EP0181253A1 - Process for the catalytic hydrotreatment of heavy hydrocarbons in fixed or mobile beds with injection of a metal compound into the feed - Google Patents

Abstract

The invention relates to a process for catalytic treatment of heavy hydrocarbons, in a fixed or moving bed, over a catalyst containing an alumina carrier and at least one catalytic metal or compound of metal from groups VB, VI B and VIII of the periodic classification of elements, characterized by the direct injection into the charge, continuously or periodically, of at least one metal compound selected from the group consisting of halides, oxyhalides, oxides, polyacids and polyacid salts of metals from groups VI B, VII B and VIII, before introducing the charge into the hydrotreatment zone.

Description

The present invention relates to a process for hydrotreating heavy hydrocarbon feedstocks containing heteroatomic impurities such as for example sulfur, nitrogenous and metallic impurities, for example those containing nickel, vanadium and / or iron. Among the charges envisaged, there may be mentioned, without this list being considered restrictive, atmospheric distillation residues, vacuum distillation residues, heavy crude oils, deasphalted oils, braised and asphalts diluted with an aromatic distillate. coming for example from a catalytic cracking process (light cycle oil) and carbon hydrogenates.

This process consists in treating with hydrogen a charge of heavy hydrocarbons in contact with at least one fixed or mobile bed of a heterogeneous catalyst containing an alumina support and at least one catalytic metal or compound of catalytic metal of l '' at least one of the metals of groups VB, VI B and VIII of the periodic table of the elements (Handbook of Chemistry and Physics 37 ^th edition, 1956 pages 392-393), said alumina support having a pore volume of 0.85 a 2 cm ³ x ^g-1 and a specific surface of 80 to 250 m ² x g- ¹ , said process being characterized in that one adds to the charge of hydrocarbons to be treated added with hydrogen in sufficient quantity to carry out the hydrotreatment reaction, continuously or periodically at least one compound of at least one metal chosen from the group formed by halides, oxyhalides, oxides, polyacids and polyacid salts of the metals of the group formed by the metals of groups VI B, VII B and VIII of the periodic table of elements before passage of said charge through the catalyst bed heterogeneous.

The purpose of refining hydrocarbon cuts is to convert heavy molecules into lighter molecules and to eliminate the maximum of sulfur, nitrogen and metallic heteroatomic impurities.

The sulfur and nitrogen heteroatoms are generally eliminated respectively in the form of hydrogen sulphide and ammonia, these compounds do not deactivate the catalyst and are found in the effluents.

On the other hand, the metals of the filler and in particular nickel and vanadium are deposited on the surface of the catalyst, generally in the form of sulphides, thus causing a significant deactivation, and hardly reversible of the catalyst, which becomes progressively incapable of carrying out the reactions. hydrodesulfurization and hydrodenitrogenation.

The processes for hydrotreating petroleum fractions, and in particular those distilling below 550 ° C., are well known to those skilled in the art. The operations are generally carried out under hydrogen pressure, in the presence of catalysts such as oxides and sulfides of molybdenum, tungsten, nickel and cobalt, for example on alumina, at temperatures generally between 250 ° C and 450 ° C.

The numerous researches carried out quickly showed that in particular an adaptation of the porous texture of the conventional hydrorefining catalysts makes it possible to clearly increase the level of activity in hydrodemetallization and in conversion of heavy molecules. This modification of the catalyst also makes it possible to appreciably increase the lifetime of the catalysts (period of time during which the catalyst used is sufficiently active so that it is not necessary to replace it with a new charge of fresh catalyst). Numerous patents or patent applications among which we can cite US-A-4,395,329, US-A-4,225,421, US-A-4,166,026, US-A-4,134,856 and EP-A-98,764 claim such an improvement. The catalysts described in patent application EP-A-98 764 having a particular porous texture and a structure resembling the image of a bunch of spiny chestnut bugs or even a bunch of sea urchins, are particularly effective. in heavy metal demetallation reactions and can be used on an industrial level.

