In the era of easy and cheap oil, the chemistry of aromatics has ever been directed towards the selective oxidation of arenes to phenols or other functionalized aromatics, which has led to processes of extreme importance and high-volume production currently present in the chemical industry. However, times are changing rapidly. The vast availability of lignin, and the fact that lignin will be released as a major waste in the production of cellulosic ethanol, should create new opportunities for the production of aromatics in the chemical and fuel industry. Indeed, for each 1 kg of cellulosic ethanol is 1-3 kg of lignin generated as waste. Thereby, depolymerization of lignin followed by hydrodeoxygenation rendering arenes with low boiling point could greatly facilitate the fractionation and further processing of the complex lignin products into chemical commodities (e.g. benzene, toluene, ethylbenzene and xylenes) by conventional refinery and petrochemical routes. Finally, even if the isolated product yields demonstrates to not be sufficient enough to give a suitable return in today's chemical industry, the mixture of arenes and aliphatics could very well serve as valuable bio-additives to synthetic fuels produced by the Fischer-Tropsch synthesis, which does not produce aromatic and branched hydrocarbons. Recently, we reported a new method for the conversion of phenols into arenes. This method involves a cascade of chemical reactions: (I) transfer hydrogenation, (II) dehydration and (III) transfer dehydrogenation. The tandem conversion is catalyzed by the concurrent use of Raney Ni and �-zeolite, which enables the easy adjustment of the interplay between metal and acid catalysts. The reaction cascade is initiated by the partial conversion of phenol into cyclohexanol through the transfer hydrogenation using 2-propanol as a starting H-donor. Next, cyclohexanol is dehydrated into cyclohexene, which is then used as the H-donor for the hydrogenation of the remaining phenol content. This reaction renders benzene as the main product. In this communication, we present the rationale behind the optimization of this method for the molecular simplification of lignin into arenes.

Lignin into arenes: A new platform for the production of liquid fuels by catalytic H-transfer reactions

248th National Meeting (2014)

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