US3841996A

US3841996A - Hydrodesulphurization process

Info

Publication number: US3841996A
Application number: US00289503A
Authority: US
Inventors: A Jacobsen
Original assignee: TOPSOL H
Current assignee: TOPSOL H; TOPSOL H DK
Priority date: 1971-09-28
Filing date: 1972-09-15
Publication date: 1974-10-15
Anticipated expiration: 1991-10-15
Also published as: GB1373791A; JPS56477B2; FR2154635B1; NL7213105A; DE2247241A1; CA977300A; NL177925C; FR2154635A1; JPS4843002A; IT975100B; DE2247241C2

Abstract

MESH-WIDTH OF SIEVES THAT RETAIN THE PARTICLES AND LET THEM PASS, RESPECTIVELY, SAID REACTING THREE-PHASE DISPERSION OCCUPYING ALL CAVITIES OF THE REACTION LOOP AND BEING SUBSTANTIALLY FREE OF CONCENTRATION GRADIENTS IN ALL PARTS OF THE REACTION LOOP; (B) WHILE MAINTAINING THE THREE-PHASE DISPERSION AND THE TEMPERATURE AND PRESSURE CONDITIONS FOR HYDROCONVERSION, CONTINOUSLY INTRODUCING INTO THE REACTION LOOP FEED STREAMS OF MEASURED AMOUNTS OF THE HYDROGEN-CONTAINING GAS, THE LIQUID OIL FEED AND THE PARTICULATE HYDROCONVERSION CATALYST; (C) SIMULTANEOUSLY HEREWITH CONTINOUSLY ALLOWING A CORRESPONDING AMOUNT OF A PRODUCT STREAM HAVING SUBSTANTIALLY THE SAME COMPOSITION AS THE REACTING THREE-PHASE DISPERSION TO FLOW FROM THE REACTION LOOP; AND (D) SEPARATING THE PRODUCT STREAM THUS FLOWING FROM THE REACTION LOOP INTO A HYDROGEN-CONTAINING GAS, A PRODUCT OIL AND A CONCENTRATED SLURRY OR PASTE OF THE PARTICULATE HYDROCONVERSION CATALYST IN OIL.

1. IN A PROCESS FOR THE CATALYTIC HYDROCONVERSION AT ELEVATED TEMPERATURE AND PRESSURE OF CRUDE OIL AND HEAVY PETROLEUM FRACTIONS, THE IMPROVEMENT COMPRISING THE STEPS OF (A) IN A REACTION LOOP, MAINTAINED AT HYDROCONVERSION CONDITIONS OF ELEVATED TEMPERATURE AND PRESSURE AND PROVIDED WITH INLETS, OUTLETS, MIXING DEVICES, AND A CIRCULATION PUMP, FIRST FORMING AND THEREAFTER MAINTAINING A REACTING THREE-PHASE DISPERSION CONSISTING OF A GASEOUS HYDROGEN CONTANING PHASE, A LIQUID PHASE OF THE OIL TO BE HYDROCONVERTED, AND A SOLID PHASE OF THE HYDROCONVERSION CATALYST IN PARTICULATE FORM RANGING IN SIZE FROM 0.02 TO 0.5 MM, MEASURED BY THE

Description

Oct. 15, 1914 A. Q'JACOBSEN' 3,341,996

I HYDRODESULPHURIZATION PROCESS Filed Sept. 15, 1972 2 Sheets-Sheet 1 M15. 1974 f km coasm 3.841.996

HYDRODESULPHURIZATION PROCESS Filed Sept. 15; 1972 2 Sheets-Sheet z United States Fatent C) 3,841,996 HYDRODESULPHURIZATIDN PROCESS Andreas Christian .lacobsen, Charlottenlund, Denmark,

assignor to Haldor Frederik Axel Topsol, Frydenlundsvej, Vedbaek, Denmark Filed Sept. 15, 1972, Ser. No. 289,503 Claims priority, application Great Britain, Sept. 28, 1971, 45,200/ 71 Int. Cl. Cltlg 13/02, 37/02 US. Cl. 208-112 Claims ABSTRACT OF THE DISCLOSURE There is provided an improved process for the hydroconversion, particularly hydrodesulphurization and hydrocracking, of crude oils and heavy petroleum fractions at elevated temperature and pressure in the presence of a solid particulate catalyst, in which process the hydroconversion is carried out in a reacting three-phase dispersion of a gaseous hydrogen-containing phase, a liquid phase of the oil and the catalyst, this three-phase dispersion being formed and maintained in a reaction loop at substantially constant conditions, a product stream having substantially the same composition as the threephase dispersion being continuously allowed to leave said reaction loop. Hereby efficient conversion is obtained without risk of clogging a catalyst bed and without risk of local disturbances, coke formation and similar disadvantages.

