Review of biodiesel composition, properties, and specifications

Biodiesel is a renewable fuel that is suitable for both stationary and automotive engines. It consists of fatty acid methyl esters and fatty acid ethyl esters when vegetable oils are transesterified with methanol and ethanol respectively. The structural configuration and properties of individual fatty acid methyl esters can significantly influence the biodiesel properties. The purpose of the present work is to review the effects of the properties and the structural configurations of fatty acid methyl esters on various biodiesel properties. The structural configuration includes the molecular structure, the chain length, the saturated or unsaturated nature, the degree of unsaturation and the position of double bonds. Important properties of fatty acid methyl esters are reviewed, and a large number of data consisting of their reported values are given. The viscosity, the cetane number, the heat of combustion, the density, the bulk modulus and compressibility, the iodine value, the oxidative stability, the low-temperature properties, the boiling point, the lubricity, the saponification value, the surface tension, the specific heat, the latent heat of vaporization and the flash point are reviewed in the present study. The reported mathematical equations for estimating the properties of fatty acid compounds and biodiesel are presented. A few studies that recommend enrichment of a particular fatty acid (or acids) which is possible through genetic modification to improve the overall biodiesel properties are also cited. The contribution of a particular fatty acid (or acids) favours some properties while it has an undesirable effect on other properties. Hence the specification of one particular fatty acid profile to improve all the properties of biodiesel is not possible. Considering the low-temperature properties and the oxidative stability, a combination of both saturated fatty acids and unsaturated fatty acids is necessary. Therefore, it is important to decide whether a biodiesel should contain a larger amount of saturated fatty acid esters or unsaturated fatty acid esters in order to obtain better fuel properties. The inherent genetic modification of the fatty acid profile could be the best possibility for addressing several fuel property issues simultaneously.

A very good understanding of the structure, level, type and physical property relationships of fatty acids in plants oils and their methyl esters (FAMEs) is of utmost importance when selecting vegetable oils for a particular desired biodiesel quality that meets the operating condition requirements of the compression-ignition diesel engine and the climatic dictate of the environment under which the engine is operated. It is on this premise that the degree of influence of fatty acid configuration, chain length, branching and unsaturation on cold flow and critical properties of biodiesel was investigated. The critical properties studied include: saponification and cetane number, iodine value, higher heating values, density, flash point and kinematic viscosity. The feed stock consists of three groups of vegetable oil biomass. The group one is made up of highly saturated, lauric coconut and palm kernel oils while group two consists of high linoleic, soyabean and corn oil biomass with low percentage of mono-unsaturated and high percentage of poly-unsaturated fatty acid. High oleic olive and canola oil constituted the third group of biomass. The triglycerides in these oils were converted to methyl esters by alkali-catalyzed transesterification reaction under standard conditions. The fatty acid methyl esters (FAMEs) compositional analyses of these feed stocks was done by using Agilent, HP 6890 Gas Chromatograph equipped with Flame ionization detector and 6890 Auto Sampler that connects with a controller box (GC-FID). The various biodiesel cold flow behaviour and critical properties under investigation were evaluated by the American society for testing materials (ASTM D6751-07b) and the European union (EN 14214) standard procedures and techniques.Better cold flow behaviour was exhibited by biomass with higher degree of unsaturation, longer chain length, higher degree of branching and with cis configuration. While critical properties showed a lot of variations based on fatty acid profile.

Mixed microalgae consortia growth under higher concentration of CO2 from unfiltered coal fired flue gas: Fatty acid profiling and biodiesel production

Efficient rapid fractionation of fatty acid methyl esters (FAMEs) through evaporative urea inclusion

A comprehensive review on properties of edible and non-edible vegetable oil-based biodiesel: Composition, specifications and prediction models

