Page 63 - Gas Purification 5E

Alkanolamines for Hydrogen Sulfide and Carbon Dioxide Removal 53

products resulting from reactions of DGA with CO, and COS (see Chapter 3). In 1996, Digly-
colamine solutions were being used in more than 100 plants (Kenney, 1996).
Diisopropanolamine

Diisopropanolamine (DIPA) has been used in the ADIP and Sulfinol processes, both
licensed by the Shell International Petroleum Company (SIPM). In the Sulfinol process, diiso-
propanolamine is used in conjunction with a physical organic solvent, and a more detailed dis-
cussion of this process is given in Chapter 14. The ADP process, which employs relatively
concentrated aqueous solutions of diisopropanolamine, has been described by Bally (1961)
and by Klein (1970). It has been widely accepted. primarily in Europe, for the treatment of
refmery gases and liquids which, besides H,S and COz, also contain COS. It is claimed that
substantial amounts of COS are removed without detrimental effects to the solution. Further-
more, diisopropanolamine solutions are reported to have low regeneration steam requirements
and to be noncorrosive (Klein, 1970). SIPM has applied the ADIP process to the selective
absorption of H2S from refinery gas streams (Abe and Petenan, 1980) and, as part of the
SCOT process, to selective absorption of H2S from Claus plant tail gas (see Chapter 8). How-
ever, SIPhl is gradually replacing DIPA with MDEA in both of these applications. A theoreti-
cal study of the absorption kinetics hV0hed in the selective absorption of H2S in DIPA has
been presented by Ouwerkerk j1978). Equations for mass transfer with chemical reaction are
utilized in the study to develop a computer program which takes into account the competition
between H?S and C02 when absorbed simultaneously.
Methyldiethanolamine

Selective absorption of hydrogen sulfide in the presence of carbon dioxide, especially in
cases where the ratio of carbon dioxide to hydmgen sulfide is very high, has recently become
the subject of considerable interest, particularly in the purification of non-hydrocarbon gases
such as the products from coal gasification processes and Claus plant tail gas. The early
work at the Fluor Corp. (now Fluor Daniel) showed that tertiary amines, especially
methyldiethanolamine, can absorb hydrogen sulfide reasonably selectively under proper
operating conditions involving short contact times (Frazier and Kohl, 1950; Kohl, 1951;
Miller and Kohl, 1953). -4 study by Vidaurri and Kahre j1977), in which selective absorption
with several ethanolamines was investigated in a pilot and commercial plant, demonstrated
that purified gas containing as little as 5 parts per million of hydrogen sulfide could be
obtained with absorption of only about 308 of the carbon dioxide contained in the feed gas.
The most selective solvent was methyldiethanolamine, although other amines also showed
some selectivity.
Additional information on selective H2S absorption with MDEA or hfDEA-based solu-
tions is presented by Pearce (1978j, Crow and Baumann (1974j, Goar (198Oj, Blanc and
Elgue (1981): Sigmund et al. (1981). Dibble (1983), Robinson et al. (1988). and Kam and
Langfitt (1986.4, 1986Bj. The papers by Sigmund et al. and Dibble describe Union Carbide
Corporation’s proprietary process using MDEA-based solutions under the trade name of
UCARSOL HS Solvents. These solvents are claimed to be more selective than conventional
MDEA and DIPA solutions and, consequently, more economical with respect to energy con-
sumption. A comparison of UCARSOL with DIPA for recovering H2S from Claus plant tail
gas (after hydrogenation) is shown in Table 24. The paper by Robinson et al. pro\ides data
on a gas treating plant that was converted from DEA to GAS/SPEC CS-3 Solvent-an