CN108031485B - Method for preparing parachloroaniline through parachloronitrobenzene selective hydrogenation - Google Patents

Abstract

The present invention provides a method for preparing p-chloroaniline by selective hydrogenation of p-chloronitrobenzene. Hydrogenation is used to prepare p-chloroaniline, so that the dechlorination side reaction is greatly reduced during hydrogenation, and the catalyst is a Pt/TiO ₂ /SBA-15 catalyst. The catalyst in the present invention exhibits excellent catalytic activity when it is used to catalyze the selective hydrogenation of p-chloronitrobenzene to prepare p-chloroaniline, the conversion rate and selectivity are very high, both can be as high as 99% or more, and the side reaction of dechlorination is greatly reduced . The composite nanostructure catalyst Pt/TiO ₂ /SBA-15 used in the method provided by the present invention has a simple preparation method, a short production cycle, and a low platinum loading, so that the catalyst cost is low, and high temperature treatment is not required, and a reducing agent is not required during preparation. Platinum has good dispersibility and high catalytic activity.

Description

A kind of method for preparing p-chloroaniline by selective hydrogenation of p-chloronitrobenzene

technical field

The invention belongs to the field of catalytic hydrogenation, in particular to a method for preparing p-chloroaniline by selective hydrogenation of p-chloronitrobenzene.

Background technique

p-Chloroaniline is an important organic intermediate, which is widely used in the synthesis of dyes, medicines and pesticides. At present, most p-chloroaniline is prepared by the reduction of p-chloronitrobenzene. The reduction methods mainly include metal reduction method, electrochemical reduction method, non-hydrogen reducing agent reduction method, catalytic hydrogenation reduction method, etc. Among them, catalytic hydrogenation The reduction method has advanced technology and high yield, which is more in line with the requirements of modern chemical industry for atomic economy. Among them, the noble metal catalytic hydrogenation method occupies the main position. In the past, the heterogeneous catalytic reduction method under high temperature and high pressure was mainly used. The surface of the carrier is easy to aggregate, which affects its dispersibility, which in turn affects the catalytic activity of the catalyst. In recent years, heterogeneous catalysis under low temperature and low pressure has gradually attracted the interest of scientific researchers. The key point of catalytic hydrogenation is how to control the selectivity of the reaction and prevent the occurrence of side reactions of dechlorination.

At present, there are two main methods: one is to prevent dechlorination by adding dechlorination inhibitors or pre-poisoning the hydrogenation catalyst, and the other is to modify the hydrogenation catalyst to achieve the purpose of inhibiting dechlorination.

For example, patent CN201510129577 uses platinum catalyst and dechlorination inhibitor to catalyze hydrogenation reaction, including first using 2-chloro-6-nitrotoluene as raw material under solvent or solvent-free conditions, in the presence of hydrogenation catalyst and dechlorination inhibitor. Under certain conditions, a hydrogenation reduction reaction is carried out, and the reaction solution is filtered at a certain temperature to obtain 3-chloro-2-methylaniline; and then the product 2,6-diaminotoluene is obtained through an ammonolysis reaction.

However, the addition of dechlorination inhibitors will increase secondary pollution and affect product quality, while poisoning the hydrogenation catalyst will greatly reduce the catalyst activity.

The modification of hydrogenation catalysts usually involves the following three aspects: (1) Selecting appropriate supports and catalyst precursors to adjust the interaction between metals and supports. (2) Alloy the catalyst active metal with other metals or add appropriate ions to treat the catalyst; (3) Change the size of the active metal particles by changing the preparation method of the catalyst.

For example, patent CN200810183391 provides a catalyst for synthesizing p-chloroaniline by hydrogenation of p-chloronitrobenzene, which contains active component platinum and carrier attapulgite. Patent CN201210366514 provides a method for preparing 3,4-dichloroaniline, comprising using 3,4-dichloronitrobenzene as a raw material, without using a solvent, and carrying out a catalytic hydrogenation reaction in the presence of a Pt catalyst, and the reaction pressure is 1.0MPa～ 3.0Mpa, the reaction temperature is 75 ℃ ~ 120 ℃; the Pt catalyst is composed of the active component Pt, the carrier C and the auxiliary agent, wherein the mass percentage of Pt is 0.5% to 5%, the auxiliary agent is Fe2O3, and the amount of the auxiliary agent is Fe2O3. The mass percentage is 0.05% to 0.5%, and the rest is C. That is, the catalyst used therein contains platinum carbon and iron oxide.

