CO₂ as a chemical feedstock Flashcards
What are some core features of CO₂
- Colourless gas
- Soluble in water (forming carbonic acids in an equilibrium reaction
- Naturally occurring in atmosphere
- Primary source of carbon for all planetary life
What is the average atmospheric increase of CO₂ per year due to anthropogenic activity
4 PgC yr⁻¹
How might we measure the concentration of non-CO₂ GHG in the atmosphere?
IR Spectroscopy
The scale of CO₂ in our atmosphere is very large and we don’t actually use that much carbon in chemicals manufacture. Why hence would we use carbon capture?
Using CO₂ as a feedstock could be see as a leaver that we could use to help manage the steady state concentration of CO₂ in our atmosphere. It can be helpful because it means we can move away from petrochemically derived carbon and by doing this we stop adding carbon to our environment
Why might capturing CO₂ into chemical feedstock not be a good idea for the long run?
We need to capture CO₂ for a long period of time, but when using it as a vector for creating new molecules the turnover is really fast, hence not ideal. In reality we need to tie it up for a really long period of time (structural material, polymers etc)
Why is CO₂ defined as a thermodynamic sink?
CO₂ is quite inert due to it having a large ΔH (enthalpy). The only way to get CO₂ to react is investing huge amounts of energy to reduce the carbon (this is the key challenge of using CO₂ as a feedstock because where will all this energy come from – burning fossil fuel)
How can we avoid the false economy associated with using CO₂ as a chemical feedstock
By using combining solar, wind, hydro instead, to create the energy instead
Direct investment in energy is not the only way of taking a molecule out of a thermodynamic sink. What can we do instead
- We can invest energy in reagents we can use to help us to extract the CO₂ by trapping it as an add on/new molecule. If we use catalysis we can lower the reaction energy in many different reactions.
- For example to addition of CO₂ to Grignard’s reagent: anion adds to the δ⁺ of the CO₂, the upon acidic workup, you can produce carboxylic acids. Allows us to have new molecule and synthetic strategies
What is the issue associated with using a reagent like Grignard’s?
Obtaining the magnesium within the reagent. We have to refine it and there is a huge amount of energy which goes into the refining process of magnesium. Similarly bromine, it is extracted from seawater by acidification also at a high energy cost
Thinking about the chemistry of CO₂, how will it react
Many molecules which react with CO₂ are nucleophilic in nature because CO₂ is electrophilic in nature
What sort of reactions can be done with CO₂
Catalytic hydrogenations, carbamations, formations of urea etc
What type of reactions may be preferred for activating CO₂ and why?
The timescale in which we can sequester CO₂ is important on the impact it will have on the atmospheric CO₂ concentration. Mineralisation reactions will form carbamates which will have a very long lifetime in the environment – seen as a longer-term strategy for the sequestration of CO₂
Name some direct uses of CO₂
- Carbonation of drinks
- Enhanced oil recovery
- Inert gas in packaging of food
- Solvent – Supercritical fluid
Name ways we can use CO₂ as a resource
- Urea synthesis
- Salicylic Acid (Kolbe Schmidt)
- Organic carbonates
- Polymer application
- Water Gas Shift (synthesis gas- Fischer Tropsch)
What is the largest chemical use of CO₂
Is as a feedstock in the production of urea (around 160m tonnes of urea made every year, with most being used in fertilisers)
Describe the Kolbe-Schmidt reaction
- This reaction involves the incorporation of CO₂ into small molecules forming Aspirin precursors (like phenolates).
- The reaction is driven by high temperatures of 125° and CO₂ must be delivered at a liquid phase of 100atm.
- BUT the benefit of this process is the sequestration could be month-years.
E.g. an aspirin tablet may not be consumed immediately
Describe cyclic Carbonate Synthesis?
- The product is used to make electrolytes or solvents for the use in batteries (lithium polymer).
- Direct reaction requires catalyst (organocatalytic like ionic liquid or inorganic materials).
- It is where CO₂ react with epoxide at modest pressures of 1atm.
Has a long sequestration due to lithium battery life being years
What is Power to X (also known as power to hydrogen)
Through reacting CO₂ with hydrogen, you can form methanol or methane which can be used to replace the petrochemical alternatives and fuels or feedstock
This reaction requires selective catalysis
What does the diagram show
Through combining carbon capture, with Green hydrogen production to produce methanol/methane
Then utilising the Fischer-Tropsch process to extend the hydrocarbon to make fuels etc