The present invention relates to a process and an apparatus for the hydroconversion of heavy petroleum oils in the presence of a solid catalyst. In particular, the invention relates to a process for hydrodesulphurization and/or hydrocracking of crude oils and heavy petroleum fractions in the presence of a hydroconversion catalyst.

Heavy petroleum oils such as residual oils, crude oils, and heavy oil fractions contain various undesired elements which can be removed more or less completely in a hydroconversion process. Sulphur is present mainly in the form of organic sulphur compounds among which tiophenic compounds predominate. Similarly, nitrogen and oxygen are present in various heteroa omic compounds. During the hydroconversion reactions these elements are liberated from the organic compounds as hydrogen sulphide, ammonia, and water, respectively. Furthermore, there are metallic contaminants in heavy petroleum oils in the form of metallo-organic complexes as well as inorganic compounds. Also the metals are partly removed from the petroleum oils in the hydroconversion process and some of them become deposited on the catalyst either as free metals or as inorganic compounds. Further reactions occurring in hydroconversion processes are hydrocracking reactions in which large hydrocarbon molecules are broken into smaller fragments which are immediately hydrogenated.

If desulphurization is the main objective of a hydroconversion process it is often referred to as a hydrodesulphurization process, while it is referred to as a hydrocracking process if hydrocracking is the main objective. However, all the above mentioned reactions will occur simultaneously in both processes, and it may not always be possible to distinguish clearly between a hydrodesulphurization process and a hydrocracking process. The term hydroconversion process used in the present specification should be understood to include both processes.

Most of the heavy petroleum oils cannot be brought in vapor form without destructions. Consequently, such oils will remain liquid in hydroconversion processes. Most of the hydroconversion reactions are hydrogen consuming. The liquid petroleum oils will, therefore, have to be brought in good contact with gaseous hydrogen. Furthermore, the desired reactions will only proceed with a practical rate in the presence of a solid catalyst. A predominant technological problem in processes for hydroconversion of heavy petroleum oils relates to the necessity of providing an intimate contact between three phases: a gaseous hydrogen phase, a liquid oil phase, and a solid catalyst phase.

In most of such conventional hydroconversion processes, gaseous hydrogen and liquid oil are passed downwards through a fixed bed of porous catalyst particles. As in other catalytic reactions in the presence of porous catalyst particles, there are in the hydroconversion reactions rate restrictions related to the transfer of reactants into and products out of the catalyst pores. The use of the smallest possible catalyst particle size will tend to decrease the length of the transfer paths and thereby reduce the rate restrictive effect. However, in fixed bed processes, the pressure drop increases with decreasing particle size and the particle size cannot be decreased below certain limits.

A particular problem in the hydroconversion processes relates to the gas-liquid contact between hydrogen and oil. If hydrogen is not readily available at all locations where reactions take place, cracking reactions may occur and lead to undesired coke formation. As the consumption of hydrogen usually is higher than the amount of hydrogen that can be dissolved in the oil, hydrogen must continuously be supplied to the oil phase. This requires a very intimate contact between the gaseous hydrogen phase and the liquid oil phase. In a conventional hydroconversion process, where the two phases flow co-currently down through a fixed catalyst bed, each catalyst particle will be surrounded by a liquid oil film. This oil film provides an area for gas-liquid contact which is practically equal to the total outer surface area of the catalyst particles. Consequently, the gas-liquid contact area will increase with decreasing particle size. However, as mentioned above, the particle size cannot be decreased below certain limits. Therefore, alternative ways of increasing the hydrogen transfer rate in fixed bed processes have been sought. Among these are an increase of the hydrogen pressure and an increase of the rate of hydrogen flow.

A further problem in hydroconversion processes is related to the deposition of solids such as metals or metal compounds and coke on the catalyst. In fixed bed processes these deposits accumulate between the catalyst particles especially in the inlet part of the bed and tend to increase the pressure drop. Furthermore, they will plug the catalyst pores and thus make the interior of the catalyst particles inaccessible to the reactants. The useful life of a catalyst bed will, therefore, be reduced and operation of a fixed bed process will have to be interrupted periodically for renewal of at least part of the catalyst bed.

Several attempts have been made to increase the rate of hydrogen transfer from the gaseous phase to the liquid oil phase by providing a better contact between these two phases.

It has been proposed in US. Pat. No. 2,968,614 to circulate a stream of a heavy hydrocarbon oil and a suspended particulate hydrogenation catalyst in a reaction zone comprising an open-ended draft tube and an annular space surrounding the draft tube. Hydrogen, hydrocarbon oil, and suspended catalyst are introduced at or near the lower end of the draft tube and flow as a turbulent three-phase mixture or dispersion upwardly through the draft tube. At the top end of the draft tube hydrogen becomes disengaged from the liquid and passes out of the reactor. The suspension of hydrocarbon oil passes downwardly through the annular space, where it becomes partly separated. Two oil product streams are continuously withdrawn from the annular space, a first stream containing catalyst in a lesser proportion of catalyst to oil than is present in the draft tube and a second stream containing catalyst in the same proportion of catalyst to oil as is present in the draft tube. Fresh oil and regenerated catalyst are introduced into the draft tube in amounts corresponding to the total amounts of oil and catalyst in the two product streams withdrawn from the annular space.