However, such catalysts, used alone, do not allow, on the one hand sufficient hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) activities and on the other hand the activities of HDS, HDN, hydrodemetallization (HDtl) and conversion of heavy molecules decrease over time, due to poisoning of the active phase by deposition of vanadium and nickel. This insufficiency in the stability of the hydrorefining activity of these catalysts generally forces a second hydrotreatment step to be used in order to obtain products which can be used as finished products or as feedstock in catalytic hydrocracking cracking units or steam cracking. The implementation of this second step is very costly because it requires investments in equipment, in particular, very large.

The object of the present invention is to overcome the above drawbacks and in particular to allow the use of catalysts supported on alumina, said alumina having a pore volume of 0.85 to 2 cm ³ xg ^-1 and a specific surface from 80 to 250 m ² xg ^-1 in industrial hydrorefining units for longer treatment times than those obtained with the methods of the prior art, and in certain cases making it possible to avoid having to carry out a second hydrotreatment step.

Surprisingly, it has been discovered that the addition to the feedstock of hydrocarbons to be treated continuously or periodically (by puffing) of at least one compound of at least one metal chosen from the metals of groups VI B, VII B and VIII of the peri classification contains elements and advantageously of at least one compound of at least one metal from the group formed by molybdenum, tungsten, nickel, cobalt and chromium, in the implementation in fixed bed or mobile catalyst supported on alumina, under conventional conditions for hydrotreating heavy products, in particular allows to significantly increase the life of these catalysts.

Not all metal compounds can be used in the present process. With the catalysts which we use in the present invention and which are defined more precisely below certain compounds and in particular organic compounds such as for example lenaphthénatee molybdenum, seem to decompose very quickly in contact with the catalyst, at the head of the bed , causing crusting and do not improve the performance of the catalysts used.

Surprisingly, it has been discovered that the compounds of the above metals chosen from the group formed by halides, oxyhalides, oxides, polyacids such as isopolyacids and heteropolyacids and the salts of these acids make it possible to obtain a clear improvement of the performance of the catalysts used and in particular of their lifetime. Among the halogenated compounds, compounds containing chlorine, bromine or iodine are advantageously used in their formulas and more particularly compounds containing chlorine or iodine in their formulas. In a very advantageous manner, molybdenum compounds will be used alone or in combination with nickel and / or cobalt compounds and, preferably, blues of molybdenum and / or phosphomolybdic acid or one of its salts will be used.

The metal compound which is injected into the charge of hydrocarbons to be treated is introduced for example in the form of a solution, or of suspension in an organic solvent having a solubility of at least 1% by weight in hydrocarbons under the conditions hydrotreatment, in the form of a solution or emulsion in a water-organic solvent mixture, or in the form of an aqueous solution of said compound if it has sufficient solubility in water.

Among the organic solvents which can be used, mention may be made of hydrocarbons, alcohols, ethers, ketones, esters, amides and nitriles. Alcohols are preferably used and especially mixtures of alcohols having 6 to 18 carbon atoms or hydrocarbons.

When water-organic solvent mixtures are used to introduce the metal compound, mixtures containing from 50 to 99% by weight and preferably from 70 to 99% by weight of organic solvent are preferably used relative to the total weight of the water-organic solvent mixture. In a preferred form of the invention, metal compounds are used in solution in hydrocarbons or in solution in mixtures of alcohols, in particular C ₇ -C ₉ alcohols or in solution in water-alcohol mixtures C ₇ - C ₉ . It is particularly advantageous to use, for example phosphomolybdic acid or its salts in aqueous solution, and / or blues of molybdenum preferably chosen from those described in FR-A-1 099 953, in solution in a mixture of alcoholen C ₇ -C ₉ or in a mixture water-alcohol C ₇ -C ₉ or hydrocarbons, for example in a fraction of the load after a previous treatment.

