A process is developed for removing the small micron-sized ash and unconverted coal material from a liquefied Emery coal. The separation is effected through constant pressure filtration using cellulose fiber filter aid as precoat. Depending upon the process and the application, the solids must be removed to avoid high sulfur concentrations in the coal-derived liquid, to minimize erosion and corrosion of equipment, and to prevent fouling and poisoning of catalysts in downstream processing, or sludge formation in storage or transportation. A fractional factorial experiment is developed for four variables and used to determine the best combination for removing the unliquefied coal and mineral matter from the liquid product. Some further tests are performed to explore the trends shown by the fractional factorial and find approximately optimum conditions for the filtration. This optimum is shown to be of interest when compared with other separation studies on an economic basis.
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