Fuel Processing Technology (v.89, #8)
Editorial Board (IFC).
Control of pore development during CO2 and steam activation of olive stones by S. Román; J.F. González; C.M. González-García; F. Zamora (715-720).
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.
Keywords: Olive stones; Activated carbon; Gasification; Steam; Carbon dioxide;
Hydroisomerization of different refinery naphtha streams by using a beta zeolite catalyst by María Jesús Ramos; Antonio de Lucas; Vicente Jiménez; Paula Sánchez; José Luis Valverde (721-727).
In this work, the evaluation of a catalyst based on beta zeolite agglomerated with bentonite in the hydroisomerization of three feeds obtained by distillation of refinery naphtha streams provided by the petroleum company REPSOL-YPF was considered. These refinery naphthas were different in composition, being constituted mostly by different proportions of paraffin, aromatic and naphthenic compounds. The highest overall paraffin conversion value was obtained with that naphtha with the highest content in linear paraffins. As the classical hydroisomerization mechanism predicts, linear alkanes were transformed into branched isomers. Thus, the relation between branched isomers and linear paraffins (iC6/nC6, iC7/nC7 and iC8/nC8) was higher in the products than in the feed. The presence of the aromatic compounds (benzene and toluene) was detected in the three feeds. In all cases, a complete benzene conversion, leading to naphthenic compounds formation, was reached. Long-term tests showed that, regardless of the type of naphtha fed to the reactor, the research octane number of the products remained practically constant.
Keywords: Hydroisomerization; Naphtha; Binder; Zeolites;
Promotional effect of Ca on the Pd/Ce–Zr/Al2O3 catalyst for low-temperature catalytic combustion of methane by Baohua Yue; Renxian Zhou; Xiaoming Zheng; Wencong Lu (728-735).
Promotional effect of Ca on the catalytic property of Pd/Ce–Zr/Al2O3 catalyst towards methane combustion is examined. The surface properties and the oxidation/reduction behavior of these catalysts are investigated by BET, TEM, XPS, TPR, TPO and TPSR techniques. Activity tests in methane combustion show that addition of Ca to Pd/Ce–Zr/Al2O3 can promote remarkably its low-temperature activity. The thermal stability of the Pd/Ce–Zr/Al2O3 catalyst to the exposure at high temperature is also enhanced by Ca loading. XPS and TEM results show that the addition of Ca to Pd/Ce–Zr/Al2O3 catalyst generates well-dispersed PdO particles on support. H2–TPR, O2–TPO and CH4/O2–TPSR experiments show that the addition of Ca improves the reduction/reoxidation properties and thermal stability of the active PdO species, which increases the catalytic activity and thermal stability of the Pd/Ce–Zr/Al2O3 catalyst.
Keywords: Catalytic combustion; Methane; Pd/Ce–Zr–Ca/Al2O3; Thermal stability;
Reactivity of several olefins in the HDS of full boiling range FCC gasoline over PtPd/USY by Szabolcs Magyar; Jenő Hancsók; Dénes Kalló (736-739).
Reactivity of C4–C6 olefins during the selective HDS of a full boiling range FCC gasoline over PtPd/USY catalyst was studied under various process conditions. Effect of the structure and carbon number of olefins on their conversion is discussed. It was found that the rate of hydrogenation decreases with the carbon number of linear olefins. Terminal olefins are readily converted to internal ones by double bond shift to approach the equilibrium composition of olefin isomers.
Keywords: HDS; FCC gasoline; Olefin hydrogenation; PtPd/USY;
Techno-economic study of different alternatives for biodiesel production by J.M. Marchetti; V.U. Miguel; A.F. Errazu (740-748).
Biodiesel has become an attractive diesel fuel substitute due to its environmental benefits since it can be made from renewable resource. However, the high costs surrounding biodiesel production remains the main problem in making it competitive in the fuel market either as a blend or as a neat fuel. More than 80% of the production cost is associated with the feedstock itself and consequently, efforts are focused on developing technologies capable of using lower-cost feedstocks, such as recycled cooking oils and wastes from animal or vegetable oil processing operations.The main issue with spent oils is the high level of free fatty acids found in the recycled materials. The conventional technology employs sodium methoxide as a homogeneous base catalyst for the transesterification reaction and illustrates the drawbacks in working with feedstocks that contain high levels of free fatty acids. On the other hand, homogeneous acidic catalysts are being used for exactly such feedstocks. Both acid and basic homogeneous catalyzed processes require downstream purification equipment to neutralize the catalyst and to purify the biodiesel as well as the glycerol.Recent studies have been conducted to employ heterogeneous catalysts, such acidic or basic solid resins, or immobilized lipases. These catalysts will allow the use of different feedstocks that will permit operation at lower investment costs and will require less downstream process equipment.A conceptual design of these alternative production plants has been done with a techno-economic analysis in order to compare these alternatives.A process simulator was employed to carry out the conceptual design and simulation of each technology. Using these models it was possible to analyze different scenarios and to evaluate productivity, raw material consumption, economic competitiveness, and environmental impacts of each process.
