Catalytic Cracking of Light Crude Oil: Effect of Feed Mixing with Liquid

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Catalytic Cracking of Light Crude Oil: Effect of Feed Mixing with Liquid Hydrocarbon Fractions Abdulhafiz Usman, Abdullah Aitani, and Sulaiman Saleh Fahad Al-Khattaf Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/ acs.energyfuels.7b02324 • Publication Date (Web): 25 Sep 2017 Downloaded from http://pubs.acs.org on September 29, 2017

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Gas/Liquid

Total Gases

Naphtha

FCC Fractionator

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AXL Feed HCO

Recycle Stream

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LCO

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Catalytic Cracking of Light Crude Oil: Effect of Feed Mixing with Liquid Hydrocarbon Fractions Abdulhafiz Usman a,b, Abdullah Aitani a, Sulaiman Al-Khattaf a,b* a

Center of Research Excellence in Petroleum Refining & Petrochemicals, King Fahd University of Petroleum & Minerals, Dhahran 31261, Saudi Arabia b

Department of Chemical Engineering, King Fahd University of Petroleum & Minerals, Dhahran 31261, Saudi Arabia

Email addresses of authors: •

Abdulhafiz O. Usman: [email protected]

•

Abdullah M. Aitani: [email protected]

•

Sulaiman S. Al-Khattaf: [email protected]

* Corresponding author: Sulaiman S. Al-Khattaf, Postal Address: Center of Research Excellence in Petroleum Refining & Petrochemicals, P.O. Box 5040, King Fahd University of Petroleum & Minerals, Dhahran 31261, Saudi Arabia, Email address: [email protected]; Phone: +966-13-8602029, Fax: +966-13-860-4509

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ABSTRACT The direct catalytic cracking of Arab Extra Light (AXL) crude oil was conducted in a microactivity test (MAT) unit at 550 °C where product recycling was simulated by mixing feed and liquid products in varying proportions. The effect of AXL mixing with total liquid product (LP) or a mixture of light cycle oil (LCO) and heavy cycle oil (HCO) was investigated at various ratios to determine the dependence of light olefins yield on feed composition. It was observed that mixing the least amount of LP with AXL yielded about 20.3 wt % light olefins and 39.6 wt % naphtha. The cracking of AXL and LCO+HCO yielded similar results as the case of cracking LP. A configuration of 100% recycle of liquid product without blending with AXL feed showed an increase in the yield of light olefins from 20 wt % to 29 wt % associated with a decrease in naphtha yield to from 40 wt % to 27 wt %. A second configuration of 100% recycle of LCO+HCO without blending with AXL feed showed that the yield of light olefins increased from 20 wt % to 26 wt % associated with an increase in naphtha yield to from 40 wt % to 50 wt %. The study has shown that the recycling of low-value heavy fraction (LCO+HCO) is a cost-effective means to supplement the AXL feed without loss in the yield of desired light olefins and naphtha. Keywords: Catalytic cracking, light olefins, crude oil, blending, heavy cycle oil, light cycle oil 1. INTRODUCTION Refiners are looking for means to enhance their profit margins by integrating fuel production with selected basic chemicals manufacture.1 Intermediate refinery streams are utilized in steam cracking for light olefins production or in catalytic naphtha reforming for aromatics production. The changing properties of transportation fuels due to environmental regulations and the stagnant growth in the demand for transportation fuels have necessitated the coproduction of light olefins (mainly propylene) from the fluid catalytic cracking (FCC) unit.2 While the FCC process remains the main conversion unit for gasoline production, it is also the second important source for propylene after steam naphtha cracking.3-5 High severity operation (high reaction temperature and high catalyst/oil ratio) has increased propylene yield in FCC units from 5 wt % to more than 20 wt % in the cracking of vacuum gas oil (VGO) and other heavy fractions.6 Enhancing the production of propylene in the FCC unit requires the utilization of USY catalyst blended with stable zeolite additive.7-9 The main additive used in FCC catalyst to increase the yield of liquefied petroleum gas (LPG) is MFI 1 ACS Paragon Plus Environment

