CN116764550A

CN116764550A - Equipment and process for producing ethylene oxide by oxidizing ethylene in two-step serial connection method

Info

Publication number: CN116764550A
Application number: CN202310767337.4A
Authority: CN
Inventors: 王刚; 卓润生; 张信
Original assignee: Shanghai Runhe Shengjian Engineering Technology Co ltd
Current assignee: Shanghai Runhe Shengjian Engineering Technology Co ltd
Priority date: 2023-06-27
Filing date: 2023-06-27
Publication date: 2023-09-19

Abstract

The application discloses equipment and a process for producing ethylene oxide by oxidizing ethylene in a two-step serial method, which relate to the technical field of petrochemical industry, wherein a gas-gas isothermal tube array reactor and a water-gas isothermal tube array reactor are arranged in series in a reaction unit, the water-gas isothermal tube array reactor is used for carrying out a first-step ethylene oxidation reaction, the gas-gas isothermal tube array reactor is used for carrying out a second-step ethylene oxidation reaction, and the using process of the equipment comprises a reaction stage, an ethylene oxide absorption and stripping stage and a carbon dioxide absorption and stripping stage.

Description

Equipment and process for producing ethylene oxide by oxidizing ethylene in two-step serial connection method

Technical Field

The application relates to the technical field of petrochemical industry, in particular to equipment and a process for producing ethylene oxide by oxidizing ethylene through a two-step serial method.

Background

Ethylene oxide is an important derivative of ethylene, and is mainly used for producing ethylene glycol, amino alcohol, halohydrin, polyoxyethylene alkyl ether, glycol ether, nonionic surfactant and the like as an intermediate product, and can also be used in the fields of plasticizers, lubricants, plastic box rubber and the like. At present, industrialized ethylene oxide is almost built in combination with an ethylene glycol production device as a raw material of the ethylene glycol device.

The industrial production method of ethylene oxide mainly comprises a chlorohydrin method and an ethylene direct oxidation method, and the ethylene direct oxidation method is divided into an air oxidation method and a pure oxygen oxidation method. The chlorohydrin method has simple process flow and low requirement on the purity of ethylene, but a large amount of highly toxic substance chlorine is consumed in the production process; the side reaction is more, and the ethylene unit consumption is high; the equipment is severely corroded, the sewage discharge amount is large, the production cost is high, and the method is replaced by an ethylene direct oxidation method.

The air oxidation method adopts purified air as an oxidant and adopts a main and auxiliary reactor design to realize the oxidation of ethylene. The main disadvantages of the air oxidation method are that the silver content of the catalyst is high in requirement, the selectivity is low, the catalyst loading is high under the same treatment scale, and the ethylene unit consumption is high; in addition, the air needs to be provided with a purification system.

Compared with the air oxidation method, the pure oxygen oxidation method has the advantages of short process flow, low silver content in the catalyst and high selectivity; the reaction temperature is low, which is beneficial to prolonging the service life of the catalyst; the ethylene content in the vent gas is lower than that in the air method, and the ethylene consumption is less. Meanwhile, as the air separation device is mature, the oxygen sources are more, and the price is low. Therefore, the pure oxygen oxidation method is widely adopted in the industrial production at present to produce the ethylene oxide.

At present, the design and the technological process of a reactor for producing the ethylene oxide by a pure oxygen oxidation method are different, and the reactor is characterized in that a silver-based catalyst is filled in a fixed bed near-isothermal reactor tube array, and then the ethylene oxide is directly produced by a one-step method. The steps of ethylene oxide recovery, carbon dioxide removal and the like are completed immediately. Some catalysts in the process for producing the ethylene oxide by a pure oxygen oxidation method have high selectivity and low raw material consumption, but the catalyst has low activity, the catalyst loading is large, and the size of a reactor is large; some of the catalyst has high activity, but the selectivity is low, the consumption of ethylene raw materials is large, and the production cost is high; still other catalysts have better selectivity and activity, but require promoters in the reaction system, which increase the difficulty of handling in subsequent passes.

In general, the existing pure oxygen oxidation method adopts a one-step synthesis method, and an isothermal tube array oxidation reactor adopts one or a plurality of parallel connection reactors. The method is characterized in that the method is subject to large heat release in the ethylene oxidation process, and the explosion risk is high after ethylene and oxygen are mixed, so that if the treatment capacity is increased, the capacity can be increased only by connecting reactors in parallel.

Ethylene oxidation is a strongly exothermic reaction, the initial stage of which is controlled by kinetic reaction, and it is necessary to increase the reaction rate by increasing the reaction temperature for increasing the conversion rate of the oxidation. And controlling the thermodynamic equilibrium at the end of the reaction. Therefore, the ideal reaction state is that the reaction temperature is low at the end of the isothermal tube reactor, which is more favorable for the balance to advance to the direction of the ethylene oxide generation. Meanwhile, the reaction temperature at the tail end is low, and the explosion hazard of mixing ethylene and oxygen is low, so that the concentration of oxygen in raw material gas can be increased theoretically, the primary conversion rate is improved, the ethylene circulation ratio is reduced, the load of a circulation compressor is reduced, and the purposes of energy conservation and consumption reduction are achieved. However, the existing one-step isothermal tube reactor cannot meet the requirement of low reaction end temperature.

US10858328B2 discloses a method for producing ethylene oxide by an oxidation method, which designs a water-cooled isothermal tube reactor, and the tube is filled with a silver catalyst. Raw materials of ethylene, oxygen and chloride inhibitor are mixed into a tube, an inhibitor is added for delaying corrosion of a reaction tube array, and the flow rate in the tube is controlled to be more than 7m/s. The patent only designs a water-cooling isothermal reactor, and the single-pass conversion rate is 8 percent, so that the thermodynamic equilibrium limit at the end of the ethylene oxidation reaction still cannot be broken, and the primary conversion rate of ethylene cannot be improved.

