A method for increasing ethylene production by utilizing ethane products produced as a by-product of methanol to olefins

Abstract

The present invention relates to a method for increasing ethylene production by utilizing an ethane product produced as a byproduct of a methanol-to-olefins (MTO) process. The method comprises the following steps: (a) mixing the ethane product produced as a byproduct of MTO with a diluent gas and an oxidant, and then feeding the mixture into an ODHE (Open Distillation Heating) reactor to generate an ethylene-rich ODHE reaction gas; (b) feeding the ODHE reaction gas into an ODHE gas-liquid separator to obtain a gaseous product, which is then fed into an ODHE product separation tower to obtain an ODHE product gas and a liquid product II; (c) feeding the ODHE product gas into an ODHE deoxygenation unit to obtain an ODHE deoxygenated product gas; (d) feeding the ODHE deoxygenated product gas into an ODHE CO2 removal unit to obtain an ODHE decarbonated product gas and a liquid product III; and (e) compressing and mixing the ODHE decarbonated product gas, followed by oxygenate separation, alkaline elution to remove CO2, drying, and olefin separation, ultimately obtaining an ethylene product, an ethane product, and other products. The ethane product is then returned to the inlet of the ODHE reactor. The present invention has a simple process flow, requires minimal equipment investment, and can effectively increase the yield of ethylene products.

Description

Technical Field

[0001] The present invention belongs to the technical field of ethane resource utilization, and in particular relates to a method for increasing ethylene production by utilizing an ethane product as a by-product of methanol to olefins. Background Art

[0002] Typical MTO process product distribution is as follows Figure 1 As shown, the main products are ethylene and propylene, and the main byproducts are ethane, propane, and mixed C4+ hydrocarbons. Patent CN109651038A proposes a method for coupling the MTO process with a propane dehydrogenation process, utilizing the MTO byproduct propane through a PDH process to increase propylene production. Patent CN102190539B proposes a method for increasing propylene yield by utilizing the mixed C4+ hydrocarbons separated from the MTO unit through a catalytic cracking system and an olefin disproportionation system. Patent CN101092322A proposes a method for converting MTO reaction byproducts into alkanes, utilizing the C4+ hydrocarbons separated from the MTO unit and reacting them with hydrogen over a hydrogenation catalyst to convert them into alkanes. None of these patents address the utilization of the MTO byproduct ethane.

[0003] Ethane, a byproduct of the MTO process, accounts for approximately 3% of the total ethylene output. Currently, this byproduct is primarily used as fuel or sold directly as ethane products, resulting in relatively low value. To unlock higher profit margins, suitable processes can be used to convert this ethane into ethylene, thereby increasing revenue for the company.

[0004] Invention patents CN104193574B, CN104151121B, CN107417481A, CN107056568A, CN104193570B, and CN104230617B all involve coupling MTO plants with steam cracking plants to produce ethylene. Steam cracking is a widely used industrial method for producing ethylene from ethane. The gas feedstock undergoes high-temperature cracking in a cracking furnace to produce olefins. However, this is a highly endothermic process that requires not only high temperatures (generally above 850°C) but also negative pressure (with the addition of large amounts of superheated steam for dilution). This results in significant energy consumption, high investment in the cracking furnace, complex operation, and the need for regular carbon removal. The ethane conversion rate in the cracking furnace is 65%, while the ethylene selectivity is relatively low, approximately 80% to 84%. The cracked gas is complex in composition, primarily containing ethane, ethylene, propylene, hydrogen, methane, and mixed C4+ gases. The use of steam cracking leads to high operating costs, complex subsequent separation systems, high equipment investment, and large land area. Therefore, a more economical and simple method is needed to convert ethane, a by-product of MTO, into ethylene.

[0005] In recent years, research on the production of ethylene (ODHE) by oxidative dehydrogenation of low-carbon hydrocarbons, especially ethane, has attracted more and more attention. Research on the catalytic oxidative dehydrogenation of ethane began in the 1970s. As early as in 1971, Gaspar et al. proposed the catalytic oxidative dehydrogenation of ethane to produce ethylene under the catalytic action of H2S in their research report. Subsequently, in 1977 and 1978, Ward and Thorsteinson also announced the oxidative dehydrogenation process using Mo, Si and Mo, V mixed oxides as catalysts. Chinese patent CN105849069A discloses the use of a catalyst with the active component MoVTe(Nb)O for the oxidative dehydrogenation of alkanes with 2 to 6 carbon atoms, with a feed gas space velocity of 7500 to 15000 h -1 At a reaction temperature of 320-420°C, the ethane conversion rate can reach 44%, corresponding to an ethylene selectivity of 92.2%. Chinese patent CN105080575B discloses the use of a catalyst containing MoVTeNbO as the active component for the catalytic oxidative dehydrogenation of ethane. At 350°C, the ethane conversion rate and ethylene selectivity can reach 70.5% and 95%, respectively.

