Insoluble Coke Research Articles

Effect of Residual Cuts on Deactivation of Hierarchical Y Zeolite-Based Catalysts during Co-Processing of Vacuum Gas Oil (VGO) with Atmospheric Residue (ATR)

The influence of residual cuts on the deactivation of hierarchical Y zeolite-based catalysts during the co-processing of vacuum gas oil (VGO) with atmospheric residue (ATR) was investigated. The experiments were conducted in a laboratory-scale MAT-type reactor. The conversion of VGO, ATR, and their 70:30 (mass basis) mixture was examined using two composite catalysts: Cat.Y.0.00 and Cat.Y.0.20. The operating conditions closely resembled those of the commercial catalytic cracking process (550 °C and contact times of 10 to 50 s). When ATR was processed individually, the conversion remained below 50 wt%. However, significant improvements in conversion rates were achieved and catalyst deactivation was mitigated when ATR was co-processed with VGO. Notably, the BET surface area and average mesopore volume were adversely impacted by ATR, which also led to the accumulation of high levels of metals and nitrogen on the spent catalyst, detrimentally affecting its acidic and structural properties. Moreover, substantial coke deposition occurred during ATR cracking. The soluble and insoluble coke analysis revealed H/C ratio values of up to 0.36, indicative of polycondensed coke structures with more than ten aromatic rings. The nature of the coke was confirmed through TPO and FTIR analyses. Interestingly, the CatY.0.20 catalyst exhibited less activity loss, retaining superior acid and structural properties. Co-processing Colombian atmospheric residue with ATR loadings of 30 wt% (higher than the typical 20 wt%) in catalysts formulated with hierarchical zeolites presents a promising alternative for commercial applications. This research opens avenues for optimizing catalytic cracking processes.

Elucidating metal composition–coking relationships and coke formation pathways during gas-phase oxydehydration of glycerol over clay mineral-supported Mo-V-O catalysts

Catalyst deactivation by carbon deposition (coking) remains a major obstacle in many important industrial processes, such as catalytic gas-phase oxydehydration of glycerol. Understanding the chemical nature and development of coke species during the time-on-stream (TOS) of the catalytic solids is therefore crucial for mitigating the extent of coking and in the design of regeneration process of the coked catalysts. In this study, multiple analytical techniques, including SEM, XRD, FTIR, Raman, GC-MS, XPS, and 13C solid-state MAS NMR were employed to gain insights into the coking behavior of acid-activated montmorillonite (HMMT) supported Mo-V-O catalysts with modulated metal ratios, along with soluble and insoluble coke compositions and their evolution over time. Insoluble coke was comprised of polycyclic aromatic compounds with 5 or more fused-benzene rings containing different types of oxygen-bonded groups, such as −OCH3, −COOH, −CHO, and −OH. The major chemical constituents of soluble coke were mononuclear aromatic derivatives (i.e., xylenes, 2,4-di-tert-butylphenol, and 1-hydroxycyclohexyl phenyl ketone) and paraffinic hydrocarbons with 12–18 carbon atoms. The latter coke species is thought to be formed via the deoxygenation of linear oligoglycerols. The insights presented in this study may aid in understanding the carbon deposition process during gas-phase oxydehydration of glycerol for improved design of supported Mo-V-O catalyst materials with high coking resistance.

Trace Compounds Confined in SAPO-34 and a Probable Evolution Route of Coke in the MTO Process.

Confined compounds in SAPO-34 cages are important to understand the activation and deactivation mechanisms of the methanol-to-olefin process. In this work, gas chromatography–mass spectrometry (GC-MS) chromatograms of CCl4-extracted samples of used SAPO-34 were denoised by subtracting signals of air compounds and stationary phase bleeding of the chromatographic column, which enhanced the identification of trace compounds. In addition to the generally noted methyl aromatics, this work also identified alkanes, cycloalkanes, alkyl (ethyl, propyl, and butyl) compounds, partially saturated compounds, and bridged compounds. These novel identified trace compounds favor the evolution route depiction of monocyclic, bicyclic, tricyclic, tetracyclic, and multicore hydrocarbons in the SAPO-34 cage. Confined compounds should grow via step-by-step alkylation, cyclization, and aromatization processes. C2+ side chains, especially C3+, favor the growth of rings. Alkyldihydroindenes should be key intermediates between monocyclic and bicyclic aromatics. Bridged soluble compounds provide evidence that insoluble coke is formed across cages in the SAPO-34 crystal.

