Method for producing catalytically reformed feedstock

Abstract

To provide hydrodesulfurized stock oil highly containing an 8C component derived from decomposed gasoline and low in nitrogen concentration and in olefin concentration which may cause excess heat evolution to a catalyst in a hydrodesulfurization step.SOLUTION: A manufacturing method of catalytically-reformed stock oil includes: a first step of fractionating desulfurized heavy cracked gasoline obtained by desulfurizing heavy cracked gasoline into a first light fraction, a second light fraction, and a heavy fraction; a second step of obtaining hydrodesulfurized stock oil by mixing the second light fraction with a full range naphtha fraction; and a third step of supplying the hydrodesulfurized stock oil to a naphtha hydrodesulfurization apparatus to be hydrodesulfurized. A ratio of a nitrogen atom amount contained in the first light fraction and the second light fraction is 3.0-15.0 mass% in the total nitrogen atom amount contained in the first light fraction, the second light fraction, and the heavy fraction, and a ratio of olefin amount contained in the second light fraction is 40 mass% or lower in the total olefin amount contained in the first light fraction and the second light fraction.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing catalytically reformed feedstock. [Background technology]

[0002] Xylene is a very important petrochemical raw material, and its demand is continuously growing while gasoline demand continues to decline, calling for a change in the supply and demand balance. Xylenes are primarily produced by catalytic reforming of feedstock oils, primarily naphtha fractions, but catalytic cracking gasoline, which is produced by catalytic cracking of heavy petroleum fractions, can be produced more economically than other naphtha fractions and has a high proportion of naphthenes and aromatics, so it has sometimes been used as a catalytic reforming feedstock. However, because catalytic cracking gasoline contains large amounts of sulfur and nitrogen, even if these are removed by methods such as hydrodesulfurization, it has been difficult to use it in large quantities as a catalytic reforming feedstock in order to avoid problems such as catalyst degradation in catalytic reforming. Regarding the study of catalytic reforming feedstock, Patent Document 1 proposes a method in which catalytic cracking gasoline, in which the aniline content has been reduced by contacting it with an acidic solution such as sulfuric acid, is mixed with a naphtha fraction and used for catalytic reforming. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-195701 Summary of the Invention [Problem to be solved by the invention]

[0004] The present invention has been made under these circumstances, and aims to provide a hydrodesulfurized feedstock that contains a large amount of components with eight carbon atoms (C8 components) derived from cracked gasoline, and has a low concentration of nitrogen and a low concentration of olefins that can cause excessive heat generation in the catalyst during the hydrodesulfurization step. [Means for solving the problem]

[0005] As a result of extensive research to solve the above problems, the present inventors have found that the above problems can be solved by fractionating a feedstock derived from cracked gasoline into three fractions: a first light fraction, a second light fraction, and a heavy fraction, and using the second fraction to provide a hydrodesulfurized feedstock with a low nitrogen concentration. That is, the present invention provides a method for producing a catalytically reformed feedstock having the following configuration.

[0006] 1. A method for producing catalytically reformed feedstock, comprising: a first step of fractionating desulfurized heavy cracked gasoline obtained by desulfurizing heavy cracked gasoline into a first light fraction, a second light fraction, and a heavy fraction; a second step of blending the second light fraction with a full-range naphtha fraction to obtain hydrodesulfurized feedstock; and a third step of supplying the hydrodesulfurized feedstock to a naphtha hydrodesulfurization unit for hydrodesulfurization, wherein the ratio of the amount of nitrogen atoms contained in the first light fraction and the second light fraction to the total amount of nitrogen atoms contained in the first light fraction, the second light fraction, and the heavy fraction is 3.0 to 15.0 mass%, and the ratio of the amount of olefins contained in the second light fraction to the total amount of olefins contained in the first light fraction and the second light fraction is 40 mass% or less. 2. The method for producing catalytically reformed feedstock oil according to item 1, wherein the ratio of the amount of nitrogen atoms contained in the second light fraction to the total amount of nitrogen atoms contained in the first light fraction, the second light fraction, and the heavy fraction is 0.5 to 5.0 mass%. 3. A method for producing catalytically reformed feedstock oil according to 1 or 2 above, wherein the proportion of aromatic hydrocarbons having 8 carbon atoms contained in the second light fraction is 90 mass% or more based on the total amount of aromatic hydrocarbons having 8 carbon atoms contained in the first light fraction and the second light fraction. 4. The method for producing catalytically reformed feedstock according to any one of 1 to 3 above, wherein in the second step, 1 to 20 parts by mass of the second light fraction is mixed with 100 parts by mass of the full-range naphtha fraction. 5. The method for producing catalytically reformed feedstock according to any one of the above 1 to 4, wherein the nitrogen atom content of the hydrodesulfurized feedstock is 2.0 ppm by mass or less. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a hydrodesulfurized feedstock that contains a large amount of C8 components derived from cracked gasoline and has a low concentration of nitrogen and a low concentration of olefins that can cause excessive heat generation in the catalyst during the hydrodesulfurization step. DETAILED DESCRIPTION OF THE INVENTION

