JPH0681749B2 - Method for producing maleic anhydride - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing maleic anhydride. More specifically, the present invention relates to improvement of reaction selectivity, operational safety, etc. in a method for producing maleic anhydride by catalytically oxidizing an aliphatic hydrocarbon in the gas phase in the presence of a vanadium-phosphorus catalyst.

[Conventional technology]

It is well known that maleic anhydride can be obtained by vapor-phase oxidation of a linear C ₄ hydrocarbon such as butane, butenes, butadiene, etc., and is widely practiced industrially. As the catalyst, a complex oxide-based catalyst containing vanadium and phosphorus as main components, and optionally a slight accelerating component added is used. In particular, in the case of gas-phase oxidation of butane, crystalline vanadium phosphate is known to exhibit high activity and high selectivity, and various contrivances have been made regarding its production method (for example, Japanese Patent Publication No. 53 -39,037, U.S. Pat.No. 4,225,465
No. 56-45,815, JP-A-56-33,038, etc.).

[Problems to be solved by the invention]

The method for producing maleic anhydride using butane obtained from natural gas or the like as a raw material is attractive because the raw material is easily available and inexpensive. However, in the production of maleic anhydride by gas phase oxidation of butane, butane is more likely to undergo autoxidation under relatively mild conditions as compared with butene, butadiene, etc., and in some cases, spontaneous combustion is likely to occur. There is.

There are various proposals regarding the process of using butane as a raw material for gas phase oxidation. For example, a method has been proposed in which the butane concentration in the air is made to be a high concentration above the upper limit of the explosion and the unreacted butane is recycled. In this case, as a result of using the catalyst in an excessively reduced state, it is extremely difficult to maintain the activity.

[Means for solving problems]

As a result of intensive studies to solve the above-mentioned problems, the inventors of the present invention have generally positively tried to reduce the sulfur content, which is usually disliked as a catalyst poison in catalytic reactions using hydrocarbons as raw materials and whose reduction is attempted. The present invention has been completed by finding that the autoxidation reaction is suppressed without suppressing the oxidation reaction of the raw material hydrocarbon to maleic anhydride when it is allowed to exist in the reaction system.

An object of the present invention is to provide a method for producing maleic anhydride having improved operational safety, and the gist thereof is the presence of an vanadium-phosphorus complex oxide catalyst in the presence of an aliphatic carbon atom having 4 or more carbon atoms. In producing maleic anhydride by catalytically oxidizing hydrogen in the gas phase, in the reaction system,
Converted into sulfur atoms based on the weight of the above aliphatic hydrocarbons
A method for producing maleic anhydride, characterized in that a sulfur compound of 4 ppm or more is present.

Hereinafter, the present invention will be described in detail.

The catalyst used in the method of the present invention is a vanadium-phosphorus complex oxide catalyst. There are amorphous and crystalline vanadium-phosphorus complex oxides, and various types are known. Of these, an appropriate activity can be selected according to the kind of the raw material hydrocarbon, but when high activity is required, a catalyst containing a crystalline complex oxide as a main active component is selected. use.

Crystalline vanadium-phosphorus composite oxides are known, and some production methods have been reported. For example, in a non-oxidizing acidic solution such as hydrochloric acid solution, pentavalent vanadium such as vanadium pentoxide is reduced with a reducing agent such as oxalic acid to prepare a solution containing tetravalent vanadium ions. Then, after reacting with a pentavalent phosphorus compound such as phosphoric acid, the resulting soluble vanadium-phosphorus complex is precipitated by adding water (JP-A-51-95990).
), A pentavalent vanadium compound such as vanadium pentoxide and phosphoric acid are reacted in an aqueous medium in the presence of a reducing agent such as hydrazine hydrochloride or hydroxylamine hydrochloride, and concentrated or evaporated to dryness. To obtain crystals (JP-A-56-45815), vanadium pentoxide is reduced in an organic medium such as ethanol, isopropanol, glycerol, reacted with phosphoric anhydride, and azeotropically dehydrated with a solvent such as benzene. To precipitate crystals (US Pat. No. 4,283,288), vanadium pentoxide is dissolved in an aqueous medium in the presence of phosphoric acid and an inorganic reducing agent to give a solution containing tetravalent vanadium ions, and then 110 It is known that a method of hydrothermal treatment in the temperature range of up to 250 ° C (JP-A-58-151,313), and the like are known.

