AU2007356234B2 - Synthesis Gas Production Method in a Process for Producing Kerosene and Gas Oil from Natural Gas - Google Patents

Description

1 DESCRIPTION Synthesis Gas Production Method in a Process for Producing Kerosene and Gas Oil from Natural Gas 5 Technical Field The present invention relates to a synthesis gas production method in a process for producing kerosene and gas oil from a natural gas which includes a synthesis gas producing step, a Fischer-Tropsch oil producing step and an upgrading step. 10 Background Art In a process for producing kerosene and gas oil from a natural gas which comprises a synthesis gas producing step for producing a synthesis gas from the natural gas, a Fischer-Tropsch oil producing step for subjecting the synthesis gas to a Fischer-Tropsch is reaction to produce heavy hydrocarbons, and an upgrading step for hydtrotreating the heavy hydrocarbons to produce product fuel oil, the desired products are kerosene and gas oil. Light hydrocarbons such as LPG and naphtha obtained as a by-product in the upgrading step have a low added value as will be appreciated from its chemical properties and is, for example, used for the production of a desired light hydrocarbon product or utilized as a raw 20 material for existing processes. Such a use or utilization is determined in view of various points such as its market value, economy, etc. The present inventors have thought that if light hydrocarbon, which is a by-product having a low added value in a process for producing kerosene and gas oil from a natural 25 gas, is able to be recycled as a raw material in the process, it is possible to improve the raw material consumption and to obtain significant economical merits. At present, however, there are no proposals which suggest how to specifically use such light hydrocarbons in the kerosene and gas oil production process.

2 The present invention has been made under such a circumstance and aims to provide synthesis gas production method in a process for producing kerosene and gas oil from a natural gas, which method is contemplated to specifically reuse light hydrocarbons being a by-product having a low added value and to improve the raw material basic unit. 5 Object of the Invention It is the object of the present invention to substantially overcome or at least ameliorate one or more of the prior art disadvantages or at least provide a useful alternative. 10 Disclosure of the Invention The present invention provides a process for producing kerosene and gas oil from a natural gas comprising: a synthesis gas producing step in which a hydrocarbon gas feed containing a natural gas is subjected to a reforming reaction with steam and/or carbon dioxide to produce 15 a synthesis gas, a Fischer-Tropsch oil producing step in which the synthesis gas is subjected to a Fischer-Tropsch reaction to produce a Fischer-Tropsch reaction product, the Fischer Tropsch reaction product being subsequently separated into a Fischer-Tropsch oil and a gaseous product, and 20 an upgrading step in which the Fischer-Tropsch oil is hydrotreated to obtain a hydrotreated product, the hydrotreated product being subsequently distilled to obtain light hydrocarbons and final products of kerosene and gas oil, wherein at least a part of the light hydrocarbons separated by distillation in said upgrading step is recycled to said synthesis gas producing step as part of the hydrocarbon 25 gas feed. The present invention in a preferred embodiment provides a process according to the above, wherein, in said synthesis gas producing step, a H 2 0/C molar ratio is in the range of 0.0 to 3.0 and/or a C0 2 /C molar ratio is in the range of 0.0 to 1.0 where C is a number of 30 moles of the carbon of hydrocarbons contained in the hydrocarbon gas feed containing the natural gas and the recycled light hydrocarbon, and H 2 0 and C02 are the steam and carbon dioxide, respectively, fed to said synthesis gas producing step.

