DEEP DESULPHURISATION OF A DIESEL BLEND IN A PILOT PLANT TRICKLE BED REACTOR

ABSTRACT

A pilot plant investigation was conducted to study the influence of hydrotreating conditions on conversion and characteristics of diesel blend and to determine the severity of operating conditions required to meet the proposed product specifications for diesel fuel in India. A typical diesel blend derived from various refinery streams with sulphur content of 2·06 wt% was hydrodesulphurised over a commercial NiO-MoO₃/Al₂O₃ catalyst in a pilot plant trickle bed reactor. The experiments were conducted at 300–370°C, 30–50 kg/cm², 2·0 3·0 hr^-1 liquid hourly space velocity and constant H₂/oil ratio of 185 m³/m³. The data showed that the diesel blend could be hydrotreated to meet revised product specifications of 0·25 wt% sulphur, 46 cetane number by increasing the severity of operation. The cetane number and aromatic saturation were limited by thermodynamic equilibrium at temperatures above 360°C. The influence of temperature was found to be more pronounced than that of pressure in the range of operating conditions studied.     

EFFECTS OF HYDROTREATING COKER LIGHT GAS OIL ON FUEL QUALITY

Coker light gas oil (LGO) derived from Athabasca bitumen was hydrotreated in a fixed bed reactor using two commercial NiO-MoO₃/Al₂0₃ catalysts. The effect of temperature on product quality was investigated in a pilot plant between 330 and 390 °C at 12.4 MPa, space velocity of 0.5 Ir1 and 700 liter of hydrogen per liter of coker LGO (L/L). The product quality was monitored by ^I3C NMR spectroscopy, elemental analysis, density and distillation techniques.

The data showed that coker LGO can be hydrotreated using nickel-molybdenum catalysts at 350 °C, 0.5 h¹, 12.4 MPa and 700 L/L to meet the diesel product specifications, namely, 0.5 wt % sulfur, 20% aromatics and cetane index of 40. The cetane index improvement and aromatic saturation, which are affected by thermodynamic equilibrium at temperature higher than 370 °C, could reach 29 and 86% respectively. The cetane improvement was attributed to aromatic saturation and hydrocracking with hydrogen consumption ranging from 215-340 L/L. The Ketjenfine KF-840 catalyst was found slightly better performance than Procatalyse HR-348 catalyst.     

Hydrotreating Activity of Heavy Gasoil over NiMo/γ-Al2O3-TiO2

Different γ-Al₂O₃-TiO₂ catalysts were tested in a pilot plant fixed-bed reactor in order to evaluate the effect of atomic ratio (Ni/Ni + Mo) on hydrotreating activity of heavy gasoil FCC feed. Hydrotreating reactions were carried out at three temperatures (330, 365, and 400°C) and LHSV of 6 h^-1. Studies of atomic ratio were done varying Ni amounts (2, 2.4, and 2.95 wt%) whereas molybdenum loading was kept constant (6 wt%) for all catalysts, the behavior of these catalysts was compared with a reference catalyst containing 11.5 wt% of Mo and 2.95 wt% of Ni, which was evaluated at the same conditions. All catalysts were prepared by incipient impregnation method over γ-Al₂O₃-TiO₂ (Ti = 5.6 wt%). Experimental results showed correlation between the atomic ratio (Ni/Ni + Mo) and the best results for hydrodemetallization where found for the catalyst with atomic ratio of (Ni/Ni + Mo) = 0.45.     

Evaluation of Diluted and Undiluted Trickle-Bed Hydrotreating Reactor with Different Catalyst Volume

In this work, a comparative study on the combined effects of hydrodynamics and kinetics on the hydrodesulfurization (HDS) of a straight-run gas oil (SRGO) using a trickle-bed reactor with and without diluent (SiC) and different catalyst volume (0.1, 0.07, and 0.050 × 10^-3 m³, respectively) was carried out. The tests were conducted in a pilot plant under conditions close to those used in industrial-scale units (5492 kPa, 445.4 m³(STP)/m³ H₂/oil ratio, 623-643K, 0.9 and 2.5 h^-1 LHSV values). The catalyst used was a commercial CoMoP/Al₂O₃ formulation shaped as tri-lobed extrudates (1/20 in, nominal size) or as crushed particles (d_p = 1.2 × 10^-3 m). Contrarily to that usually claimed, the undiluted systems showed better performance than those comprising small diluent (SiC) particles (d_p ~ 5 × 10^-5 m). Calculations to evaluate hydrodynamic variables (plug-flow behavior, wall effects, wetting, and back-mixing) were carried out in order to explain the observed facts. The possible influences of the size of the diluent particles used are discussed.     