The above crystalline composite oxides can be used alone or in combination with other active ingredients or carrier ingredients depending on the mode of use. When used as a catalyst for a fixed bed reaction, it can be molded into an arbitrary shape by a known method and used. Further, particularly when used in a fluidized bed, mechanical strength in the reaction system is required. Suitable mechanical strength-improved catalysts for such use include, for example, vanadium and phosphorus as the first component, and Table B below: A composition containing, as a second component, a crystalline complex oxide having a characteristic X-ray diffraction peak shown in FIG. 2 and an amorphous complex oxide containing vanadium and phosphorus in a uniformly dispersed state. A catalyst consisting of The catalyst preferably contains, in addition to the active ingredient consisting of the first component and the second component, a suitable carrier as the third component, in particular silica, in a uniformly dispersed state. Such catalysts contain, for example, vanadium and phosphorus as the first component and are listed in Table A or Table B below: To a crystalline complex oxide (crystalline vanadium phosphate) having a characteristic X-ray diffraction peak shown in, and an aqueous solution containing vanadium and phosphorus as a second component (preferably vanadyl phosphate aqueous solution), preferably Is further produced by mixing an appropriate carrier as the third component, particularly silica gel to form an aqueous slurry, spray-drying the slurry, and calcining the obtained solid particles (for example, JP See JP-A-58-170,542, JP-A-58-170,543, and U.S. Pat. No. 4,472,527).

The hydrocarbon raw material used in the method of the present invention is an aliphatic hydrocarbon having 4 or more carbon atoms, preferably an aliphatic hydrocarbon having 4 carbon atoms. A more preferable raw material is a linear aliphatic hydrocarbon having 4 carbon atoms, particularly n-butane, 1-butene, 2-butene, butadiene or a mixture thereof. Maleic anhydride is produced, albeit in a lower yield, from an aliphatic hydrocarbon having 4 carbon atoms and a side chain, such as isobutane or isobutylene. Further, hydrocarbons having 5 or more carbon atoms, such as pentane, isopentane, cyclopentadiene and pentenes, can be used if desired. The most economically advantageous raw material is n
-Butanes and butenes, usually C obtained by separation from natural gas or by naphtha cracking or FCC reactions
_{It is used as 4} fractions and, if desired, as the remaining mixture of butadiene and isobutylene extracted from them.
In these cases, C ₃ or C ₅ hydrocarbons are usually mixed as impurities, but there is no particular problem.

In the method of the present invention, these hydrocarbons are catalytically oxidized in the gas phase in the presence of the catalyst to produce maleic anhydride. A molecular oxygen-containing gas, usually air, is used as the oxidant.

As the reaction system, either a fixed bed system or a fluidized bed system can be adopted, but when a high concentration of hydrocarbon is used in the reaction, the fluidized bed system is adopted from the viewpoint of easy heat removal. desirable.

The reaction conditions are somewhat dependent on the reaction system, but in the case of the fluidized bed system, the reaction temperature is usually 300 to 500 ° C, preferably 350 to 480.
The reaction pressure is usually above atmospheric pressure, preferably in the range of 0.1 to 10 kg / cm ² . The concentration of the raw material hydrocarbon is usually about 0.1 to 8% by volume, but 1 to 5% by volume.
Is industrially advantageous. Space velocity (sv)
Preferably 300-3000 hr ^-1 , more preferably 500-2500
hr ^-1 .

Now, in the method of the present invention, the sulfur compound is present in the reaction system in an amount of 4 ppm by weight or more, more preferably 5 ppm or more in terms of sulfur atoms based on the raw material aliphatic hydrocarbon.

