The oxidative coupling of methane in a fluidised-bed reactor

A small fluidised-bed reactor has been used by the CSIRO Division of Coal Technology to study the oxidative coupling of methane to higher hydrocarbons. Methane conversions of 9.6 to 13.5% were obtained in preliminary experiments using a lithium-promoted magnesium oxide catalyst at 850°C and with feed gases containing 5.6 to 10.7% v/v oxygen. Total hydrocarbon selectivity declined from 82 to 72% with increasing methane conversion. When operating with ethane in the feed at concentrations found in natural ethylene, the fluidised-bed reactor converted the ethane with good selectivity to ethylene, a key result in the context of using oxidative coupling for natural gas conversion. In view of these promising results, current work is directed towards increasing methane conversion and hydrocarbon selectivity in fluidised-bed reactors by development of more active and selective catalysts.     

A sensitivity analysis and multi-objective optimization to enhance ethylene production by oxidative dehydrogenation of ethane in a membrane-assisted reactor

Owing to the importance of process intensification in the natural gas associated processes, the present contribution aims to investigate the production of an important natural gas downstream product in an improved system. Accordingly, a membrane-assisted reactor for the oxidative dehydrogenation of ethane is presented. The presented system includes a membrane for axial oxygen dosing into the reaction side. Such a strategy would lead to optimum oxygen distribution along the reactor length and prevention of hot spot formation as well. A feasibility study is conducted by developing a validated mathematical model composed of mass and energy balance equations. The effects of various operating variables are investigated by a rigorous sensitivity analysis. Then, by applying the genetic algorithm, a multi-objective optimization procedure is implemented to obtain the optimum operating condition. Considerable increase in the ethane conversion and ethylene yield are the advancements of membrane-assisted oxidative dehydrogenation reactor working under the optimum condition. More than 30% increase in the ethane conversion is obtained. Furthermore, the ethylene yield is enhanced up to 0.45.     

Fluidised bed membrane reactor for ultrapure hydrogen production via methane steam reforming: Experimental demonstration and model validation

Hydrogen is emerging as a future alternative for mobile and stationary energy carriers in addition to its use in chemical and petrochemical applications. A novel multifunctional reactor concept has been developed for the production of ultrapure hydrogen from light hydrocarbons such as methane for online use in downstream polymer electrolyte membrane fuel cells. A high degree of process intensification can be achieved by integrating perm-selective hydrogen membranes for selective hydrogen removal to shift the methane steam reforming and water-gas-shift equilibriums in the favourable direction and perm-selective oxygen membranes for selective oxygen addition to supply the required reaction energy via partial oxidation of part of the methane feed and enable pure CO₂ capture without costly post-treatment. This can be achieved in a proposed novel multifunctional bi-membrane bi-section fluidised bed reactor [Patil, C.S., van Sint Annaland, M., Kuipers, J.A.M., 2005. Design of a novel autothermal membrane assisted fluidized bed reactor for the production of ultrapure hydrogen from methane. Industrial and Engineering Chemistry Research 44, 9502-9512]. In this paper, an experimental proof of principle for the steam reforming/water-gas-shift section of the proposed novel fluidised bed membrane reactor is presented. A fluidised bed membrane reactor for steam reforming of methane/water-gas-shift on a commercial noble metal-based catalyst has been designed and constructed using 10 H₂ perm-selective Pd membranes for a fuel cell power output in the range of 50-100 W. It has been experimentally demonstrated that by the insertion of the membranes in the fluidised bed, the thermodynamic equilibrium constraints can indeed be overcome, i.e., increased CH₄ conversion, decreased CO selectivity and higher product yield (H₂ produced/CH₄ reacted). Experiments at different superficial gas velocities and also at different temperatures and pressures (carried out in the regime without kinetic limitations) revealed enhanced reactor performance at higher temperatures and pressures (3-4 bar). With a phenomenological two-phase reactor model for the fluidised bed membrane reactor, incorporating a separately developed lumped flux expression for the H₂ permeation rate through the used Pd-based membranes, the measured data from the fluidised bed membrane reactor could be well described, provided that axial gas back-mixing in the membrane-assisted fluidised bed reactor is negligible. This indicates that the membrane reactor behaviour approached that of an ideal isothermal plug flow reactor with maximum H₂ permeation.     

