Enhanced microwave assisted pyrolysis of waste rice straw through lipid extraction with supercritical carbon dioxide

Chanettee Sikhom, Thomas M. Attard, Weerapath Winotapun, Nontipa Supanchaiyamat, Thomas J. Farmer, Vitaliy Budarin, James H. Clark, Andrew J. Hunt*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


A combination of supercritical carbon dioxide (scCO2) extraction and microwave-assisted pyrolysis (MAP) have been investigated for the valorisation of waste rice straw. ScCO2 extraction of rice straw led to a 0.7% dry weight yield of lipophilic molecules, at elevated temperatures of 65 °C and pressures of 400 bar. Lipid compositions (fatty acids, fatty alcohol, fatty aldehydes, steroid ketones, phytosterols, n-alkanes and wax esters) of the waxes obtained by scCO2 were comparable to those obtained Soxhlet extraction using the potentially toxic solvent n-hexane. ScCO2 extraction positively influenced the pyrolysis heating rate, with a rate of 420 K min−1 for particles of 500-2000 μm, compared to 240 K min−1 for the same particle size of untreated straw. Particle size significantly affected cellulose decomposition and the distribution of pyrolysis products (gaseous, liquid and char), highlighting the importance of selecting an adequate physical pre-treatment. TG and DTG of the original rice straw and resulting biochar produced indicated that cellulose was completely decomposed during the MAP. While a rapid pressure change occurred at ∼120 °C (size > 2000 μm) and ∼130 °C (size 500-2000 μm) during MAP and was associated with the production of incondensable gas during cellulose decomposition, this takes place at significantly lower temperatures than those observed with conventional pyrolysis, 320 °C. Wax removal by scCO2 influences the dielectric properties of the straw, enhancing microwave absorption with rapid heating rates and elevated final pyrolysis temperatures, illustrating the benefits of combining these sustainable technologies within a holistic rice straw biorefinery.

Original languageEnglish
Pages (from-to)29-45
Number of pages17
JournalRSC Advances
Issue number1
Publication statusPublished - 2 Jan 2024

Bibliographical note

Funding Information:
Chanettee Sikhom gratefully acknowledges funding through The Oil Refinery Contract Contribution Fund and the Ministry of Energy, Thailand. This research was supported by the Fundamental Fund of Khon Kaen University. The research on “Valorisation of low value sugarcane residues through a development of sustainable advanced materials and biofuels” by Khon Kaen University, Department of Chemistry, has received funding support from the National Science, Research, and Innovation Fund. This project is funded by National Research Council of Thailand (NRCT) (Grant number: No. 42A650240). The Center of Excellence for Innovation in Chemistry (PERCH-CIC), Ministry of Higher Education, Science, Research, and Innovation is also gratefully acknowledged.

Publisher Copyright:
© 2024 The Royal Society of Chemistry.

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