阅读说明：本技术 一种流动化学在甲苯硝化中的应用 (Application of flow chemistry in toluene nitration ) 是由 黄薇 张润民 张怀 于 2020-12-18 设计创作，主要内容包括：本发明公开了一种流动化学在甲苯硝化中的应用。以甲苯为溶剂,以硝酸为硝化剂,以硫酸为催化剂,在微通道反应器中进行硝化反应。本发明通过微通道反应器应用在甲苯硝化反应上,利用微通道反应器具有目标产物选择性高、反应速度快及反应温和易控制的优点,相比传统的方法,反应温度比工业上进行甲苯硝化反应的温度要低,同时利用微通道反应器较大的比表面积,反应体系换热快,减小了因操作不当而引发事故的可能性。(The invention discloses an application of flow chemistry in toluene nitration. Toluene is used as a solvent, nitric acid is used as a nitrating agent, sulfuric acid is used as a catalyst, and nitration reaction is carried out in a microchannel reactor. The method is applied to the toluene nitration reaction by the microchannel reactor, and has the advantages of high selectivity of target products, high reaction speed, mild reaction and easy control of the reaction by utilizing the microchannel reactor.)

1. Use of flow chemistry in the nitration of toluene.

2. Use of a flow chemistry in the nitration of toluene according to claim 1, wherein: toluene is used as a solvent, nitric acid is used as a nitrating agent, sulfuric acid is used as a catalyst, and nitration reaction is carried out in a microchannel reactor.

3. Use of a flow chemistry in the nitration of toluene according to claim 2, wherein: the specific steps of the nitration reaction are as follows:

step one, mixing nitric acid and a sulfuric acid catalyst to obtain a mixed solution, and respectively conveying the mixed solution and toluene to two inlets of a microchannel reactor through a high-pressure constant-flow pump;

step two, after the two streams of liquid are mixed, contacted and reacted in the microchannel reactor, the two streams of liquid flow out from an outlet of the microchannel reactor and enter a collecting tank;

standing and layering the solution in the collecting tank, wherein the upper layer is a mixture of sulfuric acid, water and dilute nitric acid, and the lower layer is a nitration product of toluene;

step four, separating two phases by using a separating funnel, and washing, neutralizing and drying the lower layer liquid to obtain a nitration product of the toluene;

and step five, removing 85% of water and nitric acid from the upper layer liquid after reduced pressure distillation, and drying and dehydrating the residual liquid for recycling.

4. Use of a flow chemistry in the nitration of toluene according to claim 2, wherein: the preparation process of the nitric acid comprises the following steps:

firstly, air sucked into a first-stage air filter of a four-stage air filtering device is subjected to primary impurity removal, then is cooled and condensed by an ammonia air condenser, condensed water is removed by a liquid drop separator, and then is conveyed to a second-stage, a third-stage and a fourth-stage air filters of the four-stage air filtering device for dust removal, and the air after dust removal is pressurized and divided into primary air and secondary air;

step two, mixing the liquid ammonia and the primary air in the step one in an ammonia-air mixer after impurity removal, oil removal and evaporation;

thirdly, carrying out ammonia oxidation reaction on the mixed gas in the ammonia-air mixer through an oxidation furnace to obtain NOx gas;

fourthly, the NOx gas is cooled through heat exchange and then sent to a condensation separator, and the generated dilute condensed acid is cooled and sent to a tower plate in the middle of an absorption tower;

fifthly, after the cooled NOx gas is subjected to fine separation through a nitrogen oxide fine separator, sending a liquid phase to a recovery system, sending a gas phase to a nitrogen oxide compressor, and then boosting pressure, exchanging heat and cooling;

and step six, sending the NOx gas after the fine separation and the heat exchange to the bottom of an absorption tower, and carrying out gas-liquid reverse absorption with water added at the top of the tower and condensed acid added at the middle part of the tower to obtain a nitric acid solution with the concentration of 65-80%.

