CN113358812A - Quantitative analysis method for isocyanic acid radical in melamine tail gas - Google Patents
Quantitative analysis method for isocyanic acid radical in melamine tail gas Download PDFInfo
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Abstract
The invention relates to analysis of melamine tail gas, in particular to a quantitative analysis method of isocyanic acid radical in melamine tail gas. Including S1, sampling; s2, liquid transferring; s3, accurately transferring 50.0ml of a sample to be detected into an iodometric vial, adding 20ml of analytically pure formaldehyde solution, dripping a plurality of drops of phenolphthalein indicator, and neutralizing with 1.0mol/L NaOH standard solution until the solution is light red; s4, placing an iodine measuring flask on an electric furnace, and heating to boil for 1 minute; s5, cooling to room temperature after covering a stopper, adding 5mL of di-n-butylamine toluene solution into an iodometry bottle by using a pipette when negative pressure cannot be formed in the bottle, and leaching the wall of the iodometry bottle by using 10mL of toluene; s6, adding 50ml of acetone into the mixture by using a measuring cylinder, and standing the mixture for reaction for 15min at room temperature; s7, titrating the excessive di-n-butylamine by a potentiometric titration method or a chromogenic titration method; and S8, calculating the content of the isocyanate according to the titration result in the S7. The invention provides a novel method for quantitatively analyzing the isocyanic acid radical through design, and the method is simple to operate, accurate in result and significant in popularization.
Description
Technical Field
The invention relates to analysis of melamine tail gas, in particular to a quantitative analysis method of isocyanic acid radical in melamine tail gas.
Background
The melamine tail gas contains a large amount of ammonia, and the ammonia preferentially reacts with hydrochloric acid to generate ammonium chloride in the process of titrating the isocyanic acid and the esters thereof, so the ammonia and the salts thereof must be removed in advance when the isocyanic acid and the esters thereof are titrated, but the prior art does not have an effective scheme for solving the technical problems.
Disclosure of Invention
In order to solve the problems in the background art, the invention provides a quantitative analysis method of isocyanic acid radical in melamine tail gas, and the quantitative analysis of the isocyanic acid radical in the melamine tail gas is more accurate by providing a new quantitative analysis method, and the technical scheme adopted by the invention is as follows:
a quantitative analysis method of isocyanate in melamine tail gas comprises the following steps:
s1, sampling, namely collecting melamine tail gas by using an aluminum foil sampling bag, wherein the aluminum foil sampling bag is filled with distilled water, and the melamine tail gas is sampled and dissolved in the distilled water;
s2, transferring liquid, namely transferring the solution in the aluminum foil sampling bag into a 500ml volumetric flask;
s3, accurately transferring 50ml of a sample to be detected into an iodometry bottle, adding 20ml of analytically pure formaldehyde solution, dripping a plurality of drops of phenolphthalein indicator, and neutralizing the solution with 1mol/L NaOH standard solution until the solution is light red;
s4, placing an iodine measuring flask on an electric furnace, and heating to boil for 1 minute;
s5, cooling to room temperature after covering a stopper, adding 5mL of di-n-butylamine toluene solution into an iodometry bottle by using a pipette when negative pressure cannot be formed in the bottle, and leaching the wall of the iodometry bottle by using 10mL of toluene;
s6, adding 50ml of acetone into the mixture by using a measuring cylinder, and standing the mixture for reaction for 15min at room temperature;
s7, titrating the excessive di-n-butylamine by a potentiometric titration method or a chromogenic titration method;
and S8, calculating the content of the isocyanate according to the titration result in the S7.
Further, the specific step of S1 is:
the method comprises the steps of using an aluminum foil sampling bag filled with about 300ml of distilled water and provided with a spring clamp, discharging air in the aluminum foil sampling bag, clamping by the spring clamp, wiping and weighing, marking as m1, then opening a field sampling valve to discharge for a moment, connecting a sampling leather tube on the sampling bag with the sampling valve, shaking while sampling, closing the sampling valve after the sampling bag expands, shaking the sampling bag to dissolve gas in a violent manner, taking down the sampling bag after the sampling bag is warm, clamping by the spring clamp, weighing after wiping, marking as m2, and obtaining the mass difference between the front and the back as the sample mass.
Further, in the step S1, the weighing precision is accurate to 0.01 g.
