Progress in studies of natural gas conversion in China

DOI10.1007/s12182008-0011-7Progress in studies of natural gasconversion in China NYu Changchun** and Shen ShikongKey Laboratory of Catalysis under CNPC, China University of Petroleum, Beijing 102249, ChinaAbstract: Progress in natural gas conversion in China is presented in this paper, including processes ofnatural gas to synthesis gas(syngas), syngas to liquid hydrocarbons, oxygenates synthesis, methanol toolefins(MTO), methane to aromatics and oxidative coupling of methane(OCM)Key words: Methane, natural gas conversion, GTL, synthesis gas, hydrocarbons, alcohols, olefins,methanol, dimethyl ether1 Introductionto oxygenate and natural gas to hydrogen has attracted moreattention in China and worldwideAccording to the data from china State Statistics bureauResearch and development of natural gas conversionthe output of natural gas in China was less than 1x10"m3in China are presented in this paper, and suggestions onbefore 1995, of which about 45% was used as chemical utilization of natural gas are made for natural gas chemicalindustry feedstock. In 2004, the output of natural gas in China industryreached 4.07x10. of which the commercial sales volumewas 3x10 m, while the natural gas used as chemical industry 2 Conversion of natural gas to syngasfeedstock decreased to 35%, but the absolute quantity was2.3 times higher than that of 1995. Up to date, the natural gasCatalytic partial oxidation(CPO)of natural gas to syngasused as chemical industry feedstock in China for ammonia is a mild exothermic reaction(AH=-36 kJ/mol). Worldwidesynthesis accounts for 60% for methanol synthesis accounts researchers have carried out lots of studies on CPO procesfor 30%, for acetylene and all the other products accounts for since 1990(Ashcroft et al, 1990; Hickman and Schmidt,10%(Kong and wu, 2004993; Lu et al, 1998; Zhang et al, 2000 Li et al, 2001; YangUp to 2005, China had only shared 1.3% of the world total et al, 2002 ). The results indicated that both noble metalnatural gas resources, and the corresponding price was relative catalysts and nickel catalysts have very high activity for CPOhigh, which is unfavorable for the development of natural reaction, and alkaline earth metal oxide and rare earth metalas chemical industry in China. However, globalization isxide promoters can inhibit carbon deposition reactions overtrend in the future and the neighboring countries of China, nickel catalysts. Because of very high reaction rate of CPOcountries in middle east and australia have abundant natural controlling reaction temperature to avoid runaway of thegas resources, which is favorable for China to utilize these catalyst bed temperature is the key to scale up of CPO reactorforeign natural gas resources From the viewpoint of optimal (Shen et al, 2001). Currently, syngas production based onutilization of natural gas resources, the chemical industry CPO is still in the phase of laboratory research with only onein China has quite a large potential size in the utilization exception of pilot plant test of Exxon Mobils fixed fluidizedof natural gas. Chemical conversion and utilization of bed CPO process(Eisenberg et al, 1999)natural gas has always been put in an important position inHighly active anti-carbon deposition catalyst is mostChina, and a lot of progress has been made. Processes with important for the CPO process. The La2 -Ni/MgAlOindependent intellectual property rights, including MTO and Al2 O catalyst developed by Lu et al (1998)is a nickel-basedoal-based synthesized fuel were developed and achieved highly active anti-carbon deposition CPO catalyst For thepilot plant demonstration, providing strong technical support catalyst, an MgAl O4 spinel membrane formed on the surfacefor sustainable development of natural gas chemical industry of Al2O, support can prevent the reaction of high temperaturein Chinasolid phase between nickel and alumina, thus avoiding thecause of the shortage of petroleum resources and more formation of NiAl O4 spinel phase, which is an inactive phasetrict environmental regulations, the conversion of natural gas for CPo reaction and will result in catalyst deactivation. Theto liquids(GTL), natural gas to olefins(GTO), natural gas catalyst promoted by the strong basic La,O, promoter canken the metallicity of nickel and slightly decrease thethe catalyst. BSupported by the National Natural Science Foundation of China promoters'modification, once methane dissociates over(20490201,20306016)the catalyst, sus Corresponding author. e-mail: yucc(@cup. edu中国煤化工 act with surfaceoxygen speciesReceived March 11 2007YHCNMHGy Surface carbonPet. Sci.