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(ZSM-5) zeolite which allows the cracking of naphtha-range components to light olefins.10-13 MFI selectively cracks the C5+ olefins, thereby reducing the olefinicity of FCC gasoline and increasing propylene and butenes production. The flexibility of the FCC unit in handling a variety of conventional gas oils and vacuum residues has allowed refiners to utilize new feedstocks such as shale and tight crude oils. Various oil and catalyst companies have conducted research on the conversion of crude oil to naphtha and light olefins.14-17 A two-stage riser FCC unit was investigated for cracking a mixture vacuum residue and shale oil to increase propylene yield.15 Corma et al. reviewed various strategies for the direct conversion of crude oil to chemicals utilizing the FCC unit and related catalysts.16 Our previous work17 has demonstrated that light crude oils can be cracked in a MAT unit at moderate conditions to yield light olefins and naphtha. Several studies have reported the re-cracking of various liquid hydrocarbon fractions in the FCC riser to increase the yields of naphtha and light olefins.18-22 While recycling part of the liquid products is done in the same riser reactor, the re-cracking of some of the products requires a costly separate reactor. Various naphtha schemes have been proposed and the optimum scheme was co-feeding cracked naphtha with VGO using the same feed injector to increase propylene yield.22 In another study23, naphtha reactivity and propylene yield from the catalytic cracking of various types of naphtha increased in the following order: heavyFCC cracked naphtha < light straight run naphtha < heavy straight run naphtha < light cracked naphtha. It was found that the cracking of liquid hydrocarbon fractions such as FCC naphtha or LCO increased the production of high-octane gasoline or light olefins depending on the type of the feed, composition of the catalyst and operation severity.24,25 The recycling of partially hydrogenated light cycle oil (LCO) and cracking over different Y zeolites with MFI additive suppressed hydrogen transfer reaction and yielded high propylene and butenes in LPG fraction.25 In this work, liquid products from the cracking of Arab Extra Light (AXL) crude oil were recracked over commercial equilibrium catalyst (E-Cat) and MFI additive by mixing the AXL feed with liquid MAT products and commercial FCC liquid products to simulate two recycle configurations. Total liquid product and a mixture of LCO and HCO were mixed at different ratios with AXL feed in a MAT unit to study their impact on the incremental yields of naphtha and light olefins.

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2. EXPERIMENTAL SECTION 2.1.

Feedstocks. The AXL crude oil, LCO and heavy cycle oil (HCO) used in this work

were procured from an industrial FCC unit at a local refinery. LCO and HCO fractions were used as representative products obtained from the fractional distillation of the FCC liquid product in industrial FCC unit. The physical and distillation properties of AXL are presented in Table 1. AXL is a light paraffinic crude oil extracted from Saudi Aramco’s Shaybah supergiant oil field with an API gravity of 39° and a sulfur content of 1.6 wt %.17 The simulated distillation of AXL showed that AXL contains 34.2 wt % naphtha, 28.3 wt % middle distillates (221-343 °C) and 37.5 wt % heavy oil fraction (343+ °C). The analysis of AXL naphtha, determined by GC-PONA, showed a content of 64.7 wt % paraffins, 8.5 wt % naphthenes and 26.8 wt % aromatics. A secondary (derivative) feed used in was the total liquid product (LP) obtained from several MAT runs using AXL crude oil as feed at 550 °C and CTO of 3.0. The simulated distillation results of LP, LCO and HCO feeds are presented in Table 2. The naphtha content in LP was 59.6 wt % compared with 28.6 wt % in LCO and 7.1 wt % in HCO feed. LP, LCO and HCO feeds contained 40.4 wt %, 71.4 wt % and 92.9 wt % LCO+HCO fraction in the temperature range 221+ °C, respectively. LP, LCO and HCO were used as separate feeds in the MAT unit or mixed with AXL crude oil at various ratios. 2.2. Base Catalyst and MFI Additive. A commercial USY E-Cat was obtained from a local refinery and used as a base catalyst in the cracking of crude oil alone or mixed with liquid fractions. The E-Cat was calcined at 500 °C for 3 h at a rate of 5 °C/min before use. The commercial MFI additive was procured from Zeolyst Intl. in ammonium form (CBV28014 with nominal Si/Al molar ratio of 280). It was calcined in air at 550 °C for 3 h (3 °C/min) to get the H-form. The additive was pelletized, crushed and sieved out using 80-90 µ sieve. The properties of the E-Cat and MFI additive are presented in Table 3. Based on our previous work,17 E-Cat/MFI-280 additive yielded the highest light olefins in the catalytic cracking of different types of light crude oils including AXL. The E-Cat containing additive used in MAT testing was prepared by physical mixing of 25 wt % sieved MFI additive and 75 wt % E-Cat based on previous findings.17,27 2.3. Catalyst Characterization. The SiO2 and Al2O3 contents in E-Cat and MFI additive were determined using an inductively coupled plasma spectrometer (ULTIMA 2, ICP-OES) from HORIBA Scientific. The textural properties of the catalysts were measured by N2 3 ACS Paragon Plus Environment

