Contribution to emission reduction of CO2 by a fluidized-bed membrane dual-type reactor in methanol synthesis process

In this work, a fluidized-bed membrane dual-type reactor was evaluated for CO₂ removal in methanol synthesis process. The feed synthesis gas is preheated in the tubes of the gas-cooled reactor and flowing in a counter-current mode with reacting gas mixture in the shell side. Due to the hydrogen partial pressure driving force, hydrogen can penetrate from feed synthesis gas into the reaction side through the membrane. The outlet synthesis gas from this reactor is fed to tubes of the water-cooled packed-bed reactor and the chemical reaction is initiated by the catalyst. The methanol-containing gas leaving this reactor is directed into the shell of the gas-cooled reactor and the reactions are completed in this fluidized-bed side. A two-phase dynamic model in bubbling regime of fluidization was developed in the presence of long-term catalyst deactivation. This model is used to compare the removal of CO₂ in a FBMDMR with a conventional dual-type methanol synthesis reactor (CDMR) and a membrane dual-type methanol synthesis reactor (MDMR). The simulation results show a considerable enhancement in the CO₂ conversion due to have a favourable profile of temperature and activity along the fluidized-bed membrane dual-type reactor relative to membrane and conventional dual-type reactor systems.     

Methylcyclohexane dehydrogenation for hydrogen production via a bimodal catalytic membrane reactor

The dehydrogenation of methylcyclohexane (MCH) to toluene (TOL) for hydrogen production was theoretically and experimentally investigated in a bimodal catalytic membrane reactor (CMR), that combined Pt/Al₂O₃ catalysts with a hydrogen‐selective organosilica membrane prepared via sol‐gel processing using bis(triethoxysilyl) ethane (BTESE). Effects of operating conditions on the membrane reactor performance were systematically investigated, and the experimental results were in good agreement with those calculated by a simulation model with a fitted catalyst loading. With H₂ extraction from the reaction stream to the permeate stream, MCH conversion at 250°C was significantly increased beyond the equilibrium conversion of 0.44–0.86. Because of the high H₂ selectivity and permeance of BTESE‐derived membranes, a H₂ flow with purity higher than 99.8% was obtained in the permeate stream, and the H₂ recovery ratio reached 0.99 in a pressurized reactor. A system that combined the CMR with a fixed‐bed prereactor was proposed for MCH dehydrogenation. © 2015 American Institute of Chemical Engineers AIChE J, 61: 1628–1638, 2015     

Carbon dioxide separation and dry reforming of methane for synthesis of syngas by a dual‐phase membrane reactor

High‐temperature CO₂ selective membranes offer potential for use to separate flue gas and produce a warm, pure CO₂ stream as a chemical feedstock. The coupling of separation of CO₂ by a ceramic–carbonate dual‐phase membrane with dry reforming of CH₄ to produce syngas is reported. CO₂ permeation and the dry reforming reaction performance of the membrane reactor were experimentally studied with a CO₂–N₂ mixture as the feed and CH₄ as the sweep gas passing through either an empty permeation chamber or one that was packed with a solid catalyst. CO₂ permeation flux through the membrane matches the rate of dry reforming of methane using a 10% Ni/γ‐alumina catalyst at temperatures above 750°C. At 850°C under the reaction conditions, the membrane reactor gives a CO₂ permeation flux of 0.17 mL min^?1 cm^?2, hydrogen production rate of 0.3 mL min^?1 cm^?2 with a H₂ to CO formation ratio of about 1, and conversion of CO₂ and CH₄, respectively, of 88.5 and 8.1%. © 2013 American Institute of Chemical Engineers AIChE J, 59: 2207–2218, 2013     

Catalytic Oxidative Dehydrogenation of n‐Butane on Gallium Nitride‐Containing Titanosilicate Catalyst

