Efficient Utilization of Greenhouse Gas in a Gas-to-Liquids Process

Jan 15, 2010 - is composed of both steam reforming of methane (SRM) and carbondioxidereformingofmethane(CDR)toformsyngas,which gives composition ...
0 downloads 0 Views 986KB Size
Download PDF
Environ. Sci. Technol. 2010, 44, 1412–1417

Efficient Utilization of Greenhouse Gas in a Gas-to-Liquids Process Combined with Carbon Dioxide Reforming of Methane KYOUNG-SU HA, JONG WOOK BAE, KWANG-JAE WOO, AND KI-WON JUN* Petroleum Displacement Technology Research Center Korea Research Institute of Chemical Technology (KRICT), Daejeon 305-600, Korea

Received September 25, 2009. Revised manuscript received November 25, 2009. Accepted December 24, 2009.

A process model for a gas-to-liquids (GTL) process mainly producing Fischer-Tropsch (FT) synthetic oils has been developed to assess the effects of reforming methods, recycle ratio of unreacted syngas mixture on the process efficiency and the greenhouse gas (GHG) emission. The reforming unit of our study is composed of both steam reforming of methane (SRM) and carbon dioxide reforming of methane (CDR) to form syngas, which gives composition flexibility, reduction in GHG emission, and higher cost-competitiveness. With recycling, it is found that zero emission of CO2 from the process can be realized and the required amount of natural gas (NG) can be significantly reduced. This GTL process model has been built by using Aspen Plus software, and it is mainly composed of a feeding unit, a reforming unit, an FT synthesis unit, several separation units and a recycling unit. The composition flexibility of the syngas mixture due to the two different types of reforming reactions raises an issue that in order to attain the optimized feed composition of FT synthesis the amount of flow rate of each component in the fresh feed mixture should be determined considering the effects of the recycle and its split ratio. In the FT synthesis unit, the 15 representative reactions for the chain growth and water gas shift on the cobalt-based catalyst are considered. After FT synthesis, the unreacted syngas mixture is recycled to the reforming unit or the FT synthesis unit or both to enhance process efficiency. The effect of the split ratio, the recycle flow rate to the FT reactor over the recycle flow rate to the reforming unit, on the efficiency of the process was also investigated. This work shows that greater recycle to the reforming unit is less effective than that to the FT synthesis unit from the standpoint of the net heat efficiency of the process, since the reforming reactions are greatly endothermic and greater recycle to the reformer requires more energy.

1. Introduction The gas-to-liquids process based on Fischer-Tropsch (FT) synthesis is continuously drawing attention due to consistent increases in the price of oil (1). In addition, world oil consumption grows rapidly, but there are reports saying that not only the number but also the average size of newly discovered oil fields is consistently decreasing. For example, * Corresponding author phone: +82-42-860-7671; fax: +82-42860-7388; e-mail: [email protected]. 1412

