An apparatus and method for increasing ethylene production coupled with a methanol to olefins process

Abstract

The present application relates to a device and method for increasing ethylene production coupled with methanol to olefin process, which couples an ethane oxidative dehydrogenation (ODHE) system and a methanol to olefin (MTO) system, wherein the ODHE system comprises: ethane oxidative dehydrogenation and ODHE crude product gas dehydration and deacidification, oxygen removal, pressurization, decarburization and drying; the MTO system comprises: MTO reaction and pretreatment, MTO product gas compression, MTO oxygen-containing compound separation, MTO caustic washing to remove CO2, MTO product gas drying and MTO olefin separation. Compared with the prior art, the process flow of the ODHE system in the present application is simple, the obtained crude product gas is used to realize the separation and purification of ethylene in the ODHE crude product gas by using the separation device of the existing MTO system, the total investment of the device of the present application is small, and a new path is provided for increasing production and income of the existing MTO system in production.

Description

Technical Field

[0001] This invention belongs to the field of ethane resource utilization technology, and relates to an apparatus and method for increasing ethylene production by coupling with a methanol-to-olefins process. Background Technology

[0002] The main products of the MTO system are ethylene and propylene, and the byproducts are ethane, propane and mixed C4+. Currently, the ethane byproduct of the MTO process is mainly used as fuel or sold directly as ethane product. To further increase the value of ethane, a suitable process can be adopted to convert this part of ethane into ethylene, which has a higher value, and can bring greater economic benefits to enterprises.

[0003] Patent CN104193574B discloses a coupling method between the MTO process and the naphtha steam cracking to ethylene process; patent CN104151121B discloses a coupling method between the MTO process and the naphtha pre-cracking propane removal process; patent CN107056575A discloses a coupling method between the MTO process and the naphtha and propane pre-cracking ethane removal process; patent CN107417481A discloses a coupling method between the MTO process and the light hydrocarbon pre-cracking ethane removal process; patent CN107056568A discloses a coupling method between the MTO process and the naphtha and propane pre-cracking propane removal process; and patent CN104193570B discloses a coupling method between the MTO process and the naphtha cracking sequential separation process. All of these patents involve coupling the MTO system with a steam cracking to ethylene unit. However, steam cracking is a strongly endothermic process, which suffers from harsh reaction conditions, high energy consumption, and high equipment investment. To address this issue, research on oxidative dehydrogenation to ethylene (ODHE) has received increasing attention. Chinese patent CN105080575B discloses the use of a catalyst with MoVTeNbO as the active component for the catalytic oxidative dehydrogenation of ethane, achieving an ethane conversion rate of 70.5% and an ethylene selectivity of 95% at 350℃.

[0004] The main problem this invention aims to solve is how to convert ethane, a byproduct of the MTO system, into ethylene in a process with mild reaction conditions, simple procedures, low energy consumption, low investment, and minimal impact on the existing MTO system. Summary of the Invention

[0005] The purpose of this invention is to provide an apparatus and method for increasing ethylene production by coupling with a methanol-to-olefins (MTO) process. By coupling with the existing MTO system, the process flow is simplified, investment is reduced, and the yield of ethylene products from the MTO system can be effectively improved.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] One of the technical solutions of the present invention provides an apparatus for increasing ethylene production by coupling with a methanol-to-olefins (MTO) process, comprising an ODHE reactor, an ODHE acid-water separation tower, a CO2 absorption tower, an ODHE alkaline washing tower, and an ODHE dryer connected sequentially along the main material flow direction. The ODHE reactor is also connected to the ethane product outlet of the MTO system, and the ODHE dryer is also connected back to the MTO system and is separated from the MTO product gas.

[0008] Furthermore, the MTO system includes an MTO reaction and pretreatment unit, an MTO product gas compressor, an MTO oxide separation unit, an MTO alkali elution unit, an MTO product gas drying unit, and an MTO olefin separation unit connected in sequence. The MTO olefin separation unit is equipped with an ethylene product outlet, a propylene product outlet, and an ethane product outlet. The gas phase outlet of the ODHE dryer returns to the inlet connected to the MTO olefin separation unit.

[0009] Furthermore, a heat exchanger is provided between the ODHE reactor and the ODHE acid water separation tower. The ethane discharged from the ethane product outlet, together with the newly introduced oxidant and dilution gas, exchanges heat in the heat exchanger before being sent into the ODHE reactor.

[0010] Furthermore, a deacidification product gas pipeline is provided between the ODHE acid water separation tower and the CO2 absorption tower, and an ODHE deaerator and an ODHE product gas compressor are also arranged on the deacidification product gas pipeline.

[0011] Furthermore, the CO2 absorption tower is also connected to the CO2 desorption tower, and a CO2 absorbent is recycled between the two.

[0012] Furthermore, an ODHE dryer is also provided between the ODHE alkaline washing tower and the MTO system.

[0013] The second technical solution of the present invention provides a method for increasing ethylene production by coupling with a methanol-to-olefins process, which is implemented using the apparatus described above, and the method includes the following steps:

[0014] (1) MTO by-product ethane is mixed with oxidant and dilution gas, and the heat exchange forms a preheated feed gas that enters the ODHE reactor. Under the action of the catalyst, ODHE crude product gas rich in ethylene is generated.

