A method for separating sodium carbonate and sodium chloride from crude hydrazine

Abstract

This invention provides a method for separating sodium carbonate and sodium chloride from crude hydrazine. The method includes the following steps: treating the crude hydrazine solution by electrodialysis, reverse osmosis, and / or nanofiltration to separate sodium carbonate and sodium chloride from the crude hydrazine. The method of this invention is simple, has a short process flow, introduces no impurities, is easy to operate, allows for easy control of operating parameters, and has low energy consumption. Multiple separations of sodium carbonate and sodium chloride from hydrazine hydrate improve the separation efficiency of impurity salts and the purity of hydrazine hydrate, yielding a pure hydrazine hydrate solution and high-purity sodium carbonate and sodium chloride. Furthermore, the process uses a full membrane system, eliminating the need for added reagents and avoiding environmental pollution and equipment corrosion.

Description

Technical Field

[0001] This invention relates to the field of hydrazine hydrate purification technology, and in particular to a method for separating sodium carbonate and sodium chloride from crude hydrazine. Background Technology

[0002] Hydrazine hydrate (N₂H₄·H₂O), as an important chemical raw material and intermediate, is mainly used in the production of foaming agents for plastics and rubber, pharmaceuticals, pesticides, water treatment, and the synthesis of high-energy fuels in organic processes. The urea process is a commonly used method in my country, where a mixed solution of urea, sodium hypochlorite, and sodium hydroxide is fed into a reaction vessel and oxidized under the catalysis of potassium permanganate or manganese sulfate. The resulting hydrazine hydrate reaction solution is then cooled, evaporated, desalted, and distilled to obtain a purified hydrazine hydrate solution. However, the synthesis process is prone to the phenomenon of crystal re-dissolution, accompanied by the production of sodium carbonate and sodium chloride as byproducts. This leads to incomplete separation of hydrazine hydrate from sodium carbonate and sodium chloride, resulting in a decrease in the purity of hydrazine hydrate. Therefore, further separation and purification are necessary.

[0003] Currently, the process for removing impurities such as sodium carbonate and sodium chloride in the purification of hydrazine hydrate employs a combination of methods including freeze separation, evaporation crystallization desalination, and chemical dosing. However, this method suffers from problems such as poor desalination efficiency, high evaporation energy consumption, and low purity of hydrazine hydrate. Existing freeze crystallization and evaporation techniques utilize the difference in solubility between hydrazine hydrate and impurities to separate them, but these processes are cumbersome. They require first cooling and freeze crystallization to remove sodium carbonate, followed by heating and evaporation to remove sodium chloride. The temperature fluctuations result in significant heat loss, leading to high energy consumption. Furthermore, with prolonged use, equipment scaling occurs, affecting heat transfer and reducing separation efficiency. Moreover, existing hydrazine hydrate purification technologies require multiple steps including freeze separation, evaporation, chemical precipitation, separation, and desalination to obtain purified hydrazine hydrate, resulting in a long process and the introduction of impurities.

[0004] CN104860275A discloses a method for removing sodium carbonate from a crude hydrazine hydrate solution. The steps are as follows: Chloride is added to the crude hydrazine hydrate solution, causing the cations in the chloride to react with carbonate ions to form a sparingly soluble carbonate. The sparingly soluble carbonate is then separated by centrifugation. After removing sodium carbonate, the hydrazine hydrate solution is further filtered through a membrane to remove any remaining cations, thus completely removing sodium carbonate from the crude hydrazine hydrate solution. However, this method uses a chemical reaction to remove carbonate ions first, followed by membrane filtration to remove the remaining cations. This method suffers from poor desalination efficiency, low purity of hydrazine hydrate, a long process, and the introduction of chloride impurities.

[0005] CN112209410A discloses a method for treating sodium chloride brine, a byproduct of hydrazine hydrate, comprising the following steps: a) adding acid and a homogeneous catalyst to the sodium chloride brine; b) reacting the heated brine with oxygen; c) adding a homogeneous catalyst to the brine after the first reaction and reacting it with oxygen again; S5) cooling the brine after the second reaction and removing gaseous ammonia from it using an ammonia-nitrogen separation membrane; S6) evaporating and crystallizing the brine, followed by solid-liquid separation to obtain a solid salt product. Its advantages are that the TOC of the solid salt product can be controlled below 10 ppm. Its disadvantages are that the chemical reaction method for impurity removal results in a long process and the introduction of impurities (including raw materials, catalysts, and reaction products).

[0006] Therefore, it is of great significance to explore a method that can simultaneously and efficiently separate sodium carbonate and sodium chloride from hydrazine hydrate and overcome the shortcomings of existing technologies.

[0007] In view of this, the present invention is hereby proposed. Summary of the Invention

[0008] One objective of this invention is to provide a method for separating sodium carbonate and sodium chloride from crude hydrazine. The method includes the following steps: subjecting the crude hydrazine solution to electrodialysis, reverse osmosis, and / or nanofiltration to separate sodium carbonate and sodium chloride from the crude hydrazine, thus solving the problem of incomplete separation of hydrazine hydrate from sodium carbonate and sodium chloride in existing preparation processes; addressing the issues of high energy consumption and low efficiency in existing hydrazine hydrate refining methods; shortening the process route; ensuring no impurities are introduced; and ultimately achieving a sodium carbonate and sodium chloride removal rate of over 95%.

