Naphthenic Rings Research Articles

Deactivation of WNiPd/TiO 2Al 2O 3 catalyst during the upgrading of LCO

The deactivation of a novel catalyst during the production of a high-quality low-emission diesel component has been studied experimentally in a hydrotreating microplant. This process is compared with a commercial operation that used a conventional HDT catalyst. Catalysts were tested by incrementing temperature as a function of cycle length to keep the sulfur constant in the product, maintaining all other operating conditions constant. Spent catalysts were characterized using solid 13CNMR and XPS spectroscopy, pyridine adsorption, GC–MS of the coke extracted, and chemical analysis. Effective pore diffusivity was measured with pentane, and the catalyst activity and selectivity were measured with LCO and probe molecules to verify naphthenic ring opening capability. An important decline in hydrogenation and ring opening activity was detected along the cycle length due to acid site deactivation. The deactivation is attributed to LCO poly-aromatics adsorption on a particular type of acid site. A commercially deactivated HDT catalyst that operated with LCO presents a similar type of coke to that of the pilot plant.

Study of Ir/WO 3/ZrO 2–SiO 2 ring-opening catalysts: Part II. Reaction network, kinetic studies and structure–activity correlation

The present paper is the second part of a systematic study of the influence of W and Ir loading on the activity of Ir/WO 3/ZrO 2–SiO 2 catalysts for the ring-opening reaction of naphthenic molecules using methylcyclohexane (MCH) as a model compound. A series of Si-stabilized tungstated zirconias, WO x /ZrO 2–SiO 2, containing up to 3.5 atom W/nm 2, was prepared. Ir-based catalysts containing up to 1.2 wt% were obtained by impregnation of these solids. Characterization of the metal dispersion and catalyst acidity was described in a previous article. The objective of the present study was to determine the best metal/acid balance for optimal performance of Ir/WO x /ZrO 2–SiO 2 catalysts in the ring-opening reaction of MCH. Monofunctional (acid WO x /ZrO 2–SiO 2 or metal Ir/ZrO 2–SiO 2) and bifunctional (Ir/WO 3/ZrO 2–SiO 2) catalysts were examined. Based on the analysis of the yields and products distributions, a reaction network was proposed, and kinetic data (e.g., activation energies, initial rates) were calculated. Correlations between characterization results obtained earlier (e.g., acidity, dispersion) and catalytic performance are also reported. The monofunctional acid catalysts WO x /ZrO 2–SiO 2 showed a low selectivity for ring opening. The ring-contraction activity developed for W surface density above a threshold value of 1 atom W/nm 2. This was attributed to the appearance and the development of a relatively strong Brönsted acidity monitored by infrared measurements. MCH ring contraction and C5 naphthene ring opening occur according to a classic acid mechanism. For low conversions, the monofunctional metal catalysts Ir/ZrO 2–SiO 2 exhibited significant selectivity for ring opening that decreased with increasing conversion. Because of the lack of ring-contraction products, the observed activity was attributed to the direct ring opening of the MCH. Ring opening and cracking occur according to a dicarbene mechanism. The study of MCH conversion on Ir/WO x /ZrO 2–SiO 2 catalysts indicated that MCH ring contraction to alkylcyclopentanes occurs before ring opening. The best yields for ring opening were obtained with the 1.2% Ir/WO x /ZrO 2 (1.5 atom of W/nm 2). Further increases in W surface density led to a decrease in the indirect ring-opening yield, attributed to a decrease in Ir dispersion. For bifunctional metal/acid catalysts, analysis of the mechanism is less straightforward. The activation energy for C6 ring contraction and indirect C6 ring opening is a function of the metal/acid ratio. For high ratios, indirect ring opening occurs essentially over metallic sites. A decrease in the metal/acid ratio enhances the contribution of acid mechanism.