The catalysts that are used in the context of the present invention, containing an alumina support with a pore volume of 0.85 to 2 cm ³ g ^-1 and a specific surface of 80 to 250 m ² × g ^-1 .

The aluminas which can be used as a support are preferably chosen from aluminas of low or zero acidity, such as that having a heat of neutralization by absorption of ammonia preferably less than 10 calories and more particularly less than 7 calories per gram of alumina at 320 ° C under 0.04 megapascals (MPa). The so-called neutral aluminas can also be characterized by their inertness with respect to cracking and coking reactions in the presence of hydrogen. Neutrality can be determined for example by the n-heptane cracking test which consists in measuring the quantity of n-heptane converted into lighter molecules under the following operating conditions:

The conversion is measured by analysis by gas chromatography of the liquid products.

In this test, a support is said to be neutral if its cracking activity (mole / hour / m ² of support) is less than 5 x 10 ^-6 at the temperature of 470 ° C and if it is less than 15 x 10 ^-6 at the temperature of 500 ° C.

Aluminas treated with alkali metal and / or alkaline _- earth metal, for example those having a content of Na ₂ 0 to 1000 ppm by weight or more are usable, as well as the thermally stabilized with rare earth metals and / or alkaline earth metals and / or silica, generally meet the neutrality criteria defined below.

Advantageously, it is also possible to use autoclaved aluminas. The term “autoclaved alumina” denotes aluminas which have undergone a treatment with water or with steam called “autoclaving” at a temperature between approximately 80 ° C. and approximately 300 ° C. for approximately 5 minutes to 48 hours, preferably 1 to 6 hours.

Preferably, the aqueous autoclaving medium contains at least one acid capable of dissolving part of the alumina of the agglomerates, or the mixture of such an acid with at least one compound providing an anion capable of combining with aluminum ions, for example a mixture of nitric acid and acetic or formic acid. The autoclaving technique is for example described in French patent application FR-A-2 496 631.

In a particularly preferred form of the invention, an autoclaved alumina obtained according to the method described in European patent application EP-A-98 764 will be used. The alumina support obtained is formed of a plurality of needle-shaped plates, the plates of each agglomerate being oriented generally radially with respect to each other and relative to the center of the agglomerate. The aforementioned structure includes macropores and mesopores (we call mesopores, pores of size between that of micropores and that of macropores: the mesopores are therefore, roughly between 10 and 100 nanometers) and practically no micropores.

The preferred supports are those which contain a preponderant proportion of wedge-shaped mesopores.

On the alumina supports, described above, the catalytic metal or metals or compounds of catalytic metals are deposited by any at least one of the metals of groups VB, VI B, and VIII of the periodic table of the elements and preferably at least one of the metals from the group formed by molybdenum, tungsten, iron, cobalt, nickel, chromium and vanadium. Preferred combinations are molybdenum + cobalt, molybdenum + nickel, tungsten + nickel, vanadium + nickel. The metal content of the final catalyst used in the present invention is generally from 0.5 to 40% by weight of metals (expressed as oxide) relative to the weight of the finished catalyst. In a preferred embodiment of the invention, one of the combinations of metals mentioned above is used, the metal content then preferably being from 1 to 30% by weight of metals (expressed as oxide) relative to the weight. of the finished catalyst.

The catalysts described in European patent application EP-A-98 764, of which the support formed from autoclaved alumina has the structure recalled above, which have a structure identical to that of the support, and have improved resistance in clogging of mouths of pores compared for example to bimodal (macroporous and microporous) or monomodal (microporous) catalysts are preferred within the framework of the invention. The support of these catalysts is inert to the n-heptane cracking test. Were obtained spec i _{fi c} activities q _ues of 0.610 ^-6 _{mol / h / m} 2 at _{470 ° C} and _{8 ×} 10 ^-6 mol / h / m ² at 500 ° C.

