ABSTRACT
Graphene materials exhibit extraordinary properties, but are difficult to produce. The present work describes the possibility of using a plasma process to exfoliate and functionalize graphite flakes. An impulse plasma phase is generated at a liquid surface to produce chemical species and shock waves in order to modify the reactive liquid as well as the graphite flakes. With this process, industrial graphite was treated. 20% thickness diminution was observed, and the formation of a random turbostratic structure. The exfoliation occurs with small amount of functionalization of the surface. Even after treatment, the graphite flakes present a low defect density compared with other treated graphite obtained by more conventional chemical treatments. This process is a new way to exfoliate graphite and to produce functionalized graphenic materials.
ABSTRACT
Lignin is a potential renewable material for the production of bio-sourced aromatic chemicals. We present the first hydrotreatment of lignin pyrolysis vapors, before any condensation, using inexpensive and sustainable iron-silica (Fe/SiO2 ) and iron-activated carbon (Fe/AC) catalysts. Lignin pyrolysis was conducted in a tubular reactor and vapors were injected in a fixed bed of catalysts (673 K, 1 bar) with stacks to investigate the profile of coke deposit. More than 170 GC-analyzable compounds were identified by GCxGC (heart cutting)/flame ionization detector mass spectrometry. Lignin oligomers were analyzed by very high resolution mass spectrometry, called the "petroleomic" method. They are trapped by the catalytic fixed bed and, in particular, by the AC. The catalysts showed a good selectivity for the hydrodeoxygenation of real lignin vapors to benzene, toluene, xylenes, phenol, cresols, and alkyl phenols. The spent catalysts were characterized by temperature-programmed oxidation, transmission electron microscopy (TEM), and N2 sorption. Micropores in the Fe/AC catalyst are completely plugged by coke deposits, whereas the mesoporous structure of Fe/SiO2 is unaffected. TEM images reveal two different types of coke deposit: 1) catalytic coke deposited in the vicinity of iron particles and 2) thermal coke (carbonaceous particles ≈1 µm in diameter) formed from the gas-phase growth of lignin oligomers.
