The factors affecting acid treatment are as follows.
- Raw oil
The quality of saponification waste water depends on the quality of oils and fats. Generally, oils and fats contain protein, gum, pigment (chlorophyll, carotenoids, gossypol), resin, phospholipids, sterols, waxes and other impurities. If the oil has not been pretreated, these impurities will be salted out into the saponification waste liquor after the saponification, it not only affects the saponification waste liquor treatment, but also affects the quality of glycerol products.
2. influence of flocculants: The amount of ferric chloride is determined by the quality of saponified waste liquid during acid treatment.
In order to remove the impurities in the saponification waste water as much as possible, the pH and temperature of the solution must be controlled. The hydrolysis of 1mol ferric chloride produces 3mol hydrochloric acid. Under acidic conditions, the iron soap can be dissolved and the colloid of ferric hydroxide can be reduced. In this way, the precipitation of ferric chloride, electric neutralization, coagulation and adsorption at isoelectric point are reduced, and the impurities can not be completely removed. Therefore, the Ph control of general endpoints is more appropriate in 3.5-3.8. The average amount of ferric chloride is 0.3%-0.6% of saponification waste liquid. For the same waste liquor, the crude glycerol (fatty acid iron soap precipitated completely) obtained by increasing ferric chloride in proper amount has good quality and light color. However, the treatment cost is high, the filtration residue is much, and the filtration speed is slow. When the amount of ferric chloride is reduced, the amount of filter residue is low, the filtration speed is fast, and the cost is low. However, the coarse and sour color is deep and the quality is poor.
Aluminum salt is a good flocculant. When treating saponification waste liquid, aluminum hydroxide is formed by reaction with free alkali. Aluminum hydroxide is a kind of flocculant colloid with strong adsorption. At the same time, aluminum ions react with fatty acids to form fatty acid aluminum salts. Aluminum salt flocculants can completely remove higher fatty acids. The removal rate of fatty acids is also very high. The removal rate of hydrophilic impurities such as protein and amino acids can reach 80%. When using aluminium salt, the temperature should be controlled at 40-80 C, and the PH should be controlled at 4.5. But when treated with H2SO4 and AL2 (SO4) 3, Na2so4 is formed. If NA2SO4 is used in the salting out of soap glue, its effect is only half of that of Naci. Therefore, when the amount of Na2SO4 in the recovered salt exceeds 20%, the salting out effect of soap cooking operation will be affected, so it needs to be replaced. In addition, the price of aluminum salt is relatively high, so the Chinese soap making industry mostly uses FeCL3 solution.
3. Treatment temperature: When the treatment temperature is low, the coagulation and adsorption effect of iron soap precipitation formed by FeCl3 is better. The longer the static time is, the more black fatty acid is separated. In the same way, the water quality is lighter, but the filtration speed is slower. The acidification treatment temperature is 50-60 degrees.
Control points of acid treatment operation: Take 10ML filtrate into test tube, add 2 drops of 5% ferric chloride solution, shake well and place for 5 minutes. Observe that there should be no turbidity or precipitate in the filtrate. Otherwise, the ferric chloride solution should continue to be added. When Ph has reached 3.5, it is necessary to return to alkali, adjust PH with alkali, make the treatment solution alkaline and then add ferric chloride solution to treat Ph up to 3.8-4.2, until the filtrate is not turbid. When adding pH to pH value, a small test should be carried out to determine the amount of alkali added.
