CORDIS - EU research results

Measurements and modelling of the high-pressure phase equilibria related to the process of depolymerisation and cracking of lignin in near-critical water

Final Report Summary - CRACKING OF LIGNIN (Measurements and modelling of the high-pressure phase equilibria related to the process of depolymerisation and cracking of lignin in near-critical water.)

This Marie Curie Career Integration Grant focused on the thermochemical conversion of lignin to bio-fuel and valuable chemicals. Lignin is the second most abundant natural organic polymer on earth and it can be an alternative source of fuel additives and chemicals which are currently produced from petroleum. Recent improvements in the wood pulping process, as well as the emerging commercial process of bio-ethanol production from lignocellulosic materials, are making increasing amounts of lignin by-products available to be exploited for valorisation. Therefore, the development of new conversion processes for lignin will increase the overall value produced by the above-mentioned processes, supporting their development into fully developed biorefineries, i.e. industrial units aimed at producing a variety of chemicals and energy rather than a single product.
The production of valuable fuel additives and chemicals from lignin is however a difficult task. In the last decades, many researchers have been dealing with this issue, with interesting seminal results together with many technical problems still to be solved. If, on the one hand, this biopolymer is rather simple to depolymerise, it also has a tendency of producing low-value solid residuals hindering the possibility of developing a feasible pilot scale process that could be further be developed into a commercial industrial process. Among different processes, the conversion of lignin in high-pressure high-temperature water (more specifically: near-critical water, i.e. water at high-pressure in the range of temperatures 280 °C – 370 °C) has emerged as particularly promising. This process demonstrated a good potential at pilot scale at Chalmers University of Technology [1-2], which is the institution where the Marie Curie researcher (Marco Maschietti) was working at the time he got the EU-project granted.
Testing at pilot scale, albeit necessary, requires more money and more time with respect to laboratory scale testing which should be devoted to initial screening of process conditions. However, the technical difficulties related to operating with lignin in laboratory reactors operating at high pressures (above 200 bar) and temperatures (280 °C – 350 °C) have typically led to partial or inconsistent results which have not allowed the obtainment of clear indications for realising pilot units to test the process on a larger scale. In line with this, the aim of this project was to develop a new lab-scale reactor, and related operating procedure, with the capability of producing results by far more accurate than typical laboratory reactors nowadays in use. Started at Chalmers University of Technology, the project was subsequently relocated to Aalborg University (AAU), where meanwhile the research fellow got a position as Associate Professor.
At AAU a new customised laboratory batch/semibatch reactor was designed by the research fellow, realised and its operation was started in collaboration with an existing group of researchers working on high-pressure high-temperature processes at AAU. The features of the new equipment comprises the possibility of injecting the biomass in the pre-heated pre-pressurised reactor, an efficient pressure control system and the possibility of withdrawing and quenching of reaction products after the desired reaction time. In the second part of the project, an operating procedure for efficient use of the new equipment was developed and applied to study a variant of the conversion of lignin in near-critical water.
The new laboratory-scale reactor proved to be operable and to produce results by far more reliable than those typically obtained with common commercial turnkey batch reactors available on the market. An experimental campaign conducted on the new reactor supported the feasibility of the conversion of lignin in near-critical water, providing new accurate data.
Information on the project and the new reactor is provided in the project website:

[1] T.D.H. Nguyen, M. Maschietti, T. Belkheiri, L.-E- Åmand, H. Theliander, L. Vamling, L. Olausson, S.-I. Andersson, Catalytic depolymerisation and conversion of Kraft lignin into liquid products using near-critical water, Journal of Supercritical Fluids 86 (2014) 67-75.
[2] T.D.H. Nguyen, M. Maschietti, L.-E- Åmand, L. Vamling, L. Olausson, S.-I. Andersson, H. Theliander, The effect of temperature on the catalytic conversion of Kraft lignin using near-critical water, Bioresource Technology 170 (2014) 196-203.
[3] K.R. Arturi, M. Strandgaard, R.P. Nielsen, E. Søgaard, M. Maschietti, Hydrothermal liquefaction of lignin in near-critical water in an innovative batch reactor: influence of phenol and temperature, submitted to The Journal of Supercritical Fluids.