A New FCC Process MIP for Production of Clean Gasoline Component

Scientific ResearchA New FCC Process MIP for Production ofClean Gasoline ComponentXu Youhao; Zhang Jiushun; Long Jun; Wang Xieqing(Research Institute of Petroleum Processing, Beijing 100083)Abstract: A concept of two different reaction zones was proposed based on the FCC reaction mechanism,and verified by the experimental results of a fixed fluidized bed reactor. The concept was used to design anovel reactor with corresponding operation measures. Further experiments were conducted on the newlydesigned pilot scale riser reactor. In comparison with the conventional FCC at relatively equivalent conversion,the pilot test results had shown that the olefin content in the cracked naphtha dropped by 12.4%, and both ofiso-paraffin and aromatics increased by 6%, and its MON increased by 1.3 units while maintaining the RONof the naphtha unchanged, and its sulfur content was reduced by 15% with a significant extension of its .induction period for Shengli VGO + VR.Keywords: catalytic cracking; riser reactor; reaction mechanism; gasoline stock; olefin1 Introductiontions to carry out cracking reaction, bydrogen transfer andisomerization in a controllable and selective degree aimingTo meet the environmental goal in China, a new specifica- at improvement of product quality and product distribution.tion has proposed for automotive gasoline, demanding thecontentsofolefin≤35v%。 aromatics≤40v%. benzene≤2 Analysis of Reaction Mechanism2.5v%, and sulfur≤0.08m%, respectively. The finishedgasoline pool of China is composed of over 80% of FCC Under the regime of catalytic cracking the hydrocarbon va-gasoline which contains 40%-65% of olefin, making the ole- pors are subjected to a host of interrelated reactions on thefin content of finished gasoline exceed the new gasoline spec. zeolite catalyst to form a rather complicated reaction system.Therefore how to slash the olefin content in FCC naphtha is The main reactions are presented in Figure |42.an urgent and tough problem in the study of FCC process.It can be seen from Figure l that alkanes, naphthenes orAn ideal approach to reduce the olefin content of FCC naph- aromatics all are subjected to a primary reaction involvingtha is to convert the normal and iso-olefins into iso-paraf- breakage ofC- C bonds to form olefins, which then lead to .fins and aromatics to the maximum extent. In order to solve a variety of secondary reactions. The important secondarythis problem, it is necessary to study the FCC reaction reactions include: cracking, cyclization, isomerization, hy-mechanism, modify the existing reaction pattern and cata- drogen transfer and polymerization of olefins, dehydroge-lyst type in favor of cracking of heavy hydrocarbons and nation of naphthenes, condensation, transalkylation and alky-conversion of light olefins. Analysis of FCC reaction mecha- lation of aromatics, etc. It is worthy of noticing that withnism and assessment of outcome of hydrocarbon reactions the e:”中国煤化工ctions (such as dehydro-in different reactors has resulted in a novel FCC process- genacondensation andMIPI (Maximizing Io-Parffins) for production of clean transaYHCNMHGove-mentioned second-gasoline component. This technology has broken through ary reactions take place through involvement of olefins.the constraints of existing FCC process on secondary reac- Hence the carbonium ion is the intermediate of the primary43China Petroleum Processing and Petrochemical TechnologyNo.3, September 2001Paraffins+Paraffins + OlefinsCrackins+OlefinsNaphthenesDrerereatio H rast.Cyclene Dlyroygution " rustsAromaticessIsomerizuion,Naphthenes with different ringsSid: chain cracking+Aromatics + olefinsAromaticsTrasaskylation，Aromatics with different alkyl groupsDelhydrogenaion.: Polynuclear aromaticsDehydrogenation,+CokeH transfer condensationCracking, Olefinscyctizationin NaphtbenesIsmeriatio,Iso-olefins Hytrogen uraresisoparaffinsOlefins Hydrogen raser, ParafrinsHylroge ronsir. soarfins+AroatiesCyeliztion, Hydgcn transfer, Condensetionsetion +CokeAlkyatin Iso-paraffins or alkylaromaticsFigure 