Effect of acid strength distribution on de-t-butylation rate and catalyst fouling rate

De-t-butylation of t-butylbenzenes was carried out over a pyridine poisoned solid acidic catalyst to determine the effect of acid strength distribution on the reaction rate and catalyst fouling rate. The acid sites on the solid acidic catalyst were divided into three groups by their acid strength. Moderate acid sites, which were effective for the de-t-butylation but ineffective for the coke formation, were exclusively left on the catalyst surface by the partial poisoning. It is found that the present modification of the catalyst is useful in preparing an acid catalyst without catalyst fouling by coke deposition.     

Fatty acid selectivity of lipases: Erucic acid from rapeseed oil

The fatty acid selectivity of several commercial lipases was evaluated in the hydrolysis of high-erucic acid rapeseed oil (HEARO). The lipase ofPseudomonas cepacia catalyzed virtually complete hydrolysis of the oil (94–97%), while that ofGeotrichum candidum discriminated strongly against erucic acid, especially in esterification. A two-step process is suggested for obtaining a highly enriched erucic acid in which theG. candidum lipase is employed to selectively esterify the fatty acid residues of unsaturated C-18, and shorter chain acids, from a mixture of HEARO fatty acids obtained from total hydrolysis of the oil withP. cepacia lipase.     

Effect of the diffusion phenomena in the catalyst grain on the selectivity of a system of parallel-consecutive reactions involved in the process of n-heptane dehydrocyclization

Analytical relations were derived for analyzing the selectivity of consecutive-parallel reactions occurring under conditions of the reforming process. With these relations it is also possible to determine how the shape of the catalyst grain, as well as the kinetic and diffusion phenomena that govern the process, affects the efficiency of the desired final products.     

Effects of catalyst aging on the activity and selectivity of commercial three-way catalysts

A Pd catalyst is particularly effective for the oxidation of CO and C₃H₆ at low temperatures, while the Pt/Rh/Ce catalyst is active for NO reduction. The TWC activity of both catalysts generally decreased as the catalyst mileage increased. However, the NO reduction activity was less affected by catalyst aging compared to the oxidation reactions. The selectivity of the catalysts in favor of the CO–O₂ reaction (vs. C₃H₆–O₂ reaction) in the O₂ partitioning experiments became less pronounced as the catalyst aged. The NO partitioning experiments reveal the superior capability of H₂ in NO reduction to the other reductants (CO and C₃H₆) examined in the present study. The reactivities of NO with both H₂ and CO were found to decrease upon catalyst aging, resulting in decreased overall NO removal activity.     

Fatty acid selectivity: The selectivity of lipases ofGeotrichum candidum

The relative reactivities of several long-chain fatty acids in esterifications with 1-butanol catalyzed by lipases ofGeotrichum candidum were evaluated. As has been noted previously, these lipases are not uniformly highly selective forcis-9 unsaturated fatty acids. However, the lipase preparations examined do uniformly discriminate against fatty acids having a chainlength greater than C-18 such as erucic acid. The reactivities of γ-linolenic and ricinoleic acid were also low compared to that of oleic. An examination of the effect of the alcohol upon the relative reactivities of acids showed that one could enhance fatty acid selectivity by proper choices of alcohol. For example, oleic acid esterifies 2.5 times faster than palmitic acid with 1-butanol catalyzed by Amano GC-4 lipase, but esterifies over 50 times faster with 2-methyl-1-propanol or cyclopentanol.     