Study of catalyst deactivation during 1,3-butanediol dehydration to produce butadiene

Catalyst deactivation and mechanism of coke formation during the gas phase dehydration of 1,3-butanediol were studied on solid acids of different nature: Al2O3, SiO2/Al2O3, HZSM5 and tungstophosphoric acid (TPA) supported on SiO2. All the catalysts deactivated on stream with a significant coke content ranged between 9% and 14% C. Fresh and spent catalysts as well as carbonaceous deposits were thoroughly characterized using different techniques such as N2 physisorption, FTIR spectroscopy, FTIR of adsorbed pyridine, DSC-TGA, GC-MS and MALDI-TOF MS (matrix-assisted laser desorption/ionization time of flight mass spectrometry). The IR spectra of spent and washed (after direct extraction with CH2Cl2) samples and the superficial soluble coke characterized by MALDI-TOF MS showed the different nature of coke formed in each catalyst with carbonaceous products of higher molecular weights on HZSM5 and TPA/SiO2 than on Al2O3 and SiO2/Al2O3. After catalyst dissolution using hydrofluoric acid and extraction with CH2Cl2 both total soluble and insoluble coke were analyzed. Insoluble coke was only detected on TPA/SiO2 and it was attributed to the strength of its Brønsted acid sites. GC-MS chromatograms of total soluble coke showed the presence of aromatic and polyromantic species, that were very alkylated in the case of HZSM5. Particularly, the well differentiated nature of coke on HZSM5 including alkylnaftalenes and alkylantracenes suggested the coke formation by a shape selectivity mechanism.

Catalytic properties and deactivation behavior of modified H-ZSM-5 in the conversion of methanol-to-aromatics

A comparative study on the effects of SiO2 modification and mesoporous structures on catalytic performances over ZSM-5 zeolites in MTA conversion both theoretically and experimentally was done. Experimental results showed that hierarchical pores increased the production of aromatics. However, DFT calculation proved that energy barriers for producing aromatics over mesoporous ZSM-5 were larger than that of parent ZSM-5 due to decreasing acid strength after alkali treatment which significantly influenced rate-determining step. Furthermore, diffusion behaviors of toluene were studied by Molecular Dynamics. Larger pores led to the improvement of diffusion behaviors over hierarchical ZSM-5 owing to the decrease of collision frequency between molecules. Therefore, the formation of aromatics was mainly determined by diffusion limitation over hierarchical ZSM-5. The lowest BTX selectivity was obtained over SiO2 deposited mesoporous ZSM-5 due to decreasing acid strength and blockage of pore mouth. Additionally, the deactivation of ZSM-5 serial catalysts in MTA was attributed the formation of insoluble coke. Moreover, the introduction of mesopores and silylation on external surface alleviated the deactivation of catalysts.

Behavior of coking and stable radicals formation during thermal reaction of an atmospheric residue

This work studies the thermal reaction of Maoming atmospheric residue at a temperature range 400–500 °C in sealed tube reactor. It is found that the CS2 insoluble (coke) is formed at 420 °C and above and it increases with time and temperature, which can be fitted with a combination of the second-order and autocatalytic kinetics. The loss of heteroatoms in the coke such as sulfur atom accompanied with the condensation of coke. The concentration, g value and linewidth of stable radicals in residue are measured by electron spin resonance (ESR) and discussed to explore the transformation of coke structure. The formation of stable radicals can be expressed by a combination of the two first-order kinetics including CS2 soluble (oil) cracking and coke condensation with activation energies of 168 and 98 kJ/mol, respectively. More than half of stable radicals exist in oil (or in the coke presented in oil) when the coke contents are no >3.4%, while about 90% of the total stable radicals can be found in the coke when coke contents are >8.0%. In addition, the variation of g value and linewidth of stable radicals in coke are also studied.

