CN112939781B - Adiabatic process for continuous operation for the preparation of nitrobenzene by nitration of benzene - Google Patents
Adiabatic process for continuous operation for the preparation of nitrobenzene by nitration of benzene Download PDFInfo
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- CN112939781B CN112939781B CN201911268204.2A CN201911268204A CN112939781B CN 112939781 B CN112939781 B CN 112939781B CN 201911268204 A CN201911268204 A CN 201911268204A CN 112939781 B CN112939781 B CN 112939781B
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- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C201/00—Preparation of esters of nitric or nitrous acid or of compounds containing nitro or nitroso groups bound to a carbon skeleton
- C07C201/06—Preparation of nitro compounds
- C07C201/08—Preparation of nitro compounds by substitution of hydrogen atoms by nitro groups
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- C01B17/00—Sulfur; Compounds thereof
- C01B17/69—Sulfur trioxide; Sulfuric acid
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Abstract
The invention relates to a continuously operated adiabatic process for the preparation of nitrobenzene by nitration of benzene. After the nitration is finished, the crude nitrobenzene is separated from the water phase, the obtained diluted sulfuric acid enters a sulfuric acid regenerator, a reducing agent is added into the sulfuric acid regenerator, the reducing agent can decompose nitrophenol derivatization black substances dissolved in the sulfuric acid, and meanwhile, the aromatic hydrocarbon and nitrous acid can be prevented from forming resinified products, so that the black substances are prevented from being generated in the nitration process. And the regenerated sulfuric acid enters a sulfuric acid flash evaporator to remove impurities, so that the concentrated sulfuric acid is recovered and recycled.
Description
Technical Field
The invention relates to a continuously operating adiabatic process for preparing nitrobenzene by the nitration of benzene, which can inhibit the formation of black substances during the preparation of nitrobenzene by the adiabatic nitration of benzene.
Background
Nitrobenzene is an important intermediate product of the chemical industry, which is required in particular for the production of anilines and thus also for the production of diisocyanates and polyisocyanates of the diphenylmethane series and polyurethanes based thereon.
The method is mainly characterized in that no technical measures for introducing heat into a reaction system or leading out heat are adopted, the released reaction heat is absorbed by the sulfuric acid, and the heat is utilized to carry out flash evaporation concentration on the sulfuric acid.
During the nitration reaction, an excess of benzene, preferably in a 2% to 20% excess, based on the molar amount of nitric acid, is added to carry out the reaction. After the end of the reaction, the reaction mixture, which is free of nitric acid, is conducted to a phase separation apparatus, in which two phases are formed, the first phase, referred to as crude nitrobenzene, consisting essentially of nitrobenzene, benzene and sulfuric acid dissolved in nitrobenzene and the amount of water, and the second phase, referred to as recycled sulfuric acid, consisting essentially of water, sulfuric acid and nitrobenzene dissolved in sulfuric acid. The recycled sulfuric acid separated in the phase separation unit is introduced into a flash evaporator unit, in which the sulfuric acid concentration is brought back to the pre-reaction concentration by applying a negative pressure and supplementing a small amount of heat.
In the actual running process of the nitration reaction, a black substance is found in a phase separation device of the crude nitrobenzene, a crude nitrobenzene cooler and adjacent pipelines, and the continuous running of the nitration process is interrupted and the nitration process is stopped for cleaning when the black substance is serious.
The document "discussing the extraction process of waste acid MNT with toluene" mentions that when the mixed acid has insufficient nitration capability and contains nitrous acid, the toluene will undergo resinification reaction to make the reaction solution black, and the formation of complex is prevented by adding nitric acid. In the patent CN105308018A, it is mentioned that by incorporating an oxidizing agent (nitric/nitrous acid or nitrosylsulfonic acid) in an amount of 10ppm to 5000ppm in the concentrated sulfuric acid at least one minute before the concentrated sulfuric acid is brought into contact with the fresh nitric acid, the amount of black material formed in the crude nitrobenzene heat exchanger and in the phase separation apparatus can be reduced, but the formation of black material cannot be completely avoided and the black material still accumulates in the system, based on the total mass of the concentrated sulfuric acid returned to the nitration. In addition, the solution proposed in the CN105308018A patent is to add nitric acid into a pipeline between the concentrated sulfuric acid storage tank or the flash evaporator and the sulfuric acid storage tank, which inevitably increases the content of nitric acid in the concentrated sulfuric acid storage tank, and the sulfuric acid contains organic matters such as benzene and nitrobenzene, which react violently in the storage tank under the catalytic action of sulfuric acid, thereby reducing the safety of nitrification.
