SONG, In Kyu (202 958-16 Daechi-dong, Gangnam-gu, Seoul 135-280, KR)
CHO, Kyung min (9-1003 Sinsegye Apt, Suseong 1-gaSuseong-gu, Daegu 706-031, KR)
PARK, Sunyoung (316-303 Hanyang Apt, Seohyeon-dongBundang-gu,Seongnam-si, Gyeonggi-do 463-050, KR)
BAECK, Sung-Hyeon (1 Hansin Apt, Mok 6-dongYangcheon-gu, yukSeoul 158-050, 08-1509, KR)
DAELIM INDUSTRIAL CO., LTD. (146-12 Susong-dong, Jongno-gu, Seoul 110-140, KR)
DOOSAN MECATEC CO., LTD. (64 Sinchon-dong, Changwon-si, Gyeongsangnam-do 641-370, KR)
KOREA NATIONAL OIL CORPORATION (1588-14 Gwanyang-dong, Dongan-guAnyang-si, Gyeonggi-do 431-711, KR)
HYUNDAI ENGINEERING CO., LTD. (917-9 Mok-dong, Yangcheon-gu, Seoul 158-050, KR)
SK ENERGY CO., LTD. (90 Seorin-dong, Jongno-gu, Seoul 110-110, KR)
JUN, Ki-won (3 Expo Apt, Jeonmin-dongYuseong-gu, Daejeon 305-761, 05-1602, KR)
SONG, In Kyu (202 958-16 Daechi-dong, Gangnam-gu, Seoul 135-280, KR)
CHO, Kyung min (9-1003 Sinsegye Apt, Suseong 1-gaSuseong-gu, Daegu 706-031, KR)
PARK, Sunyoung (316-303 Hanyang Apt, Seohyeon-dongBundang-gu,Seongnam-si, Gyeonggi-do 463-050, KR)
BAECK, Sung-Hyeon (1 Hansin Apt, Mok 6-dongYangcheon-gu, yukSeoul 158-050, 08-1509, KR)
Claims
[1] A continuous process of preparing Ci 0 -C 2O liquid-phase hydrocarbon mixture, the process comprising: conducting Fischer- Tropsch reaction between carbon monoxide and hydrogen in a continuous-flow dual-bed catalytic reactor; wherein the reactor comprises: an upper fixed-bed reactor filled with a catalyst, a lower fixed-bed reactor filled with a catalyst, and a hydrogen- supplying pipe; and the two fixed-bed reactors are consecutively placed in the upper and lower position of the dual-bed reactor, respectively, and the hydrogen- supplying pipe is added between the two fixed-bed reactors. [2] A process of claim 1, wherein the upper fixed-bed reactor is filled with a catalyst for Fischer- Tropsch synthesis, and the lower fixed-bed reactor is filled with a catalyst for hydrocracking reaction. [3] A process of claim 1, wherein the Fischer- Tropsch synthesis is conducted in the upper fixed-bed reactor at a reactant space velocity of 100-1500 niLg^lr 1 , a temperature of 200-240 0 C and a pressure of 10-20 bar. [4] A process of claim 1, wherein the hydrocracking reaction is conducted in the lower fixed-bed reactor at 270-350 0 C, 10-20 bar and a hydrogen space velocity of 500-1000 UiLg C81 - 1 Ir 1 . [5] A process of any of claims 1-3, wherein the upper fixed-bed reactor is filled with a cobalt/titania catalyst. [6] A process of any of claims 1, 2 and 4, wherein the lower fixed-bed reactor is filled with a palladium/alumina catalyst. [7] A process of claim 1 or 2, wherein a hydrocarbon mixture obtained from the upper fixed-bed reactor comprises 30-50 wt% of Ci-C 9 hydrocarbon, 30-40 wt% of Ci 0 -C 2O hydrocarbon and 20-30 wt% of C 2 i or higher hydrocarbon. [8] A process of claim 1 or 2, wherein a hydrocarbon mixture obtained from the lower fixed-bed reactor comprises 30-45 wt% of Ci-C 9 hydrocarbon, 50-55 wt% of Ci 0 -C 20 hydrocarbon and 5-15 wt% of C 2! or higher hydrocarbon. |
Description
CONTINUOUS-FLOW DUAL-BED REACTOR FOR
PRODUCTION OF LIQUID-PHASE HYDROCARBON
MIXTURE ON FISCHER-TROPSCH CATALYSIS USING
SYNTHETIC GAS Technical Field
[1] The present invention relates to a process of preparing liquid-phase hydrocarbon mixture by using a catalyst reactor for Fischer-Tropsch synthesis. In particular, it relates to a continuous-flow dual-bed reactor for Fischer-Tropsch synthesis designed to increase the yield of Ci 0 -C 2O liquid-phase hydrocarbon mixture, and a Fischer-Tropsch reaction using the reactor. Background Art
[2] Most of transportation oil is obtained by fractionating and processing crude oil.
