Purification of urea water mixtures synthesized by stripping

Abstract

The application provides a purification method for urea water mixture synthesized by a stripping method, and a preparation method of a reverse osmosis membrane used in the method is as follows: preparing an aqueous phase containing a polyamine compound and a molecular sieve powder with a specific content, preparing an organic phase containing a multifunctional acyl halide compound and graphene with a specific content, and adding a flux enhancer with a specific content into the aqueous phase and the organic phase respectively; applying the aqueous phase to the surface of a porous support membrane to obtain a coated support membrane; applying the organic phase to the coated support membrane, and performing interfacial polymerization of the polyamine compound and the multifunctional acyl halide compound to form a distinguishing layer of a reverse osmosis membrane, wherein the reverse osmosis membrane comprises the porous support membrane and the distinguishing layer; and the flux enhancer comprises a metal chelate containing a bidentate ligand and a metal ion, and a dialkyl sulfoxide. The reverse osmosis membrane has excellent biuret rejection effect, and can further reduce the biuret content in the urea water mixture.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of urea synthesis, more particularly, to a purification method for urea aqueous mixture synthesized by stripping method. BACKGROUND

[0002] Urea is a neutral nitrogen fertilizer with high nitrogen content, which is widely used at present. It is suitable for all kinds of soil and plants, and has the advantages of easy storage, convenient use and small damage to soil.

[0003] In industry, urea is usually synthesized from ammonia and carbon dioxide under certain conditions. Its production process includes various processes, such as ammonia stripping method, carbon dioxide stripping method and water solution full cycle method. The carbon dioxide stripping method process has become the urea production process with the largest production equipment capacity and the most plants in the world.

[0004] Although the carbon dioxide stripping method process has many advantages, it needs to strictly control the ammonia-carbon ratio. If it is not controlled within the appropriate range, it is easy to cause the occurrence of side reactions, and then lead to a high content of biuret in urea products, affecting product quality.

[0005] GB959358A discloses a method for producing urea prills with low biuret content. The urea-containing degassing reactor effluent enters a second purification zone from a primary purification zone, wherein the effluent is heated under specific temperature and pressure conditions. A highly concentrated biuret-containing urea melt is taken from the second purification zone, and the biuret concentration of the urea taken from the second purification zone depends on the concentration of urea achieved. The biuret concentration is further reduced by contacting the urea melt with an ammonia-containing gas at a temperature higher than the melting point of pure urea for a sufficient time to achieve equilibrium between the reacting ammonia and biuret and urea. However, this method needs to regulate the equilibrium between ammonia and biuret and urea, which is difficult to control.

[0006] CN109070043B discloses a novel method for controlling the formation of biuret in urea production. This is achieved by reducing or preventing the formation of biuret in the concentration section, in particular in one or more concentrators or evaporators. The method includes controlling the residence time of the urea water stream treated in such concentration section independently of the volume flow of said stream entering said concentration section per time interval. The residence time can be controlled, for example, by providing a concentration section with an adjustable volume or by adding a gas to the urea stream to be treated. This method is based on how to reduce the generation of biuret, and cannot be universally applied to urea materials with high biuret content. SUMMARY

[0007] In order to solve the above technical problems, the present application provides a purification method for CO2 stripping method urea material with high biuret content caused by various factors, which has good industrial application prospect.

[0008] The embodiment of the present application provides a purification method for urea water mixture synthesized by a stripping method, comprising the step of reducing the content of biuret in urea by using a reverse osmosis membrane, and the reverse osmosis membrane is prepared by the following method:

[0009] S1, preparing an aqueous phase containing a polyamine compound and a molecular sieve powder, and an organic phase containing a multifunctional acyl halide compound and graphene, and adding a flux improving additive into the aqueous phase and the organic phase respectively;

[0010] S2, applying the aqueous phase to the surface of a porous support membrane to obtain a coated support membrane;

[0011] S3, applying the organic phase to the coated support membrane, and carrying out interfacial polymerization of the polyamine compound and the multifunctional acyl halide compound to form a distinguished layer of a reverse osmosis membrane, and the reverse osmosis membrane comprises the porous support membrane and the distinguished layer; the adding amount of the molecular sieve powder accounts for 0.05% to 0.3% of the mass of the aqueous phase, and the adding amount of the graphene accounts for 0.01% to 0.2% of the mass of the organic phase;

