Modelling and Measuring Hydrate Promotion for CO2 Capture

A novel separation concept is investigated here, whereby a precipitated, or slurry, system, enables CO₂ capture by hydrate formation – enhanced by thermodynamic promoters. We have demonstrated that a model for the hydrate phase, combined with an equation of state for associating systems – the Cubic Plus Association (CPA) equation of state enables an accurate determination of mixed hydrate dissociation pressures as well as hydrate composition.

We have subsequently presented experimental work measuring promoted gas hydrate formation with tetrahydrofuran (THF) and cyclopentane (CP), both known low-pressure/high temperature sII hydrate formers. However when applied as a mixed promoter system the hydrate formation pressures are lowered by up to 20% when compared to the pure CP promoter system, which is thermodynamically the more efficient of the two pure promoter systems.

Finally, in order to model this promoted system the complex phase behaviour between water and THF needs to be understood. This system is successfully modeled using CPA, including the complex LLE observed at high pressures. This complex system is best modeled by specifically accounting for the solvation of THF (i.e. that THF forms hydrogen bonds with water but is not self-associating), which is also the correct physical picture of what occurs.