Coke Content Research Articles

Influence on Zhundong Coal Slagging and Contamination Characteristics of Oil Shale Semi-Coke Blending Combustion

Zhundong coal has the advantages of low ignition temperature and high burning rate etc,but the high content of alkali metal in coal leads to slagging and fouling problems in the combustion process. In order to improve the coal’s slagging and fouling problems and the combustion efficiency of oil shale semi coke, XRF was used to determine the ash content of the sample to show high sodium content in coal has reached 6.41% and high silicon, aluminum content in the oil shale semi coke and alkali metal content decreased obviously after mixing. By calculating the index of slagging and contamination showed that blending oil shale semi-coke makes slagging, contamination index of Zhundong coal decrease for higher, moderate and slight degree by severity, and semi-coke mixing proportion reached more than 30%, oil shale semi-coke greatly improve the coal contamination problem.

Influence of coke content on sintering process of chromium-containing vanadium-titanium magnetite

The sintering of chromium-containing vanadium-titanium magnetite using different coke contents was studied through the sintering pot tests, X-ray diffraction analysis and mineralogical phase analysis. Results showed that, as the coke content increased from 3.2% to 4.4%, the liquid phase and combustion zone thickness increased while the vertical sintering rate and ratio of sintered product decreased. In addition, the combustion ratio of exhaust gas also increased with increasing the coke content, indicating that combustion zone temperature also increased, and the excessive the coke content in the sintering process of vanadiumtitanium magnetite is harmful. As the coke content increased, the magnetite, silicates, and perovskite contents of the sintered ore increased while the contents of hematite and calcium ferrite of sintered ore decreased; drum strength decreased, and reduction degradation properties increased while reduction ability decreased. We found that the appropriate coke content for the sintering process is 3.6 wt%.

Biomass to hydrogen-rich gas via steam reforming of raw bio-oil over Ni/La2O3-αAl2O3 catalyst: Effect of space-time and steam-to-carbon ratio

Hydrogen-rich gas production by steam reforming (SR) of the raw bio-oil was studied in a continuous two-step system, with the first unit of thermal treatment (at 500 °C) used for retaining the pyrolytic lignin. The remaining volatile stream was reformed in the second unit (fluidized bed reactor) over a Ni/La2O3-αAl2O3 catalyst at 700 °C. The effect of space-time (0.04–0.38 gcatalysth/gbio-oil) and steam-to-carbon ratio (S/C) (1.5–6) on bio-oil conversion and product yields was assessed. Temperature programmed oxidation (TPO) was used to analyze the coke deposited on the Ni/La2O3-αAl2O3 catalyst. It was found that a raise in both the space-time and the S/C ratio contribute to increasing the H2 yield and to decreasing that of CO, CH4 and C2-C4 hydrocarbons. Catalyst deactivation is highly attenuated by raising space-time because of the lower deposition of encapsulating coke, which is directly related to the concentration of bio-oil oxygenates in the reaction medium. Space-time does not affect the formation of filamentous coke (less responsible for deactivation). The S/C ratio has less influence on total coke content than space time. For 700 °C, 0.38 gcatalysth/gbio-oil and S/C = 6, a hydrogen-rich gaseous stream (66 vol% H2) is obtained, with the H2 yield being 93% based on the bio-oil entering the catalytic reactor (or 87% based on the raw bio-oil fed into the two-step system), which decreases to 70% after 7 h time on stream as a consequence of the low catalyst deactivation.

Prediction of sinter yield and strength in iron ore sintering process by numerical simulation

Sinter yield and strength were predicted by the method of numerical simulation in this study. An unsteady two-dimensional mathematical model for the iron ore sintering process was developed by taking most of the significant physical phenomena and chemical reactions into consideration. By employing FLUENT software and C language programming via custom code, numerical simulation was carried out. A sinter pot test was performed and experimental data reasonably agreed with the numerical results, which validated the model. By analyzing temperature profile and melt fraction, parameters including peak temperature, residence time, cooling rate, melt formation heat and melt fraction were analyzed. Relationship between cooling rate and sinter strength was discussed as well as relationship between melt fraction and the yield of product sinter. Results indicated that sinter strength and yield could be predicted by simulation. The effects of different coke contents and additional heat supplement on sinter strength and yield were discussed. Results showed that increasing coke content improves sinter strength. Lower coke content will lead to increasing of under-melted sinter while higher coke content will lead to increasing of over-melted sinter and decreasing of the yield. Additional heat supplement technology can not only enhance sinter strength, but also promote sinter yield significantly.

