A continuous method for the nitration of benzene series

Abstract

The present application relates to the chemical technology field, specifically to a continuous nitration method of benzene series.The method provided by the present application adopts a loop reactor to carry out the nitration reaction, the loop reactor comprises a first-stage tubular reactor, a second-stage tubular reactor and a circulating pump which are communicated with each other, benzene series, fuming nitric acid and sulfuric acid are continuously introduced into the loop reactor respectively, and then, under the action of the circulating pump, the nitration reaction occurs in the circulation flow between the first-stage tubular reactor and the second-stage tubular reactor, the ratio of the circulation flow rate to the total feed flow rate is 30-500:1, since the circulation flow rate is much larger than the total feed flow rate, the reactant material can be rapidly dispersed by a large amount of circulating material after entering the loop reactor, the mass transfer and heat transfer efficiency of the reaction is improved, the method of the present application is more safe and efficient, and the operation is simple, and the equipment investment cost is low;the present application can realize the continuous nitration of benzene series, and is suitable for the industrialized continuous production with large flux.

Description

Technical Field

[0001] This invention relates to the field of chemical technology, and specifically to a continuous nitration method for benzene compounds. Background Technology

[0002] Nitration is a common reaction type widely used in fine chemical industries such as pharmaceuticals, pesticides, dyes, and materials. Nitration is characterized by its rapid reaction rate, large exothermic reaction, and heterogeneous mass and heat transfer, and is considered one of the eighteen most hazardous processes. Traditional processes mostly employ batch production methods such as batch or semi-batch reactors, which are technologically outdated, have large material volumes per reactor, and poor mass and heat transfer efficiency. During the reaction, local overheating and thermal runaway are prone to occur, leading to side reactions such as polynitration and oxidation. In severe cases, it can even cause high-temperature decomposition of materials, resulting in safety accidents. While microchannel reactors can achieve continuous nitration, their small liquid holdup means that achieving high-throughput industrial production requires multiple microchannel reactors connected in parallel, resulting in excessively high equipment investment for the same capacity. Therefore, they are not suitable for large-scale industrial production. Summary of the Invention

[0003] In view of this, the present invention provides a continuous nitration method for benzene compounds to solve the problems of existing processes that cannot produce continuously, are difficult to operate, have poor safety, and are low in cost.

[0004] In a first aspect, the present invention provides a continuous nitration method for benzene compounds, wherein the nitration reaction is carried out in a circulating reactor, the circulating reactor comprising a first-stage tubular reactor, a second-stage tubular reactor and a circulating pump connected to each other, and the inlet and outlet of the circulating reactor being located at arbitrary positions in the circulating reactor.

[0005] Benzene compounds, fuming nitric acid, and sulfuric acid are continuously fed into the circulating reactor. Under the action of the circulating pump, the reactants circulate between the first-stage tubular reactor and the second-stage tubular reactor, where a nitration reaction occurs. The ratio of the circulating flow rate to the total feed flow rate is 30 to 500:1. The reaction liquid containing the nitration product of benzene compounds is continuously collected from the outlet of the circulating reactor.

[0006] In one alternative implementation, the ratio of the circulating flow rate of the reactants to the total feed flow rate is 50 to 300:1.

[0007] In one alternative implementation, the ratio of the circulating flow rate of the reactants to the total feed flow rate is 100 to 250:1.

[0008] In one alternative embodiment, the molar ratio of benzene series compounds to fuming nitric acid and sulfuric acid in the circulating reactor is 1:1.01 to 1.1:1 to 3.

[0009] In one alternative embodiment, the molar ratio of benzene series compounds to fuming nitric acid and sulfuric acid in the circulating reactor is 1:1.02-1.07:1.5-2.5.

[0010] In one alternative embodiment, the nitration reaction is carried out at a temperature of -10°C to 100°C.

[0011] In one alternative embodiment, the nitration reaction takes 5 to 60 minutes, preferably 5 to 40 minutes.

[0012] In one alternative embodiment, both the first-stage tubular reactor and the second-stage tubular reactor are equipped with feed distributors at their inlet ends.

[0013] In one alternative embodiment, the first-stage tubular reactor and the second-stage tubular reactor are each selected from any one of a shell-and-tube heat exchanger, a coiled-tube heat exchanger, a dynamic tubular reactor, and a static tubular reactor.

[0014] In one alternative embodiment, the circulating pump is selected from any one of axial flow pumps, centrifugal pumps, screw pumps, gear pumps, and diaphragm pumps.

[0015] In one alternative embodiment, the sulfuric acid has a mass concentration of 70%-98%.

[0016] In one alternative embodiment, the benzene compound is benzene or a substituted benzene having 1 to 3 identical or different substituents, wherein the substituents are selected from halogens or C1-C4 alkyl groups, wherein the halogen is fluorine, chlorine, bromine or iodine, and the alkyl group is a straight-chain alkyl or a branched alkyl.

[0017] In one alternative embodiment, the outlet of the circulating reactor is located at the outlet end of the second-stage tubular reactor.

[0018] In one alternative embodiment, the feed inlet of the circulating reactor includes an inlet for benzene series compounds, an inlet for fuming nitric acid, and an inlet for sulfuric acid, wherein:

[0019] The inlet of the benzene series compound is located at the inlet end of the first-stage tubular reactor or at the inlet end of the circulating pump.

[0020] The inlet of the fuming nitric acid is located at any position in the circulating reactor;

[0021] The sulfuric acid inlet is located at the inlet end of either the first-stage tubular reactor or the second-stage tubular reactor.

[0022] In one alternative embodiment, the outlet end of the second-stage tubular reactor is connected to an aging reactor for aging the material flowing out of the circulating reactor.

[0023] In one alternative embodiment, the aging temperature is 10°C to 30°C higher than the nitration reaction temperature, and the aging time is 5 min to 60 min.

[0024] In one alternative embodiment, the aging reactor is selected from any one of a static tubular reactor, a dynamic tubular reactor, a circulating reactor, and an overflow reactor.

[0025] In one alternative embodiment, the material flowing out of the circulating reactor or the aging reactor is separated into an acid phase and an organic phase. The organic phase is then washed and separated to obtain a mononitrated product of benzene series compounds.

