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Nitrogen poisoning effect on the catalytic cracking of gasoil
Abstract
This research work consisted in the assessment of the damaging effect of basic nitrogen in the performance of industrial catalytic cracking catalysts. Laboratory evaluation of an industrial equilibrium catalyst was done with four feedstocks with very distinct nitrogen contents: a gasoil with 1307ppm of basic N (feedstock A); feedstock A after an acid treatment with the objective of partially removing the basic nitrogen (feedstock B: 135ppm of basic N); feedstock B after adding 1172ppm of quinoline (feedstock C: 1307ppm of basic N); and feedstock A after adding 1172ppm of quinoline (feedstock D: 2479ppm of basic N). Characterization of the gasoils showed that only the basic nitrogen content was affected by the acid treatment. The evaluation results showed that basic nitrogen reduces the gasoil cracking conversion in 5–10wt% points, depending on the catalyst to oil ratio. In addition, at constant conversion, the increase in basic nitrogen content also resulted both in a decrease in gasoline yield and an increase in coke and hydrogen yields. Nitrogen contained in the quinoline molecule had similar effects to that present in the original gasoil.
... [5] In addition to hydrocarbons, crude oil fractions for FCC units contain non-negligible amounts of sulfur, nitrogen, carbon residue, and metals such as nickel, iron and vanadium. [19,27,57,58] The overall performance of the FCC process in the production of liquid fuels is strongly affected by the feedstock properties including the feedstock composition and contaminants. For example, the vacuum and atmospheric residue cuts consist of mainly resins and asphaltenes. ...
... [133] Li et al. [134] showed that non-basic nitrogen compounds and condensed aromatics in coker gas oil (CGO) could easily adsorb on the cracking catalyst, causing pore blockage and a decrease in conversion and light oil yields, and could also lead to higher coke yield during cracking under conventional FCC conditions. Caeiro et al. [57] investigated the effects of nitrogen poisoning on the catalytic cracking of gas oil. The catalytic evaluation indicated that basic nitrogen reduced gasoil conversion by 5-10 wt.%, depending on the CTO. ...
... The catalytic evaluation indicated that basic nitrogen reduced gasoil conversion by 5-10 wt.%, depending on the CTO. [57] Increasing the nitrogen concentration resulted in a decrease in activity and a variation in product distribution. Coke and hydrogen yields increased at the expense of gasoline. ...
The fluid catalytic cracking (FCC) technology is one of the pillars of the modern petroleum industry which converts the crude oil fractions into many commodity fuels and platform chemicals, such as gasoline. Although the FCC field is quite mature, the research scope is still enormous due to changing FCC feedstock, gradual shifts in market demands and evolved unit operations. In this review, we have described the current status of FCC technology, such as variation in the present day feedstocks and catalysts, and particularly, great attention is paid to the effects of various contaminants of the FCC catalysts of which the latter part has not been sufficiently documented and analyzed in the literature yet. Deposition of various contaminants on cracking catalyst during FCC process, including metals, sulfur, nitrogen and coke originated from feedstocks or generated during FCC reaction constitutes a source of concern to the petroleum refiners from both economic and technological perspectives. It causes not only undesirable effects on the catalysts themselves, but also reduction in catalytic activity and changes in product distribution of the FCC reactions, translating into economic losses. The metal contaminants (vanadium (V), nickel (Ni), iron (Fe) and sodium (Na)) have the most adverse effects that can seriously influence the catalyst structure and performance. Although nitrogen and sulfur are considered less harmful compared to the metal contaminants, it is shown that pore blockage by the coking effect of sulfur and acid sites neutralization by nitrogen are serious problems too. Most recent studies on the deactivation of FCC catalysts at single particle level have provided an in-depth understanding of the deactivation mechanisms. This work will provide the readers with a comprehensive understanding of the current status, related problems and most recent progress made in the FCC technology, and also will deepen insights into the catalyst deactivation mechanisms caused by contaminants and the possible technical approaches to controlling catalyst deactivation problems.
... Over the years, the poisoning effect of basic nitrogen has been extensively published [103,114,115,[125][126][127]. Recently, there has been a shift in crude oil supply towards heavier crudes. ...
... Two mechanisms have been used to explain the retarding effects of basic nitrogen compounds [114,129]. First, the basic nitrogen compounds reversibly absorb on the Brønsted or Lewis acid centres and then poison the acid centres hindering the hydrocarbon cracking ability of the FCC catalyst. Second, because of their big size and aromatic nature, the basic nitrogen compounds may be the precursors of coke. ...
The catalysts used for residue fluid catalytic cracking must have good catalyst activity, selectivity, hydrothermal stability, coke selectivity and metals tolerance to high concentrations of heteroatoms such as N, S, Fe, Na, Ni, and V. Recent increase in energy demand leads to the processing of heavy feedstocks such as atmospheric residue that hitherto have been disfavoured. Processing these feedstocks comes with several challenges due to the presence of
these heteroatom poisons that are detrimental to catalysts as they either permanently or temporarily deactivate or poison the catalysts, thereby promoting undesirable reactions such as dehydrogenation and coke production. To give perspective on these challenges, RFCC technologies, catalysts, and catalyst deactivation are discussed.
The differences and limitations of conventional fluid catalytic cracking and contemporary residue fluid catalytic cracking are also highlighted. This study emphasises the passivation of Ni using antimony, rare earth metals,
bismuth and boron compounds and passivation of V using tin, rare earth metals, and basic alkaline earth
compounds such as Mg. The work also presents new illustrations of nickel and vanadium poisoning mechanisms. While antimony successfully mitigates nickel’s deleterious effects; it leads to NOx emissions and increased bottom fouling. Boron does not exhibit such a problem and has been shown to be a good substitute for antimony
in mitigating the harmful effect of nickel.
... Nitrogen compounds are present in fuels in the form of amines, nitriles and heterocyclic aromatic compounds, as pyrrole or pyridine [4,5]. The conventional method used in the oil industry to remove these contaminants in fuel oils is the process of hydrodenitrogenation (HDN), consisting in a reduction reaction at high pressure and temperature (300-450 C) of the N components in the presence of hydrogen using catalysts to produce NH 3 [6,7]. This process is extremely expensive, and although aliphatic N compounds are reduced, it is inefficient in the reduction of aromatic compounds. ...
... IL) using CH 2 Cl 2 /CH 3 OH (9/1) as eluent. Finally, the solvent was removed by rotary evaporation and the obtained IL was dried by heating at 353. 15 7.74 (s, 1H, H-4), 4.18 (m, 2H, NCH 2 ), 2.65 (m, 2H, C(2)CH 2 ), 2.20 (s, 3H, C(5)CH 3 ), 2.14 (s, 3H, C(3)CH 3 ), 1.59 (m, 2H, NCH 2 CH 2 ), 1.27 (m, 2H, C(2)CH 2 CH 2 ), 1.14 (m, 4H, C(2)(CH 2 ) 2 CH 2 , N(CH 2 ) 2 CH 2 ), 1.02 (m, 2H, C(2)(CH 2 ) 3 CH 2 ), 0.63 (t, 3H, J = 7.4 Hz, N(CH 2 ) 3 CH 3 ), 0.54 (t, 3H, J = 7.2 Hz, C(2)(CH 2 ) 4 CH 3 ). ...
The emission of sulfur and nitrogen oxides to the atmosphere caused by the presence of heterocyclic sulfur and nitrogen compounds present in fuel oils, is one of the main environmental issues worldwide and the major contributor for acid rain and global warming. In this work, the ability of two tetraalkyl substituted pyridinium-based ionic liquids as solvents for the denitrogentation of model fuels by liquid extraction was tested. For that purpose, the liquid–liquid equilibrium data for {heptane + pyrrole, pyridine + ionic liquid} ternary mixtures were experimentally determined at T = 298 K and at atmospheric pressure. The selected designed and synthesized ionic liquids were derived from the 1-butyl-3, 5-dimethyl-2-pentylpyridinium cation, incorporating dicyanamide and bis(trifluoromethylsulfonyl) imide anions. The extraction power of these ionic liquids was evaluated in terms of selectivity and solute distribution ratio, which showed that heterocyclic nitrogen compounds are better extracted by the ionic liquid derived from dicyanamide anion than by that based on bis (trifluoromethylsulfonyl)imide. In any case, the obtained results using these ILs are very promising and they greatly improve the results achieved so far using other ILs.
... For its part, the nitrogen that was present in a greater proportion in the ATR (N = 1.40 wt%) could poison the active sites of the catalyst, especially the acid sites. Therefore, a greater impact of the residual feedstocks on the deactivation of the catalyst was expected [29]. The simulated distillations of each feedstock are also presented in Table 1. ...
The influence of residual cuts on the deactivation of hierarchical Y zeolite-based catalysts during the co-processing of vacuum gas oil (VGO) with atmospheric residue (ATR) was investigated. The experiments were conducted in a laboratory-scale MAT-type reactor. The conversion of VGO, ATR, and their 70:30 (mass basis) mixture was examined using two composite catalysts: Cat.Y.0.00 and Cat.Y.0.20. The operating conditions closely resembled those of the commercial catalytic cracking process (550 °C and contact times of 10 to 50 s). When ATR was processed individually, the conversion remained below 50 wt%. However, significant improvements in conversion rates were achieved and catalyst deactivation was mitigated when ATR was co-processed with VGO. Notably, the BET surface area and average mesopore volume were adversely impacted by ATR, which also led to the accumulation of high levels of metals and nitrogen on the spent catalyst, detrimentally affecting its acidic and structural properties. Moreover, substantial coke deposition occurred during ATR cracking. The soluble and insoluble coke analysis revealed H/C ratio values of up to 0.36, indicative of polycondensed coke structures with more than ten aromatic rings. The nature of the coke was confirmed through TPO and FTIR analyses. Interestingly, the CatY.0.20 catalyst exhibited less activity loss, retaining superior acid and structural properties. Co-processing Colombian atmospheric residue with ATR loadings of 30 wt% (higher than the typical 20 wt%) in catalysts formulated with hierarchical zeolites presents a promising alternative for commercial applications. This research opens avenues for optimizing catalytic cracking processes.
... Aromatic content also decreases due to high hydrogenating activity of the catalyst. There is also great decrease in viscosity, density and fraction composition, caused by the formation of gas products and gasoil [27,28]. ...
