Patent Application
20080047313
The invention will now be described by way of an exemplary embodiment with reference to the accompanying simplified, diagrammatic, not-to-scale drawings. In the drawings:
The present invention relates to a solid porous media produced from carbonaceous materials that are impregnated with acid, and an apparatus for removing ammonia from a gas stream by flowing the gas through the solid porous media impregnated with acid, and a composition that is the by-product of reacting ammonia with the acid impregnated in the activated carbon matrix. When describing the present invention, the following terms have the following meanings, unless indicated otherwise. 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 following description is intended to cover all alternatives, modifications and equivalents that are included in the spirit and scope of the invention, as defined in the appended claims.
“Carbonaceous material” shall mean any biomass material, which includes recently or once living biological material such as plants, animals, algae, or micro-organisms, or any materials or residues formed from once living organisms. Carbonaceous materials may include, without limitation, wood and other lignocellulosic material, animal waste or byproducts such as digested or composted animal manure, agricultural byproducts, peat moss, straw, municipal solid waste, bedding materials containing manure, nut shells, coconut coir, and fossil fuels and fossil fuel byproducts such as coal and petroleum coke.
“Liquid acid” shall mean any inorganic acid including, but not limited to, sulphuric, phosphoric, nitric, or hydrochloric acid.
“Activated carbon” shall mean a solid microporous material with high surface area comprised primarily of elemental carbon and containing small amounts of other elements originally found in the carbonaceous materials from which the activated carbon was formed, which may include but are not limited to such elements as oxygen, hydrogen, nitrogen, sulphur, silicon, aluminum, iron, calcium, magnesium, sodium, and potassium.
“Activated carbon matrix” shall mean activated carbon in a solid form sufficiently porous to allow passage of gas through its interior spaces.
“Gas” shall mean any substance or combination of substances that exists in a gaseous state at standard temperature and pressure.
“Chemisorption” shall mean the attachment or adsorption of a gas molecule onto a solid or liquid surface and any reactions that might ensue between the gas molecule and the solid or liquid.
The inventors have found that carbonaceous materials will react with liquid acid to form an activated carbon matrix impregnated with the acid. This reaction may occur under ambient conditions.
In general terms, an acid-impregnated activated carbon matrix may be formed by:
The carbonaceous material may comprise any suitable biomass material, including wood and other lignocellulosic material, animal waste or byproducts such as digested or composted animal manure, peat moss, straw, municipal solid waste, bedding materials containing manure, nut shells, coconut coir, coal and petroleum coke. Wood chips or shavings are a particularly preferred carbonaceous material.
The moisture content of the carbonaceous material depends on the feedstock and the particle size, and may have a range of about zero to 50% on a wet mass basis, preferably about 5 to 35% and more preferably about 15 to 25%. The carbonaceous material may be dried if the moisture content is higher than the desired level, or water may be added to the carbonaceous material to bring up the moisture level.
The carbonaceous material may be processed into particles of an appropriate size, depending on the intended application and the feedstock, by any suitable method, including for example, chopping, grinding, cutting or otherwise reducing the particle size. Additionally, if the feedstock consists of very small particles, the particles maybe agglomerated to create larger particles of a suitable size. The particle size of the carbonaceous material may have an average range of about 0.1 mm to 10 mm, preferably about 1 to 5 mm and more preferably about 3 mm.
The liquid acid may be any suitable mineral acid, such as sulphuric, phosphoric, hydrochloric, or nitric acid. The choice of acid will of course change the salt formed if the acid reacts with a chemisorbed molecule. Thus, if the material is being used to remove ammonia from a gas stream, then the use of sulphuric acid will result in the formation of ammonium sulphate.
The concentration of liquid acid used depends on the moisture content of the carbonaceous material, lower concentrations are suitable for lower moisture content, and may have a range of about 20 to 100%, preferably about 75 to 100% and more preferably 100% (where 100% is the concentrated form of the acid). The amount of liquid acid used depends in part on the particle size of the carbonaceous material and the concentration of the acid used, and may have a range of about 1 part acid to 1 part carbonaceous material (by weight) for smaller particles, to 10 parts acid to 1 part carbonaceous material for the largest (about 10 mm) particles. Preferably, the ratio of acid to carbonaceous material is about 2:1 to 5:1 and more preferably about 4:1 (by weight).
