CN117942873A

CN117942873A - Fixed bed reactor and method for synthesizing vinyl acetate by ethylene gas phase method

Info

Publication number: CN117942873A
Application number: CN202211331151.6A
Authority: CN
Inventors: 朱洁; 黄云群; 陈伟
Original assignee: China Petroleum and Chemical Corp; Sinopec Shanghai Research Institute of Petrochemical Technology
Current assignee: China Petroleum and Chemical Corp; Sinopec Shanghai Research Institute of Petrochemical Technology
Priority date: 2022-10-28
Filing date: 2022-10-28
Publication date: 2024-04-30

Abstract

The invention relates to a fixed bed reactor and discloses a method for synthesizing vinyl acetate by a gas phase method of ethylene, which comprises a shell and a cavity formed by surrounding the shell, wherein a first distributor, a multi-channel reaction bed layer and a second distributor are arranged in the cavity from top to bottom, the multi-channel reaction bed layer is provided with a first channel for filling a catalyst and a second channel for circulating a heat exchange medium, the axis of the cavity is outwards, and the first channel and the second channel are alternately arranged, so that the first channel and the second channel form a partition wall type heat exchange; the second channel is arranged as a closed heat exchange cavity, the upper part of the second channel is communicated with the first distributor through a plurality of first pipelines, and the lower part of the second channel is communicated with the second distributor through a plurality of second pipelines. The invention has the advantages of compact structure, large catalyst loading, uniform heat removal fluid distribution, timely heat removal, easy realization of temperature control, reduced operation difficulty, and better safety and stability.

Description

Fixed bed reactor and method for synthesizing vinyl acetate by ethylene gas phase method

Technical Field

The invention relates to a fixed bed reactor, in particular to a fixed bed reactor and a method for synthesizing vinyl acetate by an ethylene gas phase method.

Background

Vinyl acetate abbreviation: VAc is also called vinyl acetate, is a colorless transparent and strong-odor volatile liquid at normal temperature, and the vapor is a wet anesthetic, can stimulate skin and respiratory organs, is dissolved in alcohol ether and is insoluble in aliphatic hydrocarbon, and is widely applied to organic synthesis in the chemical industry. The molecular formula is C4H6O2, the structural formula is CH3COOCH=CH2, and the molecular weight is 86.09. The molecular structure contains unsaturated vinyl, has strong polymerization capability, is an important monomer, and is mainly used for producing derivatives such as polyvinyl alcohol PVA, vinyl acetate PVAc, vinyl acetate-ethylene copolymer emulsion VAE or copolymer resin EVA. Vinyl acetate has wide application prospect in various aspects such as paint, aviation, adhesive, film, vinylon, acetal resin and the like. At present, the industrial vinyl acetate production process mainly comprises an ethylene method and an acetylene method, and 80% of vinyl acetate is prepared by an ethylene gas phase method.

The ethylene gas phase process for producing vinyl acetate is to mix ethylene, oxygen and acetic acid steam, and to produce vinyl acetate through gas phase oxidation reaction under the action of noble metal catalyst and potassium acetate assistant, while producing small amount of side products acetaldehyde, ethyl acetate, methyl acetate, etc. The ethylene method is a main method for producing vinyl acetate at home and abroad at present because of good manufacturability and economy.

The ethylene gas phase method for producing vinyl acetate is an exothermic reaction, the temperature of a catalyst bed is unevenly distributed, and the heat released by the reaction is not removed in time, so that the single pass conversion rate of ethylene is reduced. Along with the continuous expansion of the production scale of vinyl acetate, the continuous expansion of the scale of a reactor, how to uniformly and rapidly remove the heat released by the reaction becomes one of the key problems of engineering development, which is also attributed to the uniform distribution of heat removal fluid in the reactor. If the heat removal fluid cannot be uniformly distributed and the heat cannot be removed in time, the flying temperature is formed, so that the local temperature is too high, the utilization efficiency of the catalyst and the reactor is influenced, the selectivity and the yield of a target product are influenced, and the danger of severe combustion and explosion of ethylene can be generated. Therefore, development of efficient reaction process technology is important for preparing vinyl acetate by ethylene gas phase method.

At present, a tubular fixed bed reaction technology is mainly adopted for producing vinyl acetate by an ethylene method. For example, CN102784596B, CN201684584U, CN203494494U, CN202893325U and the like all adopt tubular fixed bed reactors, reaction materials and catalysts are arranged in the tubes, and heat of reaction is removed by heat removal fluid outside the tubes.

CN102784596B discloses a shell side structure and a shell-and-tube vinyl acetate synthesis reactor comprising the shell side structure, catalyst is filled in the shell of the reactor, heat removal medium is arranged between the shell side and the shell side, inlet and outlet of the heat removal medium are positioned at the upper and lower ends of the shell side structure, annular distributors are respectively arranged, fluid communication of a plurality of inlet/outlet ports of the heat removal medium is realized through annular channels in the annular distributors, distribution holes which are uniformly distributed along circumference and have the same size are arranged on the inner side of the annular distributors, namely, a shell at the corresponding position of the reactor, the heat removal medium enters/exits the shell side of the reactor through the distribution holes and exchanges heat with materials in the reaction shell, and the heat removal medium in the shell side and the materials in the reaction shell are in countercurrent, so as to continuously remove reaction heat, thereby achieving the control requirement of reaction temperature. However, when the reactor diameter is large and the number of reaction tubes is large, the heat removal medium flow dead zone is inevitably generated in the center and edge areas of the reactor, the reactor adopts a scheme that a shell side is added with a disc and a circular baffle plate, and the center and edge areas are not distributed, so that the turbulence of the shell side fluid is enhanced to improve the heat transfer effect, but the effective reaction space of the reactor is also lost, and the trend is more prominent with the increase of the diameter of the reactor.

