Catalytic pyrolysis of atmospheric residue on a fluid catalytic cracking catalyst for the production

第37卷第1期燃料化学、学报Vol. 37 No. 12009年2月Jourmal of Fuel Chemistry and TechnologyFeb. 2009文章编号: 0253-2409<2009)01-0124-05Catalytic pyrolysis of atmospheric residueon a fluid catalytic cracking catalyst for the production of light olefinsYANG Lian-guo, MENG Xiang-hai, XU Chun-ming, GAO Jin-sen, LIU Zhi-chang(State Key Laboratory of Heary Oil Processing, China University of Petroleum( Beijing), Beijing 102249, China)Abstract: Catalytic pyrolysis of Chinese Daqing atmospherie residue on a commercial fluid catalytic cracking ( FCC) catalyst wasinvestigated in a confined fuidized bed reactor. The results show that the commercial FCC catalyst has good capability of crackingatmospheric residue to light olefins. The analysis of gas samples shows that the content of total light olefins in cracked gas is above80%. The analysis of liquid samples shows that the content of aromatics in liquid samples ranges from 60% to 80% , and it increaseswith the enhancement of reaction temperature. The yield of total light olefins shows a maximum with the increase of reactiontemperature, the weight ratios of catalyst to-oil and steam-to-oil, respecively. The optimal reaction temperature, the weight ratios ofcatalyst-to-oil and steam-lo-oil are about 650心, 15 and 0. 75, respectively.Key words: catalytic pyrolysis; residue; ethylene; propyleneCLC umber: TE624.4Document code: ACatalytic pyrolysis has attracted great interests inranged from 19% to 27%. The yield of total lightrecent years since it can use low value heavy oils andolefins ( ethylene + propylene + butylene ) exceededgas oils to produce such light olefins as ethylene,50% under optimal operating conditions for thepropyleneandbutylene2Compared withcatalytic pyrolysis of paraffinic atmospheric residue. Lconventional steam pyrolysis, catalytic pyrolysis canet al' 15 investigated the catalytic pyrolysis of Daqingnot only reduce reaction temperature. and energyatmospheric residue on Ag and La modified 2ZSM-5consumption, but also allow one to flexibly adjust thecatalyst using a two stage riser FCC apparatus. Theproduct distribution. Catalytic pyrolysis can alsoyields of ethylene and propylene reached 13. 0% andproduce light olefins from a wide range of feedstocks.29.9% respectively with the recycle of C4The feed for catalytic pyrolysis ranges from Chydrocarbons. Experimental research showed thathydrocarbons'3-61heptanenaphtha[81， FCCproduct yields varied greatly with catalyst properties,gasoline9.io，vacuum gas oil"， and even lowfeed properties，reactor types and operating conditions.valuable heavy oils!12-14]In this research, we first analyzed the componentsMeng et al investigated the catalytic pyrolysisin gas and liquid samples from catalytic pyrolysis ofof Daqing atmospheric residue on CPP ( catalyticatmospheric residue on a commercial fluid catalyticpyrolysis process) catalyst. The yields of light olefinscracking ( FCC) catalyst, and then studied theshowed maxima with the increase of reactioninfluence of reaction temperature, weight ratios oftemperature, the mass ratios of catalyst-to-oil andcatalyst-to-oil and steam-to-oil on product yields, andsteam-to-oil，respectively. Under optimal operatingthen determined the optimal reaction conditions.conditions， the yields of ethylene and propylene were15. 9% and 20. 7% respectively. Zhang et al'3]1 Experimentalinvestigated the catalytic pyrolysis of heavy oils on CPP1.1Feedstocks and catalyst In this research,catalyst using a pilot-scale FCC apparatus. The yieldsChinese Daqing atmospheric residue ( Daqing AR) wasof ethylene and propylene were 22. 82% and 15. 