This set of Engineering Chemistry Multiple Choice Questions & Answers (MCQs) focuses on “Cracking – 2”.
1. How can we increase the ageing of alumina-silica catalyst?
a) By making the contact of catalyst with heavy metals
b) By making the contact of catalyst with lighter metals
c) By making the contact of catalyst with heavy non-metals
d) By making the contact of catalyst with lighter non-metals
Explanation: The process of ageing can be accelerated, if the catalyst comes into the contact with compounds containing sulphur, vanadium, nickel etc. The ageing can also be increased if the conditions are more rigid.
2. How can we regenerate alumina-silica catalyst?
a) By increasing the particles of coke on the catalyst
b) By increasing the amount of catalyst
c) By decreasing the particles of coke on the catalyst
d) By making it react with suitable anion or cation
Explanation: The catalyst can be regenerated to store their activity and reactivity by burning of the coke deposited on the catalyst particles. The catalyst used in the catalytic reactions are very expensive, due to which their regeneration is necessary.
3. What happens when the crude petroleum fractions are made in contact of catalyst in cracking process?
a) Solid substances are obtained
b) Liquid substances are obtained
c) Gaseous substances are obtained
d) Solid, liquid and gaseous substances are obtained
Explanation: Gases, gasoline, coke and other liquid products are formed when a catalyst comes in contact with crude petroleum fractions in cracking process. This happens due to the various reactions such as dehydrogenation, isomerization etc.
4. Catalytic cracking process are more expensive to run than the thermal cracking process.
Explanation: The catalyst used in these processes are expensive. This type of cracking gives more stable and superior product. The yields obtained by this type of cracking are higher.
5. Which compounds can be obtained from higher percentile yields of butyne-butylene fractions?
Explanation: The octane ratings of gasoline fuel is 87 where as the octane ratings of super-gasoline is 93. These fuels are more suitable than gasoline fuels.
6. In which form does the catalyst are used in fluid-bed cracking?
a) In the form of oxides
b) In the form of vapours
c) Liquid form
d) In the form of fine powder
Explanation: In this process, the catalyst in the form of fine powder is circulated through the cracking reactor with the help of oil vapours. The catalyst accelerates and directs the cracking and also acts as a heat transfer medium.
7. In which process does the oil vapours are heated to their cracking temperatures?
a) Thermal cracking
b) Fixed-bed cracking
c) Fluid-bed cracking
Explanation: In fixed-bed cracking the oil vapours are heated to their cracking temperatures and are passed on to the fixed catalyst bed. When the catalyst gets carbonised, it is reactivated by burning off the carbon deposited.
8. At what temperature does the oil is vaporised and heated in fixed-bed cracking process?
b) 700-800 oC
c) 100-200 oC
d) More than 1000 oC
Explanation: The heavy oil charge is passed through a heater, where the oil is vaporised and heated to 400-500 oC. The hot vapours are then passed over fixed bed catalyst. The pressure is about 1-5 kg/cm2.
9. How much percentile of low molecular weight hydrocarbons are formed in fixed-bed catalytic cracking?
a) 15-20 %
b) 50-60 %
c) 30-40 %
d) 0-5 %
Explanation: About 30-40 % of the charge is converted into low molecular weight hydrocarbons, conforming the composition of catalyst. About 4 % of carbon is formed during this process.
10. What happens to the heavy gas oil fractions in the cracking process?
a) It escapes out
b) Condensed at the bottom of the column
c) It gets dissolved in the solution
d) It blocks the air holes
Explanation: The cracked vapours of the oil enters the fractionating column where the gasoline vapours and other gaseous products are recovered from the top, while the heavy gas oil fractions are condensed at the bottom of the column.
11. What happens in the stabilizer of fixed-bed catalytic cracking?
a) Coke is obtained in it
b) Coal gas is formed in it
c) Butane is formed
d) Gasoline is recovered
Explanation: The condensed vapours of the catalytic system are send to the stabilizer, where the dissolved gases are removed and gasoline is recovered. The light gases produced in cracking are no longer allowed to escape into the air.
12. Which type of raw materials are formed from the light gases produced by cracking?
a) Synthetic rubber
b) Freezing agents
d) Inorganic compounds
Explanation: These light gases form valuable raw materials for the synthesis of new types of fuel. The other materials such as antifreeze, plastics and synthetic rubber are obtained from these gases.
13. Which of the following is the main disadvantage of hydrogenation cracking?
a) It cannot achieve complete cracking
b) It creates holes in the reactor
c) It is expensive and intricate
d) It requires more human effort
Explanation: In hydrogenation cracking, the heavy oil is cracked in the presence of hydrogen under high temperature and pressure. Complete cracking can be achieved by recycling.
14. In fluid-bed catalytic cracking, cracking takes place on ___________________
a) The side walls of the turbulent
b) The surface of the turbulent
c) Upper portion of the turbulent
d) Instruments of the turbulent
Explanation: Cracking takes place on the surface of the turbulent catalyst bed as it circulates with the oil vapours in the reactor at a temperature of 530 oC and at a pressure of about 3 to 5 kg/cm2.
15. Fluid-bed catalytic cracking products contain high proportions of aromatic and iso-paraffin compounds than thermal cracking process.
Explanation: The products obtained in fluid-bed catalytic cracking are distributed in different chambers due to which it has higher proportions of aromatic and iso-paraffin compounds than thermal cracking. This process is used by the industries for the cracking process.
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