The present report is devoted to refining of thermolysis oil (TO), which was obtained from the mixture of different plastics and contained 2.24% of chlorine. The process of refining of thermolysis oil includes combination of hydrotreating of TO (80%) and SR VGO (20%) mixture with NiMo supported catalysts. The following process includes FCC treatment of the obtained hydrotreating products. All used conditions were typical for industrial FCC process of SR VGO with its preliminary hydrotreating. The influence of hydrotreating catalyst type and hydrotreating temperature on the composition and properties of hydrotreating products was studied. Moreover, the effect of these parameters on the composition and yields of FCC products was established. The main reasons of hydrotreating catalysts deactivation during refining of Cl containing thermolysis oil were investigated by XPS, HAADF, HCNS-analysis. It was revealed that the best hydrotreating temperature was 360 °C, while the best used catalyst was NiMoP/Al2O3.
... Increased content of oxygen and basic nitrogen in BFs can affect the performance of the hydrocracking catalyst due to the competitive adsorption of these heteroatoms on the catalyst's active sites. Based on the previous reports dedicated to the effect of the basic nitrogen (0.63 wt % for SBDR vs 0.04 wt% for CF) on the FCC cracking catalysts [51,52], we can assume that basic nitrogen present in high concentration in the straw SBDR can greatly suppress the conversion. ...
Utilization of waste lignocellulosic biomass to produce high-quality fuels with renewable carbon content using existing refinery infrastructure is an important step towards carbon neutrality. Direct hydroprocessing of pyrolysis bio-oil to liquid biofuels is technically challenging due to its wide fractional and complex chemical composition that requires harsh reaction conditions associated with extensive biocarbon loss to the gaseous products. We have proposed a novel bio-oil hydroprocessing strategy based on 1) bio-oil hydrotreatment (stabilization), 2) fractionation of the stabilized bio-oil and 3) co-processing of the fractions in appropriate refinery processes. In this work, we focus on the co-processing of the stabilized bio-oil distillation residue (SBDR, b.p. 360+°C) with vacuum gas-oil (VGO) in a hydrocracking fixed bed reactor under conventional conditions. This allowed us to maximize biogenic carbon content (92%) in the liquid transportation fuels as confirmed by the distribution of 14C (obtained by Accelerator Mass Spectrometry) into the corresponding fractions. i.e. gases, naphtha, kerosene, diesel and distillation residue. Reduction of the fossil CO2 emission was 3 times higher for the naphtha fraction compared with E10 gasoline; 2.4 times higher for the diesel fraction compared with B7 diesel (7 vol% FAME). Detailed analysis of the products via GC × GC-TOFMS, 13C NMR, and FTIR together with the standardized methods demonstrated that fuel distillates met requirements for conventional fuels with only negligible effect of the SBDR on physicochemical properties of products and catalyst stability. This shows that the co-hydrocracking of SBDR is a suitable process to maximize liquid fuel production with increased biogenic carbon content
... However, it was difficult to find any evidence that might contribute to an increased reformer catalyst coking and the subsequent deactivation. Based on a previous LNB study on fluid catalytic cracking (FCC) of H-Oil derived gas oils [10] and the literature data asso- ciated with the FCC study showing the poisoning effect of nitrogen [11][12][13] on the performance of acid catalysts, the LNB process engineers team directed their focus on a possible poisoning of the reformer catalytic system. Investigating the performance of the whole LNB refinery the process engineer team noted that in the second half of July 2019 experiments started in the crude distillation units (CDUs) with the substitution of NaOH by organic bases to neutralize the crude chlorides and reduce the sodium content in the vacuum residue (VR). ...
The LUKOIL Neftohim Burgas hybrid reformer has
experienced unusual reformate octane drop from 100
down to 98.7 (research octane) and from 89 down to
87.5 (motor octane) during its eighth cycle and
16-year operation with the same catalytic system.
Several hypotheses have been checked to identify the
reason for the octane reduction over a period of five
months. Finally, it was established that the basic nitrogen
containing chemical substituting caustic to
neutralize the chlorides in the crude distillation units
upstream of the reformer in order to decrease the sodium
content in the vacuum residue had been carried
over to the reformer and subsequently poisoned its catalyst.
Poisoning of the reformer catalytic system led to
both octane reduction and reformate yield decrease.
... Basic nitrogen is a well-known catalyst poison in catalytic cracking [66][67][68]. For conventional 595 refinery feedstock, the content of basic nitrogen is usually about one third of the total nitrogen 596 [68][69][70]. ...
Gasification of wheat straw, an agricultural residue with high ash content, was investigated in a low temperature circulating fluidized bed (LT-CFB) gasifier in combination with catalytic tar upgrading as a flexible process to co-produce high quality bio-oil, nutrient rich char, and utilize the producer gas for heat and power production. The change in product distribution and bio-oil quality was studied when conducting the catalytic treatment with HZSM-5/γ-Al2O3 and lower-cost γ Al2O3. The fuel properties of the raw and upgraded bio-oils were analyzed by elemental composition, moisture, total acid number, size exclusion chromatography, basic nitrogen content, gas chromatography−mass spectrometry with flame ionization detection (GC–MS/FID), 1H nuclear magnetic resonance (NMR), 13C NMR, and two-dimensional heteronuclear single-quantum correlation (2D HSQC) NMR. The operating temperature of the LT-CFB pyrolysis chamber determined the tar yield and quality in the producer gas. With decrease in pyrolysis temperature from 690 to 570 °C, the tar concentration in the producer gas increased while the higher heating value of the condensed oil phase decreased from ~35 to 30 MJ/kg and the oxygen content, moisture content and acidity of the bio-oil increased. Both HZSM-5/γ-Al2O3 and γ-Al2O3 were effective catalysts as the tar treatment improved the bio-oil quality in terms of increased heating value and revaporization efficiency, and a reduction in oxygen content, moisture content, total acid number, and basic nitrogen content. Catalytic vapor treatment, e.g. using HZSM-5/γ-Al2O3 at 500 °C, decreased the energy content in the condensed bio-oil slightly from ~22% to ~20%. The oil quality improved significantly, as the oxygen content (water-free) and TAN of the bio-oil decreased from 13 wt% O and 34 mg KOH/g to 11 wt% O and 3 mg KOH/g, respectively. The catalytically treated bio-oils are thus better suited for further processing in existing oil refineries.
... The lower activity of the ZSM-5 could also be related to the nitrogenous compounds released from the pyrolysis of PM. Nitrogenous compounds often have basic characteristics and are a poison to acidic catalytic cracking catalysts like the ZSM-5 (Bobkova et al., 2014;Caeiro et al., 2007). The basic MgO catalyst lacked acidity and was not similarly affected by the nitrogenous compounds in the pyrolysis vapours of PM. ...
The objective of this study was to examine the potential of poultry wastes to be used as feedstock in non-catalytic and catalytic fast pyrolysis processes, which is a continuation of our previous research on their conversion into biofuel via slow pyrolysis and hydrothermal conversion. Both poultry meal and poultry litter were examined, initially in a fixed bed bench-scale reactor using ZSM-5 and MgO as catalysts. Pyrolysis of poultry meal yielded high amounts of bio-oil, while pyrolysis of poultry litter yielded high amounts of solid residue owing to its high ash content. MgO was found to be more effective for the deoxygenation of bio-oil and reduction of undesirable compounds, by converting mainly the acids in the pyrolysis vapours of poultry meal into aliphatic hydrocarbons. ZSM-5 favoured the formation of both aromatic compounds and undesirable nitrogenous compounds. Overall, all bio-oil samples from the pyrolysis of poultry wastes contained relatively high amounts of nitrogen compared with bio-oils from lignocellulosic biomass, ca. 9 wt.% in the case of poultry meal and ca. 5-8 wt.% in the case of poultry litter. This was attributed to the high nitrogen content of the poultry wastes, unlike that of lignocellulosic biomass. Poultry meal yielded the highest amount of bio-oil and was selected as optimum feedstock to be scaled-up in a semi-pilot scale fluidised bed biomass pyrolysis unit with the ZSM-5 catalyst. Pyrolysis in the fluidised bed reactor was more efficient for deoxygenation of the bio-oil vapours, as evidenced from the lower oxygen content of the bio-oil.
... Many researches reported challenges with processing regular CGO using FCC, due to its high content of nitrogen (especially basic nitrogen) and condensed aromatics as well as its hydrogen deficiency [5][6][7]. Basic nitrogen compounds readily interact with Brønsted acid sites and/or Lewis acid sites, leading to rapid FCC catalyst poisoning [5,[8][9][10]. Catalyst deactivation restricts the conversion of the feedstock and reduces the yield of the valuable liquid products [5,[8][9][10]. ...
Inferior coker gas oil (I-CGO) is difficult to directly process by fluid catalytic cracking (FCC) or hydrocracking owing to its high content of nitrogen and condensed aromatics. Catalysts in these units deactivate rapidly as a result of major coking and acid site neutralization. In this work, a two-step pilot-scale process consisting of hydrotreating I-CGO followed by FCC processing is designed to effectively convert I-CGO to high-value light fuel product. The results showed that the yield of gasoline increase by 12.88 wt%, whereas the yield of the slurry decrease by 20.55 wt%. Moreover, the quality of the products; including gasoline, light cycle oil (LCO), and slurry improved, significantly. These remarkable results arise from a synergy attributed to the ease of cracking of partially saturated condensed aromatics without major coking as well as reducing the content of basic nitrogen.
... These compounds show many negative effects on downstream oil refining processes and on the specification of final products. They cause the poisoning of acidic catalysts in upgrading processes such as hydrocracking and fluid catalytic cracking, even below 50 ppm of nitrogen [1][2][3]. Moreover, literature studies demonstrated an inhibiting effect of nitrogen compounds on deep hydrodesulphurization and hydrodearomatization due to their competitive adsorption on catalytic active sites [4][5][6][7][8][9]. ...
... These compounds show many negative effects on downstream oil refining processes and on the specification of final products. They cause the poisoning of acidic catalysts in upgrading processes such as hydrocracking and fluid catalytic cracking, even below 50 ppm of nitrogen [1][2][3]. Moreover, literature studies demonstrated an inhibiting effect of nitrogen compounds on deep hydrodesulphurization and hydrodearomatization due to their competitive adsorption on catalytic active sites [4][5][6][7][8][9]. ...
