This Application claims priority to Israeli Patent Application No. 284,759, filed July 11, 2021, the contents of which are incorporated by reference as if fully set forth herein.

Field of the Invention

The present disclosure concerns, in some embodiments, an anti-aging additive for impregnated activated carbon, and more specifically, but not exclusively, to an anti aging additive comprised of a phosphate.

Background of the Invention

Activated carbon is a form of carbon processed to have small, low-volume pores that increase the surface area available for adsorption. Due to its high degree of microporosity, one gram of activated carbon may have a surface area of between 1,000 and 2,000 m ² , or even greater.

Activated carbon has many commercial uses, including particularly filtration of noxious gases from the atmosphere. In such uses, the activated carbon is included in a gas mask, NBC filter, or CBRN filter, and filters that are designated for civilian uses. Activated carbon is generally effective, without additional impregnation, in adsorbing organic compounds that do not exhibit high volatility (e.g., boiling point greater than 65°C). However, for effective filtration of volatile organic compounds and low-molecular weight gases, such as hydrogen cyanide (HCN), cyanogen chloride

(CK), sulfur dioxide, ammonia, formaldehyde, and chlorine gas, it is necessary to impregnate the activated carbon with metal additives, usually in the oxide form. It is believed that the impregnated metals bind to the pores of the activated carbon (usually as the oxide form), and chemically adsorb the target gases more effectively than the activated carbon itself. Initially, chromium, together with copper and a small amount of silver, was found to be an effective additive; however, the use of chromium has been discontinued after chromium was discovered to be a carcinogen. Commonly-used additives today include salts of copper, zinc, and molybdenum, silver, and triethylenediamine (TEDA). One commercially produced form of impregnated activated carbon with such additives is the ASZM-TEDA ^® activated carbon produced by Calgon Corporation.

Impregnated activated carbon gradually loses its efficacy when it is exposed to humidity. The adsorbed water causes changes in the impregnated metal oxide (or metal salts) crystallites and causes their migration to the external surface of the activated carbon, and also changes the metal oxide size. As a result, the metal impregnants gradually lose their efficacy against certain noxious gases, especially hydrogen cyanide and cyanogen chloride.

U.S. Patent 10,625,104 discloses a filter material including activated carbon that is impregnated with sulfate and phosphate, among other materials. In the examples given, the sulfate and phosphate were introduced as salts of zinc or ammonium. In a limited set of experiments, the impregnated filter material exhibited modest improvements in resistance to aging.

Summary of the Invention

It is accordingly an object of the present disclosure to provide an additive to activated carbon that would prolong the activated carbon's shelf life. It is a further object of the present disclosure to demonstrate the efficacy of this additive through reliable experiments detailing the composition of the additive and the way the additive is impregnated into the activated carbon.

A long shelf-life activated carbon is described herein. The long shelf-life activated carbon includes phosphates. The inventors have determined, on the basis of reliable, reproducible experiments, that phosphate alone prevents aging of impregnated activated carbon. The phosphate may be sourced from any compound, and in particular from sodium or potassium phosphates. With the phosphate additive, the activated carbon retains at least approximately 75% of its effectiveness in adsorbing cyanogen chloride after accelerated aging of three months, as opposed to less than 20% effectiveness in comparable activated carbon without the phosphate additive. The activated carbon may be implemented in an air filter, or may be used in any suitable application of activated carbon. Methods of manufacture of the long-shelf life activated carbon are also disclosed.

According to a first aspect, a long-shelf life activated carbon includes activated carbon impregnated with salts of copper, zinc, and molybdenum, and TEDA; wherein the activated carbon is also impregnated with phosphate.

In another implementation according to the first aspect, the phosphate is supplied as sodium dihydrogen monophosphate monohydrate, disodium hydrogen phosphate dihydrate, trisodium phosphate, monopotassium phosphate, dipotassium phosphate, or tripotassium phosphate. In another implementation according to the first aspect, the phosphate is supplied as zinc phosphate, copper phosphate, ammonium phosphate, or phosphoric acid.

In another implementation according to the first aspect, following closed accelerated aging of three months at 50 °C, a Ct value of the activated carbon when exposed to cyanogen chloride is at least approximately 70% of a Ct value of the activated carbon prior to the accelerated closed aging.

In another implementation according to the first aspect, following accelerated closed aging of three months at 50 °C, a Ct value of the activated carbon when exposed to cyanogen chloride is at least approximately 70% of a Ct value of the activated carbon prior to the accelerated closed aging.

