thermal methods in petroleum analysis

Thermal Methods in Petroleum Analysis
by.
Heinz
Kopsch
CopyrightoVCH Verlagsgesellschaft
mbH,
1995
Heinz
Kopsch
Thermal Methods
in
Petroleum
Analysis
0
VCH Verlagsgesellschaft mbH, D-69451 Weinheim, Federal Republic
of
Germany, 1995
Distribution:
VCH,
PO.
Box
10
11
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of
Germany
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PO.
Box, CH-4020 Basel, Switzerland
United Kingdom and Ireland: VCH,

8
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ISBN 3-527-28740-X
Heinz
Kopsch
Thermal Methods
in Petroleum Analysis
VCH
4b
Weinheim
.
New York
.
Base1
-
Cambridge
-
Tokyo
Dr. rer. nat. Heinz Kopsch
Institut fur Technische Chemie
T.U.
Clausthal

ErzstraBe 18
D-38678 Clausthal-Zellerfeld
Germany
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was
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The cover photo shows a view of part of the BASF steamcracker in Antwerp.
(Courtesy of BASF Aktiengesellschaft Ludwigshafen, Germany)
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-
CIP-Einheitsaufnahme
Kopsch,
He&
Thermal methods in petroleum analysis

/
Heinz Kopsch.
-
Weinheim
;
New York
;
Base1
;
Cambridge
;
Tokyo
:
VCH, 1995
ISBN
3-527-28740-X
0
VCH Verlagsgesellschaft mbH, D-69451 Weinheim, Federal Republic of Germany, 1995
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Preface
The monograph Thermal Methods in Petroleum Analysis is based mainly on results of
more than twelve years research work on the application
of
thermoanalytical methods to
petroleum and its products during the activities of the author at the German Institute for
Petroleum Research. It was very interesting to research the application of well defined
physical methods, such as thermogravimetry and differential scanning calorimetry, to the
multicomponent systems of petroleum and its products, and to understand the limits of
those methods on the one hand and the excellent transferability of the results to technical
processes on the other. The diversity of possible applications of thermoanalytical methods
to various problems in the petroleum laboratory can only be indicated in this mono-
graph.
Many people supported my work, either by active or by indirect help. Thanks are
expressed to Mrs. Elvira Falkenhagen, who has been a skilful and reliable assistant for
many years, as well as to Dr Ing. Maria Nagel, Dr Ing. Ulrike Tietz, Mrs. Liliane
Varoscic, Mrs. Regina Bosse, Mrs. Gerda Sopalla, and the late Mrs. Heidi Gottschalck.
An
acknowledgement should be made to the directors of the German Institute for Petroleum
Research: Professor Dr.

H.
H.
Oelert, Professor Dr.
H J.
Neumann, and Professor Dr.
D.
Kessel who granted me maximum independent research capacity. Some parts of the
research work were carried out with financial support from the German Association for
Research CD (Deutsche
Forschungsgemeinschaft).
For several years successful and plea-
sant cooperation was established with colleagues of the University of Belgrade, especially
with Professor Dr. D. Skala, Professor Dr. M. Sokic, and Professor Dr.
J.
A. Jovanovic.
Thanks are also expressed to those whose names do not appear in this list. All the
companies which supplied me with information as well as with illustrations are likewise
acknowledged; their names may be found in the appendix.
I hope that this monograph will be
of
some help to colleagues in both academic and
industrial research establishments and will encourage them towards further attempts in the
application of thermal methods of analysis, even to chemically non-defined multicompo-
nent systems. The examples presented might represent a stimulation for further experimen-
tal work.
Heinz Kopsch
Oktober
1995
Contents
1

Introduction 1
Methods and instrumentation 3
Thermal analysis on model substances
Thermogravimetry (TGA)
15
Thermogravimetry in an inert atmosphere 15
Simulated distillation 28
Thermogravimetry in an oxidizing atmosphere
Isothermal thermogravimetry
45
Experiments using the simultaneous thermal analyzer
Differential scanning calorimetry on model substances
DSC in an inert atmosphere
54
DSC in an oxidizing atmosphere
Reaction kinetics
68
Theoretical basis 68
Method according to ASTM
E
698-79 69
Method according to Borchardt and Daniels
Method according to Flynn and Wall
72
Method according to McCarthy and Green 74
Kinetic investigations on model substances 75
DSC experiments according to ASTM
E
698-79 heat of vaporization of n-alka-
nes

