Method for producing polyvinylidene fluoride in membrane reactor

Abstract

The invention relates to a method for producing polyvinylidene fluoride by polymerizing vinylidene fluoride monomers, in particular using a polymerization reactor containing a membrane.

Description

Technical Field

[0001] The present invention relates to a method for producing polyvinylidene fluoride, and more particularly to a method for forming an interface between a gaseous monomer phase and an aqueous reaction phase under conditions of vinylidene fluoride polymerization in a particularly advantageous manner. Background Art

[0002] Conventional polymerization of vinylidene fluoride (VDF) to give polyvinylidene fluoride (PVDF) is carried out in a discontinuously operated stirred tank reactor. VDF is present in the reactor as a gaseous monomer and must be dissolved in the aqueous phase for polymerization to take place. This requires a phase interface between the monomer and the aqueous phase, which is formed in a stirred tank reactor by the generation of bubbles by the agitator. More precisely, the required phase interface between the gaseous monomer and the aqueous reaction phase is formed by the generation and rupture of bubbles. Therefore, a high mechanical energy input with low efficiency is necessary with regard to the formation of the phase interface.

[0003] Since the solubility of monomers in water is very low, polymerization is severely limited by mass transfer. In addition to the process pressure, the phase interface is the decisive process parameter to reduce this limitation. In order to increase the solubility of monomers in the aqueous phase, polymerization is usually carried out at a pressure of 10-300 bar or even higher.

[0004] In addition to the additional energy input for compressing the gas, the solutions of the existing technology may also be affected by safety issues, especially in the presence of large amounts of flammable gases in the reactor at high pressures and temperatures. In addition, the traditional production of PVDF uses fluorinated emulsifiers, which are environmentally persistent and harmful to health. Although the use of earlier emulsifiers such as perfluorooctanoic acid (PFOA) has been banned in the EU since 2020, alternatives that only slightly differ from PFOA in chemical structure are used, which are also fluorinated emulsifiers with potential environmental persistence and bioaccumulation.

[0005] US2002 / 123585 A1 describes a method for continuously producing a PVDF homopolymer or copolymer. The optional comonomer is composed of a free radical polymerized vinyl group and includes at least one fluorine atom, a fluoroalkyl group or a fluoroalkoxy group, directly bonded to the vinyl group. The invention also relates to a PVDF homopolymer produced by the method. With regard to the polymerization of PVDF, the invention particularly describes a high pressure method using more than 300 bar.

[0006] DE 102020102420A1 describes a gas-liquid reactor for gasifying a process liquid with a process gas without bubbles, the reactor having at least one reactor housing, a stirring device and a gasification device, the gasification device having a feed pipe for feeding the process gas into the reactor, wherein the feed pipe for the process gas terminates in a first gas receiving space in the reactor, the membrane of which is connected to a plurality of membranes in a gas-tight manner, the membranes being selected from a group consisting of a diffusion membrane, a microfiltration membrane or a combination of at least two membrane types; the process gas passes through these membranes into a second gas receiving space in the reactor, which is connected to the other end of the membrane in a gas-tight manner. The two gas receiving spaces are arranged concentrically with the stirrer shaft of the stirring device and can be mechanically connected to each other, wherein the gas receiving space and the membrane arranged therebetween form a cylindrical shell in the reactor, and the arrangement of the membrane relative to the stirrer axis is selected from a group consisting of orthogonal-concentric or axial-concentric. This reactor is used to provide oxygen to bacteria in a nutrient medium.

[0007] However, the solutions known from the prior art may still have potential for improvement, in particular with regard to the efficient polymerization of vinylidene fluoride for the production of polyvinylidene fluoride and / or copolymers thereof. Summary of the invention

[0008] Therefore, it is an object of the present invention to provide a method which at least partially overcomes at least one disadvantage of the prior art. In particular, it is an object of the present invention to provide a solution which enables efficient production of polyvinylidene fluoride.

[0009] According to the invention, the problem is solved by a method having the features of claim 1, preferred embodiments of the invention being disclosed in the dependent claims, the description and the drawings, wherein the further features described or disclosed in the dependent claims, the description or the drawings may illustrate the subject matter of the invention alone or in any desired combination, unless the context clearly indicates otherwise.