In another implementation according to the first aspect, when the activated carbon is manufactured by impregnating the phosphate prior to impregnating the salts of copper, zinc, and molybdenum, and following accelerated open aging of three months at 50 °C, a Ct value of the activated carbon when exposed to cyanogen chloride is at least approximately 70% of a Ct value of the activated carbon prior to the accelerated open aging.

In another implementation according to the first aspect, following accelerated closed aging of three months at 50 °C, a Ct value of the activated carbon when exposed to sulfur dioxide is at least approximately 65% of a Ct value of the activated carbon prior to the accelerated closed aging.

In another implementation according to the first aspect, the activated carbon is sulfate-free. In another implementation according to the first aspect, the activated carbon includes sulfate, and the phosphate is supplied separately from the sulfate or together with the phosphate.

In another implementation according to the first aspect, an air filter includes the long shelf-life activated carbon.

According to a second aspect, a method of manufacturing a long shelf-life activated carbon is disclosed. The method includes impregnating the activated carbon with phosphate, wherein the activated carbon is impregnated with salts of copper, zinc, and molybdenum and TEDA.

In another implementation according to the second aspect, the method further includes impregnating the activated carbon with phosphate after the carbon is impregnated with the salts of copper, zinc, and molybdenum.

In another implementation according to the second aspect, the method further includes impregnating the activated carbon with phosphate during or prior to impregnating the activated carbon with the salts of copper, zinc, and molybdenum.

In another implementation according to the second aspect, the impregnating step comprises impregnating sodium dihydrogen monophosphate monohydrate, disodium hydrogen phosphate dihydrate, trisodium phosphate, monopotassium phosphate, dipotassium phosphate, or tripotassium phosphate in an aqueous solution.

In another implementation according to the second aspect, the impregnating step comprises supplying the phosphate as zinc phosphate, copper phosphate, ammonium phosphate, or phosphoric acid. In another implementation according to the second aspect, the impregnating step further comprises: preparing an aqueous solution of the phosphate; dripping the aqueous solution into the activated carbon with incipient impregnation, while stirring; and drying the activated carbon.

In another implementation according to the second aspect, the activated carbon is sulfate-free.

In another implementation according to the second aspect, the method further includes adding sulfate to the activated carbon separate from the impregnating step.

In another implementation according to the second aspect, the method further includes incorporating the activating carbon into an air filter.

Detailed Description of the Invention

The present disclosure concerns, in some embodiments, an anti-aging additive for impregnated activated carbon, and more specifically, but not exclusively, to an anti aging additive comprised of a phosphate.

Before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not necessarily limited to the details set forth in the following description and illustrated in the Examples. The invention is capable of other embodiments or of being practiced or carried out in various ways.

Experimental Setup

The present disclosure demonstrates the effectiveness of the anti-aging additive through a series of tests performed on activated carbon. The tests were performed on 12x30 activated carbon. The appellation 12x30 signifies that at least 95% of the activated carbon particles have a particle size of between 12 and 30 mesh. Certain tests were performed on commercial ASZM-TEDA ^® 12x30 activated carbon manufactured by Calgon Corporation (hereinafter, ASZMT carbon). The composition of the impregnation for ASZMT carbon is 5% copper, 5% zinc, 2% molybdenum, around 0.06% silver, and 3% TEDA. Other experiments were performed on "lab-impregnated" activated carbon other than ASZSMT, as will be described further herein.

In order to test efficiently the effect of phosphate on aging of activated carbon, impregnated activated carbon was aged using accelerated aging.

Accelerated aging is a laboratory process that is used to approximate the natural aging process, which occurs at room temperature, in less time. In general, accelerated aging techniques, as disclosed in the present disclosure, are assumed to approximate a time period around 20 times as long for a non-accelerated aging. Thus, for example, 45 days of accelerated aging corresponds to 900 days of room- temperature aging, and three months of accelerated aging corresponds to 1,800 days, which is approximately 5 years, of room-temperature aging.

In general, activated carbon may age in one of two ways: open aging and closed aging. In open aging, after water adsorbs onto the activated carbon, the filter is open and exposed to atmospheric air. In closed aging, after the water absorbs onto the carbon, the filter is closed and sealed from the atmosphere. The filter closing is accomplished by closing valves, in the case of a collective filter, or corking, in the case of a personal filter. Due to the sealing, the activated carbon keeps its water content. In order to mimic the effects of open and closed aging, the accelerated aging of the experimental activated carbon was performed in one of two ways: "closed accelerated aging" and "open accelerated aging." Closed accelerated aging refers to a procedure in which the pre-humidified carbon is placed in a sealed container (jar) under elevated temperature. For each sample, before the aging, the impregnated activated carbon was humidified by passing through the carbon bed a 20 l/min airflow at a temperature T=18.0±0.2°C and Relative Humidity=85±2% until equilibrium was reached. The final water content was approximately 30 grams for every 100 grams of dry carbon. The humidified carbon was then sealed in a closed jar and stored at 50±0.5 °C, for a duration of 45, 60, 90, or 180 days. For open accelerated aging, the carbon was pre-humidified in the same manner as close ageing and thereafter was stored in an open jar in a chamber with a temperature of 50±0.5 °C having 85±2% relative humidity (RH=85%).