[0008] A method for producing catalytically reformed feedstock according to an embodiment of the present invention (hereinafter sometimes simply referred to as "this embodiment") comprises: a first step of fractionating desulfurized heavy cracked gasoline obtained by desulfurizing heavy cracked gasoline into a first light fraction, a second light fraction, and a heavy fraction; a second step of blending the second light fraction with a full-range naphtha fraction to obtain hydrodesulfurized feedstock; and a third step of supplying the hydrodesulfurized feedstock to a naphtha hydrodesulfurization unit for hydrodesulfurization, wherein the ratio of the amount of nitrogen atoms contained in the first light fraction and the second light fraction to the total amount of nitrogen atoms contained in the first light fraction, the second light fraction, and the heavy fraction is 3.0 to 15.0 mass%, and the ratio of the amount of olefins contained in the second light fraction to the total amount of olefins contained in the first light fraction and the second light fraction is 40 mass% or less. By setting the nitrogen atom amounts in the first light fraction and the second light fraction fraction distilled in the first step and the amount of olefins contained in the second light fraction within the above ranges, it is possible to remove components that are particularly harmful to the catalytic reforming catalyst and to recover more C8 components that can be reformed into xylenes. Each step will be described in detail below.

[0009] [First step] In the first step, the desulfurized heavy cracked gasoline obtained by desulfurizing the heavy cracked gasoline is fractionated into a first light fraction, a second light fraction, and a heavy fraction, and the fractionation must be carried out so that the ratio of the amount of nitrogen atoms contained in the first light fraction and the second light fraction to the total amount of nitrogen atoms contained in the first light fraction, the second light fraction, and the heavy fraction is 3.0 to 15.0 mass%. If the ratio of the amount of nitrogen atoms contained in the first light fraction and the second light fraction is less than 3.0 mass%, the recovery rate of C8 components will decrease, and if it exceeds 15.0 mass%, a large amount of components harmful to the catalytic reforming catalyst will be contained, making it necessary to reduce the ratio of components derived from heavy cracked gasoline in the catalytic reforming feedstock. The ratio of the amount of nitrogen atoms contained in the light fraction is preferably 4.5 to 14.0 mass%, more preferably 6.0 to 13.0 mass%. Specific methods for adjusting the ratio of the nitrogen atomic weights contained in the first light fraction and the second light fraction to fall within the above range include changing the temperature conditions and pressure conditions so as to satisfy this requirement, or changing the position (stage) in the distillation column from which the second light fraction is extracted, either vertically or horizontally. Specific distillation conditions vary greatly depending on the distillation column and cannot be generally determined, but for example, the column top temperature is about 51 to 97°C and the column top pressure is about 0.02 to 0.1 MPa. Here, the ratio of the nitrogen atomic weight can be calculated based on the nitrogen concentration determined by a chemiluminescence method for each of the first light fraction, the second light fraction, and the heavy fraction.

[0010] In the first step, a specific method for fractionating the first light fraction, the second light fraction, and the heavy fraction using a distillation column includes a method in which the first light fraction is obtained from the top of the distillation column, the second light fraction is withdrawn from the middle of the distillation column, and the heavy fraction is withdrawn from the bottom of the column. Here, the middle stage portion from which the second light fraction is extracted cannot be determined in general terms because it varies greatly depending on the distillation column and operating conditions, but it can be, for example, a stage corresponding to 20 to 80% from the top of the total number of stages provided in the distillation column, and the second light fraction may be extracted from one stage or from multiple stages.

[0011] Furthermore, the ratio of the amount of olefins contained in the second light fraction to the total amount of olefins contained in the first light fraction and the second light fraction must be 40% by mass or less, preferably 18 to 35% by mass, and more preferably 24 to 32% by mass. If the ratio of the amount of olefins contained in the second light fraction is 40% by mass or less, excessive heat generation on the catalyst in the third step can be suppressed, and if it is 18% by mass or more, the recovery rate of C8 components is improved. Here, the ratio of the amount of olefins can be calculated based on the amount of olefins measured by the fluorescent indicator adsorption method of JIS K 2536 "Testing Methods for Components of Petroleum Products."

