Tyrosinase reaction/chitosan adsorption: A selective and efficient separation technique for waste minimization

A non-capital-intensive separation approach for selectively and efficiently removing phenolic contaminants from intermediate chemical process streams was investigated. This approach involves two steps in which phenol is first oxidized to its quinone by the enzyme tyrosinase. The quinone is then adsorbed to a chitosan adsorbent through strong covalent interactions. The advantage of this approach is that due to the substrate specificity of tyrosinase and the strength of quinone-chitosan adsorption, phenols can be selectively and efficiently removed from solutions without the need for multiple-staged contacting. In a series of case studies, we have demonstrated the potential of tyrosinase reaction/chitosan adsorption for: separating a contaminating byproduct to upgrade an intermediate process stream in the synthesis of fragrance compounds; selectively adsorbing a contaminant from a recycle stream in pharmaceutical manufacturing; and removing inhibitors to improve the efficiency of polymer processing.; To package two components into an appropriate configurations, tyrosinase was immobilized within chitosan gel films to yield a combined catalyst-sorbent system for phenol removal. The entrapment of tyrosinase between the films led to little loss of activity during immobilization, while tyrosinase leakage during incubation was limited. The chitosan gels rapidly adsorb the tyrosinase-generated product(s) of phenol oxidation while the capacity of the gels is substantially greater than the capacity of chitosan flakes. Using this tyrosinase-containing chitosan gel, phenol can be completely removed from the solution.; It is believed that this novel, non-capital-intensive separation approach for waste minimization can be readily incorporated into existing manufacturing operations for specialty and commodity chemicals. Such small-volume chemical producers are currently unable to implement traditional waste minimization approaches because large capital investments are typically required.