3 The present invention in another preferred embodiment provides a process according to the above, wherein, in said synthesis gas producing step, the number of the carbon atoms in the recycled light hydrocarbons is maintained in the range of 10 to 35 % based on the number of the carbon atoms in the natural gas fed to said synthesis gas 5 producing step. The present invention in another preferred embodiment provides a process according to the above, wherein, in said synthesis gas producing step, the number of carbon atoms in the final products of kerosene and gas oil is set in a range of 60 to 80% based on 10 the number of the carbon atoms in the natural gas fed to said synthesis gas producing step. The present invention in another preferred embodiment provides a process according to the above, wherein, in said synthesis gas producing step, a temperature in an outlet of a catalyst layer is 800 to 950*C, a pressure in an outlet of the catalyst layer is 1.5 to is 3.0 MPaG, and a GHSV (gas hourly space velocity) is 500 to 5,000 hr 1 . The present invention in another preferred embodiment provides a process according to the above, wherein, in said synthesis gas producing step, the natural gas contains hydrocarbons having 1 to 6 carbon atoms and containing methane in an amount of 20 at least 60 mole %. Since the present invention in a preferred embodiment is constructed such that, in a process for producing kerosene and gas oil from a natural gas, comprising: a synthesis gas producing step in which a hydrocarbon gas feed containing a natural gas is subjected to a 25 reforming reaction with steam and/or carbon dioxide to produce a synthesis gas, a Fischer Tropsch oil production step in which the synthesis gas is subjected to a Fischer-Tropsch reaction to produce a Fischer-Tropsch reaction product, the Fischer-Tropsch reaction product being subsequently separated into a Fischer-Tropsch oil and a gaseous product, and an upgrading step in which the Fischer-Tropsch oil is hydrotreated to obtain a 30 hydrotreated product, the hydrotreated product being subsequently distilled to obtain light hydrocarbon and final products of kerosene and gas oil, at least a part of the light hydrocarbon separated by distillation in said upgrading step is recycled to said synthesis gas producing step as part of the hydrocarbon gas feed, the light hydrocarbon which is a by product having a low added value in the process for producing kerosene and gas oil from the 35 natural gas is contemplated to specifically reuse and to improve the raw material basic unit.

4 Brief Description of the Drawing A preferred embodiment of the present invention will now be described, by way of an example only, with reference to the accompanying drawing wherein: 5 FIG. 1 is a scheme showing a synthesis gas production method in a process for producing kerosene and gas oil from a natural gas according to the present invention. Best Mode for Carryinq out the Invention The best mode for carrying out the present invention will be described 10 below. The present invention is directed to a synthesis gas production method in a process for producing kerosene and gas oil as an end product from a natural gas. 15 FIG. 1 is a scheme showing a synthesis gas production method in a process for producing kerosene and gas oil from a natural gas according to the present invention. As shown in FIG. 1, the process for producing kerosene and gas oil from a natural gas comprises a synthesis gas producing step 10, a Fischer-Tropsch oil producing step (FT 20 synthesis step) 20, and an upgrading step 30. In the process for producing kerosene and gas oil from a natural gas, the gist of the present invention resides in recycling light hydrocarbons separated by distillation in the upgrading step 30 to the synthesis gas producing step as a raw material for producing the 25 synthesis gas. The reference numeral 40 designates the step for recycling the light hydrocarbon. In a case where the light hydrocarbon is recycled to the Fischer-Tropsch oil producing step (FT synthesis step) 20, the recycled hydrocarbon cannot serve as a raw material and, further, causes a reduction of the partial pressure of the synthesis gas. As a consequence, the reaction rate of the Fischer-Tropsch synthesis is disadvantageously reduced. Thus, the recycling to the step 20 is not preferable. 5 The description will be first made of each of the steps constituting the process for producing kerosene and gas oil from a natural gas according to the present invention. [Synthesis gas producing step] 10 The synthesis gas producing step is to produce a synthesis gas (CO and

