S. Román

Universidad de Extremadura, Badajoz, Extremadura, Spain

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Publications (33)51.92 Total impact

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    ABSTRACT: In this work, the cyclic thermal regeneration of activated carbons saturated with p-Nitrophenol was analyzed with two complementary views: the examination of the process itself and the porosity modifications found in the adsorbents. The process, which was followed by TG/DTG/TDA analysis, showed that the regeneration process is highly dependent on the number of uses of the carbon. As it is reused, it becomes more and more resistant towards the heat treatment. Regarding the porosity, the fresh adsorbent (Vmi = 0.42 cm3 g−1), underwent a significant porosity decrease after saturation (Vmi = 0.04 cm3 g−1), mainly due to micropore blockage. The subsequent regeneration succeded to render around 70% of the adsorbent N2 uptake. However, further uses of the carbon resulted in a progressive decay of the adsorbent capacity, with a marked porosity widenning. These features were further investigated by means of Scanning Electron Microscopy and Infrared Spectroscopy.
    Journal of Analytical and Applied Pyrolysis 03/2014; · 2.56 Impact Factor
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    ABSTRACT: In this work the thermal regeneration of activated carbons saturated with p-nitrophenol has been analysed. By thermogravimetry, it was possible to elucidate the different events taking place during the thermal treatment, and relate them to the type of adsorption in the interfacial system. It was found that the mass loss during thermal treatment comprises a complex process in which different stages are involved, such as drying, desorption of physisorbed adsorbate, breaking up of surface functional groups, cracking of products from adsorbate–surface-specific interactions, etc. The analysis of the textural and surface chemistry characteristics of the pristine and regenerated adsorbent confirmed the thermal desorption mechanisms. Moreover, a kinetic study based on temperature-programmed desorption and Suzuki models was performed, using thermogravimetry data at different heating rates (5–20 K min−1). From this analysis, the values of activation energy involved in each degradation step were estimated.
    Journal of Thermal Analysis and Calorimetry 01/2014; · 1.98 Impact Factor
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    ABSTRACT: This work deals with the regeneration of p-Nitrophenol (PNP) loaded Activated Carbons by means of aqueous thermal desorption.Continuous desorption experiments were performed under different temperature (140–200 °C) and stirring (100–600 rpm) conditions. The study was made with a double point of view; firstly, desorption kinetics was analyzed by applying non-linear Lagergren model. Secondly, the improvements on the textural parameters of the regenerated adsorbents as well as the regeneration efficiency were evaluated.The results obtained revealed that the final amount of PNP desorbed was temperature dependent in the range 140–180 °C, while no improvement was found for higher temperatures, independently of the stirring speed. Likewise, temperature did not exert a marked effect on desorption kinetics.The irreversibility of the adsorption processes was confirmed from N2 and PNP adsorption analyses, although some differences were found. It is worth mentioning that increasing temperature did have a relevant influence on the adsorption regain of the adsorbents, being maximum for 200 °C (N2 and PNP adsorption efficiency values up to 61% and 80%, respectively). This might be attributed to the occurrence of some activating effect induced by water under these conditions. The study of the prevalence of desorption over adsorption for enhanced temperature was complemented by the development of an Arrhenius-based model.
    Journal of Supercritical Fluids The 01/2014; 85:24–30. · 2.73 Impact Factor
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    ABSTRACT: Biomass plays an important role as an energy source, being an interesting alternative to fossil fuels due to its environment-friendly and sustainable characteristics. However, due to the exposure of customers to emissions during biomass heating, evolved pollutants should be taken into account and controlled. Changing raw materials or mixing them with another less pollutant biomass could be a suitable step to reduce pollution. This work studied the thermal behaviour of olive pomace, pyrenean oak and their blends under combustion using thermogravimetric analysis. It was possible to monitor the emissions released during the process by coupling mass spectrometry analysis. The experiments were carried out under non-isothermal conditions at the temperature range 25-750 °C and a heating rate of 20 °C·min-1. The following species were analysed: aromatic compounds (benzene and toluene), sulphur emissions (sulphur dioxide), 1,4-dioxin, hydrochloric acid, carbon dioxide and nitrogen oxides. The results indicated that pollutants were mainly evolved in two different stages, which are related to the thermal degradation steps. Thus, depending on the pollutant and raw material composition, different emission profiles were observed. Furthermore, intensity of the emission profiles was related, in some cases, to the composition of the precursor.
