Adsorption process for recovering ethylene from refinery dry gas by combining MOF (Metal Organic Framework) and zeolite

Abstract

The invention provides an adsorption process for recovering ethylene from refinery dry gas through combination of MOF and zeolite, raw material gas is refinery dry gas, a main body contains hydrogen, carbon dioxide, C1-C3 low-carbon hydrocarbon gas and the like, the content of C2H4 is about 10%, a pre-decarburization process and an associated bed process are introduced, the adsorption capacity of an adsorbent is protected, and the content of ethylene is reduced. The non-compliant purity ethylene gas in the pressure swing adsorption process is re-enriched and recovered through an associated bed; in the initial stage of adsorption separation, after CO2 is removed through a customized or commercialized adsorbent, C2H4 enrichment and purification are directly carried out, and by introducing an associated bed, ethylene in gas passing through the adsorption process and ethylene gas in the preliminary desorption process of the adsorption bed are captured again, so that the ethylene recovery rate in the process is improved.

Description

Technical Field

[0001] The present invention belongs to the field of adsorption separation, and in particular relates to an adsorption process for recovering ethylene from refinery dry gas by combining MOF with zeolite. Background Art

[0002] The dry gas produced by the catalytic cracking process contains a variety of gas components, among which methane, ethylene, ethane, propylene, hydrogen, and nitrogen are highly valuable. However, separating and purifying these gases currently consumes excessive energy, often requiring them to be transported as fuel into the natural gas pipeline network or directly combusted, resulting in a waste of energy resources. Improving the utilization rate of these gases and converting them into economically valuable green and clean chemical products is a major challenge facing green chemical production.

[0003] In recent years, many porous materials have been found to exhibit good performance in adsorption separation at the laboratory level. However, due to the co-adsorption of CO2, the adsorption capacity of the materials is reduced, and there are unsatisfactory mass transfer kinetics, which to some extent limits their use in engineering applications. In addition, compared with hydrogen purification or nitrogen production, obtaining a single product gas from a multi-component gas is a more challenging task. Achieving the dual goals of high recovery and high purity requires designing a desorption process that adapts to multi-bed processes and sets separation purity targets.

[0004] In the prior art, CN101260017 B discloses a method for separating ethylene and hydrogen from refinery dry gas by pressure swing adsorption. The method comprises the following steps: first, carbon dioxide removal; second, dehydration; third, pressure swing adsorption extraction of ethylene; and fourth, pressure swing adsorption recovery of hydrogen. Conventional ethylene-specific adsorbents employing ethylene-specific adsorption molecular sieves, ethylene-specific adsorption ion exchange resins, ethylene-specific adsorption γ-Al2O3, or ethylene-specific adsorption layer columnar clays (i.e., PILCs) cannot guarantee the carbon dioxide removal concentration. Furthermore, ethylene-specific adsorbents cannot completely recover low-concentration ethylene, nor can they resolve the co-adsorption of ethylene in mixed gases and the low recovery rate of ethylene-depleted gas. Furthermore, adsorbent regeneration and final product times must be adjusted as needed, and the treatment process can affect the purity and yield of ethylene.

[0005] Therefore, to solve these problems, improve the utilization rate of dry gas and separate and purify it in a green and clean way to obtain economic chemical products is one of the challenges faced by ethylene green chemical production. Summary of the Invention

[0006] This invention provides an adsorption process for recovering ethylene from refinery dry gas using a combination of MOF and zeolite. By introducing a pre-decarbonization process and a companion bed process, the adsorbent's adsorption capacity is protected while the companion bed is used to re-enrich and recover ethylene gas that is not of the required purity during the pressure swing adsorption process. The specific scheme is as follows:

[0007] (1) Pretreatment: The industrial exhaust gas from refineries is used as the raw gas. After being cooled to 60-120°C, it is subjected to a pretreatment process consisting of dust removal, deoiling, demisting, and blasting and / or compression to remove impurities including solid particles, green oil, C6 and hydrocarbons above C6, and then enters the next designed process, the pre-decarbonization and purification process;

