煤液化技术

Chemical Engineering Science65(2010)12--17Contents lists available at ScienceDirect Chemical Engineering Science journal homepage:w w w.e l s e v i e r.c o m/l o c a t e/c esCoal liquefaction technologies—Development in China and challenges in chemical reaction engineeringZhenyu Liu a,∗,Shidong Shi b,Yongwang Li ca State Key Laboratory of Chemical Recourse Engineering,Beijing University of Chemical Technology,Box35,15BeiSanhuan East Road,Beijing100029,PR Chinab China Coal Research Institute,5Qingniangou Road,Beijing100013,PR Chinac State Key Laboratory of Coal Conversion,Institute of Coal Chemistry,Chinese Academy of Sciences,Taiyuan030001,PR ChinaA R T I C L E I N F O AB S T R AC TArticle history:Received16October2008Received in revised form10May2009 Accepted12May2009Available online18May2009Keywords:Reaction engineeringCatalysisEnergyFuelDirect coal liquefactionIndirect coal liquefactionFTS With fast increasing demand in liquid transportation fuels,limited and unevenly distributed petroleum resources,and volatile petroleum prices,coal liquefaction technologies have again received the world's attention since the beginning of this century.China has actively pursued R&D of coal liquefaction tech-nologies in the past decade and is deploying the first and the largest direct coal liquefaction plant since WWII and the largest indirect coal liquefaction plants after Sasol,South Africa.This paper analyzes the historical developments of coal liquefaction technologies from science point of view,presents recent de-velopments of the technologies in China,and identifies challenges of the technologies towards successful industrial application.©2009Elsevier Ltd.All rights reserved.1.IntroductionCoal liquefaction,termed coal to liquid or CTL frequently nowadays,refers to conversion of solid coal into liquid fuels and chemicals.Its main objectives are breaking down of the coal's molec-ular structure and addition of hydrogen(Dadyburjor and Liu,2004). These have been realized mainly through two routes,one is direct hydrogenation of coal,commonly termed direct coal liquefaction or DCL,and the other is breakdown of coal structure into the smallest building blocks,CO and H2,through gasification followed by reac-tions of CO and H2to synthesize liquid products,commonly termed indirect coal liquefaction or ICL.Both routes require reactions at elevated temperatures and pressures in the presence of catalysts.2.History and technological advancementsIt is generally recognized that coal liquefaction technologies were invented in the early20th century in Germany,DCL by Friedrich Bergius at1913that led to a Nobel Prize in chemistry in1931,and ICL by Franz Fischer and Hans Tropsch at1923that was termed also as F–T synthesis or FTS(Dadyburjor and Liu,2004;Schulz,1999).∗Corresponding author.Tel./fax:+861064421073.E-mail address:liuzy@(Z.Liu).0009-2509/$-see front matter©2009Elsevier Ltd.All rights reserved.doi:10.1016/j.ces.2009.05.014Since then,coal liquefaction technologies underwent various stages of development determined mainly by the availability of petroleum. The first fast development period was before and during World War II(WWII)in Germany,UK,France,and Japan due to urgent needs of liquid transportation fuels.The peak production capacities in Ger-many alone reached4.23Mt/y for DCL and0.59Mt/y for FTS.The DCL process was operated at around470◦C and70MPa with iron catalysts initially,while FTS at100–400◦C and0.1–0.2MPa over cobalt catalysts and5–100MPa over supported ruthenium catalysts (Dadyburjor and Liu,2004).The discovery of inexpensive petroleum in Mid-East in1950s ceased essentially all the coal liquefaction developments in the world except that in South Africa due to its unavailability of petroleum.This led to the greatest developments and successes in FTS in South Africa as is still being witnessed today with operation of Sasol plants and annual productions of5Mt transportation fuels and2.6Mt chemicals. The early technology was based on the developments in Germany and US.The development of Sasol FTS technology since then can be reviewed in terms of its product strategy.The earlier technology (Sasol I)produced mainly fuels with limited chemicals due to strate-gic considerations.Since mid1970s the production orientated more to chemicals(Sasol II and III),which led to significant improvements in plant economy.Starting from this century,the technology was further advanced and characterized by higher product flexibility, direct production of chemicals and lower separation costs(Gibson, 2007).This