Petroleum processing method

Abstract: A petroleum processing method comprising the steps of: performing an atmospheric distillation of crude oil; collectively hydrodesulfurizing the resultant distillates consisting of gas oil and fractions whose boiling point is lower than that of gas oil in a reactor in the presence of a hydrogenation catalyst at 310 to 370°C under 30 to 70 kg/cm 2 G (first hydrogenation step); and further performing hydrodesulfurization at lower temperatures (second hydrogenation step). When the second hydrogenation step is carried out only for the heavy naphtha obtained by separating the distillates after the first hydrogenation step, the second hydrogenation temperature can be in the range of 250 to 400°C. The hydrodesulfurization having been performed for each of gas oil, kerosene, heavy naphtha and light naphtha in the art can be collectively and efficiently carried out, so that the oil refinery plant can be simplified and so that the cost of oil refinery equipment and running cost can be reduced. The petroleum processing method and apparatus of the present invention are especially useful when the amount of crude oil to be processed is small.

Description: FIELD OF THE INVENTION The present invention relates to the separation and purification of crude oil by means of a simplified apparatus. BACKGROUND OF THE INVENTION In the art of oil refinery, it is common practice to perform an atmospheric distillation of crude oil having undergone pretreatments such as dehydration and desalting so that the crude oil is separated into bottoms and fractions of gas oil, kerosene, heavy naphtha, light naphtha, LP gas and light gas and to carry out hydrorefining for each of fractions to be subjected to hydrorefining, optionally followed by reforming. Thus, petroleum products are obtained. For example, referring to Fig. 3, the light gas (off gas) fraction among the fractions separated by an atmospheric distillation of crude oil has acid gases such as H 2 S separated by an amine treatment unit and is outputted as fuel gas. Among the above fractions, the LP gas fraction has its impurities removed by an LP gas treatment unit and is outputted as LP gas. Sulfur is recovered from the acid gases. The light naphtha fraction undergoes treatment such as sweetening by a light naphtha treatment unit to thereby remove mercaptan, H 2 S, etc. and is formulated into gasoline. The heavy naphtha fraction undergoes a hydrorefining by a heavy naphtha treatment unit and, thereafter, a catalytic reforming and is outputted as gasoline. In the use of the heavy naphtha in the catalytic reforming, the sulfur content of the heavy naphtha must not exceed 1 ppm by weight. Thus, sulfur components such as mercaptan, undesulfurized sulfides and hydrogen sulfide (H 2 S) contained in the above hydrorefined heavy naphtha are removed by treating with an adsorbent of a metal oxide such as NiO, CuO or ZnO or by an amine absorption. The kerosene and gas oil fractions are each individually hydrogenated, optionally followed by treatment with the use of, for example, an adsorbent, and outputted as kerosene and gas oil, respectively. The atmospheric distillation bottoms are distilled at reduced pressure with the use of a vacuum distiller, and the thus obtained vacuum distillates are used as a feedstock for producing gas oil. As apparent from the above, in the conventional oil refinery, the individual fractions such as light naphtha, heavy naphtha, kerosene and gas oil are purified by the respective treatment units such as a hydrorefining unit. Therefore, problems are encountered such that the constitution of the petroleum processing apparatus is complex and such that not only are complicated and large facilities required but also construction cost is high. Further, in the conventional oil refinery, it is conducted in unified form irrespective of the amount of processed crude oil. In this connection, it is demanded to simplify the petroleum processing apparatus and reduce the scale thereof to thereby lower oil refinery cost especially when the amount of processed crude oil is small. EP0635555 describes a process for refining crude oil. The document describes the use of a hydrotreating reaction, which is carried out at a temperature of 300° to 400° C. US4155835 describes a process for desulphurising naphtha. In view of the above prior art, the applicant proposed a method comprising performing an atmospheric distillation of crude oil so that the crude oil is separated into bottoms and distillates and collectively hydrogenating the distillates in a reactor and an apparatus suitable for use in the method (see Japanese Patent Laid-open Publication No. 7(1995)-82573). In this method, the distillates are collectively hydrorefined and, thereafter, fractionated into individual fractions. This method enables simplifying the petroleum