[0006] The main problem to be solved by the present invention is how to reduce the separation equipment after ethane is converted into ethylene, simplify the process flow, and reduce the energy consumption of ethylene production through process coupling. Summary of the Invention

[0007] The purpose of the present invention is to provide a method for increasing the production of ethylene by utilizing the ethane product as a by-product of methanol to olefins. The process flow of the present invention is simple, the equipment investment is small, and the yield of the ethylene product can be effectively improved.

[0008] The purpose of the present invention is achieved through the following technical solutions:

[0009] A method for increasing ethylene production by utilizing ethane as a by-product of methanol-to-olefins, the method specifically comprising the following steps:

[0010] (a) mixing ethane, a by-product of MTO (methanol to olefins), with a diluent gas and an oxidant, preheating the mixture and feeding it into an ODHE (ethane catalytic oxidative dehydrogenation) reactor to generate ethylene-rich ODHE reaction gas under the action of a catalyst;

[0011] (b) the ODHE reaction gas obtained in step (a) is sent to an ODHE gas-liquid separator after heat recovery to obtain a gaseous product and a liquid product I. The gaseous product is sent to the bottom of an ODHE product separation tower and is countercurrently contacted with a coolant I and / or an absorbent introduced from the middle and upper part of the ODHE product separation tower to obtain an ODHE product gas at the top of the tower and a liquid product II at the bottom of the tower;

[0012] (c) preheating the ODHE product gas obtained in step (b) and feeding it into an ODHE deoxygenation device, where oxygen in the ODHE product gas reacts with the deoxygenating gas and is removed from the gas phase to obtain an ODHE deoxygenated product gas;

[0013] (d) cooling the ODHE deoxygenated product gas obtained in step (c) and feeding it into an ODHE CO2 removal device, wherein the carbon dioxide in the ODHE deoxygenated product gas undergoes physical absorption and / or chemical reaction with a decarbonizing agent and is removed from the gas phase to obtain an ODHE decarbonated product gas and a liquid phase product III;

[0014] (e) The ODHE decarbonated product gas obtained in step (d) is fed into the MTO product gas compressor, mixed with the pretreated MTO product gas, and then sequentially enters the MTO oxygenate separation unit (for oxygenate separation), the MTO alkali CO2 removal unit (for alkali CO2 removal), the MTO product gas drying unit (for product gas drying) and the MTO olefin separation unit (for olefin separation), ultimately obtaining ethylene products, propylene products, ethane products and other products, and the ethane product is returned to the inlet of the ODHE reactor.

[0015] In step (a), the diluent gas is selected from methanol or a mixture of methanol and one or more of nitrogen, water vapor, and carbon dioxide, preferably methanol, which can be used as a raw material in the MTO system. The diluent gas does not participate in the ODHE reaction or participates in a trace amount.

[0016] In step (a), the oxidant is selected from pure oxygen or a mixture of one or more of air.

[0017] In step (a), the molar ratio of the ethane product to the diluent gas and the oxidant is 1: (0.6-4.65): (0.27-0.55). The amount of diluent is adjusted according to the ethane ratio and the working pressure in actual operation. When the ethane ratio is high and the working pressure is high, the amount of diluent needs to be increased to avoid the risk of explosion.

[0018] In step (a), the active component of the catalyst is a transition metal oxide.

[0019] The transition metal oxide includes one or more of Mo, V, Te or Nb, and a MoVTeNbO catalyst may be used.

[0020] In step (a), the ethane product is uniformly mixed with the diluent gas and the oxidant, and then preheated to a temperature of 150 to 340°C.

[0021] In step (a), the ODHE reaction gas contains ethylene, unreacted ethane, acetic acid, oxygen, methanol, acetic acid, carbon monoxide, carbon dioxide and water.

[0022] In step (a), the reaction temperature in the ODHE reactor is 350-450° C., preferably 380-410° C., and the reaction pressure in the ODHE reactor is in the range of 0.20-1.00 MPaG, preferably 0.20-0.80 MPaG.

[0023] In step (b), the ODHE reaction gas is cooled to 40-300° C., preferably 50-125° C., more preferably 80-95° C., and then fed into the ODHE gas-liquid separator.

[0024] In step (b), the coolant I is introduced from the middle or top of the ODHE product separation tower, and the absorbent is introduced from the top of the ODHE product separation tower.

[0025] In step (b), the coolant I is selected from water or water containing methanol.

[0026] In step (b), the absorbent is selected from water or water containing methanol.

[0027] In step (b), the liquid phase product II contains water and acetic acid.

[0028] In step (b), the liquid phase product I obtained by the ODHE gas-liquid separator and the liquid phase product II obtained by the ODHE product separation tower are mixed to obtain a mixed liquid, wherein the mass fraction of methanol in the mixed liquid ranges from 0 to 90%, but is not 0, preferably from 50 to 90%, and more preferably from 70.6 to 88.0%;

[0029] At least part of the mixed liquid is fed into the MTO feed vaporizer located before the MTO reactor as part of the feed to the MTO reactor. The reaction temperature in the MTO reactor can be 456°C and the reaction pressure can be 0.28 MPaG.

