Power to Methane

[mblakele]

NB: This discussion started in another thread and in another sub, but I felt we were getting far afield from the thread topic. Since I contributed to that, I took it on myself to start a new thread. Anyway I've been wanting a dedicated thread for power-to-methane discussion.

The story so far:

So my outsider view of things - it looks like we've got much more widespread systems for managing liquid methane (roughly the same as natural gas) than we do hydrogen, it's less dangerous to be working with at all - so why not be using the excess renewable energy to manufacture liquid methane than hydrogen?

I also like the idea of turning excess renewable energy into CH4, so we can use all the existing LNG and natural gas infrastructure. However methane is a powerful greenhouse gas itself, so we have to be careful about leaks. Also combustion of methane produces CO2; we have to find ways to capture that CO2 and feed it back into methane synthesis. That may be easy in some applications: imagine an efficient gas turbine co-located with CO2 storage and a methane synthesis plant. But capturing the CO2 from an oceangoing freight vessel sounds more difficult.

Controlling methane leaks is something to consider (since it's harder to extract from air), but the CO2 emissions isn't. There's nothing to be gained from storing the CO2 in a container versus storing it in the atmosphere and re-extracting it later for the sabatier process [for converting to methane].

So not a concern. The problem holding this idea back is that it takes much more energy to produce methane versus H2, and you don't get as much back burning methane versus running H2 through a fuel cell stack.

My understanding from reading about projects like HELMETH is that the process requires a fairly pure stream of CO2 — at least with the current state of the art, and for an end product that's pure enough to use in natural gas infrastructure. Do you know of a sufficiently efficient method for direct air capture of CO2?

On the topic of efficiency, HELMETH claimed about 75% in their pilot, and suggested that 80% would be practical at scale. As I understand it they got to that point primarily by using excess heat from one stage in the process to boost another stage.

 

[mblakele]

On the topic of efficiency, HELMETH claimed about 75% in their pilot, and suggested that 80% would be practical at scale. As I understand it they got to that point primarily by using excess heat from one stage in the process to boost another stage.

I should have added that a modern combined-cycle gas turbine is about 60% efficient. So a system based on solar or wind, HELMETH, and combined-cycle might clock in at 35-48%. That doesn't sound great, but the input energy was "free" — generally wind or solar that's excess and that we'd otherwise throw away unused. We can store methane for long periods, so this helps with inter-seasonal demand.

 

[adiggs]

Thanks for the link to that project (HELMETH). One of the idea that I got from that, that I didn't have before, is that the best feedstock for the Sabatier reaction is hydrogen. It looks like that project runs electrolysis to produce hydrogen, and then runs the hydrogen through to get methane.

I'm really wishing I hadn't missed out on chemistry lab now - not just the info; this stuff sounds like fun


The other idea, which I had and has been reinforced - I think that the main impediment to having an economical method for making methane from renewable energy today isn't the technology - it's the economics of using natural gas (mostly methane) as feedstock for making hydrogen. It's a highly related bit of chemistry, and since natural gas is so cheap, the idea of making it in a more expensive process isn't exactly attractive.

So something like SpaceX's need for the ability to manufacture methane on Mars might be the driver for developing the technology. Or at some point in the future, natural gas will be under enough price pressure from renewable energy sources that it won't be cheaply available (enough); then it might be sensible to develop a methanation process that might be competitive with hydrogen manufacturing. And it might not.

 

[mblakele]

I think that the main impediment to having an economical method for making methane from renewable energy today isn't the technology - it's the economics of using natural gas (mostly methane) as feedstock for making hydrogen. It's a highly related bit of chemistry, and since natural gas is so cheap, the idea of making it in a more expensive process isn't exactly attractive.

So something like SpaceX's need for the ability to manufacture methane on Mars might be the driver for developing the technology. Or at some point in the future, natural gas will be under enough price pressure from renewable energy sources that it won't be cheaply available (enough); then it might be sensible to develop a methanation process that might be competitive with hydrogen manufacturing. And it might not.

Yes. An effective carbon tax could change that.

So far the most interesting pilot projects have been in Europe, not in the USA or other regions. I see several reasons for that. Europe cares about decarbonizing, more than most other areas. There's an energy security angle, because most of their natural gas comes from Russia. Also they're a little further along with renewables than, say, the USA is; they can see the point of interseasonal storage, beyond what battery storage can handle.

 

[Oil4AsphaultOnly]

My understanding from reading about projects like HELMETH is that the process requires a fairly pure stream of CO2 — at least with the current state of the art, and for an end product that's pure enough to use in natural gas infrastructure. Do you know of a sufficiently efficient method for direct air capture of CO2?

On the topic of efficiency, HELMETH claimed about 75% in their pilot, and suggested that 80% would be practical at scale. As I understand it they got to that point primarily by using excess heat from one stage in the process to boost another stage.

Thanks for starting this thread!

No, I don't know of a high-efficiency process for extracting CO2. I'm just of the opinion that the filtering process would be less intensive then the capturing PLUS storage of CO2 from a combined-cycle gas power plant (the exhaust isn't pure CO2 either). Assuming the filtering process is almost equally energy intensive, at least save on the container costs.