1 Main reactions of hydrocarbons in FCC cautalysiscatalytic cracking reaction, and the olefins formed during reaction temperature would favor the cracking reaction andthe primary reaction become the intermediates of secondary would be disadvantageous to hydrogen transfer, isomeriza-reactions. The secondary reactions in connection with for- tion and alkylation reactions. Judging from the equilibriummation of iso-paraffins and aromatics include isomerization, constants of these reactions, high temperature would favorhydrogen transfer and alkylation (as shown by thick lines in the cracking reaction and would be disadvantageous to hy-Figure I), and all these reactions are related with olefins. drogen transfer, which would be affected by thermodynam-Thus it is evident that olefin is the precursor leading to for- ics to a lesser extent thanks to its larger equilibrium constant.mation of iso-paraffins and aromatics.High temperature would also be disadvantageous to isomer-ization reaction, which could be affected by thermodynam-The thermodynamic data on hydrogen transfer, isomeriza- ics to a larger extent thanks to its smaller equilibriumtion and alkylation can be used to predict the possible de- constant. Decrease of reaction temperature could favorgree of these reactions and optimal operating conditions. isomerization reaction. It can be figured out that low reac-The thermodynamic data of some reactions are presented in tion temperature can favor formation of iso-paraffins, the .Table 1. .precursors of which (olefins) can only be produced throughcracking of hydrocarbons at high temperature. These twoIt can be seen from Table I that the cracking reaction is an factors constitute a pair of contradictions. It is the crux ofendothermic reaction, whereas the hydrogen transfer, isomer- the new FCC process that can solve these contradictions.ization and alkylation are exothermic reactions. Increase of Since the precursor to iso-paraffin is olefin, which serves asTable 1 Thermodynamic data for some idealized reactions of importance in catalytic cracking: Equilibrium constant (g K)、Heat of reaction,Reaction typeChemical reaction454°C510°C527°C: kJmol"n-CJH,→nCH.+ CH。2.04。2.4633812; Crackingi-CH。→2-CH,1.682.102.2335514Hydrogen4CH。一3 CH.+CH。-115713中国煤化工transferCyclo-CH,+3i-CH。-3CH,+CH。11.22-77278Isomeriation 1CH-1-2-CH,0.32HCNMHG-51421-CH,->i-CH,0.236Alkylation1-CH+ i-CH。-i-C.H.-3.3Scientific ResearchReaction zone 2Reaction zone Ifomiezto-lso-olefins Hrase Iso-paraffinsiHydrocarbon mixture CrackinHydrocarbon mixture t(olefin' H transfer→Iso-paraffins+aromaticsAlkylation+Iso-paraffins or alkylaromaticsFigure 2 Routes of cutalytic cracking and conversion of Ihydrocarbons towards formation of iso-paraffins and aromaticsan intermediate of a series of reactions, it is possible to split approximately simulate these reactions, because the reac-the formation of olefin and the conversion of olefin into two tion of oil vapors takes place at a relatively stable tempera-different reaction zones. (Figure 2)ture and longer residence time with possible environmentfor further reaction of olefins resulted from primary crack-It can be seen from Figure 2 that the two reaction zones are ing of heavy hydrocarbons. The simulation method is basedseparated by olefin formation. The reaction zone 1 involves on cracking of heavy hydrocarbon feed on different catalystolefin formation, whereas the reaction zone 2 involves the types and reaction of naphtha feedstock on spent catalyst.olefin reactions. The main function of reaction zone 1 is the The former is used to simulate the reaction zone 1 and thequick and thorough cracking of hydrocarbon mixture into reaction zone 2, and the latter is applied to simulate the re-olefins. The operating pattern of this zone is similar to cur- action zone 2.rent FCC mode characterized by high temperature, shortcontact time and high catalyst/oil ratio. The reaction sever- The exploratory study using the Daqing atmospheric residity in this zone should exceed that currently adopted for FCC (AR) as the feed ran the small scale fixed