Capturing CO2 by itself does not provide a solution, it subsequently either needs to be stored underground or put to use. While utilizing CO2 is a hot topic and covered extensively in academic literature, studies that provide a general yet accessible overview of different CCU options and how they would fit with a certain point source profile are rare. Therefore, this part of the MAP-IT CCU project aims to provide such an overview, informing interested parties who do not have an extensive background in the field, allowing them to start reflecting on how CCU could fit in their decarbonization trajectory.
In each case study, aspects ranging from technology over economics and policy up to an overview of recent investment projects are covered. The main purpose is to allow the reader to get familiar with these cases, and evaluate whether it may be worthwhile to explore them further. As with the CO2 capture technologies, what is most suitable as utilisation option depends on the profile of the CO2 emitter. It is therefore strongly warranted to start with the executive summary of each case study, which provides a basic overview, and then to proceed with the detailed reports of cases that are deemed to be most relevant.
Process overview
There are various ways in which CO2 can be used to manufacture polymers. A critical distinction is whether the CO2 is used as the sole carbon source, or alongside with other compounds that contain carbon. In the first case, as with e-fuels, inevitably large amounts of H2 will be required, preferably produced in a clean way via water electrolysis coupled to renewable electricity. To convert the CO2 and H2 into the target polymers, multiple technology platforms are available. The methanol-to-olefins (MTO) route is a well-known and already commercially applied (albeit to grey methanol, not e-methanol) method to produce ethylene and propylene, from which the corresponding polyolefins can be produced. The Fischer-Tropsch (F-T) route similarly is a process with a certain history, and yields fractions that are suitable for plastics manufacturing along with other fractions that can be used as fuel (e.g. diesel, kerosene). Both are complex, high temperature thermocatalytical processes. In contrast, gas fermentation can convert CO2 and H2 to polymers such as PHA at mild conditions using biocatalysts.
In the second case, CO2 can be co-polymerised with epoxides (from fossil origin) to introduce carbonate groups in the polymer structure. A good example is the production of polycarbonate polyols, which can substitute for regular polyols (without carbonate groups) that are used to make polyurethanes.
Source: Von der Assen & Bardow, Green Chem., 2014, 16, 3272
This leads to a double benefit: CO2 is taken up in the polymer, and the use of the fossil feedstock required to make a certain amount of polymer is reduced. This reaction is exothermic and hence does not require energy inputs.
Scale and CO2 purity requirements
Conventional approaches such as MTO and F-T comprise a series of unit operations, at elevated pressures and temperatures, and are normally done at very large scale to compensate for the cost of this complexity. They also generally start from high purity CO2. The gas fermentation route is quite different in the sense that high purity is not required, as microbes are generally more tolerant for impurities. For gas fermentation, no data is available on typical plant scale as it is not yet commercially applied, yet taking into account also the required electrolyser and downstream processing, small plants may not be viable.
Policy aspects
No specific policy targets or other supporting measures are currently applicable in the EU. Any CO2 sent to polymer production will still be subject to the ETS carbon tax. The critical difficulty here is that CO2 cannot be considered to be permanently stored, as there is always a chance that even after a longer period of time CO2 gets released when waste plastics get incinerated. At the same time, some applications (e.g. polyurethanes for insulation foam) have a lifetime of several decades. How to best account for this non-permanent CCU in EU policy is currently an active discussion topic.