A method for quantitation of bisulfide in the aqueous phase reactions of H 2 S scavenging with MEA-triazine is proposed. The method is based on time-resolved in situ Raman spectroscopy, thus allowing in situ monitoring of the reactions. The method is applied to obtain the kinetic data of the reactions in batch configuration at room temperature for initial pH values of 9, 10, and 11 and MEA-triazine/bisulfide initial concentration ratios in the range of 0.5−10. The pH increases remarkably during the reactions, causing a substantial decrease in the rate of disappearance of bisulfide. If the system is reacidified, complete depletion of bisulfide can be achieved, evidencing the irreversibility of the scavenging reactions. The results are also supported by a qualitative analysis of the trends of the characteristic Raman peaks of MEA-triazine, dithiazine, and monoethanolamine. These trends are in line with the currently accepted reaction scheme, consisting of two scavenging reactions in series.
A novel kinetic model for the aqueous phase hydrogen sulfide scavenging reactions using MEA-triazine (HET) is proposed. The assumptions of the model are based on experimental observations obtained by NMR spectroscopy, supporting the existence of 3,5-bis(2-hydroxyethyl)hexahydro-1,3,5-thiadiazine (TDZ) as a quantitative reaction intermediate and showing the protonation behavior of HET and the lack of protonation of 5-(2-hydroxyethyl)hexahydro-1,3,5-dithiazine (DTZ). Experimental kinetic data were obtained with a new in situ Raman spectroscopy setup, which enabled monitoring the time-variation of bisulfide concentrations in a batch stirred reacting system at temperatures of up to 75 °C for HET/HS − initial concentration ratios from 0.5 to 5. The optimal model parameters were regressed from the experimental data using a brute force optimization method. The rate constants of the first and second scavenging reactions were estimated to be 0.435 and 0.004 L mol −1 s −1 at 25 °C, and the activation energies were 68 and 57 kJ mol −1 , respectively.
A model of the Coldfinger water exhauster for advanced glycol regeneration, based on two-equilibrium stages with internal recirculation of vapor, is proposed and validated on plant data of natural gas dehydration using triethylene glycol (TEG). Optimal operating regions are located for vapor recirculation ratios (𝛼𝛼) above 0.95, gas-to-liquid feed ratios in the order of 10 -4 and top temperatures in the range 50 to 80 °C. The conceptual investigation supports that the Coldfinger unit can enhance TEG purity up to approximately 99.7 wt %. Taking conventional single-stage gas stripping as reference, the model supports the possibility of achieving the same TEG enrichment levels using 10 to 100 times less gas. Non-obvious features are also highlighted, such as multiple steady-states and conditions leading to low or negative efficiency. The model provides a good fit with plant data with optimal values of 𝛼𝛼 (regression parameter) being consistent and bearing sound physical meaning.
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