[0015] (2) After heat exchange, the crude ODHE product gas is sent to the bottom of the ODHE acid water separation tower and comes into countercurrent contact with the absorbent introduced from the top of the ODHE acid water separation tower. At the bottom of the tower, a liquid product containing water and acetic acid is obtained and sent out, and at the top of the tower, a dehydrated and deacidified ODHE product gas is obtained.

[0016] (3) The dehydrated and deacidified ODHE product gas is mixed with auxiliary deoxygenating gas, preheated, and then reacted in the deoxygenator to obtain ODHE deoxygenated product gas.

[0017] (4) The ODHE deoxygenated product gas is cooled and pressurized (the pressure can be 1.7 to 3.5 MPaG, etc.) and sent to the bottom of the CO2 absorption tower, where it comes into countercurrent contact with the absorbent liquid introduced from the top of the CO2 absorption tower. The CO2-desorbed ODHE product gas is obtained at the top of the tower, and the rich liquid containing the absorbed acid gas is obtained at the bottom of the tower.

[0018] (5) The rich liquid is preheated and sent to the upper part of the CO2 desorption tower. The resulting top gas phase is cooled and sent to the gas-liquid separator. The CO2 desorbed gas obtained at the top of the separator is directly discharged. The reflux liquid obtained at the bottom of the separator is returned to the upper part of the CO2 desorption tower. The liquid at the bottom of the CO2 desorption tower is pressurized and cooled and then returned to the upper part of the CO2 absorption tower for recycling.

[0019] (6) The CO2-removed ODHE product gas is sent to the bottom of the ODHE alkaline washing tower for further decarbonization. It is contacted countercurrently with the washing liquid from bottom to top. At the top of the tower, the decarbonized ODHE product gas is obtained. After drying, it is sent to the MTO system for separation treatment together with the MTO product gas.

[0020] Furthermore, in step (1), the oxidant is selected from one or more of air, oxygen-enriched gas, or pure oxygen; the dilution gas is selected from one or more of nitrogen, water vapor, or carbon dioxide.

[0021] Furthermore, in step (1), the molar ratio of ethane to oxidant and dilution gas is 1:(0.27~0.55):(0.6~3.5).

[0022] Furthermore, in step (1), the temperature of the preheated raw material gas is 150–350°C.

[0023] Furthermore, in step (1), the reaction temperature in the ODHE reactor is 350–450°C, and the reaction pressure ranges from 0.2 to 1.0 MPa.G. Simultaneously, the active component of the catalyst in the ODHE reactor is a transition metal oxide, wherein the transition metal element in the transition metal oxide includes one or more of Mo, V, Te, or Nb, specifically a MoVTeNbO catalyst.

[0024] Furthermore, in step (2), the absorbent is water and / or an alkaline aqueous solution, and water can be used. Furthermore, in step (3), the mixing preheating temperature is 60-230°C, and the auxiliary oxygen desiccant is selected from one or more of carbon monoxide, hydrogen, and methane.

[0025] Furthermore, in step (4), the absorbent is one or a mixture of several of the following: aqueous solution of alcohol amine, aqueous solution of potassium carbonate, sulfolane, propylene carbonate, polyethylene glycol dimethyl ether, or methanol solution.

[0026] This invention introduces an oxidant (using oxygen as an example) to mix ethane and oxygen in a specific ratio, then introduces the mixture into an oxidative dehydrogenation catalyst bed. Under relatively low temperature conditions, a catalytic oxidative dehydrogenation reaction occurs to produce ethylene (ODHE process). The main chemical reaction equations for the ODHE process in this invention are as follows:

[0027] C2H6 + 0.5O2 = C2H4 + H2O (1)

[0028] C2H6 + 1.5O2 = C2H4O2 + H2O (2)

[0029] C2H6 + 2.5O2 = 2CO + 3H2O (3)

[0030] C2H6 + 3.5O2 = 2CO2 + 3H2O (4)

[0031] In this invention, the crude product gas exiting the ODHE reactor first undergoes waste heat recovery and cooling via a heat exchanger before entering the bottom of the absorption tower. There, under the action of the absorbent at the top of the tower, acetic acid is removed from the crude product gas. The absorbent can be water and / or an alkaline aqueous solution; preferably, water is used. The deacidified product gas at the top of the absorption tower is mixed with auxiliary deoxygenating gas, preheated by a heat exchanger, and then enters the deaerator to remove unreacted residual oxygen from the crude product gas.

[0032] The deoxygenation method employed in the deaerator of this invention preferably uses CO from the byproduct of the ODHE reaction, along with other auxiliary deoxygenating gases, to catalytically react with unreacted residual O2 in the crude product gas, generating H2O and CO2, thereby removing residual oxygen from the reactor effluent. The auxiliary deoxygenating gas is preferably derived from light component gas (containing H2 and CH4) obtained from a low-carbon hydrocarbon pretreatment unit, but can also be supplied from outside the reactor. The preferred chemical reaction equation for removing residual oxygen in this invention is as follows:

[0033] 2H₂ + O₂ = 2H₂O (5)

[0034] CH4 + 2O2 = CO2 + 2H2O (6)

[0035] 2CH4 + 3O2 = 2CO + 4H2O (7)

[0036] 2CO + O2 = 2CO2 (8)

[0037] The deoxygenated product gas is cooled by a heat exchanger and pressurized by a compressor before being sent to a CO2 absorption tower. CO2 is removed from the product gas through physical and / or chemical absorption, and CO2-free ODHE product gas is obtained at the top of the tower.

