Crystal regulation and control method for preparing large-particle sodium bicarbonate through reaction of sodium sulfate and ammonium bicarbonate

Abstract

The invention relates to a crystal regulation and control method for preparing large-particle sodium bicarbonate through reaction of sodium sulfate and ammonium bicarbonate. In the reaction of preparing sodium bicarbonate and ammonium sulfate through double decomposition reaction of sodium sulfate and ammonium bicarbonate, one or more crystal regulators are added to regulate the size of sodium bicarbonate crystals, so that the diameter of more than 60% of sodium bicarbonate particles is greater than 180 microns, a basis is provided for preparing heavy soda ash, and good economic and social benefits are achieved.

Description

Technical Field

[0001] The invention belongs to the field of chemical technology, and particularly relates to a crystal control method for preparing large-particle sodium bicarbonate by reacting sodium sulfate and ammonium bicarbonate. Background Art

[0002] Sodium bicarbonate is an important chemical and an intermediate for the preparation of soda ash. Sodium bicarbonate is generally produced from sodium chloride by the Solvay process or the combined alkali process, and the raw material sodium chloride is mostly obtained by drying and refining seawater or from salt wells. With the substantial increase in the demand for soda ash in industrial production, the raw material of sodium chloride is in short supply. At the same time, since the ammonia-soda process produces a large amount of useless solid calcium chloride as a by-product, the state has restricted the production scale of the ammonia-soda process, and production equipment below 600,000 tons / year will no longer be approved. Since the by-product of the combined alkali process is ammonium chloride, which contains chlorine, its use in agricultural fertilizers is subject to certain restrictions, and the development of the combined alkali process technology will also be affected by the ammonium chloride market. my country produces a large amount of sodium sulfate. If sodium sulfate can be used instead of sodium chloride as a raw material to prepare sodium bicarbonate and ammonium sulfate, the economic and environmental benefits will be extremely significant.

[0003] The earliest method for preparing soda ash from sodium sulfate was the Leblanc process, which uses sodium sulfate, coal powder, and limestone as raw materials to generate sodium carbonate through a high-temperature melting reaction, cools, crushes, and leaches the melt, then concentrates the leachate, introduces carbon dioxide for carbonization, and then removes impurities through precipitation, concentration, separation, and drying to obtain soda ash. This method has complex reactions, high operating temperatures, low product purity, low yield, and serious three-waste pollution, and has now been eliminated.

[0004] There are also many studies on the preparation of sodium bicarbonate from sodium sulfate in my country. For example, CN101544385A discloses a method for preparing sodium carbonate and calcium sulfate with sodium sulfate as raw material and organic amine as auxiliary material. This method can achieve a sodium conversion rate of more than 90%. However, organic amines have high boiling points, high viscosity, and high energy consumption for evaporation recovery; there are many organic amines entrained in sodium bicarbonate and calcium sulfate, which are difficult to recover, with many losses and high production costs. CN102198953A discloses a method for generating sodium carbonate and ammonium sulfate by reacting melammonium-containing ammonia, CO2 tail gas and sodium sulfate solution, CN109437248A discloses a method for co-producing soda ash and ammonium sulfate using sodium sulfate and ammonium bicarbonate as raw materials, and CN114436297A discloses a method for preparing soda ash using sodium sulfate. During the preparation process, ammonia is used as a salting-out agent to reduce the solubility of sodium sulfate, thereby breaking the precipitation balance of sodium sulfate and ammonium sulfate, promoting the formation of sodium sulfate precipitation, preventing the formation of sodium ammonium sulfate double salt crystals, improving the single-pass recovery rate of sodium sulfate, and avoiding the problem of difficulty in separating sodium sulfate and ammonium sulfate double salts. In order to improve the recovery rate of sodium bicarbonate and ammonium sulfate, some public patents respectively adopt the method of adding additives, such as CN111039305A discloses a method for preparing sodium bicarbonate and ammonium sulfate from sodium sulfate in a short process, by adding diammonium hydrogen phosphate, disodium hydrogen phosphate, ammonium nitrate, sodium nitrate, ammonium formate or sodium formate to the sodium bicarbonate reaction mother liquor, the presence of the promoter inhibits the generation of double salt and mixed salt. CN116199244A discloses a method for preparing sodium carbonate and ammonium sulfate from sodium sulfate, adding diammonium hydrogen phosphate and sodium formate in the double decomposition reaction, which can expand the crystallization area of ​​sodium bicarbonate, increase the precipitation rate of sodium bicarbonate, and make the recovery efficiency of sodium above 90%. CN 111039304 A discloses a method for preparing ammonium sulfate and sodium bicarbonate from sodium sulfate, using ammonium sources including diammonium hydrogen phosphate, ammonium formate or ammonium nitrate as the conversion medium for preparing ammonium sulfate and sodium bicarbonate from sodium sulfate, and the ammonium source is recycled in the system. First, sodium sulfate is reacted with an ammonium source, and high-grade ammonium sulfate is prepared by evaporation and crystallization. The mother liquor is cooled and crystallized, and then reacted with ammonium bicarbonate (or carbon dioxide + ammonia) to prepare sodium bicarbonate. The purity of ammonium sulfate prepared by this method meets the requirements of GB535-1995, the purity of sodium bicarbonate is ≥90%, and the utilization rate of sodium sulfate is >85%.

