8. Technical Chemistry

Question 1

❓ What historically drove large-scale production in the chemical industry?

Answer 1

✅ The demand for vital chemicals needed to produce other products, rather than direct consumer demand.

Question 2

❓ What was the first chemical to experience high industrial demand?

Answer 2

✅ Sodium carbonate (Na₂CO₃), also known as soda ash.

Question 3

❓ What industrial process was first developed to produce sodium carbonate?

Answer 3

✅ The Leblanc process.

Question 4

❓ What were the main reactants in the Leblanc process?

Answer 4

✅ Sodium chloride (NaCl) and sulfuric acid (H₂SO₄).

Question 5

❓ What factors must be considered when scaling up a chemical process?

Answer 5

✅
1. Availability & affordability of raw materials.
2. Scalability of machinery & processes.
3. Investment & production costs.
4. Pricing & profitability.
5. Time needed to recover the investment.

Question 6

❓ What additional factors do modern industries consider?

Answer 6

✅
1. Product quality & control.
2. Operational cost reduction.
3. Waste minimization & utilization.
4. Automation & sustainability.
5. Worker safety.
6. Use of AI in process optimization.

Question 7

❓ What is a chemical process?

Answer 7

✅ A series of transformations that convert raw materials into valuable products on an industrial scale.

Question 8

❓ What are unit operations?

Answer 8

✅ Basic steps in a chemical process, involving physical or chemical changes.

Question 9

❓ What is an example of a unit operation?

Answer 9

✅ A heat exchanger, which transfers heat between fluids without mixing them.

Question 10

❓ What is a shell-and-tube heat exchanger?

Answer 10

✅ A device that increases heat transfer by having one fluid circulate through tubes and another through an external shell.

Question 11

❓ What are process flow diagrams (PFDs)?

Answer 11

✅ Diagrams that provide an overview of a chemical process, showing unit operations and material flow.

Question 12

❓ What are piping and instrumentation diagrams (P&IDs)?

Answer 12

✅ Detailed diagrams showing pipes, control instruments, and safety features, crucial for process control and safety.

Question 13

❓ How are unit operations and valves labeled in P&IDs?

Answer 13

✅
Unit operations are labeled with a letter (e.g., “F” for filter) and a number.
Valves are labeled with a type-related letter and number.

Question 14

❓ What is a material balance?

Answer 14

✅ A mathematical model that quantifies mass flow in and out of a system using differential equations.

Question 15

❓ What factors influence material balances?

Answer 15

✅ Flows, densities, concentrations, residence times, temperature, pressure, and enthalpy.

Question 16

❓ What is an energy balance?

Answer 16

✅ Similar to material balance, but accounts for energy entering and leaving a system, based on thermodynamics.

Question 17

❓ What is fluid flow in industrial processes?

Answer 17

✅ The study of how fluids move in pipes, valves, and reactors, using models to predict pressure drops & design pipe diameters.

Question 18

❓ What is viscosity?

Answer 18

✅ A fluid’s resistance to flow, affecting fluid dynamics and energy requirements in a process.

Question 19

❓ What is heat transfer?

Answer 19

✅ The study of how heat moves in a system, influenced by thermal conductivity of materials.

Question 20

❓ What is process control?

Answer 20

✅ The use of sensors, valves, and controllers to maintain stable temperature, pressure, and flow rates in a process.

Question 21

❓ How are process control equations typically solved?

Answer 21

✅ Using differential equations and the Laplace transform.

Question 22

❓ What is the Laplace transform?

Answer 22

✅ A mathematical tool that converts differential equations into algebraic equations for easier solving.

Question 23

❓ Why is the Laplace transform important in chemical engineering?

Answer 23

✅ It simplifies process control models making it easier to analyze system behavior.

Question 24

❓ What is the purpose of studying unit operations in water treatment?

Answer 24

✅ To understand how different processes work and how assumptions impact mathematical models.

Question 25

❓ How have advancements in computer simulations affected mathematical models?

