47(3)-03(류준형).fm

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1 Korean Chem. Eng. Res., Vol. 47, No. 3, June, 2009, pp 총 설 메탄의건식개질을이용한이산화탄소의재활용 김정묵 류준형 이인범 이재성 포항공과대학교화학공학과 경북포항시남구효자동산 31 (2009 년 4 월 3 일접수, 2009 년 4 월 18 일채택 ) Recycle of Carbon Dioxide Using Dry Reforming of Methane Jeongmook Kim, Jun-hyung Ryu, In-Beum Lee and Jae Sung Lee Department of Chemical Engineering, POSTECH, San 31, Hyoja-dong, Nam-gu, Pohang, Gyeongbuk , Korea (Received 3 April 2009; accepted 18 April 2009) 요 약 온실가스배출규제에따라이산화탄소배출감축은산업계에서해결해야할가장중요한과제중하나가되었다. 이산화탄소는온실가스발생원중대부분을차지하며본논문에서는실제대규모산업현장에서의이산화탄소배출을저감하는직접적인방안으로메탄의이산화탄소개질반응을이용하는방법을고찰해보았다. 강한흡열반응형태인이반응에대해추가적인이산화탄소발생을피하며효율적으로에너지를공급하기위해서는자열개질반응을이용하는것이적합한방법으로판단된다. 생산된합성가스는환원가스로재활용하거나화학제품및연료의합성에활용할수있다. Abstract Considerable attention has been given to developing methodologies to reduce the emission of carbon dioxide from industry to meet strengthened environmental regulations. In this article, recent research trends on dry reforming of methane as an alternative method to reduce CO 2 emission from large scale industrial processes are addressed. To efficiently provide the energy needed in this strong endothermic reaction without additional CO 2 emission, it seems to be desirable to adopt autothermal reaction mode. The produced synthesis gas could be used as a reducing gas, or a feedstock for synthesis of chemicals and fuels. Key words: Carbon Dioxide, Methane, Reforming, Autothermal Reaction, Synthesis Gas 1. 서론 1992년리우기후변화협약이래, 세계각국정부와기업, 연구기관은온실가스배출을줄이려는노력을계속하고있으며 2005년발효된교토의정서는이러한노력을더욱가속화하고있다. 우리나라의경우, 주요한산업국이자온실가스배출국으로서 2013년이후새로이적용될기후변화협약에온실가스배출감축의무국으로포함될것이확실시됨에따라관련기술확보를포함한대응책마련이시급한상황이다. 특히이산화탄소는가장중요한온실가스로배출을감축하고자하는연구가다양하게이루어지고있다. 산업부문별국내온실가스배출량을살펴보면 2004년기준으로전기 수도 가스부문이 33.2%, 제조업중금속제품부문이 13.4% 등으로압도적인비중을차지한다 [1]. 이는각각발전과철강공정의배가스로배출되는이산화탄소에의한것으로이들공정은특성상에너지원혹은환원제로서다량의석탄등탄화수소를사용하고 To whom correspondence should be addressed. jlee@postech.ac.kr or jun2002@postech.ac.kr 있어특히이들공정에있어이산화탄소배출을저감할수있는기술이요구되고있다. 현재연구되고있는이산화탄소저감방법은크게에너지효율증진, 저탄소연료개발, 원자력에너지및신재생에너지사용등으로원천적으로이산화탄소의발생을줄이는방법과발생한이산화탄소를분리, 저장하는방법등이있다 [2]. 그러나에너지효율증진방법의경우, 이미국내발전, 철강산업의효율이세계최고수준에도달하여추가적인증진이쉽지않은실정이다. 또한저탄소발생연료개발, 원자력에너지및신재생에너지의사용은경제적, 사회적으로많은개발및활용비용을요구하거나규모나효율성측면에서경쟁력있는기술이개발되지못하는등의한계가있다. 분리, 저장방법은현재다양하게연구되고있으며상당히안정화된기술이개발되어있으나기존공정에추가적으로비용이이산화탄소분리에 15~115 US$/tCO 2, 그에따른저장에 0.8~30 US$/tCO 2 이나더필요하여획기적인기술개선이없는이상은경제적으로달갑지않은방법이다. 지질학적저장이나해양저장에따른환경에대한영향이충분히연구되어있지않고이에대한국제법상의 267

2 268 김정묵 류준형 이인범 이재성 규제문제또한명쾌히해결되지않고있으며우리나라의경우에는저장하기위한충분한공간을장기적으로확보하는것역시만만치않은문제이다. 이러한한계점을지닌위의방법들의다른대안으로써이산화탄소를반응물로서재활용하는것을고려해볼수있다. 화학적이산화탄소재활용방법은저장법과는달리대기중으로방출될이산화탄소의화학적전환을통해탄소를포함하고있는유용한물질을생산하는것을의미한다. 광화학적 / 전기화학적 / 생물화학적 / 촉매화학적방법등다양한화학반응을이용한방법들이제시되고있다 [3]. 이러한화학적재활용방법을설계하기위해서는여러가지사항들에대하여고려해야한다. 먼저기존의화학공정에요구되는비용, 시간, 규모와같은조건들을고려하는것에서더나아가매우안정한물질인이산화탄소를 (ΔG o f = kj/mol) 전환하는데에필요한강력한환원제의개발을전제로한다. 또한이산화탄소의절감을목적으로하기때문에재활용시에필요한외부에너지의투입으로인한이산화탄소의추가발생까지검토되어야한다. 또한생산된물질을경제적으로활용가능한시장에서의수요확보나기존공정과의연계활용가능성등이반드시고려되어야한다. 본논문에서는기존의상용화된대규모화학공정과유사하여기술적용속도나처리규모에서상대적으로유리한촉매화학적방법을이용한재활용방안중의하나로서메탄의이산화탄소개질반응에대해고찰해보고자한다. 2. 메탄의이산화탄소개질반응 이산화탄소를다른물질로전환하기위해서는환원제가반드시필요하다. 가장강력한환원제로서는수소가있으며이산화탄소와반응시켜메탄올을생산하거나이를중간체로활용하여다른물질을합성할수있다. 그러나자연상태에서수소는수소분자형태로거의존재하지않아에너지를투입하여다른물질을분해하여생산하여야만한다. 이과정에서신재생에너지를이용하여수소를생산할수있다면적절한방법이될수있겠지만경쟁력있는신재생에너지는아직까지존재하지않으며현재로서는천연가스를수증기로개질하여수소를생산하는것이가장저렴한방법인데이과정에서오히려이산화탄소가발생되므로이산화탄소총량을절감한다는목적에는적절하지않다. 하지만메탄은다음의두가지장점때문에환원제로사용할수있다고판단된다. 