80203661
Post on 03-Jun-2018
216 Views
Preview:
TRANSCRIPT
-
8/12/2019 80203661
1/11
292
Chemistry and Technology of Fuels and Oils, Vol. 48, No. 4, September, 2012 (Russian Original No. 4, July-August, 2012)
RESEARCH
THERMODYNAMIC PARAMETERS OF CONVERSION REACTIONS OF SOME
HEAVY OIL COMPONENTS UNDER THE ACTION OF STEAM AND HEAT
V. A. Lyubimenko, N. N. Petrukhina, B. P. Tumanyan,
and I. M. Kolesnikov
____________________________________________________________________________________________________
I. M. Gubkin Russian State University of Oil and Gas. Translated fromKhimiya i Tekhnologiya Topl iv i
Masel, No. 4, pp. 27 33, July August, 2012.
0009-3092/12/48040292 2012 Springer Science+Business Media, Inc.
The mechanism of the reactions of conversion of heavy oil components, viz., heteroatomic compounds
and polycyclic aromatic hydrocarbons, under conditions of steam and thermal action on the oil reservoir
is studied. Based on the calculation of the thermodynamic parameters of the reactions, conclusions are
drawn regarding the feasibility of the reactions and the primary directions of conversion of heavy oil
components at the steam and thermal action temperature. The possibility, in principle, of occurrence of
hydrogenolysis, hydrogena tion, and hydrocracking in the presence of such hydrogen donors as polycyclic
naphthenic-aromatic hydrocarbons and formic acid in the reaction system is demonstrated.
Key words: heavy oil, native asphalts, steam and thermal action, steam and gravity drainage, Gibbs
energy, aquathermolysis, hydrolysis, hydrogen donor.
Russ ia posse sse s subs tan t i a l r e se rves o f na t ive a spha l t s - va r ious ly p red ic t ed to r ange
from 30 to 75 billion tons [1], of which the recoverable reserves, even at very low recovery factors, exceed 1 billion
tons [2]. More than 500 heavy crude oil deposits are concentrated in the Volga-Ural oil- and gas-bearing
province [3] . The to ta l recoverable reserves of heavy crude o i ls in th is province comprise more
than 660 million tons. Note that the major part (97%) of these oils is high-sulfur.
These deposits cannot be recovered by traditional means, which makes search for economically efficient
techniques of heavy oil and native asphalt recovery an urgent task. Steam-thermal action (STA) on the reservoir,
such as cyclic, area, steam-gravity drainage, etc., is well studied and used widely [4]. Steam injected into the
reservoir is not only an effective heat carrier and a displacing agent, but also leads to chemical conversion of the
crude oil. This is confirmed by comparative studies of the physicochemical properties of native oil and the oil
-
8/12/2019 80203661
2/11
293
recovered by STA [5]: these specimens differ in density, fractional and group composition, IR spectral
characteristics, content of heteroatoms, etc.
In modeling STA in a flow-type reactor [6], resin-asphaltene components, in particular, were shown to
undergo transformation with increase in oil content in the transformed material. Modeling of hydrothermal
transformations of asphaltenes of native asphalt in hydrogen and steam helped detect considerable increase in
radical paramagnetism [7]. The content in the aqueous phase of products of reaction of hydrocarbons and
oxygen-containing compounds as well as redistribution of group components of native asphalt upon hydrothermal
transformation makes i t possible to suggest that asphaltene degradation occurs at a lkyl substi tuents
containing carbon-heteroatom bonds [6-8]. This is corroborated by slightly lower values of the energy of
the C-S and C-O bonds in sulfides and ethers than the energy of the C-C bond [9].
In [10, 11], modeling of STA indicated steep rise in volume of carbon dioxide and hydrogen sulfide liberated
at temperatures above 200C. It is suggested that hydrogen sulfide is formed upon thermal decomposition of
organosulfur compounds, reaction between sulfur and paraffins with formation of mercaptans and decomposition
of the latter. Steam was shown to have a catalytic effect on carbon dioxide generation. Catalytic effect of water on
transformation of organic compounds is reported also in [12]. With rise of temperature the solubility of
organic compounds in water increases and, moreover, at 250C the negative logarithm of the ionic product of water
is 11 (at 20C it is 14). So with rise of temperature water simultaneously becomes a stronger acid and a stronger
base , catalyzing reactions of hydrolysis of some heteroatomic compounds. As shown in [13], in STA water may
not only be a catalyzer but also a reagent. Analysis of thiophane and thiophene transformation products under
conditions of thermolys is in steam [13] showed relatively high carbon monoxide and carbon dioxide content in the
reaction gas, although the initial sulfur compounds do not seem to contain oxygen, i.e., water is the only source
of oxygen in the system.
