Recovery of zinc chloride catalyst from coal hydrogenation char

In the catalytic liquefaction of coal using zinc chloride, the recovery of the various spent zinc products is a prime requirement if the process is to be economically feasible. After hydrogenation, depending on the extent of coal conversion to liquid and gaseous products, about one third of the applied zinc is found with the liquids and two thirds remain with the char. The zinc associated with the liquid product is readily recovered with a water wash. The zinc associated with the char can be recovered by means of water and hydrochloric acid leaches to the extent of 70% of that present. The remaining char associated zinc (15–20% of that originally applied to the coal) is incorporated within the organic matrix of the char. A room temperature concentrated nitric acid leach is required to liberate the remaining zinc from the char. Ultimate recoveries of 98.5–99.7% are possible with the combined water, hydrochloric acid and nitric acid leach sequence.