PROJECT DESCRIPTION
BACKGROUND
Adipic acid manufactured by nitric acid oxidation of cyclohexanol-cyclohexanone results in the production of a gaseous by-product nitrous oxide (N20). This gas is known for its contribution to greenhouse effect and is suspected of increasing the depletion rate of the stratospheric ozone layer. Nitrous oxide is an endothermic compound which can be thermally converted to nitrogen, oxygen and some nitric oxide, depending on the reactions conditions and catalysts. Rhône-Poulenc together with other important Adipic acid producers have decided to substantially decrease their nitrous oxide emissions by 1998. Rhône-Poulenc, after laboratory scale experiments on synthetic mixtures, proposed to study an innovative thermal conversion process which is intended to promote nitrous oxide conversion to nitric oxide. The nitric oxide formed can be recovered as nitric acid by conventionnal technologies and recycled to Adipic acid production. The project aimed to test an innovative thermal converter on industrial gaseous effluents in order to establish its industrial feasibility and to optimize conditions for complete nitrous oxide destruction together with maximum nitric oxide yield. The new process involves preheating the effluent gas to about 700° C before sending it in a natural gas burner where it is heated to ca. 900 - 1200° C in a very short time. The gas then enters a plug flow type reactor where N20 is converted into nitric oxide, nitrogen and oxygen in an exothermic reaction raising the temperature to more than 1400° C. The reaction is then quenched to temperatures lower than 1000 ° C in order to preserve the NO formed from thermal destruction. The pilot plant was equiped with an analytical cabin which carried out a continuous analysis of incoming and outcoming gases. The influence of several parameters of the reaction on yield was studied : residence times in the burner and plug flow reactor, activation temperature and nitrous oxide concentration. The quench of the reaction mixture to 850° C was operated mainly with air but it was also demonstrated that quench with steam or water was possible without adverse effect on yield. Following this work, an industrial plant underwent construction in Alsachimie (Chalampé-France).