Aviation Biofuels Research Articles

Drop-in biofuels production from microalgae to hydrocarbons: Microalgal cultivation and harvesting, conversion pathways, economics and prospects for aviation

In the last few years, governments all around the world have agreed upon migrating towards carbon-neutral economies as a strategy for restraining the effects of climate change. A major obstacle limiting this achievement is greenhouse gases emissions, for which the aviation sector is a key contributor because of its dependence on fossil fuels. As an alternative, biofuels with similar characteristics to current fossil-fuels and fully compatible with the existing petroleum infrastructure (i.e., drop-in biofuels) are being developed. In this regard, microalgae are a promising feedstock thanks to, among other aspects, their potential for lipid accumulation. This review outlines the development status, opportunities, and challenges of different technologies that are capable of or applicable to transform microalgae into aviation fuels. To this effect, a baseline of the existing jet fuels and the requirements for potential aviation biofuels is initially presented. Then, microalgae production and valorization techniques are discussed with an emphasis on the thermochemical pathways. Finally, an assessment of the present techno-economic feasibility of microalgae-derived aviation fuels is discussed, along with the authors’ point of view on the suitability of these techniques. Further developments are needed to reduce the costs of cultivation and harvesting of microalgae, and a biorefinery approach might improve the economics of the overall process. In addition, while each of the conversion routes described has its advantages and drawbacks, they converge upon the need of optimizing the deoxygenation techniques and the proportion of the suitable type of hydrocarbons that match fuel requirements.

New approach for bio-jet fuels production by hydrodeoxygenation of higher alcohols derived from C-C coupling of bio-ethanol

A new approach for the synthesis of jet fuel hydrocarbon from bio-ethanol was developed, the integrated catalytic process of ethanol C-C coupling and heavy alcohols hydrodeoxygenation (HDO) was reported. The initial bio-ethanol C-C coupling process was fulfilled directly in aqueous environment over Na/Ni@C catalyst. The obtained high-carbon alcohols can be separated into C4-C7 and C8-C16 alcohols respectively through convenient fractional distillation. The obtained C8-C16 alcohols mainly consist of β-branched primary alcohol, which are desired precursors for jet fuel hydrocarbons. To maintain the branched carbon skeleton in the subsequent alcohol HDO process, the Co-Mo2C catalyst with excellent C-O bonds cleavage and carbon skeleton retention ability were developed. Jet fuel hydrocarbons of 56.7% yield obtained from this approach is mainly C8-C16 branched alkanes, which is beneficial for the cold flow properties. This strategy creates new opportunities for producing alternative jet fuel from the mature bio-ethanol industry.

Optimization-based framework for modeling and kinetic parameter estimation

To understand the mechanism of a catalytic system, computational analysis is essential. Additionally, process simulators play a fundamental role in the reproduction of models associated with various unit operations such as chemical reactors. However, due to the complexity that some chemical and kinetic reactions may present, it is often complicated to design a reactor considering stoichiometric and chemical kinetic relationships resorting to yield-based or Gibbs-type reactors. This barrier has limited on several occasions the adequate reproduction of kinetic processes, their dynamic study, and even the direct application of process intensification strategies. This work presents a generic optimization framework for solving parameter estimation and catalyst design problems. Using a stochastic optimization method in conjunction with Aspen Plus and experimental data, kinetic data values were predicted. The direct advantage of obtaining kinetic parameters with this methodology is to be able to represent the kinetics according to the Arrhenius equation, which is widely used in commercial simulators. To validate this method, a previously presented case of dimerization of isobutane to produce isooctane is used as a baseline. Once the proposed methodology was used, it was possible to obtain kinetic parameters like those obtained by the authors of the case study with an error lower than 0.1%. Finally, the strategy to determine the kinetic parameters of a more complex case, the kinetic values of the oligomerization and hydrogenation reactions present in the aviation biofuel production process by the ATJ method were developed obtaining results like those reported experimentally with an error percentage lower than 1%, and with statistical metrics with relatively good approximation.

