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Chemical Reaction Engineering and Kinetics
... The Ha represents the ratio between the reaction rate in the liquid phase and the physical mass transfer rates (Levenspiel, 1999). Depending on the value assumed by the Hatta number, we can have a very slow kinetic regime (Ha <0.3, reaction occurring entirely in the liquid bulk), a very fast kinetic regime (Ha >3, reaction occurring entirely in the liquid film) or an intermediate regime (reaction occurring both in the bulk and in the film) (Charpentier, 1981;Missen et al., 1999;Zarzycki and Chacuk, 1993). Once the kinetic regime has been determined, to quantify the effects of a chemical reaction in the liquid phase, the Enhancement Factor (E L ) is recommended in several textbooks and papers available in the literature (Charpentier, 1981;Flagiello et al., 2023a;Levenspiel, 1999;Missen et al., 1999;Zarzycki and Chacuk, 1993). ...
... Depending on the value assumed by the Hatta number, we can have a very slow kinetic regime (Ha <0.3, reaction occurring entirely in the liquid bulk), a very fast kinetic regime (Ha >3, reaction occurring entirely in the liquid film) or an intermediate regime (reaction occurring both in the bulk and in the film) (Charpentier, 1981;Missen et al., 1999;Zarzycki and Chacuk, 1993). Once the kinetic regime has been determined, to quantify the effects of a chemical reaction in the liquid phase, the Enhancement Factor (E L ) is recommended in several textbooks and papers available in the literature (Charpentier, 1981;Flagiello et al., 2023a;Levenspiel, 1999;Missen et al., 1999;Zarzycki and Chacuk, 1993). It is defined as the ratio between the actual mass transfer rate in the presence of chemical reactions in the liquid phase (chemical absorption) and the corresponding mass transfer rate in the presence of only diffusive and convective phenomena (physical absorption) (Charpentier, 1981;Missen et al., 1999;Zarzycki and Chacuk, 1993), thus embedding all chemical reactions' effects in a single factor. ...
... Once the kinetic regime has been determined, to quantify the effects of a chemical reaction in the liquid phase, the Enhancement Factor (E L ) is recommended in several textbooks and papers available in the literature (Charpentier, 1981;Flagiello et al., 2023a;Levenspiel, 1999;Missen et al., 1999;Zarzycki and Chacuk, 1993). It is defined as the ratio between the actual mass transfer rate in the presence of chemical reactions in the liquid phase (chemical absorption) and the corresponding mass transfer rate in the presence of only diffusive and convective phenomena (physical absorption) (Charpentier, 1981;Missen et al., 1999;Zarzycki and Chacuk, 1993), thus embedding all chemical reactions' effects in a single factor. Different expressions for the Enhancement factor correlated to the Hatta number can be adopted depending on the reaction kinetic regime established in the liquid phase (Flagiello et al., 2023a;Missen et al., 1999;Zarzycki and Chacuk, 1993). ...
This study is part of the research activities devoted to the development of new gas-cleaning technologies required
to minimize the emissions factors of sulfur compounds in chemical industries and power plants. Among flue gas
desulfurization (FGD) processes, wet scrubbing with oxidizing chemicals, e.g. sodium chlorite (NaClO2) has
appeared as a viable option for different applications. The present work aims to study the absorption kinetics of
the gas-liquid reaction between sulfur dioxide (SO2) and NaClO2, in a lab-scale falling-film absorber, investigating
the effects of the main process parameters: liquid and gas flow rates, SO2 gas-phase concentration, NaClO2
liquid-phase concentration, solution pH and process temperature. The experimental activity aims to determine
the Enhancement Factor (EL) to develop a kinetic model for reactive absorption. To this end, kinetic parameters
are calculated from experiments using the Danckwerts equation for a pseudo-second-order reaction kinetic,
determining a maximum prediction error of ±20% compared to the experimental data. Experimental data
available in the literature on pilot-scale oxidative FGD scrubbers using chlorite are used to test the validity and
robustness of the kinetic model. The kinetic model is able to predict the data with good accuracy within a
prediction error range of ±30%.
... This specific situation requires an evaluation of the catalyst effectiveness factor in each position in the catalytic bed, considering the conditions we have at any instance in that point. This subject has been previously described in many books, papers, and reviews [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]. A modern and comprehensive approach to the problem, with many solved exercises, can be found in [1]. ...
... The effectiveness factor can also be evaluated experimentally by determining the reaction rate in the presence of catalyst pellets of different diameters and on finely powdered catalyst operating in chemical regime: η = rate observed for a given particle size rate observed in chemical regime on powdered catalyst (16) We have already seen that inside the catalyst particle, in correspondence to any concentration gradient, a temperature gradient is associated, determinable with Equations (5) or (6). The evolution of the effectiveness factor with the Thiele and Weisz moduli, reported in Figures 3 and 4, corresponds The effectiveness factor can also be evaluated experimentally by determining the reaction rate in the presence of catalyst pellets of different diameters and on finely powdered catalyst operating in chemical regime: η = rate observed for a ginen particle size rate observed in chemical regime on powdered catalyst (16) We have already seen that inside the catalyst particle, in correspondence to any concentration gradient, a temperature gradient is associated, determinable with Equations (5) or (6). ...
... The effectiveness factor can also be evaluated experimentally by determining the reaction rate in the presence of catalyst pellets of different diameters and on finely powdered catalyst operating in chemical regime: η = rate observed for a given particle size rate observed in chemical regime on powdered catalyst (16) We have already seen that inside the catalyst particle, in correspondence to any concentration gradient, a temperature gradient is associated, determinable with Equations (5) or (6). The evolution of the effectiveness factor with the Thiele and Weisz moduli, reported in Figures 3 and 4, corresponds The effectiveness factor can also be evaluated experimentally by determining the reaction rate in the presence of catalyst pellets of different diameters and on finely powdered catalyst operating in chemical regime: η = rate observed for a ginen particle size rate observed in chemical regime on powdered catalyst (16) We have already seen that inside the catalyst particle, in correspondence to any concentration gradient, a temperature gradient is associated, determinable with Equations (5) or (6). The evolution of the effectiveness factor with the Thiele and Weisz moduli, reported in Figures 3 and 4, corresponds to isothermal conditions. ...
The tremendous progress in the computing power of modern computers has in the last 20 years favored the use of numerical methods for solving complex problems in the field of chemical kinetics and of reactor simulations considering also the effect of mass and heat transfer. Many classical textbooks dealing with the topic have, therefore, become quite obsolete. The present work is a review of the role that heat and mass transfer have in the kinetic studies of gas–solid catalytic reactions. The scope was to collect in a relatively short document the necessary knowledge for a correct simulation of gas–solid catalytic reactors. The first part of the review deals with the most reliable approach to the description of the heat and mass transfer outside and inside a single catalytic particle. Some different examples of calculations allow for an easier understanding of the described methods. The second part of the review is related to the heat and mass transfer in packed bed reactors, considering the macroscopic gradients that derive from the solution of mass and energy balances on the whole reactor. Moreover, in this second part, some examples of calculations, applied to chemical reactions of industrial interest, are reported for a better understanding of the systems studied.