One piece of interesting technology is to convert CO2 straight into coal: Scientists Just Pulled CO2 From Air And Turned It Into Coal

Spinning the idea of "clean coal" on its head.

 

[Oil4AsphaultOnly]

Although not 100% pure, it's pretty close and super efficient: Our Technology | Climeworks – Capturing CO2 from Air

It's a filter that passively pulls CO2 directly from the air, saturating itself, and when heated to 212F releases it back out.

 

[ItsNotAboutTheMoney]

Although not 100% pure, it's pretty close and super efficient: Our Technology | Climeworks – Capturing CO2 from Air

It's a filter that passively pulls CO2 directly from the air, saturating itself, and when heated to 212F releases it back out.

It's OK, we're literate here. You could write 100C.

 

[mblakele]

Thanks for starting this thread!

No, I don't know of a high-efficiency process for extracting CO2. I'm just of the opinion that the filtering process would be less intensive then the capturing PLUS storage of CO2 from a combined-cycle gas power plant (the exhaust isn't pure CO2 either). Assuming the filtering process is almost equally energy intensive, at least save on the container costs.

One piece of interesting technology is to convert CO2 straight into coal: Scientists Just Pulled CO2 From Air And Turned It Into Coal

Spinning the idea of "clean coal" on its head.

Although not 100% pure, it's pretty close and super efficient: Our Technology | Climeworks – Capturing CO2 from Air

It's a filter that passively pulls CO2 directly from the air, saturating itself, and when heated to 212F releases it back out.

You may be right. I'm skeptical because of entropy. I don't have the data, but I'd think it's better to use an exhaust stream that's already partway to the required purity.

Another EU project could resolve the question: it looks like a successor to HELMETH in some ways. But there are three demo sites, and each uses a different CO2 source: a bioethanol plant, a wastewater treatment plant, and direct capture.

About the Project

 

[Oil4AsphaultOnly]

You may be right. I'm skeptical because of entropy. I don't have the data, but I'd think it's better to use an exhaust stream that's already partway to the required purity.

Another EU project could resolve the question: it looks like a successor to HELMETH in some ways. But there are three demo sites, and each uses a different CO2 source: a bioethanol plant, a wastewater treatment plant, and direct capture.

About the Project

I'm really curious about the Store&Go process flow. What in the world is "Green CO2"? It's not even explained anywhere on their website.

 

[mblakele]

I'm really curious about the Store&Go process flow. What in the world is "Green CO2"? It's not even explained anywhere on their website.

I'm not sure, but I think they mean the CO2 source is renewable: for example a bioethanol plant or a wastewater treatment plant. Non-green CO2 would be extracted from mineral or fossil sources, I suppose. This poster has some discussion, and seems to use "green CO2" interchangeably with "biological CO2" — but the latter term seems inexact to me, since fossil fuels originated from once-living things.

https://www.researchgate.net/public...s_a_feedstock_for_Power_to_Gas_energy_storage

Biological CO2 sources for methanation and their P2G potential – first results

The usage of biological CO2 for methanation offers various advantages

• Renewable methane production independent of industrial plants & sectors
• CO2 footprint equals zero due to renewable resources
• Synergies between methanation and biogas injection plants
• CO2 from fermentation as a ‘Low hanging fruit’ due to high CO2 concentrations
• High social acceptance

Synthetic methane from green CO2 sources:​

largest potentials in France, Spain, Germany and Poland due to large energy crop potentials and large populations (wastes, residues)
European Potential >1.250 TWh (26 nations) --- work in progress ---
Additional forest wood potentials (predominantly located in Scandinavia), not taken into account here.​

 

[nwdiver]

I'm not sure, but I think they mean the CO2 source is renewable:

While we're still burning coal and gas... wouldn't power plant emissions be the best place to start? While it's there might as well use it. CO2 is CO2.

 

[mblakele]

While we're still burning coal and gas... wouldn't power plant emissions be the best place to start? While it's there might as well use it. CO2 is CO2.

I think you're right, but it may come down to that last bullet point from the STORE&GO poster: "High social acceptance" — which doesn't have to make sense. But it's important, because the project is funded by public money.

After successful pilots I'd expect more widespread deployments, using private money. Those should be more rational about their sources of CO2. I'd expect them to optimize for the EU emissions trading system (ETS).

 

[mblakele]

It appears that the window for petrochemicals as a growth market for crude oil might get closed in the not too distant future: New method converts carbon dioxide to methane at low temperatures

Being able to produce methane directly, at ~100C, without first producing hydrogen, would be a pretty huge step forward for net negative CO2 production.

