Experimental Methods and Instrumentation for Chemical Engineers

373 Pages·2013·16.304 MB·English

by  Gregory S. Patience (Auth.)

Experimental Methods
and Instrumentation
for Chemical Engineers
Experimental Methods
and Instrumentation
for Chemical Engineers
Gregory S. Patience
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Preface
Throughout the day, we constantly make use of experimental methods, whether
or not we are aware of it: we estimate physical properties like time, distance, and
weight, as well as probability and expectation. For example, what is the prob-
ability that I will be late if I sleep another five minutes? (What is the probability
that I will only sleep an additional five minutes?) Many of us look at the weather
forecast to gauge what clothes to wear. Following a recipe to bake or prepare a
meal is an example of an experimental procedure that includes the classic engi-
neering quantities of temperature, time, mass (volume) and length.
The principles of chemistry and chemical engineering were perhaps first
formulated in the kitchen.
The undergraduate course on Experimental Methods offered in my depart-
ment was, in the beginning, primarily based on the textbook written by J.P.
Holman entitled “Experimental Methods for Engineers.” This is an excellent
textbook and is particularly suited for mechanical (and perhaps electrical) engi-
neers, but elements particular to Chemical Engineering are lacking. For this
reason, we embarked on the daunting task of compiling a version suited to the
needs of Chemical Engineers.
The chapters often begin with a historical perspective to recognize the work
of early pioneers but also to stimulate the imagination of the students. For
example, 10 000 years ago, man created plaster from limestone. Plaster requires
temperatures nearing 900 ºC, which is well over 100 ºC hotter than an open pit
fire. This technology required considerable resources: 1 t of wood (chopped by
stone axes), 500 kg of limestone, a pit 2 m in diameter and 0.7 m deep, rocks to
insulate, and two days to burn. Modern manufacturing errors are costly and a
nuisance; in prehistoric times, errors would have been considerably more than
just an inconvenience.
In Chapter 1, the rules of nomenclature are reviewed—units of physical
quantities, abbreviations, conversion between SI and British Units—and the
various national and international standards bureaus are mentioned. Chapter 2
introduces significant figures and concepts of accuracy, precision and error
analysis. Experimental planning is discussed in some detail in Chapter 3. This
subject is enormous and we try to distil the essential elements to be able to use
the techniques. Chapters 4 and 5 cover many aspects of measuring pressure and
temperature. The industrial context is often cited to provide the student with a
picture of the importance of these measurements and some of the issues with
making adequate measurements. Flow measurement instrumentation is the
subject of Chapter 6. A detailed list of the pros and cons of most commercial
xi
xii Preface
flow meters is listed. Example calculations are detailed throughout the book to
help the students grasp the mechanics of solving problems but also to underline
pitfalls in making these calculations. Chapter 7 deals with the three major physi-
cochemical properties in Chemical Engineering, including thermal conductivity,
viscosity, and diffusion. Measuring gas and liquid concentration is the subject of
Chapter 8—many analytical instruments are mentioned but chromatography is
primarily described. Finally, in Chapter 9 we discuss powder and solids analysis—
physical characterization as well as practical examples in Chemical Engineering.
This manuscript has been a collaborative effort from the beginning. I would
particularly wish to recognize the contributions of Melina Hamdine who early
on in the project drafted several chapters in French including Physicochemical
Properties, Analysis of Powders and Solids, and Design of Experiments. Much
of the material on DOE was based on the contribution of Prof. Bala Srinivasan.
Katia Sene´cal was “instrumental” in gathering the essential elements for the
chapters including Measurement Analysis, Pressure, Temperature and Flow
Rate. Prof. Bruno Detuncq collaborated in the revision of these chapters.
Danielle Be´land led the redaction of the chapter on chromatography to deter-
mine concentration with some assistance from Cristian Neagoe. He also wrote
the section concerning spectroscopy. Amina Benamer contributed extensively
to this project, including preparing solutions to the problems after each chapter,
writing sections related to refractometry and X-ray and translating. Second-year
students from the Department also participated by proposing original problems
that were added at the end of each chapter (together with the name of the author
of the problem). Ariane Be´rard wa devout at identifying errors and proposing
additional problems. I would particularly like to recognize Paul Patience for his
tremendous contribution throughout the creative process of preparing this manu-
script. The depth of his reflection has been appreciated tremendously (LATEX).
He also co-authored the section on pyrometry. Christian Patience prepared many
of the drawings and Nicolas Patience helped with translating from French to
English, as did Nadine Aboussouan.
