Selective hydrogenation of lignin-derived model compounds to produce nylon 6 precursors
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This study investigated the conversion of monomeric lignin fragments into cyclohexanols for use as a source of lignin-derived monomers for renewable Nylon 6 production. Lignin-derived monomeric phenolic species was transformed to their cyclohexanol analogs via selective catalytic hydrogenation. A fixed-bed flow reactor was used to evaluate the selective hydrogenation of individual model phenolic species (guaiacol, 4-methylguaiacol or diphenyl ether). The catalyst composition studied was Ni/SiO₂, which was previously shown to form cyclohexanol as an intermediate from phenol. A primary focus was on tuning the reaction conditions to form desired products, while avoiding the formation of bicyclic species which can be precursors to catalyst deactivation, or fully hydrogenated products of lower value. Reaction pathways of guaiacol, 4-methylguaiacol and diphenyl ether were studied. Major products obtained from guaiacol, 4-methylguaiacol and diphenyl ether reactions were 2-methoxycyclohexanone, 4-methylcyclohexanol and cyclohexanol, respectively. Spent catalyst was analyzed for extent of deactivation.