Dual-Bed Catalytic System for Direct Conversion of Methane to Liquid Hydrocarbons

摘要

A dual-bed catalytic system is proposed for the direct conversion of methane to liquid hydrocarbons. In this system, methane is converted in the first stage to oxidative coupling of methane (OCM) products by selective catalytic oxidation with oxygen over La-supported MgO catalyst. The second bed, comprising of the HZSM-5 zeolite catalyst, is used for the oligomerization of OCM light hydrocarbon products to liquid hydrocarbons. The effects of temperature (650-800℃), methane to oxygen ratio (4-10), and SiO_2/Al_2O_3 ratio of the HZSM-5 zeolite catalyst on the process are studied. At higher reaction temperatures, there is considerable dealumination of HZSM-5, and thus its catalytic performance is reduced. The acidity of HZSM-5 in the second bed is responsible for the oligomerization reaction that leads to the formation of liquid hydrocarbons. The activities of the oligomerization sites were unequivocally affected by the SiO_2/Al_2O_3 ratio. The relation between the acidity and the activity of HZSM-5 is studied by means of TPD-NH_3 techniques. The rise in oxygen concentration is not beneficial for the C_(5+) selectivity, where the combustion reaction of intermediate hydrocarbon products that leads to the formation of carbon oxide (CO+CO_2) products is more dominant than the oligomerization reaction. The dual-bed catalytic system is highly potential for directly converting methane to liquid fuels.