첫번째로는천연가스의형태로상당히많은양이매장되어있어직접적으로활용하기가쉬우며또한수소원자의비중이높아좋은환원제이다. CO 2 +CH 4 2CO + 2H 2 (ΔH o 973 K = 261 kj/mol) (1) 메탄을이용한이산화탄소개질반응은 (1) 과같이이산화탄소의환원제로메탄을주입하여고온에서반응시켜수소와일산화탄소의혼합물인합성가스를생산하는반응으로, 1888년최초로연구된이래주로상대적으로안정된탄화수소인메탄을이용하여합성가스를생산하고자하는데주안점을두고수증기개질반응과부분산화반응등과함께연구되어왔다 [4-7]. 이들반응중특히수증기개질반응은이미 1930년대에미국뉴저지스탠다드오일사 ( 現엑손모빌 ) 에의해서상용화되어현재까지도수소의공업적생산에주된공정으로쓰이고있어촉매계등유사한공정조건을가진이산화탄소개질반응의상용화는어렵지않을것으로보이며 Fig. 1. Equilibrium mole fraction of CO 2 reforming as a function of temperature [11]. 최근일본에서파일럿테스트가수행되기도하였다 [8]. 생산된합성가스는다양한유기화합물을합성하는반응물로유용하게쓰일수있다 [4, 7, 9]. 특히, 이론적으로생산된합성가스중수소와일산화탄소의비가 1:1로서수증기개질반응이나부분산화반응에비해수소함량이적어옥소화합물의합성에적합하다. 하지만이들화합물의시장규모가이산화탄소발생량에비하여매우작으므로다른메탄개질반응을동시에실행하여수소와일산화탄소의비를조절하여좀더다양한유기화합물을생산하거나기존공정내에서합성가스를활용하는등대규모로합성가스를사용할수있는활용방안의창출이필요하다. 참고로유럽의철강관련산업체와연구기관의컨소시엄인 ULCOS(Ultra-Low CO 2 Steelmaking) 에서는메탄의부분산화반응을통해생산된합성가스를이용해철광석을환원하는직접환원법을연구중에있다 [10]. 열역학적으로메탄의이산화탄소개질반응은 Fig. 1과같이 400~700 o C 사이에서반응평형이급격하게변화하여높은평형전환율에이르므로 700 o C 이상의고온에서의운전이필수적이다 [11]. 반응평형에근접한높은전환율을보이는적합한촉매물질로는다른개질반응과유사하게주로 Ni, Ru, Rh, Pd, Ir, Pt과같은 8족전이금속들이높은활성을띄는것으로보고되었다. 이들중, Ni을제외한귀금속들은높은활성을띠면서도탄소침적에대해상대적으로높은저항성을보이지만희소성과함께원소에따라 Ni의약 500~3,000배에달하는높은가격때문에상용화공정촉매로서의사용에제약이있어 Ni계촉매에대한연구비율이높다 [12]. 하지만 Ni계촉매의경우, 높은활성을보이지만탄소침적이크게일어나고활성이빨리저하되어연구의주안점은이를어떻게제어하느냐에집중되고있다 [4-7]. 촉매상의탄소침적은다음과같은메탄분해반응 (CH 4 cracking) (2) 와 Boudouard 반응 (CO disproportionation) (3) 을통해서일어나는것으로받아들여지고있으며이것이촉매의활성을저해하는주원인으로알려져있다 [13]. CH 4 2H 2 +C (s) (ΔH o =17.9 kcal/mol C (s) ) (2) 2CO CO 2 +C (s) (ΔH o = 41.2 kcal/mol C (s) ) (3) 위두반응중주된반응이무엇인지와각기다른촉매상에서실제반응은어떤경로를거쳐일어나는지에대해서는다양하게연구되고있다 [4-7, 14-19]. Assabumrungrat 등은열역학적인분석을통 화학공학제 47 권제 3 호 2009 년 6 월

3 메탄의건식개질을이용한이산화탄소의재활용 269 와결정격자크기가유사하며높은안정성을가지는 MgO에의해높은활성과안정성을유지한다고설명하였다. Tomishige 등은다른전구체를이용하여제조한 NiO-MgO 촉매를이용하여 850 o C, 상압에서 CH 4 80% 이상의높은전환율을 100일동안유지하였다고보고한바있다 [39]. 최근에는 perovskite 구조를가지는 La-Ni 화합물혹은이에양이온을일부첨가한촉매를전구체로사용한연구도진행되고있다 [19, 25, 27, 40-45]. 공침법등을이용하여 perovskite 구조체를만들고이를소결하여표면에잘분포된작은크기의 Ni 입자를형성하는방법으로 Gallego 등은 self-combustion 법을이용하여 La 2 NiO 4 perovskite를합성하고소결하여 700 o C, 상압, 300,000 ml/ g h, dilution gas를사용한조건에서반응한결과, CH 4 85%, CO 2 93% 의높은전환율을 160시간동안유지하였다고보고하였다 [19]. Fig. 2. Values of the equilibrium constants of reactions related to CO 2 reforming of methane [20]. 해관련각반응의온도에따른반응평형상수를계산한바있는데 Fig. 2와같이 700 o C 이상에서탄소침적반응은상당히높은평형상수를가짐을확인할수있다 [20]. Gadalla와 Bower은열역학적계산을통해서이산화탄소와메탄이 1기압하에서같은비율로존재할때 870 o C 이하에서는평형상에서탄소침적이발생함을주장했다 [21]. 따라서고온에서의반응에따른외부에너지의과도한투입을최소화하기위해서는탄소침적을반응속도론적으로제어할수있는촉매의개발이필수적이라고할수있다. 상용개질반응 Ni 촉매의경우탄소침적을방지하기위해 SPARG (Sulfur Passivated Reforming) 공정을이용하는데이것은촉매표면의활성점중일부를황으로봉쇄하여탄소의침적을막고반응은유지하는 ensemble control 의일종으로탄소의침적에요구되는활성점 ensemble의크기가반응에필요한 ensemble의크기보다큰것을이용한것이다 [22,23]. Duprez 등은 filamentous carbon의경우, 활성점을이루는금속입자크기가 6nm 이상이되어야생성된다고주장한바있다 [24]. Ensemble 효과외에도촉매담체에다른물질을첨가함에따른촉매의산성 / 염기성변화나 oxygen mobility 변화의효과도다양하게연구되고있다 [25-35]. 나노구조체인촉매의특성상이같은효과들은변인이완전히통제되어독자적으로판단되기는힘드나제조공정과전처리과정에따른촉매특히활성점을이루는 Ni 금속결정과그주변의구조의변화에영향을받는다고볼수있다 [19]. 구체적으로는촉매담체를사용하여촉매와담체간, 담체와반응물간의상호작용으로안정성을높이고자하는연구는다양하게진행되었으며일정한개선효과와함께반응기작에대한연구성과가보고된바있다 [5]. Kaengsilalai 등은 KH zeolite 담체에 8% Ni을올려사용하였을때 700 o C에서 60시간의운전뒤에도평형에가까운전환율 (80% 이상 ) 을보였으며탄소침적량이 3.82%(5시간운전후 ) 에불과한것으로보고하였다 [36]. Ruckenstein과 Hu는 NiO-MgO 고용체를촉매로사용하여 790 o C, 상압, 60,000 ml/g h에서 CH 4 91%, CO 2 95% 의높은전환율을 120시간의운전동안유지하였다고보고한바있다 [37]. 이들은 MgO를담체로사용한 Ni을함침법으로제조한뒤고온에서소결하여촉매를제조하였으며 [38] NiO 이들은 XRD 분석결과표면에서 7nm의미세한 Ni 입자와 La 2 O 3 입자가형성되었음을확인되었으며이는함침법을이용해서제조한 Ni/La 2 O 3 가 11 nm의 Ni 입자크기를보인것에비해촉매분산에있어서많은개선을보인것이라주장했다. Lima 등은 La 1-x Ce x NiO 3 를합성하여 750 o C, 상압, 72,000 ml/g h에서반응한결과, CO 2 62% 의전환율을 18시간동안유지하였다고보고한바있다 [27]. 