Nitrogen oxides and sulphur dioxide removal from waste gas - with by prodn. of sulphur and sulphuric acid

摘要

Process comprises (a) contacting, at 300-350 degrees F, the gas with a first oxidation catalyst (I) at a GHSV of 500-10000 to convert all the nitrogen oxides to NO2 and part of the SO2 to SO3, (b) admixing the stream with 70-90 wt % aq. H2SO4 to form nitrosyl sulphuric acid by adsorption of the NO2, (c) sepg. the acid phase (A) and unabsorbed gas (B) contg. SO2 (d) heating (A) at 300-500 degrees F to remove N oxides, SO2 and water as overhead to obtain a sulphuric acid of higher concn. and recycling (part of) it to step, (b), (e) combining the overhead of step (d) with (B), and (f) treating the mixt. with a second oxidn. catalyst (II) at a GHSV of 500-10000 to yield N2, CO2 and S, the latter being separated as a product. Used esp. in treating the stack gases from utility plant facilities attached to e.g. petroleum refinery complexes (where significant volumes of CO are also produced in fluid catalytic cracker regenerators), and smelting plants. Marketable amts. of sulphur and sulphuric acid of sufficient purity to be reusable are obtd. Pref. (I) is V2O5 or an oxide of copper, and (II) is in oxide of copper, opt. in a complex with copper chromite, both (I) and (II) being supported on Al2O3.