| Esterification is a kind of indispensable reaction in chemical industry because of its widely use in daily chemicals, foodstuffs, medicines, petroleum, rubber, paints etc. And in actual production process, the catalyst is indispensable. Catalysts of esterification include general acid, solid acid, hydrochloride and sulfate (hydrogen) salt, solid heteropoly acid, solid super acid and non-acid etc. During recent years, dibutyl maleate (DBM) and dibutyl fumarate (DBF) which both are synthesized in the esterification of maleic anhydride with butanol have high application value in the industry of petroleum, fabric, plastic and papermaking. Using homogeneous catalyst tin chloride in this reaction have been reported in several literatureTin chloride is a Lewis acid which owes carbon coordinated and alcoholic hydroxyl group attacked capability due to its empty orbitals. Thus, it exhibits good catalytic activity for esterification. In order to obtain reusability catalyst, achieve the immobilization of tin chloride becoming a hot research topic. Supports which are widely used at home and abroad as follows:activated carbon, molecular sieve, ion exchange resin, macromolecule materials, and silica etc. In this work, we selected silica aerogels which owning specific surface areas, low bulk densities and good thermal stability as the support to synthesize the tin tetrachloride supported on silica aerogels catalyst, then applied to the esterification of maleic anhydride with butanol to explore the activity.This work includes three parts:the first part is the synthesis steps of support and supported catalyst, and the steps of characterize. The second part is the characteristic of tin tetrachloride pentahydrate supported on silica aerogels catalyst (SnCl4-5H2O/SiO2) and the activity evaluation in the esterification of maleic anhydride with butanol, besides, the analysis of deactivation reason. The third part is the characteristic of tin tetrachloride supported on silica aerogels catalyst (SnCl4/SiO2) and the activity evaluation in the esterification of maleic anhydride with butanol, besides, the analysis of activity decreaed reason.The first part corresponds to chapter two. Chapter two gives detailed instructions on the synthesis steps of silica aerogels and two catalysts of SnCl4-5H2O/SiO2and SnCl4/SiO2, and with the characteristic methods, the steps of the esterification of maleic anhydride with butanol. Using ethanol supercritical dry ness method to prepare silica aerogels. Two catalysts are prepared by refluxing under anhydrous and non-oxygen conditions, and so does the esterification of maleic anhydride with butanol. Besides, the Infrared (FTIR) spectra and’HNMR spectrum of two products DBM and DBF are both coincide with the standard spectrum nicely which is conformed that we have prepared DBM and DBF successfully and the purity up to above98%.The second part corresponds to chapter three. In chapter three, SnCl4-5H2O/SiO2catalyst was characterized by element analysis, X-ray powder diffraction (XRD), Infrared (FTIR) spectra, UV-vis diffuse reflectance spectra (DRUV-vis) and N2sorption. It is indicated that tin tetrachloride pentahydrate have been grafted on the surface of silica aerogels successfully, but immobilized ratio of active species is low and the structure of silica aerogels have been affected that appears the phenomenon of pores filling after supported reaction. The catalyst is appilied in the esterification of maleic anhydride with butanol. It is demonstrated that SnCl4·5H2O/SiO2catalyst appears good activity in this esterification which the conversion of maleic anhydride was up to78.8%, but the activity decreased considerably neared to the blank system after three recycle used which is illustrated that the stability of this catalyst is poor. The deactivation reason is analyzed by element analysis and IR as follows:1) Serious losing of Sn and Cl in the reused process;2) little reactants would adsorpt on the surface of catalyst which may lead to the decrease of active species. In order to increase the stability of catalyst, replace tin tetrachloride pentahydrate with tin tetrachloride as the active species which revealed in the third part in detail.The third part corresponds to chapter four and chapter five which is the central part of the paper. In chapter four, SnCl4/SiO2catalyst was characterized by element analysis, X-ray powder diffraction (XRD), Infrared (FTIR) spectra, UV-vis diffuse reflectance spectra (DRUV-vis) and N2sorption. It is indicated that tin tetrachloride have been grafted on the surface of silica aerogels successfully, and the immobilized ratio of active species has increased25%than SnCl4·5H2O/SiO2. Although appears the phenomenon of pores filling, it have been improved comparatively compared to the SnCl4·5H2O/SiO2. The optimal esterification conditions were confirmed as follows:mol ratio of reactants was1:2:0.0028(anhydride:butanol: catalyst),25ml of dehydrating agent (toluene) was used when each0.1mol of maleic anhydride used (4.903g maleic anhydride,7.4g butanol,0.5g catalyst,12.5ml toluene), temperature was120℃, reaction time was6h, under which the conversion of maleic anhydride was up to86.10%. It is indicated that not only the activity have been increased compared to SnCl4·5H2O/SiO2, but also the stability have been improved largely that the conversion of maleic anhydride remain two times as much as the blank system.after six times reused. As there is a little decrease of the catalyst activity in the recycle used process, in chapter five, activity results combined with element analysis, IR, DRUV-vis, N2sorption to analyze the decreased reason. It is demonstrate that strong electron deficiency of active center (Sn-Cl2) on the catalyst surface make the catalyst may react with MA and BO together to form new active species (Sn-OR, R=-O2CCH=CHCO2H、-OBu) as the catalytic was going on that may bad for the catalyst activity. |
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