Flocculation properties of polyethylene glycol-modified lignin

Polyethylene glycol (PEG)-modified lignin (glycol lignin) can be produced through an acid-catalyzed reaction of Japanese cedar using PEG as a solvolysis reagent. Acid precipitation and the following solid–liquid separation steps are the rate-determining processes for glycol lignin production. The effect of temperature on the flocculation of glycol lignin suspensions, which is necessary for effective solid–liquid separation, was evaluated. The heat treatment of glycol lignin suspensions, at temperatures of ≥50 °C, improved flocculation and decreased the average filtration resistance values of the suspensions. However, alkaline lignins, such as those in soda and kraft lignins in black liquors, did not show significant improvements in flocculation following heat treatment at 50 °C. The heat-induced flocculation property depended on the type of glycol lignin. The degree of flocculation increased with the increase in the molecular weight of PEG used for glycol lignin production. The solid–liquid separation for the glycol lignin production was highly improved by a simple heat treatment.