Aromatic Saturation Research Articles

A Novel Self-Assembled Hierarchical-Structured Catalyst for the Diffusion of Macromolecules

A novel self-assembled catalyst, FA-Z30, possessing a mesoporous/macroporous structure is prepared and applied to FCC diesel hydrodesulfurization (HDS). The catalyst has 54 % of the total pore volume lying within 30–60 nm pores, greater than 26 % of the continuous phase. This indicates interconnected pores. N2 adsorption data show a bimodal structure with pores ranging between 30–60 nm and <10 nm. Textural properties of the catalyst show that the pore volume is 0.78 cm g–1 having a specific surface area of 181 m2 g–1 with a most probable pore diameter of 20 nm. The catalyst possesses a low active metal concentration of ~154.9 g L–1 per unit volume and a low bulk density of ~0.50 g cm–3. X-Ray diffraction, high resolution transmission electron microscopy, and X-ray photoelectron spectroscopy show improved active metal dispersion with an average MoS2 layered slab number of 3–7, having lengths ranging from 5 to 10 nm. Molybdenum sulfide sulfidity at 75 % is higher than the commercial catalyst, FCB, at 62 %. The activity and stability of HDS and hydrodenitrification (HDN) are improved, as is aromatics saturation (HDAr) reflected by limited coke formation. Average conversion rates of HDS, HDN, and HDAr are 95, 97, and 67 % at 100 h on stream for FA-Z30, respectively, and their respective rates of 6.1, 6.3, and 4.3 % per unit volume of active metal is twice that of the commercial catalyst. The low bulk density of FA-Z30 improves the utilization rate and relative activity of the active metals. FA-Z30 is a promising catalyst for FCC diesel hydrogenation.

Mesoporous zeolite-supported metal sulfide catalysts with high activities in the deep hydrogenation of phenanthrene

Developing highly active hydrogenation catalysts for deep aromatics saturation is of great importance in the production of ultraclean diesel fuel at a low cost. Toward this goal, we synthesized a mesoporous zeolite ZSM-5 (MZSM-5) that was cost-effective and available on a large scale, and used it as a support for the preparation of highly efficient metal sulfide catalysts (NiMoS/MZSM-5 and CoMoS/MZSM-5) for the deep hydrogenation of phenanthrene. The intrinsic activity of the NiMoS/MZSM-5 catalyst (7.4×10−4molkg−1s−1) was much higher than that of the alumina-supported NiMo catalyst (NiMoS/γ-Al2O3, 4.8×10−4molkg−1s−1), and the selectivity of the deep hydrogenation products over NiMoS/MZSM-5 (20.9%) was higher than for NiMoS/γ-Al2O3 (15.2%). Compared with γ-Al2O3, the relatively weak metal–support interaction could facilitate the formation of polymolybdates on MZSM-5. After sulfidation, the more multistacked MoS2 active phases were formed on the MZSM-5, enhancing the hydrogenation activity of the NiMoS/MZSM-5 catalyst.

Selective cleavage of C[sbnd]O bond in benzyl phenyl ether to aromatics over Pd–Fe bimetallic catalyst supported on ordered mesoporous carbon

Bimetallic Pd–Fe catalyst supported on ordered mesoporous carbon (Pd–Fe/OMC) was prepared by a surfactant-templating method and a subsequent incipient wetness impregnation method. The catalyst was applied to the catalytic cleavage of CO bond in benzyl phenyl ether to aromatics. For comparison, monometallic Pd/OMC and Fe/OMC catalysts were also investigated. Benzyl phenyl ether was used as a lignin model compound for representing α-O-4 linkage in lignin. The combined effect of palladium and iron on the physicochemical properties and catalytic activities of Pd–Fe/OMC was investigated. Although Pd/OMC catalyst showed the highest conversion of benzyl phenyl ether, selectivity for aromatics was low due to saturation of aromatic ring. On the other hand, Fe/OMC catalyst showed lower conversion of benzyl phenyl ether than Pd/OMC, but Fe/OMC catalyst showed higher CO bond cleavage selectivity than Pd/OMC catalyst without saturation of aromatics. Bimetallic Pd–Fe/OMC catalyst showed the highest yield for aromatics. The introduction of Fe into Pd/OMC catalyst resulted in the modification of electronic properties of Pd by electron transfer from Fe to Pd, which led to the enhanced yield for aromatics.