processing apparatus as compared with the prior art in which the respective hydrorefining reactors are employed for individual fractions. This method is useful especially when the amount of processed crude oil is small. In the hydrodesulfurization of gas oil fraction containing sparingly desulfurizable sulfur compounds among the distillates obtained by the above atmospheric distillation of crude oil, the higher the desulfurization temperature, the higher the desulfurization efficiency. Thus, when the above distillates are mixed and collectively hydrogenated, it is needed to select conditions under which gas oil can efficiently be desulfurized. However, when the hydrogenation temperature is 340°C or higher, sulfur components such as H 2 S having been removed by the hydrogenation reaction are likely to undergo a recombination reaction with olefin (naphtha fraction). When the catalyst life is close to an end (EOR: end of run), the hydrogenation reaction must be carried out at high temperature, thereby increasing the likelihood of recombination reaction. When the sulfur content of light naphtha or heavy naphtha is increased by the above recombination, a new problem occurs such that the sulfur content of hydrogenated naphtha, especially, heavy naphtha may exceed the tolerance set for a feedstock for catalytic reforming. When the collective hydrogenation of the distillates is performed at relatively low temperature for avoiding this problem, there occurs another problem such that the desulfurization efficiency is lowered with the result that only gas oil with a high sulfur content can be obtained. The inventor has conducted investigations with a view toward solving the above problems once for all. As a result, it has been found that the above object can be attained by performing the collective hydrogenation of distillates in two stages, i.e., the first stage comprising performing the hydrogenation at high temperature so that the desulfurization efficiency of gas oil is high and the second stage comprising performing the hydrogenation at low temperature so that the possibility of sulfur components such as hydrogen sulfide formed by the first-stage hydrogenation undergoing a recombination with olefin is very low. The present invention has been completed on the basis of the above findings. The diesel gas oil hydrogenating method in which the hydrogenation of gas oil is performed in two stages, i.e., the first stage comprising hydrogenating gas oil to thereby effect the desulfurization thereof and the second stage comprising hydrogenating the gas oil having been colored by the first-stage desulfurization so as to improve the hue thereof is known in the art. For example, Japanese Patent Laid-open Publication No. 5(1993)-78670 describes the method in which diesel gas oil (petroleum distillate with a boiling point of 150 to 400°C) is hydrogenated at temperature as high as 375 to 450°C under a pressure of 45 to 100 kg/cm 2 to thereby effect a desulfurization to a sulfur content of 0.05% by weight or below (first stage) and, thereafter, hydrogenating the gas oil at 200 to 300°C under a pressure of 45 to 100 kg/cm 2 (second stage) so that the hue of the diesel gas oil having been colored by the first-stage hydrogenation is improved. Although the hue is improved to at least -10 in terms of Saybolt chromometry value in the second-stage hydrogenation, it is described in the Example portion of the literature that the sulfur content of the gas oil after the second-stage hydrogenation is the same as that of the gas oil after the first-stage hydrogenation, so that no desulfurizing effect is exerted in the second-stage hydrogenation. Furthermore, Japanese Patent Laid-open Publication No. 3(1991)-86793 proposed the similar method comprising desulfurizing gas oil (first stage) and performing a second-stage hydrogenation for improving the hue thereof (second stage). As in the above literature, it is described in the Example portion that no desulfurizing effect is exerted in the second-stage hydrogenation. OBJECT OF THE INVENTION It is an object of the present invention to provide a petroleum processing method which enables efficiently performing the separation and purification of crude oil by means of a simplified apparatus and to provide an apparatus suitable for carrying out the above petroleum processing. SUMMARY OF THE INVENTION The petroleum processing method of the present invention comprises the steps of: performing an atmospheric distillation of crude oil so that the crude oil is separated into bottoms and distillates, these distillates comprising gas oil and fractions whose boiling point is lower than that of gas oil; collectively hydrodesulfurizing the distillates in a reactor in the presence of a hydrogenation catalyst at 310 to 370°C under 30 to 70 kg/cm 2 G (first hydrogenation step); and further