A collaboration between gas analysis experts Servomex and engineers at ExxonMobil Chemicals at Mossmorran in Fife has solved the problem of measuring the presence of water in the Sulfinol process
A collaboration between gas analysis experts Servomex and engineers at ExxonMobil Chemicals at Mossmorran in Fife has solved the problem of measuring the presence of water in sulfinol as used in the Sulfinol process. ExxonMobil Chemicals operates an ethylene plant at Mossmorran in which Servomex gas analysers have been installed for routine process analysis for several years. The feedstock of ethane, propane and butane used for the production of ethylene comes from an adjacent natural gas processing plant and this feedstock inevitably contains levels of carbon dioxide (CO2) and hydrogen sulphide (H2S), which are corrosive and capable of causing damage to the ethylene liquefaction plant.

These corrosive gases are removed using the Sulfinol process.

This is a widely applied gas treatment process, which has been in use since the 1960s and for which some 200 installations have been licensed worldwide.

H2S and CO2 are removed using an absorbtion medium called Sulfinol, an organic solvent mixture made up of Sulfolane (tetrahydrothiophene) and alkanolamines in an aqueous mixture.

The feedstock is subjected to absorption, regeneration, heat exchange and recycling and simultaneous physical and chemical absorption of the acid gases occurs under conditions of elevated pressure and moderate pressure.

This reduces the water content of the feedstock, and its water content after processing provides a quality indicator of the efficiency with which the process is operating.

ExxonMobil had been checking the water content of the processed feedstock using off-line laboratory gas chromatograph techniques, but decided that they wanted simple on-line continuous monitoring of the water content so as to have an immediate indication if the water level increased.

The Servomex Customer Applications team asked ExxonMobil to let them have some samples of Sulfinol containing various known levels of water.

Detailed analyses at Servomex using laboratory Fourier transform infrared spectroscopy (FTIR) demonstrated that a measurement of water content at near infrared wavelengths was realistically possible at useful water concentrations.

Based on the laboratory spectroscopic data and its previous experience of Servomex infrared gas analysers, ExxonMobil installed a Servomex 2500 analyser to monitor its Sulfinol process on a continuous basis.

Servomex also designed and built a custom-made sampling system and enclosure, suitable for hazardous areas.

Experience has shown that the new system has enabled the operators to control the absorption of water more efficiently, with consequent cost savings.

The on-line analysis has also reduced the foaming of the Sulfinol, which can cause production problems downstream of the analyser.

In many other applications, the 2500 infrared gas analyser and its sampling system successfully monitor the presence of water from trace level (0-50ppm wt) to 0-50% wt in various organic solvents and liquids.

The 2500 provides reliable and accurate performance with excellent long-term stability and is certified for use in hazardous areas.