Hydrocracking of LVGO Using Dispersed Catalysts Derived from

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Kinetics, Catalysis, and Reaction Engineering

HYDROCRACKING OF LVGO USING DISPERSED CATALYSTS DERIVED FROM SOLUBLE PRECURSORS: PERFORMANCE EVALUATION AND KINETICS Ahamd Al-Rashidy, Tareq Al-Attas, Syed Ahmed Ali, Saad A. AlBogami, Shaikh Abdur Razzak, and Mohammad Mozahar Hossain Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.9b02658 • Publication Date (Web): 17 Jul 2019 Downloaded from pubs.acs.org on July 17, 2019

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Industrial & Engineering Chemistry Research

HYDROCRACKING OF LVGO USING DISPERSED CATALYSTS DERIVED FROM SOLUBLE PRECURSORS: PERFORMANCE EVALUATION AND KINETICS Ahmad H. Al-Rashidy1, Tareq A. Al-Attas1,4, Syed A. Ali2, Saad A. Al-Bogami3, Shaikh A. Razzak1, Mohammad M. Hossain1* 1Department

of Chemical Engineering, 2Center for Refining and Petrochemicals, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia

3Research

and Development Center, Saudi Arabian Oil Company (Saudi Aramco), Dhahran 31311, Saudi Arabia

4Department

of Chemical and Petroleum Engineering, University of Calgary, 2500 University Drive NW, Calgary, Alberta T2N 1N4, Canada

ABSTRACT The promotional effects of dual water-soluble and bimetallic oil-soluble precursors for the LVGO hydrocracking were investigated. The water-soluble Fe-Mo precursor caused the reduction in naphtha and coke yields while the bimetallic oil-soluble layered ammonium nickel molybdate (Ni-LTM) catalyst precursor reduced the coke deposition without affecting the naphtha yield. The synergistic effects of the Ni-LTM were investigated by employing it as a co-catalyst with a Ni-W/Al2O3-SiO2 catalyst. The Ni-LTM significantly decreased the coke deposition on the supported catalyst as noticed by the SEM images. A five-lump discrete reaction scheme was found suitable for the kinetic modeling of the LVGO hydrocracking over the co-catalytic system. The estimated kinetic parameters show that the LVGO has a higher probability of being converted to naphtha than distillate, which explains the high selectivity of naphtha compared to the other pseudo products. The catalyst decay constant decreased with the process severity indicating an enhancement of hydrogenation by the dispersed catalysts. Keywords: slurry phase hydrocracking, dispersed catalysts, LTM, coke deposition, lumped kinetic model *Corresponding author: Mohammad M. Hossain; Tel: +966 13 860 1478; Fax: +966 13 860 4234; E-mail address: [email protected]

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1.

INTRODUCTION

The depleting supply of light crude oil synchronized with the growing demand for the clean lighter fuels has compelled petroleum refiners to process the low-value streams such as bitumen, fuel oil and residual oils.1 Catalytic hydrocracking is one of the most sufficient approaches for upgrading the quality of heavy feedstocks into high-value light products.2–4 Amongst the available hydrocracking technologies, slurry-phase processing is the most flexible configuration due to its versatile characteristics.5,6 This technology can convert up to 95 % of heavy oil of vacuum residue.7 Additionally, slurry-phase hydrocracking can minimize the production losses by reducing the formation of coke. Minimum limitations of intra-particle mass transfer between the solid catalyst and the heavy hydrocarbon molecules could be achieved by using smaller catalyst particles at high agitation speeds.4 Slurry-phase hydrocrackers utilize both supported and unsupported metal catalysts. However, the supported catalysts suffer from faster deactivation due to the deposition of coke on the catalyst surface. This results in subsequent production losses and equipment fouling.8 Alternatively, the dispersed catalyst provide high hydrogenation activity because of their small sizes that are similar to reactant molecules which reduces the formation of coke and minimizes the fouling of equipment.9–11 The presence of free active metal sites, formed by in-situ sulfidation of precursors, enhances the catalytic HYD reactions. In addition, it reduces the condensation probability of polynuclear aromatic hydrocarbons (PAHs) by hindering the polymerization reactions of the free radicals formed by the thermal cracking. The high surface area-to-volume ratio of the dispersed catalysts reduces the mass transfer limitations by minimizing the gradients of concentration and facilitating the reactants diffusion inside the catalyst particles.11


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Dispersed catalysts are categorized into two general types: finely dispersed powder catalyst and soluble dispersed catalyst (water-soluble and oil-soluble).12–14 The soluble dispersed catalyst precursors are diluted in solvent (water or oil) prior to injecting to the process to ensure an effective dispersion for the in situ active metal sites formed subsequently. Therefore, the dispersion of the active metal sites derived from soluble precursors is higher compared to those obtained from the finely powder dispersed catalysts. Moreover, the soluble dispersed catalyst requires relatively low concentration to attain appreciable catalytic performance and dispersion. The use of low concentration of the soluble catalyst precursors makes them the best choice in terms of reducing the cost of catalytic materials. The difficulty of recovering these catalysts could be avoided by utilizing small amounts of the catalyst precursors, which increases the probability of trapping most of the formed metal sites within the solid (i.e. coke and solid supported catalyst).15–17 Oil-soluble dispersed catalyst are mainly organometallic compounds of nickel, molybdenum, iron naphthenates and alkyl thiometallates.3,14 Although oil-soluble dispersed catalysts have good catalytic activity and excellent dispersion characteristics, their use is restricted to 1000 ppm because they are expensive. Water-soluble catalyst precursors are adequate substitutes because of their simple synthesis and low price. Examples of water-soluble molybdenum-based catalyst precursors are ammonium molybdates, phosphomolybdic acid, ammonium tetrathiomolybdate and ammonium heptamolybdate.18 However, the water-soluble catalysts are less reactive than oil-soluble catalysts due to the rapid evaporation of water at process temperature which causes reduction in reactivity by the agglomeration and reduction in the dispersion of catalyst particles.12,13 Thus, the use of water-soluble catalyst precursors requires pretreatment, including emulsion followed by dehydration.14



