(355h) Asymmetric Hollow Fiber Membranes for Aggressive Sour Gas Purification

Carbon dioxide (CO₂) and hydrogen sulfide (H₂S)
are present in high concentration in a large fraction of natural gas reserves.
These species must be removed prior to transport through natural gas pipelines
in order to prevent corrosion, increase the heating value of natural gas and
because of the dangers associated with H₂S. A series of novel
crosslinkable materials based on the glassy polyimide 6FDA-DAM:DABA, which has
been used in the past for CO₂/CH₄ separations, has been developed
for use in the simultaneous removal of H₂S and CO₂ from
aggressive natural gas feeds. These materials exhibit significantly improved H₂S/CH₄
selectivity and plasticization resistance over the base polymer without
sacrificing the outstanding CO₂/CH₄ permselectivity of
6FDA-DAM:DABA. Following dense film permeation and sorption studies, one of these crosslinkable 6FDA-DAM:DABA derivatives was identified
as a promising candidate for asymmetric hollow fiber formation and testing. In
dense film form, this material has an H₂S/CH₄
selectivity as high as 23.5 and a CO₂/CH₄ selectivity
just below the intrinsic value when using a 20% H₂S/20% CO₂/60%
CH₄ mixture at feed pressures up to 900 psi. The dense film characterization
results as well as those for asymmetric hollow fiber spinning and preliminary
permeation testing will be discussed.