GVL pulping is the core technology of the biorefinery, enabling an effective fractionation of biomass (preferably hardwoods, annual plants or agricultural wastes) into a solid cellulosic fraction spinnable to textile fibers, and a liquid fraction containing the depolymerized and extracted hemicelluloses and lignin, upgradable to materials and chemicals. Besides the absence of sulfur-based cooking chemicals, GVL pulp can be bleached to full brightness without chlorine-based bleaching agents, thus making the GVL biorefinery comply to the strictest environmental regulations. Our laboratory covers pulping experiments from minute scale to pilot scale, conducted in a wide variety of reactors:
Max 2 g biomass/batch: fast, highly reproducible for preliminary screening of raw materials and pulping conditions. Biomass only in sawdust form.
Max 40 g biomass /autoclave: entry level for pulping experiment with wood chips, perfect for investigating the effect of different chemical dosages or pulping time
Max 400 g biomass / autoclave:
up-scaled pulping experiment with wood chips
Max 2500 g biomass/batch: advanced pilot reactor system with high versatility: steam explosion, steam prehydrolysis, liquor displacement
For the novel GVL process to be both economically feasible and environmentally sound, the recovery of the valuable products and recycling of pulping chemicals require special attention. In the present projects, these aspects are also emphasized. Both carefully designed phase equilibria studies and test extractions with liquid CO2 have been conducted. Based on these experiments, rigorous thermodynamic model has been developed and implemented in a process flowsheet simulator capable of modeling full integrated biorefinery processes. The extraction test experiments further validate the process design from a practical engineering viewpoint.
The recovery of pulping solvent (GVL) and isolation of extracted biomass fractions are conducted by combining well-established unit operations such as vacuum distillation and liquid-liquid extraction. GVL exhibits higher affinity towards liquid CO2 over water, thus can be efficiently removed from the aqueous pulping spent liquor by liquid CO2 extraction, which is more energetically favorable than vacuum distillation. Lignin precipitates upon addition of anti-solvent (water) or removal of solvent (GVL extraction). The furanics are extracted together with GVL while carboxylic acids and carbohydrates remains in the aqueous phase.
A simplified VISIO scheme showing the flow of each biomass fraction into the corresponding process streams.
The cellulose-rich pulp fraction (bleached or unbleached) is compatible with several spinning technologies (e.g. IONCELL®) to produce regenerated cellulosic fibers for textile applications.
Furfural (extracted together with GVL) are either isolated by vacuum distillation or converted in-situ to GVL.
Oligomeric carbohydrates can be hydrolyzed to xylose and precipitated by crystallization or further converted to xylitol.
Carboxylic acids are recovered by standard unit operations such as distillation.
Sulfur-free lignin is collected along the chemical recovery path in different fractions with distinct molecular weight, which offers a wide variety of applications such as solid fuel, resin (polyurethane replacement) or platform chemicals (monoaromatics).
Fundamentals of GVL biorefinery
Surprise could end in demise!
As a research institute, even with a solid proof-of-concept, before scaling the process up to a whole new level, we still invest a decent effort in investigating fundamental aspects of GVL pulping such as solvent stability and loss reaction between GVL and wood components.
GVL is a stable organic solvent under neutral conditions and at room temperature. However, as a cyclic lactone, GVL tends to hydrolyze in the presence of acids and bases into 4-hydroxyvaleric acid (4-HVA). Our latest research demonstrated that even under extreme acidic and alkaline conditions, GVL remains relatively stable, making it an excellent solvent for pulping.
Besides, no loss reaction was detected between GVL and non-phenolic lignin model compounds. Further study will be later updated.