AU688491B2 - Densified carbon black adsorbent and a process for adsorbing a gas with such an adsorbent - Google Patents

Description

WO 95/26812 PCT/US95/03806 1 DENSIFIED CARBON BLACK ADSORBENT AND A PROCESS FOR ADSORBING A GAS WITH SUCH AN ADSORBENT BACKGROUND OF THE INVENTION The present invention relates to an adsorbent comprising a densified carbon black, and a process for adsorbing a gas with such an adsorbent.

The adsorption of gases is an important component of many industrial processes. The extent of adsorption is dependent on the ability of the adsorbent to contain the gas. The effectiveness of an adsorbent may be judged from several criteria, depending on the application. The adsorption capacity of the adsorbent may be expressed in terms of the adsorption per unit mass of the adsorbent, or in terms of the adsorption capacity per unit volume of the adsorbent. For some applications, such as the adsorptive storage of natural gas, space is a constraint, and so the adsorption capacity per unit volume of the adsorbent is the criterion for measuring its effectiveness. Thus, a good adsorbent should have a high adsorption capacity both on a unit mass basis, as well as on a unit volume basis. The adsorption capacity per unit volume of adsorbent is dependent on the adsorption capacity per unit mass, as well as the bulk density of the adsorbent material. Thus, increasing the bulk density of the adsorbent will cause an increase in adsorption capacity per unit volume of the adsorbent.

A number of carbon adsorbents have been investigated in the past. For example, Mullhaupt, "Carbon Adsorbents For Natural Gas Storage", International Carbon Conference, June 21-26, 1992, discloses the use of active carbon as a methane adsorbent, as well as the use of certain carbon blacks as methane adsorbents.

U.S. Patent No. 4,999,330 to Bose, et al., describes a densified carbonaceous material for use as a methane adsorbent. As disclosed in this pal.nt, while ther- is an increase in the density of the adsorbent of from 50% to 200%, the corresponding increase in the adsorption capacity per unit volume of the adsorbent ranges from about 20% to about 100%.

It is, therefore, an object of the invention to provide a densified carbon black that exhibits an adsorption capacity per unit volume superior to that shown by undensified carbon blacks.

It is a further object of the invention to provide a process for using such a densified carbon black as an adsorbent for gases.

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SUMMARY OF THE INVENTION The present invention meets these and other objects by providing new adsorbents comprising densified carbon blacks. Upon densification, the carbon blacks preferably have an increase in methane adsorption capacity per unit volume in excess of 100% or more, up to 400% or more, as compared to an undensified carbon black.

The "carbon black" referred to in this invention may be any carbon black, furnace black, thermal black, lamp black, acetylene black, or a carbon black manufactured by any other means, including carbon black and it is formed as a by-product in a process whose primary product is not carbon black. Preferably, the carbon black is a furnace carbon black.

The present invention also provides a process for adsorbing a gas with a densified carbon black adsorbent.

According to a first aspect of this invention, there is provided an adsorbent including a densified carbon black, having a methane storage capacity increase per unit volume at 298 0 K and 35 atm of at least about 142% compared to undensified carbon black, and wherein the densified carbon black 0 0 20 has an increase in density of from about 100% to about 500% over the O 00: o* undensified carbon black.

According to a second aspect of this invention, there is provided a process for adsorbing a gas with an adsorbent including a densified carbon black, said process including the step of contacting said gas with said adsorbent for a sufficient time to adsorb at least a portion of said gas, and wherein said adsorbent has a methane storage capacity increase per unit volume at 298 0

K

and 35 atm of at least about 142% compared to undensified carbon black, and wherein the densified carbon black has an increase in density of from about 100% to about 500% over the undensified carbon black.

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WO 95/26812 PCTUS95/03806 2 -SUMMARY 2F THEI-IVENTtMN--- The present invention meets these and other objects by pro ng new adsorbents comprising densified carbon blacks. Upon densificatio e carbon blacks preferably have an increase in adsorption capacity enit volume in excess of 100% or more, up to 400% or more, as compared to undensified carbon black.

The "carbon black" referred to i is invention may be any carbon black, furnace black, thermal black, la ack, acetylene black, or a carbon black manufactured by any other me including carbon black that is formed as a byproduct in a process w e primary product is not carbon black. Preferably, the carbon black is race carbon black.

