Production method of 1, 2-propylene glycol

Abstract

The invention discloses a production method of 1, 2-propylene glycol, which is characterized by comprising the following steps: respectively and continuously feeding propylene and hydrogen peroxide into a reactor, and reacting in the presence of a titanium silicalite molecular sieve catalyst and a cocatalyst to obtain a reaction product; discharging trace non-condensable gas generated by reaction from the top of the reactor, and feeding a reaction product into a catalyst separator; the reaction product in the catalyst separator is subjected to oil-water phase separation, an upper-layer oil-phase material and propylene together serve as total propylene feed to return to the reactor through a propylene circulating pump, and a lower-layer water-phase material is fed into a membrane filter through a catalyst circulating pump; in a membrane filter, the water-phase material is filtered into a clear solution without the titanium silicalite molecular sieve and a turbid solution containing the titanium silicalite molecular sieve, the turbid solution is cooled by a heat collector and then is circulated back to the reactor, and the clear solution is sent to a reaction product separation system for separation of 1, 2-propylene glycol and reaction by-products.

Description

Technical Field

[0001] The present invention relates to a method for producing an organic chemical raw material, and more specifically to a method for producing 1,2-propylene glycol including a target product synthesis and a catalyst separation process. Background Art

[0002] 1,2-Propanediol is a colorless, odorless, viscous, water-absorbing liquid. It is an important raw material for the production of unsaturated polyesters, polyurethane resins, epoxy resins, surfactants, and plasticizers.

[0003] At present, the main industrial production processes of 1,2-propylene glycol are ester exchange, glycerol hydrogenolysis, and propylene oxide hydration.

[0004] The ester exchange method is the main production process of 1,2-propylene glycol. Although the ester exchange method is mature in technology and has high atomic utilization rate, it has problems such as poor product quality, long process flow and high energy consumption.

[0005] CN101848884A discloses a method for preparing 1,2-propylene glycol by hydrogenating glycerol. The method uses at least three fixed bed reactors connected in series. In the presence of a heterogeneous copper catalyst, at a temperature of 173-185°C and a pressure of 200 bar, glycerol is hydrogenated to obtain 1,2-propylene glycol, with a glycerol conversion rate of 99.61% and a 1,2-propylene glycol selectivity of 97.37%. Since the method has harsh reaction conditions and high requirements for equipment, its industrial application is limited.

[0006] The technology for preparing 1,2-propylene glycol by the reaction of propylene and hydrogen peroxide disclosed in CN108779053A has the characteristics of short process and low energy consumption. The technology uses propylene and hydrogen peroxide as raw materials, and heteropolytungstic acid + phase transfer catalyst + inorganic acid as catalysts. It can realize two-step reaction in one reactor, that is, propylene and hydrogen peroxide react to generate propylene oxide, and propylene oxide and water react to generate 1,2-propylene glycol. However, due to the use of a homogeneous catalyst system, the technology has the problem of difficult catalyst separation. Summary of the invention

[0007] The inventors of the present invention have found that in a solvent-free heterogeneous system, the hydrophilicity of titanium silicalite and the water solubility of 1,2-propylene glycol can be used to achieve oil-water phase separation, and the titanium silicalite is evenly dispersed in the water phase to achieve separation of unreacted propylene and titanium silicalite / reaction products, and then an external membrane filter is used to separate the titanium silicalite from the reaction products, forming a continuous and complete production method for 1,2-propylene glycol including synthesis and catalyst separation. Based on this, the present invention is formed.

[0008] Therefore, the object of the present invention is to provide a method for producing 1,2-propylene glycol in a solvent-free heterogeneous system with the participation of an external membrane filter.

[0009] In order to achieve the above-mentioned purpose, the present invention provides a method for producing 1,2-propylene glycol, characterized in that the method comprises: propylene and hydrogen peroxide are continuously fed into a reactor respectively, and react in the presence of a titanium silicon molecular sieve catalyst and a co-catalyst to obtain a reaction product; a trace amount of non-condensable gas produced by the reaction is discharged from the top of the reactor, and the reaction product enters a catalyst separator; the reaction product is subjected to oil-water phase separation in the catalyst separator, wherein the oil phase material in the upper layer is returned to the reactor together with propylene as a total propylene feed through a propylene circulation pump, and the water phase material in the lower layer is sent to a membrane filter through a catalyst circulation pump; in the membrane filter, the water phase material is filtered into a clear liquid without titanium silicon molecular sieve and a turbid liquid containing titanium silicon molecular sieve, the turbid liquid is cooled by a heat collector and then circulated back to the reactor, and the clear liquid is sent to a reaction product separation system to separate 1,2-propylene glycol and reaction by-products.

