Related Art As one result of concern with air pollution, environmental regulators have severely reduced and are continuing to reduce allowable emissions of sulfur oxides and hydrogen sulfide. As a result, a variety of technologies have been developed and are continuing to be developed for use in flue gas desulfurization (FGD).

FGD techniques can generally be classified as wet and dry scrubbing. Dry scrubbing contacts the effluent with a solid material which chemically reacts with the sulfur component and forms a compound. The system can be a fixed bed such as zinc oxide pellets that are used to react with H2S to form zinc sulfide. The zinc sulfide pellets must be removed and replaced after saturation. The dry scrubber can also be in powder or particulate injected into the stream followed by a baghouse or electrostatic filtration to remove the reacted product. An example of powder would be limestone, which would react after injection into the exhaust stream to form calcium sulfate and/or calcium sulfite hemihydrate sludge. The material is typically delivered as a wet slurry, which dries in the exhaust and reacts with the sulfur oxides. This material is then removed and typically disposed of in a landfill. There are also regenerable dry scrubber materials such as copper oxide on aluminum oxide pellets or spheres. The regenerable copper systems must be heated to and or reduced at high temperatures. This technique requires that the sorption temperature be less than the regeneration temperature.

Wet scrubbing techniques use wet slurries or amine solutions and require that the exhaust temperature be reduced to below the boiling point of the solutions to be used. These techniques give rise to losses by evaporation and entrainment and produce products which are contaminated and unusable and must be disposed of/or purified before reuse.

The present invention introduces a new technology for the removal of H2S, S02 and oxidation of CO. This technology utilizes a catalytic oxidative sorption process for the removal of the sulfur component where the sulfur component is first oxidized and preconcentrated and then released in a concentrated stream of much smaller volume which is delivered to processes for recovery as sulfur, sulfur dioxide, or sulfuric acid. This technology has tremendous advantages over the scrubbing techniques. It is an advantage that the present process operates in the exhaust stream with oxidative capture mode and reductive regeneration occurring at the same temperature. It is a further advantage that it is a dry process, which is selective for sulfur components and will produce sulfur oxide off gases with high concentration and purity. It is a feature of the present invention that it reduces the volume of sulfur containing gases thereby reducing the costs for further processing. It is a further feature that the process also operates over a wide range of temperatures (200°F to 800°F). It is another advantage of the process of the present invention that it has high capture efficiencies of over 99.75% and also has very low pressure drop.

SUMMARY OF THE INVENTION One aspect of the present invention is a process for removing gaseous sulfur compounds, particularly S02 and/or H2S from gaseous streams, such as effluent combustion and industrial process streams, comprising contacting a gaseous stream, containing gaseous sulfur compounds with a catalyst/sorber under sulfur sorbing condition, said catalyst/sorber comprising a noble metal catalyst

component, a metal oxide sorber component, and optionally modifiers consisting of oxides of Ag, Cu, Bi, Sb, Sn, As, In, Pb, Au or mixtures thereof to remove said gaseous sulfur compound from said stream to said catalyst/sorber.

In a preferred embodiment of the present process the gaseous sulfur compound containing stream is terminated and the sorbed sulfur is desorbed from said catalyst/sorber by contacting the catalyst/sorber with a regenerating gas stream under sulfur compound desorbing conditions whereby the catalyst/sorber is regenerated for reuse in the sorbing. A most preferred embodiment comprises alternating said sorbing and regeneration steps.

Preferred regenerating gases provide a reducing environment. The reducing agents include hydrogen and hydrocarbons or mixtures thereof. The hydrocarbon preferably comprises of Cl-Cl2 hydrocarbons, which may be used as one compound or mixtures of compounds. Usually the reducing agent will comprise methane and/or a mixture of hydrocarbons. The principal source of methane is natural gas. The principal component of the gaseous stream is an inert carrier gas such as nitrogen, helium, argon or steam.

The term"principal component"is used to mean over 50%.

The regeneration may also be carried out with the inert carried gases alone or with oxygen present. Air may also be used for regeneration.

