Periodic Reporting for period 1 - SmartSorp (Smart Ceramic Hollow Fibers for Energy Efficient Gas and Vapour Sorption)
Période du rapport: 2019-09-01 au 2021-08-31
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.
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.
This project has produced novel positive temperature coefficient of resistivity (PTCR) BaTiO3 hollow fibers for energy efficient gas separation applications. This has been achieved by doping of the BaTiO3 powder material with lanthanum to make it electrically conductive after sintering. The doped powder was then mixed with N-methly-2-Pyrrolidone (NMP) solvent, and a polymethyl methacrylate (PMMA) polymer, and the final mixture is known as a ceramic slurry. The ceramic slurry is then passed through a spinneret, which is a type of extruder, and the slurry is formed into a hollow fiber geometry by a process known as phase inversion. The phase inversion process produces a solid polymer-ceramic material, as the solvent in the polymer mixture is removed, leaving a solid polymer-ceramic material behind, known as a green body. This method allows ceramic materials to be shaped into hollow fibre geometries in an economical way. The green body was then subject to a process known as debinding and this burns-off most of the PMMA polymer, while the hollow fibre geometry remains. At this stage the hollow fiber is very fragile, as the ceramic grains are not connected together. The material is then sintered at high temperature (1350 °C – 1400 °C) and this causes the grains to grow and coalesce, increasing the density and strength of the ceramic. Following this, the material was then subject to a process known as annealing, which involved heating the hollow fibre in air at 1175 °C. This step is vital for the formation of the PTCR mechanism and gives the material its self-regulating heating characteristics. An adsorbent zeolite layer was then grown inside the hole of the hollow fibre, known as the lumen, using a process known as hydrothermal synthesis. This layer was then tested and was found to adsorb CO2. The smart characteristics of the hollow fibre were then tested by applying an AC electrical current through the material, a process known as Joule heating. It was found that the La-doped BaTiO3 layer could self-regulate its own Joule heating and this heat energy was directed onto the inner adsorbent layer. Hence, an energy efficient gas sorption system was formed with smart heating characteristics. The outcomes of this work have been published in several high impact scientific journals and the researcher aims to present his work at a conference hosted by the European Space Agency.
This work has involved the development of a hollow fibre material that can be used in energy efficient gas separation processes. The material contains an inner adsorbent porous layer onto which a target gas molecule can stick. Once this sticking process saturates the adsorbent bed, and the pores have become full, then the gas molecules have to be removed in order for the next process cycle to begin. This can be thought of as a molecular sorting process– separating one molecule that likes to stick from another molecule, which does not like to stick. Once the molecules are separated then they can be used in other processes, such as the synthesis of chemicals. In order to regenerate the saturated adsorbent layer, this bed must be heated. This project had developed a heating layer that surrounds the adsorbent layer, which directs heat onto the bed in a very energy efficient way. The heating layer can also regulate its own heating and can be described as a smart material. Therefore, the aim of this project was to reduce the energy penalty for separating gases compared to cryogenic separation methods, which are extremely energy intensive. The hollow fibres can be integrated into compact systems and work under any orientation. This makes them useful in transport applications. Energy efficient gas separation is extremely pertinent to topics such as climate change, where CO2 has to be recovered from a variety of sources, such as emissions from flue gases and vehicles. Due to the compact nature and portability of these devices, these materials could also be used in fire and rescue respirator systems, as well as in air processing system in the aerospace and space sectors.