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29CHEMISTRY
QUALITY OF OIL. REMOVING THE ORGANIC SULFUR COMPOUNDS FROM PETROLEUM
BSc Kabyl A. A.
Kazakhstan, Astana, Eurasian National University
Abstract. This article discusses the problem of extracting sulfur and organosulfur compounds from the oil. This topic is very important, because each method has its advantages as well as disadvantages. In an attempt to evaluate each of the methods has been identified as the authors of the research objectives. One method can distinguish oil quality as possible, but the devices may be subjected to corrosion. Another method does not cause any harm, but is not as effective. This problem is poorly understood and requires further research.
Key words: quality of the oil products, classifications, sulfur compounds, petroleum, processing
Oil is a fluid combustible mineral common in sedimentary shell of the Earth. Different oil deposits differ by physical and chemical properties. Properties of oil determine the direction of its processing, which have a decisive influence on the quality of the oil products. Therefore, oils classification is essential for selection of the best option refining, reflecting their chemical nature.
There are all sorts of chemical, industrial and technological classification of oils. The most important are the chemical and technological classification. In the chemical classification depending on the preponderance of hydrocarbons any one class (over 50%) in a fraction, oil are divided into three main types: methane (paraffinic), naphthenic and aromatic. If the content of this fraction is 25% (or more) of other hydrocarbons classes, oil are divided into mixed types: methane-naphthenic, naphthenic-methane, aromatic-naphthenic, naphthenic-aromatic, aromatic-methane, methane-aromatic and methane-aromatic-naphthenic.
Oil by technological classification depending on sulfur content is divided into three classes: I class - low-sulfur oil with sulfur content from 0 to 0.5%, II class- sulphurous oil with a sulfur content from 0.51 to 1.9%; III class - high sulfur oil with a sulfur content exceeding 1.9%. Then oil is divided into types according to the output fraction to 350C; groups - on the potential content of base oils; Subgroup - by index viscosity of base oils; species - by content solid paraffin in the oil.
The most important element in determining the quality and the price of oil is the mass fraction of sulfur in the hydrocarbon-based. A large amount of sulfur in the oil increases its transportation costs, complicates processing and degrades the quality of petroleum products. The widespread use of various types of petroleum-based fuels (gasoline, kerosene, fuel oil, etc.) in the automotive, marine and air transport and to generate electricity results in the pollution of the atmosphere by combustion products, primarily sulfur dioxide that directly threatens human health and causes acid rain reducing soil fertility.
The price of oil depends on the extent of its technological preparation. Oil, produced in different fields, has a different chemical composition and significantly different in quality. The greatest value has a crude oil which requires minimal processing, from this point of view standard grade are selected, as a higher quality and therefore expensive. To one of the parameters, which is significantly reduced the cost of oil, refers percent sulfur content. High reference varieties contain sulfur within 0.5%.
Sulfur is the most common heteroelements in oil and petroleum products. Its content in the oil ranges from hundredths of a percent to 14%. Sulfur compounds in petroleum are unevenly distributed on its fractions. Usually the content increases with increasing boiling point. However, unlike other heteroelements contained mainly in the asphalt-resinous portion of oil, sulfur is present in significant amounts in the distillate fractions.
Improving the quality of oil is possible due to its processing, namely the removal of sulfur. Desulfurization of the product is carried out by the method of destruction or extraction of organic sulfur compounds. The most interesting for the sulfur-containing products, of course, is the extractive method.
The sulfur in oil is in the dissolved state and partially goes into distillate products at distillation. Elemental sulfur is a very aggressive agent with respect to the non-ferrous metals, and especially to copper and its alloys.
Hydrogen sulfide is dissolved in some crude oils. However, its presence in the distillates is often a consequence of thermal decomposition of other sulfur compound. Hydrogen sulfide is very
toxic, corrosive. The bulk of the sulfur is a part of different organic compounds - derivatives of hydrocarbons and resinous substances.
In various oils found sulfur compounds of the following types: mercaptans and thioalcohols (thiols), aliphatic sulfides or thioethers, monocyclic sulfides, thiophene and its derivatives, polycyclic sulfur compounds.
Mercaptans (thiols) have the structure RSH. Methyl mercaptan (methanethiol) - gas with a boiling point 5.9C. Ethyl mercaptan and higher homologs - liquid, insoluble in water. Boiling point of mercaptans C2-C6 is 35-140C. Mercaptans have a very unpleasant smell. The smell of the lower representatives is so intense that is found in trace concentrations (0.6*10-4 - 2*10-6% for C2H5SH). This property is used in the practice of urban gas supply to prevent a gas line fault. They are added to a household gas as an odorant. The content of mercaptans in petroleum is small.
