(57a) Solubility and Diffusivity of Syngas Components in a Next Generation Pre-Combustion Solvent

Solubility and Diffusivity of Syngas Components in a Next
Generation Pre-Combustion Solvent

Lei Hong ^1,2, Nicholas Siefert ¹,
Robert Thompson ^1,2, Wei Shi ^1,2, Kevin Resnik ^1,2,
David Hopkinson ¹

¹National Energy Technology Laboratory,
626 Cochrans Mill Road, Pittsburgh, PA  15236

²Leidos Research Support Team, 626
Cochrans Mill Road, Pittsburgh, PA  15236

ABSTRACT.

A key to improve the
efficiency of integrated gasification
combined cycle power plants with CO₂
capture and storage is to increase the temperature at which carbon dioxide is captured
and regenerated. The current baseline for
pre-combustion carbon capture technology is a solvent based process, such as
Selexol® (mixtures of dimethylethers of polyethelenglycol) and Rectisol® (chilled
methanol).  To obtain high CO₂ capture efficiency (>90%),
sub-ambient conditions are required for those solvents. However, cooling the
syngas to below room temperature is costly and requires energy-intensive
chillers.  In addition, since both Selexol and Rectisol are highly hydrophilic,
this can introduce corrosion issues for equipment. The hydrophilic solvents are
not ideal to be used at warm temperatures partly due to water presence in the
gas stream which could be absorbed in the solvent and significantly decrease CO₂
uptake. A process based on a hydrophobic solvent which can achieve a warm CO₂
separation would improve power plant efficiency as much as 2-3% compared to
those processes requiring sub-ambient temperatures (Henry Pennline, et.al., Fuel
Processing Technology, 89 (2008) 897-907).  The National Energy Technology
Laboratory (NETL) has developed a hydrophobic solvent, i.e. disub-4PEG, which
has shown great potential to replace current solvents, Selexol or Rectisol. Preliminary
pilot scale tests demonstrated that disub-4PEG performs better than Selexol
surrogate with both higher CO₂ uptake and higher CO₂/H₂
selectivity at the same operating conditions. Absorption of water in Selexol affects
the absorption of other gases, mainly CO₂ and H₂. The
computational study shows that H₂O absorption in a Selexol surrogate
solvent could significantly decrease both CO₂ uptake and CO₂/H₂
solubility selectivity. In contrast, for disub-4PEG,  water in the fuel gas
stream will have minimal effects on CO₂ solubility and CO₂/H₂
solubility selectivity due to very small amounts of water absorption in the
hydrophobic disub-4PEG solvent.  Finally, the solubility and diffusivity of
different gases including H₂, CO₂, N₂ and CH₄,
which are the main components of syngas, will be presented, which are essential
for a reliable process design.