I.A. Vasalos

Biomass pyrolysis in a circulating fluid bed reactor for the production of fuels and chemicals

An approach for biomass flash pyrolysis in a circulating fluid bed (CFB) reactor with continuous solids regeneration is described in this study. The unit is capable of performing conventional and catalytic biomass pyrolysis with the proper solid selection. The production of improved quality liquid products in a direct step through catalytic pyrolysis is investigated in this work. Both conventional and catalytic biomass pyrolysis can be effectively performed in this CFB unit. Flash pyrolysis conditions were achieved and liquid product yields of , 70 wt% (on biomass feed) were obtained. The effect of specific operating variables including the type of inorganic solid material and the solid/biomass ratio was established on the final liquid product quality and yield. Solid materials considered included silica sand, a commercial fluid catalytic cracking catalyst and a ZSM-5 additive. Catalytic biomass pyrolysis generally leads to the production of additional water, coke and gases compared to conventional pyrolysis. However, the obtained liquid product quality and composition is improved. q 2002 Elsevier Science Ltd. All rights reserved.

Oxidative dehydrogenation of propane over vanadium oxide based catalysts: Effect of support and alkali promoter

The oxidative dehydrogenation of propane was investigated using vanadia type catalysts supported on Al2O3 ,T iO 2, ZrO2 and MgO. The promotion of V2O5/Al2O3 catalyst with alkali metals (Li, Na, K) was also attempted. Evaluation of temperature programmed reduction patterns showed that the reducibility of V species is affected by the support acid‐base character. The catalytic activity is favored by the V reducibility of the catalyst as it was confirmed from runs conducted at 450‐550 C. V2O5/TiO2 catalyst exhibits the highest activity in oxydehydrogenation of propane. The support’s nature also affects the selectivity to propene; V2O5 supported on Al2O3 catalyst exhibits the highest selectivity. Reaction studies showed that addition of alkali metals decreases the catalytic activity in the order non-doped>Li>Na>K. Propene selectivity significantly increases in the presence of doped catalysts.

Carbon dioxide reforming of methane over 5 wt.% Ni/CaO-Al2O3 catalyst

Methane reforming by carbon dioxide was investigated over 5 wt.% Ni/CaO-Al2O3 catalyst. X-ray diffraction (XRD) and temperature-programmed reduction (TPR) techniques were applied to characterise the catalyst. The catalyst exhibited high activity and very good stability at stoichiometric methane and carbon dioxide feed. The addition of steam in the reacting mixture was tested and proved beneficial for the conversion of methane and the drastic decrease in carbon deposition. The kinetic behaviour of the catalyst was investigated as a function of temperature and methane and carbon dioxide partial pressures. The apparent activation energies of the two reactants CH4 and CO2 were estimated 25.5 ± 2.0 and 23.6 ± 1.8 kcal/mol, respectively and that of CO was 24.6 ± 1.2 kcal/mol while hydrogen activation energy was estimated at 35.2 ± 3.2 kcal/mol. Partial pressure dependencies of the reaction rates were obtained at 630 ◦ C. The increase of H2 partial pressure resulted in an acceleration of the CO formation, while an increase in CO partial pressure demonstrated the inhibiting role in H 2 formation and the conversion of the reactants.

The effect of CH4, H2O and SO2 on the NO reduction with C3H6

Abstract NO reduction experiments were carried out in a fixed-bed reactor loaded with metal/alumina catalysts. Two hydrocarbons, methane and propene, were used as the reducing agents for the NO reduction. The former hydrocarbon exhibited relatively low NOx conversions and it was burned at high temperatures. The addition of methane to a propene-containing feed gas stream did not cause any inhibition or enhancement on the NO reduction activity over the Pt/alumina catalyst. The presence of water in the feed gas stream caused a small, reversible, inhibition effect over the Pt/, Cu/ and Ni/alumina catalysts. The maximum NO conversion was measured over Ni/alumina, followed by that over Cu/and Pt/alumina. The peak temperature varied with the catalyst, but it was not affected by the addition of water to the feed gas stream. The presence of SO2 in the feed gas stream did not affect the NOx conversion over Pt/alumina, it caused a significant irreversible loss of activity over other metal/alumina catalysts and it enhanced the activity of Rh/alumina.

Investigations on the oxidative dehydrogenation of n-butane over VMgO-type catalysts

The oxidative dehydrogenation of n-butane was investigated over VMgO mixed oxide and pure magnesium ortho- and pyrovanadate catalysts. The formulation containing 30 wt% V2O5 and consisting of the Mg3(VO4)2 and MgO crystal phases is more selective than the pure Mg3(VO4)2, while the Mg2V2O7 phase is the least selective. The selectivity to butenes and butadiene increases with the reaction temperature and the feed molar ratio of butane/oxygen. Addition of water tends to decrease the conversion of butane and enhances the oxydehydrogenation product selectivity. The relative importance of the primary and secondary paths of the reaction network was analyzed by the method of addition of intermediate products. # 1998 Elsevier Science B.V. All rights reserved.

