Maltene petroleum

Bitumen contains a solvent-soluble fraction referred to as maltenes, and an insoluble fraction called asphaltenes. The word bitumen is in some cases also used to indicate the residue of the distillation of petroleum. 

Maltenes that fraction of petroleum that is soluble in, for example, pentane or heptane deasphaltened oil q.v.y, also the term arbitrarily assigned to the pentane-soluble portion of petroleum that is relatively high boiling (>300°C, 760 mm) see also Petrolenes. 

Asphaltenes may contain both porphyrin and nonporphyrin metals, depending upon the origin of the crude oil. Yen et al. (1969) characterized the vanadium complexes in a petroleum asphaltene by mass spectroscopy, optical spectroscopy, and ESR. Porphyrins (Etio and DPEP), acid-resistant porphyrin macrocycles of increased aromaticity (Rhodo), and nonporphyrins with mixed donor complexes were identified. Baker (1966) and Baker et al. (1967) extracted porphyrins from Boscan crude oil asphaltenes and also found Etio and DPEP as the two major porphyrin series. These homologous series range in molecular weight by 7 to 18 methylene groups. Gallegos (1967) observed by mass spectroscopy that asphaltenes and maltenes from a Boscan crude oil had nearly identical porphyrins in terms of mass distribution. 

Percent Vanadium in Each Molecular Weight Category of Vanadyl Compounds in the Four Heavy Crude Petroleums and Their Asphaltenes, Maltenes, Asphaltene Polar Extracts, and Extracted Asphaltenes by 50/100/1000 A SEC-HPLC-GFAA Analysis"- ... 

Vanadyl salen provides a model of mixed heteroatom metal coordination characteristic of Ni and VO in the maltenes and asphaltenes. Approximately 50-90% of the metals in petroleum are not contained in the free porphyrin fraction. Yen (1975, 1978) has postulated that these metals exist in a variety of environments such as highly aromatic bound porphyrins, complexed to tetradentates of mixed N, S, and O ligands, or defect sites in large aromatic sheets. Analytical work by Fish et al. (1984) has indicated the presence of metals complexed to salen-type ligands in petroleum. 

Figure 1. Flow diagram for the separation of the sulfide and thiophene classes of compounds from the maltene fraction of petroleum. (Reproduced from Reference 34. Copyright 1989, American Chemical Society.)...

An early hypothesis of the physical structure of petroleum (52) indicated that asphaltenes are the centers of micelles formed by adsorption, or even by absorption of part of the maltenes, that is, resin material, onto the surfaces or into the interiors of the asphaltene particles. Thus, most of those substances with greater molecular weight and with the most pronounced aromatic nature are situated closest to the nucleus and are surrounded by lighter constituents of less aromatic nature. The transition of the intermicellular (dispersed or oil) phase is gradual and almost continuous. Continued attention to this aspect of asphaltene chemistry has led to the assumption that asphaltenes exist as clusters within the micelle. This arises mainly because of the tendency for asphaltenes to associate in dilute solution in solvents of low polarity and from possible misinterpretation of viscosity data (58, 64). The presence of asphaltene stacks in the solid phase, as deduced from x-ray diffraction patterns (68), also seemed to support the concept of the widespread existence of asphaltene clusters in the micelle. 

The molecular size distributions and the size-distribution profiles for the nickel-, vanadium-, and sulfur-containing molecules in the asphaltenes and maltenes from six petroleum residua were determined using analytical and preparative scale gel permeation chromatography (GPC). The size distribution data were useful in understanding several aspects of residuum processing. A comparison of the molecular size distributions to the pore-size distribution of a small-pore desulfurization catalyst showed the importance of the catalyst pore size in efficient residuum desulfurization. In addition, differences between size distributions of the sulfur- and metal-containing molecules for the residua examined helped to explain reported variations in demetallation and desulfurization selectivities. Finally, the GPC technique also was used to monitor effects of both thermal and catalytic processing on the asphaltene size distributions. 

Recently, petroleum residua have been studied extensively (I, 2) because of the increasing importance of heavier fuels. Both the asphaltene (pentane-insoluble) and maltene (pentane-soluble) components of residua are of interest, and since their properties overlap, a complete study of petroleum residua must consider both asphaltenes and maltenes. One area that has received considerable attention has been the size characterization of asphaltenes and maltenes (3, 4, 5). Size distribution data are useful both in understanding the fundamental chemistry of asphaltenes and maltenes and in observing the effects of various processes on residua sizes. 

In this study, six petroleum residua were characterized by a combination of preparative- and analytical-scale gel permeation chromatography (GPC). Each residuum was separated initially by pentane deasphalting into an asphaltene and maltene pair, both of which were separated further by... 

Finally, during the fractionation of petroleum, the metallic constituents (metalloporphyrins and nonporphyrin metal chelates) are concentrated in the asphaltene fraction. The deasphaltened oils (petrolenes and maltenes) contain smaller concentrations of porphyrins than the parent materials and usually very small concentrations of nonporphyrin metals. 