Renewable Aviation Fuel: Review of Bio-jet Fuel for Aviation Industry

The search for environmentally sound, socially responsible, and economically viable renewable fuel generation methods is a major global concern. A type of aviation fuel called jet fuel or often spelled avtur is intended for use in aeroplanes with turbine (gas) engines. Jet fuel appears colourless. The fuels Jet A and Jet A-1 are the most frequently used ones in commercial aviation sector. Other than Jet B, which is utilised for its enhanced cold-weather operation, there are no other jet fuels that are frequently used in gas-turbine-engine in the aviation industry. Renewable aviation fuel or known as bio-jet fuels represent a sizable sector for the consumption of fossil fuels. The production of bioethanol and biodiesel for piston engine vehicles in internal combustion engines has already shown that biofuel can play a significant role in the development of sustainable renewable aviation jet fuel. Here, we also provide a book review on the potential bio-jet fuel as a renewable aviation jet fuel.

Global warming potential analysis of bio-jet fuel based on life cycle assessment

Due to the large amount of greenhouse gas (GHG) emissions and the high dependence on fossil energy, the aviation industry has attracted a lot of attention for emission reduction and sustainable development. Biomass is a green and sustainable renewable resource, and its chemical conversion to produce bio-jet fuel is considered to be an effective way to replace fossil jet fuel and achieve emission reduction. In this study, the cradle-to-grave life cycle analysis is conducted for three bio-jet fuel conversion pathways, including biomass aqueous phase reforming (APR), hydrogenated esters and fatty acids (HEFA), and hydrothermal liquefaction (HTL). Compared with fossil jet fuels, the three bio-jet fuels have a great advantage on global warming potential (GWP), contributing 29.2, 43.6 and 51.2 g CO2-eq/MJ respectively. In general, as a relatively new bio-jet fuel conversion technology, the technology of aqueous phase reforming has minimal environmental impact. If the barriers of raw material availability and economy could be broken down, bio-jet fuel will have great development potential in replacing fossil jet fuel and realizing sustainable development.

Emerging technologies for the production of biojet fuels from wood—can greenhouse gas emission reductions meet policy requirements?

The transition from fossil jet fuel to biojet fuel is an important step towards reducing greenhouse gas (GHG) emissions from aviation. To enable such a fuel shift, the Swedish Government introduced a GHG emission reduction mandate of 27% by 2030 for aviation fuel sold in Sweden, forcing fuel suppliers to blend in biojet fuel in fossil jet fuel. A similar policy instrument is being discussed within the EU. Biojet fuels with life cycle GHG emissions 90% lower than those for fossil jet fuel are projected to be available by 2025, which by far exceeds the requirement of 65% lower emissions in the EU Renewable Energy Directive. The purpose of this study was to carry out life cycle assessments for a number of wood-fuel-based production chains near commercialization and to determine whether they meet the Swedish projection and the EU requirement. The study illustrates what can be achieved in a region with high availability of wood fuels and access to heat and power with low GHG emissions. The production chains studied include the production of hydrocarbon intermediates via (i) fast pyrolysis, (ii) hydrothermal liquefaction, (iii) thermal gasification followed by Fischer–Tropsch-synthesis, and (iv) cellulosic ethanol fermentation followed by upgrading of these four intermediates to biojet fuel and other liquid biofuels. The results show that all the production chains studied can deliver biojet fuels with 89–91% lower GHG emissions than fossil jet fuels. Non-fossil hydrogen is required to achieve low emissions in the upgrading of intermediates from fast pyrolysis and hydrothermal liquefaction.

