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Electron-beam radiolysis of gaseous propane in the presence of water under circulation conditions
Radiation Physics and Chemistry 65 (2002) 71–78
Electron-beam radiolysis of gaseous propane in the presence of water under circulation conditions A.V. Ponomareva, I.E. Makarova, N.R. Saifullinb, A.Sh. Syrtlanovb, A.K. Pikaeva,* a
Institute of Physical Chemistry of Russian Academy of Sciences, Leninsky Prospect, 31, Moscow 11991, Russia b Stock Oil Company ‘‘Bashneft’’, Pushkin Str. 95, Ufa 450008, Republic Bashkortostan, Russian Federation Received 12 July 2001; accepted 5 December 2001
Abstract The paper describes the data obtained from the study of electron-beam radiolysis of gaseous propane in the presence of water under circulation conditions on pilot-scale facility with electron accelerator UEVK ‘‘Avrora-9B’’ (energy 0.5 MeV, maximum beam power 40 kW). It was obtained that irradiation leads to the formation of condensable alkanes and oxygen-containing organic compounds (predominantly alcohols and ethers). The dependencies of their content in the formed mixture on cooling conditions, dose, and gas flow rate were measured. The mechanism of the formation of the mentioned compounds was discussed. r 2002 Elsevier Science Ltd. All rights reserved. Keywords: Alcohols; Alkanes; Circulation conditions; Condensable products; Electron-beam radiolysis; Ethers; Gaseous propane; Pilot-scale facility
1. Introduction Radiolysis of light alkanes has been studied by many . authors (Foldiak, 1981; Pikaev, 1986; Saraeva, 1986 and references therein). Because of this, at present, there is a lot of literature data on radiolytic conversions of alkanes in gaseous, liquid and solid phases. In particular, it was established that radiolysis leads to the formation of new compounds with lower and higher molecular masses in comparison with the initial compounds. However, virtually all the conducted studies consisted of irradiation of an individual alkane or a definite mixture of some alkanes under stationary conditions. Such a method allows one to carefully measure radiationchemical yields of initial compound degradation and radiolysis product formation at low absorbed doses, but has some limitations at high doses, when the degrada*Corresponding author. Tel.: +7-95-333-9567; fax: +7-95335-1785. E-mail address: [email protected] (A.K. Pikaev).
tion degree of the initial compound becomes noticeable and all the intermediate and final radiolysis products inevitably participate in radiolytic reactions with the initial substance. The main goal of the present work is to investigate the features of gaseous hydrocarbons radiolytic conversions (based on the example of commercial propane) under circulation conditions, i.e. upon the continuous alternations of electron-beam irradiation and separation of the formed condensable products. Upon such a regime of the treatment, the role of heavy condensable products in radiolytic conversions of the main compound is minimized. The influence of water and oxygen impurities in the initial circulating propane on the composition of its radiolysis products was also investigated in this work. The work is connected with the problem of utilization of gaseous alkane-containing effluents. This is a continuation of the studies (Gafiatullin et al., 1997; Ponomarev et al., 2000) on radiolysis of light alkanes and their mixtures under circulation conditions.
0969-806X/02/$ - see front matter r 2002 Elsevier Science Ltd. All rights reserved. PII: S 0 9 6 9 - 8 0 6 X ( 0 1 ) 0 0 6 8 5 - 5
A.V. Ponomarev et al. / Radiation Physics and Chemistry 65 (2002) 71–78
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2. Experimental Gaseous commercial propane, initially containing oxygen (0.06 wt%), nitrogen (0.20 wt%), water (0.08 wt%), methane (0.85 wt%), ethane (4.25 wt%), propane (92.75 wt%), isobutane (2.0 wt%) and n-butane (0.19 wt%), was used in the study. Together with gaseous components, initial commercial propane contained a superfluous condensed moisture. The total mean content of water in circulating propane was 3.5–4.5 wt%. Under the forced gas circulation conditions, water was converted to an aerosol. Irradiation of gas and separation of condensable radiolysis products were conducted on the pilot-scale multi-functional facility ‘‘ELCON’’ of Tuimazy gasprocessing works of Stock Oil Company ‘‘Bashneft’’. The principal scheme of the facility is shown in Fig. 1. The source of ionizing radiation was cascade accelerator UEVK ‘‘Avrora-9B’’ (electron energy 0.5 MeV, maximum beam power 40 kW) (1) supplied by Efremov Institute of Electrophysical Apparatuses (St. Petersburg, Russian Federation). Gas was irradiated at a constant pressure of 0.13 MPa in a continuous stainless-steel reactor (2) having from above a hermetic flange connection with an exit window of the accelerator. Walls of the reactor and accelerator exit window were cooled from outside by water at 161C. The mean gas outlet temperature was not over 501C. For separation of the condensable products, irradiated gas was cooled in a shell-and-tube heat exchangers with boiling propane (at 421C) (3), and circulating water (at 61C) (4) as coolants. A cooled gas was directed to an inertial gas–liquid separator (5) where it was slowed down and released from condensate droplets. A decrease in the pressure of a residual gas caused by its partial conversion to condensate was compensated by an automated inflow of the initial gas. The gas circulation via reaction contour including reactor, cooler and separator was performed by a gas blower (6). The gas flow rate in an irradiation zone was regulated within
3
1
2
4
5 6
Fig. 1. Principal scheme of pilot facility.
200–1200 m3 h1. The mean amount of the condensable products sample was 2 kg. Analysis of liquid and gaseous radiolysis products was conducted with chromato-mass spectrometer ‘‘Q-Mass, Autosystem XL’’ (Perkin–Elmer) (helium was a gascarrier, column was a glass capillary with a length of 60 m and an internal diameter of 0.25 mm).
