From liquid to solid-state, solvent-free oxidative ammonolysis of lignins - an easy, alternative approach to generate "N-lignins"

Gerhild K Wurzer; Markus Bacher; Oliver Musl; Nadine Kohlhuber; Irina Sulaeva; Theres Kelz; Karin Fackler; Robert H Bischof; Hubert Hettegger; Antje Potthast; Thomas Rosenau

doi:10.1039/d3ra00691c

From liquid to solid-state, solvent-free oxidative ammonolysis of lignins - an easy, alternative approach to generate "N-lignins"

RSC Adv. 2023 Mar 23;13(14):9479-9490. doi: 10.1039/d3ra00691c. eCollection 2023 Mar 20.

Authors

Gerhild K Wurzer¹, Markus Bacher¹, Oliver Musl^{1

2}, Nadine Kohlhuber¹, Irina Sulaeva^{1

3}, Theres Kelz¹, Karin Fackler⁴, Robert H Bischof⁴, Hubert Hettegger¹, Antje Potthast¹, Thomas Rosenau^{1

5}

Affiliations

¹ Department of Chemistry, Institute of Chemistry of Renewable Resources, University of Natural Resources and Life Sciences, Vienna (BOKU) Konrad-Lorenz-Strasse 24 A-3430 Tulln Austria thomas.rosenau@boku.ac.at.
² Department of Chemical and Biological Engineering, Biobased Colloids and Materials, UBC University of British Columbia, Vancouver 2385 East Mall Vancouver Canada.
³ Core Facility Analysis of Lignocellulosics (ALICE), University of Natural Resources and Life Sciences, Vienna (BOKU) Konrad-Lorenz-Straße 24 A-3430 Tulln Austria.
⁴ Lenzing AG, Research & Development A-4860 Lenzing Austria.
⁵ Johan Gadolin Process Chemistry Centre, Åbo Akademi University Porthansgatan 3 FI-20500 Åbo Finland.

Abstract

A new chemical modification protocol to generate N-lignins is presented, based on Indulin AT and Mg²⁺-lignosulfonate. The already known ammonoxidation reaction in liquid phase was used as a starting point and stepwise optimised towards a full solid-state approach. The "classical" liquid ammonoxidation products, the transition products from the optimization trials, as well as the "solid-state" products were comprehensively analysed and compared to the literature. The N-lignins obtained with the conventional ammonoxidation protocol showed the same properties as reported. Their molar mass distributions and the hydroxy group contents, hitherto not accessible due to solubility problems, were measured according to a recently reported protocol. N-Indulin showed an N-content up to 11 wt% and N-lignosulfonate up to 16 wt%. The transition experiments from liquid to solid-state gave insights into the influence of chemical components and reaction conditions. The use of a single chemical, the urea-hydrogen peroxide complex (UHP, "carbamide peroxide"), was sufficient to generate N-lignins with satisfying N-content. This chemical acts both as an N-source and as the oxidant. Following the optimization, a series of solid-state ammonoxidation tests were carried out. High N-contents of 10% in the case of Indulin and 11% in the case of lignosulfonate were obtained. By varying the ratio of UHP to lignin, the N-content can be controlled. Structural analysis showed that the N is organically bound to the lignin, similar to the "classical" ammonoxidation products obtained under homogeneous conditions. Overall, a new ammonoxidation protocol was developed which does not require an external gas supply nor liquids or dissolved reactants. This opens the possibility for carrying out the lignin modification in closed continuous reactor systems, such as extruders. The new, facile solid-state protocol will hopefully help N-lignins to find more consideration as a fertilizing material and in soil-improving materials.