Aircraft engine particulate matter emissions from sustainable aviation fuels: Results from ground-based measurements during the NASA/DLR campaign ECLIF2/ND-MAX

The use of alternative jet fuels by commercial aviation has increased substantially in recent years. Beside the reduction of carbon dioxide emission, the use of sustainable aviation fuels (SAF) may have a positive impact on the reduction of particulate emissions. This study summarizes the results from a ground-based measurement activity conducted in January 2018 as part of the ECLIF2/ND-MAX campaign in Ramstein, Germany. Two fossil reference kerosenes and three different blends with the renewable fuel component HEFA-SPK (Hydroprocessed Esters and Fatty Acids Synthetic Paraffinic Kerosene) were burned in an A320 with V2527-A5 engines to investigate the effect of fuel naphthalene/aromatic content and the corresponding fuel hydrogen content on non-volatile particle number and mass emissions. Reductions up to 70% in non-volatile particle mass emission compared to the fossil reference fuel were observed at low power settings. The reduction trends to decrease with increasing power settings. The fuels showed a decrease in particle emission with increasing fuel hydrogen content. Consequently, a second fossil fuel with similar hydrogen content as one of the HEFA blends featured similar reduction factors in particle mass and number. Changes in the fuel naphthalene content had significant impact on the particle number emission. A comparison to in-flight emission data shows similar trends at cruise altitudes. The measurements highlight the importance of individual fuel components in regulating engine emissions, particularly at the low thrust settings typically employed during ground operations (e.g. during idle and taxi). Therefore, when selecting and mixing SAF blends to meet present fuel-certification standards, attention should be paid to minimizing complex aromatic content to achieve the greatest possible air quality and climate benefits.

MgO-modified activated biochar for biojet fuels from pyrolysis of sawdust on a simple tandem micro-pyrolyzer

The aim of this work was to study on MgO-modified KOH activated biochar (AC) catalysts, in the pyrolysis of sawdust for the direct production of bio-jet fuels using a tandem micro-pyrolyzer. AC catalysts with various MgO contents (5 to 20 wt%) were synthesized using an impregnation method. The mesopores generated (4 to 18 nm) in the carbon has a great potential in the conversion of oxygenated to jet fuel. The importance of basic nature in the catalysts is demonstrated with the maximum bio-jet fuel yield of 29 % at 10 % MgO. Further, the temperature of 600 °C and a catalyst/sawdust ratio of 10 are identified as the optimal conditions. The nanosize of MgO and the synergism of acid and base sites seemed to enhance deoxygenation, via decarboxylation and decarbonylation, and oligomerization, which are required for jet fuel formation in high amounts from sawdust pyrolysis.

Ion Impregnation Effect of Fe, Cu, Cr-attributed Mordenite on Stearic Acid Cracking

The improvement in the design of mordenite-based catalysts focuses on the present study to fulfill the massive demand for bio-aviation fuel (BAF) as renewable energy. Modification of the mordenite through ionic impregnation of Fe, Cu, and Cr, has supported the mordenite to perform with better efficiency and activity in catalyzing the cracking process of stearic acid. The adjustment on catalytic activity was carried out by simply reacting the catalyst with stearic acid at 190 °C and investigating cracking products with Gas Chromatography-Mass Spectroscopy. The results of the GC-MS test of the cracking product showed the formation of alkane-alkene and aromatic compounds. BAF was selectively obtained (30.27%) when the reaction was catalyzed by FeCuCr/mordenite catalyst. The BAF derived from FeCuCr/mordenite contained hydrocarbons that include xylene, mesitylene, dodecane, tridecane, tetradecane, and pentadecane. However, reduced selectivity was realized (19.85%) when the reaction was catalyzed by nano FeCuCr/mordenite. Its hydrocarbon constituents include benzene, tetradecane, and pentadecane compounds.

Subnanometric Cu clusters on atomically Fe-doped MoO2 for furfural upgrading to aviation biofuels

Single cluster catalysts (SCCs) are considered as versatile boosters in heterogeneous catalysis due to their modifiable single cluster sites and supports. In this work, we report subnanometric Cu clusters dispersed on Fe-doped MoO2 support for biomass-derived furfural upgrading. Systematical characterizations suggest uniform Cu clusters (composing four Cu atoms in average) are homogeneously immobilized on the atomically Fe-doped ultrafine MoO2 nanocrystals (Cu4/Fe0.3Mo0.7O2@C). The atomic doping of Fe into MoO2 leads to significantly modified electronic structure and consequently charge redistribution inside the supported Cu clusters. The as-prepared Cu4/Fe0.3Mo0.7O2@C shows superior catalytic performance in the oxidative coupling of furfural with C3~C10 primary/secondary alcohols to produce C8~C15 aldehydes/ketones (aviation biofuel intermediates), outperforming the conventionally prepared counterparts. DFT calculations and control experiments are further carried out to interpret the structural and compositional merits of Cu4/Fe0.3Mo0.7O2@C in the oxidative coupling reaction, and elucidate the reaction pathway and related intermediates.

