Efficient Synthesis of Ethyl Levulinate Fuel Additives from Levulinic Acid Catalyzed by Sulfonated Pine Needle-Derived Carbon

The low-cost and environmentally friendly solid acid catalysts for the efficient synthesis of ethyl levulinate fuel additives were prepared from pine needles through the partial carbonization, followed by a hydrothermal H₂SO₄ sulfonation procedure. The resultant sulfonated carbon catalysts possessed an amorphous carbon structure and high contents of the sulfate groups. Other than that, they had good thermal stability and the total acid density was as high as 2.28 mmol g⁻¹. In this work, noticeably, the parameters of both synthetic and catalytic reactions were optimized to enhance the conversion of levulinic acid (LA). The results showed that the LA conversion was as high as 96.1% over the catalysts carbonizated at 700 °C for 90 min and sulfonated at 160 °C for 15 h under the optimized conditions (5:1 ethanol/LA molar ratio, 5 wt% catalyst dosage, 80 °C reaction temperature, 8 h reaction time). Meanwhile, the recyclability experiments confirmed that the resultant catalysts exhibited satisfactory reusability and the corresponding conversion of LA was maintained as 63.0% in the fourth run. Remarkably, the reused catalysts can be easily activated again and the corresponding LA conversion could reach up to 90.1%. The results demonstrated that the catalysts had great potential in the synthesis of biofuels, which could be efficient and could have excellent recyclability.