H

2 ) by reforming reaction of a natural gas fed as a raw material with steam and/or carbon dioxide. Namely, the synthesis gas producing step is to produce a synthesis gas composed mainly of CO and H 2 by reforming a hydrocarbon gas feed containing methane as a major ingredient with steam (H 2 0) and/or carbon 15 dioxide (C0 2 ) in the presence of a synthesis gas producing catalyst. In the present invention, in addition to the natural gas fed as a raw material, the light hydrocarbon separated in and recycled from the upgrading step 30, as described previously, is incorporated into the hydrocarbon gas feed for producing the synthesis gas (see the step 40 for recycling the light hydrocarbon 20 in FIG. 1). Thus, necessary additional descriptions for the synthesis gas producing step including a description of the recycled light hydrocarbon will be made hereinafter the description of the upgrading step 30. Description of synthesis gas production catalyst used in reforming reaction The catalyst for use in the synthesis gas production comprises a carrier, 25 and a catalytic metal supported on the carrier. As the carrier, a calcined molded body of magnesium oxide is preferably used. Such a molded body may be prepared by molding under pressure magnesium oxide powder in a mold into a desired shape and then calcining the molded product. The shape of the molded body is not specifically limited but is 5 generally in the industrially ordinarily employed form, such as rings, saddles, multi-hole bodies, pellets, etc. The shape of the catalyst may also be an irregular form such as crushed particles. The carrier of such a magnesium oxide molded body has a specific 5 surface area of 0.1 to 1.0 m 2 /g, preferably 0.2 to 0.5 m 2 /g. When the specific surface area exceeds 1.0 m 2 /g, there is a tendency to increase the rate of formation of carbon and to cause a disadvantage that the catalytic activity is reduced. When the specific surface area is less than 0.1 m 2 /g, there is a tendency that the catalytic activity per unit catalyst is so small that a large amount 10 of the catalyst must be disadvantageously used. The specific surface area as used herein is as measured by the so-called BET method. In general, a combination of a calcination temperature and a calcination time can control the specific surface area of the obtained carrier or catalyst. Magnesium oxide (MgO) used as a carrier may be obtained by calcining 15 commercially available magnesium oxide (MgO). The purity of magnesium oxide (MgO) must be at least 98 % by weight, preferably at least 99 % by weight. Contamination of components enhancing the carbon deposition activity or components decomposing under a high temperature or a reducing gas atmosphere, such as iron, nickel and the like metals and silicon dioxide (SiO 2 ), is 20 particularly undesirable. On such a carrier is supported ruthenium (Ru) as a catalytic metal in an amount of 10 to 5,000 wt-ppm per unit weight of carrier, preferably 100 to 2,000 wt-ppm, in terms of metal element. An amount of Ru above 5,000 wt-ppm is undesirable because the cost of the catalyst increases and because carbon 25 deposition tends to occur during production. Too small an amount of Ru below 10 wt-ppm fails to provide satisfactory catalytic activity. The amount of Ru metal is expressed in terms of the weight ppm based on the catalyst carrier. Rhodium (Rh) may be also used in lieu of ruthenium (Ru). One suitable example of the method for preparing a synthesis gas 6 production catalyst will be described below. Preparation of catalyst carrier Magnesium oxide (MgO) powder is mixed with, for example, carbon as a lubricant and the mixture is then molded under pressure into a predetermined 5 shape. The molded body is then calcined at 1,0000C or higher, preferably 1,000 to 1,3000C, more preferably 1,100 to 1,2000C, for 1 to 4 hours. The calcination is generally carried out in air. The activity of the ordinary reforming catalyst is nearly proportional to its outer surface area. Thus, as the particle size decreases, the catalytic activity 10 increases. However, this results in an increased pressure loss because the mass velocity of the gas is large. Under the above circumstance, a cylindrical shape carrier is widely used. Supporting of catalytic metal (Ru) The thus prepared carrier is impregnated with an aqueous solution of 15 ruthenium chloride. The impregnated material is then dried and calcined to support ruthenium (Ru) on outer surfaces of the magnesium oxide molded body. Illustrative of suitable methods for impregnating the carrier are an immersing method and a spray method. Among them, the spray method in which the aqueous ruthenium chloride solution is sprayed over the carrier is preferred. 20 The Ru-adsorbed carrier is dried at 50 to 1500C for about 1 to 4 hours and then calcined at 300 to 5000 C, preferably 350 to 4500 C, for about 1 to 4 hours. The drying and calcination may be performed in air. The calcination can further enhance the reaction activity of the catalytic metal. Method for producing synthesis gas 25 As described above, a synthesis gas containing CO and H 2 as major components is produced by reforming, with H 2 0 and/or C02 in the presence of the thus prepared synthesis gas production catalyst, a hydrocarbon gas feed including a natural gas containing methane as its main ingredient (generally a natural gas containing hydrocarbons which have 1 to 6 carbon atoms and which 7 contain methane in an amount of at least 60 mole %), and light hydrocarbon recycled from the upgrading step 30. In this case, when attention is focused upon methane, (i) the reaction of methane (CH 4 ) with carbon dioxide (CO 2 ) (CO 2 reforming) proceeds as shown by 5 the following formula (1):

CH

4 + C0 2 " 2CO + 2H 2 (1) and (ii) the reaction of methane (CH 4 ) with steam (H 2 0) (steam reforming) proceeds as shown by the following formula (2):

