Trans. of the Korean Hydrogen and New Energy Society(2016. 12), Vol. 27, No. 6, pp. 702~711 DOI: https://doi.org/10.7316/khnes.2016.27.6.702 ISSN 1738-7264 eissn 2288-7407 이채영 1 ㆍ한선기 2 1 수원대학교토목공학과 하천환경기술연구소, 2 한국방송통신대학교환경보건학과 Production of Biofuels and Biochemicals by Biorefinery CHAE-YOUNG LEE 1, SUN-KEE HAN 2 1 Dept. of Civil Engineering Institute of River Environment Technology, The University of Suwon, 17 Wauan-gil, Hwaseong-si, Gyeonggi-do, Korea 2 Dept. of Environmental Health, Korea National Open University, 86 Daehak-ro, Jongno-gu, Seoul, Korea Abstract >> The authors reviewed information about biorefining of biomass by using academic information databases. Feedstocks were classified into triglycerides biomass, sugar biomass, starchy biomass, lignocellulosic biomass, and organic waste biomass. Biorefinery is an integrated system converting biomass into biofuels and biochemicals by various physical, chemical, biological, and thermochemical technologies. This paper presented a comprehensive summaries of opportunities, recent trends and challenges of biorefinery. A brief overview of promising building blocks, their sources from biomass, and their derivatives were also provided. In conclusion, this paper demonstrated the feasibility of biorefinery producing biofuels and biochemicals from biomass. Key words : Biomass( 바이오매스 ), Biofuels( 바이오연료 ), Biochemicals( 바이오화합물 ), Biorefinery( 바이오리파이너리 ), Building blocks( 중간바이오화합물 ) 1. 서론현대사회는화석연료, 특히석유에크게의존하고있다. 석유가보급됨에따라서연료분야, 소재분야, 화학제품분야등에커다란변화가나타났고, 그로인해우리는석유를떼어놓고는생활을영위할수없을만큼석유와불가분의관계를유지하고있다. 하지만석유는무한한자원이아니다. 우리나라는석유의전량을수입에의존하는취약한사회구조를 Corresponding author : skhan003@knou.ac.kr Received : 2016.10.13 in revised form : 2016.11.7 Accepted : 2016.12.30 Copyright c 2016 KHNES 가지고있으며, 또한전지구적관점에서본다고해도세계자원연구소 (world resource institute) 에의하면석유의수명을향후약 40년정도로예견하고있다 1). 또한석유의사용은지구온난화에따른기후변화를유발하고있다. 우리나라는지구온난화의영향으로지난 40년간남한지표면의기온은약 1.3 C, 해양표층의수온은약 1.0 C 상승하여, 세계에서수온상승이가장빠른곳중의하나가되었다 1). 또한지구온난화에따라지구평균기온이 1880년이후 2012 년까지약 0.85 C 증가했으며, 지구평균해수면은 1901년이후 2010년까지약 19 cm 상승했다. 만약현재와같은추세로온실가스를배출한다면, 21세기 702
