Progress for this memo

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Currently, my goal is to build an electrolyzer to convert CO2 to battery-grade graphite. The main questions surrounding that are:

  1. What are the components of an electrolyzer?
  2. What is the best architecture for our goals?
  3. How do you optimize the electrolyzer for my desired output (graphite)?
  4. How do you build those components?

Today I’m focusing on the second question.

<aside> âť“ A list of common terminology is at the bottom of this memo.

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The standard Carbon Capture process.

To understand what’s different about this architecture, I want to spend some time on the default DAC system. Specifically, we are going to dive deep onto Carbon Engineering’s system which is outlined in their paper [1] .

As shown below, atmospheric air comes into contact with an alkaline solution containing KOH (Potassium Hydroxide) to yield K2CO3 (Potassium Carbonate). The K2CO3 is fed to pellet reactor where the carbonate ion is removed from K2CO3 via causticization. In solution, the Ca^2+ and CO3^2- ions react to yield CaCO3 and regenerate KOH. CO2 is liberated from the CaCO3 in the calciner, where the pellets are heated to 900°C. The pure CO2 is then compressed to be stored or utilized. The excess CaO is slaked, combining with water to yield Ca(OH)2 for use in the pellet reactor.

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Note that the calciner is the most energy-intensive part of this process. Carbon Engineering included a table showcasing their process data which I’ll summarize below for energy consumption.

Equipment Energy Consumption (MJ/t-CO2) % of total energy consumption
Contactor 295.2 6.21%
Pellet Reactor 97.2 2.04%
Calciner 4050 85.16%
Slaker (net produces energy) -162 -3.41%
Compressor 475.2 9.99%
Total 4755.6 100.00%

After the carbon capture process, we usually start to think about conversion or storage. However, to convert pure CO2, that means we must have a regeneration or calcination step which is incredibly energy-intensive.

This is exactly why I want to explore alternative conversion methods which convert the carbonates in solution rather than pure CO2. As I said in the previous memo, carbonate conversion is usually best suited for C1+ products, which is perfect for our goals.

The next portion of this memo will be focused on if the idea can work conceptually using napkin math. Afterwards, I’ll go deeper into the economics.

Is it possible to convert carbonates to graphite?