Precipitation study of CO2-loaded glycinate solution with the introduction of ethanol as an antisolvent

Abstract

Focused beam reflectance measurement (FBRM) and 13C nuclear magnetic resonance (13C NMR) analysis were used to study the precipitation process of CO2-loaded potassium glycinate (KGLY) solutions at different CO2 loadings, during the addition of ethanol as an antisolvent at a rate of 10 mL·min−1. The volume ratio of ethanol added to the KGLY solution (3.0 mol·L−1, 340 mL) ranged from 0 to 3.0. Three solid-liquid-liquid phases were formed during the precipitation process. The FBRM results showed that the number of particles formed increased with CO2 loading and ethanol addition for CO2-unsaturated KGLY solutions, whilst for CO2-saturated KGLY solution it first increased then decreased to a stable value with ethanol addition. 13C NMR spectroscopic analysis showed that the crystals precipitated from the CO2-unsaturated KGLY solutions consisted of glycine only, and the quantity crystallised increased with CO2 loading and ethanol addition. However, a complex mixture containing glycine, carbamate and potassium bicarbonate was precipitated from CO2-saturated KGLY solution with the maximum precipitation percentages of 94.3%, 31.4% and 89.6%, respectively, at the ethanol volume fractions of 1.6, 2.5 and 2.3.