5. Use of a flow chemistry in the nitration of toluene according to claim 4 wherein: the volume ratio of the secondary air to the primary air in the first step is 8-22%.

6. Use of a flow chemistry in the nitration of toluene according to claim 4 wherein: the absorption tower of the four steps is provided with 40 layers of tower plates.

7. Use of a flow chemistry in the nitration of toluene according to claim 2, wherein: the preparation process of the sulfuric acid comprises the following steps:

melting solid sulfur, filtering the molten liquid, conveying the molten liquid into a liquid sulfur storage tank, and pumping the molten liquid into a sulfur incinerator for combustion, wherein the pressure in the sulfur incinerator is 3-5MPa, and the temperature in the incinerator is 700-;

compressing the combusted flue gas, cooling to 130-160 ℃, adjusting the pressure to 7-9Mpa, then sending into an absorption system to obtain finished sulfuric acid, leading out the finished sulfuric acid from an outlet of a circulating pump of a drying tower, and collecting and storing;

step three, tail gas discharged from the absorption system in the step two enters from a lower inlet of the tail gas washing tower, and ammonia water is sprayed from an upper inlet of the tail gas washing tower;

and step four, pumping the wastewater discharged by the tail gas cleaning tower to a biochemical treatment system by using a slurry pump for separation to obtain ammonia gas and ammonium sulfate.

8. Use of a flow chemistry in the nitration of toluene according to claim 7 wherein: the pressure in the sulfur incinerator in the first step is 4MPa, and the temperature in the incinerator is 950 ℃.

9. Use of a flow chemistry in the nitration of toluene according to claim 8, wherein: and after the flue gas in the step two is compressed, cooling to 140-150 ℃, and adjusting the pressure to 7.3-8.2 Mpa.

Technical Field

The invention belongs to the technical field of chemical materials, and particularly relates to application of flow chemistry in toluene nitration.

Background

The mononitrotoluene has three isomers of o, m and p, p-nitrotoluene and o-nitrotoluene are important chemical materials, and the two compounds are the first-stage nitration products of toluene.

However, the nitration reaction is carried out in a conventional reactor, the reaction process is not easy to control, if the heat is concentrated by reaction heat and is not transferred in time, the partial reaction of the reactor is overheated, great potential safety hazard is generated, side reaction and over reaction are easy to occur, the decomposition of nitric acid can be caused by the partial high nitric acid, a great amount of nitrogen dioxide gas is generated, and the environment is polluted, so that the application of the flow chemistry in the toluene nitration is provided.

Disclosure of Invention

The object of the present invention is to provide a use of flow chemistry in toluene nitration that solves the problems set forth in the background above.

In order to achieve the purpose, the invention provides the following technical scheme: use of flow chemistry in the nitration of toluene.

Preferably, toluene is used as a solvent, nitric acid is used as a nitrating agent, sulfuric acid is used as a catalyst, and the nitration reaction is carried out in a microchannel reactor.

Preferably, the specific steps of the nitration reaction are as follows:

step one, mixing nitric acid and a sulfuric acid catalyst to obtain a mixed solution, and respectively conveying the mixed solution and toluene to two inlets of a microchannel reactor through a high-pressure constant-flow pump;

step two, after the two streams of liquid are mixed, contacted and reacted in the microchannel reactor, the two streams of liquid flow out from an outlet of the microchannel reactor and enter a collecting tank;

standing and layering the solution in the collecting tank, wherein the upper layer is a mixture of sulfuric acid, water and dilute nitric acid, and the lower layer is a nitration product of toluene;

step four, separating two phases by using a separating funnel, and washing, neutralizing and drying the lower layer liquid to obtain a nitration product of the toluene;

and step five, removing 85% of water and nitric acid from the upper layer liquid after reduced pressure distillation, and drying and dehydrating the residual liquid for recycling.