The continuous or periodic injection of metal compounds, and in particular of molybdenum compounds is carried out after adding enough hydrogen to perform. the feed hydrorefining reaction. The introduction of metal compound takes place before the passage of said charge added with hydrogen through the heterogeneous catalyst bed, in a preferred form of the invention the metal compound is introduced into the charge added with hydrogen previously carried at a temperature of at least 330 ° C, advantageously from 330 ° C to 450 ° C approximately and preferably, previously brought to a temperature of approximately 350 ° C to approximately 450 ° C.

The continuous or puff injection of this metallic compound, in particular of the molybdenum compounds, makes it possible, in addition to increasing the cycle time, to keep the demetallizing activity of the catalyst constant, to improve the hydrodenitrogenation activities, hydrodesulfurization and conversion of heavy molecules.

Without wishing to be bound by any theory, it seems that the metal compounds, in particular the molybdenum compounds, decompose on the catalyst and the metal atoms (molybdenum) then attach to the surface of the catalyst, thus making it possible to avoid deactivation thereof, by continuous or periodic regeneration of the active phase.

The injection of the metal compounds, preferably molybdenum compounds, is in an advantageous form of the present invention carried out periodically. A quantity of compound is thus introduced during a determined duration into the charge, at variable intervals, for a more or less long time; for example, this compound is introduced for 1 to 30 h every 100,200 or 300 hours and advantageously for 10 to 20 h every 200 hours.

The amount of the metal compound added to the charge is advantageously such that the concentration of metal added relative to the total weight of the charge is from 10 to 1500 ppm and preferably from 30 to 600 ppm.

The usual conditions for the hydrotreatment reaction are a temperature of about 250 to about 500 ° C and preferably about 350 to about 450 ° C, a pressure of about 5 to about 30 megapascals (MPa) and preferably from approximately 8 to approximately 20 MPa and a flow rate of hydrocarbon feedstock per volume of catalyst and per hour (VVH) of approximately 0.1 to approximately 10 and preferably approximately 0.2 to approximately 2. The flow rate d 'Hydrogen is for example from about 50 to about 5000 liters per liter of feed and preferably from about 200 to about 3000 x 1-1.

In the following examples which illustrate the invention without limiting its scope, two catalysts A and B are used, prepared according to the method described in European patent application EP-A-98 764.

The characteristics of these two catalysts are those which are described in patent application EP-A-98 764 with regard to their structures, their porous distributions and their compositions.

The support for these catalysts is alumina, it is prepared according to the method described in Example 1 of patent application EP-A-98 764 and has all the characteristics described in this example. Then deposited on this support molybdenum and nickel using the method described in Example 1 of EP-A-98 764. The metal contents expressed by weight of oxide relative to the weight of the finished catalyst A and B obtained are the following:

Example 1.

• • Test 1: 1 1 of catalyst A is placed in a hydrotreating pilot unit operating in a fixed bed. The operating conditions for using this catalyst are as follows:
  
  

The petroleum cut used to carry out the test is atmospheric petroleum residue from Safaniya (Saudi Arabia), the characteristics of which are as follows:

The pilot unit consists of a preheating oven, allowing the charge to be brought to the desired temperature for the catalytic hydrotreatment reaction, in series with a catalytic hydrotreatment reactor comprising a fixed bed of catalyst.

The above charge and the hydrogen are introduced into the preheating furnace so as to raise the temperature of this mixture to 400 ° C., this charge plus hydrogen mixture then passes into the catalytic hydrotreatment reactor.

Test 2: Under the same operating conditions, with the same apparatus and the same catalyst as that used in test 1, another test is carried out by continuously adding, in the charge-hydrogen mixture leaving the preheating oven, molybdenum, in the form of an emulsion at 5.8% by weight of molybdenum blue in a water-organic solvent mixture containing 2% by weight of water, the organic solvent being constituted killed by a mixture of C ₇ -C ₉ alcohols. The quantity of this aquo-organic emulsion introduced into the charge is such that the molybdenum content, counted by weight of metal relative to the weight of the charge, is 100 ppm.

