Undergraduate
Lectures on
Material Balances for Chemical Engineers
May 30- June 10, 2016
Chapter 1: Lecture 1:
Overview
Brian G. Higgins
Department of Chemical Engineering and
Materials Science
University of California, Davis
Class Web Site: h.ps://sites.google.com/site/ekayasolu9onsteachingvietnam/
Our schedule for the next two weeks
Tuesday, Wednesday, and Thursday: 13:30-15:30
Monday - Friday, 9:30-12:00
Homework problems due most days
Lectures will follow textbook closely.
Most problems taken from textbook
How this class relates to other classes in the program
Junior Year
Fall: ECH152A Chemical Thermodynamics Chapters 3, 4 and 5)
Winter: ECH141 Fluid Mechanics (Chapters 3 & 4)
Spring: ECH142 Heat Transfer (Chapter 8)
Spring: ECh143 Mass Transfer (Chapters 3,4,5,6,8)
Spring: ECH152b Thermodynamics (Chapters 6,7,8)
Senior Year
Winter: ECH146 Kine9cs and Reac9on Engineering (Chapters 6,7,8,9)
What is Chemical Engineering?
Chemical engineering deals with the transforma9on of ma.er through chemical
reac9ons to form new chemical, materials and products.
What is the role of Chemical Engineers?
Chemical engineers draw on fundamental sciences with sound
engineering prac9ce to design environmentally safe processes that
are economical in the global market.
Chemical engineers use principles of op9miza9on, design and process control in
developing new processes
Examples
Petrochemical industry:
Manufacture of gasoline, jet fuel, lubrica9ng oils, waxes, asphalt, coke
Chemical Industry:
New chemicals
Food Industry:
Use of heat to transform ma.er, cerviche (cold cooking), process foods
Packaging industry
Novel packaging for food products, biodegradable plas9c bo.les
Prin9ng Industry
High speed prin9ng, on-demand prin9ng, printable electronics
Electronics Industry:
Manufacture of semiconductor chips, op9cal switches, polymer photo-voltaics, fuel
cells
Biochemical Industry:
Pharmaceu9cals, enzymes bio-fuels
What is material balances all about?
Mass is conserved
or
Mass is neither created or destroyed
Example: Combus9on process
SO2 needs to be
removed from
stack gases
What is happening in a combusRon process?
The need to keep tract of molecular species!
What is happening in a scrubber process?
Limestone - Ca(OH)2 is used to absorbed unwanted SO2
(Homogeneous versus heterogeneous reacRon)
Limestone/water slurry
Material Balances and Environmental
QuesRons
Water balance for Mono Lake, Northern Sierras, Nevada
Sources and sinks of water must be in balance
Note: two major sinks: evapora9on and water export to Los Angeles
What is the nal shape/quality of the lake.
Environmental Disaster: Aral Sea in Kazakhstan
Lake Balkhash 13th largest fresh water lake
is now also threatened.
In 1980s Aral Sea was the 4th largest freshwater
lake in the world. Now, it's only 10% of its
former size!
Chemical Processes : Concept of a Flow Sheet
Flow sheet of a chemical process for manufacture
of ethyl alcohol from ethylene
Key Principles for Analysis of Reacting
Systems
Topics for this class
Mass must be conserved
Atomic species of a reacting systems cannot
be created or destroyed.
Topics for future classes
Balance of momentum must be satisfied
Balance of thermal energy must be satisfied
Thermodynamic relations must be satisfied
Analysis of Chemical Reactors and the
Connecting Disciplines
Thermodynamics Fluid Mechanics
Chemical
Kine9cs Mathema9cs
Reactor
Heat Transfer Mass Transfer
Chemical reactors are the linchpin in a chemical plant for
controlling, optimizing, manipulating
the transformation of matter through chemical reactions
Example of Reacting System
Incomplete combustion of ethane
Output of reactor can be measured
Reactor
How is the reactor performance dictated by:
reactor temperature? (how does T varying within reactor)
residence time of reactor?
inlet/exit compositions? (how does Ci varying within reactor)
laminar vs turbulent flow?
use of catalysts?(homogeneous vs hetrogeneous reactions)
Industrial Reactors
Catalytic cracker
(petroleum refinery)
Multiphase slurry reactor
Fermentors
(Pharmaceuticals)
Microuidic Reactors
(Lab -on - Chip)
Reaction front
Huang & Higgins 2008
Biochemical Reactors:
An area of increasing importance for chemical
engineers
In a chemostat, nutrients and oxygen enter a well-mixed tank containing
a cell culture, and biological reac9ons generate new cells that are harvested
in the product stream. This biological process are analyzed using Material Balances
Hierarchy of length scales associated with the
producRon of ethyl alcohol.
Concept of control volumes to analyze process at dierent length scales
The analysis of a scrubber
The concept of analyzing small parts of a problem and then assembling
the small parts into a comprehensive representaRon of the whole problem
is extremely important.
In addiRon, the concept of studying the whole problem and then breaking
it apart into smaller problems is also extremely important