3. 메탄의이산화탄소자열개질반응 앞서언급한바와같이메탄의이산화탄소개질반응은반응평형상반드시고온을유지해주어야하며또한 ΔH o 973 K = 261 kj/mol의매우강한흡열반응이다. 따라서높은전환율을위해서는많은양의에너지를공급할필요가있다. 그러나가장경제적인에너지공급원이현재로서는화석연료임을감안할때, 많은에너지의공급을요하는공정은다량의추가적인이산화탄소방출을요구하므로재고되어야할필요가있다. 이를방지하기위해이산화탄소의추가적인방출을최소화하면서에너지를공급할수있는개선방안으로다음의세가지를고려할수있다. (1) 기존공정의폐열활용 (2) 신재생에너지를이용한에너지공급 (3) 소량의산소를메탄과함께공급하는메탄의이산화탄소자열개질반응 이중 (1) 공정폐열활용의경우, 언급한바와같이산업분야이산화탄소주배출원인발전산업과철강산업의에너지효율이상 대적으로매우높은수준에있어공정내에서개질반응에요구되는규모의폐열원을찾기가쉽지않은상황이다. 또한배가스의잔류열역시배가스중대기오염물질인아황산가스등을제거하는공정을거쳐야하므로활용하기어렵다. (2) 신재생에너지의경우, 현재까지화석연료에비견할만큼경제성을갖춘기술이없으며, 특히본반응에서요구하는고온의열에너지를통제가용이하게집약적으로공급하는신재생에너지기술은아직까지개발되지않았으므로본공정에적용하기는힘들것으로보인다. (3) 메탄의이산화탄소자열개질반응의경우, 에너지공급의효율성과통제의용이성, 추가적인이산화탄소개질반응개선효과등을기대할수있어적합한방안이라할수있다. 특히일부라도기존공정내의폐열을발굴하여함께적용한다면현재로서는가장적합한방안이라할수있다. 구체적으로메탄의이산화탄소자열개질반응은메탄, 이산화탄소와함께소량의산소를공급하여다음과같은반응이병행하여 Korean Chem. Eng. Res., Vol. 47, No. 3, June, 2009

4 270 김정묵 류준형 이인범 이재성 일어나는것이다. CH 4 +1/2 O 2 CO+2 H 2 (ΔH o 973 K = 23.1 kj/mol) (4) CH 4 +3/2 O 2 CO+2 H 2 O(ΔH o 973 K = 520 kj/mol) (5) CH 4 +2 O 2 CO 2 +2 H 2 O(ΔH o 973 K= 804 kj/mol) (6) 이들반응은모두메탄의산화에따른발열반응으로서발생한열을이산화탄소개질반응에직접적으로전달하여열에너지를전환혹은전달과정을전혀거치지않고효율적으로공급해줄수있다. 또한산소공급량을조절하여개질반응의결과물인합성가스의조성을변화시킬수있는등공정의조절과통제를더욱용이하게할수있다 [7,46]. 게다가개질반응촉매의주요한난점인탄소침적을억제하는효과가있는것으로도보고되고있다 [47,48]. Amin과 Yaw는 Fig. 3에서보는바와같이메탄, 이산화탄소, 산소의공급량과온도에따른반응평형변화를반응참여물질의 Gibbs 자유에너지를계산하여그래프로나타내었다 [49]. 이를통해메탄의전환율을제외하고는산소의공급을메탄대비 0.1~0.2 정도로적게유지하고, 이산화탄소 / 메탄비를 0.8~1.0으로유지하였을때, 본반응에적합한평형을기대할수있음을알수있다. 반응의엔탈피를고려해보면, CO 2 :CH 4 :O 2 =0.9:1.0:0.2의비율로공급되고이산화탄소개질반응 (1) 외의추가공급된메탄과산소가메탄연소 반응 (6) 을따른다면평형을이룰때반응에필요한열에너지중대략 1/3을공급해줄수있음을알수있다. 이를통해다양한촉매와공급조성비에대한실제반응전환율자료를축적한다면추가적에너지공급을최소화하는공정을설계할수있음을확인할수있다. 그러나본연구에서목표로하는이산화탄소의환원을통한합성가스로의전환과재활용은필수적으로높은이산화탄소전환율을요구하는데산소의공급은이산화탄소를추가적으로발생하게한다. 산소의첨가는이산화탄소의환원제로서공급되는메탄의산화를통해열을공급하므로메탄의추가적인공급을필요로한다 [48-50]. 이는앞에서살펴본바와같이추가로공급되는산소가메탄을산화하는발열반응을통해열을공급하기때문이다. 직접적으로이산화탄소를추가발생시키는반응 (6) 뿐만아니라 (4),(5) 역시산화된탄소를시스템에공급한다. 하지만강한흡열반응인이산화탄소개질반응에있어서열공급은필수적인데 Tomishige 등이보인바와같이산소의공급은반응기내부에서에너지형태의전환과정없이직접적으로열을공급하여효율적인열공급이가능하게하므로 [51] 단순히산소공급량을최소화하기보다는외부에너지의투입과폐열의활용, 반응평형의변화등반응공정전체에대한분석을통해최적화된값을찾 Fig. 3. Equilibrium analysis of autothermal CO 2 reforming of methane as a function of CH 4 : CO 2 : O 2 feed ratios at 1000 K for: (i) CH 4 conversions (%); (ii) CO 2 conversions (%); (iii) CO yields (%); (iv) H 2 yields (%); (v) H 2 O yields (%); and (vi) H 2 / CO ratios [49]. Fig. 4. Effect of temperature on the heat of reaction (ΔH, Δ) and H 2 / CO ratio [experimental ( ) and equilibrium (dotted line)] during the autothermal CO 2 reforming of methane over a) CoO x /MgO/SA5205 catalyst and b) CoO x /CeO 2 /SA5205 catalyst [7]. 화학공학제 47 권제 3 호 2009 년 6 월

5 메탄의건식개질을이용한이산화탄소의재활용 271 는것이필요하다. Choudhary와 Choudhary는많은반응이동시에일어나는자열개질반응에있어서첨가제에서차이를갖는유사한두촉매 CoO x /MgO/SA-5205[52], CoO x /CeO 2 /SA-5205[53] 사이에서도반응결과물들이반응평형과차이를보이며서로다르게생성되며그에따라알짜반응열도 Fig. 4에서보는바와같이크게변화함을보인바있다 [7]. 이는산소공급량에대한최적화분석에있어서단순한경향성예측뿐만아니라다양한촉매계에대한반응결과의축적이필수적임을보여준다. 따라서다양한반응물공급비와반응온도에따른전환율및소모에너지의변화에대한실험결과의축적과해석을통해공정의경제성과이산화탄소저감량을최적화할수있을것이다. 메탄의산화반응 (4), (5), (6) 중이산화탄소자열개질반응과정에서무엇이주된반응인지에대해서 Wang 등과 [54] Tomishige 등은 [51,55] 반응기내부의급격한온도차이등을근거로메탄연소반응 (6) 이주된반응이라고간주하고있으나복잡한반응메커니즘상이를명확하게규명하지못하였다. Choudhary와 Choudhary 는메탄의부분산화반응 (4) 자체가촉매와온도에따라직접산화와연소생성물과미반응메탄간의반응에의한간접산화로달라진다고주장한바있다 [7]. 한편반응기내부의급격한온도차이는내부의열전달문제로인해야기되며소결을비롯한촉매의성능저하를불러일으킬수있다 [28,54]. O Connor와 Ross[56] 와 Tomishige 등은 [46] 이를실측하여나타낸바있다. 