CH

4

+H

2 0 +-+ CO + 3H 2 (2) 10 In the above reforming conditions, a water gas shift reaction of the formula (3) below also proceeds simultaneously with the above two reactions because the catalyst has a water gas shift activity. CO + H 2 0 - C0 2 + H 2 (3) Based on the above stoichiometric formulas (1) and (2), it is seen that 15 the CO 2 reforming of methane gives a synthesis gas having a H 2 /CO molar ratio of 1, while the H 2 0 reforming of methane results in the formation of a synthesis gas having a H 2 /CO molar ratio of 3. Thus, by combining these reactions it is possible to directly produce a synthesis gas having a H 2 /CO molar ratio of 1 to 3 without a need to separate hydrogen from the product gas. 20 Namely, it is possible to directly produce a synthesis gas having a H 2 /CO molar ratio of about 1 to 2 which is suitable as a raw material for methanol, FT synthesis and DME. However, under the reaction conditions for directly producing a synthesis gas having such a molar ratio range, the product gas generally has a 25 composition causing deposition of carbon on the catalyst surfaces, which in turn causes catalyst deterioration. The above-described specific catalyst for producing a synthesis gas is effectively used to solve the problem of such catalyst deterioration. Further, by using the specific synthesis gas production catalyst, it has become possible to recycle light hydrocarbons separated by 8 distillation in the upgrading step 30 to the synthesis gas producing step as part of the hydrocarbon gas feed. Such a recycling represents the essence of the present invention. If the light hydrocarbon is recycled to the synthesis gas producing step as a part of the hydrocarbon gas feed while using a catalyst 5 other than the above-described specific synthesis gas production catalyst, deposition of carbon derived from the light hydrocarbon will significantly occur to cause deactivation of the catalyst. [Fischer-Tropsch oil producing step (FT synthesis step)] 10 The Fischer-Tropsch oil producing step is a step in which the above-described synthesis gas is subjected to a Fischer-Tropsch reaction in the presence of a catalyst to produce a Fischer-Tropsch product, the Fischer-Tropsch reaction product being subsequently separated into a Fischer-Tropsch oil and a gaseous product. The FT synthesis reaction gives a 15 hydrocarbon mixture from the synthesis gas of CO and H 2 according to the following formula: CO + 2H 2 -> 1/n-(CH 2 )-n + H 2 0 The Fischer-Tropsch catalyst comprises a catalytic metal such as metallic iron (Fe), cobalt (Co), ruthenium (Ru) or nickel (Ni). If desired, such a 20 catalytic metal may be supported on a carrier such as silica, alumina, silica alumina or titania. The reaction conditions generally involve a reaction temperature of 200 to 350*C and a reaction pressure of ambient pressure to about 4.0 MPaG. When an iron catalyst is used, the reaction temperature is preferably 250 to 25 350 0 C and the reaction pressure is preferably about 2.0 to 4.0 MPaG. When a cobalt catalyst is used, the reaction temperature is preferably 220 to 2500 C and the reaction pressure is preferably about 0.5 to 4.0 MPaG. The Fischer-Tropsch reaction is a kind of polymerization. It is generally difficult to maintain the degree of polymerization (number n). Therefore, the 9 product includes a wide distribution of C1 to C100, hydrocarbons. The distribution of the carbon number follows the Schulz-Flory rule and may be expressed in terms of a chain growth probability factor ci. In the case of industrial catalysts, the value cv is in the range of about 0.85 to 0.95. 5 The FT reaction primarily produces a-olefins which undergo the following secondary reactions. Namely, the secondary reactions include hydrogenation resulting in the formation of straight chain paraffins, hydrocracking resulting in the formation of lower paraffin such as methane, secondary chain growth reactions resulting in the formation of higher hydrocarbons, etc. 10 Although in a small amount, alcohol such as ethanol, ketone such as acetone and carboxylic acid such as acetic acid are also produced. Examples of the reactor for the FT synthesis include a fixed bed reactor, a fluidized bed reactor, a slurry bed reactor and super critical reactor. Since refining treatments such as dedusting and desulfurization for 15 protecting the catalyst have been generally carried out during the production of the synthesis gas, the hydrocarbons produced therefrom by the FT synthesis are free of sulfur compounds and heavy metals and are very clean. The hydrocarbons produced by the FT synthesis are mostly composed of straight chain olefins (1-olefins) and straight chain paraffins. 20 There is no specific limitation for a device used for the separation of the Fischer-Tropsch reaction product into a gaseous product and a Fischer-Tropsch oil (hydrocarbon oil) and various known devices may be used. For example, a flash separator may be used. 25 [Upgrading step] In the succeeding upgrading step, the Fischer-Tropsch oil is hydrotreated (catalytic hydrotreatment) to obtain a hydrotreated product, the hydrotreated product being subsequently distilled to obtain light hydrocarbons and final products of kerosene and gas oil. 10 The hydrotreatment may be performed using a reactor with any catalytic bed such as a fluidized bed, a moving bed, a slurry bed or a fixed bed. The hydrotreatment conditions involve, for example, a reaction temperature of about 175 to 400'C and a hydrogen partial pressure of 1 to 25 MPaG (10 to 250 atm). 