9

ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 44, NO. 4, 2010

USGS Assessment 2000 (2) expected that the oil fields of around 20 billion barrels would be discovered annually, but at most only 10 billion barrels of 3-year-average annual production were found in recent years (3). From the viewpoint of economy, the synthetic oils are more cost-competitive than the petroleum-based oils since the formers are generally made from cheaper raw materials such as coal, natural gas, and sometimes wasted biomass. In addition, the FT synthetic oils do not require different types of infrastructure for transmission, storage, etc., and the transportation vehicles do not have to be reorganized nor redeveloped to use the oils. Also, the FT synthetic oils give other options for the countries that import almost all energy resources they need from the other countries because the raw materials are more abundant and thus more easily available than the petroleum. Although there are other forms of alternative fuels such as bioethanol, the process of producing bioethanol, for example, requires an enormous amount of agricultural produce. And these kinds of fuels derived from agricultural produce sometimes cause such controversial socioeconomic issues as the abrupt increase in the prices of crops and the shortage of foods in certain areas. As far as environmental issues are concerned, the FT synthetic oils especially from natural gas have strong advantages that they contain very little amount of sulfur compounds that can be transformed into SOx compounds when they are combusted and eventually form acid rain. If CO2, a representative greenhouse gas (GHG), is used as a carbon source to produce syngas, the processes become more environmentally benign and more economic since not only the CO2 emission but the required amount of natural gas (NG) can be significantly reduced, which will be discussed later. Therefore, many researchers are trying to find more costcompetitive ways of producing the synthetic fuels. Lee and co-workers (4) developed three kinds of process models producing FT diesel, dimethyl ether, and methanol with the help of Aspen Plus software to elucidate which process is the most cost-effective, depending on the prices of the raw materials and the products. Guetel et al. (5) established four types of reactor models and assessed the efficiencies of the reactors. The authors concluded that the slurry-bubble column reactor is far more efficient than the other types of reactors and explained that the enhanced efficiency mainly comes from smaller internal and external mass transfer resistances and completely isothermal operation. And the bubble size distribution, gas bubble holdup, Sauter-mean diameter of the SBC reactor, etc. also have been studied by other researchers (6). Especially, the behavior of the commercial scale SBC reactor could be predicted quite well with the CFD model considering simple FT reactions by Troshko and co-worker (7) and their CFD model was developed based on ANSYS Fluent software. Although many simulation works are done about specific reactor types or processes so far, there are a relatively small number of works dealing with the behavior of the entire GTL process and GHG problem under various operating conditions. Therefore, we constituted a new process model to elucidate the behavior of the main parts of a GTL process. Especially, the carbon dioxide reforming of methane (CDR) was also incorporated. And it is found that the operation of the process can be successfully done without any CO2 absorber and separation units, and GHG emission is significantly reduced by recycling some portion of the unreacted syngas mixture and CO2 generated from combustion at the reformer burner. 10.1021/es902784x

 2010 American Chemical Society

Published on Web 01/15/2010

FIGURE 1. Process scheme for a gas-to-liquids process for the production of synthetic oils.

2. Process Model Development In general, a GTL process consists of a feeding unit, a unit for the pretreatment, a reforming unit, an FT synthesis unit, an upgrading unit, and a product separation and rectification unit composed of a series of distillation and absorption columns. Among the units mentioned above, the pretreatment, the upgrading, and the product separation and rectification units are not within the scope of this work since their influence on the performance of the process is relatively small and they are well established in the field of the present petrochemical industry. Thus, we constitute rather a simplified but rigorous process model mainly depicting the feeding unit, the reforming unit, the FT synthesis unit, and the recycling unit including a few separation vessels as a whole, which is illustrated in Figure 1. The reforming unit has two parts, a prereformer and a reformer. In the prereformer, almost all C2 to C4 hydrocarbons originally contained in the natural gas are transformed into methane on a nickel-based catalyst and the RGibbs model using chemical equilibrium for C1 to C4 components is incorporated. The reaction temperature is set at around 550 °C at the exit and the pressure is 5 barg. For simulating the reformer, the RGibbs model is also used where SRM and CDR are considered as follows: CΗ4 + Η2Ο f CΟ + 3Η2

(1)

CΟ2 + CΗ4 f 2CΟ + 2Η2

(2)

The reaction temperature is 850 °C and the pressure is 5 barg. The reaction rates are so fast under very high temperature that they are properly assumed to be in chemical equilibria, which can be successfully incorporated by using “Restricted Chemical Equilibrium” option implemented in Aspen Plus. After reforming, there is no CO2 removal unit since CO2 itself is one of the main raw materials for the process and the CO2 generated at this process is recycled to be consumed at the reforming or recycled to the FT synthesis units. Depending on the reforming condition and the feed composition, various syngas compositions are possible at the exit of the reforming unit. For this reason, we have to investigate the effects of the feed composition, the amount of recycled gas, and its split ratio of the FT synthesis unit to