[0038] The CO2-removed ODHE product gas is further decarbonized in an ODHE alkaline scrubbing tower, where it is countercurrently contacted with the alkaline solution from the middle of the tower and the water (i.e., scrubbing liquid) from the top of the tower. The top of the tower yields a finely decarbonized ODHE product gas. Part of the scrubbing liquid obtained at the bottom of the upper section is recycled back to the top for continued use, while the rest is discharged from the boundary area. The waste alkaline solution obtained at the bottom of the lower section is also discharged from the boundary area. Then, the finely decarbonized ODHE product gas is dried and enters the MTO olefin separation unit, where it is separated together with the MTO product gas, which has undergone pretreatment such as oxygen-containing compound separation, alkaline scrubbing for CO2 removal, and drying, ultimately yielding ethylene, propylene, ethane, and other products. The ethane is sent to the inlet of the ODHE reactor.

[0039] Compared with the prior art, the present invention has the following advantages:

[0040] (1) The method for increasing ethylene production described in this invention is to convert ethane byproduct of MTO into ethylene through the ODHE reaction. This reaction is exothermic, the reaction conditions are mild, the reactor avoids the use of high-temperature resistant materials, and the equipment investment is low.

[0041] (2) The method for increasing ethylene production described in this invention employs an ODHE reaction, which has high ethylene selectivity. The only byproducts are acetic acid, carbon monoxide, and carbon dioxide. The crude product gas after the reaction, after dehydration, deacidification, deoxygenation, decarbonization, and drying, can be directly incorporated into an existing MTO separation unit, making full use of existing MTO process equipment to ultimately achieve the separation and purification of ethylene. This method converts ethane, a byproduct of MTO, into ethylene, providing a new path for increasing production and revenue in existing MTO systems. Attached Figure Description

[0042] Figure 1 This is a flowchart of a method for increasing ethylene production by coupling a methanol-to-olefins process according to the present invention.

[0043] Explanation of markings in the diagram:

[0044] Equipment labeling: 7 is the ODHE reactor; 13 is the ODHE acid-water separation tower; 20 is the ODHE deaerator; 23 is the ODHE product gas compressor; 25 is the CO2 absorption tower; 30 is the CO2 stripping tower; 42 is the ODHE alkaline washing tower; 49 is the ODHE dryer; 5, 11, 17, 22, 33, 35, and 37 are all heat exchangers; 32 and 41 are both pumps; 38 is a gas-liquid separator; 52 is the MTO reaction and pretreatment unit; 54 is the MTO product gas compressor; 56 is the MTO oxygen-containing compound separation unit; 58 is the MTO alkaline CO2 elution unit; 60 is the MTO product gas drying unit; 62 is the MTO olefin separation unit.

[0045] Material flow markings: 1 for ethane; 2 for oxidant; 3 for dilution gas; 4 and 6 for ODHE feed gas; 8 and 9 for ODHE crude product gas; 10 and 12 for molten salt circulating liquid; 14 for coolant; 15 for acid-containing aqueous solution; 16 and 19 for dehydrated and deacidified ODHE product gas; 18 for auxiliary deoxygenation gas; 21 and 24 for ODHE deoxygenated product gas; 26 for ODHE product gas after CO2 removal; 27 and 29 for rich liquid; 31 and 34... 36 is lean liquid; 39 is CO2-rich gas; 40 is CO2 emission gas; 43 is liquid product; 44, 44a, and 44b are washing liquid; 45 is fresh alkali solution; 46 and 47 are waste alkali solution; 48 is ODHE product gas after fine decarbonization; 50 is ODHE dried product gas; 51 is methanol; 53, 55, 57, 59, and 61 are MTO product gas; 63 is ethylene product; 64 is propylene product; and 65 is other products. Detailed Implementation

[0046] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0047] In the following embodiments, unless otherwise specified, the functional components or structures are conventional components or structures used in the art to achieve the corresponding functions.

[0048] Example 1

[0049] like Figure 1As shown, this embodiment provides a method for increasing ethylene production by coupling a methanol-to-olefins (MTO) process. An ethane oxidative dehydrogenation (ODHE) system and a methanol-to-olefins (MTO) system are coupled together. The ODHE system includes ethane oxidative dehydrogenation and processes such as dehydration, deacidification, deoxygenation, pressurization, decarbonization, and drying of the crude ODHE product gas. The MTO system includes, in sequence, an MTO reaction and pretreatment unit 52, an MTO product gas compressor 54, an MTO oxygen-containing compound separation unit 56, an MTO alkaline CO2 elution unit 58, an MTO product gas drying unit 60, and an MTO olefin separation unit 62. Methanol 51 is sequentially processed through the MTO reaction and pretreatment unit 52, the MTO product gas compressor 54, the MTO oxygen-containing compound separation unit 56, the MTO alkaline CO2 elution unit 58, and the MTO product gas drying unit 60 to obtain MTO product gases 53, 55, 57, 59, and 61, respectively.

