Traditional methods for making graphite involve heating premium needle coke and coal-tar pitch at temperatures above 3,000ºC in a process that requires several days of heating and cooling. A new process developed by researchers at the National Energy Technology Laboratory (NETL; www.netl.doe.gov) has the potential to cut the heat requirements by half and reduce process times from weeks to hours. The process could help fulfill a growing demand for crystalline graphite, which is sought after for use in battery electrodes, composite materials, steel-making and energy-industry applications.
Source: NETL
The NETL process utilizes a hematite (Fe2O3)-based catalyst and occurs at temperatures around 1,200ºC. “The interaction of the Fe and C, near the eutectic point in their phase diagram, facilitates the production of Fe-carbide materials that dissociate into crystalline graphite,” explains NETL research scientist Ki-Joong Kim, the principal investigator of the project. While there are still many mechanistic details of the chemistry to work out, it appears that carbon from coal dissolves in molten iron at or near its eutectic point (where a mixture of two substances transitions from solid to liquid simultaneously). For iron and carbon, this occurs at 1,150ºC with 4–5 wt.% carbon. “After dissolution of C in Fe, Fe3C (cementite) is formed, which is metastable at these temperatures and dissociates into Fe and crystalline graphite. The fundamental thermodynamics of Fe and C are essentially what drives the process,” Kim says.
Using the new process, NETL scientists have demonstrated the ability to produce 1 kg of graphite at a time. The hurdles for scaling it up involve “developing a reactor that can efficiently mix the catalyst and carbon feedstock during the graphitization process, reducing or eliminating the use of leaching acids for purifying the graphite, and improving process efficiency for recovering, regenerating and re-using the catalyst material,” Kim explains.
The NETL team is currently working with several industrial partners to develop pre-pilot- and pilot-scale processes based on this core catalytic graphitization technology, hoping to transfer the technology to industry. “And from a research perspective, we are trying to understand how we may reduce processing temperature and time even further by using unconventional heating approaches, such as microwaves,” Kim says.
Global production of both natural graphite and synthetic graphite is currently concentrated in China. The NETL process could lead to a new cost-effective domestic industrial manufacturing base for synthetic graphite, now considered a critical material, Kim says.