Method for preparing allyl acetate and recovering propylene and propane

Abstract

The invention provides a method for preparing allyl acetate and recovering propylene and propane, which comprises the following steps: introducing a gas raw material into a reactor for reaction, pumping out gas in the material from the top of a first absorption tower by using a first compressor to serve as a recycle gas flow, conveying one part of the recycle gas flow into the reactor, and conveying the other part of the recycle gas flow into a second absorption tower; and conveying a part of the exhaust gas flow to the bottom of the second absorption tower, discharging the rest of the exhaust gas flow, and sequentially discharging liquid in the material into a crude product storage tank and a rectifying tower from the bottom of the first absorption tower, and condensing a part of an extracted material flow entering the gas-liquid separation tank from the top of the rectifying tower, introducing the condensed material flow into the top of the second absorption tower as a first absorption liquid to obtain a rich solution, discharging the rich solution into a crude product storage tank, and pumping gas flashed from the crude product storage tank back to the bottom of the first absorption tower. The method provided by the invention is beneficial to reducing the production cost, improving the selectivity of the target product and reducing the carbon dioxide emission of the system.

Description

Technical Field

[0001] The invention relates to the technical field of gas recovery and utilization, and in particular to a method for preparing allyl acetate and recovering propylene and propane. Background Art

[0002] Allyl acetate is an important fine chemical with a wide range of uses. Allyl acetate is mainly obtained from propylene, acetic acid and oxygen under the catalytic oxidation of metal Pd.

[0003] The single-pass conversion rate of propylene in the acetyl oxidation reaction is less than 20%, so the materials after the reaction include allyl acetate, propylene, oxygen, acetic acid, water, carbon dioxide and other inert gas mixtures. After the reaction mixture is condensed and separated from the heavy components by an absorption tower, the light components contain unreacted propylene, oxygen, acetic acid, carbon dioxide and other inert gases. After the light components are pressurized by a compressor, most of them are returned to the reactor to continue to participate in the reaction.

[0004] Considering the process cost, the raw materials propylene and oxygen are both industrial raw materials, and there is no impurity gas separation process before the raw gas enters the reactor. Usually, the purity of propylene in industrial polymerization grade propylene is greater than>99.6%, and the main impurity is propane. The purity of industrial oxygen is greater than>99.5%, and the main impurity components are nitrogen and argon. These three inert gases in the circulating gas do not participate in the reaction. If the above three gases are not discharged from the reaction system, they will continue to accumulate, seriously affecting the pressure balance and chemical balance of the reaction system, and even more so causing explosions. Therefore, during the reaction process, it is necessary to discharge a part of the circulating gas continuously to the flare for incineration to discharge the inert substances out of the reaction system. Because the circulating gas contains more propylene, directly sending it for incineration not only causes economic losses, but also produces a large amount of greenhouse gases, pollutes the environment, and increases the environmental burden of the enterprise. Summary of the invention

[0005] In order to overcome the deficiencies of the prior art, the object of the present invention is to provide a method for preparing allyl acetate and recovering propylene and propane, which method is conducive to reducing production costs, improving the selectivity of target products and reducing system carbon dioxide emissions.

[0006] To solve the above problems, the technical solution adopted by the present invention is as follows:

[0007] A method for preparing allyl acetate and recovering propylene and propane comprises the following steps:

[0008] Passing a gas raw material into a reactor to react and generate allyl acetate, wherein the gas raw material comprises propylene, acetic acid, oxygen and an inert gas;

[0009] Using a first condenser to condense the material discharged from the bottom of the reactor, so that the condensed material is discharged into the bottom of the first absorption tower;

[0010] Using a first compressor to pump gas in the material out from the top of the first absorption tower as a circulating gas flow, a portion of the circulating gas flow is transported to the reactor, and the remaining portion is used as an exhaust gas flow, a portion of the exhaust gas flow is transported to the bottom of the second absorption tower, and the remaining portion of the exhaust gas flow is discharged, and the liquid in the material is discharged from the bottom of the first absorption tower into a crude product storage tank and a distillation tower in sequence, and the gas flashed out in the crude product storage tank is pumped back to the bottom of the first absorption tower using a second compressor;

[0011] A portion of the produced stream entering the gas-liquid separation tank from the top of the rectification tower is condensed in the second condenser and then introduced into the top of the second absorption tower as the first absorption liquid, so that the first absorption liquid and the exhaust gas stream are in countercurrent contact in the second absorption tower to obtain a rich liquid absorbing propylene and propane, and the waste gas from which propylene and propane are removed in the second absorption tower is combined with the exhaust portion of the exhaust gas stream and discharged together;

[0012] The rich liquid is discharged into the crude product storage tank, and the second compressor also pumps the gas flashed from the rich liquid in the crude product storage tank back to the bottom of the first absorption tower.