    International Journal of Molecular Sciences 01/2014; 15(10):18349-18361. · 2.46 Impact Factor
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    ABSTRACT: In this work, the surface free energy of biomass-based activated carbons, both fresh and impregnated with triethylenediamine, has been evaluated. The contribution of Lifshitz van der Waals components was determined by the model proposed by van Oss et al. The results obtained allowed predicting the most probable configurations of the impregnant onto the carbon surface and its influence on the subsequent adsorption of radioactive methyl iodide.
    Applied Surface Science 10/2013; · 2.54 Impact Factor
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    ABSTRACT: The adsorption of fluoxetine onto activated carbons (ACs) prepared from almond tree pruning by steam and CO2 activation under different temperature conditions (650–950°C), was studied. In both series increasing the temperature caused an increase in the BET apparent surface area, yielding ACs with SBET up to 870 and 710 m2 g−1 after steam and CO2 activation, respectively. Also, a slight widening of the porosity was found in both cases. In order to modify the functionality of the ACs, two of them were impregnated with triethylenediamine (TEDA) prior to the adsorption process, which caused a decrease in the AC apparent surface mainly due to micropore blockage. The fluoxetine adsorption isotherms at 25°C showed maximum adsorption capacities between 110 and 224 mg g−1. The adsorption isotherms were analyzed using Langmuir and Freundlich models. Although the impregnation reduced the pore volume, it did not cause a decrease in the fluoxetine maximum adsorption capacity, but a modification in the adsorption mechanism was observed.
    CLEAN - Soil Air Water 07/2012; 40(7). · 2.05 Impact Factor
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    ABSTRACT: As a result of agroindustrial activities in southwestern Europe, a great amount of residues are generated; among them, olive pomace stands out as one of the most abundant. One interesting alternative to increase its potential as biofuel can be its densification. However, in order to achieve high quality pellets, it is necessary to blend this material with other feedstocks. In this work, the properties of blends of pelletized residues from olive pomace and pyrenean oak were analyzed with a view to find the best option.In order to compare the characteristics of the obtained pellets, such as moisture content, mechanical durability, ash content and calorific value, these parameters were determined according to the Technical Specifications for Solid Biofuels CEN/TS. Moreover, the pellets produced were subjected to a combustion test in a pellet stove to analyze the emissions associated to each sample. The results show that not all residues pelletize satisfactorily, which is due to the different conditions of the precursors. Adding pyrenean oak residues to the olive pomace samples guarantees a more effective compression of the pellet, improving its manipulation and transport, without significantly modifying its thermal properties. Concerning the pellet combustion, emissions are slightly worse with olive pomace pellet, concluding that it is not recommendable to use blends with more than 50% of this product.
    Fuel and Energy Abstracts 01/2012;
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    ABSTRACT: The effective implementation of biomass gasification has to overcome some difficulties such as the minimization of tars. On the other hand, with a proper design of experimental conditions, biomass gasification can be directed towards the production of hydrogen. The aim of the present study was to investigate the use of dolomite as catalyst to improve tar removal and hydrogen production by a two-stage steam gasification process, using olive cake as raw material. Fixing the olive cake gasification conditions on the first reactor (900 °C, steam flow rate of 190 mg min−1, O2 flow rate of 7.5 cm3 min−1), the cracking of tars was prompted by: a) steam gasification (steam flow rate in the range 40–190 mg min−1) at 1000 °C, b) catalytic gasification, using dolomite (5% wt.). It was found that increasing steam flow rate up to 110 mg min−1 involves an increase in hydrogen fraction due to the enhancement of water gas and water gas shift reactions. Also, the influence of dolomite was studied at 800 and 900 °C in a second reactor, finding better results at 800 °C, which gave an hydrogen fraction of 0.51.
    Biomass and Bioenergy 10/2011; 35(10):4324-4330. · 3.41 Impact Factor
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    ABSTRACT: One possibility for the elimination of the by-products generated in the viticulture industry can be their densification for subsequent use as a solid biofuel. In this work, washed grape pomace has been considered due to its thermal characteristics. Since it could show problems in the densification process, other by-products such as pyrenean oak residues, with good pelleting properties and available in this region, are also used.So that, samples of different concentrations from both residues were densified by means of a flat die pelletizer, obtaining pellets of 6mm diameter. The densified samples were characterized in terms of the proximate and ultimate analyses, heating value and physical characteristics such as durability or bulk density. Also, the combustion profile of the pellets was studied by thermogravimetry and inorganic emissions such as sulphur dioxide and nitric oxide were considered, by means of coupled mass spectrometry (TG-MS).The results obtained showed that both residues show good characteristics for their densification and manufacture in pellets. Also, they show good physical and thermal properties for its use as biofuel, as well as its different blends. Therefore, it is possible to give a more efficient energetic use to both residues.
