Desorption of CO2by steam bubbles from amine-promoted potash solutions

Preliminary Desorption

Communication

of CO2 by steam bubbles

amine-prnated

potash

from

solutions

We have recently described (1) some experiments in which the rate of dasorprion of CO2 per unit eree of interface was measured, using potash solutions with end without the addition of small amounts of alkanolemines. The present camunication concerns experiments in which steem was bubbled through 100 cm3 of the carbonated liquor, and no attempt was made to control The experimental procedure was very similar to that the interfreial mea. described in ref. (l), except that the stripping gas was steam generated at etcmospheric ptessure (without nitrogen) end was bubbled through the potash The emergent solutions, which waa kept at 1OloC and atmospheric pressure. vepour was passed through a packed ebsorptim column in which the CO2 we8 This was subsequently acidified and the absorbed in a solution of NaOH. equivalent partial pressure of CO2 in the liquid determined with a Radiometer electrode. P =o2 In view of the fact that the actual area of the interface between liquid and gas wee not known, and certainly varied a8 between one experiment nowever, and another, no very fine quantitative conclusions can be drawn. the Table shows-that MEA. DEA and TEA all increase the rate of desorption compared to that from unpromoted potash solution to about the same extent. When the interfacial area is fixed the magnitudes of the promotion effect are DEA>HEA>TEA (indeed TEA has very little promoting power). The difference between the two situations. as can be seen by the naked eye, is that the emines affect the interfacial area. in the experiments described It is easy to see that TEA produces a froth here, to different extents. with a much larger interfacial area than the other solutions. The "promotion" brought about by TEA is thus due to physical rather then chemical effects. The effect would be apparent in bubbLe-plate but not in packed columns. The problem of foaming may arise when a promoter like TEA is used. TABLE

(K+)M

Amine

5.4 5.4 5.3 5.28

MEA DEA TEA

*

concentration

0

carbonation

RA

rate of deeorption

Mabajani

V.V. and Danckwerts

RA(mol/cm3s)x107

a

UmmoM

0.6 1.8 1.9 1.6

0.30 0.26 0.22 0.25

0.3 0.3 0.3 NOTATION of amine ratio

added

to solution

(as defined

in ref.11

of CO2 per unit volume

P.V..

Chem. Engg.

Sci.1983

V.V. Mehajani and P.V. Danckwerte. Dept. of Chemical Engineering. Pembroke Smeet. Cambridge, England. CB2 3RA. 25th November,

1982

499

of liquid

s

321