Microchannel synthesis method of dinitrobenzene
Technical Field
The invention relates to a synthesis method of an important fine chemical product, in particular to a synthesis method of dinitrobenzene in a microchannel reactor.
Background
Dinitrobenzene is an important raw material in chemical production, is mainly used for preparing dyes, paints and coatings, and is also a precursor for producing trinitrobenzene (TNT) explosive.
The production of dinitrobenzene is mainly a two-step nitration of benzene and a one-step nitration of nitrobenzene. At present, the nitration process mainly comprises two nitration processes of isothermal nitration and adiabatic nitration, and the difference mainly lies in that an energy transfer mode and a waste acid recovery mode are different, so that energy consumption is different and nitration product components are different. The constant temperature condition is favorable for product selectivity, and the adiabatic condition can integrate the reaction and waste acid concentration together to play a role in reducing energy consumption. The adiabatic nitration realizes the industrial production in the end of the 70 th 20 th century, and the basic principle is that the mixing heat and the reaction heat are fully utilized to heat the material for non-constant temperature nitration, and the nitration reaction temperature is between 90 and 135 ℃. The adiabatic nitration uses mixed acid with high sulfuric acid and low nitric acid ratio (the nitric acid content in the mixed acid is 4-7.5%, and the sulfuric acid content is 67-70%), and aims to improve the conversion rate of nitrobenzene, and simultaneously, waste acid after reaction is in a reaction temperature state, and is recycled after flash evaporation concentration. Isothermal nitration requires the construction of a waste acid concentration device, while adiabatic nitration requires the installation of a simple waste acid concentration process in dinitrobenzene production. Although the process is different, the nitration reaction is a strong exothermic fast reaction, the currently adopted kettle type or pan type reactor requires relatively mild acid conditions to reduce the intrinsic rate and match the heat transfer rate of the reactor, so that the conventional process needs a plurality of reactors connected in series to completely convert the benzene, and the equipment is large and complex; the organic phase and the acid phase are required to be prepared according to a specific proportion and the reaction time is kept long enough to control the reaction rate and the heat transfer rate; an intermediate process for generating nitrobenzene is needed; a refrigerating device is needed to quickly take away a large amount of reaction heat, and the temperature runaway caused by the formation of hot spots is avoided, so that explosion is avoided. Influenced by the batch process of the reaction kettle, the whole process needs to continuously regulate and control process parameters, the manual intervention is more, the continuous automation level of the process is not high, and the stability is general.
The synthesis technology of the microchannel reactor is a novel technology which tends to be mature in recent years, the heat and mass transfer of the synthesis technology is improved by 1-3 orders of magnitude compared with that of conventional scale equipment, technological parameters can be accurately controlled, the controllability of the technological process is strong, the continuity and the automation of a reaction process are easy to realize, and the safety and the stability of the process are improved. The invention is based on a micro-reactor synthesis technology, and uses benzene to synthesize dinitrobenzene in one step, which is not reported.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide a synthesis technology of a micro-channel reactor of dinitrobenzene, so that one-step nitration of benzene and mixed acid to dinitrobenzene is realized.
In order to realize the purpose, the invention directly synthesizes the dinitrobenzene from the benzene in the one-step method in the microchannel reactor, adopts the rapid reaction process for improving the intrinsic reaction rate of the nitration reaction, improves the benzene dinitration reaction speed and the selectivity of dinitration products, eliminates the potential safety hazard of the benzene dinitration process, and obtains the one-step preparation process with high conversion rate, high yield, safety and high efficiency. The technical scheme adopted by the invention is as follows:
a nitration process for the synthesis of dinitrobenzene, the reaction being carried out in a microreactor having two inlets and one outlet, comprising the steps of:
(1) taking mixed acid of nitric acid and sulfuric acid as a nitrating agent to prepare mixed acid solution of nitric acid and sulfuric acid;
(2) synchronously pumping two material flows of the mixed acid of the reaction materials and the benzene into two inlets of the microchannel reactor through a metering pump respectively, and controlling the molar ratio of the benzene and the mixed acid through the metering pump;
(3) mixing two raw material liquids of benzene and mixed acid in a microchannel reactor and reacting;
(4) outputting the reaction materials from the outlet of the microreactor to a collector, and continuously stirring and reacting for 0-1 hour; and then separating, washing and drying to obtain the target product.
