氢气存在下一氧化碳偶联反应的化学和性能英文

第30卷2002年　第6期12　月燃　料　化　学　学　报JOURNAL OF FUE L CHEMISTRY AND TECHNOLOGYVol 130　No 16Dec 1 2002Article ID :025322409(2002)0620573204　Receive d date :2002208206;Revise d date :2002210222　Foundation ite m :China National Ninth 2five Plan (962539201)1　Corresp ondi ng a ut hor :XU Gen 2hui ,Tel :022*********(O ),E 2mail :shenxu @public 1tpt 1tj 1cn Aut hor i nt roduction :MENG Fan 2dong (19642),male ,Ph 1D 1,Senior Engineer ,chemical technology speciality ,engaged in petrochemical research 1E 2mail :mengfandong @eyou 1comCA RBON MONO XID E COU PL IN GR EA C TION IN TH E P R ES EN C E O F H YD RO G ENMENG Fan 2dong1,2,XU Gen 2hui 1,DU Pa 1,GUO Rong 2qun2(11State K ey Laboratory of C 1Chemical Technology ,T ianjin University ,T ianjin 300072,China ;21Luoyang Petrochemical Engineering Corporation ,Luoyang 471003,China )A bst ract :The use of carbon monoxide from coal or natural gas to produce dialkyl oxalate is an important research area in C 1chemical technology 1The chemical reactions and performance in the coupling reaction system for synthesis of diethyl oxalate from carbon monoxide and ethyl nitrite were tested in the presence of hydrogen under the typical coupling reaction conditions 1The results indicated that hydrogen only reacts with ethyl nitrite to form ethanol 1The introduction of hydrogen to the reaction system lowered the conversion of carbon monoxide and the selectivity of diethyl oxalate because hydrogen competed with carbonmonoxide to adsorb on the surface of the catalyst and interrupted the normal redox process of Pd 0→Pd 2+→Pd 0necessary for the formation of diethyl oxalate 1Also ,the chemisorption measurements revealed that hydrogen and carbon monoxide adsorbed on the same active sites of the catalyst 1Key wor ds :CO coupling ;diethyl oxalate ;hydrogen effect ;reaction performance CL C n um be r :O 643132 Docume nt code :A A novel synthesis route for diethyl oxalate (DEO )from carbon monoxide and ethyl nitrite (EN )over sup 2ported palladium catalyst in a gaseous phase at atmo 2spheric pressure has been studied by several groups [1～7]1The main reactions can be described by the following two equations :Coupling reaction2CO +2EtONO →(COOEt )2+2NO(1)Regeneration reaction2NO +2EtOH +1/2O 2→2EtONO +H 2O (2)The overall equation is2CO +2EtOH +1/2O 2→(COOEt )2+H 2O(3)It is obvious that the fresh feeds in diethyl oxalate production are carbon monoxide ,oxygen and ethanol 1Generally ,in industrial practice carbon monoxide is mainly obtained from coal gas or syngas ,and in such process hydrogen is an inherent concomitant 1Now a scale 2up test in diethyl oxalate production has been com 2pleted [8]and the technology for the commercialization has been established 1So it is necessary to investigate the process behavior in the presence of hydrogen 1In the present contribution ,the chemical reactions in this process are verified experimentally and carbon monoxide conversion and diethyl oxalate selectivity are tested under typical coupling reaction conditions in the presence of hydrogen 1The observations are interpreted on the basis of hydrogen ,carbon monoxide and ethyl ni 2trite chemisorption measurements over the catalyst andthe thermodynamic principles 11　Exp e ri me nt alThe generation of ethyl nitrite was taken place in a special vessel into which an amount of 50mL ethanol was added and reacted with nitrogen monoxide and oxy 2gen at ca 1308K 1The coupling reaction experiments were performed in a flow 2type apparatus with a glass 2made fixed 2bed reactor at atmospheric pressure 1The flow scheme is depicted in Figure 11The reactor tube ,with a 2cm internal diameter and a 60cm length ,was electrically heated with a temperature control accuracy of ±015K 1The reaction zone was filled with 2mL catalyst pellets and up and down was some quartz of the same particle