CS237651B1 - Process for preparing the raw material for pyrolysis and alkylation from pyrolysis hydrocarbons - Google Patents

Abstract

The pyrolysis of these hydrocarbons, resulting from ethylene production or cracking, especially from unrefined or partially refined raw materials, especially middle and heavy distillates, is carried out after their hydrogenation in the gaseous, liquid or mixed phase and in the presence of platinum and/or palladium-based catalysts, supported on a suitable carrier, preferably on active alumina, in a concentration of 0.02 to 5% by weight, prepared specifically for this purpose and/or those that were originally intended and possibly used for the purposes of catalytic reforming, hydrogenation removal of acetylenes from pyrolysis products or isomerization. According to the invention, catalysts with a single active component or mixed or promoted ones are used, which were produced on the basis of platinum and/or palladium sulfides, and the hydrogenation is carried out at a temperature of 10 to 250 °C, preferably at 50 to 200 °C, a pressure of 0.1 to 20 MPa, preferably up to 1 MPa, a molar excess of hydrogen to olefins of 1.05 to 25 and a volume flow rate of 1 to JO kg of olefinic feed/kg/hour. The method is intended for increasing the production of ethylene»;

Description

The invention relates to a method for preparing a raw material for pyrolysis from pyrolysis hydrocarbons and cracking hydrocarbons with carbon numbers of 5 and 4 or their mixtures, resulting from the production of ethylene by their hydrogenation in the gaseous, liquid or mixed phase and in the presence of catalysts.

The purpose of the invention is to expand the raw material base for the production of ethylene, possibly also for the alkylation of paraffins with unsaturated hydrocarbons.

The capacity of units for pyrolysis of primary petroleum fractions is constantly growing worldwide, as is the consumption of the basic olefin - ethylene. The sources of the most suitable raw materials for pyrolysis, i.e. light saturated hydrocarbons, are very limited for these purposes, and most processes are therefore based on primary petroleum gasoline, the balance of which is, however, considerably strained. Therefore, the transition is made to higher-boiling fractions, the pyrolysis of which is, however, considerably more complicated and brings a whole range of operational and sales problems.

The formation of ethylene during the pyrolysis of hydrocarbons is associated with the simultaneous formation of higher olefinic fractions, mainly hydrocarbons with carbon numbers of 5 and 4, and in addition liquid fractions of a wide distillation range, such as pyrolysis gasoline and pyrolysis oil, which are rich in aromatics. These by-products also include excess propylene, which is always produced in significant quantities simultaneously with ethylene and is not always fully utilized by Jiljs.

Of the other products, butadiene is currently the most important, followed by cyclopentadiene, isoprene and some aromatics, which are selectively isolated from the pyrolysis by-products. Other chemically valuable products are used much less (recently, isobutylene has been increasingly used for the production of methyl tert-butyl ether) and

- 2 237 651 serves primarily as a fuel, which is highly uneconomical. In the pyrolysis of thermally labile raw materials, some sulfur compounds are used as coking retardants, which appear in the pyrolysis product as such or in the form of HjS, or compounds formed by the reaction of H2S with pyrolysis products. In addition, raw materials with a higher boiling point are increasingly being pyrolyzed, especially kerosene and gas oils, often unsulfurized or partially desulfurized, so that in this case sulfur compounds become a regular part of the pyrolysis products.

A significant source of C5 and C4 hydrocarbons are also cracking processes of higher oil fractions. Cracking is mostly carried out with unsulfurized feedstocks, so the content of sulfur compounds in the cracked products is usually in concentrations determined by the initial sulfur content in the cracked feedstock.

In many of the above cases, the content of sulfur compounds can reach various concentrations, from a few ppm to hundreds of ppm, i.e. concentrations that limit or completely block the efficiency of precious metal catalysts, especially platinum or palladium, during the hydrogenation treatment of these raw materials. In this case, reforming contacts, especially polymetallic ones, with significant oxidation-reduction activity, are particularly sensitive, especially in the area of highest reaction sensitivity, i.e. at lower temperatures /up to 550 °C/, higher volume velocities and low molar excesses of hydrogen.

The above-mentioned shortcomings are eliminated according to the invention by a method of preparing raw material for pyrolysis or alkylation from hydrocarbons with 5 and 4 carbon atoms or their mixtures, arising from ethylene production or cracking, especially from unrefined or partially refined raw materials, especially middle and heavy petroleum distillates, or those whose pyrolysis is carried out in the presence of hydrogen sulfide or other sulfur compounds, added in order to reduce coking, their hydrogenation in the gaseous, liquid or mixed phase and in the presence of platinum and/or palladium-based catalysts, supported on a suitable carrier, preferably on active alumina, in a concentration of 0.02 to 5% by weight, prepared

- 5,237,651 either purposefully and/or those which were originally intended and possibly used for the purposes of catalytic reforming, hydrogenation removal of acetylenes from pyrolysis products or isomerization. Its essence lies in the use of catalysts with a single active component or mixed or promoted ones, which were produced on the basis of platinum and/or palladium sulfides, at a temperature of 10 to 250 °C, preferably at 50 to 200 °C, a pressure of 0.1 to 20 MPa, preferably up to 1 MPa, a molar excess of hydrogen to olefins of 1.05 to 25 and a volume flow rate of 1 to 50 kg of olefinic feed/kg/hour.

