Enhancement in Triethylene Glycol (TEG) Purity via Hydrocarbon Solvent Injection to a TEG plus Water System in a Batch Distillation Column

Triethylene glycol (TEG) is one of the most important liquid desiccants in the natural gas dehydration industry. In enhanced TEG regeneration processes, liquid hydrocarbons such as toluene and isooctane are added to the stripping column of natural gas dehydration unit in order to boost water volatility and regenerate TEG to higher purity. In this study, isooctane and toluene were selected as liquid hydrocarbon solvents and the effect of these two solvents on TEG purity and the outlet water concentration from the reboiler of tray column were experimentally investigated and mathematically modeled. The vapor-liquid equilibrium calculations were performed using the NRTL activity coefficient model and ideal gas equation of state to represent the liquid and vapor phases, respectively. Moreover, a comprehensive model was used to determine the liquid molar flow rate on each tray where it changed with time and tray by tray. The impact of various concentrations of solvents and different operating conditions (total and no reflux) on the performance of the tray column was investigated. The modeling results were validated with the experimental data, and good agreement was observed between them. Results showed that the least water concentration in the reboiler and the highest TEG purity were achieved by adding 0.15 wt % isooctane under total reflux conditions. The achieved results can provide an initial insight into designing equipments in enhanced TEG regeneration processes with hydrocarbon solvent injection.