1. Material & Energy Balances ๐
The Foundation of All Chemical Processes
Material Balance:
In - Out + Gen - Cons = Accumulation
Steady-state, no reaction: In = Out
Energy Balance:
Q - W = ฮH + ฮKE + ฮPE
Usually: Q - W โ ฮH (neglect KE, PE)
Degrees of Freedom Analysis
DOF = Variables - Independent Equations
DOF = 0: Exactly determined | DOF > 0: Underspecified | DOF < 0: Overspecified
2. Unit Operations ๐ญ
| Operation | Principle | Key Equation |
|---|---|---|
| Distillation | Vapor-liquid equilibrium | McCabe-Thiele, Fenske |
| Absorption | Gas-liquid mass transfer | NTU, HTU |
| Extraction | Liquid-liquid equilibrium | Distribution coefficient K |
| Drying | Moisture removal | Psychrometric chart |
| Evaporation | Concentration by boiling | q = UA(ฮT) |
| Filtration | Solid-liquid separation | Darcy's law |
3. Reactor Design ๐ฌ
CSTR
(Continuous Stirred Tank)
Perfect mixing. Exit conc = tank conc
ฯ = V/vโ = (CAโ-CA)/(-rA)
PFR
(Plug Flow Reactor)
No mixing. Conc varies along length
ฯ = โซdCA/(-rA)
Batch
(Batch Reactor)
No flow. Time-dependent
t = โซdCA/(-rA)
Conversion & Selectivity
Conversion X = (nAโ - nA)/nAโ
Selectivity S = Desired product / Undesired product
4. Process Control ๐๏ธ
PID Controller
u(t) = Kc[e + (1/ฯI)โซe dt + ฯD(de/dt)]
- P (Proportional): Responds to current error
- I (Integral): Eliminates steady-state offset
- D (Derivative): Anticipates future error
Control System Elements
Feedback: Measure output, compare to setpoint
Feedforward: Measure disturbance, act before effect
Cascade: Controller outputs to another controller
Ratio: Maintain ratio between two streams
5. Process Economics & Safety ๐ฐ
Economic Analysis
- NPV = ฮฃ(CF)/(1+r)โฟ
- ROI = Net Profit / Investment
- Payback = Investment / Annual CF
- Six-tenths rule: Cโ/Cโ = (Sโ/Sโ)โฐยทโถ
Process Safety
- HAZOP - Hazard and Operability
- LOPA - Layers of Protection
- Flash point, autoignition temp
- LEL, UEL (flammability limits)
6. Practice Questions ๐
Common Board Exam Questions
Q1: A CSTR has V=100L, vโ=10 L/min, CAโ=2M. For first-order k=0.1 minโปยน, find CA.
A: ฯ = V/vโ = 10 min. ฯ = (CAโ-CA)/(kCA). 10 = (2-CA)/(0.1CA). CA = 1M
Q2: What is the minimum reflux ratio for a distillation column?
A: Rmin gives infinite stages. Found using Underwood equations or pinch point method.
Q3: If equipment cost doubles when capacity increases 2.5x, what is the cost exponent?
A: 2 = 2.5^n โ n = log(2)/log(2.5) = 0.76
๐ฅ ChE Challenge ๐ฅ
Master process engineering! Unit operations, reactors, control, economics - design and optimize chemical plants!
Transform molecules, transform the world!