US2018/0370936A1 patent provides a process for reducing the presence of gaseous iodide-containing impurities, particularly alkyl iodide impurities, in the recycle gas stream of an ethylene oxide production plant. In this method, the ethylene oxidation reactor is designed as one reactor, and thus, as in the previous example, the primary conversion rate of ethylene cannot be improved.

CN205933707U proposes an ethylene oxide production device, in which two ethylene oxide reactors are arranged and are operated in parallel, so that the circulating air flow and flow velocity are enlarged, and the purpose of expanding the device is achieved. Likewise, parallel reactors cannot change the reaction temperature in the tubular beds and cannot achieve optimal operating conditions for ethylene reaction kinetics and thermodynamic control.

CN112566888A proposes a process for producing ethylene oxide and ethylene glycol, in which the ethylene oxidation reactor is also a single-stage one-step oxidizer.

It can be seen that the current industrial device or patent refers to ethylene pure oxygen oxidation to produce ethylene oxide, which is subject to the strong exothermic nature of the reaction, adopts a steam isothermal tube reactor or the parallel operation of the same reactors for expanding the productivity. The single-stage ethylene oxidation reaction is limited by dynamics and thermodynamics of ethylene and oxygen, and the single-pass conversion rate is 8%. A large amount of unreacted ethylene is recycled through the EO absorption tower and the circulating gas compressor, so that the device has large lean solution circulation amount and high energy consumption and electricity consumption.

Disclosure of Invention

In order to solve the problems of low single pass conversion rate, large ethylene circulation amount and short service life of silver-based catalysts in the existing industrial one-step ethylene oxidation method, the application provides equipment and a process for producing ethylene oxide by oxidizing ethylene in a two-step serial method.

The equipment for producing ethylene oxide by oxidizing ethylene through a two-step serial method comprises a reaction unit, an ethylene oxide absorption and stripping unit and a carbon dioxide absorption and stripping unit, wherein a gas-gas isothermal tube array reactor and a water-gas isothermal tube array reactor are arranged in the reaction unit in series, the water-gas isothermal tube array reactor is used for carrying out a first-step ethylene oxidation reaction, and the gas-gas isothermal tube array reactor is used for carrying out a second-step ethylene oxidation reaction.

Further, the gas-gas isothermal shell-and-tube reactor comprises a gas-gas reactor shell and a gas-phase heat transfer tube bundle, wherein a shell side gas inlet tube orifice and a shell side gas outlet tube orifice are arranged on the gas-gas reactor shell, a lower gas inlet ball cavity and an upper gas outlet ball cavity are arranged on the gas-phase heat transfer tube bundle, and the gas-phase heat transfer tube bundle, the lower gas inlet ball cavity and the upper gas outlet ball cavity are all in a spherical header structure;

the spherical header structure is convenient for an maintainer to enter the spherical cavity for checking and plugging, and the catalyst is not required to be removed.

Further, the gas phase heat transfer tube bundle is provided with a bow;

the two ends of the gas phase heat transfer tube bundle adopt bow bends to eliminate thermal stress, a common straight tube bundle structure is avoided, the bow bends are of a whole seamless welded steel tube structure, the gas phase heat transfer tube bundle has good flexibility, can expand freely, can eliminate stress by means of self thermal expansion, and ensures that no stress acts on an air inlet balloon cavity.

The arched tube bundle is selected to have a diameter range according to the throughput and the heat transfer rate

Further, 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 multi-empty layer;

the gas phase heat transfer tube bundle adopts the high-flux heat exchange tube, and the heat transfer coefficient between gas and gas media is small, so that the heat transfer efficiency is improved, the high-flux heat exchange tube for strengthening tube side heat transfer is adopted, and the metal porous layer is generated by coating and sintering metal on the outer surface of the metal light tube, so that the high-efficiency heat transfer under the condition of lower heat transfer temperature difference is realized, the heat transfer tube bundle has the characteristics of strengthening boiling heat transfer, having good scale inhibition performance and the like, and is beneficial to realizing the cascade utilization of energy sources and improving the energy utilization rate.

Further, the tube side of the gas-gas isothermal tube reactor is used for filling silver-based catalyst;

further, the lower air inlet balloon cavity and the upper air outlet balloon cavity are both in spherical structures.

The lower air inlet balloon cavity and the upper air outlet balloon cavity adopt spherical structures, and have the best pressure bearing capacity relative to a flat tube plate or an elliptic structure.

In the isothermal tube array reactor for gas and gas, fresh raw material gas in a tube side is heated and takes away a large amount of reaction heat of a byproduct of ethylene oxidation in a second step, and tail burning is completely eradicated due to lower temperature control of the oxidation reaction in the second step of the shell side.

The tube side and the shell side of the gas-gas isothermal tube array reactor only bear the pressure generated by the reaction gas resistance drop, so that the manufacturing cost of the gas-gas reactor is very low.

Further, a steam drum is arranged at the upper part of a shell side of the water-gas isothermal tube array reactor, a saturated steam outlet pipe is arranged at the top of the steam drum, a plurality of ascending pipes and descending pipes are arranged at the bottom of the steam drum, the ascending pipes are connected with the top of the shell side of the reactor, the descending pipes are connected with the bottom of the shell side of the reactor, and a steam mixer is arranged at the descending pipes;

the shell side of the steam isothermal shell-and-tube reactor is provided with a set of natural circulation steam drum system: boiler water first enters the drum in the upper part of the shell-side reactor. The top of the steam drum is provided with a saturated steam outlet pipe, and a pressure regulating valve is arranged on the pipe and used for regulating the pressure of steam produced by the steam drum.

