Non-thermal gas-phase pulsed corona discharge for lignin modification

Lignin has the potential to become a significant resource of renewable aromatics for the chemical industry. The current work studies pulsed corona discharge (PCD) as an alternative method for lignin modification. The effect of initial lignin concentration and gas phase composition on aldehydes formation was studied experimentally. Kraft lignin was used as a test compound. It was concluded in the work, that treatment in low oxygen content atmosphere and high initial lignin concentration leads to higher lignin conversion to aldehydes. Despite the proven aldehydes formation, the precise nature of the changes in the lignin structure during oxidation with PCD remained unclear. To address this question, a number of advanced analytical techniques were implemented: NMR, GPC, HSQC, HPSEC, and GCMS. The effect of PCD treatment on lignin structure was studied for two types of lignin: kraft lignin, purchased from Sigma Aldrich, and birch lignin acquired from a pressurized hot water extraction and soda pulped biorefinery process (BLN lignin). Changes in solubility, molecular weight and proportion of phenolic and aliphatic OH groups, as well as lignin repolymerization were detected. The findings are of value to efforts to make lignin modification tunable to the production of desired products.