Production of 5-hydroxymethylfurfural from apple pomace in deep eutectic solvent

Apple pomace is a waste stream produced by fruit processing industry millions of tons annually. It is rich in carbohydrates making it a potential feedstock for the production of 5-hydroxymethylfurfural (HMF), one of the most valuable platform chemicals. In this work, the conversion of apple pomace carbohydrates to HMF was studied in a choline chloride:glycolic acid (1:3) deep eutectic solvent. To prevent undesired side reactions of HMF methyl isobutyl ketone was added to the reaction system as an extractive phase. The effect of reaction conditions, i.e., the amount of water added to the reaction system, the presence of Lewis acid co-catalyst, as well as the reaction temperature and time, on HMF yield were studied. The highest total HMF yield (44.5%) was achieved at 110 °C in 10 min with 15 wt% H₂O, and 0.01 g CrCl₃ as co-catalyst. Without the co-catalyst, the highest achieved HMF yield was 37.3% (120 °C, 20 min, 15 m% H₂O). The results indicated that apple pomace can be used as the feedstock for HMF production but the reaction procedure, especially the extraction process of HMF from deep eutectic solvent needs to be studied further.