JP2009046409A - Method for purifying naphthalene and method for producing phthalic anhydride - Google Patents

Abstract

The present invention relates to a method for purifying naphthalene in which sulfur compounds and nitrogen compounds, which are impurities in crude naphthalene, are reduced without causing blockage of piping, and to stably produce phthalic anhydride using the naphthalene. It aims to provide a way to do.
An addition / mixing step of adding and mixing an acid anhydride group-containing high-boiling product to crude naphthalene obtained by distillation of coal tar, and an amount of nitrogen contained in naphthalene obtained in the addition / mixing step A naphthalene having a nitrogen reduction step for reducing and a hydrodesulfurization step for reducing the amount of sulfur contained in the naphthalene by hydrodesulfurizing the naphthalene obtained in the nitrogen reduction step in this order Purification method.
[Selection figure] None

Description

  The present invention relates to a method for purifying crude naphthalene and producing phthalic anhydride from the purified naphthalene.

  In the method for producing phthalic anhydride by oxidizing naphthalene with a fluidized bed for gas phase oxidation, maintaining the activity of the oxidation catalyst is extremely important for ensuring stable production. Naphthalene is usually obtained through a distillation process using coal tar as a raw material, but contains impurities such as nitrogen compounds and sulfur compounds. In addition to poisoning the oxidation catalyst, this impurity must be removed to reduce the quality of the final product. For sulfur compounds only, removal methods applicable to industrial processes such as hydrodesulfurization have been established. For example, Patent Document 1 discloses a method for removing sulfur compounds by heating 95% naphthalene in the presence of a solid acid catalyst, followed by distillation. However, this hydrodesulfurization method alone cannot sufficiently remove nitrogen compounds, and phthalic anhydride cannot be produced stably.

  Patent Document 2 discloses a method for purifying naphthalene that removes sulfur compounds and nitrogen compounds contained in crude naphthalene. Specifically, first, an acid anhydride group-containing high-boiling product such as phthalic anhydride is added to desulfurized naphthalene obtained by removing sulfur compounds from crude naphthalene by the hydrodesulfurization method. Most of the nitrogen compounds are converted to amine compounds by the hydrodesulfurization method, and react with an acid anhydride group-containing high boiling point product to form a high boiling point imide compound. Using the fact that the boiling point of the produced imide compound is higher than the boiling point of naphthalene, only naphthalene can be obtained as a top fraction by distillation. The produced imide compound is recovered from the bottom of the column as a residue in the still. Summarizing the processes in this document, the operations are performed in the order of hydrodesulfurization of crude naphthalene, addition of an acid anhydride group-containing high-boiling product, and distillation.

JP-A-10-331080 Patent No. 3529163

  The method for purifying naphthalene in Patent Document 2 can significantly reduce the concentrations of sulfur compounds and nitrogen compounds contained in the crude naphthalene. However, the following problems were found by the inventors' investigation.

  Sulfur and nitrogen compounds in crude naphthalene are liable to become heavy due to thermal polymerization or carbonize due to thermal decomposition during the hydrodesulfurization operation. Since it adheres and accumulates, clogs the piping, and further adheres to the surface of the desulfurization catalyst in the hydrodesulfurization reactor and reduces the catalytic activity, the equipment is often shut down, the piping is cleaned, and the catalyst is clogged. There was a problem that the productivity had to be greatly impaired due to the necessity of replacement.

  On the other hand, for the purpose of solving the above-mentioned problems, a method in which crude naphthalene is subjected to precision distillation before hydrodesulfurization treatment to use highly purified naphthalene is also conceivable. However, adding additional distillation operations on an industrial scale is undesirable from the standpoint of energy costs and construction costs. Further, when the distillation before the desulfurization treatment is actually carried out for a long time, there is a problem that the piping of an apparatus such as a distillation tower is blocked. For this reason, every time the pipe is blocked, it is necessary to disassemble the distillation tower over a great amount of labor and time to remove the deposits, which has caused a significant reduction in productivity.

  Therefore, in view of the above problems, the present invention provides a method for purifying naphthalene that reduces sulfur compounds and nitrogen compounds as impurities in crude naphthalene without causing plugging of the piping, and phthalic anhydride using the naphthalene. An object of the present invention is to provide an industrially advantageous method for stably producing the above.