Swiss Patent No. 459,960 describes a process for hydrogenation of liquids such as unsaturated fatty oils. Two streams of the liquid, possibly mixed with a catalyst, are introduced into a reaction chamber through two diammetrically opposite tubes. Hydrogen is introduced into the zone, where the two streams meet, and this results in an intimate mixing of the liquid and the gas. The hydrogenated liquid from the mixing chamber is collected and separated in a vessel, from where it may be recycled to the reaction chamber for completion of the hydrogenation.

A serious defect of hitherto known processes operating with a circulating suspension of a particulate catalyst in oil is that the intimate three-phase dispersion is not maintained in all parts of the reaction zone or, in other words, in all phases of the cycle. In both processes referred to in above two patents, the cycle includes a phase in which the catalyst-oil suspension is separated more or less completely from the hydrogen phase before the reaction has been completed. This involves a serious risk of coking of the catalyst because of hydrogen deficiency.

It is an object of the present invention to provide a continuous process for hydroconversion of heavy petroleum oils in which the contacts mutually between the reactants as well as between the catalyst particles and the reactants are better than in hitherto known processes and in which such good contacts are obtained in sub stantially all parts of the reaction zone. A further object is to provide a process in which deposition of solids on the catalyst particles does not result in an increased resistance to the flow of the reactants. A still further object is to provide a process in which catalyst renewal can be accomplished, whenever necessary, either periodically or continuously without discontinuation of the operation of the process.

It is also an object of the present invention to provide an improved apparatus for conducting a process for hydroconversion of heavy petroleum oils.

I have now found that hydroconversion of heavy petroleum oils is feasible in a three-phase dispersion consisting essentially of a gaseous hydrogen phase, a liquid oil phase, and a solid catalyst phase. Accordingly, I provide a continuous process for the catalytic hydroconversion at elevated temperature and pressure of crude oils and heavy petroleum fractions, comprising the steps of (a) first forming and maintaining a reacting three-phase dispersion consisting of a gaseous hydrogen-containing phase, a liquid phase of the oil to be hydro-converted and a solid phase of the hydroconversion catalyst in particulate form, by circulating measured amounts of the three phases in a reaction loop maintained at hydroconversion conditions of elevated temperature and pressure and provided with inlets, outlets, mixing devices and a circulation pump,

(b) while maintaining the three-phase dispersion and the temperature and pressure conditions for hydroconversion, continuously introducing into the reaction loop feed streams of measured amounts of hydrogen-containing gas, liquid oil feed and particulate hydro-conversion catalyst,

(c) simultaneously herewith continuously allowing a corresponding amount of a product stream having substantially the same composition as the reacting threephase dispersion to flow from the reaction loop, and

(d) separating the product stream thus flowing from the reaction loop into a hydrogen-containing gas, a prodnet oil and a concentrated slurry or paste of the particulate hydroconversion catalyst in oil.

According to the invention, it is advantageous (e) to recycle at least part of the separated hydrogencontaining gas and at least part of the separated slurry or paste of catalyst in oil for re-use in step (b).

Furthermore, I provide an apparatus for conducting the above process of the present invention.

Methods for forming two-phase and multi-phase dis persions consisting of gasesous, liquid and/ or solid phases are well known in chemical engineering practice. It is also known how to provide a stability of such dispersions which is high enough for handling them as though they were homogeneous single-phase fluids.

A dispersion of a solid material in a liquid, often referred to as a suspension, can easily be obtained. Its stability essentially depends on the particle size of the solid material, on the concentration of solid, and on the viscosity of the liquid. For the solid catalyst and liquid petroleum oils used in the process of the present inven tion, a dispersion or suspension of the desired composition and of sufiicient stability can be formed by simple mixing means. Such a dispersion in certain respects has fluid properties as a homogeneous liquid and can be handled accordingly.

Dispersion of a gas phase in a liquid requires a more refined technique, especially when relatively large amounts of gas are to be dispersed, while the fluid properties of the resulting dispersion are still to be like the fluid properties of a homogeneous liquid. An example of a technique which will provide an intimate mixture or disper sion of a gaseous hydrogen phase, a liquid oil phase, and a solid phase of a particulate catalyst is described in the above-mentioned US. Pat. No. 2,968,614. I have further found that the technique described in US. Patent No. 3,334,868 is better suited for providing a three-phase dispersion required for the process of the present invention.

