MChem Master of Chemistry Master of Chemistry: Industrial Chemistry 4

Question 1

In the context of reactor design, what does the Damköhler number (Da) represent?

Accepted Answer

Ratio of reaction rate to mass transfer rate (or residence time)

Answer

The Damköhler number (Da = reaction rate / convective transport rate) indicates whether a system is reaction-limited (Da<<1) or transport-limited (Da>>1).

Question 2

What is 'atom economy' as defined by Paul Anastas in green chemistry principles?

Accepted Answer

The percentage of atoms in reactants that are incorporated into the desired product

Answer

Atom economy = (MW of desired product / sum of MW of all reactants) × 100%, measuring how efficiently atoms are utilized in a reaction.

Question 3

Which industrial separation technique is used to purify para-xylene from a mixed C8 aromatics stream using zeolite adsorbents?

Accepted Answer

Simulated moving bed (SMB) chromatographic separation

Answer

The UOP Parex process uses a simulated moving bed with zeolite adsorbent (e.g., faujasite) to selectively adsorb p-xylene from C8 isomers.

Question 4

What is the purpose of a 'stripping column' in a gas sweetening unit that removes H2S and CO2 from natural gas?

Accepted Answer

To regenerate the amine solvent by heating and releasing absorbed acid gases

Answer

The stripping column (regenerator) reverses absorption by heating the rich amine, driving off H2S and CO2, and regenerating lean amine for recycle.

Question 5

In a CSTR (continuous stirred tank reactor) operating at steady state, how does conversion relate to reactor volume compared to a PFR for a positive-order reaction?

Accepted Answer

CSTR requires more volume than PFR for the same conversion

Answer

Because a CSTR operates at the exit (lowest) concentration, its rate is lower than average, requiring more volume than a PFR that exploits higher inlet concentrations.

MChem Master of Chemistry Practice Test

MChem Master of Chemistry Practice Test

MChem Master of Chemistry Master of Chemistry: Industrial Chemistry 4