3. Results and discussion The condensate that evolved from separator after irradiation contained over 100 compounds with molecular masses from 32 (methanol) to 170 (dodecane). The main parts of the components were formed in small amounts (not over 0.2 wt%). Only 20 compounds had an individual portion over 1 wt%; their total amount in the condensate was B80 wt%. The qualitative condensate composition did not depend virtually on the gas flow rate in reactor and on the used condensation regime. On the contrary, the change in the conditions of irradiation and separation had a considerable effect on the quantitative ratio of the main condensable components and, to a lesser extent, on the rate of their formation. Tables 1–3 show the most important condensate components (their total number was 30) obtained at beam current 40 mA and gas flow rate 600 m3 h1 under conditions of water and boiling propane cooling. Fig. 2 illustrates the content of alkanes C6–C7 in the condensate. As expected, alkanes consisted of the main part of condensate (see Table 1). Under all experimental conditions, their portion in the obtained condensates was equal to over 50 wt%. Since the predominant component of the initial gas was propane, the most probable liquid products of its radiolysis must be hexane isomers (because of dimerization of propyl radicals dC3 H7 ) (Foldiak, . 1981; Pikaev, 1986; Saraeva, 1986): 2dC3 H7 -ðCH3 Þ2 CHCHðCH3 Þ2 ð2; 3-dimethylbutaneÞ;
ð1Þ
2dC3 H7 -CH3 ðCH2 Þ2 CHðCH3 Þ2 ð2-methylpentaneÞ;
ð2Þ
2dC3 H7 -CH3 ðCH2 Þ4 CH3 ðn-hexaneÞ:
ð3Þ
In fact, from Table 1 and Fig. 2 it can be seen that 2,3dimethylbutane and 2-methylpropane are the predominant components of the condensate obtained upon boiling propane cooling. These two isomers contained over 25 wt% for all the condensate. n-Hexane was formed with a minimal yield and its concentration in the condensate was not over 0.05 wt%. Such an effect seems to be actual because of the decreased probability for the formation and, as a consequence, mutual combination of alkyl radicals with unpaired electron at the end
A.V. Ponomarev et al. / Radiation Physics and Chemistry 65 (2002) 71–78 Table 1 Content of alkanes in the condensate (wt%)
73
Table 3 Content of ethers in the condensate (wt%)
Alkane
Cooling by water
Cooling by boiling propane
Ether
Cooling by water
Cooling by boiling propane
2,3-Dimethylbutane 2-Methylpentane 2,2,3-Trimethylbutane 2,3-Dimethylpentane 2,2,3-Trimethylpentane 3,3-Dimethylhexane 2,3,4-Trimethylpentane 2,3,3-Trimethylpentane 2-Methyl-3-ethylpentane+2,3dimethyl-hexane 2,4-Dimethyl-3ethylpentane+2,3,5-trimethylhexane 2,2,3,3-Tetramethylpentane 2,3-Dimethyl-3ethylpentane+2,3,3,4-tetramethylpentane 3,3-Dimethylheptane 2,3,3-Trimethylhexane+2methyl-3-ethyl-hexane 3-Methyl-4-ethylhexane 2,3,4-Trimethylhexane
4.56 2.80 2.80 1.41 0.64 0.92 0.34 5.69 0.55
17.82 8.11 8.43 1.59 0.55 0.56 0.33 3.84 0.39
Diisopropyl ether Tert-Butylisopropyl ether Diisobutyl ether 1,1,2-Trimethyl propyl isopropyl ether
1.46 0.60 0.70 5.00
5.15 0.51 0.27 2.29
1.14
0.73
0.78 5.51
0.33 2.34
0.71 9.36
0.24 2.33
2.35 0.61
1.08 0.28
Table 2 Content of alcohols in the condensate (wt%) Alcohol
Propanol-2 Propanol-1 2-Methylpropanol-2 Butanol-2 2-Methylbutanol-2 2,3-Dimethylbutanol-2 2-Methylpentanol-2 2,3,3-Trimethylbutanol-2 2,3-Dimethylpentanol-3 + 2methyl-hexanol-2 3-Ethylpentanol-2
Cooling by water
Cooling by boiling propane
8.72 0.54 0.64 1.07 2.50 2.86 3.14 4.00 5.86
8.39 0.05 0.63 0.21 1.29 1.06 0.55 2.13 3.40
5.60
1.61
. carbon atom (Gaumann and Hoigne, 1968; Foldiak, 1981; Ponomarev et al., 2000; Saraeva, 1986). Apparently, the formation of the other hexane isomers and also of heavier hydrocarbons was due to the participation of not only propane, but also other gaseous alkanes (methane, ethane, butanes and pentanes) in radiolytic conversions. These components were initially present in the gas; they were additionally accumulated as a result of radiolytic conversions of
propane (see Fig. 3). So the formation of 2,2-dimethylbutane (0.59 wt%) can be caused by a combination of alkyl radicals from isobutane and ethane or from isopentane and methane. In its turn, 3-methylpentane (0.13 wt%) seems to be formed upon combination of 2-butyl and ethyl radicals. Upon water cooling of irradiated gas, the predominant components of the condensate were nonane isomers (see Fig. 2). Such an effect seems to be caused by a considerable aggravation of condensation of hexanes (and, in some degree, heptanes) under water cooling. A high volatility of hexanes (boiling points from 491C to 691C) assisted their entrainment with a flow of non-condensable gas and to a repeated participation in radiolytic conversions (see Fig. 4). In irradiation zone, hexane was converted mainly to hexyl radical (Saraeva, 1986). A further combination of hexyl and propyl radicals led to the formation of a respective nonane isomer: dC6 H13
þ dC3 H7 -C9 H20 :
ð4Þ
The main nonane isomers (2,3,3,4-tetramethylpentane, 2,3,3-trimethylpentane and 3-ethyl-2-methylhexane) seem to be formed in reaction (4) with the participation of radicals from 2,3-dimethylbutane and 2-methylpentane. Concentration of hexyl radicals formed by the direct radiolysis of hexanes should be very low because of low relative concentration of hexanes in gas phase under irradiation (o0.5% when water cooling is used and o0.15% upon boiling propane cooling). Additional amount of hexyl radicals, making their concentration comparable with the concentration of propyl radicals, is formed due to three processes: (a) excitation energy transfer from propane to hexanes; (b) reaction of propyl radicals with hexanes that resulted in the formation of hexyl radicals; and, mainly, (c) capture of propyl radicals by propylene (its yield is 2.0–2.5 molecule/100 eV)–reaction (5). CH3 CH ¼ CH2 þ dC3 H7 -dC6 H13 :
ð5Þ
A relatively high content of nonanes in the condensate obtained upon boiling propane cooling, i.e. under conditions of the limited volatility of hexane isomers,
A.V. Ponomarev et al. / Radiation Physics and Chemistry 65 (2002) 71–78
74
30
Content, wt. %
Water cooling Boiling propane cooling
20
10
0 Hexanes
Heptanes
Octanes
Nonanes
Fig. 2. Content of alkanes C6–C9 in the condensate upon water and boiling propane cooling.
