Patent GB-759560-A (GB)
Title: Process for oxidising mercaptans or mercaptides to disulphides
IPC: B01D11/04
Filed: 1954-06-01
Abstract: In a process for converting into disulphides the mercaptans or mercaptides initially present in a two-phase system, one phase of which comprises a hydrocarbon oil and the other of which comprises an aqueous alkali metal hydroxide solution, the two phases are passed, in the presence of oxygen, upwardly through a column packed with material which is preferentially wetted by the aqueous phase, the flow rate of the hydrocarbon oil being from 0.1 to 3, and preferably 0.2 to 2, centimetres per second.  The ratio of the volume of hydroxide solution to the volume of hydrocarbon oil can vary within very wide limits and generally lies between 0.05 and 5, and when the process of the invention is used to remove mercaptans from a hydrocarbon oil the volume of hydroxide solution led through the column per unit of time is preferably of from 5 to 50 per cent of the volume of hydrocarbon oil led through the column per unit of time. When the process of the invention is used to regenerate an alkali metal hydroxide solution containing mercaptides, such as one which has served for the extraction of mercaptans from a hydrocarbon oil the ratio of hydroxide solution to the volume of hydrocarbon oil is preferably between 0.2 and 5.  The process is especially suitable for the removal of mercaptans from light hydrocarbon oils preferably containing less than 0.05 per cent by weight of mercaptan sulphur, such as gasolines and kerosenes, but when these contain unsaturated components, e.g. cracked or reformed gasolines, an anti-oxidant such as an aryl amine or an alkyl phenol must be added.  Suitable hydrophilic packing materials are metals, ceramics and coke which may be, for example, in the form of Raschig rings, compressed metal gauze, steel wool, beads, small cubes or nails, or porous material. The process is generally carried out at atmospheric pressure but increased pressure may be necessary.  The oxygen may be supplied conveniently as air and it can be dissolved in the hydrocarbon oil beforehand or injected into the reaction column.  The quantity of oxygen must be at least equivalent to the quantity of mercaptans to be converted and is preferably in an excess of 50 to 200 per cent of the theoretical, unless a peroxide is simultaneously used. Preferably the concentration of the aqueous alkali metal hydroxide solution is at least 2-normal and the extractive power of such solutions for mercaptans may be increased by incorporation of a solutizer, suitable solutizers being amino and hydroxy alkyl amines, glycols, amino and diamino glycols, dihydroxy or amino hydroxy dialkyl ethers or thioethers, alkali metal salts of fatty acids or of hydroxy or amino fatty acids or of unsubstituted, hydroxy or amino phenyl acetic acids, alkali phenolates, and mixtures thereof.  Solutizers to promote the solubility of oxygen may also be incorporated, phenolates being especially suitable. After the process has reached completion the two phases are separated in a settler which may be the top of the column from which packing material has been omitted; a baffle plate may also be fitted in the top of the column to promote separation. The alkali metal hydroxide solution may then be recycled.  A pretreatment of the hydrocarbon oils may be carried out with aqueous alkali metal hydroxide solution to remove acids which are stronger than the mercaptans therefrom and if a solutizer is also incorporated hydrocarbon oils having a mercaptan sulphur content of 0.05 per cent by weight or more are also freed from the greater part of the mercaptans by this pretreatment.  In examples (1) the mercaptan sulphur content of a straight-run gasoline is reduced from 0.018 to 0.0008 per cent by weight by upward passage of the gasoline, together with air and a solution consisting of approximately equal parts by weight of water, potassium hydroxide and cresols, through a column packed with steel wool, the respective rates being 200, 30 and 60 litres per hour resulting in a rate of flow of 1.25 cm/sec., the temperature being 15 DEG  C. and the pressure 1 atmosphere gauge at the bottom of the column and atmospheric at the top; after separation, the aqueous solution and one half of the gasoline are recycled; (2) under similar conditions the mercaptan content of a straight-run gasoline is reduced from 0.0172 per cent to 0.0052 per cent by weight, the supply rates of gasoline, aqueous solution and air being 1000, 100 and 75 litres per hour respectively, resulting in an upward flow rate of 0.4 cm/sec.; (3) the mercaptan sulphur content of a spent potassium hydroxide solution containing also approximately equal parts by weight of water and cresols is reduced from 0.05 to 0.002 per cent by weight under