A detailed kinetic study of the hydrodenitrogenation (HDN) network of quinoline was carried out over Ni-promoted MoS2 catalysts supported either on γ-Al2O3 or on amorphous silica alumina (ASA), the objective is to identify the role of the support acidity in HDN reactions. The kinetic data obtained from catalytic tests in a batch reactor were analyzed by a model including the liquid-vapor mass transfer. The adsorption constants of all intermediates and the kinetic constants of all elementary steps were estimated. We found that the NiMo(P)/ASA exhibited a higher rate constant in the hydrogenation of tetrahydroquinoline, which was the rate determining step of the main reaction pathway, and in exocyclic carbon-nitrogen bond cleavage reactions, than the NiMo(P)/Al2O3. Characterization data by Infra-Red spectroscopy of CO suggested that this result might be related to the modification of the electronic properties of promoted NiMoS phase due to higher acidity of ASA. However, the stronger self-inhibiting effect due to stronger adsorption of nitrogen compounds over NiMo(P)/ASA and its lower content of NiMoS phase decreased its global catalytic activity.
... As an important source of FCC feedstock, a typical vacuum gasoil (VGO) only contains approximately 25%-30% of the nitrogen existent in crude oil. However, in the last few years, more fluid catalytic crackers began to process vacuum residua (VR) containing 70%-75% of the nitrogen present in crude oil [1]. Moreover, coker gas oil (CGO), which is characterized by high nitrogen compounds and polynuclear compounds, was blended into the FCC feedstock as well [2][3][4]. ...
Nitrogen oxides (NOX) emission during the regeneration of coked fluid catalytic cracking (FCC) catalysts is an environmental issue. In order to identify the correlations between nitrogen species in coke and different nitrogen-containing products in tail gas, three coked catalysts with multilayer structural coke molecules were prepared in a fixed bed with model compounds (o-xylene and quinoline) at first. A series of characterization methods were used to analyze coke, including elemental analysis, FT-IR, XPS, and TG-MS. XPS characterization indicates all coked catalysts present two types of nitrogen species and the second type with a higher binding energy is related with the inner part nitrogen atoms interacting with acid sites. Due to the stronger adsorption ability on acid sites for basic nitrogen compounds, the multilayer structural coke has unbalanced distribution of carbon and nitrogen atoms between the inner part and the outer edge, which strongly affects gas products formation. At the early stage of regeneration, oxidation starts from the outer edge and the product NO can be reduced to N2 in high CO concentration. At the later stage, the inner part rich in nitrogen begins to be exposed to O2. At this period, the formation of CO decreases due to lack of carbon atoms, which is not beneficial to the reduction of NO. Therefore, nitrogen species in the inner part of multilayer structural coke contributes more to NOX formation. Based on the multilayer structure model of coke molecule and its oxidation behavior, a possible strategy to control NOX emission was discussed merely from concept.
... The retardation effects of nitrogen compounds and condensed aromatics in FCC process have to be figured out if shale oil is used to produce clean fuel. The retarding effects of basic nitrogen compounds may be explained by two mechanisms [7][8][9]. First, the basic nitrogen compounds reversibly absorb on the Brønsted or Lewis acid centers and then poison the acid centers, thus weaken other hydrocarbons cracking ability. Second, since their big size and aromatic nature, the basic nitrogen compounds may be the precursors of coke. ...
Untreated shale oil, shale oil treated with HCl aqueous solution and shale oil treated with HCl and furfural were used to do comparative experiments in fixed bed reactors. Nitrogen compounds and condensed aromatics extracted by HCl and furfural were characterized by electrospray ionization Fourier transform cyclotron resonance mass spectrometry and gas chromatography and mass spectrometry, respectively. Compared with untreated shale oil, the conversion and yield of liquid products increased considerably after removing basic nitrogen compounds by HCl extraction. Furthermore, after removing nitrogen compounds and condensed aromatics by both HCl and furfural, the conversion and yield of liquid products further increased. In addition, N1 class species are predominant in both basic and non-basic nitrogen compounds, and they are probably indole, carbazole, cycloalkyl-carbazole, pyridine and cycloalkyl-pyridine. As for the condensed aromatics, most of them possess aromatic rings with two to three rings and zero to four carbon atom.
... The process entails C-S and C-N bond cleavage to produce H 2 S and NH 3 , respectively. [15][16][17][18] HDS is the primary desulfurization technology used today. The HDS reaction in reneries is carried out in trickle-bed reactors. ...
The purpose of this review is to provide appropriate details concerning the applications of ionic liquids for the removal of pollutants from refinery feedstocks, like sulfur-, nitrogen- and fluor-containing compounds, aromatics, naphthenic acids and asphaltenes. Furthermore, critical considerations surrounding the problems and challenges associated with the application of these technologies in the petroleum industry are discussed.
... Moreover, the adsorption of air (N 2 ) on catalyst pores will influence the test results. Barth et al. 61 used the HF solution (40%) to extract the coke from the catalyst; however, Caeiro et al. 11 found the dissolution process is not completely effective, because some of the catalyst components are not completely destroyed by the HF treatment. Indeed, researchers care more about the SO x and NO x emissions during the regeneration of coked catalyst. ...
To investigate the effects of operating conditions and the catalyst activity on the transfer regularity of sulfur and nitrogen during the cracking process of coker gas oil (CGO), the CGO was catalytically cracked in a pilot-scale riser fluid catalytic cracking (FCC) apparatus at different test environments. Then the cracked liquid products were analyzed for sulfur and nitrogen distributions with boiling point, from which the sulfur and nitrogen concentrations of gasoline, light cycle oil (LCO), and heavy cycle oil (HCO) fractions were determined. The sulfur and nitrogen compounds in each product cut, and their possible reaction pathways were reviewed and discussed. The results show that sulfur-containing species are easier to crack but more difficult to be removed from the liquid product, while nitrogen compounds are easier to form coke, then be removed from the liquid product. The sulfur distribution of CGO is different from that of conventional feedstocks. Different processing parameters can significantly affect the sulfur and nitrogen distribution yields and concentrations in liquid products. Increasing the reaction temperature and the catalyst-to-oil ratio as well as shortening the residence time cannot only increase the light oil yield but also improve the product quality and reduce the SOx and NOx emissions in the regenerator.
... Coker gas oil (CGO), one feedstock widely used for FCC units in China, has attracted attentions from refineries, due to their increasing output and hardness to upgrade. The low hydrogen, high aromatic, and nitrogen contents (especially basic nitrogen compounds) are considered difficult during its upgrading [2,3].Work has been done to obtain the structural information of nitrogen compounds in CGO and their adverse effects caused by neutralizing or blocking the acid sites during CGO FCC [4][5][6][7]. However, the catalytic cracking reaction is a complex process where feedstock is adsorbed on the acid sites first and then chemical reactions occurred, resulting in adsorption as a necessary prerequisite for the reaction to proceed successfully. ...
The fluid catalytic cracking (FCC) performances of three typical coker gas oil (CGO) in China were investigated in a fixed fluidized-bed reactor. Effects of the blending ratio of CGO to vacuum gas oil (VGO), comparative FCC performances of different CGOs, and effects of operating conditions on CGO catalytic cracking performance were discussed. Based on these, the competitive adsorption effects on CGO catalytic cracking were analyzed. The results show that the conversion decreases with the increasing blending ratio of CGO to VGO due to lower reactivity of coker gas oils. The catalyst to oil ratio (CTO) has a larger influence on CGO catalytic cracking performance than the reaction temperature and weight hourly space velocity (WHSV) has. A competitive reaction area and a free reaction area can be distinguished based on the relation of CTO and CGO catalytic cracking performance.
This book is a guide to the application of ionic liquids (ILs) in the oil industry. It includes ten chapters that review basic and advanced topics. Starting with a general introduction to IL structure and properties, the book comprehensively explains the use of ILs in key petroleum extraction processes such as pollutant removal, demulsification, crude oil transport and oil recovery. Additional applications that are important for the sustainability management of petrochemical operations such as deepwell hydrate inhibition, CO2 capture, corrosion engineering, catalysis, hydrocarbon separation, bitumen extraction and stabilization are also included. Each chapter also provides bibliographic references for further reading. The wide range of topics makes this an informative reference to students and professionals in petroleum engineering, chemical engineering programs and any other training course that requires reading material for an understanding of the oil industry. General readers and researchers interested in the fascinating chemistry of ionic liquids will also enjoy this book.
For co-processing of bio-oil and conventional fossil feed in existing refinery fluid catalytic cracking (FCC) units, little attention has been paid to the enhanced aromatics and basic nitrogen content associated with the introduction of bio-oil and how it affects FCC performance. In this contribution, the effect of blending two bio-oils obtained from different catalytic treatment of wheat-straw pyrolysis vapors with atmospheric residue was tested using a microactivity testing unit (MAT). The catalysts used for the pyrolysis vapor phase upgrading included i) a Na/Al2O3 deoxygenation catalyst, and ii) a Pt/TiO2 catalyst in combination with H2 atmosphere. The oxygen content of both bio-oils was similar at ~7-8 wt%, but the Na/Al2O3 bio-oil had a lower total acid number (TAN) of 5 mg KOH/g and a higher basic nitrogen (BN) content of 0.7 wt% compared to the Pt/TiO2 bio-oil (15 mg KOH/g, 0.4 wt% BN).
The processing of the upgraded bio-oils in blends with atmospheric residue in MAT increased the yields of dry gas, CO, CO2, and coke at the expense of naphtha (decrease by 2.8 percentage points) and decreased the conversion by ~2.5 percentage points. This is attributed to the high aromaticity and basic nitrogen content of the two bio-oils. The lower basic nitrogen content and higher degree of saturation for the Pt/TiO2 bio-oil may explain its slightly higher conversion (by ≤1 percentage points) compared to the Na/Al2O3 bio-oil.
This contribution provides important information for refinery operators interested in FCC co-processing of fossil oils and biomass-derived pyrolysis oils with elevated content of nitrogen and aromatics.
