Sustainable biofuel and bioenergy production from biomass waste residues using microwave-assisted heating: A comprehensive review

Since the late 1980s, the scientific community has been attracted to microwave energy as an alternative method of heating, due to the advantages that this technology offers over conventional heating technologies. In fact, differently from these, the microwave heating mechanism is a volumetric process in which heat is generated within the material itself, and, consequently, it can be very rapid and selective. In this way, the microwave-susceptible material can absorb the energy embodied in the microwaves. Application of the microwave heating technique to a chemical process can lead to both a reduction in processing time as well as an increase in the production rate, which is obtained by enhancing the chemical reactions and results in energy saving. The synthesis and sintering of materials by means of microwave radiation has been used for more than 20 years, while, future challenges will be, among others, the development of processes that achieve lower greenhouse gas (e.g., CO2) emissions and discover novel energy-saving catalyzed reactions. A natural choice in such efforts would be the combination of catalysis and microwave radiation. The main aim of this review is to give an overview of microwave applications in the heterogeneous catalysis, including the preparation of catalysts, as well as explore some selected microwave assisted catalytic reactions. The review is divided into three principal topics: (i) introduction to microwave chemistry and microwave materials processing; (ii) description of the loss mechanisms and microwave-specific effects in heterogeneous catalysis; and (iii) applications of microwaves in some selected chemical processes, including the preparation of heterogeneous catalysts.

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Microwaves and heterogeneous catalysis: A review on selected catalytic processes

An attractive alternative to the use of fossil fuels is biodiesel, which can be obtained from a variety of feedstock through different transesterification systems such as ultrasound, microwave, biological, chemical, among others. The efficient and cost-effective biodiesel production depends on several parameters such as free fatty acid content in the feedstock, transesterification reaction efficiency, alcohol:oil ratio, catalysts type, and several parameters during the production process. However, biodiesel production from vegetable oils is under development, causing the final price of biodiesel to be higher than diesel derived from petroleum. An alternative to decrease the production costs will be the use of economical feedstocks and simple production processes. Castor oil is an excellent raw material in terms of price and quality, but especially this non-edible vegetable oil does not have any issues or compromise food security. Recently, the use of castor oil has attracted attention for producing and optimizing biodiesel production, due to high content of ricinoleic fatty acid and the possibility to esterify with only methanol, which assures low production costs. Additionally, biodiesel from castor oil has different advantages over conventional diesel. Some of them are biodegradable, non-toxic, renewable, they can be used alone, low greenhouse gas emission, among others. This review discusses and analyzes different transesterification processes, technologies, as well as different technical aspects during biodiesel production using castor oil as a feedstock.

Production of Biodiesel from Castor Oil: A Review

A review on the current research on microwave processing techniques applied to graphene-based supercapacitor electrodes: An emerging approach beyond conventional heating

Branched chain fatty acids in the flavour of sheep and goat milk and meat: A review

A review on microwave-assisted transesterification processes using various catalytic and non-catalytic systems

In this research, non-edible Kusum oil was used to convert the free fatty acid into its methyl esters using a silicotungstic acid catalyst. The microwave as a heat source was used to fasten the rate of esterification of Kusum oil. The parametric study of the effect of methanol to oil molar ratio, catalyst amount, temperature, and time was carried out to obtain the reasonable conversion of free fatty acid. The study revealed that 9:1 molar ratio, 65 °C, 3.6 wt% catalyst, and 13 min of reaction time gave 92% free fatty acid (FFA) conversion. Further, the present study also estimates the kinetic and thermodynamic parameters of Kusum oil esterification. The kinetic study was performed at four temperatures with a pre-optimized 9:1 molar ratio of methanol to oil, 3.6 wt.% Silicotungstic acid for different time intervals. The kinetic study revealed that microwave-assisted acid-catalyzed esterification reaction is pseudo-first-order having activation energy 38.82 kJ.mol−1 and pre-exponential factor 219,037 min−1, respectively. The higher value of pre-exponential factor and lower activation energy in the kinetic study indicates the non-thermal effect associated with microwave heating. The rate constant and Gibbs’ free energy change at 65 °C was 0.224 min−1 and 98.89 kJ.mol−1. The values of Enthalpy and Entropy changes were 36.06 kJ.mol−1 and −0.185 kJ.mol−1.K − 1. It shows the reaction is non-spontaneous and endergonic by nature.

Parametric, kinetic, and thermodynamic studies of microwave-assisted esterification of Kusum oil

Microwave-assisted transesterification of non-edible oil to produce biodiesel is gaining attention due to lower heat loss as well as rapid\nconversion. In this study, esterified kusum oil as a feedstock was transesterified in the presence of Ba(OH)2. At 800 W microwave power\nand constant magnetic stirring the effect of important process parameters such as solvent methanol molar ratio, Ba(OH)2, temperature, and\ntime on biodiesel yield were evaluated. The parametric study suggested that 9:1 M methanol, 65 ºC reaction temperature, 2.5 wt%\nBa(OH)2 catalyst and 3.5 min of transesterification time gave close to 96% biodiesel yield. At the above conditions of methanol and\ncatalyst, the reaction kinetics and thermodynamic study were performed using different time intervals. The microwave-assisted\ntransesterification followed pseudo-first-order reaction rate with 34.57 kJ/mol K activation energy and 205664 min-1 frequency factor.\nThe reduction in activation energy and increase in the frequency factor reveal the non-thermal effect associated with microwave heating.\nThe thermodynamic properties evaluated using the Eyring equation suggests non-spontaneity and endothermic nature of transesterification.

Sheetal N. Nayak

Papers

A review on microwave-assisted transesterification processes using various catalytic and non-catalytic systems

Parametric, kinetic, and thermodynamic studies of microwave-assisted esterification of Kusum oil

Microwave-Assisted Transesterification of Kusum Oil: Parametric, Kinetic and Thermodynamic Studies