RU2418037C2 - Selective catalysts for naphtha hydrodesulphurisation - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to a catalyst for hydrodesulphurisation of naphtha, a method of preparing said catalyst and a method for hydrodesulphurisation of naphtha using said catalyst. Described is a method of preparing the catalyst for hydrodesulphurisation of naphtha and versions thereof, involving: (i) saturating a silicon oxide based support, where the support contains at least approximately 85 wt % silicon oxide and has pore volume between 0.6 and 2.0 cm³/g and average pore size between 150 and 2000 Å, (a) with an aqueous solution of a cobalt salt, (b) an aqueous solution of a molybdenum salt and at least one organic additive. The said organic additive contains at least one organic acid and at least one compound selected from a group consisting of compounds containing at least two hydroxyl group and 2-20 carbon atoms, and (poly)ethers of these compounds, to obtain a catalyst precursor; (ii) drying the catalyst precursor at temperature lower than approximately 350°C to obtain a dry catalyst precursor, and (iii) possibly sulphidation of the dry catalyst precursor, provided that the dry catalyst precursor, or catalyst, is not calcined before sulphidation or use for hydrodesulphurisation. The catalyst for hydrodesulphurisation of naphtha prepared using the method given above is described. Described also is a method for hydrodesulphurisation of naphtha, having olefin content of at least 5 wt % in terms of the weight of naphtha, involving sulphidation of the catalyst and its reaction with naphtha under hydrodesulphurisation conditions.

EFFECT: low degree of saturation of olefins while also minimising loss of octane number and achieving high hydrodesulphurisation activity.

33 cl, 1 tbl, 8 ex, 1 dwg

Description

FIELD OF THE INVENTION

The invention relates to a catalyst for hydrodesulfurization of naphtha, to a method for preparing said catalyst and to a method for hydrodesulfurization of naphtha using said catalyst. In particular, the catalyst includes a metal Co / Mo hydrogenation component on a silica-based support having a defined pore size distribution and at least one organic additive. The catalyst has high dehydrosulfurization activity and minimal olefin saturation when used to dehydrosulfurize naphtha.

BACKGROUND OF THE INVENTION

Environmental legislation authorizes the reduction of sulfur levels in motor gasoline (automotive fuel). For example, this legislation is expected to require by 2006 that automotive fuel levels of sulfur be 30 ppm or less. In many cases, these sulfur levels are reached by hydrotreating naphtha obtained by Fluid Catalytic Cracking (FCC naphtha), which makes the largest sulfur contribution to the automotive fuel pool. Since sulfur in automobile fuel can also lead to reduced efficiency of catalytic converters, a target of 30 ppm of sulfur is desirable even when legislation allows a higher level. As a result, techniques are required that reduce sulfur in catalytic naphthas, while minimizing the loss of positive properties such as octane.

Conventional fixed bed hydroprocessing can reduce the level of sulfur in cracked naphtha to very low levels. However, such hydroprocessing also leads to a significant reduction in the octane number due to a large decrease in the olefin content in naphtha, as well as to excessive consumption of hydrogen when implementing the hydroprocessing method. Recently, selective hydroprocessing methods have been developed to avoid such saturation of olefins and loss of octane number. Unfortunately, in these methods, the released H ₂ S reacts with the remaining olefins to form mercaptan sulfur upon reversal. Unfortunately, the H ₂ S released in this process reacts with the remaining olefins to form mercaptan sulfur in the reverse reaction. Such methods can be implemented in harsh conditions, when the product is produced within the framework of sulfur regulation. However, there is also a significant decrease in octane number.

To preserve the octane number during sulfur removal, an approach is proposed consisting in modifying the olefin content in the feed using an olefin modification catalyst and subsequent reaction with a GDS catalyst (US Patent No. 6,602,405). The olefin modification catalyst oligomerizes olefins.

The newly developed GDS method is the SCANfining refining method, which is a method developed by Exxon Mobil Corporation. “SCANfining” is described in a National Petroleum Refiners Association report # AM-99-31 entitled “Selective Cat Naphtha Hydrofining with Minimal Octane Loss” and in US Patent Nos. 5,985,136 and 6,013,598. Typically, SCANfining conditions include one- and two-stage Methods of hydrodesulfurization of naphtha raw materials. The feed is brought into contact with a hydrodesulfurization catalyst, comprising from about 1 wt. % to about 10 wt. % MoO ₃ ; and from about 0.1 wt. % to about 5 wt. % CoO; and having an atomic Co / Mo ratio of from about 0.1 to about 1.0; and an average pore diameter of from about 6 angstroms to about 200 angstroms.

Despite the fact that the SCANfining process regulates the degree of saturation of olefins, and a high degree of GDS is achieved, there continues to be a need to improve the selectivity of the catalyst system in order to further reduce the degree of saturation of olefins, while minimizing the loss of octane number while achieving high hydrodesulfurization activity.

SUMMARY OF THE INVENTION

This invention relates to a catalyst for hydrodesulfurization of naphtha, to a method for preparing said catalyst and to a method for hydrodesulfurization of naphtha using said catalyst. One embodiment relates to a method for manufacturing a catalyst for hydrodesulfurization (GDS) of naphtha, the method comprising:

(i) impregnating a silica-based carrier, wherein the carrier contains at least about 85 wt. % silica based on silica and has a pore volume between about 0.6 cc / g and about 2.0 cc / g, and average pore sizes in the range of about 150 angstroms to 2000 angstroms, (a) an aqueous solution of a cobalt salt, (b) an aqueous solution of a molybdenum salt, and (c) at least one organic additive, said organic additive comprising at least one compound selected from the group consisting of at least one compound , two hydroxyl groups and 2-20 carbon atoms, and (poly) esters of these compounds, with a catalyst precursor;

(ii) drying the catalyst precursor at a temperature of less than about 350 ° C. to obtain a dry catalyst precursor, and

(iii) optionally, sulfiding the dry catalyst precursor, provided that the dry catalyst precursor or catalyst has not been calcined before sulfidation or use for GDS.

This method is called direct cooking. Impregnation with Co salt, Mo salt, and organic additive (s) (s) can be carried out through more than one successive stages in various orders and combinations. The dry catalyst precursor “optionally” is sulfided. The invention therefore also relates to a method for manufacturing a dry catalyst precursor in a non-sulfided form, since this is the form in which the catalyst is usually commercially available, but also to a method for manufacturing the catalyst in its active sulfated form. The term “catalyst precursor” as used herein is used to refer to the catalyst in unsulfonated form, since sulfidation is typically carried out before use for GDS. The use of this expression, however, does not exclude the fact that the non-sulfided form of the catalyst also has catalytic properties.

