CS237189B1 - A method for producing a dearomatized n-hexane concentrate with a reduced methylcyclopentane content - Google Patents

Abstract

The invention describes the production of dearomatized n-hexane concentrate for Ziegler polymerization of olefins with a reduced concentration of methylcyclopentane by catalytic hydrogenation coupled with isomerization of methylcyclopentane on a platinum catalyst supported by alumina activated with aluminum chloride under conditions that achieve a small isomerization of n-alkanes to i-alkanes.

Description

The invention describes the production of dearomatized n-hexane concentrate for Ziegler polymerization of olefins with a reduced concentration of methylcyclopentane by catalytic hydrogenation coupled with isomerization of methylcyclopentane on a platinum catalyst supported by alumina activated with aluminum chloride under conditions that achieve a small isomerization of n-alkanes to i-alkanes.

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c 07 C 9/15, C 10 G 45/62

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The invention relates to a process for producing dearomatized n-hexane concentrate with a reduced methylcyclopentane content by pressure hydrogenation in the presence of a platinum catalyst on a support formed by alumina and activated by aluminum chloride.

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Concentrates of n-hexane are very advantageous solvents in Ziegler polymerizations of olefins, because they excel in inertness to the reaction mixture and thus guarantee the formation of advantageous types of polymers, e.g. in the polymerization of propylene or ethylene-propylene, etc. In addition, their properties guarantee low catalyst deactivation and a reduced concentration of volatile components in the resulting polymerization product. The prerequisite is a low content of aromatic and unsaturated hydrocarbons and an adequate concentration of methylcyclopentane.

A maximum of one tenth of a percent of benzene and olefins are permitted. The concentration of methylcyclopentane should not exceed the order of a percent. However, the raw materials from which this concentrate is produced do not meet the strict requirements and must be complexly treated chemically and physicochemically. Desulfurized light petroleum gasoline contains hydrocarbons up to C?, in which, depending on the type of crude oil, there are up to several percent of benzene, the content of unsaturated compounds, characterized by the bromine index, is usually several hundred mg Br/100 g and the ratio of n-hexane to methylcyclopentane is usually up to 1:1 by weight. The removal of benzene and olefins is mainly carried out by catalytic hydrogenation in the vapor phase under pressure in the presence of platinum or nickel or tungsten and nickel oxides or molybdenum and nickel on alumina. The hydrogenation of benzene in particular is demanding from an energy point of view and from the point of view of the need for high conversion. Low volume rates and high operating pressure are chosen. The separation of n-hexane and methylcyclopentane is always a problem due to the close boiling points and decreasing the ratio of n-hexane to methylcyclopentane worsens the yield of n-hexane concentrate with a defined concentration of methylcyclopentane and n-hexane.

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- 2 The invention provides a new solution for the production of dearomatized n-hexane concentrate with a reduced methylcyclopentane content for Ziegler polymerization of olefins consisting of pressure hydrogenation in the presence of a platinum catalyst on a support formed by alumina and activated aluminum chloride. It is characterized in that the mixture of up to C? hydrocarbons, preferably Cg hydrocarbons with a boiling point in the range of 20 to 80 °C, is introduced with a gas containing hydrogen and hydrogen chloride under a pressure of 2 to 10 MPa and with 20 to 2000 ppm of a chlorinated hydrocarbon with at least two chlorines on one carbon at a temperature of 70 to 200 °C and with a space velocity of 0.5 to 8 h”' ¹ ' onto a catalyst containing 0.2 to 0.8 wt. % platinum on gamma-alumina with 5 wt. % chlorine and with a hydrogen to hydrocarbon ratio of 0.5 to 5 molar in a practically anhydrous environment and from the product, first all C^ hydrocarbons are separated by rectification, then a larger part of the iso-C hydrocarbons and then a 70 to 95% n-hexane concentrate.