Principal Regularities in Compositions and Structures of High-Molecular Compounds from Crude Oils and Natural Bitumens

Experimental data on structural group composition and macro-structural characteristics of hydrocarbons and petroleum high-molecular compounds (PHMC) – resins and asphaltenes – from more than 150 samples of crude oil samples extracted on the oil-fields of Pannonian (Serbia), Volgo-Ural, South-Caspian, West-Kazakhstanian, West-Siberian, and several Eastand Southeast Asian oil-bearing basins are summarized. It was shown that the number of carbon atoms in the highest n-alkane molecules reaches up to 70-71 in Cenozoic, but only 35-40 in Jurassic and Paleozoic oils. Petroleum hybrid naphtheno-aromatic hydrocarbons are compounds with up to six rings to 24 C-atoms in alkyl fragments of molecules. Resin molecules contain, on a mass weighted average, 1-3 structural blocks each consisting of 0-3 aromatic and 0-5 naphthenic rings in such combinations that the total number of cycles in each block does not exceed 5-6. The weight of average molecular masses of resins does not exceed 1000-1500 g/mole. Asphaltenes differ from resins from the same source by larger average numbers of structural blocks in molecules (up to 5), by the predominantly tri- and/or tetracycloaromatic nature of these blocks, by lesser substitution factors of aromatic nuclei and lesser proportions of C-atoms in saturated fragments. The weight of average masses of asphaltene molecules measured by cryoscopy in naphthalene does not exceed 2500 g/mole. Owing to strong intermolecular interactions, PHMC molecules form various associated structures and poly-molecular particles, including quasicrystalline “batches” and multi-batch aggregates, especially in asphaltenes. Through spontaneous decay and formation of such particles the oils have the character of dynamically equilibrium poly-disperse systems. Compositional and structural variations of PHMC were studied depending on the depths at which they occurred, age and lithological composition of oil-bearing sediments. Although thermal histories are not considered here, clear regularities are established. PHMC, consisting of chemically labile hetero-organic substances, under any bedded conditions are subjected to compositional and structural transformations which are more rapid and substantial as compared with petroleum hydrocarbons.

Analyses of mild hydrogenation products of coals treated with zinc and butyl iodide

Butylation using zinc and butyl iodide under mild conditions (130 °C and atmospheric pressure) is an effective method to convert solid coals to soluble products in poor solvents such as hexane and benzene. Because of mild conditions and high solubility, the butylation of coals is found to be applicable for estimating coal structures. Until now, two typical coals, Taiheiyo and Yubari coals, were converted to hexane soluble products significantly. However they were too heavy to obtain much information on the structure of the original coals. In order to analyze the structural features of the coals butylated with zinc and butyl iodide, the polar mixture (PM) fractions separated from hexane soluble products (HS) from butylated Yubari and Taiheiyo coals were hydrogenated using Adkins catalyst. The HS products of hydrogenated PM fractions were fractionated by gel permeation chromatography (GPC), and the GPC fractions were further analyzed. After hydrogenation, structural parameters of HS products separated from PM fractions did not change so much, but molecular weight decreased. The GPC fractions (Fr.1–Fr.7) from both coals had similar high σal (degree of aliphatic chain substitution) as well as low fa (aromaticity) to the original PM fractions. These results indicated that the GPC fractions were highly butylated. Many structural parameters of GPC fractions except for Fr.7 were similar with each other. For Taiheiyo coal, the ring sizes of GPC fractions were 1–2, and similar to those from pyridine soluble products. For Yubari coal they were 2–3, and smaller than those from pyridine soluble product, 4 due to reductive butylation. The ring sizes of the Fr.7 from both coals were as small as one. Because the solvent soluble products were subject to reductive butylation, the naphthenic rings of the fractions seemed to be ruptured by hydrogenation. These findings suggest that high hexane extractability of the coals butylated with zinc and butyl iodide was caused by reductive butylation.

Transformations of oil cut hydrocarbons in catalytic modification with α-olefins

The change in the structural and group composition of paraffins and naphthenes and aromatics in the oil cut before and after alkylation with a-olefins was investigated. Oligoalkylation of these hydrocarbons and rupture of naphthene rings in hybrid structures and isomerization of alkyl fragments are reflected in the quality of the products obtained.

