A review on biodiesel production using catalyzed transesterification

Biodiesel is a low-emissions diesel substitute fuel made from renewable resources and waste lipid. The most common way to produce biodiesel is through transesterification, especially alkali-catalyzed transesterification. When the raw materials (oils or fats) have a high percentage of free fatty acids or water, the alkali catalyst will react with the free fatty acids to form soaps. The water can hydrolyze the triglycerides into diglycerides and form more free fatty acids. Both of the above reactions are undesirable and reduce the yield of the biodiesel product. In this situation, the acidic materials should be pre-treated to inhibit the saponification reaction. This paper reviews the different approaches of reducing free fatty acids in the raw oil and refinement of crude biodiesel that are adopted in the industry. The main factors affecting the yield of biodiesel, i.e. alcohol quantity, reaction time, reaction temperature and catalyst concentration, are discussed. This paper also described other new processes of biodiesel production. For instance, the Biox co-solvent process converts triglycerides to esters through the selection of inert co-solvents that generates a one-phase oil-rich system. The non-catalytic supercritical methanol process is advantageous in terms of shorter reaction time and lesser purification steps but requires high temperature and pressure. For the in situ biodiesel process, the oilseeds are treated directly with methanol in which the catalyst has been preciously dissolved at ambient temperatures and pressure to perform the transesterification of oils in the oilseeds. This process, however, cannot handle waste cooking oils and animal fats.     

Homogeneous borotungstic acid and heterogeneous micellar borotungstic acid catalysts for biodiesel production by esterification of free fatty acid

A highly negatively charged borotungstic acid H₅BW₁₂O₄₀ had been tested as homogeneous catalyst in esterification. Compared with common used H₃PW₁₂O₄₀, it displayed a higher conversion (98.7%) and excellent efficiency (96.2%) due to its high amount of protons in methanol. In order to overcome the drawbacks of homogeneous heteropolyacid H₅BW₁₂O₄₀, a Brønsted-surfactant-combined (C₁₆TA)H₄BW₁₂O₄₀ (C₁₆TA = cetyltrimethyl ammonium) had been fabricated with strong acidity and nano-size micellar structure resulting in enhanced activity and stability during the reaction, which exhibited consistent activity during recycling in esterification reaction.     

Inorganic heterogeneous catalysts for biodiesel production from vegetable oils

Biofuels are renewable solutions to replace the ever dwindling energy reserves and environmentally pollutant fossil liquid fuels when they are produced from low cost sustainable feedstocks. Biodiesel is mainly produced from vegetable oils or animal fats by the method of transesterification reaction using catalysts. Homogeneous catalysts are conventionally used for biodiesel production. Unfortunately, homogeneous catalysts are associated with problems which might increase the cost of production due to separation steps and emission of waste water. Inorganic heterogeneous catalysts are potentially low cost and can solve many of the problems encountered in homogeneous catalysts. Many solid acid and base inorganic catalysts have been studied for the transesterification of various vegetables oils. The work of many researchers on the development of active, tolerant to water and free fatty acids (FFA), as well as stable inorganic catalysts for biodiesel production from vegetable oils are reviewed and discussed.     

Characterization and transesterification of Iranian bitter almond oil for biodiesel production

In the present work the production of biodiesel using bitter almond oil (BAO) in a potassium hydroxide catalyzed transesterification reaction was investigated. The BAO was obtained from resources available in Iran and its physical and chemical properties including iodine value, acid value, density, kinematic viscosity, fatty acid composition and mean molecular weight were specified. The low acid value of BAO (0.24 mg KOH/g) indicated that the pretreatment of raw oil with acid was not required. The fatty acid content analysis confirmed that the contribution of unsaturated fatty acids in the BAO is high (84.7 wt.%). Effect of different parameters including methanol to oil molar ratio (3–11 mol/mol), potassium hydroxide concentration (0.1–1.7% w/w) and reaction temperature (30–70 °C) on the production of biodiesel were investigated. The results indicated that these parameters were important factors affecting the tranesterification reaction. The fuel properties of biodiesel including iodine value, acid value, density, kinematic viscosity, saponification value, cetane number, flash point, cloud point, pour point and distillation characteristics were measured. The properties were compared with those of petroleum diesel, EN 14214 and ASTM 6751 biodiesel standards and an acceptable agreement was observed.     