75
Pyrolysis kinetics according to ASTM
E
698-79 82
DSC oxidation kinetics according to ASTM E 698-79
Kinetics according to Borchardt and Daniels
TGA kinetics according to Flynn and Wall
90
TGA kinetics according to McCarty and Green 94
Thermoanalytical investigations on petroleum und petroleumproducts 97
Crude oils (degasified crudes) 99
Refinery residues
11
1
Description and characterization of the samples
Implementation and evaluation of tests
Deviations in thermogravimetry
119
15
38
47
54
63
70
84
89
112
118
2
3

3.1
3.1.1
3.1.2
3.1.3
3.1.4
3.1.5
3.2
3.2.1
3.2.2
3.3
3.3.1
3.3.1.1
3.3.1.2
3.3.1.3
3.3.1.4
3.3.2
3.3.2.1
3.3.2.2
3.3.3
3.3.4
3.3.5
3.3.6
4
4.1
4.2
4.2.1
4.2.2
4.2.2.1
VIII
Contents

4.2.3
4.2.3.1
4.2.3.2
4.2.3.3
4.2.3.4
4.2.3.5
4.2.4
4.2.4.1
4.2.5
4.2.6
4.2.6.1
4.2.6.2
4.2.7
4.2.8
4.2.8.1
4.2.8.2
4.2.8.2.1
4.2.8.3
4.2.8.4
4.2.9
4.2.9.1
4.2.9.2
4.2.9.3
4.3
4.3.1
4.3.2
4.3.2.1
4.3.2.1.1
4.3.2.1.2
4.3.2.2

4.3.3
4.3.4
4.3.4.1
4.3.4.2
4.3.4.3
4.3.4.4
4.3.5
4.3.6
4.3.6.1
4.3.6.2
Thermogravimetry in an inert atmosphere
Directly measured index numbers
Derived index numbers
136
Simulated distillation
137
Directly measured index numbers in comparison with the simulated distilla-
tion
143
Derived index numbers for pracital application
Thermogravimetry in air
147
Directly measured index numbers
155
Correlations of analytical data with index numbers from thermogravime-
try
160
Simulated thermal cracking by TGA
Index numbers from simulated cracking
Correlation of index numbers from simulated cracking with analytical da-

ta
165
Start temperature of the cracking process in an inert atmosphere
Differental scanning calorimetry (DSC)
167
Experiments in argon at atmospheric pressure
Experiments in methane at
10
bar pressure
Reaction enthalpy from tests at
10
bar pressure
Start temperatures of the cracking process at different pressures
Correlation of kinetic parameters with analytical data
Conclusions from experiments on refinery residues
Thermogravimetry
18
1
Reaction kinetics
184
Correlation of data from thermoanalysis with analytical data
Investigations on bitumen
187
Description and characterization of the samples
Thermoanalytical investigations
195
Thermogravirnetry in inert gas
195
Correlation
of

index number from thermogravimetry with consistency da-
ta
202
Correlation index numbers with analysis data
21
1
Thermogravimetry in air
217
Isothermal aging tests by thermogravimetry
Differential scanning calorimetry (DSC)
233
Test in argon at atmospheric pressure
233
Tests in methane at
10
bar pressure
237
Tempratures of the cracking process
243
Oxidation in air
247
Low temperature behavior of bitumen
Conclusions from experiments on bitumen
Thermogravimetry
258
Reaction kinetics
261
123
13 1
144

162
164
166
167
171
174
175
176
18
1
186
189
225
258
258
Contents
IX
4.4
4.4.1
4.4.2
4.4.2.1
4.4.2.2
4.4.3
4.4.4
4.4.5
4.5
4.5.1
4.5.2
4.6
4.6.1

4.6.2
4.6.3
4.7
4.7.1
4.7.2
4.7.3
4.8
4.9
4.9.1
4.9.2
4.9.2.1
4.9.2.2
4.9.2.3
4.9.3
4.10
4.10.1
4.10.1.1
Investigations on polymer modified bitumens (PMB)
Description and characterization
of
the samples 265
Thermogravimetry 269
Dynamic (temperature-programed) thermogravimetry 269
Isothermal gravimetq 275
Reaction kinetics using DSC 283
Low
temperature behaviour of PMB using DSC
Aging properties of polymers for the modification of bitumen
287
Investigation on the hydrocracking reaction of heavy residues 296

