Determination of trace sulfur in light olefins by oxidation microcoulometric method (3)

6 Measurement procedure

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Table 1

Note: Depending on the instrument used, the operating conditions may vary greatly (see Appendix A), but the recovery rate must reach 75% to 95%

6.

Before each analysis of the sample, it is necessary to calibrate with an organic sulfur standard solution (4.

First use a 10uL micro syringe to draw about 8uL of organic sulfur standard solution, dry the needle, and then slowly pull the needle core until the meniscus at the junction of the liquid and air is aligned with the 1uL scale, and note the position of the needle core end The reading (V1)

The sulfur recovery rate F (%) is calculated according to formula (2):

In the formula: X—the sulfur content in the organic sulfur standard solution (4.

W—Sulfur content displayed by microcoulometer, ng;

V ₁ -V ₂ —The volume of the injected organic sulfur standard solution, uL

Each standard sample shall be determined at least five times, and the arithmetic mean of its recovery rate shall be taken as the correction factor

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Ethylene sampling shall be conducted in accordance with the provisions of Article 2.
2 of GB 7715
.

Propylene sampling shall be conducted in accordance with the provisions of Article 2.
2 of GB 7716
.

Sampling of C4 olefins shall be carried out in accordance with GB 6601
.

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3.
2 Vaporization of liquid samples

The liquid sample must be vaporized before the sulfur content can be determined
.
Connect the sampling cylinder as shown in Figure 2, open the lower valve, let the sample flow into the stainless steel heating coil, and control the constant temperature water bath at 60-80°C to ensure that the sample is completely vaporized
.
The gaseous sample is collected in the sample container 4 for measurement
.

Figure 2
1-Liquefied petroleum gas sampler (steel cylinder); 2- constant temperature water bath (60～80℃),
3- heating coil, 4- sample container: 5- gas washing bottle

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3 Sample size

According to the range of sulfur content to be measured in the sample, an appropriate amount of sample should be taken as shown in Table 2
.

Table 2

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4 Determination

Use a 5 mL medical syringe to draw a gaseous sample from the sample container
.

When sampling, replace the sample gas for 3 to 5 times before sampling, record the volume reading (V) and then inject the sample at a constant speed (2 to 3 mL/min), titrate and record the coulometer reading (ng)
.

Note: In order to avoid the contamination of the syringe with different concentrations of sulfur, the micro-injector and the syringe should be used for samples or standard solutions with large differences in concentration
.