In the related research process, it is unexpectedly found that the black substance is not only a resinated product in the aromatic hydrocarbon nitration process, but also a part of the black substance is generated by nitrophenol derivatization, the nitrophenol derivatization cannot be avoided by adding nitric acid into sulfuric acid to generate the black substance, and meanwhile, the black substance generated by the nitrophenol derivatization can be further promoted to generate the black substance by dissolving the black substance in the sulfuric acid.
In conclusion, the solution has no industrial application feasibility, can not thoroughly avoid the generation of black substances, and can still accumulate and block in a phase separator and a crude nitrobenzene heat exchanger to influence the stable operation of nitrification.
Disclosure of Invention
The invention is mainly used for solving the problem of black substance generation, avoiding shutdown and cleaning, and improving continuous, stable and safe operation of benzene adiabatic nitration. The inventor of the invention has conducted repeated studies and unexpectedly found that a reducing agent is added to sulfuric acid, and the reducing agent can decompose nitrophenol derivative black substances dissolved in the sulfuric acid and simultaneously prevent aromatic hydrocarbons and nitrous acid from forming resinated products, thereby avoiding the generation of black substances in the nitration process.
The invention provides an adiabatic process for the continuous operation of nitrobenzene production by nitration of benzene, wherein:
a) under adiabatic conditions, a nitric acid stream (a1) is reacted with sulfuric acid (a2) to form a mixed nitric-sulfuric acid, a benzene stream (a3) is reacted with nitric acid (a1) under sulfuric acid catalysis in a reactor, wherein a stoichiometric excess of benzene based on nitric acid (a1) is used; preferably, benzene is used in a stoichiometric excess of preferably 2.0% to 20%, particularly preferably 5.0% to 10%, of the theoretical value, based on nitric acid (a 1);
b) separating the reaction product obtained in step a) in a phase separation device into an aqueous phase (b1) comprising dilute sulfuric acid and an organic phase (b2) comprising nitrobenzene;
c) feeding the aqueous sulfuric acid-containing phase (b1) obtained in step b) to a sulfuric acid regenerator, feeding the aqueous sulfuric acid-containing phase (c1) from the sulfuric acid regenerator to a flash evaporator, removing water by flash evaporation to obtain a concentrated aqueous sulfuric acid-containing phase (d1) having a greater sulfuric acid concentration than the aqueous sulfuric acid-containing phase (b1), wherein the concentrated aqueous sulfuric acid-containing phase (d1) is returned to step a) and used as a component of (a2),
d) working up the organic phase (b2) obtained in step b) to pure nitrobenzene (e1),
wherein the content of the first and second substances,
the aqueous phase (b1) containing sulfuric acid obtained in the phase separator is fed first to a sulfuric acid regenerator and then to a flash evaporator, where a reducing agent (c2) is added. The nitro phenol derivative black substance dissolved in sulfuric acid is decomposed by a reducing agent, and meanwhile, the formation of resinified products by aromatic hydrocarbon and nitrous acid can be prevented, so that the generation of the black substance in the nitration process is avoided.
The reducing agent (c2) is one or more selected from thiosulfuric acid, dithionous acid, sulfurous acid, thiosulfate, dithionous acid and sulfite. Preferably, the concentration of the reducing agent (C2) is set to 100-2000ppm, the amount of the reducing agent added being based on the mass of the sulfuric acid-containing aqueous phase (b1) obtained in the phase separator. The residence time of the liquid in the sulfuric acid regenerator is 1-5min, preferably 2-3 min. The sulfuric acid regenerator comprises stirring equipment to ensure the uniform mixing of the liquid. The treatment in the sulfuric acid regenerator is carried out in a manner known in the art.
