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Class Exercise for the 24th of Feb 2010

1. EXAMPLE: Balance on a mixing unit

An aqueous solution of sodium hydroxide contains 20% NaOH by mass. It is desired to produce

an 8% NaOH solution by dilutin a stream of the 20% solution !ith a stream of pure !ater.

". #alculate the ratios $ H2O feed solution& and $ product solution feed solution&.

2. 'etermine the feed rates of 20% solution and dilutin !ater needed to produce 2("0 lb mminof the 8% solution.

2. EXAMPLE: Scale up of a separation process flowchart

A )0 * +0 mixture $by moles& of A and , is separated into t!o fractions. A flo!chart of the

process is sho!n here. It is desired to achie-e the same separation !ith a continuous feed of "20

lb*molesh. /cale the flo!chart accordinly.

. EXAMPLE: Material !alances on a "istillation column

A mixture containin +% benene $,& and % toluene $1& by mass is fed to a distillation

column. An o-erhead stream of !t% , is produced3 and 8% of the benene fed to the column

lea-es in the bottom stream. 1he feed rate is 2000 4h. 'etermine the o-erhead flo! rate and the

mass flo! rates of benene and toluene in the bottom stream

#. EXAMPLE: $wo %nit &istillation Process

A labeled flo!chart of a continuous steady*state t!o*unit distillation process is sho!n belo!.

5ach stream contains t!o components3 A and ,3 in different proportions. 1hree streams !hose

flo! rates andor compositions are not 4no!n are labeled "3 2 and (. #alculate the un4no!n flo!

rates and compositions of streams "3 23 and (.

'. EXAMPLE: (eaction Stoichiometr)

Dr M Hassan Chapter 4 for PENG 373 Pae 1

8/13/2019 class exr 1

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Class Exercise for the 24th of Feb 2010

Acrylonitrile is produced by the reaction of propylene3 ammonia3 and oxyen.

1he feed contains "0 mole% propylene3 "2% ammonia3 and 68% air. A fractional con-ersion of

(0% of the limitin reactant is achie-ed. 'etermine !hich reactant is limitin3 the percentae by!hich each of the other reactants is in excess3 and the molar flo! rates of all product as

constituents for a (0% con-ersion of the limitin reactant3 ta4in "00 mol of feed as a basis.

*. EXAMPLE:

#onsider the follo!in pair of reactions.A 7 2, $desired& A 7 # $undesired&

"00 moles of A are fed to a batch reactor and the final product contains "0 mol of A3 ")0 mol of

, and "0 mol of #. #alculate $"& percentae yield of ,3 $2& the selecti-ity of , relati-e to # and

$(& the extents of the reactions.

+. EXAMPLE: ,om!ustion of Methaneethane is burned !ith oxyen to yield carbon dioxide and !ater. 1he feed contains 20 mole%

#H+3 )0% O23 and 20% #O23 and a 0% con-ersion of the limitin reactant is achie-ed. #alculate

the molar composition of the product stream usin $"& balances on molecular species3 $2& atomic

balances3 $(& the extent of reaction.

-. EXAMPLE: (ec)cle an" Purge in the S)nthesis of Ammonia

1he fresh feed to an ammonia production process contains 2+.6 mole % nitroen3 6+.2 mole%

hydroen3 and the balance inerts $I&. 1he feed is combined !ith a recycle stream containin the

same species3 and the combined stream is fed to a reactor in !hich a 2% sinle*pass con-ersion

of nitroen is achie-ed. 1he products pass throuh a condenser in !hich essentially all of the

ammonia is remo-ed3 and the remainin ases are recycled. Ho!e-er3 to pre-ent buildup of theinerts in the system3 a pure stream must be ta4en off. 1he recycle stream contains "2. mole%

inerts. #alculate the o-erall con-ersion of nitroen3 the ratio $moles pure asmole of as

lea-in the condenser&3 and the ratio $moles fresh feedmole fed to the reactor&.

. EXAMPLE: &r) Basis et Basis

An /rsat anal)sis $a technique for stac4 as analysis& yields the follo!in dry basis

composition9 O2 "0% #O ""% #O2 "+% N2 )%

A humidity measurement sho!s that the mole fraction of H 2O in the stac4 as is 0.06. #alculate

the stac4 as composition on a !et basis.

10. EXAMPLE: $heoretical an" Excess Air

One hundred mol per hour of butane $# +H"0& and 000 mol per hour of air are fed into a

combustion reactor. #alculate the percent excess air.

11. EXAMPLE: ,om!ustion of Ethane

5thane $#2H)& is burned !ith 0% excess air. 1he percentae con-ersion of the ethane is 0%: of

the ethane burned3 2% reacts to form #O and the balance to form #O2. #alculate the

composition of the fuel as and the ratio of !ater to dry fuel as.

Dr M Hassan Chapter 4 for PENG 373 Pae 2