Ana Jakob, Blaž Likozar, Miha Grilc
Hemicelluloses, the most prevalent components of waste lignocellulosic biomass, can be efficiently converted through the hydrolysis of polysaccharides and subsequent dehydration of individual sugar units into value-added furanics. Over the past two decades, the hydroxymethylfurfural (HMF) biobased compound has demonstrated immense potential for its utilization capacity. However, the low process efficiency of the HMF production on an industrial scale has been restricting its valorization. Experimental kinetic studies are thus useful to elucidate underlying reaction mechanisms, enabling process optimization, and assessing biorefinery techno-economic operation. This review aims to present, analyze, and examine the validated characteristic activity of homogeneously, and heterogeneously catalyzed sugar dehydration, namely glucose, fructose, and xylose, as well as real wood and agricultural streams. Kinetic studies demonstrated the trend of strong temperature sensitivity for both HMF and humin formation and feedstock-dependent selectivity. Systematic testing with complex mixtures, controlled material samples, and model chemical intermediates contributes to unraveling the impact of feedstock complexity on HMF synthesis by identifying unwanted interactions and regulating the influence of impurities. Therefore, the principles of these elusive pathways are evaluated, discussing the possibilities of limiting undesired side products. Comparing the relevance of HMF, an overview is concluded with the acknowledged challenges of feedstock, impacting HMF selectivity.