the reforming unit on the H2/CO ratio of the feed for the FT synthesis unit. A series of chain growth reactions and water gas shift reaction are considered on the basis of the conversions of raw materials and the selectivities of produced hydrocarbons from Figure S3 in the Supporting Information and our previous experimental observations (8). Fourteen representative reactions for generation of paraffin species and one reaction for water gas shift are considered as listed in Table S1 (Supporting Information). The consumption ratio of H2/CO in the FT reactor was found to be in the range of 2 to 2.2 from the experimental results, which is a widely known result and is also in good agreement with our model prediction. The reactor for the FT synthesis can be properly modeled by using the RStoic model, where we designated each fractional conversion corresponding to each reaction in Table S1 based on the result in Figure S3. The reaction temperature is 235 °C and the pressure is 20 barg. After the FT synthesis unit, some portion of the unreacted syngas mixture is recycled and the other portion is vented to suppress the accumulations of byproduct and unnecessary components. In the FT reactor, the gaseous product stream is drawn out from the top or side of the reactor and goes through several separation units to eliminate water and to separate condensable hydrocarbons. The liquid product stream is drawn out from the side or the bottom of the reactor and just like the gaseous product stream, goes through separation units to eliminate water and to retrieve liquid hydrocarbons. The gaseous recycle stream is split into two recycle streams to the FT synthesis unit and to the reforming unit at a certain prescribed ratio. For example, if the split ratio is set at 60% (FT60), 60% of the recycle stream goes to the FT reactor and the other 40% goes to the reformer where recycled CO2 is consumed as a reactant and the accumulation of CO2 is quite suppressed. So, there is no need for CO2 separation units, unlike conventional autothermal reforming or steam reforming of methane.

3. Results and Discussion 3.1. Effects of Recycle Ratio on the Behavior of the GTL Process. A series of simulation runs are conducted under the prescribed process conditions mentioned in Table S2 of the Supporting Information. During this simulation study, 8 different recycle ratios are applied to investigate the effects VOL. 44, NO. 4, 2010 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

9

1413

of recycle ratio on the syngas ratio and the efficiencies of the process. The process for our study is designed to produce 1 barrel of C5+ synthetic oil per day. The reforming feed conditions are chosen to reach near equilibrium conversions with reference to the literature (9) and the molar ratio of fresh feed, NG/H2O/CO2 was set in the range of 1/1.4-1.7/ 0.39-0.42 (see Table S2 of the Supporting Information). In addition, we set the temperature and the pressure conditions where the reformer generates as small amount of carbon deposit as possible based on the simulation results from Outokumpu HSC Chemistry software and another references (10, 11). The optimum syngas ratio ranging from 2.05 to 2.10 (see Table S2 of the Supporting Information) and the prescribed production rate (1 barrel of C5+ synthetic oils per day) are simultaneously met by applying the feed composition range mentioned above. The different recycle ratios lead to the change in the syngas ratio. Therefore, a very narrow range of optimum syngas feed ratios for the FT reactor should be reached by minutely controlling the feed molar ratios as graphically represented in Figure S1 in the Supporting Information. In this reformer, there is the composition flexibility of syngas mixture due to the two competitive reforming reactions, whose rates can be successfully controlled by applying different feed molar ratios. From Figure S1(a) of the Supporting Information, the fresh CO2/NG ratio decreases as the recycle ratio increases because of CO2 accumulation around the process caused by inertness to FT catalyst and less activity in reforming than methane. Accordingly, H2O/NG ratios are adjusted to be higher to meet the syngas ratio 2.05-2.10 at the inlet of the FT reactor (Figure S1(b) of the Supporting Information). And the changes in the mass flow rates at the exits of the reformer and the FT reactor in Figure 2 are quite clear. It is obvious that the mass flow rate at the exit of FT reactor increases as the recycle ratio increases as shown in Figure 2(a) since the amount of recycle itself increases and the unreacted byproduct such as CO2 and CH4 accumulate to certain degrees as well. On the contrary, in the reformer CO2 and CH4 are consumed as two major reactants and they are also supplied from the recycle stream so the amounts of the freshly supplied CO2 and CH4 can be greatly reduced and the conversions of them are also enhanced with increasing recycle ratio, which leads to reduction in the mass flow rate of the reformer as shown in Figure 2(b). At the recycle ratio g85%, however, the tendencies of two mass flow rates are somewhat ambiguous. As shown in Table S2 of the Supporting Information, H2O feed ratio (H2O/NG) at R95 (recycle ratio of 95%) is set higher than those at R90 and R97.5 in order to meet the optimum syngas composition ratio (H2/CO) of 2.1 for FT synthesis reaction with recycle. These alterations result in relatively higher values of the flow rates at the exits of FT reactor and the reformer at R95 than the values at R90 and R97.5. It is worth noting that Figure 3(a) shows only a slight increase in CO2 level even if the recycle ratio is raised to 99% (R99), which can be explained through combined reforming reactions. In the reformer of our concern, CDR besides SRM occurs. The recycled CO2 to the reformer is consumed as a reactant and the CO2 level can be successfully suppressed. If there is no CDR in the reformer, then a much higher CO2 level is expected as the recycle ratio is raised and the size of reactor should be increased because of the increased inert material, such as CO2 and CH4 in the FT reactor. Although the fraction of CH4 increases with an increasing recycle ratio, it also remains very low in front of the FT synthesis unit since 40% of recycle gas is directed to the reformer where the CH4 gas is also consumed as a reactant just like the case of CO2. In Figure 3, the case of R95 shows somewhat unusual points compared to its neighboring cases. As we mentioned above, 1414

