Large Amount Of Coke Research Articles

A Review on Catalytic Co-Pyrolysis of Biomass and Plastics Waste as a Thermochemical Conversion to Produce Valuable Products

In order to satisfy the increasing need for renewable chemicals and fuels, it is important to replace petroleum-based products with alternative feedstocks. Lignocellulosic biomass is considered to be the most capable alternative source for producing sustainable biofuels. Catalytic co-pyrolysis (CCP) is a process that involves simultaneously pyrolyzing biomass and plastics to produce a combination of liquid and gaseous products, such as bio-oil and syngas. Catalysts are used to raise the reaction degree and the selectivity of the co-pyrolysis process, with the choice of catalyst dependent on the physico-chemical features of the feedstock. Catalytic pyrolysis is a useful method for producing high-quality biofuels directly from biomass, although it typically yields a modest amount of aromatic hydrocarbons (HCs) and a large amount of coke, even with highly effective catalysts. Adding a co-reactant high in hydrogen to the CCP process can significantly increase the yield of aromatics while reducing coke formation. The use of CCP can help to address the environmental issues related to waste plastic disposal and improve energy security. This review article thoroughly discusses the process and mechanism of catalytic co-pyrolysis, the influence of plastics on the process, and how the addition of plastics can improve the quality and output of bio-oil while reducing the production of oxygenated compounds and coke. The importance of various catalysts (such as biochar, activated carbon, and acid and base catalysts) in improving the production and quality of obtained products is also compared and discussed.

Experimental study on photothermocatalytic CO2 reforming of benzene

To improve the conversion efficiency and reduce the CO2 emissions associated with the reforming of biomass tar to syngas, photothermal catalysts were prepared in this study through various impregnation methods. Photothermocatalytic CO2 reforming (PTCR) of benzene as a tar model compound, was conducted using the prepared Ni/TiO2-Al2O3 catalysts. The results show that the introduction of TiO2 facilitates the conversion of NiO to Ni during the photothermal reaction, while the photocatalysis of TiO2 significantly enhances the photothermocatalytic activity of the Ni/Al2O3 catalysts at low temperatures. Moreover, the methodology for catalyst preparation involving the loading of NiO before TiO2 is also beneficial to catalyst performance. However, when the mass ratio of TiO2 to Al2O3 exceeds 1, the specific surface area, pore volume, and structural stability of the catalysts are reduced. The results of PTCR experiment show the following optimal Ni/TiO2-Al2O3 catalyst preparation parameters: 25% NiO content and a TiO2/Al2O3 ratio of 3:7; 450 °C calcination temperature and a nitrogen atmosphere. The maximum benzene conversion achieved through PTCR with the 0.25Ni/0.3Ti0.7Al(M2) catalyst is 88.2%. However, a large amount of coke is deposited onto the spent catalyst surface, contributing significantly to catalyst deactivation.

Mesoporous Silica SBA-15 Supported Pt–Ga Nanoalloys as an Active and Stable Catalyst for Propane Dehydrogenation

Propane dehydrogenation is one of the most admired technologies for propylene production. However, the development of an active and stable catalyst presents a significant challenge. In this study, Pt–Ga/SBA-15 catalysts were prepared via coimpregnation, followed by H2 reduction, and applied in propane dehydrogenation. The Pt–Ga/SBA-15 catalyst with a Ga/Pt molar ratio of 1 exhibited a high propane conversion of up to 60% and high selectivity toward propylene of 98.2% at 550 °C for 10 min, with a propane conversion of 51.6% and propylene selectivity of 99.5% after reaction for 25 h. The physicochemical properties characterized using N2 physisorption, XRD, TEM, XPS, CO chemisorption, and in situ CO–DRIFT spectroscopy reveal that the Pt–Ga alloy nanoparticles were formed on the SBA-15 support after direct reduction with H2. The study of coke formation via temperature-programmed oxidation showed that a large amount of coke was deposited over the support of spent Pt–Ga/SBA-15 catalyst, indicating coke mobility from the active sites to the supports and its contribution to catalyst stability. The activities of spent catalysts could be almost completely recovered via reduction regeneration, during which Pt–Ga alloy retains the original geometrical and electronic structure well. The dilution of Pt ensembles due to the addition of Ga, e.g., Pt–Ga alloy formation, plays an important role in enhancing the catalytic performance for propane dehydrogenation.