Liquid fuel prepared from crude oil contains sulfur, nitrogen and aromatic compounds, and produces air pollutants during combustion. Diesel fuel that is produced by distillation of crude oil and severe hydrogen treatment has relatively lower cetane value, normally lower than 60.
[3] Diesel fuel and kerosene may also be prepared by obtaining middle distillate by
Fischer-Tropsch process. Middle distillate is a mixture of hydrocarbons having a carbon number of about 10-20 and a boiling point of 140-370 0 C. Middle distillate contains fuels such as diesel oil and kerosene.
[4] Fischer-Tropsch process is a technique for obtaining liquefied distillate from a synthetic gas (carbon monoxide and hydrogen) obtained from, for example coal, natural gas, biomass, etc. Middle distillate that may be obtained by Fischer-Tropsch synthesis is a clean liquid fuel not containing sulfur, nitrogen and aromatic compounds. In particular, the liquid fuel prepared by Fischer-Tropsch synthesis contains a relatively larger portion of linear paraffin-based hydrocarbons, thus showing a relatively high cetane value.
[5] Fischer-Tropsch synthesis has been of great interest as an energy technique during the transitional period from fossil fuel age to hydrogen economy because petroleum resources is being exhausted while the oil price is on rapid increase.
[6] In obtaining middle distillate for the purpose of transportation fuel, the conventional
Fischer-Tropsch process is disadvantageous in that it requires a post-treatment process comprising at least two steps, due to the characteristics of the Fischer-Tropsch synthesis reaction. Fischer-Tropsch synthesis is a growth reaction of a carbon chain.
As the growth of carbon chains depends on a variable called 'Chain Growth Probability (α)', the carbon number of hydrocarbon product shows normal distribution. For this reason, it is impossible to obtain pure products having a certain range of carbon number by Fischer- Tropsch synthesis. Therefore, the total process of the conventional Fischer- Tropsch for the production of transportation fuel comprises: (a) preparing wax products with high boiling temperature (higher than 400 0 C) through Fischer-Tropsch synthesis, (b) separating gas products from liquid and solid products and treating the products under reduced or pressurized conditions and (c) de- waxing the separated liquid and solid products and conducting hydrocracking process, thereby converting into carbon component appropriate for transportation purpose.
[7] Shell and ExxonMobil have developed these processes and other similar ones for commercial purpose [J. Eilers, S. A. Posthuma, S.T. Sie, Catal. Lett., 7, 253 (1990); Korean patent publication Nos. 2003-0080077, 2003-0007490 and 2003-0010613; Korean patent No. 449,389]. The separation and post-treatment processes require a higher cost than those required for Fischer-Tropsch synthesis.
[8] For the improvement of efficiency of the process, various attempts have been made to induce the decomposition of products at the same time during the process of the Fischer-Tropsch synthesis, thereby being capable of controlling the carbon number of the products (hybrid Fischer-Tropsch catalyst process) [Z.-W. Liu, X. Li, K. Asami, K. Fujimoto, Catal. Comm., 8, 503 (2005); S. Bessell, Appl. Catal. A, 126, 235 (1995); K. Jothimurugesan, S.K. Gangwal, Ind. Eng. Chem. Res., 37, 1181 (1998); DJ. Koh, J.S. Chung, Y.G. Kim, Ind. Eng. Chem. Res., 34, 1969 (1995); J. He, Y. Yoneyama, B. Xu, N. Nishiyama, N. Tshbaki, Langmiur, 21, 1699 (2005); N. Tsubaki, Y. Yoneyama, K. Michiki, K. Fujimoto, Catal. Comm., 4, 108 (2003); F.G. Botes, W. B hringer, Appl. Catal. A, 267, 217 (2004); X. Li, K. Asami, M. Luo, K. Michiki, N. Tsubaki, K. Fujimoto, Catal. Today, 84, 59 (2003); Z.-W. Liu, X. Li, K. Asami, K. Fujimoto, Ind. Eng. Chem. Res., 44, 7329 (2005)].
[9] The hybrid Fischer-Tropsch process may be divided into two subprocesses. One is to prepare a catalyst so that the catalyst can have both a Fischer-Tropsch synthetic function and an acid catalytic function at the same time. Another process is to prepare a catalyst for each of the above two functions and allow the two reactions occur at certain time intervals.
