In a world that’s hungry for energy and showing no sign of slowing down, there is no industrial process more voracious than petrochemical manufacturing. Since the early 20th century, everything from gasoline and diesel fuel to plastics has been made by cracking complex hydrocarbon molecules found in oil and coal with tremendous amounts of heat and pressure.
The shale gas boom in the United States has driven energy costs down and opened up new possibilities to the nation’s petrochemical manufacturers. Ethane, a major component of natural gas liquids, offers a simpler hydrocarbon to refine than oil. Once ethane is converted to ethylene, it becomes the primary building block of many plastics in advanced manufacturing.
This conversion can be done thermally, the same way as it is with oil, at temperatures of up to 850 C. But a team of Idaho National Laboratory researchers has hit upon an electrochemical process that could eliminate the need for high-energy steam cracking, creating synthetic fuels and chemical building blocks while using 65 percent less energy and producing up to 98 percent less carbon dioxide.
The INL research, being conducted in conjunction with Massachusetts Institute of Technology and the University of Wyoming, is one of 24 projects being funded by the U.S. Department of Energy’s Office of Energy Efficiency and Renewable Energy (EERE). The EERE Advanced Manufacturing Office announced Feb. 5 that the project would receive $1.25 million over two years, part of $35 million awarded to 24 projects developing early-stage innovative technology for advanced manufacturing.
Both INL and University of Wyoming are members of the Center for Advanced Energy Studies (CAES), a consortium that also includes three Idaho state-supported universities. The decision to respond to DOE’s Funding Opportunity Announcement came from a CAES-sponsored meeting at UW in August 2016. With carbon conversion experts in the two partner organizations — Dr. Ting He at INL and Dr. Maohong Fan at UW — the connection they established through CAES led to the preliminary research that resulted in EERE-AMO funding.
“It’s a perfect example of the CAES model being applied,” said Don Roth, CAES’ associate director from UW. “CAES focuses on regional energy solutions with national impact, and this project is a direct outcome of our strategic planning.”
The new process involves feeding ethane to the anode in an electrochemical membrane reactor. Electricity separates protons (hydrogen ions) from the molecules, leaving ethylene, an unsaturated hydrocarbon that can be used to make polymers. Meanwhile, the protons migrate through a dense electrolyte to the cathode, where they combine with electrons to form hydrogen gas.
The ethylene on the anode can be further refined into higher hydrocarbons, including gasoline, diesel, lubricants and wax, depending on what coupling catalyst is applied and at what point the reaction is terminated.
The electrochemical process has the ability to overcome thermodynamic limitations, allowing operation at the lower temperature: 400 C compared to 850 C. Coking, side reactions and catalyst deactivation can be drastically mitigated, said Dr. Dong Ding, one of the INL researchers on the team. Further, electrochemical membrane reactors can push the overall reaction toward practical deployment through fast removal of hydrogen.
“This is totally new stuff,” Ding said. As the work progresses, MIT will provide modeling and calculations with its advanced characterization tools while UW will conduct research and development of catalysts to build higher hydrocarbons.
Several factors are driving the project, Ding said. First of all, the plentiful supply of natural gas in the United States is poised to fuel the return of chemical industries to the country. The current price of ethane is roughly 25 cents per gallon but projected to increase, which could inspire transitions toward more cost-effective production methods.
The declining cost of electricity makes electrochemical refining more economically feasible. Theoretically, if the process were to be powered by a renewable source and the captured hydrogen were to be incorporated into fuel cells, there is net gain in process energy. From a CO2 standpoint, using a noncarbon source of electricity — nuclear, hydro, wind or solar — could cut the carbon footprint down to 2 percent of traditional production methods.
In their proposal, the INL-led research team pointed out that the plastics and resins market is projected to rise 50 percent by 2030.
“This project has high potential to secure U.S. industrial competiveness in chemicals, fuels, and plastics production for the foreseeable future,” the proposal to DOE said. “This technology will fundamentally change the petrochemical manufacturing paradigm from fossil energy fueled ‘thermal’ practices to a ‘clean energy’ scheme that uses the nation’s vast resources of natural gas, while incorporating renewables such as wind and solar.”
Ding said the INL team is beginning to focus on how to convert methane into ethylene. Methane is also found in natural gas — more plentifully than ethane, in fact — but its carbon-hydrogen bond is much harder to break, Ding said.
The team recently published a paper describing this work in the journal Energy & Environmental Science. The work was later highlighted by Chemical & Engineering News.
Posted May 4, 2018
