FR2586253A1 - Improved process for sweetening petroleum cuts - Google Patents

Abstract

Process for sweetening a hydrocarbon feedstock containing sulphur products. The invention is characterised by the use of a supported catalyst treated with an anhydrous alcoholic solution containing an alkaline agent. The catalyst may also be regenerated by treatment with an alcoholic alkaline solution.

Description

The present invention relates to the softening, preferably in a fixed bed, of hydrocarbon charges containing smelly and corrosive sulfur products. It relates in particular to the oxidation of mercaptans to disulfides by air in the presence of at least one catalyst deposited on a support and operating under anhydrous conditions.

The process according to the invention makes it possible in particular to avoid the conventional alkaline regeneration of the catalysts in the oxidation reactions of mercaptans, or at least to space considerably over time of such alkaline rejuvenations.

We know the great application that is made industrially ~ the property that have the chelates of certain transition metals such as copper, cobalt, vanadium, nickel, to catalyze the transformation of mercaptans into disulfides in the presence of atmospheric oxygen. . This property is implemented, for example in the presence of sulfonated cobalt phthalocyanine, to soften, in the aquo-alkaline liquid phase, the liquefied gases, natural or cracked gasolines, naphthas, or solvents of any composition. Such a process is described for example in US Patents 2,966,453, US 2,882,224, US 2,988,500 according to which the alkaline solution containing for example as catalyst a sulfonated cobalt phthalocyanine is used to extract the mercaptans from the fuel and to oxidize them disulfides by air in the aqueous phase.

It is also possible to carry out this softening using an oxidation catalyst fixed on a support insoluble in soda and hydrocarbons. Such a process is described for example in French patents 1,301,844 or US 2,988,500 according to which the hydrocarbon charge is brought into contact with a fixed bed of cobalt phthalocyanine on activated carbon, in the presence of air and of a reagent aquoalkaline.

Although these processes are widely used in the petroleum refining industry, they have the major drawback of consuming large quantities of aqueous sodium hydroxide solution which becomes polluted during the softening operation by various products such as naphthenic acids, phenols, hydrogen sulfide, nitrogenous products, etc. The recycling of these polluted soda solutions is a difficult operation, and their disposal poses ecological problems for the environment.

Another drawback linked to the use of such methods is due to the rapid deactivation of the catalyst which is compensated by frequent rejuvenation with aqueous sodium hydroxide, and less frequently, by regeneration by washing with hot water making it possible to entrain the alkaline naphtenates and phenates which poison the catalyst. This is described, for example in US Patents 3,148,156 and US 4,009,120.

This rapid deactivation can be overcome by the use of activators such as nitrogenous bases (US patents 4,100,057, US 4,168,245) or of quaternary ammonium salts (US patents 4,159,964, US 4,124,493,
US 4,121,997, US 4,157,312 and US 4,2U6,079), but the use of these expensive activators which are found in softened charges strikes the economy of these processes.

Another drawback of the use of such methods is linked to the need to separate, at the outlet of the softening reactor, the hydro charge.
of the activating solution of aqueous sodium hydroxide. he is also
necessary to dry the softened load on a filter
salt in order to reduce the water content in the hydrocarbons as much as possible, and to eliminate the risks of settling in the tanks, and freezing in cold weather.

We have now discovered a new procedure which makes it possible to avoid the above-mentioned drawbacks by considerably increasing the activity and the stability of the supported softening catalysts.

The procedure according to the invention consists
/ aqueous
a) - impregnating the catalyst supported by a non / (substantially anhydrous) alcoholic solution with at least one alkaline agent (or post-treating the catalyst supported by a non-aqueous (substantially anhydrous) alcoholic solution with at least one agent alkaline b) - percolating the charge containing the mercaptans on the supported catalyst in the presence of air as long as the mercaptan content at the outlet of the reactor has not reached at most the maximum value of the required specification (generally 5 ppm for gasoline and 10 ppm for kerosene) and possibly thereafter,
c) - to regenerate the supported catalyst by washing
with hot water or steam to remove accumulated impurities
lées on the support, then to reactivate the supported catalyst thus washed
with a nonaqueous (substantially anhydrous) alcoholic solution of at least
an alkaline agent.

The charge is then percolated again in the presence of air on the catalyst
thus regenerated.

