The Study Of Microwave-assisted Modified Chitosan And Flocculation Property

In recent years,with the improvement of environmental quality requirements,the development of efficient, low-cost, non-toxic flocculant has become a hot research topic,in the water treatment industry. The inorganic flocculants and synthetic organic flocculants has secondary pollution、toxicity disadvantages, has been rarely used. However the natural polymer flocculants such as chitosan has lower cost, easy to graft modified biodegradable polymer and its degradation intermediates harmless advantages, has been widely used. However, chitosan as a flocculant has relatively low molecular weight and a narrow range of pH shortcomings. These shortcomings leads to its small use scope, poor flocculation. So it is necessary to modify the chitosan.The chitosan-grafting copolymer (chitosan-DMDAAC) was prepared by chitosan and dimethyl diallyl ammonium chloride (DMDAAC), using microwave irradiation method, and the modified chitosan was characterized by Infrared spectroscopy. By orthogonal experiment, the optimal reaction conditions of modified chitosan was studied to get the highest graft rate, the order of three factors(microwave reaction temperature、microwave reaction time、DMDAAC concentration) that influence on the graft copolymerization was identified. Its flocculation capability was tested by processing Kaolin suspensions、Congo red analog dyeing wastewater and actual domestic wastewater. Meanwhile, two different reaction ways of the microwave radiation heating and traditional water bath were compared. The results show that, under the optimal reaction conditions (microwave reaction temperature 55℃, microwave reaction time 20 min,0.5g chitosan, microwave power 270W, DMDAAC concentration 20%) the graft rate of modified chitosan is 80%. Furthermore,the three factors influence the size of the graft copolymerization is microwave reaction temperature> DMDAAC concentration> microwave reaction time. FTIR analysis results show that, chitosan-DMDAAC graft copolymer is successfully synthesized. The compared result of two different reaction ways (the microwave radiation heating and traditional water bath) is that microwave heating has simple, fast, energy-efficient, maintain a high grafting yield advantages. In flocculation experiments,turbidity removal efficiency of chitosan-DMDAAC graft copolymer reaches 91.2%, its COD removal efficiency reaches77.2%, decolorization rate reaches 84.9%. The results indicate that chitosan-grafting copolymer (chitosan-DMDAAC) has better flocculation properties than chitosan.