Abstract:
A highly effective catalyst for the preparation of diethyl oxalate using carbon monoxide using Pd/α-Al 2 O 3  and CeO 2  as a promoter. High conversion rates with greatly extended catalyst life is achieved with the CeO 2 -enhanced Pd catalysts. The catalysts can be used for the production of high-value diethyl oxalate, and eventually ethylene glycol, from coal-derived syngas.

Description:
CLAIM OF PRIORITY 
       [0001]    This application claims priority to U.S. patent application Ser. No. 62/018,471, filed Jun. 27, 2014, and which is incorporated herein in its entirety by this reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates generally to catalysts of the production of diethyl oxalate from carbon dioxide and, more specifically, to highly effective palladium catalysts promoted with cerium. 
         [0003]    Ethylene glycol (EG) is a crucial raw material with a global demand of around 25 million tons each year, which is mostly produced through traditional petrochemical technology.[1,2] However, the cost of this production is relatively high due to the continuous increasing price of natural gas and crude oil, and dwindling sources of petroleum. Furthermore, strong acids or alkalis such as sulfuric acid or sodium hydroxide have to be used through the traditional method, which causes severe corrosion to the equipment and environmental problems.[3] Therefore, a green route which is independent of petroleum while achieves high yield of EG is in demand and of great significance. 
         [0004]    Coal is the most abundant energy reserve in the world that some people like because of their needs while others hate due to the various emissions resulting from its combustion.[4] To reduce CO 2  emission and produce high-value fuels and chemicals from coal, coal gasification and liquefaction technologies have attracted increasing interest during the past few decades.[5-8] Coal to ethylene glycol, as a potentially green and economic coal liquefaction technology, has been attracting extensive attention in both academic and business circles in the past decades.[9-12] Although it is challenging to achieve high industrial production levels, due primarily to achieving good performance of the catalysts, this technology has been scaled-up to industrial levels of production in China and Europe. Until now, China leads the word in this area and successfully built the world&#39;s first annual 200 thousand tons coal to ethylene glycol production plant in 2009.[13] 
         [0005]    Syngas to ethylene glycol contains several steps and the step of CO oxidative coupling to di-alkyl oxalate is the critical step since di-alkyl oxalate is required for hydrogenation to EG. 
         [0000]      2 CO+2RONO→(COOR) 2 +2NO   (1)
 
         [0000]      2ROH+2NO+½O 2 →2RONO+H 2 O   (2)
 