96%used as the feedstock. The main properties of the feedrespectively under the following reaction conditions,are given in Table I.reaction temperature 640 C，reaction pressure 0. 07A commercial FCC equilibrium catalyst obtainedMPa，and steam content 54. 3%. Sha et al4from Huabei Petrochemical Company, PetroChina wasinvestigated the catalytic pyrolysis of heavy oils onused as the catalyst. The physical properties andHCC ( Heavy-oil contact cracking) catalyst using aparticle size distribution of the catalyst are listed inpilot-scale FCC apparatus. The yield of ethyleneTable 2.中国煤化工Received date: 2008-06-13; Received in revised form: 2008-10-09.Foundation item: National Science Fund for Distinguished Young Scholars ofMHCN M H Gan of the Ministy ofEducation of China (307008).Corresponding author:MENG Xiang-hai, Tel; 8610-8973-3775, E-mail: mengh@ cup. edu. en.Author introduction: YANG Lian-guo ( 1968-), male, doctral student, engaged in clean fuel production.第1期YANG Lian-guo et al. : Catalyic pyrolysis of atnospheric residue on a fluid catalytice cracking catalyst ..125_Table 1 Properties of Daqing atmospheric residueDensity Viscosity Hydrogen Carbon HCCarbonGroup analysis(20C) (50C) content content atomieAromaticityresiduew/%p/g*cm^Pa's w/%ratisalurales aromatics__ resins asphaltenes_ 0.92 0.21 13.08 86.921.7910.94.851.329.818.30.6二Table 2 Properties of the commercial FCC equilibrium catalystMiero -reaction Pore volume Surface area Packing density Coke contentParticle size distibuion w0/%activity index_ v/cm' °gA/m'.g"' .p/g.cm°/%0-20 μm 20-40 um 40~80 um >80 um0.2490. 88070.216.458.225.21.2 Apparatus In experiments of catalyticmeasure the volume percentage of components in thepyrolysis of heavy oils, a confined fluidized bed reactor;as sample. The equation of state for the ideal gaswas used, and the diagram is shown in Figure 1. It isconverts the data to mass percentages. The liquidcomprised of five sections， oil and steam inputsample was analyzed with a gas chromatogram-massmechanisms, a reaction zone， temperature controlspectrometer to get contents of the main components insystem and a product separation and collection system.liquid sample. Coke content on the spent catalyst wasmeasured with a coke analyzer.2 Results and discussion2.1 Analysis of catalytic pyrolysis products0118The components of cracked gas and liquid samples ofcatalytice pyrolysis of Daqing AR on the commercialFCC catalyst were analyzed in detail. The residence13time and the weight ratios of catalyst-to-oil and steam-10-14to-oil were kept constant at 2. 5 s，15 and 0. 75,respectively.2.1.1 Analysis of gas sample The yields of70components in gas samples are listed in Table 3.Figure 1 Diagram of the experimental setupTable 3 Yields of components in gas samples1 -constant temperature box; 2-steam fumace; 3-feedstock;8-preheater; 9-reactor fumace; l0-thermocouple; 11-reactor;625C650C675C12-inlet and oule of atalysts; l3-fiter; 14-condenser; L-oectinnHydrogen0.3 0.3 0.botle for liquid samples; 16-gas cllection vessel; 17-beaker;Methane3.1 4.0 5.5l8-gas sample bagEthane2.0 2.1 2.4Ethylene10.2 12.0 14.0The experiments were carried out at varioustemperatures between 625 C and 675 C，with thePropane0.9 0.7 0.6weight ratios of catalyst-to-oil and steam-lo-oil varyingPropylene20.2 19.9 18.2between 8 ~ 22，and 0. 5 ~ 1. 