One of my research interest is to apply zeolite membranes to organic chemical processes. We just published its application for dehydration reactions;
Ind. Eng. Chem. Res. 2007, 46, 3743.
I suppose that one of the characteristics of zeolite membranes is its high separatability, compared with polymer based membranes. (If polymer based membrane is separatable enough, DMFC should be easy to be made!) In this paper, we showed that water can be removed selectively even from methanol aqueous solution that enabled "Anti-Eastman Process".
Eastman process is to manufacture methyl acetate from acetic acid and methanol. Because its reversible nature, reactive distillation process has been applied. (Details? See Fogler's ChemE!) Eastman process is useful only when the ester is volatile enough compared with water or methanol.
In our case, we applied PV (pervaporation) by the zeolite membrane we developed in order to remove water. Water can be removed selectively owing to the separatability of our zeolite membranes. I do not think that polymer based membrane could work like this!
Also, as I mentioned as "Anti-Eastman Process", esters do not have to be volatile in order to get promotive effect from PV. - I suppose this is good news.
It is not unusual for zeolite membranes to be separative compared with polymer membrane, as the alcohol dehydration process has been already commercialized. (e. g. see PV separator - sorry, this is Japanese - Ultimately, PV can compete with distillation process, especially in small scale chemical plant. At the same time, it is better to understand why "zeolite membranes" are sometimes so separative.