    Fuel Processing Technology 02/2011; 92(2):278-283. · 2.82 Impact Factor
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    ABSTRACT: Biomass as an energy source has a lot of advantages over fossil residues, but it presents an important drawback: in local environments, such as homes, people are exposed to some harmful gases evolved during the biomass degradation process. Thus, many efforts have been made in order to dismiss these pollutants, being the blending with less pollutant biomass materials (that is, dilution), the optimization of the energy obtaining process and the use of catalysts and adsorbents the most popular ways to achieve this goal. The aim of this research was to assess the effectiveness of dilution over grape pomace, a quite abundant residue in Extremadura (Spain), blending it with Pyrenean oak. During the combustion of these blends, some parameters were measured by a coupled TG-MS technique, which allowed us to obtain much information about kinetics and evolved gases emissions. It is shown how the dilution effect affects both the amount of evolved gases (reducing them) and the combustion mechanism.
    Fuel and Energy Abstracts 01/2011;
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    ABSTRACT: Activated carbons were prepared by different series of carbon dioxide and steam activation from walnut shells for their optimal use as radioactive methyl iodide adsorbents in Nuclear Plants. The knowledge of the most favourable textural characteristics of the activated carbons was possible by the previous study of the commercial activated carbon currently used for this purpose. In order to increase their methyl iodide affinity, the effect of triethylenediamine impregnation was studied at 5 and 10wt.%. The results obtained indicated that in both cases the adsorption efficiency is markedly improved by the addition of impregnant, which allows the adsorbate uptake to occur not only by physical adsorption, via non-specific interactions (as in non-impregnated carbons) but also by the specific interaction of triethylenediamine with radioactive methyl iodide. Methyl iodide retention efficiencies up to 98.1% were achieved.
    Fuel Processing Technology - FUEL PROCESS TECHNOL. 01/2011; 92(2):247-252.
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    ABSTRACT: The thermal decomposition of pellets made from pyrenean oak (PK) and olive waste pomace (OP) mixed under different proportions (0–100wt.% of OP) was studied. Mass spectra measurements were accomplished simultaneously in order to elucidate the emissions generated during the weight loss of the lignocellulosic materials.The coupled TG–MS study allowed the monitoring of the emissions of CO2, SO2, NO, C6H6 and C7H8, and the differences found were related to the chemical composition of the precursors and also to the features of their thermal degradation. It was found that in general a high content of OP favors the release of these emissions at lower temperatures. On the other hand, the effect of OP content on the ion intensity height of the emissions is more marked in the range 25–75wt.% of OP. The analysis of the emission profiles for each case allows a proper design of the experimental conditions in order to get a better control of the process.
    Fuel Processing Technology 11/2010; 91(11):1459-1463. · 2.82 Impact Factor
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    ABSTRACT: A study of the enzymatic ethanolysis of sunflower oil has been carried out. The objective of this work, which continued previous work, was to determine the optimal conditions for the conversion of the triglycerides to ethyl esters. The operational variables were temperature (35-60 °C), the ethanol oil molar ratio (3:1 and 4:1), the lipase type (Lipozyme 62350, Lipozyme TL IM, Novozym 435 and Pseudomonas cepacia) and concentration (2% to 4% in weight). The principal esters, analyzed at different reaction times, were the linoleate (55%), the oleate (30%), the palmitate (9%) and the stearate (5%) esters. In the final biodiesel, the density, viscosity, flash point, combustion point, Conradson carbon residue, cold filter plugging point (CFPP), characteristics of distillation, high heating value, and cetane, acidity, saponification and iodine index, were determined according to ASTM norms. These parameters, except the CFPP, presented similar values to diesel oil of automotive industry. The best ethanol oil molar ratio was the 3:1. Larger ratios, such as 4:1, decreased the ethyl esters yield, since the lipases suffer a deactivation when they are in excess of ethanol. Kinetically, the reaction is slow, since, in the best reaction conditions, times of 20 to 25 h are required to achieve conversions 95-98%. The best catalyst was the Novozyme 435, followed for Pseudomonas cepacia, Lipozyme TL IM, and Lipozyme 62350. In all cases the concentration of catalyst exercised a positive effect. The best results were achieved with the concentration of 4%. Temperature, in the case of Lipozyme 62350, exerts a positive effect between 35- and 40 °C. For higher temperatures (45, 50, 55 and 60 °C), the yield diminishes when this variable increases. Following a differential method of analysis of data, a kinetic study, to determine the parameters of the models of Michaelis Menten and Ternary Complex, was carried out. The experimental data fit well to both models. Nevertheless, the model of the Ternary Complex predicts lower velocities to compared to experimental data when the concentration of oil is low.
