LU85306A1 - PROCESS FOR REMOVING CARBONYL SULFIDE FROM LIQUID HYDROCARBON FEEDSTOCKS - Google Patents

Description

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PROCESS FOR REMOVING CARBONYL SULFIDE FROM LIQUID HYDROCARBON FEEDSTOCKS

The present invention relates to a process for removing the sulfur present in the form of carbon oxysulfide or carbonyl sulfide, outside of liquid hydrocarbons, in particular the fillers of hydrocarbons containing propylene and other olefins.

In refineries, the treatment of liquid hydrocarbons for the removal or for the transformation of impurities requires complex and costly processes.

The various sulfur compounds represent the usual impurities which one seeks to eliminate. These are hydrofluoric acid, mercaptans and in particular carbonyl sulfide.

The prevailing industry practice is to reduce the sulfur content by treating the gaseous hydrocarbons. A widely accepted practice is to remove sulfides from combustible gases taken in the gaseous state with diethanolamine, diisopropanolamine, monoethanolamine, and tetraethylene glycol. It is also known that these solvents can be used to treat hydrocarbons in the liquid state.

However, when these solvents are used to extract the impurities from hydrocarbons in the liquid state, they do not make it possible to reduce the content of carbonyl sulfide, hereinafter referred to as COS for ease, to ‘less than 5 ppm.

However, it is also known that the new propylene polymerization processes use catalyzes.

Increasingly efficient mi - 2 - sors. The latter, on the other hand, are extremely sensitive to all polar impurities such as for example COS, whose dipole momert is 0.736 Debye. When using these polymerization processes, it is therefore important to purify the feed so that the residual content of impurities is extremely low.

However, with the conventional processes which treat fillers which may contain from 30 to 70 ppm COS at the start, it is possible to reach a residual COS content after purification of the order of 10 to 20 ppm.

It has already been proposed to treat feeds of liquid hydrocarbons containing in particular propylene, with 2- (2-aminoethoxy) ethanol, known under the name of diglycolamine, to remove the COS, however the residual content obtained, although low since of the order of ppm, is not yet sufficient to satisfy the conditions for polymerizations using very active Ziegler type catalysts.

In addition to the treatment technique using liquid-liquid contacts, treatments have already been proposed by liquid-solid contacts.

This type of treatment has the advantage of limiting the risks of contamination of propylene which must be polymerized later, hence the need for a second absorber.

Thus, it has already been proposed to use zinc oxides, or mixtures of Zn oxide and Ca carbonate, over which the liquefied charge is passed at a temperature of 20 to 60 ° C, thus transforming the oxides sulfides; however, the residual COS content of the feed has always remained above about 1 ppm.

; It has also been proposed to use absorbents composed of iron oxide, copper oxide or copper and chromium oxide on a support with a high specific surface such as activated carbon or alumina, so as to reduce the COS content of liquid hydrocarbons from 50-60 ppm in the initial charge up to approximately 0.5 ppm.

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However, although this content is already very low, this is not yet sufficient to be able to send the propylene thus purified to the polymerization unit using the very active Ziegler catalysts.

It has also been proposed to treat these charges by passing them over basic ion exchange resins, at ambient temperature. However, the residual COS content obtained is also of the order of ppm, which is too high to carry out the polymerization in the presence of latest generation polymerization catalysts.

There is therefore a need for a process which makes it possible to desulfurize and in particular which makes it possible to remove the COS from the charges of liquid hydrocarbons containing in particular propylene and other olefins, until the residual content of COS does not not more than 30 ppb, so that the new generation propylene polymerization catalysts are not poisoned too quickly.

The object of the present invention is a process for purifying the charges of liquid hydrocarbons which makes it possible to satisfy the criteria set out above.

The subject of the present invention is a purification process which makes it possible to remove the COS from the charges of liquid hydrocarbons containing in particular propylene, until a residual COS content of less than 30 ppb is obtained.

The purification process of the present invention for removing COS from feeds of liquid hydrocarbons comprising in particular propylene, and containing from 1 to 70 ppm of COS, is characterized in that the feed of liquid hydrocarbons is passed over an absorbent material comprising from about 50 to 85% by weight of iron oxide, en-. let / or sodium.

about 40 to 10% by weight of potassium oxide; from 0 to about 3% by weight of chromium oxide and from about 1 to about 10% by weight of alumina.

It has been found, unexpectedly, that by passing a charge of liquid hydrocarbons, in this case a charge of propylene intended for polymerization, over the absorbent material of the present invention, a purified charge is obtained which meets the purity conditions required for polymerization in the presence of the latest generation Ziegler catalyst.

