Coke Surface Research Articles

コークス反応性制御によるシャフト炉コークス比制御技術

The shaft furnace, which is a scrap melting furnace, plays an important part as an energy supplier in a steelworks, because the shaft furnace produces high calorie gas. The shaft furnace is required either to reduce coke rate or to increase exhaust gas calorie, corresponding to energy balance in the steelworks. Coke rate and exhaust gas calorie are determined by the coke gasification reactivity, so the control technique of the reactivity is very important. In this study, coke surface was coated by CaCO3, Fe2O3 and SiO2 to control the coke reactivity, and the gasification rates were measured at 1573-1773 K. As the results, the gasification rates were accelerated by CaCO3 and Fe2O3, and decelerated by SiO2. The acquired gasification rates applied to a one-dimensional mathematical model of the shaft furnace. The shaft furnace operations controlling the coke reactivity were simulated and the effects of the coke reactivity on coke rate and exhaust gas calorie were estimated.

Propane Dehydrogenation over In2O3–Ga2O3–Al2O3 Mixed Oxides

AbstractA series of ternary mixed metal oxides containing Group III A elements (In, Ga, Al) is prepared by means of an alcoholic co‐precipitation method. Specifically, oxide catalysts with a molar composition of In/Ga/Al=5:15:80, 10:10:80, and 15:5:80 are reported. The chemical composition, redox properties, and catalyst structures are fully characterized, with the results suggesting that the indium, gallium, and aluminum moieties are well‐dispersed in the catalysts. The catalysts are evaluated for propane dehydrogenation (PDH) at 570 and 600 °C under 1 atm total pressure. The most effective catalyst with a composition of In/Ga/Al=5:15:80 provides 17 % conversion and approximately 86 % C3H6 selectivity with an initial activity of 4.6 mmol h−1 gcat−1 and 24.1 μmol h−1 m−2. The intrinsic activity on an active metal (i.e. indium and gallium) basis is approximately 3 times that of the In2O3–Ga2O3 family and approximately 3–9 times that of the In2O3–Al2O3 family. The catalyst deactivates with time on stream, and regeneration tests show that removal of surface coke and recovery of an In2O3 state helps to regain the initial activity, whereas reducing In2O3 domains into In0 does not allow for recovery of the performance. Raman analysis of the carbonaceous species deposited on the catalyst indicates catalysts with higher gallium content give more graphitic carbon, which correlates with higher C3H6 selectivity, whereas catalysts with more disordered coke are associated with lower selectivity. However, higher gallium content causes more coke formation, which leads to faster deactivation. This initial study of this family of mixed oxides suggests that an ideal In/Ga ratio may exist whereby catalyst properties may be optimized.

Effects of Additives on Sulfur Transformation, Crystallite Structure and Properties of Coke during Coking of High-sulfur Coal

High-sulfur coal, as an alternative coal source, has a relatively high proportion in coal reserves. However, the feature of high sulfur content, which can cause environmental pollution and poor quality of molten iron, restrains its utilization in coking industry. Coking experiments of high-sulfur coal with Fe2O3, La2O3 and CaO as additives were carried out in order to fix the sulfur in coke. The effects of additives on sulfur distribution, crystallite structure, surface morphology and properties of coke were investigated. The results indicate that CaO can be used as sulfur-fixing agent in coking process, and CaS is the main mineralogical phase of the sulfur-contained mineral constituents in coke. Fe2O3 and La2O3 facilitate the conversion of CaO to CaS. The additives mainly influence the crystallite height and the average interlayer spacing d002 of coke. The addition of La2O3 increases the value of the crystallite height while the addition of CaO and Fe2O3 decreases it. CaO leads the pores of coke to increase with its physical action and agglomerating characteristic. Fe2O3 and C can form (Fe,C), resulting in the pulverization and erosion of the pore wall. La2O3 makes the coke surface become more compact and thinner. The reactivity of coke increases with the decrease of crystallite height and crystallite layer number.

