Experimental Study Of New Absorbents For Chemical Absorption CO₂ Capture Process

It's well accepted that the gradually increased temperature caused by large amount of greenhouse gases is constantly threatening the survival of humanity. As the major greenhouse gas, carbon dioxide (CO2) is currently responsible for over 60% of the enhanced greenhouse effect. Hence, the CO2 emitted by coal-fired plant, must be controlled. Several technologies now can be chosen to control CO2 emissions, such as post-combustion CO2 capture, pre-combustion CO2 separation and oxy-fuel combustion. However, in the short term, chemical absorption is considered as the most promising choice. Nowdays the cost of chemical is very high, because the common absorbent MEA is of high regeneration heat. There are also corrosion, degradation and other problems for MEA. Based on the analysis above, novel absorbent, which has high reaction rate, low energy consumption, is tested in this paper.Compared with MEA, aqueous ammonia has better absorption and regeneration performance. The absorption rate of aqueous ammonia is affected by temperature and concentration. The absorption rate increases as the increase of temperature and concentration. It's hard to regenerate when the solution loading is lower than 0.4 mol CO2/mol NH3.When solution loading is higher than 0.4 mol CO2/mol NH3, the regeneration efficiency increases with the solution CO2 loading. The regenerated CO2-lean solution regains the ability to capture CO2.Aqueous ammonia is easy to volatilize. The volatility increases with the increase of temperature and concentration. At 40℃, the volatility of aqueous ammonia is 6.7 times that at 0℃,and the volatility of 15% aqueous ammonia is 2 times of 5% aqueous ammonia. Adding little ammount. of additives (1 wt%) including amine and hydroxyl groups, i.e.,2-amino-2-ethyl-1,3-propandiol (AEPD), and tri(hydroxymethyl) aminomethane (THAM),can reduce ammonia volatilization by 28%-33%.At the same time,the absorption capacity is not affected.In order to meet the requirement of "high absorption rate,low regeneration energy consumption",several reaearches on the absorption and regeneration performance of blended amines have been carried out.It was found that,adding little amount of tertiary amines into primary amines can reduce the energy consumption of regeneration and meanwhile keep the absorption rate at high level. Adding some activators,such as PZ and DETA,into tertiary amines can improve the absorption performance of the solution significantly,but the regeneration performance deteriorates. Both absorption and desorption performance should be considered when choose absorbent used in chemical absorption.Derived from the comprehensive performance assessment of different absorbents, 9 mixed amines, i.e.,15%MEA+15%MDEA,are considered to be promising absorbents. Factually, more studies on the corrosion and degradation problems of the blended absorbents still need to be carried out before the large-scale industrial applications.