In the accompanying drawings,

FIG. 1 shows in diagrammatic and very simplified manner the general principles of the process of the present invention, and

FIG. 2 schematically and in vertical section shows an embodiment of an apparatus for carrying out the process.

In FIG. 1, the general principle of the present invention is elucidated in simplified manner. The hydroconversion reactions take place in a three-phase dispersion comprising a gaseou phase containing hydrogen, a liquid phase of oil, and a solid phase of a particulate hydroconversion catalyst. This dispersion is formed and maintained by being circulated in a reaction loop which on FIG. 1 is located within hatched line 11. The reaction loop comprises a dispersion tank 12, a circulating pump 13, mixing devices, various transfer lines, and various inlets and outlets.

The dispersion is circulated by pump 13 and via line 14 introduced into dispersion tank 12 through the mixing devices which may be a nozzle or a system of nozzles 15. The dispersion tank and the mixing devices are designed to form an intimate three-phase dispersion stable enough for being circulated in the loop as a homogeneous fluid.

The shape of the dispersion tank 12 is not very critical, since the mixing devices 15 can be designed to fit practically any shape of the dispersion tank. The tank can, therefore, in general be shaped with a view to obtaining a simple and economic design and manufacture. Horizontal or Vertical cylinder tanks are well suited, however, other shapes such as cubes or spheres or the like can be used as well.

The capacity of pump 13 must be designed to circulate an hourly volume of dispersion which can be as high as several thousand times the total volume of the loop. The required circulation rate depends in particular on the size and design of the dispersion tank and nozzles or, in other words, on the efliciency of the combined system to create a turbulence which is high enough for forming and maintaining a high degree dispersion. The reaction loop is kept at the conditions of temperature and pressure which have been selected for the hydroconversion process, However, means for providing and controlling these conditions have not been shown in FIG. 1. Similarly, means for cooling the products as well as other details have been omitted from the drawings as well as from the present description.

Measured amounts of a hydrogen-containing gas, a liquid oil feed, and a particulate hydroconversion catalyst are continuously introduced into the reaction loop. A corresponding amount of three-phase dispersion is allowed to flow from the loop. The volume of dispersion that leaves the loop per hour may be of the order 0.1 to

times the total volume of the loop. Since the circulation rate in the loop is very high, for example up to several thousand times the loop per hour, it will be understood that any temperature and concentration gradients resulting from the introduction of the feed components and from the reactions will be very quickly eliminated in the reaction loop. Inlets for the feed components and outlet or outlets for the stream of three-phase dispersion flowing from the loop can, therefore, be placed at practically any appropriate location on the loop. It should, of course, be avoided to place the inlets immediately before the outlets, so that elimination of the concentration gradients created at the inlets cannot be completed before the dispersion reaches the outlets.

Referring again to FIG. 1, the liquid oil feed is supplied from line 31 and by pump 32 introduced into the reaction loop 11 via line 33. The hydrogen-containing gas is supplied at the required pressure from line 34 and after addition of recycle hydrogen from compressor 21 introduced into the reaction loop 11 via line 35. The particulate hydroconversion catalyst is introduced into the loop via line 36 in the form of a thick slurry of catalyst in oil or a catalyst-oil paste.

Once a circulation in the loop has been established at the desired conditions and at the desired relative ratios of the three phases, the dispersion is maintained by being passed at a high rate into the dipersion tank via the mixing devices. By proper design of the tank and mixing devices and by operating the process at a high circulation rate, a dispersion stable enough to flow substantially as a homogeneous fluid is obtained. Consequently, there will be a perfect and complete mixing of the contents of the reaction loop. This means that the three phases will have identical residence time distributions in the loop and any concentration or temperature gradients that might occur in the dispersion will tend to become immediately eliminated. This situation is often referred to as substantially complete back-mixing.

Assuming that all other conditions are equal, the extent to which the gaseous phase and the solid phase are dispersed in the oil phase will largely determine the efliciency of the process. Thus the degree of dispersion is an important parameter, however, it is not easy to assess, since it can only be roughly and qualitatively described at is will be done below.

As mentioned above, the three-phase dispersion has in some respects fluid properties like a homogeneous fluid. This is because it has a high degree of dispersion. However, any dispersion will lack one characteristic of a homogeneou fluid: it cannot indefinitely be divided into smaller volumes which still have the same composition as the bulk dispersion. This define a dispersion No. as the maximum number of identical volumes into which any unit volume of the three-phase dispersion could be divided.

Any of these identical volumes must contain at least one catalyst particle and at least one gas bubble. It follows, therefore, that the dispersion No. can never exceed the number of catalyst particles in the unit volume or the number of gas bubbles in the unit volume, whichever is the smaller. This defines a theoretical maximum dispersion No. that can be obtained for a given set of operating conditions.

