LU85307A1 - 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 carboriyl sulfide, hereinafter referred to as COS for ease, to less than 5 pom .

However, it is also known that the new propylene polymerization processes use increasingly efficient catalysts. 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 room 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 a absorbent material comprising from about 75 to 95% by weight of iron oxide, from about 3.5 to 23% by weight of alumina optionally containing silica, and from about 0.4 to 5% by weight of a promoter chosen from the group comprising sodium, potassium, calcium, barium or magnesium oxides, the specific surface of the absorbent material being between 2 and 20 m / g.

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 corresponding to this is obtained. at 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 75 to 95% by weight, preferably from 80 to 92% by weight of iron oxide, from about 3.5 to 23% and preferably from 5 to 12% by weight of alumina or of silica alumina and from 0.4 to 5%, preferably from 0.6 to 3% by weight of a promoter chosen from oxides of sodium, potassium, calcium, barium or magnesium .

When a silica-alumina is used in the absorbent material, an amount of silica which varies between about 1 and about 15% by weight is used, the remainder being alumina.

The specific surface of the absorbent material is between 2 and 20 m / g. and preferably between 5 and 15 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 method of preparing the absorbent material is to mix alumina or a silica-alumina gel with a soluble salt of iron such as iron nitrate.

As alumina, o <^ - boehmite is generally used.

The quantity of promoter, taken in the form of oxide, is then added to this mixture and a slurry is formed which is dried, and with which pellets are formed. These pellets are subjected to a calcination step at a temperature between 500 and 650 ° C., preferably 570 at - 5 -, .620 ° C., and in the presence of water vapor. After calcination, the absorbent tablets are perfectly suitable for use in the present invention.

According to a preferred embodiment of the present invention, boehmite, as a source of alumina, is mixed with iron nitrate, and the desired amount of carbonate or carbonate is added to this mixture. potassium oxide or hydroxide. The slurry thus obtained is dried and pellets are formed which are calcined at a temperature of 600 ° C. in the presence of water vapor. An absorbent material is obtained having a specific surface 2 of between 2 and 20 m / g.

Generally, loads of liquid hydrocarbons containing more than 75% of propylene are treated, 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 feeds with a higher COS content, i.e., ^ fireYcT'500 ppm, are to be treated, they are first treated with an amino solvent, such as monoethanolamine, so as to reduce the COS level at a suitable value, less than 70 ppm.

According to an embodiment of the process of the present invention, 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 liquid phase.

The hourly liquid space velocity or LHSV, at which the charge is passed, is generally between 0.1 and 10 and preferably between 0.2 and 5.

It has been found that the presence of a promoter, such as sodium, potassium, calcium, barium or magnesium oxide, at 0.4 to 5% in the absorbent material, is of great importance in the purification process of the invention. It has been found, in fact, that

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- 6 - under the same treatment operating conditions, the residual COS content of the filler is much higher if a promoter, and in particular 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% of propylene and having a residue content of d scoop and 62 ppm of COS was passed over an absorbent material consisting of 87% by weight of iron oxide, 12% alumina and 1% potassium oxide.

The specific surface of this material was 15 m ^ /. G.

During its preparation, the mixture which contained alumina, iron nitrate and potassium oxide was subjected, after drying and tableting, to a calcination at a temperature of 600 ° C.

The charge mentioned above was thus passed over the absorbent material, at ambient temperature and at a pressure adjusted to maintain the charge in the liquid phase, and at an LHSV of 0.5.

A sample of the purified feed was taken and the COS content was determined. This was 2 2 ppb.

For comparison, the same charge was passed over an absorbent material consisting of 87% by weight of iron oxide and 13% by weight of alumina. This material had a specific surface of 15 m / g.

The operation was carried out at ambient temperature and at a pressure sufficient to maintain the charge in the liquid phase.

This charge was passed over the absorbent to an LHSV of 0.5.

Claims (5)

1. Process for the purification of charges of liquid hydrocarbons containing in particular propylene and thence 70 ppm of carbonyl sulfide, in order to remove the latter, characterized in that the charge of liquid hydrocarbons is passed over an absorbent material comprising from about 75 to 95% by weight of iron oxide, from about 3.5 to 23% by weight of alumina optionally containing from 1 to 15% by weight of silica and from about 0 , 4 to 5% by weight of a promoter chosen from the group comprising sodium, potassium, calcium, barium or magnesium oxides, the specific surface of the absorbent material 2 being between 2 and 20 m / g. Process according to Claim 1, characterized in that the charge of liquid hydrocarbons is passed over an absorbent material comprising from 80 to 92% by weight of iron oxide, from 5 to 12% by weight of alumina optionally containing from 1 to 15% of silica, and from 0.6 to 3% by weight of a promoter chosen from the group comprising sodium, potassium, barium, calcium or magnesium oxide, specific surface of this absorbent material being between 2 and 20 m / g. 3. Method according to any one of claims 1 and 2 Λ characterized in that one passes the charge of liquid hydrocarbons over the absorbent material, at a temperature between about 20 and 60 ° C, at a sufficient pressure 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 90% 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 sulfide, characterized in that this charge is passed over an absorbent material comprising from 80 to 92 % by weight of iron oxide, from 5 to 12% by weight of alumina optionally containing from 1 to 15% by weight of silica and from 0.6 to 3% of a promoter chosen from potassium oxide or of calcium, this absorbent having previously been subjected to calcination at a temperature of between 550 and 650 ° C. and in the presence of water vapor, this absorbent having a specific surface of between 2 and 20 m / g., at a temperature between 20 and 60 ° C, at a pressure sufficient to maintain the charge in the liquid phase and at an LHSV between 0.1 and 10. 6. Charges of purified hydrocarbons, with a low carbonyl sulphide 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.