Decarbonisation Technology - February 2022 Issue

EOR EGR Enhanced recovery of oil & gas

Methane via DRM Methanol via catalysis Urea via ammonia Conversion to chemical feedstocks

Polymers & co-polymers Rubbers, polymer blends Direct synthesis of CO based polymers

CO-Utilisation processes

Carbonates Mineralisation

Figure 2 CO 2 utilisation processes, Adapted from Al-Mamoori et al., 2017

CO 2 utilisation processes Al-Mamoori et. al identified a number of potential options for the utilisation of captured CO 2 (see Figure 2 ) (Al-Mamoori, et al ., 2017). The scheme includes four main processes: enhanced recovery of oil and gas, chemical conversion, mineralisation, and desalination. As desalination does not lead to the removal of CO 2 , it is not discussed further here. Enhanced oil recovery (EOR) and enhanced gas recovery (EGR) are established uses of captured CO 2 (Alvarado & Manrique, 2010). In the EOR process, CO 2 is injected into the depleted oil wells, where it mixes with the oil. The mixture is subsequently pumped to the surface and any excess CO 2 recycled to repeat the process, which ultimately leads to more barrels of oil being recovered. In chemical conversion, the CO 2 is converted into a number of different products or intermediate materials, such as methane, methanol (Zakaria & Kamarudin, 2016), syngas, and other alkanes (Zhou, et al., 2019). Two main processes are CO 2 hydrogenation (Yang, et al. , 2017) and the dry reforming of methane (DRM) for the production of hydrocarbon fuels (Aramouni, et al. , 2018). In the latter case, the high operating temperatures of the process result in difficulties in finding an appropriate catalyst for the reaction. CO 2 can also be converted into a range of fine chemicals, including urea, inorganic carbonates, polyurethane, acrylic acid, acrylate, polycarbonates, and alkylene carbonates. Further CCU processes in this scheme include mineralisation into carbonates, which unfortunately has a number of chemical process challenges and progress is slow. A range of technologies for the synthesis of CO 2 based polymers (see Figure 2 ), including co- polymers and polymer blends, such as CO 2 -based

aliphatic polycarbonates and poly (propylene carbonates), are being developed (Muthuraj & Mekonnen, 2018). Another example is the synthesis of elastomers through the reaction of CO 2 with propylene oxide and maleic anhydride, where resulting cross-linkable polyether carbonate polyols are combined with isocyanates for conversion into CO 2 -based rubbers, as a novel class of polymers (Meys, et al., 2019). Other processes include the use of CO 2 as a feedstock for the production of oxalic and glycolic acid-based polyesters (Murcia Valderrama , et al., 2019). These synthetic pathways are still at the exploratory stage of development. A recent assessment of the potential, scale, and cost for a selection of 10 CO 2 utilisation pathways is summarised in Figure 3 (Adlen & Hepburn, 2019). The CO 2 utilisation pathways can be characterised as ‘cyclic’, ‘closed’, and ‘open’. For instance, many conventional industrial utilisation pathways, such as CO 2 -based fuels and chemicals, tend to be ‘cyclic’ ( Figure 3 : light green arrows): they move carbon through industrial systems over timescales of days, weeks, or months. Such pathways do not provide net CO 2 removal from the atmosphere, but they can reduce emissions via industrial CO 2 capture that displaces fossil fuel use. By contrast, ‘closed’ pathways ( Figure 3 : red arrows) involve utilisation and near-permanent CO 2 storage, such as in the lithosphere (via CO 2 -EOR or BECCS) in the deep ocean or in mineralised carbon in the built and natural environments. Finally, ‘open’ ( Figure 3 : dark green arrows) pathways, based in biological systems, are characterised by large removal potential and storage in ‘leaky’ natural systems, such as biomass and soil, with the risk of large-scale flux back to the atmosphere. All 10 CO 2 utilisation pathways offer some kind of economic