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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.

Renewed interest in production of 1,3-butadiene from non-petroleum sources has motivated research into novel production routes. In this study, we investigated an integrated process comprising 1-butanol dehydration over a γ-Al2O3 catalyst to produce a mixture of linear butenes, coupled with a downstream K-doped Cr2O3/Al2O3 catalyst to convert the butenes into butadiene. Linear butene yields greater than 90% are achievable at 360 °C in the dehydration step, and single-pass 1,3-butadiene yields greater than 40% are achieved from 1-butene in a N2 atmosphere in the dehydrogenation step. In the integrated process, 1,3-butadiene yields are 10–15%. In all cases, linear C4 selectivity is greater than 90%, suggesting that 1,3-butadiene yields could be significantly improved in a recycle reactor. Doping the Cr2O3 catalyst with different metals to promote H2 consumption in a CO2 atmosphere did not have a large effect on catalyst performance compared to an undoped Cr2O3 catalyst, although doping with K in an N2-diluted atmosphere and with Ni in a CO2-enriched atmosphere showed slight improvement. In contrast, doping with K and Ca in a CO2-enriched atmosphere showed slightly decreased performance. Similarly, employing a CO2-enriched atmosphere in general did not improve 1,3-butadiene yield or selectivity compared to reactions performed in N2. Overall, this study suggests that an integrated dehydration/dehydrogenation process to convert 1-butanol into 1,3-butadiene could be feasible with further catalyst and process development.

We conduct a combined experimental and computational study to reveal the kinetics of tandem glucose isomerization and fructose dehydration to 5-hydroxymethylfurfural (HMF) over a bifunctional zeolite H-BEA-25 in water. The model accounts for multicomponent adsorption, homogeneous Bronsted acid catalyzed chemistry of fructose, intrinsic heterogeneous Lewis acid catalyzed isomerization, Bronsted acid catalyzed fructose dehydration, HMF rehydration, and humin formation chemistry. The octahedrally coordinated extra-framework Al sites catalyze glucose to fructose isomerization effectively. The activation energy for the isomerization in H-BEA-25 is between those reported for Ti-BEA and Sn-BEA. We reveal that tandem reactions exhibit multiple kinetic regimes. When a bifunctional catalyst with a fixed total number of acid sites is used (e.g., aluminosilicate zeolites), the HMF formation rate exhibits a volcano type curve vs. the Lewis to Bronsted acid site ratio. On the other hand, when the two types of sites are varied independently (e.g., in Sn-BEA and HCl), the HMF formation rate increases and then approaches a plateau with increasing Bronsted acid site density. These appear to be generic features of tandem reactions catalyzed by multiple or multifunctional catalysts. We show that materials with stronger sugar adsorption would produce HMF in significantly higher yields and higher rate than H-BEA. When HMF degradation reactions are suppressed, a ratio of Lewis to Bronsted acid sites of ∼0.3 maximizes the HMF rate produced from glucose and the HMF yield (which is predicted to be ∼60% at 130 °C). These predictions provide a framework for understanding and improving tandem reactions catalyzed by heterogeneous catalysts.

Catalytic partial oxidation (CPO) reactors have complex concentration and temperature gradients which make it difficult to understand the mechanism of autothermal operation. Previous research in the Schmidt group on methane CPO using the capillary sampling technique has shown the existence of two zones – oxidation and reforming [1] , [2] , [3] , [4] . Nearly (>90%) all of the oxygen in the feed is converted within the first 2 mm of the catalyst bed. In this paper, temperature and concentration profiles during the CPO of methane and dimethyl ether CH3OCH3, an oxygenated hydrocarbon, are presented. Results with the two feeds are compared and the nature of the profiles was similar, with sharp gradients existing in the oxidation zone with slower chemistries in the reforming section. The rhodium catalyst in the oxidation zone during methane CPO was also analyzed using XPS and XRD and shown to be rhodium metal.

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.