... From the experimental point of view, this source states that concentration-time profiles are measured and from them rate equations are deduced. Missen et al. (1999) operate with the extensive rate of reaction with respect to a species A that "is the observed rate of formation of A" (the intensive rate is obtained by referring, for example, to the unit reaction volume or the unit mass of catalyst). For simple (in fact, stoichiometric) reactions, they present the rate of reaction as the component rates divided by the corresponding stoichiometric coefficients. ...
... Of the monographs and textbooks referred to above, only that by Missen et al. (1999) provides some basic information on the number of independent chemical reactions (chemical equations in their terminology) and states that "[a] proper set of chemical equations for a system is made up of linearly independent equations" and that "stoichiometry tells us the maximum number of independent rate laws that we must obtain experimentally." ...
... This was realized, e.g., byMissen et al. (1999) who state that stoichiometry gives the minimum number of species to be analyzed.Frontiers in Chemistry | www.frontiersin.org ...
Linear algebra treatment of the permanence of atoms (mass conservation) naturally leads to the transformation of formation or destruction rates of components of a reaction mixture into rates of reaction steps, which are sufficient to describe the transformations mathematically. These steps form a scheme of independent reactions that can provide a rational basis for elucidating the reaction mechanism (network) while reducing both the component and parametric dimensionality of the description of kinetics. Several particular reaction examples are used to explain the method and show that rates of additional, dependent reactions cannot be unambiguously related to measured component rates. They also illustrate how the rates of dependent reactions can be correctly expressed in terms of the rates of independent reactions. The method starts only with a knowledge of the components of a reaction mixture. It is argued that the design of consistent reaction networks or mechanisms should take into account not only chemistry but also mathematics.
... Example 1: The first example is the Example 21-3 of CHE333 [3]: And the following data: ...
... 1 + 1 1 − 1 ( 13 + 12 + 1 + 1 ) + 2 21 + 3 31 = 0 2 + 2 2 − 2 ( 2 + 2 + 21 + 24 ) + 1 12 + 3 32 + 4 42 = 0 3 unknowns is involved. While simple substitution would suffice Example 2 problem, this method is used to illustrate its robustness and effectiveness, especially dealing with even larger system where simple substitution would be way too tedious. ...
... Unlike Example 1, the form of the formulae is too complex to have analytic solution. This requires numerical method to solve, as suggested by the textbook [3]. The following is the compiled algorithm: Figure 23 The further explained calculation procedure for fluidized bed reactor sizing ...
... Pore diffusion limited reactions exist when the supply of reactants to the active sites within the particle is limiting the rate (2 or 6) usually at moderate temperatures. Finally, at the highest temperature, chemical reactions and pore diffusion rates are so fast the reaction is considered limited by bulk mass transfer (1)(2)(3)(4)(5)(6)(7). ...
... The overall kinetics of a heterogeneous catalytic reaction can be controlled by any of the seven steps listed above [7][8][9][10]. We can distinguish that which rate is controlling by determining the temperature dependence of the reaction. ...
... There is also an Eley-Rideal mechanism where the chemisorbed species reacts with a gas phase molecule and the combination rapidly converts to the final product. There are many kinetic models that describe different mechanisms and the reader is directed to some outside references [7][8][9][10]. ...
Every college student of chemistry, material science, and chemical engineering should be schooled in catalysis and catalytic reactions. The reason is quite simple; most products produced in the chemical and petroleum industries utilize catalysts to enhance the rate of reaction and selectivity to desired products. Catalysts are also extensively used to minimize the harmful byproduct pollutants in environmental applications. Enhanced reaction rates translate to higher production volumes at lower temperatures with smaller reactors and less exotic materials of construction necessary. When a highly selective catalyst is used, large volumes of desired products are produced with virtually no undesirable byproducts. Gasoline, diesel, home heating oil, and aviation fuels owe their performance quality to catalytic processing used to upgrade crude oil. Intermediate chemicals in the production of pharmaceutical products utilize catalysts as well as the food industry in the production of every day edible products. Catalysts are playing a key role in developing new sources of energy and a variety of approaches in mitigating climate change and CO2 upgrading.
... Experimental work of sacrificial anode system was carried out to determine the consumption rate of zinc in artificial sea water (4% NaCl/distilled water) using weight loss for various conditions of temperature (0-45°C), flow rate (5-900 L/h), pH (2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12) and time (1-4 h). Working electrode was tube specimen of low car bon steel with dimensions of 13.50 cm length, 2.68 cm inside diameter and 0.31 cm thick. ...
... where k is rate constant and n is the order of reaction. Equation (10) can be drawn as shown in Fig. 7 at 5 L/h and pH 2, and the values of slope and intercept can be obtained. The values of rate constants were 1, 0.5, 0.35 and 0.25 h -1 at 45, 30, 15 and 0°C respectively. ...
... Therefore, this method is not suitable for the determination of order of a reac tion as well as the value of the rate constant. It is best to find a method where concentration and time can be substituted directly to determine the reaction orders [10]. The reaction rates can also be expressed in terms of half life or half life period t 1/2 . ...
... The Eq. (7) can be solved based on the following boundary conditions: [21] At x = 0, C NO = C NO, i , and x = , C NO = C NO, L . ...
... The rate of transfer or flux of NO into the liquid film, N NO (x = 0), equals the diffusion rate at the gas-liquid interface: [7,21] ...
... The following correlations (Eqs. (20)(21)(22)) are developed by López-López et al. [22] for gas hold-up and liquid phase mass transfer. ...
Aims: In present study, the mass transfer-reaction kinetic parameters of nitric oxide (NO) removal by ultraviolet (UV)/H 2 O 2 process in a bubble column reactor in the presence of SO 2 are calculated.
Materials and Methods: The mass balance equation for NO through a layer thickness of δ, under the steady state condition is solved, and NO absorption rate is calculated. The value of rate constants and Ha numbers are obtained based on experimental data under different conditions.
Results: The calculations indicate that the values of Ha number are >3. The values of rate constants (k obs) are fitted to some empirical equations for different operating conditions. It is observed that the value of k obs increases with an increase in H 2 O 2 concentration and UV radiation intensity while it decreases with an increase in NO and SO 2 inlet concentrations. The values of rate constants are in order of 10−5 , expect for SO 2 , which are in order of 10−7 . The results reveal that there is a good agreement between calculated and experimental values where the maximum absolute error is 16.18% related to UV light intensities between 0 and 0.012 W/m 3 .
Conclusion: The obtained values of Ha numbers under different condition confirm that the absorption process of gas in the liquid phase is a fast reaction. The maximum error values resulted from a comparison between the calculated NO absorption rates and the experimental ones are acceptable.
... For the batch reactor experiments, the fractional conversion of gaseous naphthalene is given by [36] ...
... The Thiele Modulus and effectiveness factor can be determined for the paint experiments. The major assumption for the calculation include: a flat plate geometry, reaction occurs on and within the paint material but only at catalyst particle, surfaces, a first-order irreversible reaction, and that the system is isothermal [36,38]. The Thiele Modulus is then calculated from the following equation [36]: ...
... The major assumption for the calculation include: a flat plate geometry, reaction occurs on and within the paint material but only at catalyst particle, surfaces, a first-order irreversible reaction, and that the system is isothermal [36,38]. The Thiele Modulus is then calculated from the following equation [36]: ...
