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Comparative Characteristics of Different Isomerization Technologies
At the present time there are three types of light naphtha isomerization processes in oil refining that differ in type of used catalysts: zeolite, chlorinated alumina and sulphated oxide catalysts.
Zeolite catalysts have sufficiently wide application in the refining due to its relative stability to sulphur and water influence. However, along with it, zeolite catalysts have one significant disadvantage: they are able to work in 250-300°С temperature range only, in which the methane hydrocarbons isomerization reactions thermodynamics is unfavourable for high-branched isomers formation. Therefore, octane number of pentane-hexane fraction of isomerate (isomerizate) cannot be more than 78-79 RON. In addition, an insufficient concentration of high-branched isomers in isomerate makes the recycle schemes with low octane isomers noncompetitive.
Chlorinated alumina catalysts has gained wider application in refining due to their operating temperature range that amounts to 130-170°С, and therefore the depth of isomerization and the octane number of the isomerate are considerably increased. The octane number of "once-through-run" isomerate (isomerizate) is 82-84 RON and the recycle flow charts of low octane isomers allow receiving the isooctane component, having 86-92 RON. Along with it, the technology based on chlorinated catalysts has serious disadvantages:
● the catalysts are notable for extremely high sensibility to the influence of trace sulphur, nitrogen and water. Contaminants content in feed must be less than 0,1 ppm, so they require special hydrogenate aftertreatment adsorption blocks. Skips of contaminants result in irretrievable activity losses of the catalysts;
● to set off the chlorine losses in the catalysts, the regular feeding of organochlorine compound to the reactor block and the alkaline scrubber unit to remove hydrogen chloride from the reaction products are required. The unit gains caustic wastes subject to utilization.
In connection with the above-mentioned disadvantages of the chlorinated alumina catalysts, research and development of new effective isomerization catalysts has been constantly conducted. The main direction of the research was development of such catalysts that could work effectively at low temperatures, but would be considerably more stable to the influence of catalyst poisons.
In the beginning of this decade such catalyst (SI-2) and such isomerization technology over the catalyst (Isomalk-2™) had been developed by JSC SIE Neftehim.
The commercial application of Isomalk-2™ technology began in 2003. Seven isomerization units operate now over this technology: five units in Russia, one unit in Ukraine and one unit in Romania. Besides, four units are in design and construction stages.
Prompt recognition of Isomalk-2™ technology is conditioned by the good performance of operating isomerization units.
The comparative analysis of isomerization technology types is presented in the table below
Thus, Isomalk-2™ technology has the advantages not only over technologies based on the zeolite and chlorinated catalysts, but also over the single industrial analogue based on the sulphated oxide catalysts – ParIsom. In 2006 the isomerization unit in Romania that had been operated over the ParIsom technology, was converted to Isomalk-2™ technology. The isocomponent octane number increased by 5 points and brought to 88 RON (unit with DIH column).
Isomalk-2™ technology can process both pentane-hexane fractions and fractions containing considerable quantities of benzene and C7 hydrocarbons.
In each case, subject to Customer's preference, we develop optimal technological design which provides required parameters for octane number and nonaromatic autocomponents yield.