Chapter 1
Introduction
1.1 OVERVIEW
Experimental methods and instrumentation—for the purpose of systematic,
quantifiablemeasurements—havebeenadrivingforceforhumandevelopment
andcivilization.Anthropologistsrecognizetoolmaking,togetherwithlanguage
and complex social organizations, as a prime distinguishing feature of Homo
sapiensfromotherprimatesandanimals.However,theanimalkingdomshares
many concepts characteristic of experimentation and instrumentation. Most
animals make measurements: cheetahs, for example, gauge distance between
themselvesandtheirpreybeforegivingchase.Manyspeciesareknowntouse
tools:largearborealprimatesusebranchesasleversfordisplacementfromone
treetoanother;chimpanzeesmodifysticksasimplementstoextractgrubsfrom
logs;spidersbuildwebsfromsilktotraptheirprey;beaverscutdowntreesand
usemudandstonestobuilddamsandlodges.Adaptingobjectsforadefined
taskiscommonbetweenmanandotheranimals.Iftheactofmodifyingatwig
toextractgrubsisconsidered“toolmaking”thenamoreprecisedifferentiating
factor is required. Man uses tools to make tools and a methodology is
adapted to improve an outcome or function. One of the earliest examples of
applying methodology is in the manufacture of chopping and core tools—
axesandfisthatchets—thathavebeenusedsincebeforetheLowerPaleolithic
period (from 650000 to 170000BC): blades and implements were produced
through cleaving rocks with a certain force at a specific angle to produce
sharp edges. The raw material—a rock—is modified through the use of an
implement—adifferentrock—toproduceanobjectwithanunrelatedfunction
(cutting,scraping,digging,piercing,etc.).Strikingrocks(flint)togetherledto
sparksandpresumablytothediscoveryofhowtomakefire.
ExperimentalMethodsandInstrumentationforChemicalEngineers.http://dx.doi.org/10.1016/B978-0-444-53804-8.00001-0
©2013ElsevierB.V.Allrightsreserved. 1
2 ExperimentalMethodsandInstrumentationforChemicalEngineers
Throughouttheday,wemakemeasurementsandemployinstrumentation.
Theclothesthatwewear,thefoodthatweeat,theobjectsthatwemanipulate
have all been developed and optimized through the use of standardized
procedures and advanced instrumentation. The transportation sector is an
example where instrumentation and sensors are commonplace: gauges in the
carassessspeed,enginetemperature,oillevel,fuellevel,andevenwhetheror
nottheseatbeltisengaged.Oneofthekeyfactorsinhomesismaintainingthe
correcttemperatureeitherinrooms,refrigerators,hotwaterheaters,ovens,or
elementsonthestove.Advancedscalesnowdisplaynotonlybodyweightbut
alsopercentfatandpercentwater!
Developmentistherecognitionandapplicationofunrelatedornon-obvious
phenomenatoaneworimprovedapplication—likemakingfire.Optimizationof
innovationsandtechnologycanbeachievedthroughaccidents,trial-and-error
testing,orsystematicapproaches.Observationisthefundamentalbasisformea-
suringdevicesanditwasthemaintechniqueemployedbymantounderstand
theenvironmentinwhichwelivedasinterpretedbyoursenses:sight,sound,
smell,touch,hearing,time,nociception,equilibrioception,thermoception,etc.
The manufacture of primitive stone tools and fire required a qualitative
appreciation for the most common measures of mass, time, number, and
length.Theconceptoftimehasbeenappreciatedformillennia.Incomparative
terms it is qualified by longer and shorter, sooner and later, more or less.
Quantitatively,ithasbeenmeasuredinseconds,hours,days,lunarmonths,and
years. Calendars have existed for well over 6000yr and clocks—instruments
tomeasuretimeintervalsoflessthanaday—werecommonaslongas6000yr
ago.Chronometersaredevicesthathavehigheraccuracyandlaboratorymodels
haveaprecisionof0.01s.
Oneofthefirst24-hclockswasinventedbytheEgyptianswith10hduring
theday,12hatnight,and1hatdawnanddusk—theshadowhours.Thenight
timewasmeasuredbythepositionofthestarsinthesky.Sundialswereusedat
thesametimebyBabylonians,Chinese,Greeks,andRomans.Thewaterclock
(clepsydra)wasdevelopedbyEgyptianstoreplacethestarsasameansoftelling
timeduringthenight:PrinceAmenemhetfilledagraduatedvesselwithwater
and pierced a hole in the bottom to allow the water to drain (Barnett, 1998).
Recordsofthehourglassdatebacktotheearly13thcenturybutothermeansto
“accurately”measuretimeincludedburningcandlesandincensesticks.
