A method for preparing diamines and polyamines containing diphenylmethane structure with low acid consumption

Abstract

The present invention relates to a method for preparing diamines and polyamines containing diphenylmethane structure with low acid consumption. S1: In the presence of an acidic catalyst, aniline undergoes a salting reaction to form anilinium salt. S2: The anilinium salt and formaldehyde solution are mixed for a condensation reaction to obtain a reaction solution containing diamine salt and polyamine salt with diphenylmethane structure. S3: The reaction solution of S2 is added to a membrane separator, and the acid catalyst in the aqueous phase is separated out with water in the form of anilinium salt, realizing the separation of the aqueous phase from the organic phase containing diamines and polyamines with diphenylmethane structure. S4: The organic phase of S3 is washed with alkali and distilled to obtain diamines and polyamines (DAM) containing diphenylmethane structure. After the aqueous phase obtained in S3 is distilled to remove part of the water, it is returned to S1 as a raw material for the condensation reaction together with the acid catalyst. The method of the present invention significantly reduces the material consumption, energy consumption and the generation of waste brine in the DAM preparation process on the premise of ensuring the quality of DAM.

Description

Technical Field

[0001] The present invention belongs to the technical field of polyamines, and mainly relates to a method for preparing diamines and polyamines containing diphenylmethane structure with low acid consumption. Background Art

[0002] MDI is one of the main raw materials in the polyurethane industry. It is a well-known method in the industry to prepare polymethylene polyphenyl polyamine (DAM) by reacting aniline and formaldehyde under an acidic catalyst, and then synthesize MDI by reacting DAM with phosgene.

[0003] In the traditional preparation process of diamines and polyamines (DAM) containing diphenylmethane structure, aniline and formaldehyde undergo a condensation reaction under the action of an acid catalyst to obtain an acidic reaction mixture of diamines and polyamines (DAM) containing diphenylmethane structure. Then, the reaction solution containing DAM salt is completely neutralized with an alkali solution and layered into an organic phase and a brine phase. The organic phase is further refined to obtain crude DAM. The process of neutralizing the reaction solution with an alkali is usually carried out at 90°C to 110°C, and hydroxides of alkali metals and alkaline earth metals are suitable as the alkali. For example, an aqueous solution of NaOH is used. In the process of completely neutralizing the diamine salt and polyamine salt containing diphenylmethane structure to obtain diamines and polyamines containing diphenylmethane structure, due to the large amount of acid catalyst used in the front-end salt formation reaction, such as hydrochloric acid catalyst, in order to fully neutralize hydrochloric acid, a large amount of caustic soda will be consumed, and the cost of caustic soda accounts for nearly 10% of the manufacturing cost of DAM. At the same time, due to the addition of caustic soda, a large amount of waste brine containing organic amines is generated, which also causes great pressure on environmental protection emissions or recycling. Moreover, due to the particularity of the neutralization reaction, if the amount of caustic soda added is insufficient or the control is unstable, the overly acidic reaction solution will corrode the downstream acid-intolerant equipment, affecting the long-term stable operation of the device.

[0004] Currently, in patents at home and abroad regarding diamines and polyamines containing diphenylmethane structure, the removal of moisture and acid catalyst mainly adopts the method of neutralizing the diamine salt and polyamine salt containing diphenylmethane structure with an alkali solution, and then separating the generated water phase and organic phase. In the current industrial production process of DAM, if the amount of acid catalyst added is reduced, the miscibility of the water phase and the oil phase in the reaction solution will decrease, changing from a homogeneous phase to a heterogeneous phase, thereby affecting the mass transfer effect and intensifying side reactions, resulting in poor DAM quality. Therefore, how to design a production process of diamines and polyamines containing diphenylmethane structure that can ensure not to affect the quality of the final product, effectively reduce the consumption of acid catalyst, reduce production costs, and reduce the generation amount of organic amine-containing wastewater has become an urgent problem in the industry. Summary of the Invention

[0005] The object of the present invention is to provide a method for preparing diamines and polyamines containing diphenylmethane structure with low acid consumption. This method can efficiently separate aniline salts from diamines and polyamines containing diphenylmethane structure, greatly reduce the consumption of lye in the production process of DAM, significantly reduce the generation amount of wastewater containing organic amines, and ensure the stable quality of DAM.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for preparing diamines and polyamines containing diphenylmethane structure with low acid consumption, the method comprising the following steps:

[0008] S1: In the presence of an acidic catalyst, aniline undergoes a salification reaction to form aniline salt.

[0009] S2: The aniline salt and formaldehyde solution are mixed for a condensation reaction to obtain a reaction solution containing diamine salts and polyamine salts with diphenylmethane structure.

[0010] S3: The reaction solution of S2 is added to a membrane separator, and the acid catalyst in the aqueous phase is separated out with water in the form of aniline salt, realizing the separation of the aqueous phase from the organic phase containing diamines and polyamines with diphenylmethane structure.

[0011] S4: The organic phase of S3 is washed with alkali and distilled to obtain diamines and polyamines (DAM) containing diphenylmethane structure. After the aqueous phase obtained in S3 is distilled to remove part of the water, it is returned to S1 as a raw material for the condensation reaction and an acid catalyst.

[0012] In the present invention, most of the acid catalyst in the diamines and polyamines is separated out with water in the form of aniline salt through the DHNTs / pGO superhydrophilic membrane, and this part of aniline salt is recycled, thereby reducing the actual addition amount of raw material aniline and acid catalyst. As a result, the consumption of lye for neutralizing the acid catalyst in the subsequent process is greatly reduced. In addition, due to the reduction of aniline feed, the energy consumption in the process of removing aniline from diamines and polyamines is further reduced. Thus, the production cost is greatly reduced without affecting the product quality. At the same time, the generation of high-concentration brine containing organic amine substances is avoided, thereby alleviating the environmental protection pressure for treating the brine to meet the discharge standards. This is because after membrane separation, most of the acidic catalyst and most of the aniline are recycled and reused in the system. The wastewater generated from washing the organic phase with dilute alkali solution and the wastewater generated from distilling the aqueous phase after membrane separation have very low salt content and small quantity, and can be sent to the biochemical treatment unit and then to the advanced treatment unit for reuse after further treatment, solving the environmental protection pressure.

[0013] In the present invention, the acidic catalyst described in S1 is selected from sulfuric acid and / or hydrochloric acid, preferably a 10 - 35 wt% hydrochloric acid solution and / or a 10 - 30 wt% sulfuric acid solution, more preferably a 20 - 30 wt% hydrochloric acid solution.

[0014] In the present invention, the molar ratio of H of all the acidic catalysts in S1 to aniline is (0.2 - 0.5):1; preferably, the molar ratio of H of the newly added acidic catalyst in S1 to aniline is (0.01 - 0.1):1, more preferably (0.01 - 0.05):1. + In the present invention, the molar ratio of H of all the acidic catalysts in S1 to aniline is (0.2 - 0.5):1; preferably, the molar ratio of H of the newly added acidic catalyst in S1 to aniline is (0.01 - 0.1):1, more preferably (0.01 - 0.05):1. + In the present invention, the molar ratio of H of all the acidic catalysts in S1 to aniline is (0.2 - 0.5):1; preferably, the molar ratio of H of the newly added acidic catalyst in S1 to aniline is (0.01 - 0.1):1, more preferably (0.01 - 0.05):1.