Such a procedure avoids the use of aqueous sodium hydroxide solutions to reactivate the catalyst, and therefore eliminates the settling and drying operations associated with the use of such aqueous sodium hydroxide solutions. It also makes it possible to considerably reduce the alkali consumption of the process, and thereby to eliminate the problems of elimination and recycling of aqueous sodium hydroxide solutions.

The activation procedure according to the invention makes it possible to considerably improve the activity and the lifetime of certain known supported softening catalysts. Such catalysts are, for example, mono or polysulfonated cobalt phthalocyanines deposited on activated carbon described for example in US patent 3,108,081, sulfonated cobalt tetraphenylporphyrins deposited on carbon (preferably active) (patent
US 2,966,453), the sulfonated cobalt corrines deposited on activated carbon (US Patent 3,252,892).

The polycarboxylated cobalt phthalocyanines deposited on activated carbon can also be activated according to the procedure of the invention.

Such chelates can be prepared, for example, by reacting a cobalt salt with an anhydride such as pyromellitic anhydride or trimellitic anhydride in the presence of urea, and ammonium molybdate.

The polycarboxylated cobalt phthalocyanine thus obtained is then dissolved in an aqueous sodium hydroxide solution, then percolated over activated carbon.

The activation procedure according to the invention consists in impregnating the solid support with an alkaline alcoholic solution of metallic chelate, or in post-treating a traditional supported catalyst with an alkaline solution of alcohol.

As solid support for the chelates or complexes which can be used in the present invention, it is possible to use activated carbon preferably, but also any other suitable support such as silicas, aluminas, silica-aluminas, aluminosilicates, zeolites, earths activated, cation exchange resins, among which may be cited as examples Amberlite A.15 (RS03H) or IRC 50 (R-COOH).

The alkaline alcoholic activation solution may contain a base such as, for example, sodium hydroxide, potassium hydroxide, lithium hydroxide, ammonia in solution in a primary or secondary alcohol such as, for example, methanol, I ' ethanol, n-propanol, isopropanol, normal or branched butanols, pentanols, hexanols, ethyl-2-hexanol.

The impregnation temperature is between 20 and 800C, preferably between 20 and 500C. The catalyst and its support impregnated with the alkaline alcoholic solution has an alkali content of between 0.1 and 10% by weight, preferably between 1 and 5% by weight.

The softening is carried out by percolation of the petroleum fraction in the presence of oxygen or air on a support catalytic bed containing in supported form the metal complex according to the invention.

No addition of alkali such as aqueous sodium hydroxide, potassium hydroxide or ammonia is necessary after the impregnation or activation of the catalyst supported by an alcoholic solution of alk ali. The present method thus makes it possible, advantageously compared to the conventional methods, to avoid the use of a decanter, a salt filter and a soda pump or any other alkaline compound.

In carrying out the softening reaction, the reaction temperature does not have a critical effect. It can operate at room temperature, but it is also possible to operate at higher temperatures, without however exceeding temperatures of the order of 1200C.

On the other hand, the pressure required is generally between approximately 0.5 and 50 bars, and preferably between 1 and 30 bars approximately. Air is the most suitable oxidizing agent. Any other oxidizing agent, such as oxygen in the pure state, can also be used as any other gas or mixture of gases containing oxygen. The latter can be introduced into the reactor in stoichiometric quantities. It is sometimes better to use it in excess.

When the softened charge at the outlet of the reactor has a mercaptan content exceeding that required by the specifications, the catalyst is regenerated by first washing with hot water (washing temperature between 60 and 1000 ° C.) or with steam until colorless effluents are obtained, in order to rid the catalyst of the accumulated impurities contained in the feed. The catalyst thus washed is then re-impregnated with an alcoholic alkali solution.

The following examples illustrate, without limitation, the implementation of the method according to the present invention:
Example 1 (comparative)
In accordance with the techniques of the prior art, a supported catalyst is prepared by percolating on activated carbon a solution of sulfonated cobalt phthalocyanine in an aqueous solution containing 3% of ammonia.

The catalyst obtained contains 0.15% by weight of cobalt and 4% by weight of ammonium. The softening of a kerosene is carried out as follows
The charge to be softened is placed in a tank which supplies a reactor with an additional air. The reaction operating conditions are as follows - catalyst volume = 20 cm3 - pressure = 1 atmosphere - temperature = 200C - hourly space velocity of the feed (vvH) 1 liter / liter cataly
s / hour.

