Environmental Engineering Reference
In-Depth Information
osmosis (RO) desalination membranes. At irst glance, bringing an advanced membrane
material to market should revolutionize energy requirements and vastly improve the com-
petitiveness of desalination. Certainly membranes with extraordinary characteristics have
been demonstrated in the laboratory, and these will undoubtedly ind application in some
industry. Thus, it is natural that advanced technology companies should at least consider
this space to see what they can offer.
Recently, a major company better known in the aerospace market announced a patent
on a “revolutionary” graphene oxide desalination membrane. According to published
interviews, the company expects to be conducting pilot testing by 2014 or 2015. It touts
the membrane as one atom thick, a thousand times stronger than steel, and vastly less
resistant to the passage of water than incumbent membranes, with the implication of an
unbeatable seawater desalination membrane.
None of these are the relevant metrics, however. What one really needs to know when
examining a new RO membrane is the answer to questions like
• Does it resist fouling and biofouling? Ordinary membranes are often function-
alized to improve this characteristic. With a single-layer nanomaterial, however,
these characteristics are pretty much ixed.
• Is it robust enough to outlast the 5-7-year lifespan of current membranes? Sure, it
is 1000× stronger than steel, weight for weight, but no one would dream of deploy-
ing a steel structure one atom thick. Structurally speaking, gold leaf is probably
a better comparison. Adding any kind of backing will add resistance and largely
negate the value of using such an exotic material. Graphene being graphene, it also
is not clear that multiple layers will “play” well together, possibly limiting options
to improve performance by layering.
• Does it require extensive pretreatment? A large chunk of the energy used in mod-
ern RO systems is actually in the pretreatment steps. If the graphene oxide mem-
brane is susceptible to fouling or microtears when particles scrape it, it will need
very similar pretreatment.
• Is it easy to clean? A major drawback of the current generation of polymeric mem-
branes is that they do not withstand cleaning with chlorine. It is not clear that
graphene oxide would do much better.
• Can large sheets be made to allow elements to it the form factor of existing mem-
branes? If so, the membranes are drop-in replacements for the large installed base
of RO plants. If not, the technology is doomed to deployment at a dusty kiosk in
EPCOT.
• Is it cost-competitive, at scale and right now, in a commodity market? Extreme
competition between major RO membrane makers has driven margins through
the loor, and a new crop of Chinese manufacturers spun up with heavy govern-
ment backing are promising to make the market even less attractive. Current RO
membranes cost no more than a few hundred dollars per square meter. Current
graphene membranes cost tens to hundreds of thousands of dollars per square
meter, pricing them completely out of the market.
By this time the thoughtful reader will be asking, yes, but what if the performance is much
better than existing membranes? Would not that make it a potential winner whatever the
current uncertainties?
