Ball milling for cellulose depolymerization and alcoholysis to produce methyl levulinate at mild temperature

The selective preparation of methyl levulinate (ML) from cellulose is an important step for utilizing natural renewable resource to produce interesting bulk chemicals. However, harsh reaction conditions, particularly high reaction temperatures (180-200 degrees C), are generally required to overcome the low reactivity of cellulose due to its high crystallinity. In this work, ball milling pretreatment was used prior to the alcoholysis of cellulose over Al-2(SO4)(3) to promote the process at mild reaction temperatures under microwave irradiation, reaching an ML yield as high as 64.92 mol% at 170 degrees C within 45 min, higher than reported results under the same reaction conditions. Ball milling was revealed to increase the accessibility of cellulose to the catalyst and disrupt the cellulose hydrogen-bonding networks, which facilitated the decomposition of cellulose. In addition, more reducing -end concentration suggested more reaction sites caused by ball milling pretreatment, contributing to the efficient conversion of cellulose. A kinetic study showed that the reaction active energies of two rate-determining steps, i.e., the decomposition of cellulose into methyl glucosides (MG) and sequent conversion of MG into ML, were reduced by the ball milling pretreatment and Al-2(SO4)(3), respectively. Furthermore, Al-2(SO4)(3) showed excellent reusability with minor loss of performance. The successful application of ball milling pretreatment prior to the alcoholysis of cellulose as well as raw biomass over Al-2(SO4)(3) makes it possible to produce ML directly from lignocellulose in industry.