Effective pretreatment is essential for producing fermentable sugars from lignocellulosic biomass. In this study, mixed-acid and organic-amine pretreatments were conducted for corncob deconstruction, component fractionation, lignin removal, and enzymatic saccharification. The sulfuric acid/maleic acid system (1:1, w/w) efficiently hydrolyzed hemicellulose, achieving glucose and xylose yields of 78.5% and 99.56%, respectively. 2D HSQC NMR analysis showed a clear decrease in the Cβ signal of β-O-4 linkages in G-type lignin units, indicating acid-catalyzed ether-bond cleavage. However, delignification in the acid system was limited to a maximum of 26.2%. In contrast, aqueous triethylamine pretreatment selectively removed lignin by cleaving ester and ether linkages in lignin-carbohydrate complexes while retaining most cellulose and hemicellulose. 2D HSQC NMR analysis revealed substantially weakened β-O-4 signals after amine pretreatment, indicating selective depolymerization with intact S and G units. Pretreatment with 30% triethylamine achieved 74% lignin removal. Enzymatic hydrolysis of the amine-pretreated residue gave 99.4% glucose, 89.1% xylose, and 93.7% total sugar yields. DFT calculations demonstrated that the amine system exhibits significantly stronger interactions with the lignin model (−32.78 kcal/mol) than organic acids (−18.52 and −15.08 kcal/mol), explaining its superior lignin affinity. These results show that mixed-acid pretreatment is suitable for xylose-oriented fractionation, whereas amine pretreatment is more suitable for delignification and glucose-oriented saccharification.
The sustainable bioeconomy is moving beyond its original role as a renewable-resource substitute for fossil production. That transition is occurring under simultaneous pressures from accelerating climate risk, transgressed Earth-system limits, biodiversity decline, resource insecurity, public-health impacts, rapid digitalization and geopolitical uncertainties. This critical review redefines the sustainable bioeconomy as a dynamic socio-ecological-technological system whose performance must be assessed across six interdependent pillars: climate mitigation and adaptation; circular and regenerative resource management; nature-positive development; human and planetary health; digital intelligence and responsible innovation; and socioeconomic resilience supported by adaptive governance. Recent high-impact evidence is synthesized to show why renewable biological origin alone is insufficient: bio-based pathways can lower emissions, recover nutrients and create new products, yet can also shift burdens to land, water, biodiversity, health, energy demand or vulnerable communities. This paper critically reviews complementary approaches relevant to bioeconomy assessment, including life-cycle assessment (LCA) and techno-economic assessment (TEA), corporate sustainability and Environmental, Social and Governance (ESG) frameworks, Sustainable Development Goal (SDG) and Earth-system-based approaches, Planetary Health and One Health frameworks, and systems, multi-criteria, and digitally enabled assessment methods. This analysis provides operational questions and maps the complementary roles and blind spots of major assessment approaches. Building on this synthesis, an integrated assessment framework and research roadmap are proposed in which minimum environmental and social safeguards, life-cycle and economic performance, resilience testing, transparent governance and continuously updated evidence are combined. The resulting perspective shifts the objectives of the bioeconomy from maximizing biomass utilization to sustaining regenerative, low-carbon and equitable system performance aligned with population health under changing climatic and societal conditions.
Sustainable aviation fuel (SAF) production from distributed biogenic carbon resources remains limited by the high capital intensity and process complexity of conventional gas-to-liquids (GTL) technologies. Here, we report the development and pilot-scale validation of Cool GTL™, an electrified, integrated GTL platform designed for the decentralized conversion of biogenic gas and CO2-derived carbon into drop-in transportation fuels. The process combines an internally electrically heated reformer, Fischer–Tropsch (FT) synthesis, and direct product upgrading in a compact configuration that eliminates external fired reformers, intermediate syngas conditioning, and stand-alone hydrocracking. The electrically heated reformer simultaneously converts CH4, C2⁺ hydrocarbons, steam, and CO2 through bi-reforming to produce synthesis gas with an H2/CO ratio of 2.0–2.55, enabling direct FT conversion without downstream adjustment. Unlike conventional GTL systems, the integrated upgrading reactor enables hydrocracking and hydroisomerization directly in the presence of CO, eliminating the need for CO removal and reducing the requirement for high-purity hydrogen supply. The fully integrated pilot plant demonstrated stable operation for more than 2,400 h using multiple carbon feedstocks and produced over 190 L of liquid hydrocarbons, with approximately 50 wt% distributed in the SAF boiling range. The optimized SAF fraction satisfied applicable ASTM fuel specifications, including freeze-point requirements. Compared with scaled-down conventional GTL designs, the simplified configuration reduced estimated capital cost by approximately 78% for a 2,500 bbl/d system. These results demonstrate an electrified, low-complexity GTL pathway that enables economically attractive decentralized production of SAF from biogenic carbon and CO2.