Further, the water-gas isothermal shell-and-tube reactor adopts a tube plate structure, and the upper tube plate adopts a flexible tube plate;

the steam isothermal shell-and-tube reactor adopts a mature tube plate structure, wherein the upper tube plate adopts a flexible tube plate, and thermal stress expansion caused by tube shell-and-tube temperature difference is prevented.

Further, the tube bundles of the water-gas isothermal tube array reactor adopt seamless steel tubes and are arranged in a shell-side water bath;

carbon steel pipes, alloy steel pipes or duplex stainless steel pipes can be selected, and the duplex stainless steel pipes are preferable in the present application.

The water-gas isothermal tube bundle also adopts a high-flux heat exchange tube, and a metal sintering coating is coated on the outer layer of the tube bundle, so that the shell is particularly suitable for the heat transfer working condition that the shell has phase transition.

Further, the tube bundle of the water vapor isothermal tube array reactor is selected to have the diameter range ofThe length is 5000-8000 mm.

Further, the tube ends of the tube bundles are provided with springs for supporting the catalyst and the magnetic balls;

a grid is typically provided on the lower flat tube sheet. However, as the reactor becomes larger and larger, more catalyst is loaded, and the grid is easily deformed by compression; the spring support is provided, and the space velocity of the catalyst bed can be increased so as to reduce the catalyst filling.

Further, the steam drum is a horizontal storage tank;

the steam drum down tube of the steam isothermal tube array reactor is provided with a steam mixer for heating the reactor in the starting stage, thereby greatly reducing the reaction starting time and saving the raw material cost.

Further, a pressure regulating valve is arranged on the pipeline of the saturated steam outlet pipe.

The steam drum of the steam isothermal tube array reactor can accurately control the temperature of a bed layer by controlling the pressure of medium pressure steam, and the pressure of the medium pressure steam ranges from 1.7 Mpa to 2.5Mpa, and the pressure of the medium pressure steam is 2.0Mpa.

Further, the ethylene oxide absorbing and stripping unit is provided with an ethylene oxide absorbing tower, an ethylene oxide stripping tower and a quenching absorption liquid stripping tower, wherein the ethylene oxide absorbing tower is provided with an upper steam stripping section and a lower glycol concentration section, and the quenching absorption liquid stripping tower is used for stripping pre-washing Duan Fuyi glycol alkali liquor;

the main components of the reaction gas are ethylene, oxygen, ethylene oxide, carbon dioxide, methane, a small amount of ethylene glycol, aldehyde, acid, inhibitor and the like.

Unlike the prior art, the ethylene oxide stripper is divided into upper and lower sections. The lower section is an ethylene glycol concentration section where the rich liquid strips the ethylene oxide out and goes to an upper column. The ethylene glycol solution is sent out as a product. The upper section of the ethylene oxide stripping column adopts steam stripping, and all ethylene oxide is stripped out and sent out as a product.

Further, a quenching section is arranged at the lower part of the ethylene oxide stripping tower, and an anti-blocking valve is arranged in the quenching section;

the quench absorber stripper was used to strip the pre-wash Duan Fuyi glycol lye in order to recover ethylene oxide absorbed in the quench section. And the glycol solution at the bottom of the quenching absorption liquid tower is taken as a product to be sent out. The design of the quenching absorption liquid stripping tower has the advantages of recovering ethylene oxide to the greatest extent, and reducing the energy consumption of the device.

The alkali liquor is used as a circulating absorbent for absorbing a small amount of acid and aldehyde impurities in the gas at the outlet of the reactor, so that the purity of the ethylene oxide product is conveniently controlled. The advantage of designing the quench section is that it allows for higher purity of the ethylene oxide product.

The ethylene oxide main absorption section filler layer is provided with two layers: the ethylene oxide is absorbed by the lean solution, and the main component of the lean solution is water. Ethylene oxide, ethylene glycol, and the like in the reaction gas are absorbed by the lean liquid to become rich liquid. The rest reaction gas is mainly ethylene, oxygen, methane and carbon dioxide, and is sent out of the carbon dioxide absorption and stripping unit.

Further, the carbon dioxide absorbing and stripping unit comprises a circulating gas compressor, a carbon dioxide absorbing tower and a carbon dioxide stripping tower which are sequentially connected, wherein the carbon dioxide stripping tower is divided into an upper section and a lower section, the upper section is a flash evaporation section, and the lower section is a steam stripping section;

further, the internal parts of the carbon dioxide absorption tower adopt a structured packing or floating valve tower tray structure;

further, the carbon dioxide absorption tower internals adopt a structured packing structure.

The using process of the equipment comprises the following steps:

reaction stage: fresh raw material gas consisting of ethylene and oxygen enters the tube pass of the gas isothermal tube array reactor, the fresh raw material gas is heated and then is sent into the tube pass of the water vapor isothermal tube array reactor, and a first-step ethylene oxidation reaction occurs in the tube pass of the water vapor isothermal tube array reactor;

the gas after the first step reaction is collected by a lower pipe box and then is sent to a shell side of a gas-gas isothermal shell-and-tube reactor for the second step oxidation reaction;

the temperature of the second ethylene oxidation reaction is lower than that of the first ethylene oxidation reaction;

ethylene oxidation is a strongly exothermic reaction, the initial stage of which is controlled by kinetic reaction, and it is necessary to increase the reaction rate by increasing the reaction temperature for increasing the conversion rate of the oxidation. And controlling the thermodynamic equilibrium at the end of the reaction. Therefore, the ideal reaction state is that the reaction temperature is low at the end of the isothermal tube reactor, which is more favorable for the balance to advance to the direction of the ethylene oxide generation. The application mainly realizes that the reaction temperature of the second step is lower than that of the first step by adding the near-isothermal reactor of the second step, not only meets the requirement of the ethylene oxide on the reaction speed, but also can improve the thermodynamic equilibrium constant of the reaction and improve the single pass conversion rate of ethylene. Thus, more products can be obtained with the same equipment size.