Comparative study of the hydrogenation of tetralin on supported Ni, Pt, and Pd catalysts

The hydrogenation of tetralin in the vapor phase has been investigated over Ni, Pt, and Pd catalysts to determine the evolution of the trans- and cis-decalin products as a function of conversion over the different catalysts. The concentration of each isomer in the product may be important in subsequent ring opening steps if cetane number improvement is desired. The cis-decalin isomer is preferred to open the naphthenic ring in a selective way instead of multiple cracking. However, thermodynamically, this isomer is the least favored; so, kinetic control is the only solution. By selecting the proper catalyst and operating conditions, one could keep the trans/cis-decalin ratio low. In this study, we have prepared a series of supported metal catalysts and tested them in a flow reactor at 3540kPa and 548K. Kinetic parameters for the hydrogenation of tetralin and the cis-to-trans-decalin isomerization over the various catalysts investigated were obtained by fitting the data with a generalized Langmuir–Hinshelwood model.The kinetic analysis revealed that the relative rates of tetralin hydrogenation, as well as the cis-to-trans isomerization are greatly affected by adsorption site competition of decalin and tetralin, which in turn has different magnitudes over the different catalysts. At tetralin conversions above 30%, the Ni catalyst yields the lowest trans/cis-decalin ratio. In contrast, the trans/cis ratio on Pd catalyst remains constant at all conversion levels and is highest at low tetralin conversion. It is concluded that the trans/cis ratio is a combination of the intrinsic selectivity of each isomer and the isomerization reaction.

Structural Characterization of Asphaltenes and Ethyl Acetate Insoluble Fractions of Petroleum Vacuum Residues

Asphaltenes and insoluble fractions of vacuum residues (VRs) of two Indian crude oils (viz. Heera and Jodhpur) of different specific gravity were obtained by precipitation of VRs in n-hexane, n-heptane, and ethyl acetate, and also by subsequent reprecipitation of n-heptane and ethyl acetate soluble fractions by n-pentane. The effect of various solvents on average molecular structure of asphaltenes and insolubles was studied using nuclear magnetic resonance spectroscopy (NMR), Fourier transform infrared spectroscopy (FTIR), and size exclusion chromatography (SEC). The asphaltenes and insolubles of Jodhpur VR have higher amounts of high molecular weight species with a high concentration of condensed and substituted aromatic rings, branched and/or short alkyl side chains, oxygen and nitrogen functionalities, compared to that of Heera VR. Ethyl acetate insolubles comprise a higher number of substituted aromatic structures, branched aliphatic structures, complex average unit structures, nitrogen and oxygen functionalities, and high molecular weight (MW) species as compared to hexane and heptane asphaltenes. Heptane insolubles consist of more naphthenic rings condensed with aromatic rings than C6A and EAI.

Effect of the hydrocarbon molecular structure in diesel fuel on the in-cylinder soot formation and exhaust emissions

Evaluations of diesel fuel effects on combustion and exhaust emissions in single-cylinder direct-injection diesel engines led to the unexpected result that a Swedish ‘class 1’ fuel generated more particulate matter (PM) than a fuel denoted ‘improved’, even though ‘class 1’ fuel had much lower distillation temperatures, aromatic concentration, sulphur level, and density than the ‘improved’ fuel. Little differences were observed in the combustion characteristics between these fuels, but detailed compositional analyses showed that ‘class 1’ fuel contains higher levels of cyclic and/or branched paraffins. Subsequent investigations in a laboratory flow reactor showed that ‘class 1’ fuel produces more soot precursors such as benzene and acetylene than the ‘improved’ fuel. In addition, experiments in a low-pressure laminar flame apparatus and shock tube with model (single-molecule) paraffin fuels showed that isoparaffins and cycloparaffins generate more soot precursors and soot than n-paraffins do. These results strongly suggested that the effect of molecular structure on exhaust PM formation should be more carefully examined. Therefore, a new series of investigations were performed to examine exhaust emissions and combustion characteristics in single-cylinder engines, with well-characterized test fuels having carefully controlled molecular composition and conventional distillation characteristics and cetane numbers (CNs). These investigations revealed the following. Firstly, under low and medium loads, cycloparaffins (naphthenes) have a higher PM formation tendency than isoparaffins and n-paraffins. Under high-load conditions, however, the paraffin molecular structure has a very small effect. Secondly, a highly n-paraffinic fuel does not yield PM reductions as high as expected, due to its high CN and corresponding shorter ignition lag, which initiates combustion under a state of insufficient fuel-air mixing. This finding was corroborated by laser-induced incandescence analyses. Thirdly, the lowest PM emissions were observed with a paraffinic fuel containing 55 per cent isoparaffins and 39 per cent n-paraffins. Fourthly, aromatics give higher soot and PM levels than paraffins do at high and medium load conditions. Smaller differences are observed at lower speeds and loads. Fifthly, the best fit to the PM emissions was obtained with an equation containing the regression variables CN, aromatic rings, and naphthene rings. This expression of the fuel effects in chemical terms allows well-to-wheel analyses of refining and vehicle impacts resulting from molecularly based fuel changes.

