Why does the Permylene membrane require a membrane hydration system?

In the Permylene membrane system, the permeate stream absorbs moisture from the silver nitrate hydration maintenance solution and the hydrogel layer as it expands through the membrane , moving from the higher pressure to the lower pressure side. This moisture loss cannot be sufficiently compensated for by humidification of the feed gas prior to entry into the membrane system. As the aqueous silver nitrate solution is continuously circulated across the surface of the membrane concurrently with the hydrocarbon gas flow, the silver nitrate content maintains the charge of silver ions within the membrane while continuously replenishing the moisture lost to the permeating gas stream. The hydration maintenance solution is automatically controlled within a target molarity range using reverse osmosis or deionized water as make up. Because only the water leaves the membrane system in the permeate and retentate streams, the silver ions remain in the membrane and hydration system and are not consumed in the process.