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The production and use of terpene-based fuels represents a renewable source of energy in the transportation sector, especially in the aviation sector. The literature on the conversion of terpenes into valuable compounds is not new but has been based on the production of products for cosmetics and pharmaceutics. Several established chemical routes are also a way to develop drop-in fuels. The present work explores all the main chemical processes that can transform terpenes into more valuable fuels or additives, focusing on the use of heterogeneous catalysis, catalyst type, operating conditions, and reaction performance. α-pinene is the most studied catalyst, since it is the main component of turpentine. Isomerization is the most frequently applied chemical pathway used to enhance fuel properties, and a wide group of heterogeneous catalysts have been reported, with sulphonic acid resin catalysts, transition metals, alumina, and silicates being the most used. This work also explores the current production and commercialization of terpenes, as well as the challenges for their use as fuels at a commercial scale. The future challenge is to discover new catalysts or to improve the performance of the current products and reduce production costs. The feasibility of the production and commercialization of terpene-derived fuels is also linked to oil prices. [ABSTRACT FROM AUTHOR]

The use of algal biomass as a renewable source of energy is potentially promising. The literature on biofuels derived from Sargassum is limited compared to other macroalgae. The unusual seaweed bloom of Sargassum from 2011 to date can be caused by the following factors: eutrophication of the sea, climate change, and other oceanographic patterns. The atypical invasion has had great ecological and economic effects in the affected regions. Traditionally, Sargassum has been recovered from coasts and beaches for use as fertilizer, but new markets need to be found to exploit the large volumes produced by the seaweed influx and mitigate its impact. The biochemical composition of Sargassum biomass defines it as a potential feedstock for biofuel production. However, the high moisture and ash content constitute the limitations for the development of some energy extraction methods. On the other hand, the costs associated with the removal of high volumes of accumulated Sargassum from coasts and beaches, transportation, cleaning, and storage are relatively high. Therefore, the production of biofuels from Sargassum seaweed is still a technical, economic, and energy challenge. This review proposes a multifactorial approach to the potential use of Sargassum biomass as feedstock for energy production, especially by thermochemical conversion (combustion, gasification, pyrolysis, and hydrothermal liquefaction). The survey analyses the chemical composition, biomass productivity and coastal impact, energy output, thermochemical conversion processes, techno-economic challenges, and future perspectives. In addition, a Sargassum biomass biorefinery approach with a circular bioeconomy approach is proposed. [ABSTRACT FROM AUTHOR]

Highlights • Fatty acid glycerol formal ester produced from waste glycerol was used in diesel blends. • Reactions are proposed to co-produce acetals as cold-flow depressors. • Glycerol formal methoxy-methyl glycerol formal were tested at different concentrations. • Optimal acetal content and composition are proposed as a compromise of properties. Abstract One of the barriers for the extended use of fatty acid methyl esters (FAME) as a diesel fuel component is the yield of raw glycerol as a by-product of the transesterification process. In fact, glycerol is considered as one of the most abundant waste feedstock in the world. A new fuel denoted as FAGE (Fatty Acid Glycerol formal Esters) produced from glycerol and waste oil has been developed. FAME is concomitantly obtained during the manufacturing process of FAGE in different proportions depending of the reaction conditions. Since FAGE cold flow properties are in disadvantage when compared to FAME, the influence of some cold-flow improvers in FAGE/FAME blends has been investigated. In this work, the use of some acetals, co-products of the FAGE production process, are proposed as cold-flow improvers, giving extra value to this new fuel since all the co-products obtained from the production process would have a new industrial use. These two acetals are GF (Glycerol Formal) and GFOMOM (Methoxy-methyl glycerol formal). The results obtained show that cold flow properties become poorer when the amount of FAGE increases in the FAGE/FAME blend, but such effect is very slight up to 50% FAGE. The use of the acetals improves cold flow properties of the blends up to 2 °C, with minor effect of the GF content in the GF/GFOMOM acetal blend. In addition, a commercial cold flow improver was tested, improving the pour point and the cold filter plugging point with only small effect on cloud point and crystallization temperature. The results obtained from the acetals and the cold flow improver are compared, and the value of the acetals as cold flow improvers has been proved. A combination of both, acetals and cold-flow improver, is proposed as an optimal method to improve cold flow properties. [ABSTRACT FROM AUTHOR]

