FR2591610A1 - Transition metal complexes prepared from tetracyanothiophene and tetracyanodithiine, and their use as catalysts for sweetening petroleum cuts in liquid and supported phase - Google Patents

Abstract

New catalyst obtained by reaction between a metal precursor, especially a transition metal salt, and a compound which is tetracyano-1,4-dithiine or tetracyanothiophene. The catalyst can be employed in processes for sweetening hydrocarbon feedstocks, either deposited on a support or in liquid phase.

Description

The present invention relates to new transition metal complexes and their manufacture from a metal salt or complex and tetracyanothiophene or tetracyanodithiine; the invention also relates to their use as catalysts for the oxidation of mercaptans to disulfides, in the liquid or supported phase.

The great application which is made industrially of the property possessed by the chelates of certain transition metals such as copper, cobalt, vanadium and nickel is known to catalyze the transformation of mercaptans into disulfides in the presence of atmospheric oxygen. This property is implemented, for example in the presence of a sulfonated cobalt phthalocyanine, to soften, in the aquo-alkaline liquid phase, the liquefied gases, natural or cracked essences, 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 2,882,224 and US 2,988,500, according to which the hydrocarbon feed is brought into contact with a fixed bed of cobalt phthalocyanine.

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 is polluted during the softening operation by various products such as that naphthenic acids, phenols, hydrogen sulfide, nitrogen products, etc., The recycling of these polluted soda solutions is a difficult operation, and their elimination poses ecological problems;
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 allowing 'entrain the naphthenates and alkaline 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 quaternary ammonium salts (US patents 4,159,964, US 4,124,493,
US 4,121,997, US 4,157,312 and US 4,206,079), 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 processes is also due to the use of sulfonated or carboxylated cobalt phthalocyanines as catalysts, which are expensive and difficult products to prepare.

Cobalt phthalocyanines, generally prepared by reaction of a cobalt salt with phthalonitrile (US Patent 3,140,292 for example) or with phthalic anhydride in the presence of urea, ammonium molybdate and ammonium salt (Belgian patent 611,062 for example) are insoluble products and therefore difficult to use as such.

In order to make these complexes soluble in the aqueous phase, sulphonation of the cobalt phthalocyanines is carried out with pure sulfuric acid or oleum (US Pat. No. 3,091,618 for example). This is difficult to control since it produces multisulfonated complexes which are easily eluted by the aqueous regeneration soda which is used in the softening process in a fixed bed. Sulfonation also has the disadvantage of producing spent sulfuric acid which is difficult to get rid of. In addition, recovery of the active catalyst from the reaction mass is difficult and costly.

An improvement described in US Pat. No. 4,088,569 consists in using 4-sulfophthalic acid as a precursor and thus avoiding the subsequent sulfonation of the cobalt complex formed.

Another improvement consisted in using as precursor 3, 3 ', 4, 4' benzophenone tetracarboxylic dianhydride, and thus obtaining, after a complicated procedure, the corresponding cobalt octacarboxylated phthalocyanine (US Pat. No. 4,243,551). However, these solutions remain expensive and not very easy to implement.

We have now discovered new catalysts and a procedure for manufacturing these catalysts, which has the advantage of being much simpler than the procedures mentioned above, and of using precursors which are much less expensive and much less difficult to prepare.

The procedure for preparing the catalysts according to the invention consists in reacting a metal precursor (transition metal or salt or complex of a transition metal) with tetracyano 1,4-dithiine (I) or tetracyano thiophene (II) , in order to obtain a complex which is directly usable, both in a liquid-liquid softening process, and in a supported phase softening process.

It is optionally possible to use a mixture of compounds 1 and II.

Tetracyano 1,4 dithiine (I) is a product whose synthesis is easily carried out, for example from sodium cyanide, carbon sulphide and an oxidizing agent such as chlorine or thionyl chloride. Its synthesis, which is carried out with a high yield, is described, for example by G. Bahr in the review "Angewandte Chemie, 1956, 68, 525" and by HE Simmons and his collaborators in the "Journal
N of the American Chemical Society, 1962, vol. 864, p. 4746 ".