[0012] The flux improving additive comprises a metal chelate containing a bidentate ligand and a metal ion, and a dialkyl sulfoxide; the adding amount of the metal chelate is to make the mass concentration of the metal chelate in the aqueous phase or the organic phase be 0.03% to 0.12%, and the adding amount of the dialkyl sulfoxide is to make the mass concentration of the dialkyl sulfoxide in the aqueous phase or the organic phase be 1.6% to 3.5%.

[0013] As a case, the bidentate ligand is selected from one or two of , and the metal ion is selected from one or two of Na + or K + .

[0014] As a case, the polyamine compound is selected from one or more combinations of ethylenediamine, propylenediamine, diaminobenzene, triaminobenzene, m-phenylenediamine, p-phenylenediamine, 2,4-diaminotoluene and 2,4-diaminoanisole.

[0015] As a case, the multifunctional acyl halide compound is selected from one or more combinations of trimesoyl chloride, trimellitic acid chloride, isophthaloyl chloride and terephthaloyl chloride.

[0016] As a case, the molecular sieve powder is pretreated as follows:

[0017] An aqueous hydrochloric acid solution with a mass fraction of 12% to 20% is prepared and heated to 50 to 60 DEG C, and then the molecular sieve powder is added, constant temperature stirring is carried out for 3 to 6 hours, and the filter cake is collected after filtration and washing;

[0018] An aqueous hydrochloric acid solution with a mass fraction of 12% to 20% is prepared and heated to 50 to 60 DEG C, and then the molecular sieve powder is added, constant temperature stirring is carried out for 3 to 6 hours, and the filter cake is collected after filtration and washing;

[0019] The filter cake is treated in a 12-20% by mass aqueous H2O2 solution for 2-4 hours.

[0020] As an example, the graphene is pretreated as follows: a 25-40% by mass sodium hypochlorite solution is prepared, the pH is adjusted to 9-10 by adding alkali, the graphene is added and stirred for 2-4 hours, filtration and washing are performed, and the solid is collected and soaked in a 1.5%-4% by mass sodium metabisulfite solution for 1-2.5 hours.

[0021] As an example, the urea concentration in the urea aqueous solution is 65-85% by weight.

[0022] As an example, in the step of reducing the biuret content in the urea using a reverse osmosis membrane, the temperature of the urea aqueous solution is controlled at 72-78°C.

[0023] Compared with the prior art, the present application has the following advantages:

[0024] 1. The method of the present application can be widely used for purifying CO2 stripping method urea materials with high biuret content caused by poor process operation, and can be conveniently combined with various existing CO2 stripping method urea production systems for use, thus having good industrial application prospects.

[0025] 2. The reverse osmosis membrane used in the method of the present application has excellent biuret interception effect, which can further reduce the biuret content in the urea aqueous solution and improve the quality of the urea product. DETAILED DESCRIPTION

[0026] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the technical solutions of the embodiments of the present application will be described below in conjunction with the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the described embodiments of the present application, all other embodiments obtained by a person of ordinary skill in the art without any inventive effort fall within the scope of protection of the present application.

[0027] The reagents used in the following examples can be obtained from the market, and the specific manufacturers are not limited.

[0028] Examples 1-5

[0029] A reverse osmosis membrane for purifying a stripping method urea aqueous solution is provided, which is prepared by the following method:

[0030] S1, an aqueous phase containing a polyamine compound and a molecular sieve powder, and an organic phase containing a multifunctional acyl halide compound and graphene are prepared, and a flux improving additive is added to the aqueous phase and the organic phase, respectively;

[0031] S2, applying the aqueous phase to the surface of the porous support membrane to obtain a coated support membrane;

[0032] S3, applying the organic phase to the coated support membrane to cause interfacial polymerization of the polyamine compound and the multifunctional acyl halide compound to form a distinct layer of a reverse osmosis membrane, the reverse osmosis membrane comprising the porous support membrane and the distinct layer; the amount of the molecular sieve powder added accounts for 0.05% to 0.3% of the mass of the aqueous phase,

[0033] the amount of the graphene added accounts for 0.01% to 0.2% of the mass of the organic phase;

[0034] the flux improving additive comprises a metal chelate containing a bidentate ligand and a metal ion, and a dialkyl sulfoxide; the amount of the metal chelate added accounts for 0.03% to 0.12% of the mass concentration of the metal chelate in the aqueous phase or the organic phase, and the amount of the dialkyl sulfoxide added accounts for 1.6% to 3.5% of the mass concentration of the dialkyl sulfoxide in the aqueous phase or the organic phase.

