强阳离子型壳聚糖改性絮凝剂的制备及其在饮用水处理中的应用研究

发布时间：2018-04-01 13:31

本文选题：强阳离子型壳聚糖絮凝剂　切入点：小试　出处：《南京大学》2012年硕士论文

【摘要】：水是人类生存最基本的需求。传统的饮用水絮凝剂,如：铝、铁盐等无机材料,在使用过程中,不可避免地会在水体中残留,从而对人体健康及环境造成危害,因而研发高效环保的新型絮凝剂材料有着重要的现实意义。近年来,兼具有环境友好、可再生、来源广泛,且完全脱离石油资源等重要特点的天然高分子材料备受关注,且其分子链上富含有大量反应性基团,具有良好的絮凝、络合等性能,因此有人将天然高分子材料誉为“21世纪的绿色絮凝剂材料”。但是天然高分子材料在实际应用中也存在着许多不足之处,如：化学性质不活泼、溶解性差、分子量相对较低等等。针对这些缺点,人们通常采用化学改性的方法进行性能改善。本工作以一种性能优越的天然高分子材料——壳聚糖为基材,以低毒性季铵试剂(3-氯-2-羟丙基三甲基氯化铵(CTA))为改性剂,采用醚化反应,通过调节反应原料投加量,制备了一系列具有不同阳离子取代度的强阳离子型壳聚糖絮凝剂。并将该絮凝剂材料应用于饮用水处理中,分别以高岭土悬浊液和长江中下游镇江段原水为模拟水样,在实验室小试及水厂中试规模条件下系统地考察了其实际水处理性能。着重研究了环境温度、原水浊度、絮凝剂投加量、pH、盐效应等因素对其絮凝性能的影响；此外还通过正交实验方法,进一步得到其中试规模下最佳絮凝实验条件,发现该强阳离子型壳聚糖絮凝剂具有良好的絮凝效果。此外,还结合双分子碰撞理论及分形理论初步研究了其实际絮凝动力学过程。最后重点考察了改性壳聚糖絮凝剂的一个重要结构因子——阳离子取代度对其絮凝性能的影响,建立了合理的构效关系,为新型天然高分子絮凝剂的研究与开发提供了理论依据。具体实验结果如下： (1)实验室小试絮凝实验结果表明,絮凝剂应在一个适中的投加量条件下具有最佳絮凝效果,且对应Zeta电位值在最佳投加量时接近于零,这说明絮凝过程主要受电中和作用控制；并且小试最佳絮凝剂投加量仅为0.05mg/L,远小于传统絮凝剂用量,因此该强阳离子型壳聚糖絮凝剂具有很高的絮凝效率。另外,原水起始浊度越大,所需絮凝剂投加量也越大；在相同原水浊度条件下,随着环境温度的升高,絮凝剂需求量下降；且絮凝剂在酸性环境下有着更好的絮凝性能；而外加盐由于能使高岭土颗粒双电层厚度被有效压缩,颗粒易于相互碰撞聚集,有利于絮凝剂絮凝性能的提高。此外,在絮凝动力学过程研究中发现,絮体的尺寸和分形维数值均在絮凝剂最佳投加量时达到最大值。且在不同投加量条件下,絮体的尺寸和分形维数均随着时间的增长而增大且逐渐达到平衡。 (2)经正交实验得到中试絮凝最佳实验条件为：絮凝剂投加量为1.1mg/L,混凝时间为20min,三联机械搅拌混凝池中搅拌速度分别为200、100及50rpm。此外,正交实验统计参数表明絮凝剂投加量在三个影响因素中对其絮凝性能影响最为重要。水样常规37项理化检验结果表明,采用天然高分子改性絮凝剂处理得到的水样符合国家新颁布实施的饮用水标准。另外,与镇江市自来水公司现行使用的絮凝剂——聚合硫酸铁的絮凝效果相比,发现强阳离子型壳聚糖絮凝剂具有更为优异的絮凝性能,所需的絮凝投加量远低于聚合硫酸铁,仅约为其四十分之一,具有很高的性价比。因此,可以认为该强阳离子型壳聚糖絮凝剂具有优良的絮凝性能。 (3)此外,分别在小试和中试规模下,系统考察了CTA改性壳聚糖絮凝剂的阳离子取代度对其实际絮凝性能影响,研究结果表明其絮凝性能随着CTA取代度的增大而不断提升。并且相应絮凝动力学研究结果表明：其絮凝动力学过程十分符合双分子碰撞模型,试验点与理论曲线的线性相关度(R2)均在0.99以上。综上,小试和中试结果一致显示：该强阳离子型壳聚糖絮凝剂具有良好的絮凝性能,有着广阔的应用前景。
[Abstract]:Water is the most basic requirement for human existence . Traditional drinking water flocculant , such as aluminum , iron salt and other inorganic materials , is of great practical significance in the use of natural polymer materials , such as aluminum , iron salt and so on .

In this paper , a series of strong cationic chitosan flocculant with different cation substitution degree was prepared by using chitosan as the base material , with low toxicity quaternary ammonium reagent ( 3 - chloro - 2 - hydroxypropyl trimethyl ammonium chloride ( CTA )) as modifier .
In addition , the effect of the cationic substitution degree on the flocculation property of the modified chitosan flocculant is studied . The reasonable structure - effect relationship is established , which provides a theoretical basis for the research and development of the novel natural polymer flocculant . The experimental results are as follows :

( 1 ) The experimental results show that the flocculating agent should have the best flocculation effect under a moderate adding quantity condition , and the corresponding zeta potential value is close to zero when the optimum dosage is added , which indicates that the flocculation process is mainly controlled by the neutralization effect ;
In addition , the greater the initial turbidity of the original water , the greater the amount of flocculant required to be added .
Under the condition of the same raw water turbidity , with the increase of ambient temperature , the demand of flocculating agent decreased ;
and the flocculating agent has better flocculation property under an acidic environment ;
In addition , it is found that the size and fractal dimension of the flocs reach the maximum when the optimum dosage of the flocculating agent is reached . In addition , the size and fractal dimension of the floc are increased with the increase of time and the equilibrium is gradually reached under different feeding conditions .

( 2 ) The best experimental conditions were obtained by orthogonal experiment : the adding amount of flocculant is 1 . 1mg / L , the coagulation time is 20min , the stirring speed of the three - linked mechanical stirring and coagulation tank is 200 , 100 and 50 rpm respectively .

( 3 ) In addition , under the scale of pilot and pilot scale , the effect of the cationic substitution degree of CTA modified chitosan flocculant on its actual flocculation property was investigated . The results showed that the flocculation performance of CTA was increased with the increase of the degree of substitution of CTA . The results showed that the flocculation kinetics was in accord with the double molecular collision model , and the linear correlation between the test point and the theoretical curve ( R2 ) was 0.99 or more .

The results show that the strong cationic chitosan flocculant has good flocculation property and has wide application prospect .

【学位授予单位】：南京大学
【学位级别】：硕士
【学位授予年份】：2012
【分类号】：TQ316.3;R123

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