703 말에는극심한기후변화로인해수많은지역이물에잠기고많은인류가가뭄과홍수, 혹한, 폭설등의피해를입을것으로전망되고있다 2). 따라서우리는친환경적으로지속가능한사회로의전환을위해서새로운대안이필요한상황이며, 그대안으로바이오매스 (biomass) 가떠오르고있다 3-7). 사용후재생이불가능한석유에비해서바이오매스는일정한시간후재생이가능하다. 그리고거의무한하다고할만큼풍부한자원이며재생되는시간이상대적으로빠른장점이있다. 또한바이오매스를이용하는과정에서이산화탄소가배출될수밖에없지만, 바이오매스가생산되는과정에서광합성을통해이산화탄소를흡수하기때문에탄소중립적인특징이있다 8,9). 따라서이러한바이오매스로부터바이오연료및바이오화합물을생산하는바이오리파이너리 (biorefinery) 에대해서그개념과다양한주요산물, 그리고기술의제한점등을살펴보고자한다. 2. 바이오리파이너리의개념 바이오리파이너리는물리적, 화학적, 생물학적및열화학적기술등을이용하여바이오매스로부터재생가능한바이오연료및바이오화합물등을생산하는것이다 4,6,8,10,11). Fig. 1에바이오리파이너리의개요가잘나타나있다. 바이오매스는광합성에의해서생성되는식물체및미생물균체, 그리고이를섭취해서살아가는동물체를포함한전체생물유기체를의미한다 3,9,12). 다시말하면미생물, 식물, 동물이직접생산한물질은물론이고그로부터유래한모든물질을포함하는것으로, 한마디로정리하면재생가능한모든유기물질이라고할수있다. 그종류를살펴보면, 첫째유지계바이오매스 (triglycerides biomass) 에는유채씨, 대두, 폐식용유, 동물성지방, 해조류등이있고, 둘째당질계바이오매스 (sugar biomass) 에는사탕수수, 사탕무등이있으며, 셋째전분질계바이오매스 (starchy biomass) 에는밀, 보리, 옥수수, 감자등이있고, 넷째목질섬유소계바이오매스 (lignocellulosic biomass) 에는초본, 볏짚, 왕겨, 임목등이있으며, 그리고다섯째유기성폐기물계바이오매스 (organic waste biomass) 에는음식물류폐기물, 하수슬러지, 가축분뇨등이있다 5-7). 기존의오일리파이너리 (oil refinery) 가원유로부터다양한연료와화합물등을통합적으로생산하는것처럼바이오리파이너리도바이오매스로부터다양한바이오연료및바이오화합물등을통합적으로생산한다 10,11). 하지만다음과같은차이점이있다 (Table 1). 첫째, 오일리파이너리는균질한 (homogeneous) 원유를사용하지만, 바이오리파이너리는일반적으로비균질한 (heterogeneous) 바이오매스를이용하여전처리가복잡하고비용이많이소요된다. 둘째, 오일리파이너리의원료인원유는재생이불가능하며이용시이산화탄소를발생시켜지구온난화를유발하지만, 바이오리파이너리의원료인바이오매스는재생이가능하며광합성의결과로서생성되기때문에대기중이산화탄소의농도를증가시키지않아탄소중립적이다. 그리고셋째, 오일리파이너리는휘발유 (gasoline), 등유 (kerosene), 경유 (diesel oil), 중유 (heavy oil) 등과같은연료와함께에틸렌 (ethylene), 프로필렌 (propylene), 부틸렌 (butylene), BTEX (benzene, toluene, ethyl benzene, xylene) 등을화합물로생산하지만, 바이오리파이너리는바이오에탄올 (bioethanol), 바이오부탄올 (biobutanol), 바이오디젤 (biodiesel), 바이오메탄 (biomethane), 바이오수소 (biohydrogen) 등과같은바이오연료와함께숙신산 (succinic acid), 3-HPA(3-hydroxypropionic acid), 레불린산 (levulinic acid), FDCA(furan-2,5-dicarboxylic acid), 글리세롤 (glycerol), 소르비톨 (sorbitol), 자일리톨 (xylitol) 등을바이오화합물로생산한다 10,13). 제 27 권제 6 호 2016 년 12 월
704 이채영ㆍ한선기 Fig. 1 Schematic diagram of biorefinery (adapted from [3]) Table 1 Comparison of oil refinery and biorefinery (adapted from [10]) 3. 바이오리파이너리의주요산물 Feedstock Oil refinery Homogeneous petroleum Biorefinery Heterogeneous biomass 3.1 화학적전환으로생산되는바이오연료 Fuel Compound Gasoline, kerosene, diesel oil, heavy oil, etc. Ethylene, propylene, butylene, BTEX (benzene, toluene, ethyl benzene, xylene), etc. Bioethanol, biobutanol, biodiesel, biomethane, biohydrogen, etc. Succinic acid, 3-HPA, levulinic acid, FDCA, glycerol, sorbitol, xylitol, etc. 바이오디젤은산, 염기또는효소촉매하에서자연에존재하는각종동식물성기름을메탄올과함께에스테르교환반응 (transesterification) 을시켜서생산되는액체연료이다. 보통반응속도가빠른염기촉매를가장많이이용한다. 동식물성기름인트리글리세 >> 한국수소및신에너지학회논문집
