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<p>This study introduces a novel, sustainable method for biodiesel production using bifunctional heterogeneous catalysts derived from black tea waste. Catalysts were synthesized via sulfonation with H<sub>2</sub>SO<sub>4</sub> followed by alkaline treatment with NaOH and KOH to produce NaS.T and KS.T, respectively. Characterization showed enhanced surface areas of 59.7&#xa0;m<sup>2</sup>/g (NaS.T) and 47.6&#xa0;m<sup>2</sup>/g (KS.T), supporting improved catalytic activity. Transesterification of waste cooking oil using these catalysts achieved maximum biodiesel yields of 98.7% (NaS.T) and 97.8% (KS.T) under optimal conditions (3 wt% catalyst, 10:1 methanol/oil ratio, 40&#xa0;°C, 45&#xa0;min). Kinetic modeling confirmed pseudo-first-order behavior (R<sup>2</sup> &gt; 0.90), with activation energies of 11.71&#xa0;kJ/mol (NaS.T) and 24.56&#xa0;kJ/mol (KS.T)—significantly lower than conventional ranges—indicating a diffusion-controlled reaction. The higher pre-exponential factor for KS.T (741.5&#xa0;min<sup>−1</sup> vs. 106.5&#xa0;min<sup>−1</sup> for NaS.T) suggests a greater frequency of effective molecular collisions. Thermodynamic analysis confirmed the endothermic nature of the process (ΔH* = 15.01–22.04&#xa0;kJ/mol) and negative entropy values (− 25.81 to − 41.9&#xa0;J/mol·K), reflecting the formation of an ordered transition state. Gibbs free energy values (ΔG* = 27.29–30.12&#xa0;kJ/mol) affirmed the feasibility and spontaneity of the reactions under studied conditions. Optimization using Response Surface Methodology yielded models with high predictive accuracy (R<sup>2</sup> = 0.979 for KS.T; 0.944 for NaS.T), enabling predicted yields of up to 99.6%. These results demonstrate the potential of black tea waste-derived catalysts for low-cost, energy-efficient biodiesel production, aligning with sustainable fuel and waste valorization goals.</p>

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Upcycling black tea waste into a bifunctional catalyst for efficient biodiesel production from waste cooking oil with kinetic and thermodynamic insights

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年7月1日

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  • May N. Bin Jumah,
  • Amna M. Farhan,
  • Ahmed A. Allam,
  • Mostafa R. Abukhadra,
  • Stefano Bellucci

摘要

This study introduces a novel, sustainable method for biodiesel production using bifunctional heterogeneous catalysts derived from black tea waste. Catalysts were synthesized via sulfonation with H2SO4 followed by alkaline treatment with NaOH and KOH to produce NaS.T and KS.T, respectively. Characterization showed enhanced surface areas of 59.7 m2/g (NaS.T) and 47.6 m2/g (KS.T), supporting improved catalytic activity. Transesterification of waste cooking oil using these catalysts achieved maximum biodiesel yields of 98.7% (NaS.T) and 97.8% (KS.T) under optimal conditions (3 wt% catalyst, 10:1 methanol/oil ratio, 40 °C, 45 min). Kinetic modeling confirmed pseudo-first-order behavior (R2 > 0.90), with activation energies of 11.71 kJ/mol (NaS.T) and 24.56 kJ/mol (KS.T)—significantly lower than conventional ranges—indicating a diffusion-controlled reaction. The higher pre-exponential factor for KS.T (741.5 min−1 vs. 106.5 min−1 for NaS.T) suggests a greater frequency of effective molecular collisions. Thermodynamic analysis confirmed the endothermic nature of the process (ΔH* = 15.01–22.04 kJ/mol) and negative entropy values (− 25.81 to − 41.9 J/mol·K), reflecting the formation of an ordered transition state. Gibbs free energy values (ΔG* = 27.29–30.12 kJ/mol) affirmed the feasibility and spontaneity of the reactions under studied conditions. Optimization using Response Surface Methodology yielded models with high predictive accuracy (R2 = 0.979 for KS.T; 0.944 for NaS.T), enabling predicted yields of up to 99.6%. These results demonstrate the potential of black tea waste-derived catalysts for low-cost, energy-efficient biodiesel production, aligning with sustainable fuel and waste valorization goals.