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adsorption at 77 K utilizing a Micromeritics ASAP-2020 analyzer. The samples (50 mg) were outgassed at 240 °C for 2 h under N2 flow prior to measurements. The surface area and pore size were obtained by employing Barrett–Joyner–Halenda (BJH) method. The BrunauerEmmett-Teller (BET) surface area was determined from the desorption data within 0.06-0.2 relative pressure (P/Po). Temperature programmed desorption (TPD) was used to measure catalyst acid properties in a Mettler Toledo Star equipment. More details on the characterization methods are presented elsewhere.17 2.4. Catalytic Cracking in a MAT Unit. A micro-activity test (MAT) unit with a fixed-bed reactor was utilized for the catalytic cracking of AXL, LP, LCO, HCO and mixtures of AXL with liquid products. While MAT testing is widely used to evaluate the performance of FCC catalysts, it has been used to assess the reactivity and selectivity patterns of different hydrocarbon feedstocks. The feed injector was modified to handle AXL feed instead of conventional VGO. For each MAT test, a full mass balance was obtained. If the mass balance was less than 97% or greater than 102%, the test was repeated.11 All MAT tests were conducted at 550 °C, catalyst-to-oil (CTO) ratio of 3.0 and 30 s time-on-stream based on results from our previous work.17 The catalyst was stripped at 550 °C using nitrogen gas at 30 cc/min for 9 min. The dry gas (H2 and C1-C2) and LPG (C3-C4) in the MAT gaseous products were analyzed using a Micro-GC Agilent 3000A utilizing multi-column, multi-channel system and four thermal conductivity detectors (TCD). Liquid products were analyzed in a simulated distillation (SimDis) using Shimadzu GC 2010 Plus with a flame ionization detector (FID) to define three fractions: naphtha (C5-221 °C), LCO (221–343 °C) and HCO (343+ °C). Naphtha composition (paraffins, olefins, naphthenes, and aromatics) in AXL was determined using a Shimadzu GC with BP-1 PONA capillary column and FID detector. A Horiba Carbon Analyzer (EMIA) was used to determine the coke deposited on the spent catalyst by combustion method. The results of the analyses were used to calculate MAT conversion and product yields for crude oil and other fractions. Conversion was defined as the amount of 221°C+ fraction (LCO+HCO) in the feed (AXL, LP, LCO or HCO) which has been cracked to lighter gaseous and naphtha fractions as given below: Conversion (wt %) =

% % %


∗ 100%

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3. RESULTS AND DISCUSSION 3.1. Catalyst Characterization. The chemical and physical properties of E-Cat and MFI additive are presented in Table 3. The SiO2/Al2O3 ratios of E-Cat and MFI obtained by ICP analysis were 3.3 and 295, respectively. The results of N2 adsorption measurements showed that the nitrogen adsorption isotherm was a type I isotherm for the two samples which is typical of microporous materials. The BET surface area, micropore volume and mesopore volume calculated from the nitrogen sorption isotherms are shown in Table 3. The micropore volume was determined using the t-plot method. The NH3-TPD profiles of E-Cat and MFI additive showed two major desorption peaks. These peaks have maxima in low temperature region (100-300 °C) and high temperature region that corresponds to around 300-600 °C.10,26 The peaks appearing at the high temperature correspond to the ammonia desorbed from the acid sites of zeolites. The peaks appearing at the low temperature were assigned to ammonia molecules adsorbed either on NH4+ species formed on Brønsted acid sites or on Na+ cations. The total acidity for E-Cat was 0.09 mmol/g and that for MFI-280 was 0.07 mmol/g.26 3.2. Effect of MFI Addition on Product Yields. In order to determine the weight ratio of MFI additive that yields the highest amount of light olefins when physically blended with ECat, AXL feed was cracked using different ratios of E-Cat/MFI mixture. Our previous studies showed that the highest yield of light olefins was obtained at MFI additive concentration of 25 wt % blended with E-Cat for the cracking of VGO.10,11,27,28 Adewuyi et al.27 reported that the highest yield of light olefins occurred at an MFI concentration of about 25 wt % associated with an increase of about 150% in propylene and isobutene yield. However, above 25 wt%, the conversion of gasoline-range olefins was essentially complete, and the major effect of MFI was dilution of E-Cat with concomitant loss in overall conversion. The results of AXL cracking over E-cat/MFI-280 at 550 °C and CTO of 3.0 are presented in Figure 1. Increasing the MFI-280 concentration from 0 to 25 wt % resulted in an increase in the yield of light olefins from 12 to 21 wt % associated with a decrease in the yield of naphtha from 51 to 43 wt %. However, the increase in MFI-280 concentration from 25 to 100 wt % resulted in a decrease in the yield of light olefins from 20 to 10 wt % associated with a decrease in the yield of naphtha from 43 to 29 wt %. Therefore, the highest yield of light olefins from the cracking of AXL was obtained at 25 wt % additive concentration in a mixture of E-Cat and MFI-280 additive. Beyond 25 wt % additive concentration, the dilution of E-Cat with MFI-280 takes place which causes reduced light olefins yield.17 This confirmed