705 리드 (triglyceride) 의 1몰은염기촉매하에서 3몰의메탄올과반응하여 3몰의지방산메틸에스테르 (fatty acid methyl ester) 와 1몰의글리세롤을만들어내는데, 여기에서지방산메틸에스테르가경유와성질이유사한바이오디젤이다 10,14). 바이오디젤은기존연료보급시설을활용하여운반및판매가가능하고, 기존디젤엔진을그대로사용하며, 경유보다인화점이높아불이잘붙지않고, 경유와달리생분해가가능하며, 독성이없고, 연소시대기오염물질의배출이크게저감된다 3,4,14). 한편, 부산물인글리세롤은계면활성제, 화장품, 의약품, 감미제, 식품제조용첨가제등으로재활용될수있다 12). 그리고생촉매하에서글리세롤로부터생산되는글리세롤카보네이트 (glycerol carbonate) 와 3-HPA는각각의학 산업용용제와아크릴수지용중간체로활용될수있어바이오디젤생산비용을 15% 이상절감할수있다 15). 3.2 생물학적전환으로생산되는바이오연료바이오에탄올은당질계바이오매스로부터당액을추출한후, 알코올발효 (alcohol fermentation) 를시켜서생산되는액체연료이다. 그리고전분질계바이오매스를이용하는경우에는당화 (saccharification) 를통해서, 목질섬유소계바이오매스를이용하는경우에는전처리후당화를통해서바이오매스내탄수화물을포도당및환원당으로전환시킨다음, 알코올발효를시켜서생산해내는액체연료이다 12). 여기에서당화는산이나효소를이용하여탄수화물을포도당및환원당으로가수분해하는것이다. 산은묽은산이나농축된산이이용되며, 효소는전분 (starch) 에대해서는아밀라아제 (amylase), 셀룰로오스 (cellulose) 에대해서는셀룰라아제 (cellulase), 헤미셀룰로오스 (hemicellulose) 에대해서는자일라나아제 (xylanase) 가이용된다. 알코올발효는산소가없는상태에서효모 (Saccharomyces cerevisiae) 나세균 (Zymomonas mobilis) 과같은미생물을이용하여포도당및환원당을바이오에탄올로전환시키는것이다 3). 바이오에탄올은가스홀 (gashol), ETBE(ethyl tertiary butyl ether), 수화에탄올등으로사용될수있다. 가스홀은휘발유 (90%) 와바이오에탄올 (10%) 의혼합물이며, ETBE는바이오에탄올과석유가스등을혼합한친환경연료첨가제이고, 수화에탄올은바이오에탄올 (95%) 과물 (5%) 의혼합물이다. 그리고바이오에탄올은기존연료보급시설을그대로활용하며, 증발잠열및옥탄가가높고, 엔진효율이높으며, 공연비 (air/fuel ratio) 가낮고, 연소시대기오염물질의배출이크게저감된다 5). 바이오부탄올은탄수화물 ( 포도당, 녹말등 ) 의 ABE 발효 (acetone-butanol-ethanol fermentation) 를통해서생산되는액체연료이다. 세균 (Clostridium acetobutylicum) 을이용하여포도당, 녹말등으로부터바이오아세톤, 바이오부탄올, 바이오에탄올이각각 3:6:1의비율로생산되는데, 기본반응은알코올발효와비슷하다 12). 가장많은양 (60%) 이생산되는바이오부탄올은바이오에탄올보다더나은성능의액체연료이다. 바이오부탄올은에너지밀도가높고, 비식용바이오매스를이용하며, 휘발유와유사하여기존연료보급시설을활용하여운반및판매가가능하고, 기존가솔린엔진을그대로사용하며, 휘발유에혼합이잘되고, 휘발유와혼합사용시연비손실이적으며, 물의존재시상분리가발생하지않고, 연소시대기오염물질의배출이크게저감된다 8). 한편, 같이생산되는바이오아세톤은용제로, 바이오에탄올은액체연료로사용된다. 바이오메탄은각종바이오매스의메탄발효를통해서얻어지는기체연료이다. 중온조건에서유기물이가수분해 (hydrolysis), 산생성 (acidogenesis), 초산생성 (acetogenesis) 및메탄생성 (methanogenesis) 의혐기성분해과정을거치면서최종적으로바이오메탄이생산된다 16). 가수분해는복합유기물질 ( 탄수화물, 지방, 단백질등 ) 이단순유기물질 ( 포도당, 지방산, 아미노산등 ) 로전환이되는것이고, 산생성은단순유기 제 27 권제 6 호 2016 년 12 월
