Efficient Coke Inhibition in Supercritical Thermal Cracking of Hydrocarbon Fuels by a Little Ethanol over a Bifunctional Coating

Abstract

Coke inhibition is one of the key issues for hydrocarbon fuel cracking. In the work reported in this paper, controllable cracking with greatly reduced coke deposits has been realized by the addition of a little ethanol over a bifunctional coating. The coating, consisting of perovskite and phosphotungstic acid, is prepared in a nickel-based super alloy tube reactor (diam. 3 mm × 0.5 mm × 1000 mm) by the wash-coating method. Scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy, and X-ray diffraction are utilized to characterize the morphology and phase composition of the coating and cokes. The results show that BaWO4, BaCeO3, SiO2, and H3PW12O40 coexist in the 4.2 μm coating with a uniform distribution. The anti-coking tests were conducted during the supercritical thermal cracking of RP-3 Chinese jet fuel with a flow rate of 1 g/s for 30 min at 700 °C and 4 MPa. The results show that the efficiency of coke inhibition reaches up to 96%, and the stability (i.e., pressure drop of tube reactor and cooler) of the system has been effectively improved. The deposited cokes were characterized by temperature-programmed oxidation and SEM. The pyrolysis products, including gas and liquid, were also analyzed. The results indicate that the strategy based on ethanol and a bifunctional coating not only plays an important role in eliminating the coke deposits on the reactor tube walls but also reduces the amount of typical coke precursors related to the aromatic condensation cokes. A possible mechanism for the process has been proposed. In general, phosphotungstic acid in the coating is capable of catalyzing the dehydration of ethanol for the production of water. Meanwhile, the perovskite structures can remove coke deposits on the coating through carbon–steam gasification reaction.

Investigation into the Anticoking Performances of Sol–Gel-Derived SiO2 and SiO2–CeO2 Coatings during Thermal Pyrolysis of Light Naphtha

“…The morphologies of SiO 2 coating are shown in Figure . Visible cracks can be found on the surface of the sol–gel-derived coating, similar to those observed in other research studies on anticoking coatings prepared by the dip-coating method. ,, The appearance of cracks is mainly due to the mismatch of thermal expansion coefficients (TECs) between the layer and the substrate during the annealing process . The TEC of the high-temperature alloy is about 16–20 × 10 –6 K –1 , while that of SiO 2 is just about 0.5 × 10 –6 K –1 at 800 °C.…”

“…Meanwhile, the product coke will diffuse into the interior of the metal . In the past 40 years, a lot of effort has been spent to find methods to inhibit coke formation, including the application of additives, − the surface coating technologies, ,− and the special-shaped tube reactor for heat transfer enhancement, resulting in lower wall temperatures and coking rates. − …”

Effects of Metal-Support Interactions and Interfaces on Catalytic Performance over M2O3- ( M = La , Al-) Supported Ni Catalysts

“…Compared with the cracking or dehydrogenation process, fuel steam reforming process can provide a higher heat sink and can meet the actual requirements of hypersonic missiles with flight speed up to Mach 10 [3]. Adding water/ethanol to fuel was based on a two-step reaction involving the lowtemperature prereforming of fuel to produce methane and carbon dioxide, and then the methane and carbon dioxide (dry) reforming under high-temperature conditions with strong endothermic effect [6]. Therefore, fuel steam reforming such as ethanol steam reforming and methane carbon dioxide reforming is expected to provide a fundamental data for improving the heat absorption capacity of fuel.…”

Experimental Study on the Ethanol-Assisted Catalytic Steam Reforming of Endothermic Hydrocarbon Fuel

“…The heat sink improvement mainly arose from the physical heat sink and dehydration of ethanol. Yang et al 38 pointed out by experiment that carbon deposition in supercritical fuel cracking can be suppressed by adding 5 wt % ethanol to the RP-3 kerosene.…”