collectively hydrodesulfurizing the above hydrodesulfurized distillates in a reactor in the presence of a hydrogenation catalyst at 280 to 330°C under 30 to 70 kg/cm 2 G (second hydrogenation step), wherein the second hydrogenation step is performed at a lower temperature than the first hydrogenation step. In this method, the second hydrogenation step is generally followed by the steps of: separating gas fractions from the hydrodesulfurized distillates (gas separating step); and separating the distillates having undergone the gas separating step into gas oil, kerosene, heavy naphtha and light naphtha fractions (fractionation step). The heavy naphtha fraction obtained in the fractionation step can be catalytically reformed to thereby obtain gasoline. Generally, the heavy naphtha fraction has a sulfur content of not greater than 1 ppm by weight. The petroleum processing apparatus suitable for carrying out the method of the present invention comprises: an atmospheric distillation unit capable of performing an atmospheric distillation of crude oil so that the crude oil is separated into bottoms and distillates, said distillates comprising gas oil and fractions whose boiling point is lower than that of gas oil; a first hydrogenation reactor capable of collectively hydrodesulfurizing the distillates separated by the atmospheric distillation unit; and a second hydrogenation reactor capable of further collectively hydrodesulfurizing the distillates hydrodesulfurized by the first hydrogenation reactor. This petroleum processing apparatus, generally further to the atmospheric distillation unit, the first hydrogenation reactor and the second hydrogenation reactor, comprises: means for separating gas fractions from the distillates hydrodesulfurized by the second hydrogenation reactor; and fractionating means for separating the distillates processed by the gas separating means into gas oil, kerosene, heavy naphtha and light naphtha fractions This petroleum processing apparatus may further comprise a catalytic reformer capable of catalytically reforming the heavy naphtha fraction separated by the fractionating means. Alternatively, the petroleum processing apparatus of the present invention may comprise: the above atmospheric distillation unit and first hydrogenation reactor; means for separating gas fractions from the distillates hydrodesulfurized by the first hydrogenation reactor; fractionating means for separating the distillates processed by the gas separating means into gas oil, kerosene, heavy naphtha and light naphtha fractions; a second hydrogenation reactor capable of hydrodesulfurizing the heavy naphtha fraction separated by the fractionating means; and an adsorber capable of removing by adsorption sulfur components from the heavy naphtha fraction hydrodesulfurized by the second hydrogenation reactor. This petroleum processing apparatus may further comprise a catalytic reformer capable of catalytically reforming the heavy naphtha fraction processed by the adsorber. BRIEF DESCRIPTION OF THE DRAWING Fig. 1 is a diagram showing the process flow of the petroleum processing method (i) of the present invention; Fig. 2 is a view showing a form of the petroleum processing apparatus (i) and Fig. 3 is a diagram showing the process flow of the conventional petroleum processing method. DETAILED DESCRIPTION OF THE INVENTION The petroleum processing method and petroleum processing apparatus according to the present invention will be described in detail below. Petroleum processing method The petroleum processing method (i) of the present invention comprises the steps of: performing an atmospheric distillation of crude oil so that the crude oil is separated into bottoms and distillates, these distillates consisting of gas oil and fractions whose boiling point is lower than that of gas oil; collectively hydrodesulfurizing the distillates in a reactor in the presence of a hydrogenation catalyst at 310 to 370°C under 30 to 70 kg/cm 2 G (first hydrogenation step); and further collectively hydrogenating and desulfurizing the above hydrogenated and desulfurized distillates in a reactor in the presence of a hydrogenation catalyst at 280 to 330°C under 30 to 70 kg/cm 2 G (second hydrogenation step). Fig. 1 schematically shows the process flow of the above petroleum processing method (i). In the crude oil distillation step, generally, base sediment and water are first removed from the crude oil, and pretreatments such as dehydration and desalting are conducted. The resultant crude oil is subjected to an atmospheric distillation so that the crude oil is separated into bottoms and distillates, these distillates consisting of gas oil and fractions whose boiling point is lower than that of gas oil. The distillates consisting of gas oil and fractions whose boiling point is lower than that of gas oil are, generally, fractions