The Removal of Aldehydes from Diesel Exhaust Gas

Abstract

Abstract This report presents the results of studies (a) to determine the relation between aldehyde content of Diesel-exhaust gas and the odorous and irritating properties of that gas; (b) to determine the effectiveness of different scrubbing media for removing aldehydes from Diesel-exhaust gas. Observations on the odor and irritation produced by Diesel exhaust gas have shown that both of these properties can be correlated with the concentration of aldehydes in the exhaust gas. The threshold concentration for perception of odor is approximately 0.2 to 0.3 ppm of aldehydes (expressed as equivalent formaldehyde). The threshold of nasal and eye irritation occurs at about 1 ppm of aldehydes (expressed as equivalent formaldehyde). A series of full-scale tests on the removal of aldehydes by scrubbing with water showed that, as the concentration of aldehydes in the scrubbing solution increases, the percentage removal of aldehydes decreases. At elevated temperatures, the removal was nil, and under no conditions was complete removal obtained. From a series of laboratory tests, it appeared that aqueous solution of sodium sulphite might be used in removing aldehydes from Diesel exhaust gas if hydroquinone was added to inhibit the oxidation of sodium sulphite. A full-scale test showed that an aqueous scrubbing solution, containing 10 per cent sodium sulphite by weight and 0.5 per cent hydroquinone, removed substantially all aldehydes for a period of 7 hr, and 90 per cent or more of the aldehydes for a period of 15 hr. In this test approximately 3000 cu ft of dry exhaust gas (at 60 F and 29.92 in. Hg) was scrubbed per hour at a scrubbing temperature of 133 F. Estimates of the cost of scrubbing Diesel exhaust gas indicate that the cost of materials would be approximately 80 cents for an engine operating continuously for 8 hr and producing an average of 5000 cu ft of dry exhaust gas (at 60 F and 29.92 in. of Hg) per hour.