Conversion of natural gas to transportation fuels via the shell middle distillate synthesis process (SMDS)

Abstract For several decades Shell's research has been involved in syngas chemistry, with special focus on routes to convert natural gas into easily transportable liquid hydrocarbons. This effort has resulted in the development of the SMDS process, for which the first commercial plant is being constructed in Sarawak, Malaysia. The heart of SMDS is an enhanced Fischer-Tropsch synthesis. Fundamentals of the Fischer-Tropsch synthesis are reviewed. The relation between catalyst characteristics and choice of the synthesis reactor is discussed. In the case of fluid-bed technology, the type of reactor places a clear limitation on product carbon numbers. For fixed and ebulliating beds diffusion limitations within the catalyst particles are quantified, while extra-particle mass-transfer limitations can be observed in slurry reactors. Cracking of Fischer-Tropsch waxes follows the synthesis step in the SMDS process. The control of the chain-length distribution in the selective hydrocracking step is elaborated. It is this combination of synthesis and hydrocracking that forms the basis of the SMDS process. The concept of the process is explained with emphasis on process integration, product quality and environmental aspects.