The carbonaceous material and the liquid acid are mixed until the reaction is substantially complete, which length of time depends on the moisture content, particle size, acid concentration and acid/feedstock ratio, but is typically between about 2 to 35 minutes, preferably about 5 to 25 minutes and more preferably about 15 minutes. In one embodiment, completion of the reaction may be monitored by temperature. As the reaction starts, the temperature typically rises to reach a maximum and falls as the reaction completes.
In one embodiment, the liquid acid is sprayed on the carbonaceous material as mixing proceeds. In another embodiment, the carbonaceous material is formed into pellets and then the liquid acid is applied to the pelletized form of carbonaceous material.
The acid converts the carbonaceous material into an activated carbon matrix, and excess acid impregnates itself onto the activated carbon matrix. Even though there are large amounts of acid impregnated in the carbon matrix, the product looks and behaves as a solid material. A solid matrix containing large amounts of a strong acid is scientifically and commercially important because gas can be flowed through porous activated carbon matrix more efficiently and inexpensively than through an equivalent amount of liquid.
In one embodiment, the conversion of the carbonaceous material to activated carbon, and the impregnation of acid, takes place in one step. Furthermore, the acid-impregnated activated carbon matrix does not require further processing prior to use as a chemisorbent. Thus, no heat treatment, washing or neutralization step, or subsequent gas sulfonation step is required or desired.
As a result, the acid-impregnated carbon matrix may be used as a chemisorbent material because of its microporosity and large surface area. Hence, any basic constituent in a gas which is flowed through the material can be more efficiently removed and converted into a solid by-product.
In one embodiment, the material may be used to remove ammonia from a gas stream. Ammonia reacts with inorganic acids to form the corresponding ammonium salt and will be retained by the solid material as the gas passes through.
A gas stream containing ammonia may be routed through a sealed reaction chamber comprising the acid-impregnated activated carbon matrix, either in solid, granular or pelletized form. The activated carbon matrix may comprise a fixed bed or may be disturbed by gas flow or by mechanical means, such as with a fluidized bed, or a pseudofluidized bed. Preferably, means are provided to periodically replenish or replace the activated carbon matrix.
The ammonia is chemisorbed by the acid-impregnated activated carbon matrix and converted to a fertilizer salt with little residual acidity and only small amounts of carbon and other elements. Thus, the spent activated carbon matrix is a useful source of selected nutrients for agriculture and horticultural applications. As such, the expense of ammonia removal is reduced and a value-added by-product is created.
The spent activated carbon matrix may be pelletized using conventional methods to form fertilizer pellets or otherwise processed into a useful agricultural or horticultural form. If pelletized or processed in granular form, the pellets may provide a slow-release mechanism for the ammonium salt fertilizer.
In one embodiment, the ammonium salt, such as ammonium sulphate, is elutriated from the activated carbon matrix with water. The ammonium sulphate solution can then be concentrated and formed as a fertilizer, leaving the activated carbon matrix.
The following examples are intended to illustrate but not limit the claimed invention.
Concentrated sulphuric acid was added to carbonaceous material in weight ratios varying from about 2.5:1 to about 4.5:1. The temperature of the material was monitored, and the final acid content of the material was recorded. The results are shown in Table 1 below.
It can also be seen from Table 1 that liquid acid not only transforms the carbonaceous material to activated carbon but results in the impregnation of acid in activated the carbon matrix. Depending on the ratio of liquid acid to carbonaceous material, as much as 82% by weight of the resulting activated carbon matrix is comprised of acid.
Furthermore, Table 1 shows that the maximum temperature of the reaction decreases as the ratio of acid to carbonaceous material increases. Although not shown in Table 1, none of the trials resulted in more than five percent loss in mass balance, that is, the sum of the loss of carbonaceous material and acid during the reaction to produce the solid product did not exceed five percent.
The extent of the reaction of several carbonaceous materials with sulphuric acid was quantified. The transformation of several carbonaceous materials into porous activated carbon matrix comprising activated carbon was demonstrated by a large change in surface area.