evolution was made possible by advancements inZ.Liu et al./Chemical Engineering Science 65(2010)12--1713T e c h n i c a l l e v e lFig.1.Developments of Sasol technology.05000100001500020000250001950YearR e a c t o r C a p a c i t y , b b l /d196019701980199020002010Fig.2.FTS reactor developments at Sasol (Geertsema,2005).reactor and catalysts as indicated in Fig.1.The development in reac-tor was from fixed-bed Arge reactors to slurry phase SSBR reactors,and from circulating fluidized-bed Synthol reactors to fix-fluidized-bed SAS reactors.The reactor capacity increased from 700bbl/d in 1985for an Arge reactor to 17000bbl/d in 2001for a SSBR reactor,and from 8000bbl/d in 1987for a Synthol reactor to 20000bbl/d in 1995for a SAS reactor as shown in Fig.2(Geertsema,2005).Different from the continued and systematic developments in FTS in South Africa,interests in DCL resumed in 1970s in many countries such as US,Germany,Japan,UK and former USSR due to high petroleum prices.Since then many processes were developed as shown in Table 1.The technology advanced significantly as in-dicated by decreases in pressure,from 70MPa to about 20MPa,increases in oil yield,from 44%of SRC-II to 58%of IGOR and NEDOL and to more than 60%of CTSL (Dadyburjor and Liu,2004)and Shen-hua,and decreases in cost,from an equivalent crude price of $50/bbl in 1970s to about $35/bbl in mid 1990s (Coal:Energy for the Future,1995).The developments,however,were discontinuous and none of the processes went to commercial production except Shenhua.It is important to note that with many processes been invented and tested in many countries in this period,the DCL processes were imprecisely categorized.Some processes contained one or two coal-to-liquid steps and were termed accordingly as single-stage or two-stage liquefaction process,respectively.But some other pro-cesses included a primary liquid product upgrading step (partially for hydrogenation of recycle solvent)in addition to a coal-to-liquid step and were termed also two-stage liquefaction process (Coal Liquefaction,1999).In principle,to produce market acceptable liquid fuels many hydrogenation steps are needed to upgrade the primary DCL liquids but these hydrogenation steps,however,should not be included in general in a DCL process.Therefore,a precise definition of a DCL process considers only the processing steps forTable 1DCL technologies developed since1970s (Dadyburjor and Liu,2004;Li,2006).Country Process Capacity (t /d )Time U.S.SCRI 61974SRCI/II 50/251974–1981EDS 2501979–1983H-Coal 6001979–1982CTSL 21985–1992HTI 31990sGermanyIGOR +2001981–1987PYROSOL61977–1988JapanBCL 501986–1990NEDOL 1501996–1998UK LSE 2.51983–1995USSR CT-571986–1990ChinaShenhua 62002–Shenhua 30002004–T e c h n i c a l l e v e lFig.3.Developments of DCL technology (Note:HP stands for high pressure).hydrogenation of coal (solid),i.e.an N -stage DCL process refers to hydrogenation of coal (solid)consecutively at N different conditions.It is recognized that DCL mechanisms are very complex and not yet known entirely.The prevailing understanding is that DCL con-sists of two fundamental and consecutive reactions,cracking of coal structure to generate free radical fragments and capping or hydro-genation of the free radical fragments into products,although the products may crack further and then be hydrogenated again.Bal-ance of these two reactions governs the performance of a DCL pro-cess.Insufficient hydrogenation of the free radical fragments would result in retrograde reactions between the free radical fragments,which lead to formation of solid coke,a group of products chemi-cally more stable than coal.Clearly,for high oil yields the coal struc-ture should be fully cracked and the free radical fragments gener-ated should be fully hydrogenated.The developments of DCL tech-nology can be viewed along this line as attempts to balance or match these two fundamental reactions.These attempts can be character-ized into three phases as shown in Fig.3.The first phase was before 1950during which the free radical fragment generation and hydro-genation reactions were conducted in a single reactor (single stage)under extremely severe conditions (especially at high H 2pressures,noted as HP in the figure)to ensure a high hydrogenation capability.The second phase was between 1970s and 1990s.Although the two reactions were still carried out in one reactor (single stage)but the conditions used were much milder,due to the use of hydrogenated recycle solvents as in EDS,IGOR +,LSE,BCL and NEDOL,and the use of active catalysts as