A method for treating ammonium bisulfate by-product of acetone cyanohydrin process for preparing alpha-hydroxycarboxylate
By adding water dropwise at high temperature and distilling under normal pressure, and using unreacted sulfuric acid as an acid hydrolysis reagent, combined with activated carbon decolorization and ammonia neutralization, the problem of efficient hydrolysis and resource recovery of ammonium bisulfate mixed salt, a byproduct of the preparation of α-hydroxycarboxylic acid esters by the acetone cyanohydrin method, was solved, achieving low-cost, green treatment and efficient recovery of ammonium sulfate.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- HEBEI CHENGXIN
- Filing Date
- 2025-10-22
- Publication Date
- 2026-08-04
AI Technical Summary
Existing technologies for processing ammonium bisulfate mixed salts, a byproduct of the preparation of α-hydroxycarboxylic acid esters using the acetone cyanohydrin method, suffer from high reagent consumption, high energy consumption, difficulty in product separation, and low economic value, failing to achieve efficient and low-cost processing and resource recovery of the mixed salts.
The byproduct ammonium bisulfate mixed salt was hydrolyzed by adding water dropwise in a molten state at high temperature. The methanol-water mixture was removed by atmospheric distillation. Unreacted sulfuric acid was used as an acid hydrolysis reagent. Combined with activated carbon decolorization and ammonia neutralization reaction, the complete hydrolysis of monomethyl sulfate and the recovery of ammonium sulfate were achieved.
Complete hydrolysis of monomethyl sulfate was achieved to obtain ammonium sulfate that meets fertilizer-grade standards, reducing processing costs and safety risks, realizing efficient resource recovery and green treatment, and making it suitable for industrial production.
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Figure CN121361812B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of chemical production technology, and in particular to a method for processing ammonium bisulfate mixed salt, a byproduct of the preparation of α-hydroxycarboxylic acid esters by the acetone cyanohydrin method. Background Technology
[0002] In the chemical industry, the process of preparing carboxylic acid esters by cyanohydrolysis of sulfuric acid and cyano compounds in methanol solvent is widely used. Among these processes, the reaction of acetone cyanohydrin with concentrated sulfuric acid in a methanol system to produce methyl 2-hydroxyisobutyrate is a core industrial method for synthesizing methyl 2-hydroxyisobutyrate, 2-hydroxyisobutyric acid, and polymethyl acrylate. This process inevitably produces a byproduct, ammonium bisulfate mixed salt. The main components of this mixed salt include ammonium bisulfate, monomethyl sulfate, unreacted sulfuric acid, and small amounts of organic impurities. The content of monomethyl sulfate is approximately 25%–35%. The presence of this substance not only severely interferes with the subsequent recovery and purification of ammonium sulfate but may also cause equipment corrosion or secondary pollution risks in subsequent processing stages. Therefore, monomethyl sulfate must be converted or decomposed before the recovery of ammonium sulfate.
[0003] Current research has reported methods to convert monomethyl sulfate in wastewater into sodium methyl sulfate by controlling the pH of the system, and then use sodium methyl sulfate to synthesize nitromethane, p-methylsulfonyl toluene, and anisole. However, this process requires the introduction of a large amount of sodium hydroxide and involves a series of operations such as high-temperature reaction, distillation, and rectification, which greatly increases the difficulty of wastewater treatment and makes industrial application difficult.
[0004] Currently, two main industrial processing routes are used: The first involves converting sodium methyl sulfate to sodium sulfate via atmospheric pressure reflux hydrolysis under sodium hydroxide conditions, using water as a solvent. The sodium sulfate is then separated by concentration and dehydration. While this method is relatively simple, it consumes a large amount of sodium hydroxide and ultimately produces a mixed salt of sodium sulfate and ammonium sulfate as a byproduct. Separating these two compounds is difficult, resulting in low added value for the obtained sodium sulfate product and thus low industrial economic value. The second route involves adding excess ammonia to the waste salt system and converting monomethyl sulfate to ammonium sulfate via high-pressure alkaline hydrolysis. However, this method requires the additional removal of excess ammonia from the system, and subsequent high-energy concentration is necessary to obtain the ammonium sulfate product. Overall, the energy consumption and operating costs are high, making it difficult to meet the economic requirements for large-scale industrial applications.