[0008] (2) Pre-decarbonization purification process: the raw gas that has undergone the pretreatment process is treated with commercial or customized materials (recommended zeolite materials with high selectivity for removing CO2 from two low-carbon hydrocarbons) to remove CO2 from the stream. The operating temperature is 25-250°C and the operating pressure is normal pressure to 1.0 MPa. The system is a purification process consisting of at least two or more purification towers connected in series or in parallel or in series and parallel. Multiple purification towers are operated in an alternating cycle. The purification tower adopts a temperature variable adsorption process to regenerate the adsorbent to ensure the continuous entry of the raw gas. The treated gas enters the next process, the C2 component purification process; the zeolite material for removing CO2 is any one of the zeolite materials in CN202211600250X or CN2022113598060 patents.

[0009] (3) C2 component purification process: The gas from the previous decarbonization purification process enters the C2 component concentration system. The system consists of a working group and a recovery group. The working group is composed of at least 2 or more working adsorption towers connected in series or in parallel or in series and parallel. Multiple adsorption towers are operated alternately and cyclically to ensure the continuous entry of raw gas. One or more adsorption towers are in the adsorption state, and the other adsorption towers are in the regeneration state. The operating temperature is room temperature and the operating pressure is normal pressure ~ 1.0MPa. The recovery group (companion bed) consists of no less than 1 companion tower. The operating temperature is room temperature and the operating pressure is The pressure is from 0.1 bar to atmospheric pressure. In the adsorption tower, the non-adsorbed phase gas discharged from the top of the tower through the bed is used as the exhaust gas, and the adsorbed phase gas discharged from the bottom of the tower due to pressure reduction is used as the product gas. The exhaust gas from the working adsorption tower will pass through the recovery tower to adsorb the residual ethylene in the exhaust gas again. As the pressure decreases, the ethylene concentration in the discharged product gas will gradually increase. During this process, some product gas that does not meet the purity requirements will also pass through the recovery tower to adsorb ethylene in the product gas again, thereby achieving two-step ethylene recovery and improving the overall C2H4 recovery rate of the process. The regeneration of the associated bed adopts the form of vacuum extraction, and the obtained gas can be incorporated into the feed gas and recycled, thereby improving the C2H4 recovery rate of the process system.

[0010] Furthermore, the raw gas includes dry gas from petrochemical refineries, naphtha cracking tail gas, ethane propane cracking gas, or ethylene-containing gas thereof, and contains C2H4 at a volume concentration of 3 to 30%. The pre-decarbonization purification process requires deep removal of CO2, wherein the concentration of CO2 in the stream must be removed to below 100 ppm, and the adsorbent must avoid co-adsorption of C2H4 as much as possible to protect the C2H4 adsorption working capacity of the adsorbent in subsequent work sections.

[0011] Furthermore, the adsorbent used in the C2 component purification process should be a MOF adsorption material that selectively adsorbs C2H4. The MOF adsorption material is a high-efficiency adsorbent for ethylene in refinery dry gas disclosed in CN2022107766961, so that C2H4 product gas can be obtained during the desorption process.

[0012] In the C2 component purification process, during the working group desorption process, the C2H4 concentration in the discharged product gas will gradually increase as the pressure decreases. The appropriate operation time for connecting the product gas and the associated bed can be selected according to the needs of the subsequent process; when the subsequent process has a supporting ethane and ethylene distillation device, the connection to the associated bed can be stopped when the ethylene concentration is >50-70%, and the product gas can be passed to the subsequent process. When the process requires high-purity ethylene, the connection to the associated bed can be stopped when the ethylene concentration is >99.5%. The operation time for the product gas to connect to the subsequent section and the associated bed can be adjusted according to actual needs.

