Page 291 - Petroleum and Gas Field Processing

Figure 9 Purisol process.

Purisol Process
This process uses N-methyl-2-pyrrolidone also known as NMP as a solvent
licensed by Lurgi. The solvent removes H 2 S, CO 2 ,H 2 O, RSH, and
hydrocarbons and elastomers. The feature of this solvent is that it is highly

selective for H 2 S, as shown in Table 3. It has a boiling point of 396 F,
which is rather low to be used in amine mixed solvents.
Figure 9 shows a typical flowsheet for the purisol process.
Regeneration is accomplished by two strippers, where dissolved hydro-
carbons are stripped off as fuel gas nitrogen in the first drum and acid
gases are stripped in the second stripper; regenerated NMP is recycled
back to the absorber.

Selexol Process
This process uses a mixture of dimethyl ether of propylene glycols as a
solvent. It is nontoxic and its boiling point is not high enough for amine
formulation. Figure 10 shows the flowsheet of the Selexol process. A cool
stream of natural gas is injected in the bottom of the absorption tower
operated at 1000 psia. The rich solvent is flashed in a high flash drum at
200 psia, where methane is flashed and recycled back to the absorber and
joins the sweet gas stream. The solvent is then flashed at atmospheric
pressure and acid gases are flashed off. The solvent is then stripped by

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