in H-Coal.14Z.Liu et al./Chemical Engineering Science 65(2010)12--17The unique feature of the third phase is to disassemble the free radical fragments generation step in two consecutive reactors,first at a low temperature and then at a high temperature (two stage),as in CTSL in late 1980s,HTI in 1990s,and Shenhua in 2000s.This sim-ple modification significantly reduced peak rates of free radical frag-ments generation,increased hydrogenation efficiency under milder conditions,and increased oil yields to about 70%even in the ab-sence of recycle solvent hydrogenation as in HTI.The oil quality was also improved as indicated by lower S and N contents and higher H contents.The development of DCL technology can also be viewed with respect to catalysts development,from micron-size iron oxides and sulfides,as in the earlier technologies and in IGOR +and NEDOL,to Co and Ni supported on alumina in H-Coal and CTSL,and then to the nano sized and disposable iron in HTI and Shenhua.This trend not only increased DCL efficiency at reduced costs but also results in advancement in DCL reactor,from bubble columns in the early days to ebullated-bed reactors in CTSL,HTI and Shenhua.3.Development and current status of coal liquefaction technologies in ChinaChina is a fast developing country with limited petroleum re-serves.Since 2000its dependence on imported petroleum became significant as indicated in Fig.4.It consumed 346Mt petroleum with 46%been imported in 2007,and is expected to need 450–610Mt petroleum per year with 60–70%been imported in 2020.Produc-tion of transportation fuels from coal has been an important option to lessen the deficiency in petroleum supply (Fletcher et al.,2004;Nolan et al.,2004;Zhao and Gallagher,2007).3.1.Development and current status of DCL in ChinaChina's DCL research started in late 1970s.The emphases were on evaluation of Chinese coals and understanding of DCL boratory reactors of various scales were used,including two 0.1t(coal)/d bench scale continues units built at China Coal Research Institute (CCRI)in 1980s based on IGOR and NEDOL processes.Since 2000,Shenhua Group,the largest coal company in China,devel-oped a two stage DCL scheme and a catalyst with support from CCRI.The scheme was fully tested in a 0.1t(coal)/d bench scale DCL unit (BSU)and a 6t(coal)/d process development unit (PDU).200050100150200250300350P e t r o l e u m , M tYear2001200220032004200520062007Fig.4.Annual petroleum consumption inChina.Fig. 5.Construction of a Shenhua DCL plant (1Mt/y)at Inner Mongolia in 2008(Sun,2008).The catalyst preparation technique was evaluated at a 0.2t/d catalyst preparation PDU.These developments led to an ambitious plan to build industrial scale DCL plants with a total capacity of 3Mt(oil)/y in 2010s.By the end of 2008,construction of the first production line with a capacity of 1Mt(oil)/y was completed in Inner Mongolia (Fig.5),which will produce 778600t/y of ultra-clean and low sul-fur diesel fuel,229800t/y of naphtha and 101800t/y of LPG.This is the only industrial DCL plant in the world since WWII.The charac-teristics of the Shenhua process include:(1)two ebullated reactors in series operated at around 455◦C;(2)nano-size iron catalyst pre-pared from Fe(SO 4);(3)hydrogenated recycle solvent for a higher hydrogen donor capability.Fundamental researches were carried out with supports mainly from Chinese government to support the fast developments in DCL.Topics cover essentially all aspects of DCL technology (Shu,2003),including process development (Shi et al.,2003;Zhang et al.,2004;Shu et al.,2006),catalysts (Yang et al.,2002;Zhang et al.,2002;Zhu et al.,2000,2001;Guo et al.,2000;Wang et al.,1999;Liu et al.,2001;Shu et al.,2003)and kinetics (Chen and Guo,2006),reaction engineering and reactor design (Mao et al.,2005)and simulation (Yang and Mao,2005;Wang et al.,2006a ),rheological properties of slurry (Chang et al.,2005;Wang et al.,2006b ;Li et al.,2006;Zhang et al.,2006a ;Zhu et al.,2006),products upgrading and utilization (Li et al.,2008;Cui et al.,2002,2003;Chu et al.,2006),process and plant optimization,and waste treatments.3.2.Development and current status of FTS in ChinaChina had FTS plants as early as in 1940s.During 1950s and early 1960s it had 74FTS units based on BASF's Co catalyst and fixed bed reactors (Li,2006).The annual production was 0.47Mt liquids in 1959(Gao and Zhang,2004)before the discovery of Daqing oil field.In late 1970s China restarted FTS research at the Institute of Coal Chemistry (ICC),Chinese Academy of Science (CAS)with emphases on fused