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Biodiesel is a mixture of fatty acid esters formed by transesterification of vegetable oil, animal fat, algae oil or waste oil with an alcohol like methanol (CH3OH), ethanol (C2H5OH) or higher alcohols. There are many important catalytic variables like catalyst type and composition, support type and pretreatment conditions (i.e. calcination temperature and time) which are utilized to achieve high yields for the transesterification reaction. In addition, operational conditions such as reaction temperature, alcohol type, alcohol to oil molar ratio and stirring speed have also quite high significance. Moreover, all these variables can be optimized under supercritical conditions by novel techniques like ultrasonic and microwave irradiation or hydrodynamic cavitation. In this work, significant catalytic and operational variables for biodiesel production are reviewed. In addition, dominant parameters together with their limitations during the application of advanced technologies are investigated in detail. Then, it has been concluded that, for better control and higher yields of biodiesel production, future research works should focus on addition of co-solvents, use of longer chain alcohols, bulky structures or ionic liquids, adjustment of mode of irradiation and modification of the instrumentation or the equipment.

This study analyzes the influence that the environmental conditions and media composition have on the quality of wastewater-grown-microalgae lipids as a feedstock for biodiesel. A two-level full factorial design with three factors (organic carbon content, CO2 supply, and light intensity), followed by a PCA were utilized to explore relations among the variables. The content of SFAs, MUFAs, and PUFAs in the algal lipids ranged between 30.9 and 56.6%, 16.4–62.1%, and 4.7–27.9%, respectively. Light intensity was the major factor affecting lipids composition, followed by CO2. Experimental conditions at the lowest light intensity and the highest CO2 content tested in the study (40 μmol·m−2·d-1 and 10% CO2) were related to enhanced productions of MUFAs and increased C16 and C18 contents, which are desirable compounds in the lipids targeted to biodiesel production. Among the components derived from the wastewater mixture used as source of nutrients to microalgae, NH3-N was related to increased MUFAs productions by the cells. Higher contents of organic carbon reduced the unsaturation value, increasing the oxidative stability of the biodiesel. Biodiesel properties of the algal lipids grown under all experimental conditions tested in this study were found to comply with ASTM D6751 and EN 14214 standards.

Current research deals with the effective, economic and ecofriendly conversion of algal oil into biodiesel using Calcium oxide (CaO) nanocatalyast. CaO nanoparticles were used as an alkaline catalyst for the transesterification of the indigenous green alga, Chlorella vulgaris oil into biodiesel. The catalyst was subjected to different calcination temperatures and their effect on complete transesterification of algal oil at different concentrations was also studied. The characteristics of the nanocatalyst were investigated using UV–Vis spectrophotometer, Fourier-Transform Infrared spectroscopy (FTIR), powder X-ray Diffractometer (XRD) and Field Emission Scanning Electron Microscopy (FESEM) equipped with Energy Dispersive Spectroscopy (EDS). It was found that various parameters such as reaction time, temperature and catalyst amount influences the fatty acid methyl esters (FAME) yield. The ideal conditions for transesterification process were optimized as a methanol to oil molar ratio of 9:0.6, a reaction period of 4 h, a catalyst loading at 4% and a reaction temperature of 80 °C. Gas chromatographic analysis revealed a fatty acid profile highly suitable for biodiesel production. A catalyst concentration of 3 mg.L-1 of CaO synthesized at 400 °C was found to be ideal for the transesterification process. These approaches could make massive impact on the large scale biodiesel production minimizing the hefty capital costs.

Nutrient supply, especially nitrogen and phosphorus, is one of the key obstacles limiting industrialization of algal biofuel. To help enhance nutrient utilization efficiency, our research focused on recycling of nutrients from lipid extracted algae biomass by the method of anaerobic digestion. Two methods of lipid extraction were performed, nutrients were released during anaerobic digestion of the lipid extracted biomass, the recycled nutrients were collected for algae cultivation, and the cycle was repeated: cultivation-extraction-digestion-cultivation. The results show that anaerobic digestion released nitrogen and phosphorus, and methane as a gaseous by-product. The algae grew well on the recycled nutrients. Ammonia is the limiting macro element, and extra trace elements enhanced algae production as well. Ash free dry weight, lipid content and lipid components were monitored and did not vary when the cycle was repeated. This system for recycling nutrients with supplementary nutrients holds potential for producing biofuel from algae.