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the results from our previous experiments on the catalytic cracking of VGO feeds in a MAT unit.11,13 3.3. Cracking of AXL Crude Oil. The catalytic cracking of AXL crude oil was investigated over E-Cat/MFI-280 at 550 °C and a CTO ratio of 3.0. At 60 wt % conversion, the product yields (gases, naphtha, LCO, HCO and coke) are presented in Table 4. From our previous work,17 the CTO ratio of 3.0 was found to be representative of the maximum light olefins yield obtained from the cracking of AXL over E-Cat/MFI-280. At CTO ratio above 3.0, only marginal increases in light olefins yield were observed. As shown in Table 4, the cracking of AXL produced a total light olefins yield of 20.4 wt % (2.8 wt % ethylene, 9.5 wt % propylene and 8.1 wt % butenes). The yield of naphtha was the highest among all products (40.3 wt %) which may be attributed to the unconverted naphtha in the AXL feed and the formation of naphtha from the cracking of LCO and HCO fractions.29 The PONA composition of naphtha in the AXL feed and product showed an increase in aromatics content from 26.8 to 48.4 wt % and substantial formation of olefins of 26.0 wt %. This was likely due to the strength of acid sites within the MFI additive. Naphtha paraffins content decreased from 64.7 to 22.0 wt % and naphthenes decreased from 8.5 wt % to 5.1 wt % due to aromatization and cracking reactions.17 The yields of LCO and HCO from AXL cracking were 17.6 wt % and 9.6 wt %, respectively. These results are quite similar to product yields obtained from the cracking of conventional FCC VGO feed.13 The yield of dry gas and coke formation in the spent catalyst were 4.4 wt % and 1.6 wt %, respectively. 3.4. Cracking of Liquid Product (LP), LCO and HCO. The liquid product (LP) fraction obtained from the cracking of AXL was cracked at the same experimental conditions in which the AXL feed was initially cracked. The conversion and product yields of LP cracking are presented in Table 4. The low conversion of LP (1.2 wt %) can be attributed to the dilution of the feed by its high naphtha content (59.6 wt %) which is highly aromatic and has a low reactivity.23 The highest product yield from LP cracking was naphtha at 40.0 wt % followed by LCO (25.4 wt %) and HCO (14.5 wt %). It is worth mentioning that naphtha molecules in the LP fraction convert easier than LCO and HCO molecules due to ease of diffusion in the zeolite pores. The naphtha yield was high because LCO and HCO fractions were also further cracked to naphtha and other light ends. The yields of ethylene, propylene and butenes were 2.3 wt %, 6.3 wt % and 4.2 wt %, respectively. These yields were lower


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than those obtained when AXL alone was cracked. This is because AXL has higher content of heavier ends (37.5 wt %), which are light olefins precursors, than the LP fraction (14.3 wt %) as shown in Table 2. Since naphtha is converted to lighter ends on the cracking of LP, it is desirable to separate the light ends and naphtha from the cycle oils (LCO and HCO) by fractional distillation in the refinery. The LCO and HCO fractions can then be further mixed and cracked with AXL feed at different ratios. The LCO and HCO fractions were cracked separately and as a 50:50 mixture to assess their contribution to the product stream. At a conversion of 31.2 wt %, the product yields obtained at a constant CTO ratio of 3.0 are shown in Table 4. For LCO feed, a naphtha yield of 31.8 wt % was obtained compared with naphtha content in the feed of 28.6 wt %. The yields of ethylene, propylene and butenes were 1.6 wt %, 5.4 wt % and 3.8 wt %, respectively. At a conversion of 27.9 wt %, about 46.8 wt % of LCO product was produced compared with 67.7 wt % in LCO feed. The high yield of LCO may be attributed to the composition of LCO feed which contains multi-ring aromatics that are difficult to crack.25,30 On the other hand, the cracking of HCO feed produced 43.2 wt % LCO which was the major product compared with 61.8 wt % in the HCO feed. At a conversion of 31.2 wt %, about 21 wt % of HCO product was produced. The other yields from HCO cracking were naphtha, ethylene, propylene and butenes at 17.3 wt %, 2.1 wt %, 6.1 wt % and 4.0 wt %, respectively. The cracking of HCO feed resulted in a higher yield of light olefins than cracking LCO (12.3 wt % vs. 10.8 wt %). This may be attributed to the presence of larger amount of light olefins precursors in heavy oil (HCO) and to the activity of the acidic matrix in the base USY catalyst.31 In general, most commercial FCC catalysts have sufficient acidic matrix activity to provide some pre-cracking of high boiling point materials. These pre-cracking molecules are small enough to enter the zeolite pores for further cracking to LPG and naphtha. The product distribution from the cracking of LCO+HCO mixture is presented in Table 4. The mixture contains complicated chemical structures that crack into various gaseous and liquid products which are more complicated in structure and composition. The results show that the yields of ethylene, propylene and butenes were 2 wt %, 6 wt % and 4 wt %, respectively, which are similar to those obtained from the HCO cracking. However, the naphtha yield increased from 17 wt % in HCO cracking to 27 wt % in the cracking of LCO+HCO. This indicates that the mixing of AXL with LCO+HCO fraction might lead to a higher overall product yields than if HCO alone is mixed. The conversion from the separate cracking of AXL and cycle oils decreased in the following order: AXL > LCO+HCO > HCO 7 ACS Paragon Plus Environment

