A method and device for recovering ethylene in ethylene gas containing seal oil

Abstract

The present invention provides a method and a device for recovering ethylene in ethylene gas containing seal oil, relating to the technical field of ethylene recovery. In the present invention, ethylene glycol diacetate is used as a solvent to absorb ethylene in the ethylene gas containing seal oil, and the obtained ethylene-rich liquid is analyzed, so as to realize the efficient separation and recovery of ethylene. The recovery rate of ethylene is high, and the recovered ethylene can be directly used in the production of vinyl acetate by the ethylene method, greatly reducing the consumption of ethylene raw materials in the process of producing vinyl acetate by the ethylene method. Moreover, ethylene glycol diacetate is produced as a by-product in the process of producing vinyl acetate by the ethylene method. In the present invention, ethylene glycol diacetate (EGDA) is used as a solvent, and no new impurities are introduced.

Description

Technical Field

[0001] The present invention relates to the technical field of ethylene recovery, and particularly relates to a method and a device for recovering ethylene in ethylene gas containing seal oil. Background Art

[0002] Vinyl acetate is an important chemical raw material and can be widely used as a raw material for the preparation of polyvinyl alcohol, ethylene-vinyl acetate copolymer, ethylene-vinyl alcohol copolymer, coatings, adhesives, textile processing, paper coatings, etc. The production methods of vinyl acetate are divided into the ethylene method and the acetylene method, and among them, the ethylene method is more widely used as an environmentally friendly route.

[0003] In the process of preparing vinyl acetate by the ethylene method, the recycle gas compressor is the core equipment of this process flow. The seal system of some models of this compressor is an oil seal system. In order to prevent the seal oil in the oil seal system from entering the process system, a stream of ethylene gas is required as a protective gas to be continuously discharged. This stream of ethylene gas will carry out a certain amount of seal oil during the discharge process, and the seal oil will cause chronic poisoning of the precious metal catalyst, resulting in the inability of this stream of ethylene gas to return to the original system for recycling, causing waste of raw material ethylene.

[0004] At present, there is already a method of using a mixed solution of acetic acid and vinyl acetate in the distillation section of vinyl acetate production as an absorbent to recover ethylene in the refined gas discharged gas. This method uses the absorbent as an absorbent and sprays deionized water in the upper section of the ethylene recovery tower to remove acetic acid in the recovered ethylene. The ethylene recovery rate of this method is 60 - 95%, but when this method is used to treat ethylene in the oil seal system, not only will the seal oil be brought into the absorbent, and this part of the absorbent will directly enter and return to the reaction section, and the seal oil will damage the catalyst, but also the entrainment of deionized water will increase the energy consumption of the distillation section. Therefore, this method is not suitable for recovering ethylene in the compressor oil seal system. The vinyl acetate process has high requirements for impurities in the recycle gas, and currently there is no efficient recovery method for recovering ethylene in the compressor oil seal system. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a method and a device for recovering ethylene in ethylene gas containing seal oil. The recovery method provided by the present invention can achieve efficient recovery of ethylene in ethylene gas containing seal oil.

[0006] In order to achieve the above-mentioned invention purpose, the present invention provides the following technical solutions:

[0007] The present invention provides a method for recovering ethylene in ethylene gas containing seal oil, comprising the following steps:

[0008] Absorbing ethylene in the ethylene gas containing seal oil with ethylene glycol diacetate to obtain an ethylene-rich liquid;

[0009] The ethylene-rich liquid is subjected to desorption to obtain recycled ethylene gas.

[0010] Preferably, the mass ratio of the ethylene gas containing seal oil to ethylene glycol diacetate is 1:50 to 100;

[0011] The mass fraction of ethylene in the ethylene gas containing seal oil is 50 to 99%.

[0012] Preferably, the pressure of the absorption is 2 to 8 bar and the temperature is 15 to 60 °C.

[0013] Preferably, the pressure of the desorption is 0 to 1 bar and the temperature is 15 to 100 °C;

[0014] The desorption includes vacuum flash separation.

[0015] Preferably, the desorption also obtains a desorption-rich liquid. The desorption-rich liquid is subjected to rectification to obtain recycled ethylene glycol diacetate, and the recycled ethylene glycol diacetate is used in the absorption step.

[0016] Preferably, the pressure of the rectification is 0 to 1 bar and the reflux ratio is 2 to 5.

