Hydrogen sulfide separation from gas streams using salt hydrate chemical absorbents and immobilized liquid membranes

Abstract

The salt hydrate tetramethylammonium fluoride tetrahydrate, [(CH 3 ) 4 N]F : 4H 2 O, in the liquid state reversibly absorbs large quantities of hydrogen sulfide, for example 0.30 mol H 2 S per mole of salt at 508C and 100 kPa. Gas absorption likely occurs by deprotonation of H 2 S to form bisulfide, HS 2 , and bifluoride, HF 2 2 . The equilibrium constant for the reaction of H 2 S with [(CH 3 ) 4 N]F : 4H 2 O is 1.4 Â 10 22 kPa 21 at 508C as determined from absorption/desorption data. The heat of H 2 S absorption was surprisingly low, 20.78 kcal mol 21 . A second salt hydrate, tetraethylammonium acetate tetrahydrate, [(C 2 H 5 ) 4 N]CH 3 CO 2 : 4H 2 O, also reversibly absorbs H 2 S but with a lower affinity. However, at higher pressures, its H 2 S capacity increases more than does that of [(CH 3 ) 4 N]F : 4H 2 O making it more suitable for use as a pressure swing absorbent. Absorption/desorption data are consistent with reaction of one mole of [(C 2 H 5 ) 4 N]CH 3-CO 2 : 4H 2 O for each mole of H 2 S and an equilibrium constant of 6.4 Â 10 24 kPa 21 mol H 2 S per mole of salt. Membranes 627

Natural gas purification using supported ionic liquid membrane

“…It is known that ILs with fluorinated anions, such as [FAP -], are unstable in the presence of water at high temperatures. They can hydrolyze and form hydrogen fluoride (HF) [30]. Because HF is volatile, it would be removed from the membrane by the gas flow [31].…”

Wastewater treatment for production of H2S‐free biogas

“…Conventional ways to combat this problem are well-known physical and chemical methods such as separation of H 2 S gas from the biogas using chemical absorbents 6 and membranes, 6 -8 pigging (in tubes) and cleaning the system and/or applying biocides. However, from an environmental point of view, it is necessary to find new ways to eliminate the H 2 S that are based on the process microbiology itself.…”

Liquid membranes for gas/vapor separations

“…one of the salt ions acts like a carrier [32,44,49]. In the following, these liquids are referred to as functionalized liquids.…”