[0030] In step (c), the ODHE product gas is heated to 100-230° C. and then fed into the ODHE deoxygenation device.

[0031] In step (c), the oxygen content in the ODHE deoxygenated product gas is in the range of 1 to 1000 ppmv, preferably 10 to 200 ppmv.

[0032] In step (c), the deoxygenating gas that reacts with oxygen in the ODHE product gas is partly derived from carbon monoxide, ethylene or ethane in the ODHE reaction product, and partly derived from the externally added auxiliary deoxygenating gas.

[0033] The auxiliary deoxygenating gas includes one or more of carbon monoxide, hydrogen, methane, ethylene or ethane.

[0034] In step (d), the ODHE deoxygenated product gas is cooled to 40-50° C. and then fed into the ODHE CO 2 removal device.

[0035] In step (d), the decarbonizing agent is selected from one or more of sodium hydroxide aqueous solution, organic amine solvent, potassium carbonate aqueous solution, sulfolane and alcoholamine aqueous solution, propylene carbonate, polyethylene glycol dimethyl ether, and methanol.

[0036] In step (d), the CO2 content in the ODHE decarbonation product gas is in the range of 1 ppm to 2 mol%.

[0037] In step (e), the operating parameters used in the MTO oxygenate separation unit, the MTO alkaline CO2 removal unit, and the MTO olefin separation unit can be set according to existing processes. The present invention has discovered through research that the catalytic oxidative dehydrogenation of ethane (ODHE) process introduces an oxidant into the reaction, making it an exothermic reaction with a lower Gibbs free energy, thereby achieving a higher equilibrium conversion rate at a lower temperature. Taking oxygen as an oxidant as an example, the reaction equation for the oxidative dehydrogenation of ethane is: C2H6 + 0.5O2 = C2H4 + H2O. At 400°C, the Gibbs free energy of this reaction is ΔG = -193.2 kJ / mol, and the exothermic heat released is 104.2 kJ / mol. The introduction of O2 makes the equilibrium conversion rate of ethane much higher than that of a simple dehydrogenation reaction (C2H6 = C2H4 + H2). The reaction involved in this process is exothermic, which is more conducive to the production of ethylene than the endothermic ethane steam cracking reaction. Under suitable catalyst conditions, ethane conversion rates are high even at relatively low temperatures. The only byproducts are acetic acid, carbon monoxide, and carbon dioxide, making the products easy to separate. Compared to ethane steam thermal cracking processes, the catalytic oxidative dehydrogenation of ethane (ODHE) reactor utilizes a tubular fixed-bed reactor, offering milder reaction conditions, high ethylene selectivity, and a simpler product. Existing MTO process equipment can be used to separate the components, significantly reducing investment and operating costs for the separation equipment. This process is highly suitable for converting ethane, a byproduct of the MTO process, into ethylene.

[0038] For ethane catalytic oxidative dehydrogenation (ODHE) reaction, since the system is an oxygen-containing flammable and explosive mixed gas, and the reaction is highly exothermic, a diluent must be introduced to dilute the reaction heat, improve the reaction heat transfer efficiency, and the introduction of the diluent simultaneously causes the mixed gas to be outside the explosion limit range, making operation safer. The introduction of a large amount of diluent is crucial to the impact of the reaction and the subsequent separation of the diluent. Patents such as CN105080575B, CN110963880A, CN110963879A, CN106660901B, and CN105727975B mention the method using inert gases such as water vapor, nitrogen, and carbon dioxide as diluents. The addition of these diluents has brought challenges to the separation and industrial application of this technology. The advantage of using water vapor as a diluent gas is that the dilution gas and the product gas can be separated by cooling, and the separation energy consumption is low. The disadvantage is that the presence of water vapor in the raw gas will greatly increase the selectivity of the by-product acetic acid product, thereby reducing the effective utilization rate of the raw material; using CO2 as a diluent gas will cause a large amount of CO2 to be recycled back to the reactor after absorption and desorption. The decarbonization unit has high energy consumption, and the desorbed CO2 is a normal pressure gas. The energy consumption and equipment investment for compressing and recycling it back to the reactor are relatively high. A large amount of CO2 needs to be introduced during startup, and its material source is limited; using nitrogen as a diluent gas has little effect on the selectivity of the reaction, but it will cause a large amount of nitrogen to mix with the ethane and ethylene in the product gas. If deep cold separation is used, the pressure needs to be increased to above 30atm and cooled to below -100℃. The compressor has a large pressure ratio and the required cooling capacity is high, resulting in high equipment investment and high energy consumption for subsequent nitrogen separation.

[0039] To address this issue, the present invention, based on the characteristics of the ODHE and MTO reactions, proposes adding some methanol as a diluent gas for the ODHE reaction. Methanol does not participate in the reaction or reacts only in trace amounts in the ODHE reactor. By adjusting the methanol feed rate, the reactor oxygen concentration is controlled within a safe range, ensuring the reactor's thermal stability and avoiding explosion risks. The post-reaction gas is cooled and washed with water to separate the diluent methanol, water, and trace acetic acid from the other reaction products. This liquid mixture can be separated from the water and trace acetic acid by a feed vaporizer preceding the MTO reactor, and the methanol can then be re-entered as a feedstock in the MTO reactor.

