Ethylene two-step series method for producing ethylene oxide and process thereof

Abstract

The application discloses a kind of ethylene two-step series method oxidation production ethylene oxide equipment and process, it is related to petroleum chemical industry technical field, gas-gas isotherm column reactor and water-gas isotherm column reactor are provided in series in reaction unit, the water-gas isotherm column reactor is used to occur first step ethylene oxidation reaction, the gas-gas isotherm column reactor is used to occur second step step ethylene oxidation reaction, the use process of equipment includes reaction stage, ethylene oxide absorption and stripping stage and carbon dioxide absorption and stripping stage, the application makes two reactors consider dynamics and thermodynamic state, improves single pass conversion, reduces ethylene circulation ratio, reduces the energy consumption of device, and improves the service life of catalyst.

Description

Technical Field

[0001] The present invention relates to the technical field of petrochemical industry, and in particular to equipment and a process for producing ethylene oxide by two-step serial oxidation of ethylene. Background Art

[0002] Ethylene oxide is an important derivative of ethylene. As an intermediate product, it is primarily used in the production of ethylene glycol, amino alcohols, haloalcohols, polyoxyethylene alkyl ethers, glycol ethers, and nonionic surfactants. It is also used in plasticizers, lubricants, plastics, and rubber. Currently, industrial ethylene oxide production is often integrated with ethylene glycol production facilities, serving as a raw material.

[0003] There are two main methods for the industrial production of ethylene oxide: the chlorohydrin process and the direct oxidation of ethylene. The latter is further divided into air oxidation and pure oxygen oxidation. The chlorohydrin process has a simple process flow and requires low ethylene purity. However, due to the large amount of highly toxic chlorine consumed during production, numerous side reactions, high ethylene consumption per unit, severe equipment corrosion, large wastewater discharge, and high production costs, the direct oxidation of ethylene has been replaced by the chlorohydrin process.

[0004] The air oxidation method uses purified air as the oxidant, employing a primary and secondary reactor design to oxidize ethylene. The main disadvantages of the air oxidation method are the high silver content required in the catalyst, low selectivity, high catalyst loading at the same processing scale, and high ethylene consumption per unit. Furthermore, the air requires a purification system.

[0005] Compared to air oxidation, pure oxygen oxidation offers a shorter process, lower silver content in the catalyst, and higher selectivity. Its lower reaction temperature extends catalyst life, and its ethylene content in the vented gas is lower than in the air method, resulting in lower ethylene consumption. Furthermore, the increasing sophistication of air separation units (ASUs) has resulted in more diverse oxygen sources and lower prices. Therefore, pure oxygen oxidation is currently the predominant method for industrial ethylene oxide production.

[0006] Currently, the reactor design and process flow for producing ethylene oxide using pure oxygen oxidation are largely similar. In all processes, a silver-based catalyst is loaded into the tubes of a fixed-bed, near-isothermal reactor, directly producing ethylene oxide in a single step. Ethylene oxide recovery and carbon dioxide removal are then completed. Some catalysts in this process offer high selectivity and low feedstock consumption, but low catalyst activity, requiring large catalyst loadings and reactor dimensions. Others offer high catalyst activity but low selectivity, resulting in high ethylene feedstock consumption and high production costs. Still others offer both high selectivity and activity, but require the addition of a promoter to the reaction system, complicating subsequent processing steps.

[0007] Generally speaking, existing pure oxygen oxidation methods all employ a one-step synthesis process, using a single isothermal tubular oxidation reactor or several reactors connected in parallel. Due to the high exothermicity of the ethylene oxidation process and the high explosion hazard associated with the mixture of ethylene and oxygen, increasing processing capacity requires parallel reactors to expand production capacity.

[0008] The ethylene oxidation reaction is a highly exothermic reaction, governed by kinetics in the early stages. Increasing the reaction temperature is necessary to increase the reaction rate and conversion rate. At the end of the reaction, it is governed by thermodynamic equilibrium. Therefore, the ideal reaction state is a low reaction temperature at the end of the isothermal tubular reactor, which is more conducive to shifting the equilibrium toward ethylene oxide production. Furthermore, a low terminal reaction temperature reduces the explosion hazard of the ethylene-oxygen mixture. This theoretically increases the oxygen concentration in the feed gas, improving the primary conversion rate and reducing the ethylene recycle ratio, thereby lowering the load on the recycle compressor and achieving energy conservation and consumption reduction. However, existing one-step isothermal tubular reactors cannot achieve the required low terminal reaction temperature.

[0009] US Patent No. 10858328B2 discloses a method for producing ethylene oxide by oxidation. The method involves designing a water-cooled, isothermal tubular reactor loaded with a silver catalyst. The raw materials ethylene, oxygen, and a chloride inhibitor are mixed and introduced into the tubes. The patent proposes adding an inhibitor to retard corrosion of the reaction tubes, and controls the flow rate within the tubes to greater than 7 m / s. This patent only designs a water-cooled, isothermal reactor, resulting in a single-pass conversion rate of approximately 8%. Therefore, the patent fails to overcome the thermodynamic equilibrium constraints of the final stage of the ethylene oxidation reaction and fails to improve the primary ethylene conversion rate.

[0010] US2018 / 0370936A1 provides a method for reducing gaseous iodide impurities, particularly alkyl iodide impurities, in the circulating gas stream of an ethylene oxide production unit. This method uses a single ethylene oxidation reactor and, as in the previous example, fails to improve the primary ethylene conversion rate.

[0011] CN205933707U proposes an ethylene oxide production device that utilizes two identical ethylene oxide reactors operating in parallel, thereby increasing the circulating gas flow rate and velocity, thereby expanding the device's capacity. However, parallel reactors cannot alter the reaction temperature within the tubular bed, preventing optimal operation for ethylene reaction kinetics and thermodynamics.

[0012] CN112566888A proposes a method for producing ethylene oxide and ethylene glycol, wherein the ethylene oxidation reactor of the method is also a one-step single-unit oxidizer.