[10] In the first process, there is used a single reactor as in the conventional Fischer-
Tropsch synthesis. This prevents the hybrid catalyst from exhibiting two or more functions because each function requires a different range of temperature and hydrogen pressure. When solid acid catalyst such as a zeolite catalyst is used in a hydrocracking reaction, an appropriate temperature is 280 0 C or higher. At this temperature, however, Fischer-Tropsch catalyst comprising cobalt increases methane production
due to insufficient chain extension. Similarly, the appropriate temperature for Fischer- Tropsch reaction is about 220 0 C, but it is difficult to efficiently conduct hydrocracking reaction and isomerization reaction by using a solid acid catalyst at this temperature. Further, a relatively higher conversion of Fischer-Tropsch reaction may cause insufficiency in hydrogen gas that is required for hydrocracking reaction and isomerization reaction by using a solid acid catalyst [T. -S. Zhao, J. Chang, Y. Yoneyama, N. Tsubaki, Ind. Eng. Chem. Res., 44, 769 (2005)]. Disclosure of Invention Technical Problem
[11] An object of the present invention is to prepare Ci 0 -C 2O liquid-phase hydrocarbon mixture by using a simple and widely applicable continuous -flow dual-bed reactor to overcome the aforementioned problems of the conventional Fischer-Tropsch synthesis, thereby achieving higher selectivity towards Ci 0 -C 2O liquid-phase hydrocarbon mixture than that of the Fischer-Tropsch synthesis. Technical Solution
[12] The present invention relates to a continuous process of preparing Ci 0 -C 20 liquid- phase hydrocarbon mixture, the process comprising:
[13] conducting Fischer-Tropsch reaction between carbon monoxide and hydrogen in a continuous -flow dual-bed catalytic reactor;
[ 14] wherein the reactor comprises :
[15] an upper fixed-bed reactor filled with a catalyst,
[16] a lower fixed-bed reactor filled with a catalyst, and
[17] a hydrogen- supplying pipe ; and
[18] the two fixed-bed reactors are consecutively placed in the upper and lower position of the dual-bed reactor, respectively, and the hydrogen-supplying pipe is added between the two fixed-bed reactors. Brief Description of the Drawings
[19] Figure 1 is a schematic drawing of a continuous -flow dual-bed reactor according to the present invention, and shows the connection of each catalyst bed and additional hydrogen- supplying pipe. Best Mode for Carrying Out the Invention
[20] The present invention relates to a method of increasing the selectivity of middle distillate in hydrocarbons produced during Fischer-Tropsch reaction by using a continuous -flow dual-bed catalytic reactor for Fischer-Tropsch catalyst reaction designed to overcome the problems of conventional Fischer-Tropsch reaction in terms of the selectivity of transportation fuel.
[21] In the present invention, middle distillate refers to liquid-phase distillate comprising
Ci 0 -C 2O saturated or unsaturated hydrocarbons. Fractionation of distillate is divided into two types, i.e., based on boiling point and carbon number. In the present invention, products are analyzed by gas chromatograph instead of being fractionated or distilled, and thus divided based on carbon number in the present invention.
[22] Further, Fischer-Tropsch reaction is a catalytic process of preparing hydrocarbons from synthetic gas obtained via various routes, and the synthetic gas refers to a mixture of carbon monoxide and hydrogen. Fischer-Tropsch process is a process of obtaining liquefied distillate by polymerizing carbon chains using carbon monoxide and hydrogen as reactants, which has been widely studied in connection with catalyst and process.
[23] Fischer-Tropsch synthesis has been conducted mainly in a fixed-bed reactor and a slurry reactor. Fixed-bed reactor is advantageous for a process where all the gas-, liquid- and solid-phase products are produced because it shows high conversion and also facilitates the collection of products like Fischer-Tropsch synthesis. If the fixed- bed reactor is designed as a dual-bed reactor, a continuous catalytic reaction may be achieved where products prepared in the first catalyst bed is directly used in the subsequent reaction without being separated.
[24] The present invention relates to a catalytic device comprising a continuous -flow dual-bed reactor for more efficiently conducting Fischer-Tropsch synthesis reaction and increasing the selectivity of Ci 0 -C 2O liquid-phase middle distillate in hydrocarbons produced during Fischer-Tropsch synthesis reaction.
[25] A catalyst device comprising a continuous-flow dual-bed reactor of the present invention is for simultaneously conducting chain growth reaction by Fischer-Tropsch synthesis and selective hydrocracking reaction process, which is an improved form of Fischer-Tropsch synthesis reaction. This is developed to efficiently carry out the steps as a single process not as two steps. Therefore, Fischer-Tropsch synthesis process using a continuous-flow dual-bed reactor is different from the post-treatment process subsequent to the conventional process.
[26] A reactor of the present invention is developed based on the simplest form of a catalyst reactor that has been used in Fischer-Tropsch synthesis, and the improved form is not totally different from that of the conventional one. Further, catalyst used in each reactor is also similar to the simplest form of the conventional catalysts used in Fischer-Tropsch synthesis and hydrocracking. That is, according to the present invention, an appropriate combination of reactor form and catalysts may lead to higher yield of middle distillate than that of the conventional Fischer-Tropsch synthesis without including processes for preparing complicated reactor or catalysts.
