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PtL, BtL: Competitive Solutions?

11.02.22 | Blog | By:

Synthetic liquid fuels, from gasification-synthesis of biomass, aka Biomass-to-Liquid (BtL), or e-fuels from CO2 and renewable electricity via hydrogen, aka Power-to-Liquid (PtL), are seen as one of the pathways for sustainable mobility. The latter is actually advocated by Germany in parallel with electromobility from 2035 onwards, when the EU intends to de facto ban internal combustion engines vehicles (ICEV) from new car sales, new truck sales being next on the chopping block. In the same vein, a recent study by McKinsey foresees a 280 million ton per annum demand for PtL aviation fuel by 2050.

But both biomass and renewable electricity are in high demand in a sustainable future, not only for renewable fuel production. A huge elephant was already in the room, it has made a lot of noise in 2022 in Europe, thanks to the bear from the East: natural gas (NG). Home heating and key industries do rely on it. Even in maritime transport, a sector with an ambitious and global decarbonization strategy toward 2050, shipping world leaders like MSC and CMA-CGM have just started operating NG-propelled ships, emitting 25% less CO2 than the legacy ones, running on heavy fuel-oil: large ships, to carry containers or passengers, are not built for just a few years, they remain on the seven seas much longer, several decades, actually.

Decarbonization of NG, a fossil energy, ranked a close third on a global basis, behind oil and coal, is no small task. Neither is its substitution, in households or in industry, or shipping, possibly implying that decarbonization could come as the top priority for the foreseeable future. So far, NG is not that green in Europe, with only 4.6% in biomethane content in 2020, mostly produced from anaerobic digestion of agricultural residues, if not from biomass grown on purpose, the latter attracting a lot of opposition from eco-radicals. The potential for this renewable gas, sometimes called biogas, biomethane or synthetic natural gas (SNG), is huge, adding to this that bio-methane also brings its contribution to supply security, as a local production, a concern that sure will stay for a long time in the back of our minds and can be found in the response of the European Commission to the energy crisis this year, RePower EU.

NG usage is not only significant, it is multi-sectoral. During a recent IEA Bioenergy workshop, we learnt that Austria, quite a green Member State in the EU (46% of land is covered by forests), also quite an industrialized nation, with a strong ambition of net zero emissions in 2040, is pessimistic about decarbonization of NG from domestic renewable resources:

Sure, imports can be considered, unlikely from neighbors, confronted to similar demand issues. If from across the Mediterranean Sea (in consideration: transport of hydrogen, produced from solar PV electricity in Saharan Africa or in the Middle East, could be a possibility for Europe), development of transport infrastructure, security of supply, financing of overseas investments and security thereof in the not always stable global south, to name some of the constraints, do complicate the timing. Conversely, hierarchy of usage seems logical to consider in the near-term, and, in a competitive world, economics will, to an extent, influence that hierarchy, once national security is taken care of: enters advocacy. Which brings us to technology.

Whether we consider synthetic or e-fuels or biomethane, there is a common part for the BtL, PtL, SNG pathways, upstream: production of syngas, a mix of H2 and CO, mainly, with CO2 and CH4 as companion molecules depending on the selected gasification technology. Syngas transformation can then produce biomethane, by methanation, or liquid fuels, by Fisher-Tropsch synthesis, a mature technology developed on coal and gas, or via fermentation to alcohols, a pathway in development (LanzaTech, for instance).

As for the two former, reasonably mature, pathways, methanation will produce methane and water, synthesis will produce hydrocarbons and water, from catalytically-enhanced and highly exothermic reactions. When methanation usually takes place in fairly standard fixed bed reactors, synthesis will use sophisticated reactional sections, for synthesis and product mix adjustment (hydrocracking), which can easily add half a billion dollars in capex for a production of 1,500 bpd of synthetic hydrocarbons, placing this technology nowhere close in the merit order to more standard thermochemical processes, like lipids hydrogenation (to produce renewable diesel and sustainable aviation fuel (SAF)), alcohol-to-jet SAF, or to fermentation processes, yielding ethanol for gasoline decarbonization.

With a strong demand for SNG, competition will be fierce to transform syngas into bio-molecules. Will the pathways to liquids, BtL or PtL, prevail or even get a seat in this green way remains a big question, in my opinion.

Philippe Marchand is a Bioenergy Steering Committee Member of the European Technology and Innovation Platform (ETIP).

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