In another embodiment, the present invention relates to a method for manufacturing a catalyst for hydrodesulfurization (GDS) of naphtha, the method comprising:

(i) impregnating a silica-based carrier, wherein the carrier contains at least about 85 wt. % silica based on silica, and has a pore volume of between about 0.6 cc / g and about 2.0 cc / g, and average pore sizes in the range of about 150 angstroms to 2000 angstroms, (a ) an aqueous solution of a cobalt salt and (b) an aqueous solution of a molybdenum salt, to obtain a first catalyst precursor;

(ii) drying the first catalyst precursor at a temperature of less than about 350 ° C. to obtain a first dry catalyst precursor;

(iii) impregnating the first dry catalyst precursor (c) with at least one organic additive, wherein the organic additive comprises at least one compound selected from the group consisting of compounds comprising at least two hydroxyl groups and 2 -20 carbon atoms, and (poly) esters of these compounds to give a second catalyst precursor;

(iv) optionally drying the second catalyst precursor at a temperature of less than about 350 ° C. to obtain a second dry catalyst precursor and

(v) optionally sulfidizing the second catalyst precursor, provided that the second dry catalyst precursor was not calcined before sulfidation or use for GDS.

This method is called a subsequent impregnation or activation method, since impregnation with additives can be applied to any commercially available or prepared catalyst that does not include the additive and has not been sulfidated.

In yet another embodiment, the invention relates to a method for producing a catalyst for hydrodesulfurization (GDS) of naphtha, the method comprising:

(i) regeneration of the spent catalyst, including a carrier based on silicon oxide, where the carrier contains at least about 85 wt. % silica based on silica, and has a pore volume between about 0.6 cc / g and about 2.0 cc / g, and average pore sizes ranging from about 150 angstroms to 2000 angstroms, which was impregnated with a cobalt salt and a molybdenum salt, to obtain a regenerated catalyst;

(ii) impregnating the regenerated catalyst with at least one organic additive, said organic additive comprising at least one compound selected from the group consisting of compounds comprising at least two hydroxyl groups and 2-20 carbon atoms and (poly) esters of these compounds to form a catalyst precursor;

(iii) optionally drying the catalyst precursor at a temperature of less than about 350 ° C. to obtain a dry catalyst precursor, and

(iv) optionally, sulfiding the dry catalyst precursor, provided that the dry catalyst precursor or catalyst has not been calcined before sulfidation or use for GDS.

This method is called the reactivation method, since the impregnation with additives can be applied to the regenerated (spent) naphtha hydrodesulfurization (GDS) catalyst, as indicated, most preferably, the catalyst which was prepared according to the method in accordance with the present invention before use in the GDS.

In another embodiment, the invention relates to a catalyst comprising a silica-based carrier, wherein the carrier contains at least about 85 wt. % silica based on silica, and has a pore volume of between about 0.6 cc / g and about 2.0 cc / g, and average pore sizes in the range of about 150 angstroms to 2000 angstroms, said the silica-based support was impregnated with a cobalt salt, a molybdenum salt and at least one organic additive, said organic additive comprising at least one compound selected from the group consisting of at least two hydroxyl groups and 2-20 carbon atoms, and (poly) esters these compounds. In particular, the invention relates to such a catalyst obtained by any of the above methods in accordance with this invention.

The invention further also relates to a catalyst in accordance with this invention, which has been sulfidized by in-situ or ex-situ sulfidation.

Another embodiment relates to a process for the synthesis of naphtha with an olefin content of at least about 5 wt.%, Based on the weight of naphtha, comprising: (i) contacting the naphtha with a selective HDS catalyst under hydrodesulfurization conditions, where a selective HDS catalyst is prepared according to any of the methods described above.

The catalyst of the invention, when used for NDS naphtha, exhibits improved selectivity for olefin saturation, while a high NDS naphtha level remains.

BRIEF DESCRIPTION OF THE DRAWING

The drawing is a graph showing the GDS activity (k _GDS ) as a function of the amount (wt.%) Of an organic additive for various additives compared to a catalyst supported on an alumina carrier.

DETAILED DESCRIPTION OF THE INVENTION

The term “naphtha” refers to a mid-range boiling hydrocarbon fraction or fractions that are the main components of gasoline, the term “FCC naphtha” referring to a preferred naphtha that has been produced by a well-known fluid catalytic cracking process. Naphthas having an average boiling range are naphthas having boiling points of from about 10 ° C (i.e., from about ₅ ) to about 232 ° C (from 50 to 450 ° F) at atmospheric pressure, preferably from about 21 ° C to about 221 ° C (70 to 430 ° F). The production of naphtha by the FCC method without added hydrogen results in naphtha, in which there is a relatively high content of olefins and aromatic compounds. Other naphthas, such as steam cracking naphthas and coke naphthas, may also contain relatively high concentrations of olefins. Typically, olefin naphthas have an olefin content of at least about 5 wt. % to about 60 wt. %, based on the weight of naphtha, preferably from about 5 wt. % to about 40 wt. %; sulfur content from about 300 ppm by weight to about 7000 ppm by weight, based on the weight of naphtha; and a nitrogen content of from about 5 parts per million by weight to about 500 parts per million by weight, based on the weight of naphtha. Olefins include open chain olefins, cyclic olefins, dienes, and cyclic olefin hydrocarbons with side chains. Since olefins and aromatic compounds are high octane components, the olefin naphtha usually exhibits higher research and motor octane values than hydrocracked naphtha. In addition to the fact that olefin naphthas, as a rule, have a high olefin content, they can also contain other compounds, especially sulfur-containing and nitrogen-containing compounds.

The catalyst for selective sulfur recovery with minimal olefin saturation of the olefin naphtha is a catalyst supported on a silica support which has been impregnated with (a) a cobalt salt, (b) a molybdenum salt, and (c) at least one organic additive. The silica-based carrier contains at least about 85% by weight. % silicon oxide based on silicon oxide, preferably at least about 90 wt. % silicon oxide, especially at least about 95 wt. % silicon oxide. Examples of silica-based supports include silica, MCM-41, silica-bonded MCM-41, white carbon black, silica-modified silica supports and diatomaceous earth.

The silica-based carrier has a pore volume between about 0.6 cm ³ / g and about 2.0 cm ³ / g, preferably between about 0.8 cm ³ / g and about 1.0 cm ³ / g, as was determined using mercury porosimetry according to ASTM D4284-03. Also, the silica-based support has an average pore size (average pore diameter) in the range of about 150 angstroms to about 2000 angstroms, preferably about 150 angstroms to about 1000 angstroms, more preferably about 200 angstroms to about 500 angstroms, as this was determined using mercury porosimetry according to ASTM D4284-03.

