A method and device for preventing blocking in alcoholysis process of preparing ethylene-vinyl acetate alcohol copolymer

Abstract

The present invention relates to a method and device for preventing blockage in the alcoholysis process of preparing ethylene-vinyl acetate alcohol copolymer. The method comprises: in an alcoholysis tower, causing an ethylene-vinyl acetate copolymer stream and a catalyst stream to contact each other with a methanol vapor stream to perform an alcoholysis reaction, wherein the pressure of the methanol vapor stream is controlled to always be greater than the pressure of the alcoholysis tower kettle; a space is reserved above the feed position of the ethylene-vinyl acetate copolymer stream; and the overhead gas stream of the alcoholysis tower passes through a cyclone separator provided at the top of the alcoholysis tower, and the heavy component liquid phase stream after cyclone separation is refluxed to the alcoholysis tower. This method has a simple process flow, is easy to operate, and the process pipeline is not prone to blockage. It can operate stably for a long period of time, reduces the total energy consumption of the equipment and the amount of fresh methanol used, and is very easy to industrialize.

Description

Technical Field

[0001] The present invention relates to the field of ethylene-vinyl acetate copolymers, and in particular to a method and a device for preventing blocking in the alcoholysis process of preparing ethylene-vinyl acetate alcohol copolymer by alcoholysis of ethylene-vinyl acetate copolymer. Background Art

[0002] Ethylene-vinyl acetate alcohol copolymer (EVOH) is generally obtained by polymerizing ethylene and vinyl acetate through conventional methods such as emulsion polymerization, solution polymerization, or suspension polymerization to form ethylene-vinyl acetate copolymer (EVAC). It is then produced through an alcoholysis reaction in the presence of an alkaline catalyst, typically with a molar ratio of 20-45% ethylene to 55-80% vinyl alcohol. The alcoholysis reaction of EVAC is a reversible equilibrium reaction. To obtain a highly alcoholyzed EVOH product, pressure equipment is typically used to increase the pressure and temperature, or nitrogen is introduced to fully remove the small molecular byproduct methyl acetate, causing the reaction to shift to the right. The alcoholysis process generally involves three types of reactions: transesterification, saponification, and side reactions. Transesterification is the primary reaction, and the specific reaction equation is shown below:

[0003] Transesterification reaction:

[0004]

[0005] Saponification reaction:

[0006]

[0007] Side effects:

[0008] CH3CPOOCH3+NaOH→CH3OH+CH3COONa.

[0009] CN104098728A discloses a simple and easy method for the alcoholysis of ethylene and vinyl acetate copolymers at normal pressure. By introducing solvent vapor to carry out the alcoholysis reaction, the alcoholysis degree is increased. The ethylene-vinyl acetate copolymer can be alcoholyzed within 1 to 3 hours to obtain EVOH with an alcoholysis degree of more than 99%. The alcoholysis efficiency is improved, and the obtained EVOH is of good quality and white in color.

[0010] CN204602161U discloses an alcoholysis reaction system for use in EVOH production. The system includes an alcoholysis unit connected to both a feed and discharge pipelines. The system also includes a gas inlet pipeline, a heat exchanger, and a condensate tank. The gas inlet pipeline is connected to the alcoholysis unit; the discharge pipeline includes an EVOH discharge pipeline that is connected to the heat exchanger and then to the outside of the system; and the heat exchanger is connected to the condensate tank. The system can stably control the pressure in the alcoholysis unit, ensuring the smooth and continuous progress of the alcoholysis reaction. It also reduces heat dissipation in the system, saving energy.

[0011] CN106146717A discloses a method for producing ethylene-vinyl alcohol copolymers, comprising, in sequence, copolymerization, monomer removal, saponification, granulation, and post-processing. In the granulation step, the ethylene-vinyl alcohol copolymer solution obtained in the saponification step is extruded through an extruder into a coagulation bath for coagulation. The method is characterized in that the extruder head is positioned below the level of the coagulation bath, and the coagulation bath is water. This method not only simplifies the structural setup, simplifies the granulation process, and improves the operating environment.

[0012] Most of the patents published so far focus on the basic operating process of EVOH production or are limited to laboratory research, while there are few reports on the industrial production method and equipment of EVOH. There are no reports on the anti-blocking method and equipment during the alcoholysis process. Therefore, the present invention proposes a method and equipment for preventing blockage during the alcoholysis process of preparing ethylene-vinyl acetate alcohol copolymer (EVOH) by alcoholysis of ethylene-vinyl acetate copolymer (EVAC), which specifically solves this problem and can be used to guide and easily realize industrial production. Summary of the Invention

[0013] In order to solve the above problems existing in the prior art, the present invention provides a method and device for preventing blockage of alcoholysis equipment and pipelines during the alcoholysis of ethylene-vinyl acetate copolymer (EVAC) to prepare ethylene-vinyl acetate alcohol copolymer (EVOH). The method and device can be used in the EVOH production process to achieve continuous, efficient and smooth alcoholysis reaction.

[0014] One of the objectives of the present invention is to provide a method for preventing blockage in an alcoholysis process for preparing ethylene-vinyl acetate alcohol copolymer, comprising: bringing an ethylene-vinyl acetate copolymer stream and a catalyst stream into contact with a methanol vapor stream in opposite directions in an alcoholysis tower to carry out an alcoholysis reaction, wherein the pressure of the methanol vapor stream is controlled to always be greater than the pressure of the alcoholysis tower kettle; reserving space above the feed position of the ethylene-vinyl acetate copolymer stream; passing the overhead gas stream of the alcoholysis tower through a cyclone separator provided at the top of the alcoholysis tower, and refluxing the heavy component liquid phase stream after cyclone separation to the alcoholysis tower.

