A review on recent biodiesel intensification process through cavitation and microwave reactors: Yield, energy, and economic analysis

The use of biodiesel as a reliable and green energy source has grown over the past few years. Biodiesel is sustainable and biodegradable because it is only made from vegetable contents and waste cooking oil. Although biodiesel has many advantages over conventional fuels, there are still a lot of technological issues that need to be addressed during the production process. The yield of biodiesel produced using conventional methods is poor and the process is time-consuming. Process enhancements like cavitation and microwave have thus been developed to address this problem. Starting with a comparison to the conventional biodiesel process, this paper has reviewed the most recent developments in the increase of mixture and transfer of heat in these two reactors. This paper examined biodiesel improvement using microwave and cavitation reactors, including biodiesel yield, by meticulously reviewing and analyzing previous works. The production of biodiesel from various raw materials using a range of catalysts, energy requirements, as well as operating factors, activation energy, and constraints also have been discussed. Additionally, the economic analysis discusses the feasibility and cost-effectiveness of implementing these technologies on a commercial scale. Overall, this review provides valuable insights into the intensification of biodiesel production using cavitation and microwave reactors while considering both the technical and economic aspects.

Advances in the fabrication, modification, and performance of biochar, red mud, calcium oxide, and bentonite catalysts in waste-to-fuel conversion

Various catalysts are being used in fuel production from biomass and polymeric waste for the obtention of an alternative energy source with both environmental friendliness and economic viability. Biochar, red mud bentonite, and calcium oxide have been shown to play a pertinent role as catalysts in waste-to-fuel conversion processes, such as transesterification and pyrolysis. In this line of thought, this paper has provided a compendium of the fabrication and modification technologies of bentonite, red mud calcium oxide, and biochar, together with their various performances in their application in the waste-to-fuel processes. Additionally, an overview of the structural and chemical attributes of these components is discussed regarding their efficiency. Ultimately, research trends and future points of focus are evaluated, and it is observed that techno-economic optimization of catalyst synthetic routes and investigation of new catalytic formulations, such as biochar and red mud-based nanocatalysts, are potential prospects. This report also offers future research directions that are anticipated to contribute to the development of sustainable green fuel generation systems.

A comprehensive review on nanocatalysts and nanobiocatalysts for biodiesel production in Indonesia, Malaysia, Brazil and USA

Biodiesel is an alternative to fossil-derived diesel with similar properties and several environmental benefits. Biodiesel production using conventional catalysts such as homogeneous, heterogeneous, or enzymatic catalysts faces a problem regarding catalysts deactivation after repeated reaction cycles. Heterogeneous nanocatalysts and nanobiocatalysts (enzymes) have shown better advantages due to higher activity, recyclability, larger surface area, and improved active sites. Despite a large number of studies on this subject, there are still challenges regarding its stability, recyclability, and scale-up processes for biodiesel production. Therefore, the purpose of this study is to review current modifications and role of nanocatalysts and nanobiocatalysts and also to observe effect of various parameters on biodiesel production. Nanocatalysts and nanobiocatalysts demonstrate long-term stability due to strong Brønsted-Lewis acidity, larger active spots and better accessibility leading to enhancethe biodiesel production. Incorporation of metal supporting positively contributes to shorten the reaction time and enhance the longer reusability. Furthermore, proper operating parameters play a vital role to optimize the biodiesel productivity in the commercial scale process due to higher conversion, yield and selectivity with the lower process cost. This article also analyses the relationship between different types of feedstocks towards the quality and quantity of biodiesel production. Crude palm oil is convinced as the most prospective and promising feedstock due to massive production, low cost, and easily available. It also evaluates key factors and technologies for biodiesel production in Indonesia, Malaysia, Brazil, and the USA as the biggest biodiesel production supply.

High Conversion of CaO-Catalyzed Transesterification of Vegetable Oils with Ethanol

Fatty acid ethyl esters (FAEEs) derived from vegetable oils and ethanol are promising bio-based chemicals for various applications such as biofuel, monomers for polyesters, and fine chemicals. However, the limited conversion and yield are obtained in the conventional methods due to low boiling point of ethanol that thus requires conducting the reaction at low temperature. This work demonstrates high yield of FAEEs from soybean, rice bran and palm oil with ethanol by performing the transesterification at high temperatures of 150-200°C by using CaO catalyst in a high pressure reactor. The results demonstrate the complete reaction for all vegetable oils with low ethanol to oil molar ratio of 6:1 and 1 wt.% CaO catalyst. Higher reaction temperature results in faster reaction while keeping high conversion of ≥ 99.0%. The unsaturated components in FAEE products are consistent with their original fatty acid chain. Moreover, the high conversion can be achieved even in the reaction conducted with low ethanol to oil molar ratio of 4.5:1 and 0.5 wt.% CaO catalyst at 180 °C in the palm oil transesterification. The catalyst can be reused for at least 3 times with the conversion higher than 94.0%. In addition, the activation energy (E_a), enthalpy of activation (ΔH^‡), entropy of activation (ΔS^‡) and Gibbs free energy of activation (ΔG^‡) are also obtained.

