A multi-membrane coupling recovery process for tail gas of ethylene oxidation deep processing device

Abstract

The application provides a multi-membrane coupling recovery process for tail gas of ethylene oxidation deep processing device, and belongs to the field of chemistry and chemical engineering. Through the complementary effect of the rubber state membrane assembly and the glass state membrane assembly in the selective aspect, the multi-membrane coupling recovery process can simultaneously ensure the control of the oxygen enrichment degree and the efficient removal of the inert gas, which can avoid the safety hidden danger of explosion of the recovery device, and weaken the negative influence of the recovery device on the production capacity of the oxidation deep processing device, so that the full recovery of the raw material ethylene is realized safely, stably and efficiently. The multi-membrane coupling recovery process can realize the ethylene recovery rate of 88.6% for the tail gas of the ethylene glycol production device, and can realize the ethylene recovery rate of 94.1% for the tail gas of the vinyl acetate production device; according to the technical and economic evaluation results, the membrane method recovery system for the tail gas of the ethylene oxidation deep processing device is established based on the process, and the payback period is not more than 4 months.

Description

TECHNICAL FIELD

[0001] The present application relates to a multi-membrane coupling process for deep recovery of ethylene in ethylene oxidation deep processing device tail gas, belonging to the field of chemistry and chemical engineering. For the tail gas discharged by the ethylene oxidation deep processing device, light hydrocarbon membrane separation technology and oxygen membrane separation technology are coupled and integrated to realize efficient recovery and utilization of the reaction raw material ethylene. BACKGROUND

[0002] Ethylene is one of the largest chemical products in the world, and its derivative products account for three quarters of petrochemical products, playing an important role in the national economy. Catalytic oxidation and ozonation processing is an important means to obtain ethylene derivative products on a large scale, and can obtain many products such as ethylene oxide, ethylene glycol, vinyl acetate, acetaldehyde and acetic acid. In order to control the oxidation degree and oxidation selectivity of ethylene deep processing, and thus efficiently obtain the target product, the catalytic oxidation and ozonation reaction process often adopts an incomplete conversion operation mode, and excess ethylene will be recycled through a combined process of reaction-separation; in addition, ethylene and oxygen contain some substances that do not participate in the reaction, such as nitrogen, argon and methane, in order to avoid excessive accumulation of these inert substances in the ethylene recycling process and thus cause a substantial decrease in the reaction raw material partial pressure and reaction rate, the ethylene oxidation deep processing device usually needs to discharge a part of the circulating gas to ensure the material balance inside the device.

[0003] The production tail gas discharged by the ethylene catalytic oxidation device and the ethylene ozonation device contains a large amount of ethylene, causing great waste of raw materials. A 200,000 tons / year vinyl acetate production device of an enterprise needs to discharge about 160 standard cubic meters of production tail gas per hour in order to ensure the material balance of argon and nitrogen, with an ethylene concentration of 75.0 mol%, a nitrogen concentration of about 5.0 mol%, an argon concentration of about 12.9 mol%, and an oxygen concentration of about 4.2 mol%; according to the calculation of 8400 hours of operation per year, the loss of ethylene reaches 1106 tons, accounting for about 1.58% of the total consumption, with a total value of more than 7 million yuan. A 750,000 tons / year ethylene glycol production device of an enterprise also needs to discharge more than 1460 standard cubic meters of production tail gas per hour in order to ensure the material balance of argon and nitrogen, with an ethylene concentration of 34.0 mol%, a methane concentration of about 47.6 mol%, a nitrogen concentration of about 4.2 mol%, an argon concentration of about 5.3 mol%, and an oxygen concentration of about 6.4 mol%; according to the calculation of 8400 hours of operation per year, the loss of ethylene reaches 4575 tons, accounting for about 0.91% of the total consumption, with a total value of nearly 30 million yuan. In summary, the recovery of ethylene from the production tail gas of the ethylene oxidation deep processing device can greatly reduce the loss of raw materials and has significant economic benefits.

[0004] For the tail gas discharged from the ethylene deep processing device, the recovery process needs to solve the following problems: 1) to realize high concentration and high yield separation and enrichment of ethylene; 2) to avoid water freezing and ensure continuous and stable operation of the system; 3) to avoid extreme operating conditions such as ultra-low temperature and improve process energy efficiency; 4) to avoid the oxygen-containing mixture at the key node position within the explosion limit range.

