A pharmaceutical product is crystallized and washed with absolute ethanol. by we

Question

A pharmaceutical product is crystallized and washed with absolute ethanol. by weight by A 100kg batch of product containing 10% ethanol by weight is to be dried 0.1% ethanol by weight by passing 0.2 m^3/min of 50 degree C nitrogen through the dryer. Estimate the rate (mol/min) that ethanol is removed from the crystals, assuming that ethanol exerts the same vapor pressure as if it were pure liquid. Based on this assumption, estimate the residence time for the crystals in the dryer. The dryer operates at 0.1 MPa and the vapor pressure of the pharmaceutical is negligible.

Explanation / Answer

Basis is 100 kg

Initially we have 10% ethanol ,so 10 kg of ethanol

Final wt% is 0.1% this means ,

x/(90+x) = 0.001

x= (90*0.001)/(1-0.001)

= 0.09 kg

Change in ethanol mass = 10 kg - 0.09 kg = 9.90 kg

Moles of ethanol = 9.90 kg / 46 = 0.215 moles

Rate of ethanol removed = 0.215 moles / min

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