Preferred silica supports have one or more of the following features: (i) surface area determined by nitrogen adsorption using the BET equation in the range of 50 to 150 m ² / g, preferably in the range of 60 to 140 m ² / g; (ii) a crush strength of at least 625 g / mm (35 lb / in), preferably in the range between 625 g / mm (35 lb / in) and 2144 g / mm (120 lb / in).

In a separate preferred embodiment, the carrier further comprises up to 10 parts by weight, preferably up to 5 parts by weight, of the polymeric material per 100 parts by weight of the carrier. Typically, the organic material is a polymeric material, for example, an organic material selected from polyvinyl alcohols, cellulose, cellulose ethers such as polymers of methyl cellulose and hydroxypropyl methyl cellulose, colloidal silicon dioxide, floridine, coal powder, graphite, polyoxyethylene, mixed walnut shell or a mixture thereof. In this preferred embodiment, the silica-based carrier is prepared in the usual manner by a method comprising the steps of: (a) molding particles from a mixture obtained from at least one silica source, a liquid medium, and at least one of the above polymeric materials; (b) drying the formed particles obtained in step (a), preferably at a temperature of less than 200 ° C; and (c) heating the formed particles to a temperature in the range of from about 500 ° C to about 800 ° C in the presence of steam or a mixture of steam and air. Stage (C) is usually carried out in an atmosphere containing at least 5 vol.% Air, or in an atmosphere containing at least 10 vol.% Steam. Also typically, the mixture that is formed in step (a) is obtained by combining at least one silica powder and at least one silica sol.

Although not intended to be limited to any particular theory, it has been postulated that silica supports with large pore sizes and large pore diameters, in combination with at least one organic additive in accordance with the invention, lead to GDS catalysts having the desired selectivity for olefin saturation while maintaining the activity of the GDS catalyst with respect to desulfurization of incoming naphtha.

In another embodiment, the silica-based support can also be doped with metals from Groups 2-4 of the Periodic Table in IUPAC format of Groups 1-18, preferably from Groups 2 and 4. Examples of such metals include Zr, Mg, Ti. See, for example, The Merck Index, Twelfth Edition, Merck & Co., Inc., 1996.

The cobalt and molybdenum salts used to impregnate the silica-based support can be any water-soluble salt. Preferred salts include carbonates, nitrates, heptamolybdates and the like. By the term “water soluble cobalt and molybdenum salts” is also meant here those cobalt and molybdenum compounds which may not be soluble in pure water, but soluble in an aqueous impregnating solution, for example, due to the presence of an acid, for example, cobalt and / or molybdenum oxides in combination with acid. The amount of salt is such that the carrier based on silicon oxide contains from about 2 wt. % to about 8 wt. %, preferably from about 3 wt. % to about 6 wt. % cobalt oxide, calculated on the catalyst, and from about 8 wt. % to about 30 wt. %, preferably from about 10 wt. % to about 25 wt. % molybdenum oxide, calculated on the carrier.

The organic additive used for impregnation is at least one compound selected from the group consisting of compounds comprising at least two hydroxyl groups and 2-20 carbon atoms, preferably 2-15 carbon atoms and, more preferably 2-10 carbon atoms, and (poly) esters of these compounds. In general, very good results were obtained when the organic additive was selected from the group consisting of polyhydroxyalkanes or polyhydroxyalkenes comprising two or more hydroxyl groups and from 1 to 4 carbon atoms per hydroxyl group and their polycondensates (polyesters).

Examples of suitable additives include aliphatic alcohols such as ethylene glycol, propylene glycol, glycerin, trimethylol ethane, trimethylol propane, etc. Esters of these compounds include diethylene glycol, dipropylene glycol, trimethylene glycol, triethylene glycol, tributylene glycol, tetraethylene glycol, tetrapentylene glycol. These compounds also include polyesters such as polyethylene glycol. Other esters that are suitable for use in the present invention include ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether and diethylene glycol monobutyl ether. Of these, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, dipropylene glycol, and polyethylene glycol with a molecular weight of between 200 and 600 are preferred.

Another group of compounds comprising at least two hydroxyl groups and 2-10 carbon atoms per molecule are saccharides. Preferred saccharides include monosaccharides such as glucose and fructose. Their ethers include disaccharides such as lactose, maltose and sucrose. The polyesters of these compounds include polysaccharides. The organic compounds of this group are preferably essentially saturated, which confirms the iodine number is less than 60, preferably less than 20.

In an even more preferred embodiment, a compound comprising two hydroxyl groups and having 2-20 carbon atoms, preferably 2-15 carbon atoms and, more preferably 2-10 carbon atoms, further comprises at least one secondary amino group. Preferably, at least 2 hydroxyl groups are separated from the secondary amino group by 1 or more carbon atoms, preferably 2-4 carbon atoms.

In general, very good results were obtained when the organic additive was selected from the group consisting of secondary amines, including alkanol or alkenol groups, and their polycondensates, for example diethanolamine or dialkanolamine. One of the advantages of the aforementioned preferred organic additives over catalysts that do not have these additives is that their GDS activity is very high, while maintaining high selectivity and, therefore, low olefinic saturation. Another non-limiting advantage is that equally good GDS activity and high selectivity can be obtained using a significantly lower metal content, which makes the catalyst much less expensive. It turned out that the catalyst according to the invention has a comparable level of activity when the metal content is reduced by at least 20%, preferably at least 30% and, most preferably, at least 40% compared with the same catalyst, having the indicated additives.

The molar ratio between the amount of additive and the amount of hydrogenated metals (total amount of Co and Mo) is preferably from 0.01: 1 to 2.5: 1. In terms of achieving increased activity, the molar ratio is preferably at least 0.05, more preferably at least 0.1, even more preferably at least 0.2, and most preferably at least , 0.3. With high metal additive ratios, an additional increase in activity is reduced, so it is preferred that the molar metal additive ratio is less than 2.5. The amount of additive (s) is at least 3 wt. %, preferably at least 5 wt. %, more preferably at least 7 wt. % relative to the total weight of the catalyst. Less is required for those supplements that better improve activity.

