CO₂ removal using 1DMA2P solvent via membrane technology: Rate based modeling and sensitivity analysis

Highlights

• A comprehensive 2−D mathematical model is developed to investigate the CO₂absorption.

• The absorption performance of novel reactive 1DMA2P is considered.

• The absorption performance of different conventional and alternative amine solutions was compared in a HFMC.

• The impact of critical operating parameters on CO₂ absorption is evaluated.

Abstract

A numerically solved reaction rate/kinetic model for CO₂ removal from a CO₂/N₂ gas mixture into novel reactive 1-dimethylamino-2-propanol (1DMA2P) solution in a gas–liquid membrane contactor was constructed. The model is assembled by considering the main transport phenomena and all possible reactions. The validated model was applied to investigate the transport phenomena in the different sides of membrane. The impact of main operation parameters on the performance of HFMC were evaluated. The influence of co- and counter-current operational modes on the absorption process was analyzed. The sensitivity analysis under moderate conditions indicated that the mass transfer resistance of gas phase is dominant with respect to liquid phase. Enhancing the liquid temperature, solvent circulation velocity, 1DMA2P concentration and also decreasing gas stream velocity increase the CO₂ absorption. The CO₂ removal using conventional and alternative amines were analyzed and compared. It is observed that due to high capacity of 1DMA2P for CO₂ capture and its low regeneration heat, it could be considered as one of the efficient solvent for CO₂ removal.

Introduction

Extensive efforts have been performed to solve environmental problems related to climate change and global warming [1], [2], [3]. The world is imposed to upgrade environmental strategies and applied efficient technologies that will reduce the greenhouse gas emissions into the atmosphere [4]. One of the main concerns for the future decades is mitigation of CO₂ emissions as the largest contributor to greenhouse pollution. Post–combustion CO₂ capture via chemical absorption process is a favorable method for carbon capture and storage (CCS). Amine solvents are usually used for this process since they represent high capture efficiency and selectivity towards CO₂, low energy requirement for regeneration, low degradation rate, and low corrosiveness. Different amine–based solvents have been widely used for CO₂ capture. Alkanolamine solvents can be categorized into three main groups, including primary, secondary and tertiary amines. Although, because of faster reaction rates of primary and secondary amines with CO₂, they are extensively used, but also their use has been recently limited because of their low CO₂ absorption capacity, solvent degradation and corrosion, high regeneration energy and cost. On the other hand, the tertiary amines represent higher absorption capacity, lower regeneration heat, as well as slower reaction rate. The tertiary amines catalyze the hydrolysis of CO₂ to bicarbonate without any direct reaction with CO₂. The superiority of lower energy consumption during regeneration of tertiary amines can provide the wide–spread employment of amine solvents. In recent years, the development of more efficient tertiary amine solvents has attracted extensive attention in the research community to provide a cost effective system. Currently, 1–dimethylamino–2–propanol (1DMA2P), a tertiary alkanolamine, introduced as an applicable solvent for large-scale use in bulk CO₂ absorption. The previous investigations confirmed that 1DMA2P represents better mass transfer performance and higher kinetics of CO₂ removal than the most common tertiary amines [5]. Liang et al. [5] investigated the CO₂ removal performance of aqueous 1DMA2P in terms of CO₂ absorption rate, CO₂ absorption heat, CO₂ equilibrium solubility, and mass transfer efficiency. Their reported results indicated that the equilibrium solubility of 1DAM2P solvent is greater than that of conventional amines such as MEA and MDEA. Kadiwala et al. [6] reported that 1DMA2P represents faster kinetics of CO₂ absorption compared to that of MDEA. Afkhamipour et al. [7] experimentally and theoretically calculated the physical properties of 1DMA2P solution such as CO₂ equilibrium solubility, density and viscosity. Liu et al. [8] determined the CO₂ solubility and absorption heat into 1DMA2P. They inferred that the CO₂ equilibrium solubility into 1DMA2P solution reduces as both reaction temperature and solvent concentration increases, and the CO₂ solubility enhances as the CO₂ partial pressure increases.

Gas-liquid absorption process is conventionally performed using sprayer, bubble, plated and packed columns, but the main challenge in designing and operating these columns is to intensify the mass transfer rate by providing as much contact area as possible. Another important drawback of these columns is the interdependence of the two fluid phases to be directly contacted, which may lead to problems such as foaming, flooding, emulsions and unloading. An alternative approach to overcome these disadvantages and provide substantially more contact area than conventional methods is non–dispersive contact via a membrane. Recently, hollow fiber membrane contactors (HFMC) are introduced as one of the most promising alternative to intensify the CO₂ removal by chemical absorption. The main advantage of HFMC is to make use of permeable membrane to enhance chemical absorption with equilibrium–limited chemical reactions. Also, since two fluid streams are independent in the HFMC, the available contact area remains unchanged at various flow rates. Indeed, the membrane acts as a physical barrier and allows non–dispersive gas–liquid contact. Moreover, membrane contactors present flexibility, modularity, compact size, high contact area, easy installation and low cost.

HFMC has been extensively considered both theoretically and experimentally, and interesting results have been achieved in terms of CO₂ removal from the flue gases. Cao et al. [9] studied the CO₂ removal by aqueous 1DMA2P solution in a polytetrafluoroethene HFMC. Their reported results indicated that the enhancement of amine temperature and concentration will improve the CO₂ removal efficiency. Experimental investigation by deMontigny et al. [10] showed that the overall mass transfer coefficient (K_Ga_v) in membrane contactor is significantly greater than that in the packed tower. Rangwala [11] studied and compared the CO₂ absorption into different solvent via traditional packed column and membrane module. They observed that the K_Ga_v in HFMC can be 3–9 times greater than traditional packed column. Iliuta et al. [12] concluded that under the same specific surface area and volume, the HFMCs has a higher CO₂ removal efficiency to the packed column. Also, they inferred that the CO₂ absorption can be significantly intensified with an enhancement in the specific area of membrane module. More detailed literature review is presented by Saidi et al. [13,14], Luis et al. [15], Cui and deMontigny [16], and Hillal and Ismail [17].

In this research, a two–dimensional reaction rate/kinetics model is developed to assess and analyze the CO₂ removal using aqueous 1DMA2P solution functioning under industrial relevant operating conditions. The intensification potential of the aqueous 1DMA2P solution for CO₂ absorption by application of a polypropylene HFMC is estimated and validated in comparison with other solvents such as monoethanolamine (MEA), diethanolamine (DEA), methyldiethanolamine (MDEA), piperazine (PZ) and 4-(diethylamino)-2-butanol (DEAB) solutions. Also, the impact of essential parameters on the CO₂ removal have been determined.