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1.3.1. Composition and structure polycyclic and alifaticheskihfragmentov structures of asphaltenes


Structure of asphaltenes - a debatable question. At studying of asphaltenes neftej Canada, the USA and Venezuela of J. G.Spejtom [38] notes following facts. The constancy of nuclear relation N/S = 1,15 0,05, despite possibility of a considerable quantity of shifts of fragments in the molecules including heteroatoms is emphasised.
The author considers, that this most weighty proof of that nativnye asphaltenes have certain composition and settle hydrocarbon solvents according to this composition. However, in the maintenance of heteroatoms (especially kislo - sorts and sulfurs) are observed appreciable distinctions.
Concerning heteroatoms it is shown [39], that nitrogen is present at asphaltenes in the form of connections of the basic and nonbasic character, including in a kind metallsoderzhashchih complexes porfirinovogo and neporfirinovogo types. Atoms of oxygen in fractions of asphaltenes according to IK spectroscopy, are present at a kind of the hydroxyl groups located in one benzene ring of a condensed system, or near to a carbonyl group, and also in ketonnyh and-or hinonnyh groups [40-44].
Summarising the obtained data, J. G.Spejt considers positioned, that the basic structural fragments of asphaltenes - condensed polycyclic (the systems including heterocyclic (and not heterocyclic are faster polyaromatic)) connections of nitrogen, oxygen and sulphur. In asphaltenes there are paraffin chains of a normal structure, basically С1-С4, but there are also long alkilnye chains to Сі6-С2о (fig. 3).

Fig. 3. Hypothetical model of a molecule of asphaltenes (according to J. G.Spejtu)
The first detailed researches of reflexes in spectrums of diffraction of Roentgen rays of asphaltenes are made by T.Ienom (Yen T.F.), I.Erdmanom (Erdman I.G.) and S.Pollack (Pollack S.S.) [45]. They have divided on rentgeno - grammes coherent and incoherent components and have found, that the first corresponds to a diffraction line uglegrafitovyh substances (002) and is caused by reflexion from the condensed aromatic beds. They have connected an incoherent component with dispersion on sated polime - tilenovyh chains. It is shown, that in kristallopodobnye structures are organised not all aromatic kernels.
Authors [46] also have shown, that for a part of asphaltenes crystalline structure is characteristic. For these structures presence of badly generated planes, free of organised geksagonal th grid is positioned. Significant microdeformations of these planes, according to authors, are defined by following factors: atoms of carbon, formi -
2 3
6

Fig. 4. Charted representation of a molecule of asphaltenes (according to I.A.posadovu) () and the same in section A-A ().
rujushchie planes (002) are, apparently, not only in sp, but also in sp - a hybrid condition; in asphaltenes the significant maintenance "destrukturujushchih" in radiographic sense of elements (About, N, S), organizujushchih heteronucleuses on planes (002) is revealed.