CN203494494U discloses a shell-and-tube fixed bed reactor for vinyl acetate synthesis, the shell side of the reactor employs a plurality of annular baffles and at least one disc-shaped baffle plate, wherein bypass holes are opened between each reaction tube perforation on the baffle plate and baffle plate to increase the fluid turbulence degree of the region, thereby reducing the flow dead zone. The inlet and outlet of the heat-carrying fluid of the reactor are respectively provided with a guide cylinder, the wall surface of the reactor cylinder body on the inner side of the guide cylinder is respectively provided with guide holes which are distributed at equal intervals, so that the heat-carrying fluid enters the guide cylinder and then enters/exits the shell side of the reactor through each guide hole arranged on the reactor cylinder body.

Disclosure of Invention

The invention aims to solve the problems of short catalyst loading amount, local temperature flying of the reactor caused by untimely heat removal due to uneven fluid distribution in a shell, premature deactivation of the catalyst, greatly shortened service cycle, poor equipment safety and process stability and the like of a reactor for synthesizing vinyl acetate by an ethylene gas phase method in the prior art, and provides a method for synthesizing vinyl acetate by a fixed bed reactor and an ethylene gas phase method.

In order to achieve the above object, the present invention provides in one aspect a fixed bed reactor comprising a housing and a cavity formed around the housing, wherein a first distributor, a multi-channel reaction bed layer and a second distributor are arranged in the cavity from top to bottom,

The multi-channel reaction bed layer is provided with a first channel for filling a catalyst and a second channel for circulating a heat exchange medium, and the first channel and the second channel are alternately arranged from the axis of the cavity to the outside, so that the first channel and the second channel form a dividing wall type heat exchange;

The second channel is arranged as a closed heat exchange cavity, the upper part of the second channel is communicated with the first distributor through a plurality of first pipelines, and the lower part of the second channel is communicated with the second distributor through a plurality of second pipelines.

Preferably, the multi-channel reaction bed layer comprises a multi-channel spiral structure formed by winding N groups of plates which are arranged at intervals, wherein N is more than or equal to 1, each group of plates which are arranged at intervals are wound to form a double-channel spiral structure, one spiral channel of the double-channel spiral structure forms a first channel, and the other spiral channel forms a second channel.

Preferably, the first distributor comprises a first spiral coil formed by horizontally winding a pipeline, two ends of the first spiral coil are closed, one end of the first spiral coil is communicated with a heat exchange medium inlet arranged on the side wall of the shell, and a plurality of first pipelines are communicated with the first spiral coil.

Preferably, the second distributor comprises a second spiral coil formed by horizontally winding a pipeline, two ends of the second spiral coil are closed, one end of the second spiral coil is communicated with a heat exchange medium outlet arranged on the side wall of the shell, and a plurality of second pipelines are communicated with the second spiral coil.

Preferably, the multi-channel helical structure is formed by winding N sets of spaced apart plates at least 3 turns.

Preferably, the ratio of the width of the first channel to the second channel is 1 to 8, preferably 1.2 to 5.

Preferably, the first spiral coil or the second spiral coil has a tube cross-sectional area that is required to maintain an average flow velocity of 0.3 to 8m/s when the heat exchange medium passes through.

Preferably, the pipe diameter of the first spiral coil positioned in the cavity is gradually reduced from the outer ring to the inner ring;

More preferably, the difference between two adjacent turns of pipe diameter is (20% -80%)/X ₁, wherein X ₁ is the number of turns of the first spiral coil;

it is further preferable that the pipe diameter of the outermost ring is 1.1 to 3 times the pipe diameter of the heat exchange medium inlet.

Preferably, the pipe diameter of the second spiral coil in the cavity is reduced from the outer ring to the inner ring, and more preferably, the difference value between the pipe diameters of two adjacent rings is (20% -80%)/X ₂, wherein X ₂ is the number of the second spiral coil;

it is further preferable that the pipe diameter of the outermost ring is 1.1 to 3 times of the pipe diameter of the heat exchange medium outlet.

Preferably, the ratio of the number of turns X ₁ of the first spiral coil to the number of turns of the multi-channel spiral structure is 0.2 to 1, and not less than 2 turns.

Preferably, the ratio of the number of turns X ₁ of the second helical coil to the number of turns of the multi-channel helical structure is 0.2 to 1, and not less than 2 turns, more preferably the number of turns of the second helical coil is the same as the number of turns of the first helical coil.

Preferably, a plurality of the first pipelines are arranged at equal intervals along the spiral direction of the first spiral coil, and more preferably, the number of the first pipelines is more than or equal to 3; more preferably not less than 23.

Preferably, a plurality of the second pipelines are arranged at equal intervals along the spiral direction of the second spiral coil, and more preferably, the number of the second pipelines is more than or equal to 3; more preferably not less than 23.

Preferably, the first pipe and the second pipe are arranged in a staggered manner along the winding direction of the multi-channel spiral structure.

Preferably, the angle α between the axis of the first pipe and the axis of the first helical coil is between 10 ° and 90 °, more preferably between 30 ° and 90 °.