Biowaste valorization is increasingly promoted as a strategy for climate-change mitigation, yet converting waste into useful products does not inherently guarantee decarbonization. This review critically examines how biowaste can function as a renewable carbon resource and identifies the conditions under which its valorization delivers genuine life-cycle greenhouse-gas benefits. Biowaste streams are first classified according to physicochemical characteristics that govern pathway selection, followed by evaluation of biological, biochemical, thermochemical, chemical, and integrated biorefinery routes. Particular attention is given to five mechanisms through which valorization can contribute to decarbonization: avoidance of conventional waste-management emissions, displacement of fossil energy, displacement of fossil-derived chemicals and materials, carbon retention and durable removal, and decarbonization of the conversion process itself. The carbon value of resulting products is further assessed according to their function and residence time, distinguishing rapidly cycled fuels from chemicals, long-lived materials, stable carbon products, and geological storage of biogenic CO2. Methodological challenges in quantifying climate benefits are critically evaluated, with emphasis on system boundaries, functional units, allocation, substitution, counterfactual waste-management scenarios, temporal carbon accounting, and geographic energy mixes. Environmental burden shifting, economic viability, technological maturity, and scale-up constraints are also considered. Based on this synthesis, harmonized metrics and a feedstock-specific decision framework are proposed for selecting valorization pathways according to carbon performance, product function, economics, technological readiness, and spatial context. The review concludes that future biorefineries should evolve from biomass-conversion facilities toward integrated carbon-management systems that optimize fossil displacement, carbon utilization and permanence, environmental performance, and economic viability simultaneously.
The catalytic hydrogenolysis of aromatic C–O bonds in lignin to produce phenolic jet fuel precursors offers a promising route for lignin valorization. However, conventional methods often suffer from reliance on noble metal catalysts, harsh reaction conditions, and external hydrogen gas. Herein, we report a strategy using isopropanol as the in-situ hydrogen donor with non-precious Ni/CeO2 catalyst to hydrogenolyze lignin and lignin dimers under N2 atmosphere. The Ni/CeO2 catalyst proved highly effective in cleaving aromatic C–O bonds, mainly producing aromatic hydrocarbons and cyclohexanol. At 240 oC for 2.5 h, complete conversion of benzyloxybenzene (BOB) and 2-phenoxyphenylethanol (POPE) was achieved, and diphenyl ether (DPE) achieved 96.9 mol% conversion. A series of control experiments confirmed that Ni0 species serve as the primary active sites of Ni/CeO2, and the strong interfacial interaction between Ni and CeO2 also plays an indispensable role. For the depolymerization of organosolv lignin, syringyl (S), guaiacyl (G), and p-hydroxyphenyl (H) phenolic monomers are the main products, with carbon numbers ranging from C7 to C11, serving as effective phenolic precursors for jet fuel. A maximum monophenol yield of 36 wt% was achieved under the conditions of 240 oC, 7.5 h, and a catalyst/lignin mass ratio of 75/100. Characterization of the lignin oil and the spent catalyst confirmed that this system effectively depolymerizes lignin, with the catalyst exhibiting excellent structural stability and regenerability. In summary, this work provided an efficient approach for producing valuable phenolic precursors for jet fuel from lignin.
