There are two general:
1) exchange lignin sulfonate via ion exchange;
2) In the process of pulping, with sodium carbonate or sodium hydroxide, instead of calcium oxide or calcium hydroxide. This method is relatively rare, because the price of sodium carbonate or sodium hydroxide is usually higher than calcium oxide or calcium hydroxide.
With the paper mill pulp waste as raw material, there are generally three kinds of preparation methods.
1. The sulfite or bisulfate contained in the pulp waste of the calcium bisulfite pulp process is directly combined with the hydroxyl groups in the lignin molecule to form lignosulfonate. 10% lime milk was added to the waste and heated at (95 ± 2) ° C for 30 min. The calcined solution will be allowed to settle and the precipitate will be filtered off, washed with water and sulfuric acid. Filter to remove calcium sulfate. Then Na2CO3 was added to the filtrate to convert lignosulfonate to sodium sulfonate. Reaction temperature is 90 ℃ is appropriate, after 2 h reaction, standing, filter to remove impurities such as calcium sulfate. The filtrate was concentrated and cooled to crystallize the product.
2. Pulp liquid pulping as raw material. First, add 50% of concentrated sulfuric acid to the waste liquid, stirring 4 ~ 6 h. And then with lime milk, by sedimentation, filtration, beating, acid, sodium carbonate conversion, concentration, drying products
3. Wastewater from grass pulp was used as raw material.