The invention also provides a method for synthesizing vinyl acetate by an ethylene gas phase method, which is carried out in the fixed bed reactor, wherein the top end of the shell is provided with a reaction gas inlet communicated with the cavity, the reaction gas inlet is provided with a gas distributor, and the bottom end of the shell is provided with a synthesis gas outlet communicated with the cavity; the method comprises the following steps:

Feeding a mixture gas containing ethylene vapor, oxygen and acetic acid vapor to the reaction gas inlet, wherein,

The heat exchange medium enters the second channel through a plurality of first pipelines through the first distributor to form dividing wall type heat exchange with the first channel filled with the catalyst, and is discharged through the second distributor through a plurality of second pipelines;

the mixed gas enters a catalyst bed layer through a gas distributor to contact with a catalyst to generate vinyl acetate, and the vinyl acetate is discharged from a synthesis gas outlet.

Preferably, the contact condition of the mixed gas and the catalyst comprises: the pressure is 0.3-1.5 MPa (G), the operating temperature is 120-260 ℃, and the reaction space velocity is 1000-2200 h ^-1.

Preferably,thecatalystisselectedfromatleastoneofPd-Au,Pd-Pt,Pd-Cd,Pd-VandPd-M-A.

Preferably, the first channel comprises inert porcelain balls, a catalyst and the inert porcelain balls from top to bottom.

Preferably, the heat exchange medium is selected from at least one of heat transfer oil, circulating hot water, steam and process materials.

Preferably, the mol ratio of ethylene vapor, oxygen and acetic acid vapor in the mixed gas is (9-100) to (1-20) to (2-12).

Preferably, the flow direction of the heat exchange medium is the same as the flow direction of the mixture in the second passage.

Through the technical scheme, the multi-channel reaction bed layer structure of the fixed bed reactor increases the loading amount of the catalyst on one hand, so that the catalyst is more uniformly distributed, and on the other hand, the first channel filled with the catalyst and the second channel filled with the heat exchange medium perform dividing wall type heat exchange, so that the contact area between the heat exchange medium and the catalyst is increased, the flow dead zone of fluid is eliminated, and the rapid and uniform heat exchange is realized; the rapid circulation of the heat exchange medium in the reactor is realized through a plurality of first pipelines and second pipelines, so that the rapid temperature rise and temperature reduction are realized; particularly, when the fixed bed reactor is applied to exothermic reaction, heat can be timely removed, the catalyst deactivation caused by local temperature flying and the influence on the selectivity and yield of target products are avoided, meanwhile, the severe combustion and explosion of combustible reaction materials are avoided, the process stability and the equipment operation safety are improved, and the large-scale requirement of the reactor can be met.

Additional features and advantages of the invention will be set forth in the detailed description which follows.

Drawings

FIG. 1 is a schematic diagram of a fixed bed reactor according to an embodiment of the present invention;

FIG. 2 is a schematic diagram of the connection structure of the first distributor, the second distributor and the dual channel spiral structure of FIG. 1;

FIG. 3 is a cross-sectional view of the dual channel reaction bed of FIG. 1;

fig. 4 is a schematic structural view of the first distributor or the second distributor in fig. 1.

Description of the reference numerals

1, A reaction gas inlet; 2 a gas distributor; 3 a first helical coil; 4a multi-channel reaction bed layer; 5 a second spiral coil; 6, a heat exchange medium inlet; 7, a heat exchange medium outlet; 8, a synthesis gas outlet; 9a first conduit; a second conduit 10; 11a first channel; 12 a second channel.

Detailed Description

The following describes specific embodiments of the present invention in detail with reference to the drawings. It should be understood that the detailed description and specific examples, while indicating and illustrating the invention, are not intended to limit the invention.

In the present invention, unless otherwise stated, terms such as "up, down, left, right" are used to generally refer to terms for describing the mutual positional relationship of the components in the direction shown in the drawings or in the vertical, vertical or gravitational directions, wherein the vertical direction is the height direction or gravitational direction, and one turn in the present invention refers to the direction of winding forming 360 ° with the winding end face, and in the present invention, without any particular description, the "upper portion" of the container refers to the position of the container from top to bottom by 0-30%; the "middle" of the container means the position of the container from top to bottom by 30-70%, and the lower means the position of the container from bottom to top by 0-30%.

As shown in fig. 1-2, in one aspect, the present invention provides a fixed bed reactor, the fixed bed reactor comprises a housing and a cavity formed by surrounding the housing, a reactant inlet and a product outlet which are communicated with the cavity are arranged on the housing, wherein the reactant inlet is provided with a material distributor in the prior art, a first distributor, a multi-channel reaction bed layer 4 and a second distributor are arranged in the cavity from top to bottom,

The multi-channel reaction bed layer is provided with a first channel 11 for filling a catalyst and a second channel 12 for circulating a heat exchange medium, and the first channel 11 and the second channel 12 are alternately arranged from the axis of the cavity to the outside, so that the first channel 11 and the second channel 12 form a dividing wall type heat exchange;

The second channel 12 is arranged as a closed heat exchange cavity, the top wall of the second channel 12 is communicated with the first distributor through a plurality of first pipelines 9, and the bottom wall of the second channel is communicated with the second distributor through a plurality of second pipelines 10.

The structure of the multi-channel reaction bed layer of the fixed bed reactor increases the loading amount of the catalyst on one hand, so that the distribution of the catalyst is more uniform, and on the other hand, the first channel filled with the catalyst and the second channel filled with the heat exchange medium perform dividing wall type heat exchange, so that the contact area between the heat exchange medium and the catalyst is increased, the flow dead zone of fluid is eliminated, and the rapid and uniform heat exchange is realized; the rapid circulation of the heat exchange medium in the reactor is realized through a plurality of first pipelines and second pipelines, so that the rapid temperature rise and temperature reduction are realized; particularly, when the fixed bed reactor is applied to exothermic reaction, heat can be timely removed, the catalyst deactivation caused by local temperature flying and the influence on the selectivity and yield of target products are avoided, meanwhile, the severe combustion and explosion of combustible reaction materials are avoided, the process stability and the equipment operation safety are improved, and the large-scale requirement of the reactor can be met.

