2 ms·

This is true but burning hydrocarbons is always going to be a dirty business. CO2 isn't the only nasty thing that comes out of a tailpipe. Theoretically impro

by mulmen 3y ago

This is true but burning hydrocarbons is always going to be a dirty business. CO2 isn't the only nasty thing that comes out of a tailpipe. Theoretically improvements can be made with synthetic hydrocarbon fuels but you're not going to collect and resynthesize 100% of tailpipe emissions. With an EV the only harmful emissions are tires and brake pads. Cleaning up the electrical grid is also a lot more attainable given current technology than scaling up synthetic hydrocarbon production. If a car has an estimated lifespan of say 20 years then I am more confident in achieving cleaner grid power than I am in clean synfuels in that lifetime. There is also the matter of where you live. Some grids are already very clean and so the EVs that operate there really are low or even zero tailpipe emission. I am curious how a synfuel ICE vehicle compares to an EV in terms of energy per distance. How much energy does it take to synthesize the fuel?

dredmorbius 3y ago
Largely agreed, though let's also note that over the long term, the principle concern is CO2 emissions. Of the secondary emissions of combustion, most of those can be controlled through ensuring the purity of the fuel mix, and if you're synthesizing the fuel in the first place, you can ensure that those components aren't present, notably sulfur and other contaminants. That still leaves partially-combusted hydrocarbons (where fuel burn is too lean and/or cold), NOx emissions (where fuel burn is too hot, and the nitrogen comes from the atmosphere itself), carbon monoxide (partial combustion, again), and ozone. Those can all be mitigated to some extent through engine, combustion, and emissions controls, though there will always be some pollutants. My understanding is that the round-trip efficiency of electricity-to-fuel synfuels based on seawater-sourced carbon is about 50-60% in the fuel synthesis, and about 25--30% for the utilisation (Carnot efficiencies are again a weak point), for a round-trip of as low as 12.5% to a high perhaps of 20%. That is admittedly not great, but what you do gain is an extremely energy-dense fuel that transports well and stores indefinitely. (Fossil fuels themselves are tens to hundreds of millions of years old.) Where those characteristics are desireable, there's simply nothing else which provides equivalent characteristics. The fuels are also remarkably non-toxic (contra ammonia), non-corrosive (contra methanol), at heavier weights non-flammable (ironic in a fuel), certainly non-explosive (contra hydrogen). I have a feeling that they'll be with us for some time yet to come.
- mulmen 3y ago
  Agreed. Hydrocarbon fuel is going to be hard to get rid of entirely. Especially in applications where energy density is important. But beyond aerospace I’m not sure what those applications actually are. Once (if?) we start accounting for actual costs the more energy efficient option should win out just based on economics. Is seawater sourced carbon actually carbon neutral? I always imagined the neutrality of synfuel relying on atmospheric carbon. I know the ocean absorbs some but is it enough to not be adding CO2 to the atmosphere? And if not then whats the energy efficiency of atmospheric carbon captured synfuels?
  - dredmorbius 3y ago
    CO2 in seawater is in equilibrium with that in the atmosphere, so there's a constant exchange, and the ocean is a primary (short-term) sink of CO2. The advantage of sourcing CO2 from seawater as opposed to the atmosphere is that the energy cost of doing so is far lower. That's a key message (unsure if it's an original finding) of 2010s USNRL research by Willauer et al I'd looked at when it made news a ways back. <https://web.archive.org/web/20230604174145/https://old.reddit.com/r/dredmorbius/comments/22k71x/us_navy_electricitytofuel_synthesis_papers_and/ https://web.archive.org/web/20230604174145/https://old.reddi...> - "The Feasibility and Current Estimated Capital Costs of Producing Jet Fuel at Sea Using Carbon Dioxide and Hydrogen". Heather D. Willauer, Dennis R. Hardy, Frederick W. Williams. Navy Technology Center for Safety and Survivability, Chemistry Division. September 29, 2010. NRL/MRi6180--10-9300 <https://web.archive.org/web/20230604174145/http://www.dtic.mil/get-tr-doc/pdf?AD=ADA539765 https://web.archive.org/web/20230604174145/http://www.dtic.m...> - "Extraction of Carbon Dioxide from Seawater by an Electrochemical Acidification Cell Part I--Initial Feasibility Studies". Felice DiMascio, Heather D. Willauer, Dennis R. Hardy, M. Kathleen Lewis, Frederick W. Williams. Navy Technology Center for Safety and Survivability, Chemistry Division. July 23, 2010. NRL/MR/6180--10-9274 <https://web.archive.org/web/20230604174145/http://www.dtic.mil/get-tr-doc/pdf?AD=ADA544002 https://web.archive.org/web/20230604174145/http://www.dtic.m...> - "Extraction of Carbon Dioxide from Seawater by an Electrochemical Acidification Cell Part II--Laboratory Scaling Studies eather D. Willauer". Heather D. Willauer, Felice DiMascio, Dennis R. Hardy, M. Kathleen Lewis, Frederick W. Williams. Navy Technology Center for Safety and Survivability, Chemistry Division. April 11, 2011. NRL/MR/6180--11-9329 <https://web.archive.org/web/20230604174145/http://www.dtic.mil/get-tr-doc/pdf?AD=ADA544072 https://web.archive.org/web/20230604174145/http://www.dtic.m...> - "Extraction of Carbon Dioxide and Hydrogen from Seawater by an Electrochemical Acidification Cell Part III: Scaled-up Mobile Unit Studies (Calendar Year 2011)". Heather D. Willauer, Dennis R. Hardy, Frederick W. Williams, Felice DiMascio. May 30, 2012. NRL/MR/6300--12-9414 <https://web.archive.org/web/20230604174145/http://www.dtic.mil/get-tr-doc/pdf?AD=ADA565466 https://web.archive.org/web/20230604174145/http://www.dtic.m...> - "Extraction of Carbon Dioxide and Hydrogen from Seawater by an Electrochemical Acidification Cell Part IV: Electrode Compartments of Cell Modified and Tested in Scaled-Up Mobile Unit". Heather D. Willauer, Dennis R. Hardy, Frederick W. Williams, Felice DiMascio. September 3, 2013. NRL/MR/6300--13-9463 <https://web.archive.org/web/20230604174145/http://www.dtic.mil/get-tr-doc/pdf?AD=ADA589263 https://web.archive.org/web/20230604174145/http://www.dtic.m...> Other and earlier research: <https://web.archive.org/web/20230601122020/https://old.reddit.com/r/dredmorbius/comments/28nqoz/electrical_fuel_synthesis_from_seawater_older/ https://web.archive.org/web/20230601122020/https://old.reddi...>