Further, the specific step of S2 is:
transferring the solution in the aluminum foil sampling bag into a 500ml volumetric flask, washing the sampling bag with distilled water for 3 times, adding the washing solution into the volumetric flask, diluting the solution to a scale with distilled water, and shaking up for later use.
Further, in S7, the potentiometric titration method specifically includes: pouring the sample in the iodometry bottle into a beaker, washing the iodometry bottle by using 25ml of acetone, placing the beaker on a magnetic stirrer, placing the beaker on a middle rotor for stirring, carrying out potentiometric titration by using a 1.0mol/L hydrochloric acid standard solution until a jump occurs, and carrying out potentiometric titration by using the hydrochloric acid standard titration solution until the end point.
Further, in S7, the color-developing titration method specifically includes: and (3) placing the iodometric flask on a magnetic stirrer for stirring, adding 0.5ml of bromocresol green indicator solution by using a single-line pipette, titrating by using a hydrochloric acid standard titration solution until the blue turns yellow, and keeping the time for 15s unchanged to obtain a titration end point.
Further, the solution developed a blue color at the start of titration, a blue-green color at the middle and a yellow color at the end.
Compared with the prior art, the invention has the beneficial effects that:
the invention provides a novel method for quantitatively analyzing the isocyanic acid radical by design, in the actual operation, the methenamine with stronger stability is generated by the reaction of formaldehyde, ammonia and salt substances thereof, and the method has the advantages of simple operation, accurate result and very obvious popularization and application significance.
Detailed Description
The technical solutions in the embodiments of the present invention are clearly and completely described below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The invention provides a quantitative analysis method of isocyanate in melamine tail gas, which comprises the following steps:
s1, sampling, namely collecting melamine tail gas by using an aluminum foil sampling bag, wherein the aluminum foil sampling bag is filled with distilled water;
s2, transferring liquid, namely transferring the solution in the aluminum foil sampling bag into a 500ml volumetric flask;
s3, accurately transferring 50.0ml of a sample to be detected into an iodometric vial, adding 20ml of analytically pure formaldehyde solution, dripping a plurality of drops of phenolphthalein indicator, and neutralizing with 1.0mol/L NaOH standard solution until the solution is light red;
s4, placing an iodine measuring flask on an electric furnace, and heating to boil for 1 minute;
s5, cooling to room temperature after covering a stopper, adding 5mL of di-n-butylamine toluene solution into an iodometry bottle by using a pipette when negative pressure cannot be formed in the bottle, and leaching the wall of the iodometry bottle by using 10mL of toluene;
s6, adding 50ml of acetone into the mixture by using a measuring cylinder, and standing the mixture for reaction for 15min at room temperature;
s7, titrating the excessive di-n-butylamine by a potentiometric titration method or a chromogenic titration method;
and S8, calculating the content of the isocyanate according to the titration result in the S7.
Further, the specific step of S1 is:
the method comprises the steps of using an aluminum foil sampling bag filled with about 300ml of distilled water and provided with a spring clamp, discharging air in the aluminum foil sampling bag, clamping by the spring clamp, wiping and weighing, marking as m1, opening a field sampling valve to discharge for a moment, connecting a sampling leather tube on the sampling bag with the sampling valve, shaking while sampling, closing the sampling valve after the sampling bag expands, shaking the sampling bag to dissolve gas in a violent mode, taking down the sampling bag after the sampling bag is warm, wherein the sample has the mass of about 50-80 g, clamping by the spring clamp, weighing after wiping, marking as m2, and obtaining the mass difference between the front and the rear as the sample mass. The weighing precision in the S1 is accurate to 0.01 g.
Further, the specific step of S2 is:
transferring the solution in the aluminum foil sampling bag into a 500ml volumetric flask, washing the sampling bag with distilled water for 3 times, adding the washing solution into the volumetric flask, diluting the solution to a scale with distilled water, and shaking up for later use.
Further, in S7, the potentiometric titration method specifically includes: pouring the sample in the iodometry bottle into a beaker, washing the iodometry bottle by using 25ml of acetone, placing the beaker on a magnetic stirrer, placing the beaker on a middle rotor for stirring, carrying out potentiometric titration by using a 1.0mol/L hydrochloric acid standard solution until a jump occurs, and carrying out potentiometric titration by using the hydrochloric acid standard titration solution until the end point.
Further, in S7, the color-developing titration method specifically includes: and (3) placing the iodometric flask on a magnetic stirrer for stirring, adding 0.5ml of bromocresol green indicator solution by using a single-line pipette, titrating by using a hydrochloric acid standard titration solution until the blue turns yellow, and keeping the time for 15s unchanged to obtain a titration end point.
