Cracking Process in Refinery

Individual inquiry 2001 Allyson Woodford Executive Summary Caltex Australia operates an Oil refinery at Lytton on the mouth of the Brisbane River The Fluidised Catalytic Cracking Unit (FCCU) has the ability to recycle both selected product and waste streams to the reactor-riser The objective of this individual inquiry was to investigate the yield effects on product, of recycling two streams to the riser Sponge Column Off Gas (SCOG) and Hydro-treated Light Cycle Oil (HT-LCO) Literature suggested that a stream rich in hydrogen would passivate nickel and heavy metal contamination on the catalyst and result in a decrease in SCOG production SCOG was recycled to the Wye junction on the riser HT-LCO is rich in olefinic material and was recycled to the riser to act as mixed temperature control (MTC) liquid increasing conversion to favour gasoline and liquid petroleum gas (LPG) Test runs, using reactor mix sampling (RMS) technique, were performed over two days (April 9th and 10th) and Caltex laboratory technicians performed subsequent analyses It resulted that SCOG did not behave in the same manner as reported in literature, resulting in an increase in SCOG and coke production HT-LCO as MTC liquid was a success as an increase in both gasoline and LPG gas was recorded This inquiry concludes that the recycle of SOCG to the riser is not a practice recommended for the Lytton refinery The recycle of HT-LCO to the riser is a practice highly recommended especially when demand for gasoline and LPG is higher than that of diesel Further investigation should be conducted into the recycle of Light Catalytic Naphtha as lift gas in the riser as an un-planned unit shut down prevented the stream from being researched Individual inquiry 2001 Allyson Woodford Contents Page Section Page 1.0 Introduction 1.1 Sponge Column Off Gas 1.2 Hydro-treated Light Cycle Oil 1.3 Experimental Objective 2.0 Background 2.1 Refinery Process Description 2.1.1 Crude Distillation Products 2.2 FCCU Process Description 2.2.1 Reactor/Regenerator 2.2.1.1 Reactor – Riser 2.2.1.2 Catalyst Deactivation 2.2.1.3 Regenerator 2.2.1.4 Mixed Temperature Control Liquid 2.2.1.5 Catalyst Addition 2.2.2 Main Fractionator 2.2.2.1 Fractionator Overheads 2.2.2.2 Light Catalytic Naphtha (LCN) 2.2.2.3 Heavy Catalytic Naphtha (HCN) 2.2.2.4 Un-treated Light Cycle Oil (UT-LCO) 2.2.2.5 Clarified Oil (CLO) 2.2.3 Product Treatment 2.2.3.1 Sponge Column Off Gas (SCOG) 2.2.3.2 Propane/Propylene (C3) and Butane/Butylene (C4) 2.3 Catalytic Cracking Theory 10 2.3.1 Reaction Mechanisms 10 2.3.2 Thermal Cracking 10 2.3.3 Catalytic Cracking 10 2.3.3.1 Catalytic Cracking Initiation 10 2.3.3.1.1 Carbonium Formation 10 2.3.3.1.2 Carbenium Formation 11 2.3.3.2 Catalytic Cracking Propagation Mechanisms 11 2.3.3.2.1 Primary Cracking Reactions 11 2.3.3.2.2 Secondary Cracking Reactions 12 2.3.4 Catalyst Properties 12 2.3.4.1 Zeolite 13 2.3.4.2 Matrix 13 2.3.4.2.1 Matrix Binder and Filler 13 2.3.4.2.2 Active Alumina 13 3.0 Literature Review 14 3.1 FCCU History 14 3.2 Recycling SCOG to the Riser 15 3.2.1 SCOG – U.S Patent 15 3.2.1.1 SCOG – U.S Patent Description 15 3.2.1.2 SCOG – Australian Patent Description 15 3.2.1.3 SCOG – U.S Patent Catalyst 16 3.2.2 SCOG – U.S Patent Testing 16 3.2.3 SCOG – U.S Patent Results 17 3.2.4 SCOG – Literature Summary 17 Individual inquiry 2001 Allyson Woodford 3.3 Recycling HT-LCO to the Riser 17 3.3.1 Split Feed Technology 17 3.3.2 HT-LCO as MTC Liquid 18 3.3.2.1 HT-LCO Chemistry 18 3.3.3 HT-LCO – Summary 19 4.0 Methodology 20 4.1 Test Runs 20 4.1.1 Normal Sampling 20 4.1.2 Reactor Mix Sampling (RMS) 20 4.1.2.1 RMS Analysis 21 4.2 Inquiry Test Run Sampling 21 4.2.1 Other Samples 21 4.2.2 Analysis Performed 21 4.2.3 Process Instrumentation Error 22 4.3 Plan of Testing 22 4.3.1 Crude Composition 23 4.3.2 Labour 23 4.3.3 Test Run Schedule 23 4.4 Implementation 24 4.4.1 Problems 24 5.0 Results 25 5.1 Mass Balance 25 5.2 SCOG Test Run Results 25 5.2.1 SCOG – Process Variables 25 5.2.2 SCOG – Normal Sampling 26 5.2.2.1 Fractionator Column Dynamics 27 5.2.3 Hysys Processing of RMS Results 28 5.3 HT-LCO Test Run