[0005] In the above patents of using sodium sulfate to prepare sodium bicarbonate and then calcining sodium bicarbonate to obtain soda ash, the density of the obtained soda ash is relatively small, mostly less than 600kg / m 3 The particle size is also relatively small, mostly less than 150 microns, belonging to the category of light soda ash. However, heavy soda ash (density 1000-1200kg / m 3, particle size greater than 150 microns), is more economical than light soda ash in terms of packaging, storage and transportation, and is widely used in glass, metallurgy and pigment industries. Therefore, the price per ton of heavy soda ash is higher than that of light soda ash. Therefore, in the process of producing soda ash using sodium sulfate as raw material, if large particles of heavy soda ash can be obtained, the economic benefits will be better than those of light soda ash. In order to obtain large particles of soda ash, large particles of sodium bicarbonate must first be obtained in the double decomposition reaction of sodium sulfate and ammonium bicarbonate.

[0006] In the existing process of producing sodium bicarbonate using sodium sulfate as raw material, there are relatively few reports on adjusting the size of sodium bicarbonate particles by process means, especially producing large particles of sodium bicarbonate, which still has shortcomings and needs to be further improved. Summary of the invention

[0007] The purpose of the invention is to overcome the defects of the prior art and provide a production technology for producing large-particle sodium bicarbonate (particles with a particle size of ≥180 μm account for more than 60%) using sodium sulfate and ammonium bicarbonate (or ammonia, CO2, water) as raw materials, while making the sodium bicarbonate solid separated after the double decomposition reaction of sodium sulfate and ammonium bicarbonate absorb less ammonia and have a lighter ammonia smell.

[0008] The technical solution to achieve the purpose of the present invention is: The inventor believes that the reaction of sodium sulfate with ammonium bicarbonate, or the introduction of CO2 into a saturated ammonia solution of sodium sulfate to generate sodium bicarbonate and ammonium sulfate is a double decomposition crystallization process, and the reaction equation is as follows: (1) or, (2)

[0009] Since sodium sulfate and ammonium bicarbonate react quickly, the solution is highly supersaturated, and the sodium bicarbonate nucleation rate is fast during the reaction process, the generated crystal nuclei will not have time to grow and grow, resulting in the accumulation of many crystal nuclei, and finally it is easy to obtain smaller particles. According to the crystal solubility curve, it can be divided into three regions-unstable zone, stable zone and metastable zone. To obtain larger crystals, the crystallization process should be controlled in the metastable zone to avoid the formation of excessive crystal nuclei, and the saturation should not be too large. Of course, there are many factors that affect the crystal size of salts, which are closely related to the nucleation rate, growth rate and residence time of crystals in the crystallizer. A trace amount of organic additives (crystal regulators) in saturated inorganic salt solutions has the effect of reducing surface tension and increasing the surface activity of the solution, changing the crystallization rate of the solution, and thus controlling the crystal size. The presence of crystal regulators can slow down the formation rate of sodium bicarbonate nuclei, increase the interfacial energy of the sodium bicarbonate crystallization process, thereby inhibiting the occurrence of spontaneous nucleation, promoting the growth of sodium bicarbonate crystals, and increasing the size of sodium bicarbonate crystals.