Catalytic pyrolysis of sugarcane bagasse over cerium (rare earth) loaded HZSM-5 zeolite

The main objective of the present work is to investigate the influence of catalyst to biomass ratio (C:B) on pyrolysis sugarcane bagasse over cerium loaded Hydrogen exchanged Zeolite Socony Mobil-5 (HZSM-5, Si/Al = 23) catalyst via in-situ fixed bed reactor. HZSM-5 catalyst was used as a support with 1 wt.% of Ce as promoter loaded via incipient wetness impregnation method. The pyrolysis oil (PO) yield and coke yield were significantly affected by the use of Ce/HZSM-5 at various C:B ratio than the none catalytic pyrolysis, in which generating low PO yields (50.0 wt.%). The increasing Ce/HZSM-5 loading has an additional effect with respect to PO and coke yields. Among the tested C:B ratio, a catalyst to biomass ratio of 1:1 has demonstrated to be potential candidates in the catalytic pyrolysis of SB into a higher yield of condensable pyrolysis oil with lower coke contents.

Promotion of the vapors from biomass vacuum pyrolysis for biofuels under Non-thermal Plasma Synergistic Catalysis (NPSC) system

Abstract Non-thermal Plasma Synergistic Catalysis (NPSC) was firstly proposed and employed in the upgrading of biomass pyrolysis vapors for preparation of biofuels. The effects of the three-way catalysis (non-thermal plasma, HZSM-5 body and modified components) on the bio-oil upgrading performance and catalyst stability were comprehensively investigated. Bio-oil yields continued to decrease, but the physicochemical properties were further improved. The contents and compositions of hydrocarbons in bio-oil were increased and improved to varying degrees. The introduction of non-thermal plasma technology enhanced performance of cracking and deoxygenation for whole catalytic process. Besides, anti-coking performance of Zn/HZSM-5 was enhanced to a certain extent, but the multiple interactions significantly improved the cracking performance when Ti species introduced, increased the coke content, and an “isomorphism” phenomenon for two kinds of coke was emerged. In general, obtained biofuels still belonged to the hydrogen-deficient fuel, lower (H/C) eff of the vapors limited substantial improvement of the fuel grade.

Effect of methane co-feeding on product selectivity of catalytic pyrolysis of biomass

Co-feeding a hydrogen-rich material with biomass feedstock is an effective approach to enhance the pyrolysis process efficiency. In this research, the effect of methane (H/Ceff ratio of 4) co-feeding on product selectivity of catalytic pyrolysis of lignin and yellow poplar was studied at 600°C using HY and HZSM-5/metal-modified HZSM-5 as in-situ and ex-situ catalysts, respectively. Fe, Cu, Zn, and Mo with a 3wt% loading and Ni with 1, 3, and 5wt% loadings were incorporated into HZSM-5 by incipient wetness impregnation method. Compared to the nitrogen pyrolysis atmosphere, methane enhanced significantly the level of hydrocarbon (BTEX, benzene derivatives and polyaromatics) production from the cellulose and hemicellulose fractions of biomass. Lignin was selectively converted to alkylphenols in catalytic pyrolysis under methane atmosphere. The maximum hydrocarbon yield of 5.86wt% was obtained from catalytic pyrolysis of yellow poplar using HY (in-situ) and 1wt% Ni/HZSM-5 (ex-situ) as catalysts, mainly due to the effects of Ni on enhanced methane activation and an increase in the acid site density of HZSM-5. Meanwhile, the coke content of HZSM-5 was increased in both lignin and yellow poplar pyrolysis by replacing the pyrolysis atmosphere of nitrogen with methane.

Characterization of the location of coke deposited on spent HZSM-5 zeolite by special temperature-programmed oxidation and isothermal oxidation methods

The location of coke deposited on HZSM-5 zeolite catalyst during the supercritical catalytic cracking (400°C, 4.0MPa) of n-dodecane was systematically characterized by special temperature-programmed oxidation (TPO) and isothermal oxidation methods, and a steric hindrance model describing the interactions of the coke deposited on different locations was proposed to support the methods theoretically. Accord to the results, the sharp shoulder peak that appears on the TPO profile at high temperature range (>700°C) with low concentration of oxygen in the oxygen/nitrogen mixed carrier gas (≤2.0 Vol.%) can be ascribed to the characteristic peak representing the oxidation of the coke blocked in micropores, while the appearance of the CO peak during the isothermal oxidation at high temperature (≥550°C) using air as carrier gas provides another method to detect the coke blocked in micropores. Through checking whether the characteristic sharp shoulder peak of the TPO profile appears or not as expected according to the steric hindrance model during the re-oxidation of several samples with different coke content and spatial distribution, which were prepared by partial oxidation of the spent catalyst using TPO and isothermal oxidation methods, the special TPO and isothermal oxidation methods combined with their theoretical support of the steric hindrance model were proved to be self-consistent in the characterization of the location of coke. The location information of coke was further verified by the typical method of nitrogen adsorption-desorption analyses of a series of partially oxidized samples prepared by TPO method.

