Method for detecting neutralization reaction endpoint in production of trisodium phosphate and application of method

Abstract

The invention belongs to the technical field of phosphate production and quality control, and particularly relates to a method for detecting a neutralization reaction endpoint in production of trisodium phosphate and application of the method. (2) potentiometric titration: titrating the to-be-detected sample solution to a reaction end point A1 by using a hydrochloric acid standard solution, recording the volume V1 of the consumed standard solution, continuously titrating to a reaction end point A2 by using a sodium hydroxide standard solution, and recording the volume V2 of the consumed standard solution; (3) calculating the reaction endpoint ratio of trisodium phosphate; (4) if the value of k is greater than 2.5, indicating that unreacted NaOH exists in the to-be-detected sample solution; if the value of k is less than 1.5, Na2HPO4 exists in the sample solution to be detected; if k is larger than or equal to 1.5 and smaller than or equal to 2.5, the content of anhydrous trisodium phosphate is larger than or equal to 97%, and the total phosphorus content is larger than 42%; the detection method provided by the invention improves the scientificity and accuracy of neutralization reaction endpoint determination, does not need electrode calibration and temperature compensation, and improves the accuracy of endpoint determination.

Description

Technical Field

[0001] The invention belongs to the technical field of phosphate production and quality control thereof, and particularly relates to a method for detecting an endpoint of a neutralization reaction in producing trisodium phosphate and an application thereof. Background Art

[0002] In the food field, trisodium phosphate (TSP) is often used to improve the complexing metal ions, pH value, and ionic strength of food, thereby improving the binding force and water retention of food. Trisodium phosphate is often compounded with other phosphates as a food additive; trisodium phosphate is compounded with disodium phosphate and used as a food desiccant. The production processes of domestic enterprises are basically the same, all using phosphoric acid as raw material, adding soda ash or caustic soda for neutralization reaction; most companies use spray drying to prepare anhydrous trisodium phosphate: after the neutralization reaction of trisodium phosphate is completed, it is sent to the drying tower through a conveying pump for spray drying to remove free water and most of the crystal water, and the rotary kiln is dried again to remove the last crystal water. The traditional process often forms compound salts Na3PO4·12H2O·1 / 7NaOH, Na3PO4·12H2O·1 / 4NaOH, 4Na3PO4·12H2O·NaOH, etc. when preparing trisodium phosphate, and it is difficult to obtain anhydrous trisodium phosphate with a content higher than 97% and a total phosphorus content greater than 42%. In addition, the existing production process only determines the endpoint of the neutralization reaction based on production experience, and then further tests the product quality through the trisodium phosphate content determination method. Therefore, it is impossible to quickly detect the degree of neutralization reaction and quickly determine the endpoint of the neutralization reaction, resulting in unstable product quality.

[0003] In addition, the current analysis methods of trisodium phosphate include gravimetric method and acid-base analysis method. The acid-base analysis method requires the use of indicators such as methyl orange, which makes it difficult to observe the end point color and the analysis results are prone to deviation; the gravimetric analysis operation is complicated and takes a long time. Some documents also disclose the use of spectrophotometry for analysis, such as "Determination of Industrial Trisodium Phosphate" disclosed by Li Taotao et al. Although the operation is simple and the analysis results are accurate, the analysis cost is high. In addition to the need for precision instruments such as spectrophotometers, it is also necessary to purchase potassium dihydrogen phosphate, ascorbic acid, ammonium molybdate, EDTA, formic acid, potassium antimony tartrate, sulfuric acid, and it is also necessary to prepare phosphate standard stock solution and working solution. More importantly, the above analysis methods are difficult to be quickly applied to the production process, which is easy to cause economic losses due to poor product quality or high post-processing production due to insufficient neutralization reaction. Therefore, it is of practical need and great significance to find a method for accurately judging the end point of the neutralization reaction, with low cost, convenient and fast operation, and accurate estimation of the content of trisodium phosphate. Summary of the invention

[0004] In view of the deficiencies of the prior art, the present invention provides a method for detecting the end point of a neutralization reaction in producing trisodium phosphate and an application thereof.

