联合两段氧化制合成气/F-T合成的GTL工艺和催化剂

Chinese J. Chem. Eng, 11(1)85-89(2003)An Integrated Process of a Two-Stage Fixed Bed SyngasProduction and F-T Synthesis for GTL in RemoteFieldDAI Xiaoping(代小平), YU Changchun(余长春), Li Qiang(李强), ZHANG Changbin(张), JIANG Qiying(江启滢) and SHEN Shikong(沈师Key Laboratory of Catalysis, CNPC, University of Petroleum, Beijing 102249, Chinane to synthesis gas (syngas), which consists of twgenerate heat or power energy. The results show that the two-stage fixed reactoress keep away from explosiongrated process is fitted to produce diesel oil andKeywords two-stage fixed reactor, syngas, Fischer- Tropsch synthesis, gas to liquid, process1 INTRODUCTIONposed and future GTL facilities will be remarkably lessInterest in the conversion of natural gas to liquid cost than their very expensive predecessors. Some new():is still needed in order to reduce the operationgascapital costs of a GTL plant, and strengthen its eco-nomic competitiveness. Owing to hot-spot formation 2 GTL PROCESS AND CATALYSTS FORand the risk of explosion with premixed CHa/O2 mix- CONVERSION OF NATURAL GAStures, the process of catalytic partial oxidation(CPO)An alternative GTL technology, which would beof methane to syngas has not been realized commer- used mainly in small gas field in remote areas, is be-cially. The choice of suitable operating conditions and ing developed 9, 10. The schematic of this process isale-up problems relating to catalyst stabilityshown in Fig. 1. This technology includes three pro-process safety still require considerable attention. At cess steps as the followingressure, hot-spot formation due to exothermal oxida- production of syngas, using Lao. 7Ca0.3Feo 3Mno703ion reactions can lead to severe catalyst deactivation. perovskite combustion catalyst and La2 O3 promotedA technology for syngas production in fuidized bed 7%(by mass)Ni/MgAl204-Al2O3 catalyst, is devel-reactor has been developed by Exxon(2,3). Alterative oped. Air and natural gas, which have to be desulfur-dual-bed or mixed-catalyst bed reactors have been rated, is used as feed stock, and the total ratio is 1:2examined by Ma and Trimm 4). Sasol Slurry Phase (volume ratio). The reaction conditions vary 653-Distillate process used autothermal reforming with 723K(in the first reactor), 973--1323K (in the sec-O2 for the production of syngas, while Shell Middle ond reactor), 2.0-2. 5 MPa and gas hourly space ve-Distillate synthesis process used noncatalytic partilocity(GHSV)is 10000-30000h -. The main reac-oxidation3.1, BP Amoco process, which integrated tions occurring in the two fixed bed reactors are ascombustion with steam reforming, leads to a 90% eff- followsciency versus 60%65%for conventional reformer(6)The first reactorEspecially, Syntroleum process uses autothermal re-forming with air to produce syngas, which from theCH4+202-+CO2+2H2Oautothermal reformer has a nearly ideal H2-to-Co ra-△H29K=-802 kJ, mol-1tio. The process used air instead of O2, and one-passdesign for Fischer-Tropsch synthesis, which competi-The second reactortive on an economic basis 3, 7, 8]. Although the meritsof new large-scale commercial F-T plants are yet tobe confirmed, there is good reason to believe that pro-△H29K=-357 kJ. mol-1Received 2001-12-18, accepted 2002-09-18Supported by the Major State Basic Research Projects of the Minist中国煤化工m(a9To whom correspondence should be addressed. E-mail: IngecabjpeuYHCNMHGChinCh. E(VoL 11, No. 1)CH4+2CO2→2CO+2H2concentration of methane in the first reactor thaan par△H298K=247kJ·mol(3) tial oxidation of methane, while the inert N 2, and CO2and H2O from the first reactor are as diluent gas in thesecond reactor, which could reduce the range of explo-CH4+H2O→CO+3Hsive limit which could become wider with increasing△H29sK=206kJ·mol-(4) initial temperature and pressure!12, 13. The first re-actor,packed with a perovskite type oxide catalyst isThe total reactionused for catalytic combustion of methane at low ini-(2)A single-pass Fischer-Tropsch synt bess (5) tial temperature(653--673K), while the second reac-CH4+0.502-+CO+2H2tor filled with a La promoted Ni-based catalyst is usedfor the partial oxidation, H2O and CO2 reforming ofcess, using ceria promoted co-based catalyst (ll. The methane to syngas. A portion of methane(ca. 69reaction is run at 488--523K, 2.0-2.5 MPa, andis oxidized completely to CO2 and H2O in the300-800h-1. The main reaction is shown in Eq (6). first reactor, in which the effluent are heated to thetemperature required for methane partial oxidationCO+2H2→+-CH2-+H2O1073 K )at adiabatic conditions. The remaining△H29s8=-165kJmo-1(6) air(ca70%--75% of the total) is introduced into the(3)Catalytic combustion technology of low mic partial oxidation of methane and the endothermicmethane concentration is for F-t offgas conversion, reforming reactions of CO2 and H2O with methane.using Lao. 7Ca0.3Feo.3Mno 703/y-Al2O3 catalyst. TheTable 1 shows that the ignition temperature ofreaction is run at 488--523K, 0. 1 MPa, and 300- the perovskite is higher than that of pd-Pt/r-Al2OA large amount of Co is formed over1 A two-stage fixed bed process of CPO for Pd-Pt/r-Al2O3 catalyst at high reaction tempera-production of synthesis gasture of 973K. The tests of 100 h on streamThis process consists of two consecutive fixed re- 1073 K, GHSV=10000h-, CH4/O2 volume ratio isactors in which air is introduced separately into the 8 at atmosphere pressure show that the activity oftwo reactors. In this way, the process is far from the Lap.7 Ca0. FeD.3Mno 3O3 catalyst is stable, and the de-explosive limit in either reactor due to increase the posited carbon is 0.6%(by mass) of the catalystcompressor stcam natural steam coho steam syngas自自自air compressorsteamcondenserventpartial oxidation.Figure 1 Schematic of GTL using two-stage flxed reactor/Fischer-Tropsch synthesisTable 1 Test results of various catalyst for combustion of rich methaneConv. of ChCatalystsSelectivity.Pd-Pt/y-Al2O3Pd.Lao. 7 Cao fEo, mNo, 7O3A0.7Cao, 3 Feo mNo.73Reaction condition: CH4/O2 volume ratio is 8, GHSV=30000h-I中国煤化工 2 mm diameter. reactorinner diameter of 14 mm-HCNMHGFebruary, 2003An Integrated Process of a Two-Stage Fixed Bed Syngas Production and F-T SynthesisTable 2 The effect of pressure on the combustion of rich methanePressureSelectivity,CatalystsMPacOmm85.8Lau.7 Cav. 3 Feo. 3Mno. 7O31.05.61.55.6Reaction condition: CH4/O2 volume rat1-2 mm diameterinner diameter of 14mmTable 2 shows that the catalyst exhibitmore exceent catalytic combustion with the pressure increasedl20The product is almost CO2 above 1.0MPaThe reaction was tested in ceramic lined stainless steel reactor(inner diameter of 19 mm). The re-sults of 300h in two-stage CPO test at 1223 K and2. 0MPa show that the both catalysts exhibit goodstability. The Lanthanum-based perovskite type oxde catalysts (Lao. 7 Cao. 3Feo 3 Mno.7O3), was used in100150200250300the first reactor, while the proprietary Lay O3 prme on strcam, hmoted Ni/MgAl2 O3 catalyst was used in the secondreactFigure 3 Time trace of hot spot temperature ofe■ hot spots temperature;·furnreactor, the same reaction conditions as in Fig. 22.2 A single-pass Fischer-Tropsch synthesisprocessHigh CO conversion is needed to a Fischer-Tropschsynthesis process without recycle F-T tail gas becauseof the air-derived syngas. At the same time, low CO050100150200250300and light hydrocarbon selectivities are desiredtime on stream hpromoted co-based catFigure 2 TheNi/MgA1O4 on the two-stage fixed bed processdeveloped(in. a syngas of H2: CO=2.02: 1 (molar ra-H4: O2: N2(air)=2: 1 4(molatio)is used for the catalyst test. The catalyst is re-ratio); at the first reactor: 673 K, reactor inner diameter of duced for 8 h in hydrogen with a gas hourly space ve-14mm,5g catalyst,1-2mm diameter, at the second reactor: locity(GHSV)of 500h -I at 673 K under atmospheric1223K,GHSV=10000h-I, reactor inner diameter of 14 mm, pressure, and then cooled to room temperature5 g catalyst, y-Al2O3 spheres of 2.5 mm diameter)■CH4 conversion;·H2 selectivity;▲ CO selectivThe catalyst(Ce/Co molar ratio is 0.28)gives 89%average conversion for CO and 81% average selectivFigure 2 shows that the CH4 conversion reaches ity for liquid hydrocarbons(C5) using quartz lined83%, CO and H2 selectivity reached 92% and 93%, stainless fixed bed reactor under 490K, 1.2 MPa andespectively. The experimental data are quite close to GHSV=500h-1 in a 1000h run(in Fig 4). The molethe