         [0006]    Two main chemical reactions are involved in the CO oxidative coupling step, coupling reaction and regeneration reaction which are shown in Eq. (1) and (2) separately. The reaction in Eq. (1) occurs on supported metal catalysts, where R could be methyl, ethyl or butyl groups. The regeneration reaction shown in Eq. (2) doesn&#39;t need any catalyst. Esterification between oxalic acid and alcohol has been employed as a traditional way of synthesizing oxalic ester. However, this method has several problems, such as severe pollution, high energy consumption and high upfront costs. Therefore, oxidative coupling reaction of CO and alkyl nitrite, forming oxalic ester, has been extensively researched in the past decades.[3,14-20] 
         [0007]    Various supported palladium catalysts for gas-phase synthesis of dimethyl oxalate (DMO) or diethyl oxalate (DEO) have been investigated, and the results have demonstrated that higher conversion and selectivity are realized on Pd/α-Al 2 O 3  compared to Pd on active carbon or γ-Al 2 O 3 .[21,22] However, the relatively high Pd loading (around 2 wt %) is always an issue for industrial application of CO oxidative coupling to OMO, which will greatly increase the cost of production. Therefore, the design of low Pd loaded catalysts with high performance is important to industry. A Pd/α-Al 2 O 3  nanocatalyst with ultra-low Pd loading that exhibits high activity and stability for CO oxidative coupling to DMO was developed recently.[23] This catalyst was prepared by a Cu 2+  assisted in situ reduction method at room temperature, which significantly increased the dispersion and the specific area of active component Pd, and also decreased the ensemble size of Pd nanoparticles dispersed over the Pd/α-Al 2 O 3 . The average size of Pd nanoparticles is 2.7 nm, and the Pd loading could be as low as 0.13 wt %. To further enhance the activity and stability of Pd/α-Al 2 O 3 , several metals such as Fe,[24,25] Ni and Ce were reported as promoters to enhance the dispersion of Pd on the support or decrease the Pd particles size.[24-27] CeO 2  was reported as a promoter and in spite of the reaction was evaluated only within 100 min, Pd—CeO 2 /α-Al 2 O 3  catalyst showed around 20% higher catalytic activity compared to Pd/α-Al 2 O 3  catalyst (without CeO 2 ) for the synthesis of DMO from CO and methyl nitrite.[28] 
         [0008]    Although methyl nitrite has been maturely used, especially in China, for the industrial synthesis of DMO, it is controlled in the US due to its highly flammable, highly explosive and toxic properties. Ethyl nitrite, however, is another safe and non-explosive alkyl nitrite that also can be used for CO oxidative coupling reaction.[18,20,29-31] Therefore, to find a good catalyst with low Pd loading and high catalytic activity for CO oxidative coupling to DEO is of great significance in the US. Herein, we report a Pd—CeO 2 /α-Al 2 O 3  nanocatalyst with 0.8% Pd (wt %) loading and 0.2 wt % Ce0 2  as a catalyst for CO oxidative coupling to DEO. We present the preparation and characterization of two catalysts with and without CeO 2  as a promoter. The comparison of catalytic activities between the two catalysts is discussed and the interaction among Pd, ceria and the support leading to the activity differences is also presented. 
       SUMMARY OF THE INVENTION 
       [0009]    The present invention involves highly effective catalysts for preparation of diethyl oxalate (DEO) using CO from coal-derived syngas. Pd/α-Al 2 O 3  nanocatalysts were synthesized and CeO 2  was used as a promoter. The nanocatalysts were characterized with various techniques including X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electronic microscopy (TEM), scanning transmission electronic microscopy (STEM) and scanning electronic microscopy (SEM), and evaluated with a packed bed reactor. The obtained best catalyst contains of 0.9 wt % Pd and 0.2 wt % CeO 2  with its size and specific surface area being 13 nm and 5.6 m 2 /g, respectively. The catalyst promoted with CeO 2  achieved as high as 62% CO conversion, more than 50% increase compared to that without CeO 2 , while the same DEO selectivity (93%). Moreover, the high CO conversion maintained as long as 72 h, about 42 times longer than that reported in literature. Therefore, a CeO 2  promoted Pd/α-Al 2 O 3  is a highly active and stable nanocatalyst for production of high-value DEO and eventually EG from coal-derived syngas. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a schematic diagram of the apparatus used in the conversion of ethylene nitrite to diethyl oxalate. 
