Study On The Preparation And Flocculation Performance Of Chitosan And Its Quaternary Ammonium Salt With Different Molecular Weight

Molecular weight is an important molecular parameter of chitosan, chitosans with different molecular weight not only have great variant properties, but also affect the preparation and properties of theirs quaternary ammonium salt directly. As natural and modified macromolecular flocculants, chitosans and theirs quaternary ammonium salt have many merits such as no toxicity, no secondary pollution, convenient application et al. However, the high cost of chitosan and its quaternary ammonium salt and the limitation of inorganic flocculants inhitit theirs use in industrial scale. Therefore, they have attracted considerable interests in the field of chitin chemistry and flocculation chemistry for how to produce the chitosans with suitable molecular weight and theirs quaternary ammonium salt in large-scale, and how to match the inorganic flocculants and natural organic flocculants perfectly.The chitosans with different molecular weight were prepared byγ-ray irradiation degradation technology and modified by introducing quaternary ammonium group. The effect of radiation to chitosan and reaction time, temperature, molar ratio to the degree of substitution of quaternary ammonium salt was studied. The results indicated that: (1) While the radiation dosage increased, the weight average molecular weight of chitosan decreased. (2) As the reaction time, temperature and molar ratio increased, the degree of substitution of quaternary ammonium salt increased gradually. The optimum conditions of preparing quaternary ammonium salt of chitosan were determined as follows: the molar ratio of chitosan to glycidyl trimethyl ammonium chloride 1:3, reaction temperature 80℃and reaction time 10 h.The flocculation performance of chitosan and quaternary ammonium salt with different molecular weight and their compounds with PAC were studied. The results showed that: (1) the molecular weight of chitosan and quaternary ammonium salt was higher, the flocculation property was better, and especially the quaternary ammonium salt of chitosan that radiated 50 kGy was best. (2) The flocculation performance of 0.5 ppm quaternary ammonium salt of chitosan radiated 50 kGy mixed with 4 ppm PAC showed better within all pH value compared with the mix of 0.7 ppm chitosan with 7 ppm PAC. The effect of 4.5 ppm pure quaternary ammonium salt of chitosan was same as the latter. (3) The flocculation effect of pure chitosan and PAC was influenced evidently by pH, and their good effect at pH=7. (4) The removal effect of several kinds of flocculants on the lead ion (Pb²⁺) attained above 97% under the optimum conditions. (5) The good flocculation of chitosan, quaternary ammonium salt of chitosan and their compounds with PAC was attributed to the cooperant utilization of the several kinds of mechanisms, such as electric neutrality, bonding and bridging, chelating et al.The research results not only have references to crossed application of chitin chemistry and inorganic flocculation chemistry, but also provide more effective approach for water treatment with flocculation methods.