Aviation sector is one of the strongest growing transport sectors. Global airline operations consumed around 1.5 billion barrels of Jet A-1 fuel. Jet fuel consumption of 705 million metric tons (Mt) generates significant greenhouse gas emissions, accounting for about 2% of global CO2 emissions each year (www.climatesolutions.org/programs/aviation-biofuels-initiative). For Egypt from 1980 to 2016, the average consumption value during that period was 19.32 thousand barrels per day, with a minimum of 7.29 thousand barrels per day in year 1980 and a maximum of 38.11 thousand barrels per day in 2010 (https://www.theglobaleconomy.com/Egypt/jet_fuel_consumption/). Awareness of greenhouse gas emissions and climate change push researchers and airlines sector to develop renewable jet fuel alternatives.
Biomass fuels (bio-jet fuel) have recently attracted considerable attention as alternatives to conventional jet fuel. They have become the focus of aircraft manufacturers, engines, oil companies, governments and researchers alike. IATA identified biofuels as the most promising strategies to reduce carbon dioxide emissions from the aviation sector in the foreseeable future (Yang et al. 2019).
The high dependence of the bio-jet production cost would be on the following parameters: (1) feedstock’s composition and cost, (2) process design, (3) product yield or conversion efficiency, (4) co-product’s valorization; and (5) energy conservation. Hence, decreasing the production cost of bio-jet fuel depends on significant hard work in all areas, including enhancements in the areas of feedstock productivity, the extracted yield of oil or sugar yield from the crops, process conservation energy, and balance between jet fuel product and co-products added value (Wang and Tao 2016).
Derived jet fuels from renewable feedstock can reduce the dependency of the aviation industry on one single energy source. Also this can decrease the petroleum prices, and essentially lowering greenhouse gas (GHG) emissions. The use of aviation biofuels could reduce greenhouse gas emissions in the life cycle of aviation by a range of 68.1% in 2050 (Staplesa et al. 2018; Blakeley 2012; Tao et al. 2017).
Investigators from different academia and organizations (the oil-refining industry, the aviation industry, government, bio fuel companies, agricultural organizations), tried to develop new commercially practicable and sustainable processes that produce renewable low cost jet fuels with low greenhouse gas emissions. Produced jet fuels must meet (ASTM) international standards and can be a 100% drop-in replacement for the current petroleum jet fuel. The emissions after combustion and engine tests show up the benefits of running the aero plane with bio-jet fuels. Technologies for producing renewable jet fuels from different pathways containing alcohols-to-jet, oil-to-jet, syngas-to-jet, and sugar-to-jet, are studied. The main challenges for each technology pathway, including feedstock availability, process conceptual design and economics, life-cycle assessment of greenhouse gas emissions, and commercial willingness, are discussed (Wang et al. 2016).
Several types of feed stocks for bio aviation fuel production are listed as (a) oil-based feedstocks, such as vegetable oils, waste oils, algal oils, and pyrolysis oils; (b) solid-based feedstocks, such as lignocellulosic biomass (including wood products, forestry waste, and agricultural residue) and organic portion of municipal waste or (c) gas-based feedstocks, such as biogas and syngas (ICCT 2019).
Using Camelina, jatropha and algae, as raw materials for Jet fuel production reduce the fuel's carbon foot print by80% relative to jet fuel without competing for food sources (Bailis and Bake 2010).
Basically, kerosene is a straight-run distillate of petroleum fraction with boiling temperature ranging from 205 to 260 °C. Increasing jet fuel production decreases obviously the production of other products (Sun 2012).
Also safety and security of supply criteria change and developed the specifications of aviation kerosene (Pires et al. 2018; Corporan et al. 2011; Hileman and Stratton 2014). Strategy of both environmentally and economically feasibility of bio fuel production is related to the development of conversion technologies and feed stock resources so that the cost-competitive production of bio fuels is compatible with the use of sustainable low cost, and diverse feed stocks (Sathaye et al. 2011; Skreiberg et al. 2013).