Genetic modification of lignocellulosic biomass can enhance its processability by reducing its recalcitrance to pretreatment and enzymatic conversion to chemicals such as biofuels. Downregulation of cinnamyl alcohol dehydrogenase 1 (CAD1) in poplar results in the increased incorporation of sinapaldehyde in the lignin polymer. Here, we investigated steam explosion as a pretreatment strategy for the enzymatic hydrolysis of field-grown CAD1-downregulated and wild-type (WT) poplar. Steam explosion at 210°C for 90 s resulted in a significantly higher lignin reduction of 25% for CAD wood, compared to 15% for WT wood. Under limited conditions at 8.4% solid loading and 8 filter paper units of Cellic Ctec3 HS per gram dry weight, enzymatic hydrolysis resulted in a significantly higher average glucose yield of 76% for CAD wood compared to 60% for WT wood. Our data show that steam explosion pretreatment of CAD1-modified poplar is a promising strategy to improve enzymatic hydrolysis without the need for additional chemicals.
Biohydrogen production offers a renewable route to convert biomass, organic residues, wastewater, and other biogenic carbon streams into a low-carbon energy carrier through biological, photochemical, electrochemical, and thermochemical pathways. Due to the complex, highly nonlinear nature of these conversion processes, conventional modeling approaches often struggle to capture system behavior across different operational scales and pathways. As a result, machine learning (ML) has emerged as a powerful tool for modeling and optimizing biohydrogen production systems. This review synthesizes ML-assisted biohydrogen production across feedstock–process–model relationships, algorithmic architectures, interpretability methods, optimization strategies, techno-economic performance, and environmental implications. The literature indicates that ML is primarily used as a surrogate modeling tool to predict hydrogen yield, production rate, syngas composition, electrochemical performance, and cost–emission trade-offs, with the greatest methodological focus on biomass gasification and fermentative systems. Across routes, influential descriptors cluster around feedstock chemistry, reaction environment, transport and electrochemical conditions, catalyst structure, irradiation regime, and residence-time effects. Despite their strong apparent predictive performance, current models remain limited by sparse and heterogeneous datasets, route-specific calibration, insufficient external validation, inadequate uncertainty quantification, and poor integration of mechanistic knowledge. Progress will require physics-informed and uncertainty-calibrated ML frameworks linked to active learning, external validation, techno-economic analysis, and life-cycle assessment. Such integration is essential for moving from local prediction toward transferable biohydrogen process design.
The chemical conversion of biomass-derived platform molecules, such as furfural, into sustainable aviation fuel (SAF) is a subject of increasing interest. This work examines the aldol condensation between two biomass-derived platforms, like furfural and methyl isobutyl ketone, to produce the corresponding adduct (FuMe), suitable as a SAF precursor. Zr-modified MOFs are typically efficient catalysts in aldol condensation. However, crystalline MOF catalysts suffer from small pore size and limited reusability, especially when applied to processes involving bulky products. To overcome these limitations, this work provided a series of zirconium MOFs supported on mesoporous SBA-15 silica, aiming at increasing both the stability and the accessibility of the Zr-MOF active phases. The characterization via XRD, TEM-EDX, XPS, ICP-AES, 13C NMR, TGA, and N2 adsorption of the MOF/mesoporous silica hybrid materials demonstrated the successful incorporation of highly dispersed Zr organo-species onto the SBA-15 surface area. As a result, the catalytic performance of the prepared hybrid materials was markedly superior to that of the corresponding free crystalline Zr-MOFs, in terms of higher condensation activity and better selectivity. The best-performing hybrid, UiO-66@SBA-15, achieved 67% furfural conversion vs 3% on the unsupported MOF, accompanied by 100% FuMe selectivity. Furthermore, reducing furfural concentration allowed achieving total conversion (100%) and FuMe selectivity (100%). This is attributed to a synergistic effect between the surface-dispersed Zr-MOF active phase and the mesoporous silica support. In addition to demonstrating enhanced catalytic activity, the synthesised materials also exhibited improved stability during subsequent condensation processes, reinforcing the benefits of supporting Zr-MOF phases onto silica surfaces.
