The primary objective of this study was to address the lack of understanding of the commercial- scale implementation of novel CO2 based carbon nanomaterial (CNM) production and its comparison with status quo CNM production processes using unsustainable fossil resources. To accomplish this objective, first, a literature review was performed on the status quo commercial- scale CNM production, the lab-scale CO2 based processes and the CNM market. In regards to the status quo processes, the literature review yielded mainly chemical vapor deposition (CVD) processes of carbon nanotubes (CNTs) and graphene production. With respect to the lab scale CO2 based processes, the literature review involved categorising the identified processes into four different approaches based on their working principles - CO2 based CVD, molten salt based electrochemical CO2 reduction, liquid metal catalyst aided CO2 reduction and metal reductant enabled CO2 reduction. With regards to the CNM market, CNT materials were found to have the highest market share followed by that of graphene. Startup spinoffs working on the graphene and CNT production from CO2 were identified with origins to university-based research groups.

Following such literature review, a framework was developed to select one process each from the status quo CVD processes and the novel CO2 based processes, which produced comparable CNM. This framework was applied to the processes obtained from the literature review, which led to the selection of a methane-based CVD process and a molten salt-based electrochemical CO2 reduction process for small-diameter multi-walled (MW) CNT production. The methane-based CVD process involved the use of Ni-Mo catalyst on MgO support and high-temperature operating condition of 975°C. The molten salt-based electrochemical CO2 reduction process involved the use of Ni and steel electrodes, pure molten Li2CO3 electrolyte and high-temperature operating condition of 750°C. These selected processes were designed and simulated in Aspen Plus at a commercial-scale production level of 5000 tonnes per operating year. The mass balance, energy balance, and equipment cost data obtained from the simulations were used to assess the technical, economic, and environmental performance of the ex-ante CO2 based production process and the status quo CVD production process.

The technical performance assessment involved the estimation of resource intensity and energy efficiency indicators of the two processes, wherein the CVD process outperformed the electrochemical process in both indicators. The economic performance assessment involved the estimation of total capital investment, operational expenditure, net present value, and payback period. The CVD process performed better than the electrochemical process in all the indicators except total capital investment. Both processes indicated positive net present values and short payback periods, indicating the realisation of commercial scale plants of both processes to be profitable. The environmental performance assessment was carried out using the life cycle assessment methodology in the CMLCA software. The climate change impact indicators at scope 1 and 2 levels along with the net avoided impact from using CO2 were estimated using the CML 2001 impact assessment family. The electrochemical process was shown to perform considerably better than the CVD process in all the climate change impact indicators. Overall, the technical and economic performance of the CVD process was better than that of the electrochemical process. However, the environmental performance of the electrochemical process was shown to outperform that of the CVD process.

The limitations associated with modeling decisions taken in the two processes and with the uncertainty associated with the lack of data were highlighted. Further, the relevance of this study was discussed with respect to the industrial symbiosis potential of using waste CO2 from industries leading to GHG emission reduction and subsequent deceleration of climate change impacts. Finally, future potential studies were highlighted that could build on the research and insights generated in this study. One of these studies involved a case study on the implementation of a commercial-scale electrochemical process for MWCNT production in Port of Rotterdam region. Another study involved a techno-economic and environmental assessment of atmospheric CO2 capture and conversion to carbon nanomaterials for applications that can potentially achieve net negative emissions.