The present invention also provides a process for adsorbing a gas with a fAied carbon backadsorbent.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a plot showing uniaxial densification curves for a carbon black, CB-1, and an activated carbon having a nitrogen BET surface area (SA) of 2050 m 2 /g.

FIG. 2 is a plot showing the methane adsorption capacity per unit volume of undensified, isostatically densified, and uniaxially densified carbon blacks.

DETAILED DESCRIPTION OF THE INVENTION When densification is carried out on carbon black as described below, there is a substantial increase in adsorption capacity per unit volume of the carbon black. One important application of densified adsorbents is in the adsorptive storage of natural gas, the efficacy of the adsorbent being measured by the adsorption capacity for methane, per unit volume of adsorbent, at a specified pressure and room temperature. The adsorption capacity per unit volume of adsorbent can be calculated by Vv=(Vw)(d) where Vw is the adsorption capacity of the material per unit mass of adsorbent, and d is the density of the adsorbent pellets. On densifying the material, the density d is increased, and so the adsorption capacity per unit volume, Vv, also increases.

The carbon black may be densified by any one of several densification techniques known in the prior art. One way of compressing the carbon black particles is by the application of pressure uniformly in all directions (isostatic densification For example, the carbon black particles may be densified in a pin pelletizer. The pin pelletizer relies on capillary forces from a wetting fluid, (usually, but not necessarily, water) to densify the carbon black particles and form pellets.. Typically, a measured ig quantity of water is added to a known quantity of carbon black in a pin pelletizer, and L- ~-I WO 95/26812 PCTUS95/03806 3 the resulting mixture is agitated. The rolling motion of the pins and capillary forces due to the wetting fluid cause the formation of pellets.

Some other types of equipment which may be used for isostatic densification in the densification of carbon black include, but are not restricted to, drum pelletizers and disc pelletizers. Operation of such equipment is well known to those skilled in the art, and particularly in the carbon black industry.

Another means of densification of carbon black is by application of pressure in one direction only (uniaxial densification). This technique is commonly used in various fields e.g. catalysis and pharmaceuticals, among others. This may be achieved, for example, by the following procedure. A known mass of carbon black is carefully loaded into a die. For the specific procedure considered here, a steel die of circular cross-secti with an internal diameter of 0.5 inches was used. A plunger of the same external diameter as the internal diameter of the die is inserted into the die and the combination is inserted between the platens of a hydraulic press. Force is applied on the plunger until the desired pressure is exerted on the carbon black within the die. For the present procedure, 0.4 gm of carbon black was subjected to a force of about 20,000 Ibs. (corresponding to a pressure greater than 100,000 psi in the inch diameter die) for a period of three hours. At the end of the constant pressure period, the pressure is gradually reduced and the pellet removed from the die. The volume of the pellet can be calculated from the height of pellet and the diameter of the die. From the weight and the volume, the density of the pellet may be calculated.

Table 1 lists several furnace carbon blacks studied for the purposes of demonstrating the present invention, along with the physical properties of these blacks.

II ,I WO 95/26812 PCT/US95/03806 4 TABLE 1: Properties of some carbon blacks.

Furnace carbon DBP Iodine No. CTAB BET black N2S.A.

m2/g BLACK PEARLS® 2000 330 1412 750 1500 carbon black CB-1 232 669 1021 1756 CB-2 340 655 1057 1936 CB-3 284 754 1081 1976 CB-4 1353 1896 Carbon Black Analytical Properties The CTAB of the carbon blacks was determined according to ASTM Test Procedure D3765-85.

The iodine absorption number (12No.) of the carbon blacks was determined according to ASTM Test Procedure D1510.

The nitrogen surface area (N2SA) of the carbon blacks was determined according to ASTM Test Procedure D3037-Method A.

The dibutyl phthalate absorption value (DBP) of the carbon was determined according to ASTM Test Procedure D3493-86.