[0017] The present invention also provides a recycling device for the recycling method described in the above technical solution, including an ethylene absorption tower 1 and an ethylene desorption tower 2;

[0018] The ethylene absorption tower 1 is provided with a raw gas inlet, a non-condensable gas outlet of the absorption tower, and an absorption tower liquid outlet;

[0019] The ethylene desorption tower 2 is provided with a desorption tower liquid inlet, a desorption tower liquid outlet, and a recycled ethylene outlet; the desorption tower liquid inlet is communicated with the absorption tower liquid outlet.

[0020] Preferably, the ethylene desorption tower 2 includes a flash tank.

[0021] Preferably, the recycling device is further provided with a solvent recovery rectification tower 3, a solvent condenser 4, and a solvent recovery tank 5;

[0022] The solvent recovery rectification tower 3 is provided with a rectification tower reboiler 7, a rectification tower liquid inlet, a recycled solvent inlet of the rectification tower, a rectification tower gas outlet, and a seal oil outlet; the rectification tower liquid inlet is communicated with the desorption tower liquid outlet;

[0023] The solvent condenser 4 is provided with a condenser inlet and a condenser outlet, and the condenser inlet is communicated with the rectification tower gas outlet;

[0024] The solvent recovery tank 5 is provided with a recovery tank inlet, a recovery tank solvent outlet, and a recovery tank non-condensable gas outlet. The recovery tank inlet is communicated with the condenser outlet, and the recovery tank solvent outlet is communicated with the rectification column recovery solvent inlet through a solvent reflux pump 6.

[0025] Preferably, the ethylene absorption tower 1 is further provided with an absorption tower recovery solvent inlet; the recovery tank solvent outlet is communicated with the absorption tower recovery solvent inlet.

[0026] In the present invention, ethylene glycol diacetate (EGDA) is used as a solvent to absorb ethylene in ethylene gas containing seal oil, and the obtained ethylene-rich liquid is analyzed to achieve efficient separation and recovery of ethylene. The recovery rate of ethylene is high, and the recovered ethylene can be directly used in the production of vinyl acetate by the ethylene method, greatly reducing the consumption of ethylene raw materials in the process of producing vinyl acetate by the ethylene method. Moreover, ethylene glycol diacetate is produced as a by-product in the process of producing vinyl acetate by the ethylene method. Using ethylene glycol diacetate (EGDA) as a solvent in the present invention will not introduce new impurities.

[0027] The present invention rectifies the analyzed rich liquid to obtain recovered ethylene glycol diacetate for the absorption step, realizing continuous and stable operation of ethylene recovery from ethylene gas containing seal oil. Moreover, deionized water is not used in the process of recovering ethylene in the present invention, and the energy consumption of the subsequent rectification section is low.

[0028] The present invention introduces ethylene gas containing seal oil and EGDA into the ethylene absorption tower 1, uses EGDA to absorb ethylene to obtain an ethylene-rich liquid, and reduces the pressure of the ethylene-rich liquid and then introduces it into the ethylene analysis tower 2 for analysis to obtain recovered ethylene gas. Using the recovery device provided by the present invention can achieve efficient recovery of ethylene from ethylene gas containing seal oil, and the recovery rate of ethylene is high.

[0029] The present invention transports the analyzed rich liquid to the solvent recovery rectification column 3 for rectification to obtain recovered ethylene glycol diacetate and recovered seal oil. The recovered ethylene glycol diacetate is discharged from the top of the solvent recovery rectification column 3, condensed by the solvent condenser 4, passed through the solvent recovery tank 5 and the solvent reflux pump 6, and then returned to the ethylene absorption tower 1 for recycling, realizing continuous and stable operation of ethylene recovery from ethylene gas containing seal oil and with low energy consumption. Description of the Drawings

[0030] Figure 1 It is a schematic structural diagram of the recovery device in the present invention, wherein 1 is an ethylene absorption tower, 2 is an ethylene analysis tower, 3 is a solvent recovery rectification column, 4 is a solvent condenser, 5 is a solvent recovery tank, 6 is a solvent reflux pump, and 7 is a rectification column reboiler. Detailed Embodiments

[0031] The present invention provides a method for recovering ethylene from ethylene gas containing seal oil, comprising the following steps:

[0032] Absorbing ethylene in the ethylene gas containing seal oil with ethylene glycol diacetate (EGDA) to obtain ethylene-rich liquid;

[0033] Analyzing the ethylene-rich liquid to obtain recovered ethylene gas.

[0034] Unless otherwise specified, the materials and equipment used in the present invention are commercially available products in the art.