(20085:67-72deposition is avoided.which is far higher than that of CPO process. In addition, theAlthough CPO is a mild exothermic reaction, very high temperature of exit gas of aTR process is about 1050C. Ingas hourly space velocity would cause a large quantity CPO process, as the feedstock temperature is limited by itsof heat release in catalyst bed in a short time period, auto-ignition temperature, in order to reach a high exit gasconsequently resulting in the formation of hot spot and temperature of ca. 1050C, a small fraction of natural gastemperature runaway. In addition, the feedstock methane and oxygen are used as fuel to be burnt to heat the reactionto oxygen molar ratio is 2: 1, which is in the range of gas. By this way, the natural gas and oxygen consumptionupper and lower limits of explosion of CH/O, mixture, CPO process is 7% and 18%, respectively, higher than thatand safe operation of cPo process is one of the key in ATR process(Bakkerud and Gol, 2004). Whether CPO ortechnologies for CPO commercialization. Lu et al(1998) ATR process is more advanced needs further researchdeveloped a new technology, which is a combination of In ATR process, oxygen production cost accounts for 40%low temperature catalytic combustion and catalytic partial of operation cost. In order to cut down the oxygen productionoxidation. It includes a serially connected cascade of two cost, ion transportation membrane (ITM)based syngasfixed bed reactors. The first one is a catalytic combustion production technology has been studied and developed byreactor, in which a perovskite type combustion catalyst 9 research organizations and universities supported by theLao Cao Feo 3 Mn,O, is packed. All the methane and 25% of US Department of Energy (DOE) since 1997( Chen et al,the total oxygen is pre-heated to 450-500 C and fed into the 2004). In the ItM process, oxygen in air obtains electronsfirst reactor. 6%-7% of methane is deeply oxidized into co, on one side of the membrane and forms oxygen anions, andand H,O, meanwhile, the feedstock is autothermally heated to the oxygen anions are transported from one side to the other800-900.C. The effluent gas of the first reactor together with side and react with natural gas to produce syngas. At the samethe rest 75% of the total oxygen is fed into the second reactor, time, the electrons of oxygen anions are released, thus thein which CH reacts with 0,, CO, and H,O over a multi- ITM cycle can carry on repeatedly. Many investigations offunctional catalyst La,O,-Ni/MgA1O3-Al,O3. In the second the ITM process were conducted (Mazanec et al, 2001; Wangreactor,the heat released by exothermic CPO reaction was et al, 2003 ), the high-temperature stability of ITM membranebalanced by the endothermic steam reforming reaction and and scale up of the membranes reactor are still problems anddry reforming reaction. In this way, an adiabatic and constant need further studiestemperature operation can be expectedA novel route for syngas production using lattice oxygerThe results of the two-stage partial oxidation in syngas of composite oxide instead of molecular oxygen wasproduction show that under the conditions of the first reactor developed (Li et al, 2004). In this route, the composite oxideinlet temperature of 400C, the second reactor temperature of acts as an oxygen carrier and syngas is produced by using a950C, feedstock composition of CH: O2 (1st): O2(2nd)=8: 1: 3 reduction-oXidation cycle. In the reduction step, the composite(molar ratio), the conversion of methane is 83%, the CO and oxide loses its lattice oxygen, which reacts with methane toH2 selectivities are 92% and 91%, respectively. In a 300-hour produce syngas, and then in the following oxidation step thestability test, the conversion of methane of 84% and syngas composite oxide that has lost lattice oxygen contacts with airselectivity of 94% are quite close to the thermodynamics and captures oxygen from air, and converts the oxygen to itsequilibrium under the same conditions. The two-stage CPO lattice oxygen. A perovskite-type oxide, LaI-xSr, FeO,, is usedprocess is now in the phase of multikilogram catalyst-based in air-methane periodically switched reactions to producbench scale testsyngas, and syngas selectivity is more than 90%process based on CPO technology. A 1000-hour stability test 3 Conversion of natural gas to liquids (gtl)ras carried out at Daqing Refining and Chemical Company Since the 1980s, Shanxi Institute of Coal Chemistryusing 500 g impregnated Ni-La/AL, catalyst at a pressure of Chinese Academy of Sciences(CAS)has carried out aof 0. 