Catalytic cracking of crude oil to light olefins and naphtha: Experimental and kinetic modeling
Graphical abstract
Introduction
While thermal cracking of various hydrocarbons remains the main source of light olefins, intense research is ongoing to develop cost-effective catalytic routes that are less energy intensive and that emit less carbon emissions (Rahimi and Karimzadeh, 2011). The major source of ethylene and propylene is the traditional steam naphtha cracker that supplies about 57% of global propylene as a by-product to ethylene production. The fluid catalytic cracking (FCC) unit is also an important source of propylene producing about 35% of world propylene as a by-product to gasoline production (Chau et al., 2016, Sadrameli, 2016). The remaining 8% of world propylene is produced by ‘on-purpose’ processes such as propane dehydrogenation, olefin metathesis and methanol-to-propylene.
The FCC process is known for its flexibility to crack a wide range of low-value heavy hydrocarbons as well as new potential feedstocks such as straight-run shale oils and bio-oils (vegetable and pyrolysis) through modifications to catalyst and operating conditions (Bryden et al., 2014, Vogt and Weckhuysen, 2015). However, light paraffinic oils contain lower molecular weight components boiling below 343 °C that are more difficult to crack especially the components below 221 °C with low coke production (Letzsch and Ashton, 1993). Corma et al. (2017) reviewed the direct catalytic cracking of crude oil to produce basic chemicals, mainly light olefins, using technologies derived from FCC. Several oil and chemical companies have patented various catalytic methods for the conversion of whole crude oil to light olefins and naphtha by integrating FCC unit with other processes (Powers, 2006, Long et al., 2014). Chen et al. (2015) suggested a two-stage FCC riser for the cracking of a mixture of shale oil and 30% vacuum residue to enhance the production of propylene.
Maximizing propylene yield in FCC unit requires specific catalysts or additives and the operation at high severity and short contact time (Buchanan, 2000). MFI additives can increase propylene yield from about 5 wt.% in conventional FCC unit to about 15 wt.% depending on the type of feedstock (Aitani et al., 2000). MFI additives crack C7–C10 gasoline range components to light olefins, mainly propylene and butenes (Arandes et al., 2000). The amount of MFI crystal added to USY-based FCC catalysts has increased with values as high as 25–30 wt.% are reported in some FCC units. High propylene yields in FCC result from naphtha over-cracking and low hydrogen transfer reactions as a function of the strength of additive acid sites and fast diffusion of desired light olefins (Awayssa et al., 2014).
Various methods have been developed for testing FCC catalysts and diverse feeds ranging from light hydrotreated vacuum gas oil (VGO) to blends containing atmospheric and vacuum residues (Corma and Sauvanaud, 2013, Bryden et al., 2015, Vogt and Weckhuysen, 2015). The early method was the Micro Activity Test (MAT) which uses a fixed-bed reactor to measure conversion by changing the catalyst-to-oil (C/O) ratio. Despite its various drawbacks related to operation mode and reactant–catalyst contact, the MAT method is still used. Other laboratory fluidized-bed techniques have been developed to overcome the above drawbacks and provide more realistic laboratory testing taking into consideration FCC process short residence time and fast catalyst deactivation. These techniques include the CREC Riser Simulator reactor (Arandes et al., 2000, Passamonti et al., 2012), ACE Advanced Cracking Evaluation (Kayser, 2000), micro-downer (Corma and Sauvanaud, 2013) and circulating riser pilot plant unit (Lappas et al., 2015, Bryden et al., 2015).
In this work, we have studied the direct catalytic cracking of three light crude oils in a MAT unit at FCC operating conditions using commercial E-Cat blended with MFI additive. The effect of MFI Si/Al molar ratio (30, 280 and 1500) and post modification by steaming on light olefins yield were evaluated. Kinetic modeling of crude oil cracking was conducted using a 4-lump model to determine the kinetic constants and the activation energies between 500 °C to 550 °C and catalyst/oil ratios of 2 to 4.
Section snippets
Feedstocks and base catalyst
The crude oils used in this study, Arab Super Light (ASL), Arab Extra Light (AXL) and Arab Light (AL), were procured from a domestic oil company. The properties of ASL, AXL and AL are listed in Table 1. ASL feed is a low-sulfur crude oil with an API gravity of 51° while AXL has an API of 39° and higher sulfur content was about 1.2 wt.%. Arab Light crude oil with an API gravity of 34 has the highest sulfur content (1.8 wt.%) of the three feeds. The naphtha fraction (C5221 °C) in ASL, AXL and AL
Catalyst characterization
XRD patterns of the MFI additives are shown in Fig. 1. All additives showed characteristic peaks of MFI between 8–9° and 22–25° (Baerlocher et al., 2001, Treacy et al., 1996). There was no change in crystallinity for all the additives.
