3.3.11Oligomerizationoflightolefinstodiesel/gasoline o 올레핀의올리고머화는에틸렌, 프로필렌, 부틸렌을올리고머화하여가솔린이나디젤을생산하는공정으로제올라이트나다양한고체산촉매를이용하여가솔린이나디젤뿐만아니라윤활유, 합성수지, 염료, 세정제및첨가제등의다양한석유화학제품을생산하는매우중요한공정이다. o 고체산촉매를이용한올레핀의올리고머화는촉매가고체담체에활성의감소없이지지될수있다면많은장점을가지는반면에올리고머화조절하는촉매시스템이적합하지않다면원하는생성물의형성에대한선택도가낮아진다는단점이있다. 또한일반적으로사용되는촉매들이산을사용하기에부식의문제가발생한다는것이다. o 특히올레핀의올리고머화반응에있어많은연구가진행되고있는제올라이트의경우에는기공의형태, 크기, 구조등이선택도에많은영향을주며반응조건 ( 온도, 압력, 공간속도등 ) 등에의해결정되므로이에대한개선및새로운촉매의개발이필요하다. 또한적절한장치디자인과촉매의비활성화에대한연구, 편리한공정및반응생성물에대한개선이이루어져야한다. o 현재국내에서는가솔린이나디젤생산을위한올리고머화기술은거의연구되고있지않으며차후외국의기술을도입할경우에는촉매성능및공정전반에관한데이터가축적될수없기때문에기술개발이더디어질수밖에없다. 따라서국가적인에너지수급문제및석유화학인프라를위하여기술개발은매우중요하며국가적차원에서의체계적인지원이필요하다. o 기술의개요 *F-T 합성으로제조되는탄화수소는유황분과방향족을함유하지않기때문에환경적으로깨끗한연료로주목되어최근기술개발과경제성이매우향상되고있다. 특히액체연료이외에부생되는알파올레핀과왁스등은화학공업의원료로사용되어그경제성이크게향상되었으며, 천연가스를원료로하여부가가치가높은화학제품의제조도포함하는액체연료제조프로젝트들이기업을중심으로계속진행되고있다.
* 촉매의특성과운전조건등에관계없이 FT 합성은항상광범위한올레핀들, 파라핀들과산소가들어있는물질, 즉알코올, 알디하이드, 산및케톤류등을생산한다. 이생성물질의분포에영향을주는변수들로는온도, 원료가스의조성, 압력, 촉매의형태와촉진제등이있다. * 올레핀의올리고머화는약 70 년전부터시작되어왔으며대부분의경우 산촉매 (acid catalyst) 를이용하여합성수지, 염료, 세정제및첨가제뿐만 아니라가솔린, 디젤, 윤활유등을생산하는매우중요한공정이다. o 올레핀의올리고머화반응 *Propylene 과 butylene 의올리고머화는 1930 년에인산을이용하여가솔린범위의이소올레핀 (C 6 -C 10 ) 을생산하는공정에처음산업적으로도입되었다. 그러나 ethylene 과 propene 는인산을포함하는산촉매를사용하였지만부식에대한문제로인하여인산을포함하는산촉매대신 zeolite 와같은다른산촉매를이용하는방법에대해논의되었다. * 이후 zeolite 촉매의기공구조의조절에의해생성물의선택도를조절하는공정이개발되었으며 ZMS-5 류의 zeolite 를사용하는 MOGD(Mobil olefin togasolineand distilate) 공정에의해저분자올레핀을고분자가솔린이나디젤로전환하는공정이나타났다. * 올레핀의올리고머화는주로산촉매의존재하에진행되는데제올라이트 를사용하는경우가대부분이며여러가지금속이온, 인산, 니켈을포함 하는촉매도사용되고있다. * 사슬의성장은반응분자의수에의존하게되며 n=2 일경우 dimerization, 2<n<100 일경우 oligomerization, n>100 일때 polymerization 이라한다.Oligomerization 은 propagation( 사슬성장 ) 과 elimination( 수소제거 ) 의두단계로이루어지며단일반응이아니라여러가지반응이동시에진행하게된다.Oligomers,aromatics,coke 및 saturates 등이얻어질수있는데이는 cracking, isomerization, dehydrocyclization,methyl 및 hydrogeltransfer 의발생을의미한다.
