High Efficiency Packed Columns For Gas Processing
Authors: Aroonwilas A. , Tontiwachwuthikul P. , Mourits F. 
Published: March 2010

The possibility of using high efficiency structured packings in CO2 absorption processes with a sterically hindered amine, 2- amino-2-methyl-1-propanol (AMP), was investigated. Performance of the structured packings was evaluated by performing CO2 absorption into sodium hydroxide (NaOH) and AMP aqueous solutions in a 0.019 m ID absorption column. The performance, presented in terms of the volumetric overall mass transfer coefficient (KGa), is reported as a function of main operating variables, namely CO2 partial pressure, gas loading, liquid loading, and liquid composition. Performance comparisons between the tested structured and typical random packings is also given.

Introduction

Carbon dioxide (CO2) absorption is considered an important step in many industrial processing operations such as natural gas purification, manufacture of hydrogen, and coal gasification. The absorption process is basically used to separate CO2 from gas streams so that gas products with higher quality can be obtained and operational difficulties can be minimized. Environmentally, this process can also alleviate the global warming problem by reducing the net CO2 emissions from industrial waste gases which would otherwise be vented to the atmosphere.

In the absorption process, CO2 in gas streams is absorbed into liquid solvents, which can be classified into physical and chemical categories. Chemical solvents are preferred for the process because they have higher absorption capacity at a low partial pressures of CO2. Alkanolamines are considered to be the most commonly used chemical solvents for CO2 removal applications(1). Among these, monoethanolamine (MEA), a primary alkanolamine, is the most popular absorption solvent(2).

Another class of acid gas absorbents so called "sterically hindered amines," has been disclosed by EXXON Research and Engineering Company(3). 2-amino-2-methyl-1-propanol (AMP) is one of the most promising solvents among the hindered amine group. On the basis of stoichiometry, AMP can react with CO2 at a theoretical ratio of one mole CO2 per mole of amine, while each mole of the conventional MEA can react with only one-half mole of CO2. In addition, the CO2 absorption system using AMP aqueous solutions is reported to induce relatively less corrosion, which is considered the most severe operational problem in conventional alkanolamine plants(4).

According to the outstanding characteristics of the solvent, use of the sterically hindered amine AMP in the CO2 absorption application is very attractive. However, it should be noted that the absorption rate in CO2-AMP system is generally lower than that in conventional CO2-MEA system, by approximately 10 times(5). To enhance efficiency of the absorption system using AMP, mass transfer performance of CO2-AMP absorption system must be improved. An approach that might lead to the improvement of the system is modifications of the interior of the absorber. Successful use of structured packings for distillation and gas dehydration applications(6, 7), suggests that use of structured packings as the absorber interior may also improve mass transfer performance of the new CO2-AMP absorption system.

The primary objective was therefore to investigate the possibility of using high efficiency structured packings in CO2 absorption processes using a sterically hindered amine, 2-amino-2-methyl-1- propanol (AMP).