Preface

The purpose of this article are as follows

to provide a basic roadmap to the undergraduate students who are interested in, or currently taking chemical engineering program, but still not sure about what they will learn in the future.
to give some insight of all the knowledge I have learned so far, and show the implicit connection.

All the content are based on my own experience of the program I have been taking and there might be some mistakes and (many) typos. It might be partially representative but hope it helps a bit:)

If you could read Chinese, I highly recommend reading this column. Other work of the author are also inspiring.

210322: These lecture note is quite helpful for Chem Eng students.

What major courses are included in Chemical Engineering Program

Here we exclude some courses that are provided and shared by other program (e.g. Calculus, Organic Chemistry, Analytical Chemistry, etc.) but focus on the particular chemical engineering programs.

The core courses in the program I have taken are listed here

———The followings are 2k courses

Process and Product Design Principles

Thermodynamics

Fluid Mechanics (or Transport Phenomena I)

———The followings are 3k courses

Separation Process (or Unit Operation)

Heat and Mass Transfer (or Transport Phenomena II)

Process Control and Dynamics

Chemical Reaction Engineering and Kinetics

Process Design and Integration

———The followings are 4k courses

Plant Design and Economics

2k courses build up the basic disciplines, while 3k courses extend them to application, consolidating the fundamental knowledge. 4k courses are a collection of knowledge of a specific field.

Introduction and personal insight to each course

All the content can be simplified into four character in Chinese 三传一反 (Three Transport - Heat, Mass and Momentum, and One Reaction - Kinetics)

Part 1. Introductory courses

Before admitted to an chemical engineering program, one might first take an introductory course about it. The introductory course I took it mainly introduced mole/mass balance, some basic thermodynamics and diffusion.

Process and Product Design Principles, however, is again an introductory course, only introducing mass and energy balance (maybe a bit more complicated). ~~Actually nothing much interesting~~

Part 2. Chemical Engineering Principles

~World Ruled by Laws of Thermo~

The following courses can be explained in series because they are centered at Thermodynamics.

Thermodynamics

Thermodynamics is some knowledge from physical chemistry and mechanic engineering - but interpreted by chemical engineer for better application. Before reading the material, keep in heart that ‘We are doing all these for engineering purpose’ - which means some terms are actually designed for convenience instead of anything else. Rather than trying to grab everything in brain by first glance, use it and apply it.

The four laws for thermodynamics rule the world, while the 【first and second Law】 rule your academic life.

【First Law】 is conversation, or in short, balance, which we use everywhere. It can be applied for mass, heat and momentum.

【Second Law】 on the other hand, give a direction in time about how it will progress in the following time - it tells that the world prefer chaos more.

The two laws together provide fundamentals to all the physical method for the following courses.

By the way, here are a twins of concepts that may be confusing - enthalpy and entropy.

Enthalpy is a measurement of heat. But different from internal energy, which is also a measurement of heat, enthalpy is more convenient. Why? The course will give the answer

Entropy on the other hand is a measurement of chaos, and all spontaneous events tend to increase the entropy. Higher entropy means stable and comfortable for molecules(if one is good enough, then the boss will not push him) and reduced disability to change (you know, everyone, every single molecule, are substantially lazy).

For more detailed interpretation of thermodynamics, please check my notes here (Some Chinese included)

Fluid Mechanics & Heat and Mass Transfer (Transport Phenomena)

Fluid Mechanics and Heat and Mass Transfer are the two courses where we describe how we transfer heat, mass and momentum to the place we want by applying the first and 【Second Law】 of thermodynamics.

For the 【First Law】, we usually write in the form of:

$ACCUMULATION=IN-OUT+GENERATION$

By the way, steady state, which we usually assume to be true in the following courses, means no ACCUMULATION with time passing, but there might be IN or OUT.

The most representative expression is Reynold Transport Theorem but most famous one is Bernoulli Equation. For more about fluid mechanics, please check this note(to be added).

The expression can be extremely complicated, since we have to use many fancy integration. If we are to simplify all the complicated terms and give a lot of smart assumptions, we come to this expression of conservation (take energy/heat as an example)

$\frac{\partial T}{\partial t} = \alpha \triangledown^2T+\frac{\dot{q}}{\rho c}$

The inversed triangle is called Laplace operator, which we might have learned in multivariable calculus. But we are not going to detail. The only thing is, it gives the spatial distribution. While the $\frac{\partial T}{\partial t} $ term gives time axis. $\frac{\dot{q}}{\rho c}$ indicates external forces.

