Optimisation of the process of abies ethanol lignin sulfation by sulfamic acid – urea mixture in 1,4-dioxane medium

Abstract

The new process of abies ethanol lignin sulfation by a low-toxic mixture of sulfamic acid and urea in 1,4-dioxane medium was optimized and the structure of sulfated ethanol lignin was studied. The process of lignin sulfation is described by a first-order equation in the temperature range 70-100˚C. The value of the rate constants are weakly dependent on the ratios of lignin and sulfating complex (sulfamic acid-urea mixture). The activation energy of the sulfation process decreaseses from 95 kJ / mol to 24 kJ / mol with an increase in the content of the sulfating complex (SC). The optimal conditions for sulfation of abies ethanol lignin with a high yield of water-soluble sulfated lignin ((100% of mass) with sulfur content of 7.9%) where found: temperature 95–100°С, L / SC ratio 1: 2,3- 1:2,9, time 2h. The composition and structure of water-soluble sulfated ethanol lignin were proven by elemental analysis, FTIR spectroscopy, two-dimensional NMR spectroscopy and gel permeation chromatography. It was shown that only alcoholic OH-groups of ethanol lignin react with sulfamic acid. Sulfated ethanol lignin has a higher molecular weight and a lower degree of polydispersity compared to the initial ethanol lignin.