Preferably, the preparation process of the nitric acid comprises the following steps:

firstly, air sucked into a first-stage air filter of a four-stage air filtering device is subjected to primary impurity removal, then is cooled and condensed by an ammonia air condenser, condensed water is removed by a liquid drop separator, and then is conveyed to a second-stage, a third-stage and a fourth-stage air filters of the four-stage air filtering device for dust removal, and the air after dust removal is pressurized and divided into primary air and secondary air;

step two, mixing the liquid ammonia and the primary air in the step one in an ammonia-air mixer after impurity removal, oil removal and evaporation;

thirdly, carrying out ammonia oxidation reaction on the mixed gas in the ammonia-air mixer through an oxidation furnace to obtain NOx gas;

fourthly, the NOx gas is cooled through heat exchange and then sent to a condensation separator, and the generated dilute condensed acid is cooled and sent to a tower plate in the middle of an absorption tower;

fifthly, after the cooled NOx gas is subjected to fine separation through a nitrogen oxide fine separator, sending a liquid phase to a recovery system, sending a gas phase to a nitrogen oxide compressor, and then boosting pressure, exchanging heat and cooling;

and step six, sending the NOx gas after the fine separation and the heat exchange to the bottom of an absorption tower, and carrying out gas-liquid reverse absorption with water added at the top of the tower and condensed acid added at the middle part of the tower to obtain a nitric acid solution with the concentration of 65-80%.

Preferably, the volume ratio of the secondary air to the primary air in the first step is 8-22%.

Preferably, the absorption tower of the four steps is provided with 40 layers of towers.

Preferably, the preparation process of the sulfuric acid comprises the following steps:

melting solid sulfur, filtering the molten liquid, conveying the molten liquid into a liquid sulfur storage tank, and pumping the molten liquid into a sulfur incinerator for combustion, wherein the pressure in the sulfur incinerator is 3-5MPa, and the temperature in the incinerator is 700-;

compressing the combusted flue gas, cooling to 130-160 ℃, adjusting the pressure to 7-9Mpa, then sending into an absorption system to obtain finished sulfuric acid, leading out the finished sulfuric acid from an outlet of a circulating pump of a drying tower, and collecting and storing;

step three, tail gas discharged from the absorption system in the step two enters from a lower inlet of the tail gas washing tower, and ammonia water is sprayed from an upper inlet of the tail gas washing tower;

and step four, pumping the wastewater discharged by the tail gas cleaning tower to a biochemical treatment system by using a slurry pump for separation to obtain ammonia gas and ammonium sulfate.

Preferably, the pressure in the sulfur incinerator in the first step is 4MPa, and the temperature in the incinerator is 950 ℃.

Preferably, after the flue gas in the second step is compressed, the temperature is reduced to 140-150 ℃, and the pressure is adjusted to 7.3-8.2 MPa.

Compared with the prior art, the invention has the beneficial effects that:

(1) the method is applied to the toluene nitration reaction by the microchannel reactor, and has the advantages of high selectivity of target products, high reaction speed, mild reaction and easy control of the reaction by utilizing the microchannel reactor.

(2) The invention reduces the generation of waste acid and byproduct nitrocresol in the reaction process and reduces the o/p value in the product by applying the microchannel reactor to the toluene nitration reaction.

Detailed Description

The technical solutions in the embodiments of the present invention are clearly and completely described, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Example 1

The invention provides a technical scheme that: use of flow chemistry in the nitration of toluene.

In this embodiment, preferably, the nitration reaction is performed in a microchannel reactor with toluene as a solvent, nitric acid as a nitrating agent, and sulfuric acid as a catalyst.

In this embodiment, preferably, the specific steps of the nitration reaction are as follows:

step one, mixing 1.0g and 15.2ml/mol of nitric acid and 0.1g of sulfuric acid catalyst to obtain a mixed solution, and respectively conveying the mixed solution and 10.0g and 21.7ml/mol of toluene to two inlets of a 50ml microchannel reactor through a high-pressure constant-flow pump;

step two, after the two streams of liquid are mixed, contacted and reacted in the microchannel reactor, the two streams of liquid flow out from an outlet of the microchannel reactor and enter a collecting tank;

standing and layering the solution in the collecting tank, wherein the upper layer is a mixture of sulfuric acid, water and dilute nitric acid, and the lower layer is a nitration product of toluene;

step four, separating two phases by using a separating funnel, and washing, neutralizing and drying the lower layer liquid to obtain a nitration product of the toluene;

and step five, removing 85% of water and nitric acid from the upper layer liquid after reduced pressure distillation, and drying and dehydrating the residual liquid for recycling.