[0005] This is achieved specifically through the following technical solutions:

[0006] The first object of the present invention is to provide: a method for detecting the endpoint of a neutralization reaction in producing trisodium phosphate, comprising the following steps:

[0007] (1) Preparation: Using water as a solvent or diluent, prepare a hydrochloric acid standard solution, a sodium hydroxide standard solution, and a sample solution to be tested, wherein the concentrations of the hydrochloric acid standard solution and the sodium hydroxide standard solution are denoted as C1 and C2, respectively;

[0008] (2) Potentiometric titration: Calibrate the automatic potentiometric titrator, place the measuring electrode in the sample solution to be tested, first titrate with hydrochloric acid standard solution to the reaction endpoint A1, and record the volume of standard solution consumed V1; then continue titrating with sodium hydroxide standard solution to the reaction endpoint A2, and record the volume of standard solution consumed V2;

[0009] (3) Calculate the neutralization degree k of the sample solution to be tested: Calculate the endpoint ratio of the trisodium phosphate reaction according to the following formula;

[0010]

[0011] Where:

[0012] k——neutralization degree of trisodium phosphate neutralization solution;

[0013] C1——Concentration of hydrochloric acid standard solution, in moles per liter (mol / L);

[0014] C2——Concentration of sodium hydroxide standard solution, in moles per liter (mol / L);

[0015] V1——The volume of hydrochloric acid standard solution consumed when the test solution is titrated to the reaction endpoint A1, in milliliters (mL);

[0016] V2——The volume of sodium hydroxide standard solution consumed when the test solution is titrated to the reaction endpoint A2, in milliliters (mL);

[0017] (4) Determine the degree of neutralization reaction: If the k value is greater than 2.5, it indicates that unreacted NaOH exists in the sample solution to be tested; if the k value is less than 1.5, it indicates that Na2HPO4 exists in the sample solution to be tested; if 2.5 ≥ k ≥ 1.5, it indicates that the content of anhydrous trisodium phosphate is ≥ 97% and the total phosphorus content is greater than 42%.

[0018] The concentration of the hydrochloric acid standard solution is 0.1 mol / L to 0.5 mol / L.

[0019] The concentration of the sodium hydroxide standard is 0.1 mol / L to 0.5 mol / L.

[0020] The test sample solution is prepared by weighing 10g-15g of the test sample, placing it in a 250mL beaker, and adding 50ml-100ml of water to dissolve it. The test sample is a trisodium phosphate neutralization solution; further, the test sample comes from the trisodium phosphate neutralization process, that is, the neutralization reaction between phosphoric acid and caustic soda.

[0021] The reaction endpoint A1 is the first chemical reaction equivalence point at which hydrochloric acid reacts completely with phosphate and sodium hydroxide in equal amounts in the titration, and the endpoint is reflected on the V / E titration curve.

[0022] The reaction endpoint A2 is the first chemical reaction equivalence point in which hydrochloric acid reacts completely with phosphate and sodium hydroxide in equal amounts during titration, and the endpoint is reflected on the V / E titration curve.

[0023] The second object of the present invention is to provide: an application of a method for detecting the endpoint of a neutralization reaction in producing trisodium phosphate in the production quality control of trisodium phosphate products.

[0024] Preferably, the trisodium phosphate product quality control includes controlling the total phosphorus content, the main content of trisodium phosphate, the sodium hydroxide content and the content of disodium hydrogen phosphate.

[0025] More preferably, the quality control of the trisodium phosphate product refers to controlling the total phosphorus content, trisodium phosphate content, sodium hydroxide content and disodium hydrogen phosphate content in the anhydrous trisodium phosphate product by adjusting k.

[0026] Beneficial effects:

[0027] The detection method of the invention does not need to use an indicator, has low detection cost, is fast and accurate, and has a small error. The content of disodium hydrogen phosphate and sodium hydroxide in the trisodium phosphate neutralization solution is determined, and the error is reduced by using a ratio method, thereby improving the scientificity and accuracy of the neutralization reaction endpoint determination in the trisodium phosphate production process. The qualified condition refers to that the anhydrous trisodium phosphate content is ≥97%, and the total phosphorus content is greater than 42%.

