WO2007041553A1

WO2007041553A1 - Method of removing contaminants from fluid streams and solid formations

Info

Publication number: WO2007041553A1
Application number: PCT/US2006/038569
Authority: WO
Inventors: Slawek Winecki; Olga Koper; David A. Jones; Janis Voo
Original assignee: Nanoscale Materials, Inc.
Priority date: 2005-09-30
Filing date: 2006-09-29
Publication date: 2007-04-12

Abstract

Methods of removing contaminants from various streams and solid formations comprising contacting the stream with a quantity of nanocrystalline particles for sorbing the contaminant are provided. In particular, such streams include streams comprising less than about 10% by weight hydrocarbon compounds, predominantly hydrogen streams, wastewater streams, syngas streams, and streams comprising hydrocarbon compounds. Preferred solid formations include subterranean formations such as coal mines, metal mines, and diamond mines. Methods according to the invention are particularly useful in protecting mine workers from exposure to hazardous or toxic materials. The nanocrystalline particles are characterized as having average crystallite sizes of less than about 20 nm and have relatively high surface areas.

Description

METBOD OF REMOVING CONTAMINANTS FROM FLUID STREAMS AND SOLID FORMATIONS

RELATED APPLICATION

The present application claims the benefit of U.S. Provisional Patent Application S/N 60/722,583, filed September 30, 2005, which is incorporated by reference herein.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention generally pertains to methods of removing contaminants from liquid or gaseous streams and subterranean solid hydrocarbon formations. More particularly, methods according to the present invention comprise contacting a stream or solid surface comprising at least one contaminant with a quantity of nanocrystalline particles selected from the group consisting of metal oxides, metal hydroxides, and combinations thereof for sorbing the contaminant.

Description of the Prior Art

The contamination of various industrial liquid and gas streams has been a long standing problem in many fields, particularly the energy industry. In many instances, fuel streams are contaminated with undesirable components that must be removed in order to make the fuel stream safe for use by consumers. Hydrogen sulfide is a particularly troublesome contaminant found in natural gas and petroleum streams. In order for natural gas to be useful, hydrogen sulfide must not be present at a level greater than about 4 ppm. Various technologies have been developed to remove sulfur from natural gas streams such as membrane separation, the Claus process, amine processes, catalytic conversion of hydrogen sulfide to sulfur dioxide and sulfur redox reactions.

Also, the presence of hydrogen sulfide gas in coal formations presents health concerns for coal mine workers. Hydrogen sulfide gas can seep from the coal formation into the air inside the mine and be inhaled by the mine workers. Conventional treatment of hydrogen sulfide typically involves ventilation of the gas from the mine. In metal mines, the ambient atmosphere may become contaminated with HCN or water used in mining operations could become contaminated with HCN, thus producing contaminated wastewater.

Various sorbent materials have also been used in order to remove sulfur compounds from natural gas and petroleum streams. However, numerous problems have been encountered with the use of these sorbents. For example, iron-containing sorbents can often lead to production of iron pyrite and activated charcoal sorbents can become rapidly saturated with condensable hydrocarbons. Also, most commercial sorbent materials do not, have a very high sorptive capacity thereby requiring frequent replacement of the material and some materials are selective for stream components other than the contaminant.

U.S. Patent No. 6,447,577, incorporated by reference herein, discloses a method for removing hydrogen sulfide and carbon dioxide from crude and natural gas streams. However, because of selectivity issues, it is unknown and impossible to accurately predict whether similar methods will effectively remove contaminants in other kinds of streams such as predominantly hydrogen streams for use in fuel cells or syngas streams produced from coal.

SUMMARY OF THE INVENTION

The present invention overcomes the above problems and provides methods of removing contaminants from a fluid stream or contaminants produced from a solid subterranean formation. In one embodiment, methods according to the present invention comprise the steps of providing a fluid stream including at least one contaminant and contacting the stream with a quantity of nanocrystalline particles for sorbing the at least one contaminant. In particularly preferred embodiments, the fluid stream will include at least one contaminant selected from the group consisting of alcohols, heavy metals, heavy metal-containing compounds, H₂SO₄, HCl, HNO₃, C1-C20 thiols, cyanides, C1-C20 sulfides, C1-C20 oxysulfides, C1-C20 disulfides, and C1-C20 thiophenes. The nanocrystalline particles are preferably selected from the group consisting of metal oxides, metal hydroxides and mixtures thereof having an average crystallite size of less than about 20 nm.