In this embodiment, preferably, the preparation process of the nitric acid includes the following steps:

firstly, air sucked into a first-stage air filter of a four-stage air filtering device is subjected to primary impurity removal, then is cooled and condensed by an ammonia air condenser, condensed water is removed by a liquid drop separator, and then is conveyed to a second-stage, a third-stage and a fourth-stage air filters of the four-stage air filtering device for dust removal, and the air after dust removal is pressurized and divided into primary air and secondary air;

step two, mixing the liquid ammonia and the primary air in the step one in an ammonia-air mixer after impurity removal, oil removal and evaporation;

thirdly, carrying out ammonia oxidation reaction on the mixed gas in the ammonia-air mixer through an oxidation furnace to obtain NOx gas;

fourthly, the NOx gas is cooled through heat exchange and then sent to a condensation separator, and the generated dilute condensed acid is cooled and sent to a tower plate in the middle of an absorption tower;

fifthly, after the cooled NOx gas is subjected to fine separation through a nitrogen oxide fine separator, sending a liquid phase to a recovery system, sending a gas phase to a nitrogen oxide compressor, and then boosting pressure, exchanging heat and cooling;

and step six, sending the NOx gas after the fine separation and the heat exchange to the bottom of an absorption tower, and carrying out gas-liquid reverse absorption with water added at the top of the tower and condensed acid added at the middle part of the tower to obtain a 65% nitric acid solution.

In this embodiment, it is preferable that the volume ratio of the secondary air to the primary air in the first step is 22%.

In this embodiment, it is preferable that the four absorption columns of the step are provided with 40 stages of trays.

In this embodiment, preferably, the preparation process of the sulfuric acid includes the following steps:

melting solid sulfur, filtering molten liquid, conveying the molten liquid into a liquid sulfur storage tank, and pumping the molten liquid into a sulfur incinerator for combustion, wherein the pressure in the sulfur incinerator is 3MPa, and the temperature in the incinerator is 700 ℃;

compressing the combusted flue gas, cooling to 130 ℃, adjusting the pressure to 7Mpa, then sending into an absorption system to obtain finished sulfuric acid, leading out the finished sulfuric acid from an outlet of a circulating pump of a drying tower, and collecting and storing;

step three, tail gas discharged from the absorption system in the step two enters from a lower inlet of the tail gas washing tower, and ammonia water is sprayed from an upper inlet of the tail gas washing tower;

and step four, pumping the wastewater discharged by the tail gas cleaning tower to a biochemical treatment system by using a slurry pump for separation to obtain ammonia gas and ammonium sulfate.

The GC analysis of the nitration reaction in this example is shown in table 1 below, where a ═ o-nitrotoluene, B ═ m-nitrotoluene, and C ═ p-nitrotoluene.

TABLE 1

Example 2

The invention provides a technical scheme that: use of flow chemistry in the nitration of toluene.

In this embodiment, preferably, the nitration reaction is performed in a microchannel reactor with toluene as a solvent, nitric acid as a nitrating agent, and sulfuric acid as a catalyst.

