Heterogeneous Reaction Model for Evaluating the Kinetics of Levulinic Acid Synthesis from Pretreated Sugarcane Bagasse

The abundance of sugarcane bagasse, a by-product of sugarcane juice extraction in sugar factories, serves as an advantage of its potential for producing chemicals such as levulinic acid (LA). Levulinic acid contains carbonyl and carboxyl groups that can be utilized for many applications, such as pharmacies, cosmetics, and solvents. Bagasse hydrolysis into LA was preceded by alkaline-acid pretreatment to separate cellulose from hemicellulose and lignin. This treatment could minimize the disturbance of these unwanted components, so that LA synthesis would be more optimal. Pretreated bagasse contained 82.64% cellulose, about two-fold from the non-pretreated one. It was hydrolyzed with hydrochloric acid (HCl), which acts as a catalyst (a Bronsted acid), at 150-170 oC, 0.1-1 M catalyst concentration, 1-10% solid-to-liquid (cellulose:catalyst-solution) ratio, and 0-200 minutes reaction time. The range of LA yield values obtained in the study were between 15-64.05%. The maximum LA yield was obtained at a temperature of 160 oC, 1 M catalyst concentration, and 1% solid-to-liquid ratio. The high LA yield indicates the importance of pretreatment supported by optimal conditions of synthetic reaction. The reaction route involved in hydrolysis was cellulose-glucose-levoglucosan (LG)-hydroxymethylfurfural (HMF)-LA. The result exhibits that temperature and catalyst concentration do not significantly affect the maximum potential LA yield. However, higher temperatures and catalyst concentration can accelerate the time to achieve the maximum potential LA yield. Meanwhile, the LA yield increases with a lower solid-to-liquid ratio. In contrast to previous studies, this study evaluated the reaction model in a more precise way using combination of models, considering that the reaction occurs between solid and liquid. The heterogeneous reaction model, namely the shrinking core model (SCM) for cellulose conversion to glucose and the first-order homogeneous reaction model for glucose to LA reaction, give good fitting results. The more appropriate reaction model is expected to be the basis of scale-up process carried out for industry one day. The results of this research have the potential to be applied for various other biomass raw materials with some improvements based on their characteristics which can be studied in the future.