Once treated in the reactor, the effluent is separated from the air it contains in a separator. A residual mercaptan is then measured qualitatively by a "doctor test" (sodium leadite and sulfur flower) and quantitatively by potentiometry every 24 hours.

The charge to be softened consists of a kerosene (160-3000C) containing 700 ppm of total sulfur and 150 ppm of mercaptan sulfur. It is percolated in the presence of air directly on the supported catalyst. After 100 hours, the mercaptan content of the softened kerosene exceeds 10 ppm.

We can therefore assess the lifetime of this catalyst at only about 100 hours.

Example 2 (comparative)
Example 1 is repeated, replacing the aqueous solution containing 3% of ammonia with an aqueous solution containing 3% of sodium hydroxide. The catalyst thus contains, by weight, 0.15% of cobalt and 4% of sodium hydroxide. Substantially the same results are obtained as in Example 1.

Example 3
A supported catalyst is prepared by percolating on activated carbon a solution of sulfonated cobalt phthalocyanine in pure methanol, therefore anhydrous, containing 5% sodium hydroxide. The catalyst obtained after washing with pentane and drying in air contains 0.15% by weight of cobalt and 4% by weight of sodium hydroxide.

The softening of a kerosene is carried out under the same conditions and with the same charge as in Example 1 (200C, atmospheric pressure, 20 cm3 of catalyst supported on activated carbon, VVH = 1, kerosene containing 150 ppm mercaptan sulfur) .

No soda injection is carried out here.

A softened kerosene containing less than 10 ppm mercaptan sulfur is collected at the outlet of the reactor for 1,700 hours of operation. During this test, 34 liters of kerosene were softened with 20. cm3 of catalyst. This test shows that the impregnation of the carbon with an anhydrous alkaline alcoholic solution of sulfonated cobalt phthalocyanine leads to a supported catalyst whose lifetime is considerably increased compared to that of the same catalyst prepared in an aqueous medium.

After softening the kerosene for 1700 hours, the deactivated catalyst is washed with hot water at 800C- until colorless effluents are obtained, then re-impregnated with a methanolic sodium hydroxide solution at 5% by weight.

We then proceed to soften the same charge of kerosene under the same conditions. The new service life during which the softened charge has a mercaptan sulfur content of less than ioppm is 1600 hours.

Example 4
The supported catalyst prepared in Example 3 is used to soften an industrial load composed of a 50/50 mixture (by volume) of light petrol and heavy petrol produced by a catalytic cracker.

This charge, whose density at 150C is 0.779 contains 34% of aromatic compounds, 27% of olefins and 39% of saturated hydrocarbons. It also contains 800 ppm of phenols, 400 ppm of mercaptan sulfur and 2000 ppm of total sulfur.

The operating conditions are as follows: - catalyst volume = 20 cm3 - relative pressure = 0.5 bar - temperature = 300C - air volume / g RSH = 2Nl / g - VVH = 1.5
The petrol is softened for 1400 hours, during which the mercaptan content is below Sppm. At this stage, the catalyst can be regenerated as indicated in Example 3 and then the softening of an industrial charge can continue.

Example 5
An octacarboxylated cobalt phthalocyanine is prepared in the following manner: - 11 g of pyromellitic anhydride, 46 g of urea, 5.5 g of cobalt chloride, 1 g of boric acid and 0.5 g are reacted of ammonium molybdate in 150 cm3 of trichlorobenzene at 2180C for 4h. After evaporation to dryness of the trichlorobenzene at 1600C under vacuum, the black residue is washed with 400 cm3 of water, then it is dried for 1 hour at 1300C under vacuum. After dissolving in 180 cm3 of 30% aqueous sodium hydroxide, evaporation, then dissolving in 2 liters of water and filtration, neutralization is carried out with concentrated sulfuric acid until a precipitate is obtained which is filtered, which the washed with distilled water, and dried under vacuum at 1300 C. The elemental analysis of this blue-black precipitate (12 g, 78% yield) corresponds to the formula of octacarboxylated cobalt phthalocyanine.

- 40 cm3 of supported catalyst are prepared by circulating a solution of 0.4 g of octacarboxylated cobalt phthalocyanine in 100 cm3 of 5% aqueous sodium hydroxide solution over 40 cm3 of activated carbon until the solution is completely discolored. After drying at 400C of the impregnated catalyst containing 0.1% by weight of cobalt, it is divided into two batches of 20 cm3 intended to carry out two comparative kerosene softening tests.