Summing up the foregoing it can be suggested that STA may stimulate reactions of thermal cracking of
hydrocarbons and heteroatomic components, high-temperature hydrolysis (aquathermolysis) of heteroatomic
compounds [14], condensation, hydrogen migration, i.e., dehydrogenation of some compounds simultaneously
with saturation and hydrogenolysis of others. It is of interest to determine the thermodynamic feasibility ofoccurrence of these reactions of transformation of some components of heavy crudes at temperatures typical
for STA. For this purpose, the thermodynamic parameters (fH
T and S
T) of the reactants considered as model
compounds of heavy crudes were calculated by the roentgenometric method PM6 using the MOPAC 2007 software
package and the change in Gibbs energy of the react ions was calculated by the equat ion rG
T =
rH
T - T
rS
T.
Transformation of organosulfur compounds. Hydrolysis of carbon-heteroatom bonds is stimulated by
part ial negative charge on the heteroatom, i.e. , by its abil ity to bind a proton (protonate), so hydrolysis intensif ies
in acidic medium. The following mechanism of high-temperature hydrolysis of cyclohexylphenyl sulfide can be
suggested [15]:
-
8/12/2019 80203661
3/11
294
or in the shortened form
(1)
(2)
(3)
For cyclic sulfides, particularly for thiophane, the following transformation chain was suggested in [13]:
To check the feasibility of the chain of transformations, the thermodynamic parameters were calculated for
the first stage:
(4)
Since hydrogen sulfide formed upon STA is a weak acid, it is capable of protonating heteroatomic
compounds of crude oil and initiating their hydrolysis, i.e., autocatalytic reactions may occur under the action
of H2S [13].
The initial reagents noted above may be a part of resin molecules and asphaltene structures. The following
aquathermolysis reaction at the CS bond can be written for the model of the molecule of resinous matter:
(5)
-
8/12/2019 80203661
4/11
295
As can be seen, destruction of C-S bonds may cause detachment of individual fragments from the resin
and asphaltene particles. Note that the chains containing heteroatoms bind aromatic plates into asphaltene
packets [16]. Upon breakup of carbon-heteroatom bonds, alongside a change in the group and fractional
composition, the structure of the asphaltene particles may undergo transformation, causing, in turn, a change in
the rheological properties of the material.
Apparently, at temperatures between 200 and 350C, reactions of thermal cracking of sulfur-containing
compounds will occur with formation of hydrogen sulfide, hydrocarbons, condensation products, etc.:
1262136136 H2CSHHCSHC (6)
In some works, [17, 18] in particular, use of hydrogen donors for accelerating transformation of heavy oil
components by STA is proposed. The most common hydrogen donor is tetralin (tetrahydronaphthalene), which is
amenable to dehydrogenation with liberation of active hydrogen:
(7)
Decomposition of formic acid may also be a source of hydrogen:
22 COHHCOOH (8)
But, according to [19], in gas phase formic acid undergoes decomposition by the reaction:
COOHHCOOH 2
(9)
Fig. 1. Dependence of change in Gibbs energy of hydrogen formation reaction on
temperature (the digits on the curves correspond to reaction numbers in the text).
Gib
bsenergy,
kJ/mole
Temperature, K
-
8/12/2019 80203661
5/11
296
In liquid phase, on the other hand, formic acid forms with water complexes that decompose to hydrogen
and carbon dioxide; this reaction is catalyzed by water, on the concentration of which depends the acid
decomposition rate [19]. Reaction between steam and carbon dioxide - a product of decarboxylation of oxygen-
containing organic compounds, may also be another source of hydrogen in the system:
222 HCOOHCO (10)
In order ascertain the thermodynamic feasibility of reactions (7)-(10), which may be sources of hydrogen
in the productive stratum, their rG
T values were calculated (Fig. 1). As will be seen, tetralin hydrogenation is
possible a t temperatures above 337C, and both formic acid decomposition reactions and reaction (10) are possible
at the STA temperature.