다음은 oligomerization 반응을간단히나타낸 [ 그림 58] 이다. [ 그림 13] 올레핀의올리고머화반응모식도 o Ethyleneoligomerization * 에틸렌의올리고머화에서가장중요한생성물은알파올레핀으로수십년간선형올레핀의생산에기여해왔다. 알파올레핀의생산은 trialkyl ammonium(chevron and Ethyl) 과 nickelcomplex(shel) 의균일촉매하에서진행되어왔으며불균일반응에서의생성물이더다양하다. * 불균일반응촉매로는제올라이트, 고체산, 니켈담지촉매로구분될수있다.Lightolefin 은 gasoline 및 lubeoil-range 생성물뿐만아니라고분자량 distilate fuel 을생성하며이는반응조건과촉매의구조에영향을받는다. * 에틸렌의경우다른 lightolefin 에비해상대적으로낮은반응성을갖으며특히 C 2 -C 5 hydrocarbon 의혼합물일경우낮은반응성을극복하기위해다양한조건과방법들이시도되어왔다. 즉다양한온도, 압력, 촉매를사용하는다단반응시스템이연구되었다. * 제올라이트를사용한에틸렌의연료및윤활유로의제조는많은연구가 되어왔다. 에틸렌의올리고머화는제올라이트의성질과산성점의수에 관련되어있다. * 일반적으로 ZSM-5 촉매를이용한에틸렌의올리고머화속도는다른올 레핀에비해느리고더높은온도에서반응하게된다. 프로필렌및부틸
렌등의전환율이약 50-90% 정도인것에비해에틸렌의전환율은 10-30% 정도이다. * 에틸렌올리고머화에서촉매의성능은제올라이트의외부나내부의표면산점에관련되어있다. 또한프로필렌올리고머화에서 ZSM-5 의촉매의성질은결정크기에관련되어있으며결정의크기는 Si/Al 의비율과관련되고 Si/Al 이감소하면올레핀의올리고머화는증가하게된다. * 촉매의수명은 coke 의생성비율에의존하게되며외부표면적보다는내부 에서발생하게되고이는외부표면적이촉매의수명을좌우하게된다. * Ni-exchanged NaY-zeolite 는낮은온도에서의에틸렌올리고머화에서 diesel-rangehydrocarbon 을생성한다. * 가솔린및디젤생산을위한에틸렌올리고머화에대한연구를아래표 에정리하였다.
< 표 12>Ethyleneoligomerization Year Catalysts Reactioncondition/remarks Products Ref. 1994 ZSM-5of SiO 2/Al 2O 3=25, OH/SiO 2=0.2-0.3, H2O/SiO2=50, (TPaBr)/SiO 2=0.01-0.1, smal crystal size (30-50nm) large externalsurface area 400,0.1MPa,C 2H 4/N 2=50/50 the external surface area was 3 times greater than that of other zeolites, which indicates that the lifetimeofzeolitein oligomerization dependsontheexternalsurfacearea or crystal size; consequently the coke selectivity was low on the zeolite with large external surface area Gasoline-range hydrocarbons 1 1993 P r i m a r y oligomerization over a surfacedeactivated (by a stericaly h i n d e r e d trialkylpyridine), medium pore zeolite (ZSM-5 or ZSM-23) and second oligomerization over a supported group VI(B) metal, SiO 2-supported reducedcroxide Multistepprocess:WHSV 0.21, 6.21 MPa,200,resulting in 91% propylene conversion and yielding 78.6% product:lubricating oil54.1, dieselfuel20.5andkerosene/jetfuel 15.0wt% Lubricating oil(bp >343,viscosity 50 cstat100 ) andhighcetane number (cetane no. 50-75 after hydrogenation) fuels(bp 177-343 ) 2 1993 ZSM-5 of medium pore size,e.g.5-7a and having a SiO2/Al2O3 ratio of about 20:1orgreater Fluidizedbed,WHSV >0.1, 0.14-1.5 MPa,342-482,suficient for concurent oligomerization of light olefins while cracking n-parafins C5+ gasoline and dewaxed distilate 3 1991 amorphoussio 2-Al 2O 3 Ion-exchanged catalystis beter for (Si/Al=72 : 1), etheneoligomerization todieselfuel, impregnated or C 10+ fraction in product was 41% ion-exchanged with vs.23% forimpregnatedcatalyst Ni 1991 HZSM-5 Fluidized catalyst bed, 5.5 MPa, 300-650,conversion50wt% Dieselfuel 4 Fuel, C 5-C 10 5 hydrocarbons
