WO2021047052A1 - System and process for enhancing toluene oxidation - Google Patents

Abstract

A system and process for enhancing toluene oxidation, belonging to the technical field of preparing benzoic acid. A traditional bubble reactor is replaced with a tubular reactor (3) to improve the controllability of the oxidation reaction process; a micro-interface generator (4) is provided in the tubular reactor (3) to increase the gas-liquid phase interface area of oxygen and toluene, so as to improve the reaction efficiency; a casing pipe having a two-layer structure of an inner tube (11) and an outer tube (12) is provided to achieve the effect of using excessive heat of a reaction product for preheating the toluene, so as to reduce the loss of energy; compared with the traditional technology for preparing benzoic acid, the tubular reactor (3) is replaced and the micro-interface generator (4) and a separation unit (5) are added into the reactor (3), so as to improve the yield of the product.

Description

System and process for strengthening toluene oxidation Technical field

The invention relates to the preparation of benzoic acid and benzaldehyde, in particular to a system and process for strengthening the oxidation of toluene.

Background technique

Benzoic acid is an important organic synthetic raw material. It is mainly used as food preservatives and alkyd resin modifiers. It can also be used in the fields of medicines, dye intermediates, plasticizers, spices, fiber intermediates, etc.; benzaldehyde is A very versatile aromatic aldehyde raw material in the chemical industry, widely used in perfumes, medicines, dyes, pesticides and other fields. The methods currently used in industry for preparing benzoic acid and benzaldehyde include trichlorotoluene hydrolysis, phthalic anhydride decarboxylation, benzyl halide oxidation and liquid-phase air oxidation. However, the main application of benzoic acid and benzaldehyde is that the pharmaceutical and food fragrance industries require them to be halogen-free products. Furthermore, from the perspective of economy and environmental protection, the method of liquid phase air oxidation of toluene has gradually become the domestic production of benzaldehyde and benzoic acid. Mainstream method.

The toluene liquid-phase air oxidation method is a catalytic oxidation reaction between toluene and air in the presence of a catalyst and a promoter to produce benzoic acid as the main product and a certain amount of benzaldehyde as a by-product. The reaction is a series reaction, and the reaction principle is as follows: in the liquid phase air oxidation process of toluene, toluene and air are firstly oxidized to form the intermediate product benzaldehyde, and the benzaldehyde further undergoes oxidation reaction to form the main product benzoic acid.

At present, in the field of industrial production of benzoic acid and benzaldehyde, the existing process reactor devices mainly have the following problems. The production reactors for benzoic acid are mainly bubble reactors, in which the reaction liquid is back mixed in the bubble reactor. The phenomenon is very serious, making the selectivity and yield of benzaldehyde as an intermediate product of the reaction low. The liquid-phase oxidation of toluene to prepare benzoic acid and benzaldehyde is a strongly exothermic reaction. The heat of reaction needs to be removed in time during the reaction. However, the addition of a heat exchange device to the bubble reactor results in a complex structure and heat transfer efficiency. Lower. The bubbling reactor is by bubbling air or high-concentration O ₂ into the reactor to undergo oxidation reaction with liquid toluene. The mass transfer rate has a greater impact on the speed of the gas-liquid reaction, while bubbling The mass transfer efficiency of the type reactor is low.

Summary of the invention

For this reason, the present invention provides a system and process for enhancing the oxidation of toluene to solve the problem of low mass transfer efficiency of the gas-liquid phase reaction in the toluene oxidation process.

In one aspect, the present invention provides a system for enhancing the oxidation of toluene, including: a toluene preheating tube, an oxygen preheating tube, a tubular reactor, a micro-interface generator, a separation unit, and a reaction product storage unit;

The toluene preheating tube includes an inner tube and an outer tube, the inner tube is connected to the tubular reactor, and the outer tube is connected to the separation unit and the reaction product storage tank;

The oxygen preheating pipe includes an inner pipe and an outer pipe. The inner pipe is connected to the micro-interface generator, and the outer pipe is connected to a steam pipe. The hot water vapor enters from below the outer pipe through the pipe and flows out from above the outer pipe. To preheat the oxygen in the inner tube;

The tubular reactor includes an inner oil inlet, an oil outlet, and an inner reaction tube. The inner reaction tube is a reaction site for toluene oxidation. The oil outlet on the top of the device leaves;

The micro-interface generator is arranged in the inner reaction tube to break the oxygen from the oxygen preheating tube into micron-sized bubbles.