size 1The gas mixtures before and after each reac 2tion were analyzed by gas chromatography equipped with a capillary column and a thermal conductivity detector 1Pd 2Fe /α2Al 2O 3with 1w /%of palladium and015w /%of iron was used as catalyst 1The catalyst was prepared by impregnation of α2Al 2O 3with 20w /%aqueous solution of PdCl 2and 5w /%FeCl 3・H 2O 1Then it was dried in air at ca 1393K for 12h 1After that ,the catalyst was pretreated in 2situ with a purge of pure hydrogen for 4h at 623K 1The measurements of hydrogen ,carbon monoxide and ethyl nitrite chemisorption on the catalyst at different temperature were performed using Micrometrics 2910in 2strument 1The catalyst sample (ca 10132018)was placed in a flow 2through cell for pretreatment (Ar ,at 623K ,2h )and then outgassing in vacuum ,and subsequentlyhydrogen ,carbon monoxide and ethyl nitrite chemisorp 2tions were measured 1An accurate volume of 5vol 1%H 2/Ar or 5vol 1%CO/Ar or 5vol 1%EN/Ar gas mix 2tures was injected to the catalyst sample repeatedly until the desorption peak remained unchanged ,which means that the chemisorption has been saturated1Figure 1　Scheme of CO coupling reaction in the presence of H 2CT —cold trap ;MF —mass flowmeter ;TC —temperature control system ;TE —thermocouple ;WFM —wet flowmeterIn the coupling reaction system ,there are two reac 2tants (CO ,EtONO )and two products [(CO 2Et )2,NO ]1The reactions between hydrogen and every component mentioned above were tested 1Following this ,the effect of hydrogen on coupling reaction of carbon monoxide to diethyl oxalate was also examined 1The reaction condi 2tions adopted were typical coupling reaction conditionsadressed in previous work [8],i 1e 1Reaction temperature :393K Residence time :118sPressure :atmosphere pressure2　Res ults a n d disc ussion211　Che mical re actions i n t he p res e nce of hy 2droge n As mentioned above ,there are four compo 2nents [i 1e 1CO ,EtONO ,(CO 2Et )2,NO ]in the cou 2pling reaction system ,thus the reactions which may take place are :2H 2+2CO →CH 4+CO 2(4)H 2+2EtONO →2EtOH +2NO(5)4H 2+(CO 2Et )2→(CH 2OH )2+2EtOH(6)5H 2+2NO →2NH 3+2H 2O(7)Table 1is the Gibbs free energy (△G 0)oftheabove reactions 1It can be seen that all the reactions ,thermodynamically ,are possible to take place 1Reaction (4)is a well 2known reaction for the methanation of car 2bon monoxide and reaction (6)is used to produce ethy 2lene glycol 1Ta ble 1　△G 0of t he reactions (4)-(7)at 393KReaction △G 0/k J ・mol -1(4)2130133(5)2163128(6)　27158(7)249817021111　Reaction of hydrogen with ethyl nitrite Hydro 2gen ,ethyl nitrite and nitrogen were fed into the reactor with a flow rate of 714mL/min ,16167mL/min and 43mL/min ,respectively 1During 10h run time under steady 2state conditions ,the conversions of hydrogen and ethyl nitrite were 7618%and 7314%,respectively ,which correspond to an absolute consumed amount of 0115mol hydrogen and 0133mol ethyl nitrite 1The liquid product collected in cold trap is pure ethanol ,weighted 1418g ,i 1e 10132mol 1So ,the ratio of stoichiometric coefficients of hydrogen ,ethyl nitrite and ethanol is e 2qual to 0115∶0133∶0132≈1∶2∶2and the reaction can be described by the equation (5)121112　Reaction of hydrogen with carbon monoxide ,diethyl oxalate and nitrogen monoxide In the same way ,hydrogen ,carbon monoxide and nitrogen were in 2troduced into the reactor with a flow rate of 714mL/min ,1313mL/min and 4513mL/min ,respectively 1During 4h run time under steady 2state conditions ,the concen 2tration of hydrogen and carbon monoxide at the inlet and the outlet of the reactor remained unchanged ,indicating that there was no occurrence of chemical reactions 1Sim 2ilarly ,carbon monoxide was replaced by diethyl oxalate or nitrogen monoxide 1Also ,it was found that there was no conversion of diethyl oxalate or nitrogen monoxide 