GB2055599A - Alumina-supported hydrotreatment catalysts - Google Patents

Abstract

A Ni-Mo catalyst on gamma -alumina is prepared by adsorbing a Ni salt on the alumina under basic conditions, calcining the product then adsorbing a Mo salt or complex on the calcined product under acid conditions and calcining the product. The product catalyst has a high octahedral/tetrahedral Mo(VI) ratio, a high tetrahedral Ni<2+> content and good dispersion of both Mo and Ni, and is especially useful in the hydrotreating of coal-derived materials.

Description

SPECIFICATION Alumina-supported catalysts This invention concerns the production of catalysts supported on alumina, especially catalysts suitable for hydrogenation of coal-derived materials.

It has previously been proposed to use Co (or Ni)-Mo (or W) supported catalysts for the hydrotreating of heavy petroleum oils and coal-derived liquors, and they have been studied experimentally with particular emphasis on the hydrodesulphurisation (HDS) capability of these catalysts. Co-Mo catalysts have been estensively studied and several are commercially available.

Ni-Mo catalysts are also commercially available. In the preparation of Co-Mo catalysts supported on y-alumina the usual procedure has been to carry out impregnation of the support under initially essentially neutral conditions, allowing the pH to vary freely as adsorption on the support material proceeds. Indeed, the pH has sometimes been used as a guide to the completion of adsorption processes.

The present invention is based on the control of pH of an impregnating solution to allow greater control over surface species present in the final species, with improvements in the subsequent activity of the catalysts. There is a tendency for y-alumina to buffer pH at a constant value and thus accurate control over pH would be expected to be difficult.

The present invention provides a novel Ni-Mo catalyst supported on y-alumina in which the catalyst in oxide form has a high octahedral/tetrahedral Mo(VI) ratio, a high tetrahedral Ni2+ content arising from inversion of the surface Ni-alumina spinel, and good dispersion of both Mo and Ni. The octahedral/tetrahedml Mo(VI) ratio is indicated by a strong, well-defined peak in the 300-360 nm region of the u.v. reflectance spectrum and a decreased absorbance in the region below 290 nm. Preferred values for the octahedml/tetrahedral Mo(VI) ratio are in excess of 0.5.

The high tetrahedral Ni2+ contend is indicated by a strong double peak in the range 500-700 nm of the u.v. reflectance spectrum. Preferred values for the tetrahedral Uni2+ content are in excess of 10% of total Ni. Good dispersion of Mo and Ni is indicated by Mo/AI and Ni/AI ratios of the peak areas as determined by X-ray photoelectron spectroscopy (ESCA) exceeding 1.5 and 0.6 respectively, preferably exceeding 1.9 and 0.95 respectively. Suitable loadings of Mo are 4 to 17%, preferably 8 to 15%, and suitable loadings of Ni are 1 to 6%, preferably 2 to 5%.

The invention also provides a method for the preparation of a Ni-Mo catalyst supported on yalumina, which method comprises the steps of impregnating a y-alumina catalyst support with a solution of a nickel salt under basic conditions then calcining the product and thereafter impregnating the calcined product with a solution of a molybdenum salt or complex under acid conditions then calcining the resulting product to yield the catalyst. Preferably the solution of molybdenum salt or complex has a pH of 2 to 4. The already mentioned property of alumina supports to buffer pH leads to a decrease in pH when contacted with the nickel salt under basic conditions and to an increase in pH when contacted with the molybdenum solution under acid conditions.It is preferred to adjust pil by restoring it to approximately its original value either continuously or step-wise, by addition of a base or an acid or by replenishing the impregnating solution. A suitable nickel salt is nickel nitrate and a suitable molybdenum complex is ammonium molybdate.

The calcination conditions may be optimised to further improve the performance of the catalyst by careful control of temperature and the moisture and oxygen content of the calcining atmosphere. Suitable calcination temperatures are 673K to 873K and the preferred temperature is approximately 773K for calcination after impregnation by Ni and after impregnation by Mo.

The preferred calcining atmospheres are water saturated (STP) air after Ni impregnation and dry air after Mo impregnation.

The alumina suitable for use in the invention is commercially available as a catalyst support from a number of firms. Preferred y-aluminas have surface areas in excess of 200 m2g-1, a pore volume in excess of 0.5 cm3g-1 and may be in the form of pellets or powder.