The basic effect of the process according to the invention is therefore that it allows the above-mentioned products to be returned to pyrolysis and thereby increase the yield of the desired ethylene. To ensure a high yield of ethylene, it is advantageous to convert these fractions into paraffins by hydrogenation. It is therefore possible to hydrogenate the olefinic by-product mixture directly and feed this hydrogenate directly to the pyrolysis furnace, whereby the saturation of the double bonds can be carried out to the required degree.

According to another feature of the invention, the temperature control in the hydrogenation reactor is carried out by mixing the starting olefinic fraction and the hydrogenate, the olefin content in the raw material being 5 to 45 wt.%.

For hydrogenation, purpose-prepared Pt and/or Pd catalysts or catalysts containing the same active ingredients, but originally intended for reforming gasoline fractions into motor gasoline, for hydrogenation removal of acetylenes in pyrolysis products, either fresh or used, can be used, while the active ingredient can be, in addition to Pt or Pd, another promoter, e.g. Re, etc.

Hydrogen or hydrogen concentrates from other processes can be used for hydrogenation. Suitable hydrogen concentrates are those that are produced during the reforming of gasoline fractions into gasoline, hydrogen from styrene production, hydrogen from electrolytic chlorine production, etc.

To implement the plan, unused equipment originally intended for hydrogenation removal of acetylenes from the pyrolysis fraction before isolation of 1,5-butadiene can be used, thereby saving investment costs.

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- 4 The above hydrogenation process can also advantageously obtain raw material for alkylation of paraffins and olefins. In this way, the necessary excess of isobutane can be easily obtained by hydrogenating isobutylene to the required degree so as to ensure a high yield of alkylate. In the case where pure isobutylene or a mixture with its high concentration is used, a raw material suitable for catalytic alkylation is obtained directly.

According to the invention, the desired technical and economic efficiency is achieved; the process is not apparatus- and energy-intensive.

The method according to the invention is explained in more detail with several examples.

Example 1

Isobutylene was hydrogenated in the gas phase in the presence of a catalyst made on the basis of Pt sulfide /designated PtS/AlsOj, 0.45% Pt/, in a flow reactor at atmospheric pressure. The conversion of isobutylene to isobutane was controlled in a wide range by using different reaction temperatures /50 to 200 °C/, different molar excesses of hydrogen /1.1 to 25/; the advantage of high excesses of hydrogen is the possibility of regulating the temperature regime in the reactor/ and different space velocities. For example, at a temperature of 100 °C, a feed rate of 15 kg isobutylene/kg catalyst/hour. and a molar ratio of isobutylene to hydrogen of 1 : 20, 80% conversion to isobutane was achieved.

Example 2

Under the conditions given in Example 1, for comparison, using the reforming catalyst Pt/Al^O^, /0.6% Pt/, 80% conversion to isobutane was achieved at a temperature of 100 °C, an isobutylene feed of 15 kg/kg catalyst/hour and a molar ratio of isobutylene to hydrogen of 1:20.

Example 5

Isobutylene was hydrogenated in a discontinuous stirred autoclave in the presence of 1 wt. % of the catalyst PtS/Al2O3 (the same catalyst as in Example 1); at an initial hydrogen pressure of 11 MPa (mol. ratio of H2 to isobutylene was 1.5 : 1); at a temperature of 100 °C and a reaction time of 60 min., quantitative conversion to isobutane was achieved.

Example 4

Under the conditions given in Example 3, for comparison, in the presence of the Pt/Al2O3 catalyst (the same catalyst as in Example 2), quantitative conversion to isobutane was achieved at 100°C.

Example 5

Under the conditions given in Example 3, quantitative conversion to isobutane was achieved on a mixed catalyst made on the basis of palladium and platinum sulfides on Al2O5 (ratio of Pt to Pd 1:1, content of both metals on alumina was 0.6%).

Example 6

Under the conditions given in Example 1, instead of pure isobutylene, the C4 fraction /composition: 1.8% isobutane, was hydrogenated.

12.5% n-butane, 75.2% isobutylene, 7.8% 1-butene, 2.5% cis-2-butene and 0.2% trans-2-butene/, with 78% saturation of double bonds in the raw material.