[0028] The present invention does not require electrode calibration and temperature compensation, improves the accuracy of endpoint determination, and ensures that each equivalence point in equivalence point titration is consistent with the theoretical true value of the chemical theoretical reaction.

[0029] The detection method of the present invention indirectly determines the neutralization reaction endpoint of trisodium phosphate, reduces the back-end process cost caused by insufficient neutralization reaction, improves the product qualification rate, and effectively controls the content of trisodium phosphate. At the same time, the detection method of the present invention realizes the control of the quality of the anhydrous trisodium phosphate product by adjusting the k value, and specifically can adjust the total phosphorus content, trisodium phosphate content, sodium hydroxide content and disodium hydrogen phosphate content, thereby realizing the efficient and accurate production of anhydrous trisodium phosphate without changing the original production process, and improving the quality of trisodium phosphate products.

[0030] The detection method of the present invention can be applied and promoted on different trisodium phosphate production devices. DETAILED DESCRIPTION

[0031] The specific embodiments of the present invention are further described in detail below, but the present invention is not limited to these embodiments, and any improvement or substitution based on the basic spirit of the present embodiment still falls within the scope of protection required by the claims of the present invention.

[0032] Example 1

[0033] A method for detecting the endpoint of a neutralization reaction in producing trisodium phosphate comprises the following steps:

[0034] (1) Preparation: Using water as a solvent or diluent, prepare 0.1 mol / L hydrochloric acid standard solution, 0.1 mol / L sodium hydroxide standard solution and the sample solution to be tested, wherein the concentrations of the hydrochloric acid standard solution and the sodium hydroxide standard solution are denoted as C1 and C2, respectively;

[0035] (2) Potentiometric titration: Calibrate the automatic potentiometric titrator, place the measuring electrode in the sample solution to be tested, first titrate with hydrochloric acid standard solution to the reaction endpoint A1, and record the volume of standard solution consumed V1; then continue titrating with sodium hydroxide standard solution to the reaction endpoint A2, and record the volume of standard solution consumed V2;

[0036] (3) Calculate the neutralization degree k of the sample solution to be tested: Calculate the endpoint ratio of the trisodium phosphate reaction according to the following formula;

[0037]

[0038] Where:

[0039] k——neutralization degree of trisodium phosphate neutralization solution;

[0040] C1——Concentration of hydrochloric acid standard solution, in moles per liter (mol / L);

[0041] C2——Concentration of sodium hydroxide standard solution, in moles per liter (mol / L);

[0042] V1——The volume of hydrochloric acid standard solution consumed when the test solution is titrated to the reaction endpoint A1, in milliliters (mL);

[0043] V2——The volume of sodium hydroxide standard solution consumed when the test solution is titrated to the reaction endpoint A2, in milliliters (mL);

[0044] (4) Determine the degree of neutralization reaction: If the k value is greater than 2.5, it indicates that unreacted NaOH exists in the sample solution to be tested; if the k value is less than 1.5, it indicates that Na2HPO4 exists in the sample solution to be tested; if 2.5 ≥ k ≥ 1.5, it indicates that the content of anhydrous trisodium phosphate is ≥ 97% and the total phosphorus content is greater than 42%.

[0045] The sample solution to be tested is prepared by weighing 10 g of the sample to be tested, placing it in a 250 mL beaker, and adding 50 ml of water to dissolve it. The sample to be tested is a trisodium phosphate neutralization solution, that is, it comes from the trisodium phosphate neutralization section.

[0046] The reaction endpoint A1 is the first chemical reaction equivalence point at which hydrochloric acid reacts completely with phosphate and sodium hydroxide in equal amounts in the titration, and the endpoint is reflected on the V / E titration curve.

[0047] The reaction endpoint A2 is the first chemical reaction equivalence point in which hydrochloric acid reacts completely with phosphate and sodium hydroxide in equal amounts during titration, and the endpoint is reflected on the V / E titration curve.

