You have said this twice, but it is really not true. Natural gas is hydrocarbon, just like oil is. The carbon chains are shorter in the gaseous than in the liquid hydrocarbons, which means they have a somewhat lower proportion of carbon as compared to hydrogen, but certainly not far less.
You are both partially correct here. What makes it really confusing is that you are not comparing apples to apples.
Let’s look at power production - not much oil is used in power production because of economic reasons. The two main fuels for power production are coal and natural gas (not considering nuclear).
The best coal plants (pulverized coal - supercritical ) can get to an thermal efficiency of about 40% while a natural gas combined cycle plant will give around 55% efficiency. Many coal plants are old and are in the 30-35% efficiency range. So switching from coal to natural gas results in less co2 for the same power generated.
When it comes to automobiles, like njtt said, there is not a big difference in CO2 emissions switching from gasoline to natural gas. In fact, over the whole well to wheel analysis, natural gas may give off more greenhouse emissions due to leaks of natural gas.
No we are not. I was correct, as you admit in your final paragraph, and kanicbird was wrong, in the statements of his that I was responding to. The rest of what you say, even if true (and I am not at all sure you are right about little oil being used in power production) is completely irrelevant to what I said, and I think pretty much irrelevant to what kanicbird was saying too. We were not discussing coal-fired power generation or the difference between fuels for power and fuels for automobiles, just how much CO2 is released by burning hydrocarbon gas (actual gas, not gasoline) as compared to burning liquid hydrocarbons.
Are any of these sentences actually true? I’m pretty sure the first and third are false, and the second seems extremely dubious, though perhaps there have been some edge cases where Bt has poisoned something other than an insect that would be considered a pest.
Relevance? Do we want as much CO2 in the atmosphere as we had before it got sequestered in the ground? Has no carbon come from upwelling? Was all Earth carbon in the atmosphere before it got sequestered as biological sediment?
Really? Why not?
Your list comprises the caveats I mentioned. What I didn’t understand was why anyone thought biofuels are or could be an improvement over fossil fuels (obvious though it should have been). You aren’t illuminating anything for me here, so your post is the dim light moment for me. Please don’t presume to tell me when I’m learning something and when I’m not. You’d be guessing, and in this case, guessing wrongly.
You can but it’s stupid impractical and expensive compared to scrubbing flue gas.
Let’s put some hard citable numbers on that and let the OP decide
From Are there CO2 emissions from natural gas? | HowStuffWorks
30 percent reduction in CO2 just by switching fuel seems pretty significant to me YMMV
I never denied that, in fact I pointed this out 2x (well that CO2 is produced), but at rates less the oil
Yes exactly, so less CO2 produced as per my cite
OK I think you may have mistyped here, I never said that Natural gas produces less CO2 the Hydrogen. Hydrogen combustion should not produce any CO2. What I said is that Nat Gas produced less CO2 then Oil, which is a start in what appears to be the OP’s request to lower CO2 emissions.
The short answer to the OP is alkenes. And I’m mystified why everyone’s gone off talking about CO2 and biofuels. Maybe it’s a Brit thing but over here we are all required by law to bore our children to death about this in schools. Maybe it’s cos the OP was focusing on ‘getting the hydrogen’ whereas cracking is focused on ‘getting the alkenes’. Also everyone’s focused on ‘getting energy’. Which cracking certainly doesn’t do.
But anyhow, cracking long chain alkanes gives you shorter chain alkenes and hydrogen. So you could then use the hydrogen as fuel if you like. No, you won’t get as much energy out of the hydrogen burning as you needed to crack the petrol, but then if you wanted energy you should have burned the petrol. In which case, of course you’ll bloody get CO2.
A lot of H2 is produced during cracking, but it’s more a byproduct of the alkenes than the alkenes are of H2 production, since most of the hydrogen is still in the alkene products.
While most large-scale H2 production is via steam reforming, which ultimately produces CO2 if it’s the H2 you’re after, you can also plasma reform to H2 and carbon black. The energy inputs are large, but the carbon also has value. I don’t have a handle on the economics.
