CO2 Absorption in a Minimodule Membrane Contactor

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G. Pantoleontos, S. P. Kaldis, D. Koutsonikolas, P. Grammelis, and G. P. Sakellaropoulos

18.1 Introduction

Undesirable species such as CO2 which is usually encountered in a coal upgrading process product gas is considered to be one of the major contributors to the global warming problem via the greenhouse effect. In fact, half of the anthropogenic CO2 emissions are produced by fossil fuels in industry and power plants (Desideri and Paolucci, 1999). Unless major policy changes and technological innovations take place, future concentrations of CO2 will continue to increase largely, mainly as a result of fossil fuel uses in transport, heating, and power generation (Wuebbles and Jain, 2001). Therefore, reduction of carbon dioxide (CO2) emissions has become an international priority, requiring the introduction of efficient and flexible technologies, capable of operating over a wide range of concentration levels and volumetric flows.

Hollow fiber membrane contactors appear as a promising alternative to conventional equipment, such as packed columns, since they are flexible, modular, and energy-efficient devices with a high specific surface area (known a priori) (Mavroudi et al., 2003). Some possible applications for the use of membrane gas absorption are listed in Table 18.1 (Klaasen et al., 1998).

Membrane gas absorption is based on a gas-liquid contact across a hydrophobic membrane. In this manner, gas-liquid membrane contactors can also be effectively applied to carbonation of beverages, nitrogenation of beer to provide a dense foam head, oxygen removal in semiconductor industry for the production of ultra-pure water, and ozonation for water treatment (Drioli et al., 2005). The principle of these devices is that the membrane forms a permeable barrier between the liquid and the gas phase and does not act selectively for one gas species over the other. The gas preferentially fills the hydrophobic membrane pores and meets the liquid at the opposite side of the membrane. The liquid phase pressure should be slightly higher than that of the gas phase to prevent dispersion of gas bubbles into the liquid.

I. Dincer et al. (eds.), Global Warming, Green Energy and Technology,

DOI 10.1007/978-1-4419-1017-2_18, © Springer Science+Business Media, LLC 2010

As long as the excess aqueous solution pressure is less than the breakthrough pressure of the membrane the solution does not penetrate the pores and the gas/liquid interface is immobilized at the pore mouth of the membrane on the solution side. As the membrane is non-selective, the chemistry of the separation is the same as for conventional equipment. The choice of a suitable combination of absorption liquid, membrane characteristics, and operation mode determines the selectivity of the process (Mavroudi et al., 2003).

Table 18.1 Applications for the use of membrane gas absorption (Klaasen et al., 1998).

SO2, HCl, CO2, NO,

From flue gases

H2O, H2S, CO2, Hg

From natural/landfill gas/biogas

O3, SO2, NO,, VOC

From indoor air

NH3, H2S, CO2

From off-gases

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