Pre-reforming of n-tetradecane over Ni/MgO–Al2O3 catalyst: effect of added potassium on the coke resistance

We investigated the pre-reforming of n-tetradecane (C14H30) over the K-promoted 50 wt% Ni/MgO–Al2O3 catalyst and also analysed the coke resistance. The 50 wt% Ni/MgO–Al2O3 catalysts were prepared by the deposition–precipitation method and 1–5 wt% of potassium was added to the catalyst using the impregnation method. The catalysts were characterized by ICP, XRD, H2-chemisorption, H2-TPR, and BET. The pre-reforming of n-tetradecane was performed under the reaction conditions of S/C = 4.0, GHSV = 3000 h−1, and 400–450 °C. The Ni crystallite size increased, whereas the Ni dispersion and surface area of catalysts decreased with increasing amounts of K. The 50 wt% Ni/MgO–Al2O3 showed large amounts of coke deposition compared to the K-promoted catalysts. It was found that the K addition over 50 wt% Ni/MgO–Al2O3 catalyst was beneficial for coke removal by promoting the coke gasification. A 1 wt%K/50 wt% Ni/MgO–Al2O3 catalyst showed stable activity during pre-reforming at S/C = 4.0, GHSV = 3000 h−1, and 400 °C. Furthermore, it had the lowest amount of surface coke, as observed by SEM, TEM, and TG analysis.

Gasification Effect of Metallurgical Coke with CO2 and H2O on the Porosity and Macrostrength in the Temperature Range of 1100 to 1500 °C

The gasification of metallurgical cokes with CO2 and H2O on their porosity and macrostrength were investigated in the current study. Cokes were reacted with CO2 or H2O in the temperature range of 1100 to 1500 °C. During the reaction, the compositional change of product gases were measured by quadruple mass spectrometry (QMS) for evaluating the gasification rate. Image analysis was carried out to measure the porosity according to the distance from the coke surface. The porosity at the surface of coke gasified with CO2 indicated low values due to its low reactivity, which resulted in the intraparticle reaction to diffuse into the pores at low temperatures while the coke gasified with H2O showed the tendency to react with the coke at the surface. This difference in the reaction behavior can be explained by Thiele modulus. Furthermore, fine powder formation and tensile strength were measured to evaluate macrostrength of cokes. According to the results, the different reaction mode caused an obvious difference ...

Steam reforming of ethanol over electrically-heated anodic aluminum catalysts for hydrogen production

Technical development of fuel cell systems that are fueled by renewably produced bioethanol is required. In this research hydrogen is generated from a low-concentration ethanol solution using a steam reforming reaction and a nickel anodic-alumina catalyst (Ni/Al2O3) with the Ni catalyst providing high selectivity of hydrogen at low cost. However, catalyst deactivation is known to occur because of oxidation of metallic Ni, sintering of Ni particles, and especially coke deposition as the significant problem. Adding Ce to Ni/Al2O3 as a new co-catalyst reduces the amount of surface coke deposition, extending the durability of the catalyst, through the ability of Ce to store oxygen. In this work catalyst durability of more than 1022 h was achieved. Furthermore, this work has demonstrated catalyst durability can be increased. XRD analysis, EDS mapping and TPR analysis clarified the catalyst durability was improved because of the synergistic effect of a firmly fixed Ni layer connected to Ce on the catalyst surface.

Interfaces Between Coke, Slag, and Metal in the Tuyere Level of a Blast Furnace

An in-depth understanding about the reactions in the high-temperature zone of a blast furnace is significant to optimize both the current and future blast furnace process. The interfaces between coke, slag, and metal were observed using scanning electronic microscope with samples obtained from the tuyere level of a blast furnace. Two types of slag phases were identified, one originating from coke ash and the other from the bosh slag. Slag formed by coke ash was seen to cover the coke surface, which may hinder the reaction of coke with both gas and liquid iron. The reduction of FeO from the bosh slag (originated from the primary slag) occurs in the coke/slag interface with the reduced iron forming a metal layer surrounding the coke surface. The reduction of SiO2 occurs both in and outside the coke, and the reduced silicon reacts with iron to form iron silicide if the two species come into contact. Further study is proposed based on the results of this study.