In practice the actual dispersion No. will be lower than the theoretical maximum dispersion No. The degree of dispersion, defined as the ratio of the actual dispersion No. to the theoretical maximum No., Will be between 0 and The degree of dispersion obtained in the process of the present invention will largely depend on the amount of kinetic energy transformed into mixing energy in the mixing devices of the reaction loop. It is assumed that by proper design of the reaction loop, particularly the mixing device, a dispersion degree considerably above 50% can be achieved.

All cavities of the reaction loop are in communication with each other and will be occupied by the reacting threephase dispersion. Therefore, when a steady state operation has ben obtained the weight amount leaving the loop per hour as a product stream will correspond to the total weight amount introduced into the loopas feed streams.

The product stream 17 from the loop has substantially the same composition as the reacting three-phase dispersion circulating in the loop. This is because of the very eflicient mixing which creates the conditions of substantially complete backmixing in the reaction loop.

The three phases of the product stream are separated in a conventional separating system 18 which may comprise several settling tanks or other separating apparatus in series and/ or in parallel. The oil product is withdrawn from the separating system 18 through line 19, while the hydrogen and the catalyst after further treatments can be used again in the process.

The gaseous phase obtained from separating system 18 consists of hydrogen and hydrogen sulphide and possible other gaseous products from the hydroconversion reactions. The undesired compounds, particularly hydrogen sulphide, are eliminated from the hydrogen in a gas separation column 20 which may for example be an amine wash. After compression in compressor 21 the purified hydrogen is combined with the stream 34 of feed hydrogen.

The solid catalyst settles in separating system 18, from where it is obtained as a thick slurry in oil or paste. This catalyst slurry or paste may be used again in the process without further treatment. However, all or part of the catalyst may first be subjected to a purification or regeneration. It is also possible at this stage to replace part of the spent catalyst by new catalyst and thus obtain a gradual renewal of the catalyst, when this is required. In that case part of the spent catalyst is withdrawn through line 22 and discarded. The remaining part of spent catalyst is introduced via line 23 into mixer 24. New catalyst to replace the discarded part of spent catalyst is introduced into the mixer via line 25. The catalyst leaves the mixer in the form of thick slurry in oil or as a catalyst-oil paste.

Several variations in the above described embodiment of the process are possible without deviating from the scope of the invention. Although only one loop and one dispersion tank is shown in FIG. 1, there may be several loops connected to the same tank and there may be several loops connected either in series or in parallel or in a combination hereof. Similarly, there may be more than one outlet from the looplocated either on the tank or on the transfer lines. There may be one or several inlets for the feed components and these may be introduced either separately as indicated in FIG. 1 or two or three in combination. For example all or part of the oil feed may be fed to mixer 24 and introduced into the loop together with the catalyst.

For any reaction system in which there is a complete back-mixing, the use of a number of reactors in series will in general provide a better conversion than the use of a single reactor provided that the total reaction volume is the same in the two cases. This also holds true for the process of the present invention. Therefore, the use of two or even more reaction loops in series may be preferred in cases where a high conversion is required.

Furthermore, the process of the present invention may be used in combination with other processes for hydroconversion of heavy petroleum oils. Thus it may be used for pretreatment of a petroleum oil before subjecting it to further treatment in a fixed bed process. An. example of such a pretreatment is the removal of a major pro portion of the metals, especially V, Ni, and Fe, by using a catalyst having a high activity for metals removal. An other example of a pretreatment is reduction of the vis cosity of the oil by using a catalyst having a high ac tivity for hydrocracking. Both kinds of pretreatment render the heavy petroleum oil better suited for further treatment in a fixed bed process.

Operating pressure and temperature for the process of the present invention may typically be almost the same as in fixed bed processes. Thus lower boiling fractions of petroleum oils such as gas oils can be hydroconverted at a pressure in the range from to 70 atmospheres. Heavier fractions such as whole crudes and residuum oils may require pressures up to 600 atmospheres, preferably from 50 to 200 atmospheres. The temperature is in the range from 260 to 485 C. A preferred temperature range for whole crudes and residuum oils is from 320 to 450 C.