MILD HYDROCRACKING OF VACUUM GAS OILS TO IMPROVE FCC PERFORMANCE AND MAXIMIZE DISTILLATE YIELDS

A pilot plant study was conducted on mild hydrocracking of heavy vacuum gas oils derived from two different crude sources over a commercially available catalyst to determine the possibility of utilizing mild hydrocracker bottoms as fluidized catalytic cracking feedstock along with improved middle distillate yields. The mild hydrocracking experiments were conducted at 390°C, 60 kg/cm², 1.0/h liquid hourly space velocity and H₂/oil ratio of 390 l/l in a pilot plant trickle bed reactor using two catalyst beds for pretreatment and mild hydrocracking reactions. The experimental results showed that mild hydrocracking would result in valuable middle distillates with low sulphur and nitrogen content. With research octane number of 78, the naphtha obtained from mild hydrocracking was found to be a good blending stock for gasoline pool. The middle distillate fraction (140-370°C) obtained from mild hydrocracking product was found to have cetane number in the range of 48-54. The bottom product from mild hydrocracking of heavy vacuum gas oils was found to be a good feedstock for fluidized catalytic cracking unit because of its low sulphur, nitrogen and aromatic contents. The data obtained from pilot plant studies showed that the processing of mild cracker bottom in FCC unit would result in better quality fuels.     

Advantages of Mild Hydrocracking FCC Feed—A Pilot Plant Study

In view of increasingly stringent environmental regulations with respect to SOx and particulate emissions, the allowable sulphur and nitrogen levels in diesel and gasoline are reducing all over the world. Fluid catalytic cracking (FCC) unit is a major source of fuels produced from a refinery. Any attempt to reduce sulphur and nitrogen content of distillates produced from FCC unit will greatly improve the quality of fuels. In the present work, pilot plant studies were conducted to evaluate the options of hydrotreating and mild hydrocracking (MHC) of FCC feedstock. Experiments were conducted on commercially available catalyst samples using high nitrogenous vacuum gas oil (VGO) as feedstock. MAT experiments were also conducted to compare the conversions and yields of untreated, hydrotreated, and MHC VGO at constant operating conditions. Pilot plant data showed that MHC of VGO would produce additional fuels to the extent of 15% under moderate operating conditions besides improving the quality of FCC feedstock. The mild hydrocracked VGO as feed was found to increase FCC conversion by 2 wt%, increase fuels by 2.5 wt%, reduce residue by 2.8 wt% compared to untreated vacuum gas oil.     

ESTIMATION OF TOXIC COKE DEPOSITS ON FRESH AND REGENERATED Pt/Al2O3 CATALYST FROM METHYLCYCLOPENTANE REFORMING IN H2 AND N2 ATMOSPHERES.

An estimate of the quantity of toxic coke deposited on fresh and regenerated Pt/Alj₂O₃ catalyst has been determined for methylcyclopentane (MCP) reforming in a Berty CSTR at 390°C, W/F=0·11 g min cm^-3, total pressure of 1 atm and MCP partial pressure of 9·2 × 10^-2 atm in H₂ or N₂ carrier. Eleven cycles consisting each of catalyst deactivation, regeneration and reduction were investigated with 3 in H₂ and 8 in N₂. Oxidizable (primary) coke deposits were higher in N₂. However, higher levels of toxic (secondary) coke were deposited in H₂. The ratio of oxidizable to toxic coke lies between 1-15×10³ in H₂ and 22 - 55 × 10³ in N₂ The coke-time profiles for secondary coke removal exhibited maxima suggestive of three types of secondary coke with varying reactivity in H₂. Furthermore, the results strongly suggest that the cokes were layered on acidic coke forming sites with the solid phase transformation of primary to secondary coke occurring at the catalyst-coke interface.     

