A mechanism study of acid-assisted oxidative stabilization of asphaltene-derived carbon fibers
Desirée LeistenschneiderPeiyuan ZuoYuna KimZahra AbediDouglas G. IveyArno de KlerkXuehua ZhangWeixing Chen
29
Citation
36
Reference
10
Related Paper
Citation Trend
Abstract:
The development of inexpensive carbon fiber precursors is necessary to meet the future demands of carbon fibers. This work shows how asphaltenes, which are obtained as a by-product in bitumen production, can play an important role as such inexpensive carbon fiber precursors. To synthesize carbon fibers from asphaltene, stabilization by means of oxidizing acids (HNO3 and H2SO4) was developed. Stabilization could not be achieved by a non-oxidizing acid (HCl). The reactions leading to fiber stabilization was investigated for nitric acid treatment, which led to oxidation and the incorporation of nitro-groups. Further thermal treatment caused an increase in C/H ratio that was related to decomposition of nitro-groups, which facilitated air oxidation and other reactions leading to the loss of volatile hydrogen-rich products, such as light hydrocarbons. Additionally, the influence of the acid concentration during treatment on fiber properties, such as fiber diameter, composition, tensile strength and elastic modulus, has been examined. The application of the acid treatment leads to carbon fibers with good tensile properties, with a tensile strength and elastic modulus of 811 MPa and 32.7 GPa, respectively. The overall yield of carbon fibers is 37 – 38 wt.%.Keywords:
Oxidizing agent
Nitric acid
Asphaltene
Carbon fibers
Oxidizing agent
Peroxide
Cite
Citations (0)
Abstract Coagulation of asphaltenes in crude oil has been studied by electronic spin resonance (ESR). Free radicals in asphaltenes with the content of vanadium less than 0.1 mass% are found to recombine when asphaltenes precipitate. Polyaromatic fragments are shown to be localized in the inner part of the asphaltene molecules. A possibility of the formation of diamagnetic compounds between vanadyl (VO2+) complexes and free radicals of asphaltenes is investigated. Introduction The study of asphaltenes from crude oil is a matter of special interest and research in oil chemistry. The constantly increasing share of heavy crude oil and bitumen in total oil production has lead to the increasing importance of studies in this area. High concentrations of asphaltenes, resins, vanadium and sulphur are characteristic for most of the heavy crude oil and bitumen deposits. That makes oil production and refining more complicated. Petroleum asphaltenes are the highest molecular species among components of petroleum and asphaltenes only —the basic carriers of oil paramagnetysm. Basically, paramagnetic components in oils are free stable radicals and vanadyl (VO2+) complexes. The behaviour of asphaltenes under reservoir conditions, and in the preparation and transportation of crude oil, is strongly related to the interactions between paramagnetic fragments in the structure of asphaltene aggregates. There is a hypothesis that asphaltene molecules, especially the large ones, are not necessarily two-dimensional flat disks but they have the capacity, owing to the presence of long polymethylene bridges, to fold upon themselves into a complex three-dimensional globular conformer with an internal structure(1). In other works, however, it has been shown it is possible for the molecules containing alkyl fragments up to C24 (paraffins, ceresines, etc.) to co-precipitate together with asphaltenes(2,3). Hypothetical structures of the asphaltene molecules have been presented(4,5). They have a different type: polyaromatic fragments are in the centre of the molecules whereas naphtene-aliphatic groups are located on the periphery. By way of explanation of the characteristics of crude oil and bitumen, the most significant model was proposed by Juan Murgich(6) to describe asphaltenes from different crude oils. According to the model, all asphaltenes are two types: A-type and S-type. A-type asphaltenes have 15 to 20 condensed aromatic rings (in the centre), alkyl substitutes and heteroatoms on the periphery. Asphaltenes of this type are flat. S-type asphaltenes have several aromatic parts (2 to 5 rings) which are connected with each other by alkyl and sulphide bridges. The molecules are almost spherical. The aromatic parts are located on the outer surface of the asphaltene molecules. In the work by Galtsev et al.(7), a conclusion is made about the low mobility of the vanadyl complexes/ asphaltene system. This conclusion is based on the reverse correlation between the relaxation characteristics of electrons in crude oil. On the basis of the time of spin-spin relaxation, the concentration of an agent responsible for widening of the signal associated with free radicals, i.e., vanadyl complexes, is calculated. The concentration of vanadyl complexes derived from the integral intensity of the signal in a spectrum is lower than that derived based on the time of spin-spin relaxation.
Asphaltene
Cite
Citations (10)
In this article,the synthesis of p-tert-butylbenzoic acid by using nitric acid as the oxidizing agent was introduced.The raw material was p-tert-butyltoluene.Three kinds of conditions which affected the reaction were discussed:The concentration of nitric acid,the temperature and time of the reaction.The best condition was also found by way of orthogonal experimental design.This simple synthetic route was appropriate for industrial production.
