| Ester compounds are widely used in coatings,medicines and cosmetics,for example,diisoamyl oxalate is a new type of diesel cetane number improver.At present,liquid sulfuric acid is often used as a catalyst in industry,but there are obvious shortcomings in separation,recovery and environmental impact.On the other hand,solid acid catalysts have the advantages of being non-corrosiveness,easy to separation and recyclable multiple times,all of which are in line with the concept of green chemistry.In this paper,chemical bonding between sulfonic acid and phosphoric acid groups on the surface of metasilic acid was used to prepare the new solid silicon sulfonic acid catalyst(SSA)and the new solid silicon phosphoric acid catalyst(SPA),which were then adopted to catalyze the esterification reactions.The catalysts have a low production cost,a high acid content,high catalytic activity and good stability.This paper focuses on the study on the performance of new solid acid catalysts in different esterification reactions.The main conclusions are as follows:Firstly,the new solid silicon sulfonic acid catalyst was prepared by chemical bonding method,and its acid content was 1.69 mmol H~+/g.Esterification of acid and alcohol catalyzed by silicon-based sulfonic acid was investigated,and the reaction conditions were optimized.Under the optimal conditions,in the synthesis of butyl acetate,3 g of acetic acid,1:2 molar ratio of acetic acid to n-butanol,110℃ of reaction temperature,2 h of reaction time,0.5 g of catalyst,the conversion of acetic acid was 90.5%,and the selectivity to butyl acetate was 100%.In the synthesis of diisoamyl oxalate,the reaction conditions were optimized and the reusability of silicon sulfonic acid catalyst was investigated.The oxalic acid was 3 g,the molar ratio of oxalic acid to 3-Methy-1-butanol was 1:6.5,the catalyst dosage was 0.8 g,the reaction time was 3 h,the reaction temperature was 120℃,the conversion of oxalic acid was 92.9%,and the selectivity to disoamyl oxalate was 100%.Furthermore,the catalyst presented good stability after 5 cycles,with the conversion of oxalic acid being nearly unchanged,and the selectivity to diisoamyl oxalate was still 100%.Compared with the existing research,the silicon sulfonic acid showed good stability in the esterification reaction.The structure and properties of silicon sulfonic acid were characterized by XRD,FT-IR,and BET.The excellent catalytic performance of silicon sulfonic acid might be resulted from its prominent B-acid site,strong acidity and surface area.The possible catalytic reaction mechanism was proposed based on the performance test and characterization results of the catalyst.Secondly,the new solid silicon phosphoric acid catalyst was prepared by chemical bonding method,its acid content was 2.36 mmol H~+/g.The catalytic performance on the esterification of oxalic acid with 3-Methy-1-butanol to diisoamyl oxalate was investigated.Meanwhile,the reaction conditions were optimized and the reusability of the catalyst was investigated.The results showed that under the optimal conditions,the oxalic acid was 3 g,the molar ratio of oxalic acid to3-Methy-1-butanol was 1:5.5,the reaction temperature was 120℃,the reaction time was 3 h,the catalyst was 0.8 g,the conversion of oxalic acid was 91.1%,and the selectivity to disoamyl oxalate was 100%.Furthermore,the conversion of oxalic acid remained basically unchanged,and the selectivity to diisoamyl oxalate was 100%after the catalyst was recycled 5 times.The structure and properties of silicon phosphoric acid were characterized by XRD,FT-IR and BET.The results showed that silicon phosphoric acid catalyst possesses high Bacid sites and strong acid sites.In conclusion,the new solid silicon sulfonic acid and the new solid silicon phosphoric acid were developed in this paper.The catalysts have the advantages of low preparation cost,simple preparation method,superior catalytic performance and reusability,therefore they have important theoretical significance and application prospects. |
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