According to results obtained by the present inventors, aging the carbon in a sealed container causes greater acceleration of aging than aging in an open container. To be considered effective at preventing aging, an additive should prevent aging, or at the least limit aging to acceptable levels, both following closed accelerated aging and following open accelerated aging. Nevertheless, it is reasonable to believe that preventing aging within a sealed container is a more significant achievement.

In addition, following accelerated aging, there are two techniques for measuring the ability of the activated carbon to withstand a noxious gas. In one technique, the activated carbon is tested in its humid state. In another technique, the activated carbon is dried after aging, but before testing. Generally, drying the activated carbon improves the protection against cyanogen chloride (CK), when it is tested after accelerated aging. For the sake of evaluating the effectiveness of the phosphate additive, tests were performed both on aged carbon that was preserved in its humidified state, and on aged carbon that was dried.

Following accelerated aging (open or closed), and optionally drying as discussed, the activated carbon was exposed to cyanogen chloride. Specifically, an activated carbon bed having height of 18.5 mm was filled into a testing tube of 60 mm diameter. Cyanogen chloride gas was flowed at an inlet concentration of 2.6 g / m ³ (which may also be expressed as 2,600 mg / m ³ ), and at a linear air flow velocity of 5.9 cm/s (flow rate 10 L/min). The relative humidity of the airflow was 75%. The testing was continued until a breakthrough concentration of 1.5 mg / m ³ , corresponding to approximately 0.5 ppm, was reached.

The ability of the activated carbon bed to protect against CK is measured based on the parameter called protection values or concentration time (Ct values). Concentration time is a measure of exposure to a gas, and is calculated as the influent concentration (C ₀ ) multiplied by the time of exposure (t _B ). It is assumed that, when the product of concentration and time is constant, over a limited range of concentration and time, so is the biological effect. Because concentration is expressed as milligram per cubic meter (mg / m ³ ) and time as minutes, concentration time is measured as milligram-minutes per cubic meter (mg*min / m ³ ). A larger value of Ct signifies that more noxious gas is required to be present in an area in order to break through the filter. Control Samples

Table 1 below compares the average Ct values for dried activated carbon and humidified activated carbon, following closed aging, when neither sample was impregnated with phosphate. The results of the experiments are shown in Table 1 below.

Table 1 - Effect of Accelerated Closed Aging and Humidity on Protection of Commercial Impregnated Activated Carbon (commercial ASZMT) Average Ct values (thousands of mg*min / m ³ )

Parenthetically, the Ct values may be converted to breakthrough time in minutes by dividing the Ct values by the cyanogen chloride concentration of 2.6 x 10 ³ mg/m ³ . Since the values listed in Table 1 are units of thousands, this requires only dividing the values listed in Table 1 by 2.6. For example, the new humidified carbon has a breakthrough time of 65 minutes, and the humidified carbon aged over three months has a breakthrough time of less than 12 minutes.

The results demonstrated that accelerated closed aging for three to six months dramatically reduced the efficacy of the carbon, whether the carbon was dried or humidified. At the same time, drying the aged carbon after aging improved the efficacy of the carbon. Impregnation with Phosphate

Impregnated activated carbon with a phosphate anti-aging additive was prepared in one of two preparations. In the first preparation, the phosphate was added to the activated carbon prior to copper, zinc, molybdenum, and TEDA additives. In the second preparation, the copper, zinc, molybdenum, and TEDA additives were added to the activated carbon prior to the phosphate.

Example 1 - Lab preparation of Impregnated Activated Carbon with Phosphate from BPL ^® Carbon

An aqueous solution containing phosphate was dripped into activated carbon while stirring. In exemplary embodiments, the source of the phosphate was sodium dihydrogen monophosphate monohydrate (Nah^PC h^O). Other sources of phosphate, and differences in the concentration of phosphate, will be discussed further below. The carbon that was used was BPL ^® 12x30 activated carbon, manufactured by Calgon Corporation. BPL ^® is a virgin granular activated carbon derived from bituminous coal. The volume of the aqueous phosphate solution was 0.7 milliliters per gram of dry carbon. This volume is less than the volume of the pores of the carbon. As a result, at the end of the process, the carbon appeared dry. This process is also known as incipient impregnation. The carbon was dried at a temperature of 120 °C for two hours. The drying evaporated the water, while the phosphate additive remained in the pores of the carbon.

