Licensed by Shell the Sulfinol® process combines the properties of a physical and a chemical solvent. The Sulfinol® solution consists of a mixture of sulfolane (tetrahydrothiophene 1-1 dioxide), which is a physical solvent, diisopropanolamine (DIPA), and water. DIPA is a chemical solvent that was discussed under the amines.
The physical solvent sulfolane provides the system with bulk removal capacity. Sulfolane is an excellent solvent of sulfur compounds such as H2S, COS, and CS2. Aromatic and heavy hydrocarbons and CO2 are soluble in sulfolane to a lesser degree. The relative amounts of DIPA and sulfolane are adjusted for each gas stream to custom fit each application. Sulfinol® is usually used for streams with an H2S to CO2 ratio greater than 1:1 or where it is not necessary to remove the CO2 to the same levels as is required for H2S removal. The physical solvent allows much greater solution loadings of acid gas than for pure amine-based systems. Typically, a Sulfinol® solution of 40% sulfolane, 40% DIPA and 20% water can remove 1.5 moles of acid gas per mole of Sulfinol® solution.
The chemical solvent DIPA acts as secondary treatment to remove H2S and CO2. The DIPA allows pipeline quality residual levels of acid gas to be achieved easily. A stripper is required to reverse the reactions of the DIPA with CO2 and H2S. This adds to the cost and complexity of the systern compared to other physical solvents, but the heat requirements are much lower than for amine systems, A reclaimer is also required to remove oxazolidones produced in a side reaction of DIPA and CO2.