반응기내부에서의직접적이고효율적인열전달을목적으로하는자열개질반응의경우, 이러한반응기내부열전달문제는특히중요하게극복되어야할문제라할수있다. Zheng 등과 [44,47,57-61] Tomishige 등은 [51,62] 이를해결하기위해유동층반응기를도입하여실험하였다. 유동층반응기는반응물유체를고정되어있지않은고체상촉매층아래에서위로불어줌으로써촉매층을유동화하여반응물과촉매의접촉과열전달개선, 촉매의재생등을꾀하는형태의반응기이다 [63]. 특히 Tomishige 등은고정층반응기와유동층반응기의비교연구를통해탄소침적억제와촉매의환원성개선을통한 CH 4 전환율증진에서유동층반응기사용시에개선된효과가있음을보고하였으며그이유로유동화된촉매가산화와환원을반복하며반응하면서촉매층상단과 하단을왕복하는 Fig. 5와같은모델을제시하였다 [55]. 유동층반응기의이같은특징은유사한촉매계를사용한메탄부분산화반응 (4) 와 [64] 메탄의이산화탄소개질반응 (1) 에 [65,66] 대해서도관찰됨이보고된바있다. 촉매연구에있어서현재까지주로연구된촉매계는 Ni[47,57,59, 61,62,67-71], Pt[51,54,56,58,72,73], Co[52,53,74,75], Ir[76] 등을활성점으로다양한담체와첨가제를넣은촉매들이연구되었다. 합성가스생산에주안점을두고연구된이산화탄소개질반응과같이이산화탄소자열개질반응연구역시메탄의전환율을높이거나, 탄소침적저하, 에너지공급저하등에초점이맞추어져왔다 [46-48,55,56,61,62,77]. 이들과뚜렷하게구별할수는없지만합성가스를생산하는다른방법인메탄의부분산화반응 (2) 에대하여과도한발열을막고합성가스조성비를조절하기위한방법으로이산화탄소를추가공급하는연구들역시많이이루어져왔다 [7,28,50,52,71]. 따라서이들연구들은직접적으로이산화탄소의저감에중점이맞추어져있지않으며특히많은양의산소를추가공급하고있는편이다. Zheng 등은활성점인 Ni 입자의크기가반응의활성과안정성에큰영향을미친다고알려진메탄의이산화탄소개질반응과같이이산화탄소자열개질반응에서도 Ni 입자의크기가중요한역할을함을보고한바있다 [47]. 4. 결론이산화탄소배출제재가곧현실화될현시점에서발전, 철강등이산화탄소를대규모로배출하는산업에대해촉매화학적방법을이용한이산화탄소재활용공정중특히상대적으로풍부한천연가스를환원제로사용하여메탄이산화탄소개질반응을통해합성가스를생산하는공정은유력한방안으로여겨진다. 이반응의실제도입을위해서는반응공정의효율과안정성을높이기위하여오랜시간높은활성을보이며탄소침적에저항성있는촉매의개발이요구된다. 또한강한흡열반응인메탄이산화탄소개질반응에대해이산화탄소의추가적인발생을최소화하며에너지를공급하는것역시반드시해결해야할과제인데소량의산소를추가로공급하는자열개질반응을통해직접적으로에너지를공급하고특히반응기내부에서의열전달문제를해결하기위해유동층반응기를사용하는것이적절할것으로보인다. 실제공정개발에있어서는좋은활성과안정성을보이는다양한촉매계에대하여반응물의공급비와반응온도에따른반응생성물과공급에너지등의자료를축적하고이를기존의발전, 철강공정내에서활용할수있는폐열의활용방안과연계하여종합적으로분석하여경제성과이산화탄소배출저감을최적화하는조건을찾는것이타당할것이다. 생산된합성가스의사용처를창출하는것역시해결되어야할중요한과제로반응물공급비조절을통해좀더다양한물질합성에활용하거나기존공정내에서활용할방안을강구할필요가있다. 감 사 Fig. 5. A model of fluidized bed reactor in autothermal CO 2 reforming of methane [55]. 본논문은포항제철주식회사의재정적지원에따라수행되었으며이에감사드립니다. Korean Chem. Eng. Res., Vol. 47, No. 3, June, 2009

6 272 김정묵 류준형 이인범 이재성 참고문헌 1. Kwon, T. H. and Choi, J. Y., Analysis on Recent Green House Gas Emission in Korea, Bank of Korea, Seoul, Korea(2008). 2. IPCC, IPCC Special Report on Carbon Dioxide Capture and Storage. Prepared by Working Group III of the Intergovernmental Panel on Climate Change [Metz, B., O. Davidson, H. C. de Coninck, M. Loos, and L. A. Meyer (eds.)], Cambridge, United Kingdom and New York, NY, USA, p. 442(2005). 3. Song, C., Global Challenges and Strategies for Control, Conversion and Utilization of CO 2 for Sustainable Development Involving Energy, Catalysis, Adsorption and Chemical Processing, Catalysis Today, 115(1-4), 2(2006). 4. Hu, Y. H. and Ruckenstein, E., Binary MgO-Based Solid Solution Catalysts for Methane Conversion to Syngas, Catalysis Reviews, 44(3), 423(2002). 5. Bradford, M. C. J. and Vannice, M. A., CO 2 Reforming of CH 4, Catalysis Reviews, 41(1), 1(1999). 6. Hu, Y. H., Ruckenstein, E., Bruce, C. G. and Helmut, K., Catalytic Conversion of Methane to Synthesis Gas by Partial Oxidation and CO 2 Reforming, Advances in Catalysis, Academic Press, (2004). 7. Choudhary, T. V. and Choudhary, V. R., Energy-Efficient Syngas Production through Catalytic Oxy-Methane Reforming Reactions, Angewandte Chemie International Edition, 47(10), 1828(2008). 8. Yagi, F., Kanai, R., Wakamatsu, S., Kajiyama, R., Suehiro, Y. and Shimura, M., Development of Synthesis Gas Production Catalyst and Process, Catalysis Today, 104(1), 2(2005). 9. Pena, M. A., Gomez, J. P. and Fierro, J. L. G., New Catalytic Routes for Syngas and Hydrogen Production, Applied Catalysis A: General., 144(1-2), 7(1996) Moon, K.