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The Lignin-First Approach for the Full Valorisation of Lignocellulosic Biomass

Periodic Reporting for period 3 - LIGNINFIRST (The Lignin-First Approach for the Full Valorisation of Lignocellulosic Biomass)

Reporting period: 2020-03-01 to 2021-08-31

The transition from fossil-based to a sustainable economy is one of the significant challenges humanity faces in the foreseeable future. Lignocellulosic biomass is one of the most abundant materials available on Earth. This feedstock has been extensively employed in the paper and pulp production, besides in the construction sector, as the case of the wood itself. However, lignocellulose can potentially serve as a raw material alternative to produce new high value-added chemicals and synthetic biofuels. In this quest, the utilization of lignin is essential to waste-free biorefinery processes. In fact, lignin constitutes around one-third of the mass of wood. It is the only abundant source of aromatics in nature. Currently, it is recognized three main routes for lignin valorization. The first consists of generating syngas to produce liquid fuels via Fischer-Tropsch synthesis. The second route focuses on the production of current platform chemicals utilized in the petrochemical industry to synthesize fine chemicals. The third route and the research problem addressed by the LIGNINFIRST project is the efficient isolation of lignin species to create new platform chemicals directly derived from the native structure of lignin.

Current pretreatment processes allow relatively good separation of lignin from cellulosic fibers. However, the lignin obtained has a high molar mass with a random structure. These features hinder its application as raw material to produce top value-added chemicals. In addition, hemicelluloses are usually degraded by pulping processes. Therefore, the development of new technologies for efficient lignin isolation, preserving most of its initial reactivity, constitutes the overarching objective of a research field so-called “Lignin-first Biorefining.”

The fundamental science developed in the LIGNINFIRST project holds the potential for translation into industrial processes of high relevance for business diversification in the pulp and paper industry. This industry generates around 100,000 jobs across Europe and 150 billion € revenues annually. However, the decreased demand for paper and the insertion of new world players in the pulp and paper market pose severe threats to the competitivity of the European pulp and paper industry. Business diversification (e.g. diversion of lignin to produce chemicals) could well offer new avenues for boosting the European pulp and paper industry.
The action's implementation in the first period included:

1. Setting up and recruiting the research team: three research associate fellows (Dr Robert Woodward; Dr Sergio Martins; Dr Ines Graca) and one research assistant (PhD student, Martin Kessler);

2. Purchasing the foreseen small pieces of equipment and other consumables required for the execution of LIGNINFIRST project;

3. Building up experimental setup and facilities for the implementation of LIGNINFIRST project;

4. Initial experiments utilizing synchrotron facilities for the advanced monitoring of lignocellulose deconstruction (by X-ray microtomography, WP1) and in-depth characterization of catalysts (by employing X-ray absorption near edge structure spectroscopy, WP2); and downstream processing of lignin oil and holocellulosic pulps (WP3)

5. Producing nine research papers and one book chapters (for activities in WP1, WP2, and WP3);

6. Dissemination of results of LIGNINFIRST in scientific conferences and in invited lectures across the globe.
A heightened understanding of efficient lignin depolymerization (and prevention of re-condensation) has been acquired. Regarding the prevention of lignin recalcitrance generation upon its removal from the lignocellulosic matrix, our research group has demonstrated the mechanisms underlining the Early-stage Catalytic Conversion of Lignin (ECCL). ECCL technology has opened a wholly new scientific avenue, as lignin streams can be tailor-made through and for catalysis. Therefore, since it is now possible to control the chemical properties of the lignin stream, the primary objective of this third work package is to understand the relationship between the lignin oil stream properties and the susceptibility of the lignin oil to downstream catalytic upgrading. As a secondary yet essential objective, the suitability of the holocellulose pulp fraction for applications in the current pulp and paper sector is under investigation.

For the utilization of each lignin fraction in the lignin liquors, the development of separation strategies to fractionate the lignin streams by molecular weight ranges constitutes a timely challenge to be tackled. Herein, membrane filtration was applied to the refining of lignin streams obtained from a lignin‐first biorefining process based on H‐transfer reactions catalyzed by Raney Ni, by using 2‐PrOH as a part of the lignin extraction liquor and as an H‐donor. A two‐stage membrane cascade was considered to separate and concentrate the monophenol‐rich fraction from the liquor. Building on the results, an economic evaluation of the potential of membrane filtration for the refining of lignin streams was undertaken. In this proof‐of‐concept study, a detailed analysis is presented of future developments in the performance required for the utilization of membrane filtration for lignin refining and, more aspiringly, solvent reclamation.

In the LIGNINFIRST biorefining, we undertake pioneering research at the border of Wood/Lignocellulose Chemistry, Catalysis and Reaction Engineering, aiming at:

1. Understanding (and control over) the solvolytic release of lignin fragments;

The expected results until the end of the project are:

a) Elucidation of the role of solvent/solvent mixtures in the extraction of lignin. Initial X-ray computer tomography results revealed that water is needed to allow the expansion of the lignocellulosic matrix allowing for the lignin release.

b) Advanced spectroscopic techniques have been employed to understand the evolution of lignin species in the liquor. We expect to solve the 'mysterious' mechanisms of lignin condensation in the liquor, generating lignin waste materials.

c) Finally, we advanced in the fractionation of the lignin stream so that advanced catalysis studies are possible. We are targeting improved understanding of the preservation of the phenolic species even under highly reductive conditions.

2. Advancing the molecular understanding of H-transfer reactions catalyzed by sponge Ni catalysts to accelerate the discovery of catalytic methods for lignin valorization;

The expected results until the end of the project are:

a) Advanced spectroscopic studies (Ni K-edge X-ray absorption near-edge spectroscopy, Ni K-edge XANES) to elucidate the transformations of Raney Ni over the catalytic fractionation process.

3. Reaction engineering of the interdependent processing steps for fractionation of the initial biomass feedstock (catalytic upstream biorefining or CUB) to the intended value-added products (downstream catalytic processing).

The expected results until the end of the project are:

a) Improved fractionation of lignin stream via membrane fractionation techniques.

b) Production of high value-added products out of the lignin fractions.