Building off of a process to efficiently manufacture graphene (see Chem. Eng., April 2022, p. 9), a team of researchers from Rice University (Houston, www.rice.edu) have uncovered that the process can be easily altered to also produce a nearly pure stream of hydrogen gas using mixed-waste plastic materials as the feedstock. The previous work focused making flash graphene using any carbon source, including petroleum coke, coal, food waste or biochar, but now the team is looking to waste plastics, such as polypropylene and polyethylene, due to their higher hydrogen content. “We noticed gas coming out of the reaction as it heats to over 3,000K in the first 3 ms. We were only trapping a small amount of this gas,” explains James Tour, professor of materials science and nanoengineering at Rice. Upon analysis, the team found that the gas was 92–94% H2. By swapping coke feedstock for waste plastics, which have a more favorable weight percentage of hydrogen (around 14 wt.%) and a very low cost the process can maximize hydrogen production while also producing graphene at a high yield.
“We take the plastic and put a high-current voltage through it and add a small amount of carbon additive, such as metallurgical coke, to increase the conductivity of the plastic, and it forms graphene and hydrogen,” explains Tour. The ability to use a low-cost feedstock, along with the purity of the H2 produced, make the process economics very favorable, emphasizes Tour. “If we can sell the graphene at $3,000/ton, the amount of H2 that comes out will essentially cost negative $4.30/ton.”
The next steps will be to find a partner to license and scale up the plastics-based technology. Universal Matter (Houston; www.universalmatter.com) is set to start up a demonstration plant for rapid flash-Joule heating in the coming months, producing 1 ton/d of graphene from metallurgical coke feedstock.