           [0011]      FIG. 2  shows the TEM results (a) and the size distribution of the Pd/α-Al 2 O 3  catalyst (b) and the TEM results (c) and size distribution of the Pd—CeO 2 /α-Al 2 O 3  catalyst (d). 
           [0012]      FIG. 3  shows the Pd 3d XPS spectra of catalysts Pd/α-Al 2 O 3  (a) before and (b) after reaction and Pd—CeO 2 α-Al 2 O 3  (c) before and (d) after reaction. 
           [0013]      FIG. 4(   a ) is a chart of the conversion of CO (blue lines) and EN (red lines) of CO oxidative coupling to DEO with different catalysts within 72 h;  FIG. 4(   b ) DEO selectivity of CO oxidative coupling to DEO with different catalysts within 72 h. 
           [0014]      FIG. 5  are graphs of the in situ FTIR spectra for the CO oxidative coupling to DEO reaction with Pd/α-Al 2 O 3  (a) and Pd—CeO 2 /α-Al 2 O 3  (b). 
           [0015]      FIG. 6(   a ) is a graph of the conversion of CO (blue lines) and EN (red lines) of CO oxidative coupling to DEO at different reaction temperatures (reaction conditions: 3.5 g of Pd—CeO 2 /α-Al 2 O 3  catalyst, 1200 h-1 of gas hourly space velocity; reactant&#39;s volume ratio CO/EN is 1.2, 0.1 Mpa), and 
           [0016]      FIG. 6(   b ) is a chart of the DEO selectivity of CO oxidative coupling to DEO with different reaction temperatures. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0017]    As used herein, a “promoter” or “enhancer” is a chemical that is added to a catalyst to improve the performance of the catalyst in catalyzing a chemical reaction. 
         [0018]    The Pd catalysts promoted by CeO 2  of the present invention had optimal performance characteristics when used at a Pd loading of between 0.1 wt % and 1.2 wt %, more preferably between 0.4 wt % and 1.4 wt %, and even more preferably between 0.7 wt % and 1.0 wt %. 
         [0019]    The Pd catalysts promoted by CeO 2  of the present invention had optimal performance characteristics when used at a CeO 2  loading of between 0.02 wt % and 1 wt %, more preferably between 0.07 wt % and 0.6 wt %, and even more preferably between 0.15 wt % and 0.25 wt %. 
         [0020]    The Pd catalysts promoted by CeO 2  of the present invention had optimal performance characteristics when the Pd particles had an average size of between 2 nm and 80 nm, more preferably between 5 nm and 40 nm, and even more preferably between 9 nm and 17 nm. 
         [0021]    The Pd catalysts promoted by CeO 2  of the present invention had optimal performance characteristics when the Pd particles had an average surface area of between 1 m 2 /g and 20 m 2 /g, more preferably between 2 m 2 /g and 12 m 2 /g, and even more preferably between 3 m 2 /g and 8 m 2 /g. 
         [0022]    The Pd catalysts promoted by CeO 2  of the present invention maintained a high conversion rate for a time between 2 and 100 times longer, more preferably between 10 and 70 times longer, and even more preferably between 30 and 55 times longer, than Pd catalysts that had not been promoted with CeO 2 . 
         [0023]    Where ranges are used in this disclosure, the end points only of the ranges are stated so as to avoid having to set out at length and describe each and every value included in the range. Any appropriate intermediate value and range between the recited endpoints can be selected. By way of example, if a range of between 0.1 and 1.0 is recited, all intermediate values (e.g., 0.2, 0.3. 6.3, 0.815 and so forth) are included as are all intermediate ranges (e.g., 0.2-0.5, 0.54-0.913, and so forth). 
       EXAMPLE 1 
     Materials 
       [0024]    Palladium (II) chlolride (PdCl 2 , ReagentPlus, 99%), potassium hexachloropalladale (IV) (K 2 PdCl 6 ), potassium chloride (KCl), L-ascorbic acid, aluminum oxide (fused, powder, a-phase, 325 mesh), ammonium cerium nitrate (CeH 8 N 8 O 18 ) and polyvinylpyrrolidone (PVP, Mw: 40 K) were purchased from Sigma-Aldrich and used as received without further purification. 