[0005] Therefore, developing a process that is simpler to operate, more economical, and can effectively process monomethyl sulfate and achieve efficient recovery of ammonium sulfate has become an urgent technical need to be addressed in this field. Summary of the Invention
[0006] To address the common problems in existing methods for processing ammonium bisulfate mixed salts, a byproduct of α-hydroxycarboxylic acid ester preparation via the acetone cyanohydrin method, such as high reagent consumption, high energy consumption, difficulty in product separation, or low economic value, which prevent efficient and low-cost processing and resource recovery of the mixed salts, this invention provides a method for processing ammonium bisulfate mixed salts, a byproduct of α-hydroxycarboxylic acid ester preparation via the acetone cyanohydrin method.
[0007] To solve the above-mentioned technical problems, the technical solution provided by the present invention is as follows: A method for processing ammonium bisulfate mixed salt, a byproduct of the preparation of α-hydroxycarboxylic acid esters via the acetone cyanohydrin method, includes the following steps: Step a: The by-product ammonium bisulfate mixed salt is heated and melted, and water is added dropwise to the molten by-product ammonium bisulfate mixed salt to carry out the hydrolysis reaction. At the same time, a methanol-water mixture is extracted under normal pressure. After the dropwise addition is completed, the temperature is kept until the hydrolysis is complete to obtain ammonium bisulfate and ammonium sulfate mixed salt. Step b: Dissolve the ammonium bisulfate and ammonium sulfate mixture in water to obtain a mixed salt solution; Step c: Add activated carbon to the mixed salt solution for decolorization, and separate the solid and liquid to obtain a decolorized mixed salt solution; Step d: Ammonia gas is introduced into the decolorized mixed salt solution to separate the solid and liquid, yielding ammonium sulfate solid and ammonium sulfate mother liquor.
[0008] The ester bond in the monomethyl sulfate molecule is affected by both the steric hindrance of the methyl group and the strong electron-withdrawing effect of the sulfate group. Compared with ordinary carboxylic acid esters (such as methyl acetate), its hydrolytic activity is significantly reduced and it is difficult to break under normal conditions. Moreover, the monomethyl sulfate content in this mixed salt is as high as 25%~35%. At high concentrations, local mass transfer resistance is easily formed, which further inhibits the hydrolysis reaction. Existing technologies generally require the introduction of additional acid and base reagents and rely on high pressure or high temperature operation, but still cannot achieve complete hydrolysis.
[0009] Addressing the critical bottleneck of inefficient hydrolysis of monomethyl sulfate in the ammonium bisulfate mixed salt byproduct of α-hydroxycarboxylic acid ester preparation via the acetone cyanohydrin method, this invention breaks through the conventional approach of requiring additional acid-base reagents. It creatively uses unreacted sulfuric acid from the ammonium bisulfate mixed salt as the acidolysis reagent. Water is added dropwise to the molten mixed salt to initiate the hydrolysis reaction, while atmospheric pressure distillation is used to remove the methanol-water mixture generated in real time. This achieves the complete hydrolysis of the high content of monomethyl sulfate in the mixed salt, ultimately yielding a mixed salt of ammonium bisulfate and ammonium sulfate, laying the foundation for the efficient recovery of ammonium sulfate in the future.
[0010] After complete hydrolysis of monomethyl sulfate, water is added to dissolve the salt to obtain a mixed salt solution. Then, the solution is decolorized to remove colored impurities, resulting in a colorless clear liquid. Ammonia gas is then introduced into the decolorized mixed salt solution to neutralize the generated ammonium bisulfate. After filtration, ammonium sulfate is obtained. The quality of this ammonium sulfate meets the fertilizer grade Type I standard (GB / T 535-2020). This achieves high-value utilization of the by-product mixed salt and provides a feasible technical path for the greening and industrial upgrading of the acetone cyanohydrin process for the preparation of α-hydroxycarboxylic acid esters.