Catalytic conversion of biomass-derivates by in situ DRIFTS: Evolution of coke

Coke deposition in the catalytic fast pyrolysis of biomass includes active coke and inert coke, which promote or inhibit the formation of hydrocarbons. This study aims at the evolution of coke formation on various catalysts in the catalytic conversion of furan as an important intermediate from biomass fast pyrolysis. The functional groups on the surface of each catalyst at every moment were recorded by in situ diffuse reflectance Fourier transform infrared spectroscopy. The results indicated that the coke formation was closely related to the structure and acid property of the catalysts combined with catalytic tests in a fixed-bed reactor. Though dealumination only changed the acid distribution, it increased the hydrocarbon yield and introduced different chemical component of active coke. Because MCM-22 had a large internal space and small windows, its coke content should be quite large. However, the coke on MCM-22 did not show large molecules in this study because of the wide acid distribution, and similar active coke species with ZSM-5 were detected of polymethyl benzaldehyde. The coke content of HY was small because of large quantities of weak acid, although HY showed a significantly large internal space. The main components of active coke on HY and Hβ were diolefinic alcohols and polymethyl benzenes. The understanding of coke formation on various catalysts will provide guidelines for catalyst design, i.e., it is suggested that 3-dimensional structures such as MCM-22 with large supercages and small windows can be introduced into the original ZSM-5 system to form a core-shell catalyst to increase the hydrocarbon yields.

Effective vacuum residue upgrading using sacrificial nickel(II) dimethylglyoxime complex in supercritical methanol

The petroleum refining industry has become more profitable in recent years owing to the extraordinary value-adding processes of petroleum and petroleum-based products that generate a minimal amount of leftover. However, effectively utilizing vacuum residue (VR) to meet the rising demand for middle distillates in the near future remains a great challenge. The high-cost and low-surplus of hydrogen source in refineries complicate the application of existing slurry hydrocracking technologies at a practical scale. As such, supercritical methanol can serve as an effective and economically viable alternative to conventional VR upgrading techniques. Herein, an effective catalytic upgrading of VR using sacrificial nickel(II) dimethylglyoxime (Ni-DMG) complex in supercritical methanol is reported. The sacrificial Ni-DMG complex prevents low-temperature poisoning, which is typically caused by the heteroatoms present in asphaltenes, as well as catalyst coking. Under an optimized reaction condition of 400°C, 30.5–31.2MPa in supercritical methanol at a reaction time of 1h, a high amount of directly distillable fraction (72.2wt.%) was obtained using Ni-DMG in supercritical methanol. In the presence of low H2 pressure (initial pressure: 1MPa), the distillable fraction increased significantly to 92.2wt.% with an extremely low coke content (6.2wt.%). In addition, the upgraded oil was completely denitrogenated with noticeable desulfurization and significant demetallization activities (60.4%, 51.2%, and 85.7% reduction of nickel, iron, and vanadium, respectively).

Aqueous phase reforming of polyols from glucose degradation by reaction over Pt/alumina catalysts modified by Ni or Co

A comparison of Pt-M/Al2O3 catalysts (M = Ni, Co, none) for the aqueous phase reforming (APR) of different polyols that can be obtained from glucose degradation was made. A standard monometallic Pt/Al2O3 catalyst was prepared by incipient wetness impregnation (IWI) of platinum on an alumina support. The bimetallic catalysts had Ni or Co promoters incorporated by the urea matrix combustion method (UCM) and Pt by IWI technique (PtNi and PtCo catalysts).The catalysts were characterized by ICP/MS analysis, CO/chemisorption, TPR, XPS, SEM-EPMA and XRD. The catalytic activity was assessed with the tests of APR of an aqueous solution of 10 %wt of ethylene glycol (EG), glycerol (Gly) or sorbitol (Sorb), in a tubular fixed bed reactor at 498 K, 2.2 MPa, WHSV = 2.3–2.5 h−1, 3 cm3min-1 He carrier. Monitored variables were: conversion to carbon product in the gas phase, hydrogen and methane yield, selectivities, TOF and coke content on the spent catalysts.PtNi and PtCo catalysts had better hydrogen yield and stability during the experiments than the un-promoted Pt catalyst, (H2 yield = 24.4, 21.2 and 15% for PtNi, 17.9 and 15.1 for PtCo and 13.7, 10.8 and 7.5% for Pt after 8 h on stream in APR of EG, Gly or Sorb solution, respectively). Especially PtNi showed excellent yield and selectivity to hydrogen and a good stability, steadily generating hydrogen for long times. Co addition mainly helped in keeping low levels of coke and a low selectivity to methane.

