Comparative study between fluidized bed and fixed bed reactors in methane reforming combined with methane combustion for the internal heat supply under pressurized condition

The effect of catalyst fluidization on the conversion of methane to syngas in methane reforming with CO₂ and H₂O in the presence of O₂ under pressurized conditions was investigated over Ni and Pt catalysts. Methane and CO₂ conversion in the fluidized bed reactor was higher than those in the fixed bed reactor over Ni_0.15Mg_0.85O catalyst under 1.0 MPa. This reactor effect was dependent on the catalyst properties. Conversion levels in the fluidized and fixed bed reactor were almost the same over MgO-supported Ni and Pt catalysts. It is suggested that this phenomenon is related to the catalyst reducibility. On a catalyst with suitable reducibility, the oxidized catalyst can be reduced with the produced syngas and the reforming activity regenerates in the fluidized bed reactor. Although serious carbon deposition was observed on Ni_0.15Mg_0.85O in the fixed bed reactor, it was inhibited in the fluidized bed reactor.     

Improvement of promoters on the Fischer–Tropsch activity of mechanically mixed Fe catalysts

The precipitated Fe₂O₃ was promoted with K, Cu, Zn and Al by impregnation and mechanical mixing. Their activity for Fischer–Tropsch (FT) synthesis was tested in fixed bed reactor under the conditions of 503 K and 1.6 MPa syngas (H₂/CO = 2). The Fe catalysts co-promoted by K, Cu, Zn and Al showed increasing CO conversion with time on stream. At present, the improvement is ascribed to the increased resistance to water oxidation on active sites and the further formation of active sites during FT synthesis with the addition of K, Cu, Zn and Al to Fe catalysts. The carbon deposition is not responsible for the variety of catalytic activity in this study.     

Temperature profile in a two-stage fixed bed reactor for catalytic partial oxidation of methane to syngas

Detailed axial temperature distribution has been studied in a two-stage process for catalytic partial oxidation of methane to syngas, which consists of two consecutive fixed bed reactors with oxygen or air separately introduced. The first stage of the reactor, packed with a combustion catalyst, is used for catalytic combustion of methane at low initial temperature. While the second stage, filled with a partial oxidation catalyst, is used for the partial oxidation of methane to syngas. A pilot-scale reactor packed with up to 80 g combustion catalyst and 80 g partial oxidation catalyst was employed. The effects of oxygen distribution in the two sections, and gas hourly space velocity (GHSV) on the catalyst bed temperature profile, as well as conversion of methane and selectivities to syngas were investigated under atmospheric pressure. It is found that both oxygen splitting ratio and GHSV have significant influence on the temperature profile in the reactor, which can be explained by the synergetic effects of the fast exothermic oxidation reactions and the slow endothermic (steam and CO₂) reforming reactions. Almost no change in activity and selectivity was observed after a stability experiment for 300 h.     

A novel low-temperature methanol synthesis method from CO/H2/CO2 based on the synergistic effect between solid catalyst and homogeneous catalyst

The activity of a binary catalyst in alcoholic solvents for methanol synthesis from CO/H₂/CO₂ at low temperature was investigated in a concurrent synthesis course. Experiment results showed that the combination of homogeneous potassium formate catalyst and solid copper–magnesia catalyst enhanced the conversion of CO₂-containing syngas to methanol at temperature of 423–443 K and pressure of 3–5 MPa. Under a contact time of 100 g h/mol, the maximum conversion of total carbon approached the reaction equilibrium and the selectivity of methanol was 99%. A reaction pathway involving esterification and hydrogenolysis of esters was postulated based on the integrative and separate activity tests, along with the structural characterization of the catalysts. Both potassium formate for the esterification as well as Cu/MgO for the hydrogenolysis were found to be crucial to this homogeneous and heterogeneous synergistically catalytic system. CO and H₂ were involved in the recycling of potassium formate.     

