CS217388B1 - A method for obtaining high density aromatic mixtures from liquid pyrolysis products - Google Patents

Abstract

The invention relates to the treatment of olefinic sulfur-containing pyrolysis products boiling in the range of 30 to 220 °C to aromatic mixtures containing predominantly Cg to Cg aromatics, suitable for petrochemical synthesis. The process consists in that the pyrolysis gasoline fraction rich in Cg to Cg aromatics is first hydrogenated, the liquid product is freed from hydrogen sulfide and water and in the next stage is subjected to reforming, the product of which is extracted with diethyl glycol and the extract is redistilled to pure aromatics. The product is a valuable petrochemical raw material.

Description

The invention relates to the treatment of olefinic sulfur-containing pyrolysis products boiling in the range of 30 to 220 °C to aromatic mixtures containing predominantly C _g to C _g aromatics, suitable for petrochemical synthesis. The process consists in that the pyrolysis gasoline fraction rich in C g to C _g aromatics is first hydrogenated, the liquid product is freed from hydrogen sulfide and water and in the next stage is subjected to reforming, the product of which is extracted with diethyl glycol and the extract is redistilled to pure aromatics. The product is a valuable petrochemical raw material.

.217388

The invention relates to a method for obtaining highly concentrated mixtures from liquid pyrolysis products by treating olefinic, sulfur-containing pyrolysis products boiling in the range of 60 to 160 °C, but especially in the range of 75 to 150 °C.

Pure aromatic hydrocarbons, benzene, toluene and Cg-aromatics are in constant demand for a number of organic syntheses and the products are used for a variety of final products. There are two sources of these hydrocarbons, namely the reforming product and the pyrolysis product of hydrocarbons. Each of them has its own specific composition and treatment methods before obtaining aromatics.

More demanding treatments are required for pyrolysis products to obtain aromatics. Pyrolysis gasoline obtained as a by-product of thermal cracking of hydrocarbons contains relatively high concentrations of sulfur compounds, unsaturated components and aromatics. Of the unsaturated components, the most harmful for further processing are the olefins that form resins, condensation products and coke when heated. Therefore, they must be selectively removed to the maximum extent before further processing, usually by low-temperature hydrogenation. Only the product of this process is used for further processing, usually for aromatics. There are many hydrogenation methods that can be used for this purpose and they can be catalytic or thermal with or without prior redistillation. For example, the conversion of the 75 to 150 °C fraction by thermocatalysis to benzene and methane in the presence of hydrogen or hydrogenation refining with subsequent extraction of aromatics from the products are known. The first method has a number of problematic points, especially the necessity of working at temperatures above 550°C, coking of the catalyst, etc. The second method has weaknesses mainly in the low efficiency of the hydrorefining stage and the non-utilization of cyclans, which are formed by hydrogenation of cyclan olefins or partially aromatics. Cyclan raffinate is a poor raw material for pyrolysis and the yields of the desired ethylene are lower than from alkanes.

The invention solves a method of obtaining highly concentrated aromatic mixtures from liquid pyrolysis products by a complex process including the isolation of the most volatile fractions, their stabilization, desulfurization and saturation of olefins and the conversion of volatile olefins into aromatics using new catalysts.

A complex process for obtaining a highly concentrated aromatic mixture from liquid products of pyrolysis of hydrocarbon gases, gasolines and middle distillates previously freed from olefins by preliminary low-temperature hydrogenation consists, according to the invention, in that pyrolysis gasoline heated between 60 and 160 °C is led in the presence of 300 to 2,000 volumes of hydrogen-containing gas and 0.5 to 200 wt. parts of an antioxidant based on substituted phenol or aromatic amine first to a hydrogenation refinery. There it comes into contact with a catalyst containing active salts of at least two metals of the sixth and eighth groups of the pearlite system on alumina, at a pressure of 3 to 6 MPa at an LHSV of 1.0 to 2.5 vol./vol. h, at a temperature of 320 to 420 °C.

If the fractionation is carried out under adlabatic conditions, preferably 5 to 50% by volume of a stable hydrocarbon feedstock with a b.p. of 80 to 200 °C without olefins is added to regulate temperature differences, on the contrary, the addition of this fraction is not necessary under isothermal conditions.

The obtained liquid product is freed from hydrogen sulfide and water at 0.15 MPa to 2.0 MPa and is introduced into several successive reforming stages, where it is heated to a temperature of 505 to 540 °C at a pressure of 2.5 to 5.0 MPa with a molar ratio of hydrogen to hydrocarbons of at least 3:1b LHSY 0.5 to 2.5 vol./vol. . h. in the presence of a catalyst containing 0.20 to 0.50 wt.% platinum and the same content of rhenium on gamma alumina containing 0.05 to 2.0 wt.% titanium dioxide. The product from the last reaction stage, which is usually the third and contains 4 parts of catalyst, while in the first two there are 1 and 2 parts of catalyst composed preferably of 0.30% to 0.35% bm. of each of the two active metals on gamma alumina. For both catalytic conditions included, it can be stated as advantageous that the desulfurization catalyst before sulfurization contains 6 to 15 wt.% MoO and 2 to 4 wt.% cobalt oxide and/or nickel oxide, and that the reforming stages operate preferably at 480 to 510 °C and at a pressure of 2 to 3 MPa.

