S.He and T.Li at University of Maryland College Park
Filtering the salt from seawater can take a lot of energy or specialised engineering. A thin membrane made of porous wood may be able to fix that.
In membrane distillation, salty water is pumped through a film, usually made of some sort of polymer with very narrow pores that filter out the salt and allow only water molecules through. Jason Ren at Princeton University in New Jersey and his colleagues developed a new kind of membrane made of natural wood instead of plastic.
“If you think of traditional water filtration, you need very high-pressure pumping to squeeze the water through, so it uses a lot of energy,” says Ren. “This is more energy efficient and it doesn’t use fossil-fuel based materials like many other membranes for water filtration.”
His team’s membrane is made of a thin piece of American basswood, which undergoes a chemical treatment to strip away extra fibres in the wood and to make its surface slippery to water molecules. One side of the membrane is heated so that when water flows over that side it is vapourised.
The water vapour then travels through the pores in the membrane toward its colder side and leaves the salt behind, condensing as fresh, cool water. This takes far less energy than simply boiling all of the saltwater because there’s no need to maintain a high temperature for more than a thin layer of water at a time, Ren says.
This method filters about 20 kilograms of water per square metre of membrane per hour, which is not quite as quick as polymer membranes. The researchers think that may be because they did not have the equipment to make their membrane as thin: it is 500 micrometres thick, whereas the polymer membranes are generally closer to 130 micrometres thick.
Making the wood membranes thinner shouldn’t be too hard with the right equipment, Ren says. “The functional part of the membrane is a micrometre thick,” he says. “The rest is just a supporting structure to make it harder to break.”
Journal reference: Science Advances, DOI: 10.1126/sciadv.aaw3203
Jackatarian on August 3rd, 2019 at 13:57 UTC »
Cue 1000's of Japanese carpenters coming out of retirement.
fromIND on August 3rd, 2019 at 13:16 UTC »
I hope this isn't one of those things you hear about once then they disappear.
mvea on August 3rd, 2019 at 11:52 UTC »
The title of the post is a copy and paste from the title, second and third paragraphs of the linked academic press release here:
Journal Reference:
Hydrophobic nanostructured wood membrane for thermally efficient distillation
Dianxun Hou1, Tian Li2, Xi Chen1,3, Shuaiming He2, Jiaqi Dai2, Sohrab A. Mofid4,5, Deyin Hou6, Arpita Iddya7, David Jassby7, Ronggui Yang4, Liangbing Hu2,* and Zhiyong Jason Ren1,3,*
Science Advances 02 Aug 2019: Vol. 5, no. 8, eaaw3203
Link: https://advances.sciencemag.org/content/5/8/eaaw3203
DOI: 10.1126/sciadv.aaw3203
Abstract
Current membrane distillation (MD) is challenged by the inefficiency of water thermal separation from dissolved solutes, controlled by membrane porosity and thermal conductivity. Existing petroleum-derived polymeric membranes face major development barriers. Here, we demonstrate a first robust MD membrane directly fabricated from sustainable wood material. The hydrophobic nanowood membrane had high porosity (89 ± 3%) and hierarchical pore structure with a wide pore size distribution of crystalline cellulose nanofibrils and xylem vessels and lumina (channels) that facilitate water vapor transportation. The thermal conductivity was extremely low in the transverse direction, which reduces conductive heat transport. However, high thermal conductivity along the fiber enables efficient thermal dissipation along the axial direction. As a result, the membrane demonstrated excellent intrinsic vapor permeability (1.44 ± 0.09 kg m−1 K−1 s−1 Pa−1) and thermal efficiency (~70% at 60°C). The properties of thermal efficiency, water flux, scalability, and sustainability make nanowood highly desirable for MD applications.