[0009] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted:

[0010] In a first aspect, the present invention provides a method for separating sodium carbonate and sodium chloride from crude hydrazine, the method comprising the following steps:

[0011] The crude hydrazine solution is subjected to electrodialysis, as well as reverse osmosis and / or nanofiltration to separate sodium carbonate and sodium chloride from the crude hydrazine.

[0012] In this invention, a combination of electrodialysis, reverse osmosis, and / or nanofiltration is employed. This is because while nanofiltration and reverse osmosis can remove sodium carbonate and sodium chloride impurities from crude hydrazine, during nanofiltration separation of sodium carbonate and hydrazine hydrate (containing sodium chloride), the product water side contains sodium chloride and hydrazine hydrate, while the concentrate side, although containing retained sodium carbonate, still contains sodium chloride and hydrazine hydrate at concentrations comparable to those in the product water. Therefore, the sodium carbonate separated by nanofiltration cannot form a single sodium carbonate salt for resource recovery. Further salt separation processes are required for sodium carbonate recovery. Electrodialysis, on the other hand, first separates sodium chloride and hydrazine hydrate (containing sodium carbonate) from the crude hydrazine. Through process design, high-purity and high-concentration sodium chloride can be obtained in the electrodialysis concentration chamber, and can be directly concentrated and evaporated for recovery.

[0013] Preferably, the process of the method includes any one of electrodialysis-reverse osmosis (ED-RO), nanofiltration-electrodialysis (NF-ED), electrodialysis-nanofiltration (ED-NF), electrodialysis-nanofiltration-reverse osmosis (ED-NF-RO), and nanofiltration-electrodialysis-reverse osmosis (NF-ED-RO), preferably electrodialysis-reverse osmosis or electrodialysis-nanofiltration-reverse osmosis, and more preferably electrodialysis-nanofiltration-reverse osmosis.

[0014] Among them, "electrodialysis-reverse osmosis" refers to treating the crude hydrazine solution with electrodialysis first, and then with reverse osmosis; "nanofiltration-electrodialysis" refers to treating the crude hydrazine solution with nanofiltration first, and then with electrodialysis; "electrodialysis-nanofiltration" refers to treating the crude hydrazine solution with electrodialysis first, and then with nanofiltration; "electrodialysis-nanofiltration-reverse osmosis" refers to treating the crude hydrazine solution with electrodialysis, nanofiltration, and reverse osmosis in sequence; and "nanofiltration-electrodialysis-reverse osmosis" refers to treating the crude hydrazine solution with nanofiltration, electrodialysis, and reverse osmosis in sequence.

[0015] Electrodialysis is an electrically driven process that, under the influence of a direct current electric field, utilizes the selective permeability of ion exchange membranes (i.e., cation exchange membranes allow only cations to pass through while repelling anions, and anion exchange membranes allow only anions to pass through while repelling cations) to cause charged ions to migrate directionally, thereby achieving the separation, concentration, and purification of salts in the solution. Under the influence of an electric field, the poor electrolysis properties of hydrazine hydrate are utilized to allow Na+ in the solution to migrate directionally. + Cl - Charged ions migrate to the concentrated water side while hydrazine hydrate does not migrate, thereby achieving the separation of hydrazine hydrate from the salt in the feed solution.

[0016] Reverse osmosis is a pressure-driven process that effectively retains all dissolved salts and organic matter while allowing water molecules to pass through. Therefore, under pressure, sodium carbonate can be effectively blocked on the concentrate side and efficiently permeate hydrazine hydrate, thus separating the two.

[0017] In this invention, a process combining electrodialysis and reverse osmosis is preferred. Electrodialysis utilizes the difference in ion migration ability under the action of an electric field to initially separate hydrazine hydrate and sodium chloride in the feed solution. Then, reverse osmosis utilizes its efficient interception of dissolved salts to further separate hydrazine hydrate and sodium carbonate, ultimately obtaining a pure hydrazine hydrate solution. The combined electrodialysis and reverse osmosis method has the following advantages: First, compared with existing technologies, the combined electrodialysis and reverse osmosis technology does not require the addition of reagents and significantly shortens the preparation process. The process is continuous and controllable, and easy to operate. Second, the crude hydrazine solution is directly fed into the electrodialysis system, allowing for preliminary separation of hydrazine hydrate from sodium carbonate and sodium chloride. Then, the hydrazine hydrate solution containing sodium carbonate in the electrodialysis is further separated by the reverse osmosis system, improving the removal rate of sodium carbonate and sodium chloride while increasing the purity of hydrazine hydrate. Furthermore, the generated sodium carbonate and sodium chloride can be reused as industrial salt resources, generating economic benefits. Third, the separation of hydrazine hydrate from sodium carbonate and sodium chloride in the solution is achieved using both electric and pressure-driven methods. The reverse osmosis permeate is a pure hydrazine hydrate solution. This method involves multiple separations to reduce the content of sodium carbonate and sodium chloride in hydrazine hydrate, and significantly reduces energy consumption compared to freeze crystallization and evaporation crystallization.