-I., Carbon Dioxide Reforming of Methane over Nickelbased Catalyst, Department of Chemical Engineering, Pohang University of Science and Technology, Pohang, 111(1996) Chubb, T. A., Characteristics of CO 2 -CH 4 Reforming-Methanation Cycle Relevant to the Solchem Thermochemical Power System, Solar Energy., 24(4), 341(1980). 14. Rostrup-Nielsen, J. and Trimm, D. L., Mechanisms of Carbon Formation on Nickel-containing Catalysts, Journal of Catalysis, 48(1-3), 155(1977). 15. Hu, Y. H. and Ruckenstein, E., The Characterization of a Highly Effective NiO/MgO Solid Solution Catalyst in the CO 2 Reforming of CH 4, Catalysis Letters, 43(1), 71(1997). 16. Snoeck, J. W., Froment, G. F. and Fowles, M., Filamentous Carbon Formation and Gasification: Thermodynamics, Driving Force, Nucleation, and Steady-State Growth, Journal of Catalysis, 169(1), 240(1997). 17. Ruckenstein, E. and Wang, H. Y., Carbon Deposition and Catalytic Deactivation during CO 2 Reforming of CH 4 over Co/γ-Al 2 O 3 Catalysts, Journal of Catalysis., 205(2), 289(2002). 18. Bychkov, V. Y., Tyulenin, Y. P. and Korchak, V. N., The Mechanism of Methane Reforming with Carbon Dioxide: Comparison of Supported Pt and Ni (Co) Catalysts, Kinetics and Catalysis, 44(3), 353(2003). 19. Sierra Gallego, G., Mondrag, F., Tatibou, J.-M., Barrault, J. and Batiot-Dupeyrat, C., Carbon Dioxide Reforming of Methane over La 2 NiO 4 as Catalyst Precursor-Characterization of Carbon Deposition, Catalysis Today, , 200(2008). 20. Assabumrungrat, S., Laosiripojana, N. and Piroonlerkgul, P., Determination of The Boundary of Carbon Formation for Dry Reforming of Methane in a Solid Oxide Fuel Cell, Journal of Power Sources., 159(2), 1274(2006). 21. Gadalla, A. M. and Bower, B., The Role of Catalyst Support on the Activity of Nickel for Reforming Methane with CO 2, Chemical Engineering Science., 43(11), 3049(1988). 22. Rostrup-Nielsen, J. R., Sulfur-passivated Nickel Catalysts for Carbon-free Steam Reforming of Methane, Journal of Catalysis., 85(1), 31(1984). 23. Rostrup-Nielsen, J. R., Calvin, H. B. and John, B. B., Promotion by Poisoning, Studies in Surface Science and Catalysis, Elsevier, (1991). 24. Duprez, D., DeMicheli, M. C., Marecot, P., Barbier, J., Ferretti, O. A. and Ponzi, E. N., Deactivation of Steam-Reforming Model Catalysts by Coke Formation : I. Kinetics of the Formation of Filamentous Carbon in the Hydrogenolysis of cyclopentane on Ni/Al 2 O 3 Catalysts, Journal of Catalysis., 124(2), 324(1990). 25. Li, L., Liu, B. S., Leung, J. W. H., Au, C. T. and Cheung, A. S. C., CH 4 /CO 2 Reforming over La 2 NiO 4 and 10%NiO/CeO 2 -La 2 O 3 Catalysts under the Condition of Supersonic Jet Expansion via Cavity Ring-down Spectroscopic Analysis, Catalysis Today, 131(1-4), 533(2008). 26. Laosiripojana, N., Chadwick, D. and Assabumrungrat, S., Effect of High Surface Area CeO 2 and Ce-ZrO 2 Supports over Ni Catalyst on CH 4 Reforming with H 2 O in the Presence of O 2, H 2, and CO 2, Chemical Engineering Journal., 138(1-3), 264(2008). 27. Lima, S. M., Assaf, J. M., Pe, M. A. and Fierro, J. L. G., Structural Features of La 1-x Ce x NiO 3 Mixed Oxides and Performance for the Dry Reforming of Methane, Applied Catalysis A: General, 311, 94(2006). 28. Choudhary, V. R., Mondal, K. C. and Mamman, A. S., High- Temperature Stable and Highly Active/selective Supported NiCoMg- CeO x Catalyst Suitable for Autothermal Reforming of Methane to Syngas, Journal of Catalysis, 233(1), 36(2005). 