The effects of sulfides and sulfur/phosphorus‐containing compounds on coke formation during thermal cracking of light naphtha

Abstract

In this study, coke deposits during thermal cracking of light naphtha in the presence of sulfur‐ and sulfur/phosphorous‐containing compounds with different addition methods were investigated from the points of morphology and structure. Sulfur/phosphorous‐containing compounds were applied by continuous addition, pretreatment, and pretreatment followed by continuous addition. As for continuous addition, the amount of coke was decreased with increasing the mass concentration of sulfides in short‐term cracking periods. Catalytic coke was inhibited because of passivating the metal by sulfides at the initial stage of coking process. When phosphides were combined with the mixture of sulfides, the coke formation was further decreased as the synergistic effects of adsorption of sulfur and phosphorous onto the metal led to the decreased activity of metal surface. In the case of pretreatment with sulfur/phosphorous, the reduction in coke formation at the initial stage of cracking process was due to the adsorption of S/P‐containing radicals on the oxide film. In further cracking operation, an enrichment of Fe and Ni in the oxide layer from the pretreatment process leads to the appearance of coke filaments in coke layers. The combined addition method, the surface pretreatment with dimethyl disulfide (DMDS)/triphenyl phosphite (TPPI) followed by continuous addition of sulfides/TPPI in the feed, shows the best coking inhibition performance. The inhibition rate is up to 88.8% and 78.5% respectively when the cracking time is 1 and 3 h. The combined application strengthened the coverage of catalytic activity sites by sulfur/phosphorous‐containing radicals. The scanning electron microscope (SEM) results showed that the structural characteristics of coke deposit at the applied conditions were mainly amorphous coke. Variant coke filaments were also observed at the conditions of pretreatment and pretreatment followed by continuous addition. The analyses of Raman spectra indicated that the application methods decreased the graphitization degree of coke deposited and increased the structure defects of the coke matrix. During naphtha cracking, sulfur/phosphorous‐containing compounds reduced dehydrogenation and condensation by which hydrocarbons were degraded to coke.

Investigation of the effect of presulphidation on coke deposition on 25Cr‐35Ni alloy during ethane steam cracking

“…A catalytic mechanism occurs due to the catalytic effect of metal particles such as Cr and Ni and its morphology is filaments of various types, such as segmented worms, spiral and rod filaments. [ 21 ] As a result, encapsulating coke is observed on the surface whenever the catalytic effect is suppressed, and carbon cannot penetrate through the metal particles. The coke morphology formed on the HP40 coupon in conditions of preoxidized and presulphided is shown in Figure 6.…”

“…The influence of the sulphurcontaining compounds on coke deposition depends on different factors, including the application methods (presulphidation and continuous addition), the nature and the amount of the sulphur compounds, and metal surface composition. [2,15,[18][19][20] Ding et al [21] used DMDS, thiophene, and benzothiophene as coke inhibitors and surveyed the influence of the application method and realized that pretreatment followed by continuous addition is the most effective procedure. In addition, Dhuyvetter et al [13] and Wang et al [15] both used DMDS in naphtha cracking and other hydrocarbons and figured out that the amount and the method of using this inhibitor make a significant change in the morphology and the amount of the coke.…”

Bi‐Reforming of Biogas for Hydrogen Production with Sulfur‐Resistant Multimetallic Catalyst

“…The usual procedure carried out is the sulfurization with dimethyl disulfide (DMDS) of the catalytic solid with the objective of minimize the material coking tendency by inducing the passivation of active metal by a strong attach of the sulfur [50,51]. The Differential Thermogravimetric analysis (DTG) profiles of used samples (Fig.…”