Patent GB-687381-A (GB)
Title: Electrolytic regeneration of spent caustic
IPC: C10G19/08
Filed: 1950-11-02
Abstract: 687,381. Electrolytic regeneration of spent caustic containing sulphur impurities. GAYLOR, P. J. Nov. 2, 1950 [Dec. 10, 1949], No. 26761/50. Class 41. A process of regenerating spent caustic containing sulphur impurity oxidizable into an insoluble form comprises subjecting the caustic to electrolysis between electrodes separated by a liquid-permeable gas-impermeable diaphragm to convert at least a substantial portion of the sulphur impurity to an insoluble form. In the apparatus shown, in which caustic becomes contaminated when used for scrubbing sour gasoline, the gasoline is fed through an inlet 2 to a scrubbing tower 1, in countercurrent to caustic supplied through a pipe 24. The spent caustic is drawn off through a pipe 5 into a surge tank 7, from which it is pumped to reservoirs 12, 36 and to an electrolyzer 13. The caustic is passed through the electrolyzer and is then discharged to a settling tank 18 where the aqueous regenerated caustic 20 settles out, disulphides forming an oily layer 19 which is removed through a pipe 77. The regenerated caustic is pumped to the line 24 for re-use. The electrolyzer, which is of filter-press type, has anode plates 29 alternately disposed with respect to cathode plates 31, with insulating diaphragm plates 30 interposed. Each electrode plate, like the anode plate 29, Fig. 3, is preferably made of iron electroplated with nickel or of graphite, and has an outer sealing edge 85 and ridged front and back faces 43. The diaphragm plates have each a central portion made of asbestos or other material which will permit flow of liquid therethrough but will prevent diffusion of gases formed by the electrolysis. Registering holes are formed at the four corners of the diaphragm plates and electrode plates. Some of the holes are sealed off from communication with the ridged surfaces of the electrode plates, and all of the holes are sealed off from the surfaces of the diaphragm plates. In anode plate 29, caustic entering through opening 47 flows towards opening 46 and during electrolysis sulphur impurities react with nascent oxygen to produce disulphides. Any excess oxygen is collected in reservoir 36. Similarly caustic enters through openings 48 in the cathode plates and flows across the cathode plates to openings 45, hydrogen produced being collected in reservoir 12. The regenerated caustic together with disulphides is passed through line 17 to the settling tank 18. The reservoirs 12, 36 are partly filled with liquid passing up through pipes 34, 35. The reservoir 12 may be dispensed with and the hydrogen collected in the settling tank 18 together with the liquid products. In a modification a foraminous conductive body such as a stack of fine mesh wire sheets, compressed knitted metal or loosely-compressed metal fibres or powder may be placed between the face of each electrode plate and the face of the diaphragm plate, the faces of the electrode plates preferably being smooth rather than ridged. The process may be used for treating caustic containing hydrogen sulphide to obtain sulphur which is removed from the liquid product by filtration.