[0026] In one alternative embodiment, at least a portion of the acid phase is directly and / or extracted, concentrated, and then reused in the circulating reactor.

[0027] In one alternative embodiment, the extraction step uses a benzene series compound as the extractant. After extraction, the extracted benzene series compound and the recovered dilute acid are obtained. At least a portion of the recovered dilute acid is concentrated to obtain a recovered concentrated acid. The recovered concentrated acid and the extracted benzene series compound are then fed into the circulating reactor.

[0028] In one alternative embodiment, the acid phase obtained from the phase separation step or the recovered dilute acid obtained from the extraction step enters the circulating reactor from the inlet end of the first-stage tubular reactor.

[0029] The recovered sulfuric acid or the concentrated acid obtained from the concentration step enters the circulating reactor from the inlet end of the second-stage tubular reactor. The recovered sulfuric acid is a mixture of at least a portion of the concentrated acid obtained from the concentration step and at least a portion of the acid phase obtained from the phase separation step or at least a portion of the dilute acid obtained from the extraction step.

[0030] In one alternative embodiment, the acid phase processed in the extraction step accounts for more than 13% of the total acid phase volume.

[0031] In one alternative embodiment, the mass concentration of the recovered concentrated acid is 70%-98%.

[0032] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0033] The continuous preparation method of benzene series compounds provided by this invention uses a circulating reactor for nitration. The circulating reactor includes a first-stage tubular reactor, a second-stage tubular reactor, and a circulating pump that are interconnected. Benzene series compounds, fuming nitric acid, and sulfuric acid are continuously introduced into the circulating reactor and circulate between the first-stage and second-stage tubular reactors under the action of the circulating pump to carry out the nitration reaction. The ratio of the circulating flow rate to the total feed flow rate is 30-500:1. Because the circulating flow rate is much greater than the total feed flow rate, the reactants can be rapidly dispersed by a large amount of circulating material after entering the circulating reactor, thus improving the mass and heat transfer efficiency of the reaction. This makes the preparation method of this invention safer, more efficient, simple to operate, and has low equipment investment costs. The preparation method of this invention allows benzene series compounds, fuming nitric acid, and sulfuric acid to continuously enter the circulating reactor to carry out the nitration reaction, and the reaction liquid containing the nitration product of benzene series compounds is continuously collected from the outlet of the circulating reactor, realizing the continuous nitration of benzene series compounds. It is suitable for large-scale industrial continuous production.

[0034] Furthermore, the continuous preparation method for benzene series compounds provided by this invention allows the acid phase obtained after phase separation of the material flowing out of the circulating reactor or aging reactor to be directly or indirectly reused in the nitration reaction, realizing the comprehensive utilization of sulfuric acid, reducing the discharge of waste acid, and being more energy-efficient and environmentally friendly. Extracting and reusing the acid phase also allows for the recovery of organic matter in the acid phase, reducing product loss, and avoiding safety hazards caused by nitrates during acid phase treatment. Attached Figure Description

[0035] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0036] Figure 1 This is a schematic diagram of the process flow of the first embodiment of the present invention;

[0037] Figure 2 This is a schematic diagram of the process flow of the second embodiment of the present invention;

[0038] Figure 3 This is a schematic diagram of the process flow of the third embodiment of the present invention;

[0039] Figure 4 This is a schematic diagram of the process flow of the fourth embodiment of the present invention;

[0040] Figure 5This is a schematic diagram of the process flow of the fifth embodiment of the present invention;

[0041] Figure 6 This is a schematic diagram of the process flow of the sixth embodiment of the present invention;

[0042] Figure 7 This is a schematic diagram of the process flow for the seventh embodiment of the present invention;

[0043] Figure 8 This is a schematic diagram of the process flow of the eighth embodiment of the present invention;

[0044] Figure 9 This is a schematic diagram of the process flow for Comparative Example 1 of the present invention.

[0045] The reference numerals in the attached figures are explained as follows:

[0046] 1. Circulating reactor; 1-1. First-stage tubular reactor; 1-2. Second-stage tubular reactor; 1-3. Circulating pump; 2. Aging reactor; 3. Feed distributor. Detailed Implementation

[0047] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0048] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0049] To address the problems existing in the aforementioned related technologies, according to a first aspect of the present invention, a continuous nitration method for benzene compounds is provided, wherein a circulating reactor is used for the nitration reaction, the circulating reactor comprising a first-stage tubular reactor, a second-stage tubular reactor, and a circulating pump that are interconnected, and the inlet and outlet of the circulating reactor are located at arbitrary positions in the circulating reactor.

[0050] Benzene compounds, fuming nitric acid, and sulfuric acid are introduced into the circulating reactor. Under the action of the circulating pump, the reactants circulate between the first-stage tubular reactor and the second-stage tubular reactor, where a nitration reaction occurs. The ratio of the circulating flow rate to the total feed flow rate is 30 to 500:1. The reaction liquid containing the nitration product of benzene compounds is continuously collected from the outlet of the circulating reactor.

[0051] The continuous preparation method of benzene series compounds provided by this invention uses a circulating reactor for nitration. The circulating reactor includes a first-stage tubular reactor, a second-stage tubular reactor, and a circulating pump that are interconnected. Benzene series compounds, fuming nitric acid, and sulfuric acid are continuously introduced into the circulating reactor. Under the action of the circulating pump, they circulate between the first-stage and second-stage tubular reactors to undergo nitration. The ratio of the circulating flow rate to the total feed flow rate is 30-500:1. Because the circulating flow rate is much greater than the total feed flow rate, the reactants can be rapidly dispersed by a large amount of circulating material after entering the circulating reactor, thus improving the mass and heat transfer efficiency of the reaction. This makes the preparation method of this invention safer, more efficient, simple to operate, and has low equipment investment costs. The preparation method of this invention allows benzene series compounds, fuming nitric acid, and sulfuric acid to continuously enter the circulating reactor to undergo nitration, and the reaction liquid containing the nitration product of benzene series compounds is continuously collected from the outlet of the circulating reactor, realizing continuous nitration of benzene series compounds. This method is suitable for large-scale industrial continuous production.

[0052] Understandably, compared to other types of reactors, tubular reactors can achieve high-throughput reactions while ensuring high mass and heat transfer efficiency, making them more suitable for this invention. In this invention, the term "total feed flow rate" refers to the sum of the feed flow rates of benzene series compounds, fuming nitric acid, and sulfuric acid.