It is like we are given a Google Map App, it gives every location, but we need to decide the starting point and ending point (or even passing by point), which are called boundary conditions. Only in this way we can figure out our route.

When it comes to Second Law, wait, we don’t want to always deal with the abstract entropy, but we want to know the direction and trend of changing, so here it comes:

$Flux = - \frac{Driving\ Force}{Resistance}$

Driving Force is the difference in temperature or concentration. Again, the world wants to homogenize all the things, so it struggle to remove every deviation. Any difference provides potential of changing, while uniform things remain uniform.

Resistance is something quite real. Everything cannot move on that fast and hasty, just like our lives are full of various challenges. Resistance is there is slow down the transport.

Flux is a vector (always perpendicular to the surface). It answers the magnitude and direction of the changing.

Direction - Combined with 【Second Law】 we can reason that lower temp/conc are of higher entropy, second low prefer higher entropy, so it flows from higher to lower temp/conc.
Magnitude - The larger the temp/conc difference, the faster the flux

While the driving forces can be determined by differentiate the distribution, we can get everything we want.

Back to our Map analogy, the driving force is when we hurry to school/work, and resistance is delaying buses. We obtain the ‘flux’, giving the direction and velocity (and thus the time) needed for the transport. We are now confident to get to anywhere throughout the world.

Separation Process

We looked from a typically specific and very useful aspect - separation. Namely we have a mixture and we want to disjoin them. How can we separate things? We can base separation on

size/density(centrifugation, filtering),
boiling point(evaporation and distillation),
solubility(absorption, extraction),
diffusivity(membrane separation),
etc.

Before we have advanced separation techniques, we just put our mixture there, look up the properties that they have most significant difference, then apply corresponding method.

We know that our total input should equals to our total output - that is again 【First Law】.

We know that mixture - with high entropy - is already stable and seem not to separate automatically, so external force (like heat or absorbent) are added to perturb the (relative) quiescence. The unhappy components are trying to make themselves most comfortable, so given enough time, they move to another state different from initial state. This progress is actually so-called separation. And every process molecules struggle to find the comfortable state is again based on 【Second Law】.

If the process is conducted once, then it is called simple stage separation, which is simple but due to insufficient external forces. If we keep adding force and push them continuously, here comes multi-stage separation, which is more efficient.

We can calculate everything, but for multi-stage, it is very complicated, since we have tons of 【First Law】 and 【Second Law】 to solve. How to solve them in the easiest way. What’s more, how many stages do we need economically?

The answer is graphical method - or Mccabe-thesis method.

It is a graphical method to decide the optimal number of stages and configurations of all stages. The procedure is surprisingly simple - drawing zig-zag between operation line and equilibrium line.

Operation line is obtained from mass balance - again here, 【First Law】 of thermo. Equilibrium line is collected from experiments but theoretically based on 【Second Law】. Then we are ruled by these two laws again.

Before computers applied in industry, the most efficient approach is graphical method. Draw straight lines, read numbers or measure the length. It sounds simple, but saving tons of time and draft paper.

Chemical Reaction Engineering and Kinetics

Chemical engineering is originated but deviated from mechanical engineering, where whether chemical reactions takes place.

Thermodynamics determine the farthest point we can reach - equilibrium point. But how long will it takes? A second, a week, or a year?

Kinetics tells how fast the reaction goes on.

The ultimate target of kinetics is to determine the reaction rate of a particular chemical reaction. The expression of rate that relates it with other parameters is called rate law.

From the last few chapters of thermodynamics, we have learned that elementary chemical reaction follow a simple rate law that

$rate = k \prod C_i^{\nu_i}$

The symbol looks similar to $\Pi$ means ‘multiply all’. $k$ in the formula is a reaction constant. $C_i$ is the concentration for species $i$, while $\nu_i$ is the stoichiometric number of $i$ in the reaction

Take the reaction $A+B\rightarrow C+D$ as and example. $rate = k \frac{C_C C_D}{C_A C_B}$

But then another question comes - the concentration changes every single second, and how can we determine the time needed? Again and again, we have to take out our first law(most time in differential and integral form), and combine it with our rate law, to fine out the variable we hope to know

Actually, time is only the variable that batch process hope to optimize. Besides batch, we have some continuous process, where time is not a factor for consideration in those cases. (Continuous means the stream is always flowing, so we may need to consider flow rate instead of time). The well-known continuous processes are

Continuous Stirred Tank Reactor(CSTR),
Plugged Flow Reaction(PFR), and
Packed Bed Reactor(PBR).

