PECULIARITIES OF SMALL STRAINED ALICYCLE COMPOUNDS FORMATION IN CATALYTIC TRANSFORMATION OF METHANOL OVER ZEOLITE H-ZSM-5

Abstract

The article presents the results of strained hydrocarbons formation study during the catalytic transformation of methanol into hydrocarbons on zeolite H-ZSM-5. The formation of the following strained cyclic compounds was determined: 1,1-dimethylcyclopropane, 1,2-dimethyl-cyclopropane, 1,1,2-trimethylcyclopropane, 1,2,3-trimethylcyclopropane, 1,1,2,2-tetramethylcyclo-propane, 1,1,2 , 3-tetramethylcyclopropane. The non-stationary character of strained cyclic hydrocarbons formation with a pronounced hydrocarbons formation rate maximum and subsequent deactivation of the catalyst was found. The temperature effect on strained hydrocarbons yield was evaluated. Thus, with an increase in the process reaction temperature up to 400 °C, a maximum of strained hydrocarbons accumulation rate was achieved as 8-8.5 g(Hyd)/(kg(Cat)·h) on 350 h of reaction, and a further increase in the reaction temperature leads to a decrease in the strained hydrocarbons accumulation rate. The effect of the methanol feed rate on the strained hydrocarbons formation rate was also studied. An increase in the methanol feed rate from 0.02 ml/min to 0.16 ml/min results in increase in the strained hydrocarbons formation rate up to 37 g (Hyd)/(kg(Cat)·h). The article presents results of H-ZSM-5 physicochemical study used by ammonia chemisorption, nitrogen phisisorption, X-ray photoelectron spectroscopy. Physicochemical studies of catalyst samples after the methanol transformation process to form strained hydrocarbons showed a twofold decrease in the number of acid sites from 1.2 mmol(NH3)/g (sample) to 0.3 mmol (NH3)/g(sample) and a significant decrease in surface area of micropores from 294 m2/g for the initial sample to 16 m2/g for the sample after the reaction. The X-ray diffraction spectroscopy method showed that the composition of the catalysts H-ZSM-5 surface includes carbon, oxygen, silicon and aluminum. Carbon concentration was found to be 4.3 at.% on the surface of the initial catalyst. While the carbon concentration increases up to 14.1 at.% during the reaction. Also oxygen content on the catalysts surface decreases from 59.9 to 53.4 at%, silica concentration decreases from 35.5 to 32.1 at.%. The following indicates the formation of a carbon surface layer over the catalysts.