Influence of heat treatment on the size of sodium lignosulfonate particles in water—ethanol media

Abstract

Dynamic light scattering and size exclusion chromatography were used to investigate the size of sodium lignosulfonate particles in water—ethanol media and the changes occurring at temperatures of 115–440 °C (13 MPa). It was found that the characteristic size (diameter) of particles of the starting sodium lignosulfonate in solutions with a concentration of 1.5 and 13.3 g L⁻¹ was 2.2−5.2 nm. Treatment in a flow reactor at temperature of 235–325 °C led to a disintegration of larger particles with an increase in the fraction of particles with size of 2.2 nm and a simultaneous formation of particles with a size of ~100 nm. Increasing the treatment temperature (>415 °C) led to a complete disappearance of particles with size of 2.2–5.2 nm and the formation of particles 100–130 nm in diameter, as well as the precipitation of large soot-like particles. IR spectroscopy showed that increasing the treatment temperature above 275 °C led to a decrease in the specific content of oxygen-containing and sulfoxyl groups in the sodium lignosulfonate structure, with the exception of carboxyl groups, whose fraction remained almost unchanged, as well as CH₃ groups (methoxy and aliphatic), whose content increased slightly. The temperature range of 235–275 °C was optimal for hydrolysis of sodium lignosulfonate and preparation of aromatic monomers.