Slurry Phase Hydrocracking Of Vacuum Residue Research Articles

Structural design and electronic regulation of atomically dispersed Mo-S4 sites by second shell N species reconfiguration for intensifying hydrogen spillover

Intensifying hydrogen spillover by regulating the atomic local structures catalysts is crucial for improving the hydrogenation performance, but still hugely challenging. Herein, we report a robust single-atom catalyst featuring Mo-S4 sites in the first shell modulated with N atoms in the second shell (Mo-S4-N/C) by an efficient cyclodextrin supramolecular self-assembly pyrolysis strategy for intensifying hydrogen spillover in slurry-phase hydrocracking of vacuum residue (VR). We discovered that the H2 is activated at the single-atom Mo-S4 sites efficiently and the spillover of active hydrogen is accelerated by the reconfiguration of N species in the second shell. Remarkably, the Mo-S4-N/C catalyst demonstrates excellent catalytic hydrogenation activity with high turnover frequency calculated for total metals up to 0.46 s−1, the VR per pass conversion of 61 wt.%, liquid product yield of 94 wt.%, and the low coke content of 0.6 wt.%, along with good stability, respectively. Theoretical calculations revealed that the N species in the second shell regulated the electronic structure of Mo-S4 sites, promoting the migration of active hydrogen species by reducing the transfer energy barrier of hydrogen spillover, thus enhancing the hydrogenation performance. This work proposed a strengthened hydrogen spillover mechanism from the atomic scale for hydrogenation reaction, offering novel concepts for designing and developing high-performance hydrogenation catalysts.

The effect of recycle stream on slurry-phase hydrocracking of vacuum residue: An experimental and modeling approach

The effect of the recycle stream on slurry-phase hydrocracking (HCK) of vacuum residue was examined using a continuous bench-scale unit with the aim of attaining process optimization. This was achieved through a model-based approach that links experimental investigations, kinetic modeling, and model-based optimization. The experiments were conducted at various reaction temperatures, liquid hourly space velocity of fresh feed (LHSVFF) and recycle ratios at a pressure of 160 bar, with the fresh feed containing 1000 wt. ppm of molybdenum. The HCK kinetic model was modified to incorporate the recycling effects and accurately predict the experimental data. The adapted model confirmed that the unconverted residue in recycle operating mode (ROM) became more refractory. By implementing the modified kinetic model in a dynamic Simulink model, the prediction accuracy of RES conversions and product yields can be improved by up to 25.1 wt.% in the case of the lowest conversion. A sensitivity analysis using the dynamic model showed that the temperature exerted a greater impact on the RES conversion and recycle ratio in ROM. An operational stability index was also proposed to prevent operation failure in ROM. Finally, an optimal operating condition from the parametric study was found to meet several process goals simultaneously.

Atomic coordination structural dynamic evolution of single-atom Mo catalyst for promoting H2 activation in slurry phase hydrocracking

Development of efficient catalysts with high atomic utilization and turnover frequency (TOF) for H2 activation in slurry phase hydrocracking (SPHC) is crucial for the conversion of vacuum residue (VR). Herein, for the first time, we reported a robust and stable single atoms (SAs) Mo catalyst through a polymerization-pyrolysis-in situ sulfurization strategy for activating H2 in SPHC of VR. An interesting atomic coordination structural dynamic evolution of Mo active sites was discovered. During hydrocracking of VR, the O atoms that coordinated with Mo were gradually replaced by S atoms, which led to the O/S exchange process. The coordination structure of the Mo SAs changed from pre-reaction Mo-O3S1 to post-reaction Mo-O1S3 coordination configurations, promoting the efficient homolytic cleavage activation of H2 into H radical species effectively. The evolved Mo SAs catalyst exhibited robust catalytic hydrogenation activity with the per pass conversion of VR of 65 wt%, product yield of liquid oils of 93 wt%, coke content of only 0.63 wt%, TOF calculated for total metals up to 0.35 s−1, and good cyclic stability. Theoretical calculation reveals that the significant variation of occupied Mo 4d states before and after H2 interaction has a direct bearing on the dynamic evolution of Mo SAs catalyst structure. The lower d-band center of Mo-O1S3 site indicates that atomic H diffusion is easy, which is conducive to catalytic hydrogenation. The finding of this study is of great significance to the development of high atom economy catalysts for the industrial application of heavy oil upgrading technology.