GaN‐containing titanosilicate catalysts were used for the first time for the oxidative dehydrogenation (ODH) of n‐butane at a relatively low reaction temperature (460 °C). Commercially available GaN powder with a wurtzite crystal structure showed superior reactivity and stability for the ODH of n‐butane. The catalytic property of GaN catalyst for ODH strongly depends on the GaN particle size. The effects of the GaN weight percentage and GaN particle size on the catalytic performance are investigated in a fixed bed reactor. Based on the physicochemical properties of the catalyst characterized via TEM, DLS, N₂ adsorption‐desorption, XRF, O₂‐TPD, XRD, XPS, and in‐situ FTIR, the textural and structural properties of catalyst were obtained. The catalytic results reveal that the presence of GaN increases the activity of the catalysts, indicating that GaN can be used as a new active phase for the ODH of n‐butane. XRD, XPS, O₂‐TPD, DLS, TEM, and in‐situ FTIR results show that activated O species exist on the surface of the GaN catalyst and enhance the catalytic performance with a decreasing GaN particle size, suggesting that smaller GaN particles possess a remarkable capability to activate O species in O₂ and C‐H bonds in light alkanes.     

Mixed oxygen ionic-carbonate ionic conductor membrane reactor for coupling CO2 capture with in situ methanation

CO₂ methanation is one of the vital reactions to utilize CO₂ and realize power to gas process. To decrease the CO₂ capture cost and alleviate the hot spots during the strong exothermic methanation reaction, here, we report a coupling of CO₂ capture process with in situ CO₂ methanation process through a ceramic-molten carbonate (MC) dual phase membrane reactor over the Ni-based catalyst. The performance of the membrane reactor was systematically investigated and compared with the traditional fixed-bed reactor. The results show that the performance of the membrane reactor is higher than that of the fixed-bed reactor, since the produced steam through the methanation process can be partially removed through the dual-phase membrane, which promotes the reaction shift to right side. A stability test shows no obvious degradation within 32 h. These results indicate that the membrane reactor is promising for coupling CO₂ capture with in situ methanation process.     

Theoretical investigation of a water‐gas‐shift catalytic membrane for diesel reformate purification

The novel application of a catalytic water‐gas‐shift membrane reactor for selective removal of CO from H₂‐rich reformate mixtures for achieving gas purification solely via manipulation of reaction and diffusion phenomena, assuming Knudsen diffusion regime and the absence of hydrogen permselective materials, is described. An isothermal, two‐dimensional model is developed to describe a tube‐and‐shell membrane reactor supplied with a typical reformate mixture (9% CO, 3% CO₂, 28% H₂, and 15% H₂O) to the retentate volume and steam supplied to the permeate volume such that the overall H₂O:CO ratio within the system is 9:1. Simulations indicate that apparent CO:H₂ selectivities of 90:1 to >200:1 at H₂ recoveries of 20% to upwards of 40% may be achieved through appropriate design of the catalytic membrane and selection of operating conditions. Under these conditions, simulations predict an apparent hydrogen permeability of 2.3 × 10^?10 mol m^?1 Pa, which compares favorably against that of competing hydrogen‐permselective membranes. © 2013 American Institute of Chemical Engineers AIChE J, 59: 4334–4345, 2013     

Enhanced Conversion in the Direct Synthesis of Diethyl Carbonate from Ethanol and CO2 by Process Intensification

To overcome the low equilibrium conversion in the direct synthesis of diethyl carbonate from ethanol and CO₂ under moderate reaction conditions, the reaction was conducted in a membrane reactor packed with pelletized Cu‐Ni:3‐1 supported on activated carbon. A SiO₂/γ‐Al₂O₃ commercial membrane and zeolite A membranes synthesized on commercial Al₂O₃ supports were evaluated in the membrane reactor. Although characterization of the membranes by X‐ray diffraction confirmed the presence of a zeolite A layer on the supports, gas permeation and permselectivity tests of ethanol and water evidenced some defects of the synthesized membranes. An increase in conversion with respect to a conventional packed‐bed reactor was observed in the membrane reactors prepared on Al₂O₃, but equilibrium conversion was not attained. However, with the commercial membrane, the ethanol conversion was higher than the equilibrium conversion.     

