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Other refinery products

In addition to finished products for the domestic market, Česká rafinérská also produces raw materials for further processing. In particular, the company supplies raw materials to the petrochemical plants of Chemopetrol, provides basic raw materials for the production of lubricating and other special oils, and manufactures raw materials for the production of hydrogen.

Sulphur. Sulphur is a chemical element that was known as early as in prehistoric times. Already Homer mentions the burning of sulphur for purposes of disinfection. Sulphur occurs naturally in a relatively high amount both in its unbound state primarily in the vicinity of volcanoes and in the form of various chemical compounds, mainly sulphates and sulphides. The accessible part of Earth’s crust contains about 0.03% (m/m) of sulphur. Sulphur is also an important biogenic element since it is found in proteins. In stores, we usually encounter sulphur in two forms – as flowers of sulphur, which are rapidly cooled sulphur vapours, or so-called roll sulphur, which is obtained by casting liquid sulphur heated to 120 °C into moulds.

In its solid state under normal conditions, sulphur is a yellow crystalline substance. Sulphur commonly occurs in several different crystalline forms depending on its origin. Sulphur melts easily – its melting point is 110°C. Liquid sulphur shows significant anomalies, which depend on the temperature and are most apparent in its viscosity. Viscosity of the liquid is lowest at a temperature of approx. 158°C, after which there is a sharp increase of more than four orders of magnitude until it reaches its maximum at approx. 187°C. As the temperature further increases, the viscosity of the molten, liquid sulphur markedly decreases again. The increase in viscosity is explained by the development of an amorphous form of sulphur, which is basically composed of polymeric chains of sulphur with molecular weights of 60,000 to 150,000. The viscosity of liquid sulphur is strongly reduced by the presence of certain admixtures, particularly hydrogen sulphide.

Sulphur is a very active chemical element, above all at higher temperatures. In particular, it is used in the production of sulphuric acid. Further, it is used in the production of carbon disulphide, ultramarine, vermilion, organic sulphurous dyes, cellulose, explosives, industrial fertilisers, matches, etc. A large amount of sulphur is used in the rubber-making industry during the vulcanisation of rubber. Burning sulphur is used for disinfection; sulphurous ointments are often applied in medicine to cure skin diseases. As can be seen from the above list, sulphur may be applied for a broad range of uses.

Sulphur is present in petroleum in the form of organic compounds ranging from several tenths of a percent up to several percent, depending on the origin of the petroleum. In the Czech Republic, Russian petroleum is processed most often – its sulphur content hovers around 1.5% (m/m). During the technological process, sulphur is removed from the individual fractions and products mainly through hydrogenation. The final sulphur content in motor fuels is approx. 100 times lower as compared to the original petroleum. Highly toxic hydrogen sulphide develops from the present sulphurous compounds during the desulphurisation of fractions. It is usually washed out from the circulating hydrogen gases using mono- or diethanolamine. Concentrated hydrogen sulphide gas is then further processed in the so-called Claus units. Here, hydrogen sulphide is oxidised to yield sulphur and in part also sulphur dioxide, which further reacts with the hydrogen sulphide to produce other elemental forms of sulphur. The efficiency of the process is very high – more than 98.5%. We thus obtain very pure sulphur that – unlike natural, mined sulphur – does not contain any physical impurities.

Sulphur is supplied by the refineries in its molten state at temperatures of approx. 140 – 160°C with qualitative parameters given in the following table. This liquid is of a dark yellow colour with an orange tinge. Supplies to our customers are transported in special railroad tanks.

Raw materials for Chemopetrol’s thermal cracking unit. Chemopetrol Litvínov is the largest buyer of raw materials for further petrochemical processing. In addition to ethylene, the thermal cracking unit (due because of its main product also called the ethylene unit) also produces propylene, C4-fractions with a large percentage of butadiene, C5-fractions, benzene, and other products. A whole range of refinery products are used as raw materials. The lightest supplied raw material is LPG; next, the unit processes petrol, gas oil, and the principal raw material is hydrocracked vacuum distillate from the hydrocracking unit built at the Litvínov refinery specifically for this purpose. This hydrocracking unit is also called the PRP unit (preparation of raw materials for petrochemical use).

Raw materials for the production of hydrogen and synthesis gas at Chemopetrol. The hydrogen plant serves mainly to produce gas for the synthesis of ammonia and for the production of higher alcohols via the Fischer-Tropsch synthesis. A smaller part of the produced hydrogen also covers the needs of the refinery. Hydrogen is produced by gasification or partial oxidation of heavy petroleum residues in Shell reactors. These heavy vacuum residues to be gasified are supplied by the refinery.

Oil-based hydrogenates for the production of priming, lubricating, and special oils. The production of oil-based hydrogenates is one of the oldest methods of deep petroleum processing in the Česká rafinérská Litvínov and this technology was the first of its kind worldwide. Production began in the late 1960s and hydrogenates have been and still are produced in high-pressure units originally intended to hydrogenate brown-coal tars. From 1967 until today oil-based fractions from vacuum distillation of petroleum have been used in the production of hydrogenates. The essential feature of hydrogenation is the use of the CHEROX 34-03 catalytic converter that works at a pressure of 22 MPa. This domestic catalytic converter is distinguished by its mild hydrocracking characteristics, high activity, and good selectivity. The produced hydrocracked oils are characterised by their high viscosity index, suitable viscosity, colour, and other properties required for the purposes of producing priming, lubricating, and special oils.

The production of hydrogenates through selective hydrocracking may be adjusted in terms of the choice of the basic raw materials and the resulting viscosity index. Depending on the conversion degree, components of lower viscosity also form and thus the final products are obtained via subsequent distillation procedures. By stripping the petrol fractions we obtain so-called stabilised hydrogenates, which are further modified by distillation in the Koramo distillation unit. In addition to the distillation residue, it is possible to obtain very narrow distillation profiles with precisely specified properties for various special applications. If mid-boiling fractions are stripped from hydrogenates along with the petrol fractions, we obtain the so-called classical hydrogenates. These are used as high-index components in Paramo and Koramo – particularly for motor oils of lower viscosity classes as a substitute for fully synthetic components.