Patent CN201310009679 provides a production method for preparing chlorinated aniline by hydrogenation of chlorinated nitrobenzene in a solvent-free method. The chlorinated nitrobenzene is used as a raw material. and react with hydrogen at 0.3-2.5MPa without adding a solvent, and after completion, water is separated to obtain chlorinated aniline. The catalyst used therein is a platinum carbon catalyst.

Patent CN2012103303921 provides a method for preparing o-chloroaniline by solvent-free catalytic hydrogenation, using o-nitrochlorobenzene as a raw material, wherein a platinum-carbon catalyst with vanadium is used to catalyze the hydrogenation to suppress the side reaction of dechlorination. Similarly, patent CN201510128466 provides a method for preparing dichloroaniline by continuous catalytic hydrogenation of dichloronitrobenzene, wherein the dechlorination side reaction is suppressed by catalytic hydrogenation using a catalyst containing platinum carbon plus vanadium or tin.

It is generally believed that a nano-platinum catalyst with excellent performance should have the following characteristics in structure: the active component platinum is highly uniformly dispersed on the surface of the carrier, the active component platinum loading is low, the surface exposed atoms are many, and the carrier specific surface area is large. However, there are always some problems in the above-mentioned prior art: for example, some preparation conditions are harsh in the preparation method, the reagents used are not friendly to the environment, the dispersibility of platinum is not good, and the particle size is large. In terms of application, the catalytic reaction temperature is required to be high, the reaction time is long, and the selective hydrogenation conversion and selectivity of p-chloronitrobenzene under mild conditions have certain limitations.

In summary, supported platinum-based catalysts have good hydrogenation performance, and are often used in the selective hydrogenation of enynes, nitro groups, aldehydes, ketones, etc.; The interaction between platinum metal and the support will affect the catalytic activity of the catalyst. At present, the commonly used methods for preparing platinum-based catalysts at home and abroad, such as impregnation method, sol-gel method, and ion exchange method, have disadvantages such as complicated preparation process, easy aggregation of platinum nanoparticles, and non-greenness, which affect the overall performance of the catalyst. Therefore, it is of great significance to develop a simple and green platinum-based catalyst with good dispersibility, low noble metal loading, high activity and stability, and to provide an excellent method for the selective hydrogenation of p-chloronitrobenzene to prepare p-chloroaniline.

SUMMARY OF THE INVENTION

Therefore, the present invention provides a method for preparing p-chloroaniline by selective hydrogenation of p-chloronitrobenzene, the method comprising using a catalyst containing platinum and titanium dioxide and catalyzing p-chloronitrobenzene under a hydrogen environment and heating conditions Selective hydrogenation is used to prepare p-chloroaniline, which greatly reduces the side reaction of dechlorination during hydrogenation, and the catalyst is a Pt/TiO ₂ /SBA-15 catalyst.

In a specific embodiment, the content of platinum in the Pt/TiO ₂ /SBA-15 catalyst is 0.01-0.3 wt %, preferably 0.05-0.15 wt %, more preferably 0.08-0.10 wt %.

In a specific embodiment, in the Pt/TiO ₂ /SBA-15 catalyst (using the principle of spontaneous monolayer dispersion) TiO ₂ is spread on the carrier SBA-15 in the form of a thin film layer, a single layer or multiple layers , while the active component platinum is anchored on the TiO ₂ thin film layer.

In a specific embodiment, absolute ethanol is used as a solvent in the selective hydrogenation reaction.

In a specific embodiment, the temperature of the selective hydrogenation is 40-90°C, preferably 50-70°C.

In a specific embodiment, in the catalyst, TiO ₂ accounts for 5-20 wt %, preferably 10-15 wt % of the total weight of the composite carrier TiO ₂ /SBA-15.

In the present invention, there is a strong interaction between platinum and the semiconducting metal oxide TiO ₂ to form a composite nanostructure catalyst Pt/TiO ₂ /SBA-15; The amount of platinum used in the catalyst of the present invention is reduced to an extremely low value.