The tetracyanothiophene (II) is prepared with a very good yield, for example by pyrolysis of the compound (I) with extrusion of a sulfur atom at a temperature of the order of 2000C (see previous reference).

The metal precursor necessary for the synthesis of the catalyst according to transition
The invention can be any salt or complex of a metal or groups
IVb, Vb or Vlb or preferably from group VIII of the periodic table; mention may, for example, be made of iron, cobalt, nickel, copper, manganese or vanadium salts. Thus, in general, any salt such as a sulfate, a nitrate, a chloride, a bromide, an iodide, a carbonate, an octoate, a stearate, or a naphthenate can be used. It is also possible to operate from a metal which gives the desired complex in situ during the reaction.

For example, cobalt or powdered copper can be used in place of the metal salt.

The reaction between the precursor and the tetracyano 1,4-dithiine (I) or the tetracyano thiophene (II) can be carried out in any solvent such as for example water, chlorobenzene, dichlorobenzenes, trichlorobenzenes, quinoline, nitrobenzenes, dimethylformamide, dimethylacetamide, lthexamethyl-phosphoramide, etc.

The ratio between the tetracyano ligand (I) or (II) and the metal or the metal salt or complex, can be between 1 and 10, and preferably between 2 and 4.

The reaction temperature between the metal precursor and the cyano ligand is between approximately 20 and 2500C, preferably between 120 and 23gel approximately.

The reaction between the ligand (I) or (II) and the metal precursor (metal salt for example) is generally accompanied by the formation of a precipitate, generally very colored, which, after filtration and washing, can be used as it is for softening reactions. Indeed, this precipitate is generally soluble in aqueous sodium hydroxide or any aqueous-alkaline solution and can therefore be used in liquid-liquid softening processes in which the catalyst is generally used in solution in an alkaline aqueous solution ç for example of aqueous soda used to extract the mercaptans from a hydrocarbon feed and to transform them into sodium mercaptide.

The aqueous alkaline, for example aqueous sodium, solution of the catalyst according to the invention can also be used as an impregnating solution for any suitable support, such as activated carbon preferably, but also any other support such as silicas, aluminas , silica-aluminas, aluminas silicates, zeolites, activated earths and ion-exchange resins, among which mention may be made, for example, of amberlite A15 (RSO3H) or IRC 50 (R-COOH).

The charges to be treated can be softened in a liquid-liquid two-phase medium, if the charge is a light essence or a naphtha.

In this case, the catalyst is dissolved in the aqueous sodium phase in which the mercaptans from the feed are extracted in the form of sodium mercaptide. The oxidation of sodium mercaptides is carried out in air in the presence of the catalyst according to the invention, and provides disulfides which are insoluble in an aqueous medium which are separated by decantation.

In the case where the load to be treated consists of heavy gasolines, catalytic cracking gasolines, kerosene, gas oil, softening is preferably carried out in a fixed bed, several versions being possible depending on whether one operates under anhydrous conditions or not.

Thus, on the one hand, softening in a fixed bed in an anhydrous medium has the advantage of requiring only rejuvenations which are spaced out over time, and considerably reducing the consumption of alkaline agent. After activation of the catalyst supported by an alkaline alcoholic solution, the petroleum fraction is percolated in the presence of oxygen or air on a fixed catalytic support bed containing the metal complex according to the invention in supported form.

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, ethanol, n-propanol, 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.

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 alkali. 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.

When the softened charge at the outlet of the reactor has a mercaptan content exceeding that required by the specifications, the catalyst is regenerated for example, Ven first washing with hot water (washing temperature between 60 and 1000C) 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.

On the other hand, in the non-anhydrous version, the charge is percolated in the presence of air or oxygen on the fixed catalytic support bed containing, in supported form, the metal complex according to the invention, but an aqueous sodium hydroxide solution is also sent to the catalyst continuously or discontinuously. The aqueous sodium hydroxide solution which settles from the hydrocarbon phase is then recovered, then recycled.

In carrying out the softening reaction, the reaction temperature does not have a critical effect. It is possible to operate at ambient 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 well 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.