With the peak in diesel consumption and the impact of new energy in the coming years, research will be focused on the treatment of excess diesel. In addition, low carbon aromatics such as benzene, toluene, and xylene (BTX) are important chemical raw materials that will be in high demand in the next few years but are still in short supply. Thus, many researchers have proposed the use of excess diesel, especially the inferior diesel-like light cycle oil (LCO) to produce BTX. The hydrocracking process is typically used to convert LCO to BTX. To provide some guidance on this topic, this review summarizes the typical group compositions in LCO from different refineries, hydrocracking reaction mechanisms of aromatics and cycloalkanes in LCO, hydrocracking catalysts, improved hydrocracking conditions, related hydrocracking technologies, and future developments in the production of BTX. The amount of aromatics with different ring numbers in LCO has been clearly analyzed, and their part types have also been studied. However, some complex types of aromatics in LCO remain unknown. In addition, the hydrocracking mechanisms and pathways of aromatics in LCO to produce BTX have garnered great attention since the 1990s. Based on this, hydrocracking catalysts and related technologies have been developed by many institutions and corporations to convert aromatics to BTX; however, there are still some problems including an insufficient selectivity of BTX, low yield of liquid products, and excessive energy consumption. In the future, more advanced technologies can be applied to analyze all types of aromatics in LCO, which, along with the aid and application of computational chemistry tools, could help deepen the understanding of the reaction pathways of aromatics and develop more efficient catalysts by balancing the properties of the active phase and supporting the surmounting of current shortcomings. Owing to this high value utilization of inferior diesel, the upcoming problem of diesel surplus can be solved effectively, and the utilization of LCO to produce BTX is one possible path.
The effect of sulfur-containing compounds on the hydrodenitrogenition (HDN) of o-propylaniline (OPA), decahydroquinoline (DHQ), 1,2,3,4-tetrahydroquinoline (14THQ) were performed at a moderate reaction conditions over NiMo/Al2O3 catalysts in a fixed-bed reactor, respectively. The presence of DMDS and DBT, converting CUS into sulfur sites (S²⁻ and SH- group), could accelerate the ring-opening reaction (Csp3-N bond cleavage) of DHQ/14THQ while inhibit the direct denitrogenation (Csp2-N bond cleavage) of OPA, indicating that the Csp3-N bond cleavage of DHQ/14THQ would require the synergistic work of S²⁻ and SH- group, but while the Csp2-N bond cleavage of OPA would take place on the CUS. An inhibitory effect of sulfur-containing compounds on the HDN of 14THQ was also observed. It could be ascribed to that the selectivity of 14THQ → OPA → PB/PCHA pathway in HDN of 14THQ was enhanced. However, the conversion of OPA is rather difficult for the reason that the inhibitory effect on the Csp2-N bond cleavage and the competitive adsorption from DHQ and 14THQ. The conversion of OPA, which is a “dead end” in the presence of sulfur-containing compounds, determines the limitation HDN conversion of 1,2,3,4-tetrahydroquinoline.
Using density functional theory (DFT) with numerical atomic functions including dispersion corrections, we establish a series of energy changes and Gibbs free energies of in situ and ex situ substitution by ammonia on Ni-Mo-S nanocluster, which includes Ni-Mo-Edge, Ni-S-Edge and Corner-Site. The results show that the in situ substitution on all active sites on Ni-Mo-S is hard to happen. The –SH group and hydrogen atom on coordinately unsaturated sites (CUS) of Ni-S-Edge can form H2S under a moderate condition, whereas the sulfur atoms on Ni-Mo-Edge are rather difficult to form H2S. The ex situ substitution of sulfur atoms on both Ni-S-Edge and Ni-Mo-Edge is energetically favored; however, the substitution may only occur on Ni-S-Edge under low partial pressure of ammonia based on the steady state of Ni-Mo-S active phase. The orbital properties show the eigenvalue has increased after substitution, which indicates the decreasing of binding electron capacity. Furthermore, the HDS performance would drop remarkably attributed to steric hindrance and lacking of activated hydrogen after substitution.
The behavior of bio-oils when co-processed with conventional fossil feed in a fluid catalytic cracking (FCC) unit is suitably tested using a microactivity testing unit (MAT). In the present study, non-catalytic fast pyrolysis oils originating from wood and wheat straw were co-processed in a MAT at a 20/80 weight blend (bio-oil/FCC feed). In addition, bio-oil obtained from deoxygenating the straw derived vapors over a steamed HZSM-5/Al2O3 extrudate catalyst was tested. The bio-oils were characterized for elemental composition and moisture content to calculate energy recoveries, amounting to 35% and 30% for the non-catalytically obtained wood and straw oils, while it was 19% for the partly deoxygenated straw oil. Wood oil showed higher acidity (61 mg KOH/g) and molar O/C ratio (0.35) compared to straw oil (54 mg KOH/g and O/C = 0.24). The acidity and O/C ratio was reduced for the straw-derived bio-oil from catalytic vapor treatment (3 mg KOH/g, O/C = 0.08). At constant conversion (77.5%) at the MAT, the wood pyrolysis oil showed a product distribution quite similar to the reference oil while the wheat straw pyrolysis oil gave a 1.6% points higher coke yield and a 1.2% points lower liquid petroleum gas (LPG) yield. For the catalytically treated wheat straw pyrolysis oil, an even higher coke yield (2.6% points) and 1.9% points lower LPG yield resulted. The observations are attributed to the higher content of aromatics, phenolics, and nitrogen containing compounds of the catalytically upgraded straw fast pyrolysis oil.
Heavy oil could be classified into two parts: one is easy-cracking part, which is the main source of liquid hydrocarbon transportation fuels and industrial chemicals; the other one is refractory-cracking part, which is failed to be cracked by present technologies and has negative effects on upgrading. Therefore, the efficient method to obtain higher conversion of heavy oil is needed for heavy oil processing industry. Coker gas oil (CGO), used as an example of heavy oil, is supposed to be hard to process during fluid catalytic cracking (FCC).The structural information in molecular level of basic nitrogen compounds, non-basic nitrogen compounds, and condensed aromatics in feedstock and liquid products from FCC was investigated. And the coked catalysts in the catalytic cracking reaction of CGO were characterized. The results showed that these compounds, especially basic ones, are more difficult to crack, which are preferential chemisorbed on the surface of catalyst leading to less acid sites for other easy-cracking hydrocarbons and the decrease of the activity of catalysts. Physical solvent removal and chemical catalytic adsorption were used to pretreat heavy oil, and the result indicated either physical solvent removal or chemical catalytic adsorption is a good way to avoid the retarding effects of refractory-cracking components and better product distributions can be obtained.
Liquid fuels rich in aliphatic and aromatic carbon compounds are utilized as the carbon precursors for the production of carbon dots (CDs) for the first time. Herein we demonstrate the preparation of liquid fuels derived CDs (d-CDs and f-CDs) via chemical oxidation approach and the subsequent application for cerebral copper ions (Cu2+) sensing in rat brain microdialysate. The as-prepared CDs exhibits different morphology and photoluminescence properties depending on the different component of precursors. The luminescence of the as-prepared d-CDs can be significantly quenched upon addition of Cu2+, in which Cu2+ are trapped by the oxygen and nitrogen functional groups surrounding the emissive d-CDs. Moreover, the fluorescence intensity of d-CDs is sensitive to the concentration of Cu2+ with a linear relationship in the range of 0-4 μM, and a detection limit was estimated to be 0.039 μM. Simultaneously, we found out that the luminescent d-CDs manifests an extraordinarily high selectivity which can clearly discriminate Cu2+ from other interference species in aqueous solution and therefore substantially endows d-CDs as a fluorescent sensing platform for Cu2+. According to this nature, we employed d-CDs for the in vivo analysis of Cu2+ in the rat brain microdialysate and the measured basal level of Cu2+ was estimated to be 2.82 ± 0.16 μM (n = 3) even in the presence of other metal ions, biological substances and amino acids that commonly existing in the rat brain.
Data are presented on the modification of cracking catalysts in order to improve their resistance to the poisoning effect of nitrous compounds of various classes. The modification of the catalyst matrix consists in that special additives are introduced into the catalyst formulation to improve its resistance to the poisoning action of nitrous compounds. Acid-activated clays and mixed oxides are considered as these additives.
Inferior coker gas oil (ICGO) derived from Venezuelan vacuum residue delayed coking is difficult to process using fluid catalytic cracking (FCC) or hydrocracking (HDC). The high content of nitrogen and condensed aromatics leads to major coking, and readily deactivates the acid catalyst. In this work, a sequence of hydrotreating (HDT) and FCC processing is used to effectively convert ICGO to high-value light oil product. The results show a higher overall conversion and a significant increase in the yield of gasoline compared with FCC processing. Molecular level characterization of the nitrogen compounds and condensed aromatics before and after HDT confirms that the nitrogen content and the 2+ ring aromatic content decreased, whereas the single ring aromatics increased. The nitrogen compounds were mainly N1, N1O1, N1O2, and N1S1 class species in basic nitrogen and N1, N1O1, N1O2, N2, and N2O1 class species in non-basic nitrogen. Moreover, the double bond equivalent of these species shifted to lower values. The decrease in the nitrogen compounds with high heteroatom content reduces coking on the FCC catalyst. Subsequently, FCC unit performance and conversion to light oil increased. Moreover, the decrease in the size of N1 class compounds and the ease of their cracking following HDT improved the performance of the FCC unit. Partial saturation of condensed aromatics following HDT also made it easier to crack these compounds.
Two narrow fractions distilled from Liaohe coker gas oil were used for the research. The distribution of basic nitrogen compounds in feedstocks and their liquid products were characterized by ESI FT-ICR MS. The results showed that N1 class species were the most predominant in both feedstocks and products. The catalytic cracking progress reduced the relative abundance of all class species, except for the N1 and N1S1 class species. Although the N1 class species had longer side chains and higher condensation in the heavier feedstock, the distribution of N1 class species became similar in the two liquid products.
The purpose of this research is to evaluate, at a molecular level, the removal of nitrogen compounds from vacuum gas oil (VGO), which is used as feedstock for fluid catalytic cracking units. Here, a VGO sample was treated with two different adsorbents: an argillaceous material specifically developed for the removal of nitrogen compounds in middle distillate cuts (kerosene and diesel) and a commercial silica adsorbent. Breakthrough curves were built on two temperature levels (80 and 150 °C), containing different rupture times (from 60 to 420 min), to determine their influence on nitrogen compound removal. All samples, produced from each condition of adsorption, were analyzed by positive and negative electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry [ESI(±)FT-ICR MS]. Besides FT-ICR MS characterization, the total nitrogen content was monitored. FT-ICR MS indicated that the removal of nitrogen compounds by the clay adsorbent was enhanced when the temperature was higher (150 °C). Conversely, silica has shown a rich adsorption capacity at moderate temperatures (80 °C). This result corroborates the existence of two different adsorption mechanisms. The clay adsorption mechanism is likely a chemisorption process, while the silica adsorption mechanism is related to physisorption. Both processes displayed better performance in short rupture times, for example, at 60 min. Longer rupture times require a saturation of the adsorption process through a packed bed. FT-ICR mass spectra detected a wide range of compounds from m/z 220 to 800, with average molecular weight distributions (Mw) that increase as a function of decreasing the total nitrogen content (424 → 711 Da). Class distribution showed a removal preferential of N[H] and N2[H] compounds with low carbon numbers (<C26) for ESI(+) data. The ESI(+)FT-ICR MS data also revealed that clay is a more efficient adsorbent than silica for the removal of nitrogen compounds and should be used in the petroleum industry. However, the ESI(−)FT-ICR MS data showed that, although adsorbents, such as clay, present acid sites and selectively adsorb basic nitrogen species, a great reduction of non-basic nitrogen species, such as carbazole and its analogues, is clearly observed mainly for VGO samples treated with clay at 150 °C and with silica at 80 and 150 °C, both with t = 60 min.