Influence of Support Acidity of NiMo Sulfide Catalysts for Hydrogenation and Hydrocracking of Tetralin and Its Reaction Intermediates

Aromatic saturation is an important reaction for improving the cetane number of diesel streams. NiMo sulfide catalysts supported on alumina (Alu), silica–alumina (Si–Al), and alumina-Y zeolite (AluZ) were prepared with similar dispersions and variable acidities. These catalysts were tested in the hydroconversion of tetralin, indan, decalins, and alkylbenzenes to evaluate the effect of the support acidity in the overall activity and the distribution of products. NiMo/Alu generated essentially hydrogenated products while the presence of an acid component on the support increased not only isomerization and cracking reactions but also hydrogenated compounds formation, especially on tetralin, indan, and butylbenzene hydroconversions over NiMo/AluZ catalyst. The better hydrogenation activity of NiMo/AluZ for these reactions was associated with the presence of strong acid sites that contribute to creating protonated species which would migrate to the sulfide phase. Such species would be easier to hydrogenate due...

Design and Synthesis of a Novel Mesoporous Composite and its Performance as the Support for the Catalyst

A novel synthesis route for a MCM-41 structure with Y zeolite seeds colloidal has been developed. The route is different from conversational method of highly ordered MCM-41 assembled from Y zeolite seed colloidal. The material was characterized by various techniques. The results indicate that the material has well-ordered hexagonal structure, with a thicker wall than that of the sample synthesized by a direct hydrothermal route (N-MCM-41). Furthermore, it has a stronger acidity. The sample was used as the support of a Pd-Pt catalyst for the polyaromatics hydrogenation. It was demonstrated that the introduction of building units of Y zeolite enhances the activity of polyaromatics hydrogenation. It can be concluded that the pore structure and acidity of support is a key factor for the design of a sulfur-resistant noble metal catalyst for aromatics saturation of diesel.

Design and Synthesis a Novel Supported Pd-Pt Mesoporous Composite as Catalysts for the Polyaromatic Hydrogenation

Hydrothermally stable mesoporous aluminosilicates with tubular morphology and hexagonal nanochannels were prepared by a new route. The route is different from conversational method of highly ordered MCM-41 assembled from Beta zeolite seed colloidal. The synthesis of Beta zeolite-like seeds is a novel route of acid treatment. The XRD results indicated that the synthesized materials were well-ordered hexagonal mesostructures of MCM-41. The highly regular hexagonal mesostructures could survive by steaming at 750 °C for 2 h, exhibiting good hydrothermal stability. Combining the SEM investigation, the as-made materials showed tubular morphology with diameter of 0.4 μm. The sample has a stronger acid strength, and was used as the support of a Pd-Pt catalyst for the polyaromatics hydrogenation. It has high activity and good sulfur tolerance towards hydrogenation of aromatics of smaller diameter. It was demonstrated that the introduction of building units of Beta zeolite enhances the activity of polyaromatics hydrogenation. It can be concluded that the pore structure and acidity of support is a key factor for the design of a sulfur tolerant noble metal catalyst for aromatics saturation of diesel.

Mechanism of Hydrodesulfurization of dibenzothiophenes on unsupported NiMoW catalyst

Hydrodesulfurization (HDS) of dibenzothiophene (DBT), 4-methyldibenzothiophene (4-MDBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) on unsupported NiMoW catalyst was studied. Moreover, mechanisms and reaction networks were revealed on the basis of GC and GC-MS analyses of the reaction products. The result shows that, the HDS rate of dibenzothiophenes is in the order of 4,6-DMDBT≈4-MDBT<DBT for the spatial restraining effect of the methyl group. Unsupported NiMoW catalyst has high hydrogenation activity in aromatics saturation, it favours the hydrogenation of alkyl-substituted aromatic ring, weakens the spatial restraining effect, leads to the effectively removing of alkyl-substituted dibenzothiophenes. The hydrodesulfurization products of DBT could be hydrogenated further and its distribution is similar to the hydrogenation products of biphenyl(BP). The hydrogenation route of the hydrodesulfurization of 4-MDBT have two reaction pathways, the electron donor induction of the methyl group could promote the hydrogenation of the adjacent phenyl. On the Lewis acid sites of catalyst, part of 4-MDBT and 4,6-DMDBT transformed into DBT through the demethylation reaction in their hydrodesulfurization process.