[0010] In view of the above technical status, the present invention aims to provide a method for producing polyvinylidene fluoride or a polyvinylidene fluoride copolymer by polymerizing at least vinylidene fluoride as a monomer, wherein the method comprises at least the following steps:

[0011] (1) providing a continuously operable polymerization reactor, the polymerization reactor comprising a monomer space and a polymerization space, wherein the monomer space and the polymerization space are separated by a preferably hydrophobic membrane;

[0012] (2) introducing vinylidene fluoride into the monomer space at a first pressure p1;

[0013] (3) introducing an aqueous polymerization solution into the reaction space at a second pressure p2; wherein

[0014] (4) p1 is greater than, equal to, or less than p2;

[0015] (5) vinylidene fluoride enters the water phase; and

[0016] (6) Vinylidene fluoride is polymerized in the reaction space to obtain polyvinylidene fluoride or a polyvinylidene fluoride copolymer.

[0017] This process can advantageously polymerize vinylidene fluoride and optionally other monomers to produce polyvinylidene fluoride or optionally polyvinylidene fluoride copolymers.

[0018] The method comprises at least the following steps, wherein the process steps described below can be performed in the specified order, but can also be performed at least partially simultaneously or in a different order:

[0019] Step (1) first includes a polymerization reactor that can be operated continuously, wherein the polymerization reactor includes a monomer space and a polymerization space, wherein the monomer space and the polymerization space are separated by a membrane.

[0020] In particular, the polymerization reactor in the method is operated continuously, and the efficiency advantages brought by it are understood by those skilled in the art. In particular, when operated in a continuous mode, the method described herein has advantages over the stirred tank reactors of the prior art, because the setup and purification time between batches greatly reduces the space-time yield of the stirred tank.

[0021] Furthermore, a polymerization reactor can in principle be any object which meets the definition and in which the process can be carried out.

[0022] To this end, the polymerization reactor comprises a monomer space and a polymerization space. Both spaces are equipped and preferably connected to suitable peripheral devices, such as, in particular, discharge and feed lines, so that one or more monomers can be introduced into the monomer space and, correspondingly, an aqueous reaction solution can be introduced into the polymerization space for polymerization.

[0023] Therefore, the monomer space and the polymerization space (also referred to as the reaction space) may preferably have corresponding pressure resistance. An appropriate temperature control device may also be provided, preferably for heating or cooling the reactor or the medium in the reactor.

[0024] The monomer space and the polymer space are further separated by a membrane.

[0025] The membrane is preferably hydrophobic. In the context of the present invention, "hydrophobic membrane" means that the membrane exhibits hydrophobic properties with respect to water. This in turn means, for example, that the contact angle (also called wetting angle) of ultrapure water (conductivity ≤ 1.1 μS / cm at 20° C., total organic carbon ≤ 0.5 mg / l, nitrate ≤ 0.2 mg / l) is greater than 75°. In the case of corresponding contact angles below 75°, reference may be made according to the present invention to the hydrophilic membrane or the hydrophilic properties of the membrane.

[0026] In principle, there are different approaches to making a membrane hydrophobic, as described in detail below. For example, the membrane itself can be formed from a hydrophobic material or it can be formed from a non-hydrophobic or slightly hydrophobic material and have a coating that exhibits or improves the corresponding hydrophobic properties.

[0027] However, according to the invention, the membrane may also be hydrophilic. Advantageously, for example, a hydrophilic membrane or a hydrophobic membrane with a hydrophilic coating, such as polyethylene glycol (PEG), polyvinyl alcohol (PVA), polyethylene glycol diacrylate (PEGDA), poloxamers, meroxapol and / or cross-linked mixtures comprising at least one of the aforementioned components, is used. The filter cake may also be hydrophilic. In particular, very thin hydrophilic layers have little effect on the gas transport, but have great advantages in preventing deposits (PVDF particles, emulsifiers) or fouling on the membrane that would reduce the mass transfer.

[0028] For example, the membrane is also porous, i.e. has pores connecting the monomer space and the polymerization space. The shape, distribution, number and size of the pores can be freely selected as long as it ensures that the monomer gas can enter the polymerization space from the monomer space, and in particular, the aqueous solution can be prevented from entering the monomer space.

[0029] In this case, the shape and size of the hole can be arranged to facilitate the monomer gas to enter the liquid in the reaction space without bubbles under the reaction conditions. For this reason, the hole can be adapted to the material of the film, particularly adapted to the characteristics of the film. Therefore, it is possible to avoid the operation of breaking bubbles by high energy input. By the hydrophobic nature of the film with appropriate pressure characteristics in the monomer space and the polymerization space, it is possible to achieve the bubble-free introduction of the monomer gas. Therefore, steps (2) and (3) preferably can introduce the monomer gas (particularly vinylidene fluoride) into the aqueous solution in a bubble-free manner.

[0030] The membrane may also be non-porous. In this case, for example, an embodiment with a PDMS (polydimethylsiloxane) coating may be provided, which is dielectrically tight or non-porous. For mass transfer, a monomer passage in the sense of a monomer or solution diffusion model may be assumed, such as described in Membrane Technology and Applications, Richard W. Baker, Wiley, 2004.