For BLACK PEARLS® 2000 furnace carbon black, manufactured and sold by Cabot Corporation, the density ranged between about 0.1 and 0.15 ;/cm 3 before densification and this increased to between 0.27 g/cm 3 and 0.3 g/cm 3 after isostatic densification in a pin pelletizer. The density attained by BLACK PEARLS® 2000 carbon black after uniaxial densification, as described above, ranged between 0.45 and 0.6 g/cm 3 Similarly, the density of another furnace black, designated herein I I I--1 II WO 95126812 PCT/US95/03806 as CB-1, before densification and after uniaxial densification changed from between 0.1 and 0.15 g/cm 3 to between 0.6 and 0.75 g/cm 3 respectively.

FIG. 1 shows uniaxial densification curves for an activated carbon powder having a nitrogen BET surface area of 2050 m 2 /gm (hereinafter the activated carbon), and the CB-1 carbon black. Clearly, the activated carbon does not densify as well as the CB-1 carbon black. Though the initial density of the carbon black is lower than that of the activated carbon, the final density of the CB-1 carbon black at the end of the densification decompression cycle is higher than that of the activated carbon.

Table 2 shows the condition of the two materials at various stages in the uniaxial densification experiment. The percentage increase in density after densification is about 96% for the activated carbon, compared to an increase of greater than 400% for the CB-1 carbon black. It was observed that while the activated carbon did not retain any semblance of shape and became a powder almost immediately after removal from the die, the CB-1 carbon black retained a pellet shape after removal from the die. The point to be noted here is that after decompression the carbon black has a much higher density than exhibited by the activated carbon. Thus it may be assumed that the difference between the structures of the activated carbon and the carbon black is responsible for the inherently superior densification behavior of carbon black.

WO 95/26812 PCT/US95/03806 6 TABLE 2: Data from uniaxial densification experiment for activated carbon and CB-1 carbon black (numbers in brackets show the percentage increase over the undensified material).

Stage in activated carbon CB-1 carbon black densification cycle Before loading material' density 0.3 g/cm 3 density 0.14 g/cm 3 into die Material in die before density 0.42 g/cm 3 density 0.25 g/cm 3 densification begins [79%] Maximum densification density 1.23 g/cm 3 density 1.33 g/cm 3 (at 80,000 psi) [310%] [850%] Material in die at the density 0.59 g/cm 3 density 0.72 g/cm 3 end of densification [414%] cycle Material removed from Does not retain Cylindrically shaped die shape, crumbles into pellet is obtained powder Several specific non-limiting examples of gas adsorption are set forth in Examples I and II. Examples I and II describe the adsorption of nitrogen at 770 K, carbon dioxide at 2730 K, methane at 2980 K and butane at 2730 K. These Examples, carried out with different gases under different conditions of temperature and pressure, demonstrate the general applicability of densified carbon black as an adsorbent. Example III demonstrates the use of several different densified carbon blacks as adsorbents to show that any carbon black can be densified as described herein for use as an adsorbent. Thus, it should be understood that the invention is in no way restricted to the specific examples herein, and that the examples serve only to illustrate the usefulness of the invention.

EXAMPLE Enhancement of the adsorption properties of BLACK PEARLS® 2000 carbon black through densification.

Table 3 shows the adsorption properties of BACK PEARLS® 2000 carbon black as determined by the adsorption of various gases under different conditions of temperature and pressure, on a unit volume basis.

~~ILrl~ WO 95/26812 PCT/US95/03806 7 TABLE 3: Adsorption properties of undensified and densified BLACK PEARLS® 2000 carbon black per unit volume of material (numbers in brackets show the percentage increase over the undensified material) Adsorption property Undensified Densified Densified per unit volume ("fluffy") isosotatically in uniaxially (cm 3 carbon (Density 0.12 a pin pelletizer (density 0.6 g/cm 3 (density 0.29 g/cm 3 g/cm 3 BET surface area, m 2 /cm 3 carbon 175.2 437 [149%] 900 [414%] Micropore volume, cm 3 /cm 3 carbon 0.1158 0.2799 [142%[ 0.579 [400%] Methane adsorption capacity at 298 0 K and 20 49 [145%] 102 [410%] atm., cm 3 STP/cm 3 carbon From the above Table 3, the following can be observed in connection with the ability of a densified carbon black to adsorb nitogen, carbon dioxide and methane gases: 1) BET surface area: The adsorption of nitrogen at 770 K is commonly used as a technique for determining the surface area of a carbon black. This may be done in accordance with ASTM Test Procedure D3037-Method A. The BET surface area is widely used by those skilled in the art as a criterion for judging the usefulness of a material as an adsorbent. The higher the BET surface area, the better the adsorption qualities of the adsorbent for nitrogen at 77 0 K. The surface area may be expressed in m 2 /gm, or m 2 /cm 3 of adsorbent. As stated previously, the objective here is to increase the surface area per unit volume of the adsorbent. Table 3 shows data for the BET surface area of BLACK PEARLS® 2000 carbon black before densification, and after densification using isostatic densification or uniaxial densification. From the data shown in Table 3 it is clear that the surface area per unit volume of the carbon black increases after densification. Thus the densification process is highly beneficial to the adsorption properties of the carbon black, and shows that nitrogen is adsorbed in an increased amount.

