United States Patent Office Patented Jan
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3,789,019 United States Patent Office Patented Jan. 29, 1974 1. 2 Temperature (C.): Percent conversion 3,789,019 400 ----------------------------------- 99.21 PREPARATION OF CATALYSTS USEFUL IN 420 -----------------'-a'-- 'mas-s-sur - - -w or un mo 98.72 OXIDATION OF SO GASES 450 ----------------------------------- 97.53 Alvin B. Stiles, Wilmington, Del, assignor to E. T. Du Pont de Nemours and Company, Wilmington, Del. 480 ----------------------------------- 95.50 No Drawing. Filed Dec. 27, 1971, Ser. No. 212,761 500 ----------------------------------- 93.53 Int, CI. B01j11/06, 11/22 520 ----------------------------------- 90.95 U.S. C. 252-440 35 Claims 540 ----------------------------------- 87.72 560 ----------------------------------- 83.79 0 600 ---------------------'oon ra aars amru as - are no 74.04 ABSTRACT OF THE DISCLOSURE From the above data it is thus seen that in going from This invention relates to a process for preparing a catar a catalyst that is effective at 480 C. to one that is effec lytic material having high efficiency in the oxidation of tive at 450° C., the SO2 leakage in the off gases of a SOa to SO3 which entails preparing a homogeneous mix converter would be reduced by 45.2% (182% more SO ture comprising a catalytically effective amount of a pri 5 leakage at 480 C. than at 450° C.). However, in going mary catalytic material selected from the group of CSVO from a temperature of 480 C. to 400° C. the SO, leak or RbVO3, a promoter, and a carrier material comprising age would be reduced by 82.4% (570% more SO, leak diatomaceous earth; and then drying the mixture to pro age at 480 C. than at 400° C.). vide the catalyst. Whenever the HO cleanup procedure for the SO 20 leakage described above is utilized, a corresponding de crease in the H2O (or peroxy acid of sulfur) consumption BACKGROUND OF THE INVENTION is achieved. In recent years the elimination of various contaminants U.S. Pat. 1,941,426 to Beardsley et al. (dated Dec. 26, 1933) discloses the preparation of cesium vanadate by from our environment has become important. One of the 25 reacting ammonium metavanadate and cesium chloride most troublesome contaminants is sulfur dioxide. Sulfur together. The catalytic material is then placed on a carrier dioxide is produced by the burning of various fuels, i.e., comprising chips of Celite. The catalytic material is stated in electric power generation, industrial, domestic and to be useful in the method of making sulfur trioxide. vehicular fuel use, the smelting of ores, the recovery of However the catalyst of Beardsley et al. does not have sulfur from a sulfur compound-bearing gas stream, oil 30 a high efficiency (see applicant's Examples 20 and 21). refining, and also as an intermediate in the manufacture It is known in the art that the chloride ions poison the of sulfuric acid. Many processes have been proposed for catalyst (see Duecker & West, The Manufacture of Sul the removal of sulfur dioxide from the off gases of these phuric Acid, Reinhold, 1959, p. 184), but most critically, processes, particularly the off gas from sulfuric acid applicant has found that the primary catalytic material manufacture. Some of these processes involves the conver 35 (cesium vanadate) must be prepared in an intimate homo sion of sulfur dioxide to elemental sulfur while others geneous mixture with the promoters and carrier material involve sulfur dioxide removal with a liquid sorbent, still as opposed to impregnating the solid support with the others with a dry sorbent and finally multiple stage cata primary catalytic material as taught by Beardsley. Ap lytic oxidation, or catalytic oxidation with interpass ab 40 plicant's procedure would seem to be in the wrong direc sorption. All of these prior art processes present an eco tion for the production of a low cost, low temperature, . nomic problem to the industry involved. catalytic material because the expensive cesium com Assignee's copending application Ser. No. 173,247, filed ponent is intermixed with and consequently diluted by the carrier which would usurp a large fraction of the Aug. 19, 1971, describes a process wherein the SO2 con surface available for reaction. This is in contrast to the tent of the off gases from sulfuric acid plants can be 45 coated Support of Beardsley which presents a surface reduced to acceptable levels by incorporating a low tem entirely coated by the coating-impregnating procedural perature, high efficiency SO2 oxidation catalyst, e.g., sup step. ported platinum, rubidium-promoted vanadate, or a ce Various combinations of cesium promoted vanadate sium promoted vanadate composition, in at least the last catalysts in conjunction with promoters and/or activators stage of a multi-stage catalytic converter, and Subse 50 have been disclosed in the