12
2
Content, wt. %
10
8
6
4
1
2
3 4
0
0
100
200
300
400
500
Irradiation time, min. Fig. 3. Accumulation of methane (1), ethane (2), isobutane (3) and n-butane (4) in the condensate (beam current 20 mA, gas flow rate 400 m3 h1, and boiling propane cooling).
indicates the significant role of the successive proceeding of reactions (5) and (4). The hard condensation conditions realized upon boiling propane cooling not only prevented the entrainment of hexanes and the other liquid components of the condensate but also minimized the content of butanes
and pentanes in circulating gas. The fresh condensate obtained upon boiling propane cooling contained up to 6 wt% of pentanes (the ratio of isopentane : n-pentane: neopentane was 4:1:0.1). However, the soft condensation conditions (water cooling) prevented an accumulation of pentanes and butanes in the condensate
A.V. Ponomarev et al. / Radiation Physics and Chemistry 65 (2002) 71–78
75
8
7
1
Content, wt. %
6
5 2
4
3
3
2 400
600
800
Gas flow rate,
m3
1000
h-1
Fig. 4. Dependence of content of 2,3-dimethylbutane (1), 2-methylpentane (2) and 2,2,3-trimethylbutane (3) in the condensate on gas flow rate (beam current 30 mA, and water cooling).
(concentration of pentanes in the condensate was not over 0.5 wt%), ensuring their return to irradiation zone with circulating gas flow. Butyl and amyl radicals, formed upon radiolysis of these alkanes, and also the respective alkenes were an additional source for the formation of heavy condensable hydrocarbons (in particular, nonanes). From Tables 2 and 3 it follows that, in addition to alkanes, oxygen-containing compounds (alcohols and ethers) consist of a, respectively, large part of the condensate. Undoubtedly, the appearance of alcohols and ethers among the radiolysis products was due to the presence of oxygen and water in the initial gas. .OH radical seems to be one of the most important precursors of alcohols upon irradiation of alkanes in the presence of the mentioned compounds. It was formed as a result of a decay of excited water molecules (Paretzke, 1987; Ponomarev et al., 1991): H2 O -H þ dOH
ð6Þ
and an interaction of H atoms (they appear with the yield X5 atom/100 eV upon alkane radiolysis) with oxygen (Woods and Pikaev, 1994): H þ O2 -dOH þ O;
ð7Þ
H þ O2 -HO2 ;
ð8Þ
H þ HOd2 -dOHþdOH;
ð9Þ
d
Note that reaction (8) proceeds in clusters of water with alkanes. The formed dOH radicals reacting with large alkyl radicals converted them directly to alcohol molecules. For example, dOHþdCn H2nþ1 -Cn H2nþ1 OH:
ð10Þ
The second pathway is an addition to alkene molecule with the formation of hydroxyalkyl radical: dOH
þ Cn H2n -dCn H2nþ1 OH:
ð11Þ
In its turn, hydroxyalkyl radical can react with alkyl radical forming a molecule of secondary alcohol: dCn H2nþ1 OHþdCm H2mþ1 -Cn H2n ðOHÞCm H2mþ1 :
ð12Þ
The formation of ethers seems to be caused by the combination of alkoxy Cn H2nþ1 Od (Pikaev, 1986; Pikaev and Ponomarev, 1989; Woods and Pikaev, 1994) and alkyl dCm H2mþ1 radicals: Cn H2nþ1 Od þ dCm H2mþ1 OH-Cn H2nþ1 OCm H2mþ1 : ð13Þ and also by the interaction of CnH+ 2n+1 carbonium ions . with alcohols (Foldiak, 1981; Pikaev, 1986; Saraeva, 1986; Woods and Pikaev, 1994): þ Cn Hþ 2nþ1 OdþCm H2mþ1 OH-Cn H2nþ1 OCm H2mþ1 þH : ð14Þ
Reaction (14) seems to proceed via the intermediate formation of CnH2n+1(OyH+)CmH2m+1 ion.
A.V. Ponomarev et al. / Radiation Physics and Chemistry 65 (2002) 71–78
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The formation of alcohols and ethers considerably depends on the gas flow rate through the irradiation zone (see Fig. 5). Obviously, the probability of reactions between transient radiolysis products of alkane with admixture compounds increases at high doses. This is due to the increase in an inflow of the last compounds with increasing gas flow rate. Besides, the increased gas flow rate prevents the condensation of water and light oxygen-containing compounds in the separator; the high-rate flow of gas is saturated with these light-volatile compounds. The composition of identified radiolysis products was not limited by alkanes, alcohols and ethers. The carbonyl compounds (aldehydes and ketones) and alkenes were also detected. Their total concentration in the final condensate was not over 1.5–2.0 wt%. It is . known (Foldiak, 1981; Saraeva, 1986; Woods and Pikaev, 1994) that alkenes are the radiolysis products of propane. Acetylene (0.11 wt%), ethylene (0.30 wt%) and propylene (2.0 wt%) appear upon propane radiolysis with the total yield of 2.4–3.4 molecule/100 eV that is comparable with the total yield of the saturated products of propane degradation, i.e. methane and ethane (3.1–3.6 molecule/100 eV). The high yield of alkenes is also characteristic of the radiolysis of high-
. molecular alkanes (Foldiak, 1981; Pikaev, 1986; Ponomarev et al., 2000; Saraeva, 1986). However, the noticeable accumulation of alkenes in the circulating irradiated gas and condensed product was not observed. Similarly, the accumulation of considerable amounts of carbonyl compounds was not found, although some processes leading to the formation of alcohols should provide the appearance of the comparable amounts of aldehydes and ketones. For example, disproportionation of hydroxyalkyl (Pikaev, 1986; Woods and Pikaev, 1994) or hydroxyalkyl (Pikaev and Ponomarev, 1989; Woods and Pikaev, 1994) radicals must give carbonyl compound (in addition to alcohol): 2Cn H2nþ1 Od2 -Cn H2nþ1 OH þ Cn H2n O þ O2 ;
ð15Þ
2dCn H2n OH-Cn H2nþ1 OH þ Cn H2n O:
ð16Þ
The noticeable accumulation of carbonyl compounds is prevented by three factors. Firstly, the low concentration of oxygen and volatile oxygen-containing compounds in gas phase causes the low probability for the combination reactions (15) and (16) (respectively), because the decay of peroxyalkyl and hydroxyalkyl radicals owing to their low concentrations is due to their
5 1
4
Content, wt. %
5
3
2
4 3
1 2
0 400
600
800
1000
Gas flow rate, m3 h-1 Fig. 5. Dependence of content of propanol-2 (1), butanol-2 (2), diisopropyl ether (3), 2-methylbutanol-2 (4) and 2,3-dimethylbutanol-2 (5) in the condensate on gas flow rate (beam current 30 mA, and water cooling).