9

ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 44, NO. 4, 2010

FIGURE 2. Mass flow rates at the exits of (a) the FT reactor and; (b) the reformer. the flow rate of H2O at R95 case was set higher than those at R90 and R97.5. As you can see in eqs 1 and 2, the reaction in eq 1 seems to be more favorable under higher H2O concentration. In addition, the conversion of CH4 was found to be higher than those at R90 and R97.5. Consequently, the mole fraction of CH4 was lower than that at R90, whereas the mole fraction of CO2 was higher than that at R97.5. As the recycle ratio decreases, the fraction of synthetic oils naturally increases as well as that of the unreacted syngas mixture through the vent stream. However, the vent stream can be used as fuel for the burner-type reformer or other uses since the vent stream is composed of synthetic oils, syngas, and hydrocarbons, etc. Figure 3(b) shows that the overall lower heating value (LHV) can be evaluated with LHV of each component. Thus, the efficiency of the entire process can be elevated by using the quantity of retrieved heat, which will be shown later. In the burner-type reformer, NG is consumed not only as a reactant but also as a burner fuel. So if the vent stream can be applied to the burner as fuel instead of NG, then a large amount of NG will be saved, as shown in Figure 3(b). 3.2. Carbon and Net Heat Efficiencies. Before we proceed further, the definitions of carbon and net heat efficiencies need to be expressed in detail. As far as the measurement of a process efficiency is concerned, there have been several similar works reported previously, in which different production way of synthesis gas has been used (12-16). In this work, we define 3 kinds of efficiencies that are interconnected. They are carbon efficiency, net heat efficiency, and stoichiometric heat efficiency, and their relation is as follows:

ΕffC ) ΕffΗ,net/ΕffΗ,stoic

(3)

burning for the reformer: 2.75CΗ4 + 5.5Ο2 f 2.75CΟ2 + 5.5Η2Ο (5)

where EffC, EffH,net, and EffH,stoic denote carbon efficiency, net heat efficiency, and stoichiometric heat efficiency, respectively. As you can see from eq 3, the carbon efficiency is defined as the ratio of EffH,net to EffH,Stoic, which means that ratio of total lower heating value of products from the process model of this study to total lower heating value of products from the virtual process without loss of any carbon sources. So, eq 3 can be utilized to show the amount of carbon source that is converted to the products. If the actual GTL process saves more carbon sources, then the value of carbon efficiency approaches 1. If there were no carbon loss, then the value would be definitely 1. The retrieved quantity of heat from vent shown in Figure 3(b) is assumed to be utilized for the reformer burner. Then, the values of EffC’s can be estimated with eqs 3, 9, and 10 and the values are represented in Figure 4. The calculation procedure is represented below. In order to compute EffH,stoic, which is calculated by using the stoichiometry of reactions only, we propose simple overall reactions as follows:

