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Process development for lignin valorisation to aromatic building blocks and further production of bio-based polymers

Project leader: dr. Miha Grilc


Project information

There is an ongoing challenge to develop economically-efficient and environmentally-harmless technologies to transform lignocellulosic biomass into value-added chemicals. Lignin is a complex branched polymer of p-coumaryl alcohol, coniferyl alcohol and sinapyl alcohol. Its diverse building blocks and their random connectivity make lignin by far the most complex lignocellulosic biopolymer, but still the only renewable source of an important and high-volume class of compounds - the aromatics. This project will not aim at the conversion of lignin into a particular drop-in chemical, but demonstrate the suitable selection of raw materials and tailored lignin isolation, eventual fractionation and depolymerisation can yield a blend of bio-aromatics with well-defined chemical properties (i.e. molecular weight distribution, concentration of free OH groups), that will be tested in final phenol-formaldehyde and epoxy resins formulations. Lignin fractions will serve as functional substitutes for phenol or bisphenol A. The project covers four consecutive objectives, which will collectively serve to develop new bio-based polymer precursors from lignin and allow establishing a lignin structure-product quality correlation. These four objectives are isolation of various lignins from different LC biomass sources and lignin fractionation according to molecular weights, depolymerisation of isolated lignin fractions, testing of obtained products in different formulations and development of kinetic modelling methodology. By tailoring the isolation, eventual fractionation, catalytic depolymerisation, and mathematical description of lignin depolymerisation, we will reach the ultimate objective of the project which is to produce aromatic products with tailored macrochemical properties.



Faculty of Polymer Technology, Slovenj Gradec, Slovenia

Slovenian NMR Centre, Ljubljana,Slovenia

Basic co-funding information 

Project is co-funded by ARRS with 2.384 annual hours of price category C for a period od 3 years. Funding started on September 1st, 2020.


Project team with links to SICRIS

Project team at the National Institute of Chemistry, Slovenia is composed of:

Project activities

Project activities

The project main activities:

Isolation and fractionation

  • Lignin isolation from various types of biomass
  • Fractionation protocol development
  • Isolation of selected fractions

Catalytic treatment of isolated lignin fractions

  • Caatalyst characterisation
  • Blank runs and support and screening hydrotreatments tests
  • Metal-supported catalysts screening hydrotreatment tests
  • Metal supported catalysts sceening oxidative tests
  • Screening of process parameters to optimise lignin valorisation chain


Pathway to the final products

  • Downstream recovery and characterisation of products
  • Preparation of formulations
  • Testing of formulations

Development of analytic techniques

  • Characterisation of lignin and lignin-derived monomers
  • Lignin characterisation by coupling ATR-FTIR with multivariate analysis
  • Method development for the lignin extraction monitoring in-situ

Development of kinetic modelling methodology

  • Reaction pathway network development
  • Descriptive lumped lignin model
  • Predictive lumped kinetic model
  • Experimental validation of optimized process parameters

Dissemination and reporting

  • Dissemination
  • Reports


Realization of project activities

WP1 Isolation and fractionation. For isolation and fractionation of lignin, the three most commonly grown wood species in Europe were selected (beech - hardwood, spruce - softwood and straw - herbaceous lignin). We developed a fractionation protocol with the aim to separate lignin fractions with different distribution of molecular weight and functionality (content of aliphatic and phenolic OH groups, ether bonds, etc.). The developed organosolv fractionation process of lignin was described mathematically, taking into account the process parameters and structural properties of lignin. This provided important insights into the prediction of the isolation and fractionation process with the target properties of lignin as a precisely designed material for depolymerization and preparation of bioaromatics for testing in phenol-formaldehyde and epoxy resins.

WP.1, Isolation and fractionation, 100% completed.


Publications from this work package:

DOI: 10.3390/polym13244443


WP2 Catalytic treatment of isolated lignin fractions. Several lignin samples and their isolated fractions were depolymerized by reductive and oxidative methods. Ni, Ru and Pt on carbon support were tested as commercial monometallic catalysts. The commercial Ni/C and Ru/C catalysts were characterized in detail prior to reaction using methods such as XRD, TEM, SEM, TPR, TPD and analysis of N2-physisorption using the BET method.