As shown in fig. 4, according to a preferred embodiment of the present invention, the first distributor comprises a first spiral coil 3 formed by horizontally winding a pipe, both ends of the first spiral coil 3 are closed, one end of which is connected to a heat exchange medium inlet 6 provided at a side wall of the housing, and the first spiral coil 3 is provided with a plurality of distribution holes communicating with the first pipe 9 in a spiral direction of itself. Through a plurality of first pipelines that evenly distributed along circumference get into the second passageway, realize the evenly distributed of heat transfer medium, effectively prevented the risk that the temperature of flight appears in the regional emergence of reactor.

According to a preferred embodiment of the present invention, the second distributor comprises a second spiral coil 5 formed by horizontally winding a pipe, both ends of the second spiral coil 5 are closed, one end of which is communicated with a heat exchange medium outlet 7 provided at a side wall of the housing, and the second spiral coil 5 is provided with a plurality of distribution holes communicated with the second pipe 10 along its own spiral direction, so that the reaction heat can be continuously and timely removed.

On the basis of rapid heat exchange, the reactor of the invention has the advantages that the inlet of the heat exchange medium is arranged outside the shell and one inlet is arranged, and the flow and the temperature of the heat exchange medium entering the reactor are controlled through a single point, so that compared with the mode of feeding the multi-point heat exchange medium in the prior art, the reactor of the invention is easy to realize temperature control, reduces the operation difficulty, and has better tightness and controllability.

Compared with the catalyst bed of the tubular reactor formed by a plurality of tubular pipes which are independent of each other, the volume rate of the reactor is obviously improved, and the distribution of the catalyst is more uniform, so that the stability of the process and the safety of equipment operation are improved.

The multi-channel reaction bed layer 4 of the invention can be formed by nesting a plurality of annular shells inside and outside, and a gap between two adjacent shells is formed into a first channel 11 and a second channel 12; or according to a preferred embodiment of the invention, the multi-channel reaction bed 4 comprises a multi-channel spiral structure formed by winding N groups of plates arranged at intervals, N is equal to or greater than 1,

Wherein, as shown in fig. 2 and 3, each group is formed by winding two plates (such as metal plates) which are arranged at intervals to form a double-channel spiral structure, one spiral channel of the double-channel spiral structure forms a first channel 11, two axial ends of the first channel are open, and the catalyst is fixed in the first channel 11 by adopting the prior art; the other spiral channel is formed as a second channel 12, and both axial ends of the second channel 12 are arranged to be closed, forming a heat exchange chamber for circulating a heat exchange medium. Thus, the structure of the spiral channel integrally enhances the turbulence effect of the fluid, eliminates the flow dead zone of the fluid, and ensures that the fluid is distributed more uniformly, thereby ensuring the uniformity of the temperature distribution in the reactor.

The invention is illustrated with the advantage of only a multi-channel reaction of 1, i.e. a set of two-channel helical structures formed by winding two spaced plates, but the invention is not limited thereto.

According to a preferred embodiment of the invention, the double channel spiral structure is formed by winding two spaced apart plates at least 3 turns. The use of the foregoing preferences facilitates the scale-up of fixed bed reactors.

According to a preferred embodiment of the invention, the ratio of the widths of the first channel 11 to the second channel 12 is 1 to 8, preferably 1.2 to 5; the adoption of the optimization is favorable for continuously and timely removing the reaction heat and avoiding local temperature runaway, so that the service life of the catalyst and the yield and selectivity of target products are improved. In some embodiments of the invention, the width of the spiral channel of the first channel 11 is not more than 120mm, more preferably not more than 80mm.

According to a preferred embodiment of the present invention, the plurality of first pipes 9 are arranged at equal intervals along the spiral direction of the first spiral coil 3, preferably the number of first pipes 9 is equal to or more than 3; more preferably not less than 23. The adoption of the optimization can realize the rapid inlet and outlet of the heat exchange medium into and out of the reactor, thereby avoiding the local temperature runaway caused by the reaction heat.

According to a preferred embodiment of the present invention, the plurality of second pipes 10 are arranged at equal intervals along the spiral direction of the second spiral coil 5, preferably the number of second pipes 10 is equal to or more than 3; more preferably not less than 23. The adoption of the optimization can realize the rapid inlet and outlet of the heat exchange medium into and out of the reactor, thereby avoiding the local temperature runaway caused by the reaction heat.

According to a preferred embodiment of the present invention, the tube cross-sectional area of the first spiral coil 3 or the second spiral coil 5 is a tube cross-sectional area required to be able to maintain an average flow rate of 0.3 to 8m/s when the heat exchange medium passes therethrough.

According to a preferred embodiment of the invention, the pipe diameter of the first spiral coil 3 decreases from the outer ring to the inner ring, preferably the difference between the pipe diameters of two adjacent rings is (20% -80%)/X ₁, wherein X ₁ is the number of the rings of the first spiral coil 3; the selectivity and the yield of the target product can be improved by adopting the optimization; more preferably, the pipe diameter of the outermost ring is 1.1-3 times of the pipe diameter of the heat exchange medium inlet 6.

According to a preferred embodiment of the invention, the pipe diameter of the second spiral coil 5 is decreased from the outer ring to the inner ring, preferably the difference between the pipe diameters of two adjacent rings is (20% -80%)/X ₂, wherein X ₂ is the number of the second spiral coil 5, and the selectivity and the yield of the target product can be improved by adopting the above preference; more preferably, the pipe diameter of the outermost ring is 1.1-3 times of the pipe diameter of the heat exchange medium outlet 7.