Evaluation of Decarbonization Technologies for ASEAN Countries via an Integrated Assessment Tool

A new assessment tool for evaluating decarbonization technologies that considers each technology’s sustainability, security, affordability, readiness, and impact for a specific country is proposed. This tool is applied to a set of decarbonization technologies for the power, transport, and industry sectors for the ten Southeast Asian countries that constitute ASEAN. This results in a list of the most promising decarbonization technologies, as well as the remaining issues that need more research and development. This study reveals several common themes for ASEAN’s decarbonization. First, carbon capture and storage (CCS) is a key technology for large-scale CO2 emission. Second, for countries that rely heavily on coal for power generation, switching to gas can halve their CO2 emission in the power sector and should be given high priority. Third, hydropower and bioenergy both have high potential for the majority of ASEAN countries if their sustainability issues can be resolved satisfactorily. Fourth, replacing conventional vehicles by electric vehicles is the overarching theme in the road transport sector, but will result in increased demand for electricity. In the medium to long term, the use of hydrogen for marine fuel and biofuels for aviation fuel are preferred solutions for the marine and aviation transport sectors. Fifth, for the industry sector, installing CCS in industrial plants should be given priority, but replacing fossil fuels by blue hydrogen for high-temperature heating is the preferred long-term solution.

Experimental Investigation on the Performance of an Aviation Piston Engine Fueled with Bio-Jet Fuel Prepared via Thermochemical Conversion of Triglyceride

Bio-jet fuels prepared by the thermochemical conversion of triglyceride can be used as complete substitutes of jet fuels. A bio-jet fuel prepared as a substitute of the RP-3 jet fuel and the RP-3 jet fuel itself were, respectively, used to fuel a small aviation piston engine. The characteristic tests of the engine were carried out, and the performances of the power, economy, emissions, and heat release law of the engine fueled with the two fuels were analyzed. The feasibility of the bio-jet fuel as a substitute for the RP-3 jet fuel was proved by the experimental results, which show that when the engine is fueled with the bio-jet fuel, the power and economy performance do not deteriorate; however, the HC emissions increase at small and medium throttle openings, while at large throttle openings, the performances of power and economy decreases, the emissions of HC and NOx increase, and the CO emission decreases. The bio-jet fuel is more prone to spontaneous combustion than the RP-3 jet fuel, so knock combustion would be more likely to occur at large throttle openings, and large cooling air flux is required to cool the cylinder because spontaneous combustion would increase heat release.

Soot Morphology and Nanostructure Differences between Chinese Aviation Kerosene and Algae-Based Aviation Biofuel in Free Jet Laminar Diffusion Flames.

Aircraft soot has a significant effect on the air quality and human health. The aim of this study is to investigate the evolution of soot morphology in free jet laminar diffusion flames between Chinese traditional aviation kerosene RP-3 and algae-based aviation biofuels. The differences in height, profile, and structural properties of soot between the RP-3 flame and biofuel flame are determined. A laboratory-made probe sampling method was applied for soot sample collection. Transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), and elemental analyzers were used to analyze the collected soot particles. The average particle size of soot increases first and then decreases in both flames, and the size of biofuel primary particles is smaller than that of jet fuel RP-3 particles along the same flame height. At the flame tip, the primary particle sizes of RP-3 soot and biofuel soot are 22.7 and 15.6 mm, respectively. In comparison with the RP-3 soot, the nanostructure of biofuel soot particles along the same flame height exhibits a shorter fringe lattice, a larger fringe tortuosity, and a larger interlayer spacing, which indicate a higher degree of oxidation reactivity. Meanwhile, RP-3 soot particles have a lower H/C atom ratio and have greater intensity in X-ray diffraction, which indicates a more orderly and compact lattice structure. This study provides some references in studying the algae-based biofuel with regard to soot formation.