Maltenes the fraction of petroleum that is soluble in, for example, pentane or heptane ... 

Historical Aspects. An early hypothesis of the physical structure of petroleum (Figure 10) (94) suggested that asphaltenes are the centers of micelles formed by adsorption or even by absorption of part of the maltene fraction, that is, resin material, onto the surfaces or into the... 

In this study, we have developed a technique to analyze directly trace and ultra trace metal elements in cmde oils and its fractions (maltenes-asphaltenes) by ICP-MS after sample dilution in xylene. This method was then used to produce a new set of data, using the above-mentioned methodology, on the distribution of metal trace elements between asphaltenes and maltenes in cmde oils from a Brazilian petroleum basin. 

Composition. Bitumen paints contain bituminous substances as binders. Bitumen is defined in DIN 55 946 as A low-volatile, darkly-colored mixture of organic substances obtained in the processing of mineral oils and petroleum, whose viscoelastic behavior changes with temperature. The typical properties of bitumen can be attributed to a colloidal system in which the disperse phase (asphaltenes) is stably distributed in a coherent phase of high-boiling oils (maltenes). ... 

Correlation of the activation energy with the concentration of maltenes (dispersion medium + petroleum resins) shows a similar trend, i. e. decrease of the activation energy with increase of the concentration of maltenes. Only one line is produced for each pressure range and the coefficients of con elation are considerably lower, so the numerical values are not listed. 

The less distinct correlation of the activation energy with the concentration of maltenes is not contradictory, because the content of petroleum resins in the maltenes includes a corresponding concentration of aromatic compounds. Those aromatics could not be pyro-lyzed under the current experimental conditions, however aliphatic side chains of substituted aromatics are pyrolysed. 

The reaction kinetic constants activation energy E and frequency factor A, can only be correlated with the concentration of paraffinic carbon, CP (from structural group analysis) with the concentration of dispersion medium (fiom colloid analysis) and with the H/C ratio (from elemental analysis). These functions show correlation coefficients of an acceptable magnitude. Examination of the correlation of the concentration of maltenes revealed a similar tendency but with very low coefficients of correlation. It is well known that the dispersion medium contains the highest concentration of chemical bonds, which can be cracked under the chosen reaction conditions [4-20]. In the pyrolysis experiments from distillation residues, about 92 % of the dispersion medium was converted, whereas conversion of the petroleum resins was only 83 %, despite the fact that the kinetic coefficients are of nearly the same magnitude for the two components. 

Fractionation by solubility is used to isolate asphaltenes from maltenes, and the standard method (ASTM-3279-97) has been used in this work. Crude petroleum is mixed with 40 volumes of heptane, heated, stirred, and left to cool. The asphaltenes form a precipitate that can be removed by filtration. Normal practice is to clean the asphaltene fraction by Soxhlet in heptane. The proportions of asphaltene in crude petroleums vary widely, from less than 0.1% in the best crudes to over 10% in the heavy crudes. In general, the heavy crudes such as Maya are of most interest. The solubility of petroleum asphaltene in NMP is of interest since the NMP-insoluble material has no fluorescence [61] and was initially assumed to be aliphatic. However, it has UV absorbance and must be aromatic [62]. The separation into NMP soluble and insoluble was achieved for several asphaltenes. A Kuwaiti asphaltene was separated into NMP-soluble and -insoluble fractions [63]. Seven crude oils were fractionated into heptane solubles and asphaltenes for comparison with an asphaltene from a heavy oil [64]. 

Alkanes form a significant proportion of crude petroleum samples (16% of Athabasca bitumen and 32% of Maya crude [89]) and would normally be heptane soluble and part of the maltene fraction. Alkanes are also found in coal tars formed by pyrolysis without extensive secondary thermal treatment [81]. LD-MS at 337 nm does not ionize alkanes [90], and therefore, ali-phatics will not appear in the mass spectra alkanes can be ionized by silver ion adduction and LD, but this method has not been applied in work discussed here. 

The physical properties of asphalt are directly related to the quantity of the dispersed phase (asphaltenes) the size of the micellar structures, which depends upon the degree of adsorption of resins the nature of the dispersion medium and maltenes (oils and resins). In heavier fractions of petroleum, single molecules contain Cp, C, and C portions. The aromatic protons near the aromatic ring system can participate in electrophilic reactions, such as nitration, sulfonation, halogenation, and others. The interaction between the molecules will determine the chemical properties of asphalt. 

A crude oil can be separated in two main components asphaltenes and maltenes. The heavy fractions of petroleum can be defined as molecules possessing more than 25 atoms of carbon distributed in polar and heavy compounds, such as asphaltenes and resins, having high boiling points (Merdrignac and Espinat, 2007). Since asphaltenes are the main constituents of heavy crude oils and their structure and composition directly affect the whole composition of the petroleum, they deserve special attention. 

Matsushita et al. (2004) defined the following relationship that takes into account the H/C atomic ratio of asphaltenes and maltenes, which gives certain information about the solubility of asphaltenes and its influence on coke formation during processing of petroleum ... 

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