Chemical absorption of carbon dioxide with asymmetrically heated polytetrafluoroethylene membranes

doi:10.1016/j.jenvman.2010.08.014

Journal of Environmental Management

Volume 92, Issue 4, April 2011, Pages 1083-1090

https://doi.org/10.1016/j.jenvman.2010.08.014 Get rights and content

Abstract

In this study, the absorption of carbon dioxide using an absorbent composed of 2-amino-2-methyl-l-propanol (AMP) + monoethanolamine (MEA) + piperazine (PZ) in asymmetric and symmetric polytetrafluoroethylene (PTFE) membrane contactors was investigated. Experiments were conducted using various gas flow rates, liquid flow rates, and absorbent blends. CO₂ recovery increased with increasing liquid flow rates. The mean pore size of PTFE membrane reduced via heating treatment. An asymmetric membrane had a better CO₂ recovery than a symmetric membrane. For the asymmetric membrane, placing the smaller pore-size side of the membrane in contact with the liquid phase, reduced the level of wetting of the membrane. The membrane mass transfer coefficient and durability of the PTFE membrane were enhanced by asymmetrically heating.

Introduction

Carbon dioxide is the most heavily emitted anthropogenic greenhouse gas and is believed to be responsible for increases of the earth’s surface temperature (Herzog et al., 2000). Half of all CO₂ emissions are from fossil fuel-burning electric power plants (Desideri and Paolucci, 1999). Therefore, the development of separation processes for removal and recovery of CO₂ from these emission sources is greatly needed. In general, bubble columns, packed towers, venturi scrubbers, and/or sieve trays can be used to remove CO₂ from process streams. The best-known commercial process for CO₂ separation is the packed-column system. However, because of the disadvantages of the packed-column system, which include flooding, channeling, and the need for large-scale equipment, new technologies are needed.

Gas absorption membrane (GAM) processes are an alternative CO₂ removal technique. Hollow fiber membrane contactors (HFMCs) offer a much larger contact area per unit volume compared to tray and/or packed columns. They have the advantages of no flooding, no entrainment, and no foaming-limited flow rate restrictions (Rangwala, 1996, Gabelman and Hwang, 1999). However, the additional mass transfer resistances of membranes limit the CO₂ absorption rate in the membrane contactor module, even though the interfacial area of the membrane is greater than that of conventional absorbers (Li and Chen, 2005). Therefore, minimization of the membrane mass transfer resistance is an important goal in gas absorption processes that use membrane contactors. It is preferable to use hydrophobic membranes for CO₂ absorption processes due to the fact that they display fewer wetting and swelling phenomena.

PTFE is considered one of the most suitable materials due to its high hydrophobicity. Yeon et al. (2003) investigated CO₂ absorption in poly (vinylidene fluoride) (PVDF) and PTFE hollow-fiber membranes using a single absorbent monoethanolamine (MEA). Kumar et al. (2002) studied CO₂ capture from dilute gas streams using a novel absorbent called CORAL in a PTFE membrane contactor. Kim and Yang (2000) used aqueous alkanolamine solutions as absorbents to separate CO₂-N₂ mixtures in PTFE hollow fiber membrane contactors. However, the broad pore size distribution and larger pore size of commercial PTFE restrict its application in CO₂ absorption. It is difficult to control the pore size of PTFE membranes, though several methods of control have been reported, including heating, plasma deposition, and sheet/film rolling and stretching (Kitamura et al., 1999, Kitamura et al., 2000). The sheet/film rolling and stretch process is the most economical method of production. Highly permeable PTFE membranes have been made with this technique (Kitamura et al., 1999, Kitamura et al., 2000, Kurumada et al., 1998).

The success of GAM technology is highly dependent on the resistance and wetting of the membrane. In this study, the sheet/film rolling and stretch process was adopted to form a symmetric PTFE membrane, and an asymmetrically heating method was applied to produce an asymmetric PTFE membrane. CO₂ recovery using an aqueous blended alkanolamines solution as an absorbent with various PTFE membranes in a plate flat-membrane contactor was investigated. The effects of liquid and gas flow rates on CO₂ recovery and absorption fluxes were examined. The mass transfer resistances, wetting, and durability of PTFE membranes were also evaluated.

