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.     

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.     

Effect of catalyst poisoning on the overall selectivity and activity

A mathematical model describing the pore-mouth poisoning of porous catalysts by a strongly adsorbed poison is presented. The effect of poisoning on catalyst selectivity and activity are examined for various pellet geometries; namely, an infinite slab, an infinite cylinder and a sphere. Three types of multiple reactions; independent, parallel and consecutive reactions are considered. For each type of multiple reaction, poisonings of the desired reaction, the undesired reaction and both the desired and the undesired reactions are treated separately.The variations in catalyst selectivity are discussed in terms of the reaction rate constants, the effective diffusities of reacting species, and the extent of catalyst poisoning.A criterion is given for selection of a catalyst that offers a high selectivity for the desired reaction.     

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     

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。     

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.     

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.     

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.     

磷钼酸在硫酸-醋酸体系中对304不锈钢的缓蚀性能研究

考察了磷钼酸在硫酸一醋酸混酸介质中对304不锈钢的缓蚀性能,对缓蚀机理进行了初步推断。实验结果表明,磷钼酸是一种阳极型缓蚀剂,在ω(H2SO4)=0．5％～1．5％、ω(CH3COOH)=58．0％、ω(HPA)=0．1％～0．2％,温度100～120℃的条件下,腐蚀速度小于0．05mm／a,缓蚀率高迭99．7％。     

De-t-butylation of t-butylphenols over dealuminated zeolites in liquid-solid system

Liquid-solid phase de-t-butylation of p-t-butylphenols was carried out over original and dealuminated zeolites to determine the effect of catalyst pore size and acidity on the reaction rate and catalyst fouling rate. The de-t-butylation rate over the original zeolites was mainly dependent upon their micro pore sizes. Although the dealumination by acid leaching decreased strong acid sites, the de-t-butylation rate over dealuminated HY zeolite was higher than that on the original zeolite. The present dealumination is a useful method to prepare an acid catalyst for de-t-butylation in a liquid-solid system.     

Effect of metal dispersion on CO hydrogenation over Pd/HZSM-5 catalysts

Pd/HZSM-5 catalysts prepared by ion-exchange method using Pd(NH₃) ₄ ²⁺ were calcined and reduced at different temperatures to provide different metal dispersions. The effect of Pd dispersion on CO adsorption characteristics and acidity were observed through FT-IR study. Methanol and dimethyl ether were the main products in CO hydrogénation over Pd/HZSM-5 catalyst with small Pd particles on which CO was weakly adsorbed, while the selectivity to methane increased with metal sizes.     

对苯二甲酸加氢精制钯炭催化剂硫中毒原因初探

通过在实验室中进行对苯二甲酸加氢精制钯炭催化剂的硫中毒试验,初步探讨了钯炭催化剂在对苯二甲酸加氢精制反应过程中发生硫中毒的可能原因和机理。