5，respectively.i-Butane0.5 0.4 0.3Experiments are conducted in a batch mode. For eachn-Butane0.8 0.2 0.2experiment, varying weights of catalyst were loadedt-2-Butylene2.6 2.6 2.1into the reactor with an effective volume of about1-Butylene2.3 2.2 1.9580 mL. Distilled water was pumped into a furmace toi-Butylene3.8 3.8 3.2form steam, which was used to fluidize the catalyst.c-2- Butylene0.6 1.4 1.5The feedstock was pumped and mixed with the steam.1 ,3-Butadiene0.4 0.6 0.5The mixture was heated to approximately 500 C in aCarbon dioxide0.4 0.6 0.8pre-heater. Reactions took place as the feed contactedTotal light olefins (A)40.1 42.5 41.4with the fluidized catalyst. The oil gas afler reactionlyd |中国煤化工7.6 7.7 9.4was cooled and separaled into liquid and gas samples.Fl8.1 50.8 51.6The spent catalyst after reaction was drawn out of theHCNMHG.19 0.18 0.23reactor by a vacuum pump.ContentofAinCw/%.83.37 83.66 80.231.3 Analytical methods An Agilent 6890 gaschromatograph with Chem Station software was used toThere are mainly light olefins in cracked gas.126燃料化学学报第37卷samples，and the content of total light olefins inincreases.cracked gas ranges from 80. 23% to 83. 66% underexperimental conditions. Furthermore , propylene yield2.2 Investigation of reaction conditions Theis much higher than that of ethylene or butylene.influence of reaction temperature, weight ratios ofThe yields of total light olefins and cracked gascatalyst-to-oil and steam-to-oil on product yields andare high， exceeding 40% and close to 50% ,distribution was studied. The optimal reactionrespectively, while that of hydrogen and total lightconditions were obtained.alkanes is below 10%. The yields of cracked gas2.2. 1 Influence of the weight ratio of catalyst-lo-oilincrease slightly as reaction temperature increases ，The influence of the weight ratio of calalyst-to-oilwhile that of total light olefins shows a maximum atwas studied in the range of 8. 7 to 21.5 by changing650 C.the catalyst loading. Reaction temperature, residenceThe desired products of catalytic pyrolysis oftime and the weight ratio of steam-to-oil were keptatmospheric residue are light olefins such as ethylene,constant at 675 C, 2.5s and 0.75, respectively.propylene and butylene， while hydrogen and lighThe experimental data are listed in Table 5. Asalkanes are undesired products. Therefore, we want tothe weight ratio of catalyst-to-oil increases, the yieldsget the low ratio of the yield of hydrogen and total lightof cracked gas, propylene , butylene , total light olefinsalkanes to the yield of total light olefins. As reactionand ethylene plus propylene show maxima at the weighttemperature increases,， the ratio of the yield ofratio of catalyst-to-oil of 15. 0, those of ethylene andhydrogen and total light alkanes to the yield of totalcoke increase, those of hydrogen and methane varylight olefins shows a minimum at 650 C .slightly , and that of liquid product shows a minimum at2.1.2 Analysis of liquid sample Table 4 lists thethe weight ratio of catalyst-to-oil of 15. 0. The optimalcontent of components in liquid samples.weight ratio of catalyst-to-oil is around 15. 0 for muchproduction of light olefins.Table 4 Contents of components in liquid samplesw/% .Table5 Product yields as a function of catalyst-to-oil625 C 650C 675 Cweight ratioAlkyl benzene31.2 32.5 32. 2w/%Benzene2.2 2.8 1.5Caalylsto-oil weight ratio 8.7 12.2 15.0 21.5Toluene10.4 12.0 12.7Cracked gas50.0 50.0 51.5 50.0Ethyl benzene2.02.2 2. sHydrogen0.40.4 0.4 0.Xylene & styrene9.5 9.2 10.6Methane5.6 5.4 5.3 5.7Cz benzene7.16.3 4.9Ethylene13.914.0 14.1 14.5Alkyl naphthalene14.218.4 23.0Propylene17.5 18.1 18.9 17.2Naphthalene1.8Butylene8.0 7.9 8.2 7.5Methyl naphthalene4.4 3.8 5.5Total light olefins39.4 40.0 41.2 39.2C2 naphthalene5.0 3.7 5.3Ethylene + propylene1.5 32.1 33.0 31.7C3 naphthalene3.04.9 4.5Liquid45.8 44.3 42.9 43.8Alkyl indene4.14.5 6.7Coke4.2 5.7 5.6 6.2Alkxyl phenathrene & anthracene7.5 8.6 10.9The main function of the catalyst is to transferAlkyl pyrene1.5 1.6 2.7energyi