CS231730B1 - A method for treating a liquid hydrocarbon swovirty for pyrolysis to unsaturated hydrocarbon gas - Google Patents

Abstract

The invention relates to improving the quality of liquid hydrocarbon feedstock for pyrolysis into gaseous unsaturated hydrocarbons by combining catalytic hydrorefining on a catalyst containing metal sulfides on alumina and catalytic dearomatization on catalysts containing platinum or rhenium on alumina containing chlorine and titanium dioxide. A feedstock for pyrolysis is obtained, providing a high yield of unsaturated gaseous hydrocarbons.

Description

The invention relates to a method for converting liquid hydrocarbon feedstock for pyrolysis into gaseous unsaturated hydrocarbons by combining two catalytic processes at medium hydrogen pressures and obtaining a feedstock for pyrolysis providing a higher yield of gaseous unsaturated hydrocarbons.

Gaseous unsaturated hydrocarbons, e.g. ethylene, propylene, or butadiene, are basic raw materials for a wide range of organic substances used in all branches of human activity. They are obtained by pyrolysis of petroleum hydrocarbon mixtures of various compositions depending on the quality of the oil, but mainly from alkane gasolines or kerosene, containing mono- and bicyclic aromatics, olefins and nitrogen compounds, or contaminated with heavy metals. Each of the impurities and secondary components has an adverse effect on pyrolysis, reduces gas yields and clogs the pyrolysis equipment.

There are a number of solutions that can improve the quality of raw materials for pyrolysis. Known processes are used to remove impurities and impurities or reduce their concentration. These include adsorption processes for removing heavy metals, extraction of aromatic hydrocarbons and olefins, hydrodesulfurization or high-pressure hydrogenation of aromatics on sulfide catalysts, or low-pressure hydrogenation on noble metals such as nickel or platinum.

The invention provides a variant in which the quality of the liquid hydrocarbon feedstock is improved by modifying the process using modern low-platinum catalysts for efficient hydrogenation.

A method of improving the quality of liquid hydrocarbon feedstock for pyrolysis into gaseous unsaturated hydrocarbons, especially petroleum gasolines, by combining hydrorefining on mixed sulfide catalysts and pressure dearoflatization on supported catalysts containing precious metals under hydrogen pressure and at elevated temperatures, according to the invention, consists in that the desulfurized hydrocarbon mixture with a boiling point of 30 to 250 °C, preferably 100 to 190 °C, is fed to a distillation column with 5 to 20 trays and the distillation residue, freed from light hydrocarbons to C _r ,, hydrogen sulfide, water and with a sulfur content of ωβχ. up to 50 ppm, is fed into two to four layers of a catalyst containing 0.2 to 0.5 wt. % rhenium 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 for at least 90% of the operating period through a desiccator, e.g. alumina or molecular sieve, under a pressure of 2 to 3 MPa, at a volume velocity of 0.5 to 1.5 volumes per volume of catalyst per hour and at gradually increasing temperatures at the inlets to the reaction layers by 5 to 50 ⁿ G in the range of 180 to 250 °C on the first layer.

The process of the invention therefore includes the treatment of petroleum gasolines, namely of a wide distillation range, or gasoline fractions, especially heavy ones, possibly also in a mixture with petroleum fractions from crude oil. Other raw materials from secondary sources or of non-petroleum origin, not yet suitable for pyrolysis, are not excluded.

A series of tests have shown that the hydrogenation platinum-rhenium catalyst defined in the subject of the invention has high saturation properties at low water concentrations, to which it is more sensitive than conventional catalysts. However, it is more economically advantageous than catalysts with high contents of noble metals. The conditions of hydrogenation of aromatics in the second stage are also an important feature of the invention, since it is necessary to distribute the hydrogenation into the optimal temperature range by varying the inlet temperatures and to exclude the transition to the dehydrogenation range. For this purpose, 1 working pressure is used.

The main effects of the process according to the invention compared to other similar processes are therefore low energy requirements given by low temperatures and reduced costs for catalysts, which contain practically lower concentrations of especially precious metals and less of them are supplied to the reaction space. Considering the effect of using the product for the production of pyrolysis gases, the advantage of the first process is also the preservation of the concentration of n-alkanes in the product. This is achieved by choosing a non-iso3 231730 nerating catalyst and reaction conditions. It is known that the yield of ethylene from n-alkane compared to i-alkane with the same number of carbons is three to four times.

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

Example

from the pyrolysis feed, heavy gasoline was selected, the analytical values of which are given in Table 1, which further shows the values of the products of its hydrogenation on a catalyst containing 4 wt. % CoqSq and 12 wt. % MoS _o on gamma alumina under the following conditions:

reaction pressure

IíHSV (volumetric velocity)

H _g : CH temperature

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

3.0 MPa vol./vol. cat h 250 vol./vol.

300°C

0.25 MPa free from HgS and HgO as well as dissolved

It was conducted in three-stage hydrogenation conditions:

P; CH

L1ÍSV (volumetric flow rate) temperature catalyst unit where dearomatization occurred at these below 3.0 MPa

00Θ volume/volume

and 2 vol./vol. h 150 to 400 °C

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

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

It is evident from the table that in the temperature range protected by the drying method t-3:·ui, deep dearomatization and practically complete removal of olefins occur. The yield of the liquid product is higher than 100% by weight. At an optimum of approximately 80% dearomatization, 10% more light unsaturated hydrocarbons and less aromatic gasoline are obtained from the same amount of feed with the same pyrolysis intensity. The selection of heavy gasoline containing predominantly C _o+ aromatics in the aromatics also leads to the fact that their content in the pyrolysis medium decreases with a milder pyrolysis regime.

gasoline decreases and increases by Table 1 Cg concentration to Cg aromatics. Raw material characteristics for pyrolysis and of its products 1 each . degree of hydrology invention. raw material product ^day 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

S ppm Br - index mg Br/100 g aromatics % wt. raw material 950 750 12.9 product under 1 160 12.7 Table 2 The effect of temperature on dearomatization desulfurized raw materials. temperature °C 150 200 250 300 350 LHSV i ,0 1.0 1.0 1.0 1.0 obj./obj. h ^day 20 0.766 0.765 0.760 0.760 0.761 Br - index 33 9 8 29 257 mg Br/100 g flavors % wt. 12.7’ 10.1 3.8 1.9 4.7 dearomatization 0 20.4 70.0 84.7 63.0 Similar results were achieved in • first stage with 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 without rhenium with titanium, chlorine and sulfur.

During dearomatization of the 100 to 170 °C fraction on the same Pt Re catalyst, aromatics decreased from 8.5 wt. % to 1.5 wt. % in the temperature range of 250 to 270 °C and the naphthenes content increased to 31 wt. %. This concentration of naphthenes is also suitable in the feedstock for pyrolysis.

The product obtained by the process according to the invention had, according to mass spectrometric analysis combined with gas chromatography, an average molar ratio of n-alkanes to i-alkanes in the range of hydrocarbon numbers 6 to 10 of 2:1. In similar processes in which some feature of the invention was omitted (increased temperature, especially due to the inability to control the exothermicity of the hydrogenation of aromatics), the ratio decreased to about 55% molar n-alkanes in the mixture of β-alkanes, up to 30% methylcyclopentanes were formed 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.