17 Questions
What is a batch reactor?
A reactor where the stirring is efficient, resulting in all fluid elements having the same composition, but the composition is time-dependent.
How does a Continuous Stirred-Tank Reactor (CSTR) differ from a batch reactor?
In a CSTR, the feed mixture continuously enters and the outlet mixture is continuously withdrawn, maintaining a constant reaction rate and identical outlet concentration to the internal composition.
What type of reactions are tubular reactors generally used for?
Tubular reactors are generally used for gaseous reactions, but are also suitable for some liquid-phase reactions.
What is a fluidized bed reactor?
A reactor where the bed of solid particles is suspended and behaves like a fluid due to the upward flow of gas.
What is a packed bed reactor?
A reactor filled with a stationary bed of solid particles, typically used for catalytic reactions.
Describe the flow pattern in a stirred tank reactor.
In a stirred tank reactor, there is a consistent mixing of the reactants due to efficient stirring, resulting in uniform composition throughout.
What is the general form of the overall material balance equation for a chemical reactor?
Overall Material Balance = Input = Output + Rate of Disappearance + Rate of Accumulation of Reactant A
What is the equation for the fractional conversion of reactant A, $X_A$, in a steady-state process?
$X_A = 1 - \frac{F_A}{F_{A0}}$
What is the space-time equation for a zero-order irreversible chemical reaction $A \rightarrow$ Products?
$\tau = \frac{V}{Q} = \frac{V}{Q_0(1-X_A)}$
What is the space-time equation for a second-order irreversible chemical reaction $2A \rightarrow$ Products?
$\tau = \frac{V}{Q_0} \left( \frac{1}{X_A} - 1 \right)$
How does the residence time requirement dictate the sizing of a Continuous Stirred-Tank Reactor (CSTR)?
The longer the residence time required, the bigger the reactor volume at a constant volumetric flow rate. The residence time requirement is the key factor that dictates the sizing of a CSTR.
What is the principal advantage of a fluidized bed reactor over a fixed bed reactor?
The principal advantage of a fluidized bed over a fixed bed is the higher heat transfer rate.
Why are small-diameter tubes used in tubular reactors when high heat-transfer rates are required?
Small-diameter tubes are used to increase the surface area to volume ratio, which enhances heat transfer.
What are the two basic types of packed-bed reactors mentioned in the text?
The two basic types of packed-bed reactors are: 1) those in which the solid is a reactant, and 2) those in which the solid is a catalyst.
What is the essential feature of a fluidized bed reactor?
The essential feature of a fluidized bed reactor is that the solids are held in suspension by the upward flow of the reacting fluid.
What is the space time ($\tau$) in a Continuous Stirred-Tank Reactor (CSTR)?
The space time ($\tau$) is the time required to process one reactor volume of feed.
Express the space time ($\tau$) in terms of the given variables ($C_{Ao}$, $V$, $F_{Ao}$, $v_o$).
$\tau = \frac{V}{v_o} = \frac{C_{Ao}V}{F_{Ao}}$
Study Notes
Material Balance and Reaction Rates
- Material balance equation: Input = output + rate of disappearance + rate of accumulation of A
- At steady-state process, rate of accumulation of reactant A = 0
- FAO = FA + (-rA)V, where FA = FAo - FAo XA, and XA is the fractional conversion of reactant A
Chemical Reaction Orders
- Zero-order irreversible chemical reaction: A → Product
- Second-order irreversible chemical reaction: 2A → Product
- N'th-order irreversible chemical reaction: nA → Product
CSTR Sizing
- CSTR sizing is dictated by residence time requirement
- Longer residence time requires a bigger reactor volume at constant volumetric flow rate
- Important factors to consider: heat transfer, safety, and confinement of hazardous reactants and products
Reactor Types
- Classified by: mode of operation, phases present, and reactor geometry
- Modes of operation: batch or continuous
- Phases present: homogeneous or heterogeneous
- Reactor geometries: flow pattern and manner of contacting the phases
- Examples: stirred tank reactor, tubular reactor, packed bed, fluidized bed
Batch Reactor
- Stirring is efficient, resulting in uniform composition throughout the reactor
- Composition is time-dependent, but no input or output until the reaction is completed
- Used in pharmaceuticals and fermentation manufacturing
Continuous Stirred-Tank Reactor (CSTR)
- Feed mixture continuously enters and outlet mixture is continuously withdrawn
- Reaction rate is approximately the same throughout the reactor
- Outlet concentration is identical to the internal composition
Tubular Reactor
- Suitable for gaseous reactions and some liquid-phase reactions
- Small-diameter tubes increase the surface area to volume ratio for high heat-transfer rates
Packed Bed Reactors
- Two types: solid is a reactant or a catalyst
- Heat-transfer rates are poor in large diameter packed beds
Fluidized Bed Reactors
- Solids are held in suspension by upward flow of reacting fluid
- Promotes high mass and heat-transfer rates, and good mixing
- Higher heat transfer rate compared to fixed bed reactors
CSTR Design Equations
- Space time (τ) is the time required to process one reactor volume of feed
- τ = V / vo, where V is the volume of the reactor, and vo is the volumetric flow rate
This quiz covers factors influencing reactor design, including heat transfer, safety considerations, reactor types based on mode of operation and phases present, and reactor geometry. Test your knowledge on reactor design characteristics and classifications.
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