In a specific embodiment, the catalyst is prepared by the following method. First, the TiO ₂ is supported on the SBA-15 by the sol-gel method to obtain one or more layers of nano-TiO ₂ on the SBA-15. The composite carrier of the thin film, and the active component platinum is supported on the composite carrier by a photocatalytic reduction method to obtain the Pt/TiO ₂ /SBA-15 catalyst.

In a specific embodiment, before the TiO ₂ is loaded on the SBA-15, the step of ultrasonically pre-processing the SBA-15 with absolute ethanol is further included.

In a specific embodiment, the sol-gel method includes adding butyl titanate to absolute ethanol containing SBA-15, adding water and continuing to stir to hydrolyze the butyl titanate, and heating the hydrolysis mixture to a temperature of 35- 45°C to make it gel-like, and then vacuum-dried at 60-90°C to obtain a TiO ₂ /SBA-15 composite carrier.

In a specific embodiment, the photocatalytic reduction method includes dispersing the TiO ₂ /SBA-15 composite carrier in deionized water, adding methanol and chloroplatinic acid solution for ultrasonic immersion, and then placing the mixed solution under ultraviolet light , stirring, solid-liquid separation, washing with water to neutrality and drying to obtain the Pt/TiO ₂ /SBA-15 catalyst, preferably the mass ratio of methanol to water used in the photocatalytic reduction is 1:5～15, And the ultraviolet irradiation time is 5 to 20 hours.

The present invention at least has the following beneficial effects:

1) The catalyst exhibits excellent catalytic activity when used to catalyze the selective hydrogenation of p-chloronitrobenzene to prepare p-chloroaniline, the conversion rate and selectivity are very high, both can be as high as 99% or more, and the side reaction of dechlorination is greatly reduced.

2) The catalyst structure is novel, and the amount of platinum in the catalyst is small, so the catalyst cost is low. The composite nanostructure catalyst Pt/TiO ₂ /SBA-15 provided by the invention has the advantages of simple preparation method, short production cycle, low platinum loading, no high temperature treatment, no need to add reducing agent during preparation, good platinum dispersibility and high catalytic activity .

3) During the catalytic hydrogenation reaction, the reaction conditions are mild, the reaction time is short, the catalyst and the reaction liquid are easy to separate, and there is a good application prospect.

4) The preparation process of the TiO ₂ /SBA-15 composite carrier in the present invention is simple, the reaction time is short, the solvent is green and pollution-free, does not require high temperature calcination, and the TiO ₂ has a high degree of dispersion on the surface of the mesoporous silicon material SBA-15, which makes the subsequent loading The nano-platinum on it and the nano-TiO ₂ produce synergistic catalysis.

5) In the present invention, when platinum is supported on a composite carrier, sufficient time and sufficient light is given during the reduction process of the photocatalyst, and Pt ²⁺ can be completely reduced to Pt ⁰ without adding an additional reducing agent. The platinum nanoparticles in the catalyst are anchored or embedded in the _TiO2 film layer. In the catalyst of the present invention, due to the modification effect of TiO ₂ , the Pt nanoparticles are completely and uniformly distributed on the SBA-15 carrier, the platinum nanoparticles are highly dispersed, and the particle size is small, so that the dosage of platinum can be very small. Catalytic hydrogenation effect.

Description of drawings

Figure 1 is the XRD pattern of the 10%TiO ₂ /SBA-15 composite support.

Figure 2 is the XRD pattern of the 15%TiO ₂ /SBA-15 composite support.

FIG. 3 is the XRD pattern of the 0.08%Pt/10%TiO ₂ /SBA-15 catalyst prepared in Example 2. FIG.

FIG. 4 is the XRD pattern of the 0.1%Pt/10%TiO ₂ /SBA-15 catalyst prepared in Example 1. FIG.

Detailed ways

The present invention will be described in detail below with reference to the accompanying drawings and embodiments.

In the present invention, the specific steps of preparing p-chloroaniline by the selective hydrogenation of p-chloronitrobenzene catalyzed by Pt/TiO ₂ /SBA-15 are as follows:

₁ ) get a certain proportion of p _- chloronitrobenzene and catalyst in the reactor, add an appropriate amount of solvent, pass in H to replace the air in the reactor, close the H valve, set the reaction temperature and _H pressure.

