Kinetics of Methanol Carbonylation to Methyl Formate Catalyzed by Sodium Methoxide

雪Joumel o NaurlGa ChenlaryJournal of Natural Gas Cemistry 13(2004)225- 230SCIENCE PRESSKinetics of Methanol Carbonylation to Methyl FormateCatalyzed by Sodium MethoxideLiang Chenl*，Jianghong Zhang2，Ping Ning'，Yunbua Chen' ,Wenbing Wul1. Research Center of C1 Chemical Technology, Kunming University of Science and Technology, Kunming 650093, China2. College of Science, Kunming Universtty of Science and Technology, Kunming, 650093, China[Manuscript received August 23, 2004; revised November 15, 2004]Abstract: Kinetics of synthesis of methyl formate from carbon monoxide and methanol, using sodiummethoxide as the catalyst and pyridine as the promoter in a batch reactor, was studied. Kinetic parameterssuch as the apparent reaction orders, the rate constant and the apparent activation energies were obtained.The experimental results showed that both the reaction orders with respect to CO and methanol equal to1, the general reaction kinetic equation is (-r)=- dp(CO)/dt: =k . p(CO)(MeOH], and the rate constant isk= -8.82x10*exp [61.19x10*/(R . T)] in the presence of pyridine. The apparent activation energies haddecreased 6.44 kJ/mol and the rate constant had increased more than 1.5 times when pyridine was usedas the promoter in the catalyst system.Key words: carbon monoxide, pyridine, methanol, methyl formate, carbonylation, kinetics1. Introductioncial production of methyl formate via carbonyla-tion of methanol and catalyzed by sodium methoxide(CH3ONa) is effective in quite large scales [20].Methyl formate (HCOOCH3) is an important andHowever, carbon monoxide (CO) obtained fromversatile chemical intermediate, which has been con-the tail gases of yellow phosphorous production con-sidered as one of the building block molecules in C1tains some impurities such as carbon dioxide, water orchemistry [1]. It demonstrates high reactivities forphosphorous compounds like PH3, which are particu-preparing formic acid [2- 5], for isomerization of aceticlarly detrimental to the usual methyl formate synthe-acid [6], for producing acetic anhydride [7], for hy-sis catalyst (CH3ONa) and must be totally removeddroesterification of alkenes [8] and for a variety obefore the reaction. Therefore, development of newC1 chemicals [9] due to its aldehyde group, carboxylcatalytic systems for carbonylation of methanol intogroup and active hydrogen. There are plenty ofmethyl formate which are less sensitive to CO im-publications on methanol carbonylation for prepar-purities has important commercial importance. Ining methyl formate by different kinds of catalysts,this connection, the reaction system of liquid phasesuch as copper- containing catalysts [10 15], Cu/SiO2methanol carbonylation to methyl formate in the pres-catalysts [16]， platinum group metal catalysts [17],ence of a CH3ONa catalyst and with pyridine as a pro-ruthenium complex catalysts [18], anionic group VIImoter [23] is of great significance in the study of themetal catalysts [19], epoxide -amine [20,21] catalysts,kinetics of methyl carbonylation to methyl formate.polymeric strongly basic resins catalysts [22], alkaliIn thi中国煤化Iihyl formate synthesismetal methoxide [23- 26], and so on. The commer-via:by using CH3ONa asCorresponding author. Email: kmcexlc@yahoo.com.cn, Tel:+86 871TCHCNM H G,This project was supported by Yunnan Science and Technology Cooperate Plan Foundation (99YT002) and Yunnan NatureScience Foundation (2003E0027M)226Liang Chen et al./ Journal of Natural Gas Chemistry Vol. 13 No. 4 2004the catalyst and pyridine as the promoter was inves-Method 1: A known amount of methanol, catalysttigated.and the promoter agent(if need) were introduced intoan autoclave, and then purged with CO gas at normal2. Experimentalpressure. After heating the mixture to the requiredtemperature, the