The nitrogen adsorption isotherms exhibited type I isotherm for all additives which is typical of microporous materials. The increase in the adsorbed amount between p/p0 of 0.9 and 1.0 is due to the adsorption in inter-particle voids. The textural parameters
Reaction scheme
A kinetic study was conducted on the catalytic cracking of one of the feeds; AL crude oil. Crude oil consists of a large number of reactants which belong to different distillation cuts and chemical groups. Since it would be complicated to represent all the equations in a kinetic scheme, lumping of the reactants and products based on their boiling points is used to simplify the kinetic model (Ancheyta-Juarez et al., 1997). For crude oil cracking, a four-lump model comprising (HCO + LCO), naphtha,
Conclusions
This study has demonstrated the ability for direct catalytic cracking of crude oils to light olefins and high-aromatics naphtha under FCC conditions. The cracking of AXL crude oil (°API = 39) over E-Cat/MFI yielded 16.5, 21.3 and 19.4 wt.% C2–C4 light olefins for MFI with Si/Al ratio of 30, 80 and 1500, respectively, compared with 13.0 wt.% over E-Cat alone (at 60% conversion). A similar trend was observed with another light paraffinic crude oil (ASL) with °API of 51, yielding 14.5 wt.% light
Acknowledgements
The authors appreciate the support from the Ministry of Education, Saudi Arabia in the establishment of the Center of Research Excellence in Petroleum Refining & Petrochemicals (CoRE-PRP) at KFUPM.
References (52)
- et al.
Effects of high-level additions of ZSM-5 to a fluid catalytic cracking RE-USY catalyst
Appl. Catal. A
(1995) - et al.
Maximization of FCC light olefins by high severity operation and ZSM-5 addition
Catal. Today
(2000) - et al.
5-Lump kinetic model for gasoil catalytic cracking
Appl. Catal. A
(1999) - et al.
Modified HZSM-5 as FCC additive for enhancing light olefins yield from catalytic cracking of VGO
Appl. Catal. A
(2014) - et al.
Five-lump kinetic model with selective catalyst deactivation for the prediction of the product selectivity in the fluid catalytic cracking process
Catal. Today
(2007) The chemistry of olefins production by ZSM-5 addition to catalytic cracking units
Catal. Today
(2000)- et al.
Mechanistic considerations in acid-catalyzed cracking of olefins
J. Catal.
(1996) - et al.
FCC testing at bench scale: new units new processes, new feeds
Catal. Today
(2013) - et al.
Synergy effects of ZSM-5 addition in fluid catalytic cracking of hydrotreated flashed distillate
Appl. Catal. A
(2002) - et al.
Role of pore structure in the deactivation of zeolites (HZSM-5, Hβ and HY) by coke in the pyrolysis of polyethylene in a conical spouted bed reactor
Appl. Catal. B
(2011)
Modified HZSM-5 zeolites for intensifying propylene production in the transformation of 1-butene
Chem. Eng. J.
Modification of ZSM-5 zeolite for maximizing propylene in FCC reaction
Catal. Commun.
Catalytic cracking of Arabian Light VGO over novel zeolites as FCC catalyst additives for maximizing propylene yield
Fuel
Feedstock and catalyst effects in fluid catalytic cracking—comparative yields in bench scale and pilot plant reactors
Chem. Eng. J.
The effect of feedstock on yields and product quality
Stud. Surf. Sci. Catal.
Effects of temperature and catalyst to oil weight ratio on the catalytic conversion of heavy oil to propylene using ZSM-5 and US-Y catalysts
J. Nat. Gas Chem.
Inter-conversion of light olefins on ZSM-5 in catalytic naphtha cracking condition
Catal. Today
ZSM-5 zeolites with different SiO2/Al2O3 ratios as fluid catalytic cracking catalyst additives for residue cracking
Chin. J. Catal.
The effect of hydrothermal treatment of FCC catalysts and ZSM-5 additives in catalytic conversion of biomass
Appl. Catal. A
Comparison between fixed fluidized bed (FFB) and batch fluidized bed reactors in the evaluation of FCC catalysts
Chem. Eng. J.
Fluid catalytic cracking: science and technology
Stud. Surf. Sci. Catal.
Catalytic cracking of hydrocarbons over modified ZSM-5 zeolites to produce light olefins: a review
Appl. Catal. A
Thermal/catalytic cracking of liquid hydrocarbons for the production of olefins: catalytic cracking review
Fuel
Optimum reference temperature for reparameterization of the Arrhenius equation part 2: problems involving multiple reparameterizations
Chem. Eng. Sci.
Enhancing propylene production from catalytic cracking of Arabian Light VGO over novel zeolites as FCC catalyst additives
Fuel
Relation between properties and performance of zeolites in paraffin cracking
J. Catal.
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