Structure de mise en forme 2 colonnes
Young Researchers

SP3 - Syngas to liquids

The synthesis of gasoline from syngas as part of the OCMOL process was shown to be feasible by integrating STO with OTL, as shown schematically in Figure 5. The products from the oxygenate reactor were directed to a separator where mainly DME and CO2 were condensed and subsequently sent to the oxygenate-to-liquids reactor. A recycle stream of CO and hydrogen was also implemented in the layout with the aim of increasing the conversion of syngas. To further reduce the concentration of reactants, the oxygenates-rich stream was mixed with a recycle stream from the post-OTL process separation step. This recycle stream contained a high fraction of light alkenes, which may react to form higher hydrocarbons and improve the gasoline yield. The addition of light alkenes improved the gasoline yield and prolonged the lifetime of the catalyst.

Figure 5: Simplified process layout involving liquid product intermediate. Oxygenate synthesis purge stream adds to the main (liquid) feed for Oxygenate-to-Liquids synthesis.

Since the conversion of oxygenates into hydrocarbons is a strongly exothermic reaction, and less than 100% conversion gives the highest gasoline yields over H-ZSM-22 or H-ZSM-23 catalysts, the use of a fluidized bed reactor is beneficial. Fluidization of the catalyst provided an excellent means for controlling the reaction temperature, ensuring homogeneous reaction conditions along the catalytic bed and minimizing the risk for a runaway or hot spots, in addition to allowing stable operation at less than 100% conversion. Further, the application of a fluidized bed process enabled continuous regeneration of the catalyst particles in a separate regenerator, which is particularly relevant for catalysts suffering from rapid deactivation such as H-ZSM-22 and H-ZSM-23.

The full conversion of syngas via DME/MeOH with light olefin recycle into higher hydrocarbons gave a gasoline product with C5+ and C4+ yields superior to 70 wt% and 80 wt%, respectively, of the total hydrocarbon product. In addition, the final product stood out by its low content in aromatics. The topology of H-ZSM-22 and H-ZSM-23 inhibits the formation of aromatic compounds, which made this process very attractive for producing environmentally friendly gasoline.

 

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