ETHYLENE OXIDATION ON SILVER CATALYSTS: EFFECT OF ETHYLENE OXIDE AND OF EXTERNAL TRANSFER LIMITATIONS

Ethylene oxidation to ethylene oxide and to carbon dioxide over silver catalysts was studied in a CSTR. The effects of two factors on the catalyst performance were examined. The first was the presence of excess ethylene oxide in the feed. A kinetic model was introduced which assumed that ethylene and ethylene oxide compete for the same sites on the catalyst surface. This model provided reasonable quantitative agreement with kinetic and potentiometric measurements. The second factor that was studied was the presence of external heat and mass transfer limitations. It was found that such limitations cause a significant decrease of the selectivity to ethylene oxide. This decrease is a result of the temperature difference between the catalyst surface and the bulk of the gas phase and of the fact that the activation energy of ethylene combustion is greater than that of ethylene epoxidation. The contribution of other factors such as inhibition by CO₂ or possible incomplete mixing in the reactor is shown to be insignificant.     

环氧乙烷反应器的安全设计问题

从环氧乙烯的易燃易爆性着手，剖析了传统式非离子表面活怀剂的生产中的不安全性，介绍了一种新型的安全性反应器。     

A REACTION-EXTRACTION-REGENERATION SYSTEM FOR HIGHLY SELECTIVE OXIDATION OF BENZENE TO PHENOL

The reaction-extraction-regeneration system for the liquid-phase oxidation of benzene to phenol in the benzene-water-oxygen system was investigated. Phenol was extracted in the extractor to reduce the concentration of phenol in the benzene phase. As vanadium catalyst was oxidized to inactive species after the oxidation reaction, the regenerator was installed in the system to reduce the oxidation state of vanadium catalyst from V⁴⁺ or VO²⁺ to the active V³⁺ under H₂ flow. The effects of various operating parameters including concentration of VCl₃ catalyst, O₂ and H₂ flow rates, benzene bubble size, pH, surface area of Pt regeneration catalyst, the metal species, and amount of ascorbic acid were investigated. Ascorbic acid was employed as a reducing agent for helping reduce the V⁴⁺ form to the active form and therefore improving the activity of vanadium catalyst. VCl₃ catalyst concentration of 10 mol/m³ with pH of 3–4 in the reactor and Pt surface area of 0.05 m² in the regenerator showed optimal conditions for the system.     

THE MECHANISM OF THE CATALYTIC OXIDATION OF SOME ORGANIC MOLECULES

The revolution in industrial organic chemistry during the last two decades is characterized by two marked changes:     

THE MECHANISM OF THE CATALYTIC OXIDATION OF SOME ORGANIC MOLECULES

The revolution in industrial organic chemistry during the last two decades is characterized by two marked changes:     

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     

PERIODIC OPERATION PERFORMANCE OF FIXED-BED REACTORS FOR SELECTIVE OXIDATION OF n-BUTANE TO MALEIC ANHYDRIDE

Ｃｕｒｒｅｎｔｌｙ ,ｔｈｅｓｅｌｅｃｔｉｖｅｏｘｉｄａｔｉｏｎｏｆｎ -ｂｕｔａｎｅｔｏｍａｌｅｉｃａｎｈｙｄｒｉｄｅ (ＭＡ)ｏｖｅｒｖａｎａｄｉｕｍｐｈｏｓｐｈｏｒｕｓｏｘｉｄｅ (ＶＰＯ)ｃａｔａｌｙｓｔｓｉｓｔｈｅｏｎｌｙｉｎｄｕｓｔｒｉａｌｐｒｏｃｅｓｓｉｎｖｏｌｖｉｎｇｔｈｅｓｅｌｅｃｔｉｖｅｏｘｉｄａｔｉｏｎｏｆａｌｉｇｈｔａｌｋａｎｅ[1].Ｓｐｌｉｔｔｉｎｇｕｐｏｆｔｈｅｏｖｅｒａｌｌｒｅａｃｔｉｏｎｉｎｓｐａｔｉａｌｏｒｔｅｍ ｐｏｒａｌｔｏｔｗｏｓｔｅｐｓａｎｄｍａｔｃｈｉｎｇｅａｃｈ…     