Results 29 5.3.1 HT-LCO – Process Variables 29 5.3.2 HT-LCO Normal Sampling 29 6.0 Discussion 31 6.1 SCOG Test Run 31 6.1.1 Error 31 6.1.1.1 Instrument Calibration 31 6.1.1.2 RMS Technique 31 6.1.2 Plant Data vs Literature Data 31 6.1.2.1 MAT Testing 31 6.1.2.2 Residence Time 31 6.1.2.3 Catalyst to Oil Ratio 32 6.1.2.4 Catalyst Formulation 32 6.1.2.5 SCOG 32 6.1.3 Fractionator Column Dynamics 32 6.2 HT-LCO Test Run 32 7.0 Conclusions and Recommendations 33 7.1 SCOG 33 7.2 HT-LCO 33 7.3 LCN 33 References 34 Individual inquiry 2001 Allyson Woodford List of Figures Title Page Figure – Refinery Flow sheet Figure – Crude Distillation Unit Figure – Basic FCCU Flow sheet Figure – Reactor-riser Figure – Temperature Profile for MTC Addition Figure – Main Fractionator Figure – Reactor Mix Sampling 21 Figure – SCOG/HT-LCO black box analysis 25 Figure – Feed rate SCOG Test Run 26 Figure 10 – Reactor Temperature SCOG Test Run 26 Figure 11 – LCN Yield – SCOG Test Run 27 Figure 12 – LCO Yield – SCOG Test Run 27 Figure 11 – CLO Yield – SCOG Test Run 27 Figure 14 – Reactor Pressure – SCOG Test Run 28 Figure 15 – Feed rate HT-LCO Test Run 29 Figure 16 – Reactor Temperature HT-LCO Test Run 29 Figure 17 – LCN yield shift - HT-LCO Test Run 30 Figure 18 – Polymerisation Unit (C3’s) yield - HT-LCO Test Run 30 List of Tables Title Page Table – Catalytic Cracking : Reactants and Products 12 Table – Test Conditions 16 Table – Patent Results 17 Table – Diesel and LCO analysis 18 Table – Laboratory Test Methods and Repeatability 22 Table – ASTMD3507 Repeatability 22 Table – SCOG RMS Results 28 Individual inquiry 2001 Allyson Woodford Individual inquiry 2001 Allyson Woodford 1.0 Introduction The focus on the optimistion of the petroleum refinery has intensified over the past decade with an increasing demand for transportation fuels as well as tightening environmental restrictions The fluidised catalytic cracking is one of the more important processes in the refinery (upgrading low-value feed stock) The FCCU at Caltex Lytton Refinery (herein referred to as the Lytton refinery) has several locations where recycled product can be injected into the reactor/riser in addition to normal feed The ability to recycle these products has recently been installed and the effect of these activities has not yet been investigated This inquiry will investigate the effect on product yields of the following recycles to the FCCU riser: 1.1 Sponge Column Off-Gas (SCOG) Often referred to as dry gas, SCOG is a light hydrocarbon mixture (comprising of mainly H2, CH4, C2H6, C2H4, N2 etc) and relatively high concentrations of H2S (1000ppm sulphur) Nickel is present in most crudes, plating out on the FCCU catalyst Nickel acts as a catalyst poison catalysing reversible dehydrogenation reactions, resulting in elevated hydrogen gas yields and a loss of valuable product Sulphur is a temporary poison for nickel-catalysed dehydrogenation reactions An excess of hydrogen will favour dehydrogenation reactants via Le Chatelier’s principle of equilibrium (Wilson, 1997) as well as reducing the nickel to a metallic state promoting selective carbonisation of contaminated sites (rendering them inactive) Pre-treating the catalyst with a gas containing hydrogen and sulphur before contacting the catalyst with the feed should render the nickel inactive However, sulphur, in high concentrations, can also act as a catalyst poison and excess gas recycle can overload product treatment compressors This inquiry will investigate whether recycling SCOG to the riser at the Lytton refinery will improve product yield by the above said mechanisms 1.2 Hydro-treated Light Cycle Oil (HT-LCO) Light cycle oil (LCO) is a product of the FCCU used as a blend stock for diesel Hydro-treating the LCO saturates olefinic (and aromatic) material By recycling this paraffinic/naphthenic stream to the riser it is proposed that the yield of gasoline and LPG will increase 1.3 Experimental Objective The purpose of this inquiry is to investigate the effects on product yields of recycling HT-LCO and SCOG to the riser To observe yield shifts with respect to a single changing variable (e.g