Effect of hydrogen combustion reaction on the dehydrogenation of ethane in a fixed-bed catalytic membrane reactor

A two-dimensional non-isothermal mathematical model has been developed for the ethane dehydrogenation reaction in a fixed-bed catalytic membrane reactor. Since ethane dehydrogenation is an equilibrium reaction, removal of produced hydrogen by the membrane shifts the thermodynamic equilibrium to ethylene production. For further displacement of the dehydrogenation reaction, oxidative dehydrogenation method has been used. Since ethane dehydrogenation is an endothermic reaction, the energy produced by the oxidative dehydrogena-tion method is consumed by the dehydrogenation reaction. The results show that the oxidative dehydrogenation method generated a substantial improvement in the reactor performance in terms of high conversions and significant energy saving. It was also established that the sweep gas velocity in the shell side of the reactor is one of the most important factors in the effectiveness of the reactor.     

Membrane Reactor/Separator: A Design for Bimolecular Reactant Addition

Abstract

A membrane reactor (MBR) is used to investigate the effect of selective reactant addition on series-parallel reaction networks, such as the oxidative dehydrogenation of ethane to ethylene. Ethylene is favored in an oxygen-lean environment, while excess oxygen favors the formation of combustion products. Control of the reactant ratio (ethane to oxygen) is crucial to both the overall selectivity and the hydrocarbon conversion. Traditional reactor designs co-feed the bimolecular reactants at the top of the reactor at some preset feed ratio. The MBR uses a tube (porous alumina membrane) and shell configuration. One reactant is fed at the top of a catalyst bed packed within the membrane core. The other reactant permeates into the tube along the length of the reactor via an imposed pressure drop. The reactant ratio is large at the top of the MBR, which leads to high selectivities; as the oxygen is consumed, it is replenished via downstream permeation to improve the ethane conversion. The MBR and a plug flow reactor (PFR) are evaluated at 600 [ddot]C, with identical space velocities, and using a magnesium oxide catalyst doped with samarium oxide. At low to moderate reactant feed ratios, the ethylene yield in the MBR exceeds the PFR by a factor of three, under some conditions. At higher feed ratios, the performance of the PFR nears or exceeds the performance of the MBR.     

Steam reforming of natural gas with intergrated hydrogen separation for hydrogen production

The development of heat resistant permeation membranes has opened up new possibilities for the conversion of fossil energy resources. In steam reforming of natural gas, such membranes even permit a direct production of hydrogen at high temperatures during the conversion of feed hydrocarbons. Further gas processing, such as required for reformer gas in existing hydrogen production processes, is not necessary. Due to continuous hydrogen discharge directly in the reformer tube, the chemical equilibrium of the occurring reactions becomes displaced towards the products, resulting in more favourable process conditions and, consequently, in improved by 36% utilization of the feed hydrocarbons. At the same time, the hydrogen yield increases by 44%. The heat required, which is provided by a high temperature reactor, is 17% in excess of that in conventional plants. It can be expected that the simplified process design will produce substantial cost advantages over the existing processes for the production of hydrogen.     

Co‐current and Countercurrent Configurations for a Membrane Dual Type Methanol Reactor

A dynamic model for a membrane dual‐type methanol reactor was developed in the presence of catalyst deactivation. This reactor is a shell and tube type where the first reactor is cooled with cooling water and the second one with feed synthesis gas. In this reactor system, the wall of the tubes in the gas‐cooled reactor is covered with a palladium‐silver membrane which is only permeable to hydrogen. Hydrogen can penetrate from the feed synthesis gas side into the reaction side due to the hydrogen partial pressure driving force. Hydrogen permeation through the membrane shifts the reaction towards the product side according to the thermodynamic equilibrium. Moreover, the performance of the reactor was investigated when the reaction gas side and feed gas side streams are continuously either co‐current or countercurrent. Comparison between co‐current and countercurrent mode in terms of temperature, activity, methanol production rate as well as permeation rate of hydrogen through the membrane shows that the reactor in co‐current configuration operates with lower conversion and also lower permeation rate of hydrogen but with longer catalyst life than does the reactor in countercurrent configuration.     