WO 95/26812 PCT/US95/03806 8 2) Micropore volume from C02 adsorption at 273 0 K: The adsorption of carbon dioxide at 273 0 K is indicative of the adsorption behavior of gases that are close to their critical temperature. It is also possible to calculate the micropore volume of the carbon black by applying an adsorption theory to the carbon dioxide adsorption data. In this instance, the micropore volume was determined using the method of Dubinin and Astakhov as found in M. M. Dubinin, Progress in Surface and Membrane Science, Vol. 9, edited by Cadenhead, t Academic Press, New York (1975).

Table 3 shows the micropore volume per unit volume of carbon black, both before and after isostatic or uniaxial densification. It is clear from Table 3 that the micropore volume available in a unit volume of adsorbent increases after densifying the carbon black. This indicates that the amount of CO2 adsorbed, per unit volume, is increased upon densification of the carbon black, since the quantity of CO2 adsorbed is directly proportional to the micropore volume.

3) Adsorption of methane at 298 0 K: One of the important future application for adsorbents is the use of such adsorbents to store natural gas for automobiles and other applications. The usefulness of the adsorbent stems from the fact that the same quantity of natural gas that is stored in a tank devoid of adsorbent at high pressures, on the order of 3000 psi, can be stored at considerably lower pressures in the range of 500-1000 psi by utilizing a tank filled with adsorbent. To gauge the suitability of an adsorbent for the storage of natural gas, the adsorption of methane is commonly carried out in the laboratory. Since natural gas consists primarily of methane, the adsorption capacity of methane can be used to gauge the performance of the adsorbent for natural gas storage applications.

Densification of the adsorbent assumes great importance for natural gas applications because the usefulness of the adsorbent is determined by measuring the quantity of methane that can be delivered by the adsorbent, per unit volume of the storage tank. The higher the density of the adsorbent, the smaller the volume of the storage tank required to accommodate a particular mass of adsorbent. Thus, if two materials have the same adsorption capacity for methane per unit weight of the adsorbent they have the same specific adsorption), the material with a higher density will have a higher adsorption capacity per unit volume of adsorbent.

FIG. 2 shows methane adsorpiton isotherms at room temperature for BLACK PEARLS® 2000 carbon black based on unit volume of adsorbent for the undensified black with a density of 0.12 g/cm 3 the black isostatically densified in a pin pelletizer with a density of 0.29 g/cm 3 and the black densified by uniaxial densification, with a density of 0.6 g/cm3. As illustrated in FIG. 2, the adsorption capacity per unit volume of the densified carbon black increases substantially over

I,

WO 95/26812 PCT/US95103806 9 that of the undensified carbon black. It is therefore clear that the increase in density of the carbon black as described herein, translates directly into an increase in adsorption capacity per unit volume of the adsorbent.

Example II-- Adsorption of butane on CB-1 carbon black at 273 0

K:

The adsorption of butane at 273 0 K was carried out on the CB-1 carbon black to establish the suitability of densified carbon blacks for the adsorption of larger gas molecules, such as normal alkanes. The quantity of butane adsorbed at a pressure of 549 Torr was used as a measure of the effectiveness of the CE-1 black as an adsorbent for larger gas molecules. Table 4 shows the change in adsorption capacity of the CB-1 black per unit volume of adsorbent, before densification and after uniaxial densification. As the data set forth in Table 4 clearly show, the adsorption capacity for butane per unit volume of the adsorbent increases after densification.