Optimisation of base-catalysed transesterification of Simarouba glauca oil for biodiesel production

Biodiesel was prepared from the crude oil of Simarouba glauca by transesterification with methanol in the presence of KOH as a catalyst. The reaction parameters such as catalyst concentration, alcohol to oil molar ratio, temperature and rate of mixing were optimised for the production of Simarouba oil methyl ester. The yield of methyl esters from Simarouba oil under the optimal condition was 94–95%. Important fuel properties of methyl esters of Simarouba oil (biodiesel) was compared with ASTM and DIN EN 14214. The viscosity was found to be 4.68 Cst at 40°C and the flashpoint was 165°C.     

Comparison of biodiesel production from crude Jatropha oil and Krating oil by supercritical methanol transesterification

This work compared the production of biodiesel from two different non-edible oils with relatively high acid values (Jatropha oil and Krating oil). Using non-catalytic supercritical methanol transesterification, high methyl ester yield (85–90%) can be obtained in a very short time (5–10 min). However, the dependence of fatty acid methyl ester yield on reaction conditions (i.e., temperature and pressure) and the optimum conditions were different by the source of oils and were correlated to the amount of free fatty acids (FFAs) and unsaturated fatty acid content in oils. Krating oil, which has higher FFAs and unsaturated fatty acid content, gave higher fatty acid methyl ester yield of 90.4% at 260 °C, 16 MPa, and 10 min whereas biodiesel from Jatropha oil gave fatty acid methyl ester yield of 84.6% at 320 °C, 15 MPa and 5 min using the same molar ratio of methanol to oil 40:1. The product quality from crude Krating oil met the biodiesel standard. Pre-processing steps such as degumming or oil purification are not necessary.     

A comparative study of KOH/Al2O3 and KOH/NaY catalysts for biodiesel production via transesterification from palm oil

The transesterification of palm oil to methyl esters (biodiesel) was studied using KOH loaded on Al₂O₃ and NaY zeolite supports as heterogeneous catalysts. Reaction parameters such as reaction time, wt% KOH loading, molar ratio of oil to methanol, and amount of catalyst were optimized for the production of biodiesel. The 25 wt% KOH/Al₂O₃ and 10 wt% KOH/NaY catalysts are suggested here to be the best formula due to their biodiesel yield of 91.07% at temperatures below 70 °C within 2–3 h at a 1:15 molar ratio of palm oil to methanol and a catalyst amount of 3–6 wt%. The leaching of potassium species in both spent catalysts was observed. The amount of leached potassium species of the KOH/Al₂O₃ was somewhat higher compared to that of the KOH/NaY catalyst. The prepared catalysts were characterized by using several techniques such as XRD, BET, TPD, and XRF.     

Screening,optimization and kinetics of Jatropha curcas oil transesterification with heterogeneous catalysts

This work investigates the production of fatty acid methyl esters (FAME) from Jatropha curcas oil using a variety of heterogeneous catalysts: resins, zeolites, clays, hydrotalcites, aluminas and niobium oxide. For this purpose, a catalyst screening was first conducted in a batch reactor at the following operating conditions: oil to methanol molar ratio of 1:9, 6 h of reaction, 5 wt% catalyst, at 333 and 393 K. From the screening step, KSF clay and Amberlyst 15 catalysts were selected to carry out a 2³ full factorial central composite rotatable design so as to elucidate the effects of process variables on FAME yield. The optimum reaction conditions for both catalysts were found to be oil to methanol molar ratio of 1:12, 5 wt% of catalyst, 433 K and 6 h of reaction with a FAME yield of about 70 wt%. A kinetic study was then experimentally performed and a semi-empirical model was built to represent the experimental data. Finally, catalyst re-utilization in five successive batch experiments was evaluated at the optimized conditions.     