[0011] This invention eliminates the need for additional acid and alkali reagents, as well as the complex operations such as high-pressure alkaline hydrolysis and distillation separation found in traditional methods. It also eliminates the need for high-energy-consuming equipment such as high-pressure reactors and distillation columns. The hydrolysis of monomethyl sulfate and recovery of methanol can be achieved simply through conventional heating and melting and atmospheric distillation, significantly reducing processing costs and production safety risks, and facilitating industrial production applications.
[0012] It should be noted that the α-hydroxycarboxylic acid ester described in this invention is prepared by cyanohydrolysis esterification of acetone cyanohydrin and sulfuric acid in an alcohol solvent. Specifically, the 2-hydroxyisobutyrate ester is prepared by the acetone cyanohydrin method, and the residue remaining in the distillation vessel after distillation to obtain the product is the byproduct ammonium bisulfate mixed salt.
[0013] Taking the preparation of 2-hydroxyisobutyrate by the acetone cyanohydrin method as an example, acetone cyanohydrin first reacts with sulfuric acid in water to form α-hydroxyisobutyramide hydrogen sulfate, and then esterifies to obtain methyl 2-hydroxyisobutyrate and ammonium bisulfate. During this process, sulfuric acid reacts with methanol to generate monomethyl sulfate. After distillation to obtain the product, the main components in the remaining residue include ammonium bisulfate, monomethyl sulfate, unreacted sulfuric acid, and a small amount of organic impurities. Among them, the content of monomethyl sulfate is about 25% to 35%.
[0014] Furthermore, in step a, the temperature for heating and melting is 120°C to 140°C.
[0015] Further, in step a, the molar ratio of the amount of water added to the monomethyl sulfate in the by-product ammonium bisulfate mixed salt is 2:1 to 5:1, and the temperature of the added water and the temperature of the hydrolysis are both 120℃ to 140℃.
[0016] The optimal amount of water added ensures sufficient contact between water and monomethyl sulfate. Combined with subsequent heat-insulating hydrolysis, this promotes the complete hydrolysis of monomethyl sulfate. The small amount of dissolved water in step b, which matches the amount of mixed salt, ensures that the final concentration of the mixed salt solution is exactly within the range where ammonium sulfate saturates after ammonia is introduced. This allows the ammonium sulfate concentration in the system to instantly reach saturation after ammonia is introduced to neutralize ammonium bisulfate and generate ammonium sulfate. Without any concentration treatment, solid ammonium sulfate can be obtained directly by centrifugation, thus improving the overall processing efficiency.
[0017] Furthermore, in step a, the water is added dropwise for 1 to 3 hours; after the addition is completed, the hydrolysis is kept at a constant temperature for 2 to 3 hours.
[0018] A water addition time of 1h to 3h allows water to slowly and continuously dissolve into the molten salt, forming a uniform water-mixed salt reaction environment. This avoids the problem of local water excess or deficiency and allows the hydrolysis rate of monomethyl sulfate to match the ability of methanol to be extracted at atmospheric pressure, thereby improving the hydrolysis rate of monomethyl sulfate.
[0019] Furthermore, the mass ratio of the water in step b to the by-product ammonium bisulfate mixture in step a is 0.5:1 to 1.5:1.
[0020] Further, in step c, the activated carbon is acidic lignocarbon, and the mass ratio of the activated carbon to the mixed salt solution is 0.001:1 to 0.01:1.
[0021] Furthermore, in step c, the waste activated carbon obtained from solid-liquid separation can be regenerated by anaerobic high-temperature calcination, and the regenerated activated carbon can be reused to reduce costs.
