Contaminants and Membrane Performance

The conundrum in designing membranes for high CO2 permeability is that the separation is enhanced by the solubility of CO2 in the polymer and that the polymer needs to be dissolved in solvents in order for the phase inversion process to occur and form the asymmetric structure. Properties that enhance CO2 performance also can make the structure sensitive to contaminants that over the long term can hurt performance and in worst case scenarios completely shut down performance. 

Liquid water collapses dried C A membrane structures, requiring in the field that natural gas streams be treated to reduce water content before they are introduced into the membrane. Simple droplet tests on the surface of flat sheet membranes also show that numerous solvents will also damage or dissolve these CA membranes. A partial listing includes acetone, 1,4-dioxane, acetonitrile, dichloromethane, chloroform, propyl acetate, ethyl acetate, 2-butanone, tetrahydrofuran and nitroethane. 

In addition to the hydrocarbons that can be expected with a natural gas stream other organics can find their way into the system, both volatile and non-volatile. A leak in a 

Glycol dehydrators are used to scrub water from natural gas to meet pipeline specifications but also pose a potential hazard to membrane systems. An upset in dehydrator operations can flood manbrane modules with triethylene glycol (TEG), commonly employed as the working fluid. 

Operations for oil and natural gas recovery can also introduce drilling additives, fracturing fluids and other processing Uquids into the ground from which natural gas is extracted. These are low cost and sometimes proprietary mixtures for which the composition can be unknown and/or unreported [20]. There are many potential chemical hazards to a membrane operation so a proper pre-treatment system is recommended for successful long-term operations. 

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