GB2106535A - Two-stage catalytic process for removing contaminants from hydrocarbonaceous feedstocks - Google Patents

Abstract

Hydrocarbonaceous feedstocks having high concentrations of metals and sulfur as contaminants are contacted with a hydrodemetalation catalyst in a first zone and then with a hydrodesulfurization catalyst in a second zone, the average temperature of the first zone being maintained at least 15 DEG C higher than the average temperature of the second zone. This increases the removal of the contaminants and provides a longer life for the catalyst system compared to both catalyst zones being kept at the same average temperature.

Description

SPECIFICATION Two-stage catalytic process for removing contaminants from hydrocarbonaceous feedstocks This invention relates to hydrodemetalation and hydrodesulfurization of feedstocks, particularly hydrodemetalization and hydrodesulfurization processes that use multiple beds.

The world supply of petroleum is shrinking, thereby forcing the utilization of feedstocks that are not considered to be readily refinable into lighter products. Examples of such heavy feedstocks are Maya Crude, Arabian Heavy Crude, California San Joaquin Crude and various Venezuelan Crudes. These crudes are characterized by low hydrogen to carbon ratios and high nonhydrocarbon contaminant content.

These contaminants include sulfur, nitrogen and metals, in particular, iron, nickel and vanadium, in the form of various soluble organometallic compounds, such as porphrins and asphaltenes.

It is preferred that sulfur and metals be removed as early as possible in the processing of contaminated feedstocks since both sulfur and metals tend to lessen the activity of downstream catalysts. In the case of metals, this deactivation tends to be irreversible. Also, when burned, products that contain less contaminants tend to require less post combustion treatment to provide an environmentally acceptable exhaust.

Many processes are known to remove metals and sulfur from feedstocks. Simple distillation will remove most of the lighter hydrocarbons, and solvent extractions can remove the asphaitene fraction which contains high concentrations of sulfur and metals. Hydroconversion processes are used extensively for desulfurization, and such processes will remove metals as well. The metals tend to deposit on the surface of the desulfurization catalyst, deactivating it. There has recently been great effort placed in hydrodemetalation. Catalysts have been made that remove most metals from the feedstock.

Various catalysts supported on alumina for demetalation of feedstocks are known.

A variety of multiple bed processing schemes are known to remove sulfur and metals before further processing. U.S. Patent No.

4,212,729 to Hensley et al discloses a two-stage catalytic process for hydrometalation and hydrodesulfurization of heavy hydrocarbon streams containing asphaltenes and a substantial amount of metals. The first stage of this process comprises contacting the feedstock in a first reaction zone with a catalyst consisting essentially catalyst comprising hydrogenation metal selected from Group VIB and/or Group VIII deposed on a large-pore, high surface area inorganic oxide support; the second stage of the process comprises contacting the effluent from the first reaction zone with a catalyst consisting essentially of hydrogenation metal selected from Group VIB deposited on a smaller pore, cataiytically active support comprising alumina, said second stage catalyst having a surface area within the range of about 1 50 meters2/gram to about 300 meters2/gram, having a majority of its pore volume in pore diameters within the range of about 80 Angstroms to about 130 Angstroms, and the catalyst has a pore volume within the range of about 0.4 cubic centimeters/gram to about 0.9 cubic centimeters/gram.

U.S. Patent No. 4,166,026 to Fukui et al discloses a process for hydrodesulfurization of heavy hydrocarbon oil containing asphaltenes and heavy metals. The heavy oil is hydrotreated in a continuous two-step process. In the first step the heavy oil is subjected to hydrodemetalation and selective cracking of asphaltenes by the use of a catalyst having a unique selectivity therefor. In the second step the effluent from the first step is subjected to hydrodesulfurization to produce desulfurized oils of high grade by the use of a catalyst having a pore volume and pore size distribution particularly adapted for the hydrodesulfurization of the effluent.

It has now been discovered in accordance with the invention that in a two-stage hydro metalation/hydrodesulfurization catalytic process where the feed stock is first contacted with a catalyst tailored for demetalation, and then is contacted with a catalyst tailored for desulfurization, if the first catalyst zone is kept at a higher average temperature than the second zone, the product from the second zone has less contaminants and the entire system has a longer life than if both catalyst zones are kept at the same average temperature.