29. Fei, J., Hou, Z., Zheng, X. and Yashima, T., Doped Ni Catalysts for Methane Reforming with CO 2, Catalysis Letters, 98(4), 241 (2004). 30. Bouarab, R., Akdim, O., Auroux, A., Cherifi, O. and Mirodatos, C., Effect of MgO Additive on Catalytic Properties of Co/SiO 2 in the Dry Reforming of Methane, Applied Catalysis A: General, 264(2), 161(2004). 31. Mattos, L. V., Rodino, E., Resasco, D. E., Passos, F. B. and Noronha, F. B., Partial Oxidation and CO 2 Reforming of Methane on Pt/ Al 2 O 3, Pt/ZrO 2, and Pt/Ce-ZrO 2 Catalysts, Fuel Processing Technology., 83(1-3), 147(2003). 32. Seok, S.-H., Choi, S. H., Park, E. D., Han, S. H. and Lee, J. S., Mn-Promoted Ni/Al 2 O 3 Catalysts for Stable Carbon Dioxide Reforming of Methane, Journal of Catalysis, 209(1), 6(2002). 33. Souza, M. M. V. M., Aranda, D. A. G. and Schmal, M., Reforming of Methane with Carbon Dioxide over Pt/ZrO 2 /Al 2 O 3 Catalysts, Journal of Catalysis, 204(2), 498(2001). 34. Xu, Z., Zhen, M., Bi, Y. and Zhen, K., Catalytic Properties of Ni Modified Hexaaluminates LaNi y Al 12-y O 19-δ for CO 2 Reforming of 화학공학제 47 권제 3 호 2009 년 6 월

7 메탄의건식개질을이용한이산화탄소의재활용 273 Methane to Synthesis Gas, Applied Catalysis A: General, 198(1-2), 267(2000). 35. Seok, S.-H., Role of Mn-oxide in Ni/MnO x -Al 2 O 3 Catalysts for Carbon Dioxide Reforming of Methane, Department of chemical engineering, Pohang University of Science and Technology, Pohang, 133(2000). 36. Kaengsilalai, A., Luengnaruemitchai, A., Jitkarnka, S. and Wongkasemjit, S., Potential of Ni Supported on KH Zeolite Catalysts for Carbon Dioxide Reforming of Methane, Journal of Power Sources, 165(1), 347(2007). 37. Ruckenstein, E. and Hu, Y. H., Carbon Dioxide Reforming of Methane over Nickel/Alkaline Earth Metal Oxide Catalysts, Applied Catalysis A: General, 133(1), 149(1995). 38. Ruckenstein, E. and Hang Hu, Y., The Effect of Precursor and Preparation Conditions of MgO on the CO 2 Reforming of CH 4 over NiO/MgO Catalysts, Applied Catalysis A: General, 154(1-2), 185 (1997). 39. Tomishige, K., Yamazaki, O., Chen, Y., Yokoyama, K., Li, X. and Fujimoto, K., Development of Ultra-stable Ni Catalysts for CO 2 Reforming of Methane, Catalysis Today, 45(1-4), 35(1998). 40. Valderrama, G., Kiennemann, A. and Goldwasser, M. R., Dry Reforming of CH 4 over Solid Solutions of LaNi 1-x Co x O 3, Catalysis Today, , 142(2008). 41. Araujo, G. C. d., Lima, S. M. d., Assaf, J. M., Pe, M. A., Fierro, J. L. G. and do Carmo Rangel, M., Catalytic Evaluation of Perovskite-type Oxide LaNi 1-x Ru x O 3 in Methane Dry Reforming, Catalysis Today, , 129(2008). 42. Gallego, G. S., Mondrag, F., Barrault, J., Tatibou, J.-M. and Batiot- Dupeyrat, C., CO 2 Reforming of CH 4 over La-Ni Based Perovskite Precursors, Applied Catalysis A: General 311, 164(2006). 43. Batiot-Dupeyrat, C., Gallego, G. A. S., Mondragon, F., Barrault, J. and Tatibou, J.-M., CO 2 Reforming of Methane over LaNiO 3 as Precursor Material, Catalysis Today, , 474(2005). 44. Guo, J., Lou, H., Zhu, Y. and Zheng, X., La-based Perovskite Precursors Preparation and Its Catalytic Activity for CO 2 Reforming of CH 4, Materials Letters, 57(28), 4450(2003). 45. Hayakawa, T., Suzuki, S., Nakamura, J., Uchijima, T., Hamakawa, S., Suzuki, K., Shishido, T. and Takehira, K., CO 2 Reforming of CH 4 over Ni/Perovskite Catalysts Prepared by Solid Phase Crystallization Method, Applied Catalysis A: General, 183(2), 273(1999). 