[0053] With a constant liquid holding volume in the circulating reactor, a slower feed flow rate results in a longer reaction time and lower production efficiency; conversely, a faster feed flow rate leads to a shorter reaction time and lower raw material conversion rate. If the circulation flow rate is too slow, the heat generated during the reaction cannot be removed in time, causing the temperature of the reaction system to rise, increasing byproducts and posing safety hazards. Conversely, a faster circulation flow rate results in greater flow resistance, causing the circulating pump to overheat and reducing its lifespan. Therefore, in this invention, the ratio of the circulating flow rate to the total feed flow rate needs to be controlled at 30–500:1, preferably 50–300:1, and more preferably 100–250:1.

[0054] In the nitration reaction of this invention, the more sulfuric acid and nitric acid are used, the faster the nitration reaction rate, but the more likely it is to generate polynitro compounds as byproducts. Therefore, this invention controls the molar ratio of benzene series compounds to fuming nitric acid and sulfuric acid in the circulating reactor to be 1:1.01 to 1.1:1 to 3. As a preferred embodiment, the molar ratio of benzene series compounds to fuming nitric acid and sulfuric acid is 1:1.02 to 1.07:1.5 to 2.5.

[0055] The appropriate concentration of sulfuric acid and reaction temperature are selected based on the nature and number of substituents in the benzene series compounds. The higher the concentration of sulfuric acid and the higher the reaction temperature, the more difficult the reaction process is to control and the easier it is to generate polynitration products. Conversely, the lower the concentration of sulfuric acid and the lower the reaction temperature, the slower the reaction rate and the lower the production efficiency. Therefore, in order to balance the reaction rate and the yield of mononitration products, the preferred mass concentration of sulfuric acid in this invention is 70% to 98%, and the nitration reaction temperature is -10℃ to 100℃.

[0056] In this invention, the reaction time is defined as the ratio of the liquid holding volume of the circulating reactor to the total feed flow rate of benzene series compounds, nitric acid, and sulfuric acid. The reaction time is related to factors such as the type and number of substituents in the benzene series compounds, the reaction temperature, and the concentration of sulfuric acid. To ensure safe and efficient industrial production, this invention preferably uses a nitration reaction time of 5 min to 60 min, and more preferably 5 min to 40 min.

[0057] The preparation method provided by this invention is applicable to benzene series compounds with the following structural formulas: Wherein, n = 1 to 3, R represents H, halogen, or C1 to C4 alkyl groups, the halogen being fluorine, chlorine, bromine, or iodine, and the alkyl group being a straight-chain alkyl or branched alkyl. Exemplarily, the benzene series compounds in this invention include, but are not limited to, benzene, toluene, o-xylene, m-xylene, p-xylene, mesitylene, fluorobenzene, chlorobenzene, bromobenzene, o-dichlorobenzene, m-dichlorobenzene, p-dichlorobenzene, o-difluorobenzene, m-difluorobenzene, p-difluorobenzene, 1,2,3-trifluorobenzene, 2,6-dichlorofluorobenzene, 2,4-dichlorofluorobenzene, etc. Substituted nitrobenzene is a benzene ring with a nitro group formed after the nitration reaction of substituted benzene with nitric acid. Depending on the substituent on the benzene ring, substituted nitrobenzene can be a single compound or a mixture of multiple isomers.

[0058] In this invention, the circulating pump is selected from any one of axial flow pump, centrifugal pump, screw pump, gear pump, and diaphragm pump. The first-stage tubular reactor and the second-stage tubular reactor can be independently selected from any one of shell-and-tube heat exchanger, coiled tube heat exchanger, dynamic tubular reactor, or static tubular reactor. Preferably, a feed distributor is provided at the inlet end of both the first-stage tubular reactor and the second-stage tubular reactor for pre-distribution of materials.

[0059] In one alternative embodiment of the present invention, the outlet of the circulating reactor is located at the outlet end of the second-stage tubular reactor, and the inlet of the circulating reactor includes an inlet for benzene series compounds, an inlet for fuming nitric acid, and an inlet for sulfuric acid, wherein: the inlet for benzene series compounds is located at the inlet end of the first-stage tubular reactor or the inlet end of the circulating pump; the inlet for fuming nitric acid is located at any position in the circulating reactor; and the inlet for sulfuric acid is located at the inlet end of either the first-stage tubular reactor or the second-stage tubular reactor.

[0060] To further improve the conversion rate of raw materials and thus the yield of the target product, in this invention, as a preferred embodiment, an aging reactor is connected to the outlet of the circulating reactor. The aging reactor is selected from any one of a static tubular reactor, a dynamic tubular reactor, a circulating reactor, or an overflow reactor. The material (nitration reaction liquid) flowing out of the circulating reactor enters the aging reactor for aging. The aging temperature is 10°C to 30°C higher than the nitration reaction temperature, and the aging time is 5 min to 60 min.

[0061] In a preferred embodiment of the present invention, the material flowing out of the circulating reactor or aging reactor is separated into an acid phase and an organic phase. The organic phase is acidic due to the presence of a small amount of acid phase. Therefore, as a preferred embodiment, the present invention washes and separates the organic phase (for example, performing pre-washing separation, alkaline washing separation, and water washing separation in sequence) until the pH value of the organic phase reaches 7-8, thereby obtaining the mononitration product of benzene series compounds. Regarding the acid phase, at least a portion of the acid phase can be directly and / or extracted, concentrated, and then reused in the circulating reactor to continue the nitration reaction. This improves the utilization rate of sulfuric acid and reduces the amount of waste acid discharged. In specific embodiments of the present invention, a portion of the acid phase is directly reused and enters the circulating reactor separately from fresh sulfuric acid, or is mixed with fresh sulfuric acid before entering the circulating reactor to promote the nitration reaction; or, a portion or all of the acid phase is extracted, concentrated, and then reused; or, a portion of the acid phase is extracted, concentrated, and then enters the circulating reactor, while the remaining portion of the acid phase enters the circulating reactor directly; or, a portion of the acid phase is extracted, concentrated, mixed with the remaining portion of the acid phase, and then enters the circulating reactor to promote the nitration reaction.

