Coke Components Research Articles

Evaluation of component interface quality in 3D micro-CT images of metallurgical coke

Metallurgical coke is a crucial component in the production of steel worldwide. It is a porous composite material, created by conversion of metallurgical coal in a coke oven. A key property of metallurgical coke is its strength, and there is evidence that poor interface quality between the two key components of coke can have deleterious effect on coke strength. Here we create small samples of coke and image them using high resolution 3D micro-CT, with pixel size of approximately \(8\,\mu\)m. We use a Gabor filter, combined with morphology techniques to isolate the different components in the samples. We then develop a measure, called excess porosity to quantify the quality of the interfaces between components. This measure enables us to highlight problem interactions between components.

A Mechanistic Model on Catalyst Deactivation by Coke Formation in a CSTR Reactor

A mechanistic model on catalyst deactivation by coke formation in a continuous stirred tank reactor (CSTR) has been developed in the paper. Catalyst deactivation by coke formation was treated as a surface reaction. Four reaction mechanisms representing coke formation through different routes were proposed. The evolved system of ordinary differential equations (ODEs) was solved numerically using MATLAB. This approach was validated by applying it to the skeletal isomerization of 1-pentene over ferrierite. Simulation results were compared qualitatively to those obtained from the literature. Simulation results indicated that coke formation is an extremely rapid process with fast formation of coke components on the strongest acid sites leading to final coke. The coke deposition is slower at higher residence times resulting in more stable product formation and weaker deactivation. The results obtained from this work revealed that the developed model is indeed able to successfully demonstrate the most essential features of catalyst deactivation by coke formation and are in agreement with the findings in the literature. Future work is aimed to extend the study to different reactors such as a plug flow reactor, in addition to analysis of the reaction system’s sensitivity to variables such as temperature and pressure.

Effects of furanic compounds from biomass pyrolysis on ketonization reaction: The role of oxygenated side groups

Ketonization of biomass-derived oxygenates is promising for sustainable production of platform chemicals, but the catalyst activity will be severely inhibited by furanic compounds. To investigate the mechanism of the inhibition effect, furanic compounds with different side functional groups were chosen for co-ketonization with propanoic acid over CeO2. Results from 12 h continuous reaction showed that conversion of propanoic acid changed slightly when furan was co-fed with propanoic acid, while decreased significantly from 100 % for sole propanoic acid feeding to <55 % when co-feeding with furfural and furfuralcohol. Therefore, the inhibition ability followed the order of furfural ≈ furfuralcohol ≫ furan, which agreed well with the coke yield on the spent catalysts (51 %, 47 %, and 22 %, respectively). DFT calculation indicated that furfural and furfuralcohol, with the adsorption energy of 17–19 kJ·mol−1, were much easier to adsorb on the catalyst than furan (11 kJ·mol−1). However, the lack of α-H of these furanic compounds led to their conversion into aromatic coke components. It is evidenced that the oxygenated side groups, rather than the furan ring, are responsible for the inhibition effect. Successive ketonization-combustion-ketonization tests revealed that simple air calcination can hardly recover the activity of the spent CeO2. This investigation gives new insights into the inhibitory impact of furans on the ketonization activity.

Coking and Deactivation Behavior of Ba–La-Modified Alumina in the Aldol Condensation of Methyl Acetate with Formaldehyde: Effect of the Reactant Composition

Catalyst deactivation caused by coking has always been a concern in the aldol condensation reaction. In this work, Ba–La-modified alumina has been characterized and tested as a catalyst in the vapor-phase aldol condensation process. The coke formation, acid–base properties, and deactivation behavior of the spent catalysts were studied through a series of characterization techniques: N2 adsorption–desorption, pyridine FT-IR, TG-DTA, TPO-MS, as well as NH3, CO2-TPD, and UV Raman spectroscopy. It was found that the main components of coke are polycyclic aromatic hydrocarbons, which can be removed by high-temperature roasting under an air atmosphere. The overactivation of formaldehyde accelerates the rate of coke deposition and ultimately aggravates the decrease in the stability of the catalyst. Furthermore, adding a proper amount of methanol to the reactants can greatly inhibit the hydrolysis of esters and improve the selectivity of the catalyst for the target reaction. Under the optimum reaction condition of Ma/FA/CH3OH = 6:2:8, the pairs of medium acidic and weakly basic sites enable Ba–La/Al2O3 to achieve the highest yield of methyl acrylate.