[0015] The anti-blocking method of the present invention can be achieved by the following aspects: providing a pressure regulating valve I on the methanol vapor logistics pipeline at the bottom of the tower to control the pressure of the methanol vapor purge to always be greater than the pressure of the alcoholysis tower kettle; providing a certain number of empty trays or no trays above the feed point of the EVAC methanol solution; providing a cyclone separator at the top of the alcoholysis tower to separate the polymer heavy components and liquid entrained in the distillate; providing a pressure regulating valve II on the gas phase logistics pipeline at the outlet of the cyclone separator to control the pressure at the top of the tower and ensure stable pressure in the tower; and providing a steam-heated coil in the alcoholysis tower to ensure stable temperature of the materials in the tower.

[0016] In the technical solution of the present invention, the ethylene-vinyl acetate copolymer flow is preferably a methanol solution of ethylene-vinyl acetate copolymer; the catalyst adopts a common catalyst in the field, and the catalyst flow is preferably a methanol solution of an alkali.

[0017] Preferably, the alcoholysis method of the present invention comprises the following steps:

[0018] a) regulating the methanol vapor logistics pressure by the pressure regulating valve I provided on the methanol vapor logistics pipeline fed through the tower bottom so that the methanol vapor logistics pressure is always greater than the alcoholysis tower reactor pressure.

[0019] b) The distance between the ethylene-vinyl acetate copolymer logistics feed position and the top outlet of the alcoholysis tower is 1 to 6 m, preferably 2 to 3 m.

[0020] c) a cyclone separator is provided on the outlet pipeline of the overhead gas of the alcoholysis tower to prevent the pipeline from being blocked by polymer heavy components and liquid carried in the distillate;

[0021] d) regulating the pressure at the top of the alcoholysis tower by means of a pressure regulating valve II provided on the gas phase logistics pipeline at the cyclone separator outlet to ensure a stable pressure in the tower;

[0022] e) The steam heating coil installed in the alcoholysis tower ensures the temperature of the logistics in the alcoholysis tower is stable.

[0023] f) The catalyst stream may be fed using one feed location or at least two different feed locations.

[0024] In the technical solution of the present invention, the setting formula of the pressure regulating valve I on the methanol vapor logistics pipeline is:

[0025] △P=P1-P2,

[0026] Among them, P1 is the methanol vapor logistics pressure, P2 is the alcoholysis tower bottom pressure, ΔP is the pressure difference between the methanol vapor logistics and the alcoholysis tower bottom pressure, and the pressure difference between the methanol vapor logistics pressure and the alcoholysis tower bottom pressure is controlled to be 1~100kPaG, preferably 20~80kPaG.

[0027] In the technical solution of the present invention, in method a), the pressure of the methanol vapor stream is 0.17 to 0.70 MPaG, preferably 0.22 to 0.50 MPaG.

[0028] In the technical solution of the present invention, the pressure of the alcoholysis tower bottom is 0.15 to 0.60 MPaG, preferably 0.20 to 0.45 MPaG.

[0029] In the technical solution of the present invention, the pressure at the top of the alcoholysis tower is 0.14 to 0.58 MPaG, preferably 0.20 to 0.45 MPaG.

[0030] In the technical solution of the present invention, in method b), 1 to 10 empty trays, preferably 4 to 6 trays, may be provided above the ethylene-vinyl acetate copolymer logistics feed position in the alcoholysis tower, or no tray may be provided above the ethylene-vinyl acetate copolymer logistics feed position.

[0031] In the technical solution of the present invention, in method c), a cyclone separator is provided on the top of the alcoholysis tower to separate the polymer heavy components entrained in the distillate, and the polymer heavy component solution after cyclone separation is refluxed to the alcoholysis tower.

[0032] In the technical solution of the present invention, in method d), a pressure regulating valve II is provided on the gas phase logistics pipeline at the outlet of the cyclone separator to regulate the pressure in the alcoholysis tower to ensure the stability of the pressure in the tower.

[0033] In the technical solution of the present invention, in method e), a steam heating coil is provided in the tower for heating the logistics in the tower to ensure that the temperature of the material in the tower is stable.

[0034] In the technical solution of the present invention, in method f), the ethylene-vinyl acetate copolymer stream and the catalyst stream feed can specifically be:

[0035] The ethylene-vinyl acetate copolymer stream and the catalyst stream are fed from the upper part of the alcoholysis column, wherein the catalyst stream is fed above the ethylene-vinyl acetate copolymer stream; or,

[0036] The catalyst stream is fed in at least two different feeding positions, wherein part of the catalyst stream is fed from the upper part of the alcoholysis tower and the catalyst stream is fed above the ethylene-vinyl acetate copolymer stream, or part of the catalyst stream and the ethylene-vinyl acetate copolymer stream are pre-mixed and then fed together from the upper part of the alcoholysis tower, and the remaining catalyst stream is fed from the middle part of the alcoholysis tower.

[0037] In the technical solution of the present invention, in method f), the pressure of the ethylene-vinyl acetate copolymer stream is 0.40 to 0.90 MPaG, preferably 0.60 to 0.80 MPaG.

[0038] In the technical solution of the present invention, the pressure of the catalyst flow is 0.40 to 0.90 MPaG, preferably 0.60 to 0.80 MPaG.

