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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.

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.