1By this token ,it is unable for the reaction (4),(6)and (7)to take place under the typical coupling reaction conditions 1It well known that reaction (6)is used in the production of ethylene glycol by hydrogenation of diethyl oxalate 1But it occurs only when Cu/SiO 2catalyst is used under higher temperature and pressure 1The typical coupling reaction conditions are also unsuited for the oc 2currence of methanation of carbon monoxide 121113　Thermodynamic analysis It is known that an RO -NO bond of alkyl nitrite is easily cleaved homoliti 2cally 1The bond dissociation energy of ethyl nitrite into ethoxy radical (EtO 2)and NO is estimated to be about 176k J ・mol -1,which is considerably low when com 2pared with the dissociation energy of C =O or N =O bond (at least twice that value )1The decomposition of ethyl nitrite is accelerated in the presence H 2,and af 2fords a fair amount of ethanol 1On the contrary ,the re 2action (4),(6)and (7),due to high dissociation ener 2gy of C =O or N =O bond ,is rather difficult to occur475　燃　料　化　学　学　报30卷under the typical coupling reaction conditions 1212　Eff ect of hydroge n on coup li ng re action p e rf or ma nce In CO catalytic coupling reaction sys 2tem ,the main product is diethyl oxalate with a small amount of by 2products of ethyl formate and diethyl car 2bonate 1The following will investigated the reaction be 2haviors after the introduction of hydrogen to the system 121211　E ffect of hydrogen on conversion and selectivity The above work revealed that in the presence of hy 2drogen the only byproduct ,ethanol ,produced in the coupling reaction system was from the reaction (5)1The conversion of carbon monoxide and ethyl nitrite before and after introducing hydrogen to the coupling reaction system is shown in Figure 21It can be seen that the CO conversion went down and EN conversion went up with the increase of H 21The reason is that H 2competes with CO to react with EN to form ethanol 1It was also discov 2ered that the mole amount of ethyl nitrite consumed is the sum of the mole amount of hydrogen and carbon monoxide consumed ,which further confirmed that only the reaction (5)occurred1Figure 2　Conversion of CO or EN as a function of H 2concentrationFigure 3　DEO selectivity as a function of H 2concentration Figure 3showed that H 2concentration has a pro 2nounced influence on DEO selectivity 1It is known thatDEO selectivity is rather high in CO coupling reaction ,with quite a small amount of diethyl carbonate and ethylformate as byproducts [8]1In the presence of hydrogen ,the reaction (5)occurred and produced another byprod 2uct ,ethanol ,in the coupling reaction 1The more the H 2concentration was ,the more the DEO electivity de 2creased because more ethanol was formed 1The results from our pilot plant test indicate that when the H 2con 2centration is more than 1000μg ・g -1,DEO selectivity will decrease appreciably 1So ,in industrial practice ,hy 2drogen should be removed from the feedstock by means of such technologies as adsorption or catalysis 1Our previous research on kinetics and mechanism of the coupling reaction revealed that the rate 2determining step of the coupling reaction is the adsorption of carbonmonoxide on the surface of the catalyst [9]1Moreover ,it was considered that the alkoxycarboxide intermediate (COOEt )possibly exists ,and further associates to di 2ethyl oxalate 1Also ,it was concluded that the catalytic coupling reaction of carbon monoxide occurs via a redox mechanism ,that is to say ,Pd 0is the active phase andundergoes the changes of Pd 0→Pd 2+→Pd 01When H 2was introduced into the coupling reaction system ,it in 2terrupted the normal redox process necessary for the for 2mation of diethyl oxalate and thus led to the decrease of DEO selectivity 121212　Hydrogen ,carbon monoxide and ethyl nitrite chemisorption measurements