GB2277513A - Disposal of material containing antimony and vanadium as landfill - Google Patents

Abstract

An FCC catalyst contaminated with antimony introduced into the FCC cycle as a means to passivate metals such as vanadium contained in gas oil feedstock is treated to reduce the leachability of antimony, as well as vanadium and other metals if present in appreciable amount, thereby rendering the material suitable for disposal as landfill. The treatment involves adding titanium or aluminum sulfate or preferably a combination of titanium and aluminum sulfate and iron sulfates when leachability of vanadium is also to minimized. The salt-treated mixture is then neutralized by lime and dried.

Description

DISPOSAL OF MATERIAL CONTAINING ANTIMONY AND VANADIUM AS LANDFILL BACKGROUND OF THE INVENTION This invention relates to the disposal of particles of cracking catalysts which are contaminated with appreciable amounts of antimony added during the cracking cycle to passivate heavy metals originally contained in the oil feedstock.

Spent fluid cracking catalyst (FCC) particles are periodically withdrawn from the FCC generator in order to permit catalytic cracking units to operate at desirable activity and selectivity levels. See, for example, U.S. Patent No. 4,268,188. Particles of spent fluid cracking catalyst normally contain deposits of metal contaminants originating in the petroleum feedstock charged to the catalytic cracking unit.

These principal metals include vanadium or nickel, usually both. Spent cracking catalyst is frequently employed to start-up FCC units. However, the majority of spent cracking catalyst, as well as fines discharged from FCC regenerators, are usually discarded and used as landfill.

There has been a trend in recent years to charge FCC units with feedstocks which contain considerably higher levels of metal contaminants than the relatively "clean" gas oils heretofore used as FCC chargestock.

Consequently, spent FCC catalysts and regenerator fines may now be expected to contain higher concentrations of metals than were encountered in the past unless high catalyst replacement rates are used.

When discarded FCC catalysts are to be disposed of as landfill, it is desirable, and in some cases essential, to minimize leaching of water-soluble heavy metals contaminants because the landfill is likely to come into prolonged contact with rain and/or surface waters, resulting in possible pollution of the waters.

Generally, such waters are mildly acidic, e.g., the pH is about 3 - 6. Further, it is desirable to accomplish this result while minimizing treatment costs associated with chemical additives and equipment. Also, it is advantageous to provide material intended for disposal or landfill in the form of a solid or semi-solid mass amenable to direct disposal without a downstream filtration or dewatering step.

In addition to vanadium and nickel, metals originating in petroleum feedstocks may, but do not necessarily, include one or more of the following contaminants: chromium, cobalt, copper, arsenic, antimony, bismuth, and barium. Except for copper, only trace amounts of these metals are usually contained in feedstocks. For example, antimony is usually not present in petroleum crudes in detectable amounts, although some Chinese crudes may contain this metal in the ppm range. See U.S. 4,668,124 for a disclosure of typical quantities of metals in spent cracking catalysts.

Leachable vanadium in spent FCC catalysts typically includes V+S and V+4 compounds. The difficulty involved in insolubilizing vanadium in spent contact material or cracking catalysts is that vanadium is an amphoteric element. Thus, vanadium is soluble at acidic pH values and is still somewhat soluble at neutral and mildly alkaline pH values at which other heavy metals such as nickel and iron are insoluble or are low in solubility. Vanadium compounds increase in solubility at strongly alkaline pH values.

U.S. 4,668,124 solves the problem of reducing the leachability of normally leachable vanadium compounds to minimum practical levels while assuring limited solubility of other metals including nickel by addition of certain polyvalent acidic salts, e.g., ferrous and ferric sulfate, aluminum sulfate, titanium sulfate and combinations thereof, followed by addition of an alkali, preferably a calcium compound, under conditions that result in a solid or semi-solid amenable to disposal as landfill.

In recent years the addition of antimony compounds to cracking catalysts or FCC feed to passivate metals, especially nickel, has become widespread. See U.S.

3,711,422 as a nonlimiting example of antimony passivation technology. As described in this patent, the quantity of antimony added is dependent on the metals content of the gas oil feedstock, e.g., from o.

to about 2 moles of contaminating metal in feed.

Whether added to an FCC unit or applied directly to catalyst, the antimony can deposit on the circulating catalyst inventory and build up to high levels, e.g., 1,000 ppm or above. Vanadium levels in spent catalysts may be 1,000 ppm or higher, with levels of 5,000 6,000 ppm being prevalent in Europe. Unexpectedly, procedures described in the above-mentioned '124 patent may not adequately solve the problem of reducing the leachability of antimony in spent FCC catalysts when antimony has been added at levels sufficiently high to effectively passivate metals. Furthermore, procedures described in the '124 patent may not always reduce the leachability of vanadium to levels satisfying the criteria of recently introduced more stringent leaching tests.

SUMMARY OF THE INVENTION The present invention comprises a process for reducing the leachability of antimony in particles of a spent cracking catalyst or regenerator fines. The method of the invention places the material in the form of a solid or semi-solidness and comprises the steps of: (a) contacting the spent catalyst or regenerator fines, or a mixture thereof, in the presence of water with an effective amount of titanium sulfate, aluminum sulfate or the combination thereof at an acidic pH, and (b) increasing the pH of the resulting mixture to a value of at least 10 by addition of a base of calcium to insolubilize the antimony and vanadium and convert sulfate to insoluble calcium sulfate, and (c) drying the resulting alkaline mixture.Preferably, the weight of chemicals added to the material during the insolubilization treatment is minimal and relatively small amounts of water are utilized. Most preferably, the treated mass is solid or semi-solid, even prior to drying.