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> LCO. This order may be consistent with the trends in the aromatics content and average molecular weight of the feeds.32 3.5. Recycle Configurations. A practical recycle approach which involves the mixing of LP with AXL feed and the use of this mixture as a feed into the MAT unit was tested.25 The mixing of AXL with LP at different ratios and re-cracking in the MAT unit results in different product distributions.21 The first recycle configuration was conducted to examine the effect of cracking total liquid product comprising naphtha, LCO and HCO fractions obtained from the cracking of AXL as shown schematically in Figure 2. The effect of various recycle ratios on the desired product yields was examined. A total LP of 67.5 wt % was obtained from the initial cracking of AXL in the MAT unit. The recycling of this entire amount and making it up to 100 wt % with 32.5 wt % of AXL feed represents 100% LP recycle. A blend of 33.8 wt % LP and 66.2 wt % AXL feed corresponds to 50% recycle while mixing only 16.9 wt % LP and 83.1 wt % AXL represents 25% LP recycle. The 0% recycle indicates that there is no liquid product (LP) in the feed stream, just AXL. The second configuration was conducted to examine the effect of AXL mixing with LCO+HCO fraction and cracking in the MAT unit as shown schematically in Figure 3. The effect of various recycle ratios on the desired product yields was investigated. A total yield of 27 wt % LCO+HCO product was obtained from the cracking of AXL in the MAT unit. Recycling this entire amount back into the MAT unit and making it up to 100 wt % with 73 wt % of AXL feed represents 100% LCO+HCO recycle. A blend of 13.5 wt % LCO+HCO and 86.5 wt % AXL feed corresponds to 50% recycle. The 0% recycle indicates that there is no LCO+HCO in the feed stream, just AXL. The results of the two recycle configurations are presented in Tables 5 and 6 and Figures 4 and 5. These results indicate that there is no change in the yield of the light olefins (about 20 wt %) as a result of AXL mixing with LP or LCO+HO feeds which have lower content of light olefinic precursors. For instance, the yield of light olefins remained at 20 wt % for 0% recycle as well as 100% recycle (Figures 4 and 5). This suggests that the low reactivity cracked naphtha fraction in the LP and LCO+HCO feeds contributed very little to the total light olefins yield when the two feeds were mixed with AXL.23 Naphtha yield decreased slightly from 40.3 wt % to 37.5 wt % and 35 wt % on increasing the recycle ratio from 0 to 100% for LP and LCO+HCO, respectively. While the yields of other products did not change, only coke content decreased from 1.6 wt % to about 1.0 wt % for all AXL mixed feeds. 8 ACS Paragon Plus Environment