提高钛白废酸提钪萃取选择性的研究

研究旨在选择合适的助萃剂LH,提高二（2-乙基己基）磷酸（P204）-磷酸三丁酯（TBP）-磺化煤油体系对钛白废酸提钪的选择性,提高钪钛分离系数和钪铁分离系数。研究采用的工艺为二次萃取富集、二次反萃成钪、化学精制提纯钪。通过正交试验确定最佳萃取工艺条件：萃取剂最佳配比V（P204）∶V（TBP）∶V（磺化煤油）=1.3∶0.7∶10,一次萃取相比为V（O）∶V（A）=1∶21,不加助萃剂二次萃取相比为V（O）∶V（A）=1∶5,加助萃剂时其加量为水相体积的1.7%,此时钪钛分离系数达到124 812,钪铁分离系数达到8 202。     

The role of shape selectivity and intrinsic selectivity of acidic sites of the catalysts in the skeletal isomerization of n-butenes

The effect upon kinetic behaviour (activity and selectivity) of the physical properties (pore volume distribution) and acidic characteristics (nature of acidic sites and acidic strength distribution) of acidic catalysts in the skeletal isomerization of n-butenes has been studied. The catalysts studied are the following: γ-alumina, alumina modified by introduction of F, Cl and Br, silica–alumina, HZSM-5 zeolite-based catalyst and SAPO-34-based catalyst. It has been proven that the selectivity of acidic catalysts towards the skeletal isomerization of n-butenes is the result of a compromise between pore shape selectivity and intrinsic selectivity of the acidic sites of different strength, this latter property being more significant. Strong acidic sites are needed for the skeletal isomerization, but sites which are too strong produce important amounts of byproducts. A chlorinated alumina is a highly active and selective catalyst for skeletal isomerization. © 1998 SCI.     

有机锆络合物在高选择性催化反应中的应用

有机锆络合物可以高选择性地催化环辛二烯加氢、烯烃与２－甲基吡啶偶合反应、环酮与醛、醇交叉缩合反应、ＭＰＶ型酮还原和ＯＰＰ型醇氧化反应及多羟基化合物酰基化等反应．这些反应在有机合成中具有应用价值。     

Studies of the fischer-tropsch synthesis on a colbalt catalyst. III. mechanistic formulation of the kinetics of selectivity for higher hydrocarbon formation

Mechanistic models are derived to quantify selectivity in the Fischer-Tropsch synthesis. The models are fitted to experimental selectivity data obtained on a cobalt catalyst and are found to give a satisfactory fit. Results show that branching reactions can be explained by assuming a rate limiting 1-2 hydrogen shift. For small molecules the 1-2 shift takes place on one site, whereas larger molecules need an adjacent sit for the shift to take place. The “break” arises from the sum of two Anderson-Schulz-Flory distributions arising on two different locations.     

Fatty acid selectivity of lipases: γ-linolenic acid from borage oil

The γ-linolenic acid (Z,Z,Z-6,9,12-octadecatrienoic acid, GLA) present in borage oil free fatty acids was concentrated in esterification reactions that were catalyzed by several preparations of the acyl-specific lipase ofGeotrichum candidum. In this manner, a 95% recovery of the GLA originally present in borage oil (25% GLA) was obtained as a highly enriched fatty acid fraction with a GLA content of >70%. Other fatty acids concentrated in this fraction were the monounsaturated fatty acids with chainlengths of C-20 and longer that were present in the oil. An immobilized preparation ofG. candidum on silica gel also was used for the enrichment of GLA in borage oil. In this instance, a 75% recovery of GLA was obtained, and the supported lipase was reusable (three cycles) with minimal loss in activity. Presented in part at the 84th Annual Meeting of the American Oil Chemists’ Society, Anaheim, California, May 1993.     

Shape selectivity as a function of pore size in epoxidation of alkenes with supported titanium catalysts

Reactant shape selectivity of supported titanium catalysts for epoxidation of cyclohexene and 2-hexene has an excellent correlation with the pore diameter of the catalysts. With titanosilicate the preference to cis isomer epoxidation is small compared to TiO₂-SiO₂ probably because of the restriction of its diffusion imposed by the zeolite micropore structure.     