[0039] In the present invention, both the ethylene-vinyl acetate copolymer (EVAC) solution and the product ethylene-vinyl acetate alcohol copolymer (EVOH) polymer solution are polymer solutions. The viscosity of the system is significantly affected by temperature. When the temperature decreases, the viscosity increases exponentially. Therefore, to avoid excessive system viscosity and blockage of equipment, and to facilitate material transportation, the reaction process is usually carried out at a relatively high temperature. As the alcoholysis reaction proceeds, the concentration of the polymer solution gradually increases from the top of the tower to the bottom of the tower, and the viscosity gradually increases, which deteriorates the heat and mass transfer efficiency. If the tower bottom reboiler is used to provide heat, blockage or local overheating is very likely to occur. Therefore, in the industrial production process, excess methanol is used for purging. On the one hand, the generated small molecular weight methyl acetate can be carried out of the alcoholysis system through azeotropy and excess methanol gas, promoting the continuous progress of the alcoholysis reaction. On the other hand, it can provide sufficient heat to the alcoholysis tower, ensuring the fluidity of the polymer solution and the heat and mass transfer efficiency within the alcoholysis tower. However, in actual industrial production processes, due to pressure fluctuations within the tower, the highly viscous polymer solution in the tower bottom can backflow into the methanol steam line or even the methanol heater, causing equipment blockage. Furthermore, due to the use of excess methanol vapor for purging, when removing the byproduct methyl acetate, some polymer solution is carried out of the alcoholysis column due to entrainment and enters the overhead condensation system, causing condensation system blockage. Therefore, the present invention first installs a pressure regulating valve on the methanol vapor pipeline to adjust the methanol vapor pressure according to changes in the tower bottom pressure to prevent polymer solution backflow and clogging the pipeline. Furthermore, a cyclone separator is installed at the top of the alcoholysis column to separate the polymer solution carried out by the overhead gas through a cyclone before returning the polymer solution to the alcoholysis column. Furthermore, the reserved space between the EVAC polymer solution feed inlet and the tower top is increased to provide sufficient time for the polymer heavy components to fall, preventing the polymer solution from being carried out of the alcoholysis column and entering the condensation system with the overhead gas and clogging the equipment. Finally, a low-pressure steam-heated coil is installed within the tower. This not only provides sufficient heat to the alcoholysis column, ensuring the fluidity of the polymer solution and the occurrence of the alcoholysis reaction, but also prevents clogging of the tower plates. It also reduces the amount of fresh methanol used, thereby lowering the energy consumption of the entire process.

[0040] A second object of the present invention is to provide an anti-blocking device for the alcoholysis process of preparing ethylene-vinyl acetate alcohol copolymer (EVOH) from ethylene-vinyl acetate copolymer (EVAC) methanol solution, which is used to perform the anti-blocking method. The anti-blocking device comprises:

[0041] Alcoholysis tower: It is configured to receive ethylene-vinyl acetate alcohol copolymer logistics at the top, catalyst logistics at the top or the top and middle, methanol vapor logistics at the bottom, discharge alcoholysis tower overhead gas logistics at the top of the tower, and discharge alcoholysis tower bottom liquid logistics at the bottom of the tower;

[0042] Cyclone separator: configured to receive the overhead gas stream of the alcoholysis tower and discharge a light component gas phase stream and a heavy component liquid phase stream;

[0043] Alcoholysis tower top condenser: it is configured to receive the light component gas phase stream separated by the cyclone separator and discharge the condensate;

[0044] Pressure regulating valve I: It is installed on the methanol vapor logistics pipeline entering the bottom of the alcoholysis tower;

[0045] Pressure regulating valve II: It is installed on the gas phase logistics pipeline at the outlet of the cyclone separator;

[0046] Steam heating coil: It is installed in the alcoholysis tower, from the top plate to the bottom of the tower, and is mainly used to heat the liquid on the tower plate.

[0047] In the technical solution of the present invention, further, the anti-blocking device also includes:

[0048] Condensate collection tank: it is configured to receive the condensate discharged from the alcoholysis tower top condenser, and discharge the alcoholysis tower top condensate and alcoholysis tower non-condensable gas;

[0049] Gear pump: It is configured to receive the alcoholysis tower bottom liquid and transport it to the downstream process;

[0050] Reflux pump: It is configured to receive the condensate from the top of the alcoholysis tower and discharge all of it as the top distillate, or discharge a part of it back into the alcoholysis tower and discharge the other part as the top distillate.

[0051] In the technical solution of the present invention, 1 to 10 empty trays, preferably 4 to 6 trays, are provided above the ethylene-vinyl acetate copolymer logistics feed position in the alcoholysis tower, or no tray is provided above the ethylene-vinyl acetate copolymer logistics feed position, and the distance between the feed position and the tower top outlet is 1 to 6 m, preferably 2 to 3 m.

[0052] The method of the present invention can realize the continuous, efficient and smooth progress of the alcoholysis reaction, has the advantages of simple process flow, easy operation, no clogging of process pipelines, long-term stable operation, reduced total energy consumption of equipment and fresh methanol consumption, and easy industrialization.

[0053] All publications, patent applications, patents, and other references mentioned in this specification are incorporated herein by reference. Unless otherwise defined, all technical and scientific terms used in this specification have the meanings conventionally understood by those skilled in the art. In the event of conflict, the definitions in this specification shall prevail.

[0054] When this specification uses the prefix "well known to those skilled in the art", "prior art" or similar terms to introduce materials, substances, methods, steps, devices or components, the objects introduced by the prefix include those commonly used in the art when this application is filed, but also include those that are not commonly used at present but will become generally recognized in the art to be suitable for similar purposes.