Pure H2 production through hollow fiber hydrogen‐selective MFI zeolite membranes using steam as sweep gas

Hollow fiber MFI zeolite membranes were modified by catalytic cracking deposition of methyldiethoxysilane to enhance their H₂/CO₂ separation performance and further used in high temperature water gas shift membrane reactor. Steam was used as the sweep gas in the MR for the production of pure H₂. Extensive investigations were conducted on MR performance by variations of temperature, feed pressure, sweep steam flow rate, and steam‐to‐CO ratio. CO conversion was obviously enhanced in the MR as compared with conventional packed‐bed reactor (PBR) due to the coupled effects of H₂ removal as well as counter‐diffusion of sweep steam. Significant increment in CO conversion for MR vs. PBR was obtained at relatively low temperature and steam‐to‐CO ratio. A high H₂ permeate purity of 98.2% could be achieved in the MR swept by steam. Moreover, the MR exhibited an excellent long‐term operating stability for 100 h in despite of the membrane quality. © 2015 American Institute of Chemical Engineers AIChE J, 61: 3459–3469, 2015     

Modeling of CO2 mass transport across a hollow fiber membrane reactor filled with immobilized enzyme

The enzyme‐based contained liquid membrane reactor to capture CO₂ from the closed spaces is a very complicated process with large numbers of interdependent variables. A theoretical and experimental analysis of facilitated transport of CO₂ across a hollow fiber membrane reactor filled with immobilized carbonic anhydrase (CA) by nanocomposite hydrogel was presented. CO₂ concentration profiles in the feed gas phase and the membrane wall were achieved by numeric simulation. The effects of CO₂ concentration, CA concentration, and flow rate of feed gas on CO₂ removal performance were studied in detail, and the model solution agrees with the experimental data with a maximum deviation of up to 18.7%. Moreover, the effect of CO₂ concentration on the required membrane areas for the same CO₂ removal target (1 kg/day) was also investigated. This could provide real‐world data and scientific basis for future development toward a final efficient CO₂ removal device. © 2011 American Institute of Chemical Engineers AIChE J, 2012     

Separation of CO2 from CH4 by pure PSF and PSF/PVP blend membranes: Effects of type of nonsolvent,solvent, and PVP concentration

Complete CO₂/CH₄ gas separation was aimed in this study. Accordingly, asymmetric neat polysulfone (PSF) and PSF/polyvinylpyrrolidone (PVP) blend membranes were prepared by wet/wet phase inversion technique. The effects of two different variables such as type of external nonsolvent and type of solvent on morphology and gas separation ability of neat PSF membranes were examined. Moreover, the influence of PVP concentration on structure, thermal properties, and gas separation properties of PSF/PVP blend membrane were tested. The SEM results presented the variation in membrane morphology in different membrane preparation conditions. Atomic forced microscopic images displayed that surface roughness parameters increased significantly in higher PVP loading and then gas separation properties of membrane improved. Thermal gravimetric analysis confirms higher thermal stability of membrane in higher PVP loading. Differential scanning calorimetric results prove miscibility and compatibility of PSF and PVP in the blend membrane. The permeation results indicate that, the CO₂ permeance through prepared PSF membrane reached the maximum (275 ± 1 GPU) using 1‐methyl‐2‐pyrrolidone as a solvent and butanol (BuOH) as an external nonsolvent. While, a higher CO₂/CH₄ selectivity (5.75 ± 0.1) was obtained using N‐N‐dimethyl‐acetamide (DMAc) as a solvent and propanol (PrOH) as an external nonsolvent. The obtained results show that PSF/PVP blend membrane containing 10 wt % of PVP was able to separate CO₂ from CH₄ completely up to three bar as feed pressure. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1139‐1147, 2013     

Dehydrogenation of propane with selective hydrogen combustion: A mechanistic study by transient analysis of products

The role of lattice and adsorbed oxygen species in propane dehydrogenation in a perovskite hollow fiber membrane reactor containing a Pt–Sn dehydrogenation catalyst was elucidated by transient analysis of products with a sub-millisecond time resolution. Propane is mainly dehydrogenated non-oxidatively to propene and hydrogen over the catalyst, while lattice oxygen of the perovskite oxidizes preferentially hydrogen to water. For achieving high propene selectivity at high propane conversions, the formation of gas phase O₂ on the shell side of the membrane reactor should be avoided. Otherwise, oxygen species adsorbed over the Pt–Sn catalyst participate in non-selective C₃H₈/C₃H₆ transformations to C₂H₄ and CO_x.     