[0013] In some possible implementations, the gas separated by the gas-liquid separation tank is also introduced into the crude product storage tank, and the second compressor also pumps the gas recovered from the gas-liquid separation tank to the crude product storage tank.

[0014] In some possible embodiments, the flow rate of the exhaust gas stream is less than 1% of the flow rate of the recycle gas stream by weight.

[0015] In some possible implementations, the flow rate of the portion of the exhaust gas stream transported into the second absorption tower is 50%-100% of the flow rate of the exhaust gas stream by weight.

[0016] In some possible implementations, the operating pressures of the first absorption tower and the second absorption tower are the same and are both lower than the operating pressure of the reactor, and the operating pressures of the first absorption tower and the second absorption tower are both 0.5-0.9 MPa.

[0017] In some possible implementations, the feed temperature of the first absorption liquid is 10-40°C.

[0018] In some possible implementations, the flow rate of the first absorption liquid is 2% to 5% by weight of the overhead extraction amount of the distillation tower.

[0019] In some possible embodiments, the second absorption tower includes a packed tower, a plate tower or a floating valve tower.

[0020] In some possible implementations, after the condensed material is discharged into the first absorption tower, the method further comprises:

[0021] A second absorption liquid is introduced from the top of the first absorption tower, and the second absorption liquid is used to absorb the uncondensed allyl acetate vapor.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] In the present application, through the coordination between the reactor, the first absorption tower, the first condenser, the first compressor, the second absorption tower, the crude product storage tank, the second compressor, the distillation tower, the gas-liquid separation tank and the second condenser, the oil phase component separated by the distillation tower is used as an absorption liquid for separating propylene, propane and other impurity gases, without introducing other organic components, which is conducive to simplifying the process of recovering propylene and propane, and the recovered propylene and propane can be transported to the reactor again to participate in the reaction, on the one hand, the recycling of the reactant propylene is realized, on the other hand, the propane content in the reaction gas is increased, which is conducive to suppressing side reactions and reducing the heat of reaction, thereby increasing the selectivity of the target product allyl acetate. In addition, the method provided by the present application can also reduce the content ratio of propylene and propane in the exhaust gas. Therefore, the method provided by the present application is conducive to reducing production costs, improving the selectivity of the target product and reducing the carbon dioxide emissions of the system.

[0024] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 A schematic diagram of the connection between the preparation and recovery system and the RTO corresponding to the method provided in one embodiment of the present application.

[0026] Figure 2 This is a connection diagram of the system used as a comparative reference standard for this application.

[0027] Description of Figure Numbers:

[0028] 10-reactor; 20-first absorption tower; 30-first condenser; 40-second absorption tower; 50-crude product storage tank; 60-rectification tower; 70-gas-liquid separation tank; 80-second condenser; 90-transfer pump; 11-first pipeline; 12-second pipeline; 21-third pipeline; 22-first compressor; 23-fourth pipeline; 24-fifth pipeline; 25-sixth pipeline; 26-fifteenth pipeline; 41-eighth pipeline; 42-thirteenth pipeline; 51-seventh pipeline; 52-second compressor; 53-ninth pipeline; 61-tenth pipeline; 62-eleventh pipeline; 71-twelfth pipeline; 72-fourteenth pipeline. DETAILED DESCRIPTION

[0029] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0030] The terms "first", "second", etc. in the specification and claims of this application and the above-mentioned drawings are used to distinguish different objects, rather than to describe a specific order. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions. It should be noted that when an element is referred to as "fixed to" another element, it can be directly on the other element or there can be a centered element. When an element is referred to as "connected to" another element, it can be directly connected to the other element or there can be a centered element. When an element is referred to as "arranged on" another element, it can be arranged on the other element or there can be a centered element.