46. Tomishige, K., Nurunnabi, M., Maruyama, K. and Kunimori, K., Effect of Oxygen Addition to Steam and Dry Reforming of Methane on Bed Temperature Profile over Pt and Ni Catalysts, Fuel Processing Technology, 85(8-10), 1103(2004). 47. Hou, Z., Gao, J., Guo, J., Liang, D., Lou, H. and Zheng, X., Deactivation of Ni Catalysts during Methane Autothermal Reforming with CO 2 and O 2 in a Fluidized-Bed Reactor, Journal of Catalysis, 250(2), 331(2007). 48. Souza, M. M. V. M. and Schmal, M., Autothermal Reforming of Methane over Pt/ZrO 2 /Al 2 O 3 Catalysts, Applied Catalysis A: General, 281(1-2), 19(2005). 49. Amin, N. A. S. and Yaw, T. C., Thermodynamic Equilibrium Analysis of Combined Carbon Dioxide Reforming with Partial Oxidation of Methane to Syngas, International Journal of Hydrogen Energy, 32(12), 1789(2007). 50. Liu, S., Xiong, G., Dong, H. and Yang, W., Effect of Carbon Dioxide on the Reaction Performance of Partial Oxidation of Methane over a LiLaNiO/γ-Al 2 O 3 Catalyst, Applied Catalysis A: General, 202(1), 141(2000). 51. Tomishige, K., Kanazawa, S., Suzuki, K., Asadullah, M., Sato, M., Ikushima, K. and Kunimori, K., Effective Heat Supply from Combustion to Reforming in Methane Reforming with CO 2 and O 2 : Comparison between Ni and Pt Catalysts, Applied Catalysis A: General, 233(1-2), 35(2002). 52. Choudhary, V. R., Mondal, K. C. and Choudhary, T. V., Oxy-CO 2 Reforming of Methane to Syngas over CoO x /MgO/SA-5205 Catalyst, Fuel, 85(17-18), 2484(2006). 53. Choudhary, V. R., Mondal, K. C. and Choudhary, T. V., Oxy-CO 2 Reforming of Methane to Syngas over CoO x /CeO 2 /SA-5205 Catalyst, Energy & Fuels, 20(5), 1753(2006). 54. Wang, W., Stagg-Williams, S. M., Noronha, F. B., Mattos, L. V. and Passos, F. B., Partial Oxidation and Combined Reforming of Methane on Ce-promoted Catalysts, Catalysis Today, 98(4), 553 (2004). 55. Tomishige, K., Matsuo, Y., Yoshinaga, Y., Sekine, Y., Asadullah, M. and Fujimoto, K., Comparative Study Between Fluidized Bed and Fixed Bed Reactors in Methane Reforming Combined with Methane Combustion for the Internal Heat Supply under Pressurized Condition, Applied Catalysis A: General, 223(1-2), 225(2002). 56. O Connor, A. M. and Ross, J. R. H., The Effect of O 2 Addition on the Carbon Dioxide Reforming of Methane over Pt/ZrO 2 Catalysts, Catalysis Today, 46(2-3), 203(1998). 57. Mo, L., Zheng, X., Chen, Y. and Fei, J., Combination of CO 2 Reforming and Partial Oxidation of CH 4 over Ni/Al 2 O 3 Catalysts Using Fluidized Bed Reactor, Reaction Kinetics and Catalysis Letters, 78(2), 233(2003). 58. Mo, L., Fei, J., Huang, C. and Zheng, X., Reforming of Methane with Oxygen and Carbon Dioxide to Produce Syngas over a Novel Pt/CoAl 2 O 4 /Al 2 O 3 Catalyst, Journal of Molecular Catalysis A: Chemical, 193(1-2), 177(2003). 59. Jing, Q., Lou, H., Mo, L., Fei, J. and Zheng, X., Reforming of CH 4 with CO 2 and O 2 to Produce Syngas over CaO Modified Ni/ SiO 2 Catalysts in a Fluidized Bed Reactor, Reaction Kinetics and Catalysis Letters, 83(2), 291(2004). 60. Guo, J., Lou, H., Zhao, H., Chai, D. and Zheng, X., Dry Reforming of Methane over Nickel Catalysts Supported on Magnesium Aluminate Spinels, Applied Catalysis A: General, 273(1-2), 75(2004). 61. Gao, J., Guo, J., Liang, D., Hou, Z., Fei, J. and Zheng, X., Production of Syngas via Autothermal Reforming of Methane in a Fluidized-Bed Reactor over the Combined CeO 2 -ZrO 2 /SiO 2 Supported Ni Catalysts, International Journal of Hydrogen Energy, 33(20), 5493(2008). 