Ethylene oxide absorption and stripping stage: after the second oxidation reaction is finished, the reaction gas flows out of the tubular reactor such as gas and the like, enters a low-pressure steam boiler, enters an ethylene oxide absorption tower for pre-washing after being cooled, enters an ethylene oxide main absorption section of the reactor after pre-washing, and the gas flowing out of the main absorption section is sent into a carbon dioxide absorption and stripping unit;

carbon dioxide absorption and stripping stage: firstly, the gas enters a circulating gas compressor for pressurization, the pressurized circulating gas enters a carbon dioxide absorption tower, the carbon dioxide absorption tower adopts polyethylene glycol dimethyl ether as absorption liquid, and the methane gas is flashed out from a carbon dioxide stripping tower after passing through the absorption liquid, and the carbon dioxide gas is resolved by adopting low-pressure steam.

The carbon dioxide absorption tower adopts polyethylene glycol dimethyl ether (NHD) as an absorption liquid, and the NHD absorption liquid has the advantages of good chemical property temperature, good thermal stability, no toxicity, good corrosiveness and good decarburization effect, and is an absorbent more excellent than potassium carbonate. A carbon dioxide stripper for separating the NHD rich liquid absorbed with carbon dioxide. The resolved NHD rich solution is called lean solution, and is recycled after being cooled by a lean-rich solution heat exchanger.

Further, in the reaction stage, the first step of ethylene oxidation reaction conditions: the temperature is 230-270 ℃, the reaction pressure is 1.0-3.0 Mpa, and the space velocity of the catalyst bed layer is selected to be 4000-12000 h ^- ；

Further, the first step ethylene oxidation reaction conditions: the temperature is 240-260 ℃, the reaction pressure is 1.8-2.2 Mpa, and the space velocity of the catalyst bed layer is selected to be 5000-9000 h ^- ；

The reaction conditions of the second ethylene oxidation reaction shell side bed layer are as follows: the temperature is 190-220 ℃, the reaction pressure is 1.0-3.0 Mpa, and the space velocity of the catalyst bed is 2000-10000 h ^- ；

Further, the reaction conditions of the shell side bed layer of the second ethylene oxidation reaction are as follows: the temperature is 200-210 ℃, the reaction pressure is 1.8-2.2 Mpa, and the space velocity of the catalyst bed is 6000-8000 h ^- 。

Further, in the ethylene oxide absorption and stripping stage, the absorption pressure of the main absorption stage is 1.7-2.0 Mpa, and the absorption temperature is 30-40 ℃.

Further, in the carbon dioxide absorption and stripping stage, the outlet of the compressor is boosted by 0.3Mpa compared with the inlet, the absorption temperature of the carbon dioxide absorption tower is controlled to be 20-40 ℃, and the absorption pressure is 1.8-2.2 Mpa.

Further, 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;

further, the absorption liquid is polyethylene glycol dimethyl ether, the active component of the polyethylene glycol dimethyl ether in the absorption liquid is more than or equal to 99%, and the moisture is less than or equal to 1.0%.

The more excellent amine salt is selected as the absorbing liquid, and can be polyethylene glycol dimethyl ether (NHD), N-Methyldiethanolamine (MDEA), diethanolamine (DEA) or a mixture thereof. As the absorption liquid, NHD is preferable, and the absorption liquid has the advantages of good chemical property temperature, good thermal stability, no toxicity, good corrosiveness and good decarburization effect.

The application has the beneficial effects that:

1. the application adopts a two-step series reaction of the gas-gas isothermal tube array reactor and the water-gas isothermal tube array reactor, so that the two reactors take the dynamics and thermodynamic states into consideration, the single-pass conversion rate is improved, the ethylene circulation ratio is reduced, the energy consumption of the device is reduced, and the service life of the catalyst is prolonged. Meanwhile, the existing ethylene oxidation isothermal fixed bed reactor generally adopts a fixed tube plate structure, the structure has weak bearing capacity and large thermal stress on the cold and hot sides, the tube bundle is easy to damage and leak, and the air tube reactor adopts a balloon collecting cavity structure, so that the problem of large thermal stress of the tube plate and the tube bundle in the isothermal tube reactor in the prior art is solved, and the equipment cost is saved.

2. The application uses polyethylene glycol dimethyl ether (NHD) to replace potassium carbonate in the traditional ethylene oxide production process as CO in the circulating gas for the first time ₂ The absorption liquid of polyethylene glycol dimethyl ether has the advantages of good chemical property temperature, good thermal stability, no toxicity, good corrosiveness and good decarburization effect, and is an absorbent more excellent than potassium carbonate.

Drawings

FIG. 1 is a flow chart of a process for producing ethylene oxide by oxidizing ethylene in a two-step serial process of the present application;

FIG. 2 is a schematic diagram of a gas-gas isothermal train reactor;

FIG. 3 is a schematic diagram of a steam isothermal tube reactor.