Performance Evaluation of Certain Commercial Hydrotreating Catalysts in a Pilot Plant Reactor

The performance of different hydrotreating catalysts was evaluated in a pilot plant trickle bed reactor using a feedstock collected from an industrial diesel hydrodesulfurization unit. The feed is a typical blend of straight run diesel fractions from crude distillation units, FCC cycle oils, heavy naphtha, etc. It contains 1.11 wt% of sulfur, 0.12 wt% of nitrogen, and 34.6 wt% of total aromatics. The catalyst samples evaluated in the present work are commercially available high activity new generation catalysts being used in many refineries for diesel hydrodesulfurization application. The experiments were carried out at a constant pressure of 40 kg/cm² and a constant H₂/oil ratio of 200 l/l. Experiments were performed to study the influence of reactor temperature and liquid hourly space velocity on product quality. The reactor temperature was varied from 320-360°C at different liquid hourly space velocities. The liquid hourly space velocity was varied from 1.0 to 2.5 h^-1 at different reactor temperatures. The feed and product samples hydrotreated in the pilot plant reactor were analyzed to determine their physical properties and measure sulfur, nitrogen, olefinic, poly-, di-, monoaromatic, and naphthenic hydrocarbons. Catalyst C was found to have the highest hydrodesulfurization activity among the catalysts studied. The hydrodesulfurization activity of catalyst A and catalyst B are similar. Catalyst D was found to have lower hydrodesulfurization and higher hydrodenitrogenation activity compared to catalyst C.     

Desulfurization of FCC Gasoline Over Mordenite Modified with Al2O3

Mordenite modified with Al₂O₃ (Al₂O₃/mordenite) was synthesized and used for the desulfurization of FCC gasoline. The influences of operating parameters on the results were studied for the model solution composed of dibenzothiophene (DBT) and isooctane. Al₂O₃/mordenite exhibits higher sulfur capacity than other kinds of chemisorbents. The suitable composition of the chemisorbent is 30 wt% Al₂O₃ to 70 wt% mordenite. The optimal operating parameters are: temperature 160°C; velocity 3 h^-1 (WHSV). Under the stated conditions, desulfurization was carried out for the FCC gasoline with sulfur content of 220.4 μg/g. The chemisorbent can maintain the sulfur content under 50 μg/g for 40 h and has good regeneration ability after desorption using benzene.     

COMPARATIVE REACTION STUDY OF METHYLCYCLOHEXANE AND 3-METHYLHEXANE IN H2 AND N2 ON Pt/Al2O3 CATALYST

The reaction of methylcyclohexane and 3-methylhexane were studied in a pulse microcatalytic reactor using H₂ and N₂ carriers on Pt/Al₂O₃ catalyst at temperatures from 350 to 500°C, contact times (W/F) of 1.25 × 10^-3-3.75 × 10^-3 g min/ml and a total pressure of 4.0 kg/cm². In N₂, there was complete conversion of methylcyclohexane to methane, benzene and toluene while similar products were produced for 3-methylhexane, albeit with diminished conversion level. In H₂, methane was produced from 3-methylhexane conversion while aromatization without demethylation was obtained in addition to some cracking for methylcyclohexane at the low temperature range (350-400°C); a higher temperature range (460-500°C) resulted in complete fragmentation for methylcyclohexane. In H₂-N₂ mixtures, the presence of N₂ of not less than 50% in the carrier gas stream yielded an aromatic catalyst at conditions where only cracking activity was previously evident. The differences in product distribution and/or product types for the two reactants in H₂ and N₂ suggest a different reaction mechanism for both reactants.     

The Role of Nitrogen in Facilitating Methylcyclohexane Aromatization on Pt/Al2O3 and Pt-Re/Al2O3 Catalysts

The kinetics of methylcyclohexane aromatization on commercial Pt/Al₂O₃ and Pt-Re/Al₂O₃ catalysts was investigated in a micro-reactor using N₂ and/or H₂ as carrier gases at temperatures ranging between 300-500°C, W/F values ranging between 0.83-3.75 mg min/mL and at a total pressure of 4.0 kg/cm². On both catalysts in N₂ atmosphere, aromatization accompanied by demethylation was observed with the formation of cracked products, benzene and toluene. However, in H₂ methane was the predominant product of methylcyclohexane reforming on PtA1₂O₃ and Pt-Re/Al₂O₃ at 500°C and 400-500°C respectively, whereas at 350°C, aromatization was predominant on Pt/Al₂O₃ but on Pt-Re/Al₂O₃, aromatization was accompanied by fragmentation to methane. In N₂-H₂ mixtures, demethylation activity was observed to decrease with H₂ content of the mixture on Pt-Re/Al₂O₃. A preliminary test of the kinetic data using Sica's method of pulse kinetic analysis suggests a first order rate in methylcyclohexane with activation energies of 3.21 kcal/gmol in N₂ and 19.70 kcal/gmol in H₂ for the Pt/Al₂O₃ catalyst and 16.66 kcal/gmol in N₂ and 34.94 kcal/gmol in H₂ for the Pt-Re/Al₂O₃ catalyst. However, a more comprehensive kinetic analysis suggested an aromatization mechanism for Pt-Re/Al₂O₃, where adsorbed H₂ was a participant. A different aromatization mechanism for the reaction in N₂ where hydrogen was not needed explained the data on Pt/Al₂O_3. In both cases, the desorption of toluene was determined as the rate determining step.     

