Wheat straw biomass: A resource for high-value chemicals

Abstract

Two methods are proposed for increasing the commercial value of wheat straw based on its chemical constituents. The first method involves the determination and extraction of the major organic components of wheat straw, and the second involves those found and extracted in the aqueous and viscous biooils derived from the straw by fast pyrolysis. We used pyrolysis-field ionization mass spectrometry to identify the fine chemicals, which have high commercial values. The most abundant organic compounds in the wheat straw and biooil used as precursors for green chemicals are N-heterocycles (16 to 29% of the Total Ion Intensities, TII) and fatty acids (19 to 26% of TIIs), followed by phenols and lignins (12 to 23% of TIIs). Other important precursors were carbohydrates and amino acids (1 to 8% TIIs), n-alkyl benzenes (3 to 5% of TIIs), and diols (4 to 9% TIIs). Steroids and flavonoids represented 1 to 5% of TIIs in the three materials. Examples of valuable chemical compounds that can be extracted from the wheat straw and biooils are m/z 256, 270, 278, 280, 282 and 284, which are the n-C16 and n-C17 fatty acids respectively, and the C18:3, C18:2 and C18:1 unsaturated fatty acids. In particular, the C18:2 (linoleic acid) is present at a concentration of 1.7% of TIIs. Pyrazole, pyrazine, pyridine, indoles, quinolines, carbazoles, and their identified derivatives are found in relatively high concentrations (1 to 8% of TIIs). Other useful compounds are sterols such as m/z 412 (stigmasterol), m/z 414 (β-sitosterol), and steroids such m/z 394 (stigmastatriene), m/z 398 (stigmastene) and m/z 410 (stigmastadienone). Relative to the wheat straw, the relative concentration of all flavonoids such as m/z 222 (flavone) and m/z 224 (flavonone) doubled in the biooils. The conversion of wheat straw by fast pyrolysis, followed by chemical characterization with mass spectrometry, and extraction of fine chemicals, opens up new possibilities for increasing the monetary value of crop residues.

Keywords:

• Wheat straw
• pyrolysis
• fine chemicals
• mass spectrometry
• flavonoids
• fatty acids
• sterols
• heterocyclic-N
• alkaloids
• cosmetics

Acknowledgments

The authors thank the Saskatchewan Research Council for providing the biooil samples for this experiment. Agriculture and Agri-Food Canada provided funding for this research. We are grateful to Dr. P. Leinweber of Rostock University for assistance with the mass spectrometric analysis, and S. Baxi for typing the manuscript.