Preparation And Application Of Mesoporous Silica Microspheres Solid Acid

With the rapid development of domestic plastic industry,the demand for nontoxic plasticizer like citroflex is getting larger and larger.At present,concentrated sulfuric acid is often used as catalysts to synthesize citroflex in industry.Howerver,these processes suffer from the disadvantages of the severe equipment corrosion,inconvenient post treatment and the pollution of by-products.So a solid acid with high catalytic activity,strong stability,repeatable use and easy separation is urgent to be developed to take the place of concentrated sulfuric acid.In recent years,mesoporous silica base solid acid is gradually becoming a new research hotspot.This kind of catalysts exhibit high specific surface area,good pore structure,high mechanical strength and high catalyticactivity and do well in various acid catalytic reactions.In this work,in order to prepare the novel solid acid,the mesoporous silica spheres prepared by hydrothermal method were used as support,and then a series of mesoporous silica solid acid microspheres were synthesized by sulfonation process and grafting method,respectively.The influences of the preparation technology on the catalytic activity of these catalysts were mainly investigated,and the application of these catalysts in the synthesis of citrate esters plasticizer were also discussed.The main results are as follows:1.Mesoporous silica microsphere was hydrothermally synthesized using nonionic copolymer?P123?and cetyl trimethyl ammonium bromide?CTAB?as template and tetraethyl orthosilicate?TEOS?as silicon source with the assistance of inorganic salt.The effect of acid concentration,the amount of CTAB and the type of inorganic salt on the morphology and pore structure of mesoporous silica microspheres were studied.When the concentration of hydrochloric acid was 1 mol/L,the amount of CTAB was0.3g,the inorganic salt was Zn Cl₂,silica microspheres with smooth appearance and uniform particle size?5⁷?m?could be facilely obtained.The silica microspheres with three-dimensional worm-like channel structure,narrow pore size distribution?average pore size 2.57 nm?and large specific surface area?730.45 m²/g?.2.A series of sulfonate silica microspheres solid acid was synthesized by sulfonated sulfonation method by using mesoporous silica spheres materials with different 3D pore structure as supports.The effects of the sulfonated temperature and time on the activity of different structure catalysts were investigated and the catalysts were applied in the synthesis of Tributyl citrate.The results show that the optimum preparation conditions of silica microspheres solid acid with different structures are closely related to the pore structure of the mesoporous silica.The worm-like mesoporous silica spheres with larger surface area possessed the highest catalytic activities after sulfonated at 240°C for 6 h.When it was used in the synthesis of plasticizer tributyl citrate ester,the esterification rate is as high as 99.04%,but which owns the poor catalytic activity for the repeated use.3.The silica microspheres solid acid was prepared by graft copolymerization method?-Pr-SO3H?,benzene sulfonic acid?-Ph-SO3H?and ammonia sulfonic acid?-A-SO₃H?group.Through the esterification reaction of citric acid and n-butanol,the catalytic capacity of different acidic groups and the optimum reaction conditions of the esterification reaction were investigated.The results show that the catalytic activity of catalyst depends on the acid strength,and the catalytic activity sequence of different catalysts is:-Ph-SO₃H>-Pr-SO₃H>-Am-SO₃H.The occurrence of such differences is mainly related to the adsorption capacity of the groups adjacent to sulfonate roots,the stronger the electronic absorption capacity is,the greater the acid strength becomes.The optimum process conditions of trioctyl citrate esterification using WSM-Ph-SO₃H are as follows:the reaction temperature was 150°C,the molar ratio of n-butanol to citric acid was 5:1,the mass of catalyst was 7.5%wt and reaction was 5 h.Under these conditions,a maximum esterification yield of 98.67%could be obtained.And the catalyst shows good recyclability.4.A series of pairs of functionalized silica microspheres solid acid were synthesized by grafting different alkyl?methyl,n-octyl or dodecyl?and sulfonic acid groups simultaneously The influence of the hydrophobic group and the ratio of sulfonic acid group on the activity of catalyst was studied.The results revealed that the catalytic activity increases with the increase of alkyl chain in hydrophobic groups.When the hydrophobic group was in octyl,the ratio of acidic group to hydrophobic group was 2:3,and the synthesized solid acid had the highest catalytic activity.When it was used in the catalytic synthesis of citric acid three dioctyl,the optimum reaction condition are as follows:the reaction temperature is 160°C,the molar ratio of n-butanol to citric acid is 5:1,the mass of catalyst was 10%wt and reaction is 5 h.Under these conditions,a maximum esterification yield of 97.88%could be obtained.After repeated use for 6 times,the esterification yield is 94.04%,which means that the catalyst has the advantages of stability and high efficiency,and is promising to be used in other acid catalytic reactions.