The present study demonstrated the growth of microalgae in wastewaters to underline a process coupled with biofuel production. Green alga, Scenedesmus sp., was cultivated in various domestic wastewaters (S1, S2, S3). Biomass 0.84, 0.68, 0.73 (g/L) and lipid productivity 8.6, 5.6, 6.2 (mg/L/d) were obtained from wastewaters S1, S2, S3 respectively in 20 days. Removal of 66% inorganic phosphorous, 99% nitrite, 86% nitrate, 80% ammoniacal nitrogen, 84% calcium and 76% sulphate from the initial high level of wastewater nutrients were achieved by algal cultivation. The total fatty acid (FA) produced by the alga in these conditions consisted of 43.3% saturated FA, 44.4% monounsaturated FA, and 12.3% polyunsaturated FA. The pilot scale study could be implemented for the simultaneous nutrient removal and algal oil production by utilizing domestic wastewaters.

Pollution is one of the major tricky issues in the world due to the negative impact of vehicle population and industrialization. Transport sector is still struggling to control the pollution in spite of making many initiatives to keep it in control. Researchers have successfully claimed that biodiesel could be a possible solution due to its closed carbon cycle. In this scenario, microalgal biodiesel has the potential resource to reduce the vehicle pollution as an alternative fuel source. In this work, microalgae cultivated in open raceway ponds in optimized composite media were harvested with low cost filters, dried and oil extracted using solvent method. Two step conversion processes was employed to convert algal oil into biodiesel using optimized process parameters. Naturally available sea shell was used as the catalyst in the transesterification process. A new comprehensive bioreactor was designed and fabricated for oil extraction, esterification, transesterification and distillation process to produce 10 l of biodiesel in a batch. The biodiesel was then tested in the internal combustion (IC) engine test rig for various blends to analyse the performance and emission at different compression ratios (CRs). The brake thermal efficiency (BTE) of 27.42% at specific fuel consumption (SFC) of 0.225 kg/kWh was obtained for B30 blend at CR of 19. The emission characteristics were also found to be low at CR 19, which is the rated CR of the engine for diesel fuel.

Effect of addition of anti-oxidants into the algae biodiesel blend with modification of its fuel injection timing was investigated for the emission control of a compression ignition (CI) engine. It was planned to control the NOx emission of the engine fuelled with algae biodiesel blend by equally concentrating on the smoke control and brake thermal efficiency (BTE). Hence NOx, smoke and BTE were the responses for the present investigation. Experiment test matrix were designed with two different anti-oxidants (Pyrogallol (PY) and Butylated hydroxytoluene (BHT)) and fuel injection timing as the factors by choosing three levels in each factor. A single cylinder stationary engine was tested with the designed test matrix as per the Taguchi Orthogonal array. Experiments results were analysed by calculating multi response signal to noise (MRSN) ratio for the loss functions of the selected responses and also by analysing the variance of obtained MRSN ratio. From the results it was observed that when fuelled with algae biodiesel blend, BHT plays a most significant role followed by injection timing for the reduction of engine NOx emission with equal importance to the smoke control and BTE. It was also observed that the influence of pyrogallol was less when compared with other factors for the NOx control of the CI engine fuelled with algae biodiesel blend.

