Temperature control production process of methylacrolein

Abstract

The invention discloses a temperature-controlled production process of methylacrolein, which specifically comprises the following steps: metering and pressurizing three materials, namely a formaldehyde solution, a propionaldehyde solution and a catalyst solution according to a preset flow rate, injecting into a temperature-controlled reactor, preheating, mixing, and carrying out condensation reaction to prepare methylacrolein, and after the reaction is finished, reducing the pressure of the reacted material to normal pressure, feeding the reacted material into a flash evaporation chiller for flash evaporation and chilling, and then carrying out water-oil two-phase separation. Preheating and reaction temperatures are controlled through temperature adjusting water, so that the reaction is quickly carried out at a stable temperature, and local high temperature is avoided; the flash chilling device can quickly cool reaction liquid, so that the materials are prevented from being in a high-temperature environment for a long time to cause polymerization to generate polymers; the production process disclosed by the invention has the advantages of high reaction speed, few byproducts and high product yield.

Description

Technical Field

[0001] The invention belongs to the technical field of methacrolein production, and particularly relates to a temperature-controlled production process for methacrolein. Background Art

[0002] Methacrolein (MAL) is an important organic synthesis intermediate and has been widely used in the fields of organic synthesis and new materials. It is mainly used in the manufacture of copolymers and resins. It is a raw material for the production of basic chemical products such as methacrylic acid (MAA), methyl methacrylate (MMA) and methallyl alcohol (MAO), and a raw material for thermoplastic monomers.

[0003] There are three main synthetic routes for methacrolein (MAL): isobutylene oxidation, isobutane oxidation, and Mannich condensation of formaldehyde and propionaldehyde. The Mannich condensation of formaldehyde and propionaldehyde to prepare methacrolein has a simple process, mild reaction conditions, a wide range of raw materials, and good selectivity for methacrolein, and is the key research direction for the synthesis of methacrolein.

[0004] The preparation of methacrolein by Mannich reaction, although the process route is simple and easy, the reaction conditions are mild, the raw material sources are wide, and the methacrolein selectivity is good, but because methacrolein is easy to polymerize at high temperature, the final methacrolein yield is not high, and the methacrolein polymer is easy to adsorb on the reactor and pipeline wall, affecting the normal production of the equipment. In order to prevent the polymerization of methacrolein at high temperature, various optimization methods are constantly proposed, such as adding inhibitors to the reaction solution (such as: CN112638856, CN114524721A) to reduce the occurrence of polymerization; or adding the circulation of inert component water to the reaction solution (such as: CN106687437A) to control the temperature of the reaction system; or controlling the reaction to be carried out at low temperature (such as: CN116554015, CN114988995A, CN114524721A). Although these measures reduce the polymerization of methacrolein, they also reduce the reaction speed; at the same time, adding inert components to the reaction system to control the temperature greatly increases material consumption and energy consumption. Summary of the invention

[0005] In order to solve the technical problems in the prior art such as slow reaction speed but low propionaldehyde conversion rate at low temperature and fast reaction speed but many side reactions at high temperature, a temperature-controlled production process of methacrolein with fast reaction speed, few by-products and high product yield is provided.

[0006] To achieve the above-mentioned purpose, the present invention provides a temperature-controlled production process for methacrolein. The production process specifically comprises the following steps: injecting three streams of materials, namely, formaldehyde solution, propionaldehyde solution and catalyst solution, into a temperature-controlled reactor at a preset flow rate, after metering and pressurization, for preheating, mixing and condensation reaction to prepare methacrolein; after the reaction is completed, the reacted materials are depressurized to normal pressure and then enter a flash chiller for flash evaporation and quenching, and then the water-oil two-phase separation is performed.

[0007] Furthermore, the temperature-controlled reactor is composed of multiple sections of shell and tube reactor units, the first section of the shell and tube reactor unit is a preheating section, the second to the last section of the shell and tube reactor units are reaction sections, and the multiple sections of the shell and tube reactors are connected by flange connections; the shell side uses temperature-adjusting water to control the temperature of the preheating section and the reaction section of the reactor, and the tube side performs preheating mixing and reaction of the materials.

