【作者】 杨凯；

【导师】 马莺；

【作者基本信息】 哈尔滨工业大学 ， 生物化工， 2008， 硕士

【摘要】 玉米粉可再生可生物降解,主要由淀粉组成,淀粉对水有特殊的亲和力,可以从乙醇及其它有机溶剂中选择性地吸收水。主要成分为淀粉的玉米粉仍然保留这种吸附特性,且可在改变颗粒大小和结构的同时仍保持对水的亲和力。基于淀粉的这种性能,人们研究了许多淀粉基的材料的吸水性能,如:玉米淀粉、玉米粉、酶解玉米粉、化学改性玉米淀粉等。本文以玉米粉为主要原料,分别对玉米粉进行酶改性、化学改性以及酶,化学联合改性得到了三种改性淀粉基干燥剂。研究了各改性方法的条件,并将改性产品的性质与原玉米粉进行比较。酶改性可以增加玉米粉的比表面积,通过对α-淀粉酶,葡萄糖淀粉酶及复合酶进行选择,以水解率、吸水率、颗粒度为评价指标得到α-淀粉酶改性玉米粉的反应条件:酶解温度为45℃、体系pH为6.5、α-淀粉酶添加量为95u/g、酶解时间为60h。得到的酶解玉米粉的水解率为11.1%、过筛率为26%、吸水率达到115.53%,是原玉米粉吸水率的2.1倍。在玉米粉表面接枝共聚丙烯酸单体,在接枝温度为60℃、引发剂用量占玉米粉干基质量的0.5%、丙烯酸单体中和至pH为6.5、接枝时间为3h、丙烯酸单体与玉米粉干基质量比为5:1时,得到接枝率为3.3%、吸水率达93%的接枝玉米粉。吸水率比原玉米粉提高了69%。以上述接枝条件对酶解率分别为4.8%、9.7%、17%的玉米粉进行接枝改性,所得产品的接枝率分别为4.02%、4.53%、5.2%,与之对应的吸水率分别为125%、134%、142%。通过10次再生实验表明:对比原玉米粉,酶解玉米粉、接枝玉米粉、接枝酶解玉米粉的吸水率分别减少了4.3%、6.5%、11%。扫描电镜观察表明α-淀粉酶处理后样品的表面形成了很多孔洞,接枝玉米粉的表面也发生了较大的变化。在实验室内模拟工业乙醇液相脱水,考察自制干燥剂的应用性能得出:四种淀粉基干燥剂均能够将乙醇浓度为95.5mass%(乙醇-水溶液共沸点)的乙醇-水溶液进一步脱水至97.5mass%。干燥剂对水的吸附量随着溶液中乙醇含量的升高而减小。在干燥剂与溶液质量比为1:5时α-淀粉酶改性玉米粉和接枝酶解改性玉米粉可以将乙醇浓度为90mass%乙醇-水溶液浓度提高至mass96%以上。更多还原

【Abstract】 Corn grits (a form of ground corn) are biodegradable and derived from a renewable resource. A major component of the corn grits, starch, is the primary adsorptive material in the corn grits. Starch has affinity for water and selectively adsorbs water vapor from air, alcohols and other organic vapors. The combinations are useful for increasing the particle size and structural stability of the materials while maintaining the water adsorptive capacity. The adsorption properties have been studied for many types of these materials, specifically, corn starch, corn grits, enzyme modified corn grits, and chemical modified corn starch .In this paper, three new starch based desiccants are produced. Corn grits were modified by enzyme and chemistry. The research involved the processing and properties of the enzyme and chemistry modified corn grits and the combination modified corn grits by chemistry and enzymes. All of the results had been compared with native corn grits.The goal of the modification of the corn grits was to create pores and increase the surface area per gram of corn grits without radically reducing the size of the particles. The enzymatic method had been applied to modification of corn grits. The enzymes tested includedα-amylase and gluco-amylase.α-amylase was selected as one of the enzymatic modifying agents because of its action on starch polymers. The corn grits were hydrolyzed byα-amylase (95u/g) at 450C, pH 6.5for 60h. The hydrolysis rate of corn grits was 11.1%, and the rate of adsorb water was115.53 mass%. Sieve size analysis was conducted to determine if a change in the mean particle size had occurred during the enzyme modification. The mean particle sizes were 74% in 22 sieve size for modified corn grits and 100% in 18/20 sieve size for native corn grits. Compared with native corn grits, the adsorb water of modified crone grits was increased to 2.1 times.The graft copolymerization of acrylic acid onto native corn grits under the initiation of ammonium ceric nitrate was investigated. This was done to maximize the graft rate and rate of adsorb water. The major factors affecting the graft copolymerization reaction such as concentration of ammonium ceric nitrate, pH and concentration of acrylic acid liquor, reaction time (duration) and temperatures had been studied. Based on the results obtained, appropriate conditions for grafting acrylic acid onto native corn grits was established and the graft yield (3.3%) and rate of adsorb water (93%) were higher under the following conditions: using 0.5 mass% ammonium ceric nitrate, the ratio of acrylic acid (pH 6.5) and corn grits (5:1), reaction time, 90 min; and polymerization temperature, 35°C. Compared with native corn grits, the adsorb water of chemical modified corn grits was increased by 69%.At the same condition of the graft copolymerization modification, three enzyme modified corn grits with different hydrolysis rates (4.8%, 9.7% and 17%) had been chemically modified by acrylic acid. The results show that the graft rate of three enzyme modified corn grits are 4.02% (4.8%), 4.53% (9.7%), and 5.2% (17%) respectively; and the rates of adsorb water were 125% (4.8%), 134% (9.7%), and 142% (17%) respectively.After tem times regeneration testing, compared with native corn grits the rates of adsorb water of three modified corn grits were cut down 4.3% (enzyme modified corn grits), 6.5% (chemistry modified corn grits) and 11% (enzyme and chemistry modified corn grits) respectively. Scanning electron microscope observations show that, there were significant changed on the surface of three desiccants after handling.The four desiccants were tested the capability of removal water from ethanol/water liquor. Four desiccants were shown to selectively adsorb water from 95.5 mass% ethanol/water liquor at room temperature which giving a resulting ethanol/water of 97.5% dryness. When the ratio of desiccant and ethanol/water liquor was 1:5, enzyme modified corn grits and combination modified corn grits removed water from 90 mass% of ethanol/water to 96 mass% of ethanol/water.更多还原