Oligomerizing Olefins in Light Coke Gasoline to Diesel

We prepare a catalyst for FCC gasoline polymerizing to produce diesel oil, which uses non-noble metal Ni as the main active component; here mesopore γ-Al₂O₃ is used as the carrier. The effects of mass fraction of active components and the condition of preparing were investigated simultaneously. The results show that mass fraction of the main active component is 8%, soakage time is 6 hr, and the roasting temperature is 500°C to roast for 4 hr, which are better conditions for preparing the catalyst. Under the condition of a reaction temperature of 210°C, reaction pressure is 3.0 Mpa, space velocity is 1.0 h^-1, and volumetric percent of diesel is 42.0%, which meet a criterion of -35^# diesel. At the same time we study the stability and regeneration of the catalyst with good results.     

REFORMING OF N-OCTANE ON A Pt/Al2O 3 CATALYST. 1. PRODUCT DISTRIBUTION AND KINETIC ANALYSIS.

The conversion of n-octane on Pt/Al₂O₃ catalyst to hydrocracked products, isooctane, ethylbenzene, o-,p-,m-xylene and toluene was investigated in hydrogen in a Berty CSTR at three different partial pressures of n-octane, 101·325 KPa total pressure, temperatures between 400°C-460°C and W/F values up to 0·33gmincm^-3. The hydrocracked products were the most predominant. Of the other products, isooctane was present in the highest yield. A sequence of elementary steps based on the suggested reaction network of Ako and Susu (1986) was found to predict the experimental conversion-W/F data with the conversion of adsorbed isooctane to adsorbed o-xylene as the rate determining step. The activation energies for the forward and backward reactions of this step were determined to be 21·2 and 14·3 Kcal/gmol, respectively.     

A Comprehensive Evaluation of High Viscous Crude Oil from Shuguang No. 1 Zone of Liaohe Oil Field

The high viscous crude oil from Shuguang No. 1 zone of Liaohe oil field has the characteristics of high density (ρ₂₀ = 0.9977 g cm^-3), great viscosity (ν₁₀₀ = 1223.9 mm² s^-1) and high pour point (48°C), which are similar to those of the residue distillation of general crude oils. It contains no gasoline distillation and the diesel oil fraction yield is just 7.19%. It is often used as fuels after emulsification. But this oil is so vicious that it cannot be atomized uniformly and burned fully. In order to make full use of it, this kind of high viscous crude oil has been evaluated comprehensively and the properties of its various distillations are analyzed respectively. The results indicate that this crude oil contains less wax, but more resins and asphaltene, which belongs to low-sulfur naphthene-base crude oils and it is the suitable material to produce high-quality paving asphalt. Based on its characteristics, the optimum processing scheme is put forward and the high-quality paving asphalt is produced by using the distillation higher than 350°C.     

Study on Improving Oxidation Stability of Catalytically-Cracked Diesel Oil

In this article, oxidation stabilities of catalytically-cracked diesel oil extracted with several solvents were studied respectively. The experimental results showed that double-solvent extraction was the better method than others, in which furfural containing transition metal ion was used as the first extraction solvent and the 95% ethanol solution was the second extraction solvent. During the course of accelerated storage test, the amount of sediment was reduced from 27.56 mg/100 mL to 0.43 mg/100 mL, and met the requirement of premium grade diesel oil. Under the experimental condition: shaking time of 3 min, the volume ratio of solvent to oil of one and operating temperature 30°C, the extraction result is most satisfied. The color and existent gum reached the standard of premium grade diesel oil. The removal rate of sulfur was up to 74.5%, the removal rate of nitrogen 93.8%. The cetane number of catalytically-cracked diesel oil was enhanced from 37.3 to 51.2. The oxidation stability was improved greatly after being treated.     

HYDROPROCESSING OF COAL-DERIVED MIDDLE DISTILLATE

Coal-derived middle distillate, boiling range 437 to 623^°K, was hydrotreated in a fixed bed reactor with a commercial N_iO-M_o0₃/ Al₂O₃ catalyst. The feedstock contained predominantly highly-substituted aromatics. The product heteroatom content and aromaticity decreased with increased process temperature or pressure. Aromaticity was proportional to liquid space velocity. Heteroatonms could be effectively reduced at hydroprocessing conditions of 653^°K, 10 MPa, and 2 WHSV. Experimentally-derived cetane number was found to be proportional to product aromaticity. Severe hydroprocessing conditions were required to produce diesel fuel of acceptable cetane number.     

