Acid gas scrubbing process using hindered amine solution with hindered amine recovery from side-product cyclic urea

An acidic gas (e.g CO2) is removed from a gas mixture containing it by contacting the gas mixture with an absorbing solution in an absorption tower (10) of a scrubbing system. The absorbing solution comprises a basic alkali metal compound and a hindered amine activator some of which is converted to a cyclic urea. Acid gas is recovered (in 28) by passing absorbing solution recovered from the absorption tower (10) to a desorption tower (20) of the scrubbing system operated at a lower pressure and/or higher temperature than the absorption tower (10), and part of the regenerated absorbing solution is returned to the absorption tower (10) for re-use. Another part of the regenerated absorbing solution is circulated to a thermal conversion zone (40) wherein it is retained for an adequate residence time and at an elevated temperature to convert at least some of the cyclic urea to hindered amine activator, whereafter the thermally treated absorbing liquid is returned from the thermal conversion zone (40) to the scrubbing system.