Catalyst for removal of sulphur oxides from flue gases of power plants

Abstract

The present invention relates to the catalytic processes for rendering harmless the flue gases of the power stations or more precisely to the catalysts for sulfur oxides reduction to elemental sulfur. The novel catalyst presents the binary polycations of copper and zinc or copper and manganese incorporated into the low silica faujasite X (LSX) having transition metals ratio Cu:Zn or Cu:Mn in the range of 2:1 to 4:1.

Claims

1. A method for removal of sulfur oxides from a gas comprising the steps of: contacting the gas with a catalyst for sulfur oxides removal; wherein the catalyst for sulfur oxides removal comprises a low-silica faujasite LSX with the binary polycations of transition metals of IB, IIB, VIIB and VIIIB groups of the Periodic System; and wherein the low-silica faujasite is characterized the ratio of SiO2:Al2O3 oxides from about 1.8 to about 2.2 and includes binary polycations of copper and zinc from about 2:1 (mole:mole) to about 4:1 (mole:mole).

2. The method of claim 1, wherein the said low-silica faujasite includes the binary polycations of copper and manganese from about 2:1 (mole:mole) to about 4:1 (mole:mole).

3. The method of claim 1, wherein the temperature is below 240° C.

4. The method of claim 3, wherein the temperature is below 220° C.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) The catalyst product of this invention is a low-silica faujasite having a molar ratio of silicon and aluminum oxides in the range of 2.0-2.2 whereas the said low-silica faujasite contains the binary polycations of transition metals copper and zinc or copper and manganese at their proportion Cu:Zn or Cu:Mn from about 2:1 to about 4:1.

(2) The procedure for low-silica faujasite synthesis has been described by G. Kül, (G. H. Kül, “Crystallization of Low-Silica Faujasite (SiO.sub.2:Al.sub.2O.sub.3˜2.0”), Zeolites, 1987, 7, 451) and has been commercialized by several zeolite manufacturers. The simple process for zeolites polycation forms synthesis has been developed by the authors of the present invention, which alongside the activity of zeolites with the transition metals polycations in reactions of carbon monoxide and organic sulfur oxides oxidation has been published in the following papers: O. P. Tkachenko, A. A. Greish, A. V. Kucherov, K. C. Weston, A. M. Tsybulevski, L. M. Kustov “Low-temperature CO oxidation by transition metal polycation exchanged low-silica faujasites”, Applied Catalysis B: Environmental, 2015, 179, 521 and A. M. Tsybulevski, O. P. Tkachenko, E. J. Rode, K. C. Weston, L. M. Kustov, E. M. Sulman, V. Y. Doluda, A. A. Greish “Reactive adsorption of sulfur compounds on transition metal polycation-exchanged zeolites for desulfurization of hydrocarbon streams”, Energy Technology, 2017, 5, 1627.

(3) An enhanced activity of the catalysts of the present invention in the oxidation reactions is caused by the transition metal polycations ability for transferring excessive oxygen atoms of polycations to the reactants. At the same time, the activity of the polycation catalysts in the reducing reactions, their capability to breaking away oxygen atoms from the reactants was unknown, was absolutely unexpected and surprisingly found by the authors of the present invention. The activity of the novel catalyst at the low temperatures range, its capability for complete elimination of sulfur dioxide even at 240° C. is also absolutely unexpected and amazing. The mentioned features of the novel catalyst open new ways for the desulfurization of flue gases of power stations.

(4) In order to illustrate the present invention and the advantages thereof for sulfur oxides removal from flue gases, the following examples are provided. It is understood that these examples are illustrative and do not produce any limitation on the invention. In particular, it is important to understand that the present invention is generally applicable for power stations that are firing gas, liquid or solid fuels.

