Chemistry of inorganic compounds – Modifying or removing component of normally gaseous mixture – Carbon dioxide or hydrogen sulfide component
Patent
1990-01-18
1993-05-11
Langel, Wayne
Chemistry of inorganic compounds
Modifying or removing component of normally gaseous mixture
Carbon dioxide or hydrogen sulfide component
252189, 423229, C01B 3120, C09K 300
Patent
active
052099148
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a liquid absorbing acidic gases containing a tertiary alkanolamine component and an activator of CO.sub.2 absorption. It also relates to the application of the said absorbent liquid to the deacidification of gases containing CO.sub.2 and possibly other acidic gaseous compounds such as H.sub.2 S or/and COS.
It is known that it is possible to rid gases of undesirable acidic gaseous compounds or acidic gases, especially CO.sub.2, H.sub.2 S and COS, which they contain by subjecting the said gases to scrubbing by means of regenerable absorbent liquids consisting of organic solvents or of aqueous solutions of organic solvents, which retain the acidic gaseous compounds. On an industrial scale, there are chiefly two categories of absorbent liquids employed for scrubbing gas containing acidic gaseous compounds, namely, on the one hand, absorbent liquids with physical action, such as sulpholane, N-methylpyrrolidone, polyethylene glycol dimethyl ether, methanol or else propylene carbonate, which absorb acidic gaseous compounds such as mentioned above without any chemical reaction, but whose major disadvantage is that of simultaneously absorbing large quantities of hydrocarbons and, on the other hand, absorbent liquids with predominant chemical action and especially aqueous solutions of alkanolamines such as monoethanolamine, diethanolamine, diglycolamine, diisopropanolamine, triethanolamine or else methyldiethanolamine, which fix acidic gaseous compounds such as CO.sub.2, H.sub.2 S and COS by chemical reaction with formation of compounds capable of being decomposed by heating, which allows the absorbent liquid to be regenerated Primary alkanolamines such as monoethanolamine, or secondary alkanolamines such as diethanolamine, are generally suitable for highly exhaustive removal of CO.sub.2, but exhibit the disadvantage of requiring a large expenditure of energy for their regeneration.
With tertiary alkanolamines, especially methyldiethanolamine and triethanolamine, the consumption of energy needed for the regeneration is lower, but the treated gas resulting from the scrubbing operation using the said tertiary alkanolamines still has CO.sub.2 contents ranging from a few thousand ppm to a few per cent, depending on the case. This is due to the fact that tertiary alkanolamines do not react directly with CO.sub.2, the result being kinetics of absorption of CO.sub.2 by the absorbent liquid containing such tertiary alkanolamines which are much slower than the kinetics of absorption of CO.sub.2 by an absorbent liquid based on primary or secondary alkanolamines, while the rate of absorption of H.sub.2 S is substantially the same whatever the alkanolamine employed in the absorbent liquid.
In order to draw maximum advantage of the saving of regeneration energy which can be achieved when an absorbent liquid based on a tertiary alkanolamine is employed for scrubbing gases containing acidic gaseous impurities such as CO.sub.2, H.sub.2 S and COS, while obtaining a suitable removal of CO.sub.2, it has been proposed to add to the said absorbent liquid a small quantity of an activator which accelerates CO.sub.2 absorption without modifying the absorption capacity for other acidic gaseous compounds and especially for H.sub.2 S, or the energy saving achieved during the regeneration of the absorbent liquid.
Among the products proposed hitherto as activators of CO.sub.2 absorption by absorbent liquids based on tertiary alkanolamines are to be found primary alkanolamines such as monoethanolamine (EP-A-0,160,203), monomethylmonoethanolamine (U.S. Pat. No. 3,622,267) and piperazine (U. S. Pat. No. 4,336,233).
It has now been found that certain other amine compounds have been shown to be effective activators of CO.sub.2 absorption by tertiary alkanolamines.
The invention proposes, therefore, a liquid absorbing acidic gaseous compounds exhibiting an improved absorption capacity for CO.sub.2, the said absorbent liquid containing a tertiary alkanolamine component made up of one or more tertiary alkanolamines and an activ
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Le Coz Philippe
Oliveau Olivier
Peytavy Jean-Louis
Elf Aquitaine Production
Langel Wayne
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