[0031] For polymerization, it is further specified that, according to step (2), vinylidene fluoride is introduced into the monomer space at a first pressure p1, and according to step (3), the polymerization aqueous solution (which can also be referred to as the reaction solution) is introduced into the reaction space at a second pressure p2. More precisely, p1 mentioned here is greater than or equal to or less than p2.

[0032] For the polymerization solution, it is preferred to remove oxygen in it and in the aqueous process fluid entering the reactor before entering the reactor. For this purpose, for example, the liquid storage container is filled with nitrogen, and a degasser, such as a membrane degasser capable of removing the gas dissolved in the liquid, is arranged upstream of the pump for transporting the aqueous process fluid. In principle, certain gases in the monomer stream, such as oxygen, should be removed as much as possible and preferably be oxygen-free.

[0033] The corresponding pressure range can be selected according to specific requirements, including the magnitude of the pressure and the ratio of p1 and p2.

[0034] For example, an operation with p2 > p1 can be carried out. This further inhibits the formation of bubbles, but since mass transfer is driven by concentration and the two phases remain in contact on the pore / membrane surface, mass transfer is still possible.

[0035] While in the case of operating with p2 < p1, gas can be introduced into the aqueous phase particularly effectively, thus ensuring a high conversion rate because the amount of gas introduced is relatively high.

[0036] In the case of operating with p2 = p1, relatively few bubbles can be introduced at a relatively high conversion rate.

[0037] Accordingly, appropriate polymerization conditions are set in the polymerization reactor, more precisely, in the monomer space and the polymerization space. More precisely, the monomer in the monomer space can pass through the membrane into the polymerization space. This is achieved according to step (5), according to which vinylidene fluoride and any provided comonomers enter the aqueous phase.

[0038] Then, according to step (6), the polymerization of vinylidene fluoride may occur accordingly in the aqueous phase of the polymerization space, thus forming polyvinylidene fluoride. As mentioned above, in addition to vinylidene fluoride, other monomers can also be introduced into the monomer space or the polymerization space to produce polyvinylidene fluoride copolymers.

[0039] The formed polymer, especially polyvinylidene fluoride, can be discharged from the reactor after the reaction. Especially in the case of continuous operation of the reactor, it can be separated from the aqueous phase and can be optionally washed and dried.

[0040] This process has obvious advantages compared with the solutions in the prior art.

[0041] Using the above method, in particular using the continuous membrane reactor described, a gas-liquid phase interface can be formed with only very few gas bubbles (if any). To this end, the membrane acts as a contactor between the two phases, namely the gaseous monomer phase and the liquid polymer phase. The membrane can separate the two phases from each other.

[0042] The invention forms the necessary phase interface in a continuous (e.g. tubular) reactor by means of a membrane and has shown that polymerization can be carried out in this reactor without the use of fluorinated emulsifiers, in other words, the process or the polymerization phase does not contain fluorinated emulsifiers. On the contrary, the process described can avoid the use of emulsifiers or use emulsifiers selected from meroxapols and poloxamers, which can be used without problems or at least with significantly reduced potential risks.

[0043] This can therefore be very advantageous, since fluorinated emulsifiers are highly polluting to the environment, their use on an industrial scale has hitherto been a problem with conventional production processes, and even obtaining substitutes for PFOA can be difficult and can only be used disadvantageously. The present invention can avoid the disadvantages of the prior art, such as the use of stirred tank reactors, which produce large amounts of aqueous solutions containing environmentally hazardous substances (e.g. PFOA or similar substitutes) that need to be disposed of.

[0044] In addition to the emulsifier, it is also important for the polymerization reaction to provide an initiator, which can be introduced, for example, with the aqueous reaction solution.

[0045] The invention also makes it possible to avoid the input of mechanical energy, for example by using an active stirrer, such as the stirred tank reactor known in the prior art. This not only reduces the energy consumption of the reaction, but also makes the design of the polymerization reactor simpler and more cost-effective. This is a significant advantage compared to the solutions in the prior art, since the use of a stirrer to generate the phase interface for the gas introduction requires a high input of mechanical energy into the reactor, of which only a small part is used to generate the phase interface between the monomer gas and the aqueous phase, and is therefore less efficient.

[0046] The present invention also avoids the use of high process pressures, which are usually necessary according to the prior art, but which are also disadvantages of the prior art production processes from the perspective of energy and process safety. For example, a large amount of flammable gases are generated in the prior art reactor under high pressure.