with a boiling point of -40°C to +400°C which, specifically, consist of gas oil, kerosene, heavy naphtha, light naphtha, LP gas (LPG) and light gas. In the distillation, either may the individual fractions be obtained separately or the distillates consisting of gas oil and fractions whose boiling point is lower than that of gas oil, exclusive of bottoms, may be obtained in the form of one fraction. Alternatively, the distillates consisting of gas oil and fractions whose boiling point is lower than that of gas oil, exclusive of distillates whose hydrogenation is not required (for example, light gas and LPG), can be obtained in the form of one fraction. The fractions having been individually separated by the distillation are mixed together and collectively hydrogenated. In the present invention, in the subsequent hydrodesulfurization of the above distillates, it is requisite that distillates whose hydrogenation is required be collectively subjected to the hydrogenation step but the distillates to be subjected to the hydrogenation step may contain or may not contain distillates whose hydrogenation is not needed. Vacuum gas oil obtained by a vacuum distillation of the bottoms produced by the atmospheric distillation of crude oil may be added to the distillates to be subjected to the hydrogenation step. In the petroleum processing method (i) of the present invention, the distillates (consisting of gas oil and fractions whose boiling point is lower than that of gas oil) obtained by the atmospheric distillation of crude oil are collectively processed by the two-stage hydrogenation. For example, a gas-liquid downstream parallel flow reactor, a gas-liquid counterflow reactor and a gas-liquid upstream parallel flow reactor can be mentioned as the reactor suitable for use in the hydrogenation step of the present invention. In the first hydrogenation step, a wide variety of conventional hydrogenation catalysts can be used as the hydrogenation catalyst. For example, use can be made of Co-Mo, Ni-Mo, Ni-Co-Mo and Ni-W catalysts. These active metals are preferably borne on a support such as alumina. In the first hydrogenation step, the above distillates are collectively hydrdesulfurized in a reactor in the presence of a hydrogenation catalyst at 310 to 370°C, preferably, 330 to 370°C, still preferably, 330 to 350°C under 30 to 70 kg/cm 2 G, preferably, 40 to 60 kg/cm 2 G. In the first hydrogenation step, it is preferred that the H 2 /oil (NL/L) ratio range from 60 to 150, especially, from 70 to 120 and that the liquid space velocity (LHSV) range from 1 to 5 hr -1 , especially, from 1.5 to 3 hr -1 . The sulfur content of the gas oil fraction can be reduced to 0.2% by weight or less, preferably, 0.05% by weight or less by this first hydrogenation step. Although the same hydrogenation catalysts as in the first hydrogenation step can be used in the second hydrogenation step, preferred use is made of catalysts with high hydrogenation capability which are especially active to induce the hydrodesulfurization of mercaptan. For example, Ni-Mo, Ni-Co-Mo and Ni-W catalysts can preferably be used. In the second hydrogenation step, the above distillates are further collectively hydrogenated and desulfurized in a reactor in the presence of a hydrogenation catalyst at 280 to 330°C, preferably, 300 to 320°C under 30 to 70 kg/cm 2 G, preferably, 30 to 60 kg/cm 2 G. From the viewpoint of operation easiness, the second hydrogenation step is preferably conducted under the same pressure as in the first hydrogenation step. In the second hydrogenation step, it is preferred that the H 2 /oil (NL/L) ratio range from 60 to 150, especially, from 70 to 120 and that the liquid space velocity (LHSV) range from 3 to 10 hr -1 , especially, from 5 to 8 hr -1 . In the above petroleum processing method (i) in which the distillates obtained by the atmospheric distillation of crude oil are collectively hydrodesulfurized in two stages, the second hydrogenation step is performed at temperature lower than in the first hydrogenation step. That is, the desulfurization of sparingly desulfurizable fraction such as gas oil is efficiently carried out in the first hydrogenation step in which the temperature is relatively high. Even if a recombination reaction occurs between sulfur components and olefin during the desulfurization, the sulfur components can be efficiently removed as H 2 S, etc. in the second hydrogenation step conducted at low temperature. In the above petroleum processing method (i), desulfurized fractions can be obtained by performing, subsequent to the second hydrogenation step, the steps of: separating gas fractions from the hydrodesulfurized distillates (gas separating step); and separating the distillates having undergone the gas separating step into gas oil, kerosene, heavy naphtha and light naphtha fractions (fractionation