Application of water vapor and hydrogen-permselective membranes in an industrial fixed-bed reactor for large scale methanol production

Coupling reaction and separation in a membrane reactor improves the reactor efficiency and reduces purification cost in the next stages. In this work a novel reactor consisting two membrane layers has been proposed for simultaneous hydrogen permeation to reaction zone and water vapor removal from reaction zone in the methanol synthesis reactor. In this configuration conventional methanol reactor is supported by a Pd/Ag membrane layer for hydrogen permeation and alumina-silica composite membrane layer for water vapor removal from reaction zone. In this reactor syngas is fed to the reaction zone that is surrounded with hydrogen-permselective membrane tube. The water vapor-permselective membrane tube is placed in the reaction zone. A steady state heterogeneous one-dimensional mathematical model is developed for simulation of the proposed reactor. To verify the accuracy of the model, simulation results of the conventional reactor is compared with the available plant data. The membrane fixed bed reactor benefits are higher methanol production rate, higher quality of outlet product and consequently lower cost in product purification stage. This configuration has enhanced the methanol yield by 10.02% compared with industrial reactor. Experimental proof-of-concept is needed to establish the safe operation of the proposed configuration.     

Hydrogen production by decomposition of ethane-containing methane over carbon black catalysts

Mixtures of methane and small amounts of ethane were decomposed in the presence of carbon black (CB) catalysts at 1,073–1,223 K for hydrogen production. Although most of the added ethane was first decomposed to ethylene and hydrogen predominantly by non-catalytic reaction, subsequent decomposition of ethylene was effectively facilitated by the CB catalysts. Because some methane was produced from ethane, the net methane conversion decreased as the added ethane increased. The rate of hydrogen production from methane was decreased by the added ethane. A reason for this is that adsorption of methane on the active sites is inhibited by more easily adsorbing ethylene. In spite of this, the hydrogen yield increased with an increase of the added ethane because the contribution of ethane and ethylene decomposition to the hydrogen production was dominant over methane decomposition. A higher hydrogen yield was obtained in the presence of a higher-surface-area CB catalyst.     

Conversion of Pyrolysis Fuel Oils by a Dielectric Barrier Discharge Reactor in the Presence of Methane and Ethane

Pyrolysis fuel oil cracking by low‐temperature plasma was investigated in a dielectric barrier discharge reactor at ambient pressure. The promoting effect of methane and ethane in the formation of products was evaluated by altering the working gas from methane to ethane. In addition, the production of hydrocarbons and hydrogen was analyzed. The main parameters were working gas type, flow rate, and applied voltage. Increasing the applied voltage enhanced the production rate of valuable petrochemical compounds like gas and liquid. Alteration of the working gas flow rate led to a higher production rate of H₂, C₂, C₃, and C₄. Chemical investigations were performed by optical emission spectroscopy of plasma and the main mechanisms are described.     

Membrane/sorption-enhanced methanol synthesis process: Dynamic simulation and optimization

In this study, a dynamic mathematical model of a Membrane-Gas-Flowing Solids-Fixed Bed Reactor (Membrane-GFSFBR) with in-situ water adsorption in the presence of catalyst deactivation is proposed for methanol synthesis. The novel reactor consists of water adsorbent and hydrogen-permselective Pd-Ag membrane. In this configuration feed gas and flowing adsorbents are both fed into the outer tube of the reactor. Contact of gas and fine solids particles inside packed bed results in selective adsorption of water from methanol synthesis which leads to higher methanol production rate. Afterwards, the high pressure product is recycled to the inner tube of the reactor and hydrogen permeates to the outer tube which shifts the reaction towards more methanol production. Dynamic simulation result reveals that simultaneous application of water adsorbent and hydrogen permeation in methanol synthesis process contributes to a significant enhancement in methanol production. The notable advantage of Membrane-GFSFBR is the continuous adsorbent regeneration during the process. Moreover, a theoretical investigation has been performed to evaluate the optimal operating conditions and to maximize the methanol production in Membrane-GFSFBR using differential evolution (DE) algorithm as a robust method. The obtained optimization result shows there are optimum values of inlet temperatures of gas phase, flowing solids phase, and shell side under which the highest methanol production can be achieved.     

Promotion of hydrogen permeation on metal-dispersed alumina membranes and its application to a membrane reactor for methane steam reforming

A mesoporous membrane for selective separation of hydrogen was prepared usingthe sol-gel method. Some metal salts such as RuCl₃, Pd(NH₃)₄Cl₂, RhCl₃,, and H ₂PtCl₆, were added to the boehmite sol and coated on a porous alumina substrate before firing at 500°C. It was foundthat the permeability of hydrogen and the separation factor for a hydrogen-nitrogen gaseous mixture of these metaldispersed membranes exceeded the limitations of the Knudsen diffusion mechanism. Although the gas permeation through a neat alumina membrane is governed by the Knudsen diffusion, the metals dispersed in alumina membranes were effective in promoting hydrogen permeation. These metaldispersed alumina membranes were also used in a membrane reactor for methane steam reforming at low temperature. In the temperature range of 300 to 500°C, the membrane reactor attained a methane conversion twice as high as the equilibrium value of the packed bed catalytic reactor system as a result of the selective removal of hydrogen from the reaction system.     