The excessive blooming of green filamentous macroalgae is a global problem due to their unwanted presence in freshwater, lakes, nursery garden and stagnant waters. An attractive solution is to use macroalgae as a biofuel feedstock. In this work, the macroalgae studied was the Chaetomorpha cf. gracilis. The macroalgae oil extraction was accomplished using Soxhlet method obtaining a yield of 1.85%. The gas chromatography analysis showed higher unsaturated fatty acids (56.14%) compared to saturated fatty acids (35.18%), highlighting the content of oleic acid, 27.89%. The kinematic viscosity and density were 0.826 mm2/s and 699.6 kg/m3, respectively. The heating value, crystallization temperature and elemental composition showed higher values than other algae oils. Nevertheless, the nitrogen content was similar to L.digitata macroalgae. The analysis conducted on the net energy ratio for the oil extraction process showed that the Chaetomorpha macroalgae oil might represent an attractive alternative for liquid biofuel production. [ABSTRACT FROM AUTHOR]

This work aims to study the properties of fatty acid methyl and ethyl esters from Tunisian oils in order to assess their potential use as biofuel sources. The oils chosen for this study have been scarcely researched by other authors and are very interesting for a possible exploitation as fuels. Most of them are nonedible sources and all of them can be grown in arid places with no need of supplementary water: the bishop’s weedAmmi visnaga, the bitter appleCitrullus colocynthis, the stramoniumDatura stramonium, the devil pickleEcballium elaterium, and the milk thistleSilybum marianum. [ABSTRACT FROM PUBLISHER]

Current trends in diesel transport anticipate that in the upcoming future a range of renewable fuels will be necessary to comply with emission and sustainability legislations. Exhaust after-treatment devices such as diesel particulate filters –DPFs– will have to operate satisfactorily with this pool of biofuels. In particular, DPF regeneration is crucial to cut the fuel penalty and guarantee an acceptable lifetime for this device. In the present work, an automotive diesel engine was run with fossil fuel and three renewable fuels: a conventional biodiesel, a fuel manufactured through Fischer-Tropsch –FT– process and a HVO biofuel. The DPF was loaded and regenerated through an active process with fuel post-injections. Additionally, soot samples were investigated with thermo-gravimetry (TGA) and calorimetry (DSC) to confirm whether these techniques obtain relevant information for explaining DPF behavior. Both methods proved that biodiesel leads to a more economical regeneration being the biodiesel soot, more reactive than the other samples, the main reason. DPF regenerations with paraffinic fuels (FT-derived and HVO) did not reveal strong differences compared to diesel, though TGA and DSC results suggested that soot from paraffinic biofuels is more reactive than that from diesel. The exhaust gas temperature and composition are behind this apparent discrepancy. [ABSTRACT FROM AUTHOR]

A new advanced biofuel –FAGE (fatty acid formal glycerol ester)– produced from crude glycerol has been blended with diesel fuel (20% FAGE content) and tested in an automotive engine following the New European Driving Cycle. Since cold flow properties, volatility and viscosity are the critical properties of this biofuel, the driving cycles were performed from both warm and cold starts. The FAGE blend showed significant benefits in hydrocarbon, carbon monoxide and particle emissions, particle number and opacity when the cycle was started from warm conditions. Such benefits were even more important during the extra-urban period, where also small engine efficiency benefits were found. Differently, the mentioned emissions increased substantially with respect to those of diesel during the first urban sub-cycle at cold start. Among the emitted hydrocarbons, the non-oxygenated ones were more sensible to the engine temperature. Also, the nucleation mode in the particle size distributions increased at cold conditions. NOx emissions were slightly increased with the FAGE blend during the extra-urban sub-cycle, and differences in the NO 2 /NO ratio were found during the initial urban sub-cycle from cold start. The results have been explained based mainly on the injection timings, the fuel–air ratio, the oxidation catalyst performance and the fuel properties. [ABSTRACT FROM AUTHOR]