When the spent antimony contaminated catalyst is one that also contains appreciable leachable vanadium, a solution of iron (fez) sulfate is preferably added with the titanium sulfate, aluminum sulfate or mixtures thereof, and the leachability of both antimony and vanadium is reduced.

Preferably the leachability of antimony is reduced to a value below 10 ppm, most preferably below 3 ppm.

The leachability of vanadium is preferably reduced to a value below 10 ppm, most preferably below 5 ppm.

In one embodiment, a salt of titanium and iron is obtained ; digesting a titaniferous slag with sulfuric acid. In another embodiment, a sulfate salt of titanium and iron is obtained by digesting ilmenite ore with sulfuric acid. In still another embodiment, a sulfate salt of aluminum and iron is obtained by digesting a bauxite ore with sulfuric acid.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT The present invention in especially preferred aspects is a simple and economical procedure for treatment of spent petroleum cracking catalyst, especially FCC catalysts, previously used to crack petroleum feedstocks contaminated with metals and cracked in the presence of added antimony to passivate metals in feedstocks. Antimony may be added directly to the particles of cracking catalyst or it may be added directly to oil feedstock. The process of the invention renders the treated materials suitable for direct disposal without the need for prior extraction of metals. This invention is especially applicable to the treatment of spent fluid cracking catalyst containing more than 100 ppm Sb and has produced acceptable results with materials containing more than 1,000 ppm Sb. Reduced Leachable vanadium levels are achievable with spent catalysts containing more than 100 ppm leachable vanadium.

Present day fluid cracking catalysts contain at least one zeolitic molecular sieve component (typically zeolite Y) and a matrix-diluent which is an inorganic oxide, usually silica-alumina. The catalyst is in the form of microspheres when used for FCC. See, for example, U.S. 4,490,902, Brown et al. Practice of the invention is applicable to a host of cracking catalysts, however, and is not restricted to catalysts produced by any specific processing techniques or based upon any specific zeolite or any specific matrix.

Thus, for example, the cracking catalyst can be one based on Zeolite Y, B, L, ZSM-5 or various combinations thereof. The invention is also applicable to the treatment of spent cracking catalysts used in moving bed processes as well as to fluid or moving bed cracking catalysts not based on zeolites. When processing spent moving bed catalyst, it may be advantageous to pregrind the catalyst pellets before treatment, e.g., grind the catalyst pellets into particles in the 10 to 200 micron size range typical of fluid catalysts. Finer grinding can be practiced.

Regenerator fines may also be subject to the process of the invention.

The especially preferred treatment of the present invention comprises the steps of: (a) contacting the cracking catalyst contaminated with leachable metals including antimony and/or vanadium at a pH below 4, preferably below 2, in the presence of water with a dry or concentrated aqueous solution of sulfate salt selected from the group consisting of: (1) titanium sulfate (2) aluminum sulfate (3) mixtures of titanium and aluminum sulfates (including mixtures having a molar ratio of TiO2 to A1203 of from 99/1 to 1/99 (4) (1), (2) or (3) plus ferrous sulfate) (5) (1), (2), (3) or (4) plus ferric sulfate.

Iron sulfate, preferably ferric sulfate, should be used when the spent catalyst contains high levels of soluble vanadium. Preferably, the molar ratio of Tio2 to iron oxide is in the range of 4:1 to 0:05, most preferable 3:1 to 1:1.

(b) pugging the material produced in step (a) with sufficient calcium hydroxide to raise the pH to at least 10 and, (c) drying the pugged material at about 1000 to 2000C.

Heat treatment after lime neutralization is essential and can reduce significantly the leaching of antimony as well as vanadium, possibly by promoting V/Ti/Fe or Sb/Ti/Fe interactions and insolubilization.

Heat treatment also removes water, thereby minimizing the weight for disposal. Further, it hardens the material.

For economic reasons, it may be desirable to utilize mixtures of acidic sulfate salts produced by treating titaniferous or aluminous ores or slags with sulfuric acid. Examples are the titanium rich-ferrous sulfate solutions produced by dissolving slags, or ilmenite ores, as well as ore by-products or aluminumiron sulfates produced by digesting iron rich bauxite ores with sulfuric acid. Mixed sulfate salts obtained by treatment with acid can be enriched in a suitable metal sulfate, such as ferric sulfate.

The added sulfate salts are preferably present in amount at least sufficient to provide at least one equivalent of cation in the salt per equivalent of combined leachable vanadium and antimony and are preferably added as aqueous solutions of maximum feasible concentrations.

Claims (7)

CLAIMS:

1. A process for reducing the leachability of antimony in an FCC catalyst contaminated therewith which comprises (a) contacting said catalyst contaminated with antimony in the presence of water with titanium sulfate, aluminum sulfates or the combination thereof and at an acidic pH, and (b) increasing tha pH of the resulting mixture to a value of at least 10 by addition of a base of calcium and (c) drying the resulting alkaline mixture.

2. The process of claim 1 wherein said catalyst also contains leachable vanadium and ferrous or ferric sulfate is also added with said titanium sulfate, aluminum sulfate and mixtures thereof.

3. The process of claims 1 or 2 wherein the leachability of antimony is reduced to a value below 10 ppm using the TCLP procedure.

4. The process of claim 2 wherein the leachability of vanadium is reduced to a value below 10 ppm using the TCLP procedure.

5. The process of claim 2 wherein said sulfate salt of titanium and ferric iron is obtained at least in part by digesting a slag with sulfuric acid.

6. The process of claim 2 wherein said sulfate salt of titanium and iron is obtained at least in part by digesting ilmenite ore with sulfuric acid.

7. The process of claim 2 wherein said sulfate salt of aluminum and ferric iron is obtained at least in part by digesting a bauxite ore with sulfuric acid.