< 표 12>( 계속 ) Year Catalysts Reactioncondition/remarks Products Ref. 1990 ZSM-5 with a SiO 2/Al 2O 3 molarratio of70:1 Multi-stage reactor:firstreactor for contactingfeed with amedium pore shape-selective zeolite catalyst for converting the C3-olefinicsto liquid hydrocarbons comprising C 5+, in second stage the process conditions should be efective to convert a majoramountofethene C 5+gasoline 6 1989 An innercore portion, e.g.zsm-5 orzsm-23, and an outer portion comprising a fluoride-containing crystalshel 1988 ZSM-5 3, 7.8 wt% WO3 on SiO2 1,and MgO 3 partsbyweight Reaction time 5 h under oligomerization conditions >99 % C 2H 4 conversion and 67-75 % selectivity 1988 Ni-exchanged ZSM-5 WHSV1,1.83MPa,376,7.5days, 89.0 wt% conversion,the selectivity toc5fraction82.3wt% 1988 Ni-exchanged zeolitey (10-40%) 3.5MPa,at100-150 orat300-330, at low temperature the oligomerization proceeds by a selective growth reaction,26% C 10+ product,athigh temperature,about 300, a purely acidcatalysed oligomerization High viscosity lubricating oils, and gasoline 7 C 5+gasoline 8 Gasoline with octane no. (R+O) 93.1 Diesel-range products 1985 ZSM-5 Fourfixed bed reactors Gasoline and jet fuels 1984 ZSM-5 Fixed-bed, staged oligomerization; zeolites partialy deactivated in a primary stage are used before regeneration in asecondary stageat hightemperature 1984 ZSM-5 type medium pore zeolites, with a SiO 2/Al 2O 3 molarratio of 70 and extruded with35% alumin 1) In distilate mode (fixed bed, WHSV 0.5-1,4-10 MPa,190-310 ; (2) in gasoline mode (0.4-3 MPa, 285-385 ) 9 10 11 Gasoline 12 (1) 80 % of the 13 product was distilate fuels C 11-C 20 with a cetane number a f t e r hydrogenation of over 50; (2) C 5+ olefinic gasoline withoctaneno.92
*Propeneoligomerization * 프로필의올리고머화는윤활유뿐만아니라 C 5 + 가솔린과디젤을생성하는반응이다. 이들생성물은같은촉매를사용하더라도반응조건에따라다양한생성물을얻을수있다. * 가솔린 (C 5 -C 10 ) 은높은온도와적당한압력 ( 상압에서 5.5 MPa 까지 ) 에서 얻을수있으며적당한온도와상대적으로높은압력에서는 C 20 + aliphatic 생성물을얻을수있다. * 현재까지 ZSM-5 가 lightolefin 을고분자량의 distilatefuel 이나 gasoline 으로전환시키는데가장우수한물질로평가되고있으며 MOGD 공정에 적용된이후최적화되어왔다. * 높은압력에서의프로필렌의올리고머화에다른형태의 zeolite(zsm-5, boralite,ofretite,hy,mordenite,omega) 는액체생성물의선택도에관련된.WHSV 가 1이고 4.8MPa 에서 silica-alumina 의비가 78 인 ZSM-5 는 300 이하에서는낮은활성을나타낸다. 그러나비슷한조건에서 boralite 는더높은활성을나타내며,H-omega 와 H-ofretite 는반응온도가 200 에서 350 로,150 에서 250 로증가함에따라활성이증가하는것으로나타났다. *HZSM-5 와같은 shape-selectiveacidiczeolite 의올리고머화는두가지가있는데하나의반응은채널내부의 brønsted acid site 에서일어나서 linearmaterial 을생성하는것이고다른하나의반응은외부표면에서발생하여 morebranched material 을생성한다는것이다. 이것은제올라이트의외부표면산점을감소시킴에따라 methylbranching 의감소가일어나고결과적으로높은점도와높은 cetane number 를갖는생성물을만들어낸다. * 프로판의올리고머화에서 ZSM-5 의 Si-Al 의비는결정크기에큰영향을 미치는데그최적조건은약 20 정도이며이조건에서우수한촉매수명 과활성을나타낸다.