Progress on Modified Calcium Oxide Derived Waste-Shell Catalysts for Biodiesel Production

The dwindling of global petroleum deposits and worsening environmental issues have triggered researchers to find an alternative energy such as biodiesel. Biodiesel can be produced via transesterification of vegetable oil or animal fat with alcohol in the presence of a catalyst. A heterogeneous catalyst at an economical price has been studied widely for biodiesel production. It was noted that various types of natural waste shell are a potential calcium resource for generation of bio-based CaO, with comparable chemical characteristics, that greatly enhance the transesterification activity. However, CaO catalyzed transesterification is limited in its stability and studies have shown deterioration of catalytic reactivity when the catalyst is reused for several cycles. For this reason, different approaches are reviewed in the present study, which focuses on modification of waste-shell derived CaO based catalyst with the aim of better transesterification reactivity and high reusability of the catalyst for biodiesel production. The catalyst stability and leaching profile of the modified waste shell derived CaO is discussed. In addition, a critical discussion of the structure, composition of the waste shell, mechanism of CaO catalyzed reaction, recent progress in biodiesel reactor systems and challenges in the industrial sector are also included in this review.

Calcium and nitrogen species loaded into SBA-15 - a promising catalyst tested in Knoevenagel condensation

Mesoporous silica of the SBA-15 type was used as a support for basic active centers generated by the incorporation of calcium species and (3-aminopropylo)trimethoxysilane (APTMS) or imidazole. The samples were characterized by low temperature N2 adsorption/desorption, XRD, XPS, FTIR spectroscopy, CO2-TPD, and elemental and thermal analyses. Calcium containing samples were analysed in 2,5-hexanedione dehydration and cyclization, while the activities of all the samples were examined in Knoevenagel condensation between benzaldehyde and malononitrile. It was demonstrated that the calcium species interacted with a silica support increasing the stabilization of organosilanes on the SBA-15 surface. A very high activity of the catalysts in Knoevenagel condensation indicated a synergistic interaction between calcium and the organic modifiers.

Synthesis and characterization of monoacylglycerols through glycerolysis of ethyl esters derived from linseed oil by green processes

The synthesis of monoacylglycerol (MAG) through the glycerolysis of ethyl ester mixture (biodiesel) was investigated in this study from linseed oil, low-cost alternative feedstock, using an alkaline catalyst with green reagent. The transesterification double step process (TDSP), reaction with ethanol to ethyl esters yielded 97%. In the glycerolysis reaction, the optimum operating condition was in a temperature of 130 °C with 5% sodium hydroxide (NaOH) in 1 : 5 biodiesel-glycerol and 12 h reaction time, in open reactor. The reaction conditions showed an interesting conversion and monoacylglycerol yield of 98% and 76%, respectively. The determination and characterization of reaction products was carried out by Gas Chromatography (GC) method, Infrared Spectroscopy (IR), Thermogravimetric Analysis (TGA) and Hydrogen Nuclear Magnetic Resonance Spectroscopy (1H NMR).

Process dynamic investigations and emission analyses of biodiesel produced using Sr-Ce mixed metal oxide heterogeneous catalyst

The present study explores the feasibility of Sr-Ce based mixed metal oxides for its performance in transesterification reaction of waste cooking oil. The catalyst synthesis was carried out through gel combustion route and was characterized through several techniques including thermal analysis (TGA-DTA), X-ray diffraction (XRD), attenuated total reflectance based Fourier transform infrared spectroscopy (ATR-FTIR), high resolution scanning electron microscopy (HR-SEM) assisted with EDX, BET specific surface area and Hammett indicator basicity. The enhanced activity of the catalyst was investigated at pH 7.0 with Sr-Ce atomic ratio of 3:1 at 900 °C of calcination temperature. Influences of various process parameters on transesterification efficiency were carefully investigated. The experimental results demonstrated that maximum transesterification efficacy of 99.5% was achieved under optimized reaction conditions with catalyst dose of 2.0 wt %, oil-to-methanol ratio 1:14, reaction time 120 min, reaction temperature 65 °C and stirring speed of 700 rpm. For better interpretation of the process, the reaction rate was computed by employing pseudo-first and pseudo-second order kinetics model at varying reaction temperature (50 °C-75 °C). The transesterification data agreed well with pseudo-first order model with highest rate constant value of 2.5 × 10^-3 min^-1 was evaluated at 65 °C. Activation energy and frequency of the reaction was quantified from the Arrhenius expression as 17.04 kJ/mol and 9.92 min^-1, respectively. Thermodynamic analysis of the reaction system suggests that the transesterification of the waste cooking oil followed endergonic reaction pathway. Synthesis of biodiesel was ascertained from the H¹-NMR and FTIR analysis of the transesterified product, further, the physicochemical properties of the biodiesel were also compared with that of diesel fuel and the resultant values were found to be within ASTM limits. Reusability study was also conducted and it indicated that the catalyst can be easily regenerated and could be effectively reused up to four runs.

Advances in porous and nanoscale catalysts for viable biomass conversion

Solid catalysts with unique porosity and nanoscale properties play a promising role for efficient valorization of biomass into sustainable advanced fuels and chemicals.

Mg–Fe mixed oxides as solid base catalysts for the transesterification of microalgae oil

Mg–Fe LDO with different Mg/Fe molar ratios as catalysts were adopted for transesterification of microalgae oil, and the catalytic performance of the catalysts was closely related to their basicity and crystallinity.

Ultrasonic-assisted biodiesel production from waste cooking oil over novel sulfonic functionalized carbon spheres derived from cyclodextrin via one-step: a way to produce biodiesel at short reaction time

A novel sulfonated carbon derived from cyclodextrin showed high catalytic activity for the ultrasonic-assisted transesterification of waste cooking oil.