Development of Silicalite-1-encapsulated Ni nanoparticle catalyst from amorphous silica-coated Ni for dry reforming of methane: Achieving coke formation suppression and high thermal stability

Dry reforming of methane (DRM) is an important reaction for converting CO2 into synthesis gas (H2 + CO). Though Ni is one of the most promising catalysts, the agglomeration of Ni particles and the formation of coke on the catalyst proceed during DRM, resulting in rapid catalyst deactivation. Therefore, the development of Ni-based catalysts that exhibit high thermal stability and suppress coke formation is indispensable. The encapsulation structure of Ni nanoparticles in porous supports is reported to be effective for high DRM activities and the suppression of coke formation.Herein, we synthesized a Silicalite-1-encapsulated Ni catalyst (Ni@Silicalite-1) for DRM using amorphous silica-encapsulated Ni-oxide nanoparticles (NiOx@SiO2) as the Ni precursor, and the effect of physicochemical properties on DRM activities was investigated using Ni@Silicalite-1, Ni@SiO2 (NiOx@SiO2 after H2 reduction), and Ni/Silicalite-1 (impregnation). For Ni@Silicalite-1, Ni phyllosilicate was formed inside Silicalite-1 during the hydrothermal synthesis, and the encapsulation structure of 4.5-nm-sized Ni particles was realized by reducing Ni phyllosilicate to Ni particles inside the zeolite. Because the small Ni particles were stabilized in the porous supports, Ni@Silicalite-1 and Ni@SiO2 exhibited high and stable activity for DRM at 600 °C with negligible coke formation (6.6 and 8.2 mg-C/g-catalyst for Ni@Silicalite-1 and Ni@SiO2 respectively), whereas a large amount of coke was formed on Ni/Silicalite-1 (532 mg-C/g-catalyst). Ni@Silicalite-1 exhibited high and stable DRM activity throughout 24 h at 600 °C and GHSV = 108000 mL/(g-cat·h). Moreover, because Silicalite1 possessed high thermal stability, the high activity of Ni@Silicalite-1 was maintained throughout the 5 h of DRM at 850 °C, whereas the activity of Ni@SiO2 decreased because of the collapse of the pore structure of SiO2. Ni@Silicalite1 exhibited a higher conversion rate of methane (13.3 mol-CH4/(g-Ni·min) at 850 °C and GHSV = 1080000 mL/(g-cat·h)) than previously reported Ni-based catalysts.

Perovskite-derived cobalt-based catalyst for catalytic propane dehydrogenation

This paper describes the synthesis and application of γ-Al2O3 supported SmCoO3 perovskite-type oxide in the catalytic propane dehydrogenation to propene. Various techniques including X-ray diffraction (XRD), H2 temperature-programmed reduction (H2-TPR), transmission electron microscopy (TEM), thermogravimetric analysis (TG) and X-ray photoelectron spectra (XPS) were used to characterize the physico-chemical properties of SmCoO3/Al2O3 and derived Co-based catalyst. The characterization results reveal that the perovskite lattice confinement can lead to better dispersed cobalt oxide and restrain the reduction to metallic Co species. Under the high weight hourly space velocity (3 h−1), the propane conversion and propene selectivity of the reduced SmCoO3/Al2O3 catalyst were 25% and 94%, respectively, and obviously higher than those of the reduced SmCoO/Al2O3 catalyst used as a referential sample prepared by an incipient wetness impregnation method. A large amount of coke was formed over the used SmCoO/Al2O3 catalyst. Instead, the SmCoO3/Al2O3-derived Co-based catalyst can greatly reduce the amount of coke deposition. The superior catalytic performance and anti-coking ability of SmCoO3/Al2O3 catalyst are attributed to the formation of a large amount of well-dispersed surface Co2+ species, especially small CoO nanoparticles, and the absence of metallic Co species.

Development of heavy oil upgrading technologies in China

Abstract Heavy oils have high viscosity, density, and Conradson carbon residue and high contents of sulfur, nitrogen, oxygen, nickel, and vanadium, as well as asphaltenes, which can cause problems for producers, leading to catalyst deactivation and fouling and plugging of tubing, pipes, valves, and reactor flow lines. Heavy oil upgrading can be classified into carbon rejection and hydrogen addition processes, mainly including four technologies: (1) the fluid catalytic cracking (FCC) process, which catalytically converts heavy oil into light fractions, like liquid petroleum gas, naphtha, and light cycle oil; (2) the hydro-processing process, which catalytically converts heavy oil to high-quality feedstock for FCC and hydrocracking processes under the hydrogen atmosphere without coke formation; (3) the coking process, which thermally converts heavy oil into light liquid fractions and large amounts of coke; and (4) the solvent deasphalting process, which fractionates distillation resid to provide feedstock for residue FCC, such as the residue oil solvent extraction. This paper reviews the progress on basic research of heavy oil chemistry and processing technology developments in China. Heavy oils were comprehensively characterized by the supercritical fluid extraction and fractionation technology and high-resolution mass spectrometry. The FCC process for maximizing iso-paraffin, new residue hydroprocessing technologies, progress in coking process, and a new process – the Supercritical Fluid Selective Extraction Asphaltene Technology – were discussed. As an emerging and promising research area, molecular management techniques were prospected, as well as a new concept of coupling the SELEX-Asp with the conventional heavy oil upgrading processes.

