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THERMOA1~ALYSIS

OF PETROLEUM PRODUCTS CRITICISM TO THE CONRADSON NUMBER AND A POSSIBILITY TO DETERMINE THE FLASH POINT*

By Z . .d..DO::,\YI

Department of Chemical Technology, Technical Llliyersity, Budapest

Introduction

From analytical aspects, testing material properties during temperature changes proved to be rather expedient. Continuously developing methods of thermal analysis are, however, applied in other fields than quantitative and qualitative analysis. As against isothermal tests, non-isothermal tests yield a lot of data from a single test. This fact has the quite natural consequence that investigators attempt to determine and understand essentials and kinetics of the invoh-ed processes from this type of measurements instead of from more tedious and time consuming isothermal test :;;eries. After initial successes, however, the:;;e uses of non-isothermal tests turned to complicated problems, to "marshland" - according to the characteristics of kinetical processes.

Hence, seemingly well-known compounds considered as safe bases such as calcium oxalate, calcium carbonate, are to he tested as models again and again.

Nevertheless, theoretical and practical analytic work to interpret and apply thermoanalytic phenomena did not meet expectations. Thermal de- composition processes could not he presented by DTA and DTG peak tempera- hues in a reassuring manner. Peak:;; becallle "'independent", their temperatures varying as a function of sample volume, heating rate etc. Ohviously, with the growth of the number of components, curves soon become confuse, especially for extremely varying composition:;;. This is the case for tcsting petroleum products when mostly neither quantity, nor quality of sample components are knowll separately but ranged into groups established, to some or other principle.

For such compounds, thermal processes with rates depending on temper- ature are overlapping in various ways. It is well-known that distinction of overlapping processes is generally still an unsolved prohlem. In testing pe- troleum products, the prohlem is made more complex hy the superposition of the evaporation of systems consisting of many components - known at most hy hydrocarbon type groups to the thermal decomposition processes. This

" Lecture presented at the Section of Thermal Analysis, Centenary Scientific Session of the Faculty of Chemical Engineering.

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286 Z. ADO"YI

fact is responsible for the low number of researchers concerned with the ther- mal analysis of petroleum products.

Inconsistent results probably due to their complexity seem to be responsible for the unclearedness and debatedness of relevant test conditions.

Contradictory opinions are known, for example, about the usefulness of TG distillation curves in connection with the siting of the microdistillating parts of the thermobalance used for analytical purposes and the heating set mounted over it [1-4], or the admixing of solids [5].

Among others, with reference to foaming, it should be noted that evap- oration is not the only physical phenomenon 'which complicates thermal processes.

Possihilities of identifying various thermal processes

Testing of petroleum products has led to the recognition that for getting convincing results partly the fixation of the thermal process has to be attempt- ed and partly thermal decomposition has to be distinguished from evaporation.

Standardization of testing conditions is no solution for fixing the thermal processes. Namely, standardization may help dissimulating causes of phenom- ena. A more important problem is that for petroleum products it is not possible to keep the sample quantity at a constant value by specifying the weighed quantity alone, because of the variable composition of the sample.

Rather than to standardize test conditions, primarily, straightening of thermo- analytic curves has been attempted in application of epistemology results of

MILL [6].

VAN KREVELEN et al. [7] succeeded to straighten thermogravimetric cun-es (TG) by means of the differential equation

where -dx/dt (a-x) n k

dxldt = k(a-x)n weight loss rate at temperature T:

the concentration of a reactant at time t;

reaction order;

Arrhenius rate constant depending on the absolute tempera- ture.

Already COATS and REDFERN [8] have indicated their anxiety that this differential equation could hardly be used for any thermal decomposition process. Among others, DRAPER [9] set forth the limitations of its use in detail. Nevertheless, it may he useful, provided that it is not applied heyond its limits. Generally spoken, it is a mathematical tool for transforming meas- urement data so as to make the thermal process more accessihle, more re- cognizahle. There are of course some cases where it can describe the kinetics of the process.

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THER.UO.·LYALYSIS OF PETROLEUJI PRODUCTS 287 The ahoye statements are illustrated hy thermogra yimetric test results in Table 1, compiling ealcium carhonate test conditions, data [10], as 'well as reaction order and activation energy values calculated by the method of

FREE;)IAN and CAROLL [11].

