Tutorial 2-Mass Balance

1. A liquid mixture containing 30.0 mole% benzene (B), 25% toluene (T) and the balance xylene (X) is fed to a distillation column. The bottoms product contains 98 mole % (X) and no B, and 96% of X in the feed is recovered in this stream. The overhead product is fed to second column. The overhead product is fed to a second column. The overhead product from the second column contains 97% of the B in the feed to this column. The composition of this stream is 94 mole% B and the balance T. (a) Draw and label a flowchart of this process.

(b) Do the degree-of-freedom analysis for this process.

(c) Calculate (i) the percentage of the benzene in the process feed that emerges in the overhead product from the second column and (ii) the percentage of toluene in the process feed that emerges in the bottom product from the second column.

2. The waste acid from a nitrating process containing 20% HNO3, 55% H2SO4 and 25% H2O by weight is to be concentrated by adding of concentrated 95% H2SO4 and concentrated 90% nitric acid to get desired mixed acid containing 26% nitric acid and 60% H2SO4. Calculate the quantities of waste acid and concentrated acids required for 1000 kg of desired mixed acid. (Basis: 1000 kg of desired mixed acid)

3. An aqueous solution of pyridine containing 27% pyridine and 73% water is to be extracted with chlorobenzene. The feed and solvent and well mixed in batch extractor and the mixture is then allowed to stand for phase separation. The extract phase contains 11% pyridine and 88.1% chlorobenzene and 0.9% water by weight. The raffinate phase contains 5% pyridine and 95% water by weight. Calculate: (a) The quantities of two phases

(b) The weight ratio of solvent to feed based on 100 kg of feed.

4. Stream 1, containing only substance A, is mixed with Stream 2, which contains substances A & B, at the mixing point. The flow rates of Streams 1 & 2 are 60.0 & 30.0 kg/h, respectively. The mass fraction of A in the Stream 2 is 0.35. Determine the composition of the output stream.

5. Evaporator is used to concentrate a dilute 4 wt% caustic soda (CS) solution to 25 wt%. Calculate the amount of water to be evaporated per 100 kg of feed.

6. Membrane separation is a new technology for separating gases. A nano-porous membrane is used to concentrate the amount of oxygen in the product stream. If the total mole of waste stream is 75% of that of the input stream, what is the molar composition (percentage) of the waste stream?

Dr Rashmi G Walvekar