[0013] Furthermore, the C2 component purification process, the working group tower, the operating temperature is room temperature - 100 ° C, the operating pressure is normal pressure ~ 3.0 MPa;

[0014] Furthermore, the operating temperature is preferably room temperature, and the operating pressure is preferably normal pressure to 1.0 MPa.

[0015] Furthermore, in the C2 component purification process, the adsorbent of the associated bed is consistent with that of the working bed, the exhaust gas and the product gas are the raw gas of the associated bed, the operating temperature is room temperature-100°C, the operating pressure is 0.01 bar~3 bar, the operating temperature is preferably room temperature, and the operating pressure is preferably 0.1 bar~normal pressure.

[0016] Furthermore, an H2 separation process unit can be set between the pre-decarbonization purification process and the C2 component purification process to increase the content of low-carbon hydrocarbon components entering the C2 component purification process.

[0017] Beneficial effects

[0018] The present invention is applicable to various recyclable C2H4-poor raw gases with different concentrations, pressures and temperatures; the adsorption capacity of the adsorbent is protected by the pre-decarbonization process, the process efficiency and the purity of the desorption product are improved, and the subsequent process is prevented from removing CO2 again; the non-compliant purity ethylene-containing stream is circulated internally by adding a recovery group (associated bed), thereby improving the process recovery rate, and the working group adopts PSA and the recovery group adopts VPSA, and there is a pressure gradient difference between the two, so no additional pressurization operation is required, thereby reducing energy consumption; the flexible characteristics of pressure swing adsorption operation are fully utilized to adjust the associated time and final product time according to actual needs, and the existing processes of the refinery are combined to achieve global optimization or directly obtain high-purity ethylene product gas.

[0019] Attached photos

[0020] Figure 1 This is a schematic diagram of the entire process;

[0021] Figure 2 This is a schematic diagram of the C2 component purification process;

[0022] Figure 3 This is a schematic diagram of the multi-tower relationship in the C2 component purification process;

[0023] Figure 4 This is a schematic diagram of the full-process combined hydrogen purification unit process;

[0024] Figure 5 It is the operation logic diagram;

[0025] Figure 6 is the ethylene stream concentration under working conditions. DETAILED DESCRIPTION

[0026] To make the objectives, technical solutions and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0027] An adsorption process for recovering ethylene from refinery dry gas using a MOF and zeolite is described. The process involves four steps: pretreatment, pre-decarbonization, and purification, and C2 component purification. The feed gas composition is shown in Table 1. The process flow is outlined below.

[0028] (1) Pretreatment: The raw gas is cooled by the cooler and then enters the treatment process consisting of dust removal, oil removal, mist removal and blower to remove suspended particulate matter, coke (green) oil and heavy hydrocarbon impurities in the raw gas.

[0029] (2) Pre-decarbonization purification process: the raw gas after the pretreatment process enters the variable temperature TSA carbon dioxide removal process composed of three adsorption towers with an operating temperature of 25-200℃ and an operating pressure of . Among them, the three adsorption towers are operated alternately and cyclically to ensure that the raw gas can be continuously decarbonized. One adsorption tower is always in the adsorption state, and the other two adsorption towers are in the regeneration cooling state. In the adsorption tower, the non-adsorbed phase gas discharged from the top of the tower through the bed is used as the exhaust gas. The CO2 content in the exhaust gas during this process is greater than or equal to 100ppm as an indicator for switching to the next adsorption tower. Subsequently, it is quickly regenerated by heating to 250℃ and vacuuming, and then cooled to room temperature and backfilled with N2 as the post-vacuum compensation gas.

