Producing high yield of levoglucosan by pyrolyzing nonthermal plasma-pretreated cellulose
Producing high yield of levoglucosan by pyrolyzing nonthermal plasma-pretreated cellulose
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DOI：
10.1039/d0gc00255k
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发表时间：
2020-03-21
期刊：
影响因子：
9.8
通讯作者：
Bai, Xianglan
中科院分区：
文献类型：
--
作者：
Lusi, A.;Hu, Haiyang;Bai, Xianglan
大气压低温等离子体处理是一种新型的、绿色的、低能耗的生物质转化方法。等离子体放电的独特物理化学使生物质内的反应成为可能，否则在传统条件下不可能发生。在这项研究中，我们提出了一个简单的方法，生产高产量的左旋葡聚糖从纤维素不使用任何催化剂，化学品，溶剂或真空，但通过使用等离子体处理来控制纤维素的解聚机制。纤维素首先在环境空气或氩气中操作的介电阻挡放电反应器中预处理10-60秒，然后在350-450 ℃下热解以产生高达78.6%的左旋葡聚糖。在没有等离子体预处理的情况下，纤维素热解的左旋葡聚糖的最大产率为58.2%。本研究的结果表明，等离子体预处理导致糖苷键的均裂。当等离子体放电停止时，所得的自由基然后被捕获在纤维素结构内，从而允许等离子体预处理的纤维素的后续热解通过基于自由基的机制进行。目前的结果还表明，虽然自由基为基础的机制是高度选择性的左旋葡聚糖形成，这种途径通常是不鼓励时，未处理的纤维素被热解，由于高能量障碍均裂。在等离子体预处理期间引发均裂也有助于预处理的纤维素使用较低的热解温度产生较高产率的左旋葡聚糖。在375 ℃下，未处理的纤维素的左旋葡聚糖产率仅为53.2%，而氩等离子体预处理的纤维素的产率达到77.6%。
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 degrees 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 degrees C, the levoglucosan yield was only 53.2% for the untreated cellulose, whereas the yield reached 77.6% for the argon-plasma pretreated cellulose.