GB810490A - Processes for sweetening hydrocarbon oils - Google Patents

Abstract

Mercaptans are removed from hydrocarbon oils by intimately contacting, in the presence of a free oxygen-containing gas, with an aqueous alkali metal hydroxide solution in and by means of a propeller mixer, the volume ratio of aqueous alkali metal hydroxide to mercaptan-containing hydrocarbon oil supplied to the propeller mixer being less than 0.5:1. Aqueous sodium and potassium hydroxide solutions may be used, to which solutizers for mercaptans and for oxygen may be added. Solutizers for mercaptans referred to are amino- and hydroxy-alkyl amines where the alkyl groups contain 2 to 3 carbon <PICT:0810490/III/1> atoms, glycols, amino-glycols and diaminoalcohols containing 3-5 carbon atoms, diamino-, dihydroxy- or aminohydroxy-dialkyl ethers or thioethers where the alkyl groups have 2-3 carbon atoms, alkali salts such as potassium salts of fatty acids containing 3-5 carbon atoms, e.g. isobutyric acid, or of hydroxy- or amino-fatty acids containing 4-7 carbon atoms, or of phenyl acetic acid or hydroxy- or aminophenyl acetic acids, and alkyl phenolates such as cresolates. Solutizers for oxygen specified are phenolates, which may be substituted by alkyl groups with a total of not more than 3 carbon atoms. An oxidation catalyst for mercaptans, such as tannin, may be used. An excess of 50-200 per cent with respect to the theoretical amount of oxygen required for oxidation of the mercaptans is preferred; 10-40 per cent of a peroxide, based on the stoichiometric quantity of oxygen, may also be added. The process may be carried out at 0-80 DEG C. and at normal or elevated pressure, and may be effected continuously. From 0.2-0.4 parts by volume of alkali to 1 part of oil may be used. The oils may be pretreated with dilute aqueous alkali metal hydroxide solution to remove hydrogen sulphide and part of the aromatic mercaptans, and also with a similar solution containing a solutizer for mercaptans to remove most of the mercaptans. Hydrocarbon oils treated may be those boiling not higher than 350 DEG C., such as straight run or cracked gasolines and kerosines, e.g. catalytically cracked gasolines, and reformed gasolines; when the oils contain unsaturated components, an antioxidant may be added, e.g. an arylamine or alkyl phenol. In the Figure, 1 designates a propeller mixer comprising a rotating vane 3 mounted on a shaft 2 and surrounded by a jacket 4, in which the mixture of oil and alkali is introduced via inlet 5. The mixture is sucked down by the vane and enters the zone between the jacket and the outer wall via the bottom of jacket 4. The mixture leaves the apparatus at outlet 6. The inner wall of the apparatus may be provided with baffles 7. The vanes may revolve at 250-2500 revolutions per minute. The mixture of oil and alkali is passed to a settling tank to separate the phases, and the aqueous alkali recycled. The process is compared with a similar process using a turbomixer instead of a propeller mixer. Specifications 499,678, 503,644, 509,669 and 712,056 are referred to.