[0040] Compared with the prior art, the present invention has the following advantages:

[0041] (1) The ODHE process for producing ethylene is an exothermic reaction with mild reaction conditions. The risk of high-temperature coking in the reactor is low, the catalyst service life is longer, and the reactor can avoid the use of high-temperature resistant materials. Compared with the ethane steam thermal cracking process for producing ethylene, the investment in the cracking furnace is large, the product composition is complex, the ethylene yield is low, the energy consumption is higher, and the equipment occupies a larger area.

[0042] (2) The present invention makes full use of the characteristics of the ODHE process, such as mild reaction conditions, high ethylene selectivity, and simple products, and proposes a method for increasing ethylene production by utilizing the ethane product as a by-product of methanol to olefins. This method greatly simplifies the process flow, reduces equipment investment, and increases the yield of ethylene products.

[0043] (3) The present invention proposes using methanol as the diluent gas for the ODHE process. Given the high boiling point and water-miscible nature of methanol, it can be separated from the ODHE product gas by cooling and water washing, which greatly reduces the energy consumption for separating the diluent gas and the product gas and saves the corresponding equipment investment. During the methanol separation process, the water and trace acetic acid in the ODHE product gas are simultaneously separated from the gas phase, reducing the separation equipment. The separated methanol and water are passed through the MTO feed vaporizer to separate the methanol from the water and trace acetic acid. The methanol is then re-entered into the MTO reactor as a raw material, avoiding the waste of diluent methanol. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 This is a typical MTO process product distribution diagram;

[0045] Figure 2 The process flow chart for Example 1 and Example 2 is as follows;

[0046] In the picture:

[0047] Device marking description: 2 is MTO feed vaporizer; 6 is heat exchanger A; 8 is MTO reactor; 10 is heat exchanger B; 12 is MTO quench tower; 16 is MTO product separation tower; 20 is heat exchanger C; 22 is MTO product gas compressor; 24 is heat exchanger H; 26 is MTO oxygenate separation unit; 28 is MTO alkali elution CO2 removal unit; 31 is MTO product gas drying unit; 33 is MTO olefin separation unit; 41 is heat exchanger D; 43 is ODHE reactor; 46 is ODHE gas-liquid separator; 49 is ODHE product separation tower; 53 is heat exchanger E; 56 is heat exchanger F; 58 is ODHE deoxygenation unit; 60 is heat exchanger G; 62 is ODHE CO2 removal unit;

[0048] Material flow markings: 1 is fresh methanol feedstock; 3 is vaporized methanol feedstock; 4, 5, and 7 are methanol-containing water; 9, 11, 15, 18, 23, 25, 27, 29, and 32 are MTO product gases; 13 is fresh alkali liquor II; 14 is wastewater containing sodium acetate; 17 is condensate from MTO product gas; 19 and 21 are coolant II; 30 is waste alkali liquor II; 34 is ethylene product; 35 is propylene product; 36 is other products; 37 is ethane product; 38 is diluent gas; and 39 is oxidant. ; 40 and 42 are ODHE raw gases; 44 and 45 are ODHE reaction gases; 47 is gaseous product; 48 is liquid product I; 50 is absorbent; 51 is liquid product II; 52 and 54 are coolant I; 55 and 57 are ODHE product gases; 59 and 61 are ODHE deoxygenated product gases; 63 is decarbonizer; 64 is ODHE deCO2 product gas; 65 is liquid product III; 66, 70 and 71 are mixed liquids; 68 is carbon dioxide; 72 is auxiliary deoxygenation gas. DETAILED DESCRIPTION

[0049] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0050] The present invention provides a method for increasing ethylene production by utilizing ethane as a by-product of methanol-to-olefins, the method specifically comprising the following steps:

[0051] (a) mixing an ethane product produced as a by-product of MTO with a diluent and an oxidant, preheating the mixture to a temperature of 150-340° C. and feeding the mixture into an ODHE reactor to generate an ethylene-rich ODHE reaction gas under the action of a catalyst, wherein the ODHE reaction gas comprises ethylene, unreacted ethane, acetic acid, carbon monoxide, carbon dioxide, and water, wherein the diluent is selected from methanol or a mixture of methanol and one or more of nitrogen, water vapor, and carbon dioxide, and the oxidant is selected from a mixture of pure oxygen or one or more of air, and the molar ratio of the ethane product to the diluent and the oxidant is 1:(0.6-4.65):(0.27-0.55), and the active component of the catalyst is a transition metal oxide including Mo, V, Te, or Nb, and the reaction temperature in the ODHE reactor is 350-450° C. and the reaction pressure in the ODHE reactor is in the range of 0.20-1.00 MPaG;

