CS255695B1 - Process for producing benzene from catalytic reforming products - Google Patents

Abstract

The present invention relates to a process for the preparation of benzene from catalytic reforming products by thermal cleavage in the presence of water vapor and the following. hydrodealkylation of the hydrogenated fraction. a thermal cracking product on chromium oxide to alumina, wherein the thermal cracking is subjected to a mixture of a reformate boiling in the range of 30 to 220 ° C or a fraction thereof and a hydrocarbon mixture boiling in the boiling range of 20 to 360 ° C with a reformate to weight ratio of hydrocarbon mixtures 1: 5 to 50.

Description

The invention relates to the production of pure benzene from the products of catalytic reforming of gasoline fractions, whereby the reformate is first thermally cracked and then the fraction rich in Cg and _Cg aromatics is catalytically hydrodealkylated.

Pure benzene is a permanent basic raw material for a number of petrochemical products and is in short supply worldwide, which makes combinations of processes leading to its production economical.

The main source for the production of benzene remains the product of pyrolysis of petroleum gasolines, or medium-boiling petroleum fractions (diesel). Catalytic reformate, which usually contains only a few percent of benzene, has ceased to be a source, and reforming benzene cuts gives poor yields and a maximum of 10 to 15% benzene in the product. However, hydrodealkylation of higher aromatics C? to Cg obtained from aromatic concentrates by extraction with solvents, e.g. diethyl glycol, is being considered, and is sometimes also implemented in production. However, aromatics isolated in this way may contain, in addition to water, also diethylene glycol, or its decomposition products. These impurities have a corrosive, coke-forming effect and deactivate catalysts operating at temperatures over 600 °C. Hydrodealkylation of higher aromatics is also demanding in terms of the consumption of valuable hydrogen under pressure, of which approximately 200 to 600 m^N/t is consumed for C _? to Cg aromatics, depending on the carbon number.

In alkylaromatics, methyl homologues predominate, giving mainly methane as a by-product.

The invention solves a method of producing benzene from catalytic reforming products by thermal cracking at 700 to 850 °C in the presence of steam, whereby gasoline is isolated from the gaseous product, which is further hydrogenated from dienes, vinylbenzenes and indenes and the hydrogenation product is redistilled to a fraction with a boiling point range of 60 to 180 °C, containing mainly Cg to Cg monocyclic aromatics and this fraction is then catalytically hydrodealkylated on a catalyst, which is chromium and aluminum oxide, and pure benzene is isolated from the reaction product by subjecting the product of catalytic reforming of gasoline with an octane number by the research method of 88 to 98, boiling in the range of 30 to 220 °C or its fraction boiling up to 170 °C, or in the range of 70 to 170 °C in a mixture with hydrocarbon mixtures to thermal cracking in the presence of steam boiling in the boiling point temperature range of 20 to 360 °C in a mass ratio of reformate to hydrocarbon mixture of 1:5 to 50. Preferably, the catalytic reformate is mixed before thermal cracking with virgin gasoline boiling in the range of 20 to 200 °C and/or with a middle oil fraction boiling in the range of 150 to 360 °C, wherein the mass ratio of reformate to oil fraction is 1:5 to 1:20.

From the gaseous product of thermal cracking, gasoline boiling between 60 and 210 °C is then isolated in a known manner by a combination of condensation and, if necessary, distillation, which is subjected to hydrorefining, e.g. over a Pd catalyst at 80 to 180 °C under a pressure of 2 to 10 MPa, the refined product is redistilled to a product with a boiling point of 60 to 180 °C, which is catalytically hydrodealkylated at temperatures of 550 to 650 °C under a pressure of 4 to 10 MPa over a catalyst containing turpentine oxides on alumina. After the isolation of benzene, the uncracked alkyl aromatics are partially or completely returned to the pyrolysis gasoline or its cuts.

Analysis of the production process according to the invention shows advantages over existing concepts. Energy is saved for isolating the cut, e.g., 150 to 155 °C from the reformate and for its extraction, which is very energy-intensive. Thermal cracking of the reformate containing approximately 55 to 70 wt. % aromatics and 30 to 45 wt. % alkanes will give a high yield of C _g to C _g aromatics when diluted, and from the alkanes, mainly up to olefins with an increased yield of propylene will be formed. The ratio between the aromatics will be shifted towards benzene or toluene by thermal dealkylation. Monocyclic aromatics do not increase coking under pyrolysis conditions. Aromatics with reduced concentrations of alkyl homologues are then subjected to hydrodealkylation, and thus less hydrogen is consumed. Hydrogen is provided by the pyrolysis of alkanes.