Keywords: Biodiesel production; Economic analysis;
Desulfurization of transportation fuels targeting at removal of thiophene/benzothiophene by Wei Dai; Yaping Zhou; Shengqiang Wang; Wei Su; Yan Sun; Li Zhou (749-755).
A new method is presented for deep desulfurization of transportation fuels targeting at the removal of thiophenic compounds. The method is based on a characteristic condensation reaction of thiophenic compounds with formaldehyde, and the reaction was designed to occur in the pore spaces of activated carbon under catalysis of sulfuric acid. The reaction is selective because the hydrocarbon components of fuels do not react with formaldehyde at the same condition. Therefore, the quality of fuel, e.g. the octane number, will not change, and the desulfurization function will not be interfered either by olefin/aromatic components or the dissolved water of fuels. Because the reaction is occurring in the pore spaces, the desulfurization function is locally intensified and the reaction products were there adsorbed. All those merits were shown firstly by different types of model fuels, and then by a commercial diesel fuel. In conjunction with an oxidation treatment, the total sulfur content of the commercial fuel dropped from 1697 ppm to 14 ppm, which meets the present fuel specification of the US.
Keywords: Desulfurization; Transportation fuel; Thiophene/benzothiophene; Characteristic reaction; Carbon pores;
Utilization of Estonian oil shale semicoke by Andres Trikkel; Rein Kuusik; Ants Martins; Tõnu Pihu; John M. Stencel (756-763).
In thermal processing of oil shale in vertical retorts huge quantities of a solid waste — semicoke are formed. It has been shown that circulating fluidized bed combustion of semicoke could be a promising technology allowing utilization of its high residual energy potential. The main parameters of combustion process and the additional heat produced were calculated and verified by combustion tests in a fluidized bed device with a thermal capacity of 50 kWth. The experiments indicated that semicoke with low moisture content can be burnt directly in fluidized bed. For the combustion of semicoke with higher moisture content (over 10%) about 10% of oil shale must be added. In addition, possibilities for utilizing residual carbon present in semicoke by obtaining carbon-rich materials with further production, for example, activated carbon were discussed. A series of experiments accompanied by SEM and EDAX analysis was carried out in order to elucidate the distribution of carbon and mineral part in semicoke and to find possibilities for their separation and subsequent enrichment. Different separation methods — selective grinding and subsequent screening, pneumatic separation and triboelectroseparation method were analyzed. It was shown that due to close integration of mineral and organic part in semicoke, the separation of carbon-rich ingredients by these methods was not enough effective to obtain enriched products suitable for the production of activated carbon.
Keywords: Oil shale semicoke; Semicoke combustion; Semicoke enrichment;
Investigation on the reactions influencing biomass air and air/steam gasification for hydrogen production by J.F. González; S. Román; D. Bragado; M. Calderón (764-772).
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).
Keywords: Olive waste; Hydrogen; Gasification; Catalyst;
Influence of crystal form and morphological characteristics of CaCO3 particles on kinetic of combustion gases desulfurization by Borivoj Adnadjevic; Aleksandar Popovic (773-776).
Influence of crystal form and morphological characteristics of CaCO3 samples with different structural (calcite, aragonite, low-crystalline and amorphous) and morphological (medium particle dimensions and shapes) characteristics on the kinetic of time-limited desulfurization process of coal combustion gases between 1030 and 1150 K was determined. Kinetic parameters (activation energies and pre-exponential factors of sulfurization reaction) were established. Correlations of the above-mentioned kinetic parameters of the reaction with size of particles (within the same crystal phase), morphology of particles or particle structure were explained by the difference in distribution of energy of active centers within border phase of interaction.
Keywords: Calcium carbonate; Desulfurization; Combustion gases;
Major gaseous and PAH emissions from a fluidized-bed combustor firing rice husk with high combustion efficiency by Kasama Janvijitsakul; Vladimir I. Kuprianov (777-787).
This experimental work investigated major gaseous (CO and NO x ) and PAH emissions from a 400 kWth fluidized-bed combustor with a cone-shaped bed (referred to as ‘conical FBC’) firing rice husk with high, over 99%, combustion efficiency. Experimental tests were carried out at the fuel feed rate of 80 kg/h for different values of excess air (EA). As revealed by the experimental results, EA had substantial effects on the axial CO and NO x concentration profiles and corresponding emissions from the combustor. The concentration (mg/kg-ash) and specific emission (μg/kW h) of twelve polycyclic aromatic hydrocarbons (PAHs), acenaphthylene, fluorene, phenanthrene, fluoranthene, pyrene, benz[a]anthracene, chrysene, benzo[b]fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene, dibenz[a,h]anthracene and indeno[1,2,3-cd]pyrene, were quantified in this work for different size fractions of ash emitted from the conical FBC firing rice husk at EA = 20.9%. The total PAHs emission was found to be predominant for the coarsest ash particles, due to the effects of a highly developed internal surface in a particle volume. The highest emission was shown by acenaphthylene, 4.1 μg/kW h, when the total yield of PAHs via fly ash was about 10 μg/kW h.
