Novel Natural Gas to Liquids Processes: Process Synthesis and Global Optimization Strategies

An optimization-based process synthesis framework is proposed for the conversion of natural gas to liquid transportation fuels. Natural gas conversion technologies including steam reforming, autothermal reforming, partial oxidation to methanol, and oxidative coupling to olefins are compared to determine the most economic processing pathway. Hydrocarbons are produced from Fischer-Tropsch (FT) conversion of syngas, ZSM-5 catalytic conversion of methanol, or direct natural gas conversion. Multiple FT units with different temperatures, catalyst types, and hydrocarbon effluent compositions are investigated. Gasoline, diesel, and kerosene are generated through upgrading units involving carbon-number fractionation or ZSM-5 catalytic conversion. A powerful deterministic global optimization method is introduced to solve the mixed-integer nonlinear optimization model that includes simultaneous heat, power, and water integration. Twenty-four case studies are analyzed to determine the effect of refinery capacity, liquid fuel composition, and natural gas conversion technology on the overall system cost, the process material/energy balances, and the life cycle greenhouse gas emissions. (C) 2013 American Institute of Chemical Engineers AIChE J, 59: 505-531, 2013