autoclave was pressurized to the re-The carbonylation reaction of CO and methanolquired pressure with CO as quickly as possible, thenairproofed the autoclave and started stirring.to methyl formate has been carried out previously byreaction was carried out at a constant temperatureusing CH3ONa as the catalyst at a suitable temper-of the autoclave, and the system pressure decreasedature and pressure, and the reaction selectivity hasgradually as the reaction proceeded. The pressure ofbeen found to be almost 100% [27]. These previousthe reaction system was recorded every 1 minute.research results [9,23] showed that no any other sub-Method 2: A known amount of methanol, cat-stances were found in the reaction product except theraw materials and the methyl formate product whenalyst and promoter agent were introduced into anMeONa was used as the catalyst and pyridine as theautoclave, then stirring was started and the mixturepromoter at temperatures of 80 -100 °C and pressuresheated. As soon as the liquid phase reached the re-of 2.04.5 MPa. So it is evident that the reaction canquired temperature, stirring was stopped, and CO gasbe expressed as:was introduced into the autoclave until the requiredpressure was attained, then stirring was resumed. TheCH,0H()+ CO(g)MoNitrndine - HCOOCH, (1)reaction was carried out at constant temperature andpressure. When the reaction proceeded to a certainlength of time, the autoclave was cooled, and both the2.1. Materialsliquid and gas products were analyzed by an HP1790gas chromatograph.The purities of the reactants were: carbonmonoxide>99.9%; methanol, AR, H2OS0.1%; Pyri-3. Results and discussiondine, AR. The sodium methoxide was prepared in ourlaboratory [9].3.1. Reaction rate of methanol carbonylation2.2. MethodsBy using CH3ONa as the catalyst and with no anypromoters, the correlations of CO pressure and reac-The procedure of methanol carbonylation ttion time with different temperatures were shown inmethyl formate is shown schematically in Figure 1.Figure 2.∞∞}4.093.0s 2.5申2.0|21.5年(4) (3)1.0Figure 1. Schematic diagram of the apparatus unitfor the synthesis of methyl formate中国煤化工060 70 801--N2 cylinder, 2- Co cylinder， 3- mass flow meter, 4-pressure gauge,5- liquid inlet, 6 stirrer, 7- gas outlet,Figur"THCN M H Gesure on recto8- indicating thermocouple, 9- autoclave controller， 10-autoclave, 11- -liquid outlet(1) 60"C, (2) 70C, (3) 80 C, (4) 90°CJournal of Natural Gas Chemistry Vol. 13 No.4 2004227It was proved that a higher temperature led toThis indicated that the reaction was first ordera faster reaction rate and a shorter equilibrium reac-with respect to the partial pressure of Co from 60 totion time, but to a lower CO conversion owing to the90 °C, i.e., β=1. Therefore, the kinetic equation ofexothermic effect of the reaction. However, becausemethanol carbonylation to methyl formate could beof the equilibrium restrain in a batch reaction, the re-represented as follows:action rate decreased very quickly, and the correlation-dp(CO)curves exhibited the lowest points of no linearity. Theat= ko . p(CO)(3)fact was that the conversion of CO was approximately40% at any temperature when the system pressureFrom the linear slope in Figure 3, the rate con-reached the lowest value, i.e., methanol carbonyla-stants (ko) at different temperatures could be ob-tion to methyl formate is close to equilibrium at atained, as listed in Table 1.40% conversion of CO in a batch reactor. This resultTable 1. Rate constants at different temperatureswas consistent with that reported by Smathers [27].without any promotersTemperature (C)ko3.2. Effect of CO partial pressure0.0129700.0291Based on the reaction of Equation (1), the reac-300.0553tion rate was expressed as:)00.0978(-r)=-dp(CO) =k. [MeOHI'e :p(Co)P (2)dt3.3. Effect of temperature on rate constantwhere p(CO) is the CO partial pressure (MPa), k is arate constant (L/ (mol:min)), [MeOH] is the concen-The kinetic curve of the natural logarithm of thetration of liquid methanol (mol/L), and a and β arerate constant (ko) and the reciprocal of reaction tem-the reaction orders.perature based on the data of Table 1 was shown inWhen this reaction was run according to MethodFigure 4.1, but without any promoters, it can be considered-2.0that the concentration of methanol was constant be-cause of the large excess of methanol in the liquidphase. So it could be considered that only the partialpressure of CO was varying with the reaction time.As shown in Figure 3, the natural logarithm o量。the CO partial pressure (lnp(CO)) versus the reaction-3.5time (t) showed good linearity at different tempera-tures when there was no promoter present.4.0-4.51.20.00270.00280.00290.0030Figure 4. Relation between natural logarithm of therate constant (k) and the reciprocal of0.8reaction temperatureg0.6EIt can be seen that the plot exhibited a good lin-(4)+(3)\(2()0.4earity, i.e.,0.2日-8135lnko=一个+ 20.124(4)2468中国煤化工BasedArrhenius equationt1 min(k =:MYHCN M H Gon energy (AEo) ofFigure 3. Relation between natural logarithm ofCO partial pressure and reaction timemethanol carbonylation to methyl formate by using(1) 60"C,(2) 70*C, (3) 80"C,(4)90°Csodium methoxide as the liquid phase catalyst and228Liang Chen et al./ Journal of Natural Gas Chemistry Vol. 13 No. 4 2004without any promoters was 67.63 kJ/mol, and thelinear slope of Figure 7 and the Arrhenius equation,preexponential factor (Ao) was 9.96x106. These in-the rate equations could be obtained for the reactiondicated that the reaction was operating in the kineticwhen there was pyridine present as a promoter, asregion.expressed by Equations (6) and (7). The activationenergy (OE1) was 61.19 kJ/mol, and the preexponen-ko= 9.96 x 10exp--67.63 x 103(5)tial factor (A1) was 8.82x108.R.Tlnk1 =- 7359.8+ 18.373(6)T3.4. Effect of methanol concentration on thereactionki = 8.82 x 10exp--61.19x 103When running the reaction according to Method2 for the preparation methyl formate, and by keepingthe CO pressure and the CH3ONa catalyst concentra-tion constant, the effect of the methanol concentra-1tion on the reaction was shown in Figure 5. It can be1.0 Fseen that the plot lnc(MeOH) of versus reaction time(t) was linear. This indicated that the reaction ratewith respect to methanol is first order, i.e., a=1.80.三0.6-3.13) (20.43.0 F0.92025302.8 Ft/minFigure 6. Relation between natural logarithm of2.7 FcO partial pressure and reaction timewith the presence of a promoter(1) 70*C,(2) 80*C, (3) 90°C508100t/ min-1.5Figure 5. Relation between natural logarithm oMeOH concentration and reaction time-2.03.5. Effect of catalytic promoter on the reac-tion查25At a partial pressure of 3.8 MPa CO, and withCH3ONa of 0.4 mol/L and pyridine of 2 mol/L in the-3.0reaction liquid phase, the reaction was run accordingto Method 2 for the preparation of methyl formate,and the result of the effect of the promoter on the re--3.50.002750.002800.002850.00290action was shown in Figure 6. The plot of the naturallogarithm of CO partial pressure (lnp(CO)) versus re-Figure 7. Relation between natural logarithm ofaction time (t) also showed good linearity at differentrate constant (k1) and reciprocal of reac-temperatures in the presence of pyridine as the pro~中国煤化工th the presence of amoter.CHby cumparng uese resulus with those of no pro-CNMHGThe rate constant (k1) could be obtained fromthe linear slope of Figure 6. Moreover, the relation ofmoters present (Equation 5), it can be found thatlnk1 U8 1/T was presented in Figure 7. Then, from the the activation energy of methanol carbonylation toJournal of Natural Gas Chemistry Vol. 13 No. 4 2004229methyl formate in the presence of 2 mol/L pyridinecarbonylation to methyI formate when added to thein the liquid