Most contaminants that result in bio oil yields can be traced back to the feedstock, such as residual solids (char), alkali metals, and high water content (Zacher et al. 2014a).
Common technologies used is catalytic hydride oxygenation at high pressure (Mante et al. 2017) which generates a hydrocarbon liquid suitable for co-processing in a petroleum refinery or blending into finished fuel (Talmadge et al. 2014). To achieve IATA goals, higher blending rates may eventually be required. In fact, this product may not be available everywhere during the growing period. The ability to mix higher ratios in some locations can help achieve the establishment objectives, taking into account the local availability of the product (Chuck and Donnelly 2014). The first task of the High Biofuel Blends in Aviation (HBBA) study was to establish the relevant range of properties of conventional kerosene properties, and to identify sources for the supply of suitable samples (Prussi et al. 2019). The target set by the European Union Flightpath for the aviation sector focuses on all methods of production, but in particular, takes into account artificial paraffin or biologically derived biomass. Aviation biofuels must be fully compatible and can be combined with standard fossil fuels (such as Jet-A fuel). These fuels should also be tested and approved before commercial use, and emissions are verified. In addition, production and use should not only be developed and verified, but also the entire transport and distribution chain (Chairamonti 2019).
Conventional biofuels cannot be mixed even in very few percentages with fossil kerosene, as the fuel standards are too strict for aircraft engines. This also applies to distilled fractions of conventional biofuels (Chuck and Donnelly 2014).
The first track relies on vegetable oils and fats, and therefore on raw materials such as oilseeds or fat-rich algae, residues such as cooking oil used or animal fat, or even common products such as tall oil from the papermaking industry (Chuck and Donnelly 2014; Prussi et al. 2019). Esterification is not a vital option for the production of aviation fuel: the so-called "biodiesel", is a mixture of fatty acid methyl esters (FAME) to be used as a low component (5–7%) in the land transport mix. On the contrary, hydrogen treatment of fats can be applied to the production of jet fuel, as has already been done by many companies (such as Neste Oil, Petrobras, ENI/UOP, etc.) to obtain high-quality biomass-derived fuel, compared with FAME (Chairamonti 2019).
It is clear that if biodiesel is to be used for aviation then it will have to contain short-chain esters rather than long-chain polyunsaturated. While hydrogen-treated triglycerides are accepted as synthetic aviation fuels, a number of studies have shown biodiesel, alkyl esters of fatty acids produced by the glyceride transformation process, to be a suitable fuel for gas turbine engines. Biodiesel typically contains straight-chain fatty acid esters ranging from 16 to 18 carbon atoms that can contain 3 double bonds. Biodiesel is suitable for aviation if composed solely of short chain saturates (Chuck and Donnelly 2014; Wang et al. 2016). However, the melting points of long-chain saturated and unsaturated esters are too high to be suitable for flight. Reducing the length of the chain or increasing the level of saturation significantly reduces the freezing point (Wahyudi 2018; Holladay 2015a; Gawron and Białecki 2018).
Numerous literatures have examined the effect of hydro treating process on bio-oil characteristics (Zacher et al. 2014b; Howe et al. 2015). The produced hydrocarbon via zinc aluminate as catalyst was mainly branched alkanes and cycloalkanes with a maximum yield ≈ 89% after upgrading and distillation processes (Hawash et al. 2017). Overall, thermo- chemical conversion is an important route for the production of biojet fuel using vegetable oils (Xu et al. 2016).
The present investigation is undertaken to study the effect of change of operating conditions in the hydro thermal catalytic cracking process for converting waste cooking oils to bio aviation fuel through the determination of different parameters representing the experimental results based on the rate of depression in freezing point of the produced bio kerosene with different reaction conditions and the test proved that the obtained thrust of using 10% blend of the produced bio aviation fuel is in a good agreement with jet A-1 specifications.