This work investigates the vapor-phase decarbonylation of furfural to furan, a key platform intermediate, using Pd/gamma-Al2O3 catalysts under conditions approaching industrial operation. Reaction parameters, including space velocity, temperature, and pressure, were systematically optimized. Although lower pressures favor catalytic activity, a compromise pressure of 10 bar was selected to facilitate downstream separation. The optimal reaction temperature was identified as 325 degrees C, providing high activity and near-complete selectivity toward furan. Catalyst stability was enhanced through modification of the alumina support with K, Ca, and La cations. The unmodified, Ca-, and La-modified catalysts exhibited rapid deactivation within the first 24 h on stream, whereas the K-modified catalyst showed significantly improved stability with no clear deactivation over this period. At longer times on stream, gradual deactivation was observed, mainly attributed to coke deposition. The superior performance of the K-modified catalyst is associated with reduced acidity and slightmodification ofpalladium electronic density and dispersion. Regeneration of severely deactivated catalysts proved challenging, resulting in poor catalytic recovery. Therefore, regeneration was performed while conversion remained above 90% and selectivity above 95% to maintain process operability. Long-term catalyst lifetime was demonstrated through multiple reaction-regeneration cycles, achieving at least 200 h on stream without significant loss of activity or selectivity for the optimal formulation
The bio-templating approach offers a promising route for preparing highly efficient bulk hydrodesulfurization (HDS) catalysts, due to its simplicity, sustainability, and cost-effectiveness. In this study, mesoporous CoMo bulk catalysts were fabricated for the HDS of thiophene using pomelo mesocarp as a sustainable hard template via the impregnation-calcination method. The characterization results confirmed that the catalysts successfully inherited the structural features of pomelo mesocarp, resulting in a mesoporous framework composed of interconnected nanoparticles. Among these catalysts, the CoMo-0.5 catalyst exhibited the highest activity, achieving a thiophene conversion of 93.5% at 1 MPa and 360 degrees C. This superior performance can be attributed to its lower stacking number, shorter slab length, higher MoS2 dispersion, and developed mesoporous channels, which collectively increase the number of accessible active sites and promote efficient mass transfer. This study demonstrates a green and cost-effective strategy for fabricating high-performance bulk HDS catalysts using renewable biomass templates. (c) 2026 Alpha Creation Enterprise CC BY 4.0
Peatlands are essential long-term carbon sinks, yet continued peat extraction for horticulture contributes to greenhouse gas emissions and ecosystem degradation. Here, we introduce artificial peat, a peat-formation-inspired material produced by selectively mimicking natural humification pathways under controlled alkaline conditions. Unlike conventional biomass conversion processes that aim for complete degradation, carbonization, or simple constituent replacement, this approach promotes controlled partial transformation of lignocellulosic biomass into artificial humic substances while preserving a stabilized fibrous framework. Batch and continuous processing routes operated under mild conditions (≤120 °C) using widely available feedstocks, including paludiculture biomass, wood residues, leaves, and agricultural by-products. Artificial humic acid yields ranged from 6.9 to 42.3 wt% in batch systems. Across both processing modes, carbohydrate fractions decreased and lignin underwent partial depolymerization followed by condensation into humified macromolecular structures, accompanied by a marked reduction of readily oxidizable organic matter. Multimodal analyses (elemental composition, Van Krevelen evolution, FTIR, microscopy/EDX, and oxidative thermogravimetry) revealed a transition toward oxygen-rich, condensed architectures with enhanced oxidative stability relative to raw biomass. The applied thermal–alkaline conditions are expected to promote hygienization and seed inactivation, while the conversion of labile biomass components into humic substances suggests improved chemical and potential biological stability. Produced within minutes rather than millennia, artificial peat combines humic functionality with preserved structural integrity, establishing a scalable and resource-efficient alternative to natural peat for sustainable growing media and carbon stabilization applications.