[27] The aforementioned combination of reactor and catalyst has never been attempted in the conventional hybrid Fischer-Tropsch process for the production of middle
distillate. A continuous-flow dual-bed catalytic reactor of the present invention has a form of a fixed-bed reactor comprising two vertically-combined fixed-bed reactors in which catalysts can be loaded. Each catalyst bed is designed so that to enable an independent temperature control. Additional hydrogen- supplying pipe lies in between the two reactors. This structure can be adopted very usefully either in a process showing limited yield like Fischer-Tropsch reaction or in a process comprising at least two consecutive catalytic processes for example a process followed by a post- treatment process.
[28] The reactor is also advantageous in flexibly change products. For example, when
Fischer-Tropsch reaction is conducted in the first catalyst bed, the length or form (linear or branched) of carbon chains in the second catalyst bed can be controlled by changing the catalytic properties or process variables.
[29] The present invention also relates to a continuous process of preparing Ci 0 -C 2O liquid- phase hydrocarbon mixture from the synthetic gas of carbon monoxide and hydrogen in Fischer-Tropsch reaction by using the continuous -flow dual-bed catalytic reactor.
[30] In the upper fixed-bed reactor, chain growth reaction is conducted according to
Fischer-Tropsch synthesis. In the lower fixed-bed reactor, selective hydrocracking reaction is conducted.
[31] Catalysts for Fischer-Tropsch synthesis reaction are filled in the upper the first catalyst bed, and the conventional catalysts used for such purpose can also be used in the present invention. Examples of the catalysts include VIII transition metal, particularly cobalt, nickel, iron and ruthenium. The length of carbon chains can vary depending on catalytic properties and process variables.
[32] As catalytic properties are very important factors in Fischer-Tropsch synthesis, at least one metal such as rhenium, cerium, thorium, zinc and copper may be used as a co-catalyst in Fischer-Tropsch synthesis to achieve additional property such as stability in addition to the carbon chain growth. Although Fischer-Tropsch synthesis reaction is conducted in the presence support and VIII metal without using co-catalyst, the present invention is not limited to such reaction. A co-catalyst may also be used in the present invention.
[33] The length of hydrocarbons varies depending on the transition metal in Fischer-
Tropsch catalyst. For the synthesis of long-chain hydrocarbons such as diesel and wax, low-temperature Fischer-Tropsch process (LTFT) is used in combination with cobalt. High-temperature Fischer-Tropsch process (HTFT) is used in combination with iron to produce hydrocarbons with relatively low carbon number such as gasoline. Low-temperature Fischer-Tropsch synthesis based on cobalt catalyst is preferred in the present invention because the present invention aims to produce middle distillate ranging Ci 0 -C 2O .
[34] Although cobalt catalyst causes the production of hydrocarbons with relatively longer chains in low-temperature Fischer- Tropsch synthesis, the distribution of carbon chains depends on the manufacturing conditions. When a continuous-flow dual-bed reactor is used, two strategies as described hereinbelow may be considered.
[35] The first method is to mainly produce hydrocarbons with relatively higher carbon number (e.g., C 30 or higher hydrocarbons having higher boiling point) than the carbon range of middle distillate by preparing cobalt catalyst such that the chain growth probability of cobalt catalyst may be nearly one, and to hydrocrack the hydrocarbons to middle distillate. This strategy needs much energy for allowing products with high boiling point produced in the first catalyst bed to smoothly flow into the second catalyst bed as well as a lot of hydrogen gas for a vigorous hydrocracking process.
[36] The second strategy is to produce a lot of hydrocarbons ranging middle distillate in
Fischer- Tropsch synthesis, and subsequently to increase the selectivity of middle distillate by selectively hydrocracking side products, C 2 o or higher wax products. According to this strategy, it is possible to allow hydrocarbons produced in the first reactor to smoothly flow down to the second reactor. Further, the second strategy requires less amount of hydrogen and heat energy because mild selective hydrocracking process is needed instead of vigorous hydrocracking process.
[37] In the commercially available Fischer- Tropsch process, middle distillate is obtained in a similar manner to the first strategy, which can be effective because separation process is added. However, the second strategy is more preferred in the present invention because products produced in the upper (first) fixed-bed reactor are moved to the lower (second) fixed-bed reactor without additional separation process in the present invention.
[38] In the present invention, the distribution of products is focused on carbon range of middle distillate during Fischer-Tropsch synthesis conducted in the first reactor, and thus prepared products are selectively decomposed by mild hydrocracking process, which differs from the conventional Fischer-Tropsch process.
[39] Hereunder is provided a detailed description of catalysts used in a continuous-flow dual-bed catalyst reaction device according to the present invention.
[40] The conventionally used catalysts for Fischer-Tropsch synthesis, where VIII metal is supported as an active metal onto support, is used in the upper fixed-bed reactor. Examples of the active metal include cobalt, ruthenium, nickel and iron, and examples of the support include silica, mesoporous silica (SBA- 15), titania, alumina and magnesia. Supports such as mesoporous silica (SBA- 15) and titania show superior chain growth probability, thus being appropriate for Fischer-Tropsch synthesis of the upper fixed-bed reactor. In particular, cobalt/titania catalyst is more profitable to the upper fixed-bed reactor.
