Relationship between hydrogenation degree and pyrolysis performance of jet fuel

Abstract

Understanding the relationship between the chemical composition and pyrolysis performance of endothermic hydrocarbon fuel (EHF) is of great significance for the design and optimization of advanced EHFs. In this work, the effect of deep hydrogenation on the pyrolysis of commercial RP-3 is investigated. Fuels with different hydrogenation degrees were obtained by the partially and completely catalytic hydrogenation and their pyrolysis performances were investigated using an apparatus equipped with an electrically heated tubular reactor. The results show that with the increase of hydrogenation degree, fuel conversion almost remains constant during the pyrolysis process (500e650 °C, 4 MPa); however, the heat sink increases slightly, and the anti-coking performance significantly improves, which are highly related to their H/C ratios. Detailed characterisations reveal that the difference of the pyrolysis performance can be ascribed to the content of aromatics and cycloalkanes: the former are prone to initiate secondary reactions to form coking precursors, while the latter could act as the hydrogen donor and release hydrogen, which will terminate the radical propagation reactions and suppress the coke deposition. This work should provide the guidance for upgrading EHFs by modulating the composition of EHFs.

1. Introduction

Thermal management of engine and airframe of aircraft vehicles under the cruising speed up to Mach 5 or higher is a challenging problem. It is generally accepted that the regenerative cooling strategy using on-board endothermic hydrocarbon fuel (EHF) as the coolant is one of the most feasible methods for heat removal [1]. EHF could provide both the physical and excess chemical heat sink through the temperature rise, phase transition, and endothermic thermal cracking reactions when it flows through the micro-channels at very high temperature [2]. However, the formation of coke deposition is inevitable during the thermal cracking process, and the excessive coking may block the channels and nozzles, decrease the heat transfer performance, and even result in the engine failure [3]. Thus, the design of advanced hydrocarbon fuels with higher heat sink and lower coking tendency is of great significance.

The composition of fuel has a significant influence on the pyrolysis performance. Many attempts, such as adding initiators, coking inhibitors and hydrogen donors, have been made to produce EHFs with high heat sink and low coking tendency [4e6]. Specifically, the hydrogenation can simply alter the hydrocarbon compositions, increase the H/C ratio, reduce the contents of unsaturated hydrocarbons, and remove hetero atomic compounds, thus significantly change the properties of the fuel [7]. As reported, the hydrogenation process could be applied in the preparation of synthetic fuel [8]. Recently, our group found that the hydrogenation was a promising approach to improve the thermal oxidative stability of jet fuel via the removal of aromatics and the inherent heteroatomic species (sulphur and phenols), and the neat heating value of jet fuel could also be improved [9]. However, there have been no reports regarding the effects of hydrogenation of jet fuels on the pyrolysis and anti-coking performance.