Another aspect of the present invention is the catalyst/sorber. The noble metal component may comprise Pt, Pd, Rh, Ru or mixtures thereof, preferably Pt. The metal oxide sorber component is an oxide of Ti, Zr, Hf, Ce, Al, Si or mixtures thereof. In addition to these components, the catalyst/sorber optionally contains a modifier comprising an oxide of Ag, Cu, Bi, Sb, Sn, As In, Pb, Au or mixtures thereof, preferably Cu, Ag, Bi and mixtures thereof. The purpose of the modifier is to inhibit the formation of H2S during regeneration.

The catalyst/sorber can be used in pellet, spheres, particulate, or extruded form. Preferably the catalyst/sorber can be coated onto a carrier with the

catalyst/sorber comprising 1 to 50 wt% of the total weight. The noble metal component is preferably present as from 0.005 to 20.0 wt% of the catalyst/sorber, the sorber component is preferably present as from 70 to 99 wt% of the catalyst/sorber, and the modifier is preferably present as from 1 to 10 wt% of the catalyst/sorber.

Although the sulfur compounds are removed from a gaseous stream on and/or onto the catalyst/sorber according to the present invention, it is not known in what form or by what mechanism the sulfur is associated with the catalyst/sorber. It is the invention that the sulfur compounds in the gaseous stream are in some manner releasably associated with the catalyst/sorber in an oxidizing atmosphere. It is believed that the sulfur is associated with the catalyst/sorber as a compound, most likely as an oxide, but not in the elemental form.

Elemental sulfur has not been observed. Preferably the sulfur is removed from the catalyst/sorber as a more concentrated stream of sulfur compounds. Unless otherwise stated percentages and ratios of compounds expressed herein are by weight.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows outlet S02 values during 300°F - 30 minute sorption runs with 30 ppm S02 and the conditions given in Table 2 with different catalyst/sorber compositions.

Figure 2 shows outlet S02 values during a 500 ppm S02 sorption run and a 60 ppm S02 sorption run at 500°F.

Figure 3 shows sulfur components released during regeneration of partially saturated Ti02/Pt catalyst/sorber.

Figure 4 shows the amount of S02 captured and released during a 20 minute run and a subsequent reductive regeneration of the Ti02/Pt catalyst/sorber at 500°F.

Figure 5 shows the amount of S02 captured and released during a 20 minute run and a subsequent regeneration of the Ti02/Pt/Cu catalyst/sorber at 500°F.

Figure 6 shows the effect of Cu loading reported as precursor Cu (NO3) 2 on the proportion of H2S and S02 released during 500°F regenerations (Table 4) with the Ti02/Pt/Cu system.

Figure 7 shows 300°F, 60 ppm S02 sorption runs with Ti02/Pt catalyst/sorbers modified with Bi, Ag or Cu.

Figure 8 shows the S02 release during regeneration of Ti02/Pt catalyst/sorbers modified with Bi, Ag or Cu.

Figure 9 shows consecutive 60 ppm S02 cycles with Ti02/Cu sorber/modifier with no noble metal catalyst component at 500°F.

Figure 10 shows the effect of Pt loading reported as wt% of sorber/carrier on the S02 breakthrough during 60 ppm S02 run cycles at 500°F.

Figure 11 shows the effect of oxygen on the S02 sorption for the Ti02/Pt catalyst/sorber system.

Figure 12 shows capture efficiencies obtained during 75 minute 60 ppm sorption cycles with the Ti02/Pt system at 520,620, and 810°F and comparatively the Ti02/Pt/Cu system at 620°F.

Figure 13 shows the H2S sorption with TiO2/Pt and Ti02/Pt/Cu catalyst sorbers with 30 ppm inlet H2S at 500°F.

Figure 14 shows desorption of captured H2S after the sorption run with the Ti02/Pt system illustrated in Figure 13.

Figure 15 shows S02 released during a 900°F desorption with inert gas, which followed a 100 ppm S02 sorption at 500°F.

Figure 16 shows 250 ppm S02 sorption runs following a standard regeneration and following a thermal regeneration with air.

PREFERRED EMBODIMENTS The sorption stage may be carried out at 100 to 1000°F, preferably 300 to 600°F at GHSV 200 to 200,000 hr-1 preferably 1,000 to 120,000 hr-1. The pressures may range from subatmospheric to 500 psig.

The desorption stage may be carried out at 100 to 1000°F, preferably 300 to 900°F at GHSV 20 to 20,000 hr°1

preferably 50 to 10,000 hr-1. The pressures may range from subatmospheric to 500 psig.