5 The hydrotreated hydrocarbon fraction is separated by distillation into light hydrocarbons containing mainly LPG and naphtha and final products of kerosene and gas oil. In the present invention, the light hydrocarbons such as LPG and naphtha, which is not objective final products, are recycled to the synthesis gas 10 producing step. Namely, the light hydrocarbons such as LPG and naphtha are recycled to the synthesis gas producing step 10 as part of the hydrocarbon gas feed for the production of the synthesis gas, as shown in FIG. 1. The description will be again made of the synthesis gas producing step 10. 15 In the synthesis gas producing step 10, a H 2 0/C molar ratio is adjusted in the range of 0.0 to 3.0 and/or a CO 2 /C molar ratio is adjusted in the range of 0.0 to 1.0 where C is a number of moles of the carbon of hydrocarbons contained in the hydrocarbon gas feed containing the natural gas and the recycled light hydrocarbons, and H 2 0 and CO 2 are the steam and carbon dioxide, respectively, 20 fed to said synthesis gas producing step. The H 2 0/C molar ratio is preferably 0.3 to 1.7, more preferably 0.7 to 1.3, while the C0 2 /C molar ratio is preferably 0.2 to 0.8, more preferably 0.4 to 0.6. Further, in the synthesis gas producing step 10 of the present invention, the number of the carbon atoms in the recycled light hydrocarbons is maintained 25 in the range of 10 to 35 %, preferably 15 to 35 %, more preferably 20 to 30%, based on the number of the carbon atoms in the natural gas fed to the synthesis gas producing step. When this value is less than 10 %, it is not possible to sufficiently accomplish the prime object to contemplate the specific reuse of the light hydrocarbons and to improve the raw material consumption. On the other 11 hand, when this value exceeds 35 %, carbon deposition on surfaces of the synthesis gas production catalyst is apt to occur. Such carbon deposition will result in the catalyst deterioration. Thus, the value of 10 to 35 % plays an important factor in determining in what proportion the light hydrocarbons should 5 be recycled. Namely, entire amount of the light hydrocarbons separated in the upgrading step 30 can be recycled without any problem as long as the above value falls within the range of 10 to 35 %. When the value exceeds 35 % by recycling the entire amount of the light hydrocarbons, then a method is adopted in which not entire amount but only a part of the light hydrocarbons is recycled. 10 Further, in the synthesis gas producing step 10 of the present invention, the number of the carbon atoms in the final products of kerosene and gas oil is set in a range of 60 to 80 %, preferably 65 to 80 %, based on the number of the carbon atoms in the natural gas fed to the synthesis gas producing step. Further, in the synthesis gas producing step of the present invention, the 15 temperature in an outlet of a catalyst layer is 800 to 950'C, preferably 850 to 920 "C, the pressure in an outlet of the catalyst layer is 1.5 to 3.0 MPaG, and the GHSV (gas hourly space velocity) is 500 to 5,000 hr 1 . [Example] 20 The present invention will be described in more detail by giving concrete examples. Example 1 A synthesis gas having H 2 /CO molar ratio of 2.0 suitable as a raw material for the FT (Fischer-Tropsch) synthesis was produced while recycling all 25 of the naphtha and LPG produced as a by-product in-an upgrading step 30 of a process for producing kerosene and gas oil from a natural gas, as shown in FIG. 1. As a catalyst for producing a synthesis gas, a catalyst having Ru supported on a MgO carrier was used. 12 The synthesis gas producing step 10 was operated at a temperature in an outlet of the catalyst layer of 900'C, a pressure in an outlet of the catalyst layer of 2.0 MPaG, a GHSV (gas hourly space velocity) of 2,000 hr', a H 2 0/C molar ratio of 1.27, and a CO 2 /C molar ratio of 0.41. The natural gas had a 5 composition of C1/C2/C3/C4/C5+/N 2 of 90.0/5.5/2.5/0.5/1.0/0.5 (mol/mol). The material balance on inlet and outlet sides of the synthesis gas producing step in FIG. 1 (materials indicated as (1), (2), (3), (4), (5) and (7) in FIG. 1) was calculated, based on which the production efficiency of the synthesis gas producing step in the kerosene and gas oil production process was evaluated. 