Mass Balance in Chemical Process

Mass Balance in Chemical Process

Process Flow Diagram (PFD)

Mass Balance in Chemical Process

Single Unit

Multiple Unit

Mass Balance with Recycle

Mass Balance with Reaction

Multiple Unit With Recycle + Reaction

Single Unit Mass Balance

Component :1. Water2. Solid

Mass

Balan

ceA

B

C

WaterSolid

WaterSolid

WaterSolid

Overall Mass Balance

A = B+C

Component Mass Balance

Water in A = Water in B+ Water in CSolid in A = Solid in B+ Solid in C

Single Unit Mass Balance

A

B

C

Water: 0.60Solid……

Water : 0.4Solid

WaterSolid : 0.3

325 kg/ hr

1. Find the Concentration of water and solid2. Find Flowrate in C and D !!

Case 1.

Single Unit Mass Balance

Case 2.

Find the concentration of acetic acid and water in stream A if the flow rate of B and C are 200 and 430 kg/ hr

Single Unit Mass Balance

Use of molar quantities (no reaction)• It is often useful to calculate a mass balance using molar quantities of materials and to

express composition as mole fractions or mole %.

• Distillation is an example, where equilibrium data is often expressed in mole fractions.

Distillation

Feed

Distillate

Residue/Bottom

𝑀𝑜𝑙𝑒 =𝑀𝑎𝑠𝑠

𝑀𝑤

Mole Frac Mole

Component 1 𝑋1 =𝐴

𝑍A

Component 2 𝑋2 =𝐴

𝑍B

Total 𝑋1+𝑋2 = 1 Z = A+B

Single Unit Mass Balance

1000 kmol/hr of an equimolar mixture of benzene and toluene is distilledin a multistage batch distillation unit. 90 % of the benzene is recovered inthe top product (distillate). The top product has a benzene mole fraction of0.95. Calculate the quantities of top and bottom products and thecomposition of the bottom product.

Case 3.

Equimolar : Containing the same number of moles% Recovery : amount pure product recovered

Feed

Distillate

Bottom

Benzene 0.95

BenzeneToluene

Single Unit Mass Balance

Case 4.

Single Unit Mass Balance

Case 5.

Single Unit Mass Balance

Case 6.

Multiple Unit Mass Balance

Combination of more than 1 equipments

AD

CE

mixer

Decanter

Reactor

Fire Heater

Multiple Unit Mass Balance

• Solving material balances in multiple unit process is basically the same as single unit processes

• In multiple unit, must isolate and write balance on several subsystems to obtain enough equation to determine all unknowns stream variables

Multiple Unit Mass Balance

Sub-system boundary Overall system boundary

Multiple Unit Mass Balance

Case 7.

A

FC

mixer

Decanter

Reactor

Fire HeaterD

E

A mixture of Water, Acetone and Chlorobenzene with different concentration are mixedtogether and flow through a decanter. The decanter was used to separate acetone formwater because the solubility of acetone in chlorobenzene is higher. Calculate the flowrateof each stream and composition (D included) based on provided information below!

A C F E

Mass Frac Mass Mass Frac Mass Mass Frac Mass Mass Frac Mass

Water 0.4 120 3 5 15 260 0.033 7Acetone 0.4 2 0.2 6 16 12 8 10

Chlorobenzene 1 60 0.3 90 17 13 0.467 11

Total 1 300 4 14 9

Multiple Unit Mass Balance

Case 8.Separation of volatile metals by staged distillation. Solid lines represent liquid phase streams, and dashed lines are gas

streams. There is actually a small amount of Zn in F2 and a small amount of Hg in F5, but these are neglected to simplify

the process.

Multiple Unit Mass Balance

Case 8.

Overall Mass Balance F1 = F2+F4+F5

Easy right?

Multiple Unit Mass Balance

Case 8.

Overall Mass Balance F1 = F2+F4+F5

Sub-System 1F1= F2+F3

Sub-System 2F3= F4+F5

Multiple Unit Mass Balance

Case 8.

Sub-System 1 mass balanceF1= F2+F3

ComponentIn Out

F1 F2 F3

% mass Mass (lb) % mass Mass (lb) % mass Mass (lb)

Hg

Cd

Zn

Total

Multiple Unit Mass Balance

Case 8.

Sub-System 2 mass balanceF3= F4+F5

ComponentIn Out

F3 F4 F5

% mass Mass (lb) % mass Mass (lb) % mass Mass (lb)

Hg

Cd

Zn

Total

Multiple Unit Mass Balance

Case 9.

A labeled flowchart of a continuous steady-state two-unit process is shown below. Each stream contains two

components, A and B, in different proportions. Three streams whose flow rates and/or compositions are not known

are labeled 1, 2, and 3.

Quote of the day

If you don't like something, change it. If you can't

change it, change your attitude.-Maya Angelou-

People may hear your words, but they feel your

attitude.

- John C. Maxwell-