Oxidizing agent
Nitric acid
Cite
Citations (0)
1H DOSY NMR experiments were used to investigate the macrostructure of the asphaltenes of Maya, Athabasca, and Buzurgan feedstocks in toluene-d8 at 20 °C. The influence of the concentration of asphaltenes on their diffusion coefficients is presented for the three asphaltenes. A separation between two classes of aggregates—one diffusing quickly and one diffusing more slowly—was observed at an onset concentration that is dependent upon the origin of the sample. This illustrates that the chemical interactions (and, hence, the chemical structures) are different for the three asphaltenes. Because asphaltenes are a continuum of both archipelago and continental asphaltenes, the interactions in the solutions differ, depending on the repartition between archipelago- and continental-type asphaltenes in the feed. Maya and Buzurgan asphaltenes show similar diffusion properties in the dilute regime, while Athabasca asphaltenes diffuse more slowly. Results obtained from DOSY experiments data seem to indicate that Buzurgan asphaltenes show a more continental character than the two other asphaltenes, while Athabasca asphaltenes seem to contain more archipelago asphaltenes. 1H and 13C NMR experiments were also performed to determine the average structural parameters of asphaltenes. Average sizes and molecular weights were determined from the 1H-DOSY NMR diffusion coefficients and compared to size exclusion chromatography (SEC) data.
Asphaltene
Archipelago
Cite
Citations (120)
The results of studies of asphaltenes of bituminous oil from the Ashalchinskoye oilfield and oil and resin-asphaltene components isolated from the liquid products of their conversion in n-hexane under supercritical conditions are presented. It is found out that the mean molecules of secondary asphaltenes and resins differ from those of asphaltenes of the initial sample by the number of structural blocks. They prevail in the mean molecule of secondary asphaltenes, while in the mean molecule of resins they are lesser in number. A feature of the structural blocks of secondary asphaltenes is a lower number of naphthenic cycles, a higher content of sulfur atoms, and a reduced content of nitrogen and oxygen atoms. The structural blocks of the resulted resins consist of minority of aromatic and naphthenic cycles and contain a lesser number of sulfur and nitrogen atoms but more of oxygen atoms than the initial and secondary asphaltenes. The qualitative composition of the compounds identified in the resulted oils is substantially identical to that of the compounds identified in oil components isolated from liquid products of autoclave thermal degradation of asphaltene substances of heavy oils.
Asphaltene
Hexane
Autoclave
Degradation
Light crude oil
Cite
Citations (0)
Abstract Asphaltenes can be dispersed in crude oils in 3 different forms; molecules, nanoaggregates (of molecules) or clusters (of nanoaggregates); these forms are codified in the Yen-Mullins model and relate to the extent of solvency of the asphaltenes in the crude oil. Many reservoir studies are used here to show the systematic behavior of the specific asphaltene species in crude oil and the corresponding magnitude of the asphaltene (and viscosity) gradients. In addition, the specific asphaltene species is related to the chemical origin controlling asphaltene onset pressure (AOP) and tar formation and depends on 1) the quality of the live crude oil solvent for asphaltenes and 2) the concentration of asphaltenes. Elevated quantities of solution gas of a reservoir crude oil significantly reduce the solvency of asphaltenes in crude oil. For low concentrations and/or good solvency, asphaltenes are dispersed in crude oils as molecules with small gradients (unless there are large GOR gradients). For moderate concentrations and/or moderate solubility, asphaltenes are dispersed as nanoaggregates with intermediate (gravity) gradients of asphaltenes. With large concentrations and/or poor solvency, asphaltenes are dispersed as clusters with very large gradients in reservoirs. These crude oils can also exhibit higher asphaltene onset pressures and/or phase separated bitumen or tar in the reservoir depending on the origin of asphaltene cluster formation. Secondary gas charge into oil reservoirs can yield tar and/or a high AOP. The effect of biodegradation on these factors is also discussed. The systematics presented here are helpful in understanding a variety of reservoir concerns associated with asphaltenes.
Asphaltene
tar (computing)
Cite
Citations (2)
Hydrogen peroxide (H2O2) is a central molecule in plant stress responses as a potential oxidizing agent or a signal molecule, depending on its localization and cellular concentrations. The work compares the versatility of three simple and rapid, potentially high through-put photometric assays to detect this reactive oxygen species in leaf extracts.
Oxidizing agent
Peroxide
Cite
Citations (20)
Chemical inhibition of asphaltene deposition is considered a cost-effective way to prevent the harsh consequences of asphaltene instability in the produced crude. Thus, a careful screening of asphaltene inhibitors is crucial for an efficient prevention. However, the characteristics of asphaltenes such as their acid–base properties will influence the selection of an asphaltene inhibitor and the inhibition mechanism. Therefore, improved knowledge on asphaltene acidic and basic fractions is important. In this work, the separation of asphaltenes into acid, base, neutral, and amphoteric fractions was performed. Among the existing techniques to fractionate asphaltenes, the method of Ramljack was adopted and applied on a light oil extracted asphaltene. However, this oil was sampled from one of the wells in the Hassi Messaoud field in Algeria that experienced a recurring deposition of asphaltenes. The results of asphaltene fractionation reveal that the half composition of this heavy part of crude oil is active functions gathered acid and base components. However, the main contribution is reported to the neutral fraction. The characterization results of infrared and elementary analyses show that both active fractions are aromatic and polar. Moreover, the acid fraction contains in its structure carboxylic acids, phenols, sulfoxide groups, and aliphatic chains, while the structure of the base fraction contains amines, sulfoxide groups, and aliphatic chains.
Asphaltene
Fraction (chemistry)
Sulfoxide
Base (topology)
Cite
Citations (15)