[0062] It is understood that, in this invention, "the material flowing out of the circulating reactor" refers to the reaction liquid containing the mononitration product of benzene series compounds taken from the outlet of the circulating reactor; "the material flowing out of the aging reactor" refers to the material after aging treatment of the reaction liquid containing the mononitration product of benzene series compounds taken from the outlet of the circulating reactor.

[0063] To improve the utilization rate of benzene compounds, recover organic matter in the acid phase, and avoid coking of organic matter entrained in the acid phase during the concentration process, thereby causing safety accidents, as a preferred solution, at least a portion of the acid phase is extracted with benzene compounds from the reaction raw materials to obtain extracted benzene compounds and recovered dilute acid. At least a portion of the recovered dilute acid is concentrated to obtain recovered concentrated acid, and the recovered concentrated acid and extracted benzene compounds are sent to the circulating reactor.

[0064] In one alternative embodiment of the present invention, the acid phase obtained from the phase separation step or the recovered dilute acid obtained from the extraction step enters the circulating reactor from the inlet end of the first-stage tubular reactor.

[0065] In one alternative embodiment of the present invention, the recovered sulfuric acid or the recovered concentrated acid obtained from the concentration step enters the circulating reactor from the inlet of the second-stage tubular reactor. The recovered sulfuric acid is a mixture of at least a portion of the recovered concentrated acid obtained from the concentration step and at least a portion of the acid phase obtained from the phase separation step or at least a portion of the recovered dilute acid obtained from the extraction step. The recovered concentrated acid obtained after concentration, or the recovered sulfuric acid formed by mixing the recovered concentrated acid with the acid phase or the recovered dilute acid, enters the circulating reactor from the inlet of the second-stage tubular reactor. Benzene compounds enter the circulating reactor from the inlet of the first-stage reactor. This staggered feeding of benzene compounds and concentrated acid avoids direct contact between benzene compounds and concentrated acid, which could accelerate the nitration reaction and cause localized overheating, leading to safety issues and increased byproduct substitution of dinitrobenzene. It also ensures a continuous and rapid nitration reaction, improving reaction efficiency.

[0066] Because water is generated during the nitration reaction of benzene compounds with nitric acid, the acid concentration decreases. Preferably, the acid phase treated by the extraction step accounts for 13% to 100% of the total acid phase volume, and the mass concentration of the recovered concentrated acid is 70% to 98%.

[0067] The continuous preparation method for benzene series compounds provided by this invention allows the acid phase obtained after phase separation of the material flowing out of a circulating reactor or aging reactor to be directly or indirectly reused in the nitration reaction. This achieves comprehensive utilization of sulfuric acid, reduces waste acid emissions, and is more energy-efficient and environmentally friendly. Extracting and reusing the acid phase also allows for the recovery of organic matter from the acid phase, reducing product loss and avoiding safety hazards caused by nitrates during acid phase treatment.

[0068] The present invention will be further described in detail below with reference to specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed by the present invention. It is understood that the concentrations of fuming nitric acid and sulfuric acid in the embodiments of the present invention refer to mass concentrations, and v% represents volume percentages.

[0069] Example 1

[0070] The circulating reactor in this embodiment includes two-stage tubular reactors connected in series with circulating pump 1-3. The outlet of the first-stage tubular reactor 1-1 is connected to the inlet of the second-stage tubular reactor 1-2. The outlet of the second-stage tubular reactor 1-2 is connected to the inlet of circulating pump 1-3. The outlet of circulating pump 1-3 is connected to the inlet of the first-stage tubular reactor 1-1. The feed inlets for benzene and nitric acid are located at the inlet end of the first-stage tubular reactor 1-1. The inlet for sulfuric acid is located at the inlet end of the second-stage tubular reactor 1-2. The outlet of the circulating reactor is located at the outlet end of the first-stage tubular reactor 1-1.

[0071] like Figure 1As shown, toluene and 98% fuming nitric acid enter the circulating reactor from the inlet of the first-stage tubular reactor at flow rates of 10.64 mL / min and 4.5 mL / min, respectively, to undergo nitration. 75% sulfuric acid enters the circulating reactor from the inlet of the second-stage tubular reactor at a flow rate of 15.2 mL / min to promote the nitration reaction. The molar ratio of toluene to nitric acid and sulfuric acid is 1:1.05:2. The circulation flow rate is controlled at 2.43 L / min using a centrifugal pump, the reaction temperature is controlled at 25℃, and the reaction time is 35 min. A nitration reaction solution containing o-nitrotoluene and p-nitrotoluene is obtained from the outlet of the circulating reactor, with a toluene conversion rate of 99.6%.

[0072] Example 2

[0073] In this embodiment, the circulating reactor 1 includes two-stage tubular reactors connected in series with the circulating pump 1-3. The outlet of the first-stage tubular reactor 1-1 is connected to the inlet of the second-stage tubular reactor 1-2, the outlet of the second-stage tubular reactor 1-2 is connected to the inlet of the circulating pump 1-3, and the outlet of the circulating pump 1-3 is connected to the inlet of the first-stage tubular reactor 1-1. The feed inlet for the substituted benzene is located at the inlet end of the circulating pump 1-3, the inlets for nitric acid and sulfuric acid are located at the inlet end of the first-stage tubular reactor 1-1, and the outlet of the circulating reactor is located at the outlet end of the second-stage reactor 1-2.

[0074] like Figure 2 As shown, m-xylene enters the circulating reactor from the inlet of the circulating pump at a flow rate of 12.35 mL / min. 98% fuming nitric acid and 73% sulfuric acid enter the circulating reactor from the inlet of the first-stage tubular reactor at flow rates of 4.4 mL / min and 8.2 mL / min, respectively, to undergo a nitration reaction with m-xylene. The molar ratio of m-xylene to nitric acid and sulfuric acid is 1:1.03:1. The circulation flow rate is controlled at 1.25 L / min by a centrifugal pump, the reaction temperature is controlled at 25 °C, and the reaction time is 40 min. A nitration reaction solution containing 2,6-dimethylnitrobenzene and 2,4-dimethylnitrobenzene is obtained from the outlet of the circulating reactor. The conversion rate of m-xylene is 99.7%.

