An official website of the United States government
Fast pyrolysis of lignocellulosic biomass is a promising approach for producing biofuels and renewable chemicals, but the resultant bio-oil quality and diverse product distributions limit its widespread adaptation. Concurrently, the accumulation of waste plastics in the environment, particularly polyolefin thermoplastics, is becoming a growing threat. Co-pyrolysis of biomass with hydrogen-rich thermoplastics has shown promise for producing high-quality bio-oils, presenting an attractive solution to waste management. However, a molecular-level understanding of the synergy of the two components in the molten phase during co-pyrolysis is still lacking. In this work, we report the discovery of catalytic and inhibitory effects on cellulose fast pyrolysis caused by noncovalent interactions (NCIs) induced by molten plastics. Our microreactor experiments demonstrated that selectivity toward cellulose-derived anhydrosugars, small oxygenates, or furans increased due to the presence of polyketone, polyethylene glycol, or polystyrene, respectively, which are three thermoplastics with distinct functional groups. Density functional theory calculations reveal that key cellulose pyrolysis pathways leading to major products are catalyzed or inhibited due to perturbations of transition state geometries and partial charges caused by the NCIs induced by plastic functional groups. This discovery offers insights and opportunities for tuning cellulose fast pyrolysis via NCIs using a new family of unconventional molten plastic catalysts or inhibitors
more »
« less
Catalytic and Inhibitory Effects Induced by Noncovalent Interactions between Cellulose and Lignin during Fast Pyrolysis
Biomass fast pyrolysis has emerged as a highly promising technology for producing renewable fuels and chemicals. However, the inherent multi-scale and multiphase nature of the process and the heterogeneous nature of biomass feedstocks typically lead to low selectivity toward each bio-oil molecule, posing significant commercialization challenges. Molecular-level understanding of the biomass pyrolysis reaction kinetics considering the interactions between the main constituents (i.e., cellulose, hemicellulose, and lignin) is essential to advance the macroscopic design, scale-up, and optimization of the process. In this work, microreactor experiments were conducted to determine the effects of lignin structures on the yields of cellulose-derived products during pyrolysis. We show that levoglucosan formation is inhibited by the β-O-4 lignin linkages or catalyzed by the 5-5 linkages, glycolaldehyde formation is catalyzed by the β-O-4 linkages or inhibited by the 5-5 linkages, and 5-hydroxymethylfurfural formation is inhibited by either linkage. Density functional theory calculations reveal that these catalytic and inhibitory effects on cellulose fast pyrolysis are induced by noncovalent interactions between cellulose and lignin. The molecular-level picture of cellulose–lignin interactions uncovered in this work paves the way for further use of genetic engineering to grow new genotypes of biomass for selective production of value-added chemicals and machine learning approaches to obtain correlations between biomass structures and product yields for biomass fast pyrolysis.
more »
« less
- Award ID(s):
- 1847289
- PAR ID:
- 10543420
- Publisher / Repository:
- American Chemical Society
- Date Published:
- Journal Name:
- ACS Sustainable Chemistry & Engineering
- Volume:
- 12
- Issue:
- 26
- ISSN:
- 2168-0485
- Page Range / eLocation ID:
- 9591 to 9601
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Lignin depolymerization to aromatic monomers with high yields and selectivity is essential for the economic feasibility of many lignin-valorization strategies within integrated biorefining processes. Importantly, the quality and properties of the lignin source play an essential role in impacting the conversion chemistry, yet this relationship between lignin properties and lignin susceptibility to depolymerization is not well established. In this study, we quantitatively demonstrate how the detrimental effect of a pretreatment process on the properties of lignins, particularly β-O-4 content, limit high yields of aromatic monomers using three lignin depolymerization approaches: thioacidolysis, hydrogenolysis, and oxidation. Through pH-based fractionation of alkali-solubilized lignin from hybrid poplar, this study demonstrates that the properties of lignin, namely β-O-4 linkages, phenolic hydroxyl groups, molecular weight, and S/G ratios exhibit strong correlations with each other even after pretreatment. Furthermore, the differences in these properties lead to discernible trends in aromatic monomer yields using the three depolymerization techniques. Based on the interdependency of alkali lignin properties and its susceptibility to depolymerization, a model for the prediction of monomer yields was developed and validated for depolymerization by quantitative thioacidolysis. These results highlight the importance of the lignin properties for their suitability for an ether-cleaving depolymerization process, since the theoretical monomer yields grows as a second order function of the β-O-4 content. Therefore, this research encourages and provides a reference tool for future studies to identify new methods for lignin-first biomass pretreatment and lignin valorization that emphasize preservation of lignin qualities, apart from focusing on optimization of reaction conditions and catalyst selection.more » « less
