The effects of water vapor on the separation of methane and carbon dioxide by gas permeation through polymeric membranes

Abstract

Three commercially available films and a vinylidene fluoride film modified with sulfolene were tested for the separation of carbon dioxide from carbon dioxide, methane and water vapor mixtures. Flux and separation factor values were obtained over a temperature range from 23 to 90°C and a feed gas moisture content from 0.0 to 1.32%. A feed gas containing 60% carbon dioxide and 40% methane on a dry basis was used at an operating pressure of 2068 kPa. The commercially available films tested were cellulose acetate, polysulfone and polyethersulfone. All three films provided good separation. For example, the polysulfone film produced a permeate containing 96.0% carbon dioxide at room temperature and 0.12% water. Separation factor values for carbon dioxide ranged from 4.6 to 45.1. Flux values for the commercial films ranged from less than 10.E-05 to 1.9xl0E-03 cu cm(STP)/sq cm(sec). The sulfolene modified film also provided good separation. Separation factor values for carbon dioxide ranged from 9.6 to 33.6. Flux values ranged from 10.E-05 to 5.7xl0E-05 cu cm(STP)/sq cm(sec). Strong trends towards increasing flux and decreasing percentage of carbon dioxide in the permeate with increasing temperature were observed with all films. A trend towards decreasing percentage of carbon dioxide in the permeate with increasing water content was observed with cellulose acetate, polysulfone and polyethersulfone films. These films demonstrated a strong trend towards increasing flux with increasing water content at low levels of water content. As the feed stream approached saturation, gas flux tended to become constant or actually decrease. The sulfolene modified film tended towards constant or increasing percentage of carbon dioxide in the permeate with increasing water content. The flux tended to remain constant or decrease with increasing water content.

Water vapor permeation in polyimide membranes

“…The implementation of such gas separation systems poses significant challenges. One of them is the presence of water vapor, a known plasticizer in membrane separation [1][2][3]. Water vapor is usually considered as a minor component of the system in such industrial carbon capture applications [4,5].…”

Membrane pilot plant trials of CO2 separation from flue gas

“…For example, a similar reduction in CO 2 permeability is recorded in a fluorinated polyimide (6FDA‐TMPA) when the water activity is increased from zero to 0.8. Conversely, while Paulson et al observed a significant decrease in selectivity, these authors observe a flux increase for a CO 2 /CH 4 methane mixture through a polysulfone membrane when the gas stream was humidified. However, their water concentrations (1 mol%) are significantly lower than those observed here (∼10 mol%).…”

Effect of humidified feeds on oxygen permeability of mixed matrix membranes

“…As water swelled PVAc, the diffusion coefficient of oxygen was increased, and hence so was the oxygen permeability, as shown in Figure 2. Typically, such swelling causes plasticization and disproportionate increases in the diffusivities of the slower penetrants, such as nitrogen, so that the overall effect is decreased selectivity 29. In more rigid glassy polymers the major effect of water is the occupation of sorption sites usually available to other penetrants,9, 30 so the decline in selectivity may be less severe.…”