Biojet fuel production from oleaginous crop residues: thermoeconomic, life cycle and flight performance analysis
Graphical abstract
Introduction
Air transport is a cornerstone in current globalization, supporting the movement of more than 4.5 billion passengers and nearly 55 Mt of goods equivalent to €5.58 trillion in 2019, before the SARS-CoV-2 [1]. At a European level, 700 large commercial airports home to over 4000 civil aircraft, managing a quarter of the passengers worldwide. On average, 27,400 daily flights pass over its airspace, accounting for around 28% of global air traffic [2]. Nonetheless, the economic outlook for the next 20 years anticipates the number of air passengers to double. Simultaneously, aviation fuel (Jet A1) consumption will rise accordingly, leading to increased greenhouse gas (GHG) emissions (976 Mt of CO2 in 2019). In addition, Petroleum-derived Jet A1 affects the atmosphere due to pollutant emissions such as NOx, CO2, sulphate, aerosols, and soot, contributing to climate change and depleting the ozone layer [3].
In this regard, the aviation industry has committed to the third phase of the Carbon Offsetting and Reduction Scheme for International Aviation (CORSIA), which aims to cut net emissions in half by 2050 compared to 2005 levels while reducing reliance on conventional aviation fuels [4]. Nevertheless, better performance in modern engines, aerodynamic enhancements, and effective air traffic control is insufficient for offsetting the expected emissions [5]. In contrast, alternative jet fuel derived from renewable sources can significantly reduce the aviation industry's net GHG emissions [6]. Therefore, its production is imperative for a carbon–neutral expansion and ensuring energy security.
Lignocellulosic biomass is the most abundant renewable energy source globally. It is primarily composed of two biopolymers: aromatic (lignin) and polysaccharides (cellulose and hemicellulose). Its chemical composition ranges between 40 and 50 wt% of cellulose, 25–35 wt% of hemicellulose, 15–25 wt% of lignin, and, to a lesser extent, 3–7 wt% of extractives and inorganics (ash) [7]. Agriculture, forest, and industry sectors offer most of the lignocellulosic biomass; nonetheless, agricultural wastes are ideal because of their relatively low cost and ease of transportation/storage [8]. With this in mind, oleaginous crops account for about 18% of the global cultivated area, producing 210 Mt of vegetable oil in 2020. Also, the annual per capita consumption is projected to reach 20 kg by 2026 [9], [10]. The production of main vegetable oils includes coconut (3%), cottonseed (4%), olive (2%), palm (32%), palm kernel (4%), peanut (4%), rapeseed (14%), soybean (29%), and sunflower oil (8%). Throughout the extracting process of vegetable oil from the fresh fruit bunches (FFB), lignocellulosic biomass is obtained, such as empty fruit bunches (EFB) (23 wt%), oilseed kernel (7 wt%), mesocarp fibre (15 wt%), shell (7 wt%) and decanter cake (6 wt%). At the same time, the plantation area produces plant fronds (24%) and trunk residues (15%) during FFB harvesting [11]. Moreover, lignocellulosic biomass from oleaginous crops contains a higher sugar fraction, releasing more glucose and xylose during Biomass-to-Liquid conversion, achieving higher efficiencies [12].
Globally, primary biofuels used in gasoline blending of land transport are cellulose-derived oxygenates. However, their suitability as jet fuel blending components is constrained due to their lower volumetric energy density, increased volatility, corrosivity, and incompatibility with existing infrastructure [13]. Hence, synthesized paraffinic kerosene (SPK) from renewable sources is required. In addition, the SPK or biojet fuel contains no sulphur or nitrogen, avoiding the formation of SO2 and H2SO4 during combustion [14]. In this sense, biojet fuel produced through the certified routes by the American Society for Testing and Materials (ASTM) comprises linear, branched, and cyclic hydrocarbons compatible with Jet A1 as 'drop-in' fuels, i.e. blending components at a determined ratio. Biojet fuel can not replace Jet A1 completely; for this to happen, the synthesis of a certain fraction (about 20 wt%) of aromatics in the C9-C13 range would be needed [15].
Nonetheless, biojet fuel must suit aircraft engines' design and fuel distribution systems. Physico-chemical homogeneity between both fuels is crucial for combusting behaviour due to specific conditions regarding viscosity, non-freezing or cloudiness phenomena at low temperature, freezing point, etc. Also, to meet storage and transport safety requirements [16]. Approved technologies involve the conversion of (i) Hydrogen, carbon monoxide, and dioxide carbon mixture (syngas) in a Fischer-Tropsch (FT) reactor into a wide range of hydrocarbons via power-to-liquid (PtL) process [17]; (ii) Hydroprocessed esters and fatty acids (HEFA) by reacting triglycerides from fats and oils with hydrogen; (iii) Synthesized iso-paraffin produced through hydroprocessed fermented sugars (SIP-HFS) employing farnesene as feedstock; (iv) Synthesized kerosene with increased aromatics content (FT-SPK/A) by alkylation of light aromatic compounds from renewable sources [17]; (v) Alcohol-to-jet synthetic paraffinic kerosene (ATJ) from lignocellulosic-derived alcohols; (vi) and recently, Catalytic hydrothermolysis jet (CHJ) and co-processing jet from triglycerides and vegetable, waste, or algal oils [18], [19], [20].
A detailed scheme describing the ASTM routes is contained in the supplementary information (SI1). The ATJ and HEFA pathways were selected for the biorefinery design. The ATJ upgrades the cellulose-derived alcohol into biojet fuel, whereas the HEFA pathway processes vegetable oil, as shown in Fig. 1.
