Process for filtering tar

Claim 1

THE PROCESS FOR TREATING HEAVY COAL TAR HYDROCARBONS CONTAINING NATURALLY OCCURRING FINELY DIVIDED PARTICLES SUSPENDED THEREIN, SELECTED FROM THE GROUP CONSISTING OF COAL TARS AND PITCHES DERIVED THEREFROM, CONTAINING AT LEAST ABOUT 1% OF QUINOLINE-INSOLUBLE MATERIAL AND HAVING VISCOSITIES AT TEMPERATURES BETWEEN ABOUT 185* AND ABOUT 500* F. NOT GREATER THAN ABOUT 100 SSU, WHICH COMPRISES PASSING SAID HYDROCARBON AT TEMPERATURES OF THE RANGE BETWEEN ABOUT 175* F. AND ABOUT 500* F. UNDER PRESSURES OF BETWEEN ABOUT 20 P.S.I.G. AND ABOUT 200 P.S.I.G. THROUGH VERTICAL LEAF FILTE SCREENS HAVING OPENINGS NO GREATER THAN ABOUT 162 MICRONS, CONTINUING SAID PASSAGE OF SAID HYDROCARBON THROUGH SAID FILTER SCREENS AT AN AVERAGE FILTRATION RATE BETWEEN ABOUT 0.75 GALLON PER SQUARE FOOT OF FILTER AREA PER HOUR AND ABOUT 2.5 GALLONS PER SQUARE FOOT PER HOUR, UNTIL A SUBSTANTIAL FILTER CAKE HAS ACCUMULATED ON THE OUTER SURFACES OF THE FILTER SCREENS, DISCONTINUING THE FILTRATION BEFORE THE ACTUAL FILTRATION RATE DROPS BELOW ABOUT 0.5 GALLON PER SQUARE FOOT PER HOUR, RECOVERING THE RESULTING CLARIFIED FILTRATE, AND SUBSTANTIALLY IMMEDIATELY AFTER CESSATION