Chemical Reactors | Applications of Chemical Reactors

Chemical Reactors and their Applications:

Chemical reactions occur almost everywhere in the environment; however, a chemical reactor is defined as a device properly designed to let reactions occur under controlled conditions toward specified products. To a visual observation, chemical reactors may strongly differ in dimensions and structure; nevertheless, in order to derive a mathematical model for their quantitative description, essentially two major features are to be considered: the mode of operation and the quality of mixing.

Batch Reactor:

A batch reactor is a type of reactor in which reactants are added, kept for some time, and after processing are withdrawn as product. Each batch is a closed system and the total mass of each batch remain fixed till the end of reaction. As far as volume is concerned, the volume or density of each batch may vary as reaction proceeds. With the proceeding of reaction, heat may be evolved in the reactor due to the exothermic reaction. To control the evolved heat, Batch Reactor is equipped with a heat exchanger like cooling jacket or coils.

Mean Residence Time:

The time for which reactants are kept in the Batch Reactor is known as Mean Residence Time. It is taken as a measure of performance of Batch Reactor.

t = v/u = volume of the reactor/flow rate of feed in the reactor

Working Principle of a Batch Reactor:

§  As mentioned before in Batch Reactor, reactants are added in the reactor of fixed volume and size, and after certain time products are withdrawn. A batch reactor has neither inflow nor outflow of reactants or products while the reaction is being carried out.

§  This is an unsteady state operation, where composition changes with time; however, at any instant the composition and temperature throughout the reactor is uniform due to vigorous stirring.

Application of Batch Reactor:

§  Typically for liquid phase reactions that require long reaction time.

§  Used only when a small amount of product is required.

§  Used when different batches of different products are required as in Pharmaceutical Industries.

Favored when a process is in the development stage or to produce expensive products.

Continuous Stirrer Tank Reactor:

As name shows, CSTR is a type of reactor in which feed is entered continuously with the continuous withdrawal of the product (Steady State Process). A stirrer is present in CSTR with the help of which fluid particles that enter the reactor are instantaneously dispersed throughout the reactor volume. CSTR may be employed in series as well as parallel arrangement. At steady state conditions, the flow rate in must be equal the mass flow rate out.

Residence Time in CSTR:

The average amount of time a discrete quantity of reagents spends inside the tank.

Residence Time = Vol. Flow Rate/Vol. of the tank

Applications of CSTR:

§  CSTR are most commonly used in industrial processing, primarily in homogeneous liquid phase flow reactions where constant agitation is required. They may be used by themselves, in series, or in a battery.

§  Fermenters are CSTRs used in biological processes in many industries such as brewing, antibiotics, and waste treatment. In fermenters, large molecules are broken down into smaller molecules, with alcohol produced as a by-product.

Plug Flow Reactor:

Plug Flow Reactor (sometimes called Continuous Tubular Reactor or Piston Flow Reactor) is a model used to describe chemical reactions in continuous, flowing systems of cylindrical geometry. The necessary and sufficient condition for Plug flow is the residence time in the reactor to be the same for all elements of the fluid.

Applications of Plug Flow Reactor:

1. Plug Flow Reactor employed in the industrial applications where a highly exothermic or explosive process is involved.

2. It ensures the safe heat transfer between the instrument and the surrounding.

3. It is commonly used to ensure the static mixing of the components.