Method for determining ammonium ion content in molecular sieve

Abstract

The invention relates to the technical field of molecular sieves, in particular to a method for measuring the content of ammonium ions in a molecular sieve, which comprises the following steps: (1) weighing a molecular sieve sample, and adding acid to adjust the pH value of the sample to be less than 2.0; (2) transferring the sample to a distillation flask, adding distilled water, and adjusting the pH value of the system to 6.0-7.4; (3) connecting a distillation flask with a nitrogen ball and a condensation pipe for heating and distilling, and collecting distillate; and (4) dropwise adding an indicator into the distillate, titrating with a hydrochloric acid standard solution to an end point, and calculating the ammonium ion content in the molecular sieve. The method provided by the invention can accurately and timely measure the ammonium content in the molecular sieve, instructs the catalyst production to timely and accurately control the addition amount, avoids the waste of raw materials, and is beneficial to environmental protection.

Description

Technical Field

[0001] The invention relates to the technical field of molecular sieves, and in particular to a method for determining the content of ammonium ions in a molecular sieve. Background Art

[0002] Molecular sieve is a synthetic hydrated aluminosilicate (zeolite) or natural zeolite with the function of screening molecules. Molecular sieve has the functions of screening molecules, adsorbing ion exchange and catalysis. It has high adsorption capacity, strong selectivity and high temperature resistance. Therefore, it is widely used in the fields of organic chemical industry and petrochemical industry. It is also an excellent adsorbent for coal gas dehydration. In terms of waste gas purification, molecular sieve is also increasingly valued.

[0003] During the industrial production of molecular sieves, a large amount of exchange liquid such as ammonium sulfate is added for exchange filtration and sodium removal. The purpose is to use ammonium ions to replace sodium ions in the molecular sieve, so that the sodium ions in the molecular sieve are reduced to less than 2% to ensure the activity of the molecular sieve. Therefore, the molecular sieve contains a large amount of ammonium ions. The molecular sieve containing a large amount of ammonium ions enters the microsphere device for further processing of catalytic cracking catalysts. In the catalyst production process, the content of ammonium ions must be known as accurately as possible to ensure the addition of a certain amount of rare earth solution and hydrochloric acid, etc., so as to ensure that ammonium ions are removed to the greatest extent and that excessive addition is not added to cause exhaust gas to exceed the standard and cause environmental accidents.

[0004] Among the existing methods for determining ammonium ions, the commonly used method is the determination of ammonia nitrogen content in water - distillation neutralization titration method. It does not involve the determination of ammonium ion content in special forms of liquid and solid phases produced in the molecular sieve production process, and cannot fully guarantee the timeliness of reporting the measurement results, which is not conducive to adjusting the process in the first time. Summary of the invention

[0005] In view of the technical problems in the prior art such as the untimely determination of ammonium ions, the present invention provides a method for determining the ammonium ion content in a molecular sieve, which can accurately and timely measure the ammonium content in the molecular sieve, guide the catalyst production to timely and accurately control the addition amount, avoid the waste of raw materials, and benefit environmental protection.

[0006] The present invention provides a method for determining the content of ammonium ions in a molecular sieve, comprising the following steps: (1) Weigh the molecular sieve sample and add acid to adjust the sample pH to less than 2.0; (2) Transfer the sample to a distillation flask and add distilled water to adjust the pH of the system to 6.0-7.4; (3) Connect the distillation flask to the nitrogen ball and condenser for heating and distillation, and collect the distillate; (4) Add an indicator to the distillate and titrate to the endpoint with a standard hydrochloric acid solution. Calculate the ammonium ion content in the molecular sieve using formula 1. Formula 1: ; ω(NH4 + ,%)─mass percentage of ammonium ions in molecular sieve, %; C HCl ─Concentration of hydrochloric acid standard solution, mol / L; V HCl ─Volume of hydrochloric acid standard solution consumed, mL; V0─The volume of hydrochloric acid standard solution consumed by the blank group, mL. There is no sample to be tested in the blank group, and only the same volume of distilled water is added to the distillation flask; 18─NH4 + Molecular weight, g / mol; m─ molecular sieve sample mass, g; d─density of molecular sieve, g / cm 3 ; Y─molecular sieve content, g / L.

[0007] Furthermore, the acid in step (1) is a sulfuric acid aqueous solution with a volume ratio of 1:1.

[0008] Furthermore, in step (1), after adding acid to adjust the pH of the sample, the sample is left to stand for 2 hours, in order to ensure that the acid is in full contact with the molecular sieve sample.

[0009] Furthermore, in step (2), the volume of distilled water added is 250 mL.