Using forest area for carbon footprint analysis of typical steel enterprises in China

Steel industry is an important mainstay industry and key greenhouse gas emitter of China. Employing life cycle assessment method of cradle-to-gate and establishing material flow model for steel production processes, this paper analyzed carbon footprints of steel enterprises to reduce carbon emission efficiently. Taking the function of forest to capture carbon into account, carbon footprint was expressed as the forest area instead of carbon dioxide equivalent (CO2e). Taking five typical steel enterprises (J, A, T, N, B) in China as examples, the carbon footprint per ton of steel in each process was calculated and its influence factors were analyzed. Results show that (1) from the perspective of process, the carbon footprint of iron-making, in which a large amount of coke and coal is consumed, is the largest, followed by the process of coking and sintering; (2) analyzing the type of gas, CO2 contributes over 70% of the total carbon footprint in the whole production process; (3) the average carbon footprint per ton of steel was 0.325hm2/t. Among five companies, carbon footprints of company N were up to 0.342hm2/t, while company B had the lowest carbon footprint, at only 0.291hm2/t. The gaps of carbon footprint are mainly due to geographical differences, energy consumption construction and product equipment and technology. The carbon footprint of enterprises was compared with the local carbon capacity, and analysis results show that the steel output and local forest areas could be significant factors determining whether the carbon emissions discharged by steel mills exceed the local carbon capacity and cause environment problems. According to analysis results, corresponding opinions and policies were proposed.

Influence of historical industrial epochs on pore water and partitioning profiles of polycyclic aromatic hydrocarbons and polychlorinated biphenyls in Oslo Harbor, Norway, sediment cores

Contaminant levels in urban harbor sediments vary with contaminant emission levels, sedimentation rates, and sediment resuspension processes such as propeller wash. Levels of polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) are decreasing in many urban harbors, as heavily contaminated sediments that accumulated during past decades are being buried by less-contaminated sediments. However, PAHs and PCBs remain a concern in areas where burial is slow or resuspension processes re-expose heavily contaminated older layers. Chronostratigraphic sediment core studies typically characterize contaminant level histories by using total sediment concentrations, C(sed) , and do not determine the freely dissolved porewater concentrations, C(pw) , which provide a better measure of bioavailability. Here both C(sed) and C(pw) profiles were established for PAHs and PCBs in dated sediment cores from diverse areas of Oslo Harbor, Norway. Sediment-porewater partitioning profiles were established alongside profiles of various sorbing carbonaceous phases, including total organic carbon (TOC), black carbon, and diverse carbonaceous geosorbents identified by petrographic analysis. Stratigraphic trends in carbonaceous phases and C(sed) could be associated with different industrial epochs: hydropower (post-1960, approximately), manufactured gas (∼1925-1960), coal (∼1910-1925), and early industry (∼1860-1910). Partitioning was highly variable and correlated best with the TOC. Hydropower-epoch sediments exhibit decreasing C(sed) with time and a relatively strong sorption capacity compared with the manufactured-gas epoch. Sediments from the manufactured-gas epoch exhibit substantial PAH and metal contamination, large amounts of coke and char, and a low sorption capacity. Reexposure of sediments of this epoch increases risks to local benthic species. Implications on natural recovery as a sediment management strategy are discussed.

Catalytic behavior of Ni/Zr xTi 1−xO 2 and the effect of SiO 2 doping in oxidative steam reforming of n-butane

Catalytic behaviors of TiO 2-, Zr 0.5Ti 0.5O 2-, and ZrO 2-supported Ni catalysts were investigated for oxidative steam reforming of n-C 4H 10 at 723 K. The composite oxide support, Zr 0.5Ti 0.5O 2, shows high specific surface area (136 m 2/g), leading to fine Ni particles. Thus, the Ni/Zr 0.5Ti 0.5O 2 catalyst exhibits higher and more stable activity than that exhibited by other catalysts. However, relatively large amounts of coke are deposited on the catalyst during reaction. Thus, to retard carbon deposition, the influence of SiO 2 additive was studied. Large amounts of SiO 2 additive (5 or 10 mol%) decrease initial activity; at 10 mol%, degradation is also induced by oxidation of Ni 0. However, small amounts of SiO 2 additive (1.5 mol%) effectively retard coking without lowering initial activity. The resultant Ni/Zr 0.5Ti 0.5O 2–SiO 2 (1.5 mol%) catalyst exhibits high and stable activity without coking.

