Factors Affecting Reactor Design

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Questions and Answers

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In a CSTR, the feed mixture continuously enters and the outlet mixture is continuously withdrawn, maintaining a constant reaction rate and identical outlet concentration to the internal composition.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. Signup and view all the answers

What is a packed bed reactor?

A reactor filled with a stationary bed of solid particles, typically used for catalytic reactions. Signup and view all the answers

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. Signup and view all the answers

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 Signup and view all the answers

What is the equation for the fractional conversion of reactant A, $X_A$, in a steady-state process?

$X_A = 1 - \frac{F_A}{F_{A0}}$ Signup and view all the answers

What is the space-time equation for a zero-order irreversible chemical reaction $A \rightarrow$ Products?

$\tau = \frac{V}{Q} = \frac{V}{Q_0(1-X_A)}$ Signup and view all the answers

What is the space-time equation for a second-order irreversible chemical reaction $2A \rightarrow$ Products?

$\tau = \frac{V}{Q_0} \left( \frac{1}{X_A} - 1 \right)$ Signup and view all the answers

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. Signup and view all the answers

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. Signup and view all the answers

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. Signup and view all the answers

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. Signup and view all the answers

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. Signup and view all the answers

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. Signup and view all the answers

Express the space time ($\tau$) in terms of the given variables ($C_{Ao}$, $V$, $F_{Ao}$, $v_o$).

$\tau = \frac{V}{v_o} = \frac{C_{Ao}V}{F_{Ao}}$ Signup and view all the answers

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

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Description

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.