Reference numerals: 1-isothermal tube array reactor; 101-a gas reactor shell; 102-tube bundle; 103-upper balloon cavity; 104-lower air inlet ball cavity; 105-a gas phase heat removal tube bundle; 106-catalyst discharge port; 107-fresh gas inlet; 108-a preheated gas outlet; 109-a synthesis gas inlet after the first step of oxidation reaction; 110-a synthesis gas outlet after the second step of oxidation reaction; 2-an intermediate heat exchanger; 3-a water-gas isothermal tube reactor; 301-a water vapor reactor shell side; 302-flexible tube sheet; 303-heat exchange tube bundles; 304-preheating a feed gas inlet; 305-a synthesis gas outlet after the first step of oxidation reaction; 306-raising the pipe orifice of the boiler water; 307-boiler water downcomer orifice; 308-supporting a spring; 4-medium pressure steam drum; 5-a venturi; 6-a pressure regulating valve; 7-a low pressure steam generator; 8-a reaction gas cooler; 9-quenching section of ethylene oxide absorption tower; an absorption section of the 10-ethylene oxide absorption tower; 11-lean solution chiller; 12-liter of air cap; a 13-ethylene oxide stripper steam direct stripping section; a 14-ethylene oxide stripping tower glycol concentration section; 15-stripper lean liquid pump; 16-stripper feed heater; 17-quench stripper; 18-a product cooler; 19-a recycle gas compressor; 20-a carbon dioxide absorption tower; a flash section of a 21-carbon dioxide stripping tower; 22-a carbon dioxide stripper steam stripping section; a 23-NHD lean-rich liquid heat exchanger; 24-fresh gas; 25-synthesizing gas after the first step of oxidation reaction; 26-synthesizing gas after the second step of oxidation reaction; 27-carbon dioxide-rich recycle gas; 28-medium pressure saturated steam; 29-boiler water; 30-starting steam; 31-a downcomer; 32-preheating the feed gas; 33-sodium hydroxide absorption liquid; 34-ethylene glycol-rich liquid; 35-ethylene glycol solution; 36-ethylene oxide product liquid; 37-quench section base fluid; 38-an ethylene oxide rich absorption liquid; 39-lean absorption liquid; 40-quench stripping overhead gas; 41-circulating gas; 42-methane-rich gas; 43-carbon dioxide gas; 44-NHD lean solution; 45-NHD rich solution.

Detailed Description

The following description of the present application will be made clearly and fully, and it is apparent that the embodiments described herein are only some, but not all, of the embodiments of the present application. All other embodiments, which can be made by those skilled in the art based on the embodiments of the application without making any inventive effort, are intended to fall within the scope of the application.

Example 1

As shown in figures 1-3, a process for producing ethylene oxide by oxidizing ethylene in two steps in series is characterized in that ethylene and oxygen are subjected to oxidation reaction in the presence of a silver-based catalyst to prepare ethylene oxide, and the process mainly comprises a reaction stage, an ethylene oxide absorption and stripping stage and a carbon dioxide absorption and stripping stage. In this example, the reactant composition is primarily ethylene oxide, ethylene, carbon dioxide, water, methane, trace amounts of aldehydes, organic acids.

In the embodiment, the silver catalyst comprises 17 weight percent of silver, 0.05 weight percent of strontium, 0.5 weight percent of magnesium, 0.65 weight percent of fluorine, 0.05 weight percent of cerium, 0.25 weight percent of tin, 0.15 weight percent of phosphorus and 0.15 weight percent of boron, based on the total weight of the dry basis of the silver catalyst; the silver catalyst has water absorption rate of 55%, specific surface area of 0.91 square meter/g and pore volume of 0.52 ml/g, wherein the pores with pore diameter of 5-30 microns account for 89%, and the pores with pore diameter of more than or equal to 30 microns account for 11%. Under the condition, the catalyst has excellent heat transfer, conduction, diffusion and reaction activity, and is suitable for two filling forms of the tube side and the shell side of the fixed bed reactor. In this example, the reference reaction pressure of the reactor was 2.0MPa.

Reaction stage: the ethylene oxidation reaction is carried out in two steps. The first step is carried out at a higher temperature of 250 ℃, and the reaction site is the tube side of the steam isothermal tube reactor 3; the second step is carried out at 210 ℃, and the reaction site is the shell side of the shell-and-tube reactor 1 with isothermal gas.

First, the fresh gas 24 containing ethylene and oxygen is mixed with the recycle gas 41, and the mole fractions of the mixed gas are as follows: 28% of ethylene, 8% of oxygen, 5% of carbon dioxide, 50% of methane, 7% of nitrogen and 2% of argon; a trace of 1,2 dichloroethane is also added to the feed gas as an inhibitor. The mixed fresh gas is then fed through fresh gas inlet 107 to the lower inlet balloon 104 of the tube side of the gas isothermal tube reactor 1. The isothermal shell-and-tube reactor 1 for gas consists of gas reactor shells 101 and 102. The ends of the tube bundle 105 are in a bowed and spherical cavity configuration with optimal pressure resistance and flexibility. Fresh gas 24 flows through the gas phase heat transfer tube bundle 105 from bottom to top to exchange heat with the synthesis gas after the first oxidation reaction in countercurrent, and the temperature is heated from 40 ℃ to 170 ℃. And then is discharged through a preheated gas outlet 108 pipe after being collected by the upper balloon chamber 103. The preheated raw material gas 32 is continuously preheated for the second time by the intermediate heat exchanger 2, and enters the tube pass of the water-gas isothermal tube reactor 3 to perform the first-step oxidation reaction after being preheated to 200 ℃. The synthesis gas 25 after the first oxidation step flows through the shell-side catalyst bed layer from top to bottom in the shell-side of the gas-gas isothermal tube reactor 1, undergoes the second oxidation step, and finally leaves the reaction unit through the synthesis gas outlet 110 after the second oxidation step. The temperature of the bed layer of the second oxidation reaction is controlled at 210 ℃ because the fresh gas 24 in the pipe takes heat. The reaction thermodynamic equilibrium constant is helped to shift towards the production of ethylene oxide at low temperature, thereby breaking the single-step oxidation reaction conversion limit.