Improving metal dusting resistance of. transition‐metals and Ni‐Cu alloys

AbstractThe present study focuses on a new technique for the prevention of metal dusting in carbonaceous gas environments at intermediate temperature. Preliminary laboratory metal dusting test was conducted for transition‐metals and Ni‐x%Cu binary alloys in a simulated 60%CO‐26%H2‐11.5%CO2‐2.5%H2O (in vol.%) gas mixture at 650°C for 100 h. The metal dusting caused no coke deposition on transition‐metals of Cu, Ag, and Pt, while those of Fe, Co, and Ni have a large amount of coke and lost mass. Whether or not coking behavior of Ni‐Cu binary alloys formed any oxide scales in the simulated gas environment depended on the Cu content. Specimens containing low Cu were entirely covered with coke and showed rough metal surfaces due to the degradation of metal. Alloys of 20% and more Cu, on the contrary, had no coke deposition and smooth metal surfaces, suggesting alloys with an adequate Cu do not react with CO in the gas mixture without an oxide scale barrier. Based on these results, we conclude that Cu does not protect by formation of the oxide scale but has a “Surfactant‐Mediated Suppression” against metal dusting. This effect can be explained in terms of atomistic interaction of CO with transition‐metal surfaces by electronic structure analyses. The concept can be also useful for the practical material design of Ni‐Cr base alloy with excellent metal dusting resistance.

CO<sub>2</sub> Reforming of Methane on Ni- and Co-based Intermetallic Compound Catalysts

Catalytic properties of Ni- and Co-based intermetallic compound (IMC) were assessed for the CO2 reforming of methane. Single-phase IMCs were prepared by arc-melting mixtures of stoichiometric amounts of nickel or cobalt and a second element. IMCs were crushed into particles and used as a catalyst for the CO2 reforming of methane at 1073 K. Ni- and Co-IMCs containing Ta, Hf and Sc showed higher initial activity than Ni and Co powders. Stability of these IMCs was examined for the reaction at 923 K because lower temperatures favor coke formation. Among Ni-IMCs, Ni7Hf2, NiHf and NiHf2 showed high stability for CO2 conversion. However, temperature programmed oxidation revealed that a relatively large amount of coke was formed on these catalysts. Filamentous carbon was observed by TEM on NiHf. High activity for the hydrogenation of ethene suggested that the surface of Ni-Hf IMCs is separated into Ni particles and Hf species. Among Co-IMCs, Co2Sc and CoHf2 showed stable CO2 conversion at 923 K. Low ethene hydrogenation activity suggested that the surface of these Co-IMCs consists of each IMC phase. CoHf2 formed less coke than Co2Sc. Only a slight decrease in CO2 conversion was observed on CoHf2 after 100 h of the reforming reaction at 923 K. CoHf2 is a good catalyst for the CO2 reforming of methane with high stability for reforming activity and low activity for coke formation.

Influence of the reduction temperature on catalytic activity of Co/TiO 2 (anatase-type) for high pressure dry reforming of methane

0.5 wt.% Co/TiO 2 was prepared by incipient wetness impregnation with Co(NO 3) 2·6H 2O and TiO 2, which contains only anatase as crystal structure. The influence of reduction temperature (973–1223 K) on the catalytic activity of the 0.5 wt.% Co/TiO 2 was investigated for the CH 4/CO 2 reaction under 2.0 MPa mainly at a space velocity (SV) of 6000 ml g −1 h −1. Co/TiO 2 reduced below 1123 K lost its activity completely at the beginning of the reaction. The results of TPO revealed that large amounts of coke (≧2.9 wt.% carbon for 24 h) were deposited on the catalysts during the CH 4/CO 2 reaction. On the other hand, Co/TiO 2 reduced at and above 1123 K kept relatively stable activity for 24 h and did not show significant amounts of deposited coke (≦0.25 wt.% carbon). The natures causing different catalytic behavior among the catalysts were discussed with the results of TEM, XRD, and TPR. In addition, slow deactivation of the Co/TiO 2 reduced at 1123 K, probably due to the oxidation of the metallic cobalt, was inhibited by the addition of small amount of ruthenium (Ru/Co=0.05) and it was found that the strong resistance to the coking of the Co/TiO 2 reduced at 1123 K was retained after the addition of ruthenium.

