Mechanistic and kinetic investigation on maximizing the formation of levoglucosan from cellulose during biomass pyrolysis
Mechanistic and kinetic investigation on maximizing the formation of levoglucosan from cellulose during biomass pyrolysis
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DOI：
10.1016/j.fuel.2020.119444
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发表时间：
2021-02
期刊：
影响因子：
7.4
通讯作者：
Alexander Shaw;Xiaolei Zhang;L. Kabalan;L. Jun
中科院分区：
文献类型：
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作者：
Alexander Shaw;Xiaolei Zhang;L. Kabalan;L. Jun
左旋葡聚糖是生物质热解过程中的重要中间体，近年来，人们对左旋葡聚糖的生成进行了大量的实验和计算研究。虽然已经提出了有希望的机制来解释左旋葡聚糖的形成，但抑制纤维素化学计量产率的因素还有待澄清，并且目前可用的机制采用短链寡糖结构的模型化合物而不是纤维素聚合物。在这项工作中，构建了描述纤维素（聚合度DP为2048）分解和左旋葡聚糖形成的动力学模型。发现温度和停留时间协同影响左旋葡聚糖的产率，即在600 °C下在80 s内可以达到最大产率，然而，在550 °C下需要约10 min。大于DP8的脱水低聚糖将产生，然后在热解温度为500 °C及以上的情况下在60秒内消耗。结果还表明，目前可用的协同引发和解聚反应不足以解释实验观察到的纤维素解聚和左旋葡聚糖形成的高速率，必须考虑其他关键因素，如副反应。此外，还发现左旋葡聚糖的生成速率与初始纤维素链长无关，这一发现将促进生物能源和生物质分解领域的未来研究。
Attempts to understand and control the formation of levoglucosan, as a key bio-oil compound and an important intermediate chemical, during biomass pyrolysis have recently generated a large number of experimental and computational studies. Whilst promising mechanisms have been put forward to explain levoglucosan formation, there has yet to be clarity on the factors that inhibit the stoichiometric yields from cellulose, and, current available mechanisms adopt model compounds of short chain oligosaccharide structures rather than cellulose polymer. In this work, kinetic models describing cellulose (with Degree of Polymerisation DP of 2048) decomposition and levoglucosan formation have been constructed. It was found that temperature and residence time co-ordinately influenced the yield of levoglucosan, i.e. maximum yield can be reached within 80 s at 600 °C, however, around 10 min is required at 550 °C. Anhydro-oligosaccharides greater than DP8 will be generated and then consumed in 60 s with pyrolysis temperatures of 500 °C and over. The results also showed that the current available concerted initiation and depropagation reactions are insufficient to explain the experimentally observed high rates of cellulose depolymerisation and levoglucosan formation, other key factors such as side reactions have to be considered. Additionally, it was found that the rate of levoglucosan generation is independent of the initial cellulose chain length, which is a finding that will facilitate future studies in the area of bioenergy and biomass decomposition.