对煤分子中活性基团氧化机理的分析

根据煤分子结构的研究成果,推断桥键中的次甲基醚键、α位碳原子带羟基和带支链亚甲基的次烷基键、与两个芳环相连的次甲基键,以及侧链中的甲氧基、醛基、α位碳原子带羟基的烷基为常温常压下发生煤氧复合的活性结构。其氧化活性以醛基侧链、次甲基西边键、α位带羟基的次烷基键、α位带亚甲基的次烷基键、甲氧基、α位带羟基的烷基侧链、与两个芳环相连的次甲基键的顺序排列。由于氧分子存在两个未饱和分子轨道,煤分子活性基团在共轭效应和诱导效应作用下,呈现部分未成对的电子云进入氧分子轨道产生化学吸附,进而有部分发生各步氧化反应,放出热量。根据每步反应的键能变化,采用加权平均法可推算出煤氧复合每产生1mol CO,CO2和H2O的热效应值。由于煤中七种活性结构的氧化性不同及不同种类煤中各种活性结构的数量不同,煤氧化反应放出的热量不同,煤自然性也就不同。     

回收乙烯产品冷量降低乙烯装置能耗

兰州石化乙烯厂460 kt/a乙烯装置采用KBR公司脱乙烷塔技术,脱乙烷塔顶可生产出三分之一的产品乙烯。脱乙烷塔顶的乙烯进入乙烯制冷压缩机四段压缩后,送往下游聚烯烃装置。脱乙烷塔顶乙烯温度在-36℃,通过改造后,回收此冷量,降低了装置丙烯冷剂的用量,降低了装置的能耗。     

DIRECT OXIDATION OF ETHYLENE TO ACETALDEHYDE IN A HOLLOW FIBER MEMBRANE REACTOR†

A hollow fiber membrane reactor, which resembles a tube-and-shell heat exchanger, was developed for homogeneous catalytic reactions with gas reactants and products. The gas stream flows through the tube side while the reaction takes place in the catalyst solution which fills the shell side. The separation load of product from the catalyst solution can be reduced by using a hollow fiber membrane reactor instead of a conventional bubble column reactor. The reactor operates in a plug-flow pattern with a large mass transfer area per unit volume of catalyst solution

This concept was investigated experimentally using the direct oxidation of ethylene to acetaldehyde reaction in an aqueous solution of palladium (H) chloride-cupric chloride with a silicone rubber membrane reactor and a polypropylene membrane reactor. It was experimentally demonstrated that membrane reactors could achieve higher production rates per unit volume of catalyst than the conventional sparged reactor. The experimental data were in good agreement with the predictions by the mathematical model. The conditions under which the membrane reactor will be more advantageous than the conventional sparged reactors can be readily ascertained with the analytical solution of the simplified membrane reactor model.     

THE SELECTIVE CATALYTIC REDUCTION OF NITRIC OXIDE WITH METHANE OVER NONZEOLITIC CATALYSTS

This article deals with recent progress in the development of nonzeolitic catalysts for the selective catalytic reduction (SCR) of nitrogen oxides (NO_x) with methane. Although metal-exchanged zeolitic catalysts exhibit high activities for this reaction, most of these metastable structures suffer from deactivation problems when exposed to wet exhaust streams at elevated temperatures. Nonzeolitic oxide catalysts have the potential for improved durability because many of these are thermodynamically stable structures.

The NO_x reduction activity and poisoning resistance of lanthanide oxides, Group IIA oxides, Group IIIB oxides, as well as gallium-, tin-, and palladium-based catalysts are reviewed. Current opinions on mechanistic aspects of the SCR reaction are discussed in relation to the development of more active catalytic systems.

A detailed experimental study of the SCR of NO_x over rare earth oxides has also been performed. The role of absorbed oxygen in the activation of CH₄ and consumption of CH₃ radicals is discussed and related to the catalytic properties of the rare earth oxides. The presence of highly basic centers is shown to promote catalytic activity, and the presence of weakly absorbed oxygen species is found to be detrimental to catalytic selectivity. Oxides with lower electronic conductivities are found to be more selective than catalysts with higher conductivities. The selectivities of rare earth oxides for the SCR of NO_x with methane and the oxidative coupling of methane are also compared and contrasted.     

丙烯选择催化还原NO的研究

在以蜂窝陶瓷为载体的Pt/Al₂O₃催化剂上,对采用丙烯选择催化还原方法来脱除稀燃发动机尾气中NO的反应进行了实验与理论研究.建立了一维非均相反应模型,对反应过程进行了模拟,从实验与理论两方面讨论了反应温度、反应物浓度、通道特征尺度等因素的影响;并对反应过程中的内、外扩散作用作了理论分析.     

