Preparation Of Chitosan Derivatives And Their Application Of Treatment With The Waste Water From The Middle Process In Making Paper

Chitosan is a straight chain multi-polysaccharide of amino-glucose with a formula of C6H11NO4)n and similar to cellulose in chemical structure. It is the deacetylated product of chitin. Chitosan is a half-transparent sheet solid and behaves alkaline properties due to the amino-group(-NH2) in its molecule. It can be dissolved in dilute acid such as formic acid, acetic acid and hydrochloric acid etc hut the degree of polymerization will reduced when it is dissolved in strong acid. Generally chitosan cannot be dissolved in organic solvent because of the strong inter-molecular hydrogen bonds. Chitosan is a straight-chain polymer with amino-group(-NH2) and hydroxyl(-OH) so it can induce some reaction such as hydrolysis, hydroxymethylation, sulfonation, oxidation, complexation, condensation etc. Because of the amino-group in its molecular structure, chitosan can be used directly as a flocculant or improving its flocculation by modifying its structure. The main results of this study are as following:Considering the chitosan used mainly in acid medium, its utilization is limited. In order to expand its utilization study, chemical modification has been conducted. The chitosan and chitin were used as parent materials to prepare water-soluble chitosan, O- carboxymethylchitosan, and O- carboxymethylchitin etc. which were used flocculants with anion or cation. The optimal reaction conditions have been obtained to prepare them. The products of a series derivatives prepared in this study can be directly used as flocculants or as a coagulant aid to other flocculants, which show a good flocculating effects to treatment with inorganic solid suspensions or many kinds of organic compounds. In this paper, the flocculating characteristics of modifying chitosan and chitin have been systematically investigated in treatment with the waste water from the middle process in making paper and expected results have beenobtained.In order to compared the flocculating effects between the inorganic flocculants and chitosan and its derivatives, poly-aluminium sulfate(PACS) with different ratio of mole Al3+/ SO42- were synthesized under preferential preparing conditions. A series of compounds including derivatives of chitosan, aluminium salt, iron salt, calcium oxide, poly-aluminium sulfate, and polyacrylamide with anion or cation have been used respectively as a flocculant in treatment with the waste water from the middle process in making paper. The optimal pH value and amount of the flocculants addition of treating with the waste water have been determined experimentally and a tentative flocculating mechanism for the samples above mentioned has been discussed.The results show that chitosan and its derivatives have better flocculating effects than inorganic flocculants and polyacrylamide with anion or cation. The ratio of elimination of chemical oxygen demand measured by potassium dichromate (CODcr), suspension, and colority reaches up to 78 ~ 85 %, 63 ~ 74 %, and 50-80%, respectively.A complex flocculant including chitosan and its derivatives, aluminium sulfate and calcium oxide has been investigated in order to improving the treatment effects and reducing the treatment cost of the waste water. The complex flocculant shows better flocculating effects than single one of them. The ion Al3+ neutralizes the negative charges of the waste water and the chitosan or its derivatives adsorbs and binds the particles of the solution and flocculation occurs. The ratio of elimination of CODcr, suspension, and colority reaches up to 90 ~ 99 %, 78 ~ 88 %, and 79-95%, respectively when the concentration of the chitosan or its derivatives, aluminium sulfate, and calcium oxide is 10-50 ppm, 300~500ppm and 300 ppm, respectively. The concentration of CODcr, suspension and colority reduces up to 7-72 mg/L, 25~40mg/L, and 4-16 times, respectively in the treated waste water which is transparent liquid and no color is found. The quantity of the treated waste water accords with the first-order national standard of waste water exhaust.The procedure of treatment with the waste...