8 MPa and CH: Air H,0=1: 2.4: 2(molar ratio). The exitgas composition was 44. 4% H2, 36. 4%N2,9.6%CO, 1.0%research on coal-based syngas and iron-based catalyst usingCH, and 8.6%CO,(volume percentage)at a gas hourly space a 160 kt/a coal-based FTS plant was built at ChangzhiShanxi province. In the latest decade, Shanxi Institute ofgood activity, selectivity and stability, and no hot spot was Coal Chemistry of Cas(Chen and Sun, 2004), Dalianobserved in the reactor during the test periodInstitute of Chemical Physics of CAS and China UniversityWith regard to feedstock composition and productomposition, CPO process and autothermal reforming(ATR)of Petroleum(Beijing) have carried out research on naturalprocess has no distinct difference. As the reactor effluent gas tube fixed-bed reactor FTS has been developed by the threecomposition is nearly in thermodynamics equilibrium, theproduct gas compositions of CPO and ATR are quite closeunder similar operation conditions. For CPO process, the 4 Synthesis of methanol and other alcoholsauto-ignition temperature of feedstock CH4: 02=2: 1(molarratio) is 250C, the pre-heat temperature of feedstock carIn the traditional methanol synthesis process, a largenot be higher than its auto-ignition temperature. While, for amount of unconATR process, natural gas and oxygen are fed into reactor this disadvantage中国煤化工 n order to avoidchnology underseparately, so the feedstock can be pre-heated up to 650C, supercritical corHC N MH GShanxi Instituteet. Sci.(2008)5:67-72of Coal Chemistry of CAs(Wei et al, 1999). In the methanol Shaanxi Provincial Investment Corporation and luoyangnthesis process, a supercritical solvent, for example Petrochemical Engineering Corporation to build a 10 kt/an-hexane or n-heptane, is added, thus the formed methanol scale MTO pilot plant in Shaanxi province since Augustcan be successively transferred from gas phase to supercritical 2004. The plant was put into operation in February 2006phase. By this way, the thermodynamics equilibrium in the Gas to olefins (Gto) process is quite important for themethanol synthesis process is broken, and the Co conversion development of petrochemical industry in the areas, whichreaches 90%. Because a large amount of supercritical solvent have abundant natural gas resources but are short of oiladded to the process, energy consumption and supercritical Both Southwest Petroleum Administration of China Nationalsolvent consumption increase. Reducing the negative effects Petroleum Corporation(CNPC) and Daqing Refiningcaused by the use of supercritical solvent is the critical issue and Chemical Company of CNPC have planned theirof this procespetrochemical development program of GtO. ConceptualSynthesis of ethanol and higher alcohols mixture also design of gto by Daqing refining and Chemical Companyattract researchers'attention. Dalian Institute of Chemical of CNPC shows good economic benefit at a price of naturalPhysics of CAs has successfully developed a rhodium-based gas below RMB Yl/mcatalyst for ethanol synthesis, in which the content of rhodiumis less than 1 wt%, and a 1000-hour continuous pilot-scale 6 Syngas to DMEtest had been carried out. The results show that the catalysthas good stability, and the ethanol selectivity is 90% after DME is one of the important derivatives of methanol andhydrogenation of the product. Ethanol and ethyl acetate can ben be prepared by dehydration of methanol. The physicalprepared with high-selectivity by changing catalyst componentsproperties of DME are similar to liquid petroleum gas (LPg),and operation conditions. This process shows high potential for So DME is considered as synthesized LPG. DME has a highfuture applications (Yin et al, 2003a; 2003b; Yin, 2003)cetane number and good compression ignition performance,A catalyst, Mn-Ni-K-MoS2, has been developed by the and it is easily converted to hydrogen by reforming reactionShanxi Institute of Coal Chemistry of CAS for C,+ higherLots of research had been carried out by Amoco and Haldoralcohols synthesis, and a 1000-hour bench-scale test hasTopsoe for DME synthesis and application in 1990s(Fleischeen performed(Qi et al, 2003 ). The results indicate that the and Sills, 2004)catalyst has good activity, and the C2+ alcohols selectivity isDME can also be synthesized from syngas directlythis way, methanol synthesis and dehydration take40%-50%. The results have been repeated in a pilot-scale test place simultaneously in one reactor, which contains bothf single tube reactormethanol synthesis catalyst Cu-Zn-AL2O3 