[0013] As can be seen, current industrial plants or patents for the pure oxygen oxidation of ethylene to produce ethylene oxide rely on a single water-gas isothermal tubular reactor or parallel operation of similar reactors to expand production capacity due to the highly exothermic reaction. This single-stage ethylene oxidation reaction, constrained by the kinetic and thermodynamic limitations of ethylene and oxygen, results in a single-pass conversion rate of approximately 8%. A large amount of unreacted ethylene is recycled through the EO absorber and recycle gas compressor, resulting in high lean liquid circulation and high energy and electricity consumption. Summary of the Invention

[0014] In order to solve the problems of low single-pass conversion rate, large ethylene circulation volume and short life of silver-based catalysts in the current industrial one-step ethylene oxidation process, the present invention provides an ethylene oxide production equipment and process by a two-step tandem ethylene oxidation process. By adopting a gas-gas isothermal tubular reactor and a water-gas isothermal tubular reactor for a two-step tandem reaction, the two reactors take into account both kinetic and thermodynamic states, thereby improving the single-pass conversion rate, reducing the ethylene circulation ratio, reducing the energy consumption of the device, and increasing the service life of the catalyst.

[0015] Disclosed is an apparatus for producing ethylene oxide by a two-step serial oxidation process of ethylene, comprising a reaction unit, an ethylene oxide absorption and stripping unit, and a carbon dioxide absorption and stripping unit. A gas-gas isothermal tubular reactor and a water-gas isothermal tubular reactor are arranged in series within the reaction unit. The water-gas isothermal tubular reactor is used for the first step ethylene oxidation reaction, and the gas-gas isothermal tubular reactor is used for the second step ethylene oxidation reaction.

[0016] Furthermore, the gas-gas isothermal tubular reactor comprises a gas-gas reactor shell and a gas-phase heat transfer tube bundle, the gas-gas reactor shell is provided with a shell-side air inlet and a shell-side air outlet, the gas-phase heat transfer tube bundle is provided with a lower inlet spherical cavity and an upper outlet spherical cavity, and the gas-phase heat transfer tube bundle, the lower inlet spherical cavity and the upper outlet spherical cavity all adopt a spherical header structure;

[0017] The spherical header structure makes it easy for maintenance personnel to enter the spherical cavity to inspect and plug leaks without removing the catalyst.

[0018] Furthermore, the gas phase heat transfer tube bundle is provided with an arcuate bend;

[0019] The gas phase transfer heat pipe bundle adopts bow-shaped bends at both ends to eliminate thermal stress, avoiding the use of the commonly used straight pipe bundle structure. This bow-shaped bend pipe bundle is a whole seamless steel pipe structure without welding, has good flexibility, and the pipe bundle can expand freely. It can eliminate stress by relying on its own thermal expansion, ensuring that no stress acts on the air inlet and outlet cavities.

[0020] The diameter of the bow-shaped curved tube bundle is selected according to the processing volume and heat transfer rate.

[0021] Furthermore, the gas phase heat transfer tube bundle adopts a high flux heat exchange tube, and the outer surface of the gas phase heat transfer tube bundle is provided with a metal porous layer;

[0022] The gas phase heat transfer tube bundle adopts high-flux heat exchange tubes. Since the heat transfer coefficient between gas media is small, in order to improve the heat transfer efficiency, high-flux heat exchange tubes with enhanced tube heat transfer are adopted. By applying and sintering metal on the outer surface of the metal plain tube, a metal porous layer is produced, which realizes efficient heat transfer under a relatively low heat transfer temperature difference. It has the characteristics of enhanced boiling heat transfer and good scale inhibition performance, which is conducive to realizing the cascade utilization of energy and improving energy utilization rate.

[0023] Furthermore, the tube side of the gas-gas isothermal tubular reactor is used to load a silver-based catalyst;

[0024] Furthermore, the lower air inlet cavity and the upper air outlet cavity both adopt a spherical structure.

[0025] The lower inlet ball cavity and the upper outlet ball cavity adopt a spherical structure, which has the best pressure bearing capacity compared with a flat tube plate or an elliptical structure.

[0026] In the gas-gas isothermal tubular reactor, the fresh feed gas in the tube side is heated and takes away a large amount of reaction heat of the second-step ethylene oxidation by-product. Since the temperature of the second-step oxidation reaction in the shell side is controlled at a low level, the occurrence of tail burning is completely eliminated.

[0027] The tube side and shell side of the gas-gas isothermal tubular reactor only bear the pressure generated by the resistance drop of the reaction gas, which determines that the manufacturing cost of the gas-gas reactor is very low.

[0028] Furthermore, a steam drum is provided on the upper part of the shell side of the water-gas isothermal tubular reactor, a saturated steam outlet pipe is provided on the top of the steam drum, and a plurality of risers and downcomers are provided at the bottom of the steam drum, the risers are connected to the top of the reactor shell side, the downcomers are connected to the bottom of the reactor shell side, and the downcomers are provided with a steam mixer;

[0029] The shell side of the water-gas isothermal tubular reactor is equipped with a natural circulation drum system: boiler water first enters the drum at the top of the shell side reactor. A saturated steam outlet pipe is designed at the top of the drum, and a pressure regulating valve is installed on the pipe to adjust the steam pressure produced by the drum.

[0030] Furthermore, the water-gas isothermal tube reactor adopts a tube sheet structure, and the upper tube sheet adopts a flexible tube sheet;

[0031] The water-gas isothermal tube reactor adopts a mature tube sheet structure, wherein the upper tube sheet adopts a flexible tube sheet to prevent thermal stress expansion caused by temperature difference between the tube and shell.

[0032] Furthermore, the tube bundle of the water-gas isothermal tubular reactor is made of seamless steel pipes and is arranged in a shell-side water bath;

[0033] Carbon steel pipes, alloy steel pipes or duplex stainless steel pipes can be selected. In the present invention, duplex stainless steel pipes are preferably selected.

[0034] The water-gas isothermal tube bundle also uses high-flux heat exchange tubes, and a metal sintered coating is applied to the outer layer of the tube bundle, which is particularly suitable for heat transfer conditions where the shell has phase change.

[0035] Furthermore, the diameter range of the tube bundle of the water-gas isothermal tubular reactor is The length is 5000~8000mm.