According to a preferred embodiment of the invention, the ratio of the number of turns X ₁ of the first helical coil 3 to the number of turns of the double channel helical structure is between 0.2 and 1 and not less than 2.

According to a preferred embodiment of the invention, the ratio of the number of turns X ₂ of the second helical coil 5 to the number of turns of the double channel helical structure is between 0.2 and 1 and not less than 2, preferably the number of turns of the second helical coil 5 is the same as the number of turns of the first helical coil 3. The characteristics of spiral continuous baffling and no flow dead zone of the spiral channel are fully utilized, so that the heat exchange medium enters the second channel 12 from the first spiral coil 3 through the plurality of first pipelines 9, and under the action of the spiral plate wall, the heat exchange medium also forms circumferential continuous baffling while flowing axially, and enters the second spiral coil 5 through the plurality of second pipelines 10 after passing through the plurality of circles of second channels. The use of the aforesaid preference facilitates the formation of a circumferential turbulence of the heat exchange medium in the second channels.

According to a preferred embodiment of the invention, the first conduit 9 and the second conduit 10 are arranged offset in the winding direction of the double-channel spiral structure. The use of the foregoing preference results in the heat exchange medium forming a circumferential flow in the heat exchange chamber.

According to a preferred embodiment of the invention, the angle α of the axis of the first conduit 9 to the axis of the first helical coil 5 is between 10 ° and 90 °, preferably between 30 ° and 90 °. The selectivity and yield of the target product can be improved by adopting the above preference.

The invention also provides a method for synthesizing vinyl acetate by an ethylene gas phase method, which is carried out in the fixed bed reactor, wherein the top end of a shell is provided with a reaction gas inlet 1 communicated with a cavity, the reaction gas inlet 1 is provided with a gas distributor 2, and the bottom end of the shell is provided with a synthesis gas outlet 8 communicated with the cavity; the method comprises the following steps:

Feeding a heat exchange medium to a heat exchange medium inlet 6, feeding a mixed gas containing ethylene vapor, oxygen and acetic acid vapor to a reaction gas inlet 1, wherein,

The heat exchange medium enters the second channel 12 through the plurality of first pipelines 9 to form dividing wall type heat exchange with the first channel 11 filled with the catalyst, and is discharged through the heat exchange medium outlet 7 through the plurality of second pipelines 10;

The mixed gas enters the first channel 11 through the gas distributor 2 to contact with the catalyst to generate vinyl acetate, and the vinyl acetate is discharged from the synthesis gas outlet 8.

According to the invention, vinyl acetate is synthesized in the fixed bed reactor by an ethylene gas phase method, so that on one hand, the loading amount of the catalyst is increased, the mixed gas is more fully contacted with the catalyst, on the other hand, the catalyst bed layer and the heat exchange cavity through which the heat exchange medium flows perform dividing wall type heat exchange, the contact area of the heat exchange medium and the catalyst is increased, the flow dead zone of fluid is eliminated, the temperature distribution is uniform, the reaction is facilitated, and more importantly, the heat exchange medium absorbing the reaction heat can be timely removed from the reactor through a plurality of second pipelines, so that the local temperature flying is avoided, the service cycle of the catalyst and the selectivity and the yield of the vinyl acetate are improved, and the product quality is ensured; the spiral coil pipe structure in the fixed bed reactor can self-compensate the thermal stress of the pipeline, effectively avoids the problem that the pipeline is deformed to generate the pipeline stress due to thermal expansion, and is beneficial to the stable operation and the safety of equipment; in addition, compared with the flow regulation of a plurality of heat exchange medium inlets in the prior art, the method greatly reduces the control difficulty and is beneficial to the stability requirement of the process.

In the invention, the contact conditions of the mixed gas and the catalyst comprise: the pressure is 0.3-1.5 Mpa (G), the operating temperature is 120-260 ℃, and the reaction space velocity is 1000-2200 h ^-1.

Inthepresentinvention,thecatalystisatleastoneselectedfromPd-Au,Pd-Pt,Pd-Cd,Pd-VandPd-M-A.

In the invention, the catalyst bed layer sequentially comprises inert porcelain balls, a catalyst and the inert porcelain balls from top to bottom.

In the invention, the heat exchange medium is selected from at least one of heat conduction oil, circulating hot water, water vapor and process materials.

In the invention, the mol ratio of ethylene vapor, oxygen and acetic acid vapor in the mixed gas is (9-100) to (1-20) to (2-12).

In the invention, the flow direction of the heat exchange medium is the same as the flow direction of the mixed gas in the first channel 11, and the mixed gas flows from top to bottom, so that the reaction heat can be continuously and timely removed from the reactor.

The advantages of the present invention are illustrated by the following examples, but the present invention is not limited thereto.

Example 1

The ethylene gas phase method is adopted to synthesize the vinyl acetate in the fixed bed reactor; wherein,

Structural parameters of fixed bed reactor: the double-channel spiral structure is formed by winding two metal plates at intervals for 20 circles, and the ratio of the widths of the first channel 11 to the second channel 12 is 1.5; the number of turns of the first spiral coil 3 is 6, and the number of turns of the second spiral coil 5 is 6; the tube cross-sectional areas of the first spiral coil 3 and the second spiral coil 5 are each the tube cross-sectional areas required to maintain an average flow velocity of 3m/s when the heat exchange medium passes through; the pipe diameter of the first spiral coil 3 is gradually decreased from the outer ring to the inner ring, the difference value between the pipe diameters of two adjacent rings is 12%, and the pipe diameter of the outermost ring is 2 times of the pipe diameter of the heat exchange medium inlet 6; the pipe diameter of the second spiral coil 5 is gradually decreased from the outer ring to the inner ring, the difference value between the pipe diameters of two adjacent rings is 12%, and the pipe diameter of the outermost ring is 2 times of the diameter of the heat exchange medium outlet 7; the number of the first pipelines 9 is 88, and the number of the second pipelines 10 is 88; the angle α of the axis of the first conduit 9 to the axis of the first helical coil 3 is 30 °.