2) When the temperature in the kettle reaches the set reaction temperature, pass in H ₂ , turn on stirring, and start the reaction.

3) After the reaction is completed, cool, take an appropriate amount of the reaction solution for centrifugal separation, and carry out gas chromatographic analysis.

Example 1

The mesoporous silicon material SBA-15 was added to 15 mL of anhydrous ethanol, and ultrasonically oscillated for 2 h to obtain a mixed solution of treated SBA-15 and anhydrous ethanol. Under stirring conditions, 0.5 mL of butyl titanate was added dropwise to the above mixture, and stirred for 1 h; 1 mL of water was slowly added to the mixture to hydrolyze the butyl titanate, and the stirring was continued for 1 h to complete the hydrolysis of the butyl titanate. . The mixture was heated and stirred at 40°C so that the mixture was gel-like. Vacuum drying at 80° C. overnight to obtain a 10% TiO ₂ /SBA-15 composite support (the content of TiO ₂ in the composite support is 10 wt %). Disperse 0.702g of TiO ₂ /SBA-15 composite carrier in 100mL of deionized water, add 10mL of anhydrous methanol, ultrasonically disperse for 10min, then add 0.1mL of chloroplatinic acid solution, ultrasonically disperse for 20min, and then place the solution in stirring condition. The resulting solution was filtered and washed under ultraviolet light for 12 h, and dried in vacuum at 80 °C to obtain a Pt/TiO ₂ /SBA-15 catalyst with a Pt mass fraction of 0.1% (the Pt content in the catalyst was 0.1 wt%), that is, 0.1% Pt/10 % _TiO2 /SBA-15.

Example 2

Same as Example 1, the difference is that the mass fraction of Pt in Pt/TiO ₂ /SBA-15 is 0.08%, that is, 0.08% Pt/10% TiO ₂ /SBA-15.

Example 3

The same as Example 1, the difference is that the mass fraction of TiO ₂ in the composite carrier in Pt/TiO ₂ /SBA-15 is 15%, that is, 0.1% Pt/15% TiO ₂ /SBA-15.

Example 4

The 0.1%Pt/10% _TiO2 /SBA-15 prepared in the above Example 1 was used to catalyze the hydrogenation of p-chloronitrobenzene. Take 0.401g p-chloronitrobenzene, 0.1g 0.1%Pt/10%TiO ₂ /SBA-15 and 20mL absolute ethanol in the autoclave, pass H ₂ to replace the air in the reactor, close H ₂ valve, when the temperature in the kettle reaches 70°C reaction temperature, pass in H ₂ , turn on the stirring, start the reaction, react for 1 hour, after the reaction is completed, cool, take 10 mL of the reaction solution by centrifugation, and conduct gas chromatography analysis. The conversion rate of p-chloronitrobenzene was 100%, and the selectivity of p-chloroaniline was 98.44%.

Example 5

Same as Example 4, add catalyst 0.1%Pt/10%TiO ₂ /SBA-15 0.1g prepared in Example 1, 0.401g p-chloronitrobenzene, 20mL absolute ethanol, and react at 70°C for 0.5h. The conversion rate of p-chloronitrobenzene was 98.32%, and the selectivity of p-chloroaniline was 98.60%.

Example 6

Same as Example 4, add catalyst 0.1%Pt/10%TiO ₂ /SBA-15 0.1g prepared in Example 1, 0.401g p-chloronitrobenzene, 20mL absolute ethanol, and react at 50°C for 1.5h. The conversion rate of p-chloronitrobenzene was 99.36%, and the selectivity of p-chloroaniline was 99.13%.

Example 7

Same as Example 4, add catalyst 0.08%Pt/10%TiO ₂ /SBA-15 0.1g prepared in Example 2, 0.317g p-chloronitrobenzene, 20mL absolute ethanol, and react at 70°C for 1h. The conversion rate of p-chloronitrobenzene was 84.71%, and the selectivity of p-chloroaniline was 99.50%.

In this example, when the platinum content is relatively low, the catalytic reaction time is not long enough, resulting in a low conversion rate of p-chloronitrobenzene.

