Abstract:
The various embodiments of the invention relates to the composition of a hydrogen sulfide capture material and the related method of manufacture. The hydrogen sulfide capture material is formed by solubilizing an iron source in acid to form an aqueous solution comprising iron chloride, neutralizing the aqueous solution with a caustic solution to form a neutralized solution, washing the neutralized solution to separate it into water and a slurry, forming a thickened slurry by removing additional water from the slurry, separating the thickened slurry to produce filtered water and a wet filter cake, and drying the wet filter cake to form granules. The hydrogen sulfide capture material of the present invention removes hydrogen sulfide for a longer time and at a faster rate than the materials of the prior art, thereby improving the efficiency and decreasing the cost of sour gas treatment.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part application which claims priority to U.S. patent application Ser. No. 12/899,515, filed Oct. 6, 2010, which claimed priority of the provisional application with Ser. No. 61/249,141 titled “Material and Method for the Sorption of Hydrogen Sulfide” filed on Oct. 6, 2009. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable 
     FIELD OF THE EMBODIMENTS 
     The field of the embodiments is generally gas and vapor stream processing. More specifically, the field of the embodiments is capture of hydrogen sulfide laden fluid streams. 
     BACKGROUND OF THE EMBODIMENTS 
     Hydrogen sulfide is a highly dangerous and corrosive gas that is contained in a variety of man-made and naturally occurring fluid streams. One of these fluid streams is the flow of natural gas from a well. Many natural gas wells contain an appreciable amount of hydrogen sulfide, and this hydrogen sulfide must be removed to make the gas marketable to natural gas gathering and transmission systems. One of the purposes of the embodiments described in this patent application is to remove hydrogen sulfide from fluid streams, including natural gas streams to make the natural gas marketable. 
     One of the most technically challenging and economically costly aspects of removing hydrogen sulfide with granular/solid scavengers is removing the spent capture material from the sulfur removal vessel. In many cases, the physical and chemical reaction that occurs when hydrogen sulfide is removed from the gas or vapor stream, changes the capture material from free-flowing particles into monolithic mass. This solid mass sometimes requires workers to enter the vessel through manways and hammer and chisel the material into smaller pieces for removal from the vessel. This operation is not only extremely unpleasant, but time consuming and costly for the operator of the hydrogen sulfide capture process and potentially unsafe for the laborers. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a flow diagram of the process of making the hydrogen sulfide capture material. 
         FIG. 2  shows an embodiment of the process of using the hydrogen sulfide capture material to strip hydrogen sulfide from the natural gas. 
         FIG. 3  shows the performance of a representative sample of a prior art invention in removing hydrogen sulfide from a gas stream. 
         FIG. 4  shows the performance of an embodiment of the prior art in removing hydrogen sulfide from a gas stream. 
         FIG. 5  shows the performance of an embodiment of the instant invention in removing hydrogen sulfide from a gas stream over a long period showing the relatively long breakthrough behavior of the embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The embodiments of this invention relate to a composition of matter and method remove hydrogen sulfide (H 2 S) from gas or vapor streams. The material is manufactured from steel or iron. The iron or steel can be scrap materials from manufacturing operations or can be recycled material. In other embodiments, the material is manufactured from iron oxide powders used as starting material. The various embodiments described herein make economic use of this scrap steel or iron. 
     In the preferred method of manufacture  101  of the hydrogen sulfide capture material (hereinafter “Capture Material” or SULFABATE™ (CalTech Global, LLC, Sapulpa, Okla.)), the iron is solubilized with hydrochloric acid (HCl)  102  into an aqueous solution of hydrochloric acid and iron chloride. In one embodiment the iron chloride is ferric chloride, FeCl 3 . In another embodiment, the iron chloride is ferrous chloride, FeCl 2 . In another embodiment, the iron chloride is a mixture of ferric chloride, FeCl 3 , and ferrous chloride, FeCl 2 . The iron chloride and hydrochloric acid solution is then combined with caustic solution  103  to adjust the pH to between 4.0 and 5.0 pH units. The base used in the caustic solution may be a metal hydroxide, such as sodium hydroxide or calcium hydroxide. The solution that results from combining the iron chloride and hydrochloric acid solution and caustic solution  103  is comprised mostly of suspended and solubilized iron, and is further neutralized  104  to a pH of between 7 and 10 pH units, preferably between 7 and 8 pH units. Next, flocculent may be added  105  and mixed with the solution. The solution is now comprised of mainly suspended iron hydroxide/iron oxide solids. The solution then proceeds to a water-clarifier system  106  where the solids are washed and separated by gravity and the cleaned water is discarded  107 . The slurry proceeds to the next step of the manufacturing process where the slurry from the flocculent step goes to a settling tank  108  and then the thickened slurry goes to a filter press  109  where the wet filter cake is collected. The wet filter cake is then subsequently dried to between 0 and 30 percent moisture content. Excess calcium hydroxide from the neutralization step may act as a binding agent when the wet filter cake is dried. The dry filter cake granules are then crushed and screened between No. 4 to No. 40 mesh size screens and packaged. The granules that are larger than the size of No. 4 mesh are crushed, screened and then sacked. The dust from the entire process is collected and pelletized in a rolling pan using a binder, preferably lime. 
     An embodiment of the Capture Material was analyzed using x-ray diffraction analysis and energy-dispersive x-ray spectroscopy. As shown in Table I, an embodiment of the Capture Material contains calcite, maghemite, amorphous mineral constituents, and trace amounts of quartz and lepidocrocite. Table II identifies the concentration of various elements in the same embodiment of the Capture Material in terms of percent by weight. The Capture Material contains approximately 55% iron and 25% calcium, as well as lesser amounts of silicon, phosphorus, sulfur, titanium, manganese, copper, and zinc. However, these lesser amounts may not be present if different raw materials are used. The composition of the Capture Material may vary depending upon the type of raw materials and chemicals used to make the Capture Material. In addition, the Capture Material has a preferred particle size of less than 1,000 nanometers. 
     The effectiveness of the Capture Material is due in part to the large surface area that results in the manufacturing of the Capture Material. This increase in surface area is due to a combination of process of the scrap steel, the addition of the flocculants, surfactants and the presence of the trace metals. In addition, the effectiveness of the Capture Material is in part due to the presence of both crystalline and amorphous material. 
     In addition, the Capture Material contains approximately 25% water. Therefore, the Capture Material is approximately the composition of Fe(OH) 3 . The high level of Fe(OH) 3  processed in the manner discussed herein leads to the high surface area of Capture Material, which may range from approximately 50 m 2 /g to approximately 400 m 2 /g. 
