Cyclohexane assisting preparation of starch esterification in supercritical CO2

Auxiliary effect of additives, such as cyclohexane, in supercritical CO2 fluid on the preparation of octenyl succinic acid cassava starch was investigated, and the types of additives, volume rate of additive to supercritical CO2, amount of esterification agent, reaction temperature, pressure and reaction time on the effect of degree of substitution and reaction efficiency were explored in a bath reactor set-up. The NMR, SEM and XRD were used to examine esterification groups, particle surface morphology and crystalline structure. The results revealed that the additive could improve the solubility of the supercritical CO2 medium to esterification agent, and the cyclohexane additive showed the optimal synergistic effect with reaction efficiency of about 3.0 times higher than that without the additive when 1.5% cyclohexane was added. Meanwhile, the optimum reaction conditions were found as follows: reaction temperature of 90℃, pressure of 12 MPa, time of 3 h and esterification agent of 4% with the degree of substitution and the reaction efficiency are 0.0191 and 61%, respectively, and even the reaction efficiency was up to 83% by using 2% esterification agent. Analysis of product structure characterization showed that the esterification groups were introduced into the starch molecules, and small particle characteristics and A-type crystal structure were still remained, but the particle surface morphology was partially destroyed and the crystallinity was reduced. All the results indicated that the cyclohexane can increase reaction efficiency and improve esterification reaction condition. © All Right Reserved.