Further, a feed pump is provided on the toluene feed pipe for transporting toluene into the toluene preheating pipe.

Further, a catalyst addition pipe is provided on the pipe connecting the toluene preheating pipe and the tubular reactor.

Further, the micro-interface generator is a pneumatic generator.

Further, the micro-interface generator breaks the oxygen bubbles to form micron-sized bubbles with a diameter greater than or equal to 1 μm and less than 1 mm, thereby increasing the mass transfer area between the oil-coal slurry and the hydrogen.

Further, at least one micro-interface generator is provided at each concave pipe of the inner reaction tube.

Further, the separation unit includes: a separation tank, a condenser and a circulating pump;

The separation tank is connected to the tubular reactor for separating reaction products;

The gas phase product separated by the separation tank is condensed by the condenser, and the condensed liquid phase toluene enters the toluene preheating tube for cyclic reaction;

The liquid phase product separated from the separation tank is passed through the circulating pump into the outer tube of the toluene preheating tube, and is used to preheat the toluene in the inner tube of the toluene preheating tube.

Further, the reaction product storage unit includes a heat exchanger and a storage tank, and the heat exchanger is arranged on a pipe connecting the outer pipe of the toluene preheating pipe and the storage tank.

On the other hand, the present invention provides a process for enhancing the oxidation of toluene, which includes the following steps:

Pass protective gas N ₂ into the system to a system pressure of 0.7 MPa, turn on the feed pump, deliver the toluene reaction raw material solution into the toluene preheating tube, and feed at a mass flow rate of 0.007 wt% relative to the mass fraction of toluene Add the cobalt naphthenate catalyst to toluene at a high rate, inject heat transfer oil into the tubular reactor, and raise the reaction temperature of the tubular reactor to 158°C;

After the system temperature reaches the set temperature of 158°C, oxygen is introduced into the oxygen preheating tube, and hot steam is used to preheat the oxygen, and the preheated oxygen is passed into the micro-interface generator for Make the gas-liquid two-phase mixing more fully;

During the oxidation reaction process, the heat transfer oil is used to remove the heat released by the reaction in time, and the temperature in the tubular reactor is always maintained at 158°C by controlling the flow rate of the heat transfer oil;

After the reaction materials are reacted in the tubular reactor, they enter the separation tank, and the gas phase components condense toluene in the gas components through the condenser and then enter the toluene preheating tube with the raw materials, and the liquid phase components The toluene preheating tube is pumped into the outer tube of the toluene preheating tube through the material circulation pump, the toluene in the toluene preheating tube inner tube is preheated by the liquid phase temperature, and then it is returned to the reaction product storage tank through the heat exchanger in.

Compared with the prior art, the beneficial effect of the present invention is that at least one micro-interface generator is arranged at each concave pipe of the tubular reactor, and the oxygen is broken into micron-level micro-interface generators in the micro-interface generator. Bubbles. These micro-sized bubbles have additional pressure, and they are not easy to merge with each other when they collide with each other. Therefore, they have a larger phase boundary area than the unbroken oxygen, which makes these micro-sized bubbles easier to mix with toluene. A gas-liquid emulsion is formed, which increases the product yield during the toluene oxidation reaction.

In particular, the gas enters the tubular reactor from bottom to top. Under the agitation of the gas, the catalyst is always suspended in the tubular reactor without deposits, which improves the reaction efficiency.