[0012] Furthermore, the ratio of the amount of nitrogen atoms contained in the second light fraction to the total amount of nitrogen atoms contained in the first light fraction, the second light fraction, and the heavy fraction is preferably 0.5 to 5.0 mass%, more preferably 1.3 to 4.0 mass%, and even more preferably 1.6 to 3.5 mass%. If the ratio of the amount of nitrogen atoms contained in the second light fraction is 5.0 mass% or less, the adverse effect on the catalytic reforming catalyst can be further reduced, and if it is 0.5 mass% or more, the recovery rate of C8 components is improved. Here, the ratio of the nitrogen atomic weights can be calculated based on the nitrogen concentrations determined by a chemiluminescence method for each of the first light fraction and the second light fraction.

[0013] Furthermore, from the viewpoint of improving the recovery rate of xylene, the ratio of aromatic hydrocarbons having 8 carbon atoms contained in the second light fraction to the total amount of aromatic hydrocarbons having 8 carbon atoms contained in the first light fraction and the second light fraction is preferably 90 mass% or more, more preferably 95 mass% or more, and even more preferably 98 mass% or more. Here, the ratio of aromatic hydrocarbons having 8 carbon atoms can be calculated based on the concentration of each component measured by the total component test method using gas chromatography in JIS K 2536 "Testing Methods for Components in Petroleum Products."

[0014] (Desulfurized heavy cracked gasoline) The desulfurized heavy cracked gasoline is obtained, for example, by desulfurizing heavy cracked gasoline having an initial distillation point of 90°C or higher, which is obtained by cracking feedstock oil using a fluid catalytic cracking unit (also called an "FCC unit"), at a desulfurization rate such that the sulfur content is approximately 10 ppm by mass or less, and preferably contains 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more, of hydrocarbon components having 7 to 10 carbon atoms. The nitrogen concentration of the desulfurized heavy cracked gasoline is usually about 5 to 100 mass ppm, and the olefin content is about 5 to 30 mass %. The methods for measuring the nitrogen concentration and olefin content are the same as those for the second light fraction.

[0015] Examples of the feedstock oil include desulfurized heavy oil (DSAR) obtained by hydrodesulfurization treatment in a heavy oil direct desulfurization unit, heavy gas oil (HGO) and vacuum gas oil (VGO) obtained by atmospheric distillation and vacuum distillation of other crude oils, desulfurized vacuum gas oil (VHHGO) obtained by desulfurizing these heavy gas oils and vacuum gas oils in an indirect desulfurization unit, deasphalted oil (DAO) obtained from indirect desulfurized heavy oil and a solvent deasphalting unit, vacuum heavy oil (VR), coker gas oil, coker bottom oil, and other various heavy oils.

[0016] Furthermore, the fluid catalytic cracking unit can be any unit known as a fluid catalytic cracking unit that is typically installed in oil refineries, without any particular limitations. For example, a unit can be used that includes a reaction tower having a cyclone, a cracked product discharge line, a stripper, a spent catalyst transfer line, a riser, etc., in which fluid catalytic cracking of feedstock oil is carried out, and a regeneration tower having an air blower, an air grid, a cyclone, a regenerated catalyst transfer line, an exhaust gas line, etc., in which the catalyst is regenerated.

[0017] [Second process] In the second step, the second light fraction, or the first and second light fractions, are mixed with a full-range naphtha fraction to obtain a hydrodesulfurized feedstock. In the second step, it is preferable to mix only the second light fraction with the full-range naphtha fraction, since this reduces the olefin content of the hydrodesulfurized feedstock. In addition, the nitrogen atom content of the hydrodesulfurized feedstock is preferably 2.0 ppm by mass or less. The heavy fraction cannot be mixed with the hydrodesulfurized feedstock because it contains a large amount of nitrogen compounds that adversely affect the catalyst in catalytic reforming.

[0018] In the second step, by mixing 1 to 20 parts by mass of the second light fraction with 100 parts by mass of the full-range naphtha fraction, it becomes relatively easy to avoid problems such as catalyst poisoning in catalytic reforming while recovering C8 components derived from catalytic reformed gasoline.