and to offer location and active centers forOthers41.5 34.4 24.5cracking reactions. The value of the weight ratio ofThe content of aromatics in liquid samples rangescatalyst-to-oil not only denotes the contact conditionfrom 60% to 80% under experimental conditions, ancbetween oil vapor and the catalyst, but also indicatesit increases with thenhancement of reactionthe average activation of the catalyst. As the weighttemperature. The aromatics in liquid samples areratio of catalyst-to-oil increases， the contactmainly composed of alkyl benzene, alkyl naphthalene.opportunities between oil vapor and active centersalkyl indene, alkyl phenathrene, alkyl anthracene andbecom中国煤化工of active centersalkyI pyrene. The yield of alkyl benzene varies slightlycontacactive centers willas reaction temperature increases, while that of alkyldeclinTYHC NMH Ge centers on thenaphthalene increases. This indicates that the pyrolysissurlace per unit catalyst will be covered by coke. Largedegree becomes higher, and the condensation degree ofweight ratio of catalyst-to-oil means that much energypyrolysis liquid increases as reaction temperaturecan be transferred in the reaction process, which can第1期YANG Lian-guo et al. : Catalytic pyrolysis of atmospheric residue on a fuid catalytice cracking catalyst ..127accelerate thermal cracking reactions. To a certaincatalytic cracking reactions following the carbonium ionextent, a large weight ratio of catalyst-to-oil means amechanism, and they are intermediate products, whichthorough pyrolysis.can undergo such secondary reactions as hydrogenMoreover，the increase of the weight ratio oftransfer,aromatization，crackingandcatalyst-to-oil can enhance the back-mixing degree ofpolymerizationEthylene is primarily formed fromcatalyst particles，which can reinforce the back -rmixingthermal cracking reactions fllowing the free radicaldegree and prolong the residence time of part of the oilmechanism, and it is close to the end product, so it isgas, and then increase the secondary crackingunlikely to undergo secondary reactions.reactions of intermediate products. Since ethylene isAs reaction temperature increases, the reactionclose to final pyrolysis product, so its yield increasesrates of both catalytic cracking and thermal crackingall the time, but the increasing scope is not obvious,increase, causing pyrolysis to be more thorough, andwhich indicates that the weight ratio of catalyst-to-oil istherefore, the yields of light products increase. W ithnot the main factor influencing ethylene yield. In thefuther increase of reaction temperature, the proportioncase of propylene and butylene, they can take placeof catalytic crackingreactions decreases and that offurther cracking reactions of both catalytic pyrolysis andthermal cracking reactions increases. The yield ofthermal pyrolysis because they are not final pyrolysisethylene becomes close to that of propylene as reactionproducts, especially at large weight ratio of catalyst-to-temperature increases. Since the increase of reactionoil. As a result, their yields show maxima at the weighttemperature can accelerate the secondary reactions ofratio of catalyst-to-oil of 15.0.intermediate products, the yield of propylene decreases2.2.2 Infuence of reaction temperatureTheas reaction temperature increases, and that of butyleneinfluence of reaction temperature was investigated onshows a maximum.product yields in the reaction temperature range ofIn order to achieve high yields of light olefins with625 C ~675 C. Residence time and the weight ratioslow energy consumption， the appropriate reactionof catalyst-to-oil and steam-to-oil were kept constant attemperature is around 650 C. Under such reaction2.5s, 15 and 0. 