[0052] (b) The ODHE reaction gas obtained in step (a) is cooled to 40-300° C. after heat recovery and then fed into an ODHE gas-liquid separator to obtain a gaseous product and a liquid product I. The gaseous product is fed into the bottom of an ODHE product separation tower and countercurrently contacts with a coolant I and / or an absorbent introduced from the middle and upper part of the ODHE product separation tower to obtain an ODHE product gas at the top of the tower and a liquid product II at the bottom of the tower. The liquid product II comprises water and acetic acid, wherein the coolant is introduced from the middle or top of the ODHE product separation tower and the absorbent is introduced from the top of the ODHE product separation tower. The coolant I is selected from water or water containing methanol, and the absorbent is selected from water or water containing methanol. The liquid product I obtained from the ODHE gas-liquid separator and the liquid product II obtained from the ODHE product separation tower are mixed to obtain a mixed liquid, at least part of which is fed into an MTO feed vaporizer located before the MTO reactor as part of the raw material for the MTO reactor.

[0053] (c) preheating the ODHE product gas obtained in step (b) to 100-230° C. and then feeding it into an ODHE deoxygenation device, where oxygen in the ODHE product gas reacts with a deoxygenating gas and is removed from the gas phase to obtain an ODHE deoxygenated product gas, wherein the oxygen content in the ODHE deoxygenated product gas is in the range of 1-1000 ppmv, wherein the deoxygenating gas reacting with the oxygen in the ODHE product gas is partially derived from carbon monoxide, ethylene or ethane in the ODHE reaction product and partially derived from an externally added auxiliary deoxygenating gas;

[0054] (d) cooling the ODHE deoxygenated product gas obtained in step (c) to 40-50° C. and then feeding it into an ODHE CO2 removal device, wherein the carbon dioxide in the ODHE deoxygenated product gas undergoes physical absorption and / or chemical reaction with a decarbonizing agent and is removed from the gas phase to obtain an ODHE decarbonated product gas and a liquid phase product III, wherein the CO2 content in the ODHE decarbonated product gas is in the range of 1 ppm to 2 mol%;

[0055] (e) The ODHE decarbonated product gas obtained in step (d) is fed into the MTO product gas compressor, mixed with the pretreated MTO product gas, and then sequentially enters the MTO oxygenated compound separation unit, the MTO alkaline CO2 removal unit, the MTO product gas drying unit, and the MTO olefin separation unit to finally obtain ethylene product, propylene product, ethane product and other products, and the ethane product is returned to the inlet of the ODHE reactor.

[0056] The above implementation is further described below with reference to specific examples.

[0057] In the following embodiments, unless otherwise specified, functional components or structures are conventional components or structures used in the art to achieve corresponding functions.

[0058] Example 1

[0059] In this embodiment, a 600,000 ton / year MTO system with a by-product of 8,500 ton / year ethane is combined with an ODHE system to convert ethane into ethylene. The ethane feed in the ODHE system is 2.86 t / h (1.00 t / h fresh ethane as a by-product of MTO + 1.86 t / h recycled ethane). Oxygen is used as the oxidant and methanol as the diluent. After the ethane is converted into ethylene, the product gas is separated by the method of this embodiment. The process flow is as follows: Figure 2 As shown, the process includes the following steps:

[0060] Fresh ethane, a byproduct of MTO, and recycled ethane are mixed together to form ethane product 37, which is then mixed with methanol (as diluent 38) and oxygen (as oxidant 39) in a molar ratio of 1:0.6:0.27. (This embodiment operates under low-pressure conditions with a low oxygen-to-methane ratio, requiring less diluent to avoid the risk of ODHE feed gas explosion.) This produces ODHE feed gas 40. ODHE feed gas 40 is preheated to 150°C in heat exchanger D 41, becoming ODHE feed gas 42 and fed into ODHE reactor 43. Over the catalyst (MoVTeNbO), ethane and the oxidant undergo oxidative dehydrogenation to produce ethylene-rich ODHE reaction gas 44. The temperature within ODHE reactor 43 is 350°C, the pressure is 0.20 MPaG, the ethane conversion is 35.0%, and the selectivities for ethylene, acetic acid, carbon monoxide, and carbon dioxide are 95.0%, 0.7%, 2.9%, and 1.4%, respectively. The molar flow rate of the ODHE reaction gas 44 is 191.9 kmol / h, and the composition is (mol%): C2H4: 16.5%; C2H6: 32.2%; O2: 2.4%; CH3OH: 28.2%; H2O: 18.8%; CO: 1.0%; CO2: 0.5%; CH3COOH: 0.1%; others: 0.3%.

