Patent Application: US-201414470289-A

Abstract:
a hydrogen sulphide adsorbent is formed from an alkali metal nanotitanate having a portion of the alkali metal cations exchanged with metal cations reactive with hydrogen sulphide , and heat treated . a method for producing the adsorbent includes the steps of mixing an alkali metal nanotitanate in powder form into an aqueous metal cation solution to produce a slurry , which is subsequently dehydrated to produce a powder , which is heat treated . a low temperature method for removing hydrogen sulphide from a gaseous mixture involves exposing the gaseous mixture to the aforementioned adsorbent , at a temperature less than 250 ° c . the adsorbent maintains a high adsorption capacity over a range of activation temperatures and humidity conditions .

Description:
the present invention relates to a hydrogen sulphide adsorbent . when describing the present invention , all terms not defined herein have their common art - recognized meanings . to the extent that the following description is of a specific embodiment or a particular use of the invention , it is intended to be illustrative only , and not limiting of the claimed invention . the scope of the claims should not be limited by specific embodiments set forth in the description or the examples , but should be given the broadest interpretation consistent with the description as a whole . to facilitate understanding of the invention , the following definitions are provided . “ breakthrough capacity ” means the capacity of an adsorbent bed at which unadsorbed gas begins to be emitted at a concentration of 0 . 5 ppm . “ ets zeolite ” refers to a family of crystalline titanium silicate molecular sieve zeolites as disclosed in u . s . pat . no . 4 , 853 , 202 and u . s . pat . no . 4 , 938 , 939 ( the entire contents of both which are incorporated herein by reference , where permitted ), referred to as ets , including family members ets - 1 , ets - 2 , ets - 4 and ets - 10 . the thermal stability of ets - 4 and ets - 10 have been reported in the literature . an investigation into the thermal stability of ets - 4 activated at different temperatures in the air showed a partial loss of crystallinity at temperatures equal to or greater than 200 ° c . and complete collapse of the crystalline structure at 500 ° c . ( naderi et al ., 1996 ). however , it has been shown that ets - 10 is stable at a wider temperature range up to 550 ° c . ( anderson et al ., 1995 ) and that copper exchanged ets - 10 is stable up to 550 ° c . ( gervasini et al ., 2000 ). “ ets - 2 ” refers to a titanium oxide phase essentially devoid of silica , as disclosed in u . s . pat . no . 4 , 853 , 202 to kuznicki , examples of which may have an x - ray diffraction ( xrd ) pattern having the significant lines and relative intensities as set forth in table 1 . ets - 2 is a high surface area sodium nano - titanate with superior ion - exchange capabilities formed by the alkaline digestion of tio 2 . the caustic digestion converts the surface of the tio 2 particles into sodium titanate , which is an effective ion - exchanger ; particularly for transition metals . the material has no measurable microporosity which makes it immune to pore blockage or capillary condensation . having no measurable microporosity , its surface area can be as high as 250 m 2 / g due to the nano - scale particles . ets - 2 particles are on the order of 50 - 100 nanometers long . the core of these particles is presumed to be tio 2 while the surface titania species carry a net negative charge which is offset by sodium ions . “ ets - 4 ” refers to a crystalline titanium silicate molecular sieve zeolite , as disclosed in u . s . pat . no . 4 , 938 , 939 to kuznicki , having a pore size of approximately 3 to 5 angstrom units and a composition in terms of mole ratios of oxides as follows : wherein m is at least one cation having a valence of n , y is from 1 . 0 to 100 , and z is from 0 to 100 , said zeolite being characterized by an xrd pattern having the lines and relative intensities set forth in table 2 . “ ets - 10 ” refers to a crystalline titanium silicate molecular sieve zeolite , as disclosed in u . s . pat . no . 4 , 853 , 202 , having a pore size of approximately 8 angstrom units and a composition in terms of mole ratios of oxides as follows : wherein m is at least one cation having a valence of n , y is from 2 . 