We show that in the aqueous-phase dehydration of fructose to 5-hydroxymethyl furfural (HMF) with zeolite catalysts, about 1–2 wt% of the zeolite dissolves, resulting in a solution of aluminosilicate species with Al 1.2–26.2 mg/L and Si up to 226 mg/L. The actual concentration of these species depends on the zeolite type used and on its Si/Al ratio. These species homogeneously catalyze side reactions of fructose and sequential reactions of HMF, but not glucose–fructose isomerization. This is in contrast to what has been observed using zeolites and several Al3+ salts. Fructose conversion to glucose, HMF, and levulinic acid was observed with several dissolved Al and Si salts (e.g., aluminum formate, Al(HCO2)3, aluminum lactate, Al(C3H5O3)3, and AlCl3). Detailed characterization using NMR, FTIR, DLS and XRD suggests that the active species dissolved from the zeolites are probably oligomeric aluminosilicate fragments in which the Al O Si and Si O Si connectivity is similar to that of amorphous aluminosilicate solids that do not catalyze hexose isomerization reactions.

The main paths by which zeolites carry out the dehydration of fructose to HMF and the rehydration of HMF to levulinic acid in aqueous solutions are elucidated using an H-BEA zeolite with SiO2/Al2O3 = 18 (H-BEA-18) as a representative solid acid catalyst. Specifically, the relative role of homogeneous chemistry (both solvent- and zeolite-induced), the effect of external surface acid sites, and the effect of adsorption of products and reactants on the catalyst for these reactions is delineated. We found that H-BEA-18 increases the conversion of fructose and HMF in part by catalyzing fructose isomerization to glucose and HMF rehydration to formic and levulinic acids, respectively. The glucose-to-fructose isomerization is caused by octahedral aluminum atoms that act as Lewis acid sites as shown by 1H and 13C NMR. These Lewis sites are formed during calcination and are stable under reaction conditions. They also catalyze reactions to unknown products from both fructose and HMF. The acids produced from HMF rehy...

The development of biofuels produced from biomass-derived pyrolysis oils (bio-oil) requires a deeper understanding of the bio-oil vaporization required for catalytic hydrodeoxygenation, reforming and combustion processes. Through the use of high-speed photography, bio-oil droplets on a 500 °C alumina disk in nitrogen gas were observed to undergo violent microexplosions capable of rapidly dispersing the fuel. High speed photography of the entire droplet lifetime was used to determine explosion times, frequency and evaporation rates of the bio-oil samples that have been preprocessed by filtering or addition of methanol. Filtration of the oil prior to evaporation significantly reduced the fraction of droplets that explode from 50% to below 5%. Addition of methanol to bio-oil led to uniform vaporization while also increasing the fraction of droplets that exploded. Experiments support the necessity of dissolvable solids for the formation of a volatile core and heavy shell which ruptures and rapidly expands to ...

The four isomers of butanol offer an interesting platform from which to study the reaction pathways of alcohols in an autothermal partial oxidation system, as they comprise one tertiary, one secondary, and two primary alcohols with the same number of carbon atoms. We demonstrate high yields of syngas or unsaturated molecules at contact times on the order of 10 ms, and investigate the reaction pathways of each isomer over Rh, RhCe, Pt, and PtCe catalysts for a range of carbon-to-oxygen (C/O) ratios. For each isomer, conversion to equilibrium syngas products is essentially complete at C/O = 0.8. As C/O ratio increases, the major product from the primary and secondary butanols switches to the corresponding carbonyl, producing butyraldehyde, isobutyraldehyde, and butanone from 1-butanol, isobutanol and 2-butanol, respectively. Selectivity to the carbonyls approached 30–50% as C/O approached 2.0. Dehydration to the corresponding butenes is relatively minor in comparison, representing less than 20% selectivity at C/O = 2.0. tert -butanol reacted differently, selecting mainly for the dehydration product isobutene. Acetone was the main carbonyl product from tert -Butanol, but selectivity to acetone was always ≤10%. Global mechanisms in an autothermal reactor, based on pyrolysis, combustion and surface science literature, are proposed for each alcohol. Surface chemistry likely accounts for much of the syngas formation and heat generation, while the carbonyls and alkenes may be formed primarily through homogeneous routes.