[0022] For example, the temperature of the oxygen-free high-temperature calcination is 700℃~900℃, and the calcination time is 1h~3h.
[0023] Furthermore, in step d, the endpoint of introducing ammonia gas is when the pH of the feed liquid is 6~7.
[0024] Furthermore, in step d, the ammonia gas is introduced for 2 to 3 hours, and the ammonia gas is introduced at a temperature of 20°C to 50°C.
[0025] The optimal ammonia flow rate and flow time ensure that ammonium bisulfate in the system is fully converted into ammonium sulfate, while avoiding excessive free ammonia levels that would fail to meet the GB / T 535-2020 fertilizer-grade ammonium sulfate standard.
[0026] Furthermore, step d also includes: returning the ammonium sulfate mother liquor to step b to dissolve the mixed salt of ammonium bisulfate and ammonium sulfate.
[0027] Furthermore, in step d, the solid-liquid separation method is filtration, and the filtration temperature is 20℃~30℃.
[0028] The present invention provides a method for treating ammonium bisulfate mixed salt, a byproduct of the preparation of α-hydroxycarboxylic acid esters using the acetone cyanohydrin method. This method utilizes unreacted sulfuric acid in the mixed salt, and simultaneously extracts a methanol-water mixture at high temperature by adding water dropwise. This allows monomethyl sulfate to be fully hydrolyzed into sulfuric acid and methanol, avoiding the problem of generating large amounts of additional waste salt from the decomposition of monomethyl sulfate using strong alkali and high temperature. Furthermore, by controlling the amount of water added, the hydrolysis of monomethyl sulfate is complete, and after passing ammonia gas through the brine, no concentration treatment is required; direct centrifugation yields fertilizer-grade Type I standard (GB / T 535-2020) ammonium sulfate. The ammonium sulfate mother liquor after centrifugation is not directly discharged from the system but is recycled back to dissolve the mixed salt after high-temperature acid hydrolysis, further recovering ammonium sulfate. This achieves resource utilization of the ammonium sulfate mother liquor, and no hazardous liquid waste is generated in the entire system. It is a green, energy-saving, and resource-efficient treatment method with high application value. Attached Figure Description
[0029] Figure 1 This is a schematic diagram of the process flow for treating the by-product ammonium bisulfate mixed salt in an embodiment of the present invention. Detailed Implementation
[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.
[0031] To better illustrate the present invention, further examples are provided below.
[0032] The following examples and comparative examples illustrate the treatment of waste salt containing ammonium bisulfate, monomethyl sulfate, sulfuric acid, and a small amount of organic impurities generated during the synthesis of methyl 2-hydroxyisobutyrate.
[0033] The methyl 2-hydroxyisobutyrate waste salt described in the following examples and comparative examples comes from the production process of synthesizing methyl 2-hydroxyisobutyrate using acetone cyanohydrin, sulfuric acid and methanol as raw materials, wherein the methyl 2-hydroxyisobutyrate waste salt contains 25% to 35% monomethyl sulfate.
[0034] Preparation of mixed salts containing ammonium bisulfate: Concentrated sulfuric acid, water, and acetone cyanohydrin were mixed and heated to 40-50°C for 1 hour. Methanol was then added, and the mixture was heated to reflux and held at that temperature for 12 hours. After the reflux was completed, methanol and methyl 2-hydroxyisobutyrate were distilled off under reduced pressure. The remaining material was a mixed salt of ammonium bisulfate as a byproduct. The byproduct ammonium bisulfate was tested for the following index: SO42-. 2- 52.54%, total nitrogen 11.20% (as N), acidity 0.52% (as sulfuric acid), monomethyl sulfate: 27.72%.
[0035] The following examples directly weigh the above-mentioned mixed salt and process it.