5 to 25 , and z is from 0 to 100 , said zeolite being characterized by an xrd pattern having the lines and relative intensities set forth in table 3 . “ xrd pattern ” refers to an x - ray powder diffraction pattern for a substance as determined using standard crystallography techniques , and is defined by lines having d - spacings expressed as two times the bragg angle , and relative intensity i / i 0 wherein i is the intensity count of the line and i 0 is the intensity count of the strongest line in the pattern , as read from a scintillation counter spectrometer chart . in one aspect , the invention comprises novel alkaline metal nanotitanates which have been ion exchanged with a metal which his reactive with hydrogen sulphide , such as barium , copper or zinc . in embodiments , these materials exhibit high exchange capacity for solution cations of 7 meq / g of titanium oxide , all on crystallite exteriors with surface areas of approximately 250 to 300 m 2 / g . in one embodiment , the nanotitanates comprise an ets zeolite such as ets - 2 , ets - 4 or ets - 10 . in one embodiment , and without restriction to a theory , it is believed that effective forms of the metal ion - exchanged ets zeolite are converted to an amorphous form during ion - exchange . the amorphous forms may be characterized by having metal ion - to - titanium atomic ratio of greater than 0 . 05 , preferably greater than 0 . 10 , and more preferably greater than about 0 . 20 . in one embodiment , it may be about 0 . 21 . the amorphous forms may also be characterized by having a sodium - to - titanium atomic ratio of less than about 0 . 12 , preferably less than about 0 . 10 , and more preferably equal to or less than about 0 . 05 . in one embodiment , the morphology of the ion - exchanged ets zeolite is not significantly changed by the metal exchange process . preferably , xrd patterns do not reflect any significant diffraction peaks for compounds of the exchanged metal cation . the metal - exchanged ets zeolite may be formed by suspending a slurry of the ets zeolite in an aqueous solution of the metal salt for a sufficient period of time , in one embodiment , the weight proportion of the ets to metal salt to water may be 1 : 2 : 10 . heat may increase the rate of reaction , allowing the metal exchange to take place more quickly . thus , the slurry may be heated , for example to about 80 ° c . the ion - exchanged ets zeolite may then be filtered and washed with de - ionized water , and dried to produce a metal ion - exchanged powder . in another aspect , the invention may comprise a method of adsorbing hydrogen sulphide in a gas stream , using the metal ion - exchanged ets zeolites described herein . the metal ion - exchanged ets zeolites may be formed into particulates and used in a fixed bed , fluidized bed , or semi - fluidized bed reactors , or may be packed into a column or cartridge through which the gas stream flows . embodiments of the present invention are further described by way of the following examples , which are not intended to be limiting of the claimed invention . this example describes the preparation of three embodiments of the adsorbent using ets - 2 , ets - 4 and ets - 10 , respectively . ets - 2 , ets - 4 and ets - 10 were hydrothermally synthesized in accordance with the method disclosed in u . s . pat . no . 4 , 853 , 202 . in general , the method involves the following steps : preparing a reaction mixture of a titanium source , a silica source , an alkaline source , water , and optionally an alkali metal fluoride , with a certain range of mole ratios ; heating the reaction mixture ; allowing crystal formation ; and separating , washing , and drying the crystalline ets product . the silica source was sodium silicate ( 28 . 7 % sio 2 , 8 . 9 % na 2 o ) for each of ets - 2 , ets - 4 and ets - 10 . the titanium source was solid titanium ( iii ) oxide ( ti 2 o 3 ) for ets - 2 , and solubilized titanium ( iii ) chloride ticl 3 for ets - 4 and ets - 10 . copper ( ii ) nitrate ( cu ( no 3 ) 2 ) salt was added to water to create an aqueous copper nitrate solution in three separate vessels . the synthesized ets - 2 , ets - 4 and ets - 10 were each added in powder form to the aqueous copper ( ii ) nitrate solution in one of the vessels and agitated to create three slurries . in each of the slurries , the weight proportion of the ets to salt to water was 1 : 2 : 10 . the vessels containing the slurries were heated in an oven at 80 ° c . for approximately 18 hours . the samples were filtered and washed with de - ionized water and dried overnight at 80 ° c . to produce a cu - exchanged powder . the cu - exchanged powder was mixed with colloidal silica preparation ( sigma - aldrich ™ ludox ® hs - 40 , 40 wt . % suspension in water ) to produce a relatively dry adsorbent mixture . the adsorbent mixture was then placed in a cylindrical mold ( 2 . 54 cm in diameter ), and compressed in an axial press at a force of 6 metric tonnes for 1 minute to produce an adsorbent disk . the adsorbent disk was crushed and sieved to obtain adsorbent pellets having a standard mesh size of 20 - 50 mesh . the adsorbent pellets were heated in a muffle furnace , at a rate of approximately 4 ° c . per minute , to the desired activation temperature , and an isothermal dwell time of 2 hours . for comparative purposes , three metal oxide samples were also obtained from basf chemical company : r3 - 11g ( 36 wt . % cuo ); r3 - 12 ( 40 wt . % zno and 40 wt . % cuo ); and zinc oxide ( 100 wt . % zno ). the metal oxide samples were used as received and sieved to obtain pellets having a standard mesh size of 20 - 50 mesh . table 4 below summarizes the loading weights of the copper and zinc , as the case may be for the adsorbent samples . this example describes testing of the adsorbent performance of the samples prepared as described in example 1 . the following testing procedure was followed separately with respect to each of the adsorbents . a 50 mg sample of the pelletized adsorbent was packed between glass wool plugs in a stainless steel column having a length of 4 cm and an inside diameter of 0 . 