The uses of metal oxide nanoparticles in modern paint and sunscreen formulations are widespread. Through materials characterization and kinetic experiments, it is demonstrated that fresh surface coatings of paint and sunscreen photocatalytically degrade gaseous naphthalene. The primary metal oxides are TiO2 in the form of the rutile phase in paint and as anatase in sunscreen formulations. Other metal oxides present are Al2O3 and ZnO. Several organic fillers that are photochemically active are also present in paint and sunscreen samples but are unidentified. Reaction rate constants increased with increasing air relative humidity, due to the production of surface hydroxyl radical, and decreased with increasing coating thickness, due to mass transfer limitations. Photocatalytic degradation on these freshly generated surfaces is observed to be fast, with naphthalene half-lives shorter than 30 minutes. This work demonstrates that large, semivolatile organic compounds can react photochemically on freshly generated paint- and sunscreen-coated surfaces and may impact air quality in both indoor and outdoor environments.
... Experimental work of sacrificial anode system was carried out to determine the consumption rate of zinc in artificial sea water (4% NaCl/distilled water) using weight loss for various conditions of temperature (0-45°C), flow rate (5-900 L/h), pH (2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12) and time (1-4 h). Working electrode was tube specimen of low car bon steel with dimensions of 13.50 cm length, 2.68 cm inside diameter and 0.31 cm thick. ...
... where k is rate constant and n is the order of reaction. Equation (10) can be drawn as shown in Fig. 7 at 5 L/h and pH 2, and the values of slope and intercept can be obtained. The values of rate constants were 1, 0.5, 0.35 and 0.25 h -1 at 45, 30, 15 and 0°C respectively. ...
... Therefore, this method is not suitable for the determination of order of a reac tion as well as the value of the rate constant. It is best to find a method where concentration and time can be substituted directly to determine the reaction orders [10]. The reaction rates can also be expressed in terms of half life or half life period t 1/2 . ...
Corrosion of steel tube in sea water was controlled by cathodic protection. Sacrificial anode technique was used. In this technique, weight loss method was used to determine the rate of zinc consumption as a function of temperature, time, pH and solution velocity. Reaction kinetics studies showed that the rate of zinc consumption was first order. Activation parameters were obtained from Arrhenius equation and transition state equation. Two mathematical models were suggested to represent the consumption data. Statistical analysis proved that the second-order multi-terms model was better than the one-term model.
... The amount of UO 2 2+ adsorbed was calculated by numerical integration of the BTC describing the UO 2 2+ concentration in time. The values were subtracted from the integration of the same curve describing the outflow concentration of an inert species, which is described by Eq. (3) in a perfectly stirred media (Missen et al., 1999): ...
... where t is the time, and t is the mean residence time given by the ratio between the reactor volume (V) and the flux (q). The equation of material balance for continuous stirred flow-through reactor within a constant density solution is given by Eq. (4) of Missen et al. (1999): ...
... The extensive rate of adsorption/desorption was obtained at any point in the experiment (for a reactor of volume V) by rearranging Eq. (4) according to Missen et al. (1999) as follows: ...
Adsorption of uranyl ions onto kaolinite, montmorillonite, humic acid and composite clay material (both clays
and humic acid) was studied by measuring the system response to clay suspensions (pre-equilibrated with or
without uranyl) and to perturbations of the solution chemistry. Adsorption behavior of selected materials
under the frame of batch experiments was tested at high uranyl concentrations (6–1170 μg/mL; 2.5 × 10−2 to
4.9 μM), whereas that under flow through continuous stirred reactor experiments was tested at low concentrations
(1.00 × 10−4 to 1.18 × 10−4 M). Both experiments were developed at pH 4.5 and ionic strength 0.2 mM.
The adsorption experiments follow a Langmuir isotherm model with a good correlation coefficient (R2 N 0.97).
The calculated amount of adsorbed and desorbed uranyl was carried out by numeric integration of the experimental
data,whereas the desorption rates were determined fromthe breakthrough curve experiments. Kaolinite
with highly disordered structure adsorbed less uranyl (3.86 × 10−6 mol/g) than well-ordered kaolinite
(1.76 × 10−5 mol/g). Higher amount of uranyl was adsorbed by montmorillonite (3.60 × 10−5 mol/g) and
only half of adsorbed amountwas desorbed (1.85 × 10−5 mol/g). The molecular interactions between kaolinite,
montmorillonite, humic acid, composite material and saturated uranyl ion solutions were studied by molecular
fluorescence, infrared and X-ray photoelectron spectroscopy. The Stern–Volmer constant obtained for montmorillonite
(2.6 × 103 M−1) is higher than for kaolinite (0.3 × 103 M−1). Molecular vibrations of Si\O stretching
and Al\OH bending related to hydroxylated groups (`SiOH or `AlOH) of kaolinite and montmorillonite
show structural changes when uranyl ions are adsorbed. X-ray photoelectron spectroscopy shows that the
U 4f7/2 core level signals occur at 380.5 eV in either kaolinite or montmorillonite that resulted from the interaction of aluminol surface sites with the (UO2)3(OH)5+.
... In each experiment, 1-pentanol conversion, selectivity to DNPE, and DNPE yield were computed. 1-pentanol conversion, X 1-PeOH , was defined as usually by [32] ...
... The overall fractional yield of DNPE with respect to 1-pentanol was selected as a measure of the selectivity of 1-pentanol towards DNPE. It was defined as [32] [30]. e Values obtained from molecular models [31]. ...
... Likewise, selectivity to alkenes (S ALKENES ), branched ethers (S ETHERS ), 2-pentanol (S 2-PeOH ), and pentene dimers (S DIMERS ), were defined. The yield of DNPE with respect to 1-pentanol was defined as [32] ...
The present paper deals with the liquid-phase synthesis of di-n-pentyl ether (DNPE) by dehydration of 1-pentanol over H-Beta, H-ZSM-5, H-mordenite and H-Y zeolites. Their SiO2/Al2O3 ratios were about 25 for H-Beta, 28 for H-ZSM-5, 35 for H-mordenite and 6 for H-Y. Experiments were performed in a batch reactor in the temperature range 140–180°C at 1.6MPa. Comparison of the catalysts behaviour shows that H-Beta is the most active and selective to DNPE, although it is less active than microporous ion-exchange resins. Kinetics of DNPE synthesis was studied. The best kinetic model for all the catalysts stems from a reaction mechanism whose rate-limiting step is the surface reaction between two 1-pentanol molecules adsorbed on adjacent sites, to yield DNPE and water both adsorbed on single site. Activation energy, on each single catalyst, was estimated to be in the range 94–118kJmol−1.
... The presence of the catalyst does not affect the Gibbs energy of reactants or product therefore it does not affect the equilibrium constant for the reaction (Missen et al., (1999)). ...
... These assumptions are based on the simplest rational explanation of surface catalytic kinetics and models are formulated by Langmuir and Hinshelwood (Missen et al., (1999)). Figure (2) represent Lamgmiur-Hinshelwood mechanism. ...
In this research hydrogenation kinetic of alpha-methylstyrene (AMS) on Pd/Al2O3
catalyst was studied. The reaction is mildly exothermic (ΔH=-109 kJ/mol). Intrinsic
kinetic law was investigated under wide range of operating conditions 0.1 and 0.2 gm
catalyst loading, 0.5-100 wt% AMS, 10, 15 and 20 bar pressure and 343-373 K
temperature.
