近临界异丙醇中Cu-Pd/Al_2O_3催化转移氢化糠醛制备糠醇

糠醇是重要的有机化工原料,用途广泛。现行糠醛催化加氢制备糠醇的技术存在氢耗大、成本高等缺点。本文提出了一种在近临界异丙醇中,Cu-Pd/Al_2O_3催化糠醛转移氢化制备糠醇的方法。采用共沉淀法制备了不同Cu、Pd负载量的Cu-Pd/Al_2O_3催化剂,并进行了XRD、氮气吸脱附表征。考察了催化剂中Cu-Pd的负载量、催化剂用量、糠醛浓度、反应温度和反应时间对反应的影响。结果表明:18%Cu-2%Pd/Al_2O_3双金属催化剂对糠醛催化转移氢化反应效果最好;在18%Cu-2%Pd/Al_2O_3催化剂作用下,反应温度为190℃、反应时间为3h时,糠醛转化率为100%、糠醇收率达到86.4%;催化剂重复使用四次后依然保持良好的活性。本文提出的方法具有非临氢、糠醇收率高、催化剂重复使用性能好等优点。     

糠醛液相催化加氢制糠醇金属催化剂的研究进展

糠醛催化加氢是将糠醛转化为生物燃料、医药农药中间体等精细化学品的最常用的反应之一,如糠醇、2-甲基四氢呋喃、内酯、乙酰丙酸盐、环戊酮等皆由糠醛催化加氢制取.当前糠醛催化加氢的过程主要有液相、气相以及催化转移加氢等.综述了近年来糠醛液相催化加氢制备糠醇的不同金属基催化剂的研究进展.从不同过渡金属和贵金属作为催化活性中心制备的单金属及双金属催化剂着手,讨论了部分金属基催化剂用于糠醛液相催化加氢制糠醇反应过程的催化性能.     

铬形态及使用条件对糠醛催化加氢反应产物分布的影响

采用共沉淀法制备系列Cu-Cr糠醛加氢催化剂,考察不同铬形态对催化剂反应性能的影响。采用管式连续流动固定床积分反应器, 研究糠醛在Cu-Cr催化剂上的气-液相加氢反应规律。结果表明,制备催化剂时的铬原料不同,将极大地影响催化剂的加氢活性和产物选择性,以硝酸铬形式加入制备的催化剂对糠醇的生成较为有利,而以醋酸铬形式加入制备的催化剂对甲基呋喃的形成有利;在(70～110) ℃,随着温度升高,糠醛转化率和糠醇选择性增加,2-甲基呋喃选择性降低;糠醛流速为(0.01～0.06) mL·min^-1时,随着流速的增加,糠醛转化率下降,0.03 mL·min^-1时糠醇选择性出现极大值,而副产物2-甲基呋喃和呋喃类则在此处出现极小值。副产物戊二醇和四氢康醇的选择性则随着糠醛流速的增大上升。     

糠醛液相化学选择性加氢制糠醇的研究

本文主要介绍了间歇式反应釜中糠醛在Cu-Zn/γAl2O3催化剂条件下在不同温度、时间、糠醛浓度和溶剂体系中的催化加氢制糠醇,从糠醛转化率和糠醇选择性两方面对加氢效果进行比较。通过实验,我们得到了糠醛加氢制糠醇的最佳工艺条件为反应温度为160℃、反应时间为3 h、催化剂用量为糠醛的7wt%、糠醛浓度为5wt%~25wt%、溶剂为甲苯时,糠醛的转化率和糠醇的选择性最好,分别为99%和98%。     

非晶态CoNiB合金催化糠醛液相加氢制糠醇

采用化学还原法制备了CoNiB非晶态合金催化剂,并用于糠醛液相加氢制糠醇反应。考察了Ni/Co摩尔比,NaBH4滴加速率等催化剂制备条件对催化性能的影响,以及反应压力、反应时间、反应温度等反应条件对糠醛转化率和糠醇选择性的影响。结果表明:最佳的催化剂制备条件是Ni/Co摩尔比为5/5,NaBH4滴加速率为2.6mL·min-1;最佳的反应条件为反应压力2MPa,反应时间3h,反应温度80℃。在此条件下糠醛的转化率为46.2%,糠醇的选择性为90.4%。     

