Furfural is one of the most promising platform chemicals for a future biobased industry and can already be produced from renewable raw materials. However, its production processes suffer from yield loss and fouling problems due to degradation reactions. To increase our understanding of furfural stability, we investigated the kinetics of its degradation (i) without acid catalyst and (ii) in 10 different acids that are frequently used in biomass processing or that are naturally present in biomass hydrolysates. The batch experiments were conducted in a parallel minireactor setup at temperatures ranging from 125 to 200 C. The results showed that acid-catalyzed furfural degradation reactions depend mainly on acid strength and give rise to a set of common degradation products (formic acid, glycolic acid, pyruvate, etc.). Sulphurous acid and lignosulphonic acid led to greater furfural degradation than expected, which appears to be driven by specific side reactions. Adding formic acid, in contrast, led to a lower degradation rate than expected. In general, we observed two distinct, competing degradation mechanisms. Selectivity for formic acid as a degradation product depends on temperature, furfural concentration, and the presence of an acid catalyst. A more detailed study of the formic acid yielding reaction showed it to be reversible, and we provide the first quantitative description of this reaction for any furan. The proposed kinetic model, together with the results presented, contributes to the development of more efficient furfural production processes.

No 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.