Transformation of the energy state of the molecular structure of coal in the process of metamorphism

This article discusses processes of rock-mass geothermal and geomechanical energy transfer on the nanolevel and describes different mechanisms of potential energy absorption, distribution and usage by the molecular structure of the coal substance. We show that mechanical and thermal energies in the molecular structure of the coal substance are transformed into quantum-mechanical energy which feeds the structural transformations and generation processes in the substance. At the nanolevel, the energy inflow transforms the atomic-molecular structure, changes the physical and chemical properties of the coal and may cause fluid (including methane) emission. The availability of a general solution for energetic problems of different hierarchical levels is evidence of the possibility of using a fractal approach for researching the energy re-distribution in the system.


Introduction.
In the process of geological history, rocks of the coal-bearing stratum are subject to changes in temperature, geostatic and tectonic pressure.Geodynamic conditions are periodically changed, thus, the system receives geothermal and geomechanical energies which differ by intensity and impact on the structure and properties of the entire rock mass at the macro-and micro levels (Lukinov at all, 2010, Tektono-heokhimichna. Lukinov at all, 2011).However, the same external processes occurring at different levels activate different mechanisms of the inflow energy absorption and re-distribution.On the scale of the rock massif, the laws of classical physics and thermodynamics work well and exactly describe the processes occurring in the macroscopic systems; while the laws of quantum mechanics are good for the atomic-molecular level, where the principle of energy uncertainty acts in the system.
Formulation of the problem.The IGTM , NANU, researched the effect of thermal and mechanical actions at the nanolevel with the help of the spectral method.The experimental studies of transformations in the atomic-molecular structure of coal (Burchak at all, 2010. Balalaev at all, 2011) proved that geological processes with associated pressure and temperature growth impacted on the state, composition and properties of the coal substance.At the nanolevel, the energy inflow transforms atomic-molecular structure, the consequence of which is emission of methane and changes in the coal's physical and chemical properties (Burchak, 2012).However, mechanisms of the transformations take place at different levels and their interdependence has been insufficiently studied.Therefore, research on the energy transfer from the macro level to the nanolevel and mechanisms of the accumulated energy distribution and usage in a large scale macro system by molecular volumes of the substance is the subject of this article.Presentation of the general material.In the process of metamorphism, a coal substance is in an energetic state close to equilibrium.When external conditions are changed, it is profitable for this system to transfer its composition and state in accordance with the Le Chatelier-Broun principle as such transformations soften the action of the external factors.So, the carbonization process, by its essence, is an energetic response of a closed system to an external impact, i.e. it is a relaxation which should be accompanied with increase of entropy and reduction of the internal energy of the substance.The increase of entropy, in its turn, is impossible without destruction of macro molecules and formation of low-molecular compounds.
Free energy ( F ) is connected with the energy ( E ) of the entire system, temperature ( T ) and entropy ( S ) by an equation The energy coming into the system from outside changes T and S, or, more specifically, increases the product TS, and the value of F is reduced, correspondingly, approaching its minimum.It means that the system accumulates an external energy and will relax it in such a way as to reduce the F. In a closed system, free energy can be reduced only through certain transformations in the molecular structure (Semenov, 1986), breakup of high-molecular compounds and structuring of the group.
Figure 1 presents the scheme of a coal fragment with cyclic and linear sections.Macromolecules of the carbonized organic substance have carbon compounds of the linear type with concentration n1, which, in the process of transformation transfer to cyclic compounds with concentration n1.In this case, the system entropy change, per 1 mol of the substance, is: where R is a universal gas constant ( R = 8.31 J/mol•К); n1 -is concentration of the compounds with the linear structure, mol -1 ; n2 -is concentration of the compounds with the cyclic structure, mol -1 .It results from this that it is profitable for this system to become structured by transforming linear compounds into cyclic compounds with emission of energy.The similar structural transformations are associated not only with inflow of energy from outside but with the internal entropic factor as well.At the same time, the molecular structure of the substance is rebuilt spontaneously resulting in reduced energy of the system and increased entropy.