A.V. Ponomarev et al. / Radiation Physics and Chemistry 65 (2002) 71–78
reactions with alkyl radicals [reaction of type (12)]. This feature leads to the accumulation of heavier alcohols. Secondly, the volatility of carbonyl compounds is considerably higher than that of alcohols with the same number of carbon atoms. For instance, boiling points of propanal and acetone are 48.81C and 56.21C, respectively, while these points for 2-propanol and 1-propanol are 82.41C and 97.21C, respectively. It is only natural that propanols were much better separated from the circulating gas mixture than propanal and acetone. Thirdly, carbonyl compounds, as alkenes, have the highest reactivity towards electrons, H atoms and alkyl radicals among the molecular radiolysis products (Pikaev, 1986; Woods and Pikaev, 1994). This leads to the effective conversion of carbonyl compound to hydroxyalkyl radical: Cn H2n O þ H-dCn H2n OH
ð17Þ
or to alkoxyalkyl radical: Cn H2n OþdCn H2nþ1 -dCn H2n OCn H2nþ1 :
ð18Þ
The analogous fast reactions also proceed with the participation of alkenes: Cn H2n þH-dCn H2nþ1 ;
ð19Þ
Cn H2n þ dCm H2mþ1 -dCnþm H2ðnþmÞþ1 :
ð20Þ
It is necessary to note that the content of oxygencontaining compounds in the formed condensate was high in spite of the comparatively low concentration of oxygen and water in the used gas. Upon boiling propane cooling, the portions of alcohols and ethers were up to 25–30 and 5–10 wt%, respectively. Upon water cooling, the portion of alcohols increased and reached B50 wt%. As follows from Tables 2 and 3, alcohols and ethers with higher molecular masses dominated in the condensate obtained with water cooling. The mean compositions of oxygen-containing compounds upon boiling propane and water cooling approximately corresponds to the formulas of amyl alcohol C5H11OH and hexyl alcohol C6H13OH, respectively. From this it follows that the total content of atomic oxygen in the condensed compounds was B6.0– 7.5 wt%. It is almost 30–40 times higher than the content of dissolved oxygen and water in the initial propane. Obviously, the main reason for this effect is the participation of water aerosol in radiolytic conversions. The water radiolysis products very often have a higher reactivity towards hydrocarbon radicals than the radicals themselves in reaction with each other. The portion of gas subjected to radiolytic conversions in the reactor is lower by several orders of magnitude than the total volume of gas circulating in the facility. Because of this, oxygen and water excess wereretained upon irradiation for many hours. This feature provided
77
the accumulation of the high amounts of oxygencontaining compounds. It is also necessary to mention that gaseous alkanes (from methane to butane) consisted of the considerable part of radiolysis of propane itself; these products were not accumulated in the condensate. On the contrary, even the lightest alcohol (methanol) has a sufficiently high boiling point (64.61C) which allows it (and its homologues) to pass from gas to the condensate. At the same time, the alcohol molecules escaping the condensation can noticeably increase the solubility of water vapors in the circulating gas flow (Bell, 1973) and, because of the formation of water– alkane and water–alcohol clusters, intensify the energy transfer to water molecules (Bell, 1973; Paretzke, 1987; Shakhparonov, 1980; Traven’, 1989). The effective formation of oxygen-containing compounds upon electron-beam radiolysis of gaseous alkanes in the presence of small amounts of oxygen and water is important both from the scientific viewpoint and also for the practical use of irrradiation treatment of the real hydrocarbon systems. At present, the additional experiments are conducted for detailed elucidation and computer simulation of the alkanes radiolysis mechanism (in particular, of the formation of oxygen-containing compounds) under circulation conditions. It will allow to compare more precisely the data obtained with the data of previous investigations on alkanes radiolysis including yields of specific radiationchemical processes that were hardly derived in the present work.
4. Conclusion The described peculiarities of electron-beam irradiation of gaseous propane in the presence of water under circulation conditions on pilot-scale facility allow us to draw the following main conclusions: 1. The mentioned irradiation techniques enable the production of the condensable products of commercial propane radiolysis (alkanes with higher molecular masses, alcohols, ethers). 2. The presence of oxygen and water in the circulating gaseous mixture causes the formation of oxygencontaining compounds (predominantly alcohols and ethers). 3. The quantitative composition of the condensable products strongly depends on the type of coolant (boiling propane or water).
References Bell, R.P., 1973. The Proton in Chemistry. Chapman & Hall, London.
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. Foldiak, G. (Ed.), 1981. Radiation Chemistry of Hydrocarbons. Elsevier, Amsterdam. Gafiatullin, R.R., Makarov, I.E., Ponomarev, A.V., Pokhilo, S.B., Rygalov, V.A., Syrtlanov, A.Sh., Khusainov, B.Kh., 1997. Method of treatment of gaseous alkanes. Pat. 2099317 RF; Bull. Isobret. 35, 3–10. Gaumann, T., Hoigne, J. (Eds.), 1968. Aspects of Hydrocarbon Radiolysis. Academic Press, London. Paretzke, H.G., 1987. Radiation track structure theory. In: Freeman, G.R. (Ed.), Kinetics of Nonhomogeneous Processes. Wiley, New York, pp. 89–170. Pikaev, A.K., 1986. Modern Radiation Chemistry: Radiolysis of Gases and Liquids. Nauka, Moscow. Pikaev, A.K., Ponomarev, A.V., 1989. The track and bulk reactions of solvated electrons in irradiated monobasic aliphatic alcohols. Radiat. Phys. Chem. 34 (4), 693–698.
Ponomarev, A.V., Makarov, I.E., Pikaev, A.K., 1991. Dynamics of electron tracks in liquid water. Khim. Vys. Energ. 25 (4), 311–317. Ponomarev, A.V., Syrtlanov, A.Sh., Pikaev, A.K., 2000. Condensable products of radiolysis of multicomponent mixtures of gaseous alkanes. Dokl. RAN 372 (2), 195–198. Saraeva, V.V., 1986. Radiolysis of Hydrocarbons in Liquid Phase. Izd-vo MGU, Moscow. Shakhparonov, M.I., 1980. Mechanisms of Fast Processes in Liquids. Vysshaya Shkola, Moscow. Traven’, V.F., 1989. Electronic Structure and Properties of Organic Molecules. Khimiya, Moscow. Woods, R.J., Pikaev, A.K., 1994. Applied Radiation Chemistry: Radiation Processing. Wiley, New York.