[0075] The nitration reaction solution was subjected to phase separation at 25°C to obtain an acid phase and an organic phase. 61% of the acid phase was mixed with fresh 93% sulfuric acid to prepare 73% sulfuric acid, which was then reused in the nitration reaction. The organic phase was successively separated by pre-washing, alkali washing, and water washing to obtain substituted nitrobenzene (a mononitration product containing 2,6-dimethylnitrobenzene and 2,4-dimethylnitrobenzene), with a molar yield of 99.2%.

[0076] Example 3

[0077] The circulating reactor in this embodiment includes two-stage tubular reactors connected in series with circulating pump 1-3. The outlet of the first-stage tubular reactor 1-1 is connected to the inlet of the second-stage tubular reactor 1-2, the outlet of the second-stage tubular reactor 1-2 is connected to the inlet of circulating pump 1-3, and the outlet of circulating pump 1-3 is connected to the inlet of the first-stage tubular reactor 1-1. The inlets for substituted benzene, nitric acid, and sulfuric acid are all located at the inlet end of the first-stage tubular reactor 1-1, and the outlet of the circulating reactor is located at the outlet end of the first-stage tubular reactor 1-1.

[0078] like Figure 3 As shown, o-dichlorobenzene, 98% fuming nitric acid, and 98% sulfuric acid entered the circulating reactor from the inlet of the first-stage tubular reactor at flow rates of 12.2 mL / min, 4.7 mL / min, and 16.4 mL / min, respectively, to undergo nitration. The molar ratio of o-dichlorobenzene to nitric acid and sulfuric acid was 1:1.1:3. The circulation flow rate was controlled at 16.68 L / min by a centrifugal pump, the reaction temperature was controlled at 100℃, and the reaction time was 5 min. A nitration reaction solution containing 3,4-dichloronitrobenzene and 2,3-dichloronitrobenzene was obtained from the outlet of the circulating reactor, and the conversion rate of o-dichlorobenzene was 99.9%.

[0079] The nitration reaction solution was subjected to phase separation at 80°C to obtain an acid phase and an organic phase. All the acid phase was extracted with o-dichlorobenzene to obtain extracted o-dichlorobenzene and dilute acid. The extracted o-dichlorobenzene was reused in the nitration reaction. All the dilute acid was concentrated to obtain 98% recovered concentrated sulfuric acid, which was reused in the nitration reaction. The organic phase was successively separated by pre-washing, alkali washing, and water washing to obtain substituted nitrobenzene (containing the mononitration products of 3,4-dichloronitrobenzene and 2,3-dichloronitrobenzene) with a molar yield of 99.3%.

[0080] Example 4

[0081] The reaction apparatus in this embodiment includes a circulating reactor and an aging reactor 2 connected in series. The circulating reactor includes two-stage tubular reactors connected in series with a circulating pump 1-3. The outlet of the first-stage tubular reactor 1-1 is connected to the inlet of the circulating pump 1-3, the outlet of the circulating pump 1-3 is connected to the inlet of the second-stage tubular reactor 1-2, and the outlet of the second-stage tubular reactor 1-2 is connected to the inlet of the first-stage tubular reactor 1-1. The inlets for substituted benzene and nitric acid are both located at the inlet end of the first-stage tubular reactor 1-1, and the inlet for recovering concentrated sulfuric acid is located at the inlet end of the second-stage tubular reactor 1-2. The outlet of the circulating reactor is located at the outlet end of the second-stage tubular reactor 1-2, and the outlet of the circulating reactor is connected to the inlet of the aging reactor 2.

[0082] like Figure 4As shown, o-xylene and 98% fuming nitric acid enter the circulating reactor from the inlet of the first-stage tubular reactor at flow rates of 12.06 mL / min and 4.36 mL / min, respectively, to undergo nitration. 70% (w / w) recovered concentrated sulfuric acid enters the circulating reactor from the inlet of the second-stage tubular reactor at a flow rate of 13.1 mL / min to promote the nitration reaction. The molar ratio of o-xylene, nitric acid, and recovered concentrated sulfuric acid is 1:1.02:1.5. The circulation flow rate in the circulating reactor is controlled at 0.89 L / min using a centrifugal pump, the reaction temperature is controlled at -10℃, and the reaction time is 60 min. The reaction solution flowing out of the circulating reactor enters the aging reactor, where the aging temperature is controlled at 0℃ and the aging time is 60 min. A nitration reaction solution containing 3-nitro-o-xylene and 4-nitro-o-xylene is obtained from the outlet of the aging reactor, with an o-xylene conversion rate of 99.6%.

[0083] The nitration reaction solution was subjected to phase separation at 35°C to obtain an acid phase and an organic phase. All the acid phase was extracted with o-xylene to obtain extracted o-xylene and dilute acid. The extracted o-xylene was reused in the nitration reaction. All the dilute acid was concentrated to obtain 70% concentrated sulfuric acid, which was reused in the nitration reaction. The organic phase was successively separated by pre-washing, alkali washing, and water washing to obtain substituted nitrobenzene (a mononitration product containing 3-nitro-o-xylene and 4-nitro-o-xylene), with a molar yield of 99.2%.

[0084] Example 5

[0085] The reaction apparatus in this embodiment includes a circulating reactor and an aging reactor 2 connected in series. The circulating reactor includes two-stage tubular reactors connected in series with a circulating pump 1-3. The outlet of the first-stage tubular reactor 1-1 is connected to the inlet of the circulating pump 1-3, and the outlet of the circulating pump 1-3 is connected to the inlet of the second-stage tubular reactor 1-2. A feed distributor is provided at the inlet end of the first-stage tubular reactor 1-1. The outlet of the second-stage tubular reactor 1-2 is connected to the inlet of the feed distributor at the inlet end of the first-stage tubular reactor 1-1. The inlets for benzene and nitric acid, as well as the recovered acid phase, are all located on the feed distributor at the inlet end of the first-stage tubular reactor. The inlet for the recovered concentrated sulfuric acid is located at the inlet end of the second-stage tubular reactor. The outlet of the circulating reactor is located at the outlet end of the second-stage reactor and is connected to the inlet of the aging reactor.