Based on a polyglycidyl methacrylate-co-ethylene glycol dimethacrylate copolymer (PGMA-co-EGDMA), nitrogen, sulfur, and aromatic compounds were removed from light and heavy gas oil feeds. The method in which PGMA-co-EGDMA is synthesized can influence the textural and chemical characteristics of the polymer, and thus its adsorption capacity. Studies have shown that using cerium initiated graft polymerization in PGMA-co-EDGMA synthesis can improve the adsorption capacity of the polymer. In this work, nitrogen, sulfur, and aromatics removal capacity of (PGMA-co-EGDMA) polymer incorporated with tetranitrofluorenone (TENF) via 1,3 diaminopropane (PDA) using cerium initiated graft polymerization were compared with the same polymer without using cerium. A third polymer with different linker, ethylenediamine (EDA) instead of PDA, was synthesized using cerium initiated graft polymerization to inspect the impact of the linker on the removal efficiency. The synthesized polymers were characterized using different characterization methods. The synthesized polymers were tested at different nitrogen, sulfur, and aromatic content using light and heavy gas oil feeds. In addition, the removal capacity of the synthesized polymers toward non-basic nitrogen were determined using automatic potentiometric titrator. Results have shown that using cerium graft polymerization on the synthesis of PGMA-co-EGDMA polymer reduced surface area, pore size and volume, and amount TENF grafted, thus decreasing the removal efficiency of nitrogen, sulfur, and aromatics. However, polymer selectivity toward non-basic nitrogen was not affected by cerium graft polymerization. Furthermore, the adsorption capacity of the PGMA-co-EGDMA decreased with increasing linker length due to steric hindrance effect that influences the adsorption capacity of the polymer.
In this work, pyrolysis photoionization time-of-flight mass spectrometry (Py-PI-TOFMS) was applied to study the behavior of ammonia poisoning on H-form ultra stable Y (HUSY) zeolite for the catalytic pyrolysis of polypropylene (PP). Firstly, ammonia poisoning on HUSY was performed to obtain the suitable catalysts with different strength and amounts of acid sites. Secondly, online photoionization mass spectra for the pyrolysis products of PP and HUSY with various acid strength were recorded at different pyrolysis temperatures. Finally, the formation curves of various pyrolysates of PP/HUSY with the increase of temperature were determined. Our results indicate that the formation temperatures, yields and selectivity of the pyrolysis products of PP demonstrate obvious relationship with the acid strength of HUSY.
New functionalized 1-butyl-3-Xpyridinium dicyanamide ionic liquids (ILs) were synthesized by adding groups (X = cyano, amino, chlorine, alkyl) with different substituent effects. Experimental and computational analyses were performed to evaluate the role of the pyridinium substituent on IL solvent properties, particularly as an extracting agent of pyridine from fuels. Quantum chemical calculations and NMR measurements indicated that the hydrogen bond (HB) donor character of the cation was successfully tuned by an adequate substitution. The COSMO-RS study showed that pyridine produces exothermic mixtures with these ILs, mainly due to favorable HB interactions. However, the mixture behavior was found to be controlled by entropy. Experimental and calculated Liquid–Liquid Equilibrium (LLE) data of pyridine-heptane-IL mixtures revealed that the new functionalized ILs present favorable partition coefficients and selectivity for extracting N-compounds from aliphatic mixtures. It was possible to enhance the solvent performance by using tetraalkyl substituents, which increases the entropy of the system.
This study was designed to investigate the use of commercial adsorbent materials for the removal of nitrogen compounds from a vacuum gas oil obtained from an industrial atmospheric distillation unit. Two types of adsorbents were tested: a clay developed specifically for the removal of nitrogen compounds from middle distillates (jet fuel and diesel); and a silica used in a variety of industries. Kinetic and thermodynamic equilibrium experiments were conducted at three temperatures: 80, 100, and 120 °C. The variation in the concentration of nitrogen and aromatic compounds was monitored throughout the kinetic adsorption and thermodynamic equilibrium experiments. When an adsorbent/gas oil mass ratio of 0.75 was used, the clay removed around 70 % of the basic nitrogen compounds from the gas oil, while the silica removed 80 % of the same compounds, which are the ones that effectively hamper catalytic cracking. The silica also removed 14.2 % of the aromatic compounds, while the clay only removed 4.1 %. This study shows that it is possible to treat a viscous hydrocarbon feed using an adsorption process to remove nitrogen compounds without the need to dilute the feed. Using a fluidized bed advanced cracking evaluation (ACE) unit, which simulates a fluid catalytic cracking unit on a bench scale, the gas oil treated with silica produced 3 % more liquid petroleum gas (LPG) and 4 % more gasoline, while the gas oil treated with clay produced 2 % more LPG and 3 % more gasoline than the untreated gas oil.
The poisoning mechanisms of FCC catalysts with azotic compounds, including the acid-alkali neutralization theory, competitive adsorption theory, inductive effect and steric hindering effect, were summarized. The poisoning extent is closely related to proton affinity, adsorption and complexing capability, molecular size and structure of the azotic compounds and pore structure of the catalysts. The measures of improving the nitrogen-resistant performance of the FCC catalysts were reviewed, such as increasing the acid sites, choosing active matrixes, modifying the zeolites and heightening the reaction temperature and the ratio of the catalysts to oil. The processes for treating coker gas oil with high content of azotic compounds were introduced. The trend of improving FCC unit to process feedstocks with high content of azotic compounds was prospected.
This paper proposes a mechanism for the inductive effect of quinoline on coke formation during the catalytic cracking of o-xylene. Quinoline preferentially adsorbs on the acidic sites to induce coke formation and promote the conversion of o-xylene via electrophilic substitutions and hydrogen transfer reactions. The presence of naphthyl-quinolines and benzyl-quinolines in soluble coke identified by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry and the characterization of two types of nitrogen species in coke by XPS both confirm that the mechanism is reasonable. Basic nitrogen compounds poison the acidic sites of catalysts and induce the coke formation from aromatics.
A kinetic study of the hydrodenitrogenation of quinoline is performed in a batch reactor, over a NiMo(P)/γ-Al2O3 sulfide catalyst, in the range of temperature of 340-360 °C and concentration of 1-2 wt % of quinoline. Liquid-vapor mass transfer is considered in the reactor model, and the kinetic expression using Langmuir-Hinshelwood model considers competitive adsorption of reactants, products, and solvents. The activation energies of every elementary reaction and adsorption enthalpies of nitrogen compounds are calculated. The kinetic modeling shows that the hydrogenation of 1,2,3,4-tetrahydroquinoline into decahydroquinoline is the rate-determining step of the principal reaction pathway. The self-inhibition effect due to competitive adsorption of nitrogen-containing compounds is confirmed. The adsorption constants of nitrogen compounds decrease in the order saturated amines > NH3 > aromatic amines, showing that their adsorption strength is related to the basicity of molecules. Moreover, the kinetic model is validated by an additional experiment using ammonia as an inhibitor.
The effect of the content and nature of nitrogen compounds on the distribution of target products in transforming model hydrocarbons under cracking conditions over equilibrium zeolite-containing catalyst was studied. Using cracking of n-undecane as an example, a nearly 50% drop in the conversion and in yields of propane-propene (PPF) and butane-butene fractions (BBF) was observed when the pyrrol content in the feed was raised to 3000 ppm of nitrogen. Increasing the nitrogen content in the feed led to a nonlinear reduction in the rate constants of n-undecane cracking. It was found that the dependence of the yields of PPF, BBF, and isobutane in BBF on the conversion remained constant upon the cracking of n-undecane with various of nitrogen compounds; poisoning was likely to proceeds only because the acidic sites of the catalyst were blocked. The high poisoning effect of pyrrol and indole upon the cracking of n-undecane and decalin (strong proton donors) was observed along with the formation of ammonia. Quinoline exhibited high poisoning ability in the catalytic cracking of cumene with low [H]-donor activity. Quinoline poisoned catalysts to a greater degree than indole, during the catalytic cracking of non-hydrofined vacuum gasoil with a high content of aromatic structures. Indole exhibited the highest poisoning ability in processing heavy hydrocracking residue which was rich of paraffin-naphthene hydrocarbons.
Adsorption behaviors of pyridine, quinoline and isoquinoline in ZSM-5 and USY zeolites at 773 K were studied by Grand Canonical Monte Carlo simulations. Interaction energy, adsorption isothermal and localization for each adsorbate were obtained. The results show that pyridine and quinoline/isoquinoline molecules have different adsorption behaviors in the zeolite, while quinoline and isoquinoline molecules have similar adsorption behaviors. The maximum interaction energy between quinoline/isoquinoline and zeolite is more negative than that of pyridine and zeolite, which indicates that the quinoline/isoquinoline can be adsorbed more stable than pyridine. But the loadings of pyridine are significantly larger than that of quinoline/isoquinoline at the same pressure. Otherwise, pyridine can be adsorbed on most sites while quinoline/isoquinoline can only enter the large channels or cages. And the adsorption quantities in USY zeolite are much more than the adsorption quantities in ZSM-5 zeolite for each adsorbate.
Recent studies show that chabazite can catalyze cracking reactions and remove nitrogen and heavy metals from bitumen derived from oil sands. In this study, it was found that, after reaction at 400 degrees C for 1 h, indole concentration was reduced by 43% and nitrogen removals up to 17% were obtained. Pyridinic nitrogen containing compounds were also found to react in the presence of natural zeolites although the reaction rates are much slower. Experimental evidence suggests that indole is converted into aniline and the nitrogen removed remains on the surface of the catalyst as aniline or aniline derivatives. Two possible reaction paths for the conversion of indole into aniline are presented. Experimental evidence suggests that the water affects the nitrogen adsorption but not the reaction pathway. A better understanding of the reaction path and adsorption phenomena of this system may lead to an improved process for heavy oils.