Further, the solution developed a blue color at the start of titration, a blue-green color at the middle and a yellow color at the end. The color change was determined by titrating the solution quickly with acid to a few tenths of a milliliter to the end point when the first flash of yellow color was observed.
The invention relates to the following principle:
the melamine tail gas contains a large amount of ammonia, and the ammonia preferentially reacts with hydrochloric acid to generate ammonium chloride in the process of titrating the isocyanic acid and the esters thereof, so the ammonia and the salts thereof must be removed in advance when the isocyanic acid and the esters thereof are titrated. In actual operation, the urotropine with stronger stability is generated by the reaction of formaldehyde, ammonia and salt substances thereof. The reaction principle is as follows:
4NH4 ++6HCHO＝＝＝＝(CH2)6N4H++3H++6H2O
formation of protonated hexamethylenetetramine acid (CH)2)6N4H+(Ka ═ 7.1X 10-6) and free H+All can be neutralized by NaOH standard solution. The end product is (CH2)6N4, the aqueous solution is slightly alkaline, and phenolphthalein can be used as an indicator during neutralization.
Removing ammonia and salt thereof from the melamine tail gas aqueous solution, quantitatively reacting isocyanic acid and ester thereof with di-n-butylamine in toluene to generate corresponding substituted urea, adding cosolvent acetone, carrying out potential or color-developing back titration on the excessive di-n-butylamine by using a hydrochloric acid standard solution, and then calculating the mass fraction of the isocyanic acid and ester groups thereof. The reaction principle is as follows:
isocyanic acid and its ester group and di-n-butylamine (C)8H19N) reaction to form urea:
(C4H9)2NH+R—NCO→R—NHCON(C4H9)2
reacting excessive di-n-butylamine with a hydrochloric acid standard solution:
(C4H9)2NH+HCl→(C4H9)2NH·HCl
the reagent adopted by the invention is as follows:
1. the reagent and water used in the method should be analytically pure reagent and water conforming to GB/T6682 grade III.
2. Toluene (GB 684): dehydrating and drying by a 4A molecular sieve.
3. HCL standard solution: and C is 1 mol/L.
4. NaOH standard solution: and C is 1.0 mol/L.
5. Formaldehyde solution (40%).
6. di-N-butylamine toluene solution C (N4H9NHN4H9) 0.1 mol/L: 12.9g of di-n-butylamine were weighed into a 1000mL volumetric flask, dissolved in toluene dehydrated over 4A molecular sieves and diluted to the mark.
7. 2g/L phenolphthalein indicator: 200mg of phenolphthalein are dissolved in 100mL of ethanol solution with volume fraction of 60%
8. 0.1% bromocresol green indicator: 0.1g of bromocresol green was dissolved in 100m1 volume fraction 20% ethanol.
The apparatus used in the present invention comprises:
1. potentiometric titrators or PH meters: the precision is not lower than 0.1mV, and a glass electrode or a calomel electrode and a 20ml burette with a plug are arranged.
2. Single line pipette: 1ml and 25 ml.
3. Magnetic stirrer (with heating).
4. Iodine amount bottle: 500ml with a ground plug.
5. Other conventional instruments.
The invention discloses a result calculating and representing method
The percentage of isocyanate (NCO) is calculated according to the following formula:
in the formula: v1The dosage of the hydrochloric acid standard solution is mL when the blank is dripped;
V2the dosage of the hydrochloric acid standard solution is mL when the sample is dripped;
c is the concentration of the hydrochloric acid standard solution, mol/L;
42.02-constant, -value for the molar mass of NCO, g/mol;
m1-mass of the sampling bag before sampling, g;
M2-mass of the sampled bag, g;
1000-factor from grams to milligrams.
The precision of the invention is as follows:
reproducibility (same analyst): the relative error of the parallel sample obtained by the same analyst using the same equipment is less than 0.4% (95% confidence) by using the chromogenic titration method; the relative error should be less than 0.2% (95% confidence) using potentiometric titration.
Reproducibility (between laboratories): the relative error of the difference between the mean results of parallel samples of the same substance from different laboratories should be less than 0.8% (95% confidence).
Although only the preferred embodiments of the present invention have been described in detail, the present invention is not limited to the above embodiments, and various changes can be made without departing from the spirit of the present invention within the knowledge of those skilled in the art, and all changes are encompassed in the scope of the present invention.