The following examples illustrate, without limitation, the implementation of the method according to the present invention:
Example 1- a) - Preparation of a catalyst from a cobalt salt and tretracyano thiophene (catalyst A).

179 tetracyano thiophene, 11.59 cobalt octoate in solution in xylene (11% by weight of cobalt) and 1 liter of trichlorobenzene are introduced into a 2 liter flask. The mixture is stirred and the solution is refluxed at 2200C for 4 hours. A black precipitate is then obtained which is filtered, which is washed with acetone and which is dried under vacuum. 189 of catalyst A are obtained. Elemental analysis of this complex A indicates that it contains (by weight) 7% of cobalt, 42% of carbon, 19% of nitrogen, 16% of sulfur, and 2% of hydrogen.

b) - Softening in a liquid-liquid two-phase medium.

100 mg of catalyst A are dissolved in 20 cm 3 of sodium hydroxide at P / o (weight), then 80 cm 3 of heptane are introduced, then 59 of tert-butyl mercaptan.

(tbu= tertiobutyle) (1 mole d'oxygène est absorbée pour 4 moles de mercaptans consommés). En fin de réaction, la teneur en mercaptan résiduel dans les deux phases est mesurée par potentiométrie. Au bout de 30 minutes, on absorbe 0,33 l d'oxygène, ce qui correspond à la quantité estimée pour la consommation de l'intégralité de la charge de tertiobutyl mercaptan. La potentiométrie au nitrate d'argent indique que la teneur en mercaptan résiduel est inférieure à lmm. The sealed reactor is connected to a pure oxygen supply, and the two-phase mixture is stirred vigorously. The oxygen consumption is monitored at room temperature over time linked to the softening reaction

(tbu = tertiobutyle) (1 mole of oxygen is absorbed for 4 moles of mercaptans consumed). At the end of the reaction, the residual mercaptan content in the two phases is measured by potentiometry. After 30 minutes, 0.33 l of oxygen is absorbed, which corresponds to the amount estimated for consumption of the entire load of tert-butyl mercaptan. The silver nitrate potentiometry indicates that the residual mercaptan content is less than 1 mm.

Successive charges of 59 of tert-butyl-mercaptan are then introduced in order to evaluate the stability of the catalyst over time. It is found that the softening time remains constant at around 30 minutes for 8 successive loads of 59 of tert-butyl mercaptan.

c) - Softening in a fixed bed and in an anhydrous medium.

1.2 g of catalyst A are dissolved in 250 cm 3 of an aqueous sodium hydroxide solution at 5% (by weight), and a dark green solution is obtained. This solution circulates by means of a peristatic pump on 200 cm3 of NORIT PKDA activated carbon until the solution is completely discolored.

After draining the catalyst on carbon, the catalyst is activated with 200 cm3 of a methanolic sodium hydroxide solution at 5% (weight) for 1 hour at 400C. The supported catalyst, after drying, contains about 0.07% (weight) of cobalt and 4% (weight) of sodium hydroxide.

The charge to be softened is placed in a tank which supplies the reactor with an additional air. The operating conditions of the reaction are as follows: - catalyst volume = 20 cm3 - pressure = 1 atmosphere - temperature = 200C - hourly space velocity of the feed (VVH = 11/1 catalyst / hour)
Once treated in the reactor, the effluent is separated from the air it contains in a separator. A residual mercaptan is then assayed 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.

The mercaptan content of softened kerosene is less than 1 ppm for approximately 50 hours, then gradually increases until it reaches 10 ppm after 800 hours of walking. The lifetime of the catalyst can thus be evaluated at approximately 800 hours.

After having softened the kerosene for 800 hours, the deactivated catalyst is washed with hot water at 80 ° C. until colorless effluents are obtained, 7 then re-impregnated with an equivolume of 5% ethanolic sodium hydroxide solution. One then proceeds to soften the same charge of kerosene according to the conditions of example le. The service life of the catalyst during which the softened charge has a mercaptan sulfur content of less than 10 ppm is 600 hours.

d) - Softening in a fixed bed and in an aqueous-sodium medium.

