ECH Sample Loop vs Mass Flow Controller for ppm water in LPG determination according to ASTM D7995

Water is one of the leading causes of corrosion and creates numerous safety hazards during the storage, distribution and use of liquified petroleum gases (LPG) and pressurised low molecular weight hydrocarbons and their different mixtures. Recent advances have been made in adapting coulometric Karl Fischer titration to analyse the water content in problematic samples such as LPG and LNG. Globally, coulometric Karl Fischer titration is recognised as the leading method of water content determination due to its greater sensitivity and ability to analyse both free and dissolved water.

In 2019, the standard Test Method for Total Water in Liquid Butane by Liquefied Gas Sampler and Coulometric Karl Fischer Titration was approved. Subsequently, the new Aquamax KF Pro LPG coulometric titrator was awarded full compliance to this method. The method describes two principles for sample introduction. One uses a temperature and pressure regulated fixed volume sample loop with internal pressure reducer for highly accurate dosing of liquefied and gaseous samples. The second administration is a dosing principle using an electronic mass flow controller.

Both principles of introduction conform to ASTM D7995. However, there are several notable differences between the principles. The below table describes some of the key reasons ECH decided to apply the Sample Loop procedure in the Aquamax KF Pro LPG in favour of standard mass flow controller.

Electronic Mass Flow

1. Rinsing gas (typically Nitrogen) is required for all measurements.
2. Background drift and detection limit are dependent on the quality of the rinsing gas used.
3. High continuous gas flow through the measuring cells means fast evaporation of the KF reagent leading to regular replacement.
4. Mass flow controller must be calibrated for all different gas samples individually.
5. Single measurements only with additional rinsing for each run.
6. Maximum external sample pressure of 40 bar only.

Sample Loop

1. No need for additional rinsing gases i.e., Nitrogen.
2. Large, fixed volume sample loop for accurate dosing of liquefied & gaseous samples..
3. No calibration required when switching samples or cylinders.
4. External sample pressure of 200 bar.
5. Determination of pressure & temperature of sample loop mean an accurate determination of known and unknown gas mixtures.
6. Automatic measuring sequences available, up to 125 over 48 hour period.

Each individual part of the Aquamax KF Pro LPG was specifically designed with the demanding petroleum industry in mind. All parts are fully enclosed in protective housing allowing you to use the instrument in the laboratory with full automation (125 measurements in a 48 hour period) Alternatively due to the enclosure you can take the system directly onsite to the sampling point or even be integrated into your process as an on-line analyser. The system still retains a direct injection port on the front of the titration cell meaning users can conform to additional coulometric KF methods such as ASTM D6304 and ASTM D4928.

To learn more about the Aquamax KF Pro LPG or ASTM D7995 please feel free to reach to one of our product experts.

Read more about the advances ECH have made in total automation of coulometric Karl Fischer analysis in solid and liquid samples using the popular Closed Loop carrier gas technique - ECH Closed Loop Technique for ppm water in oil determination (new revisions to ASTM D6304).

Book your session in the ECH Studio to learn about all aspects on coulometric Karl Fischer titration - ECH Product Demonstration Studio.