Hydrotreatment screening tests were performed to gain insight into the catalytic activity of the catalysts. Lignin model components were used to test the catalyst activity and to determine the most promising catalyst (Ni/C). Using the lignin model components, we were able to demonstrate various mechanisms of defunctionalization, modification, and bond cleavage that may have a significant impact on the formulation of the final products. Using the Ni/C catalyst, experimental tests were performed with lignin and isolated fractions under a wide range of reaction conditions (variation of temperature, pressure, gas composition).

The final part of WP2 involves a review of process parameters to optimize the valorization of lignin, which we hope will increase the yield of depolymerized products. The optimized process parameters are temperature, initial hydrogen pressure, catalyst to lignin ratio, and solvent. After developing a kinetic modeling methodology (WP5), we will use a combined lignin model to guide the optimization of process conditions to obtain depolymerization products with specific properties (structure, molecular weight distribution, and functionality) that meet the requirements of the final polymer formulations.

WP.2, Catalytic treatment of isolated lignin fractions, 85% completed.


Publications from this work package:

DOI: 10.1016/j.biortech.2021.125655



WP3 Pathway to final products. The low molecular weight lignin fractions obtained by precipitation (WP1) and the monomer/oligomer mixtures obtained in WP2 were tested for further processing and purification of the products. Identification and comprehensive characterization were performed by NMR, SEC, GC-MS, HPLC and HR-MS, of which the three most important methods (NMR, SEC and GC-MS) were selected.

The selected products were tested in the most commercially relevant formulations for polymers. We used them as phenolic monomers to prepare phenol formaldehyde-like resins. We also synthesized epoxy resins using various phenolic to epichlorohydrin ratios. Resins with different molecular weights, viscosities and epoxy equivalent were obtained. These resins, after curing with amines or anhydrides, gave products with the full range of physical properties.

WP.3, Pathway to final products, 70% completed.


WP4 Development of analytical techniques. The main objective of WP4 was to develop analytical techniques to characterise lignin in order to monitor its structural changes, purity and functionality during the isolation process and fractionation protocol development. Special attention was given to the development of the straightforward analytical methods using FTIR spectroscopy for direct analysis of reactants and products, based on correlations between detailed analyzes of lignin using NMR and SEC. We concluded that fractionation of lignin affects the structural properties of lignin, which are reflected as a key to further depolymerization of lignin, the amount of products obtained and their properties.

WP.4, Development of analytical techniques, 100% completed.


WP5 Development of kinetic modelling methodology. The results collected in WP2 will be used to develop the microkinetic model and optimize the model parameters. The model will describe the conversion kinetics of lignin, which will be based on the microkinetics of cleavage and defunctionalization of the lignin model components (dimers and monomers). In order to identify the optimal conditions and catalysts for individual batches of lignin, a suitable understanding of the relationship between its characteristics and the required depolymerization conditions is paramount.

The kinetic model will include the following contributions: hydrodynamic conditions in the reactor, transport phenomena, homogeneous chemical reactions, and the rate of chemical reactions on the active sites of the catalyst. To predict the distribution of molecular weight fragments, we have already optimized parameters such as the length of the lignin chain and the sites where cleavages preferentially occur.

WP.5, Development of kinetic modelling methodology, 50% completed.

Publications from this work package:



WP6 Dissemination and reporting. Results were published in 20 scientific journals. Of these, 8 articles were published in journals with an impact factor greater than 10 and 13 articles were published in journals in the first quartile of the field. The published articles were cited 210 times. The results were also presented at 5 international and Slovenian conferences. The annual report was prepared within the deadline required by the Slovenian Research Agency.

WP.6, Dissemination and reporting, 70% completed.


Literature references published from the implementation of the project

Listed as part of the realization of project activities (above).

ARRS (Slovenian Research Agency) logo and other co-funders

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