Methanol is probably one of the most versatile solvents in the natural gas processing industry. Historically, methanol was the first commercial organic physical solvent and has been used for hydrate inhibition, dehydration, gas sweetening and liquids recovery. Most of these applications involve low temperature where methanol’s physical properties are advantageous compared with other solvents which exhibit high viscosity problems or even solids formation. Operation at low temperatures tends to suppress methanol’s most significant disadvantage, high solvent loss.

Methanol has been extensively used as a hydrate inhibitor for conditions where the Hammerschmidt equation is applicable. Outside this range, predicting methanol’s behavior is more complicated than the empirical correlations that are provided in industrial standard data books. In fact, the thermodynamic properties and phase equilibrium of mixtures of methanol, water and hydrocarbons are notoriously difficult to predict. Methanol shows both polar and non-polar characteristics. Consequently, these characteristics give methanol the unique ability to be used in an extensive range of applications. This paper will review some of these diverse applications: hydrate inhibition, gas dehydration, sweetening and liquids recovery.

This paper will discuss and compare the methods used to suppress hydrate formation in natural gas streams. Included in the comparison will be regenerated systems using ethylene glycol and non-regenerated systems using methanol. A comparison will be made between the quantities of methanol and ethylene glycol required to achieve a given suppression. A discussion of BTEX emissions resulting from the ethylene glycol regenerator along with the effect of process variables on these emissions is also given.

BTEX emissions from glycol dehydration units have become a major concern and some form of control is necessary in many cases. One method of reducing BTEX emissions that is often overlooked is in the selection of the proper dehydrating agent. BTEX compounds are less soluble in diethylene glycol (DEG) than triethylene glycol (TEG) and considerably less soluble in ethylene glycol (EG). If the use of DEG or EG achieves the required gas dew point in cases where BTEX emissions are a concern, a significant savings in both operating costs and the cost of treating still vent gases may be achieved. This paper compares plant operations using TEG, DEG, and EG from the viewpoint of BTEX emissions, circulation rates, utilities, and dehydration capabilities.

In designing dehydration units for natural gas, several critical parameters exist which can be varied to achieve a specified dew point depression. This paper studies the effects of varying the glycol flow rate, number of stages in the contactor, reboiler temperature, and stripping gas rate on water content in glycol dehydration units. The effect of high carbon dioxide composition in the feed is also presented. Finally, the emissions of aromatic (BTEX) and other VOC's from the regenerator and flash will be considered.