DavidPBL

Process efficiency can be measured in different ways. I can't give you a number on energy efficiency yet but what I can say is that the carbon efficiency of the process can get close to 100% yield. We aren't there yet for a number of reasons, but to provide details, two things it is related to are mass transfer (how much of the gas is dissolved into the water) and the residence time (how long the gases are in the bioreactor). With our current setup, neither of these has been optimised so the yield isn't great. But this is part of developing the process. We will soon be switching to better bioreactor designs to improve on these fronts.

Your other comment relates to productivity and can be expressed as space time yield (STY). Like the above we need to improve on this and is part of our next steps.

Thank you! Long journey ahead but I hope we can rise to the challenge.

Thank you!

We are going to need low cost green hydrogen. Existing electrolyser technology uses precious metals and so they are expensive/current limiting factor. However there are lots of startups working on bringing to market electrolysers that use non precious metals.

In terms of chemical processes, fermentation is quite simple. In addition to the bioreactor you need a device to control the gas inputs and you need some downstream processing (product extraction). For ethanol distillation is most commonly used but there are newer lower energetically demanding techniques that can be used for extraction. Not all products can be distilled out though, so extraction is somewhat product dependent.

Thank you!

The stoichiometric equation is:

2CO2 + 6H2 > C2H5OH (ethanol) + 3 H2O [∆G -107.4 +/- 36.8 kJ/mol]

You're absolutely right, we require low cost green hydrogen (electricity). The carbon balance depends a bit on what kind of carbon you use.

We use an autotrophic microorganism called an acetogen. Autotrophic means it can use inorganic carbon to feed itself. Plants are another example of an autotroph. Humans are heterotrophs, meaning we depend on other sources for food.

Thank you!

I agree, Daniel Nocera's team have done some really cool research and you're right that renewable fuels in general would be too expensive. I would argue that the cost of fossil fuels are artificially low because their current cost doesn't account for the environmental damage they cause. If we had to pay their true cost, the difference might not be so great.

I like to dream and so our long term ambition is to try and make complex molcules like cannabinoids directly from CO2, but we're some ways off.

Thank you very much for the suggestion!

We take a small sample out the bioreactor (1-2 milliliters) and run it through HPLC (high pressure liquid chromatography). This is manual and labour intensive. There are newer techniques like raman spectroscopy which measure products in real time.