Example 8

Same as Example 4, add catalyst 0.08%Pt/15%TiO ₂ /SBA-15 0.1g prepared in Example 2, 0.317g p-chloronitrobenzene, 20mL absolute ethanol, and react at 70°C for 1.5h. The conversion rate of p-chloronitrobenzene was 99.25%, and the selectivity of p-chloroaniline was 99.22%.

Example 9

The solution after the reaction in Example 4 was centrifuged, the reaction solution was removed, centrifuged and washed with absolute ethanol for several times, and then placed in a vacuum drying oven at 40 ° C to dry overnight, and the catalyst after secondary recovery was carried out according to the method in Example 4. Steps to carry out the reaction, the conversion rate of p-chloronitrobenzene is 97.77%, and the selectivity of p-chloroaniline is 97.23%. It shows that the catalytic activity of the catalyst recovered for the second time is still very high.

As can be seen from the above examples, the catalysts of different platinum mass fractions prepared by this method are active for the selective hydrogenation of p-chloronitrobenzene, and as a whole, the consumption of platinum is low and is in the high catalytic hydrogenation conversion rate. At the same time, the dechlorination side reaction is less.

Comparative Example 1

The preparation of the catalyst is roughly the same as that in Example 1, but the catalyst is not provided with a titanium dioxide layer, and a 0.1% Pt/SBA-15 catalyst is prepared by the photocatalytic reduction method (the mass fraction of platinum in the catalyst is 0.1%).

The method for catalytic selective hydrogenation of the catalyst is the same as that in Example 4. 0.1 g of 0.1% Pt/SBA-15 catalyst, 0.401 g of p-chloronitrobenzene, 20 mL of anhydrous ethanol are added, and the reaction is carried out at 70° C. for 2.0 h. The conversion rate of p-chloronitrobenzene is 13.05%, and the selectivity of p-chloroaniline is about 100%.

Comparative Example 2

The preparation of the catalyst is roughly the same as that in Example 1, but the catalyst is not provided with a titanium dioxide layer, and a 0.1% Pt/SBA-15 catalyst is prepared by the photocatalytic reduction method (the mass fraction of platinum in the catalyst is 0.1%).

The method for catalytic selective hydrogenation of the catalyst is the same as that in Example 4. 0.1 g of 0.1% Pt/SBA-15 catalyst, 0.401 g of p-chloronitrobenzene, 20 mL of anhydrous ethanol are added, and the reaction is carried out at 70° C. for 3.0 h. The conversion rate of p-chloronitrobenzene was 53.7%, and the selectivity of p-chloroaniline was about 100%.

Comparative Example 3

The preparation of the catalyst was roughly the same as that in Example 1, but the catalyst was not provided with a titanium dioxide layer, and a 2% Pt/SBA-15 catalyst was prepared by the photocatalytic reduction method (the mass fraction of platinum in the catalyst was 2%).

The method for catalytic selective hydrogenation of the catalyst is the same as that in Example 4. 0.1 g of 2% Pt/SBA-15 catalyst, 0.401 g of p-chloronitrobenzene, 20 mL of anhydrous ethanol are added, and the reaction is carried out at 70° C. for 1.0 h. The conversion rate of p-chloronitrobenzene was 91.51%, and the selectivity of p-chloroaniline was 86.56%.

From the comparison between Comparative Example 1 and Comparative Example 3, it can be seen that if the titanium dioxide is not dispersed on SBA-15 first, but platinum is directly supported on SBA-15, the platinum content required in the catalyst is higher, and the catalyst can have better performance. At this time, the conversion rate of raw materials increases, but at the same time, the side reaction of dechlorination is also significantly strengthened. Only by dispersing TiO2 on SBA-15 first, and then dispersing platinum on TiO2, can a catalyst with excellent catalytic activity and target product selectivity be prepared when the platinum loading is very low.

From the comparison of Comparative Examples 1 to 3 and the examples, it can be seen that during the preparation process of the catalyst of the present invention, titanium dioxide and platinum are successively dispersed on the carrier SBA-15, which are used to catalyze the selective hydrogenation of p-chloronitrobenzene to prepare p-chloroaniline At the same time, only a small amount of precious metal platinum can be used to achieve excellent catalytic activity, and the occurrence of dechlorination side reactions can be significantly reduced.