706 이채영ㆍ한선기 물질이다양한유기산 (volatile fatty acids) 으로전환이되는것이며, 초산생성은다양한유기산이초산 (acetic acid) 과수소로전환이되는것이고, 메탄생성은초산과수소가메탄가스로전환이되는것이다. 초산생성균은수소소비메탄생성균과공생관계에있는데, 초산생성균이선호하는낮은수소분압이수소를이용하여메탄을생성하는수소소비메탄생성균에의해서이루어진다 17). 메탄발효는산소의공급이필요없어운전비용이저렴하고, 메탄가스를회수하여대체에너지로이용할수있으며, 세포수율이낮아슬러지발생량이상대적으로적고, 고농도유기성폐기물을처리할수있는장점이있다 18). 바이오수소는각종바이오매스의혐기성수소발효를통해서얻어지는기체연료이다. 열처리 (90 100 C, 10분이상 ) 를통해서선별된수소발효균 (Clostridium butyricum) 이중온및최적 ph(4.5 5.5) 의조건에서유기물로부터바이오수소를생산한다 19). 혐기성수소발효는광합성수소발효와비교시, 반응속도가빠르고, 반응조가작고간단하며, 태양광이필요치않고, 산소에의한제한이없으며, 유기성폐자원을처리함과동시에바이오수소를생산할수있다 20). 다만, 바이오수소와함께유기산이생성되기때문에, 이에대한후처리가필요하다. 후처리방법에는다음과같은방법이있다. 첫째, 앞서설명한메탄발효를이용하여유기산으로부터추가적으로바이오메탄을생산할수있다. 둘째, 미생물연료전지 (microbial fuel cell, MFC) 를이용하여유기산으로부터추가적으로전기를생산할수있다. MFC는전기화학적활성을지닌혐기성미생물의촉매작용을이용하여유기물에함유된화학에너지를직접전기에너지로전환시키는것이다. 그리고셋째, 미생물전해전지 (microbial electrolysis cell, MEC) 를이용하여유기산으로부터추가적으로수소를생산할수있다. MEC는 MFC의구조및운전방법을간단히변형함으로써전기대신높은수율의수소를얻는것이다. 즉, 환원전극에대한산소공급을중단하고전기회로에약간의전압을공급하면환원전극으로부터수소가생산된다 21). 3.3 물리적전환으로생산되는바이오연료 바이오고형연료제품 (biomass-solid refuse fuel, BIO- SRF) 은바이오매스를파쇄, 선별, 건조및성형등의과정을거쳐생산되는고체연료이다. 성형을거치면그크기가직경 5 cm 이하및길이 10 cm 이하로유지되며 ( 성형을거치지않으면그크기가가로 12 cm 이하및세로 12 cm 이하로유지 ), 수분은 10%( 중량비 ) 이하로유지되고, 저위발열량은제조고형연료제품인경우에는최소 3,000 kcal/kg 이상 ( 수입고형연료제품인경우에는최소 3,150 kcal/kg 이상 ) 으로유지된다. 코르크나펠릿형태로제작돼전용발전소, 산업용보일러등에서다양하게이용된다. BIO-SRF 에는폐지류, 농업폐기물, 폐목재류 ( 침목, 전신주제외 ), 식물성잔재물 ( 음식물류폐기물제외 ), 초본류폐기물등이포함된다 22). 3.4 열화학적전환으로생산되는바이오연료및바이오화합물 직접연소는바이오매스를직접태우는것이다. 이때발생하는열을바로이용하거나또는그열로수증기를만들어터빈을돌림으로써전기를생산할수있다. 열분해는무산소이거나저산소인상태에서바이오매스를가열하여고체, 액체및기체연료를생산하는것이다. 저온열분해 ( 약 500 900 C) 에서는고체및액체연료가많이생성되며, 고온열분해 ( 약 1,100 1,500 C) 에서는기체연료가많이생성된다 18). 직접액화는목질계바이오매스를분쇄나탈수한후, 알칼리금속염촉매하에서고온및고압으로반응을시켜액체연료를생산하는것이다 3). >> 한국수소및신에너지학회논문집
707 직접가스화는고온에서바이오매스에공기, 산소, 수증기등의가스화제를단독또는서로배합하여작용시켜수소, 일산화탄소, 메탄등을주성분으로하는합성가스를얻는것이다 3,23). 가스화를통한간접액화는가스화를통해서얻어진합성가스를이용하여메탄올, 합성가솔린등을생산하는것이다. 메탄올은 Cu-Zn 혼합금속촉매를이용하여기체상고온, 고압의조건에서합성가스로부터생산이된다. 합성가솔린은 F-T(Fischer-Tropsch) 와 MTG(methanol to gasoline) 법등이있다. F-T법은 Fe, Co, Ru 등의촉매를사용하여고온, 고압의조건에서합성가스로부터합성가솔린이만들어지고, MTG법은합성가스로부터메탄올을합성한후제올라이트촉매하고온, 고압의조건에서메탄올로부터 합성가솔린이만들어진다 3,10,23). 