[0031] One embodiment of the present application provides a method for preparing allyl acetate and recovering propylene and propane. The method provided in the present application can be used as follows Figure 1 The preparation and recovery system shown. The method provided in this application comprises the following steps:

[0032] Step S101: introducing a gas raw material into a reactor 10 to react and generate allyl acetate, wherein the gas raw material includes propylene, acetic acid, oxygen and an inert gas. For example, the inert gas may include one of carbon dioxide or nitrogen. A corresponding catalyst, such as PD, may be provided in the reactor 10.

[0033] In some embodiments, the reaction temperature in the reactor 10 is 140-220° C., and the reaction pressure is 0.6-1.0 MPa.

[0034] Specifically, the top of the reactor 10 is connected to a first pipe 11 for introducing gas materials. Propylene, acetic acid, oxygen and inert gas can be introduced into the reactor 10 through the first pipe 11 for reaction, and a corresponding catalyst, such as a supported PD catalyst, can be provided in the reactor 10.

[0035] Step S102 : using the first condenser 30 to condense the material discharged from the bottom of the reactor 10 , so that the condensed material is discharged into the bottom of the first absorption tower 20 .

[0036] Specifically, the bottom of the first absorption tower 20 is connected to the bottom of the reactor 10 through the second pipeline 12. The first condenser 30 is installed on the second pipeline 12 to condense the materials discharged from the reactor 10, so that the products discharged from the bottom of the reactor 10 are passed into the first absorption tower 20 in the form of liquid, and the residual gas materials can enter the first absorption tower 20 in the form of gas. The gas materials entering the first absorption tower 20 include propylene, oxygen, uncondensed propylene acetate vapor and inert gas (including inert gases such as propane, nitrogen and argon).

[0037] In some embodiments, the method further comprises the steps of:

[0038] A second absorption liquid is introduced from the top of the first absorption tower 20, and the second absorption liquid is used to absorb the uncondensed allyl acetate vapor. Exemplarily, the second absorption liquid can be an acetic acid aqueous solution or acetic acid. The mass fraction of acetic acid in the acetic acid aqueous solution is greater than or equal to 50%.

[0039] Specifically, the top of the first absorption tower 20 is also connected to a fifteenth pipeline 26 for feeding the second absorption liquid. The second absorption liquid is used to absorb uncondensed product vapor, thereby improving the process yield while reducing the possibility of product vapor being pumped into the reactor 10, thereby helping to increase the life of the catalyst in the reactor 10.

[0040] Step S103: Use the first compressor 22 to pump the gas in the material from the top of the first absorption tower 20 as a circulating gas stream. Part of the circulating gas stream is transported to the reactor 10, and the remaining part is used as an exhaust gas stream. Part of the exhaust gas stream is transported to the bottom of the second absorption tower 40, and the remaining part of the exhaust gas stream is discharged. The liquid in the material is discharged from the bottom of the first absorption tower 20 into the crude product storage tank 50 and the distillation tower 60 in sequence, and the gas flashed in the crude product storage tank 50 is pumped back to the bottom of the first absorption tower 20 using the second compressor 52.

[0041] In some embodiments, the flow rate of the vent gas stream is less than 1% of the flow rate of the recycle gas stream by weight.

[0042] In some embodiments, the flow rate of the portion of the exhaust gas stream delivered to the second absorption tower 40 is 50% to 100% by weight of the flow rate of the exhaust gas stream.

[0043] In some embodiments, the operating pressures of the first absorption tower 20 and the second absorption tower 40 are the same and lower than the operating pressure of the reactor 10 , and the operating pressures of the first absorption tower 20 and the second absorption tower 40 are both 0.5-0.9 MPa.

[0044] Specifically, the top of the first absorption tower 20 is connected to the first pipeline 11 through the third pipeline 21, so that the gas material in the first absorption tower 20 can be circulated to the reactor 10. The first compressor 22 is installed on the third pipeline 21 for pumping the gas discharged from the first absorption tower 20 (as a circulating gas flow). The bottom of the second absorption tower 40 is connected to the part of the third pipeline 21 adjacent to the first pipeline 11 through the fourth pipeline 23, that is, the access point of the fourth pipeline 23 to the third pipeline 21 is placed on the side of the first compressor 22 away from the first absorption tower 20, so that the first compressor 22 can be used as a transmission power source for both the third pipeline 21 and the fourth pipeline 23. It can be understood that a regulating valve can be respectively set on both the third pipeline 21 and the fourth pipeline 23 to adjust the flow of the corresponding pipeline. The fourth pipeline 23 is set so that a part of the circulating gas flow in the third pipeline 21 is separated as an exhaust gas flow, and a part of the exhaust gas flow enters the second absorption tower 40 through the fourth pipeline 23. The fourth pipeline 23 is connected to the fifth pipeline 24 for discharging part of the material from the system, that is, another part of the exhaust gas flow in the fourth pipeline 23 is discharged from the system through the fifth pipeline 24. For example, the exhaust gas flow discharged through the fifth pipeline 24 can be passed into a regenerative thermal incinerator (RTO) for incineration. For example, a regulating valve can be provided on each of the fourth pipeline 23 and the fifth pipeline 24 to adjust the flow entering the second absorption tower 40 and the flow discharged from the system.