Further, the mass ratio of the sulfuric acid to the nitric acid is 23: 1-25: 1.
Further, the benzene-containing stream (a3) was reacted with sulfuric acid (a2) and nitric acid (a1) in a reactor at 95-135 ℃ for 50-60 s.
It has been found that the formation of black material can be completely avoided by feeding the aqueous phase containing sulfuric acid obtained in the phase separator into a sulfuric acid regenerator, adding a reducing agent, preferably thiosulfuric acid, into the sulfuric acid regenerator, and recycling the regenerated sulfuric acid to the nitration reaction via a sulfuric acid flash evaporator.
The steps of the present invention are explained in detail below. The various embodiments can be combined with one another in any desired manner, if the person skilled in the art does not explicitly derive any indication to the contrary from the context.
In principle, step a) can be carried out according to all adiabatic nitration processes known from the prior art. In order to carry out this step of the process according to the invention, preference is given to using a tubular reactor in which a plurality of dispersing elements are arranged dispersedly along the length of the reactor, said dispersing elements ensuring thorough mixing of the benzene, nitric acid and sulfuric acid. It is preferred here that nitric acid (a1) is initially introduced into the sulfuric acid pump inlet, and benzene (a3) is subsequently metered into sulfuric acid (a 2).
The phase separation in step b) is likewise carried out in a separation vessel known to the person skilled in the art according to methods known per se in the prior art.
In principle, the concentration of the aqueous phase (b1) in step c) is carried out as known from the prior art. Concentrated sulfuric acid is obtained by removing water under reduced pressure (7 to 9kPa (a) pressure range) in a flash evaporator (process parameters of the flash evaporator such as a temperature of 95 to 105 ℃).
In principle, the working up of the organic phase (b2) in step d) is carried out as is known from the prior art. The preferred process is described below: the organic phase (b2), which usually also contains traces of acid, is washed once to twice, preferably once, with an aqueous wash solution and subsequently separated from the acidic aqueous phase by phase separation; in this process, the residual acid contained in the crude nitrobenzene (b2) is washed out; this process step is therefore also referred to as pickling. The organic phase thus obtained is subsequently subjected to one to two, preferably one, alkaline washing with an aqueous solution of a base, preferably selected from sodium hydroxide, sodium carbonate or sodium bicarbonate, and subsequently separated from the alkaline washing liquor by phase separation; the organic phase thus obtained is then subjected at least once, preferably twice, to water. Finally, the washed nitrobenzene is freed of dissolved water, unreacted benzene and possibly organic impurities by further work-up. Preferably by treatment, preferably using a rectification column, in which steam water and benzene and possibly organic impurities present are taken off via the top of the column, which is re-introduced into the reaction as recovered benzene (e 2). The bottom product, which is fed as pure nitrobenzene (e1) to further applications, such as the hydrogenation of aniline.
It is essential to the invention that the aqueous phase (b1) containing sulphuric acid obtained in the phase separator is fed first to a sulphuric acid regenerator and then to a flash evaporator, and that a reducing agent (c2) is added to the sulphuric acid regenerator, which agent decomposes the nitrophenol-derived black material dissolved in the sulphuric acid and at the same time prevents the formation of resinated products of aromatic hydrocarbons with nitrous acid, thus avoiding the formation of black material during nitration. Wherein the reducing agent (c2) is thiosulfuric acid, dithionous acid, sulfurous acid, thiosulfate (such as sodium salt, potassium salt), dithionous acid (such as sodium salt), sulfite (such as sodium salt) or a mixture of at least two of these reducing agents, for example, a mixture of thiosulfuric acid, dithionous acid and sulfurous acid in a mass ratio of 1:0.5-1.5:0.5-1.5, or a mixture of thiosulfate (such as sodium salt, potassium salt), dithionous acid (such as sodium salt) and sulfite (such as sodium salt) in a mass ratio of 1:0.5-1.5: 0.5-1.5. Wherein the concentration of the reducing agent (C2) was set to 100-2000ppm and the amount of the reducing agent added was based on the mass of the sulfuric acid-containing aqueous phase (b1) obtained in the phase separator. The residence time of the liquid in the sulfuric acid regenerator is 1-5min, preferably 2-3 min. The sulfuric acid regenerator comprises stirring equipment to ensure the uniform mixing of the liquid.