3.5 생물학적또는화학적전환으로생산되는바이오화합물 미국에너지부 (Department of Energy) 의에너지효율및재생에너지국 (Energy Efficiency and Renewable Energy Office) 에서 2004년에발간한 Top Value Added Chemicals from Biomass-Volume 1 을보면바이오매스로부터다양한화학제품이생산될수있음을알수있다 12,13). Table 2에서보는바와같이바이오매스원료 ( 전분, 셀룰로오스, 헤미셀룰로오스 ) 의당화를통해포도당, 과당 (fructose), 자일로오스 (xylose), 아라비노오스 (arabinose), 젖당 (lactose), 자당 (sucrose) 을얻 Table 2 Top 12 building blocks produced from biomass by biorefinery and their derivatives (adapted from [13]) Biomass feedstocks Intermediate platforms Building blocks Derivatives Glycerol Glyceric acid, glycidol, 1,3-propanediol, propylene glycol, glycerol carbonate, propanol, diglyceraldehyde, mono-, di-, or triglycerate, branched polyesters and nylons etc. 3-hydroxypropionic acid 1,3-propanediol, acrylic acid, methyl acrylate, malonic acid, acrylamide, propiolactone, acrylonitrile etc. Starch Cellulose Glucose Fructose Xylose Arabinose 1,4-diacids (succinic, fumaric and malic acids) 3-hydroxybutyrolactone Aspartic acid Itaconic acid Levulinic acid g-butyrolactone, 1,4-butanediol, succindiamide, tetrahydrofuran, 1,4-diaminobutane, 2-pyrrolidone, succinonitrile, 4,4-bionolle etc. 3-hydroxytetrahydrofuran, g-butenyl-lactone, 3-aminotetrahydrofuran, epoxy-lactone, 2-amino-3-hydroxy tetrahydrofuran, acrylate-lactone etc. 3-aminotetrahydrofuran, amino- -butyrolactone, 2-amino-1,4-butanediol, aspartic anhydride, amino-2-pyrrolidone etc. 2-methyl-1,4-butanediamine, itaconic diamide, 3-methylpyrrolidine etc. g-valerolactone, angelilactones, acrylic acid, 1,4-pentanediol, levulinate esters, d-aminolevulinate, b-acetylacrylic acid, diphenolic acid etc. Hemicellulose Lactose Sucrose Glutamic acid Xylitol /arabinitol Glucaric acid Glutaminol, glutaric acid, norvoline, 1,5-pentandiol, 5-amino-1-butanol, pyroglutaminol, proline, prolinol, pyroglutamic acid, polyglutamic acid etc. Xylaric acid, propylene glycol, ethylene glycol, glycerol, lactic acid, mixture of hydroxy furans etc. Glucaro- -lactone, glucaro- -lactone, glucarodilactone, polyhydroxypolyamides, -ketoglucarates etc. Sorbitol Isosorbide, propylene glycol, 1,4-sorbitan, lactic acid, 2,5-anhydrosugars, ethylene glycol, glycerol etc. Furan-2,5- dicarboxylic acid 2,5-furandicarbaldehyde, 2,5-dihydroxymethyl furan, 2,5-bis(aminomethyl)-tetrahydrofuran, succinic acid, 2,5-dihydroxymethyl tetrahydrofuran etc. 제 27 권제 6 호 2016 년 12 월
