Vliv kovových katalyzátorů na syntézu aminů ve vícefázových reaktorech

Abstract

The heterogeneous catalytic reactions of special amine preparations in trickle bed reactors were tested. The continual reactors are situated in Borsodchem MCHZ in Ostrava. The three-phase system (gas-liquid-solid) is a basic principle of studied procedures when a reaction mixture is liquid sprinkling over a solid catalytic bed. Hydrogen as a reducing gas ensemble with the reaction mixture has the same direction as liquid (downflow). A chemical technologist must solve lots of problems associated with scale-up of trickle bed reactors. Transfer of laboratory results to the production equipment is very difficult because the laboratory reactor is characterized by very short and narrow catalytic bed. Therefore, the hydrodynamic conditions of liquid flow over the catalytic bed and obtained conversions and selectivities of studied reactions in laboratory reactors are quite different from production reactors. Nevertheless the reaction parameters are comparable in both reactor scales. The development of new technologies and optimalization of established processes must often be realized in a pilot plant, but these experiments are very time and financially demanding. Thus, it is always desirable to find the way how to avoid pilot plant experiments. The thesis shows differences among the performance of several BC MCHZ reactors and selectivities of tested reactions. It also tries to explain and propose such steps, so as it would be possible to transfer the laboratory results directly from the laboratory to production line. For these purposes, two reaction types were chosen, the first one was the preparation of N-ethylaniline (MEA) and N,N-diethylaniline (DEA) by hydrogenation alkylation of aniline using ethanol over copper catalyst and the second one was the synthesis of N,N-dimethylcyclohexylamine (DMCHA) by hydrogenation methylation of cyclohexylamine using formaldehyde over nickel catalysts. Conversions of reactions decreased with shortening the catalytic bed length in both reactions, whereas pilot plant already provided the similar yield of products as the production equipment. It was caused mainly by different sprinkling efficiency of catalyst  (for example the value reached 90 % in production reactor in contrast with 15 % in laboratory reactor during the preparation of DMCHA), and by high ratio of wall flow and axial dispersion of the reaction mixture in small laboratory reactor. The sprinkling efficiency of catalytic bed is very closely connected with flow rate of liquid phase over the bed and with external mass transfer between catalyst surface and flowing reaction mixture. The partial improvement of efficiency of laboratory reactor R01 was achieved by using tablets of nickel catalyst with smaller particle size dp (reduction of the value dp from 5.78 mm up to 3.25 mm). This caused decrease in catalyst bed porosity and limitation of axial dispersion. Another improvement was noted when the centric temperature tube was excluded from laboratory reactor (R01), probably it enabled better embedding of catalyst tablets inside the reactor R01 and to minimize dead space there. It supports the fact that the reactor R01 approached adiabatic regime. The dilution of catalytic bed by fine inert material (SiC) presented the most significant increase of laboratory reactor performance, wherewith the smaller particle size of inert and catalyst was used, the better results were obtained. Considering the fact that the hydrogenation methylation of cyclohexylamine by formaldehyde has exothermic character, the temperature influences up to conversion and selectivity of studied reactions were monitored very rigorously in all experiments when the catalytic bed was modified because of rising reaction heat and heat losses outside the reactor R01 which are various.