Microwave-assisted separation hemicellulose from hemp stalk: Extracting performance, extracting mechanism and mass transfer model

Abstract

Herein, a novel microwave-assisted alkali extraction process was proposed for further high-efficiency extraction of hemicellulose from hemp stalk. The hemicellulose extraction yield of the peeled hemp stalk surpasses 60% under mild conditions (4% alkali content, 80 °C, 30 min). Meanwhile, the hemicellulose presented a high weight-average and number-average molecular weight of 25331, 6067 g/mol. The improved efficiency could be thanks to the looser structure created by microwave expansion pretreatment via breaking the intricate structure and shielding of the hemp stalk cell wall, detailed as the specific surface area, total pore volume, and average pore size of the hemp stalk increased from 1.30 m²/g, 0.003 cm3/g, 10.66 nm to 1.85 m²/g, 0.006 cm3/g and 13.08 nm after the microwave expansion pretreatment. Furthermore, the higher expansion rate (36.74%) and water retention value (265%) of the hemp stalk also demonstrated the effective disrupting effect on the fiber structure. Finally, the empirical mass transfer model of extraction hemicellulose from hemp stalk was established. The predicted value and the experimental data showed a good correlation (R2 = 0.9998) and the model displayed excellent stability (relative deviation within 5%). Therefore, microwave-assisted alkali extraction has great potential application in the hemicellulose separation industry.