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We use the configuration of film boiling on a horizontal tube positioned in a stagnant pool of saturated diethyl carbonate (DEC, (C2H5O)2CO) to study DEC decomposition at temperatures up to 1500 K. The composition of bubbles that percolate through the liquid pool is measured and the results are used to infer the decomposition reactions. The results show that below tube temperatures of about 1100 K, the decomposition products are ethylene (C2H4), carbon dioxide (CO2), and ethanol (EtOH, C2H5OH) with a molar ratio nC2H4/nCO2∼1, which is consistent with a first-order decomposition process. At higher temperatures, nC2H4/nCO2 > 1 which is explained by an additional route to forming C2H4 from radicals in the system (created by EtOH decomposition) attacking DEC. The presence of H2, CO, CH4, and C2H6 in the product stream was noted at all temperatures examined with concentrations that increased from trace values at low temperatures to values comparable to the DEC unimolecular process at the highest temperatures. Formation of a carbon layer on the tube was observed but did not appear to influence the decomposition process. A scale analysis shows that the rate constant controls decomposition compared to the residence time, which has a weaker dependence on temperature.

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This paper presents a new approach for promoting thermal decomposition reaction of subcooled liquids. It is based on establishing film boiling of the liquid. The process is illustrated by converting aqueous glycerine to synthesis gas (a mixture of carbon monoxide and hydrogen) and methane. A horizontal tube is immersed into a pool of aqueous glycerine (water weight fractions of 3% and 10%) and film boiling is established on the tube. Because of the large temperature drop that occurs across the vapor film that surrounds the tube, the potential exists to drive pyrolytic or thermal cracking reactions at high temperature but in a comparatively cold bulk liquid. The reaction products are transported away from the tube under the action of buoyancy. The reactor volume essentially forms by itself solely as a result of heating the tube.