Thermal and Element Analyses for Supercritical RP-3 Surface Coke Deposition under Stable and Vibration Conditions

A surface coke deposition mechanism on the supercritical aviation kerosene RP-3 was studied under stable and vibration conditions. The flowing RP-3 kerosene is pressurized to 5 MPa and heated from 400 to 723 K in a stainless tube (inner diameter, 1.8 mm; outer diameter, 2.2 mm; and length, 1800 mm) with a constant heat flux. The experimental mass flow rate is fixed at 3 g/s (1180 kg m–2 s–1), and the working fuel flows downward through the test tube. The 1 h stable, 1 h with 600 Hz vibration, and long duration with 566 Hz vibration tube jam experiments were performed. The two vibration frequencies are close to the main frequencies of the combustion chamber vibration when it works. Flow resistance, heat-transfer characteristics, coking amount, and component analysis were compared between stable and vibration conditions. The results indicate that vibration can affect the coking distribution much more uniformly and extend the tube working time. Also, vibration inhibits the exponential growth of flow resistan...

The promoting role of Ag in Ni-CeO2 catalyzed CH4-CO2 dry reforming reaction

The catalytic performance of Ag promoted Ni/CeO2 catalyst has been investigated in methane and carbon dioxide dry reforming reaction. The temperature-dependent catalytic activity and time-on-stream catalytic performance at 760°C under different feeding conditions have been explored. Pristine Ni/CeO2 is not stable as a result of coke deposition and surface reconstruction. In addition, co-feeding of H2 can adversely influence the long-term stability of Ni/CeO2. Ag severely reduces the intrinsic catalytic activity of Ni/CeO2 catalyst, while enhances the long-term stability by diminishing coke deposition. Ag is applicable as a promoter under various reaction conditions, from N2 diluted feedstock to H2 co-fed and carrier-gas free feedstock. Kinetic studies show that Ag elevates the activation energy from 91 to ca. 140kJ/mol by a loading of 0.3mol.%, excessive Ag loading does not affect activation energy. The role of Ag is to block step sites on Ni surface that is associated with carbon nucleation and growth, and to promote gasification of coke formed. Besides, Ag alters the type of coke formed over Ni surface from recalcitrant whisker/encapsulating carbon to easily gasifiable amorphous carbonaceous species.

Mechanism of Fe additive improving the activity stability of microzeolite-based Mo/HZSM-5 catalyst in non-oxidative methane dehydroaromatization at 1073 K under periodic CH4–H2switching modes

The catalytic stabilities of Fe-modified and -unmodified 5% Mo/HZSM-5 catalysts in non-oxidative methane dehydroaromatization were compared at 1073 K and three reaction/H2-regeneration cycle periods: 5 min CH4–5 min H2, 5 min CH4–10 min H2, and 5 min CH4–20 min H2. Fe addition proved capable of remarkably increasing the catalyst stability over the cycles of 5 min CH4–20 min H2 but was hardly effective over the cycles of 5 min CH4–5 min H2. On the other hand, SEM observation of all spent samples revealed that Fe addition causes a massive accumulation of carbon nanotubes under the latter cyclic condition but little in the former. Thus several sets of comparative tests were specially designed and performed to gain an insight into the role of Fe-catalyzed cyclic formation of carbon nanotubes in stabilizing the activity under the cyclic condition of 5 min CH4–20 min H2. The results further confirmed that at this condition, cyclic formation of carbon nanotubes enhances cyclic evolution of H2 and increases the H2 concentration of the system, which is thermodynamically beneficial for suppression of formation of the activity-deactivating surface coke. Finally, it was further confirmed that at least a 20 min H2 exposure is required to remove most of the carbon nanotubes and surface coke formed during a 5 min CH4 exposure and reactivate most of the Fe nanoparticles and make them available again for formation of catalytic carbon nanotubes with an enhanced H2 evolution, i.e., with a controlled formation of the surface coke in the next CH4 exposure.