  As a result of intensive studies to solve the above problems, the present inventors have obtained the following knowledge.

(i) In the distillation operation of the crude naphthalene before the desulfurization treatment, a part of the nitrogen compound in the crude naphthalene is thermally polymerized, and the produced polymer adheres to and accumulates on the piping of the distillation tower, resulting in blockage of the piping. Turned out to be.

(ii) It has been found that the imide compound obtained by the reaction of the above-described nitrogen compound exhibiting polymerizability and an acid anhydride group-containing high-boiling product does not exhibit polymerizability under the heating conditions of the distillation operation.

  Therefore, based on the above findings, the present inventors added an acid anhydride group-containing high-boiling product to crude naphthalene to produce an imide compound, and then carried out distillation and hydrodesulfurization operation, so that there was no blockage of piping. In addition, the inventors have found an industrially advantageous purification method capable of greatly reducing the concentration of sulfur compounds and nitrogen compounds, and have completed the invention. Summarizing the steps of the present invention, operations are performed in the order of addition of an acid anhydride group-containing high-boiling product to crude naphthalene, distillation, hydrodesulfurization treatment, and phthalic anhydride production step.

That is, the gist of the present invention resides in the following (1) to (7).
(1) Addition / mixing step of adding and mixing acid anhydride group-containing high-boiling products to crude naphthalene obtained from distillation of coal tar, and reducing the amount of nitrogen contained in naphthalene obtained in the addition / mixing step And a hydrodesulfurization step for reducing the amount of sulfur contained in the naphthalene by hydrodesulfurizing the naphthalene obtained in the nitrogen reduction step in this order. Purification method.
(2) The method for purifying naphthalene according to (1), wherein the nitrogen is an imide compound formed by a reaction between a nitrogen compound contained in the crude naphthalene and the acid anhydride group-containing high-boiling product. .
(3) The method for purifying naphthalene as described in (1) or (2), wherein the boiling point of the acid anhydride group-containing high-boiling product is higher than 218 ° C.
(4) The method for purifying naphthalene according to any one of (1) to (3), wherein the acid anhydride group-containing high-boiling product is phthalic anhydride.
(5) The method for purifying naphthalene according to any one of (1) to (4), wherein the reduction of the nitrogen amount is reduction by distillation.
(6) A method for producing phthalic anhydride, wherein naphthalene obtained by any of the purification methods according to (1) to (5) is oxidized under a catalyst to produce phthalic anhydride.

  The present invention relates to a method for purifying naphthalene that reduces sulfur compounds and nitrogen compounds, which are impurities in crude naphthalene, without causing blockage of the piping, and a method for stably producing phthalic anhydride using the purified naphthalene. I will provide a. The present invention enables continuous and stable operation on an industrial scale. Therefore, the present invention is an economical method and has great industrial value.

Next, the present invention will be described in more detail with reference to preferred embodiments.
In the present invention, phthalic anhydride is produced in the following four steps.
(1) Addition / mixing step of adding / mixing an acid anhydride group-containing high-boiling product to crude naphthalene obtained from distillation of coal tar (2) The amount of nitrogen contained in naphthalene obtained in the addition / mixing step Reduced nitrogen reduction step (3) Hydrodesulfurization of naphthalene obtained in the nitrogen reduction step to reduce the amount of sulfur contained in the naphthalene (4) Obtained in the hydrodesulfurization step A process for producing phthalic anhydride by oxidizing naphthalene under a catalyst to produce phthalic anhydride is described in detail below.

(1) Addition / mixing step The first step is a step of adding and mixing an acid anhydride group-containing high-boiling product to crude naphthalene obtained from distillation of coal tar. In this step, the amine-based nitrogen compound contained in the crude naphthalene reacts with the added acid anhydride group-containing high-boiling product to produce a high-boiling imide compound.

  The crude naphthalene used in the present invention is not particularly limited, but can be obtained through separation and recovery operations such as distillation and crystallization using coal tar generated from a coke oven, coal liquefied oil or the like as a raw material. The purity of the crude naphthalene is usually 90 to 99.9% by mass, preferably 95 to 99% by mass.