And
The X-ray diffraction technique in asphaltenes fixes presence of two phases: polynaphthenic and ірафитоподобной [47, 48]. The essential deviation of base units from coplanarity speaks authors that as a part of aromatic and naphthenic fragments of asphaltenes there are heteroatoms and consequently there is no full division of polyaromatic and polynaphthenic fragments (fig.
4, projection АА1).
In search of paths of profound research of resins and asphaltenes in IHN the Siberian Branch of the Russian Academy of Science is tested set of variants and schemas of their allocation and fractionation, possibilities of use of different physical and physical and chemical methods of an establishment of composition and structural characteristics CAB are studied. The method of an integrated functional group analysis for calculation of parametres of "a centre molecule" on the basis of the yielded NMR, element and functional analyses and data on molecular weights [47,49] is widely used.
The received results show [49], that the major structural differences of asphaltenes from resins consist: 1) in bolshem number of the base units connected together, 2) in the big centre sizes poliarenovyh kernels, 3) in smaller centre length or in smaller prevalence of large aliphatic substituents and 4) in smaller development of the alicyclic fragments condensed with aromatic kernels. These features asfaltenovyh molecules also define their specific feature to formation of spatially ordered particulates.
At the present stage of researches of structure of asphaltenes the tendency to a consensus concerning construction and centre molecular composition of asphaltenes is observed.
It is necessary to note powerful development of methods of studying of structure of asphaltenes by chemical influence [50] and partial change and destruction of molecules of asphaltenes [34, 51-55], with the subsequent analysis of formed connections.
For example, the oxidation of asphaltenes catalyzed by ions of ruthenium, will transform aliphatic substituents of aromatic systems to their carboxylic derivatives. The carboxyl group corresponds to a place soedine - nija with aromatic system. Restoration by nickel boride (N12B) is result ined to destruction of a part of communications C-S, by processing by boron bromide (ВВг3) - to destruction of ethereous communications.
Thus, in works [52-55] it is shown, that hydrocarbonaceous substituents of aromatic systems vary under the maintenance of carbon links in limits (С1-С30) among which there are fragments-biomarkers (scale-sterany, gopany, regular izoprenody, etc.). Aromatic systems svjazanny the polymethylene (to С25) and sulphidic bridges. Formed arilkarbonovye acids specify in the basic ways of condensation of aromatic systems. Besides, proves to be true, that perikon - densirovannye aromatic structures (a crystal phase) make an insignificant share from a lump of asphaltenes.
Science team of leading universities of the USA, Venezuela and Mexico at studying of structure and properties of asphaltenes and resins widely use a method of molecular mechanics. The essence of a method consists in definition of stable conformstion of molecules and their aggregates (in vacuo and in a solution) [56]. For representation of a various sort of internuclear and intermolecular communications analytical functions are used, the initial configuration, interatomic distances and angles are considered, communications are corrected. Further it is used iterative (iterative) a computing method, for a finding of the minimum power configuration of molecules.
Resulted hypothetical molecular compositions of asphaltenes will well be co-ordinated with thermodynamic calculations of energy of their interaction with resins [57, 58], kaolin [59] etc.
In work X, Murgicha (Juan Murgich) [57] the important conclusion becomes: molecules of asphaltenes, especially big sizes, not certainly two-dimensional flat disks, but can be and volume, because of presence of the long polymethylene bridges. Asphaltenes of studied oil objects Atabaski represent a complex of the globular form with nebol - shimi the shank bores caused by polymethylene bridges, connecting aromatic fragments (fig. 5).

Rice 5. Hypothetical structure of asphaltenes neftej Atabaski (according to calculations X. Murgicha)
However there are works [60, 61] in which possibility from sedimentation with evolved asphaltenes of molecules (paraffin is shown, ceresines etc.), containing alkilnye fragments (to С24) - In this connection, long lo - limetilenovye the fragments fixed in a lump of asphaltenes, probably, do not enter into molecular composition of asphaltenes.
In other works X. Murgicha [58, 59] the calculated molecular compositions of asphaltenes Venezuelan neftej and petroleum residue have some other type of construction of polyaromatic and nafteno-aliphatic fragments (fig. 6).

Cassocks. 6. Hypothetical structure of asphaltenes neftej Venesuelly (according to calculations X. Murgicha)
In works X. Groenzina (Henning Groenzin), O.Mullinsa (Oliver S Mullins), etc. [30, 32, 62] is considered correlation of molecular size of asphaltenes with the size of polyaromatic system (the relation aromatich - nost/alifatichnost). This correlation is carried out in case the molecule contains no more than two polyaromatic systems. And (according to RSA, NMR, rentgeno-fluorescent, optical and emissive fluorescent spectroscopy, etc.) centre condensed systems of asphaltenes contain from 4 to 10 benzene rings (fig. 7). The Molecular structure of asphaltenes is defined by balance between kondensirovannostju aromatic systems of asphaltenes (propensity to formation of the hardware-tg-communications, umen - * sheniju solubilities) and, on the contrary, steric difficulties p - % stekinga alkilnymi groups (propensity to solubility increase).
There is a set of publications into which typification of asphaltenes [17] is entered. Division into types and subtypes is based on distinction of data on element composition of asphaltenes, the spectral characteristics yielded PC And, PMR etc. However not in all publications there are conclusions about features of spatial structure of specified types of asphaltenes.