According to the invention, a process is provided for hydroconversion of hydrocarbonaceous feedstocks containing as contaminants both sulfur and metals by passing the feedstock through multiple catalyst beds, wherein an inverse temperature profile is maintained in the beds.

Thus in accordance with the invention contaminants are removed from a feedstock containing both metals and sulfur by contacting the feedstock with catalysts in two zones, the first zone containing a demetalation catalyst and the second zone containing a desulfurization catalyst, with the average temperature of the first zone being maintained at least 1 50C higher than the average temperature of the second zone.

In the accompanying drawing, Figure 1 is a graphical representation of a conventional temperature profile through a reaction vessels with multiple quenches; and Figure 2 is a graphical representation of a temperature profile of a process in accordance with this invention.

The feedstocks for the present invention are hydrocarbonaceous feedstocks that contain sulfur and metal. Frequently hydrocarbonaceous feedstocks will contain .5 percent sulfur, up to 4 percent sulfur and in extreme cases, over 6 percent sulfur, and 35 ppm metals, up to 200 ppm metals and in extreme cases, over 1 ,000 ppm metals. Unless specifically denoted to the contrary, as used herein, "percent sulfur," or "percent," refers to weight percent based on total elemental sulfur in the feedstock. Such feedstocks include crude oils, topped crudes, atmospheric and vacuum residua, solvent deasphalted oil, liquids from oil shales and tar sands and coalderived liquids. The feedstocks of the present invention have boiling points that will frequently exceed 4000F and may exceed 1 ,0000F.

The feedstock of the present invention will contact, in a first zone, a catalyst tailored for hydrodemetalation, and then will contact, in a second zone, a catalyst tailored for desulfurization. The "first and second zones," as used herein, refer to temperature controlled zones; that is, the first zone will have an average temperature at least 1 50C higher than that of the second zone. The catalyst in the first zone may be the same as the catalyst in the second zone, and each zone may contain more than one catalyst.

The catalyst of the first zone can be any of a class of well-known and defined hydro metalation catalysts. Catalysts supported on alumina are known and are generally characterised by the presence of at least 5% of macropores, herein defined as pores larger than 1,000 Angstroms in diameter, and an average calculated micropore diameter of at least 100 Angstroms when calculated by the formula: 4xPV > c104 Average Micropore Diameter= SA where PV is micropore volume expressed in cubic centimeters/gram of catalyst where micropores are those pores of less than 1 ,000 Angstroms in diameter, and SA is surface area expressed in meters2/gram of catalyst.

Such catalysts may contain catalytic metals, in particular, metals from the group consisting of Group VIB and Group VIII Transition metals of the Periodic Table of Elements, particularly, molybdenum, tungsten, nickel and cobalt. The Group VI metals may be present in a quantity of at least 1.5 weight percent, preferably from 1.5 weight percent to 20 weight percent, based on the total catalyst weight. The Group VIII metals may be present in quantities up to 1 5 percent.

There may be no Group VIII metals at all on some alumina-supported hydrodemetalation catalysts.

Clay-supported demetalation catalysts may also be the catalyst of the first zone. Such catalyst supports may be made from sepiolite, attapulgite, polygorskite, and similar fibrous magnesium silicate clays or halloysite and similar fibrous or rod-like aluminum silicate clays. These catalysts are physically characterised by large calculated average pore diameters, frequently over 200 Angstroms, and few macropores.

Generally they will have at least 70 percent of the pore volume provided by pores of between 200 and 700 Angstroms. These catalysts may contain catalytic metals, and in particular, those selected from the group consisting of Group VI and Group VIII Transition metals, particularly, molybdenum, tungsten, nickel and cobalt and various combinations of these metals.

Any other catalyst that shows substantial hydrodemetalation activity can be used in the first zone of this invention. "Substantial hydrometalation activity" is herein defined as the ability to remove at least 25 percent of the metals content of a feedstock continuously for a period of time not less than 500 hours under hydroprocessing conditions.