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3.6. Strategy for Increasing Light Olefins Yield. A quantitative examination of the absolute product distributions obtained on cracking AXL feed followed by separate cracking its liquid products (naphtha, LCO and HCO) was carried out. This was done to gain insight into the relative increases in light olefins yield and loss of naphtha fraction that may be achieved on recycling liquid product from crude oil cracking. This approach is not a practical recycle scheme since it involves a separate FCC riser for the cracking of liquid product streams. Two separate cases were considered for this scheme. The first case considered was the separate cracking of total LP in the MAT unit. In Table 7, the results obtained from cracking the total LP yield of 67.5 wt % are shown. This fraction was cracked separately and added to the initial AXL product yields as shown in Table 7. Some important conclusions can be drawn from these results. It can be observed that the overall yield of light olefins on recycling the entire liquid product was 29 wt % which represents a 42% increase compared to cracking AXL without recycle (20.4 wt %). The naphtha yield, decreased from 40 wt % to 27 wt % while the LCO+HCO yield remained almost unchanged at 27 wt %. While these results suggest that when LP is recycled into the MAT unit, only the naphtha fraction gets converted to light olefins, the LCO and HCO fractions are also re-cracked to lighter ends. The total yield of LCO and HCO (27 wt %) is the net yield from the conversion of all fractions in the LP feed (naphtha, LCO and HCO). The re-cracking of the three fractions in the MAT unit at 550 °C and 3.0 CTO has made these liquid fractions less reactive due to the formation of heavier compounds.32 The second case considered for enhancing the yield of light olefins was the cracking of LCO+HCO fraction in the MAT unit without mixing with AXL feed. Table 8 shows that the overall yield of light olefins obtained upon recycling the LCO+HCO fraction is 25.8 wt % which represents a 26.5 % increase compared to the cracking of AXL alone (20.4 wt %). The naphtha yield increased from 40.3 wt % to 50.1 wt %. This scheme, shown in Figure 6, provides a more attractive option than the cracking of LP because the amount of naphtha produced was significantly higher when LCO+HCO was cracked (27 wt % vs 50.1 wt %). Besides, the relatively low-value LCO+HCO fraction gets reduced significantly in the product stream from 27 wt % to 9 wt % when LCO+HCO fraction was recycled. However, in the case of LP recycling, the LCO+HCO content remained the same at 27 wt %. The two quantitative cases demonstrated that in order to maintain a balance between high naphtha and light olefins yield, it is better to recycle LCO+HCO only after fractionation of the products rather than the entire liquid product stream. 9 ACS Paragon Plus Environment

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4. CONCLUSIONS It has been shown that the recycling of liquid hydrocarbon fractions obtained from the catalytic cracking of AXL crude oil is a viable means for increasing the yield of light olefins. Total light olefins yield increased from 20 wt % to 29 wt % on the separate cracking of total liquid product obtained from AXL cracking over E-Cat/MFI-280. A practical recycle configuration which involves the mixing of AXL with its liquid product at different ratios resulted in different product yields depending on the composition of the mixed feed. The separation of LCO+HCO fraction from the liquid product stream and its recycling for further reprocessing with AXL in the same riser reactor seems to be a more viable recycle configuration than the cracking of the total liquid product. It is concluded that the recycle of low-value heavy fraction (LCO+HCO) is a cost-effective means to supplement the AXL feed without loss in the yield of desired light olefins and naphtha. This route is attractive to petrochemicals industries that are interested in the direct conversion of crude oil to petrochemicals. The study has shown that at the laboratory level, it was possible to blend crude oil feed with its liquid products, crack them further and obtain light olefins comparable to that obtained by the cracking of crude oil alone. 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 (1) Dharia, D, Batachari, A, Naik, P, Bowen, C. Catalytic cracking for integration of refinery and steam crackers, In: Advances in Fluid Catalytic Cracking: Testing, Characterization, and Environmental Regulations, Occelli, M, Ed. 2010, 119-126. (2) Akah A, Al-Ghrami M. Maximizing propylene production via FCC technology. Appl. Petrochemical Res. 2015, 5, 377-392. (3) Bryden, K, Singh, U, Berg, M, Brandt, S, Schiller, R, Cheng, WC. Fluid catalytic cracking (FCC): catalysts and additives. In: Kirk-Othmer Encyclopedia of Chemical Technology, 5th ed. Wiley, New York, 2015, 1-37. (4) Sadrameli, SM. Thermal/catalytic cracking of liquid hydrocarbons for the production of olefins: catalytic cracking review. Fuel 2016, 173, 285-297. (5) Vogt, ET, Weckhuysen, BM. Fluid catalytic cracking: Recent developments in the grand old lady of zeolite catalysis. Chem. Soc. Rev. 2015, 44, 7342–7370. 10 ACS Paragon Plus Environment