RECOVERY OF ASPHALTENES FROM TAR SAND BY SUPERCRITICAL FLUID EXTRACTION

Many non-oil producing countries are enriched with other sources of energy, for example tar sand, oil shale, coal, biomass, and uranium, that are not fully utilized. Supercritical fluid extraction (SFE) of tar sand was carried out in a batch autoclave at different temperatures. Extracts recovered from SFE were fractionated into oils, asphaltenes, preasphaltenes and gases by solvent extraction. The highest yield) of SFE (24.3 wt % dry basis) from tar sand was obtained with n-pentane/benzene (1/1, v/v') mixture at 655 K. Comparison of the amount of n-alkanes (C1-C4) evolved at 585 K and 685 K shows that the amount of methane is significantly increased at 685 K whereas the amount of C4 alkane is reduced. At 685 K, hydrogen and methane represent 45·1 vol % of the gases evolved from the SFE. The yields of C1-C3 alkane hydrocarbons were higher for supercritical fluid extracts at 685 K as compared to those obtained at 585 K. The quantity of olefines (C₂H₄ + C₃H₆) was found between 5·1 and 10·1 vol %.     

A Pipe-Loop Apparatus to Investigate Asphaltene Deposition

A circulating pipe-loop has been designed to measure asphaltene deposition under flowing conditions. Bitumen and n-heptane are combined to induce asphaltene precipitation at the entrance of a test section in which deposition is to be measured. The n-heptane is separated from the bitumen at the exit of the test section allowing the asphaltenes to redissolve in the bitumen before it is pumped back to the test section. In the test section, solid deposits are measured nonintrusively with X-ray tomography using a computer assisted tomographic (CAT) scanner. A segment of the test section is also removable for direct gravimetric measurement and collection of deposits. The pipe-loop is designed to investigate the effect of flow rate, solvent type, solvent-to-bitumen ratio, metal type, temperature, and pressure on asphaltene deposition. The effect of additives can also be assessed. The system is rated for pressures upto 7 MPa, temperatures from 25 to 100°C, and flow rates up to 0.1 m³/h.     

A STUDY ON THE EFFECT OF PREPARATION PARAMETERS ON THE CATALYTIC PERFORMANCE AND ACTIVE COMPONENTS OF A NEW TYPE HYDRODESULFURIZATION CATALYST

The effects of the impregnating conditions on the contents of the active components of a new type hydrodesulfurization (HDS) catalyst have been studied by ICP technique in this paper. Meanwhile, the effects of the activation temperature, the activation time and the calcining temperature on the catalytic properties of the CoMo/(TiO₂ + Al₂O₃) catalyst have also been studied. The results show that at the given hygroscopicity of the support, the contents of the Co and the Mo, both of which are the active components of the catalyst, change linearly with the changes of the concentrations of the solvents in the impregnant. When the catalyst is impregnated at 40°C for 2 h, the contents of the active components reach the maximum values. The calcining temperature sharply affects the dispersed state of the active components on the surface of the support. When calcined at 500°C for 2 h, this HDS catalyst obtains the best catalytic activity. Even when the catalyst has been calcined at 600°C for 3 h, its activity is still good, which indicates that the heat resistance of this new type catalyst is satisfactory.     

REFORMING OF N-OCTANE ON A Pt/Al2O3 CATALYST. II. KINETIC ANALYSIS OF HYDROGEN DEPENDENCE.

The conversion of n-octane on Pt/Al₂O₃ catalyst was found to pass through pronounced maxima with the variation of the partial pressure of hydrogen at temperatures between 420°C-460°C, P_N = 7·63 × 10^-3 atm and W/F = 0·11lg min cm_-3. The products of reaction were hydrocracked products, octane, ethylbenzene, o-.p-,m,-xylene and toluene. The order of appearance of the optimum PH for the various reactions were: Isooctane>Dehydrocyclized products>Hydrocracked products.

A sequence of elementary steps earlier postulated was found to predict the maximum in the n-octane P_H profiles for the three temperatures investigated. The rate determining steps for the two rate equations that were found suitable were conversion of adsorbed isooctane to adsorbed o-xylene and ethylbenzene.