Keywords: Combustion efficiency; CO and NO x emissions; Polycyclic aromatic hydrocarbons;
HDS, HDN and HDA activities of nickel–molybdenum catalysts supported on alumina by M.A. Domínguez-Crespo; A.M. Torres-Huerta; L. Díaz-García; E.M. Arce-Estrada; E. Ramírez-Meneses (788-796).
In this work, NiMo–Al2O3 catalysts were prepared by using different alumina precursors. The supports were impregnated by means of the spray at incipient wetness technique in both basic and acid media. Both the supports and fresh catalysts were characterized by the adsorption–desorption isotherms, Temperature-Programmed Reduction (TPR), Thermal Pyridine Adsorption–Desorption (TPD) and X-Ray Diffraction analyses (XRD). After sulfidation, the NiMoS metallic particles were characterized by Transmission Electron Microscopy (TEM). The initial analyses were performed in a trickle-bed reactor by using a real feedstock (Mexican heavy gas oil) and performing hydrotreating reactions (HDS, HDN and HDA) at three different temperatures: 613, 633 and 653 K; and 54 kg cm− 2. The catalytic activities are discussed in relation to the physicochemical properties of the NiMo catalysts, alumina phase and pH of the impregnating solution. The catalytic results show an increase in the conversion profiles with temperature. The sulfur conversion was increased from 89 to 99.25%, 91–99%, 90.8–97%, 83–95% and 78–96% when the crystal size of the support varied from 3 to 20 nm, respectively. The nitrogen and aromatic conversions were also increased in the range of 23–45 wt.%. It was found that the γ phase reached a higher catalytic performance than the η phase. The NiMo catalysts synthesized in a basic medium showed a better catalytic performance than that obtained with those prepared in acid solutions. The significance of the kinetic data to compare the catalysts is discussed. The maximum value of the catalytic activity was reached with the catalysts with the smallest particle sizes.
Keywords: Catalysis; Hydrotreating; Heavy gas oil; NiMoS particles;
Influence of reaction conditions and the char separation system on the production of bio-oil from radiata pine sawdust by fast pyrolysis by Hyun Ju Park; Young-Kwon Park; Joo Sik Kim (797-802).
Radiata pine sawdust was pyrolyzed in a bubbling fluidized bed equipped with a char separation system. The influence of the reaction conditions on the production of bio-oil was investigated through the establishment of mass balance, and the examination of the products' chemical and physical characteristics. The optimal reaction temperature for the production of bio-oil was between 673 and 723 K, and the yield was above 50 wt.% of the product. An optimal feed size also existed. In a particle with a size that was less than 0.3 mm, the bio-oil yield decreased due to overheating, which led to gas formation. A higher flow rate and feeding rate were found to be more effective for the production of bio-oil, but did not significantly affect it. The main compounds of bio-oil were phenolics, including cresol, guaiacol, eugenol, benzendiol and their derivatives, ketones, and aldehydes. In addition, high-quality bio-oils, which contained less than 0.005 wt.% of solid, no ash and low concentrations of alkali and alkaline earth metals, were produced due to the char removal system.
Keywords: Fast pyrolysis; Char separation system; Reaction temperature; Feed size; Flow rate; Feeding rate;
Synthesis of methyl benzoate by methoxycarbonylation of acetophenone with dimethyl carbonate over solid base catalysts by Dudu Wu; Wenming Chang; Xia Wen; Fukui Xiao; Junping Li; Ning Zhao; Wei Wei; Yuhan Sun (803-807).
A convenient and simple route for synthesis of methyl benzoate from dimethyl carbonate and acetophenone has been exploited for the first time in the presence of solid base catalysts. The results showed that solid base with moderate strength, such as MgO, facilitated the formation of methyl benzoate and the function of basic catalysts could mainly be attributed to the activation of ketone via the abstraction of Hα by base sites.
Keywords: Methyl benzoate; Acetophenone; Dimethyl carbonate; Solid base catalysts;
The effect of aromatics on paraffin mild hydrocracking reactions (WNiPd/CeY–Al2O3) by Roberto Galiasso Tailleur; Juan Ravigli Nascar (808-818).
The conversion of heavy paraffin and aromatics into a high-quality diesel fraction was performed in a microplant using a WNiPd/CeY-alumina catalyst. The effects of aromatics and naphtheno-aromatics on mild hydrocracking of hexadecane were studied at different concentrations. Two catalysts, with and without Pd and thermal treatment, were characterized by FTIR, XPS, and TPD of ammonia and ammonia plus naphthalene to complement previous study about the surface composition. The hydrocracking activity and selectivity were tested using different amounts and types of aromatics. This study demonstrated the presence of two acid strengths that contribute in different ways to paraffin and aromatics isomerization, ring opening, and cracking reactions. The product distribution obtained by mild hydrocracking of n-C16 is between amorphous (SiO2Al2O3) and Y-zeolite type of support. The aromatic adsorption on acid sites reduces the cracking rate and improves the survival of di- and tri-branched paraffin. A model for the path of reaction is discussed to explain the results.
Keywords: Mild hydrocracking; Modified Y-zeolite; Aromatics; Metallic acid site;