MChem Master of Chemistry Master of Chemistry: Industrial Chemistry 3 — Questions and Answers
Question 1: What is the primary advantage of a fluidized bed reactor over a fixed bed reactor for highly exothermic reactions?
- Lower capital cost
- Superior heat transfer and isothermal temperature control (Correct answer)
- Higher catalyst loading per unit volume
- Lower pressure drop across the bed
Correct answer: Superior heat transfer and isothermal temperature control
Fluidized beds provide intense gas-solid mixing and excellent heat transfer coefficients, preventing hot spots in strongly exothermic reactions.
Question 2: In the Wacker process, ethylene is oxidized to acetaldehyde using what catalytic system?
- Fe2O3 / V2O5
- PdCl2 / CuCl2 in aqueous HCl (Correct answer)
- Rh(CO)2I2
- Co2(CO)8 / iodide
Correct answer: PdCl2 / CuCl2 in aqueous HCl
The Wacker process uses PdCl2 as the stoichiometric oxidant, regenerated by CuCl2, which is re-oxidized by O2 from air.
Question 3: What is 'turndown ratio' in the context of industrial distillation columns?
- Ratio of reflux to distillate flow rates
- Range of operating capacity over which a column functions adequately (Correct answer)
- Ratio of feed to bottoms flow rates
- Temperature difference between top and bottom trays
Correct answer: Range of operating capacity over which a column functions adequately
Turndown ratio is the ratio of maximum to minimum operable throughput, reflecting operational flexibility of a distillation column.
Question 4: Which gas-phase industrial process produces maleic anhydride by selective oxidation of benzene or n-butane?
- Andrussow process
- SOHIO/BP process using vanadium phosphorus oxide catalyst (Correct answer)
- Wacker oxidation
- Monsanto acetic acid process
Correct answer: SOHIO/BP process using vanadium phosphorus oxide catalyst
Maleic anhydride is produced by selective oxidation over a vanadium phosphorus oxide (VPO) catalyst, with n-butane now preferred over benzene.
Question 5: In polymer production, what distinguishes a Ziegler-Natta catalyst from a metallocene catalyst?
- Ziegler-Natta catalysts require higher temperatures
- Metallocene catalysts produce narrower molecular weight distributions due to single-site active centers (Correct answer)
- Ziegler-Natta catalysts only polymerize ethylene
- Metallocene catalysts are heterogeneous while Ziegler-Natta are homogeneous
Correct answer: Metallocene catalysts produce narrower molecular weight distributions due to single-site active centers
Metallocenes are single-site catalysts giving narrow PDI (~2), whereas Ziegler-Natta catalysts have multiple active sites producing broader distributions.
Question 6: What is the function of a 'scrubber' in an industrial gas treatment system?
- To compress gas to high pressure
- To remove gaseous pollutants or particulates by contacting gas with a liquid or solid sorbent (Correct answer)
- To crack heavy hydrocarbons into lighter fractions
- To measure gas composition by spectrometry
Correct answer: To remove gaseous pollutants or particulates by contacting gas with a liquid or solid sorbent
Scrubbers absorb or react acidic gases (e.g., SO2, HCl, H2S) or particulates from process or flue gas streams using aqueous or alkaline solutions.
Question 7: The Ostwald process converts ammonia to nitric acid. Which intermediate is formed when ammonia is oxidized over a platinum-rhodium gauze?
- N2O (nitrous oxide)
- NO (nitric oxide) (Correct answer)
- NO2 (nitrogen dioxide)
- N2O4 (dinitrogen tetroxide)
Correct answer: NO (nitric oxide)
Ammonia is selectively oxidized to NO over Pt-Rh gauze at ~850°C, which is then further oxidized to NO2 and absorbed in water to form HNO3.
MChem Master of Chemistry Master of Chemistry: Industrial Chemistry 3
What is the primary advantage of a fluidized bed reactor over a fixed bed reactor for highly exothermic reactions?