[0030] (3) C2 component purification process, the decarbonized gas from the previous decarbonization purification process, the system consists of a working group and a recovery group, the working group consists of 6 adsorption towers, 3 as Group A (Group A), the other 3 as Group B (Group B), the two groups of adsorption towers are operated alternately and cyclically to ensure the continuous entry of raw gas, one or more adsorption towers are in the adsorption state, and the other adsorption towers are in the regeneration state, the operating temperature is room temperature, the operating pressure is normal pressure ~ 0.5MPa, the recovery group (Group C, Group B) C) (companion bed) consists of two companion towers (X, Y), operating at room temperature and pressures ranging from 0.1 bar to atmospheric pressure. Within the adsorption towers, non-adsorbed gas permeates the bed and is discharged from the top as exhaust gas, while adsorbed gas, due to reduced pressure, is discharged from the bottom as product gas. The exhaust gas from Group A adsorption tower passes through recovery tower X to reabsorb any remaining ethylene in the exhaust gas. The indicator here is that the ethylene content of Group A exhaust gas is >1% before it is connected to Tower X. At this time, Group B is undergoing a regeneration process. As the pressure decreases, the ethylene concentration in the exhausted product gas gradually increases. During this process, some product gas that does not meet the purity requirements will also pass through the recovery tower to reabsorb ethylene from the product gas. After the adsorption stage of Group A, the pressure gradually decreases from 5 bar, while the ethylene purity during this stage increases from 10%. When it reaches the target purity, Group A is connected to Tower X, and the desorbed gas from Group A is subsequently produced as high-purity ethylene product gas, thereby achieving ethylene recovery in the desorption step and improving the overall C2H4 recovery rate of the process. The regeneration of the associated beds X and Y is carried out in the form of vacuum pumping, and the obtained gas can be incorporated into the raw gas and recycled to improve the C2H4 recovery rate of the process system.

[0031] In addition, the desorption process can be adjusted to control the purity of the ethylene product gas at this stage, and it can be used in conjunction with existing supporting equipment and processes to minimize the overall energy consumption. In addition, we can add an additional H2 separation process unit between the pre-decarbonization purification process and the C2 component purification process. This unit operation is common in refinery hydrogen purification, which can increase the content of low-carbon hydrocarbon components entering the C2 component purification process and improve the overall efficiency of the system.

[0032] Table 1 Refinery dry gas after pretreatment

[0033]

[0034] The core ethylene capture process is carried out and described through examples.

[0035] Example

[0036] A dual-stage, four-bed, six-step VPSA separation unit was designed using a C2H4 / C2H6 / N2 (10 / 10 / 80; v / v / v) mixture to simulate low-concentration ethylene refinery dry gas. This design validated the potential for industrial application of existing materials in adsorption separation processes, given the common issues of low bed utilization, low selectivity, low single-pass recovery, and difficulty in ethylene desorption. The developed pressure swing adsorption unit, consisting of a main unit, control system, and analysis system, also incorporates a tail gas companion bed to address the low single-pass ethylene-depleted gas recovery. Theoretically, no additional lean gas is generated, allowing for full recovery of the lean gas throughout the entire process.

[0037] The UTSA-280 adsorption column was used for the activation process. During the activation process, the column was heated to 373 K and evacuated for 12 hours, then purged with argon to room temperature. For the zeolite adsorption column, during the activation process, the column was heated to 473 K and evacuated for 12 hours, then purged with argon to room temperature.

[0038] Working logic of adsorption device:

[0039] Step 1: Bed A is fed with gas and pressurized to the specified pressure. The pressure is maintained until the predetermined adsorption degree is reached. The outlet of bed A is connected to bed C, which is then connected to Release Poor C2H4 gas. At this time, bed B is evacuated to obtain product gas.

[0040] Step 2-Quick Step: Open the valve between beds A and B, allowing the pressure in bed A to drop, then close the valve.

[0041] Step 3: Bed B is fed with gas and pressurized to the specified pressure. The pressure is maintained until the predetermined adsorption degree is reached. The outlet of bed B is connected to bed C, and bed C is connected to Release Poor C2H4 gas. At this time, bed A is evacuated to obtain product gas.

[0042] Step 4-Quick Step: Open the valve between bed B and bed A, so that the pressure of bed B drops, and then close the valve;

[0043] Step 1 / 5: At this time, the C bed has undergone two rounds of exhaust gas re-enrichment and needs to be connected to vacuum regeneration, and the tail gas is merged into Cyclegas.