In general, the absorbent material of the present invention contains from about 50 to about 80% and preferably from about 60 to about 75% by weight of iron oxide, from about 40 to about 10% and preferably from about 30 to about 15% and / or sodium, by weight of potassium oxide and about 1 to about 10%, preferably about 2 to about 5% by weight of alumina.

The absorbent material of the present invention may also contain from about 1 to about 10% by weight of chromium oxide. The specific surface of the absorbent material is generally between approximately 1 and approximately 2200 m / g, and in particular between 1 and 20 m / g.

The absorbent material of the present invention can be prepared using the mixing techniques well known to those of skill in the art.

A typical mode of preparation of the absorbent material consists in mixing an iron salt such as iron nitrate, with alumina in the presence of water so as to obtain a paste ensuring an intimate mixture. The mixture obtained is then dried, and the resulting product is mixed with oxide and / and / or sodium, or potassium hydroxide and / or carbonate; Orf performs this mixture in an anhydrous medium, or in the presence of as little water as possible. It is then dried at a temperature of 150 to 350 ° C. As examples of absorbent material suitable for use in the present invention, mention may be made in particular the materials usually used as a dehydrogenation catalyst and whose composition in the various oxides corresponds to the proportions defined above, the specific surface of these catalysts being relatively small and generally comprised between 1 and 30 m / g.

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- 5 - Γ -, Generally we treat loads of liquid hydrocarbons containing more than 75% of propylene, more particularly loads containing up to 85% and 99% of propylene, the COS content generally being of the order of 1 to 70 ppm. When loads contain more COS, i.e. up to 500 ppm, they are first treated with an amino solvent such as monoethanolamine, so as to reduce the COS level to a suitable value , or less than 70 ppm. The charge of liquid hydrocarbons containing propylene is passed over the absorbent material of the present invention, at a temperature generally between 20 and 60 ° C. and at a pressure sufficient to maintain the medium in the liquid phase. The hourly space velocity of liquid at which the charge is passed is generally between 0.1 and 10 and preferably between 0.2 and 5.

It was found that the presence of potassium oxide in the absorbent material and used in the proportions defined above was of great importance in the purification process of the invention. It has in fact been found that, under the same processing operating conditions, the residual COS content of the filler is much greater if potassium oxide is not used in the absorbent material.

The following examples are given to better illustrate the present invention, but without limiting its scope.

Example 1

A charge of liquid hydrocarbons containing 99% propylene and having a residual COS content of 52 ppm of COS is passed over an absorbent material consisting of 68% by weight of iron oxide, 22% by weight of potassium, 8% by weight of alumina and 2% by weight of chromium oxide.

The specific surface of this material was L J

Claims (6)

1. Process for the purification of charges of liquid hydrocarbons containing, in particular, propylene and from i to 70 ppm of carbonyl sulfide, for removing the carbonyl sulfide, characterized in that the charge d liquid hydrocarbons on an absorbent material comprising from about 50 to about 85% by weight of iron oxide, of ... and / or .sodium. about 40 to about 10% by weight of potassium oxide 0. about 3% by weight of chromium oxide and about 1. about 10% by weight of alumina. 2. Method according to claim 1, characterized in that the charge of liquid hydrocarbons is passed over an absorbent material comprising from 60 to 75% by weight of iron oxide, from 30 to 15% by weight of potassium oxide -__ and / or sodium. siuntycteO has 3% by weight of chromium oxide and 2 to 5% by weight of alumina. 3. Method according to any one of claims 1 and 2, characterized in that the charge of liquid hydrocarbons is passed over the absorbent material, at a temperature between about 20 and about 60 ° C, at a pressure sufficient to maintain the charge in the liquid phase and at an hourly space velocity of liquid of between 0.1 and 10, preferably between 0.2 and 5 4. Method according to any one of claims 1 to 3, characterized in that one passes a charge of liquid hydrocarbons containing more than 75% of propylene. 5. Process for the purification of charges of liquid hydrocarbons containing more than 95% of propylene and containing from 1 to 70 ppm of carbonyl sulphide in order to remove the carbonyl sulphide therefrom, characterized in that this charge is passed over a absorbent material comprising from 60 to 75% by weight of iron oxide, from 30 to 15% by weight of potassium oxide, from 2 to 5% by weight of alumina, this absorbent having a specific surface of between 2 1 and 200 m / g, at a temperature between 20 and 60 ° C, at a pressure sufficient to maintain the load in the liquid phase and at an LHSV between - 8 - 0.1 and 10. 6. Charges of purified hydrocarbons, with a low carbonyl sulfide content and obtained according to the process described in any one of claims 1 to 5. Brussels, the Par Pon of the company called LABOFINA S.A.