       Preparation of Catalysts 
       [0025]    Pd/α-Al 2 O 3 : In a typical synthesis, K 2 PdC 16  (0.25 mmol), PdCb (0.25 mmol), KCl (7.5 mmol), L-ascorbic acid (1 mmol) and PVP (10 mmol) were dissolved in 100 mL of deionized water. The mixed solution was refluxed at 100° C. for 3 h. Al 2 O 3  (5 g) were added in the solution and the mixture was stirred at 60° C. until all the solvents evaporated. The product was washed with ethanol/water and ethanol for several times and vacuum dried at 60° C. overnight. 
         [0026]    CeO 2 /α-Al 2 O 3 : Ammonium cerium nitrate (0.05 mmol) was dissolved into 10 mL of deionized water. Al 2 O 3  (5 g) were added in the solution and the mixture was stirred at 60° C. until all the solvents evaporated. The mixture was dried at 100° C. overnight and then calcined at 500° C. for 5 h to get CeO 2 /α-Al 2 O 3 . 
         [0027]    Pd—CeO 2 /α-Al 2 O 3  catalysts: 0.25 mmol K 2 PdCl 6 , 0.25 mmol PdCl 2 , KCl (7.5 mmol), L-ascorbic acid (1 mmol), and PVP (10 mmol) were dissolved in 100 mL of deionized water, followed by refluxing at 100° C. for 3 hrs. Then CeO 2 /α-Al 2 O 3  (5 g) was added to the solution and the mixture was stirred at 60° C. until the complete evaporation of all the solvents. The resulting mixture was washed with ethanol/water and then ethanol for several times, and vacuum dried at 60° C. for 12 h. 
       Characterization of Catalysts 
       [0028]    The surface areas of the catalysts were measured using nitrogen physisorption by standard Brunauer-Emmet-Teller (BET) analysis (MicromeriticsTriStar 3000 V 6.04 A). The surface areas were calculated with TriStar II 3000 software. 
         [0029]    X-ray photoelectron spectroscopy (XPS) was measured with a Physical Electronics ESCA 5800 spectrometer which is equipped with a monochromatic Al Ka X-ray source (E =1486.6 eV). The scanning step and working pressure were 0.1 eV and 2×10 −9  mbar, respectively. Binding energies were calibrated to Cl s peak at 284.5 eV. 
         [0030]    X-ray diffraction (XRD) analyses were performed on a Rigaku Smartlab X-ray diffraction system. A Cu Kβ radiation source (λ=1.392 Å) working at 40 kV and 40 mA was used in the tests. The range of 28 measurements was between 20° to 80’ with 0.02° steps. 
         [0031]    The morphology and the particle size as well as the dispersion of the catalysts were studied by a scanning electron microscope (SEM-EDS, FEI, Quanta FEC MK2; Oxford Instruments America, Model #51-XMX0005) and a transmission electron microscopy. (TEM, FEI Tecnai G2 F20 S-Twin 200 kV). Samples for TEM observations were prepared by dispersing the catalysts in ethanol and drying one drop of the solution on copper grids. The particle size distribution was calculated by using Image J software. 
         [0032]    In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) measurements were performed on a Nicolet iS50 FT-IR spectrometer (Thermo Scientific, Waltham, Mass., USA) equipped with a DRIFTS system with reaction chamber (Praying Mantis model, Barrick Scientific Products, Pleasantville, N.Y., USA) employing ZnSe windows. After loading 20 μL of powder samples, the cell temperature was raised to 140° C. and allowed to thermally equilibrate for ten minutes, after which the gaseous reactants were introduced at constant flow with pressure inside the reaction chamber maintained at 2 atm. The spectra are a composite of 16 scans recorded at aresolution of 4 cm −1  . 
       Synthesis 
       [0033]    The measurement of catalytic activity was performed in a fix-bed continuous flow reactor. The reactor configuration is shown schematically in  FIG. 1 . The catalyst (3.5 g, 2 mL) was sandwiched with sands in as stainless steel tube reactor with an inner diameter of 1.2 cm. The reactant gases (18% CO, 15% CH 3 CH 2 ONO, and N 2  balance) were passed through the reactor at a gas hourly space velocity (GHSV) of 600-3000 h −1 . The DEO production was carried out at a temperature of 100-160° C. and under a pressure of 0.1 MPa. A thermocouple was inserted into the catalyst bed to detect the reaction temperature. Therefore, the temperature reported here is the catalyst bed temperature. A SRI 8610C gas chromatography (GC) fitted with a capillary column (Restek MXT-1 60 m ×0.53 mm ×5 μm) and a molecular sieves column (MS 13×) was used to analyze the tail gases. Gas chromatography/mass spectroscopy (GC-MS) for liquid products were performed with an Agilent Technology 7890A GC system with a split-splitless injector (model 7863 Auto-sampler Injector) fitted with a 5957C VLMSD MS system using a capillary column (HP-5MS, 30 m×0.250 mm ×0.25 μm). When the GC analysis results show that the reaction is in steady state, the sample cylinder vessel is emptied and the start time of the reaction is recorded. Samples from the sample cylinder vessel are collected in every 6 hours and the liquid products were collected and analyzed by offline GC-MS. 