[0010] Furthermore, in step (2), bromothymol blue indicator is added dropwise to the system, and the pH of the system is adjusted to 6.0 (indicator is yellow) to 7.4 (indicator is blue) using sodium hydroxide or sulfuric acid solution.

[0011] Furthermore, in step (3), during heating and distillation, light magnesium oxide and glass beads are added into the distillation flask.

[0012] Furthermore, in step (3), the volume of the collected distillate is 200 mL.

[0013] Furthermore, in step (4), a methyl red-methylene blue mixed indicator is added dropwise to the distillate, and the solution is titrated with a standard hydrochloric acid solution until the distillate changes from green to lavender.

[0014] The measuring principle of the present invention is as follows: the present invention targets the ammonium ions contained in the molecular sieve, destroys the inherent structure by adding acid and blocks the ammonium ions to prevent overflow, fully releases the ammonium ions from the molecular sieve structure, collects ammonia gas by distillation, neutralizes and titrates with hydrochloric acid, and uses the titration to measure the ammonia nitrogen content to calculate the ammonium content in the molecular sieve, which can better guide the subsequent microsphere device to perform precise control.

[0015] The beneficial effects of the present invention are: (1) The present invention adds acid to adjust the pH of the molecular sieve to avoid overflow of ammonia generated by ammonium ions under alkaline conditions, which would result in a smaller result, thereby improving the accuracy of the determination.

[0016] (2) The present invention uses a method of weighing solids instead of the method of measuring the volume of liquid directly in the prior art, and can determine the ammonium ion content in a substance with a special form of liquid and solid phases.

[0017] (3) The determination method of the present invention saves time and ensures the timeliness of the results, which is convenient for the process to be adjusted in the first place, replacing the cumbersome process of calculating the ammonium content by the original subtraction method.

[0018] (4) The present invention ensures the accuracy of the results, and the actual measurement error is controlled within ±0.03%, thereby avoiding the problem that the theoretical dosage of ammonium radicals deviates from the actual dosage when calculating the ammonium radical content by the original subtraction method, and the filtrate is not representative. DETAILED DESCRIPTION

[0019] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0020] The method of the present invention is used to determine the ammonium ion content of a molecular sieve sample with an unknown content. Whether this method is applicable and whether the result is accurate requires preparing a molecular sieve sample containing a known and accurate ammonium ion content, and then performing the determination based on the method of the present invention to verify whether this determination method is consistent with the actual theoretical value.

[0021] Example 1 A semi-finished molecular sieve without ammonium ions was taken from the molecular sieve device, and it was known that the content of the semi-finished molecular sieve was 177.2 g / L; solid ammonium oxalate and ammonium sulfate solution were quantitatively added to exchange the molecular sieve sample to be tested with a dry basis weight of 50 g of the molecular sieve as a unit; it was calculated that the total mass of the added ammonium ions was 3.858 g, and the mass of the ammonium ions lost with the filtrate after the exchange was 2.320 g, so the ammonium ion content (theoretical value) in the molecular sieve sample to be tested was 2.98%.

[0022] Accurately weigh the molecular sieve sample to be tested (its density is 1.294 g / cm 3, content is 458g / L) 4.2840g into a glass beaker, add 1:1 sulfuric acid while stirring, and measure the pH in real time. After adjusting the pH to 1.8, let it stand for 2 hours. The treated sample is completely transferred to a distillation flask, and distilled water is added to the distillation flask to 250mL. Two drops of bromothymol blue indicator are added, and the pH is adjusted to 7.0 with sodium hydroxide solution. 0.25g of light magnesium oxide and several glass beads are added. Immediately connect the nitrogen ball and condenser to start heating distillation. The distillate rate is 10mL / min. When the distillate reaches 200mL, stop distillation. Transfer all the distillate to a conical flask, add 2 drops of methyl red-methylene blue mixed indicator, and titrate with 0.1000mol / L hydrochloric acid standard solution until the distillate changes from green to lavender as the end point, consuming 24.85mL of hydrochloric acid standard solution, and use 250mL of distilled water to replace the molecular sieve sample to be tested for a blank experiment, and the blank experiment consumes 0.00mL of hydrochloric acid standard solution. Substitute into formula 1 for calculation, and the ammonium ion content in the molecular sieve sample to be tested is 2.95%. The determination error between the measured value of 2.95% and the theoretical value of 2.98% is -0.03%.