[41] The conventionally used catalyst can also be used in the present invention without limitation to the preparation process. An incipient wetness method is used in the present invention, and this method is easy to conduct, thus providing superior reproducibility.
[42] As an embodiment, a process of preparing cobalt/silica catalyst by using incipient wet method is described in detail.
[43] Cobalt precursor (cobalt nitrate) is dissolved in distilled water. The amount of water is maintained at minimum level. Silica is added to this solution in such an amount that the weight ratio of cobalt : silica may be 0.1-0.4 : 1, and impregnation is conducted by delivering physical force. Here, a very little amount of water is added very slowly until it wets silica. The impregnated cobalt/silica specimen is dried at 20-200 0 C, preferably 100-150 0 C for about 12 hours or more, preferably 16-20 hours or more, thereby completely eliminating moisture. Catalyst is calcined in a high-temperature electrical furnace at 200-800 0 C, preferably 300-700 0 C, more preferably 400-500 0 C for about 4 hours or more, preferably 5-7 hours or more. Thus prepared cobalt/silica catalyst is reduced and reacted at zero- valence state.
[44] The reduction conditions depend on the kind of catalyst. For example, cobalt/silica catalyst is reduced at 300-600 0 C, preferably 400-500 0 C for 4 hours or more, preferably 6-8 hours under hydrogen condition.
[45] It is preferred to vary the aforementioned conditions such as the amount of water, drying time and calcination time depending on the kind of support and active metal.
[46] Typically, catalytic activity increases as the amount of active metal increases.
However, the catalytic activity levels off when the amount increases. Therefore, it is preferred to maintain the amount of active ingredient within 15-20 wt%. When the amount of the active metal is less than 15 wt%, the activity may not be satisfied due to insufficient number of active sites for Fischer-Tropsch synthesis. When the amount is higher than 20 wt%, the active sites for Fischer-Tropsch synthesis become saturated.
[47] When conducting Fischer-Tropsch synthesis by using thus prepared catalyst, catalytic reaction conditions can be optimized by controlling process variables, particularly space velocity of reactants. Although optimum space velocity depends on the performance of catalysts, it is preferred to control the space velocity of cobalt/titania catalyst within 100-1500 mLg ^ ^h 1 , preferably 300-1000 InLg 031 1 Ir 1 , more preferably 500-800 mLg cat 'h 1 . When the space velocity is lower than 100 HiLg 031 - 1 Ii" 1 , methane production may increase due to insufficient circulation of reaction heat, and the transportation of products may also be difficult. When the space velocity is higher than 1500 mLg cat "1 !! "1 , the amount of hydrocarbon products having high boiling point may be low due to the relatively short contact time between catalyst and reactant.
[48] As other variables, it is preferred to control temperature within 200-240 0 C and
pressure at 10-20 bar, and the temperature at the connection portion between the upper and the lower reactors above 200 0 C for better circulation of products. In cobalt catalyst, when reaction temperature is lower than 200 0 C, Fischer- Tropsch catalyst may show insufficient activity. When the temperature is higher than 240 0 C, catalytic deactivation may be accelerated and the methane production may increase. As reported, the selectivity of products with high boiling temperature increases as reaction pressure increases in Fischer- Tropsch synthesis (10 bar or higher is preferred). In the present invention, 10-20 bar is preferred to obtain the desired product distribution.
[49] The composition of thus obtained products in the first reactor is 30-50 wt% of Ci-C 9 hydrocarbon, 30-40 wt% of Ci 0 -C 2O hydrocarbon and 20-30 wt% of C 2 i or higher hydrocarbon.
[50] Selective hydrocracking reaction process is conducted in the lower fixed-bed reactor. The conventionally used catalysts can be used in the hydrocracking reaction without limitation. Catalysts showing two activities are preferred.
[51] Active metals used in hydrocracking reaction have a hydrogenation activity, and is known to promote the decomposition reaction on solid acid by facilitating the hydrogen supply and to prevent carbon deposition on catalyst acid site. Examples of active metal include nickel, palladium, platinum and molybdenum, and cobalt may be used as co-catalyst. Solid acid may be used as a support, and acts as a catalyst by allowing decomposition of hydrocarbons to occur on acid sites. Examples of solid acid include silica-alumina, zeolites and clays.
[52] In an embodiment of the present invention, solid acid catalyst usually used in the process of cracking and modifying crude oil is used as support component in the present invention. Examples of the solid acid catalyst include commercially available zeolite, in particular ZSM-5, modernite, zeolite beta and alumina. Aluminum site in zeolite structure has an anion charge, and this site is substituted with a cation, particularly with sodium or ammonium ion in commercially available zeolites. Thus, thermal treatment or ion exchange is preferred for substituting hydrogen ion in zeolites for cations. Although most zeolites tested during this process showed a superior decomposition activity and decomposed smaller hydrocarbons in addition to wax, alumina showed a preferable decomposition activity, thereby increasing the selectivity of middle distillates.