  Normally, crude naphthalene contains sulfur compounds such as thiophenes, thiols, and thionaphthenes. The sulfur atom content contained in the crude naphthalene is usually about 1000 to 10000 mass ppm (hereinafter referred to as ppm) in terms of mass ratio to the naphthalene, and can be used within this range. The sulfur atom content is measured by a known method such as a GC-FTD method or a combustion method.

  In addition to aromatic primary amines such as aniline and toluidine, the crude naphthalene contains nitrogen-containing heterocyclic compounds such as quinoline and isoquinoline and various nitrogen-containing compounds having a nitrile group. The content of nitrogen atoms contained in the crude naphthalene is generally about 50 to 500 ppm in terms of mass ratio to the naphthalene, and any naphthalene within the range can be used. The nitrogen atom content is measured by a known method such as chemiluminescence. Among the nitrogen compounds, in particular, amine compounds such as aniline and toluidine are likely to react with an acid anhydride group-containing high-boiling product described later.

  The crude naphthalene used in the present invention may contain other compounds in addition to the sulfur compound and the nitrogen compound. Specific examples include tetralin, 1-methylnaphthalene, 2-methylnaphthalene, and alkylbenzenes. The concentration of these compounds is usually 1 to 2 mass% in total with respect to the naphthalene.

  The acid anhydride group-containing high boiling point product used in the present invention means a high boiling point compound having an acid anhydride group. The high boiling point is over 218 ° C., and if it is lower than 218 ° C., the acid anhydride group-containing high boiling point product may evaporate during the reaction in the addition / mixing step described later. It is preferable not to distill with naphthalene even when an acid anhydride group-containing high-boiling product is excessively added. Specifically, aromatic carboxylic anhydrides such as phthalic anhydride, trimellitic anhydride, tetrahydrophthalic anhydride, copolymers of maleic anhydride, styrene-maleic acid resin, indene-maleic acid resin, maleic anhydride-polyolefin And high molecular weight acid anhydride group-containing compounds such as acid resins and maleic anhydride-modified nylon resins. Among these, a low molecular weight acid anhydride group-containing compound is preferable, and phthalic anhydride is particularly preferably used. These may be used alone or in combination of two or more. Moreover, if necessary, the acid anhydride group-containing high-boiling product and other compounds may be mixed and used as a mixture having an acid anhydride group-containing high-boiling product content of 1% by mass or more. For example, a combination of phthalic anhydride and naphthalene, phthalic anhydride and anthracene, or the like can be given.

  The boiling point of the acid anhydride group-containing high-boiling product is preferably 220 ° C. or higher, more preferably 280 ° C. or higher. The higher the boiling point of the acid anhydride group-containing high-boiling product, the higher the boiling point of the imide compound produced by the reaction, and the easier the imide compound and naphthalene (boiling point: 218 ° C.) in the distillation operation in the nitrogen reduction step described later. Can be separated.

  The addition amount of the acid anhydride group-containing high-boiling product is not particularly limited, but is 0.2 to 10 times, preferably 0.5 to 8 times, in mass ratio to the nitrogen atom content (T-Nppm) in the naphthalene. It is. If the amount added is too small, the reaction with the nitrogen compound does not proceed sufficiently. Moreover, when there is too much addition amount, it is economically unpreferable.

  Although it is a method of mixing crude naphthalene and acid anhydride group-containing high-boiling products, it is not particularly limited, but even if the total amount of acid anhydride group-containing high-boiling products is first added to crude naphthalene, it is also divided during the reaction. It is also possible to add them.

  In the addition / mixing step, a mixture of crude naphthalene and an acid anhydride group-containing high-boiling product may be heated, and the mixing temperature is usually not lower than the melting point (80 ° C.) of naphthalene, preferably 90 to 140 ° C. The mixing time is appropriately selected depending on the scale to be used and the apparatus to be used, but is usually about 2 hours to 2 days. The operation pressure in the addition / mixing step is usually atmospheric pressure, and may be increased or reduced as required.

  Although it does not specifically limit in an addition and mixing process, A solvent can be used or it can also carry out without a solvent. When a solvent is used, specific examples include tetralin, toluene, xylene, and alkylbenzenes. These solvents may be used alone or as a mixture of two or more solvents.

