JPS6229556A - Vapor-phase nitration of benzene - Google Patents

Abstract

PURPOSE:To obtain nitrobenzene useful as a raw material for aniline and synthetic intermediate for organic industrial chemicals in good yield with almost no formation of by-products, by nitrating benzene with a nitrating agent in the vapor phase in the presence of a niobium oxide catalyst. CONSTITUTION:Benzene is nitrated with NO2 or N2O4 as a nitrating agent in the presence of a niobium oxide catalyst, preferably in the presence of an inert gas, e.g. nitrogen, which is a diluent in the vapor phase at 80-250 deg.C. The amount of the nitrating agent based on the benzene is as follows; 0.1-3.0, preferably 0.2-2.0 molar ratio of NO2 to the benzene and 0.05-1.5, preferably 0.05-1.0 molar ratio of the N2O4 used to the benzene. The niobium oxide is readily obtained by heat-treating niobium hydroxide, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for nitrating benzene in a gas phase, and more specifically, the method for nitrating benzene in a gas phase using NO2 or N2O4 is characterized by using niobium oxide as a catalyst. This invention relates to a method for gas phase nitration of benzene.

Nitrobenzene obtained by nitration of benzene is used in large quantities as a raw material for aniline and as an intermediate for organic industrial chemicals, and is an important key industrial chemical in the chemical industry. The method for producing nitrobenzene was first developed in 1884.
Since the nitration of benzene was first carried out by Mitscherlich, the principle has not changed to this day.

That is, this is a method of nitration in a liquid phase using a mixed acid that is a mixture of nitric acid and concentrated sulfuric acid. Although this process has progressed from the initial batch process to the current continuous process, the problems associated with the liquid phase process of waste sulfuric acid and wastewater treatment remain unsolved.

On the other hand, the gas phase nitration method using N(Jx) has been studied because it is expected to have advantages such as the simplicity of the process, no waste sulfuric acid, and the use of nitrogen oxides, which are cheaper than concentrated nitric acid. However, unfortunately, it is not as good as the liquid phase method in terms of reaction yield and catalytic activity, and has not been industrialized to date.

Gas-phase nitration of benzene (the following methods are known in this regard:

l) U.S. Patent No. 2,109,878 and Industry and Engineering Chemistry June
, 1986, page 662, there is a description that gas phase nitration of benzene with NOx is carried out using silica gel as a catalyst. According to that description, silica gel with a particularly high surface area is highly active, but even in that case, the reaction temperature is as high as 810"C, and the molar ratio of NO27 benzene is 2.
Under the conditions, WH5V (weight hourly space velocity) of benzene = 0
．． Space-time yield = 0.0145-0.0 at extremely slow feed rate of 0206~0.165~/~catalyst/hr
518, the formation remained at a low level of #.nitrobenzene/co-catalyst.hr.

According to the description in the same document, only silica gel has catalytic activity, and bauxite, activated alumina, and Ti0g-
Pumice and other materials are said to be ineffective for gas-phase nitration of benzene. It is also estimated that the reaction follows the following equation.

2) British Patent No. 586,782 describes HNU of benzene.
There is a description that gas phase nitration using s or NO2 is carried out using a phosphoric acid salt or a calcined product of phosphoric acid supported on a solid absorbent as a catalyst. According to that example, nitrobenzene was obtained by nitration of benzene with HNOs using calcium metaphosphate as a catalyst, iN08/benzene molar ratio = 0.864, temperature = 176°C1Wl (SV
=0.176Ky/l・Catalyst・hr Space-time yield of nitrobenzene under null conditions=0.074Kl/l・Catalyst・h
The result has been as low as r. Note that this document does not contain any examples using Now as a nitration agent, and the substantial embodiment of the invention is interpreted as nitration with nitric acid.

On the other hand, gas phase nitration has been studied for the purpose of controlling the isomer ratio (para/ortho ratio) of nitrochlorobenzene produced in the nitration of chlorobenzene. JP-A-1988-1986 - 1988-2007 - 2003-2012 - 2004-2012 - 2008-2012 - Nitrochlorobenzene with a para/ortho ratio controlled over a wide range can be obtained by nitrating chlorobenzene in the gas phase with Now in the presence of a molecular sieve catalyst (zeolite catalyst) having a pore size. There is a description. In this case, examples of specific zeolite catalysts include [ZEOLON-900H
”, “AW-500 Sheave”, “Zeoron 800J
rtax molecular sieve" is listed. As for the reaction results, for example, "When Zeolon 900-HJ is used as a catalyst, the reaction temperature is 200°C, the NO2/chlorobenzene molar ratio = 2.37, and the WH8V of chlorobenzene = 0.289 Ky/l-catalyst. hr null feed rate (however, diluted with 30 times nitrogen gas), space-time yield (
STY) = 0.098 Ky/l・catalyst・br results, but the activity is still insufficient.

Note that this document does not mention that gas phase nitration of benzene is performed using the zeolite catalyst.

Furthermore, a series of patents are known for the purpose of controlling the P2O ratio in the nitration of halobenzenes. That is, JP-A-1850-121284, JP-A-50-126626
No., JP-A-50-126627, JP-A-51-698
No. 1 and JP-A-J [51-19784]. Both of these patents relate to the gas phase nitration of halobenzene, but judging from the descriptions and examples of the specifications, the embodiments of the invention are substantially limited to methods using nitric acid as the nitration agent. It is something.

Although there is a statement in the above patent specification that NO2 is also used as a nitrating agent, there is no specific example in the Examples to support this. Furthermore, nitric acid and NOx have N oxidation numbers of pentavalent and tetravalent, respectively, and are clearly different in terms of chemical mildness. Therefore, embodiments in which nitric acid is the nitrating agent and embodiments in which NO2 is the nitrating agent should be considered to be different systems of technology.

