Diethanolamine (DBA) is a secondary arnine that has in recent years replaced MEA as the most common chemical solvent. As a secondary amine, DEA is a weaker base than MEA, and therefore DEA systems do not typically suffer the same corrosion problems, In addition, DEA has lower vapor loss, requires less heat for regeneration per mole of acid gas removed, and does not require a reclaimer, DEA reacts with H2S and CO2 as follows:
These reactions are reversible. DBA reacts with carbonyl sulfide (COS) and carbon disulfide (CS2) to form compounds that can be regenerated in the stripping column. Therefore, COS and CS2 are removed without a loss of DEA. Typically, DBA systems include a carbon filter but do not include a reclaimer.
The stoichiometry of the reactions of DEA and MEA with CO2 and H2S is the same. The molecular weight of DEA is 105, compared to 61 for MEA, The combination of molecular weights and reaction stoichiometry means that approximately 1.7 Ib of DEA must be circulated to react with the same amount of acid gas as 1.0 Ib of MEA. However, because of its lower corrosivity, the solution strength of DEA ranges up to 35% by weight compared to only 20% for MEA. Loadings for DEA systems range
to 0.65 mole of acid gas per mole of DEA compared to a maximum of 0.4 mole of acid gas per mole of MEA. The result of this is that the circulation rate of a DEA solution is slightly less than for a comparable MEA system.
The vapor pressure of DEA is approximately l/30th of the vapor pressure of MEA; therefore, amine losses as low as 1/4-1/2 Ib/MMscf can be expected.