顺酐生产用VPO催化剂的研究进展

综述了正丁烷选择性氧化制顺酐VPO催化剂的研究进展,介绍了催化剂制备过程中添加载体及助剂对催化剂性能的影响,讨论了正丁烷选择氧化制顺酐的反应机理,并结合国内外研究现状对VPO催化剂未来的发展方向作了展望.     

Characterization of cobalt-impregnated VPO catalysts

Cobalt-impregnated VPO catalysts containing 1–6% of the metal by weight were prepared. The catalytic tests showed that cobalt impregnation significantly increased the overall activity while slightly decreasing the maleic anhydride selectivity. To investigate the origin of the cobalt effect, the solids were characterized using XRD, Raman spectroscopy, FT-IR, TPR and XPS. No structural effects were detected through XRD. TPR showed that the non-equilibrated catalysts contain cobalt oxides which react with the VPO solids to yield a hard to reduce system. Non-equilibrated umpromoted and promoted (low cobalt loadings) catalysts contain small proportions of V(V) phases. After several 100 h on stream, the only phase detected in all cases was V(IV) vanadyl pyrophosphate. The surface oxidation state of vanadium was V(IV). The maleic anhydride yield correlates with the increased exposure of cobalt on the catalysts surface.     

The beneficial effect of cobalt on VPO catalysts

The addition of Co to VPO formulations improves the yield of n-butane to maleic anhydride. In this work, different modes of impregnation and two different organic cobalt salts were used. The equilibrated catalysts were characterized using XRD, ³¹P SEM NMR, FT-IR and acetonitrile adsorption to evaluate Lewis acidity.

The best catalyst was obtained using Co acetyl acetonate for impregnation of the VOHPO₄·0.5H₂O precursor. This catalyst after equilibration had an optimum concentration of very strong Lewis acid sites, very low concentration of isolated V(V) centers, and no V(V) phases.     

The reaction network of the selective oxidation of n-butane on (VO)2P2O7 catalysts: Nature of oxygen containing intermediates

The reaction network of the partial oxidation of n-butane to maleic anhydride on (VO)₂P₂O₇ has been investigated using steady-state and transient experiments in a Temporal-Analysis-of-Products (TAP) reactor under vacuum conditions to identify by mass spectrometry possible intermediate products and in a tubular fixed bed reactor at atmospheric pressure to derive information on the role of the detected and other potential intermediates in the reaction network. The oxidation of butane, butadiene, tetrahydrofuran, dihydrofuran, and furan has been studied in the TAP reactor and, additionally to these compounds, crotonaldehyde, crotonlactone, and malealdehydic acid were oxidized in the tubular flow reactor. From the results obtained it can be concluded that the main reaction pathway from butane to maleic anhydride proceeds via the intermediate products n-butenes, butadiene, crotonaldehyde, dihydrofuran, furan, and crotonlactone.     

正丁烷选择氧化中吸附氧与晶格氧的作用

引　言丁烷选择氧化制顺酐是以廉价低碳烷烃作为原料的直接选择氧化反应 ,近年来已引起广泛关注并进行了较多的研究[1] .普遍认为 ,这是一个以复合氧化物VPO作为催化剂 ,晶格氧参与催化循环、按氧化还原机理进行的反应[2 ] .为了提高这一反应的选择性 ,杜邦公司按照序贯氧化 还原原理重新组织催化循环的思想 ,率先提出了双反应器循环流化床 (CFB)的专利 ,并进行了晶格氧正丁烷选择氧化制顺酐的技术开发 ,建立了大规模工业示范装置 ,显示了改善性能的潜力[3] .鉴于在空间上和在时间域内使催化循环各步骤分离进行这两类非定态操作在实质上…     

