Engine exhaust, formic acid

This paper describes the analysis of formic acid in diesel engine exhaust and mine air using ion chromatography (IC) and ion chromatography exclusion (ICE). 

Collection Method. The goal of the initial phase of our work was to determine the concentration of formic acid in engine exhaust subject to different forms of control, e.g., catalytic oxidation. Initially, samples were collected from diesel engine... 

In a later phase of work, the formic acid concentration in mine air subject to diesel emissions was measured. The expected concentrations were about one hundred times lower than those found in engine exhaust. The efficiency of the collection scheme was again measured under these conditions of challenge concentration (0.06 mg/m3). The collection efficiency was found to be 92.2% at this level (Table IV). 

To determine the fate of formaldehyde and formic acid in a coal mine, an unused shaft about 120 m long and 6 m2 in cross sectional area was selected for study. With a ventilation air flow of 190 m3/min and an engine exhaust flow of 1.5 m3/min, complete exhaust dispersion and dilution was observed in about 10 m. Samples collected in the mine air downstream of the diesel engine indicate no significant change in formic acid concentration at increasing distances from the engine (Table VIII). This is certainly not consistent with the loss of formaldehyde in the same interval. The mechanism for loss of formaldehyde is apparently not a gas phase oxidation to formic acid. Interaction with surfaces may be a more suitable explanation of the observed reduction in formaldehyde concentrations. 

Two ion chromatographic techniques were utilized to quantify formic acid in both diesel engine exhaust and mine air subjected to diesel emissions. A commonly used anion separation system utilizing a weak borate eluent adequately separated the acids of interest in diesel exhaust. It was, however, affected by the presence of strong acids during subsequent consecutive analyses. 

Results of analysis of formic acid in diesel engine exhaust subjected to various forms of post-combustion control, i.e., catalytic oxidation and water conditioning, indicate both a reduction of formic acid due to oxidation in the catalyst and dissolution in the water scrubber. In-mine analysis of formic acid at increasing distances from a source of diesel exhaust indicates that no significant change in concentration occurs. This finding contradicts a hypothesis that formaldehyde concentration decreases with increasing distance due to gas phase oxidation to formic acid. Surface reactions may, however, be important sinks for formaldehyde. 

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