Methanol oxidative dehydrogenation in a catalytic packed-bed membrane reactor: experiments and model

Methanol oxidative dehydrogenation to formaldehyde over a Fe-Mo oxide catalyst was studied experimentally in three reactor configurations: the conventional fixed-bed reactor (FBR) and the packed-bed membrane reactor (PBMR), with either methanol (PBMR-M) or oxygen (PBMR-O) as the permeating component. The kinetics of methanol and formaldehyde partial oxidation reactions were determined independently from FBR experiments. A steady state plug-flow PBMR model, utilizing these kinetics and no adjustable parameters, fit the experiments accurately. It is shown experimentally and in accordance with the model that for given overall feed conditions, the reactor performance for methanol conversion and formaldehyde yield is in the order PBMR-M < FBR < PBMR-O.     

An investigation of the comparative reactivities of ethane and ethylene in the presence of oxygen over Li/MgO and Ca/Sm2O3 catalysts in relation to the oxidative coupling of methane.

In order to examine the importance of the further oxidation of the desired C₂ products in the oxidative coupling of methane, ethylene and ethane have been added to the feed (containing methane and oxygen) to a Li/MgO or Ca/Sm₂O₃ catalyst. The results of these measurements show that neither of these C₂ molecules is stable under these conditions with either of the catalysts. Additionally, the rates of the oxidation of ethane and of ethylene alone have been measured using a gradientless reactor for both catalysts as well as for a quartz bed. It was found that the Ca/Sm₂O₃ material had higher activities for the oxidation of C₂H₆ and C₂H₄ (and also of CH₄) than had the Li/MgO material. These higher activities result in a lower optimal reaction temperature for the oxidative coupling of methane and are (at least partially) responsible for the lower selectivity to C₂ products observed with the Ca/Sm₂O₃ catalyst compared to that with the Li/MgO catalyst.     

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.     

Enhancement of acetylene and ethylene yields in partially decoupled oxidation of ethane by changing the composition of heat carrier

In our previous work, a partially decoupled process(PDP) was proposed for efficient conversion of ethane to increase the ethylene yield and a new structural reactor called forward-impinging-back reactor(FIB)was proposed for scale-up. In this work, the influence of changing the composition and temperature of the heat carrier was investigated by simulations with detailed chemistry to further increase of the C₂(C₂ H₂+ C₂ H₄) yield in the PDP of...     

The selective oxidation of methane to ethane and ethylene in a solid oxide electrolyte reactor

A study of the selective oxidative coupling of methane (OCM) to C₂ hydrocarbons (ethane and ethylene) in a solid-state electrochemical reactor made from yttria-stabilized zirconia (YSZ) has been made. Three different catalyst–electrode systems based on silver and two trimetallic formulations of Mn modified alkali (Na and K) tungstates supported on silica were used. A comparison is made between co-fed and electrochemically-supplied oxygen. The electrochemically-supplied oxygen gave higher overall C₂ selectivities than the co-fed method under low current conditions, which was attributed to differences in local methane to oxygen ratios at the catalyst surface. The potassium tungstate supported catalyst gave the best overall C₂ selectivity (86% at 4% C₂ yield).     

SrFe0.6Cu0.3Ti0.1O3-δ透氧膜反应器中甲烷部分氧化反应工艺及膜稳定性考察

采用SrFe_0.6Cu_0.3Ti_0.1O_3-δ混合导体透氧膜组装成膜催化反应器,进行甲烷部分氧化制合成气反应,考察了反应温度、空速、催化剂粒径等条件的影响,并分析了反应气氛引起的透氧膜结构变化情况。结果表明,在膜反应器内,催化反应与透氧过程存在相互制约和相互促进的关系。在膜反应器内进行甲烷部分氧化反应后,透氧膜的两侧表面均发生蚀刻现象,结晶度显著降低,反应侧蚀刻现象较为严重,膜表面形成了疏松的多孔层,反应气氛使膜表面晶体结构发生了较大改变,Sr容易从钙钛矿结构中析出并与CO₂结合形成SrCO₃,Sr的析出导致组成不平衡,促进了钙钛矿结构分解及其他物相的产生。     

