Process for absorbing toxic gas

#This invention relates to solid sorbent materials ("acceptors") for use in removing ("accepting") sulfur oxides, nitrogen oxides (NO.sub.x), hydrogen halides and/or other noxious components (e.g. hydrogen sulfide, carbonyl sulfide, sulfur trioxide, etc.) from a gas, particularly a waste gas stream, and to improvements in process for making, using and regenerating the acceptors. Of these contaminants the ones specially targetted here are SO.sub.2 and NO.sub.x (typified by NO.sub.2) as they as the most common and usually most difficult to remove virtually completely amongst those above specified.

#Flue or vent gases from the combustion of fuels such as coal or residual oil, the pyrolysis of solid waste, and the venting of chemical processes has been a matter of increasing concern for many years. Components such as sulfur dioxide and nitrogen oxides (NO.sub.x) are accused of fostering acid rain, having toxic effect on human, lower animal and plant life, and being generally dangerous or obnoxious even in quite low concentrations.

#As a result, many approaches have been proposed to cleanse the waste gases of their toxic components. Scrubbing with a compound in slurry form with water has been by far the most popular approach. Wet scrubbing systems, although effective in removing toxic gases, have been very expensive and highly corrosive and have often simply converted an air-pollution problem into a sludge-disposal or water-pollution problem. Even with wet scrubbing processes involving reactants that are regenerable, thus producing no waste sludge, problems have occurred. In the magnesium oxide wet scrubbing process, for example, major technical difficulties have been encountered in handling the corrosive liquid slurries, and large energy costs have been incurred in drying the slurries and in regenerating the magnesium oxide.

#Two 20-gram quantities of acceptor (MgO coated onto exfoliated vermiculite) were conditioned by heating each at 550.degree. C. for 30 minutes, then cooled and moistened. Two other like batches simply were air dried for 2 hours. All were tested with a gas stream flowing at two liters per minute and containing 931 ppm of NO.sub.2, 210 ppm of NO, and the balance nitrogen. The NO.sub.2 removal even after two hours was extremely high for the conditioned acceptors and essentially zero for the unconditioned ones. About half of the NO was removed by the conditioned acceptors while significantly less NO was removed by the unconditioned ones.

#The tests are summarized below; they demonstrate that conditioning definitely improves sorptive performance of the acceptor.

#TABLE I ______________________________________ NO.sub.2 Removal Efficiency, Percent After After After Acceptor 2 min. 10 min. 120 min. ______________________________________ Unconditioned #1 67.8 46.3 0 Unconditioned #2 66.7 35.6 0 Conditioned #1 100.0 97.3 87.1 Conditioned #2 100.0 97.9 87.1 ______________________________________