10 As a result, it was found that the percentage, calculated on the basis of the material balance, of the number of the carbon atoms in the recycled gas relative to the number of the carbon atoms in the hydrocarbons contained in the natural gas was 25.8 %. The yield of the products (kerosene and gas oil) based on the carbon atoms in the natural gas was found to be 67.4 %. The feed 15 amount of the natural gas was able to be reduced by 17.5 % as compared with a case where no recycling was conducted. Example 2 A synthesis gas having H 2 /CO of 2.0 suitable as a raw material for the FT (Fischer-Tropsch) synthesis was produced while recycling only the 20 naphtha produced as a by-product in an upgrading step 30 of a process for producing kerosene and gas oil from a natural gas, as shown in FIG. 1. The synthesis gas producing step 10 was operated at a temperature in an outlet of the catalyst layer of 9000C, a pressure in an outlet of the catalyst layer of 2.0 MPaG, a GHSV (gas hourly space velocity) of 2,000 hr', a H 2 0/C 25 molar ratio of 1.27, and a C02/C molar ratio of 0.41. The raw material natural gas had a composition of C1/C2/C3/C4/C5+/N 2 of 90.0/5.5/2.5/0.5/1.0/0.5 (mol/mol). The material balance on inlet and outlet sides of the synthesis gas producing step in FIG. 1 (materials indicated as (1); (2), (3), (4), (5) and (7) in FIG. 13 1) was calculated, based on which the production efficiency of the synthesis gas producing step in the kerosene and gas oil production process was evaluated. As a result, it was found that the percentage, calculated on the basis of the material balance, of the number of the carbon atoms in the recycled gas 5 relative to the number of the carbon atoms in the hydrocarbons contained in the natural gas was 24.1 %. The yield of the products (kerosene and gas oil) based on the carbon atoms in the natural gas was found to be 66.6 %. The feed amount of the natural gas was able to be reduced by 16.4 % as compared with a case where no recycling was conducted. 10 Example 3 A synthesis gas having H 2 /CO of 2.0 suitable as a raw material for the FT (Fischer-Tropsch) synthesis was produced while recycling only a half the amount of the naphtha produced as a by-product in an upgrading step 30 of a process for producing kerosene and gas oil from a natural gas, as shown in FIG. 15 1. The synthesis gas producing step 10 was operated at a temperature in an outlet of the catalyst layer of 900 C, a pressure in an outlet of the catalyst layer of 2.0 MPaG, a GHSV (gas hourly space velocity) of 2,000 hr', a H 2 0/C molar ratio of 1.25, and a C0 2 /C molar ratio of 0.44. The raw material natural 20 gas had a composition of C1/C2/C3/C4/C5+/N 2 of 90.0/5.5/2.5/0.5/1.0/0.5 (mol/mol). The material balance on inlet and outlet sides of the synthesis gas producing step in FIG. 1 (materials indicated as (1), (2), (3), (4), (5) and (7) in FIG. 1) was calculated, based on which the production efficiency of the synthesis gas 25 producing step in the kerosene and gas oil production process was evaluated. As a result, it was found that the percentage, calculated on the basis of the material balance, of the number of the carbon atoms in the recycled gas relative to the number of the carbon atoms in the hydrocarbons contained in the natural gas was 11.0 %. The yield of the products (kerosene and gas oil) based 14 on the carbon atoms in the natural gas was found to be 60.6 %. The feed amount of the natural gas was able to be reduced by 8.2 % as compared with a case where no recycling was conducted. Comparative Example 1 5 A synthesis gas having H 2 /CO of 2.0 suitable as a raw material for the FT (Fischer-Tropsch) synthesis was produced without recycling the naphtha and LPG produced as a by-product in an upgrading step 30 of a process for producing kerosene and gas oil from a natural gas, as shown in FIG. 1. The synthesis gas producing step 10 was operated at a temperature in 10 an outlet of the catalyst layer of 9000C, a pressure in an outlet of the catalyst layer of 2.0 MPaG, a GHSV (gas hourly space velocity) of 2,000 hrl, a H 2 0/C molar ratio of 1.24, and a C02/C molar ratio of 0.46. The raw material natural gas had a composition of C1/C2/C3/C4/C5+/N 2 of 90.0/5.5/2.5/0.5/1.0/0.5 (mol/mol). 15 The material balance on inlet and outlet sides of the synthesis gas producing step in FIG. 1 (materials indicated as (1), (2), (3), (4), (5) and (7) in FIG. 1) was calculated, based on which the production efficiency of the synthesis gas producing step in the kerosene and gas oil production process was evaluated. As a result, it was found that the yield, calculated on the basis of the 20 material balance, of the products (kerosene and gas oil) based on the carbon atoms in the natural gas was found to be 55.6 %. From the above results, the effects of the present invention are apparent. Namely, since the present invention is constructed to recycle light hydrocarbons separated by distillation in the upgrading step to a synthesis gas producing step 25 as a part of raw material for producing the synthesis gas, a process for producing kerosene and gas oil from a natural gas exhibits extremely excellent effect that the light hydrocarbons being a by-product having a low added value can be specifically reused and the raw material basic unit can be improved. 15 Industrial Applicability The present invention is utilizable to an industry of chemically converting a natural gas to produce a synthesis gas for the preparation of methanol, DME, synthetic petroleum, etc. 5 16