[0019] The full-range naphtha fraction is a naphtha fraction obtained by atmospheric distillation of crude oil, and has a boiling point range of approximately 30 to 180° C. The full-range naphtha fraction is usually used as is as a catalytic reforming feedstock, but in this embodiment, by mixing the full-range naphtha fraction with the second light fraction, or the first light fraction and the second light fraction, it becomes possible to efficiently recover C8 components contained in the desulfurized heavy cracked gasoline and convert them into xylene. In this embodiment, imported naphtha can also be used as the full-range naphtha fraction.

[0020] The nitrogen concentration of the full-range naphtha fraction is usually about 0.01 to 5 mass ppm, and the olefin content is about 0.1 to 10 mass %. The methods for measuring the nitrogen concentration and olefin content are the same as those for the second light fraction.

[0021] [Third step] The third step is a step of supplying the hydrodesulfurized feed oil to a naphtha hydrodesulfurization unit and carrying out hydrodesulfurization.

[0022] The reaction conditions for the hydrodesulfurization cannot be uniquely determined because they vary depending on the type of feedstock oil and the like. However, from the viewpoint of more efficient operation and reducing the sulfur content, the reaction temperature (temperature at the inlet of the hydrodesulfurization reactor) is preferably 260°C or higher and 340°C or lower, more preferably 270°C or higher and 330°C or lower, and even more preferably 280°C or higher and 320°C or lower, the hydrogen partial pressure is preferably 0.3 MPa or higher and 1 MPa or lower, more preferably 0.4 MPa or higher and 0.8 MPa or lower, and the ratio of hydrogen to feedstock oil (hydrogen / feedstock oil) is preferably 30 Nm 3 / kL or more 100Nm 3 / kL or less, preferably 35Nm 3 / kL or more 80Nm 3 / kL or less, more preferably 40Nm 3 / kL or more 70Nm 3 / kL or less, and the liquid hourly space velocity (LHSV) is preferably 2 h -1 More than 20h -1 Less than 2.5 hours, preferably -1 Over 18 hours -1 In particular, when the hydrogen partial pressure is within the above range, coke deterioration can be further suppressed, and when the reaction temperature, hydrogen partial pressure, and liquid hourly space velocity are all within the above ranges, the occurrence of sulfuric acid recombination can be further suppressed.

[0023] The hydrodesulfurization produces a desulfurized light naphtha and a desulfurized heavy naphtha. The desulfurized heavy naphtha is a fraction having a boiling point range of typically 60°C to 200°C, preferably 70°C to 195°C, and more preferably 75°C to 190°C, and typically has a sulfur content of approximately 0.5 mass ppm or less. While the initial boiling point may exceed 80°C within the boiling point range, this does not pose a particular problem in this embodiment. Desulfurized light naphtha is a fraction having a boiling point range of typically 30°C or higher and 140°C or lower, preferably 35°C or higher and 100°C or lower, and more preferably 40°C or higher and 90°C or lower, and typically has a sulfur content of approximately 0.5 mass ppm or lower. The desulfurized light naphtha is either used as a gasoline base stock as is or introduced into an isomerization unit where the low-octane normal paraffins are isomerized into high-octane isoparaffins, and the resulting isomerized gasoline (isomerate) is used as a gasoline base stock. This desulfurized light naphtha is also used as a petrochemical raw material for the production of ethylene, propylene, etc. Meanwhile, desulfurized heavy naphtha can be introduced into a catalytic reforming unit, where its main components, paraffins and cycloparaffins, are converted (reformed) into aromatic hydrocarbons to produce naphtha reformate. This naphtha reformate can be used directly as high-octane reformed gasoline or used to produce gasoline base stock. It is also particularly suitable for producing xylene, a petrochemical raw material. [Example]

[0024] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples in any way.

[0025] Example 1 The desulfurized heavy cracked gasoline obtained by desulfurizing the heavy cracked gasoline was fractionated into a first light fraction, a second light fraction, and a heavy fraction. The distillation conditions were targeted to achieve a ratio of the amount of nitrogen atoms contained in the first light fraction and the second light fraction to the total amount of nitrogen atoms contained in the first light fraction, the second light fraction, and the heavy fraction of about 8%. The mass ratio, nitrogen concentration, olefin concentration, C8 concentration, and C8A concentration (concentration of aromatic hydrocarbons with a carbon number of 8) of each fraction, the desulfurized heavy cracked gasoline before fractionation, and the full-range naphtha fraction were measured using the following methods. The measurement results are shown in Table 1.

