Preparation And Catalytic Performance Of Supported Phosphotungstic Acid Catalyst For Esterification Reaction

Phosphotungstic acid (PW) can be used as catalyst for numerous organicreactions because of its unique acidic and redox properties. Supporting PW onvarious porous carriers by impregnation methods can improve the surface area ofphosphotungstic acid, thermal stability, catalytic activity and reusability. Nevertheless,these systems suffer from the the leaching of PW active phase, and cannot give highcatalytic reusability. Therefore, it is much desirable to design new PW catalysts toovercome the solubilization of active component in the reaction medium.In this study, ultra-stable Y zeolite (USY), dealuminated USY (DUSY) andSBA-15were used as catalyst carriers, a series of supported phosphotungstic acidcatalysts were prepared by impregnation method、in-situ synthesis method and graftedmethod. The catalytic activities were tested for the esterification of adipic acid withn-butanol. The research focus is placed on the catalysts preparation conditions and thecatalysts reusability. In addition, structure, composition and surface acidity ofcatalysts were characterized by FT-IR、XRD、NH3-TPD、N2adsorption-desorptionand UV-Vis etc.A series of catalysts with different loading of PW and cesium salt of PW onDUSY were prepared by impregnation method. The optimum reaction conditions foresterification over DUSY supported PW catalyst are reaction temperature383K,mole ratio of n-butyl alcohol to adipic acid3.3:1, mass fraction of toluene (as waterremoval agent) in the reaction medium is22%, mass ration of the catalyst used in thereactants is2.0%. Under the above reaction conditions, the better catalyticperformance can obtained over40%PW/DUSY and50%Cs2.5H0.5PW/DUSY, with theadipic acid conversion reached up to96.3%and86.7%respectively after reaction5h..Repeated use tests showed that the activity stability of supported cesium salt of PWcatalysts is far better than that of supported PW catalysts.A new type of PW encaged USY zeolite catalysts were prepared by in-situsynthesis method. The influence of catalysts preparation conditions on the catalytic performances were investigated in detail. An active and stable catalyst can be obtaiedunder the optimum preparation conditions of mole ratio of Na2HPO4to Na2WO4is3:12, amount of HCl is5mL and the theoretical loading of PW is40%. Furthermore,in-situ synthesis method can overcome the leakage problem of active component inpolar reaction media. The PW-USY catalysts prepared by this method have goodcatalytic reusability and adipic acid conversion dropped less than5.0%after fourtimes of reaction cycle.Mesoporous silica SBA-15functionalized with amine group by different silanecoupling agents were synthesized by grafting method and phosphotungstic acid weresubsequently immobilized on the functionalized SBA-15for the further evaluation asa catalyst of adipic acid esterification. Silane coupling agents were grafted onto thepore walls of SBA-15successfully and SBA-15maintained the ordered mesoporousstructure. The esterification results showed that SBA-15were functionalized withsingle amino silane coupling agent and the density of amine sites on SBA-15surfaceswere controlled using benzyl spacers and hydrophobic group was immobilized onSBA-15surfaces can improve the activity of catalyst. The catalyst prepared bygrafted method showed excellent catalytic stability, and adipic acid conversion onlydropped4.0%after five times of reaction cycle.