In particular, compared with the bubble reactor, the flow state of the reactants in the tubular reactor system is similar to the plug flow, which greatly reduces the degree of backmixing of the reactants in the reactor. In terms of oxidation reaction, the controllability of the oxidation reaction process is greatly improved, which is beneficial to increase the yield of intermediate products.

Further, it realizes the function of using the excess heat of the reaction product to preheat toluene by arranging a sleeve having a two-layer structure of an inner tube and an outer tube, thereby reducing energy loss.

Description of the drawings

Fig. 1 is a schematic structural diagram of an embodiment of the present invention.

detailed description

In order to make the purpose and advantages of the present invention clearer, the present invention will be further described below in conjunction with the embodiments; it should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention.

The preferred embodiments of the present invention will be described below with reference to the drawings. Those skilled in the art should understand that these embodiments are only used to explain the technical principles of the present invention, and are not intended to limit the protection scope of the present invention.

It should be noted that in the description of the present invention, the terms "upper", "lower", "left", "right", "inner", "outer" and other terms indicating directions or positional relationships are based on the attached drawings. The direction or position relationship shown is only for ease of description, and does not indicate or imply that the device or element must have a specific orientation, be configured and operated in a specific orientation, and therefore cannot be understood as a limitation of the present invention.

In addition, it should be noted that, in the description of the present invention, unless otherwise clearly defined and limited, the terms "installation", "connection", and "connection" should be understood in a broad sense, for example, it may be a fixed connection or It is a detachable connection or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the internal communication between two components. For those skilled in the art, the specific meaning of the above-mentioned terms in the present invention can be understood according to specific circumstances.

Refer to Figure 1, which is a schematic structural diagram of a system for enhancing toluene oxidation provided by the present invention. The system includes: toluene preheating tube 1, oxygen preheating tube 2, tubular reactor 3, micro-interface generator 4, separation Unit 5, reaction product storage unit 6, steam pipe 7, catalyst dosing pipe 8, and feed pump 9.

Continuing to refer to Figure 1, the toluene preheating tube 1 is provided with an inner tube 11 and an outer tube 12; the liquid toluene is passed into the inner tube 11 through the feed pump 9; the hot material from the separation unit 5 is passed into the outer tube 12, The toluene in the inner tube 11 is preheated; the oxygen preheating tube 2 is provided with an inner tube 21 and an outer tube 22, and oxygen passes into the inner tube 21; the hot water vapor enters the outer tube 22 through the steam tube 7, and the inner tube 21 Preheat the oxygen in the air. The preheated toluene is mixed with the catalyst from the catalyst dosing pipe 8 and then passed into the tubular reactor 3; the preheated oxygen is passed into the micro-interface generator 4 arranged in the tubular reactor 3.

Continuing to refer to FIG. 1, the tubular reactor 3 includes an inner reaction tube 31, an oil inlet 32 and an oil outlet 33. The micro-interface generator 4 is arranged in the inner tube 31, and at least one micro-interface generator 4 is arranged at the bottom of each concave pipe of the inner tube to break the oxygen into micron-level small bubbles, making it easier to form gas with the toluene liquid. Liquid emulsion, thereby increasing the reaction rate. The heat transfer oil enters the tubular reactor 3 from the oil inlet 32 and leaves the reactor from the oil outlet 33 to raise the temperature in the reactor to the required temperature for the reaction and to remove the oxidation of toluene in time after the reaction starts. The heat released by the reaction.

Continuing to refer to Figure 1, the separation unit includes a separation tank 51, a condenser 52 and a circulating pump 53, the reaction product enters the separation tank 51 for gas-liquid separation, the separated gas is condensed by the condenser 52, and the condensed liquefied toluene is Pass into the toluene preheating pipe 1 for circulation reaction; the separated liquid passes through the circulation pump 53 and then enters the outer pipe 12 to preheat the toluene. After the preheating is completed, it is passed into the storage tank 62 through the heat exchanger 61 to cool down. , To prepare to enter the follow-up section for rectification and purification and other operations.

