Optimization and kinetic study of methyl laurate synthesis using ionic liquid [Hnmp]HSO4 as a catalyst.

Benyong Han,Hong Yang,Changmei Wang,Fang Yin,Jing Liu,Shiqing Liu,Xingling Zhao,Wudi Zhang

doi:10.1098/rsos.180672

Abstract

Methyl laurate was synthesized from lauric acid (LA) and methanol via an esterification reaction using ionic liquids (ILs) as catalysts. The efficiencies of three different catalysts, 1-methylimidazole hydrogen sulfate ([Hmim]HSO4), 1-methyl-2-pyrrolidonium hydrogen sulfate ([Hnmp]HSO4) and H2SO4, were compared. The effect of the methanol/LA molar ratio, reaction temperature, reaction time and catalyst dosage on the esterification rate of LA was investigated by single-factor experiments. Based on the single-factor experiments, the esterification of LA and methanol was optimized using response surface methodology. The results showed that the most effective catalyst was the IL [Hnmp]HSO4. The optimal conditions were as follows: [Hnmp]HSO4 dosage of 5.23%, methanol/LA molar ratio of 7.68 : 1, reaction time of 2.27 h and reaction temperature of 70°C. Under these conditions, the LA conversion of the esterification reached 98.58%. A kinetic study indicated that the esterification was a second-order reaction with an activation energy and a frequency factor of 68.45 kJ mol−1 and 1.9189 × 109 min−1, respectively. The catalytic activity of [Hnmp]HSO4 remained high after five cycles.

Highlights

Esters obtained from esterification reactions have attracted widespread attention due to their extensive applications in the food, cosmetic, plasticizer, pharmaceutical, plastic and chemical industries [1,2]
The esterification reaction can be catalysed by a homogeneous acid [10], such as H2SO4, HCl and organic sulfonic acids, which are traditionally selected as the acid catalyst [7]
Based on the comprehensive analysis of the response surface, we found that the interaction effects of [Hnmp]HSO4 dosage, methanol/acid molar ratio and reaction time were not significant parameters affecting the conversion of lauric acid (LA)

Summary

Introduction

Esters obtained from esterification reactions have attracted widespread attention due to their extensive applications in the food, cosmetic, plasticizer, pharmaceutical, plastic and chemical industries [1,2]. There is a high concentration of free fatty acids (FFAs) in non-edible oils. To achieve a reasonable conversion to biodiesel, the FFAs of non-edible oils should be converted to fatty acid methyl esters by esterification with methanol. Homogeneous acid-catalysed reactions can suffer from environmental and corrosion problems, which together negatively impact their applications in continuous processing, especially during neutralization and separation steps. Other issues, such as unfavourable by-products and difficult catalyst recovery and reuse [11], hinder the large-scale production of biodiesel from high FFA oils using homogeneous acid catalysts. Solid super acids [12], heteropolyacids [13], metal oxides [14], zeolites [15], molecular sieves [16] and enzymes [17] have been used for biodiesel production

Methods

Results

Conclusion