Operating parameters: the mol ratio of ethylene vapor, oxygen and acetic acid vapor in the mixed gas is 20:5:4, the catalyst Pd-Au, the heat exchange medium is circulating hot water and the reactant flow forward, and the reaction heat is continuously removed; contact conditions: the pressure is 0.7MPa, the operating temperature is 180 ℃, and the reaction space velocity is 1200h ^-1.

Results: the yield of vinyl acetate was 99.1%, the reaction selectivity was 97.8%, and the volume fraction of the reactor catalyst bed was 59.8%.

Example 2

Structural parameters of fixed bed reactor: the double-channel spiral structure is formed by winding two metal plates at intervals for 10 circles, and the ratio of the widths of the first channel 11 to the second channel 12 is 1.25; the number of turns of the first spiral coil 3 is 3, the number of turns of the second spiral coil 5 is 3, and the pipe cross sections of the first spiral coil 3 and the second spiral coil 5 are respectively pipe cross sections required for maintaining an average flow velocity of 2.0m/s when a heat exchange medium passes through; the pipe diameter of the first spiral coil 3 is gradually decreased from the outer ring to the inner ring, the difference value between the pipe diameters of two adjacent rings is 10%, and the pipe diameter of the outermost ring is 1.5 times of the pipe diameter of the heat exchange medium inlet 6; the pipe diameter of the second spiral coil 5 is decreased from the outer ring to the inner ring, the difference value between the pipe diameters of two adjacent rings is 10%, and the pipe diameter of the outermost ring is 1.5 times of the pipe diameter of the heat exchange medium outlet 7; the number of the first pipelines 9 is 23, and the number of the second pipelines 10 is 23; the angle α of the axis of the first conduit 9 to the axis of the first helical coil 3 is 90 °.

Operating parameters: the mol ratio of ethylene vapor, oxygen and acetic acid vapor in the mixed gas is 80:16:8, the catalyst is Pd-Cd, the heat exchange medium is circulating hot water and the reactant flow forward, and the reaction heat is continuously removed; contact conditions: the pressure was 0.6MPa, the operating temperature was 160℃and the reaction space velocity was 1500h ^-1.

Results: the yield of vinyl acetate was 98.7%, the reaction selectivity was 97.3%, and the volume fraction of the reactor catalyst bed was 58.6%.

Example 3

Structural parameters of fixed bed reactor: the double-channel spiral structure is formed by winding two metal plates at intervals for 20 circles, and the ratio of the widths of the first channel 11 to the second channel 12 is 1.25; the number of turns of the first spiral coil 3 is 6, the number of turns of the second spiral coil 5 is 6, and the pipe cross sections of the first spiral coil 3 and the second spiral coil 5 are respectively pipe cross sections required for maintaining an average flow velocity of 2.8m/s when a heat exchange medium passes through; the pipe diameter of the first spiral coil 3 is gradually decreased from the outer ring to the inner ring, the difference value between the pipe diameters of two adjacent rings is 12%, and the pipe diameter of the outermost ring is 2 times of the pipe diameter of the heat exchange medium inlet 6; the pipe diameter of the second spiral coil 5 is gradually decreased from the outer ring to the inner ring, the difference value between the pipe diameters of two adjacent rings is 12%, and the pipe diameter of the outermost ring is 2 times of the diameter of the heat exchange medium outlet 7; the number of the first pipelines 9 is 88, and the number of the second pipelines 10 is 88; the angle α of the axis of the first conduit 9 to the axis of the first helical coil 3 is 60 °.

Operating parameters: the mol ratio of ethylene vapor, oxygen and acetic acid vapor in the mixed gas is 50:10:6, the catalyst Pd-Pt, the heat exchange medium is circulating hot water and the reactant flow forward, and the reaction heat is continuously removed; contact conditions: the pressure was 0.78MPa, the operating temperature was 180℃and the reaction space velocity was 1400h ^-1.

Results: the yield of vinyl acetate was 99.6%, the reaction selectivity was 98.4%, and the volume fraction of the reactor catalyst bed was 59.5%.

Example 4

Structural parameters of fixed bed reactor: the double-channel spiral structure is formed by winding 22 circles of two metal plates which are arranged at intervals, and the ratio of the widths of the first channel 11 to the second channel 12 is 3; the number of turns of the first spiral coil 3 is 5, the number of turns of the second spiral coil 5 is 5, and the pipe cross sections of the first spiral coil 3 and the second spiral coil 5 are respectively pipe cross sections required for maintaining the average flow velocity of 3.5m/s when a heat exchange medium passes through; the pipe diameter of the first spiral coil 3 is gradually decreased from the outer ring to the inner ring, the difference value between the pipe diameters of two adjacent rings is 15%, and the pipe diameter of the outermost ring is 1.5 times of the pipe diameter of the heat exchange medium inlet 6; the pipe diameter of the second spiral coil 5 is gradually decreased from the outer ring to the inner ring, the difference value between the pipe diameters of two adjacent rings is 8%, and the pipe diameter of the outermost ring is 1.5 times of the pipe diameter of the heat exchange medium outlet 7; the number of the first pipelines 9 is 58, and the number of the second pipelines 10 is 58; the angle α of the axis of the first conduit 9 to the axis of the first helical coil 3 is 90 °.