thermodynamic equilibrium data of the reaction percent of CH, is 8.5%. H2O is the main byprod-condition. The amount of deposited carbon over the uct and CO 2 is the minor one. The hydrocarbon dis-second reactor is about 4.1%(by mass). Fig 3 shows tribution indicates that the chain growth factorthat the temperature of the hot spot increase in the proaches 0.9 over ceria promoted Co/SiOz catalystfirst 80h, and then keep almost constant at about (shown in Fig. 5), while typical chain growth factor ac-1243K. The location of the hot spot is in the mid- cording to ASF rule is 0.78 over Co/Sioz catalyst/44dle of the catalyst bed. The hot spot constitutes no The mass fraction distribution of products is C7--C10serious problem at the present scale test, and it needs 11.3%, C1-C20 58.4%, C#, 30.3% over ceria pro-further attestation as the test is carried out on a larger moted Co/SiO2 catalyst. The result shows that ceriascale. The two-stage fixed reactor process avoids more promoted Co/SiO catalyst is favorable to producingfavorably the risk of explosion of CH4/O2, due to the diesel oil and lubricating oilintroduction of O2 into the two reactors separately closeand the dilution by N, in the air中国煤化工四吗CNMHG1(1)85(200Ch.E(Vol. ll, No. 1)7before regenationregenationImm01015202530300200300400500600Figure 5 The hydrocarbon distribution of CeoFigure 4 The stability test of CeOa promotedpromoted 15%(by mass)Co/SiOz catalysts15%(by mass)Co/SiOa catal000h on streamF-T synthesisThe reaction conditions are the same as in Fig 4■ Co conversion;· CE selectivity;A CHa selectivity: V CO2 selectivformation of nitric oxides. This is a promising newReaction conditions: 1. MPa, Ha C0-2 1(contain 3: N2, technology for the production of energy/l61. A cat-pheres of 0. 45--0. 90 mm)alytic combustion technology has been investigated forthe F-T offgas to generate heatthat Co-Ce/SiO2 catalyst(Ce/ Co=0. 28, molar ratio) heat can be used for heating the feed-stock gasgives 92.6% conversion for CO and 86.8% selectivityThe F-T tailgas from air-derived syngas containsfor liquid hydrocarbons(Ct )using fixed bed reactor methane 5.7%, CO 3.5%, C2 0.4%, C3 0.5%, C40.4under 491K, 2.0MPa and GHSV=500h-l. The mole CO 2 0.7% and a larger amount of nitrogen(volumefraction of CH4 is 7.1%. The result is close to that of ratio). Catalytic combustion of CHa at low concen-the same partial pressure of Co+H2 from the stan- tration has been investigated over Al2O3-supporteddard syngas!l5)perovskite catalysts. Test of catalysts for combustioatalytic combustion for F-T offgasof low CH4 content gas under oxygen-rich conditionCatalytic combustion of methane and light hydro- at low temperature has been carried out. The resultsarbors at a relatively lower temperature preventsare shown in Table 4Table 3 Test results of Fischer-Tropsch synthesis over Ce-Co/SiOz catalyst at different temperature fromsyngas(40% H2: 20%CO: 40%N2, volume ratioco conversionCK yield91.138L.742128680.4Reaction conditions: 2.0 MPa, GHSh, reactor inner diameter of 8 mm, l g catalyst, 0.45--0.90 mmTable 4 Evaluation of various catalysts for combustion of methane at low concentration[GHSV=10000h-, CH4: O2: N2=1: 5: 20(molar ratio), atmosphere, I g catalyst, 1 mm diameterNo. 1 5%(by mass)Lao. 7 Ca0.3Feo.3Mno 703/a-Al2O3No,27.5%(b)Lao. 7 Cao fEo mNo 703/a-Al2O3No. 3 45%(by mass)Lao.7Cao, fEo. Mno. 7O3/a-Al2O309No 4 5.2%(by mass)Lao .Cao.3Feo.3Mno 7O3/7-Al2O3中国煤化工100otes: aqueous solution for catalyst No. 1 and Ntrate mCNMHGAn Integrated Process of a Two-Stage Fixed Bed Syngas Production and F-T SynthesisTable 4 shows that the catalysts have quite high REFERENCESctivities at low temperature than those prepared by 1 Michael, J.C., Purvin, E.G., " GTLthe aqueous solution method. The selectivity to CO,ering costa", Oil Gas J, 98(38)very high (close to 100%)in the range of 873- 2 Benjamin, E, Rocco, AF, Thomas,GK, et al., "The ev1023K,especially at 1073 K. High conversion is exhib-lution of advanced gas-to-liquid technology, Chemtech(10),32-37(1999ited above 973 K, and in this range of temperature, the 3 Alan, H.S., "Advances make gas-to-liquids process competconversion of methane approaches 100%. 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