整體型催化劑上甲烷自熱氧化制合成氣

第7卷(2001)第2期燃燒科學(xué)與技術(shù)ol.7(2001)No.2JOURNAL OF COMBUSTION SCIENCE AND TECHNOLOGYPartial Oxidation of Methane to Syngas autothermalover Monolithic CatalystsWANG Ya-quan, HOU Yong-jiang, QI Sui-tao(State Key laboratory of Ci Chemical Technology, School of Chemical EngineeringTianjin University, Tianjin 300072 China)Abstract: A monolithic Ni metal catalyst was prepared and its performace in the partial oxidation of methane to syngas was compared with that of supported Rh and Pt catalysts. It was shown that the Ni metal catalyst gave the siilar methane conversion and selectivity to H, and CO as supported Ni and Rh catalysts, but had excellent stability.The results with H,O and CO addition in the reaction indicate that H2 /CO ratio in the products can be adjusted di-rectly in the reactionKeywords: Ni; monolith; methane; partial oxidation syngas整體型催化劑上甲烷自熱氧化制合成氣王亞權,侯永江,齊隨濤(天津大學(xué)化工學(xué)院,一碳化工國家重點(diǎn)實(shí)驗室,天津300072)摘要:用鎳金屬制備了一整體催化劑并與負載銠和鉑比較了甲烷氧化制合成氣的性能。結果表明,鎳金屬催化劑上甲烷轉化率、H和CO的選擇性與銠催化劑相當,而且穩定性非常好。反應中加入H2O和CO2的實(shí)驗表明,產(chǎn)物中H2/CO的比例可以直接調節。關(guān)鍵詞:鎳;整體型;甲烷;部分氧化;合成氣中圖分類(lèi)號:TQ426文獻標識碼:A文章編號:1006-8740(2001)02-0105-05As the recovery of petroleum becomes more difCurrently, the conversion of natural gas to synficult and expensive, the utilization of natural gas gas is carried out by catalytic steam reforming. This(mainly methane ) is more and more important. Cuprocess is highly endothermic, and so energy-inten-rently, the natural gas is turned into syngas (H2sive that in the reaction. excess steam must be used inCO)first, then syngas can be converted into gaso- order to prevent carbon formation on the catalystsline, methanol and other important products. In thesMoreover, H, /CO ratio in the product is 3, not suitprocesses, around 60%-70% cost of the overall pro- able for gasoline, methanol and some other importantcess is associated with syngas generation. Reductionprocesses[in syngas generation would have a large and direct inrs. many research efforts have beenfluence on the overall economics of these downstream devote中國煤化工idation of natural gasprocesses.to syCNMHGoxidation reaction is*收稿日期:1999-11-12;修回日期:1999-12-30?；瓞F方瘧自然科學(xué)基金資助項目(98360341作者簡(jiǎn)介:王亞權(1961—),男,工學(xué)博土,教授。燃燒科學(xué)與技術(shù)第7卷第2期slightly exothermic, so the process is energy effiwere sealed in the reactor by silica-alumina cloth andcient Oxidation reactions are also faster than steam the reactor was insulated by wrapping with high tem-therefore smaller reactors are required. perature insulation outside. The reaction temperaFurthermore, H, /CO ratio in the final product is 2, tures were measured by a Pt-Rh /Pt thermocouplesuitable for gasoline, methanol and some other impor- placed between the catalyst and the back ceramictant processesmonolith Flow rates of hgih purity O2 CO2 and CHUp to now, most laboratory studies on partial (99. 5%) were controlled by mass flowmeters. Theoxidation of methane (POM) have been conducted in reaction was ignited by passing a NH3 /air mixturefixed-bed microreactors 2, 4-8. In these processes, wallhrough the catalyst and preheating using a bunsenol thetemperature. Schmidt and coworkers 4.10 studied a ucts were analyzed by Gas Chromatograph For exnovel monolithic reactor. Using this kind of reactorperiments in which steam was added to the feed, wathe reaction can be operated at high gas hour space ter was pumped through a long, thin tube inserted invelocity (GHSV) and autothermally with no external to the preheated section of the reactor that permittedfurnace being required. The results showed that sup- the water to be completely vaporized before reachingported Pt, Rh, Ir and Ni are very active and selectivefor POm reaction. 80% methane conversion, 90% Hand 95% CO were obtained on Rh catalysts. Ni 2 Results and Discussionactivated within a few hours [9J2. 