[ replying in what I see as a more appropriate thread ]

Thanks, that's interesting. Here's the paper: the full PDF is freely available.

https://www.journal.csj.jp/doi/full/10.1246/cl.190930

CO2 methanation was conducted at low temperatures with an electric field. Results show that 5 wt %Ru/CeO2 catalyst exhibited high and stable catalytic activity for CO2 methanation with the electric field. The kinetic investigations and in-situ DRIFTS measurements revealed that Ru/CeO2 catalyst promoted CO2methanation and Ru at the Ru–CeO2 interface (low-coordinated Ru sites) contributes to the reverse water gas shift reaction at low temperatures in the electric field.​

 

[Oil4AsphaultOnly]

[ replying in what I see as a more appropriate thread ]

Thanks, that's interesting. Here's the paper: the full PDF is freely available.

https://www.journal.csj.jp/doi/full/10.1246/cl.190930

CO2 methanation was conducted at low temperatures with an electric field. Results show that 5 wt %Ru/CeO2 catalyst exhibited high and stable catalytic activity for CO2 methanation with the electric field. The kinetic investigations and in-situ DRIFTS measurements revealed that Ru/CeO2 catalyst promoted CO2methanation and Ru at the Ru–CeO2 interface (low-coordinated Ru sites) contributes to the reverse water gas shift reaction at low temperatures in the electric field.​

Just thinking out loud, would the reduction in activation temperature be enough of an efficiency improvement to make this the go-to product versus simply using H2 directly?

On the first page of that journal, they show CO2 + H2 -> CH4 + H20, which doesn't balance out chemically, but I think indicates that H2 is needed as a feedstock along with CO2. So if you're using renewable energy to electrolyze water into H2 + O2, is the savings from NOT compressing H2 greater than the additional energy cost of converting H2 to CH4?

 

[mblakele]

Just thinking out loud, would the reduction in activation temperature be enough of an efficiency improvement to make this the go-to product versus simply using H2 directly?

On the first page of that journal, they show CO2 + H2 -> CH4 + H20, which doesn't balance out chemically, but I think indicates that H2 is needed as a feedstock along with CO2. So if you're using renewable energy to electrolyze water into H2 + O2, is the savings from NOT compressing H2 greater than the additional energy cost of converting H2 to CH4?

Good question. I don't think I can answer it, but maybe the next pilot project like HELMETH will take that on.

Another potential advantage of renewable CH4 over renewable H2 is that CH4 can use existing natural gas tech and infrastructure. That could be part of the overall cost picture.

Of course CH4 has its disadvantages. Burning CH4 emits CO2 again, so that loop has to be closed somehow; for example by only burning CH4 in large-scale operations, where carbon capture can be practical and economic. Also we'd need to be careful about leaks, because CH4 is a potent GHG on its own.

 

[miimura]

I think CO2 methanation is a good bridge technology because it allows carbon neutral use of millions of existing gas appliances. Getting individuals to replace gas appliances is going to take a very long time. Centrally synthesizing a carbon neutral fuel to supply through the existing gas network is far easier to accomplish on a relatively short timeline. I'm all for pushing to all-electric new buildings, but this kind of bridge to support existing buildings and appliances has great value. Capturing CO2 from the atmosphere over and over again with renewable energy is pretty easy, technologically speaking.

 

[Oil4AsphaultOnly]

I think CO2 methanation is a good bridge technology because it allows carbon neutral use of millions of existing gas appliances. Getting individuals to replace gas appliances is going to take a very long time. Centrally synthesizing a carbon neutral fuel to supply through the existing gas network is far easier to accomplish on a relatively short timeline. I'm all for pushing to all-electric new buildings, but this kind of bridge to support existing buildings and appliances has great value. Capturing CO2 from the atmosphere over and over again with renewable energy is pretty easy, technologically speaking.

For the short term, and maybe producing plastics as a sort of long-term CO2 sequestration? After all, one of the biggest issues of plastics is that they don't easily decompose.

Maybe millions of years into the future, with the help of geology, our hydro-carbon end products might get compressed into a plastic tar that future sentient beings could refine into their fuel? Our trash being someone else's treasure! /only-half-jesting

 

[TheTalkingMule]

Gas appliances is a drop in the bucket for the methane world. We can all use gas to cook(and heat when absolutely necessary) without impacting climate goals. Power/LNG/cracking take up the bulk of supply.

 

[miimura]

Gas appliances is a drop in the bucket for the methane world. We can all use gas to cook(and heat when absolutely necessary) without impacting climate goals. Power/LNG/cracking take up the bulk of supply.

While I agree that gas cooking is a meaningless quantity, home heating (I consider a furnace to be an appliance in a residential setting) and industrial nat-gas process heat is non-trivial and would be well served by synthetic methane.

 

[ItsNotAboutTheMoney]

For the short term, and maybe producing plastics as a sort of long-term CO2 sequestration? After all, one of the biggest issues of plastics is that they don't easily decompose.

Maybe millions of years into the future, with the help of geology, our hydro-carbon end products might get compressed into a plastic tar that future sentient beings could refine into their fuel? Our trash being someone else's treasure! /only-half-jesting

Oh my God. That's an awesome idea.

Sea + Power -> Water + salt.
Salt + power -> Metals
Power + water + CO2 -> Methane + O2
Power + methane -> Plastic

Metal + Plastic + power -> Erector/Meccano + Lego

Now we just need cheap power and some engineers to create the machine.
Saltwater in, toys out.