[0036] Furthermore, the ends of the tube bundle are provided with springs for supporting the catalyst and the magnetic balls;

[0037] Generally, a grid is installed on the lower flat tube plate. However, as the reactor becomes larger and more catalyst is loaded, the grid is easily deformed by pressure. Spring supports can be installed to increase the space velocity of the catalyst bed, thereby reducing the catalyst loading.

[0038] Furthermore, the steam drum is a horizontal storage tank;

[0039] The steam drum downcomer of the water-gas isothermal tubular reactor is provided with a steam mixer for heating the reactor during the start-up phase, thereby greatly reducing the reaction start-up time and saving raw material costs.

[0040] Furthermore, a pressure regulating valve is installed on the saturated steam outlet pipe.

[0041] The steam drum of the water-gas isothermal tubular reactor can accurately control the bed temperature by controlling the pressure of the produced medium-pressure steam. The medium-pressure steam pressure ranges from 1.7 to 2.5 MPa, and the medium-pressure steam pressure of the present invention is 2.0 MPa.

[0042] Furthermore, the ethylene oxide absorption and stripping unit is provided with an ethylene oxide absorber, an ethylene oxide stripper and a quenched absorption liquid stripper, the ethylene oxide absorber is provided with a steam stripping section in the upper section and an ethylene glycol concentration section in the lower section, and the quenched absorption liquid stripper is used to strip the ethylene glycol-rich alkali solution in the pre-wash section;

[0043] The main components of the reaction gas are ethylene, oxygen, ethylene oxide, carbon dioxide, methane, a small amount of ethylene glycol, aldehydes and acids, inhibitors, etc.

[0044] Unlike existing technologies, the ethylene oxide stripping tower is divided into two sections, the lower section being the ethylene glycol concentration section, where the rich liquid strips out the ethylene oxide and sends it to the upper section. The ethylene glycol solution is delivered as the product. The upper section of the ethylene oxide stripping tower uses steam stripping, where all the ethylene oxide is stripped out and sent as the product.

[0045] Furthermore, a quenching section is provided at the lower part of the ethylene oxide stripping tower, and an anti-blocking valve is provided in the quenching section;

[0046] The quench absorbent stripper is used to strip glycol-rich caustic solution from the pre-wash section, recovering the ethylene oxide absorbed in the quench section. The glycol solution at the bottom of the quench absorbent stripper is delivered as product. The advantage of the quench absorbent stripper design is maximum ethylene oxide recovery, which reduces energy consumption.

[0047] Alkali liquor is used as a circulating absorbent to absorb small amounts of acid and aldehyde impurities in the reactor outlet gas, making it easier to control the purity of the ethylene oxide product. The advantage of designing a quenching section is that it can achieve higher purity of the ethylene oxide product.

[0048] The primary ethylene oxide absorption section has two packing layers. Lean liquid, primarily composed of water, absorbs ethylene oxide. Ethylene oxide and ethylene glycol in the reaction gas are absorbed by the lean liquid, turning it into rich liquid. The remaining reaction gas, primarily composed of ethylene, oxygen, methane, and carbon dioxide, is sent to the carbon dioxide absorption and stripping units.

[0049] Furthermore, the carbon dioxide absorption and stripping unit comprises a circulating gas compressor, a carbon dioxide absorption tower and a carbon dioxide stripping tower connected in sequence, the carbon dioxide stripping tower is divided into two sections, the upper section is a flash section, and the lower section is a steam stripping section;

[0050] Furthermore, the internals of the carbon dioxide absorption tower adopt structured packing or a floating valve tray structure;

[0051] Furthermore, the internals of the carbon dioxide absorption tower adopt a structured packing structure.

[0052] The use process of the equipment includes the following:

[0053] Reaction stage: Fresh feed gas consisting of ethylene and oxygen enters the gas-gas isothermal tubular reactor tube side. After being heated, the fresh feed gas is sent to the water-gas isothermal tubular reactor tube side. The first step of ethylene oxidation reaction occurs in the water-gas isothermal tubular reactor tube side.

[0054] The gas after the first step reaction is collected by the lower pipe box and sent to the shell side of the gas-gas isothermal tubular reactor for the second step oxidation reaction;

[0055] The temperature of the second-step ethylene oxidation reaction is lower than the temperature of the first-step ethylene oxidation reaction;

[0056] The ethylene oxidation reaction is a highly exothermic reaction. In the early stage of the reaction, it is controlled by kinetic reactions. It is necessary to increase the reaction temperature to increase the reaction rate in order to increase the conversion rate of the oxidation reaction. At the end of the reaction, it is controlled by thermodynamic equilibrium. Therefore, the ideal reaction state is that at the end of the isothermal tubular reactor, the reaction temperature is low, which is more conducive to the equilibrium being pushed towards the formation of ethylene oxide. This application mainly realizes that the reaction temperature of the second step is lower than that of the first step by adding a second-step near-isothermal reactor. This not only takes into account the requirements of ethylene oxide for the reaction rate, but also increases the thermodynamic equilibrium constant of the reaction and improves the single-pass conversion rate of ethylene. As a result, more products can be obtained under the same equipment size.

[0057] Ethylene oxide absorption and stripping stage: After the second step of oxidation reaction is completed, the reaction gas flows out of the gas-gas isothermal tubular reactor and enters the low-pressure steam boiler. After cooling, it enters the ethylene oxide absorption tower for pre-washing. After pre-washing, the reactor enters the ethylene oxide main suction section, and the gas flowing out of the main suction section is sent to the carbon dioxide absorption and stripping unit;

[0058] Carbon dioxide absorption and stripping stage: First, the circulating gas enters the circulating gas compressor for pressurization, and the pressurized circulating gas enters the carbon dioxide absorption tower. The carbon dioxide absorption tower uses polyethylene glycol dimethyl ether as the absorption liquid. After passing through the carbon dioxide stripping tower after the absorption liquid, methane gas is flashed out, and low-pressure steam is used to decompose the carbon dioxide gas.

