Classification of reactions and reactors

Basic Problems of Chemical Reaction Engineering andPotential of Membrane Reactors

Department of Chemical Engineering,University of Engineering & Technology Peshawar, PAKISTAN

Challenges in Chemical Reaction Engineering

More then 30 000 specialty chemicalsapproximately 300 intermediate chemicals

produced industrially from

The vast majority of these intermediates are produced from a verylimited number of approximately 20 simple base chemicals forexample, ethylene, propylene, butane, ammonia, methanol,sulfuric acid and chlorine.

To perform efficiently the large spectrum of chemical reactions ofinterest an arsenal of specific reactor types and dedicatedoperating regimes has been developed and is applied in variousindustries.

The design of efficient and reliable reaction processes is the coresubject of Chemical Reaction Engineering, a discipline which can beconsidered nowadays as rather mature.

29 May 2016 Dr. Saeed GUL, Department of Chemical Engineering, UET Peshawar, Pakistan2


The main starting point of an analysis of reacting systems is typicallyan evaluation and quantification of the rates of the reactions ofinterest.

Based on the specific physical and chemical properties of thereactants and products a wider range of temperature and pressureconditions has to be considered during the early developmentphases.

The spectrum of reactor types available and operating principles applicableis very broad.

Reactions and reactors are often classified according to the phases present.

There are reactions that can be carried out in a single phase.However, in a reaction system often more phases are presentrequiring more sophisticated configurations and operation modes



The energy efficiency of endothermal and exothermal reactions performedindustrially is often not satisfactory.

In reaction networks, the selectivities and yields with respect to a certaintarget product are limited

Dr. Saeed GUL, Department of Chemical Engineering, UET Peshawar, Pakistan

429 May 2016

Another useful classification is based on the character of theprocess and distinguishes between continuous and discontinuous(batch) operations.

To accelerate the desired reactions and/or to influence theselectivity in reaction networks with respect to the targetproducts, frequently specific catalysts are applied.

These catalysts might be present in the same phase as the reactants(homogeneous catalysis).

To fix these often expensive materials in continuously operated

reactors, catalysts are often deposited (immobilized) on the

surface of solid porous supports (heterogeneous catalysis).





529 May 2016

Despite the large efforts devoted to further develop the field ofChemical Reaction Engineering, the performance of how chemicalreactions are carried out industrially still suffers from severalsevere limitations. Very important and not sufficiently solvedproblems are:

The rates of chemical reactions leading to desired products are often too lowto establish economically attractive processes.

The conversion of many reactions of interest isthermodynamically limited, that is, the reactions proceed also inthe opposite direction and convert products back (reversiblereactions).





629 May 2016

Despite the large efforts devoted to further develop the field ofChemical Reaction Engineering, the performance of how chemicalreactions are carried out industrially still suffers from severalsevere limitations. Very important and not sufficiently solvedproblems are:

The rates of chemical reactions leading to desired products are often too lowto establish economically attractive processes.

The conversion of many reactions of interest isthermodynamically limited, that is, the reactions proceed also inthe opposite direction and convert products back (reversiblereactions).

Concepts of Membrane Reactors

In the above figure the classic tubular reactor is shown.

This reactor possesses closed walls. Thus, the reactantsintroduced together at the reactor inlet (co - feed mode).

are typically

Often tubular reactors are filled with solid catalyst particles in order toincrease the rates and selectivities.

This classic fixed - bed or packed – bed reactor ( PBR ) is intensively studiedand used widely.


Different concepts of membrane reactors

Concept I: Retainment of homogeneous catalysts

The membrane reactor concept shown in Figure exploits themembrane to retain in the reactor soluble (homogeneous) catalysts.

Thus, it allows for continuous operation without the need to separate andrecycle the typically valuable catalysts.

Successful application for various synthesis reactions are described, forexample, by (Kragl and Dreisbach,2002).


Classification of Reactions & Reactors

Reaction:-Chemical Reactions are classified as:

Syntheses Reaction

Decomposition Reaction

Single-Displacement Reaction

Double-Displacement Reaction

Combustion Reaction

Precipitation Reaction

Oxidation/Reduction Reaction

Acid-Based Reaction


Classification of Reactions

10Dr. Saeed GUL, Department of Chemical Engineering, UET Peshawar, Pakistan29 May 2016

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