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Atmospheric pressure nonthermal plasma treatment can be a novel, green and low energy method to convert biomass to biobased chemicals. The unique physiochemistry of plasma discharge enables reactions within biomass that otherwise could not possibly occur under traditional conditions. In this study, we present a simple method of producing a high yield of levoglucosan from cellulose without using any catalysts, chemicals, solvents or vacuum, but by using plasma treatment to control the depolymerization mechanism of cellulose. Cellulose was first pretreated in a dielectric barrier discharge reactor operating in ambient air or argon for 10–60 s, followed by pyrolysis at 350–450 °C to produce up to 78.6% of levoglucosan. Without the plasma pretreatment, the maximum yield of levoglucosan from cellulose pyrolysis was 58.2%. The results of this study showed that the plasma pretreatment led to homolytic cleavage of glycosidic bonds. The resulting free radicals were then trapped within the cellulose structure when the plasma discharge stopped, allowing subsequent pyrolysis of the plasma-pretreated cellulose to proceed through a radical-based mechanism. The present results also revealed that although the radical-based mechanism is highly selective to levoglucosan formation, this pathway is usually discouraged when the untreated cellulose is pyrolyzed due to the high energy barrier for homolytic cleavage. Initiating homolytic cleavage during the plasma pretreatment also helped the pretreated cellulose to produce higher yields of levoglucosan using lower pyrolysis temperatures. At 375 °C, the levoglucosan yield was only 53.2% for the untreated cellulose, whereas the yield reached 77.6% for the argon-plasma pretreated cellulose.
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Remarkable selectivity of polyvinyl alcohol oxidation: An insight from ambient air plasma in the presence and absence of TiO2
Initiating depolymerization at ambient temperature by nonthermal air plasma provides a novel and promising route to convert polymer wastes to valuable small molecules. This study showed that the selectivity of partial oxidation of polyvinyl alcohol (PVA) initiated by nonthermal air plasma can be controlled by the polymer to TiO2 ratio and AC (alternative current) voltage and frequency. Transient responses to applying AC (alternating current) power showed that the CO2 led to the formation of CO, propionaldehyde, and acetaldehyde. Significant formation of propionaldehyde showed that -C-OH in PVA can be directly converted to CH3 in propionaldehyde, unraveling a new reaction pathway in nonthermal plasma chemistry. The selectivity of aldehydes is at the same level as that of CO2. The selectivity of aldehydes was further enhanced by nitrogen plasma while the selectivity toward CO2 was increased in the presence of TiO2. This study demonstrated that ambient nonthermal air plasma could provide a potentially effective approach for the selective conversion of polymers to desired small molecules.
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- Award ID(s):
- 2132178
- PAR ID:
- 10539709
- Publisher / Repository:
- Elsevier
- Date Published:
- Journal Name:
- Applied Catalysis O: Open
- Volume:
- 192
- Issue:
- C
- ISSN:
- 2950-6484
- Page Range / eLocation ID:
- 206921
- Subject(s) / Keyword(s):
- Partial oxidation Transient response Acetaldehyde Propionaldehyde Nonthermal plasma chemistry
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1016/j.apcato.2024.206921