During these two tests, the analyzes of the sulfur, nickel, vanadium and asphaltenes content of the effluents at the outlet of the catalytic hydrotreatment reactor are carried out, in order to compare over time the performance evolution with each of the two systems. .

The results are given in Table I below:

The results therefore very clearly show that the activities of _HDS , HDM and HDA (asphaltene hydroconversion) are always higher when molybdenum blue is added to the charge. It is clear that deactivation after 500 hours is much less important when molybdenum blue is added, which makes it possible to have a longer cycle time.

Example 2.

• • Test 1: 1 1 of catalyst B is placed in a pilot hydrotreatment unit operating in a fixed bed. The apparatus, the operating conditions and the test load used are identical to those of test 1 of Example 1.
• • Test 2: 1 1 of the same Best catalyst placed in the same pilot unit, under the same operating conditions. However, in the feed, phosphomolybdic acid in aqueous solution is added at the outlet of the preheating oven before its injection into the catalytic hydrotreatment reactor. The amount of acid added is such that the molybdenum content in the feed is 50 ppm.

The results obtained during each of these two tests are shown in Table II.

It therefore appears that even with a more active catalyst, an injection, in moderate quantity, of molybdenum into the charge makes it possible to improve the activity of the catalytic system and to have better stability over time.

Example 3.

• Test 1: 1 1 of catalyst A is loaded into a pilot hydrotreating unit in a fixed bed identical to that of Example 1. The operating conditions are as follows:

The test load is an asphalt diluted with 35% by weight of light cycle oil (LCO).

The characteristics of this charge are as follows:

The charge-hydrogen mixture is brought to 410 ° C. in the preheating oven and then introduced into the catalytic hydrotreatment reactor.

• Test 2: 1 1 of catalyst A is loaded into the same pilot unit and is placed under the same operating conditions as those of test 1. In the same test load as that used in test 1, the following is added to the out of the preheating oven of molybdenum blue in solution at 5.8% by weight in a mixture of C ₇ -C ₉ alcohols. The amount of solution added is such that the molybdenum content in the feed is 150 ppm by weight.

• Test 3: This test is identical to test 2 except that the blue of molybdenum is replaced by molybdenum trioxide in a water-alcohol mixture C ₇ -C ₉ at 10% by weight d water and a sufficient amount of this composition is introduced to have 150 ppm by weight of molybdenum in the feed.

• Test 4: This test is identical to test 2 with the exception that the molybdenum blue prepared using the method described in FR-A-1 099 953 is used. A sufficient quantity of this compound is introduced to have 150 ppm by weight of molybdenum in the feed. These four tests are summarized in Table III below:

These results show that the addition of molybdenum blue, or molybdenum trioxide, to the charge makes it possible to increase the activities of HDS, HDM and HDA, and also to have a more stable catalytic activity during time.

Example 4.

₀ Test 1: 1 1 of catalyst A is placed in a hydrotreating pilot unit identical to that described in Example 1. The operating conditions are as follows:

The hydrocarbon charge used to carry out the test is Boscan crude deasphalted with pentane (Venezuelan crude from the Orinoco belt), the characteristics of which are:

The charged hydrogen mixture is brought to 380 ° C. in the preheating oven and then introduced into the catalytic hydrotreatment reactor.

• Test 2: 1 1 of catalyst A is placed under the same conditions as those of test 1. The test charge used is also that of test 1. But during the test, every 200 hours, for 12 hours phosphomolybdic acid in aqueous solution is added to the charge at the outlet of the preheating oven, in an amount such that the molybdenum concentration in the feed which is introduced during these 12 hours is 600 ppm by weight.

The results obtained during each of these two tests are collated in Table IV.

These results clearly show that the addition, at regular intervals, of a molybdenum compound makes it possible to increase the catalytic activity and to keep it more stable during the operation of the catalytic system.