     It is important during the process to keep the maximum temperature of the filter cake below 250° F. Above 250° F., the material loses activity. A variety of materials could be used as a binder. If the filter cake is sufficiently dry, no binder is required. Because a binder is not required, the dry filter cake has a very high porosity and low bulk density. The dry filter cake is very hydrophobic and does not readily pick up water. The filter cake contains trace amounts of copper, zinc and lead as well as other heavy metals. These trace elements may help improve the performance of the material. Upon drying, the material shrinks to about 50% of its initial volume. 
     In other embodiments of the Capture Material, it is possible to add liquid triazine as an additional hydrogen sulfide scavenger to the filter cake and collected processing dust to act as a binder and thereby increasing the capacity and the rate of hydrogen sulfide uptake in subsequent processing. 
     In yet another embodiment of the instant invention it is also possible to add H 2 S-consuming bacteria along with sodium nitrite (NaNO 2 ) and sodium nitrate (NaNO 3 ) to the filter cake to increase the hydrogen sulfide uptake capacity of the Capture Material. 
     The resulting Capture Material is subsequently used to remove hydrogen sulfide from a variety of gaseous and vapor streams. In all embodiments, the Capture Material possesses both a faster reaction rate and greater uptake capacity of hydrogen sulfide than comparable prior art materials. The result of the increased rate is that more gas or vapor containing hydrogen sulfide can processed in an equal amount of time or in a smaller bed depth of Capture Material. The result of the increased capacity is that the Capture Material must be replaced less often than comparable prior art material. In one application, the Capture Material is used to remove hydrogen sulfide from sour natural gas thereby making the gas acceptable for purchase by gas distribution systems and for subsequent residential and commercial use. 
     Hydrogen sulfide is a particularly dangerous material that is toxic at relatively low levels, therefore the utility of this material is to remove hydrogen sulfide and convert the hydrogen sulfide into less toxic elemental sulfur. The spent/reacted Capture Material product is not hazardous and therefore approved for disposal in municipal landfills. The Capture Material pellets are sized and screened to a narrow-mesh range to ensure minimum pressure drop through a contact tower. The Capture Material pellets can be shipped in super sacks to minimize labor and expense during installations. The Capture Material granules are also easily removed from the contact tower when saturation is realized. The various embodiments remain granular and therefore allow for easy removal from the vessel, which is a significant advantage over similar hydrogen sulfide removal materials. The capture material pellets are comprised of waste material and therefore are a recyclable and green product. 
     An embodiment for the process for using the Capture Material pellets is to place the Capture Material pellets in a sorption tower as shown in  FIG. 2 . In this embodiment, there is a bed of sorbate Capture Material  207 . The Capture Material pellets are supported by a filter foam support  208  and added to the bed to form an absorption volume. In this embodiment, the filter foam support  208  is supported by a 40-mesh screen support  209 . The 40-mesh screen support  209  is in turned supported by a 4-mesh screen support  210 . The 4-mesh screen  210  is supported by a permanently affixed support grid  211 . Sour gas, that is gas that is high in hydrogen sulfide, is added at the sour gas inlet,  203 . The sour gas is first diverted by an inlet gas deflector  204  then proceeds downward through the Capture Material bed. 
     The sour gas proceeds downward through the Capture Material bed  207 . Hydrogen sulfide is sorbed by the Capture Material in the Capture Material bed  207 . The treated gas continues downward through the filter foam support  208 , 40-mesh support  209 , 4-mesh support  208 , and the permanent support grid  209 . The treated gas then exits the sorption tower through the treated gas outlet  212 . The embodiment is also comprised of a loading man way  206  and a cleanout man way  202  for charging new material and removing spent Capture Material. 
     A significant advantage of the Capture Material over the prior art materials is in the ease of removal of the spent Capture Material from the sorption tower. In many cases with the prior art materials, those materials bind into larger clumps and lumps of material making the removal from the tower difficult. In all embodiments of the Capture Material, the sorption of hydrogen sulfide does not bind the material. 
       FIGS. 3 ,  4 , and  5  demonstrate the performance of the prior art and embodiments of the instant invention.  FIG. 3  shows the results of a performance test of the “Iron Sponge” prior art material. As shown in  FIG. 3 , the concentration of H 2 S in the gas after it has passed through a sorption tower containing iron sponge was approximately 1,300 ppm at the beginning of the test. That concentration began to rise almost immediately and leveled off at approximately 1,400 ppm after only ten minutes.  FIG. 4  shows the results of a performance test of the SULFATREAT® (M-I L.L.C., Houston, Tex.) prior art material, which is comprised of clay particles coated with iron oxide. As shown in  FIG. 4 , the concentration of H 2 S in the gas after it has passed through a sorption tower containing SULFATREAT® was initially zero. However, “breakthrough” occurred after only four minutes, when the concentration increased to approximately 400 ppm and remained relatively constant for the duration of the test. Finally,  FIG. 5  shows the results of a performance test of an embodiment of the instant invention. As shown in  FIG. 5 , the concentration of H 2 S in the gas after it has passed through a sorption tower containing the Capture Material was approximately zero for 337 minutes, meaning that the Capture Material removes H 2 S for a much longer time than either the iron sponge or SULFATREAT®. As a result, the Capture Material in the sorption tower does not have to be removed and replaced as often as conventional materials, which increases the efficiency and decreases the costs of removing H 2 S from sour gas. In addition, because breakthrough for the Capture Material occurs much later, it is likely that the Capture Material reacts with H 2 S at a faster rate than either iron sponge or SULFATREAT®, thereby improving the efficiency of sour gas treatment. 
     The tests shown in  FIGS. 3 ,  4  and  5  are conducted using the same testing parameters. The inlet gas was a gas blend containing nitrogen, 10,000 parts per million (ppm) carbon dioxide, and 2,000 ppm H 2 S, and was hydrated to duplicate field conditions. The flow rate of the inlet gas was 5.5 standard cubic feet per hour, with a pressure of 5 pounds per square inch and a temperature of 70° F. The volume of iron sponge, SULFATREAT®, or the Capture Material through which the inlet gas was passed was 27 milliliters, and each material was screened to achieve granules ranging in size from 8- to 16-mesh. The concentration of H 2 S in the outlet gas was then measured and graphed in  FIG. 3  (iron sponge),  FIG. 4  (SULFATREAT®), and  FIG. 5  (Capture Material). 
     With respect to the above description then, it is to be realized that the optimum relationships for the parts of the invention, to include variations in materials, shape, form, function and manner of operation, assembly and use, are deemed readily apparent and obvious to one skilled in the art, and all equivalent relationships to those illustrated in the drawings and described in the specification are intended to be encompassed by the present invention. 
     Therefore, the above is considered as illustrative only of the principles of the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described, and accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention. 
     