As in any conventional process, it is essential for the process of the invention that hydrogen is present every where in the loop, where reactions occur. Otherwise, cracking reactions leading to detrimental coke formation may predominate. Therefore, hydrogen is added in an excess. The amount of hydrogen that is consumed by the hydroconversion reactions varies with the composition of the oil and with the degree of desulphurization. It is typically of the order of 20 to 300 Normal liter of hydrogen per liter of oil (Ni/l. oil). In the process in accordance with the present invention hydrogen is introduced into the loop at a rate of to 600 Nl/l. feed oil depending on operating pressure and desired degree of conversion. Part of the hydrogen will dissolve in the oil. The solubility will typically be between 10 and Nl/l. oil. The remaining part of hydrogen, which does neither react nor become dissolved in the oil, will be present as a gaseous phase in the dispersion. Because of the high pressure in the loop, this part of the hydrogen will actually occupy a volume which is much smaller than its Normal volume. It has been found expedient to relate the actual volume of the gas phase present in the dispersion to the volume of liquid oil phase present in the dispersion. This ratio will be referred to as the gas to liquid ratio. According to the present invention this gas to liquid ratio should preferably be from 0.25:1 to 4:1. If the ratio is much higher there are difiiculties in the pumping the dispersion, and it may not be possible to maintain a continuous liquid phase. On the other hand, if the gas to liquid ratio is too low, the concentration of hydrogen sulphide, which is liberated during the process, will become so high that the desulphurization rate is unfavourably effected.

Any type of catalyst which is useful in conventional hydroconversion processes may be used in the process of of the inventionfprovided that it is capable of being shaped as very small particles. Examples of suitable catalyst compositions are oxides or sulphides or combinations of oxides or sulphides of nickel, cobalt, molybdenum, and tungsten supported on alumina, silica, magnesia or similar support materials. Other types of suitable support materials in clude the group of zeolitic materials, particularly aluminosilicate zeolites. The catalyst is used in the form of discrete particles having a typical particle size from 0.02 to 0.5 mm. diameter. The shape of the catalyst particles may conveniently be spheres, extrudates, cylinders or irregularly-shaped particles. The amount of catalyst present in the circulating dispersion is related to the amount of oil. It will typically be from 0.05 to 0.40 kg. of catalyst per kg.

of oil. However, it may in certain cases be preferable to use up to 1 kg. of catalyst per kg. of oil.

The space velocity for the process of the invention can be defined as in a conventional hydroconversion process. For this purpose the loop is regarded as a reactor. Accordingly, the weight hourly space velocity, often abbreviated to WHSV, is defined as the weight of oil introduced into the loop per hour per unit weight of catalyst present in the loop. The WHSV in the process of the invention may be of the same order as in a conventional hydroconversion process. However, more often it may be higher. It may for example be from 0.5 to 50 kg. oil per kg. catalyst per hour, preferably from 2 to 20 kg. oil per kg. catalyst per hour. This is somewhat higher than in a conventional process, where the preferred range is from 0.2 to 3 kg. oil per kg. catalyst per hour.

Very often the main objective of a hydroconversion process is desulphurization. The degree of desulphurization obtained in the process of the invention will vary Widely with operating conditions and with average residence time in the loop. The average residence time in hours which is the total loop volume divided by the volume of dispersion leaving the loop per hour may typically vary from 0.2 to 2 hours. By selectin appropriate values of all operating parameters such as temperatures, pressure, residence time, catalyst composition, circulation rate, etc. it is possible to obtain any degree of desulphurization. If a high desulphurization degree is desired, however, the process of the invention may conveniently be conducted in two or more steps in which product from one loop is transferred as feed to a similar subsequent loop with or without separation of the three phases between the steps, and with or without an exchange of feed or product streams between the steps.

It is an important feature of the present invention that very small catalyst particles can be used. Because of the shorter distance in small particles, the rate restrictive effect of pore diffusion has been eliminated and a larger proportion of the total active inner surface of the catalyst particles can be utilized.

Another important feature is the good contact between the gaseous hydrogen phase and the liquid oil phase. This means that the rate of hydrogen transfer is high and hydrogen is readily available everywhere where reactions occur. The use of a large excess of hydrogen is, therefore, not necessary.

There are several other advantageous features of the process of the present invention. It will be understood that deposition of metals and coke on the catalyst is less harmful than in a conventional hydroconversion process. Firstly, such deposition does not result in an increasing pressure drop, because there is no fixed catalyst bed in which the deposits would otherwise accumulate. Secondly, since the catalyst circulates with the dispersion, all catalyst particles are equally exposed to the deposition. Thirdly, the total outer surface of the catalyst particles is much larger than in a conventional process. Since the deposition predominantly occurs on and near the outer surface it takes longer to reach a critical degree of deposi tion. For all these reasons the useful life of a catalyst is several times higher in the process of the present invention than in a conventional hydroconversion process operating under similar conditions.

Example 1 The hydroconversion process in accordance with the present invention will now be further illustrated by some experiments designated as ruus Nos. 1-4 and conducted in a laboratory scale apparatus. The main objective of the experiments was to demonstrate the feasibility of the process in desulphurization of heavy petroleum oils.