Electron-beam radiolysis of gaseous propane in the presence of water under circulation conditions A.V. Ponomareva, I.E. Makarova, N.R. Saifullinb, A.Sh. Syrtlanovb, A.K. Pikaeva,* a
Institute of Physical Chemistry of Russian Academy of Sciences, Leninsky Prospect, 31, Moscow 11991, Russia b Stock Oil Company ‘‘Bashneft’’, Pushkin Str. 95, Ufa 450008, Republic Bashkortostan, Russian Federation Received 12 July 2001; accepted 5 December 2001
Abstract The paper describes the data obtained from the study of electron-beam radiolysis of gaseous propane in the presence of water under circulation conditions on pilot-scale facility with electron accelerator UEVK ‘‘Avrora-9B’’ (energy 0.5 MeV, maximum beam power 40 kW). It was obtained that irradiation leads to the formation of condensable alkanes and oxygen-containing organic compounds (predominantly alcohols and ethers). The dependencies of their content in the formed mixture on cooling conditions, dose, and gas flow rate were measured. The mechanism of the formation of the mentioned compounds was discussed. r 2002 Elsevier Science Ltd. All rights reserved. Keywords: Alcohols; Alkanes; Circulation conditions; Condensable products; Electron-beam radiolysis; Ethers; Gaseous propane; Pilot-scale facility
1. Introduction Radiolysis of light alkanes has been studied by many . authors (Foldiak, 1981; Pikaev, 1986; Saraeva, 1986 and references therein). Because of this, at present, there is a lot of literature data on radiolytic conversions of alkanes in gaseous, liquid and solid phases. In particular, it was established that radiolysis leads to the formation of new compounds with lower and higher molecular masses in comparison with the initial compounds. However, virtually all the conducted studies consisted of irradiation of an individual alkane or a definite mixture of some alkanes under stationary conditions. Such a method allows one to carefully measure radiationchemical yields of initial compound degradation and radiolysis product formation at low absorbed doses, but has some limitations at high doses, when the degrada*Corresponding author. Tel.: +7-95-333-9567; fax: +7-95335-1785. E-mail address: [email protected] (A.K. Pikaev).
tion degree of the initial compound becomes noticeable and all the intermediate and final radiolysis products inevitably participate in radiolytic reactions with the initial substance. The main goal of the present work is to investigate the features of gaseous hydrocarbons radiolytic conversions (based on the example of commercial propane) under circulation conditions, i.e. upon the continuous alternations of electron-beam irradiation and separation of the formed condensable products. Upon such a regime of the treatment, the role of heavy condensable products in radiolytic conversions of the main compound is minimized. The influence of water and oxygen impurities in the initial circulating propane on the composition of its radiolysis products was also investigated in this work. The work is connected with the problem of utilization of gaseous alkane-containing effluents. This is a continuation of the studies (Gafiatullin et al., 1997; Ponomarev et al., 2000) on radiolysis of light alkanes and their mixtures under circulation conditions.
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2. Experimental Gaseous commercial propane, initially containing oxygen (0.06 wt%), nitrogen (0.20 wt%), water (0.08 wt%), methane (0.85 wt%), ethane (4.25 wt%), propane (92.75 wt%), isobutane (2.0 wt%) and n-butane (0.19 wt%), was used in the study. Together with gaseous components, initial commercial propane contained a superfluous condensed moisture. The total mean content of water in circulating propane was 3.5–4.5 wt%. Under the forced gas circulation conditions, water was converted to an aerosol. Irradiation of gas and separation of condensable radiolysis products were conducted on the pilot-scale multi-functional facility ‘‘ELCON’’ of Tuimazy gasprocessing works of Stock Oil Company ‘‘Bashneft’’. The principal scheme of the facility is shown in Fig. 1. The source of ionizing radiation was cascade accelerator UEVK ‘‘Avrora-9B’’ (electron energy 0.5 MeV, maximum beam power 40 kW) (1) supplied by Efremov Institute of Electrophysical Apparatuses (St. Petersburg, Russian Federation). Gas was irradiated at a constant pressure of 0.13 MPa in a continuous stainless-steel reactor (2) having from above a hermetic flange connection with an exit window of the accelerator. Walls of the reactor and accelerator exit window were cooled from outside by water at 161C. The mean gas outlet temperature was not over 501C. For separation of the condensable products, irradiated gas was cooled in a shell-and-tube heat exchangers with boiling propane (at 421C) (3), and circulating water (at 61C) (4) as coolants. A cooled gas was directed to an inertial gas–liquid separator (5) where it was slowed down and released from condensate droplets. A decrease in the pressure of a residual gas caused by its partial conversion to condensate was compensated by an automated inflow of the initial gas. The gas circulation via reaction contour including reactor, cooler and separator was performed by a gas blower (6). The gas flow rate in an irradiation zone was regulated within
3
1
2
4
5 6
Fig. 1. Principal scheme of pilot facility.
200–1200 m3 h1. The mean amount of the condensable products sample was 2 kg. Analysis of liquid and gaseous radiolysis products was conducted with chromato-mass spectrometer ‘‘Q-Mass, Autosystem XL’’ (Perkin–Elmer) (helium was a gascarrier, column was a glass capillary with a length of 60 m and an internal diameter of 0.25 mm).
