Vapor phase dehydrogenation of methanol to methyl formate in the catalytic membrane reactor with Cu/SiO2/ ceramic composite membrane

The Cu/SiO₂/ceramic composite membrane was prepared on the SiO₂/ceramic mesoporous membrane by an ion exchange method, and vapor phase dehydrogenation of methanol to methyl formate in the catalytic membrane reactor was investigated. It showed much better performance in the catalytic membrane reactor than that in the fixed-bed reactor under the same reaction conditions. At 240 °C, 57.3% conversion of methanol and 50.0% yield of methyl formate were achieved in the catalytic membrane reactor and only 43.1% conversion of methanol and 36.9% yield of methyl formate were achieved in the fixed-bed reactor.     

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.     

LTA zeolite composite membrane preparation,characterization and application in a zeolitic membrane reactor

An LTA membrane has been crystallized inside a porous ceramic tube and applied to synthesis of methanol from carbon dioxide and hydrogen in a zeolite membrane reactor (ZMR). The results obtained with the ZMR were compared with those gained from one traditional reactor (TR) used under the same operating conditions. CO₂ conversion obtained with the ZMR at 210 °C reached 17% under conditions where the equilibrium value without zeolite membrane (TR) is equal to about 6%.     

A catalytic membrane reactor for water-gas shift reaction

We conducted the WGS reaction on a catalytic membrane reactor consisting of a WGS catalyst bed, Pt/CeO₂ and thin, defect-free, Pd-Cu alloy membranes. The presence of CO and other gases with H₂ reduced the H₂ permeation through the membrane by more than 50% and the effect of the other gases on the permeation reduction decreased in the following order: CO>CO₂>N₂. In a catalytic membrane reactor with helium sweep gas, the CO conversion was improved by about 65% compared with the catalyst without any membrane, and the CH₄ formed from an undesirable side reaction was significantly reduced. Although the H₂ permeation was severely reduced by surface phenomena such as blocking of available H₂ dissociation sites by CO, CO₂ and steam, the CO conversion was notably improved by the membrane presence. Moreover, the CO conversion was maintained at 98% even after 60 h of reaction and our Pd-Cu-Ni alloy membrane withstood the exposure of CO and the other gases. However, for separation of pure H₂, a newly designed, catalyst-membrane system is required with better sealing and the ability to withstand the high operating pressure that drives the H₂ permeation.     

Beneficial effects of the use of a nickel membrane reactor for the dry reforming of methane: Comparison with thermodynamic predictions

The development of a nickel composite membrane with acceptable hydrogen permselectivity at high temperature in a membrane reactor for the highly endothermic dry reforming of methane reaction was the purpose of this work. A thin, catalytically inactive nickel layer, deposited by electroless plating on asymmetric porous alumina, behaved simply as a selective hydrogen extractor, shifting the equilibrium in the direction of a higher hydrogen production and methane conversion. The main advantage of such a nickel/ceramic membrane reactor is the elimination or limitation of the side reverse water gas shift reaction. For a Ni/Al₂O₃ catalyst, containing free Ni particles, normally sensitive to coking, the use of the membrane reactor allowed an important reduction of carbon deposition (nanotubes) due to restriction of the Boudouard reaction. For a Ni–Co/Al₂O₃ catalyst, where the metallic nickel phase was stabilized by the alumina, the selective removal of the hydrogen significantly enhanced both methane conversion (+67% at 450 °C, +22% at 500 °C and +18% at 550 °C) and hydrogen production (+42% at 450 °C, +32% at 500 °C and +22% at 550 °C) compared to the results obtained for a packed-bed reactor. The hydrogen selectivity during the catalytic tests at 550 °C, maintained with constant separation factors (7 for H₂/CH₄, 8 for H₂/CO and 10 for H₂/CO₂), higher than Knudsen values, attested to the high thermal stability of the nickel composite membrane.     

Continuous phenol hydroxylation over ultrafine TS-1 in a side-stream ceramic membrane reactor

A side-stream ceramic membrane reactor system was developed that can facilitate the in situ separation of ultrafine catalysts from the reaction mixture and make the production process continuous. Continuous hydroxylation of phenol to dihydroxybenzene over ultrafine titanium silicalites-1 (TS-1) was taken as a model reaction to evaluate the feasibility and performance of the membrane reactor system. The effects of membrane pore size and operation conditions (residence time, temperature, catalyst concentration, phenol/H₂O₂ molar ratio) on the performance of the reactor system were examined via single factor experiments. We demonstrated that the membrane pore size and operation conditions greatly affect the conversion, selectivity and filtration resistance. The phenol conversion and dihydroxybenzene selectivity remain stable at about 11% and 95% in a 20-h continuous run, respectively.     