[0086] like Figure 5As shown, benzene, 98% fuming nitric acid, and the recovered acid phase enter the circulating reactor from the inlet of the first-stage tubular reactor at flow rates of 8.7 mL / min, 4.3 mL / min, and 24.3 mL / min, respectively, to undergo nitration. 98% recovered concentrated sulfuric acid enters the circulating reactor from the inlet of the second-stage tubular reactor at a flow rate of 2.44 mL / min to promote the nitration reaction. The molar ratio of benzene, nitric acid, and sulfuric acid (total amount of recovered acid phase and recovered concentrated sulfuric acid) is 1:1.01:3. In the circulating reactor, the circulation flow rate is controlled at 3.73 L / min using a centrifugal pump, the reaction temperature is controlled at 20℃, and the reaction time is 20 min. The reaction solution flowing out of the circulating reactor enters the aging reactor, where the aging temperature is controlled at 35℃ and the aging time is 20 min. A nitration reaction solution containing nitrobenzene is obtained from the outlet of the aging reactor, with a benzene conversion rate of 99.8%.

[0087] After phase separation at 20°C, the nitration reaction solution yields an acid phase and an organic phase. 13% of the acid phase is extracted with benzene to obtain extracted benzene and dilute acid. The extracted benzene is recycled back to the nitration reaction. All the dilute acid is concentrated to obtain 98% recovered concentrated sulfuric acid, which enters the circulating reactor from the inlet of the second-stage tubular reactor and is recycled back to the nitration reaction. The remaining 87% of the acid phase is recycled as acid phase and enters the circulating reactor from the feed distributor at the inlet of the first-stage tubular reactor and is recycled back to the nitration reaction. The organic phase is sequentially pre-washed, alkali-washed, and water-washed to obtain nitrobenzene with a molar yield of 99.5%.

[0088] Example 6

[0089] The reaction apparatus in this embodiment includes a circulating reactor and an aging reactor 2 connected in series. The circulating reactor includes two-stage tubular reactors connected in series with a circulating pump 1-3. The outlet of the first-stage tubular reactor 1-1 is connected to the inlet of the circulating pump 1-3, the outlet of the circulating pump 1-3 is connected to the inlet of the second-stage tubular reactor 1-2, and the outlet of the second-stage tubular reactor 1-2 is connected to the inlet of the first-stage tubular reactor 1-1. The inlets for substituted benzene and recovered dilute acid are both located at the inlet end of the first-stage tubular reactor, and the inlets for nitric acid and recovered concentrated sulfuric acid are located at the inlet end of the second-stage tubular reactor. The outlet of the circulating reactor is located at the outlet end of the second-stage reactor and is connected to the inlet of the aging reactor 2.

[0090] like Figure 6As shown, toluene and recovered dilute acid enter the circulating reactor from the inlet of the first-stage tubular reactor at flow rates of 10.6 mL / min and 6.4 mL / min, respectively. 98% fuming nitric acid and 80% recovered concentrated sulfuric acid enter the circulating reactor from the inlet of the second-stage tubular reactor at flow rates of 4.5 mL / min and 7.8 mL / min, respectively. The molar ratio of toluene, nitric acid, and sulfuric acid (total amount of recovered dilute acid and recovered concentrated sulfuric acid) is 1:1.05:2. In the circulating reactor, the circulation flow rate is controlled at 4.4 L / min using a centrifugal pump, the reaction temperature is controlled at 30℃, and the reaction time is 10 min. The reaction solution flowing out of the circulating reactor enters the aging reactor, where the aging temperature is controlled at 50℃ and the aging time is 5 min. A nitration reaction solution containing o-nitrotoluene and p-nitrotoluene is obtained from the outlet of the aging reactor, with a toluene conversion rate of 99.8%.

[0091] The nitration reaction solution was subjected to phase separation at 50°C to obtain an acid phase and an organic phase. All the acid phase was extracted with toluene to obtain extractable toluene and dilute acid. The extractable toluene was recycled back to the nitration reaction. 60% of the dilute acid was concentrated to obtain 80% concentrated sulfuric acid, which was then fed into the circulating reactor from the inlet of the second-stage tubular reactor and recycled back to the nitration reaction. The remaining 40% of the dilute acid was recycled back to the circulating reactor from the inlet of the first-stage tubular reactor and recycled back to the nitration reaction. The organic phase was successively subjected to pre-washing separation, alkali washing separation, and water washing separation to obtain substituted nitrobenzene (a mononitration product containing o-nitrotoluene and p-nitrotoluene) with a molar yield of 99.6%.

[0092] Example 7

[0093] The reaction apparatus in this embodiment includes a circulating reactor and an aging reactor 2 connected in series. The circulating reactor includes two-stage tubular reactors connected in series with a circulating pump 1-3. The outlet of the first-stage tubular reactor 1-1 is connected to the inlet of the circulating pump 1-3, the outlet of the circulating pump 1-3 is connected to the inlet of the second-stage tubular reactor 1-2, and the outlet of the second-stage tubular reactor 1-2 is connected to the inlet of the first-stage tubular reactor 1-1. The inlet for substituted benzene is located at the inlet end of the first-stage tubular reactor, and the inlets for nitric acid and recovered sulfuric acid are located at the inlet end of the second-stage tubular reactor. The outlet of the circulating reactor is located at the outlet end of the second-stage tubular reactor and is connected to the inlet of the aging reactor.

[0094] like Figure 7As shown, chlorobenzene enters the circulating reactor from the inlet of the first-stage tubular reactor at a flow rate of 10.2 mL / min. 98% fuming nitric acid and 85% (w / w) recovered sulfuric acid enter the circulating reactor from the inlet of the second-stage tubular reactor at flow rates of 4.5 mL / min and 14.3 mL / min, respectively, to react with the chlorobenzene in a nitration reaction. The molar ratio of chlorobenzene, nitric acid, and recovered sulfuric acid is 1:1.06:2.2. In the circulating reactor, the circulation flow rate is controlled at 7.28 L / min using a centrifugal pump, the reaction temperature is controlled at 50°C, and the reaction time is 40 min. The reaction solution flowing out of the circulating reactor enters the aging reactor, where the aging temperature is controlled at 80°C and the aging time is 30 min. A nitration reaction solution containing o-chloronitrobenzene and p-chloronitrobenzene is obtained from the outlet of the aging reactor, with a chlorobenzene conversion rate of 99.8%.