feed rate, MTC rate or reactor temperature) a step test is often conducted The system is held at steady state with no recycle and product yields are recorded A recycle stream is then added, at a specified time and rate, in a single step The system returns to steady state and the new product yields are recorded The yield shift observed is then attributed to the change in variable In order to observe these shifts a material/mass balance must be closed around the FCCU To understand the implications of such a change a detailed background into the process and supporting theory is also presented in this inquiry (see note*) Note*: In the original thesis proposal a third variable (Light Catalytic Naphtha) was scheduled to be tested on the 26th of April 2001 Due to an un-planned FCCU shut down, this trial was aborted and the scope of the inquiry was re-defined to Page of 36 Individual inquiry 2001 Allyson Woodford include a detail background investigation Page of 36 Individual inquiry 2001 Allyson Woodford 2.0 Background To understand the impact of yield changes within the FCCU it is important to have sufficient background knowledge of the refinery process itself as well as cracking mechanisms and catalyst properties Crude oil is found in deposits deep below the earth’s surface as a result of carbonaceous (plant and animal) material decomposing over millions of years (hence the term fossil fuel) The major components of crude oil are hydrocarbons (paraffins, olefins, naphthenes and aromatics) in the range CH4 to material with boiling point in excess of 750°C, sulphurous compounds, and traces of metals such as Ni, Va, Fe, Cu etc Crude Oil is refined/processed into a variety of fuels to meet the energy demands of today’s society The operational aim of a refinery is to produce high yields of gasoline (30°C – 185°C) kerosene (jet fuel) (160° C- 230°C) and diesel distillate (230°C – 330°C) and to minimise the production of fuel oil (> 360°C) and dry gas (C2 and lighter), (see Figure – Refinery Flow sheet over page) 2.1 Refinery Process Description Crude oil is drawn from wells and transported to the refinery where it undergoes primary atmospheric distillation in a crude distillation unit (CDU), separating products on a boiling point/component basis Crudes processed at the Lytton refinery are purchased primarily from South East Asia and Australia and are low in sulphur to meet state regulations on sulphur content of salable fuels ( Heptane Oxygen Nitrogen CO CO2 52.96 0.00 45.55 67.36 79.75 97.49 145.15 32.30 0.00 192.83 13.25 9.11 29.68 4.14 73.48 40.04 77.56 62.53 0.00 11.60 4.55 9.53 -4.89 0.00 2.10 -4.19 -1.97 -5.55 -3.13 5.68 0.00 -5.10 83.84 6.38 3.91 307.59 -12.58 -3.65 -18.13 10.81 0.00 5.70 21.65 32.72 -21.12 0.00 5.24 0.06 0.25 -5.20 -0.97 11.68 0.00 0.32 21.78 14.62 10.35 335.55 -20.73 -2.13 -4.88 24.49 0.00 67.84 45.85 79.38 5.3 HT-LCO Test Run Results 5.3.1 HT-LCO Process Variables Reactor temperature, feed rate and composition were stable (within ± 2σ of the mean value) for the hours prior and duration of the test run (6:00am to 1:30pm) No change in feed rate or composition was experienced 5190 Feed Rate HT-LCO Test Run Feed Rate (tpd) 5170 5150 5130 5110 5090 5070 4/10/01 4/10/01 4/10/01 4/10/01 4/10/01 4/10/01 4/10/01 4/10/01 4/10/01 4:48 6:00 7:12 8:24 9:36 10:48 12:00 13:12 14:24 Time Figure 15 – Feed Rate HT-LCO Test Run Page 30 of 36 Individual inquiry 2001 Allyson Woodford Reactor Temperature HT-LCO Test Run 507.5 Reactor Temperature (°C) 507 506.5 506 505.5 505 504.5 504 503.5 4/10/01 4/10/01 4/10/01 4/10/01 4/10/01 4/10/01 4/10/01 4/10/01 4/10/01 4:48 6:00 7:12 8:24 9:36 10:48 12:00 13:12 14:24 Time Figure 16 – Reactor Temperature HT-LCO Test Run 5.3.2 HT-LCO - Normal Sampling The normal sampling method can be used to show gross changes in product yields and quality This evidence is conclusive enough for a liquid recycle such as HT-LCO It is obvious from the gross plant data where yield shifts are experienced Large yield shifts were recorded in the following streams: Page 31 of 36 Individual inquiry 2001 Allyson Woodford LCN Yield - HT-LCO Test Run 50 250 49.5 LCN Yield (% feed) 48.5 150 48 47.5 100 47 50 46.5 46 MTC Flow (tpd) 200 49 45.5 45 10/04/01 10/04/01 10/04/01 07:12 08:24 09:36 LCN Yield MTC Flow (tpd) 10/04/01 10/04/01 10:48 Time 12:00 10/04/01 13:12 10/04/01 14:24 -50 10/04/01 15:36 Figure 17 – LCN yield shift -HT-LCO Test Run Polymerisation Unit Feed Yield - HT-LCO Test Run 5.8 250 200 5.7 5.65 150 5.6 5.55 100 5.5 50 5.45 5.4 MTC flow (tpd) Poly feed yield (% feed) 5.75 5.35 5.3 10/04/01 07:12 -50 10/04/01 08:24 Poly Feed Yield (% feed) 10/04/01 09:36 10/04/01 10:48 MTC Flow (tpd) 10/04/01 12:00 10/04/01 13:12 10/04/01 14:24 10/04/01 15:36 Time Figure 18 – Polymerisation Unit feed (C3’s) Yield – HT-LCO Test Run The product yields of interest are: • SCOG, C3 (Polymerisation Unit feed), C4 (Alkylation Unit feed) • LCN, LCO, CLO and Coke The product qualities of interest are • Cloud point • C3 and C4 composition (on-line analysers) All graphs can be found in appendix Page 32 of 36 Individual inquiry 2001 6.0 Allyson Woodford Discussion 6.1 SCOG test runs As discussed in the literature review, the production of hydrogen was expected to decrease with the introduction of SCOG to the riser In fact, the opposite was observed as the production of SCOG increased by 30% with the addition of 20 tpd SCOG to the riser (Table 7) 6.1.1 Error Possible errors that would attribute to the failure of SCOG to act as predicted include: 6.1.1.1 Instrumentation Calibration The flow meters measuring SCOG at different points around the refinery are calibrated for various assumed molecular weights and operating temperatures These flow meter calibrations cannot be adjusted on a daily basis (to comply with incoming crude changes) and an in-line analyser would be too expensive to install to determine the composition of waste refinery fuel gas (SCOG) A more sensible approach would be to calibrate the meters all to the same molecular weight 6.1.1.2 RMS Student Allyson Woodford performed the RMS for the first time collecting results for this inquiry Test runs are not performed on a weekly basis so there was no in-house training available to her The first sample exploded and the student was very cautious filling the next two samples Consequently the masses of the first two bags were considerably lower the other samples collected throughout the test runs This problem would not hinder the results considerably but has the potential to be a problem in the future 6.1.2 Plant data vs Literature data The main difference between the results obtained by Hayes and Castillo to those obtained from this series of test runs is the test conditions themselves 6.1.2.1 MAT testing Hayes and Castillo carried out all testing on a micro activity reactor Lytton refinery uses MAT testing to evaluate the FCCU catalyst but has found that the results can only be compared qualitatively to plant data (Laurie Palmer Verbal reference) As with all experimentation, actual implementation of the procedure on the plant will always give different responses to a laboratory or pilot plant 6.1.2.2 Residence time The residence time used by Hayes and Castillo is more than 20 minutes of SCOG contact with the regenerated catalyst before it is subjected to feed (15 minutes H2 gas followed by minutes of CH4) The FCCU riser at the Lytton refinery has between 1-2 second’s contact with the regenerated catalyst before contacting the feed It is possible that there is not enough time for the hydrogen to completely reduce the nickel to a free metallic state and then Page 33 of 36 Individual inquiry 2001 Allyson Woodford become selectively carbonised and inactivated It is most likely that nickel on the catalyst surface is becoming partially reduced to the metallic state, hereby accelerating the catalysis of dehydrogenation reactions rather then suppressing the action 6.1.2.3 Catalyst to oil ratio The testing performed by Hayes and Castillo had a low catalyst to oil ratio of only 3:1 The catalyst to oil ratio at the Lytton refinery is up to 8:1 As with the shortened residence time, the regenerated catalyst may not be fully reduced to the metallic state before contact with the feed A larger flow rate of SCOG may be able