Characteristics of integrated micro packed bed reactor-heat exchanger configurations in the direct synthesis of dimethyl ether

The performance of three integrated micro packed bed reactor-heat exchangers (IMPBRHEs) for direct DME synthesis over physical mixtures of CuO–ZnO–Al₂O₃ and γ-Al₂O₃ catalysts was experimentally investigated. Systematic variations in reactor and slit dimensions and configuration were analyzed in terms of thermal behaviour, mass transfer, pressure drop and residence time distribution (RTD). The pressure drop was always small (<0.12 bar) relative to the total pressure (50 bar), and linear dependence with GHSV confirms the predicted laminar flow for Re = 0.1–2. A narrow RTD was estimated by the dispersion analysis. Careful temperature measurements confirmed that the reaction temperature is mainly controlled by the oil heat exchange to give a practically uniform temperature profile for set inlet oil temperatures of 220–320 °C. The micro packed beds were found free of the internal as well as external mass transfer limitations, as showed by no significant change in the CO conversion and DME yield for different catalyst particle sizes, no effect of varying the linear gas velocity, and no effect of manipulating reactant diffusion coefficient. Packed bed microstructured reactors hence provide an isobaric and isothermal environment free from transport limitations for the direct DME synthesis, in the kinetic regime as well as at equilibrium conversion.     

CO2 reforming of CH4 in coke oven gas to syngas over coal char catalyst

The CO₂ reforming of methane (in coke oven gas) on the coal char catalyst was performed in a fixed bed reactor at temperatures between 800 and 1200 °C under normal pressure. The effects of the coal char catalyst pretreatment and the ratio of CO₂/CH₄ were studied. Experimental results showed that the coal char was an effective catalyst for production of syngas, and addition of CO₂ did not enhance the CH₄ reforming to H₂. It was also found that the product gas ratio of H₂/CO is strongly influenced by the feed ratio of CO₂/CH₄. The modified coal char catalyst was more active during the CO₂–CH₄ reforming than the coal char catalyst based on the catalyst volume, furthermore the modified catalyst exhibited high activity in CO₂–CH₄ reforming to syngas. The conversion of methane can be divided into two stages. In the first stage, the conversion of CH₄ gradually decreased. In the second stage, the conversion of methane maintained nearly constant. The conversion of CO₂ decreased slightly during the overall reactions in CO₂–CH₄ reforming. The coal char catalyst is a highly promising catalyst for the CO₂ reforming of methane to syngas.     

Process modelling of dimethyl ether production from Victorian brown coal—Integrating coal drying,gasification and synthesis processes

Power plants using Victorian brown coal operate at low efficiency. Being reactive and spontaneously combustible, dried brown coals cannot be exported either. Synthesis of dimethyl ether (DME) is one option for the production of liquid fuel, an exportable product for power generation and transportation. This paper presents a steady-state process model for DME production using brown coal including drying, gasification and DME synthesis. The yield of the DME was a maximum for H₂ to CO molar ratio of 1.41 and 0.81 at the gasifier outlet and the DME reactor inlet respectively. A process efficiency of 32% and CO₂ emission of 2.91 kg/kg of DME was obtained. Improved yield of DME is achieved when CO₂ is removed from the fuel gas prior to feeding to the synthesis reactor. Integration of waste heat and design of appropriate catalyst for gasification and DME synthesis can result in further improvements in the process.     

An integrated biomass-derived syngas/dimethyl ether process

A Cu-Zn-Al methanol catalyst combined with HZSM-5 was used for dimethyl ether (DME) synthesis from a biomass-derived syngas containing nitrogen. The syngas was produced by air-steam gasification of pine sawdust in a bubbling fluidized bed biomass gasifier with a dry reforming reaction over ultra-stable NiO-MgO catalyst packed in a downstream reactor for stoichiometric factor (H₂, CO, CO₂) adjustment. It constantly gave syngas with H2/CO ratio of 1.5 and containing trace CH₄ and CO₂ during a period of 150 h. The obtained N₂-containing biomass-derived syngas was used directly for DME synthesis. About 75% CO per-pass conversion and 66.7% DME selectivity could be achieved under the condition of 533 K, 4MPa and 1,000-4,000 h^-1. The maximized DME yield, 244 g DME/Kgbiomass (dry basis), was achieved under a gasification temperature of 1,073 K, ER (Equivalence Ratio) of 0.24, S/B (Steam to Biomass Ratio) of 0.72 and reforming temperature of 1,023 K with the addition of 0.54 Nm³ biogas/Kg_biomass (dry basis).     