Tough and wear-resistant carbon fiber reinforced TiC-based composite prepared by alloyed melt infiltration at low temperatures

To improve the toughness and friction properties of carbon fiber reinforced ceramic matrix composite, a Cu alloy modified carbon fiber reinforced TiC based ceramic matrix composite was designed and prepared by TiCu alloy melt infiltration at low temperatures up to 1100 °C. The as-produced composite was mainly composed of carbon, TiC, Ti₃Cu₄, TiCu₄ and Cu phases. Due to the ductile Cu alloy introduced into the matrix, the composite showed good mechanical performance especially the fracture toughness. The flexural strength reached about 248.36 MPa while the fracture toughness was up to 15.78 MPa·m^1/2. The high toughness of the composite was mainly attributed to the fiber bridging, fiber pull-out, interface debonding, crack propagation and deflection. The tribological performance of the as-produced composite was measured using SiC and 440C stainless steel balls as counterparts, respectively. The as-prepared composite exhibited good wear resistance and the wear mechanism was discussed based on the microstructural observations.     

钯复合膜反应器中异丁烷催化脱氢反应

引　言异丁烷脱氢反应是一个受热力学平衡限制的反应 ,平衡转化率很低 ,若将膜反应器用于该反应 ,则可以通过膜不断地从反应区选择性分离出氢气 ,克服了反应受热力学平衡制约的缺点 ,这样就可降低反应温度和减压程度的要求 ,改善反应的工艺条件 ,从而达到高效和节能的目的 .文献中已分别对钯 /陶瓷复合膜[1,2 ]和钯 -钌 (钌的质量分数为 2 % )合金膜[3]反应器中的异丁烷脱氢反应进行了初步研究 .前文[4 ]已对用改进的化学镀新工艺制备的钯和钯 -银 /陶瓷复合膜进行了表征 ,本文将用钯-银 /陶瓷复合膜反应器进行异丁烷脱氢反应的研究 .本工作…     

Theoretical study of a membrane reactor for the water gas shift reaction under nonisothermal conditions

A simulation of a membrane reactor for the water gas shift reaction is carried out by means of a 1D pseudo‐homogeneous nonisothermal mathematical model. The composite membrane consists of a dense layer of Pd (selective to H₂) supported over a porous ceramic layer. The effect of temperature, overall heat‐transfer coefficient, and mode of operation on the membrane reactor performance and stability are analyzed, and the results obtained are compared with those corresponding to a reactor with no hydrogen permeation. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

PROMOTION EFFECT OF Mo IN AMORPHOUS Ni-P CATALYSTS FOR THE LIQUID-PHASE CATALYTIC HYDROGENATION OF NITROBENZENE TO ANILINE

Amorphous Ni-P catalysts were prepared by a chemical reduction method, and the promotional effects of Mo on the hydrogenation of nitrobenzene to aniline on Ni-P catalyst were investigated. However, the two crystallization temperatures of the 1% Ni-Mo-P catalyst were 644 K and 723 K, which were 15 K and 43 K higher, respectively, than those of the Ni-P catalyst itself; these results indicate that the presence of Mo increased the thermal stability of the Ni-P catalysts. SEM results showed that the particle size of the active component of Ni-P in the 1.0% Ni-Mo-P catalyst was smaller than that in the amorphous Ni-P catalyst. The N₂ adsorption isotherms for the amorphous Ni-Mo-P catalysts were the III-type, and the N₂ isothermal adsorption-desorption curves exhibited H₃-type hysteresis loops. H₂-TPR results showed that the addition of Mo had no effect on the reduction of NiO in the catalyst but negatively affected the reduction of Ni-P-O. H₂-TPD results showed that the hydrogen adsorption capacity of the amorphous Ni-P catalysts can be enhanced through the addition of Mo, and the optimal amount of Mo was determined to be 1.0%. The XPS results indicated the presence of a small amount of free metallic Mo in the amorphous Ni-Mo-P catalysts in addition to the Mo in MoO₃. The use of 1% amorphous Ni-Mo-P catalyst at 383 K and under 1.0 MPa of hydrogen for 3.0 h resulted in a nitrobenzene conversion rate and aniline selectivity of 64.5% and 98.8%, respectively.     

