Selecting an absorbent — Why is a low-viscosity absorbent generally preferred?

Introduction:
Absorber performance hinges on both thermodynamics (solubility/selectivity) and hydraulics (mass transfer, pressure drop, capacity). While solvent choice often starts with solubility, the fluid's viscosity strongly affects transfer rates and column operability. This question highlights the multifaceted benefits of low viscosity.

Given Data / Assumptions:

• Packed or tray absorber operating at near-ambient to moderate temperatures.
• Comparable solvent volatility and chemical stability among candidates.
• Mass-transfer coefficients depend on diffusivity and film thickness; hydraulics depend on liquid properties.

Concept / Approach:

Low-viscosity liquids exhibit thinner boundary layers and higher diffusivities, boosting liquid-side mass-transfer coefficients, which accelerates absorption. They also distribute better over packings, enhancing wetting and heat removal. Hydraulically, lower viscosity reduces friction losses (pressure drop), and delays onset of flooding (higher capacity) due to improved film flow and reduced holdup. Thus, low viscosity supports rapid absorption, improved flooding behavior, and lower pumping energy simultaneously.

Step-by-Step Solution:

Verification / Alternative check:

Packed column design correlations (e.g., Sherwood–Lobo–Evans) and flooding charts show clear viscosity effects on k_L, pressure drop, and capacity.

Why Other Options Are Wrong:

A/B/C each capture only part of the benefit; the comprehensive, correct choice is all of them. E contradicts standard design practice.

Common Pitfalls:

Choosing a very viscous but highly soluble solvent without accounting for severe mass-transfer penalties and hydraulic limitations.

Final Answer:

all (a), (b) and (c)