In another embodiment of the present invention, there is provided a method of removing contaminants from a solid subterranean formation, especially a subterranean mine such as a coal mine, metal mine, or diamond mine. Preferably, the contaminants are contacted with nanocrystalline particles, such as those described above. Even more preferably, the particles are contacted with the contaminant while the contaminant is still within the mine so as to prevent its escape therefrom and also to enhance the safety of those working inside the mine. Contacting of the nanocrystalline particles with the contaminant may occur in several fashions . For example, the particles can be incorporated into a foam, suspension, sol, liquid carrier, or gel that is sprayed onto an exposed surface of the mine. The particles may also be placed in some kind of filtration media through which a fluid stream containing the contaminant produced from the mine is passed.

In yet another embodiment of the present invention, there is provided a method of removing a contaminant from a fluid stream comprising between about 5-99% by weight hydrogen and less than about 10% by weight hydrocarbon compounds. All weight percentages expressed herein are based upon the weight of the entire stream unless otherwise stated. Preferably, hydrogen is the predominant component or at least one of the two most prevalent components in the stream. Exemplary streams include streams of synthesis gas and feed streams for hydrogen fuel cells. The contaminant present in the stream is preferably selected from the group consisting of acids, alcohols, compounds having at least one atom of P, S, N, Se or Te, hydrocarbon compounds, toxic metal compounds, bacteria, fungi, spores, viruses, toxins, and mixtures thereof. The stream, and contaminant present therein, is contacted with a quantity of nanocrystalline particles for sorbing the contaminant. The nanocrystalline particles are preferably selected from the group consisting of metal oxides, metal hydroxides, and combinations thereof having an average crystallite size of less than about 20 nm.

In still a further embodiment of the present invention, there is provided a method of removing at least one contaminant from a stream comprising from about 1-50% by weight hydrocarbon compounds and at least one contaminant. The stream is contacted with a quantity of nanocrystalline particles, such as those discussed above, for sorbing the at least one contaminant.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The present invention generally relates to the removal of harmful or toxic materials from fluid streams and solid subterranean formations. A number of contaminants may be removed using methods according to the present invention. Selection of the appropriate nanocrystalline particulate material for use herewith will largely depend upon the contaminant to be targeted. Different nanocrystalline materials are selective and/or most effective for certain kinds of contaminants. The chemistry involved in the sorptive operation varies between nanocrystalline materials and the target contaminant. Thus, a nanocrystalline particle that effectively absorbs one type of contaminant, may not effectively adsorb other contaminants.

Preferably, the nanocrystalline particles used in conjunction with the present invention are selected from the group consisting of metal oxides, metal hydroxides, and combinations thereof. As used herein, the terms "metal oxides" and "metal hydroxides" refer to compounds containing a single metal ion (mono-metal oxides and hydroxides), compounds containing more than one metal ion (e.g., mixed metal oxides of the formula (M^MQ_yOJ, and intimate mixtures of metal oxides and hydroxides. More preferably, the nanocrystalline particles are selected from the group consisting of metal oxides and metal hydroxides of Mg, Sr, Ba, Ca, Ti, Co, Fe, V, Mn, Ni, Cu, Al, Si, Zn, Ag, Mo, Zr and mixtures thereof. In alternate embodiments, the metal portion of the oxide or hydroxide is selected from the group consisting of calcium, magnesium, zinc, iron, and other metals from groups 8, 9, or 10 of the IUPAC periodic table of elements (CAS Group VDI), with zinc oxide being most preferred. However, it is within the scope of the invention to employ any nanocrystalline metal oxide or hydroxide material including those recited in U.S. Patent No. 6,860,924, incorporated by reference herein. The outer surface of the nanocrystalline particles maybe modified, or coated, especially with a second oxide or hydroxide different from the core material. Iron oxide (Fe₂O₃) is the most preferred surface modifier, however, any metal oxide or hydroxide including metal oxides and hydroxides of Ti, V, Cr, Mn, Ni, Co, Cu, and Fe and those disclosed in U.S. Patent No. 5,914,436, incorporated by reference herein, may be used. Preferably, the nanocrystalline particles have average crystallite sizes of less than about 20 nm, and more preferably from about 4-10 nm. The nanocrystalline particles also exhibit average surface areas of at least about 20 m²/g, more preferably from about 80-300 m²/g, and most preferably from about 85-150 m²/g.

The nanocrystalline particles may be in the form of a powder or the particles can be agglomerated into granules having particle sizes of between about 1 μm and 1 mm. The particles can be placed in a porous media, such as a filter, a fixed bed, or a fluidized bed, through which the stream comprising the at least one contaminant is passed or a batch-type vessel such as a continuously stirred tank reactor (CSTR). In the context of mine operations, the filtration media containing the nanocrystalline particles may be located in an air filtration device or air purification system that is installed inside the mine.