[0018] Furthermore, nanofiltration is added between electrodialysis and reverse osmosis to further improve the separation rate of hydrazine hydrate from sodium carbonate and sodium chloride, and better solve problems such as incomplete separation of hydrazine hydrate from sodium carbonate and sodium chloride, low purity of hydrazine hydrate, and high loss rate of hydrazine hydrate.

[0019] Preferably, the concentration of sodium carbonate in the crude hydrazine solution is in the range of 50–150 g / L, for example, it can be 50 g / L, 60 g / L, 70 g / L, 80 g / L, 90 g / L, 100 g / L, 110 g / L, 120 g / L, 130 g / L, 140 g / L, 150 g / L, etc.

[0020] Preferably, the concentration of sodium chloride in the crude hydrazine solution is in the range of 80–200 g / L, for example, it can be 80 g / L, 90 g / L, 100 g / L, 110 g / L, 120 g / L, 130 g / L, 140 g / L, 150 g / L, 160 g / L, 170 g / L, 180 g / L, 190 g / L, 200 g / L, etc.

[0021] Preferably, the mass percentage of hydrazine hydrate in the crude hydrazine solution ranges from 2% to 8%, for example, it can be 2%, 3%, 4%, 5%, 6%, 7%, 8%, etc.

[0022] Preferably, the electrodialysis treatment is used to remove sodium chloride from crude hydrazine.

[0023] In this invention, the selective permeability of electrodialysis to charged ions is utilized, allowing chloride and sodium ions in the solution to migrate to the concentrate side under the influence of an electric field, while uncharged hydrazine hydrate molecules remain on the desalination side. The desalination chamber contains sodium carbonate and hydrazine hydrate, with only a very small amount of sodium chloride impurities.

[0024] Preferably, the exchange membrane used in the electrodialysis treatment is a monovalent selective ion exchange membrane.

[0025] Preferably, after electrodialysis, the crude hydrazine solution yields a sodium chloride solution in the concentration chamber and a sodium carbonate-containing hydrazine hydrate solution in the dilute chamber.

[0026] Preferably, the conductivity of the sodium chloride solution in the concentrated chamber is 100–300 mS / cm, for example, 100 mS / cm, 150 mS / cm, 200 mS / cm, 250 mS / cm, 300 mS / cm, etc.; the conductivity of the hydrazine hydrate solution containing sodium carbonate in the dilute chamber is 20–100 mS / cm, for example, 20 mS / cm, 30 mS / cm, 40 mS / cm, 50 mS / cm, 60 mS / cm, 70 mS / cm, 80 mS / cm, 90 mS / cm, 100 mS / cm, etc.

[0027] Preferably, the electrodialysis membrane stack in the electrodialysis treatment consists of 5 to 500 electrodialysis membrane pairs (e.g., 5, 50, 100, 150, 200, 250, 300, 350, 400, 450, 500, etc.); each membrane has an effective area of ​​0.08 to 1.2 m². 2 For example, it could be 0.08m 2 0.1m 2 0.2m 2 0.5m 2 0.8m 2 1m 2 1.2m 2 wait.

[0028] Preferably, the voltage of the feed solution in the electrodialysis treatment is 5 to 300V, for example, 5V, 10V, 50V, 100V, 150V, 200V, 300V, etc., the current is 4 to 200A, for example, 4A, 10A, 50A, 80A, 100A, 120A, 150A, 180A, 200A, etc., and the operating temperature is 20 to 40℃, for example, 20℃, 25℃, 30℃, 35℃, 40℃, etc.

[0029] Preferably, the reverse osmosis treatment is used to retain sodium carbonate.

[0030] In this invention, a combination of electrodialysis and reverse osmosis membrane technology is used, and then the high efficiency of the reverse osmosis membrane in intercepting dissolved salts is used to separate hydrazine hydrate and sodium carbonate in the dilute chamber of electrodialysis, so that the removal rate of sodium carbonate and sodium chloride is above 95%.

[0031] Preferably, the reverse osmosis membrane used in the reverse osmosis treatment is a spiral wound high-pressure reverse osmosis membrane or a disc tube membrane.

[0032] Preferably, the reverse osmosis membrane has a molecular weight cutoff greater than 100 Da, such as 105 Da, 110 Da, 120 Da, 125 Da, 150 Da, 200 Da, 500 Da, 1000 Da, etc.

[0033] Preferably, the pressure of the feed solution in the reverse osmosis treatment is 1-12 MPa, for example, 1 MPa, 2 MPa, 3 MPa, 4 MPa, 5 MPa, 6 MPa, 7 MPa, 8 MPa, 9 MPa, 10 MPa, 11 MPa, 12 MPa, etc., and the temperature is 10-50℃, for example, 10℃, 15℃, 20℃, 25℃, 30℃, 35℃, 40℃, 45℃, 50℃, etc.

[0034] Preferably, the nanofiltration process is used to retain sodium carbonate.

[0035] Preferably, the nanofiltration membrane used in the nanofiltration treatment is any one or a combination of at least two of spiral wound nanofiltration, high-pressure nanofiltration, alkali-resistant nanofiltration, or high-temperature resistant nanofiltration membranes.

[0036] Preferably, the pressure of the nanofiltration membrane in the nanofiltration process is 1 to 8 MPa, for example, 1 MPa, 2 MPa, 3 MPa, 4 MPa, 5 MPa, 6 MPa, 7 MPa, 8 MPa, etc., and the temperature is 10 to 80°C, for example, 10°C, 20°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, etc.

