Methanol-to-hydrocarbons reaction over SAPO-34. Molecules confined in the catalyst cavities at short time on stream

In order to obtain more insight into the methanol-to-hydrocarbons (MTH) rea ction the organic molecules confined in a working SAPO-34 catalyst have bee n studied. The reaction was run for varying times, 30 s to 30 min. At a pre determined time the reaction was stopped and the catalyst dissolved in 1 M HCl. The gas phase above the solution as well as a CCl4 extract were analyz ed by gas chromatography (MS detector). The gas phase consists mainly of is oalkanes C4-6. The less volatile organic molecules were concentrated in the CCl4 extract. More than 200 different species are present, but polymethylb enzenes, with one to six methyl groups, are always dominating. They constit ute 30-50% of the samples. Penta- and hexamethylbenzene easily split off sm all hydrocarbons and turn into di- and trimethylbenzenes. it is speculated that methylations of arenes which thereupon split off small alkenes and the n are remethylated again may be an essential part of the catalytic activity in the MTH reaction.