Mercaptans of oil are well studied. Many individual compound of this class were allocated from oils, including primary, secondary, tertiary and monocyclic mercaptans with carbon atoms from C1 to C8. For example:
C2H5SH
Ethyl mercaptan
C2H5 \ C2H5 -CSH C2H5 /
Tert-hexyl mercaptan Cyclohexanethiol
(3-methyl pentanethiol-3)
Mercaptans are very harmful impurity to commodity products, as corrosive, promote resinification in cracking gasoline and petroleum products give a disgusting smell.
Elemental sulfur, hydrogen sulfide and mercaptans as a very aggressive substances are the most undesirable part of the oil. They have to be completely removed during cleaning and to strictly control their presence in commercial products.
Aliphatic sulfides have the structure RSR'. This is liquid substance with an unpleasant odor. C2-C7 sulfides have low boiling point (37-150C) and at oil refining get into gasoline distillate.
Sulphides account for the bulk of the sulfur compounds, getting into light distillates at distillation. Their content in gasoline, kerosene, diesel fuel ranges from 50 to 80% of the amount of sulfur compound in these fractions. As mercaptans, sulfides in oil are well studied. About 180 individual representatives of sulfides and mercaptans are marked or identified in many oils. Disulfides RSSR is also found in small quantities. They release sulfur, hydrogen sulfide and mercaptans at heating.
Development of new methods for the isolation and concentration of sulfur compounds of oil is a part of the study of their composition, structure and properties. Therefore, an important issue is the creation of an efficient integrated circuit identification and isolation of organic sulfur compounds from the oil and all its factions, which will go to their detailed study.
Currently, a variety of methods known concentration and extraction of organosulfur compounds from a hydrocarbon feedstock. Industrial schemes obtaining concentrates of sulphide, sulfoxides and sulfones of oils and petroleum distillates is developed, which also played a positive role in the study of oil sulfur compounds and allows now to define the real ways of their skilled use. In particular, they can be used in hydrometallurgy in the beneficiation of ore, and extraction of many metals, including noble and to solve environmental problems, in the treatment of animals and crop improvement are the feedstock in various reactions of organic and petrochemical synthesis. Large-scale use of oil sulfur compounds is constrained by the lack of commercially acceptable methods of their removal from the petroleum and petroleum products. Therefore, the possibility of their wide use necessitates the development of simple and promising methods for allocating industrial realization of sulfides, mercaptans and thiophenes, as well as finding industrially acceptable methods of converting them into bi- and polyfunctional derivatives with even more interesting properties than the starting products.
The most reliable and affordable methods for isolating organic sulfur compounds are the oxidation with a variety of oxidants, adsorption onto silica and aluminum oxide, sulfuric acid and alkaline extraction. In this each method has possible many variants differing nature of the used oxidizing agent, the extractant, oxidation catalyst, solvent, and process emissions volume etc. Of all
CH3CH( SH)C2H5 Sec-butyl mercaptan (2-butanethiol) SH
these methods, methods based on the principle of extraction seem more promising, which involve simple technological realization and well established in the industry.
Therefore, work on selection of different solvents for the separation and concentration of sulfur compounds of oil do not stop. Common shortcomings of different solvents are the low selectivity and a sufficiently high dissolving power in respect paraffin-naphthenic hydrocarbons. In connection with this in selective purification processes of oil are selected various additives to solvents (alcohols, water) governing selectivity.
Thus, there are various methods of desulfurization of the petroleum feedstock. The most promising and necessary direction is selection of organic compounds in native form. Unfortunately, there are the negligible amount of research in this field, and if they are carried out, then it is closed.
It should be noted that the discussed methods for isolating organic sulfur compounds are mainly used for gasoline and in rare cases - for middle distillates. In all the methods fail to achieve complete cleaning of the desired product and part of organosulfur compounds lost through oxidation and gum formation. However, it must be emphasized that hydrogen peroxide oxidation, adsorption on silica and alumina catalyst, sulfuric acid and alkaline extraction to extract organic sulfur compounds from petroleum distillates are the most reliable and available methods.
On the other hand, the study of the distribution of organic sulfur compounds in fractions of oil shows that the bulk of the residual sulfur is concentrated in the high-boiling distillates, whose composition is insufficiently studied.
Data on the composition of organic sulfur compounds such distillates are of considerable interest in connection with the further deepening of oil refining and involvement in the processing of heavy oil and oil residues, when the influence of sulfur compounds becomes more tangible and raises the question of environmental protection from pollution by industrial emissions.
All this makes it necessary to develop new economically clean and waste-free methods of extraction of organic sulfur compounds from the heavy hydrocarbon feedstock, as well as the further generalization and separate consideration of accumulated information on the subject.
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