[0015] In the present invention, the temperature of the salt - forming reaction in S1 is 35 - 50 °C.

[0016] In the present invention, the molar ratio of formaldehyde in the formaldehyde solution in S2 to aniline in the aniline salt is 0.3 - 0.6:1, more preferably 0.35 - 0.5:1; the concentration of the formaldehyde solution is preferably 35 - 50 wt%, more preferably 37 - 42 wt%.

[0017] In the present invention, the reaction time of the aniline salt and formaldehyde in S2 is 3 - 5 h, and the reaction temperature is 50 - 100 °C.

[0018] In one embodiment, it is preferred that when the molar ratio of formaldehyde to aniline in S2 is higher than 0.45:1, before performing the membrane separation of the oil - water phase, aniline is added to the reaction solution; the molar amount of the added aniline should ensure that the overall aniline content exceeds the total molar amount of H in the reaction solution by 5 - 10%. + In one embodiment, it is preferred that when the molar ratio of formaldehyde to aniline in S2 is higher than 0.45:1, before performing the membrane separation of the oil - water phase, aniline is added to the reaction solution; the molar amount of the added aniline should ensure that the overall aniline content exceeds the total molar amount of H in the reaction solution by 5 - 10%.

[0019] In the present invention, the aqueous phase of S3 contains: 35 - 55 wt% of aniline salt, 2 - 8 wt% of diamine and polyamine salt, and the remaining part is water.

[0020] In the present invention, the oil phase of S3 contains: 60 - 85 wt% of diamine and polyamine, 1 - 9 wt% of diamine and polyamine salt, 1 - 4 wt% of aniline salt, 1 - 3 wt% of water, and the remaining part is aniline.

[0021] In the present invention, the membrane separator in S3 is a shell - and - tube membrane separator.

[0022] In the present invention, the membrane in the membrane separator of S3 is a modified halloysite nanotube / porous graphene oxide super - hydrophilic membrane; preferably, the conditions for the membrane separation operation are an operating temperature of 60 - 100 °C and an operating pressure difference between the feed side and the aqueous phase extraction side of 0.05 - 0.2 MPa.

[0023] In one embodiment, the shell-and-tube membrane separator includes a shell, a head, a tube sheet, and membrane separation tubes; among them, the membrane separation membrane tubes are made of the aforementioned DHNTs / pGO superhydrophilic membrane. The upper head is connected to a vacuum unit, and the lower head is provided with a water-phase inlet and outlet pipe orifice for collecting the water phase after membrane separation. The two ends of the heads and the tube sheets fixed at both ends of the shell are connected by flanges; the shell is provided with an inlet and outlet for the organic phase, and several baffle support plates are arranged inside the shell; preferably, the inner diameter of the shell is 0.1 - 0.3 m, the length of the membrane separation tube is 0.2 - 0.5 m, the inner diameter is 5 - 10 mm, the thickness of the membrane separation tube is 0.5 - 1.5 mm, the number of membrane tubes is 10 - 50, and the distance between the support baffle plates is 40 - 100 mm.

[0024] In the present invention, the caustic washing in S4 uses a sodium hydroxide solution; preferably, the concentration of the sodium hydroxide solution is 3 - 5%, and the molar ratio of the sodium hydroxide solution to the hydrochloric acid added in S2 is 1.05 - 1.5:1.

[0025] In the present invention, the deviation between the mass of the water removed from the water phase in S4 by distillation and the total water brought in by the raw materials and generated by the reaction, after deducting the water taken away by the oil phase after membrane separation in S3 and the remaining water in the concentrated water phase, is less than 3%, preferably less than 1%.

[0026] In one embodiment, in S4, a small amount of dilute alkali solution is used to wash the organic phase containing diamines and polyamines (DAM) with a diphenylmethane structure, and it is phase-separated again into an organic phase and a water phase; the water phase containing aniline, diamines, and polyamines is sent to a brine treatment process for treatment, and the organic phase containing diamines and polyamines with a diphenylmethane structure is separated by distillation to remove the organic solvent, aniline, and water therein, obtaining diamines and polyamines with a diphenylmethane structure; the gas phase of the distilled organic phase is cooled and recycled as the organic solvent in S2.

[0027] Preferably, the dilute alkali solution washing process is as follows: at 80 - 95 °C, the sodium hydroxide solution and the organic phase containing diamines and polyamines with a diphenylmethane structure are fully mixed in a mixer, and through caustic washing, the residual trace aniline salts, diamine salts, and polyamine salts in the organic phase containing diamines and polyamines with a diphenylmethane structure are removed. Then it is sent to an oil-water separator for phase separation.

[0028] Preferably, in S4, an evaporator is used to remove part of the water from the water phase containing anilinium salts generated in S3. The dehydrated anilinium salt aqueous solution is cooled to 30 - 50 °C and used as the raw material for the condensation reaction in S1. The dehydrated water phase containing anilinium salts should satisfy that the mass ratio of the acid catalyst to water is basically the same as that in S1, ensuring the stability and balance of the water content in the condensation reaction process; the gas phase generated by distillation is cooled and merged with the water phase generated by the caustic washing of the organic phase, and then sent to the brine treatment process for treatment together.

[0029] Another object of the present invention is to provide a superhydrophilic membrane.

[0030] A superhydrophilic membrane used in the above method, wherein the superhydrophilic membrane is a modified halloysite nanotube / porous graphene oxide superhydrophilic membrane.

[0031] The DHNTs / pGO superhydrophilic membrane of the present invention has a uniform pore distribution, no defects, high selectivity, and high temperature resistance. In addition, after the graphene oxide is modified with nitric acid, nanopores are formed on the surface as mass transfer channels, greatly improving the treatment flux of the superhydrophilic membrane.

[0032] Another object of the present invention is to provide a method for preparing a superhydrophilic membrane.

[0033] A method for preparing a superhydrophilic membrane, wherein the superhydrophilic membrane is the superhydrophilic membrane used in the above method, or the above-mentioned superhydrophilic membrane, and the superhydrophilic membrane is prepared by the following steps:

[0034] SS1: Add graphene oxide (GO) powder to water for dispersion, mix the dispersion with concentrated nitric acid and continue to disperse, then perform centrifugal separation, washing, suction filtration, and drying to obtain porous graphene oxide (pGO);

[0035] SS2: Dissolve dopamine in Tris-HCl solution, react after mixing, adjust the pH value of the mixed solution, add HNTs, react after dispersion, perform centrifugal separation, washing, suction filtration, and drying to obtain modified halloysite nanotubes (DHNTs);

[0036] SS3: Dissolve pGO in water to obtain a pGO dispersion; dissolve DHNTs in water to obtain a DHNTs dispersion;

[0037] SS4: Mix the pGO dispersion and the DHNTs dispersion and disperse them, then mix with an ethylenediamine solution, disperse and perform suction filtration, load the mixed solution onto a microporous filter membrane, wash and dry to obtain a DHNTs / pGO superhydrophilic membrane.

[0038] In the present invention, the dispersion method for the dispersion in any one of SS1, SS2, SS3, and SS4 is ultrasonic dispersion; preferably, the frequency of ultrasonic dispersion is 30 - 40 kHz, and the time is 1 - 2 h.