Hydrocarbon Bio-Jet Fuel from Bioconversion of Poplar Biomass: Life Cycle Assessment of Site-Specific Impacts

Hydrocarbon drop-in bio-jet fuels could help to reduce greenhouse gas emissions within the aviation sector. Large tracts of land will be required to grow biomass feedstock for this biofuel, and changes to the management of these lands could have substantial environmental impacts. This research uses spatial analysis and life cycle assessment methodologies to investigate potential environmental impacts associated with converting land to grow poplar trees for conversion to bio-jet fuel from different regions within the western United States. Results vary by region and are dependent on land availability, type of land converted, prior land management practices, and poplar growth yields. The conversion of intensively managed cropland to poplar production results in a decrease in fertilizer and a lower annual global warming potential (GWP) (Clarksburg CA region). Bringing unmanaged rangeland into production results in increases in fertilizers, chemical inputs, fuel use, and GWP (Jefferson OR region). Where poplar yields are predicted to be lower, more land is converted to growing poplar to meet feedstock demands (Hayden ID). An increased use of land leads to greater fuel use and GWP. Changes to land use and management practices will drive changes at the local level that need to be understood before developing a drop-in biofuels industry.

Areas Available for the Potential Sustainable Expansion of Soy in Brazil: A Geospatial Assessment Using the SAFmaps Database

Recently, soybean production almost doubled in Brazil, reaching 122 million tonnes, and it is expected to increase even more. Brazil is the world’s largest producer and is primarily an exporter. From a sustainability point of view, soy production has been strongly criticized mainly in relation to deforestation, albeit for indirect effects. Soybean oil is a potential feedstock for the production of bio-jet fuels, which needs to be sustainable according to international criteria (sustainable aviation fuels—SAF). This paper aims to estimate the areas still available for soy expansion in Brazil, considering conditions that would allow the production of SAF. We used the SAFmaps platform, a geospatial database with information on the most promising bioenergy crops for SAF and their supply chains. Just by displacing pastures and observing a set of constraints, the total area available for expansion was estimated at 192.8 thousand km2, of which 43% is of high suitability. These areas are concentrated in the Center-West region. Assuming a vertical supply chain, the results of the case studies of SAF production indicate potential feasibility, but some hypotheses considered are optimistic. Moreover, the results indicate that there can be sustainable production of soybean oil and contribution to the production of SAF.

The balance of contradictory factors in the selection of biodiesel and jet biofuels on algae fixation of flue gas

The purpose would discover the impacts of the contradictory factors in application of algae in CO2 sequestration with sustainable biofuel benefit. Based on LCA approach, the quantitively AI assessment model and approach have been established coupling upstream CO2 source and downstream algal product at the uniform algae level of Nannochloropsis oceanica, which would benefit for algae biofuel deliverables choice. The AI model investigated the effects of interaction factors on the energy consumption, including transportation distances with purification modes coupling with CO2 concentration in flue gas, lipid content with specific productivity coupling the nutrient supply, refining process with final products. Computational framework of AI model is classified into three sub-models, including CO2 capture and purification model, algae cultivation and harvesting model, refining process and biofuel product model. According to uncertainty analysis by AI model, the positive energy gains have been conducted at a wide range of lipid contents despite of jet biofuel or biodiesel coupling solar energy utilization and by-product of bioactive nutrients effects. Biodieselwet and HTL-HRJ jet biofuel performed the priorities in energy consumption in three pathways of jet biofuel and three pathways of biodiesels. The allocation analysis confirmed that algae biofuel will be promising in the direction of cultivating appropriate algae for the target biofuel product requirement and enhancing by-product recovery. The results would enhance the interests in both LCA and CO2 sequestration with sustainable biofuel benefit.