Operating parameters: the mol ratio of ethylene vapor, oxygen and acetic acid vapor in the mixed gas is 30:6:4, the catalyst is Pd-V, the heat exchange medium is circulating hot water and the reactant flow forward, and the reaction heat is continuously removed; contact conditions: the pressure is 1.1MPa, the operating temperature is 220 ℃, and the reaction space velocity is 1600h ^-1.

Results: the yield of vinyl acetate was 98.1%, the reaction selectivity was 96.5%, and the volume fraction of the reactor catalyst bed was 60.1%.

Example 5

Structural parameters of fixed bed reactor: the double-channel spiral structure is formed by winding two metal plates at intervals for 16 circles, and the ratio of the widths of the first channel 11 to the first channel 12 is 5; the number of turns of the first spiral coil 3 is 4, the number of turns of the second spiral coil 5 is 4, and the pipe cross sections of the first spiral coil 3 and the second spiral coil 5 are respectively pipe cross sections required for maintaining the average flow velocity of 3.8m/s when a heat exchange medium passes through; the pipe diameter of the first spiral coil 3 is gradually decreased from the outer ring to the inner ring, the difference value between the pipe diameters of two adjacent rings is 10%, and the pipe diameter of the outermost ring is 2.5 times of the pipe diameter of the heat exchange medium inlet 6; the pipe diameter of the second spiral coil 5 is gradually decreased from the outer ring to the inner ring, the difference value between the pipe diameters of two adjacent rings is 8%, and the pipe diameter of the outermost ring is 2.5 times of the pipe diameter of the heat exchange medium outlet 7; the number of the first pipelines 9 is 26, and the number of the second pipelines 10 is 26; the angle α of the axis of the first conduit 9 to the axis of the first helical coil 3 is 80 °.

Operating parameters: themolratioofethylenevapor,oxygenandaceticacidvaporinthemixedgasis60:12:5,thecatalystPd-M-A,theheatexchangemediumisheatconductionoilandreactantflowforward,andthereactionheatiscontinuouslyremoved; contact conditions: the pressure was 0.9MPa, the operating temperature was 210℃and the reaction space velocity was 1800h ^-1.

Results: the yield of vinyl acetate was 97.5%, the reaction selectivity was 95.7%, and the volume fraction of the reactor catalyst bed was 59.4%.

Example 6

Unlike example 1, the ratio of the width of the first channel 11 to the second channel 12 is 6; the cross-sectional areas of the first spiral coil 3 and the second spiral coil 5 are each the tube cross-sectional areas required to maintain an average flow velocity of 10m/s when the heat exchange medium passes through; the number of first pipes 9 is 18 and the number of second pipes 10 is 18.

Results: the yield of vinyl acetate was 95.3%, the reaction selectivity was 94.6% and the volume fraction of the reactor catalyst bed was 60%.

Example 7

Unlike example 1, the following is: the angle α of the axis of the first conduit 9 to the axis of the first helical coil 3 is 10 °.

Results: the yield of vinyl acetate was 97.9%, the reaction selectivity was 95.9%, and the volume fraction of the reactor catalyst bed was 59.8%.

Example 8

Unlike example 1, the following is: the pipe diameters of the first spiral coil 3 and the second spiral coil 5 are not changed, but the same pipe diameter.

Results: the yield of vinyl acetate was 97.2%; the reaction selectivity was 95.4% and the volume fraction of the reactor catalyst bed was 59.8%.

Comparative example 1

Unlike example 1, the following is: a tubular fixed bed reactor with the same volume as the fixed bed reactor in the example 1 in the prior art is adopted, the reaction operation temperature is 160 ℃, the operation pressure is 0.75MPa, and the reaction airspeed is 1200h ^-1; the device is provided with an annular guide cylinder at the inlet and outlet of a heat exchange medium, adopts circulating hot water as heat removal fluid, flows reversely with the material flow in a reaction tube array, has the yield of the vinyl acetate of 92.5 percent, the reaction selectivity of 85 percent and the volume ratio of a catalyst bed of a reactor of 35.5 percent.

Comparative example 2

Unlike example 1, the following is: the multistage spiral plate reactor of CN108114672B having the same volume as the fixed bed reactor of example 1 was used, the yield of vinyl acetate was 92.8%, the reaction selectivity was 88%, and the volume ratio of the reactor catalyst bed was 54%.

The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited thereto. Within the scope of the technical idea of the invention, a plurality of simple variants of the technical proposal of the invention can be carried out, comprising that each specific technical feature is combined in any suitable way, and in order to avoid unnecessary repetition, the invention does not need to be additionally described for various possible combinations. These simple variations and combinations should also be considered as being within the scope of the present disclosure;

The endpoints and any values of the ranges disclosed herein are not limited to the precise range or value, and are understood to encompass values approaching those ranges or values. For numerical ranges, one or more new numerical ranges may be found between the endpoints of each range, between the endpoint of each range and the individual point value, and between the individual point value, in combination with each other, and are to be considered as specifically disclosed herein.

Claims

1. A fixed bed reactor is characterized by comprising a shell and a cavity formed by surrounding the shell, wherein a first distributor, a multi-channel reaction bed layer (4) and a second distributor are arranged in the cavity from top to bottom,

The multi-channel reaction bed layer is provided with a first channel (11) for filling a catalyst and a second channel (12) for circulating a heat exchange medium, the axes of the first channel (11) and the second channel (12) are alternately arranged outwards from the cavity, so that the first channel (11) and the second channel (12) form dividing wall type heat exchange;

The second channel (12) is arranged as a closed heat exchange cavity, the upper part of the second channel (12) is communicated with the first distributor through a plurality of first pipelines (9), and the lower part of the second channel is communicated with the second distributor through a plurality of second pipelines (10).