Based on the technical scheme, preferably, in the step (1), the molar ratio of the nitric acid to the sulfuric acid is 0.2-1.0, preferably 0.2-0.5, and the mass concentration of water is 3-10%.
Based on the technical scheme, preferably, in the step (2), the molar ratio of the benzene to the nitric acid is 1: (2.0-2.4).
Based on the technical scheme, preferably, in the step (3), the reaction temperature is 60-80 ℃, and the residence time is 8-500 seconds.
Based on the technical scheme, preferably, in the step (4), the reaction materials are output from the microreactor to a collector, and the reaction is continuously carried out for 0-1 hour under the condition of heat preservation and stirring; then separating, washing and drying by using a conventional method to obtain a target product.
The separation of the product and the concentration and purification of the aqueous phase can be carried out by means of conventional methods and equipment, and the aqueous phase can be reused after dehydration, concentration and purification.
The material proportion and the reactor operating temperature of the main product dinitrobenzene with the selectivity of more than 40-99% can be (1) the molar ratio of mixed acid, nitre and sulfur is 0.2-0.5, the mass concentration of water is less than 5%, the molar ratio of feed nitric acid and benzene is 2.0-2.4, the reactor temperature is controlled (60-80 ℃), the content of nitrobenzene is 1-5%, and the dinitrobenzene is 95-99%; or (2) the molar ratio of mixed acid, nitre and sulfur is 0.2-0.5, the mass concentration of water is 5-10%, the molar ratio of feed nitric acid to benzene is 2.0-2.4, the temperature of the reactor is controlled (60-80 ℃), the content of nitrobenzene is 30-60%, and the content of dinitrobenzene is 40-70%.
The device for realizing the synthesis method comprises at least three parts, wherein the first part is at least two metering pumps for quantitatively pumping initial reaction material benzene and mixed acid, the second part is at least one substrate, the substrate at least comprises two inlet connecting ends for pumping the initial reaction material benzene and mixed acid reagents and a measurement and control thermocouple jack, at least one microchannel reaction plate for prolonging the residence time is connected in series behind the mixing plate, and a channel with the width of 2-6mm is arranged on the microchannel reaction plate; at least two heat medium channel plates distributed on the upper and lower sides of the mixing plate; the second substrate is provided with an outlet connecting end for outputting products, and the third part is a collector for collecting materials and continuing reaction.
Based on the technical scheme, the preferable material of the pipeline involved in the microreactor is stainless steel or PTFE material, the inner diameter of the channel in the microreactor is 0.2-1 mm, and the length range of the microchannel is 50-500 cm.
Based on the technical scheme, preferably, the pumping speed of the initial raw materials, namely the benzene and the mixed acid, into the microreactor is 0.3-44 ml/min.
Based on the technical scheme, the flowing pressure of the benzene and the mixed acid in the microchannel reactor is preferably 0.0-0.7 MPa.
Based on the technical scheme, preferably, after the synthesis reaction is finished, the sulfuric acid is recovered in a concentration mode and is directly used for the synthesis reaction.
Compared with the prior art, the process for preparing dinitrobenzene in the microreactor has the following technical results:
1. benzene and mixed acid are mixed and reacted in a micro reactor channel by a one-step method to directly and continuously synthesize dinitrobenzene.
2. Compared with the defects of a common reaction kettle by utilizing the advantages of a microreactor, the method has the advantages that raw materials and products with flammable and explosive characteristics exist, potential dangers are different in the microchannel reactor, and hot spots existing in the kettle type reaction can induce rapid temperature rise of a large amount of materials until a large accident happens. The mass transfer and heat transfer efficiency in the microchannel reactor is 1-3 orders of magnitude higher than that of a kettle type reactor, and heat generated by reaction can be taken away rapidly, so that the possibility of accidents is reduced, and meanwhile, the quantity of materials participating in the reaction is lower than 3-5 orders of magnitude, and the severity of accidents caused by a large quantity of materials is completely eradicated.
3. The water content of the mixed acid can reach about 8 percent, and the concentrated sulfuric acid (about 90 percent) recovered in the industrial production process can be directly used for continuous nitration without generating a large amount of waste acid.