[0044] Considering the low ethylene concentration in the feed gas, adopting a downward inlet allows for more complete contact between the adsorbent and the feed gas, making it more suitable for high-throughput operation. Therefore, a three-tower, one-companion bed operation model was proposed. This operation is based on three main adsorption towers and one companion tower, with three stages of zeolite enrichment (adsorption beds ABC) and a primary MOF recovery (adsorption bed D). The process uses a gas distribution method to simulate continuous circulating gas and secondary purification. The specific steps are as follows:

[0045] (1) Step 1: The C2H4 / C2H6 / N2 mixed gas is passed into adsorption bed A, and the pressure is increased to 5 bar, completing the stamping step (Step 1-①). The pressure is then maintained for the adsorption step (Step 1-②), and the tail gas is passed into the MOF companion bed D. After adsorption is completed in adsorption bed A, it is connected to bed D for pressure equalization to increase the concentration of desorbed gas, causing the pressure of bed A to drop to 2.5 bar (Step 1-③), thereby increasing the concentration of desorbed tail gas. After that, adsorption bed A and adsorption bed B, which are in a vacuum state, are pressure-equalized once (Step 1-④). When beds AB reach the specified pressure, the first-level pressure equalization purification is completed.

[0046] (3) Second step: Pressurize bed B (Step 2-①) and adsorb (Step 2-②). After bed B completes adsorption, it is connected to bed D for pressure equalization to increase the concentration of desorbed tail gas (Step 2-③). Bed B is pressure-equalized with bed C, which is in a vacuum state (Step 2-④). After that, bed B and bed C reach the specified pressure to complete the secondary pressure equalization purification.

[0047] (4) Step 3: Pressurize bed C (Step 3-①) and perform adsorption (Step 3-②). After bed C completes adsorption, it is connected to bed D for pressure equalization to increase the concentration of desorbed tail gas (Step 3-③). Bed C is then vacuumed out to the product tank to become product gas (Step 3-④). Beds A and B are vacuumed out to the gas storage tank to become reflux feed gas (Steps 1, 2, 3-⑤). All beds are regenerated and ready for the next cycle.

[0048] By evaluating the single-pass production data, Figure 6 This demonstrates the potential of the adsorbent for engineering applications. After Steps 1, 2, and 3, the C2H4 concentration is significantly increased. Furthermore, through continuous circulation, the resulting exhaust gas concentration is high, reaching over 90%, effectively absorbing the entire ethylene-depleted gas. Using a gas distribution method to simulate the circulating gas during the cycle and the feed gas required for secondary continuous purification, the existing laboratory data provides a highly effective reference for engineering applications.