62. Matsuo, Y., Yoshinaga, Y., Sekine, Y., Tomishige, K. and Fujimoto, K., Autothermal CO 2 Reforming of Methane over NiO-MgO Solid Solution Catalysts under Pressurized Condition: Effect of Fluidized Bed Reactor and Its Promoting Mechanism, Catalysis Today, 63(2-4), 439(2000). 63. Kunii, D. and Levenspiel, O., Fluidization Engineering, Wiley, New York(1969). 64. Santos, A., Menendez, M., Monz, A., Santamaria, J., Miro, E. E. and Lombardo, E. A., Oxidation of Methane to Synthesis Gas in a Fluidized Bed Reactor Using MgO-Based Catalysts, Journal of Catalysis, 158(1), 83(1996). 65. Effendi, A., Hellgardt, K., Zhang, Z. G. and Yoshida, T., Char- Korean Chem. Eng. Res., Vol. 47, No. 3, June, 2009

8 274 김정묵 류준형 이인범 이재성 acterisation of Carbon Deposits on Ni/SiO 2 in the Reforming of CH 4 -CO 2 Using Fixed- and Fluidised-Bed Reactors, Catalysis Communications, 4(4), 203(2003). 66. Chen, X., Honda, K. and Zhang, Z.-G., A Comprehensive Comparison of CH 4 -CO 2 Reforming Activities of NiO/Al 2 O 3 Catalysts under Fixed- and Fluidized-Bed Operations, Applied Catalysis A: General, 288(1-2), 86(2005). 67. Choudhary, V. R., Rajput, A. M. and Prabhakar, B., Energy Efficient Methane-to-Syngas Conversion with Low H 2 /CO Ratio by Simultaneous Catalytic Reactions of Methane with Carbon Dioxide and Oxygen, Catalysis Letters, 32(3), 391(1995). 68. Choudhary, V. R., Uphade, B. S. and Mamman, A. S., Simultaneous Steam and CO 2 Reforming of Methane to Syngas over NiO/ MgO/SA-5205 in Presence and Absence of Oxygen, Applied Catalysis A: General, 168(1), 33(1998). 69. Ruckenstein, E. and Hu, Y. H., Combination of CO 2 Reforming and Partial Oxidation of Methane over NiO/MgO Solid Solution Catalysts, Industrial & Engineering Chemistry Research, 37(5), 1744(1998). 70. Song, C. and Pan, W., Tri-reforming of Methane: A Novel Concept for Catalytic Production of Industrially Useful Synthesis Gas with Desired H 2 /CO Ratios, Catalysis Today, 98(4), 463(2004). 71. Choudhary, V. R., Mondal, K. C. and Choudhary, T. V., Partial Oxidation of Methane to Syngas with or without Simultaneous Steam or CO 2 Reforming over a High-Temperature Stable-NiCoMg- CeO x Supported on Zirconia-Hafnia Catalyst, Applied Catalysis A: General, 306, 45(2006). 72. Larentis, A. L., de Resende, N. S., Salim, V. M. M. and Pinto, J. C., Modeling and Optimization of the Combined Carbon Dioxide Reforming and Partial Oxidation of Natural Gas, Applied Catalysis A: General, 215(1-2), 211(2001). 73. Souza, M. M. V. M., Macedo Neto, O. I. R. and Schmal, M., Synthesis Gas Production from Natural Gas on Supported Pt Catalysts, Journal of Natural Gas Chemistry, 15(1), 21(2006). 74. Choudhary, V. R. and Mamman, A. S., Simultaneous Oxidative Conversion and CO 2 or Steam Reforming of Methane to Syngas over CoO-NiO-MgO Catalyst, Journal of Chemical Technology & Biotechnology, 73(4), 345(1998). 75. Ruckenstein, E. and Wang, H. Y., Combined Catalytic Partial Oxidation and CO 2 Reforming of Methane over Supported Cobalt Catalysts, Catalysis Letters, 73(2), 99(2001). 76. Ashcroft, A. T., Cheetham, A. K., Green, M. L. H. and Vernon, P. D. F., Partial Oxidation of Methane to Synthesis Gas Using Carbon Dioxide, Nature, 352(6332), 225(1991). 77. Pant, B. and Stagg-Williams, S. M., Investigation of the Stability of Pt/LaCoO 3 during High Temperature Reforming Reactions, Catalysis Communications, 5(6), 305(2004). 화학공학제 47 권제 3 호 2009 년 6 월