Stability of gamma-valerolactone under pulping conditions as a basis for process optimization and chemical recovery

Abstract

This study focuses on the investigation of the extent of the γ-valerolactone (GVL) hydrolysis forming an equilibrium with 4-hydroxyvaleric acid (4-HVA) in aqueous solutions over a wide pH range. The hydrolysis of a 50 wt% GVL solution to 4-HVA (3.5 mol%) was observed only at elevated temperatures. The addition of sulfuric acid (0.2 × 10–5 wt% to 6 wt%) at elevated temperatures (150–180 °C) and reaction times between 30 and 180 min caused the formation of 4 mol% 4-HVA. However, with decreasing acidity, the 4-HVA remained constant at about 3 mol%. The hydrolysis reactions in alkaline conditions were conducted at a constant time (30 min) and temperature (180 °C) with the variation of the NaOH concentration (0.2 × 10–6 wt% to 7 wt%). The addition of less than 0.2 wt% of NaOH resulted in the formation of less than 4 mol% of sodium 4-hydroxyvalerate. A maximum amount of 21 mol% of 4-HVA was observed in a 7 wt% NaOH solution. The degree of decomposition after treatment was determined by NMR analysis. To verify the GVL stability under practical conditions, Betula pendula sawdust was fractionated in 50 wt% GVL with and without the addition of H2SO4 or NaOH at 180 °C and a treatment time of 120 min. The spent liquor was analyzed and a 4-HVA content of 5.6 mol% in a high acidic (20 kg H2SO4/t wood) and 6.0 mol% in an alkaline (192 kg NaOH/t wood) environment have been determined.

Birch fractionation in γ-valerolactone with the emphasis on pulp properties: prehydrolysis, acid-catalyzed, and alkaline-catalyzed concept

“…Simultaneously, the concentration of free hydroxyl ions at pH 8.6 was not sufficient to cleave the lignin bonds, which require pH > 11. Possible shift of the equilibrium of GVL to 4-hydroxyvaleric acid, catalyzed by higher alkalinity, 22 could reduce the delignification capability of GVL. Additionally, an S-free nucleophile effective in the neutral or slightly acidic pH range would be required to further improve the efficiency and selectivity of delignification.…”

“…Neither prehydrolysis nor alkaline catalysis had a significant effect on the acceleration of the delignification of GVL pulping compared to the reference uncatalyzed conditions. Similar to one-stage alkaline pulping, NaOH undergoes the neutralization reaction with 4-hydroxyvaleric acid 22 and acid products generated from GVL hydrolysis and hemicellulose degradation, respectively. As a result, even at the highest NaOH dosage, the proton concentration is too low so that no free hydroxyl ions are available for the degradation reaction.…”

“…Being renewable with low toxicity, low volatility, high chemical stability, and high solubility in water while staying zeotropic, GVL was rst proposed as a sustainable chemical for the production of energy and carbon-based chemicals. 21,22 Dumesic et al expanded the application of GVL to the production of soluble carbohydrates from biomass by applying the pre-treatment in acid-catalyzed GVL/water solution with the subsequent ethanol production. 23 Meanwhile, Luterbacher et al aimed not only for biomass pretreatment in GVL/ water but also for the simultaneous production of less condensed lignin by the addition of formaldehyde.…”

Suppression Effect of Gamma-Valerolactone on the Mild Alkaline Pretreatment of Hybrid Pennisetum

“…As discussed above, under the experimental condition (37 °C for 24 h), the addition and increase of GVL in alkaline solutions strongly suppressed the delignification performance of alkaline. Given that the decomposition of GVL via ring-opening reactions into acids is minimal under such conditions, , reactions between GVL and biomass or NaOH are unlikely to have a major effect on the resulting low delignification. In addition, time-dependent changes of GVL concentrations under 37 °C for 24 h were determined by a UV–visible spectrophotometry method.…”

High-Quality Cellulosic Fibers Engineered from Cotton–Elastane Textile Waste

“…1,5-Diazabicyclo[4.3.0]­non-5-ene (DBN, C 7 H 12 N 2 , M = 124.18 g/mol, CAS: 3001-72-7, purity 99.0%) was provided by Fluorochem. GVL (C 5 H 8 O 2 , M = 100.12 g/mol, CAS: 108-29-2) was produced in the laboratory following published procedures . All solvents were used without further purification.…”