Coke Rate Research Articles

Nonthermal Plasma‐Catalytic Dry Reforming of Methane in Parallel‐Plate Dielectric Barrier Discharge Reactor Using Mg‐Modified Ni Catalysts

The conversion of greenhouse gases, particularly CO2 and CH4, into syngas via dry reforming of methane (DRM) has effectively mitigated global warming and climate change issues. The research objectives are to enhance the DRM efficiency and reduce coke formation using Ni catalysts supported on Mg‐modified Al2O3 in parallel plate dielectric barrier discharge. Raising the Ni calcination temperature from (Ni/Mg–Al2O3‐500) to 700 °C (Ni/Mg–Al2O3‐700) enhances NiO reduction temperatures, thus diminishing their reducibility. This indicates that Ni/Mg–Al2O3‐700 exhibits stronger NiO–Al2O3 interaction, resulting in increased metal dispersion and decreased crystallite and particle sizes. As the Ni calcination temperature increases from 700 to 800 °C (Ni/Mg–Al2O3‐800) the intensity of the Ni0.8Mg0.11Al2O4 spinel structure is enhanced. The increased Ni calcination temperature enhances the metal‐support sintering processes and promotes the metal nanoparticle cluster formation, leading to increased particle and crystallite sizes, alongside decreased dispersion of Ni and Mg particles on the catalyst surface. The Ni/Mg–Al2O3‐700 exhibits lowest NiO reducibility, strongest NiO–Al2O3 interaction, highest metal dispersion, highest specific surface area, smallest particle, and crystallite sizes. Consequently, it attains the highest CH4 and CO2 conversions, H2 and CO selectivities, and energy efficiency, as well as the lowest coking rate, carbon deposition, carbon loss, and specific energy consumption.

Combination of Hollow Capsule Structure and Zn Uniform Load for the Conversion of Methanol to Aromatics over Zn/ZSM-5 Zeolites.

As an important nonoil route for acquiring aromatics, the highly efficient conversion of methanol to aromatics over Zn/ZSM-5 zeolites remains an ongoing challenge. In this work, we developed a uniform loading approach of zinc and further combined it with a hollow capsule structure to design the high-performance Zn/ZSM-5 catalyst. The electrostatic assembly among EDTA3-, n-butylamine+ and negative silica-alumina gel gave rise to an "Inorganic-Organic Hybrid Sphere" in form of Na(l+m+n+3x)-(y+z)·{[(SiO)4Al-]l/(SiO-)m(n-butylamine+)y(EDTA3-)x(n-butylamine+)z(SiO-)n, which further transformed into mesoporous aluminosilicates sphere (MASS) through calcination. The characteristic of abundant mesopore guaranteed MASS fantastic ability to evenly incorporate Zn ingredient inside, and the resultant Zn/MASS further served as a "hard template" for the direct synthesis of Hollow Zn/ZSM-5 capsules, rather than after impregnation. When tested in the methanol-to-aromatics (MTA) process, the direct synthesis method not only facilitated the homogeneous dispersion of the Zn ingredient, but also benefited for the generation of more (ZnOH)+ sites and strengthened their synergism with zeolite acid for the superior aromatics selectivity (50.63%). Meanwhile, the hollow capsule structure increased the contact time of MTA intermediate products with the Zn/ZSM-5 shell, and it increased the coke-admitting capacity and suppressed the coke rate, which maintained quite an excellent stability (131 h). Therefore, the above combination of hollow capsule structure and uniform load of Zn ingredient brings forward a wide prospect to develop zeolite materials with excellent properties in catalysis.

Preparation of a polyurethane‐coated expandable graphite and its flame retardant application in rigid polyurethane foams

AbstractExpandable graphite (EG) is widely used in rigid polyurethane (PU) foam (RPUF) as flame retardant, however, the mechanical properties of RPUF would deteriorate with the increase of its content. To alleviate this problem, PU‐coated EG (PUEG) is prepared by coating PU on the surface of EG via interface polymerization. PUEG is characterized by FTIR, XPS, and SEM. The results show that PUEG is successfully prepared. Compared with the RPUF add with the pure EG, the compressive strength and flame retardancy of the RPUF prepared by adding 15% PUEG have been improved to varying degrees. A 15% PUEG and 20% PUEG modify RPUFs obtained both UL‐94 V‐0 rating with LOI values of 29.7% and 31.2%, respectively. The improvement in the flame retardancy and compressive strength of RPUF is due to the good interfacial compatibility between the RPUF and PU on the surface of the EG and the increased coking rate of the EG, which accelerates the formation of the thermal barrier carbon layer. The preparation process of PUEG is simple and suitable for large‐scale production.

