Ethylene glycol lignin

Production and Hydrolytic Depolymerization of Ethylene Glycol Lignin... 

Set-up for Ethylene Glycol Lignin Production. A process development unit (PDU), previously described by Chornet and co-workers (11), was used for the experiments. A typical preparation consists of initially mixing 1-1.2 kg of wood meal with 10 1 of ethylene glycol. The mixture is allowed to stand overnight for imbibition to take place. To enhance solvent to substrate penetration, the slurry is homogenized at 200°C in the pretreatment section of the PDU. It is then pumped through the treatment section which consists of a tubular reactor at 220°C. The product slurry is collected in a receiver. The detailed procedure and choice of conditions above have been published elsewhere (11,12). 

As far as the ethylene glycol lignin is concerned, it has been shown to be a native-like lignin which can be produced and recovered by direct solvolytic treatment of the initial lignocellulosic substrate. It would also be possible to remove the hemicelluloses via an aqueous/steam treatment prior to solvolytic separation of the lignin and cellulose. Such an option would facilitate the recovery of the three main constitutive fractions of lignocellulosics in significant yields. Work in this direction is now underway. 

The efficiency of ethylene glycol-water as a delignifying solvent has been demonstrated by Gast and Puls (10). Results showed that sufficiently delignified pulps could be obtained. Also, the lignins produced showed promising results as extenders in phenolic resin adhesives. 

Low copolymer to propylene oxide ratios make it obviously difficult to totally liquefy lignin, Table II. Such conditions, however, seem to favor polyols with low total hydroxyl numbers. The oxyalkylation reaction appears to require catalyzation by zinc chloride or base catalysts in concentrations of about 10% or less for successful completion. The presence of an initiator (ethylene glycol) helps completion of the reaction in particular when the unhydrolyzed copolymer is used as substrate (Table III). 

An approach to reduce the deleterious effects of lignin is delignification of pre-treated UgnoceUulosic biomass. Another approach is the introduction of additives to hydrolysis mixtures, including surfactants, proteins and other lignin-binding polymers. In particular, poly (ethylene glycol) has been foxmd to be effective (32). 

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