[0036] Example 1 This embodiment provides a method for treating ammonium bisulfate mixed salt, a byproduct of methyl 2-hydroxyisobutyrate, which specifically includes the following steps: Step a: Take 200g of the prepared by-product ammonium bisulfate mixed salt, heat it to 130℃ to melt it, and then add 44.5g of water dropwise to the molten by-product ammonium bisulfate mixed salt, while collecting the methanol-water mixture dropwise. The dropwise addition time is 3h. After the dropwise addition is completed, keep it at 130℃ for 2h to obtain brownish-yellow ammonium bisulfate and ammonium sulfate mixed salt. Step b: Add 100g of water to the ammonium bisulfate and ammonium sulfate mixture obtained in step a, stir to dissolve the salt, and obtain a brownish-yellow mixed salt solution; Step c: Heat the above mixed salt solution to 75°C, add 0.32g of acidic charcoal, stir and keep warm for 4 hours, filter, and obtain 307g of colorless and transparent decolorized mixed salt solution and 1.03g of waste acidic charcoal. In step d, the decolorized mixed salt solution was cooled to 20°C, and 24.96g of ammonia gas was introduced into it at this temperature until the pH reached 6-7. The aeration time was 2 hours. After filtration, 129.3g of wet ammonium sulfate was obtained (after drying, the nitrogen (N) content was 20.72% and the sulfur (S) content was 24.10%), and 198.42g of slightly yellow ammonium sulfate mother liquor was obtained. This was reused in the next batch of dissolved and acid-hydrolyzed ammonium bisulfate and ammonium sulfate mixed salt.
[0037] Example 2 This embodiment provides a method for treating ammonium bisulfate mixed salt, a byproduct of methyl 2-hydroxyisobutyrate, which specifically includes the following steps: Step a: Take 200g of the prepared by-product ammonium bisulfate mixed salt, heat it to 120℃ to melt it, and then add 17.82g of water dropwise to the molten by-product ammonium bisulfate mixed salt, collecting the methanol-water mixture while adding the water dropwise. The addition time is 3h. After the addition is completed, keep it at 120℃ for 3h to obtain brownish-yellow ammonium bisulfate and ammonium sulfate mixed salt. Step b: Add 198g of the ammonium sulfate mother liquor obtained in step d of Example 1 to the ammonium bisulfate and ammonium sulfate mixed salt obtained in step a, stir to dissolve the salt, and obtain a brownish-yellow mixed salt solution; Step c: Heat the above mixed salt solution to 80°C, add 4.02g of acidic charcoal, stir and keep warm for 1 hour, filter, and obtain 394g of colorless and transparent decolorized mixed salt solution and 5.32g of waste acidic charcoal. Step d: Cool the decolorized mixed salt solution to 50°C, and at this temperature, introduce 24.43g of ammonia gas until the pH reaches 6-7. The aeration time is 3h. After filtration, 153g of wet ammonium sulfate (after drying, the nitrogen (N) content is 20.65% and the sulfur (S) content is 24.18%) and 257g of slightly yellow ammonium sulfate mother liquor are obtained. These can be reused in the next batch of dissolved and acid-hydrolyzed ammonium bisulfate and ammonium sulfate mixed salt.
[0038] Example 3 This embodiment provides a method for treating ammonium bisulfate mixed salt, a byproduct of methyl 2-hydroxyisobutyrate, which specifically includes the following steps: Step a: Take 200g of the prepared by-product ammonium bisulfate mixed salt, heat it to 140℃ to melt it, and then add 35.64g of water dropwise to the molten by-product ammonium bisulfate mixed salt, collecting the methanol-water mixture while adding the water dropwise. The addition time is 1h. After the addition is completed, keep it at 140℃ for 2h to obtain brownish-yellow ammonium bisulfate and ammonium sulfate mixed salt. Step b: Add 287g of ammonium sulfate mother liquor obtained in step d of Example 2 to the mixed salt of ammonium bisulfate and ammonium sulfate obtained in step a, stir to dissolve the salt, and obtain a brownish-yellow mixed salt solution; Step c: Heat the above mixed salt solution to 70°C, add 2.55g of acidic charcoal, stir and keep warm for 2 hours, filter, and obtain 493g of colorless and transparent decolorized mixed salt solution and 4.55g of waste acidic charcoal. Step d: Cool the decolorized mixed salt solution to 30°C, and at this temperature, introduce 24.49g of ammonia gas until the pH reaches 6-7. The aeration time is 2 hours. After filtration, 222g of wet ammonium sulfate (after drying, the nitrogen (N) content is 20.56% and the sulfur (S) content is 24.07%) and 270g of slightly yellow ammonium sulfate mother liquor are obtained. These can be reused in the next batch of dissolved and acid-hydrolyzed ammonium bisulfate and ammonium sulfate mixed salt.