Favorable formation of needle-shaped NiAl2O4 phase over macroporous Ni/CexZr1-xO2–Al2O3 catalysts in one-pot preparation and coke-resistant catalytic performance in dry reforming of methane

In this study, we report the formation of needle-shaped NiAl2O4 via favorable interactions between Ni and Al species over macroporous Ni/CexZr1-xO2–Al2O3 catalysts for dry reforming of methane (DRM) and its remarkable improvement in the catalytic performance. The macroporous catalysts prepared by a one-pot (OP) method promote a favorable interaction between Ni and Al species that results in the formation of unique needle-shaped NiAl2O4 due to easy access to each other compared with that by incipient wetness impregnation. The NiAl2O4 phase in the calcined catalysts transforms into highly dispersed Ni and defective Al2O3 via the Ni exsolution in the reduction step. The presence of oxygen vacancies near Ni0 species facilitates the CO2 activation and enhances the catalyst stability over DRM. The optimized distribution of active sites with abundant defects over macroporous Ni/CexZr1-xO2-Al2O3 catalysts (OP) result in high conversions of CH4 and CO2 and a low coking rate in DRM.

Fluoride- and OSDA-free synthesis of ZSM-5 with controllable b-axis orientation: Insights into the role of medium alkalinity and seed induction

MFI-topology nanosheets with a b-axis-oriented structure are valuable catalysts in diffusion-controlled acid-catalyzed reactions. Therefore, b-axis-oriented ZSM-5 nanosheets were synthesized herein in a fluoride-free solution without using special additives and complex methods. The initial gel pH of mixed raw materials was adjusted to approximately 5–7 (weak acidity) to direct nanosheet structure formation. The target ZSM-5 zeolite with a b-axis-oriented structure was achieved through the synergistic effect between the involved gel pH and seed solution. The seed solution directed the formation of an MFI structure, and the low alkalinity of the gel limited crystal growth in the b plane, thereby affording b-axis-oriented thin sheets. The ratio of the lengths of the c and b axes of the obtained ZSM-5 could be effectively tuned by adjusting the pH of the initial gel. Compared with the nanosized hexagonal ZSM-5 sample synthesized in a strong-basic system, the as-synthesized b-axis-oriented ZSM-5 exhibited a lower coking rate and higher propylene yield during the considered 1-hexene cracking reaction.

Enhancement of non-thermal plasma-catalytic CO2 reforming of CH4 using Ni/Mg–Al2O3 catalysts in a parallel plate dielectric barrier discharge reactor

CO2 and CH4 are converted to syngas by dry reforming of methane (DRM) reaction. This research investigated the effects of the Mg promoter on Al2O3-supported Ni catalysts and Mg calcination temperature on the DRM performance in a parallel plate dielectric barrier discharge reactor. The Mg promoter played a crucial role in the DRM performance, as increasing the Mg calcination temperature from 700 °C to 800 °C significantly improved the DRM performance and catalyst properties, including increased specific surface area, decreased total acidity, reduced crystallite and particle sizes, and more uniform dispersion of the Ni nanoparticles. Under these conditions, the H2 and CO selectivity were 77.0 % and 70.7 %, the CH4 and CO2 conversion were 25.1 % and 20.6 %, and the energy efficiency was 8.4 %. In addition, the catalyst was associated with a lower coking rate (0.5 mg C/gcat h), a relatively low carbon deposit of 1.5 %, and a carbon loss of 2.8 %, possibly because the weak acidity hindered the Boudouard reaction and CH4 decomposition. However, increasing the Mg calcination temperature to 900 °C increased the total acidity and Ni particle size, decreasing H2 and CO selectivities and increasing carbon deposits on the catalyst surface.

