The effects of combined catalysis of oxalic acid and seawater on the kinetics of xylose and arabinose dehydration to furfural

Abstract

It is known that both acids and salts have a positive catalytic effect on the dehydration of pentoses to form furfural, a potentially attractive platform chemical. In this study the effects of the combined usage of an organic acid, instead of stronger mineral acids, and a saline catalyst is investigated. In order to assess these effects, the kinetics of pentose dehydration to furfural are studied using oxalic acid as the primary catalyst and NaCl or seawater as the secondary saline catalyst. The interactions between these two types of catalysts are complex and are, therefore, also assessed thermodynamically. The addition of salts lowers the activity coefficient of the hydronium ions, but simultaneously favours the dissociation of the organic acid. It turned out that these two effects are of similar magnitude, resulting in a fairly constant hydronium ion activity. Because nonetheless higher furfural yields are obtained using the salts as a secondary catalyst, it is concluded that the salts influence the pentose dehydration mechanism directly. The final furfural yields obtained using oxalic acid as the primary catalyst were only slightly lower than those for similar experiments using HCl. The most distinctive difference between the two acids is the lower reaction rate (and thus longer reaction times) when using oxalic acid. Finally, it was observed that if no acidic catalyst is used, the salts tend to catalyse a loss reaction, which is suppressed when an acid is present.

Experimental studies of furfural production from water hyacinth (Eichhornia Crassipes)

“…16 Furthermore, oxalic acid experiments at 180°C under the presence of seawater, performed with 50 mmol L −1 and 100 mmol L −1 of acid, led to the same conclusion upon comparison. 16 Furthermore, oxalic acid experiments at 180°C under the presence of seawater, performed with 50 mmol L −1 and 100 mmol L −1 of acid, led to the same conclusion upon comparison.…”

“…This behavior can be attributed to the fact that high salt concentration impacts negatively the acid activity, ultimately leading to a lower furfural yield (Figure 3). 2,[13][14][15][16] The Cl ions improve the transition states of xylose during the dehydration step, thus promoting furfural formation. [28][29][30][31] The addition of NaCl as a secondary catalyst for pure C5 sugar conversion can lead to a significant increase in the furfural yield.…”

“…16 This different behavior can be attributed to two potential effects of the presence or absence of salts. 16 This different behavior can be attributed to two potential effects of the presence or absence of salts.…”

“…9 Water hyacinth has recently been found to be valuable for lignocellulosic content-based sugar production. 2,[13][14][15][16] The chemical composition of water hyacinth will be identified, followed by the experimental study of its hydrolysis and dehydration characteristics regarding furfural production. 5 In this study, the furfural production from water hyacinth is addressed.…”

Enhancement of furfural formation from C5 carbohydrates by NaCl in a green reaction system of CO2–water–isopropanol

“…Hongsiri et al. applied hydrochloric acid and oxalic acid in the conversion of arabinose to FF at 200°C, and moderate FF yields of 24.5% and 44.7%, respectively, were obtained. When they added NaCl to the aqueous solvent, the yields of FF from arabinose catalyzed by hydrochloric acid or oxalic acid increased to 34.5% and 49.1%, respectively.…”