The organic additive preferably has a not too low boiling point, preferably in the range of 80-500 ° C, and good solubility in water, usually at least 5 grams per liter at room temperature (20 ° C) (atmospheric pressure )

After impregnation with at least one organic additive, it is essential for the method in accordance with the invention to carry out any drying step in such a way that at least part of the additive remains in the catalyst. The catalyst, therefore, does not calcinate after impregnation with at least one organic additive. Therefore, the drying conditions to be applied depend on the temperature at which the additive boils or decomposes. In the context of the present invention, the drying step should be carried out under conditions in which at least 50%, preferably at least 60%, more preferably at least 70%, most preferably at least 90% additives introduced into the catalyst in the impregnation step are still present in the catalyst after the drying step. Of course, it is preferable to keep as many additives as possible in the catalyst during the drying step, but in the case of more volatile compounds, evaporation during the drying step cannot always be avoided. The drying step can, for example, be carried out in air, in vacuum or in an inert gas. Usually, preferably drying is carried out at a temperature below about 350 ° C, such as below about 300 ° C, usually below about 250 ° C, most preferably below about 200 ° C.

In a particularly preferred embodiment, the at least one organic additive further comprises an inorganic acid, an organic acid, or a mixture of an inorganic acid and an organic acid. Inorganic acids are defined as acidic components that do not contain carbon atoms. Examples of inorganic acids include HCl, H ₂ SO ₄ , HNO ₃ , H ₃ PO ₄ , (NH ₄ ) H ₂ PO ₄ , (NH ₄ ) ₂ HPO ₄ , H ₂ PHO ₃ , H ₂ P ₂ H ₂ O ₅ and H _{(n + 2)} P _n O _{(3n + 1)} ). In the group of inorganic acids, phosphorus-containing acids are preferred, since phosphorus itself can positively affect the activity of the hydroprocessing catalyst. H ₃ PO ₄ is particularly preferred.

The disadvantage of using inorganic acids is that counterions, such as chloride, sulfate or nitrate, are part of the catalyst. If the impregnation method of the additive of the present invention is repeated several times, this can lead to undesirable accumulation of these counterions in the composition of the catalyst. However, this may not be a problem, depending on the nature of the counterion and on the number of stages impregnated with the additive. Organic acids are preferred because they do not have this drawback.

In the context of the present description, an organic acid is defined as a compound comprising at least one carboxyl group (COOH). An organic acid is typically a carboxylic acid comprising at least one carboxyl group and 1-20 carbon atoms (including carbon atoms of a carboxyl group). Suitable acids include acetic acid, citric acid, malic acid, maleic acid, formic acid, glycolic acid, hydroxypropionic acid, hydroxybutyric acid, hydroxycaproic acid, tartaric acid, glyceric acid, gluconic acid, polyacrylic acid, oxaloic acid, oxaloic acid, oxalic acid and N-containing acids such as EDTA (ethylenediaminetetraacetic acid) and CDTA (1,2, -cyclohexanediaminetetraacetic acid), etc. Acids comprising at least two carboxyl groups are preferred in this group of compounds. For reasons of overall cost and activity, citric acid, malic acid, maleic acid, malonic acid, and tartaric acid are preferred. Citric acid is particularly preferred.

In a preferred embodiment, the at least one organic additive comprises an organic acid and at least one compound selected from the group consisting of polyhydroxyalkanes or polyhydroxyalkenes comprising 2 or more hydroxyl groups and from 1 to 4 carbon atoms per hydroxyl group their polycondensates and secondary amines, including alkanol or alkenol groups, and their polycondensates.

Acid and additive can be introduced into the catalyst simultaneously or sequentially; not following a certain order. The advantage of introducing the acid and the additive into the catalyst at separate stages may be that the properties of the impregnating solutions can be selected to meet the acid and additive requirements. However, for reasons of effectiveness, it is preferable to bring the carrier into contact with a single impregnating solution, including both acid and the additive, possibly followed by an aging step and / or a drying step under such conditions that at least 50% of the additives remain in the catalyst.

Silica-based supports are impregnated with aqueous solutions of Co and Mo salts using conventional techniques. At least one organic additive may be added to one or both aqueous solutions of Co and Mo salts before contact with a silica-based support. One embodiment of the impregnation of a carrier based on silicon oxide with a metal salt is carried out by the initial wetting method. In this method, an aqueous solution containing metal salts and an organic additive is mixed with the carrier to the point of initial wetting using conventional techniques, i.e. techniques that are well known in the technology of preparation, production and use of hydroprocessing catalysts.

An alternative way to impregnate a silica-based support with a metal salt may be to impregnate the silica-based support with a cobalt salt mixture and, using initial wetting, dry the impregnated support and then impregnate the dry support with a molybdenum salt solution or a molybdenum salt solution to the initial wetting point, where the solution salts of Co and / or Mo contain some or all of the organic additives (y). In another embodiment, the order of impregnation with a cobalt salt and then with a molybdenum salt may be reversed. In yet another embodiment, the carrier can be simultaneously impregnated with a mixture of cobalt salt and molybdenum salt plus an organic additive prior to initial wetting. The impregnated carrier can be dried and the co-impregnation method repeated.

In yet another embodiment, the silica-based extruded carrier is impregnated with a mixture of cobalt salt, molybdenum salt and organic additive, and the impregnated carrier is dried. Processing may be repeated if desired.

In yet another embodiment, the silica-based support is impregnated with an aqueous solution of a cobalt salt and an aqueous solution of a molybdenum salt, or a solution of a cobalt salt and a molybdenum salt, to obtain a first catalyst precursor. The first catalyst precursor is dried and then the first dry catalyst precursor is impregnated with at least one organic additive to give a second catalyst precursor.

In all of the above embodiments, the organic additive may be a single additive or a mixture of additives, and the impregnation sequences can be repeated several times if it is necessary to achieve the desired metal and additive concentrations. After impregnation, heating and drying is carried out at temperatures ranging from about 50 ° C to about 350 ° C, preferably below about 300 ° C, to obtain a dry catalyst precursor. The drying may be under vacuum, or in air, or in an inert gas such as nitrogen. The applicable temperature conditions are generally chosen so as to ensure drying with minimal loss of additive due to evaporation.

As noted previously, it is important that at least a portion of the organic additives impregnated with the catalyst remain in the catalyst before the catalyst is used in the catalytic process. Therefore, the catalyst is not heated to temperatures above about 350 ° C. before catalytic use. However, due to the deactivation of the catalyst during its catalytic use, the catalyst will require regeneration. The regeneration of the catalyst can be carried out by any method known to specialists in technology. For catalysts in accordance with the invention, the preferred regeneration conditions are the reaction of the spent catalyst with an oxygen-containing gas at temperatures below about 350 ° C, preferably below about 325 ° C, more preferably below about 315 ° C and most preferably below about 300 ° C . The regeneration temperature is usually chosen as low as possible, and a long regeneration time is avoided. Regeneration temperatures in the range of 310 ° C to 340 ° C are generally suitable for these types of catalysts.

