Better, More Efficient Watermakers Are on The Horizon

[Chotu]

Desalination Breakthrough Could Lead to Cheaper Water Filtration


The paper documents an increase in efficiency in the membranes tested by 30%-40%, meaning they can clean more water while using significantly less energy.


https://news.utexas.edu/2020/12/31/d...er-filtration/

[dougweibel]

Here is another article that does a bit better job of explaining what they actually did.
https://scitechdaily.com/desalinatio...er-filtration/

Here is a citation for the actual paper (just out). I have not found a copy of the paper outside of a paywall yet.

Nanoscale control of internal inhomogeneity enhances water transport in desalination membranes
BY TYLER E. CULP, BISWAJIT KHARA, KAITLYN P. BRICKEY, MICHAEL GEITNER, TAWANDA J. ZIMUDZI, JEFFREY D. WILBUR, STEVEN D. JONS, ABHISHEK ROY, MOU PAUL, BASKAR GANAPATHYSUBRAMANIAN, ANDREW L. ZYDNEY, MANISH KUMAR, ENRIQUE D. GOMEZ
SCIENCE01 JAN 2021 : 72-75

Looks like some chemistry and materials science way above my head

[David Chop]

I couldn’t find a non-paywalled copy either, but I think the bottom line for sailors is in the available writeups if we read them a bit carefully. Spoiler alert: improved water makers not coming any time soon.


From the Science teaser,

“Culp et al. (8) leverage advances in microscopy and modeling to provide critical insights into structure–property relationships for current state-of-the-art RO membranes that could be used to rationally improve their performance.”

First, it helps to think of a desalination membrane as a net. If the holes in the net are large enough to let water molecules through yet small enough to block the passage of salt molecules, when you force salt water at it you get salt trapped on the high pressure side and pure water out the other. This is a bit over-simplified of course, but work with me. It’s just an analogy. All I’m really after is the net bit.


Normally we think of a net as an orderly pattern of knots and holes; equal string length between knots making a pattern of equal sized holes^(*). In nature (reality), the pattern is imperfect. There are flaws and impurities in the structure that lead to some larger holes and, important to the study, clusters of smaller holes. These flaws affect performance.


The researchers noted that 1) some naturally occurring membranes are more efficient than manufactured (man-made) ones, and 2) some manufactured membranes are more(!) efficient when they’re thicker. They used a very whiz-bang microscope to scan some of these membranes, then built a computer/math simulation that accurately models the differences in performance^(**). In the net analogy: they built a computer model that says a net with ‘x’ less small hole clusters has a ‘y’ improvement in performance.


They neither made any new membranes, nor improved any existing ones. All they did is make a tool for measuring the performance of existing membranes, and predicting the performance of theoretical future membranes. There’ve been no actual advancements in either the fundamental chemistry (material science) or manufacturing processes.


Bottom line for sailors: don’t expect any sudden improvements in water makers due to this study.



(*) Where I come from we’d call this structure the atomic lattice. They’re calling it nano-scale micro-structure or some such. Kids now days are much cooler than when I was in it.
(**) Explaining the more(!) efficient at greater thickness bit. This is why they got published. It’s valuable work.