Decaffeination in a Single-Equilibrium Stage

To gain an idea of the CO2 requirements in decaffeination, we consider a hypothetical process in which the carbon dioxide is circulated through the extraction vessel until it is in equilibrium with its charge of coffee. We term this contact an equilibrium stage, a concept that is discussed more fully in Chapter 7. 

Suppose the requirement is to reduce the caffeine content from 1 to 0.05%, which is typical of commercial decaffeination processes. The task is to calculate the ratio G/S kg C02/kg coffee required to achieve this reduction. 

Caffeine equilibrium distribution at 60°C, 272 atm. (From McHugh, M. and Krukonis, V. Supercritical Fluid Extraction, 2nd ed., Butterworth-Heinemann, Boston, 1994. Wth permission.) 

The carbon dioxide is assumed to be devoid of caffeine initially. The equilibrium content in the gas at the end of the operation is given by 

A caffeine mass balance for the process leads to the expression 

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