Ti/Zr助剂掺杂VPO催化正丁烷选择性氧化制顺酐

采用有机相法制备钒磷氧(VPO)催化剂,并在合成过程中加入Ti/Zr助剂,使用微型固定床反应器评价其催化正丁烷选择性氧化制顺酐的性能,考察了不同助剂元素及其化合物形式和添加量对催化剂性能的影响,分析了添加助剂对催化剂晶相及微观形貌的影响. 结果表明,加入助剂未改变催化剂的晶相结构,但促进了活性相(VO)2P2O7生成,且使反应后催化剂微观形貌发生改变,片层更破碎,活性相暴露,同时生成了利于反应的微量V5+;助剂金属Ti和Zr与V元素间的相互作用对催化剂表面P浓度及V价态都有一定影响;与不加助剂的VPO催化剂相比,相同反应条件下,Ti/Zr助剂修饰的VPO催化性能显著提高,摩尔比Zr/V为1.5%的Zr(NO3)4为助剂的催化剂的催化性能最佳,稳定状态下正丁烷的转化率高达99.1%,顺酐收率为54.4%.     

Membrane pilot reactor applied to selective oxidation reactions

The partial oxidation of butane to maleic anhydride was studied in a conventional fixed bed as well as a novel reactor configuration consisting of a porous metallic membrane immersed in a gas–solid fluid bed. The diameter of both reactors was at a commercial scale greater than 30 mm. A range of gas flow rates, temperatures and butane concentrations were tested. Maleic anhydride yield was generally higher in the membrane reactor due to higher butane conversion. Maleic productivity in the fixed bed equalled that observed in the membrane reactor when the gas–solid fluid bed was maintained at a higher temperature of as much as 30 °C. The butane feed rate to the membrane reactor was limited by hot spots. These hot spots were unanticipated and underscore the importance of increasing heat transfer in order to commercialize this technology.     

A Model for the Phosphorus Dynamics of VPO Catalysts during the Selective Oxidation of n‐Butane to Maleic Anhydride in a Tubular Reactor

A model for the phosphorus dynamics in vanadium‐phosphorus oxide (VPO) catalysts for the oxidation of n‐butane to maleic anhydride was developed. According to the model, reversible sorption processes determine the phosphorus content of the catalyst. Simulations reveal that several phenomena can be successfully described. If no phosphorus is added to the reactant feed, the catalytic activity increases until runaway occurs. With addition of a proper amount of phosphorus, the loss can be compensated while excessive phosphorus addition results in complete catalyst deactivation. Adjusting the model parameters to experimental data may result in a model that can be used to optimize the performance of maleic anhydride reactors.     

Controlling factors in the selective conversion of n-butane over promoted VPO catalysts at low temperature

Unpromoted and 1.2, 2.3 and 4.3 molar % Co:V cobalt-promoted vanadium-phosphorous-oxide (VPO) catalysts were synthesized via an organic route. The catalyst precursors were calcined and then conditioned in a reactor, forming the active vanadyl pyrophosphate (VO)₂P₂O₇ phase, which was confirmed via X-ray diffraction studies (XRD). The effect of co-promotion on the yield of maleic anhydride (MA) from n-butane oxidation was examined at different temperatures and gas hourly space velocities (GHSV). 2.3% Co:V was the optimum promoter loading for a high yield towards MA. Higher GHSV's proved to enhance the selectivity towards MA.

The catalysts were tested over a 200 h period, generally taking some 24 h to reach steady-state performance. The best performing catalyst yielded 45% MA at 275 °C and a GHSV of 7200 ml g⁻¹ h⁻¹, with an n-butane conversion of 73%, whilst all previously reported VPO catalysts produced far lower MA yields at this temperature.     

