Studies Of The Metal Oxides And Solid Acid Catalysts In The Condensation Reactions

The reactions for condensation are very important, and their products of ethylacetate and isoprene have a wide range of applications in various fields. Ethylacetate is an important chemical materials and a useful solvent that is widely used inperfume industry, food industry, textile industry, etc. Isoprene is the importantmonomer for synthetic rubber (SR), and it is mainly used for synthesis isoprenerubber (IR), butyl rubber (IIR) and styrene-isoprene-styrene block copolymer (SIS)etc.The liquid acid catalysts have many defects in reactions for condensation, suchas: corrosion of equipment, pollution of the environment, separation and recyclingdifficulties. A lot of research works have been carried out to solve these problems.The the metal oxides and solid acid catalysts have been used to replace liguid acidcatalysts, due to their advantages of non-corrosive, environmentally friendly,reusable. However, for the condensation reaction, the catalytic properties, activecenter, reaction mechanism over the solid acid catalysts still need furtherimprovement and research.The reaction of ethanol one-step synthesis to ethyl acetate and the vapor phasecondensation of isobutene and formaldehyde reactions have been investigated overmetal oxides and solid acid catalysis. The structure and surface texture of thecatalysts were studied with different characterization means. The active sites on thecatalysts and the reaction mechanism were also discussed combining with thecatalytic performance of catalysts. The main experimental results and conclusionsare as follows:1. Cu/SiO2catalysts for ethanol one-step synthesis to ethyl acetate Cu/SiO2catalysts, which contain copper phyllosilicate, were successfullyprepared using the ammonia-evaporation method. The formation of the copperphyllosilicate species significantly affected the structural properties and caused theCuO nanoparticles to become highly dispersed, and they would also provide accessto the Lewis acidic Cu+species. The Cu/SiO2catalyst with a23.7wt%copperloading exhibited the best ethanol conversion and ethyl acetate selectivity.Compared to the IM catalyst, the AE catalysts exhibited a much higherdispersion, a smaller copper particle size and a larger surface area, in addition to theformation of copper phyllosilicate, which could be reduced to Cu+. The AE catalystsexhibited superior ethanol conversion and selectivity for ethyl acetate formation inthe reaction of ethanol one-step synthesis to ethyl acetate. We proposed that thesynergistic effect of Cu0and appropriate amount of Lewis acidic sites generatedfrom Cu+cause this effect.2. The one-step synthesis of ethanol to ethyl acetate over Cu-based catalystsmodified by ZrA series of Cu/Zr/SiO2catalysts have been prepared through impregnationmethod. The introduction of Zr could not only improve the dispersion of CuO andrestrict the growth of Cu particle, but also provide a certain amount of acid L and Bacid sites for the surface of catalysts. We suggested that the synergistic effect of Cu0and amount of acidic sites was beneficial for the reaction.The Cu/ZrO2catalysts were modified by alkali metal and alkaline earth metal,the introduction of Mg could neutralize the medium strength acid sites, and inhibitthe occurrence of side reactions, enhance the selectivity of ethyl acetate. But, theaddition of Na, K decreased the selectivity of ethyl acetate, which may be due to thestrong basicity of Na and K, and reduced esterification center.3. Modified HZSM-5molecular sieves for the condensation of isobutene andformaldehydeThe high silica of HZSM-5zeolite applied in the vapor phase condensation reaction isobutylene and formaldehyde. Experimental results showed that Si/Al ratiohave a certain impact on the catalytic performance the catalysts. The selectivity ofisoprene increased gradually with the silica to alumina ratio increasing. We proposedthat the strong acid sites were not conducive to the generation of isoprene.The HZSM-5molecular sieves modified with transition metal and nonmetalwere prepared and successfully applied to the condensation of isobutene andformaldehyde. We found that the sample with P content of5wt%showed the bestcatalytic performance. The results suggested that appropriate amount of the weakacid sites could improve the condensation of isobutene with formaldehyde.Other acidic zeolites such as HY, H-beta, TS-1were also applied in the vaporphase condensation reaction isobutylene and formaldehyde. The results furtherillustrated that a appropriate amount of weak acids were in favor of the condensationreaction, and confirmed that the acid type was not related with the catalyticperformance directly.4. Supported heteropoly acid catalysts for the condensation of isobutene andformaldehydeThe type of heteropoly acids and supports had been filtered, and it was foundthe SiO2supported heteropoly acid catalysts showed high catalytic performance. Theconversion and selectivity were related with the concentration and strength of acidsites. Appropriate amount of the weak Lewis acid sites could improve thecondensation of isobutene with formaldehyde.The relationship between acidity of the surface catalyst and the coke depositshas been investigated. The side effects and coke deposits were caused by themedium-strong acid sites. The coke deposits could cover the moderately strong acidsites as the reaction continued which inhibited the side reactions and enhanced theselectivity to isoprene.