Fischer–Tropsch synthesis: effect of small amounts of boron,ruthenium and rhenium on Co/TiO2 catalysts

The effect of the addition of small amounts of boron, ruthenium and rhenium on the Fischer–Tropsch (F–T) catalyst activity and selectivity of a 10 wt.% Co/TiO₂ catalyst has been investigated in a continuously stirred tank reactor (CSTR). A wide range of synthesis gas conversions has been obtained by varying space velocities over the catalysts. The addition of a small amount of boron (0.05 wt.%) onto Co/TiO₂ does not change the activity of the catalyst at lower space times and slightly increases synthesis gas conversion at higher space times. The product selectivity is not significantly influenced by boron addition for all space velocities investigated. Ruthenium addition (0.20 wt.%) onto Co/TiO₂ and CoB/TiO₂ catalysts improves the catalyst activity and selectivity. At a space time of 0.5 h-g cat./NL, synthesis gas conversion increases from 50–54 to 68–71% range and methane selectivity decreases from 9.5 to 5.5% (molar carbon basis) for the promoted catalyst. Among the five promoted and non-promoted catalysts, the rhenium promoted Co/TiO₂ catalyst (0.34 wt.% Re) exhibited the highest synthesis gas conversion, and at a space time of 0.5 h-g cat./NL, synthesis gas conversion was 73.4%. In comparison with the results obtained in a fixed bed reactor, the catalysts displayed a higher F–T catalytic activity in the CSTR.     

High performance Cu–ZnO/Pd-β catalysts for syngas to LPG

The catalytic performance of Cu–ZnO/Pd-β catalyst for syngas to LPG (Liquefied Petroleum Gas) has been investigated in this paper. The kind of zeolite, SiO₂/Al₂O₃ ratio in Pd-β, Pd-β particle size, Pd content in Pd-β, and reaction conditions, have been optimized. The results showed that the suitable reaction conditions for syngas to LPG over Cu–ZnO/Pd-β are: 325–350 °C, 2.1–3.6 MPa, 4.5–9 g h/mol gas velocity (W/F), and 37–75 ratio of SiO₂/Al₂O₃. At the optimal conditions, Cu–ZnO/Pd-β could exhibit an excellent catalytic performance for syngas to LPG: 72.2% CO conversion, 45.3% hydrocarbon yield and 78.0% LPG selectivity in hydrocarbons could be achieved.     

Low-temperature catalytic conversion of lignite: 3. Tar reforming using the supported potassium carbonate

Alumina-supported K₂CO₃–LaMn_0.8Cu_0.2O₃ was investigated for the catalytic conversion of tar, produced from lignite, into syngas under inert and steam-reforming conditions. A double-bubble fluidized bed reactor system, equipped with a micro gas chromatograph and a collecting system to analyze permanent gases and condensable species, was developed to screen the catalytic conversion of tar components below 700 °C. The redox properties of catalysts, estimated by hydrogen temperature programmed reduction analyses, were correlated with their catalytic performance in tar conversion. The synthesized catalyst effectively converted tars into hydrogen-rich syngas and also improved tar reforming by inhibiting coke deposition.     

Specifics of dimethyl ether synthesis from syngas over mixed catalysts

Dimethyl ether (DME) synthesis from syngas over a mixture of a methanol synthesis catalyst (ZnO, 25.10 wt %; AuO, 64.86 wt %; Al₂O₃, 10.04 wt %) and a methanol dehydration catalyst (γ-A1₂O₃) has been investigated for one-, two-, and three-layer catalyst beds. There is a common regularity for these three variants: with an increasing temperature, the total CO conversion decreases, the CO-to-methanol conversion decreases, and the CO-to-DME conversion increases. The largest values of DME selectivity and DME yield have been attained with the three-layer bed. The highest DME yield has been obtained at 250–285°C. Use of a mechanical mixture of the methanol synthesis catalyst and alumina makes it possible to efficiently obtain DME from syngas ballasted with nitrogen (20 vol %) at an H₂/CO ratio of 1, which is unfavorable for methanol synthesis. The DME yield on the syngas input basis in this case with the ballast gas (nitrogen or CO₂) taken into account can be about 10 wt %.     