[0039] Example 4 This embodiment provides a method for treating ammonium bisulfate mixed salt, a byproduct of methyl 2-hydroxyisobutyrate, which specifically includes the following steps: Step a: Take 200g of the prepared by-product ammonium bisulfate mixed salt, heat it to 130℃ to melt it, and then add 35.64g of water dropwise to the molten by-product ammonium bisulfate mixed salt, collecting the methanol-water mixture while adding it dropwise. The addition time is 3h. After the addition is completed, keep it at 130℃ for 2h to obtain brownish-yellow ammonium bisulfate and ammonium sulfate mixed salt. Step b: Add 270g of ammonium sulfate mother liquor obtained in step d of Example 3 to the mixed salt of ammonium bisulfate and ammonium sulfate obtained in step a, stir to dissolve the salt, and obtain a brownish-yellow mixed salt solution; Step c: The waste acidic charcoal obtained in step c of Examples 1 to 3 is calcined at 800°C in an oxygen-free environment for 2 hours to obtain 5.32g of regenerated acidic charcoal; The above mixed salt solution was heated to 72°C, and 5g of the above regenerated acidic charcoal was added. The mixture was stirred and kept warm for 4 hours. After filtration, 477g of colorless and transparent decolorized mixed salt solution and 7.02g of waste acidic charcoal were obtained. Step d: Cool the decolorized mixed salt solution to 40°C, and at this temperature, introduce 25.46g of ammonia gas until the pH reaches 6-7. The aeration time is 3h. After filtration, 213g of wet ammonium sulfate (after drying, the nitrogen (N) content is 20.55% and the sulfur (S) content is 24.03%) and 286g of slightly yellow ammonium sulfate mother liquor are obtained. These can be reused in the next batch of dissolved and acid-hydrolyzed ammonium bisulfate and ammonium sulfate mixed salt.
[0040] Example 5 This embodiment provides a method for treating ammonium bisulfate mixed salt, a byproduct of methyl 2-hydroxyisobutyrate, which specifically includes the following steps: Step a: Take 200g of the prepared by-product ammonium bisulfate mixed salt, heat it to 130℃ to melt it, and then add 44.55g of water dropwise to the molten by-product ammonium bisulfate mixed salt, collecting the methanol-water mixture while adding the water dropwise. The addition time is 3h. After the addition is completed, keep it at 130℃ for 3h to obtain brownish-yellow ammonium bisulfate and ammonium sulfate mixed salt. Step b: Add 100g of water to the ammonium bisulfate and ammonium sulfate mixture obtained in step a, stir to dissolve the salt, and obtain a brownish-yellow mixed salt solution; Step c: Heat the above mixed salt solution to 75°C, add 0.32g of acidic charcoal, stir and keep warm for 4 hours, filter, and obtain 303g of colorless and transparent decolorized mixed salt solution and 1.56g of waste acidic charcoal. In step d, the decolorized mixed salt solution was cooled to 20°C, and 24.87g of ammonia gas was introduced into it at this temperature until the pH reached 6-7. The aeration time was 2h. The solution was concentrated under reduced pressure to remove water, and ammonium sulfate was obtained. The nitrogen (N) content was 20.59% and the sulfur (S) content was 24.13%.