The laboratory apparatus is shown in the accompanying drawing FIG. 2. The loop in which the reacting three phase dispersion of gaseous hydrogen, liquid oil, and solid catalyst was being circulated was contained in an electrically heated and insulated box 51. The tank 52 had a volume of 2.5 liters and was provided with an inlet pipe 53 with nozzle 54. Centrifugal pump 55 had a capacity for circulating about 5000 liters of dispersion per hour. During the experiments the pump was operated at about three quarters of its maximum capacity. The total volume of the loop including tank, centrifugal pump, and pipes was 5.0 liters.

Before being introduced into the loop, feed oil was mixed with catalyst in a 20 liter slurry reservoir 56 equipped with a propeller 57 and a circulation pump 58 for keeping the catalyst suspended in the feed oil. Feed oil and catalyst were supplied to the slurry reservoir 56 from time to time to compensate for the amount that was continuously fed to the loop by piston pump 59. Hydrogen was continuously fed to the loop via rotameter 60.

Hydrodesulphurized product oil was continuously flowing from the loop as a three-phase dispersion which was separated in a separating system. The separating system comprised a high pressure separator 61 for separation of gas, a settling tank 62 from which the product oil was isolated via line 66 and a slurry recipient 63 from where the catalyst was collected in the form of a thick slurry via line 67. The catalyst was periodically transferred to slurry reservior 56 for mixing with feed oil before it was used again in the process. The gas from separator 61 was discarded since its amount was too small to justify a purification and reuse in the process.

The accompanying Table I gives further details about the four runs 1-4 conducted in the laboratory apparatus. In all cases the catalyst was an alumina supported cobaltmolybdenum catalyst containing 1.4 wt. percent cobalt and 7.0 wt. percent molybdenum. The catalyst was in the form of spherical particles having a particle diameter from 0.03 to 0.08 mm.

The heavy petroleum oils used in the experiments were all of Middle-East origin. They are described in the table by usual standard terms. HGO stands for Heavy Gas Oil and HVGO for Heavy Vacuum Gas Oil.

In addition to operating data the table gives the sulphur content in wt. percent of the oil before and after the process and the hydrogen consumption in term of moles hydrogen per atom sulphur removed from the oil. In one of the experiments, run No. 4, the table also gives the content of metals (V+Ni) in p.p.m. (wt.) of the oil before and after the process.

TABLE I Run number Feed oil:

Type oioll HGO HVGO HVGO Specific gravity, g./c 0. 84 0. 90 0. 90 0.98 Sulphur, wt. percent 1. O 2. 4 2. 4 3. 5 Metals (V +Ni), p.p.m. (wt.) 80 Process conditions:

Temperature, C 311 345 375 387 Pressure, atms. abs 51 51 51 51 Hydrogen feed rate, Nl/h 50 110 150 172 Oil feed rate, kg./h 1.5 1. 6 2. 5 1. 6 Gas to liquid ratio, vol. v 0. 33:1 1:1 1:1 0.96:1 Catalyst to oil ratio, kg. kg 0. 093 0. 090 0. 088 0.089 Circulation rate, percent of max 75 83 83 83 Space velocity, WHSV, kg.l

kgJh 5.2 8 0 12. 6.8 Average residence time, hours 2. 2 1 5 0.9 1. 0 Results:

Sulphur in product oil, wt.

percent 0. 48 1. 11 1. 30 2. 04 Metals (V+Ni) in product oil,

p.p.m. (wt.) 47 Hydrogen consum tion mole H /atom S 5. 0 4. 1 4. 7 5.9

1 Am. residue.

As defined in the specification (col. 7).

10 Example II Another laboratory experiment designated as run No. 5 simulated operation of the process of the present invention in two steps. A two-step process would normally be conducted in an apparatus having two reaction loops in series. The product stream from the first step would be used as a feed stream for the second step. Preferably, however, the gaseous phase would first be more or less completely separated between the step for removal of hydrogen sulphide and for addition of a fresh hydrogen containing gas.

A laboratory apparatus having two loops in series was not available for run 5. The two-step operation was therefore simulated by first operating the process in one step for about hours. The oil product from this operation was stored and afterwards used again in a new operation in one step for another 150 hours at the same conditions.

The catalyst had the same composition and particle size as the one used in Example I. The same charge of catalyst was used in the two operations of run 5.

Operating data and results from the two steps are given in Table II. The space velocity (WHSV) and average residence time given in the table are related to each of the steps. Related to a true two-step operation the figure for space velocity would be halved, while the figure for residence time would be doubled. Also the consumption of hydrogen is related to each of the two steps. The results indicate that when two reaction loops are used in series a better removal of sulphur and metals will be obtained than when only one reaction loop is used.

TABLE II Run number 6 (second step) step) Average residence time, hours Results:

Sulphur in product oil, wt. percent Metals (V&Ni) in product oil, p.p.m. (wt.).