Production of low aromatics and low sulfur diesel in a hydrodesulfurization (HDS) pilot plant unit

The present work investigates the hydrotreating process of a diesel in order to achieve lower sulphur and aromatics content. The entire work was performed in a Hydrodesulphurization (HDS) pilot plant unit located in Chemical Process Engineering Research Institute (CPERI). For the tests, a commercial HDS catalyst (CoMo) was used while the feed was provided by the deep desulphurization unit of a Greek refinery (Motor-Oil refinery). For the determination of diesel aromatics, a method based on the ASTM D- 2549-85 was applied. The objective of the work was to investigate the ability of a typical HDS catalyst for aromatics saturation. The effect of the main hydrotreating operating parameters (T, P, WHSV, H2/Oil ratio) on sulphur and aromatics removal was also investigated. In general, the data showed that the product density and the aromatic and sulphur content of diesel decreased as the temperature or pressure increased or space velocity decreased. It was concluded that with the present catalyst an aromatics saturation degree of up to 40% could be achieved, giving a diesel product with aromatics content of about 20-25% wt. However, high temperatures (&gt;370°C) were required in order to achieve 500 ppmw sulphur in this feedstock.

Distillate Hydrotreating to Ultra-low-sulfur Diesel – the Impact of Aromatics

Distillate hydrotreating has become a key concern in the refining industry owing to ultra-low-sulfur diesel legislation. Rate-limiting parameters that had previously been overlooked, such as aromatic inhibition, may need to be considered for the production of ultra-low-sulfur diesel (<10 weight parts per million wppm sulfur). As hydrodesulfurization (HDS) and aromatic saturation (HDA) reactions occur in parallel in a shared environment, they compete for the necessary resources, namely, hydrogen and catalyst sites. A series of pilot plant and numerical simulation experiments were completed in order to explore how the competition for hydrogen and catalyst sites impacts the rate of HDS in the presence of poly-cyclic aromatics. A diagnostic pilot plant test showed that external mass transfer was not rate-limiting. Intra-particle mass and energy transport were investigated by calculating the concentration and temperature gradients in a catalyst pellet. The effectiveness factors for HDS and HDA decreased in the presence of increased aromatics concentrations. However, the magnitude of the changes was insufficient to conclude that the competition for hydrogen was the sole mechanism needed to explain the suppression of HDS activity. Furthermore, the pilot plant data indicated that the presence of poly-aromatics has a more significant impact on the slower HDS reactions (sterically hindered dibenzothiophenes). As a result, it was concluded that aromatics inhibition (competitive adsorption on catalyst sites) impacted the rate of HDS most significantly. Although the consequences were significant, the impact of aromatic inhibition was minor relative to the analogous nitrogen inhibition.

A Novel Synthesis Route for Highly Ordered MCM-41 Assembled from Y Zeolite Seed Colloidal and its Performance as the Support for the Catalyst

A novel synthesis route for a MCM-41 structure with Y zeolite seeds colloidal has been developed. The route is different from conversational method of highly ordered MCM-41 assembled from Y zeolite seed colloidal. The material was characterized by various techniques. The results indicate that the material has well-ordered hexagonal structure, with a thicker wall than that of the sample synthesized by a direct hydrothermal route (N-MCM-41). SEM images show a very uniform net-like morphology, which is different from the loose appearance of N-MCM-41. Furthermore, it has a stronger acid strength and a higher hydrothermal stability. The sample was used as the support of a Pd-Pt catalyst for the polyaromatics hydrogenation. It was demonstrated that the introduction of building units of Y zeolite enhances the activity of polyaromatics hydrogenation. It can be concluded that the pore structure and acidity of support is a key factor for the design of a sulfur tolerant noble metal catalyst for aromatics saturation of diesel.