[0045] The crude product storage tank 50 is connected to the bottom of the first absorption tower 20 through the sixth pipeline 25 and to the middle and lower part of the first absorption tower 20 through the seventh pipeline 51, so that the access point of the seventh pipeline 51 to the first absorption tower 20 is higher than the access point of the sixth pipeline 25 to the first absorption tower 20, and the material discharged from the bottom of the first absorption tower 20 can flow into the crude product storage tank 50 through the sixth pipeline 25. The flashed gas in the crude product storage tank 50 can be passed into the first absorption tower 20 through the seventh pipeline 51, and then this part of the gas can also be pumped out of the first absorption tower 20 through the first compressor 22. Exemplarily, the access point of the seventh pipeline 51 can be above the liquid phase space at the bottom of the tower and below the packing in the tower. Exemplarily, both the sixth pipeline 25 and the seventh pipeline 51 can be connected to the top of the crude product storage tank 50. The second compressor 52 is installed on the seventh pipeline 51 to pump the flash gas in the crude product storage tank 50 into the first absorption tower 20. The distillation tower 60 is used for distilling and separating the materials discharged from the crude product storage tank 50. The middle of the distillation tower 60 is connected to the crude product storage tank 50 through a ninth pipeline 53. The bottom of the distillation tower 60 is provided with a tenth pipeline 61 for draining liquid.

[0046] Step S104: a portion of the produced flow entering the gas-liquid separation tank 70 from the top of the distillation tower 60 is condensed in the second condenser 80 and then passed into the top of the second absorption tower 40 as the first absorption liquid, so that the first absorption liquid and the exhaust gas flow are in countercurrent contact in the second absorption tower 40 to obtain a rich liquid for absorbing propylene and propane, and the waste gas from which propylene and propane are removed in the second absorption tower 40 is combined with the exhaust part of the exhaust gas flow and discharged together, thereby helping to reduce the ratio of propylene and propane in the waste gas, thereby helping to reduce the carbon dioxide emissions of the system.

[0047] In some embodiments, the feed temperature of the first absorption liquid is 10-40°C.

[0048] In some embodiments, the flow rate of the first absorption liquid is 2% to 5% by weight of the overhead extraction amount of the distillation tower 60 .

[0049] In some embodiments, the second absorption tower 40 includes one of a packed tower, a plate tower, or a valve tower.

[0050] In some embodiments, the method further comprises:

[0051] The gas separated by the gas-liquid separation tank 70 is also introduced into the crude product storage tank 50, and the second compressor 52 also pumps the gas recovered from the gas-liquid separation tank 70 to the crude product storage tank 50, thereby further improving the recovery ratio of propylene and propane.

[0052] Specifically, the gas-liquid separation tank 70 is connected to the distillation tower 60 through at least two eleventh pipelines 62 for separating the materials after distillation and realizing the reflux of the distillation tower 60. The bottom of the gas-liquid separation tank 70 is connected to the top of the second absorption tower 40 through the twelfth pipeline 71. The second condenser 80 is installed on the twelfth pipeline 71 for condensing the materials discharged from the gas-liquid separation tank 70, so that a part of the materials discharged from the gas-liquid separation tank 70 are condensed and used as the top feed of the second absorption tower 40 to absorb propylene and propane. Exemplarily, a regulating valve can be provided on each of the eleventh pipeline 62 and the twelfth pipeline 71 for reflux, so as to adjust the flow of the corresponding pipeline.

[0053] The top of the second absorption tower 40 is connected to the fifth pipeline 24 through the thirteenth pipeline 42, so that the waste gas from which propylene and propane are removed is combined with the discharged part of the exhaust gas flow into one gas flow and discharged out of the system together. For example, it can be discharged into the RTO for incineration treatment.