[0050] In this embodiment, taking a domestically produced MTO system as an example, its by-product ethane volume is 7840 tons / year. Through the method of coupling with the methanol-to-olefins process to increase ethylene production as described in this embodiment, ethane is converted into ethylene. The ethane feed rate in the ODHE system is 1849 kg / h, of which 980 kg / h is fresh ethane from MTO by-product and 869 kg / h is recycled ethane. Oxygen is used as the oxidant, and nitrogen and water vapor are used as dilution gases.

[0051] This embodiment of a method for increasing ethylene production by coupling with a methanol-to-olefins process includes the following steps:

[0052] (a) Ethane Oxidative Dehydrogenation: Ethane 1 from the MTO system is mixed with oxygen 2 and dilution gas 3 (nitrogen + water vapor) in a molar ratio of 1:0.43:1.94 to obtain ODHE feed gas 4. ODHE feed gas 4 is preheated to 350°C by heat exchanger 5 to obtain ODHE feed gas 6, which is then sent to the inlet of ODHE reactor 7. Under the action of a transition metal oxide catalyst (MoVTeNbO catalyst), ethylene-rich ODHE crude product gas 8 is generated. The reaction temperature in ODHE reactor 7 is 3... At 70℃ and a pressure of 0.34 MPaG, the conversion rate of ethane is 53%, and the selectivities for ethylene, acetic acid, carbon monoxide, and carbon dioxide are 89%, 3.3%, 3.5%, and 3.8%, respectively. The molar flow rate of the ODHE reaction gas 8 is 223.6 kmol / h, and its composition (mol%) is: C2H4: 13%, C2H6: 12.9%, O2: 1.3%, N2: 44.2%, H2O: 26%, CO: 1%, CO2: 1.1%, and C2H4O2: 0.5%. Additionally, the ODHE reactor 7 is externally equipped with a cooling medium pipeline with a heat exchanger 11, through which molten salt circulating liquids 10 and 12 are circulated.

[0053] (b) Dehydration and deacidification of ODHE crude product gas: The ODHE crude product gas 8 from the outlet of ODHE reactor 7 is cooled to 120°C by heat recovery in heat exchanger 5 and sent to the bottom of ODHE acid-water separation tower 13, where it comes into countercurrent contact with coolant 14 (i.e., water) introduced from the top of ODHE acid-water separation tower 13. At the top of the tower, dehydrated and deacidified ODHE product gas 16 is obtained, and at the bottom of the tower, a liquid product containing water and acetic acid (i.e., acid-water mixture 15) is obtained and sent out of the boundary area.

[0054] (c) Deoxygenation of ODHE product gas: ODHE product gas 16 from the top of the ODHE acid water separation tower is preheated to 190°C by heat exchanger 17 and then sent to ODHE deoxygenator 20. The oxygen in the ODHE product gas 16 reacts with the deoxygenating gas, which is CO in the ODHE product gas and an added auxiliary deoxygenating gas 18 (which can be hydrogen). ODHE deoxygenated product gas 21 is obtained at the outlet of ODHE deoxygenator 20, wherein the oxygen concentration is ≤10ppm.

[0055] (d) ODHE product gas pressurization: ODHE deoxygenated product gas 21 from the outlet of ODHE deaerator 20 is cooled by heat exchanger 22 and sent to the inlet of ODHE product gas compressor 23, pressurized to 1.8MPaG and then sent to the bottom of CO2 absorption tower 25 in ODHE decarbonization unit.

[0056] (e) Decarbonization of ODHE product gas: The pressurized ODHE product gas 24 flows from bottom to top in the CO2 absorption tower 25, countercurrently contacting the MDEA absorbent (i.e., lean liquid 34) flowing down from the top of the tower. The top of the tower yields ODHE product gas 26 with CO2 removed, where the CO2 content is ≤100ppm. The bottom of the tower yields rich liquid 27, which has absorbed acid gas. Rich liquid 27, exiting from the bottom of the CO2 absorption tower 25, is heated by heat exchanger 28 to obtain rich liquid 29, which is then sent to the top of the CO2 desorption tower 30, flowing from top to bottom with the gas generated by the reboiler 35 at the bottom of the tower. The steam is brought into countercurrent contact to desorb CO2. The top of the CO2 desorption tower 30 yields CO2-rich gas 36, which is cooled by heat exchanger 37 and enters gas-liquid separator 38. The liquid product 40 obtained at the bottom of gas-liquid separator 38 is pressurized by pump 41 and returned to the tower. The CO2 exhaust gas 39 obtained at the top of gas-liquid separator 38 is directly discharged into the atmosphere. The bottom of the CO2 desorption tower 30 yields regenerated lean liquid 31, which recovers heat by heat exchanger 28, is then pressurized by pump 32 and cooled by heat exchanger 33 to generate lean liquid 34, which is then recycled to the top of CO2 absorption tower 25.

