CC BY
9PACS:: 621.436
POST-RADIATION PROCESSES IN OLEFINITE LIQUID SYSTEMS
L. JABBAROVA, I. MUSTAFAYEV, R. AKBAROV
Institute of Radiation Problems, Azerbaijan National Academy of Sciences, 9 F. Agayeva str. Baku,
AZ1143, Azerbaijan.
Abstract: The main reason for the low stability in hydrocarbon fuels is the presence of olefin compounds. Alkenes are very reactive, they enter into bonds at the sites of double and triple bonds, polymerization reactions are characteristic. The study of the radiolysis of mixtures of saturated and unsaturated hydrocarbons at various concentrations makes it possible to draw conclusions about the nature of the main radiation-chemical processes. In fuels containing a large amount of unsaturated hydrocarbons, coking capacity increases and color deteriorates during irradiation. Structuring is physically manifested in organic liquids in a change in viscosity and density. The amount of decomposed hydrocarbon increases with an increase in the total radiation dose. Changes occurring at the time of irradiation may be reversible or irreversible. Reversible effects depend on the dose rate. Irreversible changes in the properties of organic fuels depend on the absorbed dose, temperature and persist after irradiation, causing chemical transformations of molecules. The studies were performed using radiolysis of a model hydrocarbon mixture, the hexane / hexene system. Changes in the iodine number and molecular structure of liquid fuels, as well as the kinetics of gas formation were studied as indicators of the processes. The dependence of the speed of the post-polymerization process on the concentration and dose of olefin was studied.
Keywords: olefin, iodine number, post-polymerization, liquid fuel.
INTRODUCTION
Under the influence of radioactive radiation, the structuring of organic compounds and their decomposition occur simultaneously. Decomposition always continues because gas is released during the radiolysis of all organic compounds. Decomposition leads to a decrease in viscosity in liquids and an increase in softness in solids. Clarifying the effect of radiation on the overall composition of the fuel, the relationship between the requirements for the composition of a fuel and its radiation resistance is a very important task of research. As a result, the performance of the fuel deteriorates at ambient temperatures. To date, many works have been published on the effects of ionizing radiation on various hydrocarbons and liquid fuels [1-11], and these studies allow us to establish the general laws of radiolysis of organic compounds.
METHODOLOGY
The studies were performed using radiolysis of hexane / hexene mixture. The kinetics of the processes were studied at temperature T=20oC, radiation dose rate P=0.072 Gy/s, absorbed dose D = 27-78 kGy, olefins at concentrations of 5, 10, 20 and 40%. Iodine number was determined in BRUKER MPA spectrometer, Density was determined by pycnometers in accordance with GOST 3900-85, Viscosity was measured by VPZh-2 type viscometers in accordance with GOST 33-66 and GOST 10028-81.
EXPERIMENTAL PART
The effect of hexane-hexene mixture on the system density at different concentrations and absorbed doses one and two months after gamma irradiation (post radiation effect) is shown in Figure 1(a,b).
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Fig. 1 (a, b). The effect of gamma irradiation on the density of the hexane-hexene mixture at different concentrations after 1 month (a) and 2 months (b)
The graphs describing the effect of the radiation dose on the system density show that small dose values are more effective in changing the density. Saturation is observed after 64 hours of radiation. Dose dependence of the density associated with changes in mixture shows that as the amount of olefin in the system increases, the density changes more, which is due to the increase in the density of the liquid during polymerization. As the amount of olefin increases, the viscosity increases rapidly as the radiation dose increases, which can be explained by the polymerization process. The varying degrees of dose dependence can be explained by the dose-dependent nature of the intermolecular interactions that determine viscosity. Dose dependence of viscosity is shown in Figure 2 (a, b).
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The effect of gamma irradiation on the viscosity of the hexane-hexane mixture at different concentrations 2 months later (%)
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Fig. 2 (a, b). The effect of gamma irradiation on the viscosity of the hexane-hexene mixture at
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As can be seen, the viscosity of the system increases monotonically with increasing radiation, there is a weak dose dependence, and at values greater than 64 hours there is a relatively rapid increase in viscosity. As the dose of ionizing radiation increases, the density of the hexane-hexene mixture increases. In order to be sure that the change in the physical characteristics of the model hydrocarbon mixture is due to the radiation-stimulated polymerization process, it is necessary to study the process of changing double bonds in the system experimentally. Iodine is an indicator of the presence of unsaturated hydrocarbons, which determines the chemical instability of quantitative fuels. Changes in the iodine number of samples of hexane-hexane mixtures at different concentrations were shown to be irradiated and 1 month after irradiation (Figure 3).
Fig. 4. The effect of gamma radiation on Hexane and Hexene's iodine number change after 1 month
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Fig.5. Change in iodine numbers of hexane-hexene mixtures at different concentrations and
absorbed doses after 2 months of irradiation
Change in iodine numbers of hexane-hexene at different
Fig 6. Change in iodine numbers of hexane-hexene at different concentrations and absorbed doses
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RESULTS AND DISCUSSIONS
While studying the effects of ionizing radiation on organic compounds, there are two periods -immediately after radiation and after radiation. Changes that occur during radiolysis may be reversible. These deductions are due to the occurrence of secondary reactions of unsaturated hydrocarbons accumulated during radiation. In the conditions of our experiments, the dose rate of P = 0,076 Gy/s at the Co60 gamma source of hexane / hexene mixture (5,10,20,40%) s, at different absorbed doses (D = 25-78 kGy), the density and viscosity increase, the iodine number changes. As can be seen, a change in the hexene concentration in hexane from 5% to 40% changes the iodine number from 3 to 10, and this change is very close to linear.
Analysis of IR- spectra shows that the predominant direction of radiation-chemical processes in binary systems with no or little olefins (5-10%) is dehydrogenation and the formation of olefins. At values greater than 168 hours (D= 48 kGy) of irradiation, the olefins present in the system begin to polymerize and the iodine number decreases. In olefin-rich mixtures (20-40%), both processes of olefin formation and polymerization begin simultaneously in the process of radiolysis. The post-polymerization process in hydrocarbon systems containing more than 20% olefin will be studied in the coming years.
Conclusion: The rate of polymerization during radiolysis of olefin-paraffin mixture depends on the concentration of olefin in the system and the absorbed dose. At systems with a dose greater than 45 kGy, polymerization becomes a dominant process in systems containing more than 20% olefin.
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