Fig. 7. Structurally-spatial model of asphaltenes (on representation X. Groenzina and O.Mullinsa)
The most significant, from the point of view of an explanation of observable properties neftej and native bitumens, is entered X. Murgichem typification of asphaltenes of various oil objects [63]. According to which, asphaltenes are divided into two types:
Type - containing a site from 15-20 the condensed benzene rings (in the centre), alkilnye substituents and heteroatoms on periphery (fig. 6). Asphaltenes of this type have a flatness.
-S type - containing aromatic areas (from 2 to 5 rings), is connected th among themselves alkilnymi and sulphidic bridges (rice, 5), the Form of molecules is close to the spherical. Aromatic areas are on an external surface of molecules of asphaltenes.
The specified types of asphaltenes differ both interaction energy among themselves, and interaction energy with molecules of resins. Ener - gija interactions between And - S-ASPHALTENES and molecules of resins (R) decreases among: A-A> A-S> S-S = S-R> A-R.
Both specified types of asphaltenes contain the paramagnetic centres. It is possible to assume, that if the aromatic sites containing nespa - rennye electrons, are on an external surface of molecules at sedimentation of asphaltenes CP will be inclined to the mutual recombination. If on-liaromaticheskie sites are localised in the internal (closed) part of molecules of asphaltenes recombination CP at sedimentation of asphaltenes will be sterically complicated.
Presence in neftjah two types of asphaltenes is marked S.Asevedo's by group (Socrates Acevedo) [50]. And it is underlined, that, possibly, nizkorastvorimye asphaltenes (А1) should form a colloidal phase, dis-pergirovannuju in well soluble asphaltenes (А2).
In work [64] it is noticed, that in the studied oil systems, pripoljusnoe an environment asfaltenovogo kernels make mainly molecules of resins, equatorial — molecules of lube cuts. Possibly, studied oil contain asphaltenes And type (on X. Murgichu).
Generalising set of works on revealing of the centre constitutional formula of asphaltenes, there is a question on practical value of numerous hypothetical models of molecular composition of asphaltenes. For revealing of the centre constitutional formula, the set of assumptions and assumptions becomes, therefore it is represented to more true to describe such substances, as asphaltenes, structural types, instead of one molecular structure.
Structural features of asphaltenes define they are chemical properties, propensity to formation of a various kind of oil associates and, finally, behaviour of the VAT. Earlier selection of reagents for an intensification of extraction, preparation, and petroleum refining was based on data of numerous tests, distinction of componental composition neftej. Now it is obviously necessary, more effective and, probably, quite sufficient to investigate feature of composition and structure of asphaltenes for creation and selection of chemical reagents expressly or by implication attacking on asfaltenovuju a phase of oil systems.
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A source: Tagirzjanov, Marseilles Ilgisovich. ASPHALTENES VANADIJSODERZHASHCHIH neftej (on an example of oil objects of deposits of Tatarstan) the Dissertation on competition of a scientific degree of a Cand.Chem.Sci. Kazan - 2003. 2003

More on topic 1.3.1. Composition and structure polycyclic and alifaticheskihfragmentov structures of asphaltenes:

  1. 1.3. Structure of oil asphaltenes
  2. 3.1. Laws of interrelation of the maintenance vanadilovyh complexes with the maintenance of sulphur, asphaltenes and free radicals in neftjah and asphaltenes.
  3. 3.2. Mineral structure, structures and structures of ores of the South Kirov deposit.
  4. 2.2. The analysis of a phase composition, crystalline structure and a microstructure of samples.
  5. Chapter 3. Effects of examinations of a phase state, structure and a composition of thin films TSTS
  6. influence of composite composition of a chain of an ionomer on membrane morphology. A case of a regular structure of a chain
  7. 6.2. Comparison of spectral characteristics of asphaltenes
  8. Z.Strukturnye types of asphaltenes with the various maintenance of vanadium
  9. 6.1. Degree of extraction of free stable radicals and vanadilovyh complexes asphaltenes from neftej
  10. 5.2. Studying of interrelation of the maintenance vanadilovyh complexes isvobodnyh radicals in neftjah and asphaltenes
  11. 2.2.7 Technique of definition of maintenance VK and CP in neftjah and asphaltenes method EPR
  12. 4.2. Fenalenilnyj a radical as a part of heavy resin of pyrolysis iosobennosti technogenic asphaltenes
  13. 6. STUKTURNYE FEATURES of ASPHALTENES neftej With the VARIOUS MAINTENANCE of VANADIUM
  14. 2.2.1. Definition of group composition neftej and neftepodobnyhsistem