Membrane modules for CO 2 capture based on PVDF hollow fibers with ionic liquids immobilized

Abstract

Hollow fiber membrane contactors with ionic liquids are promising alternatives to traditional spray towers and amines for carbon dioxide absorption. Ionic liquids have emerged as new alternative solvents because of their zero emission features compared with amines. The aim of this work was to compare fibers based on PVDF and different additives, as well as fibers including two different ionic liquids. On the one hand, 1-ethyl-3-methylimidazolium ethyl sulfate [emim][EtSO 4 ] presents physical absorption, and on the other hand, 1-ethyl-3-methylimidazolium acetate [emim][Ac] presents chemical absorption. To compare the fibers under study, the thickness of the composite fiber was examined using scanning electron microscopy (SEM). The mechanical properties and the bubble point were also evaluated.Permeability tests were conducted, and the gas permeation of the composite hollow fibers was measured using pure CO 2 . Laboratory-made stainless steel modules were used for the tests.All of the above tests were performed with the fibers in both wet and dry conditions. It was determined that the fibers with the ionic liquid immobilized would be promising for CO 2 capture because the CO 2 permeance significantly increased. Namely, D+[emim][EtSO 4 ] achieved a 43% increase compared with the fibers without the addition of the ionic liquid, resulting in a CO 2 permeance value of 57040 NL/(h m 2 bar), which is higher than the values reported in the literature for PVDF. Moreover, the overall mass transfer coefficient for CO 2 capture using the D+[emim][Ac] fibers also presented highly competitive values.

Hybrid Solvent ([emim][Ac]+water) To Improve the CO2 Capture Efficiency in a PVDF Hollow Fiber Contactor

“…From the sensitivity analysis some conclusions were obtained: (i) Koverall values upper than 1.70·10 -4 m s -1 allow CO2 capture efficiencies higher than 90%, (ii) using only two hollow fiber membrane contactors in series (0.6 m total length) were required in order to achieve the target CO2 capture efficiency, that provide competitive results comparing with traditional absorption towers, given an significant intensification factor, up to 4, related to the absorption with MEA solution. 0% water [14] 10% water 30% water 40% water 20% water 30% water 0% water [14] 10% water 20% water 40% water Figure 5. 0% water [14] 10% water 20% water 30% water 40% water 0 0,5 Sh=4.70·10 -4 Sh=2.58·10 -3 0% wáter [14] 30% water…”

“…0% water [14] 10% water 30% water 40% water 20% water 30% water 0% water [14] 10% water 20% water 40% water Figure 5. 0% water [14] 10% water 20% water 30% water 40% water 0 0,5 Sh=4.70·10 -4 Sh=2.58·10 -3 0% wáter [14] 30% water…”

“…For the carbon dioxide capture, a Polyvinylidene fluoride (PVDF) improved with the ionic liquid 1-ethyl-3-methylimidazolium acetate [emim][Ac] hollow fiber membrane contactor was home-made by phase inversion. The complete description of the fiber manufacturing method is explained in previous works [14,42,43]. The absorption membrane contactor was manufactured by gluing hollow fiber in a PVC shell [14].…”

“…In addition, with a water volume around 30% in the [emim][Ac], the mass transfer was benefited for the process. The overall mass transfer coefficient, Koverall expressed in m s -1 was calculated as in previous works according to the equation 2 [14,30,50]. , , ,…”

“…The main disadvantage in typical capture process is the low concentration of CO2 in power-plant flue gas, around 15%, means that a large volume of gas has to be handled, which results in large equipment sizes and high capital costs. Traditional solvents such as monoethanolamine (MEA), have been used for CO2 capture, achieving an outlet stream with a very low CO2 concentration [14]. However, the cost of aqueous alkanolamines based absorption/desorption processes is high because of more heat duty requirements for the absorbent regeneration [15].…”