# PTG-HEFA Hybrid Refinery as Example of a SynBioPTx Concept--Results of a Feasibility Analysis
###### Abstract  
Limited alternative fuels for a CO\({}_{2}\)-neutral aviation sector have already been ASTM certified; synthetic parafnific kerosene from hydrotreated esters and fatty acids (HEFA-SPK) is one of these--a sustainable aviation fuel. With the hypothesis to improve the greenhouse gas (GHG) balance of a HEFA plant by realizing the required hydrogen supply via electrolysis--power to gas (PTG)--an exemplary SynBioPTx approach is investigated in a comprehensive feasibility study, which is, regarding this comparatively new approach, a novelty in its extent. About 10 scenarios are analysed by technical, environmental, and economic aspects. Within the alternative scenarios on feedstocks, electricity supply, necessary hydrogen supply, and different main products are analysed. For different plant designs of the hybrid refinery, mass and energy balances are elaborated, along with the results of the technical assessment. As a result of this environmental assessment, the attainment of at least 50% GHG mitigation might be possible. GHG highly depends on the renewability grade of the hydrogen provision as well as on the used feedstock. One important conclusion of this economic assessment is that total fuel production costs of 1295 to 1800 EUR t\({}^{-1}\) are much higher than current market prices for jet fuel. The scenario in which hydrogen is produced by steam reforming of internally produced naphtha proves to be the best combination of highly reduced GHG emissions and low HEFA-SPK production costs. hybrid refinery; power-to-gas; biofuel; jet fuel; feasibility study +
Footnote †: journal: Applied Soft  
drop in fuels that can be used similarly to conventional fossil jet fuel. Related to climate protection strategies, the demand on such renewable SAF is increasing in the medium-term [1; 2]. Figure 1 shows the jet fuel demand of all flights departing in Germany, the CO\({}_{2}\) emissions to be reduced, and the share of required renewable jet fuels to fulfill targets of the Aviation Initiative for Renewable Energy in Germany e.V. (aireg), International Air Transport Association (IATA), and Climate Action Plan 2050 for Germany (CAP), as well as the required energy-related amounts of renewable SAF with specific greenhouse gas (GHG) mitigation potentials. According to this, a massive demand on SAF with high specific GHG mitigation compared to fossil jet fuel is required. Referring to the ASTM standards, which are binding in the aviation sector, only HEFA-SPK will short- to medium-term be available on the market in significant amounts [1]. Worldwide production capacities of HVO/HEFA (hydrotreated vegetable oils/esters and fatty acids) were about 224 Petajoule (PJ) in 2018 [4], of which about 5 PJ was HEFA-SPK. According to ASTM D7566 Annex 2, HEFA-SPK can be blended to a maximum of 50% (v/v) to conventional jetfuel, which has been demonstrated several times but is not part of regular operation yet. To produce HEFA, hydrogen is required. It was a hypothesis that renewable-based hydrogen might have a favorable GHG performance and--based on electrolysis (so called power-to-gas (PTG))--allow one to integrate renewable electricity. Therefore, it was the target when investigating a PTG-HEFA hybrid refinery as an example of SynBioPTx concepts in a comprehensive feasibility study. SynBioPTx stands for using synergies (syn) of biomass-based (bio) and electricity-based (PTx) fuels and product processes. This novel approach has got increasing interest in recent years, especially from the viewpoint  
Figure 1: Jet fuel demand of all flights departing in Germany, emissions to be reduced, and the share of required renewable jet fuels to fulfill targets like of aireg, IATA, and climate protection plan (adapted from [3]). of Germany where PTx fuels are seen as an important solution for climate-friendly transport and especially aviation (e.g. [5; 6; 7; 8; 9]).