In this embodiment, preferably, the specific steps of the nitration reaction are as follows:

step one, mixing 2.0g and 30.4ml/mol of nitric acid and 0.1g of sulfuric acid catalyst to obtain a mixed solution, and respectively conveying the mixed solution and 10.0g and 21.7ml/mol of toluene to two inlets of a 50ml microchannel reactor through a high-pressure constant-flow pump;

step two, after the two streams of liquid are mixed, contacted and reacted in the microchannel reactor, the two streams of liquid flow out from an outlet of the microchannel reactor and enter a collecting tank;

standing and layering the solution in the collecting tank, wherein the upper layer is a mixture of sulfuric acid, water and dilute nitric acid, and the lower layer is a nitration product of toluene;

step four, separating two phases by using a separating funnel, and washing, neutralizing and drying the lower layer liquid to obtain a nitration product of the toluene;

and step five, removing 85% of water and nitric acid from the upper layer liquid after reduced pressure distillation, and drying and dehydrating the residual liquid for recycling.

In this embodiment, preferably, the preparation process of the nitric acid includes the following steps:

firstly, air sucked into a first-stage air filter of a four-stage air filtering device is subjected to primary impurity removal, then is cooled and condensed by an ammonia air condenser, condensed water is removed by a liquid drop separator, and then is conveyed to a second-stage, a third-stage and a fourth-stage air filters of the four-stage air filtering device for dust removal, and the air after dust removal is pressurized and divided into primary air and secondary air;

step two, mixing the liquid ammonia and the primary air in the step one in an ammonia-air mixer after impurity removal, oil removal and evaporation;

thirdly, carrying out ammonia oxidation reaction on the mixed gas in the ammonia-air mixer through an oxidation furnace to obtain NOx gas;

fourthly, the NOx gas is cooled through heat exchange and then sent to a condensation separator, and the generated dilute condensed acid is cooled and sent to a tower plate in the middle of an absorption tower;

fifthly, after the cooled NOx gas is subjected to fine separation through a nitrogen oxide fine separator, sending a liquid phase to a recovery system, sending a gas phase to a nitrogen oxide compressor, and then boosting pressure, exchanging heat and cooling;

and step six, sending the NOx gas after the fine separation and the heat exchange to the bottom of an absorption tower, and carrying out gas-liquid reverse absorption with water added at the top of the tower and condensed acid added at the middle part of the tower to obtain a nitric acid solution with the concentration of 80%.

In this embodiment, the volume ratio of the secondary air to the primary air in the first step is preferably 8%.

In this embodiment, it is preferable that the four absorption columns of the step are provided with 40 stages of trays.

In this embodiment, preferably, the preparation process of the sulfuric acid includes the following steps:

melting solid sulfur, filtering molten liquid, conveying the molten liquid into a liquid sulfur storage tank, and pumping the molten liquid into a sulfur incinerator for combustion, wherein the pressure in the sulfur incinerator is 5MPa, and the temperature in the incinerator is 1100 ℃;

compressing the combusted flue gas, cooling to 160 ℃, adjusting the pressure to 9Mpa, then sending into an absorption system to obtain finished sulfuric acid, leading out the finished sulfuric acid from an outlet of a circulating pump of a drying tower, and collecting and storing;

step three, tail gas discharged from the absorption system in the step two enters from a lower inlet of the tail gas washing tower, and ammonia water is sprayed from an upper inlet of the tail gas washing tower;

and step four, pumping the wastewater discharged by the tail gas cleaning tower to a biochemical treatment system by using a slurry pump for separation to obtain ammonia gas and ammonium sulfate.

The GC analysis of the nitration reaction in this example is shown in table 2 below, where a ═ o-nitrotoluene, B ═ m-nitrotoluene, and C ═ p-nitrotoluene.

TABLE 2

Example 3

The invention provides a technical scheme that: use of flow chemistry in the nitration of toluene.

In this embodiment, preferably, the nitration reaction is performed in a microchannel reactor with toluene as a solvent, nitric acid as a nitrating agent, and sulfuric acid as a catalyst.