高炉炉下部における溶鉄および溶融スラグの流下挙動

In-situ observations of the liquid high carbon iron (HCI) and slag flows in the packed coke bed was carried out by using high temperature X-ray fluoroscopy at 1773 K. Along with the observation, 2-dimensional multiphase computational simulations of the liquid HCI and slag flows in the coke bed was carried out to investigate the effect of the slag on the HCI flow in the coke bed. It is found that the liquid HCI or slag could not pass through the coke bed with the coke diameter of 3-5 mm, however, the HCI can pass through the same size coke bed if the HCI is contacted with the slag through the X-ray fluoroscopic observation and the computational flow simulation. When the HCI and slag contacted each other on the coke surface, the contact angle of the HCI with slag decreased and the initially non-wettable characteristic of the HCI changed to wettable one. On the other hand, the slag’s contact angle is increased and changed to non-wettable. Based on the experimental and simulated results, it is confirmed that the contact angle change due to the HCI-slag contact make it possible for the liquid HCI and slag to pass though the narrow coke slit that is small enough to prevent each liquid’s flow down if they are not contacted. Based on the capillary rise model, the driving force of the HCI penetration into the coke bed will be the energy reduction by extending area of the coke surface covered with the liquid HCI.

Syngas production via combined steam and carbon dioxide reforming of methane over Ni–Ce/MgAl2O4 catalysts with enhanced coke resistance

A Ni–Ce/MgAl2O4 catalyst was prepared by the co-impregnation method by adjusting the Ce/Ni ratio in a range of 0.0–1.0 for the combined steam and carbon dioxide reforming of methane (CSCRM). The characterization as to surface area, metal dispersion, NiO crystallite size as well as reduction temperature and basicity of prepared catalysts was analyzed by BET, H2-chemisroption, XRD, TPR and CO2-TPD. The used catalysts were collected to investigate the coke formation and surface characteristics through SEM, TGA, XPS and Raman analysis. The Ce addition to Ni/MgAl2O4 catalyst has significant effects on the NiO crystallite size, metal dispersion and reduction degree. The Ni–Ce/MgAl2O4 catalyst with the Ce/Ni ratio of 0.25 showed the smallest NiO crystallite size of 8.3nm and the highest metal dispersion of 4.91%. Meanwhile, in the Ni/MgAl2O4 (Ce/Ni=0) catalyst, the NiO crystallite size was found to be as large as 11.0nm and showed a low metal dispersion of 3.49%. The Ni–Ce/MgAl2O4 (Ce/Ni=0.25) catalyst shows the highest activity and coke resistance in CSCRM due to the improvement of metal dispersion, excellent reducibility as well as effective surface oxygen transfer as evidenced by XPS results.

Oxidative dehydrogenation of ethylbenzene to styrene over alumina: effect of calcination

Commercially available γ-Al2O3 was calcined at temperatures between 500 and 1200 °C and tested for its performance in the oxidative ethylbenzene dehydrogenation (ODH) over a wide range of industrially-relevant conditions. The original γ-Al2O3, as well as η- and α-Al2O3, were tested. A calcination temperature around 1000/1050 °C turned out to be optimal for the ODH performance. Upon calcination the number of acid sites (from 637 to 436 μmol g−1) and surface area (from 272 to 119 m2 g−1) decrease, whereas the acid site density increases (from 1.4 to 2.4 sites per nm2). Less coke, being the active catalyst, is formed during ODH on the Al-1000 sample compared to γ-Al2O3 (30.8 wt% vs. 21.6 wt%), but the coke surface coverage increases. Compared with γ-Al2O3, the EB conversion increased from 36% to 42% and the ST selectivity increased from 83% to 87%. For an optimal ST selectivity the catalyst should contain enough coke to attain full conversion of the limiting reactant oxygen. The reactivity of the coke is changed due to the higher density and strength of the Lewis acid sites that are formed by the high temperature calcination. The Al-1000 sample and all other investigated catalysts lost ODH activity with time on stream. The loss of selectivity towards more COX formation is directly correlated with the amount of coke.