FT synthesis step: 12CΟ + 25Η2 f 12C12Η26 + 12Η2Ο (6)

reforming step: 2.75CΟ2 + 9.25CΗ4 + 6.5Η2Ο f 12CΟ + 25Η2 (4)

net reaction: 12CΗ4 + 5.5Ο2 f C12Η26 + 11Η2Ο

(7)

Equation 4 denotes overall reaction considering SRM and CDR. Equation 5 implies that the proposed reformer is a burner-type one. In eq 6, the average chain length of paraffin is assumed to be 12. If we combine all of these reactions together, then the net reaction is obtained as shown in eq 7. Thus, we can estimate the value of EffH,stoic as follows: ΕffΗ,stoic ) product combustion heat/ raw material combustion heat

(8)

) lower heating value of synthetic hydrocarbons/ lower heating value of NG

(9)

The estimated EffH,stoic value is about 0.8. For the calculation of EffH,net, we need heat duty of the reformer resulted from Aspen plus simulation study. We suggest a simple EffH,net calculation equation as follows: ΕffΗ,net ) quantity of heat from product/ quantity of heat entered

(10)

where the numerator is lower heating values (LHV’s) of C5+ synthetic hydrocarbons and the denominator is LHV’s of raw materials plus required heat quantity in the reformer considering heat transfer efficiency minus the retrieved quantity of heat from vent that is also computed from our Aspen Plus based process model. Figure 5(a) shows the net heat efficiencies considering C5+ synthetic oils. For the R70 ∼ R99 cases, the differences between them are not very large, although the R95 case shows the best result. This result implies that more recycle cannot guarantee higher efficiency. It should be kept in mind that more vent gas resulting from less recycle can be used as fuel for the burner-type reformer, which compensates for the lowered efficiency. If we keep reducing the amount of recycle, then it is not the case below a certain critical recycle ratio around 70%. It should be noted that the process efficiency falls apparently downward when the quantity of heat retrieved from the vent exceeds the necessary quantity of heat for the reformer since the extra quantity of heat cannot be used for the burner-type reformer directly, but should be used indirectly for generating steam that is less efficient method, or wasted. According to the simulation study of 50% recycle,

FIGURE 3. FT synthesis unit simulation results at various recycle ratios; (a) mole fractions of inert components to FT catalyst at FT reactor inlet, hollow bars: CO2, solid bars: CH4; (b) utilization of vent stream after FT reaction. Bar graph: NG saved/fresh NG feed × 100. Line with square symbols: the lower heating values of the vent streams.

FIGURE 4. Carbon efficiencies (C5+) at recycle ratio ranging from 40% to 99%. VOL. 44, NO. 4, 2010 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

9

1415

FIGURE 6. Required NG (kg) to produce 1 kg of syngas whose H2/CO ratio is about 2.0 under various reforming conditions without recycle: at 900 °C(case 1), 920 °C(case 2), 950 °C(case 3) under the pressure of 15 barg and at 850 °C under 5 barg (case 4).

FIGURE 5. Efficiencies at recycle ratio ranging from 40% to 99%; (a) net heat efficiency (C5+); (b) ratios of generated CO2 from vent gas incineration at the reformer to net amount of consumed CO2 with various recycle ratios. the quantity of heat retrieved from the vent stream is larger than the necessary quantity of heat for the reformer by about 11% and the value of EffH,net (C5+) falls to 62.6%, which is lower than the values of R70 ∼ R99 cases by 2-3% points. If we reduce recycle below 50%, then the gap is expected to be larger, as shown in Figure 5(a). 3.3. Reduction in GHG Emission and Its Use As a Feedstock Material. Besides the syngas composition flexibility due to employing both SRM and CDR mentioned already, the other benefits of this method are reduction in GHG emission and higher cost-competitiveness. According to Jaramillo et al. (17), the emission of CO2, a representative GHG, ranges from 3 to 3.8 kg per one liter of FT-diesel from the case where FT-diesel is produced with imported NG, and this value is not lower than that of traditional petroleumbased fuels. So, they argued that these conventional types of GTL processes do not help reduce GHG emission and concluded that the production of GTL-based fuel does not seem a reasonable path to follow. Even with domestic NG, the results showed a slight reduction in GHG emission. There is, however, another option to reduce GHG emission if the synthetic fuels are produced from the distinct GTL process in which a GHG gas is reused as a reactant. According to our study, about 15-17 g CO2/MJ of synthetic fuel is directly consumed to produce synthetic fuels, and this value is equivalent to 0.5-0.7 kg CO2 per one liter of the synthetic fuel, which means that in the least optimistic scenario of Jaramillo et al. (17) the level of GHG emission from this kind of GTL process is comparable to that from the conventional petroleum based process and in the most optimistic scenario, the level of GHG emission is lower than 0.5-0.7 kg CO2 per one liter of the synthetic fuel. It is also pointed out that the 1416