[0039] In the present invention, the centrifugation in any one of SS1, SS2, SS3, and SS4 is at a rotational speed of 3000 - 5000 rpm / min for a time of 5 - 30 min.

[0040] In the present invention, the operating pressure for the suction filtration in any one of SS1, SS2, SS3, and SS4 is 5 - 10 kPaA.

[0041] In the present invention, the mass ratio of GO to water in SS1 is 1:100 to 500, preferably 1:200 to 300.

[0042] In the present invention, the volume ratio of the GO dispersion in SS1 to concentrated nitric acid is 1:5 to 20, preferably 1:10 to 15.

[0043] In the present invention, the washing in SS1 is ultrasonic washing with deionized water; preferably, the washing is carried out until the pH value reaches 6 - 7. In the present invention, the drying temperature in SS1 is 25 - 50 °C and the time is 12 - 24 h.

[0044] In the present invention, the mass ratio of dopamine to Tris - HCl solution in SS2 is 1:500 - 1000, where the concentration of the Tris - HCl solution is 10 - 50 mmol / L.

[0045] In the present invention, before adding HNTs in SS2, the stirring rate of the reaction is 100 - 300 rpm, the temperature is 20 - 50 °C, and the reaction time is 8 - 24 h;

[0046] In the present invention, the pH value of the solution in SS2 is adjusted to 7 - 9.

[0047] In the present invention, the mass ratio of HNTs to the mixed solution in SS2 is 1:1000 - 2000.

[0048] In the present invention, the washing in SS2 is ultrasonic washing alternately with acetone and deionized water.

[0049] In the present invention, the drying temperature in SS2 is 50 - 70 °C and the time is 36 - 60 h.

[0050] In the present invention, the mass ratio of pGO to water in the pGO dispersion of SS3 is 1:2000 - 10000.

[0051] In the present invention, the mass ratio of DHNTs to water in the DHNTs dispersion of SS3 is 1:2000 - 20000.

[0052] In the present invention, the mass ratio of the DHNTs dispersion of SS4 to the pGO dispersion is 1:1 - 5.

[0053] In the present invention, the mass ratio of the ethylenediamine solution of SS4 to the DHNTs / pGO mixed solution is 1:5 - 10, and the ethylenediamine content in the ethylenediamine solution is 10 - 40 mmol / L.

[0054] In the present invention, the microporous membrane of SS4 is one or more of cellulose acetate membrane (CA), polyethersulfone (PES), and polyvinylidene fluoride (PVDF), preferably polyvinylidene fluoride.

[0055] In the present invention, the washing in SS4 is to clean the surface of the microporous filter membrane with flowing deionized water, and the washing time is 15 - 60 s.

[0056] In the present invention, the drying in SS4 is natural air drying at room temperature, and the drying time is 24 - 72 h.

[0057] Compared with the prior art, the beneficial effects of the technical solution of the present invention are as follows:

[0058] (1) Reduce the actual addition amount of raw material aniline and acid catalyst, thereby greatly reducing the consumption of subsequent lye; in addition, due to the reduction of aniline feed, the energy consumption in the process of removing aniline from diamine and polyamine is also reduced. Thus, the production cost is greatly reduced without affecting the product quality.

[0059] (2) Avoid the generation of high-concentration brine containing organic amine substances, thereby reducing the environmental protection pressure.

[0060] (3) The modified hydrophilic membrane greatly improves the treatment flux of the super-hydrophilic membrane, and the improvement amplitude can reach more than 40%. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Figure 1 is a schematic flow chart of a production process of the present invention. In the figure: 1 - aniline feed pipeline; 2 - hydrochloric acid feed pipeline; 3 - salt-forming mixer; 4 - formaldehyde feed pipeline; 5 - aniline hydrochloride / formaldehyde mixer; 6 - condensation reaction kettle; 7 - membrane separator; 8 - aniline acid salt solution storage tank; 9 - rising film evaporator; 10 - lye feed pipeline; 11 - neutralization mixer; 12 - neutralization stirring kettle; 13 - oil-water separation tank; 14 - polyamine storage tank; 15 - DAM refining process; 16 - alkali-washing wastewater storage tank; 17 - wastewater treatment process; 18 - aniline supplementary feed pipeline; 19 - aniline acid salt solution circulation pipeline; 20 - vacuum unit. DETAILED DESCRIPTION OF THE INVENTION

[0062] The technical solution and its effects of the present invention will be further described below in conjunction with embodiments. The following embodiments are only used to illustrate the content of the present invention and do not limit the protection scope of the present invention. Simple changes made to the present invention using the concept of the present invention are within the scope of protection required by the present invention.

[0063] <Source of raw materials>

[0064] Aniline: provided by Ningbo Wanhua Industrial Park, with a concentration of 99.9 wt%;

[0065] Hydrochloric acid: provided by Ningbo Wanhua Industrial Park, with a concentration of 33 wt%;

[0066] Formaldehyde: provided by Ningbo Wanhua Industrial Park, with a concentration of 37 wt%;

[0067] Sodium hydroxide solution: provided by Ningbo Wanhua Industrial Park, with a concentration of 5 wt%;

[0068] Halloysite nanotubes (95 at%), provided by Jiangsu Xianfeng Nano Materials Technology;

[0069] Graphene oxide, monolayer, 98%, provided by Shanghai Yuanye Bio-Technology Co., Ltd.;

[0070] Tris(hydroxymethyl)aminomethane hydrochloride (Tris-HCl), 99%, provided by Aladdin Reagent;

[0071] Polyvinylidene fluoride membrane, with an average microfiltration pore size of 0.22 μm, provided by Beijing Solarbio Science & Technology Co., Ltd.;

[0072] Cellulose acetate membrane: with a membrane pore size of 0.1 μm, provided by Zibo Dongqiang Membrane Technology Co., Ltd.;

[0073] Diethylamine (99%), acetone (99.5%), dopamine (98%) are provided by Sinopharm Reagent;

[0074] <Testing method>

[0075] Determination of the content of each component in aniline and DAM: Using an Agilent 1260 liquid chromatograph, after diluting the sample 100 times with methanol, liquid phase analysis is carried out;

[0076] Determination of chloride ion content: Using a Metrohm 905 potentiometric titrator, the titrant is silver nitrate solution, and titration is carried out in the DET u mode.

[0077] Determination of the oil droplet contact angle: Using a JC2000D1 type contact angle measuring instrument from Shanghai Zhongchen Digital Technology Equipment Co., Ltd., a fixed image when a 0.2 μL oil droplet drops on the surface of the prepared superhydrophilic membrane for 10 s under the conditions of room temperature and 60% humidity.

