US3036968A - Removal of metals and nitrogen from hydrocarbon feed stocks - Google Patents

Description

United States Patent lroducts Company, Des Plaines, Ill, a corporation of Delaware No Drawing. Filed Feb. 8, 196b, Ser. No. 7,674

4 Claims. (Cl. 208-25l) This invention relates to a process for the treatment of hydrocarbon oils whereby certain metallic and nitrogencontaining contaminants present in the oil are removed therefrom prior to use of the oil in a hydrocarbon conversion process in which these contaminants are detrimental to the catalysts utilized in the process. More specifically, this invention concerns primarily the treatment of crude oil stocks for the removal therefrom of naturally occurring nickel and vanadium-containing porphyrin complexes and nitrogen-containing compounds, all of which have an undesirable deactivating effect on cracking and reforming catalysts when the hydrocarbon stock is subsequently utilized in such processes, said treatment comprising mixing said hydrocarbon stock with from 2 to 1 to about 12 to 1 volumes of a normal paraflinic hydrocarbon diluent containing up to about 1 percent by weight of dissolved hydrogen fluoride and thereafter removing the resultant precipitate comprising said metal and nitrogenous contaminants from the hydrocarbon stock.

It is well known that certain so-called heavy metals occur naturally in petroleum stocks of both high and low boiling points, particularly in the form of certain porphyrin complexes therewith, including complexes of such metals as vanadium, nickel, cobalt, etc. erally recognized that certain nitrogen-containing compounds occur naturally in petroleum crude oils and distillate fractions thereof, including the low as well as the fi high boiling point cuts, being present in the hydrocarbon fractions particularly in the form of amines and certain heterocyclic nitrogen compounds, such as the indoles, pyrroles, pyridines and other heterocyclic nitrogen derivatives.

The present process has as its primary objective theremoval, by means of a precipitation procedure, of these heavy metal and nitrogen-containing contaminants from petroleum crude oils and stocks derived from petroleum crudes as specific fractions thereof. More specifically,- the present process is intended to reduce the concentration of these contaminants in the petroleum feed stock to a low value, at which level the concentration of these contaminants in the feed stock can be tolerated by most cracking and reforming catalysts without unduly rapid deactivation of the catalyst activity or alteration of its catalytic properties in forming products other than those intended to be formed via the catalysis. The metallic impurities occur in petroleum crudes in the form of highly stable, refractory, metal-containing complexes, such as the vanadium and nickel porphyrins, while the nitrogencontaining impurities occur in the. form of organicallybound, naturally-occurring nitrogen compounds such as some of the asphaltenes and various heterocyclic compounds of generally complex aromatic structure. These impurities, although having high boiling points, nevertheless appear in the distillate fractions of petroleum and particularly, in fractions boiling above the gasoline boiling range, because of entrainment and/ or distillation with the desired hydrocarbon components during distillation of the crude. At the high temperatures encountered during the exothermic cracking and reforming reactions, in the presence of a reducing atmosphere of hyrogen, and in the presence of the conversion catalyst, the contami- It is also gennants present in the charge stock, such as the metal porphyrins, tend to break down into simpler molecular structures or into the metals themselves, being thereafter deposited on the catalyst in amounts which increase with time and use of the catalyst. Although these contaminants are present in extremely small quantities in petroleum crudes, their effect on the catalytic activity of the cracking or reforming catalyst is very pronounced, even in the small quantities deposited on the catalyst during the conversion process. In the case of such catalysts as the silica-alumina composites, the metallic nickel and vanadium rapidly increase the destructive cracking activity of the composite, resulting in a rapid increase in the amounts of hydrogen and light gases, such as methane and propane, produced from a given quantity of feed stock and at the same time, reduce the yield of useful products from the feed stock. These metallic contaminants, there fore, reduce the effectiveness of the catalyst for producing desirable products and necessitate its replacement, with non-contaminated, fresh catalyst more frequently than would be the case of utilizing a feed stock free of such contaminants. The catalyst itself is costly and replacement incurs not only the cost of new catalyst, but also the substantial loss in production as a result of the reactor being out of service. In the case of reforming catalysts containing an acidic component essential to the hydrocracking activity of the catalyst composite, the presence of nitrogen-containing compounds in the feed stock contacted with the catalyst also markedly reduces the activity of these catalysts for hydro-cracking. In order to use such catalysts economically, therefore, it is necessary to treat the crude or fraction subjected to conversion prior to such conversion whereby the metallic and nitrogen-containing contaminants are removed from the charge stock. It is the object of the present invention to provide a method of treating petroleum-derived charge stocks whereby the metallic and nitrogen-containing contaminants initially present in these feed stocks are reduced to a level at which the catalyst will not become deactivated at a more rapid rate than would occur utilizing a feed stock devoid of such contaminants. The present process makes the realization of such an objective feasible in providing a method of treating hydrocarbon fractions intended for cracking or reforming conversions whereby the contamination by metals is reduced to less than 1.0 ppm. of heavy metals and to less than 0.1 percent by weight of nitrogen.

