Catalyst for use in hydrotreatment, comprising metals from groups VIII and VIB, and preparation with citric acid and C1-C4 dialkyl succinate

Abstract

A catalyst which comprises an amorphous support based on alumina, a C1-C4 dialkyl succinate, citric acid and optionally acetic acid, phosphorus and a hydrodehydrogenating function comprising at least one element from group VIII and at least one element from group VIB; the most intense bands comprised in the Raman spectrum of the catalyst are characteristic of Keggin heteropolyanions (974 and/or 990 cm.sup.−1), C1-C4 dialkyl succinate and citric acid (in particular 785 and 956 cm.sup.−1). Also a process for preparing said catalyst in which a catalytic precursor in the dried, calcined or regenerated state containing the elements of the hydrodehydrogenating function, and optionally phosphorus, is impregnated with an impregnation solution comprising at least one C1-C4 dialkyl succinate, citric acid and optionally at least one compound of phosphorus and optionally acetic acid, and is then dried. Further, the use of said catalyst in any hydrotreatment process.

Claims

1. A catalyst comprising an amorphous support based on alumina, at least one C1-C4 dialkyl succinate, citric acid, phosphorus, acetic acid and a hydrodehydrogenating function comprising at least one element from group VIB and at least one element from group VIII of the Periodic Table, with the Raman spectrum of the catalyst comprising a band at 896 cm.sup.−1, characteristic of acetic acid and comprising bands at 990 cm.sup.−1, at 974 cm.sup.−1 or at both 990 cm.sup.−1 and 974 cm.sup.−1, characteristic of at least one Keggin heteropolyanion, the characteristic bands of said succinate and the principal characteristic bands of citric acid, the catalyst being prepared from a precursor having: a molar ratio of dialkyl succinate to the at least one element from group VIB of the precursor in the range 0.15 to 2 mole/mole a molar ratio of citric acid to element(s) from group VIB of the precursor in the range 0.5 to 4 mole/mole a molar ratio of acetic acid to the element(s) from group VIB of the precursor in the range 0.5 to 5 mole/mole the molar ratio of citric acid+acetic acid to the element(s) from group VIB of the precursor in the range 1.0 to 6 mole/mole.

2. The catalyst according to claim 1, in which the dialkyl succinate is dimethyl succinate and in which the Raman spectrum of the catalyst has principal bands at 990 cm.sup.−1, at 974 cm.sup.−1 or at both 990 cm.sup.−1 and 974 cm.sup.−1, characteristic of Keggin heteropolyanions, and at 853 cm.sup.−1, characteristic of dimethyl succinate and at 785 and 956 cm.sup.−1, characteristic of citric acid and at 896 cm.sup.−1, characteristic of acetic acid.

3. The catalyst according to claim 1, in which the dialkyl succinate is diethyl succinate, dibutyl succinate or diisopropyl succinate.

4. The catalyst according to claim 1, in which the support contains more than 25% by weight of alumina.

5. The catalyst according to claim 1, comprising a support constituted by alumina or constituted by silica-alumina.

6. The catalyst according to claim 1, also comprising boron and/or fluorine.

7. The catalyst according to claim 1, in which the hydrodehydrogenating function comprises molybdenum, nickel, cobalt or a mixture of any of these metals.

8. The catalyst according to claim 1, which is sulphurized.

9. A process for preparing a catalyst according to claim 1, said process comprising the following steps in succession: a) preparing a catalytic precursor containing the elements of the hydrodehydrogenating function, and optionally phosphorus, said precursor having undergone a heat treatment; b) at least one impregnation with an impregnation solution comprising at least one C1-C4 dialkyl succinate, citric acid and at least one compound of phosphorus, if the phosphorus has not been introduced in totality by impregnation in step a), and acetic acid; c) maturation; d) drying at a temperature of less than 200° C., without a subsequent calcining step, in which the dialkyl succinate and citric acid are introduced into the impregnation solution of step b) in a quantity corresponding to a molar ratio of dialkyl succinate to the impregnated element(s) from group VIB of the catalytic precursor in the range 0.15 to 2 mole/mole, and in a molar ratio of citric acid to the impregnated element(s) from group VIB of the catalytic precursor in the range 0.5 to 4 mole/mole, the molar ratio of acetic acid to the impregnated element(s) from group VIB of the catalytic precursor is in the range 0.5 to 5 mole/mole, and the molar ratio of citric acid+acetic acid to the impregnated element(s) from group VIB of the catalytic precursor is in the range 1.0 to 6 mole/mole.