Algae-based fuels are considered to be the most sustainable, renewable, effective and environment friendly response to climate change and food–feed security, as well as the only renewable energy resource that has the capacity to meet the global demand for fuels in the long-term. Therefore, an extended overview of the composition, properties and challenges of algae biomass for biofuel application was conducted based on reference peer-reviewed data plus own investigations. Initially, some general considerations such as current bioenergy situation and significance of biofuel generations, as well as different aspects related to biomass use as biofuels are discussed. Then, common issues concerning taxonomical classification, habitat environment, carbon reserve capacity, production, use, and main advantages and disadvantages of algae or algae biofuel are addressed. Further, more than 135 characteristics related to the chemical, phase and mineral composition and properties of algae and algae ash are evaluated and compared to those of terrestrial biomass, coal and their ashes. As a result specific benefits and obstacles connected with the composition and properties of algae and algae ash are discussed. The behaviour of organic and inorganic matter during algae combustion is also described. Finally, the major technological and environmental challenges related to algae-based fuels are emphasized. The present data demonstrate that the high contents of inorganic matter with unfavourable modes of element occurrences (chlorides, sulphates, carbonates, oxalates, nitrates and some oxyhydroxides, phosphates and amorphous material) in algae and algae ash provoke the most critical technological and environmental challenges during algae processing for biofuel application and especially during algae thermochemical conversion. Another very important challenge addressed is the indefinite availability of sustainable algae resources for production of biofuels and biochemicals and certain recommendations are given. It was found that the disadvantages of algae biofuel application prevail significantly over the advantages; however, the major economic, environmental and social benefits appear to compensate the technological and other barriers caused by the unfavourable composition and properties of algae.

The extraction, characterization, purification and upgrading of algal lipids was examined, utilizing Scenedesmus acutus microalgae grown with flue gas from a coal-fired power plant. Lipid extraction was achieved using a procedure based on the Bligh–Dyer method, modified so as to utilize a significantly decreased solvent:biomass ratio than the original protocol. Both activated carbon and K10 montmorillonite were found to function as efficient adsorbents for the removal of chlorophyll, phospholipids and sterols from the crude algae oil. The yield of purified lipids using this approach was similar to that obtained by in situ transesterification of the lipids in S. acutus, confirming that adsorption is an effective method for the removal of non-esterifiable lipids. During the deoxygenation of the purified algae oil at 260 °C over a Ni–Al layered double hydroxide catalyst, deactivation of the catalyst was observed, attributed to the presence of highly unsaturated lipid chains which can act as poisons by adsorbing strongly to the catalyst surface and/or acting as precursors to coke formation. However, upgrading at 300 °C gave better results, the liquid product consisting of ∼99 wt% hydrocarbons, diesel-like (C10–C20) hydrocarbons constituting 76 wt% of the liquid after 4 h on stream.

The aim of the present study is to analyse the transesterification of blend of high free fatty acid FFA) sunflower oil with low free fatty acid algae oil. The high FFA content of sunflower oil is reduced by blending it with low FFA algae oil so that the resultant oil will be converted into biodiesel at low temperature using single-step base-catalyzed transesterification process. The process parameters of transesterification were optimized using response surface methodology (RSM). Box–Behnken experimental design was adopted and the three process parameters considered were methanol to oil percentage (v/v) (20–60%), catalyst concentration (0–2 wt%) and reaction time (60–180 min) at constant temperature of 50 °C. The results of the present work indicate that RSM has good predictability with an optimized biodiesel yield of 95%. The optimum conditions for the reaction were found to be methanol/oil percentage of 60% (v/v), catalyst amount of 1.392% (w/w) for a reaction time of 130 min at a constant temperature of 50 °C. A significant quadratic regression model with a value of R2 of 0.99 was obtained.

Biodiesel production from algae oil at low temperature as well as a comparative study of response surface methodology (RSM) and artificial neural networks (ANN) for the modeling of yield and process parameters was carried out in this research work. Box–Behnken experimental design was adopted and the three process parameters considered were methanol to oil percentage (v/v) (20–60%), catalyst concentration (0–2 wt%) and reaction time (60–180 min) at constant temperature of 50 °C. The results of the present work indicate that ANN has good predictability as compared to RSM. A significant quadratic regression model with value of R2 of 0.99 and 0.96 was obtained in case of ANN and RSM respectively.