Further details can be given to this basic essence of the invention, which will deepen the advantages of the invention. The level of pre-purification of the Cg to Cg fraction under hydrorefining conditions is determined by the quality of the catalyst. To obtain active sulfides, it is necessary to conduct the sulfurization of metal oxides in such a way that metals, especially cobalt or nickel, are not formed instead of sulfides. Although these hydrogenate olefins better, they are poisoned by sulfur compounds. Considering the next step, reforming the formed olefins and alkanes in the presence of a highly active and stable catalyst, it is necessary to combine the hydrorefining conditions to achieve the removal of sulfur compounds to a level of at least 2 to 3 ppm of sulfur, preferably below 1 ppm, and at the same time reduce the olefin content below 0.1 to 0.5% by weight.

The above conditions allow working with gas circulation, or using a single flow with a lower hydrogen to hydrocarbon ratio. The combination of increased pressure, which is preferably above 3.0 MPa, and an oxidation inhibitor ensures that the residual potential resins are not converted into coke-like solids that could clog the heat exchangers, the furnace, and the inlet to the catalytic space. The advantage of the proposed reforming catalyst is that it works satisfactorily even at a few ppm S in the feedstock, which is due, although the principle is not yet fully explained, to the combination with the ttandlox present in gamma alumina. Also in the reforming conditions, the most favorable for removing higher alkanes by hydrocracking and dehydrocyclization can be selected and the cyclans can be selectively converted to other aromatics. The reforming conditions and the catalyst allow for isomerization of the Cg-aromatics present and, in the case of wider fractions, for partial 1 transalkylation reactions. The composition of the feedstock after hydrorefining allows for operation at very low hydrogen to hydrocarbon ratios without affecting catalyst stability.

The conditions also include a very advantageous ascending temperature regime of three reaction stages arranged in succession. In the first stage, the olefin components are brought into equilibrium at low temperature and the six-membered olefins formed are selectively dehydrogenated, in the subsequent stages the dehydroalkylation, transalkylation and isomerization reactions are then selectively carried out. The product is practically suitable for direct extraction of aromatics by distillation, only the olefins must be removed by percolation on clay. The advantage of mixing the feedstock with primary gasolines lies primarily in ensuring a low sulfur concentration in the product and adjusting the product between Cg and Cg aromatics, since heavy gasoline mainly produces C? and Cg aromatics. In this way, ideally balanced feedstock compositions for aromatics extraction can be prepared. For this complex process, a reforming unit can be used, operating even under relatively unfavorable conditions, i.e. at high pressures and with a low hydrogen to hydrocarbon ratio. The composition of the feedstock ensures increased isothermality of the reforming stage, and conversely, the exothermic reaction of olefin hydrogenation can be used to energetically favor the process, while the mixing of both feedstocks regulates the temperature increase in the hydrogenation stage.

The following are examples of intensive utilization of the feedstock from thermal cracking by combining hydrogenation and reforming to more than 90% aromatic concentrates in the case of separate processing. The conditions illustrate the entire invention, but do not limit its scope.

Examples

By pyrolysis of a mixture of gasoline and middle distillates, gasoline with a boiling point range of 30 to 220 °C was obtained as a by-product. Its redistillation to low-temperature hydrogenation prepared a fraction containing Cg to Cg aromatics. Its characteristics are given in Table 1. To study the changes in hydrocarbons from the Cg to Cg fraction, no stabilizing feedstock without olefins was added, since the experiments were carried out in the first phase under cryothermal conditions. The addition of stabilizing feedstock is selected in an adlabatlok system to regulate temperature differences.

Table 1

Characteristics of the raw material for the production of aromatics (hereinafter referred to as BIX)

⁴ 20 dest. curve °C Oi start 78 10 # order 88 50 f> ebj. 101 90 1> vol. 129 95 <f> vol. 132 to the destination 149 Br. number gBx/100 g 16 With ppm 440

This raw material is stabilized without the addition of stabilizers, free of olefins;

mg of antioxidant based on aromatic amine/l, was subjected to isothermal hydrogenation refining over a cobalt-molybdenum catalyst containing active sulfides of both metals under the following conditions:

pressure

LHSY olxkulaoe gas catalyst composition (before sulfurization)

4.0 MPa

2.0 vol./vol. . h 250 vol.: vol. gasoline 12 # Me0 ₃ \

3.5# CoO on gamma alumina

217368

Table 2 shows the hydxogenae at different temperatures. Table 2

Effect of temperature on hydrogenaol BIX

reaction temperature °C 300 325 350 375 400 product: Br. number gBr/lOOg 4.9 2.7 2.0 1.2 0.5 With ppm 2.9 - 2.2 - 1.6 It is obvious that it is also possible delete 95 56 olefins and practically all the sulfur, so it is found·

The same level of hydrogenation was achieved at temperatures 20 to 30 °C lower on a catalyst containing 12% MoO^, 2% CoO and 2.56% NiO in the oxidic state on gamma alumina.