       Results and Discussion 
       [0034]    Characteristics of Catalysts 
         [0035]    The textural characteristics of Pd—CeO 2 /α-Al 2 O 3  catalyst were investigated by TEM, STEM and SEM ( FIG. 2 ). TEM images presented in  FIGS. 2   a  and  2   c  clearly indicate that the Pd nanoparticles of Pd—CeO 2 /α-Al 2 O 3  are highly dispersed on the α-Al 2 O 3  while the dispersion of Pd nanoparticles of Pd/α-Al 2 O 3  is poor. Moreover, the results in  FIGS. 2   b  and  2   d  show that the average Pd nanoparticles size of the Pd—CeO 2 /α-Al 2 O 3  catalyst is 13.2 nm which is smaller than that of the Pd/α-Al 2 O 3  catalyst (17.3 nm). The Pd nanoparticles size distribution of the Pd—CeO 2 /α-Al 2 O 3  catalyst is narrower than that of the Pd/α-Al 2 O 3  catalyst in the meanwhile. CeO 2  was difficult to detect by TEM maybe due to its low loading concentration. However, the red circles in  FIG. 4   a  indicate the dispersion of CeO 2  on the α-Al 2 O 3  support, which is confirmed by energy dispersive X-ray (EDX) spectra. The dispersion of CeO 2  particles was not as good as Pd particles. They were aggregated into large nanoparticles with the diameters around 200 nm. In summary of the results from TEM and SEM, it can be concluded that the promoter CeO 2  not only promotes the dispersion of Pd on the support, but also decreases the nanoparticle size of Pd. 
         [0036]    The two catalysts, Pd/α-Al 2 O 3  and Pd—CeO 2 /α-Al 2 O 3 , were detected with XPS (Pd 3d) before and after the reaction with CO and EN at 140° C. ( FIG. 3 ). Although there were small differences between Pd/α-Al 2 O 3  and Pd—CeO 2 /α-Al 2 O 3 , the obtained Pd 3d 3/2  and Pd 3d 5/2  values for both Pd(0) and Pd(II) were consistent with the published literatures.[32-34] In  FIGS. 3   a  and  3   c , both the Pd 3d 5/2 and Pd 3d 3/2  of catalysts Pd/α-Al 2 O 3  and Pd—CeO 2 /α-Al 2 O 3  are around 335 and 340 eV, respectively, which indicates that the oxidation state of Pd in the catalysts is Pd(0). However, after reaction, two new peaks appeared in both the two catalysts ( FIGS. 3   c  and  3   d ), which are assigned to Pd(II),[34] indicating that some Pd(0) in the two catalysts was oxidized to Pd(II) by methyl nitrite to form an intermediate, CH30-Pd(II)—OCH3.[13] The peaks area of the Pd(II) in  FIG. 3   d  is much bigger than the peaks area in  FIG. 3   b , which indicates that more intermediate were generated on the surface of Pd—CeO 2 /α-Al 2 O 3  catalyst, and therefore Pd—CeO 2 /α-Al 2 O 3  may have higher catalytic activity with the addition of CeO 2 . Furthermore, the percentage of the Pd on both catalysts was calculated using the peaks area of the XPS. The Pd—CeO 2 /α-Al 2 O 3  catalyst showed higher Pd concentration (0.92%) than that of the Pd/α-Al 2 O 3  catalyst (0.81%), which strongly suggests that the promoter CeO 2  can also enhance the Pd loading concentration on the support. XPS was also detected to further confirm the XPS results. However, no detectable CeO 2  or Pd peak was found maybe due to their low concentrations and the high dispersion of Pd.[28] 
       Factors Affecting the Conversion of COSEN to DEO 
       [0037]    Addition of CeO 2    
         [0038]    The catalytic performances of the two catalysts were evaluated under the same conditions. With the addition of CeO 2 , the conversion of CO and EN was increased from 39% to 65% and 64% to 92%, respectively ( FIG. 4   a ). There is 50% more of conversion for both of the reactants. The STY of DEO with Pd—CeO 2 /α-Al 2 O 3  was also greatly increased, which is 60% higher than that of Pd/α-Al 2 O 3  at 140° C. (Table 1). 
         [0000]    
       
