METHOD AND SYSTEM FOR PURIFICATION OF NATURAL GAS USING MEMBRANES
Natural gas may be purified by removing C 3+ hydrocarbons and CO 2 in respective first and second gas separation membrane stages to yield conditioned gas lower in C 3+ hydrocarbons and CO 2 in comparison to the un-conditioned natural gas.
1 . A method for purification of natural gas including methane, CO2, and C 3+ hydrocarbons, comprising the steps of:
feeding a feed gas consisting of the natural gas to a first gas separation membrane stage comprising one or more membranes having a selective layer that is selective for C 3+ hydrocarbons over methane;
withdrawing a first permeate stream from the membrane(s) of the first stage that is enriched in C 3+ hydrocarbons in comparison to the feed gas;
withdrawing a first retentate stream from the membrane(s) of the first stage that is deficient in C 3+ hydrocarbons in comparison to the feed gas;
feeding the first retentate stream to a second gas separation membrane stage comprising one or more membranes having a selective layer that is selective for CO 2 over methane;
withdrawing a second permeate stream from the membrane(s) of the second stage that is enriched in CO 2 in comparison to the feed gas; and
withdrawing a first retentate stream from the membrane(s) of the first stage that is deficient in CO 2 in comparison to the feed gas.
2 . The method of claim 1 , further comprising removing water from the feed gas prior to feeding the feed gas to the first gas separation membrane stage.
3 . The method of claim 2 , wherein said step of removing water comprises feeding the feed gas to a molecular sieve adapted and configured to remove water from fluids.
4 . The method of claim 2 , wherein said step of removing water comprises feeding the feed gas to a dehydration gas separation membrane.
5 . The method of claim 1 , further comprising the step of combusting the first and/or the second permeate streams as a flare gas.
6 . The method of claim 1 , wherein the feed gas is obtained from natural gas extracted from a subterranean or subsea geological formation and said step further comprises injecting the first and/or second stage permeate streams into the geological formation.
7 . The method of claim 6 , further comprising dehydrating the first and/or second permeate streams prior to injection into the geological formation such that a water content in the first and/or second permeate stream injected into the geological formation is no more than 50 ppm (vol/vol).
8 . The method of claim 1 , wherein the one or membranes of the first gas separation membrane stage have a separation layer made of a copolymer or block polymer of tetramethylene oxide, and/or propylene oxide, or ethylene oxide.
9 . The method of claim 8 , wherein a pressure drop between a pressure of the feed gas and a pressure of the retentate gas is less than 50 psi (3.45 bar).
10 . The method of claim 8 , wherein a pressure drop between a pressure of the feed gas and a pressure of the retentate gas is less than 30 psi (2.07 bar).
11 . The method of claim 8 , wherein a pressure drop between a pressure of the feed gas and a pressure of the retentate gas is less than less than 20 psi (1.38 bar).
12 . The method of claim 8 , wherein the one or more membranes of the first gas separation membrane stage have a methane permeance of less than 68 gas permeation units (22.4 mol/m 2 ·sec·Pa).
13 . The method of claim 8 , wherein the one or more membranes of the first gas separation membrane stage have a methane permeance of less than 34 GPU.
14 . The method of claim 8 , wherein the one or more membranes of the first gas separation membrane stage have a methane permeance of less than 20 GPU.
15 . The method of 8, wherein the one or membranes of the first gas separation membrane stage have a separation layer made of a copolymer or block polymer of the formula:
where PA is an aliphatic polyamide having 6 or 12 carbon atoms and PE is either poly(ethylene oxide) poly(tetramethylene oxide).
16 . The method of claim 8 , wherein one or membranes of the first gas separation membrane stage have a separation layer made of repeating units of the following monomers:
17 . The method of claim 8 , wherein the one or more membranes of the first gas separation membrane stage are formed as flat films or as a plurality of hollow fibers.
