What is the difference between acid refining and alkali refining?
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What is the difference between acid refining and alkali refining? Which option is better from an economic perspective, which one is more cost-effective, and what should be done with the acidic and alkaline residues thereafter?
Acid refining generally uses strong acids such as concentrated sulfuric acid, hydrochloric acid, and phosphoric acid. Pickling can remove various non-hydrocarbon compounds such as thioalcohols, thiophenols, thioethers, alkyl disulfides, thiophenes, sulfones, basic nitrides, and carboxylic acids present in oxides; it can also remove some non-basic nitrides, olefins, and aromatics. Alkali refining involves treating diesel with a low-concentration alkali solution, usually a sodium hydroxide solution with a mass fraction of around 10%, and sometimes an alcohol solution of sodium hydroxide is also used. Alkali washing can remove acidic substances in diesel, such as thiolues, thiophenes, and phenols. Since the action of alkali can only remove hydrogen sulfide as well as most naphthenic acids, phenols, and thiols, the alkali washing process is sometimes not used alone but in combination with sulfuric acid washing; this combined method is referred to as \"acid-base refining\". The alkali washing carried out before sulfuric acid purification is called pre-alkali washing, and its main purpose is to remove hydrogen sulfide ； The alkali washing after sulfuric acid purification is intended to remove the residual acid residues in the oil product after acid washing.