[seanhunt1]

Hey! We're really excited too. The biggest challenge with reactor design is getting excellent oxygen mass transfer (called the Kla "Kay el aye"). Typical fermentation reactors see a background dissolved oxygen concentration of around 8 ppm. The enzymes in the cell can see much lower concentrations, around 1 or 2. Our reactor delivers 450 ppm of dissolved oxygen to nearly every point in the reactor, greatly boosting the kinetics (and efficiency) while also mitigating the effects of H2O2 inhibition on the enzyme. Second, our reactor is also the separator (we use molecular weight cutoff membranes) so that we can continuously remove the peroxide as we make it while retaining the enzyme. The last challenge is materials. Metals decompose hydrogen peroxide and also leach out slowly into the water, lowering purity and reducing the shelf life. Thus, we are using a lined reactor. For non-peroxide producing enzymes, we can design a 316L steel version of our reactor for interested customers that is less expensive.

[semi-extrinsic]

Interesting stuff!

What sort of temperatures and pressures do you have in the reactor?

[Edit: Temperature is around human body temp, of course. I assume it's pressurised in order to get the O2 concentration way up there. So a little north of 800 psi, if my math checks out?]

Do you need to care about hydrogen embrittlement?

Do you have any numbers on CAPEX per production rate as compared to traditional production?

[seanhunt1]

Thanks! We are finding that sub-ambient temperatures are working the best (ca. 10-20 celsius). For improving reaction rates, elevating pressure is much less energy intensive than elevating temperatures, and is extremely useful for improving dissolved oxygen concentrations. Currently, we use class 150 lb components and operate around 100 psig but are looking to test out higher pressures in the future for even better efficiency. Your match checks out, but we also use a pressure swing adsorption system to send in >95% O2 rather than 21% air. We also use a proprietary sparging unit to get super-fine gas bubbles with low rise velocities. Enzymes appear quite resilient to high pressures vs. high temperatures. I suppose this is because water is largely incompressible so it does not affect the enzyme geometry even at high pressures. Yes, we do need to care about hydrogen embrittlement (always a problem) but hydrogen processing is tried and true in the industry and we operate at pretty low temperatures. CAPEX-wise, we are around 10x lower (at equal production rates) because we combine several unit operations into a single unit and we have eliminated the need for a liquid-liquid extractor. Around 50% of the CAPEX costs and >50% of the energy costs with the current anthraquinone process are related to distillation. Because we are much more efficient, we are hoping to have smaller units on site with customers that will eliminate the need for distillation all together, which removes a large portion of both the CAPEX and operating costs associated with the traditional process

[semi-extrinsic]

Thank you for the long answer!

Yeah, few biological processes care about the effect of pressure other than the changes caused in solubilities etc. The physics of the sparging process is very interesting. Do you also do countercurrent (downwards) flow of the water in the sparging unit? (Settling velocities of microdroplets is a subject close to my heart.) I guess anti-foaming is also a big concern there.

A word of caution on pressure classes: in some conservative industries (e.g. oil and gas) they won't let you get away with using piping components rated at some pressure class as pressure vessels at the same pressure class without additional certification. Say, if you were using a piece of large diameter 150 lb rated pipe with flanges at each end as your reactor body. Certification as a pressure vessel is more exhaustive/expensive than certification for piping components.

Nice trick going with the PSA unit instead of accepting the large O2 partial pressure penalty. It sounds like you guys run a tight ship, all the best of luck!

[seanhunt1]

Thanks so much for this advice, very helpful!