Pyrolysis of hydrocarbon mixtures characteristic of coal: Application to dibenzyl mixture

Thermal cracking of dibenzyl dissolved in two solvents, tetralin and decalin, has been studied in a flow reactor, in the presence of steam, under atmospheric pressure and at temperatures between 600 and 750 °C. The nature of the products obtained depends upon the structure of the hydrogen-donor agent, but is independent of the structure of dibenzyl. Valuable products such as ethylene and a benzene, toluene and xylene (BTX) mixture, obtained by a β-scission reaction with a monomolecular mechanism, are predominant when decalin is used as solvent. The dehydrogenation of tetralin to naphthalene precedes cracking reactions of the bimolecular type, which lead to significant production of hydroaromatics such as indene. Cracking of dibenzyl, followed by hydrogen transfer from the solvent to the radicals formed, leads to toluene irrespective of the chemical nature of the hydrogen donor.     

Oxidative activation of ethane on catalytic modified dense ionic oxygen conducting membranes

A reactor using dense mixed ion electron conducting membranes was successfully studied in the oxidative dehydrogenation of ethane to ethylene. Already bare Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ membranes allowed reasonable operation with yields beyond state-of-the-art steam cracking. The application of a surface catalyst was found to enhance performance even further. Long term stable operation and ethylene yields of about 75% were observed when using membranes with V/MgO micron grain or Pd nano cluster modified surfaces at temperatures of 1040 or 1050 K, respectively. Being one key factor for the performance of the membrane reactor, the influence of the surface catalysts on the oxygen permeation is reported in a detailed study. Parameters for a model describing the oxygen permeation were determined. The nature of the model indicates the importance of the surface exchange for oxygen permeation, explaining in this way the observed enhancement after application of surface catalysts at the permeate side.     

Methane steam reforming in a Pd-Ru membrane reactor

Methane steam reforming has been carried out in a Pd-Ru membrane reactor at 500–600 ‡C. The membrane reactor consisted of a Pd-6%Ru tube of 100 mm wall thickness and commercial catalysts packed outside of the membrane. The methane conversion was significantly enhanced in the membrane reactor in which reaction equilibrium was shifted by selective permeation of hydrogen through the membrane. The methane conversion at 500 ‡C was improved as high as 80% in the membrane reactor, while equilibrium conversion in a fixed-bed reactor was 57%. The effect of gas flow rate and temperature on the performance of the membrane reactor was investigated and the results were compared with the simulated result from the model. The model prediction is in good agreement with the experimental result. In order to apply the membrane in practice, however, the thickness of the membrane has to be reduced. Therefore, the effect of membrane thickness on performance of the membrane reactor was estimated using the model.     

New Integrated Catalytic Membrane Processes for Enhanced Propylene and Polypropylene Production

Newly reported integrated processes are discussed for aliphatic (paraffin) hydrocarbon dehydrogenation into olefins and subsequent polymerization into polyolefins (e.g., propane to propylene to polypropylene, ethane to ethylene to polyethylene). Catalytic dehydrogenation membrane reactors (permreactors) made by inorganic or metal membranes are employed in conjunction with fluid bed polymerization reactors using coordination catalysts. The catalytic propane dehydrogenation is considered as a sample reaction in order to design an integrated process of enhanced propylene polymerization. Related kinetic experimental data of the propane dehydrogenation in a fixed bed type catalytic reactor is reviewed which indicates the molecular range of the produced C₁-C₃ hydrocarbons. Experimental membrane reactor conversion and yield data are also reviewed. Experimental data were obtained with catalytic membrane reactors using the same catalyst as the non-membrane reactor. Developed models are discussed in terms of the operation of the reactors through computational simulation, by varying key reactor and reaction parameters. The data show that it is effective for catalytic permreactors to provide streams of olefins to successive polymerization reactors for the end production of polyolefins (i.e., polypropylene, polyethylene) in homopolymer or copolymer form. Improved technical, economic, and environmental benefits are discussed from the implementation of these processes.     

