Cleavage of Covalent Bonds in the Pyrolysis of Lignin, Cellulose, and Hemicellulose

Abstract

This study examines the cleavage of covalent bonds and the radical behavior in the pyrolysis of lignin, cellulose, and hemicellulose at 350, 400, and 440°C. In the presence of a sufficient amount of a hydrogen donor solvent, i.e., 9,10-dihydrophenanthrene (DHP), the quantity of covalent bonds cleaved is determined, and the quantity of stable radicals formed is measured. It is found that more than 99.9% of the radicals generated in the pyrolysis are coupled to hydrogen donated by DHP. The pyrolysis of the biomass can be characterized as cleavage of two types of covalent bonds, weak and strong. The cleavage of the weak bonds dominates the pyrolysis in the early stage, less than 10 min at 440°C, whereas that of the strong bonds becomes significant in the later stage, and its rate is promoted by DHP. The amounts of the weak bonds are 0.89 × 10 −2 , 0.63 × 10 −2 , and 0.68 × 10 −2 mol/g in lignin, cellulose, and hemicellulose, respectively. These values correspond to the sum of the C al −O and C al −C al bonds linking the unit structure in lignin and the C al −O bonds in the glucosidic linkage in cellulose and hemicellulose, respectively. Activation energies for the cleavage of these bonds in lignin, cellulose, and hemicellulose are 90.5, 129.7, and 126.5 kJ/mol, respectively.

The radical and bond cleavage behaviors of 14 coals during pyrolysis with 9,10-dihydrophenanthrene

“…DHP can donate hydrogen to radicals from coals by converting itself to phenanthrene (PHE). PHE may also form from disproportion and ring-opening reactions of DHP [16] but its amount is low (less than 4.7%) and can be determined by the amounts of 1,2,3,4-tetrahydrophenanthrene (THP) and 2-ethylbiphenyl (EBP) as reported previously [16]. Therefore, the amount of hydrogen donated to coal radicals, R H , is determined by Eq.…”

“…The amounts of DHP and its reaction products were determined by a high performance liquid chromatograph (HPLC) as reported previously [16]. DHP can donate hydrogen to radicals from coals by converting itself to phenanthrene (PHE).…”

“…This indicates that in the presence of a sufficient amount of a hydrogen donor solvent the majority of the active radicals generated in coal pyrolysis can be coupled by hydrogen from the donor solvent, which minimizes the coupling of coal radicals and allows determination of the quantity of active radicals by the amount of aromatics formed from the donor solvent. This method has been applied recently to a study of biomass pyrolysis [16], which showed that more than 99.9% of the radicals generated in the pyrolysis of lignin, cellulose and hemicellulose at temperatures of 350, 400 and 440°C acquired hydrogen from DHP at a DHP to biomass mass ratio of 8 while the stable radicals measured by ESR accounted only less than 0.1% of the total radicals.…”

Effect of Hydrolysis Treatment on Cellulose Nanowhiskers from Oil Palm (Elaeis guineesis) Fronds: Morphology, Chemical, Crystallinity, and Thermal Characteristics

“…The polyethylene bag containing reaction mixture was kept for 1 h at 70 o C. During this process lignin and hemicellulose were dissolved (Naran et al 2009;Banerjee et al 2011;Liu et al 2015), and the resulting pulp slurry was pressed at 15 psi and refined using DD series double disc refiner (Finland Metso corporation) operated at 120 kw power at 5% consistency.…”

Effective Cleavage of β-1,4-Glycosidic Bond by Functional Micelle with l-Histidine Residue

“…The efficient utilization of lignocellulosic biomass is of great practical significance to solve the problems of resource shortage, energy depletion and environmental pollution [1][2][3]. Cellulose is generally the main component of lignocellulosic biomass [4,5].…”