10. The process for preparing a catalyst according to claim 9, said process comprising the following steps in succession: a) at least one impregnation of an amorphous support based on alumina with at least one solution containing the elements of the hydrodehydrogenating function, and optionally phosphorus; b) drying at a temperature below 180° C. optionally followed by calcining at a temperature of at least 350° C.; c) at least one impregnation with an impregnation solution comprising at least one C1-C4 dialkyl succinate, citric acid, at least one compound of phosphorus, if the phosphorus has not been introduced in its entirety in a), and acetic acid; d) maturation; e) drying at a temperature of less than 200° C., without a subsequent calcining step, in which the dialkyl succinate and citric acid are introduced into the impregnation solution of c) in a quantity corresponding to a molar ratio of dialkyl succinate to the impregnated element(s) from group VIB of the catalytic precursor in the range 0.15 to 2 mole/mole, and in a molar ratio of citric acid to the impregnated element(s) from group VIB of the catalytic precursor in the range 0.5 to 4 mole/mole, the molar ratio of acetic acid to the impregnated element(s) from group VIB of the catalytic precursor is in the range 0.5 to 5 mole/mole, and the molar ratio of citric acid+acetic acid to the impregnated element(s) from group VIB of the catalytic precursor is in the range 1.0 to 6 mole/mole.

11. The process according to claim 10, in which the whole of the hydrodehydrogenating function is introduced during step a).

12. The process for preparing a catalyst according to claim 9, said process comprising the following steps in succession: a) regenerating spent catalyst comprising a hydrodehydrogenating function and optionally phosphorus; b) at least one impregnation with an impregnation solution comprising at least one C1-C4 dialkyl succinate, citric acid, optionally at least one compound of phosphorus if the phosphorus has not been introduced into the catalyst in its entirety in step a), and acetic acid; c) maturation; d) drying at a temperature of less than 200° C., without a subsequent calcining step, in which the dialkyl succinate and citric acid are introduced into the impregnation solution of step b) in a quantity corresponding to a molar ratio of dialkyl succinate to the impregnated element(s) from group VIB of the catalytic precursor in the range 0.15 to 2 mole/mole, and in a molar ratio of citric acid to the impregnated element(s) from group VIB of the catalytic precursor in the range 0.5 to 4 mole/mole, the molar ratio of acetic acid to the impregnated element(s) from group VIB of the catalytic precursor is in the range 0.5 to 5 mole/mole, and the molar ratio of citric acid+acetic acid to the impregnated element(s) from group VIB of the catalytic precursor is in the range 1.0 to 6 mole/mole.

13. The process according to claim 9, in which step b) is carried out in the presence of water and/or ethanol.

14. The process according to claim 9, in which step c) is carried out at a temperature of 17° C. to 50° C.

15. The process according to claim 9, in which step d) is carried out at a temperature of 80° C. to 180° C., without subsequent calcining.

16. The process according to claim 9, in which the quantity of phosphorus introduced by impregnation is in the range 0.1% to 20% by weight expressed as the weight of oxide with respect to the catalytic precursor after heat treatment in step a) or b), the quantity of element(s) from group VIB is in the range 5% to 40% by weight expressed as the weight of oxide with respect to the catalytic precursor after heat treatment in step a) or b), and the quantity of element(s) from group VIII is in the range 1% to 10% by weight expressed as the weight of oxide with respect to the catalytic precursor after heat treatment in step a) or b).

17. The process according to claim 9, in which the product obtained at the end of step e) undergoes a sulphurization step.

18. A process for the hydrotreatment of a hydrocarbon feed in the presence of a catalyst in accordance with claim 1, which comprises contacting the hydrocarbon feed with the catalyst in accordance with claim 1.

19. The process according to claim 18, in which the hydrotreatment is hydrodesulphurization, hydrodenitrogenation, hydrodemetallization, hydrogenation of aromatics or hydroconversion.

20. The process according to claim 19, in which the hydrotreatment is deep gas oil hydrodesulphurization.

Description

EXAMPLE 1

Preparation of Comparative Regenerated Catalysts B1 and B2

(1) A matrix was used which was composed of ultrafine tabular boehmite or alumina gel sold by the supplier Condea Chemie GmbH. This gel was mixed with an aqueous solution containing 66% nitric acid (7% by weight of acid per gram of dry gel) then mixed for 15 minutes. At the end of mixing, the paste obtained was passed through a die having cylindrical orifices with a diameter of 1.6 mm. The extrudates were then dried overnight at 120° C. and calcined at 600° C. for 2 hours in moist air containing 50 g of water per kg of dry air. Extrudates were obtained of a support composed solely of low crystallinity cubic gamma alumina.