Section snippets

Film model

Mass transfer between gas and liquid through a flat-plate membrane contactor occurs in three places: the gas film, the membrane, and the liquid film (Yeon et al., 2003). The CO₂ flux, J (kmol m⁻² s⁻¹), can be expressed by Eq. (1): $\begin{array}{l} J = K_{L} (\frac{P_{g}}{H_{e}}) = k_{g} (P_{g} - P_{m}) \\ = (\frac{k_{m}}{R T}) (P_{m} - P_{i}) = k_{L} E (\frac{P_{i}}{H_{e}}) \end{array}$ where k_L, k_m, and k_g are the mass transfer coefficients of the liquid phase (ms⁻¹), membrane (ms⁻¹), and gas phase (kmol s⁻¹ m⁻² kPa⁻¹), respectively; K_L is an overall mass transfer coefficient (m s⁻¹); P_g, P_i, and P_m, are

Materials

The piperazine (PZ), MEA, and 2-amino-2-methyl-l-propanol (AMP) were purchased from Aldrich Chemicals Co. The various pore sizes and symmetric and asymmetric PTFE membranes were made by the Research and Development Center for Membrane Technology (CMT). The preforming and paste extrusion, stretching and asymmetric heating processes were described in our previous study (Huang et al., 2008). Details of the membranes are listed in Table 1. All chemicals were used without any further purification.

Asymmetric heating process

The characteristic of PTFE membranes

A symmetric porous PTFE membrane was formed after the extrudate passed through the rolling and two-dimensional stretching process. The SEM image of Fig. 2(a) showed the symmetric membrane surface, it can be observed that the pores were reticular structures, which resulted in higher membrane porosity (0.85 ± 0.03). The symmetric membrane was passed the asymmetrically heating system at various heating temperature (260, 340 °C). Fig. 2(b) and (c) showed the 260, 340 °C-heated membrane surfaces,

Conclusions

The absorption of carbon dioxide using an absorbent composed of APM + MEA + PZ in asymmetric and symmetric PTFE membrane contactors was investigated. CO₂ recovery and absorption fluxes increased with increasing liquid flow rates. Although the asymmetric membrane had a slightly better CO₂ recovery than the symmetric membrane, the membrane mass transfer coefficient, the operational stability, and the durability were enhanced via asymmetrically heating. So it is a feasible and easy method to

Acknowledgement

The current research is supported by The Center-of-Excellence Program on Membrane Technology from the Ministry of Education and the project of the specific research fields in the CYCU, Taiwan and National Science and Technology Program – Energy, National Science Council.

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Chemical absorption of carbon dioxide with asymmetrically heated polytetrafluoroethylene membranes

Abstract

Introduction

Section snippets

Film model

Materials

Asymmetric heating process

The characteristic of PTFE membranes

Conclusions

Acknowledgement

Diffusion

Using polypropylene and polytetrafluoroethylene membranes in a membrane contactor for CO2 absorption

J. Memb. Sci.

Performance modeling of a carbon dioxide removal system for power plants

Energ. Convers. Manage.

Hollow fiber membrane contactors

J. Memb. Sci.

Diffusion of vapors into air streams

Ind. Eng. Chem.

Capturing greenhouse gases

Sci. Am.

Pore size control of PTFE membranes by stretch operation with asymmetric heating system

Desalination

Characteristics of porous polycarbonate membrane with polyethylene glycol in supercritical CO2 and effect of its porosity on tearing stress

J. Supercrit. Fluids

Absorption of carbon dioxide through hollow fiber membranes using various aqueous absorbents

Sep. Purif. Technol.

Formation mechanism of porous structure in polytetrafluoroethylene (PTFE) porous membrane through mechanical operations

Polym. Eng. Sci.

Morphology change in polytetrafluoroethylene (PTFE), porous membrane caused by heat treatment

Polym. Eng. Sci.

Using polypropylene and polytetrafluoroethylene membranes in a membrane contactor for CO₂ absorption

Characteristics of porous polycarbonate membrane with polyethylene glycol in supercritical CO₂ and effect of its porosity on tearing stress