By carrying out the present sorption/desorption the sulfur compounds in the feed may be concentrated from 5 to 100 times.

If a carrier is utilized, the carrier may be characterized as ceramic or metal monolith having a honeycomb structure. Preferably a carrier is used to distribute the catalyst/sorber and any modifier. The components are deposited onto the carrier in the proportions desired. The composition of the ceramic carrier can be any oxide or combination of oxides.

Suitable oxide carriers include the oxides of A1, Zr, Ca, Mg, Hf, Ti, and various mixtures of the oxides, such as cordierite and mullite.

The structure and composition of the carrier is of great importance. The structure of the carrier affects the flow patterns through the catalyst/sorber system which in turn affect the transport to and from the catalyst surface. The ability of the structure to effectively transport the compounds to be catalyzed to the catalyst surface influences the effectiveness of the catalyst/sorber. The carrier is preferably macroporous with 64 to 600 cells (pores) per square inch (cpsi) which is about 25 to 80 pores per linear inch (ppi), although carriers having 5 to 90 ppi are suitable The catalyst/sorber may be conditioned by repeated sorption/desorption cycling. The amount of sulfur components released during this conditioning increases with each regeneration until it equals the amount sorbed. It was found that by pretreating the catalyst/sorber with dilute H2SO4, that the conditioning time was dramatically reduced. For example, instead of 12 hours, conditioning after H2S04 treatment only required several hours at 300°F.

The conditioning time was also found to be dependent on the temperature at which the sorption and regenerations were conducted. By increasing the temperature one can increase the amount released, hence, decreasing the conditioning

time. A special conditioning may not be necessary, since the catalyst/sorber will become conditioned after several cycles of sorption/regeneration and remain so thereafter.

The amount of SO2 capable of being consumed by the catalyst/sorber will be referred to as the capacity of the catalyst/sorber. From a short capacity study it was concluded: 1. When the sorption/desorption temperature increases, the capacity increases.

2. When the catalyst/sorber loading is increased, the capacity increases.

3. When the noble metal content in the catalyst/sorber is increased, the capacity increases.

The catalyst/sorber used during this study was coated onto a ceramic honeycomb carrier. The catalyst/sorber/carrier contained 3.48 grams/in3 Ti02/Pt with a platinum content of 0.5%. The capacity of this <BR> <BR> sample was determined to be 20 cc S02/in3. This value was<BR> <BR> determined with an S02 breakthrough less than 10%, hence, 20 cc is a minimum value.

Experimental data gave a S02/Pt mole ratio of 10 during catalyst/sorber saturation. One theory which is not intended to reduce the scope of the present invention is that this large excess of sorbed S02 suggests that the role of the platinum is not of a sorber. The platinum under this theory promotes the sorption of S02 through the catalytic oxidation of SO2 and the sulfur subsequently sorbs onto the conditioned Ti02/Pt surface.

The capacity of a Ti02/Pt/Cu system was examined in a manner similar to that conducted with the Ti02/Pt system.

The results were almost identical. The conclusions were: 1. When the sorption/desorption temperature increases, the capacity increases.

2. When the Ti02/Pt loading is increased, the capacity increases.

3. When the platinum content in the Ti02/Pt is increased, the capacity increases. The copper modifier had little effect on sorber capacity.

According to the present invention sulfur can be captured and released by the catalyst/sorber, for example, a Ti02/Pt system at temperatures as low as 300°F, however, the desorbed components released during regeneration consisted mainly of a mixture of H2S and S02. The ratio of H2S/SO2 depended on residence time and/or the presence of modifiers. In some applications the H2S would not be desirable ; hence it would be preferably to release the sulfur components as 502.

The nature of the desorbed sulfur components can be changed by adding a modifier to the catalyst/sorber. A variety of modifiers have been utilized but to date the most efficient have been copper, silver and bismuth. It was found that the addition of modifiers to the catalyst sorber increased the release of sulfur as S02 and diminish or inhibit the formation of H2S. The modifiers may be deposited directly onto the catalyst/sorber or deposited within. A variety of modifies were determined to work; however, the most efficient were found to be copper, bismuth, and silver.