Example 1

This embodiment provides a process for enhancing the oxidation of toluene, the steps of which include:

Pass protective gas N ₂ into the system to a system pressure of 0.3 MPa, turn on the feed pump, and deliver a toluene reaction raw material solution containing 0.01 wt% benzaldehyde relative to the mass fraction of toluene into the toluene preheating tube; The mass fraction of toluene is 0.007wt% mass flow rate. Cobalt naphthenate is added to the toluene at the feed rate; thermal oil is injected into the tubular reactor to raise the reaction temperature of the tubular reactor to 158°C.

After the system temperature reaches the set temperature of 158°C, oxygen is fed into the oxygen preheating tube, and hot steam is used to preheat the oxygen. The preheated oxygen is fed into the micro-interface generator to make the gas-liquid two-phase The mixing is more complete and the mass transfer efficiency is improved.

The reaction is a strong exothermic reaction. By controlling the preheating temperature of the gas preheating tube, the preheating temperature of the toluene preheating tube, the temperature of the heat transfer medium and the flow rate of the heat transfer oil between the reaction tube and the tube, the oxidation reaction can release heat in time. Remove to control the temperature of the reaction system to 158°C.

After the reaction material has been reacted in the tubular reactor system, it enters the separation tank. The gas phase component condenses toluene from the gas component through the condenser and then enters the toluene preheating tube with the raw material. In the outer tube of the heat pipe, the liquid phase temperature is used to preheat the raw materials, and then return to the reaction product storage tank through the heat exchanger.

The height of the tubular reactor in the example is 10m, and the inner diameter of the inner reaction tube of the tubular reactor is 200mm. It has 15 concave pipes, and a micro-interface generator is provided at the bottom of each concave pipe.

After the above process is completed, the annual production capacity will be 13970t/a for benzoic acid and 3400t/a for benzaldehyde (the annual working day is 300 days, and the continuous operation is 24h per day). 99% toluene is added with 50000t/a, the conversion rate is 27.94%, the selectivity of benzoic acid is 73.2%, and the benzaldehyde is 25.8%.

Example 2

The process of this embodiment is the same as that of embodiment 1, but the tubular reactor used is different. The height of the tubular reactor in this embodiment is 10m, the inner diameter of the inner reaction tube of the tubular reactor is 200mm, and it has 15 concave pipes. , Two micro-interface generators are installed at the bottom of each concave pipe.

After the completion of the above process, the annual production capacity is 14780t/a for benzoic acid and 3180t/a for benzaldehyde (the annual working day is 300 days, and the continuous operation is 24 hours per day). 99% toluene is added with 50000t/a, the conversion rate is 29.56%, the selectivity of benzoic acid is 75.5%, and the benzaldehyde is 23.9%.

Example 3

This example is the same as the process of Example 1 for preparing benzoic acid. The tubular reactor used is different. The height of the tubular reactor in this example is 10m, and the inner diameter of the inner reaction tube of the tubular reactor is 200mm. There are 20 concave pipes, and two micro-interface generators are installed at the bottom of each concave pipe.

After the completion of the above process, the annual production capacity will be 15132t/a for benzoic acid and 2846t/a for benzaldehyde (the annual working day is 300 days and the continuous operation is 24h per day). 99% toluene is added with 50000t/a, the conversion rate is 30.46%, the selectivity of benzoic acid is 77.5%, and the benzaldehyde is 21.2%.

Comparative example 1

The tubular reactor in the reaction system of this comparative example is not equipped with a micro-interface generator. The other conditions are the same as those in Example 1. The effect is as follows: the annual production capacity is 11988t/a for benzoic acid and 2890t/a for benzaldehyde; 99 % Toluene is added 50000t/a, the conversion rate is 26.38%, the selectivity of benzoic acid is 72.9%, and the benzaldehyde is 26.4%.

