The carbohydrate-rich food waste is a potential renewable feedstock for biorefinery to produce value-added chemicals such as hydroxymethylfurfural (HMF). This study aimed to examine the kinetics and thermodynamics of conversion of bread waste i.e., starchy food waste to HMF over the trivalent and tetravalent metal chloride catalysts under heating at the temperature range of 140-160oC for 0-120 min in dimethyl sulfoxide (DMSO)/water (1:1 v/v). The results showed that the kinetics was enhanced by increasing the temperature since the optimum time for HMF generation was shortened over AlCl3 and SnCl4. However, the equilibrium remained the same in view of the similar maximum HMF yields over the tested temperature range. The highest HMF production of 29.5 Cmol% was achieved over the tetravalent SnCl4 at 160oC within 20 min. In contrast, FeCl3 produced a significant quantity of glucose but a trivial amount of HMF at the low-side temperature possibly because of its poor catalytic activity on the glucose-fructose transformation, leading to the accumulation of glucose. Nevertheless, the improved HMF yield at 160oC over FeCl3 suggested that sufficient heat could overcome the energy barrier of an alternative catalytic pathway without isomerization as the intermediate step. In addition, the stability of products formed over FeCl3 was found higher than that in AlCl3 and SnCl4. The emergence of levulinic acid implied HMF loss via rehydration, while the decline of total detectable products indicated humins formation at a high temperature and long reaction time over AlCl3 and SnCl4. The results of this study reveal the kinetic and thermodynamic characteristics of the desirable pathways and side reactions under metal catalysis, and thus expand our understanding on the dynamics in between them during the food waste valorization process.

Kinetic and thermodynamic insights into catalytic conversion of food waste to hydroxymethylfurfural

253rd National Meeting (2017)

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