The input mixture consists of 10 to 60 wt. % C^-hydrocarbons and the remainder consists of Cg-hydrocarbons including benzene. The mass ratio between methylcyclopentane and n-hexane is 1:1 to 1:2 by mass, the benzene content is 0.2 to 5 wt. %. The mixture originates from the distillation of crude oil and/or from the distillation of other secondary products from crude oil, e.g. from reformate. The liquid hydrocarbons emerging then contain below 0.05 wt. % benzene, preferably below 0.01 wt. %, the mass ratio between methylcyclopentane and n-hexane is 1:2.5 to 1:5 with a reduction in the n-hexane content of 5 to 30 % relative. Preferably, a mixture with 10 to 40 wt. % C^-hydrocarbons is used in addition to predominantly Cg-hydrocarbons with a methylcyclopentane to cyclohexane ratio of 2 to 10:1 by mass. and a circulating gas with 70 to 95 vol. % hydrogen in addition to C^ to saturated hydrocarbons and 10 to 2000 ppm vol. hydrogen chloride. Preferably, a temperature of 90 to 140°C, a space velocity of 2 to 6 h"\ 50 to 200 ppm chlorinated hydrocarbons, especially tetrachloroethane, and a molar ratio of hydrogen to hydrocarbons of 1 to 3 are further selected.

The analysis of the invention reveals a number of advantages over the prior art. It is clear from the description that the reaction is carried out in the liquid phase under very favorable energy conditions (low temperature, low gas circulation, high space velocity). The described catalyst is also used for the isomerization of n-alkanes C^ to Cg at temperatures of 130 to 220 °C with a lower space velocity. The conditions specified in the feature of the invention allow the isomerization catalyst to practically completely remove benzene (possibly also other aromatics), isomerize methylcyclopentene to a state close to equilibrium with cyclohexane, while only slightly isomerizing n-alkanes, especially n-hexane. It is also clear from the description that the milder conditions allow the operating cycles to be extended, since the formation of coke on the catalyst surface is almost completely prevented. The range of conditions also includes higher temperatures, which implicitly includes the use of a catalyst partially deactivated in the reaction space, with prior isomerization of C^ to Cg-alkenes, in particular with water and coke. It also follows from the description that the described production can be carried out on units used for low-temperature isomerization of C^ to Cg hydrocarbons.

The reduced concentration of methylcyclopentane in the mixture with n-hexane and the overall composition of the product allows for a significantly more productive isolation of n-hexane concentrate on superfractionation columns. It is possible to choose an increased hourly amount of injection into the distillation column, increase the yield of n-hexane and reduce its losses. Economically, this means a reduction in the energy requirements of superfractionation separation, i.e. saving steam for heating the columns.

If the new process replaces the old one, implemented in the co-extraction of aromatics from aromatic raw materials, e.g. reformates, there are energy savings and possibly an increase in capacity in parallel production of aromatics. All of these advantages are included in the implementation of the invention in the refinery.

Although the description of the invention clearly shows all the advantages, an example is provided to illustrate the invention in even more detail.

Example

From petroleum gasoline after hydrotreating, the C^ to Cg fraction was separated by rectification, the composition of which is given in Table 1.

The fraction was dried with a mixture of molecular sieve and alumina to a moisture content below 1 ppm wt. and together with 200 ppm carbon tetrachloride and a gas containing 85% by volume hydrogen next to C^ to C^

- */ 237 189 hydrocarbons saturated in a molar ratio of 1:3 were fed under a pressure of 3.5 MPa into a reactor containing a platinum catalyst. Catalyst composition: 0.35 wt. % platinum, 5 wt. % aluminum chloride on alumina. Space velocity 2.0 vol. fraction/vol. cat. h”^, reaction temperature 120°C. Table 1 shows the chromatographic composition of the product.