18 . The method of claim 8 , wherein each of the one or more membranes of the first gas separation membrane stage has a separation layer that is supported by a support layer.
19 . The method of claim 18 , wherein each of the support layers is made of a polyimide, polysulfone, or polyether ether ketone.
20 . The method of claim 19 , wherein each of the support layers is porous and is made of polyether ether ketone.
21 . The method of claim 1 , wherein each of the membranes of the second gas separation membrane stage is made of cellulose acetate, a polysulfone, or a polyimide.
22 . A system for purification of natural gas including methane, CO2, and C 3+ hydrocarbons, comprising:
a source of natural gas;
a first gas separation membrane stage comprising one or more membranes fluidly communicating with said source, each membrane of the first gas separation membrane stage having a selective layer that is selective for C 3+ hydrocarbons over methane; and
a second gas separation membrane stage comprising one or more membranes fluidly communicating with a retentate outlet(s) of the membranes of the first gas separation membrane stage so as to receive retentate from the first gas separation membrane stage as a feed gas in the second gas separation membrane stage, each membrane of the second gas separation membrane stage having a selective layer that is selective for CO 2 over methane.
23 . The system of claim 22 , further comprising a water removal apparatus adapted and configured to remove water from the feed gas prior to feeding the feed gas to the first gas separation membrane stage.
24 . The system of claim 23 , wherein said water removal apparatus is a molecular sieve adapted and configured to remove water from fluids.
25 . The system of claim 23 , wherein said water removal apparatus is a dehydration gas separation membrane.
26 . The system of claim 22 , wherein each of the one or membranes of the first gas separation membrane stage has a separation layer made of a copolymer or block polymer of tetramethylene oxide, and/or propylene oxide, or ethylene oxide.
27 . The system of claim 26 , wherein each of the one or membranes of the first gas separation membrane stage exhibits a pressure drop between a pressure of the feed gas and a pressure of the retentate gas is less than 50 psi (3.45 bar).
28 . The system of claim 26 , wherein each of the one or membranes of the first gas separation membrane stage exhibits a pressure drop between a pressure of the feed gas and a pressure of the retentate gas is less than 30 psi (2.07 bar).
29 . The system of claim 26 , wherein each of the one or membranes of the first gas separation membrane stage exhibits a pressure drop between a pressure of the feed gas and a pressure of the retentate gas is less than less than 20 psi (1.38 bar).
30 . The system of claim 26 , wherein each of the one or membranes of the first gas separation membrane stage exhibits a methane permeance of less than 68 gas permeation units (22.4 mol/m 2 ·sec·Pa).
31 . The system of claim 26 , wherein each of the one or membranes of the first gas separation membrane stage exhibits a methane permeance of less than 34 GPU.
32 . The system of claim 26 , wherein each of the one or membranes of the first gas separation membrane stage exhibits a methane permeance of less than 20 GPU.
33 . The system of claim 26 , wherein the one or membranes of the first gas separation membrane stage have a separation layer made of a copolymer or block polymer of the formula:
where PA is an aliphatic polyamide having 6 or 12 carbon atoms and PE is either poly(ethylene oxide) poly(tetramethylene oxide).
34 . The system of claim 26 , wherein one or membranes of the first gas separation membrane stage have a separation layer made of repeating units of the following monomers:
35 . The system of claim 26 , wherein the one or more membranes of the first gas separation membrane stage are formed as flat films or as a plurality of hollow fibers.
36 . The system of claim 26 , wherein each of the one or more membranes of the first gas separation membrane stage has a separation layer that is supported by a support layer.
37 . The system of claim 36 , wherein each of the support layers is made of a polyimide, polysulfone, or polyether ether ketone.
38 . The system of claim 37 , wherein each of the support layers is porous and is made of polyether ether ketone.
39 . The system of claim 22 , wherein each of the membranes of the second gas separation membrane stage is made of cellulose acetate, a polysulfone, or a polyimide.