Synthesis and performance of mesoporous iron oxide in vacuum residue slurry-phase hydrocracking

In order to develop a high-efficiency iron oxide catalyst for the slurry-phase hydrocracking of poor heavy oil, the mesoporous iron oxide was successfully synthesized by using the waste wood powder as a template, and the influence of alkali concentration in the resulting solution on crystal phase, morphology and pore structure of the synthesized samples was investigated. The crystal phase of the synthesized iron oxide transfers from α-Fe2O3 to γ-Fe2O3, and their crystal sizes gradually decrease with an increase of alkali concentration based on the XRD and HRTEM results. Additionally, the iron oxide with mesoporous structure, larger surface area and pore volume is obtained at the higher concentration of alkali in solution confirmed by N2 adsorption-desorption analysis. The assessment result of the iron oxide catalyst employed in the slurry-phase hydrocracking of vacuum residue (VR) illustrates that the yields of gasoline and diesel distillates obtained over Fe-O-B20, Fe-O-B24 and Fe-O-B30 catalysts are higher compared with those over Fe-O-B2 and Fe-O-B14 catalysts, it can be attributed that more exposure Fe active sites derived from their larger surface area and pore volume availably improve the catalyst hydrogenation activity, which can inhibit the over-cracking reaction of intermediate products and the condensation of polycyclic aromatic hydrocarbon in VR to enhance the yields of gasoline and diesel distillates.

Influence of ASA composition on its supported Mo catalyst performance for the slurry-phase hydrocracking of vacuum residue

To deeply illuminate the effect of ASA composition on its corresponding Mo catalyst properties and performance for the slurry-phase hydrocracking of vacuum residue, the amorphous silica-alumina (ASA) samples with the various ratios of Al to Si were successfully synthesized by a simple co-precipitation method, which have the different acid properties and pore structure, especially ASA-1 with lowest ratio of Al to Si owning the largest number of B acid sites and the highest volume of mesoporous. Additionally, the Mo catalyst supported on ASA-4 possesses the highest dispersion of MoS2 slabs and largest amount of Mo atoms located at the edge sites among all the catalyst, possibly due to the appropriate surface properties of ASA-4 derived from the ratio of Al to Si, it demonstrates that the most exposure Mo active sites are present on Mo/ASA-4 catalyst. The hydrocracking evaluation results show that the VR conversion over the different catalysts are similar, it may be ascribed to the variation of acid properties and pore structure insufficient to change VR cracking pathway because of the low catalyst dosage. Furthermore, the Mo/ASA-4 catalyst exhibits the higher yield of naphtha and middle distillate and inversely the lower yield of gas and coke in comparison with other catalysts, it should be attributed that the higher hydrogenation activity derived from the more exposure Mo active sites can efficiently restrain the over-cracking of the intermediate product and aggregation of the polycyclic aromatic hydrocarbon in the hydrocracking process.

Mo supported on natural rectorite catalyst for slurry-phase hydrocracking of vacuum residue: An effect of calcination

In order to develop high-efficiency and low-cost catalyst for the slurry-phase hydrocracking of vacuum residue (VR), the catalyst supported on natural rectorite was prepared, and the effect of calcination modification of rectorite on the catalyst properties and performance was investigated. The support of rectorite and catalyst were characterized by XRD, FTIR, Py-FTIR, H 2 -TPR and XPS to examine their structures and properties. The comparative reaction results show that VR conversions for the catalysts supported on calcined rectorite were similar with that on raw rectorite, possibly due to the VR cracking reaction controlled by the thermal cracking following free radical mechanism because of few acid sites observed on the catalysts surface. However, the yields of naphtha and middle distillates for the various catalysts were obviously different, and increased following as Rec-Mo (40.4 wt%) < Rec-600-Mo (52.7 wt%) < Rec-450-Mo (53.5 wt%) < Rec-500-Mo (61.7 wt%), indicating that the calcination of rectorite favored the enhancement of the yields of naphtha and middle distillates for the catalyst in the slurry-phase hydrocracking process, it is attributed that the higher sulfidation degree of molybdenum oxide species on the catalyst surface promoted hydrogenation reaction, thus restrained over-cracking reaction of intermediate product to produce gas.