The industrialisation of photofermentative biohydrogen production (PFHP) using purple non-sulfur bacteria (PNSB) is constrained by inefficient light harvesting and suboptimal photon utilisation. This study systematically investigated narrow-bandwidth monochromatic single-stimulated wavelength light (SSWL) across the ultraviolet-infrared (UV-IR) spectrum to enhance light capture and biohydrogen conversion in Rhodopseudomonas palustris. Compared with white light, SSWL at 520, 810, and 850 nm significantly increased biomass accumulation by 53.83%, 47.65%, and 40.00%, respectively. Irradiation at these wavelengths also enhanced fructose-1,6-bisphosphatase activity, reaching 1072, 1047, and 978.94 & micro;g g-1 biomass, respectively, compared with 897 & micro;g g-1 under the control spectrum. The highest accumulated biohydrogen volume (28 mL) was obtained at 520 nm, followed by 810 nm (26.02 mL) and 850 nm (23.33 mL). Enhanced hydrogen production at wavelengths above 500 nm correlated with increased photopigment synthesis, biomass assimilation, and dehydrogenase activity, which improved by 55.6%, 44.4%, and 36.8% at 520, 810, and 850 nm, respectively. Microbial community analysis further demonstrated wavelength-dependent shifts in microbial structure, with Firmicutes, Bacteroidetes, and Proteobacteria dominating across all bioreactors (99-99.80% relative abundance). Enrichment of Clostridium_sensu_stricto groups (1, 12, 13, 14, and 15) ranged from 60% to 82% under SSWL conditions. Mass and energy balance analysis revealed a significant reduction in energy requirements, with the lowest values observed at 520 nm (135 J mol-1 H2), followed by 810 nm (154.27 J mol-1 H2) and 850 nm (162.02 J mol-1 H2), compared with 1048.03 J mol-1 H2 for an incandescent light source. These findings identify 520, 810, and 850 nm as optimal wavelengths for enhancing PNSB growth and PFHP, providing mechanistic insights into wavelength-engineered metabolic regulation and establishing a foundation for the development of energy-efficient, scalable photobioreactor systems. (c) 2026 Alpha Creation Enterprise CC BY 4.0
The newly isolated Burkholderia sp. SCN-KJ, which is capable of simultaneously producing intracellular polyhydroxybutyrate (PHB) and exopolysaccharide (EPS) from biodiesel-derived crude glycerol, presented a significant challenge in this study because of interference from EPS synthesis. The bceA gene, which encodes a bifunctional protein responsible for mannose-6-phosphate isomerization and the mannose-1-phosphate guanylyltransferase reaction, was identified as a key regulator of EPS production. To address this issue, CRISPR interference (CRISPRi) was employed to target the bceA gene, leading to the complete suppression of EPS synthesis and a significant improvement in PHB yield. Under optimized culture conditions, the ΔbceA mutant strain exhibited complete inhibition of EPS production, resulting in a 1.75-fold increase in the PHB concentration and PHB of a higher molecular weight than that of the wild-type Burkholderia sp. SCN-KJ. These results highlight the effectiveness of dCas9-mediated silencing of the bceA gene in overcoming the challenges posed by EPS interference and underscore its potential for increasing PHB production in Burkholderia sp. SCN-KJ.
Lignocellulose, as a plentiful and renewable carbonaceous resource, presents an alluring alternative to fossil fuels for sustaining industries in the pursuit of a resilient bio-based economy. Sugars derived from lignocellulosic biomass play a central role as versatile platform intermediates for feeding microorganisms or as starting chemicals for manufacturing value-added fuels, chemicals, and materials. However, commercialization faces challenges due to the complexity and high costs associated with feedstock logistics and conversion processes. Pelleting offers a potential solution by addressing logistical issues while providing additional benefits for downstream conversion that may outweigh the extra costs associated with pelleting. To fully unlock the economic and sustainable potential of lignocellulosic biomass in biorefineries, recent advances in pelleting technologies and their impacts on downstream pretreatments and enzyme-mediated conversion are critically reviewed. Pelleting has been shown to improve enzymatic digestibility yields by 5‒20%. The process variables, product attributes, and their influences on bioconversion are discussed. More significantly, a thorough discussion of the effect of pelleting on various pretreatments, concerning diverse feedstocks, as well as their interplay, is provided to inform the design of future pelleting and pretreatment processes. Finally, practical considerations, including energy consumption, costs, and environmental impacts, are discussed, alongside an exploration of cutting-edge technologies and strategies in this field.
