Available Membranes

The development of catalytic membrane reactors is limited by the availability of membranes capable of controlling the reaction environment that are stable at reaction conditions. A brief review of transport through membranes is provided and then the additional membrane requirements are summarized. Figure 4 provides a schematic of a membrane employed for the transport of a gaseous component.

Transport of a component through a solid is only possible if there are differences between the chemical potential of the component on the two faces of the solid. For gas-phase systems that operate at moderate pressures and can be considered to be ideal, transport can be described by:

Figure 4 Schematic of transport through a solid.

pressure of component i on the low pressure side and 1 is the membrane thickness.

Thus, the difference in the partial pressure of the component to be transported controls the rate of transport. A high partial pressure driving force can be produced through:

• high total pressure on the feed side

• high concentration of the component of interest on the feed side

• low total pressure on the permeate side (using a vacuum)

• very low concentration of i on the permeate side using a very high dilution ratio of sweep gas

The rate at which a component is transported through a solid is defined as the flux of the component, (eqn [1]). To facilitate the comparison of a variety of materials, the properties of the material (permeability) have been separated from the process conditions (membrane thickness, pressures and concentrations). For equivalent process conditions, the material with the highest permeability will have the fastest transport.

The selectivity of a membrane for any pair of gases (A, B) is usually defined by the term aA/B, equal to the ratio of the gas permeabilities:

where P, is the permeability of component i through the membrane, pHi is the partial pressure of component i on the high pressure side, pLi is the partial

For membrane reactors, membranes with high selectivities are required, so only the required component enters or leaves the reactor.

Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

Get My Free Ebook

Post a comment