(1)Derived from anaerobic digestion
Reacting a carbonaceous material with a liquid acid leads to a large increase in surface area of the carbon matrix, especially of wood. The surface area of wood shavings prior to the reaction was approximately two square meters per gram; after the reaction the surface area increased to more than six hundred square meters per gram. This represents approximately a three-hundred fold increase in surface area. It should be noted that biosolids originating from the anaerobic digestion of cattle manure showed approximately a ten-fold increase in surface area as a consequence of treatment with sulphuric acid, while commercial peat moss showed approximately a five-fold increase in surface area from the same treatment.
It has been surprisingly found that any concentration of ammonia in a gas stream will be completely and rapidly chemisorbed by the acid-impregnated activated carbon matrix.
(1)Relative Humidity
(2)Derived from anaerobic digestion
The results tabulated in Table 3 shows that ammonia in a gas stream, ranging from ninety five parts per million by volume to one hundred fifty thousand parts per million by volume, is chemisorbed by the activated carbon matrix so that outlet concentrations of ammonia are less than one part per million. Furthermore, Table 3 shows that varying temperature or relative humidity of the gas does not affect ammonia chemisorption, provided that a significant decrease in temperature does not occur.
In order to determine critical response variables, testing was conducted to determine the minimum bed depth and reaction time required to adsorb 100% of ammonia present in a gas stream.
(1)Critical response variables are the minimum parameter values required to adsorb 100% of the NH3
(2)Derived from anaerobic digestion
Table 4 shows that only seven to eleven millimetres of acid-impregnated activated carbon matrix is needed to quickly (sixty one to one hundred and nine milliseconds) chemisorb all ammonia (approximately two thousand parts per million by volume) from a gas flowing at ten to seventeen centimetres per second. Our conclusion is that ammonia chemisorption is very rapid and needs very little exposure to the mass of acid-impregnated activated carbon matrix to be completely removed. Table 4 shows that high gas temperatures (60° Celsius) do not affect the retention time needed to chemisorb ammonia, as long as the gas does not drop in temperature as it passes through the activated carbon matrix (all gas streams were saturated with moisture at their respective temperatures). It is also noteworthy that Table 3 and Table 4 show that the source of the carbonaceous material, whether it originates from wood shavings or biosolids from cattle manure, does not significantly affect the required retention time for ammonia chemisorption.
We determined by testing that the acid-impregnated activated carbon matrix, even when it has been converted to its fertilizer salt, will facilitate the flow of gas with minimum pressure drop even, and even when flow rates are high. The graph shown in
The amount of ammonia adsorbed by acid-impregnated activated carbon matrix was measured by the ratio of ammonia adsorbed per unit mass of the activated carbon matrix. Table 6 shows that the acid-impregnated activated carbon matrix adsorbs between two hundred and two hundred and twenty three milligrams of ammonia per gram of activated carbon matrix, representing twenty to twenty three percent of ammonia by weight.
Table 6 also shows that the bulk density of the activated carbon matrix after chemiadsorption of ammonia increases to approximately five hundred to seven hundred kilograms per cubic meter.
Testing was conducted to determine the chemical composition of acid-impregnated activated carbon matrix after chemisorption of ammonia. The fully converted acid-impregnated media is termed “spent” activated carbon matrix. Table 7 shows the chemical composition of the spent activated carbon matrix after full chemisorption of ammonia has been completed. It can be seen from
(1)Includes elements in ammonium sulphate and residues from adsorbent matrix.
Furthermore, Table 7 shows that only six tenths of one percent of the original acid remains in the spent activated carbon matrix. The elemental composition of the spent activated carbon matrix is consistent with the large proportion of fertilizer salt, which is ammonium sulphate in the case of the experiment giving rise to the data presented in Table 7. The carbon content remaining from the original wood shavings or other carbonaceous materials is less than six percent by weight.
This application claims the priority benefit of U.S. Provisional Application No. 60/823,347 filed on Aug. 23, 2006 entitled “Preparation of Ammonia-Chemisorbent Carbonaceous Material Using Liquid Acid”, the contents of which are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 60823347 | Aug 2006 | US |