[0055] In the context of this specification, except for the contents explicitly stated, any matters or issues not mentioned are directly applicable to those known in the art without any changes. Moreover, any embodiment described herein can be freely combined with one or more other embodiments described herein, and the technical solutions or technical ideas formed thereby are considered part of the original disclosure or original description of the present invention, and should not be regarded as new content not disclosed or anticipated herein, unless a person skilled in the art considers that the combination is obviously unreasonable.

[0056] The present invention will be further described below by way of examples, but is not limited thereto. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Figure 1 Schematic diagram of the process of alcoholysis of ethylene-vinyl acetate copolymer (EVAC) according to an embodiment of the present invention.

[0058] Figure 1 Marking Description:

[0059] 101 alkaline catalyst solution;

[0060] 102 Ethylene vinyl acetate copolymer (EVAC) polymerization liquid;

[0061] 103 methanol vapor;

[0062] 104 Alcoholysis tower overhead gas;

[0063] 105 light component gas phase flow;

[0064] 106 cyclone separator reflux stream;

[0065] 107 light component gas phase condensate;

[0066] 108 Alcoholysis tower does not condense gas;

[0067] 109 alcoholysis tower top condensate;

[0068] 110 alcoholysis tower reflux stream;

[0069] 111 alcoholysis tower overhead stream;

[0070] 112 Alcoholysis tower bottom liquid;

[0071] T101 alcoholysis tower;

[0072] E101 alcoholysis tower top condenser;

[0073] S101 condensate collection tank;

[0074] X101 Cyclone Separator

[0075] H101 steam heating coil;

[0076] P101 reflux pump;

[0077] P102 gear pump;

[0078] PC I pressure regulating valve I;

[0079] PC II Pressure Regulating Valve II.

[0080] Figure 1 In the process, a polymer stream 102 of ethylene-vinyl acetate copolymer (EVAC) is fed into the upper portion of an alcoholysis tower T101. Simultaneously, an alkaline catalyst solution 101 is added from the upper portion of the alcoholysis tower (the alkaline catalyst solution 101 may be added entirely above the polymer stream 102 of ethylene-vinyl acetate copolymer, or may be divided into two streams, one portion added above the polymer stream 102 of ethylene-vinyl acetate copolymer, and the other portion added from the middle portion of the alcoholysis tower). Fresh methanol vapor 103 is introduced into the bottom of the alcoholysis tower. A steam heating coil H101 is provided in the alcoholysis tower for heating the polymer solution in the tower to ensure a stable temperature of the solution in the tower. A pressure regulating valve IPC is provided on the pipeline of the methanol vapor stream 103. I, adjust the pressure of the methanol vapor stream entering the tower to always be greater than the tower reactor pressure; the alcoholysis tower overhead gas stream 104 containing methyl acetate and methanol vapor is obtained at the top of the alcoholysis tower, the alcoholysis tower overhead gas stream 104 is subjected to gas-liquid separation by a cyclone separator X101, the cyclone separator reflux stream 106 (containing the heavy component liquid phase stream of the polymer) is refluxed to the alcoholysis tower, and the light component gas phase stream 105 (gas phase stream) is sent to the alcoholysis tower top condenser E101 for condensation, and a pressure regulating valve II PC is set on the light component gas phase stream 105 pipeline II, control the pressure in the tower to be stable; after condensation, the light component gas phase condensate 107 is sent to the condensate collection tank S101, the non-condensable gas 108 of the alcoholysis tower is discharged, and the alcoholysis tower top condensate 109 is sent to the downstream process as the alcoholysis tower top distillate logistics 111 through the centrifugal pump P101, or the alcoholysis tower top condensate 109 is divided into two streams through the reflux pump P101, one stream is the alcoholysis tower reflux logistics 110 sent to the alcoholysis tower top as reflux, and the other stream is the alcoholysis tower top distillate logistics 111 sent to the downstream process; the alcoholysis tower bottom liquid 112 is sent to the downstream process through the gear pump P102, or is post-treated, and the EVOH product is obtained by washing and drying.

[0081] Figure 2 Schematic diagram of the process of alcoholysis of ethylene-vinyl acetate copolymer (EVAC) according to the comparative example of the present invention.

[0082] Figure 2 Marking Description:

[0083] S101 alkaline catalyst solution;

[0084] S102 Ethylene vinyl acetate copolymer (EVAC) polymer solution;

[0085] S103 methanol vapor;

[0086] S104 alcoholysis tower overhead gas;

[0087] S105 alcoholysis tower overhead gas condensate;

[0088] S106 Alcoholysis Tower Non-condensable Gas;

[0089] S107 alcoholysis tower overhead condensate;

[0090] S108 alcoholysis tower reflux stream;

[0091] S109 alcoholysis tower overhead distillate stream;

[0092] S110 alcoholysis tower bottom liquid;

[0093] T alcoholysis tower;

[0094] E alcoholysis tower top condenser;

[0095] S condensate collection tank;

[0096] P1 reflux pump;

[0097] P2 gear pump;

[0098] H steam heating coil;

[0099] PC pressure regulating valve.

