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Hydrogen sulfide

Eastman AdapT for H2S removal

Sulfur species like hydrogen sulfide (H2S) must be removed to very low concentrations for safety, corrosion and environmental impact reasons and for downstream catalytic processes. Sulfur removal targets are often driven by global standardization, such as maximum allowable concentration in natural gas transported over pipeline or in liquid form. 

A gas station pipeline system.
Aerial view of a refinery worker checking production plant data.

Complete sulfur removal

Typical pipeline specifications are between 4 and 16 parts per million by volume (ppmv). Specifications may also be expressed in grains of sulfur per 100 SCF; 0.5 grains/100 SCF is equivalent to 4 ppmv. In certain applications such as refinery gases and syngas treatment, there is a general desire to reduce H2S to very low levels, although the exact specification can be plant specific.

Sulfur removal necessitates thermal regeneration of the solvent.

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A light blue gas pipeline system.

Selective sulfur removal

Besides achieving complete sulfur removal, minimizing carbon dioxide (CO2) absorption is crucial. When an acid gas stream is to be processed in a sulfur recovery unit based on Claus technology, the acid gas must contain a minimum concentration of H2S of, e.g, 40 volume percent. In natural gas treatment for pipeline transport, CO2 removal can be unnecessary and costly because it increases system size and reduces the amount of gas that can be sold.

In tail gas treatment and acid gas enrichment, low feed gas pressure poses a challenge. Tertiary amines like MDEA are preferred for selective sulfur removal due to slow CO2 kinetics. They are also “weaker” amines, lowering the driving force for absorption at lower pressure. Eastman AdapT solvents accommodate through improved mass transfer and solvent regeneration, improving the chemical equilibrium for H2S absorption.

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H2S absorption reaction chemistry

All amines react in a similar fashion to H2S. H2S is transferred quickly into the liquid phase, where it forms bisulfide, protonating an amine in the process. These reactions are fast as illustrated in the following reaction table.

Even though the effect is not as strong as in CO2 removal, the absorption of H2S can also be impacted through selection of the type and concentration of amines.

Hydrogen sulfide quickly transfers to the liquid phase, forming bisulfide and protonating an amine. Hydrogen sulfide quickly transfers to the liquid phase, forming bisulfide and protonating an amine.

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