Claims (7)

1. A process for producing kerosene and gas oil from a natural gas, comprising: a synthesis gas producing step in which a hydrocarbon gas feed containing a s natural gas is subjected to a reforming reaction with steam and/or carbon dioxide to produce a synthesis gas; a Fischer-Tropsch oil producing step in which the synthesis gas is subjected to a Fischer-Tropsch reaction to produce a Fischer-Tropsch reaction product, the Fischer Tropsch reaction product being subsequently separated into a Fischer-Tropsch oil and a 10 gaseous product, and an upgrading step in which the Fischer-Tropsch oil is hydrotreated to obtain a hydrotreated product, the hydrotreated product being subsequently distilled to obtain light hydrocarbons and final products of kerosene and gas oil; wherein at least a part of the light hydrocarbons separated by distillation in said 15 upgrading step is recycled to said synthesis gas producing step as part of the hydrocarbon gas feed.

2. A process as recited in claim 1, wherein, in said synthesis gas producing step, a H 2 0/C molar ratio is adjusted in the range of 0.0 to 3.0 and/or a C02/C molar ratio is 20 adjusted in the range of 0.0 to 1.0 where C is a number of moles of the carbon of hydrocarbons contained in the hydrocarbon gas feed containing the natural gas and the recycled light hydrocarbons, and H 2 0 and C02 are the steam and carbon dioxide, respectively, fed to said synthesis gas producing step. 25

3. A process as recited in claim 1, wherein, in said synthesis gas producing step, the number of carbon atoms in the recycled light hydrocarbons is maintained in the range of 10 to 35% based on the number of the carbon atoms in the natural gas fed to said synthesis gas producing step. 30

4. A process as recited in claim 1, wherein, in said synthesis gas producing step, the number of carbon atoms in the final products of kerosene and gas oil is set in a range of 60 to 80% based on the number of the carbon atoms in the natural gas fed to said synthesis gas producing step. 18

5. A process as recited in claim 1, wherein, in said synthesis gas producing step, a temperature in an outlet of a catalyst layer is 800 to 95000, a pressure in an outlet of the catalyst layer is 1.5 to 3.0 MPaG, and a GHSV (gas hourly space velocity) is 500 to 5,000 hr 1 . 5

6. A process as recited in claim 1, wherein, in said synthesis gas producing step, the natural gas contains hydrocarbons having 1 to 6 carbon atoms and containing methane in an amount of at least 60 mole %. 10

7. A process for producing kerosene and gas oil from a natural gas, the process substantially as hereinbefore described with reference to the accompanying drawing. 18 May, 2011 is Chiyoda Corporation Patent Attorneys for the Applicant/Nominated Person SPRUSON & FERGUSON