[53] Further, as a result of testing the performance of catalyst where nickel and palladium are supported to determine an appropriate active metal for the alumina support, it was ascertained that nickel supported onto alumina showed relatively smaller amount of liquefied distillate with large amount of methane. In contrast, palladium showed preferable decomposition behavior because the selectivity of middle distillate was increased while causing the production of relatively small amount of gas. Therefore,
palladium/alumina catalyst is preferred in hydrocracking reaction of the present invention.
[54] Conventional catalysts may be used in the present invention without limitation to the preparation method.
[55] Hydrocracking reaction is conducted by using thus prepared catalyst at 270-350 0 C and 10-20 bar and at the space velocity of 500-1000 niLg^lr 1 of hydrogen.
[56] Generally, catalysts used in hydrocracking reaction show activity at 270 0 C or higher. According to experiments, when the temperature is higher than 350 0 C, gas- phase hydrocarbon products are produced in large amount. Although the upper and the lower reactors become the same in pressure when a continuous -flow dual-bed reactor is used, 10-20 bar is sufficient because hydrocracking reaction is also conducted preferably under a relatively high pressure. Further, the space velocity is important except the first reactant because hydrogen partial pressure is important in hydrocracking reaction. For appropriate hydrocracking reaction, the aforementioned space velocity, 500 mLg cat 'h '-lOOO niLg^lr 1 is preferred. When the space velocity is higher than 1000 niLg^lr 1 , gas-phase products are produced in a large amount due to vigorous decomposition.
[57] These conditions are adopted when reactants passing through the upper catalyst bed has the aforementioned distribution. Although it may depend on the kind of catalyst, the aforementioned conditions are preferred when optimum catalyst, palladium/ alumina catalyst, is used in the present invention.
[58] Hydrocarbon mixture that may be prepared under the above reactions in the lower fixed-bed reactor comprises 30-45 wt% of Ci-C 9 hydrocarbon, 50-55 wt% of Ci 0 -C 2O hydrocarbon and 5-15 wt% of C 2 i or higher hydrocarbon.
[59] In conclusion, cobalt/titania catalyst is preferred for Fischer- Tropsch synthesis in the upper fixed-bed reactor of the present invention, while palladium/alumina catalyst is preferred for hydrocracking reaction in the lower fixed-bed reactor.
[60]
[61] The following examples illustrate the invention but they should not be construed as limiting the scope of the present invention.
[62]
[63]
[64] Preparatory Example 1 : Catalyst for Fischer-Tropsch reaction
[65] Preparatory Example 1-1 : Preparation of cobalt/silica catalyst
[66] Cobalt nitrate (3.9504 g) was dissolved in distilled water (2 g). The amount of water was maintained to minimum. Silica was added in such an amount that the weight ratio of cobalt : silica can be 0.15:1, 0.2:1 and 0.4:1, respectively, and impregnated by delivering physical force. Water was added very slowly in such an amount as to wet
silica (Incipient Wetness Method), thereby preparing impregnated cobalt/silica specimens.
[67] The impregnated cobalt/silica specimens were dried at 120 0 C for more than 24 hours to completely remove moisture, and calcined in a high-temperature electric furnace at 500 0 C for about 4 hours, thereby providing cobalt/silica catalysts with different weight ratios.
[68]
[69] Preparatory Example 1-2 : Preparation of cobalt/SBA-15 catalyst
[70] Cobalt/SBA-15 catalyst was prepared the same as in Preparatory Example 1-1 except that the weight ratio of cobalt : SBA- 15 was maintained to 0.2 : 1.
[71]
[72] Preparatory Example 1-3 : Preparation of cobalt/titania catalyst
[73] Cobalt/titania catalyst was prepared the same as in Preparatory Example 1-1 except that the weight ratio of cobalt : titania was maintained to 0.15 : 1. Calcination was conducted at 300 0 C for 20 hours.
[74]
[75] Preparatory Example 2 : Catalyst for hydrocracking
[76] Preparatory Example 2-1 : Substitution of hydrogen cation in commercially available zeolite
[77] Commercially available zeolite (ZSM-5, zeolite beta and modernite) maintain ammonium form, and ammonia was removed by conducting heat treatment in a high- temperature electrical furnace at 500 0 C for about 20 hours, thereby providing zeolite catalyst substituted with hydrogen ion.
[78]
[79] Preparatory Example 2-2 : Preparation of nickel/alumina catalyst
[80] Nickel nitrate (3.963 g) was dissolved in distilled water (2 g). The amount of water was maintained to minimum. Alumina was added in such an amount that the weight ratio of nickel : alumina can be 0.2 : 1, and impregnated by delivering physical force. Water was added very slowly in such an amount as to wet silica (Incipient Wetness Method), thereby preparing impregnated nickel/alumina specimen.