9

ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 44, NO. 4, 2010

FIGURE 7. Effects of recycle ratio and split ratio on the required amount of NG (kg) to produce 1 kg of syngas; (a) split ratio ) 60%; (b) recycle ratio ) 95%. CO2 generated from combustion of vent gas to heat up the reformer can be properly reused as a carbon source for the reformer. Our calculation shows that the amount of CO2 from vent gas incineration at about 77% recycle is nearly close to the net amount of consumed CO2, which can be inferred from Figure 5(b). And this means that CO2 emission is nearly zero from the process of our concern. If recycle ratio is raised above 77%, then more CO2 can be consumed than the process gives off. The denominator in Figure 5(b), the net amount of consumed CO2, corresponds to purely reacted amount of

Supporting Information Available Additional figures, tables, and the calculation procedure for process efficiencies.This material is available free of charge via the Internet at http://pubs.acs.org.

Literature Cited

FIGURE 8. Efficiencies at split ratio ranging from 40% to 60%; circles: EffC (C5+), squares: EffH,net (C5+). CO2 gas that can be expressed as fresh CO2 feedsCO2 in vent gassCO2 in product streams. In addition, the required NG is greatly reduced since CO2 also plays a role as one of the carbon sources. According to Choudhary et al. (18), autothermal reforming process requires about 0.53-0.61 kg NG to produce 1 kg syngas (H2/CO ratio is about 2.0). In comparison to that, the SCR (combinational method of SRM and CDR) requires 20-30% less NG, 0.42-0.46 kg per 1 kg syngas (H2:CO Z 2.0) as shown in Figure 6. If we recycle the unreacted syngas mixture to save more NG, then the required NG/syngas ratio is greatly reduced to 0.23-0.37 as shown in Figure 7(a). Also, it can be seen in Figure 7(b) that more recycling flow rate to the reformer, i.e., the lower split ratio requires less NG mainly because of the CDR in the reformer. 3.4. Effects of Split Ratio of Recycle. As the split ratio of the FT reactor to the reformer increases, the greater the amount of the unreacted syngas mixture from the FT reactor goes out through the vent, which can be also inferred from Figure S2(a) in the Supporting Information since the saved NG flow rate is equivalent to the retrieved heat flow rate from vent gas combustion when it is directly used as fuel in the burner-type reformer. And the recycle flow rate in Figure S2(b), the feed flow rates of NG and CO2 in Figure S2(b) should be increased to meet the mass balance. It is quite difficult to predict EffH,net and EC values only with results from Figure S2 of the Supporting Information which seems that less split ratio could make those efficiencies higher. On the contrary, less split ratio in Figure 8, which means, more recycle to the reformer unit, leads to lower net heat efficiency since the reforming reactions are greatly endothermic and the reformer consumes more energy to run the reformer.

Acknowledgments The authors would like to acknowledge the financial support of the Korea Energy Management Corporation (KEMCO) and GTL Technology Development Consortium under “Energy & Resources Technology Development Programs” of the Ministry of Knowledge Economy, Republic of Korea.

