碱性添加剂在钛硅分子筛/H2O2催化丙烯环氧化反应中的作用

考察了反应溶液中碱性添加剂{氨水（NH₄OH）、氢氧化钠（NaOH）、碳酸钠（Na₂CO₃）、碳酸铵[(NH₄)₂CO₃]和四甲基氢氧化铵（TMAOH）}及其浓度对钛硅分子筛（TS-1）催化丙烯环氧化反应性能的影响，并采用紫外拉曼光谱（UV-Raman）与气相色谱（GC）联用原位分析（Raman-GC）碱性添加剂的作用机理。结果表明：反应体系中添加碱性添加剂可有效改善TS-1催化丙烯环氧化反应的选择性。不同碱性添加剂对TS-1催化丙烯环氧化活性和稳定性影响不同，NaOH、Na₂CO₃和TMAOH的添加造成催化活性和稳定性降低。NH₄OH或(NH₄)₂CO₃作为添加剂改善环氧化反应选择性的同时提高了反应稳定性，其中以(NH₄)₂CO₃效果最佳。添加(NH₄)₂CO₃浓度为8.0×10^-4mol/L时，TS-1催化丙烯环氧化在固定床反应器上连续运行336h时，X(H₂O₂)仍保持在90%以上。原位Raman-GC分析发现，反应体系中NH₄OH和(NH₄)₂CO₃添加可加快反应活性中间体Ti-OOH(η²)基团的生成，促进反应产物从活性中心快速扩散，从而提高丙烯环氧化反应选择性和稳定性。     

Can lanthanum doping enhance catalytic performance of silver in direct propylene epoxidation over NaMoAg/SiO_2?

In the attempt to reduce surface free energy of silica to improve interaction of silica with silver, silica was doped by different amounts of low surface energy lanthanum, La_2O_3, through impregnation. The doped and undoped silica were used as supports for preparation of Na/Ag/Mo/La_2O_3-SiO_2 catalysts. Catalytic performances of the catalysts were evaluated in direct epoxidation of propylene(DPO) using molecular oxygen under atmospheric pressure and without adding hydrogen. Adding 5 wt%La to the Na/Ag/Mo/SiO_2 catalyst improves both the catalysts electivity in DPO and its stability over 20h of time-on-stream.The characterization results show that La_2O_3 species interact strongly with silver particles on the silica surface which result in significant improvement in the dispersion profile of silver and marked decrease in the size of silver nanoparticles(AgNPs). The estimated mean diameter of AgNPs is ca. 4.0 nm in Na/Ag/Mo/5 wt%La_2O_3-SiO_2, which is smaller than that(53.9 nm) found in Na/Ag/SiO_2. The presence of subnanometer AgNPs on Ag/La_2O_3-SiO_2 prior addition of MoO_3 and NaCl to the sample can enhance the mutual electronic synergism between Ag, MoO_3 and Na for selective production of propylene oxide.     

Modeling of an industrial scale hydrodynamic cavitation multiphase reactor for Prileschajew epoxidation

The hydrodynamic cavitation multiphase reactor (HCMR) is emerging as a promising alternative for the intensification of liquid–liquid heterogeneous reactions, but research on HCMR modeling is lacking. In this article, an HCMR model was developed using Prileschajew epoxidation as the model system. First, based on experimental measurements of oil/water two-phase flow downstream of hydrodynamic cavitation devices, semiempirical correlations were proposed to describe the droplet size and droplet size distribution (DSD) as functions of flow conditions and geometry parameters. Then, with boundary conditions calculated by the DSD correlation, a droplet dynamics simulation in a reaction tank was performed by computational fluid dynamics coupled with population balance model to obtain the two-phase interfacial area. Finally, the acquired reactor model was substituted into an overall kinetic model, to simulate the epoxidation reaction in HCMR. Model predictions were verified by experimental results measured on an industrial scale HCMR.     

Oxoiron(V) Complexes of Relevance in Oxidation Catalysis of Organic Substrates

The selective oxidation of alkane and olefin moieties are reactions of fundamental importance in both chemical synthesis and biology. Nature efficiently catalyzes the oxidation of hydrocarbons using iron-dependent enzymes, which operate through the mediation of oxoiron(IV) or oxoiron(V) species. In the quest for chemo, regio and stereoselective transformations akin to those taking place in nature, bioinspired iron catalysts have been developed and understanding their mechanism of action has become a particularly relevant area of research. While a prominent advance in the preparation and characterization of oxoiron(IV) species has been accomplished, oxoiron(V) species remain exceedingly rare, presumably because the high reactivity that makes them particularly interesting also makes them difficult to observe. This review summarizes the advances in the field, focusing in synthetic systems for which the oxoiron(V) species relevant in these transformations have been directly detected and spetroscopically characterized.     

