Construction Of Starch-based Pickering Catalyst System And Its Application In Phase Transfer Catalytic Reaction

Phase transfer catalysis(PTC)is an important new technology for organic synthesis and has been widely used in the synthesis of textile chemicals,daily chemicals and medicine.A large phase interfacial area is the key to ensure the efficient PTC reaction.At present,large interfacial area is provided by mechanical shearing,which causes the problems of high energy consumption in the reaction process and difficult treatment of reaction solution.Ensuring the efficiency of PTC reaction with low energy consumption and employing green methods into reaction process have become the focus of current research.Pickering emulsion(PE),with solid particle as emulsifier,has the advantages of stable system,large phase interface area.PE system,which can accomplish the reaction without mechanical shearing,has become one of the common systems for heterogeneous reaction.Compared to inorganic particle and polymer particle,starch-based Pickering particle is regarded as a non-toxic,renewable and environmentally friendly resource,which is more in keeping with the concept of green chemistry.In the paper,starch-based Pickering particles were prepared by octenyl succinic anhydride(OSA)and styrene oxide(STO)grafting modification on starch,respectively.The effects of pH,PTC catalyst type and amount on the interfacial activity of Pickering particle and emulsion stability were studied.Then,the feasibility of two PE catalytic systems applied to highsalt and strongly basic PTC reactions was explored.The catalytic activities of mechanical shearing system and PE system were compared and the applicability of the PE system was studied.It provided a theoretical basis for the application of PE system in heterogeneous reaction such as PTC reaction.The main research contents and conclusions are as follows:(1)Preparation of esterified starch and study on the stability of PE.The esterified starch was prepared by grafting of OSA on starch.The effect of PTC catalyst type on the stability of PE was analyzed.The results showed that OSA was grafted onto starch in the form of ester bond and the substitution degree of the prepared esterified starch was 0.07.After modification,the starch adhesion occurred with the complete destruction of crystallization region.The esterified starch had the ability to stabilize the PE with highly saline conditions.PTC Catalyst type had great influence on the stability of PE.The addition of tetrabutylammonium bromide(TBAB)caused the reduce in the droplet size and the improvement in the stability of PE.The PE demulsified with the addition of dodecyl trimethylammonium bromide(DTAB).(2)Studies on catalytic reaction in PE system stabilized by esterified starch.The esterification reaction of sodium acetate and p-nitrobenzyl bromide was used as a model,the effects of various factors on the catalytic activity were studied.And the recycling performance and applicability of the PE system were analyzed.The results showed that an excellent catalytic performance appeared in PE system,and the conversion rate achieved 100% within 3 h without mechanical shearing.The hydrolysis of ester bond was occurred with increasing the pH of aqueous phase,leading the disappearance of emulsification property of particle.Then,the aqueous phase can be reused for 5times and the conversion rate can still reach 80%.The PE system was also suitable for the reaction with potassium thiocyanate in aqueous phase but not for the reaction with strong alkali in aqueous phase.(3)Preparation of etherified starch and study on the stability of PE.The etherified starch was prepared by grafting of STO on starch.The effects of pH,PTC catalyst type on the stability of PE were analyzed.The results showed that STO was grafted onto starch in the form of ether bond and the substitution degree of the prepared etherified starch was 0.13.After modification,the fine starch grains were bonded to each other,the large particles were hollow and sunken with the complete destruction of crystallization region.The pH had little effect on the interfacial activity and zeta potential of particle.PE system stabilized by etherified starch performed an excellent alkali resistance.PTC catalyst type had great influence on the stability of PE.No significant effect was observed on the stability and diameter of PE with the addition of TBAB.And demulsification of PE was observed with the addition of fatty alcohol polyoxyethylene ether 7(AEO-7)or DTAB.(4)Studies on catalytic reaction in PE system stabilized by etherified starch.The etherification reaction of p-cresol sodium and p-nitrobenzyl bromide was used as a model,the effect of PTC catalyst amount on the catalytic activity was investigated.And the applicability of the PE system was analyzed.The results showed that TBAB accelerated reactant transport.The conversion rate was 100% within 3 h with the addition of 5% TBAB.The PE system was also suitable for the reaction with highly saline conditions but the stability of the PE system was not as good as the PE system stabilized by esterified starch.