Calcium lignosulfonate manufacture process
Calcium lignosulfonate is obtained from soft wood processed in sulfite pulping method for producing paper.
They small pieces of softwood is put into reaction tank to react with acidic calcium bisulfite solution for 5-6 hours under the temperature of 130 degree Centigrade.
During the process the bisulfite ions reacted with native lignin to for sulfonated lignin, that is lignosulfonate. Also the calcium ion stabilize the anionic lignosulfonate group. After complete reaction the insoluble cello use and soluble calcium lignosulphonate is separated by filter.
After filtration the filtrate contains some lignosulfonate, bisulfite salts and reducing agent monomers. Thus will add into sulfuric acid then through evaporation to evaporate the water and sulfite like sulfur oxide.
Then the filtrate will be diluted with water for further purification by ultrafiltration when the temperature is slightly going up. Ultrafiltration is liquid /liquid separation to separate the filtrate by a semi permeable membrane.
Then the filtrate is added into diluted sulfuric acid to adjust PH the evaporate around 100 degree Centigrade for spray dry.