  The reaction system can be either a batch system or a continuous system, but if it can be carried out in a continuous system, it is industrially advantageous.

  The addition / mixing step may be performed in a distillation pot used in a distillation operation in a nitrogen reduction step described later. In addition, the method is a method of mixing crude naphthalene and acid anhydride group-containing high-boiling product at that time, but there is no particular limitation. First, the entire amount of acid anhydride group-containing high-boiling product and crude naphthalene may be mixed in a distillation kettle. It is also possible to divide both and add them to the distillation column.

(2) Nitrogen reduction process Next, a 2nd process is demonstrated. The second step is a nitrogen reduction step for reducing the amount of nitrogen contained in the naphthalene obtained in the addition / mixing step. Specifically, the nitrogen compound contained in the crude naphthalene is removed by a known method such as filtration, distillation, crystallization, solvent extraction, and adsorption separation. In particular, a distillation operation is preferred. The imide compound obtained in the addition / mixing step is usually a compound having a boiling point higher than that of naphthalene, and can be recovered as a residue from the bottom of the distillation column.

  The distillation operation will be specifically described below. In the distillation operation, the naphthalene containing the imide compound obtained in the addition / mixing step is introduced into a distillation column, a high boiling point compound such as an imide compound is extracted from the bottom of the column, and naphthalene is distilled from the top of the column. Can do.

  Although the kind of distillation tower is not specifically limited, For example, a packed tower, a plate tower, etc. are mentioned. Moreover, you may carry out by a single distillation column or may be carried out by a plurality of distillation columns. The distillation may be either batch type or continuous type, but industrially, the continuous type is preferable. In the case of a continuous type, crude naphthalene and an acid anhydride group-containing high-boiling product may be mixed at a temperature of 90 to 120 ° C. in a premixing tank or the like, reacted, and then supplied to the distillation column. At this time, the residence time in the preliminary mixing tank is not particularly limited, but is usually 2 hours to 2 days.

  The distillation pressure of the distillation column to be used can be arbitrarily set, but is usually a normal pressure. If necessary, the tower top pressure can be lower than atmospheric pressure. By making the pressure lower than atmospheric pressure, the thermal energy used for distillation can be reduced.

  Although the tower top temperature and the tower bottom temperature vary depending on the tower top pressure, the type of the distillation tower, etc., in the case of continuous atmospheric distillation, the tower top temperature is usually 219 to 230 ° C, preferably 220 to 224 ° C. The tower bottom temperature is usually 220 to 240 ° C, preferably 223 to 230 ° C.

  Refluxing is possible without performing, and the reflux ratio is preferably 3 or less, although it depends on the column top pressure and the type of distillation column. When the reflux ratio is larger than 3, the amount of heat energy required for distillation increases, which is not economically preferable.

  The number of theoretical columns in the distillation column is sufficient even with a single distillation, but it is also possible to carry out with 10 or less. Further, a distillation column having more than 10 stages is not preferable from the viewpoints of economics of construction of the distillation column, operational difficulty, and safety management.

  The unreacted acid anhydride group-containing high-boiling product remaining at the bottom of the column by distillation may be recovered and reused.

(3) Hydrodesulfurization step Next, the third step will be described. The third step is a hydrodesulfurization step in which naphthalene obtained in the nitrogen reduction step is hydrodesulfurized to reduce the amount of sulfur contained in the naphthalene. Specifically, it is a step of purifying naphthalene by adding hydrogen and reacting with a sulfur compound in the presence of a catalyst. Sulfur compounds need to be removed because they cause poisoning of the oxidation catalyst of naphthalene in the phthalic anhydride production process and have the adverse effect of shortening the catalyst life and also cause corrosion of equipment and piping.