(1) U.S. EIA. World Oil Prices; http://tonto.eia.doe.gov/dnav/pet/ PET_PRI_WCO_K _W.htm (accessed July 7, 2009). (2) USGS. USGS Assessment 2000; U.S. Geological Survey, June 2000. (3) APSO. ASPO Newsletter No. 71; The Association for the Study of Peak Oil & Gas, November2006. (4) Lee, C.-J.; Lim, Y.; Kim, H. S.; Han, C. Optimal gas-to-liquid product selection from natural gas under uncertain price scenarios. Ind. Eng. Chem. Res. 2009, 48, 794–800. (5) Guetel, R.; Turek, T. Comparison of different reactor types for low temperature Fischer-Tropsch synthesis: A simulation study. Chem. Eng. Sci. 2009, 64, 955–964. (6) Behkish, A.; Lemoine, R.; Sehabiague, L.; Oukaci, R.; Morsi, B. I. Gas holdup and bubble size behavior in a large-scale slurry bubble column reactor operating with an organic liquid under elevated pressures and temperatures. Chem. Eng. J. 2007, 128, 69–84. (7) Troshkoa, A. A.; Zdravistch, F. CFD modeling of slurry bubble column reactors for Fischer-Tropsch synthesis. Chem. Eng. Sci. 2009, 64, 892–903. (8) Woo, K.-J.; Kang S.-H.; Kim S.-M.; Bae, J.-W.; Jun, K.-W. Performance of a slurry bubble column reactor for FischerTropsch synthesis: Determination of optimum condition, Fuel Process. Technol. in press, 2009. (9) JOGMEC Development of Japanese GTL technology; JCOAL Annual Conference on Clean Coal Technology: Tokyo, Japan, November 2006. (10) Jun, K.-W.; Baek, S.-C.; Bae, J.-W.; Min, K.-S.; Song S.-Y.; Oh, T.-Y.; Catalyst for the preparation of synthesis gas from natural gas with carbon dioxide and the preparation method thereof, Korea patent, Application number 10-2008-0075787, 2008. (11) Roh, H.-S.; Koo, K. Y.; Yoon, W. L. Combined reforming of methane over co-precipitated Ni-CeO2, Ni-ZrO2, and NiCe0.8Zr0.2O2 catalysts to produce synthesis gas for gas to liquid (GTL) process. Catal. Today, in press, 2009. (12) Sudiro, M.; Bertucco, A.; Ruggeri, F.; Fontana, M. Improving process performances in coal gasification for power and synfuel production. Energy Fuels 2008, 22, 3894–3901. (13) Mukoma, P.; Hildebrandt, D.; Glasser, D.; Coville, N. Synthesizing a process from experimental results: A Fischer-Tropsch case study. Ind. Eng. Chem. Res. 2007, 46, 156–167. (14) Hao, X.; Djatmiko, M. E.; Xu, Y.; Wang, Y.; Chang, J.; Li, Y. Simulation analysis of a gas-to-liquids process using aspen plus. Chem. Eng. Technol. 2008, 31, 188–196. (15) Mukoma, P.; Hildebrandt, D.; Glasser, D. A Process synthesis approach to investigate the effect of the probability of chain growth on the efficiency of Fischer-Tropsch synthesis. Ind. Eng. Chem. Res. 2006, 45, 5928–5935. (16) Hamelinck, C. N.; Faaij, A. P. C.; Uil, H. d.; Boerrigter, H. Production of FT transportation fuels from biomass; technical options, process analysis and optimization, and development potential. Energy 2004, 29, 1743–1771. (17) Jaramillo, P.; Griffin, W. M.; Matthews, H. S. Comparative analysis of the production costs and life-cycle GHG emissions of FT liquid fuels from coal and natural gas. Environ. Sci. Technol. 2008, 42, 7559–7565. (18) Choudhary, V. R.; Mondal, K. C.; Mamman, A. S. Hightemperature stable and highly active/selective supported NiCoMgCeOx catalyst suitable for autothermal reforming of methane. J. Catal. 2005, 233, 36–40.

ES902784X

VOL. 44, NO. 4, 2010 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

9

1417