Process could cut carbon footprint of plastic manufacturers

By Jennifer A. Dlouhy

Bloomberg

Exxon Mobil and the Georgia Institute of Technology have discovered an alternative to an energy-hogging step used to manufacture plastics, potentially keeping 45 million tons of carbon dioxide out of the atmosphere each year.

This may allow chemical plants to shrink their carbon footprints and help the world meet ambitious targets for paring 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 percent of current global energy demand, with the share projected to grow dramatically as developing countries use more electronics, housing materials and plastic products.

The research by the Exxon and Georgia Tech team ultimately could shake up the way most plastics are manufactured.

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.

Researchers came up with a way to use less energy when pulling a chemical building block called para-xylene away from similarly sized hydrocarbon molecules. It uses a filter with a membrane of hollow polymer fibers that are barely thicker than a human hair. And when a liquid hydrocarbon mixture is drawn through it, the para-xylene molecules slip out of microscopic, perfectly sized holes.

Carbon fiber membranes have been used with gas previously, but the new process is believed to be the first to separate liquid hydrocarbons using reverse osmosis.

“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, a 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 percent of the desalination market uses that reverse osmosis process.

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 percent 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.

— Bloomberg