Which of the following statements about residence time distribution (RTD) is correct?
Answer: B
RTD characterizes how long different fluid elements spend in a reactor and is fundamental to reactor design, independent of whether flow is laminar or turbulent.
Q.62Medium
A CSTR operating at steady state processes an exothermic reaction. If the inlet temperature increases by 10°C while maintaining constant coolant flow rate, which parameter is most likely to increase?
Answer: B
Higher inlet temperature increases reaction rate (via Arrhenius equation) in an exothermic reaction, leading to higher conversion. Heat removal capacity depends on coolant flow and ΔT.
Q.63Medium
For a reversible reaction A ⇌ B with equilibrium constant Ke = 4, what is the maximum theoretical conversion in a batch reactor at equilibrium?
Answer: B
At equilibrium: Ke = [B]/[A] = 4. If initial [A]₀ = C, then at equilibrium: 4 = X/(1-X), solving X = 0.8 or 80%
Q.64Medium
In a semi-batch reactor where reactant A is fed continuously to a batch of reactant B, which advantage is realized?
Answer: A
Continuous feeding of A reduces the instantaneous reaction rate and heat generation, allowing better temperature control and potentially reducing side reactions.
Q.65Easy
The Damköhler number (Da) for a chemical reaction is defined as the ratio of:
Answer: B
Da = (residence time)/(characteristic reaction time) = kτC^(n-1). When Da >> 1, reaction is fast; Da << 1, reaction is slow.
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Q.66Medium
A series of 3 identical CSTRs in cascade is used to process a first-order reaction with overall conversion X = 90%. Which statement is true?
Answer: C
For equal volume CSTRs in series processing first-order reaction: C = C₀/(1+kτ)ⁿ, showing exponential decrease in concentration.
Q.67Medium
In a fixed-bed catalytic reactor, what is the primary cause of catalyst deactivation by sintering?
Answer: B
Sintering involves migration of metal atoms on the catalyst surface, leading to agglomeration and reduction of active surface area, particularly at high temperatures.
Q.68Hard
For a second-order reaction in a PFR, increasing the inlet concentration while maintaining constant volumetric flow rate will result in:
Answer: C
In a PFR, conversion (fractional) depends on space-time and reaction kinetics but is independent of inlet concentration for a given residence time.
Q.69Medium
Which reactor configuration would be best suited for a fast, highly exothermic reaction where precise temperature control is critical?
Answer: B
Semi-batch allows controlled feeding of reactants, limiting instantaneous heat generation while maintaining good mixing and temperature control.
Q.70Hard
The Weisz-Prater criterion is used to determine:
Answer: A
Weisz-Prater number: CWP = (k''ρcRp²)/De. If CWP << 0.15, internal diffusion limitations are negligible.
Q.71Medium
In a membrane reactor for an equilibrium-limited reaction, what is the primary advantage?
Answer: B
By selectively removing product through the membrane, the equilibrium constant expression is displaced, allowing conversion beyond the thermodynamic limit.
Q.72Medium
The mean residence time in a reactor can be calculated from RTD data using:
Answer: D
Both equations are valid: the integral formulation and the volumetric flow definition give the same mean residence time.
Q.73Hard
For parallel reactions where A → B (desired) with rate constant k₁ and A → C (undesired) with rate constant k₂, the selectivity towards B is maximized by:
Answer: A
If Ea1 > Ea2, increasing temperature favors the desired reaction with higher activation energy, improving selectivity to B.
Q.74Easy
The conversion in a batch reactor at any time can be found by integrating the rate equation. For a first-order reaction, the half-life is:
Answer: D
For first-order: t₁/₂ = ln(2)/k = 0.693/k, which is independent of C₀ and inversely proportional to k.
Q.75Medium
In a tubular reactor with axial dispersion, increasing the Peclet number (Pe) results in:
Answer: A
Peclet number Pe = uL/D. High Pe means low diffusion relative to convection, approaching ideal PFR behavior with narrow RTD.
Q.76Easy
For the reaction 2A + B → Products, if the reaction is 2nd order in A and 1st order in B, the rate equation is:
Answer: A
Reaction order is determined by experimental data, not stoichiometry. The given orders are 2nd in A and 1st in B, so rate law is r = k[A]²[B].
Q.77Medium
In a heterogeneous catalytic reaction, the overall rate is limited by which step if the external mass transfer coefficient is very small?
Answer: C
A very small external mass transfer coefficient creates a large resistance to diffusion from bulk to particle surface, making external mass transfer the rate-limiting step.
Q.78Hard
For a polymerization reaction in a batch reactor, the polydispersity index (PDI) and average molecular weight depend on:
Answer: B
PDI and molecular weight distribution in batch polymerization depend on the relative magnitudes of propagation and termination reactions and the degree of conversion achieved.
Q.79Medium
In a plug flow reactor (PFR), what is the relationship between conversion and reactor volume for a first-order reaction?
Answer: B
For a first-order reaction in PFR, X = 1 - exp(-kτ), showing exponential relationship with residence time and thus volume.
Q.80Easy
What is the order of reaction if the half-life period is independent of initial concentration?
Answer: B
For first-order reactions, t₁/₂ = 0.693/k, which is independent of initial concentration C₀.