Activity of homogeneous and heterogeneous catalysts,spectroscopic and chromatographic characterization of biodiesel: A review

Biofuel has got tremendous attraction for the last decade as an alternative source of energy. Bioethanol and biodiesel are two main products of first generation biofuel. Biodiesel is chemically fatty acid methyl esters prepared from various edible and non-edible oils. It has been used as a substitute to mineral diesel during the last decade. This review is about generation, transesterification, factors affecting transesterification, catalysts (homogeneous and heterogeneous) and physico-chemical characterization of biodiesel by chromatographic and spectroscopic techniques. The alkaline homogeneous catalysts (NaOH or KOH) have been used on commercial scale for production of biodiesel because these are cheap and reaction occurs in less time. The heterogeneous catalysts such as metal oxides, e.g., CaO, MgO, SrO, ZnO, La₂O₃, Mg–Al hydrolalcite have been used for transesterification of vegetable oil due to their easy separation and reuse but these catalysts take more time for completion of reaction. The yield of biodiesel may be affected by alcohol/oil ratio, concentration of catalyst, time required for reaction, temperature free fatty acid moisture. The prepared biodiesel has been characterized by chromatographic techniques like gas chromatography, gas chromatography–mass spectroscopy, high performance liquid chromatography and spectroscopic techniques like nuclear magnetic resonance and infrared spectroscopy.     

Study on the use of MgAl hydrotalcites as solid heterogeneous catalysts for biodiesel production

This paper, reports experimental work on the use of new heterogeneous solid basic catalysts for biodiesel production: double oxides of Mg and Al, produced by calcination, at high temperature, of MgAl lamellar structures, the hydrotalcites (HT). The most suitable catalyst system studied are hydrotalcite Mg:Al 2:1 calcinated at 507 °C and 700 °C, leading to higher values of FAME also in the second reaction stage. One of the prepared catalysts resulted in 97.1% Fatty acids methyl esters (FAME) in the 1st reaction step, 92.2% FAME in the 2nd reaction step and 34% FAME in the 3rd reaction step. The biodiesel obtained in the transesterification reaction showed composition and quality parameters within the limits specified by the European Standard EN 14214. 2.5% wt catalyst/oil and a molar ratio methanol:oil of 9:1 or 12:1 at 60–65 °C and 4 h of reaction time are the best operating conditions achieved in this study. This study showed the potential of Mg/Al hydrotalcites as heterogeneous catalysts for biodiesel production.     

A green route for biodiesel production from waste cooking oil over base heterogeneous catalyst

The present work describes the synthesis of porous BaSnO₃ by eco‐friendly sol‐gel method using albumin as a bio‐template agent, and its application as a solid base catalyst in biodiesel production from waste cooking oil. The physico‐chemical, textural, and morphological properties of the catalyst were evaluated by X‐ray diffraction (XRD), Brunauer‐Emmett‐Teller (BET), field emission scanning electron microscopy (FESEM), and temperature programmed desorption (TPD)–CO₂ techniques. The synthesized catalyst showed considerable stability, efficient catalytic activity, and negligible metal leaching. The satisfactory performance of the catalyst could be ascribed to the presence of basic sites of different strength on the surface of the catalyst. The catalyst produced maximum biodiesel yield of 96% at optimum reaction conditions of 90°C reaction temperature, methanol to oil molar ratio of 10:1, catalyst dosage of 6 wt%, and reaction time of 2 hours. Moreover, the catalyst showed substantial reusability up to five reaction cycles without any considerable decrease in transesterification activity.     

Microalgae for biodiesel production and other applications: A review

Sustainable production of renewable energy is being hotly debated globally since it is increasingly understood that first generation biofuels, primarily produced from food crops and mostly oil seeds are limited in their ability to achieve targets for biofuel production, climate change mitigation and economic growth. These concerns have increased the interest in developing second generation biofuels produced from non-food feedstocks such as microalgae, which potentially offer greatest opportunities in the longer term. This paper reviews the current status of microalgae use for biodiesel production, including their cultivation, harvesting, and processing. The microalgae species most used for biodiesel production are presented and their main advantages described in comparison with other available biodiesel feedstocks. The various aspects associated with the design of microalgae production units are described, giving an overview of the current state of development of algae cultivation systems (photo-bioreactors and open ponds). Other potential applications and products from microalgae are also presented such as for biological sequestration of CO₂, wastewater treatment, in human health, as food additive, and for aquaculture.     