腐殖酸聚集体对膜蒸馏过程膜污染的作用机理

膜污染是膜蒸馏过程应用于工业水处理中遇到的主要问题之一。选取水体中具有代表性的有机物（腐殖酸）、微溶无机盐（碳酸钙）作为典型污染物,研究有机腐殖酸聚集体对于膜蒸馏过程膜污染进程的影响规律,探讨天然有机物-无机微溶盐混合水体中腐殖酸聚集体对于无机盐结晶过程的控制机理。结果表明：膜蒸馏通量的衰减大致可分为由滤饼层的形成造成的不可恢复部分以及由浓差极化、膜孔“半润湿”而造成的可部分恢复的通量降低。Ca²⁺通过加速腐殖酸分子的聚集过程,使表面负电性降低的腐殖酸聚集体率先吸附在聚偏氟乙烯中空纤维膜内表面,形成有机基质污染层;碳酸钙在有机腐殖酸聚集体的诱导下在膜内表面异相成核,最终成长为稳定的晶体。腐殖酸聚集体为无机盐晶体在疏水性膜内表面的生长提供了异相成核的基础。可通过控制污染水体中有机物的含量控制微溶碳酸钙在膜内表面成核及生长,实现控制其在膜内表面附着进而诱发疏水膜发生亲水化的过程。     

A consecutive microreactor system for the synthesis of caprolactam with high selectivity

A microreactor system containing two consecutive microreactors and a stirred vessel was developed for the improvement of selectivity of caprolactam (CPL) synthesis. The first microreactor was used to conduct the reaction of cyclohexanecarboxylic acid and oleum, and 97% selectivity for the intermediate product, named mixed anhydride, was obtained. The mixed anhydride then quickly reacted with nitroso‐sulfuric acid in the second microreactor, and the reaction was completed in the vessel, where CPL selectivity reached 93.9%, a much higher value than that achieved either in a control experiment with a batch reactor or in industrial process. The advantage of microreactors is that they can provide high‐quality mixed anhydride and can mix it quickly with the nitroso‐sulfuric acid prior to reaction in the vessel reactor, which, from an engineering standpoint, gives better performance than the traditional syringe‐fed method that is common in chemical synthesis. © 2015 American Institute of Chemical Engineers AIChE J, 61: 1959–1967, 2015     

乙酸(酯)-甲醛缩合制丙烯酸(酯)研究进展

近年来,通过乙酸（酯）和甲醛缩合制备丙烯酸的新路线吸引了学术界和工业界的广泛关注。此新路线的优点是过程简单,原料可从天然气、煤化工产品中获得,成本低廉,对可持续生产丙烯酸具有十分重要的意义。国内外研究者针对这一反应开发了多种类型的催化剂,包括钒磷氧（VPO）类催化剂、负载型碱金属/碱土金属以及离子液体等。本文综述了不同种类催化剂近期的研究成果,总结了三类催化剂的优缺点。指出均相的离子液体催化剂具有反应温度低、能耗少、选择性高的特点,但反应为间歇操作,产物分离困难、催化剂较难重复利用,催化效率偏低。VPO类催化剂和碱金属/碱土金属类催化剂,反应温度较高（320～400℃）,但可实现连续反应,产物分离方便,催化效率较高。相比于VPO类催化剂,碱金属/碱土金属类催化剂涉及的反应较少,对目标产物的选择性较高,但整体催化效能低于VPO类催化剂,且失活催化剂再生困难。最新的研究结果表明,经典的有机相法制备VPO前体可以被更加简便、经济与环境友好的一锅水相法取代。空气氛中简单焙烧即可完成催化剂前体的活化。不仅大大简化了催化剂制备,而且所得催化剂的小试性能优异,从而为后续应用奠定了重要基础。     

干燥方式对丙烯醛部分氧化制丙烯酸催化剂的影响

钼钒钨复合金属氧化物是典型的丙烯醛部分氧化制丙烯酸催化剂,铜、锑是良好的助剂.干燥方式对催化剂性能有较大影响.评价结果表明,喷雾干燥得到无定型的催化剂粉末,较结晶干燥方式具有更好的催化活性和选择性,适应的温度范围较宽.采用XRD、SEM和EDX方法对催化剂进行了表征,表明喷雾干燥所得样品元素分布更均匀.     