Investigation on a vacuum residue from Kirkuk 297
Investigation on residues of different origins
Oil shale and shale oil
Investigation using TGA and DSC
Modelling and simulation
of
oil shale pyrolysis
Fingerprinting of oil shale by oxidation
Lubricants
348
Evaporation behavior
of
lubrication oils
Oxidation behavior of lubrication oils
Comparison of the oxidation stability of virgin oils, reclaimed oils, and synthe-
tic lubrication oils
365
Silicone oils 376
Relation of the kinetics of pyrolysis and oxidation reactions to the system
pressure: Investigations on tertiary oil recovery by in situ combustion
Pyrolysis tests
405
Oxidation tests 410
Range of
low
temperature oxidation (LTO)
Range of fuel deposition
415
Range of fuel combustion 421
Discussion 424

Comparison of commercial computer programs for investigation of kinetics of
pyrolysis and oxidation reactions of heavy petroleum products
Pyrolysis reaction
429
Kinetics according to ASTM
E
698-79 429
265
285
304
321
322
331
345
349
358
400
412
427
4.10.1.1.1
DSC (DTA) experiments 429
4.10.1.1.2 Kinetics according to ASTM
E
698-79 from simultaneous TGA/DTA experi-
4.10.1.2 Kinetics according to Borchardt and Daniels 440
4.10.1.3 Kinetics according to Flynn and Wall 442
4.10.1.4
Kinetics according to McCarty and Green 453
4.10.2
Oxidation reaction 458

4.10.2.1
Kinetics according to ASTM
E
698-79 460
4.10.2.1.1 DSC (DTA) experiments 460
4.10.2.1.2
Experiments using Simultaneous Thermal Analyzer
4.10.2.2 Kinetics according to Borchardt and Daniels 468
ments 439
467
X
Contents
4.10.2.3 Kinetics according to Flynn and Wall 469
4.10.2.4 Kinetics according to McCarty and Green 473
4.10.3 Conclusions 477
5
Final consideration 485
5.1
Other applications 485
5.2
Summary on progress of instrumentation (hard and software) and advice 487
6 Appendix: Manufacturers of thermoanalytical instrumention 495
References 499
References Chapter 1 499
References Chapter 2
500
References Chapter 3
500
References Chapter 4 502
References Chapter

5
506
List
of
Symbols
A
AR
ASTM
BP
CCR
CR
DDK
DIN
DSC
DTA
DTG
Frequency or Pre-exponential Factor (min
')
Atmospheric residue
American Society for Testing and Materials
Boiling Point ("C)
Conradson Carbon Residue
(%)
Crackable part of the sample
(%)
Dynamic Difference Calorimetry (see DSC)
Deutsches Institut kr Normung e.
V.
(German Institute for Standardization)
Differential Scanning Calorimetry

Differential Thermal Analysis
Differential Thermogravimetry (First differential quotient of weight loss
with respect to time)
(%
min
')
Activation Energy
(J
.
Mol-l)
Base of natural logarithm
Exponent with base
e
Residual weight at the point of inflexion of the TGA curve
(%)
Energy flow
(pW)
Enthalpy
of
pyrolysis
(J
.
g-1)
Heat of fusion
(J
.
g-1)
Heat of vaporization
(J
.

g-1)
Infrared Spectroscopy
Reaction (Rate) Constant (min-')
Natural logarithm
Decimal logarithm
Mean relative particle mass (Mean molecular weight)
Melting Point ("C)
Non-distillable part of the sample
(%)
Nuclear Magnetic Resonance Spectroscopy
Reaction order (dimensionless)
XI1
List
of
Symbols
P
Pressure (bar)
PCR Practical thermal crackable part of the sample
(%)
Pen Needle penetration at
25
"C
(0.1
mmj
PMB Polymer modified Bitumen
Q
Quotient of weight loss in air divided by weight
loss
in inert gas (Isother-
mal Gravimetry)

R
Universal Gas Constant
(J
Mol-'
K-')
R600
Residue
(%)
at
600
"C experimental temperature
R800 Residue
(%) at
800
"C experimental temperature
r
Coefficient of correlation (dimensionless)
SAR Simulated atmospheric residue
(%)
S.P.R&B Softening Point Ring and Ball ("C)
STA
SVR
S
T
TA
TGA
Tcrack
Tm
Tonset
Tw

T1
%
T5
%
t
512
U
V
VR
VVR
x
01
P
6
A
AGlOO
AG200
AG300
AG400
Simultaneous Thermal Analysis (or Analyzer)
(TGA+DTA or TGA+DSC)
Simulated vacuum residue
(%)
Standard deviation
Temperature (Generally OC, except kinetics with absolute temperature
K)
Thermal Analysis
Start temperature of the thermal crack reaction ("C)
Thermogravimetry
Temperature of peak maximum ("C)

