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When excess base is required to drive desired reactions, such as in lignin alkaline oxidation, Sr(OH)2 can offer a reversibly-soluble alternative to NaOH that allows simple recycle of the excess base with concomitant cost and environmental benefits.

Reductive catalytic fractionation (RCF) is a promising approach to fractionate lignocellulose and convert lignin to a narrow product slate. To guide research towards commercialization, cost and sustainability must be considered. Here we report a techno-economic analysis (TEA), life cycle assessment (LCA), and air emission analysis of the RCF process, wherein biomass carbohydrates are converted to ethanol and the RCF oil is the lignin-derived product. The base-case process, using a feedstock supply of 2000 dry metric tons per day, methanol as a solvent, and H2 gas as a hydrogen source, predicts a minimum selling price (MSP) of crude RCF oil of $1.13 per kg when ethanol is sold at $2.50 per gallon of gasoline-equivalent ($0.66 per liter of gasoline-equivalent). We estimate that the RCF process accounts for 57% of biorefinery installed capital costs, 77% of positive life cycle global warming potential (GWP) (excluding carbon uptake), and 43% of positive cumulative energy demand (CED). Of $563.7 MM total installed capital costs, the RCF area accounts for $323.5 MM, driven by high-pressure reactors. Solvent recycle and water removal via distillation incur a process heat demand equivalent to 73% of the biomass energy content, and accounts for 35% of total operating costs. In contrast, H2 cost and catalyst recycle are relatively minor contributors to operating costs and environmental impacts. In the carbohydrate-rich pulps, polysaccharide retention is predicted not to substantially affect the RCF oil MSP. Analysis of cases using different solvents and hemicellulose as an in situ hydrogen donor reveals that reducing reactor pressure and the use of low vapor pressure solvents could reduce both capital costs and environmental impacts. Processes that reduce the energy demand for solvent separation also improve GWP, CED, and air emissions. Additionally, despite requiring natural gas imports, converting lignin as a biorefinery co-product could significantly reduce non-greenhouse gas air emissions compared to burning lignin. Overall, this study suggests that research should prioritize ways to lower RCF operating pressure to reduce capital expenses associated with high-pressure reactors, minimize solvent loading to reduce reactor size and energy required for solvent recovery, implement condensed-phase separations for solvent recovery, and utilize the entirety of RCF oil to maximize value-added product revenues. ispartof: Energy & Environmental Science vol:14 issue:8 pages:4147-4168 ispartof: location:England status: published

The inherent reactivity of lignin in conventional biomass processing commonly prevents isolation of native lignin and limits monomer yields from catalytic depolymerization strategies that target aryl-ether bonds. Here we show that flow-through solvolysis with methanol at 225 °C produces native-like lignin from poplar, enabling the study of intrinsic lignin properties and evaluation of steady-state lignin depolymerization processes.

Correction for ‘Flow-through solvolysis enables production of native-like lignin from biomass’ by David G. Brandner et al., Green Chem., 2021, 23, 5437–5441, DOI: 10.1039/D1GC01591E.

Co-production of high-value chemicals such as succinic acid from algal sugars is a promising route to enabling conversion of algal lipids to a renewable diesel blendstock. Biomass from the green alga Scenedesmus acutus was acid pretreated and the resulting slurry separated into its solid and liquor components using charged polyamide induced flocculation and vacuum filtration. Over the course of a subsequent 756 hours continuous fermentation of the algal liquor with Actinobacillus succinogenes 130Z, we achieved maximum productivity, process conversion yield, and titer of 1.1 g L−1 h−1, 0.7 g g−1 total sugars, and 30.5 g L−1 respectively. Succinic acid was recovered from fermentation media with a yield of 60% at 98.4% purity while lipids were recovered from the flocculated cake at 83% yield with subsequent conversion through deoxygenation and hydroisomerization to a renewable diesel blendstock. This work is a first-of-its-kind demonstration of a novel integrated conversion process for algal biomass to produce fuel and chemical products of sufficient quality to be blend-ready feedstocks for further processing.

Oleaginous microbes are promising platform strains for the production of renewable diesel and fatty-acid derived chemicals given their innate capacity to produce high lipid yields from lignocellulose-derived sugars. Substantial efforts have been conducted to engineer model oleaginous yeasts primarily on model feedstocks, but to enable lipid production from biomass, judicious strain selection based on phenotypes beneficial for processing, performance on realistic feedstocks, and process integration aspects from sugars to fuels should be examined holistically. To that end, here we report the bench-scale production of diesel blendstock using a biological-catalytic hybrid process based on oleaginous yeast. This work includes flask screening of 31 oleaginous yeast strains, evaluated based on baseline lipid profiles and sugar consumption with corn stover hydrolysate. Three strains were down-selected for bioreactor performance evaluation. The cultivation results reveal that Cryptococcus curvatus ATCC 20509 and Rhodosporodium toruloides DSM-4444 exhibit equivalent fatty acid methyl ester (FAME) yield (0.24 g g−1), whereas the highest overall FAME productivity (0.22 g L−1 h−1) was obtained with C. curvatus, and R. toruloides displayed the highest final FAME titer (23.3 g L−1). Time-resolved lipid profiling (including neutral and polar lipid classing) demonstrated triacylglycerol accumulation as the predominant lipid class in all strains. When evaluating tolerance mechanisms to inhibitory compounds, all strains could reduce and oxidize 5-(hydroxymethyl)furfural, illustrating parallel detoxification mechanisms. The R. toruloides strain was also capable of growth on four aromatic compounds as a sole carbon source, suggesting its use as a strain for simultaneous sugar and lignin conversion. Lipids from R. toruloides were recovered using a mild acid treatment and extraction, hydrogenated, and isomerized to produce a renewable diesel blendstock. The blendstock exhibited a cloud point of −14.5 °C and simulated distillation showed that approximately 75% of the product was in the diesel range with a T90 consistent with no. 2 diesel fuel. Taken together, these results demonstrate an integrated process for renewable diesel production, identify oleaginous strains for further development, and highlight opportunities for improvements to an oleaginous microbial platform for the production of renewable diesel blendstock.

