Kinetics of methanol steam reforming over COPZr-2 catalyst

Available online at www.sciencedirect.comDOURMLOFScienceDirect(9NATURAL GASCHEMISTRYEL SEVIERJournal of Natural Gas Chemistry 17(2008)171-174www.elsevier.com/locate/jngcKinetics of methanol steam reforming over COPZr-2 catalystYongfeng Lil*，Weiming Lin2，Lin Yu'，Zhifeng Hao', Rongjian Mail1. Faculty of Chemical Engineering and Light Industry, Guangdong University of Technology, Guangzhou 510006, Guangdong, China;2. School of Chemical and Energy Engineering, South China Universiry of Technology, Guangzhou 510640, Guangdong, China[Manscript rceived October 17. 2007:; revised December 3.2007 ]Abstract: The COPZr-2 catalyst, which was prepared in our prophase research, showed good catalytic performance inmethanol steam reforming reaction. In this article, the best one was chosen as an example to study the reaction kinetics ofmethanol steam reforming over this type of catalyst. First, the effects of methanol conversion to outlet CO2 and methanolconversion to outlet CO on methanol pseudo contact time W/F McOH were investigated. Then by applying the reaction route thatmethanol direct reforming (DR) and methanol decomposition (DE) were carried out in parallel, the reaction kinetic model withpower function type was established. And the parameters for the model were estimated using a non-linear regression programwhich computed weighted least squares of the defined objects function. Finally, the kinetic model passed the crrelation testand the F-test.Key words: methanol; reforming; kinetics; COPZr-21. Introduction2. ExperimentalTo reduce pollution from internal combustion engine2.1. Catalytic reaction(ICE) vehicles, polymer electrolyte membrane fuel cell(PEMFC) vehicle is regarded as the best substitute. NowThe reaction kinetic experiments were conducted using afor PEMFC vehicle, hydrogen is usually supplied from afixed-bed flow reactor at 483- -543 K under atmospheric pres-H2 generator onboard. There are several routes for thesure. The catalyst diluted with quartz sand was packed in aproduction of hydrogen from various fuels. A promis-stainless steel tubular reactor with an inner diameter 7 mm.ing route is the steam reforming of methanol (SRM). NowAfter reduction in 10 vol% H2 flowing for5 h at 573 K, it wasthe kinetics of SRM reaction over Cu/ZnO/AI2O3 cata-premixed with water and methanol at a certain H2OMeOHlyst has been studied widely [1-6]. And the kinet-molar ratio and fed into the pre-heater using a micro-feeder.ics of SRM reaction over other Cu-containing catalysts,The reaction products first passed through a cold trap, thensuch as Cu/Mn/Al2O3, Cu/ZnO/CeO2/AI2O3, Cu/ZrO2/CeO2,the gaseous products such as H2, Co, CO2, and CH4 wereCuSiO2, and Cu/Cr2O3/Fe2O3, has also been studied [7-12].detected on-line by the HP4890 gas chromatograph equippedAfter the preparation of other special catalysts, such aswith thermal conductivity detectors and TDX-01 column; thePdZnO and ZrO2/ZnO, the kinetics of SRM reaction overliquid products such as water and methanol were detectedthem was also studied [13-15]. The COPZr-2 catalyst, by ShangFen 102G gas chromatograph equipped with ther-one type of CuZnAlO catalysts with ZrO2 promoter, whichmal conductivity detectors and 401 organic supporter column.showed good catalytic performance in SRM, was prepared inUnless otherwise mentioned, the experimental data were col-our prophase research. The 150h stability test of COPZ-2lected between 5 h and 6 h in the on-stream operation.catalyst showed that the catalyst had good stability: Methanolconversion and H2 yield were kept at 88% and 83%, re-2.2. Prophase experimentspectively; and outlet H2 and CO content were > >63% and0.20% -0.31%, respectively [16,17]. Therefore, it is ncessaryThe blank experiment showed that quartz material had noto pay more atention to study the kinetics of SRM reactionffect on SRM reactinn And several nther experiments with-over COPZx-2 catalyst, to give primary data for the further out th中国煤化_ I ffusion were also donedesign of onboard methanol reformer.in advYHCNMH(3ures 1 and 2. The ex-Corresponding autbor. Tel: 020-31281539, 39322201; E-mai: gdliyf@ 163.comThis work was supported by the Natural Science Foundation of Guangdong Province (05300127, 06021469) and Science and Technology Program ofGuangdong Province (2005B10201053)172Yongfeng Li et al/Jourmal of Natual Gas Chenistry Vol. 17 No.22008perimental results showed that internal diffusion could be ne-Water-gas shift reaction (WGS)glected when particle size was either smaller than or equalCO+ H20- +C02+H2(3)to 0.72 mm, and extermal diffusion could be neglected whenpseudo contact time of input W/F was either less than or equalAs there are only two independent reactions in SRMto 6.74 g-h/mol.system, at least two reaction steps should be