Assessment and comparison of the properties of biodiesel synthesized from three different types of wet microalgal biomass

Abstract

In recent years, microalgae-based carbon-neutral biofuels (i.e., biodiesel) have gained considerable interest due to high growth rate and higher lipid productivity of microalgae during the whole year, delivering continuous bio-mass production as compared to vegetable-based feedstocks. Therefore, biodiesel was synthesized from three different microalgal species, namely Tetraselmis sp. (Chlorophyta) and Nannochloropsis oculata and Phaeodactylum tricornutum (Heterokontophyta), and the fuel properties of the biodiesel were analytically determined, unlike most studies which rely on estimates based on the lipid profile of the microalgae. These include density, kinematic viscosity, total and free glycerol, and high heating value (HHV), while cetane number (CN) and cold filter plugging point (CFPP) were estimated based on the fatty acid methyl ester profile of the biodiesel samples instead of the lipid profile of the microalgae. Most biodiesel properties abide by the ASTM D6751 and the EN 14214 specifications, although none of the biodiesel samples met the minimum CN or the maximum content of poly-unsaturated fatty acids with ≥4 double bonds as required by the EN 14214 reference value. On the other hand, bomb calorimetric experiments revealed that the heat of 2 combustion of all samples was on the upper limit expected for biodiesel fuels, actually being close to that of petrodiesel. Post-production processing may overcome the aforementioned limitations, enabling the production of biodiesel with high HHV obtained from lipids present in these microalgae.

Isolation of a euryhaline microalgal strain, Tetraselmis sp. CTP4, as a robust feedstock for biodiesel production

“…Such oxidative stability is probably related with the FAME profile of CTP4 and consequently of the produced biodiesel that revealed only trace values of long-chain PUFA, and high contents of palmitic, oleic and linoleic acids, accounting for nearly 75% of the TFA. The FAME profile of the biodiesel produced from CTP4 presents a lower degree of unsaturation than those of other Tetraselmis strains previously published in the literature 10 31 43 44 . The same is observed when the lipid profile of CTP4 is compared with that of most common commercial strains of microalgae, such as Nannochloropsis oculata and Phaeodactylum tricornutum 10 .…”

“…The FAME profile of the biodiesel produced from CTP4 presents a lower degree of unsaturation than those of other Tetraselmis strains previously published in the literature 10 31 43 44 . The same is observed when the lipid profile of CTP4 is compared with that of most common commercial strains of microalgae, such as Nannochloropsis oculata and Phaeodactylum tricornutum 10 . The low unsaturation degree of Tetraselmis sp.…”

“…Most microalgae strains fail to address the properties related with the saturation of the lipid profile, namely, the content of linolenic acid, PUFA ≥4 db, IV, CN, and most importantly, the oxidation stability 8 10 36 . In fact, the oxidative stability of the produced biodiesel (4.74 h) is to the authors’ knowledge the highest value reported for B100 microalgae-based biodiesel, except for that of Scenedesmus sp.…”

“…Since unsaturated lipids are essential metabolites for the proper development of fish larvae and bivalve growth 7 , microalgal strains with high contents of polyunsaturated fatty acids (PUFA) have been selected and commercialized. However, microalgal feedstocks with high amounts of PUFA are not suitable for biodiesel production, because the large number of double bonds present in these fatty acids decrease the oxidation stability of the end product 8 9 10 . In fact, both European (EN14214) and American (ASTM D6751) specifications impose strict limits concerning the presence of PUFA in biodiesel.…”

“…In fact, both European (EN14214) and American (ASTM D6751) specifications impose strict limits concerning the presence of PUFA in biodiesel. Therefore, screening for strains containing high lipid content with low levels of unsaturated fatty acids is crucial to enhance the productivity and quality of the feedstock used for biodiesel production 10 11 12 and decreases the costs of biodiesel refining 11 .…”