Unfortunately, regeneration conditions can sometimes lead to the removal of most, if not all, of the organic additive necessary for optimal catalyst performance. The present invention therefore also relates to a method for manufacturing a catalyst in which a spent catalyst that has been regenerated is again impregnated with at least one organic additive, or even again subjected to any of the aforementioned impregnation methods.

In a separate embodiment, the present invention also relates to a method for manufacturing a naphtha hydrodesulfurization (GDS) catalyst, the method comprising: (i) regenerating a spent catalyst comprising a silica-based support, wherein the support contains at least about 85 wt. % silica based on silica, and has a pore volume of between about 0.6 cc / g and about 2.0 cc / g, and an average pore size in the range of about 150 angstroms to 2000 angstroms; which has been impregnated with a cobalt salt and a molybdenum salt to prepare a regenerated catalyst, (ii) impregnating the regenerated catalyst with at least one organic additive, said organic additive comprising at least one compound selected from the group consisting of compounds, comprising at least two hydroxyl groups and 2-20 carbon atoms, and (poly) esters of these compounds, to obtain a catalyst precursor; (iii) drying the catalyst precursor at a temperature of less than about 350 ° C. to obtain a dry catalyst precursor; and (iv) optionally, sulfiding the dry catalyst precursor, provided that the dry catalyst precursor or catalyst has not been calcined before sulfidation or use for GDS. In this embodiment, it is not necessary that the spent catalyst be pre-impregnated with at least one organic additive before catalytic use, but it is preferable that it is also a catalyst according to the invention.

As noted previously, the invention provides catalysts that are particularly useful as a hydrodesulfurization catalyst. For such a catalytic use, dry catalyst precursors typically undergo a sulfurization step prior to catalytic use. When carrying out such sulfonation, the dry catalyst precursor is treated with hydrogen sulfide in a concentration of from about 0.1 vol.% To about 10 vol.% Calculated on the total volume of gases present, over time and at a temperature sufficient to convert the metal oxide, metal salt or complex the metal into the corresponding sulfide to prepare the GDS catalyst. Hydrogen sulfide may be formed due to the sulfidizing agent present in or on the catalyst precursor. In one embodiment, the sulfidation agent is combined with a diluent. For example, dimethyl disulfide may be combined with a naphtha diluent. Smaller amounts of hydrogen sulfide may be used, but this may lengthen the time required for activation. An inert carrier may be present, and activation may occur either in the liquid or in the gas phase. Examples of inert carriers include nitrogen and light hydrocarbons such as methane. When they are present, inert gases are included as part of the total gas volume. Temperatures range from about 150 ° C to about 700 ° C, preferably from about 160 ° C to about 343 ° C. The temperature can be kept constant or can be changed by starting at a lower temperature and increasing the temperature during activation. The total pressure is in the range up to about 5,000 gps. psi (34576 kPa), preferably from about 0 gig psi up to approximately 5,000 h. psi (101 to 34576 kPa), more preferably about 50 gigabytes. psi to about 2,500 h. psi (446 to 17338 kPa). If a liquid carrier is present, then the hourly volumetric rate of the liquid (COS) is from about 0.1 hour ^-1 to about 12 hour ^-1 , preferably from about 0.1 hour ^-1 to about 5 hour ^-1 . LSS refers to continuous mode. However, activation can also be carried out periodically. The total gas velocity can be from about 89 m ³ / m ³ to about 890 m ³ / m ³ (from 500 to 5000 cubic feet / barrel).

Sulfidation of the catalyst can be carried out either in situ or ex situ. Sulfidation can be carried out by reacting the catalyst with a sulfidation agent, and can occur with either a liquid or gas phase sulfidation agent. Alternatively, the catalyst may be pre-sulfonated so that H ₂ S may form during sulfidation. With the liquid phase sulfidation agent, the catalyst to be sulfidated is contacted with a liquid carrier containing a sulfidation agent. The sulfidation agent may be added to the liquid carrier, or the liquid carrier itself may be a sulfidation agent. The liquid carrier is preferably a stream of pure hydrocarbon and may be a feed to be reacted with a hydrogenation catalyst, but may be a stream of any hydrocarbon, such as a distillate obtained from mineral (oil) or synthetic sources. If a sulfidation agent is added to the liquid carrier, then the sulfidation agent itself may be a gas or liquid capable of forming hydrogen sulfide under activation conditions. Examples include hydrogen sulfide, carbonyl sulfide, carbon disulfide, sulfides such as dimethyl sulfide, disulfides such as dimethyl disulfide, and polysulfides such as di-tert-nonyl polysulfide. Sulfides are present in some types of raw materials; for example, petroleum feeds can act as a sulfidation agent and include a wide variety of sulfur-containing particles capable of forming hydrogen sulfide, including aliphatic, aromatic and heterocyclic compounds.

After sulfidation, the catalyst can be brought into contact with naphtha under hydrodesulfurization conditions. Hydrodesulfurization conditions include temperatures from about 150 ° C to about 400 ° C; pressures from about 445 kPa to about 13,890 kPa (50 to 2,000 psi), hourly volumetric fluid velocities from about 0.1 to about 12 hours ^-1, and processing gas velocities from about 89 m ³ / m ³ up to about 890 m ³ / m ³ (from 500 to 5000 cubic feet / barrel). After hydrodesulfurization, the desulfurized naphtha can be removed for storage or further processing, such as purification, to remove hydrogen sulfide. Desulfurized naphtha can be used to mix with other hydrocarbons boiling in the naphtha range to prepare automotive fuel.

Selected embodiments, including preferred embodiments, are illustrated in the following examples.

Example 1 (comparison)

A silica-based carrier was prepared using 80 wt. % Ultrasil VN3SP of SiO ₂ powder and 20 wt.% Nyacol 2034 DI aqueous colloidal sol of silicic acid, both based on the dry weight of the carrier after treatment at 600 ° C. These sources of silicon oxide were mixed with 4 wt. % polyvinyl alcohol (PVA) based on the dry mixture of silicon oxide with OH number 78-82 mol. %, where PVA was previously mixed with water to obtain an aqueous solution. Additional water was added as required to obtain an extrudable mixture. The mixture was extruded to obtain 1.3 mm four leaf particles. The extrudates were dried at 120 ° C. for about 1 hour. The dry support was calcined at 790 ° C in 25 wt. % steam in the air for about 1 hour.