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Energy & Fuels

(6) Aitani, A. Maximization of FCC light olefins by high severity operation and ZSM-5 addition. Catal. Today 2000, 60, 111-117. (7) Triantafillidis, C, Evmiridis, NP, Nalbandian, L, Vasalos, I. Performance of ZSM-5 as a fluid catalytic cracking catalyst additive: effect of the total number of acid sites and particle size. Ind. Eng. Chem. Res. 1999, 38, 916-927. (8) Buchanan, J. The chemistry of olefins production by ZSM-5 addition to catalytic cracking units. Catal. Today 2000, 55, 207-212. (9) Arandes, J, Abajo, I, Fernández, I, Azkoiti, MJ, Bilbao, J. Effect of HZSM-5 zeolite addition to a fluid catalytic cracking catalyst: study in a laboratory reactor operating under industrial conditions. Ind. Eng. Chem. Res. 2000, 39, 1917-1924. (10) Siddiqui MAB, Aitani AM, Saeed MR, Al-Yassir N, Al-Khattaf S. Enhancing propylene production from catalytic cracking of Arab Light VGO over novel zeolites as FCC catalyst additives. Fuel 2011, 90, 459-466. (11) Awayssa O, Al-Yassir N, Aitani A, Al-Khattaf S, Modified HZSM-5 as FCC additive for enhancing light olefins yield from catalytic cracking of VGO. Appl. Catal. A 2014, 477, 172-183. (12) Lappas, AA, Iatridis, DK, Papapetrou, MC, Kopalidou, EP,Vasalos, IA. Feedstock and catalyst effects in fluid catalytic cracking-comparative yields in bench scale and pilot plant reactors. Chem Eng J 2015, 278, 140–149. (13) Hussain AI, Aitani AM, Kubů M, Čejka J, Al-Khattaf S. Catalytic cracking of Arab Light VGO over novel zeolites as FCC catalyst additives for maximizing propylene yield. Fuel 2016, 167, 226-239. (14) Powers, D. Olefins production utilizing whole crude oil and mild catalytic cracking. US Patent No. 7,019,187, 2006. (15) Chen, X., Li, N., Yang, Y., Yang, C., Shan, H., 2015. Novel propylene production route: utilizing hydrotreated shale oil as feedstock via two-stage riser catalytic cracking. Energy Fuels 2015, 29, 7190-7195. (16) Corma A, Corresa E, Mathieu Y, Sauvanaud L, Al-Bogami, S, Al-Ghrami, M, Bourane A. Crude oil to chemicals: light olefins from crude oil. Catal. Sci. Technol. 2017, 7, 12-46. (17) Usman A, Siddiqui, M, Hussain A, Aitani A, Al-Khattaf S. Catalytic cracking of crude oil to light olefins and naphtha: Experimental and kinetic modelling. Chem. Eng. Res. Des. 2017, 120, 121-137. (18) Lacalle A, Bilbao J, Arandes M, De Puente G, Sedran U. Recycling hydrocarbon cuts into FCC units. Energy Fuels 2002, 14, 615-621. (19) Fernandez, ML, Lacalle, A, Bilbao, J, Arandes, JM. Recycling hydrocarbon cuts into FCC units, Energy Fuels, 2002, 16, 615-621. (20) Tiscornia, IS, de la Puente, G, Sedran, U. Recycling of low-value hydrocarbon cuts by means of multiple injections to FCC units, Ind. Eng. Chem. Res. 2002, 41, 5976-5982. 11 ACS Paragon Plus Environment

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(21) Verstraete V, Coupard V, Thomazeau C, Etienne P. Study of direct and indirect naphtha recycling to a resid FCC unit for maximum propylene production. Catal. Today 2005, 106, 62-71. (22) Corma, A., Melo, FV, Sauvanaud, L, Ortega, FJ. Different process schemes for converting light straight run and fluid catalytic cracking naphthas in a FCC unit for maximum propylene production, Appl. Catal. A 2004, 265, 195-206. (23) Akah, A, Al-Ghrami, N, Saeed, M, Siddiqui, MAB. Reactivity of naphtha fractions for light oleﬁns production, Int. J. Ind. Chem. 2017, 8, 221-233. (24) Jin, N, Wang, G, Yao, L, Hu, M, Gao, J. Synergistic process for FCC light cycle oil efficient conversion to produce high-octane number gasoline. Ind. Eng. Chem. Res. 2016, 55, 5108-5115. (25) Zhang, H, Zhu, X., Chen, X, Miao, P, Yang, C, Li, C. Fluid catalytic cracking of hydrogenated light cycle oil for maximum gasoline production: Effect of catalyst composition. Energy Fuels 2017, 31, 2749-2754. (26) Arudra, P, Bhuiyan, T, Akhtar, M, Aitani, A, Al-Khattaf, S, Hattori, H. Silicalite-1 as efficient catalyst for production of propene from 1-butene. ACS Catal. 2014, 4, 4205-4214. (27) Adewuyi, YG, Klocke, DJ Buchanan, JS. Effects of high-level additions of ZSM-5 to a fluid catalytic cracking (FCC) RE-USY catalyst, Appl. Catal. A 1995, 131, 121-133. (28) Hussain, AI, Palani, A, Aitani, AM, Čejka, J, Shamzhy, M, Kubů, M, Al-Khattaf, S. Catalytic cracking of vacuum gasoil over -SVR, ITH, and MFI zeolites as FCC catalyst additives, Fuel Process. Tech. 2017, 161, 23-32. (29) Bryden K, Federal M, Habib, TE, Schiller R. Processing tight oils in FCC: Issues, opportunities and flexible catalytic solutions. Grace Cat. Tech. Catalagram 2014, 114, 3-22. (30) Corma A, Gonzalez-Alfaro V, Orchillés A. Decalin and tetralin as probe molecules for cracking and hydrotreating the light cycle oil. J. Catal. 2001, 200, 34-44. (31) Arandes JM, Torre I, Azkoiti MJ, Ereña J, Olazar M, Bilbao J. HZSM-5 zeolite as catalyst additive for residue cracking under FCC conditions, Energy Fuels, 2009, 23, 42154223. (32) Lee, FM. Effects of recycle on heavy oil cracker, Ind. Eng. Chem. Res., 1989, 28, 542546.