An impregnation solution including carbonate salts of copper, zinc, and molybdenum was prepared. The impregnation solution further included ammonia as ammonium hydroxide and ammonium carbonate, for aiding the dissolution of the copper and zinc salts in the aqueous solution. The impregnation solution was dripped into the activated carbon at a volume of 0.7 milliliters / gram. The activated carbon was dried at 100 °C for 30 minutes and then at 130 °C for another 30 minutes. The impregnation solution was then dripped into the activated carbon a second time, this time at a volume of 0.55 milliliters / gram. The activated carbon was dried at 100 °C for 30 minutes, then at 130 °C for another 30 minutes, then at 160 °C for 45 minutes, then at 180 °C for 45 minutes. During this drying process, the water, ammonia, and ammonium carbonate evaporated. The carbonate ions that were originally in the metallic salts also evaporated as C0 . The copper and zinc ions descended into the pores of the activated carbon, and as a result of the high temperature, were converted to zinc oxide (ZnO) and cupric oxide (CuO), both of which have extremely low solubility in water. TEDA was added to the activated carbon, via incipient impregnation, while mixing. The carbon was dried again at 80 °C, a temperature that is low enough to ensure that the TEDA evaporation from the carbon is negligible.

The resulting impregnated activated carbon had 5% copper, 5% zinc, 2% molybdenum, and 3% TEDA. This impregnated activated carbon was similar but not identical to ASZMT carbon (with respect to ingredients other than the phosphate). Specifically, unlike ASZMT, which contains about 0.05% silver, the resulting concentration did not contain any silver.

Activated carbon prepared according to the methods of Example 1 will also be referred to herein as lab-impregnated activated carbon. The relative order of impregnation of the phosphate, metal salts, and TEDA may be changed. For example, the phosphate may be impregnated in between the metal salts and the TEDA. As another example, the TEDA may be impregnated at the same time as the phosphate, after the impregnation of the metal salts. In still another example, the phosphate is impregnated at the same time as the metal salts, when the metal salts have phosphate anions instead of carbonate anions (for example, zinc phosphate, copper (I) phosphate, or copper(ll) phosphate. The common feature of all these embodiments, however, is that the metal salts and TEDA are impregnated in the lab.

Example 2 - Impregnation of Phosphate into Commercial ASZMT

An aqueous solution of phosphate was dripped into ASZMT carbon, while stirring, at a volume of 0.5 ml / gram of the activated carbon. At the end of the process, the carbon appeared dry. The carbon was dried at 80°C for three hours. The drying removed the water, while the phosphate additive was presumably retained in the pores of the activated carbon, which also contained the metals and the TEDA.

In experimental data given below, the amount of phosphate is expressed as a percentage, for example, 7% NaH ₂ P0 ₄ -H ₂ 0. The percentages are expressed as a percentage, by weight, of the phosphate-containing ingredient, as compared to the activated carbon prior to the commencement of phosphate addition. For example, in Example 1 above, 7% NaH ₂ P0 ₄ -H ₂ 0 is added to lab-impregnated BPL carbon, while in Example 2, 7% NaH ₂ P0 ₄ -H ₂ 0 is added to ASZMT carbon. It should be appreciated to those of skill in the art that the resulting compounds have slightly different net percentages of NaH ₂ P0 ₄ -H ₂ 0, because, in example 1, additional materials are also added to the activated carbon, which would thereby lower the effective percentage of NaH ₂ P0 ₄ -H ₂ 0. Thus, in Example 2, the net weight percentage of NaH ₂ P0 ₄ -H ₂ 0 is 6.54% (7/(100+7)). In Example 1, addition of the metal salts and TEDA to 100 grams of activated carbon increases the total weight to approximately 129 grams. Addition of an additional 7 grams of NaH ₂ P0 ₄ -H ₂ 0 (7% vis a vis the original activated carbon) brings the total weight to 136 grams, thereby giving an effective weight percentage of 5.2% (7/(129+7)). Certain experimental results will be reported below comparing the effect of a given percentage of phosphate, when the same concentration was added via the method of Example 1 or the method of Example 2. In light of the above, such experimental materials should be understood as having equivalent initial weights of phosphate, but not necessarily equivalent final weight percentages of phosphate.

