Alumina-based Coating for Coke Reduction in Steam Crackers

Abstract

Alumina-based coatings have been claimed as being an advantageous modification in industrial ethylene furnaces. In this work, on-line experimentally measured coking rates of a commercial coating (CoatAlloy™) have pointed out its superiority compared to an uncoated reference material in an electrobalance set-up. Additionally, the effects of presulfiding with 500 ppmw DMDS per H2O, continuous addition of 41 ppmw S per HC of DMDS, and a combination thereof were evaluated during ethane steam cracking under industrially relevant conditions (Tgasphase = 1173 K, Ptot = 0.1 MPa, XC2H6 = 70%, dilution δ = 0.33 kgH2O/kgHC). The examined samples were further evaluated using online thermogravimetry, scanning electron microscopy and energy diffractive X-ray for surface and cross-section analysis together with X-ray photoelectron spectroscopy and wavelength-dispersive X-ray spectroscopy for surface analysis. The passivating coating illustrated a better performance than the reference Ni-Cr Fe-base alloy after application of an improved pretreatment, followed by piddling changes on the product distribution. Presulfiding of the coating affected negatively the observed coking rates in comparison with the reference alloy, so alternative presulfiding and sulfur addition strategies are recommended when using this barrier coating.

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

“…Comparing the data obtained from different coupons after five cracking cycles, it is obvious that the Al-Enhanced coupon is superior to the others, with an average coke weight of 4.3 mg (i.e., 94% less coke tendency than the worst performance coupon of 27/34 Cr–Ni). This is in accordance with the previous results of Jakobi et al and other researchers who have performed their lab-scale experiments at lower temperatures and concluded the superior performances of Al-containing material relative to non-Al-containing ones. ,, The current study demonstrates how exposing this alloy to higher temperatures near the end of the cracking cycles does not involve the deterioration of the material. The low and similar catalytic and asymptotic coking rates for this alloy indicate that the catalytic mechanism at the beginning of the reaction is mitigated by the aluminum oxide surface layer formed during pretreatment.…”

“…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.…”

Preoxidation Film and Its Anticoking Behavior on an Optimized HP40Nb Alloy with Al, Zr, Y Addition

“…Al 2 O 3 oxide layer is formed by preoxidation in low oxygen pressure. The Al 2 O 3 oxide layer can prevent Fe and Ni elements from diffusing outward, colliding with C and H free radicals, and reducing surface catalytic coking. − The cracking depth and conversion rate of feedstock are reduced, the final reaction rate is reduced, and the amount of small molecule hydrocarbons and unsaturated hydrocarbons is reduced.…”

Effect of Phosphine on Coke Formation during Steam Cracking of Propane

“…The initial coking rate reported is the mean measured value between the initial 15 and 60 min and is used to characterize the catalytic activity of the sample. The initial coking rate is mainly representative of the metal-catalyzed reactions [ 32 ]. The asymptotic coking rate is related to the radical coking mechanism and is reported as the mean measured coking rate between the 3rd and 4th hour of cracking.…”