iron catalysts and fixed-bed reactors in 1979–1987and precipitated iron and fixed-bed reactors in 1986–1993.The largest unit was 50bbl/d (Li,2006).ICC/CAS switched research to the slurry phase technology in 1995and had successfully operated a 750t/y slurry phase unit using iron catalysts since 2001(Fig.6).In 2003a Chinese coal company,Yankuang Group,built a 4500t/y FTS facility using also iron catalysts and a slurry reactor.Fundamental researches were also carried out especially at ICC/CAS,including low temperature and high temperature iron catalysts (Zhang et al.,2006b ;Yang et al.,2004,2005;Liu et al.,2008;Chang et al.,2007)and cobalt catalysts (Zhou et al.,2006,2008;Liu et al.,2007;Ma et al.,2004;Zhang et al.,2003,2005;Xiong et al.,2005),reaction mechanisms and kinetics (Teng et al.,2006;Yang et al.,2003),hydrodynamics and reactor designZ.Liu et al./Chemical Engineering Science65(2010)12--1715Fig.6.A750t/y FTS unit at ICC/CAS.Table2Coal liquefaction R&D in China.Types Affiliation Capacity(t/d)Time LocationDCL(oncoal ba-sis)CCRI0.11980s–BeijingShenhua62003(2004a)ShanghaiShenhua60002004(2008a)In.MongoliaF–T(on oilbasis)ICC61980s–ShanxiICC 2.52000–ShanxiYankuang152003–ShandongYitai/ICC5002006(2008a)In.MongoliaLu'an/ICC5002006(2008a)ShanxiDCL Shenhua150002010s In.Mongolia Planned capacity and estimated construction years(on oil basis)F–T Yankuang30002008b ShannxiShenhua/Sasol11000×22016Shannxi/NingxiaShenhua/Shell100002012NingxiaYitai/ICC150002014In.MongoliaLu'an/ICC160002014ShanxiYankuang150002013Shannxia Year in parentheses:operation date.b Estimated construction date.(Wang et al.,2003),product separation and upgrading,process-ing simulation and system integration and optimization.The most notable work was systematic and closely correlated researches on catalysis,mechanism and kinetics,which combined experimental evaluation with advanced instrumental characterization and quan-tum chemistry computation(Wen et al.,2006;Cao et al.,2005a,b; Huo et al.,2007).Based on these developments two160000t/y demonstration plants have been completed at Yitai Group in Inner Mongolia and Lu'an Group in Shanxi through joint venture with Synfuels China and ICC/CAS.Both of the plants use low temperature FTS iron catalysts and are scheduled in operation at the end of2008.Many Chinese coal companies are also active in acquiring FTS technologies,including Yankuang Group,who planned to build a 1Mt/y plant in Shannxi province,and Shenhua Group,who planned to use Sasol and Shell technologies to build three plants with a ca-pacity of3Mt/y each in2010s,as well as Yitai Group and Lu'an Group,each of them planned to built a5Mt/y plant in2010s.These activities are listed in Table2.3.3.Development on CO2sequestrationCO2sequestration has been a major concern in application of coal liquefaction technologies because in a typical coal liquefaction process,about50%carbon in coal is released in the form of CO2. However,it is important to note that this CO2is generated from the gasification or H2making unit and is of high purity,more than98% pure in some cases.To utilize this capture ready CO2,China started CO2sequestration projects with support from the government and foreign countries,including US/DOE(Sun,2008),European Union and international companies such as Shell.The researches include enhanced oil recovery,deep saline water storage and deep coal seam storage.Due to the availability of a huge amount of pure CO2from coal liquefaction plants,these researches may turn into the largest CO2sequestration demonstration project in the world in the near term(Sun,2008).4.Chemical reaction engineering challenges in coal liquefactionAs discussed earlier,DCL and FTS technologies have undergone significant advancement in the past.However,DCL is still immature with little chemical reaction engineering data available in the litera-ture and challenges in almost every aspect of the process.Although FTS is mature and has been successfully practice at industrial scale for50y at Sasol very limited chemical reaction engineering in-formation can be found in the open literature.Furthermore,with increasingly stringent specifications for transportation fuels and environmental requirements for waste management and CO2se-questration,new chemical reaction engineering challenges emerge and need to be addressed also.Low thermal efficiency,about45–55%,has been a major argu-ment of those who oppose practice of coal liquefaction techniques. Since DCL and FTS are all exothermic reactions and the reaction heat released corresponds to about20%of the heat