[0078] Preparation of DHNTs / pGO superhydrophilic membrane

[0079] Preparation Example 1

[0080] The DHNTs / pGO superhydrophilic membrane of the membrane separation device is prepared according to the following steps:

[0081] Preparation of Porous Graphene Oxide (pGO): 1 g of graphene oxide was mixed with deionized water at a mass ratio of 1:100, and dispersed under ultrasonic wave at room temperature and 30 kHz for 1 h to obtain a dispersion. Subsequently, 100 g of the dispersion was mixed with concentrated nitric acid at a mass ratio of 1:5, and subjected to ultrasonic reaction for 1 h. Then, centrifugation was carried out at 3000 rpm for 30 min to remove the supernatant. The precipitate was washed with 100 mL of deionized water and centrifuged to remove the washing solution. The above operations were repeated until the pH of the washing solution was 6.2. Then, the precipitate was placed in an oven at 30 °C and dried for 12 h to obtain porous graphene oxide;

[0082] Preparation of Modified Halloysite Nanotubes (DHNTs): 0.1576 g of Tris-HCl was dissolved in 100 mL of deionized water to prepare a 10 mmol / L Tris-HCl buffer solution. Then, 0.1 g of dopamine was weighed and mixed with the Tris-HCl buffer solution at a mass ratio of dopamine:Tris-HCl buffer solution of 1:1000. After adjusting the pH of the solution to 8.5 with 0.1 wt% sodium hydroxide solution, 50 mg of HNTs was weighed and mixed with the mixture at a mass ratio of HNTs:mixture of 1:2000. After dispersing under ultrasonic wave at 30 kHz for 1 h, a magnetic stir bar was added at 25 °C, the rotation speed was set at 200 rpm, and the reaction was continued for 24 h. After the reaction, the product was washed and centrifuged alternately with 100 mL of deionized water and acetone until the washing solution became clear. Then, the product was placed in an oven at 55 °C and dried for 48 h to obtain modified halloysite nanotubes;

[0083] Preparation of Superhydrophilic Membrane: 50 mg of DHNTs and 25 mg of pGO were weighed respectively. Then, DHNTs was mixed with deionized water at a mass ratio of 1:10000, and pGO was mixed with deionized water at a mass ratio of 1:20000. Then, they were respectively dispersed under ultrasonic wave at 30 kHz for 30 min. Subsequently, the DHNTs dispersion and the pGO dispersion were mixed at a mass ratio of 1:1 and ultrasonic dispersion was continued for 1 h. 1.202 g of ethylenediamine was dissolved in 1 L of deionized water to prepare a 20 mmol / L ethylenediamine solution. 100 g of the ethylenediamine solution was weighed and mixed with the DHNTs / pGO dispersion at a mass ratio of 1:10, and ultrasonic dispersion was carried out at 60 °C for 2 h. Then, after the dispersion cooled to room temperature, it was added to a sand core filtration device equipped with a PVDF membrane, and suction filtration was carried out at a pressure of 0.01 MPa(A). After suction filtration, the surface of the membrane was washed with deionized water for 30 s and naturally air-dried at room temperature for 48 h to remove the solvent, obtaining the 1# superhydrophilic membrane; its oil droplet contact angle was 167.2°.

[0084] Preparation Example 2

[0085] The DHNTs / pGO superhydrophilic membrane of the membrane separation device was prepared according to the following steps:

[0086] Preparation of Porous Graphene Oxide (pGO): 1 g of graphene oxide was mixed with deionized water at a mass ratio of 1:500, and dispersed under ultrasound at room temperature and 30 kHz for 2 h to obtain a dispersion. Subsequently, 100 g of the dispersion was mixed with concentrated nitric acid at a mass ratio of 1:20, and subjected to ultrasonic reaction for 1 h. Then, centrifugation was carried out at 4500 rpm for 10 min to remove the supernatant. The precipitate was washed with 100 mL of deionized water and centrifuged to remove the washing solution. The above operations were repeated until the pH of the washing solution was 6.4. The precipitate was then placed in an oven at 50 °C and dried for 24 h to obtain porous graphene oxide;

[0087] Preparation of Modified Halloysite Nanotubes (DHNTs): 0.788 g of Tris-HCl was dissolved in 100 mL of deionized water to prepare a 50 mmol / L Tris-HCl buffer solution. Then, 0.2 g of dopamine was weighed and mixed with the Tris-HCl buffer solution at a mass ratio of dopamine:Tris-HCl buffer solution of 1:500. After adjusting the pH of the solution to 7.2 with 0.1 wt% sodium hydroxide solution, 100 mg of HNTs was weighed and mixed with the mixture at a mass ratio of HNTs:mixture of 1:1000, and dispersed under ultrasound at 30 kHz for 1 h. Then, a magnetic stirring bar was added at 50 °C, the rotation speed was set at 200 rpm, and the reaction was continued for 12 h. After the reaction, the product was washed and centrifuged alternately with 100 mL of deionized water and acetone until the washing solution became clear. Then, the product was placed in an oven at 70 °C and dried for 36 h to obtain modified halloysite nanotubes;

[0088] Preparation of Superhydrophilic Membrane: 20 mg of DHNTs and 167 mg of pGO were weighed respectively. Then, DHNTs were mixed with deionized water at a mass ratio of 1:5000, and pGO was mixed with deionized water at a mass ratio of 1:3000, and dispersed under ultrasound at 30 kHz for 30 min respectively. Subsequently, the DHNTs dispersion and the pGO dispersion were mixed at a mass ratio of 1:5 and ultrasonic dispersion was continued for 1 h. 0.9015 g of ethylenediamine was dissolved in 1 L of deionized water to prepare a 15 mmol / L ethylenediamine solution. 120 g of the ethylenediamine solution was weighed and mixed with the DHNTs / pGO dispersion at a mass ratio of 1:5, and ultrasonic dispersion was carried out at 60 °C for 2 h. Then, after the dispersion cooled to room temperature, it was added to a sand core filtration device equipped with a CA membrane, and suction filtration was carried out at a pressure of 0.01 MPa(A). After suction filtration, the membrane surface was washed with deionized water for 50 s and air-dried naturally at room temperature for 48 h to remove the solvent, and the 2# superhydrophilic membrane was prepared; its oil droplet contact angle was 163.4°.

[0089] Preparation Example 3

[0090] The superhydrophilic membrane of the membrane separation device was prepared according to the method described in Preparation Example 1, except that:

[0091] Preparation of porous graphene oxide (pGO): The mass ratio of graphene oxide to deionized water was 1:300, the ultrasonic frequency was 35 kHz, the volume ratio of the dispersion liquid to concentrated nitric acid was 1:12, and the reaction time was 2 h;

[0092] Preparation of modified halloysite nanotubes (DHNTs): The concentration of Tris-HCl buffer solution was 30 mmol / L, the mass ratio of dopamine to Tris-HCl buffer solution was 1:800, and then the pH was adjusted to 8.9 with 0.1 wt% sodium hydroxide solution. The mass ratio of HNTs to the mixed solution was 1:1500. After mixing, the reaction was carried out at 50 °C for 18 h. The drying temperature of the reaction product was 70 °C and the drying time was 60 h;

[0093] Preparation of superhydrophilic membrane: The mass ratio of DHNTs to deionized water was 1:3000, the mass ratio of pGO to deionized water was 1:2000, and the mass ratio of the DHNTs dispersion liquid to the pGO dispersion liquid was 1:3. The concentration of the ethylenediamine solution was 30 mmol / L, and the mass ratio of the ethylenediamine solution to the DHNTs / pGO dispersion liquid was 1:5, to prepare the No. 3 superhydrophilic membrane; its oil droplet contact angle was 168.8°.

