Fractionation of lignosulfonates: comparison of ultrafiltration and ethanol solubility to obtain a set of fractions with distinct properties

Abstract

Commercial lignosulfonates (LS), recovered from bisulfite pulping processes, are known for their wide polydispersity. In this study, LS were fractionated by ultrafiltration (UF) and based on their solubility in ethanol (EtOH) solutions. The combination of both methods leads to a set of fractions of varying properties, suitable for several applications. UF gives well-separated fractions, with low polydispersity, and increasing functionality (sulfonate and phenolic hydroxyl groups) with decreasing molecular weight (MW). EtOH solubility yields more polydisperse fractions but still appears to be an easy and rapid way to obtain fractions with increasing MW. The residual sugars in LS, resulting from incomplete removal of hemicelluloses, were found to be mainly in the form of low MW oligomers, which were not bound chemically to lignin. Thermal degradation of the different fractions was also compared, giving better comprehension of the influence of the structure and composition. A glass transition temperature (T g ) could be measured for some fractions and was correlated to their MW.

The current and emerging sources of technical lignins and their applications

“…Ultrafiltration gave products with polydispersity between 1.3-2.4, 76 or 1.25-1.98. 77 Both were much lower than the values by amine extraction or ethanol precipitation.…”

“…With a combination of Sephacryl‐100 (2–20 kDa) and Sephadex LH20 (2–6 kDa), lignosulfonate could be purified to fractions with polydispersity between 1.76 and 1.07 . Ultrafiltration has been compared with amine extraction and ethanol precipitation to fractionate lignosulfonate. Ultrafiltration gave products with polydispersity between 1.3–2.4, or 1.25–1.98 .…”

“…Ultrafiltration has been compared with amine extraction and ethanol precipitation to fractionate lignosulfonate. Ultrafiltration gave products with polydispersity between 1.3–2.4, or 1.25–1.98 . Both were much lower than the values by amine extraction or ethanol precipitation.…”

COST Action FP1105: effect of raw materials and pulping conditions on the characteristics of dissolved kraft lignins

“…The reported results are very preliminary in terms of lignin utilization, as it is obvious that for value-added lignin applications fractionation and upgrading is necessary (Brodin et al 2009(Brodin et al , 2012Gosselink et al 2010;Ropponen et al 2011;Duval et al 2015Duval et al , 2016Fang et al 2015). Selective precipitation and ultrafiltration are potentially useful techniques, depending on the intended lignin application (Brodin et al 2009;Toledano et al 2010;Ponomarenko et al 2014;Sevastyanova et al 2014;Duval et al 2015).…”

“…Selective precipitation and ultrafiltration are potentially useful techniques, depending on the intended lignin application (Brodin et al 2009;Toledano et al 2010;Ponomarenko et al 2014;Sevastyanova et al 2014;Duval et al 2015). It has been demonstrated that an increased content of OH aliph and OH phen groups improves the acetone solubility of lignin, which would be beneficial for fractionation based on acetone and hexane (Cui et al 2014).…”