*ZSM-5 이외에도다양한제올라이크들이프로필렌의올리고머화에사용되었으며 HZSM-5, ZSM-22, ZSM-23, ZSM-35, HZSM-22, MCM-22, MCM-49 등과이들의표면산도를개선한제올라이트가사용되었다. * C 2 -C 4 alkene 의올리고머화에 NiSO 4 /γ-al 2 O 3 가많이사용되어왔다. WOx/ZrO 2 촉매는높은수율의디젤과윤활유를생성한다. * 가솔린및디젤생산을위한프로필렌올리고머화에대한연구를아래 < 표 65> 에정리하였다. *C 2 -C 4 올레핀은가장중요한화학물질로서 C 4 올레핀의올리고머화는액 체연료나윤활유를생산하는매우유용한방법이다. * 제올라이트가여러가지목적을위해 butene 의올리고머화에사용되어 왔으며, 올리고머화에대한촉매의성능은촉매제조, 전처리, 그리고반 응조건에따라매우다양하게변화한다. * 가솔린및디젤생산을위한부틸렌올리고머화에대한연구를 < 표 66> 에정리하였다.
< 표 13>Propyleneoligomerization Year Catalysts Reactioncondition/remarks Products Ref. 1997 ZrO2-supported WO 3 using impregnation and co-precipitation methods Fixed-bed tubular reactor,7 mlh -1, 2.76 MPa, 160 ; the conversion was 94.4 and 69.8 % for co-precipitated and impregnated catalyst,respectively For co-precipitated 14 catalyst,thec 5+ distributionwas29.5 gasoline,61.6 diesel and 8.9% lube;for im pregnated catalyst, the C 5+ distributionwas38.5 gasoline, 56 diesel and 5.5% lube 1995 (1) Fe-silicate, with a GHSV of1000-5000,290,tubular Gasoline synthesis 15 Si/Fe atomic ratio of reactor from lightolefins 100; (2) Pt/H-Fe-silicate for oligomerization and hydrogenation (0.01 wt% Pt) 1995 A m o r p h o u s WHSV: 4 g propene/g active micro/mesoporous phase/h,3.8 MPa,120-180,and silica-alumina gel reactiontimeabout240h having surface area of 500m 2 g -1 with amolar ratio of SiO 2/Al 2O 3 30:1 1993 Medium pore, WHSV about1,6mpa,130-250 shape-selectivezeolite 1991 Silica-alumina co-gel dispersed in alumina matrix 1989 Mixtureofpilared clay (e.g., bentonite) and WO3SiO2 Gasoline and jet fuel Gasoline and diesel hydrocarbons Gasoline and diesel fuel The catalyst was more active for C 5+ hydrocarbons 19 conversion of C 3H 6 to liquid fuel (liquid fuel) than a mixture of unpilared clay andwo 3/SiO 2 1988 Ni-exchanged pilared 10.03MPa,150 for24h Liquid product 20 silicotitanate (surface gasoline, containing area 299 m 2 g -1, C 616.6, C 956.7, C 12 containing TiO 2 70.2, 17.7, C156.7, C182, SiO2 21.7,and Na 3.3 and C 210.4wt% wt%) 16 17 18
< 표 13>( 계속 ) Year Catalysts Reaction condition/remarks Products Ref. 1986 ZSM-5zeolite,HZSM-5 of 1.22 wt% alumina, ZSM-5 poisoned with a large excess of hexamethyldisilazane in orderto replacethe acidicsurfacehydroxyl groups by trimethylsiloxylgroups, addition 4-methylquinoline of to the feed supposed to neutralizethesitesdue to alumina atexternal Fixed bed, 2.4 MPa, 189-359. Low temperature gives dimer, trimer, tetramer, etc. without shapeselectivity;reaction occurson the externalsurface ofthe zeolite ratherthan within the channel.at higher temperature the external surface is poisoned and shape-selectivityisapparent 4.2-10.4MPa,205-290 Dieselfuel 21 surfaceofzeolite 1986 HZSM-5 3 catalyst beds, 0.6-1 VHSV, C 9-10 fraction with 1986 ZSM-5 Oligomerization conditions as function of temperature, pressure and spacevelocity10.4mpa,110 