The catalysts of the invention show good activity in the hydrotreating of model compounds, a model coal derived oil and coal-derived oils, and therefore the invention includes the use of the catalysts in the hydrotreating of coal-derived materials.

The invention will now be illustrated by way of example.

EXAMPLE A series of catalysts were prepared by impregnating yalumina (Norton SA-6175); particle diameter 0.45-0.65 mm; surface area 259 rn2g' and water pore volume 0.55 cm3 at room temperature (293K) with the following solutions.

(a) Soln. of ammonium molybdate, pH = 8 and pH = 2 (b) Soln. of nickel nitrate, pH = 8 and pH = 2 (c) Mixed soln. of ammonium molybdate and nickel nitrate, pH 3 = 2 and pH = 7 209 of the support was placed in a beaker, the necessary volume of the solution of the required concentration and pH was added and the suspension agitated while maintaining the temperature at 293 i- 1 K for 40 hours using a water bath. The pH I was periodically adjusted to the desired value. The catalyst was then filtered off and dried at room temperature for 24 hours and at 3931 < for eight hours in an oven.For catalysts prepared in steps (i.e. not a concurrent impregnation and not a single impregnation), the support was impregnated with the first solution, dried and calcined before it was impregnated with the second solution using the same procedure. Calcination was at a temperature of 6731 < in dry air. The same final loading of each componsnt was achieved for each catalyst tested, that is 1 5% w Mo as MoO3 and 4% Ni as NiO on the y-alumina support.

i) The initial activity of the test catalysts was determined for the hydrodesulphurisation of thiophene after loading 3g of catalyst into a fixed bed steady state plug flow microreactor and activating in situ by passing 100cm3 min-1, of a 10% v H2S in H2 mixture at 573K for 1 hour.

The reactor was a 2.2 cm i.d. silica glass tube with a sintered glass disc in the middle of the tube on which the catalyst bed was supported.

An atmospheric test for HDS activity was carried out for each catalyst under the following standard conditions:- temperature = 623K, hydrogen flow rate = 500 cm3 min-1, hydrogen/ thiophene molar ratio = 13, pressure = 1 36 < Pa. Under these conditions no mass transfer limitation existed. Analysis of feed and products was carried out by gas-liquid chromatography.

The measured valued of the apparent kinetic constant for thiophene H HDS assuming a pseudofirst order reaction mechanism are given below in Table 1. No decay in activity was observed for any of the catalysts during a 2 hour run.

TABLE 1 Catalyst Activity for Thiophene HDS at Atmospheric Pres sure Catalysta Apparent Kinetic Constant/mo (g-cat)-1S-1 Ni(B)-Mo) 0.465 Ni(A)-Mo(A) 0.453 Ni Mo(A) b 0.417 Ni (6)-Mo(S) 0.395 Ni lVlo(N) b 0.384 Mo(A)-ili(B) 0.373 Mo(A)-Ni(A) 0.363 Mo(B)-Ni(A) 0.353 AKZO-1535c 0.353 a (A) = acid conditions, (B) = basic conditions, (N) = neutral con ditions The order of component gives the order of impregnation.

b prepared by co-impregnation c a cornrnercial Ni-Mo hydrntreating catalyst.

ii) A continuous high pressure tnc1de-bed reactor was employed in which a liquid feed, which was a model coal extract liquor containing 20% w quinoline, 5% w dibutylsulphide, 7% w dibenzofuran, 8% w phenanthrene and 60% w heptane, metered by a positive displacement pump was mixed with hydrogen and passed downwards through the reactor. The reactor tube consisted of a 15 cm length of a 10 mm i.d. stainless steel tube containing approximately 8.5 9 of catalyst. The catalysts were presulphided for a period of 1 hour in a 500 cm3 min-1 flow of 10% H2S in H2 at 503K and a total pressure of 680 KPa.

A high pressure hydrotreating test was carried out on certain of the catalysts tested in i) above, under the following standard conditions: temperature = 623 K, pressure = 6890 KPa, hydrogen flow rate = 500 cm3min-1 liquid hour space velocity = 4 g hr- (g - cat)-1.