[0037] Preferably, the crude hydrazine solution needs to be diluted by a factor of 1 to 10, for example, by 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 times.

[0038] Preferably, the crude hydrazine solution further requires pretreatment, which includes filtration.

[0039] Preferably, the filtration used to separate crude hydrazine includes any one of sand filtration, microfiltration, ultrafiltration, or multi-media filtration.

[0040] In this invention, the method for removing and separating sodium carbonate and sodium chloride from crude hydrazine using a combination of electrodialysis and reverse osmosis specifically includes the following steps:

[0041] (A) Use pretreatment equipment to remove suspended solids, colloids and other impurities from the crude hydrazine solution to obtain crude hydrazine treated solution;

[0042] (B) The crude hydrazine treatment solution obtained in step (A) is sent to an electrodialysis device to separate sodium chloride from the crude hydrazine treatment solution, and a hydrated hydrazine solution containing sodium carbonate and a sodium chloride solution are obtained.

[0043] (C) The sodium carbonate-containing hydrazine hydrate solution obtained in step (B) is sent to a reverse osmosis device to separate the hydrazine hydrate from the sodium carbonate, resulting in a pure hydrazine hydrate solution and sodium carbonate-containing reverse osmosis concentrate.

[0044] Compared with the prior art, the present invention has the following beneficial effects:

[0045] (1) The method for separating sodium carbonate and sodium chloride from crude hydrazine described in this invention solves the problem of incomplete separation of hydrazine hydrate from sodium carbonate and sodium chloride in the existing preparation process, so that the removal rate of sodium carbonate and sodium chloride is above 95%.

[0046] (2) The method for separating sodium carbonate and sodium chloride from crude hydrazine described in this invention greatly reduces separation energy consumption and improves separation efficiency.

[0047] (3) The method for separating sodium carbonate and sodium chloride from crude hydrazine described in this invention has no reagent addition, a short process flow, and a high degree of automation, which can ensure the purity of hydrazine hydrate and the process is green and reliable.

[0048] (4) This invention obtains high-purity and high-concentration sodium chloride in the electrodialysis concentration chamber, which can be directly concentrated, dried, and recycled. The dilute chamber contains sodium carbonate and hydrazine hydrate, with only a very small amount of sodium chloride impurities. Sodium carbonate can be further removed using reverse osmosis technology, and a high-purity sodium carbonate solution is obtained in the reverse osmosis concentrate, with hydrazine hydrate as the product water. Thus, while purifying hydrazine hydrate, sodium carbonate and sodium chloride are obtained and can be reused as industrial salt resources, generating economic benefits. Attached Figure Description

[0049] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0050] Figure 1 This is a process flow diagram of the electrodialysis-reverse osmosis treatment method used in this invention. Detailed Implementation

[0051] Unless otherwise defined herein, the scientific and technical terms used in conjunction with this invention shall have the meanings commonly understood by one of ordinary skill in the art. The meaning and scope of terms shall be clear; however, in any case of potential ambiguity, the definitions provided herein shall prevail over any dictionary or foreign definitions. In this application, unless otherwise stated, the use of "or" means "and / or". Furthermore, the use of the term "comprising" and other forms is non-limiting.

[0052] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0053] The present invention will be further illustrated by the following examples. Unless otherwise specified, the materials in the examples are prepared according to existing methods or purchased directly from the market.

[0054] The instrument model sources in the following embodiments are shown below:

[0055]

[0056] Example 1

[0057] This embodiment provides a method for removing sodium carbonate and sodium chloride from hydrazine hydrate by combining electrodialysis and reverse osmosis. The method includes the following steps:

[0058] S1 Pretreatment: A crude hydrazine solution dilution with hydrazine hydrate content of 24.2 g / L, sodium carbonate content of 43.5 g / L, and sodium chloride content of 61.8 g / L was used. The crude hydrazine solution was first filtered using microfiltration to remove impurities, resulting in a crude hydrazine treated solution.

[0059] S2 electrodialysis treatment: The crude hydrazine solution is subjected to electrodialysis treatment. This equipment uses two-stage electrodialysis to separate hydrazine hydrate and sodium chloride in the first stage of treatment. The concentrated chamber yields sodium chloride solution, and the dilute chamber yields hydrazine hydrate solution containing sodium carbonate.

[0060] The conductivity of the sodium chloride solution in the concentrated chamber is 72 mS / cm; the conductivity of the hydrazine hydrate solution containing sodium carbonate in the dilute chamber is 42 mS / cm; the electrodialysis membrane stack in the electrodialysis treatment consists of 10 electrodialysis repeaters; each membrane has an effective area of ​​0.01 m². 2 The voltage is 15V, the current is 2A, and the operating temperature is 25℃.

[0061] S3 Reverse Osmosis Treatment: The sodium carbonate-containing hydrazine hydrate solution obtained from the above dilute chamber is fed into the reverse osmosis equipment. The hydrazine hydrate solution is then subjected to a second separation of hydrazine hydrate and sodium carbonate using reverse osmosis treatment. The reverse osmosis concentrate is the sodium carbonate solution, and the reverse osmosis permeate is the pure hydrazine hydrate solution.