Demonstrating Effectiveness of the Phosphate Additive for Inhibiting Aging

Tables 2a and 2b below illustrate the ability of phosphates to inhibit the aging of impregnated activated carbons regarding cyanogen chloride adsorption. The ability of the cyanogen chloride to adsorb onto the activated carbon is measured based on the parameter of concentration time (Ct values). In some cases below, only values for humidified aged activated carbon are given, since carbons that were dried after aging provided better results, as discussed above.

Table 2a shows the effect of 7% NaH ₂ P0 ₄ -H ₂ 0 on the Ct values of cyanogen chloride for impregnated ASZMT activated carbon. The commercial ASZMT with phosphate was prepared according to the method of Example 2 above. The impregnated carbon was either tested immediately, or aged for 45 days up to six months in closed or open accelerated aging conditions, as described above.

Table 2a - Effect of Phosphate on Protection of Humidified Impregnated Activated Carbon, for Commercial ASZMT Carbon Ct values (thousands of mg*min / m ³ )

Table 2b reports the results of similar experiments, using lab-impregnated carbon instead of ASZMT carbon.

Table 2b - Effect of Phosphate on Protection of Humidified Impregnated Activated

Carbon, for Lab-Impregnated Carbon

Ct values (thousands of mg*min / m ³ )

A number of conclusions may be drawn from Tables 2a and 2b. First, considering the two left columns of each table, in each instance of impregnated carbon without phosphate, aging dramatically decreased the ability of the carbon to filter cyanogen chloride after three months, to the point of being rendered virtually ineffective. The accelerated closed aging was more detrimental to protection values than open accelerated aging. In both Table 2a and Table 2b, the deterioration of the protection over time was significantly greater for closed aging.

In addition, as seen in the two right columns of Tables 2a and 2b, the phosphate additive is effective at preventing aging. In three of the four examples in which phosphate was added, the efficacy of the filter decreased by only around 20- 30% after three months. In addition, in these measurements, the activated carbon in which the phosphate was impregnated prior to the metals and TEDA (lab impregnated carbon with phosphate) performed better than the alternative (commercial ASZMT with phosphate). This difference was especially striking with regard to six months accelerated aging, in which the lab-impregnated activated carbon dramatically outperformed the ASZMT carbon, for both open and closed aging. This difference is further striking when considering that the effective weight percentage of the phosphate in the lab-impregnated activated carbon was actually approximately 1.2% lower than that of the ASZMT carbon, as discussed. Also of note, the phosphate had significantly less efficacy on the commercial ASZMT carbon that was aged with open aging, as seen in the rightmost column of Table 2a.

Further of note, in both preparations of activated carbon, the phosphate reduced the initial Ct value before aging - from 170 to 117 for the commercial ASZMT, and from 171 to 152 for the lab-impregnated carbon. This reduction is not significant, and in a real-life scenario is relevant just for a short time after the exposure to humid air before aging starts to be significant. That is, shortly after exposure of the activated carbon to humidity, the humidity causes an equivalent reduction in the Ct value. This is especially the case because, usually, in commercially-produced gas filters, activated carbon is included in excess of the minimum amounts needed for protection against cyanogen chloride. The extension of the life of the activated carbon far outweighs the minor initial loss in protection.

Effect of Drying

The same experiments as those summarized in Tables 2a and 2b were also performed on activated carbon that was dried after closed aging. The results of impregnation with 7% NaF^PC I-^O, for both commercial ASZMT activated carbon and for lab-impregnated activated carbon, are summarized below in Table 3:

Table 3 - Effect of Phosphate on Protection of Dried Impregnated Activated Carbon.

Closed Aging

Ct values (thousands of mg*min / m ³ )

In general, drying the aged carbon before measurement increased the Ct values, compared to the results reported in the third columns of Tables 2a and 2b. It is presumed that one of the reasons for improvement in Ct values for dried charcoal is because dried charcoal also adsorbs the relevant gases in a physical manner that is not significantly affected by aging, in addition to the chemical adsorption that is affected by aging. In practice, this means that even when activated carbon with the phosphate additive has aged past its expected shelf life, the protection capability may be recovered to a large degree by drying the activated carbon. The improvement in performance was also observed with regard to the fresh carbon (top row of Table 3), which showed no loss of effectiveness following inclusion of the phosphate additive.