Under these conditions, the main products were: butane (from dibutylsulphide HDS), propylcyclohexane and o-propyl aniline (from quinoline hydrodenitrogenation (HDN), cyclohexyl benzene (from hydrodeoxygenation (H DO) of dibenzofuran), a mixture of di-, tetra-, octa- and per-hydrophenanthrenes (from phenanthrene hydrogenation) and dicyclic derivatives (from phenanthrene hydrocracking). Analysis of feed and product was carried out by gas liquid chromatography, and the apparent kinetic constants were calculated for the main reactions occurring and are listed in table 2 TABLE 2 Apparent kinetic constants/g (g - cat)-1 hr-l Phenanthrene Phenanthrene Catalyst HDO HDN hydrogenation hydrocracking Ni(B)-Mo(A) 0.46 1.64 4.05 0.88 Mo(A)-Ni(B) 0.31 1.01 3.33 0.50 Mo(B)-Ni(A) 0.27 0.91 3.57 0.72 AKZO-153S 0.28 1.01 3.60 0.71 iii) The catalyst Ni(B)-Mo(A) and the AKZO-153S catalyst were tested under identical conditions (pressure 21 000 KPa, temperature in middle of catalyst bed approx. 710K) in the same apparatus for their ability to hydrotreat an oil derived from the liquid extraction of coal.

The results are given below in Table 3.

TABLE 3 Product Product Feed (Ni(B)-Mo(A)) AKZO-153S Distillation Curves (in wt%) IBP-170 C 0.2 4.4 1.4 170-250 2.4 10.8 11.3 250-300 8.3 29.4 28.9 300-355 35.1 33.6 33.8 355-420 24.6 16.3 18.0 > 420 C 29.4 5.5 6.6 Conversion > 420 C (wt %) 81.3 77.6 Conradson Carbon 9.0 0.15 0.4 It can readily be seen that the catalyst according to the invention achieves a higher conversion of the heavy materials and a significantly lower Conradson Carbon number.

iv) The catalysts tested as decribed in (i) and (ii) above were studied in their calcined states and in comparison with pure compounds and with single component catalysts, using ESCA to determine binding energies. The binding energies and other data are given in Table 4 below.

The ESCA data shows that when alumina is impregnated with Mo under acid conditions high Mo/AI peak area ratios are obtained compared to impregnation under basic conditions indicating better dispersion in the former case.

TABLE 4 Binding Energies (eV)a and Peak Area Ratios from ESCA Compound or Catalystb Mo 3dw2 Ni 2ply2 Mo/AI Ni/AI MoO3 232.8 - - Mo7024- 232.8 - - NiMoO4 232.2 - - 8%w Mo(B) 232.2 - 0.64 8%w Mo(A) 232.2 - 1.50 15%w Mo(A) 232.2 - 2.6 4%w Ni(A) - 856.2 - 0.61 4%w Ni(B) - 856.2 - 1.00 Ni(B)-Mo(A)C 233.1 856.0 2.04 1.01 N i(A)- M o(A)" 232.9 856.1 1.92 -0.71 NiMo(A)C 233.1 8.55.9 1.79 0.41 Ni(B)-Mo(B)c 233.1 8.55.8 1.50 1.00 NiMo(N)c 233.1 856.0 1.76 0.74 Mo(A)Ni(B)C 233.0 856.1 1.99 1.05 Mo(A)-Ni(A)C 233.1 856.1 1.91 0.81 Mo(B)-Ni(A)C 233.1 856.0 1.73 0.79 Al < ZO-1 53S d 233.2 856.0 1.47 0.62 (a) Binding energies referred to C = 284.3 eV or Al 2ply2 = 74.5 eV (b) (B) = basic (A) = acid (N) = neutral (c) 15%w MoO and 4%w NiO (d) 1 5%w MoO and 3%w NiO.

Similarly, higher Ni/A1 peak area ratios, and therefore better dispersion, are obtained when alumina is impregnated with Ni under basic rather than acid conditions. The catalyst with the highest Mo/AI and Ni/AI ratios, Ni(B)-Mo(A), is the most active.

U.v. reflectance spectra showed that catalysts in which Mo is deposited under acid conditions consist largely of octahedral Mo(Vl) species, but since the spectra were ill defined compared to pure compounds, it is thought that t. .e Mo is present as a mixture of octahedral structures with the possible presence of a small amount of a tetrahedral species. Similarly, u.v. studies of Ni in the catalysts show that, under basic conditions, Ni is adsorbed as predominately octahedral Uni2+; upon calcining it appears that the Ni concentration at the surface is reduced, and significant amounts of tetrahedral Ni2+ formed probably by diffusion of Ni into the buik alumina and the formation of a NiAl204 spinel surface phase with a degree of spinel inversion.