An improved coking model for simulating reactive transport phenomena and coking behavior in sucrose hydrolysis

Levulinic acid (LA) holds great significance as a biomass platform chemical in the production of bio-aviation fuel and the utilization of bioenergy. Heterogeneous acid-catalyzed polysaccharide hydrolysis has emerged as a promising method for LA production. Understanding the coupling mechanisms of the physicochemical processes are fundamentally important to optimize the reaction system. In this work, a pore-scale multicomponent reactive transport model based on lattice Boltzmann method was developed to simulate the hydrolysis of sucrose. Considering the significant effect of active sites distribution density on coking formation, an improved coking model was proposed. Systematic investigations of reactive transport and coking behavior were conducted. Simulation results demonstrated that, initial sucrose concentration had a substantial impact on the coking rate of catalyst, when sucrose concentration exceeded 250 mmol/L, the catalyst became fully deactivated before complete hydrolysis of reactant occurred. Furthermore, a marginal benefit was found for the synergistic effect of protons in solution and solid catalysts on sucrose hydrolysis, when proton concentration reached the marginal value of 0.12 mol/L, further increases in proton concentration resulted in only marginal improvements in reaction efficiency. This work underscores the importance of the catalyst morphological character engineering and processes controlled for enhancing overall performance in LA production.

Process optimization, exergy analysis, and GHG emissions of ammonia production systems by gasification of high-sulfur petroleum coke with CO2 capture

High-sulfur petroleum coke is commonly used as a fuel because of its high carbon content and calorific value. Direct combustion of high-sulfur petroleum coke has the problem of emitting a lot of CO2 and sulfide. Gasification is an environmentally friendly way to utilize high-sulfur petroleum coke. Therefore, this study first established hydrogen production systems with CO2 capture through high-sulfur petroleum coke gasification. The hydrogen is then reacted with nitrogen from air separation unit for producing ammonia, which is easy to transport and store. After optimizing and analyzing the key parameters of the established models, exergy and life cycle GHG emissions analysis are carried out to evaluate the technical performance and environmental impact. In the system with an 85 % gasification conversion rate of petroleum coke, the ammonia production capacity, exergy efficiency, and GHG emissions are 2300 kmol/h, 45.39 %, and 1468 kg CO2-eq/t NH3. When the conversion rate is elevated by ten percentage points, the ammonia production and exergy efficiency are increased to 2664 kmol/h and 51.95 %, while the GHG emissions are only reduced by 85 kg CO2-eq/t NH3 since most of the CO2 produced by the system is captured. Improving the petroleum coke conversion rate can significantly increase the exergy efficiency of ammonia production system, but has little impact on reducing GHG emissions during the process.

Study on the Role of Additives in Calcination Desulfurization Process of High Sulfur Petroleum Coke

Due to the high sulfur content of high sulfur petroleum coke, sulfur-containing gas will be produced in the production process, reducing product quality and other problems, resulting in increased production costs and equipment corrosion. How to reduce the sulfur content of high sulfur petroleum coke is of great significance to improve the utilization rate of high sulfur petroleum coke and the sustainable development of related industries. In this paper, the desulfurization of high sulfur petroleum coke was carried out by using the additive-assisted high-temperature calcination method. It was found that the desulfurization effect of different kinds of desulfurization additives was different, among which MO1, MC2, MC1 desulfurization effect was better, and the desulfurization rate could reach 68%, 58%, 56%. After compounding the three desulfurizers, the desulfurization rate can be up to 75%, and then the influence of calcination temperature and time on the desulfurization rate was investigated. Finally, the physicochemical properties of petroleum coke before and after desulfurization were analyzed by X RD, FT-IR.

Disinfectant-Assisted Preparation of Hierarchical ZSM-5 Zeolite with Excellent Catalytic Stabilities in Propane Aromatization.

