Identification, quantification and Chrastil modelling of wheat straw wax extraction using supercritical carbon dioxide

Abstract

Supercritical carbon dioxide (scCO 2 ) can be used as a ''green'' selective solvent for extractions of wheat straw waxes. For the first time, the crude extraction yields of wheat straw waxes and the yields of a single high value group of components (wax esters) using various scCO 2 conditions (305.15 to 373.15 K and 7.5 to 40 MPa) have been modelled using the Chrastil equation (Chrastil, 1982). The model accurately predicts both the crude yield and percentage of valuable wax esters within the extracts enabling maximum extraction efficiency. The key compounds within the waxes (fatty acids, sterols, fatty alcohols, wax esters, b-diketones and alkanes) have been identified and quantified. This study highlighted that, 14,16 hentriacontanedione was extracted at critical temperature and pressure in concentrations of 1000 mg.g À1 straw. This molecule could demonstrate significant potential as a natural chelate for metal recovery and also in the formation of super-hydrophobic coatings.

Sugarcane waste as a valuable source of lipophilic molecules

“…These hydrophobic compounds have found uses in a host of applications from cosmetics to nutraceuticals, coatings, polishes, detergents among other things (Sin et al, 2014). Natural waxes are in high demand due to the diminishing supply of petroleum waxes, together with the transition to greener products by consumers.…”

Biomass as a Feedstock

“…In the majority of plant waxes, the hydrocarbon fraction consists of a number of n-alkanes varying in chain length from C 25 to C 35 . The predominant n-alkanes are those which contain an odd number of carbon atoms.…”

“…The extraction of waxes from biomass using supercritical carbon dioxide has been previously carried out [28,[32][33][34][35]. Supercritical carbon dioxide was found to be an ideal solvent for the extraction of plant lipids.…”

“…This is ideal, especially if a holistic biorefinery approach is considered. The supercritical extraction of wax from wheat straw has been described in detail by Deswarte et al, Sin et al and Athukorala et al [28,35,60].…”

“…The β-diketone constituents of the wax are of particular interest due to their potential industrial applications, including their use as a natural chelating agent for metal removal, and utilisation for their hydrophobic properties in coatings. Supercritical extractions of wheat straw wax have demonstrated that 1000 µg g −1 of 14,16 hentriacontanedione can be obtained leading to a wax with a 35% purity of this β-diketone [35].…”