Plants do it all the time. I don’t get what you’re trying to say. While it’s true that there are issues with biofuels, those issues present technical problems, not theoretical ones.
No argument about scrubbing flue gases as preferable, with current technology. I’ll take your word for that. If that’s all you’re saying, then fine, no argument.
Those interested in getting H2 from plants might be like to read about biomass gasification.
Sundrop Fuels has been making gasoline this way, although the H2 yield from biomass is shit, so they supplement by reforming methane.
Since the process is endothermic (although they avoid an ASU), so they heat it with solar.
I suppose you could skip the methane reforming and just shift the biomass output to the desired H2/CO ratio, but there will be a large economic hit.
I’m not entirely sure what question(s) we’re even trying to answer at this point.
What’s an ASU?
FYI, my underlying reason for asking this is the realization that fossil fuels won’t (and, realistically, can’t) go away any time soon (I was mostly thinking about energy used for transport). H2 has great energy density, even greater than gasoline, except that the storage is bulky and heavy and negates that advantage. Leaving that problem aside for the moment, I thought, “what if we could just make hydrogen from fossil fuels, rather than fuels that produce CO2 as a reaction product? Then, if we could solve the storage problem, we could continue to use fossil fuels without contributing CO2 to the atmosphere.”
That thought is probably folly for some of the reasons pointed out here.
So, we are back to square one. We have a massive base of infrastructure that is dependent on fossil fuels for a feedstock. We have a massive industry, the biggest in the world, that is dedicated to providing that resource. How do we balance these needs against the need to produce less CO2?
I am familiar with many schemes, such as use methanol, ethanol, bio-fuels, fuel cells, batteries, hybrid drives, etc., but none really seem to have the capacity to meet our current needs (if you want to go back to the hut, that’s your business, but I like the modern world), nor are really economically viable, at least not yet.
Thanks,
Rob
It has a high gravimetric energy density, which matters in a space ship, but its volumetric energy density is much, much lower. This is a huge problem for using it in vehicles. It’s hard to find a better energy storage and transfer medium than gasoline.
You chopped off the important half of the cite.
Nitpick : is produced, not ‘gets out’ - it’s CO2, not Phlogiston. (the CO2 is a product of the carbon from the fuel and the oxygen from the atmosphere)
I said “somewhat less” but your original claim was “far less”, that is what I was disputing. (I also dispute that 30% figure, and I do not recognize howstuffworks.com as a reliable source that trumps knowledge of basic chemistry.)
No I didn’t mistype, you misread. I was talking about the ratio of carbon to hydrogen within different types of hydrocarbon, not the difference between burning hydrocarbons and burning hydrogen. Please try and keep up!
Burning natural gas as opposed to burning oil (although it may have other advantages) is not going to lead to any very significant improvement in greenhouse gas emissions. Furthermore, the more you try to use natural gas, the more of it will escape into the atmosphere, and natural gas itself is a much worse greenhouse gas than CO2 is.
I understand it’s important to be factual in these topics, and I’m sorry I didn’t provide any cites (was too lazy). However, I don’t want to derail this thread with an argument on GMOs. I’m OK with you disagreeing, and urge other interested participants to do their own research and come to their own conclusions.
If this matters a lot to you, please feel free to start a separate thread and link to it instead.
To a rounding error, if you convert an alkane (other than the trivially light ones) to hydrogen and carbon dioxide, you get equal volumes of each, but the CO[sub]2[/sub] molecule is 15 times heavier than the hydrogen. You can’t make hydrogen this way without getting a buttload of carbon, and if the latter is in the form of carbon dioxide, then you may be able to sequester it at the point of production, but sequester it you must or you’ve gained nothing on the deal (and wasted a lot of energy).
The energy requirements of the whole shooting match are left as an exercise for the student.
IIRC Spacecrafts use liquid cyrogenic H2 which takes care of the volumetric density issue you state.