Fatty acid methyl ester production from wet microalgal biomass by lipase-catalyzed direct transesterification

The aim of this work was to optimize the production of fatty acid methyl ester (FAME, biodiesel) from wet Nannchloropsis gaditana microalgal biomass by direct enzymatic transesterification. This was done in order to avoid the high cost associated with the prior steps of drying and oil extraction. Saponifiable lipids (SLs) from microalgal biomass were transformed to FAME using the lipase Novozyme 435 (N435) from Candida antarctica as the catalyst, and finally the FAME were extracted with hexane. t-Butanol was used as the reaction medium so as to decrease lipase deactivation and increase mass transfer velocity. A FAME conversion of 99.5% was achieved using wet microalgal biomass homogenized at 140 MPa to enhance cell disruption, a N435:oil mass ratio of 0.32, methanol added in 3 stages to achieve a total of 4.6 cm³ g⁻¹ of oil and 7.1 cm³ g⁻¹ oil of added t-butanol, with a reaction time of 56 h. The FAME conversion decreased to 57% after catalyzing three reactions with the same lipase batch. This work shows the influence of the polar lipids contained in the microalgal biomass both on the reaction velocity and on lipase activity.     

Biodiesel production by ultrasound-assisted transesterification: State of the art and the perspectives

In the present paper state-of-the art and perspectives of ultrasound-assisted (UA) biodiesel production from different oil-bearing materials using acid, base and enzyme catalysts are critically discussed. The ultrasound action in biodiesel production is primarily based on the emulsification of the immiscible liquid reactants by microturbulence generated by radial motion of cavitation bubbles and the physical changes on the surface texture of the solid catalysts generating new active surface area. The importance of ultrasound characteristics and other process variables for the biodiesel yield and the reaction rate is focused on. UA transesterification is compared with other techniques for biodiesel production. Several different developing methods reducing the biodiesel production costs such as the optimization of process factors, the development of the process kinetic models, the use of phase transfer catalysts, the application of the continuous process, the design of novel types of ultrasonic reactors and the in situ ultrasound application in transesterification of oily feedstocks are also discussed.     

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.     

Biodiesel from corn germ oil catalytic and non-catalytic supercritical methanol transesterification

Transesterifications of grain of corn oil samples in KOH catalytic and in supercritical methanol were studied without using any catalyst. Biodiesel, an alternative biodegradable diesel fuel, is derived from triglycerides by transesterification with methanol and ethanol. The transesterification reaction is affected by the molar ratio of glycerides to alcohol, catalysts, reaction temperature, reaction time and free fatty acids and water content of oils or fats. It was observed that increasing the reaction temperature, especially to supercritical temperatures, had a favorable influence on methyl ester (biodiesel) conversion. The molar ratio of methanol to corn germ oil is also one of the most important variables affecting the yield of methyl esters. Higher molar ratios result in greater ester production in a shorter time. In the transesterification, free fatty acids and water always produce negative effects, since the presence of free fatty acids and water causes soap formation, consumes catalysts, and reduces catalyst effectiveness, all of which result in a low conversion.     

Biodiesel production from Calophyllum inophyllum oil using lipase producing Rhizopus oryzae cells immobilized within reticulated foams

Biodiesel production from non-edible Calophyllum inophyllum linn oil with high levels of Free Fatty Acid (FFA) (acid value −6.732 mg KOH/g of oil) was investigated using whole-cell biocatalysts. Rhizopus oryzae cells immobilized within reticulated polyurethane foams were used as biocatalysts for biodiesel production. The effects of reaction parameters such as methanol-to-oil molar ratio, water content, and temperature for the production of biodiesel through methanolysis in a packed-bed reactor (PBR) were studied. Molar ratio of methanol-to-oil – 12:1, water content – 15%v/v, cell concentration – 20% and temperature 35 °C were found to be the optimum. The yield of biodiesel obtained in batch methanolysis from C. inophyllum oil under optimized condition was 92%. Long-term stability of immobilized cells for methanolysis was verified using re-usability studies.     

Biodiesel production from Cedrus deodara oil in different types of ultrasonic reactors and energy analysis

This paper deals with the production of biodiesel using vegetable oil, extracted from Deodar (Cedrus deodara) in various types of ultrasonic reactors. The biodiesel so produced is tested for its property and stability. Biodiesel yield is optimized as a function of reaction time for various ultrasonic reactors. The biodiesel production through the triple-frequency flow cell ultrasonic reactor is found the most energy efficient when compared to other types of ultrasonic reactors. Biodiesel so produced from deodar oil is stable under atmospheric conditions with its various physicochemical properties within the range of acceptable limits of the diesel engine.     