A series of quaternary ammonium or phosphonium salts were applied as zeolite growth modifiers in the synthesis of hierarchical ZSM-5 zeolite. The results showed that the use of methyltriphenylphosphonium bromide (MTBBP) could yield nano-sized hierarchical ZSM-5 zeolite with a "rice crust" morphology feature, which demonstrates a better catalytic performance than other disinfect candidates. It was confirmed that the addition of MTBBP did not cause discernable adverse effects on the microstructures or acidities of ZSM-5, but it led to the creation of abundant meso- to marco- pores as a result of aligned tiny particle aggregations. Moreover, the generation of the special morphology was believed to be a result of the coordination and competition between MTBBP and Na+ cations. The as-synthesized hierarchical zeolite was loaded with Zn and utilized in the propane aromatization reaction, which displayed a prolonged lifetime (1430 min vs. 290 min compared with conventional ZSM-5) and an enhanced total turnover number that is four folds of the traditional one, owing to the attenuated hydride transfer reaction and slow coking rate. This work provides a new method to alter the morphological properties of zeolites with low-cost disinfectants, which is of great potential for industrial applications.

Hydrogen production by biogas reforming using Ni/MgO-Al2O3 catalysts

Hydrogen has been pointed out as a highly potential energy source for the future due to its flexibility in production and utilization. In order to obtain hydrogen sustainably, technologies that use renewable raw materials must be developed. In this context, this work proposes hydrogen production from biogas reforming. Ni/MgO-Al2O3 catalysts, containing 20 wt% of NiO and 10 wt% of MgO, were prepared by three methodologies (wet impregnation, coprecipitation, and citrate) and compared with Ni/Al2O3. The catalyst prepared by impregnation exhibited the highest Ni dispersion and basicity, with the highest activity in methane reforming with CO2 (CO2/CH4 = 1) at temperatures between 600 and 800 °C. This catalyst presented high stability during 100 h of reaction at 700 °C (92 % of CH4 conversion and 95 % of CO2 conversion), with a lower coking rate than Ni/Al2O3. Coke was predominantly graphitic for all catalysts, but the catalyst prepared by coprecipitation showed a higher proportion of amorphous coke and the lowest coking rate.

Alkaline earth metal modified La-Fe based perovskite enhances hydroxyl radicals for efficient coke cleaning

The low conversion rate of coke during online coke cleaning is due to the stable structure of graphite carbon, which makes it difficult to react with steam. Therefore, there is an urgent need to design a catalyst for catalytic graphite carbon conversion to achieve efficient in situ coke cleaning. Alkaline earth metal Sr modified La-Fe based perovskite LSF-x (x = 0, 0.2, 0.4, 0.6, 0.8, 1) were prepared by hydrothermal method. DFT and experimental results indicate that doping Sr at the A-site reduces the adsorption energy barrier of water molecules, promotes the decomposition of water molecules to produce absorbed and free hydroxyl radicals, and thereby enhances the conversion of graphite carbon. At 900 °C, a catalytic coke conversion of 97.32% in the presence of La0.2Sr0.8FeO3 was achieved, which was 2.09 times the value without a catalyst. The research results provide a certain theoretical basis for catalytic heterogeneous reactions.

Evolution and process analysis of the hearth activity in hydrogen-rich blast furnace

Blast furnace (BF) hydrogen-rich smelting is an important way for the green and low-carbon development of iron and steel industry. The injection volume of hydrogen-rich gas is limited due to the need for hearth activity, which is related to the stable and smooth operation of BF. In this study, the change of coke properties after hydrogen-rich smelting was summarized, the detailed evolution process of hearth activity after hydrogen-rich smelting was analyzed. The results show that: the pores on the surface of coke are enlarged after hydrogen-rich smelting. The gasification rate of coke with H2O is significantly higher than that of CO2 due to the lower activation energy and smaller molecular diameters of H2O and H2. The interlayer spacing of coke decreases and the stacking height further increases rapidly, the degree of coke graphitization is the highest after hydrogen-rich smelting. The weakening of carbon anisotropy is the fundamental reason for the increase in the degree of graphitization of coke. The strong gasification reaction causes the coke to lose a lot of carbon, and its matrix becomes loose and incomplete, so the strength after reaction decreases sharply. The wetting model is established to analyze changes in wettability. The rough surface of coke improves the wettability between slag iron and coke at high temperature. The good wettability makes it easier for slag iron to adhere to the surface of coke. The smoothness of slag iron passing through coke is reduced, the retention amount of liquid slag iron in coke layer increases. It leads to a decrease in hearth activity, the stable and smooth operation of BF is difficult to guarantee. This is the main issue limiting the injection volume of hydrogen-rich gas in BF.

