Lignin processing

Biorefinery includes fractionation for separation of primary refinery products. The fractionation refers to the conversion of wood into its constituent components (cellulose, hemicelluloses and lignin). Processes include steam explosion, aqueous separation and hot water systems. Commercial products of biomass fractionation include levulinic acid, xylitol and alcohols. Figure 3.3 shows the fractionation of wood and chemicals from wood. 

Because of the recalcitrance of lignin, processing of Ugnin-rich biomass by solvents requires the use of aggressive solvents (Abels et al., 2013). Two commercial treatment jM ocesses of wooden biomass with strong solvents have been developed (1) the Kraft process and (2) the Organosolv process (Figure 11.3). 

Ragauskas AJ, Beckham GT, Biddy MJ, Chandra R, Chen F, Davis MF, et al. Lignin valorization improving lignin processing in the biorefinery. Science 2014 344. http //dx.doi.org/10.1126/science.1246843. 

Guaiacol (2-metho)typhenol), one of the compounds found in lignin processing, can be deoxygenated by a hydrodeoxygenation process. Monometallic catalysts exhibit poor activity and are prone to deactivation due to the presence of the phenolic compounds. At 400 °C and 0.1 MPa in a gas-phase flow reactor, monometallic tin and platinum/Inconel catalysts... 

Chakar.F. S.,and Ragauskas, A J. (2004). Review of currentand future softwood kraft lignin process chemistry. Ind. Crops Prod., 20,131-141. 

Cleavage of Carbon—Carbon Bonds. Under appropriate conditions, the propanoid side chain in lignin maybe mptured to form three-, two-, or one-carbon fragments. This carbon—carbon fragmentation occurs in a variety of laboratory treatments and technical processes such as in bleaching of chemical pulps with CI2, CIO2, and O2, in microbial degradation (15), and in photooxidation (16). 

Substitution Reactions on Side Chains. Because the benzyl carbon is the most reactive site on the propanoid side chain, many substitution reactions occur at this position. Typically, substitution reactions occur by attack of a nucleophilic reagent on a benzyl carbon present in the form of a carbonium ion or a methine group in a quinonemethide stmeture. In a reversal of the ether cleavage reactions described, benzyl alcohols and ethers may be transformed to alkyl or aryl ethers by acid-catalyzed etherifications or transetherifications with alcohol or phenol. The conversion of a benzyl alcohol or ether to a sulfonic acid group is among the most important side chain modification reactions because it is essential to the solubilization of lignin in the sulfite pulping process (17). 

Applications. These materials are stiU in developmental infancy. Current production is limited to one commercial process in Europe and a demonstration-scale process in North America. The lignins produced in these processes have potential appHcation in wood adhesives, as flame retardants (qv), as slow-release agents for agricultural and pharmaceutical products, as surfactants (qv), as antioxidants (qv), as asphalt extenders, and as a raw material source for lignin-derived chemicals. 

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