HELP! Filtration Recycle Loop on Batch Reactor-Residence Time Distrib

[rideox4]

I have a batch reactor where one of the intermediate steps is to pass the entire contents of the batch (reactor 1) over to reactor 2 for the mere purpose of passing the batch through a filter to remove solids on its way to reactor 2. Because we are processing it this way, 100% of the batch gets filtered. I want to change the process so that the filtration occurs via a recycle loop in reactor 1...instead of pumping it over to reactor 2 and then back to reactor 1. The problem with the recycle loop for filtration is that we can never be sure that 100% of the batch will actually make it through the recycle loop due to residence time distribution issues.

question: Is there a rule-of-thumb for the recycle time required or # of batch turnovers required to assume that 100% (or 99%+) of the product makes it through the recycle loop? I assume it is related to a rule-of-thumb of Residence Time Distributions for a batch reactor and may be related to the recylce rate, mixing rate, etc. Let's assume perfect mixing.

Help!!
Thank You

 

[StoneCold]

rideox4
We do the recycle method. We are able to put a sight glass on the inlet and the outlet and pump our material through until it is not cloudy for our filtration. I suppose that you could also measure the pressure drop through the filter as you get to the end of the batch on the once through method. The final pressure drop on the recycle method should be close to the final pressure drop on the once through method. I would also guess that we run the reactor volume through the filter at least four times before it is all filtered.

Regards
Stonecold

 

[rideox4]

thanks for the info. unfortunately, i'm talking about a high viscosity, shear-thinning lotion....so visual really won't cut it. i was hoping somebody might know of a rule of thumb for batch turnovers...maybe as a function of batch viscosity, reynold's number etc. i thought i had read somewhere that 5-10 turnovers is generally accepted as nearly 100% certainty of every moving element of fluid making it to your recyle loop (not including dead spaces in the batch, etc.)

thanks

 

[tickle]

Can't you work it out mathematically?

If it is a CSTR, and you know withdrawl rate and that is returned to the tank with an efficiency of filtration. I am assuming that there will be an exponential and an integral in the answer.

 

[rideox4]

in a CSTR the feed concentration is constant while the discharge changes. in this case, since it's recycle what would the equation look like? i assume it's exponential in nature...i'm just curious what the constants would be as a rule of thumb relating to turnover rate required for 99%+ conversion.