Enhanced Coke Gasification Activity of the Mn_1.5Cr_1.5O₄ Spinel Catalyst during Coking in Ethylene–Steam Mixtures

Abstract

Mn−Cr−O spinel catalysts (MnCr 2 O 4 and Mn 1.5 Cr 1.5 O 4 ) and single oxides of Mn and Cr are coked under ethylene and ethylene−steam mixtures to simulate reaction conditions occurring in steam cracker furnaces. The coking rates are measured using thermogravimetric analysis, and the Mn 1.5 Cr 1.5 O 4 catalyst displayed considerably less coke deposition (an order of magnitude) under ethylene−steam flow. Analysis of the outlet gas flow suggests the Mn 1.5 Cr 1.5 O 4 catalyst gasified the radically formed coke into carbon oxides without significantly affecting ethylene conversion. The anticoking performance of the Mn 1.5 Cr 1.5 O 4 catalyst is attributed to the presence of Mn 3+ species in the spinel phase structure that are active for coke gasification in the presence of steam. No significant changes in structure or performance are observed for the Mn 1.5 Cr 1.5 O 4 catalyst across several coking and decoking cycles. The Mn−Cr−O spinel oxide with higher Mn content is suggested to have desirable activity and stability to limit coke deposition during steam cracking.

Anticoking Performance of Electrodeposited Mn/MnO Surface Coating on Fe–Ni–Cr Alloy during Steam Cracking

“…An Ar + ion laser (λ = 488 nm) was used to collect first-order Raman spectra, with a laser source intensity of 5 mW for 2 s. The sample was placed onto a glass slide to analyze at least three different coked spots. The collected Raman spectra were deconvoluted using constrained peak fitting settings in OriginPro software. , …”

“…All of the thermal pretreatments and coking tests were conducted in a customized thermogravimetric analyzer system (TGA, NETZSCH STA449F3) (Supporting Information (SI) Figure S1), as reported and validated in our previous work. ,− Prior to the first coking cycle, the Mn-plated/anodized Incoloy 800H sample (hereafter, Mn-Inc.) was placed inside an alumina crucible and thermally pretreated under a H 2 –H 2 O atmosphere. The TGA system was evacuated and purged with nitrogen three times, and the Mn-Inc. sample was then heated inside the TGA under nitrogen (130 mL/min) up to 825 °C at 10 °C/min.…”

“…The collected Raman spectra were deconvoluted using constrained peak fitting settings in OriginPro software. 34,35 ■ RESULTS AND DISCUSSION Initial Characterization of Mn-Plated/Anodized incoloy 800H…”

Carburization of High-Temperature Alloys during Steam Cracking: The Impact of Alloy Composition and Temperature

“…For instance, the oxide layer of Al-Coated regenerated itself after each cracking cycle. On the other hand, the non-aluminum-containing alloys of 33/43 Cr–Ni, Cr–Mn-Coated, and 27/34 Cr–Ni showed some fluctuations in coke formation corresponding to cracking cycles, which might indicate deterioration and recovery of the oxide layer during cracking/decoking cycles . 33/43 Cr–Ni and Cr–Mn-Coated coupons showed some aging after the second and third cracking cycles, respectively, which demonstrates that the negative effect of aging was superior to the positive effect of oxide layer recovery.…”

“…To reduce coke formation in reactor furnaces, researchers have examined numerous methodologies, mostly categorized into three groups: three-dimensional (3D) reactor technology, ,,− surface modification, − and feed additives. ,− Surface technologies, the focus of this work, aim to mitigate or eliminate catalytic coke formation by covering up the surface catalytic sites (nickel and iron). In fact, at the beginning of the reaction, highly active catalytic sites on the surface of the metals are in direct contact with the carbon-rich atmosphere.…”