[0100] Figure 2In the process, a polymer liquid stream S102 containing ethylene-vinyl acetate copolymer (EVAC) is fed into the upper part of the alcoholysis tower T. At the same time, an alkaline catalyst solution S101 is added from the upper part of the alcoholysis tower, and fresh methanol vapor S103 is introduced into the bottom of the alcoholysis tower. An alcoholysis tower overhead gas stream S104 containing methyl acetate and methanol vapor is obtained at the top of the alcoholysis tower. The alcoholysis tower overhead gas stream S104 is fed into the alcoholysis tower top condenser E for condensation. A pressure control valve is provided on the alcoholysis tower overhead gas stream S104 pipeline to control the pressure in the tower to be stable. After condensation, the alcoholysis tower overhead gas condensate S104 is obtained. 05 is sent to the condensate collection tank S, the non-condensable gas logistics S106 of the alcoholysis tower is discharged, and the condensate S107 at the top of the alcoholysis tower is sent to the downstream process as the alcoholysis tower top distillate logistics S109 through the centrifugal pump P1, or the condensate S107 at the top of the alcoholysis tower is divided into two streams through the centrifugal pump P1, one is the alcoholysis tower reflux logistics S108 sent to the top of the alcoholysis tower as reflux, and the other is the alcoholysis tower top distillate logistics S109 sent to the downstream process; the alcoholysis tower bottom liquid S110 is sent to the downstream process through the gear pump P2, or is post-processed, and the EVOH product is obtained by washing and drying. DETAILED DESCRIPTION

[0101] The present invention will be described in detail below with reference to specific embodiments. It is necessary to point out that the following embodiments are only used to further illustrate the present invention and are not to be construed as limiting the scope of protection of the present invention. Non-essential improvements and adjustments made by those skilled in the art to the present invention based on the contents of the present invention still fall within the scope of protection of the present invention.

[0102] The technical solution of the present invention is described through embodiments.

[0103] [Example 1]

[0104] The process flow of this embodiment is as follows Figure 1 As shown, the polymerization liquid flow of ethylene-vinyl acetate copolymer (EVAC) contains, by weight percentage, 75 wt% methanol, 25 wt% ethylene-vinyl acetate copolymer, the temperature is 55° C., and the pressure is 0.8 MPaG.

[0105] In terms of weight percentage, the concentration of the sodium hydroxide lye is 5 wt %, the temperature is 25° C., and the pressure is 0.50 MPaG.

[0106] The steam pressure of the heating coil is 0.2MPaG.

[0107] The distance between the EVAC methanol solution feed position and the tower top outlet is 1m.

[0108] The operating pressure of the alcoholysis tower's kettle is set at 0.22±0.01MPaG, and the operating pressure of the methanol vapor is set at 0.25±0.01MPaG. The setting logic for pressure regulating valve I on the methanol vapor logistics pipeline is pressure differential ΔP = 30kPaG. When the kettle's gas-phase pressure exceeds the set value, the valve opening of pressure regulating valve I on the methanol pipeline is increased to increase the methanol vapor flow rate. When the kettle's gas-phase pressure falls below the set value, the valve opening of pressure regulating valve I on the methanol pipeline is increased or maintained to increase or maintain the methanol vapor flow rate until the kettle pressure reaches the set value, ensuring that the methanol vapor logistics pressure remains greater than the pressure within the kettle.

[0109] The operating pressure setting value of the top of the alcoholysis tower is 0.20±0.01MPaG. When the gas phase pressure at the top of the tower exceeds the set value, increase the opening of the pressure control valve to reduce the pressure at the top of the tower to the set value; when the gas phase pressure at the top of the tower is lower than the set value, reduce the opening of the pressure control valve to make the pressure at the top of the tower reach the set value to ensure the stability of the pressure in the tower.

[0110] The unit operated smoothly, with no blockages observed in the methanol vapor or overhead gas pipelines. The pressure within the tower was stable, enabling long-term continuous operation. The alcoholysis tower consumed 10 t / h of methanol vapor stream 103, and the alcoholysis degree of the polymer solution in the alcoholysis tower (EVAC) reached 98.73%.

[0111] [Example 2]

[0112] The process flow of this embodiment is as follows Figure 1 As shown, the polymerization liquid flow of ethylene-vinyl acetate copolymer (EVAC) contains, by weight percentage, 75 wt% methanol, 25 wt% ethylene-vinyl acetate copolymer, the temperature is 55° C., and the pressure is 0.8 MPaG.

[0113] In terms of weight percentage, the concentration of the sodium hydroxide lye is 5 wt %, the temperature is 25° C., and the pressure is 0.50 MPaG.

[0114] The steam pressure of the heating coil is 0.2MPaG.

[0115] The distance between the EVAC methanol solution feed position and the tower top outlet is 1.5m.

[0116] The operating pressure of the alcoholysis tower's kettle is set at 0.24±0.01MPaG, and the operating pressure of the methanol vapor is set at 0.26±0.01MPaG. The setting logic for pressure regulating valve I on the methanol vapor logistics pipeline is pressure differential ΔP = 20kPaG. When the kettle's gas-phase pressure exceeds the set value, the valve opening of pressure regulating valve I on the methanol pipeline is increased to increase the methanol vapor flow rate. When the kettle's gas-phase pressure falls below the set value, the valve opening of pressure regulating valve I on the methanol pipeline is increased or maintained to increase or maintain the methanol vapor flow rate until the kettle pressure reaches the set value, ensuring that the methanol vapor logistics pressure remains greater than the pressure within the kettle.

[0117] The operating pressure setting value of the top of the alcoholysis tower is 0.22±0.01MPaG. When the gas phase pressure at the top of the tower exceeds the set value, increase the valve opening of the pressure regulating valve II to reduce the pressure at the top of the tower to the set value; when the gas phase pressure at the top of the tower is lower than the set value, reduce the valve opening of the pressure regulating valve II to make the pressure at the top of the tower reach the set value to ensure the stability of the pressure in the tower.

