Dissolution of kraft lignin in alkaline solutions

Abstract

Lignins are among the most abundant renewable resources on the planet. However, their application is limited by the lack of efficient dissolution and extraction methodologies. In this work, a systematic and quantitative analysis of the dissolution efficiency of different alkaline-based aqueous systems (i.e. lithium hydroxide, LiOH; sodium hydroxide, NaOH; potassium hydroxide, KOH; cuprammonium hydroxide, CuAOH; tetrapropylammonium hydroxide, TPAOH and tetrabutylammonium hydroxide, TBAOH) is reported, for the first time, for kraft lignin. Phase maps were determined for all systems and lignin solubility was found to decrease in the following order: LiOH N NaOH N KOH N CuAOH N TPAOH N TBAOH, thus suggesting that the size of the cation plays an important role on its solubility. The π * parameter has an opposite trend to the solubility, supporting the idea that cations of smaller size favor lignin solubility. Dissolution was observed to increase exponentially above pH 9-10 being the LiOH system the most efficient. The soluble and insoluble fractions of lignin in 0.1 M NaOH were collected and analyzed by several techniques. Overall, data suggests a greater amount of simple aromatic compounds, preferentially containing sulfur, in the soluble fraction while the insoluble fraction is very similar to the native kraft lignin.

Levulinic acid: A novel sustainable solvent for lignin dissolution

“…Data suggest that increasing polarizability of the acidic solvents favors lignin dissolution; acids with high polarizability (π* > 0.9) were the most effective to dissolve lignin. This trend is opposite to what was verified for the alkaline systems [25]. Furthermore, the trend observed for carboxylic acids, in which solubility is favored by a higher π* and a smaller carbon chain, is similar to alcohols, where it has already been described that π* of methanol is higher than that of 2-propanol [26] and the lignin solubility is higher in methanol [27,28].…”

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

“…This was further explained by Xue et al; GVL can form strong hydrogen bonds with water under near room temperature (40–70 °C), which is capable of breaking the hydrogen bonding in lignin and the combinations of aromatic nucleus, thus resulting in high lignin dissolution (38.1 g/100 g solvent for alkaline lignin under 40 °C). As for NaOH/water, the solubility of lignin also increases with the increase of NaOH concentration and is positively correlated to the pH of solutions (dissolution for kraft lignin is >30 wt % at room temperature with 4 wt % of NaOH) . Given that hydroxide ions can catalyze the decomposition of lignin, the dissolution of lignin in NaOH should be combined with the partial degradation of large lignin molecules.…”

Electrochemical Performance of Coaxially Wet-Spun Hierarchically Porous Lignin-Based Carbon/Graphene Fiber Electrodes for Flexible Supercapacitors

“…In detail, as shown in Figure 1, the weighed lignin powders were first dissolved in 5 mL of aqueous KOH solution, where the mass ratio of KOH/lignin was tuned to 2:1. The main purpose of adding KOH in the spinning solution is to promote lignin dissolution under alkaline conditions 36 and obtain a homogenous spinning dope. It should be noted that at 0% lignin, the solvent was merely water with no KOH.…”