Hierarchical porous carbon catalyst derived from sodium lignosulfonate for efficient biodiesel production: high turnover frequency and economic viability

Li/La bimetallic catalyst supported on hierarchical porous carbon was prepared. • RSM-BBD optimization yielded 99.5% oil conversion at 60.14°C in 2.47 h. • High TOF, low E-factor and PMI meet green chemistry principles. Sodium lignosulfonate, a major byproduct of the sulfite pulping industry, can be converted into carbonaceous materials for catalyst preparation, enabling high‑value utilization of industrial waste. In this study, a hierarchical porous carbon support (HPC) was prepared from sodium lignosulfonate and sodium humate through a two‑step process of carbonization and KOH activation. Subsequently, a series of heterogeneous base catalysts, were synthesized by loading bimetallic active components (Li and La) onto HPC via an ultrasonic‑assisted impregnation method. Optimization of the reaction parameters was conducted utilizing response surface methodology in conjunction with the Box-Behnken experimental design (RSM-BBD). The optimum reaction conditions were identified as catalyst amount of 6.96 wt%, methanol/oil molar ratio of 28.52:1, temperature of 60.14°C, and reaction duration of 2.47 h, under which an oil conversion rate of 99.5% was achieved. Kinetic analysis indicated that the transesterification process conformed to pseudo-first-order kinetic behavior, with an apparent activation energy determined to be 48.06 kJ·mol −1 . Thermodynamic parameters (ΔH = 45.42 kJ·mol −1 , ΔS = -142.19  J·mol −1 ·K −1 ) confirmed that the reaction is endothermic and nonspontaneous. The catalyst maintained a soybean oil conversion of 79.5% after five consecutive cycles, with an estimated production cost of approximately $4.74 per kilogram. Additionally, the catalyst demonstrated a high turnover frequency (TOF) value of 30.06 h −1 along with low E‑factor (0.105) and process mass intensity (PMI) (1.105) values, consistent with green chemistry principles. Download: Download high-res image (196KB) Download: Download full-size image