The thiophane hydrogenolysis reaction in the presence of tetralin as the hydrogen donor can be written
a s
(11)
Upon dissociation of formic acid to the ions H +and HCOO-, the latter will react with the organosulfur
compounds following the scheme [20]:
or in the shortened form
(12)
A similar reaction for thiophane is:
(13)
-
8/12/2019 80203661
6/11
297
The results of calculation of the Gibbs energy of reactions (1) (6) and (11)(13) at various
temperatures are plotted in Fig. 2a . The positive rGT values of cyclohexylphenyl sulfide hydrolysis
reactions (1) and (2) attest to occurrence of these reactions with low yield of products; the equilibrium is shifted
toward the initial reagents. Reaction (1) is somewhat more probable than reaction (2). At the same time,
decomposition of cyclohexylphenyl sulfide to thiophenol and cyclopentane (3) is possible at temperatures
above 227C. Hydrolysis of the CS bond in the model resin compound (5) is thermodynamically feasible in the
whole STA temperature range, so transformation of resins and asphaltenes with detachment of side fragments and
formation of hydrocarbons and heteroatomic components with a lower molecular weight is possible. The
calculated rG
Tvalues for the first stage of thiophane transformation (4) are positive, which indicates that this
reaction is improbable under the STA conditions. From a comparison of reactions (1), (4), and (5) it is obvious that
as the structure becomes more complex and the molecular weight of the organosulfur compounds increases, the
probabil ity of occurrence of hydrolysis reactions increases. Hydrolysis wi th ring sc ission , on the other hand, is
highly improbable.
Fig. 2. Dependence of change in Gibbs energy of reactions of transformation of heavy
oil componen ts by STA on temperatu re: a- organosulfur compounds; b- organooxygen
and organonitrogen compounds; c - PCAH (the digits on the curves correspond to
reaction numbers in the text).
Gibbsenergy,
kJ/mole
Temperature, K
c
b
a
-
8/12/2019 80203661
7/11
298
Calculations show that thermal degradation of dihexyl sulfide (6) is possible at temperatures not
below 227C. It is interesting to note that reactions (12) and (13) of sulfur compound hydrolysis in the presence
of formic acid may occur in the whole investigated temperature range, whereas thiophane hydrogenolysis reaction
in the presence of tetralin (11) may occur at temperatures above 120C, i.e., it is also possible under STA.
Note that in th is work tetral in is considered as one of the polycycl ic naphthenic aromatic crude oil
hydrocarbons that exhibit hydrogen donor properties. Thus, under STA hydrogen will be transferred from these
hydrocarbons to other components, heteroatomic in particular, and the latter will undergo hydrogenolysis.
Transformation of oxygen- and nitrogen-containing organic compounds. The structure of resins and
asphaltenes contain ROR2 groups whose hydrolysis will probably occur with formation of phenols [20]:
(14)
For the model of the molecule of resinous matter, referred to above, we may write two hydrolysis reactions
occurring with breakup of only the CO bond of aliphatic ether and breakup of CO bonds of both aliphatic and
cyclic ether:
(15), (16)
-
8/12/2019 80203661
8/11
299
Akin to reactions (1) and (3), reactions of phenylcyclohexylamine hydrolysis and degradation may occur
as follows [15]:
(17), (18)
In the presence of formic acid, aniline and cyclohexane may form:
(19)
The results of calculation of the change in Gibbs energy of reactions (14)(19) at various temperatures are
plot ted in Fig. 2b. As can be seen, the referred reactions of hydrolysis of oxygen-containing compounds are
possible in the whole STA tempera ture range. Thus, hydrolysis of CO bonds will occur with greater transformation
than hydrolysis of CS bonds. Hydrolysis of phenylcyclohexylamine by reaction (17) is possible only
at 230C and above, and its decomposition by reaction (18), at a temperature above 130C. Transformation of
nitrogen-containing compounds in the presence of formic acid, like oxygen-containing compounds, is
thermodynamically possible in the whole investigated temperature range.
Transformation of polycyclic aromatic hydrocarbons (PCAH). Calculation of thermodynamic characteristics
of PCAH transformation reactions under STA conditions is of interest from the standpoint of determination of the
most probable paths of their transformation: condensation, hydrogenation, hydrogen rearrangement, and breakup
of CC bonds joining the rings. The latter reaction helps get an idea of the possibility of detachment of aromatic
fragments from resins and asphaltenes as a result of breakup of the CC bond rather than the carbonheteroatom
bond as was shown earl ier. Let u s examine the t rinaphthyl transformation reactions.
Condensation:
(20)
-
8/12/2019 80203661
9/11
300
Hydrolysis in the presence of hydrogen donors:
(21), (22)
For phenanthrene, we may suggest hydrogenolysis reaction in the presence of hydrogen donors in the
system:
(23), (24)
The results of calculation of Gibbs energy of reactions (20)-(24) at various temperatures are plotted
in Fig. 2c. It is quite predictable that from the point of thermodynamics condensation reaction (20) may occur in
the whole investigated temperature range. Reactions of PCAH hydrogenolysis in the presence of formic acid as
the hydrogen donor many also occur in the whole STA temperature range. This cannot be said, however, about
polycycl ic naphthenic aromat ic hydrogen donors . Thus, reaction (21) of hydrogen transfer from te tral in to
trinaphthyl is possible at a temperature higher than 227C, but reaction (24) of hydrogen transfer from tetralin to
phenanthrene is not poss ible at al l.