The supported catalyst is used containing 0.07% (weight) of cobalt prepared in example le, but without proceeding to the start of the activation with a methanolic sodium hydroxide solution.

The kerosene is softened under the same conditions as in example îc. This time, it can be seen that the mercaptan content of the softened charge increases rapidly, reaching 10 ppm during 100 hours of operation.

The catalyst is then rejuvenated with a 7% aqueous sodium hydroxide solution. This allows the catalyst to recover its activity and provide a kerosene containing less than 10 ppm mercaptan sulfur for about 90 hours. The same operation is repeated approximately every 90 hours and shows that the catalyst has satisfactory stability.

Example 2a) Preparation of a catalyst from a cobalt salt and tetracyano 1,4-dithiine (catalyst B).

19.59 of tetracyanodithiin, 11.59 of cobalt octoate in solution in xylene (11% by weight of cobalt) and 1 liter of trichlorobenzene are introduced into a 2 liter flask. Stir and bring the solution to reflux at about 2200C for 4 hours. A black precipitate is then obtained which is filtered, which is washed with acetone and which is dried under vacuum. The yield is 199. The elemental analysis of this complex B indicates that it contains by weight 5% of cobalt, 40% of carbon, 22% of nitrogen, 24% of sulfur and 4% of hydrogen.

b) - Softening in a two-phase liquid medium.

The procedure is as in Example 1b by dissolving 100 mg of catalyst B in 20 cm 3 of sodium hydroxide at P / o (weight), then adding 80 cm 3 of heptane, and 59 of tert-butyl mercaptan. The time after which all of the mercaptan is transformed into disulfide by molecular oxygen is approximately 40 minutes. The same reaction time is obtained for the softening of 6 consecutive loads of 59 of mercaptan.

c) - Softening in a fixed bed and in an anhydrous medium.

The procedure is as in example 1c by percolating 250 cm 3 of an aqueous sodium hydroxide solution at 5% (weight) containing 1.39 of catalyst B in dissolved form. Then the catalyst obtained is activated with a methanolic sodium hydroxide solution at 5% (weight).

We then proceed to soften a kerosene identical to that of Example 1c and under the same conditions. The lifetime of the catalyst during which the residual mercaptan content of the softened charge is less than 10 ppm is 600 hours.

d) - Softening in a fixed bed and in an aqueous sodium medium.

The procedure is as in Example 1d using the catalyst prepared in Example 1c, but not activated by methanolic sodium hydroxide.

The service life of the catalyst is 80 hours. After successive rejuvenation of the catalyst with an aqueous sodium hydroxide solution at 7%, several successive softening cycles are obtained of a duration approximately equal to 70 hours of operation.

Claims (7)

Claims 1 / Hydrocarbon softening catalyst obtained by making  react a metallic precursor chosen from the group consisting  with a transition metal, a salt of a transition metal and a  transition metal complex, with at least one selected compound  among the tetracyano 1,4-dithiine of formula (I) and the tetracyano  thiophene of formula (II):

 21 The method of claim 1 wherein the transition metal  is chosen from the group consisting of iron, cobalt, nickel,  copper, manganese and vanadium. 3 / Catalyst according to one of claims 1 and 2, obtained by reaction  between the metal precursor and the compound of formula I or  formula 11, at a temperature between 20 and 2500C approximately. 4 / Catalyst according to one of claims 1 and 2, obtained by reaction  between the metal precursor and the compound of formula I or  formula II, the ratio between compound I or II and the precursor  metallic being between 1 and 10. 5 / Use of the catalyst according to one of claims 1 to 4 in  a liquid-liquid softening process, the catalyst being  used in solution in an alkaline aqueous solution using  which extracts the mercaptans from a hydrocarbon feed. 6 / Use of the catalyst according to one of claims 1 to 4 in  a process for softening hydrocarbons, the so-called catalyst  being used on a solid support. 7 / Use of the catalyst according to claim 6 on a support  chosen from the group consisting of activated carbon, silicas,  aluminas, silica aluminas, aluminosilicates, zeolites,  activated earths and ion exchange resins. 8 / Use according to one of claims 6 or 7 of a catalyst  containing a mixture of the compounds of formula I and II.