[0005] Compression condensation, adsorption, absorption and membrane separation are commonly used ethylene separation and recovery process technologies. Due to the limitation of oxygen and water vapor on the recovery process, compression condensation (water vapor freezing blocks the pipeline), adsorption (there is a risk of combustion and explosion in the oxygen-containing system during the adsorption exothermic process) cannot meet the requirements. In the absorption process, volatile absorption medium will be used, which has the risk of entrainment affecting the ethylene oxidation deep processing device, in addition, the absorption process includes large tower devices such as absorption tower and desorption tower, which has the problem of site limitation for tail gas recovery process and high construction difficulty. Gas membrane separation is a new type of high-efficiency separation technology based on the difference in permeation rate, which can realize target directional enrichment without phase change, and is not affected by water vapor freezing; the membrane separation process has no obvious heat effect, and the risk of combustion and explosion is low; the membrane assembly increases the production capacity through modular assembly, and the equipment in the membrane system can be customized according to the space of the construction site. In summary, gas membrane separation is a key technology for recycling ethylene from the tail gas discharged from the ethylene oxidation deep processing device.

[0006] The membrane method ethylene recovery process is not limited by oxygen, water vapor and construction site in the mixed system. However, the recovery rate of the ethylene recovery process is limited by the enrichment of oxygen, and improving the recovery rate while ensuring the safe and stable operation of the system is the first key problem that needs to be solved in process design and development. In addition, improving the ethylene recovery rate often accompanies higher accumulation of inert gas, which seriously affects the production capacity of the ethylene oxidation deep processing device, and at the same time, ensuring high recovery rate and high concentration enrichment of ethylene is the second key problem that needs to be solved in process design and development.

[0007] In view of the two key problems of recovering reaction raw materials in the membrane method ethylene oxidation deep processing device tail gas, the present application integrates rubbery membrane components that preferentially permeate ethylene and glassy membrane components that preferentially permeate oxygen, and realizes the control of oxygen enrichment degree and efficient removal of inert gas through the complementary selectivity of the two membrane permeations, to build a multi-membrane coupling recovery process that can safely, stably and efficiently realize the full recovery and utilization of ethylene. SUMMARY

[0008] The application aims to provide a multi-membrane coupling process for deeply recycling ethylene in ethylene oxidation deep processing device tail gas.

[0009] The technical scheme of the application is as follows:

[0010] A multi-membrane coupling recovery process for ethylene oxidation deep processing device tail gas, ethylene oxidation deep processing device production tail gas S1 is controlled in flow by an adjusting valve and then enters a first buffer tank 1, enters a precision filter 2 after pressure stabilization, obtains solid particle-containing waste gas S2 in the interception channel of the precision filter 2, and obtains pre-treatment qualified membrane unit feed gas S3 in the permeation channel of the precision filter 2, the membrane unit feed gas S3 enters a first membrane separation unit 3 assembled by a rubbery membrane assembly; ethylene-enriched first permeation gas S4 is obtained in the low-pressure side channel of the first membrane separation unit 3, enters a first compressor 5 after pressure stabilization by a second buffer tank 4, then enters a first cooler 6, and finally obtains circulating product gas S5; first retentate gas S6 from which most of the ethylene is removed is obtained in the high-pressure side channel of the first membrane separation unit 3, and then enters a second membrane separation unit 7 assembled by a glassy membrane assembly as raw material gas; oxygen-enriched second permeation gas S7 is obtained in the low-pressure side channel of the second membrane separation unit 7, enters the second buffer tank 4 to be compressed with the first permeation gas S4; second retentate gas S8 from which part of the oxygen is removed is obtained in the high-pressure side channel of the second membrane separation unit 7, and then enters a third membrane separation unit 8 assembled by a rubbery membrane assembly as raw material gas; residual tail gas S9 after membrane recovery is obtained in the high-pressure side channel of the third membrane separation unit 8, and is sent to a fuel gas pipe network; ethylene preliminarily enriched third permeation gas S10 is obtained in the low-pressure side channel of the third membrane separation unit 8, enters a second compressor 10 after pressure stabilization by a third buffer tank 9, then enters a second cooler 11, and finally obtains ethylene-enriched circulating gas S11 inside the recovery device, which enters the first buffer tank 1 to be precision filtered with the ethylene oxidation deep processing device production tail gas S1.

