Question 1

Which property of supercritical fluids (SCFs) is most similar to that of gases, and why is this important for chemical engineering applications?

Accepted Answer

Viscosity and diffusivity, because they enable rapid transport and penetration into porous materials.

Question 2

At the critical point, the phase boundary between liquid and vapor disappears. Which of the following best describes the behavior of a substance at this point?

Accepted Answer

It shows continuous variation in properties such as density, viscosity, and heat capacity.

Question 3

Supercritical CO$$_2 is $$widely used in the decaffeination of coffee. Which advantage of SCFs does this process primarily utilize?

Accepted Answer

Tunable solvent properties, allowing selective extraction of caffeine without affecting other compounds

Question 4

Which equation of state is commonly used to model phase equilibria in supercritical fluid processes?

Accepted Answer

Peng–Robinson equation

Question 5

A pharmaceutical company wants to micronize a drug to improve its bioavailability. Which property of SCFs is most beneficial for this application?

Accepted Answer

Gas-like diffusivity and low viscosity, which enable rapid penetration and efficient mass transfer

Question 6

Why is supercritical CO$$_2$$ considered environmentally friendly compared to traditional organic solvents?

Accepted Answer

It is non-toxic, non-flammable, and can be recovered and reused, reducing environmental impact.

Question 7

Which of the following is a major engineering constraint when scaling up supercritical fluid processes from laboratory to industrial scale?

Accepted Answer

The need for precise control of phase equilibria and transport phenomena under supercritical conditions

Question 8

Supercritical water oxidation (SCWO) is used for the destruction of hazardous wastes. Which property of supercritical water is most critical for this application?

Accepted Answer

Enhanced solubility of both organic compounds and oxygen, leading to faster reaction rates

Question 9

Which statement best explains why SCFs can be used as reaction media in chemical engineering?

Accepted Answer

SCFs combine liquid-like density with gas-like diffusivity, enhancing solubility and transport for reactants.

Question 10

A process engineer is designing an SCF extraction for a heat-sensitive compound. Which advantage of SCFs is most relevant?

Accepted Answer

Mild operating conditions, as the critical point for SC-CO$$_2 is $$close to ambient temperature and moderate pressure

Question 11

Which of the following best describes the duality of SCF properties and its importance in chemical engineering design?

Accepted Answer

SCFs exhibit liquid-like density (favorable for solvation) and gas-like diffusivity (favorable for transport), requiring a balance for efficient process design.

Question 12

Which disadvantage of SCFs is most likely to increase operational costs in an industrial setting?

Accepted Answer

High pressure requirements for specialized equipment

Question 13

Which real-world application leverages the enhanced mass transfer properties of SCFs?

Accepted Answer

Micronization of drugs to improve solubility and bioavailability

Question 14

Which thermodynamic concept is essential for understanding selectivity in SCF extraction processes?

Accepted Answer

Gibbs free energy of solvation $$\Delta G_{solv}$$

Question 15

Why do SCFs have limited solubility for polar compounds, such as salts, unless co-solvents are added?

Accepted Answer

SCFs like CO$$_2$$ are nonpolar and have poor solvating power for polar or ionic compounds.

Question 16

A chemical engineer is tasked with designing a separation process for heat-sensitive pharmaceuticals. Which SCF property should be prioritized?

Accepted Answer

Mild operating conditions, preserving compound integrity

Question 17

Which of the following is NOT a current industrial use of supercritical fluids?

Accepted Answer

Electrolysis of water for hydrogen production

Question 18

Which property of SCFs allows for the recovery and reuse of the fluid, reducing both cost and environmental impact?

Accepted Answer

Recyclability

Question 19

In the context of phase equilibria, which variable must be controlled to tune the solubility and selectivity of SCFs?

Accepted Answer

Temperature and pressure

Supercritical Fluids in Chemical Engineering Physical Chemistry

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