Optimization of Process Conditions for Styrene Epoxidation Based on the Artificial Intelligence Method

A novel prediction and optimization method based on improved generalized regression neural network (GRNN) and particle swarm optimization (PSO) algorithm is proposed to optimize the process conditions for styrene epoxidation to achieve higher yields. This model was designed to optimize the five input parameters reaction temperature and time as well as catalyst, solvent, and oxidant dosage. The output of the improved GRNN was given to the PSO algorithm to optimize the process conditions. The optimal smoothing parameter σ of GRNN was chosen from the training sample with a minimum cross validation error. Under the five optimized process conditions the maximum yield reached 95.76 %. This innovative model of improved GRNN hybrid PSO algorithm proved to be a useful tool for optimization of process conditions for styrene epoxidation.     

磷钨酸插层锌钛水滑石的制备及催化脂肪酸甲酯环氧化反应

采用离子交换法制备了一系列磷钨酸根插层Zn-Ti水滑石,利用XRD、FTIR、SEM对所制催化剂进行了表征。结果表明,磷钨酸根插层锌钛水滑石后仍保持原有的骨架结构。用制备的类水滑石催化脂肪酸甲酯环氧化反应,考察了所制催化剂的催化性能。当n(过氧化氢)∶n(原料双键)=1.5∶1,催化剂用量为脂肪酸甲酯质量的7.0%,在70℃下反应7 h时,脂肪酸甲酯转化率可达90.6%,环氧化产物选择性可达86.0%,优于Zn-Ti水滑石,其对脂肪酸甲酯环氧化反应显示出较高的催化活性。插层水滑石重复使用5次后,催化性能仍较稳定。     

一种新型环己烯合成环氧环己烷催化剂的制备及表征

针对现有固载型相转移催化剂制备过程中存在的问题,对环己烯合成环氧环己烷工艺进行了改进。在固载型过氧化磷钨杂多酸季铵盐PSC的制备中,对质子酸N的选用和磷酸的加入方式以及原料配比等问题进行了重新优化,并对优化工艺后制备的催化剂结构进行表征和性能实验。结果表明,改进后的催化剂制备工艺,不仅提高了原料钨酸的利用率,简化了操作,降低了成本,而且所制备的催化剂使用多次后仍能保持较高的催化活性及稳定性。     

用于合成叔胺的脂肪族环氧化物的合成

随着我国裂解制乙烯的工业不断壮大,副产物C4烯烃的产量大幅提高,如何有效利用大量生产的C4烯烃是我国亟待解决的问题。实验组以省部级项目"C4烯烃叠合生产高碳烯烃关键技术开发"为背景,研究C4烯烃下游产品的开发利用。本课题以烯烃环氧化胺化路线合成叔胺,主要研究高碳烯烃在胺化过程中环氧化物的合成,将C4烯烃最终转化到精细化工领域,在有效的解决我国大量C4烯烃的同时,提高了精细化工产品的利用率。烯烃的环氧化物在有机化学中应用广泛,它即可以做一些有机合成反应的中间体,也可以作为有机原料,在有机合成,如药物、精细产品、高分子化合物的合成方面应用非常广泛。因此,烯烃环氧化胺化路线不仅可以实现烯烃到脂肪胺的转化,还可以拓宽高碳烯烃的有效利用途径。     

N-甲基吗啉钨酸盐催化环氧化环辛烯反应研究

合成一种新型N-甲基吗啉钨酸盐[Mor1,n]Na W2O11(n=2,5,8),并考察了在以30%H2O2为氧化剂,乙腈为反应溶剂,[Mor1,2]Na W2O11为催化剂的催化环氧化环辛烯的反应体系中反应溶剂的量、催化剂的量、氧化剂的量和反应温度的变化对产率的影响,最终确定了最佳反应条件:反应温度70℃,环辛烯1 mmol,催化剂量30μmol,H2O2(30%)量2 mmol,乙腈0.5 m L,反应6 h,产率96%。