[0041] Comparative Example 1 This comparative example provides a method for treating ammonium bisulfate mixed salt, a byproduct of methyl 2-hydroxyisobutyrate. The only difference from Example 5 is that the acidolysis temperature is reduced to 90°C, and the acidolysis water is added all at once. Specifically, the method includes the following steps: Step a: Take 200g of the prepared by-product ammonium bisulfate mixed salt, heat it to 90℃, then add 44.5g of water at once, keep it warm for 3h, and obtain brownish-yellow ammonium bisulfate and ammonium sulfate mixed salt; Step b: Add 100g of water to the ammonium bisulfate and ammonium sulfate mixture obtained in step a, stir to dissolve the salt, and obtain a brownish-yellow mixed salt solution; Step c: Heat the above mixed salt solution to 75°C, add 0.32g of acidic charcoal, stir and keep warm for 4 hours, filter, and obtain 321g of colorless and transparent decolorized mixed salt solution and 1.23g of waste acidic charcoal. In step d, the decolorized mixed salt solution was cooled to 20°C, and 18.21g of ammonia gas was introduced into it at this temperature until the pH reached 6-7. The aeration time was 2 hours. The solution was then concentrated under reduced pressure to remove water, yielding ammonium sulfate. The nitrogen (N) content was measured to be 17.47%, and the sulfur (S) content was 17.62%. The ammonium sulfate obtained in this comparative example does not meet the requirements of fertilizer grade type I standard.
[0042] Comparative Example 2 This comparative example provides a method for treating ammonium bisulfate mixed salt, a byproduct of methyl 2-hydroxyisobutyrate, using an alkaline neutralization and hydrolysis method, specifically including the following steps: Take 200g of the prepared by-product ammonium bisulfate mixed salt, add 135g of water, stir to dissolve the salt, add 0.5% by weight of acidic charcoal, decolorize at 75℃ for 1h, filter, adjust the pH of the filtrate to 13-14 with 32% liquid alkali, heat to reflux and keep warm for 5h, continuously add liquid alkali to maintain the pH of the solution at 13-14, after the holding time is over, adjust the pH of the solution to 6-7 with sulfuric acid to obtain sodium sulfate brine, concentrate under reduced pressure to remove water, dry to obtain sodium sulfate, the sodium sulfate content is 98.53%, and the ammonium sulfate content is 0.52%.
[0043] Comparative Example 3 This comparative example provides a method for treating ammonium bisulfate mixed salt, a byproduct of methyl 2-hydroxyisobutyrate, using a high-pressure alkaline hydrolysis method with ammonia gas. The method specifically includes the following steps: Take 200g of the prepared by-product ammonium bisulfate mixed salt, add 135g of water, stir to dissolve the salt, add 0.5% (by weight) of acidic charcoal, decolorize at 75℃ for 1h, filter, and pass ammonia gas through the filtrate at 20-25℃ until the pH of the solution reaches 7. Continue to pass 26.77g of ammonia gas, transfer to an autoclave, heat to 120℃, pressurize and hold for 7h, cool to 20-30℃ to release pressure, and obtain an ammonium sulfate solution. Concentrate under reduced pressure to remove ammonia and water, dry, and obtain ammonium sulfate salt. The nitrogen (N) content is 20.39%, and the sulfur (S) content is 23.04%. The ammonium sulfate obtained in this comparative example does not meet the requirements of fertilizer grade Type I standard.