Onset temperature ("C)
Temperature of the point
of
inflexion of the TGA curve ("C)
Temperature ("C) at
1
%
weight loss
Temperature ("C) at
5
%
weight loss
Time (min)
Half life time (minj
Conversion
(%)
Coefficient of variation
(%
j
Vacuum residue
Visbreaker residue
Arithmetic mean
Fractional conversion (dimensionless)
Heating rate
(K
min-')
Solubility parameter according to Hildebrandt
(~MJ
m-3)
Difference

Weight
loss
up to
100
"C (%)
Weight loss up to
200
"C
(%)
Weight loss up to
300
"C (%)
Weight loss up to
400
"C
(%)
Thermal Methods in Petroleum Analysis
by.
Heinz
Kopsch
CopyrightoVCH
Verlagsgesellschaft
mbH,
1995
1
Introduction
Analytical methods describing the thermal behavior of substances during programmed
temperature changes, like thermogravimetry, differential thermoanalysis, or differential
scanning calorimetry are old methods, which were applied at first to problems of inorganic
chemistry, mainly to minerals. The analysis

of
petroleum and petroleum products has been
mentioned relatively late. In the literature survey by Weselowski
[
1-11 the first citation
dates from 1958. Also, the oldest citation in the research report by Kettrup and Ohrbach
[1-21 dates from
1965.
Petroleum, especially heavy crudes, is recovered sometimes by the use of thermal
processes like steam flooding or by in situ combustion. The processing
of
the recovered
crudes in the refineries is usually done by thermal methods at very different temperatures.
A review of the temperatures applied in refinery operations is given in Table 1-1. These
thermal processes are performed partly by sequential heating until the desired products are
obtained. The operating parameters for the different processes have been obtained to a
large extent by empirical experience or partly by simulation of the processes in laboratory
installations or in pilot plants. For that reason thermoanalytical methods are considered to
be very useful in obtaining data concerning the thermal behavior i. e. data describing the
Table
1-1:
Temperature Ranges in Petroleum Processing
Process Temperature Range ("C)
Atmospheric Distillation
Vacuum Distillation
Thermal Cracking
Catalytic Cracking
Steam Cracking
High Temperature Pyrolysis
Hydrocracking (Gas Phase)

Hydrocracking (Liquid Phase)
Visbreaking
Reforming (Thermal Treating)
Reforming (Catalytic Treating)
Isomerization
Alkylation (Catalytic)
Polymerization
Hydrotreating
Steam Reforming
Bitumen Blowing
350
.
. .
380
350

.
380
400
.
.
.
650
450
. . .
540
650
.
.
.

1000
1000
340
.
.
.
430
340
.
.
.
470
460
. .
.
480
510
.
.
.
580
500
.
.
.
550
60
.
. .
200

0
.
. .
200
170
.
. .
215
250
.
.
.
430
700
.
.
.
800
230
.
.
.
300
2
1
Introduction
thermal and oxidation stability of petroleum and its products; data predicting the manner
and quantity
of
products gained in the processes; and data concerning reaction kinetics

which can be used to optimize the refinery processes.
Thermogravimetry (TGA), differential thermoanalysis (DTA), and differential scanning
calorimetry (DSC) are the main methods which can be used in the analysis of petroleum
and its products. DSC is preferred to DTA, because DSC supplies values of energies
directly, whereas the DTA supplies only temperature differences.
These thermal methods of analysis have been described in several basic books
[l-3 to 1-17]. The application to polymers is described likewise [l-18, 1-19].
So
far no
compilation on the application to petroleum and its products exists. The situation in the
field of standards is similar. The NormenausschuB Materialpriifung im Deutschen Institut
fur Normung (Committee for Testing and Materials
of
the German Institute for Standardi-
zation e.
V.,
DIN) has approved only two standards (one of them contains terms of thermal
analysis
[
1-20], the other is the standard for thermogravimetry [l-211). Furthermore there
are three proposals (principles of differential thermal analysis
[
1-22], determination of
melting temperatures of crystalline material by DTA [l-231, and testing of plastics and
elastomers by DSC
[
1-24]). The American Society for Testing and Materials (ASTM) has
to date approved forty standards for the application of thermal methods of analysis. Among
them, seven standards are concerned with the testing of petroleum and its products [l-251
to [l-321, six standards are general methods [l-321 to [l-381, and four standards concerning