Preferably, contaminants to be targeted by the present invention are selected from the group consisting of acids, alcohols, compounds having at least one atom of P, S, N, Se or Te, hydrocarbon compounds, heavy metals and heavy metal containing compounds (especially Hg, Se, Pb, Cd, As, and compounds thereof), toxic metal compounds, bacteria, fungi, spores, viruses, toxins, and mixtures thereof. More preferably, the contaminant is selected from the group consisting of H₂S, H₂SO₄, HCl, HNO₃, C1-C20 thiols, cyanides (e.g., HCN), C1-C20 sulfides, C1-C20 oxysulfides (e.g., COS), C1-C20 disulfides, C1-C20 thiophenes, rickettsiae, and chlamydia. However, in certain applications, the contaminant maybe any undesirable substance except for H₂S and CO₂. More preferably, the contaminant is selected from one of the materials described above, except for H₂S and CO₂.

Prior to contact with the nanocrystalline particles, the contaminant may initially be present in an amount in excess of the accepted safety exposure limit for the contaminant. Such accepted safety exposure limits are available from a number of government agencies including the EPA and OSHA. In certain situations, the contaminant maybe present at alevel of about 50- 5000 ppm, preferably between 100-3000 ppm. However, after contact with the nanocrystalline particles, the contaminant may be present in an amount less than the accepted safety exposure limit. In some applications, the contaminant is present at a level of less than about 50 ppm, more preferably less than about 0.1 ppm. Even more preferably, the stream or atmosphere adj acent the solid formation is essentially free of the contaminant (i.e., less than about 0.01 ppm).

The contacting or application step may be carried out under a wide range of conditions, however, it is preferable for the contacting or application step to be performed at a temperature from about -20 to about 400 ° C, more preferably from about 30-150⁰C, and most preferably from about 30-90⁰C. Likewise, the contacting or application step may be carried out under varying pressure conditions, however, it is preferable for the contacting or application step to occur at or near ambient pressure conditions.

In the context of removing contaminants from fluid streams, the fluid stream may comprise a gas or a liquid. More specifically, the fluid stream preferably comprises at least one component selected from the group consisting of synthesis gas, flue gas, natural gas, hydrogen, hydrocarbon compounds, air, and mixtures thereof. The fluid stream may also be a liquid hydrocarbon or aqueous stream. Exemplary liquid streams include unrefined petroleum streams, petroleum distillate streams, and wastewater streams.

As used herein, "synthesis gas" or "syngas" refers to a liquid or gaseous mixture of which hydrogen and carbon monoxide comprise the primary components. Synthesis gas may be produced in a number of ways such as the steam reforming of natural gas or liquid hydrocarbons, or through the gasification of coal, for example. Thus, various contaminants that are commonly present in the raw materials for synthesis gas production can be carried over into the synthesis gas product itself. The level of these contaminants should be reduced as much as possible to avoid their escape into the environment upon combustion of the syngas or their incorporation into other products produced from the synthesis gas. Synthesis gas is preferably low in hydrocarbon compound content, but may contain some residual amounts of hydrocarbons derived from the raw materials from which the synthesis gas is produced. Preferably, the synthesis gas comprises less than about 10% by weight hydrocarbon compounds, more preferably less than about 5% by weight hydrocarbon compounds, and most preferably is essentially free of hydrocarbon compounds. As used herein, the term "essentially free of hydrocarbon compounds" means that the fluid stream comprises less than about 1 % by weight, more preferably less than about 0.1% by weight, of hydrocarbon compounds.

As used herein, the term "flue gas" refers to exhaust gases produced by the combustion of hydrocarbon compounds. Flue gas streams generally comprise levels of carbon dioxide that are higher than that of ambient air. Generally, flue gas comprises between 0.1-25% by weight carbon dioxide. The balance of the flue gas is primarily nitrogen and oxygen taken in from the ambient air that is fed to the combustion process. Flue gas may also contain trace amounts of the hydrocarbon materials that were fed to the combustion process. Flue gas may also be at an elevated temperature between just above ambient temperature to 400° C. A preferred method of treating flue gas is powder injection. The nanocrystalline materials, in powder form are injected directly into the flue gas generated by the combustion of hydrocarbon materials, particularly those emanating from a coal or natural gas power plant. Powder injection of the particles minimizes the pressure drop associated with contacting the gas with the particles compared to other means of contacting. Powder injection can be highly effective in removing mercury contaminants from flue gases before they are released into the atmosphere. In one aspect, the stream from which contaminants are being removed is preferably low in hydrocarbon compounds. In these streams, it is preferable that the stream comprise less than about 10% by weight hydrocarbon compounds, more preferably less than about 5% by weight hydrocarbon compounds, and most preferably is essentially free of hydrocarbon compounds. In certain applications, streams use in accordance with the present invention are not produced from subterranean formations, and thus are not petroleum or natural gas streams. Exemplary streams which can meet the above limitations are streams having a low hydrocarbon content including synthesis gas streams, flue gas streams, predominately hydrogen streams, and air streams. As used herein, the term "predominately hydrogen streams" means streams where hydrogen is the most abundant component. Preferably, predominately hydrogen streams comprise greater than about 40% by weight hydrogen, more preferably greater than about 60% by weight, and most preferably greater than about 85% by weight. As used herein, the term "air streams" refers to streams wherein nitrogen and oxygen are the two most abundant components. Preferably, nitrogen is present between about 65-80% by weight, and oxygen is present between about 16-23% by weight.