1 Comparison between metal Ni and supportedSince supported Ni catalysts lost the activityRh and Pt catalystsklyal foIts obtained on the nimonolithic catalyst. In this paper, the Ni catalyst was al, and supported rh and Pt monolithic catalysts. Thecompared with supported Rh and Pt catalysts and the reactions were conducted at GHSV of 1X10 h witheffects of H,O and CO, addition in the reaction were an inlet temperature of 298 K. It is seen in Fig. la thatalso studiedin comparison with the two precious metal catalystsRh and Pt, Ni catalyst gave the similar methane cor1 Experimentalversions as Rh, which are higher than Pt. Methaneconversions increase with the decrease of CH, / OraA 9 10 mm length Ni monolith was made as tio. This is what we expect because no oxygen breakfollows: 0. 7 mm Ni spheres were packed in a 9 mm through was observed under the present conditionsquartz tube with a-Al,O3 foams at the front and e all the oxygen was consumed in the reaction. Atback. In the presence of hydrogen, the temperature CH,/O2=1.8,methane converrsion is near to 80%was increased at 1 K/min from ambient temperaAccording to the partial oxidation reactionto 1 473 K, kept at the final temperatue for 6 h2CH4+O2=2H2+2CO(1)then cooled down to ambient temperaturethe theoretical ratio of Ch,/o, is 2. But it should be3.2%Rh/a-Al2O,(wt) and 3. 6%Pt/a-Al2O3 pointed out that the theoretical ratio might not be therere prepared by impregnating a-Al2O3 foams with optima中國煤化工less there would beaqueous solutions of rhodium chloride or palladiumCNMHGd into cO and H,Oacetate, followed by drying at 393 K for 12 h, calcin- Slightly lower than Z might be optimal for practicaling at 673 K for 6 h, and then reduced in H2 for 6 husePartial oxidation reaction was conductedAgain, the selectivities to H2(Fig. 1b)on both niquartz reast 5*s catalyst and two straight channel and Rh are much higher than Pt which is only aroundextruded ceramic monoliths at the front and back 55% at CH /0,=1.8. For the selectivities to CO2001年5月WANG Ya-quan, et al: Partial Oxidation of Methane to(Fig. Ic), there are not many differences on the threeowever. Schmidt and coworkers ' remetals. They are slightly lower over Ni than Rh and sults 9 showed that supported Ni catalysts lost thePt, but are still around 90activity within a few hours. The present Ni catalystThe reaction temperatures on Ni are around was used for many times for the reaction. When one273K at CH/O,=1.7-2.0. similar to those on run was finished, O, in the feed must be first shutPt, but slightly higher than Rh(Fig. 1d). Thermodyoff, then methane could be switched off in order tonamic calculation shows that at 95% conversion of prevent the explosion. During this process, muchmethane with a selectivity of 95% to both H, and bon deposited on the catalyst. When the catalyst wasCO, the reaction has an adiabatic temperature rise used again. the deposited carbon must be removed byperatures are near to the adiabatic tempertures. In be ignited. This catalyst was ale t reaction could notfrom 298K to 1 273 K. The measured reaction tem- brn oxygen. otherwise, thd for the stud,summary, results in Fig. 1 show that in the partial of the effects of H, O and CO, additions(see discuxidation of methane in autothermal conditions with sions below ). After dozens of runs with the total orCH/O2=1.8,80% methane conversion, 85% and line time for more than 50 hours, there was not any90% selectivities to H, and CO, respectively, can be deterioration of the performance in terms of the activobtained on the present Ni metal monolithic catalyst. ity and selectivities. These results demonstrate thatThese results are similar to those on supported Ni the present Ni catalyst is very stable for the reacitonCHO3〔 mol ratioCH/O, (mol ratioPR1050CH/o, (mol ratioCH,, (mol ratio)Fig. 1 Methane partial oxidation result中國煤化工2 Reaction with H, 0 and CO, additionCNMHG(2)Usually, after generation the H,O/CO ratio in By adding suitable amount of water, a certain amountthe syngas must be adjusted so as to be used in down- of CO can be transformed into H2, and thus the de萬(wàn)7es. This is done by a water-gas shift sired H, /CO ratio can be obtained In industry, a sep方數據reactionarate unit must be used for this reaction燃燒科學(xué)與技術(shù)第7卷第2期Here we study the effects of CO, and H, O addirepresented by XcH. g and Sco,eg, respectively,are alsotion in the partial oxidation to determine if the H,/ given Fig. 2 shows that with