[0010] The crystal control method for preparing large-particle sodium bicarbonate by reacting sodium sulfate with ammonium bicarbonate of the present invention comprises: A crystal modifier polyphosphate is added during the double decomposition reaction of sodium sulfate and ammonium bicarbonate.

[0011] The crystal regulator polyphosphate is one or more of sodium tripolyphosphate, sodium hexametaphosphate, sodium pyrophosphate, ammonium tripolyphosphate, ammonium hexametaphosphate, ammonium pyrophosphate, potassium tripolyphosphate, potassium hexametaphosphate, and potassium pyrophosphate.

[0012] The amount of the crystal regulator added is 2 mg / L to 250 mg / L.

[0013] The material molar ratio of sodium sulfate to ammonium bicarbonate is 1:1.5-1:2.5.

[0014] The sodium sulfate and ammonium bicarbonate are reacted at 30-50° C. for 0.5-3 hours.

[0015] After the double decomposition reaction, the sodium bicarbonate crystals are separated from the solution, and the mother liquor is evaporated and crystallized to recover the ammonium sulfate solid, and the remaining solution is returned to the double decomposition reaction process for repeated use.

[0016] By adopting the above technical solution, the purity of sodium bicarbonate can reach over 98.5%, and particles with a diameter of ≥180 μm account for over 60%. DETAILED DESCRIPTION

[0017] The present invention is further described below by way of examples, the purpose of which is only to provide a better understanding of the content of the present invention. Therefore, the examples cited do not limit the scope of protection of the present invention: Example 1

[0018] Sodium tripolyphosphate was added to 300ml 30% sodium sulfate solution at 35℃ to make the concentration of sodium tripolyphosphate 50ppm, stirred, and 108g ammonium bicarbonate solid was gradually added. The reaction was carried out under normal pressure for 1h, and the reaction temperature was maintained at 35℃. After the reaction, the slurry was filtered to obtain the alkali mother liquor and NaHCO3 filter cake respectively. The filter cake was washed with a small amount of clean water to obtain pure NaHCO3 crystals. NaHCO3 was directly dried for 2h at a drying temperature of 90℃ to obtain NaHCO3 product with a purity of 98.7%. According to SEM analysis, particles with a particle size greater than 180μm accounted for 65%.

[0019] Example 2

[0020] In 300ml 30% sodium sulfate solution at 37℃, add sodium hexametaphosphate solution to make the sodium hexametaphosphate concentration 100ppm, stir, gradually add 112.5g ammonium bicarbonate solid, react for 1.5h under normal pressure, keep the reaction temperature at 37℃, filter the slurry after the reaction to obtain alkali mother liquor and NaHCO3 filter cake respectively, wash the filter cake to obtain pure NaHCO3 crystals, directly dry NaHCO3 for 1.5h, drying temperature 100℃, obtain NaHCO3 product with purity 98.9%. According to SEM analysis, particles with a particle size greater than 180μm account for 72%.

[0021] Example 3

[0022] Sodium pyrophosphate solution was added to 300ml 30% sodium sulfate solution at 33°C to make the sodium pyrophosphate concentration 100ppm, stirred, and 108g of ammonium bicarbonate solid was gradually added. The reaction was carried out at normal pressure for 2h, and the reaction temperature was maintained at 33°C. After the reaction, the slurry was filtered to obtain the alkali mother liquor and NaHCO3 filter cake respectively. The filter cake was washed to obtain pure NaHCO3 crystals. NaHCO3 was directly dried for 3h at a drying temperature of 80°C to obtain sodium bicarbonate product with a purity of 99.0%. According to SEM analysis, particles with a particle size greater than 180μm accounted for 77%.

[0023] Example 4

[0024] Add ammonium tripolyphosphate solution to 300ml 30% sodium sulfate solution at 35℃ to make the concentration of ammonium tripolyphosphate 90ppm, stir, gradually add 108g ammonium bicarbonate solid, react for 1h under normal pressure, keep the reaction temperature at 35℃, filter the slurry after the reaction to obtain alkali mother liquor and NaHCO3 filter cake respectively, wash the filter cake to obtain pure NaHCO3 crystals, directly dry NaHCO3 for 2h, dry at 90℃ to obtain sodium bicarbonate product with a purity of 98.8%. According to SEM analysis, particles with a particle size greater than 180μm account for 66%.