2. The fixed bed reactor according to claim 1, wherein the multichannel reaction bed (4) comprises a multichannel spiral structure formed by winding N groups of plates arranged at intervals, N is equal to or greater than 1,

Wherein each group is wound by two plates arranged at intervals to form a double-channel spiral structure, one spiral channel of the double-channel spiral structure is formed into the first channel (11), and the other spiral channel is formed into the second channel (12);

and/or

The ratio of the width of the first channel (11) to the second channel (12) is 1-8, preferably 1.2-5.

3. The fixed bed reactor according to claim 2, wherein the multi-channel spiral structure is formed by winding N sets of spaced plates at least 3 turns;

and/or

The first distributor comprises a first spiral coil (3) formed by horizontally winding pipelines, two ends of the first spiral coil (3) are closed, one end of the first spiral coil is communicated with a heat exchange medium inlet (6) arranged on the side wall of the shell, and a plurality of first pipelines (9) are communicated with the first spiral coil (3);

and/or

The second distributor comprises a second spiral coil (5) formed by horizontally winding pipelines, two ends of the second spiral coil (5) are closed, one end of the second spiral coil is communicated with a heat exchange medium outlet (7) arranged on the side wall of the shell, and a plurality of second pipelines (10) are communicated with the second spiral coil (5).

4. A fixed bed reactor according to claim 3, wherein the tube cross-sectional area of the first spiral coil (3) or the second spiral coil (5) is the tube cross-sectional area required to maintain an average flow rate of 0.3 to 8m/s when the heat exchange medium passes through;

and/or

The pipe diameter of the first spiral coil pipe (3) is decreased from the outer ring to the inner ring;

Preferably, the difference value of the pipe diameters of two adjacent circles is (20% -80%)/X ₁, wherein X ₁ is the number of circles of the first spiral coil pipe (3);

more preferably, the pipe diameter of the outermost ring is 1.1-3 times of the pipe diameter of the heat exchange medium inlet (6);

and/or

The pipe diameter of the second spiral coil pipe (5) is decreased from the outer ring to the inner ring;

Preferably, the difference value of the pipe diameters of two adjacent circles is (20% -80%)/X ₂, wherein X ₂ is the number of circles of the second spiral coil (5);

more preferably, the pipe diameter of the outermost ring is 1.1-3 times of the pipe diameter of the heat exchange medium outlet (7).

5. The fixed bed reactor according to claim 3 or 4, wherein the ratio of the number of turns X ₁ of the first helical coil (3) to the number of turns of the multi-channel helical structure is 0.2 to 1 and not less than 2 turns;

and/or

The ratio of the number of turns X ₂ of the second spiral coil (5) to the number of turns of the multi-channel spiral structure is 0.2-1, and is not less than 2, preferably the number of turns of the second spiral coil (5) is the same as the number of turns of the first spiral coil (3).

6. The fixed bed reactor according to any one of claims 1 to 5, wherein a plurality of the first pipes (9) are arranged at equal intervals along the spiral direction of the first spiral coil (3), preferably the number of the first pipes (9) is not less than 3; more preferably greater than or equal to 23;

and/or

The second pipelines (10) are arranged at equal intervals along the spiral direction of the second spiral coil (5), and preferably the number of the second pipelines (10) is more than or equal to 3; more preferably not less than 23.

7. The fixed bed reactor according to any one of claims 1 to 6, wherein the first pipe (9) and the second pipe (10) are arranged offset in the winding direction of the multi-channel spiral structure;

and/or

The included angle alpha between the axis of the first pipeline (9) and the axis of the first spiral coil (5) is 10-90 degrees, and preferably alpha is 30-90 degrees.

8. A method for synthesizing vinyl acetate by an ethylene gas phase method, which is characterized in that the method is carried out in the fixed bed reactor of any one of claims 1 to 7, wherein the top end of a shell is provided with a reaction gas inlet (1) communicated with the cavity, the reaction gas inlet (1) is provided with a gas distributor (2), and the bottom end of the shell is provided with a synthesis gas outlet (8) communicated with the cavity; the method comprises the following steps:

feeding a mixed gas containing ethylene vapor, oxygen and acetic acid vapor to a reaction gas inlet (1), wherein,

The heat exchange medium enters the second channel (12) through the first distributor through the plurality of first pipelines (9) to form dividing wall type heat exchange with the first channel (11) filled with the catalyst, and is discharged through the second distributor through the plurality of second pipelines (10);

The mixed gas enters a first channel (11) through a gas distributor (2) to contact with a catalyst to generate vinyl acetate, and the vinyl acetate is discharged from a synthesis gas outlet (8).

9. The method according to claim 7, wherein,

The mol ratio of ethylene vapor, oxygen and acetic acid vapor in the mixed gas is (9-100) to (1-20) to (2-12);

and/or

The contact conditions of the mixed gas and the catalyst comprise: the pressure is 0.3-1.5 MPa, the operating temperature is 120-260 ℃, and the reaction space velocity is 1000-2200 h ^-1.

10. The method according to claim 7 or 8, wherein,

ThecatalystisatleastoneofPd-Au,Pd-Pt,Pd-Cd,Pd-VandPd-M-A;

and/or

The first channel (11) sequentially comprises inert porcelain balls, a catalyst and the inert porcelain balls from top to bottom;

and/or

The heat exchange medium is at least one of heat conduction oil, circulating hot water, steam and process materials;

and/or

The flow direction of the heat exchange medium is the same as the flow direction of the mixed gas in the first channel (11).