Upgrading of LCO by partial hydrogenation of aromatics and ring opening of naphthenes over bi-functional catalysts

Available options to upgrade LCO to diesel fuel are: i) aromatic saturation (ASAT) ii) mild hydrocracking and iii) aromatic saturation followed by selective ring opening (SRO) of naphthenic structures. Although the above mentioned routes lead to significant product quality enhancement, they suffer from several disadvantages. Hydrocracking leads to significant yields in gasoline-range products, ASAT is characterized by a relatively high consumption of hydrogen with only limited improvement of product quality in terms of density and cetane properties, ASAT + SRO route leads to higher improvements of product quality but it requires a very high hydrogen consumption which strongly affects the economics of the process. An alternative upgrading route consists in partial polyaromatic compound saturation and selective opening of both naphthenic and benzo-naphthenic structures to produce less condensed naphthenic structures and alkyl-benzenes respectively. In this case the hydrogen needed to improve product quality at the same level, of cetane properties and density, is lower in comparison with ASAT. This paper reports the results obtained during a research program aimed at upgrading LCO via selective ring opening. The hydroconversion of a low sulfur hydrotreated LCO has been studied over iridium and platinum loaded on different supports. The results of this study indicate that the properties of products heavily depend on the characteristics of the support and the metal used. The data obtained with the Ir/amorphous silica-alumina (MSA) show the possibility to get a clear increase of CN and decrease of density in comparison with the mere aromatic saturation. The practical consequence of this result is the possibility of producing products with CN and density similar to products obtained by complete dearomatization but still containing a significant percentage of aromatic structures so allowing a consistent saving of hydrogen.

Ring opening and kinetics study of hydrotreated LGO on Ni-Mo carbide supported on HY and H-Beta catalysts

Pt-Ir/HY, Ni-Mo carbide/HY and Ni-Mo carbide/H-Beta catalysts were used to improve the fuel quality of Hydrotreated Light Gas Oil (HLGO). All the catalysts are well characterized by using BET, Elemental, TPR, TPD and XRD analyzers. Screening of the catalysts were done and observed that Ni-Mo carbide/HY is an effective catalyst for improvement in cetane index of HLGO. A 12 unit increase in cetane index was observed on Ni-Mo carbide/HY at 325 °C, whereas Ni-Mo carbide/H-Beta could not improve the cetane index effectively. The Pt-Ir/HY deactivates in three days even though its activity is comparable with that of Ni-Mo carbide/H-Beta. NMR analysis showed that the Ni-Mo carbide/HY catalyst improves the cetane index of the fuel by selectively converting the naphthenes to paraffins in the temperature range of 300–325 °C. Low cetane index was observed above 325 °C due to the dominance of dehydrogenation and secondary cracking reactions. Simulated distillation results indicated the presence of high percentage of naphtha fraction above 325 °C, which decrease the fuel quality due to their low cetane values. A first order kinetic model was proposed and the model was well fit with the experimental values. Arrhenius activation energies of 111, 89 and 42 kJ/g mol were observed for dehydrogenation, aromatic saturation and cracking reactions, respectively.

Recovery of Value Added Products Can Help Survival of Solvent Extraction Unites in a Lube Processing Refinery: A Case Study

In a refinery, crude petroleum oil is distilled in an atmospheric column to separate fuel gases and distillates. Reduced crude oil (RCO) from the atmospheric distillation unit is further distilled under a vacuum, yielding varieties of distillates like vacuum gas oil and light to heavy viscous distillates. In a typical lubricating base oil–producing refinery, viscous distillates from intermediate to heavy are available from such a unit. Highly viscous distillate is also recovered from the vacuum residue. Solvent extraction takes place (Sequeira and Dekker, 1993c, p. 81; 1993b, p. 153) next to selectively dearomatize the distillates to yield high viscosity index (VI) oil. In order for the pour point to be improved, selective removal of paraffin wax is carried out in a solvent dewaxing unit. Finally this dewaxed oil is selectively hydrogenated to remove unwanted sulfur, nitrogen, and oxygen and also for improving color. Though modern catalytic aromatic saturation and dewaxing (Sequeira and Dekker, 1993a, p. 194; Raseev, 2003, p. 674) are replacing the traditional solvent refining processes, valuable products like wax, carbon black, and bitumen are available only from solvent refining processes. A typical solvent extraction unit has been studied for enhancing quality and quantity of value-added products like lube base stock, wax, carbon black feed stock (CBFS) and bitumen.