We performed a long-term study of the autothermal reforming of glycerol. Liquid glycerol and water were introduced into a quartz reactor at room temperature and mixed with air in a nebulizer. The aerosol reacted to form H2, H2O, CO, and CO2 over a bed of spherical Rh−Ce/CeO2/Al2O3 particles, with minor production of C2+ species. Catalyst deactivation was exhibited by a decrease in the production of H2 and CO2 and increases in CO and temperature over 450 h. The product changes suggest reduction in the water−gas shift reaction, which is typically promoted by Ce. SEM analysis indicated sintering of the catalyst due to high reaction temperatures, and EDS showed inorganic deposits on the walls of the quartz reactor and on the catalyst spheres. Etching of the quartz reactor shell was also observed.

Glycerol, a commodity by-product of the biodiesel industry, has value as a fuel feedstock and chemical intermediate. It is also a simple prototype of sugars and carbohydrates. Through catalytic partial oxidation (CPOx), glycerol can be converted into syngas without the addition of process heat. We explored the CPOx of glycerol using a nebulizer to mix droplets with air at room temperature for reactive flash volatilization. Introducing this mixture over a noble-metal catalyst oxidizes the glycerol at temperatures over 600 degrees C in 30-90 ms. Rhodium catalysts produce equilibrium selectivity to syngas, while platinum catalysts produce mainly autothermal non-equilibrium products. The addition of water to the glycerol increases the selectivity to H(2) by the water gas shift reaction and reduces non-equilibrium products. However, water also quenches the reaction, resulting in a maximum in H(2) production at a steam/carbon ratio of 2:3 over a Rh-Ce catalyst. Glycerol without water produces a variety of chemicals over Pt, including methylglyoxal, hydroxyacetone, acetone, acrolein, acetaldehyde, and olefins.

Catalytic partial oxidation (CPO) of isobutanol to produce synthesis gas with varying H2/CO ratios has been performed autothermally in a staged millisecond-contact-time reactor. A 1 wt% Rh-1 wt% Ce/α-alumina catalyst was used to carry out CPO of isobutanol over a range of fuel to oxygen ratios (C/O) in ∼20 ms residence times. Steam was added (S/C = 0 to S/C = 3) to promote the water gas shift (WGS) reaction and increase hydrogen production. Without steam addition, the maximum CO and H2 selectivities obtained were greater than 70%. Steam addition increased the maximum hydrogen selectivity to 103%, at C/O = 1 and S/C = 2. Conversion of isobutanol and oxygen was always > 99% at all C/O and S/C ratios after CPO where the autothermal temperatures were typically between 600 and 1000 °C . A 1 wt% Pt–1 wt% Ce catalyst was added downstream of the CPO stage to further reduce the CO and increase the H2 concentrations by the WGS reaction. Addition of the WGS stage resulted in a product stream containing 1.7 to 3 mol% CO at S/C of 2 and 3 which is comparable to the exit stream CO concentration of an industrial high temperature shift catalyst. With steam addition, selectivities to hydrogen greater than 100% were obtained at all C/O ratios, with a maximum of 122% at C/O = 0.9 and S/C = 3. At S/C = 3, the H2/CO ratio increased from ∼3 after the CPO stage to ∼12 after the WGS stage. Also, the WGS catalyst reduced the selectivities of non-equilibrium products like isobutylene and isobutyraldehyde by almost half compared to that after the CPO stage, which can reduce syngas cleanup costs after a reformer. Since the total residence time in the reactor is ∼100 ms and the product distribution can be tuned by addition of steam, this represents a compact and simple system for producing renewable syngas or hydrogen.

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.