Why are membrane tubes sensitive to water and ammonia?

There is no such thing as a membrane that is afraid of water or ammonia; water can pass through membranes (porous membranes)； Separating gases generally requires dense membranes; water forms a film on the surface of these membranes, which hinders gas mass transfer, so it is best to have no water in the mixed gas ； As for ammonia, I guess it’s because its permeation rate is higher than that of hydrogen; therefore, if ammonia is present in the mixture, it will reach the permeation side before hydrogen (I’m not sure if this statement is correct – please consider it yourselves)

What was said upstairs is incorrect. It is certain that hydrogen separation membranes are sensitive to ammonia; this is because it causes changes in the properties of the membrane material (which generally becomes more brittle). Therefore, there are specific concentration limits for both ammonia (and hydrogen sulfide). As for the water issue, generally, hydrogen separation is said to be unaffected by water. The increase in temperature in front of the membrane is primarily aimed at preventing dew formation; if water forms on the membrane surface, it reduces the effective area of the membrane, thereby affecting the separation efficiency. But a small amount of water will not cause permanent damage to the membrane.

Let me add that there are currently two main materials used for gas separation membranes: one is polyimide, and the other is polysulfone. Poly sulfone materials have better resistance to ammonia than polyimides. The membranes used in chemical plants are made of poly sulphone, with a requirement of 100 ppm; the requirement for polyimides is lower, at around 10 ppm. The reason for this, as mentioned by others above, is the fear that ammonia will react with the separation material and cause complete damage to the membrane. Currently, the pre-treatment processes for hydrogen recovery in ammonia synthesis plants all involve ammonia washing; when water is fed into the membrane separator, it is usually ammonia water. This makes it easier to cause damage to the membrane. I once conducted an experiment: polyimide film filaments were immersed in ammonia solution at a 10% concentration, and after 2 hours the filaments were no longer visible – they had completely reacted with the ammonia. No significant changes were observed in the polysulfone membrane filaments after 8 hours, but it was impossible to determine any changes in the separation layer due to the lack of a microscope; it is estimated that it can no longer be used.

I study PSA; my mentor once said that membrane separation is a good method for separation. It seems I should also learn *membrane separation technology! I would like to know whether the membrane separation process is continuous Could you provide the separation flowchart? Among some of my clients, there are many who are concerned about hydrogen recovery in the presence of ammonia and water.

PSA and membrane separation each have their own advantages and application ranges. Membrane separation is generally continuous, whereas PSA usually requires regeneration. However, if a very high purity is required, membrane separation has no advantages. Some separations are first concentrated using membranes and then purified using PSA. It really doesn’t matter what you learn. The membrane separation process is quite simple: pre-treatment comes first, followed by the membrane; generally, there is one inlet (feed gas) and two outlets (tail gas and permeate gas). Just do a search – the websites of manufacturers that use membrane technology all have pictures and photos of the actual products.

In fact, when it comes to membrane separation, both materials have their own advantages.