CeO2‐CrOy/γ‐Al2O3 redox catalyst for the oxidative dehydrogenation of propane to propylene

CeO₂‐CrO_y loaded on γ‐Al₂O₃ was investigated in this work for the oxidative dehydrogenation (ODH) of propane under oxygen‐free conditions. The ODH experiments of propane were conducted in a fluidized bed at 500°C‐600°C under 0.1 Mpa. The prepared catalyst was characterized by N₂ adsorption‐desorption measurements, H₂‐temperature‐programmed reduction, O₂‐temperature‐programmed desorption, NH₃‐temperature‐programmed desorption, x‐ray photoelectron spectroscopy, and x‐ray diffraction. The change in the selectivity of propylene resulted from the thermal cracking of the propane and the competition for lattice oxygen in the catalyst between propylene formation and propane and propylene combustion. Therefore, to achieve higher propylene yield in the industry, the reaction temperature should be 550°C‐575°C for the 17.5Cr‐2Ce/Al catalyst. The results of H₂‐TPR (from 0.2218 mmol/g‐0.3208 mmol/g) revealed that the addition of CeO₂ can enhance the oxygen capacity of CrO_y. Compared with that for 17.5Cr/Al, the conversion can be enhanced from 22.4% to 28.5% and the selectivity of propylene can be improved from 72.2% to 75.9% for the 17.5Cr‐2Ce/Al catalyst. In addition, CeO₂ can inhibit the evolution of lattice oxygen (O^2?) to electrophilic oxygen species (O₂^?), causing the average CO_x (CO and CO₂) selectivity to decrease from 9.64% to 6.31%.     

Synthesis of V‐MCM‐41 Catalysts and Their Application in CO2‐Assisted Isobutane Dehydrogenation

A series of V‐MCM‐41 were in situ synthesized. The textual properties and vanadium species were systematically characterized. The results showed that the catalysts could still maintain a mesoporous structure and high specific surface area. The vanadium species were highly dispersed on the surface, with the coexistence of polymeric vanadium species. Isobutane dehydrogenation was performed by employing CO₂ as a soft oxidant. The results revealed an almost linear relationship between the activity and surface vanadium sites. Isolated vanadium species were more active for isobutane dehydrogenation. The isobutane dehydrogenation reaction in the presence of CO₂ could proceed simultaneously through oxidative dehydrogenation and non‐oxidative dehydrogenation followed by the reverse water gas shift reaction.     

Syngas production from H2O and CO2 over Zn particles in a packed‐bed reactor

The solar thermochemical production of H₂ and CO (syngas) from H₂O and CO₂ is examined via a two‐step cycle based on Zn/ZnO redox reactions. The first, endothermic step is the thermolysis of the ZnO driven by concentrated solar energy. The second, nonsolar step is the exothermic reaction of Zn with a mixture of H₂O and CO₂ yielding syngas and ZnO; the latter is recycled to the first step. A series of experimental runs of the second step was carried out in a packed‐bed reactor where ZnO particles provided an effective inert support for preventing sintering and enabling simple and complete recycling to the first, solar step. Experimentation was performed for Zn mass fractions in the range of 33–67 wt % Zn‐ZnO, and inlet gas concentrations in the range 0–75% H₂O–CO₂, yielding molar Zn‐to‐ZnO conversions up to 91%. A 25 wt % Zn‐ZnO sample mixture produced from the solar thermolysis of ZnO was tested in the same reactor setup and exhibited high reactivity and conversions up to 96%. © 2011 American Institute of Chemical Engineers AIChE J, 2012     

Transient Effects during Dynamic Operation of a Wall‐Cooled Fixed‐Bed Reactor for CO2 Methanation

The power‐to‐gas process is an option to transform fluctuating renewable electric energy into methane via water electrolysis and subsequent conversion of H₂ by methanation with CO₂. The dynamic behavior of the methanation reactor may then be a critical aspect. The kinetics of CO₂ methanation on a Ni‐catalyst were determined under isothermal and stationary conditions. Transient isothermal kinetic experiments showed a fast response of the rate on step changes of the concentrations of H₂, CO₂; in case of H₂O, the response was delayed. Non‐isothermal experiments were conducted in a wall‐cooled fixed‐bed reactor. Temperature profiles were measured and the effect of a changing volumetric flow was studied. The experimental data were compared with simulations by a transient reactor model.     