In this work, the use of microalgae biodiesel-diesel blend has been investigated as an alternative fuel for compression ignition engine. Tests have been performed at different loads and the acquired data have been studied for various performance and emission parameters such as brake thermal efficiency (BTE), unburnt hydro carbons (UBHC), carbon monoxide (CO), oxides of nitrogen (NOx), and smoke opacity. It can be seen that while running with algae biodiesel blend CO, UBHC and smoke opacity were decreased by 28%, 15% and 21% respectively with 38% increase in NOx emission and marginal variation in BTE. As a result of adding antioxidant into the algae biodiesel blend NOx emission was reduced by 25% and CO, UBHC and smoke emissions were increased by 32%, 50% and 36% respectively. To reduce these side effects attempt was made to test the engine at advanced and retarded injection timing. As a result of the combined effect of modified injection timing and antioxidant, a decrease in CO, UBHC and smoke opacity by an average of 20% with 30% increase in NOx emission were observed at advanced injection timing and vice versa. A trade off injection timing of 24.5, 23.5, 24 and 24 CAD was also obtained for NOx between smoke, UBHC, CO and BTE respectively for the engine NOx control with less compromise on its CO, UBHC, smoke and BTE.

Energy, having primary importance in ensuring the prosperity and development of countries, has recently become one of the most strategic parameters in the international arena. Although there is no problem with oil and gas reserves for the next few decades, the issues such as searching for new alternative energy sources, producing and delivering them to consumers will be the most critical issues in energy sector. Today, almost all countries of the world (developed and developing) put in place new energy strategies to increase the share of alternative energy sources in their total energy consumption. Biodiesel is one of the most promising alternative energy sources. Biodiesel can be produced from a lot of different feedstocks such as vegetable oils, waste frying oils and fats, soapstock, algae, etc. However, produced biodiesel’s fuel properties significantly depend on the physico-chemical properties and fatty acid composition of its feedstock. In this study, methyl ester biodiesel fuels were produced by using the same transesterification reaction conditions from ten different vegetable oils including soybean, sunflower, corn, cottonseed, canola, olive, safflower, hazelnut, rapeseed, and algae. These oils’ fatty acid distributions and some critical fuel properties of biodiesel fuels obtained from these oils were detected and compared with each other to determine the best feedstock type for biodiesel production. The highest ester content value was measured for the biodiesel fuels produced from algae (98.7%) and olive oil (98.6%). In addition, cetane numbers of these two biodiesels were the highest (59 for algae biodiesel and 58 for olive oil biodiesel). The best cold flow properties were determined for biodiesel fuels obtained from algae, corn, and canola oils with the cold filter plugging point (CFPP) values of −14 °C, −13 °C and −13 °C, respectively.

A technique to produce biodiesel from Caulerpa peltata algal oil having high free fatty acids (FFA) has been developed. The algal oil was extracted from C. peltata biomass and extracted algal oil was converted into biodiesel by two-step process under ultrasonic irradiation. The first pretreatment step was carried out to reduce acid value from 19.35 to 0.51 mg KOH/g with 2% H 2 SO 4 , 15:1 methanol-to-oil molar ratio, 30 min at 65 °C under 500 rpm. The pretreated algal oil was subjected to transesterification and achieved highest conversion of 98.11% with optimized parameters of 1% NaOH, 12:1 methanol–oil molar ratio, 600 rpm at 60 °C for 16 min. The fuel properties of biodiesel were found to be within the limits of American standards. Consequently, C. peltata appears as a renewable raw-material for biodiesel production.

Microalgae have been proposed as potentially promising feedstock for the production of renewable transportation fuels. The plants are intriguing for their capacity to serve both as a source of renewable carbon fuels and as a powerful tool for carbon sequestration. Microalgae remnant, a low-cost by-product of microalgae lipid extraction, is a particularly appealing candidate for these processes. Through catalytic pyrolysis, microalgae remnant is capable of producing aromatic hydrocarbons that could be used for the production of drop-in biofuels. One of the most challenging barriers to this promising pathway is the high moisture content of harvested microalgae. The goal of this study is to compare the economics of two catalytic pyrolysis pathways for the production of drop-in biofuels, each pathway employing its own distinct method of feedstock dewatering: thermal drying or partial mechanical dewatering. The study presents chemical process models, capital expense and operating cost estimates, and sensitivity analyses of both scenarios. Results indicate that thermal drying prior to catalytic pyrolysis (TDCP) incurs capital costs similar to those incurred in partial mechanical dewatering prior to catalytic pyrolysis (MDCP) ($346 million vs. $409 million). TDCP and MDCP yield minimum fuel-selling prices (MFSPs) of $1.80/l and $1.49/l, respectively. Energy analysis shows that TDCP achieves 16.8% energy efficiency and MDCP achieves 26.7% efficiency.