Variables such as conversion, volume of reaction, and initial reactant concentration required can be determined by the combination of rate law + 【First Law】.

There are many special cases we have to learn about. For example, difference between liquid phase & gas phase is one of the most significant difference. If it is liquid phase, we have to consider viscosity. If it is gas phase reaction, then we have to consider Isothermal case, Pressure Drop case, etc.. Also, if it is bioreaction, the raw law could be different. But our core principal remains the same.

Part 3. Applications and Practices

Process Control and Dynamics

This course is originally a 4k course, but the course code is changed to 3k now. Maybe it is because in the first several slide we still base our equation on 【First Law】. By the way, there is a similar course in electronic engineering.

In many other chemical engineering courses we usually assume steady state, where we can use our equations and models to deal with various questions.

However, here we have to face that most of our real-life process are unsteady. How to model and ultimately predict our process?

A mathematical solution is here: Since it is very hard to obtain the function or relationship for original form (for example, concentration vs time), we can translate it to another form, in which we can recognize the function easily. Then we translate the recognized function back, and obtain the wanted model.

The translation process is called Laplace Transform. We might have heard of it when learning differential equation or integration. Later you will find this course is full of Laplace transform.

But don’t be scared of the complicated integration. We do not need to calculate the integration ourselves. Instead, a table is provided, which saves our life.

After acquiring the method, we first deal with a single dynamic unit operation, then whole process, whose modeling process is a Laplace enclosed in another Laplace. So it is fair to say this course is all about application of Laplace transform.

Process Design and Integration

When your boss want to have XX tones of some chemicals to be produced every year, how to design a plant from draft?

From conceptual design to flow diagram to calculate the throughput and raw material needed with MS Excel(theoretically, just mass balance, but more details). Then is calculating the exact unit operation required with ASPEN+, as well as Heat Exchange Network Design. It is just everything needed for designing a factory.

Plant Design and Economics

As a future engineer, we always have to keep in mind that we learn to apply knowledge.

Factory is one of the most common form that theoretical knowledge is converted to economic value. We have to, we must learn about how it works, to accommodate ourselves in the real world.

The first part is about economics, or rather call accounting. How to read the accounting table is the major topic.

The second part is some detail about things to be considered with when it comes to a real factory. For example, Hazard Analysis(HAZOP or HAZEN), and pressure relief(how to minimize the loss when a real incident occur).

Basically, as most of the 4k courses, it is a collection of some useful knowledge. This course is quite useful for students hope to commit to the industry, whether or not it is chemical engineering related.

Part 4. Electives

Numerical Modeling

Numerical Modeling is using a mathematical function to represent a real-life event. Modeling itself covers multiple disciplines, while considered to be rather useful especially in bioengineering.

Modern modeling involves the powerful tool of computer, enabling the processing of huge amount of data. One of the important software is MATLAB. For machine learning, Python is more widely used while R for statistics.

This course introduce several important models for chemical engineering, like first and second order ordinary differential equations(ODE), partial differential equation(PDE) and some statistics terminology. The principles are actually covered in all the other courses, while this course, from my point of view, mainly develop the programming and debugging skills, which is extremely important in this information technology era.

But remember, no model is perfect.

Bioproduct and bioprocessing

This 4k course is another collection of knowledge about cells(culture) and their process&product, from upstream (pre-processing and reaction) to downstream (separation and purification).

The upstream part cover some kinetics, some thermo, some fluid mech to be considered.

The downstream part is generally similar to the separation course. One of the exceptional point is cell lysis, where we disrupt the cell in order to take the intracellular product.

Pharmaceutical Engineering

Pharmaceutical Engineering is not about discovering new drugs (that’s Pharmacy guys’ job) but analyzing how to manufacturing them. Pharmakinetics and Pharmadynamics are taken into consideration but in more general aspects. To be specific, the chemical formula is determined by Pharmacy, but the orientation and dosage of drug needs Pharmaceutical Engineering.

When it comes to manufacturing of pharmaceutical, the type of orientation (pills, topical…) are studies to compared with each other.

Food Processing Technologies

Food engineering is a branch of chemical engineering, where food products are typical objectives. The unit operation in food processing is no other than other in other chemical engineering processes - mixing, thermal processes, separation etc. Usually, in a mild condition.

While another aspect to look at is about Safety, or to be specific, microbiological issues. How to kill harmful bacteria properties while not hurting food itself become a topic.