4. The collector in the invention has the main functions of: the device is arranged between a continuous channel synthesis process and intermittent post-treatment, and plays roles in connection and conversion; secondly, controlling the temperature and stirring according to requirements, namely serving as a part of a synthesis function, continuously reacting for a certain time to improve the conversion rate of the raw materials, and also serving as a part of a post-treatment function, and carrying out quenching reaction to enter a subsequent conventional treatment process.
The invention realizes the synthesis of dinitrobenzene by benzene dinitration under the condition of strong nitrating acid by utilizing the high-efficiency mass and heat transfer capacity of the microchannel reactor, and has safe and high-efficiency process. The conversion per pass of benzene is close to 100 percent, the yield of dinitrobenzene is higher than 99 percent, and the content of 1, 3-dinitrobenzene which is a main component reaches 84 percent.
Drawings
FIG. 1 is a schematic diagram of an apparatus for a microchannel reactor synthesis process according to the present invention; in the figure: 1. 2 are two feeding connecting ends respectively, 3 is a thermocouple socket end, and 4 is an outlet connecting end;
FIG. 2 is a graph showing the effect of different reaction temperatures on the reaction performance in example 1;
FIG. 3 is a graph showing the effect of different water contents on the reaction performance in the mixed acid of example 2.
Detailed Description
The invention will be further illustrated and described with reference to practice of the invention.
The device schematic diagram of the synthetic method of the invention is shown in figure 1, and comprises three parts, wherein the first part is two metering pumps (a metering pump A and a metering pump B) for quantitatively pumping initial reaction materials benzene and mixed acid, the second part is a microchannel reactor provided with a substrate, the substrate comprises two inlet connecting ends for pumping the initial reaction materials benzene and mixed acid reagents and a measurement and control thermocouple jack, an outlet connecting end for outputting products, and the third part is a collector for collecting materials to continue to react;
the mixed acid used in the invention is prepared from fuming nitric acid, concentrated sulfuric acid and water, the molar ratio of the nitric acid to the sulfuric acid in the mixed acid is in the range of 0.2-0.5, when the concentration of dinitrobenzene as a main product is required to be higher than 95%, the molar ratio of the nitric to the sulfur is preferably 0.5, and the mass concentration of water in the mixed acid is 3% -10%, under the condition, the mixed acid has strong nitration capability and can improve the nitration reaction speed, so the reactor can be operated at 60-80 ℃;
the micro-channel reactor can perform dinitration under the condition of strong mixed acid at the temperature of 60-80 ℃, and the process is safe. However, under the process conditions, a certain amount of organic components can be dissolved in the acid phase of the reaction product, and in order to weaken the solubility of concentrated acid and ensure the selectivity of dinitrobenzene, the invention provides two methods: firstly, the mixed acid with the water mass concentration of 5-10% is used for dinitration, only the mild temperature control state is implemented on the reactor, the temperature can be specifically controlled at 60-80 ℃, and secondly, cold shock treatment is carried out at the outlet point of the reactor or a proper amount of ice water is injected into a product collecting device.
When the nitrobenzene concentration in the product is allowed to be less than 10%, there are three routes: firstly, strong nitration ability acid is used, namely the N/S value is 0.2-0.5 and the water content is lower than 10 percent (mass), and the feeding ratio of the key reaction material nitric acid and benzene is controlled to be more than 2.2, so that under the same nitration reaction speed, the nitrobenzene generated in the reaction process has enough available nitric acid to continue to react to generate dinitrobenzene, but the benzene is completely converted or nearly completely converted. Secondly, the concentration of nitric acid is increased and the mixed acid nitration capability is improved under the condition that the equivalence ratio of nitric acid to benzene is kept to be more than 2.0, so that the dinitration reaction speed is accelerated, and the nitrobenzene intermediate product is continuously nitrated into dinitrobenzene within a short retention time. Therefore, the method of keeping the water content in the mixed acid unchanged and independently increasing the nitric acid concentration is adopted, specifically, the N/S value in the nitrating acid is between 0.5 and 1, and the water concentration is lower than 10 percent (by mass). Thirdly, the mass concentration of water in the mixed acid is 3-5%.