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Energy & Fuels

List of Figures Figure 1. Effect of MFI-280 addition to E-Cat on product yields from the cracking of AXL crude oil at 550 °C and 3.0 CTO. Figure 2. Configuration for the catalytic cracking of AXL crude oil mixed with recycled total liquid product (LP) fraction. Figure 3. Configuration for the catalytic cracking of AXL crude oil mixed with recycled LCO+HCO fraction. Figure 4. Product yields (naphtha, light olefins and propylene) from the cracking of total liquid product (LP) and AXL mixture at different recycle ratios. Figure 5. Product yields (naphtha, light olefins and propylene) from the cracking of LCO+HCO with AXL mixture at different recycle ratios. Figure 6. Schematic representation of LCO+HCO recycle configuration for catalytic cracking of AXL crude oil with product yields (RP = recycled product; GP = gas product).


Energy & Fuels

60 Light Olefins LPG

50

Naphtha 40

Yield, wt %

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Figure 1. Effect of MFI-280 addition to E-Cat on product yields from AXL cracking at 550 °C and 3.0 CTO.


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Gas/Liquid Total Gases

Naphtha

FCC Fractionator

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Energy & Fuels

LCO

AXL Crude Oil Feed HCO

LP Recycle Stream Figure 2. Configuration for the catalytic cracking of AXL crude oil mixed with recycled total liquid product (LP) fraction.


Energy & Fuels

Gas/Liquid Total Gases

FCC

AXL Crude Oil Feed

Naphtha

Fractionator

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LCO

HCO

Recycle Stream

Figure 3. Configuration for the catalytic cracking of AXL crude oil mixed with recycled LCO+HCO fraction.


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Figure 3. Product yields (naphtha, light olefins and propylene) from the cracking of total liquid product (LP) and AXL mixture at different recycle ratios.

Yield, wt %

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Energy & Fuels

Yield, wt %

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LCO+HCO recycle ratio, % Naphtha

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Figure 5. Product yields (naphtha, light olefins and propylene) from the cracking of LCO+HCO and AXL mixture at different recycle ratios.


Energy & Fuels

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GP and Coke Yield (wt.%) Dry Gas 4.4 LPG 25.6 Coke 1.6

AXL Composition (wt.%) Naphtha 34.2 Middle Distillates 28.3 Heavy Oil 37.5

MAT UNIT C/0 = 3.0 E-Cat/Z280 550°C

RP Yield (wt.%) Dry Gas 1.1 LPG 6.6 Naphtha 9.8 LCO 6.7 HCO 2.8 Coke 0.3

Total Product Yield (wt.%) Dry Gas 5.5 LPG 32.2 Naphtha 50.1 LCO 6.7 HCO 2.8 Coke 1.9

100% Recycle

100% Recycle

LCO+HCO Yield (wt.%) LCO 17.6 HCO 9.6

Figure 6. Schematic representation of LCO+HCO recycle configuration for catalytic cracking of AXL crude oil with product yields (RP = recycled product; GP = gas product).


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Energy & Fuels

sssssss

Table 1. Properties of Arab Extra Light (AXL) Crude Oil Feed. Property

Value 39.3 828 1.6 2.7

Catalytic Cracking of Light Crude Oil: Effect of Feed Mixing with Liquid

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