GB710972A - Process for refining petroleum and coal tar distillates - Google Patents

Abstract

Petroleum and coal tar distillates, such as benzene, which are substantially free from unsaturated hydrocarbons but contain both mercaptans and other organic sulphur compounds, are refined, first by extraction with aqueous alkali metal hydroxide solution in presence of a solutizer to remove the mercaptans, and then by treatment with sulphuric acid, oleum or a sulphonic acid, followed by removal of the acid. The refined distillates may further be washed with water and, if desired, with a small quantity of dilute aqueous alkali solution, but redistillation is unnecessary. When the crude distillate contains hydrogen sulphide, this may be removed by a preliminary wash with a small amount of dilute alkali metal hydroxide solution. Examples of solutizers are amino- and hydroxy-alkyl amines in which the alkyl groups contain 2-3 carbon atoms, glycols, amino-glycols and diamino-alcohols with 3-5 carbon atoms, diamino-, dihydroxy- or amino-hydroxy-dialkyl ethers or thioethers in which the alkyl groups have 2-3 carbon atoms, alkali (particularly potassium) salts of fatty acids (e.g. isobutyric acid) with 3-5 carbon-atoms or of hydroxy- or amino-fatty acids with 4-7 carbon atoms, or of phenyl acetic acid or hydroxy- or amino-phenyl acetic acids, or of alkyl phenols, or mixtures of two or more of the said compounds. Sulphonic acids mentioned are the lower alkyl (e.g. methyl, ethyl, propyl and isopropyl) sulphonic acids. In an example, extraction with aqueous caustic potash containing potassium cresolate and potassium picramate is followed by treatment with sulphuric acid.ALSO:Petroleum and coal tar distillates, which are substantially free from unsaturated hydrocarbons but contain both mercaptans and other organic sulphur compounds, are refined, first by extraction with aqueous alkali metal hydroxide solution in presence of a solutizer to remove the mercaptans, and then by treatment with sulphuric acid, oleum or a sulphonic acid, followed by removal of the acid. The refined distillates may further be washed with water and, if desired, with a small quantity of dilute aqueous alkali solution, but redistillation is unnecessary. When the crude distillate contains hydrogen sulphide, this may be removed by a preliminary wash with a small amount of dilute alkali metal hydroxide solution. Distillates mentioned are gasoline, kerosene and hydrogenation gasoline. Examples of solutizers are amino- and hydroxy-alkyl amines in which the alkyl groups contain 2-3 carbon atoms, glycols, amino-glycols and diamino-alcohols with 3-5 carbon atoms, diamino-, dihydroxy- or aminohydroxy-dialkyl ethers or thioethers in which the alkyl groups have 2-3 carbon atoms, alkali (particularly potassium) salts of fatty acids (e.g. isobutyric acid) with 3-5 carbon atoms or of hydroxy- or amino-fatty acids with 4-7 carbon atoms, or of phenyl acetic acid or hydroxy- or amino-phenyl acetic acids, or of alkyl phenols, or mixtures of two or more of the said compounds. Sulphonic acids mentioned are the lower alkyl (e.g. methyl, ethyl, propyl and isopropyl) sulphonic acids. The aqueous alkali metal hydroxide solution, which has been employed in extracting mercaptans according to the invention, may be regenerated for further use. Regeneration may be carried out by removing the absorbed mercaptans from the solution, for example with the aid of steam, or by oxidizing the mercaptans with an oxidant, such as air or another oxygen-containing gas, and separating the oxidation products or extracting the oxidation products with a hydrocarbon oil such as gasoline or kerosine. The oxidation of the mercaptans with an oxidant may be carried out in the presence of an oxidation catalyst, such as hydroxy- and aminophenols which may contain other substituents, for instance one or more carboxyl groups or nitro groups. Tannic acid, tannin and picramic acid are particularly suitable. In an example, straight run gasoline is extracted with aqueous caustic potash containing potassium cresolate and potassium picramate and then treated with sulphuric acid.