3. Results and discussion The condensate that evolved from separator after irradiation contained over 100 compounds with molecular masses from 32 (methanol) to 170 (dodecane). The main parts of the components were formed in small amounts (not over 0.2 wt%). Only 20 compounds had an individual portion over 1 wt%; their total amount in the condensate was B80 wt%. The qualitative condensate composition did not depend virtually on the gas flow rate in reactor and on the used condensation regime. On the contrary, the change in the conditions of irradiation and separation had a considerable effect on the quantitative ratio of the main condensable components and, to a lesser extent, on the rate of their formation. Tables 1–3 show the most important condensate components (their total number was 30) obtained at beam current 40 mA and gas flow rate 600 m3 h1 under conditions of water and boiling propane cooling. Fig. 2 illustrates the content of alkanes C6–C7 in the condensate. As expected, alkanes consisted of the main part of condensate (see Table 1). Under all experimental conditions, their portion in the obtained condensates was equal to over 50 wt%. Since the predominant component of the initial gas was propane, the most probable liquid products of its radiolysis must be hexane isomers (because of dimerization of propyl radicals dC3 H7 ) (Foldiak, . 1981; Pikaev, 1986; Saraeva, 1986): 2dC3 H7 -ðCH3 Þ2 CHCHðCH3 Þ2 ð2; 3-dimethylbutaneÞ;
ð1Þ
2dC3 H7 -CH3 ðCH2 Þ2 CHðCH3 Þ2 ð2-methylpentaneÞ;
ð2Þ
2dC3 H7 -CH3 ðCH2 Þ4 CH3 ðn-hexaneÞ:
ð3Þ
In fact, from Table 1 and Fig. 2 it can be seen that 2,3dimethylbutane and 2-methylpropane are the predominant components of the condensate obtained upon boiling propane cooling. These two isomers contained over 25 wt% for all the condensate. n-Hexane was formed with a minimal yield and its concentration in the condensate was not over 0.05 wt%. Such an effect seems to be actual because of the decreased probability for the formation and, as a consequence, mutual combination of alkyl radicals with unpaired electron at the end
A.V. Ponomarev et al. / Radiation Physics and Chemistry 65 (2002) 71–78 Table 1 Content of alkanes in the condensate (wt%)
73
Table 3 Content of ethers in the condensate (wt%)
Alkane
Cooling by water
Cooling by boiling propane
Ether
Cooling by water
Cooling by boiling propane
2,3-Dimethylbutane 2-Methylpentane 2,2,3-Trimethylbutane 2,3-Dimethylpentane 2,2,3-Trimethylpentane 3,3-Dimethylhexane 2,3,4-Trimethylpentane 2,3,3-Trimethylpentane 2-Methyl-3-ethylpentane+2,3dimethyl-hexane 2,4-Dimethyl-3ethylpentane+2,3,5-trimethylhexane 2,2,3,3-Tetramethylpentane 2,3-Dimethyl-3ethylpentane+2,3,3,4-tetramethylpentane 3,3-Dimethylheptane 2,3,3-Trimethylhexane+2methyl-3-ethyl-hexane 3-Methyl-4-ethylhexane 2,3,4-Trimethylhexane
4.56 2.80 2.80 1.41 0.64 0.92 0.34 5.69 0.55
17.82 8.11 8.43 1.59 0.55 0.56 0.33 3.84 0.39
Diisopropyl ether Tert-Butylisopropyl ether Diisobutyl ether 1,1,2-Trimethyl propyl isopropyl ether
1.46 0.60 0.70 5.00
5.15 0.51 0.27 2.29
1.14
0.73
0.78 5.51
0.33 2.34
0.71 9.36
0.24 2.33
2.35 0.61
1.08 0.28
Table 2 Content of alcohols in the condensate (wt%) Alcohol
Propanol-2 Propanol-1 2-Methylpropanol-2 Butanol-2 2-Methylbutanol-2 2,3-Dimethylbutanol-2 2-Methylpentanol-2 2,3,3-Trimethylbutanol-2 2,3-Dimethylpentanol-3 + 2methyl-hexanol-2 3-Ethylpentanol-2
Cooling by water
Cooling by boiling propane
8.72 0.54 0.64 1.07 2.50 2.86 3.14 4.00 5.86
8.39 0.05 0.63 0.21 1.29 1.06 0.55 2.13 3.40
5.60
1.61
. carbon atom (Gaumann and Hoigne, 1968; Foldiak, 1981; Ponomarev et al., 2000; Saraeva, 1986). Apparently, the formation of the other hexane isomers and also of heavier hydrocarbons was due to the participation of not only propane, but also other gaseous alkanes (methane, ethane, butanes and pentanes) in radiolytic conversions. These components were initially present in the gas; they were additionally accumulated as a result of radiolytic conversions of
propane (see Fig. 3). So the formation of 2,2-dimethylbutane (0.59 wt%) can be caused by a combination of alkyl radicals from isobutane and ethane or from isopentane and methane. In its turn, 3-methylpentane (0.13 wt%) seems to be formed upon combination of 2-butyl and ethyl radicals. Upon water cooling of irradiated gas, the predominant components of the condensate were nonane isomers (see Fig. 2). Such an effect seems to be caused by a considerable aggravation of condensation of hexanes (and, in some degree, heptanes) under water cooling. A high volatility of hexanes (boiling points from 491C to 691C) assisted their entrainment with a flow of non-condensable gas and to a repeated participation in radiolytic conversions (see Fig. 4). In irradiation zone, hexane was converted mainly to hexyl radical (Saraeva, 1986). A further combination of hexyl and propyl radicals led to the formation of a respective nonane isomer: dC6 H13
þ dC3 H7 -C9 H20 :
ð4Þ
The main nonane isomers (2,3,3,4-tetramethylpentane, 2,3,3-trimethylpentane and 3-ethyl-2-methylhexane) seem to be formed in reaction (4) with the participation of radicals from 2,3-dimethylbutane and 2-methylpentane. Concentration of hexyl radicals formed by the direct radiolysis of hexanes should be very low because of low relative concentration of hexanes in gas phase under irradiation (o0.5% when water cooling is used and o0.15% upon boiling propane cooling). Additional amount of hexyl radicals, making their concentration comparable with the concentration of propyl radicals, is formed due to three processes: (a) excitation energy transfer from propane to hexanes; (b) reaction of propyl radicals with hexanes that resulted in the formation of hexyl radicals; and, mainly, (c) capture of propyl radicals by propylene (its yield is 2.0–2.5 molecule/100 eV)–reaction (5). CH3 CH ¼ CH2 þ dC3 H7 -dC6 H13 :
ð5Þ
A relatively high content of nonanes in the condensate obtained upon boiling propane cooling, i.e. under conditions of the limited volatility of hexane isomers,
A.V. Ponomarev et al. / Radiation Physics and Chemistry 65 (2002) 71–78
74
30
Content, wt. %
Water cooling Boiling propane cooling
20
10
0 Hexanes
Heptanes
Octanes
Nonanes
Fig. 2. Content of alkanes C6–C9 in the condensate upon water and boiling propane cooling.