Simultaneous pretreatment and catalytic conversion of polyolefins into hydrocarbon fuels over acidic zeolite catalysts

The effect of pre-degradation treatment in catalytic pyrolysis of polymer was assessed using thermogravimetric analysis (TGA) and pyrolysis reactor experiments of different polymers on various catalysts. Intimate contact between the polymer and catalyst was achieved using physical, mechanical and thermal treatments. The results from the TGA analysis show that pre-degradation treatment has greatly improved the performance of the catalyst attaining maximum degradation at lower temperature. Pre-degradation treatment had increased the liquid yield and lowered the coke yield at various extents depending on the catalyst structure and acidity. The ZSM-5 catalyst with high Si/Al ratio showed maximum amount of (C5–C9) and ZSM-5 with lower Si/Al ratio has maximum percentage of (C14–C20). Based on the performance of the pre-degradation treatment methods, normal mixing produced the maximum amount of lighter fractions and therefore pre-degradation treatment can serve to enhance the gasoline fraction while the diesel fraction can be optimised using the co-pressing method, where polymer and catalyst particles were thoroughly mixed and co-pressed together into mixed particles. Coke characterisation showed coke formed by linear low density polyethylene contained more volatile coke components while polypropylene coke had higher percentage of hard coke. ZSM-5 had lower retention of coke components with volatile coke precursors. The volatility of the coke increases while coke concentration and decreases as the catalyst amount decreases. Pre-degradation treatment facilitated the formation of soft coke components that are easy to remove in inert atmosphere.

Catalytic degradation of linear low-density polyethylene over HY-zeolite via pre-degradation method

The catalytic degradation of linear low-density (lldPE) polyethylene over HY-zeolite catalyst was studied in a semi-batch reactor. One of the important problems encountered during catalytic pyrolysis of macromolecules is the contact with the catalyst, which is known to affect the product distribution and the quality of the coke formed. A pre-degradation procedure was introduced to achieve efficient contact between the LLDPE macromolecules and the catalyst. The influence of the pre-degradation to the reaction conditions including holding time, temperature, polymer to catalyst ratio and flow rate of carrier gas was examined. Moreover, the pre-degradation results were compared with the results obtained using normal mixing procedure. The results obtained showed that, pre-degradation promotes the liquid fraction by a factor of more than one-fold increase at the expense of the gas fraction and the coke yield. The optimal liquid fraction with pre-degradation was obtained at low reaction temperature and catalyst amount respectively, i.e. high polymer to catalyst ratio, making it economically viable method for the degradation of lldPE.The coke content was analysed using TGA in nitrogen atmosphere to remove the soft coke and then in air isothermally at the final temperature to burn the hard coke. The TGA results of the coked sample show less concentration of coke components on the catalyst using the pre-degradation method as compared to the normal mixing which shows high concentration of coke components especially at low reaction temperature. Moreover, the majority of the coke components produced using the pre-degradation method were soft coke, making it more efficient for the re-usability of the catalyst.The liquid samples collected were analysed using gas chromatography and the products distribution were presented in the form of boiling point distribution curves. The bulk of the liquid products produced were lighter fractions with a peak around the gasoline range.