Although the liquid phase treatment of petroleum stocks with hydrofluoric acid for removal of various impurities in these stocks has been dealt with extensively by the prior art, the processes heretofore utilized for hy drofluoric acid treatment are in actuality liquid-liquid phase extraction procedures wherein the contaminants dissolve in the separate liquid hydrogen fluoride or hydrofluoric acid phase which is decanted from the hydrocarbon stock as a separate phase. These processes depend upon solute transfer factors existing between an essentially hydrocarbon phase and an essentially hydrofluoric acid phase, each phase taking with it a substantial proportion of the other phase. In fact, the liquid hydrofluoric acid phase extracts an inordinate proportion of the hydrocarbon stock, generally from 10 to 30 percent, depending upon the concentration of the acid and, usually, less than percent of the orginal hydrocarbon charge is recovered. The cost of recovering the hydrocarbons from the extract phase and their change in molecular composition as a result of the conversion of these hydrocarbons which takes place in the presence of concentrated hydrofluoric acid makes the use of the extraction principle for removal of contaminants from these stocks uneconomical. In contrast to the costly extrac- Fat-exited May 29, 1962 tion methods of the prior art, the process of this invention does not result in a dual-phase liquid system, there being only sutlicient hydrogen fluoride present in the system to react with the contaminants; very little, if any, of the desired hydrocarbon stock is lost and the separation of the solid precipitate (comprising the undesired contaminants) from the treated stock is readily effected by a simple recovery procedure, without undue loss of reagents, or charge stock and without the necessity of reconstituting the hydrogen fluoride reagent, as in the liquid-liquid phase extraction method.

In one of its embodiments, this invention relates to a process for treating a hydrocarbon fraction intended for conversion in the presence of a catalyst which comprises mixing said fraction with from 1 to l to about 12 to 1 volumes per volume of a parafiinic hydrocarbon selected from propane and n-butane maintained in liquid phase and containing not more than 1 percent by weight of hydrogen fluoride, at a temperature whereby the metallic contaminants of the fraction react with the hydrogen fluoride to form a precipitate comprising said metallic contaminants and separating said precipitate from the resulting treated fraction.

Other objects and embodiments of this invention will be referred to in greater detail in the following further description of the invention.

The preferred aplication of the present treating process is in the removal of metallic and nitrogen-containing contaminants from crude oil as it is recovered from its natural sources, that is, prior to fractionation or other treatment whereby the crude oil is divided into separate fractions or prior to its use in a specific conversion process. Although, advantageously, the present method of treatment is applied to the crude oil prior to fractionation, in particular instances it may be preferable to utilize a specific boiling range fraction as charge stock to the present treating process. Thus, fractions particularly suitable as feed stocks for catalytic cracking are the kerosene and gas oil fractions of petroleum, boiling, for example, above about 400 F. In particular instances, therefore, it may be preferable to separate the desired cracking charge from the crude oil prior to the present treatment thereof. In other instances the present treatment may be extended merely to certain cycle stock fractions of the product recovered from a prior catalytic cracking process or to the lubricating oil fraction of a crude oil. In other words, the present method may be utilized in connection with the treatment of any stock of whatever derivation which is contaminated with an excessive amount or concentration of heavy metals or nitrogen-containing compounds for the specific purpose of reducing or eliminating completely these contaminants from the oil. It is true, of course, that crude oils from certain sources are more highly contaminated with undesirable metallic and nitrogen-containing compounds than crudes from other sources, but it is found generally that all crudes contain a significant and detrimental con centration of these contaminants, regardless of the source of the crude. Hence, all crudes are benefited to a considerable degree by application of the present treating method thereto, although certain crudes are benefited to a greater degree than others, depending upon the concentration of these contaminants in the crude.

