Dimethyl ether conversion to light olefins in slurry and fixed‐bed reactors: coke nature and location on Mg/ZSM‐5 catalyst

Abstract

BACKGROUND The goal of this study was to investigate the deactivation of ZSM‐5 in the DTO process (dimethyl ether to light olefins) in a slurry reactor (SLR) in polydimethylsiloxane dispersion medium compared with its deactivation in a fixed‐bed reactor (FBR), and to unveil reasons behind the rapid deactivation of the catalyst in the SLR. RESULTS Under suspension conditions coke formation proceeds more slowly compared with fixed‐bed conditions: The amount of coke formed under suspension conditions is less than under fixed‐bed conditions, 1.4 mg versus 1.7 mg, respectively. Also, in terms of the chemical composition the coke is lighter (xylenes and trimethylbenzenes versus С4,5,6‐substituted benzenes). Using thermogravimetric analysis and gas chromatography/mass spectrometry pyrolytic system, it was shown that the decomposition products of the dispersion medium contribute to the blocking of micropores and the rapid deactivation of the catalyst in SLR. The localization of coke in both SLR and FBR occurs primarily in the microporous channels of the zeolite (>60%). In SLR, the weight fraction of coke on the external catalyst surface was 11% higher than that on the FBR. This finding can be attributed to the blocking of micropores by decomposition products of the dispersion medium. CONCLUSION Under suspension conditions, сoke formation in the DTO process proceeds more slowly compared with fixed‐bed conditions. The rapid loss of catalyst activity in the SLR was related not to coke formation, but instead to the blocking of catalyst pores by products of thermal decomposition of the dispersion medium. For the same reason, in SLR the weight fraction of coke on the external surface of the catalyst was higher than that in the FBR. © 2021 Society of Chemical Industry (SCI).

Organo-metallic electrolyte additive for regulating hydrogen evolution and self-discharge in Mg–air aqueous battery

“…These observations validate the presence of the inorganic-organic hybrid structure of D3. 48,49 Fig. 3(c) (XPS) shows the steady Si 2p peak of Si-O-Si at a binding energy of 105.5 eV, followed by 283.7 eV, indicating the C1s peak of C-Si (Fig.…”

A Review on Deactivation and Regeneration of Catalysts for Dimethyl Ether Synthesis

“…In addition, mass loss at temperatures from 200 to 500 • C is caused by the removal of amorphous carbon through the oxidation of CO to CO 2 , while fibrous and graphitic carbons undergo gasification at higher temperatures [75]. T. K. Obukhova et al [76] carried out tests in a tubular-bore reactor (FBR) and in a slurry suspension reactor (SLR) using the Mg/ZSM-5 catalyst. The TGA tests showed that, at a temperature of about 100 degrees, water desorption and the degassing of weakly bound hydrocarbon-derived impurities take place in the pores of the catalyst.…”

“…Another issue that needs to be addressed is the implementation of temperature control and cooling systems due to the exothermic nature of the DME synthesis reaction. Conducting the DME synthesis at temperatures above 300 • C leads to the deactivation of the metal catalyst through the deposition of coke on the walls of the reactor [76,[86][87][88].…”

“…In both slurry reactors and fixed-bed reactors, the localisation of coke occurs primarily in the microporous channels of the zeolite (>60%). In the synthesis of dimethyl ether in slurry reactors, the catalyst activity is related to the blocking of the catalysts' pores by products originating from the thermal decomposition of the dispersion medium [76]. An important aspect is the selection of an appropriate catalyst for the reactions taking place.…”