Question

In supercritical fluid extraction, what will be the critical temperature (CT) and critical pressure (CP)?

• A. 34°C and 50 atm
• B. 31.1°C and 73.8 atm
• C. 54°C and 78 atm
• D. 40°C and 60 atm

Hint:

CO$_2$ is the preferred supercritical fluid due to its moderate critical point and safety profile in pharmaceutical processes.

Answer 1

The Correct Option is B

Supercritical fluid extraction (SFE) uses a fluid above its critical temperature and pressure, where it exhibits unique solvent properties between those of liquids and gases. The most commonly used supercritical fluid in pharmaceutical and food industries is carbon dioxide (CO$_2$) because of its relatively low critical temperature and pressure, non-toxicity, and inertness. - The critical temperature (CT) of CO$_2$ is 31.1°C. - The critical pressure (CP) of CO$_2$ is 73.8 atm (approximately 7.38 MPa). Above these conditions, CO$_2$ becomes a supercritical fluid, which can diffuse through solids like a gas and dissolve substances like a liquid, making it an excellent extraction solvent for sensitive compounds without thermal degradation. This critical point is important because: - It allows extraction at relatively mild conditions preserving thermolabile substances. - It eliminates the use of organic solvents, making the process environmentally friendly. - Adjusting temperature and pressure near the critical point allows selective extraction by changing solvent power.

Answer 2

Supercritical fluid extraction needs a solvent whose critical point is easy to reach under practical operating conditions. Carbon dioxide is the standard choice in pharmaceutical and food processing because of where its critical point falls, so checking each pair of numbers against known solvent data settles this question.

1. 34°C and 50 atm: These numbers are close to CO2's true critical constants but not exact. The real critical pressure of CO2 is meaningfully higher than 50 atm, so this option undersells the pressure needed.
2. 31.1°C and 73.8 atm: This is the accepted critical temperature and critical pressure of carbon dioxide. It sits just above room temperature, which is exactly why CO2 became the preferred supercritical solvent: it avoids the heat damage that steam distillation or hot organic solvents can cause to delicate drug molecules.
3. 54°C and 78 atm: The temperature here is far higher than CO2's real critical temperature, closer to the critical point of a heavier compound, so it does not describe CO2.
4. 40°C and 60 atm: Both figures undershoot the true critical pressure of CO2 and slightly overshoot the temperature, so neither number lines up with the accepted constants.

Only one pair of values matches the documented critical constants of carbon dioxide, the solvent that supercritical fluid extraction in pharmacy almost always refers to.

So the correct answer is 31.1°C and 73.8 atm.