Are fee-and-dividend schemes the savior of environmental taxation? Analyses of how different revenue use alternatives affect public support for Sweden’s air passenger tax

This article studies if, how, and why different revenue uses affect public attitudes to environmental taxation. More specifically, using a large-scale (N = 4292) randomized survey experiment with a 2 × 3 factorial design, the article analyses how attitudes towards a proposed increase in the current air passenger tax in Sweden are altered when combining a tax increase with three different suggestions for revenue use. The increasingly popular fee-and-dividend solution, where revenues are distributed back to the public, thus decreasing negative distributive tax effects, is compared with two additional revenue uses: unspecified government spending on welfare services, and re-investment of revenues into aviation biofuels. Our results show that, although some of the commonly used independent variables such as climate concern, personal norms and political-ideological orientation are significant in determining policy attitudes, varying both tax level and revenue use also tangibly affects how a policy proposal is received. Interestingly, however, the fee-and-dividend approach does not yield the most positive policy attitudes. Rather, directing the revenues to fund an increased use of biofuels for aviation is the alternative that most clearly drives positive attitudes to this policy, and is also the alternative that is perceived as the most effective and fair in both the high tax and the low tax alternatives.

Production of Biojet Fuel from Octadecane and Derivatives of Castor Oil Using a Bifunctional Catalyst Ni–Pd@Al-MCF in a Pressurized CO2–Hexane–Water Solvent

Production of Biojet Fuel from Octadecane and Derivatives of Castor Oil Using a Bifunctional Catalyst Ni–Pd@Al-MCF in a Pressurized CO₂–Hexane–Water Solvent

Mapping Research Trends in Publications Related to Bio-Jet Fuel: A Scientometric Review

It is a fact that society has increased the need for mobility throughout the world. In that regard, it has become aware of the problems associated with the use of fossil fuels such as jet-fuel. As alter-natives, the use of bio-jet fuel has been proposed, which is a biofuel that researchers have evaluated and developed as an environmentally friendly alternative. The development of research on the topic of biofuels has generated a growing number of alternatives in the methods, technologies and raw materials for the production of bio-jet fuel. In this work, a bibliometric study has been developed to analyze the evolution of publications, the contribution of authors, countries, in terms of citation productivity on the topic of bio-jet fuel. Scientific publications were searched in the Scopus database for the period 2001 to 2021. The results showed that the publications have grown exponentially in the last 10 years. The most influential institution and country are from China. “Renewable and Sustainable Energy Reviews” is the most cited journal in the field of bio-jet fuel. The growth rate of publications was estimated using the Gompertz model, the rate was 0.2232 y-1. Most of the documents were published in journals Q1.

Production of Jet Biofuels by Catalytic Hydroprocessing of Esters and Fatty Acids: A Review

The transition from fossil to bio-based fuels is a requisite for reducing CO2 emissions in the aviation sector. Jet biofuels are alternative aviation fuels with similar chemical composition and performance of fossil jet fuels. In this context, the Hydroprocessing of Esters and Fatty Acids (HEFA) presents the most consolidated pathway for producing jet biofuels. The process for converting esters and/or fatty acids into hydrocarbons may involve hydrodeoxygenation, hydrocracking and hydroisomerization, depending on the chemical composition of the selected feedstock and the desired fuel properties. Furthermore, the HEFA process is usually performed under high H2 pressures and temperatures, with reactions mediated by a heterogeneous catalyst. In this framework, supported noble metals have been preferably employed in the HEFA process; however, some efforts were reported to utilize non-noble metals, achieving a similar performance of noble metals. Besides the metallic site, the acidic site of the catalyst is crucial for product selectivity. Bifunctional catalysts have been employed for the complete process of jet biofuel production with standardized properties, with a special remark for using zeolites as support. The proper design of heterogeneous catalysts may also reduce the consumption of hydrogen. Finally, the potential of enzymes as catalysts for intermediate products of the HEFA pathway is highlighted.