38 cm to form an adsorbent bed within the column . the adsorbents were activated at a temperature of 100 ° c . the outlet of the column was connected to a gas chromatograph equipped with an column ( restek corporation ™ mxt ®- 1 ) having a length of 60 m and an internal diameter of 0 . 53 mm and a flame photometric detector ( fpd ) ( sri instruments ™) able to detect h 2 s at concentrations of 200 ppb . n 2 gas with 10 ppm h 2 s was continuously flowed through the adsorbent at a rate of 100 ml per minute , as controlled by needle valves and as measured using a bubble flow meter . it was noted that the cu - ets - 2 pellets changed from blue - green to dark olive green with exposure to h 2 s . the breakthrough capacity of the adsorbents was determined as the time required to first measure an h 2 s concentration at the outlet of the stainless steel column of 0 . 5 ppm using the gas chromatograph . atomic absorption spectrophotometry was used to analyze the copper content ( wt . %) in cu - ets - 2 , cu - ets - 4 and cu - ets - 10 . a quantity of the adsorbent was weighed using a balance with 0 . 1 mg resolution . nitric acid was then added to the sample to extract the copper species and build - up 10 milliliters of solution . the copper concentration in the solution was subsequently measured with atomic absorption spectrophotometer ( varian 220fs ). in addition , the metal ion utilization rate was determined by converting the time of the breakthrough capacity to moles of h 2 s , and then dividing that value by the moles of copper on the adsorbent sample as measured by atomic adsorption . table 4 below summarizes the results of the copper contents and metal utilization rates for each of the adsorbents . without restriction to any theory , it is believed that the different copper utilization rates for cu - ets - 4 , cu - ets - 2 and cu - ets - 10 can be explained by their microstructure . cu - ets - 4 and cu - ets - 10 both have crystalline microporous frameworks . in cu - ets - 4 , the pore blockage effect may explain the relatively low copper utilization rate . that is , in crystalline materials with very small pores and channels in their structure , the copper in sites nearest to the exposed surface of the adsorbent reacts first . the copper and h 2 s react to form copper sulphide which partially blocks the pore openings , thereby impeding gas from accessing the rest of the crystal ( kyotani et al ., 1989 ). in cu - ets - 10 , the larger pore diameter allows atomic dispersion of copper in the microporous framework and allows gas passage even if a channel is partially blocked , thereby allowing an almost complete copper utilization rate . unlike cu - ets - 4 and cu - ets - 10 , cu - ets - 2 has a non - porous structure composed of finely divided nano - sized platelets that provide a relatively high external surface area . the substantial , but incomplete , copper utilization of cu - ets - 2 may be due to inconsistencies in the sample structure that prevent some of the exchanged copper ions from reacting with h 2 s , or may be the result of active copper sites being blinded by copper sulphide formation on the surface of the particles . fig1 illustrates the time to breakthrough capacity of the cu - ets - 2 adsorbent compared to r3 - 11g , r3 - 12 and zno adsorbents . cu - ets - 2 had a time to breakthrough capacity of approximately 27 hours . among the commercial adsorbents , only r3 - 11g had a time to break - through capacity that surpassed that of cu - ets - 2 . however , as shown in table 4 , the copper utilization rate of r3 - 11g is lower than that of cu - ets - 2 . without restriction to any theory , it is believed the copper and h 2 s react to form dense copper sulphide which blinds the r3 - 11g particles to further reaction with h 2 s ( kyotani et al ., 1989 ). in contrast , it is believed that the significantly higher copper utilization rate for cu - ets - 2 is attributable to an increase in the dispersion of copper in the ets - 2 support via ion - exchange . this example compares the effect of humidity on the performance of cu - ets - 2 and r3 - 11g . cu - ets - 2 and r3 - 11g were exposed to h 2 s at an inlet concentration of 10 ppm , at ambient temperature , and a relative humidity of 45 percent . fig2 shows the h 2 s breakthrough capacity per gram of adsorbent , and fig3 shows the copper utilization rate calculated on a mole / mole basis , under these conditions . the cu - ets - 2 adsorbent exhibits a higher breakthrough capacity than r3 - 11g , which corresponds to an approximately four - times higher copper utilization rate than r3 - 11g . in view of the results in table 