[81] The impregnated nickel/alumina specimen was dried at 120 0 C for more than 12 hours to completely remove moisture, and calcined in a high-temperature electric furnace at 500 0 C for about 4 hours, thereby providing nickel/alumina catalyst.
[82]
[83] Preparatory Example 2-3 : Preparation of palladium/alumina catalyst
[84] Palladium/alumina catalyst was prepared the same as in Preparatory Example 2-2 except that the weight ratio of palladium : alumina was maintained to 0.01 : 1.
[85]
[86] Example 1 : Fischer-Tropsch synthesis
[87] Fischer-Tropsch synthesis reactivity was measured by using catalysts prepared in
Preparatory Example 1-1 (cobalt/silica), Preparatory Example 1-2 (cobalt/SBA-15), and Preparatory Example 1-3 (cobalt/titania). Products were obtained by filling catalysts in the upper fixed-bed reactor of a continuous -flow dual-bed reactor, while allowing the lower fixed-bed reactor empty, followed by the analysis of the products.
[88] Before the reaction, catalysts prepared in Preparatory Example 1-1 (cobalt/silica),
Preparatory Example 1-2 (cobalt/SBA-15), and Preparatory Example 1-3 (cobalt/titania) were reduced under an atmospheric pressure. The volumetric ratio of nitrogen : hydrogen was 1:1, and the space velocity of the gas mixture was about 2000 mLg cat 'h 1 . Although the reduction temperature and time depend on the kind of catalyst, the reduction was conducted at 400 0 C for about 12 hours.
[89] Carbon monoxide and hydrogen were used as the reactants for Fischer-Tropsch synthesis, and internal standard material was nitrogen. Inert gas such as nitrogen was introduced to facilitate the thermal circulation of catalyst bed and the transportation of the reactants. The volumetric ratio of the reactants (nitrogen : carbon monoxide : hydrogen) was 0.67 : 1 : 2. Stainless steel micro reactor was used, and reaction temperature and pressure were maintained to 220 0 C and 10 bar, respectively.
[90]
[91] Test Example 1 : Catalytic activity of Fischer-Tropsch synthesis reaction
[92] Fischer-Tropsch synthesis was conducted by using the catalysts prepared Example 1
(cobalt/silica, cobalt/SBA-15, cobalt/titania catalysts), and the results are presented in Table 1. Products were analyzed with gas chromatograph. Among the products, Ci 0 or lower hydrocarbons were analyzed in situ, and liquid- or solid-phase products were collected in a trap and analyzed after the completion of the reaction.
[93] Conversion of carbon monoxide, mass selectivity of middle distillate and mass selectivity of liquid-phase residues (C 5 or higher mass selectivity) were calculated by using the following formulas. As previously mentioned, Ci 0 -C 2O residues were considered as middle distillate.
[94] MathFigure 1
[Math.l]
Conversion(% ) = (Mass of reacted carbon monoxide/mass of supplied carbon monoxide)X100 [95] MathFigure 2
[Math.2]
Methane selectivity (% )= (Mass of produced methane/ total mass of produced hydrocarbon)X100
[96] MathFigure 3
[Math.3]
C10-C20 selectivity(%)=(Mass of C10-C20 hydrocarbon/ total mass of produced hydrocarbon)X100
[97] MathFigure 4
[Math.4]
Selectivity of C21 or higher hydrocarbon(%)=(Mass of produced C21 or higher hydrocarbon/ total mass of produced hydrocarbon)X100
[98] MathFigure 5
[Math.5]
Selectivity of C5 or higher hydrocarbon(%)=(Mass of produced C5 or higher hydrocarbon/ total mass of produced hydrocarbon)X100
[99] MathFigure 6
[Math.6]
VnZn = ( 1- α r ,2 α _ n-1
[100] Wn is mass of produced hydrocarbon having n carbons, and n is the number of carbons. For example, when n is 4, Wn is total mass of butane isomers. The equation is converted into logarithm values, and the values are plotted on plane having x axis (n) and y axis (ln(Wn/n)). The slope of thus obtained line is 'In α', and chain growth probability (α) was finally obtained.
[101] Table 1
[Table 1] [Table ]
[102] As shown in Table 1, titania is superior to other supports in performance.
Specifically, the present invention aims to increase the selectivity of middle distillate by obtaining Ci 0 -C 2O middle distillate with relatively high selectivity in the upper fixed- bed reactor, while selectively hydrocracking wax products having high boiling temperature produced in the lower fixed-bed reactor using a solid acid catalyst. Therefore, cobalt/titania catalyst is considered to show a performance appropriate for the purpose of the present invention because the selectivity of middle distillate approaches 40 wt% and wax selectivity also exceeds 20%.