Synthesis gas generation by chemical-looping reforming in a continuously operating laboratory reactor

Chemical-looping reforming is a technology that can be used for partial oxidation and steam reforming of hydrocarbon fuels. This paper describes continuous chemical-looping reforming of natural gas in a laboratory reactor consisting of two interconnected fluidized beds. Particles composed of 60 wt% NiO and 40 wt% MgAl₂O₄ are used as bed material, oxygen carrier and reformer catalyst. There is a continuous circulation of particles between the reactors. In the fuel reactor, the particles are reduced by the fuel, which in turn is partially oxidized to H₂, CO, CO₂ and H₂O. In the air reactor the reduced oxygen carrier is reoxidized with air. Complete conversion of natural gas was achieved and the selectivity towards H₂ and CO was high. In total, 41 h of reforming were recorded. Formation of solid carbon was noticed for some cases. Adding 25 vol% steam to the natural gas reduced or eliminated the carbon formation.     

Improving the POM performance of YBa2Cu3O7−δ membrane reactor by Co doping

The performance of Co doped YBa₂Cu₃O_7−δ (YBCO) membrane reactor have been investigated in a process of the partial oxidation of methane (POM) to syngas. The results shows that doping YBCO membrane with a little Co can enhance its oxygen permeation flux and improve its stability in reducing atmosphere noticeably. At 900 °C, with feed flow at 50 ml/min, CH₄ 6.0 v%, SV = 12,000 h⁻¹, and Ni/ZrO₂ catalyst, CH₄ conversion rate, CO selectivity, and oxygen permeation flux can reach to 98%, 92% and 1.41 ml min⁻¹ cm⁻² respectively.     

Coconut shell activated carbon tethered ionic liquids for continuous cycloaddition of CO2 to epichlorohydrin in packed bed reactor

Various ionic liquids (ILs) were in situ prepared on coconut shell activated carbon (CSAC) granules. Cycloaddition of CO₂ to epichlorohydrin (ECH) was continuously carried out in a packed-bed reactor without using solvent or cocatalyst. The conversion rates of ECH over the CSAC tethered Bmim/Br, Bmim/BF₄, Bmim-OH/Br and Bmim-COOH/Br were 63.4%, 74.5%, 83.4% and 85.9% at 140 °C and 1.4 MPa, respectively. The selectivities to epichlorohydrin carbonate (ECHC) were over 98% for the four catalysts. The ECH conversion stabilized at 82% for the CSAC tethered Bmim-COOH/Br after 50 h of continuous performance in the packed bed reactor.     

Effect of temperature on bitumen conversion in a supercritical water flow

This article deals with a study of bitumen conversion (the gross-formula CH_1.47N_0.01S_0.007) in a supercritical water (SCW) flow continuously supplied at the bottom of the vertically located tubular reactor. At the first stage, bitumen was continuously supplied from the top of the reactor into a counter-current SCW flow (400 °C, 30 MPa) for 60 min. At the second stage (after ceasing the supply of bitumen into the reactor), SCW was pumped through the layer of bitumen residue at uniform (2.5 °C/min) temperature increase from 400 to 700 °C at 30 MPa. The amount and composition of the liquid and volatile conversion products were measured. It is revealed that during bitumen supply into the reactor and subsequent pumping of SCW through the layer of bitumen residue in the temperature increasing mode from 400 to 500 °C, the yields of liquid conversion products are equal to 26.9 and 45.4%, respectively, relative to the weight of bitumen supplied into the reactor. Oils are the major components of these liquid products. Participation of H₂O molecules in redox reactions became evident due to the formation of CO and CO₂ even at 400 °C. A significant increase in the yields of H₂, CH₄, and CO₂ are detected at T > 600 °C. Based on the sulfur balance, it can be stated that the degree of bitumen desulfurization at 400–700 °C due to sulphur removal in form of H₂S accounts for 21.6 wt.% A solid carbonaceous bitumen residue, obtained after SCW conversion, is characterized by high specific surface (224 m²/g).     