[0008] Furthermore, the flash chiller includes a flash tank, a flash liquid phase nozzle system arranged on the top of the flash tank, a vapor phase cooler and a liquid phase heat exchanger. The flash liquid phase outlet at the bottom of the flash tank is connected to the tube side of the liquid phase heat exchanger. One path of the tube side of the liquid phase heat exchanger is connected to the phase separation tank, and the other path is connected to the flash liquid phase nozzle system through a pipeline; the non-condensable gas outlet is connected to the tube side of the vapor phase cooler. One path of the tube side of the vapor phase cooler is connected to the next process, and the other path flows back to the flash tank.

[0009] Furthermore, after the post-reaction material is depressurized to normal pressure, the flash liquid phase after flash evaporation in the flash tank is cooled by a liquid phase heat exchanger, and a part of it is sprayed back to the flash chiller through a flash liquid phase nozzle system to absorb all or part of the flash vapor phase into the flash liquid phase, and the other part is transported to a phase separation tank; the unabsorbed flash vapor phase and the unabsorbed non-condensable gas are converted into a flash liquid phase after passing through a vapor phase cooler and refluxed into the flash tank to merge into the flash liquid phase, and the non-condensable gas is sent to tail gas treatment.

[0010] Furthermore, the flash liquid phase entering the phase separation tank is separated into an organic phase and an aqueous phase. The organic phase is a crude methacrolein product sent to a product refining tower, and the aqueous phase is sent to a catalyst recovery tower for further distillation to remove low-boiling substances and part of water, and then the catalyst is recovered.

[0011] Furthermore, the preheating temperature of the formaldehyde solution, propionaldehyde solution and catalyst solution is 70-130°C.

[0012] Furthermore, the reaction temperature of the formaldehyde solution, propionaldehyde solution and catalyst solution is 110-180° C., and the residence time in the temperature-controlled reactor is 5-180 seconds.

[0013] Furthermore, the residence time of the formaldehyde solution, propionaldehyde solution and catalyst solution in the reaction section is 10 to 60 seconds.

[0014] Furthermore, the formaldehyde solution is a formaldehyde aqueous solution with a mass concentration of 37-55%.

[0015] Furthermore, the flash liquid phase spray head system comprises a plurality of spray pipes and a plurality of spray heads arranged on each spray pipe. The number of the spray pipes is 2 to 8 and they are evenly arranged along the circumference.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] 1) A combined preheating, mixing and reaction temperature-controlled reactor is used. The equipment has a compact and simple structure, an adjustable residence time, and is suitable for a variety of working conditions. The reaction temperature is stably controlled, which can effectively reduce local high temperatures during the reaction and reduce the polymerization of methacrolein;

[0018] 2) Use integrated flash evaporation quenching equipment to quickly cool down the flash evaporation and refrigerate / absorb the flash vapor phase through circulating coolant, so that the reacted materials can quickly leave the high temperature environment and reduce the polymerization of methacrolein;

[0019] 3) By adjusting the raw material preheating temperature of the temperature-controlled reactor, the reaction is in the high efficiency zone of the catalyst thermodynamic reaction, the reaction speed is fast, the reaction temperature is stable, and the side reactions are few;

[0020] 4) Using thermostatic water to control the operating temperature of the temperature-controlled reactor, so that the reaction can be carried out stably within a certain temperature range, reduce the occurrence of side reactions, and reduce the risk of catalyst deactivation;

[0021] 5) It adopts continuous production process with simple process flow, stable reaction operation, high catalyst stability and safe and reliable operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The present invention is a temperature control production process flow chart of methacrolein;

[0023] Figure 2 It is a one-line diagram of a temperature-controlled reactor;

[0024] Figure 3 It is the U-shaped diagram of the temperature-controlled reactor;

[0025] Figure 4 Schematic diagram of a flash chiller. DETAILED DESCRIPTION

[0026] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0027] like Figure 1 The temperature control production process of methacrolein shown in the figure is as follows:

[0028] The three streams of materials, namely, formaldehyde solution, propionaldehyde solution and catalyst solution, are metered and pressurized at a preset flow rate and injected into a temperature-controlled reactor 1 for preheating, mixing and condensation reaction to prepare methacrolein. After the reaction is completed, the reacted materials are depressurized to normal pressure and then enter a flash chiller 2 for flash evaporation and quenching, and then the water-oil two phases are separated.

