PROVIDES obtained the following achievements:
• More than one hundred new Deep Eutectic Solvents, including the first hydrophobic DES ever
• 95% lignin removal by DES delignification
• Cellulose fibres with good tensile strength and extreme internal bond
• Total DES pulping concept with similar energy consumption and operational costs compared to kraft pulping
• Proof of principle for lignin recovery
Fundamental research provides answers to questions as to ‘why’ DESs are effective, supporting the search for even more effective DESs and assisting application-oriented research. At the same time, the preparations for the pilot phase have been started to study the DES process at a larger scale to gain better insight into the process kinetics and physical transport required for further upscaling, using larger amounts of products for application testing, and validating production costs, climate benefits and environmental effects. Application-oriented research was performed on the functionality of DES as a dissolving/separation agent for lignin, cellulose, stickies and ink.
DES delignification
The main aim of the PROVIDES project was to develop radically new, sustainable and techno-economically feasible pulping technologies. This includes both an energy-efficient pulping process to separate high-quality fibres and lignin, as well as an efficient process to recover and recycle DES while maintaining its physico-chemical and dissolving properties. So far, two potential DESs for pulping by dissolving hardwood and softwood lignin are known: (1) Lactic Acid : Choline Chloride and (2) Malic Acid : Tetraethyl Ammonium Chloride. Temperature, pulping time, wood/DES ratio, pre- and post-treatments were optimised to improve the efficiency of the process, the extent of lignin isolation and the pulp quality. A technology roadmap was prepared, elaborating on all the parallel steps that need to be taken in the technology development in order to allow implementation in 2030.
DES recovered paper processing
The aim was to develop DESs that were able to either dissolve and isolate contaminants from ‘paper for recycling’ to achieve clean fibres for recycling or dissolve cellulose to obtain pure cellulose. For this purpose, hydrophobic DESs were developed. Hydrophobic DESs do not mix with water, significantly facilitating the process of isolating components from aqueous pulp.
A variety of hydrophobic DESs were tested on the dissolution of specific contaminants. Hydrophobic DESs appear able to dissolve volatile fatty acids, metal ions and some ink and sticky contaminants. Although the mineral oil content was halved, deinking trials did not lead to higher brightness.
DES and component recovery
Research was also performed on efficient recovery technologies for both the DESs and the dissolved components. Although dissolved components can easily be separated from DESs by adding water as an anti-solvent, this process is not favoured, as the subsequently required water evaporation implies high energy consumption. A liquid-liquid extraction technology was therefore developed, achieving energy savings of 80% in the recovery process.
Fibres obtained from the DES pulping process are well shaped and straight, with normal drainage. Paper produced from the fibres has extremely good internal bond and good tensile strength. The tear strength is still somewhat lower than regular kraft fibres.
Lignin isolated by DES pulping of Eucalyptus was characterised by GPC and HSQC spectroscopy.