[0054] The gas-liquid separation tank 70 is connected to the crude product storage tank 50 through the fourteenth pipeline 72 for introducing the separated gas into the crude product storage tank 50. Exemplarily, the fourteenth pipeline 72 can be connected to the top of the gas-liquid separation tank 70 and the top of the crude product storage tank 50.

[0055] Step S105 : the rich liquid is discharged into the crude product storage tank 50 , and the second compressor 52 also pumps the gas flashed from the rich liquid in the crude product storage tank 50 back to the bottom of the first absorption tower 20 .

[0056] Specifically, the bottom of the second absorption tower 40 is connected to the crude product storage tank 50 through the eighth pipeline 41, so that the rich liquid obtained after the exhaust gas flow in the second absorption tower 40 is treated is introduced into the crude product storage tank 50, and the absorbed propylene and propane are introduced into the crude product storage tank 50 through the eighth pipeline 41 and then flash evaporated, and the flashed propylene and propane are re-pumped into the circulating gas flow, thereby facilitating the increase of the content ratio of propylene and propane in the circulating gas flow, and further facilitating the inhibition of the generation of 10 side reactions in the reactor and reducing the thermal effect of the reaction to increase the selectivity of the target product allyl acetate.

[0057] In the present application, by the coordination between the reactor 10, the first absorption tower 20, the first condenser 30, the first compressor 22, the second absorption tower 40, the crude product storage tank 50, the second compressor 52, the rectifying tower 60, the gas-liquid separation tank 70 and the second condenser 80, the oil phase component separated by the rectifying tower 60 is used as an absorption liquid for separating propylene, propane and other impurity gases, and other organic components are not introduced, which is conducive to simplifying the process of recovering propylene and propane, and the recovered propylene and propane can be transported to the reactor 10 again to participate in the reaction, on the one hand, the recycling of the reactant propylene is realized, and on the other hand, the propane content in the reaction gas is increased, which is conducive to suppressing side reactions and reducing the heat of reaction, thereby increasing the selectivity of the target product allyl acetate. In addition, the method provided in the present application can also reduce the content ratio of propylene and propane in the exhaust gas. Therefore, the method provided in the present application is conducive to reducing production costs, improving the selectivity of the target product and reducing the carbon dioxide emissions of the system.

[0058] In some embodiments, the first compressor 22 is a centrifugal compressor or an axial compressor.

[0059] In some embodiments, the second compressor 52 is a liquid ring compressor, a reciprocating compressor or a screw compressor. The types of the first compressor 22 and the second compressor 52 are selected to have both low equipment cost and high pumping efficiency, thereby further reducing production costs.

[0060] In some embodiments, the reactor 10 is a shell-and-tube reactor, which has the advantages of good heat transfer performance and good mixing performance.

[0061] In some embodiments, the preparation and recovery system further includes a delivery pump 90, which is installed on the twelfth pipeline 71 to deliver the material discharged from the gas-liquid separation tank 70. The delivery pump 90 is arranged between the second condenser 80 and the gas-liquid separation tank 70. The delivery pump 90 delivers the material to overcome the pressure difference.

[0062] In some embodiments, the first absorption tower 20 may be a packed tower, a plate tower, or a valve tower.

[0063] Specific:

[0064] Embodiment [1-5]:

[0065] Taking the process of producing 50,000 tons / year of allyl acetate as an example, the second absorption tower 40 adopts a packed tower, the flow rate of the first absorption liquid is 3% of the top extraction amount of the distillation tower 60, the operating pressure of the second absorption tower 40 is 0.8Mpa, the feed temperature of the first absorption liquid is 20°C, and the ratio of the flow rate of the part of the exhaust gas flow transported into the second absorption tower 40 to the flow rate of the exhaust gas flow is changed to investigate the propylene mass concentration of the gas discharged to the RTO (exhaust gas from the system), the change of the propane mass concentration in the circulating gas flow and the change of the selectivity of the target product allyl acetate. Among them, the reference standard for the change of the propane mass concentration in the circulating gas flow and the selectivity of the process allyl acetate is the allyl acetate device without the second absorption tower 40 process (reference Figure 2 ).

[0066] Figure 2 The inert gas discharge process without the second absorption tower 40 process has a propylene content of about 45% discharged into the RTO. Figure 1 The implementation results of the inventive method are shown in Table 1.

