GB819121A - Improved dewaxing and dehazing process - Google Patents

Abstract

Waxy and/or haze-forming constituents are removed from mineral oils by contacting the oil with a molecular sieve an adsorbent having a uniform pore size of 4.5 to 5.5 A DEG at a temperature above 300 DEG F. and withdrawing the purified oil. Oils mentioned are petroleum oils, e.g. middle distillates, lubricating oils, diesel oils and jet fuels, particularly those containing less than 4 wt. per cent of wax. Preferred contacting temperatures are 400 DEG to 800 DEG F. The dewaxing may be carried out (a) in the vapour phase at reduced pressure or with a non-adsorbable carrier oil, or (b) in the liquid phase at elevated temperature or using a diluent oil having a molecular diameter greater than 5 A DEG , e.g. an iso- or cyclo paraffin or an aromatic hydrocarbon. The adsorbent may be used as a fixed or fluidized bed or as a slurry. The wax may be recovered from the adsorbent for purification by treatment with hot water at 150 DEG to 300 DEG F. Other desorbents mentioned are olefines, e.g. propylene and butylenes, lower-boiling n-paraffins, and normal primary alcohols, e.g. methanol, ethanol and butanol. Modifications include (i) removal of the higher-melting waxes only by treating only the higher boiling fractions of the oil, e.g. the 750-900 DEG F. cut of a lube oil or the 650-750 DEG F. cut of a diesel oil; (ii) combining the dewaxing with the fractionation of the oil by introducing the adsorbent to the trays of a fractionating tower; (iii) combining the dewaxing with the removal of aromatic impurities by mixing a 6-15 A DEG molecular sieve adsorbent with the 5 A DEG adsorbent. Examples illustrate the effect of the treatment on gas oil, a middle distillate, lube oils and diesel oils, by slurry vapour phase or fixed bed contacting, at temperatures of 200 DEG to 800 DEG F. at pressures of 0.4 mm. to atmospheric and varying feed rates. In an embodiment of the invention the sieve is introduced into the trays of a fractionating tower wherein a lubricating oil fraction is being distilled and the wax subsequently removed from the tower by desorbtion. Molecular sieves.-The sieves may be prepared by replacing Na by Ca in natural zeolites, e.g. NaAlSi2O6.H2O --> CaAl2Si4O12.2H2O; 4CaO.Al2O3.4SiO2 can be obtained in similar manner. The sieves may also be completely synthesized by mixing a sodium silicate with sodium aluminate to give a sodium aluminosilicate which is then base-exchanged with a metal ion such as calcium. The sodium silicate should have a Na2O/SiO2 ratio of at least 0.8/1 and the aluminate a Na2O/Al2O3 ratio of 0.8/1 to 3/1 . The aluminate is added to the silicate at room temperature, stirred to give a homogeneous paste, heated to 180-215 DEG F. for 0.5 to 3 hours at a pH above 12, washed, added to a solution of a calcium salt for 5 minutes to 1 hour (to exchange at least 65 per cent of the Na for Ca), filtered, washed and calcined at 700 DEG to 900 DEG F. In an example this method is used to synthesize a 4 A DEG sieve Na2O.Al2O3.2SiO2 which is converted to a 5 A DEG sieve by replacement of 70 per cent of the Na by Ca. The sieves may be regenerated by air or steam desorption at up to 1000 DEG F. (optionally at reduced pressure), or stripping with an inert gas, e.g. N, CH4, CO2, NH3 or refinery gas streams preferably containing olefines, e.g. ethylene, propylene, or butylenes.