| Summary: | Natural gas is among the most dominant resources to provide energy supplies and Saudi
Arabia ranks among the top 5 producers worldwide. However, prior to use of methane, natural
gas has to be treated to remove other feed gas components, such as H2O, CO2, H2S, N2 and C2+
hydrocarbons. Most NG fields in KSA contain about 10 mol% carbon dioxide that has to be
reduced to less than 2 mol% for pipeline delivery.
The conventional unit operations for natural gas separations, that is, molecular sieves, amine
absorption, cryogenic distillation, and turbo expansion exhibit some disadvantages in terms of
economics, operational flexibility or system footprint. One of the most attractive alternative is
membrane technology in either standalone- or hybrid system configuration. Currently, the only
two membrane materials used in industrial natural gas applications are cellulose acetate and
polyimide, which have moderate permeability and fairly low selectivity when tested under
realistic industrial conditions. The goal for future research is to develop unique polymeric
membranes, which can at least partially replace conventional gas processing in future natural gas
projects. This will support global economics and specifically the economy of Saudi Arabia.
Newly developed polymeric materials must meet certain criteria to be used on a commercial
scale. These criteria include: (i) high permeability and selectivity, (ii) processability into thin
films, (iii) mechanical and thermal stability, and (iv) chemical stability against feed gas
components.
This project focused on the removal of carbon dioxide from natural gas by
developing and characterizing functionalized aromatic polyimide membrane materials that
exhibit very high selectivity under aggressive mixed-gas conditions. 6FDA-DAR demonstrated a
mixed-gas CO2/CH4 selectivity of 78 at a CO2 partial pressure of 10 bar with no pronounced
indication of plasticization. Combining hydroxyl- and carboxyl groups in a miscible polyimide
blend led to mixed-gas CO2/CH4 selectivity of 100 with no aging and no plasticization effects.
This burgeoning membrane material has very high potential in large-scale natural gas separations
with the best overall performance of any type developed to date.
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