Liposome−Prilocaine Interaction Mapping Evaluated through STD NMR and Molecular Dynamics Simulations

We have examined the interaction of the neutral and protonated species of the local anesthetic prilocaine (PLC) with phosphatidylcholine (PC) bilayers combining experimental ((1)H NMR) and theoretical (molecular dynamics simulations) approaches. DOSY experiments allowed the determination of the association constants of protonated (Ka = 9 L/mol) and neutral (Ka = 21 L/mol) PLC to egg PC liposomes. Saturation transfer difference (STD) experiments showed a different trend depending on pH: At high pH the PLC hydrogen saturation was essentially uniform and at pH 5.5 the experiments show an enhancement of the aromatic moiety hydrogen saturation, with respect to the tail. Molecular dynamics simulations, performed with PLC molecules on planar bilayers of palmitoyloleyl-PC, revealed a preferential orientation for the protonated PLC species at the polar interface of the bilayer, and a nonoriented and deeper insertion for neutral PLC. Such preferential location of protonated and neutral PLC inside the bilayer can be described as different transient sites which could modulate the access of these molecules to their binding site(s) in the voltage-gated sodium channel, justifying differences in the anesthetic's potency upon ionization.

Fuel constituent effects on fuel reforming properties for fuel cell applications

The effect of different types of compounds commonly found in diesel fuel (e.g., paraffins, naphthenes, and aromatics), as well as their chemical structure (e.g., branched versus linear paraffins) on fuel reforming has been investigated. Diesel reforming is very complicated because diesel is a complex mixture of hundreds of compounds with greatly different reactivities. The syngas production rates at the same conditions were observed in this order: paraffins > naphthenes ≫ aromatics. Additionally, the type of reforming performed (OSR, CPOX, or SR) as well as the process parameters (space velocity and reaction temperature) significantly affected the syngas production rates as well as carbon formation. The reactivity of one fuel component can affect the conversion pattern of others, e.g., overall yields from the reforming of a fuel mixture are not additive of yields from individual fuel components, rather the more reactive component is consumed first. Furthermore, the type of substituent in aromatics and naphthenes, the carbon chain length in n-paraffins, branching in paraffins, and degree of aromatic saturation affect the overall hydrocarbon conversion, syngas selectivity, and carbon formation. The presence of sulfur compounds in the fuel caused significant drops in H 2 yields compared to CO yields.

High Quality Diesel by Hydrotreating Gas Oil over Modified Titania-supported NiMo Catalysts

In this work, two methods of preparing alumina-titania and ceria-titania mixed oxide supports were studied: In the first method, alumina or ceria were precipitated on the surface of a commercial titanium oxide. In the second method, alumina or ceria were impregnated on the surface of titania. In all catalysts under study, NiO comprises 3 wt% while MoO3 comprises 8 wt% in addition to 89 wt% of the support material. Surface area and pore volume measurements for the supports and catalysts were obtained from the analysis of nitrogen adsorption-desorption isotherms. Al, Ce, Ni, and Mo contents and coke percent of the spent catalysts were determined by x-ray fluorescence method. Characterization of the samples have been studied by DTA and XRD. The HDS activities have been studied, and two types of catalytic tests were used. One type of measurement was a screening test using the pulse technique. The second type was focused on studying the effect of important process variables as reaction temperature, hydrogen pressure, and LHSV on the extent of HDS of real gas oil (GO) feedstock and simultaneous HDS and HDN on the selected screened catalysts by using the continuous-flow high-pressure fixed-bed cata-test unit. The results revealed that titania containing Al or Ce catalysts are much more active than the conventional NiMo/Al2O3 catalysts on HDS and HDN reactions. They also demonstrate high aromatic saturation capabilities.

