Different Pathways To Make Glucose
My Climate Journey (Update 4)
Recap
Carbon capture is the most important technology to address climate change.
Glucose is the best product we can make from captured carbon.
What I’m Sharing Today
For this update, I attempted to create a new method for producing glucose using existing reaction steps.
It didn’t work.
Below is a summary of what I did and what I learned.
How Can You Make Glucose?
The only synthetic path I found to produce glucose is the formose reaction.
This reaction begins with formaldehyde (CH₂O), which is heated in a reactor.
The issue is that only 1% of the formaldehyde converts into glucose.
This result is poor, but it shows that glucose synthesis is possible.
Using this as a starting point, I explored ways to increase glucose yield using only existing reaction steps.
I started with CO₂ and H₂O as the input molecules.
I used formaldehyde as the intermediate.
I aimed for glucose as the final product.
Pathway 1
This is the initial process pathway I planned:
CO₂ → CO + O₂
H₂O → H₂ + O₂
CO + 2H₂ → CH₃OH (methanol)
CH₃OH + 1/2 O₂ → CH₂O (formaldehyde) + H₂O
CO₂ → Acetyl-CoA → Acetaldehyde
Acetaldehyde + formaldehyde → Pyruvic Acid
Pyruvate + CO₂ + ATP → OAA + ADP + Pᵉ
OAA + GTP → PEP + CO₂ + GDP
PEP → G3P (via intermediates)
G3P + DHAP → Fructose-6-Phosphate
F6P → Glucose
As I continued researching, I realized I hadn’t accounted for all the intermediate steps.
The full process likely involves 15+ steps.
Problem With Pathway 1
The reaction required:
2.97 tonnes of CO2 at $100/tonne = $296.75
12,719.55 kWh of energy at $0.01/kWh = $130.68
0.34 tonnes of hydrogen at $1,500/tonne = $504.13
The total cost came to $931.56 per tonne of glucose.
The market price for glucose is around $600/tonne.
This pathway is not economically viable.
Pathway 2
I explored another pathway:
CO₂ + NADH + H⁺ → HCOO⁻ (formate) + NAD⁺
HCOO⁻ + NADH + H⁺ → CH₂O (formaldehyde) + NAD⁺ + H₂O
2 CH₂O → C₂H₄O₂
CH₂O + C₂H₄O₂ → C₃H₆O₃
C₃H₆O₃ + ATP → G3P + ADP
G3P → DHAP
G3P + DHAP → FBP
FBP + H₂O → F6P + Pᵉ
F6P → G6P
G6P + H₂O → Glucose
The production cost was $948/tonne of glucose.
As with the previous pathway, this is not profitable.
Lessons Learned
More Reaction Steps Kill Your Economics
Hess’s law says the number of steps doesn’t affect the energy requirement for a reaction.
The energy requirement depends only on the input and output.
This is true for the minimum energy needed to make the reaction happen.
However, Hess’s law doesn’t account for efficiency losses at each step.
In a 10-step process with 90% efficiency per step, overall efficiency drops to 35%.
This means only one-third of the input becomes useful output. This is terrible.
For my process, low efficiency doubled my CO₂ costs.
It also tripled my energy costs.
This happened because the reaction had too many steps.
From this, I learned that reducing reaction steps is essential for good economics.
Avoid Hydrogen At All Costs
Hydrogen is a major constraint for these pathways.
It was the key factor that made these processes unprofitable.
I learned that I must create a reaction pathway from CO₂ and H₂O to glucose without using hydrogen.
This will improve my economics.
Next Steps
I need to develop a new selective pathway for the formose reaction.
Researchers know formaldehyde forms larger molecules, but the step-by-step process is unclear.
In a previous update, I mentioned needing to develop enzymes.
This does not make sense.
Enzymes can only be designed when you know the inputs and the desired outputs.
Since the step-by-step process from formaldehyde to glucose is unknown, I need to figure that out first.
Once I understand all the reaction steps, I can develop enzymes to create a more selective reaction.
The main challenge in producing glucose is connecting carbon atoms correctly.
I don’t know how to connect carbon atoms.
This means I need to learn about the fundamentals of organic (or carbon-based) chemistry.
Until next time,
Ahmed