Answer 25

✅ They have led to the development of more complex and sophisticated models based on simplified assumptions.

Question 26

❓ How can unit operations be classified?

Answer 26

✅ They can be classified into:Units involving chemical reactions.Units involving physical or chemical separation.Units using heat as a driving force (e.g. distillation heat exchangers).

Question 27

❓ What is the function of a shell-and-tube heat exchanger?

Answer 27

✅ To transfer heat between two fluids without mixing them.

Question 28

❓ What are the basic assumptions of a heat exchanger model?

Answer 28

✅There are two separate fluids that exchange heat.The fluids move in parallel or counter flow.The cold fluid is heated and the hot fluid is cooled.There are no heat losses during transfer.

Question 29

❓ What are parallel flow and counter flow?

Answer 29

✅Parallel flow: Both fluids move in the same direction.Counter flow:Fluids move in opposite directions maximizing heat transfer efficiency.

Question 30

❓ What is the driving force of heat exchange in a heat exchanger?

Answer 30

✅ The temperature difference between the hot and cold fluids at each point.

Question 31

❓ What does the heat transfer equation show?

Answer 31

✅ That heat transfer is proportional to:The heat transfer coefficient.The surface area available for heat exchange.The log-mean temperature difference (LMTD).

Question 32

❓ What is the log-mean temperature difference (LMTD)?

Answer 32

✅ A calculated value that ensures the heat transfer equation remains realistic considering the temperature variations along the heat exchanger.

Question 33

❓ Why is the log-mean temperature difference always positive?

Answer 33

✅ Because it represents a decreasing function of temperature difference ensuring accurate calculations.

Question 34

❓ Why are simplified mathematical models useful in engineering?

Answer 34

✅ They allow for quick estimations design criteria development and an initial understanding of system behavior.

Question 35

❓ When do simplified models become realistic?

Answer 35

✅ When the assumptions closely reflect reality making them useful for engineering applications.

Question 36

❓ What is chemical reaction engineering?

Answer 36

✅ It involves designing reactors for industrial chemical reactions ensuring proper mixing contact time and controlled conditions.

Question 37

❓ Why are simplified mathematical models important in chemical reaction engineering?

Answer 37

✅ They help understand complex reactions predict outcomes and design reactors efficiently.

Question 38

❓ What are the two main types of ideal reactors?

Answer 38

✅Ideal continuous reactors (steady-state): Includes stirred-tank and plug flow reactors.Ideal batch reactors: No flow in or out reactions occur in a closed system.

Question 39

❓ What are the key assumptions of an ideal batch reactor?

Answer 39

✅Perfectly stirred – uniform concentration throughout.No inflow or outflow – closed system.Reaction rate depends on reactant concentrations.

Question 40

❓ What does the mass balance equation describe in a batch reactor?

Answer 40

✅ The change in reactant concentration over time showing that the concentration decays exponentially if assumptions hold.

Question 41

❓ How can we express conversion in a batch reactor?

Answer 41

✅ Conversion (X) of reactant A is defined as the fraction of A reacted:𝑋=(𝐶𝐴0−𝐶𝐴)/𝐶𝐴0When volume is constant:𝐶𝐴=𝐶𝐴0(1−𝑋)

Question 42

❓ What are the key assumptions of a stirred-tank reactor?

Answer 42

✅Perfect mixing – uniform concentration.Steady-state operation – no accumulation over time.Outlet concentration equals the reactor concentration.

Question 43

❓ What is the mass balance equation for a CSTR?

Answer 43

✅ Since there is no accumulation the mass balance simplifies to an algebraic equation relating conversion and residence time (τ):𝑋=𝑘𝜏/(1+𝑘𝜏) Where:X = Conversionk = Reaction rate constantτ = Residence time

Question 44

❓ How does increasing residence time affect conversion in a CSTR?

Answer 44

✅ A higher residence time (τ) increases conversion (X) but is limited due to complete mixing reducing efficiency.

Question 45

❓ What are the key assumptions of a plug flow reactor?