708 이채영ㆍ한선기 Table 3 New top 14 building blocks produced from biomass by biorefinery and their evaluated results against criteria 24) Compound Extensive recent literature Multiple product applicability Direct substitute High volume product Platform potential Industrial scaleup Existing commercial product Primary building block Commercial biobased product Ethanol +++ a +++ +++ +++ +++ +++ +++ +++ +++ Furfural +++ ++ b + c ++ + + +++ ++ +++ HMF +++ ++ + + ++ + + ++ + FDCA +++ + + +++ ++ + + + + Glycerol/ derivatives +++ +++ +++ +++ +++ +++ +++ +++ +++ Isoprene +++ ++ +++ +++ + +++ +++ + + Biohydrocarbons +++ ++ +++ + + + + ++ + Lactic acid +++ +++ + +++ ++ + ++ + + Succinic acid +++ +++ + + +++ +++ + + + 3-HPA +++ + +++ +++ ++ + + + + Levulinic acid +++ ++ +++ ++ +++ +++ + +++ + Sorbitol +++ +++ +++ +++ +++ +++ +++ +++ +++ Xylitol +++ +++ + + +++ + ++ +++ ++ a Good performance against criterion; b emerging performance against criterion; c lower performance against criterion. 은후, 이러한당류의생물학적또는화학적전환을통해다양한고부가가치의중간바이오화합물 (building blocks) 을생산한다. 이중에서선정된 12개의유망한중간바이오화합물에는글리세롤, 3-HPA, 1,4-diacids ( 숙신산, 푸마르산 (fumaric acid), 말산 (malic acid)), 3-히드록시부티로락톤 (3-hydroxybutyrolactone), 아스파르트산 (aspartic acid), 이타콘산 (itaconic acid), 레불린산, 글루타민산 (glutamic acid), 자일리톨 / 아라비니톨 (arabinitol), 글루카르산 (glucaric acid), 소르비톨, FDCA가있다. 예를들어, 글리세롤의경우에는글리세린산 (glyceric acid), 글리시돌 (glycidol), 1,3-프로판디올 (1,3-propanediol), 프로필렌글리콜 (propylene glycol), 글리세롤카보네이트, 프로판올 (propanol), 디글리세르알데히드 (diglyceraldehyde), 모노-, 디-, 또는트리글리세르산염 (mono-, di-, or triglycerate), 가지형폴리에스테르및나일론 (branched polyesters and nylons) 등을유도체로생산한다. 그리고 2004년에발표된 12개의유망한중간바이오화합물은그후 2010년에그동안의기술발전을고려하여 9개의평가기준을거친다음 Table 3과같이 14개로갱신되었다,12,24). 새롭게선정된 14개의유망한중간바이오화합물에는에탄올, 푸르푸랄 (furfural), HMF(hydroxymethylfurfural), FDCA, 글리세롤 / 유도체, 이소프렌 (isoprene), 바이오탄화수소 (biohydrocarbons), 젖산 (lactic acid), 숙신산, 3-HPA, 레불린산, 소르비톨, 자일리톨이해당된다. 예를들어, 에탄올의경우에는 9개평가기준모두에대해서좋은평가결과를보여주었다. Table 4는갱신된 14개의유망한중간바이오화합물에대하여향후필요한기술적사항을보여주고있다 24). 예를들어, 에탄올의경우에는선택적알코올탈수기술, 바이오매스를이용한향상된생화학적알코올생산기술, 그리고대사공학을이용한최적발효균주의개발기술등이필요하다. >> 한국수소및신에너지학회논문집