similar conditions to the above, a gas oil being supplied at 160 litres per hour and air being blown in at 25 litres per hour, resulting, with the hydroxide being supplied at 20 litres per hour, in a flow rate of 0.9 cm/sec.ALSO:Mercaptans are removed from a hydrocarbon oil by passing the oil together with an aqueous alkali metal hydroxide solution, in the presence of oxygen, upwardly through a column packed with material which is preferentially wetted by the aqueous phase, the flow rate of the oil being from 0.1 to 3, and preferably 0.2 to 2, cm./sec., whereby the mercaptans are converted to disulphides. The volume of the hydroxide solution led through the column per unit of time is preferably of from 5 to 50 per cent of the volume of hydrocarbon oil led through the column per unit of time.  The process is especially applicable to light hydrocarbon oils, preferably containing less than 0.05 per cent by weight of mercaptan sulphur, such as gasolines and kerosines, but when these contain unsaturated components, e.g. cracked or re-formed gasolines, an anti-oxidant such as an aryl amine or an alkyl phenol must be added.  Suitable hydrophilic packing materials are metals, ceramics and coke which may be, for example, in the form of Raschig rings, compressed metal gauze, steel wool, beads, small cubes or nails, or porous material.  The process is generally carried out at atmospheric pressure, but increased pressure may be necessary.  The oxygen may be supplied conveniently as air and it may be dissolved in the hydrocarbon oil beforehand or injected into the reaction column. The quantity of oxygen must be at least equivalent to the quantity of mercaptans to be converted and is preferably in an excess of 50 to 200 per cent of the theoretical, unless a peroxide is simultaneously used.  Preferably the concentration of the aqueous alkali metal hydroxide solution is at least 2-normal and the extractive power of such solutions for mercaptans may be increased by incorporation of a solutizer, suitable solutizers being amino and hydroxy alkyl amines, glycols, amino and diamino glycols, dihydroxy or amino hydroxy diakyl ethers or thioethers, alkali metal salts of fatty acids or of hydroxy or amino fatty acids or of unsubstituted, hydroxy or amino phenyl acetic acids, alkali phenolates, and mixtures thereof.  Solutizers to promote the solubility of oxygen may also be incorporated, phenolates being especially suitable.  After the process has reached completion the two phases are separated in a settler which may be the top of the column from which packing material has been omitted; a baffle plate may also be fitted in the top of the column to promote separation. The alkali metal hydroxide solution may then be recycled.  A pretreatment of the hydrocarbon oils may be carried out with aqueous alkali metal hydroxide solution to remove acids which are stronger than the mercaptans therefrom, and if a solutizer is also incorporated, hydrocarbon oils having a mercaptan sulphur content of 0.05 per cent by weight or more are also freed from the greater part of the mercaptans by this pretreatment.  The process of the invention is also applicable to the regeneration of spent alkali metal hydroxide solutions containing mercaptides such as those which have served for the extraction of mercaptans from hydrocarbon oils.  In this case the ratio of hydroxide solution to the volume of hydrocarbon oil led through the column is preferably between 0.2 and 5.  In examples (1) the mercaptan sulphur content of a straight run gasoline is reduced from 0.018 to 0.0008 per cent by weight by upward passage of the gasoline together with air and a solution consisting of approximately equal parts by weight of water, potassium hydroxide and iresols, through a column packed with steel wool, the respective rates being 200, 30 and 60 litres per hour resulting in a rate of flow of 1.25 cm./sec., the temperature being 15 DEG C. and the pressure being 1 atmosphere gauge at the bottom of the column and atmospheric at the top; after separation the aqueous solution and onehalf of the gasoline are recycled; (2) under similar conditions the mercaptan content of a straight-run gasoline is reduced from 0.0172 per cent to 0.0052 per cent by weight, the supply rates of gasoline, aqueous solution and air being 1,000, 100 and 75 litres per hour respectively, resulting in an upward flow rate of 0.4 cm./sec.; (3) the mercaptan sulphur content of a spent potassium hydroxide solution containing also approximately equal parts by weight of water and cresols is reduced from 0.05 to 0.002 per cent by weight under similar conditions to the above, a gas oil being supplied at 160 litres per hour and air being blown in at 25 litres per hour, resulting, with the hydroxide being supplied at 20 litres per hour, in a flow rate of 0.9 cm. sec.