[0044] In summary, this invention utilizes unreacted sulfuric acid in a mixed salt solution as an acidolysis reagent. The byproduct ammonium bisulfate mixed salt solution is heated to a molten state, and water is added dropwise to hydrolyze monomethyl sulfate while simultaneously collecting a methanol-water mixture at atmospheric pressure (the methanol can be reused in the main reaction). By precisely controlling the amount of water added, the hydrolyzed mixed salt solution is dissolved, decolorized with activated carbon, neutralized with ammonia, and directly centrifuged to obtain ammonium sulfate conforming to the GB / T 535-2020 fertilizer grade type I standard. The mother liquor from centrifugation is recycled back to the mixed salt solution dissolution process to recover residual ammonium sulfate. This method requires no additional strong alkali, distillation, or evaporation concentration processes, achieving efficient conversion of monomethyl sulfate in the byproduct mixed salt solution and resource utilization of methanol and ammonium sulfate. The entire process generates no liquid or solid hazardous waste, offering advantages in energy saving, environmental protection, and economy. It can promote the green upgrading of the acetone cyanohydrin process for preparing α-hydroxycarboxylic acid esters, demonstrating significant application value.
[0045] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.
Claims
1. A method for processing ammonium bisulfate mixed salt, a byproduct of the preparation of α-hydroxycarboxylic acid esters via the acetone cyanohydrin method, characterized in that, Includes the following steps: Step a: The by-product ammonium bisulfate mixed salt is heated and melted, and water is added dropwise to the molten by-product ammonium bisulfate mixed salt to carry out the hydrolysis reaction. At the same time, a methanol-water mixture is extracted under normal pressure. After the dropwise addition is completed, the temperature is kept until the hydrolysis is complete to obtain ammonium bisulfate and ammonium sulfate mixed salt. Step b: Dissolve the ammonium bisulfate and ammonium sulfate mixture in water to obtain a mixed salt solution; Step c: Add activated carbon to the mixed salt solution for decolorization, and separate the solid and liquid to obtain a decolorized mixed salt solution; Step d: Ammonia gas is introduced into the decolorized mixed salt solution to separate the solid and liquid phases, yielding ammonium sulfate and ammonium sulfate mother liquor; In step a, the temperature for heating and melting is 120℃~140℃; in step a, the molar ratio of the amount of water added to the monomethyl sulfate in the by-product ammonium bisulfate mixed salt is 2:1~5:1; the temperature of the added water and the temperature for hydrolysis are both 120℃~140℃; in step a, the time for adding water is 1h~3h; after the addition is completed, the time for hydrolysis is 2h~3h. The mass ratio of water in step b to the by-product ammonium bisulfate mixture in step a is 0.5:1 to 1.5:1; In step c, the decolorization temperature is 70℃~80℃, and the decolorization time is 1h~4h; In step d, the temperature of the ammonia gas introduced is 20℃~50℃.
2. The method for treating ammonium bisulfate mixed salt, a byproduct of the acetone cyanohydrin method for preparing α-hydroxycarboxylic acid esters, as described in claim 1, is characterized in that... The α-hydroxycarboxylic acid ester was prepared by cyanohydrolysis esterification of acetone cyanohydrin and sulfuric acid in an alcohol solvent.
3. The method for treating ammonium bisulfate mixed salt, a byproduct of the acetone cyanohydrin method for preparing α-hydroxycarboxylic acid esters, as described in claim 1, is characterized in that... In step c, the activated carbon is acidic lignocarbon, and the mass ratio of the activated carbon to the mixed salt solution is 0.001:1 to 0.01:
1.
4. The method for treating ammonium bisulfate mixed salt, a byproduct of the acetone cyanohydrin method for preparing α-hydroxycarboxylic acid esters, as described in claim 1, is characterized in that... In step d, the endpoint of introducing ammonia gas is when the pH of the feed liquid is 6~7.
5. The method for treating ammonium bisulfate mixed salt, a byproduct of the acetone cyanohydrin method for preparing α-hydroxycarboxylic acid esters, as described in claim 4, is characterized in that... In step d, the ammonia gas is introduced for 2 to 3 hours.
6. The method for treating ammonium bisulfate mixed salt, a byproduct of the acetone cyanohydrin method for preparing α-hydroxycarboxylic acid esters, as described in claim 1, is characterized in that... Step d also includes: returning the ammonium sulfate mother liquor to step b to dissolve the mixed salt of ammonium bisulfate and ammonium sulfate.