Abstract: Sooting tendencies have been measured for 29 compounds with 5 carbon atoms and different oxygen contents, along with 12 additional oxygenated pure compounds and 10 blends of commercial fuels. The test compounds include alcohols, ethers, aldehydes, ketones, acids, esters, keto-esters and hydroxy-esters. The Threshold Sooting Index (TSI), as defined and used in the literature, was primarily used to quantify the sooting tendency of the compounds. It is shown that this index does not account for the presence of oxygen atoms in the fuel molecules, and the impact of fuel oxygen on the stoichiometric air requirement. The application of TSI to oxygenated fuels leads to sooting tendencies inconsistent with those reported in the literature. A new sooting index is proposed for oxygenated and non-oxygenated compounds, which considers the relation between the height of the flame tip and the volumetric stoichiometric air requirement of the flame. This new index is denoted as the Oxygen Extended Sooting Index (OESI). The results obtained by this new index corroborate that not only the oxygen content but also the molecular structure has an influence on the sooting tendency of fuels. Different functional groups, not only those including oxygen atoms, impart different sooting tendencies. A structural group contribution approach based on group additivity is proposed to interpret experimental observations on the effect of oxygen functional groups on the sooting tendency of fuels using the example of C-5 oxygenated fuels. Groups with a higher fraction of carbon–carbon bonds showed a higher contribution to the sooting tendency than those with a higher concentration of carbon–hydrogen bonds. Among the C-5 mono-oxygenated compounds, the sooting tendency increased in this order: aldehydes

Abstract: Binary and ternary blends of fossil diesel fuel, conventional biodiesel and hydrotreated vegetable oil (HVO), both derived from soybean oil, have been proposed as a means to increase the fraction of renewable energy in automotive fuels and to boost the blending possibilities depending on the desired fuel characteristics. Biofuels can be obtained in a specialized bio-refinery for a combined production of biodiesel and HVO or in a conventional refinery (with savings of costs as a consequence of the already existing installations). Two examples of these scenarios have been set out, and the most important physical and chemical properties of the final fuel blends measured and compared. The results proved that fuel properties depend greatly on the scenario considered, and consequently the biofuel production path must be carefully decided if the fuel potential is to be fully exploited. While a simultaneous production of HVO-diesel and a later blend with biodiesel fuels produced a neutral fuel in terms of cetane number and sooting tendency, the combined production of HVO-biodiesel to be afterwards blended with fossil diesel fuel is able to change the cetane number from 45 to 65, approximately, and reduce soot by roughly 30%. [Copyright &y& Elsevier]

Abstract: A gas-to-liquid (GTL) fuel derived from Low Temperature Fischer–Tropsch process has been tested in an automotive diesel engine fulfilling Euro 4 emissions regulations. Both regulated and non-regulated emissions have been compared with those of a commercial diesel fuel, a commercial biodiesel fuel and a GTL–biodiesel fuel (30% and 70% v/v, respectively) in order to check blending properties, synergistic effects and compatibility between first and second generation production technologies for biofuel consumption in current diesel engines. After presenting a detailed literature review, and confirming that similar efficiencies are attained with the four tested fuels under identical road-like operating conditions (this meaning fuel consumption is inversely proportional to their heating values), significant reductions in smoke opacity, particulate matter emissions and particle number concentration were observed with both GTL and biodiesel fuels, with small changes in NO x emissions. Compared with the reductions in PM emissions derived from the use of biodiesel fuels, those derived from using GTL fuels were quite similar, despite its lower soot emissions reductions. This can be explained by the lower volatile organic fraction of the PM in the case of GTL. By adequately blending both fuels, a considerable potential to optimise the engine emissions trade-off is foreseen. [Copyright &y& Elsevier]

Biofuels composed by fatty acid methyl esters are widely used as partly substituting fuels for diesel fossil fuels. Additionally, it is expected that the diesel biofuel norms will be extended to ethyl esters produced from bioethanol in the upcoming years. A precise knowledge of the standard enthalpy of formation is necessary for the calculation of some parameters useful for the analysis of the combustion process and emissions of a diesel engine operating with different fuels, such as the heating value, the adiabatic flame temperature or the kinetic mechanisms. However, experimental data for this property are scarce, and only available for short-chain, saturated methyl esters. In this work, four estimation methods for the calculation of the enthalpy of formation are examined and compared. Three of them are simple methods based on groups or bonds contribution, and another one is a computational method (with Gaussian 03 software). After presenting the implementation rules for each of them, conclusions are stated based on the results attained. Gaussian and Benson-Groups methods seem to be more accurate in predicting the actual values of the enthalpy of formation, both methods considering the separation between double bonds and the edge effects in the molecule. However, only the Gaussian method considers the effect of the position of the double bond in the molecule for all the unsaturated esters. [Copyright &y& Elsevier]