TC5t

3

·1 5*

6**

Tahle 1

Effect of sample quantity, heating rate and crucible shape on DTG peak temperature

and on kinetic constants

"-ei!!hcd Heating DTG Reaction Actiyation

saIl~ple rate peuk order energy

mg i oC/min 'C kcal/ill~ol

-""---

·10

T

I 12.6 792 0.25 ·16.7

2000 I lOA 9-1,7 0.25 51.6

200 3.7 825 0.25 -1,3.3

200 11.7 870 0.25 36.3

190 1.3 680 0.25 50.8

:!OO 7.5 892 0.0

·n.o

" Polyplate sample holder

*'" Crucible with lid

This table illustrates the often tested and well-known fact that the shape of TG, DTG and for the latter, the peak temperature depend on the sample cluantity, the heating rate and other test conditions. Besides, it is also obvious that the reaction order is permanent; it little changed at the fundamental alteration of the character of test conditions. Actiyation energy ranged about an average value, 'while DTG peak temperatures differed hy as much as 260 GC in extreme cases.

It has to he rememhered also that the logarithm of the rate constant as a function of liT is expected to be linear, and a different behaviour induces

10 search for its cause. The quoted differential equation seems to offer a possihility to systematize and survey thermal decomposition processes. In- stead of the confusion of curve distorsions due to parameter changes, modi- fication of sample weight, of heating rate etc. offers a deeper insight into the process. The thermal decomposition process is hetter descrihed hy determining the so-called "kinetic constants" than the peak temperature.

In testing petroleum products hy thermoanalytic methods, study of the evaporation phenomenon cannot he avoided. It could be stated [12]

that when treated hy the quoted differential equation, evaporation rate of chemically pure materials invariahly appeared to he of zero reaction order, thus, it could be considered as linear function of the reciprocal of temperature.

This is to say that for zero apparent reaction order, the possibility of evaporation of chemically pure material has to be reckoned with. There is a strict rela-

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288 z. ADO.\TI

tionship between equilibrium yapour pressure and eyaporation rate at a giyen temperature.

It was expedient to introduce the notion of fictiye eyaporation surface expressing the de·dation from the equilibrium state during testing. FictiYe evaporation surface depends on the temperature, 011 the composition of the gaseous phase, and is characteristic to the substance.

Testing the evaporation from a mixture gaye an unexpected result.

Applying the differential equation to this thermal process, partly, the appar- ent reaction order of eyaporation was rather different from zero, as against chemically pure materials, and partly, it much depended on heating rate, as against the thermal decomposition illustrated in Table 1.

Determination of the eyaporation from a mixture by means of the com- mon method [11] is rather cumbersome an operation, and the logarithm of the apparent reaction rate constant is no linear function of the reciprocal of absolute temperature - as against most thermal decomposition processes.

According to the presented results, thus, the same formula enables to distinguish between the three phenomena - eyaporation of a pure material, eyaporation from a mixture, and thermal decomposition - eyen for an un- known material. This would be impossible from the knowledge of the cun-es alone, from their shape.

The Conradson number and thermogl'avimetric testing of the Conradson coke

Determination of the Conradson number is an important standard test in the petroleum industry. Applying to it the statements on thermal decom- position and eYaporation, observations can bc recapitulated as follows [13].

The Conradson number expresses the percentage by weight of Con- radson coke deyeloping ·when the tested petrolcum product is heated in a space-excluding comhustion, it heing the solid product of quite a series of thermal processes. It can be preassumed that, hy tracing decomposition pro- cesses, a correlation can he found hetween some characteristic thermogravi- metric data and the Conradson numher, lending a hasis for the exact deter- mination of the coke residue, in a less empirical manner.

Tweh·e different suhstances -with ConradsoIl numbers of 3.5 to 17.6 per ccnt, have heen subjected to thennogravimetric analyses in a P.P.E. deriyato- ILraph [14].

V-arious fuel oils have heen dcmonstrated to have peculiar DTG curves [15]. Such a simplified, generalized DTG curve is shown in Fig. 1. The peak traced with a dashed line appears if the fuel oil contains some light hydro- carhon, e. g. petroleum or gas oil. The other peaks are due to thermal decompo-

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THER_1IOAiYAL YSIS OF PETROLEClI PKOVC:CTS 280

--~--~~~~~---~---

20.0. 30.0. 400 50.0. 50.0

Fig. 1. Simplified DTG curves for fuel oils

0.00.0.

u

\lJ

~ 0> 0,0.20.