Numerical study of the feasibility of injecting CO2-containing off-gas in an ironmaking blast furnace

The injection of CO2-containing blast furnace top gas (BFTG) to replace reducing gas partially in an ironmaking blast furnace (BF) is a promising approach to achieve carbon neutralisation while potentially maintaining or improving BF performance. However, the feasible injection operating strategy for using CO2-containing BFTG and its effects on in-furnace phenomena are not well understood. In this study, a multi-fluid industrial-scale BF model with a tuyere injection submodel is developed to investigate the impacts of injecting CO2-containing BFTG at the BF tuyere on the in-furnace phenomena in terms of gas flow, temperature field, iron oxides distribution, and BF performance. The results show that: the maximum reducing gas replacement ratio by BFTG is ∼ 15 %, and a further increase leads to an unacceptable flame temperature. As more reducing gas is replaced by the BFTG, the start temperature of the intensified reduction for hematite and magnetite increases while those for wustite and iron decreases; the indirect reduction of iron oxides is improved in 1073–1273 K. The coke rate is increased by around 0.87 kg-coke/tHM with every 1 % reducing gas replaced by the BFTG. The top CO2 emission rate is decreased. This work provides a cost-effective tool to understand the flow-thermal-chemical behaviours inside a BF when CO2-containing gases are recycled in the BF ironmaking process.

Impact of chute cross-sectional shape on the ironmaking blast furnace performance: A numerical investigation

Rotating chutes play a critical role in determining burden distribution on the throat of blast furnaces, thereby influencing the overall ironmaking process. This study aims to explore the influence of chute cross-sectional shape at an industrial scale using a numerical approach. The simulation results demonstrate that the semicircular chute results a lower ore/coke ratio in the central area compared to the trapezoidal chute, while exhibiting a higher ratio at the periphery. Correspondingly, this leads to a lower productivity, higher coke rate, and increased pressure drop within the furnace. These effects can be attributed to the more coke is loaded in central region which has an elevated cohesive zone. Furthermore, with the chute angle for ore increasing, the blast furnace performance with the trapezoidal chute exhibits greater stability compared to that with the semicircular chute. This investigation provides valuable insights for selecting appropriate chute designs to enhance performance and efficiency.

Controlling the Coke Formation in Dehydrogenation of Propane by Adding Nickel to Supported Gallium Oxide

AbstractAtomic layer deposition was applied on mesoporous silica to synthesize a highly dispersed gallium oxide catalyst. This system was used as starting material to investigate different loadings of nickel in the dehydrogenation of propane under industrially relevant, Oleflex‐like conditions. The formation of NiGa alloys was confirmed by X‐ray diffraction analysis and electron microscopy. Surprisingly, the nanoalloys enhanced the selectivity towards C3H6 while decreasing the tendency for coking. Herein, in situ thermogravimetry, and measured mass fractions of carbon revealed that the coking rate was reduced by over 50 % compared to the pristine gallium oxide. Generally, the increased selectivity can be explained by the partial hydrogenation and reduction of the gallium oxide surface. The optimum temperature for the removal of deposited carbon was evaluated by a temperature programmed oxidation. Finally, the best‐performing Ni−GaOx catalyst was employed in a cycled experiment with periodic reaction and regeneration tests. After regeneration, the selected Ni−GaOx catalyst provided a higher yield of propylene compared to the unmodified gallium oxide.

Combustion characteristics of charcoal, semicoke, and pulverized coal in blast furnace and their impacts on reactor performance

Injecting new fuels like charcoal and semicoke into ironmaking blast furnaces (BF) helps reduce pulverized coal and coke consumption, leading to significant environmental and economic benefits. This paper comprehensively assesses the performance of blast furnace with the injection of charcoal, semicoke, or pulverized coal. For this purpose, a recently integrated BF model that simulates the whole BF below the burden surface in terms of the gas-solid-liquid-powder multiphase reacting flows is extended to simulate the application of charcoal and semicoke injection. The combustion characteristics of charcoal, semicoke, and pulverized coal in raceways are first revealed. Then, the effects of the combustion on the in-furnace states and overall BF performances are compared in detail. The results show that the overall BF performance in terms of gas flame temperature, coke rate, and hot metal temperature is susceptible to specific components in the injected fuels, including moisture content and fixed carbon ratio. A lower moisture and a higher fixed carbon ratio result in a higher gas flame temperature and fuel-coal replacement ratio and thus a lower coke rate. Overall, the charcoal and semicoke injection is feasible, however, subject to approximate pre-treatment. This integrated BF model can offer a cost-effective way to explore the injection of new fuels of various types to reduce carbon dioxide emissions.