Investigation of hydrodearomatization of prehydrogenated gas oil fractions on Pt–Pd/H-USY catalysts

Hydrodearomatization (HDA), hydrodenitrogenation (HDN) and hydrodesulphurization (HDS) of real gas oils (various sulphur, nitrogen and total aromatic content) was investigated over Pd, Pt catalysts supported on USY zeolite, whose Pd/Pt mass ratio was varied between 6:1 and 1:3, and total metal contents were between 0.90 and 0.93. The effect of Pd/Pt ratio on HDA, HDN and HDS activities is presented. The advantageous process parameters for HDA, HDN and HDS of gas oils over a selected catalyst (e.g. Pd/Pt mass ratio 3:1) were determined. Additionally, the effect of key process parameters (temperature, pressure, LHSV) on the yield and quality of products was studied. Under optimal process parameters the HDA efficiency decreased with sulphur and nitrogen content of feed. The rate of HDA enhanced with Pt content of the catalyst while HDS and HDN efficiency increased with Pd content. The maximum aromatic saturation was 85% and it decreased with sulphur and nitrogen content of the feed.

Ring contraction and selective ring opening of naphthenic molecules for octane number improvement

Different catalytic strategies have been evaluated to maximize the production of non-aromatic compounds with high octane number, starting from naphthenic molecules, which are typically obtained from the saturation of aromatics. The research octane number (RON), the motor octane number (MON), and the specific volume of the product mixtures were evaluated in each case. The product distribution obtained on acidic and Ptcontaining zeolites was investigated in the temperature range 533‐563 K in the presence of hydrogen at a total pressure of 2 MPa. It was found that skeletal isomerization (ring contraction) was the primary reaction in both HYand Pt/HY catalysts. The presence of Pt was found to enhance the stability of the catalyst, but also greatly altered the distribution of RC products, enhancing 1,1-dimethylcyclopentane. This enhancement can be explained in terms of a higher rate of hydride transfer caused by the presence of the metal. Evaluation of the octane numbers of the product indicated that a mixture of RC products results in rather high RON, but the MON and specific volume were about the same as that of the feed. To improve MON and specific volume an Ir/SiO2 catalyst with high hydrogenolysis activity was added to realize the ring opening (RO). The combination of RC and RO was tested on physical mixtures and segregated beds of Pt/HYand Ir/SiO2 catalysts in order to optimize the production of the iso-alkanes with highest octane number. It was found that with segregated catalyst beds, a better control of the selective breaking of C‐C bonds of RC isomers can be achieved, which optimizes octane number and specific volume. # 2007 Elsevier B.V. All rights reserved.

Effect of Operating Conditions on Aromatic Content at Basrah Crude Oil Hydrotreating

In Trickle Bed Reactor Basrah crude oil was hydrotreated using a common hydrotreating catalyst (Co-Mo/γ-Al2O3) . The operating conditions of this treating was, temperature (600 – 675 K) , Liquid hourly space velocity (LHSV) (0.6 – 1.9 hr-1) , constant pressure (3 Mpa) and H2/Oil ratio 300 L/L were performed. Experiments results show that aromatic content was reduced as temperature increases and LHSV decreases, as well as the aromatic saturation were greatly enhanced at the same condition .

Unsupported transition metal sulfide catalysts: From fundamentals to industrial application

In the open literature, there are numerous papers related to the chemical and physical properties of unsupported transition metal sulfides. Besides characterization studies, the performance of a large variety of mono-, bi- and multi-metallic materials in various test reactions has been examined. The performance studies identified several unsupported materials with higher activity and/or selectivity than the traditional γ-Al 2 O 3 supported Ni/Co–Mo/W catalysts. This has resulted in numerous patents disclosing the preparation of unsupported transition metal sulfides and their use as hydroprocessing catalysts. However, for several reasons (high price and too high activity for existing refinery process equipment), the commercial use of unsupported catalysts in refinery processes has so far been limited to the NEBULA ® catalysts. Catalysts based on NEBULA technology provide unprecedented activity for hydrodesulfurization (HDS), hydrodenitrogenation (HDN) and aromatics saturation (HDA).