Impact of intermolecular interactions on the nanofiltration of pulping liquor
Sprache des Titels:
Sulfite spent liquor, a side stream of the pulping process, is an abundantly available source for bio-based platform chemicals. Lignosulfonates can be separated from the other organic components and pulping chemicals by ultrafiltration. The ultrafiltration permeate can either be used directly in a fermentation process or may be further treated by nanofiltration to reduce the fermentation inhibitor concentration. FilmTec NF270 was used to study different intermolecular interactions in the ultrafiltration permeate at various pH values and lignosulfonate concentrations. Intermolecular interactions between lignosulfonates and inhibitor components decrease membrane selectivity. Several furan derivatives interact via hydrogen bonds with the hydroxyl groups of the lignosulfonates. The oxygen of the aldehyde group or the ring oxygen atom with two lone pairs were found to form hydrogen bonds and thereby affect the retention. By comparison, the hydrogen bonds of the alcohol group did not noticeably affect the retention. Magnesium as counter ion of the lignosulfonate interacts with acetate and formate ions, thereby increasing their retention. Substitution of magnesium with sodium prevents a lignosulfonate ion interaction. The investigated interactions of lignosulfonates in sulfite spent liquor may help to improve the applicability of nanofiltration processes for the detoxification of lignocellulose-derived fermentation feed. Furthermore, insights can be used for other separation methods as well because they are not specified for membrane separation processes.