Reuse of Spent Hydrotreating Catalyst of the Middle Petroleum Fractions

Reuse of spent hydrodesulphurization (HDS) of middle petroleum fractions catalyst CoMo/γAl2O3 was accomplished via removal of coke and contaminants such as vanadium, Iron, Nickel, and sulfur. Three processes were adopted; extraction, leaching, decoking. Soluble and insoluble coke was removed. Leaching step used three different solvents (oxalic acid, ammonium peroxydisulfate and oxalic acid + H2O2) in separate in order to remove contaminant metals (V, S, Ni and Fe).
 The effect of soluble coke removal on leaching step was studied. It was found that the removal of soluble coke significantly enhances the leaching of contaminants and barely affected the removal of active metals (Co and Mo). It was found that the best route (sequence) was soluble coke extraction followed by contaminants leaching then decoking process and the best leaching solvent was oxalic acid. According to this determination, the removed contaminants were 79.9 % for sulfur, 13.69% for vanadium, 82.27 % for iron, and 76.34 % for nickel. The active components loss accompanied with this process were 5.08 % for cobalt and 6.88% for molybdenum. Leaching process conditions (leaching solvent concentration, temperature and leaching time) were studied to determine the best-operating conditions. The rejuvenated catalyst activity was examined by a pilot scale HDS unit of naphtha. Sulfur content removal of naphtha was found to be 85.56 % for single pass operation under typical operating conditions of refinery HDS unit of naphtha which are 1 ml/min feed flow rate, 200 H2/HC ratio, 32 bar operating pressure and 320 °C operating temperature.

Water inhibits the conversion and coking of olefins on SAPO-34

The inhibition effects of water on the conversion and coking of olefins on SAPO-34 were investigated on fixed bed reactor. Remarkable reduction effects of water on the conversion and coking of ethene, ethene+propene and ethene+1-butene were observed. The conversion and coking of propene and 1-butene were also inhibited, though less noticeable. The co-feeding of water strongly suppressed the formation of insoluble coke and had little effect on the formation of soluble coke. It is supposed that the conversion and coking of olefins is initiated with the oligomerization and alkylation of olefins which lead to the formation of long intermediates. Then these long molecules undergo cracking to form small species or cyclization and aromatization to form confined cokes. Water competes with olefins for the accessing of acidic sites and leads to desorption of olefins, which reduces the formation of long intermediates. Ethene can be easily desorbed while water is co-fed. The oligomerization and alkylation of ethene is suppressed greatly by water which reduces intermediates for the following cracking, cyclization and dehydro-aromatization, thus the conversion and coking of ethene-rich streams were remarkably reduced. The effect of water on the adsorption of propene and 1-butene is much weaker than that on the adsorption of ethene. Therefore, some inhibition effects of water on the conversion and coking of propene and 1-butene was observed, but much less significant than that of ethene. The role of water in MTO process can be well interpreted with the inhibition effects of water on further conversions and coking of olefins.

Coke evolution on mesoporous ZSM-5 during methanol to propylene reaction

Coke evolution during MTP reaction over mesoporous ZSM-5 zeolite was investigated at 480 °C in a fixed-bed reactor. Fresh and deactivated mesoporous ZSM-5 zeolites at different stages were characterized by TG, N2 adsorption-desorption, GC–MS, XRD, TEM as well as NH3-TPD. The characterization results showed the ‘S’ type curve of coke depositions with three stages along TOS. Internal coke was initially deposited in micropores of zeolite with initial soluble carbonaceous species identified as bulky alkylbenzenes such as tetraMBs and pentaMBs. Along TOS, the initial soluble carbonaceous species could grow into insoluble coke leading to rapid occupation in mesopores.

Solid Catalyst Alkylation of C2–C3 Olefins with Isobutane in the Presence of Hydrogen Using a Slurry Transport Reactor–Hydrocyclone–Regenerator System and PtSO4TiZr/SiO2 Catalyst: Part 2. Regeneration of Spent Catalysts in Pilot Plants and a Simulation of a Fluidized Bed Reactor

A continuous regeneration process was developed to treat spent PtTiZrSO4/SiO2 alkylation catalyst with hydrogen in a fluidized-bed reactor. Catalyst that alkylated isobutane with olefins (C2= and C3=) in a pilot plant accumulated soluble and insoluble coke on the surface in several passes through the system. It was regenerated on a small scale and in a pilot plant fluidized-bed reactor (FBR). Tests in semibatch reactors generated data to develop the apparent kinetic rate and the stoichiometry of the reaction. The information obtained in the pilot plant was used to determine fluid dynamic correlations, a new set of kinetic rate constants, the number of compartments in the dense phase, and the catalyst efficiency factor and to confirm the effects of operating variables. Simulations of the pilot plant and commercial size fluidized-bed reactor were performed using three fluid dynamic models, the kinetic rate equation, and the new fluid dynamic correlations. The effect of operating variables in alkylation cost...

