Study of Paraffins in Petroleum Oils by Nuclear Magnetic Resonance Relaxometry

Using method of pulse nuclear magnetic resonance relaxometry (NMRR) were studied paraffins in Romashkino deposit oils (Republic of Tatarstan, Russian Federation) and oils of BaCH-Ho deposit (Vietnam). As a studied samples was used Romashkino oils, in which paraffin was dissolved. Was used isoparaffin i-C22H46 (docozan). For NMR-relaxation structure-dynamical parameters measurements: spin-lattice T1i, spin-spin T2i relaxation times, their proton phases P1i and P2i, was used NMR relaxometer NMR-NP2 on resonance frequency Vo = 18,45 MHz. Dependences of spin-lattice T1A(ms) and spin-spin T2A,B (ms) relaxation times from inverse temperature 103/T K and time t (min) of cooling were received. They are described by equations with regression coefficient R2 = 0.94 and demonstrate spasmotic T1A,B,C and T2A,B,C decrease with temperature rise with jumps of their values, reaching ± 20%. So was revealed the processes of structure-dynamical (SD) ordering, which can be considered as a long time hardening phase transition with activation energies EAi through many stage exo/endothermic local phase transitions with formation/melting of temporary ordered state. Obviously it is connected with ordering of paraffins. After super high frequency (SHF) irradiation at frequency n = 2.45 GHz, with power P = 180W, 2 minutes, the relaxation times increased. This is the evidence of the viscosity reduction of all proton phases. At temperature dependences of relaxation times T2i for isoparaffin several temperature ranges with different behavior of T2i were elucidated. They are the following: i) Range of monotone T2A and T2B decrease with the activation energies EAA2 = 12.35 kJ/mol, EAB2 = 13.6 kJ/mol (left part of the curves 1 and 2) at the paraffin melting. The end of this range correspond to the temperature 43oC of allotrope transformation; ii) Below this temperature range T2B of B proton phase has an uneven behavior with oscillations We suppose they are caused by structure-dynamical processes of temporal ordering of paraffin molecules before the final crystallization, at which T2B falls to value T2B = 6.3 ms. iii) For relaxation times T2A of paraffine proton phase the decrease of T2A with three clear extremes (minimums) of T2A were observed. Probably they related to three-stage process of pre crystallization ordering of –CH2-CH3- groups. Then was observed oscillations T2A which ended with the full crystallization of phase A and sharp fall of T2A. State of paraffin in this range may be named as “rigid lattice” state. iiii) In the melt state of paraffine proton phase A population has value P2A = 65%. At the temperature of the full cooling its value reach value P2A = 98%, which is the evidence that at low temperatures main contribution in relaxation descend from the end –CH3 chains. Molecular fragments of B phase have already reached the solid crystallized (ordered) state. We connected this peculiarities in T2i behavior with SD phase transitions, which appear as a result of temporary (dynamical) formation and following melting of the clusters of supermolecular structures on the paraffin base. In our case they are accompanied by the structure ordering with decreasing of inter atomic distances Rij in structure units. This process is exo/endothermic, the last resulting to the negative local EACA and is the manifestation of open dissipative systems aspiration to the minimum of the free energy and entropy with more sufficient decrease of the enthalpy H contributing in EASD, than entropy S decrease ( H < 0, S < 0, | H} > | S|), which gives negative EASD = H - T S < 0.