Recovery of benzene and benzene derivatives from gasoline fractions and refinery streams

Abstract

A process for the separation of the aromatic compounds benzene, toluene and xylene from an aromatics-containing reformate gasoline and pyrolysis gasoline or a coke-oven light oil or an aromatics-containing refinery stream, in which the aromatics are separated by an extractive distillation uses a novel solvent combination made up of the compounds n,n′-diformyl piperazine or 2,2-bis-(cyanoethyl)ether in a combination with n-formyl morpholine as a second solvent for extractive distillation so that the solvent combination obtained shows a higher selectivity with regard to the aromatics to be extracted so that a lower solvent load is required. The aromatics-containing feed mixture is first submitted to a pre-distillation so that the obtained fraction has a narrow boiling point range. This fraction is then submitted to an extractive distillation in a first column, in which an aromatics-lean head product of predominantly paraffinic hydrocarbons is obtained as well as an aromatics-enriched bottom product. The bottom product is passed to a second column in which an aromatics-rich raffinate is obtained by reducing the pressure or increasing the temperature so that the extracting solvent combination obtained as bottom product can be recycled into the process.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This application is a divisional application of U.S. Ser. No. 12 / 733,204, filed May 27, 2010, which was a US National Phase application of International Application PCT / EP2008 / 006415, which has an International Filing Date of Aug. 5, 2008. U.S. Ser. No. 12 / 733,204 was pending as of the filing date of this application, and PCT / EP2008 / 006415 was pending as of the filing date of U.S. Ser. No. 12 / 733,204, and each of these applications is expressly incorporated by reference as if set forth in their entirety herein.BACKGROUND OF THE INVENTION[0002]The recovery of aromatics from gasoline fractions and refinery streams is an important process step in petrochemistry and coke over and refinery technology. Especially benzene and simple derivatives of benzene are important raw materials in the production of dyestuffs, plastics, solvents and varnishes. As these compounds in aromatics-containing fractions frequently occur in mixtures with non-aromatic...

AI Technical Summary

Benefits of technology

[0016]The aim of the invention is to find a solvent and a suitable process for the extractive distillation of benzene derivatives from gasoline fractions, which is characterized by improved properties as regards the aspects of selectivity and capacity. The capacity of the solvent should be adequately high so that a relatively little amount of circulated solvent is required. The solvent cost should be low and the demand for equipment low. The achieved selectivity of the solvent should be high so to ensure adequate shifting of the boiling point of the aliphatic component and easy isolation of the paraffinic and aromatic hydrocarbons from the gasoline fraction.

[0017]The present invention achieves the aim by using a new solvent mixture which meets the specified requirements. It was found that the two solvent additives n,n′-bis-(formyl)piperazine or 2,2′-bis-(cyanoethyl) either in combination with n-formyl morpholine are especially well-suited for the extractive distillation of aromatics. The capacity of this solvent combination is so high that the aromatics can be separated from the gasoline fraction with an only small amount of extracting agent. The selectivity in relation to aromatics is so high that, after addition of the extracting solvent, the boiling points of the aromatic compounds differ sufficiently enough for a distillative separation. By the high selectivity of the solvent combination according to the invention, the non-aromatic hydrocarbons are almost completely separated from the gasoline fraction so that, after the removal of the extracting solvent, it will be possible to carry out a simple distillation separation of the aromatics benzene, toluene and of the xylenes.

[0018]By the variable selectivity-increasing effect of the additional solvent components according to the invention, it is possible to reduce the amount of circulated solvent mixture to an extent that the capacity limit or, in other words, the phase separation of solvent and aromatics mixture is almost reached. The solvent combination can be optimized such that it will bring a maximum saving of solvent load for every gasoline fraction. A lower amount of circulated solvent involves lower investment cost and utility cost with plant capacity and product purity remaining the same.

Problems solved by technology

It is not possible to simply separate aromatics from gasoline fractions containing aromatics by way of distillation since the gasoline or its fractions consist of a large variety of substances of very similar boiling ranges.

The central problem to be solved when performing an extractive distillation is the selection of a suitable solvent.

Owing to the relatively low solvent capacity this process requires a high amount of solvent and involves high constructional cost.

A disadvantage of this process is that the separating efficiency can only be improved if a certain amount of water is added.

The disadvantage of this process is a large amount of circulated solvent and a relatively large column for extractive distillation, as a large portion of extracting solvent combination as compared to the hydrocarbon must be used.

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