3.5 Gas-to-liquids conversion

One future means of processing the CO2 produced from high-CO2 gas discoveries is to convert the raw gas stream into synthetic crude oil ("syncrude") in a "gas-to-liquids" ("GTL") process. Syncrude is essentially light crude oil that can be upgraded into naphtha, kerosene and diesel. One new version of GTL technology reforms methane with CO2 and steam to produce "syngas" (carbon monoxide and hydrogen). The technology can be applied to the development of high-CO2 gas fields [34] and so a brief review of its potential is appropriate for this report.

The syngas produced by the CO2/steam reforming process is converted into syncrude in a Fischer-Tropsch process. The process is made possible by proprietary and special noble metal catalysts. The produced syncrude is upgraded by conventional refinery processes into common refinery products (naphtha, kerosene, and diesel).

A review of the process initially suggested that CO2 emissions from high-CO2 gas developments might be significantly reduced. The process does not require the CO2 to be removed from the feed gas. The CO2 contained in the raw gas potentially can be converted to GTL products. Instead of reforming methane with oxygen and steam, as in conventional GTL processes, the required syngas is made by reacting the CO2 component of the raw gas with the methane component in the presence of steam.

Further review of the published technical information [35] shows that when there is 40% CO2 in the raw gas feed, only 66% of the carbon entering the plant is transferred to the GTL products sold to the customer. For an equivalent LNG production option, 51% of the carbon is transferred to the customer in the LNG product. Therefore, not all the carbon is transferred to the customer. The loss of carbon mass across the process manifests itself as CO2 emissions. If a hypothetical future technology enabled close to 100% conversion of feed carbon content (produced by reforming methane with CO2 and steam) into syncrude, then CO2 emissions would be almost eliminated from the production facilities of high-CO2 gas discoveries.

Our simple analyses suggest that CO2 emissions from this CO2/steam reforming GTL process are 15% lower than from an LNG plant of the same capacity that requires the total removal of CO2 from the raw high-CO2 gas prior to liquefying the methane. However, the GTL process inevitably emits CO2 which must either be emitted to the atmosphere (or subsequently captured and stored).

Appendix 2 shows our analysis of the published GTL process assuming that the CO2 is 40% of the raw gas by volume.

From the perspective of reducing CO2 emissions, GTL production cannot be compared to CO2 storage in saline formations or depleted oil or gas fields. GTL basically converts hydrocarbons into different energy forms, namely liquids. The liquids are ultimately burned and therefore cause CO2 emissions unless they are captured and stored.