Fate of Lipophilic Wood Extractives in Oxygen-Based Cellulose Bleaching

Sebastian España Orozco,Karin Fackler,Robert H Bischof,Stefano Barbini,Antje Potthast,Dev Sriranganadane

doi:10.1021/acssuschemeng.1c00109

Abstract

The impact of totally chlorine-free (TCF) bleaching chemicals on the composition and behavior of detrimental lipophilic wood extractives in a mixed hardwood sulfite pulp was studied to determine their potential for pitch control without the need for additional reagents. Toward this end, the acetone extracts of pulp were analyzed with commonly used gas chromatography (GC) and more sophisticated ultraperformance convergence chromatography (UPC2). During EO(P)–Z–P bleaching, the highest decrease in the lipophilic extractive content was achieved after ozone bleaching (Z), with a 38% reduction of GC-FID/MS-detectable resins. Oxygen-reinforced alkaline extraction EO(P) and peroxide bleaching (P) were less effective in terms of resin quality and quantity (−30 and −27%, respectively). Analyzing the acetone extracts after alkaline hydrolysis revealed a different pattern: EO(P) with −44%, P with −20%, and Z with only −8% less lipophilic extractives. A series of oxidized compounds, such as acyl chain-oxidized sterol esters and acylglycerols, and acidic secosterol analogues, were detected for the first time with UPC2-ESI-QToF-MS after ozone bleaching. These compounds lead to an underestimation of the GC-detectable resin content and may be involved in the formation of deposits during lignocellulosic processing. Reaction pathways for lipophilic extractives during ozone bleaching were established.

Highlights

Lipophilic extractives are the low molecular weight fraction of lignocellulosic biomass that can be extracted with nonpolar solvents and that do not contribute to structural stability
Determining the impact of ozone on lipophilic extractives is of utmost importance for wood and nonwoody biorefineries given the similarity of the resinous fraction in both renewable resources,[13] and the increasing interest in ozone as a potential pretreatment for nonwoody biomass.[14−16]. To address these limitations in previous research, we studied the fate of lipophilic wood extractives in a sulfite pulp mill with a totally chlorine-free (TCF) bleaching sequence that involved a combined oxygen and alkaline extraction stage and integrated ozone bleaching
35−46% of the total amount could be assigned by gas chromatography (GC)-FID and identified as the major lipophilic extractive families, e.g., fatty acids, sterols, diglycerides, sterol esters, and triglycerides

Summary

Introduction

Lipophilic extractives are the low molecular weight fraction of lignocellulosic biomass that can be extracted with nonpolar solvents and that do not contribute to structural stability. More resistant lipophilic extractives, such as sterols and sterol esters, cause production downtimes due to deposition, referred to as pitch deposits.[10] Less research has been conducted on the chemical pulping of wood under acidic or neutral conditions with consecutive totally chlorine-free (TCF) bleaching, such as production of dissolving pulp by the sulfite process. In both cases, hydrolyzable lipophilic components, such as waxes, sterol esters, and triglycerides, are less prone to hydrolysis and enter subsequent bleaching stages.[11] During bleaching, chemical alterations of lipophilic wood extractives occur. The growth in demand for ecological sustainability, chlorine-free processes, and environmental legislation is leading to an increased interest in TCF bleaching protocols that can operate with oxygenbased bleaching chemicals, such as molecular oxygen, ozone, Received: January 6, 2021 Revised: March 2, 2021 Published: March 24, 2021

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Conclusion