of combustion of the product,reaction temperature control and optimal used of the reac-tion heat are the major challenges in chemical reaction engineering to all coal liquefaction processes.Improvements on this subject re-quire knowledge and advancements in catalysis,reaction kinetics, reactor design,and system modeling and optimization.Coal gasification is a key common unit in all coal liquefaction pro-cesses,for synthesis gas preparation in FTS and H2making in DCL. Pressurized gasifiers with a large throughput and suitable product composition are important for higher thermal efficiency of coal liq-uefaction processes.4.1.Challenges in DCLOne of the major challenges in an industrial DCL process is that the newer technologies,although much more advanced than that of 1940s,have not been demonstrated at large scales,detailed chemical reactions information in the three-phase(gas–liquid–solid)system are not yet known entirely,and the reliability of the key equipments designed today is not confirmed by long-time operations.One ex-ample which had caused suspicion on reliability of a large scale DCL plant is mixing of gas–liquid–solid three-phase system in a large di-ameter slurry phase reactor,poor mixing may result in insufficient hydrogenation of free radical fragments,which leads to coking,as well as sedimentation of solid particles in the reactor.A slurry phase circulating pump was proposed to be installed at the reactor bottom to enforce slurry circulation.However,there has not been such a large scale pump operated at around450◦C and20MPa for a long pe-riod of time.Flow patterns,concentration distributions of coal,cata-lyst and hydrogen,as well as reaction rates of free radical fragments generation and hydrogenation are practically unknown entirely re-gardless the presence or absence of the slurry pump.The lack of this16Z.Liu et al./Chemical Engineering Science65(2010)12--17information made design of the reactor as well as the slurry pre-heater and the high temperature product separator difficult tasks.Reaction mechanism and kinetics are major challenges in DCL also.The present knowledge is superficial with no relation to the molecular structure of coal,little consideration on fundamental steps of hydrogenation or hydrogen-donating and the role of the catalyst. The kinetic models are oversimplified,which has no ability to predict reaction behaviors of other coals and under other conditions.The aromatic nature of DCL products may be another challenge. Although it can be upgraded to meet all the current specifications for transportation fuels,it might be difficult to keep up with the increas-ingly stringent specifications in future at an acceptable cost.Better control of DCL reactions and novel products upgrading techniques are much needed.In summary challenges in DCL technology may include(Coal liquefaction—A research and development needs assessment,1989):•Identify coal structures and structural changes during heating in slurry and correlate them with behaviors of free radical fragments generation.•Design better catalysts for coal liquefaction and product upgrading, especially for feeds of high aromatic and nitrogen contents.•Identify catalysis,mechanism and kinetics for hydrogenation of free radical fragments of coal especially on control of retrograde reactions,as well as the role of H-donor/transfer.•Understand the complex reaction and transport behaviors in three-phase systems.•Design and model high throughput liquefaction reactor and slurry preheaters.•Improve product separation technique especially for liquid–solid separation and for chemical production.•Develop residue processing routes for value added products.•Perform system integration for less utility demands and higher overall efficiency.4.2.Challenges in FTSMuch of the research and process developments in FTS since 1990s were aimed at matching the synthesis conditions with mod-ern coal gasifiers such as those developed by Texaco and Shell,which produce synthesis gases of low H2/CO ratios.While the gasification being a major cost in FTS,gas separation units are the major cost within a gasification process,especially oxygen making,CO2sepa-ration and H2separation units.To directly use the syngas produced from the new gasifiers slurry reactors and iron catalysts were used, separation of the catalysts from the slurry medium,therefore,had been an important challenge,which relates to sizing and chemical and physical stability of the catalyst,properties and hydrodynamics of the slurry medium,and design of the reactor.FTS produces a wide range of products,including light hydrocar-bon gases,paraffinic waxes,and oxygenates.Further processing of these products is crucial for quality diesel and gasoline fractions,and for value added chemicals.In summary challenges and improvements required in FTS may include:•Match FTS reactors with large gasifiers.