[0059] The CO2 absorption tower uses polyethylene glycol dimethyl ether (NHD) as the absorption liquid. NHD absorption liquid has excellent chemical properties, thermal stability, is non-toxic, corrosive, and has excellent decarbonization efficiency, making it a superior absorbent compared to potassium carbonate. The CO2 stripping tower is used to separate the NHD rich liquid that has absorbed CO2. The stripped NHD rich liquid, known as the lean liquid, is cooled in a lean-rich liquid heat exchanger and then recycled.

[0060] Furthermore, in the reaction stage, the first step of ethylene oxidation reaction conditions are: temperature 230-270°C, reaction pressure 1.0-3.0 MPa, catalyst bed space velocity selection range 4000-12000 h - ;

[0061] Furthermore, the first step of ethylene oxidation reaction conditions are: temperature 240-260°C, reaction pressure 1.8-2.2 MPa, catalyst bed space velocity selection range 5000-9000 h - ;

[0062] The reaction conditions of the shell-side bed of the second step ethylene oxidation reaction are: temperature 190-220°C, reaction pressure 1.0-3.0 MPa, catalyst bed space velocity 2000-10000 h - ;

[0063] Furthermore, the reaction conditions of the shell-side bed of the second step ethylene oxidation reaction are: temperature 200-210°C, reaction pressure 1.8-2.2 MPa, catalyst bed space velocity 6000-8000 h - .

[0064] Furthermore, in the ethylene oxide absorption and stripping stage, the absorption pressure of the main absorption section is 1.7-2.0 MPa, and the absorption temperature is 30-40°C.

[0065] Furthermore, in the carbon dioxide absorption and stripping stage, the compressor outlet pressure is increased by 0.3 MPa compared to the inlet pressure, the carbon dioxide absorption tower absorption temperature control range is 20-40°C, and the absorption pressure is 1.8-2.2 MPa.

[0066] Furthermore, in the carbon dioxide absorption and stripping stage, the absorption liquid is selected from one or more of polyethylene glycol dimethyl ether, N-methyldiethanolamine or diethanolamine;

[0067] Furthermore, the absorption liquid is polyethylene glycol dimethyl ether, and the active component of polyethylene glycol dimethyl ether in the absorption liquid is ≥99%, and the water content is ≤1.0%.

[0068] Select a superior amine salt as the absorption liquid, which can be polyethylene glycol dimethyl ether (NHD), N-methyldiethanolamine (MDEA), diethanolamine (DEA), or a mixture thereof. NHD is preferred as the absorption liquid. NHD absorption liquid has good chemical properties, good temperature and thermal stability, is non-toxic, has good corrosiveness, and has excellent decarburization effect.

[0069] Beneficial effects of the present invention:

[0070] 1. The present invention utilizes a two-step tandem reaction system consisting of a gas-gas isothermal tubular reactor and a water-gas isothermal tubular reactor. This allows the two reactors to balance kinetic and thermodynamic conditions, improving single-pass conversion, reducing ethylene recycle ratio, reducing device energy consumption, and extending catalyst life. Existing isothermal fixed-bed ethylene oxidation reactors generally employ a fixed tubesheet structure, which has weak pressure bearing capacity, high thermal stress on the hot and cold sides, and is prone to tube bundle damage and leakage. The gas-gas tubular reactor employs a concentrated spherical cavity structure, resolving the high thermal stress in the tubesheet and tube bundle that plagues existing isothermal tubular reactors, thereby reducing equipment costs.

[0071] 2. The present invention is the first to use polyethylene glycol dimethyl ether (NHD) to replace potassium carbonate in the traditional ethylene oxide production process as an absorption liquid for CO2 in the circulating gas. The polyethylene glycol dimethyl ether absorption liquid has good chemical properties such as temperature and thermal stability, is non-toxic, has good corrosiveness, and has an excellent decarbonization effect. It is a better absorbent than potassium carbonate. BRIEF DESCRIPTION OF THE DRAWINGS

[0072] Figure 1This is a process flow chart of producing ethylene oxide by two-step tandem oxidation of ethylene according to the present invention;

[0073] Figure 2 Schematic diagram of gas-gas isothermal tube reactor;

[0074] Figure 3 It is a schematic diagram of the water-gas isothermal shell-and-tube reactor.

[0075] Figure numerals: 1-gas-gas isothermal tubular reactor; 101-gas-gas reactor shell; 102-tube bundle; 103-upper gas outlet cavity; 104-lower gas inlet cavity; 105-gas phase heat transfer tube bundle; 106-catalyst discharge port; 107-fresh gas inlet; 108-preheated gas outlet; 109-synthesis gas inlet after the first oxidation reaction; 110-synthesis gas outlet after the second oxidation reaction; 2-intermediate heat exchanger; 3-water-gas isothermal tubular reactor; 301-water-gas reactor shell side; 302-flexible Tube sheet; 303-heat exchange tube bundle; 304-preheated raw gas inlet; 305-synthesis gas outlet after the first oxidation reaction; 306-boiler water riser; 307-boiler water downpipe; 308-support spring; 4-medium-pressure steam drum; 5-venturi tube; 6-pressure regulating valve; 7-low-pressure steam generator; 8-reactor cooler; 9-quenching section of ethylene oxide absorber; 10-absorption section of ethylene oxide absorber; 11-lean liquid cryocooler; 12-gas lift cap; 13-ethylene oxide stripping tower Steam direct stripping section; 14-ethylene oxide stripping tower ethylene glycol concentration section; 15-stripping tower lean liquid pump; 16-stripping tower feed heater; 17-quench liquid stripping tower; 18-product cooler; 19-circulating gas compressor; 20-carbon dioxide absorption tower; 21-carbon dioxide stripping tower flash section; 22-carbon dioxide stripping tower steam stripping section; 23-NHD lean and rich liquid heat exchanger; 24-fresh gas; 25-synthesis gas after the first oxidation reaction; 26-synthesis gas after the second oxidation reaction; 27-rich Carbon dioxide circulating gas; 28-Medium-pressure saturated steam; 29-Boiler water; 30-Start-up steam; 31-Downcomer; 32-Preheated raw gas; 33-Sodium hydroxide absorption liquid; 34-Ethylene glycol-rich liquid; 35-Ethylene glycol solution; 36-Ethylene oxide product liquid; 37-Quench section bottom liquid; 38-Ethylene oxide-rich absorption liquid; 39-Lean absorption liquid; 40-Quench liquid stripping tower top gas; 41-Circulating gas; 42-Methane-rich gas; 43-Carbon dioxide gas; 44-NHD lean liquid; 45-NHD rich liquid. DETAILED DESCRIPTION

