TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Components: (a) comprises trialkylamines, dialkylmonohydroxyalkylamine, monoalkyldihydroxyalkylamine or trihydroxyalkylamine. (a) is N-methyldiethanolamine or triethanolamine. (b) is an aliphatic amine compound of formula (NH2-(CH2-CH2-NH)z-CH2-CH2-NH2) having two or more primary amino groups and one or more secondary amino groups. (b) is diethylenetriamine or triethylenetetramine. The total amount of (a) and (b) is 10-50 wt.%, where the amount of (a) is 1.5-5 times the amount of (b). The molar ratio of (b) to total number of moles of (b) and (a) is 0.3-0.5. The ratio of required amount of contaminated wash solution for the concentration to the quantity of added fresh or purified washing solution is 1:1-5:1, preferably 3:1. The inlet temperatures of raw gas and washing solution is 15-60 degrees C.z = 1-5.Preferred Method: In the method, a required amount of contaminated washing solution is driven in a circular manner for the concentration step. The washing solution in the fine and coarse purification step is exposed to different irrigation densities, where the ratio of the irrigation density is at least 1:1.5. The fine and coarse purification steps are carried out without pressure (atmospheric pressure) or at low pressure of 100 mbar. The raw gas is subjected to a gas washing process by venturi- or jet scrubber, before supplying to purification process, where the contaminated wash solution from the coarse purification step is used as a liquid propellant. The regeneration of contaminated washing solution is performed at 110-200, preferably 120-165 degrees C, where bound hydrogen sulfide and carbon dioxide in the washing solution are separated. A multi-step regeneration of contaminated washing solution is carried out by desorption at a pressure of 2-10 bar, where a gradation is made from a lower to a higher pressure or vice versa. The non-desorbed compounds such as thiosulfate and heat-stable salts contained in the washing solution are removed in downstream adsorption step of the regeneration process, where a heavy metal of I, II or VIII subgroup of the periodic system, activated carbon or an ion exchange resin are used as an adsorbent in the adsorption step. EXAMPLE - Typical composition comprised (in wt.%) of: N-methyldiethanolamine (20); diethylenetriamine (10); and water (70).