Ligand structure effect in oil-soluble phosphorus-containing molybdenum precursors for slurry-phase hydrocracking of heavy oil

Slurry-phase hydrocracking for heavy oil upgrading is a challenging technology in the petroleum refining industry. We prepared various P-containing Mo precursors to elucidate the effect of their ligand structures on the slurry-phase hydrocracking of vacuum residue. Characteristic analyses of the Mo precursors were performed by first determining their dispersibility and decomposition patterns, followed by evaluating the sulfidation degree and morphology of the resulting MoS2 catalyst. The dispersibility of the Mo precursors was evaluated by a method of measuring the solubility parameter based on the oil compatibility model. The slurry-phase hydrocracking results revealed that the H2 consumption rate, residue conversion, hydrodesulfurization, and asphaltene conversion were dependent on the Mo precursor. The Mo triethylphosphite species, which had the largest number of active sites, was found to be the most efficient precursor for improving product distribution and product quality.

Hydrocracking and hydrotreating reaction kinetics of heavy oil in CSTR using a dispersed catalyst

A kinetic model for the slurry-phase hydrocracking of vacuum residue was proposed under conditions of: 410–450 °C, 0.25–1 hr−1, 160 bar, 1500 Nm3/m3 of H2 to oil ratio, and 500 ppm catalyst (Mo-octoate). A five-lump model with ten reaction pathways was adopted to describe the hydrocracking kinetics, while the hydrotreating reactions were modeled by the power-law approach. The kinetic parameters were estimated considering the change in liquid density with reaction time. The kinetic model predicted product yields and concentrations with an average error of less than 10%. As for the hydrocracking reaction, it was demonstrated that the secondary cracking of VGO mainly produced MD at high temperature and the high conversion of RES. As for hydrotreating, it was confirmed that asphaltene conversion proceeded to increase the removal level of other impurities. Finally, a hydrogen consumption rate model was proposed based on HCK and HDT, which provides consistent information for further uses in reactor modeling and process modeling.

Slurry-phase hydrocracking of heavy oil over Mo precursors: Effect of triphenylphosphine ligands

A practical approach to enhancing the performance of dispersed catalysts during slurry-phase hydrocracking is the modification of the ligand structure of the catalyst precursor. An oil-soluble Mo precursor with triphenylphosphine ligands (Mo-TPP) was prepared and further applied to the slurry-phase hydrocracking of vacuum residue (VR). For comparison, a commercial precursor termed Mo-octoate was also used. In a dispersibility test, Mo-TPP was completely dissolved at 200 °C and then finely dispersed in the VR. Thermogravimetric analysis revealed that Mo-TPP decomposed rapidly in the range 220–270 °C to produce zerovalent Mo. During the decomposition process, direct conversion of Mo-TPP to MoS2 was favored via reaction with H2S gas generated from the VR at 250 °C. The sulfidation behavior of Mo-TPP reduced the average size and stacking number of the resulting unsupported MoS2 catalyst, which led to greater exposure of the rim sites (Morim) on the catalyst surface than when Mo-octoate was used. The Mo-TPP precursor resulted in better catalytic performance than the Mo-octoate precursor in a semibatch reactor at 410 °C and under 110 bar H2. In particular, the use of Mo-TPP enhanced the radical scavenging and hydrodesulfurization activities, owing to excellent hydrogenation ability originating from the initial number of Morim sites. The phosphate compound, derived from the TPP ligands, promoted the conversion of asphaltenes via demetallization of the intrinsic V species in the VR. These results demonstrated that Mo-TPP is an efficient precursor for achieving coke suppression that also improves product quality.

