Research On The Clean Preparation Processes Ofchitosan And Carboxymethyl Chitosan

Shells are one of the most abundant natural resource.At present,most of the ways of utilization of abandoned shells need to be calcined at high temperature,which destroys the chitin as a key component of shells and fails to realize its valuable use value.The typical method of extracting chitosan from shrimp and crab shells included the decalcification with dilute acid and deproteinization with dilute alkali and then deacetylation with concentrated alkali.There are many shortcomings such as high consumption of acid and alkali solution,long treatment time and serious waste water pollution.At present,the preparation of carboxymethyl chitosan generally requires a large number of organic solvents and alkali solution.Moreover,the experimental steps are complex,the production period is long and the harsh conditions,which will cause serious pollution to the environment.Therefore,it is of great value to develop new preparation process of chitin and its derivatives,which are clean,high-quality,environmentally friendly,low-cost and easy to industrialize.In this paper,the direct preparation of chitosan from shell powder in alcohol-sodium hydroxide-water system was studied.Furthermore,a clean production process for preparing carboxymethyl chitosan from self-made chitosan by mechanochemical method was realized.The main achievements are as follows:1.Through the experiment of single factor.The optimal conditions for preparing chitosan from shell powder were determined as follows:The reaction material ratio(sodium hydroxide:shell powder)was set to 1:3.42.10%isopropanol alkali aqueous solution.The reaction temperature is 60?and the reaction time was 6h.The degree of deacetylation of chitosan was 0.81.The product were confirmed by FT-IR analysis.2.The optimum conditions for the preparation of carboxymethyl chitosan were as follows:The reaction material ratio(chitosan:sodium hydroxide:sodium chloroacetate)was set to 1:4:4.The basification time of ball milling is 5h.The carboxymethylation time is 5h.The speed of ball crusher is 600 r/min.Ball milling medium accounts for 12%of reactor volume.The mass ratio of sodium chloroacetate to catalyst sodium iodide is 1:0.4.The substituting degree of carboxymethyl chitosan was 0.95,the yield was 76%,and viscosity of 1%aqueous solution is 78 mPa.s.The product were confirmed by FT-IR and ~1H-NMR analysis.3.The process of preparing chitosan directly from shell powder has been successfully developed in this paper.The preparation conditions are mild.The consumption of acid and alkali solution in the process was significantly reduced,and the production of salt waste solution was substantially reduced.Amino acids and small peptides produced by protein degradation can be used to produce feed,fertilizer,etc.Full-component utilization of shells has been realized.4.The mechanochemical preparation of carboxymethyl chitosan is simple and solvent-free.Ethanol precipitant can be recycled.Replacing chloroacetic acid in traditional process with sodium chloroacetate made lower production cost possible.It has pentential application in industrialization.