If the aqueous phase containing sulfuric acid obtained in the phase separator according to the invention (b1) is fed first to a sulfuric acid regenerator and then to a flash evaporator, and the reducing agent (c2) is fed to the sulfuric acid regenerator, the following advantages for the preparation of nitrobenzene are obtained:
i) a reducing agent is added into the sulfuric acid regenerator, the reducing agent can decompose nitrophenol derivatization black substances dissolved in sulfuric acid, and meanwhile, the resinification product of aromatic hydrocarbon and nitrous acid can be prevented from being formed, so that the black substances are prevented from being generated in the nitration process;
ii) no black substance appears in the phase separation device and the crude nitrobenzene heat exchanger, so that the stable operation period of the device is greatly prolonged;
and iii) the emergency stop of the device is avoided, and the maintenance cost is reduced.
Drawings
FIG. 1 is a flow diagram of a nitration process.
Detailed Description
The invention is further illustrated below with reference to the figures and examples.
As shown in figure 1, the nitration process system comprises a mixer 1, a reactor 2, a phase separator 3, a washer 4, a sulfuric acid regenerator 5, a flash evaporator 6 and a sulfuric acid tank 7, wherein sulfuric acid (a2) from the sulfuric acid tank, nitric acid (a1) and benzene (a3) enter the mixer 1 to be mixed and then are fed to the reactor 2, the mixture enters the phase separator 3 after reacting in the reactor 2, the mixture is separated into crude nitric acid (b2) and sulfuric acid (b1) in the phase separator 3, the crude nitric acid (b2) is washed by the washer 4 to obtain nitrobenzene (e1), the sulfuric acid (b1) is fed into the sulfuric acid regenerator 5 added with reducing liquid (c2) to be regenerated, the regenerated sulfuric acid (c1) enters the flash evaporator 6 to be subjected to flash evaporation treatment, acid gas is discharged outside, and the obtained sulfuric acid (d1) is fed into the sulfuric acid tank 7.
The general conditions for preparing nitrobenzene in the process flow for preparing nitrobenzene by adiabatic nitration of benzene in the examples are as follows:
the nitration reaction system establishes a sulfuric acid cycle, the temperature is raised to 100 ℃, 67% nitric acid (the dosage of pure nitric acid is 147kg/min, the mass ratio of sulfuric acid to nitric acid is 24:1) is added at the inlet of a sulfuric acid pump, and then the recovered benzene and the fresh benzene are mixed and then added into a mixing element at the inlet of the reactor according to the benzene excess rate of 10%. The benzene addition amount is 200kg/min, the nitric acid and the benzene completely react to generate nitrobenzene under the catalysis of sulfuric acid (the reaction time is 55s, the temperature is 100 ℃ and 130 ℃), and the reaction liquid is sent to a phase separator to obtain a crude nitrobenzene organic phase and a sulfuric acid aqueous phase. And (3) enabling a sulfuric acid water phase discharged from the phase separator to enter a sulfuric acid regenerator, adding a reducing agent into the sulfuric acid regenerator, enabling the sulfuric acid subjected to reduction treatment to enter a sulfuric acid flash evaporator, and removing moisture through flash evaporation in an absolute pressure (absolute pressure 8kPaa) environment to enable the sulfuric acid concentration to be recovered to the concentration (70 percent concentration) before reaction. The concentrated sulfuric acid is stored in a sulfuric acid tank and participates in the nitration again. The crude nitrobenzene obtained in the phase separator is cooled to 70 ℃ by a heat exchanger and sent to an acid washer, and acid content in the crude nitrobenzene is washed off by acid (the mass ratio of washing water to crude nitrobenzene is 1.1:1, and the temperature is 50 ℃). And (3) carrying out alkaline washing and neutral washing on the washed nitrobenzene to remove nitrophenol and salt to obtain washed nitrobenzene (the mass ratio of washing water to crude nitrobenzene is 1.1:1, the temperature is 60 ℃), removing excessive benzene in a rectifying tower (the operating pressure is 3kpa, the bottom temperature is 100.5 ℃), carrying out phase separation on the condensed liquid at the top of the tower, recovering benzene, sending the recovered benzene to the reaction again, and carrying out phase separation on the product at the bottom of the tower to obtain the product nitrobenzene.