Functionalized polymers, which consist of polymer support, linker, and π-acceptor, have shown promising results in removing nitrogen and sulfur compounds from heavy gas oil via charge transfer complex (CTC) mechanism. In this work, the effect of polymer support in the efficiency and selectivity of the functionalized polymers toward nitrogen removal was studied by synthesizing three different polymers, consisting of hydrophilic and hydrophobic polymer supports, with the same linker and π-acceptor. Hydrazine (-H2N-NH2) and 2,4,5,7-Tetranitro-9-fluorenone (TENF) were chosen as the common linker and π-acceptor, respectively. The polymer supports were: polyacrylamide (PAM), polystyrene-co-divinylbenzene (PS-DVB), and polyglycidyl methacrylate-co-ethylene glycol dimethacrylate (PGMA-co-EGDMA). In the first stage, the functionalized polymers, PGMA-NN-TENF, PS-NN-TENF, and PAM-NN-TENF, were synthesized and characterized using different methods and techniques including Fourier Transform Infrared Spectroscopy (FT-IR), Brunauer-Emmett-Teller (BET), Scanning Electron Microscopy (SEM), Thermogravimetric Analysis/Differential Thermal Analysis (TGA/DTA), CHNS elemental analysis, and Nuclear Magnetic Resonance (NMR) spectroscopy. A Nitrogen/Sulfur analyzer was used to determine total nitrogen and sulfur adsorption by the synthesized polymers in 4 different feeds: model compound (MC), light gas oil (LGO), heavy gas oil (HGO), and a blend of heavy and light gas oil (BGO). Results have shown that PGMA was the best polymer support with LGO, HGO, and BGO feeds, while PS-DVB showed the highest nitrogen removal with MC feed. The higher efficiency and selectivity of PGMA-NN-TENF toward nitrogen species, in the presence of sulfur and other aromatic species in the feed, were due to the combination of hydrophilic nature and high surface area of PGMA-NN-TENF compared to other polymers. Modifying the pretreatment conditions of the polymers with BGO feed showed that increasing temperature, contact time, and polymer to oil ratio increased the efficiency of the PGMA-NN-TENF polymer.
The hydrodenitrogenation (HDN) performance of a Chinese coker gas oil (CGO) was tested in a micro-fixed bed reactor over a nickel–tungsten supported on citric-treated Y zeolite mixed with a titania–silica composite catalyst (NiW/CYCTS) within the temperature range of 360–420 °C, operating pressure range of 5.0–8.0 MPa, liquid hour space velocity (LHSV) range of 0.5–2 h− 1, H2/CGO ratio range of 400–1200 (v/v), and H2S concentration range of 1–5 wt.%. The effects of these parameters on the relative conversions of total nitrogen (TN), basic nitrogen (BN), and non-basic nitrogen (NBN) compounds were determined. The conversion of TN compounds enhanced as the temperature and operating pressure increased and as LHSV decreased. BN compounds were easier to be removed than NBN compounds; they were also affected more significantly by the reaction conditions. With increasing H2/CGO ratio, the conversion of BN and NBN compounds initially increased and then decreased thereafter. This finding may be attributed to the addition of phenyl-sulfide (PHS) in the feedstock. The kinetic study of the HDN reaction showed that TN, BN, and NBN compounds accorded with the pseudo-first-order kinetic model. The calculation of the rate constants and activation energies indicated that the HDN of NBN compounds controlled the removal of TN compounds. Moreover, the hydrogenation of N-heterocyclic was the controlling step for the conversion of NBN compounds. The results above can guide the development of CGO hydrotreating catalyst. With the information from this paper, the development of CGO hydrotreating catalyst can adjust the properties of the catalyst by decided technology which will favor the removal of NBN containing compounds.
The most critical problem of processing coker gas oil (CGO) is its high nitrogen content, especially the basic nitrogen compounds, which limits its cracking performance in the fluid catalytic cracking (FCC) process. For enhancing the conversion of CGO, three processing schemes were evaluated in a pilot-scale riser FCC unit. Four indexes (thermal cracking index, dehydrogenation index, hydrogen transfer coefficient, and isomerization reaction index) were used to investigate the effects of operating conditions on the reactions of CGO cracking. Results show that the optimal operating conditions for CGO cracking are high reaction temperature and large catalyst-to-oil ratio with a short residence time. Therefore, we proposed a synergistic process by selectively recycling light FCC gasoline (LCG) from the upper position of the riser reactor, which can provide a high-severity reaction zone for CGO cracking and a low-severity reaction zone for gasoline upgrading. To further investigate the mutual effect of the two feeds, different recycle ratios of LCG were tested. Results indicate that the conversion of CGO significantly increased with the LCG recycle ratio. When the recycle ratio reached 50 wt %, the gasoline could be upgraded at a higher efficiency. To ensure the optimal recycle ratio and improve the gasoline quality, a two-stage synergistic (TSS) process was proposed. The simulated experiments of the TSS process show that the higher conversion and more desired products can be achieved, even though under a high processing ratio of CGO to conventional feeds.
There is currently a growing need to process heavier and tougher feedstocks with increased nitrogen content for fluid catalytic cracking (FCC) units. A coker gas oil with high nitrogen content was catalytically cracked in a pilot-scale riser FCC apparatus under different conditions based on different FCC processes. Then the nitrogen balance and the conversion of saturates, aromatics, resins, and asphaltenes (SARA) were calculated, and the acid amounts of coked catalysts were analyzed by the NH3-TPD method. The results show that in the synergistic process the adsorption of nitrogen-containing species on the catalyst was controlled and more acid sites were available, thus more nitrogen-free hydrocarbons, mainly the saturates, could be cracked, while the nitrogen compounds were enriched in the cracked heavy oil. Furthermore, the compositional and structural identification of nitrogen compounds in cracked heavy oils was carried out by electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Six nitrogen class species, N1, N2, N1O1, N1O2, N1S1, and N1O1S1, were assigned in the positive-ion spectrum, while only three class species, N1, N1O1, and N1S1, were assigned in the negative-ion spectrum. The N1 class nitrogen compounds were the dominant species, and the N1O1S1 species were generated during the FCC process. Most of the nitrogen-containing species were 4–5 rings with short alkyl side chains. The MS data also show that the synergistic process not only inhibited the adsorption of nitrogen compounds on the catalyst but also changed their reaction pathways.
The coking phenomenon of coker gas oil (CGO) feedstock during fluid catalytic cracking (FCC) using a commercial equilibrium catalyst was investigated. Different types of coke formed via coker gas oil (CGO) catalytic cracking were also analyzed. The coke formed was composed of adsorption coke (Cad), dehydrogenation condensation coke (Cdh), and hydrogen transfer coke (Cht). Cad, derived from nitrogen compounds, adsorbed on the acid sites of the catalyst and accounted for 37 wt % of the total coking content under conventional reaction conditions. Cdh was formed by the dehydrogenation condensation of polycyclic aromatic hydrocarbons and accounted for about 43 wt % of the total coking content. The coking content of Cht was greatly determined by the degree of the secondary reaction. Coke selectivity can be decreased and Cht yield can be controlled by simultaneously increasing the reaction temperature and shortening the reaction time.
The influences of the boiling point and fractional composition of coker gas oil (CGO) on the fluid catalytic cracking performance were investigated. Nitrogen compounds and condensed aromatics in CGO were identified by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS) and gas chromatography-mass spectrometry (GC-MS), respectively, and their effects were studied systematically. The result shows that the catalytic cracking performance of CGO does not correspond to the boiling point of narrow fractions but rather to the basic nitrogen compounds and condensed aromatics that have high molecular weight and/or high condensation tendencies adversely. On the basis of these results, a divisional fluid catalytic cracking (DFCC) process was proposed where a separate reaction zone was added to reduce the contents and effects of the adverse compounds in CGO during catalytic cracking. The simulation experiments of the DFCC process show that improved conversion and enhanced yield of light oil can be achieved when an appropriate reaction condition is applied to every reaction zone.
As the FCC process has evolved over decades, several laboratory scale equipment have appeared to maintain a proper assessment of catalysts activity. Several laboratory equipments are available for simulating the FCC process, from the well known fixed bed, MicroActivity Test to newer, fluid bed or transported bed units. As well, a number of units have been created to simulate other parts of the process such as regenerator or stripper, The increased pressure for treating non-conventional feeds, from reprocessing gasoline to extra-heavy feeds or oils produced from biomass containing large amounts of heteroatoms, increase the needs to have a laboratory test which is as close as possible to the process so that data extraction from the laboratory test are simplified, thus less prone to errors or misunderstanding.
Over the course of the commercial fluid catalytic cracking (FCC), catalyst deactivation occurs both reversibly, as a result of side reactions that eventually yields coke, and irreversibly, due to contaminants present in the feedstock or to the dealumination of the zeolite catalyst component. Herein, we discuss the deactivation of HY zeolite and FCC catalysts from a fundamental as well as an applied point of view. Aspects related to the various causes of FCC catalysts (and additives) deactivation under industrial conditions are also summarized.
Zeolites, or more broadly molecular sieves, can be found in a majority of the major catalytic processes in today’s petroleum
refinery. This paper provides an overview of the use of zeolite catalysts in today’s petroleum refineries, and emphasizes
some of the newer refining applications including gasoline sulfur removal and dewaxing via isomerization. Zeolite catalysts
are also finding new applications at the refinery–petrochemical complex interface. These applications will also be highlighted.
The influence of the nature and amount of basic, nitrogen-containing organic molecules (pyridine, 2,6-dimethylpyridine, and quinoline) in the feed on the activity and selectivity of a series of ultrastable Y zeolites during n-heptane cracking has been studied. The effect of the framework SiO//2/Al//2O//3 ratio and procedure of dealumination on the resitance of the Y zeolite to deactivation are described and the results compared with those obtained with other zeolites such as Beta and H-ZSM-5. The observations have been extrapolated to a gas oil cracking, and it is predicted that the selectivity to gasoline and the RON decreases when increasing the nitrogen content in feed and the proton affinity of the poisons.