Answer 45

✅No axial mixing – reactants move in a uniform flow.Radial concentration is uniform.Concentration changes along the reactor length.

Question 46

❓ How does the mass balance equation differ in a PFR?

Answer 46

✅ The differential mass balance equation shows that conversion changes gradually along the reactor:𝑑𝑋/𝑑𝑉=𝑟𝐴/𝐹𝐴0​After integration it relates conversion to reactor volume.

Question 47

❓ How does conversion in a PFR compare to a CSTR?

Answer 47

✅ PFR achieves higher conversion for the same reactor volume because reactants do not mix maintaining a higher driving force.

Question 48

❓ How do real reactors compare to ideal reactors?

Answer 48

✅Real reactors behave somewhere between a PFR and a CSTR due to imperfect mixing and axial dispersion.

Question 49

❓ What factors increase complexity in real reactors?

Answer 49

✅Multiple reactions.Reversible reactions.Temperature variations requiring energy balances.Heterogeneous catalysts.

Question 50

❓ Why are simple models still valuable?

Answer 50

✅They provide a foundation for understanding reactor behavior and serve as a starting point for complex designs.

Question 51

❓ What is process design?

Answer 51

✅ It involves making decisions on how materials will be chemically or physically transformed to achieve a desired product while considering constraints such as regulations budgets and resources.

Question 52

❓ How does process design differ from product design?

Answer 52

✅ Process design focuses on "how" to produce a known product while product design focuses on "what" the product will be.

Question 53

❓ What are the main steps in process design?

Answer 53

✅Define output specifications (composition purity quantity and budget constraints).Generate potential engineering solutions.Compare and optimize solutions.Implement the best solution.

Question 54

❓ What are common challenges faced in process design?

Answer 54

✅Unknown input or steps – defining output without knowing how to achieve it.Unknown steps – input and output are known but the process isn't.Optimization – process is known but needs improvement.Adaptation – modifying a process due to new regulations or constraints.

Question 55

❓ Why is rescaling a process difficult?

Answer 55

✅ Scaling is nonlinear and must consider constraints like:Regulations (health safety environmental).Financial constraints (investment & operational costs).Final product properties.

Question 56

❓ What are key goals of process optimization?

Answer 56

✅Reducing environmental impact.Utilizing waste streams.Enhancing safety.Lowering energy use.Reducing production times.

Question 57

❓ What is the bootstrapping method in process design?

Answer 57

✅ It focuses on meeting constraints with low-detail estimates refining solutions over time as more information is gathered.

Question 58

❓ What key documents are generated in process design?

Answer 58

✅Early stages ("Front End One")Process flow diagrams.Basic mass & energy balances (for economic feasibility).Later stagesPiping & Instrumentation Diagrams (P&IDs).Specification datasheets.Equipment & instrument lists.

Question 59

❓ How are documentation revisions tracked?

Answer 59

✅ Documents are labeled iteratively (e.g. A B C for revisions) ensuring all lines valves instruments and units are identified with operating conditions like pressure temperature and flow rate.

Question 60

❓ How are early process calculations performed?

Answer 60

✅ Basic unit operations (e.g. cooling towers dewpoint vessels) are calculated using spreadsheets.

Question 61

❓ What software is commonly used for process simulations?

Answer 61

✅ Advanced unit operations (e.g. distillation & absorption columns) use simulation software like Aspen-Hysys or ChemCAD.

Question 62

❓ Why are initial approximations important in simulations?

Answer 62

✅ Many simulations require initial values and results can be sensitive to them. Engineers must generate realistic approximations before refining them with complex models.

Question 63

❓ What is a HAZOP analysis and why is it important?

Answer 63

✅ Hazard and Operability (HAZOP) studies identify potential faults in P&IDs assess risks and develop safety measures to prevent incidents.

Question 64

❓ When does detailed design begin and what does it involve?

Answer 64

✅ After finalizing process design and HAZOP studies civil and mechanical engineers work on:3D piping models.Electrical wiring diagrams.Instrumentation layouts.