Examples 1-3

The Catalyst Samples Preparation

(5) The preparation procedures, which are given below, are designated for obtaining ˜140 g of the final product. The all catalyst samples were prepared on the basis of sodium-potassium form of zeolite LSX of the M Chemical Co manufacturing

Example 1. Catalyst (Cu).SUB.p.(Zn).SUB.p.CaLSX-4

(6) Although the cations of alkali and alkaline-earth metals play a balanced role in the low-silica zeolite X structure, the preliminary conversion sodium-potassium form into calcium form is useful for the following synthesis of copper and zinc polycations. Thus, the preparation procedure includes the following operations: a) Exchange of the alkali cations for Ca.sup.2−+ cations. Prepare 1 L of the 1N solution of calcium chloride by dissolution of 73.5 g CaCl.sub.2.Math.2(H.sub.2O) in deionized water (DIW); Treat 100 g granule of the origin zeolite by 1 L of 1.0 N solution of CaCl.sub.2 at the ambient temperature and proper mixing. Maintain the pH of the exchanged solution in the range of 6.5-7.0 to obtain ˜55-60%-exchanged CaLSX sample; Wash the granules in ˜10 L of DIW. b) Cu.sup.2+-exchange. Prepare the buffer solution—0.05 M basic sodium dihydro phosphate by dissolution of 6 g anhydrous NaH2PO.sub.4 in 1 L DIW; Prepare 1 L of 1N CuCl.sub.2 solution by dissolution of 85.6 g CuCl.sub.2.Math.H.sub.2O in 1 L DIW and lower pH of the exchange solution by addition of 35 ml of buffer to avoid a spontoon hydroxide precipitation; Treat the washed granules of CaLSX by 1 L of 1N solution of CuCl.sub.2 at ambient temperature and instant agitation over 4 hours. Maintain pH of the exchange solution on the level of 5.0-5.4 with the use of sodium-dihydrophosphate buffer. The achieved ion exchange degree should be about ˜50% Cu, 40% Ca; Wash the exchange product by 10 L DIW. B) Zn.sup.2+-exchange Prepare buffer solution—0.03 M basic potassium hydro phosphate (K.sub.2HPO.sub.4). Dissolve 5.25 g K.sub.2HPO.sub.4 in 1 L DIW. Prepare 1 L of 1.5 N zinc chloride solution. Dissolve 102 g anhydrous ZnCl.sub.2 in 1 L DIW and to avoid the intense precipitation of zinc hydroxide, lower the solution pH by addition of 60 mL buffer. Treat CuCaLSF, as it was obtained in the operation b) of the catalyst sample (Cu).sub.p(Zn).sub.pCaLSX-4 synthesis by 1 L of 1.5 N ZnCl.sub.2 solution for 4 hours maintaining pH of the exchange solution on the level of 5.6-6.0 by buffer—0.03 M K.sub.2HPO.sub.4.Math.solution. The final cation ion exchange degrees in the catalyst sample are: Ca—15%, Cu—50%, Zn—12.5% equivalent. Wash the product by DIW up to the negative reaction for chloride ion by 0.028 N AgNO.sub.3 solution.

Example 2. Catalyst (Cu).SUB.p.(Zn).SUB.p.CaLSX-2

(7) Replicate operations a) and b) of the above described procedure for (Cu).sub.p(Zn).sub.pLSX-4 the catalyst synthesis. c) Zn.sup.2+-exchange Prepare 1 L of 2.5 N zinc chloride solution. Dissolve 170 g anhydrous ZnCl.sub.2 in 1 L DIW and lower pH solution by 75 mL buffer addition to avoid zinc hydroxide precipitation applying for the purpose 0.03 M K.sub.2HPO.sub.4 solution; Treat the product of stage b) of the previous sample preparation procedure, CuCaLSF sample by 1 L of 2.5 N zinc chloride solution over 4 hours maintaining pH of the exchange solution on the level of 5.2-5.6 applying the K.sub.2HPO.sub.4 buffer solution. The achieved ion exchange degrees in the final product are: Ca—12%, Cu—45%, Zn—22% 3 KB.

Example 3. Catalyst (Cu).SUB.p.(Mn).SUB.p.LSX-2

(8) Replicate a) and b) steps of the above described procedure for the catalyst (Cu).sub.p(Zn).sub.pLSX-4 synthesis. B) Mn.sup.2+-exchange Prepare 1 L of 2 N manganese chloride solution. Use 198 g MnCl.sub.2.Math.4H.sub.2O and dissolve it in 1 L DIW with the addition of 100 mL of buffer—potassium hydro phosphate to avoid manganese hydroxide precipitation. Treat the (Cu).sub.pCaLSF sample, which was obtained on the step b) of the catalyst preparation over 4 hours by 1 L of 2N manganese chloride solution maintaining pH of the exchange solution on the level of 5.1-5.4 by means of K.sub.2HPO.sub.4 buffer. The cation composition in the obtained product is: Ca—15%, Cu—50%, Mn—25% equiv.

