%0 Journal Article
%T Influence of RANEY Nickel on the Formation of Intermediates in the Degradation of Lignin
%A Daniel Forchheim
%A Ursel Hornung
%A Philipp Kempe
%A Andrea Kruse
%A David Steinbach
%J International Journal of Chemical Engineering
%D 2012
%I Hindawi Publishing Corporation
%R 10.1155/2012/589749
%X Lignin forms an important part of lignocellulosic biomass and is an abundantly available residue. It is a potential renewable source of phenol. Liquefaction of enzymatic hydrolysis lignin as well as catalytical hydrodeoxygenation of the main intermediates in the degradation of lignin, that is, catechol and guaiacol, was studied. The cleavage of the ether bonds, which are abundant in the molecular structure of lignin, can be realised in near-critical water (573 to 673£¿K, 20 to 30£¿MPa). Hydrothermal treatment in this context provides high selectivity in respect to hydroxybenzenes, especially catechol. RANEY Nickel was found to be an adequate catalyst for hydrodeoxygenation. Although it does not influence the cleavage of ether bonds, RANEY Nickel favours the production of phenol from both lignin and catechol. The main product from hydrodeoxygenation of guaiacol with RANEY Nickel was cyclohexanol. Reaction mechanism and kinetics of the degradation of guaiacol were explored. 1. Introduction Earth£¿s resources of crude oil are limited [1]. An important challenge for scientists and engineers is to develop technologies that are largely independent from fossil crude oils. Biomass, especially organic waste material, has a high potential to replace crude oil as a basic input material for the production of many organic chemicals. Lignocellulosic biomass is one of the most abundant renewable organic materials in the world. Lignin, a major component of lignocellulosic biomass, is mostly available as waste material. The paper industry produces more than 50 million tons of dry lignin every year worldwide [2]. It is mainly burned to recover its energetic value. Lignin has a structure similar to brown coal, being an aromatic heteropolymer. The three basic building blocks, p-coumaryl alcohol, coniferyl alcohol, and sinapyl alcohol. are interlinked by C¨CC or ether bonds. The latter is the weaker one of the two bonds mentioned and thus of high interest for lignin degradation. As lignin is relatively resistant to chemical or enzymatic degradation, harsh reaction conditions are required to break down this polymer [3]. By cleavage of the ether bonds, aromatic monomers are formed. Thus lignin provides high potential to serve as a renewable source for phenol or benzene [4]. Phenol is extremely interesting as building block for synthetic polymers, resins, and epoxy- or polyurethane [3]. It is however a challenge to gain a high-value product from a chemically complicated and inhomogeneous component as lignin. In order to do so, char formation is to be avoided. Char formation can be
%U http://www.hindawi.com/journals/ijce/2012/589749/