Coke and Byproduct Formation during 1,2-Dichloroethane Pyrolysis in a Laboratory Tubular Reactor

A laboratory quartz tube reactor apparatus was used to study coke and byproduct formation in 1,2-dichloroethane, also known as ethylene dichloride (EDC), pyrolysis. The effects of metal coupons, feed purity, and temperature on the amount of coke deposited and exit gas-phase compositions were analyzed. Coke formation on nickel, chromium, iron, and stainless steel metal coupons was investigated by scanning electron microscopy/energy-dispersive X-ray spectroscopy and ion-coupled plasma atomic adsorption spectroscopy. Based on scanning electron micrographs, different metals have little effect on the nature of coke formed, and it appears that coke is formed by tar droplet formation in the gas phase with subsequent impingement on surfaces. FeCl2 formation and migration along the reactor accompanied coke formation on the metal coupons. It was determined that the presence of metals coupons increases EDC conversion as well as coke formation. Two distinct types of coke are formed: hard coke is formed in the hot zone of the reactor and soft coke is formed at the exit. Increases in reaction temperature, CCl4 in the feed, and presence of FeCl2 all increase both types of coke formation, but hard coke in particular. A total of 0.3 wt % Cl2 in the feed resulted in 60% EDC conversion at 380 °C. This also reduced by more then half the total amount of hard coke formed, as compared to the lowest amount of hard coke formed by all other runs, but increased the total byproduct formation. EDC feed obtained from a commercial vinyl chloride monomer manufacturing plant produced 28% EDC conversion at 480 °C and large amounts of coke. Chloroprene was the only chemical species that strongly correlated with total coke formation.

LABORATORY STUDY OF REAL-TIME OPTICAL MICROSCOPE TRACKING OF THERMAL REACTION PROGRESS OF VACUUM RESIDUA II: CHEMICAL RELEVANCE OF PHYSICAL PROCESSES IN THERMAL REACTION SYSTEMS OF VACUUM RESIDUA

ABSTRACT It has been indicated from analyses of the vicissitude of chemical states and their comparisons with the occurring physical processes in the thermal reaction systems of vacuum residua that the first characteristic state point coincides with the induction period of coke formation, and the third characteristic state point, immediately after which a large amount of coke is yielded, manifests the critical point at which concentration of the neo-asphaltenes generated in-situ by the fast-reaction resins is high enough to approach its phase separation. The industrial implication of the second characteristic state point is not clear enough. It is accordingly pointed out, in combination with the conclusions drawn in the first part of the serial, that the real-time optical microscope tracking of the thermal reaction progress of vacuum residua based on the first and third characteristic state points is feasible on the laboratory scale for forecasting the sudden changes of the physical and/or chemical states of the thermal reaction systems of vacuum residua, and is expected to find applications in the industrial visbreaking process.

Carbon deposition on supported platinum particles

A combination of electron microscopy and thermogravimetric techniques have been used to investigate the characteristics of coke formation and the associated changes in platinum particle morphology in real and model reforming catalysts. Despite the fact that used commercial catalysts contained large amounts of coke, metal particles were clearly evident and appeared to reach an average size of 1.7 nm, indicative of only a limited degree of sintering during the reforming reaction. Decoking studies showed that the deposit was predominantly isotropic in nature and did not contain any filamentous or graphitic components. In situ electron microscopy studies performed on model supported platinum catalyst systems showed that upon reaction in a hydrocarbon environment, the metal particles were capable of hydrogasifying carbon in their immediate vicinity and during this process underwent a wetting and spreading action at the deposit interface which resulted in redispersion of the platinum. This phenomenon was limited to a narrow temperature range between 480 and 600°C, and was believed to be a key factor in the maintenance of the small metal particle size during the reforming reaction.

Regeneration of the finely dispersed aluminum-cobalt-molybdenum catalyst used for hydrocracking in a fluid bed

1. The conditions suited for desorption from and regeneration of an aluminum-cobalt-molybdenum catalyst covered with a large amount of coke have been determined in a pilot equipment. 2. A rate of catalyst regeneration equal to 20 kg/ton · h is recommended. 3. It has been proved that the catalyst can be regenerated with a gasair mixture.