A review on microwave-assisted production of biodiesel

Energy is the most important necessity for human existence on the earth. Limited crude petroleum resources and increasing awareness regarding the environmental impacts of fossil fuels are driving the search for new energy sources and alternative fuels. Biodiesel is a fuel which is renewable, biodegradable, environmentally friendly, and non-toxic in nature and has attracted considerable attention during the past decades. The costs of feedstock and the production process are two major hurdles to large-scale biodiesel production in particular. Various technologies have been developed to reduce the production cost. This paper attempts to extensively review microwave-assisted technology for biodiesel production. Additionally, different types of feedstocks for biodiesel production have been summarized in this paper. It is concluded that the microwave-assisted technique reduces the reaction time significantly in comparison with conventional methods. In addition, a high quality biodiesel can be obtained from microwave-assisted transesterification of different kinds of oils. Finally, the energy payback for 1kg biodiesel produced by microwave-assisted technology is calculated in this paper and it indicated that the system is sustainable. Therefore it can be a suitable method of decreasing the cost of biodiesel and can also help the commercialization of this fuel.     

Cyprinus carpio fish oil: A novel feedstock for biodiesel production

Biodiesel was developed from a novel nonedible oil source, namely Cyprinus carpio fish oil. The acid value of fish oil was very low (0.70 mg KOH/g oil, 0.35 free fatty acid content). As a result, biodiesel was produced through a one-step transesterifcation process, i.e. alkali-catalyzed transesterification with methanol. The optimal conditions for producing biodiesel from fish oil were investigated. The highest biodiesel yield (97.22% ~ 96.88% w/w ester content) was obtained under optimum conditions of 0.75% KOH w/w, 7:1 methanol to oil molar ratio, 60°C reaction temperature and 60-minute duration. Properties of the produced biodiesel as well as its blends with petro-diesel fulfilled the standard limits as prescribed by ASTM D6751 and EN 14214 indicating its suitability as a fuel for diesel engines.     

Brassica carinata as an alternative oil crop for the production of biodiesel in Italy: agronomic evaluation, fuel production by transesterification and characterization

In this study, the non-food use of Brassica carinata oil for biodiesel production was investigated. B. carinata, a native plant of the Ethiopian highlands widely used as food by the Ethiopians, has recently become object of increasing interest. This is due to its better agronomic performances in areas such as Spain, California and Italy that are characterized by unfavorable environmental conditions for the cultivation of Brassica napus (by far the most common rapeseed cultivated in continental Europe). The agronomic performance and the energetic balance described here confirmed that B. carinata adapted better and was more productive both in adverse conditions (clay- and sandy-type soils and in semi-arid temperate climate) and under low cropping system when compared with B. napus. The biodiesel, produced by transesterification of the oil extracted from the B. carinata seeds, displayed physical–chemical properties suitable for the use as diesel car fuel. A comparison of the performance of B. carinata oil-derived biodiesel with a commercial biodiesel and petroleum diesel fuel was conducted as regards engine performance, regulated and unregulated exhaust emissions. These results make B. carinata a promising oil feedstock for cultivation in coastal areas of central-southern Italy, where it is more difficult to achieve the productivity potentials of B. napus, and could offer the possibility of exploiting the Mediterranean marginal areas for energetic purposes.     

Preparation, characterization and application of heterogeneous solid base catalyst for biodiesel production from soybean oil

A solid base catalyst was prepared by neodymium oxide loaded with potassium hydroxide and investigated for transesterification of soybean oil with methanol to biodiesel. After loading KOH of 30 wt.% on neodymium oxide followed by calcination at 600 °C, the catalyst gave the highest basicity and the best catalytic activity for this reaction. The obtained catalyst was characterized by means of X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Scanning electron microscopy (SEM), Thermogravimetric analysis (TGA), N₂ adsorption-desorption measurements and the Hammett indicator method. The catalyst has longer lifetime and maintained sustained activity after being used for five times, and were noncorrosive and environmentally benign. The separate effects of the molar ratio of methanol to oil, reaction temperature, mass ratio of catalyst to oil and reaction time were investigated. The experimental results showed that a 14:1 M ratio of methanol to oil, addition of 6.0% catalyst, 60 °C reaction temperature and 1.5 h reaction time gave the best results and the biodiesel yield of 92.41% was achieved. The properties of obtained biodiesel are close to commercial diesel fuel and is rated as a realistic fuel as an alternative to diesel.     