As the sulfur compound, various compounds can be used. Specifically, for example, inorganic sulfur compounds such as carbonyl sulfide and carbon disulfide; alkanethiol, alkyl sulfide, alkyl disulfide, alkyl sulfoxide, Examples include organic sulfur compounds such as alkyl sulfones.

These sulfur compounds may be contained in natural gas or liquefied petroleum gas at a very low concentration. According to the knowledge of the present inventors, the content in this case is as low as 0.1 to 2 ppm with respect to butane in terms of sulfur atoms. At such a low concentration, the effect of suppressing the self-ignitability of butane is insufficient, and 4 ppm or more to achieve the object of the present invention,
More preferably, a high concentration of 5 ppm or more is required. Note that the butane recovered by crude oil topping may have a relatively higher sulfur content than liquefied petroleum gas or natural gas-based butane, but if the sulfur content is at a level of 4 ppm or more, it will be convenient for the maleic anhydride synthesis raw material. Can be used as The presence of a large amount of sulfur compounds is acceptable in terms of the effect of suppressing autoxidation, but if the amount of sulfur present is too large, it may impose a heavy burden on waste gas treatment, etc. Preferably 5000ppm or less,
It is more preferably 1000 ppm or less.

As a method of adding the sulfur compound to the reaction system, it is general to add it to the reaction vessel in a liquid state by a pump or the like, and to add the vapor by mixing it with an entrained gas. The addition position in the reactor may be before the gas enters the catalyst layer or after passing through the catalyst layer. It is also possible to add it to butane in advance, supply it, and evaporate it together to introduce it into the catalyst layer. Further, when the amount of the sulfur compound added is small, it can be dissolved in a solvent such as water, methanol, butanol, benzene or the like which does not interfere with the reaction and prepared as a diluted solution.

The effect on the reaction when a sulfur compound is present in the reaction system according to the present invention is different depending on the catalyst, but when the crystalline vanadium phosphate catalyst is used, the effect on the yield is slight, and particularly, Complete oxidation products (co, c
The production ratio of o ₂ ) changes slightly and co ₂ production tends to decrease. This is an advantageous direction in terms of removal of reaction heat, and is an advantage of the present invention together with suppression of autoxidation.

〔Example〕

Next, specific examples of the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples unless the gist thereof is exceeded.

Production Example 1 of Catalyst (A) Production of First Component: A crystalline active ingredient precursor showing the X-ray diffraction peaks in Table A was produced as follows.

A glass-lined 100 liter capacity pressure-resistant container with a jacket was charged with deionized water 38.0 kg, 85% phosphoric acid 21.83 kg, and 80% hydrazine hydrate solution 2.85 kg, and then with stirring, foam vanadium pentoxide powder 16.40 kg. Carefully added and dissolved little by little. During this period, in order to suppress the temperature rise due to heat generation and maintain the liquid temperature at 60 to 80 ° C, the heat medium was circulated in the jacket to remove heat. The addition of vanadium pentoxide was completed in about 4 hours, and a blue vanadyl phosphate solution was obtained. To this, 1.0 kg of seed crystals were added, and then a heating medium at 160 ° C. was circulated in the jacket to heat the same. Liquid temperature is raised to 140 ℃ in 2 hours,
The hydrothermal treatment was carried out for 10 hours as it was. During this time the pressure is about
It was 0.24 MPa (gauge pressure). After cooling to 90 ° C,
Deionized water (10.3 kg) was added to adjust the solid concentration in the slurry to about 35%, and the mixture was extracted. When X-ray diffraction measurement of this solid was performed, it was found that the main diffraction peaks shown in Table A were exhibited, and it was confirmed to be a pure crystalline oxide. This oxide slurry was dried using a spray dryer to obtain 29.8 kg of a pale blue powder of crystalline oxide. The P / V atomic ratio on the basis of the charge of the oxide slurry was 1.05, but the crystalline solid obtained by overwashing was substantially (V ₂ O ₄ ) (P ₂ O ₅ ) (2H
₂ O) was confirmed by the composition formula. The powder obtained by the above spray drying was used as it was as the first component.

