羟丙基和羧甲基复合醚化豌豆淀粉的制备

Hydroxypropylation and carboxymethylation of pea starch prepared by etherification

为了拓宽豌豆淀粉的应用,以豌豆淀粉为原料,氢氧化钠为催化剂,氯乙酸、环氧丙烷为醚化剂,采用乙醇溶剂法,通过分步连续反应制备具有较高取代度的羟丙基和羧甲基复合醚化豌豆淀粉。以羟丙基取代度、羧甲基取代度及羧甲基化反应效率作为优化指标进行单因素及正交优化试验。优化探究得到最佳制备工艺条件:羟丙基化反应体系中的淀粉乳质量分数为40%,氢氧化钠与淀粉干基的质量比为5.5%,环氧丙烷与淀粉干基的质量比为23%,反应温度为60℃,反应时间为16 h;羧甲基化反应的氢氧化钠与淀粉的物质的量比(n(NaOH)∶n(AGU))为3.25,氯乙酸(MCA)与淀粉的物质的量比(n(MCA)∶n(AGU))为1,反应温度为60℃,反应时间为5 h。通过优化工艺制备的复合醚化豌豆淀粉的羟丙基取代度为0.197 9,羧甲基取代度为0.780 2,羧甲基化反应效率为78.02%。此优化工艺具有产品取代度高、反应效率高、耗时短等特点,在工业化生产中能够大大降低生产成本、提高生产效率。

In order to explore the application of pea starch in industry, a new preparation process of etherified pea starch was studied in this paper. The hydroxypropyl-carboxymethyl pea starch was prepared by a stepwise continuous reaction method using sodium hydroxide(NaOH) as a catalyst, monochloroacetic acid(MCA) and propylene oxide as the etherification agent in an ethanol solvent. The optimal reaction conditions for the hydroxypropylation and carboxymethylation of pea starch were determined through a single factor and orthogonal experiment with hydroxypropylation degree, carboxymethyl degree and reaction rate as indexes. The optimal parameters in hydroxylpropyl reaction were sodium hydroxide dosage(1%, 2%, 3%, 4%, 5%), mass fraction of starch milk(25%, 30%, 35%, 40%, 45%), propylene oxide dosage(5%, 10%, 15%, 20%, 25%), reaction time(8 h, 12 h, 16 h, 20 h, 24 h) and reaction temperature(35 ℃, 40 ℃, 45 ℃, 50 ℃, 55 ℃). The optimal parameters in carboxymethylation reaction were monochloroacetic acid to starch material molar ratio(1.0, 1.5, 2.0, 2.5, 3.0), sodium hydroxide to starch material molar ratio(2.75, 3.25, 3.75, 4.25, 4.75), reaction time(1 h, 2 h, 3 h, 4 h, 5 h), reaction temperature(45 ℃, 50 ℃, 55 ℃, 60 ℃, 65 ℃). According to the single factor test results, orthogonal test was carried out to determine the optimal preparation process. The optimized conditions of the hydroxypropylation was 40% of the starch concentration, 5.5% of NaOH(starch dry basis mass), 23% of the propylene oxide(starch dry basis), and the reaction time 16 h at 60 ℃. The optimal reaction conditions for the carboxymethylation was the molar ratio of NaOH to AGU of 3.25, the molar ratio of MCA to AGU of 1, and 5 h reaction time at 60 ℃. The hydroxypropylation degree, carboxymethyl degree and reaction rate of the optimized product were up to 0.197 9, 0.780 2 and 78.02%, respectively. The results showed that the process performed a high degree of etherification and efficiency, and low energy consumption and cost in industrial production.