[0094] Preparation of diamines and polyamines containing diphenylmethane structure

[0095] Example 1

[0096] The process flow for preparing diamines and polyamines containing diphenylmethane structure is as Figure 1 shown. Material 1 aniline (concentration 99.9 wt%, 50 kg / h) was mixed with Material 2 catalyst hydrochloric acid solution (concentration 25 wt%, 2.9 kg / h) and the in-system recycled Material 19 aniline hydrochloride solution in static mixer 3, and reacted at 40 °C to form aniline hydrochloride. At this time, the molar ratio of HCl to aniline in the system was 0.3:1, while the molar ratio of HCl in the actually added hydrochloric acid to aniline was 0.03:1. Subsequently, it was mixed with Material 4 formaldehyde solution (concentration 37.0 wt%, 24.8 kg / h) in static mixer 5. The molar ratio of formaldehyde to aniline in the formaldehyde solution was 0.45:1. Subsequently, the mixed solution entered reactor 6 and reacted at 70 °C for 4 h to form a reaction solution containing DAM salt, aniline salt, DAM and aniline. In this example, since the molar content of aniline in the reaction solution has exceeded H +Content, so there is no need to supplement additional material 18 aniline. The reaction solution is sent from the bottom of the reactor 6 to the membrane separator 7 equipped with a #1 super-hydrophilic membrane through a pump from bottom to top. The inner diameter of the shell of this membrane separator is 0.2 m, the length of the membrane separation tube is 0.2 m, the inner diameter is 10 mm, the thickness of the membrane separation tube is 0.5 mm, the number of membrane tubes is 100, and the distance between the supporting baffle plates is 50 mm. The membrane separation temperature is 85 °C, and the pressure difference between the oil phase and the water phase is 0.10 MPa. The water phase separated by the membrane separator (aniline hydrochloride concentration 46.2 wt%, 4.7 kg / h) enters the storage tank 8 containing aniline hydrochloride water phase through the tube side, and then is sent to the rising film evaporator 9 for evaporation and concentration at 110 °C. The deviation of the water content in the concentrated system is 0.9%. After the aniline / water vapor is condensed, it is sent to the wastewater treatment process for treatment 17. The concentrated water phase (26.4 kg / h, containing 15.9 kg / h of aniline and 6.6 kg / h of HCl) is mixed with aniline and hydrochloric acid in the static mixer 3 as the raw material and catalyst for the condensation reaction; the organic phase separated by the membrane separator is sent to the static mixer 11 through the shell side and mixed with 5% sodium hydroxide solution (19.9 kg / h). The molar flow ratio of sodium hydroxide solution to hydrochloric acid in material 2 is 1.11:1. The temperature after mixing is 85 °C, and the mixture is sent to the washing kettle 12 for stirring and mixing, and then overflows to the oil-water separator 13 for phase separation at 85 °C. The phase separation time is 30 min. The water phase is sent to the wastewater treatment process 17 after passing through the alkali-washed wastewater storage tank 16. After washing, the organic phase at 90 °C is sent to the DAM refining process 15 for treatment after passing through the storage tank 14 to obtain the DAM product. The treatment flux of the #1 super-hydrophilic membrane is 178.1 Lm -2 h -1 。

[0097] Example 2

[0098] The process flow for preparing diamines and polyamines containing diphenylmethane structure is as Figure 1 shown. Mix material 1 aniline (concentration 99.9 wt%, 50 kg / h), material 2 catalyst hydrochloric acid solution (concentration 25 wt%, 4.8 kg / h), and the circulating material 19 aniline hydrochloride solution in the system in the static mixer 3 to react at 50 °C to form aniline hydrochloride. At this time, the molar ratio of HCl to aniline in the system is 0.4:1, while the molar ratio of HCl in the actually added hydrochloric acid to aniline is 0.047:1. Subsequently, it is mixed with material 4 formaldehyde solution (concentration 42.0 wt%, 25.3 kg / h) in the static mixer 5. The molar ratio of formaldehyde to aniline in the formaldehyde solution is 0.50:1. Then the mixed solution enters the reactor 6 and reacts at 80 °C for 3 h to form a reaction solution containing DAM salt, aniline salt, DAM, and aniline. In this example, since the molar content of aniline in the reaction solution has exceeded H +Content, so there is no need to supplement additional material 18 aniline. The reaction solution is fed from the bottom of the reactor 6 to the membrane separator 7 equipped with a #2 superhydrophilic membrane through a pump from bottom to top. This membrane separator is the same as the membrane separator in Example 1. The membrane separation temperature is 70 °C, and the pressure difference between the oil phase and the water phase is 0.20 MPa. The water phase separated by the membrane separator (aniline hydrochloride concentration 52.3 wt%, 4.9 kg / h) enters the storage tank 8 containing the aniline hydrochloride water phase through the tube side, and then is sent to the rising film evaporator 9 for evaporation and concentration at 110 °C. The deviation of the water content in the concentrated system is 1.2%. After the aniline / water vapor is condensed, it is sent to the wastewater treatment process for treatment 17. The concentrated water phase (26.6 kg / h, containing 15.9 kg / h of aniline and 9.0 kg / h of HCl) is mixed with aniline and hydrochloric acid in the static mixer 3 as the raw material and catalyst for the condensation reaction; the organic phase separated by the membrane separator enters the static mixer 11 through the shell side and is mixed with a 4% sodium hydroxide solution (35.6 kg / h). The molar flow ratio of the sodium hydroxide solution to the material 2 hydrochloric acid is 1.1:1. The temperature after mixing is 92 °C. After mixing, it is sent to the washing kettle 12 for stirring and mixing, and then overflows to the oil-water separator 13 for phase separation at 85 °C. The phase separation time is 30 min. The water phase is sent to the wastewater treatment process 17 after passing through the alkali-washing wastewater storage tank 16. After washing, the organic phase at 90 °C is sent to the DAM refining process 15 for treatment to obtain the DAM product. The treatment flux of the #2 superhydrophilic membrane is 176.2 Lm -2 h -1 。

[0099] Example 3

[0100] The process flow for preparing diamines and polyamines containing diphenylmethane structures is as Figure 1 shown. The material 1 aniline (concentration 99.9 wt%, 50 kg / h), the material 2 catalyst hydrochloric acid solution (concentration 30 wt%, 2.4 kg / h), and the system's internal circulating material 19 aniline hydrochloride solution are mixed in the static mixer 3 to react at 35 °C to form aniline hydrochloride. At this time, the molar ratio of HCl to aniline in the system is 0.27:1, while the molar ratio of HCl to aniline in the actually added hydrochloric acid is 0.029:1. Subsequently, it is mixed with the material 4 formaldehyde solution (concentration 50.0 wt%, 14.8 kg / h) in the static mixer 5. The molar ratio of formaldehyde to aniline in the formaldehyde solution is 0.35:1. Subsequently, the mixed solution enters the reactor 6 and reacts at 95 °C for 3 h to form a reaction solution containing DAM salt, aniline salt, DAM, and aniline. In this example, since the molar content of aniline in the reaction solution has exceeded H +Content, so there is no need to supplement additional material 18 aniline. The reaction solution is fed from the bottom of the reactor 6 to the membrane separator 7 equipped with a #3 super-hydrophilic membrane through a pump from bottom to top. This membrane separator is the same as the membrane separator in Example 1. The membrane separation temperature is 90 °C, and the pressure difference between the oil phase and the water phase is 0.05 MPa. The water phase separated by the membrane separator (aniline hydrochloride concentration 49.7 wt%, 4.3 kg / h) enters the storage tank 8 containing the aniline hydrochloride water phase through the tube side, and then is sent to the rising film evaporator 9 for evaporation and concentration at 110 °C. The deviation of the water content in the concentrated system is 1.8%. After the aniline / water vapor is condensed, it is sent to the wastewater treatment process for treatment 17. The concentrated water phase (23.5 kg / h, containing 15.4 kg / h of aniline and 6.2 kg / h of HCl) is mixed with aniline and hydrochloric acid in the static mixer 3 and used as the raw material and catalyst for the condensation reaction; the organic phase separated by the membrane separator enters the static mixer 11 through the shell side and is mixed with a 3% sodium hydroxide solution (30.0 kg / h). The molar flow ratio of the sodium hydroxide solution to the hydrochloric acid in material 2 is 1.11:1. The temperature after mixing is 81 °C, and the mixture is sent to the washing kettle 12 for stirring and mixing, and then overflows to the oil-water separator 13 for phase separation at 85 °C. The phase separation time is 30 min. The water phase is sent to the wastewater treatment process 17 after passing through the alkali-washing wastewater storage tank 16. After washing, the organic phase at 90 °C is sent to the DAM refining process 15 for treatment through the storage tank 14 to obtain the DAM product. The treatment flux of the #3 super-hydrophilic membrane is 174.5 Lm -2 h -1 。