(B) Production of Second Component: A vanadium phosphate solution was produced as follows.

29.56 kg of 85% phosphoric acid was dissolved in 30 kg of demineralized water, 25.5 kg of oxalic acid (H ₂ C ₂ O ₄ .2H ₂ O) was further added, and dissolved by heating.
The solution was heated to 80 ° C., 18.42 kg of vanadium pentoxide was added little by little while paying attention to foaming, dissolved, and then heated for 10 minutes in a boiling state to complete the reduction. The liquid was concentrated and the total amount was adjusted to 79.5 kg. This solution has a P / V atomic ratio of 1.266 and an oxide (V ₂ O ₄ + P ₂ O ₅ ) concentration of 44 wt%. This was used as the second component.

(C) Production of catalyst: 3.936 kg of the dry powder obtained in (A) above, 9.092 kg of the vanadium phosphate solution obtained above in (B), and 12.50 kg of a commercially available 20% concentrated colloidal silica solution were mixed. Then, the mixture was treated with a continuous wet pulverizer to be sufficiently homogenized. This slurry was dried using a spray dryer to obtain spherical catalyst particles having an average particle diameter of 60 μm. This was calcined in a kiln at a temperature of 300 ° C. for a residence time of 17 minutes in an air stream, and then in a kiln at a temperature of 580 ° C. for a residence time of 17 minutes in a nitrogen stream to obtain a fluidized bed catalyst (catalyst I). ) Got. The bulk composition of catalyst I is the first component (crystalline PV oxide) / second component (amorphous PV oxide) / third component (silica) = 35/40/25 (weight ratio) , The overall P / V ratio was 1.16.

Comparative Example 1 10 kg of the catalyst I was placed in a fluidized bed reactor having an inner diameter of 82 mmφ and a height of 5 m, pressure 1.5 kg / cm ² G, reaction temperature 440 ° C., GHSV900,
Butane (sulfur content: 0.1 ppm or less) was reacted at a concentration of 2.0%. The results are shown in Table 1.

Example 1 In Comparative Example 1, butane was replaced with dimethyl sulfide.
7ppm, carbon disulfide 0.2ppm, thiophene 1.1ppm, dimethyldisulfide 3.3ppm, methylethyldisulfide 8.8pp
The reaction was carried out in the same manner except that makeupbutane (total sulfur content: 10.4 ppm) added with m and diethyl disulfide 3.7 ppm was used. The results are shown in Table 1.

Example 2 A reaction was carried out in the same manner as in Comparative Example 1 except that a methanol solution of methyl mercaptan was added to the reaction system so that the amount of sulfur atoms in the supplied butane was 100 ppm. The reaction results are shown in Table 1.

As a result of calculation based on the above reaction results, the heat generation amount per unit butane reacted was higher in Comparative Examples 1 and 2 in Examples 1 and 2.
The reduction is estimated to be 15 to 20 KJ / mol, which is industrially shown to be advantageous in terms of reaction heat removal.

〔The invention's effect〕

The method of the present invention improves reaction selectivity and operational safety in the method of producing maleic anhydride by catalytically oxidizing an aliphatic hydrocarbon in the vapor phase in the presence of a vanadium-phosphorus catalyst.

Claims (2)

[Claims] 1. A method for producing maleic anhydride by catalytically oxidizing an aliphatic hydrocarbon having 4 or more carbon atoms in the gas phase in the presence of a vanadium-phosphorus complex oxide catalyst, the reaction system comprising: A method for producing maleic anhydride, characterized in that 4 ppm or more of a sulfur compound in terms of sulfur atom relative to the weight of the aliphatic hydrocarbon is present. 2. The method for producing maleic anhydride according to claim 1, wherein the vanadium-phosphorus complex oxide catalyst contains a carrier.