[0035] the bidentate ligand is selected from one or both of and the metal ion is selected from one or both of Na + or K + .

[0036] the polyamine compound is selected from one or more combinations of ethylenediamine, propylenediamine, diaminobenzene, triaminobenzene, m-phenylenediamine, p-phenylenediamine, 2,4-diaminotoluene, and 2,4-diaminobenzoic anisole.

[0037] the multifunctional acyl halide compound is selected from one or more combinations of trimesic acid chloride, trimellitic acid chloride, isophthalic acid chloride, and terephthalic acid chloride.

[0038] Other auxiliary agents not specifically limited or disclosed above, for example, a desiccant, a surfactant, etc. that can be added in the aqueous phase, and an antioxidant, etc. that can be added in the organic phase, can all use the general applicable components disclosed in the prior art, without affecting the realization of the corresponding effects of the innovative concept of the present application.

[0039] The porous support membrane can be obtained by market purchase, for example, a polyether sulfone membrane, a polyacrylonitrile membrane, a polyvinyl chloride membrane, a polyester membrane, a polystyrene membrane, a polysulfone membrane, a polypropylene membrane, a nitrocellulose membrane, or a cellulose acetate membrane. The thickness of the porous support membrane is usually 120 to 180 microns, and a 120-micron polystyrene membrane is used as an example in the following cases.

[0040] The surface area of the porous support membrane can be set according to the size of the reverse osmosis interface provided in the reverse osmosis device.

[0041] The aqueous or organic phase can be applied to the porous support film by existing means such as dipping, immersion, coating, spraying, etc.

[0042] The raw material compositions of Examples 1-5 are shown in Tables 1-5 below.

[0043] Table 1 Raw material composition of Example 1

[0044]

[0045] Table 2 Raw material composition of Example 2

[0046]

[0047] Table 3 Raw material composition of Example 3

[0048]

[0049] Table 4 Raw material composition of Example 4

[0050]

[0051] Table 5 Raw material composition of Example 5

[0052]

[0053] Example 6

[0054] The only difference compared to Example 1 is that the molecular sieve is treated as follows before use: an aqueous hydrochloric acid solution with a mass fraction of 20% is prepared and heated to 60°C, then the molecular sieve powder is added, constant temperature stirring for 6h, filtration, washing, and the filter cake is collected; the filter cake is placed in an aqueous H2O2 solution with a mass fraction of 12% for 4h.

[0055] Example 7

[0056] The only difference compared to Example 1 is that the graphene is pretreated as follows: a sodium hypochlorite solution with a mass fraction of 40% is prepared, the pH is adjusted to 10 with sodium hydroxide, the graphene is added and stirred for 2h, filtered, washed, the solid is collected and soaked in a sodium salt of metabisulfite with a mass fraction of 1.5% for 2.5h.

[0057] Comparative Example 1

[0058] The only difference compared to Example 1 is that the amount of molecular sieve powder added is 0.4% of the mass of the aqueous phase.

[0059] Comparative Example 2

[0060] The only difference compared to Example 1 is that the amount of graphene added is 0.25% of the mass of the organic phase.

[0061] Effect test

[0062] Referring to the reverse osmosis segment scheme disclosed in the prior art CN115066414A embodiment, the urea water mixture synthesized by the stripping method with a urea concentration of 70wt% and a biuret content of 0.6wt% is heated to 75℃, and then is respectively subjected to tests under the same test conditions in the reverse osmosis segments equipped with the reverse osmosis membranes of the above embodiments and the comparative examples.

