Reduction of losses of the initial n-hexane reactant with commercial isomerizate

Abstract

The isomerization processes of paraffin hydrocarbons ensure a reduction in the content of aromatic and low-octane hydrocarbons in gasoline. The octane number of the commercial isomerizate used in compounding in gasoline depends on the clarity of separation of the components of the isomerization reaction mass, in particular, the presence of non-converted reactants in it leads to a decrease in the octane number and loss of these raw material components. The commercial isomerization unit of a typical low-temperature isomerization unit of the light gasoline fraction PGI-DIG, together with the target products, contains low-branched and raw normal hydrocarbons, in particular, n-hexane is present, which degrades the quality of the commercial isomerization due to its low octane number (OCI= 25). One of the flows of the technological scheme forming the commercial isomerizate from the installation is the cubic product of the deisohexanizer column, the content of n-hexane in which is up to 3.5% by weight. Therefore, in industrial conditions it is advisable to extract it from the cubic product of the deisohexanizer with subsequent recycling into the raw material stream. The paper proposes a change in the technological scheme of the low-temperature isomerization installation in order to reduce the loss of raw hydrocarbons with commercial isomerization by including an additional Kdop distillation column in it. The research was carried out using the Unisim Design modeling program. The calculations performed have obtained appropriate technological modes of operation and structural parameters of the Kdop column: the number of single-flow valve plates is 30, the pressure in the Rniz column = 160kPa and Rvc = 110kPa, the temperature in the reboiler and condenser is 102.4 and 81.3 ℃, respectively, the phlegm number R = 2.5. The inclusion of an additional Kdop distillation column in a typical technological scheme ensures a reduction in losses of n-hexane with commercial isomerizate by 1.78% while simultaneously increasing its octane number by up to 2.4 points.