Biodiesel production from vegetable oils via catalytic and non-catalytic supercritical methanol transesterification methods

This paper reviews the production and characterization of biodiesel (BD or B) as well as the experimental work carried out by many researchers in this field. BD fuel is a renewable substitute fuel for petroleum diesel or petrodiesel (PD) fuel made from vegetable or animal fats. BD fuel can be used in any mixture with PD fuel as it has very similar characteristics but it has lower exhaust emissions. BD fuel has better properties than that of PD fuel such as renewable, biodegradable, non-toxic, and essentially free of sulfur and aromatics. There are more than 350 oil bearing crops identified, among which only sunflower, safflower, soybean, cottonseed, rapeseed and peanut oils are considered as potential alternative fuels for diesel engines. The major problem associated with the use of pure vegetable oils as fuels, for Diesel engines are caused by high fuel viscosity in compression ignition. Dilution, micro-emulsification, pyrolysis and transesterification are the four techniques applied to solve the problems encountered with the high fuel viscosity. Dilution of oils with solvents and microemulsions of vegetable oils lowers the viscosity, some engine performance problems still exist. The viscosity values of vegetable oils vary between 27.2 and 53.6 mm²/s whereas those of vegetable oil methyl esters between 3.59 and 4.63 mm²/s. The viscosity values of vegetable oil methyl esters highly decreases after transesterification process. Compared to no. 2 diesel fuel, all of the vegetable oil methyl esters were slightly viscous. The flash point values of vegetable oil methyl esters are highly lower than those of vegetable oils. An increase in density from 860 to 885 kg/m³ for vegetable oil methyl esters or biodiesels increases the viscosity from 3.59 to 4.63 mm²/s and the increases are highly regular. The purpose of the transesterification process is to lower the viscosity of the oil. The transesterfication of triglycerides by methanol, ethanol, propanol and butanol, has proved to be the most promising process. Methanol is the commonly used alcohol in this process, due in part to its low cost. Methyl esters of vegetable oils have several outstanding advantages among other new-renewable and clean engine fuel alternatives. The most important variables affecting the methyl ester yield during the transesterification reaction are molar ratio of alcohol to vegetable oil and reaction temperature. Biodiesel has become more attractive recently because of its environmental benefits. Biodiesel is an environmentally friendly fuel that can be used in any diesel engine without modification.     

Biodiesel fuels from palm oil via the non-catalytic transesterification in a bubble column reactor at atmospheric pressure: A kinetic study

Biodiesel has become more attractive recently because of its environmental benefits and the fact that it is made from renewable resources. Transesterification of vegetable oils with short-chain alcohol has long been a preferred method for producing biodiesel fuel. A new reactor was developed to produce fatty acid methyl esters (FAME) by blowing bubbles of superheated methanol vapor continuously into vegetable oil without using any catalysts. A kinetic study on the non-catalytic transesterification of palm oil was made in a reactor without stirring at atmospheric pressure. The effects of reaction temperatures (523, 543, and 563 K) on the rate constant, conversion, yield of methyl esters (ME) and composition of the reaction product under semi-batch mode operation are investigated. The activation energy and the frequency factor values of the transesterification reaction obtained in this experiment are 31 kJ/mol and 4.2, respectively. The optimum reaction temperature which gives the highest ME content (95.17% w/w) in the reaction product is 523 K, while the rate constant of the total system increased with reaction temperature.     

Lipase-catalysed transesterification: Viewpoint of the mechanism and influence of free fatty acids

A series of lipase-catalysed transesterification experiments were carried out to study the effect of the presence of free fatty acids on synthesis reaction rate and the stability of the biocatalyst, and also to elucidate the underlying process, which remains a subject of debate. Based on the results, the reaction rate and biocatalyst stability increased with increasing content in free fatty acids of the reaction mixture. Also, tests carried out with a mixture of triolein and linoleic acid revealed that the transesterification is a combination of direct alcoholysis of triacylglycerols and a two-step reaction involving hydrolysis of acylglycerols and further esterification of previously released free fatty acids. The time course of triacylglycerols and diacylglycerols revealed that the enzyme is similarly selective for both types of substrate.     

Biocatalytic production of biodiesel from cottonseed oil: Standardization of process parameters and comparison of fuel characteristics

The enzymatic production of biodiesel by transesterification of cottonseed oil was studied using low cost crude pancreatic lipase as catalyst in a batch system. The effects of the critical process parameters including water percentage, methanol:oil ratio, enzyme concentration, buffer pH and reaction temperature were determined. Maximum conversion of 75–80% was achieved after 4 h at 37 °C, pH 7.0 and with 1:15 M ratio of oil to methanol, 0.5% (wt of oil) enzyme and water concentration of 5% (wt of oil). Various organic solvents were tested among which a partially polar solvent (t-butanol) was found to be suitable for the reaction. The major fuel characteristics like specific gravity, kinematic viscosity, flash point and calorific value of the 20:80 blends (B20) of the fatty acid methyl esters with petroleum diesel conformed very closely to those of American Society for Testing Materials (ASTM) standards.     