75, respectively.conditions, the yield of propylene is much higher thanThe experimental data are listed in Table 6. Asthat of ethylene , and the yield of butylene is lower thanreaction temperature increases, the yields of crackedthat of ethylene.gas, coke, hydrogen, methane, ethylene and ethylene2.2.3 Infuence of the weight ratio of steam-to-oilplus propylene inerease , those of propylene and liquidReaction temperature and the weight ratio of catalyst-decrease, and that of butylene shows a maximum atto-oil were kept constant at 675 C and 15,650 C. The yield of total light olefins varies slighly asrespectively. The influence of the weight ratio of steam-reaction temperature increases from 650 C to 675 C，to-oil on product yields was investigated in the range ofbut the distribution of light olefins is different.0.5 to 1.5 by altering the feeding rate of atmosphericresidue.Table6 Product yields as a function of reaction temperatureTable 7 lists the experimental data._to/%625C650C665C675CTable 7 Product yields as a function of steam-to-oilCracked gas47.5 50.5 51.0 51.5weight ratioHydrogen0.20.3 0.4 0.4w/%Methane3.2 4.0 4.8 5.3Steam-to-oil weight ratio0.5 0.75 1.0 1.Ethylene10.5 12.0 13.4 14.141.9 50.5 50.6 49.7Propylene21.019.9 19.4 18.90.3 0.3 0.3 0.5Butylene8.1 9.5 8.9 8.23.6 4.0 3.8 4.3Total light olefns39.641.4 41.7 41.210.1 12.0 12.2 13.0Ethylene + propylene31.5 31.9 32.8 33.015.9 19.9 19.6 18.1Liquid47.744.6 44.4 42.98.2 9.5 10.4 9.8_Coke4.84.9 4.6 5.634.2 41.4 42.2 40.9中国煤化工1.9 31.8 31.1In practice， the catalytic pyrolysis processYHCNMHG4.6 44.4 46.6involves catalytic cracking reactions on catalyst surfacesLoke4.3 4.9 _ 5.0 3.7and thermal cracking reactions both on catalyst surfacesand in the interspaces between catalyst particlesLl .As the weight ratio of steam-to -oil increases, thePropylene and butylene are mainly generated from yields of cracked gas, butylene, total light olefins and128燃料化学学报第37卷coke show maxima at the weight ratio of steam)-to-oil of3 Conclusions1.0, those of propylene and ethylene plus propyleneThe commercial FCC catalyst has good capabilityshow maxima at the weight ratio of steam-to-oil ofof cracking atmospheric residue to light olefins, and0.75, those of hydrogen and methane increase, andpropylene yield is much higher than that of ethylene orthat of liquid shows a minimum at the weight ratio ofbutylene.steam-to-oil of 1.0.There are mainly light olefins in cracked gasIncreasing the weight ratio of steam-to-oil cansanple, and the content of total light olefins in crackedreduce the partial pressure of oil vapor, which favorsgas is above 80% .the cracking of hydrocarbons into low molecular weightThe content of aromatics in liquid samples rangesproducts. Therefore , the yields of light olefins increasefrom 60% to 80%， and it increases with thegradually, and reach maxima in the range of 0.75 to .enhancement of reaction temperature.1.0. However, the yields of propylene and butyleneReaction temperature and the weight ratios ofdecrease slightly when. the weight ratio of steam-to-oilcatalyst-to-oil and steam-to-oil have some influence dnis above 1.0. In that case, the residence time of oilproduct yields. The yield of total light olefins shows avapor becomes long, and accordingly, parts of lightmaximum with the increase of reaction temperature ,olefins undergo secondary reactions.the weight ratios of catalyst-to-oil and steam-to-oil,As for this study, the maximal yields of lightrespectively.olefins can be obtained when the weight ratio of steam-The opimal reaction temperature， the weightto-oil ranges from 0.75 to 1.0. 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