Separation and Purification of ω-6 Linoleic Acid from Crude Tall Oil

Md Shariful Islam,Lew P Christopher,Md Nur Alam

doi:10.3390/separations7010009

Abstract

Crude tall oil (CTO) is the third largest by-product at kraft pulp and paper mills. Due the large presence of value-added fatty and resin acids, CTO has a huge valorization potential as a biobased, readily available, non-food, and low-cost biorefinery feedstock. The objective of this work was to present a method for the isolation of high-value linoleic acid (LA), an omega (ω)-6 essential fatty acid, from CTO using a combination of pretreatment, fractionation, and purification techniques. Following the distillation of CTO to separate the tall oil fatty acids (TOFAs) from CTO, LA was isolated and purified from TOFAs by urea complexation (UC) and low-temperature crystallization (LTC) in the temperature range between −7 and −15 °C. The crystallization yield of LA from CTO in that range was 7.8 w/w at 95.2% purity, with 3.8% w/w of ω-6 γ-linolenic acid (GLA) and 1.0% w/w of ω-3 α-linolenic (ALA) present as contaminants. This is the first report on the isolation of LA from CTO. The approach presented here can be applied to recover other valuable fatty acids. Furthermore, once the targeted fatty acid(s) are isolated, the rest of the TOFAs can be utilized for the production of biodiesel, biobased surfactants, or other valuable bioproducts.

Highlights

The pulp and paper industry has joined the global movement toward cleaner and greener products in their effort to transition to forest biorefineries
Black liquor is first partially concentrated to 20–30% solids w/v and allowed to settle; (2) the top layer of the partially concentrated black liquor, known as tall oil soap, is skimmed off; and (3) the tall oil soap is acidified with sulfuric acid to form Crude tall oil (CTO) and remove impurities such as sodium salts, dissolved lignin, unreacted soap or acid, residual pulping chemicals, etc
This study presents an example that demonstrates how the circular bioeconomy concept can be applied to upgrade low-value industry by-products such as CTO

Summary

Introduction

The pulp and paper industry has joined the global movement toward cleaner and greener products in their effort to transition to forest biorefineries. This transition is based on the circular bioeconomy concept, which implies the most efficient recycling of wastes, co-products, and residues as a strategy to preserve our bio-based resources and minimize the use of fossil fuel-derived products of environmental concern. CTO is the third largest chemical by-product in a kraft pulp and paper mill, with a yield from highly resinous coniferous species in the range of 30–50 kg per ton pulp [1]. The exact yield and composition of CTO depend on a number of factors such as pulping conditions, wood species, and their length of storage prior to pulping, geographical location, climate conditions, etc. [3]

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