© The Royal Society of Chemistry 2018. Lignin conversion to renewable chemicals is a promising means to improve the economic viability of lignocellulosic biorefineries. Alkaline aerobic oxidation of lignin has long been employed for production of aromatic compounds such as vanillin and syringaldehyde, but this approach primarily focuses on condensed substrates such as Kraft lignin and lignosulfonates. Conversely, emerging lignocellulosic biorefinery schemes enable the production of more native-like, reactive lignin. Here, we revisit alkaline aerobic oxidation of highly reactive lignin substrates to understand the impact of reaction conditions and catalyst choice on product yield and distribution. The oxidation of native poplar lignin was studied as a function of temperature, NaOH loading, reaction time, and oxygen partial pressure. Besides vanillin and syringaldehyde, other oxidation products include acetosyringone and vanillic, syringic, and p-hydroxybenzoic acids. Reactions with vanillin and syringaldehyde indicated that these compounds are further oxidized to non-aromatic carboxylic acids during alkaline aerobic oxidation, with syringaldehyde being substantially more reactive than vanillin. The production of phenolic compounds from lignin is favored by high NaOH loadings and temperatures, but short reaction times, as the products degrade rapidly, which is further exacerbated by the presence of oxygen. Under optimal conditions, a phenolic monomer yield of 30 wt% was obtained from poplar lignin. Testing a range of catalysts showed that Cu-containing catalysts, such as CuSO4 and LaMn0.8Cu0.2O3, accelerate product formation; specifically, the catalyst does not increase the maximum yield, but expands the operating window in which high product yields are obtainable. We also demonstrate that other native and isolated lignin substrates that are significantly chemically modified are effectively converted to phenolic compounds. Finally, alkaline aerobic oxidation of native lignins was compared to nitrobenzene oxidation and reductive catalytic fractionation, as these methods constitute suitable benchmarks for lignin depolymerization. While nitrobenzene oxidation achieved a somewhat higher yield, similar monomer yields were obtained through RCF and alkaline aerobic oxidation, especially for lignins with a high guaiacyl- and/or p-hydroxyphenyl-content, as syringyl units are more unstable during oxidation. Overall, this study highlights the potential for aerobic lignin oxidation revisited on native-like lignin substrates.

Lignin depolymerisation is traditionally facilitated with homogeneous acid or alkaline catalysts. Given the effectiveness of homogeneous basic catalysts for lignin depolymerisation, here, heterogeneous solid-base catalysts are screened for C–O bond cleavage using a model compound that exhibits a common aryl–ether linkage in lignin. Hydrotalcite (HTC), a layered double hydroxide (LDH), is used as a support material as it readily harbours hydroxide anions in the brucite-like layers, which are hypothesised to participate in catalysis. A 5 wt% Ni/HTC catalyst is particularly effective at C–O bond cleavage of a model dimer at 270 °C without nickel reduction, yielding products from C–O bond cleavage identical to those derived from a base-catalysed mechanism. The 5% Ni-HTC catalyst is shown to depolymerise two types of biomass-derived lignin, namely Organosolv and ball-milled lignin, which produces alkyl-aromatic products. X-ray photoelectron spectroscopy and energy dispersive X-ray spectroscopy show that the nickel is well dispersed and converts to a mixed valence nickel oxide upon loading onto the HTC support. The structure of the catalyst was characterised by scanning and transmission electron microscopy and X-ray diffraction, which demonstrates partial dehydration upon reaction, concomitant with a base-catalysed mechanism employing hydroxide for C–O bond cleavage. However, the reaction does not alter the overall catalyst microstructure, and nickel does not appreciably leach from the catalyst. This study demonstrates that nickel oxide on a solid-basic support can function as an effective lignin depolymerisation catalyst without the need for external hydrogen and reduced metal, and suggests that LDHs offer a novel, active support in multifunctional catalyst applications.

The generation of primary aerosols from biomass hinders the production of biofuels by pyrolysis, intensifies the environmental impact of forest fires, and exacerbates the health implications associated with cigarette smoking. High speed photography is utilized to elucidate the ejection mechanism of aerosol particles from thermally decomposing cellulose at the timescale of milliseconds. Fluid modeling, based on first principles, and experimental measurement of the ejection phenomenon supports the proposed mechanism of interfacial gas bubble collapse forming a liquid jet which subsequently fragments to form ejected aerosol particles capable of transporting nonvolatile chemicals. Identification of the bubble-collapse/ejection mechanism of intermediate cellulose confirms the transportation of nonvolatile material to the gas phase and provides fundamental understanding for predicting the rate of aerosol generation.