Application of D-optimal design and RSM to optimize the transesterification of waste cooking oil using natural and chemical heterogeneous catalyst

This work illustrates a comparative study on the applicability of the natural calcium oxide (CaO) prepared from waste eggshells and chemical CaO as basic heterogeneous catalyst in the transesterification of waste cooking oil (WCO) with methanol for production of biodiesel. Response surface methodology (RSM) based on D-optimal design of experiments was employed to study the significance and interactive effect of methanol-to-oil (M:O) molar ratio, catalyst concentration, reaction time, and mixing rate on biodiesel yield. Second-order quadratic model equations were obtained describing the interrelationships between dependent and independent variables to maximize the response variable (biodiesel yield) and the validity of the predicted models were confirmed. The activity of the produced natural biocatalyst was comparable to that of chemical CaO, producing high yield of biodiesel ≈91 and 98% at 8.57:1 M:O, 3.99 catalyst wt%, 31 min reaction time, and 398.88 rpm mixing rate at 60°C, respectively. Fuel properties of the produced biodiesel were measured and compared with those of Egyptian petro-diesel and international biodiesel standards. The overall biodiesel characteristics either prepared using natural or chemical CaO were comparable and acceptable, encouraging the application of CaO prepared from waste eggshells for production of biodiesel as an efficient, environmentally friendly, sustainable, and low cost heterogeneous catalyst.     

Biodiesel production from Nerium oleander (Thevetia peruviana) oil through conventional and ultrasonic irradiation methods

In the present research work, Nerium oleander oil has been used as raw material for producing biodiesel using both ultrasonic transesterification and a magnetic stirrer method. A two-step transesterification process was carried out for optimum condition of 0.40% V/V methanol to oil ratio, 1% V/V H₂SO₄ catalyst, 55°C temperature, and 60 min reaction time followed by treatment with 0.2% V/V methanol to oil ratio, 1% V/W KOH alkaline catalyst, 55°C temperature, and 60 min reaction time. The process is repeated with an ultrasonic method at the frequency of 28 kHz using ultrasonic horn type reactor (50 W) for about 10–15 min. Biodiesel obtained from ultrasonic method and magnetic stirrer was then compared for their percentage yield and physiochemical properties. Ultrasonic transesterification process gave a maximum yield of 97% by weight of oleander biodiesel along with improved physiochemical characteristics. Therefore, it is concluded that ultrasonic method is the most effective method for converting crude oleander oil into biodiesel.     

Improved transesterification of waste cooking oil into biodiesel using calcined goat bone as a catalyst

In this study, potassium hydroxide-treated animal bones were employed? as a solid heterogeneous catalyst in transesterification of waste cooking oil. This catalyst was characterized by the Fourier-transform infrared spectroscopy (FTIR), and it displayed high-catalytic activity for biodiesel production. Optimum conditions for biodiesel production were catalyst loading 6.0% (w/w) of oil, methanol/oil molar ratio 9:1, calcination temperature 800°C, reaction temperature 65°C, and reaction time of 5 h, which gave maximum biodiesel yield of 84%. Reusability of the catalyst was also confirmed by repeated use of the same catalyst three times without losing much of its activity. Hence, calcined goat bones were found to be a potentially applicable catalyst for biodiesel production at industrial scale.     

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.     

Effect of reaction parameters on the catalytic transesterification of cottonseed oil using silica sulfuric acid

Transesterification of refined cottonseed oil was studied in the presence of silica sulfuric acid as a new heterogeneous solid acid catalyst to overcome the drawbacks of homogeneous alkali and acid catalysts. The effect of various reaction parameters, such as oil to methanol ratio, reaction temperature, reaction time, and catalyst amount, was investigated. The highest methyl ester conversion was obtained at 373 K using 5% catalyst amount and 1:20 methanol ratio within 8 h. Silica sulfuric acid was found to be a promising catalyst for cleaner biodiesel production without tedious post treatments for the product purification.     