[0010] In the production method of the present invention, the reactor may be one reactor or multiple reactors, for example, the total number of reactors is 2-6, preferably 2-3. When there are multiple reactors, a series connection method may be adopted, and overflow operation is achieved through the height difference between the reactors, and multiple reactors are arranged from high to low according to the height difference to achieve the flow of materials. When the reactor adopts a multiple reactor series connection method, hydrogen peroxide adopts a multi-stage feeding method in which multiple reactors are fed simultaneously.

[0011] A hydrogen peroxide feed distributor is arranged in the reactor, and the feed distributor is of an annular tube type, a branch tube type or a nozzle type, and the preferred feed distributor is an annular tube type.

[0012] In the production method of the present invention, the titanium silicon molecular sieve catalyst comprises titanium silicon molecular sieve or titanium silicon molecular sieve containing tin and / or zirconium. The framework titanium species of titanium silicon molecular sieve has the excellent performance of activating oxidant catalyzing the oxidation of organic molecules. The titanium silicon molecular sieve is a common titanium silicon molecular sieve, for example, the titanium silicon molecular sieve can be MFI type titanium silicon molecular sieve (such as TS-1 molecular sieve), MEL type titanium silicon molecular sieve (such as TS-2 molecular sieve), BEA type titanium silicon molecular sieve (such as Ti-β molecular sieve), MWW type titanium silicon molecular sieve (such as Ti-MCM-22 molecular sieve), MOR type titanium silicon molecular sieve (such as Ti-MOR molecular sieve), TUN type titanium silicon molecular sieve (such as Ti-TUN molecular sieve), hexagonal titanium silicon molecular sieve (such as Ti-MCM-41 molecular sieve, Ti-SBA-15 molecular sieve) and other structures of titanium silicon molecular sieve (such as Ti-ZSM-48 molecular sieve) and the like. Preferably, the titanium silicon molecular sieve is at least one selected from MFI type titanium silicon molecular sieve, MEL type titanium silicon molecular sieve and BEA type titanium silicon molecular sieve. Further preferably, the titanium silicon molecular sieve is an MFI type titanium silicon molecular sieve. The MFI type titanium silicon molecular sieve can be a TS-1 molecular sieve prepared by conventional methods such as hydrothermal synthesis, post-treatment synthesis, etc., can be a titanium silicon molecular sieve with a multi-level pore structure (i.e., according to the N2 adsorption and desorption curve, the BJH fitting molecular sieve pore distribution curve is performed, and there is a pore distribution in the range of 2-50nm in the molecular sieve crystal), can be a hollow titanium silicon molecular sieve HTS with a hollow structure in the crystal (i.e., after TEM characterization, it can be seen that there are one or more intracrystalline cavities in the molecular sieve crystal), can be a titanium silicon molecular sieve with a sheet-like, spherical, hexagonal column shape, and a surface opening, and the present invention does not specifically limit this. In order to achieve better technical effects, the more preferred MFI type titanium silicon molecular sieve of the present invention is a titanium silicon molecular sieve with a multi-level pore structure as described above and / or a hollow titanium silicon molecular sieve HTS with a hollow structure.

[0013] In the production method of the present invention, the co-catalyst is one or more of phosphoric acid solution, hydrochloric acid solution and sulfuric acid solution. Alternatively, the co-catalyst is one or more of cation exchange resin, tin silicon molecular sieve and zirconium silicon molecular sieve. The co-catalyst can also be a combination of one or more selected from phosphoric acid solution, hydrochloric acid solution and sulfuric acid solution and one or more selected from cation exchange resin, tin silicon molecular sieve and zirconium silicon molecular sieve (for example, synthesized according to the method described in patent CN113509958A).

[0014] When one or more of phosphoric acid solution, hydrochloric acid solution and sulfuric acid solution is used as the co-catalyst, the co-catalyst is continuously added to the reactor, or the co-catalyst can be mixed with hydrogen peroxide and introduced into the reactor.