VPO催化剂上正丁烷选择氧化制顺酐反应动力学

对一种工业钒磷复合氧化物 (VPO)催化剂上正丁烷选择氧化制顺酐的反应动力学特性进行了系统的实验研究 .在空速大于 30 0 0h^-1、温度 35 0～ 44 5℃ ,进口总压约为 0 .2MPa和原料气组成为丁烷 0 .5 %～ 3.2 %、氧 5 .5 %～ 2 6 .5 %的条件下测得 45套本征反应动力学数据 .按照三角形反应网络处理实验数据 ,经参数估计、模型识别和统计检验得到了诸反应速率的表达式及相关参数数值     

Effect of different calcination environments on the vanadium phosphate catalysts for selective oxidation of propane and n-butane

Vanadium phosphate catalysts were synthesized via VOPO₄·2H₂O and were calcined in two different hydrocarbon reaction environments, i.e. n-butane/air and propane/air. Both catalysts are denoted VPDB and VPDP, respectively. Both catalysts exhibited a good crystalline with characteristic peaks of pyrophosphate phase. However, the peaks for VPDP are shown to be more prominent than those of VPDB. BET surface area showed that VPDB gave higher surface area (23 m² g⁻¹) compared to VPDP (18 m² g⁻¹). The average V valence state for VPDP is 4.08 and the higher V valence state for VPDB is 4.26 due to higher amount of V^V for VPDB. Furthermore 14.2% of V^III was found for VPDP but none for VPDB. SEM micrographs clearly revealed that the morphologies of both catalysts composed of plate-like crystallite that was arranged into the characteristic of rosette cluster. However, the catalyst calcined in n-butane/air environment (VPDB) resulted in an increment of the amount of plate-like crystal formed in the rosette rosebud agglomerates. TPR in H₂ profiles of both catalysts gave two reduction peaks corresponding to two kinetically different oxygen species which were associated with V^V and V^IV phases, respectively. VPDB removed larger amount of active oxygen species linked to V^IV phase which eventually caused a higher conversion rate in the selective oxidation of n-butane and propane to maleic anhydride and acrylic acid, respectively.     

VPO催化剂催化正丁烷氧化工艺条件的研究

采用有机相还原法制备了VPO催化剂,并将其用于正丁烷催化氧化合成顺酐。利用单因素实验考察反应温度、原料气组成和空速对催化反应的影响。结果表明,在反应温度420℃、正丁烷物质的量分数1.5%和体积空速1 800 h-1工艺条件下,正丁烷转化率83.23%,顺酐选择性70.59%。     

A Study on VPO Specimen Supported on Aluminum-Containing MCM-41 for Partial Oxidation of n-Butane to MA

Dispersed vanadium–phosphorus oxide species supported on Al-MCM-41 with different vanadium loadings have been synthesized for the first time for partial oxidation of butane to MA. It was found that the VPO species was dispersed over the Al-MCM-41 support material, both in the internal channel and on the external surface. With increasing vanadium loading, n-butane conversion increased but MA selectivity decreased considerably under the same reaction conditions. At lower conversions (<30%), rather high MA selectivity (ca. 70%) can be achieved on the low loading sample. Compared with the amorphous structure of large pore SiO₂ support, the unique structure of the MCM-41 and the incorporated Al³⁺ in the framework do have an impact on the reaction behavior of the supported VPO specimen. The chemical nature of the supported VPO species and the interaction between the applied VPO species and the support was found to vary notably with the content of vanadium in the sample and likewise affected the related physico-chemical characteristics and their reaction behaviors.     

丁烷氧化法顺酐生产的技术进展

系统介绍了丁烷法生产顺酐的工艺技术和技术进展 ,并对顺酐的发展提出了建议。     

合成温度对VPO催化剂比表面的影响

在不同的温度下制备VPO催化剂，采用BET、XRD和SEM等测试手段考察制备温度对催化剂的比表面及晶相结构的影响。实验结果表明，温度对比表面和晶相结构的影响存在一个最佳值。选择适宜的制备温度可以使催化剂晶粒变小，比表面增大，活性相含量增加。     