Modifiers were also examined without a noble metal, e. g., Pt, i. e., sorber only in the washcoat, for example Tio2/Cu. Although many were examined and found to capture the sulfur, the release of the S02 or H2S during regenerations was not accomplished and the sorbers soon became saturated. This is illustrated in Figure 9 where consecutive 60 ppm S02 sorption cycles were carried out with a Tio2Cu sample. Intermediate regenerations followed each sorption cycle. The results show decreasing removal efficiency with each run.

By adding the modifier, e. g., Cu to the catalyst/sorber, the S02 captured during the sorption cycles was found to be released during the standard regeneration cycles. This is illustrated in Figure 5 where both the sorption and desorption cycles reached 7.7 cc SO2.

The sulfur released during the regeneration was SO2. No H2S was detected during this regeneration.

The Cu (N03) 3 precursor loading on the catalyst/sorber used in Figure 5 was 0.3 g/in3. Figure 6 illustrates the effect of the Cu (N03) 3 loading on the proportion of sulfur released as S02 and H2S. This figure demonstrates that in the vicinity of 0.3 g/in3 and greater, all the sulfur compounds released during the regenerations was released as S02 ; however, below 0.3 g/in3 H2S is released and the amount of H2S released increases with decreasing Cu (N03) 3 loading. This effect was also observed with the other Ti02/Pt/X (where X is the metal modifier as defined) modifiers such as the bismuth and silver. The ability to change the H2S/SO2 ratio with modifier loading is a tremendous asset of this new technology. The ability to adsorb sulfur from a dilute stream and then release it in a concentrated stream with appropriate H2S/SO2 ratio for use in the Claus process has not been heretofore disclosed.

Figure 6 clearly illustrates that the Cu (N03) 2 loading can be used for this purpose.

Figure 12 shows the S02 removal efficiency of the Ti02/Pt system at various temperatures and the removal efficiency of the Ti02/Pt/Cu system at 620°F. From this figure, it is evident that the capacity of the Ti02/Pt system increases with temperature. The role of the copper and other modifiers appears to reside only in changing the regeneration of the catalyst to diminish H2S formation.

By increasing the S02 inlet concentration or lengthening the sorption time, the Ti02/Pt catalyst/sorber will eventually become saturated; hence, producing S02 breakthrough. This is illustrated in Figure 2 where both a 500 ppm and a 60 ppm sorption run were conducted for 10 minutes.

Figure 2 shows that there is no evidence of SO2 breakthrough during the 60 ppm run. The 500 ppm run, in contrast, does show breakthrough. During this sorption run, the S02 breakthrough is relatively low (<40 ppm) for the first 3 minutes, however, after 3 minutes the SO2 breakthrough increases dramatically. This breakthrough

results when the majority of sorption sites have been consumed.

EXAMPLES The catalyst/sorbers used in the examples were prepared on 200-cell-per-square-inch cordierite square-cell honeycomb. The Tio2/Pt washcoat was prepared by incipient wetness. Pt content ranged from 0.1 to 2.2%. After drying and calcining at 500°C, the solids were then dispersed in 7% acetic acid and ball milled overnight. The ceramic honeycombs were then dipped into the slurry of washcoat/Pt, removed, blown off, and then dried at 150°C.

The Ti02/Pt/X samples were prepared by immersing the Ti02/Pt honeycomb sample into a modifier solution. The sample was then removed, blown off, and finally dried at 150°C. The catalyst/sorbers had a nominal composition as shown in Table 1.

Table 1: Catalyst/sorber Composition (except as otherwise noted): Ti02 0.4 - 3.5 g/in3 Pt 0 -. 08 g/in3 X 0 - 0. 3 g/in3 For testing, the samples were placed into a 304 stainless steel tubular reactor and placed inside a three- zone furnace. The reactor was connected to a gas delivery system which delivered mixed gases simulating a gas turbine exhaust. The gases were measured and controlled by Matheson mass flow transducers. Water was injected into a preheat furnace using a Cole Palmer instrument number 74900 precision syringe pump. Unless stated otherwise, the test gas compositions are given in Table 2. All sorption runs were conducted with a space velocity of 30,000 hr-1.