[0047] The invention further makes it possible to realize a continuous process in a flow tube reactor, which eliminates the cleaning and set-up times in batch operation. This is particularly advantageous because batch operation in PVDF production to date has been characterized by long polymerization times and long cleaning and set-up times required before the next batch can be produced in the reactor. Due to the strong growth in the demand for PVDF on the world market, especially due to the use of this material in battery production, economical and efficient production processes will become increasingly important in the future, and the process according to the invention can also achieve particular advantages in this regard.

[0048] The use of this polymerization reactor to polymerize vinylidene fluoride can advantageously control local reaction conditions such as pressure, temperature and concentration (p, T, C). This can eliminate the corresponding defects of batch reactors, and complex design, process and product quality control that cannot be achieved using current batch reactors will become possible.

[0049] The use of stirred tanks according to the invention, in particular with regard to the prior art, is also advantageous, since the mixing effect is very good, the residence time of the reactants is very uniform, and the concentration distribution in the reaction phase is also very uniform. This in turn allows the reaction conditions to be very defined and reliable.

[0050] The present invention also overcomes the disadvantages of stirred reactors, namely, the generation of temperature gradients in the stirred tank due to the low volume-to-surface ratio and poor heat input / output, which in turn leads to uneven reaction conditions.

[0051] Therefore, the method of the present invention can make the product quality very uniform and avoid the variation of product quality between different batches. Although the polymerization reaction is very sensitive to the variation of process parameters, according to the above-mentioned present invention, the process parameters are uniform and determined, so there will be no problem. In contrast, in the prior art stirred tank, the failure to reach the so-called steady state in the reactor leads to the process parameters constantly changing, and the variation varies from batch to batch, which has an adverse effect on the product quality.

[0052] Finally, in the case of stirred tanks, scale-up would lead to an exacerbation of the above problems, but this is easily achieved according to the present invention.

[0053] Preferably, the membrane comprises at least one of a ceramic and a polymer. It has been found that in particular these materials can be used to form membranes which are or may be particularly advantageous in terms of porosity and hydrophobicity for the method according to the invention, in particular can withstand the reaction conditions or show long term stability. The membrane may comprise only ceramic, only polymer or a combination of ceramic and polymer.

[0054] When using polymers, such as polyolefins or polyolefin copolymers, in particular preferably polypropylene, it may be advantageous that the above-mentioned properties are accompanied by inherent hydrophobic properties. Therefore, its production may be particularly advantageous. The membrane can also be made of polydimethylsiloxane (PDMS) or polytetrafluoroethylene (PTFE), for example in a media-tight or non-porous form or in a porous form.

[0055] Particularly advantageous stability properties can be achieved by using ceramic materials, such as preferably aluminum oxide (Al2O3), to produce the membrane. Therefore, the membrane may in particular include a carrier layer, also referred to as a support, made of aluminum oxide. Aluminum oxide can also be used as an active layer for controlling or influencing the passage of gases. Ceramic membranes can also include an active layer of titanium dioxide (TiO2) or zirconium dioxide (ZrO2), which can be arranged, for example, on the aluminum oxide layer.

[0056] As mentioned above, membrane also includes ceramics and plastics. In order to obtain hydrophobic properties, for example, a hydrophobic coating can be provided for ceramics. Suitable materials for this coating also include polymers, such as polytetrafluoroethylene (PTFE) or polydimethylsiloxane (PDMS), which can also be used for ceramic supports, such as supports composed of aluminum oxide. The coating can especially be located on the reaction side, i.e., one side of the aqueous medium, and can further be used as an active layer.

[0057] Thus, the polymer can be applied as a coating or, for example, act as a filter cake, introduced between the support layer and the active layer of the membrane.Polymer particles, such as PTFE particles or PDMS particles, may be present in the membrane structure close to the surface.

[0058] Therefore, it is preferred in principle that the membrane is made of a material selected from the group consisting of aluminum oxide, titanium dioxide, zirconium dioxide, polytetrafluoroethylene, polydimethylsiloxane and polypropylene.

[0059] Alternatively, the membrane may also exhibit hydrophilicity, including, for example, polyethylene glycol (PEG), polyvinyl alcohol (PVA), polyethylene glycol diacrylate (PEGDA), poloxamer, meroxapol, and / or a cross-linked mixture comprising at least one of the foregoing.

[0060] Preferably, the pressure difference between p1 and p2 is in the range of ≤2 bar. Particularly preferably, the embodiment can introduce the monomer into the aqueous polymerization phase without bubbles. In particular, in the embodiment, it is further possible to operate at low pressure, which can reduce the requirements for equipment settings and simplify the entire process. In particular, a low transmembrane pressure may be particularly advantageous for the choice of membrane, because the membrane is not subjected to any significant mechanical forces due to the pressure difference. Therefore, the process pressure (i.e. p1 and p2) may be relatively high, without the membrane being subjected to high mechanical stress.