The experiment data are fitted to estimate the kinetic parameters for different reaction
mechanisms by using ACM (Aspen Custom Modeler) software. Finally the results of
produced reaction mechanisms are compared with experimental results to obtain the
optimum reaction mechanism.
... Traditional cellulose hydrolysis models [12,23] have been based on the Shrinking Core Model [30]. Specifically, in the approach which considers that once that the liquid molecules reach the solid particles, the reaction is produced on their surface decreasing the solid mass. ...
Conventional kinetic models of cellulose hydrolysis in supercritical water do not accurately represent the operation with concentrated suspensions since they neglect the mass transfer effects. This work proposes a kinetic model which is able to reproduce cellulose hydrolysis at high concentrations providing the optimum reaction conditions to obtain nanocellulose particles and oligomers of controlled size. The basic idea of the model, which is applicable to other lignocellulosic materials, is that the hydrolysis of the cellulose particles generates an oligosaccharides layer which creates a mass transfer resistance. Therefore, it considers both the diffusion of the water molecules from the bulk phase to the surfaces of the cellulose particles and the superficial hydrolysis kinetics. Experimental points were obtained working with two different cellulose types (Dp = 75 µm and Dp = 50 µm) at 390 °C and 25 MPa, residence times between 50 ms and 250 ms and initial cellulose suspension concentration from 3% to 7% w/w (1% to 2.3% w/w at the inlet of the reactor). The average deviation between the experimental points and the theoretical values is lower than 10% proving the applicability of the kinetic model. The experimental and theoretical results demonstrated that increasing the total number of cellulose particles, either increasing the initial concentration or decreasing the average particle diameter, reduces the hydrolysis rate.
... The usual synthesis involves the reaction of syngas (carbon monoxide and hydrogen) over a highly selective catalyst which is in most cases made of copper, zinc oxide and alumina oxide. The exothermic, reversible, catalytic reaction usually takes place at 50–100 bar [6]. The equilibrium normally favours low temperatures, however, to achieve the highest conversion rates at present pressures a temperature of Here, the methanol synthesis is investigated two-fold: first by looking at the gaseous equilibrium of the synthesis at ambient pressure (section 2), second by reviewing data of experimental reactor set-ups (section 3). ...
... ([33] strand is 1.24 m min À1 . The volume fractions of all gas species are specified, and inlet pressure is defined as 1.0 atm. ...
A relatively more comprehensive 1D mathematical model, compared to previous models, is proposed for flue gas recirculation sintering (FGRS). The proposed model considers multiphase theory, eight major reactions significantly affected by the input gas conditions, and various heat transfer processes within/between different solid and gas phases. Characteristic size distributions of materials including coke, limestone and dolomite are used to correct the reaction rates of key sub-models, as well as specific kinetic parameters determined via thermogravimetric analysis instead of empirical values. Geometric changes caused by the reactive and melting factors are described in improved manners. This model is validated by contrasting the modeling results and the measured data from sinter pot tests. Parametric studies show FGRS technology can significantly enhance combustion characteristic within sinter bed, meaning to increase maximum temperature and melt fraction, improve the uneven distribution of heat. Therefore, the quality of sintered ore can be improved. However, the slightly reduced flame front speed deserves further attention. The velocity of input flue gas exerts the most significant effect, followed by O2 concentration, and then, temperature. The operating parameters of FGRS must be carefully determined. Three measures, which still require further investigations, can be proposed to optimize the process.
... Once the steady state flow field is obtained, the transport of a conservative tracer scalar quantity C is simulated by solving the three-dimensional Reynolds-averaged advection-diffusion equation. The turbulent Schmidt number is given the standard value of S c = 0.7 as suggested in Launder (1978). The low-diffusive and oscillation-free Hybrid Liner/Parabolic Approximation (Zhu, 1991) approximates the convective term and the central differencing scheme the diffusion term. ...
With the aim of optimising contact tank design through numerical model simulations, results are presented herein of an experimental and computational fluid dynamics (CFD) study in a scaled laboratory model. Three-dimensional numerical simulations of flow and transport characteristics were conducted using a Reynolds Averaged Navier-Stokes equation approach. Experimental results were obtained through Acoustic Doppler Velocimetry measurements and a series of conservative tracer experiments. Focus is given on turbulent structures and undesirable flow patterns that lead to a reduced disinfection efficiency, through phenomena such as short circuiting and recirculation zones. The laboratory data analysis indicates extensive three-dimensionality as a result of the current inlet geometry with a confirmed negative impact on the disinfection performance of the contact tank model, as demonstrated by Residence Time Distribution curves. Disinfection performance is evaluated through hydraulic efficiency indicators commonly used in the industry to monitor field-scale disinfection facilities. Correlations between CFD and experimental data confirm the adequate reproduction of hydrodynamic conditions and reinforce the predictive capabilities of numerical models as tools to simulate field scale tanks or optimize existing designs. 1 INTRODUCTION Serpentine contact tank units suggest plug flow to be the ideal hydrodynamic condition at which disinfection performance is maximized (Falconer and Tebbutt, 1986; Markse and Boyle, 1973). Under such flow conditions, disinfectant transport becomes ideal by remaining in the tank for a uniform time interval whilst achieving the desired disinfection. However, previous studies (e.g. Teixeira, 1993) indicate that flow exhibits a residence time distribution (RTD) which can be significantly different from what is dictated by plug flow. The shape of the tracer RTD curves can provide an insight into the hydrodynamic and mixing conditions, as explained by Levenspiel (1999). For example, the residence time at 10% cumulative RTD constitutes a crucial indicator (t 10) for the evaluation of disinfection efficiency and design suitability at water treatment works. Digression from plug flow can be attributed to the complex hydrodynamics, namely short-circuiting and recirculation zone formation (Kim et al., 2010). Short-circuiting occurs when particles pass through a reactor quicker than the theoretical hydraulic residence time. Recirculation zones not only promote short-circuiting (since they occupy a considerable part of the tank volume) but they also trap solutes and particles (or pathogens), which are then retained in the tank for a longer period than the theoretical hydraulic residence time. The occurrence of such flow patterns has a detrimental effect on the overall efficiency, because contact times of pathogens with the
... However, for the bed weights in the range of 150-250 g, a downfall in Umf was observed in these investigations. According to the Ergun equation (Kunii and Levenspiel 1991;Missen, Mims, and Saville 1998) initially high force is required to lift and fluidized the particles bed of increased weight. Once the bed enters into incipient regime, a slight decrease in velocity can takes place due to the settlement of the bed. ...
The increased biomass utilization has triggered the use of palm oil waste as fuel for gasification in Malaysia. In this study, pioneering work was conducted on three types of palm oil wastes namely palm kernel shell (PKS), palm oil fronds (POF) and empty fruit bunches (EFB). Minimum air velocity (Umf) required for fluidization of the tested biomass was determined experimentally in a swirling fluidized bed, by considering the effect of bed weight, density, particle size, fluidized bed height, pressure drop and bed voidage. It was revealed that higher is the particle size the smaller will be the voidage which consequently affect the minimum fluidization velocity. Umf was increased with a decrease in voidage size. However, a direct relationship was found between particle size and Umf. Overall highest Umf was determined for EFB followed by POF and PKS. Fluidized bed height was increased by decreasing the particle size regardless of the biomass type. Highest unsettled bed height was obtained with PKS on account of its low density among all the test fuels. It was concluded that optimization of the fluidized bed for each type of biomass, particle size and density is explicitly required for a low cost energy conversion process.