Concentration of Phosphate

In order to evaluate the optimum phosphate concentration, further experiments were conducted varying the concentration of NaH ₂ P0 ₄ -H ₂ 0. In each case, ASZMT carbon impregnated with phosphate was pre-humidified at a relative humidity of 85%, sealed in a closed jar while humidified, and aged for three months and 6 months at 50 °C. The activated carbon was then subjected to a flow of air with RH=75%, and contaminated with cyanogen chloride in the manner described above. In addition, similar experiments were conducted on fresh carbon. The results of these experiments are summarized in Tables 4a and 4b below.

Table 4a - Effect of Phosphate Concentration for Fresh and Aged Carbon (commercial ASZMT, Closed Accelerated Aging)

Ct values (thousands of mg*min / m ³ )

As can be seen, there was no significant difference in the efficacy of the phosphate additive between concentrations of 3.5%, 5%, and 7%.

Table 4b includes results of the same concentration experiments for lab- impregnated carbon.

Table 4b - Effect of Phosphate Concentration for Fresh and Aged Carbon flab- impregnated, Accelerated Closed Aging)

Ct values (thousands of mg*min / m ³ )

According to the data of Table 4B, the concentration of NaH ₂ PC> ₄ -H ₂ C> that is most effective is greater than 4.5%, particularly 7% or more.

It should be noted that, for the monohydrate form of sodium dihydrogen monophosphate, 69% of the mass of the complex is attributed to the phosphate group, since the molar mass of P0 ₄ is 94.97 and the molar mass of the entire complex is 136.99. Thus, concentrations of 3.5%, 5%, and 7% of the NaH ₂ P0 ₄ -H ₂ 0 correspond to concentrations of 2.4%, 3.5%, and 4.9% of just the phosphate, rounded to one decimal place. The effective concentration of the phosphate is measured based on addition of the phosphate to ASZMT carbon, as discussed. When the same amount of phosphate is added to the BPL carbon, the range of effective concentration is reduced to 2.0%, 2.8%, and 4.0%, respectively.

Sources of Phosphates

As mentioned above, in exemplary embodiments, the phosphate for the additive is sourced from NaH ₂ P0 ₄ -H ₂ 0. In order to evaluate whether the source of the phosphate contributes to its efficacy in preventing aging, experiments were performed on phosphate additives sourced from various chemicals. Of these chemicals, the most efficient source was NaH ₂ P0 ₄ -H ₂ 0. A runner-up source that was still highly efficient was phosphoric acid (H ₃ P0 ₄ ).

Table 5 below summarizes the results of testing conducted with H ₃ P0 ₄ . The phosphate additive was impregnated into commercial ASZM-TEDA ^® at different concentrations, and was subjected to accelerated aging in the manner discussed above. Certain measurements were obtained only with humidified carbon, and certain measurements were obtained with activated carbon that was dried after closed aging, with the effect of drying being an increase in the Ct value, as previously observed in connection with Table 3.

Table 5 - Effect of Phosphate Concentration for Fresh and Aged Carbon (commercial ASZMT, Accelerated Closed Aging) - H P0 ₄ Ct values (thousands of mg*min / m ³ )

The results demonstrate that H ₃ P0 ₄ actually reduces the initial efficacy of the activated carbon by a small amount for lower concentrations, on approximately the same level as the N3H ₂ R0 ₄ ·H ₂ 0. For a concentration of 7% H ₃ P0 ₄ , the reduction in initial efficacy was more significant. Nevertheless, the H ₃ P0 ₄ was to some extent effective at inhibiting aging. For example, the 3.8% H ₃ P0 ₄ had a Ct value of 65 after 3 months, as opposed to the 0% H ₃ P0 ₄ which had a Ct value of 30 after 3 months. Similarly, after 6 months, the 7% H ₃ P0 ₄ had a Ct value of 29, as opposed to the unmodified aged activated carbon which had a Ct value of just 5.

H ₃ P0 ₄ was much more effective in preventing aging of activated carbon in which the metal additives were impregnated in the lab. Table 6 reviews some experimental results obtained on humid activated carbon, with closed aging. Table 6 - Effect of Phosphate Concentration for Lab-Impregnated Carbon - H P0 ₄

Ct values (thousands of mg*min / m ³ )

As can be seen, H ₃ P0 ₄ is highly effective for preventing aging of lab- impregnated carbon, even after accelerated closed aging of 6 months. As previously mentioned, unlike the commercial ASZMT carbon, in the lab impregnated carbon, the phosphate was added before the metals and the TEDA. The phosphoric acid, however, did not provide significant protection with respect to activated carbon that underwent open accelerated aging, compared to the control sample.