In another aspect, the fluid stream may comprise from about 5-99% by weight hydrogen, more preferably between about 20-50% by weight hydrogen, and most preferably between about 25-40% by weight hydrogen. It is also preferable for these streams to comprise low amounts of hydrocarbon compounds, most preferably less than about 2% by weight. Such hydrogen streams are particularly useful as feed streams to hydrogen fuel cells. Thus, the present invention also includes, after contacting the hydrogen stream with nanocrystalline particles, the step of feeding the stream to a hydrogen fuel cell.

Methods according to the present invention are also highly useful in removing contaminants from streams containing significant amounts ofliydrocarbons, particularly streams produced from subterranean wells. In certain embodiments, the streams comprise substantially all hydrocarbon compounds, however, it is possible for the hydrocarbon compounds to simply be more prevalent than any other component. For example, the stream may comprise between about 1-50% by weight hydrocarbon compounds, more preferably between about 2-30% by weight hydrocarbon compounds, and most preferably between about 5-25% by weight hydrocarbon compounds. The fluid streams containing at least one contaminant may also include a number of additional components such as nitrogen, carbon dioxide, and carbon monoxide. The additional components may be present in the stream at a level of about 1-50% by weight, more preferably from about 10-40% by weight. As will be explained in greater detail below, the presence of these compounds does not appear to foul or meaningfully reduce the sorptive capacity of the sorbent material for the contaminant.

As noted above, the present invention is also useful to remove contaminants from petroleum distillate streams. Such distillate streams include gasoline, kerosene, diesel, and naphthalene streams. Thus, methods of removing contaminants according to the present invention may be used in conjunction with, and preferably downstream from, distillation equipment. Therefore, methods according to the present invention also include forming a petroleum distillate stream including at least one contaminant and then contacting the stream with a plurality of nanocrystalline particles, such as those described herein, in order to remove contaminants present within the stream. In the context of removing contaminants from solids and solid surfaces, the present invention is particularly useful for removing contaminants contained in or released by solid subterranean formations. The present invention is also well suited for preventing release of a contaminant from the solid subterranean formation into a subterranean atmosphere adjacent the formation. Exemplary subterranean formations include coal formations such as found in coal mines, formations containing a metal ore such as found in a metal mine, more specifically gold, silver, iron, copper, or platinum mines, and diamond mines. As used herein, the term "subterranean formation" refers to the actual coal or mineral deposit including the rock formations immediately surrounding or intermingled therewith. Thus, the present invention provides for control of undesirable harmful or toxic compounds that are commonly associated with mine operations, especially hydrogen sulfide, cyanides, and methane.

In the removal of contaminants from a mine, the nanoparticles are preferably included within a foam, suspension, spray, fog, aerosol, paste, sol, liquid carrier, or gel and then sprayed onto the exposed surfaces of the subterranean formation (e.g., the mine walls). The nanoparticles may also be applied to the formation in dry form without the aid of a liquid, foam, or gel carrier. Regardless of how the particles are applied, the nanocrystalline particles are deposited on the surface of the formation so as to adsorb contaminants as they become liberated from the formation thus preventing the contaminants from becoming dispersed in the gaseous atmosphere adjacent the formation. By adsorbing the contaminant as closely as possible to the point of its

, escape or release from the formation, the dangers to workers in the mine, particularly inhalation of the contaminant, are significantly reduced. The foam, suspension, sol, liquid carrier or gel can be applied using a pressurized fluid stream such as water, steam, a compressed gas, such as air, nitrogen, or other inert gas, or simply a pressurized stream of the material containing the nanocrystalline particles. The foam, suspension, sol, liquid carrier or gel may include another material such as a surfactant to assist in suspending the nanocrystalline particles therein or to assist in creation of the foam or gel while applying the particles to the formation surface. The foam, suspension, sol, liquid carrier or gel is preferably applied by a miner working in the mine, or can be applied by a remotely controlled robotic device. This type of subterranean application is to be distinguished from injection into a petroleum or natural gas producing well. In a well injection treatment, the particles are not sprayed directly onto the surfaces of a subterranean formation, but rather are dispersed through a production fluid which resides in or has been injected into the formation. In this particular aspect of the present invention, the nanocrystalline particles are sprayed onto the surface of the solid formation so as to become physically adhered thereto and remain in place so as to most effectively adsorb the contaminant as it escapes or is released from the formation. Thus, the nanocrystalline particles may be directly applied to discrete locations of the solid subterranean formation where they will be most effective rather than having to flood an entire formation with a fluid containing the nanocrystalline particles.