A new technique has been developed for characterizing the carbonaceous compounds deposited in zeolites, responsible for their deactivation ("coke"). The technique consists in treating the coked samples at room temperature by a so1ution of hydrofluoric acid at 40 % in order to disso1ve the zeo1ite and to liberate the internal "coke". This treatment does not cause any transformation of the carbonaceous compounds as shown by the tests carried out wi th two reactive hydrocarbons: l-tetradecene and 9-methylphenanthrene impregnated on an inert solid. The soluble components of "coke" extracted by an organic solvent (CH2Cl2) are analyzed by classical techniques: G.C., H.P.L.C., H-N.M.R., M.S.. Two examp1es are gi ven here to show the interest of thi s techni que. The fi rst concerns the effect of the reaction temperature (120-450°C) on the composition of the "coke" formed during propene transformation on a USHY zeolite ; the reactional steps involved in "coke" formation were able to be defined. In the second example, the mode of deactivation of three protonic zeolites : USHY, Hmordenite and HZSM5, during dimethyl ether conversion into hydrocarbons, was specified by using results obtained from adsorption measurements on the "coked" zeolites and from analysis of the carbonaceous compounds.
A qualitative explanation of the low dehydrogenation/cracking ratio observed in reactions with long-chain n-alkanes catalyzed by superacids is attempted via calculation of the MINDO/3 reaction profiles for the complete dehydrogenation ⇆ intermolecular interconversion ⇆ cracking (D.I.C.) set of unimolecular processes that a protonated n-alkane can undergo. It is shown that the three simplest systems can suitably model all possible D.I.C. surfaces that can be found in a long-chain linear alkane. The importance of the primary protonation site in the distribution of products is discussed.Some experimental results from cracking of n-heptane over a set of acid zeolites are used, together with those of this theoretical study, to show that a recent controversy about the presence of methane and hydrogen as primary or secondary products in saturated alkane cracking catalyzed by zeolites can be settled.
2,6-Dimethylpyridine and pyridine adsorption on CaY, HY and NaY zeolites is followed by quantitative infrared spectroscopy. 2,6-Dimethylpyridine reacts selectively with the hydroxyl groups. After adsorption of the base at temperatures from 25 up to 400 °C the OH groups are titrated first and only thereafter the Lewis sites interact with the base. The selectivity of pyridine towards Brønsted and Lewis sites is much less pronounced. Infrared identification of the ion or of the Lewis bound base was made through the frequency shift of the ν8a and ν8b vibrations.Poisoning with 2,6-dimethylpyridine of the cumene cracking activity of the HY samples amounts to an upper limit of active sites of 1.8 × 1020 per gram. This number is much lower than the amount titrated with pyridine.
The rate of isotopic exchange between H2 and D2 was followed over NaY, NaX, HY, hydrolyzed HY and LaY zeolites with controlled amounts of iron impurities.
Two maxima have been observed in the equilibration rates, one after activation at 520 °C, and another at 670 °C. At the two maxima, a linear correlation was found between equilibration rates and the iron content of the respective catalysts. The active sites at the first maximum were assumed to be cationic iron, while the activity at the second maximum was ascribed to an iron oxide species. Evaluation of the kinetic parameters showed that the data are consistent with a Bonhoeffer-Farkas mechanism.
A method for the decomposition/deconvolution of the OH region of the infrared spectrum of US-Y is proposed. it is based on the stepwise thermodesorption of ammonia combined with FTIR. The analysis shows that the complex IR band from Bronsted acid sites in US-Y can be deconstructed into acidic and nonacidic parts. The acidic part, in its turn, consists of four overlapping bands. These correspond to the conventional OH groups in siliceous zeolite Y (at 3627 and 3554 cm-1) and to hydroxyls associated with enhanced acidity, which has been attributed to the interaction of extraframework aluminum species with framework Bronsted sites.
A kinetic study of hydrogen transfer and isomerization reactions has been carried out for cyclopentene and cyclohexene. For both cycloolefins, the limiting step of hydrogen transfer is the hydride ion transfer. Isomerization of cyclohexene is rate limited by the proton transfer from a methylcyclopentyl cation to a cycloolefin molecule. Decay parameters have been determined as a function of temperature. Activation energies have also been measured.
The ratio of cracking to hydrogen transfer for n-heptane and gasoil increases with increasing dealumination of HYUS samples. In gasoil cracking, a sharp increase in this ratio occurs for samples with less than 10 Al per unit cell (uc). The adsorption of n-butane and 1-butene on HYUS samples shows that the amount of these gases adsorbed decreases with increasing dealumination. A decrease in the effective concentration of the product on the zeolites would favour monomolecular (cracking) over bimolecular (hydrogen transfer) reactions. The ratio of 1-butene to n-butane adsorbed decreases considerably below 10 Al/uc, indicating a less selective adsorption of olefins with respect to paraffins when the hydrophobicity (framework silicon-to-aluminium ratio) of the zeolites increases. These adsorption effects have an important influence on the cracking-to-hydrogen transfer ratio observed, as the hydrogen transfer reactions necessarily involve olefins, whereas cracking of n-heptane at low conversions and of paraffinic gasoil involves mainly paraffins.
This review paper presents the significant advances which were made in the last decade in the understanding of the transformation over acid and bifunctional zeolite catalysts of the cheap and readily available C2–C4 alkanes into more valuable products: mechanism of activation, reaction scheme, nature of the active sites. Both the transformations of pure alkanes: n-butane isomerization, C2–C4 alkane aromatization and of alkanes in mixture with alkenes: isobutane–butene alkylation or with aromatic hydrocarbons: benzene alkylation with ethane or propane are considered.
In this research work the deactivation of an H-MFI (Si/Alfr = 12) zeolite was studied during the methylcyclohexane transformation at 350 °C. Besides the normal activity decay with time on stream due to the formation of coke molecules, the poisoning with three nitrogen basic compounds (3-methylpyridine, quinoline and 2,6-dimethylpyridine) was studied. All three bases cause a strong decrease in conversion. The decrease in activity is proportional to the amount of nitrogen retained in the zeolite. On the other hand, the intrinsic poisoning effect of the bases seems to correlate well with its proton affinity, following the order: 2,6-dimethylpyridine > quinoline > 3-methylpyridine. Although the relatively small pores of the MFI structure, until a saturation amount, the total injected amount of nitrogen bases stays in the zeolite in the protonated form. Even so, results show that the bulkier base cannot penetrate as deep into zeolites crystallites and accumulates on the external surface which can partially explain its higher poisoning ability. Besides the actual bases, no nitrogen coke molecules were found by GC–MS coupling; soluble coke molecules were polyaromatics with 2–4 rings.
1. Basic organic nitrogen compounds, such as quinoline, are held on silica-alumina (-magnesia, -zirconia) catalyst surfaces by physical and chemical forces. These forces are widely different so that at 250-500° the physically-held quinoline can be distinguished from that chemically-held. At a given temperature the amount of physically-held nitrogen compound is increased with an increase in its partial pressure. The amount chemisorbed is decreased with an increase in temperature. 2. The cracking activity of the catalysts studied was proportional to their capacity to chemisorb quinoline at cracking temperatures. 3. Catalysts which have basic nitrogen compounds chemisorbed or which have potassium added by base exchange are poisoned for cracking. From a study of partial poisoning an exponential relationship was found between the amount of certain nitrogen compounds chemisorbed and the yield of benzene from the dealkylation of cumene. 4. A relatively small fraction of the total surface of silica-metal oxide cracking catalysts is responsible for catalytic activity. The chemical properties exhibited by this part of the surface identify the active principle as an "acid.".
The characterization of industrial coked resid fluid catalytic cracking (RFCC) catalysts is reported. The aim is to provide insight into the coke deposition on commercial resid fluid catalytic cracking catalysts sampled after the stripper of a commercial RFCC unit and to relate it to the potential process chemistry. Physicochemical techniques were used to characterize the used catalysts and the deposited coke. 95% of the coke was insoluble in CH2Cl2. This coke was located in the mesopores of the catalyst matrix. The results suggest the existence of domains of polyaromatic and heterogeneously distributed coke, in which saturated hydrocarbons are trapped. IR spectroscopy of adsorbed pyridine shows that the largest fraction of strong Brønsted acid sites is free after the catalyst has passed the stripper. The results indicate that for RFCC not the local deactivation of the acid sites but rather blocking of domains of the catalyst is the most important mode of deactivation after passing through the riser reactor.
The regeneration of FCC catalysts leads to significant NOx emissions. Hence, the identification of surface deposits and reaction intermediates is important for understanding the mechanisms by which nitrogen-containing species are converted into NOx or N2. Characterization of the feed and of carbonaceous deposits on spent FCC catalysts by IR and NMR spectroscopy as well as by (MA)LDI-TOF mass spectrometry showed that polyaromatic pyrrole derivatives (alkylcarbazoles, alkylbenzocarbazoles, alkylindoles) are the main source of nitrogen in the feed of FCC units. Consequently, (poly-)aromatic compounds (m/z = 350−850) such as carbazole and quinoline derivatives are the main nitrogen-containing components in the coke. During oxidative regeneration, these pregraphitic species are converted into smaller aromatic compounds similar to the nitrogen molecules originally present in the feedstock. With increasing temperature, nitrogen-containing coke species accumulate on the catalyst surface and can only be removed by oxidative regeneration at 550−700 °C.
In a paper of the same title, Fu and Schaffer reported on the poisoning effects of more than 30 individual nitrogen and aromatic compounds on cracking catalysts. A significant outcome of their study was a database on the relative poisoning potency of a variety of nitrogen compounds. On the basis of the database, this study was aimed at correlating the poisoning power of nitrogen compounds with their structures. For each compound, we determined 24 structural variables; of these, the dominant ones were identified by a chemometric technique. This provides a basis for developing a simple nonlinear correlational model for practical applications. It is shown that the poisoning power of a nitrogen or aromatic compound is primarily determined by a balance between its heaviness/size and basicity. The former may be measured by molecular weight, while the latter by proton affinity.