step). Gas fractions remaining in the distillates after the gas separating step can be separated from the other fractions in the fractionation step. For example, the distillates having been hydrodesulfurized in the second hydrogenation step are led into a gas-liquid separator in which the distillates are separated into purified oil and gas (hydrogen, product gas, etc.). The separated purified oil is introduced into a stripper to thereby remove gas fractions (product gases such as LPG, light gas and H2S) remaining in the oil. After the gas removal, the purified oil is subjected to the fractionation step in which the purified oil can be separated into fractions by, for example, distillation. The hydrogen containing gas having been separated by, for example, a gas-liquid separator in the gas separating step can be circulated to the first hydrogenation step and/or the second hydrogenation step. The gas oil having been separated in the fractionation step can be returned according to necessity to the first hydrogenation step and/or the second hydrogenation step so that the gas oil is hydrodesulfurized once more. In the present invention, the heavy naphtha obtained by the fractionation step can be catalytically reformed into gasoline. Prior to the catalytic reforming, the heavy naphtha can be subjected to adsorption treatment in which use can be made of an H 2 S adsorber such as ZnO. The sulfur content of the heavy naphtha to be subjected to the above catalytic reforming is generally lowered to 1 ppm by weight or less. Common processes such as the UOP platforming method in which, for example, Pt-Al 2 O 3 catalyst is used, the IFP catalytic reforming method and the power forming method can be employed in the catalytic reforming. In the petroleum processing method (i), hydrogen containing gases whose hydrogen concentration is at least about 60% can be used as hydrogen source. Examples of such hydrogen sources include the hydrogen formed as by-product in a heavy naphtha catalytically reforming device and the hydrogen containing gas separated by the above gas-liquid separator. The above petroleum processing methods of the present invention enable collectively and efficiently performing the hydrodesulfurization purification, which is commonly carried out individually for each of gas oil, kerosene, heavy naphtha and light naphtha fractions in the art. Further, the petroleum processing methods enable satisfactorily reducing the sulfur content of obtained individual fractions, especially, heavy naphtha and enable simplifying the oil refining equipment. Thus, oil refining equipment cost and running cost can be reduced. Petroleum processing apparatus Referring to Fig. 2, the petroleum processing apparatus (i) comprises: atmospheric distillation unit 1 capable of performing an atmospheric distillation of crude oil so that the crude oil is separated into bottoms and distillates, these distillates comprising gas oil and fractions whose boiling point is lower than that of gas oil; first hydrogenation reactor 2 capable of collectively hydrodesulfurizing the distillates separated by the atmospheric distillation unit 1; and second hydrogenation reactor 3 capable of further collectively hydrodesulfurizing the distillates hydrodesulfurized by the first hydrogenation reactor 2. The atmospheric distillation unit 1 is furnished with crude oil feeding line 1a, bottoms withdrawing line 1b and line 10 for introducing the distillation fractions into the first hydrogenation reactor 2. The distillation fraction introducing line 10 may be a single line adapted to withdraw as one fraction the distillates comprising gas oil and fractions whose boiling point is lower than that of gas oil from the atmospheric distillation unit 1. Alternatively, the distillation fraction introducing line 10 may be a single line adapted to withdraw as one fraction the distillates comprising gas oil and fractions whose boiling point is lower than that of gas oil, from which the LPG and light gas not requiring hydrogenation have been removed. Still alternatively, the distillation fraction introducing line 10 may be a line comprising a combination of distillation unit gas oil withdrawing line 1c, kerosene withdrawing line 1d, heavy naphtha withdrawing line 1e, light naphtha withdrawing line 1f, LPG withdrawing line 1g and light gas withdrawing line 1h. The first hydrogenation reactor 2 is furnished with hydrogen feeding line 2a and line 2b adapted to introduce the fraction hydrodesulfurized in the first hydrogenation reactor 2 into the second hydrogenation reactor 3. The second hydrogenation reactor 3 is furnished with hydrogen feeding line 3a and distillate withdrawing line 3b. The hydrogen supply to each of the hydrogenation reactors can be separately performed as shown. Alternatively, it can be performed by collectively feeding hydrogen in an