CaC2 Production from Pulverized Coke and CaO at Low Temperatures—Reaction Mechanisms

CaC2 production with pulverized feeds was proven viable at temperatures about 400 °C lower than that required by the current electric arc technology (2100–2200 °C), which led to development of an autothermal process. For the purpose of reactor design, the reaction mechanism of coke (C) with CaO at temperatures up to 1750 °C is studied in a thermogravimetric analyzer (TGA) coupled with a mass spectrometer (MS). Results indicate that the reaction of C with CaO generally proceeds in three stages, starting at 1460 °C for CaC2 formation, followed by reaction of CaC2 with CaO and by decomposition of CaC2. The second stage is observable only at the complete consumption of C while the third is controlled by surface evaporation of Ca. Reaction behavior at the surface of coke and CaO particles is proposed, including the three-stage reactions and the role of CaC2–CaO eutectics, that promotes CaO diffusion and CaC2 production.

Effects of chromium ion on sulfur removal during pyrolysis and hydropyrolysis of coal

The effects of impregnated Cr3+ on sulfur removal during pyrolysis and hydropyrolysis of coal were investigated by loading CrCl3 into raw, demineralized and pyrite removed coal, respectively. The results indicate that Cr has no effect on the removal of pyrite. Cr affects the removal of total sulfur by forming Cr7S8 and affecting the removal of organic sulfur. Cr acts as the sulfur removing agent by promoting the decomposition of the unstable organic sulfur at low temperature. However, it behaves to be sulfur fixing agent between 400 and 700°C so as to inhibit the evolution of H2S, even in hydropyrolysis. With the increase of temperature from 700 to 1050°C, a certain ratio of Cr7S8 is converted into organic sulfur during pyrolysis; however, almost all the Cr7S8 is reduced into Cr at 1050°C during hydropyrolysis. And Cr significantly promotes the removal of organic sulfur at high temperature within reducing atmosphere. The XPS results indicate that the sulfur is enriched on coke surface by Cr, which is attributable to the formation of Cr7S8 as well as the transfer of organic sulfur from bulk to surface during pyrolysis and hydropyrolysis.

Wettability and interfacial phenomena investigations on high‐density polyethylene and petroleum coke

AbstractAn in‐depth wettability and interfacial phenomena investigation was carried out to study interactions between high density polyethylene (HDPE) and petroleum coke. The aim is to investigate the effect of temperature and contact times on possible interactions and adhesion characteristics for partially substituting coal‐tar pitch binder with waste polymers. Using a sessile drop arrangement, experimental assemblies consisting of ground HDPE and a petroleum coke substrate were heat treated in the temperature range of 150–350°C for 15–60 min. Contact angles between molten HDPE and petroleum coke surface and depth of penetration of HDPE into petroleum coke substrate were measured. The highest contact angle (131.5°) was observed at 250°C after 15 min. and lowest contact angle (30.9°) was observed at 350°C after 60 min. Highest penetration depth (75 μm) was observed at 350°C after 60 min and lowest penetration (13 μm) at 200°C after 15 min. Analysis of results showed that increasing time and temperature of heat treatment had a significant impact on the interactions of molten HDPE with petroleum coke. Longer residence time and higher temperatures increased the extent of melting of HDPE, which in turn resulted in improved wettability and deeper penetration into petroleum coke substrate. HDPE was found to bind and adhere strongly with petroleum coke. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Cover Picture: Competitive Reactions of Organophosphorus Radicals on Coke Surfaces (Chem. Eur. J. 43/2011)