[0023] Example 2 A semi-finished molecular sieve without ammonium ions is taken from the molecular sieve device, and it is known that the content of the semi-finished molecular sieve is 200.8g / L; solid ammonium oxalate and ammonium sulfate solution are quantitatively added to exchange with 50g of the dry basis of the molecular sieve to obtain the molecular sieve sample to be tested; it is calculated that the total mass of the added ammonium ions is 3.858g, and the mass of the ammonium ions lost with the filtrate after the exchange is 2.338g, so the ammonium ion content (theoretical value) in the molecular sieve sample to be tested is 2.95%.

[0024] Accurately weigh the molecular sieve sample to be tested (its density is 1.296 g / cm 3, content is 466g / L) 4.1891g into a glass beaker, add 1:1 sulfuric acid while stirring, and measure the pH in real time. After adjusting the pH to 1.7, let it stand for 2 hours. Transfer the treated sample completely to a distillation flask, continue to add distilled water to the distillation flask to 250mL, add 2 drops of bromothymol blue indicator, adjust the pH to 7.2 with sodium hydroxide solution, add 0.25g of light magnesium oxide and several glass beads, immediately connect the nitrogen ball and condenser to start heating distillation, the distillate rate is 10mL / min, and stop distillation when the distillate reaches 200mL. Transfer all the distillate to a conical flask, add 2 drops of methyl red-methylene blue mixed indicator, and titrate with 0.1000mol / L hydrochloric acid standard solution until the distillate changes from green to lavender as the end point, consuming 24.77mL of hydrochloric acid standard solution, and use 250mL of distilled water to replace the molecular sieve sample to be tested for a blank experiment, and the blank experiment consumes 0.00mL of hydrochloric acid standard solution. The analysis shows that the ammonium ion content in the molecular sieve sample to be tested is 2.96%. The determination error between the measured value of 2.96% and the theoretical value of 2.95% is 0.01%.

[0025] Although the present invention has been described in detail by way of preferred embodiments, the present invention is not limited thereto. Without departing from the spirit and essence of the present invention, a person of ordinary skill in the art may make various equivalent modifications or substitutions to the embodiments of the present invention, and such modifications or substitutions shall be within the scope of the present invention. Any person of ordinary skill in the art may easily conceive of changes or substitutions within the technical scope disclosed by the present invention, and such changes or substitutions shall be within the scope of protection of the present invention.

Claims

1. A method for determining the content of ammonium ions in a molecular sieve, characterized in that: The steps include: (1) Weigh the molecular sieve sample and add acid to adjust the sample pH to less than 2.0; (2) Transfer the sample to a distillation flask and add distilled water to adjust the pH of the system to 6.0-7.4; (3) Connect the distillation flask to the nitrogen ball and condenser for heating and distillation, and collect the distillate; (4) Add an indicator to the distillate and titrate to the endpoint with a standard hydrochloric acid solution. Calculate the ammonium ion content in the molecular sieve using formula 1. Formula 1: ; ω(NH4 + ,%)─mass percentage of ammonium ions in molecular sieve, %; C HCl ─Concentration of hydrochloric acid standard solution, mol / L; V HCl ─Volume of hydrochloric acid standard solution consumed, mL; V0─volume of hydrochloric acid standard solution consumed by the blank group, mL; 18─NH4 + Molecular weight, g / mol; m─ molecular sieve sample mass, g; d─density of molecular sieve, g / cm 3 ; Y─molecular sieve content, g / L.

2. The method for determining the ammonium ion content in a molecular sieve according to claim 1, wherein: The acid in step (1) is a sulfuric acid aqueous solution with a volume ratio of 1:

1.

3. The method for determining the ammonium ion content in a molecular sieve according to claim 1, characterized in that: In step (1), after adding acid to adjust the pH of the sample, the sample was allowed to stand for 2 hours.

4. The method for determining the ammonium ion content in a molecular sieve according to claim 1, wherein: In step (2), the volume of distilled water added is 250 mL.

5. The method for determining the ammonium ion content in a molecular sieve according to claim 1, characterized in that: In step (2), bromothymol blue indicator is added dropwise to the system, and the pH of the system is adjusted to 6.0-7.4 using sodium hydroxide or sulfuric acid solution.

6. The method for determining the ammonium ion content in a molecular sieve according to claim 1, characterized in that: In step (3), during heating and distillation, light magnesium oxide and glass beads are added into the distillation flask.

7. The method for determining the ammonium ion content in a molecular sieve according to claim 1, characterized in that: In step (3), the volume of the collected distillate is 200 mL.

8. The method for determining the ammonium ion content in a molecular sieve according to claim 1, characterized in that: In step (4), a methyl red-methylene blue mixed indicator is added dropwise to the distillate, and the solution is titrated with a standard hydrochloric acid solution until the distillate changes from green to lavender.

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