Example 4

(Catalyst (Cu).SUB.p.(Zn).SUB.p.CaLSX-2 EXAFS Specters—Confirmation of the Catalyst Polycation Structure)

(9) EXAFS-specters of the catalyst (Cu).sub.p(Zn).sub.pCaLSX-2 sample were recorded at the BM23 European Synchrotron Radiation Station (ESRF, Grenoble, France). The specters of metal foil were recorded simultaneously for comparison. The measured parameters of copper and zinc cations are presented in Table 1.

(10) TABLE-US-00001 TABLE 1 Polycations Cu and Zn Structure Parameters in the Catalyst (Cu).sub.p(Zn).sub.pCaLSX-2 Cation Oxygen Surface Area Cation Me—O bond length, Å Content, N σ × 10.sup.−3, Å.sup.−2 Cu—O 1.97 ± 0.01 3.08 ± 0.19 4.7 ± 0.1 Zn—O 2.05 ± 0.01 3.75 ± 0.16 9.4 ± 1   The results of spectral measurements unambiguously confirm copper and zinc polycations presence in the (Cu).sub.p(Zn).sub.pCaLSX-2 catalyst. The length of cation measured radii significantly exceeds the standard bond length in monocations (1,97; 2.05 versus 1.95), while an average oxygen content is essentially higher than stoichiometric one and the surface that is occupied by Cu and Zn polycations is 2-3 pa3a larger than monocation size.

Example 5

The Catalyst Activity Test

(11) The catalyst samples of Examples 1-3 were tested for activity in the reaction of sulfur dioxide reduction by carbon monoxide alongside the La.sub.2O.sub.3.Math.TiO.sub.2 (anatase) catalyst sample, which is known from U.S. Pat. No. 5,213,779. The activity measurements were conducted with use of metal reactor of 9 mm diameter and 40 cm length. The sample granulation size was 1.6-2.0 MM. Preliminary samples training was carried out at 250° C. over 2 hours in nitrogen flow. The composition of initial gas mixture was: SO.sub.2—0.5%, CO—1.5%, He—98%. The gas volume rate—120-160 cm.sup.3/min. The reaction temperature was varied in the 220-380° C. range.

(12) The reaction products analysis was conducted by GC with the katharometer detector with the use of three packed columns: Column 1—length 1.5 M, stationary phase—molecular sieve 5 A; Column 2—length 1.5 M, stationary phase—Parapack Q; Column 3—length 2M, stationary phase—Chromosorb SE-54.

(13) The test results are disclosed in Table 2.

(14) TABLE-US-00002 TABLE 2 SO.sub.2 Conversion Degree over Various Catalysts Depending on the Reaction Temperature Conversion Degree, % mole Temperature, ° C. Catalyst 220 240 280 300 380 (Cu).sub.p(Zn).sub.pCaLSX-2. 92 100 100 n/d n/d (Cu).sub.p(Zn).sub.pCaLSX-4. 90 95 100 n/d n/d (Cu).sub.p(Mn).sub.pLSX-2 95 100 100 H/¤ H/¤ La.sub.2O.sub.3 .Math. TiO.sub.2 0 0 15 42 98

(15) The catalysts, according to the present invention demonstrated outstanding efficiency in sulfur dioxide elimination and therefore in the environment protection performance. As it can be seen from Table 2, the catalysts of the present invention are able to provide a practically complete sulfur dioxide removal at the temperature that is 150° C. lower than the highest ability of the catalysts of prior art. Thus, it is apparent that the catalysts of the present invention can provide substantial technical and economic achievements at their implementation at the power stations.

(16) While the above description contains many specifics, these should not be considered as limitations on the scope of the invention, but rather an exemplification of one preferred embodiment thereof. Many other variations of the catalyst composition are possible.