... Similarly, compar-665 ing the two catalysts, NiO x /Al 2 O 3 has comparably lower value. Ac-666 cording to collision theory[34], the higher values observed when 667 Ni/Al 2 O 3 was used could be due to the catalyst's inability to initi-668 ate faster reaction rates to use up the continuous inflow of H 2 gas, 669 hence the collision rate increases since the H 2 flow rate was kept 670 constant and the temperature was elevated. On the other hand, 671 the low A o observed in NiO x /Al 2 O 3 could imply that the H 2 gas 672 was quickly used up since NiO x /Al 2 O 3 has comparable higher reac-673 tivity. ...
The effect of ethanedioic acid (EdA) functionalization on Al2O3 supported Ni catalyst was studied on the hydrodeoxygenation (HDO), isomerization, kinetics and Arrhenius parameters of octadec-9-enoic acid (OA) into biofuel in this report. This was achieved via synthesis of two catalysts; the first, nickel alumina catalyst (Ni/Al2O3) was via the incorporation of inorganic Ni precursor into Al2O3; the second was via the incorporation nickel oxalate (NiOx) prepared by functionalization of Ni with EdA into Al2O3 to obtain organometallic NiOx/Al2O3 catalyst. Their characterization results showed that Ni species present in Ni/Al2O3 and NiOx/Al2O3 were 8.2% and 9.3%, respectively according to the energy dispersive X-ray result. NiOx/Al2O3 has comparably higher Ni content due to the EdA functionalization which also increases its acidity and guarantees high Ni dispersion with weaker metal-support-interaction leading to highly reducible Ni as seen in the X-ray diffraction, X-ray photoelectron spectroscopy, TPR and Raman spectroscopy results. Their activities tested on the HDO of OA showed that NiOx/Al2O3 did not only display the best catalytic and reusability abilities, but it also possesses isomerization ability due to its increased acidity. The NiOx/Al2O3 also has the highest rate constants evaluated using pseudo-first-order kinetics, but the least activation energy of 176 kJ/mol in the biofuel formation step compared to 244 kJ/mol evaluated when using Ni/Al2O3. The result is promising for future feasibility studies toward commercialization of catalytic HDO of OA into useful biofuel using organometallic catalysts.
... Both classical and innovative issues are treated by Doraiswamy and Uner (2013). Regarding chemical kinetics issues we recommend the book of Missen et al. (1999). Topics related to dynamics and control of chemical reactors, including Aspen Plus simulation, are presented by Luyben (2007). ...
This chapter presents elements from chemical reaction engineering necessary to consider in the conceptual design of a process as a system. The selection and the design of the reactor must be done in the context of interactions with the whole process, particularly with the separation system. The preliminary section reviews basic concepts with regard to stoichiometry, kinetics and chemical equilibrium. Then, design principles are discussed in the field of homogeneous reactions with reference to ideal reactor models, followed by heterogeneous reactions, where specific modelling problems are highlighted. Attention is paid to thermal design issues, related to safety and heat integration. Guidelines for the reactor selection are presented. The final section is devoted to new systematic methods developed by the process systems community.
... Both classical and innovative issues are treated by Doraiswamy and Uner (2013). Regarding chemical kinetics issues we recommend the book of Missen et al. (1999). Topics related to dynamics and control of chemical reactors, including Aspen Plus simulation, are presented by Luyben (2007). ...
This chapter develops a generic knowledge-based framework for developing flowsheets for the separation of complex mixtures. The approach relies on generating alternatives taking into account the relation between some characteristic properties of the components and the target assigned for separation, as well as the evaluation of the appropriate separation methods. The task-oriented methodology incites the application of novel techniques. The chapter describes in detail vapour and gas separations, including recent techniques based on exploiting both the size and shape properties and chemical affinities. In the field of liquid separations, the residue curve map technology is a valuable tool for getting thermodynamic insights, namely, for the separations of azeotropes. Enhanced distillation makes use of a mass separation agent, while in hybrid separations, the distillation is combined with other methods, such as liquid-liquid extraction, adsorption, crystallisation, and membranes, or even with reaction.
... The bed voidage is the ratio of the inter-particle void space to the total volume. The bed voidage was determined using [21] ...
A laboratory scale downdraft biomass gasifier was designed to deliver a mechanical power of 4 kW and thermal power of about 15 kW. The gasifier was manufactured as a single piece having a water seal and cover. The gasifier was tested in natural downdraft and forced downdraft mode. Ignition of the fuel beneath the grate, during natural downdraft mode, using wood shavings as fuel, produced gas which burned with a blue flame for 15 minutes. Ignition at the throat, using either palm kernel shells or wood shavings, during the natural downdraft mode, the gasifier did not produce syngas. During the forced downdraft mode, fuel was ignited at the throat. Gasification was successful with the palm kernel shells, during forced downdraft, which produced gas which burned steadily with luminous flame for 15 minutes per kilogram of biomass fed. However, wood shavings experienced some bridging problems during the forced downdraft mode of operation. The fuel conversion rate of the gasifier, when using palm kernel shells as fuel in forced downdraft mode, was 4 kg/h. Forced downdraft mode of operation yielded better results and is the preferred operation of the gasifier.
... So ist bekannt, dass die Geschwindigkeit der Gasphasenreaktion mit porösen Katalysatoren stark von der Diffusion des Gasmoleküls zu den aktiven Zentren beeinflusst wird. Diese als "Reaction in pore" [41] bezeichnete Theorie wurde bei der Ziegler-Natta-Polymerisation von BULS et al. [42] , SCHMEAL et al. [43] , SINGH et al. [44] sowie RAY et al. [45] angewendet. Dabei fand jedoch RAY et al. [45] mit hoch aktiven MgCl 2 -geträgerten TiCl 4 ...
... Řešení dynamických systémů (viz. [5]) je poměrně složitý proces. Za dobu, jež jsou tyto systémy řešeny bylo vyvinuto mnoho metod, jak dynamiku soustav vyšetřovat. ...
... The reaction that occurs in the pipe can be modelled as an isothermal, isobaric plug flow reactor (the change in mole number is negligible given the small concentration of NCl 3 ). The design equation [14] is: ...
