GB614406A - Process for the removal of wax contaminants from finely divided catalysts used in hydrocarbon synthesis processes - Google Patents

Abstract

Heavy hydrocarbons and waxes are removed from finely divided catalysts which have been used in the production of hydrocarbons from hydrogen and carbon monoxide by passing the catalysts in the form of a slurry in counter current flow to a stream of solvent for the contaminants in an extraction zone such a solvent also being used for slurrying the catalyst. The catalysts may be led into one <PICT:0614406/III/1> <PICT:0614406/III/2> end of the extraction zone as a slurry in a body of solvent, a stream of the solvent being led into the other end of the extraction zone from which end a slurry of washed solids is withdrawn. Preferably the solids flow downwardly and the solvent upwardly in the extraction zone. In Fig. III, a slurry of fouled catalyst and a wax solvent in proportions of less than 4 lb. (preferably 2 lb.) catalyst per 1 gallon solvent, enters mixer 302 through line 301. Tubes 305 allow the mixed slurry to flow into tube waste elements 306 up which solvent is flowing, the catalyst particles falling there-through, and the wax-solvent solution rising into zone 308 surrounding mixer 302 and thence via overflowing means 309 into annular space 310 and being withdrawn through pipes 311. Solvent is supplied at the bottom of the vessel through line 307 at such a rate that a slurry of catalyst and solvent may be withdrawn through line 312 and the upward rate of solvent in tubes 306 may be between 0.1 and 1.5 inches per minute. Tubes 306 may contain sloping circular baffles, particularly when the solvent is introduced in surges as by a reciprocating pump or by varying the pressure in the space between tubes 306, the external wall of the vessel, the upper tube sheet, and the level of liquid surrounding the tubes. Fig. II shows a two stage washing process suitable for dewaxing a powdered catalyst used for synthesising hydrocarbons from carbon monoxide and hydrogen. Gaseous synthetic product containing entrained catalyst enters scrubber 103 through line 101 into which a high boiling hydrocarbon oil such as the heaviest portions of the synthetic product or the wax itself (in liquid form) enters through line 104, the gas leaving through line 105. Catalyst-oil slurry is withdrawn from vessel 103, a level being maintained therein by level device 110 acting on valve 109, and enters mixer 112 where it is mixed with a portion of the solvent-wax mixture from washer 140 (see below) the main portion thereof entering the base of washer 115 through line 116. Fresh solvent may, alternatively be used. Solvent-wax mixture passes through pipe 120 to receiver 121, and thence to a fractionating system through pipe 122. Line 174 is used to control the system pressure to a lower value than that of the main synthesis system. Catalyst-solvent slurry is withdrawn from washer 115 through line 128 and passes into scrubbing tower 129 and thence to mixer 141 into which the main portion of fouled catalyst is fed by line 161. Occluded gases rise through scrubbing tower 129 through line 130 and pass through cooler 131 which condenses out any vaporized solvent and returns it through line 133, while the gases pass through pressure controller 163 to the main recovery system. The solvent-wax mixture from washer 140 passes into receiver 167 and is pumped into washer 115 (see above). Fresh solvent enters washer 140 through line 144, and a catalyst-solvent slurry leaves through line 150, is pumped to settler 152, from which slurry containing up to 4 lb. catalyst per gallon solvent is passed to flash coil 156 and thence to cyclones to separate the solvent vapours from the catalyst, which may be brought back to the reactor by the reactant gases. Part of the solvent in settler 152 is recycled to the washer 140 through pipe 154. Alternatively, the catalyst-solvent slurry may be separated by a filter or may be recycled to the reactor. A one-stage modification is also described, in which the catalyst-solvent mixer and washer are separate, and in which the washer consists of one wide tube provided with baffles to prevent stratification. In both modifications, the solvent is preferably a portion of the synthetic product boiling between 250 DEG and 450 DEG F., and is heated before use to between 150 DEG and 300 DEG F. The Specification as open to inspection under Sect. 91 describes the process as being applicable to the removal of soluble contaminants from finely divided solids generally. This subject-matter does not appear in the Specification as accepted.