the testings of polymers are applicable
to petroleum and its products too [l-391 to
11-42].
Thermal Methods in Petroleum Analysis
by.
Heinz
Kopsch
CopyrightoVCH
Verlagsgesellschaft
mbH,
1995
2
Methods and instrumentation
Using thermogravimetry (TGA), the dependence of the change in sample weight (mass)
on the temperature during programmed temperature changes in a chosen gas atmosphere
can be measured. The first derivative of the weight (mass) signal with respect to time is
called derivative thermogravimetry (DTG) and is a criterion for the reaction rate. It is
usual
to record both the slope of the weight (mass) versus the time or temperature (TGA), and the
differentiatoed curve versus the time or temperature (DTG). The heating rate dictates the
actual position
of
the TGA and DTG graphs; it is therefore advisable always to use the
same heating rate
(p)
so
that different tests may be compared. For small sample weights
(masses), up to approximately 10 rng, a standard heating rate of 10 K/min is practicable.
This heating rate is slow enough to avoid any temperature gradient inside the sample while
permitting a reasonable utilization of the available workmg time. The shift to higher

temperatures of the TGA and DTG curves as a consequence of faster heating rates permits
calculation of the Arrhenius kinetic parameters and hence investigation of the reaction
kinetics (see chapter 3.3). Furthermore, the position
of
the TGA and DTG curves will be
influenced by the shape of the sample pan, especially by the ratio of surface to volume of
the sample, and lastly by the quantity of gas flowing through the oven (gas flow rate).
Therefore it is important that variations in sample quantity are minimized and that the gas
flow rate is maintained as constant as possible. However, the gas flow rate must not fall
below a certain minimum value in order to avoid condensation of evaporated sample
fractions on the hangdown of the sample holder or in the gas outlet tubes. The minimum
gas flow rate depends on the geometric shape of the oven and the position of the gas inlet
and outlet tubes and therefore differs for different instruments. If the gas flow rate is
sufficient, the evaporated portions of the sample will be discharged immediately and
therefore no equilibrium between liquid and vapor will be attained. As a consequence the
boiling (evaporation) temperature of the sample will decrease adequately. That can be used
to perform a simulated distillation (see chapter 3.1.2). However, the application of ther-
moanalytic methods is limited to substances having a start temperature of evaporation at
atmospheric pressure not far below 200
"C.
Otherwise there is the risk that evaporation in
the gas flow will begin at room temperature and thus the correct start temperature of
evaporation (zero point of the TGA curve) cannot be ascertained.
In principle
all
except very corrosive gases can be passed through a thermobalance; in
practice the inert gases nitrogen, helium, and argon and the reactive gases air, oxygen, and
hydrogen will be used.
The weight calibration of thermobalances
is

done using standard weights. The tempera-
ture calibration is more difficult. The method using the Curie point temperature, as
4
2
Methods
and
Instrumentation
described in ASTM
E
914-83,
does not work if a magnetic field from outside the oven is
prevented from reciprocal action with the standard inside the oven, by the construction or
the material of the oven. Calibration using calcium oxalate monohydrate for standard is
very common, since it has exhibited three clearly-defined steps of weight
loss
during
heating (Fig.
2-1
to
2-3).:
Reaction
Temperature Residue DTG Maximum
Range at Temperature
p=
10
K/min
("C)
(%I
("C)
CaC,O,.H,O

-+
CaC,04
+
H,O
t
135
.
175
87.7
163
CaC,04
+
CaCO,
+
Cot 463
,502
68.5
49
1
CaCO,
CaO+CO,T
660.
.
.740
38.4
722
As
can be seen from the figures, the
DTG
maximum is found at conversions which are

smaller than the maximum conversion of the reaction step concerned. The onset temperatu-
res as well as the
DTG
maximum temperatures can be reproduced with coefficients of
variation
<
2
%
of the corresponding mean value.
The thermogravimetric experiments are
run
using open platinum sample pans. Pans
made from aluminium, platinum,
quartz,
glass, stainless steel etc. were also available. The
110
I00
90
U
no
U
L
PI
a
70
60
50
40
llNT
TABLE

TGA
TGA
__.
I
I
I
I
100
too
300
4bO
500
600 700
800
<
Deg
c
Fig.
2-1:
Thermogravimetry
of
CaC,O,. H,O
Plot
of
STA
780:
TGA
and
DTA
Atmosphere: Argon 30

+
20 cm3/min
Heating Rate
p:
10
K/min
5
0
-5
m
-10
::
0
>
-15
r(
x
-20
-25
-30
-35
2
Methods and Instrumentation
5
110
-
100
-
90
-