Biodiesel production using gel‐type cation exchange resin at different ionic forms

In this study, a strong acidic‐type cation exchange resin was used in the transesterification of corn oil to fatty acid methyl esters (FAME). The gel‐type cation exchange resin (Purolite‐PD206) was used in H⁺ and Na⁺ forms to utilize ion‐exchange resin as effective heterogeneous catalyst in the production of biodiesel. Effect of ionic forms of ion exchange resin on free fatty acid (FFA) conversion and composition was investigated by using different amounts of ion exchange resin (12, 16, and 20 wt%), various mole ratios of methanol to oil (1:6, 1:12, and 1:18 mol/mol), reaction temperatures (63, 65, and 67°C), and reaction time (24, 36, and 48 h) during transesterification reaction. The highest FFA conversions of 73.5% and 79.45% were obtained at conditions of 20 wt% of catalyst, 65°C of reaction temperature, 18:1 as methanol to oil ratio, and 48 h of reaction time for H⁺ and Na⁺ forms of ion exchange resin, respectively. These results were obtained from regression equations established by using analysis of variance (ANOVA) model according to the experimental results of selected parameters. Gas chromatography analysis revealed that FAME is mainly composed of C16:0 (palmitic), C18:1 (oleic), and C18:2 (linoleic) acids of methyl ester.     

Biodiesel purification using micro and ultrafiltration membranes

Biodiesel is an environmental-friendly fuel that can replace petroleum diesel. However, after transesterification reaction of vegetable oils, the obtained crude biodiesel must be purified. The commonly applied purification step is water washing. This step is a concern in biodiesel production, since large quantities of clean water are used, generating a wastewater stream to be further treated. Here we propose the application of micro and ultrafiltration processes to purify crude biodiesel. Crude biodiesel was filtrated in a dead-end process at different transmembrane pressures and using membranes of different pore sizes. Flux results showed that greater transmembrane pressures, as well as greater pore sizes, enable greater fluxes. Density, viscosity and acid values of purified biodiesel (washed and filtrated) are in accordance to the international legislation for biodiesel quality. Both processes (water washing and membrane separation) were able to reduce the amount of soap detected in crude biodiesel. However, the proposed microfiltration membranes were not efficient as the washing method to reduce the free glycerol content. The ultrafiltration membrane of 30 kDa was also not able to produce a purified biodiesel according to the international legislation for free glycerol content. Between the analyzed membranes, the glycerol content limit (less than 0.02 wt%) was achieved only with the ultrafiltration membrane of 10 kDa. Water addition in the crude biodiesel improved the glycerol removal by membrane filtration. The obtained results showed that the membrane separation process is a suitable alternative for biodiesel purification.     

Optimization of biodiesel produced from watermelon (Citrullus vulgaris) using batch-type production unit

In the present work the production of a biodiesel from watermelon seed oil (Citrullus vulgaris) by methanol-induced transesterification using an alkaline catalyst (potassium hydroxide, KOH) has been examined. The influence of the operating variables such as agitation speed, temperature, reaction time, alcohol amount, and catalyst concentration was determined experimentally and found to be 550 rpm agitation rate, 60°C reaction temperature, 55 min reaction time, 20% of methanol, and 13 g of catalysts concentration for 2.5 liters of oil. The yield of biodiesel from the watermelon methyl ester (WME) under optimized conditions is found to be 91%. The properties of biodiesel are measured as per ASTM standards and compared with the base diesel.     

Biodiesel production from degummed Jatropha curcas oil using constant-temperature ultrasonic water bath

This paper studied tri-basic potassium phosphate for transesterification process with degummed crude Jatropha curcas oil using constant-temperature, ultrasonic water bath generating low-intensity pulses with good energy distribution converting the maximum amount of biodiesel. Tri-basic potassium phosphate is suitable for J. curcas oil when the free fatty acid (FFA) content is less than 2%. The optimal reaction levels are catalyst 1.0 wt%, temperature of 50°C, and methanol-to-oil molar ratio of 12:1. The yield is 98% after 45 min, at 20 kHz frequency. The catalytic activity is found similar to potassium hydroxide and the catalyst solubility is only 4.27 ppm.     

Biodiesel production from mixed soybean oil and rapeseed oil

The biodiesel (fatty acid methyl esters, FAME) was prepared by transesterification of the mixed oil (soybean oil and rapeseed oil) with sodium hydroxide (NaOH) as catalyst. The effects of mole ratio of methanol to oil, reaction temperature, catalyst amount and reaction time on the yield were studied. In order to decrease the operational temperature, a co-solvent (hexane) was added into the reactants and the conversion efficiency of the reaction was improved. The optimal reaction conditions were obtained by this experiment: methanol/oil mole ratio 5.0:1, reaction temperature 55 °C, catalyst amount 0.8 wt.% and reaction time 2.0 h. Under the optimum conditions, a 94% yield of methyl esters was reached ∼94%. The structure of the biodiesel was characterized by FT-IR spectroscopy. The sulfur content of biodiesel was determined by Inductively Coupled Plasma emission spectrometer (ICP), and the satisfied result was obtained. The properties of obtained biodiesel from mixed oil are close to commercial diesel fuel and is rated as a realistic fuel as an alternative to diesel. Production of biodiesel has positive impact on the utilization of agricultural and forestry products.