[0061] Regarding the specific reaction pressure, as one of the preferred embodiments, the pressure in the polymerization reactor, i.e., the pressure of the monomer phase (i.e., in the monomer space) and the pressure of the reaction phase (i.e., in the polymerization space) are both within the range of ≤50 bar (e.g., ≤30 bar), particularly preferably ≤10 bar. This can reduce equipment requirements, thereby increasing complexity and reducing costs.

[0062] With regard to the structure of the reactor, it may be further advantageous if the polymerization reactor comprises a plurality of tubular membranes, in particular connected in series, arranged in a common reactor housing. This embodiment ensures in a simple manner, through the series connection of the individual component membranes, that the travel path of the components along the reactor is very long. This makes it possible to achieve a long contact between the monomer phase and the reaction phase in a relatively compact reactor, thereby ensuring a high conversion rate and increasing the efficiency of the process. This also makes it possible to achieve the production of polymers with a relatively high molecular weight.

[0063] In this embodiment, for example, the aqueous reaction medium can react inside the preferably cylindrical membrane and the monomer gas can react in a reactor outside the membrane. However, in principle, the opposite reaction mode can also be adopted, i.e. the monomer gas reacts inside the membrane and the reaction medium reacts in a reactor outside the membrane. However, the former mode may be particularly advantageous in terms of the molecular weight produced.

[0064] Further preferably, the membrane comprises a plurality of fluid channels connected in series. In this embodiment, there may be multiple channels inside the membrane, so that the path of travel of the assembly along the reactor can be ensured to be very long by the series connection of each membrane. This makes it possible to achieve a relatively compact reactor with a longer contact time of the monomer phase and the reaction phase, thereby ensuring a high conversion rate and / or achieving a high molecular weight. The aqueous phase is preferably supplied to the inner cavity of the membrane, and the gas phase is located at the shell side, wherein the reactor shell can surround the membrane. In other words, monomer gas can flow from the outside around the membrane. This structure can achieve a particularly high pressure, thereby improving the solubility of the monomer in the aqueous reaction medium.

[0065] However, the parallel connection of a plurality of membranes or a plurality of flow channels may in principle also be advantageous. This allows more reaction medium to flow through the reactor simultaneously, which can also lead to advantages in terms of throughput (ie reaction volume).

[0066] In principle, when the reactor has a cylindrical winding-like structure, i.e. the overall structure of the membrane and the reactor housing comprises the corresponding windings. This makes it possible to further minimize the size of the reactor and further generate secondary flows in the form of Taylor vortices, which lead to better mixing of the aqueous phase. This makes it possible to further improve the polymerization conditions. In particular in this embodiment, the parallel connection of a plurality of membranes or polymerization spaces can be advantageous, since the winding ensures a long residence time even in the case of limited space, so that a series connection is generally not required.

[0067] For the above-mentioned series connection of the individual channels, it is possible to provide that the membrane of the polymerization reactor is sealed at the respective axial end by a cap structure, which comprises a deflection structure connecting the individual channels. The connection of the individual channels is easy to implement in terms of equipment and at the same time allows simple maintenance and safe sealing of the reactor membrane.

[0068] Preferably, a static mixer structure is provided in the polymerization space. This mixer structure can also be understood as a structure capable of introducing radial flow components into the liquid reaction medium. This makes the concentration in the reaction phase more uniform, allowing more monomers to be absorbed in the reaction phase without changing the maximum monomer concentration. This can improve the polymerization conversion rate and / or the efficiency of the polymerization process. It can also prevent the initial solid particles of the polymer formed on the membrane from being deposited, thereby preventing the polymerization reactor from being blocked. It can also reduce the sediment on the membrane surface and the adverse effects on the reaction thereby produced (these sediments may not necessarily cause blockage, but will hinder or delay the transportation of monomers from the monomer space to the reaction space).

[0069] Further preferably, at least one of the membrane and the mixer structure is provided with a catalyst. For example, the catalyst may be fixed on the surface of the membrane or the mixer structure, or may be contained in an additional coating. The catalyst that may be selected includes, but is not limited to, a Ziegler-Natta catalyst. Providing a catalyst on the membrane or the mixer structure may have a further positive effect on the polymerization, for example, may have a positive effect on the distribution of molecular weights.

[0070] Further preferably, the process is carried out in at least two polymerization reactors connected in series. This embodiment can substantially achieve the advantages described above for the series connection of membranes. In particular, the residence time of the polymerization solution in the polymerization reactor and the polymerization time may be extended, which can have a favorable effect on the molecular weight of the produced polymer. This is also possible when the residence time of the individual membranes is relatively short. This also allows simple changes in temperature management during the reaction. For example, different heating belts are arranged around the reactors so that the first reactor is heated to a greater extent than the subsequent reactors.