The present invention is also useful in the treatment of air, or the ambient atmosphere, within a mine. The air within a mine can have a chemical makeup that is significantly different than the makeup of the above-ground atmosphere. For example, the air within a mine can include significant amounts of ammonia, carbon dioxide, carbon monoxide, hydrogen, hydrogen sulfide, sulfur dioxide, methane, and oxides of nitrogen in addition to oxygen and nitrogen. Exemplary ranges for the levels of these components are shown in the table below.

The air within the mine can be contacted with the nanocrystalline particles in any manner described above for removing, or reducing the level of, any of those materials that are hazardous to the mine workers.

Often, large quantities of water are used during mining operations thereby generating a significant amount of wastewater that will include contaminants found in the mining formation. The present invention is useful in removing such contaminants present in the wastewater produced from the mine. The wastewater stream may be treated according to any of the methods described above, however, it is preferable to pass the wastewater stream through a filtration medium such as a fixed bed, packed column, or fluidized bed, or continuously stirred tank reactor so that the nanocrystalline particles contact, adsorb, and remove the contaminants present in the wastewater. Following contaminant removal, the wastewater may undergo further treatment so that it can be released into the environment or recycled to the mine. It is also within the scope of the present invention for the wastewater to be contacted with the nanocrystalline particles in treatment tank or other reservoir. The particles may then be added to the tank, and then the contents of the tank can be agitated so as to disperse the particles and maximize contaminant removal. Once the contaminant level has been sufficiently reduced, the particles maybe allowed to settle or float and the treated wastewater drained from the tank. The high sorptive capacity of the nanocrystalline particles may allow for several treatment cycles to occur before having to replace the sorbent.

The nanocrystalline sorbent materials are capable of being regenerated so that they can be used over and over again. Preferred methods of regenerating the sorbent materials include moist air-heating, dry air-heating, and steam-heating methods. The moist air and dry air methods are similar in that they both involve passing a stream of air that is heated to a temperature of between 300-400⁰C through the spent sorbent material. However, in the moist air method, the air stream is humidified by passing the stream through a water bubbler prior to heating. The regeneration process for the moist air and dry air methods is carried out for a period of time of about 3-8 days, and more preferably for about 3 days.

In the steam-heating method, steam at a temperature of about 200-300⁰C and at a pressure of 300-500 psig is passed through the spent sorbent. The steam-heating method can be carried out for considerably less time than either the moist air or dry air methods (i.e., less than about 1 day, more preferably less than about 1 hour), however, caution must be exercised as this method can result in the generation of hazardous byproducts such as hydrogen sulfide gas.

The methods of regenerating the spent sorbent material preferably result in at least a 25 % reduction of the contaminant content of the spent sorbent material, more preferably at least a 33% reduction, and most preferably at least a 50% reduction.

Examples

The following examples set forth preferred methods of sorbing contaminants from various streams using nanocrystalline materials. It is to be understood, however, that these examples are provided by way of illustration and nothing therein should be taken as a limitation upon the overall scope of the invention.

Example 1

In this example, the efficacy of various nanocrystalline materials in removing hydrogen sulfide from a gas stream was determined. The gas stream tested comprised 41.3% hydrogen,

300 ppm hydrogen sulfide, 34.5% nitrogen, 13% carbon dioxide, 10.4% carbon monoxide, and 0.8% methane. All percentages herein are expressed in terms of weight percentages based upon the weight of the entire stream unless otherwise stated.

The gas stream was passed through several different sorbent materials available from NanoScale Materials, Inc., Manhattan, Kansas, under the name NANOACTIVE. These tests were run for 11 days at 400 ° C without significant H₂S breakthrough detected. This corresponds to H₂S adsorption exceeding 0.4 lbs H₂S/lb sorbent. Example 2

In this example, the efficacy of various nanocrystalline materials in removing hydrogen sulfide from a syngas stream produced from coal was determined. The gas stream tested contained 27-37%hydrogen, 14-22% carbonmonoxide, 22-50% carbon dioxide, 4- 19% nitrogen, about 2% methane and other organics, and 750-1500 ppm hydrogen sulfide. Again, this gas stream was tested with several different NANO ACTIVE materials. At 150⁰C in the presence of steam, capacities of 0.2-0.37 lbs of H₂S/lb sorbent were observed.