amount matching the sum of the amounts required by the first hydrogenation reactor 2 and the second hydrogenation reactor 3 into the first hydrogenation reactor 2 through the hydrogen feeding line 2a and by feeding hydrogen into the second hydrogenation reactor 3 through the line 2b. In this construction, the hydrogen feeding line 3a is not needed. For example, a gas-liquid downstream parallel flow reactor, a gas-liquid counterflow reactor or a gas-liquid upstream parallel flow reactor can be mentioned as the first hydrogenation reactor 2 or second hydrogenation reactor 3 for use in the hydrogenation step of the present invention. The petroleum processing apparatus (i) of the present invention, generally further to the atmospheric distillation unit 1, the first hydrogenation reactor 2 and the second hydrogenation reactor 3, comprises: means for separating gas fractions, such as hydrogen, LPG, light gas and other product gas, from the distillates hydrodesulfurized by the second hydrogenation reactor 2; and fractionating means for separating the distillates freed of the gas fractions into gas oil, kerosene, heavy naphtha and light naphtha fractions. For example, a gas-liquid separator or a stripper can be mentioned as the means for separating the gas fractions from the distillates. For example, the distillates having been withdrawn from the second hydrogenation reactor 3 through the line 3b are passed through gas-liquid separator 5 and stripper 6 as the gas separating means and fed into fraction separating means (e.g., distillation column) 4. The fraction separating means 4 separates the distillates into gas oil, kerosene, heavy naphtha and light naphtha fractions. The gas fractions such as LPG and light gas which remain in the distillates having been processed by the stripper 6 can also be separated by the distillation column 4. This mode of the invention will be described in greater detail. The line 2b of the first hydrogenation reactor 2 is generally connected through cooler 2c to the second hydrogenation reactor 3. The distillate withdrawing line 3b of the second hydrogenation reactor 3 is generally connected through cooler 3c to the gas-liquid separator 5. This petroleum processing apparatus may be furnished with line 5a which leads the gas phase separated by the gas-liquid separator 5, through cooler 5b, to gas-liquid separator 7, line 7a which circulates the gas phase separated by the gas-liquid separator 7, through compressor 7b, to the hydrogen feeding line 2a, and line 7c which leads the liquid phase separated by the gas-liquid separator 7 to liquid phase withdrawing line 5d of the gas-liquid separator 5. The line 7a of the gas-liquid separator 7 may be fitted with an amine treatment device (not shown) capable of separating and removing H 2 S and other product gas from the gas phase before the introduction of the gas phase into the compressor 7b. The liquid phase withdrawing line 5d of the gas-liquid separator 5 is connected to the stripper 6. Gas fractions such as H 2 S, LPG and light gas are withdrawn through line 6a from the stripper 6. Liquid phase is fed through line 6b into the distillation column 4. The liquid phase withdrawing line 6b of the stripper 6 may be fitted with heater 6c. The distillation column 4 is furnished with gas oil line 4a, kerosene line 4b, heavy naphtha line 4c and light naphtha line 4d for withdrawing separated fractions. The line 4a of the distillation column 4 may be fitted with line 4f for circulating gas oil through heater 4g to the distillation column 4. The petroleum processing apparatus (i) may be furnished with, in addition to the distillation column 4, a catalytic reforming unit (not shown) capable of catalytically reforming the heavy naphtha separated by the distillation column 4 into gasoline. The catalytic reforming unit which has heavy naphtha fed through the heavy naphtha line 4c and converts it to gasoline is generally furnished with a gas-liquid separator (not shown). The catalytic reforming unit may be furnished with a line for withdrawing gasoline through the gas-liquid separator and a line (not shown) for subjecting hydrogen formed as by-product in the catalytic reforming unit to gas-liquid separation and circulating the resultant hydrogen to the first hydrogenation reactor 2 and/or second hydrogenation reactor 3. The forms of petroleum processing apparatus of the present invention are not limited to those shown in the appended drawings. EFFECT OF THE INVENTION The present invention enables collectively and efficiently performing the hydrogenation purification of crude oil distillates, which is commonly carried out individually for each of gas oil, kerosene, heavy naphtha and light naphtha fractions in the art. Further, the present invention enables satisfactorily reducing the sulfur content of obtained individual fractions, especially, heavy