硅橡胶/陶瓷复合膜反应器中CO2合成甲醇(Ⅲ)过程实验研究

对在由硅橡胶 /陶瓷复合膜所构成的膜反应器中进行的CO₂ 加氢合成甲醇的复杂反应体系CO₂ +3H₂=CH₃ OH +H₂ O与CO₂ +H₂=CO +H₂ O开展实验研究 .考察了硅橡胶 /陶瓷复合膜在合成含氧化合物反应过程中的作用 ,并讨论了CO₂ 与H₂ 合成甲醇反应的膜反应过程参数对反应行为的影响 ,对部分理论分析结果进行验证 .在实验条件下 ,CO₂ 合成甲醇复杂反应体系中的主反应转化率较传统的固定床反应器提高了 2 2 %     

The Interaction Between SrFeCo0.5O x Ceramic Membranes and Pt/CeZrO2 During Syngas Production from Methane

Non-porous ceramic membranes with mixed ionic and electronic conductivity have received significant interest as membrane reactor systems for the conversion of methane to higher value products. In this work, the role of the membrane in the conversion of methane and the interaction with a Pt/CeZrO₂ catalyst has been studied. Pulse studies of reactants and products over physical mixtures of crushed membrane material and catalyst have clearly demonstrated that a synergy exists between the membrane and the catalyst under reaction conditions. The degree of catalyst/membrane interaction strongly impacts the conversion of methane and the catalyst performance.     

Continuous and complete conversion of high concentration p-nitrophenol in a flow-through membrane reactor

Here, we report on a green and effective method for the continuous and complete conversion of high concentrations of p-nitrophenol (PNP) using a flow-through membrane reactor and less NaBH₄. The catalytic membrane was successfully fabricated by loading Pd nanoparticles onto the surface of a branched TiO₂ nanorod-functionalized ceramic membrane. The modification with branched TiO₂ nanorods can significantly improve the loading amount of Pd nanoparticles onto ceramic membranes, resulting in enhanced catalytic performance. With 6 mg of Pd, 93 L m⁻² hr⁻¹ of flux density and 8.04 cm² of membrane surface area in the flow-through membrane reactor, PNP at a concentration of 4,000 ppm can be converted to high-value p-aminophenol using less NaBH₄ (using a molar ratio of NaBH₄:PNP of 9.6) within 24 s at 30°C. More importantly, the conversion can be continuously and stably performed for 240 min.     

Membrane supported catalytic dehydrogenation of iso-butane using an MFI zeolite membrane reactor

A H₂-selective MFI zeolite membrane has been crystallized as layer on a porous ceramic tube. At 510 °C, this membrane can separate H₂ from iso-butane/iso-butene with mixture separation factors of 70 and H₂ permeances of ca. 1 m³ (STP)/m² hbar. In membrane supported iso-butane dehydrogenation the conversion of iso-butane was increased by almost a factor of 2. However, a detailed analysis of the experiment showed that 2/3 of the conversion increase is based on the dilution of the feed by the sweep gas and 1/3 is due to the H₂ removal.     

Electrochemically induced alumina coatings on stainless steel: composition and behaviour at high temperature

Alumina coatings were formed by electrolytic treatment on an Fe-17% Cr stainless steel functionalized by surface conversion treatment to induce a particular surface morphology, suited to anchoring the ceramic layer. As deposited, the coatings appeared amorphous. They were composed of two layers: the superficial layer was constituted only of aluminium compounds while the deep layer had a composition gradient. Heating the coated steel caused interface reactions between the electrochemically-induced deposit and the initial conversion coating compounds. These reactions act to strengthen coat adhesion to the substrate with formation of crystallized mixed oxide such as Fe(Cr,AI)₂O₄. Moreover, Al₂O₃ phases appeared and acted as a barrier which prevented the thermal oxidation of the stainless steel.     