The isothermal shell-and-tube reactor of the embodiment is also provided with a catalyst discharge port 106 at the shell-side bed, so that the shell-side bed catalyst is conveniently discharged. The diameter of the gas-gas reactor is 3000 mm-4600 mm, the length of the tube bundle is 5000 mm-7000 mm, and the diameter range of the tube bundle is selected as followsThe shell side material is carbon steel, alloy steel or dual-phase steel, preferably carbon steel.

In this embodiment, the gas phase heat transfer tube bundle 105 employs a high-flux heat exchange tube, and the thickness of the porous layer of the high-flux heat exchange tube is in the range of 0.1mm to 0.3mm, preferably 0.2mm. The porosity of the porous layer of the high-flux heat exchange tube is between 30% and 70%, preferably 50%. The metal powder adopted by the outer layer of the L-shaped bent pipe bundle is mainly Cu-based or Ni-containing Cu-based or Fe-based alloy powder with the average particle size of more than 70 mu m, and preferably Fe-based alloy powder.

The preheated gas exiting the intermediate heat exchanger enters the steam isothermal shell and tube reactor 3 through the preheated feed gas inlet 304, and the synthesis gas 25 after the first-step oxidation reaction exits through the synthesis gas outlet 305 after the first-step oxidation reaction. The steam isothermal shell-and-tube reactor 3 consists of a steam reactor shell side 301 and a heat exchanger tube bundle 303, the shell-and-tube sides being separated by a flexible tube sheet 302. The embodiment adopts the flexible tube plate, can completely eliminate the thermal expansion caused by the temperature difference of the tube side, prevent the leakage of the reactor and prevent the high-pressure water of the tube side from entering the tube side catalyst bed layer.

The silver-based catalyst is filled in the tube of the water-gas isothermal tube array reactor 3 to provide a place for the first-step ethylene oxidation reaction, about 70% of the oxidation reaction occurs in the water-gas isothermal tube array reactor 3, and the rest 30% of the oxidation reaction occurs in the gas-gas isothermal tube array reactor 1. The temperature of the water side of the water gas reactor shell side 301 and the water heat extraction speed are further adjusted by controlling the pressure of the medium pressure saturated steam 28 of the water gas reactor shell side 301 and the medium pressure steam drum 4, so as to control the temperature of the bed layer in the pipe, and in the embodiment, the reaction temperature of the bed layer is controlled at 250 ℃. At this temperature, the ethylene oxidation rate is controlled by the kinetic equation, and the temperature is high, the reaction rate is high, the treatment capacity is strong, and the required catalyst loading is small. The synthesis gas 25 after the first oxidation reaction is sent to the intermediate heat exchanger 2 to continuously recycle the reaction heat.

The water gas reactor shell side 301, the medium pressure steam drum 4, the down pipe 31 and the ascending pipe form a closed loop. The adding amount of the outside boiler water entering the medium-pressure steam drum 4 is controlled by a flow regulating valve 29, the boiler water enters from the lower part of the steam isothermal tube array reactor 3 through a boiler water descending tube orifice 307 through thermosiphon natural circulation, the boiler water performs countercurrent heat exchange with the synthesis gas 25 after the first-step oxidation reaction in the tube from bottom to top, absorbs 80% of heat discharged by the reaction, and the boiler water is changed from liquid phase to gas-liquid phase and finally circulates into the medium-pressure steam drum 4 from a boiler water ascending tube orifice 306.

In the embodiment, the upper layer of the medium-pressure steam drum 4 provides a space for water-gas separation of the boiling boiler, and the byproduct medium-pressure saturated steam is led out from the top of the drum. A6-pressure regulating valve is arranged on the saturated steam pipeline and is used for controlling the steam pressure of the steam packet to be 1.7-2.5 Mpa, and preferably, the medium-pressure steam pressure is 2.0Mpa. The steam pressure is controlled, so that the temperature of the circulating boiler water at the shell side of the reactor is controlled, the reaction temperature of the bed layer is controlled, and the method is suitable for the condition that different requirements are set on the temperature of the bed layer at the initial end of the catalyst reaction. The control method is safe and has quick response time.

With this embodiment, a set of start-up steam system is provided, and the water-gas heat exchanger is preheated in the start-up stage, so that the start-up time is shortened, and the consumption of ethylene and oxygen is saved. The start-up steam system consists of a venturi tube 5 and start-up steam 30.

In this embodiment, the diameter of the water-gas reactor is 3200mm4800mm, preferably 4000mm, the length of the tube bundle is 4000mm to 8000mm, preferably 6000mm, and the diameter of the tube bundle is selected to be in the range ofPreferably-> Preferably, the shell side material is carbon steel, alloy steel or dual-phase steel, preferably carbon steel.

Ethylene oxide absorption and stripping stage: in this example, the synthesis gas 26 temperature after the second oxidation reaction reached 200 ℃, and the single pass conversion of ethylene reached 10% by the inventive two-step reaction. The composition of the mole percent of the synthesis gas 26 after the second oxidation reaction is as follows: ethylene 25.54%; 5.05% of oxygen; carbon dioxide 6.42%; 48.52% methane; 8% of nitrogen; 3% of argon; 1.2% of water; ethylene oxide 2.2%, and also a trace amount of aldehydes and acid by-products.

