*For pure R; commercial-grade R freezes at 109.6°C (min).

*For pure R; commercial-grade R freezes at 109.6°C (min).

The density of crude R is 8 lb/gal, and the density of commercial-grade R is 10.6 lb/gal.

R, C, and P are members of a homologous series, so it is reasonable to assume that their mixtures are ideal and, therefore, may be represented by constant relative volatilities. W is not a member of the homologous series, but its vapor pressure is so high compared to the other compounds that it will have been totally distilled off before the real separation process begins.

Unfortunately, C is only produced during the manufacture of R by some side reaction whose mechanism is not understood, and the amount of C present in any particular still charge cannot be predicted. Therefore, the design will have to be based on the relative volatilities of R and P, and the capabilities of the design for removing C acceptably will have to be checked later. (Fortunately, the quality of R can be easily assessed during the course of the distillation by observing product color and measuring product freezing point. When freezing point has attained a particular minimum value, and the product is essentially colorless, product quality is acceptable.)

Specification-grade R has been obtained from crude R in a number of laboratory distillations. The research chemists have decided that the distillations should be performed at 10 mmHg absolute in order to minimize the thermal degradation of R. The results obtained in the research work have been averaged, and the following values have been obtained.

S 4250

Tailings 75.2

Foreruns 212.5 P 317.8

Loss 108.4

5000 g

Thus, the problem resolves itself into the following assignment: "'Using the data provided by the research department, design and specify a complete distillation system for a plant which must produce 10.000 lb per day of specification-grade R while operating 330 days per year. The design should be based on recovering P, which has a purity high enough to be commercially attractive. C has no known commercial uses at this time."

Because 10,000 lb of R must be produced daily to meet plant capacity requirements, the laboratory distillation results must be scaled up to this basis. Doing so produces the following values:


Quantity, lb


Mole fraction

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