Characterization of electrolyzed magnesium spent-sulfite liquor

Abstract

Spent sulfite liquor derived from magnesium bisulfite pulping of beech was electrolyzed in a pilot-plantelectrolysis cell. During the electrochemical treatment (125 mA cm−2; 60°C; 180 min), desalination of the anolyte took place and the magnesium concentration was reduced to approximately 60%. In addition, the pH decreased from 5 to 1. Three differently treated liquors (SSL pH 5; SSLe pH 2.5; SSLe pH 1) were chosen for further analysis. The average molar mass of the fractions was determined by size exclusion chromatography. Extended electrolysis time increased the molar mass of the lignosulfonates (M w: SSL pH 5, 5700 g mol−1; SSLe pH 2.5, 6500 g mol−1; SSLe pH 1, 7400 g mol−1). The content of phenolic hydroxyl and sulfonic acid groups did not undergo significant changes. Nevertheless, lignosulfonates obtained after electrolysis showed higher charge densities than the unmodified product (SSL pH 5, 1590 μeq g−1; SSLe pH 2.5, 1760 μeq g−1; SSLe pH 1, 1920 μeq g−1). Separation of the liquors into five fractions was performed using four ultrafiltration membranes (100, 50, 10 and 1 kDa). This allowed detailed structural analysis of high- and low-molar-mass lignosulfonate fractions in terms of the modifications induced by electrolysis.

Production and Application of Lignosulfonates and Sulfonated Lignin

“…In this process, lime (calcium oxide)i sa dded to the spent liquor initially to precipitate calcium sulfite at pH 8.5, which can be filtered and removed. [3,64] Ion-exchange resin separation may use sandstoneo rl imestone as an adsorbent for lignosulfonates. [60] The addition of lime to the system in the following step, shown as the second precipitation stage in Scheme 3, leads to the productiono fc alcium lignosulfonates, which are solid at ap Hg reater than 12.…”

The current and emerging sources of technical lignins and their applications

“…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.…”

Production of lignosulfonate in NSSC‐based biorefinery

“…In one report, it was stated that decreasing pH to 3.5–4 resulted in a significant lignin removal from black liquor . In contrast, acidification resulted in insignificant lignosulfonate isolation from sulfite‐based spent liquor in another study . The limited removal of lignosulfonate via acidification in the current work is attributed to the fact that lignin is sulfonated (i.e., water soluble) in the SL of NSSC process.…”

“…The limited removal of lignosulfonate via acidification in the current work is attributed to the fact that lignin is sulfonated (i.e., water soluble) in the SL of NSSC process. It was stated in the literature that sodium sulfite treatment of wood chips produces lignosulfonate that was soluble in acidic pH . Since the SL contains a significant amount of lignosulfonate, the main focus of this study was to investigate the impact of an acidification/solvent extraction process on the properties of the isolated lignosulfonate.…”