Structural Studies of Vacuum Gas Oil Distillate Fractions of Kuwaiti Crude Oil by Nuclear Magnetic Resonance

Nitrogen-free vacuum gas oil (VGO) distillate was separated, using preparative column chromatography, into five hydrocarbon groups: saturates (SAs), monoaromatics (MAs), diaromatics (DAs), polycyclic aromatic hydrocarbons (PCAHs), and polar hydrocarbons (POLHs). The hydrocarbon groups MA, DA, PCAH, and POLH were separated into low- and high-sulfur compounds (LSCs and HSCs, respectively) on silica gel impregnated with PdCl2 (aqueous). SAs and LSCs obtained from MAs, DAs, PACHs, and POLHs were further fractionated into subfractions using gel permeation chromatography (GPC), based on their molecular size in solution. All the GPC subfractions were analyzed for elemental carbon, hydrogen, nitrogen, and sulfur, and for molecular weight. Nuclear magnetic resonance (NMR) spectroscopic techniques also were applied to elucidate the average molecular structure of selected GPC subfractions, POLHs, and HSCs. The SAs had average alkyl chain lengths of n = 13−15 and two naphthenic rings, and they were free of aromatics. The average molecule in the three groups (MAs, DAs, and PCAHs) contained (i) one aromatic ring, two cyclo-paraffinic rings, two alkyl groups on aromatic rings, and no bridged aromatic carbon; (ii) two aromatic rings, two naphthenic rings, five alkyl-substituted groups, and two bridged aromatic C atoms; or (iii) three aromatic rings, one naphthenic ring, four bridged aromatic C atoms, and four alkyl-substituents attached to the aromatic or naphthenic ring(s), with an average chain length of seven C atoms. The average molecule of the POLH group contained one S atom, four aromatic rings, four naphthenic rings, five bridged aromatic C atoms and four alkyl substituents attached to the aromatic or naphthenic ring with an average chain length of seven C atoms.

Ring opening of decalin and tetralin on HY and Pt/HY zeolite catalysts

The removal of polynuclear aromatics from diesel fuel in response to increasingly stringent environmental legislation has stimulated intense research. In addition to the hydrogenation reaction that saturates aromatics, an interesting possibility is the opening of naphthenic rings derived from the saturation of aromatics to produce molecules of higher cetane numbers. In this contribution, we have investigated a series of HY and Pt/HY catalysts of varying acidity densities. Under the conditions of this study, mainly ring-contraction and one-ring opening reactions take place over these catalysts. Although the products from these reactions do not have cetane numbers significantly higher than those of the saturated aromatics, they can be important intermediates to high cetane number compounds, such as normal paraffins and some iso-paraffins. The results of this investigation show that HY zeolites can be effective catalysts for the ring contraction and one-ring opening of decalin if their acidity density is adjusted to an intermediate optimum, that is, high enough to achieve conversion, but not too high that would result in fast deactivation. The low cis-to- trans ratios obtained in the products are due both to the cis-to- trans isomerization, but more importantly, to a much higher reactivity of cis-decalin than trans-decalin. Also, cis-decalin converts much more selectively to ring-opening products than trans-decalin, which mainly converts to cracking products. The production of ring-contraction and ring-opening products from tetralin is greatly enhanced in the presence of Pt due to hydrogenation of tetralin to decalin. In the presence of hydrogen Pt/HY catalysts as well as physical mixtures of HY and Pt are much more effective than HY catalysts.