Example 1 (comparative example)
The preparation of nitrobenzene was carried out as described in the general conditions for the preparation of nitrobenzene. In the phase separation device, suspended black oil drops generated by reaction are gathered on a nitrobenzene layer in the phase separator, black solid particles are separated out and formed on equipment parts such as a flange and a gasket where the nitrobenzene layer of the phase separation device is located, the black solid particles flow through a crude nitrobenzene cooler along with crude nitrobenzene to block the nitrobenzene cooler, the device is stopped, and the phase separator and the crude nitrobenzene cooler need to be opened for cleaning 6-8 times every year.
Example 2 (according to the invention)
The preparation of nitrobenzene is carried out as described in the general conditions for preparing nitrobenzene, with the following additional measures: the aqueous phase (b1) containing sulfuric acid obtained in the phase separator was fed to a sulfuric acid regenerator, to which a reducing agent (C2) was added, wherein the reducing agent (C2) was sulfurous acid, and the concentration of the reducing agent was controlled at 1000ppm based on the mass of the aqueous phase (b1) containing sulfuric acid obtained in the phase separator. By the long-cycle operation, no black material was found in the phase separator and in the crude nitrobenzene cooler.
Example 3 (according to the invention)
The preparation of nitrobenzene is carried out as described in the general conditions for preparing nitrobenzene, with the following additional measures: the aqueous phase (b1) containing sulfuric acid obtained in the phase separator enters a sulfuric acid regenerator, and a reducing agent (C2) is added into the sulfuric acid regenerator, wherein the reducing agent (C2) is a mixture of sulfurous acid, thiosulfuric acid and dithionous acid (the mass ratio of the sulfurous acid, the thiosulfuric acid and the dithionous acid is 1: 1: 1), the concentration of the reducing agent is controlled to be 1000ppm based on the mass of the aqueous phase (b1) containing sulfuric acid obtained in the phase separator. By the long-cycle operation, no black material was found in the phase separator and in the crude nitrobenzene cooler.
Example 4 (according to the invention)
The preparation of nitrobenzene is carried out as described in the general conditions for preparing nitrobenzene, with the following additional measures: the aqueous phase (b1) containing sulfuric acid obtained in the phase separator was fed to a sulfuric acid regenerator, to which was added a reducing agent (C2), wherein the reducing agent (C2) was a mixture of sodium sulfite, sodium thiosulfate and sodium dithionite (the mass ratio of sodium sulfite, sodium thiosulfate and sodium dithionite was 1: 1: 1), and the concentration of the reducing agent was controlled at 2000ppm based on the mass of the aqueous phase (b1) containing sulfuric acid obtained in the phase separator. By the long-cycle operation, no black material was found in the phase separator and in the crude nitrobenzene cooler.
Claims (10)
1. A continuously operated adiabatic process for the production of nitrobenzene by nitration of benzene, the process comprising:
a) under adiabatic conditions, the nitric acid stream (a1) and sulfuric acid (a2) form a nitric-sulfuric mixed acid, the benzene stream (a3) is reacted with the nitric acid stream (a1) under sulfuric acid catalysis in the reactor, wherein a stoichiometric excess of benzene based on the nitric acid stream (a1) is used;
b) separating the reaction product obtained in step a) in a phase separation device into an aqueous phase (b1) comprising dilute sulfuric acid and an organic phase (b2) comprising nitrobenzene;
c) feeding the aqueous phase containing dilute sulfuric acid obtained in step b) (b1) to a sulfuric acid regenerator, feeding the aqueous phase containing sulfuric acid from the sulfuric acid regenerator (c1) to a flash evaporator, removing water by flash evaporation to obtain a concentrated aqueous phase containing sulfuric acid (d1) having a greater sulfuric acid concentration than the aqueous phase containing dilute sulfuric acid (b1), wherein the concentrated aqueous phase containing sulfuric acid (d1) is returned to step a) and used as a component of sulfuric acid (a 2);
d) working up the nitrobenzene-containing organic phase (b2) obtained in step b) to pure nitrobenzene (e1),
wherein a reducing agent (c2) is added into the sulfuric acid regenerator, wherein the reducing agent (c2) is one or more of sulfurous acid, thiosulfuric acid, dithionous acid, sulfite, thiosulfate and dithionous acid.