The effect of water-soluble catalyst precursors from metallic sulfates was studied by Luo et al.12 in slurry-phase hydrocracking of Liaohe vacuum residue. The group used ferrous sulfate (FeSO4∙7H2O) and nickel sulfate (NiSO4∙6H2O) as the catalyst precursors.12 The effect of using the water-soluble catalyst precursors on heavy oil upgrading was further investigated by OrtizMoreno et al.18 by studying the influence of the concentration of catalyst precursors, reaction temperature and pressure. Ammonium tetrathiomolybdate and ammonium heptamolybdate were used as the water-soluble precursors that are in-situ activated to form molybdenum sulfides.18 A bimetallic oil-soluble catalyst precursors were prepared by Jeon et al.19 using the layered ammonium nickel molybdate (Ni-LTM). More recently, Nguyen et al.20 reported the use of molybdenum naphthenate, nickel octoate and vanadium acetylacetonate as oil-soluble precursors for dispersed catalysts.20 Bellussi et al.21,22 showed that the use of an oil-soluble catalyst can boost the conversion of hydrocracking in the presence of an acidic solid supported catalyst.21,22 Most of the reported studies discuss experimental investigations of dispersed precursors on hydrocracking of heavy feeds as standalone catalysts or in the presence of another soluble precursor as a dual function. Moreover, very few studies have explored the approach of implementing both homogenous soluble dispersed catalyst and solid supported catalyst to study its synergic effects.23–25 Hence, the present research is aimed at investigating the promotional effects that can be attained dual water-soluble precursors and a bimetallic oil-soluble precursor for the light vacuum gas oil (LVGO) hydrocracking in a slurry-phase reactor. Furthermore, the synergistic effects of the bimetallic oil-soluble catalyst precursor were investigated by introducing a first-stage solid supported hydrocracking catalyst. A five-lump discrete reaction scheme is developed to further study the reaction kinetics of the LVGO hydrocracking over the co-catalytic system.


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2.

MATERIALS AND METHODS

2.1

Materials

All chemicals were of analytical grade were obtained from Sigma-Aldrich (USA) and used as received without any further purification. For preparing the water-soluble dispersed catalyst precursor, ammonium thiomonomolybdate, nickel(II) nitrate hexahydrate (Ni(NO3)2∙6H2O, 99.999% trace metals basis) and iron(III) nitrate nonahydrate (Fe(NO3)3∙9H2O, ≥99.95% trace metals basis) were selected. The sorbitan monooleate (C24H44O, Span® 80 for synthesis) was chosen as an emulsifier. The bimetallic oil-soluble precursor is synthesized by adopting ammonium heptamolybdate tetrahydrate ((NH4)6Mo7O24·4H2O, cryst. extra pure), nickel(II) nitrate hexahydrate (Ni(NO3)2∙6H2O, 99.999% trace metal basis), ammonium hydroxide (NH3, 28.8%) and oleic acid (CH3(CH2)7CH=CH(CH2)7COOH, ≥99% (GC)). The gases used in the catalysts evaluation, i.e. hydrogen and nitrogen, were purchased from the Saudi Industrial Gas Company (SIGAS) with a purity of 99.999%. The feedstock for the process is light vacuum gas oil (LVGO) and was obtained from a Saudi Aramco refinery. A commercial supported catalyst for first-stage hydrocracking was used to study the synergetic effects with the dispersed catalysts. The catalyst is composed of nickel and tungsten metal oxides anchored on amorphous Al2O3-SiO2. Table 1 lists the textural and structural properties of the solid supported catalyst. 2.2 Preparation of the Water-Soluble Catalyst Precursor The water-soluble bimetallic dispersed catalyst precursor is prepared by mixing 250 ppm (0.0125 g) of ammonium thiomonomolybdate with 250 ppm (0.0125 g) of nickel nitrate or iron nitrate. The catalyst precursors are mixed with 30 mL of sorbitan monooleate (Span® 80) emulsifier and 100 mL of water to form an aqueous solution. Then, the catalyst precursor’s mixture is added drop-wisely to the heated LVGO at 80 °C. The mixture of catalyst precursors



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and feed is stirred at 80 °C and 2000 rpm for one hour. Figure 1 shows a demonstration of the feed/catalyst precursor preparation process. Upon completion, the mixture is heated to ~180 °C and bubbled with nitrogen to remove the water. Table 1. Properties of the commercial solid supported hydrocracking catalyst. Property

Unit

Value

Average length

mm

1.90

Compacted bulk density

g/cc

0.71

BET surface area

m2/g

288

Mean pore radius

nm

4.0

Pore volume

ml/g

0.56

Attrition loss

%

Hydrocracking of LVGO Using Dispersed Catalysts Derived from

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