[0011] The beneficial effects of the present application are: by integrating the rubbery membrane module which preferentially permeates ethylene and the glassy membrane module which preferentially permeates oxygen, the highly enriched recovery of ethylene is achieved, while avoiding the highly enriched oxygen in the tail gas of the membrane device, ensuring that the tail gas membrane recovery process of the ethylene oxidation deep processing device can be safely, stably and efficiently operated; on the basis of the safe and stable operation ensured by the rubbery membrane module and the glassy membrane module, the efficient removal of inert gases such as argon and nitrogen is realized through the two-stage circulating membrane separation process, which greatly reduces the adverse effects of the membrane recovery device on the production capacity of the ethylene oxidation deep processing device; taking the tail gas recovery process of the ethylene glycol production device as an example, the traditional membrane separation recovery process using only the rubbery membrane module, when the ethylene recovery rate reaches 75%, the composition of the tail gas of the membrane device is very close to the explosion limit (oxygen concentration is more than 8.8 mol%), and at the same time, the tail gas flow of the ethylene glycol production device is increased to 2.17 times of the original process, while the recovery process of the multiple membrane technologies coupled in the present application can ensure that the composition of the tail gas of the membrane device is far away from the explosion limit (oxygen concentration is less than 8.0 mol%) even if the ethylene recovery rate is increased to more than 88%, and at the same time, the tail gas flow of the ethylene glycol production device is only increased to 2.13 times of the original process. In summary, the recovery process of the multiple membrane technologies coupled in the present application can simultaneously meet the two key requirements of oxygen enrichment degree control and inert gas efficient removal, thereby safely, stably and efficiently realizing the full recovery and utilization of raw material ethylene in the tail gas of the ethylene oxidation deep processing device. BRIEF DESCRIPTION OF DRAWINGS

[0012] Figure 1 is a multi-membrane coupling recovery process flow diagram for the tail gas of the ethylene oxidation deep processing device.

[0013] Symbols and numbers in the figure: S1, tail gas of the ethylene oxidation deep processing device; S2, waste gas containing solid particles; S3, membrane unit feed gas; S4, first permeate gas enriched in ethylene; S5, circulating product gas; S6, first retentate gas; S7, second permeate gas enriched in oxygen; S8, second retentate gas; S9, residual tail gas after membrane recovery; S10, third permeate gas preliminarily enriched in ethylene; S11, ethylene-rich circulating gas inside the recovery device; 1, first buffer tank; 2, precision filter; 3, first membrane separation unit assembled from the rubbery membrane module; 4, second buffer tank; 5, first compressor; 6, first cooler; 7, second membrane separation unit assembled from the glassy membrane module; 8, third membrane separation unit assembled from the rubbery membrane module; 9, third buffer tank; 10, second compressor; 11, second cooler. DETAILED DESCRIPTION

[0014] The present application will be further described below in conjunction with the drawings and specific examples.

[0015] Example 1

[0016] Example 1 is directed to the tail gas generated by the oxidation process of a 750,000 tons / year ethylene glycol production device of a certain petrochemical enterprise, and the multi-membrane coupling process specially proposed by the present application is used to safely, stably and efficiently realize the full recycling of raw material ethylene. When there is no ethylene recovery device, the ethylene glycol device generates tail gas of 1460 standard cubic meters per hour, wherein the ethylene concentration is 34.0 mol%, the methane concentration is 47.6 mol%, the nitrogen concentration is 4.2 mol%, the argon concentration is 5.3 mol%, and the oxygen concentration is 6.4 mol%; In addition, the production tail gas also contains a small amount of ethane, ethylene oxide, carbon dioxide and water vapor. According to the estimation, the ethylene glycol device loses about 621.0 kilograms of ethylene per hour, and according to the annual operation of 8400 hours, it loses 5216.4 tons of ethylene per year, and the total value is expected to exceed 33.9 million yuan.

[0017] The pressure of the tail gas S1 of the ethylene oxidation deep processing device is about 1.78 MPaG, and the temperature is about 40°C. After controlling the flow through the regulating valve, it enters the first buffer tank 1, and after the pressure is stabilized, it enters the precision filter 2, the pressure drop is less than 0.03 MPaG, the filtration precision is 0.10 μm, the waste gas S2 containing solid particles is obtained in the interception channel, and the pretreated qualified membrane unit feed gas S3 is obtained in the transmission channel, which enters the first membrane separation unit 3 assembled by the rubber state membrane assembly;