[0015] In the production method of the present invention, when one or more of cation exchange resin, tin silicon molecular sieve and zirconium silicon molecular sieve is used as a promoter, the weight ratio of the promoter to the titanium silicon molecular sieve is preferably (0.2-5):1.

[0016] In the production method of the present invention, the reaction temperature of propylene and hydrogen peroxide is 20-100°C, preferably 30-80°C; propylene reacts under liquid phase conditions, the reaction pressure is 1.0-5.0MPaG, preferably 1.2-3.8MPaG. The molar ratio of propylene in the total propylene feed to hydrogen peroxide in the hydrogen peroxide feed is 1-30:1, preferably 2-10:1. The mass ratio of the circulating catalyst titanium silicon molecular sieve catalyst to hydrogen peroxide is 0.2-20:1, preferably 1-5:1.

[0017] In the production method of the present invention, a stirring paddle is provided in the reactor, and the stirring paddle is of paddle type, propeller type, turbine type or a combination thereof, and the number of stirring paddle layers is 1 to 3. A baffle is provided in the reactor, and the number of baffles is preferably 2 to 6. In order to better achieve discharge, an overflow weir is preferably provided in the reactor. In order to strengthen mixing and optimize the fluid flow pattern, the reactor is provided with a guide tube.

[0018] In the production method of the present invention, when one or more of phosphoric acid solution, hydrochloric acid solution and sulfuric acid solution is used as a promoter, by adjusting the amount of the promoter added, the H + The concentration was maintained at 10 -6 -10mol / L, preferably maintained at a concentration of 10 -3 -1mol / L.

[0019] In the production method of the present invention, the reaction product is separated into oil and water phases in the catalyst separator. The upper oil phase is mainly unreacted propylene, which is circulated back to the reactor through a propylene circulation pump; the lower water phase is mainly titanium silicon molecular sieve, co-catalyst, water, 1,2-propylene glycol, a small amount of unreacted hydrogen peroxide and reaction by-products, which are sent to the membrane filter through a catalyst circulation pump. A stirring paddle is provided in the catalyst separator to stir the lower water phase material to prevent the titanium silicon molecular sieve from settling due to long residence time. The stirring paddle is a propulsion type, a turbine type, an anchor type, a frame type or a combination thereof, and the number of stirring paddle layers is 1 to 3. An overflow weir is provided in the catalyst separator.

[0020] In the production method of the present invention, the reactors and the reactor and the catalyst separator are arranged from high to low according to the height difference to realize the flow of materials.

[0021] In the production method of the present invention, the membrane filter adopts an external membrane form outside the catalyst separator. Although the external membrane filter has the disadvantages of relatively high investment and occupying more space, it also has the characteristics of easy maintenance. In the membrane filter, the aqueous phase is filtered into a turbid liquid containing titanium silicon molecular sieve and a clear liquid without titanium silicon molecular sieve. The turbid liquid is cooled by the reaction heat collector and circulated back to the reactor. The clear liquid is sent to the reaction product separation system for separation of 1,2-propylene glycol and reaction by-products. According to the scale of the reaction device, the membrane filter is composed of a plurality of membrane components, and the membrane components are connected in parallel and / or in series. Each membrane component is composed of a shell, a tube sheet, a head and a plurality of parallel membrane tubes. The membrane tubes are placed in parallel in the shell, and tube sheets are provided at both ends of the membrane tube to separate the materials on both sides of the membrane tube. The aqueous phase material passes through the center of the membrane tube, penetrates into the membrane component shell from the inner side of the membrane tube, and is discharged as clear liquid through the clear liquid discharge pipeline on the shell side. A backwashing pipeline is provided on the clear liquid discharge pipeline on the shell side for backwashing operation of the membrane tube. The filter cake layer of the external membrane filter is relatively thick, and a large amount of medium is required for backwashing operation. The medium for the backwashing operation can be a reaction clear liquid or deionized water. Since the reaction clear liquid has a similar composition to the reaction system material, it has little effect on the reaction. Therefore, the preferred medium for the backwashing operation is the reaction clear liquid. The membrane tube is made of ceramic, metal or high-density polyethylene, preferably ceramic or metal, and the filtration accuracy is preferably 0.01 to 50 μm.

