Integrated near infrared and ultraviolet spectroscopy techniques for determination of hydrate inhibitors in the presence of NaCl

Injection of chemical inhibitors is the most widely used method to prevent the formation of gas hydrates in gas transporting pipelines. It is usual that a high dosage of hydrate inhibitors has to be applied to minimize the risk of hydrate blockages, which can cause more operation costs and severe environmental damage. Monitoring the concentration of hydrate inhibitors in the pipeline could help the operator to determine the hydrate safety margin accurately therefore optimizing the inhibitor injection rate (i.e., ensuring adequate inhibition and avoiding over inhibition). In this study, the application of spectroscopic techniques was investigated to measure the concentration of both thermodynamic and low dosage hydrate inhibitors in water/brine by coupling UV and NIR spectra.Various partial least-squares (PLS) regression models were developed and evaluated at three different spectral regions (1400-1600, 1600-1850, and 1400-1850 nm) to determine the concentration of hydrate inhibitors and NaCl in three different inhibition systems: (a) monoethylene glycol (MEG)-NaCl, (b) methanol (MeOH)-NaCl, and (c) poly(N-vinylcaprolactam) (PVCap)-MEG-NaCl. The developed PLS models were further evaluated for a typical MEG-NaCl inhibition system by determining the concentration of MEG and NaCl during natural gas hydrate formation and dissociation. The results confirmed that the integrated NIR-UV spectroscopy technique can be used as a simple, quick, and reliable means for monitoring simultaneously the hydrate inhibitors and NaCl in pipelines.