Growth of aromatic component in the process of the metamorphism draws no objections.However, the system under this consideration is in the state close to equilibrium irrespective of the processes occurring.So, when no external sources of energy are available, the driving force for the carbonization should be an entropic factor, i.e. spontaneous structural transformations leading to cyclization of the linear compounds in the molecular structure of the coal substance.This thesis requires further explanation and confirmation.
Let's randomly choose a sector of molecular structure of the substance of linear patterns (Fig. 2а).
Let's consider a system of carbon atoms CFGHL.This system has the following energy: ). ( Statistic entropy (S0) is defined by a number of micro states (W), which realize a macro state of a particular structural unit.For the linear sector: where k is a Boltzmann constant ( k = 1.38•10 -23 J/К), (W0 = 2 for the systems with two basic quantum states).If as a result of conformational deformation or structural defects a weak link is formed between the carbon atoms in the neighbouring chains, then new states appear in this system which are characterized by a nonzero probability of energy flow, i.e. that the energy could be "pumped" via these bunches ("sewing together") (Fig. 2в).For the absolute values, the entropy change is: In natural conditions, the molecular structure of the coal substance is very compact, and the spatial structures of the chains are in harmony with each other.In this case, intermolecular space is minimal; the chain buckling with further cyclization is hardly probable.A more realistic scenario is that the linear (aliphatic) linking will be "sewed together", and energy needed for developing the substance catagenetic transformations with possible detachment of the end groups and formation of methane will move via these newly formed links.On the plane, it looks like the formation of a cyclic compound.Thus, in the process of metamorphism, the structural transformations occur in the coal substance at the molecular level and lead to the energy transfer via the bunches between the molecules.
Similar mechanism of the bunch formation and energy transportation is a process of percolation, abstract theorems of which are used for describing processes of polymerization and linking small molecules into macro molecules (Tarasevich, 2002. Astahov at all, 2005).The process of the percolation conduces to self-organization, and structures formed in these cases have a fractal nature (Tarasevich, 2002).The fractal dimension is closely connected with an entropy which is characterized by energetic and dynamic peculiarities of the physical system, and these peculiarities define the system genesis.As coal is a thermodynamic system in the quasi-static state, and the link between the entropy and energy here is simple (energy transfer from the state with entropy S0 into the state S1 is more probable), so energy (Е) transferred to the unit of the substance mass is equal to: Е=Т•(S1-S0).Thus, it can be stated that natural macro processes, from time to time, "pump" energy into the system and regulate the substance structure at the atomic-molecular level.As a result of such structural transformations occurring in the coal substance under the action of external factors the system entropy increases.
By analogy with an approach presented in the article (Pines at all, 1966), coal substance can be conventionally considered as a set of molecular compounds of aliphatic and aromatic type with complicated chemical composition and structure which chemically link with the jellylike complexes.Electrons of the atoms in molecules of the coal substance are in the same energetic state and form a "quantum liquid" (it is an analogue of the Bose condensate) which contains the electrons' proton skeletons.Under the thermal and mechanical action in the coal stratum, the energetic state of the electron "jelly" is changed, and the proton skeletons "adjust" their quantum-mechanical state to such change.In a closed unstable system, the changed energetic state conduces to conformation transitions in the hydrocarbon compounds where a carbon atom is located in the electron cloud.Energy in this system can be presented as a sum of energies of the "jellylike complexes" and the energy of their interaction.Atoms forming the coal substance are located in the electron gas with energy Ее.The equation for the state of non interacting electron gas (electron "jelly"), linking pressure and this system's volume and energy is the following (Pines at all.1966): , 3 2 e e E P = Ω where e P is pressure of the electron "jelly", Ω is volume of the system, e E is energy of electron gas.This equation shows that atoms, under increased pressure, transfer to the higher energetic levels, and, therefore, the energetic potential of the system increases.The closed thermodynamic system should relax the accumulated free energy.
