Catalytic methane halogenation by bromine over microporous SAPO-34 zeolite material towards methyl bromide, dibromomethane and hydrogen bromide

Abstract

Background:Bromination-based methane conversion is one of the promising separate ways of CH4 valorisation. Both methyl bromide/dibromomethane that are formed can be subsequently transformed into more useful compounds. SAPO-34 could also improve the selectivity (S) towards bromomethane during bromination.Methods:To evaluate the performance of SAPO-34 in this reaction process, the influence of time, temperature (T) and weight hourly space velocity (WHSV) rate was investigated in a packed-bed reactor. T was in the range of 310–420 ∘C, while WHSV was 0.22–1.20 h−1. The molar CH4 to bromine ratio was 5.4:1. GC–MS was used for analysis of products. Material was characterized by XRD, SEM, NH3-TPD, N2 physisorption.Significant findings:In the material used for the reaction crystallinity was decreased, solid surface area was reduced, and the density of Brønsted acid sites was also reduced compared to the fresh material. Changes can be attributed to Al2O3 loss or also the breakage of Al–O–P bonds, caused by hydrogen bromide ions that are produced. A presence of coke was observed on the zeolite at T higher than 360 ∘C. CH2Br2 decomposes, while CH3Br is released in intermediate gas phase. Catalytic yield increase compared to homogeneous one was not notable, which indicates on the prevalence of elementary radical mechanism. The highest S for CH3Br was around 90% at 310 ∘C with the WHSV of 1.20 h−1.