Pretreatment of yellow pine in an acidic ionic liquid: extraction of hemicellulose and lignin to facilitate enzymatic digestion.

The acidic ionic liquid 1-H-3-methylimidazolium chloride can effectively pretreat yellow pine wood chips under mild conditions for enzymatic saccharification. Wood samples were treated at temperatures between 110 and 150°C for up to 5 h in the ionic liquid and three fractions collected; a cellulose rich fraction, lignin, and an aqueous fraction. This treatment caused the hemicellulose and the lignin to be degraded and dissolved from the cell walls of the pine wood. The lignin was depolymerized and subsequently dissolved in the ionic liquid. This process occurred more quickly at higher temperatures, although at the highest temperatures tested, significant cellulose degradation also occurred. The cellulose rich fraction was saccharified using cellulase from Trichoderma viride, with longer pretreatment times at 130°C resulting in higher glucose yields.

Depolymerization of oak wood lignin under mild conditions using the acidic ionic liquid 1-H-3-methylimidazolium chloride as both solvent and catalyst.

Oak wood lignin, which was separated from the wood using dissolution in the ionic liquid 1-methyl-3-ethylimidazolium acetate and subsequent precipitation, was successfully depolymerized in the acidic ionic liquid 1-H-3-methylimidazolium chloride under mild conditions (110-150 °C). Based on gel permeation chromatography results, an increase in temperature from 110 to 150 °C increased the rate of reaction, but did not significantly change the final size of the lignin fragments. Nuclear magnetic resonance and infrared spectroscopy were utilized to demonstrate that the depolymerization proceeded via a hydrolysis reaction that cleaved the alkyl-aryl ether linkages. Coupling of the lignin fragments was also shown to occur in the reaction mixture. These hydrolysis results are consistent with the literature on acid catalyzed depolymerization of lignin in conventional solvents and with recent model compound studies involving guaiacylglycerol-ß-guaiacyl ether and veratrylglycerol-ß-guaiacyl ether done in acidic ionic liquids.

Cleaving the ß--O--4 bonds of lignin model compounds in an acidic ionic liquid, 1-H-3-methylimidazolium chloride: an optional strategy for the degradation of lignin.

The hydrolysis of ß--O--4 bonds in two lignin model compounds was studied in an acidic ionic liquid, 1-H-3-methylimidazolium chloride. The ß--O--4 bonds of both guaiacylglycerol-ß-guaiacyl ether and veratrylglycerol-ß-guaiacyl ether underwent catalytic hydrolysis to produce guaiacol as the primary product with more than 70 % yield at 150 °C. Up to 32 wt % substrate concentration could be treated in the system without a decrease in guaiacol production. The ionic liquid could be reused without loss of activity in guaiacol production from both guaiacylglycerol-ß-guaiacyl ether and veratrylglycerol-ß-guaiacyl ether. A possible mechanism accounting for the guaiacol production is presented.