Controlled Synthesis of Smaller than 100 nm Lignin Nanoparticles in a Furnace Aerosol Reactor

Lignin, a constituent of biomass, is a byproduct waste of the pulp and paper industry that may have several potential applications in nanoparticle form. Conventional synthesis of lignin nanoparticles (LNPs) involves physicochemical batch and multistep processes. We report here a continuous and single-step process for the synthesis of LNPs in a furnace aerosol reactor (FuAR) starting from bulk powders with minimal use of solvents. The synthesized LNPs were analyzed for their size distribution and functional group composition. Based on the changes in functional groups, the maximum temperature in the FuAR for obtaining LNPs without significant chemical degradation was found to be around 300 °C at a residence time of 5.8 s. The as-produced LNPs had a geometric mean diameter between 50 and 68 nm. Furthermore, the bulk and as-synthesized LNPs were tested for UV protection applications. The observed improvement in UV protection with a decrease in lignin particle size is systematically investigated using the optical absorption parameter, which provides a quantitative correlation for the effect of lignin particle size and mass concentration on UV protection performance. Overall, this study contributes to advancing lignin valorization by demonstrating the synthesis of LNPs using the scalable FuAR method and providing a novel quantitative correlation for the design of high-performance lignin-based UV protection materials

Reuse of Lignin to Synthesize High Surface Area Carbon Nanoparticles for Supercapacitors Using a Continuous and Single-Step Aerosol Method

There is a growing demand for the synthesis of high surface area carbons, also known as carbon nanoparticles (CNPs). Existing synthesis methods for high surface area carbons have limited environmental benignity and economic viability due to the requirement of multistep and batch processes and harsh activating and/or templating chemicals. Herein, we demonstrate the synthesis of high surface area CNPs from lignin, a waste byproduct, through a single-step, continuous gas phase aerosol technique without the use of activating or templating chemicals. This continuous approach requires significantly less time for synthesis: on the order of seconds in comparison to hours for conventional methods. Properties of carbon materials synthesized from lignin are controlled by temperature and residence time, and the role of these parameters inside the aerosol reactor on carbon nanoparticle size, morphology, molecular structure, and surface area is systematically investigated. Furthermore, the as-obtained carbon nanoparticles are tested for specific capacitance, and the best-performing material (surface area 925 m2/g) exhibited a specific capacitance of 247 F/g at 0.5 A/g with excellent capacity retainment of over 98% after 10,000 cycles. This is a clear demonstration of their superior performance compared with supercapacitors synthesized earlier from lignin. Overall, the simple (single-step, continuous, and rapid) operation and the avoidance of the use of activating/templating chemicals make the aerosol technique a promising candidate for the scalable and sustainable synthesis of CNPs from lignin

Enhancing Aromatic Production from Reductive Lignin Disassembly: <i>in Situ</i> O‑Methylation of Phenolic Intermediates

The selective conversion of lignin into aromatic compounds has the potential to serve as a “green” alternative to the production of petrochemical aromatics. Herein, we evaluate the addition of dimethyl carbonate (DMC) to a biomass conversion system that uses a Cu-doped porous metal oxide (Cu₂₀PMO) catalyst in supercritical methanol (sc-MeOH) to disassemble lignin with little to no char formation. While Cu₂₀PMO catalyzes C–O hydrogenolysis of aryl–ether bonds linking lignin monomers, it also catalyzes arene methylation and hydrogenation, leading to product proliferation. The MeOH/DMC co-solvent system significantly suppresses arene hydrogenation of the phenolic intermediates responsible for much of the undesirable product diversity via O-methylation of phenolic −OH groups to form more stable aryl-OCH₃ species. Consequently, product proliferation was greatly reduced and aromatic yields greatly enhanced with lignin models, 2-methoxy-4-propylphenol, benzyl phenyl ether, and 2-phenoxy-1-phenylethan-1-ol. In addition, organosolv poplar lignin (OPL) was examined as a substrate in the MeOH/DMC co-solvent system. The products were characterized by nuclear magnetic resonance spectroscopy (³¹P, ¹³C, and 2D ¹H–¹³C NMR) and gas chromatography–mass spectrometry techniques. The co-solvent system demonstrated enhanced yields of aromatic products

Understanding Multiscale Structural Changes During Dilute Acid Pretreatment of Switchgrass and Poplar

Biofuels produced from lignocellulosic biomass hold great promise as a renewable alternative energy and fuel source. To realize a cost and energy efficient approach, a fundamental understanding of the deconstruction process is critically necessary to reduce biomass recalcitrance. Herein, the structural and morphological changes over multiple scales (5–6000 Å) in herbaceous (switchgrass) and woody (hybrid poplar) biomass during dilute sulfuric acid pretreatment were explored using neutron scattering and X-ray diffraction. Switchgrass undergoes a larger increase (20–84 Å) in the average diameter of the crystalline core of the elementary cellulose fibril than hybrid poplar (19–50 Å). Switchgrass initially forms lignin aggregates with an average size of 90 Å that coalesce to 200 Å, which is double that observed for hybrid poplar, 55–130 Å. Switchgrass shows a smooth-to-rough transition in the cell wall surface morphology unlike the diffuse-to-smooth transition of hybrid poplar. Yet, switchgrass and hybrid poplar pretreated under the same experimental conditions result in pretreated switchgrass producing higher glucose yields (∼76 wt %) than pretreated hybrid poplar (∼60 wt %). This observation shows that other aspects like cellulose allomorph transitions, cellulose accessibility, cellular biopolymer spatial distribution, and enzyme–substrate interactions may be more critical in governing the enzymatic hydrolysis efficiency