Analysis of feed stream acid gas concentration effects on the transport properties and separation performance of polymeric membranes for natural gas sweetening: A comparison between a glassy and rubbery polymer

• Published in: Journal of membrane science 2014-09, Vol.465, p.107-116
• Main Authors: Vaughn, Justin T., Koros, William J.
• Format: Article
• Language: English
• Subjects: Applied sciences; Carbon dioxide; Chemistry; Colloidal state and disperse state; Exact sciences and technology; Exchange resins and membranes; Forms of application and semi-finished materials; General and physical chemistry; Glassy; Hydrogen sulfide; Membranes; Mixed gas permeation; Natural gas; Natural gas purification; Polyamide resins; Polyamide–imides; Polymer industry, paints, wood; Selectivity; Separation; Sour gas sweetening; Streams; Technology of polymers
• ISSN: 0376-7388; 1873-3123
• DOI: 10.1016/j.memsci.2014.03.029

A 6FDA based polyamide-imide, 6F-PAI-1, is compared to Pebax®, a commercially available rubbery polyether/polyamide block copolymer, for the simultaneous separation of CO2 and H2S from CH4. Feed streams of 20/20/60 and 5/45/50H2S/CO2/CH4 were used to compare the effect of acid gas concentration on the separation efficiency of 6F-PAI-1 and Pebax® under industrially relevant conditions. 6F-PAI-1 showed CO2/CH4 selectivities at 850psia total feed pressure of 30 and 40 for the 20/20/60 and 5/45/50 feed streams, respectively, while selectivity for H2S/CH4 was approximately 20 for both feeds. Pebax® showed selectivities of 40 and 10 for H2S/CH4 and CO2/CH4, respectively. Both selectivities were mostly independent of acid gas concentration in the feed, an unsurprising trend considering the non-glassy nature of this material. The selectivities in 6F-PAI-1 translated to less than 6% CH4 lost in the permeate stream for both feeds, while for the 5/45/50 feed, CH4 fraction in the permeate at 850psia was less than 4%. These promising results suggest that glassy polymers possessing favorable intrinsic plasticization resistance, such as 6F-PAI-1, may be appropriate for the typical case of natural gas sweetening where CO2 concentration in the feed is higher than it is for H2S. •Lower fluorinated 6F-PAI-2 became highly plasticized in the presence of H2S.•More fluorinated 6F-PAI-1 showed better plasticization resistance against H2S.•6F-PAI-1 showed higher CO2/CH4 selectivity compared to rubbery Pebax®.•CH4 loss in the permeate for 6F-PAI-1 was less than Pebax®.