Fatty acid ester and glycerol are the important reactions in oil chemical industry. A variety of ester products can be obtained by this reaction. The most widely used products in industry are methyl ester of fatty acid and glycerol. Fatty acid methyl ester is an important basic oil chemical raw material. Many compounds can be derived from fatty acid methyl ester. Fatty acid methyl ester has always been the research object of oil chemical workers. In recent years, due to the fierce competition in the oil price war, the contradiction between fuel supply and demand has intensified, and the research of fuel substitutes has been widely carried out. The production of biodiesel has developed to a considerable scale. The production of biodiesel has directly impacted the structure of glycerol production.
The raw materials of biodiesel are oil and methanol or ethanol. For every 10 tons of biodiesel, 1 ton of glycerol by-product is produced. Vegetable oils such as rapeseed oil, soybean oil, palm oil, butter, industrial lard and other oils can be used, as well as various kinds of recycled oils, such as fried waste oil, refined oil foot recycled oil, etc. China has made great progress in the research and production of biodiesel. At present, there are 2 million tons of low-grade oil and fat in China. There are abundant raw materials for the production of biodiesel (low-grade fatty acid esters – methyl esters, ethyl esters). It is expected that biodiesel will develop rapidly to make up for the shortage of more than one million tons per year. The rapid development of biodiesel will provide abundant raw materials for glycerol production, which will inevitably attract the attention of the glycerol industry.
The alcoholysis process of oil and fat is to produce fatty acid esters and glycerol by alcoholysis of oil and low-carbon alcohols under the condition of alkaline catalyst. In order to obtain high ester conversion rate, the grease used should be degummed and deacidified so that the acid value is less than 0.5 mg KOH/g, and methanol should be anhydrous. The alcoholysis reaction can be carried out under pressure and high temperature (9.OMPa, 240 C, glycerol concentration up to 90%) or under normal pressure of 50-70 C. There are batch and continuous processes. Intermittent production, quick product turnaround, can be applied to a variety of oils and fats raw materials. Continuous type is suitable for large-scale production with low energy consumption. The concentration of alcoholic glycerol is much higher than that of oil-hydrolyzed sweet water, which can reach more than 70%.
In order to reduce the cost of raw materials, when low-grade oils (high acid value oils) are used, pre-esterification technology can be used to make free fatty acids into fatty acid esters, and then methyl esterification can be carried out. The alcoholysis reaction under pressure and high temperature has fast reaction speed, but it requires high equipment. In order to reduce the investment cost of equipment, the reaction device under low temperature and normal pressure is often used.
Oil, methanol and catalyst (sodium methanol, etc.) were put into the reactor in batches. The material remained boiling and refluxed for 2 to 3 hours at 70 (?) C. The ester conversion rate was above 95%. If the content of free fatty acid in oil is more than 2%, the oil must be alkali refined or pre-esterified with methanol (commonly used catalysts are H2SO4, HCl, p-toluene sulfonic acid, strong acid resin, etc.) to reduce the amount of catalyst and the content of soap in sweet water. The reactant is stationary in the settling stratifier and crude glycerol is separated. Methanol in crude glycerol is evaporated and reused by methanol evaporator, and crude glycerol is sent to the post-processing and refining process. A small amount of glycerol in methyl ester is recovered by heating crude methyl ester to recover methanol, then adding water to crude methyl ester to dilute acid (3% of the reaction mixture, the amount of acid is equal to that of catalyst), so as to wash out glycerol in methyl ester and decompose soap and catalyst in methyl ester. Static stratification, crude glycerol sent to the post-processing refining process.