糠醇加氢制1,2-戊二醇催化剂的制备及性能研究

采用化学共沉淀方法制备了铜氧化物催化剂FAH-1。在30 mL绝热微型固定床反应器上,研究了催化剂催化糠醇加氢制备1,2-戊二醇的性能,并对相关工艺条件进行了考察。实验结果表明：FAH-1催化剂表现出良好的糠醇加氢活性和选择性,在反应温度为160 ℃、反应压力为6 MPa、液时体积空速为0.3 h ^-1、氢油体积比为10 000∶1条件下,糠醇加氢反应的转化率和选择性分别为91.80%和41.52%,1,2-戊二醇单程收率达到38.12%,1 000 h长周期评价催化剂性能稳定。制得的1,2-戊二醇样品纯度高、质量好,满足后续加工对1,2-戊二醇的质量要求。反应过程采用固定床反应器,具有较好的工业化前景。     

糠醛气相加氢制2-甲基呋喃新型配合物催化剂研究

制备了一种新型、无毒Cu-Zn-Ca/γ- Al₂O₃配合物催化剂。采用固定床反应器,进行糠醛常压气相催化加氢反应,考察反应温度、催化剂组成、空速和氢醛比等因素的影响。结果表明,在508 K、空速0.32 h^-1、还原温度保持（493～513） K、活化6 h和氢醛物质的量比为10∶1条件下,糠醛转化率达到98.90%,2-甲基呋喃选择性达92.30%,2-甲基呋喃收率达91.28%。作为一种新型的无Cr催化剂,无毒,无污染,可代替Cu-Cr催化剂用于糠醛加氢过程,高活性和高选择性地制取2-甲基呋喃。     

糠醛选择性催化加氢的研究进展

糠醛是种可再生的生物质能源,可从农副产品中萃取得到。糠醛加氢可合成很多高附加值的产物,如糠醇、四氢糠醇、2-甲基呋喃、呋喃、2-甲基四氢呋喃、环戊酮、环戊醇和1,4丁二醇等。糠醛氢化反应除了碳碳双键、呋喃环氢化外,还有其他衍生副反应(脱羰、开环反应、缩合反应、C O键氢化等)。糠醛催化加氢催化剂主要为金属催化剂以及非晶态合金催化剂,单金属催化剂用于反应时的选择性和活性较低,通常采用添加助剂或是另一种金属以提高催化剂的活性和选择性,目前糠醛选择性催化加氢的研究主要集中在催化剂载体和双金属催化剂的研制上。主要阐述糠醛选择性催化加氢催化剂研究进展,指出在研制低成本、高选择性、稳定性、绿色环保的催化剂同时,催化剂的工业化应用研究有待进一步完善,最终以实现糠醛高效高选择性加氢工业应用为目的。     

流态化床内糠醛气相加氢制糠醇

进行了流态化床中糠醛气相催化加氢制糠醇的研究。研究了反应温度、分子比、空间速度对反应的影响。研究结果表明,最适宜的反应条件为:空间流速2.6—3.0升/分/100毫升催化剂,温度140℃,糠醛:氢气（分子比）=1∶40—45。糠醇的单程产率在90％以上,出口混合物中没有未反应的糠醛。     

以类水滑石为前躯体的铜镍基催化剂催化糠醛液相加氢

该文以类水滑石为前驱体经500℃焙烧得到铜镍基催化剂(Cu11.2Ni4.7-MgAlO)及相应的单组分铜基(Cu11.2-MgAlO)或镍基催化剂(Ni4.7-MgAlO),并采用X射线粉末衍射(XRD)、程序升温还原(H2-TPR)等技术对催化剂进行了表征.以糠醛液相加氢为探针反应,考察了3种催化剂的催化性能,并详细研究了催化剂还原活化温度、加氢反应温度、加氢压力、反应时间及催化剂用量等工艺条件对Cu11.2Ni4.7-MgAlO催化糠醛液相加氢反应的影响.结果表明,Cu11.2Ni4.7-MgAlO的催化性能均优于Cu11.2-MgAlO和Ni4.7-MgAlO;在最佳反应条件下,以Cu11.2Ni4.7-MgAlO为催化剂的糠醛转化率和糠醇选择性均可分别达到95.6%和93.1%,Cu11.2Ni4.7-MgAlO循环使用6次后,催化性能无明显下降,具有较好的稳定性.     