phase had decreased by 6.44 kJ/mol.CH3ONa catalyst system. At a pyridine concentra-Comparison of the results indicating the effect oftion of 2 mol/L in the liquid phase and at tempera-:he pyridine promoter on the reaction rate and the ac-tures of 60-80 °C; the reaction rate constant increasedtivation energy was listed in Table 2. It was evident1.52-1.58 times, showing that pyridine had a goodthat pyridine accelerated the reaction of methanolpromoter function on the carbonylation reaction.Table 2. Comparison of kinetic parameters with and without a promoterko (Without pyridine)k1 (Pyridine of 2 mol/L)k1/ko70 (°C)0.02910.04561.58Rate constant (L/(mol.min))0.05530.08461.5390 (°C)0.09780.14871.52Activation energy (O E)(kJ/mol)67.63 .61.19△Eo-OE1 -6.44A9.66x1068.82x1064. Conclusions4] Hohenschutz H, Kiefer H, Schmidt J E. USP 5 206433.1993(1) Kinetic study on methanol carbonylation to[5] Li Zh F, Chen L, Zhang J H et al. Tianranqi Huagongmethyl formate in the presence of sodium methoxide(Natural Gas Chemical Industry), 2002, 27(3): 1catalyst and the pyridine promoter showed that the6] Kawataka F, Shima Y, Nakamura K. USP 5 969 183,1999reaction orders of CO and methanol was found to beapproximately 1 at the temperature range of 60 to 90[7] Seuillet B, Castanet Y, Mortreux A et al. AppliedCatalysis A: General, 1993, 93(2): 219°C . The reaction equation can be described as (-r)=-dp(CO)/dt=k:[MeOH]p(CO).[8] Yang X G, Zhang J Q, Liu Zh T. Applied CatalysisA: General, 1998, 173(1): 11(2) The rate constants without or with pyri-[9] Zhang J H. [Master Thesis]. Kunming: Kunming Uni-dine in the sodium methoxide catalyst system canversity of Science & Technology, 2001be described as ko=9.96x 10*exp[- -67.63x 103/(R .T)]10] Joerg K, Mueller F J, Irgang M et al. USP 5 194 675,and k1 =8.82x 10'exp[- 61.19x103/(R . T)]. Adding19932 mol/L pyridine in the reaction liquid phase could[11] Chen Sh Ch, Cheng W J, LinF Shet al. USP 5144cause the reaction rate constant to increase 1.52-062, 19921.58 times at temperatures of 60 -80 °C, and reducing[12] Yoneoka M, Ikarashi T, Watabe K et al. USP 5 399the reaction temperature can give a better promoter745, 1995effect on methanol carbonylation to methyl formate.[13] Shreiber E H, Roberts G W. Applied Catalysis B: En-(3) The activation energy was found to be 67.63vironmental, 2000, 26(2): 119kJ/ mol without the promoter, but it was reduced to[14] Guerrero Ruiz A, Rodriguez -Rarmos 1, Fierro J L G.61.19 kJ/mol in the presence of pyridine as the pro-Applied Catalysis, 1991, 72(1): 119moter. It was found that the reaction proceeded in[15] Minyukova T P, Simentsova I I, Khasin A V et al.the kinetic region. Compared with no any promoters,Applied Catalysis A: General, 2002, 237(1): 171the activation energy decreased by 6.44 kJ/mol in the[16] Guerreiro E D, Gorriz 0 F, Larsen G et al. Appliedpresence of 2 mol/L pyridine and at temperatures ofCatalysis A: General, 2000, 204(1): 3360- 90 °C.[17] Aplin R P, Maitlis P M, Smith T A. USP 4 778 923,1988References[18] Choi S J, Lee J s, Kim Y G. Journal of MolecularCatalvsis. 1993. 85(2): L109[1] LeeJS, KimJ C, Kim Y G et al. Applied Catalysis,[19]中国煤化工xdi Bhupendra C. USP1990, 57(1): 1CNMHG2] Leonard J D. USP 4 299 981. 1981[20] Gerara D,uotz n, rellegrum D et al. Applied Catal-(3] Lynn J B, Homberg 0 A, Singleton A H. USP 3 907ysis A: General, 1998, 170(2): 297884. 1975[21] Green M J. EP 0 104 875, 1988230Liang Chen et al./ Journal of Natural Gas Chemistry Vol. 13 No.42004[22] Di Girolamo M D, Lami M, Marchiona M et al.1999Catalysis Letters, 1996, 38: 127[25] Couteau W, Ramioulle J. USP 4 216 339, 198023] Chen L. Tianranqi Huagong (Natural Gas Chemical [26] Bai L, Zhao Y L, Hu Y Q et al. J Nat Gas Chem,Industry), 2002, 27(1): 141996, 5(3): 229[24] Ferdinand L, Arthur H, Jurgen D. USP 5 917 085，[27] Lee D s. USP 4 100 360, 1978中国煤化工MYHCNMHG