[0057] (f) ODHE product gas alkaline washing and decarbonization: The ODHE product gas 26, which has been decarbonized from the top of the CO2 absorption tower 25, is sent to the bottom of the ODHE alkaline washing tower 42 for further decarbonization. It is in countercurrent contact with the fresh alkaline solution 45 coming down from the middle of the tower and the fresh water 43 coming down from the top of the tower, respectively. The top of the tower yields the decarbonized ODHE product gas 48, in which the CO2 content is <10ppm. The washing liquid 44 obtained at the bottom of the upper section of the tower is partially recycled back to the top of the tower for continued use as washing liquid (i.e., washing liquid 44a), and partially (i.e., washing liquid 44b) is discharged from the boundary area. The waste alkaline solution 46 obtained at the bottom of the lower section of the tower is mixed with the liquid phase product containing water and acetic acid (i.e., acid-containing aqueous solution 15) at the bottom of the ODHE acid-water separation tower 13 and then discharged from the boundary area. The waste alkaline solution can partially neutralize the acid-containing wastewater.

[0058] (g) ODHE product gas drying: The decarbonized ODHE product gas 48 obtained from the top of the ODHE alkaline washing tower 42 is sent to the inlet of the ODHE dryer 49 to remove the moisture. The ODHE dryer 49 outlet yields ODHE dried product gas 50 that meets the requirements for subsequent cryogenic separation.

[0059] (h) ODHE product gas separation and purification: The ODHE dried product gas 50 obtained from the outlet of ODHE dryer 49, which meets the requirements of subsequent cryogenic separation, is sent to MTO product gas drying unit 60. After being mixed with dried MTO product 61, it is sent to MTO olefin separation unit 62. The ethylene product 63 that is finally separated is exported, and the ethane 1 that is separated is returned to ODHE reactor 7. In addition, propylene product 64 and other products 65 are also separated here at the same time.

[0060] Using the method described in this embodiment, the existing MTO plant can increase its ethylene production by 6,512 tons per year.

[0061] Example 2

[0062] Similar to Embodiment 1 above, such as Figure 1 As shown, this embodiment also provides a method for increasing ethylene production by coupling a methanol-to-olefins (MTO) process. An ethane oxidative dehydrogenation (ODHE) system and a methanol-to-olefins (MTO) system are coupled together. The ODHE system includes ethane oxidative dehydrogenation and processes such as dehydration, deacidification, deoxygenation, pressurization, decarbonization, and drying of the crude ODHE product gas. The MTO system includes, in sequence, an MTO reaction and pretreatment unit 52, an MTO product gas compressor 54, an MTO oxygen-containing compound separation unit 56, an MTO alkaline CO2 elution unit 58, an MTO product gas drying unit 60, and an MTO olefin separation unit 62. Methanol 51 is processed sequentially through the MTO reaction and pretreatment unit 52, the MTO product gas compressor 54, the MTO oxygen-containing compound separation unit 56, the MTO alkaline CO2 elution unit 58, and the MTO product gas drying unit 60 to obtain MTO product gas 61.

[0063] In this embodiment, taking a domestically produced MTO system as an example, its by-product ethane volume is 10,240 tons / year. Through the method of coupling with the methanol-to-olefins process to increase ethylene production as described in this embodiment, ethane is converted into ethylene. The ethane feed rate in the ODHE system is 2,327 kg / h, of which 1,280 kg / h is fresh ethane from the MTO by-product and 1,047 kg / h is recycled ethane. Oxygen is used as the oxidant and nitrogen is used as the dilution gas.

[0064] This embodiment of a method for increasing ethylene production by coupling with a methanol-to-olefins process includes the following steps:

[0065] (a) Ethane Oxidative Dehydrogenation: Ethane 1 from the MTO system is mixed with oxygen 2 and dilution gas (nitrogen) 3 in a molar ratio of 1:0.46:1.61 to obtain ODHE feed gas 4. ODHE feed gas 4 is preheated to 320°C by heat exchanger 5 and then sent to the inlet of ODHE reactor 7. Under the action of a catalyst, ethylene-rich ODHE crude product gas 8 is generated. The reaction temperature in ODHE reactor 7 is 375°C, the pressure is 0.3 MPaG, and the ethane conversion rate is 55%. The selectivity for ethylene, acetic acid, carbon monoxide, and carbon dioxide was 88%, 3.4%, 4.9%, and 3.8%, respectively. The molar flow rate of the crude ODHE gas 8 was 260 kmol / h, and its composition (mol%) was: C2H4: 14.44%, C2H6: 13.42%, O2: 3.57%, N2: 48.02%, H2O: 17.13%, CO: 1.61%, CO2: 1.25%, and C2H4O2: 0.56%.

[0066] (b) Dehydration and deacidification of ODHE crude product gas: The ODHE crude product gas 8 from the outlet of ODHE reactor 7 is cooled to 100°C after heat recovery by heat exchanger 5 and sent to the bottom of ODHE acid water separation tower 13, where it comes into countercurrent contact with water 14 introduced from the top of ODHE acid water separation tower 13. Dehydrated and deacidified ODHE product gas 16 is obtained at the top of the tower, and liquid product 15 containing water and acetic acid is obtained at the bottom of the tower and sent out of the boundary area.

