Preparation And Catalytic Performance Of Solid Acid Catalysts

It is well known that acid catalysts are essential in esterification reactions,which are common and necessary reactions in the synthesis of many fine chemicals such as perfumes,solvents,pharmaceuticals,food preservatives,cosmetics and biofuels.Homogeneous inorganic acids(such as sulfuric acid)are commonly used as acid catalysts in industrial esterification,which have high catalytic activity and low cost.However,liquid acid catalysts are highly corrosive,which makes them difficult to separate and unfriendly to the environment,it doesn’t fit with the current theme of green chemistry.Therefore,the development of solid acid catalysts with high stability and environmental protection is the focus of research in the field of catalysis today,it is very necessary to replace these homogeneous acid catalysts with heterogeneous acid catalysts.Alumina is widely used in the field of catalyst and adsorbent,so the preparation of alumina with large pore and large specific surface area is the focus of current research.The main contents of this paper are as follows:(1)Alumina was prepared by hydrothermal method,sodium aluminate solution and aluminum sulfate solution were mixed and stirred,by changing the p H of the solution,the boehmite prepared by different terminal p H was obtained.Boehmite with different anions was prepared by using different acidic aluminum sources,and alumina with different anions and terminal p H was prepared by calcination.The prepared alumina is loose and porous flake structure,in which the specific surface area of alumina with terminal p H=8.0 can reach 542.4 m~2/g and the pore volume is 2.51 cm~3/g.The specific surface area of the sample containing phosphate is 512.2 m~2/g,the pore volume is up to 3.96 cm~3/g,and the maximum pore size is 21 nm.Alumina with both large pore and large specific surface area has been successfully prepared.(2)In order to explore the optimum reaction conditions of esterification reaction,the sample prepared with aluminum sulfate as raw material was selected as catalyst.By discussing the separation method and reaction conditions of the experiment,the separation method of the experiment is determined as membrane filtration.,when the reaction mixture was 6.67g,the reaction temperature was 115oC,the molar ratio of alcohol to acid was 5:3,and the catalyst was 0.5 g,the catalyst had the best catalytic effect and the highest esterification rate.Different kinds of alumina prepared were used as the esterification reaction of acetic acid and n-butanol to explore the catalytic activity of different kinds of alumina and their influence on the esterification reaction.Under the condition of no water separator,within 6 h of reaction time,the alumina with terminal p H=8.0 had the highest catalytic activity and the esterification rate reached65.4%.The esterification rate of commercial alumina SB powder is 49.2%.It indicates that the alumina with large pore and specific surface area prepared in this paper has higher catalytic activity.(3)The alumina powders prepared by different anions in Chapter 2and commercial alumina SB powders were used as catalyst supports to prepare solid acid catalysts loaded with ammonia bisulfate by grinding and impregnation methods,respectively.A series of solid acid catalysts with different preparation conditions and different kinds were prepared by changing calcination temperature and load content.The catalyst with commercial alumina SB powder and desulfurized alumina as carrier prepared by grinding method has improved the catalytic effect by 10%and3%,respectively,compared with the previous,but the specific surface area of different anionic alumina decreases greatly after loading,resulting in no obvious improvement of catalytic effect.Impregnation method is more uniform,so the activity of catalyst prepared by impregnation method with large pore and large ratio surface alumina as the carrier is greater than that prepared by grinding method,while the result of catalyst prepared by commercial SB powder as the carrier is opposite.Finally,the repeated use effect of the catalyst was explored.After 5 times of repeated use,the catalytic effect of the catalyst was slowly reduced.The sample with self-made alumina as the carrier was reduced by 10%,and the initial activity was restored after washing and roasting.