Upgrading of Simulated Syngas by Using a Nanoporous Silica Membrane Reactor

The permeance properties of a nanoporous silica membrane were first evaluated in a laboratory‐scale porous silica membrane reactor (MR). The results indicated that CO, CO₂, and N₂ inhibited H₂ permeation. Increased H₂ permeability and selectivity were obtained when gas was transferred from the lumen side to the shell side. This was therefore selected as a suitable permeation direction. On this basis, upgrading of simulated syngas was experimentally investigated as a function of temperature (150 – 300 °C), feed pressure (up to 0.4 MPa), and gas hourly space velocity (GHSV), by using a nanoporous silica MR in the presence of a Cu/ZnO/Al₂O₃ catalyst. The CO conversion obtained with the MR was significantly higher than that with a packed‐bed reactor (PBR) and broke the thermodynamic equilibrium of a PBR at 275 – 300 °C and a GHSV of 2665 h^–1. The use of a low GHSV and high feed pressure improved the CO conversion and led to the recovery of more H₂.     

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.     

Optimum operation of oxidative coupling of methane in porous ceramic membrane reactors

This paper presents analysis of oxidative coupling of methane on Li/MgO packed porous membrane reactor (PMR) by the fixed-bed reactor (FBR) model with reliable reaction kinetic equations. PMR can improve the selectivity and yield by controlling the oxygen feed to the catalyst bed through manipulating the feed pressure. At a fixed methane feed rate there is an optimal oxygen feed pressure that will achieve the highest yield. With a commercial ultrafiltration ceramic membrane, theoretical analysis shows that PMR can achieve, by operating with both side pressures at 1 bar at 750 °C, a maximal 30% yield at 53% selectivity. The maximal yield achieved in the FBR of identical dimension and temperature is 20.7% at 52.5% selectivity. Parametric study shows that lowering the membrane permeability improves the performance. Higher oxygen feed pressure will reduce the yield as well as the selectivity. Homogeneous reactions at high shell-side pressure can have adverse effect on the performance due to the fact that homogeneous reaction rates are strongly pressure dependent. The shell (oxygen feed) side volume must be minimized to reduce the homogeneous reactions. The results of PMR model calculation fit the published experimental result unexpectedly well.     

A dense Pd/Ag membrane reactor for methanol steam reforming: Experimental study

This paper focuses on an experimental study of the methanol steam reforming (MSR) reaction. A dense Pd/Ag membrane reactor (MR) has been used, and its behaviour has been compared to the performance of a traditional reactor (TR) packed with the same catalyst type and amount. The parameters investigated are reaction time, temperature, feed ratio and sweep gas flow rate. The few papers dealing with MR applications for the MSR reaction mainly analyse the effect of temperature and pressure on the reaction system. The investigation of new parameters permitted to better understand how the fluid-dynamics of the MR influences the hydrogen separation effect on methanol conversion and product selectivity. The comparison between MR and TR in terms of methanol conversion shows that the MR gives a higher performance than the TR at each operating condition investigated. Concerning hydrogen production, the experiments have shown that the overall selectivity towards hydrogen is identical for both MR and TR. However, the MR produces a free-CO hydrogen stream, which could be useful for direct application in proton exchange membrane fuel cells. A comparison, in terms of methanol conversion versus temperature, with literature data is also included.     

CO‐Free Hydrogen Production by Ethanol Steam Reforming in a Pd–Ag Membrane Reactor

In this work, the ethanol steam reforming (ESR) reaction has been studied by using a dense Pd–Ag membrane reactor (MR) by varying the water/ethanol molar ratio between 3:1 and 9:1 in a temperature range of 300–400 °C and at 1.3 bar as reaction pressure. The MR was packed with a commercial Ru‐based catalyst and a constant sweep gas flow rate in counter current mode was used. The influence of the temperature and the feed molar ratio on different parameters such as the ethanol conversion, the hydrogen production, the hydrogen yield and the CO‐free hydrogen recovery has been evaluated.     

