CS231730B1 - Preparation of hydrocarbon liquid for pyrolisis to gaseous unsaturated hydrocarbon - Google Patents

Abstract

The invention relates to improving the quality of the liquid hydrocarbon feedstock for gaseous pyrolysis unsaturated hydrocarbons by catalytic combination catalyst hydrotreating containing metal sulfides on aluain and catalytic dearomatizacl on catalysts containing platinum, or rhenium on alumina containing chlorine and thiamine dioxide. The raw material for pyrolysis is obtained, providing high yield of unsaturated gaseous hydrocarbons.

Description

The present invention relates to a process for treating a liquid hydrocarbon feedstock for pyrolysis to gaseous unsaturated hydrocarbons by combining two catalytic processes at medium hydrogen pressures and obtaining a feedstock for pyrolysis providing a greater yield of gaseous unsaturated hydrocarbons. '

Gaseous unsaturated hydrocarbons, es. ethylene, propylene or butadiene are the basic raw materials for a wide range of organic substances used in all sectors of human activity. They are obtained by pyrolysis of petroleum hydrocarbon mixtures of different composition according to the quality of the oil, but mostly from alkane gasoline or kerosene containing both mono- and bicycles! Aromatic aromatics, olefins and nitrogen compounds, possibly contaminated with heavy metals. Each of the impurities and by-products is unfavorable in pyrolysis, reducing gas yields and fouling the pyrolysis device.

There are a number of solutions to improve the quality of pyrolysis raw materials. Known processes are used to remove impurities and impurities or reduce their concentrations. These are adsorption processes to remove heavy metals, extraction of aromatic hydrocarbons and olefins, hydrogenation desulphurisation or high pressure hydrogenation of aromatics on sulfide catalysts, or low pressure hydrogenation on precious metals such as nickel or platinum.

The invention provides a variant in which a process modification using modern low-platinum catalysts for catalytic hydrogenation is used to improve the quality of the liquid hydrocarbonaceous feedstock.

A method for improving the quality of a liquid hydrocarbon feedstock for pyrolysis to gaseous unsaturated hydrocarbons, in particular petroleum naphtha, by combining hydrogenation refining on mixed sulfur catalysts and pressure dearofflateization on supported catalysts containing precious metals under hydrogen pressure and at elevated temperatures the mixture having a boiling point of 30 to 250 ° C, preferably 100 to 190 ° C, leads to a distillation column with 5 to 20 plates and a distillation residue depleted of light hydrocarbons into C _r , hydrogen sulphide, water and sulfur content ωβχ. up to 50 ppm is introduced into two to four catalyst layers containing 0.2 to 0.5 wt. rhania on alumina with 0.05 to 5 wt. titanium dioxide,

0.1 to 0.5 wt. % sulfur and 0.5 to 1.5 wt. chlorine together with hydrogen which circulates at least 90% of the working time through a desiccator, eg alumina or molecular sieve, at a pressure of 2 to 3 MPa, at a volumetric rate of 0.5 to 1.5 volumes per catalyst volume per hour. at progressively higher temperatures at the entrances to the reaction layers of 5-50 G ⁿ in the range from 180 to 250 ° C on the first layer.

The process of the invention thus involves the treatment of petroleum naphtha over a wide distillation range, or gasoline fractions, particularly heavy, possibly also in admixture with petroleum petroleum fractions. Other raw materials from secondary sources or non-petroleum sources not yet suitable for pyrolysis are not excluded.

It has been found by a number of tests that the hydrogenated platen-rhenium catalyst defined in the present invention has a high saturation property at a low water concentration to which it is more sensitive than conventional catalysts. However, it is economically more advantageous than catalysts with high noble metal contents. Also, the hydrogenation conditions of the aromatics in the second stage are an important feature of the invention, since by varying the inlet temperatures, it is necessary to decompose the hydrogenation to the optimum temperature range and to avoid the transition to the dehydrogenation region. One working pressure is used for this.

Thus, the main effects of the process of the invention over other similar processes are low energy demands due to low temperatures and reduced catalyst costs, which contain practically lower concentrations of particularly precious metals and are less supplied to the reaction space. Due to the effect of using the product to produce pyrolysis gases, the advantage of the first process is also the maintenance of the concentration of n-alkanes in the product. This is achieved by selecting a non-catalyst catalyst and reaction conditions. It is known that the yield of ethylene from n-allran versus i-alkane with the same number of carbon is three to four times.

The main data for illuminating the process according to the invention are given in the following example.

Example

The pyrolysis feedstock was selected from heavy naphtha, the analytical values of which are given in Table 1 below, and the hydrogenation products thereof on a catalyst containing 4 wt. % CoqSq and 12 wt. MoS _o on gamma alumina under the following conditions:

reaction pressure

IHSV (volumetric rate)

H _g: Temperature CH

The product was on a column of about 20 TP at a pressure of light hydrocarbons Cg to 0.