  As the catalyst used in this step, a known hydrodesulfurization catalyst can be used. For example, an inorganic oxide support in which molybdenum is an essential component and at least one component selected from cobalt and nickel is supported can be used. The inorganic oxide carrier is not particularly limited, and alumina, silica, carbon, zeolite, activated carbon and the like are used, and preferably alumina. Suitable combinations include a cobalt-molybdenum / alumina catalyst, a nickel-molybdenum / alumina catalyst or a cobalt-nickel-molybdenum / alumina catalyst. The amount of each element supported in this case is not particularly limited, but the nickel content is 0.1 to 5% by mass, the cobalt content is 0.1 to 8% by mass, and the molybdenum content with respect to the mass combined with the carrier. Is preferably in the range of 5 to 20% by mass. In addition, you may add elements other than the above to the catalyst used at this process in the range which does not impair the objective.

  The method for preparing the catalyst used in this step is not particularly limited, and examples thereof include known methods such as an impregnation method, a deposition method, and a spray drying method.

  The amount of catalyst used in the hydrodesulfurization step varies depending on the type of the reactor and is not particularly limited. However, in the case of a fixed bed flow (continuous) reactor, the value of W / F is 0.2. The catalyst amount is preferably -0.5 h, more preferably 0.25-0.4 h. The W / F is a catalyst weight ratio in the reactor per unit amount of naphthalene supply, W is a catalyst mass (t), and F is a naphthalene supply amount (t / h).

  The hydrogen pressure in hydrodesulfurization varies depending on the type of reactor, the amount and amount of catalyst used, and the amount of naphthalene treated, and is not particularly limited, but in the case of a fixed bed flow (continuous) reactor, it is 0. 2-10 MPa is preferable. More preferably, it is 0.5-5 MPa. When the hydrogen pressure is less than 0.2 MPa, the desulfurization rate is lowered, and the throughput is remarkably impaired. On the other hand, when it exceeds 10 MPa, the nuclear hydrogenation reaction such as conversion of naphthalene to tetralin is promoted, and the amount of hydrogen used increases and the yield of naphthalene decreases.

  The temperature in hydrodesulfurization varies depending on the type of reactor, catalyst type and amount used, and the amount of naphthalene treated, and is not particularly limited. In the case of a fixed bed flow (continuous) reactor, the temperature is 220 to 300. ° C is preferred. More preferably, it is 240-280 degreeC.

  Usually, before supplying raw materials to the phthalic anhydride production process described later, the contents of sulfur compounds and nitrogen compounds in naphthalene desulfurized in the third step can be confirmed by a known method such as gas chromatography analysis, The result is fed back to the operating conditions such as the flow rate, temperature, pressure and the like in the first process to the third process, and the optimum condition is appropriately selected. The control means can be performed by appropriately combining offline analysis, online automatic analysis, manual control, online automatic control, and the like.

  The content of nitrogen compound and sulfur compound in naphthalene desulfurized in the third step varies depending on the raw material and desulfurization operation, but typically, the sulfur atom content of the sulfur compound is the mass ratio to the naphthalene. In general, the total amount is 50 to 600 ppm. Moreover, the nitrogen atom content of the nitrogen compound is a mass ratio with respect to the naphthalene, and is generally 80 to 300 ppm in total. If the nitrogen atom content of the nitrogen compound is 150 ppm, the activity decrease of the catalyst for the gas phase catalytic oxidation reaction in the phthalic anhydride production process described later is suppressed, and the quality of the final product is not affected.

  Even in the long-time operation from the first step to the third step, the piping such as the distillation column is not blocked, and the operation can be performed continuously and stably. The period during which this continuous operation is possible is usually 2 years or longer, preferably 5 years or longer, more preferably 8 years or longer.

(4) Phthalic anhydride production process Next, the fourth process will be described. The fourth step is a phthalic anhydride production step for producing phthalic anhydride by oxidizing the naphthalene obtained in the hydrodesulfurization step under a catalyst. Specifically, phthalic anhydride is obtained by subjecting naphthalene and oxygen subjected to the desulfurization treatment to a gas phase catalytic oxidation reaction in the presence of a composite metal oxide catalyst.

The catalyst for the gas phase catalytic oxidation reaction used in this step is not particularly limited, and those having any composition can be used. In particular, a silica carrier catalyst mainly composed of a vanadium compound or an alkali metal compound is preferable. For example, the vanadium compound as V ₂ O ₅ is 1 to 10% by mass, preferably 2 to 7% by mass, the alkali metal compound is sulfate: M ₂ SO ₄ (M represents an alkali metal), 2 to 10% by mass, The catalyst preferably contains 5 to 12% by mass, and contains a sulfur compound as SO _{3 in} an amount of 1 to 20% by mass, preferably 2 to 10% by mass. Elements other than the above active components may be added to the catalyst as long as the purpose is not impaired.