[103] [104] Example 2 : Solid acid catalyst for hydrocracking reaction [105] Hydrocracking reaction was conducted in the lower fixed-bed reactor after the same procedure as Example 1. When the non-supported solid acid catalyst is filled in the lower fixed-bed reactor, Fischer-Tropsch catalyst filled in the upper fixed-bed reactor can be reduced, and the resultant impurities can deactivate the solid acid catalyst. Therefore, in this case, solid acid catalyst was loaded in the lower fixed-bed reactor when the catalyst reduction was completed and activated after Fischer-Tropsch reaction was initiated in the upper reactor. This is a special test example that is employed only when the activity of non-supported solid acid catalyst is tested. [106] Appropriate temperature in the lower fixed-bed reactor was 270 0 C, and pressure was
the same as in the upper fixed-bed reactor. The space velocity of hydrogen introduced into the upper catalyst bed was maintained to 500 HiLg 031 - 1 Ii" 1 .
[107] [108] Test Example 2 : Activity of solid acid catalyst for hydrocracking reaction [109] Hydrocracking reaction was conducted by using non-supported solid acid catalyst prepared in Example 2, and the results are presented in Table 2.
[HO] Table 2 [Table 2] [Table ]
[111] As in Table 2, zeolite substituted with hydrogen ion showed relatively active decomposition performance when it reacts with products prepared from the upper fixed-bed reactor. In this case, the decomposition proceeded more actively than expected, thereby increasing the selectivity of hydrocarbon gas lighter than middle distillate and gasolines (C 5 -C 9 ). However, although alumina also increased the selectivity of gasoline, mainly wax products were transformed, thereby increasing the selectivity of middle distillate. Based on the aforementioned results, alumina support was determined as appropriate for catalysts for hydrocracking reaction.
[112] [113] Example 3 : Metal-supported solid acid catalyst for hydrocracking reaction [114] Reaction was conducted by using catalysts prepared in Preparatory Examples 1-2 in a
continuous -flow dual-bed reactor. Because Fischer-Tropsch catalyst and hydro- cracking catalyst were zero-valenced, the two catalysts were simultaneously reduced when they were supported onto metal. Reactions were also allowed to proceed at the same time.
[115] Both the catalysts were reduced at atmospheric pressure, and the volumetric ratio of nitrogen : hydrogen for the upper Fischer-Tropsch catalyst was 1 : 1. The space velocity of the gas mixture was 2000 niLg^lr 1 , and the reaction was conducted under atmospheric pressure. Reduction temperature and time was 250 0 C and 15 hours as recommended in relevant arts although it depends on the kind of catalyst.
[116] Although other conditions for the reduction of the lower hydrocracking catalyst was similar to those of the reduction in the upper reactor, an appropriate temperature was 400 0 C. The catalyst filled in the lower fixed-bed reactor was conducted by using hydrogen- supplying pipe. The space velocity of hydrogen was appropriately 2000 mLg cat 'h 1 , and the two kinds of catalysts were reduced for the same time.
[117] After the reduction, reaction was also initiated at the same time. Reactants were introduced into the upper fixed-bed reactor, while maintaining the molar ratio of reactants (nitrogen : carbon monoxide : hydrogen) to 0.67 : 1 : 2. Appropriate reaction temperature of the lower fixed-bed reactor was 270 0 C, and pressure was maintained at the same level with the first catalyst bed. The space velocity of hydrogen for hydro- cracking reaction was controlled to 500 niLg^lr 1 .
[118]
[119] Test Example 3 : Activity of a metal-supported solid acid catalyst for hydro- cracking reaction
[120] Hydrocracking reaction was conducted by using metal- supported solid acid catalyst prepared in Example 3, and the results are presented in Table 3.
[121] Table 3
[Table 3] [Table ]
[122] As shown in Table 3, nickel/alumina remarkably increases the production of methane. In contrast, palladium/alumina increases the selectivity of middle distillate, while decreasing wax amount and maintaining similar production level of methane and lighter hydrocarbon gas. When applied to the lower fixed-bed reactor, palladium/ alumina increased the selectivity of middle distillate by about 10% as compared in upper fixed-bed reactor. Further, the selectivity of middle distillate was further increased by another kind of alumina under the same condition.
[123] [124] Accordingly, when hybrid Fischer- Tropsch reaction was conducted by using a continuous -flow dual-bed reactor according to the present invention, higher selectivity of middle distillate(Ci O -C 2 o) was achieved than in the conventional Fischer-Tropsch
synthesis by using the combination of cobalt/titania catalyst (the upper fixed-bed reactor) and palladium/alumina catalyst (the lower fixed-bed reactor). Industrial Applicability
[125] A continuous -flow dual-bed reactor of the present invention has a relatively simple structure, and makes it possible to control the production of products depending on the combination of catalysts, thus being advantageous in actively cope with the change in demand for synthesis oil when used in the commercial process.
[126] When hybrid Fischer- Tropsch synthesis is conducted, the use of the continuous-flow dual-bed reactor enables to increase the selectivity of hydrocarbons (transportation fuel) without conducting a separation process. The thermal efficiency is also high because thermal energy of the first reaction can be used in the second reaction because no separation process is required.