709 Table 4 Technology needs for new top 14 building blocks produced from biomass by biorefinery 24) Compound Ethanol Furans (furfural, HMF, and FDCA) Glycerol and derivatives Biohydrocarbons (isoprene and other biohydrocarbons) Lactic acid Succinic acid Hydroxypropionic acid/aldehyde Levulinic acid Sorbitol Xylitol General biorefinery technology needs - Selective alcohol dehydrations - Improved biochemical production of alcohols from biomass (rate, yield, titer, product, ph, inhibitor tolerance) - Engineering of optimal fermentation organisms - Selective dehydrations of carbohydrates - New catalysts and reaction media for dehydration - Reactive separations - Selective oxidations of alcohols; improved oxidation and dehydration catalysts - Catalytic systems for reactions in aqueous solution - Reactions in aqueous solution - Selective reductions and oxidations of polyols - Improved biological conversions of polyols - Improved biohydrocarbon production - Engineering of organisms to convert sugars to hydrocarbons - Optimizing rate, yield, titer, product tolerance - Optimization of bioconversion of carbohydrates - Bioprocesses with high rate, yield, titer, product, ph and inhibitor tolerance - Engineering of organisms to produce single materials - Bioconversion of carbohydrates - Optimization of yield, rate, titer, separation - Engineering of organisms for optimal production of target - Optimization of bioconversion of carbohydrates - Bioprocesses with high rate, yield, titer, product and inhibitor tolerance - Engineering of organisms to produce single materials - Selective dehydrations of alcohols - Selective reductions of carbonyl groups - New selective hydrogenation catalysts - Chemical processes in aqueous solution - Selective dehydrations of carbohydrates - Improved separations of products - Utility of co-product schemes by biorefinery - Improved catalysts for selective carbohydrate conversion processes - Selective hydrogenolysis of polyols - New catalysts for reduction of carbohydrate derivatives - Selective dehydrations of polyols - Comparative assessment of chemical and biochemical conversion technology - Selective bond breaking/bond making technology for polyols - Selective hydrogenolysis of polyols - New catalysts for reduction of carbohydrate derivatives - Selective dehydrations of polyols - Comparative assessment of chemical and biochemical conversion technology - Selective bond breaking/bond making technology for polyols 4. 바이오리파이너리의제한점 바이오리파이너리는무한한가능성을가지고있지만, 아직까지는초기단계라고할수있다. 따라서다음과같은제한점을극복해야만상업화단계로진입할수있다. 첫째, 바이오리파이너리는미생물발효공정및효소 화학적전환공정이주로사용되기때문에무엇보다도기질로부터바이오연료및바이오화합물을생산하는생물학적및화학적전환경로가최대한명확히규명되어야한다 8). 둘째, 원료물질인바이오매스는원유에비해가격 제 27 권제 6 호 2016 년 12 월