    Journal of Biobased Materials and Bioenergy 02/2010; 4(1):87-94. · 0.83 Impact Factor
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    ABSTRACT: The influence of carbon dioxide and steam as activating agents on the porosity development of activated carbons produced from walnut shells was investigated. The study was made covering a wide range of burnoff (12−76%) and employing different temperatures and times: in carbon dioxide activation, 850 °C varying the activation time in the range 60−480 min, and in steam activation, 700, 850, and 900 °C (for 30−120 min). It was found that the gasifying agent has a profound influence on the activated carbon porosity development. First, steam is more reactive and produces, in general, activated carbons with greater N2 adsorption capacity. Second, the increase in the fraction of mesopores with activation time is more pronounced for steam. While steam generates micro-, meso-, and macropores from the early stages of the process, carbon dioxide produces highly microporous carbons, with broadening of the microporosity only for long activation times.
    Industrial & Engineering Chemistry Research 08/2009; 48(16). · 2.24 Impact Factor
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    ABSTRACT: Biomass samples (almond shell, walnut shell, almond tree pruning and olive stone) were subjected to thermoanalytical investigation to evaluate their thermal behaviour and its correlation with their lignocellulosic composition. Then, the pyrolysis process of these materials was studied in terms of the energy content of the phases generated (gas and liquid). Finally, the feasibility of obtaining effective adsorbents from the char generated was studied. With this aim, the char was used to prepare activated carbons (ACs) by steam gasification at fixed activation temperature and time, identical for the four chars. The differences found in the porosity development of the activated carbons were related to the lignocellulosic composition of the raw material. It is shown that the four biomass residues used are versatile precursors that allow the preparation of adsorbent materials with different textural characteristics.
    Journal of Analytical and Applied Pyrolysis 05/2009; In Press, Accepted Manuscript. · 2.56 Impact Factor
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    ABSTRACT: The adsorption of phenol from dilute aqueous solutions onto new activated carbons (AC) was studied. The novel activated carbon was produced from lignocellulosic (LC) precursors of rapeseed and kenaf. Samples oxidised with nitric acid in liquid phase were also studied. The results have shown the significant potential of rapeseed and kenaf for the activated carbon production. The activated carbons produced by carbon dioxide activation were mainly microporous with BET apparent surface area up to 1350 m(2)g(-1) and pore volume 0.5 cm(3)g(-1). The effects of concentration (0.1-2 mM) and pH (3-13) were studied. The phenol adsorption isotherms at 25 degrees C followed the Freundlich model with maximum adsorption capacities of approximately 80 and 50 mg g(-1) for the pristine and oxidised activated carbons, respectively. The influence of pH on the adsorption has two trends for pH below and above 10. It was possible to conclude that when phenol is predominantly in the molecular form the most probable mechanism is based on the pi-pi dispersion interaction between the phenol aromatic ring and the delocalised pi electrons present in the activated carbon aromatic structure. When phenolate is the major component the electrostatic repulsion that occurs at high pH values is the most important aspect of the adsorption mechanism.
    Journal of hazardous materials 02/2009; 167(1-3):904-10. · 4.33 Impact Factor
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    ABSTRACT: The interest on energy recovery from renewable sources is increasing due to the global warming and fossil fuels limitation. Biomass thermochemical conversion methods present some significant advantages such as zero net emissions and the use of agricultural by-products. In this work, a study of the catalytic and non-catalytic pyrolysis of an exhausted olive waste was carried out. The objective was to characterize the solid, liquid and gaseous phases in terms of their energy content. Two experimental series were conducted: uncatalyzed processes, studying the influence of temperature in the range 400–900°C; and catalyzed ones, investigating the influence of temperature (500–800°C) and quantity of catalyst (0–100g). Also, the dolomite effectiveness as catalyst was evaluated. For this motive, consecutive experiments, without reactivating dolomite, were carried out (0–6 runs), and the yields of solids, liquids and gases were determined. It was found that increasing temperature leads in both series to a decrease in the solid and liquid yields and to an increase in the gas yield. The presence and amount of catalyst caused a significant decrease in the liquid phase yield and a high increase in the gas phase yield giving rise to a vast rise in hydrogen production. On the other hand, the catalyst proved to be stable and did not lose activity during at least six pyrolysis cycles.Finally, as a previous step to the design of industrial installations, a kinetic study of the process was performed, based on the generation of the principal gases, considering that these are formed through parallel independent first-order reactions, with different activation energy.