art as being advantageous in quently contacting the off gas with an aqueous sulfuric obtaining low temperatures and greater efficiency in the acid solution containing H2O2 or a peroxy acid of sulfur. conversion of SO2 to SO (see Duecker & West, The Man Therefore a highly efficient, low temperature oxidation ufacture of Sulphuric Acid, Reinhold, 1959; pp. 171-176). catalyst in the converter is important in order to reduce However, cesium is expensive and also catalysts thus far SO levels in the off gas, thus reducing peroxide or 55 taught in the art are inadequate in the objective at low peroxy acid consumption which concomitantly permits a SO2 leakage and consequently catalysts having even great large reduction in size of the peroxide or peroxy acid con er activity are desired. w tacting tower. The catalyst produced by the process of this invention It is important to have a low temperature catalyst in at 60 provides such a catalyst having greater efficiency in the least the final stage of SO2 to SO3 conversion since equi conversion of SO2 to SOs and requires less expensive in librium favors SOs as the temperature is lowered. For gredients than previously known catalysts. instance, the equilibrium relationship where the inlet SO SUMMARY OF THE INVENTION percent is 10% in the range of 400 to 600 is pointed It has been discovered that a catalyst having a high effi out below: 65 ciency for the oxidation of SOa to SO is provided by a 3,789,019 3 4 process which comprises preparing a homogeneous mix illustrating this invention as well as performance data for ture comprising a catalytically effective amount of a pri art comparisons or control experiments are recorded in mary catalytic material selected from the group of CSVO: Table I. or RbWO, a promoter, and a carrier material comprising Example 1 diatomaceous earth; and then drying the mixture to pro vide the catalyst. u A solution is prepared by dissolving 40 parts by weight CsVO is preferred as the primary material and it. IS of ammonium metavanadate and 56 parts by Weight of a also preferred to preform the CsVOa prior to peparing 50% solution of cesium hydroxide in 350 parts by Weight the homogeneous mixture in the form of a slurry. Good of distilled water at 95° C. At this temperature, Solution results are obtained, however, by forming the CSVO3 in 10 is complete and a reaction product forms between the situ in the mixture by including reactants that provide the cesium and the vanadate ions to form cesium vanadate. CSVO upon heating. Preferred reactants are NHVO3 A solution-slurry is prepared by dissolving a promoter and CsoH and a temperature within the range of 50 of 40 parts by weight of potassium chrome alum (K2Cr2 100° C. is preferable. (SO).24HO), 40 parts by weight of potassium sulfate, A preferred promoter is an alkali metal sulfate with 5 and 150 parts by weight of powdered diatomaceous earth chromium potassium sulfate being most preferable. Good in 600 ml, of distilled water, and an activator of 50 parts results are also obtained by including Cs2SO4 and/or by weight of a solution of 0.75 part each of the sulfates KSO, along with the cromium potassium sulfate. of Co, Ni, and Fe as their normal hydrates. The Solution It is desirable to include at least one activator selected slurry is very rapidly agitated to effect complete solution from the group of sulfates of cobalt, nickel, and iron as of the soluble salts and complete suspension of the finely their normal hydrates in the homogeneous mixture. 20 powdered diatomaceous earth. Desirable results are provided by including NaVO3 There is separately weighed out 450 parts by weight along with CsVO as the primary catalytic material. of a colloidal dispersion of silica having a solids content of It is most preferred that the carrier material comprise 30% and being comprised of spheroidal particles 70A. in a mixture of diatomaceous earth and colloidal silica. In 25 diameter. addition to diatomaceous earth, other refractory oxides With the cesium vanadate solution of the first para such as alumina, quartz, silica-alumina, mullite, titania, graph being rapidly agitated, the solution slurry of the zirconia and others can be used as carriers. These ordi second paragraph is rapidly added over a 15-second narily will have a strong X-ray crystal orientation pattern. period. Agitation is continued until the slurry becomes When considering the amorphous nature of the finished 30 uniform, requiring approximately 1 minute. Thereafter, catalyst, the crystallinity of the carrier is of course of no the colloidal silica is also added to the rapidly agitating consequence, the pattern can be isolated and is ignored. slurry over a period of 15 seconds. Agitation and heating The amorphous nature of the catalyst characterizes all are continued until the temperature reaches 70 at which components other than the highly crystalline carrier.