Recording time required a numbering system and a means of detecting a
changeinquantity.Inthesimplestformofawaterclock,timewasreadbased
ontheliquidlevelinthevesselsasindicatedbyanotchontheside.Thesystem
ofusingnotchesonbones,wood,stone,andivoryasameansofrecord-keeping
dates before the Upper Paleolithic (30000BC). Notch marks on elongated
objectsarereferredtoastallysticks.MedievalEuropereliedonthissystemto
recordtrades,exchanges,andevendebt,butitwasmainlyusedfortheilliterate.
It was accepted in courts as legal proof of a transaction. Western civilization
continues to use tally marks as a means of updating intermediate results.
Chapter | 1 Introduction 3
This unary numeral system is written as a group of five lines: the first four
runverticallyandthefifthrunshorizontallythroughthefour.
Perhaps one of the driving forces throughout the ancient civilizations for
numbering systems was for taxation, lending, land surveying, and irrigation.
The earliest written records of metrology come from Sumerian clay tablets
dated 3000BC. Multiplication tables, division problems, and geometry were
subjectsofthesetablets.Thefirstabacus—anancientcalculatorusedtoperform
simplearithmeticfunctions—appearedaround2700–2300BC.Latertablets—
1800–1600BC—included algebra, reciprocal pairs, and quadratic equations.
◦
Thebasisfor60sinaminute,60mininanhour,and360 inacirclecomesfrom
the sexagesimal numeral system of the Sumerians (Mastin, 2010). Moreover,
unliketheGreeks,Romans,andEgyptians,theyalsohadadecimalsystem.The
Pythagoreandoctrinewasthatmathematicsruledtheuniverseandtheirmotto
was“allisnumber.”
1.2 UNITS OF PHYSICAL QUANTITIES
The notion of weight, or mass, emerged during the same period as counting.
Throughouthistory,systemshavebeendevelopedforweights,measures,and
time. Often these systems were defined by local authorities and were based
on practical measures—the length of an arm, a foot, or a thumb. In the late
18thcenturytheFrenchNationalAssemblyandLouisXVIcommissionedthe
French Academy of Science to conceive a rational system of measures. The
basisforthemodernstandardsofmassandlengthwasadoptedbytheNational
Conventionin1793.
Originally,themeterwastobedefinedasthelengthofapendulumforwhich
thehalfcyclewasequalto1s:
(cid:2)
L
t =π , (1.1)
g
where L is the length of the pendulum and g is the gravitational constant.
Eventually,theAssembléeConstituantedefinedthemeterasoneten-millionth
of the distance between the equator and the North Pole. In 1795, the gram
was defined as the mass of melting ice occupying a cube whose sides equal
◦
0.01 m the reference temperature was changed to 4 C in 1799. At the Metre
Convention of 1875, the Système international (SI) was formally established
andanewstandardformeasuringmasswascreated:analloycomposedof90%
Ptand10%Irthatwasmachinedintoacylinderofheightanddiameterequalto
39.17mm.Iridiumwasincludedinthenew“InternationalPrototypeKilogram”
toincreasehardness.Thekilogramistheonlyunitbasedonaphysicalartifact
andnotapropertyofnatureaswellastheonlybaseunitwithaprefix.
Thedefinitionofthemeterandthetechniquesusedtoassessithaveevolved
with technological advances. In 1799, a prototype meter bar was fabricated
4 ExperimentalMethodsandInstrumentationforChemicalEngineers
to represent the standard. (It was later established that this bar was too short
by0.2mmsincethecurvatureoftheEarthhadbeenmiscalculated.)In1889,
the standard Pt bar was replaced with a Pt(90%)-Ir(10%) bar in the form of
an X. One meter was defined as the distance between two lines on the bar
◦
measuredat0 C.In1960,thestandardwaschangedtorepresentthenumber
ofwavelengthsofalineintheelectromagneticemissionof86Krundervacuum.
Finally,in1983,thestandardwasdefinedasthedistancethatlighttravelsina
vacuumin1/299792458s.
The standard to measure the base unit of time—the second—has evolved
asmuchasthestandardtomeasuredistance.Duringthe17–19thcenturies,the
secondwasbasedontheEarth’srotationandwassetequalto1/86400ofamean
solarday.In1956,recognizingthattherotationoftheearthslowswithtimeas
theMoonmovesfurtheraway(about4cmyr−1),EphemerisTimebecamethe
SIstandard:1/31556925.9747thelengthofthetropicalyearof1900.In1967,
thesecondwasbasedonthenumberofperiodsofvibrationradiationemitted
byaspecificwavelengthof133Cs.