Slurry phase hydrocracking of vacuum residue in the presence of presulfided oil-soluble MoS2 catalyst

Herein, a simple method for the preparation of presulfided oil-soluble MoS2 catalysts was proposed. The catalyst precursor, cetyltrimethyl ammonium heptamolybdate (CTATTM) was easily synthesized by dissolving ammonium tetrathiomolybdate in an aqueous solution containing excess cetyltrimethyl ammoniumbromide, which could be directly dissolved in a vacuum residue (VR). The obtained catalyst was evaluated in slurry phase hydrocracking of VR at 410 °C with an initial H2 pressure of 10 MPa for 1 h. It showed remarkable hydrocracking activity, with a reduction of the resin content from 25.21 to 3.54 wt% and of the C7-asphaltene content from 6.82 wt% to almost zero. With using the catalyst, as the yield of the liquid product increased from 75.03 to 96.43 wt%, yields of the coke and gas would be only 0.19, and 3.38 wt%, respectively, significantly lower than the values of 14.05, and 10.92 wt%, respectively, obtained without using the catalyst. Moreover, with increasing Mo content, hydrodemetalization conversion increased from 42.5 to 83.4 wt%, while hydrodesulfurization conversion increased from 21.6 to 59.2 wt%. In addition, a higher initial H2 pressure over 10 MPa can more efficiently promote the conversion of VR to light oil products with a significantly lower formation of coke and gas than the cases under conditions below 10 MPa. Multiple techniques, including X-Ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), and Fourier-transform infrared spectroscopy (FT-IR), were employed to determine a plausible correlation between the structure and performance. The CTATTM precursor shows good solubility and stability in heavy oil, leading to easy formation of small MoS2 particles with stacking numbers of 1 and 2, and slab lengths of 5–11 nm. This presulfided oil-soluble MoS2 catalyst with good hydrocracking activity for VR shows greatpotential for further industrial applications.

Active phase of dispersed MoS2 catalysts for slurry phase hydrocracking of vacuum residue

Different morphologies of oil-dispersed MoS2 catalysts were obtained by a ligand stabilization method using Mo(CO)6 as a Mo precursor and trioctylphosphine oxide (TOPO) as a coordinating agent to identify the active site of MoS2 in the hydrocracking (HCK) of vacuum residue (VR). Transmission electron microscopy (TEM) and extended X-ray absorption fine structure (EXAFS) spectroscopy were used to obtain structural properties of the dispersed catalyst. It was observed that the MoS2 forms a nanoscaled monolayer from 5 to 10 nm in size. The effect of the oil-dispersed MoS2 catalysts having different morphology on the slurry phase HCK of VR was investigated at 673 K and 9.5 MPa H2. The turnover frequency (TOF) of the dispersed MoS2 catalysts in the VR HCK was found to show a good correlation with the rim-site Mo dispersion of the MoS2 slabs based on the same metal loading of 0.113 mmol at 673 K and 9.5 MPa H2.

Effect of reaction temperature and time on the products and asphaltene dispersion stability in slurry-phase hydrocracking of vacuum residue

The effect of reaction temperature and time on the products and the asphaltene dispersion according to the residue conversion was investigated in a slurry-phase hydrocracking reaction. The experiments were carried out with two different approaches to control the hydrocracking reaction, which the reaction time was changed from 4 h to 20 h (at 410 °C) and the reaction temperature from 430 °C to 453 °C (for 1 h) at 100 bar (at 80 °C) of initial hydrogen pressure and 500 wt.ppm of molybdenum concentration. As a result, it was found that the control of the reaction time and reaction temperature may give different effect to the stability of the asphaltene in the liquid phase in spite of the same VR conversion. In order to understand this, the dipole moments of the liquid product and structural change of the asphaltene was compared. And it was found that enhancing hydrogenation reaction by increasing reaction time at low temperature delayed the time of decreasing point for dipole moments of the liquid phase and increased the length of alkyl chain of remaining asphaltene. Therefore, it is considered that the dispersibility of asphaltene with high polarity is increased. Additionally, it was found that enhancing hydrogenation can also improve the catalyst dispersion in the liquid phase below 80% of residue conversion.