[0018] The permeation pressure of the first membrane separation unit 3 is 0.05 MPaG, and the permeation cut ratio is 57%; The first permeation gas S4 enriched in ethylene is obtained in the low-pressure side channel, wherein the ethylene concentration is 48.0 mol%, the methane concentration is 37.8 mol%, the nitrogen concentration is reduced to 1.9 mol%, the argon concentration is reduced to 3.8 mol%, and the oxygen concentration is reduced to 4.9 mol%; The first permeation gas S4 enters the first compressor 5 after the pressure is stabilized by the second buffer tank 4, and is pressurized to more than 1.90 MPaG, and then enters the first cooler 6 and is cooled to 40°C, and finally obtains the circulating product gas S5; The first permeation gas S6 is obtained in the high-pressure side channel, wherein the ethylene concentration is reduced to 12.3 mol%, the methane concentration is increased to 64.2 mol%, the nitrogen concentration is increased to 7.1 mol%, the argon concentration is increased to 7.4 mol%, and the oxygen concentration is increased to 8.4 mol%; The first permeation gas S6 then enters the second membrane separation unit 7 assembled by the glass state membrane assembly as the raw material gas;

[0019] The permeation pressure of the second membrane separation unit 7 is 0.05 MPaG, and the permeation cut ratio is 4%; the oxygen-enriched second permeation gas S7 is obtained in the low-pressure side channel, wherein the ethylene concentration is 8.2 mol%, the methane concentration is 40.0 mol%, the nitrogen concentration is 5.8 mol%, the argon concentration is 12.5 mol%, and the oxygen concentration is increased to 30.6 mol%; the second permeation gas S7 enters the second buffer tank 4, and the oxygen concentration of the first permeation gas S4 is 5.7 mol%, far from the explosion limit for compression treatment; the second residual gas S8 with part of the oxygen removed is obtained in the high-pressure side channel, wherein the ethylene concentration is 12.5 mol%, the methane concentration is 65.2 mol%, the nitrogen concentration is 7.2 mol%, the argon concentration is 7.2 mol%, and the oxygen concentration is reduced to 7.5 mol%; the second permeation gas S7 then enters the third membrane separation unit 8 equipped with a rubbery membrane assembly as a raw material gas;

[0020] The permeation pressure of the third membrane separation unit 8 is 0.05 MPaG, and the permeation cut ratio is 35%; the residual tail gas S9 after membrane recovery is obtained in the high-pressure side channel, wherein the ethylene concentration is 5.8 mol%, the methane concentration is 69.1 mol%, the nitrogen concentration is 9.1 mol%, the argon concentration is 7.9 mol%, and the oxygen concentration is not more than 8.0 mol%, far from the explosion limit, which can be directly sent to the fuel gas pipeline network after pressure reduction; the third permeation gas S10 with preliminary enrichment of ethylene is obtained in the low-pressure side channel, wherein the ethylene concentration is 24.7 mol%, the methane concentration is 58.2 mol%, the nitrogen concentration is 3.6 mol%, the argon concentration is 5.9 mol%, and the oxygen concentration is about 6.7 mol%, far from the explosion limit, which enters the second buffer tank 9 after stable pressure, then enters the second compressor 10, is pressurized to above 1.85 MPaG, then enters the second cooler 11, is cooled to 40℃, and finally the ethylene-rich circulating gas S11 inside the recovery device is obtained, which enters the first buffer tank 1 and is mixed with the ethylene oxidation deep processing device production tail gas S1 for precise filtration treatment.

[0021] According to the calculation, after adding the multi-membrane coupling process system of the present application, the production tail gas S1 discharged by the 750,000 tons / year ethylene glycol production device per hour increases to 3118 standard cubic meters, of which the ethylene flow is 1326.7 kg; the circulating product gas S5 returned from the membrane separation system to the ethylene glycol production device per hour is 2141 standard cubic meters, of which the ethylene flow is 1256.0 kg; the residual tail gas S9 discharged from the membrane separation system to the fuel gas pipeline network per hour is 977 standard cubic meters, of which the ethylene flow is 70.7 kg; compared with the ethylene loss amount before the recovery device is set, the ethylene recovery rate of the multi-membrane coupling process system of the present application reaches 88.6%, about 550.3 kg of ethylene can be recovered per hour, about 4622.5 tons of ethylene can be recovered per year, and the total value is about 30.04 million yuan.

[0022] The utilities of the membrane process ethylene recovery system are mainly the electricity consumption of the compressors and the circulating water consumption of the cooling process. The motor power of the first compressor 5 is about 260 kW, the motor power of the second compressor 10 is about 75 kW; the total circulating water consumption of the two compressors and the two coolers is 30 tons per hour. The technical and economic evaluation results show that based on the multi-membrane coupling process system described in the application, the recovery of raw material ethylene from the tail gas of a 750,000 tons / year ethylene glycol production device can create economic benefits of more than 26 million yuan per year, and the investment recovery period is expected to be no more than 4 months.

