A pharmaceutical product is crystallized and washed with absolute ethanol. A 100

Question

A pharmaceutical product is crystallized and washed with absolute ethanol. A 100 kg batch of product containing 10% ethanol by weight is to be dried to 0.1% ethanol by weight by passing 0.2 m3/min of 50C 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: 1 minute of operation

Feed = 100 kg /min

Ethanol percent in feed = 10%

Let product = P kg /min

Ethanol percent in product = 0.1%

Let E be ethanol flow rate

Flow rate of nitrogen = 0.2 m^3/min

Density of nitrogen @50°c and 0.1 Mpa = 1.043kg /m^3

Mass flowrate of nitrogen = 0.2*1.043= 0.2086kg/min

Mass balance for overall drier

100+0.2086= P+E...........(1)

Ethanol wt% balance

(0.1)100=E+(0.001)P.........(2

Solving 1 and 2 we get

E = 9.909 kg/min

P= 90.298 kg/min

E = 9.909/46 = 0.2154 mole/ min

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