[0062] In the reverse osmosis process, the pressure of the feed solution is 6 MPa and the temperature is 30℃.

[0063] The final pure hydrazine hydrate solution contained 27.41 g / L of hydrazine hydrate, 1.62 g / L of sodium carbonate, and 1.82 g / L of sodium chloride. The removal rates of sodium carbonate and sodium chloride were calculated to be 96.28% and 97.06%, respectively.

[0064] Example 2

[0065] This embodiment provides a method for removing sodium carbonate and sodium chloride from hydrazine hydrate by combining electrodialysis and reverse osmosis. The method includes the following steps:

[0066] S1 Pretreatment: A crude hydrazine solution with hydrazine hydrate content of 64.77 g / L, sodium carbonate content of 88.53 g / L, and sodium chloride content of 151.18 g / L was used. The crude hydrazine solution was first filtered by ultrafiltration to remove impurities and obtain crude hydrazine treated solution.

[0067] S2 electrodialysis treatment: The crude hydrazine treatment solution is subjected to electrodialysis treatment. The equipment uses two-stage electrodialysis to separate hydrazine hydrate and sodium chloride in the first stage of the treatment solution. The concentrated chamber yields a sodium chloride solution, and the dilute chamber yields a hydrazine hydrate solution containing sodium carbonate.

[0068] The conductivity of the sodium chloride solution in the concentrated chamber is 186 mS / cm; the conductivity of the hydrazine hydrate solution containing sodium carbonate in the dilute chamber is 67 mS / cm; the electrodialysis membrane stack in the electrodialysis treatment consists of 20 electrodialysis repeaters; each membrane has an effective area of ​​0.02 m². 2 The electrodialysis treatment voltage is 25V, the current is 4A, and the operating temperature is 30℃.

[0069] S3 Reverse Osmosis Treatment: The sodium carbonate-containing hydrazine hydrate solution obtained from the above dilute chamber is fed into the reverse osmosis equipment. The hydrazine hydrate solution is then subjected to a second separation of hydrazine hydrate and sodium carbonate using reverse osmosis treatment. The reverse osmosis concentrate is the sodium carbonate solution, and the reverse osmosis permeate is the pure hydrazine hydrate solution.

[0070] In the reverse osmosis process, the pressure of the feed solution is 9 MPa and the temperature is 40℃.

[0071] The final pure hydrazine hydrate solution contained 69.74 g / L of hydrazine hydrate, 3.40 g / L of sodium carbonate, and 1.61 g / L of sodium chloride. The removal rates of sodium carbonate and sodium chloride were calculated to be 96.16% and 98.93%, respectively.

[0072] Example 3

[0073] This embodiment provides a method for removing sodium carbonate and sodium chloride from hydrazine hydrate by combining electrodialysis and reverse osmosis. The method includes the following steps:

[0074] S1 Pretreatment: A crude hydrazine solution with hydrazine hydrate content of 48 g / L, sodium carbonate content of 142.9 g / L, and sodium chloride content of 171.8 g / L was used. The crude hydrazine solution was filtered using a multi-media filter to remove impurities and obtain a crude hydrazine treated solution.

[0075] S2 electrodialysis treatment: The above crude hydrazine treatment solution is diluted by 1 time and then subjected to electrodialysis treatment. The equipment uses two-stage electrodialysis to separate hydrazine hydrate and sodium chloride in the first stage of treatment solution. The concentrated chamber yields sodium chloride solution, and the dilute chamber yields hydrazine hydrate solution containing sodium carbonate.

[0076] The conductivity of the sodium chloride solution in the concentrated chamber is 162 mS / cm; the conductivity of the hydrazine hydrate solution containing sodium carbonate in the dilute chamber is 98 mS / cm; the electrodialysis membrane stack in the electrodialysis treatment consists of 50 electrodialysis repeaters; each membrane has an effective area of ​​0.02 m². 2 The electrodialysis treatment voltage is 35V, the current is 4A, and the operating temperature is 30℃.

[0077] S3 Reverse Osmosis Treatment: The sodium carbonate-containing hydrazine hydrate solution obtained from the above dilute chamber is fed into the reverse osmosis equipment. The hydrazine hydrate solution is then subjected to a second separation of hydrazine hydrate and sodium carbonate using reverse osmosis treatment. The reverse osmosis concentrate is the sodium carbonate solution, and the reverse osmosis permeate is the pure hydrazine hydrate solution.

[0078] In the reverse osmosis process, the pressure of the feed solution is 11 MPa and the temperature is 40℃.

[0079] The final pure hydrazine hydrate solution contained 49.30 g / L of hydrazine hydrate, 4.80 g / L of sodium carbonate, and 1.96 g / L of sodium chloride. The removal rates of sodium carbonate and sodium chloride were calculated to be 96.64% and 98.86%, respectively.

[0080] Example 4

[0081] This embodiment provides a method for removing sodium carbonate and sodium chloride from hydrazine hydrate by combining electrodialysis and nanofiltration. The method includes the following steps:

[0082] S1 Pretreatment: A crude hydrazine dilution solution with a hydrazine hydrate content of 24.2 g / L, a sodium carbonate content of 43.5 g / L, and a sodium chloride content of 61.8 g / L was used. The crude hydrazine solution was first filtered using microfiltration to remove impurities, resulting in a crude hydrazine treated solution.