[0076] The following is a clear and complete description of the technical solution of the present invention. Obviously, the embodiments described here are only part of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0077] Example 1

[0078] like Figure 1-Figure 3 As shown, a two-step tandem oxidation process for producing ethylene oxide involves the oxidation of ethylene with oxygen in the presence of a silver-based catalyst to produce ethylene oxide. The process primarily involves a reaction phase, an ethylene oxide absorption and stripping phase, and a carbon dioxide absorption and stripping phase. In this example, the reactants primarily include ethylene oxide, ethylene, carbon dioxide, water, methane, trace amounts of aldehydes, and organic acids.

[0079] The present invention uses a silver catalyst for ethylene oxide oxidation, disclosed in application number CN112206798B, as its catalyst. In this embodiment, the silver catalyst, based on the total dry weight of the silver catalyst, is supported on a composite carrier of α-silicon carbide and α-alumina. The catalyst contains 17 wt% silver, 0.05 wt% strontium, 0.5 wt% magnesium, 0.65 wt% fluorine, 0.05 wt% cerium, 0.25 wt% tin, 0.15 wt% phosphorus, and 0.15 wt% boron. The silver catalyst has a water absorption rate of 55%, a specific surface area of ​​0.91 m2 / g, and a pore volume of 0.52 ml / g, of which pores with a pore diameter of 5 to 30 microns account for 89% and pores with a pore diameter of 30 microns or greater account for 11%. Under these conditions, the catalyst exhibits excellent heat transfer, conductivity, diffusion, and reaction activity, making it suitable for both tube-side and shell-side loading in fixed-bed reactors. In this embodiment, the reactor's base reaction pressure is 2.0 MPa.

[0080] Reaction Stage: The ethylene oxidation reaction is carried out in two steps. The first step is carried out at a higher temperature of 250°C in the three-tube side of the water-gas isothermal tubular reactor; the second step is carried out at 210°C in the one-shell side of the gas-gas isothermal tubular reactor.

[0081] First, fresh gas 24 containing ethylene and oxygen is mixed with recycle gas 41. The resulting mixture has the following molar fractions: 28% ethylene, 8% oxygen, 5% carbon dioxide, 50% methane, 7% nitrogen, and 2% argon. A trace amount of 1,2-dichloroethane is also added to the feed gas as an inhibitor. The mixed fresh gas is then delivered through fresh gas inlet 107 to the lower inlet spherical cavity 104 of the gas-gas isothermal tubular reactor 1. The gas-gas isothermal tubular reactor 1 consists of a gas-gas reactor shell 101 and a tube bundle 102. The gas-phase heat transfer tube bundle 105 features bow-shaped bends and spherical cavities at both ends, providing optimal pressure resistance and flexibility. Fresh gas 24 flows upward through the gas-phase heat transfer tube bundle 105, exchanging countercurrent heat with the synthesis gas after the first oxidation reaction, heating it from 40°C to 170°C. The fresh gas is then collected by the upper outlet spherical cavity 103 and discharged through the preheated gas outlet 108. The preheated feed gas 32 is then preheated a second time in the intermediate heat exchanger 2 to 200°C before entering the water-gas isothermal tubular reactor 3 for the first oxidation reaction. The synthesis gas 25 after the first oxidation reaction flows downward through the shell-side catalyst bed in the gas-gas isothermal tubular reactor 1, undergoing the second oxidation reaction and ultimately exiting the reactor through the second-step oxidation reaction synthesis gas outlet 110. Due to the heat removal from the fresh gas 24 within the tubes, the second-step oxidation bed temperature is controlled at 210°C. This low temperature favors a shift in the reaction thermodynamic equilibrium constant toward ethylene oxide production, thus breaking the conversion limit of the single-step oxidation reaction.

[0082] The gas-gas isothermal tubular reactor of this embodiment is also designed with a catalyst discharge port 106 on the shell side bed layer to facilitate the unloading of the catalyst on the shell side bed layer. The diameter of the gas-gas reactor is 3000mm-4600mm, the length of the tube bundle is 5000mm-7000mm, and the diameter range of the tube bundle is The shell side material is carbon steel, alloy steel or duplex steel, preferably carbon steel.

[0083] In this embodiment, the gas-phase heat transfer tube bundle 105 utilizes high-flux heat exchange tubes. The porous layer thickness of the high-flux heat exchange tubes ranges from 0.1 mm to 0.3 mm, preferably 0.2 mm. The porosity of the porous layer of the high-flux heat exchange tubes ranges from 30% to 70%, preferably 50%. The metal powder used in the outer layer of the L-shaped bend tube bundle is primarily a Cu-based, Ni-containing, or Fe-based alloy powder with an average particle size of 70 μm or greater, preferably an Fe-based alloy powder.

[0084] In this embodiment, the preheated gas exiting the intermediate heat exchanger enters the water-gas isothermal tubular reactor 3 via the preheated feed gas inlet 304. The synthesis gas 25 after the first oxidation reaction exits through the synthesis gas outlet 305. The water-gas isothermal tubular reactor 3 consists of a water-gas reactor shell 301 and a heat exchange tube bundle 303, separated by a flexible tube sheet 302. The flexible tube sheet used in this embodiment completely eliminates thermal expansion caused by temperature differences between the shell and tube sides, preventing reactor leakage and preventing high-pressure water from the shell side from entering the catalyst bed in the tube side.

