Synthesis of liquefied petroleum gas via methanol and/or dimethyl ether from natural gas (Part 3) investigation of reaction variables, ethene recycling and catalyst regeneration at high conversion from methanol and/or dimethyl ether to LPG

Conversion of methanol and/or dimethyl ether into LPG, previously proposed as a potential route for fuel synthesis from natural gas, was evaluated over H-ZSM-5 and H-FeAlMFI-silicate catalysts to optimize LPG fractional selectivity at high conversion, to simulate C-2 recycling by co-feed conversion of ethene with oxygenates, and to assess deactivation and regeneration. Selectivity for the desired product depended not only on catalyst performance but also on reaction conditions. The effect of feedstock partial pressure on product distribution could be explained by the concentrations of the active olefin intermediates. Ethene was selectively converted into the LPG fraction by co-feed reaction with oxygenates over H-ZSM-5 catalyst. The large scale process yield of LPG could be increased by recycling C-2 components according to the available recycling ratio. However, H-FeAlMFI-silicate catalyst was effective for one-pass conversion but not for recycled ethene conversion. The two catalysts deactivated during one-pass conversion could be regenerated well by a moderate carbon combustion process. Good reproducibility of fractional selectivity was achieved by the regenerated catalyst. H-FeAlMFl-silicate catalyst suffered relatively little deactivation compared with H-ZSM-5 catalyst, and showed high resistance to deactivation after ageing. The improvement in stability of H-FeAlMFI-silicate catalyst may originate from the elimination of some strong acid sites via the ageing process. H-FeAlMFI-silicate catalyst was superior to H-ZSM-5 catalyst except for recycled ethene conversion.