[0083] S2 electrodialysis treatment: The crude hydrazine solution is subjected to electrodialysis treatment. This equipment uses two-stage electrodialysis to separate hydrazine hydrate and sodium chloride in the first stage of treatment. The concentrated chamber yields sodium chloride solution, and the dilute chamber yields hydrazine hydrate solution containing sodium carbonate.

[0084] The conductivity of the sodium chloride solution in the concentrated chamber is 73 mS / cm; the conductivity of the hydrazine hydrate solution containing sodium carbonate in the dilute chamber is 34 mS / cm; the electrodialysis membrane stack in the electrodialysis treatment consists of 10 electrodialysis repeaters; each membrane has an effective area of ​​0.01 m². 2 The electrodialysis treatment voltage is 15V, the current is 2A, and the operating temperature is 25℃.

[0085] S3 Nanofiltration Treatment: The sodium carbonate-containing hydrazine hydrate solution obtained from the above dilute chamber is fed into the nanofiltration equipment. The obtained hydrazine hydrate solution is subjected to a second separation of hydrazine hydrate and sodium carbonate using nanofiltration treatment. The nanofiltration concentrate is a sodium carbonate and sodium chloride solution, and the nanofiltration permeate is a pure hydrazine hydrate solution.

[0086] The nanofiltration membrane has a pressure of 3 MPa and a temperature of 30℃.

[0087] The final pure hydrazine hydrate solution contained 25.99 g / L of hydrazine hydrate, 3.07 g / L of sodium carbonate, and 4.38 g / L of sodium chloride. The removal rates of sodium carbonate and sodium chloride were calculated to be 92.938% and 92.91%, respectively.

[0088] Example 5

[0089] This embodiment provides a method for removing sodium carbonate and sodium chloride from hydrazine hydrate by combining nanofiltration and electrodialysis. The method includes the following steps:

[0090] S1 Pretreatment: A crude hydrazine dilution solution with a hydrazine hydrate content of 24.2 g / L, a sodium carbonate content of 43.5 g / L, and a sodium chloride content of 61.8 g / L was used. The crude hydrazine solution was first filtered using microfiltration to remove impurities, resulting in a crude hydrazine treated solution.

[0091] S2 Nanofiltration Treatment: The above crude hydrazine treatment solution is fed into a nanofiltration device. The crude hydrazine treatment solution is subjected to the first separation of hydrazine hydrate and sodium carbonate using nanofiltration treatment. The nanofiltration concentrate is a mixture of sodium carbonate and sodium chloride, and the nanofiltration permeate is a hydrazine hydrate solution containing sodium chloride.

[0092] S3 electrodialysis treatment: The hydrazine hydrate solution containing sodium chloride is subjected to electrodialysis treatment. This equipment uses two-stage electrodialysis to separate the hydrazine hydrate and sodium chloride in the treatment solution for the second time. The concentrated chamber yields a sodium chloride solution, and the dilute chamber yields a pure hydrazine hydrate solution.

[0093] The conductivity of the sodium chloride solution in the concentrated chamber is 77 mS / cm; the conductivity of the pure hydrazine hydrate solution in the dilute chamber is 17 mS / cm; the electrodialysis membrane stack in the electrodialysis treatment consists of 10 electrodialysis repeaters; each membrane has an effective area of ​​0.01 m². 2 The voltage during electrodialysis is 15V, the current is 2A, and the operating temperature is 30℃.

[0094] The final pure hydrazine hydrate solution contained 25.43 g / L of hydrazine hydrate, 3.44 g / L of sodium carbonate, and 1.89 g / L of sodium chloride. The removal rates of sodium carbonate and sodium chloride were calculated to be 92.10% and 96.94%, respectively.

[0095] Example 6

[0096] This embodiment provides a method for removing sodium carbonate and sodium chloride from hydrazine hydrate by combining electrodialysis-nanofiltration-reverse osmosis, the method comprising the following steps:

[0097] S1 Pretreatment: A crude hydrazine dilution solution with a hydrazine hydrate content of 24.2 g / L, a sodium carbonate content of 43.5 g / L, and a sodium chloride content of 61.8 g / L was used. The crude hydrazine solution was first filtered using microfiltration to remove impurities, resulting in a crude hydrazine treated solution.

[0098] S2 electrodialysis treatment: The crude hydrazine treatment solution is subjected to electrodialysis treatment. The equipment uses two-stage electrodialysis to separate hydrazine hydrate and sodium chloride in the first stage of the treatment solution. The concentrated chamber yields a sodium chloride solution, and the dilute chamber yields a hydrazine hydrate solution containing sodium carbonate.

[0099] The conductivity of the sodium chloride solution in the concentrated chamber is 70 mS / cm; the conductivity of the hydrazine hydrate solution containing sodium carbonate in the dilute chamber is 36 mS / cm; the electrodialysis membrane stack in the electrodialysis treatment consists of 10 electrodialysis repeaters; each membrane has an effective area of ​​0.01 m². 2 The voltage during electrodialysis is 15V, the current is 2A, and the operating temperature is 25℃.

