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.