[0085] A silver-based catalyst is loaded into the water-gas isothermal tubular reactor 3, providing a catalyst for the first ethylene oxidation reaction. Approximately 70% of the oxidation reaction occurs within the water-gas isothermal tubular reactor 3, while the remaining 30% occurs in the gas-gas isothermal tubular reactor 1. By controlling the pressure of the medium-pressure saturated steam 28 in the water-gas reactor shell 301 and the medium-pressure steam drum 4, the water-side temperature of the water-gas reactor shell 301 and the water heat extraction rate are adjusted, thereby controlling the bed temperature within the tubes. In this embodiment, the bed reaction temperature is controlled at 250°C. At this temperature, the ethylene oxidation rate is controlled by the kinetic equations, resulting in high temperatures, high reaction rates, and high processing capacity, while requiring a low catalyst loading. The post-first oxidation synthesis gas 25 is then fed to the intermediate heat exchanger 2 for further reaction heat recovery.

[0086] The water-gas reactor shell 301, the intermediate-pressure steam drum 4, the downcomer 31, and the riser form a closed-loop water circuit. The amount of boiler water entering the intermediate-pressure steam drum 4 is controlled by a flow control valve 29. The water then circulates naturally through thermosiphoning. Boiler water enters the lower portion of the water-gas isothermal tubular reactor 3 through the boiler water downcomer 307. From bottom to top, the boiler water undergoes countercurrent heat exchange with the synthesis gas 25 after the first oxidation reaction within the tubes, absorbing approximately 80% of the heat released by the reaction. The boiler water itself then transforms from a liquid phase into a gas-liquid phase before finally circulating through the boiler water riser 306 into the intermediate-pressure steam drum 4.

[0087] In this embodiment, the upper layer of the medium-pressure steam drum 4 provides a space for separating the boiling boiler water vapor and liquid. The by-product, medium-pressure saturated steam, is drawn from the top of the drum. A pressure regulating valve 6 is installed on the saturated steam line to control the steam pressure produced by the drum within a range of 1.7 to 2.5 MPa. Preferably, the medium-pressure steam pressure in this embodiment is 2.0 MPa. By controlling the steam pressure, the temperature of the circulating boiler water on the shell side of the reactor is controlled, thereby controlling the reaction temperature of the bed. This method is suitable for applications where different bed temperature requirements exist at the initial and final stages of the catalyst reaction. This control method is safe and has a fast response time.

[0088] In this embodiment, a startup steam system is provided to preheat the gas heat exchanger during the startup phase, thereby accelerating the startup time and saving the consumption of ethylene oxygen. The startup steam system is composed of a venturi tube 5 and startup steam 30.

[0089] In this embodiment, the diameter of the water-gas reactor is 3200 mm to 4800 mm, preferably 4000 mm, the length of the tube bundle is 4000 mm to 8000 mm, preferably 6000 mm, and the diameter range of the tube bundle is The shell side is preferably made of carbon steel, alloy steel or duplex steel, preferably carbon steel.

[0090] Ethylene oxide absorption and stripping stage: In this embodiment, the temperature of the synthesis gas 26 after the second oxidation reaction reaches 200°C. Through the innovative two-step reaction, the single-pass ethylene conversion rate reaches 10%. The molar composition of the synthesis gas 26 after the second oxidation reaction is as follows: ethylene 25.54%; oxygen 5.05%; carbon dioxide 6.42%; methane 48.52%; nitrogen 8%; argon 3%; water 1.2%; ethylene oxide 2.2%, and trace amounts of aldehydes and acids as byproducts.

[0091] The reaction gas temperature remains at 200°C. To recover waste heat, it first enters a low-pressure steam generator 7, producing low-pressure steam (0.3 MPa) as a byproduct to preheat desalted water, lowering the reactor temperature to 75°C. The cooled rich liquid is then further cooled to 45°C in a reactor cooler 8 before entering the quenching section 9 of the ethylene oxide absorber. This section utilizes an anti-blocking valve and sodium hydroxide absorbent 33 as a circulating absorbent to absorb small amounts of acid and aldehyde impurities in the reactor outlet gas, facilitating control of the purity of the ethylene oxide product.

[0092] The quenching liquid 37, which has absorbed the acid and aldehyde, is discharged from the bottom of the ethylene oxide absorber and transferred to a quenching liquid stripping tower 17, where trace amounts of dissolved ethylene oxide are recovered using low-pressure steam. The ethylene oxide-containing quenching liquid stripping tower overhead gas 40 is recovered at the top of the tower. The bottom of the tower contains ethylene glycol solution 35. The quenching liquid stripping tower is a packed tower.

[0093] Gas from the top of the quenching section is fed into the absorption section 10 of the ethylene oxide absorber via a gas lift cap 12. In this embodiment, the absorption tower absorbs ethylene oxide from the reaction gas and recovers unreacted ethylene and oxygen. As the primary absorption of ethylene oxide, the absorption section 10 of the ethylene oxide absorber can typically be a packed tower or a plate tower. Generally, absorption is favored at high pressure and low temperature. The operating pressure of the absorption tower ranges from 1.0 to 3.0 MPa, preferably 1.5 to 2.0 MPa, and is determined by the operating pressure of the oxidation reactor. The absorption temperature ranges from 10 to 45°C, preferably 20 to 30°C. Furthermore, water is used as the ethylene oxide absorption liquid, with a molar flow ratio of the absorption liquid to the reaction gas ranging from 0.2 to 3.0.

[0094] The ethylene, oxygen, carbon dioxide, methane, nitrogen, etc. that are not absorbed by the absorption liquid are discharged from the top of the main absorption section and sent to the carbon dioxide absorption and stripping unit as carbon dioxide-rich circulating gas 27.

[0095] In this embodiment, the ethylene oxide-rich absorption liquid 38, primarily composed of ethylene oxide, water, and low-boiling-point impurities such as formaldehyde and acetic acid, is discharged from the bottom of the primary absorption stage. It is first passed through the reactor cooler 8 and the stripper feed heater 16 to recover cooling, where it is heated to 100°C. It then enters the steam direct stripping section 13 of the ethylene oxide stripper. The purpose of the ethylene oxide stripper is to recover ethylene oxide and regenerate rich absorption liquid for recycling.

