Mass Balance Lecture

7/31/2019 Mass Balance Lecture

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Material Balance

Lecture by :

Ir. Dewi Tristantini MT. PhD.

University of Indonesia


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MaterialsBalance analysis (MB) is asystematic reconstruction of the way

in which a chemical element, acompound or material passes through

a natural cycle and/or its economicalbenefits. An analysis of the materialflow, usually is based on the origin of aphysical balance.

German investigation Committe, 1993

Definition


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Uses

day to day operation of process for

monitoring operating efficiency

Making calculations for design and

development of a process i.e. quantities

required, sizing equipment, number of items

of equipment


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Basic Knowledge

BASIS

The basis is the reference chosen for the

calculations in any particular problems. A

proper choice of basis frequently makes the

problem much easier to solve.

For selecting a suitable basis, ask yourself the

following questions:

1. What do I have to start with?

2. What answer is called for?

3. What is the most convinient basis to use?


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Basic Knowledge

CHEMICAL EQUATION AND STOICHIMETRY

Chemical equation provides both qualitativeand quantitative information essential for thecalculation of the combining moles of

materials involved in a chemical process.

Stoichiometry: quantitative relation ship

between reactants and products. Stoichiometric ratios: ratios obtained from the

numerical coefficients in the chemicalequation.


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Basic Knowledge

CHEMICAL EQUATION AND STOICHIMETRY

Chemical equation provides both qualitativeand quantitative information essential for thecalculation of the combining moles of

materials involved in a chemical process.

Stoichiometry: quantitative relationship

between reactants and products. Stoichiometryc ratios: ratios obtained from

the numerical coefficients in the chemicalequation.


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Basic Knowledge


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Basic Knowledge


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Example

Antimony is obtained by heating pulverized stibnite

(Sb2S3) with scrap iron and drawing off the moltenantimony from the bottom of reaction vessel.

Sb2S3+ 3Fe 2Sb + 3FeS

Suppose that 0.600 kg of stibnite and 0.250 kg of iron

turnings is heated together to give 0.200 kg of Sbmetal. Determine:

a. The limiting reactant

b. The percentage of excess reactant

c. The degree of completion (fraction)

d. The percent conversion

e. The yield


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Solution


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Solution


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Solution


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Its Very Simple Right ? =)

Just Like a Piece of Cake =)

Now Lets See The Real Mass Balance Calculation


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Conservation mass principle is used because it

indicates that:

Input Material = Output Material

whereas :

Units of measurements given in kg or moles or m3

per time

Material Balance


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Flow diagram

Graphic interpretation of the materials flows.It shows volumes, proportions, ecologicalrelevance among other characteristics.

Indicate the sequence or steps of theproductive process.


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Example 1: Input and Output diagram

Auxiliary materials

UnitOperation

Raw material

Product

(expected)

byproduct(usable)

Waste

Water Energy

Waste easilyassimilated by

theenvironment

Inert wastealways available

toxic/dangerouswaste


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Plant, Processor UnitOperation

Gaseous emissionsRawmaterials

Catalyst

Air/Water

Energy

Recycle

Reusable residues in otheroperation

Products

By-products

Wastewater

Liquid waste

Solid waste

Examples of Input and Output


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Examples of the Flow Diagram

Usage


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Mass balance filtration/centrifuge

feed suspension

wash water/solvent

solid

waste water filtrate


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Filtration

F1

5000 kg DM water

Impurity 55 kg

Water 2600 kg

API 450 kg

Water 7300 kg

Impurity 50 kg

API 2kg

Water 300 kg

API 448 kgImpurity 5 kg


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Mass balance - drier

feed

product

water/evaporated solvent

water/evaporated solvent

+ dried material


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Mass balance extraction/phase split

A + B

S

A + B

S + B

A = feed solvent; B = solute; S = extracting solvent


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Mass balances multiple units

Overall balance

Unit balances

Component balances


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Multiple units

E = evaporator; C = crystalliser; F=filter unit

F1 = fresh feed; W2=evaporated water; P3 = solid product;

R4 = recycle of saturated solution from filter unit

R4

E C FF1

W2

P3


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Mass balance procedures

1. Process description

2. Flowsheet

3. Label

4. Assign algebraic symbols to unknowns(compositions, concentrations, quantities)

5. Select basis

6. Write mass balance equations (overall, total,

component, unit)

7. Solve equations for unknowns


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ProblemsPROBLEMS

1. A cereal product containing 55% water is made at the rate of 500 kg/hr.

You need to dry the product so that it contains only 30% water. Howmuch water has to be evaporated per hour?

2. To prepare a solution of 50.0% sulfuric acid, a dilute waste acidcontaining 28.0% H2SO4 is fortified with a purchased acid containing

96.0% H2SO4 . How many kilograms of the purchased acid must bebought for each 100 kg of dilute acid?

3. An aqueous etching solution containing 8.8% KI is to be prepared toetch gold in printed circuit boards. The desired solution is to be formedby combining a strong solution (12% KI and 3% I2 in H2O) with a weak

solution (2.5% KI and 0.625% I2 in H2O)What should be the value of R, the ratio of the weights of the strong tothe weak solution, to make up the desired etching solution? What willbe the concentration of I2 in the final solution?

Mass Balance Lecture

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