Abstract
The reuse of steeping lye is crucial for the sustainable production of viscose fibers. Steeping lye contains hemicellulose and many alkaline degradation products, such as organic acids, so that its purification can be evaluated in terms of total organic carbon removal. When considering purification by membrane filtration, intermolecular interactions between hemicellulose and organic acids can strongly affect their retention efficiency. Herein, we give more insights into the ultrafiltration and nanofiltration of steeping lye and corresponding model solutions. Furthermore, we studied the impact of total organic carbon concentration, hemicellulose concentration and sodium hydroxide concentration on the membrane performance. Hydrogen bonds between hemicellulose and certain types of hydroxy acids increased the retention of the latter. In contrast, charge based repulsion forces led to a decreased retention of a certain type of hydroxy acids. It can be clearly shown that taking intermolecular interactions into account is highly important for the description of complex multicomponent mixtures. In addition, the results can be extended to other, highly alkaline process streams with organic content, such as Kraft pulping liquors.
Highlights
Received: 18 November 2020Cellulose is the most abundant biopolymer on earth
We provide detailed analyses of the retention of sugars and several hydroxy acids, such as glucoisosaccharinic acid, xylo isosaccharinic acid, glycolic acid, etc., i.e., organic acids formed through alkaline polysaccharide degradation, which are leading constituents of the γ-cellulose fraction
The intermolecular interactions that play an important role in the processing of steeping lye are discussed
Summary
Cellulose is the most abundant biopolymer on earth. Wood is mainly composed of cellulose, hemicellulose, and lignin. Cellulose must be separated from hemicellulose and lignin during the production of dissolving pulp. The pulp is subjected to washing, bleaching and further treatment for use as dissolving grade pulp. In the production of viscose fibers, which utilizes dissolving wood pulp as raw material, several processing steps are conducted in highly concentrated sodium hydroxide solutions. Sodium hydroxide concentrations ranging from 17.5 to 19.5 w%
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