The role of metal sites during the coupled hydrogenation and ring opening of tetralin on bifunctional Pt(Ir)/USY catalysts

The influence of the metal function in bifunctional Pt/USY catalysts in the combined hydrogenation and ring opening of tetralin has been investigated. The key step in the reaction pathway leading to the formation of the desired ring opening products (ROPs) was the isomerization (ring contraction) of the C6 naphthenic rings of decalins. The presence of Pt in the bifunctional Pt/USY catalyst significantly increased the rate of isomerization and hence the formation of ROP as compared to the monofunctional USY sample. The formation of the high cetane ROP increased with increasing the proximity between the Pt and acid sites and with increasing the Pt loading (i.e. the metal/acid ratio) in the range of 0.25–4wt.%. Ring opening of naphthenes was seen to occur exclusively on the Brönsted acid sites of the zeolite. Incorporation of a hydrogenolysis metal (Ir) to the bifunctional Pt/USY catalyst did not lead to a further increase in the formation of ROP and significantly reduced the sulfur tolerance of Pt. This was ascribed to a higher electron density on the Pt sites induced by Ir in bimetallic Pt–Ir particles, as evidenced by XPS.

Study on Composition and Structure of Liaoshu Asphalt

In this article, the structure characteristics of Liaoshu paving asphalts have been studied by the methods of element analysis, SARA and E-D-M. At same time, the relation between composition and structure and using performance of Liaoshu paving asphalt were established. The experimental results show that carbon and hydrogen contents were more than 95%, the hydrogen/carbon atom ratio was about 1.5 in the Liaoshu paving asphalts. The content of saturates is between 20 and 25% in the Liaoshu paving asphalt, aromatics 35–40%, resin 25–30%, and asphaltene 8–10%. There are 45 carbon atoms in asphalt average molecule, which contain 16–17 aromatic carbon atoms. The number of total ring in asphalt average molecule is 5–6, the aromatic ring is 3–4, the naphthene ring is 1–2.

Study on Composition and Structure of Liaoshu Asphalt

In this article, the structure characteristics of Liaoshu paving asphalts have been studied by the methods of element analysis, SARA and E-D-M. At same time, the relation between composition and structure and using performance of Liaoshu paving asphalt were established. The experimental results show that carbon and hydrogen contents were more than 95%, the hydrogen/carbon atom ratio was about 1.5 in the Liaoshu paving asphalts. The content of saturates is between 20 and 25% in the Liaoshu paving asphalt, aromatics 35 and 40%, resin 25 and 30%, and asphaltene 8 and 10%. There are 45 carbon atoms in the average asphalt molecule, which contain 16–17 aromatic carbon atoms. The number of total ring in the average asphalt molecule is 5–6, the aromatic ring is 3–4, and the naphthene ring is 1–2.

Study and Evaluation of Aging Performance of Petroleum Asphalts and Their Constituents During Oxygen Absorption. III. Average Molecular Structure Parameter Changes

The changes of the structural parameters of the average molecules of Chinese Shanjiasi and Shengli petroleum asphalts and their constituents during oxygen absorption were studied based on the oxygen absorption behaviors and the chemical group composition and structure changes. The results show that all the structural parameters of the average molecules of asphalts and their constituents increase clearly after oxygen absorption with the exceptions of the naphthene carbon rates and the paraffin carbon rates. The parameters include the total carbon numbers, the aromatic carbon numbers, the naphthene carbon numbers, the paraffin carbon numbers, the total ring numbers, the aromatic ring numbers, the naphthene ring numbers, the total hydrogen numbers, the aromaticities, and the concentration indexes. The most obvious are the structural parameter changes of the average molecules of the asphalt resin and asphaltene constituents. The structural parameter changes of the average molecules of Shengli asphalt and its constituents are remarkably greater than those of Shanjiasi asphalt and its constituents. The clearer changes of all the average molecular structure parameters of SHL asphalt resin and asphaltene, especially resin could possibly be one of the key factors leading to the much clearer deterioration of the colloidal stability and the serviceability than SJS asphalt in oxygen absorption.