[0096] The direct steam stripping section 13 of the ethylene oxide stripping tower uses low-pressure steam to provide stripping heat. Ethylene oxide is produced at the top of the tower and cooled to a liquid state in the product cooler 18 as ethylene oxide product liquid 36, which is then sent to the downstream reabsorption and purification section for purification. Lean absorbed liquid 39, completely regenerated in the direct steam stripping section, is discharged from the bottom of the tower and pressurized by the stripping tower lean liquid pump 15 before being split into two paths. The majority of the lean liquid is cooled by the stripping tower feed heater 16 and the lean liquid cryocooler 11 before being sent to the absorption tower for further use. The lean liquid cryocooler 11 is cooled with chilled water. A small portion of the lean liquid is sent to the ethylene glycol concentration section 14 of the ethylene oxide stripping tower for further stripping. The overhead gas from this section returns to the direct steam stripping section 13 of the ethylene oxide stripping tower to replace some of the low-pressure steam, and the bottom of the tower is sent to the boundary area as ethylene glycol-rich solution 34. This completes a closed-loop ethylene oxide absorption and desorption recovery process.

[0097] Carbon dioxide absorption and stripping stage:

[0098] In this embodiment, carbon dioxide-rich recycle gas 27 first enters recycle gas compressor 19 for pressurization to compensate for pressure loss and allow the recycle gas to re-enter the reactor. Carbon dioxide in the recycle gas can increase inert gas levels within the system, affecting reaction conversion and selectivity. To remove some of the carbon dioxide from the recycle gas, a carbon dioxide absorption tower 20 is designed.

[0099] In this embodiment, polyethylene glycol dimethyl ether (NHD) is selected as the absorption liquid. The carbon dioxide absorption tower 20 is packed with gas. Carbon dioxide-rich recycle gas 27 enters the tower from the bottom and undergoes countercurrent gas-liquid exchange with NHD lean liquid 44 injected from the top. During this process, most of the carbon dioxide in the recycle gas is absorbed. The purified recycle gas 41 is mixed with fresh gas 24 and fed into the reactor for further reaction. The NHD rich liquid 45, which has absorbed carbon dioxide, is first heated in the NHD lean-rich liquid heat exchanger 23 before entering the flash section 21 of the carbon dioxide stripping tower. The flash section 21 of the carbon dioxide stripping tower recovers useful gases such as methane and ethane absorbed by the NHD liquid. Because the solubility of methane and ethane is lower than that of carbon dioxide, the pressure in the flash section is controlled at 0.3 MPa. Methane-rich gas 42 is discharged from the top of the flash section and sent to downstream processing equipment. The carbon dioxide-rich NHD liquid at the bottom of the flash section 21 of the carbon dioxide stripping tower flows by gravity into the steam stripping section 22 of the carbon dioxide stripping tower.

[0100] Stripping and desorption must be performed at high temperature and low pressure. In this embodiment, the steam stripping section of the carbon dioxide stripping tower operates at a temperature of 110°C and an operating pressure of 0.15 MPa. The tower bottom is stripped by steam, which can be done indirectly using a vertical thermosyphon heat exchanger or directly by passing steam into the tower. In this embodiment, indirect stripping using a vertical thermosyphon heat exchanger is preferred. Carbon dioxide gas 43 stripped from the rich liquid is discharged from the top of the tower. The tower bottom contains lean liquid, which is essentially free of carbon dioxide and is then cooled by the NHD lean-rich liquid heat exchanger 23 before being recycled.

[0101] Example 2

[0102] In this example, the equipment and process for the two-step serial oxidation of ethylene oxide by ethylene are identical to those of Example 1. However, a different, more heat-resistant silver-based catalyst is used as the bed layer in the first step of the water-gas isothermal tubular reactor. The specific composition is as follows: 17 wt% silver, 0.05 wt% strontium, 0.45 wt% magnesium, 0.56 wt% fluorine, 0.07 wt% cerium, 0.26 wt% tin, 0.15 wt% phosphorus, and 0.16 wt% boron. The catalyst has a water absorption rate of 51%, a specific surface area of ​​0.90 m² / g, and a pore volume of 0.50 ml / g. Pores with a pore size of 5 to 30 μm account for 85%, and pores ≥30 μm account for 15%. Because this catalyst is more heat-resistant, the reaction temperature can be controlled at 260°C.

[0103] In this example, the shell-side bed of the second-step gas-gas isothermal tubular reactor was again prepared using the silver-based catalyst of Example 1, and the reaction temperature was controlled at 210°C. The results showed that the total ethylene conversion reached 10%, with a slight decrease in selectivity from 84% to 83.5%.

[0104] The above description is only a preferred embodiment of the present application and an illustration of the technical principles used. Those skilled in the art should understand that the scope of the invention involved in this application is not limited to the technical solutions formed by the specific combination of the above-mentioned technical features, but should also cover other technical solutions formed by any combination of the above-mentioned technical features or their equivalents without departing from the inventive concept. For example, a technical solution formed by replacing the above-mentioned features with (but not limited to) technical features with similar functions disclosed in this application.

Claims

1. An apparatus for producing ethylene oxide by two-step serial oxidation of ethylene, comprising a reaction unit, an ethylene oxide absorption and stripping unit, and a carbon dioxide absorption and stripping unit, characterized in that: The reaction unit is provided with a gas-gas isothermal tubular reactor and a water-gas isothermal tubular reactor in series, wherein the water-gas isothermal tubular reactor is used for the first step ethylene oxidation reaction, and the gas-gas isothermal tubular reactor is used for the second step ethylene oxidation reaction; The gas-gas isothermal tubular reactor comprises a gas-gas reactor shell and a gas-phase heat transfer tube bundle. The gas-gas reactor shell is provided with a shell-side air inlet and a shell-side air outlet. The gas-phase heat transfer tube bundle is provided with a lower inlet spherical cavity and an upper outlet spherical cavity. The gas-phase heat transfer tube bundle, the lower inlet spherical cavity and the upper outlet spherical cavity all adopt a spherical header structure. The shell side of the gas-gas isothermal tubular reactor is used to load the silver-based catalyst; The water-gas isothermal tubular reactor is provided with a steam drum at the upper part of the shell side, a saturated steam outlet pipe is provided at the top of the steam drum, and a plurality of risers and downcomers are provided at the bottom of the steam drum, wherein the risers are connected to the top of the reactor shell side, the downcomers are connected to the bottom of the reactor shell side, and the downcomers are provided with a steam mixer; Fresh feed gas consisting of ethylene and oxygen enters the tube side of the gas-gas isothermal tubular reactor. After being heated, the fresh feed gas is sent to the tube side of the water-gas isothermal tubular reactor. The first step of ethylene oxidation reaction occurs in the tube side of the water-gas isothermal tubular reactor. The gas after the first step reaction is collected through the lower pipe box and then sent to the shell side of the gas-gas isothermal tubular reactor for the second step ethylene oxidation reaction; The temperature of the second-step ethylene oxidation reaction is lower than the temperature of the first-step ethylene oxidation reaction.