[0029] The temperature-controlled reactor 1 is composed of multiple sections of shell-and-tube reactor units. The first section of the shell-and-tube reactor unit is a preheating section, and the second to last sections of the shell-and-tube reactor units are reaction sections. The multiple sections of the shell-and-tube reactor are connected by flange connections, such as Figure 2 As shown, a straight connection is formed, or as Figure 3 The shell side uses thermostatic water to control the temperature of the preheating section and the reaction section of the reactor, and the tube side performs preheating, mixing and reaction of the materials; the residence time of the materials in the temperature-controlled reactor is achieved by increasing or decreasing the number of sections of the shell and tube reactor.

[0030] like Figure 4 The flash chiller 2 shown includes a flash tank 8, a flash liquid phase nozzle system 7 arranged at the top of the flash tank 8, a vapor phase cooler 9 and a liquid phase heat exchanger 10. The flash liquid phase outlet at the bottom of the flash tank 8 is connected to the tube side of the liquid phase heat exchanger 10. One path of the tube side of the liquid phase heat exchanger 10 is connected to the phase separation tank 3, and the other path is connected to the flash liquid phase nozzle system 7 through a pipeline; the non-condensable gas outlet is connected to the tube side of the vapor phase cooler 9. One path of the tube side of the vapor phase cooler 9 is connected to the next process, and the other path is refluxed to the flash tank 8, so that the reduced pressure flash time is less than 5 seconds. That is, after the reaction material is depressurized to normal pressure, the flash liquid phase after flash evaporation in the flash tank 8 is cooled by the liquid phase heat exchanger 10, and a part of it is sprayed back to the flash chiller through the flash liquid phase nozzle system 7 to absorb all or part of the flash vapor phase into the flash liquid phase, and the other part is transported to the phase separation tank 3; the unabsorbed flash vapor phase and the unabsorbed non-condensable gas are transformed into the flash liquid phase after passing through the vapor phase cooler 9 and refluxed to the flash tank 8 to merge into the flash liquid phase, and the non-condensable gas is sent to the tail gas treatment; the flash liquid phase entering the phase separation tank 3 is separated into an organic phase and an aqueous phase, the organic phase is the crude methacrolein product sent to the product refining tower 4, and the aqueous phase is sent to the catalyst recovery tower 5 for further distillation to remove low boiling points and part of water, and then the catalyst is recovered.

[0031] The preheating and reaction temperatures are controlled by thermostatic water, so that the reaction can proceed rapidly at a stable temperature to avoid local high temperature; the flash chiller can quickly cool the reaction liquid to avoid the material being in a high temperature environment for a long time to initiate polymerization to form polymers; the production process of the present invention has the advantages of fast reaction speed, less by-products and high product yield.

[0032] The formaldehyde solution is a formaldehyde aqueous solution with a mass concentration of 37-55%, or a hydrolyzed paraformaldehyde solution with a higher formaldehyde content; the catalyst solution is prepared by a neutralization reaction of an organic acid and an organic amine, wherein the acid is slightly excessive (pH=6-7); the preheating temperature of the formaldehyde solution, the propionaldehyde solution and the catalyst solution is 70-130° C., the reaction temperature is 110-180° C., and the residence time of the reaction section is 5-180 seconds (preferably 10-60 seconds).

[0033] The flash liquid phase spray nozzle system 7 includes multiple spray pipes and multiple spray nozzles arranged on each spray pipe. The number of spray pipes is 2 to 8 and they are evenly arranged along the circumference. The multiple spray nozzles on each spray pipe spray the flash liquid phase into mist or raindrops to cool and absorb the flash gas phase.

[0034] Example 1

[0035] A dimethylamine-acetic acid catalyst solution (the pH value is adjusted to 7.0 with acetic acid) is prepared, a formaldehyde aqueous solution with a normal temperature mass concentration of 37%, a propionaldehyde solution with a mass concentration of 99%, and a prepared catalyst solution are pressurized and metered by a pressure pump, and then pumped into a temperature-controlled reactor at a molar ratio of formaldehyde: propionaldehyde: catalyst of 1.1:1:0.04, and a preheating section of the temperature-controlled reactor is heated to 70°C using 90°C temperature-controlled water; the three streams of materials are mixed while being preheated in the preheating section, and a slow Mannich reaction is started, the reaction exotherm rapidly raises the temperature of the reaction liquid, the reaction heat is rapidly removed by the temperature-controlled water, the reaction temperature is controlled to be 110°C, the reaction pressure is 3MPa, and the reaction residence time is 180s, and a reacted material is obtained.

