Scientists at Exxon Mobil Corp. (IW 500/1) and the Georgia Institute of Technology have discovered an alternative to the most energy-hogging part of manufacturing plastics, potentially keeping 45 million tons of carbon dioxide out of the Earth’s atmosphere each year.
The breakthrough, set to be published in the Aug. 19 issue of the journal Science, ultimately may help chemical plants shrink their carbon footprint and help the world meet ambitious targets for paring the greenhouse gas emissions blamed for climate change. Although nearly 200 nations agreed last December to rein in carbon dioxide emissions by boosting energy efficiency and shifting to cleaner sources of electricity, experts say it’s also essential to green up industrial manufacturing.
Chemical plants account for about 8% of current global energy demand, with the share projected to grow dramatically as developing countries use more electronics, housing materials and plastic products.
These types of breakthroughs can make an absolute step change in the amount of energy needed to convert a raw material to a plastic."
— Vijay Swarup, vice president of research and development, ExxonMobil Research and Engineering Co.
The research by the Exxon and Georgia Tech team ultimately could shake up the way most plastics are manufactured, making it easier to pull a chemical building block called para-xylene away from similarly sized hydrocarbon molecules. Right now, manufacturers typically turn to crystallization techniques that involve repeatedly freezing the molecules, or adsorption processes that involve boiling and distilling hydrocarbon mixtures.
And even the most cutting-edge alternatives, which haven’t made their way out of the laboratory and into the market, require boiling to vaporize xylenes before passing them through a membrane.
Whether hot or cold, the processes involve a lot of energy, said Ryan Lively, an assistant professor in Georgia Tech’s School of Chemical and Biomolecular Engineering.
Filter Dials Down Energy Use
The researchers came up with a filter to remove the para-xylenes with less energy. The membrane is constructed with hollow polymer fibers that, at 200 microns (.008 inches) in diameter, are barely thicker than the average human hair. And when a liquid hydrocarbon mixture is drawn through it, the para-xylene molecules slip out of microscopic, perfectly sized holes.
Although carbon fiber membranes have been used with gas, the new process is believed to be the first time reverse osmosis and carbon membranes have been used to separate liquid hydrocarbons.
"These types of breakthroughs can make an absolute step change in the amount of energy needed to convert a raw material to a plastic," said Vijay Swarup, vice president of research and development at ExxonMobil Research and Engineering Co., a subsidiary of the energy company.
The same basic approach is already used to desalinate seawater. Where heat-based techniques can be used to strip out salt, reverse-osmosis membranes do the same work with only a fraction of the energy the thermally driven processes require. The breakthrough membranes were discovered in the 1960s and began being mass manufactured in the mid 1970s. Now, about 60% of the desalination market uses that reverse osmosis process.
An Uncertain Milestone
If the new plastic-focused membrane can be mass-produced and widely adopted -- an uncertain milestone researchers openly acknowledge would require years more R&D -- it could save $2 billion in annual energy costs. The calculations reported in Science are based on the amount of energy used in separation processes globally, an assumption that half of it could be displaced by the new technology and the average greenhouse gas emissions for each kilowatt hour of electricity produced in the U.S.
Swarup cautioned that "this is very early stages" but stressed that "being published in a prestigious journal like Science speaks to the fact that we think the fundamentals are very strong."
Molecular separation processes are essential to produce clean water, pharmaceuticals, chemicals and fuels. About 40% to 60% of the energy used producing those materials is spent on separation and purification processes, the paper’s authors say.
"We’re confident that there could be really dramatic energy savings if this technology could be commercialized and adopted by the industry," said Benjamin McCool, an advanced research associate at Exxon, which funded the research.
Exxon’s collaboration with Georgia Tech -- formally initiated in 2014 -- comes as the company is aiming to green up its image, while its use of climate change research is being probed by a handful of state attorneys general. New York, Massachusetts and other states are investigating whether Exxon misled investors by not fully disclosing how climate change could affect its business.
By Jennifer A. Dlouhy