Test A (comparative)
We proceed to the softening of a kerosene charge containing 150 ppm mercaptan sulfur according to the conditions of Example 1 (200C, VVH = 1
P atm) using 20 cm3 of catalyst prepared above. After 60 hours, the mercaptan content of the softened kerosene exceeds 1 Oppm.

Test B
The remaining 20 cm 3 of catalyst are treated with 50 cm 3 of pure methanol solution containing 5% by weight of sodium hydroxide.

After drying of the catalyst, the kerosene is softened according to Example 1 and under the same conditions as in test A. A softened kerosene containing less than 10 ppm mercaptan sulfur is collected at the outlet of the reactor for 950 hours of operation. .

Example 6
cobalt /
A phthalocyanine / tetracarboxylated is prepared in the following manner: - 9.6 g of trimellitic anhydride, 46 g of urea, 5.4 g of cobalt chloride, 0.9 g of boric acid and 0 are reacted , 47 g of ammonium molybdate in 100 cm3 of nitrobenzene at 2100C for 4 hours.

After evaporation to dryness of the nitrobenzene at 1600 ° C. under vacuum, a blue-black residue is collected, which is washed with 500 cm 3 of distilled water, and which is dried under vacuum. The yield is 11 g. This solid is used as it is for the preparation of softening catalysts.

40 cm3 of supported catalyst are prepared by circulating a solution of 0.5 g of tetracarboxylated cobalt phthalocyanine dissolved in 100 cm3 of 5% aqueous sodium hydroxide solution over 40 cm3 of activated carbon until the solution is completely discolored. After drying at 400 ° C. under vacuum, 40 cm 3 of impregnated charcoal containing approximately 0.1% by weight of cobalt are collected, which are divided into two batches of 20 cm 3 intended to carry out two comparative tests for kerosene softening.

Test A (comparative)
A kerosene feed containing 150 ppm of mercaptan sulfur is softened according to the conditions of Example 1 (200C, VVH 1, P atm) using 20 cm3 of catalyst prepared according to the method described above. After 50 hours of walking, the mercaptan content of the softened kerosene exceeds 10 ppm.

Test B
The remaining 20 cm 3 of catalyst are treated with 50 cm 3 of pure methanol solution containing 5% by weight of sodium hydroxide. After drying the catalyst, the kerosene is softened according to Example 1 and under the same conditions as in test A above. In this case, a softened kerosene containing less isoppm of mercaptan sulfur is collected at the outlet of the reactor for 1200 hours of operation.

Claims (9)

Claims 1.- Process for softening a hydrocarbon feed containing sulfur products, in the presence of a supported catalyst, the process consisting in previously impregnating the supported catalyst with a substantially anhydrous alcoholic solution of at least one alkaline agent. 2.- Method according to claim 1 wherein the alcoholic solution is a solution in an alcohol. 3.- Method according to claim 2 wherein the alcohol is a primary or secondary alcohol. 4.- The method of claim 3 wherein the alcohol is selected from the group consisting of methanol, ethanol, n-propanol, isopropanol, butanols, pentanols, hexanols and ethyl -2-hexanol. 5.- Method according to one of claims 1 to 4 wherein the alkaline agent is selected from the group consisting of sodium hydroxide, potassium hydroxide, lithium hydroxide and ammonia. 6.- Method according to one of claims 1 to 5 wherein the alkali content in the supported catalysts is between 0.1 and 10% by weight. 7.- Method according to one of claims 1 to 6 wherein the regeneration of the catalyst is carried out by washing it with hot water or steam, then treating it with an alcoholic solution substantially anhy  of at least one alkaline agent. 8.- Method according to one of claims 1 to 7 wherein the catalyst is chosen from the group consisting of cobalt phthalocyanines mono or polysulfonated deposited on a support, cobalt tetra phthalocyanines or octa carboxylated deposited on a support, sulfonated cobalt tetraphenylporphyrins deposited on a support, and sulfonated cobalt corrines deposited on a support. 9.- Method according to one of claims 1 to 8, wherein the catalyst, after impregnation with an anhydrous alcoholic medium, containing an alkaline agent, is dried before use for softening.