The viability of algae-based biodiesel industry depends on the selection of adequate strains in regard to profitable yields and oil quality. This work aimed to bioprospecting and screening 12 microalgae strains by applying, as selective criteria, the volumetric lipid productivity and the fatty acid profiles, used for estimating the biodiesel fuel properties. Volumetric lipid productivity varied among strains from 22.61 to 204.91 mg l−1 day−1. The highest lipid yields were observed for Chlorella (204.91 mg l−1 day1) and Botryococcus strains (112.43 and 98.00 mg l−1 day−1 for Botryococcus braunii and Botryococcus terribilis, respectively). Cluster and principal components analysis analysis applied to fatty acid methyl esters (FAME) profiles discriminated three different microalgae groups according to their potential for biodiesel production. Kirchneriella lunaris, Ankistrodesmus fusiformis, Chlamydocapsa bacillus, and Ankistrodesmus falcatus showed the highest levels of polyunsaturated FAME, which incurs in the production of biodiesels with the lowest (42.47–50.52) cetane number (CN), the highest (101.33–136.97) iodine values (IV), and the lowest oxidation stability. The higher levels of saturated FAME in the oils of Chlamydomonas sp. and Scenedesmus obliquus indicated them as source of biodiesel with higher oxidation stability, higher CN (63.63–64.94), and lower IV (27.34–35.28). The third group, except for the Trebouxyophyceae strains that appeared in isolation, are composed by microalgae that generate biodiesel of intermediate values for CN, IV, and oxidation stability, related to their levels of saturated and monosaturated lipids. Thus, in this research, FAME profiling suggested that the best approach for generating a microalgae-biodiesel of top quality is by mixing the oils of distinct cell cultures.

Biodiesel or fatty acid methyl ester (FAME) can be produced by transesterification of vegetable oils with methanol in the presence of a catalyst. However, some biodiesel properties such as oxidative stability and cold flow properties depend on the degree of unsaturation in FAME chains. If vegetable oils contain higher amounts of unsaturated fatty acid, they have lower oxidative stability but good cold flow properties. Therefore, the quality of biodiesel can be improved by partial hydrogenation. This research focused on the catalytic performance of partial hydrogenation of polyunsaturated FAMEs from palm oil using palladium supported on silica (Pd/SiO2), prepared by the incipient wetness impregnation method, as a catalyst. The effects of pore size of the support and Pd loading on catalytic activity were also studied. The partial hydrogenation reaction was performed in a batch reactor. The Pd/SiO2 were characterized by Gas Chromatograph, X-ray Diffractometer, Scanning Electron Microscope with Energy Dispersive Spectrometer, Temperature Programmed Desorption / Reduction / Oxidation analyzer and Atomic Absorption Spectrometer. The catalysts with large pore size (Q50) had higher activity and produced more trans-isomers.

This study evaluated the microbial conversion of coconut oil waste, a major agro-residue in tropical countries, into single cell oil (SCO) feedstock for biodiesel production. Copra cake was used as a low-cost renewable substrate without any prior chemical or enzymatic pretreatment for submerged growth of an oleaginous tropical mangrove fungus, Aspergillus terreus IBB M1. The SCO extracted from fermented biomass was converted into fatty acid methyl esters (FAMEs) by transesterification and evaluated on the basis of fatty acid profiles and key fuel properties for biodiesel. The fungus produced a biomass (8.2 g/l) yielding 257 mg/g copra cake SCO with ~98% FAMEs. The FAMEs were mainly composed of saturated methyl esters (61.2%) of medium-chain fatty acids (C12-C18) with methyl oleate (C18:1; 16.57%) and methyl linoleate (C18:2; 19.97%) making up the unsaturated content. A higher content of both saturated FAMEs and methyl oleate along with the absence of polyunsaturated FAMEs with ≥4 double bonds is expected to impart good fuel quality. This was evident from the predicted and experimentally determined key fuel properties of FAMEs (density, kinematic viscosity, iodine value, acid number, cetane number), which were in accordance with the international (ASTM D6751, EN 14214) and national (IS 15607) biodiesel standards, suggesting their suitability as a biodiesel fuel. The low cost, renewable nature, and easy availability of copra cake, its conversion into SCO without any thermochemical pretreatment, and pelleted fungal growth facilitating easier downstream processing by simple filtration make this process cost effective and environmentally favorable.