[0101] Example 4

[0102] The process flow for preparing diamines and polyamines containing a diphenylmethane structure is as Figure 1 shown. Mix material 1 aniline (concentration 99.9 wt%, 50 kg / h), material 2 catalyst hydrochloric acid solution (concentration 20 wt%, 1.9 kg / h), and the circulating material 19 aniline hydrochloride solution in the system in the static mixer 3 to react at 40 °C to form aniline hydrochloride. At this time, the molar ratio of HCl to aniline in the system is 0.20:1, while the molar ratio of HCl in the actually added hydrochloric acid to aniline is 0.013:1. Subsequently, it is mixed with material 4 formaldehyde solution (concentration 35.0 wt%, 20.1 kg / h) in the static mixer 5. The molar ratio of formaldehyde to aniline in the formaldehyde solution is 0.30:1. Then the mixed solution enters the reactor 6 and reacts at 50 °C for 4 h to form a reaction solution containing DAM salt, aniline salt, DAM, and aniline. In this example, since the molar amount of aniline in the reaction solution is less than H +Content, so a stream of fresh aniline (concentration 99.9 wt%, 8.8 kg / h) needs to be added to the reaction solution. At this time, the molar ratio of aniline to H⁺ in the reaction solution is 1.1:1. The reaction solution is fed from the bottom of the reactor 6 to the membrane separator 7 equipped with a #3 superhydrophilic membrane by a pump from bottom to top. This membrane separator is the same as the membrane separator in Example 1. The membrane separation temperature is 60 °C, and the pressure difference between the oil phase and the water phase is 0.15 MPa. The water phase separated by the membrane separator (concentration of aniline hydrochloride 37.2 wt%, 6.2 kg / h) enters the storage tank 8 for the water phase containing aniline hydrochloride through the tube side, and then is sent to the rising film evaporator 9 for evaporation and concentration at 110 °C. The deviation of the water content in the concentrated system is 2.7%. After the aniline / water vapor is condensed, it is sent to the wastewater treatment process for treatment 17. The concentrated water phase (35.2 kg / h, containing 22.8 kg / h of aniline and 5.4 kg / h of HCl) is mixed with aniline and hydrochloric acid in the static mixer 3 and used as the raw material and catalyst for the condensation reaction; the organic phase separated by the membrane separator enters the static mixer 11 through the shell side and is mixed with a 5% sodium hydroxide solution (12.2 kg / h). The molar flow ratio of the sodium hydroxide solution to the hydrochloric acid in material 2 is 1.09:1. The temperature after mixing is 90 °C. After mixing, it is sent to the washing kettle 12 for stirring and mixing, and then overflows to the oil-water separator 13 for phase separation at 85 °C. The phase separation time is 30 min. The water phase is sent to the wastewater treatment process 17 after passing through the alkali-washed wastewater storage tank 16. The washed organic phase is sent to the DAM refining process 15 for treatment at 90 °C through the storage tank 14 to obtain the DAM product. The treatment flux of the #1 superhydrophilic membrane is 213.5 Lm -2 h -1 。

[0103] Comparative Example 1

[0104] This comparative example is compared with Preparation Example 1. The difference is that during the preparation of the hydrophilic membrane, graphene oxide was not modified into porous graphene oxide (pGO). Finally, a #5 hydrophilic membrane was prepared, and its underwater oil droplet contact angle was 147.3°. This membrane was installed in the membrane separator, and the structural dimensions of this membrane separator were the same as those in Example 1.

[0105] The process flow for preparing diamines and polyamines containing diphenylmethane structures is as Figure 1As shown, material 1 aniline (concentration 99.9 wt%, 50 kg / h) is mixed with material 2 catalyst hydrochloric acid solution (concentration 25 wt%, 8.0 kg / h) and the recycled material 19 aniline hydrochloride solution in the system in static mixer 3, and reacts at 40°C to form aniline hydrochloride. At this time, the molar ratio of HCl to aniline in the system is 0.3:1, while the molar ratio of HCl in the actually added hydrochloric acid to aniline is 0.083:1. Subsequently, it is mixed with material 4 formaldehyde solution (concentration 37.0 wt%, 24.2 / h) in static mixer 5. The molar ratio of formaldehyde to aniline in the formaldehyde solution is 0.45:1. Subsequently, the mixed solution enters reactor 6 and reacts at 70°C for 4 h to form a reaction solution containing DAM salt, aniline salt, DAM and aniline. In this example, since the molar content of aniline in the reaction solution has exceeded the H + content, there is no need to supplement additional material 18 aniline. The reaction solution is sent from the bottom of reactor 6 to the membrane separator 7 equipped with a 5# super hydrophilic membrane by a pump from bottom to top. The inner diameter of the shell of this membrane separator is 0.2 m, the length of the membrane separation tube is 0.3 m, the inner diameter is 10 mm, the thickness of the membrane separation tube is 0.5 mm, the number of membrane tubes is 100, and the distance between the support baffle plates is 50 mm. The membrane separation temperature is 85°C, and the pressure difference between the oil phase and the water phase is 0.10 MPa. The water phase separated by the membrane separator (aniline hydrochloride concentration 53.3 wt%, 3.1 kg / h) enters the storage tank 8 containing aniline hydrochloride water phase through the tube side, and then is sent to the rising film evaporator 9 for evaporation and concentration at 110°C. After the aniline / water vapor is condensed, it is sent to the wastewater treatment process for treatment 17. The concentrated water phase (23.9 kg / h, containing 11.9 kg / h of aniline and 4.8 kg / h of HCl) is mixed with aniline and hydrochloric acid in static mixer 3 and used as the raw material and catalyst for the condensation reaction; the organic phase separated by the membrane separator is sent to static mixer 11 through the shell side and mixed with 3% sodium hydroxide solution (81.0 kg / h). The molar flow ratio of sodium hydroxide solution to material 2 hydrochloric acid is 1.1:1. The temperature after mixing is 88°C. After mixing, it is sent to washing kettle 12 for stirring and mixing, and then overflows to oil-water separator 13 for phase separation at 85°C. The phase separation time is 30 min. The water phase is sent to the wastewater treatment process 17 after passing through the alkali washing wastewater storage tank 16. The washed organic phase is sent to the DAM refining process 15 for treatment at 90°C after passing through storage tank 14 to obtain DAM products. The treatment flux of this hydrophilic membrane is 124.5 Lm -2 h -1 。

[0106] Comparative Example 2

[0107] This comparative example is compared with Example 1. The difference is that the hydrophilic membrane in the membrane separator uses a common purchased PALLRTM 41HF050E hydrophilic membrane, and the structural dimensions of this membrane separator are the same as those in Example 1.