[0071] Preferably, in a polymerization reactor, a material flow can be introduced or discharged between two membranes in series or between two flow channels in series or between two polymerization reactors in series. Thus, a polymer flow can be removed or further initiators or chain transfer agents can be introduced into the polymer flow more advantageously, thereby influencing the molecular weight distribution of the product. The length of the connected reactors or membranes can be adjusted so that the initiator or other additives can be added precisely at the desired time. BRIEF DESCRIPTION OF THE DRAWINGS

[0072] Figure 1: shows an apparatus including a polymerization reactor for use in the process of the present invention;

[0073] Figure 2 : Shows the Figure 1 An enlarged view of an embodiment of a polymerization reactor of the apparatus;

[0074] Figure 3 : shows the film of the polymerization reactor;

[0075] Figure 4 : Shows the Figure 3 A membrane polymerization reactor;

[0076] Figure 5 : Displayed Figure 4 A detailed view of the polymerization reactor and in particular the cap structure shown;

[0077] Figure 6 : A further embodiment view of a polymerization reactor is shown.

[0078] Explanation of the reference numerals: 10 device; 12 polymerization reactor; 13 pressure controller; 14 liquid reservoir; 16 tank; 17 degasser; 18 liquid reservoir; 19 pump; 20 filtering device; 21 overflow valve; 22 polymer medium product; 24 filtrate; 26 recovery stream; 28 purge stream; 30 monomer space; 32 monomer stream; 34 membrane; 36 polymerization space; 38 polymerization medium stream; 40 reactor housing; 42 phase interface; 46 heating belt; 48 flow channel; 50 cap; 51 seal; 52 deflection structure; 53 seal; 54 end piece. DETAILED DESCRIPTION

[0079] The following examples are used to further illustrate the present invention, but are not intended to limit the effective scope of the present invention in any way.

[0080] The present invention is explained by referring to the drawings and embodiments. The features shown below may represent one aspect of the present invention alone or in combination. The present invention includes but is not limited to the following drawings, the following description and the following exemplary embodiments.

[0081] Figure 1 An apparatus 10 is shown, which includes a polymerization reactor 12 for performing the method of the present invention. The method can produce polyvinylidene fluoride by polymerizing vinylidene fluoride. In addition to vinylidene fluoride, other monomers can also be added to produce polyvinylidene fluoride copolymers, and the following embodiments related to the production of polyvinylidene fluoride are also applicable accordingly.

[0082] exist Figure 1In the device 10 shown, the gaseous monomer vinylidene fluoride is taken from a reservoir 14 and enters a polymerization reactor 12. A pressure controller 13, such as a pressure reducer or a compressor, which can be selected according to the prevailing pressure in the reservoir 14, is arranged downstream of the reservoir 14. In addition, an aqueous polymerization solution is passed to the polymerization reactor 12. For example, water, optionally including an initiator, can be drawn from a tank 16, and an emulsifier can be added to a tank 18, for example also in the form of an aqueous solution, mixed with the water. One or both of the tanks 16, 18 can be preheated to achieve an initial decomposition of the initiator and to ensure that free radicals that promote polymerization are already present at the reactor inlet. Of course, preheating can also be carried out in the conduit leading to the polymerization reactor 12. It is also possible not to separate the two tanks 16, 18, but to use only one tank containing the initiator and the emulsifier in water.

[0083] The figure also shows that a degasser 17, such as a membrane degasser, can be provided between the tanks 16, 18 and the polymerization reactor 12, for example upstream of the pump 19, to remove as much oxygen as possible from the solution in the polymerization reactor 12. This is important because oxygen has an inhibitory effect on the reaction and should be removed from all process streams. Therefore, the tanks 16, 18 can also be purged with an inert gas (e.g. nitrogen or argon) to minimize the initial oxygen content upstream of the degasser 17.

[0084] The polymerization reaction is carried out in the polymerization reactor 12, as described in detail below. In general, the polymerization reactor 12 is provided with a membrane 34, for example, which is porous and hydrophobic or hydrophilic, to ensure an optimal phase interface between the gaseous monomer and the aqueous phase, as described below.

[0085] The outlet of the polymerization reactor 12 is connected to an optional filtering device 20, in which the polymer product 22, i.e., solid PVDF particles, produced can be selectively separated from the aqueous phase. Thus, water or filtrate 24 can be recovered in a recovery stream 26 and further purified in a loop to be reused in the polymerization process. A purge stream 28 can be used to prevent the enrichment of additives or impurities during the reaction. The polymer product 22 can be purified and correspondingly obtained in the form of a purified product. Of course, the product stream extracted from the polymerization reactor 12 can also be used immediately.