Table 3 shows a detailed analysis of the intermediate by capillary gas chromatography.

Table 3

Detailed analysis of intermediates (after hydrogenaol BTX) composition ^C 5 ^1C 6 nC ₆ MoC ₅ oCg B 1^7 nCy OCy T Cg+ near. 56 wt. 0.1 1.0 1.7 4.7 1.5 31.9 0.8 1.0 3.6 23.8 2.3 composition BB MX PX OX unidentified 56 wt. 13.4 6.3 2.3 3.0 2.3 This product is further processed in three-stage serially included reformlngu.

The following constant conditions were adjusted during the reform:

pressure 3 MPa

LHSV 1.5 hr/hr. . h gas circulation 1,000 vol. : vol. raw material catalyst composition 0.30 wt. % Pt + 0.30 56 wt. Re + + 0.15 56 wt. TiO on gamma alumina distributed in three layers 1:2:4.

Table 4 shows the product analyses at different reforming temperatures. Table 4

Effect of temperature on reforming of intermediates 3TX reaction temperature °C 475 500 514 525 raw material product composition determined by chromatography on a selective cartridge

neornates 16.3 10.9 8.0 5.1 21.5 benzene 31.7 34.2 35.8 38.5 31.8 toluene 25.5 26.7 28.1 29.4 22.4 ethylbenzene 12.6 13.8 13.7 13.1 13.4 m-xyleneη p-xyleneJ 9.9 10.3 10.5 10.2 8.1 •-xylene 3.4 3.5 3.4 3.2 2.8 Cg+ aromatics 0.6 0.6 0.5 0.5 - increased Cg of aromatics 56 22 27 28 21 -

A gradual decrease in nonaromatics and a change in the ratio of Cg-aromatics and their amount can be observed. Aromatics were determined on a selective gas chromatography cartridge, with a certain difference in the analytical values of the remaining nonaromatics compared to the results obtained by capillary gas chromatography.

Table 5 then shows a detailed chromatographic analysis of the product, which shows the distribution of non-aromatics and thus the possibility of isolat- ing aromatics. After distilling off the light hydrocarbons to n-Cg, practically pure aromatics are obtained.

Table 5

Typical properties and composition of products of complex conversion of BIX feedstock to hydrogenaol under conditions on page 3 and temperature 330 °C and after reforming under conditions on page

and a temperature of 525 °C.

*20 0.850 Br.index 870 mg Br/100 g With 1-2 ppm dest. crotch-start. 62 ®C. 10 # 86 . 30 # 94 Chromatographic analysis capillary gas chromatography in # wt. n- and 1-alkanes to Cg 2-A n— and 1-alkanes from C? .0.8 cycloalkanes up to Cg*) 0.9 benzene 39.2 toluene 29.5 ethylbenzene 12.9 p-xylene 3.0 m-xylene 7.2 o-xylene 3.2 Cg + aromatics 0.7 unidentified 2.0

(s) predominantly methylcyclopentane

Claims (4)

1. A process for obtaining high-aromatized aromatic mixtures from liquid products of the pyrolysis of hydrocarbon gases, gasolines and middle petroleum distillates devoid of long-term low-temperature hydrogenolysis, characterized in that the pyrolysis fraction is boiled between 60-160 ° C, preferably 75-150 ° C. 2,000 vol. Of hydrogen-containing gas and 0.5 to 200 ppm of substituted phenol or aromatic amine-based antloxldant, contacted with a catalyst comprising active cations of at least two metals of the sixth and eighth groups of the periodic system, on alumina in gamma form at a pressure of 3; 0 to 6.0 MPa and at LHSV 1.0 to 2.5 v / v. . h, at a temperature of 320 to 420 ° C, the liquid product is freed from hydrogen sulphide and water at 0.15 to 2.0 MPa and introduced into at least two consecutive reforming reaction stages, where it is heated to a temperature of 505 to 540 ° C, at a pressure of 2.5 to 5.0 MPa with a molar ratio of hydrogen to hydrocarbons of at least 3: 1hm ·, with a 1HSV of 0.5 to 2.5 v / v. H in the presence of catalysts containing from 0.20 to 0.50 wt. % of platinum and the same conoentraoe xhenla on gamma alumina containing an additional navi of 0.05 to 2.0 wt. titanium dioxide. 2. Process according to claim 1, characterized in that 5 to 50% by volume of a stable hydrocarbon feedstock and a boiling point of 80 to 200 [deg.] C. without olefins are preferably added before hydrogenation. 3. A process according to claim 1, wherein the desulfurization catalyst comprises 6 to 15 wt. MoO 3 and 2 to 4 wt. cobalt oxide and / or nickel oxide. 4. A process according to claim 1 wherein the reforming steps are three and a catalyst which preferably contains from 0.30 to 0.35% by weight. of each of the two metals present, is distributed in the composition in a 1: 2: 4 ratio.