Syngas Stoichiometric Adjustment for Methanol Production and Co-Capture of Carbon Dioxide by Pressure Swing Adsorption

Abstract

Methanol is an important raw material in industry and is commonly produced from syngas. The stoichiometric ratio (H₂–CO₂)/(CO + CO₂) of the methanol synthesis reactor feed stream must be adjusted to approximately 2.1. In this study, the replacement of the solvent unit within a coal to methanol process by a pressure swing adsorption (PSA) unit is proposed. The PSA produces a hydrogen enriched stream, to adjust the stoichiometric ratio of the methanol feed stream, and simultaneously captures the carbon dioxide for future sequestration. The feed flow rate is sub divided into eight 4-bed PSA units, operated with a defined phase lag between them in order to flatten the products (composition and flow rate) oscillations. The results show that the stoichiometric adjustment is possible and that oscillations on the products flow rate and composition are reduced to less than 3%. A carbon dioxide stream of 95.15% is obtained with a recovery of 94.2% and a productivity of 82.7 mol CO₂/kg/day. The power consumption of the global process is 119.7 MW, which includes the requirements for the rinse stream (64.4 MW) and the compression of the CO₂ product to 110 bar for sequestration (55.3 MW).

Keywords:

• CO₂ capture
• PSA
• stoichiometric adjustment

ACKNOWLEDGEMENTS

The authors thank LSRE financing by FEDER/POCI/2010.

Notes

*Fraction of the flow rate out of H₂S removal process that goes to the CO shift reactor.

*fraction of the flow rate out of H₂S removal process that goes to the CO shift reactor.

*fraction of the flow rate out of H₂S removal process that goes to the CO shift reactor.