Nitrogen trichloride (NCl3) is a by-product of electrolytic chlorine manufacture, produced when the brine is contaminated with ammonia. A common treatment method is a thermal destruction process in which the NCl3 is absorbed in a solvent (CHCl3) using a distillation column with no liquid bottoms product. The chlorine gas is cooled through direct contact with liquid chlorine, which flashes and condenses the solvent and NCl3 vapours. The condensate drains through trays to a reboiler in which the NCl3 decomposes while the chlorine, solvent, NCl3 solution boils. This process is well-known and widely practiced but is known to experience catastrophic detonations. A vapour phase thermal decomposition of NCl3 does occur, particularly when the heat added through compression is considered. The known data on this decomposition reaction have been collected and converted in a rate expression that allows for integration within an ASPENPLUS process model. Different options for the compressor, precooler, intercooler and liquefier operations are considered, and their impact on the compressor and liquefier duties is reported. A different approach to the design and operation for a chlorine compression/liquefaction train is presented and discussed. © 2013 Canadian Society for Chemical Engineering
... [24] For similar performance, plug-flow reactors (PFR) theoretically necessitate smaller vessels than completely stirred tank reactors (CSTR). [25] Recently, Yue et al. [26] demonstrated that the removal of animal manure COD in a PFR (44%) was higher than the 37% COD removal achieved in a CSTR (with sludge recirculation) given that both reactors operated at a hydraulic retention time (HRT) of 20 d and a temperature of 40 • C. The PFRs are also usually simpler to operate than SBRs principally due to the absence of mixing and of operating steps. In addition, PFR initial investments for installation and start-up are typically lower than other kinds of reactor configurations, because they do not have internal moving parts and they usually require less computer control and human intervention. ...
A low-temperature (25 degrees C) anaerobic eight-compartment (PF01 to PF08) cascade reactor simulating a plug-flow reactor (PFR) treating pig manure was monitored for a year. The bioreactor was fed at an average loading rate of 2.4 +/- 0.2 g of total chemical oxygen demand (TCOD) per litre of reactor per day for a theoretical hydraulic retention time (HRT) of 67 +/- 7 d. An average of 79% of TCOD was removed from pig manure (converted into biogas and in sediments), whereas specific methane yields ranging from 397 to 482 NL CH4 kg(-1) VS (148.6 to 171.4 NL CH4 kg(-1) TCOD) were obtained. After 150 d, fluctuating performances of the process were observed, associated with solids accumulation in the upstream compartments, preventing the complete anaerobic digestion of swine manure in the compartments PF01 to PF04. Low-temperature anaerobic PFR represents an interesting alternative for the treatment of pig manure and recovery of green energy. Further investigations regarding a modified design, with better accumulating solids management, are needed to optimize the performance of this low-temperature PFR treating pig manure.
... But, when T is higher than 1273 K, the reaction will be greatly restricted by the chemical equilibrium constant. Thus the net reaction rate will be lowered and the coal conversion will be consequently reduced [39]. Fig. 5(b) shows that increasing p t can greatly increase x coal . ...
Coal hydrogasification is a key component of zero emission coal (ZEC) power generation system which discharges little CO2 and other pollutants at a thermal efficiency close to 70%. In addition, coal hydrogasification itself has many advantages. A hydrogasification kinetic model including ten homogeneous reactions and four heterogeneous reactions is established in this work and is validated against experiment data available in literatures. The validated model is then used to predict the effects of different reaction conditions including the reaction temperature T, the reaction pressure pt, the H2/coal mass ratio U and the reaction time t on coal hydrogasification properties. The results indicate that coal hydrogasification is facilitated by the increased pt and t. When T is not higher than 1273 K, the gasification process is promoted with T increment. Increasing U can promote the coal hydrogasification process on the whole. When U is larger than 0.5, however, the coal conversion ratio (xcoal) will slightly decrease with U increment.
In the paper is presented a theoretical analysis of the methods for chemical engineering processes modeling. The methods for modeling specific processes may be different, but in all cases they must bring the mathematical description closer to the real process by using appropriate experimental data. These methods are presented in the cases of co-current absorption column without packings, counter-current absorption column with random packings and modeling of processes with unknown mechanism.
This chapter uses the recipe presented in Chap. 2 to develop models for different systems related to chemical engineering. The examples presented in this chapter deal with lumped-parameter problems, in which spacial variations in a physical quantity of interest are ignored. As shown in Fig. 1.1, lumped-parameter problems in a steady state are represented by algebraic equations, and, in a transient regime, by ordinary differential equations. In this chapter, we will only develop mathematical models using the recipe presented in Chap. 2. Numerical solution (using Excel) of algebraic and ordinary differential equations will be seen in Chaps. 5 and 6, respectively.
Integration of rate laws to obtain the several concentrations in terms of time is well described in books of General Chemistry, Physical Chemistry, or Chemical Engineering including mathematical and graphical descriptions. When several reactions have to be considered simultaneously, the mathematical solution of involved differential equations became difficult for students and is a good task from the mathematical point of view. Qualitative interpretation has interest from the chemical and engineering point of view and it is usually related with the change of concentrations along reactions which in turns modifies the rate of the several processes involved. In this work, no differential equations are solved analytically and no functions are obtained in order to reduce the mathematical complexity for students but a numerical solution is obtained by using the differential method and the computation of changes in concentration. A general formulation of the involved equations is presented including the effect of reactant concentration in the rate laws and an arbitrary number of simultaneous reactions. Details for numerical solution of involved equations are indicated and the task for students is to create their own program to solve the rate laws. Student should be able to input a set of compounds and reactions, to compute the evolution of concentrations of the several species with time and to plot such concentrations. Some applications with increasing complexity were computed and analyzed. In order to show the quantitative obtained results, comparison with analytical functions was carried out for simple systems.
Anode reaction characteristics in a molten carbonate fuel cell (MCFC) have been investigated in terms of overpotential by varying the temperature for 100 cm² class single cells. The temperature range was from 823 to 973 K under atmospheric conditions. Anodic overpotential was measured with the methods of electrochemical impedance spectroscopy (EIS), inert gas step addition (ISA), and reactant gas addition (RA). The cells successfully showed anodic overpotential at the very extreme temperatures of 823 and 973 K. The results of EIS and ISA revealed that anodic overpotential rose when the temperature increased. This is attributed to the fact that mass-transfer resistance through the porous electrode, that is, pore diffusion resistance, was increased at higher temperature. When using the RA method, it was also found that enlarged mass-transfer resistance of the reaction species, H2, CO2, and H2O, was responsible for the increase in overpotential at higher temperatures.
Removal process for corrosive, noxious and offensive odorous hydrogen sulfide (H2S) is often needed in waste to energy conversion system based on biogas. A hydrated iron oxide based reactive adsorbent that called iron oxide impregnated coco coir (IOCC) has been prepared for supporting H2S removal from biogas. For establishing its optimized separation performance, a series of laboratory scale experiments have been carried out in 100 mm bed length of fixed bed reactors and using synthetic biogas with 1000 ppm H2S concentration under plug flow condition. It was applied two level factorial design of experiment for parameters: pH 6.5 and 9; superficial gas velocity (v) 1.0 and 2.5 m/min; and two level regeneration treatments. The main indicator of reactor performance was characterized with sulfur removal capacity (SCb) that calculated from breakthrough curves with 100 ppm maximum outlet H2S concentration. The results showed that, under the experimental conditions, the separation process was not controlled by the external diffusion mass transfer step, but controlled by the chemical reaction step. The reactor performance could be improved by increasing pH with Na2CO3 addition and increasing the contact time with decreasing superficial velocity. The optimum operating conditions are pH=9 and superficial velocity v=1.0 m/min. Besides that, the sulfur capacity of saturated adsorbent could be recovered partially by oxidation reaction with air. This study constitutes the basis data for the next step of the scale-up experimentation at pilot scale fixed bed reactor.