2. The process of claim 1, wherein the liquid residence time in the sulfuric acid regenerator is 1-5 min.
3. The process of claim 2, wherein the liquid residence time in the sulfuric acid regenerator is 2-3 min.
4. Process according to any one of claims 1-3, wherein benzene is used in a stoichiometric excess of 2.0 to 20% of theory, based on the nitric acid stream (a 1).
5. The process of claim 4 wherein benzene is used in a stoichiometric excess of 5.0% to 10% of theory based on nitric acid stream (a 1).
6. The process of any one of claims 1 to 3 wherein the sulfuric acid regenerator includes agitation equipment to ensure uniform mixing of the liquids.
7. The process as claimed in any of claims 1 to 3, wherein the concentration of the reducing agent (c2) is set to 100-2000ppm, the amount of reducing agent added being based on the mass of the aqueous phase (b1) containing dilute sulfuric acid obtained in the phase separator.
8. The method according to any one of claims 1 to 3, wherein the mass ratio of sulfuric acid to nitric acid is 23:1 to 25: 1.
9. The process of any of claims 1-3, wherein the reaction of benzene stream (a3) with sulfuric acid (a2) and nitric acid stream (a1) in a reactor is carried out at 95-135 ℃ for a time of 50-60 s.
10. The method according to claim 1, wherein the reducing agent (c2) is a mixture of thiosulfuric acid, dithionous acid and sulfurous acid in a mass ratio of 1:0.5-1.5:0.5-1.5, or a mixture of thiosulfuric acid, dithionous acid and sulfurous acid in a mass ratio of 1:0.5-1.5: 0.5-1.5.
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| EP0436443A2 (en) * | 1990-01-04 | 1991-07-10 | Nrm International Technologies C.V. | Nitration process |
| US5313009A (en) * | 1990-01-04 | 1994-05-17 | Nrm International Technologies C.V. | Nitration process |
| US5763697A (en) * | 1995-10-22 | 1998-06-09 | Josef Meissner Gmbh & Co. | Process for the nitration of aromatic compounds |
| CN104487413A (en) * | 2012-07-27 | 2015-04-01 | 拜耳材料科技股份有限公司 | Method for producing nitrobenzene by adiabatic nitriding |
| CN104507903A (en) * | 2012-07-27 | 2015-04-08 | 拜耳材料科技股份有限公司 | Method for producing nitrobenzene by adiabatic nitriding |
| CN105308018A (en) * | 2013-04-29 | 2016-02-03 | 科思创德国股份公司 | Method for producing nitrobenzene by adiabatic nitration |
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2019
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|---|---|---|---|---|
| US2256999A (en) * | 1939-03-08 | 1941-09-23 | Du Pont | Nitration of organic compounds |
| EP0436443A2 (en) * | 1990-01-04 | 1991-07-10 | Nrm International Technologies C.V. | Nitration process |
| US5313009A (en) * | 1990-01-04 | 1994-05-17 | Nrm International Technologies C.V. | Nitration process |
| US5763697A (en) * | 1995-10-22 | 1998-06-09 | Josef Meissner Gmbh & Co. | Process for the nitration of aromatic compounds |
| CN104487413A (en) * | 2012-07-27 | 2015-04-01 | 拜耳材料科技股份有限公司 | Method for producing nitrobenzene by adiabatic nitriding |
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| CN105308018A (en) * | 2013-04-29 | 2016-02-03 | 科思创德国股份公司 | Method for producing nitrobenzene by adiabatic nitration |
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