不同P与V比的Mo/VPO催化剂物相组成及其催化性能

采用有机相法制备了不同P与V物质的量比的Mo掺杂VOHPO₄·0.5H₂O前驱体,并通过体积分数为50%空气-40%氮气-10%水蒸汽混合气氛活化得到Mo/VPO催化剂,采用固定床反应器评价其催化正丁烷氧化制顺酐的性能。结果表明,Mo/VPO催化剂催化活性随P与V物质的量比的增大而降低,但顺酐选择性与P与V物质的量比并不呈线性关系,P与V物质的量比为0.9的Mo/VPO催化剂具有最佳的催化性能。XRD分析表明,Mo/VPO催化剂催化正丁烷氧化制顺酐的主要活性物相为(VO)₂P₂O₇和钒磷云母相,形成的主要因素不是P与V物质的量比,而是由焙烧条件决定。低P与V物质的量比的Mo/VPO中存在的少量V₂O₅物相能够提升催化剂的活性和顺酐选择性,但含量过高会因深度氧化降低催化性能。催化剂中存在的钒磷云母相有利于缩短催化剂稳定时间并提升催化性能。     

A generalized kinetic model for the partial oxidation of n-butane to maleic anhydride under aerobic and anaerobic conditions

The kinetics of n-butane oxidation for the production of maleic anhydride (MA) over a commercial VPO catalyst has been investigated under aerobic and anaerobic conditions and at a temperature range of 400-. A kinetic model that can be applied under both aerobic and anaerobic conditions is presented. The model considers three types of oxygen: adsorbed oxygen, surface lattice oxygen and sub-surface lattice oxygen. Both adsorbed and surface lattice oxygen are considered active for the production of maleic anhydride and CO_x.     

Dual role of Fe boost lattice oxygen oxidation of Mo-based materials from kinetics and thermodynamics

High-valent Mo-based oxides are easily dissolved in alkaline electrolyte resulting in complete surface reconstruction of catalyst. Therefore, there are few researches on the oxygen evolution reaction (OER) process of this material, especially the reaction mechanism. Herein, Fe-Mo₂C@CN was synthesized by introducing 3d metal Fe into the Mo-based catalyst, which inhibited the complete dissolution of Mo. The overpotential is only 226 mV at a current density of 10 mA cm⁻². Experimental and density functional theory (DFT) results demonstrate that excellent electrocatalytic performance derives from the dual role of Fe and the thermodynamically favorable single-site lattice oxygen oxidation mechanism (LOM). Electronic-rich pure Fe inhibits the molybdenum dissolution while enhancing the reaction kinetics. And the doped Fe decreases the d‐band center, weakens the M-O (metal-oxygen) bond, and promotes the involvement of lattice oxygen in the OER process. This work provides theoretical basis for the engagement of Mo-based catalysts in water splitting.     

Low temperature gasification using lattice oxygen

Low temperature pyrolysis and gasification has been investigated based on the chemical looping combustion (CLC), where insufficient amount of lattice oxygen was reacted with hydrocarbons. Metal oxides such as nickel oxide, iron oxide and titanium oxide were used as lattice oxygen source and were coated on silica gel or porous aluminum. Single column reactor was used for experiments and 36.1 mmol of polyethylene was dropped to the column whose temperature was ranged from 693 to 1073 K. For the pyrolysis, hydrogen yield was 100% of polyethylene contained hydrogen, while methane, CO and CO₂ were minor products and almost half of the supplied carbon was deposited on the particle surface. On the other hand, for the steam gasification, 2-3 mol of the hydrogen was generated from 1 mol of carbon and almost no carbon deposition was observed. It is found that no wax and heavy tar was observed in the exhaust. Therefore, the lattice oxygen was able to be applied to the low temperature gasification of hydrocarbons.     

工业级原料制备正丁烷氧化制顺酐VPO催化剂及其催化性能

采用工业级原料制备正丁烷氧化制顺酐VPO催化剂,在固定床反应器中测试催化剂性能。采用粉末X射线衍射表征合成的催化剂样品。结果表明,在反应温度372℃、空速1 500 h~(-1)和反应压力0.11 MPa下,催化剂活性较好,正丁烷转化率达到86.27%,顺酐选择性73.27%,顺酐收率63.11%。长周期试验结果表明催化剂稳定性良好。