In this embodiment, preferably, the specific steps of the nitration reaction are as follows:

step one, mixing 2.0g and 45.7ml/mol of nitric acid and 0.1g of sulfuric acid catalyst to obtain a mixed solution, and respectively conveying the mixed solution and 10.0g and 21.7ml/mol of toluene to two inlets of a 50ml microchannel reactor through a high-pressure constant-flow pump;

step two, after the two streams of liquid are mixed, contacted and reacted in the microchannel reactor, the two streams of liquid flow out from an outlet of the microchannel reactor and enter a collecting tank;

standing and layering the solution in the collecting tank, wherein the upper layer is a mixture of sulfuric acid, water and dilute nitric acid, and the lower layer is a nitration product of toluene;

step four, separating two phases by using a separating funnel, and washing, neutralizing and drying the lower layer liquid to obtain a nitration product of the toluene;

and step five, removing 85% of water and nitric acid from the upper layer liquid after reduced pressure distillation, and drying and dehydrating the residual liquid for recycling.

In this embodiment, preferably, the preparation process of the nitric acid includes the following steps:

firstly, air sucked into a first-stage air filter of a four-stage air filtering device is subjected to primary impurity removal, then is cooled and condensed by an ammonia air condenser, condensed water is removed by a liquid drop separator, and then is conveyed to a second-stage, a third-stage and a fourth-stage air filters of the four-stage air filtering device for dust removal, and the air after dust removal is pressurized and divided into primary air and secondary air;

step two, mixing the liquid ammonia and the primary air in the step one in an ammonia-air mixer after impurity removal, oil removal and evaporation;

thirdly, carrying out ammonia oxidation reaction on the mixed gas in the ammonia-air mixer through an oxidation furnace to obtain NOx gas;

fourthly, the NOx gas is cooled through heat exchange and then sent to a condensation separator, and the generated dilute condensed acid is cooled and sent to a tower plate in the middle of an absorption tower;

fifthly, after the cooled NOx gas is subjected to fine separation through a nitrogen oxide fine separator, sending a liquid phase to a recovery system, sending a gas phase to a nitrogen oxide compressor, and then boosting pressure, exchanging heat and cooling;

and step six, sending the NOx gas after the fine separation and the heat exchange to the bottom of an absorption tower, and carrying out gas-liquid reverse absorption with water added at the top of the tower and condensed acid added at the middle part of the tower to obtain a nitric acid solution with the concentration of 70%.

In this embodiment, the volume ratio of the secondary air to the primary air in the first step is preferably 10%.

In this embodiment, it is preferable that the four absorption columns of the step are provided with 40 stages of trays.

In this embodiment, preferably, the preparation process of the sulfuric acid includes the following steps:

melting solid sulfur, filtering molten liquid, conveying the molten liquid into a liquid sulfur storage tank, and pumping the molten liquid into a sulfur incinerator for combustion, wherein the pressure in the sulfur incinerator is 4MPa, and the temperature in the incinerator is 950 ℃;

compressing the combusted flue gas, cooling to 140 ℃, adjusting the pressure to 8Mpa, then sending into an absorption system to obtain finished sulfuric acid, leading out the finished sulfuric acid from an outlet of a circulating pump of a drying tower, and collecting and storing;

step three, tail gas discharged from the absorption system in the step two enters from a lower inlet of the tail gas washing tower, and ammonia water is sprayed from an upper inlet of the tail gas washing tower;

and step four, pumping the wastewater discharged by the tail gas cleaning tower to a biochemical treatment system by using a slurry pump for separation to obtain ammonia gas and ammonium sulfate.

The GC analysis of the nitration reaction in this example is shown in table 3 below, where a ═ o-nitrotoluene, B ═ m-nitrotoluene, and C ═ p-nitrotoluene.

TABLE 3

Example 4

The invention provides a technical scheme that: use of flow chemistry in the nitration of toluene.

In this embodiment, preferably, the nitration reaction is performed in a microchannel reactor with toluene as a solvent, nitric acid as a nitrating agent, and sulfuric acid as a catalyst.