    Journal of Analytical and Applied Pyrolysis - J ANAL APPL PYROL. 01/2009; 85(1):197-203.
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    ABSTRACT: The pyrolysis process of Jerusalem artichoke (Heliantuhus tuberosus L.) waste was carried out. The objective of this work was to characterize the solid, liquid and gaseous phases, studying the influence of the operating variables and determining the optimal conditions. Thus, the influence of temperature (400–800°C), particle size (0.63–2.00mm), N2 flow rate (75–300mLmin−1) and initial sample mass (2.5–10g) were investigated. In these series, the yields of the three phases, their higher heating value and the proximate analysis of the solid phase were determined. Under the conditions of this study, an increase in reaction temperature leads to a decrease in the solid and liquid yields and to an increase in the gas phase yield. However, the variation of the initial sample mass and the particle size do not exert a defined influence in the yield of the three phases. On the other hand, increasing the N2 flow causes a decrease in the liquid and an increase in the gas yields. According to the energetic characterization of the phases generated, different uses were proposed. Finally, as previous step to the design of the industrial equipments, a kinetic study of the process, based on the generation of the principal gases, was accomplished. With this purpose, it was considered that the gases are formed through parallel independent first-order reactions, with different activation energies. From this model, rate constants for the formation of each gas and their corresponding activation energies were determined.
    Journal of Analytical and Applied Pyrolysis - J ANAL APPL PYROL. 01/2009; 85(1):294-300.
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    ABSTRACT: Several series of activated carbons were prepared from olive stones by means of carbonization followed by activation with carbon dioxide, water steam and a mixture of them, under different experimental conditions. The changes in porosity of the original char during activation were studied by adsorption of N2 at 77 K, CO2 at 273 K and Hg porosimetry. The study was carried out covering a wide range of burn-off (19–83%) using activation times of 20–120 min, and temperatures between 650 and 950 °C. It is shown quantitatively how the individual factors influence the development of microporosity. It was found that in general terms, increasing activation produces a continuous increase in the volume of micropores and mesopores. However, this development occurs in a different proportion whether CO2 or steam are used: while CO2 produces narrow micropores on the carbons and widens them as time is increased, steam yields pores of all the sizes from the early stages of the process. The simultaneous use of these two activating agents resulted positive at times higher than 1 h, since it yielded carbons with higher volumes of pores.
    Fuel Processing Technology 08/2008; 89(8):715–720. · 2.82 Impact Factor
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    ABSTRACT: Hydrogen could be the energy carrier of the next world scene provided that its production, transportation and storage are solved. In this work the production of an hydrogen-rich gas by air/steam and air gasification of olive oil waste was investigated. The study was carried out in a laboratory reactor at atmospheric pressure over a temperature range of 700 ­ 900 °C using a steam/biomass ratio of 1.2 w/w. The influence of the catalysts ZnCl2 and dolomite was also studied at 800 and 900 °C. The solid, energy and carbon yield (%), gas molar composition and high heating value of the gas (kJ NL− 1), were determined for all cases and the differences between the gasification process with and without steam were established. Also, this work studies the different equilibria taking place, their predominance in each process and how the variables considered affect the final gas hydrogen concentration. The results obtained suggest that the operating conditions were optimized at 900 °C in steam gasification (a hydrogen molar fraction of 0.70 was obtained at a residence time of 7 min). The use of both catalysts resulted positive at 800 °C, especially in the case of ZnCl2 (attaining a H2 molar fraction of 0.69 at a residence time of 5 min).
    Fuel Processing Technology. 01/2008;

Publication Stats

118 Citations
51.92 Total Impact Points

Institutions

  • 2005–2011
    • Universidad de Extremadura
      • • Department of Applied Physics
      • • School of Industrial Engineerings
      • • Departamento de Ingeniería Química y Química Física
      Badajoz, Extremadura, Spain
  • 2009
    • Universidade de Évora
      • Department of Chemistry
      Évora, Distrito de Evora, Portugal
  • 2006
    • Universidade da Beira Interior
      Ковильян, Castelo Branco, Portugal