Twenty-one organosolv ethanol lignin samples were prepared from hybrid poplar (Populus nigra xP. maximowiczii) under varied conditions with an experimental matrix designed using response surface methodology (RSM). The lignin preparations were evaluated as potential antioxidants. Results indicated that the lignins with more phenolic hydroxyl groups, less aliphatic hydroxyl groups, low molecular weight, and narrow polydispersity showed high antioxidant activity. Processing conditions affected the functional groups and molecular weight of the extracted organosolv ethanol lignins, and consequently influenced the antioxidant activity of the lignins. In general, the lignins prepared at elevated temperature, longer reaction time, increased catalyst, and diluted ethanol showed high antioxidant activity. Regression models were developed to enable the quantitative prediction of lignin characteristics and antioxidant activity based on the processing conditions.

An organosolv process involving extraction with hot aqueous ethanol has been evaluated for bioconversion of hybrid poplar to ethanol. The process resulted in fractionation of poplar chips into a cellulose-rich solids fraction, an ethanol organosolv lignin (EOL) fraction, and a water-soluble fraction containing hemicellulosic sugars, sugar breakdown products, degraded lignin, and other components. The influence of four independent process variables (temperature, time, catalyst dose, and ethanol concentration) on product yields was analyzed over a broad range using a small composite design and response surface methodology. Center point conditions for the composite design (180 degrees C, 60 min, 1.25% H(2)SO(4), and 60% ethanol), yielded a solids fraction containing approximately 88% of the cellulose present in the untreated poplar. Approximately 82% of the total cellulose in the untreated poplar was recovered as monomeric glucose after hydrolysis of the solids fraction for 24 h using a low enzyme loading (20 filter paper units of cellulase/g cellulose); approximately 85% was recovered after 48 h hydrolysis. Total recovery of xylose (soluble and insoluble) was equivalent to approximately 72% of the xylose present in untreated wood. Approximately 74% of the lignin in untreated wood was recovered as EOL. Other cooking conditions resulted in either similar or inferior product yields although the distribution of components between the various fractions differed markedly. Data analysis generated regression models that describe process responses for any combination of the four variables.

A comparative study on decomposition of cellulose between supercritical water (400°C, 40 MPa) and subcritical water (280°C, 40 MPa) treatments was made to elucidate the difference in their decomposition behavior. Consequently, the supercritical water treatment was found to be more suitable for obtaining high yields of hydrolyzed products. However, cellulose was found to be more liable to fragment under supercritical water treatment, resulting in a decrease in the yield of hydrolyzed products. On the contrary, cellulose was found to be liable to more dehydration in the subcritical water treatment. Based on these results, we have proposed the combined process of short supercritical water treatment followed by subcritical water treatment so as to inhibit fragmentation. Consequently, this combined treatment was able to effectively control the reaction condition, and to increase the yield of hydrolyzed products.

Sugi (Cryptomeria japonica D. Don) and buna (Fugus crenata Blume) woods were treated with supercritical water (> 374~ > 22.1 MPa) and fractionated into a water-soluble portion and a water-insoluble residue. The latter was washed with methanol to be fractionated further into a methanol-soluble portion and a methanol-insoluble residue. Whereas the carbohydrate-derived products were in the water-soluble portion, most of the lignin-derived products were found in the methanol-soluble portion and methanol-insoluble residue. The lignin-derived products in the methanol-soluble portion were shown to have more phenolic hydroxyl groups than lignin in original wood. The alkaline nitrobenzene oxidation analyses, however, exhibited much less oxidation product in the methanol-soluble portion and methanol-insoluble residue. These lines of evidence suggest that the ether linkages of lignin are preferentially cleaved during supercritical water treatment. To simulate the reaction of lignin, a study with lignin model compounds was performed; 13-O-4-type lignin model compounds were found to be cleaved, whereas biphenyl-type compounds were highly stable during supercfitical water treatment. These results clearly indicated that the ligninderived products, mainly consisting of condensed-type linkages of lignin due to the preferential degradation of the ether linkages of lignin, occurred during supercritical water treatment.

No abstract