2. The device according to claim 1, characterized in that The gas phase heat transfer tube bundle is provided with an arcuate bend; The gas phase heat transfer tube bundle adopts a high flux heat exchange tube, and the outer surface of the gas phase heat transfer tube bundle is provided with a metal porous layer; The lower air inlet cavity and the upper air outlet cavity both adopt spherical structures.

3. The device according to claim 1, characterized in that The water-gas isothermal tube reactor adopts a tube sheet structure, wherein the upper tube sheet adopts a flexible tube sheet; The tube bundle of the water-gas isothermal tubular reactor is made of seamless steel pipes and is arranged in a shell-side water bath; The water-gas isothermal tubular reactor tube bundle selection diameter range is φ40-φ50mm, length is 5000~ 8000mm; The ends of the tube bundle are provided with springs for supporting the catalyst and the magnetic balls; The steam drum is a horizontal storage tank; A pressure regulating valve is installed on the pipeline of the saturated steam outlet pipe.

4. The device according to claim 1, characterized in that The ethylene oxide absorption and stripping unit is provided with an ethylene oxide absorption tower, an ethylene oxide stripping tower and a quenched absorption liquid stripping tower. The ethylene oxide absorption tower is provided as the upper ethylene oxide absorption tower absorption section. and the quenching section of the lower ethylene oxide absorber; A quenching section is provided at the lower part of the ethylene oxide stripping tower, and an anti-blocking valve is provided in the quenching section.

5. The device according to claim 1, characterized in that The carbon dioxide absorption and stripping unit comprises a circulating gas compressor, a carbon dioxide absorption tower and a carbon dioxide stripping tower connected in sequence, wherein the carbon dioxide stripping tower is divided into two sections, the upper section is a flash section, and the lower section is a steam stripping section; The internals of the carbon dioxide absorption tower adopt structured packing or floating valve tray structure; The internals of the carbon dioxide absorption tower adopt a structured packing structure.

6. The process for using the device according to any one of claims 1 to 5, characterized in that: Includes the following: Reaction stage: Fresh feed gas consisting of ethylene and oxygen enters the gas-gas isothermal tubular reactor tube side. After being heated, the fresh feed gas is sent to the water-gas isothermal tubular reactor tube side. The first step of ethylene oxidation reaction occurs in the water-gas isothermal tubular reactor tube side. The gas after the first step reaction is collected through the lower pipe box and then sent to the shell side of the gas-gas isothermal tubular reactor for the second step ethylene oxidation reaction; The temperature of the second-step ethylene oxidation reaction is lower than the temperature of the first-step ethylene oxidation reaction; Ethylene oxide absorption and stripping stage: After the second step of oxidation reaction is completed, the reaction gas flows out of the gas-gas isothermal tubular reactor and enters the low-pressure steam boiler. After cooling, it enters the ethylene oxide absorption tower for pre-washing. The pre-washed reaction gas enters the ethylene oxide main suction section, and the gas flowing out of the main suction section is sent to the carbon dioxide absorption and stripping unit; Carbon dioxide absorption and stripping stage: First, the circulating gas enters the circulating gas compressor for pressurization, and the pressurized circulating gas enters the carbon dioxide absorption tower. After passing through the absorption liquid, the circulating gas enters the carbon dioxide stripping tower to flash out methane gas, and low-pressure steam is used to decompose the carbon dioxide gas.

7. The process according to claim 6, characterized in that Reaction stage, The first step of ethylene oxidation reaction conditions: temperature 230 ~ 270 ℃, reaction pressure 1.0 ~ 3.0 MPa, catalyst bed space velocity selection range 4000 ~ 12000 h - ; The reaction conditions of the shell-side bed of the second step ethylene oxidation reaction are: temperature 190-220 ℃, reaction pressure 1.0-3.0 MPa, catalyst bed space velocity 2000-10000 h - .

8. The process according to claim 7, characterized in that The first step of ethylene oxidation reaction conditions: temperature 240 ~ 260 ℃, reaction pressure 1.8 ~ 2.2 MPa, catalyst bed space velocity selection range 5000 ~ 9000 h - .

9. The process according to claim 7, characterized in that The reaction conditions of the shell-side bed of the second step ethylene oxidation reaction are: temperature 200-210℃, reaction pressure 1.8-2.2Mpa, catalyst bed space velocity 6000-8000h - .

10. The process according to claim 6, characterized in that In the ethylene oxide absorption and stripping stage, the absorption pressure of the main absorption section is 1.7-2.0 MPa, and the absorption temperature is 30-40°C.

11. The process according to claim 6, characterized in that During the carbon dioxide absorption and stripping stage, the compressor outlet pressure is increased by 0.3 MPa compared to the inlet pressure. The carbon dioxide absorption tower has an absorption temperature control range of 20-40°C and an absorption pressure of 1.8-2.2 MPa.

12. The process according to claim 6, characterized in that In the carbon dioxide absorption and stripping stage, the absorption liquid is selected from one or more of polyethylene glycol dimethyl ether, N-methyldiethanolamine or diethanolamine.

13. The process according to claim 12, characterized in that The absorption liquid is polyethylene glycol dimethyl ether, and the active component of polyethylene glycol dimethyl ether in the absorption liquid is ≥ 99% and the water content is ≤ 1.0%.

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