Effect of Microstructure in MOR Membrane on Its Adsorption and Permeation Properties for Water and Acetic Acid

The effect of crystal orientation on the permeation and separation performance of MOR-type membrane for water/acetic acid mixtures was investigated. The crystal orientation of MOR membrane was controlled by changing the water content of the synthesis gel. The orientation gradually changed from c-orientation to random orientation with increasing water content. Regardless of their crystal orientation, both membranes exhibited the extremely high separation performances (α > 10,000). c-Oriented MOR membrane showed a higher water flux than that through randomly oriented membrane in the unary systems. In contrast, the water flux through c-oriented membrane decreased in the binary system, because acetic acid molecules in the 12-ring along the c-axis hindered water permeation. The randomly oriented membrane maintained a relatively high water flux even in the binary system possibly because the 8-ring along b-axis avoided the entering of acetic acid. From the results of the adsorption test of acetic acid on MOR powder and randomly oriented membrane, the adsorbed amount on the membrane was approximately 30% less than that on MOR powder, suggesting that acetic acid can only access the part of crystals in a membrane layer. The region inside the membrane, where acetic acid cannot enter, contributes to its extremely high separation performance.