Physical and chemical properties of biodiesel are influenced by structural features of the fatty acids, such as chain length, degree of unsaturation and branching of the carbon chain. This study investigated if microalgal fatty acid profiles are suitable for biodiesel characterization and species selection through Preference Ranking Organisation Method for Enrichment Evaluation (PROMETHEE) and Graphical Analysis for Interactive Assistance (GAIA) analysis. Fatty acid methyl ester (FAME) profiles were used to calculate the likely key chemical and physical properties of the biodiesel [cetane number (CN), iodine value (IV), cold filter plugging point, density, kinematic viscosity, higher heating value] of nine microalgal species (this study) and twelve species from the literature, selected for their suitability for cultivation in subtropical climates. An equal-parameter weighted (PROMETHEE-GAIA) ranked Nannochloropsis oculata, Extubocellulus sp. and Biddulphia sp. highest; the only species meeting the EN14214 and ASTM D6751-02 biodiesel standards, except for the double bond limit in the EN14214. Chlorella vulgaris outranked N. oculata when the twelve microalgae were included. Culture growth phase (stationary) and, to a lesser extent, nutrient provision affected CN and IV values of N. oculata due to lower eicosapentaenoic acid (EPA) contents. Application of a polyunsaturated fatty acid (PUFA) weighting to saturation led to a lower ranking of species exceeding the double bond EN14214 thresholds. In summary, CN, IV, C18:3 and double bond limits were the strongest drivers in equal biodiesel parameter-weighted PROMETHEE analysis.

Iso-fatty acids (FAs) are the dominant FA family in all myxobacteria analyzed. Furthermore, it was postulated that iso-FAs or compounds derived thereof are involved in fruiting body formation in Myxococcus xanthus, since mutants with a reduced level of iso-FA due to a reduced level of the precursor isovaleryl-CoA, are delayed in aggregation and produce only few myxospores. To elucidate the function of iso-FAs and their corresponding lipids we have analyzed the developmental phenotype of mutants having different levels of iso-FAs resulting in a clear correlation between the amount of iso-FAs and the delay of aggregation and reduction in spore yield. Addition of either isovalerate or 13-methyltetradecanoic acid resulted in restoration of the wild-type FA profile and normal development. Detailed analysis of the fatty acid (FA) profile during fruiting body formation in Myxococcus xanthus wild-type revealed the specific accumulation of 13-methyltetradecanal and 1-O-13-methyltetradecylglycerol which were produced specifically in the myxospores and which are derived from 1-O-(13-methyl-1-Z-tetradecenyl)-2-O-(13-methyltetradecanoyl)-glycero-3-phosphatidylethanolamine (VEPE) and 1,2-di-(13-methyltetradecanoyl)-3-(13-methyltetradecyl)glycerol (TG-1), respectively. The structures of these unusual ether lipids have been determined by spectrometric methods and synthesis (for TG-1). Analysis of several mutants blocked at different stages of development indicated that the biosynthesis of TG-1 is developmentally regulated and that VEPE might be an intermediate in the TG-1 biosynthesis. Finally, addition of TG-1 to mutants blocked in the biosynthesis of isovaleryl-CoA could restore aggregation and sporulation emphasizing the important role of iso-branched lipids for myxobacterial development.

Enhancement of lipid production and fatty acid profiling in Chlamydomonas reinhardtii, CC1010 for biodiesel production

