How do I get this thing to stir ?

I was looking at my collection of literature and decided to pull out a interesting article that I had found, not in my favourite journals but a new one.  (Maybe this could be the new favourite one, now)

R. Eric Berson et al, “A Scraped Surface Bioreactor for Enzymatic Saccharification of Pretreated Corn Stover Slurries” in Energy & Fuels, Volume 23, p. 492-7 (2009).

Can you actually imagine a situation where you had tried to stir a reaction and your overhead stirrer actually ceased ?  I am sure some of the old process development jockeys have had that happen to them at one time or another.  And this could happen for various reasons, you developed a leak in your system where solvent evaporated away for some reason or another, the viscosity of the system is greater than the torque your stirrer can deliver, blah blah blah at infinitum.

What if you started with something that had the consistency of muck and had to work with this ?  In this paper, it is described that one runs into problems when you are dealing with high solids processing above 15 %.   You have problems with heat transfer and mixing.  If you are going to break down this material into simple sugars (saccharification), the enzyme needs to mix throughout your slurry.  This is going to be a major hurdle not to mention the fact that the enzyme will need to be evolved to improve its performance in your saccharification process.

A scraped surface bioreactor (SSBR) is what you may need to carry through your saccharification.  This, apparently, is something that you would find in the food processing industry for thick emulsions, like ketchup, peanut butter, etc.  The SSBR has several advantages, according to Berson.  They are:  1) This type of configuration will operate horizontally, so the formation of a dead zone or settling of particles is limited, 2)  Because the stirring is performed horizontally, it requires less power to suspend the particles (Big points here !!) 3) The scraping action cleans the sides of the reactor so there is increase in heat transfer.   This is interesting.

I will just add, that  I appreciate the traffic I have been getting to this website.  If you have questions, don’t be afraid to ask.  I won’t post unless I think it adds value to the discussion.


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