The investigation of individual reaction steps in the oxidative coupling of methane over lithium doped magnesium oxide

To elucidate the importance of various reaction steps in the oxidative conversion of methane, experiments were carried out with three reaction products: ethane, ethylene and carbon monoxide. These products were studied separately in oxidation experiments with and without a catalyst. Moreover, the effect of admixing them to a methane/oxygen feed was investigated. All experiments were carried out in a micro flow tubular quartz reactor which was either empty or filled with catalyst at a temperature of 800 °C. The ethane and ethylene experiments showed that the conversion of ethane to ethylene is much more rapid than ethane combustion, irrespective of the presence of a catalyst. The main combustion path goes via ethylene. Ethane is converted much more rapidly than methane and this imposes serious constraints on the maximum attainable yields. The principal combustion product in the absence of a catalyst is CO but with a catalyst, CO₂ dominates, in agreement with rapid catalytic oxidation observed with CO/O₂ feeds.

The conclusions are summarized in a simplified overall reaction scheme.     

Influence of the operating conditions on yield and selectivity for the partial oxidation of ethane in a catalytic membrane reactor

In this study, simulation results are presented for the partial oxidation of ethane to ethylene in a Catalytic Membrane Reactor (CMR) under isothermal and non-isothermal conditions. Considering the importance of the transport processes, a 2D model was developed and implemented in FLUENT^® using self-designed program modules for reaction kinetics, transport properties and post-processing. An analysis of significance of the influencing variables is carried out on the basis of a reference case. The number of parameters were minimized by the dimensionless formulation of the model. One of the most important variables is the oxygen dosage through the membrane. Both velocity and oxygen concentration of the trans-membrane stream were varied with the aim of attaining maximum ethylene yield. The results of the different simulations clearly show the advantages of the CMR compared to the Catalytic Wall Reactor (CWR). The numerical simulations are essential in order to reduce the experimental costs and to evaluate different reactor concepts.     

AgBiVMo oxide catalytic membrane for selective oxidation of propane to acrolein

A metal ions (Ag, Bi, V, Mo) modified sol–gel method was used to prepare a mesoporous Ag_0.01Bi_0.85V_0.54Mo_0.45O₄ catalytic membrane which was used in the selective oxidation of propane to acrolein. By optimizing the preparation parameters, a thin and perfect catalytically active membrane was successfully prepared. SEM results showed that the membrane thickness is 5 μm. XRD results revealed that Ag_0.01Bi_0.85V_0.54Mo_0.45O₄ with a Scheelite structure, which is catalytically active for the selective oxidation of propane to acrolein, was formed in the catalytic membrane only when AgBiVMoO concentrations were higher than 40%. Catalytic reaction results demonstrated that the selective oxidation of propane could be controlled to a certain degree, such as to acrolein, in the catalytic membrane reactor (CMR) compared to the fixed bed reactor (FBR). For example, a selectivity of 54.85% for acrolein in the liquid phase was obtained in the CMR, while only 8.31% was achieved in the FBR.     

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.     

Cr/SSZ-13催化二氧化碳氧化乙烷脱氢反应的研究

通过脱氢反应将低碳烷烃转化为同碳数的烯烃是烷烃高值化利用和烯烃原料多元化的重要途径。烷烃氧化脱氢制烯烃的反应具有不受反应平衡限制、积炭少、反应温度低等优点,一直是研究的热点。通过利用浸渍法制备不同铬（Cr）负载量的Cr_x/SSZ-13系列催化剂,采用氮气物理吸附、氨程序升温脱附（NH₃-TPD）、二氧化碳程序升温脱附（CO₂-TPD）、氢气程序升温还原（H₂-TPR）、紫外-可见吸收光谱（UV-Vis）以及高角度环形暗场-扫描透射电镜（HAADF-STEM）与耦合能谱分析（EDX-Mapping）等方法对催化剂进行了物性表征,并用微型固定床反应器评价催化剂对乙烷氧化脱氢制乙烯的催化性能,最终建立了Cr/SSZ-13催化剂的构效关系。研究发现,当n（二氧化硅）/n（氧化铝）=10时,Cr_1.5/SSZ-13-10催化剂上含有丰富的Cr³⁺物种,其中配位不饱和Cr³⁺是优异的脱氢活性位,有利于二氧化碳氧化乙烷脱氢反应的进行。因此,Cr_1.5/SSZ-13催化剂在650 ℃时表现出优异的催化性能,即二氧化碳转化率和乙烷转化率分别达到26.41%和53.2%,乙烯产率为38.83%。     

