Abstract:

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.

Key words: supercritical CO₂, preparation, octenyl succinic acid starch, cyclohexane, esterification, auxiliary effect

摘要：

利用环己烷等助剂辅助超临界CO₂流体制备辛烯基琥珀酸淀粉酯，研究助剂辅助效果，优化超临界酯化反应条件，并采用NMR、SEM和XRD等进行结构表征。结果表明：环己烷有助于改善超临界CO₂对酯化剂的溶解性能，酯化反应效率约为无助剂时的3.0倍；反应温度、压力、时间及酯化剂用量等对反应也有重要影响，当温度90℃、压力12 MPa、酯化剂用量2%、时间3 h时，反应效率高达83%以上；酯化剂用量为4%时，取代度为0.0191，反应效率可达61%。结构表征发现淀粉分子中引入了酯化基团，产品依然保持淀粉颗粒特征和A型结晶结构，但颗粒表面遭到局部破坏，结晶度降低。以上结果说明，环己烷提高了超临界淀粉酯化反应效率，改善了酯化反应条件。

关键词: 超临界CO₂, 制备, 辛烯基琥珀酸淀粉酯, 环己烷, 酯化, 辅助效果