Example 5 (comparative)

. Test 1: 1 liter of catalyst A is placed in a pilot hydrotreatment unit operating in a fixed bed. The apparatus, the operating conditions and the test load used are identical to those of test 1 of Example 4.

. Test 2: 1 liter of the same catalyst A is placed in the same pilot unit, under the same operating conditions. However, in the charge-hydrogen mixture, molybdenum naphthenate is added at the outlet of the preheating oven, before its injection into the catalytic hydrotreatment reactor, in the form of a 6% by weight solution in a mixture of alcohols. C ₇ -C ₉ . The amount of solution added is such that the molybdenum content in the feed is 600 ppm.

The results obtained during each of these two tests are given in Table V below.

On the other hand, during test 2, from the 400th hour, significant pressure drops were observed.

Claims (11)

1.- Process for hydrotreating a charge of heavy hydrocarbons in contact with at least one fixed or mobile bed of a heterogeneous catalyst, containing an alumina support and at least one catalytic metal or compound of catalytic metal at least one of the metals of groups VB, VI B and VIII of the periodic table, said alumina support having a pore volume of 0.85 to 2 cm ³ xg ^-1 , and a specific surface of 80 to 250 m ² xg ^-1 characterized in that one operates by introducing into said hydrocarbon charge added with hydrogen in an amount sufficient to carry out the hydrotreatment reaction, continuously or periodically, at least one compound of minus one metal, chosen from the group formed by halides, oxyhalides, oxides, polyacids and polyacid salts of the metals of the group formed by the metals of groups VI B, VII B and VIII of the periodic table before passage of said charge through the bed of heterogeneous catalyst. 2. A method according to claim 1 wherein the metal compound is mixed with the charge previously brought to a temperature of at least 330 ° C. ₃ .- Method according to claim 1 or 2 wherein the alumina support is chosen from aluminas of low or zero acidity, thermally stabilized aluminas, autoclaved aluminas inert with respect to the n- cracking test heptane. 4.- The method of claim 3 wherein the alumina support is an autoclaved alumina formed of a plurality of needle-shaped platelets, the platelets of each agglomerate being oriented generally radially with respect to each other and relative to the center of the agglomeration. 5.- Method according to one of claims 1 to 4 wherein the metal compound is introduced into the feed in the form of a solution or an emulsion in a water-organic solvent mixture containing from 70 to 99% in weight of organic solvent, solution in organic solvent or solution in water. 6. A method according to claim 5 wherein the metal compound is introduced into the feed in the form of a solution or an emulsion in a water-organic solvent mixture, said organic solvent containing at least one alcohol having from 6 to 18 carbon atoms. 7.- Method according to one of claims 1 to 6 wherein the metal compound is introduced into the charge in an amount such that the metal content added to the charge is from 10 to 1500 ppm by weight. 8.- Method according to one of claims 1 to 7 wherein the metal compound introduced into the feed is a molybdenum compound selected from the group formed by molybdenum blues, phosphomolybdic acid and the acid salts phosphomolybdic. 9.- Method according to one of claims 1 to 8 wherein the heterogeneous catalyst comprises from 1 to 30% by weight (expressed as oxide) of a combination of nickel and molybdenum, or cobalt and molybdenum or nickel and tungsten. 10.- Method according to one of claims 1 to 9 wherein the metal compound is introduced periodically into the load. 11.- Method according to one of claims 1 to 10 wherein the hydrocarbon charge to be treated is chosen from the group formed by atmospheric distillation residues, vacuum distillation residues, heavy crude oils, deasphalted oils , the pitches and the asphalts diluted by an aromatic distillate and the hydrogen carbonates and the hydrotreatment is carried out at a temperature of approximately 250 to approximately 500 ° C, a pressure of approximately 5 to approximately 30 MPa, an hourly space speed (VVH) of about 0.1 to about 10 liters per liter of catalyst per hour and a hydrogen flow rate of about 50 to about 5000 liters per liter of feed.