Concept: Designing a Chemical Process –Unit Operations and Process Flowsheets

Context: Hydrazine Synthesis (exercise 2.27 – solution is posted)

Defining Questions: Why does every recycle loop need a purge?What is the preferred method for separating substances?

Key Point: You are not expected to provide the chemical reactions.Chemical reactions will always be given.

Read Chapter 2, pp. 19-25.

EngrD 2190 – Lecture 2

If you donot submit

a questionnaire,you will workindependently

DueWednesday

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must submityour name.

Each student individually works through the problems prior to meeting. In this waythree novel solutions might be produced, each of which reflected that student’s individualapproach. I greatly benefited from this diversity because it often allowed me to shift howI approached the same type of problem in future assignments. TA Andrew Simon

Collaborative Learning – Homework Teams

I always found that I learned how to solve problems a lot better when working with mygroup, because we were able to bounce ideas off each other and get multiple perspectivesthroughout the process. TA Drew Lazarow

The ChemE major is challenging and demanding. Forming homework groups early-onsets up a culture that values friendship, teamwork, and support. That culture is somethingI have always appreciated about this major, and something that I want to make sure thisnew class of students gets. TA Ann Metzloff

People can bounce ideas off each other and get more work done overall. These groupsare good resources for other courses in the sophomore fall. TA Tommy Bradford

Teams can be an important way to meet other people in the ChemE class. As someonewho did not take Intro to ChemE freshman year, I knew no other ChemE's prior to myfirst day in 2190. I believe teams to be an important part of the learning process.

TA Gavin Batsimm

I really enjoyed getting to know the other students in ChemE through homework teams.These teams increase group bonding and make ChemE feel more like a community,which I think is unique. TA Emily Spiek

Collaborative Learning – Homework Teams, cont’d

Last semester, I worked on a group design project virtually for ChemE 3700 and whileit was difficult, having a team to work with allowed us to bounce design ideas/pitfallsoff one another. Having a team also shows different methods of thinking through problemswhich is very helpful for exams. TA Apoorva Agarwal

I was grateful to have my EngrD 2910 homework group to work not only on myEngrD 2190 problem sets, but also on my pchem and physics problem sets. I appreciatedthe collegial and cooperative environment EngrD 2190 homework groups set up.

TA Ann Metzloff

“Chemical engineers design processes based on chemical change.”

represented by process flowsheets

Every chemical process comprisesdiscrete steps, called units. Units are connected by steams.

Principle of Unit Operations.

Unit Operations was the original paradigmof chemical engineering (ca. 1910).

Exercise 2.27: Synthesis of Hydrazine

How to start the design of a process flowsheet?Don’t fixate on where to start. Choose a part of the chemical process and begin.

I like to start with a key reaction.

H2O2 + 2C3H6O + 2NH3 C6H12N2 + 4H2O

H2O2C3H6ONH3

acetazinesynthesisreactor

C6H12N2H2O

omitstoichiometric

coefficients

H2O2C3H6ONH3

H2O (solvent)

5 substances in reactor effluent. Separate into 5 streams?

to second reactor

recycle to first reactor

Separate into 2 streams?

How to separate? Basis for separation? Gas-liquid separator (preferred method)

What temperatures in the gas-liquid separators?

Need boiling points.

to 2nd reactor recycle to 1st reactor

H2OC6H12N2

H2O2NH3 C3H6O

separator 1 separator 2 use excessNH3 and C3H6O

How many separators?

Separator temperatures?

• You may assume that if acetone and ammonia are in excess in the acetazine synthesis,the H2O2 is completely consumed.

H2O2C3H6ONH3

acetazinesynthesisreactor

C6H12N2H2O

H2O2C3H6ONH3

H2O (solvent)

to second reactor

recycle to first reactor

(excess)(excess)

Return to the process flowsheet …

Why purges?

impurity

Impurityaccumulatesin process!

Why make-upinputs?

Intermediateacetone lostin purges!

Visual Assimilation!

Active Processing!

Why no purgeon the lowerrecycle loop?

So, is the purgeon the middlerecycle loopnecessary?

Defining Questions: Why does every recycle loop need a purge?

“It’s always something. If it’s not one thing it’s another.”

Gilda Radner, SNL 1978-1980

How to design a chemical process?

Start at a key process unit - usually a reactor.

Grow incrementallyby successive problem solving.

Define the real problem.