Synthesis of bifunctional nanocatalyst from waste palm kernel shell and its application for biodiesel production

Abstract

The potential of bifunctional nanocatalysts obtained from waste palm kernel shell (PKS) was investigated for one-step transesterification-esterification under mild conditions. State-of-the-art characterization illustrated that the synthesized catalyst has high stability through the thermal test, high BET surface area of 438.08 m² g^-1, pore volume of 0.367 cm³ g^-1 and pore width of 3.8 nm. The high amount of basicity (8.866 mmol g^-1) and acidity (27.016 mmol g^-1) promoted the successfulness of simultaneous transesterification-esterification. The investigation revealed that the combination of potassium and copper on activated carbon surface showed good catalytic activity by giving 95.0% FAME yield and 97.3% FFA conversion at a relatively mild condition of 5 wt% catalyst loading, 12 : 1 methanol to oil molar ratio at 80 °C for 4 hours with FAME yield > 80% after 5 reaction cycles. Characterization of the spent catalyst showed that the amount of basicity was reduced to 3.106 mmol g^-1, which validated the reduction of the catalytic performance. The usage of waste material was successfully discovered in producing an effective bifunctional catalyst for biodiesel production from waste cooking oil (WCO) and has high potential for commercialization in the future.

Fig. 1. TGA profile for PKSAC-KOH_(30%)CuO_(5%), PKSAC-K₂CO_3(30%)CuO_(5%), PKSAC-K₃PO_4(30%)CuO_(5%) and PKSAC-NaOH_(30%)CuO_(5%).

Fig. 2. Nitrogen adsorption/desorption isotherms of the raw PKS, PKSAC and PKSAC derived catalysts.

Fig. 3. Pore diameter distribution of the raw PKS, PKSAC and PKSAC derived catalysts.

Fig. 4. XRD diffractogram for PKSAC and PKSAC derived catalysts.

Fig. 5. FTIR for PKSAC and PKSAC derived catalysts.

Fig. 6. FESEM images for (a) raw PKS, (b) PKSAC, (c) PKSAC-K₂CO_3(20%)CuO_(5%), (d) PKSAC-K₂CO_3(30%)CuO_(5%), (e) PKSAC-K₂CO_3(40%)CuO_(5%) and (f) PKSAC-K₂CO_3(50%)CuO_(5%) analysed at 20 000× magnification.

Fig. 7. TGA profile of PKSAC and PKSAC-K₂CO_3(30%)CuO_(5%) catalyst.

Fig. 8. (a) Effect of K₂CO₃ wt% with Cu(NO₃)₂ fixed at 5 wt% for transesterification–esterification of WCO and (b) effect of Cu(NO₃)₂ wt% with K₂CO₃ fixed at 30 wt% for transesterification–esterification of WCO. Reaction condition: 5 wt% catalyst loading, 15 : 1 methanol-to-oil ratio at 70 °C for 4 hours.

Fig. 9. (a) The effect of catalyst loading on the FAME yield percentage (methanol : oil molar ratio of 15 : 1 at 70 °C for 4 hours). (b) The effect of reaction temperature on the FAME yield percentage (catalyst loading of 5 wt%, methanol : oil molar ratio of 15 : 1 for 4 hours). (c) The effect of methanol-to-oil molar ratio on the FAME yield percentage (catalyst loading of 5 wt% at 80 °C for 4 hours). (d) The effect of duration on the FAME yield percentage (catalyst loading of 5 wt%, methanol : oil molar ratio of 12 : 1 at 80 °C).

Fig. 10. (a) The effect of reusability study on the FAME yield percentage. Reaction condition; catalyst loading of 5 wt%, MeOH : oil molar ratio of 12 : 1, 80 °C for 4 hours. (b) XRD for fresh and spent PKSAC-K₂CO_3(30%)CuO_(5%) catalyst. (c) FTIR for fresh and spent PKSAC-K₂CO_3(30%)CuO_(5%) catalyst.