From atoms to the

enterprise, the many scales of

Chemical Engineering
Srinivas Rangarajan

IIT Madras CH1010 Intro to ChE Lecture (Sep 17th 2021)

Chemical Engineering: Addressing global grand challenges in energy, health, water, food, and environment
Several of the fourteen grand challenges in
engineering identified by the National Academy
of Engineers require significant research and
development by future generations of chemical
engineers (ChemEs)
• Make solar energy economical: Chemical Engineers are
actively involved in developing new materials for
harnessing solar energy to produce electrons or split water
• Develop carbon sequestration methods: ChemEs are at the
forefront of efforts of developing materials and devices to
capture CO2 from power plants AND even directly from the
air!
• Managing nitrogen cycle & Provide access to clean water:
ChemEs are engineering new technologies that address the
nexus of food, water, and energy. Technologies being
developed include: sustainable production of ammonia,
National Academy of Engineers: Fourteen grand challenges removal of nutrients and waste from water, and producing
energy from waste.
• Engineer better medicines and advance health informatics:
• Reverse-engineer the brain: ChemEs are helping to
ChemEs are at the forefront of designing and producing next-
understand how the brain works to design solutions to
generation medicines, developing models for personalized
address neurological disorders and engineer brain-machine
medicine, and understanding the spread of epidemics.
interfaces of smart prosthetics.
Finally, ChemEs at Lehigh are committed to advancing personalized
learning and engineering next-generation tools of scientific
My journey so far
• Born and raised in Chennai – lived in Adyar from the age of 7 to 21.

• Graduated from IIT Madras – 2007: BTECH project with Prof. Nagarajan:
Study of the generation, transport, and deposition of particles in a clean
room environment
• Internship: Reliance Industries, Mathematical models for ethylene vinyl acetate
copolymerization

• Worked at Shell Technology India and Shell Global Solutions, NL (2007-

08)
• Hydroprocessing group: Developed mathematical models for hydrocracking of
Fisher Tropsch waxes
My journey so far (contd…)
• PhD, University of Minnesota (2008-13): Thesis – Generation, analysis,
and modeling of complex reaction networks using RING

• Postdoc, University of Wisconsin-Madison (2013-16): Ab initio analysis

of heterogeneous catalytic modeling

• Assistant professor, Lehigh University (2017-)

• A computational group at the intersection of heterogeneous catalysis,
machine learning, optimization, and informatics
Computational
catalysis and
materials design
group
Current research: Multiscale computational catalysis and materials
design
Sour gas treatment Ethylene oxidation Liquid organic hydrogen carriers

H2
CO2
H2S

CO H2O

H2
Collaborator: Jonas Baltrusaitis Collaborator: Israel Wachs

Machine learning in mechanistic Molecule design Covalent organic frameworks

modeling

Collaborator: Mark Snyder, Jeetain Mittal

6
 Multiple scales of modeling in
chemical engineering Month - year Enterprise

103-5 m
Time scales

Process units &

Mins to days plants
1-100 m

Clusters of
Milliseconds molecules/material

10-6 m

Picoseconds – Atoms and

microseconds molecules

10-10 m 10-9 m Length scales

 Ammonia synthesis

Ammonia is the largest produced chemical globally. It’s used in fertilizer

production (urea for instance). Ammonia is produced using nitrogen in the air
and hydrogen produced from methane (a chemistry known as steam
methane reforming). Imagine you have a supplier that can give you natural
gas and you can just suck air from the atmosphere

Discuss the different units the process should have so that you can get a pure
product stream of ammonia in the end.
Answering different questions requires considering differing scales
Identify the scales of this process
• What is the kinetics of SMR and ammonia synthesis?
• What is the equilibrium of these reactions?
• What is the heat capacity of the reactant mixture?
• How much energy is required to heat the reactants to reaction temperature?
• What material to use to separate O2 and N2?
• What is the optimal reactor temperature?
• What is the overall cost of for producing 1 Kg of ammonia?
• How much ammonia should be produced in the plant?
• Where to locate the ammonia plant?
 A schematic of biomass conversion options…

Daoutidis AIChE J,
59, 3-18 (2013)
 Example: Cellulose conversion

Ethanol
Enterprise scale

Process

Atom/molecule
scale

CO2 + H2
 Developing a mechanistic model of formic acid
Formic acid
(FA) CO2 + H2

