Recycling H2SO4 and Dimethyl Isopropylamine from an Acid Scrubber

Alkaline or acid scrubbers are often used to remove components that are harmful to the environment, such as NOx, SO2 or certain amines from waste air streams. In these processes large amounts of acids or bases are consumed and salts are produced. In general, only dilute acids and bases are required in scrubbers. This makes the use of electrodialytic water dissociation with bipolar membranes a very suitable process to recover the acids or bases from the corresponding salts. The recovery of base from scrubbers used to remove SO2 and NO, from coal-burning power plants is described in detail in the literature.

Another similar application is the recovery of dimethylisopropylamine removed from a waste air stream by a sulfuric acid scrubber. This type of waste air stream is generated when aluminium casting moulds are made from a sand/epoxy resin mixture by injecting dimethylisopropylamine in a mixture with air as catalyst to cure the resin instantaneously. The amine is not consumed in the process and is emitted in a waste air stream containing ca. 0.5 g amine per m3 waste air. The amine can be recovered as amine sulfate in an acid scrubber, as indicated in Figure 5. The amine can then be regenerated by adding sodium hydroxide and distilled. The net result of the process, however, is the production of large amounts of sodium sulfate.

A complete recycling of the amine, the sulfuric acid and water is achieved without the production of a salt by combining the electrodialytic water dissociation with distillation. The process is illustrated in Figure 6. The waste air stream containing the amines is fed into an acid scrubber where the free amine is converted into amine sulfate. The effluent of the acid scrubber containing about 10% amine sulfate in a mixture with sulfuric acid is then fed into the electrodialytic water dissociation apparatus

Acid Scrubber Flow Chart
Figure 5 Schematic diagram illustrating a conventional process for recovering an amine from a contaminated air stream using an acid scrubber.
Figure 6 Schematic diagram illustrating the recovery of dimethylisopropyl amine from a waste air stream by combination of acid scrubber, diffusion dialysis and electrodialytic water dissociation using bipolar membranes and distillation.

containing bipolar membranes and anion and cation exchange membranes in alternating series between two electrodes. Here the amine sulfate is converted to the free amine while the sulfate ions form sulfuric acid which is recycled to the acid scrubber. The amine-water mixture is distilled to recover the amine and the water is recycled to the electrodialysis unit. Thus, the process allows complete recovery of the amine from a waste air stream by combination of an acid scrubber and electrodialytic water dissociation.

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