The International System of Units (Système international d’unités or SI)
recognizes seven base properties as summarized in Table 1.1—time, length,
mass, thermodynamic temperature, amount of matter, electrical current, and
luminousintensity.Othermeasuresincludetheplaneangle,solidangle,sound
intensity, seismic magnitude, and intensity. The standard changed from the
cgs—centimeter,gram,second—standardtothepresentonein1960.In1875
attheConventionduMètre, threeinternational organizations wereformed to
overseethemaintenanceandevolutionofthemetricstandard:
● General Conference on Weights and Measures (Conférence générale des
poidsetmesures—CGPM).
● International Bureau of Weights and Measures (Bureau international des
poidsetmesures—BIPM).
● International Committee for Weights and Measures (Comité international
despoidsetmesures—CIPM).
(cid:2) (cid:4)
TABLE1.1 SIBaseUnits
Property Quantity Measure Unit Symbol
Time t T second s
Length l,x,y,z,r L meter m
Mass m M kilogram kg
Amountofmatter n N mole mol
Temperature T θ kelvin K
Luminousintensity lv J candela cd
Electricalcurrent I,i I ampere A
(cid:3) (cid:5)
Chapter | 1 Introduction 5
1.3 WRITING CONVENTIONS
Table 1.1 lists not only the seven standard properties recognized by the
International System of Quantities (SIQ) but also the symbols representing
each property and its dimension as well as the base unit and its symbol. All
other quantities may be derived from these base properties by multiplication
anddivision(BureauInternationaldesPoidsetMesures,2006).Forexample,
speed equals distance (or length) divided by time and is expressed as L/T.
Several forms of energy have now been defined—kinetic, potential, thermal,
etc.—butenergywasoriginallydefinedbyLeibnizastheproductofthemass
of an object and its velocity squared. Thus, energy is expressed as ML2/T2
and the units are kg m2 s−2. The kg m2 s−2 has also been designated as the
Joule (J) in honor of the contributions of the 19th century English physicist.
Pressureisdefinedastheforce(ML/T2)exercisedonaunitareaandhasunits
ofML−1T−2.ThestandardunitforpressureisthePascal(Pa)aftertheFrench
physicistwhodemonstratedthechangeinatmosphericpressurewithelevation.
Quantitiesorpropertiesmayeitherbeextensive—propertiesthatareadditive
forsubsystems,forexamplemassanddistance—orintensive,inwhichcasethe
valueisindependentofthesystem,liketemperatureandpressure.Prefixesare
addedtosomepropertiestofurtherqualifytheirmeaning,forexample“specific”
and“molar.”Specificheatcapacityistheheat,orenergy,requiredtoraisethe
temperature of a given mass by an increment. The SI units for specific heat
capacityareJkg−1 s−1.TheunitsofmolarheatcapacityareJmol−1 s−1.The
volume occupied by 1mol of a substance is referred to as the molar volume.
Several derived quantities together with their SI derived unit, symbol, and SI
baseunitsareshowninTable1.2.Thoseunitsthatareacombinationofthefirst
fourderivedunitswillhavetheirnameomittedforreasonsofspace.
Other symbols that are recognized as part of the SI unit system but fall
outsidethestandardizednomenclatureareshowninTable1.3.
Units with multiple symbols should be separated by a space or a half-
◦
highdot:theviscosityofwaterat0 Cequals0.001Pas.Negativeexponents,
asolidus,orahorizontallinemaybeusedforthecaseofderivedunitsformed
bydivision.Onlyonesolidusshouldbeused,thusatmosphericpressuremaybe
expressedas101325 kg or101325kgm−1 s−2.Asinthecaseforthesymbol
ms2
forpressure“Pa,”symbolsofunitsnamedafterapersonarecapitalized(“N”—
Newton, “Hz”—Hertz, “W”—Watt, “F”—Faraday). Note that since symbols
areconsideredasmathematicalentities,itisincorrecttoappendaperiodafter
thesymbol—“min.”isunacceptable(exceptattheendofasentence).Moreover,
symbolsdonottakean“s”toindicatetheplural.Regardlessofthefontused,
unitsymbolsshouldbeexpressedinromanuprighttype.
TheCGPMhasmadeseveralrecommendationsandstandardstorepresent
a quantity including the numerical value, spacing, symbol, and combinations
ofsymbols.Aspaceshouldfollowthenumericalvaluebeforetheunitsymbol:
454kg.Inthecaseofexponentialnotation,themultiplicationsymbolshouldbe
precededandfollowedbyaspace:4.54×103 kg.Theplaneangularsymbols