Pine Wood Powder Treatment to B<sub>X</sub>H<sup>+</sup> Homogeneous Catalyst (H<sup>+</sup>/H<sub>2</sub>SO<sub>4</sub>) Supported on Its Aromatics’ and PNA’ Alkenes – Application in Black Citric Acid Polymer Synthesis

For a long time, many chemical reactions drew on catalysts, products used in smallest quantities compared to products-reagents, to accelerate their kinetics. In certain cases, one of the determining factors to improve these catalysts activities is the use of supports allowing dispersions and thereafter the effectiveness of its active sites.. It is the goal of our study, to increase the pine wood powders value like support of active acid H+ sites of sulphuric acid molecules by hydrogen bond connection with alkenes of aromatics and polynuclear aromatics which were pine wood components and their derivatives obtained after sulphuric acid solution (98%) treatment. Among these derivatives we quote water molecules formed during dehydration and esterification of wood components. Thus, we obtained homogeneous catalysts BXH+, (H+/H2SO4) supported on pine wood powder which we tested by a test reaction: citric acid dehydration to prop-1-ene 1, 2, 3 acid- tricarboxylic acid. Also, the active acid sites (H+/H2SO4) contents and alkenes on BXH+ catalysts were quantified by measuring out respectively with NaOH 0.05N and hydrofluoric acid (HF). This last measuring out enabled us to evaluate the nature of the aromatics and polynuclear aromatics which were the real supports contained in pine wood. At the end, we used these BXH+ synthesized catalysts to catalyze the citric acid black polymer synthesis (PN). The soluble coke and insoluble coke in polar solvent dichloromethane and non-polar solvent hexane of citric acid black polymer synthesized by each catalyst were quantified.

The Molecular Structure and Morphology of Insoluble Coke in SAPO‐34 Catalyst

AbstractThe insoluble coke in SAPO‐34 catalyst is investigated by mass spectrometry and scanning electron microscopy (SEM). Results indicate the insoluble coke in SAPO‐34 catalyst is a reticulate structure composed of carbon‐chain bridged cycloalkanes and aromatics. This reticulate structure located near the surface of SAPO‐34 crystal. It is proposed that the continue alkylation and cyclization of cycloalkanes or aromatics with olefins is the main cause of the coke formation. Moreover, the coke preformed by olefins in downstream catalyst bed reduces the active region for methanol conversion.

Conversion and coking of olefins on SAPO-34

Olefins' reactions lead to the formation of soluble and insoluble coke at the near-surface region of a SAPO-34 crystal.

Dual coke deactivation pathways during the catalytic cracking of raw bio-oil and vacuum gasoil in FCC conditions

Coke deposition pathways have been studied during the fluid catalytic cracking of bio-oil, vacuum gasoil (VGO) and a blend of the previous two (80wt% VGO and 20wt% bio-oil), under realistic riser conditions of the fluid catalytic cracking (FCC) unit, using a commercial catalyst at 500°C and contact times of 1.5–10s. Amount and composition of soluble and insoluble coke in dichloromethane have been analyzed using a set of techniques (TPO, FTIR, 13C NMR, XPS, Raman, GC–MS and MALDI-TOF MS, among others). The relationship of coke deposition with its composition and the reaction medium has allowed us to set two pathways of coke formation: (i) heavy hydrocarbon pathway tend to form ordered polycondensed aromatic nanostructures; whereas (ii) oxygenate pathway tend to form a lighter fraction of coke containing oxygen, less ordered and more aliphatic coke. A synergy between the two pathways have been verified due to the lower coke deposition of the blend compared to the individual components, and this has been explained in terms of (i) attenuation of the heavy hydrocarbon pathway caused by the steam contained or originated from the bio-oil, and (ii) the hydride transfer from hydrocarbons to the precursors of the oxygenate pathway.