Table 4: Adsorption capacity of CB-1 carbon black for butane, before and after densification (numbers in brackets show the percentage increase over the undensified material) Adsorption property per Undensified Densified uniaxially unit volume (cm 3 carbon ("fluffy") (density 0.72 g/cm 3 (density 0.14 g/cm 3 Butane adsorption capacity of CB-1 at 549 34 184 [441 Torr and 0 oC, cm 3 STP/cm 3 carbon Example III-- Adsorption of gases on different types of undensified and densified carbon blacks: Example Ill considers the adsorption of gases on several different carbon blacks before and after densification to show that the present invention is applicable to using ary densified carbon black as an adsorbent.

Table 5 shows the BET surface areas as determined from nitrogen adsorption at 77 0 K, for several carbon blacks. Table 5 shows the BET surface area

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WO 95/26812 PCT/US95/03806 per unit volume, before and after densification. The BET surface area per unit volume of all the carbon blacks listed in Table 5 show significent increases after densification.

Table 5: BET surface area for various densified and undensified carbon blacks (numbers in brackets show the percentage increase over the undensified material) Carbon black BET surface area, BET surface a~r', m 2 /cm 3 carbon, m 2 /cm 3 carbon, undensified densified uniaxially BLACK PEARLS® 175 900 [414%] 2000 (density 0.12 g/cm 3 (density 0.6 g/cm 3 carbon black CB-1 260 1289 [396%] (density 0.12 g/cm 3 (density 0.72 g/cm 3 CB-4 183 1037 [467%] (density 0.1 g/cm 3 (density 0.57 glcm 3 Table 6 presents data showing the methane adsorption capacities per unit volume of various caoxon blacks, at a temperature of 298 0 K, and 35 atm.

pressure. The data show the adsorption capacities on a unit volume basis, both before and after densification. As the data set forth in Table 6 show, there is a large increase in the adsorption capacity per unit volume of each of the densified carbon blacks over the undensified carbon blacks.

4 1 4-= WO 95/26812 PCT/US95/03806 11 Table 6: Methane adsorption capacities per unit volume of various carbon blacks, before and after densification (numbers in brackets show the percentage increase over the undensified material) Carbon black Methane adsorption Methane adsorption capacity, cm 3 STP/cm 3 capacity, cm 3 STP/cm 3 carbon for undensified carbon for uniaxially material densified material BLACK PEARLS® 20 102 [410%] 2000 (density 0.12 g/cm 3 (density 0.6 g/cm 3 carbon black CB-1 22 115 [423%] (density 0.14 g/cm 3 (density 0.72 g/cm 3 CB-2 20 102 [410%] (density 0.12 g/cm 3 (density 0.61 g/cm 3 CB-3 17 95 [459%] (density 0.1 g/cm 3 (density 0.55 g/cm 3 CB-4 18 105 [483%] (density 0.1 g/cm 3 (density 0.57 g/cm3) Expressed in other units, Table 7 shows the methane adsorption capacity of BLACK PEARLS® 2000 carbon black before and after densification. The gas storage capacity, as shown in Table 7, clearly increases by an amount of W)m 142 to 402 after densification of the carbon black either by isostatic or uniaxia densification.

WO 95/26812 PCT/US95/03806 12 Table 7: The effect of densification on metl ie storage capacity (at 3.54 Mpa and 298 0 K of BLACK PEARLS® 2000 carbon black Adsorbent Density, Specific Storage g/cm 3 adsorption, capacity, g CH4/100 g g CH4/I adsorbent adsorbent Undensified ("fluffy") 0.12 10.7 12.8 Isostatically densified in a pin 0.29 10.7 31 pelletizer (142%) Uniaxially densified to 100,000 psi 0.6 10.7 64.2 (402%) The purpose of the above examples and the data set forth in the associated tables was to demonstrate the superiority of utilizing the densified carbon blacks as adsorbents. Whereas known prior art carbonaceous materials, when densified, are characterized by an increase in adsorption capacity per unit volume of up to 100%, the densified carbon blacks of the present invention show an increase in adsorption capacity for a gas per unit volume of the adsorbent in excess of 100 or more, and reach values of as much as 400 or more, as compared to undensified carbon blacks. The examples provided herein demonstrate the adsorption of various gases on a range of carbon blacks, under various conditions, to show that the present invention is applicable to any carbon black for the adsorption of any gas.