(2) Cobalt, molybdenum and phosphorus were added to the alumina support described above which was in the extruded form. The impregnation solution was prepared by dissolving molybdenum oxide (24.34 g) and cobalt hydroxide (5.34 g) in hot phosphoric acid solution (7.47 g) in aqueous solution. After dry impregnation, the extrudates were left to mature at ambient temperature (20° C.) in an atmosphere saturated with water for 12 h, then they were dried overnight at 90° C. and calcined at 450° C. for 2 hours. The calcined catalyst A was obtained. The final composition of catalyst A, expressed in the form of the oxides, was thus as follows: MoO.sub.3=22.5±0.2 (% by weight), CoO=4.1±0.1 (% by weight) and P.sub.2O.sub.5=4.0±0.1 (% by weight).

(3) The calcined catalyst A was charged into a traversed bed unit and sulphurized with a straight run gas oil supplemented with 2% by weight of dimethyldisulphide. A HDS test of a mixture of straight run gas oil and gas oil from catalytic cracking was then carried out for 300 h. After the test, the spent catalyst was discharged, recovered and washed with toluene under reflux then separated into two batches. The first batch was regenerated in a combination furnace controlled by introducing increasing quantities of oxygen for each temperature stage, which limited the exothermicity linked to combustion of the coke. The final regeneration stage was 450° C. The regenerated catalyst was analyzed by XRD. The absence of a line at 26°, characteristic of the presence of crystalline CoMoO.sub.4, was noted. This catalyst will henceforth be denoted B1. The second batch of washed spent catalyst was regenerated in a muffle furnace at 450° C. without controlling the exothermicity of the coke combustion. XRD analysis carried out after regeneration showed the presence of a thin line at 26°, characteristic of the presence of crystalline CoMoO.sub.4. Further, this catalyst, henceforth denoted B2, had a very pronounced bright blue colour.

EXAMPLE 2

Preparation of a Regenerated Catalyst C1 in Accordance with the Invention—Production with Citric Acid

(4) Catalyst C1 was prepared by dry impregnation of a solution of citric acid and dimethyl succinate diluted in ethanol onto catalyst B1. The intended quantities of citric acid (CA) and dimethyl succinate (DMSU) were respectively 15% by weight and 10% by weight (i.e. AC/Mo=0.50 mole/mole and DMSU/Mo=0.44 mole/mole). After a maturation period of 24 hours in a closed vessel at ambient temperature, the catalyst was dried in a stream of nitrogen (1 NL/g/g) for 1 hour.

(5) Catalyst C1 was analyzed by Raman spectroscopy. In particular, it had a principal band of the Keggin HPA at 990 cm.sup.−1 and characteristic bands of citric acid and dimethyl succinate respectively at 785 cm.sup.−1 and 851 cm.sup.−1.

EXAMPLE 3

Preparation of a Regenerated Catalyst C2 in Accordance with the Invention—Production with Citric Acid and Acetic Acid

(6) Catalyst C2 was prepared by dry impregnation of a solution of citric acid, dimethyl succinate and acetic acid diluted in ethanol onto catalyst B2 which had a crystalline CoMoO.sub.4 phase. The intended quantities of citric acid (CA), dimethyl succinate (DMSU) and acetic acid (AA) were respectively 15% by weight, 10% by weight and 20% by weight (i.e. AC/Mo=0.50 mole/mole, DMSU/Mo=0.44 mole/mole and AA/Mo=2.13 mole/mole). After a maturation period of 24 hours in a closed vessel at ambient temperature, the catalyst was dried in a stream of nitrogen (1 NL/g/g) for 1 hour.

(7) Catalyst C2 was analyzed by Raman spectroscopy. In particular, it had a principal band of the Keggin HPA at 990 cm.sup.−1 and characteristic bands of citric acid, dimethyl succinate and acetic acid respectively at 785 cm.sup.−1, 851 cm.sup.−1 and 896 cm.sup.−1.

EXAMPLE 2BIS

Preparation of a Regenerated Catalyst C1Bis in Accordance with the Invention—Production with Citric Acid and Acetic Acid

(8) The catalyst was prepared in the same manner as for Example 3, but using regenerated catalyst B1.

EXAMPLE 3BIS

Preparation of a Regenerated Catalyst C2Bis in Accordance with the Invention—Production with Citric Acid

(9) The catalyst was prepared in the same manner as for Example 2, but using regenerated catalyst B2.