[0022] The production method of 1,2-propylene glycol provided by the present invention utilizes the hydrophilicity of the titanium silicon molecular sieve catalyst, effectively integrates the reaction steps and the process of separating the external membrane products in a solvent-free heterogeneous reaction system, and can smoothly achieve oil-water phase separation. By setting stirring in the lower water phase area of ​​the catalyst separator, under the premise of oil-water phase separation, the stirring paddle is used to achieve uniform dispersion of the catalyst, so that the titanium silicon molecular sieve catalyst is uniformly dispersed in the water phase without sinking.

[0023] The production method of 1,2-propylene glycol provided by the present invention adopts a slurry bed reaction process, propylene and hydrogen peroxide are continuously fed, and a continuous reaction is realized. By adjusting the feed ratio and the catalyst ratio, efficient operation of the reaction is realized, and the yield of 1,2-propylene glycol (including dipropylene glycol) and the conversion rate of hydrogen peroxide both reach more than 94%.

[0024] The production method of 1,2-propylene glycol provided by the present invention also has the following advantages: (1) no solvent is used, thus avoiding the separation of the solvent and reducing energy consumption; (2) propylene and the reaction product are separated by oil-water phase separation, thus reducing energy consumption; and (3) the problem of catalyst sedimentation is solved. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The accompanying drawings are used to provide further understanding of the present invention and constitute a part of the specification. Together with the following specific embodiments, they are used to explain the present invention, but do not constitute a limitation of the present invention.

[0026] Figure 1 It is a schematic diagram of the reaction and catalyst separation process of a single reactor.

[0027] Figure 2 It is a schematic diagram of the reaction and catalyst separation process of three reactors in series.

[0028] In the figure, 1. propylene; 2. hydrogen peroxide; 3. co-catalyst (phosphoric acid or hydrochloric acid or sulfuric acid solution); 4. reactor; 4-1. reactor; 4-2. reactor; 4-3. reactor; 5. reaction product; 6. catalyst separator; 7. oil phase material; 8. propylene circulation pump; 9. water phase material; 10. catalyst circulation pump; 11. external membrane filter; 12. clear liquid; 13. turbid liquid; 14. heat collector; 15. non-condensable gas; 16. total propylene feed. DETAILED DESCRIPTION

[0029] The present invention is further described below in conjunction with the accompanying drawings and embodiments, but they are not intended to limit the present invention.

[0030] The technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other. In addition, the following are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0031] Example 1

[0032] Propylene and hydrogen peroxide react in a stirred kettle with an effective volume of 5.2L at a temperature of 45°C and a pressure of 2.0MPaG. The reactor is filled with 150g of titanium silicon molecular sieve catalyst. The feed rate of the device is: 12g / h of fresh propylene and 35g / h of hydrogen peroxide (30w%). A 2mol / l H3PO4 solution is added to the reactor through a hydrogen peroxide feed line to maintain the pH value of the lower aqueous phase in the catalyst separator at 1.75. The circulating propylene amount is 24g / h and the circulating catalyst amount is 100g / h. Baffles and overflow weirs are provided in the reactor and the catalyst separator. The reactor agitator is a propeller agitator with a rotation speed of 500rmp, and the catalyst separator agitator is an anchor agitator with a rotation speed of 80rmp. The bottom outlet of the catalyst separator is connected to a pump and an external membrane filter. The membrane filter is equipped with a metal sintered membrane tube with a diameter of 10 mm and a length of 200 mm. The filtration accuracy is 0.2 μm. The catalyst slurry flows through the center of the membrane tube, and the filtered clear liquid flows out from the shell side of the membrane filter. The recoil medium is the filtered clear liquid.

[0033] After the device was stably operated for 6 hours, the clear liquid discharged from the membrane filter was sampled and analyzed, wherein the unreacted hydrogen peroxide in the reaction product was analyzed by titration, and the composition of the reaction product was analyzed by gas chromatography. The data are shown in Table 1.

[0034] Example 2

[0035] Example 1 was repeated, propylene and hydrogen peroxide were reacted at a temperature of 60° C. and a pressure of 2.8 MPaG, and other parameters remained unchanged.

[0036] After the device was running stably for 6 hours, the clear liquid discharged from the membrane filter was sampled and analyzed. The data are shown in Table 1.

