Use of Carbon Dioxide in Decaffeination Process

Question

Decaffeinated coffee produced using carbon dioxide is often considered to have the best taste. CO₂, at 90°C and 250 bar, is fed into an extraction unit where it contacts the green coffee beans, removing most of the caffeine. CO₂ at these conditions is an excellent solvent for caffeine and selectively absorbs only caffeine from the coffee beans. The CO₂, containing 2.5 weight percent caffeine, is then sent to a caffeine removal unit operation, where its temperature is reduced to 30°C and the caffeine precipitates out of solution and is filtered out.  The CO₂ is then heated, and recycled back to the extraction unit. A schematic of the process is shown in figure below. Please note that the pressure is approximately constant throughout the process. 

a) Draw and label a pressure versus temperature phase diagram for carbon dioxide. Include on the diagram the operating points of both the extraction unit and caffeine removal unit.

b) Why is CO₂ at 90°C a good solvent for caffeine but at 30°C is a poor solvent.

c) Determine the flow rate of CO₂ (in m3/min) entering the extractor.

Summary

The question belongs to Chemical Engineering and it is about the process of applying CO₂ for caffeine extraction from green coffee beans. The solution discusses some variations in the process.

Note: The solution is in handwritten format.