The Study On Acid Gas Absorption From Natural Gas Of Sterically Hindered Amine

Natural gas has got more and more attention all around the world as one of the most important fue havingl less pollutant emissions, energy efficiency and higher heating value energy. The acid gases including H2S and CO2 in natural gas will not only cause environmental pollution, but bring the issues of the catalyst poisoning, corrosion of metal equipment and the decreasing of the heating value of natural gas, etc. So the H2S and CO2 must be removed from the natural gas before the transport and use.Alcoholamine method is the most commonly used means in the desulfurization and decarbonization industry of natural gas. MDEA becomes the most widely used agent for desulfurization and decarbonization with the advantages of high selectivity of H2S, low regeneration energy, good chemical stability, low resistance, not easy to foaming and degradation, etc. Sterically hindered amine CB could be widely applied in the field of desulfurization and decarbonization in the future, because CB, as a secondary amine with a higher Taft coefficient, has higher selectivity for H2S, greater capacity for CO2 and lower energy consumption of the regeneration than MDEA.The core content of this paper is to verify the sterically hindered amine’s excellent characteristics in the field of desulfurization and decarbonization of natural gas, including larger H2S and CO2 contents, high selectivity for H2S and less regeneration energy. Firstly, the reaction temperature of 40℃ and the volume fraction of 35%～45% of the amine solution are the optimal reaction conditions. Secondly, the effect of desulfurization and decarbonization is compared between CB and MDEA solution. It results that CB solution is better than MDEA solution in not only the effect of desulfurization and decarbonization but the selectivity for H2S.The mixed solution is made of CB and MDEA with different proportions, with certain amount of total amines content. It results that the selectivity and the acid gas load increase gradually along with the increase of the proportion of the mixed solution of CB.Regeneration experiments investigate mixed lean solution and MDEA lean solution’s acid gas content under the same regeneration conditions, it results that the mixed solution is able to resolve more acid gas and own better effect of desulfurization and decarbonization after the first regeneration than MDEA solution. It verifies that the energy consumption of CB is less than MDEA.The paper investigates the effects of the gas-liquid contact time and different acid gas composition of feed gas on the desulfurization and decarbonization and the selectivity for H2S of mixed solution and MDEA solution. It results that the H2S and CO2 contents decrease and the selectivity for H2S increases with the gas-liquid contact time increasing. The H2S and CO2 contents and the selectivity for H2S of mixed solution are higher than that of MDEA solution in any gas-liquid contact time. The H2S content uniformly increases proportionately with the increasing of H2S content when the H2S content is 1%～6% of the feed gas and the mixed solution’s absorption on CO2 reaches to saturation when the CO2 content of the feed gas reaches to 5% in the precondition of the total acid gas content is 8% of the feed gas.The corrosion rate of rich solution is greater than that of lean solution. The mixed solution absorbs more acid gas but due to a lower corrosion rate than MDEA solution. The method of adding imidazoline inhibitor can effectively alleviate causticity of rich solution with an optimum volume fraction amount of 5‰.The foaming height and defoaming time of CB solution are greater than MDEA solution and the foaming tendency of mixed solution is more serious than that of MDEA and CB solution. There is no effect on the foaming height and defoaming time of the mixing ratio of MDEA and CB in mixed solution. The adding of FeS will strengthen the foaming tendency of mixed solution.The foaming case reaches to the maximum when the content of FeS is 3g/L and continue to adding FeS, the foaming case will not be strengthen any more. The foaming height keep less than 5cm and defoaming time becomes less than 10s for mixed solution when the content of FeS is 3g/L by adding defoamer of CW-3 with volume fraction amount of 3%o.