The individual effects of over 25 different nitrogen compounds were studied. It was demonstrated that not all nitrogen compounds are equally harmful. There is a good correlation between a molecule's gas phase proton affinity and its effect on cracking. Moreover, proton affinities can be used to explain how poisoning depends on the structure of the nitrogen compound. For example, it was shown that such factors as the type of nitrogen heterocyclic (pyrrolic or pyridine) and the size of the molecule are important. Thus, in order to predict the effect of nitrogen in an fluid catalytic cracking feed, it is not sufficient to use the total N (or even basic nitrogen) concentration. Quantitative predictions on the effects of nitrogen will, therefore require a better understanding of the specific structures of the nitrogen containing compounds in the FCC feed. (JMT)
Some effects of nitrogen poisoning and recycle on the kinetics of catalytic cracking of gas oils have been established. The dependence of catalyst decay and cracking rate constants on these two parameters have been quantified. Nitrogen poisoning slightly reduces the catalyst decay constant but significantly lowers the rate constants for gas oil cracking, gasoline formation, and gasoline cracking. Recycle addition increases (on total feed basis) the rate constants and catalyst decay for gasoline cracking and reduces those for gas oil cracking and gasoline formation.
A predictive kinetic model has been developed for fluid catalytic cracking (FCC). The kinetic scheme involves lumped species consisting of paraffins, naphthenes, aromatic rings, and aromatic substituent groups in light and heavy fuel oil fractions. The kinetic model also incorporates the effect of nitrogen poisoning, aromatic ring adsorption, and time dependent catalyst decay. The rate constants for these lumped species are invariant with respect to charge stock composition. The predictive capabilities of the model have been verified for wide ranges of charge stocks and process conditions.
Selective adsorption of pyridine was studied by infrared (IR) spectroscopy at 470 K on a series of HY zeolites, including samples dealuminated either by isomorphous substitution or steaming followed by acid leaching. Molar extinction coefficients of framework hydroxyls at high and low frequency, ϵHF and ϵLF, and of pyridinium ions characterized by the 1545 cm−1 band, ϵpyH+, were determined. These values do not vary with the Si/AlF ratios. In the case of steamed samples, strongly acidic sites give rise to additional OH bands at 3596 and 3522 cm−1. Pyridine adsorption at 620 K allows their mean molar extinction coefficient, ge3596 + 3522, to be determined. From the decomposition/deconvolution of the v(OH) massif of acidic OH groups, it is possible to count each type of acidic OH group and, by comparison with the number of framework Al per unit cell, to determine the cationic charges of extraframework Al-containing species counterbalancing the negative framework charge. This study evidences the substantial contribution of the (3522)OH groups; moreover, the results are in agreement with the assumption that 3596 and (3522)OH bands are due to the shift of the HF and LF framework hydroxyls, respectively, provoked by the presence of extraframework species.
The composition of coke and its effect on the acid sites were determined with samples of a USHY zeolite (with total and framework Si/Al ratios of 3.1 and 5.4, respectively) used for m-xylene transformation at 520 and 720 K. At low coke contents, coke is mainly constituted by methyl substituted polyaromatic compounds with three (520 K) or four (720 K) aromatic rings trapped in the zeolite pores. Coke causes a decrease in the intensity of the IR hydroxyl band. The most acidic hydroxyls, i.e., the bridging hydroxyls in interaction with extra-framework aluminum species are most affected by coke, whereas no interaction is observed between the non-acidic hydroxyls and the coke molecules. Pyridine adsorption shows that, while the number of protonic sites able to retain pyridine adsorbed decreases by coking, this was not the case for the Lewis sites. Pyridine adsorption facilitates the desorption under vacuum of coke molecules from the coked zeolites, the effect being more significant for coking at 520 K. This indicates that the retention of coke molecules is not only due to their low volatility (at 520 K) or to their steric blockage (720 K), but also to their adsorption on the acid sites.
Zeolites play an important role in many catalytic processes of modern refining and petrochemistry. Their shape selectivity
is always a key factor and here we look at the ways it operates in the principal processes either industrialized or with a
good industrial potential: cracking, hydrocracking, isomerization of short or long paraffins and of butene, aromatic transformations
by isomerization, disproportionation/transalkylation, and alkylations.
The modes of formation of carbonaceous deposits (“coke”) during the transformation of organic compounds over acid and over bifunctional noble metal-acid catalysts are described. At low reaction temperatures, (<200°C) “coke” formation involves mainly condensation and rearrangement steps. Therefore, the deposits are not polyaromatic and their composition depends very much on the reactant. The retention of the “coke” molecules on the catalysts is mainly due to their strong adsorption and to their low volatility (gas-phase reactions) or to their low solubility (liquid-phase reactions). At high temperatures (>350°C), the coke components are polyaromatic. Their formation involves hydrogen transfer (acid catalysts) and dehydrogenation (bifunctional catalysts) steps in addition to condensation and rearrangement steps. On microporous catalysts, the retention of coke molecules is due to their steric blockage within the micropores.
The influence of 0.5 wt.% of quinoline (540 ppm of nitrogen) in the feed was tested for the methylcyclohexane transformation at 350 °C over an H-USY zeolite (framework Si/Al ratio of 5.4). The selectivities for the fresh catalyst do not seem to be altered by the presence of quinoline. Oppositely, for the deactivated zeolite, the aromatics yield increases for the tests performed with quinoline. Deactivation with time on stream is very pronounced, even for tests carried out without the base molecule; this can be attributed to the formation of highly polyaromatic coke molecules that block the acid sites and the microporous structure. In presence of quinoline, deactivation is enhanced due to its cumulative poisoning effect, especially for smaller contact times. This deactivation is caused by the strong interaction of the nitrogen base with the Brønsted acid sites responsible for the cracking mechanism. Quinoline molecule also participates in coke formation reactions, leading to an increase in the produced amount of coke, particularly of the more polyaromatic compounds insoluble in dichloromethane.
A vacuum gasoil has been cracked on USY containing catalysts in which the matrix is either an amorphous silica-alumina or an aluminium containing sepiolite. After steaming, the aluminous sepiolite containing catalyst is more active and selective than the silica-alumina one, and the former produces a gasoline with higher alkenes and lower aromatics content. When those catalysts were used to crack a vacuum gasoil containing 5000 ppm of basic nitrogen, the catalyst with the aluminous sepiolite was more efficient to trap the poisoning molecules, preserving the zeolite activity. It was confirmed by IR spectroscopy that the aluminous sepiolite removes higher amounts of basic nitrogen compounds than amorphous silica-alumina. With the high nitrogen containing feed, the sepiolite catalyst gives a higher cracking conversion, while it is more selective to middle distillates than the amorphous silica-alumina. Finally, in the presence of basic nitrogen the former gives a higher content of linear and branched alkenes in the gasoline fraction.
The deactivation of a standard 4-component FCC catalyst has been examined using a MAT reactor for a number of additives to a n-hexadecane feedstock. The additives included, benzofuran, indene, phenanthrene, quinoline and thianaphthene and were present at levels of 1% and 10% in the feedstock. Conversions decreased with all additives, but the most severe reduction occurred with quinoline. Benzofuran and indene gave most coke formation and analysis of the coke deposited on the catalyst indicated that this was initially mainly aliphatic in nature.A simple model has been developed for the coke deactivation process, which suggests that for the present results the major deactivation effect occurs in the production of C5–C6 hydrocarbons.
In this work, the hydrogen transfer activity of two series of HY zeolites dealuminated by steam and by SiCl4 (24.47-24.24 Å unit cell) has been measured from the butene/butane ratio in the products obtained during the cracking of a vacuum gas oil at 756 K. With the steam-dealuminated zeolites, a sharp decrease in the ratio of hydrogen transfer to cracking is observed when the number of Al atoms per unit cell falls below 10. On the other hand, in samples dealuminated by SiCl4, this ratio changes very little with dealumination. These results cannot be explained assuming the need for adjacent acid sites for the hydrogen transfer. We have found, by adsorption measurements of n-butane and 1-butene, that the changes in the relative rates of bimolecular (hydrogen transfer) to monomolecular (cracking) reactions, observed with dealuminated HY zeolites, can be explained by the changes in the adsorption capacity and adsorption selectivity which occur on zeolites dealuminated at different levels by different dealumination procedures, and which are due to changes in the electric fields inside the pores.
A study of the reactions of n-octane and n-dodecane on HY zeolite has shown that molecular hydrogen is not formed as an initial product of catalytic cracking of n-paraffins on this zeolite. Hydrogen gas was not detected as a product at any level of conversion up to 25% at 400 °C. The observation of hydrogen as an initial product by other workers may be related to the presence of a hydrogen at a tertiary carbon in the reactant molecules used in such studies. Initial molar ratios of paraffin/olefin in the cracking products were found to be other than unity, confirming previous reports. However, consideration of the selectivities of all primary products formed, including the aromatics and coke, shows that the overall hydrogen balance closes without stoichiometric anomalies or the requirement that hydrogen ions associated with the active sites of the catalyst are consumed irreversibly.
The oil crisis of recent times has caused a drastic decrease in the total consumption of oil and changed the demand pattern for the products of petroleumrefining. The demand for heavier fractions or residual oils has steadily decreased, making it imperative to convert these into gasoline, diesel and such lighter fractions. Fluid catalytic cracking (FCC) of these heavier fractions, however, poses several serious problems, caused mainly by their much higher hetero-atom concentration, metal contents and coking tendency, as compared to earlier feedstocks. Several process and catalyst innovations have been made to tackle these problems. A new generation of FCC catalyst technology has emerged with tailor-made catalysts for higher structural stability and attrition strength, more complete CO combustion during regeneration, reducing SOx emissions from FCC stacks, enhancing the gasoline octane number, passivating the harmful effects of metals like Ni and V accumulating on the catalyst, etc., These developments contain valuable lessons for the science and technology of catalysis.
A kinetic model has been developed to describe the product distribution of the reaction of cyclohexene on acidic zeolite catalysts. The model was used to estimate the rate constants for hydrogen transfer, isomerization, oligomerization, cracking and coking for various zeolite catalysts. Over Y-zeolites, the selectivity toward hydrogen transfer increases by a factor of 1.7 as the number of Al atoms per unit cell increases from 4.6 to 33.4. The selectivity toward hydrogen transfer can be correlated with the fraction of paired Al sites in the zeolite as estimated by a statistical calculation. Over zeolites of comparable silica to alumina ratio, the ratio of isomerization selectivity to hydrogen transfer selectivity was the highest for H-ZSM-5, followed by H-beta and REUSY.
A technique for the quantitative determination of adsorbed species on zeolites and other solids was designed by coupling infrared spectroscopy and in situ thermogravimetry. The weight of H-Y zeolites in an infrared spectrometer was monitored upon pyridine adsorption by a McBain type microbalance. Improved extinction coefficients for the pyridinium band and for ν(OH) bands were determined on these reference materials. The influence of the temperature used for desorption of physisorbed pyridine was studied.
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