MChem Master of Chemistry Master of Chemistry: Industrial Chemistry 5 — Questions and Answers
Question 1: In industrial electrochemical production of chlorine and sodium hydroxide, what is the name of the modern membrane cell process that replaced the mercury cell?
- Hall-Héroult process
- Chlor-alkali membrane cell process (e.g., Nafion membrane) (Correct answer)
- Downs cell process
- Bayer process
Correct answer: Chlor-alkali membrane cell process (e.g., Nafion membrane)
Modern chlor-alkali plants use ion-exchange membranes (e.g., DuPont Nafion) to separate the anode (Cl2) and cathode (NaOH) compartments without mercury.
Question 2: What is 'selectivity' in industrial heterogeneous catalysis, and how does it differ from 'conversion'?
- Selectivity is the fraction of reactant consumed; conversion is the fraction forming desired product
- Selectivity is the fraction of reacted feedstock forming the desired product; conversion is the fraction of feed that has reacted (Correct answer)
- Selectivity measures catalyst lifetime; conversion measures throughput
- They are interchangeable terms for overall process efficiency
Correct answer: Selectivity is the fraction of reacted feedstock forming the desired product; conversion is the fraction of feed that has reacted
Conversion = (moles reacted)/(moles fed); selectivity = (moles to desired product)/(moles reacted), so yield = conversion × selectivity.
Question 3: Which Fischer-Tropsch derived fuel synthesis product distribution is described by the Anderson-Schulz-Flory (ASF) distribution?
- Molecular weight distribution of polymers formed on Ziegler-Natta catalysts
- Carbon number distribution of hydrocarbons produced as a function of chain growth probability α (Correct answer)
- Particle size distribution of catalyst after attrition in a fluidized bed
- Isomer ratio of branched versus linear alkanes from reforming
Correct answer: Carbon number distribution of hydrocarbons produced as a function of chain growth probability α
The ASF distribution predicts the mole fraction of each Cn hydrocarbon product from Fischer-Tropsch synthesis using the chain growth probability parameter α.
Question 4: What is the purpose of 'recycle' streams in industrial chemical processes?
- To dilute the feed before entering the reactor
- To return unconverted reactants from the separator back to the reactor, improving overall yield (Correct answer)
- To remove heat from exothermic reactors
- To purge inert gases that accumulate in the system
Correct answer: To return unconverted reactants from the separator back to the reactor, improving overall yield
Recycle streams allow per-pass conversion to be kept low (better selectivity) while achieving high overall yield by returning unreacted feed to the reactor.
Question 5: In industrial polymerization, what is 'living polymerization' and why is it industrially valuable?
- Polymerization conducted in aqueous emulsion to produce latex particles
- A chain-growth process with no termination, enabling precise control of molecular weight and block copolymer synthesis (Correct answer)
- A step-growth process producing polymers with exactly two end groups
- Polymerization using biological enzymes as catalysts for biodegradable plastics
Correct answer: A chain-growth process with no termination, enabling precise control of molecular weight and block copolymer synthesis
Living polymerization (e.g., ATRP, RAFT) lacks irreversible termination, producing narrow PDI polymers and enabling sequential block copolymer formation.
Question 6: What is the significance of the 'E-factor' (environmental factor) introduced by Roger Sheldon for evaluating industrial chemical processes?
- It measures the energy consumption per mole of product in kWh/mol
- It is the mass of waste generated per mass of desired product, with lower values indicating greener processes (Correct answer)
- It quantifies the toxicity of effluents relative to regulatory limits
- It compares the exothermicity of a reaction to its activation energy
Correct answer: It is the mass of waste generated per mass of desired product, with lower values indicating greener processes
The E-factor = kg waste / kg product; pharmaceutical synthesis has E-factors of 25–100, while bulk chemicals aim for <1, driving green chemistry improvements.
Question 7: In the industrial production of ethylene oxide, what hazard makes the direct oxidation of ethylene with O2 over a silver catalyst particularly challenging to control?
- The reaction is strongly endothermic requiring high furnace temperatures
- Ethylene/oxygen mixtures are flammable and the reaction is highly exothermic, requiring precise temperature control to avoid runaway (Correct answer)
- The silver catalyst is rapidly poisoned by CO2 at low concentrations
- High pressure causes catalyst sintering within hours of operation
Correct answer: Ethylene/oxygen mixtures are flammable and the reaction is highly exothermic, requiring precise temperature control to avoid runaway
Ethylene oxide synthesis is exothermic (ΔH ≈ −105 kJ/mol) and the mixture is flammable, so multi-tubular reactors with coolant control hot spots and prevent thermal runaway.
MChem Master of Chemistry Master of Chemistry: Industrial Chemistry 5
In industrial electrochemical production of chlorine and sodium hydroxide, what is the name of the modern membrane cell process that replaced the mercury cell?