Effects of CaO addition on the reactivity and reaction kinetics of coke

ABSTRACTIn recent years, researches have shown that highly reactive coke for blast furnace ironmaking not only reduces fuel ratio but also reduces carbon emissions. Therefore, the research on developing high reactivity coke has received unprecedented attention. In this work, CaO was added into coals with different degrees of metamorphism to caking coke to study the effect of CaO amount on the non-isothermal gasification reaction behavior of coke. Results showed that the reactivity is significantly improved as the mass of added calcium oxide accounting for less than 0.4% of the dry coal mass. However, CaO exerted little effect on the micro-strength and structural strength of coke. The analysis of Mercury intrusion porosimetry of coke samples demonstrates that the addition of CaO increased the porosity of coke, resulting in the contact area with CO2, leading further to an increase in coke reactivity. At different heating rates, as the amount of CaO added increased, both the initial reaction temperature and the corresponding temperature of the maximum reaction rate of the gasification from CO2 decreased little by little. The addition of CaO was increased from 0% to 0.6%, the activation energy of the reaction was decreased by 16.41 kJ/mol. The kinetic model of the gasification of coke by CO2 conforms to the unreacted shrinking core model. The reaction mechanism function is converted from f(α) = 3(1-α)2/3 to f(α) = 2(1-α)1/2 (α means carbon conversion ratio), indicating that the addition of CaO accelerates the dissolution rate of coke by CO2.

A Study on the Potential of Carbon Dioxide Utilization Through its Co‐Injection with Hydrogen into the Blast Furnace Tuyeres

The potential of CO2 utilization through its injection into blast furnace (BF) tuyeres is studied using the 1D steady‐state zonal model. Scenarios with the injection of CO2, hydrogen, and their co‐injection at various H2/CO2 mass ratios are analyzed. The impacts on factors affecting vertical temperature patterns and the position of the cohesive zone in the BF are identified. A life cycle assessment for several scenarios with various carbon emissions intensities of hydrogen production, carbon capture, and grid electricity generation is performed. Injection of CO2 without the addition of hydrogen increases the coke rate, reduces productivity, and increases direct CO2 emissions; however, thanks to producing top gas with higher calorific value, injection of CO2 may reduce the global warming potential (GWP) if the electric grid carbon intensity is above 654 kg‐CO2 kWh−1, while carbon capture is powered by green electricity. Although the injection of hydrogen alone would result in a more substantial reduction of GWP from the baseline than the injection of H2/CO2 mix at any mass ratio, considering the identified impacts on heat exchange and the position of the cohesive zone in the BF, co‐injection might be an enabling solution for the adoption of hydrogen injection.

Numerical Investigation of the Inner Profiles in Ironmaking Blast Furnace: Effect of the Ratio of Belly Diameter to Effective Height

The elaborate and appropriate design of blast furnace (BF) inner profile is indispensable. In practice, in this work, dumpiness, quantified by the ratio of belly diameter to effective height (RD–H), primarily determines the inner profile and significantly affects the BF performance. However, the effects of RD–H on BF operation are not investigated thoroughly, and an optimal range of RD–H is not yet proposed. In this work, a numerical study on this topic is presented to recommend an RD–H range for BF designers. This is achieved by using a recently developed 3D multi‐fluid BF process model based on a 380 m3 industrial BF. In the results, it is shown that both too slender and too dumpy BFs do not favor BF production. Excessively slender BF leads to a dramatic increase in gas pressure drop; however, the saving of coke or the improvement of productivity is insignificant. In contrast, excessively dumpy BF leads to a dramatic increase in coke rate and a significant decrease in productivity. Under the current conditions, the recommended dumpiness exists in the value of RD–H at around 0.35, where a low coke rate, low gas pressure drop, high productivity, and high thermal energy utilization are all ensured.