Intensified and safe ozonolysis of fatty acid methyl esters in liquid CO2 in a continuous reactor

We demonstrate a continuous reactor for performing the ozonolysis of fatty acid methyl esters (FAMEs) using liquid CO₂ as solvent. The fast reaction kinetics allows the use of small‐volume reactors to completely convert the FAMEs, forming secondary ozonides as the primary products. The short residence times also help maximize the yields of the secondary ozonides by minimizing over‐oxidation and the formation of oligomeric products. The liquid CO₂ medium promotes safe reactor operation by providing an essential fraction of overall reactor cooling and by diluting the vapor phase organics. We also demonstrate a continuous stirred reactor for the safe thermal decomposition of the secondary ozonides to their corresponding acids and aldehydes. Using a lumped kinetic model for the thermal decomposition of the ozonolysis products, we estimate activation energy values of 108.6 ± 0.6 kJ mol^?1 for the decomposition of secondary ozonides and 122 ± 3 kJ mol^?1 for the decomposition of the undesired oligomeric species. © 2017 American Institute of Chemical Engineers AIChE J, 63: 2819–2826, 2017     

A comparative simulation analysis of propane dehydrogenation in composite and microporous membrane reactors

Propane dehydrogenation has been simulated for a composite membrane reactor and a microporous membrane reactor using plug‐flow reactor models, in which both were packed with Pt/Al₂O₃ catalyst in the tube‐side. The reaction kinetics employed in the analysis were obtained from experimental data produced in an integral fixed bed reactor with the same catalyst. Comparative studies were carried out to analyse the performances of reactors containing the different membranes in terms of contact time, flow pattern and flow rate of sweep gas, and pressure. In general, the composite membrane reactors gave the better performance for all cases investigated. © 2002 Society of Chemical Industry     

Development and Application of Oxygen Permeable Membrane in Selective Oxidation of Light Alkanes

In this paper, oxygen permeable membrane used in membrane reactor for selective oxidation of alkanes will be discussed in detail. The recent developments for the membrane materials will be presented, and the strategy for the selection of the membrane materials will be outlined. The main applications of oxygen permeable membrane in selective oxidation of light alkanes will be summarized, which includes partial oxidation of methane (POM) to syngas and partial oxidation of heptane (POH) to produce H₂, oxidative coupling of methane (OCM) to C₂, oxidative dehydrogenation of ethane (ODE) to ethylene and oxidative dehydrogenation of propane (ODP) to propylene. Achievements for the membrane material developments and selective oxidation of light alkanes in membrane reactor in our group are highlighted.     

Dual-membrane reactor for methane oxidative coupling and dry methane reforming: Reactor integration and process intensification

A novel dual-membrane reactor concept was introduced for integrating the oxidative coupling of methane (OCM) and CO₂ methane reforming (dry reforming) reactors. The OCM reactions occur in a conventional porous packed bed membrane reactor structure and a portion of the undesired produced CO₂ and generated heat are transferred through a molten-carbonate perm-selective membrane and consumed in the adjacent dry methane reforming catalytic bed. This integrated reactor provides a very promising thermal performance by controlling the temperature peak to be below 50 °C in reference to the average operating temperature in the OCM section. This was achieved even for the low methane-to-oxygen ratio 2 by introducing 10% CO₂ as the diluent agent and reactant in this integrated reactor structure. This contributed to the improved selective performance of 32% methane conversion and 25% C₂-yield including 21% C₂H₄-yield in the OCM section which also enhances the performance of the downstream units consequently. Around half of the unconverted methane leaving the OCM section was converted to syngas in the DRM section.The dual-membrane reactor alone can utilize a significant amount of the carbon dioxide generated in the OCM catalytic bed. In combination with adsorption unit in the downstream of the integrated process, 90% of the produced CO₂ can be recovered and further converted to valuable syngas products. The experimental data, obtained from a mini-plant scale experimental facility, were exploited to verify the performance of the OCM reactor and the CO₂ separation section.