[0067] (c) Deoxygenation of ODHE product gas: ODHE product gas 16 from the top of the ODHE acid water separation tower is preheated to 180°C by heat exchanger 17 and then sent to ODHE deoxygenator 20. The oxygen in the ODHE product gas 16 reacts with the deoxygenating gas, which is CO in the ODHE product gas and hydrogen gas added as an auxiliary deoxygenating gas. ODHE deoxygenated product gas 21 is obtained at the outlet of ODHE deoxygenator 20, wherein the oxygen concentration is ≤10ppm.

[0068] (d) ODHE product gas pressurization: ODHE deoxygenated product gas 21 from the outlet of ODHE deaerator 20 is cooled by heat exchanger 22 and sent to the inlet of ODHE product gas compressor 23, pressurized to 3.5MPaG, and then sent to the bottom of CO2 absorption tower 25 in ODHE decarbonization unit.

[0069] (e) Decarbonization of ODHE product gas: The pressurized ODHE product gas 24 flows from bottom to top in the CO2 absorption tower 25, countercurrently contacting the MDEA absorbent liquid 34 flowing down from the top of the tower. The top of the tower yields ODHE product gas 26 with CO2 removed, where the CO2 content is ≤100ppm. The bottom of the tower yields a rich liquid 27 that has absorbed acid gas. The rich liquid exiting from the bottom of the CO2 absorption tower 25 is heated by the heat exchanger 28 and then sent to the top of the CO2 stripping tower 30, where it undergoes top-down stripping with the gas generated by the reboiler 35 at the bottom of the tower. The gas flows counter-currently, releasing CO2. The top of the CO2 stripping tower 30 yields CO2-rich gas 36, which is cooled by heat exchanger 37 and enters gas-liquid separator 38. The liquid phase 40 obtained at the bottom of gas-liquid separator 38 is pressurized by pump 41 and returned to the tower. The CO2 exhaust gas 39 obtained at the top of separator 38 is directly discharged into the atmosphere. The bottom of the CO2 stripping tower 30 yields regenerated lean liquid 31, which recovers heat through heat exchanger 28, is then pressurized by pump 32, cooled by heat exchanger 33, and then enters the top of CO2 absorption tower 25 for recycling.

[0070] (f) ODHE product gas alkaline washing and decarbonization: The ODHE product gas 26, which has been decarbonized from the top of the CO2 absorption tower 25, is sent to the bottom of the ODHE alkaline washing tower 42 for further decarbonization. It is contacted countercurrently with the alkaline solution 45 coming down from the middle of the tower and the water 43 coming down from the top of the tower, respectively. The top of the tower yields the decarbonized ODHE product gas 48, in which the CO2 content is <10ppm. The washing liquid 44 obtained at the bottom of the upper section of the tower is partially recycled back to the top of the tower for continued use as washing liquid, and partially discharged from the boundary area. The waste alkaline solution 46 obtained at the bottom of the lower section of the tower is mixed with the liquid product 15 containing water and acetic acid at the bottom of the ODHE acid-water separation tower 13 and then discharged from the boundary area. The waste alkaline solution can partially neutralize the acidic wastewater.

[0071] (g) ODHE product gas drying: The decarbonized ODHE product gas 48 obtained from the top of the ODHE alkaline washing tower 42 is sent to the inlet of the ODHE dryer 49 to remove the moisture. The ODHE dryer 49 outlet yields ODHE dried product gas 50 that meets the requirements for subsequent cryogenic separation.

[0072] (h) ODHE product gas separation and purification: The ODHE dried product gas 50 obtained from the outlet of ODHE dryer 49, which meets the requirements of subsequent cryogenic separation, is sent to MTO product gas drying unit 60, mixed and then sent to MTO olefin separation unit 62. The ethylene product 63 that is finally separated is exported, and the ethane 1 that is separated is returned to ODHE reactor 7.

[0073] Using the method described in this embodiment, the existing MTO plant can increase its ethylene production by 8,410 tons per year.

[0074] Example 3

[0075] Similar to Embodiment 1 above, such as Figure 1 As shown, this embodiment also provides a method for increasing ethylene production by coupling a methanol-to-olefins (MTO) process. An ethane oxidative dehydrogenation (ODHE) system and a methanol-to-olefins (MTO) system are coupled together. The ODHE system includes ethane oxidative dehydrogenation and processes such as dehydration, deacidification, deoxygenation, pressurization, decarbonization, and drying of the crude ODHE product gas. The MTO system includes, in sequence, an MTO reaction and pretreatment unit 52, an MTO product gas compressor 54, an MTO oxygen-containing compound separation unit 56, an MTO alkaline CO2 elution unit 58, an MTO product gas drying unit 60, and an MTO olefin separation unit 62. Methanol 51 is processed sequentially through the MTO reaction and pretreatment unit 52, the MTO product gas compressor 54, the MTO oxygen-containing compound separation unit 56, the MTO alkaline CO2 elution unit 58, and the MTO product gas drying unit 60 to obtain MTO product gas 61.

[0076] In this embodiment, taking a domestically produced MTO system as an example, its by-product ethane volume is 10,240 tons / year. Through the method of coupling with the methanol-to-olefins process to increase ethylene production as described in this embodiment, ethane is converted into ethylene. The ethane feed rate in the ODHE system is 2,327 kg / h, of which 1,280 kg / h is fresh ethane from the MTO by-product and 1,047 kg / h is recycled ethane. Oxygen is used as the oxidant and water vapor is used as the dilution gas.