E=

<:.;J

0.,0.40.

h Cl

0.,0.60.

100.

-e: 80 -~ Cl)

::;: 60. I--+---'--~-J'--'--- en 40 I---f--.--'---,p---'---.-

U1

"

20 I - - + - - - , F - - - -

a

L-_~~~ _ _ _ _ _ _ _ _ _ _ ~_~

(j 100 20.0. 300 !'OO 50.0 600 70.0 T eC)

Fig. 2. TG and DTG curves for sulphur-free light f[,cl oil. Conradson number -1.6%. related temperature 590 GC

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290 Z. ADO,'-YI

sition accompanied by weight loss. For the Conradson number, peak 2 in Fig.

1 is of importance, appearing in the range 475 to 610 QC and for some DTG cunres it seems eyen without kinetic analysis to be the result of several pro- cesses. This temperature range includes the decomposition point for the Conradson number that cannot, however, be co-ordinated neither to the be- ginning, nor to the end point or any other characteristic point of the peak.

DTG and TG diagrams of some tested substances indicate the temperature 0,0.00.

'-' Q)

-!:!}

0; 0.0.20.

EO C!l f-... 0,0.40,

Cl

0,,0,60.

10,0.

*

80. J

-c ~

'"

(lJ 60.

~ '--.

a

V) 1;0. I - - - - o - - - f ! - - - -

'0 a

-J

20 I - - - - ' - - } ' - . , - - - , - - - - -

0. ~~~ __ ~ ______________ ~5~3_5_cC~I __ ___

0. 10.0 20.0. :;0.0. 40.0. 50.0. 60.0. 700 T (CC)

Fig. 3. TG and DTG curves for a light fuel oil (about 30% gas oil, 70°;0 DT-I Soviet artificial oil), Conradson number 3.5~~, related temperature 535 QC

where the weight of material that remained in the crucible in thermogravi- metric measurement is equivalent to the Conradson number (Figs 2 through 7).

The Conradson number determined according to the standard method appears to pertain to a peculiar thermal decomposition section but even so, it cannot directly be determined by thermogravimetry. On the basis of thermo- gravimetric knowledge it is obvious that this can be attrihuted to shortcomings of the method of determining the Conradson number.

Presented data show that the point in DTG curves equivalent to the Conradson number is related at random to sections of different ratcs of com- plex thermal decomposition processes concomitant to weight loss. Hence, determination of the Conradson number means the interruption of a charac- teristic group of processes in a section of undefined rate and the freezing of

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\J

<ll

"

THERJIOA.YAL YSIS OF PETROLEClI PRODt:CTS

t;:; 0,020 f - - - -

E'

(!J

~ 1),040 I---\-'---~---

0060 I---~-~-t---

:J2 80

0

-C

-:?' 50

QJ

~ '--Q 40

c"

co

0 20

-.l

o~ ______ ~ ____ ~ ________ ~ ____ ___

o

;00 200 300 400 500 600 700

291

Fig. 4. TG and DTG curves of pure paraffin distillate from ;'\agylene;ycl crnde. Conradson number 5.4%, related temperature 550 cC

0,000

II QJ

c,

C;; 0,020 E'

<:.:J

!-- 0,040 Cl

0,060 100 :J2 80

0

-c

'2' 50

QJ

:;:

'-- 40

Q V)

V) 20

0 -.l

°

~--~~~--~--~--~--~--~

o

100 200 300 400 500 600 700 T (OC)

Fig. 5. TG and DTG curves for goudron. Conradson number 15.4%, related temperature- 605 QC

(8)

292

v 0,000

'"

Z

Z. ADO.YY[

:?' t:: 0,020 /---~----'<--+--

100 ,.,.,

....

