Improvement of the technological scheme of the installation of low-temperature isomerization of light gasoline fraction

The isomerization processes of paraffin hydrocarbons ensure a reduction in the content of aromatic and low-octane hydrocarbons in gasoline. The octane number of a commercial isomerizate largely depends on the clarity of separation of the components of the isomerization reaction mass and the degree of recirculation of non-converted paraffin hydrocarbons of normal structure. The reaction mass of the technological installation for low-temperature isomerization of the light gasoline fraction PGI-DIH, together with the target products, contains low-branched and normal hydrocarbons, in particular, up to 12% by weight of n-pentane is present in the industrial isomerizate, which degrades the quality of the commercial isomerizate due to its low octane number (RON=61.7). One of the flows of the technological scheme forming the isomerizate flow from the installation is the distillate of the deisohexanizer column, the content of n-pentane in which is up to 14.6% by weight therefore, in industrial conditions, it is advisable to extract it from the distillate of the deisohexanizer with subsequent recycling into the raw material stream. The paper proposes a change in the technological scheme of a low-temperature isomerization installation in order to maximize the extraction of raw hydrocarbons from a stable isomerizate by including a system of two additional distillation columns Cadd and DP. The research was carried out using the Honeywell Unisim Design modeling program. The calculations performed show the appropriate technological modes of operation and structural parameters of the columns: the Cadd column contains 61 three-flow valve plates, the pressure in the column Pbot = 245kPa and Ptop = 196kPa, the temperature Treb = 81.7 °С and Tcond = 47.9 °С; the DP column has 60 two-flow valve plates, the pressure Pbot = 400kPa and Ptop = 200kPa, temperature Treb = 83.4 °С and Tcond = 45.5 °С. The proposed technological scheme provides almost complete extraction of n-pentane (99.9% by weight) from a stable isomerizate with a simultaneous increase in its octane number by 2 points.