[0037] Example 3

[0038] Example 1 was repeated, propylene and hydrogen peroxide were reacted at a temperature of 30° C. and a pressure of 1.6 MPaG, and other parameters remained unchanged.

[0039] After the device was running stably for 6 hours, the clear liquid discharged from the membrane filter was sampled and analyzed. The data are shown in Table 1.

[0040] Example 4

[0041] Example 1 was repeated, propylene and hydrogen peroxide were reacted at a temperature of 45° C. and a pressure of 2.0 MPaG, the feed rates of the device were: 35 g / h of fresh propylene and 100 g / h of hydrogen peroxide (30 w %); a 2 mol / h H3PO4 solution was added to the reactor using a hydrogen peroxide feed line, and the pH value of the aqueous phase in the catalyst separator was maintained at 1.75; the circulating propylene amount was 70 g / h, and the circulating catalyst amount was 300 g / h.

[0042] After the device was running stably for 3 hours, the clear liquid discharged from the membrane filter was sampled and analyzed. The data are shown in Table 1.

[0043] Example 5

[0044] Example 1 was repeated, and a H3PO4 solution with a concentration of 2 mol / h was added to the reactor, and the pH value of the aqueous phase in the catalyst separator was maintained at 5. Other conditions remained unchanged.

[0045] After the device was running stably for 6 hours, the clear liquid discharged from the membrane filter was sampled and analyzed. The data are shown in Table 1.

[0046] Example 6

[0047] Example 1 was repeated, and a H2SO4 solution with a concentration of 2 mol / h was added to the reactor, and the pH value of the aqueous phase in the catalyst separator was maintained at 1.75, while other conditions remained unchanged.

[0048] After the device was running stably for 6 hours, the clear liquid discharged from the membrane filter was sampled and analyzed. The data are shown in Table 1.

[0049] Example 7

[0050] Propylene and hydrogen peroxide reacted in a stirred kettle with an effective volume of 5.2L at a temperature of 60°C and a pressure of 2.0MPaG. The reactor was filled with 150g of titanium silicon molecular sieve catalyst and 150g of zirconium silicon molecular sieve. The feed rate of the device was: 12g / h of fresh propylene, 35g / h of hydrogen peroxide (30w%), 24g / h of circulating propylene, and 100g / h of circulating catalyst. After the device was stably operated for 6 hours, the clear liquid discharged from the membrane filter was sampled and analyzed, wherein the analysis of unreacted hydrogen peroxide in the reaction product was carried out by titration, and the composition of the reaction product was analyzed by gas chromatography. The data are shown in Table 1.

[0051] Table 1

[0052]

[0053] The "other" item in Table 1 is the sum of small amounts of by-products such as acetaldehyde, propylene oxide, and acetic acid.

Claims

1. A method for producing 1,2-propylene glycol, characterized in that The method comprises: propylene and hydrogen peroxide are respectively and continuously fed into a reactor, and reacted in the presence of a titanium silicon molecular sieve catalyst and a co-catalyst to obtain a reaction product; a trace amount of non-condensable gas generated by the reaction is discharged from the top of the reactor, and the reaction product enters a catalyst separator; the reaction product is subjected to oil-water phase separation in the catalyst separator, wherein the oil phase material of the upper layer is returned to the reactor together with propylene as a total propylene feed through a propylene circulation pump, and the water phase material of the lower layer is sent to a membrane filter through a catalyst circulation pump; in the membrane filter, the water phase material is filtered into a clear liquid without titanium silicon molecular sieve and a turbid liquid containing titanium silicon molecular sieve, the turbid liquid is cooled by a heat collector and then circulated back to the reactor, and the clear liquid is sent to a reaction product separation system to separate 1,2-propylene glycol and reaction by-products.

2. The production method according to claim 1, characterized in that The reactor comprises a plurality of reactors, and the plurality of reactors are connected in series. The total number of reactors is 2-6, preferably 2-3, and overflow operation is achieved through height differences between the plurality of reactors.

3. The production method according to claim 2, characterized in that: When the reactor adopts the mode of multiple reactors connected in series, hydrogen peroxide adopts a multi-stage feeding mode of simultaneously feeding multiple reactors.

