Analytical Instrumentation

  • Total chloride analysis - The Absolute Reference Method

Total chloride analysis - The Absolute Reference Method

Feb 20 2020 Read 206 Times

For decades, the presence of organic bonded chloride has been a relevant parameter for refinery and petrochemical processes. Challenges in recent years have been the increasing need of a matrix independent refence method and an ever decreasing detection limit. Why is chloride such an important parameter and which benefits does Oxidative Combustion Microcoulometry offer?

Refineries convert crude oil into all kinds of petroleum products. The presence of chloride in crude oil can lead to catalyst poisoning, which has a negative impact on the profitability of the refinery unit. Chlorides in the refining process are difficult to control, especially the organic chlorides. They cause various forms of corrosion at different temperatures and pressure levels, downstream of the distillation unit. Besides the corrosive effects, chloride also deteriorates the quality of the final product. Petrochemical facilities can transform refinery intermediates such as gas and liquid hydrocarbons into a wider range of petrochemical products. Feedstocks used to produce these chemicals (e.g. LPG, naphtha, and gasoil) often come from refineries. The presence of organic chloride in these feedstocks also promotes the risk of corrosion in the chemical production process. Maximum chloride levels are often specified for process streams and hydrocarbon products such as aromatic hydrocarbons.

So the crucial question is: how do you detect (organic) chloride content? Several international test methods focus on the analysis of (organic) chloride, often expressed as Total Chloride (TX), in crude oil, petroleum distillates, intermediates and aromatic hydrocarbons. Oxidative combustion microcoulometry is the benchmark technique to which relevant test methods such as the ASTM D4929, ASTM D5808, ASTM D7457, and UOP779 refer. TE Instruments’ XPLORER-TX is fully compliant with these test methods.

Recently, XRF related techniques presented themselves as an alternative way to analyse chloride in petroleum products. When compared, microcoulometric detection technique offers numerous benefits. Microcoulometry is an absolute detection technique. All (organic) chloride components are converted to hydrochloric acid (HCl). The XPLORER-TX achieves a 100% recovery. Therefore, calibration of the  XPLORER-TX whilst being doable, is not even necessary. Microcoulometric titration can be applied to a much wider range of sample types, including liquids, solids, gas and LPG. Microcoulometry is not affected by the matrix and inhomogeneity of the sample. This can be seen as a major issue for XRF technique. Sulphur is another component which is ubiquitous in petroleum products. Microcoulometry does not experience interferences of sulphur to the chloride signal. No sulphur analysis or dilution is required prior to chloride analysis. The measuring range of the XPLORER-TX (25 ppb – 1000 ppm), makes it the most versatile analyser for chloride analysis. Analysing samples < 1 ppm is challenging for most XRF techniques. At ppb level, the performance of the XPLORER-TX is unrivaled within the industry.

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