[0035] The present invention absorbs ethylene in the ethylene gas containing seal oil with ethylene glycol diacetate to obtain ethylene-rich liquid.

[0036] In the present invention, the mass fraction of ethylene in the ethylene gas containing seal oil is preferably 50-99%, and in specific embodiments, it can be 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 95.3%, 95.5%, 95.8%, 96%, 96.2%, 96.5%, 96.6%, 96.8%, 97% or 97.3%. In the present invention, the ethylene gas containing seal oil preferably includes the ethylene-rich gas discharged from the compressor oil seal system in the vinyl acetate plant.

[0037] In the present invention, the mass ratio of the ethylene gas containing seal oil to ethylene glycol diacetate is preferably 1:50-100, and in specific embodiments, it can be 1:50, 1:55, 1:60, 1:65, 1:67, 1:70, 1:75, 1:80, 1:85, 1:86, 1:90, 1:95 or 1:100. Since a part of EGDA is generated in the process of producing vinyl acetate by the ethylene method, the small amount of EGDA entrained in the recovered ethylene gas will not affect the system and catalyst for producing vinyl acetate by the ethylene method.

[0038] In the present invention, the pressure of the absorption is preferably 2-8 bar, and in specific embodiments, it can be 2 bar, 2.5 bar, 3 bar, 3.5 bar, 4 bar, 4.5 bar, 5 bar, 5.5 bar, 6 bar, 6.5 bar, 7 bar, 7.5 bar or 8 bar; the temperature of the absorption is preferably 15-60 °C, and in specific embodiments, it can be 15 °C, 20 °C, 25 °C, 30 °C, 35 °C, 40 °C, 45 °C, 50 °C, 55 °C or 60 °C.

[0039] After obtaining the ethylene-rich liquid, the present invention analyzes the ethylene-rich liquid to obtain recovered ethylene gas.

[0040] In the present invention, the pressure for desorption is preferably 0 to 1 bar, and in specific embodiments, it can be 0 bar, 0.1 bar, 0.2 bar, 0.3 bar, 0.4 bar, 0.5 bar, 0.6 bar, 0.7 bar, 0.8 bar, 0.9 bar or 1 bar; the temperature for desorption is preferably 15 to 100 °C, and in specific embodiments, it can be 15 °C, 20 °C, 25 °C, 30 °C, 35 °C, 40 °C, 45 °C, 50 °C, 55 °C, 60 °C, 65 °C, 70 °C, 75 °C, 80 °C, 85 °C, 90 °C, 95 °C or 100 °C. In the present invention, the desorption preferably includes vacuum flashing separation. The recovered ethylene gas obtained in the present invention is used for the production of vinyl acetate by the ethylene method.

[0041] In the present invention, the desorption preferably further yields a desorbed rich liquid. The desorbed rich liquid is rectified to obtain recovered ethylene glycol diacetate, and the recovered ethylene glycol diacetate is used in the absorption step.

[0042] In the present invention, the pressure for rectification is preferably 0 to 1 bar, and in specific embodiments, it can be 0 bar, 0.1 bar, 0.2 bar, 0.3 bar, 0.4 bar, 0.5 bar, 0.6 bar, 0.7 bar, 0.8 bar, 0.9 bar or 1 bar; the reflux ratio for rectification is preferably 2 to 5, and in specific embodiments, it can be 2, 2.5, 3, 3.5, 4, 4.5 or 5.

[0043] The present invention also provides a recovery device for use in the above-described recovery method. The structural schematic diagram is shown in Figure 1 and will be described in detail below in conjunction with Figure 1 the recovery device.

[0044] The recovery device for ethylene in ethylene gas containing seal oil provided by the present invention includes an ethylene absorption tower 1 and an ethylene desorption tower 2, and preferably further includes a solvent recovery rectification tower 3, a solvent condenser 4, a solvent recovery tank 5 and a solvent reflux pump 6.

[0045] In the present invention, the ethylene absorption tower 1 is provided with a raw gas inlet, an absorption tower non-condensable gas outlet and an absorption tower liquid outlet, and preferably further includes an absorption tower recovered solvent inlet. In the present invention, the non-condensable gas is nitrogen that permeates out, and the amount is very small.

[0046] In the present invention, the ethylene desorption tower 2 is provided with a desorption tower liquid inlet, a desorption tower liquid outlet and a recovered ethylene outlet; the desorption tower liquid inlet is communicated with the absorption tower liquid outlet. In the present invention, the ethylene desorption tower is preferably a flash tank.

