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Multi-Step Reactions

Multi-Step Reactions

Chemical reactions often occur in a stepwise fashion involving two or more distinct reactions taking place in a sequence. A balanced equation indicates the reacting species and the product species, but it reveals no details about how the reaction occurs at the molecular level. The reaction mechanism (or reaction path) provides details regarding the precise, step-by-step process by which a reaction occurs. Each of the steps in a reaction mechanism is called an elementary reaction. These...

Chemical Equilibria: Systematic Approach to Equilibrium Calculations

Chemical Equilibria: Systematic Approach to Equilibrium Calculations

Equilibrium calculations for systems involving multiple equilibria are often complex. For example, to calculate the solubility of a sparingly soluble salt in an aqueous solution in the presence of a common ion, one must consider all the equilibria in this solution. Calculations for these systems can be complicated and tedious, so a systematic approach with a series of steps is often helpful. The process is detailed below.
The first step is to identify all the chemical reactions involved, The...

Reaction Mechanisms

Reaction Mechanisms

Chemical reactions often occur in a stepwise fashion, involving two or more distinct reactions taking place in a sequence. A balanced equation indicates the reacting species and the product species, but it reveals no details about how the reaction occurs at the molecular level. The reaction mechanism (or reaction path) provides details regarding the precise, step-by-step process by which a reaction occurs.
For instance, the decomposition of ozone appears to follow a mechanism with two steps:

Rate-Determining Steps

Rate-Determining Steps

Relating Reaction Mechanisms
In a multistep reaction mechanism, one of the elementary steps progresses significantly slower than the others. This slowest step is called the rate-limiting step (or rate-determining step). A reaction cannot proceed faster than its slowest step, and hence, the rate-determining step limits the overall reaction rate.
The concept of rate-determining step can be understood from the analogy of a 4-lane freeway with a short-stretch of traffic-bottleneck caused due to...

Molecular Weight of Step-Growth Polymers

Molecular Weight of Step-Growth Polymers

Step growth polymerization involves bi or multifunctional monomers. Bifunctional monomers react to form linear step growth polymers, whereas multifunctional monomers react to form non-linear or branched polymers.
As the step-growth polymerization involves step-wise condensation of monomers, the molecular weight also builds up eventually. Consequently, high molecular weight polymers are obtained at the late stages of the polymerization, where 99% of monomers have been consumed.
The extent of the...

Free-Radical Chain Reaction and Polymerization of Alkenes

Free-Radical Chain Reaction and Polymerization of Alkenes

The conversion of alkenes to macromolecules called polymers is a reaction of high commercial importance. The structure of the polymer is defined by a repeating unit, while the terminal groups are considered insignificant. The average degree of polymerization represents the number of repeating units in the polymer molecule and is denoted by the subscript n.

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Updated: May 17, 2025

Multiscale Sampling of a Heterogeneous Water/Metal Catalyst Interface using Density Functional Theory and Force-Field Molecular Dynamics

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Published on: April 12, 2019

Population Balance Models for Catalytic Depolymerization: From Elementary Steps to Multiphase Reactors.

Lela K Manis¹, Jiankai Ge¹, Changhae Andrew Kim¹

¹Chemical and Biomolecular Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States.

Accounts of Chemical Research

|May 16, 2025

Summary

This summary is machine-generated.

Developing advanced population balance models (PBMs) enables accurate kinetic modeling for polymer recycling. These models bridge fundamental calculations and complex polymer transformations for effective waste upcycling.

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Area of Science:

Chemical Engineering
Materials Science
Computational Chemistry

Background:

Plastic waste accumulation necessitates innovative recycling solutions.
Traditional kinetic models fail for complex polymer systems with numerous reactants and intermediates.
Advanced modeling is crucial for understanding and optimizing polymer upcycling processes.

Purpose of the Study:

To develop and apply population balance models (PBMs) for accurate kinetic analysis of polymer recycling.
To couple PBMs with adsorption, desorption, and rate equations for comprehensive process simulation.
To utilize these models for mechanistic hypothesis testing, parameter extraction, and catalyst design.

Main Methods:

Development of coupled population balance models (PBMs) accounting for macromolecular species.
Integration of polymer adsorption/desorption models and small-molecule reaction kinetics.
Application of PBMs with experimental data for parameter extraction and mechanistic analysis.
Construction of PBMs from elementary rates and first-principles calculations ('bottom-up') and data analysis ('top-down').

Main Results:

PBMs successfully model complex polymer recycling kinetics, including macromolecular reactants and intermediates.
The models facilitate quantitative comparison of catalyst activities and account for mass transfer effects.
Novel catalyst architectures mimicking enzymatic depolymerization can be designed using these models.
A quantitative link is established between first-principles calculations and polymer upcycling kinetics.

Conclusions:

Population balance models offer a powerful framework for understanding and optimizing polymer recycling.
These models enable the design of more efficient catalysts and processes for plastic waste upcycling.
The integration of theoretical calculations and experimental data accelerates advancements in polymer science and sustainability.