The table shows that benzene was practically completely hydrogenated, methylcyclopentane was partially isomerized to cyclohexane and alkanes were isomerized to a very small extent. The product was distilled twice on an 80-tray column to obtain n-hexane concentrate, ^which was practically completely free of benzene and olefins and contained less methylcyclopentane compared to the commercial product prepared from the same raw material by a combination of liquid extraction of aromatics and rectification. (Table 2)

Conditions for obtaining n-hexane concentrate superfractionation

nations changed as a result of the invention: old procedure new procedure degree no. 1 2 1 -'·· 2 spray m^/h 10 2-3 21 3-4 loss of n-hexane % - 30 - 10 steam consumption t/t 1.5 1.5 0.5 1.2 From the comparison it is clear, even that the energy level 1 difficulty

increased three times, that the losses of n-hexane according to the invention were one third of the losses in the conventional process.

The effect of introducing the process according to the invention was also manifested in the refinery in that the aromatics extraction capacity was released by 14-15%. It was possible to increase production proportionally or save energy in the stated proportion for the same production.

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Table 1

Composition of the CL-Cg-fraction from crude oil (raw material for n-hexane production) and the product. product Hydrocarbon raw material butane 3.8 3.8 i-pentane 21.3 23.0 n-pentane 32.2 30.5 i-hexane 23.2 27.0 n-hexane 12.7 H,9 methylcyclopenta n 5.0 2.5 cyclohexane. 0.8 3.2 benzene 0.4 0 ⁺ C^ ₊ hydrocarbons 0.6 0 olefins according to Br-index mg Br/100 g 8 1 ratio nCg/McC^ 2.54 4.76

according to UV spectrometry - below 10 ppm

Table 2

Comparison of commercial n-hexane concentrate with the product of the invention.

Claims (6)

Process for the preparation of a dearomatized n-hexane concentrate with reduced methylcyclopentane content for Ziegler polymerization of olefins by pressure hydrogenation in the presence of a platinum catalyst on an alumina-activated aluminum chloride support, characterized in that the mixture Cg to C? hydrocarbons, preferably Cg and Cg hydrocarbons having a boiling point of 20 to 80 ° C, reports with a gas containing hydrogen and hydrogen chloride at a pressure of 2 to 10 MPa and 20 to 2000 ppm chlorinated hydrocarbon with at least two chlorines per carbon at 70 to 200 ° % At a volumetric rate of 0.5 to 8 h ^-1 per catalyst containing 0.2 to 0.8 wt. % platinum on gamma-alumina with 5 wt. of chlorine with a ratio of hydrogen to hydrocarbons of 0.5 to 5 molar in practically anhydrous medium and from the product first all Cg hydrocarbons and most of the isomeric Cg hydrocarbons are separated by rectification and then 70 to 95% n-hexane concentrate. 2. Process according to claim 1, characterized in that the feed mixture consists of 10 to 60 wt. The C ^-hydrocarbons and the remainder are predominantly Cg-hydrocarbons, including benzene, wherein the weight ratio between methylcyclopentane and n-hexane is 11, the benzene content is 0.2 to 5% by weight. and the blend comes from the distillation of crude oil and / or from the distillation of other secondary petroleum products, reformate. 3. Process according to claim 1 or 2, characterized in that the exiting liquid hydrocarbons contain below 0.05% by weight. % benzene, preferably below 0.01 wt%, the weight ratio between methylcyclopentane and n-hexane is 1: 2.5 to 1: 5 while reducing the n-hexane content by 5 to 30% relative. 4. Process according to claim 1, characterized in that a mixture with 10 to 40 wt. The C8 hydrocarbons, in addition to the predominantly C8 hydrocarbons, have a methylcyclopentane: caclohexane ratio of 2 to 10: 1 wt. and circulating gas with 70 to 95% by volume of hydrogen in addition to % Of saturated hydrocarbons and from 10 to 2000 ppm by volume of hydrogen chloride. 237 189 5. Process according to claim 1, characterized in that a temperature of 90 to 140 ° C, a volumetric rate of 2 to 6 h ^-1 , 50 to 200 ppm of a chlorinated hydrocarbon, in particular carbon tetrachloride, and a molar ratio of hydrogen to hydrocarbons are preferably selected. 1 to 3 6. The method of claim 1, wherein the gas and liquid streams supplied contain less than 1 ppm by volume or less. .hmot. water.