Thermal desorption and characterization of carbonaceous deposits in Mo/HZSM-5 catalyst

Mo/HZSM-5 is the most active catalyst for dehydroaromatization of methane to benzene reaction. In this process, coking is the major problem to develop technically and economically successful process, as the catalyst gets deactivated due to blocking of active sites, pores and cavities, resulting in site poisoning. Hence, detailed information on the nature of the coke, its structure and composition are important factors to understand the performance of the catalyst. In the present paper, we present characterization of carbonaceous deposits formed on the surface of Mo/HZSM-5 catalyst using multi analytical techniques such as TDS-GC–MS, TGA, CHN and TEM. Investigated the structures of soft coke species using N2, and H2 temperature programmed desorption by applying in-house designed micro reactor for coke desorption from spent catalyst, followed by detailed composition analysis by TDS-GC–MS technique. The thermal desorption GC–MS method has advantages over the existing solvent extraction methods, in terms of sensitivity, overall analysis time and sample quantity requirements for complete studies. Additionally, this setup provides flexibility to understand the regeneration mechanism of catalyst under various environment and temperature conditions. The new in-house setup has given useful insights into structures of coke components and possible regeneration protocols.

Operando UV-Raman study of the methanol to olefins reaction over SAPO-34: Spatiotemporal evolution monitored by different reactor approaches

A molecular understanding of coke formation during the methanol to olefins (MTO) reaction is of great importance in order to adopt strategies that can improve the lifetime of the catalyst. UV-Raman has proven to be a valuable characterization tool, because of the favorable resonance conditions achieved towards key coke components, e.g. aromatic and olefinic compounds. Still, the applicability of UV-Raman in MTO is limited by the high risk of inducing sample damage under the exposure to the intense UV excitation laser. This drawback has been addressed by specific experimental setups, exploiting the concept of sample movement under the laser beam during the measurement, so that the laser-sample interaction is minimized by averaging over a wider sample surface. In this work, the impact of two different experimental setups, both relying on sample movement, are evaluated for the operando investigation of the MTO reaction over a SAPO-34. While in one case the whole catalytic bed is moved (fluidized bed), in the other case the sample is pressed into a pellet and rotated. Due to the peculiar spatial evolution of the reaction zone during MTO in a fixed-bed reactor, each method provides valuable information, but at very different spatiotemporal scales.

Highly Efficient Dehydration of Glycerol to Acrolein Over Isomorphously Substituted Fe-MFI Zeolites

Gas phase dehydration of glycerol formerly in aqueous solution to acrolein was studied over iron MFI zeolites prepared by post-synthesis isomorphous substitution with different iron contents, Si/Al and substitution ratios. High Si/Al (60) ratios led to high conversion in presence of air and the insertion of iron in the zeolite framework greatly improved the catalytic performances by altering the amount and the nature of the coke components reducing dramatically the deactivation. Over the most efficient sample, acrolein yield reached a stabilized value of 68% with an excellent selectivity (80%), which ranked this catalyst among the best for the selective conversion of crude glycerol.

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.

Experimental Study of Gas-Phase Pyrolysis Reaction of Benzene to Investigate the Early Stage of Coke Formation

Gas phase pyrolysis of benzene was performed at 1,123, 1,173, and 1,223 K using a flow type reactor to examine the mechanism of the initial stage of coke (poly-aromatic hydrocarbons; PAHs) formation. The pyrolysis products including hydrogen, tar, and coke were quantified as the function of benzene residence time using gas chromatography, gas chromatography-mass spectrometry, LDI-TOFMS, and elemental analysis to establish the carbon balance within 95 to 105% for all of the experiments. Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR MS) was applied to determine individual components in coke. Main tar components quantified were biphenyl (C12H10), terphenyl isomers (C18H14), quaterphenyl isomers (C24H18), phenanthrene (C14H10), and triphenylene (C18H12). Phenanthrene was found to be formed by the H-abstraction-C2H2-addition (HACA) mechanism and the other components were judged to be formed by the phenyl addition (PA) and the phenyl addition/cyclization (PAC) mechanisms. One of the smallest molecules identified within the coke was dibenzo[fg,op]naphthacene (C24H14) that is formed from triphenylene by the PAC mechanism. Larger molecules formed by the PAC mechanism and the HACA mechanism were also identified as coke components at the initial stage of pyrolysis. The phenyl addition to PAHs by the PAC mechanism and the HACA mechanism were judged to be main pathways to form larger PAHs. Main reaction mechanisms at the early stage of coke formation were suggested based on the detailed experimental data.