by mulmen 3y ago

dredmorbius 3y ago

Largely agreed, though let's also note that over the long term, the principle concern is CO2 emissions. Of the secondary emissions of combustion, most of those can be controlled through ensuring the purity of the fuel mix, and if you're synthesizing the fuel in the first place, you can ensure that those components aren't present, notably sulfur and other contaminants. That still leaves partially-combusted hydrocarbons (where fuel burn is too lean and/or cold), NOx emissions (where fuel burn is too hot, and the nitrogen comes from the atmosphere itself), carbon monoxide (partial combustion, again), and ozone. Those can all be mitigated to some extent through engine, combustion, and emissions controls, though there will always be some pollutants. My understanding is that the round-trip efficiency of electricity-to-fuel synfuels based on seawater-sourced carbon is about 50-60% in the fuel synthesis, and about 25--30% for the utilisation (Carnot efficiencies are again a weak point), for a round-trip of as low as 12.5% to a high perhaps of 20%. That is admittedly not great, but what you do gain is an extremely energy-dense fuel that transports well and stores indefinitely. (Fossil fuels themselves are tens to hundreds of millions of years old.) Where those characteristics are desireable, there's simply nothing else which provides equivalent characteristics. The fuels are also remarkably non-toxic (contra ammonia), non-corrosive (contra methanol), at heavier weights non-flammable (ironic in a fuel), certainly non-explosive (contra hydrogen). I have a feeling that they'll be with us for some time yet to come.