Claims (9)

1. A system for enhancing the oxidation of toluene, which is characterized by comprising: a toluene preheating tube, an oxygen preheating tube, a tubular reactor, a micro-interface generator, a separation unit, and a reaction product storage unit;

   The toluene preheating tube includes an inner tube and an outer tube, the inner tube is connected to the tubular reactor, and the outer tube is connected to the separation unit and the reaction product storage tank;

   The oxygen preheating pipe includes an inner pipe and an outer pipe. The inner pipe is connected to the micro-interface generator, and the outer pipe is connected to a steam pipe. The hot water vapor enters from below the outer pipe through the pipe and flows out from above the outer pipe. To preheat the oxygen in the inner tube;

   The tubular reactor includes an inner oil inlet, an oil outlet, and an inner reaction tube. The inner reaction tube is a reaction site for toluene oxidation. The oil outlet on the top of the device leaves;

   The micro-interface generator is arranged in the inner reaction tube to break the oxygen from the oxygen preheating tube into micron-sized bubbles.
2. The system for enhancing the oxidation of toluene according to claim 1, wherein a feed pump is provided on the toluene feed pipe.
3. The system for intensifying toluene oxidation according to claim 1, wherein a catalyst addition pipe is provided on the pipe connecting the toluene preheating pipe and the tubular reactor.
4. The system for enhancing the oxidation of toluene according to claim 1, wherein the micro-interface generator is a pneumatic generator.
5. The system for enhancing the oxidation of toluene according to claim 1, wherein the micro-interface generator breaks the oxygen bubbles to form micron-sized bubbles with a diameter greater than or equal to 1 μm and less than 1 mm.
6. The system for enhancing the oxidation of toluene according to any one of claims 1 to 5, wherein at least one micro-interface generator is provided at the bottom of each concave pipe of the inner reaction tube.
7. The system for enhancing toluene oxidation according to claim 1, wherein the separation unit comprises: a separation tank, a condenser and a circulating pump;

   The separation tank is connected to the tubular reactor for separating reaction products;

   The gas phase product separated by the separation tank is condensed by the condenser, and the condensed liquid phase toluene enters the toluene preheating tube for cyclic reaction;

   The liquid phase product separated from the separation tank is passed through the circulating pump into the outer tube of the toluene preheating tube, and is used to preheat the toluene in the inner tube of the toluene preheating tube.
8. The system for enhancing toluene oxidation according to claim 1, wherein the reaction product storage unit includes a heat exchanger and a storage tank, and the heat exchanger is arranged in a pipe connecting the outer pipe of the toluene preheating pipe and the storage tank. on.
9. A process for strengthening the oxidation of toluene, characterized in that it comprises the following steps:

   Pass the protective gas N ₂ into the system to the system pressure of 0.7 MPa, turn on the feed pump, and deliver the toluene reaction raw material solution into the toluene preheating pipe, and the feed rate is 0.007wt% relative to the mass fraction of toluene. Add cobalt naphthenate catalyst to toluene, inject heat transfer oil into the tubular reactor, and raise the reaction temperature of the tubular reactor to 158°C;

   After the system temperature reaches the set temperature of 158°C, oxygen is introduced into the oxygen preheating tube, and hot steam is used to preheat the oxygen. The preheated oxygen is passed into the micro-interface generator, and the micro-interface generator blows the oxygen. Broken into micron-sized bubbles, the small bubbles merge into the liquid to form a gas-liquid emulsion, which undergoes oxidation reaction under the action of the catalyst;

   During the oxidation reaction process, the heat transfer oil is used to remove the heat released by the reaction in time, and the temperature in the tubular reactor is always maintained at 158°C by controlling the flow rate of the heat transfer oil;

   After the reaction materials have been reacted in the tubular reactor, they enter the separation tank. The gas phase components pass through the condenser to condense the toluene in the gas components and then enter the toluene preheating tube with the raw materials, and the liquid components pass through the materials. A circulating pump is driven into the outer tube of the toluene preheating tube, the liquid phase temperature is used to preheat the toluene in the inner tube of the toluene preheating tube, and then the toluene preheating tube is returned to the reaction product storage tank through the heat exchanger.

Images