Extraction of Wheat Straw with Aqueous Tetra-n-Butylphosphonium Hydroxide

• Main Authors: Uula Hyväkkö, Alistair W. T. King, Ilkka Kilpeläinen
• Format: Article
• Language: English
• Published: North Carolina State University 2014-01-01
• Series: BioResources
• Subjects: Ionic liquid; Electrolyte; Biomass; Wheat straw; Fractionation; Cellulose; Phosphonium; Hydroxide; Lignin; Hemicellulose
• Online Access: http://ojs.cnr.ncsu.edu/index.php/BioRes/article/view/BioRes_09_1_1565_Hyvakko_Extraction_Wheat_Straw
• ISSN: 1930-2126; 1930-2126

The stability of tetra-n-butylphosphonium hydroxide ([P4444][OH](aq)) solutions and their potential for wheat straw extraction are investigated. Under certain concentration ranges, aqueous [P4444][OH](aq) is known to rapidly dissolve up to 20 wt% of cellulose at 25 ºC. However, at elevated temperatures and at the high concentration ranges required for cellulose dissolution, [P4444][OH](aq) irreversibly decomposes. This was determined by following the kinetics of decomposition at different temperatures and concentrations, using 31P NMR analysis of the solutions. A lower concentration range of 40 wt% [P4444][OH](aq) was observed for fractionation of wheat straw, avoiding significant decomposition of the expensive phosphonium component. Herein, the possibilities for producing cellulose-rich fractions with reduced lignin contents and hemicellulose-rich extracts are discussed. A proposal is given for a full process cycle using [P4444][OH](aq), where the phosphonium salt is used in fractionation and recovered by anion metathesis as a chloride salt. Although not demonstrated in this article, the chloride salt may be converted back to the hydroxide by means of, e.g., ion exchange.