--

:J2 0 80 /----'----,...--_. __ ._-_._---.p.--_ .. - - - - - ..c:

.:?>

60

Cl>

} '--0

'" 40

V)

0 -.J

OL-__ ~~~ __ ~ ________ ~ ____ __

o 100 200 300 400 500 600 700 T (OC)

Fig. 6. TG and DTG curves for common fuel oil (about 45°" bitumen, ~5° u ga" oil from Lispe). Conradsoll number 12.7°,,, related temperature 5·10 ~C

100

"*

801---

..c:

.~ 60 1 - - - . - - . -

Q)

}

40

2 0 / - - - - -

o

~

______

~~~

______________________ __

o 700 2DG 3(;0 50]

Fig. 7. TG and DTG curves of sulphuric light fuel oil (about 85% mazout, 15~o mixed dilut- ing material). Conradson number 12.7%, related temperature 5,15 cC

(9)

THER1IOA_YAL YSIS OF PETROLECJ1 PRODCCTS

DTG 0 mm

20 40 DTA 0 mm

20 40 60

100 ~---~----~---r----~--~---r-----i

~ 80 ~--~--~----~---r---~----~---~-~~=---

::>

<lJ

~ 60 ~ __ ~ ____________ ~ ______ - L _ _ _ _ _ _ _ _ ~ _ _ _ _ _ _ _ _ _ _ _ _ _ _

"- a

~ 4 0 ~---:---'--I---­

a

--.J

20 ~--~.---~--~~---~--~---

o I

21.:13

o 100 200 300 ,0] 500 600 700 600 900 "DOe 1100 T ,-oC;

Fig. 8. TG. DTG and DTA curyes for Conradson coke

reactions, instead of fixing some state previous to or following some thermal decomposition process. Thus, Conradson number is an ill-defined value, since it depends in an uncertain manner on factors governing the rate of reactions producing the Conradson coke, and is also a function of factors acting at the interruption of reactions.

Thermogravimetric analysis of Conradson cokes from eight different substances under lid, in nitrogen atmosphere, proves that the material evolving at the determination of the Conradson number is a product of incomplete ther- mal process. TG, DTG and DTA curves of one sample are shown in Fig. 8, those of the others being of the same character.

CUr-HS presented for the sake of illustration (Fig. 8) demonstrate the Conradson number to issue from a non-complete thermal process. It is unex- pected to see a weight loss between 100 to 200:C apparent from the DTG curve, although the substance formed at or over 500:C. Evidently, this weight loss is due to desorption: evaporation process, rather than to thermal decom-

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294 Z. ADO,'-'-]

position. Formation of the so-called Conradson coke is accompanied by the condensation of part of light hydrocarbons present in the air-free space, adding to the Conradson number, the poor definition of which being again apparent from this phenomenon.

In any case, the second DTG peak is a complex l'emltant of several thermal processes. This fact is ohvious from calculations hy the CHATTERYEE method [16] using the already presented differential equation.

1,6 1 - - - + - \ ' - - - ' - - - · - - - -

0,8

Q6 1---1-...;.--..,.----,/---;---

0,2 '--_ _ _ ... _ _ -'-_-'-) _ _ '--_-'--_...J.1 _ _ - ' - _ - ' - _ - - - '

o WO 200 300 'tOO 500 600 700 800 900 T (OC)

Fig. 9. Temperature dependence of reaction order as calculated from TG and DTG values of Conradson coke, assuming a single thermal process to exist

According to this differential equation, the reaction order is constant for a single thermal decomposition process. Attrihuting the weight loss of the so-called Conradson coke in the temperature range 70 to 1000°C to a single process, calculated reaction orders vs. temperature are shown in Fig. 9. These calculations show the weight loss to result from several decomposition pro- cesses.

Calculated reaction orders for ranges 40 to 160°C, 530 to 680 QC and 680 to 860°C are shown in Figs 10, 11 and 12.

For the 40 to 160°C temperature range, the character of the change of reaction order reminds of evaporation from a mixture. Kno'wing the agent applied for testing, this claims for the statement that the first DTG peak is due to other than thermal decomposition. (Thus, it can be stated that one result of the calculations is the possibility of distinction between weight losses

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THER.iIOA.'·ALYSIS OF PETROLE[;JI PRODCCTS 295

tJ 1,0

0,8 0,6

0,4

0,2

i

0 2D ~O 60 80 lOO 120 140 160 T (DC)

Fig. la. Temperature dependence of reaction order as calculated from TG and DTG data of Conradson coke in the 40 to 160 QC range