[0077] This embodiment of a method for increasing ethylene production by coupling with a methanol-to-olefins process includes the following steps:

[0078] (a) Ethane Oxidative Dehydrogenation: Ethane 1 from the MTO system is mixed with oxygen 2 and dilution gas (water vapor) 3 in a molar ratio of 1:0.42:0.61 to obtain ODHE feed gas 4. ODHE feed gas 4 is preheated to 150°C by heat exchanger 5 and then sent to the inlet of ODHE reactor 7. Under the action of a catalyst, ethylene-rich ODHE crude product gas 8 is generated. The reaction temperature in ODHE reactor 7 is 370°C, and the pressure is 0.4 MPaG. The conversion of ethane... The yield was 53.5%, and the selectivity for ethylene, acetic acid, carbon monoxide, and carbon dioxide was 82.2%, 10.5%, 3.6%, and 3.2%, respectively. The molar flow rate of the crude ODHE gas 8 was 175 kmol / h, and its composition (mol%) was: C2H4: 19.49%, C2H6: 20.6%, O2: 2.74%, H2O: 51.45%, CO: 1.71%, CO2: 1.52%, C2H4O2: 2.49%.

[0079] (b) Dehydration and deacidification of crude ODHE product gas: The crude ODHE product gas 8 from the outlet of ODHE reactor 7 is cooled to 100°C after heat recovery by heat exchanger 5 and sent to the bottom of ODHE acid-water separation tower 13, where it comes into countercurrent contact with water 14 introduced from the top of ODHE acid-water separation tower 13. At the top of the tower, dehydrated and deacidified ODHE product gas 16 is obtained, and at the bottom of the tower, liquid product 15 containing water and acetic acid is obtained and sent out of the boundary area for acetic acid purification.

[0080] (c) Deoxygenation of ODHE product gas: ODHE product gas 16 from the top of the ODHE acid water separation tower is preheated to 180°C by heat exchanger 17 and then sent to ODHE deoxygenator 20. The oxygen in the ODHE product gas 16 reacts with the deoxygenating gas, which is CO in the ODHE product gas and hydrogen gas added as an auxiliary deoxygenating gas. ODHE deoxygenated product gas 21 is obtained at the outlet of ODHE deoxygenator 20, wherein the oxygen concentration is ≤10ppm.

[0081] (d) ODHE product gas pressurization: ODHE deoxygenated product gas 21 from the outlet of ODHE deaerator 20 is cooled by heat exchanger 22 and sent to the inlet of ODHE product gas compressor 23, pressurized to 1.8MPaG, and then sent to the bottom of CO2 absorption tower 25 in ODHE decarbonization unit.

[0082] (e) Decarbonization of ODHE product gas: The pressurized ODHE product gas 24 flows from bottom to top in the CO2 absorption tower 25, countercurrently contacting the MDEA absorbent liquid 34 flowing down from the top of the tower. The top of the tower yields ODHE product gas 26 with CO2 removed, where the CO2 content is ≤100ppm. The bottom of the tower yields a rich liquid 27 that has absorbed acid gas. The rich liquid exiting from the bottom of the CO2 absorption tower 25 is heated by the heat exchanger 28 and then sent to the top of the CO2 stripping tower 30, where it undergoes top-down stripping with the gas generated by the reboiler 35 at the bottom of the tower. The gas flows counter-currently, releasing CO2. The top of the CO2 stripping tower 30 yields CO2-rich gas 36, which is cooled by heat exchanger 37 and enters gas-liquid separator 38. The liquid phase 40 obtained at the bottom of gas-liquid separator 38 is pressurized by pump 41 and returned to the tower. The CO2 exhaust gas 39 obtained at the top of separator 38 is directly discharged into the atmosphere. The bottom of the CO2 stripping tower 30 yields regenerated lean liquid 31, which recovers heat through heat exchanger 28, is then pressurized by pump 32, cooled by heat exchanger 33, and then enters the top of CO2 absorption tower 25 for recycling.

[0083] (f) ODHE product gas alkaline washing and decarbonization: The ODHE product gas 26, which has been decarbonized from the top of the CO2 absorption tower 25, is sent to the bottom of the ODHE alkaline washing tower 42 for further decarbonization. It is contacted countercurrently with the alkaline solution 45 coming down from the middle of the tower and the water 43 coming down from the top of the tower, respectively. The top of the tower yields the decarbonized ODHE product gas 48, in which the CO2 content is <10ppm. The washing liquid 44 obtained at the bottom of the upper section of the tower is partially recycled back to the top of the tower for continued use as washing liquid, and partially discharged from the boundary area. The waste alkaline solution 46 obtained at the bottom of the lower section of the tower is mixed with the liquid product 15 containing water and acetic acid at the bottom of the ODHE acid-water separation tower 13 and then discharged from the boundary area. The waste alkaline solution can partially neutralize the acidic wastewater.

[0084] (g) ODHE product gas drying: The decarbonized ODHE product gas 48 obtained from the top of the ODHE alkaline washing tower 42 is sent to the inlet of the ODHE dryer 49 to remove the moisture. The ODHE dryer 49 outlet yields ODHE dried product gas 50 that meets the requirements for subsequent cryogenic separation.

