Regeneration of spent caustic

摘要

Caustic employed in the removal of organic impurities from hydrocarbon oils is at least partially regenerated by foaming the spent caustic to form distinct foam and liquid layers in which the organic impurities are concentrated in the foam layer, the foam and liquid layers being thereafter separated. The caustic may be a solution of an alkali metal, preferably sodium or potassium hydroxide, carbonate or other salt having basic properties in solution and having a concentration of 0,1-5% at and containing no more than 1,0% wt. of impurities. Foaming may be carried out by the use of gases or vapours, e.g. CO2, air, N2, NH3, hydrocarbon gases or steam, or by the use of mechanical agitation, or by opposing jets of caustic. Gases which react with the organic impurities, particularly with the sulphur compounds may also be employed to produce foaming, the reacted impurities being removed in the foam layer together with unreacted impurities. Temperatures during foaming may be 40 DEG -150 DEG F. preferably 70 DEG -80 DEG F. with gas velocities to cause foaming of 1-50 ft./sec. The process may be used in conjunction with known regeneration processes, e.g. carbonation and hydrolysis, of the caustic to form carbonate solution in which the organic impurities, such as phenols and acid oils, are insoluble, particularly as a final clean-up step. A hydrocarbon oil stream 55, e.g. crude oil or oil distillate from petroleum refining, is washed with caustic stream 56 in vessel 50. Sweetened oil is removed through line 57 whilst contaminated caustic, containing phenols, naphthols, and naphthenic acids, is fed into carbonation unit 51 by line 58, where it is converted at say 100 DEG -150 DEG F. into Na2CO3 solution by CO2 gases entering under pressure below 10 p.s.i.g. through line 59. Residual gases are vented at 60. Organic impurities precipitate in settler 52 and are removed at 61. Carbonate solution containing soluble impurities is passed to tower 53 where it is foamed by flue gas introduced through line 64 and distributer 65. Impurity-rich foam is led off at 66 to coalescing zone 67, where the foam is collapsed by standing, mechanical action, increased temperature, or electrical means. Purified carbonate solution is passed through 71 to hydrolyser 54 where it is hydrolysed by steaming at 400 DEG -510 DEG C. and 250-1400 p.s.i.g. to form NaOH by steam entering at 72. Caustic together with make-up introduced at 75 is returned through 74, 70, and 56 to vessel 50 for further use. To improve stability of the foam in tower 53, foam stabilizing agents, e.g. detergents or surface active dyes, may be added.