Cyclohexane Assisting Preparation Of Octenyl Succinate Starch In Superctritical CO₂

Supercritical CO₂ media is a kind of green chemical reaction medium,which is widely used in chemical reaction engineering.In this paper,cassava starch and octenyl succinic anhydride as raw materials and strong alkali as catalysis,octenyl succinic acid cassava starch is prepared by supercritical CO₂ technology to optimize the starch ester preparation process and find the suitable additives assisting supercritical CO₂ solubilize OSA to improve the degree of substitution and reaction efficiency of esterification reaction.the structure and characterization of starch after esterification were analyzed,meanwhile,the kinetics of supercritical starch esterification was explored to investigate esterification reaction rate and activation energy and reveal supercritical starch esterification reaction competition mechanism and OSA hydrolysis in the reaction system.Various additives was used to assist supercritical CO₂ preparing octenyl succinic acid starch ester,respectively.The results revealed that additive could improve the solubility of the supercritical CO₂ medium to esterification agent,and the cyclohexane additive showed the optimal synergistic effect that reaction efficiency is about 3.0 times higher than that without the additive when 1.5%cyclohexane is added,meanwhile,the optimum reaction conditions were found as follows:reaction temperature of 90?,pressure of 12MPa,time of 3h and esterification agent of 4%that the degree of substitution and the reaction efficiency are 0.0191 and 62%,respectively,and even the reaction efficiency is up to 83%by using 2%esterification agent.All the results indicated that cyclohexane to increase reaction efficiency and improve esterification reaction condition have good synergistic effect on starch esterification in supercritical CO₂ medium.The product structure was characterized by FIRT,NMR,SEM and XRD,and the properties of starch gelatinization were investigated.Analysis of product structure characterization showed by FIRT,NMR,SEM and XRD that the esterification groups are introduced into the starch molecules,and small particle characteristics and A-type crystal structure are still remained,however,the particle surface morphology is partially destroyed and the crystallinity is reduced.Analysis of product characteristics show that the transparency,freeze-thaw stability,cohesion and emulsification of the product after esterification in supercritical CO₂ media are improved with that of the original starch,and product brabender viscosity is increased.Based on the dynamics model that has been studied,the kinetics of the preparation of octenyl succinate starch in supercritical CO₂ media was explored,and it was validated at the reaction pressure of 12 MPa,as follows:esterification reaction:r1=6.513 x 108e-65609/RTCAGU · COSA acid anhydride hydrolysis reaction:r2= 2.259 x 1010e-77133/RTCH2O· COSADynamic model analysis show that temperature is the main factor affecting starch esterification reaction selectivity,and it is more conducive to increase acid anhydride hydrolysis rate with the increase of reaction temperature,meanwhile,the esterification reaction selectivity is related to the water concentration and AGU concentration,which is independent of the concentration of OSA,and then the effect of reaction time on product substitution performed a growing trend when prolonging reaction time?...