Sustainable Conversion of Lignocellulose to High-Purity, Highly Crystalline Flake Potato Graphite

Abstract

The carbon net negative conversion of biochar, the byproduct of pyrolysis bio-oil production from biomass, to very high-purity (99.95%), highly crystalline flake graphite that is essentially indistinguishable from high-grade commercial Li-ion grade graphite, is reported. The flake size of the graphite is determined by the physical dimensions of the metal particles imbedded in the biochar, demonstrated in the range of micrometers to millimeters. “Potato”-shaped agglomerates of graphite flakes result when the flake diameter is in the 1–5 μm range. The process is shown to work with a variety of biomass, including raw lignocellulose (sawdust, wood flour, and corn cob) and biomass components (cellulose and lignin), as well as lignite. The synthesis is extremely rapid and energy efficient (0.25 kg/kWh); the graphite is produced with a very high yield (95.7%), and the energy content of its coproduct, bio-oil, exceeds that needed to power the process. The demonstrated process is a tremendous advance in the sustainability of graphite production, currently commercially mined or synthesized with very high environmental impacts, and results in a value-added product that could economically advantage carbon-neutral bio-oil production.

Are lignin-derived carbon fibers graphitic enough?

“…16 XRD diffractograms of (A) lignin, (B) wood flour, (C) corn cob, and (D) cellulose catalytically graphitized via a 2-step procedure involving carbonization at 600°C and laser irradiation. 40 Reprinted with permission from the American Chemical Society.…”

“…However, there is an emerging field of research targeting the development of new methods to convert lignin and other bioresources into graphite for electrochemical applications, such as anodes for Li-ion batteries. 35,[38][39][40][41][42][43][44][45] The lignin graphitization procedures used in these studies are similar to those used in carbon fiber studies, with the major exception being that strength properties are not optimized since electrode applications do not require such. Instead, lignin graphitization studies optimize for graphitic structure formation, and usually small graphitic particles are produced, not fibers.…”

“…Multiple studies that successfully graphitized lignin used intensive milling or other techniques to reduce particle size to the micron level prior to thermal treatment, indicating that initial particle size may play a major role in the degree of graphitization. 38,40,49 Yoon et al (2018) carbonized acid hydrolysis lignin at 900 and 1300°C for use as anode material in a Na-ion battery. 43 As shown in Fig.…”

“…15, the X-ray diffr-actograms for kraft lignin carbonized under inert gases show poor graphitic structure development. Banek et al (2018) recently developed an innovative method to catalytically graphitize multiple biomass resources, including whole biomass, cellulose, and lignin. 40 Their method involves vigorously ball milling a mixture of iron and lignin prior to a 2-step graphitization procedure: step 1 involves carbonization under nitrogen at 600°C for 30 minutes and step 2 involves laser irradiation to induce graphitization.…”

High-Grade Flake Graphite Deposits in Metamorphic Schist Belt, Central Finland—Mineralogy and Beneficiation of Graphite for Lithium-Ion Battery Applications

“…Graphite electrodes (anodes and cathodes) can only be produced from natural graphite ores by several beneficiation processes, which include repeated crushing, milling, and flotation to separate the graphite flakes from their ore body. Ultra-high-purity (>99.95% C) with fine particle size ranging from 10 to 30 µm of battery grade could be achieved by further purification with alkali roasting pretreatment and acid leaching process [3]. In practical terms, graphite is one of the easiest minerals to segregate into a rough concentrate, but one of the most difficult to refine into a commercially useful product.…”