[0063] In the above tests, the flow rates of the materials in the reverse osmosis segments are the parameters disclosed in the prior art, and the content of the biuret in the urea water mixture obtained after the final treatment is investigated.

[0064] It should be noted that the prior art is only used as an example scenario to facilitate a more specific understanding of the advantages of the present application, and is not limited to only using the system or the reverse osmosis segment.

[0065] The test results are shown in Table 6 below.

[0066] Table 6

[0067] Case % biuret content in final urea water mixture Example 1 0.22 Example 2 0.24 Example 3 0.23 Example 4 0.20 Example 5 0.24 Example 6 0.18 Example 7 0.16 Comparative Example 1 0.43 Comparative Example 2 0.36

[0068] Although the embodiments of the present application are disclosed as above, the content described is only used to facilitate the understanding of the embodiments of the present application, and is not intended to limit the present application. Any person skilled in the art of the present application can make any modification and change in the form and details without departing from the spirit and scope of the present application. The patent protection scope of the present application shall be subject to the scope defined by the appended claims.

Claims

1. A method for purifying an aqueous mixture synthesized by steam stripping, characterized in that, The step includes using a reverse osmosis membrane to reduce the biuret content in urea, wherein the reverse osmosis membrane is prepared by the following method: S1, prepare an aqueous phase containing polyamine compounds and molecular sieve powder, and an organic phase containing polyfunctional acyl halide compounds and graphene, and add flux-enhancing agents to the aqueous phase and the organic phase respectively; S2, the aqueous phase is applied to the surface of the porous support membrane to obtain a coated support membrane; S3, the organic phase is applied to the coated support membrane, causing the polyamine compound and the polyfunctional acyl halide compound to polymerize at the interface to form a differentiating layer of the reverse osmosis membrane, the reverse osmosis membrane comprising the porous support membrane and the differentiating layer; The amount of molecular sieve powder added accounts for 0.05% to 0.3% of the mass of the aqueous phase, and the amount of graphene added accounts for 0.01% to 0.2% of the mass of the organic phase; The flux-enhancing agent includes a metal chelate containing a bidentate ligand and a metal ion, and a dialkyl sulfoxide; the amount of the metal chelate added is such that the mass concentration of the metal chelate in the aqueous phase or the organic phase is 0.03% to 0.12%, and the amount of the dialkyl sulfoxide added is such that the mass concentration of the dialkyl sulfoxide in the aqueous phase or the organic phase is 1.6% to 3.5%. The molecular sieve powder undergoes the following pretreatment: Prepare a 12-20% hydrochloric acid aqueous solution and heat it to 50-60°C. Then add molecular sieve powder, stir at a constant temperature for 3-6 hours, filter, wash, and collect the filter cake. Place the filter cake in a 12-20% H2O2 aqueous solution for 2-4 hours. The graphene undergoes the following pretreatment: Prepare a sodium hypochlorite solution with a mass fraction of 25-40%, adjust the pH to 9-10 with alkali, add graphene and stir for 2-4 hours, filter and wash, collect the solid and soak it in an alkali metal salt of metabisulfite with a mass fraction of 1.5%-4% for 1-2.5 hours; The urea concentration in the urea-water mixture is 65-85 wt%; in the step of using a reverse osmosis membrane to reduce the biuret content in the urea, the temperature of the urea-water mixture is controlled at 72℃-78℃.

2. The purification method for the aqueous mixture of urea synthesized by stripping according to claim 1, characterized in that, The bidentate ligand is selected from or One or two of the metal ions, wherein the metal ions are selected from Na + or K + One or two of them.

3. The purification method for the aqueous mixture of urea synthesized by stripping according to claim 1, characterized in that, The polyamine compound is selected from one or more combinations of ethylenediamine, propylenediamine, diaminobenzene, triaminobenzene, m-phenylenediamine, p-phenylenediamine, 2,4-diaminotoluene, and 2,4-diaminoanisole.

4. The purification method for the aqueous mixture of urea synthesized by stripping according to claim 1, characterized in that, The polyfunctional acyl halide compound is selected from one or more combinations of pyromellitic acyl chloride, trimellitic acyl chloride, isophthaloyl chloride, and p-phthaloyl chloride.

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