Claims (7)
1. A quantitative analysis method for isocyanate in melamine tail gas is characterized by comprising the following steps:
s1, sampling, namely collecting melamine tail gas by using an aluminum foil sampling bag, wherein the aluminum foil sampling bag is filled with distilled water, and the melamine tail gas is sampled and dissolved in the distilled water;
s2, transferring liquid, namely transferring the solution in the aluminum foil sampling bag into a 500ml volumetric flask;
s3, accurately transferring 50ml of a sample to be detected into an iodometry bottle, adding 20ml of analytically pure formaldehyde solution, dripping a plurality of drops of phenolphthalein indicator, and neutralizing the solution with 1mol/L NaOH standard solution until the solution is light red;
s4, placing an iodine measuring flask on an electric furnace, and heating to boil for 1 minute;
s5, cooling to room temperature after covering a stopper, adding 5mL of di-n-butylamine toluene solution into an iodometry bottle by using a pipette when negative pressure cannot be formed in the bottle, and leaching the wall of the iodometry bottle by using 10mL of toluene;
s6, adding 50ml of acetone into the mixture by using a measuring cylinder, and standing the mixture for reaction for 15min at room temperature;
s7, titrating the excessive di-n-butylamine by a potentiometric titration method or a chromogenic titration method;
and S8, calculating the content of the isocyanate according to the titration result in the S7.
2. The method for quantitatively analyzing isocyanate in melamine tail gas according to claim 1, wherein the step S1 comprises the following steps:
steaming with about 300mlThe aluminum foil sampling bag with distilled water and spring clamp is characterized by that firstly, the air in the aluminum foil sampling bag is discharged, then the aluminum foil sampling bag is tightly clamped by spring clamp, dried and weighed, and its mark is m1Opening the on-site sampling valve for discharging for a moment, connecting the sampling leather tube on the sampling bag with the sampling valve, sampling while shaking, closing the sampling valve if the sampling bag is expanded, shaking the sampling bag to dissolve the gas, taking down the sampling bag after the sampling bag is warm, clamping by a spring clamp, weighing after wiping, and recording as m2And the mass difference between the front mass and the rear mass is the sample mass.
3. The method for quantitatively analyzing isocyanate in melamine tail gas according to claim 1, wherein the weighing precision in S1 is up to 0.01 g.
4. The method for quantitatively analyzing isocyanate in melamine tail gas according to claim 1, wherein the step S2 comprises the following steps:
transferring the solution in the aluminum foil sampling bag into a 500ml volumetric flask, washing the sampling bag with distilled water for 3 times, adding the washing solution into the volumetric flask, diluting the solution to a scale with distilled water, and shaking up for later use.
5. The method for quantitatively analyzing isocyanate in melamine tail gas according to claim 1, wherein in S7, the potentiometric titration method comprises the following specific steps: pouring the sample in the iodometry bottle into a beaker, washing the iodometry bottle by using 25ml of acetone, placing the beaker on a magnetic stirrer, placing the beaker on a middle rotor for stirring, carrying out potentiometric titration by using a 1.0mol/L hydrochloric acid standard solution until a jump occurs, and carrying out potentiometric titration by using the hydrochloric acid standard titration solution until the end point.
6. The method for quantitatively analyzing isocyanate in melamine off-gas according to claim 1, wherein in S7, the chromogenic titration method comprises the following specific steps: and (3) placing the iodometric flask on a magnetic stirrer for stirring, adding 0.5ml of bromocresol green indicator solution by using a single-line pipette, titrating by using a hydrochloric acid standard titration solution until the blue turns yellow, and keeping the time for 15s unchanged to obtain a titration end point.
7. The method for quantitatively analyzing isocyanate groups in melamine tail gas according to claim 6, wherein: the solution developed a blue color at the beginning of titration, a blue-green color in the middle and a yellow color at the end.
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN114778761A (en) * | 2022-04-20 | 2022-07-22 | 西安近代化学研究所 | QPQ process radical cyanate content determination device and method |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN114778761A (en) * | 2022-04-20 | 2022-07-22 | 西安近代化学研究所 | QPQ process radical cyanate content determination device and method |
| CN114778761B (en) * | 2022-04-20 | 2023-09-08 | 西安近代化学研究所 | QPQ process base salt cyanate radical content determination device and method |
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Application publication date: 20210907 |