Concentration of the paramagnetic centers in the carbonate fossil organics reaches n•10 19 g -1 , and most of this part is, depending on the rate of the substance carbonization, in the form of free radicals.Besides, it is proved that free radicals can be initiated by the walls of reaction vessels (Semenov, 1986).As the coal stratum is constantly under tectonic impact, role of such walls can be played by mineral inclusions in the coal stratum and zones contacting with the enclosing rocks.The wall activity is explained by the fact that it serves a source of radicals and place of their death.Activation energy of the radical transition into a volume of the coal substance is small (Semenov, 1986).The matter is that the system receives a weakly conjugate radical and forms a strongly conjugate radical.Availability of free radicals in the high-molecular organic substance can activate and develop chain reactions, the product of which is always low-molecular compounds.The difference of the energies remains within the system and presents an additional source of energy which reduces thermodynamic limitations of the transformations in the solids (Galimov, 1973).
In accordance with the model of electronic "jelly", any impact on the coal substance will, due to the action of the mineral components, excite the system and the energy transfer (Maradulin at all, 1968), create chain reactions of the free radicals and phase transition of the 2 nd level, change the chemical composition of the system, and, consequently, conduce to the process of the methane generation.
As a result of mechanical impact, some structural transformations occur in the coal, which reduce free energy in the entire system to its minimum.One of the possible processes of such reduction is formation and distribution of excitation waves.Processes in the substance excited by the gravity and tectonic forces conduce to the re-building of molecular compounds in the coal, and these compounds are, at the same time, elements transporting energy to the whole system.In a closed system (coal stratum), energy of vibration changes the molecule structure in the organic substance in the form of conformation deformation.As a result of the mechanical impact, chain sector and flat grids approach each other, and thermal fluctuations form links between the neighboring conjunctions.
The process of energy migration in the solid phase (rigidly fixed molecules) is based on the energetic resonance, i.e. an overlapping of the emission spectrums, and this is in harmony with conditions for exciting free excitons (Zhevandrov, 1987).Energy in such condition can be transferred to the defective areas of the structures and to other molecules.The energy is transferred because a coal substance being a thermodynamic system trends to the state of equilibrium with minimal energy.Such transfer can be a result of either energy burst (for example, a sudden coal-gas outburst) or relaxation of accumulated energy with further changing of the substance's chemical composition, state and properties.
As a result of catagenetic transformations occurring in the coal substance both chemical composition and physical state of the substance are changed, which is manifested in the fractality of the system (Pymonenko at all, 2011. Lukinov, 2010, Fraktal'nost').The external impact on the system which is a natural fractal (Bulat, 1993) conduces to the fact that the energy, at the molecular level, causes changes in fractality (changed geometry and state of the surface) and growth of the system symmetry.
Thus, energy entering the system from external sources is used in accordance with the changed geometry of the system, i.e. it is also fractally absorbed.
Conclusions.The research showed that energy transformations occurred in the molecular structure of the coal substance.Mechanical and thermal energy is transformed into quantum-mechanical energy, which feeds structural transformations and generation processes in the substance.
The study of processes of different types of energy transferring from macro level to the nanolevel showed that energies at various hierarchical levels are linked with each other functionally.Redistribution of accumulated energy conduces to the system fractality at all levels.The availability of a general solution for energetic problems of different hierarchical levels is evidence of the possibility of using a fractal approach for researching the energy re-distribution in systems.

Fig.. 1 .
Fig.. 1. Scheme of a coal fragment with cyclic and linear sections.
Scheme of cyclization of the molecular structure of coal substance: а is a sector which can be approximated as a linear structure, б are the main and additional micro states of the energy pumping (Е0 is energy of the basic micro state, Е1 is energy of additional micro state)Then we have the following equation for the statistical entropy of the flat sector: a Boltzmann constant, ( i W = 4 for the sys- tems with four quantum states).