Synthesis of ethyl levulinate over sulfonated lignin-based carbon catalyst as a fuel additive to biodiesel-diesel blends towards engine emissions. by Hassan, Abdull Hafidz, Zainol, Muzakkir Mohammad, Samion, Muhammad Alif, Azlan, Muhammad A‘qil, Mohd., Asmadi, Mohamad Daud, Ahmad Rafizan, Saad, Idris, Mohd. Nor Azman, Nur Aina Najwa