[0036] After the reaction, the material enters the flash tank after decompression and is divided into a flash steam phase and a flash liquid phase. The flash liquid phase flows out from the bottom of the flash tank and enters the liquid phase heat exchanger to further cool down to 50°C. After cooling, 1 / 3 of the mass liquid of the flash liquid phase is sprayed into the flash tank through the flash liquid phase nozzle system to absorb and quench the flash steam phase to reduce the temperature of the flash liquid phase to 90°C. The unabsorbed flash steam phase is condensed by the vapor phase cooler and returned to the flash tank; the remaining 2 / 3 of the flash liquid phase enters the phase separation tank for phase separation to obtain a methacrolein oil phase and a catalyst-containing water phase. The methacrolein oil phase is sent to the product refining tower, and the catalyst-containing water phase is sent to the catalyst recovery tower. After evaporation and dehydration, the catalyst is recovered and recycled.

[0037] The residence time of the preheating section of the temperature-controlled reactor is 60 s, and the residence time of each reaction section is 60 s, with a total of three sections. The reaction tubes of the preheating section and the reaction section are both in the tube-in-tube type, and the sections are connected in a U shape.

[0038] According to the sampling analysis at the outlet sampling point of the temperature-controlled reactor, it can be obtained that the conversion rate of propionaldehyde is 99.4%, the selectivity of methacrolein is 93%, and the selectivity of methacrolein dimer is 0.5%.

[0039] Example 2

[0040] A diethylamine-acetic acid catalyst solution (the pH value is adjusted to 6.0 with acetic acid) is prepared, a formaldehyde aqueous solution with a normal temperature mass concentration of 55%, a propionaldehyde solution with a mass concentration of 99.5%, and a prepared catalyst solution are pressurized and metered by a pressure pump, and then pumped into a temperature-controlled reactor at a molar ratio of formaldehyde: propionaldehyde: catalyst of 1.05:1:0.12, and a preheating section of the temperature-controlled reactor is heated to 130°C using 150°C temperature-controlled water; the three streams of materials are mixed while being preheated in the preheating section, a slow Mannich reaction is started, the reaction exotherm rapidly raises the temperature of the reaction liquid, the reaction heat is rapidly removed by 90°C temperature-controlled water, the reaction temperature is controlled to be 180°C, the reaction pressure is 5MPa, and the reaction residence time is 5s, and a reacted material is obtained.

[0041] After the reaction, the material enters the flash tank after decompression and is divided into a flash steam phase and a flash liquid phase. The flash liquid phase flows out from the bottom of the flash tank and enters the liquid phase heat exchanger to further cool down to 45°C. After cooling, 2 / 3 of the mass liquid of the flash liquid phase is sprayed into the flash tank through the flash liquid phase nozzle system to absorb and quench the flash steam phase to reduce the temperature of the flash liquid phase to 90°C. The unabsorbed flash steam phase is condensed by the vapor phase cooler and returned to the flash tank; the remaining 1 / 3 of the flash liquid phase enters the phase separation tank for phase separation to obtain a methacrolein oil phase and a catalyst-containing water phase. The methacrolein oil phase is sent to the product refining tower, and the catalyst-containing water phase is sent to the catalyst recovery tower. After evaporation and dehydration, the catalyst is recovered and recycled.

[0042] The residence time of the preheating section of the temperature-controlled reactor is 15s, and the residence time of each section of the reaction section is 5s, totaling one section. The reaction tubes of the preheating section and the reaction section are both tube-in-tube type, filled with twisted iron-shaped fillers, and the sections are connected in a straight line. According to the sampling analysis of the sampling point at the outlet of the temperature-controlled reactor, the conversion rate of propionaldehyde is 99.8%, the selectivity of methacrolein is 97.5%, and the selectivity of methacrolein dimer is 0.1%.