and acidic5 Conversion of methanol to olefins(MTO)methanol dehydration catalyst (Wang, 2003 ). Because ofhigh equilibrium conversion of syngas to DIn the mto process, dimethyl ether (dMe) is the pass syngas conversion can reach 70% by this route, whichintermediate of methanol dehydration to olefins. Based on significantly higher than that of methanol synthesis processthis knowledge, Dalian Institute of Chemical Physics of CAs In this process, catalyst Cu-Zn-AL2O3 also catalyzes water gashas proposed an olefins synthesis route, in which olefins are shift reactionsynthesized from syngas via methanol or DME For coal-based syngas, the H,/Co molar ratio is approximately 1One-step DME synthesis reactionwhich is the stoichiometric ratio of one-step DME synthesis3CO+3H2→>CH3OCH3+COfrom syngas. Thus . the conversion of one-step dme synthesifrom syngas is significantly higher than that of methanoTwo-step DME synthesis reactionsynthesis using coal-based syngas as feedstock, in addition2CO+4H2→>2CHOH→ CH,OCH+HOthe capital cost and operation cost of dme to olefins DTO)process can be cut down compared with MTO processThe two DME synthesis routes above show that the twoInvestigations of MTO and DTO processes have been step DME synthesis is more suitable for natural gas-basedconducted by Dalian Institute of Chemical Physics of CAs syngas (Hy CO molar ratio of 2)as feedstock, while one-stepnce 1990(Liu et al, 2000). New silicoaluminophosphateDME Synthesis is more suitable for coal-based syngas(H2/(SAPO) and metal silicoaluminophosphate(MeAPSo) CO molar ratio of 1)as feedstock. The cost of one-step Dmemolecular sieves with a small pore size have been synthesized synthesis is lower than that of two-step DME synthesis, andby using cheap raw materials and metal hetero-atom one-step DME synthesis in slurry-bed reactor is the directionmodification of sApo-34. Furthermore, microspherical of the process. One-step DME synthesis has been studiedcatalyst preparation technology by the spray method has by Tsinghua University (Wang et al,2004),Shanxi Institutebeen developed. The catalyst prepared by this technology canof Coal Chemistry of CAs(Xie et al, 2004), and daqingsatisfy the requirement of industrial fluidized-bed reactorsRefining and Chemical Company of CNPC (Xu et al, 2004a)he methanol conversion is 100%, and the total selectivity 7 Methane direct conversionof ethylene and propene is higher than 90%. In addition, theethylene to propene ratio is adjustable in a certain rangeMethane dehydrogand aromatization (MDA)Dalian Institute of Chemical Physics of CAs, owner of a new process中国煤化工 ute of chemicalindependent intellectual property rights, has collaborated with Physics of CACNMHGlethane can bePet. Sci.(20085:67-72converted to benzene and hydrogen with high selectivity by MoO /La-Co oxide catalyst for methanol synthesis. Underusing Mo-modified ZSM-5 molecular sieve as catalyst at the reaction conditions of 420C, 4.20 MPa, space velocity700C. Hydrogen is a future clean fuel, and benzene is an of 1.44 L/(gh) and a feedstock composition of CH4: O N2important petrochemical feedstock. This reaction has attracted 9: 1: I(molar ratio), methanol yield and selectivity were 6.7lots of attention. Research shows that a small amount of and 60 %, respectively. Direct selective oxidation of methanenaphthalene and C2 hydrocarbons are obtained besides to methanol is far away from commercialization. Economicbenzene in the product(Shu and Ichikawa, 2001; Huang et assessment suggests that more than 10% of per pass methaneal, 2004; Xu et al, 2003). The catalyst deactivates easily, conversion, and more than 90% of the sum of methaned the deactivated catalyst is hard to return to its original conversion and methanol selectivity, should be achieved foractivity after regeneration. Mo, Re and w supported on commercialization of the process(Fould and Gray, 1995)HZSM-5, HMCM-22 and HZSM-ll molecular sieves shows A new way of conversion of methane to methanol basedgood catalytic performance In MDa process, the catalyst on liquid mercury sulfate catalyst has been developed bydeactivation caused by carbon deposition is the key problem Periana et al (1998). The catalysis cycle includes three mainto be solved. Studies on theory and experiments conducted stepsover Mo/HZSM-5 by Xu et al (2003)show that the valenceand position of atom Mo, and the channel structure and I. Esterification: CH+2H SO4CH3OSO, H+ 2H20+SO2Bronsted acid sites distribution of the molecular sieve, are 2. Hydrolyzation: CH, OSO, H+H,0-CH,OH+ H2SOthe key factors for catalyst performance. The results of in