[0118] The unit operated smoothly, with no blockages observed in the methanol vapor or overhead gas pipelines. The pressure within the tower was stable, enabling long-term continuous operation. The alcoholysis tower consumed 10 t / h of methanol vapor stream 103, and the alcoholysis degree of the polymer solution in the alcoholysis tower (EVAC) reached 98.82%.

[0119] [Example 3]

[0120] The process flow of this embodiment is as follows Figure 1 As shown, the polymerization liquid flow of ethylene-vinyl acetate copolymer (EVAC) contains, by weight percentage, 75 wt% methanol, 25 wt% ethylene-vinyl acetate copolymer, the temperature is 55° C., and the pressure is 0.8 MPaG.

[0121] In terms of weight percentage, the concentration of the sodium hydroxide lye is 5 wt %, the temperature is 25° C., and the pressure is 0.50 MPaG.

[0122] The steam pressure of the heating coil is 0.2MPaG.

[0123] The distance between the EVAC methanol solution feed position and the tower top outlet is 2m.

[0124] The operating pressure of the alcoholysis tower's kettle is set at 0.26±0.01MPaG, and the operating pressure of the methanol vapor is set at 0.30±0.01MPaG. The setting logic for pressure regulating valve I on the methanol vapor logistics pipeline is pressure differential ΔP = 40kPaG. When the kettle's gas-phase pressure exceeds the set value, the valve opening of pressure regulating valve I on the methanol pipeline is increased to increase the methanol vapor flow rate. When the kettle's gas-phase pressure falls below the set value, the valve opening of pressure regulating valve I on the methanol pipeline is increased or maintained to increase or maintain the methanol vapor flow rate until the kettle pressure reaches the set value, ensuring that the methanol vapor logistics pressure remains greater than the pressure within the kettle.

[0125] The operating pressure setting value of the alcoholysis tower top is 0.24±0.01MPaG. When the gas phase pressure at the top of the tower exceeds the set value, increase the valve opening of the pressure regulating valve II to reduce the pressure at the top of the tower to the set value; when the gas phase pressure at the top of the tower is lower than the set value, reduce the valve opening of the pressure regulating valve II to make the pressure at the top of the tower reach the set value to ensure the stability of the pressure in the tower.

[0126] The unit operated smoothly, with no blockages observed in the methanol vapor or overhead gas pipelines. The pressure within the tower was stable, enabling long-term continuous operation. The alcoholysis tower consumed 10 t / h of methanol vapor stream 103, and the alcoholysis degree of the polymer solution in the alcoholysis tower (EVAC) reached 98.95%.

[0127] [Example 4]

[0128] The process flow of this embodiment is as follows Figure 1 As shown, the polymerization liquid flow of ethylene-vinyl acetate copolymer (EVAC) contains, by weight percentage, 75 wt% methanol, 25 wt% ethylene-vinyl acetate copolymer, the temperature is 55° C., and the pressure is 0.8 MPaG.

[0129] In terms of weight percentage, the concentration of the sodium hydroxide lye is 5 wt %, the temperature is 25° C., and the pressure is 0.50 MPaG.

[0130] The steam pressure of the heating coil is 0.2MPaG.

[0131] The distance between the EVAC methanol solution feed position and the tower top outlet is 2.5m.

[0132] The operating pressure of the alcoholysis tower's kettle is set at 0.28±0.01MPaG, and the operating pressure of the methanol vapor is set at 0.32±0.01MPaG. The setting logic for pressure regulating valve I on the methanol vapor logistics pipeline is pressure differential ΔP = 40kPaG. When the kettle's gas-phase pressure exceeds the set value, the valve opening of pressure regulating valve I on the methanol pipeline is increased to increase the methanol vapor flow rate. When the kettle's gas-phase pressure falls below the set value, the valve opening of pressure regulating valve I on the methanol pipeline is increased or maintained to increase or maintain the methanol vapor flow rate until the kettle pressure reaches the set value, ensuring that the methanol vapor logistics pressure remains greater than the pressure within the kettle.

[0133] The operating pressure setting value of the top of the alcoholysis tower is 0.26±0.01MPaG. When the gas phase pressure at the top of the tower exceeds the set value, increase the valve opening of the pressure regulating valve II to reduce the pressure at the top of the tower to the set value; when the gas phase pressure at the top of the tower is lower than the set value, reduce the valve opening of the pressure regulating valve II to make the pressure at the top of the tower reach the set value to ensure the stability of the pressure in the tower.

[0134] The unit operated smoothly, with no blockages observed in the methanol vapor or overhead gas pipelines. The pressure within the tower was stable, enabling long-term continuous operation. The alcoholysis tower consumed 10 t / h of methanol vapor stream 103, and the alcoholysis degree of the polymer solution in the alcoholysis tower (EVAC) reached 99.03%.

[0135] [Example 5]

[0136] The process flow of this embodiment is as follows Figure 1 As shown, the polymerization liquid flow of ethylene-vinyl acetate copolymer (EVAC) contains, by weight percentage, 75 wt% methanol, 25 wt% ethylene-vinyl acetate copolymer, the temperature is 55° C., and the pressure is 0.8 MPaG.

[0137] In terms of weight percentage, the concentration of the sodium hydroxide lye is 5 wt %, the temperature is 25° C., and the pressure is 0.50 MPaG.

[0138] The steam pressure of the heating coil is 0.2MPaG.