Characterization of Coke Deposition in the Catalytic Fast Pyrolysis of Biomass Derivates

Coke deposition on the zeolite catalysts in the conversion of furan (a main intermediate of biomass fast pyrolysis) is of serious concern for catalyst deactivation and product distribution. It is important to find out the nature and composition of coke on the spent ZSM-5 catalyst to study the coke-depositing behaviors. In this work, spent ZSM-5 catalysts obtained from furan catalytic conversion for chemicals at different reaction times and pyrolysis temperatures were characterized. The spent catalysts were first treated with hydrofluoric acid, and then the organics were extracted with CH2Cl2. The characterization of the origin coke and the treated insoluble coke were analyzed by the combination of some analytical techniques, including Fourier transform infrared spectroscopy (FTIR), high-performance liquid chromatography (HPLC), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and thermogravimetric analysis (TGA). The extracted organics were analyzed by HPLC to determine the chemical composition of the soluble coke. The results show that coke formation mainly involves condensation and rearrangement steps at a low reaction temperature (<200 °C). Coke components are polyaromatics, which formed by hydrogen transfer in addition to condensation and rearrangement steps at high temperatures (>200 °C). In the FTIR analysis, high aromaticity of coke species was obtained with increasing temperature, which indicates that the pyrolysis temperature plays a dominant role in the coke formation. TGA reveals that high temperature favors the formation of hard coke. The results enhance the understanding of coke formation and adjusting mechanism in biomass catalytic pyrolysis process.

Properties and CO2 reactivity of the inert and reactive maceral-derived components in cokes

The response of coke to gasification affects its degradation in the blast furnace. Coke gasification with carbon dioxide at high temperature is selective, with the inert maceral-derived component reacting more readily than the reactive maceral-derived component. Previous reactivity studies on carbonised vitrinite- and inertinite-rich fractions indicated that the amount of catalytic mineral phases control their reactivity. However, total Fe, Ca, K and Na from the ash chemistry were used as indicators of the abundance of catalytic material rather than the concentration of the catalytic mineral phases. Additionally, there is disagreement regarding the influence of micropore surface area and average carbon crystallite size on reactivity of the inert maceral-derived component and reactive maceral-derived component. Here we examine the influence of the abundance of the catalytic mineral phases on the reactivity of the inert maceral-derived component and reactive maceral-derived component, and also the influences of micropore surface area and average carbon crystallite size. Cokes from inertinite- and vitrinite-rich fractions prepared from four Australian bituminous coals were reacted with carbon dioxide at temperatures between 855 °C and 934 °C. The major factors that make inert maceral-derived component more reactive than reactive maceral-derived component at the initial stages were found to be the concentration of catalytic mineral phases and micropore surface area. The catalytic mineral phases identified in the coked inertinite- and vitrinite-rich fractions were metallic iron, pyrrhotite, troilite, wustite, magnetite and hematite. No Ca, K and Na catalytic mineral phases were identified in any of the studied cokes. The average crystallite height was not found to be a major factor controlling coke reactivity at the initial stages.