The present treating reagent is a light n-paraflin selected from propane and/or butane containing up to about 1 percent by weight of hydrogen fluoride, but not more than that which will completely dissolve in the liquid paraffin. The light n-parafiin comprising the treating agent thus acts in the capacity of a carrier fluid for the hydrogen fluoride, but it also acts partially as a deasphalting agent, causing the precipitation of the nitrogen-containing asphaltenes when mixed with, for example, a crude oil or a high boiling cut of petroleum. When contacted with the charge stock to be treated, the hydrogen fluoridc dissolved in the liquefied light n-paraflin reacts with the metallic and nitrogenous contaminants of the hydrocarbon fraction to remaining hydrocarbon mixture of light n-paraffin andtreated hydrocarbon charge stock, for example, by filtration, centrifugation, flocculation, or settling, or by other available separation means.

The light paraffins utilizable as carrie'rfluid for the hydrogen fluoride dissolved therein are selected'from -the low molecular weight normal paraffins which are essen-- tially non-reactive with the hydrogen fluoride treating reagent, including propane and normal butane. Isoparaffins in general are not suitable for use as the ca rier fluid, since these hydrocarbons are capable of under going condensation and conjunct polymerization reacy tions in the presence of hydrogen fluoride to form products which are not initially present in the charge stock, Normal paraffins of higher molecular weight than normal butane are not sufficiently selective in the present process to be etfective carrier fluids for the purpose intended herein. Thus, normal pentane, although sufficiently inert in the presence of hydrofluoric acid, is not suf ficiently selective as a deasphalting agent to reduce the metal contamination of the hydrocarbon charge stock to below less than 2 p.p.m.; hence its use in the prosent process as carrier fluid for the hydrogen fluoride is not contemplated herein.

The present method of treatment comprises mixing the treating agent comprising the carrier fluid in liquid form and containing not more than one percent by weight of dissolved hydrogen fluoride with the hydrocarbon charge stock to be treated at a temperature within the range of from about 0 to about 150 C. and more preferably, within the range of from about 30 to about C. and at a sufliciently superatmospheric pressure to main- 0 tain the hydrogen fluoride component of the system, as

well as the light normal paraflin component, in essentially liquid phase. Generally, pressures up to about 30 atmospheres are suflicient to maintain the required liquid phase conditions.

The present process is operated by intimately contact ing the hydrocarbon feed stock in liquid phase with the light n-paraffin carrier fluid containing the dissolved hydrogen fluoride, also in liquid phase. The intimate con tact between the treating agent and charge stock may be obtained, for example, by adding the light n-paraflin-hy drogen fluoride solution to the hydrocarbon charge stock in a suitable mixing device such as a stirred pressure autoclave, or in a sealed pressure container which can be shaken to intimately mix the phases.

Following the foregoing treatment, the precipitate of insoluble fluoride salts in admixture with precipitated asphalt sludge is allowed to settle out of the supernatant liquid hydrocarbon phase, the resulting phases being thereafter separated, for example, by decantation of the upper, treated hydrocarbon stock from the lower solid or sludge phase. Because of the presence of dissolved excess hydrogen fluoride in the hydrocarbon phase, the treated by drocarbon layer is thereafter desirably washed, for example, with water, or passed over an adsorbent, such as pelleted alumina or clay to remove the small amount of dissolved hydrogen fluoride, although most of the hydrogen fluoride contained in the hydrocarbons is generally removed completely by stripping (distilling) the light n-paraflin carrier fluid, from the treated hydrocarbon stock, which is left as a residue in the stripping column. The overhead, comprising stripped excess hydrogen fluoride and light n-paraflin carrier fluid, is generally con densed and recycled directly to the contacting or mixing step for reuse in treating additional stock, after adding make-up hydrofluoric acid.