Die Reintegration und Nutzung industrieller Abwärme weist ein hohes Potential zur Einsparung von Primärenergieträgern und damit zur Reduktion von Kohlendioxidemissionen auf. Allerdings wird die Weiterverwertung durch die fluktuierende Verfügbarkeit und das unzureichende Temperaturniveau der Abwärme erschwert. Thermochemische Energiespeicher auf Basis von Gas-Feststoff-Reaktionen bieten nicht nur die Möglichkeit zur Speicherung thermischer Energie mit hoher energetischer Speicherdichte, sondern sie ermöglichen gleichzeitig auch ein Anheben des Temperaturniveaus durch Wärmetransformation. In der vorliegenden Arbeit wurde daher eine Gas-Feststoff-Reaktion für die chemische Speicherung und Transformation thermischer Energie zwischen 100 °C und 200 °C identifiziert, charakterisiert, modelliert und im Labormaßstab demonstriert. Ausgehend von einer Literaturrecherche wurden zunächst sechs Salzhydrate ausgewählt und experimentell untersucht. Dabei stellte sich Calciumchlorid als geeignetes Referenzmaterial für weitergehende Analysen heraus. Ausgehend von einer detaillierten Untersuchung der Thermodynamik und Kinetik der Reaktion mit Wasserdampf sowie der thermophysikalischen Größen des Materials, wurde ein FEM-Modell entwickelt. Damit wurden entscheidende Grundlagen für die Analyse und das Modellverständnis von Hydraten geschaffen. In einer Sensitivitätsanalyse wurden die Permeabilität der Feststoffschüttung sowie deren Wärmeleitfähigkeit als einflussreichste Parameter für den Speicherbetrieb identifiziert. Das Modell wurde anhand experimenteller Daten eines Rohrbündelreaktors im Labormaßstab mit einer Kapazität von 550 kJ validiert. Dabei konnte die chemische Speicherung und Tansformation thermischer Energie mit einer energetischen Speicherdichte von 216 kWh/m^3 und einer thermischen Aufwertung von 130 °C auf 165 °C erstmals demonstriert werden.
The world is presently witnessing the advancement and development of a new multidisciplinary technology, “Nanotechnology.” The concepts that seeded nanotechnology was first discussed in 1959 by renowned physicist Richard Feynman in his talk.
In response to increasing concerns in the literature about human toxicity of microcystin-LR (MC-LR) in drinking water at very low concentrations, this study investigated the destruction of MC-LR down to ng L-1 concentrations by chlorine and permanganate. Results showed that decomposition in the low concentration range (1-2 ng L-1) exhibits a pseudo-first-order reaction with respect to both oxidants in pure water solutions. However, when the reaction proceeded down to a very low concentration (<10 ng L-1) a much smaller rate constant dictates the kinetics. In the presence of humic acids, the reaction rates and the final concentration removal were affected. The extent of such influence varied between the two oxidants, likely due to the different reaction mechanisms involved. This creates some profound effects of the governance of an oxidant exposure CT (residual oxidant concentration (C) x contact time (T)) over MC-LR degradation between the two oxidants. This study indicates that chlorine and permanganate may be still effective for MC-LR decomposition down to a concentration of 10 ng L-1 or below. However, the influence of solution chemistry must be carefully examined before a feasible CT is determined for the control of this toxin in a water treatment system.
The performance of catalysts for the recombination of oxyhydrogen gas was measured and compared with the results obtained from theoretical model. The oxyhydrogen gas was generated by the electrolysis cell and recombined through the fixed bed catalytic reactor. The yield that is the ratio of water-amount produced to the water-amount consumed in the electrolysis cell was increased with the increase of KOH concentration in electrolysis cell and the applied current. The catalyst 1 showed the best performance and the yield was under 60 %. The faradic yield calculated by Faraday's law showed about 100% in maximum with catalyst 1. The production rate of water generated by the recombination was 5-40 g/day dependent on the flow rate of mixed gas. Considering the results calculated from the pseudo-homogeneous catalytic reactor model, the hot point inside the reactor was moved to the direction of outlet and the maximum temperatures were when the gas flow rate increased. The production rate of water calculated from the theoretical model showed good agreement with experimental results below the flow rate of , but there were much differences above that flow rate.
The effect of different temperatures and acid concentrations on the corrosion of mild steel in nitric acid are addressed in this work. The effect of temperature is explained by the application of the Arrhenius equation and transition state theory, while the acid concentration effect is explained using reaction kinetic equations. The combined effect of temperature and acid concentration is then modeled using a nonlinear regression method. Thermodynamic parameters of activation (E, ΔH* and ΔS*) and detailed kinetic studies for the corrosion reaction are carried out. Nonlinear corrosion rates as a function of temperature and acid concentration are estimated with a good prediction of corrosion rate values. The values of activation energy E and enthalpy of activation ΔH* decrease with an increase in acid concentration indicating the increasing reaction rate. Entropies of activation ΔS* tend to lower values with increasing acid concentration, which indicates that the activated complex is more orderly relative to the initial state. The corrosion reaction was approximately first order.
The aim of this work was to model the catalytic oxidation of n-butane and butenes (Raffinate II) mixture to maleic anhydride (MAN) over a vanadium- phosphorus oxide (VPO) catalyst in a fluidized bed reactor (FBR). The three phase Kunni-Levenspiel hydrodynamic model (K-L) was used to describe the reactor. The obtained differential equations were solved by the fourth order Runge-Kutta numeric method. The K-L model was validated by a fitting comparison with reported experimental data for MAN production from nbutane. For the n-butane and Raffinate mixture, the maximum calculated MAN yield wasabout 52% over the FBR emulsion with a 49% of Raffinate conversion, and 51% of MAN selectivity. As a conclusion, the simulation program demonstrated a suitable performance to predict MAN selectivity, reactants conversion, and MAN and reactants concentration profiles.
In this paper we present the results of the identification of parameters of the mathematical model of non-isothermal adsorption of surfactants at the oil-bearing rocks of the porous medium. Developed the method to calculate the diffusion and kinetic coefficients of the models. The empirical formula for these coefficients is obtained in the form of polynomials.
Objective. Determine the effect of sucrose on the productivity of BC by Gluconacetobacter xylinus IFO 13693 in static condition. Materials and methods. The synthesis of bacterial cellulose (BC) by Gluconacetobacter xylinus was carried out in a discontinuous static culture at room temperature, in the presence of sucrose as the main carbon source at initial concentrations of 0.8 to 7.6% (p/v). The residual concentrations of BC, sucrose, glucose and fructose were measured every week. The Microcal Origin 6.0®. Software used to determine the kinetics of hydrolysis of sucrose and formation of cellulose and the coefficient of performance of the product Results. In the fourth week the BC values were between 32.5 to 39.5 g/L for the different concentrations of sucrose. The kinetics for the hydrolysis of sucrose fits the Michaelis-Menten model, with a Vmax of 0.0002 mol L-1 h-1 and Km of 0.018 M. The production of BC follows the model proposed by Marx-Figini and Pion, with a value of the slope (kc) between 0.0018 and 0.0024 h-1 for different initial concentrations of sucrose. The yield coefficients have values of 0.8 to 2.4 g of BC produced / g of sucrose consumed. Conclusions. The hydrolysis of sucrose, fructose consumption and glucose is reflected in cellulose synthesis. The hydrolysis of sucrose and production of BC fit the Michaelis-Menten model and the model proposed by Marx-Figini and Pion, respectively. Finally, the performance depends on the concentration of sucrose. Key words: Cellulose, Gluconacetobacter xylinus, kinetics, sucrose (Source:CAB).