In this embodiment, preferably, the specific steps of the nitration reaction are as follows:

step one, mixing 2.0g, 60.9ml/mol of nitric acid and 0.1g of sulfuric acid catalyst to obtain a mixed solution, and respectively conveying the mixed solution and 10.0g, 21.7ml/mol of toluene to two inlets of a 50ml microchannel reactor through a high-pressure constant-flow pump;

step two, after the two streams of liquid are mixed, contacted and reacted in the microchannel reactor, the two streams of liquid flow out from an outlet of the microchannel reactor and enter a collecting tank;

standing and layering the solution in the collecting tank, wherein the upper layer is a mixture of sulfuric acid, water and dilute nitric acid, and the lower layer is a nitration product of toluene;

step four, separating two phases by using a separating funnel, and washing, neutralizing and drying the lower layer liquid to obtain a nitration product of the toluene;

and step five, removing 85% of water and nitric acid from the upper layer liquid after reduced pressure distillation, and drying and dehydrating the residual liquid for recycling.

In this embodiment, preferably, the preparation process of the nitric acid includes the following steps:

firstly, air sucked into a first-stage air filter of a four-stage air filtering device is subjected to primary impurity removal, then is cooled and condensed by an ammonia air condenser, condensed water is removed by a liquid drop separator, and then is conveyed to a second-stage, a third-stage and a fourth-stage air filters of the four-stage air filtering device for dust removal, and the air after dust removal is pressurized and divided into primary air and secondary air;

step two, mixing the liquid ammonia and the primary air in the step one in an ammonia-air mixer after impurity removal, oil removal and evaporation;

thirdly, carrying out ammonia oxidation reaction on the mixed gas in the ammonia-air mixer through an oxidation furnace to obtain NOx gas;

fourthly, the NOx gas is cooled through heat exchange and then sent to a condensation separator, and the generated dilute condensed acid is cooled and sent to a tower plate in the middle of an absorption tower;

fifthly, after the cooled NOx gas is subjected to fine separation through a nitrogen oxide fine separator, sending a liquid phase to a recovery system, sending a gas phase to a nitrogen oxide compressor, and then boosting pressure, exchanging heat and cooling;

and step six, sending the NOx gas after the fine separation and the heat exchange to the bottom of an absorption tower, and carrying out gas-liquid reverse absorption with water added at the top of the tower and condensed acid added at the middle part of the tower to obtain a nitric acid solution with the concentration of 75%.

In this embodiment, the volume ratio of the secondary air to the primary air in the first step is preferably 15%.

In this embodiment, it is preferable that the four absorption columns of the step are provided with 40 stages of trays.

In this embodiment, preferably, the preparation process of the sulfuric acid includes the following steps:

step one, melting solid sulfur, filtering molten liquid, conveying the molten liquid into a liquid sulfur storage tank, and pumping the molten liquid into a sulfur incinerator for combustion, wherein the pressure in the sulfur incinerator is 3.5MPa, and the temperature in the incinerator is 800 ℃;

compressing the combusted flue gas, cooling to 150 ℃, adjusting the pressure to 7.3Mpa, then sending into an absorption system to obtain finished sulfuric acid, leading out the finished sulfuric acid from an outlet of a circulating pump of a drying tower, and collecting and storing;

step three, tail gas discharged from the absorption system in the step two enters from a lower inlet of the tail gas washing tower, and ammonia water is sprayed from an upper inlet of the tail gas washing tower;

and step four, pumping the wastewater discharged by the tail gas cleaning tower to a biochemical treatment system by using a slurry pump for separation to obtain ammonia gas and ammonium sulfate.

The GC analysis of the nitration reaction in this example is shown in table 4 below, where a ═ o-nitrotoluene, B ═ m-nitrotoluene, and C ═ p-nitrotoluene.

TABLE 4

The working principle and the advantages of the invention are as follows: the method is applied to the toluene nitration reaction by the microchannel reactor, and has the advantages of high selectivity of target products, high reaction speed, mild reaction and easy control of the reaction by utilizing the microchannel reactor; by applying the microchannel reactor to the toluene nitration reaction, the generation of waste acid and the generation of a byproduct, namely nitrocresol, in the reaction process are reduced, and the o/p value in the product is reduced.

Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.