Example 3

In this example the competitive adsorption capacity of several ZnO nanocrystalline materials was tested for carbon dioxide and hydrogen sulfide. A simulated natural gas stream comprising 93 mol% methane, 7.0 mol% carbon dioxide and 3000 ppm hydrogen sulfide was used in this trial. Table 1 lists the materials tested along with several physical properties thereof.

Table 1

NA-nanocrystalline sorbent CM-Commercial sorbent MeO[NA-ZnO] -nanocrystalline ZnO sorbent having a metal oxide modified surface * indicates an alternative formulation

Initially, each sample was pretreated with carbon dioxide under the following conditions. Approximately 0.1 g of the sorbent was packed in a sorbent column. At ambient conditions, the column was then exposed to a dynamic stream of carbon dioxide at a flow rate of 5 rnL/min. Purging with carbon dioxide continued for more than 10 hours. The simulated natural gas stream was then passed through the sorbent bed at approximately 10 mL/min at 30° C and 90° C. Gas sample aliquots were removed from the gas stream after it had passed through the sorbent bed. These aliquots were analyzed by gas chromatography equipped with a thermo-conductivity detector to determine gas component (namely hydrogen sulfide and carbon dioxide) breakthrough the sorbent bed.

For NA-ZnO at 30° C, carbon dioxide breakthrough occurred after 8 minutes and the sorbent remained saturated for carbon dioxide showing no more sorption. In contrast, hydrogen sulfide breakthrough was first recorded at approximately 73 minutes and sorbent saturation was reached at approximately double this time. Similar results were experienced with the other nanocrystalline sorbents. These results indicate that the nanocrystalline ZnO sorbents are selective for adsorbing hydrogen sulfide over carbon dioxide and that the presence of carbon dioxide in the sample gas did not poison the nanocrystalline ZnO sorbents for their capability to remove hydrogen sulfide.

Example 4

In this example, the ability of several nanocrystalline sorbents to remove hydrogen sulfide from the simulated natural gas stream described in Example 3 was tested. The sorbents were prepared in powder and granule form (mesh size 60-35) and tested under dry and humidified conditions at 30°C and 90°C. About 0.1 g of each sorbent was packed into a sorbent column. The simulated natural gas stream was then passed through the sorbent bed at approximately 10 mL/min until the sorbent was determined to be saturated by GC analysis of gas sample aliquots after passage through the sorbent bed. The hydrogen sulfide capacity of the sorbents were then determined and are noted in Tables 2-6.

Table 2-Sorbency of powder sorbent using dry sample gas

NA-nanocrystalline sorbent

MeO[NA-ZnO]-nanocrystalline ZnO sorbent having a metal oxide modified surface * indicates an alternative formulation

The sorbency of a number of species of nanocrystalline sorbents increased at least 1.5 times when the experiments were performed at elevated temperatures. Generally, NA-ZnO performed just as well as NA-ZnO* and Fe₂O₃[NA-ZnO]*. It is also noteworthy that no zinc- carbonate formation was detected in the spent sorbents.

The sorbency of NA-ZnO in powder and granular form was tested under dry and humidified gas conditions. As shown in Table 3, the granular form out performed the powder under both dry and humidified gas conditions. Most remarkably, the sorbency of the granular form at 30 ° C under humidified gas conditions showed an increase in hydrogen sulfide scrubbing activity of 167% compared to that of the powder. Table 3-Sorbency of powder NA-ZnO v. granular NA-ZnO using dry and humidified gas sam les

Using the same test method as described in Example 3, the selectivity of the sorbent material NA-ZnO for hydrogen sulfide versus carbon dioxide were tested for both the powder and granular forms. Samples of powder and granular NA-ZnO were first saturated with carbon dioxide and then tested for hydrogen sulfide sorption capacity at 30⁰C. These results were compared to the hydrogen sulfide sorption capacity for powder and granular NA-ZnO that were not pre-treated with carbon dioxide. The results, which are shown in Table 4, confirm the findings of Example 3 in that carbon dioxide does not poison the sorbent material and a significant hydrogen sulfide capacity remains.