[0067] Table 1

[0068]

[0069] It can be seen from Table 1 that the higher the ratio of the exhaust gas flow transported into the second absorption tower 40, the lower the propylene content in the exhaust gas discharged from the system, and it is much lower than Figure 2 The propylene content in the RTO gas emitted from the process. Figure 2 In the inert gas discharge process without the second absorption tower 40, the mass concentration of propane in the circulating gas stream increases from 20% to about 30%, which is increased by about 10 percentage points. As a result, the selectivity of allyl acetate in the process increases by about 1 percentage point.

[0070] Embodiment [6-9]:

[0071] Taking the process of producing 50,000 tons / year of allyl acetate as an example, the second absorption tower 40 adopts a packed tower, the flow rate of the first absorption liquid is 3% of the top extraction amount of the distillation tower 60, the flow rate of the part of the exhaust gas flow transported into the second absorption tower 40 is 70% of the flow rate of the exhaust gas flow, the operating pressure of the second absorption tower 40 is 0.8Mpa, and the feed temperature of the first absorption liquid is changed to investigate the changes in the mass concentration of propylene discharged into the RTO gas, the mass concentration of propane in the circulating gas flow, and the selectivity of the target product allyl acetate. The reference standard for the changes in the mass concentration of propane in the circulating gas flow and the selectivity of the process allyl acetate is the allyl acetate device without the second absorption tower 40 process.

[0072] according to Figure 1The implementation results of the inventive method are shown in Table 2.

[0073] Table 2

[0074]

[0075] It can be seen from the table that the lower the first absorption liquid feed temperature, the lower the propylene content in the exhaust gas discharged from the system. Figure 2 In the inert gas emission process without the second absorption tower 40 process, the mass concentration of propane in the circulating gas stream is increased by about 10 percentage points, resulting in an increase of about 1 percentage point in the selectivity of allyl acetate in the process. This application does not use a lower feed temperature, mainly because a lower feed temperature requires higher refrigeration energy consumption, so this application prefers a feed temperature in the range of 10-40°C.

[0076] Embodiment [10-12]:

[0077] Taking the process of producing 50,000 tons / year of allyl acetate as an example, the flow rate of the first absorption liquid is 3% of the top extraction of the distillation tower, the flow rate of the exhaust gas flow transported to the second absorption tower is 70% of the flow rate of the exhaust gas flow, the operating pressure of the second absorption tower is 0.8Mpa, the feed temperature of the first absorbent is 20°C, and the type of the second absorption tower 40 is changed to investigate the changes in the mass concentration of propylene discharged into the RTO gas, the mass concentration of propane in the circulating gas flow, and the selectivity of the target product allyl acetate. The reference standard for the changes in the mass concentration of propane in the circulating gas flow and the selectivity of the process allyl acetate is an allyl acetate device without the second absorption tower 40 process.

[0078] Table 3

[0079]

[0080]

[0081] It can be seen from Table 3 that the form of the tower has little effect on the absorption effect, and the use of a packed tower, a plate tower, or a floating valve tower as the second absorption tower 40 has little effect on the results of the embodiment.

[0082] Embodiment [13-17]:

[0083] Taking the process of producing 50,000 tons / year of allyl acetate as an example, the second absorption tower 40 adopts a packed tower, the flow rate of the first absorption liquid is 3% of the top extraction of the distillation tower, the flow rate of the exhaust gas flow transported into the second absorption tower 40 is 70% of the exhaust gas flow, the feed temperature of the first absorption liquid is 20°C, and the operating pressure of the second absorption tower 40 is changed to investigate the changes in the mass concentration of propylene discharged into the RTO gas, the mass concentration of propane in the circulating gas flow, and the selectivity of the target product allyl acetate. The reference standard for the changes in the mass concentration of propane in the circulating gas flow and the selectivity of the process allyl acetate is the allyl acetate device without the second absorption tower 40 process.

[0084] Table 4

[0085]

[0086]

[0087] It can be seen from Table 4 that the higher the operating pressure of the second absorption tower 40, the better the absorption effect of the first absorption liquid on propylene and propane. Due to the influence of the first compressor 22, the operating pressure of the second absorption tower 40 is preferably in the range of 0.5-0.9 MPa.