化学链干重整联合制氢热力学分析及实验

提出了一种化学链甲烷干重整联合制氢工艺。该工艺由还原反应器、干重整反应器、蒸汽反应器和空气反应器组成，在实现制氢的同时获得可变H₂/CO比的合成气。借助ASPEN plus软件和小型流化床实验台，在等温条件下，温度900℃，采用Fe₂O₃/Al₂O₃载氧体，对该工艺进行热力学分析和实验验证。结果显示，当铁氧化物被还原至FeO/Fe时，干重整反应器内甲烷转化率可以达到98%，CO产率可以达到94%。干重整反应器中同时发生甲烷干重整和部分氧化反应，载氧体内部晶格氧可以有效降低积炭并提高合成气H₂/CO比。积炭发生于晶格氧消耗殆尽时。积炭进入蒸汽反应器，发生气化反应，降低氢气纯度。     

Reaction and oxygen permeation studies in Sm0.4Ba0.6Fe0.8Co0.2O3 − δ membrane reactor for partial oxidation of methane to syngas

A disk-type Sm_0.4Ba_0.6Co_0.2Fe_0.8O_3 − δ perovskite-type mixed-conducting membrane was applied to a membrane reactor for the partial oxidation of methane to syngas (CO + H₂). The reaction was carried out using Rh (1 wt%)/MgO catalyst by feeding CH₄ diluted with Ar. While CH₄ conversion increased and CO selectivity slightly decreased with increasing temperature, a high level of CH₄ conversion (90%) and a high selectivity to CO (98%) were observed at 1173 K. The oxygen flux was increased under the conditions for the catalytic partial oxidation of CH₄ compared with that measured when Ar was fed to the permeation side. We investigated the reaction pathways in the membrane reactor using different membrane reactor configurations and different kinds of gas. In the membrane reactor without the catalyst, the oxygen flux was not improved even when CH₄ was fed to the permeation side, whereas the oxygen flux was enhanced when CO or H₂ was fed. It is implied that the oxidation of CO and H₂ with the surface oxygen on the permeation side improves the oxygen flux through the membrane, and that CO₂ and H₂O react with CH₄ by reforming reactions to form syngas.     

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.     

CHLORINE-CATALYZED OXIDATIVE PYROLYSIS OF METHANE: A PARAMETRIC STUDY

Conversion of methane and monochtoromethane to acetylene, ethane, and ethylene via homogeneous oxidative pyrolysis is investigated in an isothermal continuous flow reactor employing steam and/or oxygen as oxidizing agents. The effects of monochloromethane to methane ratio in the feed (0.304-9.981), reactor temperature (973-1423 K), and reactor space time (0.0-3.76 s) on product distribution in the reactor effluent are studied. Steam is shown to be a more effective oxidizing agent than oxygen as far as production of C₂ species is concerned. Addition of steam in the feed suppresses formation of coke, carbon monoxide, and carbon dioxide. The efficacy of oxidative pyrolysis with steam is demonstrated by the substantially high selectivity of C₂ species (up to 74%).     

负载型Mn-Fe/γ-Al2O3低温脱硝催化剂的性能

采用共沉淀法制备了负载型Mn-Fe/γ-Al₂O₃低温SCR催化剂,运用固定床催化反应器,以氨气为还原剂,考察了负载量、活性组分配比、焙烧温度等制备条件和空速、O₂体积分数、NH₃/NO摩尔比等操作条件对Mn-Fe/γ-Al₂O₃催化剂低温脱硝性能的影响,并通过X射线衍射仪(XRD)、比表面积测定仪(BET)等手段对催化剂进行表征.结果表明,负载质量分数为20%、n(Mn):n(Fe)=4:1、焙烧温度为600℃、空速为16000h^-1、O₂体积分数为4%、NH₃/NO摩尔比为1.2、反应温度为200℃的条件下,NO转化率达到了96%以上.     