[0085] (h) ODHE product gas separation and purification: The ODHE dried product gas 50 obtained from the outlet of ODHE dryer 49, which meets the requirements of subsequent cryogenic separation, is sent to MTO product gas drying unit 60, mixed and then sent to MTO olefin separation unit 62. The ethylene product 63 that is finally separated is exported, and the ethane 1 that is separated is returned to ODHE reactor 7.

[0086] Using the method described in this embodiment, the existing MTO plant can increase its annual production by 7,913 tons of ethylene and 2,150 tons of acetic acid.

[0087] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, these embodiments are not limited to the above-described embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of these embodiments without departing from the scope of these embodiments should be within the protection scope of these embodiments.

Claims

1. A method for increasing ethylene production by coupling with a methanol-to-olefins process, characterized in that, The apparatus used in this method includes an ODHE reactor, an ODHE acid-water separation tower, a CO2 absorption tower, an ODHE alkaline washing tower, and an ODHE dryer connected sequentially along the main material flow direction. The ODHE reactor is also connected to the ethane product outlet of the MTO system, and the ODHE dryer is also connected back to the MTO system and is separated together with the MTO product gas. The method includes the following steps: (1) The by-product ethane of MTO is mixed with oxidant and dilution gas, and the heat exchange forms a preheated feed gas that enters the ODHE reactor. Under the action of the catalyst, ODHE crude product gas rich in ethylene is generated. (2) After heat exchange, the crude ODHE product gas is sent to the bottom of the ODHE acid water separation tower and comes into countercurrent contact with the absorbent introduced from the top of the ODHE acid water separation tower. At the bottom of the tower, a liquid product containing water and acetic acid is obtained and sent out. At the top of the tower, the dehydrated and deacidified ODHE product gas is obtained. (3) The dehydrated and deacidified ODHE product gas is mixed with auxiliary deoxygenation gas, preheated, and then reacted in the deoxygenator to obtain ODHE deoxygenated product gas; (4) The ODHE deoxygenated product gas is cooled and pressurized and then sent to the bottom of the CO2 absorption tower, where it comes into countercurrent contact with the absorbent liquid introduced from the top of the CO2 absorption tower. The CO2-degraded ODHE product gas is obtained at the top of the tower, and the rich liquid containing the absorbed acid gas is obtained at the bottom of the tower. (5) The rich liquid is preheated and sent to the upper part of the CO2 desorption tower. The resulting top gas phase is cooled and sent to the gas-liquid separator. The CO2 desorbed gas obtained at the top of the separator is directly discharged. The reflux liquid obtained at the bottom of the separator is returned to the upper part of the CO2 desorption tower. The liquid at the bottom of the CO2 desorption tower is pressurized and cooled and then returned to the upper part of the CO2 absorption tower for recycling. (6) The CO2-removed ODHE product gas is sent to the bottom of the ODHE alkaline washing tower for further decarbonization. It is contacted countercurrently with the washing liquid from bottom to top. At the top of the tower, the decarbonized ODHE product gas is obtained. After drying, it is sent to the MTO system and enters the inlet of the MTO olefin separation unit together with the MTO product gas for separation treatment. In step (1), the oxidant is selected from one or more of air, oxygen-enriched gas, or pure oxygen; the dilution gas is selected from one or more of nitrogen, water vapor, or carbon dioxide. The molar ratio of ethane to oxidant and diluent gas is 1:(0.27~0.55):(0.6~3.5); The temperature of the preheated raw material gas is 150~350℃; The reaction temperature inside the ODHE reactor is 350~450℃, and the reaction pressure ranges from 0.2~1.0 MPa.G. In step (2), the absorbent is water and / or an alkaline aqueous solution; In step (3), the mixing preheating temperature is 60~230℃, and the auxiliary oxygen deoxygenating gas is selected from one or more of carbon monoxide, hydrogen, and methane; In step (4), the absorbent is one or a mixture of several of the following: aqueous solution of alcohol amine, aqueous solution of potassium carbonate, sulfolane, propylene carbonate, polyethylene glycol dimethyl ether or methanol solution.

2. The method for increasing ethylene production by coupling with a methanol-to-olefins process according to claim 1, characterized in that, The MTO system includes an MTO reaction and pretreatment unit, an MTO product gas compressor, an MTO oxide separation unit, an MTO alkali elution unit, an MTO product gas drying unit, and an MTO olefin separation unit connected in sequence. The MTO olefin separation unit has an ethylene product outlet, a propylene product outlet, and an ethane product outlet. The gas phase outlet of the ODHE dryer returns to the inlet connected to the MTO olefin separation unit.

3. The method for increasing ethylene production by coupling with a methanol-to-olefins process according to claim 1, characterized in that, A heat exchanger is also provided between the ODHE reactor and the ODHE acid water separation tower. Ethane discharged from the ethane product outlet, together with the newly introduced oxidant and dilution gas, is heated by the heat exchanger and then sent into the ODHE reactor.

4. The method for increasing ethylene production by coupling with a methanol-to-olefins process according to claim 1, characterized in that, The ODHE acid-water separation tower and the CO2 absorption tower are also connected by a deacidification product gas pipeline, which is equipped with an ODHE deaerator and an ODHE product gas compressor.

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