The carrier fluid containing the dissolved hydrogen fluoride is supplied at a rate sufiicient to provide from 1 to 1 to about 12 to 1, preferably from about 5 to 1 to about 7 to 1 volumes of liquefied paraffin diluent per volume of feed stock.

form a hydrocarbon-imsoluble precipitate which is readily separable from the It will be found that by virtue of the present treatment, the proportion of heavy metals present in the feed stock will be reduced to a level generally substantially below about 0.5 p.p.m. and the proportion of nitrogen-containing asphaltenes and other undesirable nitrogenous com pounds originally present in the feed stock, will be substantially reduced. Such treatment is accomplished with a net loss of feed stock of less than 15 percent, and generally, less than 10 percent by volume thereof. In its thus purified form, the feed stock may be utilized directly in a catalytic cracking process without appreciable long term reduction of the catalyst activity as a result of accumulation of the deactivating metal in the cracking catalyst. The treated hydrocarbon stock provided by the present process may also be utilized as charge to a reforming process in which the stock is contacted at reforming conditions with a catalyst comprising a hydrogenating component composited with an acidic support, such as platinum deposited on a support comprising alumina containing combined halide. Such catalysts may be used indefinitely in the process when the nitrogenous contaminants of the feed stock, which deactivate the catalyst by reaction with the catalyst, are removed.

The present invention is further described with respect to several of its specific embodiments in the following examples, which, however, are not intended to restrict the scope of the invention necessarily in accordance therewith.

EXAMPLE I In the following example a Velma crude oil obtained from D-X Sunray Oil Company, was utilized as feed stock to a catalytic cracking process. The physical and chemical properties of the crude oil, as received, are as follows:

Table 1 PROPERTIES AND ANALYSIS OF CRUDE OIL FEED STOCK Gravity, API, 60 F 26.8 Specific gravity 60 F 0.8939 Sulfur, percent... 1.50 Mercaptan sulfur, percent 0.0034 Hydrogen sulfide, percent 0.0002 Nitrogen content, percent 0.32 Basic nitrogen, p.p.m./sp. gr 861 Basic nitrogen, p.p.m 963 Ash content, p.p.m 137 Viscosities:

Kinematic 100 F., cs 8.770 Universal 100 F., secs 54.7 Reid vapor press, lbs 3.6 Oliensis test, original Negative Oliensis test, after 24 hours Negative Pentane insoluble, percent by weight 1.70

Distillation, 100 ml.:

IBP Boiling point, F 164 5% do 234 do 288 do 396 30% do 506 40% do 6'15 50% do 664 60% do 691 70% dn 712 80% do 726 90% do 746 95% do 760+ Percent recovered 95.0 Percent coke, by wt 4.7 Percent recovered 400 F 20.5 Percent recovered 525 F 32.0

Spectrographic analysis of the ash recovered by ignition of the crude oil indicates that the oil contains 0.31 p.p.m. of iron, 23.4 p.p.m. of nickel, 37.1 p.p.m. of vanadiuni and from 00.1 to 0.6 p.p.m. of manganese, tin, cop per, magnesium, calcium, and sodium.

In the following runs, the crude oil charge stock from the above-indicated source was mixed with various parafiin hydrocarbon diluents and/or with various sources of hydrogen fluoride to determine the effectiveness of the reagents and methods utilized. Where suflicient acid was utilized to form a separate acid phase, the latter was allowed to settle from the treated upper layer hydrocarbon phase by standing. Thereafter, the lower acid layer was withdrawn from the upper hydrocarbon phase and the latter washed with water to remove unreacted acid. In those instances in which no separate acid layer was formed, the metallic and nitrogen-containing impurities originally present in the crude oil precipitated with the asphalt, from which the hydrocarbon was decanted and analysis taken of the treated crude oil to determine the extent of contaminant removal. The treated crude oil containing the paramn hydrocarbon diluent is thereafter distilled until the original volume of paraflin is recovered, leaving a residue of the treated crude oil.