Optimal design and operation of an industrial fluidized catalytic cracking reactor

Fluidized catalytic cracking (FCC) is regarded one of the most significant operations in the oil refining industries to convert feedstock (mainly vacuum gasoil) to valuable products (namely gasoline and diesel). The behavior of the fluidized catalytic cracking process is playing a main part on the overall benefits of refinery units and improving in process or control of fluidized catalytic cracking plants will result in exciting benefits economically. According to these highlights, this study is aimed to develop a new mathematical model for the FCC process taking into account the complex hydrodynamics of the reactor regenerator system with a new six lumps kinetic model for the riser. The mathematical model, simulation and optimization have done utilizing vacuum gas oil (VGO) as a feedstock and zeolite as a catalyst under the following operating conditions: temperature (733K, 783K, and 813K), weight hourly space velocity (5, 20 and 30h−1) and catalyst to oil ratio (4, 7 and 10). The best kinetic parameters of the relevant reactions are estimated using the optimization technique based on the experimental results taken from literature. The effect of operating condition (mainly, reaction temp (T), catalyst to oil ratio (CTO) and weight hourly space velocity (WHSV) on the product composition has also been discussed. The optimal kinetic parameters obtained from the pilot plant scale have been employed to develop an industrial FCC process, where optimal operating condition based on maximum conversion of VGO with minimum cost in addition to maximizing the octane number of gasoline (GLN), have been studied. Minimum coke content deposition the catalyst within the regenerator is also investigated here. New results (the highest conversion and octane number, and the lowest coke content) have obtained in comparison with those reported in the literature.

Near-Graphite Coke Deposit on Nano-HZSM-5 Aggregates for Methanol to Propylene and Butylene Reaction

Nanocrystal HZSM-5 zeolite aggregates with different SiO2/Al2O3 molar ratios were prepared under low temperature and were used to catalyze the conversion of methanol to propylene and butene. The coke location, coke content, and coke species deposited on HZSM-5 aggregates were investigated. The near-graphite carbon on the external surface of HZSM-5 zeolite (SiO2/Al2O3 molar ratio = 400) was distinguished by transmission electron microscopy (TEM) and energy dispersive spectrometer (EDS). The carbon distributions in the micropores and on the external surface of the spent HZSM-5 were revealed by thermogravimetric analysis (TGA) and Brunauer-Emmett-Teller (BET) results. Coke preferred to deposit in the mircopores of low SiO2/Al2O3 molar ratio samples (200, 300) with relatively uniform Al distribution, while coke also preferred to deposit on the external surface and in the intergranular spaces of high SiO2/Al2O3 molar ratio sample (400) with an obviously poor Al core and rich Al shell.

Kinetics of coke formation in the dimethyl ether-to-olefins process over SAPO-34 catalyst

A kinetic of coke formation during dimethyl ether (DME) conversion to light olefins over SAPO-34 was studied by the use of a thermogravimetry (TG) reactor. Coke formation experiments were conducted at the heating rate from 4K/min to 10K/min and DME partial pressure between 40.53kPa and 101.325kPa. The effects of reaction temperature, DME partial pressure and coke content of catalyst on coking rate were investigated. The results showed that high reaction temperature and DME partial pressure led to high coking rate. The coking rate increased with coke content during the early stage of the DME to olefins (DTO) reaction, indicating that the coking reaction was autocatalytic reaction. A mechanism was proposed for the coke formation and a kinetic equation was established to correlate the rate of coke formation with DME partial pressure, reaction temperature and coke content of catalyst. The activation energies of coke formation and adsorption of DME onto the active sites of catalyst surface in DTO reaction were found to be 99kJ/mol and 49kJ/mol, respectively.

The formation of NOx during sintering

ABSTRACTThe release regulations of nitrogen oxides (NOx) during the sintering process have been studied in this paper, and the factors of NOx release were systematically investigated, such as sinter temperature, coke content, and basicity. Results indicated that NOx produced from sintering includes NO, NO2, and N2O. Analysis on the material composition suggested that the NOx concentration was mainly related to the sinter temperature and the N content of the coke breeze. The material accouting of sintering mixture on N element indicated that 94.59% of NOx in sintering flue gas are fuel NOx .

