Microwave-assisted p-TsOH hydrotropic delignification of oil palm biomass for dual recovery of functional lignin and crystalline cellulose

The selective and efficient extraction of lignin from lignocellulosic biomass remains a key challenge in biorefinery development. In this study, microwave-assisted hydrotropic delignification of oil palm empty fruit bunch (EFB) was performed using p-toluenesulfonic acid (p-TsOH) as a single-component system. The minimum hydrotropic concentration (MHC) of p-TsOH was determined to be 35 wt%, representing the critical threshold at which p-TsOH starts forming hydrotropic aggregates, which are necessary to begin dissolving lignin effectively. Therefore, the delignification was evaluated above the MHC value, which is at 50–80 wt% p-TsOH at 120 °C, for 30 and 60 min. The highest lignin yield of 85.27 % was achieved at 80 wt% for 30 min. Structural analysis confirmed the retention of aromatic and methoxy units, while molecular weight and thermal analysis showed that the optimized lignin exhibited the highest DTGmax (412.5 °C) and glass transition temperature (129.8 °C). The cellulose-rich residue obtained under the same conditions showed enhanced crystallinity (71.36 %) and surface fibrillation. These findings demonstrate that the combination of p-TsOH and microwave heating offers a rapid and effective route for lignin and cellulose fractionation from EFB, with potential downstream applications in thermoplastics, carbon materials, and nanocellulose production.