The capture of CO2 from stationary sources of emission is one of the fundamental approaches of climate change mitigation. One of the main obstacles in the way of implementing many of the introduced technologies for CO2 capture from stationary sources of emission is the associated high cost. For this purpose, dynamic research is focusing on the development of low cost CO2 capture technologies. Knowing that two of the highest cost components of CO2 capture are the capture and the regeneration steps, many research studies are focusing on improving and optimizing CO2 capture and sorbent regeneration to reduce their associated costs. This can be achieved through increasing the amount of CO2 captured by a sorbent, and regenerating the sorbent without using excessive energy.
In this context, this thesis targeted the improvement of CO2 adsorption capacity of electrically conductive activated carbon by combining it with materials with a higher adsorption capacity, namely; zeolite type-A and layered double hydroxide. The resulting composite materials can be directly heated and regenerated using Joule effect, potentially reducing the costs of material regeneration using electrical swing adsorption.
In this thesis, four types of electrically conductive composite CO2 sorbents were synthesised and characterized: carbonized Purolite® MN200/zeolite NaA composite; carbon supported zeolite NaA composite (zeolite NaA/AC), carbon supported dual-cation containing zeolite type-A composite (ZMG/AC), and carbon supported layered double hydroxide composite (LDH/AC).
For the first composite material, a new method was explored for the synthesis of carbonized Purolite® MN200/zeolite NaA composite, where zeolite NaA was synthesised inside the pores of phenolic resin. After synthesis, the composite material was carbonized and activated. The resulting composite material has a unique spherical carbon beads cluster morphology that is expected to reduce pressure drop during CO2 capture. Additionally, the material can easily be shaped and customized according to the shape of the reactor or application requirements. Improving the porosity, mechanical strength, and electrical conductivity of the developed material is expected to make it a suitable material for CO2 capture using electric swing adsorption.
Activated carbon beads from MatrixCarbon™ were chosen to be the support material for zeolite NaA, dual-cation containing zeolite type-A (ZMG), and layered double hydroxide (LDH), to synthesise the remaining three composite materials. MatrixCarbon™ activated carbon beads were chosen due to their high porosity and superior electric conductivity.
Scanning Electron Microscopy analysis of the internal formation of the composite materials showed the successful growth of zeolites and LDH in the macropores of the carbon beads. The ion exchange process with magnesium in zeolite NaA proved that the material’s CO2 adsorption properties can be modified to work under different sets of operation temperatures.
Energy Dispersive X-Ray and X-Ray Diffraction analyses confirmed the formation zeolite NaA, dual-cation containing zeolite type-A, and LDH in the pores of the synthesised composite materials. The amounts of impregnated zeolites or LDH in the composite material was found to range between 4.5 and 6.0 wt% in the composite material. Brunauer-Emmett-Teller (BET) analysis showed that zeolite NaA/AC, ZMG/AC, and LDH/AC composite materials maintained high surface areas of 911, 917, and 1043 m2/g respectively. Temperature Programmed Desorption showed that combining activated carbon with zeolites or LDH crystals not only increases CO2 adsorption capacity but also decreases the desorption temperature of CO2, potentially increasing the cost effectiveness of the materials.
Flux response technology was used to investigate CO2 adsorption by the synthesised materials at isothermal and non-isothermal temperatures. The technique proved to be an effective tool for the measurement of CO2 adsorption in solid sorbents. This was demonstrated by the ability to detect the non-linear CO2 adsorption in zeolite NaA and LDH at increasing temperatures (22, 100, 200, and 300 °C), which was reported in previous studies.