On the Reaction Mechanism for Hydrocarbon Formation from Methanol over SAPO-34 2. Isotopic Labeling Studies of the Co-reaction of Propene and Methanol

13C-Methanol and 12C ethene (fed as ethanol) have been co-reacted over SAPO-34 in a flow system at 400°C using argon as a carrier (diluent) gas. The feed contained an equal number of 13C and 12C atoms. The products were analyzed by GC-MS, allowing the determination of the isotopic composition of the reactor effluent. The ethanol was immediately converted to ethene, so the reaction system was equivalent to a feed consisting of methanol/ethene/water. While the methanol was completely or almost completely converted to hydrocarbons, the larger part of the ethene emerged unreacted. The products propene and butenes were mostly formed from methanol and contained a large excess of 13C atoms. The ethene effluent consisted mainly of all 12C or all 13C atoms, and only to a small extent of 12C-13C molecules. The reaction system was followed from an initially very active catalyst until the catalyst was sufficiently deactivated that C1 was not completely converted to hydrocarbons. The tendency for ethene to emerge unreacted, and for all new hydrocarbons to be formed from methanol became more pronounced with progressing catalyst deactivation. The results show clearly that the higher hydrocarbons are, over this catalyst, not formed by successive methylations of ethene. A previously proposed "carbon pool" mechanism can explain the gross effects seen in the product and isotopic distribution.