α-Ketoglutarate, a key intermediate in the TCA cycle, is crucial for amino acid synthesis and nitrogen transport. However, microbial engineering for α-ketoglutarate production is hindered by the intrinsic inefficiency of the metabolic network. In this study, transcription factor engineering was performed for the reconstruction of the metabolic network to boost α-ketoglutarate biosynthesis in Candida glabrata. Transcription factors GCR2 and RTG1 were first reinstalled to kick-start the glycolytic pathway and the TCA cycle, respectively, and then optimized to redistribute carbon flux between the two pathways. In addition, pyruvate carriers, MPC1 and MPC2, were introduced to facilitate the transport of cytoplasmic pyruvate to mitochondria, thereby feeding it into the TCA cycle for α-ketoglutarate biosynthesis. Next, transcription factor HAP4 was utilized to rewire the electron transport chain for improving redox balance and reducing overflow metabolism, thereby channeling more carbon flux to α-ketoglutarate production. Finally, the engineered strain C. glabrata KGA17 was capable of producing 210.4 g/L α-ketoglutarate in a 5-L bioreactor. This approach showed significant promise for developing efficient microbial cell factories for high-value chemical production.
The transformation of poplar biomass into bio-based chemicals, fuels, and lignin-derived products through an integrated biorefinery is essential for realizing its full potential as a sustainable and economically viable feedstock. This study presents a poplar biorefinery approach using mild biphasic pretreatment (p-toluenesulfonic acid/pentanol + AlCl3, 110°C, 40 min) to produce bio-based platform multiple products. The pretreatment achieved efficient fractionation, with 83.2% delignification, 95.2% xylan removal, and minimal cellulose loss (7.8%), enabling high-yield one-pot furfural production (68.5%, 11.3 g/L). Enzymatic hydrolysis of the cellulose-rich residue, combined with fermentation by Clostridium acetobutylicum, produced a bio-solvent mixture of 16.2 g/L, including 10.5 g/L butanol. Depolymerized lignin was recovered and subjected to catalytic hydrogenolysis, yielding 46.4% monomers, 9.3% dimers, and 17.4% oligomers. Processing 140 Mt of poplar biomass annually at scale could deliver substantial environmental and economic gains, avoiding approximately 64.12 Mt of CO2-eq emissions and generating an estimated USD 2.97 billion in annual socioeconomic benefits. Sensitivity analysis confirmed biomass availability as the dominant factor influencing emission reduction. Economic evaluation demonstrated strong financial viability, with an aggregate net present value of USD 65.7 billion projected for full national implementation. This work establishes a holistic and economically compelling biorefinery strategy for the sustainable production of bio-based chemicals and fuels.
The biomaterial polyhydroxybutyrate (PHB) is a promising, renewable, and green alternative polymer. In this study, a method to incorporate gluconate 6-phosphate dehydratase (edd) deletion in Escherichia coli expressing PHB biosynthesis genes from Cupriavidus necator strain A-04 was proposed. The growth of the edd-deficient strain, which is defective in the glycolytic Entner–Doudoroff pathway, decreased significantly in Luria-Bertani (LB) medium supplemented with glucose. Surprisingly, compared with the wild-type strain, the recombinant edd-deficient strain expressing PHB biosynthesis genes exhibited expeditious PHB accumulation with a high PHB content. The edd-deficient strain reached the highest PHB concentration of 7.6 g/L and a 93 wt% PHB content within 30 h of flask-scale cultivation when commercial glucose was used as the sole carbon source. In addition, the resulting strain was able to utilize crude glycerol waste from the biodiesel industry for PHB accretion with a 74.8 wt% content in 24 h. The PHB yields obtained from glucose and crude glycerol waste were 0.37 and 0.20 g PHB/g substrate, respectively. These findings not only broaden the understanding of the effect of glucose metabolism on PHB production but also provide promising candidates for the production of polyhydroxyalkanoates in the future.