The catalyst carrier had a total pore volume of 0.91 ml / g, as determined using mercury porosimetry according to ASTM D 4284-03, assuming that the contact angle of the mercury with silicon oxide was 130 ° using a Micromeritics AutoPore IV 9500, The BET surface area was 80 m ² / g, the average pore diameter calculated from the aforementioned mercury porosimetric volume measurements was 445 angstroms, and the crush strength was 72 psi.

A solution of CoMo-LK was prepared using 30.9 g of CoCO ₃ (44.5 wt.% Co), 70.0 g of MoO ₃ and 24.7 g of citric acid. The volume was adjusted to 300 g of MoO ₃ / L. 75 g of the prepared silica-based support were impregnated using the initial wetting method so that the product contained 20 wt. % MoO ₃ and 5 wt. % CoO calculated on the dry weight of the catalyst after treatment at 600 ° C. An aliquot of 66.7 ml of the prepared metal solution was diluted with 9.7 ml of water in order to equate to 105% of the pore volume of the substrate. The impregnated catalyst was held for 1 hour. The catalyst was dried to a product temperature of 50 ° C. using dry air at 90 ° C. The final product was removed from the vessel and placed in a closed vessel under air. This catalyst sample will hereinafter be referred to as catalyst A.

The prepared catalyst was charged into a fixed bed reactor, which was sulfidized using 3% H ₂ S in H ₂ and pure naphtha under sulfidation conditions. The hydrodesulfurization and olefin saturation characteristics of the supported CoMo catalyst supported on silica were estimated using raw FCC naphtha with an initial boiling point of 10 ° C and a final boiling point of 177 ° C, containing 1408 ppm sulfur and 46.3 wt. % olefins, based on the mass of raw materials. These characteristics were tested at a temperature of 274 ° C (525 ° F) at a pressure of 220 g. psi using H ₂ . The flow rate of the feed was set so as to obtain a desulfurization range of 2-methylthiophene of 65 wt. % to 99 wt. %, based on the mass of raw materials. Product streams were analyzed using real-time gas chromatography (GC) and sulfur determination by chemiluminescence (OCX). The C ₅ olefin content of the product was compared with the C ₅ olefin content of the feed, based on the weight, to calculate the percentage of olefin saturation (% HO). The results were stable after about 30 hours of operation of the catalyst on the stream, and they were used to evaluate the saturation of olefins at various conversions of the GDS (% GDS).

The GDS activity of catalyst A was evaluated based on a reaction rate of 1.5 orders of magnitude for the 2-methylthiophene desulfurization reaction. This calculation was carried out for all feed rates that were used. The performance was compared with the performance of the commercially available RT225 naphtha hydrodesulfurization catalyst. It is a supported on alumina catalyst containing 4.3 wt. % MoO ₃ and 1.2 wt. % CoO calculated on the dry weight of the catalyst. In the preparation did not use the organic additives described in this invention. This catalyst showed a constant reaction rate of 1.77. The reaction order ratio for catalyst A and for commercial Al ₂ O ₃ / CoMo catalyst expresses the relative GDS activity of the catalyst. For the SiO ₂ / CoMo catalyst of this example prepared using citric acid as an organic additive, the reaction rate was constant 1.72 and the relative GDS activity was 97%. The test results of the characteristics are shown in the table.

At 90% GDS, the conversion of BUT was approximately 8.4 wt. % for CoMo / SiO ₂ catalyst described in this example. This is much less than HO 13.3 wt.%, Which was demonstrated by a commercial CoMo / Al ₂ O ₃ catalyst.

These results show that a CoMo supported silica catalyst with citric acid as an organic additive exhibits reduced olefin saturation at 90% GDS conversion and a constant 1.5 GDS reaction for this catalyst containing 20 wt.% And 5 wt.% CoO calculated on the dry matter, it is almost equal to the constant GDS of the reaction of 1.5 orders of magnitude for the catalyst, taken for comparison, supported on aluminum oxide CoMo containing 4.3 wt. % MoO ₃ and 1.2 wt. % CoO calculated on the dry matter.

Example 2

Catalyst B was prepared and tested in accordance with the procedure described in Example 1, except that in addition to citric acid, a second organic additive was added to the metal solution before impregnation. The impregnation solution thus consisted of 66.7 ml of CoMo-LK solution, 8.1 g (= 7.4 ml) of diethylene glycol (DEG) and 2.3 ml of water.

The olefin saturation at 90% GDS conversion was 8.3 wt. %, and the relative activity of the catalyst compared to CoMo / Al ₂ O ₃ catalyst, taken for comparison, amounted to 135%. This shows that the addition of diethylene glycol to the impregnation solution increases the relative GDS activity of the catalyst, while improved olefin saturation of catalyst A is maintained.

Example 3

Catalyst C was prepared and tested in accordance with the procedure described in Example 1, except that in addition to citric acid, a second organic additive was added to the metal solution before impregnation. The impregnation solution thus consisted of 66.7 ml of CoMo-LK solution and 10 g (= 9.2 ml) of diethanolamine (DEA) and there was no additional water.

The olefin saturation at 90% GDS conversion was 8.0 wt. %, and the relative activity of the catalyst compared to CoMo / Al ₂ O ₃ catalyst, taken for comparison, amounted to 238%. This shows that the addition of diethanolamine to the impregnation solution greatly increases the relative GDS activity of the catalyst, while improved olefin saturation of catalyst A is maintained.

Example 4

Catalyst D was prepared and tested in accordance with the procedure described in Example 3, except that the amount of diethanolamine that was added to the metal solution was increased. The impregnation solution now consisted of 66.7 ml of CoMo-LK solution and 16.4 g (= 15.0 ml) of diethanolamine (DEA) and there was no additional water. The total volume of the impregnating solution was 112% of the total pore volume of the carrier.

The olefin saturation at 90% GDS conversion was 8.0 wt. %, and the relative activity of the catalyst compared to CoMo / Al ₂ O ₃ catalyst, taken for comparison, amounted to 282%. This shows that the increased addition of diethanolamine to the impregnation solution further increases the relative GDS activity of the catalyst while maintaining improved olefin saturation of catalysts A and C.