[0025] Example 5

[0026] Add ammonium hexametaphosphate solution to 300ml 30% sodium sulfate solution at 34℃, make the polyammonium hexametaphosphate concentration 120ppm, stir, gradually add 112.5g ammonium bicarbonate solid, react for 1h under normal pressure, keep the reaction temperature at 34℃, filter the slurry after the reactor to obtain alkali mother liquor and NaHCO3 filter cake respectively, wash the filter cake to obtain pure NaHCO3 crystals, directly dry NaHCO3 for 2h, drying temperature 90℃, obtain sodium bicarbonate product with purity 99.5%. According to SEM analysis, particles with a particle size greater than 180μm account for 73%.

[0027] Example 6

[0028] Add ammonium pyrophosphate solution to 300ml 30% sodium sulfate solution at 36℃, make the ammonium pyrophosphate concentration 110ppm, stir, gradually add 108g ammonium bicarbonate solid, react under normal pressure, keep the reaction temperature at 36℃, filter the slurry after the reaction, respectively obtain alkali mother liquor and NaHCO3 filter cake, wash the filter cake, obtain pure NaHCO3 crystals, directly dry NaHCO3 for 3h, drying temperature 80℃, obtain sodium bicarbonate product, purity 99.3%. According to SEM analysis, particles with a particle size greater than 180μm account for 79%.

[0029] Example 7

[0030] In 300ml 30% sodium sulfate solution at 36℃, add a mixed solution of sodium hexametaphosphate and ammonium hexametaphosphate, wherein the molar ratio of sodium hexametaphosphate to ammonium hexametaphosphate is 1:1, so that the total concentration of hexametaphosphate is 120ppm, stir, gradually add 108 grams of ammonium bicarbonate solid, react under normal pressure, keep the reaction temperature at 36℃, filter the slurry after the reaction, and obtain the alkali mother liquor and NaHCO3 filter cake respectively. After washing the filter cake, pure NaHCO3 crystals are obtained. NaHCO3 is directly dried for 3h at a drying temperature of 80℃ to obtain sodium bicarbonate product with a purity of 99.1%. According to SEM analysis, particles with a particle size greater than 180μm account for 74%.

[0031] Example 8

[0032] In 300ml 30% sodium sulfate solution at 36℃, add a polyphosphate mixed solution of sodium tripolyphosphate, ammonium hexametaphosphate and potassium pyrophosphate, wherein the molar ratio of sodium tripolyphosphate, ammonium hexametaphosphate and potassium pyrophosphate is 1:1:1, so that the total concentration of polyphosphate is 150ppm, stir, gradually add 108 grams of ammonium bicarbonate solid, react under normal pressure, keep the reaction temperature at 36℃, filter the slurry after the reaction, respectively obtain alkali mother liquor and NaHCO3 filter cake, wash the filter cake, obtain pure NaHCO3 crystals, directly dry NaHCO3 for 3h, drying temperature 80℃, obtain sodium bicarbonate product, purity 99.3%. According to SEM analysis, particles with a particle size greater than 180μm account for 80%.

Claims

1. A crystal control method for preparing large-particle sodium bicarbonate by reacting sodium sulfate and ammonium bicarbonate, characterized in that: A crystal modifier polyphosphate is added during the double decomposition reaction of sodium sulfate and ammonium bicarbonate.

2. The method according to claim 1, characterized in that The crystal regulator polyphosphate is one or more of sodium tripolyphosphate, sodium hexametaphosphate, sodium pyrophosphate, ammonium tripolyphosphate, ammonium hexametaphosphate, ammonium pyrophosphate, potassium tripolyphosphate, potassium hexametaphosphate, and potassium pyrophosphate.

3. The method according to claim 1 or 2, characterized in that: The amount of the crystal modifier added is 2 mg / L to 250 mg / L.

4. The method according to claim 1, characterized in that The material molar ratio of sodium sulfate to ammonium bicarbonate is 1:1.5-1:2.

5.

5. The method according to claim 1, characterized in that The double decomposition reaction of sodium sulfate and ammonium bicarbonate is carried out at 30-50° C. for 0.5-3 hours.

6. The method according to claim 1, characterized in that After the double decomposition reaction, the sodium bicarbonate crystals are separated from the solution, and the mother liquor is evaporated and crystallized to recover the ammonium sulfate solid, and the remaining solution is returned to the double decomposition reaction process for repeated use.