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Chemical transformation of enzymatic hydrolysis lignin (EHL) with catalytic solvolysis to fuel commodities under mild conditions

Periodic Reporting for period 2 - EHLCATHOL (Chemical transformation of enzymatic hydrolysis lignin (EHL) with catalytic solvolysis to fuel commodities under mild conditions)

Reporting period: 2022-05-01 to 2023-04-30

The EHLCATHOL project, Horizon 2020 H2020-LC-SC3-2018-2019-2020 (BUILDING A LOW-CARBON, CLIMATE RESILIENT FUTURE: SECURE, CLEAN AND EFFICIENT ENERGY), with a topic Chemical transformation of enzymatic hydrolysis lignin (EHL) with catalytic solvolysis to fuel commodities under mild conditions, was designed based on the state-of-the-art of catalytic solvolysis of lignin and the important results of the consortium members obtained in the past decade. Specifically, they were the first to achieve complete conversion of technical lignin to fuel-range precursor molecules. However, they as well as others in follow-up works encountered typical challenges in scaling up this process, such as, recondensation of the monomers during distilling the products, a relatively low lignin-to-solvent ratio in the feed, low reaction rates and yields of desired products. The key to overcome these challenges enroute to commercialization of this promising approach is to build up the needed fundamental knowledge about the underlying chemistry and process steps aimed to optimization towards specific product classes.

The EHLCATHOL project is aimed to boost 2G Advanced Bioethanol Technologies, which utilizes lignocellulose, the material making up the cell wall of land-based plants, to produce fuel-grade ethanol. The solar synthesis of green leaves consumes CO2 and H2O and produces a large amount of lignocellulose, which is a promising feedstock for obtaining renewable fuels and chemicals. Bioethanol production via fermentation of non-edible lignocellulose biomass has been demonstrated at the commercial scale at all continents in the past decade. As such, it is also expected to contribute to the EU’s 2050 carbon neutral renewable fuel goals. Nevertheless, fermentation primarily converts saccharide polymers, i.e. cellulose and hemicellulose, to fuel ethanol, leaving EHL as a waste. Therefore, the profitability of 2G bioethanol plants is hampered by the lack of efficient methods to valorise EHL, i.e. transforming the current waste by-product from which mostly energy is recovered into more valuable products, such as fuel blends. Furthermore, even for energy crops, the amount of lignin in dried biomass can be in the 10-15 wt% range. The mid-to-long term target of the 2G bioethanol technology is to utilize forestry and agricultural residues, which contain lignin in larger amounts, roughly 35-45% in terms of energy content. It can therefore be foreseen that, as the efficiency and scale of the 2G bioethanol technology is improved, the switch of the feed to lignin-rich biomass would make EHL utilization even more demanding.
EHLCATHOL gathers the most promising teams in Europe to carry out the tasks aimed at adding more value to EHL. Prof. Beller and Prof. Rajenahally from the Leibniz-Institut für Katalyse (LIKAT) investigate the key reaction mechanism of the EHL catalytic solvolysis reaction suppressing recondensation reactions of the monomeric reaction products obtained during solvolysis and in consequent separation steps (WP2). Prof. Chen’s team of Norges Teknisk-Naturvitenskapelige Universitet (NTNU) focuses on tuning of different fuel-cuts with suitable C-C coupling, hydrogenation, alkylation and isomerization catalytic tools (WP5). Prof. Dyson of École Polytechnique Fédérale de Lausanne (EPFL) aims to reveal, using operando spectroscopy techniques, the mechanism of the key steps of catalysed solvolysis and solvolysis oil regulation reactions, and the roles of capping agents (WP3). Aalto university (Prof. Li) and Technische Universiteit Eindhoven (Prof. Hensen) teams work on the different aspects of catalyst development, reactor and process configurations of the EHL solvolysis process (WP1&7). Dr. Boot leads the VERTORO team to take care of the reaction at the bench-scale, sample delivery, separation and scale-up (WP4). Dr. Battin-Leclerc, Director of Research of Centre National de la Recherche Scientifique (CNRS) in Nancy, and her team focus on the fuel combustion properties and the related pollutant formation of the refined EHL solvolysis products, and of the separated commodity fuels (WP6). To efficiently implement the EHLCATHOL project, we designed WP8-11 to take care of Exploitation, Dissemination, Communication, Project Management and Ethics issues.

The EHLCATHOL tasks has been successfully carried out during the past 30 months. The major outcomes in this period provide a solid base for achieving the goals of the whole project and indicate that the work formulated in the WPs and associated Tasks are well on track and efficiently going forward towards their individual goals in the form of defined deliverables.
The major scientific and technological outputs and their impacts of this M30 milestones are summarized as follows:

We successfully enhanced the catalytic reaction rate of lignin solvolysis by developing novel and improved catalysts. Modifications were made in terms of catalyst composition, preparation techniques as well as using novel promoters and supports. We effectively lowered the reaction temperature by using novel fuel compatible solvents and cascade catalysis in the reaction.

Our work on capping and elimination of functional groups of model compounds provides new understanding on the reaction mechanism of both the solvolysis and the upgrading steps. Based on advanced techniques such as operando NMR and FTIR, further understanding about reaction mechanism is obtained with an additional benefit that the use of advanced operando spectroscopy under demanding biomass conversion conditions is now possible. The mechanisms of guaiacol hydrogenation and the capping reaction steps for too reactive functional groups have been investigated in detail; such knowledge is very useful to the design of new solvolysis and upgrading catalysts.

We have established litre-scale catalytic solvolysis and successfully supplied to other partners samples of solvolysis products. We have successfully started combustion testing and made a detailed literature survey of the combustion performance of oxygenated aromatic compounds. We also investigated the formation of EHL and fuel compatible solvent slurries and extended the flowable range, explored the possibility of further lowering the reaction temperature and obtained data on the solubility and dissolution of different EHL and other technical lignin samples in the interested solvent. We further established the reactor and molecular level models of the lignin dissolution and solvolysis reaction.

We carefully analysed the materialized risks and the mitigation measures in the past 30 months, especially the challenges arisen due to the recent political crisis and the severer competitions which push the renewable energy developments.
Chemical transformation of EHL with catalytic solvolysis to fuel commodities under mild conditions