Removal of 5-hydroxymethylfurfural and Furfural in Sugar Hydrolysate by Wood Charcoal Treatment

Process Development for the Detoxification of Fermentation Inhibitors from Acid Pretreated Microalgae Hydrolysate

The aim of this study was to remove 5-hydroxymethyl furfural (5-HMF) and furfural, known as fermentation inhibitors, in acid pretreated hydrolysates (APH) obtained from Scenedesmus obliquus using activated carbon. Microwave-assisted pretreatment was used to produce APH containing glucose, xylose, and fermentation inhibitors (5-HMF, furfural). The response surface methodology was applied to optimize key detoxification variables such as temperature (16.5–58.5 °C), time (0.5–5.5 h), and solid–liquid (S-L) ratio of activated carbon (0.6–7.4 w/v%). Three variables showed significant effects on the removal of fermentation inhibitors. The optimum detoxification conditions with the maximum removal of fermentation inhibitors and the minimum loss of sugars (glucose and xylose) were as follows: temperature of 36.6 °C, extraction time of 3.86 h, and S-L ratio of 3.3 w/v%. Under these conditions, removal of 5-HMF, furfural, and sugars were 71.6, 83.1, and 2.44%, respectively, which agreed closely with the predicted values. When the APH and detoxified APH were used for ethanol fermentation by S. cerevisiae, the ethanol produced was 38.5% and 84.5% of the theoretical yields, respectively, which confirmed that detoxification using activated carbon was effective in removing fermentation inhibitors and increasing fermentation yield without significant removal of fermentable sugars.

In Situ Chemical Locking of Acetates During Xylo-Oligosaccharide Preparation by Lignocellulose Acidolysis

Xylo-oligosaccharides with high value could be obtained by acidolysis of lignocellulosic biomass with acetic acid, which was an urgent problem to solve for the separation of acetic acid from crude xylo-oligosaccharides solution. Four neutralizers, CaCO₃, CaO, Na₂CO₃, and NaOH, were used for in situ chemically locking the acetic acid in the acidolyzed hydrolysate of corncob. The chemically locked hydrolysate was analyzed and compared using vacuum evaporation and spray drying. After CaCO₃, CaO, Na₂CO₃, and NaOH treatment, the locking rates of acetic acid were 92.62%, 94.89%, 95.05%, and 95.58%, respectively, and 39.55 g, 41.13 g, 41.78 g, and 41.87 g of the compound of xylo-oligosaccharide and acetate were obtained. Sodium neutralizer had lesser effect on xylo-oligosaccharide content, and Na₂CO₃ was the best chemical for locking acetic acid among these four neutralizers. This process provides a novel method for effectively utilizing acetic acid during the industrial production of xylo-oligosaccharides via acetic acid.