1,4

r-r-...-:--rI==:I==:i l ==1===1==:1

1

==rl,_--_--r-+-I~:i

1,2

~il..l.:!1111

tJ

!

I

~--y6-1

---,1...

I

i !

I !

~O~-+I--+i--+I--+I--~!~~!~~I~~I==~I==~!

0,8 1--+

1

- +

1

- 1 -

1 --+1 -+--1 ----t-! --t-! ---,Ic---t-

j -

I

0,6

1---+--1 -T-j----i-

I -t-I ----1-1 ----t-I---t--I --;--1 ---:--\ ~i

0, it

1--+-1----J-

1 --il----T-I ----t--I ---t-I---t-I ---11----t-J ----"11

0,2 ~--~--~--~--~--~--~--~----~--~--- 560 570 580 590 600 610 620 630 640 650 660 T (DC)

Fig. 11. Temperature dependence of reaction order as calculated from TG and DTG data of Conradson coke in the 530 to 680 cC range

V 1,1

i i

1

!

J

I

0

!

1

;

i

! :

i

! I

! i i

1,0

0,9

0,8

J.

I

:

. i i :

0,7

0,6 i

700 720 740 760 780 800 820 840 860 TrC)

Fig. 12. Temperature dependence of reaction order as calculated from TG and DTG data of Conradson coke in the 680 to 860 QC range

9 Periodica Polytechnica Chem. X\"I/3.

(12)

296 Z. ADO.\TI

due to thermal decomposition and to other processes. This is impossible if only cun'e shapes are known.)

Fig. 11 presenting the 530 to 680 :C range indicates there two thermal decomposition processes. The second is not disturbed by o\-erlapping in the range 610 to 660 :C. Reaction ordcr of this process is 1, activation energy being 36.5 kcalJmole.

Decomposition process in the range 680 to 860 °c, is a single process without any oHrlapping (Fig. 12). This decomposition is also of order 1, the activation energy is 25.1 kcaljmole in the 730 to 780 cC range.

Determination and comparison of weight losses of different Conradson cokes in tnnperature intervals belonging to each decomposition process leads to the conclusion that the prime material quality is strictly related to three processes in the 400 to 680°C range, dependent on the chemical composition of the sample applied for determining the Conraclson number.

The presented results seem to be sufficient to demonstrate that system- atic thermoanalyses and kinetic calculations yield much more valuable kno\dcdge of petroleum products such as fuel oil than determination of the f'mpirical, undefined Conradson number does.

Consequently, though for the time being the industry cannot renounce the use of the Conradson number because of the experience available, anyhow it is worth while to complete the determination of the Conradson number by thermogravimetric tests. It is advisable to indicate residual percentages at the end of thermal processes leading to the so-called Conradson coke and at the end of its decompositions (higher and lower than the standard Conradson number, respectively). Inasmuch as temperatures helonging to the percentages by 'weight are indicated, thermal tests are to he standardized.

Thermogravimetric flash point determination

Another important standard test to rate petroleum products is the determination of the flash point (ignition point). Therl1logravimetry lends itself to this aim.

In flash point determination, a certain quantity of hydrocarbons got upon thermal effect into the gas space has to be mixed with air to produce flash. Hydrocarbon content of the gas space is proportional to the vapour pressure of the test material. In conformity ,,-ith those stated in the introduc- tion, vapour pressure and weight loss rate are strictly related, therefore it seemed expedient to find a correlation between the logarithm of weight loss rate and the flash point. In the log. DTG vs. liT diagram indicating the re- corded flash points, these latter are connected by a straight line. Temperatures

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THERJIOASAL YSIS OF PETROLEC_\[ PRODl-CTS 297 at the intersection of this straight line and the log. DTG n. liT curyes of each sample are compared to standard flash points in Table 2.

Table 2 exhibits a strict correlation between thermograyimetric data and flash points. According to tests in nitrogen atmosphere and ,~ith poly-

Table 2

Comparison of flash points determined by tests and from diagrams

Sample Flash point, cC

::\0.

Te" Diagrnm

1 81. 63 80

"

122. 104 112