       
         
               
             
               
               
               
               
             
           
               
                 TABLE I 
               
             
             
               
                   
               
               
                 X-ray Diffraction Analysis of H 2 S Removal Compound 
               
             
          
           
               
                   
                 MINERAL 
                 CHEMICAL 
                 RELATIVE 
               
               
                   
                 CONSTITUENTS 
                 FORMULA 
                 ABUNDANCE (%) 
               
               
                   
               
               
                   
                 Quartz 
                 SiO 2   
                 Trace 
               
               
                   
                 Calcite 
                 CaCO 3   
                   5 
               
               
                   
                 Maghemite 
                 γ-Fe 2 O 3   
                  70 
               
               
                   
                 Lepidocrocite 
                 γ-FeOOH 
                 Trace 
               
               
                   
                 Amorphous 
                   
                  25 
               
               
                   
                   
                 TOTAL 
                 100 
               
               
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
               
               
             
               
               
               
               
             
           
               
                 TABLE II 
               
             
             
               
                   
               
               
                 Energy Dispersive X-ray Analysis Results 
               
             
          
           
               
                   
                   
                   
                 Concentration  
               
               
                   
                   
                 Element 
                 (Wt. %) 
               
               
                   
               
             
          
           
               
                   
                 Silicon 
                 Si 
                 3.84 
               
               
                   
                 Phosphorous 
                 P 
                 3.26 
               
               
                   
                 Sulfur 
                 S 
                 3.9 
               
               
                   
                 Calcium 
                 Ca 
                 25.18 
               
               
                   
                 Titanium 
                 Ti 
                 1.55 
               
               
                   
                 Manganese 
                 Mn 
                 2.13 
               
               
                   
                 Iron 
                 Fe 
                 54.67 
               
               
                   
                 Copper 
                 Cu 
                 2.97 
               
               
                   
                 Zinc 
                 Zn 
                 2.49 
               
               
                   
                   
                 TOTAL 
                 100