[0139] The distance between the EVAC methanol solution feed position and the tower top outlet is 3m.

[0140] The operating pressure of the alcoholysis tower's kettle is set at 0.30±0.01MPaG, and the operating pressure of the methanol vapor is set at 0.35±0.01MPaG. The setting logic for pressure regulating valve I on the methanol vapor logistics pipeline is pressure differential ΔP = 50kPaG. When the kettle's gas-phase pressure exceeds the set value, the valve opening of pressure regulating valve I on the methanol pipeline is increased to increase the methanol vapor flow rate. When the kettle's gas-phase pressure falls below the set value, the valve opening of pressure regulating valve I on the methanol pipeline is increased or maintained to increase or maintain the methanol vapor flow rate until the kettle pressure reaches the set value, ensuring that the methanol vapor logistics pressure is always greater than the pressure within the kettle.

[0141] The operating pressure setting value of the top of the alcoholysis tower is 0.28±0.01MPaG. When the gas phase pressure at the top of the tower exceeds the set value, increase the valve opening of the pressure regulating valve II to reduce the pressure at the top of the tower to the set value; when the gas phase pressure at the top of the tower is lower than the set value, reduce the valve opening of the pressure regulating valve II to make the pressure at the top of the tower reach the set value to ensure the stability of the pressure in the tower.

[0142] The unit operated smoothly, with no blockages observed in the methanol vapor or overhead gas pipelines. The pressure within the tower was stable, enabling long-term continuous operation. The alcoholysis tower consumed 10 t / h of methanol vapor stream 103, and the alcoholysis degree of the polymer solution in the alcoholysis tower (EVAC) reached 99.21%.

[0143] [Comparative Example 1]

[0144] The process flow of this comparative example is as follows Figure 2 As shown, there is no cyclone separator at the gas phase outlet at the top of the tower.

[0145] The EVAC polymer liquid stream contains, by weight percentage, 75 wt % methanol and 25 wt % EVAC, at a temperature of 55° C. and a pressure of 0.8 MPaG.

[0146] In terms of weight percentage, the concentration of the sodium hydroxide lye is 5 wt %, the temperature is 25° C., and the pressure is 0.50 MPaG.

[0147] The operating pressure of methanol steam is 0.26±0.01MPaG, and there is no pressure regulating valve on the pipeline.

[0148] The operating pressure setting value of the alcoholysis tower kettle is 0.24±0.01MPaG, and the operating pressure setting value of the alcoholysis tower top is 0.22±0.01MPaG.

[0149] The distance between the EVAC methanol solution feed position and the tower top outlet is less than 1m.

[0150] During the operation of the device, the pressure in the tower fluctuated, causing the material to backflow into the steam pipe and even into the methanol steam generator, blocking the pipes and equipment; white polymers were found in the gas phase pipeline at the top of the tower, blocking the instruments and related equipment.

[0151] [Comparative Example 2]

[0152] The process flow of this comparative example is the same as that of comparative example 1, except that a pressure regulating valve is provided on the methanol vapor logistics pipeline.

[0153] The EVAC polymer liquid stream contains, by weight percentage, 75 wt % methanol and 25 wt % EVAC, at a temperature of 55° C. and a pressure of 0.8 MPaG.

[0154] In terms of weight percentage, the concentration of the sodium hydroxide lye is 5 wt %, the temperature is 25° C., and the pressure is 0.50 MPaG.

[0155] The operating pressure of the alcoholysis tower's kettle is set at 0.25±0.01MPaG, and the operating pressure of the methanol vapor is set at 0.26±0.01MPaG. The setting logic for the pressure regulating valve on the methanol vapor logistics pipeline is pressure differential ΔP = 10kPaG. When the kettle's gas-phase pressure exceeds the set value, the valve opening of the methanol pipeline's pressure regulating valve is increased to increase the methanol vapor flow rate. When the kettle's gas-phase pressure falls below the set value, the valve opening of the methanol pipeline's pressure regulating valve is increased or maintained to increase or maintain the methanol vapor flow rate until the kettle pressure reaches the set value, ensuring that the methanol vapor logistics pressure is always greater than the pressure within the kettle.

[0156] The distance between the EVAC methanol solution feed position and the tower top outlet is less than 1m.

[0157] During the operation of the unit, a large amount of white polymer was found in the gas phase pipeline at the top of the tower, blocking the instruments and related pipeline equipment, causing the unit to shut down.

[0158] [Comparative Example 3]

[0159] The implementation of this comparative example is the same as that of Example 5, except that no low-pressure steam heating coil is provided in the alcoholysis tower.

[0160] During operation, the temperature difference within the tower was large, resulting in frequent pressure fluctuations at the bottom and top of the tower. The overall pressure differential in the alcoholysis tower was high, making it prone to backwashing of alcoholysis liquid into the methanol vapor and / or the overhead condensation system pipes and equipment, causing blockage. To maintain the heat of the alcoholysis reaction, the alcoholysis tower consumed a significantly increased volume of methanol vapor stream 103, reaching 15 t / h. The alcoholysis degree of the polymer solution in the alcoholysis tower EVAC reached 99.08%.

