Title : Comparative study of sawdust and corn stover biomass: Evaluating the influence of reaction temperature on lignin depolymerization, sugar extraction, and reaction kinetics.
Abstract:
Lignin, composed of monomeric aromatic compounds, holds significant promise as a feedstock for producing value-added products. Despite this potential, lignin derived from biomass has conventionally been regarded as a mere waste byproduct, often utilized solely for its calorific value through combustion in various applications. In this study, we present the catalytic conversion of lignin derived from sawdust and corn stover biomass into phenolic monomers and the temperature dependency on the total yield of lignin and sugars and followed by calculation of reaction kinetic parameters. Biomass was analyzed to determine the total percentages of cellulose, hemicellulose, lignin, inorganics, and wax. A 100 ml batch Parr Reactor was used to run the reactions with temperatures ranging from 160oC-300oC and pressure ranging from 30-200 bar. A nickel on activated carbon catalyst was prepared using an incipient impregnation method with 11% metal loading. Methanol was used as a solvent and reactions were conducted at a supercritical temperature and pressure. The output of the reactor was analyzed for the (i) percentage of lignin extracted from the available lignin using Mass Balance analysis, (ii) the concentration of lignin in the cellulose fraction, (iii) the amount of cellulose, hemicellulose, and sugars in the depolymerized lignin fraction and (iv) weight percentage of phenolic components in the depolymerized lignin sample using GC-FID analysis. At 160oC, 4% (±0.4%) of the available lignin was extracted for sawdust and 1% (±0.6%) for corn stover. The extraction substantially increases at 300oC to 95% (±1.2%) for sawdust and 92% (±2.2%) for corn stover. Of the total extracted lignin at 300oC, 87% (±0.2%) and 80% (±0.6%) were identified as phenolic monomers for sawdust and corn stover, respectively. A total of 12 phenolic monomers were identified using GC-FID analysis. A possible temperature dependent depolymerization pathway was analyzed. The reaction rate of lignin depolymerization directly correlates to the temperature and pressure generated within the reactor. Above 240oC, the rate increases by almost two-fold as methanol behaves as a supercritical solvent. The calculated activation energies for sawdust and corn stover biomass were 54.33 kJ/mol (R2 = 0.9220) and 62.32 kJ/mol (R2 = 0.9740), respectively. Corn stover has a more complex matrix than sawdust which makes lignin more recalcitrant to extraction, thereby increasing the activation energy required.