situMAS NMR prove that carbon deposition occurs on Bronsted 3. Re-oxidization: SO2+O2+ H2O>H SO 4acid center. The stability of catalyst Mo/HZSM-5 can beimproved by steam treatment of the catalystselectivity of 85% is achieved at a temperature of 180 6QA methane conversion of 50% and methyl bisulfatLiu et al (1998)found that addition of 3 vol% of COz However. the reaction rate of the process is quite slow. Xu etinto methane could slow down the carbon deposition al(2004b ) reported that methane conversion of 72% and sumof the catalyst, and improve the stability of the catalyst. selectivity of CH,OSO, H and CH, OH of 81% was achievedAccordingly, Li et al(2004) proposed combining exothermicunder conditions of 220 C. 3. 4 MPa, reaction time of 2.5reaction of oxidative coupling of methane(OCM) withendothermic reaction of MDA. By such a way, the byproducthours, CH4 to catalyst molar ratio of 2.3 and using dichloro-CO, of OCM reaction can be used to improve the stabilify (n2-( 2, 2'-bipyrimydl platinum(II) complex instead of toxicof catalyst Mo/HZSM-5 for MDA reaction. In a fixed-bed mercury sulfate. They also reported another system usingquartz reactor, 0.15 g OCM catalyst and 1.0 g MDA catalyscatalyst (NH3) PtCl,, which is more active than dichloro(6 wt% Mo/HZSM-5)were packed in sequence, and under (n"-(2, 2'-bipyrimydl; )platinum( complex, but less stablethe reaction conditions of feed gas composition of CH4: 0, Although low-temperature liquid-phase homogeneousN2=9: 0. 11: 1(molar ratio) and temperature of 730 C. the complex catalysis, dichloro-(n-(2, 2'-bipyrimydl))methane conversion and the aromatics yield reached 20.1 Platinum(II), has an advantage of high methanol yield,and 10.9 %, respectively, after 60 min of reaction, and 15.9% but the problems of very low reaction rate, requirement ofand 8.9%, respectively, after 960 min of reaction. While theoncentrated sulfuric acid, complex product separation, SO2absence of OCM catalyst and the feed gas composition ofoxidation and recycle, and free of water during reaction areCH: N2=9: 1(molar ratio), resulted in methane conversion and still the challenge. Thus, conversion of methane to methanolaromatics yield being 17. 7% and 12. 8%, respectively, after 60based on this way is not possible for commercialization atmin of reaction, and only 0.9% and 0. 1%, respectively, after960 min of reaction. The results indicated that the stability beer omprehensive investigations on OCM to ethylene haveof MDa catalyst was highly improved by combination ofcatalysts reach the level that the sum of methane conversionoCM and mda reactions However with consideration ofcommercial application, long-time stability and regeneratiand C, hydrocarbons selectivity equal to or greater than100%. Na, WO4-Mn/SiO, is still the best catalyst reportedof Mda catalyst is still the main challenge to MDa process. for OCM up to date(Li, 2003). Ji and co-works(2004)The investigation of catalytic and non-catalyticconversion of methane to methanol and formaldehyde extends reported that methane conversion reached 29.5%, ethyleneover seven decades(Bone, 1931; Hall et al, 1995). However. Selectivity reached 42.6% and ethane selectivity reachedthere is no breakthrough. Methane conversion and methanol 23. 8% over Na2- Mn/SiO, catalyst under conditionsselectivity reached 8.1% and 84.6%, respectively, over 1.7 of 800oC, atmospheric pressure, space velocity of 254wt%MoO,/SiO, catalyst and N,0 as oxidant at 560C(Liu g h)and feedstock composition of CH4: 02=3.2: 1(molaret al, 1982). When using quartz sands instead of MoO /Sioratio). Economic assessment suggests that OCM might becatalyst, methane conversion and methanol selectivity reached commercialized only when per pass methane conversion is8%0-10% and 70%-80%, respectively, under the conditionsmore than 30% and the total C2 hydrocarbons selectivity ismore than 80%(Gradassi and Green, 1995)of 400-500C, 2.5-6.5 MPa, and 2.5-10.0 wt% MoO, SiO2catalyst and Oz as oxidant (Yarlagadda et al, 1988). Up to 8 Conclusiondate the above data are the best results of direct catalytic andnon-catalytic conversion processes of methane to methanol Great progre中国煤化工ect natural gas(Liu et al, 1984). Zhang et al(2004)developed a 7 wt% conversion and ulYHCNMH Gades Oil and gaset. Sci.(2008)5:67-72processes will gradually be unified by integration of hydrogen nitrous oxide over molybdenum on silica. Journal of the Americanduction, GTL, GTO and oxygenates production processesChemical Society. 1984. 106: 4117-4121with refinery and petrochemical processes. 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