Table 4:H₂S capacity of carbon dioxide pre-treated NA-ZnO using the dry sample gas at 30⁰C

Next a comparison between nanocrystalline sorbent materials and several commercial materials described above using a humidified sample gas at 30⁰C and 90⁰C was performed. As shown in Table 5, the commercial materials performed so poorly when compared with the nanocrystalline sorbent materials (an order of magnitude of difference) that the trials for the commercial materials were not performed at the higher temperatures. Table 5: Comparison of NA-ZnO materials versus commercial materials in powder form using a humidified sample gas

Lastly, the hydrogen sulfide sorption capacity was compared among NA-ZnO granules and several commercial sorbents using a humidified sample gas at 30⁰C. Again, the NA-ZnO material performed about an order of magnitude better than the commercial sorbents in hydrogen sulfide sorption capacity. The results are shown in Table 6.

Table 6: H₂S capacity of NA-ZnO granules mesh 60-35 versus commercial material for humidified as at 30° C

Example 5

In this example, the regeneration of spent sorbent powder was examined using several methods: a moist air-heating method, a dry air-heating method , and a steam-heating method. In the moist air-heating method, approximately 1 g of spent sorbent with a composition of 96.6% zinc and 2.5% sulfur was placed in a sample holder. The sampled holder was then lowered into a heating mantle. A dry air stream with a flow rate of 37 ml/min was humidified through a water bubbler before reaching the sample holder. The heating temperature was monitored and maintained at 36O⁰C for 3 days at ambient pressure.

Ih the dry air-heating method, a similar procedure as the moist air-heating method was employed except that the moisture source (i.e., the bubbler) was removed. Approximately, 2-4 g of spent sorbent material was heated using a tube furnace at 360⁰C for 3 to 8 days. At the conclusion of each regeneration trial, the sample was recovered and submitted for EDX analysis. The results of these trials are shown in Table 6 and demonstrate that the time required for the regeneration process can be greatly reduced simply by heating the spent sorbent under a wet environment.

Table 7: Regeneration of spent NA-ZnO sorbent using dry air- and moist air-heating methods

In the steam-heating method, a different batch of spend sorbent in granulated form with a composition of 92.4% zinc and 6.9% sulfur was used. The spent sorbent was suspended in a reaction vessel and 20 mL of distilled water was added at the bottom of the vessel. The regeneration study was carried out using an autoclave model Parr 4563 at 250° C and 400 psig for 1 hour. The sample was then recovered and submitted for EDX analysis. The results are noted in Table 8.

Table 8 : Regeneration study of spent sorbent NA-ZnO granules using the steam-heating method

The results show that the steam-heating method was highly effective in regenerating the sorbent in a short amount of time. However, caution should be exercised when performing this regeneration method as the generation of a hazardous by product hydrogen sulfide gas was detected.

Claims

We claim:

1. A method of sorbing a contaminant produced from a subterranean mine comprising contacting said contaminant with a quantity of nanocrystalline particles, said nanocrystalline particles being selected from the group consisting of metal oxides, metal hydroxides, and mixtures thereof having average crystallite sizes of less than about 20 nm.

2. Themethodof claim 1, saidnanocrystallineparticlesbeing contacted with said contaminant inside said mine.

3. The method of claim 1 , said method comprising contacting an exposed surface of said subterranean mine with a quantity of nanocrystalline particles under conditions for sorbing said contaminant.

4. The method of claim 3 , said nanocrystalline particles being incorporated into a foam, suspension, spray, fog, aerosol, paste, sol, liquid carrier, or gel that is sprayed onto said exposed surface of said subterranean mine.

5. The method of claim 4, said foam, suspension, sol, liquid carrier or gel including at least one surfactant.

6. The method of claim 1, said subterranean mine selected from the group consisting of a coal mine, a metal mine, and a diamond mine.

7. The method of claim 6, said metal mine being selected from the group consisting of a gold mine, a silver mine, an iron mine, a copper mine, and a platinum mine.

8. The method of claim 1 , said contaminant being present in a wastewater stream produced during mining operations.

9. The method of claim 8, said contaminant being a cyanide.

10. The method of claim 1 , said contaminant being present in the air within said mine.

11. The method of claim 1 , the air within said mine comprising between about

0.01-50 ppm of hydrogen sulfi.de.

12. The method of claim 1 , said at least one contaminant selected from the group consisting of acids, alcohols, compounds having at least one atom of P, S, N, Se or Te, hydrocarbon compounds, heavy metals and heavy metal containing compounds, toxic metal compounds, bacteria, fungi, spores, viruses, toxins, and mixtures thereof.

13. The method of claim 12, said contaminant being selected from the group consisting of H₂S, H₂SO₄, HCl, HNO₃, C1-C20 thiols, cyanides, C1-C20 sulfides, C1-C20 oxysulfϊdes, C1-C20 disulfides, C1-C20 tliiophenes, rickettsiae, and chlamydia.