[0048] Example 2

[0049] A method for detecting the endpoint of a neutralization reaction in producing trisodium phosphate comprises the following steps:

[0050] (1) Preparation: Using water as a solvent or diluent, prepare 0.3 mol / L hydrochloric acid standard solution, 0.3 mol / L sodium hydroxide standard solution and the sample solution to be tested, wherein the concentrations of the hydrochloric acid standard solution and the sodium hydroxide standard solution are denoted as C1 and C2, respectively;

[0051] (2) Potentiometric titration: Calibrate the automatic potentiometric titrator, place the measuring electrode in the sample solution to be tested, first titrate with hydrochloric acid standard solution to the reaction endpoint A1, and record the volume of standard solution consumed V1; then continue titrating with sodium hydroxide standard solution to the reaction endpoint A2, and record the volume of standard solution consumed V2;

[0052] (3) Calculate the neutralization degree k of the sample solution to be tested: Calculate the endpoint ratio of the trisodium phosphate reaction according to the following formula;

[0053]

[0054] Where:

[0055] k——neutralization degree of trisodium phosphate neutralization solution;

[0056] C1——Concentration of hydrochloric acid standard solution, in moles per liter (mol / L);

[0057] C2——Concentration of sodium hydroxide standard solution, in moles per liter (mol / L);

[0058] V1——The volume of hydrochloric acid standard solution consumed when the test solution is titrated to the reaction endpoint A1, in milliliters (mL);

[0059] V2——The volume of sodium hydroxide standard solution consumed when the test solution is titrated to the reaction endpoint A2, in milliliters (mL);

[0060] (4) Determine the degree of neutralization reaction: If the k value is greater than 2.5, it indicates that unreacted NaOH exists in the sample solution to be tested; if the k value is less than 1.5, it indicates that Na2HPO4 exists in the sample solution to be tested; if 2.5 ≥ k ≥ 1.5, it indicates that the content of anhydrous trisodium phosphate is ≥ 97% and the total phosphorus content is greater than 42%.

[0061] The sample solution to be tested is prepared by weighing 12g of the sample to be tested, placing it in a 250mL beaker, and adding 88ml of water to dissolve it. The sample to be tested is a trisodium phosphate neutralization solution, that is, it comes from the trisodium phosphate neutralization section.

[0062] The reaction endpoint A1 is the first chemical reaction equivalence point at which hydrochloric acid reacts completely with phosphate and sodium hydroxide in equal amounts in the titration, and the endpoint is reflected on the V / E titration curve.

[0063] The reaction endpoint A2 is the first chemical reaction equivalence point in which hydrochloric acid reacts completely with phosphate and sodium hydroxide in equal amounts during titration, and the endpoint is reflected on the V / E titration curve.

[0064] Example 3

[0065] A method for detecting the endpoint of a neutralization reaction in producing trisodium phosphate comprises the following steps:

[0066] (1) Preparation: Using water as a solvent or diluent, prepare 0.5 mol / L hydrochloric acid standard solution, 0.5 mol / L sodium hydroxide standard solution and the sample solution to be tested, wherein the concentrations of the hydrochloric acid standard solution and the sodium hydroxide standard solution are denoted as C1 and C2, respectively;

[0067] (2) Potentiometric titration: Calibrate the automatic potentiometric titrator, place the measuring electrode in the sample solution to be tested, first titrate with hydrochloric acid standard solution to the reaction endpoint A1, and record the volume of standard solution consumed V1; then continue titrating with sodium hydroxide standard solution to the reaction endpoint A2, and record the volume of standard solution consumed V2;

[0068] (3) Calculate the neutralization degree k of the sample solution to be tested: Calculate the endpoint ratio of the trisodium phosphate reaction according to the following formula;

[0069]

[0070] Where:

[0071] k——neutralization degree of trisodium phosphate neutralization solution;

[0072] C1——Concentration of hydrochloric acid standard solution, in moles per liter (mol / L);

[0073] C2——Concentration of sodium hydroxide standard solution, in moles per liter (mol / L);