Claims

1. A method for preventing blockage in an alcoholysis process for preparing ethylene-vinyl acetate alcohol copolymer, comprising contacting an ethylene-vinyl acetate copolymer stream and a catalyst stream with a methanol vapor stream in opposite directions in an alcoholysis tower to carry out an alcoholysis reaction, wherein: The pressure of the methanol vapor stream is controlled to be always greater than the pressure of the alcoholysis tower kettle; space is reserved above the feed position of the ethylene-vinyl acetate copolymer stream; the overhead gas stream of the alcoholysis tower passes through a cyclone separator installed at the top of the alcoholysis tower, and the heavy component liquid phase stream after cyclone separation is refluxed to the alcoholysis tower; The pressure of the methanol vapor logistics is regulated by a pressure regulating valve I provided on the methanol vapor logistics pipeline introduced into the bottom of the alcoholysis tower so that the methanol vapor logistics pressure is always greater than the pressure of the alcoholysis tower kettle; the pressure at the top of the alcoholysis tower is regulated by a pressure regulating valve II provided on the gas phase logistics pipeline at the outlet of the cyclone separator; and the temperature of the logistics in the alcoholysis tower is ensured to be stable by a steam heating coil provided in the alcoholysis tower.

2. The anti-blocking method according to claim 1, characterized in that: The pressure difference between the methanol vapor flow pressure and the alcoholysis tower kettle pressure is controlled to be 1 to 100 kPaG.

3. The anti-blocking method according to claim 1, characterized in that: The pressure difference between the methanol vapor flow pressure and the alcoholysis tower bottom pressure is controlled to be 20 to 80 kPaG.

4. The anti-blocking method according to claim 1, characterized in that: The distance between the ethylene-vinyl acetate copolymer logistics feed position and the top outlet of the alcoholysis tower is 1 to 6 meters.

5. The anti-blocking method according to claim 4, characterized in that: The distance between the ethylene-vinyl acetate copolymer logistics feed position and the top outlet of the alcoholysis tower is 2 to 3 meters.

6. The anti-blocking method according to claim 1, characterized in that: The pressure of the methanol vapor stream is 0.17 to 0.70 MPaG; and / or, The pressure of the ethylene-vinyl acetate copolymer stream is 0.40 to 0.90 MPaG; and / or, The pressure of the catalyst flow is 0.40-0.90 MPaG.

7. The anti-blocking method according to claim 6, characterized in that: The pressure of the methanol vapor stream is 0.22 to 0.50 MPaG; and / or, The pressure of the ethylene-vinyl acetate copolymer stream is 0.60 to 0.80 MPaG; and / or, The pressure of the catalyst flow is 0.60-0.80 MPaG.

8. The anti-blocking method according to claim 1, characterized in that: The pressure of the alcoholysis tower kettle is 0.15-0.60 MPaG; and / or, The pressure at the top of the alcoholysis tower is 0.14~0.58MPaG.

9. The anti-blocking method according to claim 8, characterized in that: The pressure of the alcoholysis tower kettle is 0.20-0.45 MPaG; and / or, The pressure at the top of the alcoholysis tower is 0.20~0.45MPaG.

10. The anti-blocking method according to claim 1, characterized in that: The ethylene-vinyl acetate copolymer stream and the catalyst stream are fed from the upper part of the alcoholysis column, wherein the catalyst stream is fed above the ethylene-vinyl acetate copolymer stream; or, The catalyst stream is fed in at least two different feeding positions, wherein part of the catalyst stream is fed from the upper part of the alcoholysis tower and the catalyst stream is fed above the ethylene-vinyl acetate copolymer stream, or part of the catalyst stream and the ethylene-vinyl acetate copolymer stream are pre-mixed and then fed together from the upper part of the alcoholysis tower, and the remaining catalyst stream is fed from the middle part of the alcoholysis tower.

11. A device for preventing blockage in the alcoholysis process for preparing ethylene-vinyl acetate alcohol copolymer, for carrying out the anti-blockage method according to any one of claims 1 to 10, comprising: Alcoholysis tower: It is configured to receive ethylene-vinyl acetate alcohol copolymer logistics at the top, catalyst logistics at the top or the top and middle, methanol vapor logistics at the bottom, discharge alcoholysis tower overhead gas logistics at the top of the tower, and discharge alcoholysis tower bottom liquid logistics at the bottom of the tower; Cyclone separator: configured to receive the overhead gas stream of the alcoholysis tower and discharge a light component gas phase stream and a heavy component liquid phase stream; Alcoholysis tower top condenser: it is configured to receive the light component gas phase stream separated by the cyclone separator and discharge the condensate; Pressure regulating valve I: It is installed on the methanol vapor logistics pipeline entering the bottom of the alcoholysis tower; Pressure regulating valve II: It is installed on the gas phase logistics pipeline at the outlet of the cyclone separator; Steam heating coil: It is installed in the alcoholysis tower.

12. The anti-blocking device according to claim 11, characterized in that Further including: Condensate collection tank: it is configured to receive the condensate discharged from the alcoholysis tower top condenser, and discharge the alcoholysis tower top condensate and alcoholysis tower non-condensable gas; Gear pump: It is configured to receive the alcoholysis tower bottom liquid flow and transport it to the downstream process; Reflux pump: It is configured to receive the condensate from the top of the alcoholysis tower and discharge all of it as the top distillate, or discharge a part of it back into the alcoholysis tower and discharge the other part as the top distillate.

13. The anti-blocking device according to claim 11, characterized in that: 1 to 10 empty trays are arranged above the feeding position of the ethylene-vinyl acetate copolymer logistics in the alcoholysis tower, or no tray is arranged above the feeding position of the ethylene-vinyl acetate copolymer logistics.

14. The anti-blocking device according to claim 13, characterized in that: 4 to 6 empty trays are arranged above the ethylene-vinyl acetate copolymer flow feed position in the alcoholysis tower.

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