-
The cleavage of lignin ether bonds via transfer hydrogenolysis remains a promising route for the valorization of lignin. To make this process efficient, a method would need to be developed that utilizes mild conditions and a renewable hydrogen donor solvent, in addition to avoiding high pressure of hydrogen. Herein, we demonstrate the efficient catalytic transfer hydrogenolysis of lignin model compounds possessing aromatic ether bonds, including α-O-4, β-O-4 and 4-O-5 linkages, using Pd-doped hydrotalcites as heterogeneous catalysts and ethanol as the hydrogen donor. Catalysts that can carry out transfer hydrogenolysis and decarbonylation in tandem are yet to be reported. Quantitative conversions and yields were realized for all model compounds studied, demonstrating the utility of the metal-doped hydrotalcites for this catalytic application. The system was applied to whole pine biomass to achieve delignification (86%) and a phenolic monomer yield of 39%.more » « less
-
Abstract BackgroundCellulose degradation by cellulases has been studied for decades due to the potential of using lignocellulosic biomass as a sustainable source of bioethanol. In plant cell walls, cellulose is bonded together and strengthened by the polyphenolic polymer, lignin. Because lignin is tightly linked to cellulose and is not digestible by cellulases, is thought to play a dominant role in limiting the efficient enzymatic degradation of plant biomass. Removal of lignin via pretreatments currently limits the cost-efficient production of ethanol from cellulose, motivating the need for a better understanding of how lignin inhibits cellulase-catalyzed degradation of lignocellulose. Work to date using bulk assays has suggested three possible inhibition mechanisms: lignin blocks access of the enzyme to cellulose, lignin impedes progress of the enzyme along cellulose, or lignin binds cellulases directly and acts as a sink. ResultsWe used single-molecule fluorescence microscopy to investigate the nanoscale dynamics of Cel7A fromTrichoderma reesei, as it binds to and moves along purified bacterial cellulose in vitro. Lignified cellulose was generated by polymerizing coniferyl alcohol onto purified bacterial cellulose, and the degree of lignin incorporation into the cellulose meshwork was analyzed by optical and electron microscopy. We found that Cel7A preferentially bound to regions of cellulose where lignin was absent, and that in regions of high lignin density, Cel7A binding was inhibited. With increasing degrees of lignification, there was a decrease in the fraction of Cel7A that moved along cellulose rather than statically binding. Furthermore, with increasing lignification, the velocity of processive Cel7A movement decreased, as did the distance that individual Cel7A molecules moved during processive runs. ConclusionsIn an in vitro system that mimics lignified cellulose in plant cell walls, lignin did not act as a sink to sequester Cel7A and prevent it from interacting with cellulose. Instead, lignin both blocked access of Cel7A to cellulose and impeded the processive movement of Cel7A along cellulose. This work implies that strategies for improving biofuel production efficiency should target weakening interactions between lignin and cellulose surface, and further suggest that nonspecific adsorption of Cel7A to lignin is likely not a dominant mechanism of inhibition.more » « less
-
Atmospheric pressure nonthermal plasma treatment can be a novel, green and low energy method to convert biomass to biobased chemicals. The unique physiochemistry of plasma discharge enables reactions within biomass that otherwise could not possibly occur under traditional conditions. In this study, we present a simple method of producing a high yield of levoglucosan from cellulose without using any catalysts, chemicals, solvents or vacuum, but by using plasma treatment to control the depolymerization mechanism of cellulose. Cellulose was first pretreated in a dielectric barrier discharge reactor operating in ambient air or argon for 10–60 s, followed by pyrolysis at 350–450 °C to produce up to 78.6% of levoglucosan. Without the plasma pretreatment, the maximum yield of levoglucosan from cellulose pyrolysis was 58.2%. The results of this study showed that the plasma pretreatment led to homolytic cleavage of glycosidic bonds. The resulting free radicals were then trapped within the cellulose structure when the plasma discharge stopped, allowing subsequent pyrolysis of the plasma-pretreated cellulose to proceed through a radical-based mechanism. The present results also revealed that although the radical-based mechanism is highly selective to levoglucosan formation, this pathway is usually discouraged when the untreated cellulose is pyrolyzed due to the high energy barrier for homolytic cleavage. Initiating homolytic cleavage during the plasma pretreatment also helped the pretreated cellulose to produce higher yields of levoglucosan using lower pyrolysis temperatures. At 375 °C, the levoglucosan yield was only 53.2% for the untreated cellulose, whereas the yield reached 77.6% for the argon-plasma pretreated cellulose.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1021/acssuschemeng.4c00481