80
-
70
-
60
-
50
-
U
c
0
L
m
m
a
a
-
.
.3-
>
4
k
.2-
0
4l
m
.i-
.,
0.0
-

l
-
2
-
110
-
100
-
90
-
U
0
L
a
;
80
-
m
70
-
60
-
50
-
40
-
-
9
40
L y.r

0
100
200
300
400 500
600
700
800
900
Deg
C
Fig.
2-2:
Thermogravimetry of CaC,O,. H,O
Plot of STA
780:
TGA and DTG
Atmosphere: Argon
30
+
20
cm3
Heating Rate
p:
10
K/min/min
136.13
c

171.08
C
463.21
C
661.26
C
601.36
C
I
1
I
I
0
100
200 300 400
500
600
700 800
I0
6
2
Methods and Instrumentation
catalytic effect of the pan material on the pyrolysis reaction could not be ascertained when
comparing the reaction in platinum and quartz pans, however, it could not be completely
excluded. All thermogravimetric experiments carried out by the author were run in plati-
num pans. Argon was used as the inert atmosphere. Oxidation experiments were run in air
because the reactions are too fast in oxygen.
The first stage of experiments was carried out using a Stanton-Redcroft TG
750
thermo-

balance connected to a three-pen recorder, recording weight (mass)
loss
(TGA), derivative
thermogravimetry (DTG), and temperature
(q.
For documentation the graphs of weight
(mass) versus temperature were drawn manually. Later
on,
the experiments were perfor-
med using a simultaneous thermal analyzer Stanton-Redcroft STA
780
(STA
1
000),
which
is equipped with a personal computer for control, data sampling, and data evaluation (Table
2-1).
Using this device the curves of TGA, DTG, and DTA (differential thermal analysis)
versus temperature
can
be plotted. Furthermore, the
PC
is equipped with extensive softwa-
re to evaluate the results under varying conditions.
Table
2-1:
Thermobalances
Instrument:
System:
Pressure Range

Heating Rates:
Recording:
Evaluation:
Instrument: TG
750
Stanton-Redcroft
System:
Pressure Range:
Heating Rates:
Recording:
3
pen recorder
Evaluation: manually
TGA
+
DTG up to
1000°C
normal pressure and vacuum
0.5 .
.
.
100
K/min
TGA empirical index numbers
evaporation
pyrolysis
oxidation
simulated distillation
kinetics according to ASTM
E

698-79
DTG empirical index numbers
STA 780 Stanton-Redcroft (STA
1000)
TGA
+
DTG
+
DTA simultaneous up to
1000°C
normal
pressure and vacuum
0.5 .
PC
PC
TGA
DTG
DTA
50
K/min
empirical index numbers
evaporation
pyrolysis
oxidation
simulated distillation
kinetics according to Flynn
&
Wall
kinetics according to McCarty
&

Green
empirical index numbers
kinetics according to ASTM E 698-79
specific heat
conversion temperatures
kinetics according
to
Borchardt
&
Daniels
kinetics according
to
ASTM E 698-79
2
Methods and Instrumentation
7
1-
2a-
2-
3-
12-
WALE!
IN
B-‘
9-
WATER
OUT
10-
‘6
-5

i
i
I
t4
i
1
GA
S
tN
.

-7
-
13
\
FURNACE LIFTING SYSTEM’
11
Fig.
2-4:
Diagram of the Thermobalance Stanton-Redcroft TG
750
1
Balance glass housing
8
Cooling water flow meter
2 Glass protection tube
9
Furnace
2a Brackets 10 Furnace lifting system
3

Glass protection tube
11
Spirit level
4
Counter weight glass housing 12 Support for glass protection tube
5
Gas inlet
13
Lower cover
6
Protection lid (Figure by Stanton-Redcroft Ltd.)
7
Gas flow meter
8
2
Methods and Instrumentation
A
schematic digaram
of
the TG
750
is shown in Fig. 2-4,
of
the STA
780
in Fig.
2-5.
The recorder script
of
an experiment with a hydrocarbon using the TG

750
is depicted
schematically in Fig. 2-6. Curve
I
represents the weight (mass) signal
(TGA),
curve
I1
that
of the first derivative (DTG), and curve
I11
the temperature
(T>
of the thermocouple directly
below the sample
pan.
Point
A
marks the start
of
the weight (mass)
loss
1
%
and the
corresponding temperature T1
%;
point
B
is the weight (mass) loss

5
%
and the correspon-
ding temperature
T5
%.
Point C corresponds to the weight (mass)
loss
at
400°C
(AG400).
This is the temperature limit of the thermal stability
of
most non-aromatic hydrocarbons
and
of
the heterocompounds. Point D marks the weight (mass) of the coked residue at
600 "C
(R600)
or at
800
"C
(R800).
Point
E
represents the maximum of the DTG curve
Fig.
2-5:
Cross-Section
of

