Determining Halogens and Sulfur in LPG According to ASTM D7994

Determining Halogens and Sulfur in LPG According to ASTM D7994

The ASTM D7994 - 17 standard describes the determination of sulfur, chlorine and fluorine in liquefied petroleum gas (LPG) by oxidative pyrohydrolytic combustion followed by ion chromatography (IC).

In this study a synthetic butane sample is examined. Using the LPG Module, 50 µL of the sample is injected into the combustion system. The combustion products are then analyzed by ion chromatography, applying intelligent Partial Loop Injection Technique post Inline Matrix Elimination.

Results

Mean [mg/kg] RSD [%] n = 3
1 Fluorine 26.33 1.5
2 Chlorine 17.23 1.1
4 Bromine 37.83 1.2
6 Sulfur 13.08 0.5

Peak 3 and 5 are nitrite and nitrate, respectively. Both are not quantified.

Sample

Liquefied butane gas

Sample preparation

The sample is examined by Combustion IC as well as intelligent Partial Loop Injection Technique with Inline Matrix Elimination.

Columns

Metrosep A Supp 5 - 150/4.0 6.1006.520
Metrosep A Supp 5 Guard/4.0 6.1006.500
Metrosep A PCC 2 HC/4.0 6.1006.340

Solutions

. .
Eluent 3.2 mmol/L sodium carbonate 1.0 mmol/L sodium hydrogen carbonate
Suppressor regenerant 500 mmol/L sulfuric acid
Rinsing solution STREAM
Absorber solution 150 mg/L hydrogen peroxide

Parameters

Flow rate 0.7 mL/min
Injection volume (IC) 200 µL (MiPT)
Pmax 15 MPa
Recording time 20 min
Column temperature 30 °C

Combustion parameters

Argon 100 mL/min
Oxygen 300 mL/min
Oven temperature 1050 °C
Post-combustion time 120 s
Initial volume of absorption solution 2.0 mL
Water inlet 0.1 mL/min
Injection Volume (LPG) 50 µL

Analysis

Conductivity after sequential suppression

Instrumentation

. .
930 Compact IC Flex Oven/SeS/ Deg 2.930.2460
IC Conductivity Detector 2.850.9010
920 Absorber Module 2.920.0010
800 Dosino (suppression) 2.800.0010
MSM Rotor A 6.2832.000
Adapter sleeve for Suppressor Vario 6.2842.020
Combustion Oven 2.136.0750
LPG Module 2.136.0740

Determining Halogens and Sulfur in LPG According to ASTM D7994

System Graphic

Determining Halogens and Sulfur in LPG According to ASTM D7994

Liquid handling of absorber solution is carried out by the 10 mL-Dosino – that is, before combustion, the initial volume is set into the absorber vessel. During combustion, the absorber solution is dosed (0.2 mL/minute) to the T-piece placed at the end of the combustion tube in order to achieve instant absorption of combusted products (Post-combustion rinse).

The connection between the absorption vessel and after combustion is completed,  the combustion tube is washed with 1 mL (final rinse). Next, water inlet into the combustion tube for pyrohydrolytic environment is performed by the 5 mL-Dosino with a rate of 0.1 mL/minute. Since MagIC Net is capable of recording all the volumes added to the absorber solution during and after combustion in the most accurate way, no internal standard was required.

The transfer of standards and samples into the loop of the 920 Absorber Module is carried out by the 5 mL-Dosino using partial loop injection (MiPT); this provides complete flexibility to injection volumes in the range of 4 to 200 µL. In this analysis, a fixed volume of 200 µL was employed for all MiPT injection volumes. With regard to LPG analysis, the flame sensor is not used for combustion control.

As a result, the combustion time is controlled only by 1) the time needed to inject the sample by the LPG module and 2) the post-combustion time indicated in the instrument method.

A 1 µL sample loop is included in the LPG module and this can be filled and injected up to 50 times. Eventually, this configuration can inject a variable LPG sample volume ranging between 1 and 50 µL. It takes approximately 5 minutes to inject the sample (1µL × 50 loop-fills).

This information has been sourced, reviewed and adapted from materials provided by Metrohm AG.

For more information on this source, please visit Metrohm AG.

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