Table 2: Test Gas Compositions Gas Component Concentration S02 30-500 ppm 02 14-52 0 C02 3. 05% H20 10. 20% 2 Balance

Before passing processed gas through the analytical instruments, the water was removed with a chiller. The dried exhaust was then analyzed with the instruments shown in Table 3. To measure H2S, the exhaust was first directed through a H2S to S02 converter. This converter consisted of a heated (900°F) stainless steel tube. During regenerations, oxygen was added to the exhaust before entering the converter. Laboratory tests with calibration gas showed virtually 100% H2S conversion to SO2. During some experiments the H2S was measured with a BOVAR model 922 analyzer.

Table 3: Analytical Instruments Used During Testing Gas Constituent Instrument S02 BOVAR model 721-M CO TECO model 48 NO, NO2 TECO model 10S NH3 TECO model 300/10S C02 Horiba model DIA 510 H2S BOVAR model 922 Standard regeneration cycles were conducted with the gas composition given in table 4 at a space velocity of 2000 hr-1.

Table 4: Regeneration Gas Composition Gas Component Concentration CO 0.02% C02 1.00% N2 57.14% H20 40. 84% H2 4.00% Catalyst Preparation The catalyst for the following examples was prepared as follows: - Ceramic honeycomb carrier.

- Sorber component of 2.2 g/in3.

- Platinum loading from 0.25 to 1.1 wt % of the sorber component.

- Metal modifier prepared with the metal nitrate precursor (0.00 to 0.30 g/in3).

Example 1 Example 1 shows 30 minute, 30 ppm S02 sorption runs with the Ti02 Ti02/Pt, Zr02/Pt and CeO2/Pt systems at 300°F. With the Ti02 sample there is little S02 capture, however, the Ti02/Pt, Zr02/Pt, and CeO2/Pt catalyst/sorbers gave significant S02 captured as shown in Figure 1. This illustrates the effectiveness of the Ti, Zr, and Ce and the importance of the noble metal component. Ti02 loading 2.18g/in3 ; X02/Pt loading 2.18g/in3 ; 1.1% Pt where X = Ti, Zr, or Ce.

Example 2 Example 2 illustrates the effect of inlet S02 concentration (60 ppm vs 500 ppm) during 10 minute, 500°F sorption runs with a Ti02/Pt catalyst/sorber (2.18g/in3 ; 0. 5% Pt). Figure 2 shows S02 breakthrough with the higher (500 ppm) S02 inlet. This breakthrough results when the catalyst/sorber becomes saturated. After or during saturation, the catalyst/sorber can be revitalized with a reducing gas or a thermal desorption.

Example 3 Example 3 shows the regeneration of a partially saturated Ti02/Pt catalyst/sorber at 500°F. Regeneration of the catalyst/sorber revitalizes the sorber and produces a concentrated stream of sulfur compounds with the primary compound being H2S. The regeneration cycle was about 10 minutes as shown in Figure 3.

Example 4 Example 4 shows the amount of sulfur captured and released with a Ti02/Pt catalyst/sorber during a 30 minute, 30 ppm SO2 sorption cycle at 500°F and a standard desorption cycle at 500°F. The results in Figure 4 show that the amount of sulfur compounds desorbed was equivalent to the amount of SO2 sorbed during the previous sorption cycle and that the desorbed gas was composed of a mixture of H2S and SO2.

Example 5 Example 5 shows the amount of sulfur sorbed and desorbed with a Ti02/Pt/Cu sample during a 20 minute, 60

ppm S02 sorption cycle at 500°F and a standard desorption cycle at 500°F. The results in Figure 5 demonstrates that the amount of sulfur components desorbed was equivalent to the amount of S02 sorbed during the previous sorption cycle and that the components desorbed was primarily SO2.

Example 6 Example 6 shows the effect of copper loading (metal modifier) on the proportion of sulfur released as S02 or H2S during regeneration cycles of partially saturated Tio2/Pt catalyst/sorber. This example shows in Figure 6 that with 0.3 g/in3 of Cu (N03) 2 and higher, all the sulfur is released as SO2. With no Cu (N03) 2,90% of the sulfur is released as H2S and 10% is releases as SO2. This effect was also obtained with other modifiers.