[0061] ODHE reaction gas 44 is cooled to 40°C via heat exchanger D 41 to form ODHE reaction gas 45, which is then fed into ODHE gas-liquid separator 46 for gas-liquid separation, yielding gaseous product 47 and liquid product I 48. Gaseous product 47 is fed into ODHE product separation tower 49, where it undergoes countercurrent contact with water (serving as absorbent 50) introduced from the top of the tower and coolant I 54 (water is used; in actual operation, coolant I 52 can be recovered from the bottom of the tower and subsequently passed through heat exchanger E 53 to yield coolant I 54) (the amounts of absorbent and coolant used are not specific and depend on the absorption and cooling effects). ODHE product gas 55 is obtained at the top of the tower, and liquid product II 51 containing methanol, water, and trace amounts of acetic acid is obtained at the bottom of the tower. The liquid product II 51 of the ODHE product separation tower 49 is mixed with the liquid product I 48 flowing out of the ODHE gas-liquid separator 46 to obtain a mixed liquid 66, which is then fed into the MTO feed vaporizer 2 (the mixed liquid 66 can be fed entirely into the MTO feed vaporizer 2, or it can be divided into a mixed liquid 70 and a mixed liquid 71, wherein the mixed liquid 70 enters the MTO feed vaporizer 2 and the mixed liquid 71 leaves the boundary area. The latter is adopted in this embodiment), and then used as part of the raw material for the MTO reactor 8, wherein the mass flow rate of the mixed liquid 66 is 2.6 t / h, and the composition is (mass%): CH3OH: 66.0%, H2O: 33.0%, CH3COOH: 0.5%, and others: 0.5%. The mixed liquid 70 is separated from methanol, water and trace acetic acid in the MTO feed vaporizer 2, wherein the methanol and the fresh methanol feed 1 are vaporized to obtain vaporized methanol feed 3 (methanol-containing water flows out from the bottom of the MTO feed vaporizer 2 and is divided into two streams of methanol-containing water 4 and methanol-containing water 5. Subsequently, the methanol-containing water 4 flows out of the boundary area, and the methanol-containing water 5 is heated by the heat exchanger A 6 to obtain methanol-containing water 7, which then enters the MTO feed vaporizer 2). The mixed liquid 70 then enters the MTO reactor 8, where the reactor temperature is 456°C and the reactor pressure is 0.28 MPaG. Methanol is converted into MTO product gas 9 containing ethylene, propylene, methane, ethane, propane, carbon monoxide, carbon dioxide, acetic acid, water vapor and other oxygenates in the MTO reactor 8, and is cooled to 267°C by heat exchanger B10 to become MTO product gas 11 and enter the MTO quenching tower 12. Fresh alkali solution II 13 is introduced into the middle part of the MTO quenching tower 12, and MTO product gas 15 is obtained at the top of the tower, and sodium acetate-containing wastewater 14 is obtained at the bottom of the tower. The MTO product gas 15 enters the MTO product separation tower 16, and MTO product gas 18 is obtained at the top of the tower, and MTO product gas condensate 17 is obtained at the bottom of the tower. Coolant II 21 is introduced into the upper part of the MTO product separation tower 16 (in actual work, coolant II 19 can be recovered from the bottom of the tower, and then coolant II 21 is obtained through heat exchanger C 20), and the MTO product gas 18 enters the MTO product gas compressor 22.

[0062] The resulting ODHE product gas 55 is heated to 100°C in heat exchanger F 56, becoming ODHE product gas 57, which is then fed into an ODHE deoxygenation unit 58. The deoxygenated gas comprises the carbon monoxide contained in ODHE product gas 57 and auxiliary deoxygenation gas 72, which is hydrogen. The carbon monoxide and hydrogen react with oxygen to reduce the oxygen content in ODHE product gas 57 to 10 ppmv, producing deoxygenated ODHE product gas 59.

[0063] The resulting ODHE deoxygenated product gas 59 is cooled to 40° C. in a heat exchanger G 60 and then becomes an ODHE deoxygenated product gas 61, which is then fed into an ODHE CO2 removal unit 62. Since the ODHE product gas needs to undergo an alkali wash after mixing with the MTO product gas 18 after entering the MTO system, the ODHE CO2 removal unit 62 of the ODHE system only needs to remove most of the CO2 in the ODHE deoxygenated product gas 61. In this embodiment, the decarbonizing agent 63 is a sodium hydroxide aqueous solution (hereinafter referred to as "alkali solution"). To reduce the consumption of fresh alkali solution, the "long-tailed Caoda method" with low alkali consumption is used to remove CO2. During operation, fresh alkali solution I 63 is introduced from the upper part of the ODHE alkali washing tower 62. Under the action of the fresh alkali solution I 63, the carbon dioxide in the ODHE deoxygenated product gas 61 reacts with the alkali solution and is removed from the gas phase, thereby obtaining an ODHE CO2 deoxygenated product gas 64 and a liquid product III 65. The liquid product III 65 mainly contains NaHCO3 and Na2CO3. In this embodiment, the molar flow rate of the ODHE CO2 removal product gas 64 is 96.1 kmol / h, and the composition is (mol%): C2H4: 32.8%, C2H6: 64.3%, H2O: 2.3%, others: 0.6%, and the CO2 content is 100 ppm.