One-step production of biodiesel through simultaneous esterification and transesterification from highly acidic unrefined feedstock over efficient and recyclable ZnO nanostar catalyst

Zinc oxide (ZnO) nanostar synthesized by simple and up-scalable microwave-assisted surfactant free hydrolysis method was applied as catalyst for biodiesel synthesis through one-step simultaneous esterification and transesterification from high free fatty acid (FFA) contaminated unrefined feedstock. It was found that ZnO nanostar catalyst was reacted with FFA to yield zinc oleate (ZnOl) as intermediate and finally became zinc glycerolate (ZnGly). With the re-deposition of ZnGly back to the ZnO nanostar catalyst at the end of the reaction, the catalyst can be easily recovered and stay active for five cycles. Furthermore, the rate of transesterification is highly promoted by the presence of FFA (6 wt.%) which makes it an efficient catalyst for low grade feedstock like waste cooking oil and crude plant oils.     

Transesterification of non-edible seed oil for biodiesel production: characterization and analysis of biodiesel

Evaluation of Radish (Raphanus sativus) seed oil (RSO) as a non-edible feedstock for biodiesel production was the main target of the present study. Extraction by solvent disclosed that radish seeds contains 33.50 wt.% of oil. Therefore, biodiesel production from it could be beneficial. Optimized base-catalyzed transesterification of RSO with methanol, ethanol and mixed methanol/ethanol was performed, to produce fatty acid methyl esters, fatty acid ethyl esters and mixed fatty acid methyl ethyl esters, respectively. The optimal yields of the methyl esters, ethyl esters and mixed methyl ethyl esters, were 95.55wt.%, 90.66 wt.% and 93.33 wt.%, respectively when the optimal reaction conditions were attained. Fuel properties of the parent oil were positively changed as consequence of transesterification reaction such that they fulfilled the standard limits as prescribed by ASTM D6751. Moreover, fuel properties of (biodiesels + petro diesel) blends conformed ASTM D7467-17 standards indicating their suitability as a fuel for diesel engines. Biodiesels form RSO were analyzed by thin layer chromatography and FTIR spectroscopy, and both techniques conformed its conversion into its corresponding alkyl esters.     

A green catalyst for biodiesel production from jatropha oil: Optimization study

In this study, a simple and solvent-free method was used to prepare sulfated zirconia-alumina (SZA) catalyst. Its catalytic activity was subsequently investigated for the transesterification of Jatropha curcas L. oil to fatty acid methyl ester (FAME). The effects of catalyst preparation parameters on the yield of FAME were investigated using Design of Experiment (DOE). Results revealed that calcination temperature has a quadratic effect while calcination duration has a linear effect on the yield of FAME. Apart from that, interaction between both variables was also found to significantly affect the yield of FAME. At optimum condition; calcination temperature and calcination duration at 490 °C and 4 h, respectively, an optimum FAME yield of 78.2 wt% was obtained. Characterization with XRD, IR and BET were then used to verify the characteristic of SZA catalyst with those prepared using well established method and also to describe the catalyst characteristic with its activity.     

Variability in sunflower oil quality for biodiesel production: A simulation study

Biodiesel is an alternative fuel made from vegetable oils or animal fats. The fatty acid composition of the feedstock, which varies among and within species, is the main determinant of biodiesel quality. In this work we analyze the variability in biodiesel quality (density, kinematic viscosity, heating value, cetane number and iodine value) obtained from sunflower oil, by means of a validated crop model that predicts the fatty acid composition of one high-oleic, and three traditional (high-linoleic) sunflower hybrids. The model was run with a 10-year average weather data from 56 weather stations in Argentina, and simulation results were compared to the biodiesel standards of Argentina, USA and Europe. We show that biodiesel produced from sunflower oil does not have one fixed quality, but different qualities depending on weather conditions and agricultural practices, and that intraspecific variation in biodiesel quality can be larger than interspecific differences. Our results suggest that (a) sunflower oil from high-oleic hybrids is suitable for biodiesel production (within limits of all analyzed standards), regardless of growing conditions and (b) sunflower oil from traditional hybrids is suitable for biodiesel production under the standards of Argentina and USA, while only certain hybrids grown in warm regions (e.g., Northern Argentina, Southern USA, China, India, Pakistan) are suitable for biodiesel production according to the European standard.