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

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. [Figure not available: see fulltext.].