Organic sources of biodiesel such as microalgae are considered as potential renewable energy resources. These organisms are considered as sunlight-driven cellular factories that convert carbon dioxide to high amounts of lipids that can be used for biofuel production. This paper describes the possibility of using Desmodesmus sp. (I-AU1) for biodiesel production by evaluating its fatty acid profile distribution pattern and estimating the fuel-derived physical and chemical properties from fatty acid methyl esters (FAMEs) obtained from the trans-esterified microalgal oil. Growth rate, oil content, biomass, and lipid productivity of the algal strain have been investigated under nitrogen-starved (0.375 g L−1 NaNO3 in BG 11 medium) autotrophic condition for 22 days. Maximum average biomass yield of Desmodesmus sp. (I-AU1) is 0.745 g L−1 having 36.14% lipid content per dry weight of biomass, with a specific growth rate of 0.20 day−1. Fatty acid profiling of the biodiesel obtained from Desmodesmus sp. (I-AU1) contained total saturated fatty acid (SAFA) methyl esters of 31.02%, while the total monounsaturated fatty acid (MUFA) (C18:1) is 25.64%. Percentage composition of SAFA and MUFA for the microalga was 56.66%, which is high compared to that of most of related studies. Fuel properties were determined by empirical equations and were found to be within the limits of biodiesel standards ASTM D6751 (American) and EN 14214 (European). The quality properties of the biodiesel were low density (0.88 g cm−3), low kinematic viscosity (2.81 mm2 s−1), cetane number (43.47), oxidation stability (5.96 h), and cold filter plugging point (−7.41 °C). Hence, Desmodesmus sp. (I-AU1) has potential as a feedstock for the production of quality biodiesel.

The growth kinetics and the lipid and protein content of the microalgal species Chlorella sorokiniana (CS) grown heterotrophically in growth media containing glycerol and increasing amounts of anaerobic digestate (AD) equal to 0%, 15%, 30%, and 50% was studied. The effect of the AD on the fatty acid (FA) distribution of the bio-oil extracted from the CS, as well as on the fatty acid methyl ester (FAME) properties such as the saponification number (SN), the iodine value (IV), the cetane number (CN), and the higher heating value (HHV) was also estimated. The percentage of AD in the growth medium affects the rate of carbon uptake. The maximum carbon uptake rate occurs at about 30% AD. Protein and lipid content ranged from 32.3–38.4% and 18.1–23.1%, respectively. Fatty acid distribution ranged from C10 to C26. In all AD percentages the predominant fatty acids were the medium chain FA C16 to C18 constituting up to about 89% of the total FA at 0% AD and 15% AD and up to about 54% of the total FA at 30% AD and 50% AD. With respect to unsaturation, monounsaturated FA (MUFA) were predominant, up to 56%, while significant percentages, up to about 38%, of saturated FA (SFA) were also produced. The SN, IV, CN, and HHV ranged from 198.5–208.3 mg KOH/g FA, 74.5–93.1 g I/100 g FAME, 52.7–56.1, and 39.7–40.0 MJ/kg, respectively. The results showed that with increasing AD percentage, the CN values tend to increase, while decrease in IV leads to biofuel with better ignition quality.

Optimization of cotton seed biodiesel quality (critical properties) through modification of its FAME composition by highly selective homogeneous hydrogenation

Phenotypic variation of important seed traits like seed length, seed breadth, seed thickness, 100 seed weight and seed oil content were recorded in a total of 157 collected accessions of Pongamia. Out of these, fatty acid profiles of 38 accessions selected based on their high and low oil content was analyzed. Fatty acid profile revealed high variability in stearic, oleic and linoleic acid which varied from 0.42 to 10.61%, 34.34 to 74.58%, and 7.00 to 31.28% respectively. Variations in palmitic and linolenic acid were small. Iodine value, saponification number and cetane number (CN) of fatty acid methyl esters (FAME) of seed oil ranges from 186.99 to 201.25, 81.13 to 108.19 and 46.16 to 56.47 respectively. Fatty acid compositions, degree of unsaturation and CN are the important parameters, which are used to determine quality of FAME were used as biodiesel. Some of the Pongamia accessions identified were higher in oil content while some accessions showed higher degree of unsaturation and a few of them had CN values higher than 55. Genetic diversity analysis with six TE-AFLP primers generated a total of 334 bands out of which 174 (52.10%) were polymorphic. The genetic similarity ranged from 0.11 to 0.47. These findings clearly showed high level of genetic diversity and all economically desirable traits were not present in a single genotype of Pongamia. All these traits could be selected from these CPTs and transfer to a single elite variety through selection and breeding programme and could be utilized for large scale multiplication and plantation to produce high quantity and quality biodiesel in future.