[0100] S3 Nanofiltration Treatment: The sodium carbonate-containing hydrazine hydrate solution obtained from the above dilute chamber is fed into the nanofiltration equipment. The obtained hydrazine hydrate solution is subjected to a second separation of hydrazine hydrate and sodium carbonate using nanofiltration treatment. The nanofiltration concentrate is the sodium carbonate solution, and the nanofiltration permeate is the crude hydrazine hydrate solution.

[0101] The nanofiltration membrane has a pressure of 3 MPa and a temperature of 30℃.

[0102] S4 Reverse Osmosis Treatment: The above crude hydrazine hydrate solution is fed into the reverse osmosis equipment. The resulting hydrazine hydrate solution is purified for the third time by reverse osmosis treatment to remove a small amount of sodium carbonate and sodium chloride from the crude hydrazine hydrate solution. The reverse osmosis concentrate is a mixed solution of sodium carbonate and sodium chloride, and the reverse osmosis permeate is a pure hydrazine hydrate solution.

[0103] In the reverse osmosis process, the pressure of the feed solution is 4 MPa and the temperature is 40℃.

[0104] The final pure hydrazine hydrate solution contained 28.64 g / L of hydrazine hydrate, 0.50 g / L of sodium carbonate, and 0.51 g / L of sodium chloride. The removal rates of sodium carbonate and sodium chloride were calculated to be 98.86% and 99.17%, respectively.

[0105] Comparative Example 1

[0106] This comparative example provides a method for removing sodium carbonate and sodium chloride from hydrazine hydrate using evaporative distillation, the method comprising the following steps:

[0107] S1 Pretreatment: A crude hydrazine dilution solution with a hydrazine hydrate content of 24.2 g / L, a sodium carbonate content of 43.5 g / L, and a sodium chloride content of 61.8 g / L was used. The crude hydrazine solution was first filtered using microfiltration to remove impurities, resulting in a crude hydrazine treated solution.

[0108] S2 Evaporation of High-Saline Hydrazine Solution: The above high-saline hydrazine solution was placed in a 90℃ electric heating blast drying oven (model DHG-9070A) for evaporation. When the evaporation rate of the solution reached 10%, crystals began to appear in the device. When the evaporation rate of the solution reached 35%, the optimal evaporation rate was reached, and evaporation was stopped. The solution was cooled at room temperature for 48 hours and then filtered to obtain crystals and filtrate.

[0109] The filtered NaCl crystals were dried at 105℃ to constant weight, and then calcined in a muffle furnace (model SX2-8-10) at 300℃ for 2 hours to obtain crude NaCl product.

[0110] S3 Distillation Separation and Recovery of Hydrazine Hydrate: During the evaporation of the high-salt hydrazine solution in step S2, the generated steam (containing hydrazine hydrate and water) is condensed and then separated and recovered by distillation equipment. Part of the condensate after separation is returned to the filtrate produced by filtration after evaporating and crystallizing NaCl in step 2 to obtain concentrated brine containing Na2CO3 and NaCl. The remaining condensate is used as production water.

[0111] S4 High-purity Na2CO3 product recovery: The concentrated brine in step 3 is frozen and crystallized at 0°C (without adding any seed crystals) to obtain sodium carbonate crystals.

[0112] S5 Saturated sodium carbonate solution recycling: The remaining saturated sodium carbonate solution after freezing and crystallization in step 4 is refluxed to the high-salt hydrazine solution raw water that has not yet started evaporation in step 2 to obtain mixed raw water, and then a new round of evaporation and crystallization begins.

[0113] The final pure hydrazine hydrate solution contained 19.84 g / L of hydrazine hydrate, 17.71 g / L of sodium carbonate, and 14.32 g / L of sodium chloride. The removal rates of sodium carbonate and sodium chloride were calculated to be 59.29% and 76.83%, respectively.

[0114] As can be seen from the comparison between Example 1 and Comparative Example 1, the existing technology often requires a variety of complex combined processes of evaporation-distillation and desalination to separate and purify hydrazine hydrate, sodium carbonate and sodium chloride. The process is complicated and introduces new impurities. In order to achieve the purpose of material separation, a large amount of heat is often required, resulting in high equipment energy consumption. Furthermore, over time, problems such as scaling on the evaporator and heater affect heat transfer and reduce evaporation efficiency.

[0115] Comparative Example 2

[0116] This comparative example provides a method for removing sodium carbonate and sodium chloride from hydrazine hydrate using a combination of nanofiltration and reverse osmosis, the method comprising the following steps:

[0117] S1 Pretreatment: A crude hydrazine dilution solution with a hydrazine hydrate content of 24.2 g / L, a sodium carbonate content of 43.5 g / L, and a sodium chloride content of 61.8 g / L was used. The crude hydrazine solution was first filtered using microfiltration to remove impurities, resulting in a crude hydrazine treated solution.

[0118] S2 Nanofiltration Treatment: The above crude hydrazine treatment solution is fed into a nanofiltration device. The crude hydrazine treatment solution is subjected to the first separation of hydrazine hydrate impurities by nanofiltration treatment. The nanofiltration concentrate is a sodium carbonate and sodium chloride solution (sodium carbonate concentration 70.50 g / L, sodium chloride concentration 53.58 g / L). The nanofiltration permeate is a crude hydrazine hydrate solution containing sodium chloride.