The danger of introducing catalytic poisons, especially residues of extraction agents and their products, is completely eliminated. The procedure is advantageous especially in situations where there is free capacity of a modern pyrolysis unit, in which the energy demand is reduced by very advanced

255693 heat exchange methods. However, the capacity of the unit is increased only by aromatics from reformate, since non-aromatics obtained during aromatics extraction from reformates are usually also sent to pyrolysis to produce ethylene and propylene.

The advantages of the invention are documented in the present example. The fractions and conditions chosen are for illustrative purposes only and are not intended to limit the scope of the claims.

Example

A liquid product was prepared by catalytic reforming heavy gasoline, the analyses of which are given in Table 1.

The reformate was blended at a concentration of 10 to 20% with light gasoline containing predominantly _Cg hydrocarbons with a boiling point range of 60 to 90 °C, practically free of benzene. The light gasoline was used to accurately and correctly monitor the conversion of Cg to Cg aromatics from the reformate.

The mixtures were thermally cleaved at 790 to 830 °C in the presence of water vapor in the ratio m _{H 0} :m _c jj= - 0.7 with a residence time of less than 1 s. The outlet pressure was 30 kPa. ²

Table 2 shows the BTX ratios in the thermal decomposition products of reformate and the effect of temperature and dilution on the level of thermal dealkylation of aromatics from reformate.

The fraction 65 to 165 °C was isolated from gasoline by distillation and, after hydrogenation removal of dienes, vinylbenzenes and indenes, it was hydrodealkylated in a known manner at 630 °C under pressure.

5.5 mPa on a Cr2O4 - Al2O4 catalyst in the presence of hydrogen to pure benzene, e.g. on a Pyrotol unit.

A series of pyrolysis experiments were also carried out with mixtures of reformate with whole petroleum gasolines and heavy gasolines. The B:T:X ratios of the pyrolysis products at the indicated temperatures with light gasoline were practically no different from the ratios achieved without the addition of reformate. No increased formation of heavy pyrolysis fractions was noted.

Table 1

Catalytic reforming product

0.792 composition · mass ,, 20 dest. curve start non-aromatic 10% volume to °C 84 benzene 2.2 50% volume to °C 126 toluene 16.5 95% volume to °C 174 Cg-aromatics 17.1 end : °C/% vol. 204/99 C ₉₊ -aromatics 22.6

Table 2

BTX ratios in thermal decomposition products of reformate ⁴ and its blends with light gasoline

Dilution with light itself 1:4 1:9 gasoline reformat (mass ratio reform to gasoline num) B:T:X B:T:X B:T:X temperature 790 °C 12.8:44.9:42.3 27.0:40.5:32.5 35.7:39.3:25.0 temperature 830 °C 18.9:41.5:39.6 33.3:36.7:30.0 45.5:36.4:18.1

⁺ B:T:X = 6.1:46.1:47.8

Claims (2)

SUBJECT OF THE INVENTION A process for the production of benzene from a catalytic reforming product by thermal resolution at 700 to 850 ° C in the presence of water vapor, wherein gasoline is isolated from the gaseous product which is further hydrotreated from dienes, vinylbenzenes and indenes and the hydrogenation product is redistilled to a fraction boiling temperatures of 60 to 180 ° C, containing predominantly C8 to C5 The C8 monocyclic aromatics and this fraction are then catalytically hydrodealkylated on a chromium-aluminum oxide catalyst and pure benzene is isolated from the reaction product, characterized in that the thermal cracking in the presence of water vapor is subjected to catalytic reforming of octane gasoline by research method 88 to 98, boiling in the range of 30 to 220 ° C or a fraction thereof boiling in the range of 170 to 170 ° C, optionally in the range of 70 to 170 ° C in admixture with hydrocarbon mixtures boiling in the boiling range of 20 to 360 ° C. mixtures of 1: 5 to 50. 2. A process according to claim 1, characterized in that the catalytic reformate is mixed with primary gasoline boiling in the range of 20 to 200 [deg.] C. prior to thermal digestion, and / or a medium petroleum fraction boiling in the range 150 to 360 [deg.] of the reformate to the oil fraction is 1: 5 to 1:20.