mulmen 3y ago
Agreed. Hydrocarbon fuel is going to be hard to get rid of entirely. Especially in applications where energy density is important. But beyond aerospace I’m not sure what those applications actually are. Once (if?) we start accounting for actual costs the more energy efficient option should win out just based on economics. Is seawater sourced carbon actually carbon neutral? I always imagined the neutrality of synfuel relying on atmospheric carbon. I know the ocean absorbs some but is it enough to not be adding CO2 to the atmosphere? And if not then whats the energy efficiency of atmospheric carbon captured synfuels?
- dredmorbius 3y ago
  CO2 in seawater is in equilibrium with that in the atmosphere, so there's a constant exchange, and the ocean is a primary (short-term) sink of CO2. The advantage of sourcing CO2 from seawater as opposed to the atmosphere is that the energy cost of doing so is far lower. That's a key message (unsure if it's an original finding) of 2010s USNRL research by Willauer et al I'd looked at when it made news a ways back. <https://web.archive.org/web/20230604174145/https://old.reddit.com/r/dredmorbius/comments/22k71x/us_navy_electricitytofuel_synthesis_papers_and/ https://web.archive.org/web/20230604174145/https://old.reddi...> - "The Feasibility and Current Estimated Capital Costs of Producing Jet Fuel at Sea Using Carbon Dioxide and Hydrogen". Heather D. Willauer, Dennis R. Hardy, Frederick W. Williams. Navy Technology Center for Safety and Survivability, Chemistry Division. September 29, 2010. NRL/MRi6180--10-9300 <https://web.archive.org/web/20230604174145/http://www.dtic.mil/get-tr-doc/pdf?AD=ADA539765 https://web.archive.org/web/20230604174145/http://www.dtic.m...> - "Extraction of Carbon Dioxide from Seawater by an Electrochemical Acidification Cell Part I--Initial Feasibility Studies". Felice DiMascio, Heather D. Willauer, Dennis R. Hardy, M. Kathleen Lewis, Frederick W. Williams. Navy Technology Center for Safety and Survivability, Chemistry Division. July 23, 2010. NRL/MR/6180--10-9274 <https://web.archive.org/web/20230604174145/http://www.dtic.mil/get-tr-doc/pdf?AD=ADA544002 https://web.archive.org/web/20230604174145/http://www.dtic.m...> - "Extraction of Carbon Dioxide from Seawater by an Electrochemical Acidification Cell Part II--Laboratory Scaling Studies eather D. Willauer". Heather D. Willauer, Felice DiMascio, Dennis R. Hardy, M. Kathleen Lewis, Frederick W. Williams. Navy Technology Center for Safety and Survivability, Chemistry Division. April 11, 2011. NRL/MR/6180--11-9329 <https://web.archive.org/web/20230604174145/http://www.dtic.mil/get-tr-doc/pdf?AD=ADA544072 https://web.archive.org/web/20230604174145/http://www.dtic.m...> - "Extraction of Carbon Dioxide and Hydrogen from Seawater by an Electrochemical Acidification Cell Part III: Scaled-up Mobile Unit Studies (Calendar Year 2011)". Heather D. Willauer, Dennis R. Hardy, Frederick W. Williams, Felice DiMascio. May 30, 2012. NRL/MR/6300--12-9414 <https://web.archive.org/web/20230604174145/http://www.dtic.mil/get-tr-doc/pdf?AD=ADA565466 https://web.archive.org/web/20230604174145/http://www.dtic.m...> - "Extraction of Carbon Dioxide and Hydrogen from Seawater by an Electrochemical Acidification Cell Part IV: Electrode Compartments of Cell Modified and Tested in Scaled-Up Mobile Unit". Heather D. Willauer, Dennis R. Hardy, Frederick W. Williams, Felice DiMascio. September 3, 2013. NRL/MR/6300--13-9463 <https://web.archive.org/web/20230604174145/http://www.dtic.mil/get-tr-doc/pdf?AD=ADA589263 https://web.archive.org/web/20230604174145/http://www.dtic.m...> Other and earlier research: <https://web.archive.org/web/20230601122020/https://old.reddit.com/r/dredmorbius/comments/28nqoz/electrical_fuel_synthesis_from_seawater_older/ https://web.archive.org/web/20230601122020/https://old.reddi...>