Water-cooled Furnance for
STA
1
000
(STA
780)
A
Water cooled cold finger
B
Ceranuc baffles
C Ceramic tube
D
Micro-enviromental cup
E
Ceramic stem gas inlet
F
Furnace winding
G
STA
hangdown assembly
(Figure by Rheometnc Scientific, Polymer Laboratories GmbH)
2
Methods and Instrumentation
9
E
D
Fig.
2-6:
Schematic Diagram
of

Recorder Diagram
of
a
Test in Protecting Gas by means of
TG
750.
I
TGA signal
II
DTG signal
I11
Temperature signal
A
B
C
D
E
Start
of
weight
loss
(T1
%)
Start
of
weight loss
(T5
%)
Weight loss up
to

400
"C
(AG400)
Residue at
600
"C
(R600)
or
at
800
"C
(R800)
Maximum
of
DTG curve (T-)
with the corresponding temperature
T
The amplitude of the DTG curve corresponds to
the reaction rate. The temperature of the DTG maximum shows whether the reaction
remains in the evaporation (distillation) range
(Tmx
<
400
"C)
or if a pyrolysis (cracking)
reaction has occurred
(T-
>
400
"C).

An example of rescaling the plot of weight versus time to weight versus temperature is
shown in Fig. 2-7. Here, the point of intersection of the tangents (offset point) represents
the weight (mass)
Gw
of generated coke at the temperature Tw at the point of inflexion of
the TGA curve. This happens
only
during experiments in inert gas. Using ash-free substan-
ces in experiments in air, a TGA curve passing through zero weight is obtained, while
ash-containing substances give a constant residual weight.
The DTG graph
of
the experiment in air always shows more than one maximum, the first
of which can represent vaporization as well as oxidation.
In
this case the TGA graph in
protecting gas must be consulted for comparison.
Figs. 2-1 to 2-3 demonstrate possible evaluations using the STA
780
in an experiment
with calcium oxalate monohydrate. In Fig. 2-1 the TGA curve is evaluated with respect to
the weight (mass) losses of
1
%,
5
%,
10
%,
and further in 10
%

steps, whereas in the DTA
curve the peak maximum temperature and the corresponding residual weight (mass) are
plotted. Fig. 2-2 again shows the TGA and DTG curves with peak maximum temperatures
and corresponding residual weights. Fig. 2-3 demonstrates the onset and offset temperatu-
10
2
Methods
and
Instrumentation
100
80
60.
LO
20.
Residue
(%I
(c-

-
-
-
-
-9-
___
z
I
I
I
Tw
I

*
1
-
100
300
500
7M
800
res of
the
three reaction steps. Theoretically all three evaluations could be drawn in one
plot,
but
that would be very difficult to interpret.
With the help of differential scanning calorimetry
(DSC),
events can be observed which
are created by energy transfer (take
up
or delivery) during programmed heating or cooling
of a sample,
i.
e. melting, crystallization, second order transitions, evaporation, pyrolysis,
oxidation etc. The energetic effect in the sample is compared to a thermally inert reference
substance which undergoes the same temperature programme. The differences between
sample and reference in uptake or delivery of energy will be recorded as energy flows
versus temperature or time. Using DSC it is likweise possible to differentiate the resulting
data with respect to time (dimensions W/s) or to temperature (dimensions
W/O
C). Neither

differential quotient has any meaning in the physical sense. They serve only to elucidate
effects of the graph of energy flows versus temperature
or
time. Therefore it is not
surprising, that only a very few literature references exist where differentiated curves are
described.
Using DSC, the position of the energy flows versus temperature curve as well as the rate
of an event were influeced by the heating rate, too. Therefore the DSC tests were run
likewise, using
a
standard heating rate
p=
10
K/min with the exception of the investiga-
2
Methods and Instrumentation
11
tion of reaction kinetics. There the shift
of
the maxima
of
the energy flow curve to higher
temperatures as a result of increasing heating rates permits the calculation
of
the Arrhenius
lanetic parameters (see Chapter
3.3).
All the influences, such as oven geometry, shape of
the sample pan, position
of

gas inlet and gas outlet, on the results
of
DSC are the same as in
TGA. The gas purge with a minimum flow rate is also necessary in DSC to avoid
condensations, when petroleum and its products or generally volatile substances are tested.
As a consequence, the boiling (evaporation) temperature will decrease in a similar way to
that in TGA. The gases used in TGA can be used also in DSC. Some additional experi-
ments have been carried out in methane to study the influence
of
a hydrocarbon atmos-
phere.
For
calibration, the melting point
of
indium were measured, which has
a
temperature of
fusion
(MP)
=
156.4"C and a heat of fusion
Hf=
28.46 J/g (Fig. 2-8). Because reactions at
higher temperatures occur in experiments with petroleum refinery residues, additional
calibration runs were performed using pewter (MP
=
231.84"C,
H,=
59.61 J/g) and lead
(MP