Coking behavior on a Ni–Mo/Al2O3 catalyst for the hydrocracking of vacuum residue

In this study, we performed the hydrocracking of vacuum residue (VR) in an autoclave reactor using a Ni–Mo/Al2O3 catalyst at 450 and 500 °C under 150 bar of pressure and characterized coke structure generated over the catalyst during the reaction in order to understand the coking behavior in the hydrocracking of vacuum residue. The insoluble coke generated during VR hydrocracking was characterized by N2 sorption, TGA, XRD, FE-SEM (EDX), EPMA, FT-IR, Raman, and 13C CP/MAS–NMR techniques. In the absence of catalyst, dominant thermal hydrocracking at 500 °C produced pregraphite coke containing sulfur compounds since sulfur components in the feed could not be removed by thermal hydrocracking. With catalyst, the coke structures generated during a reaction depended on the reaction temperature. The NMR, Raman, XRD, TPO, and FT-IR spectra showed that amorphous coke containing highly branched oligomers and polycyclic aromatics were generated during hydrocracking at 450 °C, whereas hydrocracking at 500 °C mainly produced pregraphite coke. The presence of the catalyst in hydrocracking of VR played an important role in increasing decomposition of VR and decreasing coke deposition.

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.

The importance of pre-treatment of spent hydrotreating catalysts on metals recovery

This work describes a three-step pre-treatment route for processing spent commercial NiMo/Al2O3 catalysts. Extraction of soluble coke with n-hexane and/or leaching of foulant elements with oxalic acid were performed before burning insoluble coke under air. Oxidized catalysts were leached with 9 mol L-1 sulfuric acid. Iron was the only foulant element partially leached by oxalic acid. The amount of insoluble matter in sulfuric acid was drastically reduced when iron and/or soluble coke were previously removed. Losses of active phase metals (Ni, Mo) during leaching with oxalic acid were compensated by the increase of their recovery in the sulfuric acid leachate.

Evolution of the deactivation mode and nature of coke of HZSM-5 and USY zeolites in the catalytic cracking of low-density polyethylene during successive cracking runs

The coke deposited in the HZSM-5 zeolite at higher coke levels causes a more important pore blockage than the coke deposited in the HZSM-5 zeolite at low coke content. On the other hand, it would appear that there is an important deactivation mode change in the USY coked zeolites during the cracking runs and when the coke level in the catalyst increases an important pore blockage is observed. In the HZSM-5 zeolite, it seems that the formation of insoluble coke during the several polymer cracking runs, as well as the possible location in the external surface could be responsible for the important pore blockage observed in this zeolite. In the USY coked zeolites, the study of the nature of the soluble coke suggests that the pyrene compounds and their evolution to insoluble coke could probably be responsible for the important pore blockage observed after the second cracking run.

Coke deposition and characterization on titanium silicalite-1 catalyst in cyclohexanone ammoximation

In this work, the changes of catalytic activity, as well as the main deactivation mode were investigated on a commercial titanium silicalite-1 (TS-1) catalyst under simulated industrial conditions in continuous tank slurry reactor. The conclusions about deactivation behavior have been achieved based on the changes of activity, conversion and selectivity. XRD and FTIR analyses indicate the MFI framework structure of zeolite cannot be changed evidently during the reaction. It is found by comparative experiments that the main reason for catalyst deactivation is coke formation on the surface of TS-1. Results from TGA-DTA, N 2 adsorption and pyridine TPD analyses of used catalysts demonstrate there are two types of coke deposited mainly on micropores. Soft coke is located near Ti sites and can be removed by oxidation under 350 °C, while refractory coke can be oxidized by air until 700 °C. Analysis results of GC–MS for soluble coke and NMR, FTIR spectra for insoluble coke indicate that N-containing polycyclic aromatic and/or polyalkene species are the main components of coke deposits.

Isomerization of n-butane to isobutane over Pt-modified Beta and ZSM-5 zeolite catalysts: Catalyst deactivation and regeneration

This work addresses the deactivation behavior of H-Beta, H-ZSM-5, Pt-Beta and Pt-ZSM-5 catalysts in the isomerization of n-butane to isobutane. Furthermore, the type of coke formed inside these catalysts was characterized. The regeneration of Pt-Beta and Pt-ZSM-5 with synthetic air was also investigated. Most of the coke was formed during the first 70 min of TOS. Linear long-chain olefins formed the soluble coke, which was mainly determined by the reactant molecule and formed by consecutive oligomerization of n-butane molecules. On the other hand, the amount of insoluble coke is influenced by the reaction conditions, carrier gas and, most of all, zeolite structure. Pt and hydrogen inhibit successive reactions, i.e. alkylation, cyclization, that soluble coke undergoes before becoming insoluble. The beneficial effect of coke on the shape selectivity was observed, which increased the isomerization efficiency, defined as IE = iC4/(iC4 + C3 + C5). The activity on Pt-Beta was completely restored by oxidative regeneration, showing a higher IE than the fresh one.