Question

Solvent S is used to extract a drug D from ground-up plant matter, but S must be recycled to cut costs. A fresh feed of pure S is joined with a recycle stream containing pure S at a different mass flow rate, and the combined stream is fed into an extractor, where it mixes with 1 kg/min D. The mixture of D and S leaving the extractor is fed to a separator. There are two streams leaving the separator. The first contains a mixture of D and S. The mass of S in this stream is 5% of the total S fed to the extractor. The second stream contains pure S, which is recycled and fed back to a point upstream of the extractor. If the stream directly into the extractor is 100 kg S/min, how much S must be fed into the process to maintain steady-state?Solvent S is used to extract a drug D from ground-up plant matter, but S must be recycled to cut costs. A fresh feed of pure S is joined with a recycle stream containing pure S at a different mass flow rate, and the combined stream is fed into an extractor, where it mixes with 1 kg/min D. The mixture of D and S leaving the extractor is fed to a separator. There are two streams leaving the separator. The first contains a mixture of D and S. The mass of S in this stream is 5% of the total S fed to the extractor. The second stream contains pure S, which is recycled and fed back to a point upstream of the extractor. If the stream directly into the extractor is 100 kg S/min, how much S must be fed into the process to maintain steady-state?

A.) 5 kg/min

B.) 10 kg/min

C.) 20 kg/min

D.) 50 kg/min

E.) 100 kg/min

F.) 200 kg/min

G.) Not enough information to determine

Answer 1

The flow chart is shown below

Under steady state conditions, the amount of S entering need to leave from first stream ( since the second stream is recycled).

The total feed to the extractor contains 100 kg S/ min. The first stream contains 5% of total S fed to the extractor. This is equal to 100*5/100= 5 Kg s/min

Remaining 95 kg/min of A need to be recycled.

The feed to the extractor inlet contains 100 kg/min out of which 95 kg/min is coming from recycle. Hence   Feed S entering the extractor = feed S from recycle+ fresh S feed =

Fresh S = 100-95= 5 kg/min

The calculations are presented. The correct answer is 5 kg/min