fluidized bed reac-to enhance cracking of heavy feedstock into olefin which tor and the pilot scale riser reactor with the same catalystshould not be subjected to further cracking in order to pre- RAG-1, respectively. The test conditions and results are pre-serve medium molecules of olefins. In the meantime, high sented in Table 2.reaction severity can suppress formation of low-octane nor-mal alkanes and cyclanes, which would help to increase the It can be seen from Table 2, that the small scale fixed fluid-octane rating of FCC naphtha. The main function of reac- ized bed reactor can be used to simulate the specific featurestion zone 2 is to maintain low reaction temperature and long of catalytic cracking of hydrocarbons to make isoparaffins.reaction time, because olefins can be converted into iso-par- As compared to the pilot scale riser reactor, catalytic crack-affins through parallel reactions and serial reactions. Since ing in small scale fixed fluidized bed reactor at similar con-low reaction temperature can favor formation of iso-paraffin，version rate of feedstock can make products rich inthe operating mode in reaction zone 2 should be different to isoparaffins. The isobutane content in LPG was by 37%the current FCC operating mode. These measures can guar- higher in the small-scale fixed fluidized bed reactor thanantee the formation of olefins and facilitate moving the re- that from the pilot scale riser reactor, while the olefin con-action of olefins towards formation of iso-paraffins or iso- tent in gasoline was reduced to 25.55% from 49.20% of theparaffins/ aromatics.pilot scale unit, with the normal paraffin content increasedto 5.88% from 3.54% of the pilot scale unit. It is clear that3 Exploratory Study of Test Methodthe aromatics and iso-paraffins content in gasoline obtainedin the small scale fixed fluidized bed reactor was increasedAs the heavy hydrocarbons are exposed to two reaction zones with a中国煤化工content.with different operating modes, the existing test facilitiesYHCNMHGcannot precisely simulate the characteristics of two reaction The olefin rich FCC naphtha as the feedstock was exposedzones. The small scale fixed fluidized bed reactor can only to spent catalyst to simulate the reaction environment of the45Scientific ResearchTable 4 Comparison of product distribution+ Outletand gasoline properties for both processes*MIP: FCCProcess type| Product distribution, m%:Dry gas: 3.082.97. Reaction zone 2LPG16.9215.33Gasoline45.0743.70LCC22.0221.69HCO6.4410.14Quench medium-Coke6.47.6.17Reaction zone IConversion,%71.5468.17 :Hot regenerated catalyst、 Feed-in systemLight dillate (gasoline + diesel)Pre-lift mediumyield, m%67.0965.39Fig. 3 Sketch of novel riser reactorLight ends (LPG+gasoline+diesel)84.0180.72at higher reaction temperature and catalys/oil rati) to give Gasoline properties:more olefns during processing of heavier fedstock; the oil: Density (20°C) g/cm'0.7614菜0.7597vapors after a short residence time enter the lower section ofSulfur content, wppm11291329the reaction zone 2 with an expanded diameter designed toNitrogen content, wppm26reduce the flow velocity of oil vapors and catalyst. A quenchCarbon, m%86.96! 86.52medium or other meanslHI can be adopted to reduce the reac-Hydrogen, m%.12.9212.95tion temperature in this reaction zone in order to suppressDiolefin number,g l/l00g1.11.8the secondary cracking reaction and enhance isomerizationInduction period, min>1000572and hydrogen transfer reaction, so that the iso-parafins andOctane numberaromatic content of gasoline can be increased. The streamsMON79.878.5can stay longer in this reaction zone prior lo exiting the con-RON: 91.7 ;; 91.7traction section which is similar to the configuration of tra-Hydrocarbon group analysis byditional top section of riser reactor that restricts the resi-chromatography, m%:dence time of streams to suppress over-cracking and increase: Paraffins28.9425.43the linear velocity of fluids. Streams are then subjected toNaphthenes? 