[0043] Example 3

[0044] A diethylamine-oxalic acid catalyst solution (the pH value is adjusted to 6.3 with acetic acid) is prepared, a formaldehyde aqueous solution with a normal temperature mass concentration of 60%, a propionaldehyde solution with a mass concentration of 99.5%, and a prepared catalyst solution are pressurized and metered by a pressure pump, and then pumped into a temperature-controlled reactor at a molar ratio of formaldehyde: propionaldehyde: catalyst of 1.05:1:0.08, and a preheating section of the temperature-controlled reactor is heated to 90°C using 150°C temperature-controlled water; the three streams of materials are mixed while being preheated in the preheating section, and a slow Mannich reaction is started, the reaction exotherm rapidly raises the temperature of the reaction liquid, the reaction heat is rapidly removed by 90°C temperature-controlled water, the reaction temperature is controlled to be 130°C, the reaction pressure is 4MPa, and the reaction residence time is 50s, and a reacted material is obtained.

[0045] After the reaction, the material enters the flash tank after decompression and is divided into a flash steam phase and a flash liquid phase. The flash liquid phase flows out from the bottom of the flash tank and enters the liquid phase heat exchanger to further cool down to 50°C. After cooling, 1 / 2 of the mass liquid of the flash liquid phase is sprayed into the flash tank through the flash liquid phase nozzle system to absorb and quench the flash steam phase to reduce the temperature of the flash liquid phase to 90°C. The unabsorbed flash steam phase is condensed by the vapor phase cooler and returned to the flash tank; the remaining 1 / 2 of the flash liquid phase enters the phase separation tank for phase separation to obtain a methacrolein oil phase and a catalyst-containing water phase. The methacrolein oil phase is sent to the product refining tower, and the catalyst-containing water phase is sent to the catalyst recovery tower. After evaporation and dehydration, the catalyst is recovered and recycled.

[0046] The residence time of the preheating section of the temperature-controlled reactor is 20s, and the residence time of each section of the reaction section is 50s, with a total of five sections. The reaction tubes of the preheating section and the reaction section are both in a tube-in-tube type, with fillers inside the tubes, and the sections are connected in a U-shaped shape. According to the sampling analysis of the sampling point at the control reactor outlet, the propionaldehyde conversion rate is 99.7%, the methacrolein selectivity is 96%, and the methacrolein dimer selectivity is 0.2%.

[0047] Example 4

[0048] A diethylamine-acetic acid catalyst solution (the pH value is adjusted to 6.5 with acetic acid) is prepared, a formaldehyde aqueous solution with a normal temperature mass concentration of 44%, a propionaldehyde solution with a mass concentration of 99.5%, and a prepared catalyst solution are pressurized and metered by a pressure pump, and then pumped into a temperature-controlled reactor at a molar ratio of formaldehyde: propionaldehyde: catalyst of 1.05:1:0.1, and a preheating section of the temperature-controlled reactor is heated to 110°C using 150°C temperature-controlled water; the three streams of materials are mixed while being preheated in the preheating section, and a slow Mannich reaction is started, the reaction exotherm rapidly raises the temperature of the reaction liquid, and the reaction heat is rapidly removed by 90°C temperature-controlled water, the reaction temperature is controlled to be 150°C, the reaction pressure is 5MPa, and the reaction residence time is 10s to obtain a reacted material.

[0049] After the reaction, the material enters the flash tank after decompression and is divided into a flash steam phase and a flash liquid phase. The flash liquid phase flows out from the bottom of the flash tank and enters the liquid phase heat exchanger to further cool down to 50°C. After cooling, 3 / 5 of the mass liquid of the flash liquid phase is sprayed into the flash tank through the flash liquid phase nozzle system to absorb and quench the flash steam phase to reduce the temperature of the flash liquid phase to 90°C. The unabsorbed flash steam phase is condensed by the vapor phase cooler and returned to the flash tank; the remaining 2 / 5 of the flash liquid phase enters the phase separation tank for phase separation to obtain a methacrolein oil phase and a catalyst-containing water phase. The methacrolein oil phase is sent to the product refining tower, and the catalyst-containing water phase is sent to the catalyst recovery tower. After evaporation and dehydration, the catalyst is recovered and recycled.