Low-temperature catalytic conversion of lignite: 1. Steam gasification using potassium carbonate supported on perovskite oxide

The catalytic conversion of alkali metal carbonate (K₂CO₃) catalyst supported on perovskite oxide was carefully examined as an effective catalyst for low-temperature catalytic gasification of lignite. It showed much higher activity than K₂CO₃ alone as well as K₂CO₃ supported on γ-alumina under gasification conditions below 800 °C. Furthermore, catalyzed syngas had higher H₂ and lower CO₂ ratios than non-catalyzed syngas. Promisingly, there was also much less tar formation, less than 50 wt.% compared to non-catalyzed gasification. Also, less loss of K₂CO₃ and no coke formation on the catalyst surface were confirmed, comparing to the catalytic gasification with K₂CO₃ supported on γ-alumina.     

Catalytic depolymerisation and conversion of Kraft lignin into liquid products using near-critical water

A high-pressure pilot plant was developed to study the conversion of LignoBoost Kraft lignin into bio-oil and chemicals in near-critical water (350 °C, 25 MPa). The conversion takes place in a continuous fixed-bed catalytic reactor (500 cm³) filled with ZrO₂ pellets. Lignin (mass fraction of approximately 5.5%) is dispersed in an aqueous solution containing K₂CO₃ (from 0.4% to 2.2%) and phenol (approximately 4.1%). The feed flow rate is 1 kg/h (reactor residence time 11 min) and the reaction mixture is recirculated internally at a rate of approximately 10 kg/h. The products consist of an aqueous phase, containing phenolic chemicals, and a bio-oil, showing an increased heat value (32 MJ/kg) with respect to the lignin feed. The 1-ring aromatic compounds produced in the process are mainly anisoles, alkylphenols, guaiacols and catechols: their overall yield increases from 17% to 27% (dry lignin basis) as K₂CO₃ is increased.     

Hydrothermal gasification of Rosa Damascena residues: Gaseous and aqueous yields

The gasification of Rosa Damascena residues – by-products of the rose-oil industry – was investigated under hydrothermal conditions at 500 °C and 600 °C, 35–45 MPa pressure with a reaction time of 1 h. The experiments were performed in the absence and presence of catalysts of K₂CO₃ and trona in a batch type reactor. The composition of the gaseous and aqueous products was determined by gas chromatography and high performance liquid chromatography, respectively. H₂, CO₂ and CH₄ are the main gaseous products while carboxylic acids (formic acid, acetic acid, glycolic acid) are the main components found in the aqueous phase followed by furfurals, phenols, aldehyde and ketones. More gaseous products were obtained at the higher temperature of 600 °C. Adding catalyst was found to aid the conversion process but the effect was only slight. Rosa Damascena residues have the potential to be a useful source for H₂ production in the future.     

Hydrodesulfurization of diesel in a slurry reactor

The need for more complete removal of sulfur from fuels is due to the lower allowable sulfur content in gasoline and diesel, which is made difficult by the increased sulfur contents of crude oils. This work reports an experimental study on the hydrodesulfurization (HDS) of diesel in a slurry reactor. HDS of straight-run diesel using a NiMoS/Al₂O₃ catalyst was studied in a high-pressure autoclave for the following operating conditions: 4.8–23.1 wt% catalyst in the reactor, 320–360 °C, 3–5 MPa pressure, and 0.56–2.77 L/min hydrogen flow rate. It was found that the reaction rate was proportional to the catalyst amount and increased with temperature, pressure and hydrogen flow rate. The reaction kinetics for the HDS reaction in the slurry reactor was obtained. As compared with HDS in a fixed bed reactor, HDS in a slurry reactor is promising because of the uniform temperature profile, high catalyst efficiency, and online removal and addition of catalyst.