Calcium lignosulfonate manufacturing starts from the spent liquor produced during sulfite pulping of wood. The process below describes a typical purification and finishing route used in industry; exact parameters vary by producer and are confirmed against the current batch TDS/COA for any specific lot.
From pulping liquor to purified calcium lignosulfonate
After pulping is complete, water-insoluble cellulose fiber is separated from the soluble calcium lignosulfonate fraction by filtration. The resulting brownish filtrate contains the lignosulfonates along with residual sulfite salts and reducing-sugar monomers released from wood cellulose during pulping. The filtrate’s pH is typically adjusted with concentrated sulfuric acid, and its water and sulfite (sulfur dioxide) content is reduced through evaporation.
Following initial evaporation, the filtrate may be diluted and passed through ultrafiltration at moderately elevated temperature. Ultrafiltration separates components by molecular size across a semi-permeable membrane, allowing the higher-molecular-weight lignosulfonate fraction to be separated from lower-molecular-weight depolymerization products and residual sugar monomers. Softwood is generally preferred as the source material in this process, since it is reported to yield a product with a more favorable high-molecular-weight distribution than other wood sources.
The purified calcium lignosulfonate solution from ultrafiltration may be pH-adjusted again with dilute sulfuric acid, then evaporated at approximately 95–105°C to a dry-matter content suitable for spray-drying. The final product is spray-dried to the moisture content specified for loss-on-drying and packed into containers appropriate for its intended grade.
Product Documentation and Supply Enquiries
Batch COA, TDS, SDS/MSDS, samples, packaging options and commercial quotations are available on request. Contact info@greenagrochem.com or use the contact form.