•Develop efficient and low cost syngas cleaning techniques,and gas separation techniques for O2,H2and CO2.•Engineer catalysts of high activity and low selectivity to CH4and coke at higher temperatures for higher productivity and better energy recovery.•Design high throughput reactors with better energy recovery and catalyst separation.•Identify and model the slurry reactor with detailed reaction kinetics,hydrodynamics and transport phenomena.•Develop better catalysts for heavy product processing and chem-ical production.•Study system integration for less utility usage and higher thermal efficiency and integration for polygeneration.5.Concluding remarksCoal liquefaction technologies have advanced significantly since 1970s and are reviving in respond to volatile oil supply and fast demand for liquid transportation fuels.DCL technology is not yet mature entirely with limited scientific and engineering informa-tion in many aspects.Although ICL is considered mature limited information in chemical reaction engineering is available in the liter-ature.Due to special circumstances China is actively practicing large scale coal liquefaction technologies with support of fundamental and applied researches.These will lead to accumulation of valuable ex-perience and reliable data,identification of new problems in science and engineering,advancement of the technologies,and promotion of China's capability on research and development.The generation of large amounts of pure CO2in coal liquefaction processes will pro-mote CO2sequestration research and lead to large scale demonstra-tions in China.AcknowledgmentsThe supports from National Science Foundation of China (20821004and20625620)and the Ministry of Science and Technol-ogy(2004CB217600)are acknowledged.ReferencesCao,D.,Zhang,F.,Li,Y.,Wang,J.,Jiao,H.,2005a.Density functional theory study of hydrogen adsorption on Fe5C2(001),Fe5C2(110),and Fe5C2(100)D.J.Phys.Chem.B109,833–844.Cao,D.,Zhang,F.,Li,Y.,Wang,J.,Jiao,H.,2005b.Structures and energies of co-adsorbed CO and H2on Fe5C2(001),Fe5C2(110),and Fe5C2(100).J.Phys.Chem.B109,10922–10935.Chang,H.,Han,W.,Zhang,D.,Gao,J.,2005.Study on swelling kinetics of Shenhua coal in some organic solvents.Coal Convers.(Chinese)28,25–28.Chang,J.,Bai,L.,Teng,B.,Zhang,R.,Yang,J.,Xu,Y.,Xiang,H.,Li,Y.,2007.Kinetic modeling of Fischer–Tropsch synthesis over Fe–Cu–K–SiO2catalyst in slurry phase reactor.Chem.Eng.Sci.62,4983–4991.Chen,H.,Guo,Z.,2006.Study on hydroliquefaction behavior and rules of Shendong coal macerals.Coal Convers.(Chinese)29,9–12.Chu,X.,Li,W.,Li, B.,Chen,H.,Bai,Z.,2006.Gasification characteristics of coal liquefaction residue with carbon dioxide.J.Fuel Chem.Technol.34,146–150. Coal:Energy for the Future,mittee on the Strategic Assessment of the US Department of Energies Coal Program,Nation Research Council,pp.102. Coal liquefaction—A research and development needs assessment,1989.DOE/ER-0400,February.Coal liquefaction,1999.Technology Status Report010,Department of Trade and Industry,UK,DTI/Pub Urn99/1120,October /ent/coal .Cui,H.,Yang,J.,Liu,Z.,Bi,J.,2002.Effects of remained catalysts and enriched coal minerals on devolatilization of residual chars from coal liquefaction.Fuel81, 1525–1531.Cui,H.,Yang,J.,Liu,Z.,Bi,J.,2003.Characterization of the residue from thermal and catalytic coal hydroliquefaction.Fuel82,1549–1556.Dadyburjor, D.,Liu,Z.,2004.Coal liquefaction.In:Kirk-Othmer Encyclopedia of Chemical Technology.vol.6,fifth ed.,Wiley-Interscience,Wiley,Hoboken,New Jersey,pp.832–869.Fletcher,J.,Sun,Q.,Bajura,R.,Zhang,Y.,Ren,X.,2004.Coal to clean fuel—The Shenhua investment in direct coal liquefaction.In:21st Annual International Pittsburgh Coal Conference,September13–17,Osaka,Japan.Gao,J.,Zhang,D.,2004.Coal Liquefaction Technology(Chinese).Chemical Industry Press,Geertsema,A.,2005.Prospects and potential impact of coal to liquid fuels,Lecture at MIT,June29.Gibson,P.,2007.Coal to liquids at Sasol,Presented at Kentucky Energy Security Summit,October11.Guo,J.,Yang,J.,Liu,Z.,2000.Characterization of in-situ impregnated direct coal liquefaction catalyst.J.Catal.(Chinese)21,165–168.Huo,C.,Ren,J.,Li,Y.,Wang,J.,Jiao,H.,2007.CO dissociation on clean and hydrogen precovered Fe(111)surfaces.J.Catal.249,174–184.。