to perform this duty however more 40tpd of fluidising gas in the riser will damage the catalyst and possible increase the pressure past the trip pressure for the unit 6.1.2.4 Catalyst formulation All testing by Hayes and Castillo was performed prior to 1984 Since then large advancements have been made in the tailoring of catalyst to suit the customer The commercial Akzo-Nobel catalyst used at the Lytton refinery is different to the three catalysts used by Hayes and Castillo The nickel content of the Lytton FCCU catalyst is approximately 2500pm compared to 5000ppm in the literature Nickel was the only contaminant introduced to the catalyst used in the literature however E-cat used by Lytton refinery has high contents of iron and vanadium as well 6.1.2.5 SCOG One obvious difference between the literature and the inquiry conditions is the use of SCOG instead on hydrogen SCOG has many catalyst poisons such as sulphur and nitrogen that may adversely affect cracking mechanisms in the unit 6.1.3 Fractionator Column Dynamics SCOG replaced steam to the Wye as fluidising gas however this caused a large pressure difference in the reactor (figure XX ) The fractionator pressure is directly linked to the reactor pressure and hence the corresponding high column pressure caused a shift in boiling points down the column (ie raising pressure results in a raised boiling point for a specific material.) This increase in pressure corresponds to an increase in CLO yield as well as a drop in LCN yield The CLO passes through a heat exchanger preceding the de-propaniser in the product treatment section of the FCCU A sudden increase in CLO flow rate will ultimately shift the boiling point in the de-propaniser column resulting in a momentary change in alky feed : poly feed ratio 6.2 HT-LCO test run As expected the recycle of HT-LCO as MTC liquid to the riser resulted in an increased yield of LCN, polymerisation and alkylation unit feeds For a 200 tpd addition of HT-LCO was recycled to the riser resulting in a 8% increase of C3 and an increase of 6% more LCN This increase has come at the expense of increasing coke and SCOG yields and an overall decrease in LCO production Recycling HTLCO to the riser as MTC liquid is a way of increasing the yield of C3 and C4 rapidly Another way to increase conversion is to increase the catalyst activity by Page 34 of 36 Individual inquiry 2001 Allyson Woodford increasing catalyst addition however the response time is in the order of weeks and cannot be used for short-term demand of these (valuable) products 7.0 Conclusions and Recommendations 7.1 SCOG It can be concluded from this inquiry that the recycle of SCOG to the Wye at the Lytton refinery does not result in a reduction of dry gas production as claimed in literature There is other reaction mechanisms taking place Another inquiry could be pursued in an attempt to understand these mechanisms It is recommended that further investigation be conducted into the use of SCOG as riser fluidising gas on a laboratory scale simulating Lytton FCCU conditions It would also be advisable to attempt to simulate patent trials to see if the results can actually be reproduced It may also be beneficial to perform test runs for SCOG recycle on different feed stocks The re-calibration of all SCOG flow meters to correct the molecular weights is also advised 7.2 HT-LCO The trial of HT-LCO as MTC liquid was a success by refinery production standards Recycling HT-LCO to the riser as MTC liquid is a rapid way of increasing the yield of C3 and C4 as well as the conversion of HT-LCO to gasoline Research and development needs to be conducted into the mechanisms by which HT-LCO increases conversion to fully understand how the process can be optimised for this type of operation It is recommended that the tests performed in this inquiry are reproduced and the results are statistically analysed to prove repeatability As with the SCOG trials, further test runs recycling HT-LCO to the riser as MTC liquid should be conducted with different FCCU feed stock The use of HT-LCO as MTC liquid should be incorporated into operational procedures For periods of