Our research revealed that ethyl nitrite does not adsorbed on the coupling reaction catalyst 1Figure 4showed the saturated amount of hydro 2gen and carbon monoxide adsorbed in dependence on temperature 1It was discovered that the saturated amount of hydrogen adsorption had a maximum at ca 1353K and it was always greater than that of carbon monoxide ad 2sorption at the same temperature 1Assuming that hydro 2gen and carbon monoxide adsorbed on the same active sites ,the adsorption competition of H 2with CO lowered the concentration of CO on the catalyst surface 1Hence ,the DEO selectivity is decreased because the rate 2deter2Figure 4　Saturated chemisorption of H 2or CO and S DE O selectivity at different temperature(C H 2=5V /%)5756期孟凡东等:氢气存在下一氧化碳偶联反应的化学和性能mining step of the coupling reaction ,as mentioned above ,is the adsorption of carbon monoxide on the sur 2face of the catalyst 1The increase of DEO selectivity with the amount of H 2adsorption decrease over a temperature range of 353K ～393K,as shown in Figure 4,also con 2firmed that hydrogen was adsorbed on the same active sites as carbon monoxide sorbed and its introduction in the coupling reaction system decreased the concentration of CO on the surface of catalyst 13　Concl usions(a )In the presence of hydrogen ,the only byprod 2uct ,ethanol ,was formed according to the reaction (5)in the coupling reaction system 1It was unable to occurfor the reactions of (4),(6)and (7)under the typical coupling reaction conditions 1(b )Hydrogen exerts a pronounced ,undesired in 2fluence on CO conversion and DEO selectivity 1In in 2dustrial practice ,the H 2mole concentration in the fresh feed gases should be kept below 1000μg ・g -11(c )Hydrogen was adsorbed on the same active sites as carbon monoxide sorbed and its introduction in the coupling reaction system decreased the concentration of CO on the surface of catalyst and thus caused the de 2crease of CO conversion and DEO selectivity 1But ,DEO selectivity increased at higher temperature ,say 393K,due to the decrease of the amount of H 2adsorption 1Ref e re nces[1]　XU Gen 2hui ,MA Xin 2bin ,HE Fei ,et al 1Characteristics of catalyst for carbon monoxide coupling reaction [J ]1Ind Eng ChemRes ,1995,34(7):2379223821[2]　Uchiumi S ,Ataka K,Matsuzaki T 1Oxidative reactions by a palladiumalkyl nitrite system[J ]1J Org Chem ,1999,576(3):27822891[3]　CHEN Geng 2shen ,Y AN Hui 2min ,XUE Biao 1Systhesis of oxalate and oxalic acid via coupling of CO with nitrous acid esters [J ]1The Chemical Engineering of Natural Gas (China ),,20(4):52101[4]　SONG Ruo 2jun ,ZHANG Xou 2jun ,HE De 2hua ,et al 1Study on the synthesis of CO catalytic coupling to diethyl oxalate in vaporphase[J ]1The Chemical Engineering of Natural Gas (China ),1987,2(4):142191[5]　王保伟,许根慧,马新宾,等1CO 气相氧化偶联制草酸二乙酯催化剂研究[J ]1燃料化学学报,2000,28(3):262-2671(WANG Bao 2wei ,XU Gen 2hui ,MA Xin 2bin ,et al 1Study of catalyst of CO coupling to diethyl oxalate in gaseous phase [J ]1J ournal of Fuel Chemistry and Technology (Chinese ),2000,28(3):26222671)[6]　Ohdan ,Kyoji 1Process for the preparation of diesters of oxalic acid[P]1EP 0802175A 1,19971[7]　XUAN Zhen 2jiang ,Y UE Hua 2su ,Bor J L ,et al 1A study on the synthesis of diethyl oxalate over Pd/α2Al 2O 3catalysts [J ]1ApplCatal A :General ,2001,211(1):472511[8]　MENG Fan 2dong ,XU Gen 2hui ,WANG Bao 2wei ,et al 1Synthesis of diethyl oxalate by a coupling 2regeneration reaction of carbonmonoxide[J ]1J of Natural Gas Chemistry ,2002,11(1):572621[9]　MA Xin 2bin ,XU Gen 2hui ,CHEN Jin 2wen ,et al 1K inetics of carbon monoxide catalytic coupling to diethyl oxalate in gaseous phase[J ]1J Chem Eng (China ),1995,46(1):502561氢气存在下一氧化碳偶联反应的化学和性能孟凡东1,2,许根慧1,杜　葩1,郭荣群2(11天津大学C 1化工国家重点实验室,天津　300072;21洛阳石化工程公司炼制研究所,河南洛阳　471003)摘　要:实验研究了在氢气存在下,一氧化碳与亚硝酸乙酯偶联合成草酸二乙酯反应体系在典型操作条件下的化学反应和反应性能,结果表明氢气只与反应体系中的亚硝酸乙酯反应生成乙醇。