Activity of catalyst coatings in reactors for waste gas purification

Abstract

The coating must have high mechanical and thermal strength, ensuring its integrity in installation of the reactor and during service. The components of the catalyst coating must be readily available; and the technology of preparing the compositions, applying them to the support plates, drying, and calcining must be relatively simple~ The activity of the catalyst coating must be sufficient to ensure total, exhaustive oxidation of the organic purities in the waste gas. The results obtained in previous studies provide a basis for recommending as the catalyst coatings a mixture of a catalyst, a binder ("talum" cement [a mixture of calcium monoand dialuminates]), and an adhesive (a solution of polymethylphenylsiloxane resin in toluene, similar in composition to KO-08 varnish) [4, 5]. The macromolecular polymethylphenylsiloxane resins used in the adhesive form an elastic network when the coating is dried and baked, compensating the deformation of the catalyst coating when the metal support plates are deformed through mechanical or thermal action. It is also possible that the adhesive interacts chemically with the oxide catalysts during baking and in the course of service of the coating [6]. In order to determine the specific factors influencing the catalytic activity of the coating and interchangeability of the catalyst componentp most of the coatings we have tested have consisted of one part of commercial catalyst, one part of cement of the "talum" type (technical calcium aluminate), and two parts of KO-08 varnish. As the catalyst component we used a crushed platinized aluminum catalyst AP-64, a batch of copper--chromium-berium oxide catalyst GIPKh-105-B, or a crushed iron--chromium oxide catalyst STK-I-7. In a number of experiments, we used as the catalyst coating a 1:4 mixture of the STK-I-7 catalyst and the cement GIPK-12R-10* as the adhesive -- a material with a higher thermal stability. The catalyst coatings ~ere applied to a metal module shaped as a six-sided prism with three internal baffles along diagonals of the prism (prism height i00 mm, length of side 30 mm, equivalent diameter 10.8 mm). Coatings with a thickness of 0.1-0.2 mm were applied to both sides of the elements of the module; the total surface area of the coating on the module was 752 cm 2. After drying and baking at 300=C for 2-3 h, the modules with the catalyst coating were tested in an integral laboratory reactor in purifying a model vapoz'-air mixture (V~O. As the organic component of the VA}I we used isopropylbenzene and paraffinic hydrocarbons (liquid and n-paraffins, 210-370~ cut), this mixture modeling the products contained, in particular, in gas from the regeneration of adsorbent used in purifying liquid paraffins. The catalytic activity of the catalyst coatings was investigated over a temperature range of 185-500~ V~M flow rate i-I0 liters/min, and concentration of organic substances in mixture 0.5-5 g/m 3. The completeness of oxidation of the organic substances in the reactor was rated by the barite method~ The reaction rate constant k (sec -~) was determined from the degree of purification x of the model mixture