FLUIDIZED COMBUSTION PROCESS FOR REGENERATION OF SPENT ZINC CHLORIDE CATALYSTS

Spent melts from the hydrocracking of coal extract with molten ZnCl2 catalyst have been regenerated in a continuous bench-scale unit by combustion with air in a fluidized bed of inert solids. The combustion process removes the C, N, and S impurities from the melt and simultaneously vaporizes the zinc chloride. Carbon is removed as a mixture of CO and CO2, and sulfur as SO2. Ammonia is decomposed to N2 and H2 at low air inputs and burned to N2 and H2O at higher air inputs. Recondensed ZnCl2 is in regenerated form suitable for recycle to hydrocracking. Fluidizing velocities of 0.16 to 2.67 feet per second, pressures from 15 to 46 p.s.i.a., superficial vapor residence times from 0.4 to 6.3 seconds, and temperatures from 1800° to 1900° F., have been investigated. The process was operable under all conditions studied. No difficulty due to agglomeration in the fluidized solids bed was encountered. Feed rates of spent melt up to 347 pounds per hour per square foot have been demonstrated. Two operating regimes of potential commercial interest have been found. The first utilizes a relatively low-carbon melt and near stoichiometric air input. By fine adjustment of the air input sufficient CO can be generated to permit subsequent reduction of the SO2 in the off-gas to elementary sulfur. The second handles a relatively high-carbon melt and uses a deficiency of air (35 to 60% of the stoichiometric). A low-sulfur fuel gas is produced, while the sulfur is retained in the bed as ZnS. The ZnS may be oxidized to ZnO and SO2 in a secondary oxidation treatment. © 1969, American Chemical Society. All rights reserved.