γ-valerolactone (GVL) is a green solvent which has been proven effective for biomass fractionation. Since the early 2010s, Aalto University has been developing a biorefinery concept based on GVL fractionation, aiming at the selective isolation and valorization of all lignocellulosic fractions, such as dissolving pulp for textile applications from cellulose, furfural and sugars from hemicelluloses and sulfur-free lignin. The scalability of the process depends on a close-loop operation, which motivated the investigation on quantitative solvent recovery and make-up GVL synthesis from the extracted carbohydrates from the spent liquor.
In this joint FinnCERES project of Aalto and VTT, the fundamental chemistry of γ-valerolactone in aqueous solution under different reaction conditions was investigated, including the study on GVL equilibrium with 4-hydroxyvaleric acid, advanced characterization of the fractionation process, which serve as a basis for GVL recovery from the fractionation spent liquor by liquid-CO2 extraction. Simultaneously, GVL pulping was piloted in kg-scale. Furthermore, the fractionated and extracted sulfur-free lignin was targeted to the synthesis o polyhydroxyurethane resin prepared by isocyanate-free procedure.
The catalyzed GVL pulping of birch wood were conducted in laboratory scale and the optimum conditions were transferred to the pilot scale.
In-depth structural characterization of lignin and carbohydrate fractions along the process chain, including the recovery process, to elucidate delignification chemistry and loss of GVL were performed.
The pulp (unbleached and unbleached) was spun into fibers by the Ioncell® process, and bleached fibers were further processed into yarns and demonstration fabrics.
The sulfur-free, higher-molecular-weight lignin fraction was precipitated from the spent liquor and upgraded into lignin-containing polyhydroxyurethane prepared by isocyanate-free procedure. As such the resin would be thermosetting and involve formation of polyurethane linkages. Thus, the product would be suitable for thermosetting coatings or as an alternative to formaldehyde-based thermosetting binder resins.
The lignin-lean spent liquor was subjected to GVL extraction with liquid CO2 for solvent recovery, isolation of the lower-molecular-weight lignin fraction, as well as purification and valorization of other extracted wood components such as sugars, furanics and carboxylic acids.
The GVL recovery in continuous mode was tested on a synthetic mixture as well as the real spent liquor. The continuous extraction of GVL reached steady-state operation, where the composition of the extract and raffinate matched well with the phase equilibria.
Short video about GVL recovery
Fabric made from GVL pulp
Pokki, J-P., Lê, H., Uusi-Kyyny, P., Alopaeus, V., & Sixta, H. (2018). Isobaric Vapor–Liquid Equilibrium of Furfural + γ-Valerolactone at 30 kPa and Isothermal Liquid–Liquid Equilibrium of Carbon Dioxide + γ-Valerolactone + Water at 298 K. Journal of Chemical Engineering Data, 63 (12), 4381–4391. https://doi.org/10.1021/acs.jced.8b00451
Lê, H. Q., Pokki, J. P., Borrega, M., Uusi-Kyyny, P., Alopaeus, V., & Sixta, H. (2018). Chemical Recovery of γ-Valerolactone/Water Biorefinery. Industrial and Engineering Chemistry Research, 57(44), 15147-15158. https://doi.org/10.1021/acs.iecr.8b03723
Granatier, M., Schlapp-Hackl, I., Lê, H. Q., Nieminen, K., Pitkänen, L., & Sixta, H. (2021). Stability of gamma-valerolactone under pulping conditions as a basis for process optimization and chemical recovery. Cellulose, 28(18), 11567-11578. https://doi.org/10.1007/s10570-021-04243-5
Shokri, S., Hedjazi, S., Lê, H. Q., Abdulkhani, A., & Sixta, H. (2022). High-purity cellulose production from birch wood by γ-valerolactone/water fractionation and IONCELL-P process. Carbohydrate Polymers, 288, . https://doi.org/10.1016/j.carbpol.2022.119364
Granatier, M., Lê, H. Q., González Carmona, E., & Sixta, H. (2023). Birch fractionation in γ-valerolactone with the emphasis on pulp properties: prehydrolysis, acid-catalyzed, and alkaline-catalyzed concept. RSC Sustainability, 1(1), 97-106. https://doi.org/10.1039/d2su00046f
Granatier, M., Lê, H. Q., Ma, Y., Rissanen, M., Schlapp-Hackl, I., Diment, D., Zaykovskaya, A., Pokki, J-P., Balakshin, M., Louhi-Kultanen, M., Alopaeus, V., & Sixta, H. (2023). Gamma-valerolactone biorefinery: Catalyzed birch fractionation and valorization of pulping streams with solvent recovery. Heliyon, 9(6), [e17423]. https://doi.org/10.1016/j.heliyon.2023.e17423