No abstract

Lignin solvolysis from the plant cell wall is the critical first step in lignin depolymerization processes involving whole biomass feedstocks. However, little is known about the coupled reaction kinetics and transport phenomena that govern the effective rates of lignin extraction. Here, we report a validated simulation framework that determines intrinsic, transport‐independent kinetic parameters for the solvolysis of lignin, hemicellulose, and cellulose upon incorporation of feedstock characteristics for the methanol‐based extraction of poplar as an example fractionation process. Lignin fragment diffusion is predicted to compete on the same time and length scales as reactions of lignin within cell walls and longitudinal pores of typical milled particle sizes, and mass transfer resistances are predicted to dominate the solvolysis of poplar particles that exceed approximately 2 mm in length. Beyond the approximately 2 mm threshold, effectiveness factors are predicted to be below 0.25, which implies that pore diffusion resistances may attenuate observable kinetic rate measurements by at least 75 % in such cases. Thus, researchers are recommended to conduct kinetic evaluations of lignin‐first catalysts using biomass particles smaller than approximately 0.2 mm in length to avoid feedstock‐specific mass transfer limitations in lignin conversion studies. Overall, this work highlights opportunities to improve lignin solvolysis by genetic engineering and provides actionable kinetic information to guide the design and scale‐up of emerging biorefinery strategies.

Four principal intra-particle phenomena occur in a highly concerted manner during the pyrolysis of lignocellulosic materials: heat transfer, mass transfer, chemical reactions, and phase changes.

This paper presents results on the primary pyrolysis products of organosolv lignin at temperatures between 360 and 700 °C. To study the primary products, a vacuum screen heater (heating rate of 8000 °C/s, deep vacuum of 0.7 mbar, and very fast cooling at the wall temperature of −100 °C) was used. The effect of the temperature on the primary and secondary lignin products was studied with a fluidized-bed pyrolysis reactor (T reactor between 330 and 580 °C) with pine wood. The results obtained with the screen heater show that the primary products of lignin were oligomers. Between 450 and 700 °C, the yield of these oligomers was very high, between 80 and 90%. After formation, the oligomers left the particle by evaporation or thermal ejection. Monophenols and other light compounds were formed by secondary reactions inside the particle or in the vapor phase. In the fluidized-bed reactor, significant quantities of lignin oligomers were formed along with monophenols, water, and other light compounds. The changes on the yield and composition of the lignin-derived oligomers as a function of the pyrolysis temperature are reported. The lignin oligomers were isolated by cold-water precipitation and analyzed with thermogravimetry (TG), Fourier transform infrared (FTIR) spectroscopy, pyrolysis−gas chromatography/mass spectrometry (Py−GC/MS), electrospray ionization−mass spectrometry (ESI−MS), gel permeation chromatography (GPC), and proton nuclear magnetic resonance ( 1 H NMR). The yield of lignin-derived oligomers reached a maximum between 450 and 580 °C. The differential thermogravimetry (DTG) results show the existence of three major peaks, which where maximal between 450 and 480 °C, indicating that not only the yield but also the structure of the lignin oligomers changed at higher pyrolysis temperatures. Py−GC/MS and 1 H NMR results indicated that, as the temperature increased, the content of methoxylated phenols decreased and the content of alkylated phenols increased. FTIR spectroscopy revealed an increase in carbonyl groups produced by carbonylation reactions, from the hydroxyl groups or the cleavage of ether bonds. Both ESI−MS and GPC results show a negligible effect of the pyrolysis temperature on the molar weight distribution. This result differs with the increase in the molecular weight observed for organosolv lignin pyrolyzed in the screen heater and highlights the importance of secondary reactions on the outcome of fast pyrolysis reactors.

Applications and associated processing technologies of lignocellulosic biomass are becoming increasingly important as we endeavor to meet societal demand for fuels, chemicals, and materials from renewable resources. Meanwhile, the rapidly expanding availability and capabilities of high-performance computing present an unprecedented opportunity to accelerate development of technologies surrounding lignocellulose utilization.In order to realize this potential, suitable modeling frameworks must be constructed that effectively capture the multiscale complexity and tremendous variety exhibited by lignocellulosic materials. In our assessment of previous endeavors toward this goal, several important shortcomings have been identified: (1) the lack of multiscale integration strategies that capture emergent properties and behaviors spanning different length scales and (2) the inability of many modeling approaches to effectively capture the variability and diversity of lignocellulose that arise from both natural and process-induced sources. In this Perspective, we survey previous modeling approaches for lignocellulose and simulation processes involving its chemical and mechanical transformation and suggest opportunities for future development to enhance the utility of computational tools to address barriers to widespread adoption of a renewable bioeconomy.