  Although it does not specifically limit as said vanadium compound, It is soluble in water and becomes vanadium oxide by baking in the air, for example, ammonium metavanadate, vanadyl sulfate (vanadium oxysulfate), vanadium acetate, vanadium oxalate, vanadium oxalate Examples thereof include ammonium and vanadium oxyhalide.

  As the alkali metal of the alkali metal compound, one or more selected from lithium, sodium, potassium, rubidium, and cesium are used, and potassium and cesium are particularly preferably used. Examples of the potassium compound include potassium hydroxide, potassium sulfate, potassium chloride, potassium oxyhalide, potassium thiosulfate, potassium nitrite, potassium sulfite, potassium hydrogen sulfite, potassium hydrogen sulfate, and the like. Particularly preferred is potassium sulfate in which the remaining part is the active ingredient. As the cesium compound, a solution obtained by dissolving a soluble salt such as cesium hydroxide, cesium sulfate, cesium chloride, cesium oxyhalide, cesium hydrogen sulfate, cesium hydrogen carbonate, cesium acetate, and cesium oxalate with an acid. Among them, cesium sulfate and cesium hydrogen sulfate are preferable. Similarly, hydroxides, sulfates, chlorides, nitrates, nitrites, oxalates, carbonates, and the like can be used for other alkali metals.

  The method for preparing the catalyst used in this step is not particularly limited, and examples thereof include known methods such as an impregnation method, a deposition method, and a spray drying method.

  The spray drying method is a drying method including a step of spraying a solution or slurry to form fine droplets, and can be carried out using a commercially available spray dryer. There is no particular limitation on the method for preparing a solution or slurry of a compound containing a catalyst constituent element, but there is a method in which a predetermined amount of a vanadium compound, an alkali metal compound or a precursor compound thereof is sequentially added to water with stirring. It is common. If necessary, the temperature, the concentration of the solution or the slurry are set, and concentration or aging may be performed. Further, a silica-based carrier can be added during the operation of preparing the solution or slurry. The obtained mixed slurry is spray-dried to obtain fine spherical particles. The obtained spherical particles are fired at a temperature of 300 to 600 ° C. in air. The firing time is usually 0.1 to 10 hours. Firing may be performed in an oxygen atmosphere, and is performed in an inert gas atmosphere such as nitrogen, argon, helium, or in a vacuum as necessary.

  The average particle diameter of colloidal silica is preferably in the range of 1 to 10 nm. When the average particle size is small, the particle shape is deteriorated.

In the case of producing by an impregnation method, a vanadium compound, an alkali metal compound or a precursor thereof is impregnated and supported in the form of an aqueous solution on silica gel having a specific surface area of 50 to 700 m ² / g and an average particle size of 40 to 200 μm. Good. After the impregnation treatment, it is usually possible to use the catalyst as a catalyst after drying moisture and the like at room temperature to about 200 ° C. If necessary, the firing may be performed again usually in the range of 300 to 600 ° C. Firing may be performed in an oxygen atmosphere, and is performed in an inert gas atmosphere such as nitrogen, argon, or helium or in a vacuum as necessary.

  The reactor is not particularly limited, and examples thereof include a fixed bed or a fluidized bed reactor, but a fluidized bed reactor is preferred in that the heat of reaction can be easily removed and temperature can be controlled throughout the catalyst bed.

  Although reaction temperature is not specifically limited, It is 340-380 degreeC, Preferably it is 355-365 degreeC. If the reaction temperature is too low, sufficient catalytic activity cannot be obtained. When the reaction temperature is too high, the amount of maleic anhydride due to excessive oxidation and the increase in carbon dioxide due to complete oxidation are accompanied by many other by-products, resulting in a decrease in the yield of phthalic anhydride.

  The amount of catalyst used in the oxidation step varies depending on the type of the reactor and is not particularly limited. However, in the case of a fluidized bed reactor, the value of W / F is 15 to 50 h, more preferably 20 to 40 h. A catalytic amount such that The W / F is the catalyst weight ratio in the reactor per naphthalene supply unit, W is the catalyst mass (t), and F is the naphthalene supply amount (t / h).

