High-performance syngas upgrading into medium-chain carboxylates in high mass transfer gas-phase bioreactors with in situ product extraction (Syn2Value)

Project Information

Syn2Value

Grant agreement ID: 101109547

DOI

10.3030/101109547

Project closed

EC signature date 4 May 2023

Start date 22 January 2024

End date 21 February 2026

Funded under

• Marie Skłodowska-Curie Actions (MSCA)

Total cost

No data

EU contribution

€ 181 152,96

Coordinated by

UNIVERSIDAD DE VALLADOLID
Spain

Periodic Reporting for period 1 - Syn2Value (High-performance syngas upgrading into medium-chain carboxylates in high mass transfer gas-phase bioreactors with in situ product extraction (Syn2Value))

Reporting period: 2024-01-22 to 2026-02-21

Summary of the context and overall objectives of the project

Humanity faces an urgent, converging set of crises: climate change, resource depletion, and a waste management challenge of staggering scale. The global economy remains overwhelmingly dependent on fossil carbon, not only for energy, but for the chemicals, materials, and fuels that underpin modern industry. Transitioning away from this dependency is no longer optional. The European Green Deal, the EU's defining policy framework for the coming decades, sets the ambition of making Europe the first climate-neutral continent by 2050, with decarbonization of industry and the consolidation of a circular bioeconomy as explicit priorities.
Biorefineries (facilities that convert biological feedstocks into a spectrum of valuable products) are widely recognized as a cornerstone technology for this transition. They hold the potential to replace fossil-derived chemicals with bio-based equivalents, while simultaneously addressing a massive and largely untapped resource: organic waste. Globally, over 88 million tons of municipal organic waste and up to 9,400 million tons of agricultural lignocellulosic residues are generated annually. These are not just disposal problems, they also represent an enormous reservoir of carbon that, if valorized, could supply significant portions of the demand for bio-based chemicals and fuels. The carboxylates market alone (one family of platform chemicals producible from biomass) is projected to reach ~€16 billion by 2028.
Yet realizing this potential requires solving a fundamental technical obstacle. The dominant fraction of globally available waste biomass is lignocellulosic (woody, fibrous, and chemically recalcitrant) resistant to most direct biological conversion routes. Gasification into syngas (CO, H2, CO2) offers a way through: it homogenizes any organic feedstock, regardless of origin or composition, into a clean, pathogen-free gas stream that microorganisms can ferment. This syngas fermentation route is one of the few pathways capable of unlocking the full breadth of waste biomass at scale. However, it remains in an early technological stage, held back by poor gas-liquid mass transfer, low product selectivity, and the absence of integrated process designs capable of reaching industrially relevant yields.
Syn2Value addresses precisely this gap. The project will develop and validate an integrated platform coupling high-performance syngas fermentation with anaerobic chain elongation, engineered to convert lignocellulosic waste into medium-chain carboxylates (MCC, C6–C12) increasing production rates and selectivity. To achieve this, Syn2Value combines novel bioreactor engineering, tailored microbial co-cultures, and in-situ product extraction into a coherent, scalable process.
The significance of this work extends beyond the laboratory. A validated syngas-to-MCC platform would provide European industry with a competitive, fossil-free route to a family of high-value chemicals currently derived from petroleum, directly advancing EU decarbonization, circular economy, and bioeconomy objectives. Moreover, the Syn2Value concept aims at demonstrating that intractable organic waste can become a feedstock for the industries of tomorrow.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

Syn2Value investigated the development of an integrated bioprocess for the direct conversion of lignocellulosic waste-derived syngas into medium-chain carboxylates (MCC), with n-hexanoic acid as the primary target product.
The central experimental achievement of the project was the development of a thermophilic microbiome capable of simultaneously performing syngas fermentation and chain elongation within a single microbial community. A dedicated enrichment strategy was designed in which synthetic syngas was supplied at progressively increasing CO concentrations (16–64%), while acetate, ethanol, and lactate were added as supplementary electron donors to favour chain-elongating activity. Selection was conducted under thermophilic conditions (55–60 °C) to restrict microbial diversity and improve community robustness. The resulting microbiome, dominated by Moorella thermoacetica and Coprothermobacter proteolyticus, demonstrated the capacity to convert syngas directly into n-hexanoic acid.
This microbiome was subsequently used to inoculate a 5 L bubble column bioreactor operated under thermophilic conditions with a continuous syngas feed. Efficient syngas consumption and its conversion into a mixture of carboxylic acids, including n-hexanoic acid, were demonstrated at reactor scale. The emergence of methanogenic activity during reactor operation was characterised in detail, and effective mitigation strategies, including operation under mildly acidic conditions and controlled reactor re-startup, were identified and investigated.
In parallel, a stoichiometric metabolic model was developed integrating the Wood–Ljungdahl pathway and reverse β-oxidation under thermodynamic constraints. The model enables quantitative prediction of carboxylic acid yields — including n-hexanoic acid — from defined H2, CO, and CO2 feed compositions, providing a mechanistic tool to guide future process optimisation and scale-up.
Taken together, the results establish the scientific feasibility of single-stage syngas-to-MCC conversion using a thermophilic microbiome, and provide both the biological material and the predictive framework needed to advance this bioprocess toward higher technology readiness levels.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

One of the most significant and unexpected findings of Syn2Value concerns the role of methanogenesis as a persistent competitive process in thermophilic syngas fermentation. While methanogenic competition is a recognised challenge in anaerobic bioprocesses, its extent and resilience under the thermophilic conditions investigated here had not been adequately characterised in the literature. Syn2Value provides systematic evidence that methanogenic activity can establish itself robustly in thermophilic syngas-fermenting microbiomes and persist despite the application of conventional suppression strategies.
Specifically, methanogenesis was not eliminated by operation at mildly acidic pH conditions (pH 5.5–6.0) which are generally considered inhibitory to methanogens, nor by the use of methanogenesis inhibitors. This persistence had a material impact on process performance, diverting H2 and CO2 away from the carboxylate-producing community and destabilising steady-state operation. The finding challenges the assumption (implicit in much of the syngas fermentation literature) that thermophilic and acidic operating conditions provide sufficient selective pressure against methanogenic competitors.
This result has direct implications for the field. Future development of thermophilic syngas-to-MCC bioprocesses will need to incorporate more robust methanogenesis control strategies from the outset, whether through targeted inhibition approaches, microbiome engineering, or reactor design features that structurally disadvantage methanogens. Establishing a clearer mechanistic understanding of why methanogenesis persists under these conditions, whether through thermophilic methanogen diversity, syntrophic protection, or other mechanisms, represents a key open question that warrants dedicated research effort.
Beyond methanogenesis, the project demonstrated for the first time the feasibility of single-stage syngas-to-MCC conversion using a thermophilic co-culture, and delivered a thermodynamic-stoichiometric model that extends the predictive toolkit available to the field. Together, these results advance the scientific foundation for syngas biorefinery development, while clearly delineating the technical barriers that must be resolved before the process can progress to higher technology readiness levels.