In view of the above-summarized results, it may be said that, overall, phosphoric acid is a less-effective source for the phosphate than NaH ₂ P0 ₄ .

Studies were also conducted on Na ₂ HP0 ₄ -2H ₂ 0, on lab-impregnated activated carbon, after closed aging. All studies were performed on humidified carbon. The results of these studies are summarized in Table 7.

Table 7 - Effect of Phosphate Addition for Lab-Impregnated Carbon - Na HPQ ₄ -

(Accelerated Closed Aging)

Ct values (thousands of mg*min / m ³ ) These studies appear to demonstrate that phosphate sourced from Na ₂ HP0 ₄ -2H ₂ 0 is also effective at preventing aging, but not as effective as NaH ₂ P0 ₄ -H ₂ 0, as can be seen from a comparison of Table 2 (Ct of 115 for 3 month aged carbon) and Table 7 (Ct of 88 for 3 month aged carbon).

Studies were also performed on trisodium phosphate (Na ₃ P0 ₄ -12H ₂ 0). Table 8 summarizes the results of the experiments on Na ₃ P0 ₄ -12H ₂ 0, which were performed on commercial ASZM-TEDA ^® carbon that was dried after aging.

Table 8 - Effect of Trisodium Phosphate Concentration for commercial ASZMT Carbon (Accelerated Closed Aging) - Na PQ ₄ -12H ₂ 0 Ct values (thousands of mg*min / m ³ )

The experiments appear to demonstrate that Na ₃ P0 ₄ -12H ₂ 0 exhibited no benefit in preventing closed aging after three months, and certainly that the Na ₃ P0 ₄ -12H ₂ 0 is less effective than NaH ₂ P0 ₄ -H ₂ 0, as can be seen by comparing Table 8 with Table 3 (showing, for the commercial ASZM-TEDA carbon, 3 month Ct values of 119 and 6 month values of 97).

Similar experiments were performed with Na ₃ P0 ₄ -12H ₂ 0 on lab-impregnated activated carbon, which was dried after aging, the results of which are summarized in Table 9: Table 9 - Effect of Phosphate Concentration for Lab-impregnated Carbon -

Na P0 ₄ -12H 0 (Accelerated Closed Aging) Ct values (thousands of mg*min / m ³ )

It is evident, based on the results, that phosphate sourced from trisodium phosphate, in the absence of acidic conditions, is not efficient for inhibiting aging. However, it may be that if Na ₃ P0 ₄ were added in an acidic environment, or if the Na ₃ P0 ₄ were added together with an acid or acidic compound, the efficiency of Na ₃ P0 ₄ would be better. This is because the acidic conditions may contribute hydrogen to the phosphate and cause the sodium phosphate to function effectively as Na ₂ HP0 ₄ or NaH ₂ P0 ₄ .

The foregoing experimental results have demonstrated that the phosphate additive enhances the efficacy of activated carbon against aging. The experiments further demonstrate that, generally, NaH ₂ P0 ₄ is the most reliable source of phosphate, although other sources of phosphate are also effective under certain conditions. The best 3 month accelerated aging results, for both open and closed aging, were for lab-impregnated carbon, with 7% NaH ₂ P0 ₄ , as shown in Table 2B.

However, the results do not address whether the addition of phosphate negatively impacts any features of the activated carbon. To address this concern, additional experiments were conducted on both the structure of the activated carbon and on the efficacy of activated carbon against gases other than cyanogen chloride.

With regard to the structure of the activated carbon, two standard diagnostic tests were performed, comparing characteristics of ASZMT activated carbon both before and after impregnation with 7% NaH ₂ P0 ₄ -H ₂ 0. The surface area of the activated carbon was calculated according the Brunauer-Emmett-Teller (BET) method. In addition, the micropore volume was measured according to the t-plot method. The results of these experiments are displayed below in Table 10.

Table 10 - Effect of Phosphate on Structural Features of Activated Carbon

As can be seen, there were no significant differences to the surface area and micropore volume of the activated carbon.

The effect of the phosphate additive was evaluated for sulfur dioxide, toluene, and ammonia.

Regarding sulfur dioxide, S0 ₂ adsorption tests were performed according to the following procedure. Sulfur dioxide gas was flowed at an inlet concentration of 1000 ppm, and at a linear air flow velocity of 5.9 cm/s (flow rate 10 L/min). The relative humidity of the air flow was 70%. The testing was continued until a breakthrough concentration of 5 ppm was reached. Table 11 shows the effect of 7% NaH ₂ P0 ₄ -H ₂ 0 on the Ct values for S0 ₂ for impregnated activated carbon. The commercial ASZMT with phosphate was prepared according to the method of Example 2 above. The lab impregnated carbon without phosphate was prepared according to Example 1 above, but skipping the impregnation with phosphate. The impregnated carbon was either tested immediately, or aged for 3 and 6 months in pre-humidified conditions, with closed aging, as described above.