Investigation of Asphaltene Precipitation Process for Kuwaiti Reservoir

As part of an Enhanced Oil Recovery (EOR) research program, Asphalting precipitation processes were investigated for a Kuwaiti dead oil sample using different hydrocarbons and carbon dioxide as precipitants at the ambient and high pressure of 3000 psig conditions. The hydrocarbons used as precipitants were ethane (C2), propane (C3), butane (C4), normal pentane (n-C5), normal hexane (n-C6), and normal heptane (n-C7). The equipment used for this investigation was a mercury-free, variable volume, fully visual JEFRI-DBR PVT system with laser light scattering. The minimum critical value of precipitants concentration for the oil sample has been identified at the ambient and high-pressure conditions for each precipitant. Our investigation has revealed that for this oil sample the most powerful asphaltene precipitant were CO2 followed by C2, C3, C4, n-C5, n-C6, and n-C7. Moreover, the effect of pressure and temperature on the asphaltene precipitation has been investigated experimentally for CO2, n-C5, n-C6, and n-C7. The precipitation and redissolution of asphaltene upon the addition and removal of CO2 and light alkanes (C2–C4), at 3000 psig and ambient temperatures, have shown evidence of reversibility of asphaltene precipitation. A comprehensive fluid characterization analysis for the oil sample has been performed including, physical properties of crude oil, compositional, molecular weight (Mw), and SARA analyses. Advanced analytical techniques such as 1H and 13C NMR and IR spectrometers have been utilized to investigate the molecular structure of the asphaltene for this sample. It was concluded that the asphaltene molecules for this oil contain 120 total aromatic carbons with 42 aromatic rings, 114 naphthenic rings, and 5–7 sets of condensed aromatic rings.

Desulfurization of Vacuum Gas Oil Based on Chemical Oxidation Followed by Liquid−Liquid Extraction

Desulfurization of vacuum gas oil (VGO) has been investigated based on chemical oxidation of sulfur-containing compounds using H2O2 and acetic acid (AcOH), followed by extraction of the oxidized compounds from the resulting VGO using an aqueous acetonitrile solution. The desulfurization behavior of VGO was compared with that of light oil feedstocks, and the reactivities of the individual sulfur compounds in VGO were studied by field ionization−mass spectrometry (FI-MS) analysis. By use of the desulfurization process, the sulfur content of the VGO was decreased successfully to less than 11% of the corresponding feed values, and the desulfurization yield of the VGO was significantly higher than that of light oils. This is because polyaromatic thiophenes in the VGO that possess at least one naphthenic ring adjacent to the thiophenic ring have higher electron density on the sulfur atom than the sulfur compounds contained in light oils, and are oxidized more effectively.

Selective Ring Opening of Naphthenic Molecules

Ring opening as practiced in hydrocracking of naphthenic molecules results from multiple cleavages of both endo- and exocyclic C–C bonds. Selective ring opening requires that only one endocyclic C–C bond per naphthene ring be severed, preserving thereby reactant molecular weight. The products of selective ring opening are alkanes and alkylnaphthenes. Over hydrocracking catalysts the yield of alkanes with the same number of carbon atoms as the reactant naphthenes is unacceptably low as a result of extensive dealkylation of alkylnaphthenes and secondary cracking of alkanes. Alkylcyclopentanes, in contrast, selectively ring open by hydrogenolysis over a number of noble metal catalysts. Under similar reaction conditions the selective ring-opening rates of alkylcyclohexanes are, however, one to two orders slower than those of alkylcyclopentanes. Addition of a ring-contraction acidity function converts alkylcyclohexanes into more easily ring-opened alkylcyclopentanes, greatly facilitating selective ring opening. Selective ring-opening rates and selectivities are optimum when ring isomerization occurs by a nonbranching ring contraction. Branching ring contraction, creating increased numbers of ring substituents, is detrimental to both ring-opening rates and selectivities. When an effective acidity function is coupled with a high-activity hydrogenolysis metal, such as iridium, the resulting bifunctional catalyst system greatly outperforms conventional hydrocracking catalysts for the selective conversion of naphthenes to alkanes.