Pd/C catalyst

Active site?
Surface environment?
Reaction mechanism?
Palladium

13
 The reaction network has 27 steps, and 12 intermediates
H
OH Formyl pathway

OH
O
H H H H

CO + H2O +H Carboxyl Formate +H CO2 + H2

pathway pathway
CO2 +O
CO2 + OH +O CO2 + OH
H+H
+OH OH O+H +OH
CO2 + H2O CO2 + H2O
H
+CO +CO
CO2 + HCO CO214+ HCO
 Compute energetics using Density Functional Theory
Carboxyl pathway
HCOOH(g)  HCOOH*  COOH*  CO2
100
Pd(111)

Formate pathway
HCOOH(g)  HCOOH*  HCOO*  CO2

Pd(100)

111
Calcs with DACAPO, USPP, PW91 15
1 eV = 96.5 kJ/mol
 Compute energetics using Density Functional Theory
From Density
Microkinetic model (CSTR) functional
∆𝑆
¿
− ∆𝐻
¿
theory (DFT)
 𝑑 𝐹𝑖 𝐺
 
𝑘 𝑓=
𝑘𝐵𝑇
𝑒 𝑅
𝑒 𝑅𝑇
=𝐹𝑖𝑛 , 𝑖 − 𝐹 𝑖+ ∑ 𝜈 𝑖𝑗 𝑟 𝑗 ∀ 𝑖 ∈ 𝐼 h From
𝑑𝑡 𝑗 ∈𝐽   𝑘𝑓 Statistical
𝑘𝑟 =
 𝑑 𝜃  1= 𝐾 mechanics
𝑖 𝑆 ∑ 𝜃𝑖
= ∑ 𝜈 𝑖𝑗 𝑟 𝑗 ∀ 𝑖 ∈ 𝐼  
−∆ 𝐺 𝑟𝑥𝑛 ∆ 𝑆 𝑟𝑥𝑛 − ∆ 𝐻 𝑟𝑥𝑛

𝑑𝑡 𝑗 ∈ 𝐽
𝑆
𝑖∈ 𝐼 𝐾 =𝑒 𝑅𝑇
=𝑒 𝑅
𝑒 𝑅𝑇

𝑟  𝑗=𝑓 (𝑘 , 𝐾 , 𝐹 , 𝜃)
𝑖 + 𝐵𝐸 𝑖 ∀ 𝑖∈ 𝐼
 𝐻 𝑔𝑎𝑠
𝑖 =𝐻  

Gas phase enthalpy Binding energy Set of species

16
 Experimental information

Catalyst Flow reactor conditions

• 5 wt.% Pd/C: Sigma Aldrich • Feed: 2-5% FA, 0-2% cofeed, balance He

• Pd dispersion: 18% • 1 atm, 353-393 K

• Site density: 81 µmol/gcat • Carbon support inert under these

conditions

• Gas chromatograph (GC-TCD) used to STEM image of the supported

determine effluent-composition Pd/C catalyst

CO2 carbon selectivity is 98-99%

17
Dual site model is accurate and requires smaller deviations
(100) : (111) = 50:50 (first approximation)

CO2 turnover frequency CO turnover frequency

18
Reaction pathways of the dual site model
Carboxyl pathway CO2
H2

Pd-111

Formate pathway

Dehydration is only on
60% flux Pd-100 111
All flux through 111
under CO cofeed
conditions
19
Emerging picture: Dual site model are both likely
Active site?
Dual site model
Either 111 alone or dual
100 site
Surface environment?
CO covered
Reaction mechanism?
Formate on 100 and
carboxyl on 111

111 20
 Example: Cellulose conversion

Ethanol
Enterprise scale

Process

Atom/molecule
scale

CO2 + H2
 Designing a biphasic reactor-process system
• Fructose is water soluble sugar
• HMF is soluble in an organic solvent
• Biphasic systems are useful in such
cases… carry out the reaction in an
aqueous:organic mixture; the
reactant is in aqueous phase, the
product prefers the organic phase
• Le Chatelier’s principle…

Torres et al. Energy Environ Sci, 3, 1560-1572 (2010)

Example: Process design allows technoeconomic evaluation

Red and blue are two different solvents

 Example: Cellulose conversion

Ethanol
Enterprise scale

Process

Atom/molecule
scale

CO2 + H2
Given the distributed nature of biomass, where to locate biorefineries?

Marvin et al. Chem Eng

Sci, 67, 68-79 (2012)
Case study: Upper midwest

Decide in which of the candidate

locations to build the biorefinery to
maximize net present value of the
investment (keeping in mind the
capital and operating costs + the
revenue generated by selling the
product locally)
Best biorefinery locations are shown as diamonds