Natural gas to synthesis gas – Catalysts and catalytic processes

Abstract

Natural gas is a dominating feedstock for the production of several bulk chemicals such as ammonia, methanol, and dimethyl ether (DME), and for the increasingly important production of synthetic liquid fuels by Fischer–Tropsch synthesis (FT synthesis) and similar processes. A major step in the conversion of natural gas to products is the production of synthesis gas with the desired composition – ranging from the 3:1 mixture of hydrogen and nitrogen used for production of ammonia to the 1:1 mixture of hydrogen and carbon monoxide preferred for production of DME. Catalysts and catalytic processes are important in the production of synthesis gas from natural gas. As an example, production of ammonia synthesis gas may in modern plants involve up to 8 separate catalytic process steps. In the article, relevant catalytic technologies are reviewed with emphasis on the present status and possible future developments. The relevant technologies are: • Final feed gas purification • Adiabatic prereforming • Fired tubular reforming • Heat exchange steam reforming • Adiabatic, oxidative reforming, mainly autothermal reforming (ATR) and secondary reforming • Other reforming technologies such as Catalytic Partial Oxidation (CPO) and Ceramic Membrane Reforming (CMR). • Conversion of carbon monoxide to carbon dioxide by the shift reaction • Final purification of synthesis gas, mainly removal of nitrogen compounds and removal of carbon oxides by methanation. After the discussion of the individual catalysts and catalytic process steps, applications are illustrated by summary descriptions of complete process concepts for production of ammonia, methanol, and hydrocarbons by low temperature FT synthesis (GTL). In a final section, future trends in the area are briefly discussed.