8.42gas-solid separation in the separation system, where the gas-Olefins24.532.78cous phase exits from the cyclone outlet and catalyst par-Aromatics: 37.5631.52ticles enter regenerator after stripping.fuorescence method, m%:5 Comparison of Pilot Test Results of MIPParaffinstnaphthenes41.6 :35.2Process Versus FCC Process27.239,631.225.2The test of MIP process was conducted in a novel pilotNote*: The catalyst was LV-23, and the fedstock was Shenglireactor, while the pilot tcst of FCC process was crriedout VGO中国煤化工in an existing pilt riser reactor. The reactin regimes, prod-uct dstribution and gasoline properties are isted in Table4. out al.MYHCNMHGatesof71.54%forMIPprocess and 68.17% for FCC process. The dry gas and cokeIt can be sen from Table 4 that a comparison was caried yiels were 3.08% and 2.97%; and 6.47% and 6.17%，47China Petroleum Processing and Petrochemical TechnologyNo.3, September 2001respectively. The LCO yield was 22.02% and 21.69%，eration mode, can apparently reduce olefin content in gaso-respectively. The LPG yield was 16.92% and 15.33%，line and increase isobutane yield. The existing FCC unitsrespectively. The gasoline yield was 45.07% and 43.70%，can be easily retrofitted into MIP unit, which can be coupledrespectively, with MIP process leading to higher gasoline with other unis to provide feedstock for other process units.yield. The HCO yield was 6.44% and 10.14%, respectively,with MIP process leading to lower HCO yield. The advan- 6 Conclusionstage of MIP process over FCC process was evidenced by thefact that the light ditillate (gasoline+LCO) yield was 67.09% A concept of two reaction zones in catalytic cracking reac-and 65.39%，respectively, and light ends yield (LPG+ tions was proposed based on catalytic cracking mechanism,gasoline+LCO) was 84.01% and 80.72%, respectively. The and was verified by tests in small -scale fixed fluidized reactor.selectivity of both processes for dry gas and coke was basi- The serial type riser reactor designed according to the re-cally equal.sults of small-scale tests has not only retained the high reac-tion severity at the initial stage of riser reactor, but also in-It can also be seen from Table 4 that the olefin content (by creased the duration of secondary reaction to meet the needsFIA method) of gasoline manufactured by MIP process was for formation of iso-paraffins in the course of FCC process.27.2%, which was lower by 12.4% as compared to 39.6% Thus emerges the novel MIP process. The pilot tests haveolefins in FCC gasoline. The paraffin (mostly iso-paraffin) revealed that the MIP process has a stronger capability forcontent of MIP gasoline was increased by 6.4% and its aro- heavy oil cracking, leading to a higher yield of lightmatic content was increased by 6%. The olefin content (by hydrocarbons. The LPG obtained is rich in isobutane, whereaschromatographic analysis) of gasoline manufactured by MIP the gasoline is rich in iso-paraffins.process was 24.5%, which was lower by 8.28% as comparedto 32.78% olefins in FCC gasoline. The relative sulfur con- Referencestent in gasoline dropped by 15% with its induction periodextended. The MON rating of the MIP gasoline was increased [1] Xu Youhao et al,“A catalytic conversion method forby 1.3 units with RON kept unchanged. In summary, the production of isobutane and gasoline rich in iso-paraffins",gasoline quality of the MIP gasoline was better that that of Chinese Patent, CN 1232069A (1999).FCC gasoline.[2] Julius Scherzer, “Octane- Enhancing Zeolitic FCCCatalysts: Scientific and Technical Aspects", Catal. Rev.-The MIP technology has provided a new approach for pro- Sci. Eng., 1989, 3(31),215-354.duction of the component for clean gasoline. This process [3] Xu Youhao et al,“A riser reactor applied in fluidizedhas broken through the constraints of existing FCC process catalytic conversion”, Chinese Patent, CN 1237477A (1999). .on secondary reactions to realize the cracking reaction, hy- [4] Xu Youhao et al,“A catalytic conversion method fordrogen transfer and isomerization in a controllable and se- reduction of olefin content in LPG and gasoline", Chineselective manner. The MIP process, which is flexible in op- Patent, CN 1245202A (1999).中国煤化工MYHCNMHG