1985 ZSM-5 Approx.5.8MPa,315,conversion 1983 Al2O3-free silicate molecularsieve 1983 CZM or zeolite impregnated with Cd about95% bp165-290, dieselfueland/or jetaircraftfuels Gasoline (C 5-10), anddiesel(c 10-20) Gasoline dieselfuels and Oligomerizationconditions Liquid fuel-range products Oligomerizationconditions Liquid fuel-range products and/ orzn 1981 Zeolites Oligomerizationconditions Liquidfuel 27 1979 SiO 2 -A l 2 O 3 or 1.4MPa,100-300 Hydraulic fluids, fluorinatedsio 2-Al 2O 3 gasolinewithhigh 1970 Mixture of SiO2 and polyphosphoricacid *Buteneoligomerization octaneno.,and jet fuels or white spiritypesolvent Gasoline highoctaneno. with 22 23 24 25 26 28 29
< 표 14>Buteneoligomerization Year Catalysts Reactioncondition/remarks Products Ref. 1996 HZSM-5 impregnated Oligomerizationconditions diesel fuel and 30 withcrsalts lubricantoil 1985 AcidicAl2O 3 0.1MPa,310 15.4 wt% C 5+ 31 fraction(at84.8% conversion) and motor octane no. 94 and 81, respectively 1996 A novelzeolite NESKO process Diesel,solvent,and lubeoil 32 1994 Zeolites Catalytic distilation reactor system, Gasoline, diesel 33 temperaturerangefrom ca.150 to fuel,solvents,and approx.350 dependingoncatalyst lubricantstock type 1992 Halogen-stabilized silicalite,orazeolite Oligomerizationconditions Gasoline with high octaneno. 34 1992 Large pore size WHSV 1, 3.45 MPa, 96 and For propylene 35 metalosilicate structure conversion 84wt% propylene, the WHSV 0.25, 3.45 of MCM-41with same conditions except WHSV 0.25 MPa,96,C 6=2, uniformly distributed conversion >98 wt%. Increasing C 9=43,C 12 =34, honeycomb pores in temperature results in high MW C 15 =12, C 18= 5, the100-200a range product, increasing pressure causes and C 21 =3 wt%, increase in activity and a shift in C 9 and C 12 selectivity to lower MWproducts, hydrogenated to improved activity compared with provide clean ZSM-5 and ZSM-23 also provide gasoline and diesel higher C 9 and C 12 for propylene fuel. oligomerization 1977 Zeolite 288-482 Gasoline with a 36 good octaneno.
o 국내외기술동향 가. 국내기술동향 * 국내의경우 GTL 이나 FT 반응에대한연구들은계속수행되어왔으나 FT 반응부산물의활용, 특히올레핀을가솔린이나디젤로전환하는연구는다른선진국에비해거의전무한실정이며, 단지알파올레핀에대한연구가한국화학연구원, 엘지환경연구원, 경희대등에서연구가수행되어지고있다. 나. 국외기술동향 *FT 공정은남아프리카공화국의 Sasol 공장은가장먼저가동된곳으로 1 단계로석탄으로부터합성가스를얻고있다. 현재상업적으로가동중 인곳은 Sasol,Mossgas,Shel 등이있다. *GTL 에집중하고있는기업중에서보유기술및자금력을바탕으로현 재 Sasol,Shel,ExxonMobil 의 3 개사가주도적인위치를차지하면서우 위를점하고있으며,ConocoPhilips 가그뒤를따르고있다. *Lightolefin 으로부터 gasoline,diesel,distilateproducts 를얻는공정은 ExxonMobile 을중심으로진행되고있으며새로운촉매의개발및제조 공정최적화를중심으로수행되고있다. *Isomerization,hydrogentransfer/cyclizaiton 과같은올레핀의산촉매반응들은중간크기의기공을가지는 zeolite 를사용함으로써상용화되어 MOGD (Mobil's olefin to Gasoline and Distilate process) 와 MOG (Mobil'solefintoGasolineprocess) 같은공정들이 1990 년이후로진행되었으며,MOGD 는 lightolefin 을전환하는가장안전하고환경친화적인공정으로인식되고있다. * 현재 MOGD 공정의경우원유에비해경제성은떨어지지만현재와같 이원유의가격이높거나향후원유의생산량이감소할경우에는상대적 으로경제적으로우위에설수있다.