Fixed‐Bed Multi‐Tubular Reactors for Oxidative Dehydrogenation in Ethylene Process

An industrial‐scale reactor for ethylene production was modeled using the oxidative dehydrogenation of ethane (ODHE) in a multi‐tubular reactor system, examining a variety of parameters affecting reactor performance. The model showed that a double‐bed multi‐tubular reactor with intermediate air injection scheme was superior to a single‐bed design, due to the increased ethylene selectivity while operating under lower oxygen partial pressures. The optimized reactor length for 100 % oxygen conversion was theoretically determined for both reactor designs. The use of a distributed oxygen feed with a limited number of injection points indicated a significant improvement on the reactor performance in terms of ethane conversion and ethylene selectivity. This concept also overcame the reactor runaway temperature problem and enabled operations over a wider range of conditions to obtain enhanced ethylene production.     

Flash hydrogenation of coal. 3. A sample of US coals

The susceptibility of a group of US coals to the production of light gaseous and liquid hydrocarbons during flash hydrogenation is examined. Eight coals ranging from lignite to high-volatile A bituminous and representing five provinces, have been flash heated in 101.3 MPa of flowing hydrogen using a bench scale reactor. A 0.6 s gas phase residence time was provided to hydrocrack the vapour products. Temperatures ranged from 750 to 850°C, where maximum yields of ethane and BTX (benzene+toluene + xylene) are found. The carbon conversion decreased with increasing rank at fixed reaction conditions. Methane yields are highest for lignite. Peak ethane yields range from 6.4 to 9% carbon conversion. BTX yields have a shallow maximum at intermediate ranks, decreasing towards high and low rank coals. Total liquid yields range from 14 to 43%. Although a definite variation of yield with rank is evident, the trends, especially total liquid yields, are attended by considerable scatter. Rank is not the only, and indeed may not be the most significant variable in determining the yield of individual species in flash hydrogenation. To establish the significant variables a stepwise regression procedure was applied to the experimental data using information from the elemental, proximate and petrographic compositions of the coals as independent variables. Two variables are adequate in all cases to correlate species yield and coal properties. Exinite appears to be capable of increasing the amount of liquid obtained from other macerals.     

Direct hydroxylation of aromatic compounds by a palladium membrane reactor

Direct hydroxylation of aromatic compounds was effectively achieved by using a newly developed Pd membrane reactor in which the Pd membrane is thin enough (ca. 1 μm) to allow permeation of hydrogen below 500 K. In this reactor, the active oxygen species is formed on the surface of Pd via the reaction between oxygen and permeated hydrogen from opposite sides of the membrane. Hydroxylation occurs on the surface of Pd via reaction of the aromatic compound and active oxygen. In the reaction of benzene at a reaction temperature of 423 K, the reactor achieved a benzene conversion of 15% and a phenol selectivity of 95%. An increase in reaction temperature, however, caused simultaneous hydrogenation. In the reaction of methyl benzoate, the reaction products were not only methyl salicylate, which is a hydroxylation product, but also numerous hydrogenation and oxidation compounds via side reactions. These side reactions were related to the gas balance between oxygen and hydrogen; oxygen-rich conditions caused complete oxidation, whereas oxygen-poor conditions (i.e., high amount of permeated hydrogen) induced high hydrogenation activity.     

A process concept for the production of benzene-ethylene-SNG from coal using flash hydropyrolysis technology

Flash hydropyrolysis (FHP) of coal is an emerging technology for the direct production of methane, ethane and BTX in a single-stage, high throughput reactor. The FHP technique involves the short residence time (1–2 seconds), rapid heatup of coal in a dilute-phase, transport reactor. When integrated into an overall, grass-roots conversion complex, the FHP technique can be utilized to generate a product slate consisting of SNG, ethylene/propylene, benzene and Fischer-Tropsch-based alcohols.This paper summarizes the process engineering and economics of a conceptualized facility based on an FHP reactor operation with a lignitic coal. The plant is hypothetically sited near the extensive lignite fields located in the Texas region of the United States. Utilizing utility-financing methods for the costing of SNG, and selling the chemicals co-generated at petrochemical market prices, the 20-year average SNG cost has been computed to vary between $3–4/MM Btu, depending upon the coal costs, interest rates, debt/equity ratio, coproduct chemicals prices, etc.