New Selective Solvent Developed For Purifying Natural Gas
Authors: Woertz Byron B. 
Published: December 2007

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Bench experiments and laboratory and field pilot plant testing have led to the development of a solvent that is selective in the removal of CO2 and H2S from natural gas at pipeline pressure. The acid gases are physically absorbed in the solvent; no chemical reaction takes place.

Comparative data indicate that our solvent, identified as Solvent P, has certain advantages over a leading competitive, commercially available solvent, which we have labeled Solvent A. Based upon our field pilot plant study, Solvent P has the following advantages over Solvent A as an acid gas removal agent:

Higher selectivity, resulting in higher gas yield, smaller refrigeration requirement, or a combination of the two. Higher heating value of the treated gas under comparable treating conditions. Less stripping gas required for solvent regeneration when making 1/4 grain H2S/100 SCF pipeline gas. Higher purity of the flash gases, improving their value for other uses.

Introduction

Until recently, essentially all commercial acid gas removal processes involved the use of either amines or potassium carbonate solutions. These materials chemically react with hydrogen sulfide and carbon dioxide, giving off appreciable quantities of heat. Heat must be supplied to regenerate the solutions.

In recent years, selective solvents have been developed by several companies for the removal of acid gases from natural gas and synthesis gas. The selective solvents operate on the principle of pure physical absorption, as one would calculate using vapor-liquid equilibrium ratios (K-values) for the appropriate systems. Whereas there is a heat of absorption and desorption involved, the heat effects are much smaller than with solutions involving chemical reactions, and the selective solvent can be regenerated without reboiling. Solvent extraction is especially useful in cases where the partial pressure of the acid gas is over 150 psia, preferably over 200 psia. The cost advantage of the solvent extraction process arises largely from the saving of heat ordinarily used in the regeneration of amines and hot potassium carbonate solutions, which is substantial when large volumes of acid gas are involved.