In today's world, there is a compelling necessity to recover and reuse greenhouse gases such as CO2. We can no longer exploit dirtier energy sources, such as fossil fuels without knowingly contributing to global warming. The ideal situation, in the short to medium term, is to build a cyclic economy using the infrastructure that already exists, and capture greenhouse gases, such as CO2 and CH4, and reuse them, thus reducing the net rate of emissions. Current-ly, many atmospheric gases are separated and recovered using cryogenic methods, a process that involves cooling gas mixtures to very low temperatures and this is extremely energy inten-sive. The energy required to cool will generate more greenhouse gases and so this energy dif-ference must be reduced. An alternative method to separate gases from the atmosphere is to trap or make the gas stick in the cavities of porous materials. This process requires much less energy, as the pores of the material are doing the work, through a process known as adsorp-tion. However, these pores must be tuned to match the sizes of the target gas molecules and this is a current hot topic in scientific research. The rational design of materials for gas separa-tion, purification and storage would create a paradigm shift in the way energy can be recycled. Adsorption-based separation on porous materials is the ideal alternative to the cryogenic-based processes, thanks to their low-energy and low-cost requirements. Adsorption-based gas sepa-ration technologies use beds of porous material through which the target gases flow. However, heating these packed beds is very energy inefficient and can take many hours to regenerate the bed for the next process cycle. Also, the porous material in these pack beds can be displaced if the system is also moved. The target gases can then by-pass the porous material and the sepa-ration becomes poor. For instance, if the packed bed is used on compressed air drying on trains, the vibration from the movement can cause the adsorbent bed to move, resulting in by-passing of the compressed air. Consequently, problems with the train's compressed air driven systems can arise.
Hollow fibres are tubular materials with an inner hole, which travels down the length of the tube and can also contain an adsorbent layer. These materials are excellent for situations where gas by-pass has to be avoided, due to vibration or changes in vehicle orientation. In this project a hollow fibre material has been formed for energy efficient gas adsorption pro-cesses. The material has an inner adsorbent layer with an outer heating layer. An electrical cur-rent is passed through the outer layer and this causes the material to heat in a process known as Joule heating. The outer layer has a positive temperature coefficient of resistance property, which means the material can regulate its own Joule heating. Therefore, the material will never overheat and is inherently safe. This heat energy is directed onto the inner adsorbent layer and the adsorbent regeneration is very energy efficient.
