Differential Method, Order Types, Catalysts, and Chemical Reactors

Posted on Feb 8, 2025 in Chemistry

Differential Method and Types of Orders

The differential method, attributed to Van’t Hoff, is based on the actual rates of reactions, determined by measuring the slopes in concentration-time curves. However, the determination of these slopes is not very precise. The equation v = KCn can be linearized as Ln v = Ln K + n Ln C. Plotting Ln v versus Ln C should yield a straight line. The slope represents the reaction order with respect to the substance whose concentration is changing, and the intercept corresponds to Ln K.

  • Order with respect to concentration (nc): Using the initial rate procedure eliminates potential complications from product interference, leading to a reaction order corresponding to the simplest situation (the *real* order).
  • Order with respect to time: The order can vary with time.

Integration Method: Advantages and Drawbacks

The integration method is the most widely used in the interpretation of kinetic data. A drawback is that it requires some “trial and error.” One might initially assume a first-order reaction and then check if it fits the experimental results. When applied to a single kinetic curve, it tends to yield a higher order than the true order.

Classification of Catalysts

Catalysts can be classified as follows:

  1. Chemical Catalysts (Homogeneous Phase)
  2. Contact Catalysts (Heterogeneous Phase). Within contact catalysts, we have:
    • Catalytic Catalysts: Their surface is usually small, and the effect of the metal decreases with temperature. A problem is chemisorption.
    • Supports (Insulation): Increase the surface area of the former.
    • Promoters:
      • Physical Promoters: Increase stability and strength.
      • Chemical Promoters: Increase activity and selectivity.

Chemical Reactors

Understanding Reactor Capability

To understand what a reactor is capable of, we need to know:

  • Kinetics: How quickly equilibrium is reached. This informs us whether heat and mass transfer will allow the reactor to reach equilibrium.
  • Contact Model: How reagents circulate through the reactor and the type of contact they have with each other.
  • Performance Equation: The relationship between the output and input.

Information Needed for Chemical Reactor Design

  1. Degree of mixing (ideal or real).
  2. Phases present (homogeneous or heterogeneous).
  3. Transport phenomena (momentum, mass, energy).
  4. Thermodynamics: Heat of reaction, chemical equilibrium.
  5. Regime: Isothermal, adiabatic.
  6. Type of operation: Continuous, discontinuous, or semi-continuous.
  7. Chemical kinetics: Reaction rate equation.

Advantages of Continuous Monitoring Systems

Advantages of a continuous monitoring system over a discontinuous one, in the context of a reactor, include:

  • Lower labor costs due to the elimination of manual operations.
  • Ease of implementing automatic control.
  • Greater consistency in reaction conditions, leading to better product quality.

Types of Single Reactors and General Characteristics

  • Intermittent Reactor (Batch Reactor): The composition within the reactor is uniform at any given position, but it changes over time.
  • Plug Flow Reactor (Stationary Condition): The flow passes through the reactor without mixing.
  • Mixed Flow Reactor (Stationary): The feed enters the reactor, and mixing occurs instantaneously and uniformly. The composition is the same inside the reactor and at the outlet. There are molecules of reactants added initially or products that were obtained for the first time.
  • Recycle Reactor.
  • Reactors in Series.