As the oxidizing agent in the oxidation step, air is usually used, and the amount used varies depending on the type of the reactor and is not particularly limited. In the case of a fluidized bed reactor, the air ratio defined by the following formula is 5 to 15, preferably 7 to 13.
Air ratio = (Air supply flow rate (Nm ³ /h)×1.293)/(Naphthalene supply flow rate (m ³ / h) × Naphthalene liquid density)

  Although it is economical to use air as an oxidation source for the oxidation reaction, it is also possible to use oxygen-enriched air to which pure oxygen is added. In this case, the oxygen concentration is 21 to 50% by volume. If the oxygen concentration exceeds 50% by volume, the cost of pure oxygen increases and it becomes uneconomical.

  To control the reaction rate and fluidized bed height in the catalyst layer, particles that are substantially inert to the reaction, for example, metal oxides such as silica, alumina, titania, zirconia, aluminosilicate, or composite metal oxides Silicon nitride, carbon, etc. may coexist with the catalyst.

  The recovered phthalic anhydride can be further purified to a high purity by a general method such as distillation, crystallization, or extraction, if necessary. A part of phthalic anhydride may be used as an acid anhydride group-containing high boiling point product in the method for purifying naphthalene of the present invention.

  The atmosphere in which the operation is performed through all the first to fourth steps in the present invention is not particularly limited, but is usually an air atmosphere. If necessary, an inert gas atmosphere such as nitrogen, carbon dioxide, argon, helium, or a reduced pressure can be used.

  EXAMPLES The present invention will be described in more detail with reference to the following examples, but the present invention is not limited by these examples.

(Catalyst for gas phase catalytic oxidation reaction)
V ₂ O ₅ ; 4% by mass, K ₂ SO ₄ : 7.5% by mass, Cs ₂ SO ₄ ; 7.5% by mass, SO ₃ ; 6% by mass, SiO ₂ ; The spherical catalyst was used.

Example 1
(Addition / mixing process)
As raw material, crude naphthalene having a purity of 97% obtained by distillation of coal tar was used. The sulfur atom content in this raw material was 4500 ppm. The nitrogen content in this raw material was 90 ppm for nitrogen of primary amines of aniline and toluidine, and 180 ppm for compounds of compounds other than primary amines such as quinoline and isoquinoline, by mass ratio to the naphthalene. This raw material and 90 ppm of phthalic anhydride (mass ratio with respect to naphthalene) were charged, and mixed and stirred at 120 ° C. for 2 hours.
(Nitrogen reduction process)
Subsequently, the obtained mixture was flash-distilled in a single distillation column at normal pressure to obtain a naphthalene purity of 97.5% as a column top component.
(Hydrogen desulfurization process)
The hydrodesulfurization catalyst (commercially available Co-Mo catalyst) 10g was used to desulfurize naphthalene obtained in a fixed bed flow reactor (reaction conditions: reaction temperature 270 ° C, pressure 3MPa, hydrogen flow rate 100ml). The naphthalene raw material was supplied at a rate of 20 g / h at / min.) After the desulfurization reaction, naphthalene having a purity of 98% by mass was obtained. In the obtained naphthalene, the nitrogen content was 25 ppm and the sulfur content was 190 ppm.
(Phthalic anhydride production process)
A fluidized bed reactor was charged with a V ₂ O ₅ —K ₂ SO ₄ —SiO ₂ fluid catalyst and a gas phase catalytic oxidation reaction was carried out. (Reaction conditions: reaction temperature 350 ° C., normal pressure, W / F = 12 h, air ratio 8). As a result of analyzing the recovered reaction product and the gas on the outlet side of the reactor by gas chromatography, the yield of phthalic anhydride was 90% by mass. There was no blockage of the piping throughout the entire process. In addition, the activity of the oxidation catalyst was not reduced, and stable operation was possible.