The method comprises the following steps of inputting benzene serving as a starting material into a connecting end 1 through a metering pump A, inputting mixed acid into an inlet connecting end 2 through a metering pump B, mixing and reacting the two starting materials in a microreactor, detecting the reaction temperature by a thermocouple through a thermocouple jack 3, stopping the reaction for 8-500 seconds at the reaction temperature of 60-80 ℃, outputting the reaction materials to a collector from an output connecting end 4 of the microreactor, continuing to keep the temperature and stir the reaction for the reaction time, stopping the reaction, and separating, washing and drying the reaction products based on a conventional method to obtain a target product.
The reaction route of the synthesis method of the microchannel reactor is as follows:
benzene is taken as a starting material, and mixed acid is taken as a nitration reagent; the starting material benzene enters the reaction device through a metering pump, and the speed of the two metering pumps is determined based on the molar ratio of the benzene to the nitric acid in the mixed acid; the feeding rate is selected based on the optional range of the metering pump, a lower feeding rate is not favorable for obtaining a better reaction rate, a higher feeding rate is favorable for leading overpressure and shutdown of the metering pump, the higher feeding rate is favorable for obtaining a higher feeding rate under the condition of not leading overpressure to shutdown of the pump, the feeding rate ensures the reaction rate, but possibly leads the reactor to be out of an optimal mass and heat transfer state, so that the reaction material is not completely reacted in the micro-channel, for this purpose, the length of the channel can be increased in series or a static mixer is added, or the heat preservation reaction is continuously carried out in a collector for a proper time, so that the benzene and the nitrobenzene in the reaction are fully converted into the dinitrobenzene as far as possible, and the better material conversion rate and the yield of the dinitrobenzene are obtained.
The invention is described above and the working results of the invention are demonstrated in the following examples, all percentages in the examples being percentages by mass.
The nitric acid is fuming nitric acid with the concentration of more than 98%, the sulfuric acid is concentrated sulfuric acid with the concentration of more than 98%, and the benzene is an industrial product with the content of more than 99%.
Examples 1 to 6
Preparing mixed acid with fuming nitric acid (more than or equal to 98%) and concentrated sulfuric acid (more than or equal to 98%) according to the molar ratio of the fuming nitric acid to the concentrated sulfuric acid of 0.5 and the water concentration of 3%. The temperature can be controlled below 25 ℃ in the process of preparing the mixed acid. Under the condition of normal temperature, mixed acid and benzene are continuously pumped into the microreactor by a trace advection pump and react in the microreactor channel, and the reaction temperature is 60 ℃, 70 ℃ and 80 ℃ respectively. The molar ratio of the nitric acid to the benzene is controlled to be more than or equal to 2.0 and less than or equal to 2.4. Wherein the specific conditions of the microreactor reaction are shown in Table 1.
TABLE 1
And continuously flowing the reaction product out of the reactor, feeding the reaction product into a collector, keeping the reaction product at the same reaction temperature with the microreactor for 1 hour, feeding the reaction product into a separator, adding a proper amount of ice water to stop the reaction and ethyl acetate, separating acid liquor, washing an organic phase with water and alkali to be neutral, drying anhydrous sodium sulfate, evaporating the solvent, and drying to obtain a product, wherein the result is shown in the attached figure 2.
The results in FIG. 2 show that, at the same N/B, the reaction temperature is increased, i.e.from 60 ℃ to 80 ℃, the yield of dinitrobenzene is increased, the increase in temperature being favourable for the reaction; at the same temperature, the yield of dinitrobenzene is increased along with the increase of N/B.
Examples 13 to 24
The process and the used reactor are the same as those of the embodiment 1-5, the molar ratio of the nitric acid to the sulfuric acid is 0.5, the water content in the mixed acid is respectively 2%, 8% and 10%, the molar ratio of the nitric acid to the benzene is not less than 2.0 and not more than 2.4, and the microreactor and the collector operate at 70 ℃. Wherein the reaction conditions of the microreactor are shown in Table 2. The results are shown in FIG. 3.
As can be seen from FIG. 3, the dinitrobenzene content increases with increasing N/B, which favors the nitration reaction. The water content in the mixed acid is increased, the nitration capability of the mixed acid is reduced, and the content of dinitrobenzene is reduced.
Although the present invention and its practical results have been described in detail in the foregoing illustrative description, it should be understood that the details are for illustration only, and that various changes and modifications may be effected therein by one skilled in the art within the spirit and scope of the invention as defined by the appended claims.