Structure–deactivation relationships in zeolites during the methanol–to-hydrocarbons reaction: Complementary assessments of the coke content

Catalyst deactivation during the methanol-to-hydrocarbons (MTH) reaction was investigated using five different commercially prepared microporous catalysts, including Mordenite, ZSM-22, ZSM-5, zeolite Beta and SAPO-34. The reaction was carried out in a fixed bed reactor at a constant feed rate per gram of catalyst. Deactivated and partially deactivated catalysts were obtained at increasing reaction times. The whole of the catalyst beds was characterized using nitrogen adsorption, thermogravimetric analysis, a dissolution-extraction protocol, and UV-Raman spectroscopy, focusing primarily on methods suitable for the quantification of the coke. The results illustrate that topology is the dominant parameter that influences not only catalyst lifetime and product distribution, but also the nature of the species causing the deactivation. For all catalyst topologies, when the entire catalyst bed is examined together, the micropore volume and BET surface area decrease more rapidly than total coke from TGA increases at short reaction times. In the materials with the more restricted access to the internal voids, such as ZSM-22 and SAPO-34, the loss of activity is to a large extent due to species which are soluble in dichloromethane and give rise to distinct features in the Raman spectra. For the Mordenite and Beta catalysts, which have larger pores comprising three dimensional networks, and to some extent for the ZSM-5 catalyst employed, the accumulation of more coke species which are insoluble in dichloromethane, presumably on the external surface of the zeolite crystals, is observed. This is linked to the appearance of more pronounced D and G bands in the Raman spectra, indicative of extended carbon species.

Catalytic Performance of Ferrierite with Different Crystal Grain Sizes during Skeletal Isomerization of 1‐Butene

AbstractFerrierite (FER) zeolite with small crystal grain size was successfully prepared by a kind of hydrothermal synthesis with aging procedure using ethylenediamine (EDA) as template. The zeolite was characterized by a series of analyses. Aging procedure decreased the crystal grain sizes and no significant change was found in the ratio of Si/Al and acid sites. Eventually, FER zeolite with small crystal grain size ranging from 150nm to 800nm showed high isobutene selectivity and good stability during skeletal isomerization of 1‐butene. The reaction was divided into two stages because of the change in the conversion of 1‐butene. Coke deposited at reaction stage II primarily caused the deactivation of FER zeolite. FER Zeolite with small crystal grain led to not only a lower rate of coke deposition but also more coke content than FER zeolite with normal crystal grain size.

Effect of Metal Loading in NiMo/Al2O3 Catalysts on Maya Vacuum Residue Hydrocracking

Hydrocracking catalysts with large porosity need to be developed to treat heavy oil feedstocks rich in large molecular weight components such as asphaltenes and withstand deactivation due to coke formation. In this work, catalysts were prepared by impregnation of varying NiMo loadings on a mesoporous Al2O3 support. The effect of metal loading on the hydrocracking of a vacuum residue at three temperatures (400, 425, and 450 °C) was studied in a batch microbomb reactor. Catalysts were reutilized in a second reaction with fresh feed to assess their activity following the initial period where results are dominated by a large carbon deposition. The textural properties and the coke content on the spent catalysts were evaluated after both reactions. It was found that the reaction temperature had an important effect on the conversion of the fraction with a boiling point above 450 °C, whereas metal loading had minimal impact. On the other hand, metal loading had a significant effect on hydrodeasphaltenization (HDA...

Kinetic and regenerator modeling of the coke combustion in the moving bed MTP process

A moving bed regenerator concept is introduced to the regeneration of HZSM-5 catalyst in the methanol to propylene process. A coke combustion kinetic model has been obtained by considering the effect of coke content and oxygen pressure. Then a moving bed regenerator model is proposed, implying a radial cross flow between catalyst and regeneration gas. An industrial scale regeneration process has also been investigated. A “reversal phenomena” has been observed both in the temperature and coke distribution in the regenerator. A multi-zone and a flow direction changing operation mode have been advanced thus making the whole regeneration process more effective.

Application of Brazilian dolomites and mixed oxides as catalysts in tar removal system

Two different classes of catalysts, three dolomites with different origins and two Ni- based mixed oxides containing cerium or lanthanum, were used on tar removal by steam reforming. Mixed oxides presented higher toluene conversion than dolomites, which lost activity due to hydration and carbonation. Mixed oxides were quite active for toluene steam reforming, obtaining high conversions for long periods, 16h at 700°C and 70h at 800°C. Despite the good activity, the samples showed high coke content after reaction, probably caused by the low steam/carbon ratio. The coked catalyst can be completely regenerated by steam. Thermodynamic simulation of coking tendency showed that carbon is formed at low temperatures even at high steam/carbon ratios.