Deactivating species in the transformation of crude bio-oil with methanol into hydrocarbons on a HZSM-5 catalyst

A study has been carried out by using different techniques (TPO, FTIR, Raman, 13C NMR, GC/MS of the coke dissolved in CH2Cl2) on the nature of the coke deposited on a HZSM-5 catalyst modified with Ni in the transformation of the crude bio-oil obtained by flash pyrolysis of lignocellulosic biomass (pine sawdust) into hydrocarbons. The reaction system has two steps in-line. In the first one, the components of crude bio-oil derived from the pyrolysis of biomass lignin are polymerized at 400°C. In the second one, the remaining volatile oxygenates are transformed into hydrocarbons in a fluidized bed catalytic reactor at 450°C. The reaction has been carried out with different bio-oil/methanol mass ratios in the feed (from 100/0 to 0/100). Co-feeding methanol significantly attenuates coke deposition, and the nature of the coke components varies according to the bio-oil/methanol ratio in the feed. When bio-oil is co-fed, the coke deposited on the catalyst has a significant content of oxygenates and oxo-aromatics and consists of two fractions, identified by temperature programmed oxidation, corresponding to external and internal coke in the zeolite crystals. The fraction of external coke is soluble in CH2Cl2, with a high content of oxygenates and oxo-aromatics, and is generated by polymerization of products derived from biomass lignin pyrolysis activated by the zeolite acid sites. The fraction of coke retained within the zeolite crystals is partially insoluble and is formed by several routes: from the intermediates in the transformation of both methanol and bio-oil oxygenates into hydrocarbons; by evolution of the other coke fraction; from the hydrocarbons (with high aromatics content) in the reaction medium.

The role of H 2 in n-butane isomerization over Al-promoted sulfated zirconia catalyst

C, H, N-elemental analyzer, and NH 3-TPD, FTIR, XPS and reactor system are used to investigate the function of hydrogen in n-butane isomerization over the Al-promoted (3 mol% as Al 2O 3) sulfated zirconia catalyst (Al/SZ). Findings show relatively stable Al/SZ catalyst activity at 250 °C with H 2 introduction; however it decreases very quickly when N 2 replaces H 2. Deactivation is attributed to coke formation. The main components of coke are graphite and polymeric hydrocarbons. Activity can be recovered about 70% when H 2 is admitted again. Conversely, catalytic activity is lower but more stable in the presence of H 2 than in that of N 2 at 150 °C. Findings also show that activity cannot be restored if n-butane conversion is down to zero (i.e., the catalyst is completely deactivated). This study infers that H 2 reacts with coke at 250 °C, but inhibits isobutane formation and cannot react with coke at 150 °C. Catalytic activity restoration is via the reaction between coke and adsorbed hydrogen on the Brønsted acid sites. Although many researchers report that decayed sulfated zirconia regenerates by burning coke off with oxygen, this work finds that the fouled catalyst regenerates, though not completely, by hydrogen, provided it is not fully deactivated.

Crystalline Structure Transformation of Carbon Anodes during Gasification

The crystalline structure transformation of five carbon anodes during gasification in air and carbon dioxide was studied using quantitative X-ray diffraction (XRD) analysis and high-resolution transmission electron microscopy (HRTEM). XRD analysis and HRTEM observations confirmed that anodes have a highly ordered graphitic structure. The examination of partially gasified samples indicated that crystalline structure transformation occurred in two stages during gasification. The first stage involved the consumption of disorganized carbon matter in the initial 15% conversion. Oxygen was found to be more reactive toward disorganized carbon at this stage of the gasification process compared to carbon dioxide. Following this stage, as more carbon was consumed, especially with the removal of smaller crystallites, it was found that the crystalline structure became more ordered with increasing conversion levels. This is due to the merging of neighboring crystallites, required to maintain the minimum energy configuration. In addition, the interaction between the pitch and the coke components was found to be strongly linked to the initial coke structure. “Stress graphitization” occurred at the pitch−coke interface, which helps to enhance the structural development of the anodes.