U.v. spectra of the catalysts and the ESCA data taken together indicate that the following features are correlated with increased activity: (i) a high octahedral/tetrahedral Mo(VI) ratio (ii) an increased tetrahedral/octahedral Ni2+ ratio (iii) an increased Ni dispersion in the catalyst surface (iv) an increased Mo dispersion in the catalyst surface.

Careful control of calcination conditions allows these features to be further optimised.

Increasing the temperature of calcination increased the amount of tetrahedral Ni2+ formed, but tended to adversely affect the octahedral/tetrahedral Mo ratio. An optimum calcination temperature is 773K.

The method of the invention permits the achievement of these features and the production of a novel catalyst of improved properties.

Claims (15)

1. A Ni-Mo catalyst supported on y-alumina, in which the catalyst in oxide form has a high octahedral/tetrahedral Mo(VI) ratio, a high tetrahedral Ni2+ content and good dispersion of both Mo and Ni.

2. A catalyst according to claim 1, in which the Mo loading is in the range from 4 to 17% by wt.

3. A catalyst according to claim 2, in which the Mo loading is in the range from 8 to 15% bywt.

4. A catalyst according to any one of the preceding claims, in which the Ni loading is in the range from 1 to 6% by wt.

5. A catalyst according to claim 4, in which the Ni loading is in the range from 2 to 5% by wt.

6. A catalyst according to any one of the preceding claims, in which the octahedral/tetrahedral Mo(Vl) ratio is in excess of 0.5, as determined by u.v. reflectance spectroscopy.

7. A catalyst according to any one of the preceding claims, in which the tetrahedral Ni2+ content is in excess of 10% of total Ni, as determined by u.v. reflectance spectroscopy.

8. A catalyst according to any one of the preceding claims, in which the Mo/AI and Ni/AI ratios of the peak areas, as determined by X-ray photoelectron spectroscopy exceed 1.5 and 0.6 respectively.

9. A catalyst according to claim 8, wherein the Mo/AI and Ni/Al ratios exceed 1.9 and 0.95 respectively.

1 0. A catalyst according to any one of the preceding claims, wherein the y-alumina has a surface area in excess of 200 m2g-' and a pore volume in excess of 0.5 cm3g-l.

11. A catalyst according to claim 1, substantially as hereinbefore described with reference to the Example.

1 2. A method for the preparation of a Ni-Mo catalyst supported on y-alumina, which method comprises the steps of impregnating a y-alumina catalyst support with a solution of a nickel salt under basic conditions then calcining the product and therefter impregnating the calcined product with a solution of a molybdenum salt or complex under acid conditions then calcining the product to yield the catalyst.

1 3. A method according to claim 12, wherein the impregnating solution of nickel salt has a pH of 7.5 to 8.0.

14. A methad according to claim 1 2 or 13, wherein the impregnating solution of molybdenum salt or complex has a pH of 2 to 4.

15. A method according to claim 13 or 14, wherein the pH is maintained within the ranges of 7.5 to 8.0 for Ni and 2 to 3 for Mo during the course of impregnation.

15. A method according to claim 13 or 14, wherein the pH is maintained within the ranges of 7.5 to 8.0 for Ni and 2 to 4 for Mo during the course of impregnation.

1 6. A method according to any one of claims 1 2 to 15, wherein calcination is carried out at a temperature of 673 to 873K.

1 7. A method according to claim 16, wherein calcination is carried out at a temperature of approximately 773K.

1 8. A method according to any one of claims 1 2 to 17, wherein the calcining atmospheres are water saturated air (STP) after Ni impregnation and dry air after Mo impregnation.

1 9. A method according to claim 12, substantially as hereinbefore described with reference to the Example.

20. A Ni-Mo catalyst whenever prepared by a method according to any one of claims 1 2 to 19.

21. The use of a Ni-Mo catalyst according to any one of claims 1 to 11 and 20 in the hydrotreatig of a coal-derived material.

CLAIMS (1 July 1980)

6. A catalyst according to any one of the preceding claims, in which the octahedral/tetrahedral Mo(Vl) ratio is in excess of 0.5, as indicated by u.v. reflectance spectroscopy.

7. A catalyst according to any one of the preceding claims, in which the tetrahedral Ni2+ content is in excess of 10% of total Ni, as indicated by u.v. reflectance spectroscopy.

14. A method according to claim 1 2 or 13, wherein the impregnating solution of molybdenum salt or complex has a pH of 2 to 3.