Example 7 Example 7 shows the S02 capture during 20 minute, 60 ppm sorption cycles using Ti02/Pt with Cu, Ag and Bi modifiers (Ti02/Pt/Cu 2.18 g/in3; 1.1% Pt; 0.3 g/in3 X (N03) y; where X=Cu, Ag, Bi). All exhibit similar characteristics with initially 100% capture efficiency until reaching a point where S02 breakthrough begins. The amount of breakthrough then steadily increases with time as can be seen in Figure 7.

Example 8 Example 8 demonstrate the S02 released during the regeneration of Ti02/Pt catalyst/sorber with Bi, Ag, and Cu metal modifiers. These regenerations followed 20 minute, 30 ppm S02 sorption cycles and appear to be almost identical with liberation of SO2 as shown in Figure 8.

Example 9 Example 9 illustrates consecutive 60 ppm S02 sorption cycles with a Ti02/Cu modifier/sorber (2.18g/in3 Ti02 0.3g/in3 Cu (N03) 2) with no noble metal component at 500°F.

This result shown in Figure 9 illustrates that the TiO2/metal modifier will capture the sulfur, however, the catalyst/sorber is not regenerated during the regeneration cycle.

Example 10 Example 10 illustrates the effect of Pt loading on the S02 breakthrough during 60 ppm S02 sorption cycles with a Ti02/Pt/Cu catalyst/sorber (2.18 g/in3 Ti02/Pt : 0.3 g/in3 Cu (N03) 2) at 500°F. Figure 10 shows that the efficiency of the Ti02/Pt/Cu is directly related to the Pt loading, such that the higher the loading the higher the sulfur capture capacity.

Example 11 Example 11 illustrates the effect of oxygen in the flue gas during 25 minute, 250 ppm S02 sorption cycles with a Ti02/Pt/Cu catalyst sorber at 500°F. Figure 11 shows that sorption of the sulfur components is significantly reduced in the absence of oxygen.

Example 12 Example 12 shows the sulfur removal efficiency obtained during 75 minute, 60 ppm S02 sorption runs with a Ti02/Pt catalyst/sorber at various temperatures and a Ti02/Pt/Cu catalyst/sorber at 620°F is shown. Figure 12 shows that the removal efficiency increases with temperature and that the removal efficiency is slightly decreased by the addition of the metal modifier.

Example 13 Example 13 shows that H2S is removed during sorption cycles with both the Ti02/Pt and Ti02/Pt/Cu catalyst/sorbers at 500°F. Figure 13 shows the results and demonstrates that H2S is also captured by the catalyst/sorbers.

Example 14 Example 14 shows that sulfur is released primarily as H2S during a desorption run of a partially saturated Ti02/Pt catalyst sorber at 500°F. The preceding sorption run utilized a 20 minute, 20 ppm H2S cycles at 500°F. This result, shown in Figure 14, demonstrates that the catalyst/sorbers can be regenerated after H2S capture.

Example 15 In this Temperature Programmed Desorption (TPD) experiment a 4-minute sorption cycle with 100 ppm of S02

was conducted at 300°F (13 cc Ti02/Pt 3.0 g/in3 Ti02 : 1. 1% Pt), space velocity = 30,000 hr-1). After the temperature was increased to 900°F, nitrogen was then passed over the catalyst as a space velocity of 30,000 hr-1. From the TPD experiment it was determined that all the sulfur captured during the 4 minute run cycle was released during the high temperature regeneration; however, no H2S was detected, hence all the sulfur released was in the form of SO2.

This illustrates that the H2S formation occurs only in the presence of the H2. Figure 15 shows that the sulfur is released in two pulses. The first being much sharper than the second.

Example 16 In this Temperature Programmed Desorption (TPD) experiment a 10 minute sorption cycle with 250 ppm of 502 was conducted at 500°F (13 CC Ti02/Pt 3.0 g/in3 Ti02 : 1. 1% Pt), space velocity = 20,000 hr-1). After the temperature was increased to 900°F, air (approximately 20. 90 02) was then passed over the catalyst for 10 minutes at a space velocity of 10,000 hr-l. During the desorption no S02 or H2S was detected, however, continuous cycling showed that the Ti02/Pt catalyst/sorber was revitalized during each 900°F air regeneration. This is illustrated in Figure 16.

The regeneration gas was also bubbled through isopropanol and analyzed for sulfur. A significant amount of dissolved sulfur was found suggesting that S03 was released during regenerations.