3 203, 217. 216 217 I 20l. 212, 206 211

"

169, 171, 175 149

6 290 268

7 176. 182 170

8 165. 165 171

9 78, 62 69

10 137 147

11 282, 285 293

12 lll, 106 105

13 1"-.. :1. 125 148

14 137. 135 U3

1.:; 154 163

16 75~ 66 82

17 219 221

18 260. 254. 270 265

19 277 276

plate sample holder, this corrrelation is greatly affected by the gas atmosphere and the crucible shape, without affecting its strictness. Thus, thermogravi- metry lends itself both to determine the flash (ignition) point and to descrihe the combustion properties of the material.

Further research is needed to refine this method, likely to clear devia- tions apparent for samples 5,6 and 13 in Table 2. Flash point determined by thermogravimetry can probably be related to the mean molar weight and the chemical group composition of the tested material.

9*

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298 Z. ADOSYI

Summary

Thermoanalysis of petroleum products is hampered by the complexity of thermal processes, by physical processes superimposed to the thermal decomposition of multicomponent materials, first of all, by evaporation. Differential equation -(dx/dt) = k(a - x)n lends itself to distinguish between these processes. Accordingly, apparent reaction order of evaporation of single-component substances is invariably zero, while for mixtures it is non-zero and much dependent on heating rate. In case of thermal decomposition, the reaction order is essentially independent of the test conditions. These findings encourage the use of thermogravimetry for petroleum product testing, what is more, for determining empirical data accessible to standard tests only but of industrial importance. Among these latter, the Conradson number proved to be an ill-defined value. TG and DTG data yield more comprehensive, unambiguous data than are characteristics resulting from the Conradson number. DTG curves help to determine another empiric characteristic ef petroleum products viz. flash point (ignition point).

References

1. ,\VELTNER, M.: Intermediate Report of the Derivatography Testing of Carbons and Oils.

Subject 1\0. 032-V. Report No. 455. Thermal Research Institute. Budapest 1961.

(In Hungarian.)

2. PAULIK, F.-PAULIK, J.-ERDEY, L.: Fresenius' Zeitschrift ftir Analytische Chemie 160, 321 (1958).

3. PAULIK, F.-PA'CLIK, J.-G.-iL, S.: Fresenius' Zeitschrift fUr Analytische Chemie 163, 321 (1958).

4. VOLKER, H. J.-FISCHER, N.: Konf. tiber die Chemie und chem. Yerarbeitung des Erd- 015 und Erdgases. Akademiai Kiad6, Budapest, 1968. p. 650 .

.5. V.bIOS, E.-FLORA, T.: Konf. tiber die Chemie und chem. Verarbeitung des Erdols und Erdgases. Akademiai Kiad6, Budapest, 1968. p. 254.

6. PAUER, 1.: Fundamentals of Logic. Franklin-Tarsulat, Budapest, 1901. p. 121 (In Hungar- ian.)

7. KREVELEl'O, D. W. VAl'O-HERDEl'O, C. VAl'O-HuNTJEl'OS, F. J.: Fuel 30, 253 (1951).

8. COATS, A. W.-REDFERN, J. P.: The Analyst 88, 906 (1963).

9. DRAPER, A. L.: Proc. Toronto Symp. Therm. Anal. 3, 63 (1971).

10. ADONYI, Z.: Periodica Polytechnic a Chem. Eng. 11, 325 (1967).

11. FREEMAN, E. S.-CARROLL, B. J.: J. Phys. Chem. 62, 394 (1958).

12. ADONYI, Z.: Investigation of evaporation by thermogravimetry. Lecture at 3rd ICTA, August 22- 28, 1971.

13. ADONYI, Z.-YktlIOS, E.-Kov.-ics, L.: Thermogravimetric Analysis of the Conradson Number and the Conradson Coke. (In Hungarian.) Lecture at the Conference "Devel- opment of Petroleum Industry in the Period of the Fourth Five-Year Plan", Gyor, October 20 to 22, 1970.

14,. PAULIK, F.-PA17LIK, J.-ERDEY, L.: Fresenius' Zeitschrift fUr Analytische Chemie 160, 241 (1958).

15. ADONYI, Z.: Derivatograph Testing of Fuel Oils. (In Hungarian.) Report for NUr. Buda- pest 1966. Manuscript.

16. CHATTERYEE, G. K.: J. Polymer Sci. A3, 4253 (1965).

Dr. ZolHin ADONYI, Budapest XI., Budafoki ut 8, Hungary.

Printed zn Hungary

.A kiauu::crt felel az Akademiai Kiad6 igaz?!atoja A kezirat nyollldaba erkezett: 1972. Y. 16.

~Iu5zaki szerke~zto: Botya1l5zky Pal Terjedclem: 1l~5/A/5 IV, 79 ubra

72.73585 Akndemiai l'\yomda, Budapest - Felelo5 vezeto: Bernat Gyorgy

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