[0074] V1——The volume of hydrochloric acid standard solution consumed when the test solution is titrated to the reaction endpoint A1, in milliliters (mL);

[0075] V2——The volume of sodium hydroxide standard solution consumed when the test solution is titrated to the reaction endpoint A2, in milliliters (mL);

[0076] (4) Determine the degree of neutralization reaction: If the k value is greater than 2.5, it indicates that unreacted NaOH exists in the sample solution to be tested; if the k value is less than 1.5, it indicates that Na2HPO4 exists in the sample solution to be tested; if 2.5 ≥ k ≥ 1.5, it indicates that the content of anhydrous trisodium phosphate is ≥ 97% and the total phosphorus content is greater than 42%.

[0077] The sample solution to be tested is prepared by weighing 15g of the sample to be tested, placing it in a 250mL beaker, and adding 100ml of water to dissolve it. The sample to be tested is a trisodium phosphate neutralization solution, that is, it comes from the trisodium phosphate neutralization section.

[0078] The reaction endpoint A1 is the first chemical reaction equivalence point at which hydrochloric acid reacts completely with phosphate and sodium hydroxide in equal amounts in the titration, and the endpoint is reflected on the V / E titration curve.

[0079] The reaction endpoint A2 is the first chemical reaction equivalence point in which hydrochloric acid reacts completely with phosphate and sodium hydroxide in equal amounts during titration, and the endpoint is reflected on the V / E titration curve.

[0080] Example 4

[0081] A method for detecting the end point of a neutralization reaction in producing trisodium phosphate is used in the production quality control of trisodium phosphate products, specifically:

[0082] Add 70mm high water into the neutralization tank, heat and stir, and control the temperature at 50-80℃; slowly add 1.0-1.5m 385% phosphoric acid and liquid caustic soda are reacted, and the addition is controlled completely according to the theoretical value during the feeding stage. Solid flake caustic soda is continued to be added to slowly adjust the k value to 1.5-2.5 and the degree of beauty to 37±1°Bé, wherein the k value is determined according to the method of Example 2. After the adjustment, stirring is continued for 30 minutes, and then the neutralized liquid is transported to the polymerization storage tank. The temperature of the neutralized liquid storage tank is controlled to 70°C-90°C. The pressure of the high-pressure pump is 8.0-10.5Mpa, the temperature of the drying tower is 90-120°C, and the polymerization process is a polymerization tail gas temperature of 360°C-390°C. The final product is tested, and the results are shown in Table 1:

[0083] Table 1

[0084] Case k value Trisodium phosphate content / % Total phosphorus / % Loss on ignition / % Case 1 1.5～2.5 97～100 41.8～45 0.04

[0085] Comparative case (PH value production method)

[0086] Add 70mm high water into the neutralization tank, heat and stir, and control the temperature at 50-80℃; slowly add 1.0-1.5m 3 85% phosphoric acid and liquid alkali react, and the addition is controlled completely according to the theoretical value during the feeding stage. Continue to add solid flake alkali to slowly adjust the pH value to 12.1-12.4 and the degree of beauty to 37±1°Bé. After the adjustment, continue stirring for 30 minutes, and then transport the neutralized liquid to the polymerization storage tank. Control the temperature of the neutralized liquid storage tank to 70℃~90℃. The pressure of the high-pressure pump is 8.0~10.5Mpa, the temperature of the drying tower is 90~120℃, and the polymerization process is the polymerization tail gas temperature of 360℃~390℃. The final product is tested, and the results are shown in Table 2:

[0087] Table 2

[0088] Case pH Trisodium phosphate content / % Total phosphorus / % Loss on ignition / % Comparative Example 1 12.1 89.5 46 0.04 Comparative Example 2 12.2 91.3 43 0.03 Comparative Example 3 12.3 95.7 42 0.01 Comparative Example 4 12.4 102 36 0.02

