Integrated Near Infrared and Ultraviolet Spectroscopy Techniques for Determination of Hydrate Inhibitors in the Presence of NaCl

Abstract

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(Nvinylcaprolactam) (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.

Recent Advances in Methods of Gas Recovery from Hydrate-Bearing Sediments: A Review

“…The inhibitor types, injection rate, injection concentration, and injection volume all significantly affect the process of NGH dissociation . Their optimal design can effectively change the NGH phase equilibrium conditions and artificially control the rate of NGH dissociation and gas production .…”

“…To achieve the elevation of an inhibitory effect of inhibitors, the mixture of multiple THIs comes into being. , However, sometimes harmful interactions exist among them to form cross-inhibition. In detail, alcohol inhibitors may restrain the solubility of salts, finally causing a “salting-out effect” and stopping the produced gas from migrating to the production well. , Furthermore, the dilution problem of inhibitors caused by decomposed water and initial free water in HBS also has been severe, resulting in the low use frequency in hydrate exploitation because of their characteristics of high dosage, high pollution, substantial capital, and cost of chemicals. , Indeed, one method encapsulates high-concentration THIs in microcarriers and releases them at a fixed point and quantitatively has been introduced to alleviate the problem of high pollution, but the feasibility of this method still to be further studied …”

“…278,279 The inhibitor types, injection rate, injection concentration, and injection volume all significantly affect the process of NGH dissociation. 280 Their optimal design can effectively change the NGH phase equilibrium conditions and artificially control the rate of NGH dissociation and gas production. 4 However, these inhibitors only work well at higher concentrations (usually >10 wt %), and the application of too low a concentration of inhibitors may abnormally facilitate the NGH growth.…”

ATR-FTIR Model Development and Verification for Qualitative and Quantitative Analysis in MDEA–H2O–MEG/TEG–CO2 Blends

“…The number of factors (loading vectors) was based on the standard error of cross-validation (SECV), which corresponds to the predictive error obtained at the cross-prediction stage, root mean square error (RMSE), and maximum possible correlation coefficient (R 2 ) for each component to generate calibration curves. Outliers in the calibration dataset were detected by calculating residuals with a 95% confidence level during the development of the model [29,36,37]. Equation 3was used to measure RMSE, Equation (4) was used for SECV and standard error (SE) and Equation (6) was used to calculate the validation number (VN) of each component in a system.…”

“…Cuccia et al reviewed the data available in the literature where FTIR was used to analyze degradation byproducts in the liquid phase for post-combustion CO 2 capture processes [27]. Handojo et al [28] used FTIR to identify thermal degradation byproducts in aqueous MDEA degradation at 120 • C with continuous CO 2 absorption and verified it with GC-MS. Haghi et al [29] used a PLS model with both near-infrared and ultraviolet spectroscopy to determine the concentration of both MEG and sodium chloride in solutions. A combined acid gas and water removal system solvent can consist of amine and MEG/TEG, and during the regeneration step it will also have absorbed water and acid gas, which need to be stripped for the regeneration of the solvent.…”