[0023] Example 2

[0024] Example 2 is directed to the tail gas generated by the oxidation process of a 200,000 tons / year vinyl acetate production device of a certain petrochemical enterprise, which uses the multi-membrane coupling process specially proposed by the application to safely, stably and efficiently realize the full recovery and utilization of raw material ethylene. Without an ethylene recovery device, the vinyl acetate production device generates tail gas of 140.0 standard cubic meters per hour, of which the ethylene concentration is 75.2 mol%, the nitrogen concentration is 5.0 mol%, the argon concentration is 13.0 mol%, and the oxygen concentration is 4.2 mol%; in addition, the production tail gas also contains a small amount of methane, ethane, carbon monoxide, carbon dioxide and water vapor. According to the calculation, the vinyl acetate production device loses about 131.7 kilograms of ethylene per hour, and according to the calculation of 8400 hours of annual operation, it loses 1106.3 tons of ethylene per year, with a total value of more than 7.19 million yuan.

[0025] According to the calculation, after adding the multi-membrane coupling process system described in the application, the production tail gas S1 flow of the 200,000 tons / year vinyl acetate production device per hour increases to 206.6 standard cubic meters, of which the ethylene flow is 194.4 kilograms; the circulating product gas S5 flow returned to the vinyl acetate production device from the membrane system per hour is 167.5 standard cubic meters, of which the ethylene concentration reaches 89.1 mol%, the nitrogen concentration decreases to 1.1 mol%, the argon concentration decreases to 5.1 mol%, and the mass flow of ethylene is 186.7 kilograms; the residual tail gas S9 flow discharged from the membrane separation system to the fuel gas pipe network per hour is 39.1 standard cubic meters, of which the ethylene flow is 7.7 kilograms; with reference to the ethylene loss before the recovery device is set, the ethylene recovery rate of the multi-membrane coupling process system described in the application reaches 94.1%, about 124.0 kilograms of ethylene can be recovered per hour, about 1041.6 tons of ethylene can be recovered per year, and the total value is about 6.77 million yuan.

[0026] The utilities of the membrane ethylene recovery system are mainly the electricity consumption of the compressors and the circulating water consumption of the cooling process. The motor power of the first compressor 5 is about 18 kW, and the motor power of the second compressor 10 is about 12.5 kW; the total circulating water consumption of the two compressors and the two coolers is 5 tons per hour. The technical and economic evaluation results show that based on the multi-membrane coupling process system described in the application, the raw material ethylene is recovered from the tail gas of a 200,000 tons / year vinyl acetate production device, and more than 6 million yuan of economic benefits can be created per year, and the expected investment recovery period is not more than 4 months.

Claims

1. A multi-membrane coupled recovery process for tail gas of ethylene oxidation deep processing device, characterized in that: the tail gas (S1) of ethylene oxidation deep processing device is controlled by a regulating valve to flow into a first buffer tank (1), and then enters a precision filter (2) after pressure stabilization, and the exhaust gas (S2) containing solid particles is obtained in the interception channel of the precision filter (2), and the membrane unit feed gas (S3) qualified for pretreatment is obtained in the permeation channel of the precision filter (2), and the membrane unit feed gas (S3) enters a first membrane separation unit (3) assembled by a rubbery membrane module; the first permeation gas (S4) enriched in ethylene is obtained in the low-pressure side channel of the first membrane separation unit (3), and then enters a first compressor (5) after pressure stabilization by a second buffer tank (4), and then enters a first cooler (6), and finally the circulating product gas (S5) is obtained; the first retentate gas (S6) from which most of the ethylene is removed is obtained in the high-pressure side channel of the first membrane separation unit (3), and then enters a second membrane separation unit (7) assembled by a glassy membrane module as raw material gas; the second permeation gas (S7) enriched in oxygen is obtained in the low-pressure side channel of the second membrane separation unit (7), and then enters the second buffer tank (4) to be compressed with the first permeation gas (S4); the second retentate gas (S8) from which part of the oxygen is removed is obtained in the high-pressure side channel of the second membrane separation unit (7), and then enters a third membrane separation unit (8) assembled by a rubbery membrane module as raw material gas; the residual tail gas (S9) after membrane recovery is obtained in the high-pressure side channel of the third membrane separation unit (8), and is sent to a fuel gas pipeline network; the third permeation gas (S10) preliminarily enriched in ethylene is obtained in the low-pressure side channel of the third membrane separation unit (8), and then enters a second compressor (10) after pressure stabilization by a third buffer tank (9), and then enters a second cooler (11), and finally the ethylene-rich circulating gas (S11) inside the recovery device is obtained, and enters the first buffer tank (1) to be subjected to precision filtration with the tail gas (S1) of ethylene oxidation deep processing device. ​

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