GB901610A - Contacting liquids - Google Patents

Abstract

<PICT:0901610/III/1> Immiscible liquids are contacted by passing said liquids in sequence through two pairs of perforate or foraminous electrodes insulated from the wall of the contacting vessel, a voltage of the same polarity being applied between each pair of electrodes and said vessel and the voltage applied to the first pair of electrodes and the spacing therebetween being such as to effect dispersion of the liquid and the voltage applied to the second pair of electrodes and the spacing between them being such as to effect separation of the liquids. For a given electrode spacing, the potential difference for dispersion (emulsification or haze-formation) is higher than that for separation and for a given potential the electrodes are closer together for dispersion. The dispersion and separation process may be employed to treat copper-sweetened naphthas with aqueous sodium sulphide and petroleum oils containing mercaptans and naphthenic acids with aqueous sodium hydroxide; in an experiment, a gas oil is treated with caustic solution with formation or destruction of haze according to the applied potential. Other oils mentioned are light and heavy naphtha and diesel oils, catalytic reformates and products of cracking vegetable oils and natural or synthetic esters such as castor oil or synthetic ester lubricants. Aqueous solutions may contain cuprous ammonium acetate or carbonate, cupric chloride or sulphate, sodium hypochlorite, sodium, potassium or lithium hydroxides or carbonates, calcium or barium hydroxide or hydrochloric or sulphuric acid. One form of apparatus for carrying out the process is shown in Fig. 3: a conductor E, insulated from the vessel C at I supports electrodes e1-e8 in the form of grids or foraminous plates. The outer pairs of electrodes e1, e2 and e7, e8\t serve to coalesce the particles of an emulsion formed by the remaining electrodes, which are more closely spaced. Oil is introduced through pipe 1 and aqueous reagent through pipe 2, said pipes being of such form as to distribute the liquids uniformly over the vessel. Purified oil leaves through line 3 and reagent through line 4 for recycling with fresh reagent from line 8, or through line 6 for removal. Earthed grids EGB and EGT are provided to confine the effects of the electrodes to the contacting zone. In other embodiments, the oil and aqueous phase may be introduced into the vessel as a coarse suspension. For emulsification, the electrodes may be at right angles or parallel to the flow of liquids or at other angles; for coalescing they should be normal to said flow. The electrodes are preferably all at the same potential, although for dispersion an A.C. or D.C. potential may be employed whereas for coalescing D.C. is preferred. To avoid corrosion it is preferred that the vessel be earthed and the electrodes at a negative potential. To disperse a hydrofined gas oil a potential above 8000 volts per inch separating the grids may be employed; to coalesce the dispersion the potential should be below 4000 volts/in. Suitable electrode spacing is 1-3 ins. for emulsification and more than 3 ins. for phase separation. Voltages of 20,000-30,000 volts per inch between the electrodes and the vessel may result in flashover, which places an upper limit on the voltage to be employed.