Determination of Halogen and Sulfur Contents in LPG

The ASTM D7994 – 17 standard describes the determination of sulfur and halogens such as chlorine and fluorine in liquefied petroleum gas (LPG) by oxidative pyrohydrolytic combustion and subsequent ion chromatography.

This work involves the analysis of a synthetic butane sample. An LPG module is used to inject 50 μL of the synthetic butane sample into the combustion system. The analysis of the combustion products is performed using IC applying intelligent Partial Loop Injection Technique followed by Inline Matrix Elimination.

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Sample

Liquefied butane gas

Sample preparation

The sample is analyzed by Combustion IC and 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/minutes

Injection volume (IC)

200 μL (MiPT)

Pmax

15 Mpa

Recording time

20 minutes

Column temperature

30 °C

Combustion parameters

Argon

100 mL/minutes

Oxygen

300 mL/minutes

Oven temperature

1050 °C

Post-combustion time

20 s

Initial volume of absorption solution

2.0 mL

Water inlet

0.1 mL/minutes

Injection Volume (LPG)

50 μL

Analysis

Conductivity after the sequential suppression

Instrumentation

930 Compact IC Flex Oven/SeS/ Deg

2.930.2460

IC Conductivity Detector

2.850.9010

920 Absorber /minutesModule

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

System graphic

The 10 mL-Dosino is used to perform liquid handling of absorber solution, i.e., the initial volume is set into the absorber vessel before performing combustion. For the combusted products to be absorbed immediately (post-combustion rinse), the absorber solution is loaded at a rate of 0.2 mL/minute into the T-piece at the end of the combustion tube.

The connection between absorption vessel, and after combustion is over, the combustion tube is rinsed with 1 mL (final rinse). 5 mL-Dosino is used for water inlet at a rate of 0.1 mL/minute into the combustion tube for pyrohydrolytic environment. The internal standard is not required as the addition of volumes to the absorber solution during and after combustion is recorded exactly by MagIC Net.

The 5 mL-Dosino is used to transfer the samples and standards into the loop of the 920 Absorber Module using partial loop injection (MiPT), offering full flexibility to injection volumes in a range of 4-200 μL. For MiPT injection volumes, a fixed volume of 200 μL was used in this work.

Since the LPG analysis does not use the flame sensor for combustion control, the combustion time depends on 1) the time needed for sample injection by the LPG module and 2) the post-combustion time defined in the instrument method.

The LPG module comprises of a 1 μL sample loop that may be filled and injected up to 50 times. Ultimately, this setup can inject a variable LPG sample volume range of 1-50 μL. The time needed for sample injection (1μL × 50 loop-fills) is roughly 5 minutes.

Results

[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.

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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