Cover Picture: Competitive Reactions of Organophosphorus Radicals on Coke Surfaces (Chem. Eur. J. 43/2011)

Improving effect of Fe additive on the catalytic stability of Mo/HZSM-5 in the methane dehydroaromatization

The promotional effects of eight kinds of transition metal additives (0.5wt%) on the activity and stability of 5wt%Mo/HZSM-5 were screened at 1073K and 10,000mL/g/h in a continuous CH4 feed mode. Only Fe was observed to improve the activity stability. Subsequently, confirmation tests were performed with other three Fe-modified catalysts containing 0.3, 1.0 and 2.0wt% of Fe in the same continuous operation mode and also with the 0.5wt%Fe–5wt%Mo/HZSM-5 under periodic CH4–H2 switch operation for 1650min. It was confirmed that Fe indeed enhanced the stability of Mo/HZSM-5 catalyst. Then, TPO, TG and BET measurements and SEM observations were performed for almost all spent samples to gain insight into the promotion mechanism of Fe additive. The results revealed that over short time frames in the continuous CH4 feed mode the formation of Fe-induced carbon nanotubes is the origin of its promotional effect, while under the long-term periodic CH4–H2 switch operation the catalytic involvement of Fe in the surface coke removal during the H2 flow periods is the main cause of Fe-modified catalyst being much more stable than the unmodified Mo/HZSM-5 catalyst

Competitive Reactions of Organophosphorus Radicals on Coke Surfaces

The efficacy of organophosphorus radicals as anticoking agents was subjected to a computational study in which a representative set of radicals derived from industrially relevant organophosphorus additives was used to explore competitive reaction pathways on the graphene-like coke surface formed during thermal cracking. The aim was to investigate the nature of the competing reactions of different organophosphorus radicals on coke surfaces, and elucidate their mode of attack and inhibiting effect on the forming coke layer by use of contemporary computational methods. Density functional calculations on benzene and a larger polyaromatic hydrocarbon, namely, ovalene, showed that organophosphorus radicals have a high propensity to add to the periphery of the coke surface, inhibiting methyl radical induced hydrogen abstraction, which is known to be a key step in coke growth. Low addition barriers reported for a phosphatidyl radical suggest competitive aptitude against coke formation. Moreover, organophosphorus additives bearing aromatic substituents, which were shown to interact with the coke surface through dispersive π-π stacking interactions, are suggested to play a nontrivial role in hindering further stacking among coke surfaces. This may be the underlying rationale behind experimental observation of softer coke in the presence of organophosphorus radicals. The ultimate goal is to provide information that will be useful in building single-event microkinetic models. This study presents pertinent information on potential reactions that could be taken up in these models.

Combustion Kinetics of Heavy Oils in Porous Media

In this study, the kinetics of heavy crude-oil combustion in porous media are reported. Ramped temperature oxidation (RTO) tests with effluent gas analysis are conducted to probe in situ combustion (ISC) reaction kinetics along with isothermal coke formation experiments. The role of oxygen on coke formation reactions (i.e., fuel formation for ISC) is investigated using X-ray photoelectron spectroscopy (XPS) of intermediate reaction products. The XPS data is analyzed along with companion RTO experiments to obtain a simplified multistep reaction scheme. Synthetic cases illustrate the connection between a proposed reaction scheme for oil/matrix pairs and one-dimensional combustion front propagation. Analysis of experimental results illustrate that the reaction scheme is capable of reproducing experimental results including the basic trends in oxygen consumption and carbon oxides production for RTO experiments as a function of heating rate for both good and poor ISC candidates. The combination of XPS and RTO studies indicates that the quality (or reactivity) of coke formed during the process is a function of oxygen presence/absence. Coke formed in the presence of oxygen is significantly more reactive due to additional oxygen functional groups on the coke surface in comparison to coke formed under an inert atmosphere. Additionally, this work extends relatively easy to perform RTO tests as a screening tool for ISC performance.