CS260563B1 - The process for producing pure aromatic hydrocarbons from the product is catalytically deformed - Google Patents

Abstract

The solution describes a technological process for the production of pure aromatic hydrocarbons from the product of catalytic reforming after extraction of aromatics, in which the entire aromatic extract is not percolated, but only the distilled toluene freed from water and decomposition products of diethylene glycol. The technical xylene produced is obtained only by rectification.

Description

The invention relates to a method for producing pure aromatic hydrocarbons from the product of catalytic reforming after extraction with diethylene glycol. The obtained aromatic extract is freed from water by distillation, only toluene is percolated and the mixture of Cg-aromatics is separated from impurities by distillation rectification.

Aromatic hydrocarbons zvi. C _? and C _g monocyclic types are permanently the basic raw material for a number of organic syntheses. Their main source is the product of catalytic reforming of heavy gasoline. This product contains 60 to 75 wt. % aromatics mainly C _? and Cg types and is usually separated from non-aromatics by extraction. A common solvent is diethylene glycol and the extract obtained with it is redistilled after percolation on activated clay to pure aromatics, zvi. to toluene and Cg-aromatics. The aromatic extract contains water, dissolved and apparent, and residues of diethylene glycol, which decompose at 160 °C to organic acids, aldehydes and resinous substances. Percolating natural clay quickly loses its activity, because it is deactivated by water, resins and unsaturated hydrocarbons. It must work at high temperature, i.e. with high energy requirements. Its service life is limited and the quality of zvi. for toluene, less for Cg-aromatics.

The process according to the invention solves the problem of producing aromatics from diethylene glycol extract. The aromatic extract containing C? to C^g aromatic hydrocarbons contaminated with olefins, diethylene glycol residues and water is first freed from water by distillation, the residue is distilled to toluene distillate, which is converted at 20 to 250 °C through natural clay under a pressure of 0.2 to 1.5 MPa, the residue is then redistilled without percolation to technical xylene and another residue containing Cg to C|g alkyl aromatics. The percolation of toluene is preferably carried out at temperatures of 30 to 120 °C with a volume ratio of toluene to clay of 0.2 to 1:1 per hour. When redistilling the residue after toluene, preferably 0.001 to 0.01 volume of Cg-aromatics per volume of Cg-aromatics present is removed as the main distillate, and technical xylene containing ethylbenzene and a mixture of dimethylbenzenes is removed from the 1st to 5th distillation plate.

The description of the process shows that only pure toluene, freed from water and diethylene glycol decomposition products, is subjected to percolation under very mild conditions. Technical xylene is not percolated and its purity corresponds to the standard. This simultaneously reduces the penetration on the percolation clay and thus improves the removal of polymerizable substances at low temperatures. In the case of a higher concentration of olefinic impurities passing into the column in which xylenes are obtained, a small amount of distillate containing these impurities is advantageously discharged from the top of the column. This distillate can be returned to the extraction raw material or discharged for other uses where olefins are not required.

The following example presents the results of an operational test of the process according to the invention.

Example

For the production of _C7 and C8 aromatics from catalytic reformate, its 100 to 160°C fraction was extracted with diethylene glycol at 145°C and an aromatic extract containing C7 to C8 aromatics was obtained.

In the usual procedure, the aromatic extract was introduced into a percolation reactor filled with fine-grained natural clay at temperatures between 125 and 190 °C and under a pressure of 1.5 MPa with a space velocity of 2 to 3 h ^-1 . The obtained percolate was introduced gradually into 3 columns, in which the following were gradually separated: water with a small amount of toluene, toluene, technical xylene and any remaining Cg to C ₁₀ aromatics. The temperature on the percolation clay increased to a maximum due to the loss of activity and after 1,000 to 1,500 hours the clay had to be replaced or subjected to steam regeneration. Table 1 lists the qualities of the products. The measure of the purity of aromatic hydrocarbons is the sulfuric acid test, the layer of which becomes colored after shaking with the product and the intensity of the color is compared with the scale modeled by chemical solutions zvi. compounds of chromium, iron and cobalt.

The same table shows the data on the process according to the invention. It was implemented in such a way that the extract was fed directly to a column removing water with a small amount of toluene, pure toluene taken from the second column was fed at a temperature of 50 to 60 °C to a percolation reactor. There it was contacted with fine-grained natural clay under a pressure of 0.35 MPa with a space velocity of 0.5 to 1 h ^-1 . There was no decrease in the activity of the clay during 2,000 hours. Technical xylene obtained without percolation by distillation of the residue from the second toluene column met the quality requirements of the standard. By correcting the process according to the invention, the water separated in 1 column did not have an acidic corrosive character and the distillation residue after xylene was not darkly colored by the diethylene glycol decomposition products.

Table

Comparison of pure aromatic production processes conventional according to the invention standard

extract t/h 10 10 - water from 1 column pH 3 to 5 7 to 7.5 - toluene X ) coloration with H ₂ SO ₄ 0 to 3 ^xx) 0 to 1 max. xylene coloration with HjSO^ 2 to 4 4 to 5 max Cg + C _1Q aromatics color brown yellowish - percolation temperature °C beginning 125 55 after 1,000 hours 190 65 x 1 scale is 0 to 6, 0 is best (ASTM-D 848-62)

at the beginning and end of the cycle

Claims (4)

SUBJECT OF THE INVENTION Process for the production of pure aromatic hydrocarbons from a product of catalytic reforming of gasoline after extraction with diethylene glycol, characterized in that the aromatic extract containing C? aromatic hydrocarbons, especially C? monocyclic alkylbenzenes, frees water by distillation, the residue is distilled to toluene distillate, which is transferred at 20 to 250 ° C through natural clay under a pressure of 0.2 to 1.5 MPa, then the residue is redistilled to technical xylene and the residue containing Cg to C 1-6 alkylaromates. 2. Process according to claim 1, characterized in that the percolation is preferably carried out at temperatures of 30 to 120 [deg.] C. with a volume ratio of toluene to clay of 0.2 to 1: 1 per hour. 3. Process according to claim 1, characterized in that, in the redistillation of the toluene residue, preferably from 0.001 to 0.01 volumes of xylene per volume of C8 aromatics present and from 1 to 1 volume of xylene are removed. In the distillation tray, technical xylene containing ethylbenzene and a mixture of dimethylbenzenes is obtained.