[0047] In the present invention, the solvent recovery rectification column 3 is preferably provided with a rectification column reboiler 7, a rectification column liquid inlet, a rectification column recovered solvent inlet, a rectification column gas outlet, and a seal oil outlet; the rectification column liquid inlet is communicated with the outlet of the stripping column. In the present invention, the rectification column reboiler preferably includes a steam heating thermosyphon reboiler.

[0048] In the present invention, the solvent condenser 4 is preferably provided with a condenser inlet and a condenser outlet, and the condenser inlet is communicated with the rectification column gas outlet.

[0049] In the present invention, the solvent recovery tank 5 is preferably provided with a recovery tank inlet, a recovery tank solvent outlet, and a recovery tank non-condensable gas outlet. The recovery tank inlet is communicated with the condenser outlet, and the recovery tank solvent outlet is respectively communicated with the rectification column recovered solvent inlet and the absorption column recovered solvent inlet through a solvent reflux pump 6.

[0050] The following Figure 1 will describe in detail the method for recovering ethylene in the ethylene gas containing seal oil.

[0051] The ethylene gas containing seal oil and EGDA are introduced into the ethylene absorption column 1, and EGDA is used to absorb ethylene to obtain an ethylene-rich liquid. The ethylene-rich liquid is introduced into the ethylene stripping column 2 under reduced pressure for stripping to obtain recovered ethylene gas and stripped rich liquid respectively.

[0052] After obtaining the stripped rich liquid, the present invention preferably further includes transporting the stripped rich liquid to the solvent recovery rectification column 3 for rectification to obtain recovered ethylene glycol diacetate and recovered seal oil respectively; the recovered ethylene glycol diacetate is discharged from the top of the solvent recovery rectification column 3, condensed by the solvent condenser 4, passed through the solvent recovery tank 5 and the solvent reflux pump 6, and returned to the ethylene absorption column 1 for the absorption step; the recovered seal oil is discharged from the bottom of the solvent recovery rectification column 3. In the present invention, the recovered seal oil also contains a part of the solvent EGDA. Discharging the recovered seal oil can ensure the purity of the recovered EGDA, so that the seal oil will not return to the system to cause entrainment of seal oil in the system, thereby contaminating the noble metal catalyst.

[0053] To further illustrate the present invention, the following will describe in detail the method and device for recovering ethylene in the ethylene gas containing seal oil provided by the present invention with reference to embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0054] In the following embodiments, the ethylene-rich gas is the ethylene-rich gas discharged from the compressor oil seal system in the vinyl acetate plant.

[0055] Example 1

[0056] Adopt Figure 1The ethylene recovery device shown recovers ethylene, and the specific steps are as follows: The ethylene-rich gas (ethylene mass concentration is 97.3%, and other components are seal oil) is fed into the ethylene absorption tower 1 at a flow rate of 40 kg / h. EGDA (flow rate is 3000 kg / h) is fed into the top of the ethylene absorption tower 1, and EGDA is used to absorb ethylene to obtain ethylene-rich liquid (containing ethylene, seal oil and EGDA). The ethylene-rich liquid is discharged from the bottom of the ethylene absorption tower 1, and after depressurization, it is fed into the flash tank in the ethylene stripping tower (flash tank) 2 for vacuum flash separation to obtain recovered ethylene gas (containing a small amount of EGDA) and stripped rich liquid respectively; The recovered ethylene gas (flow rate is 34 kg / h, purity is 99.6%) returns from the top of the ethylene stripping tower 2 to the vinyl acetate recycle gas system for reuse. The stripped rich liquid (containing seal oil and EGDA) enters the solvent recovery distillation column 3 for distillation to obtain recovered ethylene glycol diacetate and recovered seal oil respectively; The recovered ethylene glycol diacetate is discharged from the top of the solvent recovery distillation column 3, condensed by the solvent condenser 4, passed through the solvent recovery tank 5 and the solvent reflux pump 6, and then returned to the ethylene absorption tower 1 for recycling. The recovered seal oil is discharged from the bottom of the solvent recovery distillation column 3. Among them, the pressure of the ethylene absorption tower 1 is 6 bar and the temperature is 35 °C; the temperature inside the ethylene stripping tower 2 is 57 °C and the pressure is 0.8 bar; the recovery ratio inside the solvent recovery distillation column 3 is 4. In this embodiment, the recovery rate of ethylene is 85%, which greatly reduces the consumption of ethylene. Since a part of EGDA is generated during the production of vinyl acetate by the ethylene method, the small amount of EGDA entrained in the recovered ethylene will not affect the system and catalyst for the production of vinyl acetate by the ethylene method.