[0108] The process flow for preparing diamines and polyamines containing a diphenylmethane structure is as follows Figure 1 shown. Material 1, aniline (concentration 99.9 wt%, 50 kg / h), is mixed with Material 2, a catalyst hydrochloric acid solution (concentration 30 wt%, 17.2 kg / h), and the recycled Material 19, aniline hydrochloride solution, in a static mixer 3 to react at 38°C to form aniline hydrochloride. At this time, the molar ratio of HCl to aniline in the system is 0.3:1, while the molar ratio of HCl in the actually added hydrochloric acid to aniline is 0.26:1. Subsequently, it is mixed with Material 4, a formaldehyde solution (concentration 37.0 wt%, 19.9 kg / h), in a static mixer 5. The molar ratio of formaldehyde to aniline in the formaldehyde solution is 0.40:1. Then the mixed solution enters a reactor 6 and reacts at 75°C for 3 h to form a reaction solution containing DAM salt, aniline salt, DAM, and aniline. In this example, since the molar content of aniline in the reaction solution has exceeded the H + content, there is no need to supplement additional Material 18, aniline. The reaction solution is pumped from the bottom of the reactor 6 upwards through a pump and sent to a membrane separator 7 equipped with a #5 super-hydrophilic membrane. The membrane separation temperature is 85°C, and the pressure difference between the oil phase and the water phase is 0.10 MPa. The water phase separated by the membrane separator (aniline hydrochloride concentration 6.3 wt%, 2.2 kg / h) enters a storage tank 8 for aniline hydrochloride aqueous solution through the tube side, and then is sent to a rising film evaporator 9 for evaporation and concentration at 110°C. After the aniline / water vapor is condensed, it is sent to a wastewater treatment process for treatment 17. The concentrated water phase (5.1 kg / h, containing 1.0 kg / h of aniline and 0.4 kg / h of HCl) is mixed with aniline and hydrochloric acid in a static mixer 3 and used as the raw material and catalyst for the condensation reaction; the organic phase separated by the membrane separator is sent to a static mixer 11 through the shell side and mixed with a 3% sodium hydroxide solution (208.3 kg / h). The molar flow ratio of the sodium hydroxide solution to Material 2, hydrochloric acid, is 1.1:1. The temperature after mixing is 84°C. After mixing, it is sent to a washing kettle 12 for stirring and mixing, and then overflows to an oil-water separator 13 for phase separation at 85°C. The phase separation time is 30 min. The water phase is sent to a wastewater treatment process 17 after passing through an alkali-washed wastewater storage tank 16. The washed organic phase at 90°C is sent to a DAM refining process 15 for treatment after passing through a storage tank 14 to obtain a DAM product.

[0109] Comparative Example 3

[0110] In this comparative example, according to the traditional process, diamines and polyamines containing a diphenylmethane structure are prepared by adding caustic soda to completely neutralize the acid catalyst.

[0111] Material 1, aniline (concentration 99.9 wt%, 50 kg / h), is mixed with Material 2, hydrochloric acid (25 wt%, 23.5 kg / h), in static mixer 3 and reacts at 40°C to form aniline hydrochloride. At this time, the molar ratio of HCl to aniline is 0.3:1. Subsequently, it is mixed with Material 4, formaldehyde solution (concentration 37.0 wt%, 19.6 kg / h), in static mixer 5. The molar ratio of formaldehyde to aniline in the formaldehyde solution is 0.45:1. Subsequently, the mixed solution enters reactor 6 and reacts at 70°C for 5 h to form a reaction solution containing DAM salt, aniline salt, DAM, and aniline. Subsequently, the reaction solution is mixed with sodium hydroxide solution (5%, 141.7 kg / h). The molar flow rate ratio of the sodium hydroxide solution to Material 2 hydrochloric acid is 1.1:1. After mixing, the temperature is 85°C. After mixing, it is sent to washing kettle 12 for stirring and mixing, and then overflows to oil-water separator 13 for phase separation at 85°C. The phase separation time is 30 min. The aqueous phase is sent to wastewater treatment process 17 for treatment after passing through alkali-washing wastewater storage tank 16. The washed organic phase is sent to DAM refining process 15 for treatment at 90°C after passing through storage tank 14 to obtain DAM product.

[0112] Table 1 Compositions of oil and water phases after membrane separation in each example and comparative example

[0113]

[0114] Table 2 Comparison of alkali consumption in each example and comparative example

[0115] Consumption of pure sodium hydroxide, g / h Example 1 0.99 Example 2 1.42 Example 3 0.90 Example 4 0.61 Comparative Example 1 2.43 Comparative Example 2 6.26 Comparative Example 3 7.08

[0116] The embodiments of the present invention have been described above. The above description is exemplary and not exhaustive, and is not limited to the disclosed embodiments. Many modifications and variations are obvious to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A method for preparing diamines and polyamines containing diphenylmethane structure with low acid consumption, characterized in that, The method comprises the following steps: S1: In the presence of an acidic catalyst, aniline undergoes a salting reaction to form anilinium salt. S2: The anilinium salt and formaldehyde solution are mixed for a condensation reaction to obtain a reaction solution containing diamine salt and polyamine salt with a diphenylmethane structure. S3: The reaction solution of S2 is added to a membrane separator, and the acid catalyst in the aqueous phase is separated out with water in the form of anilinium salt, realizing the separation of the aqueous phase from the organic phase containing diamine and polyamine with a diphenylmethane structure. S4: The organic phase of S3 is subjected to alkali washing and distillation to obtain diamine and polyamine with a diphenylmethane structure. After the aqueous phase obtained in S3 is distilled to remove part of the water, it is returned to S1 as a raw material for the condensation reaction and the acid catalyst. Among them, the membrane separator in S3 is a shell-and-tube membrane separator. Among them, the membrane in the S3 membrane separator is a modified halloysite nanotube / porous graphene oxide superhydrophilic membrane; the superhydrophilic membrane is prepared by the following steps: SS1: Graphene oxide GO powder is added to water for dispersion, and the dispersion is mixed with concentrated nitric acid and then continuously dispersed. After centrifugal separation, washing, suction filtration, and drying, porous graphene oxide pGO is obtained. SS2: Dopamine is dissolved in Tris-HCl solution, mixed and reacted, the pH value of the mixed solution is adjusted, HNTs are added, dispersed and reacted, and after centrifugal separation, washing, suction filtration, and drying, modified halloysite nanotubes DHNTs are obtained. SS3: pGO is dissolved in water to obtain a pGO dispersion; DHNTs are dissolved in water to obtain a DHNTs dispersion. SS4: The pGO dispersion and the DHNTs dispersion are mixed and dispersed and then mixed with an ethylenediamine solution, dispersed and suction filtered, and the mixed solution is loaded on a microporous membrane, washed and dried to obtain a DHNTs / pGO superhydrophilic membrane. Among them, the conditions for the membrane separation operation are an operating temperature of 60 - 100 °C and an operating pressure difference between the feed side and the aqueous phase extraction side of 0.05 - 0.2 MPa.

