Preparation of sulfonated incomplete carbonized glucose acid catalyst via microwave irradiation for mehtyl ester production

Abstract

The usage of homogeneous catalyst in esterification process of feedstock with high free fatty acid (FFA) resulted in higher cost for post-production, wastewater treatment, and also catalysts loss. This gives reason for development of catalyst to substitute sulphuric acid in the industry. Conventional heating method of heterogeneous acid catalyst seems promising however, the heating time of carbonization and sulfonation always take longer and is not economically viable. Catalysts prepared by conventional heating also have low surface area and acid site density. Microwave-assisted sulfonated glucose was proposed in this study with several modifications of its parameter to fit in the industry scale. Microwave-assisted heating method initiates the rate of reaction and shortens the time and energy required using the power of radiation. A catalyst made from renewable resources, D(+)-Glucose was carbonized based on a few screening processes and the incomplete carbonized glucose (ICG) was then sulfonated with H2SO4 (SO3H/ICG). SO3H/ICG was characterized by using elemental analysis, X-ray diffraction, temperature programmed desorption of ammonia, field emission scanning electron microscope, Brunauer-Emmett-Teller, Fourier transform infrared spectroscopy as well as the dielectric constant (e'), loss factor (e") and tangent loss (tan d). D catalyst which was prepared at 20 min heating time, 20g D(+)-Glucose using 400W microwave power level showed remarkable surface area of 16.94 ± 0.30 m2/g, highest acid site density of 25.65 mmol/g and lowest e', e", tan d of 11.275, 10.691 and 0.948 respectively. Then, the catalyst was tested in esterification process of palm fatty acid distillate (PFAD) and analysis of the PFAD biodiesel was done through gas chromatography -flame ionization detector. The best performing catalyst, SO3H/ICG(7) with 91.41 % yield and 90.93 % conversion was then optimized via response surface methodology in order to obtain the optimum operating condition for sulfonation process. Through optimization, the most optimum reaction time, H2SO4 volume, power level of microwave and stirring rate were found to be 7.53 minutes, 159.51 ml, 413.64W and 670.53 rpm in order to obtain highest percentage yield of 94.01% and percentage conversion of 91.89%. Kinetic study was developed throughout the esterification process and activation energy from the forward and reverse reaction were found to be 3.36 kJ/mol and 11.96 kJ/mol respectively. The cost of biodiesel production from PFAD using microwave heating system on the other hand was higher for laboratory scale which was RM 31.33/kg compared to pilot and industrial scale of RM 3.29/kg and RM 1.76/kg, respectively. However these costs were much cheaper compared to conventional cost which reached RM 57.57/kg for laboratory scale. In conclusion, esterification process of PFAD to biodiesel using sulfonated glucose prepared via microwave-assisted heating method offers a greener procedure for catalyst preparation which is more convenient in time and cost saving.