[0057] Example 2

[0058] Ethylene is recovered according to the method of Example 1. The difference from Example 1 is only that: the mass concentration of ethylene in the ethylene-rich gas is 96.6%, and the flow rate of the ethylene-rich gas is 50 kg / h; the flow rate of EGDA fed into the top of the ethylene absorption tower 1 is 4000 kg / h; the pressure of the ethylene absorption tower 1 is 5.6 bar and the temperature is 25 °C; the temperature inside the ethylene stripping tower 2 is 40 °C and the pressure is 1.2 bar; the flow rate of the recovered ethylene gas is 41 kg / h, and the purity of the recovered ethylene gas is 99.9%; the recovery ratio inside the solvent recovery distillation column 3 is 3.5. In this embodiment, the recovery rate of ethylene is 82%.

[0059] Example 3

[0060] Ethylene is recovered according to the method of Example 1, with the only difference from Example 1 being that: the mass concentration of ethylene in the ethylene-rich gas is 95.3%, and the flow rate of the ethylene-rich gas is 30 kg / h; the flow rate of EGDA introduced from the top of the ethylene absorption column 1 is 2000 kg / h; the pressure of the ethylene absorption column 1 is 7 bar and the temperature is 30 °C; the temperature inside the ethylene desorption column 2 is 60 °C and the pressure is 1 bar; the flow rate of the recovered ethylene gas is 26 kg / h, and the purity of the recovered ethylene gas is 99.5%; the recovery ratio in the solvent recovery distillation column 3 is 4.5. The recovery rate of ethylene in this example is 86%.

[0061] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for recovering ethylene from ethylene gas containing sealing oil, comprising the following steps: Using ethylene glycol diacetate to absorb ethylene in ethylene gas containing sealing oil to obtain ethylene-rich liquid; Decomposing the ethylene-rich liquid to obtain recovered ethylene gas and decomposed rich liquid; The analyzed rich liquid is distilled to obtain recovered ethylene glycol diacetate, and the recovered ethylene glycol diacetate is used in the absorption step.

2. The recycling method according to claim 1, characterized in that: The mass ratio of the ethylene gas containing sealing oil to ethylene glycol diacetate is 1:50-100; The mass fraction of ethylene in the ethylene gas containing sealing oil is 50-99%.

3. The recovery method according to claim 1 or 2, characterized in that: The absorption pressure is 2-8 bar and the temperature is 15-60°C.

4. The recycling method according to claim 1, characterized in that: The analysis pressure is 0~1 bar and the temperature is 15~100°C; The analysis includes vacuum flash separation.

5. The recycling method according to claim 1, characterized in that: The distillation pressure is 0-1 bar, and the reflux ratio is 2-5.

6. The recovery method according to claim 1, 2, 4 or 5, characterized in that: The recovery device used includes an ethylene absorption tower (1), an ethylene analysis tower (2), a solvent recovery distillation tower (3) and a solvent recovery tank (5); The ethylene absorption tower (1) is provided with a raw gas inlet, an absorption tower non-condensable gas outlet, an absorption tower liquid outlet and an absorption tower recovery solvent inlet; The ethylene desorption tower (2) is provided with a desorption tower liquid inlet, a desorption tower liquid outlet and a recovered ethylene outlet; the desorption tower liquid inlet is connected to the absorption tower liquid outlet; The solvent recovery distillation tower (3) is provided with a distillation tower reboiler (7), a distillation tower liquid inlet, a distillation tower recovery solvent inlet, a distillation tower gas outlet and a sealing oil outlet, and the distillation tower liquid inlet is connected to the analytical tower liquid outlet; The solvent recovery tank (5) is provided with a recovery tank inlet, a recovery tank solvent outlet and a recovery tank non-condensable gas outlet. The recovery tank inlet is connected to the condenser outlet. The recovery tank solvent outlet is connected to the distillation tower recovery solvent inlet via a solvent reflux pump (6). The recovery tank solvent outlet is connected to the absorption tower recovery solvent inlet.

7. The recycling method according to claim 6, characterized in that: The ethylene analysis tower (2) comprises a flash tank.

8. The recycling method according to claim 7, characterized in that: The recovery device is also provided with a solvent condenser (4) and a solvent recovery tank (5); The solvent condenser (4) is provided with a condenser inlet and a condenser outlet, and the condenser inlet is communicated with the gas outlet of the distillation tower.

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