The temperature of the reaction gas is still 200 ℃, in order to recycle the residual heat of the reaction gas, the reaction gas firstly enters a low-pressure steam generator 7, low-pressure steam (pressure 0.3 mpa) is by-produced and desalted water is preheated, and the temperature of the reactor is reduced to 75 ℃. The cooled rich liquid in the reaction gas cooler 8 is then cooled to 45 c and then enters the quench section 9 of the ethylene oxide absorber. The quenching section 9 of the ethylene oxide absorption tower adopts an anti-blocking valve, and adopts sodium hydroxide absorption liquid 33 as a circulating absorbent for absorbing a small amount of acid and aldehyde impurities in the gas at the outlet of the reactor, so that the purity of the ethylene oxide product is convenient to control.

The bottom liquid 37 of the quenching section, which absorbs acid and aldehyde, is discharged from the bottom of the ethylene oxide absorption tower and sent to the quenching liquid stripping tower 17, and the dissolved trace ethylene oxide is recovered by adopting low-pressure steam. The top gas 40 of the quenching liquid stripping tower containing ethylene oxide is obtained and recovered, the tower bottom is the ethylene glycol solution 35, and the quenching liquid stripping tower is a filler tower.

The top gas of the quenching section is sent to the absorption section 10 of the ethylene oxide absorption tower by a gas lift cap 12. In this example, the absorber acts to absorb ethylene oxide in the reaction gas and recover unreacted ethylene and oxygen. As the main absorption of ethylene oxide, the ethylene oxide absorber section 10 may generally employ a packed column or a tray column. In general, absorption is advantageous at high pressure and low temperature, the operating pressure of the absorption column being from 1.0 to 3.0Mpa, preferably from 1.5 to 2.0Mpa, and being determined by the operating pressure of the oxidation reactor; the absorption temperature ranges from 10 to 45℃and preferably from 20 to 30 ℃. In addition, water is selected as the ethylene oxide absorption liquid, and the molar flow ratio of the absorption liquid to the reaction gas is in the range of 0.2-3.0.

Ethylene, oxygen, carbon dioxide, methane, nitrogen, etc. which 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 a carbon dioxide-rich recycle gas 27.

In this embodiment, the ethylene oxide-rich absorption liquid 38 contains low boiling impurities such as ethylene oxide, water, a small amount of formaldehyde, acetic acid and the like as main components, is discharged from the main absorption tower, and is first cooled by the reactor cooler 8 and the stripper feed heater 16, and is then heated to 100 ℃. And then into the ethylene oxide stripper steam direct stripping section 13. The purpose of the ethylene oxide stripper is to recover the ethylene oxide and regenerate the rich absorption liquid for recycle.

The ethylene oxide stripper vapor direct stripping section 13 provides stripping heat with low pressure vapor, with ethylene oxide being obtained overhead and cooled to a liquid state by product cooler 18 as an ethylene oxide product liquid 36 which is sent to a downstream reabsorption clean section for purification. The lean absorption liquid 39 after the complete regeneration of the steam direct stripping section is discharged from the tower kettle and is pressurized by the lean liquid pump 15 of the stripping tower and is divided into two paths. Most of the lean solution is cooled by a stripper feeding heater 16 and a lean solution chiller 11 and then sent to an absorption tower for continuous use. Wherein the lean solution chiller 11 is chilled water cooled; a small portion of the lean liquid is sent to the ethylene oxide stripper glycol enrichment section 14 for continued stripping. The overhead gas from this section is returned to the ethylene oxide stripper steam direct stripping section 13 to replace part of the low pressure steam and the bottoms is sent to the boundary zone as ethylene glycol rich solution 34. From this point on, a closed loop ethylene oxide absorption and analytical recovery process is completed.

Carbon dioxide absorption and stripping stage:

in this embodiment, the carbon dioxide rich recycle gas 27 is first admitted to the recycle gas compressor 19 for pressurization to compensate for the pressure loss so that the recycle gas can be admitted again to the reactor. Carbon dioxide in the recycle gas can cause the increase of inert gases in the system, and the reaction conversion rate and selectivity are affected. In order to remove part of the carbon dioxide in the recycle gas, a carbon dioxide absorption tower 20 is designed.

In this embodiment, polyethylene glycol dimethyl ether (NHD) is selected as the absorption liquid, the carbon dioxide absorption tower 20 adopts a filler form, and the carbon dioxide-rich recycle gas 27 enters from the bottom of the tower and is countercurrent to the NHD lean liquid 44 sprayed from the top of the tower for gas-liquid exchange. Here, most of the carbon dioxide in the recycle gas is absorbed. The purified recycle gas 41 is mixed with fresh gas 24 into the reactor for further reaction. The NHD rich solution 45 absorbed with carbon dioxide is heated by the NHD lean-rich solution heat exchanger 23, and finally enters the flash evaporation section 21 of the carbon dioxide stripping tower. The flash evaporation section 21 of the carbon dioxide stripping tower is used for recovering useful gases such as methane, ethane and the like absorbed by NHD liquid, and the pressure of the flash evaporation section is controlled to be 0.3Mpa because the solubility of methane and ethane is relatively low compared with that of carbon dioxide. The top of the flash section discharges methane-rich gas 42 and is sent to downstream processing units. The carbon dioxide-rich NHD liquid at the bottom of the flash evaporation section 21 of the carbon dioxide stripping tower enters the steam stripping section 22 of the carbon dioxide stripping tower by gravity flow.

Stripping resolution needs to be performed at high temperature and low pressure. In this example, the carbon dioxide stripper steam stripping section was operated at 110℃and at a pressure of 0.15MPa. Steam stripping is adopted in the tower kettle, and the steam stripping can be performed by adopting a vertical thermosiphon heat exchanger for indirect steam stripping, or can be performed by adopting a direct steam stripping method of directly introducing steam into the tower. In this embodiment, the indirect stripping method of the vertical thermosiphon heat exchanger is preferred. The carbon dioxide gas 43 stripped from the rich liquid is discharged from the top of the column. The tower bottom is lean solution which does not contain carbon dioxide basically, and the lean solution is recycled after being cooled by the NHD lean-rich solution heat exchanger 23.