naphtha and enables simplifying the oil refining equipment. Thus, oil refining equipment cost and running cost can be reduced. The petroleum processing method and petroleum processing apparatus of the present invention are especially useful when the amount of processed crude oil is small. EXAMPLE The present invention will now be illustrated in greater detail with reference to the following Examples, which in no way limit the scope of the invention. Examples 1 to 6 Crude oil (crude oil consisting of a 50:50 (volume ratio) mixture of Arabian light crude oil and Arabian heavy crude oil, having a sulfur content of 2.40% by weight) was processed by the process shown in Fig. 1. Fraction ratios and sulfur contents (% by weight) of the distillates obtained by the atmospheric distillation of the crude oil are listed in Table 1. Distillate Fraction ratio (vol %) S content (wt %) Composition of distillate to be collectively processed (vol %) LPG, light gas 1.8 - light naphtha 11.9 0.038 12.1 heavy naphtha 28.0 0.028 28.5 kerosene 16.7 0.139 17.0 gas oil 41.6 1.013 42.4 Of these fractions, light naphtha, heavy naphtha, kerosene and gas oil fractions were collectively subjected to the first hydrogenation step and the second hydrogenation step. Hydrogenation conditions employed in the first hydrogenation step and the sulfur contents of the thus obtained fractions are as described below and as given in Table 2. The sulfur content of the whole processed oil was 0.02% by weight. First hydrogenation step: Reactor: gas-liquid downstream parallel flow coil reactor (inside diameter of 8 mm x length of 3500 mm), Catalyst: commercially available Co-Mo catalyst (produced by Catalysts & Chemicals Industries Co., Ltd.), and Amount of catalyst: 175 ml. 1st hydrogenation step Pressure kg/cm 2 G 40 Temperature °C 350 H 2 /oil Nℓ/ℓ 90 LHSV hr -1 2.84 Results (S content) Light naphtha S:wtppm 1.1 Heavy naphtha S:wtppm 1.6 Kerosene S:wtppm <100 Gas oil S:wt% 0.05 Whole processed oil S:wt% 0.02 Hydrogenation conditions employed in the second hydrogenation step and the sulfur contents of the thus obtained fractions are as described below and as given in Table 3. Second hydrogenation step: Reactor: gas-liquid downstream parallel flow coil reactor (inside diameter of 8 mm x length of 2000 mm), Catalyst: commercially available Ni-Co-Mo catalyst (produced by Catalysts & Chemicals Industries Co., Ltd.), and Amount of catalyst: 100 ml. Comparative Examples 1 and 2 The crude oil was processed in the same manner as in Example 1 except that the hydrogenation conditions of the second hydrogenation step were changed as specified in Table 3. Processing conditions and results are given in Table 3. 2nd hydrogenation step Results (S content) Pressure kg/cm 2 G Temperature °C H 2 / oil Nl/l LHSV hr -1 Light naphtha S:wtppm Heavy naphtha S:wtppm Kerosene S:wtppm Gas oil S:wt% Ex.1 40 300 90 5 0.2 0.4 <100 0.05 Ex.2 40 320 90 5 0.2 0.3 <100 0.05 Ex.3 40 330 90 5 0.2 0.4 <100 0.04 Ex.4 30 320 90 5 0.1 0.3 <100 0.05 Ex.5 50 320 90 5 0.3 0.5 <100 0.04 Ex.6 40 320 90 8 0.4 0.5 <100 0.05 Comp Ex.1 40 270 90 5 0.5 1.3 <100 0.05 Comp Ex.2 40 340 90 5 0.6 1.5 <100 0.05

Claims: A petroleum processing method comprising the steps of: performing an atmospheric distillation of crude oil so that the crude oil is separated into bottoms and distillates, said distillates comprising gas oil and fractions whose boiling point is lower than that of gas oil; collectively hydrodesulfurizing the distillates in a first hydrogenation step in a reactor in the presence of a hydrogenation catalyst at 310 to 370°C under 30 to 70 kg/cm 2 G ; and further collectively hydrodesulfurizing the above hydrodesulfurized distillates in a second hydrogenation step in a reactor in the presence of a hydrogenation catalyst at 280 to 330°C under 30 to 70 kg/cm 2 G, wherein the second hydrogenation step is performed at a lower temperature than the first hydrogenation step. The method as claimed in claim 1, which further comprises the steps to be performed after the second hydrogenation step: separating gas fractions from the hydrodesulfurized distillates; and separating the distillates having undergone the gas separating step into gas oil, kerosene, heavy naphtha and light naphtha fractions. The method as claimed in claim 2, wherein the heavy naphtha fraction obtained in the fractionation step is catalytically reformed to thereby obtain gasoline. The method as claimed in claim 3, wherein the heavy naphtha fraction has a sulfur content of not greater than 1 ppm by weight.

Inventors: INOMATA MAKOTO, NIGAMATSU SHIGEKI, OKUMURA TOSHIYA, INOMATA, MAKOTO, NIGAMATSU, SHIGEKI, OKUMURA, TOSHIYA, Okumura, Toshiya, c/o JGC Corporation
Applicants: JGC CORP, JGC CORPORATION
Application year: 1998
Main classification: C10G65
IPC codes: C10G65, C10G69, C10G67, C10G45, C10G7, C10G35