SELECTIVE OXIDATION OF ALCOHOLS BY REDOX MOLECULAR SIEVES

High-throughput synthesis and screening of libraries consisting of redox zeolites and molecular sieves have been developed for the selective oxidation of 2-butyl-5-hydroxymethyl-imidazole to the corresponding aldehyde in the liquid phase. Libraries consisting of 96 catalysts were prepared and screened for catalytic activity using high-throughput software, robotics, reactor, and screening technologies. The integrated synthesis and screening workflow allowed ∼5000 samples to be screened in less than one month. Promising hits identified in the high-throughput primary screens were successfully scaled up and optimized in conventional laboratory test units. Best results have been obtained with doubly or triply doped mesoporous sieves containing both an impregnated and framework-substituted metal. PtBi-doped framework-substituted V-MCM-41 redox mesoporous sieves were found to be efficient catalysts for aerobic oxidation under relatively mild reaction conditions (100-150°C, 15-400 psi air, 4-10 h reaction time). MIBK/H₂O/t-BuOH mixtures were identified as efficient solvent systems for this reaction. Isolated yields confirm high selectivities of more than 90% with quantitative conversions. Spent catalysts were shown to be fully regenerable by high temperature calcination in air.     

SELECTIVE CATALYTIC REDUCTION OF NITRIC OXIDE BY AMMONIA ON PILLARED CLAY CATALYSTS: POSSIBLE MECHANISM AND PROMOTERS

The delaminated Fe₂0₃-pillared clay shows high activities for selective catalytic reduction (SCR) of NO by NH₂. Temperature program desorption (TPD) studies show that large amounts of NO., are adsorbed on the pillared clay catalyst at the SCR reaction temperatures (i.e. near 400°C). This result indicates that a Langmuir-Hinshelwood type mechanism (for reaction between chemisorbed NO, and NH, on the surface to form N₂) is operative for the pillared clay catalyst, which is in contrast to the SCR reaction on the commercial vanadia-based catalysts. The SCR activities for the delaminated Fe₂0₃-pillared clay catalyst are higher than that of a commercial-type V₂O₅ + WO₃/TiO₂ catalyst under SO₂ + H₂0 free conditions, but became lower in the presence of SO₂ +l H₂0. However, when promoted by doping 1-3% Cr₂0₃, the pillared clay catalyst exhibits higher SCR activities than the commercial-type catalyst in the presence of S0₂ + H₂O at all practical SCR reaction temperatures     

SELECTIVE OXIDATION OF ALCOHOLS BY REDOX MOLECULAR SIEVES

High-throughput synthesis and screening of libraries consisting of redox zeolites and molecular sieves have been developed for the selective oxidation of 2-butyl-5-hydroxymethyl-imidazole to the corresponding aldehyde in the liquid phase. Libraries consisting of 96 catalysts were prepared and screened for catalytic activity using high-throughput software, robotics, reactor, and screening technologies. The integrated synthesis and screening workflow allowed ～5000 samples to be screened in less than one month. Promising hits identified in the high-throughput primary screens were successfully scaled up and optimized in conventional laboratory test units. Best results have been obtained with doubly or triply doped mesoporous sieves containing both an impregnated and framework-substituted metal. PtBi-doped framework-substituted V-MCM-41 redox mesoporous sieves were found to be efficient catalysts for aerobic oxidation under relatively mild reaction conditions (100–150°C, 15–400 psi air, 4–10 h reaction time). MIBK/H₂O/t-BuOH mixtures were identified as efficient solvent systems for this reaction. Isolated yields confirm high selectivities of more than 90% with quantitative conversions. Spent catalysts were shown to be fully regenerable by high temperature calcination in air.     

INFLUENCE OF ACTIVATED CARBON OXIDATION TREATMENTS ON THE SELECTIVE REMOVALOF COPPER AND LEAD

Air, acid, and electrochemical oxidation treatments have been employed to carefully control the amount and distribution of acidic surface groups in a series of activated carbons prepared from apricot stones. The surface reactivity and functional group distribution of oxidized active carbons have been assessed using numerous analytical and surface measurement techniques including nitrogen sorption, elemental analysis, potentiometric titrations, zeta potential measurements, and Boehm's titrations. Preliminary electrochemical oxidation results suggest that this treatment provides better control of the resultant surface acidity of the prepared carbons. Lead and copper sorption studies indicate that it is possible to alter the selectivity of the oxidized active carbons towards heavy metals by changing the quantity and/or relative proportion of the individual oxygenated surface functional groups.