         
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 CO oxidative coupling to DEO with different catalysts a   
               
             
          
           
               
                   
                 Pd 
                 Ce 
                   
                   
                   
               
               
                   
                 content 
                 content 
                 Conversion b   
                 Selectivity 
                 STY 
               
               
                 Catalysts 
                 (wt %) 
                 (wt %) 
                 (%) 
                 (%) 
                 (gL −1 h −1 ) 
               
               
                   
               
               
                 Pd/α-Al 2 O 3   
                 0.8 
                 — 
                 39 
                 95 
                 195 
               
               
                 Pd—CeO 2 / 
                 0.8 
                 0.15 
                 65 
                 93 
                 318 
               
               
                 α-Al 2 O 3   
               
               
                 CeO 2 /α-Al 2 O 3   
                 — 
                 0.2  
                 — 
                 — 
                 — 
               
               
                   
               
               
                   a Reaction conditions: 3.5 g of catalyst, 1200 h −1  of gas hourly space velocity (GHSV), reactants&#39; volume ratio CO/EN is 1.2 0.1 Mpa, 140° C. 
               
               
                   b Conversion of CO 
               
             
          
         
       
     
         [0039]    In the meanwhile, the selectivity of DEO with these two catalysts was almost the same (around 92%). Since there was no catalytic activity found for the catalyst CeO 2 /α-Al 2 O 3 , the CeO 2  plays an important role as a promoter and the interaction of CeO 2  with Pd was responsible for the high activity and selectivity in CO oxidative coupling to DEO. Most of all, the catalytic activity of catalyst Pd—CeO 2 /α-Al 2 O 3  can be maintained for at least 72 h ( FIG. 4   b ), which lays a good foundation for long-term stability. 
         [0040]      FIGS. 5  illustrate the in situ DR-FTIR spectra for the reaction of CO with ethyl nitrite to DEO. The band at 1774 cm −1  is attributed to the C═O stretching vibrations of the DEO product. It is important to note that the intensity of the band at 1774 cm −1  in the spectrum of  FIG. 5   b  is stronger than that in the spectrum of  FIG. 5   a  and from the integration results of the two peaks, the peak area of Pd—CeO 2 /α-Al 2 O 3  catalyst is 20% bigger than that of the catalyst without CeO 2 , which demonstrates the superior catalytic activity of Pd—CeO 2 /α-Al 2 O 3  relative to Pd/α-Al 2 O 3 , consistent with the results of catalytic activity evaluation and TEM, XPS results. 
         [0041]    Temperature 
         [0042]      FIG. 6   a  shows the effect of temperature on both EN and CO conversion where Pd—CeO 2 /α-Al 2 O 3  was used as the catalyst for CO oxidative coupling to DEO reaction. The conversion of EN and CO became higher with the temperature increasing, especially when the temperature increased from 120° C. to 140° C. Both EN and CO conversion increased 20% accordingly. However, with the temperature increasing, the selectivity of DEO had almost no change except when the temperature reached to 180° C. Both the CO conversion and DEO selectivity decreased at 180° C. due to the decomposition of the EN. The Pd—CeO 2 /α-Al 2 O 3  catalyst can be optimized to achieve a lower reaction temperature with high DEO selectivity. 
       Conclusion 
       [0043]    In summary, a low Pd loading Pd/α-Al 2 O 3  nanocatalyst with 0.8% Pd (wt %) loading and the average Pd size of 13.2 nm was synthesized for CO oxidative coupling to DEO. After the introduction of 0.2 wt % Ce0 2 , Pd—CeO 2 /α-Al 2 O 3  catalyst showed remarkably higher catalytic activity compared with the catalyst without CeO 2 . The CO conversion was increased SO % more (from 39% to 62% with the DEO selectivity higher than 90% when the CeO 2 , was used as a promoter and, importantly, the high activity and selectivity could be maintained up to 72 h without visible decrease. TEM results is showed clearly that CeO 2  not only improved the dispersion of palladium on the surface of the support but also decreased the palladium size as well, thus resulted in the excellent catalytic activity. In consideration of the facile synthesis and low Pd loading of this catalyst as well as the insecurity factors of methyl nitrite, this highly efficient and stable nanocatalyst may have a promising industrial application, especially in the US, of the coal to ethylene glycol. 
         [0044]    The foregoing exemplary descriptions and the illustrative preferred embodiments of the present invention have been explained in the figures and tables herein and attached to this application and have been described in detail, with varying modifications and alternative embodiments being taught. While the invention has been shown, described and illustrated herein, it should be understood by those skilled in the art that equivalent changes in form and detail may be made therein without departing from the spirit and scope of the invention, and that the scope of the present invention is to be limited only as precluded by prior art. Moreover, the invention as described and disclosed herein may be suitably practiced in the absence of the specific elements which are described and disclosed herein. 
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