How a chemical process works: reactions, separations, catalysts and flowsheets

By the end you will be able to

• Identify the main blocks of a chemical plant and the utilities that support it
• Distinguish conversion, selectivity and yield, and calculate theoretical raw material use from an equation
• Explain how temperature, pressure and product removal shift equilibrium, and why rate and equilibrium conflict
• Describe what a catalyst changes, how homogeneous and heterogeneous catalysts differ, and why catalysts deactivate
• Estimate the energy and utility costs of key unit operations from source tables
• Read a flowsheet and material and energy balance, and apply inherent safety principles to judge a design

Contents

1. Part 1 The anatomy of a chemical plant

   Every chemical plant, whether it makes sulphuric acid or a medicine, is built from the same few blocks: prepare the feed, react it, separate what comes out, send the unreacted part back, purify the product and ship it. Around this sits a second plant that supplies steam, cooling water, power, fuel and nitrogen. Knowing the blocks lets you read any process and see where the money goes.

   • A plant is a reactor wrapped in separations and recycle
   • Utilities are a second plant that runs alongside the first
   • Raw materials usually dominate cost, so yield is the first lever
2. Part 2 Reaction basics that decide the economics

   A handful of ideas from chemistry decide whether a process makes money: how much raw material the equation demands, how much of the feed reacts, how much of what reacts becomes the right product, where equilibrium lets the reaction stop, how fast it goes, and how much heat it gives off. Each one translates directly into tonnes, equipment size and energy.

   • Stoichiometry sets the floor on raw material use
   • Conversion, selectivity and yield are three different numbers
   • Equilibrium decides where a reaction wants to stop
   • Rate, temperature and heat removal pull in opposite directions
3. Part 3 Catalysts: what they change and what they cannot

   Wittcoff estimates that about 90% of industrial chemical processes use a catalyst. A catalyst speeds a reaction without being used up, but its real commercial value is usually selectivity: steering molecules towards one product among several possible ones. It cannot move an equilibrium, it has to be separated from the product, and it slowly dies.

   • A catalyst opens a lower road but does not move the destination
   • Homogeneous or heterogeneous: the choice is really about separation
   • Every catalyst dies, and plants are built around that fact
4. Part 4 Unit operations, their energy bills, and batch versus continuous

   Around 1910 engineers at MIT noticed that the physical steps in chemical plants repeat across industries: heat transfer, fluid flow, distillation, filtration and so on. They called them unit operations. Most of a plant's energy goes into these steps rather than into the reaction. How they are run also depends on scale: tonnes a year in batches, or hundreds of thousands of tonnes continuously.

   • Every separation exploits a difference in a physical property
   • Distillation and evaporation are paid for in steam
   • Heat exchange and compression decide the energy bill
   • Scale and product type decide between batch and continuous
5. Part 5 Reading a flowsheet, and safety as a design input

   A flowsheet compresses a whole plant into one diagram: what goes in, what happens at each step, and what comes out. With a material and energy balance attached, it shows where money and risk sit. Working through the contact process for sulphuric acid ties together everything so far. Then we look at hazards, because Kent's safety chapter treats them as a design input from the first sketch.

   • Walking through the contact process step by step
   • The material and energy balance tells you what the plant earns
   • Inherent safety: remove the hazard before adding protection
   • Flixborough and Bhopal turned inventory into a design variable
6. Wrap-up Key terms, try it in the table, final quiz, sources