Example 5

Catalyst E was prepared and tested in accordance with the procedure described in Example 3, except that the amount of the metal solution and diethanolamine was reduced to obtain a reduced content of MoO ₃ , CoO, citric acid and diethanolamine on the catalyst. The relative ratio of these components was left the same. Additional water was added to maintain saturation of the pore volume. The impregnation solution now consisted of 49.6 ml of CoMo-LK solution, 8.0 g (= 7.3 ml) of diethanolamine (DEA) and 18 ml of water, so that the dry catalyst contained 16 wt. % MoO ₃ and 4 wt. % CoO.

Olefin saturation at 90% GDS conversion was 8.6 wt. %, and the relative activity of the catalyst compared to CoMo / Al ₂ O ₃ catalyst, taken for comparison, amounted to 145%. This shows that a decrease in the metal content from 20/5 wt. % MoO ₃ / CoO in catalyst C up to 16/4 wt. % MoO ₃ / CoO in catalyst E reduces the relative GDS activity of the catalyst while maintaining improved olefin saturation of catalyst C.

Example 6

Catalyst F was prepared and tested in accordance with the procedure described in Example 5, except that the amount of the metal solution and diethanolamine was further reduced to obtain a reduced content of MoO ₃ , CoO, citric acid and diethanolamine on the catalyst. The relative ratio of these components was left the same. Additional water was added to maintain saturation of the pore volume.

The impregnation solution now consisted of 35.0 ml of CoMo-LK solution, 6.0 g (= 5.5 ml) of diethanolamine (DEA) and 36.3 ml of water, so that the dry catalyst contained 12 wt. % MoO ₃ and 3 wt. % CoO.

The olefin saturation at 90% GDS conversion was 8.1 wt. %, and the relative activity of the catalyst compared to CoMo / Al ₂ O ₃ catalyst, taken for comparison, amounted to 101%. This shows that a decrease in metal content from 16/4 wt. % MoO ₃ / CoO in the catalyst E to 12/3 wt. % MoO ₃ / CoO in catalyst F further reduces the relative GDS activity of the catalyst while maintaining improved olefin saturation of catalysts C and E.

Example 7

Catalyst G was prepared and tested in accordance with the procedure described in Example 2, except that the amount of diethylene glycol that was added to the metal solution was increased. The impregnation solution now consisted of 66.7 ml of CoMo-LK solution and 12.6 g (= 11.6 ml) of diethylene glycol (DEG) and there was no additional water.

The olefin saturation at 90% GDS conversion was 8.0 wt. %, and the relative activity of the catalyst compared to CoMo / Al ₂ O ₃ catalyst, taken for comparison, amounted to 171%. This shows that the increased addition of diethylene glycol to the impregnation solution further increases the relative GDS activity of the catalyst, while improved olefin saturation of catalysts A and B is maintained.

Example 8

Catalyst H was prepared and tested in accordance with the procedure described in Example 7, except that the amount of diethylene glycol that was added to the metal solution was further increased. The impregnation solution now consisted of 66.7 ml of CoMo-LK solution and 16.8 g (= 15.4 ml) of diethylene glycol (DEG) and there was no additional water. The total volume of the impregnating solution was 113% of the total pore volume of the carrier.

Olefin saturation at 90% GDS conversion was 9.1 wt. %, and the relative activity of the catalyst compared to CoMo / Al ₂ O ₃ catalyst, taken for comparison, amounted to 190%. This shows that an additionally increased addition of diethylene glycol to the impregnation solution further increases the relative GDS activity of the catalyst while maintaining improved olefin saturation of catalysts A, B and G.

The results of Examples 1-8 are summarized in the table.

Catalyst Additive MoO ₃ wt.% CoO wt.% % BUT at 90% GDS conversion 1.5 order kGDS The relative activity of the catalyst Al ₂ O ₃ compared. - 4.3 1,2 13.3 1.64-1.77 * one hundred BUT LK twenty 5 8.4 1.72 97 AT LC + DEG twenty 5 8.3 2.21 135 FROM LC + DEA twenty 5 8.0 3.91 238 D LC + DEA (2x) twenty 5 8.0 4.62 282 E LC + DEA 16 four 8.6 2.47 145 F LC + DEA 12 3 8.1 1.71 101 G LC + DEG (1.5x) twenty 5 8.0 2.81 171 N LC + DEG (2x) twenty 5 9.1 3.11 190

* kGDS = 1.64 for series of tests with catalysts B, C, D, G and H; 1.70 - for test series with catalysts E and F; and 1.77 for test series with catalyst A.

Claims (33)