[0050] The residence time of the preheating section of the temperature-controlled reactor is 15s, and the residence time of each section of the reaction section is 5s, with a total of two sections. The reaction tubes of the preheating section and the reaction section are all wound tube-type, and the sections are connected in a straight line. According to the sampling analysis of the sampling point at the outlet of the temperature-controlled reactor, the conversion rate of propionaldehyde is 99.9%, the selectivity of methacrolein is 98%, and the selectivity of methacrolein dimer is 0.05%.

Claims

1. A temperature control production process for methacrolein, characterized in that: The production process is specifically as follows: three streams of materials, namely, formaldehyde solution, propionaldehyde solution and catalyst solution, are metered and pressurized at a preset flow rate and injected into a temperature-controlled reactor for preheating, mixing and condensation reaction to prepare methacrolein; after the reaction is completed, the reacted materials are depressurized to normal pressure and then enter a flash condenser for flash evaporation and quenching, and then the water-oil two-phase separation is performed.

2. The temperature control production process of methacrolein according to claim 1, characterized in that: The temperature-controlled reactor is composed of multiple sections of shell and tube reactor units, the first section of the shell and tube reactor unit is a preheating section, the second to the last section of the shell and tube reactor units are reaction sections, and the multiple sections of the shell and tube reactor are connected by flange connections; the shell side uses temperature-adjusting water to control the temperature of the preheating section and the reaction section of the reactor, and the tube side performs preheating, mixing and reaction of materials.

3. The temperature control production process of methacrolein according to claim 1, characterized in that: The flash chiller includes a flash tank, a flash liquid phase nozzle system arranged on the top of the flash tank, a vapor phase cooler and a liquid phase heat exchanger. The flash liquid phase outlet at the bottom of the flash tank is connected to the tube side of the liquid phase heat exchanger. One path of the tube side of the liquid phase heat exchanger is connected to the phase separation tank, and the other path is connected to the flash liquid phase nozzle system through a pipeline; the non-condensable gas outlet is connected to the tube side of the vapor phase cooler. One path of the tube side of the vapor phase cooler is connected to the next process, and the other path flows back to the flash tank.

4. The temperature-controlled production process for methacrolein according to claim 3, characterized in that: After the pressure is reduced to normal pressure, the post-reaction material is flashed in a flash tank, and the flash liquid phase is cooled in a liquid phase heat exchanger. A part of it is sprayed back to the flash chiller through a flash liquid phase nozzle system to absorb all or part of the flash steam phase into the flash liquid phase, and the other part is transported to a phase separation tank; the unabsorbed flash steam phase and the unabsorbed non-condensable gas are converted into a flash liquid phase after passing through a vapor phase cooler and refluxed into the flash tank to merge into the flash liquid phase, and the non-condensable gas is sent to tail gas treatment.

5. The temperature control production process of methacrolein according to claim 4, characterized in that: The flash liquid phase entering the phase separation tank is separated into an organic phase and an aqueous phase. The organic phase is a crude methacrolein product and is sent to a product refining tower. The aqueous phase is sent to a catalyst recovery tower for further distillation to remove low-boiling substances and part of water, and then the catalyst is recovered.

6. The temperature control production process of methacrolein according to claim 1, characterized in that: The preheating temperature of the formaldehyde solution, propionaldehyde solution and catalyst solution is 70-130°C.

7. The temperature control production process of methacrolein according to claim 1, characterized in that: The reaction temperature of the formaldehyde solution, propionaldehyde solution and catalyst solution is 110-180° C., and the residence time in the temperature-controlled reactor is 5-180 seconds.

8. The temperature-controlled production process for methacrolein according to claim 1, characterized in that: The residence time of the formaldehyde solution, propionaldehyde solution and catalyst solution in the reaction section is 10 to 60 seconds.

9. The temperature-controlled production process for methacrolein according to claim 1, characterized in that: The formaldehyde solution is a formaldehyde aqueous solution with a mass concentration of 37-55%.

10. The temperature-controlled production process for methacrolein according to claim 3, characterized in that: The flash liquid phase spray head system comprises a plurality of spray pipes and a plurality of spray heads arranged on each spray pipe. The number of the spray pipes is 2 to 8 and they are evenly arranged along the circumference.

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