Extraction of flax shive using sodium ethoxide catalyst in anhydrous ethanol

This work investigated the yield and nature of solvent-soluble organic compounds extracted from flax shive using a room temperature reaction (20°C) with sodium ethoxide catalyst at four different concentrations (0.2, 0.5, 0.7, and 1.0M) in anhydrous ethanol. Results were compared with the use of aqueous sodium hydroxide (1.0M) at two different reaction temperatures (20°C and 100°C). Quantitative yield from flax shive varied linearly with sodium ethoxide concentration and averaged 54.5mg/g on a dry-mass basis (db) at 1.0M. In contrast, the quantitative yield using 1.0M sodium hydroxide was much lower, averaging 2.2mg/g (db). Yield did not differ significantly due to changes of particle size in either case, or due to changes of temperature over the range considered in the case of sodium hydroxide. Analyses using proton nuclear magnetic resonance (¹H NMR) confirmed all extracts to contain aromatic compounds, thus likely lignin derived, but found differences in chemical characteristics between the two extraction methods. One key difference was the presence of compounds with methyl ether groups in sodium hydroxide extracts that were absent in the case of sodium ethoxide extracts. Given that flax contains a mixed guaiacyl–syringyl lignin, methyl ether groups would be expected to be present. Control reactions on three model compounds were carried out to confirm that transesterification occurred with sodium ethoxide. These control reactions also demonstrated that methyl ether groups would be expected to remain intact under the extraction conditions reported here. In light of the higher yield of solvent soluble compounds recovered by extraction with basic ethanol, flax shive may represent a source of value-added phenolic constituents. This processing method may also represent a useful pre-treatment prior to the production of biofuels by cellulose degrading organisms.