Claims

1. An adsorption process for recovering ethylene from refinery dry gas using a combination of MOF and zeolite, characterized in that: The following steps are involved: (1) Pretreatment The industrial exhaust gas from refineries is used as the raw gas. After being cooled to 60-120°C, it undergoes a pre-treatment process consisting of dust removal, deoiling, demist removal, and air blowing and / or compression to remove impurities including solid particles, green oil, C6 and hydrocarbons above C6, and then enters the next designed process, the pre-decarbonization and purification process; (2) Pre-decarbonization and purification process The raw gas that has undergone the pretreatment process is treated to remove CO2 from the stream through commercial or customized materials. The operating temperature is 25-250°C and the operating pressure is normal pressure to 1.0 MPa. The system is a purification process consisting of at least 2 or more purification towers connected in series or in parallel or in series and parallel. Multiple purification towers are operated alternately in a cycle. The purification tower uses a temperature swing adsorption process to regenerate the adsorbent to ensure the continuous entry of the raw gas. The treated gas enters the next process, the C2 component purification process; the zeolite material for removing CO2 is any one of the zeolite materials in CN202211600250X or CN2022113598060 patents, and the adsorbent used in the C2 component purification process is a MOF adsorption material that selectively adsorbs C2H4. (3) C2 component purification process The gas from the previous decarbonization and purification process enters the C2 component concentration system. The system consists of a working group and a recovery group. The working group is composed of at least two or more working adsorption towers connected in series, parallel or series-parallel. Multiple adsorption towers are operated alternately and cyclically to ensure the continuous entry of raw gas. One or more adsorption towers are in the adsorption state, and the remaining adsorption towers are in the regeneration state. The operating temperature is room temperature and the operating pressure is normal pressure to 1.0 MPa. The recovery group is the associated bed, which is composed of no less than one associated tower. The operating temperature is room temperature and the operating pressure is 0.1 bar to normal pressure. In the adsorption tower, the non-adsorbed phase gas discharged from the top of the tower through the bed is used as the exhaust gas, and the adsorbed phase gas discharged from the bottom of the tower due to pressure reduction is used as the product gas. The exhaust gas from the working adsorption tower will pass through the recovery tower to adsorb the residual ethylene in the exhaust gas again; as the pressure decreases, the ethylene concentration in the discharged product gas will gradually increase. In this process, some product gas that does not meet the purity requirements will also pass through the recovery tower to adsorb ethylene in the product gas again, thereby realizing two-step ethylene recovery and improving the overall C2H4 recovery rate of the process.

2. The adsorption process for recovering ethylene from refinery dry gas using a MOF and zeolite according to claim 1, characterized in that: The raw gas includes dry gas from petrochemical refineries, naphtha cracking tail gas, ethane propane cracking gas, or ethylene-containing gas thereof, and the volume concentration of C2H4 is 3 to 30%. The pre-decarbonization purification process requires deep removal of CO2, wherein the concentration of CO2 in the stream must be removed to below 100 ppm.

3. The adsorption process for recovering ethylene from refinery dry gas using a MOF and zeolite according to claim 1, characterized in that: The MOF adsorption material is a high-efficiency adsorbent for ethylene in refinery dry gas disclosed in CN2022107766961, so that C2H4 product gas can be obtained during the desorption process.

4. The adsorption process for recovering ethylene from refinery dry gas using a MOF and zeolite according to claim 1, characterized in that: In the C2 component purification process, during the working group desorption process, the C2H4 concentration in the discharged product gas will gradually increase as the pressure decreases. The appropriate operation time for connecting the product gas and the associated bed can be selected according to the needs of the subsequent process; when the subsequent process has a supporting ethane and ethylene distillation device, the connection to the associated bed can be stopped when the ethylene concentration is >50-70%, and the product gas can be passed to the subsequent process. When the process requires high-purity ethylene, the connection to the associated bed can be stopped when the ethylene concentration is >99.5%. The operation time for the product gas to connect to the subsequent section and the associated bed can be adjusted according to actual needs.

5. The adsorption process for recovering ethylene from refinery dry gas using a MOF and zeolite according to claim 1, characterized in that: The C2 component purification process, the working group tower, has an operating temperature of room temperature-100°C and an operating pressure of normal pressure-3.0MPa.

6. The adsorption process for recovering ethylene from refinery dry gas using a MOF and zeolite according to claim 1, characterized in that: In the C2 component purification process, the adsorbent of the accompanying bed is the same as that of the working bed, the exhaust gas and the product gas are the raw gas of the accompanying bed, the operating temperature is room temperature to 100°C, and the operating pressure is 0.01 bar to 3 bar.

7. The adsorption process for recovering ethylene from refinery dry gas using a MOF and zeolite according to claim 1, characterized in that: An H2 separation process unit can be set between the pre-decarbonization purification process and the C2 component purification process to increase the content of low-carbon hydrocarbon components entering the C2 component purification process.

8. The adsorption process for recovering ethylene from refinery dry gas using a MOF and zeolite according to claim 1, characterized in that: The regeneration of the associated bed is carried out in a vacuum form, and the obtained gas can be incorporated into the raw gas and recycled.

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