氢气分压对对苯二甲酸加氢反应的影响

在实验装置和工业装置上分别考察了氢气分压对对苯二甲酸(TA)加氢反应的影响,实验室研究表明,氢气分压对TA中的对羧基苯甲醛(4-CBA)的加氢速率有一定影响,氢气分压在0.5-1.5 MPa均能较快使4-CBA还原降到25μg/g以下,在工业装置上要根据催化剂的不同活性周期来调节氢气分压,合理的氢气分压操作范围为0.5-1.2 MPa。     

FCC催化剂酸性与孔结构对焦炭选择性的影响

分别制备酸性和孔体积不同的催化剂,并通过红外光谱、N₂吸附和ACE评价等方法,考察B酸与L酸的调变以及催化剂孔体积的变化对焦炭选择性的影响。结果表明,催化剂B酸量增加,L酸量在一定范围适度减少,均有利于焦炭选择性的提高;催化剂孔体积低于0.39 mL·g^-1时,随着孔体积增加,生焦因子呈降低趋势;孔体积高于0.39 mL·g^-1时,由孔体积增加带来焦炭选择性的优势便无法体现。     

Effect of surface diffusion on the selectivity of catalytic reactions

Analysis is made on the effect of surface diffusion on the selectivity of a catalyst for a consecutive reaction A→B→C in a well-mixed stirred tank reactor. The catalyst is composed of an α region despersed on the β region. A→B is assumed to occur on the α region and B→C on the β region. Migration of B from α to B proceeds both by surface diffusion and gas phase transport. Influence of the flow rate through the reactor, the crystallite size of α, and the loading of the catalyst on the selectivity for C in the presence of surface diffusion are discussed. Under otherwise identical conditions, selectivity is increased by surface diffusion. The optimum condition for the production of C is also discussed.     

The electrochemical hydrogenation of edible oils in a solid polymer electrolyte reactor. II. Hydrogenation selectivity studies

Soybean oil has been hydrogenated electrochemically in a solid polymer electrolyte (SPE) reactor at 60°C and 1 atm pressure. These experiments focused on identifying cathode designs and reactor operation conditions that improved fatty acid hydrogenation selectivities. Increasing oil mass transfer into and out of the Pd-black cathode catalyst layer (by increasing the porosity of the cathode carbon paper/cloth backing material, increasing the oil feed flow rate, and inserting a turbulence promoter into the oil feed flow channel) decreased the concentrations of stearic acid and linolenic acid in oil products [for example, an iodine value (IV) 98 oil contained 12.2% C_18:0 and 2.3% C_18:3]. When a second metal (Ni, Cd, Zn, Pb, Cr, Fe, Ag, Cu, or Co) was electrodeposited on a Pd-black powder cathode, substantial increases in the linolenate, linoleate, and oleate selectivities were observed. For example, a Pd/Co cathode was used to synthesize an IV 113 soybean oil with 5.3% stearic acid and 2.3% linolenic acid. The trans isomer content of soybean oil products was in the range of 6–9.5% (corresponding to specific isomerization indices of 0.15–0.40, depending on the product IV) and did not increase significantly for high fatty acid hydrogenation selectivity conditions.     

Effects of acid strength and micro pore size on -caprolactam selectivity and catalyst deactivation in vapor phase Beckmann rearrangement over acid solid catalysts

The vapor phase Beckmann rearrangement of cyclohexanone oxime (CHO) over solid acid catalysts including zeolites was carried out to elucidate the effects of the acid strength and the micropore size of the catalysts on the selectivity of -caprolactam (CL) and the catalyst deactivation rate. It was found that the catalyst deactivation rate was strongly dependent on the acid strength of the acid catalysts. The improvement of catalyst life was achieved by using MFI-type metallosilicates having weak acid sites. The CL selectivity decreased over the acid catalysts with micropores larger than those of the MFI zeolites. Furthermore, using methanol and carbon dioxide as the diluent solvent and diluent gas improved CL selectivity and catalyst life, respectively.