the addition of H, O, theCo ratio in the products can be adjusted directly In selectivity to CO decreases over all the three cataFig 2 reported are the results of the metal Ni and su- lysts. The curves of the selectivity to CO are roughlyported Rh and Pt catalysts with H,O addition. In the parallel to, but lower than the thermodynamic line onreaction, the flow rates of CH, and O, were kept con- all the three catalysts. The decrease of co concentrastant with CH/02=1.8. The reaction temperature tion with the addition of H,O can be attributed to thewas also kept constant as the one without H,O addi- water-gas shift reaction (equaiton 2) because no othtion with the regulation of inlet temperature. In the er products were found in the reactionxperiments, it was found that with addition of aThe results with CO, addition in the reactionlarge amount of H, O, the selectivity to Ha can not be over the three catalysts are given in Fig 3. The reacdetermined accurately, so only the selectivity to COtion was conducted as for H,O addition except that nowas reported. In Fig. 2, methane conversion and theH,O but CO, was added. Similarly, with the additionselectivity to CO at thermodynamical equilibriumof a large amount of CO 2, the selectivity to CO canCOy%中國煤化工CNMHGFig. 2 Effects of HO addition on the partial oxidationFig 3 Effects of CO, addition on the partial oxidationrm片數據ando: ows were held constant atof methane CH and O, flows were held constant1. 67 and 0.93 standard liter per minute, respectivelyat 1. 67 and 0.93 standard liter per minute, respectively2001年5月WANG Ya-quan, et al: Partial Oxidation of Methane tonot be determined accurately, so only the selectivityThe present catalyst system can be operated atto H2 was reported In Fig 3, methane conversion and high GhSv autothermally with no external furnacethe selectivity to H2 at thermodynamical equilibrium, being required. It may be suitable for any size ofepresented by XCH, eg and SH, eg, respectively, are alsogiven Fig 3 shows that the selectivity to H2 decreasReferenceses with the addition of co, on all the three catalystsIn combination with the H,o addition results. this [1] Bharadwaj S Schmidt L D Catalytic Partial Oxidation of Natufurther demonstrates that the weter-gas shift reactionral Gas to Syngas[J]. Fuel Process Tech, 1995, 42: 109-12[2 Ashcroft A T, Cheetham A K, Foord J S,et al. Selective Oxidatin(equation 2) prevails in the partial oxidation reactionof Methane to Syngas Using Transition Metal Catalysts [J]. Na-and the H2/CO ratios can be adjusted directly byadding h,o or Co[3 Hickman D A, Schmidt L D. Production of Syngas by DirectCatalytic Oxidation of Mthane[J]. Science, 1993:259: 3433 Conclusion[4] Choudhary V R, Rajput A M, Prabhakar B Nonequilibrium Oxidative Conversion of Methane to CO and H with High Selectity and Productivity over Ni/Al,O3 at low Temperatures [J]. JI Ni metal monolithic catalyst has beenCatal,1993,139:326-328prepared and proved to be suitable for the partial oxi[5 Lu Y, Deng C, Ding x, et al. Catalytic Partial Oxiddation of methane to syngas autothermally. It showsMethane to Syngas over Ni/Al,O3 Catalyst[J]. Chinese J Catalsimilar activity and selectivities as supported Ni as1996,17(1):28-33well as precious metals such as rh in the reaction. At[6 Yu J. Zhang L, Yu Z. Study on the Partial Oxidation of MethaneGHSV of 1 h, CH / O2=2 and inlet temperato Syngas[J]. J Nat Gas Chem Tech, 1996,21(4): 5-8.[7 Cao L, Chen Y, Li W,et al. Effects of Supports on the Direct Oxiture of 298 K, 80%methane conversion, 85% anddation of Methane to Syngas[J]. J Nat Gas Chem Tech,1996.2190% selectivities to H, and CO, respectively, can be(3):12obtained. The catalyst is very stable with many times [8 Chu Y, Li S Lin J et al. Methane Partial Oxidation to Carbonigniting and shutting off and long time online operaMonoxide and Hydrogen[J]. J Mol Catal, 1996.10(5):328-332tion without any deterioration[9 Torniainen P M. Chu X, Schmidt L, D. Comparison of Monolithorted Metals for the Direct Oxidation of Methane to SyThe H2/CO ratios can be adjusted directly byLJ]. J Catal,1994,146:1-10adding H,O or CO2 in the reactionV凵中國煤化工CNMHG