$1.$ What goes into choosing a solvent for gas absorption$,$ and why is it crucial?

a$.$ Can you talk about the role solvent volatility plays here?

b$.$ Why should we care about the viscosity of the solvent?

c$.$ What makes solvent selectivity so important for getting the results we want?

$2.$ Let's dive into why we fuss over finding the minimum solvent flow rate in gas absorption$.$

a$.$ How does hitting this "minimum" mark impact the overall process efficiency?

b$.$ Could you explain the relationship between this rate and the system's operating costs?

c$.$ Is there a direct link between the minimum solvent flow rate and the absorption column's design?

$3.$ Ponder the Height Equivalent to a Theoretical Plate $($HETP$)$ in packed columns.

a$.$ What's the deal with HETP, and why does it matter for column design?

b$.$ How does changing the packing material affect HETP?

c$.$ Could you shed some light on how HETP influences the column's efficiency?

$4.$ Think about the number of transfer units $($NTU$)$ in the context of gas absorption$.$

a$.$ How does NTU tie into the column's design?

b$.$ What happens to the column height as NTU changes, and why?

c$.$ How do you see the solvent flow rate playing into the NTU value?