710 이채영ㆍ한선기 이저렴하지만, 바이오매스를바이오연료및바이오화합물등으로전환할때소요되는비용은원유를이용할때보다고가이다. 따라서전환비용의감소를위해물리적, 화학적, 생물학적및열화학적전환기술의효율향상및최적화를위한연구개발이지속적으로필요하다. 또한기존의오일리파이너리시설을그대로바이오리파이너리에이용하는시설의호환성이중요하다. 이렇게하면자본집약적인고가의시설비용을들이지않을수있다 12). 더불어부산물의효과적인재활용도비용을감소시키는데필요하다. 셋째, 식용바이오매스를바이오리파이너리의원료로이용하면식량가격의상승을가져오기때문에, 비식용바이오매스인농업폐기물, 산림폐기물, 도시고형폐기물등을효과적으로이용하는것이필요하다 9,25). 다만, 목질계바이오매스의전처리시여러가지물리 화학적방법들이복합적으로사용되는데, 이과정에서발효의저해물질들이생성될수있다. 따라서발효효율을최대화하면서저해물질의발생을최소화하는전처리과정의효율향상및최적화가필요하다. 그리고전처리에서얻어진셀룰로오스와헤미셀룰로오스의당화에는셀룰라아제와자일라나아제라는효소가사용되는데고율의효소를저렴하게대량생산하는것과이를효율적으로이용하는공정개발이필요하다 10). 넷째, 대사공학, 시스템생물공학및합성생물학을이용함으로써고율균주의개발, 균주의안정성개선, 핵심효소의개량, 배양의최적화, 전환공정의수율향상, 생산물에대한미생물의내성향상, 그리고균주에대한맞춤식대량생산등이필요하다 8). 더불어대사산물의분리및정제가보다용이하게이루어지도록하는것도필요하다 10). 다섯째, 대규모의중앙집중형통합바이오리파이너리시설은바이오매스발생원으로부터멀리떨어져있기때문에수집및운반비가많이소요된다 12). 따라서소규모의분산형바이오리파이너리시설을 발생원가까이에설치함으로써수집및운반비를감소시킬수있다. 5. 결론 우리사회는앞으로도수십년간석유에의존할것이다. 그러나석유의고갈이그리멀지않았고석유의사용으로인한지구온난화로인해서이에대한대비가필요하기때문에, 그대안으로서바이오리파이너리가전세계적인관심을받고있다. 하지만바이오리파이너리의많은기술들은초기개발단계에머무르고있어서정부의지속적인투자와산학연의끊임없는기술개발이매우중요하다. 그리고향후석유기반의산업구조는바이오매스기반의산업구조로대체될것이며, 이에있어서바이오리파이너리는핵심적인역할을수행할것이다. References 1. Ministry of Environment, White paper of environment, Ministry of Environment, Seoul, Republic of Korea, 2016. 2. Intergovernmental Panel on Climate Change (IPCC) Working Group I contribution to the IPCC Fifth Assessment Report (WGI AR5), Climate Change 2013: The Physical Science Basis, WMO & UNEP, 2013. 3. S.-P. Lee, H. M. Kang and D. W. Park, Biomass, Korea Institute of Science and Technology Information, Daejeon, Republic of Korea, 2002. 4. J.-H. Jo, Foreign status and policy implications of biorefinery, Environmental Forum, Vol, 15, No. 6, 2011, pp. 1-8. 5. J.-H. Jo and H.-S. Lee, A preliminary study for environmentally-friendly application of biofuel using marine biomass, Korea Environment Institute, Seoul, Republic of Korea, 2011. 6. R. Parajuli, T. Dalgaard, U. Jørgensen, A. P. S. >> 한국수소및신에너지학회논문집
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