[0088] Embodiment [18-21]:

[0089] Taking the process of producing 50,000 tons / year of allyl acetate as an example, the second absorption tower 40 adopts a packed tower, the operating pressure of the second absorption tower 40 is 0.8Mpa, the flow rate of the exhaust gas flow transported into the second absorption tower 40 is 70% of the flow rate of the exhaust gas flow, the feed temperature of the first absorption liquid is 20°C, and the feed amount of the first absorption liquid in the second absorption tower 40 is changed to investigate the changes in the mass concentration of propylene discharged into the RTO gas, the mass concentration of propane in the circulating gas flow, and the selectivity of the target product allyl acetate. The reference standard for the changes in the mass concentration of propane in the circulating gas flow and the selectivity of the process allyl acetate is an allyl acetate device without the second absorption tower 40 process.

[0090] Table 5

[0091]

[0092]

[0093] It can be seen from Table 5 that the more the first absorption liquid, the better the absorption effect of the first absorption liquid on propylene and propane. When the first absorption liquid accounts for 4% to 5% of the top extraction of the distillation tower, the absorption effect of the first absorption liquid on propylene and propane has not changed significantly. Increasing the first absorption liquid will increase the energy consumption of the distillation tower 60, so the process preferably has a flow rate of the first absorption liquid accounting for 2%-5% of the top extraction of the distillation tower 60.

[0094] The above-mentioned embodiments are only preferred embodiments of the present invention and cannot be used to limit the scope of protection of the present invention. Any non-substantial changes and substitutions made by technicians in this field on the basis of the present invention shall fall within the scope of protection required by the present invention.

Claims

1. A method for preparing allyl acetate and recovering propylene and propane, characterized in that: The steps include: Passing a gas raw material into a reactor to react and generate allyl acetate, wherein the gas raw material comprises propylene, acetic acid, oxygen and an inert gas; Using a first condenser to condense the material discharged from the bottom of the reactor, so that the condensed material is discharged into the bottom of the first absorption tower; Using a first compressor to pump gas in the material out from the top of the first absorption tower as a circulating gas flow, a portion of the circulating gas flow is transported to the reactor, and the remaining portion is used as an exhaust gas flow, a portion of the exhaust gas flow is transported to the bottom of the second absorption tower, and the remaining portion of the exhaust gas flow is discharged, and the liquid in the material is discharged from the bottom of the first absorption tower into a crude product storage tank and a distillation tower in sequence, and the gas flashed out in the crude product storage tank is pumped back to the bottom of the first absorption tower using a second compressor; A portion of the produced stream entering the gas-liquid separation tank from the top of the rectification tower is condensed in the second condenser and then introduced into the top of the second absorption tower as the first absorption liquid, so that the first absorption liquid and the exhaust gas stream are in countercurrent contact in the second absorption tower to obtain a rich liquid absorbing propylene and propane, and the waste gas from which propylene and propane are removed in the second absorption tower is combined with the exhaust portion of the exhaust gas stream and discharged together; The rich liquid is discharged into the crude product storage tank, and the second compressor also pumps the gas flashed from the rich liquid in the crude product storage tank back to the bottom of the first absorption tower.

2. The method according to claim 1, characterized in that The gas separated by the gas-liquid separation tank is also introduced into the crude product storage tank, and the second compressor also pumps the gas recovered from the gas-liquid separation tank to the crude product storage tank.

3. The method according to claim 1, characterized in that The flow rate of the exhaust gas stream is less than 1% by weight of the flow rate of the recycle gas stream.

4. The method according to claim 3, characterized in that The flow rate of the portion of the exhaust gas stream transported into the second absorption tower is 50% to 100% of the flow rate of the exhaust gas stream by weight.

5. The method according to claim 1, characterized in that The operating pressures of the first absorption tower and the second absorption tower are the same and lower than the operating pressure of the reactor. The operating pressures of the first absorption tower and the second absorption tower are 0.5-0.9 MPa.

6. The method according to claim 1, characterized in that The feed temperature of the first absorption liquid is 10-40°C.

7. The method according to claim 6, characterized in that By weight, the flow rate of the first absorption liquid is 2%-5% of the overhead output of the distillation tower.

8. The method according to claim 1, characterized in that The second absorption tower comprises a packed tower, a plate tower or a floating valve tower.

9. The method according to claim 1, characterized in that After the condensed material is discharged into the first absorption tower, the method further comprises: A second absorption liquid is introduced from the top of the first absorption tower, and the second absorption liquid is used to absorb the uncondensed allyl acetate vapor.

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