[0086] The overflow valve 21 , which may also be referred to as a back pressure regulator, is disposed downstream of the polymerization reactor 12 , for example, upstream of the filtering device 20 .

[0087] Various embodiments of polymerization reactor 12 are described below. Polymerization reactor 12, as shown below, may be used in apparatus 10 as described above, including but not limited to.

[0088] like Figure 2As shown, the polymerization reactor 12 includes a monomer space 30 and a polymerization space 36, wherein the monomer space 30 is used to receive the monomer gas as a monomer flow 32, and the polymerization space 36 is separated from the monomer space 30 by a hydrophobic or hydrophilic and optionally porous membrane 34, and is used to receive an aqueous polymerization solution as a flow 38 of the polymerization medium. The polymerization space 36 is delimited outwardly by a reactor shell 40, and the reactor shell 40 can have a tubular structure like the membrane 34. The monomer space 30 and the polymerization space 36 can also be interchangeable in principle. In the figure, the monomer flow 32 and the polymerization flow 38 are in the same direction, but they can also be countercurrent in principle.

[0089] Figure 2 The enlarged view of the embodiment of the invention particularly shows the monomer space 30 and the polymerization space 36, wherein the monomer flow 32 and the polymerization medium flow 38 separated by the membrane 34 are shown. The membrane 34 can be porous or dielectric-tight. The monomer gas can enter the polymerization solution through the membrane 34, in particular to form polymers by emulsion polymerization. For this purpose, the aqueous phase or the polymerization solution can be preheated before entering the polymerization reactor 12, and the polymerization reactor 12 itself can be temperature-controlled, for example by means of heating belts 46 on the reactor housing 40 or by immersing the polymerization reactor 12 in a heating bath, for example using temperature-controlled oil. As mentioned above, the process pressure can be established by a proportional relief valve.

[0090] The membrane 34 and the pressure difference between the two phases stabilize the phase interface 42 and prevent water or gas from breaking through to the other side of each. This allows the monomer to enter the aqueous reaction phase without bubbles throughout the length of the polymerization reactor 12, thereby ensuring that the aqueous phase is completely saturated with monomer and that the maximum amount of monomer is available for polymerization.

[0091] The continuously operable polymerization reactor 12 and its improved mass transfer performance enable continuous production of PVDF at lower process pressures, without mechanical energy input, and with shorter residence times. In particular, PVDF can be continuously produced at pressures below 20 bar and residence times of less than 1 hour. It is preferred not to use fluorinated emulsifiers. Available emulsifiers include various meroxapols or poloxamers. These emulsifiers are harmless to humans and the environment and are also used in products such as cosmetics, so they can also be used without problems in the polymerizations performed here.

[0092] Figure 3 An embodiment of a membrane 34 is shown, Figure 4 Shows Figure 3 The corresponding use of the membrane 34 in the polymerization reactor 12. The polymerization reactor 12 can be particularly suitable for non-flexible or rigid membranes 34.

[0093] The membrane 34 comprises a plurality of fluid channels 48, which can be connected in series or are connected in series, and which can also be referred to as lumens. For example, up to 19 or more fluid channels 48 can be provided. For example, the membrane 34 has an average pore size of 50 nm and a length of 200 mm, which in the present case is 19 parallel fluid channels 48. Thus, the polymerization medium stream 38 can flow through these fluid channels in sequence, and then the monomer stream 32 can flow out of the membrane 34 and flow into the interior of the reactor housing 40.

[0094] To achieve the serial connection of the flow channels 48 , a suitable cap 50 may be provided having a deflection structure 52 that deflects the polymerizing medium flow 38 between the flow channels 48 . Figure 5 These structures are shown in more detail in This gives an example lumen-side total length of membrane 34 of 3.8 m.

[0095] Figure 4 and Figure 5 The polymerization reactor 12 shown can also be further configured as follows Figure 1 The overflow valve 21 is shown.

[0096] The polymerization reactor 12 may be sealed in the axial direction using corresponding end pieces 54 . Figure 4 and Figure 5 Further shown is the seal 51, here an O-ring, by means of which the cap 50 can be connected in a liquid-tight and gas-tight manner to the end piece 54. Also shown is a seal 53, in particular in the form of a sealing disc, by means of which the membrane 34 can be connected in a liquid-tight and gas-tight manner to the cap 50.

[0097] Figure 6 A further embodiment of a polymerization reactor 12 is shown. Figure 6 As shown, the polymerization reactor 12 comprises a plurality of tubular membranes 34, which are in particular connected in parallel and arranged in a common reactor housing 40. This embodiment may be particularly suitable for flexible membranes 34.