[0064] The obtained ODHE CO2-free product gas 64 is sent to the existing MTO system, and the ODHE CO2-free product gas 64 is mixed with the pretreated MTO product gas 18 in the first section of the MTO product gas compressor 22. The mixed MTO product gas 23 is cooled to 43°C by the heat exchanger H24 to become MTO product gas 25 and enters the MTO oxygen-containing compound separation unit 26 to remove the oxygenated substances therein. The obtained MTO product gas 27 enters the MTO alkali elution CO2 unit 28 to remove the CO2 therein to 1 ppm. The waste alkali liquid I 30 is discharged from the MTO alkali elution CO2 unit 28. The obtained MTO product gas 29 then enters the MTO product gas drying unit 31 to remove the water therein. The obtained MTO product gas 32 finally enters the MTO olefin separation unit 33 to separate and obtain ethylene product 34, propylene product 35, other products 36 and ethane product 37. The ethane product 37 is a mixture of ethane produced as a by-product of the MTO system and unreacted circulating ethane in the ODHE system, and returns to the ODHE reactor 43.

[0065] For an MTO unit with an annual capacity of 600,000 tons, the method of this embodiment can increase the company's ethylene production by 7,090 tons per year.

[0066] Example 2

[0067] This embodiment adopts Figure 2 The process shown in the figure uses the method of increasing ethylene production by using the ethane product produced as a by-product of methanol to olefins except that:

[0068] (1) The ethane feed in the ODHE reactor 43 is 1.54 t / h (1.00 t / h fresh ethane + 0.54 t / h recycled ethane).

[0069] (2) The ethane product 37 formed by mixing the fresh ethane produced as a by-product of MTO and the recycled ethane is mixed with methanol (as a diluent 38) and oxygen (as an oxidant 39) in a molar ratio of 1:4.65:0.55 (in this embodiment, the ethane content is relatively high and the process is under high pressure, so a large amount of diluent is required to keep the oxygen concentration below 10% to avoid the risk of explosion. In this embodiment, the oxygen concentration is 8.9%) to obtain ODHE feed gas 40. The ODHE feed gas 40 is preheated to 340°C in a heat exchanger D41 to become ODHE feed gas 42 and is fed into the ODHE reactor 43. Under the action of the catalyst (MoVTeNbO catalyst), the ethane and the oxidant undergo an oxidative dehydrogenation reaction to produce ethylene-rich ODHE reaction gas 44.

[0070] (3) The temperature in the ODHE reactor 43 was 450°C and the pressure was 0.80 MPaG. The ethane conversion was 65.0%, and the selectivities for ethylene, acetic acid, carbon monoxide, and carbon dioxide were 89.0%, 0.8%, 2.7%, and 7.5%, respectively. The molar flow rate of the ODHE reaction gas 44 was 334.1 kmol / h, and the composition (mol%) was: C2H4: 8.9%, C2H6: 5.4%, O2: 0.5%, CH3OH: 70.6%, H2O: 12.0%, CO: 0.5%, CO2: 1.5%, CH3COOH: 0.1%, and others: 0.4%.

[0071] (4) The ODHE reaction gas 44 is cooled to 150°C and fed into the ODHE gas-liquid separator 46 for gas-liquid separation. The gaseous product 47 is fed into the ODHE product separation tower 49, where it is countercurrently contacted with water 50 introduced from the top of the tower and coolant I 54 (using water) introduced from the middle of the tower. ODHE water product gas 55 is obtained at the top of the tower, and a liquid product II 51 containing methanol, water, and a trace amount of acetic acid is obtained at the bottom of the tower. The liquid product II 51 from the ODHE product separation tower 49 is mixed with the liquid product I 48 from the gas-liquid separator 46 to obtain a mixed liquid 66. The mixed liquid 66 is fed to the MTO feed vaporizer 2 located before the MTO reactor 8 as part of the feed to the MTO reactor 8. The mass flow rate of the mixed liquid 66 is 8.68 t / h, and the composition (mass %) is as follows: CH3OH: 88.0%, H2O: 11.3%, CH3COOH: 0.2%, and others: 0.5%.

[0072] (5) ODHE product gas 55 is heated to 230°C in heat exchanger F56 to become ODHE product gas 57, which is then fed into ODHE deoxygenation unit 58. The deoxygenated gas comprises carbon monoxide contained in ODHE product gas 57 and auxiliary deoxygenation gas 72, wherein auxiliary deoxygenation gas 72 is carbon monoxide. The reaction of carbon monoxide with oxygen reduces the oxygen content in ODHE product gas 57 to 200 ppmv, producing ODHE deoxygenated product gas 59.

[0073] (6) ODHE deoxygenated product gas 59 is cooled to 50°C in heat exchanger G60 and becomes ODHE deoxygenated product gas 61, which is then fed into ODHE CO2 removal unit 62. A decarbonizing agent 63, comprising an organic amine MDEA solution, reduces the CO2 content in ODHE CO2 deoxygenated product gas 64 to 2 mol%. Liquid product III 65 primarily contains MDEA, water, and CO2. The molar flow rate of ODHE CO2 deoxygenated product gas 64 is 49.6 kmol / h, and its composition (mol%) is: C2H4: 59.6%, C2H6: 36.1%, CO2: 2.0%, H2O: 2.2%, and others: 0.1%.