The catalyst of the second zone can be any catalyst that shows substantial hydrodesulfurization activity. These catalysts, frequently supported on alumina or alumina in combination with silica, boria, titania, magnesia, or other refractory inorganic oxides, are characterized by calculated average pores diameters of greater than 50 Angstroms and few macropores. Typically, desulfurization catalysts have more catalytic metals, giving them higher intrinsic activities. The catalytic metals are selected from the group consisting of Group VI and Group VIII Transition metals. Thus the hydrodesulfurization catalyst may contain at least 2 weight percent of Group VI Transition metal and at least 1.5 weight percent of Group VIII Transition metal, based on the total catalyst weight.

Any catalyst that shows substantial desulfurization activity can be used. "Substantial desulfurization" is herein defined as the activity required to remove at least 25 percent of the sulfur content of a feedstock for at least 500 hours under hydroprocessing conditions.

As used herein, hydroprocessing conditions are those conditions that are known to the art to give catalytic hydroconversion of hydrocarbonaceous feedstocks. Typical conditions of the present invention are 3550C to 4500C for the first zone average temperature, and 340 OC to 4500C for the second zone average temperature, while maintaining at least a 1 50C temperature difference. Space velocity of feedstock is between 0.1 and 1.5. Total pressure is between 500 and 3,000 psig, and partial pressure of hydrogen is between 300 and 2,800. Recycle rate for hydrogen is between 2,000 and 10,000 SCF/BBL.

Normally as the activity of the catalysts decrease, the temperature of the reaction vessels will be adjusted upward to maintain a specified quality in the product, usually a maximum tolerable amount of contaminants.

It is possible that the same catalyst might be used both for demetalation and desulfurization.

The catalyst charge of the first zone would tend to lose activity for desulfurization relatively rapidly, but could maintain demetalation activity for some time. Desulfurization reactions are believed to be reactions where sulfur is hydrogenated to hydrogen sulfide and thereafter passes out of the reaction zone. Demetalation deposits metals on the outer surface or inner pore surface of the catalyst. It has been observed that a catalyst can therefore lose the property of catalytically hydrogenating sulfur, but stili deposit metals.

It may be desirable to shape both the hydrodemeta lation and desulfurization catalyst particles in some shape other than the conventional round cylinder. If such shaped catalysts are used, it is preferred that the diameter of the smallest circle that can be circumscribed around the particle be 1/64 to 1/2 inches.

Another embodiment of the present invention is having more than one catalyst in either or both of the zones. For example, a macroporous, large pore demetalation catalyst can be used in the first zone, at high temperature, the second zone can be charged with firstly, a large pore desulfurization catalyst that can also remove metals and then secondly, a smaller pore desulfurization catalyst that has poor metals capacity, both catalysts maintained at a temperature of at least 15 OC less than the first zone.

The present invention requires at least a 1 50C temperature difference between the first zone and the second zone. Referring to Fig. 1 , the temperature profile of a conventional multiple catalyst bed reaction vessel is shown. Bed 1 would be the first bed the feedstock would contact, and, in the operation shown, the coolest.

Three temperature zones are shown, separated by hydrogen quenches. The average temperature for each zone is denoted by T, ave, T2 ave and T3 ave.

At each quench point there is a drop in temperature, for example, Q,. In this way the temperature increase of the exothermic catalytic hydrogenation reactions of each zone are controlled. In operation, the average temperatures of each catalyst bed tend to rise, for example, T, ave will frequently be 1 00C cooler than T2 ave.

Economic operation of the reactor dictates using less quench gas than is necessary to achieve T, ave=T2 ave. The change in temperature (AT) for any bed in commercial operation will frequently be from 1 00C to 200C.