Hydrogen has shown enormous potential to be an alternative fuel of the future. Hydrogen production technology has gained much attention in the last few decades due to advantages such as its high conversion efficiency, recyclability and nonpolluting nature. Over the last few decades, biological hydrogen production has shown great promise for generating large scale sustainable energy to meet ever increasing global energy demands. Various microorganisms, namely bacteria, cyanobacteria, and algae which are capable of producing hydrogen from water, solar energy, and a variety of organic substrates, are explored and studied in detail. Current biohydrogen production technologies, however, face two major challenges such as low-yield and high production cost. Advances have been made in recent years in biohydrogen research to improve the hydrogen yield through process modifications, physiological manipulations, through metabolic and genetic engineering. Recently, cell immobilization such as microbes trapping with nanoparticles within the bioreactor has shown an increase in hydrogen
production. This review critically evaluated various biological hydrogen production technologies, key challenges, and recent advancements in biohydrogen research and development.
Pd nanoparticles supported on basic layered double hydroxide (LDH) as highly efficient and reusable catalysts are prepared and characterized. The layered structure of LDH support could be reconstructed to different extent by controlling the activation conditions, which presented changing quantity of Brønsted-base sites. Besides, with the changing calcination temperature the LDH substrate imposed a restricted nano-size effect on the supported Pd particles under identical reduction condition, which demonstrated a convenient approach for controlling the size of supported Pd particles. The resulting Pd/LDH samples were tested as heterogeneous catalysts for solvent-free oxidation of benzyl alcohol using molecular oxygen. The sample with a larger amount of Brønsted-base sites is more active in the oxidation of benzyl alcohol, and after five catalytic runs it still gives benzaldehyde in excellent yields. The promotional effect of Brønsted-base sites of the LDH support on the catalytic activity for benzyl alcohol oxidation over Pd/LDH is studied.
Graphical Abstract
The mathematic model of combined converter with two different flow modes of gas-cooled reactor was established. The effects
of gas flow mode in gas-cooled reactor on combined converter was investigated with the yield of methanol was 1 400 kt/a. The
results show that if the flow mode of the cooling pipe gas and the catalytic bed gas change from countercurrent to concurrent,
the catalytic bed temperature distribution does not fit the most optimum temperature curve of reversible exothermic reaction
and the heat duty of heat changer in whole process increased seriously, which means that there is much more equipment investment
and more operating cost. The gas flow mode of gas-cooled reactor affects the methanol yield slightly. Therefore, the countercurrent
gas flow mode of gas-cooled reactor is more lucrative in the combined converter process.
Verfahrenstechnik ist Stoffwandlungstechnik. Sie befaßt sich mit der industriellen Umwandlung von Ausgangsstoffen in einer Folge von physikalischen, chemischen oder biologischen Prozessen zu verkaufsfähigen Zwischen- oder Endprodukten. Sie hat ihren Ursprung in der chemischen Industrie, wobei die Ingenieure insbesondere die Aufgabe hatten, die vom Chemiker in Laborversuchen erarbeiteten Ergebnisse in den technischen Produktionsmaßstab zu übertragen. Diese (Maschinenbau-)Ingenieure waren dafür verantwortlich, daß die Vorstellungen der Chemiker, Physiker und Biologen interdisziplinär verbunden wurden. Aus ihrer Tätigkeit hat sich eine eigenständige Ingenieurwissenschaft, die Verfahrenstechnik entwickelt. Hier war es zunächst der Apparatebau, der Forderungen an die Entwicklung neuer Fertigungsverfahren und neuer Werkstoffe stellte. Besonders erfolgreich wurden die Kenntnisse des Maschinenbaus bei der Entwicklung der Hochdruckverfahren, z.B. der Ammoniak- und der Methanolsynthese umgesetzt.
The effects of resin type and content as well as graphite content on physical and mechanical properties of MgO-C refractories, such as density, porosity and strength were studied. The samples were formulated with various amounts of graphite and resin, and their oxidation behavior was isothermally investigated using a thermo gravimeter (TG), in air and at a temperature ranges from 900 to 1300°C. The results indicated that, low-viscosity resins improved compressibility, but it degraded the strength. Higher resin content also improved the compressibility, but it caused higher porosity after preheating at 600°C. The results also showed that the porosity and density of tempered samples were decreased when graphite content were increased. During oxidation process, the rate of weight loss was high at the beginning, but it was gradually decreased when the thickness of decarbonized layer increased. Higher graphite content increased the weight loss, but it would reduce the thickness of oxidized layer.
This work reported the full degradation of an azo dye in a synthetic effluent by Pseudomonas oleovorans immobilized in polyurethane foam (PUF). For each fed-batch experiment, a screw-top vessel containing 160 mL of nutrient broth was inoculated with 0.16 g L À1 of fresh culture, incubated at 32 W C and supplemented with 50 mg L À1 of dye every 24 hours. Afterwards, the P. oleovorans were immobilized in PUF and inoculated in an anoxic reactor. The results showed that at fed-batch conditions, P. oleovorans was capable of removing 50 mg of dye in 192 hours. However, when the decolorization was performed in an anoxic reactor, it was capable of fully degrading 25 mg of dye in only 24 hours.
The objective of this paper is to investigate characteristics of an autothermal reformer at various operating conditions. Numerical method has been used, and simulation model has been developed for the analysis. Pseudo-homogeneous model is incorporated because the reactor is filled with catalysts of a packed-bed type. Dominant chemical reactions are Full Combustion reaction, Steam Reforming(SR) reaction, Water-Gas Shift(WGS) reaction, and Direct Steam Reforming(DSR) reaction. Simulation results are compared with experimental results for code validation. Operating parameters of the autothermal reformer are inlet temperature, Oxygen to Carbon Ratio(OCR), Steam to Carbon Ratio(SCR), and Gas Hourly Space Velocity(GHSV). Temperature at the reactor center, fuel conversion, species at the reformer outlet, and reforming efficiency are shown as simulation results. SR reaction rate is improved by increased inlet temperature. Reforming efficiency and fuel conversion reached the maximum at 0.7 of OCR. SR reaction and WGS reaction are activated as SCR increases. When GHSV is increased, reforming efficiency increases but pressure drop from the increased GHSV may decrease the system efficiency.
Jordanian iron ore samples, obtained from Warda area, were reduced using hydrogen gas and preliminary kinetic observations and results were obtained. Samples of iron ore were carefully sized, weighed and reduced using flowing hydrogen in a tubular furnace. Constant temperature experiments were conducted to examine the effect of particle size (180 to 710 ?m), temperature (400 to 600°C) and gas flow rate (1 to 3 L min–1 at STP) on the percentage of reduction with time. It was found that the reduction rate increased with decreasing particle size, increasing gas flow rate, and increasing temperature. In general, the course of ore reduction was observed to follow three distinct stages; an initial stage of increasing percentage of reduction at an increasing rate, followed by a stage of decreasing rate, and a final stage with constant percentage of reduction. The initial stage was successfully modelled using the shrinking core model with the chemical reaction step controls, probably combined by gas diffusion. The observed activation energy of reduction for this period was 29 kJ mol–1.
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