Biologically inspired membrane purges coal-fired smoke of greenhouse gases
April 11, 2018
ALBUQUERQUE, N.M. -- A biologically inspired membrane intended to cleanse carbon dioxide almost completely from the smoke of coal-fired power plants has been developed by scientists at Sandia National Laboratories and the University of New Mexico.
The patented work, reported recently in Nature Communications , has interested power and energy companies that would like to significantly and inexpensively reduce emissions of carbon dioxide, one of the most widespread greenhouse gases, and explore other possible uses of the invention.
The memzyme meets the Department of Energy's standards by capturing 90 percent of power plant carbon dioxide production at a relatively low cost of $40 per ton.
Researchers term the membrane a "memzyme" because it acts like a filter but is near-saturated with an enzyme, carbonic anhydrase, developed by living cells over millions of years to help rid themselves of carbon dioxide efficiently and rapidly.
"To date, stripping carbon dioxide from smoke has been prohibitively expensive using the thick, solid, polymer membranes currently available," says Jeff Brinker, a Sandia fellow, University of New Mexico regents' professor and the paper's lead author.
"Our inexpensive method follows nature's lead in our use of a water-based membrane only 18 nanometers thick that incorporates natural enzymes to capture 90 percent of carbon dioxide released. (A nanometer is about 1/700 of the diameter of a human hair.) This is almost 70 percent better than current commercial methods, and it's done at a fraction of the cost."
Coal power plants are one of the United States' largest energy producers, but they have been criticized by some for sending more carbon dioxide into the atmosphere than any other form of electrical power generation. Still, coal burning in China, India and other countries means that U.S. abstinence alone is not likely to solve the world's climate problems. But, says Brinker, "maybe technology will."
The device's formation begins with a drying process called evaporation-induced self-assembly, first developed at Sandia by Brinker 20 years ago and a field of study in its own right.
The procedure creates a close-packed array of silica nanopores designed to accommodate the carbonic anhydrase enzyme and keep it stable. This is done in several steps. First, the array, which may be 100 nanometers long, is treated with a technique called atomic layer deposition to make the nanopore surface water-averse or hydrophobic. This is followed by an oxygen plasma treatment that overlays the water-averse surface to make the nanopores water-loving or hydrophilic, but only to a depth of 18 nanometers. A solution of the enzyme and water spontaneously fill up and are stabilized within the water-loving portion of the nanopores. This creates membranes of water 18 nanometers thick, with a carbonic anhydrase concentration 10 times greater than aqueous solutions made to date.