Characteristics of slurry-phase hydrocracking for vacuum residue with reaction temperature and concentrations of MoS2 dispersed catalysts

This study investigated the characteristics of slurry-phase hydrocracking of vacuum residue (VR >524°C) at a high conversion (40–95wt.%) with a change of reaction temperatures and concentrations of the dispersed molybdenum (Mo Conc. 100–2000wt.ppm) catalyst. Experiments were carried out with an initial hydrogen pressure of 80bar (at 80°C) at a reaction temperature from 385 to 440°C for four hours in a batch reactor. As results, it was found that the sediment formation is mainly dependent on the VR conversion by the reaction temperature and started over 70wt.% of VR conversion. Up to 70–80wt.% of VR conversion, the higher catalysts showed the higher asphaltene conversion and prevented the sediment formation at the boundary of its formation, but it didn’t show any effect over 80wt.% of VR conversion anymore. Based on the analysis of the structural change and ξ-potential of asphaltene from the liquid and sediment, and SARA compositional change in the liquid, the reason for sediment formation was explained.

Slurry-Phase Hydrocracking of Residue with Ultradispersed MoS2 Catalysts Prepared by Microemulsion Methods

Slurry-phase hydrocracking of vacuum residue using a dispersed catalyst has been investigated in this work. The liquid yield and coke formation in this process mostly depend upon the catalyst particle size and its distribution. Three emulsion methods, colloidal emulsion liquid (CEL), emulsion liquid membrane (ELM), and reverse micelle (RM), are used to synthesize the dispersed MoS2 catalyst. Dynamic light scattering results show that the colloidal particle of molybdenum sulfide in the RM catalyst is smaller in size and narrowly distributed in comparison to the catalysts prepared by CEL and ELM methods. Our scanning electron microscopy and transmission electron microscopy analysis results also support the smaller particle size of the active metal in the RM catalyst. Hydrotreating and hydrocracking activities of the RM catalyst are higher, and it is due to its smaller particle size and its narrow distribution. Moreover, coke formation in this catalyst is very low. It is found that the residue (550 °C+ hydro...

Role of macroporosity in macro-mesoporous red mud catalysts for slurry-phase hydrocracking of vacuum residue

To improve the catalytic performance of red mud (RM) for slurry-phase hydrocracking of vacuum residue, macro-mesoporosity was introduced into RM using polystyrene and Pluronic F-127 as co-templates in this study. The obtained macro-mesoporous red mud (Ma-RM) catalysts were characterized by nitrogen adsorption, X-ray diffraction, ammonia temperature-programmed desorption, scanning electron microscopy, and transition electron microscopy. Subsequently, they were applied to the slurry-phase hydrocracking of vacuum residue at 490°C for 2h. Comparative reaction tests revealed that Ma-RM exhibited better catalytic behavior for the VR hydrocracking compared to activated RM without macropores. Ma-RM successfully suppressed coke formation and increased liquid yield in products distribution. The macroporous structure of Ma-RM was connected by mesopores containing active sites for hydrogenation. The presence of a macro-mesoporous structure enhanced hydrogenation over the catalysts due to better accessibility to the active sites for hydrogenation, which induced less coke and more liquid yield.

Slurry-phase hydrocracking of vacuum residue with a disposable red mud catalyst

In this study, red mud (RM) was used as a catalyst in slurry-phase hydrocracking of vacuum residue (VR) in batch system. Without RM, thermal cracking occurred and a lighter fraction and higher conversion was achieved than in the presence of catalyst. However, the catalytic cracking obviously inhibited both the coke formation and residue cracking reaction. We investigated the influence of reaction temperature, reaction time and RM concentration on VR conversion. Reaction temperature and time significantly improved the yield of naphtha, diesel and vacuum gas oil; unfortunately, they also increased the gas fraction, which is an undesirable product. Catalyst concentration negligibly affected the VR conversion while vacuum gas oil fraction in product distribution increased with catalyst concentration, indicating that the cracking reaction was suppressed in the presence of catalyst. Through the characterization of fresh and spent catalysts by diverse techniques, it has been determined that the crystalline iron oxide of RM transforms into pyrrhotite (Fe(x−1)Sx), an active phase for the hydrocracking reaction, due to presence of sulfur in VR. Our results show that RM is possibly self-activated during the reaction and the pretreatment step can be eliminated.