[0026] (Various measurement methods) Nitrogen concentration It was determined by chemiluminescence. Olefin content Measurement was performed using the fluorescent indicator adsorption method of JIS K 2536 "Testing methods for petroleum product components." Analysis of hydrocarbons with 8 carbon atoms Measurement was performed using the total component test method by gas chromatography in JIS K 2536 "Testing Methods for Components in Petroleum Products."

[0027] [Table 1]

[0028] 449 parts by mass of the second light fraction obtained as described above and 3011 parts by mass of the full-range naphtha fraction were mixed to obtain a hydrodesulfurized feedstock. As is clear from Table 1 above, the ratio of the amount of nitrogen atoms contained in the first light fraction and the second light fraction to the total amount of nitrogen atoms contained in the first light fraction, the second light fraction, and the heavy fraction was 8.1 mass%.

[0029] (Comparative Example 1) 576 parts by mass of the first light fraction obtained in Example 1, 449 parts by mass of the second light fraction, and 3011 parts by mass of the full-range naphtha fraction were mixed together to obtain a hydrodesulfurized feedstock.

[0030] (Comparative Example 2) 449 parts by mass of the second light fraction obtained in Example 1, 621 parts by mass of the heavy fraction, and 3011 parts by mass of the full-range naphtha fraction were mixed together to obtain a hydrodesulfurized feedstock.

[0031] (Comparative Example 3) 576 parts by mass of the first light fraction obtained in Example 1 and 3011 parts by mass of the full-range naphtha fraction were mixed to obtain a hydrodesulfurized feedstock.

[0032] The nitrogen atom concentration, olefin concentration, and C8 concentration in the hydrodesulfurized feedstocks obtained in Example 1 and Comparative Examples 1 to 3 were measured in the same manner as above. The measurement results are shown in Table 2.

[0033] [Table 2]

[0034] The hydrodesulfurized feed oil obtained in Example 1 satisfied the requirement for a hydrodesulfurized feed oil of a nitrogen concentration of 2.0 ppm by mass or less from the standpoint of catalyst poisoning, and also had a low olefin concentration, which made it possible to suppress excessive heat generation on the catalyst during hydrodesulfurization.Furthermore, it was confirmed that the hydrodesulfurized feed oil obtained in Example 1 was suitable as a hydrodesulfurized feed oil to be used as a raw material for xylene, due to its high C8 concentration. In contrast, the hydrodesulfurized feedstock of Comparative Example 1, which used the first light fraction obtained from desulfurized heavy cracked gasoline, had a high olefin concentration, and the hydrodesulfurized feedstock of Comparative Example 2, which was obtained by blending the heavy fraction with a full-range naphtha fraction, had an extremely high nitrogen concentration, confirming that neither was suitable as a hydrodesulfurized feedstock. Furthermore, the hydrodesulfurized feedstock of Comparative Example 3, which was obtained by blending the first light fraction with a full-range naphtha fraction, was confirmed to have a low ratio of C8 components and an insufficient xylene recovery rate.

Claims

1. The method for producing catalytically reformed feedstock comprises: a first step of fractionating desulfurized heavy cracked gasoline obtained by desulfurizing heavy cracked gasoline into a first light fraction, a second light fraction, and a heavy fraction; a second step of blending the second light fraction with a full-range naphtha fraction to obtain a hydrodesulfurized feedstock; and a third step of supplying the hydrodesulfurized feedstock to a naphtha hydrodesulfurization unit for hydrodesulfurization, wherein the ratio of the amount of nitrogen atoms contained in the first light fraction and the second light fraction to the total amount of nitrogen atoms contained in the first light fraction, the second light fraction, and the heavy fraction is 3.0 to 15.0 mass%, the ratio of the amount of nitrogen atoms contained in the second light fraction is 0.5 to 5.0 mass%, and the ratio of the amount of olefins contained in the second light fraction to the total amount of olefins contained in the first light fraction and the second light fraction is 18 to 35 mass%.

2. 2. The method for producing catalytically reformed feedstock oil according to claim 1, wherein the ratio of aromatic hydrocarbons having 8 carbon atoms contained in the second light fraction to the total amount of aromatic hydrocarbons having 8 carbon atoms contained in the first light fraction and the second light fraction is 90 mass% or more.

3. 3. The method for producing catalytically reformed feedstock according to claim 1 or 2, wherein in the second step, 1 to 20 parts by mass of the second light fraction is mixed with 100 parts by mass of the full-range naphtha fraction.

4. The method for producing catalytically reformed feedstock according to any one of claims 1 to 3, wherein the nitrogen atom content of the hydrodesulfurized feedstock is 2.0 ppm by mass or less.

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