Example 2

In this embodiment, the apparatus and process for the two-step tandem oxidation of ethylene to ethylene oxide are the same as those of embodiment 1, and only the first-step isothermal shell-and-tube reactor tube bed layer is selected from another silver-based catalyst which is more resistant to high temperature, and the specific components are as follows: 17wt% silver, 0.05wt% strontium, 0.45wt% magnesium, 0.56wt% fluorine, 0.07wt% cerium, 0.26wt% tin, 0.15wt% phosphorus, 0.16wt% boron. The catalyst has water absorption rate of 51%, specific surface area of 0.90 square meter/g and pore volume of 0.50 ml/g, wherein pores with pore diameter of 5-30 microns account for 85%, and pores with pore diameter of more than or equal to 30 microns account for 15%. Since this catalyst is more resistant to high temperatures, the reaction temperature can be controlled at 260 ℃.

In this example, the silver-based catalyst in example 1 was still selected for the shell-side bed of the second-stage gas-isothermal train reactor, and the reaction temperature was controlled at 210 ℃. As a result, it was found that the total conversion of ethylene was 10%, and the selectivity was slightly lowered from 84% to 83.5%.

The above description is only illustrative of the preferred embodiments of the present application and of the principles of the technology employed. It will be appreciated by persons skilled in the art that the scope of the application referred to in the present application is not limited to the specific combinations of technical features described above, but also covers technical features described above or equivalents thereof without departing from the inventive concept. And other technical schemes formed by any combination are carried out. Such as the above-mentioned features and the technical features disclosed in the present application (but not limited to) having similar functions are replaced with each other.

Claims

1. The equipment for producing the ethylene oxide by oxidizing the ethylene through a two-step serial method comprises a reaction unit, an ethylene oxide absorption and stripping unit and a carbon dioxide absorption and stripping unit, and is characterized in that a gas-gas isothermal tube array reactor and a water-gas isothermal tube array reactor are arranged in the reaction unit in series, wherein the water-gas isothermal tube array reactor is used for carrying out a first-step ethylene oxidation reaction, and the gas-gas isothermal tube array reactor is used for carrying out a second-step ethylene oxidation reaction.

2. The device according to claim 1, wherein the gas-gas isothermal shell-and-tube reactor comprises a gas-gas reactor shell and a gas phase heat transfer tube bundle, wherein a shell side gas inlet tube orifice and a shell side gas outlet tube orifice are arranged on the gas-gas reactor shell, a lower gas inlet ball cavity and an upper gas outlet ball cavity are arranged on the gas phase heat transfer tube bundle, and the gas phase heat transfer tube bundle, the lower gas inlet ball cavity and the upper gas outlet ball cavity are in a spherical header structure;

further, the gas phase heat transfer tube bundle is provided with a bow;

3. The apparatus of claim 1, wherein the shell side upper portion of the water-gas isothermal shell-and-tube reactor is provided with a steam drum, the top of the steam drum is provided with a saturated steam outlet pipe, the bottom of the steam drum is provided with a plurality of ascending pipes and descending pipes, the ascending pipes are connected with the top of the shell side of the reactor, the descending pipes are connected with the bottom of the shell side of the reactor, and the descending pipes are provided with a steam mixer;

further, the steam drum is a horizontal storage tank;

4. The plant according to claim 1, characterized in that the ethylene oxide absorption and stripping unit is provided with an ethylene oxide absorption column, an ethylene oxide stripping column and a quench absorption liquid stripping column, the ethylene oxide absorption column being provided as an upper steam stripping and a lower glycol concentration section, the quench absorption liquid stripping column being used for stripping pre-wash Duan Fuyi glycol lye;

further, the lower part of the ethylene oxide stripping tower is provided with a quenching section, and an anti-blocking valve is arranged in the quenching section.

5. The apparatus of claim 1, wherein the carbon dioxide absorption and stripping unit comprises a recycle gas compressor, a carbon dioxide absorption column and a dioxide column stripper column connected in sequence, the carbon dioxide column stripper column being divided into an upper section and a lower section, the upper section being a flash evaporation section, the lower section being a steam stripping section;

6. A process for using the device according to any one of claims 1 to 5, comprising the following:

carbon dioxide absorption and stripping stage: firstly, the gas enters a circulating gas compressor for pressurization, the pressurized circulating gas enters a carbon dioxide absorption tower, the circulating gas after absorption liquid enters a carbon dioxide stripping tower, methane gas is flashed out, and the carbon dioxide gas is resolved by adopting low-pressure steam.

7. The process according to claim 6, wherein the first ethylene oxidation reaction conditions: the temperature is 230-270 ℃, the reaction pressure is 1.0-3.0 Mpa, and the space velocity of the catalyst bed layer is selected to be 4000-12000 h ^- ；

8. The process according to claim 6, wherein the main absorption stage absorbs the pressure of 1.7-2.0 MPa and the absorption temperature of 30-40 ℃ in the ethylene oxide absorption and stripping stage.

9. The process according to claim 6, wherein the carbon dioxide absorption and stripping stage and the carbon dioxide absorption and stripping stage are performed with a pressure of 0.3Mpa at the outlet of the compressor higher than the pressure at the inlet, and the absorption temperature of the carbon dioxide absorption tower is controlled to be 20-40 ℃ and the absorption pressure is controlled to be 1.8-2.2 Mpa.

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