Figures 1 and 2 are the XRD patterns of the TiO ₂ /SBA-15 composite support, and Figures 3 and 4 are the XRD patterns of the Pt/TiO ₂ /SBA-15 catalyst. From the comparison of Figures 3 to 4 with Figures 1 to 2, it can be seen that the diffraction peaks of platinum are basically not observed in the XRD pattern, which indicates that the platinum loading in the catalyst prepared by the method described in the present invention is very low.

The scope of the present invention is not limited to the above examples, as long as the mass fraction of the active components of the catalyst and the reaction conditions including temperature and time are well controlled, the catalyst of the present invention can achieve very good performance in the hydrogenation reaction of p-chloronitrobenzene. Good results.

The above content is a further detailed description of the present invention in conjunction with specific preferred embodiments, and it cannot be considered that the specific implementation of the present invention is limited to these descriptions. For those of ordinary skill in the technical field to which the present invention pertains, without departing from the concept of the present invention, some simple deductions and substitutions can also be made, all of which should be regarded as belonging to the protection scope of the present invention.

Claims (8)

1. a method for the selective hydrogenation of p-chloronitrobenzene to prepare p-chloroaniline, the method comprises using a catalyst containing platinum and titanium dioxide and catalyzing the selective addition of p-chloronitrobenzene under hydrogen environment and heating conditions. Hydrogen is used to prepare p-chloroaniline, which greatly reduces the side reaction of dechlorination during hydrogenation. The catalyst is a Pt/TiO ₂ /SBA-15 catalyst, and the content of platinum in the Pt/TiO ₂ /SBA-15 catalyst is 0.01-0.3 wt%, in the Pt/TiO ₂ /SBA-15 catalyst, TiO ₂ is in the form of a thin film layer, which is spread on the carrier SBA-15 in the form of a single layer or multiple layers, and the active component platinum is anchored by a photocatalytic reduction method on the _TiO2 thin film layer. 2. The method for preparing p-chloroaniline according to claim 1, wherein dehydrated alcohol is used as solvent in the selective hydrogenation reaction. 3 . The method for preparing p-chloroaniline according to claim 1 , wherein the temperature of the selective hydrogenation is 40-90° C. 4 . 4 . The method for preparing p-chloroaniline according to claim 1 , wherein, in the catalyst, TiO ₂ accounts for 5-20 wt % of the total weight of the composite carrier TiO ₂ /SBA-15. 5 . 5. the method for preparing p-chloroaniline according to claim 1, is characterized in that, described catalyzer is prepared by following method, first adopts sol-gel method to load _TiO on SBA-15, obtain SBA-15 A composite carrier with one or more layers of nano-TiO ₂ thin films is laid on top, and the Pt/TiO ₂ /SBA-15 catalyst is obtained by loading the active component platinum onto the composite carrier by a photocatalytic reduction method. 6 . The method for preparing p-chloroaniline according to claim 5 , characterized in that, before the TiO ₂ is loaded on the SBA-15, the method further comprises the step of using absolute ethanol to perform ultrasonic pretreatment on the SBA-15. 7 . 7. The method for preparing p-chloroaniline according to claim 6, wherein the sol-gel method comprises adding butyl titanate to the dehydrated alcohol containing SBA-15, adding water and continuing to stir to make the titanic acid The butyl ester is hydrolyzed, the hydrolyzed mixture is heated to 35-45° C. to make it gel-like, and then vacuum-dried at 60-90° C. to obtain a TiO ₂ /SBA-15 composite carrier. 8. The method for preparing p-chloroaniline according to claim 7, wherein the photocatalytic reduction method comprises dispersing the TiO ₂ /SBA-15 composite carrier in deionized water, adding methanol and chloroplatinic acid solution to ultrasonically Immersion, then place the mixed solution under ultraviolet light, stir, separate from solid and liquid, wash with water to neutrality and dry to obtain the Pt/TiO ₂ /SBA-15 catalyst. The methanol and water used in the photocatalytic reduction The mass ratio is 1:5-15, and the ultraviolet irradiation time is 5-20 hours.

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