# Synthetic fuels

The technological options for synthetic fuels in TIAM-FR encompasses 3 routes:
+ hydrogenation of CO<sub>2</sub> into methanol
+ methanaton of CO<sub>2</sub> into methane
+ Fischer-Tropsch process into a range of synthetic fuels

For routes converting CO<sub>2</sub> into synthetic fuels, several designs are implemented depending on the nature of the CO<sub>2</sub> processed and the type of hydrogen, i.e. either generated by dedicated variable renewable assets or centralized electricity. Concerning the nature of CO2, we distinguish fossil and process CO<sub>2</sub> from biogenic and atmospheric CO<sub>2</sub>. As hydrogen is not involved in the mineralization of CO<sub>2</sub>, only the nature of CO<sub>2</sub> processed in differentiated.

![CCU designs](CCU-designs.png)
Fig. 1: Different designs for CO<sub>2</sub> utiliation in TIAM-FR

As it is assumed that 90% of the CO<sub>2</sub> processed is actually converted, and residual emissions are accounted for 1% of the CO<sub>2</sub> flow in the case where fossil CO<sub>2</sub> is employed. For processes convertin CO<sub>2</sub> into synthetic fuels, capacity designs are assumed to a commercial capacity of 11.2 PJ/y (Winchester et al., 2013). All CO<sub>2</sub> utilization processes are commercially available as of 2030.

## Hydrogenation

Methanol (CH₃OH or MeOH) is an alcohol used as a fuel for transportation demands such as buses, heavy trucks, light trucks, and cars. The main process to generate methanol is to make CO<sub>2</sub> react with H<sub>2</sub>, also yielding water as a by-product:

$$
CO_2 + 3H_2 \leftrightarrow CH_3 OH + H_2O
$$

The techno-economic assumptions for this processes are taken from Zhang et al. (2019) and summarized in Table 1.

Tab. 1: Techno-economic properties of the hydrogenation process in TIAM-FR
|Properties|Units|Values|
|----------|-----|------|
|Hydrogen efficiency|J/J|1.08|
|CO<sub>2</sub> efficiency|g/J|75.4|
|CAPEX|$/GJpa|20|
|Fixed O&M|$/GJpa|0.7|
|Availability factor||90%|
|Life|years|20|
|Discount rate||8%|

The techno-economic assumptions for CO<sub>2</sub> capture can be found in sections related to [the power sector](power-sector.md), [biofuels](biofuels.md), [industry](../industry/index.md), and [direct air capture](/backstop/dac.md). The techno-economic assumptions for hydrogen supply can be found [here](hydrogen.md).  

Besides, methanol turned into gasoline through the so-called Methanol-to-Gasoline (MtG) process for which liquified petroleum gas (LPG) and electricity are co-products. Likewise, the MtG process can employ fossil-based or climate-neutral methanol. The techno-economic assumptions for this process are extrated from Hennig and Haase (2021) and summarized in Table 2:

Tab. 2: Techno-economic properties of Methanol-to-Gasoline in TIAM-FR (Henning and Haase, 2021)
|Properties|Units|Values|
|----------|-----|------|
|Gasoline yield|J/J|0.52|
|LPG yield|J/J|0.40|
|Electricity generation|J/J|0.1|
|CAPEX|$/GW|5|
|Fixed O&M|$/GW|0.04|
|Availability factor||90%|
|Life|years|15|
|Discount rate||7%|

In TIAM-FR, methanol is only modeled as an energy carrier, not as a chemical good. The energy demand for methanol as a chemical is implicitly modeled and included in the overall energy demand of the chemical industry.  

## Methanation
Methanation is a process turning CO<sub>2</sub> and H<sub>2</sub> into synthetic CH<sub>4</sub> through the following reaction:

$$
CO_2 + 4H_2 \leftrightarrow CH_4 OH + H_2O
$$

The synthetic methane can be utilized in end-use processes to substitute for natural gas. The techno-economic properties of methanation processes implemented in TIAM-FR are taken from Chauvy et al. (2021) and summarized in Table 3.

Tab. 3: Techno-economic properties of methanation processes in TIAM-FR (Chauvy et al., 2021)
|Properties|Units|Values|
|----------|-----|------|
|CO2 input|kg/GJ|50.5|
|Hydrogen input|J/J|1.2|
|Electricity consumption|J/J|0.002|
|Excess heat|J/J|0.18|
|CAPEX|$/GW|86.5|
|Fixed O&M|$/GW|6.5|
|Availability factor||90%|
|Life|years|20|
|Discount rate||8%|

## Fischer-Tropsch

The Fischer-Tropsch reaction consists in processing CO<sub>2</sub> with hydrogen in the presence of a catalyst at temperatures between 150-200°C to generate a slate of liquid hydrocarbons, generally diesel, gasoline, and kerosene. The generation shares depend on the catalyst employed. In TIAM-FR, the Fischer-Tropsch processes implemented follow the assumptions of Zang et al. (2021), as Table 4 summarizes.

Tab. 3: Techno-economic properties of Fischer-Tropsch processes in TIAM-FR (Zang et al., 2021)
|Properties|Units|Values|
|----------|-----|------|
|CO2 input|kg/GJ|50.5|
|Hydrogen input|J/J|1.2|
|Electricity consumption|J/J|0.002|
|Excess heat|J/J|0.18|
|CAPEX|$/GW|86.5|
|Fixed O&M|$/GW|6.5|
|Availability factor||90%|
|Life|years|20|
|Discount rate||8%|

The synthetic liquids supply all sectors of the economy, just like conventional fossil fuels, thus assuming for instance that synthetic kerosene is a perfect subsitute for conventional jet fuels, which is yet to be proven technically.

**References**  
Zhang, H., Wang, L., Van herle, J., Maréchal, F. & Desideri, U. Techno-Economic Optimization of CO2-to-Methanol with Solid-Oxide Electrolyzer. Energies 12, 3742 (2019).  
Hennig, M. & Haase, M. Techno-economic analysis of hydrogen enhanced methanol to gasoline process from biomass-derived synthesis gas. Fuel Processing Technology 216, 106776 (2021).  
Chauvy, R., Verdonck, D., Dubois, L., Thomas, D. & De Weireld, G. Techno-economic feasibility and sustainability of an integrated carbon capture and conversion process to synthetic natural gas. Journal of CO2 Utilization 47, 101488 (2021).  
Zang, G., Sun, P., Elgowainy, A. A., Bafana, A. & Wang, M. Performance and cost analysis of liquid fuel production from H2 and CO2 based on the Fischer-Tropsch process. Journal of CO2 Utilization 46, 101459 (2021).