Mechanistic and kinetic investigation on maximizing the formation of levoglucosan from cellulose during biomass pyrolysis

Abstract

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 seconds at 600 o C, however, around 10 minutes is required at 550 o C. Anhydro-oligosaccharides greater than DP8 will be generated and then consumed in 60 seconds with pyrolysis temperatures of 500 o 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.

Commodity Chemicals and Fuels from Biomass: Thermodynamic Properties of Levoglucosan Derivatives

“…An essential aspect of the use of renewable carbon sources is the production of platform molecules from biomass and the upgrading of these molecules into valuable products . Levoglucosan is the valuable intermediate obtained from thermal degradation of the cellulose component of biomass . The general reaction for this process is shown in Figure .…”

Insight into the production of phenol from co‐pyrolysis of cellulose and sodium borohydride

“…Each glucose unit contains hydroxyl groups on C 2 , C 3 and C 6 , which can form stable hydrogen bonds within and between molecules of cellulose macromolecules 16,17 . In an earlier study, the Broidio–Shafizadeh model believed that cellulose would first decompose into an intermediate during pyrolysis, which they called ‘active cellulose’, and then this intermediate decomposed into volatiles and fixed carbon, and there would be a competitive reaction between volatiles and fixed carbon 18–22 . It is recognized that the pyrolysis of cellulose will have three product components: gas, liquid product and carbon residue (or char).…”

“…16,17 In an earlier study, the Broidio-Shafizadeh model believed that cellulose would first decompose into an intermediate during pyrolysis, which they called 'active cellulose' , and then this intermediate decomposed into volatiles and fixed carbon, and there would be a competitive reaction between volatiles and fixed carbon. [18][19][20][21][22] It is recognized that the pyrolysis of cellulose will have three product components: gas, liquid product and carbon residue (or char). Through the detection of pyrolyzed cellulose and its substitutes by gas chromatography/mass spectrometry (GC/MS), the main products are sugars, furans, acids, ketones and aldehydes, e.g.…”