Hydrogen consumption, mole Hzlatom S..-

1 Atm. residue. 2 Product from first step. a As defined in the specification (col. 8).

I claim:

1. In a process for the catalytic hydroconversion at elevated temperature and pressure of crude oils and heavy petroleum fractions, the improvement comprising the steps of (a) in a reaction loop, maintained at hydroconversion conditions of elevated temperature and pressure and provided with inlets, outlets, mixing devices, and a circulation pump, first forming and thereafter maintaining a reacting three-phase dispersion consisting of a gaseous hydrogen containing phase, a liquid phase of the oil to be hydroconverted, and a solid phase of the hydroconversion catalyst in particulate form ranging in size from 0.02 to 0.5 mm., measured by the mesh-width of sieves that retain the particles and let them pass, respectively, said reacting three-phase dispersion occupying all cavities of the reaction loop and being substantially free of concentration gradients in all parts of the reaction loop;

(b) while maintaining the three-phase dispersion and the temperature and pressure conditions for hydroconversion, continuously introducing into the reaction loop feed streams of measured amounts of the hydrogen-containing gas, the liquid oil feed and the particulate hydroconversion catalyst;

(0) simultaneously herewith continuously allowing a corresponding amount of a product stream having substantially the same composition as the reacting three-phase dispersion to flow from the reaction loop; and

(d) separating the product stream thus flowing from the reaction loop into a hydrogen-containing gas, a product oil and a concentrated slurry or paste of the particulate hydroconversion catalyst in oil.

2. The process according to claim 1, wherein the reacting three-phase dispersion has a gas/liquid ratio between 0.25:1 and 4:1 and a catalyst concentration between 0.05 and 1.0 kg. of catalyst per kg. of oil.

3. In the process according to claim 2, the further step of recycling at least part of the separated hydrogen-containing gas and at least part of the separated slurry or paste of catalyst in oil for re-use in step (b).

4. In the process according to claim 2, the step of using mixing devices comprising at least one nozzle placed in a dispersion tank included in the reaction loop.

S. In the process according to claim 2, the further step of maintaining the reacting three-phase dispersion under hydroconversion conditions of elevated temperature and pressure in at least one further reaction-loop connected in series with the first reaction-loop, any reaction loop in the series after the first being fed with the product stream from the immediately preceding reaction-loop together with additional hydrogen-containing gas.

6. In the process according to claim 1, wherein the hydroconversion temperature is in the range 260-484 C. and the pressure in the range 25-600 atmospheres absolute.

7. In the process according to claim 1, wherein the weight hourly space velocity is between 0.5 and 50 kg. of oil per kg. of catalyst per hour.

8. The process according to claim 1 wherein the hydroconversion catalyst is one having substantial hydrosulphurization activity.

9. The process according to claim 1, wherein the hydroconversion catalyst is one having substantial hydrocracking activity.

10. The process according to claim 1, wherein the particulate hydroconversion catalyst contains at least one catalytically active material selected from the class consisting of oxides and sulphides of cobalt, nickel, molybdenum, tungsten, vanadium and chromium, on an alumina-containing support.

References Cited UNITED STATES PATENTS 2,968,614 1/1961 Brooks et al 208-264 3,079,329 2/1963 Browning 2081 57 3,151,054 9/1964 Layng 20811 3,183,178 5/1965 Wolk 20858 3,368,965 2/1968 Schuman 208143 3,410,792 11/1968 Van Driesen et al. 208l43 3,457,161 7/1969 Tulleners 2081 11 3,600,300 8/1971 Steenberg 208-108 3,617,503 11/1971 Rogers et a1. 208-97 3,617,524 11/1971 Conn 208157 3,635,943 1/1972 Stewart 208-157 DELBERT E. GANTZ, Primary Examiner GEO. E. SCHMITKONS, Assistant Examiner US. Cl. X.R.

Claims

1. IN A PROCESS FOR THE CATALYTIC HYDROCONVERSION AT ELEVATED TEMPERATURE AND PRESSURE OF CRUDE OIL AND HEAVY PETROLEUM FRACTIONS, THE IMPROVEMENT COMPRISING THE STEPS OF (A) IN A REACTION LOOP, MAINTAINED AT HYDROCONVERSION CONDITIONS OF ELEVATED TEMPERATURE AND PRESSURE AND PROVIDED WITH INLETS, OUTLETS, MIXING DEVICES, AND A CIRCULATION PUMP, FIRST FORMING AND THEREAFTER MAINTAINING A REACTING THREE-PHASE DISPERSION CONSISTING OF A GASEOUS HYDROGEN CONTANING PHASE, A LIQUID PHASE OF THE OIL TO BE HYDROCONVERTED, AND A SOLID PHASE OF THE HYDROCONVERSION CATALYST IN PARTICULATE FORM RANGING IN SIZE FROM 0.02 TO 0.5 MM, MEASURED BY THE