In each of the following runs 200 g. of crude oil was utilized as charge stock. The hydrogen fluoride was either mixed with a paraflinic hydrocarbon diluent and the resulting solution mixed with the crude oil or the hydrogen fluoride was added to a mixture of the crude oil and n-paraflin. The mixture was thereafter thoroughly shaken, followed by separation of the resulting phases.

In the following run No. l, 200 grams of the aforementioned Velma crude was mixed with 1020 grams of liquid propane and the mixture thereafter shaken to effect intimate mixing of the liquids. Upon standing, two liquid phases separated, an upper propane-treated oil phase and a lower precipitated asphalt phase which was drained from the bottom of the upper propane phase. The propane solution of the treated crude was thereafter heated to evaporate the propane, leaving 166 grams of recovered oil (representing 83 percent of the charge stock). The recovered oil contained 1.6 p.p.m. of nickel, 3.4 p.p.m. of vanadium and 1120 p.p.m. of total nitrogen. Analysis of the asphalt residue indicates that it contains 172 p.p.m. of nickel, and 184 p.p.m. of vanadium.

Utilizing pentane as a source of the light paraffin for deasphalting purposes, 88 percent of the original crude was recovered by evaporation of the pentane, but the treated crude still contained 20 p.p.m. of nickel and 45 p.p.m. of vanadium.

In the following run No. 2, 200 grams of Velma crude having the above specification was mixed with 1000 grams of normal pentane and 200 grams of liquid anhydrous hydrogen fluoride was added to the mixture. The liquids were thereafter stirred and the resulting layers separated. grams of treated crude (75 percent of the charge stock containing 0.1 p.p.m. of nickel, 0.35 p.p.m. of vanadium and 374 p.p.m. of total nitrogen was recovered from the pentane layer. It will be noted that in this method of treatment, utilizing a liquid phase extraction procedure, the loss of charge stock to extract is excessive (25 percent by weight of the initial charge), as was also the case in the following run No. 3.

In the following run No. 3, 200 grams of the Velma crude oil was mixed with 1000 grams of propane and 200 grams of anhydrous hydrogen fluoride in liquid phase, the mixture being thereafter stirred and allowed to settle to separate the two phases. 59 grams of treated crude oil was recovered from the propane solution (29.9 percent of the original charge stock) containing 0.07 p.p.m. of nickel and 0.01 p.p.m. of vanadium. In a separate run utilizing grams of anhydrous hydrogen fluoride, 200 grams of crude oil and 1000 grams of liquid propane, followed by separating the resulting hydrogen fluoride sludge phase, 114 grams of treated crude oil (57 percent of the original charge stock) was recovered, the oil containing 0.9 percent p.p.m. of nickel, 3.2 p.p.m. of vanadium and 476 p.p.m. of total nitrogen.

In the following run No. 4, 200 grams of the Velma crude oil specified above was mixed with 1000 grams of normal pentane and 200 grams of a hydrogen fluoride sludge recovered from the hydrogen fluoride catalyzed alkylation of isobutane with butylene, the sludge containing 96 percent by weight of hydrogen fluoride, 1.2 percent by Weight of Water and 0.9 percent by weight of hydrocarbons. The mixture was shaken in a pressure cylinder for minutes and the resulting phases separated by decantation. 120 grams of treated crude oil (60.5 percent by Weight of the original crude oil charge stock) was recovered from the pentane layer, the recovered oil containing 0.43 p.p.m. of nickel, 0.83 p.p.m. vanadium and 500 p.p.m. of total nitrogen.

