Method 1. Use dried kelp or dried sargassum as raw material
Soaking and color fixation Take 120kg of dried kelp or 180kg of dried sargassum (generally the glue content is greater than 15%), remove sediment and other substances, add water (or seaweed lotion containing less than 2% mannitol) 2-3t, soak at room temperature For two hours, scrub with water to remove impurities such as mannitol, and recover mannitol from the solution. Wash the clean raw materials, add 1% formaldehyde solution of 15 times the dry weight of the raw materials, soak at room temperature for 16-24 hours, wash the fixed raw materials with water once, and chop them as appropriate.
Dried kelp (or dried sargassum) [water, HCHO]→[16-24h] finely ground kelp
Digestion Take 10-15g/L (1%-1.5%) sodium carbonate solution of 10-15 times the amount according to the dry weight of the raw material, and steam it to 40-45°C (spring, autumn) or 30-40°C (summer) or 50-55°C (winter) (Sargassum 65-70°C), add the color-fixed raw materials, heat and digest for 4 hours, until the materials become paste and reach the end of digestion to obtain a paste-like glue.
Color-fixing kelp [Na2CO3]→[heating and digesting for 4h] pasty glue
Precipitation Dilute the pasty glue solution with water to 60-70 times the dry weight of the raw material, stir evenly, let it settle at room temperature for 16-20 hours, release the supernatant, filter it through 80-100 mesh silk silk, and filter it with a fine cloth bag. A clear sodium alginate solution was obtained. The glue solution extruded from the lower layer of sediment was re-precipitated for 4-8 hours, finely filtered with a fine cloth bag, the residue was discarded, and the clarified filtrate was combined to obtain the glue solution.
Acid coagulation Add 60-70L of hydrochloric acid (or 40-50L of sulfuric acid) into 20000L of clarified glue in a trickle, stir slightly, let it stand for a while, the pH reaches 1-1.5, and the waste acid solution released from the lower part is clear and transparent, reaching the end point. The alginic acid after acid coagulation is washed with water until the pH of the lotion reaches 1.5-2, packed into bags, self-filtered for a while, and squeezed to obtain alginic acid.
Supernatant [HCl]→[pH1-1.5] seaweed liquid
Bleaching and degradation Take 200kg of alginic acid (moisture less than 90%) and mash it, add 80-100kg of ethanol with a volume fraction of 90% and 10-14L of 300g/L (30%) NaOH solution to obtain sodium alginate slurry, neutralization time No more than 8h, control pH7-8. After neutralization, add 24-30L of sodium hypochlorite solution (content 30-50g/L) for bleaching, then use about 5-7L of sodium sulfite solution (content 20-27g/L) to reduce the excess sodium hypochlorite, and control the pH to 8 until starch potassium iodide does not appear. until blue, ethanol was filtered off, and dried to obtain oligomeric sodium alginate.
Alginic acid [ethanol, NaOH] → [8h, pH7-8] sodium alginate slurry [NaClO, Na2SO3] → [pH8] oligomeric sodium alginate
Drying and pulverization Take the wet oligomeric sodium alginate, spread it evenly in a baking tray, dry it at 60-80°C for 2-8 hours, and pulverize it to obtain the finished product of white oligomeric sodium alginate.
Wet oligomeric sodium alginate[60-80℃,2-8h]→Oligomeric sodium alginate finished product
Method two, the preparation method of raw material with sea-tangle (mixed with 1/3 seaweed)