Table 11: Effect of Phosphate (NaH2PQ4-H 0) for Humidified Impregnated Activated Carbon against SO _?, Accelerated Closed Aging Ct values (thousands of mg*min / m ³ )

The table above shows that NaH ₂ P0 ₄ is an effective aging inhibitor with regard to

S0 ₂ adsorption. For commercial ASZMT carbon, the effect is clear after aging for 3 months. Moreover, the ASZMT carbon without phosphate aged significantly more quickly than lab impregnated carbon with the phosphate.

Regarding toluene, unlike cyanogen chloride and S0 ₂ , toluene is physically

(not chemically) adsorbed onto activated carbon. Aging does not significantly decrease the efficiency of impregnated carbon against toluene under dry conditions. Accordingly, as with sulfur dioxide, it was deemed sufficient to measure the toluene adsorption with fresh activated carbon (without aging), to make sure that the phosphate addition did not significantly decrease the Ct values against physically adsorbed organic compounds. Experimental results demonstrated that toluene adsorption was not affected by addition of 7% NaH ₂ P0 ₄ -H ₂ 0. This result also accords with results obtained in Table 9, above, Because the phosphate did not change the surface area or micropore volume, it is logical that there should be no effect on the adsorption of toluene.

Regarding ammonia, the phosphate appears to even improve the protection of the activated carbon against ammonia, if the activated carbon had been pre humidified. The impregnation of the activated carbon certainly does not negatively impact the adsorption of ammonia.

Further experimentation may help determine optimum conditions for reducing the effects of aging on adsorption of hydrogen cyanide (HCN), and whether the optimum conditions for preventing aging with respect to HCN are the same as those with respect to cyanogen chloride.

In view of the above-described experimental results, the phosphate additive described above is very different from the phosphate additive described in U.S. Patent 10,625,104. First, the phosphate additive used in the above experiments lacks the presence of any sulfates. Thus, it is possible to isolate the effect of the phosphate in preventing the aging. It is possible, in embodiments of the present disclosure, that sulfates may be used in addition to phosphates, for enhanced protection against other gases such as ammonia, as is known to those of skill in the art. In such embodiments, the sulfate may optionally be supplied separate from the phosphate. Regardless, the above-described results demonstrate that the phosphate is effective even in sulfate-free impregnations.

Second, the above-described experiments demonstrate that the phosphate additive is effective when it is added as a salt of various cations, and particularly when it is sourced as NaH ₂ P0 ₄ . In addition, the percentage of the phosphate used greatly exceeds the percentages of phosphate suggested to be effective in that disclosure.

In addition, the experimentation supporting the present disclosure is significantly broader. In the present disclosure, the phosphate was shown to be effective in preventing aging even for accelerated aging of up to 180 days. The experiments described above further demonstrate that the order of addition of ingredients and the method of aging may influence the efficacy of the additive. Finally, the samples of aged activated carbon used in the above-described experiments were aged according to industry standards, and included experimental controls, in order to verify the effectiveness of the phosphate. The experimental controls included studies of the Ct values for carbon without phosphate, both fresh and aged with open and closed aging, and for fresh carbon with phosphate, as discussed above.

Many alternatives are possible to the embodiments described herein. For example, instead of the activated carbon being sourced from coal, it may be sourced from any other source of activated carbon that is known or that may become known, such as bamboo, coconut husks, willow peat, wood, coir, lignite, or petroleum pitch. The phosphate may be added to different commercial activated carbons, as well as activated carbons impregnated with different metals, or different concentrations of copper, zinc, molybdenum, and/or silver. In addition, while the disclosed concentration of B.5%-7% of NaH ₂ P0 ₄ -H ₂ 0, corresponding to 2.4-4.9% P0 ₄ , has been shown to be effective, other concentrations of phosphate may prove to be equally effective. The phosphate may also be sourced from alternative sources such as zinc phosphate or copper phosphate, supplied to the impregnation in place of zinc carbonate and copper carbonate, or ammonium phosphate in place of ammonium carbonate or ammonium hydroxide. In particular, because potassium ions are similar to sodium ions in many respects, it is expected that monopotassium phosphate, dipotassium phosphate, or tripotassium phosphate would exhibit similar effectiveness as the corresponding sodium phosphates.