The Effect of Pressure in Membrane Reactors: Trade-Off in Permeability and Equilibrium Conversion in the Catalytic Reforming of CH4 with CO2 at High Pressure

The antagonistic effects of pressure on reaction equilibrium and permeability were studied for the first time in a membrane reactor (MR). The reaction employed was the catalytic dry-reforming of methane with carbon dioxide (CH₄ + CO₂ ? 2CO + 2H₂) which produces a net increase in moles and is disfavored by high pressure. The studies were conducted at non-equilibrium conditions in a MR containing a hydrogen-selective ceramic membrane and a packed-bed reactor (PBR) at various pressures (1–20 atm) and temperatures (873 and 923 K) using a Rh/Al₂O₃ catalyst. Because of the concurrent and selective removal of hydrogen from the reaction in the MR significant enhancements over the PBR in the yields for H₂ (>170%) and CO (>130%) in the reaction products were obtained. However, as pressure was increased the enhancement in H₂ and CO yields in the MR went through a maximum and then declined. This occurred because, although the rate of hydrogen separation increased with increasing pressure, the conversions of the reactants decreased with increasing pressure. Thus, the maximum was due to a tradeoff between a transport property (hydrogen separation) and a thermodynamic quantity (hydrogen production) which had opposing pressure dependencies. It was also found that the reverse water–gas shift (RWGS) reaction (H₂ + CO₂ ? CO + H₂O) occurred simultaneously with the reforming reaction, and at high pressures significantly reduced the amount of hydrogen production in favor of water. The results are general and make the dry-reforming reaction impractical for commercial hydrogen generation regardless of the type of catalyst or reactor used.     

Oxidative coupling of methane in Ba0.5Sr0.5Co0.8Fe0.2O3−δ tubular membrane reactors

A dense membrane tube made of Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ (BSCF) was prepared by plastic extrusion from BSCF oxide synthesized by the complexing EDTA-citrate method. The membrane tube was used in a catalytic membrane reactor for oxidative coupling of methane (OCM) to C₂ without an additional catalyst. At high methane concentration (93%), about 62% C₂ selectivity was obtained, which is higher than that achieved in a conventional reactor using the BSCF as a catalyst. The dependence of the OCM reaction on temperature and methane concentration indicates that the C₂ selectivity in the BSCF membrane reactor is limited by high ion recombination rates. If an active OCM catalyst (La-Sr/CaO) was packed in the membrane tube, C₂ selectivity and CH₄ conversion increased compared to the blank run. The highest C₂ yield in the BSCF membrane reactor in presence of the La-Sr/CaO catalyst was about 15%, similar to that in a packed-bed reactor with the same catalyst under the same conditions. However, the ratio of C₂H₄/C₂H₆ in the membrane reactor was much higher than that in the packed-bed reactor, which is an advantage of the membrane reactor.     

Modeling and simulation of biodiesel production using a membrane reactor integrated with a prereactor

To enable the transesterification performed as quickly as possible, whereas the purification of product simultaneously carried out as completely as possible, the biodiesel production using a membrane reactor integrated with a prereactor is developed in this work. The set of mathematical model equations for the whole system includes the kinetics of the transesterification, the phase equilibrium, the mass balance of the prereactor, and the equations for the tubular ceramic membrane derived from mass balances of both the feed side and the permeate side coupled with the mass transfer across the membrane. The integrated reactor performances are then investigated in terms of the permeated biodiesel flux and selectivity over a range of methanol to oil ratio in the feed, the initial reaction time in the prereactor, the volume ratio of the prereactor to the tube membrane, and the length of the tube membrane module. The results show that the prereactor can be used for the purpose of carrying out a substantial part of the transesterification reaction in the early stage. The subsequent membrane reactor, when the operating conditions are controlled at methanol to oil molar ratio in the feed of 24:1, the catalyst concentration to the oil of 0.05 wt% at 65 ^oC, can serve to separate the unreacted emulsified oil from the product stream. The production of biodiesel with high purity using this proposed system is further validated experimentally and found in agreement considerably well with the simulated ones by adjusting the operating conditions, including the initial reaction time in the prereactor and the tube membrane length.