Patent GB-546148-A (GB)
Title: Improvements in or relating to the extraction of components from solutions containing the same
IPC: B01D11/04
Filed: 1941-01-31
Abstract: 546,148. Purifying hydrocarbons or derivatives thereof. SHELL DEVELOPMENT CO. Jan. 31, 1941, No. 1328. Convention date, Jan. 12, 1940. [Class 91] In the extraction of components from a solution containing them by means of a solvent immiscible and chemically inert to the solution, the latter is fractionated into at least two fractions, each of which contains a portion of the components of different degrees of ease of transference toward the solvent, and the fractions are caused to flow through an extraction zone by admitting them thereto at different points, the solvent flowing through the extraction zone at least in part in countercurrent to the fractions. The fractions are admitted to the extraction zone in the order of the decreasing ease of transference of their solutes to be extracted and are combined therein, the raffinate and the solvent being separately withdrawn therefrom. The solution may be fractionated, e.g., by distillation, fractional precipitation or fractional solvent extraction and the fractions may contain varying proportions of the components. Specified solutions to be treated comprise hydrocarbon oils, such as sour gasoline distillates; lubricating oils and coal tar distillates, aliphatic and aromatic hydrocarbons, chlorinated hydrocarbons, and basic organic liquids such as quinolines, alkylated pyridines and water-insoluble amines. In the application to a sour gasoline distillate, two fractions may be segregated, one containing difficultly removable high-boiling mercaptans and the other more easily removable low-boiling mercaptans; intermediate fractions may be introduced to the extracting zone between these two fractions. Three such fractions are withdrawn through lines 4, 5 and 6 from a fractionating column 3 and after condensing in coolers 7, 8 and 9, are supplied by lines 13, 14 and 12 respectively to an extraction column 10 which receives the extracting solution or solvent, in this case an aqueous caustic alkali, through line 11. The combined sweetened raffinate is withdrawn through line 15, the heaviest fraction containing the high-boiling mercaptans thus being treated with a higher ratio of solvent to solution than the remaining fractions. The spent alkali solution, laden with mercaptides, is supplied by line 16, through a heater 17, to a steam stripping column 18, and the regenerated solution returned to the column 10 through line 11. Since the extracting solution is regenerated by steam stripping, the dissociation constants of the components to be extracted should be less than 10<SP>-5</SP> and stronger acid components such as H 2 S, naphthenic acids and thiophenols, are pre-removed; components, such as alkyl phenols, which raise the viscosity of the extracting solution unduly, are also pre-removed. The sour distillate is therefore fractionated to obtain these components in the heaviest fraction, which is pre-treated with aqueous caustic alkali, in a settling tank 23. The extracting solution should preferably contain a solubility promoter for the mercaptans and groups of substances are specified for this purpose and include potassium isobutyrate, with or without an alkyl phenolate. The temperature in column 10 is preferably 0-60‹C., and 'the lower part may be refrigerated. Details are also given of the removal of mercaptans from a polymer naphtha and a West Texas straight-run gasoline respectively. Specification 519,397 is referred to.