Succinic acid is a crucial four-carbon dicarboxylic acid with widespread applications in the detergent, food, and pharmaceutical industries. However, its microbial production on a large scale is limited by the utilization of neutralizing agents and high cooling costs. In this study, we conducted metabolic engineering of the thermotolerant and acid-tolerant yeast Kluyveromyces marxianus to facilitate the efficient biosynthesis of succinic acid at high temperature and low pH. A robust genetic manipulation platform for K. marxianus was established by developing gene editing tools, characterizing neutral integration sites, and identifying endogenous promoters. Leveraging this efficient platform, we systematically constructed and optimized the biosynthetic pathway of succinic acid through many metabolic engineering strategies, such as the knockout of byproduct pathways, the redistribution of carbon flux, and the enhancement of the succinic acid transport system. Finally, the engineered strain K. marxianus KmSA12 was able to produce 50.6 g/L succinic acid with a yield of 0.31 g/g and productivity of 0.42 g/L/h in a 5-L bioreactor. These results demonstrate the potential of K. marxianus as a promising platform for the large-scale production of various organic acids.
The photoenzyme fatty acid photodecarboxylase (FAP) has emerged as a promising catalyst for the redox-neutral biological production of hydrocarbons. Previous studies have shown that FAP can efficiently convert medium-chain fatty acids such as n-octanoic acid into hydrocarbons, outperforming its natural long-chain fatty acid substrates (C16-C18). Such observation expands the potential applications of FAP to include solvents and jet fuels. However, the limited availability of natural sources of n-octanoic acid poses a challenge to the industrial implementation of n-heptane bioproduction. This study investigates the hydrocarbon synthesis capacity of an E. coli strain that expresses FAP and produces n-octanoic acid, the precursor to n-heptane, via a specific octanoyl-ACP thioesterase. Several FAPs and thioesterases were tested. A blue light-inducible promoter ensured high expression of both enzymes, eliminating the need for chemical inducers. Fusion of FAP with thioredoxin increased n-heptane production 12-fold. Using a co-cultivation strategy, where one strain produces n-octanoic acid and another strain converts it to n-heptane, increased hydrocarbon production 14-fold compared to co-expressing FAP and thioesterase. Co-cultures operated in batch mode in 100-mL photobioreactors enabled the recovery of >90%-pure n-heptane, yielding 272 mg·L-1 over 56 h. This work lays the foundation for the development of an industrial bioproduction of n-heptane.
Exploring the potential of advanced distillable solvents as efficient biomass pretreatment agents is critical for biorefineries, enhancing fermentable sugar yields while enabling solvent recovery and recycling without suffering significant losses. Here, we employ distillable amine-based solvents for pretreating a wide range of lignocellulosic feedstocks, aiming to facilitate the industrial release of fermentable sugars from diverse feedstocks through enzymatic hydrolysis. Twenty-two diverse feedstocks, sourced from different geographical regions and representing various biomass categories, were surveyed for chemical (mainly carbohydrates and lignin) and lignin (S, G, and H units) profiles. Several solvents, including ethanolamine, ethanolammonium acetate, butylamine, butylammonium acetate, and triethylamine, were tested for the pretreatment of eight selected biomasses. Among these solvents, butylamine emerged as the most effective due to its favorable sugar release, excellent solvent removal rate, and low boiling point, facilitating solvent recovery and recycling. Extending butylamine pretreatment to all 22 feedstocks demonstrated desirable sugar yields and highly efficient solvent removal in the majority of the biomass sources tested. Agricultural residues and their mixtures showed particularly favorable sugar release. Despite minimal changes in cellulose crystallinity, XRD characterization of sorghum, poplar, and pine before and after butylamine pretreatment showed a decrease in intensity and a slight shift of certain peaks, indicating alterations in cellulose structure. Fourier-transform infrared spectroscopy and thermogravimetric analysis analyses suggested disruption of biomass linkages in hemicellulose and lignin, enhancing enzymatic digestibility. Scale-up experiments of the mixed agricultural feedstocks in a 1 L Parr reactor achieved over 90% glucose liberation and more than 99% butylamine removal, highlighting the scalability of the method. The resulting hydrolysates supported the growth of diverse bacterial and fungal strains, indicating downstream compatibility with commercial fermentation processes. This study presents butylamine as an effective, recoverable pretreatment solvent for a wide range of lignocellulosic feedstocks, offering a promising solution to key biorefinery challenges. The demonstrated scalability and compatibility with various biomass types and blends underscore its potential for industrial application, advancing sustainable biofuel and biochemical production.