[0095] After phase separation at 85°C, the nitration reaction solution yields an acid phase and an organic phase. 59% of the acid phase is extracted with chlorobenzene to obtain extractable chlorobenzene and dilute acid. The extractable chlorobenzene is reused in the nitration reaction. All the dilute acid is concentrated to obtain 90% concentrated sulfuric acid. The 90% concentrated sulfuric acid is mixed with the remaining 41% of the acid phase to obtain 85% concentrated sulfuric acid, which enters the circulating reactor from the inlet of the second-stage tubular reactor and is reused in the nitration reaction. The organic phase is sequentially pre-washed, alkali-washed, and water-washed to obtain substituted nitrobenzene (containing mononitration products of o-chloronitrobenzene and p-chloronitrobenzene) with a molar yield of 99.6%.

[0096] Example 8

[0097] The reaction apparatus in this embodiment includes a circulating reactor and an aging reactor connected in series. The circulating reactor includes two-stage tubular reactors connected in series with circulating pump 1-3. The outlet of the first-stage tubular reactor 1-1 is connected to the inlet of circulating pump 1-3, the outlet of circulating pump 1-3 is connected to the inlet of the second-stage tubular reactor 1-2, and the outlet of the second-stage tubular reactor 1-2 is connected to the inlet of the first-stage tubular reactor 1-1. The inlet for substituted benzene is located at the inlet end of the first-stage tubular reactor, and the inlets for nitric acid and recovered sulfuric acid are located at the inlet end of the second-stage tubular reactor. The outlet of the circulating reactor is located at the outlet end of the second-stage tubular reactor and is connected to the inlet of the aging reactor.

[0098] like Figure 8As shown, m-dichlorobenzene enters the circulating reactor from the inlet of the first-stage tubular reactor at a flow rate of 12.3 mL / min. 98% fuming nitric acid and 90% mass-concentration recovered sulfuric acid enter the circulating reactor from the inlet of the second-stage tubular reactor at flow rates of 4.6 mL / min and 15.1 mL / min, respectively, to react with chlorobenzene in a nitration reaction. The molar ratio of m-dichlorobenzene, nitric acid, and recovered sulfuric acid is 1:1.07:2.5. In the circulating reactor, the circulation flow rate is controlled at 9.56 L / min using a centrifugal pump, the reaction temperature is controlled at 80℃, and the reaction time is 30 min. The reaction solution flowing out of the circulating reactor enters the aging reactor, where the aging temperature is controlled at 90℃ and the aging time is 10 min. A nitration reaction solution containing 2,4-dichloronitrobenzene and 2,6-dichloronitrobenzene is obtained from the outlet of the aging reactor, with a conversion rate of 99.9% for m-dichlorobenzene.

[0099] The nitration reaction solution was subjected to phase separation at 80°C to obtain an acid phase and an organic phase. All the acid phase was extracted with m-dichlorobenzene to obtain extracted m-dichlorobenzene and dilute acid. The extracted m-dichlorobenzene was recycled to the nitration reaction. 70 vol% of the dilute acid was concentrated to obtain 93% concentrated sulfuric acid. The 93% concentrated sulfuric acid was mixed with the remaining 30 vol% of the acid phase to obtain 90% concentrated sulfuric acid, which was then fed into the circulating reactor from the inlet of the second-stage tubular reactor and recycled to the nitration reaction. The organic phase was successively subjected to pre-washing separation, alkali washing separation, and water washing separation to obtain substituted nitrobenzene (a mononitration product containing 2,4-dichloronitrobenzene and 2,6-dichloronitrobenzene) with a molar yield of 99.6%.

[0100] Comparative Example 1

[0101] The reaction apparatus in this comparative example includes a feed distributor 3, a two-stage tubular reactor, and an aging reactor 2 connected in series. The outlet of the feed distributor 3 is connected to the inlet of the first-stage tubular reactor 1-1, the outlet of the first-stage tubular reactor 1-1 is connected to the inlet of the second-stage tubular reactor 1-2, and the outlet of the second-stage tubular reactor 1-2 is connected to the inlet of the aging reactor 2. The inlets for benzene, nitric acid, and the recovered acid phase are located at the inlet end of the first-stage tubular reactor, and the inlet for the recovered concentrated sulfuric acid is located at the inlet end of the second-stage tubular reactor.

[0102] like Figure 9As shown, benzene, 98% fuming nitric acid, and the recovered acid phase are introduced into the first-stage tubular reactor at flow rates of 8.7 mL / min, 4.3 mL / min, and 24.3 mL / min, respectively, to undergo nitration. 98% recovered concentrated sulfuric acid is introduced into the second-stage tubular reactor at a flow rate of 2.44 mL / min to promote the nitration reaction. The molar ratio of benzene, nitric acid, and sulfuric acid (total amount of recovered acid phase and recovered concentrated sulfuric acid) is 1:1.01:3. The reaction temperature is controlled at 20℃, and the reaction time is 20 min. The reaction solution flowing out of the second-stage tubular reactor enters an aging reactor, where the aging temperature is controlled at 35℃ and the aging time is 20 min. A nitration reaction solution containing nitrobenzene is obtained from the outlet of the aging reactor, with a benzene conversion rate of 39.8%.

[0103] After phase separation at 20°C, the nitration reaction solution yields an acid phase and an organic phase. 13% of the acid phase is extracted with benzene to obtain extracted benzene and dilute acid. The extracted benzene is recycled back to the nitration reaction. All the dilute acid is concentrated to obtain 98% recovered concentrated sulfuric acid, which is recycled back to the nitration reaction from the inlet of the second-stage tubular reactor. The remaining 87% of the acid phase is recycled back to the nitration reaction from the inlet of the first-stage tubular reactor. The organic phase is sequentially pre-washed, alkali-washed, and water-washed to obtain a mixture of nitrobenzene and benzene. After distillation, the molar yield of nitrobenzene is 38.5%.