12
2
Content, wt. %
10
8
6
4
1
2
3 4
0
0
100
200
300
400
500
Irradiation time, min. Fig. 3. Accumulation of methane (1), ethane (2), isobutane (3) and n-butane (4) in the condensate (beam current 20 mA, gas flow rate 400 m3 h1, and boiling propane cooling).
indicates the significant role of the successive proceeding of reactions (5) and (4). The hard condensation conditions realized upon boiling propane cooling not only prevented the entrainment of hexanes and the other liquid components of the condensate but also minimized the content of butanes
and pentanes in circulating gas. The fresh condensate obtained upon boiling propane cooling contained up to 6 wt% of pentanes (the ratio of isopentane : n-pentane: neopentane was 4:1:0.1). However, the soft condensation conditions (water cooling) prevented an accumulation of pentanes and butanes in the condensate
A.V. Ponomarev et al. / Radiation Physics and Chemistry 65 (2002) 71–78
75
8
7
1
Content, wt. %
6
5 2
4
3
3
2 400
600
800
Gas flow rate,
m3
1000
h-1
Fig. 4. Dependence of content of 2,3-dimethylbutane (1), 2-methylpentane (2) and 2,2,3-trimethylbutane (3) in the condensate on gas flow rate (beam current 30 mA, and water cooling).
(concentration of pentanes in the condensate was not over 0.5 wt%), ensuring their return to irradiation zone with circulating gas flow. Butyl and amyl radicals, formed upon radiolysis of these alkanes, and also the respective alkenes were an additional source for the formation of heavy condensable hydrocarbons (in particular, nonanes). From Tables 2 and 3 it follows that, in addition to alkanes, oxygen-containing compounds (alcohols and ethers) consist of a, respectively, large part of the condensate. Undoubtedly, the appearance of alcohols and ethers among the radiolysis products was due to the presence of oxygen and water in the initial gas. .OH radical seems to be one of the most important precursors of alcohols upon irradiation of alkanes in the presence of the mentioned compounds. It was formed as a result of a decay of excited water molecules (Paretzke, 1987; Ponomarev et al., 1991): H2 O -H þ dOH
ð6Þ
and an interaction of H atoms (they appear with the yield X5 atom/100 eV upon alkane radiolysis) with oxygen (Woods and Pikaev, 1994): H þ O2 -dOH þ O;
ð7Þ
H þ O2 -HO2 ;
ð8Þ
H þ HOd2 -dOHþdOH;
ð9Þ
d
Note that reaction (8) proceeds in clusters of water with alkanes. The formed dOH radicals reacting with large alkyl radicals converted them directly to alcohol molecules. For example, dOHþdCn H2nþ1 -Cn H2nþ1 OH:
ð10Þ
The second pathway is an addition to alkene molecule with the formation of hydroxyalkyl radical: dOH
þ Cn H2n -dCn H2nþ1 OH:
ð11Þ
In its turn, hydroxyalkyl radical can react with alkyl radical forming a molecule of secondary alcohol: dCn H2nþ1 OHþdCm H2mþ1 -Cn H2n ðOHÞCm H2mþ1 :
ð12Þ
The formation of ethers seems to be caused by the combination of alkoxy Cn H2nþ1 Od (Pikaev, 1986; Pikaev and Ponomarev, 1989; Woods and Pikaev, 1994) and alkyl dCm H2mþ1 radicals: Cn H2nþ1 Od þ dCm H2mþ1 OH-Cn H2nþ1 OCm H2mþ1 : ð13Þ and also by the interaction of CnH+ 2n+1 carbonium ions . with alcohols (Foldiak, 1981; Pikaev, 1986; Saraeva, 1986; Woods and Pikaev, 1994): þ Cn Hþ 2nþ1 OdþCm H2mþ1 OH-Cn H2nþ1 OCm H2mþ1 þH : ð14Þ
Reaction (14) seems to proceed via the intermediate formation of CnH2n+1(OyH+)CmH2m+1 ion.
A.V. Ponomarev et al. / Radiation Physics and Chemistry 65 (2002) 71–78
76
The formation of alcohols and ethers considerably depends on the gas flow rate through the irradiation zone (see Fig. 5). Obviously, the probability of reactions between transient radiolysis products of alkane with admixture compounds increases at high doses. This is due to the increase in an inflow of the last compounds with increasing gas flow rate. Besides, the increased gas flow rate prevents the condensation of water and light oxygen-containing compounds in the separator; the high-rate flow of gas is saturated with these light-volatile compounds. The composition of identified radiolysis products was not limited by alkanes, alcohols and ethers. The carbonyl compounds (aldehydes and ketones) and alkenes were also detected. Their total concentration in the final condensate was not over 1.5–2.0 wt%. It is . known (Foldiak, 1981; Saraeva, 1986; Woods and Pikaev, 1994) that alkenes are the radiolysis products of propane. Acetylene (0.11 wt%), ethylene (0.30 wt%) and propylene (2.0 wt%) appear upon propane radiolysis with the total yield of 2.4–3.4 molecule/100 eV that is comparable with the total yield of the saturated products of propane degradation, i.e. methane and ethane (3.1–3.6 molecule/100 eV). The high yield of alkenes is also characteristic of the radiolysis of high-
. molecular alkanes (Foldiak, 1981; Pikaev, 1986; Ponomarev et al., 2000; Saraeva, 1986). However, the noticeable accumulation of alkenes in the circulating irradiated gas and condensed product was not observed. Similarly, the accumulation of considerable amounts of carbonyl compounds was not found, although some processes leading to the formation of alcohols should provide the appearance of the comparable amounts of aldehydes and ketones. For example, disproportionation of hydroxyalkyl (Pikaev, 1986; Woods and Pikaev, 1994) or hydroxyalkyl (Pikaev and Ponomarev, 1989; Woods and Pikaev, 1994) radicals must give carbonyl compound (in addition to alcohol): 2Cn H2nþ1 Od2 -Cn H2nþ1 OH þ Cn H2n O þ O2 ;
ð15Þ
2dCn H2n OH-Cn H2nþ1 OH þ Cn H2n O:
ð16Þ
The noticeable accumulation of carbonyl compounds is prevented by three factors. Firstly, the low concentration of oxygen and volatile oxygen-containing compounds in gas phase causes the low probability for the combination reactions (15) and (16) (respectively), because the decay of peroxyalkyl and hydroxyalkyl radicals owing to their low concentrations is due to their
5 1
4
Content, wt. %
5
3
2
4 3
1 2
0 400
600
800
1000
Gas flow rate, m3 h-1 Fig. 5. Dependence of content of propanol-2 (1), butanol-2 (2), diisopropyl ether (3), 2-methylbutanol-2 (4) and 2,3-dimethylbutanol-2 (5) in the condensate on gas flow rate (beam current 30 mA, and water cooling).
