Chitosan manufacturing process

Abstract

A method for producing chitosan from naturally occurring chitin-containing raw material, such as crustacean shells, includes an optional pretreatment step to remove non-chitin rich organic material for example, shrimp flesh, from the raw material, e.g., shrimp shells. The optional pretreatment is followed by a demineralization step utilizing a mild hydrochloric acid solution and a deproteination step utilizing a mild sodium hydroxide solution. The deproteination step is followed by a deacetylation step to remove the acetyl group from N-acetylglucosamine (chitin) to form an amine group, yielding d-glucosamine (chitosan). Each step is followed by a washing step and the product is dried, preferably at a temperature not in excess of about 65° C. Known purification and grinding steps may also be used to produce the final chitosan product. The process is carried out in equipment comprising a series of substantially identical or similar tanks ( 18, 26, 36, etc.) and dryers ( 62, 62 ′), suitably interconnected.

What is claimed is: 
     
         1 . A process for the manufacture of chitosan from a naturally occurring chitin source consists essentially of the following steps:
 (a) a naturally occurring chitin source is demineralized by immersing it in a demineralization (“DMIN”) hydrochloric acid solution of from about 0.5 to about 2 M at a temperature of from about 20° C. to about 30° C. and for a DMIN time period of from about 0.5 to about 2 hours to demineralize the chitin source, and then separating the resulting demineralized chitin source from the acid solution, washing the chitin source in a DMIN wash water for a DMIN wash period of from about 0.5 to about 2 hours to remove the hydrochloric acid and calcium salts therefrom, and then separating the demineralized chitin source from the DMIN wash water;   (b) subjecting the demineralized chitin source to deproteination (“DPRO”) by treating the demineralized chitin source in a DPRO sodium hydroxide solution containing from about 1% to about 10% w/w NaOH for a DPRO time period of from about 4 to about 24 hours and at a temperature of from about 60° C. to about 80° C. to deproteinize the demineralized chitin source, and then separating the resulting demineralized and deproteinized chitin source from the deproteination sodium hydroxide solution, washing the separated demineralized and deproteinized chitin source in a DPRO wash water for a DPRO wash period of from about 0.5 to about 2 hours to remove the sodium hydroxide from the demineralized and deproteinized chitin source, and then separating the demineralized and deproteinized chitin source from the deproteination wash water;   (c) separating residual water from the chitin source obtained in step (b);   (d) immersing the chitin source obtained from step (b) into a sodium hydroxide deacetylation (“DEAC”) solution containing from about 40% to about 50% w/w NaOH and carrying out deacetylation at a temperature of from about 90° C. to about 110° C. and for a DEAC time period of from about 1 to about 3 hours to convert acetyl groups of the chitin source obtained from step (c) to amine groups, to thereby form a chitosan biopolymer having d-glucosamine as the monomer of the chitin biopolymer, then separating the resulting chitosan biopolymer from the DEAC solution and washing the separated chitosan biopolymer in a DEAC wash water for a DEAC wash period sufficient to remove sodium hydroxide from the chitosan polymer, and then separating the chitosan biopolymer from the DEAC wash water; and   (e) residual water is then separated from the chitosan biopolymer which is then dried in air at a temperature of not more than about 65° C. for a drying time period sufficient to reduce the moisture content of the chitosan biopolymer to below about 10% by weight to provide a medical-grade quality chitosan.   
     
     
         2 . The process of  claim 1  wherein step (e) is carried out under conditions comprising that the temperature is from about 50° C. to about 65° C. and the drying period is from about 2 to about 5 hours. 
     
     
         3 . The process of  claim 1  wherein:
 step (a) is carried out under conditions comprising that the hydrochloric acid solution is from about 0.9 to about 1.1 M, the temperature is from about 22° C. to about 26° C., the DMIN time period is from about 0.75 to about 1.25 hours, and the DMIN wash period is from about 0.9 to about 1.1 hours; 
 step (b) is carried out under conditions comprising that the sodium hydroxide solution contains from about 4% to about 6% w/w NaOH, the temperature is from about 70° C. to about 75° C., the deproteination period is from about 4 to about 6 hours, and the DPRT wash period is from about 0.9 to about 1.1 hours; and 
 step (d) is carried out under conditions comprising that the sodium hydroxide solution contains from about 45% to about 50% w/w NaOH at a temperature of from about 100° C. to about 110° C. and the deacetylation wash period is from about 0.9 to about 1.1 hours.