Fig. 2 shows an example of the present invention, a reactor containing 3 catalyst beds in which the first bed operates at a higher temperature than the down-stream beds. Bed 1 is the first catalyst bed the feedstock contacts, but unlike conventional operation, it is the hottest bed the feedstock contacts. The change in average temperature in the operation of the present invention is at least 1 50C. T2 ave and T3 ave are preferably held closer together than typical in conventional operation. In Fig. 2 the first zone comprises Bed 1 and the second zone comprises Beds 2 and 3. It will be noted that AT ave is much greater in the operation of this invention than it is conventionally, thereby providing a second, cooler temperature zone.

The temperature profile will be observed to have several sharp drops at various points along the length of the reaction vessel. These correspond to gaseous hydrogen quenches inside the reaction vessel. For the maintenance of the desired temperature profile of the present invention, more hydrogen must be used at the junction of the first and second bed than at any other quenching point.

It should be appreciated that although the temperatures of Fig. 1 are of a single reactor, multiple temperature controlled reactors can be used. For example, guard bed reactors in separate vessels, at a temperature 1 50C hotter, could be substituted. The temperature of the catalyst beds generally increases during the life of the catalysts of the beds to maintain a preselected quality of product. The temperature cannot increase beyond certain limits dictated by metallurgic constraints of the reaction vessel. When the first zone, the hottest, reaches the maximum temperature which the reaction vessel can tolerate, the temperature of that zone must be held at a constant value, allowing the temperature of the second zone to eventually equal that of the first zone.When the two zones are at the same temperature, the end of run of that catalyst charge has been reached.

Although Applicants do not wish to be bound to any particular theory of operation, it is believed that the demetalation catalyst of the first zone has contamination removal activity similar to the desulfurization catalyst of the second zone, which has more metals than the demetalation catalyst, even though the demetalation catalyst has less intrinsic activity, because of the temperature differential. More metals are removed in the first zone, which does not lose activity rapidly, and the catalyst of the second zone does not lose activity for desulfurization as rapidly. The total catalyst system, therefore, has longer life than otherwise would be possible.

Example The following catalysts were prepared to use in a reactor with the inverse temperature profile of the present invention. Catalyst A is prepared as follows: Eight milliliters of 88 percent formic acid (specific gravity 1.2) was added to 300 milliliters of distilled water. This solution was added to 500 grams of Kaiser alumina at about 500C and about 50 milliliters every minute while mixing. The mixing continued for 20 minutes after all the solution had been added. A second solution made from 6 milliliters of 58 percent ammonium hydroxide, 45 milliliters of a molybdenum solution, and 200 milliliters of distilled water was added at a rate of 50 milliliters per minute while stirring. The molybdenum solution was prepared by dissolving 17.4 grams of MoO3 in 17.2 milliliters of 30 percent NH4OH and 26 milliliters of distilled water.The temperature during the second addition was approximately 600C to 650C. The doughy mixture was extruded with a trilobal fluted die and dried on a screen tray in a preheated oven at 1 200C for 2 hours and then at 2000C for 2 hours. The dried extrudate was calcined at 6800C in a steam atmosphere. After one hour, fresh dry air replaced the steam and the extrudate was calcined for another half an hour at 6800C Catalyst B is prepared according to the procedure described in U.S. Patent No.

4,113,661 issued to P. W. Tamm, September 12, 1978, entitled "Method for Preparing a Hydrodesulfurization Catalyst." An 80/20 by weight mixture of Catapal, made by Conoco, alumina and Kaiser alumina are sized in the range below about 1 50 microns and treated by thoroughly admixing the mixed powders with an aqueous solution of nitric acid, were for each formula weight of the alumina (Al203) about 0.1 equivalent of acid is used. The treated alumina powder is in the form of a workable paste. A sample of this paste completely disperses when one part is slurried in four parts by weight of water. The pH of the slurry is in the range of about 3.8 to about 4.2, usually about 4.0.After aqueous acid treatment of the powders, aqueous ammonium hydroxide is thoroughly admixed into the paste in an amount equivalent to about 80 percent of the ammonium hydroxide theoretically required to completely neutralize the nitric acid; that is, about 0.08 equivalent of the hydroxide is added to the paste per formula weight of the alumina present. The ammonium hydroxide used is desirably about an 11 percent by weight solution because the volatile material evolved during drying and calcination content of the treated and neutralized solids should be in the range of 50 to 70 weight percent. With the addition and thorough admixing of ammonium hydroxide, the past changes to a free-flowing particulate solid suitable as a feed to an extruder.