新型惰性膜反应器中丁烷氧化脱氢制丁二烯和丁烯

The oxidative dehydrogenation of butane to butadiene and butene was studied using a conventional fixed-bed ractor (FBR), inert membrane reactor (IMR) and mixed inert membrane reactor (MIMR). When IMR and MIMR were employed, a ceramic membrane modified by partially coating with glaze was used to distribute oxygen to a fixed-bed of 24-V-Mg-O catalyst. The oxygen partial pressure in the catalyst bed could be decreased. The effect of feeding modes and operation conditions were investigated. The selectivity of C4 dehydrogenation products (bntene and bntadiene) was found to be higher in IMR than in FBR. The feeding mode with 20% of air mixing with butane in MIMR was found to be more efficient than the feeding mode with all air permeating through ceramic membrane. The MIMR gave the most smooth temperature profile along the bed.     

Effect of incipient removal of hydrogen through palladium membrane on the conversion of methane steam reforming: Experimental and modeling

This paper presents a mathematical model based on the reaction rate expressions to describe the displacement of methane conversion in the steam reforming. The effect of several parameters including weight hourly space velocity (WHSV), load-to-surface ratio, reaction pressure, hydrogen partial pressure in permeate side and reaction temperature were investigated. Simulation and experimental results showed that a conversion higher than 80% could be achieved in a palladium membrane reactor at reaction temperature of 500 °C relative to 850 °C in a conventional fixed bed reactor (FBR). Besides, the yield of CO (<2%) in membrane reactor was much lower than that (>50%) in the FBR, which indicated the significant depression of CO production in use of membrane reactor.     

Effect of the pretreatment with oxygen and/or oxygen-containing compounds on the catalytic performance of Pd-Ag/Al2O3 for acetylene hydrogenation

Catalytic performance of Pd-Ag/-Al₂O₃ was studied for the selective hydrogenation of acetylene in the presence of excess ethylene. The catalyst activation was undertaken prior to the reaction test by the pretreatment with oxygen and/or oxygen-containing compounds, i.e. O₂, NO, N₂O, CO and CO₂. The enhancement of catalytic performances by the pretreatment was a consequence of an increase in accessible Pd sites responsible for acetylene hydrogenation to ethylene. Furthermore, the sites involving direct ethane formation from acetylene could be suppressed by NO_x treatment.     

Oxidative coupling of methane over K/Ni/Ca oxide and K/Ni/Mg oxide catalysts

The oxidative coupling behaviour of a series of K/Ni/Ca oxide catalysts with low nickel-to-calcium ratios has been examined and the results are compared with those for a magnesium-based catalyst. The effect of gas composition and the stability of ethylene under reaction conditions have also been studied. The catalysts were calcined at 1200°C unless otherwise stated. Potassium was added after the calcination stage. It is found that a high calcination temperature of 1200°C is necessary to give a Ca-based catalyst with high activity and selectivity. The catalysts based on MgO were less selective. Substitution of K for Li in the MgO based catalyst gave a slight improvement in the selectivity. A series of experiments was carried out with the K_0.1Ni_0.012 Ca material with the aim of optimising the yield. It was found that the selectivity could be improved by increasing the concentration of CH₄ or by adding CO₂ to the feed. However the addition of CO₂ decreased the activity of the catalyst. The activity could be increased by increasing the H₂O concentration. An increase of the O₂ concentration in the feed from 10.85 to 13% with 31% of CH₄ and 21% H₂O increased the C₂ yield from 15.1% to 17.8%. In a series of experiments in which different concentrations of C₂H₄ were added to the feed, it was found that the main oxidation product of ethylene was CO₂. The formation of ethane was unaffected by the addition of ethylene. It is therefore proposed that two different sites are required for the oxidation of ethylene and the activation of methane to form ethane.