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SMDS technology is a modern version of the Fisher-Tropsch process which was invented back in 1920s. The SMDS process, however, uses a much more active and selective proprietary Shell catalyst, which enables the technology to be brought to full commercial operations. |
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The SGP Reactor
The HPS Reactor
The HPC Conversion Reactor
SMDS Technology Development
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 In essence, the Shell MDS technology is a three-stage process. In the first stage synthesis gas is obtained by partial oxidation of natural gas with pure oxygen in the Shell Gasification Process (SGP) In the second stage, Heavy Paraffin Synthesis (HPS), the synthesis gas is converted into liquid hydrocarbons. In the third and final stage, the waxy syncrude is fractionated into high-quality products, a part of which is converted into middle distillates by means of the Heavy Paraffin Conversion (HPC). |
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 The Shell Gasification Process was first developed in the 1950s, primarily with the objective of gasifying heavy residues; commercial plants have been in operation since 1956. The reactor is also capable of using natural gas as feedstock. The process is operated at 1300 to 1500°C and pressures up to 70 bar; carbon efficiency is in excess of 95% with a methane slip of about 1%. For the Shell MDS product slate, the SGP gas requires little adjustment of the H2/CO ratio, giving a high overall process efficiency and producing water as the only by-product. |
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 The heart of Shell MDS technology is the Heavy Paraffin Synthesis process. Here, synthesis gas is converted into high-value synthetic paraffins via Fischer-Tropsch (FT) reaction. The history of Fischer-Tropsch (FT) chemistry dates back to the early 1920s in Germany. The multi-tubular fixed bed reactor is filled with a Shell proprietary Fischer-Tropsch catalyst. The Fischer-Tropsch synthesis reaction can be modelled as a chain growth reaction of CO and hydrogen on the surface of a heterogeneous catalyst.
The synthetic crude carbon number distribution follows the Anderson-Schulz-Flory (ASF) distribution. This simple statistical model predicts a linear relationship between the logarithm of the molar amount of a paraffin and its carbon number. The growth probability, which fixes the slope of the ASF distribution, is catalyst dependent and the design of the catalyst largely defines the product slate.
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 The Heavy Paraffin Conversion reactor is used to fine tune the unique properties of the Shell MDS products. The waxy part of the raw synthesis product is selectively hydrocracked to the desired middle distillate products. Simultaneously the product is isomerised to improve the cold flow properties. Crucial for the performance is the use of the proprietary hydrocracking catalyst. The HPC product is subsequently fractionated in a conventional distillation column.
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The Shell MDS process was developed at the Shell Research and Technology Centre, Amsterdam. The development was a multi-disciplinary project with early involvement of all expertise areas of the Amsterdam Laboratory (from basic and exploratory, to engineering, catalyst and process development). This joint achievement has not only led to the successful commercialisation of Shell MDS Bintulu, but has also resulted in numerous patents and publications.
At the start of the S-Curve. Scanning Tunnelling Microscopy reveals the dynamic behaviour of a Fischer-Tropsch catalyst surface at the atomic scale after exposure to representative high pressure reaction conditions. These images show the state of a model catalyst surface before reaction (large atomically flat terraces - left) and after reaction (restructured surface - right). Each of the 'particles' visible in the case of the restructured surface corresponds to a small island of metal just 8 atoms in diameter and 1 atom in height. Atomic scale restructuring turns out to be an important process in determining the actual working state of the catalyst surface.
Literature for further reading: - Shell Research and Technology Centre, Amsterdam WWW site
- Engineering aspects of the conversion of natural gas into middle distillates, M.M.G. Senden, S.T. Sie, M.F.M. Post, J. Ansorge, Chemical Reactor Technology for Environmental Safe Reactors and Products, 227-247, 1992
- The Shell Middle Distillate Synthesis Process, J. Eilers, S.A. Posthuma and S.T. Sie, Catalysis Letters, 7 (1990), 253-270
- Conversion of natural gas to transportation fuels via the Shell Middle Distillate Synthesis Process, H.M.H. van Wechem and M.M.G. Senden, Natural Gas Conversion Symposium, Sydney, July 4-9 1993
- The Markets for Shell Middle Distillate Synthesis products, P.J.A. Tijm, J.M. Marriott, H. Hasenack, M.M.G. Senden and Th. van Herwijnen, Alternate Energy 1995, Vancouver, Canada, May 2-4 1995
- Atomic-scale restructuring in high-pressure catalysis, J.H. Wilson and C.P.M. de Groot, J. Phys. Chem, volume 99, 20, 7860-7866, 1995
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