Ignition delay time measurements were made using the shock tube method for a conventional petroleum-derived military diesel fuel, F-76, and an alternative hydroprocessed renewable diesel fuel derived from hydroprocessing algal oils, HRD-76. Measurements were made in the reflected shock region using pressure and chemiluminescence and carried out for temperatures ranging from 671 to 1266 K, at nominal pressures of 10 and 20 atm, and for fuel–air equivalence ratios of 0.5 and 1.0. The measurements show that the high-temperature (>1000 K) reactivity of the two fuels is indistinguishable and very similar to that for petroleum-derived and alternative jet fuels and biodiesels. While at low temperatures (

This report includes assessments of comparative studies on the physical, chemical, and motor properties of diesel fuels containing 30% (vol.) algae oil methyl esters (AME). The properties of this biofuel were compared with the properties of fossil diesel fuel and those of diesel fuel mixtures containing 30% conventional diesel fuel – standardized rapeseed oil methyl esters (RME). Motor studies were performed on a VALMET 320 DMG diesel generator onboard a ship while using fuel blends consisting of 30% AME (B30AME) or RME (B30RME) and 70% fossil diesel fuel. The B30AME’s environmental and energy indicators were compared with indicators related to the B30RME and fossil diesel fuel (D). The experiments allowed the researchers to establish that the quality of the algae oil methyl esters and their mixing with the fossil diesel fuel complied with standard requirements. After measuring the emission of hazardous components, it was found that the main improvement to environmental indicators was related to a 10–75% reduction in the smokiness of the exhaust gas and a 5–25% reduction of hydrocarbons (HC) emissions compared to those of D. The smokiness of the exhaust gas when the engine was running at capacities close to the maximum was approximately 10% lower for B30RME compared to B30AME.

Rise in global fuel demands and approaching towards the ‘peak-oil,’ liquid fuels from non-fossil resources are being considered as promising alternatives. Yeast single cell oil is gaining significant attention as feedstock for biofuels or oleochemicals over tree-borne or algal oil. In the present work, the oil-producing capacity of an oleaginous yeast Rhodotorula mucilaginosaIIPL32 has been enhanced to 1.18-fold by overexpressing the cytosolic malic enzyme through genome integration and cultivating the yeast on sugarcane bagasse derived xylose on 15 L fermenter scale. Detailed in silico modeling and docking study of the malic enzyme of R. mucilaginosa was also carried out to understand its interaction with cofactors involved in lipogenesis. Estimation of fuel properties revealed that the lipid produced by transformed yeast complies with fourteen out of the seventeen fuel properties in the EU, Indian and US standards. We conclude with the plausible use of the engineered yeast for industrial production of oil as an alternative to plant-borne oil for biofuel production in a lignocellulosic-biomass-based biorefinery.

Algae oil is an underutilized carbon neutral oil that is considered to be a drop-in replacement for transportation fuels in the future. In this work, an acid-catalyzed esterification process which uses an acid loaded KIT-5 mesoporous material was investigated for the production of algal biodiesel. The optimum conditions for transesterification of algal oil with methanol, using mesoporous framework loaded with acid catalyst, were found to be 60 °C reaction temperature, 6 hour reaction time, 1:2 vol/vol ratio of algal oil to methanol and 1.5% catalyst (w/w). Under these optimal conditions, the use of 35% phosphotungstic acid loaded KIT-5 catalyst led to a 98% conversion of algal oil to fatty acid methyl esters. Catalyst recycling and regeneration studies were also conducted.