[0104] Therefore, it is evident that the mass transfer efficiency of a conventional two-stage series reactor is low. Under the same reaction time and temperature conditions as a circulating reactor, the conversion rate of the raw material is reduced. Both the raw material and product remain in the organic phase in the reaction liquid exiting the reactor, requiring distillation to obtain the nitration product. Reducing the feed flow rate in this comparative example and extending the reaction time by four times would increase the conversion rate of benzene to 98%, but this would obviously reduce the reaction efficiency. Replacing the tubular reactor with a microchannel reactor can achieve a benzene conversion rate of 98% under the same reaction time and temperature, with a significantly shortened reaction time, even to less than one minute. However, due to the small liquid holdup of the microchannel reactor, high-throughput industrial production requires multiple microchannel reactors connected in parallel. In Example 5 of this invention, a throughput of 10,000 tons is achieved with a total liquid holdup of less than 1 m³ in the circulating reactor. 3 Inexpensive and readily available, microchannel reactors, when used for a residence time of 1 minute, can achieve a total liquid holding volume of nearly 25L. However, due to the specialized manufacturing process of microchannel reactors, the liquid holding volume of a single unit is relatively small, typically 2-3L. At least eight industrial-grade microchannel reactors with a single liquid holding volume of 3L would be required, while a liquid holding volume of 1m³ would be significantly higher. 3The value of the circulating reactor is lower than that of a single industrial microchannel reactor with a liquid holdup of 3L. Therefore, achieving the same throughput using a microchannel reactor results in higher equipment costs and makes it unsuitable for large-scale industrial production. Thus, compared to existing technologies, the method of this invention is applicable to large-scale industrial production with lower equipment investment costs.

[0105] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A continuous nitration method for benzene compounds, characterized in that, The nitration reaction is carried out using a circulating reactor, which includes a first-stage tubular reactor, a second-stage tubular reactor, and a circulating pump that are interconnected. The outlet of the circulating reactor is located at any position in the circulating reactor. The feed inlets of the circulating reactor include an inlet for benzene series compounds, an inlet for fuming nitric acid, and an inlet for sulfuric acid, wherein: the inlet for benzene series compounds is located at the inlet end of the first-stage tubular reactor or the inlet end of the circulating pump; the inlet for sulfuric acid is located at the inlet end of the second-stage tubular reactor; and the inlet for fuming nitric acid is located at any position in the circulating reactor. Benzene compounds, fuming nitric acid, and sulfuric acid are continuously fed into the circulating reactor. Under the action of the circulating pump, the reactants circulate between the first-stage tubular reactor and the second-stage tubular reactor, where a nitration reaction occurs. The ratio of the circulating flow rate to the total feed flow rate is 30-500:

1. The reaction liquid containing the nitration product of benzene compounds is continuously collected from the outlet of the circulating reactor. In the circulating reactor, the molar ratio of benzene series compounds to fuming nitric acid and sulfuric acid is 1:1.01~1.1:1~3; The sulfuric acid has a mass concentration of 70%-98%; The material flowing out of the circulating reactor or the aging reactor is separated into an acid phase and an organic phase. The organic phase is washed and separated to obtain the mononitration product of benzene series compounds. At least a portion of the acid phase is directly and / or extracted, concentrated, and then reused in the circulating reactor. After extraction, extracted benzene series compounds and recovered dilute acid are obtained. At least a portion of the recovered dilute acid is concentrated to obtain recovered concentrated acid. The recovered concentrated acid and the extracted benzene series compounds are fed into the circulating reactor. The recovered sulfuric acid or the recovered concentrated acid obtained from the concentration step enters the circulating reactor from the inlet end of the second-stage tubular reactor. The recovered sulfuric acid is a mixture of at least a portion of the recovered concentrated acid obtained from the concentration step and at least a portion of the acid phase obtained from the phase separation step or at least a portion of the recovered dilute acid obtained from the extraction step.

2. The continuous nitration method for benzene compounds according to claim 1, characterized in that, The ratio of the circulating flow rate of the reactants to the total feed flow rate is 50~300:1, preferably 100~250:1; And / or, in the circulating reactor, the molar ratio of benzene series compounds to fuming nitric acid and sulfuric acid is 1:1.02~1.07:1.5~2.

5.

3. The continuous nitration method for benzene compounds according to claim 1, characterized in that, The nitration reaction is carried out at a temperature of -10℃ to 100℃. And / or, the nitration reaction time is 5 min to 60 min, preferably 5 min to 40 min.

4. The continuous nitration method for benzene compounds according to claim 1, characterized in that, Both the first-stage tubular reactor and the second-stage tubular reactor are equipped with feed distributors at their inlet ends. And / or, the first-stage tubular reactor and the second-stage tubular reactor are selected from any one of shell-and-tube heat exchangers, coiled-tube heat exchangers, dynamic tubular reactors, and static tubular reactors, respectively; And / or, the circulating pump is selected from any one of axial flow pumps, centrifugal pumps, screw pumps, gear pumps, and diaphragm pumps; And / or, the benzene series compound is benzene or a substituted benzene having 1 to 3 identical or different substituents, wherein the substituents are selected from halogens or C1-C4 alkyl groups, wherein the halogen is fluorine, chlorine, bromine or iodine, and the alkyl group is a straight-chain alkyl or a branched-chain alkyl.

5. The continuous nitration method for benzene compounds according to claim 1, characterized in that, The outlet of the circulating reactor is located at the outlet end of the second-stage tubular reactor.

6. The continuous nitration method for benzene compounds according to claim 5, characterized in that, The outlet end of the second-stage tubular reactor is connected to an aging reactor to age the material flowing out of the circulating reactor. Preferably, the aging temperature is 10°C to 30°C higher than the nitration reaction temperature, and the aging time is 5 min to 60 min. Preferably, the aging reactor is selected from any one of a static tubular reactor, a dynamic tubular reactor, a circulating reactor, and an overflow reactor.

7. The continuous nitration method for benzene compounds according to claim 6, characterized in that, The extraction step uses a benzene series extractant.

8. The continuous nitration method for benzene compounds according to claim 7, characterized in that, The acid phase obtained from the phase separation step or the recovered dilute acid obtained from the extraction step enters the circulating reactor from the inlet end of the first-stage tubular reactor.

9. The continuous nitration method for benzene compounds according to claim 8, characterized in that, The acid phase processed in the extraction step accounts for more than 13% of the total acid phase volume; And / or, the mass concentration of the recovered concentrated acid is 70%-98%.

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