Note that all of these are only descriptions regarding the nitration of halobenzene, and there is no description at all about the method for producing nitrobenzene by nitration of benzene, which is the object of the present invention.

By the way, as mentioned at the beginning, nitrobenzene is a key industrial chemical, and its production volume far exceeds that of Yaguchi nitrobenzene. Therefore, if a superior new process is developed, the benefits are expected to be enormous.

The present inventors, in view of the possibility that gas phase nitration of benzene with NOx or N2O4 has the various advantages mentioned above in terms of the process, have diligently searched for catalysts active in gas phase nitration, and have found that: If an acidic composite oxide containing more than one species of oxide is used, the catalytic activity of the nitration reaction is extremely high.
It has already been found that nitrobenzene hardly produces by-products such as dinitrobenzene, and the selectivity for nitrobenzene is extremely high (Japanese Patent Application Laid-Open No. 58-162557, 58-180).
Publication No. 460).

Furthermore, as a result of our search for catalysts for nitration reactions, the present inventors found that niobium oxide has extremely high catalytic activity and selectivity when used alone, without coexisting with other metal oxides to form a composite acidic oxide. The present invention was based on the discovery that the following is true.

That is, the present invention provides an industrially excellent method for nitrating benzene in a gas phase using NO2 or N2O4, which is characterized by using niobium oxide as a catalyst. It is.

The niobium oxide catalyst used in the present invention can be easily obtained, for example, by heat-treating niobium hydroxide.

The heating temperature may be, for example, 100 to 400"C as described in JP-A-60-44089, or even higher 5"C.
00 to 600''C.

As the nitrating agent in the method of the present invention, NO! and N
Examples include 2O4, but Not is particularly preferred. Also, N
Since it is well known that O is readily oxidized to Now in the coexistence of oxygen, the method of the present invention may also employ a method in which a mixed gas of NO and 02 is used as the nitration agent.

The gas phase nitration in the present invention is carried out at a reaction temperature of 80"C to 25"C.
It is carried out by continuously feeding a gas phase mixture of benzene and a nitrating agent over a niobium oxide catalyst bed while maintaining a temperature of 0° C., and separating the formed nitrobenzene from said gas phase mixture. Preferably, the gas phase nitration reaction is carried out in the presence of an inert gas such as nitrogen as a diluent. A specific example of how the reaction occurs in this case is as follows.

Benzene is preheated and vaporized, mixed with a constant flow rate of diluent nitrogen gas, and then mixed with a gaseous stream of nitrating agent before being introduced into a heated catalyst bed for catalytic reaction.

The nitrating agent preferably used in the present invention is NO2, and the molar ratio of N02 to benzene is generally from 0.1 to
The molar ratio is 8.0, more preferably 0.1 to 2.0. In addition, when N2O4 is used, the molar ratio is generally 0.05 to 1.5 with respect to benzene, preferably 0.
．． The molar ratio is 0.06 to 1.0.

Each reaction component and diluting nitrogen gas can be fed into the reactor at an arbitrary space velocity while maintaining a predetermined composition ratio.

In order to explain the present invention in more detail, specific examples are given below, but the present invention is not limited thereto.

The calculation methods for conversion rate, yield, and selectivity in Examples are as follows.

Example 1 Using hydrous niobium oxide (manufactured by CBMB International Limited), the particle size was adjusted to 24 to 48 mesh, and the particle size was 8.87f (5CC) with a length of 82mm and an inner diameter of 1.5mm.
A 0 m quartz glass reaction tube was filled with the mixture. Next, it was heat-treated at 500°C for 4 hours under a stream of air, and then kept at 125°C.

No gas 29 tut/hr (7
7.44 mmol/hr) and O! Ga x 14.45
6.04 f/hr of benzene vaporized by a vaporizer filled with molten alumina and NO2 gas produced by mixing mol/hr (88.72 mmol/hr).
(77.44 mmol/hr) was fed to cause a catalytic reaction. The temperature of the catalyst bed was maintained at 125°C. At this time, W/F (catalyst jl for raw material feed amount per unit time) = 501-Cat-hr/mo
It was l/< .

After leaving the reaction tube, the reaction mixture gas was trapped in an ice-cooled trap, and the exhaust gas was neutralized with alkaline water and then purged.

The trapped substances were analyzed by gas chromatography. The results are shown in Table 1.

Table 1 s'ry: 4 nitrobenzene/cocatalyst/hr (empty yield) W/F: Kg -Cat -hr/mo
1-Benzene Comparative Example 1 Molybdenum oxide (Mo0a), tungsten oxide (
11, manufactured by Kyoto Tungsten ■, Fl-WOa) were thoroughly mixed with 0.5 f/, 9.5 f and water 12 in a mortar and then pressure molded. After pulverizing this, the particle size was made uniform to 24 to 48 meshes, and it was calcined at 500°C for 8 hours in a stream of air to obtain Moon-Won (atomic ratio Mo/W = 0.0
85) A composite oxide was prepared.

This catalyst is 8.871! was filled into the same reaction tube as in Example 1, and the nitration reaction was carried out in the same manner as in Example 1. The results are shown in Table 2.

Table 2 Comparative Example 2 Tungsten oxide (Tokyo Tungsten ■, Fl-won
) 8.879 wo 24-48) The particles were filled in the same reaction tube as in Example 1 with the same particle size, and heat treatment and nitration reaction were performed under the same conditions as in Example 1. The results are shown in Table 8.

Table 8

Claims (1)

[Claims] A method for nitrating benzene in a gas phase using NO_2 or N_2O_4, the method comprising using niobium oxide as a catalyst.