In run No. 5, 200 grams of the Velma crude oil was mixed with 1000 grams of propane containing 2 grams of anhydrous hydrogen fluoride. No liquid acid phase was present, although a precipitate formed which separated from the hydrocarbon phase and was'recovered from the propane solution by filtration. 169 grams (84.5 percent of the original crude) was recovered from the hydrocarbon phase after evaporation of the propane; the treated crude contained 0.22 p.p.m. of nickel, 0.56 p.p.m. of vanadium and 537 p.p.m. of total nitrogen. In the same type of operation, except that 1000 grams of normal pentane was substituted in place of 1000 grams of propane, 172 grams (86 percent of the original crude) of treated oil was recovered from the pentane solution, the recovered oil containing 2.2 p.p.m. of nickel, 5.0 p.p.m. of vanadium and 973 p.p.m. of total nitrogen. Normal butane is substantially as efiective as propane for purposes of the treatment, 87 percent of the crude oil being recovered. The treated oil contains about 0.3 p.p.m. of nickel, 0.6 p.p.m. of vanadium and less than 500 p.p.m. of nitrogen.

The above results indicate that the precipitation procedure utilizing a normal paraflin diluent containing a small amount of anhydrous hydrogen fluoride (less than enough to form a separate acid phase) constitutes the only practical means for separating the metallic and nitrogenous contaminants of the crude oil utilizing hydrofluoric acid as the extractant. Thus, 85 percent or more of the original crude is recovered and the combined nickel and vanadium content of the oil is reduced to a level less than 1 p.p.m. Although the use of a separate phase of an anhydrous hydrogen fluoride extractant also reduces the metal contamination of the oil, the presence of a separate liquid phase of the extractant results in excessive loss of crude oil charge stock to the extractant (less than percent of the original crude oil being recovered by this method of treatment). It will be further noted that only propane and normal butane are useful and practical as the hydrocarbon diluent for treatment of the crude oil stock, normal pentane, for example, resulting in retention of excessive quantities of heavy metals in the crude oil.

1 claim as my invention:

1. A process for treating a hydrocarbon fraction containing heavy metal and nitrogenous contaminants which comprises mixing said fraction with from 1 to 1 to about 12 to 1 volumes per volume of a liquid parafiinic hydrocarbon selected from the group consisting of propane and normal-butane containing anhydrous hydrogen fluoride in an amount not exceeding about 1 percent by weight and only sufiicient to react with said contaminants, thereby precipitating said contaminants while avoiding the formation of a dual-phase liquid system, and thereafter separating the resultant precipitate of metallic and nitrogenous contaminants from the treated hydrocarbon fraction.

2. The process of claim 1 further characterized in that said hydrocarbon fraction is crude oil.

3. The process of claim 1 further characterized in that from 5 to 1 to about 7 to 1 volumes of said paraflinic hydrocarbon per volume of hydrocarbon fraction is mixed with said fraction.

4. The process of claim 1 further characterized in that said fraction is selected from the group consisting of a kerosene fraction, a gas oil fraction and a lubricating oil fraction of petroleum.

References Cited in the file of this patent UNITED STATES PATENTS 2,352,236 Thomas June 27, 1944 2,590,490 Benedict Mar. 25, 1952 2,800,427 Junk et al July 23, 1957

Claims (1)

1. A PROCESS FOR TREATING A HYDROCARBON FRACTION CONTAINING HEAVY METAL AND NITROGENOUS CONTAMINANTS WHICH COMPRISES MIXING SAID FRACTION WITH FROM 1 TO 1 TO ABOUT 12 TO 1 VOLUMES PER VOLUME OF A LIQUID PARAFFINIC HYDROCARBON SELECTED FROM THE GROUP CONSISTING OF PROPANE AND NORMAL-BUTANE CONTAINING ANHYDROUS HYDROGEN FLUORIDE IN AN AMOUNT NOT EXCEEDING ABOUT 1 PERCENT BY WEIGHT AND ONLY SUFFICIENT TO REACT WITH SAID CONTAMINANTS, THEREBY PRECIPITATING SAID CONTAMINANTS WHILE AVOIDING THE FORMATION OF A DUAL-PHASE LIQUID SYSTEM,AND THEREAFTER SEPARATING THE RESULTANT PRECIPITATE OF METALLIC AND NITROGENOUS CONTAMINANTS FROM THE TREATED HYDROCARBON FRACTION.