time where diesel is in low demand recycling HT-LCO is one way of improving refinery profitability 7.3 LCN The use of LCN as fluidising riser steam should be investigated as it was not possible to carry out the test planned for this inquiry due to an un-planned FCCU shutdown Page 35 of 36 Individual inquiry 2001 Allyson Woodford References Ashland Oil, (1984) Australian Patent AU-A-43111/85 Residual oil cracking process using dry gas as lift gas initially in riser reactor Chia Dr D A (2000) Deactivation of Industrial Fluid Catalytic Cracking Catalysts – CATALYTIC CRACKING CATALYST DEACTIVATION – IMPACT ON SELECTIVITY FOR COMPLEX FEEDS Doctoral Thesis, Department of Chemical Engineering and Industrial Chemistry, University of New South Wales de la Puente, G., Chiovetta, G., Sedran, U (1999) FCC Operation with Split Feed Injectors Ind Eng Chem Res American Cemical Society, USA Grace, W.R (1993) The Grace Davidson Guide to Fluid catalytic cracking Part One W.R Grace and Co., Connecticut USA Hayes, J Castillo, C (1983) United States Patent, 4,447,552 Passivation of metal contaminants on cracking catalyst Krishna, A.S., Skocpol, R.C., English, A.R., Sadeghbeigi, R (1994) Split feed injection: Another tool for increasing light olefin yields and gasoline octanes AkzoNobel FCC Australian Catalyst Seminar Papers Sadeghbeighi, R (1995) Fluid Catalytic Cracking Handbook Gulf Publishing Company, Houston Texas Wilson, J.W (1997) Fluid Catalytic Cracking PennWell Publishing Company, Tulsa Oklahoma Technology and Operations Woodford A.M (2001) Vacation Student Report 2001 Caltex Lytton Refinery, Brisbane Page 36 of 36 Individual inquiry 2001 Appendix One Allyson Woodford - Test Procedure (See files for other Appendicies Test Procedure Conditions - No recycles including slops to main frac, MTC, LCN, SCOG etc (except the recylce being tested) Partial burn operation of regenerator Maintain constant operating conditions eg reactor severity, regenerator bed temmperature and main fractionator tray temperatures Stable operation at least 6-12hrs before testing to proceed (no crude diet changes) SCOG Procedure Collect feed sample of cracker feed Collect catalyst sample (warning – hot) Collect bags of reactor overhead sample Collect bombs of regenerator flue gas Collect SCOG sample Replace 25tpd of riser fluidising steam at the Wye with 25tpd of SCOG (same MW) Leave system for hour to stabilise Repeat steps – Replace a further 25tpd (50tpd in total) of steam with 25tpd SCOG (total of 50tpd of SCOG addition) 10 Leave system for hr to stabilise 11 Repeat steps – 12 Prepare samples for analysis LCN Procedure Collect feed sample of cracker feed Collect catalyst sample (warning – hot) Collect bags of reactor overhead sample Collect bombs of regenerator flue gas Collect LCN sample Replace 10tpd of riser fluidising steam at the wye with 50tpd of LCN Leave system for hour to stabilise Repeat steps – Replace a further 10tpd (20tpd in total) of steam with 50tpd LCN (total of 100tpd LCN addition) 10 Leave system for hr to stabilise 11 Repeat steps – 12 Prepare samples for analysis Hydrotreated LCO Procedure Collect feed sample of cracker feed Collect catalyst sample (warning – hot) Collect bags of reactor overhead sample Collect bombs of regenerator flue gas Collect Hydrotreated LCO sample Add 100tpd of HT-LCO as MTC Leave system for hour to stabilise Repeat steps – Add further 100tpd (200tpd total) of HT-LCO as MTC 10 Leave system for hr to stabilise 11 Repeat steps – 12 Prepare samples for analysis Page 37 of 36 ... thermal cracking polymerise and condense directly to coke (Sadeghbeigi 1995) Thermal cracking should be avoided as the main cracking mechanism in the FCCU 2.3.3 Catalytic Cracking Catalytic cracking. .. poly-gasoline (increasing the octane) over a platinum-based catalyst The heavy fraction is processed into gasoline blend stock isomerising and dehydrogenating the hydrocarbons over a platinum/rhenium/tin-based... an increasing demand for transportation fuels as well as tightening environmental restrictions The fluidised catalytic cracking is one of the more important processes in the refinery (upgrading