4 , the performance of cu - ets - 2 in terms of copper utilization rate is relatively less sensitive to humidity , than the performance of r3 - 11g . this example describes the testing of cu - ets - 2 prepared as described in example 1 , and subjected to testing as described in example 2 except at different activation temperatures . fig4 shows the h 2 s breakthrough capacity per gram of cu - ets - 2 adsorbent samples after exposure to temperatures ranging from as - prepared temperature to 600 ° c . the h 2 s breakthrough capacity of cu - ets - 2 remains relatively unchanged even after the material has been exposed to temperatures of up to 500 ° c . the decrease in breakthrough capacity after exposure to temperatures exceeding 500 ° c . correlates with an increase in the intensity of anatase reflections seen in the xrd patterns and is attributed to a re - crystallization event which renders cu - ets - 2 inactive toward h 2 s , as discussed under example 5 below . this example describes the morphology and composition of cu - ets - 2 prepared as described in example 1 at different activation temperatures . cu - ets - 2 samples in powder form were dispersed in methanol in an ultrasonic bath for 10 minutes . one or two drops of the suspension was placed on a carbon type b , au grid ( 300 mesh ) and dried prior to analysis . the samples were then deposited in a transmission electron microscope ( tem ) ( jeol ltd . model 2010 ) and subjected to selected area electron diffraction ( saed ) to analyze the structure of the sample , and point - specific energy dispersive x - ray spectroscopy ( edx ) to analyze the elemental composition of different components of the sample . the results of the tem imaging and saed analysis revealed the presence of a crystalline needle - like component and a non - crystalline amorphous component in the cu - ets - 2 . the structure is non - porous . fig5 and 6 depict the tem images of the crystalline needle - like component and the non - crystalline amorphous component , respectively , of ets - 2 . fig7 and 8 depict the tem images of the crystalline needle - like component and the non - crystalline amorphous component , respectively , of cu - ets - 2 . as can be seen , the copper ion exchange process in the preparation of cu - ets - 2 from ets - 2 does not change the morphology of ets - 2 . the edx analysis results , as summarized in table 5 , indicate that the crystalline component of cu - ets - 2 contained predominantly sodium ions , and a relatively low copper to titanium content . the amorphous component of cu - ets - 2 has a relatively high copper to titanium content , which is approximately 10 times higher than that of the crystalline component of cu - ets - 2 . for this reason , it is believed that the amorphous component of cu - ets - 2 is principally responsible for h 2 s adsorption . in addition , the cu - ets - 2 samples at different activation temperatures were subjected to xrd analysis using a diffractometer ( rigaku geigerflex ™ model 2173 ) equipped with a cobalt rotating anode source ( wave length of 1 . 79021 å ) and a graphite monochromator for filtering the k - beta wavelengths . fig9 shows the xrd patterns for ets - 2 and as - prepared cu - ets - 2 . the xrd pattern for cu - ets - 2 indicate that it has a semi - crystalline morphology , with the crystalline component detected in the tem analysis being a minor phase relative to the amorphous component . the xrd patterns also indicate that the copper - ion exchange process in the preparation of cu - ets - 2 does not introduce any significant changes to the ets - 2 morphology . further , the absence of diffraction peaks for copper compounds , confirms the high atomic dispersion of copper ions in the ets - 2 structure . fig1 shows the xrd patterns for cu - ets - 2 samples exposed to different activation temperatures . the xrd pattern of cu - ets - 2 activated at 700 ° c . shows reflections for anatase ( tio 2 ) and copper oxide ( cuo ). the emergence of these crystalline phases suggests that the amorphous components of cu - ets - 2 change to crystalline components at higher activation temperatures . in addition , the surface areas of ets , as - prepared cu - ets - 2 , ets - 2 and commercial adsorbents were measured by n 2 adsorption using a volumetric measuring system ( quantachrome instruments autosorb - 1 ™). the surface areas of the material were calculated using the bet method , which is most appropriate for ets - 2 as it is composed of platelets having an exposed surface area rather than a macroporous structure . table 6 summarizes the specific surface areas of ets - 2 and the adsorbents . the following references are incorporated herein by reference ( where permitted ) as if reproduced in their entirety . all references are indicative of the level of skill of those skilled in the art to which this invention pertains . abbasian , j ., hill , a . h ., wangerow , j . r ., flytzani - stephanopoulos , m ., bo , l ., patel , c ., & amp ; chang , d . 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