Carbon Capture and Storage Flashcards
Over exploitation of natural resources and human activities are relentlessly fuelling the emission of CO₂ into the atmosphere
What is a possible solution to address this?
- The reduction of CO₂ offers an alternative to fossil fuels for various organic industrial feedstocks and fuels
- The efficient and scalable approaches for the reduction of CO₂ to products such as methane and methanol can generate value from its emissions
- Transition metal-based catalysts are the most efficient for activation of CO₂ owing to their ability to interact with CO₂ molecules in various ways
What are the problems of just taking out some of the CO₂ which we have already emitted into the atmosphere
- Although levels are higher now, relative CO₂ concentrations in the atmosphere are dilute
- Hence the energy need to move this quantity of air would be vast
Hence catching CO₂ as you release it, is a better solution
How we capture CO₂ requires high selectivity
Explain why?
- Some porous materials are very selective in the absorption of CO₂
- BUT the absorption needs to be reversible and unaffected by H₂O or pollutants
Materials must be cheap
Which sources of CO₂ would be good for carbon caputure and storage?
Fixed sorces like factories, power stations etc which often emit CO₂ on a huge scale
Some (e.g. cement or steel manufacture) emit relatively pure CO₂
Why is carbon caputre not a desirable practice for businesses
Caputuring CO₂ is an ‘added cost’ to production (reduces profit)
(therefore carbon capture can only use inexpensive materials and must be as energy efficient as possible)
Define the 3 stages to carbon capture and storage
1) Capturing & Purifying CO₂
2) Compressing & Transporting CO₂ via pipeline
3) Finding somewhere to store it
Where is CO₂ stored once it is captured?
CO₂ is often stored underground or undersea (there needs to be sufficient space)
The choice of where to store is relatively limited, hence places like depleted gas fields rather than solid ground as there is nowhere for the CO₂ to go
How can you created an economic benefit from storing CO₂
- When you extract oil from porous rock, you can normally extract about 50% or less of the oil
- But if you pump a lot of CO₂ in, you can remove more oil AND can store CO₂ gas
- On land, there are deep abandoned coal mines which CO₂ could be stored
This is a benefit as the rocks are porous and often too deep to mine economically
What is a drawback of using oil fields to store captured CO₂
If you are getting more oil (fossil fuel) out which is then going to be burned, there is no gain to capturing the CO₂ in the first place, as more CO₂ will be emitted from burning the fuel
What are some issues which must be overcome when compressing and transporting captured CO₂ gas?
- Transport of CO₂ at pressures of >100 atm which requires a considerable amount of energy
- Residual water can precipitate out as the temperature drops and the steel will rust when wet. Hence you have a problem of corrosion (hence drying the CO₂ is very important)
- if a pipe leaks, large quantities of CO₂ can collect in low lying areas and suffocate people
What happened at Lake Nyos, Cameroon (1986)
The Volcano at Lake Nyos emits CO₂ which collects in high concentrations in Lake Nyos
Every so often you can get a catrastrophic bubbling of CO₂ which can result in a huge discharge like in 1986
Resulted in many casualties (demonstrates the potential danger of having large quantities of CO₂ unless handled safely)
Name a process which can utilise the capture of CO₂
- In ammonia production, the H₂ needs to be seperated from CO₂
- CH₄ + 2H₂O → 4H₂ + CO₂ (steam reforming)
- Therefore relatively pure CO₂ is ready to be stored/reused
- Results in ‘blue ammonia’ where CO₂ is captured and stored
What is the Water Gas shift Reaction?
Some of the CO₂ can react with hydrogen to form CO and water
However the reaction is reversible
CO + H₂O → CO₂ + H₂
How can you apply the carbon caputre approach to power stations?
1) Carry out stream reforming (reacting methane and water)
2) Seperate the hydrogen from CO₂ which is sent to CCS
3) Burn the hydrogen to generate electricity without releasing any CO₂
(you will however get less energy than the direct buring of methane)
What is Oxyfuel
- Burning methane is pure oxygen
- Then seperating the water out from the CO₂ which is the stored
(undiluted oxyfuel is used in glass making which needs higher temps)
What is the problem with Oxyfuel
Burning methane in oxygen produces much higher temperature flames
(however you could recycle some of the CO₂ into combustion to cool flames)
If fuel is burned in air, any CO₂ for carbon capture and storage needs to be seperated from nitrogen (and water/impurities etc)
What two possible strategies for seperating CO₂
1) Selective reversible solid absorbetns (i.e. materials which selectively absorb CO₂ and then release it)
These materials have to be inexpensive and long-lived
2) Liquid absorber - for example amines: reversible formation of carbamates (RNH₂ + CO₂ → RNH-CO₂H)
3) Also proposals for using ionic liquids, either as liquids or as thin films on solid support
(all are expensive and have reduced efficiency)
What are the two main problems with reusing capture CO₂
1) Scale - CO₂ is generated on a huge scales; most uses (chemicals, fire extinguishers etc) are on much smaller scales
So the rate of producting CO₂ is likely to exceed the rate at which the CO₂ can be reused
2) The CO₂ is likely to be impure - so some applications (e.g. food) may not be appropriate
Between 90-95% of petroleum production goes into energy application (fuels, power stations, etc)
The remain 5-10% is used for manufacturing chemicals and plastics
How much profit comes from making chemicals
50% of the total profits from petrochemicals comes from making chemicals
How can we make CO₂ sustainable to capture?
CO₂ must have an economic value to make it sustainable to capture
Therefore, a key objective is how to make ‘value’ from captured CO₂
(no current answer for this)
What industrial scale process used supercrital CO₂, hence giving some econmic value to CO₂
using supercritical CO₂ in hydrogenation of isophorone to trimethylcyclohexanone
It had a 100% yield and was a successful process
(however it reality the issue was the cost of this process was too high, and industry moved abroad. This was due to cost of compressing CO₂ and wouldn’t meet Green Chemistry Principle 6 - design for energy efficiency)
Powerstations will have large amounts of compressed CO₂
One could tap into that supply to feed a supercritical hydrogenation plant
What however is the problem with this?
CO₂ will have impurities N₂, H₂O and CO
Will these poison the heterogeneous Pd Catalysts?
(to answer this question, you would actually have to try the experiment and see)
What affect will N₂ impurities have on the hydrogenation of isophorone
In order to get hydrogenation with impure CO₂ (i.e. N₂ impurity), you have to run it with a slightly higher temperature
However the overall reaction is exothermic, so running it at a higher temperature doesn’t really hace an additional cost
(isophorone is just one reaction, power stations could supply and compress CO₂ to many different processes making chemicals and making money to partly subsidies the CCS)
Carbon capture and storage can be impactful but under what circumstance?
CCS needs to be a hude scale enterprise if it is to make make any difference to the atmosphere