Semihydrogenation of a propargylic alcohol over highly active amorphous Pd81Si19 in “supercritical” carbon dioxide

The semihydrogenation of a propargylic alcohol (dehydroisophytol) has been studied using glassy Pd₈₁Si₁₉ as a catalyst and “supercritical” CO₂ as a solvent. The continuous fixed-bed reactor experiments were performed in the pressure range 50–250 bar and at temperatures from 42 to 120°C. Parallel studies of the phase behavior of the reaction system in a high-pressure view-cell revealed that the number, nature and composition of the mutually saturated phases depended strongly on temperature and pressure. Correlation of the phase behavior with the catalytic studies indicated that a single-phase system is an ideal reaction medium for this catalytic system. In combination with the high activity of the amorphous metal alloy catalyst high conversion and selectivity could be reached at significantly lower temperature than when working in the two-phase region. Comparative catalytic tests revealed that the glassy alloy exhibits a more than 50 times higher turnover frequency than a conventional silica-supported palladium catalyst under similar conditions. Selectivity to isophytol was 100% at low conversion and declined to 77% at around 70% conversion due to overhydrogenation. The combined application of a glassy palladium–silicon alloy together with “supercritical” CO₂ seems to be promising for this type of Lindlar reactions.     

硅橡胶/陶瓷复合膜反应器中CO2合成甲醇(Ⅱ)过程行为分析

以在膜反应器中进行的CO₂ 加氢合成甲醇的复杂反应 (平行反应 )体系为模型反应建立了等温一维拟均相膜反应器并流模型 ,运用Runge -Kutta法对膜反应器中的反应过程行为进行模拟 ,并讨论了Da、α、Φ、p_r、q₁、T、γ和L₁等参数对反应过程行为的影响     

非晶Ni-P合金镀层的制备及应力腐蚀研究

为了探究非晶Ni-P合金镀层对304不锈钢应力腐蚀的影响,通过优化工艺配方制备非晶Ni-P合金镀层,并对其结构和耐蚀性进行了分析。结果表明:非晶Ni-P合金镀层表面平整,P的质量分数为10.72%;非晶Ni-P合金镀层的耐蚀性优于304不锈钢的,接近耐腐蚀材料等级;非晶Ni-P合金镀层的应力腐蚀敏感指数更低,起到较好的机械隔离和电化学保护作用。     

Dynamic modeling and operability analysis of a dual-membrane fixed bed reactor to produce methanol considering catalyst deactivation

The goal of this research is dynamic operability analysis of dual-membrane reactor considering catalyst deactivation to produce methanol. A dynamic heterogeneous one-dimensional model is developed to predict the performance of this configuration. In this configuration, a conventional reactor has been supported by a Pd/Ag membrane tube for hydrogen permeation and alumina–silica composite membrane tube to remove water vapor from the reaction zone. To verify the accuracy of the considered model, the results of conventional reactor are compared with the plant data. The main advantages of the dual-membrane reactor are: higher catalyst activity and lifetime, higher CO₂ conversion and methanol production.     

Facile method to prepare Pd/Polystyrene composite microspheres and investigation on their catalytic properties

Nano-sized Pd/polystyrene composite nanoparticles were prepared via surfactant-free emulsion polymerization. The as-prepared composite particles were used as a catalyst for Suzuki reaction, and they showed excellent catalytic properties in the conversion and recyclability. First, polystyrene (PS) latex particles bearing carboxyl groups on the surfaces were synthesized via one-stage surfactant-free emulsion polymerization employing acrylic acid as the functional monomer. Thus, made the PS particles negatively charged and could attract positively charged Pd²⁺ ions. By adding PdCl₂ solution to this functional polystyrene emulsion, Pd²⁺ ions were attached to the surfaces and reduced to zero valent particles by the reducing agent, NaBH₄. Nano-sized Pd/PS composite particles could be synthesized via this facile method. The amount of the functional monomers, the Pd²⁺ content and the amount of the initiator played important roles to the final morphologies of the composite particles. The resulting composite microspheres were observed by TEM. Furthermore, catalytic properties of the as-prepared Pd/PS composite particles were studied via Suzuki reaction, and the results were characterized by FTIR and ¹H-NMR. The Pd/PS composite particles showed excellent conversion and could be recycled easily for reuse. After each round of Suzuki reaction, the Pd/PS composite particles could be separated just by filtration, the conversion still remained as high as 70.2?%, even when used 5 times.