14. A method of removing a contaminant from a fluid stream comprising the steps of: providing a fluid stream including at least one contaminant selected from the group consisting of alcohols, heavy metals, heavy metal-containing compounds, H₂SO₄,

HCl, HNO₃, C1-C20 thiols, cyanides including HCN, C1-C20 sulfides, C1-C20 oxysulfϊdes, C1-C20 disulfides, C1-C20 thiophenes; and contacting said stream with a quantity of nanocrystalline particles for sorbing said at least one contaminant, said nanocrystalline particles being selected from the group consisting of metal oxides, metal hydroxides, and mixtures thereof having an average crystallite size of less than about 20 nm.

15. The method of claim 14, said contaminant being present in said stream prior to said contacting step at a level of about 50-5000 ppm.

16. The method of claim 15, said contaminant being present in said stream after said contacting step at a level of less than about 50 ppm.

17. The method of claim 16, said contaminant being present in said stream after said contacting step at a level of less than about 0.1 ppm.

18. The method of claim 14, said nanocrystalline particles being selected from the group consisting of metal oxides, metal hydroxides of Mg, Sr, Ba, Ca, Ti, Co, Fe, V, Mn, Ni, Cu, Al, Si, Zn, Ag, Mo, Zr and mixtures thereof.

19. The method of claim 14, each of said nanocrystalline particles presenting an outer surface, said outer surface being modified with a compound selected from the group consisting of oxides and hydroxides of Ti, V, Cr, Mn, Ni, Co, Cu, and Fe.

20. The method of claim 14, said nanocrystalline particles having surface areas of at least about 20 m²/g.

21. The method of claim 14, said contacting step being performed at a temperature from about -20 to about 400° C.

22. The method of claim 14, said nanocrystalline particles forming a part of a fluidized bed through which said stream is passed.

23. The method of claim 14, said nanocrystalline particles forming a part of a fixed bed through which said stream is passed.

24. The method of claim 14, said nanocrystalline particles forming a part of a continuously-stirred tank reactor.

25. The method of claim 14, said^'nanocrystalline particles being placed within filter media through which said stream is passed.

26. The method of claim 25, said filter media being placed within a subterranean well.

27. The method of claim 14, said stream being a fluid stream produced from a subterranean mine.

28. The method of claim 27, said stream being a wastewater stream produced from a mine contaminated with a heavy metal or heavy metal-containing compound.

29. The method of claim 14, said stream comprising synthesis gas.

30. The method of claim 14, said stream comprising flue gas produced by the combustion of hydrocarbons.

31. The method of claim 14, said stream comprising hydrogen as the primary constituent.

32. The method of claim 14, said stream comprising from about 1-50% by weight hydrocarbon compounds.

33. A method of removing a contaminant from a fluid stream comprising the steps of: providing a fluid stream comprising at least one contaminant, between about 5-99% by weight hydrogen, and less than about 10% by weight hydrocarbon compounds, said at least one contaminant selected from the group consisting of acids, alcohols, compounds having at least one atom of P, S, N, Se or Te, hydrocarbon compounds, toxic metal compounds, bacteria, fungi, spores, viruses, toxins, and mixtures thereof; contacting said stream with a quantity of nanocrystalline particles for sorbing said at least one contaminant, said nanocrystalline particles selected from the group consisting of metal oxides, metal hydroxides, and combinations thereof having an average crystallite size of less than about 20 nm.

34. The method of claim 33, said stream comprising less than about 2% by weight hydrocarbon compounds.

35. The method of claim 33, said stream comprising from about 20-50% by weight hydrogen.

36. The method of claim 33 , further comprising, after contacting said stream with said nanoparticles, feeding said stream to a hydrogen fuel cell.

37. The method of claim 33, said contaminant being present in said stream prior to said contacting step at a level of about 50-5000 ppm.

38. The method of claim 33, said fluid stream comprising synthesis gas.

39. Amethod of removing at least one contaminant from a stream comprising the steps of: providing a stream comprising from aboutl-50%by weight hydrocarbon compounds and at least one contaminant; and contacting said stream with a quantity of nanocrystalline particles for sorbing said at least one contaminant, said nanocrystalline particles selected from the group consisting of metal oxides, metal hydroxides, and combinations thereof having an average crystallite size of less than about 20 nm.

40. The method of claim 39, said stream comprising from about 2-30% by weight hydrocarbon compounds.

41. The method of claim 39, said contaminant being selected from the group consisting of acids, alcohols, compounds having at least one atom of P, S, N, Se or Te, hydrocarbon compounds, toxic metal compounds, bacteria, fungi, spores, viruses, toxins, and mixtures thereof.