The extruder has a die plate that will extrude the shaped particles of the present invention. The extrudate precursor is freed of loosely-held water by an initial moderate drying step, for example, at a temperature in the range of 750C to 2500C.

The preparation of the carrier is then completed by calcining the dried extrudate at a temperature between 2500C to 8500C in a dry or humid atmosphere. The resulting carrier has a pore volume of about 0.7 cubic centimeters/gram, of which at least about 85 percent is furnished by pores having a diameter in the range between about 80 and 1 50 Angstroms. Less than about 1.0 percent of pore volume is furnished by pores larger than 1,000 Angstroms. By calcining the catalyst in a 100 percent steam atmosphere at 4500C to 6000C, larger pores, for example, 160 Angstroms to 1 90 Angstroms, may be obtained.

A reactor was charged with two layers of catalyst. The first layer and first zone was Catalyst A and the second layer and second zone was Catalyst B. An Arabian Heavy Atmospheric residue of 4.4 weight percent sulfur, 26 ppm nickel and 89 ppm vanadium was contacted with Catalysts A and B in series. Initially, conditions were 2,200 psig, about 1,800 psig average pressure of hydrogen and about 0.35 hr-1 space velocity, with the first catalyst kept at about 1 40C hotter than the second catalyst. The temperature of the two beds was increased to maintain a constant sulfur concentration of 0.6 weight percent in the effluent from the second zone. At mid-run, the length of run possible for this system was extrapolated. End of run for this system is the metallurgical limit of the reaction vessel. The temperature difference between the first and second zone was increased to 28"C. The temperature of the vessel was increased until the first zone was 4270C, the metallurgical limit of the reaction vessel and the temperature of the first zone was held constant as the temperature of the second zone was increased to 427 OC, the end of the run. The actual time of this run was about 25 percent better than the length of run estimated from mid-run extrapolations. the increase in catalyst life is believed to be a function of the larger difference in average temperature.

Claims (9)

Claims

1. A process for hydrotreating a hydrocarbonaceous feedstock containing as contaminants both sulfur and metal, the process comprising: contacting the feedstock with hydrogen at a first elevated average temperature and elevated pressure in a first zone containing a catalyst having substantial demetalation activity thereby producing an effluent; and contacting said effluent with hydrogen in a second zone containing a catalyst having substantial desulfurization activity at a second elevated average temperature and elevated pressure, said second elevated average temperature being at least 1 50C less than said first elevated average temperature.

2. A process according to Claim 1, wherein the hydrodemetalation catalyst has an alumina support having at least 5 percent of its pore volume provided by macropores and a calculated - micropore diameter of at least 100 Angstroms.

3. A process according to Claim 1, wherein the hydrodemetalation catalyst has a support selected from fibrous magnesium silicate clays and fibrous aluminum silicate clays having at least 70 percent of its pore volume provided by pores of between 200 and 700 Angstroms.

4. A process according to Claim 3, wherein the support is selected from sepiolite, polygorskite, attapulgite and halloysite.

5. A process according to any preceding claim, wherein said hydrodemetalation catalyst contains a Group VIB Transition metal in an amount of at least 1.5 weight percent, when weight percent is calculated as percent metal to total catalyst weight.

6. A process according to any preceding claim, wherein the hydrodesulfurization catalyst has a support having an average calculated pore diameter of greater than 50 Angstroms, and comprises at least 2 weight percent of Group VI Transition metal and at least 1.5 weight percent of Group VIII Transition metal, when weight percent is calculated as percent metal to total catalyst weight.

7. A process according to any preceding claim, wherein the hydrodemetalation catalyst consists of shaped particles of between 1/64 inches and 1/2 inches in circumscribed diameter.

8. A process in accordance with Claim 1, substantially as hereinbefore described with reference to the accompanying drawing.

9. A process in accordance with Claim 1, substantially as described in the foregoing Example.