Example 7

Under the conditions given in Example 3, quantitative saturation of double bonds was achieved during hydrogenation of the C4 fraction.

Example 8

Propylene containing 50 ppm hydrogen sulfide in the cross-section was hydrogenated at 2 MPa in a continuously operating adiabatic flow reactor. The hydrogenation was carried out in the presence of a sulfurized Pt/AlO catalyst with a feed rate of 10 l of liquid propylene/l catalyst/hour, at a molar ratio of propylene : H2 = 1 : 1.2 and an inlet temperature of the mixture of 150 °C; 85% conversion of propylene to propane was achieved.

Example 9

Under the same reaction conditions as in Example 8, in the presence of Pt-Pd/AlO catalyst/total metal content

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- 6 1.2% wt., weight ratio Pt : Pd = 1 : 5/, produced from the sulphide form, achieving propylene conversion above 95%

Example 10

Under the same conditions as in Example 8 (mol. ratio olefins:H2 = 1:1.5, injection rate 10 l/l/hour), a C4 fraction containing 25 wt. % olefins and 50 ppm S in the Αθ form of dimethyl sulfide was hydrogenated, achieving approximately 90% hydrogenation of the unsaturated hydrocarbons present.

Example 11

A tubular reactor, which was originally intended for hydrorefining, in which the acetylenes contained in the C4 fraction were removed before 1,5-butadiene was isolated, can also be used for hydrogenation of the pyrolysis C4 fraction.

The C4 pyrolysis fraction can be dosed as a raw material as it is discarded from the separation of pyrolysis products, as well as ^{the C4} pyrolysis fraction after separation of the contained 1,5-butadiene by extractive distillation, using dimethylformamide, or the C4 pyrolysis fraction after separation of the butadiene and the contained isobutylene, whereby the contained isobutylene was converted to ethyl tert-butyl ether.

The composition of the processed C4 fraction was as follows:

Pyrolysis C4 fraction after separation of 1,5-butadiene /% wt./ after separation of 1,5-butadiene and iso butylene /% wt./ alkanes 20.76 55.85 propadiene, methylacetylene and residual 1,5-butadiene 0.88 1.52 alkenes 78.56 , 62.65

The processed C4 fraction contained predominantly C4 hydrocarbons, the content of C2 and C5 hydrocarbons was 4.15 and 7.15 wt%, respectively.

In order to maintain the reaction temperature within the required limits, the fresh O4 fraction was diluted with hydrogenate so that the resulting mixture contained unsaturated hydrocarbons usually in the range of 5 to

%.

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The hydrogenation of the pyrolysis C4 fraction after separation of 1,3-butadiene and isobutylene was carried out under the following conditions:

a tubular reactor containing 30 tubes with an internal diameter of 57 mm, a length of 1 m contained 250 l of tableted PtS/AlO catalyst containing approximately 0.6 wt. % Pt.

2,330 kg of pyrolysis C4 fraction diluted with 3,300 kg of hydrogenate and 1,650 Nn^ of hydrogen from the reforming of gasoline containing 75 vol. % hydrogen, 17.1 vol. % methane, 6.9 vol. % ethane and 6 vol. % other hydrocarbons were dosed per hour.

The reaction temperature was in the range of 60 to 183 °C and the inlet pressure was 0.45 MPa. The hydrogenate obtained contained 1.9 wt. % unsaturated hydrocarbons. The separated hydrogen was not recirculated. The intertube space was cooled with water.

Claims (2)

1. A process for the preparation of a feedstock for pyrolysis or alkylation from pyrolysis hydrocarbons having a carbon number of 5 θ 4 or mixtures thereof resulting from the production of ethylene, in particular from unrefined or partially refined feedstocks, in particular medium and heavy petroleum distillates, or the presence of hydrogen sulphide or other sulfur compounds added to reduce coking by hydrogenating them in the gas, liquid or mixed phases and in the presence of platinum and / or palladium catalysts supported on a suitable support, preferably active alumina, at a concentration of 0, 02 to 5% by weight of the prepared beeches and / or those originally intended and possibly used for the purposes of catalytic reforming, hydrogenation removal of acetylenes from pyrolysis products or isomerization, characterized in that single active catalysts are used component or mixed, optionally promoted, which have been produced on the basis of platinum and / or palladium sulfides, at a temperature of 10 to 250 ° C, preferably at 50 to 200 ° C, a pressure of 0.1 to 20 MPa, preferably up to 1 MPa, by molar excess hydrogen to olefins of 1.05 to 25 and a bulk rate of 1 to 50 kg of olefin feed / kg / hr. 2. Process according to claim 1, characterized in that the temperature control in the hydrogenation reactor is carried out by mixing the starting olefinic fraction and the hydrogenate, the olefin content of the feedstock being 5 to 45% by weight.