included tocompletely describe the kinetic behavior of this system. Atpresent, dual rate model are studied mostly. And this modelconsiders that there are usually three different reaction routes)0 tin SRM system: (a) Methanol direct reforming and methanol区decomposition carried out in parallel to generate CO2, CO,38and H2, as shown in Equations (1) and (2); (b) First, methanoldecomposes to generate CO and H2, and then Co continuesreacting to generate CO2 and H2 by water-gas shift reaction,86as shown in Equations (2) and (3); (C) First, methanol directlyreforms with vapor to generate CO2 and H2, and then CO284 tcontinues reacting to generate co and H2O by inverse water-gas shift reaction, as shown in Equations (1) and (3). .The results obtained by applying the three reaction routes0.2 0.40.6 0.8 1.0 1.2 1.4 1.6respectively to verify the experimental data showed thatGrain diameter (mm)the reaction route that methanol direct reforming (DR) andFigure 1. Infuence of inner dffusion on SRM. Reaction conditions: 250 °C,methanol decomposition (DE) carried out in parallel is most0.1 MPa, molar ratio of H2O/MeOH 1.3, WHSV 3.56 hr-', no carier gassuitable. This conclusion was in agreement with the report ofWang et al. [19]. According to Equations (1) and (2) and theliteratures [5-7], the rate of methanol direct reforming (rDR)00 rwas related to the partial pressure of CH3OH, H2O, CO2, andH2. And the rate of methanol decomposition (rDE) was related)0 Eto the partial pressure of CH3OH, CO and H2. So the reactionkinetic model with power function type was established as fol-80上lows:70 560'DR = kone-B(/RT! PieoH:Piho(-Kp,DR. PMeOH PHOPCO2 唱(40E●0.2 g calyst。0.1 g calystrDE = kone~-B2/R' PMcOHPCO .际(5]Kp,DE . PMeOH,30123.2. Parameter estimationWIF (gh/mol)Figure 2. Influence of outer diffusion on SRM. Reaction conditions:With Equation (6) as object function, the parameters for250 °C, 0.1 MPa, molar ratio of H2OMeOH 1.3, no carrier gasthe model could be determined using a non-linear regres-sion program, which computes weighted least squares of the3. Data processingdefined objects function.3.1. Kinetic modelS= Z(rR- FDR)?+ Z(me-FDE)P (6There are generally three reaction steps in SRM systemsas fllows [18]:4. Results and discussionMethanol direct reforming (DR)CH3OH + H2O-→CO2 + 3H2(1)4.1.L中国煤化工Methanol decomposition (DE)"THC N M H Gal flow reactor, the rateof methanol direct reforming (rDR) and the rate of methanolCH3OH-→CO+ 2H2(2)decomposition (rDE) could be expressed as follows:Jounal of Natural Gas Chemistry VoL. 17No. 22008173YDR=:dXco2(7)d(W/FMeon)dXco: 543K(8)●523Kd(W/FMcOH)●503KSo using the kinetic data obtained from SRM reactionover COPZr-2 catalyst, the effects of methanol conversion tooutlet CO2 and methanol conversion to outlet Co on methanolpseudo contact time W/FMeOH could be determined, which are2displayed in Figures 3 and 4.10E70WFuow(urh/mo)Figure 4. Effeet of methanol conversion to outlet CO (Xco) on methanolpseudo contact time (W/FMeOH) in SRM40By linking Equations (4), (5), (7) and (8), using a non-■523Klinear regression program which computed weighted least30503 Ksquares of the defined objects function to process data dis-played in Figures 3 and 4, the parameters in Equations (4) and(5) could be determined. Therefore, the rate of methanol di-W/Fseow (..*h/mol)rect reforming (rDR) and the rate of methanol decompositionFigure 3. Effect of methanol conversion to outlet CO2 (Xoo2) on methanol(TDE) could be expressed as follows:pseudo contact time (W/FMecoH) in SRMPCO2喝rDR = 6.147 x 10'5e-151462/RTPAR28H P啦_682(9)Kp,DR . PMcOH PH2OPCO.啼。E =2.883 x 181919/9TpR2(10)Kp,DE "PMcOH )where, the units of rate r, reaction temperature T and out-F0.9 and *The values in the parentheses denote the degrce of feedom174Yongfeng Li et al/ Jounal of Naural Gas Chemistry Vol. 17 No.220085. Conclusionstype was established. And the parameters for the model wereestimated using a non-linear regression program which com-puted weighted least squares of the defined objects function.(1) By applying the reaction route that methanol direct re-Therefore, the rate of methanol direct reforming (rpR) and theforming (DR) and methanol decomposition (DE) were carriedrate of methanol decomposition (rDE) could be expressed asout in parallel, the reaction kinetic model with power functionfollows:rDR =6.147 x 101-156162/2P2A81 :phz52po:嘱Kp,DR' PMeOH PH2O,PCo喘rDE = 2.883 x 1018-195720/RT pAM204PMcOHKp,DE . PMecOHAnd the kinetic model passed the crrelation test and theReferencesF-test.(2) From the kinetic model, it can be found that the ac-[1] Patel S, Pant K K Chemical Engineering Science, 2007, 62(19):5425tivation energy of DR (151 kJ/mol) is less than that of DE[2] Choi Y T, Stenger H G. Jourmal of Power Sources, 2005,(196 kJ/mol). 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