[0074] Except for this, the rest are the same as in Example 1.

[0075] For an MTO system with an annual capacity of 600,000 tons, the method of this embodiment can increase the company's ethylene production by 6,630 tons per year.

[0076] The above description of the embodiments is intended to facilitate understanding and use of the invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without requiring inventive effort. Therefore, the present invention is not limited to the above-described embodiments. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention, without departing from the scope of the present invention, should be within the scope of protection of the present invention.

Claims

1. A method for increasing ethylene production by utilizing ethane as a by-product of methanol to olefins, characterized in that: The following steps are involved: (a) The ethane product produced as a by-product of MTO is mixed with a diluent gas and an oxidant, and after preheating, is fed into an ODHE reactor to generate ethylene-rich ODHE reaction gas under the action of a catalyst; (b) The ODHE reaction gas obtained in step (a) is sent to the ODHE gas-liquid separator after heat recovery to obtain a gaseous product and a liquid product I, wherein the gaseous product is sent to the bottom of the ODHE product separation tower and is countercurrently contacted with the coolant I and / or absorbent introduced from the middle and upper part of the ODHE product separation tower to obtain an ODHE product gas at the top of the tower and a liquid product II at the bottom of the tower; (c) preheating the ODHE product gas obtained in step (b) and feeding it into the ODHE deoxygenation device to react with the deoxygenated gas to obtain the ODHE deoxygenated product gas; (d) cooling the ODHE deoxygenated product gas obtained in step (c) and feeding it into an ODHE CO2 removal device to undergo physical absorption and / or chemical reaction with a decarbonizing agent to obtain an ODHE decarbonated product gas and a liquid phase product III; (e) The ODHE decarbonated product gas obtained in step (d) is fed into the MTO product gas compressor of the MTO system, mixed with the MTO product gas, and then sequentially enters the MTO oxygenate separation unit, the MTO alkaline CO2 removal unit, the MTO product gas drying unit, and the MTO olefin separation unit to ultimately obtain ethylene product, propylene product, ethane product, and other products, wherein the ethane product is returned to the inlet of the ODHE reactor; In step (a), the diluent gas is selected from methanol or a mixture of methanol and one or more of nitrogen, water vapor, and carbon dioxide; In step (a), the oxidant is selected from a mixture of one or more of pure oxygen and air; In step (a), the molar ratio of ethane product to diluent gas and oxidant is 1: (0.6~4.65): (0.27~0.55); In step (b), the liquid phase product I obtained from the ODHE gas-liquid separator and the liquid phase product II obtained from the ODHE product separation tower are mixed to obtain a mixed liquid, and at least a portion of the mixed liquid is fed to the MTO feed vaporizer of the MTO system and fed to the MTO reactor as a raw material.

2. The method for increasing ethylene production by utilizing ethane as a by-product of methanol to olefins according to claim 1, characterized in that: In step (a), the active component of the catalyst is a transition metal oxide.

3. The method for increasing ethylene production by utilizing ethane as a by-product of methanol to olefins according to claim 1, characterized in that: In step (a), the ethane product is mixed with the diluent gas and the oxidant, and then preheated to a temperature of 150-340°C; In step (a), the reaction temperature in the ODHE reactor is 350-450° C., and the reaction pressure ranges from 0.20-1.00 MPaG.

4. The method for increasing ethylene production by utilizing ethane as a by-product of methanol to olefins according to claim 1, characterized in that: In step (b), the ODHE reaction gas is cooled to 40-300°C and then fed into the ODHE gas-liquid separator.

5. The method for increasing ethylene production by utilizing ethane as a by-product of methanol to olefins according to claim 1, characterized in that: In step (b), the coolant I is water or water containing methanol; In step (b), the absorbent is water or water containing methanol.

6. The method for increasing ethylene production by utilizing ethane as a by-product of methanol to olefins according to claim 1, characterized in that: In step (c), the ODHE product gas is heated to 100-230°C and then fed into the ODHE deoxygenation device; In step (c), the deoxygenating gas reacting with the ODHE product gas is partly derived from carbon monoxide, ethylene or ethane in the ODHE product gas and partly derived from an externally added auxiliary deoxygenating gas; The auxiliary deoxygenating gas is selected from one or more of carbon monoxide, hydrogen, methane, ethylene or ethane.

7. The method for increasing ethylene production by utilizing ethane as a by-product of methanol to olefins according to claim 1, characterized in that: In step (d), the ODHE deoxygenated product gas is cooled to 40-50°C and then fed into the ODHE CO2 removal device; The decarbonizing agent is selected from one or more of sodium hydroxide aqueous solution, organic amine solvent, potassium carbonate aqueous solution, sulfolane and alcoholamine aqueous solution, propylene carbonate, polyethylene glycol dimethyl ether, and methanol.

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