=
327.40°C,
Hf
=
26.47 J/g).
If
a calibration at higher temperatures is necessary,
potassium perrhenate KReO,
(MP
=
550°C,
H,=
294.8 J/g) can be used.
All
DSC tests carried
out
by the author were run using open aluminium pans. For
reference an empty pan were used. Comparative tests with platinum pans gave no indica-
0
Temperature
CoC)
Fig.
2-8:
Indium
Calibration
Curve
of
DSC
MP
:

156.4
"C
Hf
:
28.46
J/g
12
2
Methods
and Instrumentation
tion that the pan material had any influence, neither
for
pyrolysis
nor
for oxidation
reactions. The first experiments were carried out with the help of
a
DuPont 990 Thermo-
analysis System connected to a 910
DSC.
This system used
a
two pen x-y recorder; the
resultant graphs were evaluated manually.
Later,
a
DuPont 9900 Thermoanalysis System
was used, which is equipped with
a
PC

for control, data sampling, and data evaluation
(Table 2-2).
A
cross-section of the
DSC
cell is shown in Fig. 2-9.
Table
2-2:
Differential Scanning Calorimetry
Instrument:
System:
Heating Rates:
Cooling Rates:
Recording:
Evaluation:
DuPont 9900 Thermal Analysis
System
DuPont 910 DSC
Pressure DSC Cell
DSC
-75
"C
. . .
+250
"C, normal pressure
DSC RT
.
.
.
+650

"C
vacuum till
bar
pressure up to
70
bar
0.5
.
.
.
50K/min
0.5
.
.
.
5K/min
PC
PC
specific heat
conversion temperatures
reaction enthalpy
heat
of
conversions
kinetics according
to
ASTM E 698-79
Fig.
2-9:
DSC

1
2
3
4
5
6
7
8
Cell Cross-Section
Gas purge inlet
Lid
Reference pan
Silver ring
Furnace winding
Furnace block
Radiation
shield
Sample platform
9 Chromel disk
10
Chromel wire
11
Alumel wire
12
Thermocouple junction
13 Thermoelectric disk (Constantan)
14
Samplepan
15
Lid

(Figure
by
TA Instruments Inc.)
2
Methods
and
Instrumentation
13
Petroleum and its products are multicomponent systems of varying chemical composi-
tion. They are predominantly a mixture of hydrocarbons, usually accompanied by a small
quantity of heterocompounds which contain in addition to carbon (C) and hydrogen
(H)
other atoms such as sulfur
(S),
nitrogen
(N),
and/or oxygen
(0).
Metals are present in very
small concentrations, such as vanadium and nickel in organically bound forms. The
average elementary composition
of
petroleum in weight-% lies between the following
limits
[2-11:
C83

87%
H11
14%

S
0.01
.
8
%
0
0

2
%
N
0.01
. .
.
1.7
%
Metals
0
. . .
0.1
%
Petroleum contains four groups of hydrocarbons:
-
alkanes (unbranched
n-
and branched i-alkanes)
-
cycloalkanes (naphthenes, unsubstituted and substituted)
-
aromatics (unsubstituted and substituted)

-
complex hydrocarbons (naphthenoaromatics)
Alkenes (olefins) and alkynes (acetylenes) are not found in petroleum (crude oils). Howe-
ver, they were formed during the processing of petroleum at high temperatures.
With regard to the boiling behavior, the full range of substances occur, from those which
evaporate early during the recovery, as a result of pressure decrease, through to substances
which cannot evaporate without decomposition. It is possible to separate individual chern-
cally-defined substances from the low boiling fractions. From medium and high boiling
fractions and from the non-distillable residues only multicomponent systems can be
obtained, which can be separated into groups characterized by a similar chemical and
physical behavior. Separation into individual compounds is almost impossible.
Under these circumstances, it seems reasonable to study the thermal reactions such as
boiling, pyrolysis, and the oxidation behavior of defined model substances first, in order to
understand the behavior
of
petroleum and its main products and to draw some analogous
conclusions.