Preparation and evaluation of catalysts for the production of ethylene via steam cracking: Effect of Operating Conditions on the Performance of 12CaO-7Al2O3 Catalyst

Various types of catalyst samples selective for the production of ethylene via steam cracking were prepared. Controlled ratios of two or more oxides and high calcination temperatures were used in order to obtain the desired crystal phases. BET surface-area measurement and X-ray diffraction techniques were used for the examination of the samples. The prepared samples were tested in an experimental pyrolysis unit using n-hexane as a feed. It was found that a catalyst with the formula 12CaO-7Al2O3 has the highest selectivity ratios. The catalyst activity varied widely depending on the operating conditions. At short residence times the catalyst increases the conversion of the feed and hence the olefin yields compared with “inert” α-alumina and thermal cracking (empty reactor). At relatively long residence times and high hydrocarbon partial pressure the catalyst promotes the formation of carbon oxides. Therefore, with a judicious choice of the operating conditions, the catalyst 12CaO-7Al2O3 can act as a steam cracking and/or a steam reforming catalyst. Testing of a sample following treatment with hydrogen at high temperature showed no catalytic activity. It is believed that the increased catalyst activity is due to the excess of oxygen that exists in the crystal phase Ca12Al14O33 of the 12CaO-7Al2O3 catalyst.

Surface properties and reactivity of Al2O3-supported MoO3 catalysts in ethane oxidative dehydrogenation

The effect of MoO3 loading on the properties and the catalytic performance of a series of alumina-supported molybdena catalysts (0–30 wt% MoO3) was investigated in the oxidative dehydrogenation of ethane. The molybdena species on alumina were found to be amorphous at submonolayer coverages. At higher loadings, the formation of Al2(MoO4)3 crystallites was detected by XRD. XPS revealed the existence of both Mo(VI) and Mo(V) sites on the catalyst surface, the concentration of which depends on the MoO3 loading. In terms of catalytic performance, the activity increases with increasing loading in the submonolayer regime, decreasing for higher loadings. High selectivity to ethene is obtained even at relatively high conversion levels for catalysts exceeding monolayer coverage.

HdPro: a mathematical model of trickle-bed reactors for the catalytic hydroprocessing of oil feedstocks

Abstract A steady-state model for trickle-bed reactors was developed, primarily concerning hydroprocessing of light oil feedstocks containing volatile compounds. The case of a homogeneous plug flow fixed bed reactor with axial dispersion was considered. Catalyst particles were assumed to be isothermal and isoconcentrational. Mass balances, overall two-phase flow momentum balance and phase energy balances were written in detail. Hydrodynamic flow of the two phases and specifically the flow regime under which the bed was operated, the liquid holdup, the wetting efficiency of the solid particles, the two-phase flow pressure drop and the gas–liquid and liquid–solid interfacial areas were all predicted using carefully selected industrial engineering correlations. In addition, all necessary thermophysical properties, such as phase densities, viscosities, conductivities, diffusivities, interfacial tension, latent heats of vaporization, specific heats, and molar partial enthalpies were continuously calculated as functions of the system pressure, temperature and phase composition. A suitable numerical package was developed for this kind of calculations. Phase equilibrium was calculated with the aid of the same package and the non-ideal phase behavior was taken into account, as well. Mass transfer rates were calculated by the effective diffusivity method. Compared to a set of experimental data taken from the operation of a pilot scale hydrodesulfurization plant, excellent agreement was found. A user-friendly interface was developed to facilitate the use of the numerical package.

Catalytic Conversion of N2O to N2 over Metal-Based Catalysts in the Presence of Hydrocarbons and Oxygen

The catalytic conversion of N2O to N2 in the presence or the absence of propene and oxygen was studied. The catalysts examined in this work were synthesized impregnating metals (Rh, Ru, Pd, Co, Cu, Fe, In) on different supports (Al2O3, SiO2, TiO2, ZrO2 and calcined hydrotalcite MgAl2(OH)8·H2O). The experimental results varied both with the type of the active site and with the type of the support. Rh and Ru impregnated on γ-alumina exhibited the highest activity. The performance of the above most promising catalysts was studied using various hydrocarbons (CH4, C3H6, C3H8) as reducing agents. These experimental results showed that the type of reducing agent does not affect the reaction yield. The temperature where complete conversion of N2O to N2 was measured was independent of the reductant type. The activity of the most active catalysts was also measured in the presence of SO2 and H2O in the feed. A shift of the N2O conversion versus temperature curve to higher temperatures was observed when SO2 and H2O were added, separately or simultaneously, to the feed. The inhibition caused by SO2 was attributed to the formation of sulfates and that caused by water to the competitive chemisorption of H2O and N2O on the same active sites.

Selective catalytic reduction of NO with C3H6 over Rh/alumina in the presence and absence of SO2 in the feed

Abstract The selective catalytic reduction of NO in excess O2 with C3H6 as reductant was studied over a Rh/alumina catalyst. The effect of SO2 on the extent of NO reduction and product formation was extensively examined. TPD and FT-IR studies using different feeds aimed at the identification of species adsorbed on alumina and Rh/alumina samples. Experiments were also carried out in a differential fixed-bed reactor to estimate apparent orders of reaction and activation energies. The rate-controlling step of the proposed reaction mechanism for the NO reduction is the reaction of Rh–NCO and Rh–NO+ for an SO2-free feed. In the presence of SO2 in the feed the NO and C3H6 oxidation over the catalyst were inhibited and a less complicated reaction mechanism is proposed, based on the reaction of Rh–NO+ and partially oxidized C3H6.