[0119] The nanofiltration membrane has a pressure of 6 MPa and a temperature of 25℃.

[0120] S3 Reverse Osmosis Treatment: The above crude hydrazine hydrate solution is fed into the reverse osmosis equipment. The resulting hydrazine hydrate solution is subjected to a second impurity separation process using reverse osmosis. The reverse osmosis concentrate is sodium chloride solution, and the reverse osmosis permeate is pure hydrazine hydrate solution.

[0121] In the reverse osmosis process, the pressure of the feed solution is 8 MPa and the temperature is 30℃.

[0122] The final pure hydrazine hydrate solution contained 20.48 g / L of hydrazine hydrate, 4.30 g / L of sodium carbonate, and 12.89 g / L of sodium chloride. The removal rates of sodium carbonate and sodium chloride were calculated to be 90.11% and 79.14%, respectively.

[0123] As can be seen from the comparison between Example 1 and Comparative Example 2, nanofiltration can only ensure the purity of sodium chloride in the product water, while the purity of sodium carbonate in the concentrate is not high (there is still a large amount of sodium chloride). However, the concentrate chamber of the electrodialysis process contains sodium chloride, and through process control, the sodium carbonate impurity is very low. The sodium carbonate and hydrazine hydrate remaining in the dilute chamber also have very low sodium chloride impurity content. After desalination by nanofiltration or reverse osmosis, sodium carbonate with low impurity content can be obtained. Therefore, the method of the present invention yields three substances with low impurity content, which is both economical and efficient.

[0124] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for separating sodium carbonate and sodium chloride from crude hydrazine, characterized in that, The method includes the following steps: The crude hydrazine solution is subjected to electrodialysis, as well as reverse osmosis and / or nanofiltration to separate sodium carbonate and sodium chloride from the crude hydrazine. The process of the method is either electrodialysis-reverse osmosis or electrodialysis-nanofiltration-reverse osmosis; The crude hydrazine solution contains sodium carbonate in a concentration range of 50–150 g / L; sodium chloride in a concentration range of 80–200 g / L; and hydrazine hydrate in a mass percentage range of 2–8%. The electrodialysis treatment is used to remove sodium chloride from the crude hydrazine. After electrodialysis treatment, the crude hydrazine solution yields a sodium chloride solution in the concentrate chamber and a sodium carbonate-containing hydrazine hydrate solution in the dilute chamber. The reverse osmosis treatment is used to remove sodium carbonate, and the reverse osmosis membrane used in the reverse osmosis treatment is a spiral wound high-pressure reverse osmosis membrane or a disc tube membrane, and the molecular weight cutoff of the reverse osmosis membrane is greater than 100 Da. The nanofiltration process is used to retain sodium carbonate, and the nanofiltration membrane used in the process is any one or a combination of at least two of spiral wound nanofiltration, high-pressure nanofiltration, alkali-resistant nanofiltration, or high-temperature resistant nanofiltration membranes.

2. The method for separating sodium carbonate and sodium chloride from crude hydrazine according to claim 1, characterized in that, The process of the method is electrodialysis-nanofiltration-reverse osmosis.

3. The method for separating sodium carbonate and sodium chloride from crude hydrazine according to claim 1 or 2, characterized in that, The exchange membrane used in the electrodialysis treatment is a monovalent selective ion exchange membrane.

4. The method for separating sodium carbonate and sodium chloride from crude hydrazine according to claim 1, characterized in that, The conductivity of the sodium chloride solution in the concentrated chamber is 100~300 mS / cm; the conductivity of the sodium carbonate-containing hydrazine hydrate solution in the dilute chamber is 20~100 mS / cm.

5. The method for separating sodium carbonate and sodium chloride from crude hydrazine according to claim 1, characterized in that, The electrodialysis treatment process involves an electrodialysis membrane stack consisting of 5 to 500 membrane pairs; each membrane has an effective area of ​​0.08 to 1.2 m². 2 .

6. The method for separating sodium carbonate and sodium chloride from crude hydrazine according to claim 1, characterized in that, The electrodialysis treatment involves a feed liquid voltage of 5~300 V, a current of 4~200 A, and an operating temperature of 20~40℃.

7. The method for separating sodium carbonate and sodium chloride from crude hydrazine according to claim 1, characterized in that, The pressure of the feed solution in the reverse osmosis process is 1~12 MPa, and the temperature is 10~50℃.

8. The method for separating sodium carbonate and sodium chloride from crude hydrazine according to claim 1, characterized in that, The nanofiltration process involves a nanofiltration membrane with a pressure of 1-8 MPa and a temperature of 10-80℃.

9. The method for separating sodium carbonate and sodium chloride from crude hydrazine according to claim 1, characterized in that, The crude hydrazine solution needs to be diluted by a factor of 1 to 10.

10. The method for separating sodium carbonate and sodium chloride from crude hydrazine according to claim 1, characterized in that, The crude hydrazine solution also needs to undergo pretreatment, which includes filtration.

11. The method for separating sodium carbonate and sodium chloride from crude hydrazine according to claim 10, characterized in that, The filtration used to separate crude hydrazine includes any one of sand filtration, microfiltration, ultrafiltration, or multi-media filtration.

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