Carbon cryogel production from lignin, ionic liquid and liquefied oil palm frond as catalyst for esterification of levulinic acid

Abstract

Carbon cryogel synthesized from lignin, ionic liquid (IL) and mixtures of liquefied oil palm frond-ionic liquid (LOPF-IL), was used as an acid catalyst for esterification of levulinic acid in ethanol. Commercial lignin was reacted with furfural via sol-gel poly-condensation reaction at 90 °C for 30 min and the gel was freeze-dried and finally carbonized or calcined to produce carbon cryogel. Parametric study for the gel preparation was conducted to evaluate the carbon cryogel surface area and acidity. Similar parametric study was also performed on gel synthesis from IL and furfural. The selected gel condition of IL and furfural was applied for gel preparation from LOPF-IL and furfural. Nitrogen physisorption and temperature programmed desorption of ammonia measurements revealed the selected carbon cryogels obtained a large total surface area (>200 m2/g) and high acidity (>10 mmol/g). The selected carbon cryogels from lignin-furfural (CCLF), IL-furfural (CCIL) and liquefied OPF-IL-furfural (CCOPF) were further characterized using thermogravimetric analyzer, Fourier transform infrared spectroscopy, x-ray diffraction and field emission scanning electron microscopy with energy dispersive x-ray spectrometry. The phase structure of the synthesized spherical carbon cryogel was amorphous, has micro structures (microspheres) and thermally stable. The synthesized CCLF, CCIL and CCOPF were tested as catalyst in the esterification of levulinic acid. Carbon cryogels showed high potential as an acid catalyst for levulinic acid esterification with above 70.0 mol.% yield of ethyl levulinate. The kinetic studies using CCLF and CCIL revealed the esterification of levulinic acid followed pseudo-first order kinetics and have low activation energy. Meanwhile, the thermodynamic parameters conferred the reaction was endergonic and more ordered.