SU1396014A1 - Method of analyzing methyl mercaptane in the air - Google Patents

Abstract

The invention relates to analytical chemistry, in particular determination. methyl mercaptan in the air of the working area of coke-chemical, oil refining and pulp and paper production. An air sample is passed into the 5M NaOH absorption solution, followed by its subsequent treatment with tetrart-acetate-fluorescein solutions, 5M CHDSAN solution to pH 3.5-5 and 5M NaOH solution to pH 12-13. The analysis is carried out by measuring the intensity of luminescence. This method allows the determination of the concentration of methyl mercaptan to be 0.037 mg / m, which is not known in the known case. 3 dw., 2 tabl. i cl

Description

00 with

ABOUT)

The invention relates to analytical chemistry and can be used for the analysis of sulfur-containing compounds in the atmospheric air and the air of the working area of coke-chemical, non-refining, pulp and paper and a number of other enterprises.

The aim of the invention is to increase the detection sensitivity.

FIG. depicted; a graph of luminescence intensity versus methyl mercaptan concentration at pH 32-13 and pH 3.5-5; Fig. 2 is a graph of the dependence of the luminescence intensity on the pH of the solutionJ in Fig. 3 - Graduation plots of the intensity of the luminescence at various pK values

The method is carried out in the following way.

A sample of the analyzed gas of 10–20 l is aspirated at a rate of 0.4 l / min after three Richter absorbers filled with an aqueous 5 M solution of sodium hydroxide in 0 ml each. During sampling, scavengers are cooled to. The contents of the three absorbers are discharged together, the volume is measured and analyzed according to the method: in triplicate flasks with a capacity of 50 ml; 2.0 MP of alkaline absorption solution were added, 3.0 5 M sodium hydroxide solution, 5.0 TPAF solution with concentration of 8 mg / l, 18 ml of 5 M solution of acetic acid with concentration up to pH 3.5- five. Let stand for 2-3 minutes, and then add 10 MIL of 5M sodium hydroxide solution (flasks are necessarily closed with stoppers after the introduction of each reagent and thoroughly mixed). The contents of the flasks are cooled to room temperature and brought to the mark with distilled water. At the same time, a blank experiment is prepared: 5 ml of sodium hydroxide, 5 ml of TRAF solution with a concentration of 8 mg / l, 18 MP of 5m acetic acid solution, 10 ml of 5M sodium hydroxide solution.

Luminescent measurements are performed on a G1MF-72 M instrument. According to the idle experience, the instrument's scale is set to 90 units. Scales are set on distilled water in cuvettes 2 cm thick. Then the residual luminescence of TPAF is measured in working solutions and on a graduation scale. found the content of methyl mercaptan in 1 liter of the working solution. The concentrate

The methyl mercaptan radio in the analyzed gas is calculated by the formula:

...

e

P

P

five

am V / them /. mg / m3,

0

five

V-20

where is the amount of methyl mercaptan in 50 ml of the working solution, calculated from the calibration curve data, mg;

in d, dd is the total volume of the absorption solution, ml; mm volume of absorption solution, taken for analysis, ml;

V is the volume of the selected day of gas analysis, reduced to NU.

The calibration curve for the determination of methyl mercaptan by the luminescence method is as follows. In six volumetric flasks with a capacity of 50 ml, (0.5-5.0) ml of a standardized solution of methyl mercaptan, 5M sodium hydroxide solution, 5 ml of the working solution TRAPH with a concentration of 8 mg / l, 18 ml of 5M acetic acid solution (to pH 3, 5-5). Let stand for 2-3 minutes, then neutralize the solution with 0 ml of 5M sodium hydroxide solution, cool the solutions to room temperature (in cold water) and bring to the mark with distilled water. At the same time, a blank solution containing no standardized methyl mercaptan solution is conducted through all the operations. The calibration curve is plotted in the following coordinates: the instrument scale (I) shows the concentration of methyl mercaptan.

In the implementation of the method, the property of a sharp increase in quenching is detected, the daminescence of TRAF determined by methyl mercaptan, which has not appeared in the known methods and is unknown from other sources.

The essence of the proposed method is that at pH 3.5-5 the reaction between methyl mercaptan and tetramercury acetate fluorescein (TRAF) probably goes better than in an alkaline medium. The quenching of the luminescence and reagent with the same additions of met1 | amercaptan increases, as can be seen from a comparison of the curves shown in Fig. 1. Curve 1 reflects the quenching of the luminescence of TRAF with methyl mercaptan at pH 12-13, curve 2 at pH 3.5-5. Curve 2 is used as graduation. Table 1

0,645 0,675 0,705 0,690 0,660 0,050 0,055 0,060 0,063 0,057 0,040 0,045 0,050 0,037 0,050

S 2,372-lO S 1,57% 4,36%

Is determined by

S 0.462-10S f 3.88% He is determined by 10.78%

S 0,462-10

S 4.65% He is determined: 12.91%

Is determined by

table 2

± 2.72

313

good graph for determining methyl mercaptan. The pH range of 3.5-5 is selected on the basis of experimental data; upon acidification to pH 3.5, followed by alkalinization to pH 1213, the luminescence of TRAF is reversible depending on the pH of the solution. Acidification to pH 5 does not produce the desired result. The pH range of 3.5-5 is the optimum for achieving the goal,

Example. According to the presented methodology, the air of the working area of several pulp and paper workshops was analyzed. The results are presented in table 1. The pH of the medium after the addition of 3 t of hydrochloric acid is 4.2, after addition of sodium pdroxide, pH 12.5 (Fig. 2).

When going beyond the pH value of 5.5; 11 |

14, a decrease in the sensitivity of the method is observed by reducing the intensity of the intrinsic luminescence of the reagent C (pH 11, 14 (see FIG. 2) and reducing the angle of inclination of the calibration curve at pH 5.5 (see FIG. 3).

Preparation of TRAF Solution 80 g of TRAF is dissolved in 50 cm 2M potassium hydroxide solution. The resulting solution was quantitatively transferred to a 1000 cm volumetric flask and made up to the mark with distilled water. The resulting concentrated solution of TRAF is stable for a long time when stored in the dark. Working solutions of TRAF with a concentration of 8 mg / dm are prepared for daily use.

Table 1

The results of the determination of methyl mercaptan in the air of the working area.

0

five

01

0

five

0

five

 i.

but diluted the original solution in mer-.

Noah flask with distilled water 10 times.

Table 2 shows the comparative metrological characteristics of the known and proposed methods.

In comparison with the known, the proposed method has a higher sensitivity (sensitivity increased from 0.5 to 0.05) μg in the analyzed volume.

The method error varies from 8.75% to 13.84% depending on the range of varying concentrations, i.e. The proposed method is sufficiently accurate for the determination of trace amounts of methyl mercaptan in gases.

Claims (1)

Invention Formula t The method of determining methyl mercaptan in air by aspirating the sample being analyzed through the absorption solution, treating the absorption mixture with chemical reagents with a subsequent analysis of the resulting solution, characterized in that, in order to determine the sensitivity of the solution, a 5M sodium hydroxide solution is used to determine the sensitivity. The treatment is carried out sequentially with tetragfluoride acetate fluorescein solutions, 5N acetic acid solution to pH 3.5-5 and then 5M sodium hydroxide solution to pH 12-13 and The analysis is carried out by measuring the luminescence intensity. roV at f2 G6 Fie.1 20 /" C / M Mr / 3f i -fff tft PH /, 8 12 16 20 21, .5 Fig.ZSmmMG / dm