Chemical, microstructural and thermal analyses of a naphthalene-derived mesophase pitch

A detailed characterisation of a synthetic naphthalene-derived mesophase pitch, in its as-received state and during pyrolysis, has been performed. The study has been conducted by means of various techniques and with a particular attention to Raman microspectroscopy. The Raman spectra show features in common with the naphthalene precursor, i.e., a broad and complex band at 1150–1500 cm −1 and a multicomponent G band at 1600 cm −1. These features correspond to the vibration modes of the molecules of the pitch and more especially to the non-aromatic C–C bonds involved in alkyl groups, aryl–aryl bonds or naphthenic rings. The pyrolysis of the pitch into coke takes place within a narrow temperature range (480–500 °C) through the elimination of hydrogen and light alkanes resulting from the breaking of homolytic C–H bonds and naphthenic cycles, respectively. This process initiates a swelling of the pitch. The analysis of the Raman features shows that the structure of the pitch is only slightly affected within this temperature range. Conversely, significant structural changes of the material (as shown by the vanishing of the multicomponent bands at 1600 and 1150–1500 cm −1) are evidenced beyond 750 °C, simultaneously with a hydrogen release and an increase of the true density. This phenomenon corresponds to the extension of the graphene layers of the coke and the formation of a distorted carbon network.

Decalin and Tetralin as Probe Molecules for Cracking and Hydrotreating the Light Cycle Oil

Cracking of tetralin and decalin was carried out over several zeolites to establish the effect of the pore topology of the catalyst on product distribution. These molecules were chosen as probe molecules, because they indicate which catalyst is the best for cracking or hydrotreating the light cycle oil (LCO) fraction, which is obtained directly from fluid catalytic cracking units. A set of zeolites with medium-sized (ZSM-5, MCM-22, ITQ-2), large (USY, Beta), and ultralarge pores (UTD-1), as well as a mesoporous MCM-41, were used as catalysts at 723 K. The results demonstrate that pore size and topology have a strong influence on diffusion, and consequently, on activity and selectivity in reactions such as ring opening, dealkylation, transalkylation, hydride transfer, and coke formation. UTD-1 generally has the highest activity per framework Al owing to the pore size and topology of this zeolite that enables flat molecules to diffuse easily inside the pores. According to the results, zeolites with medium-sized pores are adequate in combination with large-pore zeolites to crack naphthenes and fused aromatic–naphthenic rings, of the type present in LCO, to produce propene. Large-pore zeolites show good selectivity for naphthenic ring opening and appear to be better suited for hydrotreating LCO. Beta zeolite is a catalyst that is especially suitable for both processes.

Deactivation of Hydrodesulfurization Catalysts in Two-stage Resid Desulfurization Process. (Part 5). Characterization of Asphaltenes after Hydrodemetallization and Subsequent Hydrodesulfurization Reactions.

Hydrodemetallization (HDM) and subsequent hydrodesulfurization (HDS) of Arabian light (AL) atmospheric residues were performed with a bench-scale unit, and the structure of the asphaltenes obtained from each reaction was characterized. The HDM reaction caused a decrease in the number of aromatic rings, an increase in aromaticity, and a decrease in the number of alkyl side chains, but no formation of naphthenic rings. In contrast, HDS reaction formed naphthenic rings, but their number decreased with an increase of HDS temperature, thus leading to an increase of aromaticity. Using the structural parameters obtained by using a computer program based on the SAAH system developed by Katayama et al., we modeled the structure of asphaltenes after HDM and HDS reactions and found that the aromatic unit structure of AL asphaltenes became coronene-type as hydrotreatings proceed.