Setup of glycine continuous synthesis by ammonolysis of monochloroacetic acid

Abstract

This article describes the continuous production of glycine by catalytic ammonolysis of monochloroacetic acid in an aqueous medium. The synthesis and crystallization of glycine are carried out in a battery of three stirred double-jacketed reactors while temperature and pH values are controlled. The results of the kinetic study allow one to calculate the residence time in each tank for a desired conversion ratio and are first checked with the setup. Then, some parameters (concentration of reagents, regulation of pH, residence time, catalyst) are modified to improve the final yield in crystallized glycine. The best yield resulting from a flow process (96.6%) is better than that resulting from a batch process (93%) and is obtained in the following conditions: the first step is performed at 75°C and pH 5.4 with a 10 mol L−1 monochloroacetic acid solution and a 17 mol L−1 ammonia aqueous one with a 0.2 molar ratio of hexamethylenetetramine; the second step is carried out at 75°C and pH 8.0; the optimal residence times are respectively 1 and 4 hours. Replacement of hexamethylenetetramine by formaldehyde can also be considered even if the yield is slightly lower. © 1999 John Wiley & Sons, Inc. Lab Robotics and Automation 11: 29–35, 1999