1. A method of preparing a catalyst for hydrodesulfurization (GDS) of naphtha, comprising: (i) impregnating a silica-based support, wherein the support contains at least about 85 wt.% Silica based on silica and has a pore volume between about 0, 6 and about 2.0 cc / g and average pore sizes from about 150 to 2000 Å, (a) an aqueous solution of a cobalt salt, (b) an aqueous solution of a molybdenum salt and at least one organic additive, said organic additive comprising at least one organic acid and at least at least one compound selected from the group consisting of compounds comprising at least two hydroxyl groups and 2-20 carbon atoms, and (poly) esters of these compounds to obtain a catalyst precursor;
(ii) drying the catalyst precursor at a temperature of less than about 350 ° C to obtain a dry catalyst precursor and,
(iii) optionally, sulfiding the dry catalyst precursor, provided that the dry catalyst precursor or catalyst has not been calcined before sulfidation or use for GDS. 2. A method of preparing a catalyst for hydrodesulfurization (GDS) of naphtha, including:
(i) impregnating a silica-based support, wherein the support contains at least about 85 wt.% silica based on silica and has a pore volume of between about 0.6 and about 2.0 cc / g and average sizes then from about 150 to 2000 Å, (a) an aqueous solution of a cobalt salt and (b) an aqueous solution of a molybdenum salt to obtain a first catalyst precursor;
(ii) drying the first catalyst precursor at a temperature of less than about 350 ° C. to obtain a first dry catalyst precursor;
(iii) impregnating the dry catalyst precursor (c) with at least one organic acid and at least one organic additive, the organic additive comprising at least one compound selected from the group consisting of compounds comprising at least two hydroxyl groups and 2-20 carbon atoms, and (poly) esters of these compounds, to obtain a second catalyst precursor; (iv) optionally drying the second catalyst precursor to obtain a second dry catalyst precursor and,
(v) optionally sulfidizing the second catalyst precursor, provided that the second dry catalyst precursor or catalyst has not been calcined before sulfidation or use for GDS. 3. A method of preparing a catalyst for hydrodesulfurization (GDS) of naphtha, including:
(i) regeneration of a spent catalyst comprising a silica-based support, wherein the support contains at least about 85 wt.% silica and has a pore volume between about 0.6 and about 2.0 cc / g and average pore sizes from about 150 to 2000 Å, which was impregnated with a cobalt salt and a molybdenum salt, to obtain a regenerated catalyst;
(ii) impregnating the regenerated catalyst with at least one organic additive, said organic additive comprising at least one organic acid and at least one compound selected from the group consisting of compounds comprising at least two hydroxyl groups and 2-20 carbon atoms and (poly) esters of these compounds to form a catalyst precursor;
(ii) drying the catalyst precursor at a temperature of less than about 350 ° C. to obtain a dry catalyst precursor; and (iii) optionally sulfiding the dry catalyst precursor, provided that the dry catalyst precursor or catalyst was not calcined before sulfidation or use for GDS. 4. The method according to any one of claims 1 to 3, where the compound comprising two hydroxyl groups and 2-20 carbon atoms, further comprises at least one secondary amino group. 5. The method according to claim 4, where at least 2 hydroxyl groups are separated from the secondary amino group by 1 or more carbon atoms, preferably 2-4 carbon atoms. 6. The method according to claim 1 or 2, where the organic additive is selected from the group consisting of polyhydroxyalkanes and polyhydroxyalkenes, including two or more hydroxyl groups and from 1 to 4 carbon atoms per hydroxyl group, and their polycondensates, and secondary amines, including alkanol or alkenol groups, and their polycondensates. 7. The method according to claim 1 or 2, where the additive is at least one compound selected from ethylene glycol, diethylene glycol, polyethylene glycol, diethanolamine or dialkanolamine. 8. The method according to any one of claims 1 to 3, where the molar ratio between the amount of additive and the amount of cobalt and molybdenum is in the range from 0.01: 1 to 2.5: 1. 9. The method according to any one of claims 1 to 3, where the amount of additive is at least 5% relative to the total weight of the catalyst. 10. The method according to any one of claims 1 to 3, where the silica-based carrier has a pore volume between about 1.0 and about 1.5 cm ³ / g. 11. The method according to any one of claims 1 to 3, where the average pore sizes of the carrier based on silicon oxide before impregnation are in the range from about 150 to about 1000 Å. 12. The method according to any one of claims 1 to 3, where the carrier based on silicon oxide contains at least about 90 wt.% Silicon oxide. 13. The method according to any one of claims 1 to 3, where the amounts of cobalt salt and molybdenum salt are sufficient to obtain a catalyst containing from about 2 to about 8 wt.% Cobalt oxide and from about 8 to about 30 wt.% Molybdenum oxide onto a silica-based carrier. 14. The method according to any one of claims 1 to 3, where the catalyst precursor is sulfided in situ or ex situ in the presence of at least one sulfidation agent. 15. The method according to 14, where the sulfidation agent is a hydrogen sulfide in a concentration of from about 0.1 to about 10%, based on the total amount of gases present. 16. The method according to any one of claims 1 to 3, where the dry catalyst precursor or sulfidized catalyst is not heated to temperatures above about 350 ° C before sulfidation or use for GDS. 17. A catalyst suitable for hydrodesulfurization (GDS) of naphtha obtained by the method according to any one of claims 1 to 16. 18. A catalyst suitable for hydrodesulfurization of naphtha, comprising a silica carrier, which has a silica content of at least about 85 wt.% Based on silica and has a pore volume between about 0.6 and about 2.0 cubic cm / g and average pore sizes from about 150 to 2000 Å, wherein said silica support is impregnated with a cobalt salt, a molybdenum salt and at least one organic additive, said organic additive comprising at least one organic acid and at least one compound selected Fifth of the group consisting of compounds comprising at least two hydroxyl groups and 2-20 carbon atoms, and (poly) esters of these compounds. 19. The catalyst according to claim 18, wherein the compound comprising two hydroxyl groups and 2-20 carbon atoms further comprises at least one secondary amino group. 20. The catalyst according to claim 19, where at least 2 hydroxyl groups are separated from the secondary amino group by 1 or more carbon atoms, preferably 2-4 carbon atoms. 21. The catalyst according to claim 18, where the organic additive is selected from the group consisting of polyhydroxyalkanes and polyhydroxyalkenes, including two or more hydroxyl groups and from 1 to 4 carbon atoms per hydroxyl group, and their polycondensates, and secondary amines, including alkanol or alkenol groups, and their polycondensates. 22. The catalyst of claim 18, wherein the additive is at least one compound selected from ethylene glycol, diethylene glycol, polyethylene glycol, diethanolamine, or dialkanol diamine. 23. The catalyst according to claim 18, wherein the molar ratio between the amount of additive and the amount of cobalt and molybdenum is in the range from 0.01: 1 to 2.5: 1. 24. The catalyst of claim 18, wherein the amount of additive is at least 5% relative to the total weight of the catalyst. 25. The catalyst of claim 18, wherein the silica-based support has a pore volume of between about 1.0 and about 1.5 cc / g. 26. The catalyst according to p, where the average pore size of the carrier based on silicon oxide before impregnation are from about 150 to about 1000 Å. 27. The catalyst of claim 18, wherein the silica-based support comprises at least about 90% by weight of silica. 28. The catalyst according to p. 18, where the amounts of cobalt salt and molybdenum salt are sufficient to obtain a catalyst containing from about 2 to about 8 wt.% Cobalt oxide and from about 8 to about 30 wt.% Molybdenum oxide based on a carrier based silicon oxide. 29. The catalyst according to any one of claims 18 to 28, which has been sulfided by in-situ or ex-situ sulfidation. 30. A method of hydrodesulfurization of naphtha having an olefin content of at least about 5% based on the weight of naphtha, comprising reacting naphtha under hydrodesulfurization conditions with a catalyst prepared by the method according to any one of claims 1-16, or with a catalyst in accordance with clause 17 or 29. 31. A method for hydrodesulfurization of naphtha having an olefin content of at least about 5% based on the weight of naphtha, the method comprising: (a) sulfiding the catalyst in accordance with any one of claims 18 to 28 to obtain a sulfated catalyst; (b) reacting a sulfidated catalyst with naphtha under hydrodesulfurization conditions. 32. The method according to item 30 or 31, where the naphtha is at least one naphtha selected from naphtha obtained by fluid catalytic cracking (FCC naphtha), steam cracking naphtha or coke naphtha. 33. The method according to any one of claims 30 and 31, where the naphtha fraction has an olefin content of from about 5 to about 60 wt.%, A nitrogen content of from about 5 to about 500 million ^-1 by mass and a sulfur content of from about 300 to about 7000 million ^-1 by mass relative to the mass of naphtha.