[0098] also, Figure 6 The polymerization reactor 12 is also shown to have a cylindrical wound structure. Although the reaction duration is relatively long, this embodiment can save space or be compact.

[0099] More specifically, for example, a membrane 34 made of polypropylene, having an average pore size of 100 nm and a length of 3 m is used. A plurality of membranes 34 as described above are mounted in a cylindrically wound stainless steel tube, the total length of the reactor housing 40 being 2.5 m, and sealed at the ends of the reactor, for example with epoxy resin, so that the gas phase is introduced into the lumen channel or fluid channel 48 of the membrane 34, and the aqueous phase flows around the membrane 34 on the shell side. In order to provide the minimum temperature required for the reaction of about 75° C., the polymerization reactor 12 can be temperature-controlled accordingly. In order to establish the necessary process pressure in the aqueous phase, for example, a proportional overflow valve 21 can be used downstream of the reactor outlet, such as Figure 1 In principle, it is advantageous to control the temperature of the polymerization solution within the range of 50°C to 100°C.

Claims

1. A method for producing polyvinylidene fluoride or a polyvinylidene fluoride copolymer by polymerization of at least a monomer of vinylidene fluoride, wherein: The method comprises at least the following steps: (1) A continuously operable polymerization reactor (12) is provided, wherein the polymerization reactor (12) comprises a monomer space (30) and a polymerization space (36), wherein the monomer space (30) and the polymerization space (36) are separated by a membrane (34); (2) introducing vinylidene fluoride into the monomer space (30) at a first pressure p1; (3) introducing an aqueous polymerization solution into the polymerization space (36) at a second pressure p2; wherein (4) p1 is greater than, equal to, or less than p2; (5) vinylidene fluoride enters an aqueous polymerization solution; and (6) Vinylidene fluoride is polymerized in the polymerization space (36) to obtain polyvinylidene fluoride or a polyvinylidene fluoride copolymer.

2. The method according to claim 1, characterized in that The membrane (34) includes at least one of a ceramic and a polymer.

3. The method according to claim 2, characterized in that The membrane (34) is made of a material selected from the group consisting of aluminum oxide, titanium dioxide, zirconium dioxide, polytetrafluoroethylene, polydimethylsiloxane and polypropylene.

4. The method according to any one of claims 1 to 3, characterized in that Steps (2) and (3) are performed in such a manner that the monomer gas can be introduced into the aqueous polymerization solution without bubbles.

5. The method according to any one of claims 1 to 4, characterized in that: The pressure difference between p1 and p2 is in the range of ≤ 2 bar.

6. The method according to any one of claims 1 to 5, characterized in that: The pressure in the polymerization reactor (12) is in the range of ≤ 50 bar.

7. The method according to any one of claims 1 to 6, characterized in that: The polymerization reactor (12) comprises a plurality of tubular membranes (34), in particular connected in series, which are arranged in a common reactor housing (40).

8. The method according to any one of claims 1 to 7, characterized in that: The membrane (34) comprises a plurality of fluid channels (48) which are connected in series.

9. The method according to any one of claims 1 to 8, characterized in that: The polymerization reactor (12) has a cylindrical wound structure. In particular, at least two membranes (34) connected in parallel are present in the polymerization reactor (12).

10. The method according to any one of claims 1 to 9, characterized in that: A static mixer structure is arranged in the polymerization space (36).

11. The method according to any one of claims 1 to 10, characterized in that: At least one of the membrane (34) and the mixer structure has been provided with a catalyst.

12. The method according to any one of claims 1 to 11, characterized in that: The process is carried out in the absence of emulsifiers.

13. The method according to any one of claims 1 to 12, characterized in that: The method is carried out using an emulsifier selected from the group consisting of meroxaban and poloxamers.

14. The method according to any one of claims 1 to 13, characterized in that: The polymerization solution is heated to a temperature in the range of ≥50°C to ≤100°C.

15. The method according to any one of claims 1 to 14, characterized in that: The process is carried out in at least two polymerization reactors (12) connected in series.

16. The method according to any one of claims 1 to 15, characterized in that: In the polymerization reactor (12), a material flow is introduced or discharged between two membranes (34) connected in series or between two fluid channels (48) connected in series or between two polymerization reactors (12) connected in series.

17. The method according to any one of claims 1 to 16, characterized in that: The membrane (34) separating the monomer space (30) and the polymerization space (36) exhibits hydrophobicity.

18. The method according to any one of claims 1 to 16, characterized in that: The membrane (34) separating the monomer space (30) and the polymerization space (36) exhibits hydrophilicity.

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