Photodecomposition kinetics of formic acid in aqueous solution

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Abstract
The photodecomposition of aqueous solutions of formic acid was studied as a model reaction for removing organic pollutants from water. The process was carried out in a tubular‐flow reactor, operated continuously. The cylindrical reactor was irradiated from the outside by placing the cylindrical lamp and the reactor at the foci of an elliptical reflector. Measurements made at differential operating conditions permitted calculation of rates of reaction as a function of formic acid concentration and light intensity for the temperature range 25° to 60°C. Carbon dioxide and carbon monoxide were the only observed products of the decomposition.The rate was first order in absorbed light intensity and between zero and first order in formic acid. These results correspond to a combination of chain and non‐chain kinetics occurring simultaneously. Rate constant ratios and quantum yields were calculated from the data and the kinetics model.A few measurements were made by adding ferric chloride and ferrous chloride to the feed to the reactor. An order of magnitude increase in rate was observed with these sensitizers.