4. The production method according to claim 3, characterized in that: A hydrogen peroxide feed distributor is arranged in the plurality of reactors. The feed distributor is of a ring pipe type, a branch pipe type or a nozzle type. The preferred feed distributor is of a ring pipe type.

5. The production method according to claim 1, characterized in that: The titanium silicon molecular sieve catalyst includes titanium silicon molecular sieve or titanium silicon molecular sieve containing tin and / or zirconium.

6. The production method according to claim 1, characterized in that: The co-catalyst is one or more of a phosphoric acid solution, a hydrochloric acid solution and a sulfuric acid solution.

7. The production method according to claim 6, characterized in that: The cocatalyst is continuously added to the reactor.

8. The production method according to claim 7, characterized in that: The co-catalyst is mixed with hydrogen peroxide and then enters the reactor.

9. The production method according to claim 1, characterized in that: The co-catalyst is one or more of a cation exchange resin, a tin silicon molecular sieve and a zirconium silicon molecular sieve.

10. The production method according to claim 1, characterized in that: The co-catalyst is a combination of one or more selected from phosphoric acid solution, hydrochloric acid solution and sulfuric acid solution and one or more selected from cation exchange resin, tin silicon molecular sieve and zirconium silicon molecular sieve.

11. The production method according to claim 9, characterized in that: The weight ratio of the co-catalyst to the titanium silicon molecular sieve is (0.2-5):

1.

12. The production method according to claim 1, characterized in that: The reaction temperature of propylene and hydrogen peroxide is 20-100°C, preferably 30-80°C; propylene reacts under liquid phase conditions, and the reaction pressure is 1.0-5.0 MPaG, preferably 1.2-3.8 MPaG.

13. The production method according to claim 1, characterized in that: The molar ratio of propylene to hydrogen peroxide in the reactor is 1 to 30:1, preferably 2 to 10:

1.

14. The production method according to claim 1, characterized in that: The mass ratio of the titanium silicon molecular sieve catalyst to hydrogen peroxide in the reactor is 0.2 to 20:1, preferably 1 to 5:

1.

15. The production method according to claim 1, characterized in that: The reactor is provided with a stirring paddle, which is a paddle type, a propeller type, a turbine type or a combination thereof, and the number of layers of the stirring paddle is 1 to 3.

16. The production method according to claim 1, characterized in that: The reactor is provided with baffles, and the number of the baffles is 2 to 6.

17. The production method according to claim 1, characterized in that: An overflow weir is arranged in the reactor.

18. The production method according to claim 1, characterized in that: The reactor is provided with a draft tube.

19. The production method according to claim 1, characterized in that: In the catalyst separator, H + The concentration is 10 -6 -10mol / L, the preferred concentration is 10 -3 -1mol / L.

20. The production method according to claim 1, characterized in that The catalyst separator is provided with a stirring paddle to stir the aqueous phase material in the lower layer. The stirring paddle is of propulsion type, turbine type, anchor type, frame type or a combination thereof. The number of stirring paddle layers is 1 to 3.

21. The production method according to claim 1, characterized in that An overflow weir is arranged inside the catalyst separator.

22. The production method according to claim 1, characterized in that The membrane filter is composed of a plurality of membrane components, and the membrane components are connected in parallel and / or in series.

23. The production method according to claim 22, characterized in that Each membrane module consists of a shell, a tube sheet, a head and a plurality of parallel membrane tubes. The membrane tubes are placed in parallel in the shell, and tube sheets are provided at both ends of the membrane tubes to separate the materials inside and outside the membrane tubes.

24. The production method according to claim 22, characterized in that In the membrane filter, the aqueous phase material passes through the center of the membrane tube, permeates into the membrane module shell from the inner side of the membrane tube, and is discharged as clear liquid through the clear liquid discharge pipeline on the shell side.

25. The production method according to claim 23, characterized in that: A backwashing pipeline is provided on the clear liquid discharge pipeline on the shell side for backwashing operation of the membrane tube.

26. The production method according to claim 25, characterized in that In the backwashing operation, the medium is a reaction clear solution or deionized water, preferably a reaction clear solution.

27. The production method according to any one of claims 23 to 25, characterized in that: The membrane tube is made of ceramic, metal or high-density polyethylene, and preferably made of ceramic or metal.

28. The production method according to claim 27, characterized in that The membrane tube has a filtration accuracy of 0.01 to 50 μm.

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