Abstract: Flexibility in the supply of biomass to the energy conversion facility, as a function of the seasonal availability, is considered as one of the keys to guarantee their continuous operation and the yield of the investments. The kinetics of devolatilisation of the two most typical biomass wastes in the middle-south regions of Spain, wastes from pruning of pine and olive trees, were studied using thermogravimetric analysis, in order to evaluate their use in combination as an energy feedstock throughout the year. A kinetic devolatilisation model was fitted to the experimental results and the kinetic parameters were obtained. Although slightly different behaviour was found between different categories of the same sample (large branches, small branches and needles or leaves), the differences between pine and olive wastes were not significant, which indicates that they can be combined for use in combustion or gasification systems. [Copyright &y& Elsevier]

Abstract: Methyl esters obtained from the most interesting Spanish oleaginous crops for energy use—sunflower and Cynara cardunculus—were both used as diesel fuels, pure and in 25% blends with a commercial fuel which was also used pure. A stationary engine test bed, together with the instrumentation for chemical and morphological analysis, allowed to study the effect of these fuels on the engine emissions, soluble organic fraction of the particulate matter, origin of adsorbed hydrocarbons, sulphate content, particle number per unit filter surface, and mean particle diameter. Both the consideration of the thermochemical properties of the tested fuels and the computations of a chemical equilibrium model were helpful for the results analysis. These results proved that the use of these vegetable esters provides a significant reduction on particulate emissions, mainly due to reduced soot and sulphate formation. On the contrary, no increases in NOx emissions nor reductions on mean particle size were found. [Copyright &y& Elsevier]

Abstract Residues from wine industry constitute an interesting feedstock for biodiesel in wine-producing countries like Spain. The use of grape seed oil together with bioethanol obtained from wine surplus or distillation of grape skins and stalks in the transesterification reaction results in fatty acid ethyl esters (FAEE), which is a fully renewable and waste-derived biofuel. In this work, FAEE from the grape seed oil obtained from the vine variety Tempranillo has been produced and some of their properties have been measured and estimated. Only the oxidation stability would fall below the minimum value established for biodiesel in Europe, thus requiring additivation with antioxidants to fulfill the standard. The remaining properties are within the range. Noteworthy, the cold flow behaviour is very promising. Highlights • Fatty acid ethyl esters (FAEE) were produced from wine industry feedstocks. • A fully renewable biofuel of waste origin was produced. • This biofuel has good cold flow behaviour but poor oxidative stability. [ABSTRACT FROM AUTHOR]

The use of conventional and advanced biofuels is part of the efforts to reduce greenhouse gases and harmful exhaust gaseous emissions. This study investigates the unregulated emissions in gas and particles from a Euro 6b diesel engine, operated with four unconventional and advanced biofuels (two hydrogenated terpenic biofuels, a polyoxymethylene dimethyl ether, and a glycerol-derived biofuel), blended with diesel fuel and pure hydrotreated vegetable oil as base biofuel. The engine was operated following WLTC starting from cold-engine conditions. Gas phase samples were collected at each phase of the driving cycle and particulate matter (PM) samples were collected from a dilution tunnel at the end of the driving cycle. A total of 16 PAH and 13 carbonyls were analyzed. In addition, the apoptotic index induced by gas and particle emissions was determined. In the gaseous phase, the total PAH and carbonyl emission factors were higher at the low-speed phase for all fuels. Gas-phase PAH emission factors exceeded particle-bound PAH. Carbonyl emission factors ranged from 0.12 ± 0.012 to 25.3 ± 4.2 mg/km, markedly exceeding gaseous PAH emissions, which ranged from 20.7 ± 1.5 to 51.7 ± 8.9 μg/km. Diesel fuel exhibited the highest carbonyl emissions and its blend with 20% of hydrogenated turpentine exhibited the highest PAH emissions at the end of the WLTC, both due to high emissions at the low-speed phase. Although particle-bound PAH comprise only a small fraction of total PAH emissions, both phases (gas and particles) contributed approximately equal to the toxicity associated with carcinogenic PAH. The apoptotic cells percentage increased in a dose-dependent manner and was significantly higher in cells exposed to gas phase-derived samples. The apoptotic index induced by particulate matter samples did not show a concentration-response effect for any of the fuels. [Display omitted] • Four advanced biofuels, diesel and HVO were tested in a modern engine under WLTC. • PAH, carbonyl emissions and apoptotic index from gas and particles were assessed. • More than 85% of the total PAH emissions were distributed in the gas phase. • Carbonyl and PAH were more sensitive to engine temperature than to fuel properties. • Apoptosis was induced from all fuels, but did not correlate with PAH or carbonyls. [ABSTRACT FROM AUTHOR]