Integrated capture and conversion of CO2 to methanol

Processes that capture carbon dioxide from industrial fluegas and simultaneously convert it into useful chemicals are desirable because they offer an opportunity to produce CO₂-derived chemicals more efficiently and economically than conventional approaches, where costs are driven up by the energy-intensive regeneration of the capture solvent. By integrating CO₂ capture with conversion to methanol (flowsheet), scientists at Pacific Northwest National Laboratory (PNNL; Richland, Wash.; www.pnnl.gov) have developed a process that could eventually reach cost parity with producing methanol derived from fossil fuels, the PNNL team says.

For the CO₂ capture component, the team used 2-EEMPA (N-(2-ethoxyethyl)-3-morpholinopropan-1-amine), an advanced, water-lean, amine-based capture solvent. To produce methanol, the CO₂-containing solvent is exposed to a catalyst that consists of platinum metal atoms on a titanium-oxide support. The heterogeneous catalyst allows a reaction pathway that avoids methylation (and thus deactivation) of the capture solvent. Other catalysts used for methanol synthesis in the gas phase tend to deactivate the capture solvent by promoting a route that methylates the amine site.

With an integrated capture and conversion process, the exothermic CO₂-to-methanol conversion process partially offsets the energy that would normally be required in conventional carbon capture and utilization for the regeneration of the capture solvent, the PNNL team explains. Further, “because the captured CO₂ is converted directly in the capture-solvent medium, there is also energy saved on the CO₂ compression and transportation that would otherwise be required with gas-phase conversion, thus reducing additional energy inputs and associated equipment costs,” PNNL says.

The PNNL research, reported in the journal Advanced Energy Materials, includes a technoeconomic analysis (TEA) of capturing CO₂ from a natural-gas combined-cycle power plant and converting it to methanol in the condensed phase. The TEA suggests that the minimum selling price for methanol can be significantly reduced, and may reach price parity with conventional methanol synthesis, if faster kinetics and higher selectivity can be achieved through catalyst and reactor development. Current efforts are focused in those areas, the PNNL team says.