EXAMPLE 4

Comparative Test of Catalysts B1, B2, C1, C2, C1Bis and C2Bis in the Hydrogenation of Toluene in Cyclohexane Under Pressure and in the Presence of Hydrogen Sulphide

(10) The catalysts described above were sulphurized dynamically in situ in the traversed fixed bed of a tube reactor of a Microcat type pilot unit (made by Vinci), the fluids moving from top to bottom. Hydrogenating activity measurements were carried out immediately after sulphurization under pressure and with no ingress of air, using the hydrocarbon feed which served to sulphurize the catalysts.

(11) The sulphurization and test feed was composed of 5.8% of dimethyldisulphide (DMDS), 20% of toluene and 74.2% of cyclohexane (by weight).

(12) The sulphurization was carried out from ambient temperature to 350° C. with a temperature ramp-up of 2° C./min, a HSV of 4 h.sup.−1 and H.sub.2/HC=450 NL/L. The catalytic test was carried out at 350° C. at a HSV of 2 h.sup.−1 and H.sub.2/HC equivalent to that of sulphurization, with a minimum of 4 samples being taken for analysis by gas chromatography.

(13) In this way, the stabilized catalytic activities of equal volumes of catalysts was measured for the toluene hydrogenation reaction.

(14) The detailed conditions of the activity measurement were as follows: total pressure: 6.0 MPa; toluene pressure: 0.37 MPa; cyclohexane pressure: 1.42 MPa; methane pressure: 0.22 MPa; hydrogen pressure: 3.68 MPa; H.sub.2S pressure: 0.22 MPa volume of catalyst: 4 cm.sup.3 (extrudate length between 2 & 4 mm); hourly space velocity: 2 h.sup.−1; test and sulphurization temperature: 350° C.

(15) The liquid effluent samples were analyzed by gas chromatography. The molar concentrations of unconverted toluene (T) and the concentrations of its hydrogenation products (methylcyclohexane (MCC6), ethylcyclopentane (EtCC5) and dimethylcyclopentanes (DMCC5)) were used to calculate a degree of toluene hydrogenation, X.sub.HYD, defined by:

(16) $\hspace{1em}{X}_{\mathrm{HYD}}\left(\%\right)=100\times \frac{\mathrm{MCC}6+\mathrm{EtCC}5+\mathrm{DMCC}5}{T+\mathrm{MCC}6+\mathrm{EtCC}5+\mathrm{DMCC}5}$

(17) Since the toluene hydrogenation reaction is first order under the test conditions employed and the reactor behaves as an ideal piston reactor, the hydrogenating activity A.sub.HYD of the catalysts could be calculated by applying the formula:

(18) $\hspace{1em}{A}_{\mathrm{HYD}}=\frac{\ln \left(100\right)}{\left(100-X_{\mathrm{HYD}}\right)}$

(19) Table 1 compares the relative hydrogenating activities of catalysts B1 and B2 (not in accordance), and catalysts C1 and C2 (in accordance with the invention), equal to the ratio of the activity of the catalyst to the activity of catalyst B2 (not in accordance) taken as the reference (100% activity).

(20) TABLE-US-00001 TABLE 1 Relative activities with respect to calcined catalyst B2 (not in accordance) Quantity Quantity of Relative of acid organic A.sub.HYD (wt % with additive (wt with respect Type of % with respect Type of to final organic respect to to B2 Catalyst acid catalyst) additive final catalyst) (%) Regenerated — 0 — 0 100 B1, not in accordance Regenerated — 0 — 0 87 B2, not in accordance C1, in CA 15  DMSU 10 116 accordance C2, in CA + 15 + 20 DMSU 10 119 accordance AA C1bis (from CA + 15 + 20 DMSU 10 120 B1) in AA accordance C2bis (from CA 15  DMSU 10 108 B2) in accordance

(21) The catalyst regenerated under uncontrolled conditions, B2, (not in accordance), had a lower activity than the regenerated catalyst B1 (not in accordance).

(22) Table 1 shows that the supplemented catalyst C1 (in accordance) prepared by adding 15% by weight of citric acid (CA) and 10% of dimethyl succinate (DMSU) to catalyst B1, had an improved activity, compared with the starting catalyst, of 16%; adding acetic acid increased the gain to 20% (catalyst C1bis).

(23) Table 1 shows that the supplemented catalyst C2bis (in accordance) prepared by adding 15% by weight of citric acid (CA) and 10% of dimethyl succinate (DMSU) to catalyst B2, had an improved activity compared with the starting catalyst, of 24%; adding acetic acid increased the gain to 37% (catalyst C2).

(24) These catalytic results show the particular and surprising effect of a combination of citric acid (AC) and dimethyl succinate (DMSU) on regenerated catalyst (in accordance with the invention) and in particular on a regenerated catalyst which has crystalline phases (B2). This effect is further improved by adding acetic acid.