3.0 MPa v / v kot. h 250 v / v

300 [deg.] C

0.25 MPa free of HgS and HgO dissolved

It led to three-stage hydrogenation points:

P; CH

L1ISV (vol. Velocity) temperature catalyst unit where it dearomatizevel at these below 3.0 MPa

00Θ obj./obj.

and 2 v / v h 150-400 ° C

0.3 wt.%, Pt and 0.30 wt. Ko on alumina · - 0.7 wt. chlorine and 0.15% pot. Ϊ: 0 ,,

Table 2 shows the hydrogenation results using a dried gas with a moisture content below 10 ppm vol. The temperature on the 3rd catalyst layer is shown (the temperatures in the 1st and 2nd layers were reduced by 10 and 5 ° C, respectively).

It can be seen from the table that deep dearoraatt zuei occurs in the temperature range protected by the invention when drying t-3: · ui and virtually complete removal of olsfins. The yield of the liquid product is greater than 100% by weight. At an optimum ca 80% oderatisation, with the same pyrolysis sharpness, 10% more light unsaturated hydrocarbons and less aromatic gasoline are obtained from the same feed rate. In addition, the choice of heavy naphtha containing predominantly C _{o +} aromatics in aromatics results in their content being reduced by pyrolysis

Gasoline decreases and increases by this Table 1 Cg concentration up to Cg of aromatics. Characteristics of raw material for pyrolysis a of its products after 1 . degree hy drugstore invention. raw material product ^d 20 0,766 0,764 distillation curve ° C beginning 130 120 10% vol. 142 140 50% vol. 147 146 90% vol. 160 160 95% vol. 164 1 64 end 1 77 175

With ppm Br - index mg Br / 100 g aromatics raw material 950 750 12.9 product under 1 160 12.7 Table 2 Influence of temperature on dearomatization desulphurised raw materials. temperature ° C 150 200 250 300 350 LHSV i, 0 1.0 1.0 1.0 1.0 obj./obj. h ^d 20 0,766 0.765 0.760 0.760 0,761 Br - index 33 9 8 29 257 mg Br / 100 g % aromatics 12.7 ’ 10.1 3.8 1.9 4.7 dearomatizace 0 20.4 70.0 84.7 63.0 Similar results have reached in • first stage with a catalyst containing 2.5 % COgSg,

1.6% Ni ^ Sg β 14% MoSg and in the second stage with a catalyst containing 0.6% wt. Pt free from titanium, chlorine and sulfur.

When the fraction 100 to 170 ° C was dearomatized on the same Pt Re catalyst, the aromatics were reduced from 8.5 wt. % to 1.5 wt. and the naphthenic content increased to 31 wt. This concentration of naphthenes is also suitable in the raw material for pyrolysis.

The product obtained by the process of the invention had a molar ratio of n-alkanes to i-alkanes in the range of hydrocarbon numbers 6 to 10 on average 2: 1 according to mass spectrometric analysis associated with gas chromatography. In similar processes, omitting some feature of the invention (elevated temperature especially due to the lack of control of the exothermicity of aromatic hydrogenation), a ratio of up to about 55 mole% of n-alkanes in the alkane β mixture resulted in up to 30% methylcyclopentanes from aromatics.

Claims (1)

Process for the treatment of liquid hydrocarbon feedstock for pyrolysis to gaseous unsaturated hydrocarbons, in particular petroleum naphtha, by a combination of hydrotreating on mixed sulphide catalysts and pressure dearomatization on supported catalysts containing precious metals under hydrogen pressure at elevated temperatures, characterized in that the desulphurized hydrocarbon mixture 30 to 250 [deg.] C., preferably 100 to 190 [deg.] C., is fed to a 5 to 50 tray distillation column and the distillation residue free of light hydrocarbons in, hydrogen sulphide and water and having a sulfur content of up to 50 ppm is introduced into two to four layers of catalyst containing 0.2 % to 0.5 wt. % platinum and 0.2 to 0.5 wt. rhenium on alumina with 0.05 to 5 wt. % of titanium dioxide, 0.01 to 0.5 wt. % sulfur and 0.5 to 1.5 wt. chlorine together with hydrogen, which circulates at least 90% of the working time through a desiccator, eg alemine or molecular sieve, at a pressure of 2 to 3 MPa, at a volume rate of 0.5 to 1.5 volumes per catalyst volume per hour and gradually increasing the inlet temperatures of the reaction layers by 5 to 50 ° C in the range of 180 to 250 ° C on the first layer.