Optimization of Extraction of Wax from Flax Straw by Supercritical Carbon Dioxide

Abstract

Response surface methodology (RSM) was used to optimize supercritical carbon dioxide (SC-CO2) extraction of wax from flax straw. SC-CO2 variables included flow rate (24.8, 35, 50, 65, and 75.2 g/min), pressure (132, 200, 300, 400, and 468 bar), and temperature (34.8, 45, 60, 75, and 85.2°C). The SC-CO2 extraction technique was optimized for the extraction of flax straw wax and its main constituents (fatty acids, alkanes, sterols, aldehydes, and wax esters). A second order polynomial model provided a good fit (R2 value of 0.90) for the yield of wax from flax straw. Canonical analysis revealed a maximum stationary point for wax yield of 1.26 g/100 g at a flow rate of 61.1 g/min, a pressure of 378 bar and a temperature of 75°C. The fatty acid and wax ester contents of flax wax were also fitted with a second order polynomial model with R2 values of 0.94 and 0.87, respectively. The temperature was found to be the most important factor affecting the recovery of wax. Linear and quadratic effects of temperature and interaction effects of temperature and pressure had a significant effect on the total wax yield and on the content of fatty acids, fatty alcohols, and sterols in the wax.