2. The method according to claim 1, characterized in that, The acidic catalyst in S1 is selected from sulfuric acid and / or hydrochloric acid. and / or, the molar ratio of H of all the acidic catalysts in S1 + to aniline is (0.2 - 0.5):1; And / or, the temperature of the salting reaction in S1 is 35 - 50 °C.

3. The method according to claim 2, wherein The acidic catalyst in S1 is selected from 10 - 35 wt% hydrochloric acid solution and / or 10 - 30 wt% sulfuric acid solution. The molar ratio of H of the newly added acidic catalyst in S1 + to aniline is (0.01 - 0.1):

1.

4. The method according to claim 3, wherein The acidic catalyst in S1 is selected from 20 - 30 wt% hydrochloric acid solution. The molar ratio of H of the newly added acidic catalyst in S1 + to aniline is (0.01 - 0.05):

1.

5. The method according to claim 1 or 2, characterized in that, The molar ratio of formaldehyde in the formaldehyde solution in S2 to aniline in the anilinium salt is 0.3 - 0.6:1; the concentration of the formaldehyde solution is 35 - 50 wt%. And / or, the reaction time of anilinium salt and formaldehyde in S2 is 3 - 5 h, and the reaction temperature is 50 - 100 °C.

6. The method according to claim 5, characterized in that, The molar ratio of formaldehyde in the formaldehyde solution in S2 to aniline in the anilinium salt is 0.35 - 0.5:1; the concentration of the formaldehyde solution is 37 - 42 wt%.

7. The method according to claim 1, wherein The aqueous phase in S3 contains: 35 - 55 wt% anilinium salt, 2 - 8 wt% diamine and polyamine salt, and the remaining part is water. And / or, the oil phase in S3 contains: 60 - 85 wt% diamine and polyamine, 1 - 9 wt% diamine and polyamine salt, 1 - 4 wt% anilinium salt, 1 - 3 wt% water, and the remaining part is aniline.

8. The method according to claim 1, wherein The alkali washing in S4 uses a sodium hydroxide solution. And / or, the deviation of the mass of water removed from the aqueous phase of S4 by distillation from the total water brought in by the raw materials and generated by the reaction, after deducting the water carried away by the oil phase after membrane separation in S3 and the remaining water in the concentrated aqueous phase, is less than 3%.

9. The method according to claim 8, characterized in that The concentration of the sodium hydroxide solution in S4 is 3-5 wt%, and the molar ratio of the sodium hydroxide solution to the hydrochloric acid added in S2 is 1.05-1.15:1; And / or, the deviation of the mass of water removed from the aqueous phase of S4 by distillation from the total water brought in by the raw materials and generated by the reaction, after deducting the water carried away by the oil phase after membrane separation in S3 and the remaining water in the concentrated aqueous phase, is less than 1%.

10. A superhydrophilic membrane used in the method according to any one of claims 1-9, characterized in that, The superhydrophilic membrane is a modified halloysite nanotube / porous graphene oxide superhydrophilic membrane.

11. A method for preparing a superhydrophilic membrane, the superhydrophilic membrane being the superhydrophilic membrane used in the method according to any one of claims 1-9, or the superhydrophilic membrane according to claim 10, characterized in that, The superhydrophilic membrane is prepared by the following steps: SS1: Add graphene oxide GO powder to water for dispersion, mix the dispersion with concentrated nitric acid and continue to disperse, then perform centrifugal separation, washing, suction filtration, and drying to obtain porous graphene oxide pGO; SS2: Dissolve dopamine in Tris-HCl solution, react after mixing, adjust the pH value of the mixed solution, add HNTs, react after dispersion, perform centrifugal separation, washing, suction filtration, and drying to obtain modified halloysite nanotubes DHNTs; SS3: Dissolve pGO in water to obtain a pGO dispersion; dissolve DHNTs in water to obtain a DHNTs dispersion; SS4: Mix the pGO dispersion and the DHNTs dispersion and disperse them, then mix with an ethylenediamine solution, disperse and perform suction filtration, load the mixed solution onto a microporous membrane, wash and dry to obtain a DHNTs / pGO superhydrophilic membrane.

12. The method according to claim 11, wherein The dispersion method for the dispersion in any of the steps SS1, SS2, SS3, and SS4 is ultrasonic dispersion; And / or, the centrifugation is at a rotational speed of 3000-5000 rpm / min for 5-30 min; And / or, the operating pressure for the suction filtration is 5-10 kPa.

13. The method according to claim 12, wherein The ultrasonic dispersion frequency in SS1, SS2, SS3, and SS4 is 30-40 kHz, and the time is 1-2 h.

14. The method according to claim 11, wherein The mass ratio of GO to water in SS1 is 1:100-500; And / or, the volume ratio of the GO dispersion to concentrated nitric acid in SS1 is 1:5-20; And / or, the washing in SS1 is ultrasonic washing with deionized water; And / or, the drying temperature in SS1 is 25-50 °C, and the time is 12-24 h.

15. The method according to claim 14, characterized in that, The mass ratio of GO to water in SS1 is 1:200-300; And / or, the volume ratio of the GO dispersion to concentrated nitric acid in SS1 is 1:10-15; The washing in SS1 is until the pH value is 6-7.

16. The method according to claim 11, wherein The mass ratio of dopamine to the Tris-HCl solution in SS2 is 1:500-1000, where the concentration of the Tris-HCl solution is 10-50 mmol / L; And / or, the stirring rate before adding HNTs in SS2 for the reaction is 100-300 rpm, the temperature is 20-50 °C, and the reaction time is 8-24 h; And / or, the pH value of the solution is adjusted to 7-9 in SS2; And / or, the mass ratio of HNTs to the mixed solution in SS2 is 1:1000-2000; And / or, the washing in SS2 is ultrasonic washing alternately with acetone and deionized water; And / or, the drying temperature in SS2 is 50 - 70 °C and the time is 36 - 60 h.

17. The method according to claim 11, wherein In the pGO dispersion of SS3, the mass ratio of pGO to water is 1:2000 - 10000; And / or, in the DHNTs dispersion of SS3, the mass ratio of DHNTs to water is 1:2000 - 20000.

18. The method according to claim 11, wherein The mass ratio of the DHNTs dispersion to the pGO dispersion in SS4 is 1:1 - 5; And / or, the mass ratio of the ethylenediamine solution to the DHNTs / pGO mixture in SS4 is 1:5 - 10, and the ethylenediamine content in the ethylenediamine solution is 10 - 40 mmol / L; And / or, the microporous filter membrane of SS4 is one or more of cellulose acetate membrane, polyethersulfone, and polyvinylidene fluoride; And / or, the negative pressure operating pressure for suction filtration in SS4 is 5 - 10 kPa; And / or, in SS4, the washing is to clean the surface of the microporous filter membrane with flowing deionized water, and the washing time is 15 - 60 s; And / or, in SS4, the drying is natural air drying at room temperature, and the drying time is 24 - 72 h.

19. The method according to claim 18, wherein The microporous filter membrane of SS4 is polyvinylidene fluoride.

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