Based on the results of the performed calculations it can be concluded that the following chemical
transformations are most likely when heavy crude oils and native asphalts are recovered by steam-thermal technique:
hydrolysis of ether, sulfide, and amine bridges with detachment of lower-molecular fragments such as
paraffinic, aromatic, he teroatomic, etc.;
thermal cracking of heteroatomic components and PCAH, including with formation of gases,
lower-molecular components, and condensation products;
-
8/12/2019 80203661
10/11
301
transfer of hydrogen from polycyclic naphthenic aromatic hydrocarbons to organic sulfur compounds
and PCAH with formation of hydrogen sulfide and lower-molecular products, respectively;
hydrogenolysis of heteroatomic compounds and hydrocracking of PCAH with involvement of the hydrogen
formed in the reaction of carbon monoxide conversion with steam.
When formic acid is used as the hydrogen donating additive, hydrolysis of nitrogen- and sulfur-containing
compounds and hydrocracking and hydrogenation of PCAH may also occur.
REFERENCES
1. R. Kh. Muslimov, G. V. Romanov, G. P. Kayukova, et al.,kon. Org. Prom. Proizvod., No. 1, 35-40 (2012).
2. V. P. Yakutseni, M. D. Belonin, and V. V. Gribkov, Geol. Nefti i Gaza, No. 12, 35-39 (1994).
3. V. N. Makarevich, N. I. Iskri tskaya, and S. A. Bogoslovskii,Neftegaz. Geol. Teor. Prak., 5, No. 2 (2010).
4. N . K . Ba ibakov and A. R. Garushev, Thermal Methods of Oil Deposit Exploitation[in Russian], Nedra,
Moscow (1988), p. 343.
5. G. P. Kayukova, G. P. Kurbskii, E. V. Lifanova, et al.,Nef tekhimiya, 33 , No. 1, 19-29 (1993).
6 . V. R. Ant ipenko and O. A. Go lubina,Izv. Tomsk. Politekh . Univ., 309, No. 2, 174-179 (2006).
7. A. M. Kiyamova, G. P. Kayukova, V. I. Morozov, et al., Tekhnol. Nefti i Gaza, No. 1, 40-47 (2007).
8. G. P. Kayukova, A. M. Kiyamova, L. Z. Nigmedzyanova, et al.,Nef tekhimiya, 47 , No. 5, 349-361 (2007).
9. L. V. Gurvich, G. V. Karachevtsev, V. N. Kondratev, et al.,Energy of Chemical Bond Breakup. Ionization
Potentia ls and Electron Aff inity[in Russian], Nauka, Moscow (1974), p. 351.
10. L. M. Ruzin, O. E. Pleshkova, and L. V. Konovalova,Nef t. Khoz. , No. 11, 59-62 (1990).
11. L. M. Ruzin, L. V. Konovalova, and A. V. Petukhov, Geol. Nefti i Gaza, No. 7, 43-46 (1988).
12. Wang Yuanqing, Chen Yanglin, He Jing, et a l. ,Energy & Fuels , 24 , 1502-1510 (2010).
13. P. D. Clark, J. B. Hyne, and J. D. Tyrer,Fuel, 62, 959-962 (1983).
14. J. B. Hyne, J. W. Greidanus, J. D. Tyrer, e t a l. , In: 2nd Intl. Conf. The Future of Heavy Crude and Tar
Sands,Caracas, Venezuela, 7-17 February 1982, McGraw Hill, New York (1984), pp. 404-411.
15. A. R. Katr itzky and S. M. All in ,Acc . Chem. Res. , 29 , 399-406 (1996).
16. V. D. Ryabov, Chemistry of Oil and Gas[in Russian], Tekhnika, Moscow (2004), p. 288.
17. L iu Yangji an and Fan Hongfu,Energy & Fuels, 16 , 842-846 (2002).
18. C. Ovall es and H. Rodriguez,J. Canad. Petr. Technol., 47 , No. 1, 43-51 (2008).
19. Yu. J inal i and P. E. Savage,Ind. Eng. Chem. Res., 37, 2-10 (1998).
20. A. R. Katritzky, D. A. Nichols, M. Siskin, et al., Chem. Rev., 101, No. 4, 837-892 (2001).
-
8/12/2019 80203661
11/11
Copyright of Chemistry & Technology of Fuels & Oils is the property of Springer Science & Business Media
B.V. and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright
holder's express written permission. However, users may print, download, or email articles for individual use.