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TENDENCY OF ISOMERIZATION PROCESS DEVELOPMENT （1）
TENDENCY OF ISOMERIZATION PROCESS DEVELOPMENT
IN RUSSIA AND FOREIGN COUNTRIES
E.A. Yasakova, A.V. Sitdikova
Ufa State Petroleum Technological University
Problems of Russian Refineries in term of toughening of requirements to up-to-date automotive gasoline quality are considered in the article. Review of existing technologies of isomerization process and their main performances are represented here. The data about existing state of isomerization process and tendency of development of this process in Russia and foreign countries are given in the article.
Keywords: isomerization process, high-quality gasoline, isomerization catalyst, technology of isomerization process, reducing of benzene content in gasoline
1. TOUGHENING OF UP-TO-DATE GASOLINE REQUIREMENTS
In worldwide production of automotive gasoline permanent tendency to the toughening of not only its operating but also its ecological characteristics is observed.So, international and domestic regulations to automotive gasoline considerably limit the content of benzene, aromatic hydrocarbons, olefin hydrocarbons and sulfur.
The special technical regulation “About requirements to gasoline, diesel and some fuels and lubricants” was approved in Russia since February of 2008. The date of Euro-2, 3, 4, 5 ecological class automotive gasoline productions are defined in it.
Particularly it is necessary to switch over the automotive gasoline of Euro-4 class production with aromatic compounds content equal 35 % including benzene content less than 1 % since 1-st January of 2012 [1,2]. The benzene limits up to 0.96 % have already been introduced in USA currently. The Regulations Mobile Source Air Toxics (MSATII), which limit the benzene content in gasoline up to 0.62 % become operative since 1st
January of 2011 .
In 1970s the variants of hydrogenation of the benzene, contained in the reformate, proceeding without the decrease of product octane number have been offered .
However for decrease of the total aromatics content the dilution of reformate (being the base component of high-octane gasoline in Russia) with high-octane nonaromatic components is required. This situation is complicated by refusal from tetraethyl lead (TEL) and deficit of butane-butylene fraction (because of the lack of FCC duty), which is used for the production of high-octane alkylate in the world practice.
Thereby the development of isomerization process is one of the effective methods for solution of this problem. It allows the producing of commercial gasoline which corresponds to the current and perspective requirements to the fuels and provides necessary flexibility of processing.
2. TYPES OF ISOMERIZATION PROCESSES
Three types of industrial isomerization processes are worked out currently [5, 6]:
― high-temperature isomerization process (360-440 °\u1057X) on fluorinated-alumina catalysts;
― medium-temperature isomerization process (250-300 °\u1057X) on zeolite catalysts;
― low-temperature isomerization process on chlorinated-alumina catalysts (120-180 °\u1057X) and sulfated metal oxides (180-210 °\u1057X).
3. THERMODYNAMIC AND KINETIC LAWS OF ISOMERIZATION PROCES
The schemes of proposing processes are analogous generally. The differences are defines by performances of usable catalysts due to their type. Main parameter which is the octane number of produced isomerizate depends on process temperature.
That’s why we will dwell on the issue of thermodynamic of isomerization reaction. First of all hydrocarbons isomerization reaction is balanced reaction, and equilibrium yield of isoparaffins increases with temperature reducing, but it can be reached only after an “infinite residence time” of the feed in reaction zone or an equivalent very small value for LHSV. On the other hand an increase in temperature always corresponds to an increase in reaction velocity. So that at low temperature the actual yield will be far below the equilibrium yield, because of low reaction velocity. On the contrary, at higher temperature, the equilibrium yield will be more easily reached, due to a high reaction rate. Consequently, at higher temperature the yield of isoparaffins is limited by the thermodynamic equilibrium, and at lower temperature it is limited by low reaction rate (kinetic limitation) (Figure 1) .
The comparative estimation of isopentanes content in sum of pentanes for different types of isomerization catalysts is represented below (Figure 2) .