A.V. Ponomarev et al. / Radiation Physics and Chemistry 65 (2002) 71–78
reactions with alkyl radicals [reaction of type (12)]. This feature leads to the accumulation of heavier alcohols. Secondly, the volatility of carbonyl compounds is considerably higher than that of alcohols with the same number of carbon atoms. For instance, boiling points of propanal and acetone are 48.81C and 56.21C, respectively, while these points for 2-propanol and 1-propanol are 82.41C and 97.21C, respectively. It is only natural that propanols were much better separated from the circulating gas mixture than propanal and acetone. Thirdly, carbonyl compounds, as alkenes, have the highest reactivity towards electrons, H atoms and alkyl radicals among the molecular radiolysis products (Pikaev, 1986; Woods and Pikaev, 1994). This leads to the effective conversion of carbonyl compound to hydroxyalkyl radical: Cn H2n O þ H-dCn H2n OH
ð17Þ
or to alkoxyalkyl radical: Cn H2n OþdCn H2nþ1 -dCn H2n OCn H2nþ1 :
ð18Þ
The analogous fast reactions also proceed with the participation of alkenes: Cn H2n þH-dCn H2nþ1 ;
ð19Þ
Cn H2n þ dCm H2mþ1 -dCnþm H2ðnþmÞþ1 :
ð20Þ
It is necessary to note that the content of oxygencontaining compounds in the formed condensate was high in spite of the comparatively low concentration of oxygen and water in the used gas. Upon boiling propane cooling, the portions of alcohols and ethers were up to 25–30 and 5–10 wt%, respectively. Upon water cooling, the portion of alcohols increased and reached B50 wt%. As follows from Tables 2 and 3, alcohols and ethers with higher molecular masses dominated in the condensate obtained with water cooling. The mean compositions of oxygen-containing compounds upon boiling propane and water cooling approximately corresponds to the formulas of amyl alcohol C5H11OH and hexyl alcohol C6H13OH, respectively. From this it follows that the total content of atomic oxygen in the condensed compounds was B6.0– 7.5 wt%. It is almost 30–40 times higher than the content of dissolved oxygen and water in the initial propane. Obviously, the main reason for this effect is the participation of water aerosol in radiolytic conversions. The water radiolysis products very often have a higher reactivity towards hydrocarbon radicals than the radicals themselves in reaction with each other. The portion of gas subjected to radiolytic conversions in the reactor is lower by several orders of magnitude than the total volume of gas circulating in the facility. Because of this, oxygen and water excess wereretained upon irradiation for many hours. This feature provided
77
the accumulation of the high amounts of oxygencontaining compounds. It is also necessary to mention that gaseous alkanes (from methane to butane) consisted of the considerable part of radiolysis of propane itself; these products were not accumulated in the condensate. On the contrary, even the lightest alcohol (methanol) has a sufficiently high boiling point (64.61C) which allows it (and its homologues) to pass from gas to the condensate. At the same time, the alcohol molecules escaping the condensation can noticeably increase the solubility of water vapors in the circulating gas flow (Bell, 1973) and, because of the formation of water– alkane and water–alcohol clusters, intensify the energy transfer to water molecules (Bell, 1973; Paretzke, 1987; Shakhparonov, 1980; Traven’, 1989). The effective formation of oxygen-containing compounds upon electron-beam radiolysis of gaseous alkanes in the presence of small amounts of oxygen and water is important both from the scientific viewpoint and also for the practical use of irrradiation treatment of the real hydrocarbon systems. At present, the additional experiments are conducted for detailed elucidation and computer simulation of the alkanes radiolysis mechanism (in particular, of the formation of oxygen-containing compounds) under circulation conditions. It will allow to compare more precisely the data obtained with the data of previous investigations on alkanes radiolysis including yields of specific radiationchemical processes that were hardly derived in the present work.
4. Conclusion The described peculiarities of electron-beam irradiation of gaseous propane in the presence of water under circulation conditions on pilot-scale facility allow us to draw the following main conclusions: 1. The mentioned irradiation techniques enable the production of the condensable products of commercial propane radiolysis (alkanes with higher molecular masses, alcohols, ethers). 2. The presence of oxygen and water in the circulating gaseous mixture causes the formation of oxygencontaining compounds (predominantly alcohols and ethers). 3. The quantitative composition of the condensable products strongly depends on the type of coolant (boiling propane or water).
References Bell, R.P., 1973. The Proton in Chemistry. Chapman & Hall, London.
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. Foldiak, G. (Ed.), 1981. Radiation Chemistry of Hydrocarbons. Elsevier, Amsterdam. Gafiatullin, R.R., Makarov, I.E., Ponomarev, A.V., Pokhilo, S.B., Rygalov, V.A., Syrtlanov, A.Sh., Khusainov, B.Kh., 1997. Method of treatment of gaseous alkanes. Pat. 2099317 RF; Bull. Isobret. 35, 3–10. Gaumann, T., Hoigne, J. (Eds.), 1968. Aspects of Hydrocarbon Radiolysis. Academic Press, London. Paretzke, H.G., 1987. Radiation track structure theory. In: Freeman, G.R. (Ed.), Kinetics of Nonhomogeneous Processes. Wiley, New York, pp. 89–170. Pikaev, A.K., 1986. Modern Radiation Chemistry: Radiolysis of Gases and Liquids. Nauka, Moscow. Pikaev, A.K., Ponomarev, A.V., 1989. The track and bulk reactions of solvated electrons in irradiated monobasic aliphatic alcohols. Radiat. Phys. Chem. 34 (4), 693–698.
Ponomarev, A.V., Makarov, I.E., Pikaev, A.K., 1991. Dynamics of electron tracks in liquid water. Khim. Vys. Energ. 25 (4), 311–317. Ponomarev, A.V., Syrtlanov, A.Sh., Pikaev, A.K., 2000. Condensable products of radiolysis of multicomponent mixtures of gaseous alkanes. Dokl. RAN 372 (2), 195–198. Saraeva, V.V., 1986. Radiolysis of Hydrocarbons in Liquid Phase. Izd-vo MGU, Moscow. Shakhparonov, M.I., 1980. Mechanisms of Fast Processes in Liquids. Vysshaya Shkola, Moscow. Traven’, V.F., 1989. Electronic Structure and Properties of Organic Molecules. Khimiya, Moscow. Woods, R.J., Pikaev, A.K., 1994. Applied Radiation Chemistry: Radiation Processing. Wiley, New York.