【作者】 许永亮；

【导师】 赵思明；

【作者基本信息】 华中农业大学 ， 食品科学， 2008， 硕士

【摘要】 絮凝法是水处理中的关键环节之一,我国絮凝剂产品品种齐全,但阳离子絮凝剂较少,阳离子淀粉絮凝剂有较广的应用前景,但其反应效率较低。本文以不同来源的淀粉为原料,采用浆法、球磨辅助浆法、干法和球磨辅助干法制备淀粉絮凝剂,研究制备工艺对淀粉絮凝剂絮凝效果、取代度和反应效率的影响,获得淀粉絮凝剂最佳的制备工艺,分析淀粉絮凝剂的絮凝性能,采用红外光谱仪、X-衍射、扫描电镜技术进行结构表征和微观结构观察,采用电荷密度分析和Zeta电位分析探索淀粉絮凝剂的絮凝机理,为高效果、低成本的阳离子淀粉絮凝剂的开发提供理论依据。主要结论如下:1.淀粉絮凝剂的制备工艺:考察了机械活化时间、反应时间、淀粉浓度、引发剂浓度、单体浓度、反应温度对醚化反应的影响,结果表明,浆法、球磨辅助浆法、干法和球磨辅助干法制备的淀粉絮凝剂的取代度分别为0.03～0.07、0.07～0.14、0.18～0.30、0.30～0.35,反应效率为4%～10%、9%～20%、32%～42%、75%～87%;4种制备方法中,以球磨辅助干法制备的淀粉絮凝剂的取代度、反应效率和得率最高,絮凝效果最好,对淀粉来源的依赖性最小。球磨辅助干法为季铵化淀粉絮凝剂最佳的制备方法,其制备条件为:淀粉球磨5h,2,3-环氧基三甲基氯化铵与淀粉的摩尔比为0.40:1.00,90℃反应2.5h,体系水分含量低于20%,该工艺过程不需添加碱。机械活化后进行醚化改性可以得到取代度高、絮凝效果良好的阳离子淀粉絮凝剂。2.机械力活化在淀粉改性中的作用:粒度分析和凝胶色谱分析表明球磨后淀粉粒度先减小后增大,表面积先增大后减小,球磨后淀粉分子的长链和支叉结构断裂,淀粉中大分子数量减少,小分子数量增加,分子量分布发生变化。X-射线衍射和扫描电镜结果显示球磨破坏淀粉分子空间排列,球磨后淀粉产生晶格畸变、最终非晶化,单体试剂更容易渗透到颗粒内部使淀粉发生醚化反应。机械活化使部分机械能转变为化学能储存起来,使物质处于不稳定的高能状态,从而也使淀粉的反应活性提高。本试验首次将机械力活化作用应用于淀粉的醚化改性,制备阳离子淀粉絮凝剂。3.淀粉絮凝剂的絮凝特性:絮凝评价实验表明,絮凝剂母液浓度稍低于临界交叠浓度,污水中絮凝剂分子链间动态接触有利于絮凝;固形物含量为1%的悬浊液沉降效果最好;制备的淀粉絮凝剂的pH和水温适用范围广,其中水温为15℃左右时絮凝效果最好;淀粉絮凝剂的高岭土澄清效果较明矾和聚合氯化铝的好,絮凝后絮凝体的体积较小。4.淀粉絮凝剂的絮凝机理:自制的季铵化阳离子淀粉絮凝剂(球磨后干法制备)优异的絮凝性能是直链和支链淀粉絮凝剂共同作用的结果,絮凝过程中表现出电中和、吸附架桥和网捕卷扫作用,直链淀粉絮凝剂以列车式和尾式与胶体颗粒结合,支链淀粉絮凝剂以尾式或环式与胶体颗粒结合。更多还原

【Abstract】 Flocculation process is one of the key links in the wastewater treatment.In China, the flocculation product is rich,but the cationic flocculant is rare.Cationic starch flocculants have a well prospect in practice,but have low production efficiency.In this paper,cationic starch flocculants were synthesized by wet process,wet process assistanted with ball-milling treatment,dry process and dry process assistanted with ball-milling treatment.The effect of preparation technologies on the flocculation efficiency,degree of substitution and reaction efficiency of products were discussed. Optimal procedure for cationic starch flocculant was obtained,and flocculation performance was analysised.Microstructure of starch and starch flocculation were elucidated by means of infrared spectrum(IR),x-ray diffraction(XRD) and scanning electron microscopical technique(SEM).The mechanism of flocculation was explored by charge density analysis,ubbelohde viscosimeter and zeta potentiometric analysis.The above analysis could provide a sound theoretical basis for good effect and low cost cationic starch flocculants preparation.1.Preparation process for starch flocculationThe effect of activation time,reaction time,starch concentration,initiator concentration,monomer concentration and reaction temperature on the etherify reaction were investigated.The degree of substitution and reaction efficiency of products synthesized by wet process,wet process assistanted with ball-milling treatment,dry process and dry process assistanted with ball-milling treatment were 0.03～0.07, 0.07～0.14,0.18～0.30,0.30～0.35 and 4%～10%,9%～20%,32%～42%,75%%～87% respectively.The dry process assistanted with ball-milling treatment was the best method for starch flocculation preparation.The degree of substitution,reaction efficiency,yield rate and flocculation efficiency of products synthesized by dry process assistanted with ball-milling treatment was the highest among the four processing methods and had less dependence upon the starch source.The optimal reaction conditions were as following: starches were mechanically activated by a stirring-type ball mill for 5h.Then the activated starches were used to fabricate etherify copolymer in the presence of monomer of 2,3-epoxypropyltrimethylammonium with the molar ratio of 0.40:1.00.Etherifying reaction was carded at 90℃for 2.5h with initial system moisture content less than 20%.2.Function of ball milling in starch modificationParticle size and gel permeation chromatography analysis results demonstrated that particle size,surface area of starch granule and molecular weight distribution of starch molecules exhibited major changes after ball milling.After subjected to ball-milling treatment,long chain and branch structure of starch molecules were broken,which resulted in a remarkable increase in small molecular segmer and decrease in large molecular segmer.XRD and SEM analysis revealed that the etherifying reaction occured not only in the amorphous region,but also in the crystalline region of the starch when ball-milling caused the molecular arrangement disorder,crystal structure destruction and lattice distortion.In addition,mechanical energy exchanging into chemical energy in polymer chain made the starch molecular groups be in an unstable state with high energy, and therefore enhanced the starch etherifying modification.3.Flocculation performance of starch flocculantsOptimal dose of flocculant in solution was slightly lower than the critical concentration,in which molecular chain had partly overlapped.Good flocculation performance existed in certain suspension solid content of kaolin suspension(1%). Excessively high or low kaolin suspension concentration could decrease the flocculation effect.It was found that the starch flocculation was comparatively more effective than potassium alum and polymeric aluminum chloride flocculant in kaolin suspension clarification.The starch flocculation had wide feasible pH and temperature range and small volume of floes afer flocculation.The best adsorption effect could be obtained when temperature was 15℃.4.Flocculation mechanism of starch flocculationComprehensive analysis showed its outstanding flocculation performance depended on its special molecular structure of amylose flocculation and amylopectin flocculation, and was the result that electriciy counteract was in cooperation with adsorption bridge building and the net rooling-sweeping action.Amylose flocculation was preferred to adsorb the colloidal particle at solid-liquid interface by train and taile type,while amylopectin flocculation was likely to adsorb by loop and tail type.更多还原