Deactivation studies during 1-pentene reactions over HUSY zeolite

In this paper we report about catalyst deactivation during reactions of 1-pentene over acidic ultrastable Y zeolite in a fixed-bed reactor. The effects of reaction temperature and time-on-stream (TOS) on product distribution, conversion and coke formation are discussed. At this work various coke groups – coke precursors, hard coke as well as total coke amount – were followed with TOS. Furthermore, the effects of coking on 1-pentene reactions were also studied. Cracking and hydride transfer were the predominant reactions in the first minute of TOS which deactivated rapidly allowing isomerisation to become the main reaction afterwards. A steep increase of the amount of coke formed was observed initially which was in good correlation with the initial rapid deactivation. The hydrogen freed during this initial time from the formation of high a carbon-to-hydrogen (C/H) ratio coke components contributed to the formation of hydride transfer products.

Deactivation of zeolite catalysts for benzene oxidation to phenol

Abstract Coking and deactivating experiments were carried out in a fixed-bed reactor for benzene oxidation to phenol (BTOP). The catalyst used in this study was HZSM-5 (SiO 2 /Al 2 O 3 = 20) treated by high temperature steam at 700 °C. Then the catalysts undergoing different reaction time were analyzed and characterized. The amount of coke was measured by TG. The coke components were detected by infrared. At the same time, the main physics properties of the catalyst with coke deposition were characterized. The pores of the catalyst before and after coking were measured by N 2 adsorption at −196 °C. The amount of hexane and cyclohexane adsorption was measured by weight continuous flow. The acid sites of Bronsted and Lewis were characterized by pyridine adsorption-infrared measurements. Our results show that the deactivation of ZSM-5 in the BTOP reaction system is caused by the coke deposition in the mouth of pores and blocking the pores of the catalyst. It can also be found that the present process agrees with most coking processes over ZSM-5 caused by organic compounds, the Bronsted acid sites are the active sites of the coking.

Initial coke deposition on hydrotreating catalysts. Part 1. Changes in coke properties as a function of time on stream

Initial coke deposition on an industrial Mo/Al 2O 3 hydrodemetallization catalyst was studied as a function of operating time during hydrotreating of Kuwaiti atmospheric residue ( T; 380 °C, LHSV; 1 h −1). The primary objective of the study was to examine the nature of the initial coke and to determine coke's possible role in catalyst deactivation. The amount of coke on the catalyst increased rapidly and climbed up to 15 wt% within 12 h, but then, coke formation slowed down and reached about 20 wt% after 240 h. Used catalyst samples from experiments conducted at different time on stream periods (1, 3, 12, 48, 120 and 240 h) were subjected to temperature programmed oxidation and diffuse reflectance infrared Fourier transform spectroscopy to obtain information on the nature of the initial coke and changes in the coke properties with increasing run time. Additionally, the 1, 12, 48 and 120 h aged catalysts were extracted with tetrahydrofuran (THF). The results showed the presence of two types of coke on the catalyst, an easy removable soft coke and a more refractory surface coke. After 240 h of operation, a large fraction of the soft coke had been converted into refractory coke. The refractory coke contained substantial amounts of nitrogen and sulfur, whereas their concentration in soft coke was rather low. Nitrogen species, e.g. NH x , were found to deposit at the active metal sulfide crystallites, whereas coke was formed predominantly at the surface of the support. The THF extraction removed mainly heterocompounds and aliphatic coke components.

Organic chemistry of coke formation

The modes of formation of carbonaceous deposits (“coke”) during the transformation of organic compounds over acid and over bifunctional noble metal-acid catalysts are described. At low reaction temperatures, (<200°C) “coke” formation involves mainly condensation and rearrangement steps. Therefore, the deposits are not polyaromatic and their composition depends very much on the reactant. The retention of the “coke” molecules on the catalysts is mainly due to their strong adsorption and to their low volatility (gas-phase reactions) or to their low solubility (liquid-phase reactions). At high temperatures (>350°C), the coke components are polyaromatic. Their formation involves hydrogen transfer (acid catalysts) and dehydrogenation (bifunctional catalysts) steps in addition to condensation and rearrangement steps. On microporous catalysts, the retention of coke molecules is due to their steric blockage within the micropores.