Comparative Example 1
(Nitrogen reduction process and hydrodesulfurization process)
The same raw material as in Example 1 was used. The addition / mixing step of adding phthalic anhydride was omitted, the raw materials were charged into a distillation column, and a nitrogen reduction step and a hydrodesulfurization step were performed under the same conditions as in Example 1. After the desulfurization operation, the nitrogen atom content of the nitrogen compound in naphthalene was 180 ppm, and the sulfur atom content of the sulfur compound was 200 ppm. In addition, blockage of the piping was confirmed by continuous operation for 200 hours.
(Phthalic anhydride production process)
Using the obtained desulfurized naphthalene, phthalic anhydride was produced under the same conditions as in Example 1. The yield of phthalic anhydride was 65% by mass. 25% by mass of naphthoquinone was obtained as a by-product.

Comparative Example 2
(Pre-distilled)
The same raw material as in Example 1 was used. The raw material was charged into a distillation column, and a distillation operation was performed under the same conditions as in the same nitrogen reduction step of Example 1. Pipe clogging was confirmed by continuous operation for 200 hours.
(Hydrogen desulfurization process)
Using the obtained naphthalene, a hydrodesulfurization step was carried out under the same conditions as in Example 1.
(Addition / mixing process and nitrogen reduction process)
The obtained naphthalene and 90 ppm of phthalic anhydride were charged and mixed and stirred at 120 ° C. for 2 hours. The obtained reaction mixture was again charged into the distillation column, and a nitrogen reduction step was performed under the same conditions as in Example 1. After the nitrogen reduction step, the nitrogen atom content of the nitrogen compound in naphthalene was 5 ppm, and the sulfur atom content of the sulfur compound was 190 ppm.
(Phthalic anhydride production process)
Using the obtained naphthalene, a gas phase catalytic oxidation reaction was carried out under the same conditions as in Example 1. The yield of phthalic anhydride was 90% by mass.

The steps of the above examples and comparative examples are summarized as follows.

table 1

  From Table 1 above, in Example 1, a sufficient reduction in sulfur content and nitrogen content was confirmed. Moreover, there was no blockage of the piping and continuous operation was possible. Furthermore, in the phthalic anhydride production process, there was no decrease in the activity of the oxidation catalyst, and no influence of the remaining sulfur compound and nitrogen compound on the catalyst was observed. The yield of the obtained phthalic anhydride was also good.

  In Comparative Example 1, since there was no nitrogen reduction step, sufficient nitrogen compounds could not be removed, and piping clogging and reduction in oxidation catalyst activity were confirmed. In Comparative Example 2, reduction of the sulfur content and the nitrogen content was achieved, but the blockage of the piping was confirmed by predistillation, and continuous operation was not possible.

  According to the present invention, sulfur compounds and nitrogen compounds in crude naphthalene, which is a raw material of phthalic anhydride, can be effectively removed without causing a decrease in activity due to line blockage or catalyst poisoning. Accordingly, it is possible to suppress downtime due to cleaning of the closed portion and cost increase due to replenishment of the catalyst for maintaining productivity, thereby ensuring stable production.

Claims (6)

  Addition / mixing step of adding and mixing acid anhydride-containing high-boiling products to crude naphthalene obtained from coal tar distillation, and nitrogen reduction to reduce the amount of nitrogen contained in naphthalene obtained in the addition / mixing step A method for purifying naphthalene comprising: a step, and a hydrodesulfurization step for reducing the amount of sulfur contained in the naphthalene by hydrodesulfurizing the naphthalene obtained in the nitrogen reduction step in this order.   2. The method for purifying naphthalene according to claim 1, wherein the nitrogen is an imide compound formed by a reaction between a nitrogen compound contained in the crude naphthalene and the acid anhydride group-containing high-boiling product.   The method for purifying naphthalene according to claim 1 or 2, wherein the boiling point of the acid anhydride group-containing high-boiling product is higher than 218 ° C.   The method for purifying naphthalene according to any one of claims 1 to 3, wherein the acid anhydride group-containing high-boiling product is phthalic anhydride.   The method for purifying naphthalene according to any one of claims 1 to 4, wherein the reduction of the nitrogen amount is reduction by distillation.   A method for producing phthalic anhydride, wherein naphthalene obtained by the purification method according to any one of claims 1 to 5 is oxidized under a catalyst to produce phthalic anhydride.