Currently, several companies are producing biojet fuel. For instance, Byogy Renewables Inc. technology can effectively process ethanol, propanol or butanol via catalytic synthesis to obtain biojet fuel [21], [22]. Among cellulosic alcohols, ethanol is a versatile platform molecule to form long-chain hydrocarbons [20]. Ethanol processing is a well-understood industrial-scale technology, environmentally sustainable and cost-effective, with production capacity reaching near-theoretical thermodynamic yields [23], [24]. Besides, it is the most prevalent liquid fuel produced from biomass presently. One way to meet the growing demand for middle and heavier distillate fuels (jet fuel and diesel) is to derive these from ethanol [25]. The ethanol is dehydrated during the ATJ route to produce ethylene, which is subsequently oligomerized over a solid acid catalyst in a single or double processing phase to obtain linear α-olefins. An alternative approach involves a single-stage oligomerization; however, up to 40% of undesirable selectivity to C1–C4 light hydrocarbons have been reported [26], [27]. Efficient conversion of ethylene to heavier hydrocarbons (C8+) has been observed through a two-step oligomerization process, minimizing the formation of aromatics and naphtha-like compounds by shorter chain product recycling [28]. Products distribution is determined by the water content in the feed, reaction conditions, and the catalysts’ surface acidity regulated by zeolites additives and Si/Al ratio [29].
On the other hand, the HEFA route employs thermal hydrolysis, decarboxylation, hydrocracking, and isomerization to treat triglycerides from vegetable oil [30], [31]. It is currently the most well-known and fully commercialized on an extensive industrial-scale process [5], [30]. Many companies opt to implement biorefineries using the HEFA technology because much lower capital is required than lignocellulose-based technologies [32]. For example, Neste® operates two refineries in Finland and two others in the Netherlands and Singapore, target to increase waste and residues share from the current 83% to 100% of renewable raw material inputs by 2025 [33]. Plant kernel is a valuable residue from vegetable oil processing due to its oil content ranging between 5 and 12 wt%, depending on the type and cultivation conditions [34]. Furthermore, fatty acid distillates (FAD) recovered from the stripping and deodorisation stages (5–10 wt%) during vegetable oil alkali refining contain unsaturated and saturated free fatty acids (C12 to C30) for increasing decarboxylation reactor yield [35]. Both feedstocks have received significant interest owing to their potential to produce biojet fuel with a higher cetane number and lower aromatic content.
Biojet fuels techno-economic and environmental assessments are widely available in the literature. For example, Atsonios et al. determined that biochemical alcohol fermentation with subsequent upgrading is more economically feasible than the production via mixed-alcohol synthesis [13]. In comparison, Tanzil et al. found that HEFA is the most competitive biojet fuel technology on the market today. Its costs are relatively low and have a high fuel yield than lignocellulosic biomass-based technology, notwithstanding triglycerides are several times the price of those inputs [36]. While the studied feedstocks are entirely characterized, detailed information on their composition and availability exists, there is a general lack of understanding of their effect on hydrocarbon yield, particularly biojet fuel blend yield and overall process thermoeconomics. Therefore, new detailed information is required to approach a substantial improvement in developing a sustainable Jet A1 surrogate, combining thermodynamics and physico-chemical properties with the produced biojet fuels' combustion behaviour.
The research examines a biorefinery simulation to produce biojet fuel via the ATJ and HEFA processes from oleaginous crop waste. It describes lignocellulosic ethanol production as an intermediate molecule in the ATJ route and kernel oil and FAD as feedstocks for the HEFA route. The process feasibility and efficiency were evaluated through comprehensive thermodynamic and techno-economic analyses and complemented with a life cycle assessment (LCA). Furthermore, both biojet fuels' combustion properties were estimated and compared to the ASTM physico-chemical specifications. Finally, a payload vs range calculation was conducted to evaluate biojet fuels' performance when replacing Jet A1 during a flight.
Section snippets
Process design and basic assumptions
The ATJ and HEFA routes were modelled and simulated in the chemical engineering software AspenPlus® v.11 (Aspen Technology Inc., USA) based on experimentally obtained data and approved methodologies. The NRTL (non-random two liquid) property method was selected for the vapour-liquid equilibrium calculations and thermodynamic and transport properties estimation. The simulation models were used to evaluate optimal operating conditions and perform precise mass and energy balances. The
Simulation description
The feedstock streamflows (S1ATJ and S2ATJ) of the ATJ sequentially go through hydrolysis, SSCF, dehydration, oligomerization, and hydroprocessing. The HEFA feedstock (S1HEFA, S26HEFA and S10HEFA) are transformed through hydrolysis, decarboxylation and hydroprocessing reactions, as shown in Fig. 5.
The physico-chemical properties of all flow streams from the simulated biorefinery are summarized in the SI8 section. The mass and energy balances and the primary process results are described in
Conclusions
The simulated processes for biojet fuel production from lignocellulosic biomass through the ATJ and HEFA thermochemical routes achieved a highly efficient production rate. From the techno-economic analysis, it is concluded that even though the HEFA process has better performance than the ATJ route in terms of carbon utilization and thermal efficiency, the minimum biojet fuel selling price remains higher than the Jet A1 price. On the other hand, the ATJ minimum selling price almost double Jet A1
CRediT authorship contribution statement
Nicolas Vela-García: Conceptualization, Methodology, Software, Investigation, Writing - review & editing. David Bolonio: Conceptualization, Methodology, Validation, Visualization, Project administration. María-Jesús García-Martínez: Methodology, Software, Resources, Formal analysis. Marcelo F. Ortega: Software, Resources, Formal analysis. Daniela Almeida Streitwieser: Conceptualization, Investigation, Writing - review & editing. Laureano Canoira: Supervision, Validation, Investigation, Writing
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
The authors of this research would like to thank Alberto Peset, Patricia Lorente, Luis Uruburu, and Alejandro Torre Sainz, all from UPM, who provided technical work.
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