[0089] As can be seen from Table 1 and Table 2, the method of the present invention has the following advantages in controlling the quality of trisodium phosphate products compared with the pH value method: ① The detection method of the present invention can directly determine the content of sodium hydroxide in trisodium phosphate in the neutralization section of trisodium phosphate, which cannot be directly measured by the pH value method. ② The detection method of the present invention can directly determine the content of trisodium phosphate in trisodium phosphate in the neutralization section of trisodium phosphate, which cannot be directly measured by the pH value method. ③ The detection method of the present invention can directly determine the content of disodium hydrogen phosphate in trisodium phosphate in the neutralization section of trisodium phosphate, which cannot be directly measured by the pH value method. ④ The detection method of the present invention can exclude the influence of compound salts such as Na3PO4·12H2O·1 / 7NaOH, 4Na3PO4·12H2O·NaOH on the endpoint of trisodium phosphate, which cannot be excluded by the pH method. ⑤ The detection method of the present invention can realize the online detection of trisodium phosphate neutralization solution by making simple changes, and the pH method is difficult to realize the online detection of trisodium phosphate neutralization solution due to the material of the pH probe.

Claims

1. A method for detecting the end point of a neutralization reaction in producing trisodium phosphate, characterized in that: The steps include: (1) Preparation: Using water as a solvent or diluent, prepare a hydrochloric acid standard solution, a sodium hydroxide standard solution, and a sample solution to be tested, wherein the concentrations of the hydrochloric acid standard solution and the sodium hydroxide standard solution are denoted as C1 and C2, respectively; (2) Potentiometric titration: Calibrate the automatic potentiometric titrator, place the measuring electrode in the sample solution to be tested, first titrate with hydrochloric acid standard solution to the reaction endpoint A1, and record the volume of standard solution consumed V1; then continue titrating with sodium hydroxide standard solution to the reaction endpoint A2, and record the volume of standard solution consumed V2; (3) Calculating the neutralization degree k of the sample solution to be tested: Calculate the endpoint ratio of the trisodium phosphate reaction according to the formula k = (V1×C1) / (V2×C2), and obtain the neutralization degree k of the sample solution to be tested; (4) Determine the degree of neutralization reaction: If the k value is greater than 2.5, it indicates that unreacted NaOH exists in the sample solution to be tested; if the k value is less than 1.5, it indicates that Na2HPO4 exists in the sample solution to be tested; if 2.5 ≥ k ≥ 1.5, it indicates that the content of anhydrous trisodium phosphate is ≥ 97% and the total phosphorus content is greater than 42%.

2. A method for detecting the neutralization endpoint of producing trisodium phosphate according to claim 1, characterized in that: The concentration of the hydrochloric acid standard solution is 0.1 mol / L to 0.5 mol / L.

3. A method for detecting the neutralization endpoint of producing trisodium phosphate as claimed in claim 1, characterized in that, The concentration of the sodium hydroxide standard is 0.1 mol / L to 0.5 mol / L.

4. A method for detecting the neutralization reaction endpoint of producing trisodium phosphate as claimed in claim 1, characterized in that, The test sample solution is prepared by weighing 10 g to 15 g of the test sample, placing it in a 250 mL beaker, and adding water to dissolve it.

5. A method for detecting the neutralization reaction endpoint of producing trisodium phosphate as claimed in claim 1, characterized in that, The sample to be tested is trisodium phosphate neutralized solution.

6. A method for detecting the endpoint of a neutralization reaction for producing trisodium phosphate as claimed in claim 1, characterized in that: The reaction endpoint A1 is the first chemical reaction equivalence point at which hydrochloric acid reacts completely with phosphate and sodium hydroxide in equal amounts in the titration, and the endpoint is reflected on the V / E titration curve.

7. A method for detecting the end point of a neutralization reaction in producing trisodium phosphate according to claim 1, characterized in that: The reaction endpoint A2 is the first chemical reaction equivalence point at which hydrochloric acid reacts completely with phosphate and sodium hydroxide in equal amounts during titration, and the endpoint is reflected on the V / E titration curve.

8. Application of a method for detecting a neutralization reaction endpoint for producing trisodium phosphate as claimed in claim 1 in the production quality control of trisodium phosphate products.

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