While preferred embodiments have been shown and described, various modifications and substitutions may be made without departing from the spirit and scope of the invention. Accordingly, it is to be understood that the present invention has been described by way of example and not by limitation.

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Claims (25)

1. An adsorbent including a densified carbon black having a methane storage capacity increase per unit volume at 298 0 K and 35 atm of at least about 142% compared to undensified carbon black, and wherein the densified carbon black has an increase in density of from about 100% to about 500% over the undensified carbon black.

2. The adsorbent of claim 1 wherein the densified carbon black has a nitrogen surface area of at least about 600 m 2 /g.

3. The adsorbent of claim 1 wherein the densified carbon black has a DBP of at least about 150 cc/100g.

4. The adsorbent of claim 1 wherein the densified carbon black has a bulk density of at least about 0.3 g/cm3.

5. The adsorbent of claim 1 wherein the densified carbon black has a micropore volume per cm 3 of carbon increase determined by C02 adsorption at 273 0 K increase over the undensified carbon black of at least about 142%.

6. The adsorbent of claim 1 wherein the densified carbon black is a densified furnace carbon black.

7. The adsorbent of claim 1 wherein the adsorbent is an adsorbent for a gas.

8. The adsorbent of claim 7 wherein the gas includes methane, butane, nitrogen or carbon dioxide.

9. The adsorbent of claim 8 wherein the gas is methane. 14 The adsorbent of claim 1 wherein the densified carbon black has an increase in density of from about 100% to about 500% over the undensified carbon black, a nitrogen surface area of at least about 600m 2 and a DBP of at least about 150 cc/100g.

11. The adsorbent of claim 10 wherein the densified carbon black has an increase in methane adsorption per cm 3 of carbon at 35 atm and 298 0 K over the undensified carbon black of at least 145%.

12. A process for ads. h'ng a gas with an adsorbent including a densified **carbon black, said process including the step of contacting said gas with said adsorbent for a sufficient time to adsorb at least a portion of said gas, and wherein said adsorbent has a methane storage capacity increase per unit volume at 298 0 K and 35 atm of at least about 142% compared to undensified carbon black, and wherein the densified carbon black has an increase in density of from about 100% to about 500% over the undensified carbon black.

13. The process of claim 12 wherein the densified carbon black has a nitrogen surface area of at least about 600 m 2 /g.

14. The process of claim 12 wherein the densified carbon black has a DBP of at least about 150 cc/100g. The process of claim 12 wherein the densified carbon black has a bulk density of at least about 0.3 g/cm 3

16. The process of claim 12 wherein the densified carbon black has an increase in methane adsorption per cm3 of carbon at 298 0 K and 35 atm over the undensified carbon black of at least about 145%.

17. The process of claim 12 wherein the densified carborn black includes a densified furnace carbon black. I I

18. The process of claim 12 wherein the gas includes methane, butane, nitrogen, or carbon dioxide.

19. The process of claim 18 wherein the gas is methane. The process of claim 12 wherein the densified carbon black has an increase in density of from about 100% to about 500% over the undensified carbon black, a nitrogen surface area of at least about 600 m 2 and a DBP of at least about 150 cc/100g.

21. The adsorbent of claim 1, wherein said densified carbon black has a methane storage capacity increase of from about 142% to about 402% compared to the undensified carbon black.

22. The adsorbent of claim 1, wherein said adsorbent has an increase in methane adsorption per cm 3 of carbon at 298 0 K and 35 atm of at least about 145% compared to the undensified carbon black.

23. The adsorbent of claim 22, wherein said adsorbent has an increase in methane adsorption per cm 3 of carbon at 298 0 K and 35 atm of from about 145% "to about 483% compared to the undensified carbon black.

24. The process of claim 12, wherein said adsorbent has a methane storage capacity increase of from about 142% to about 402% compared to the undensified carbon black. An adsorbent consisting essentially of a densified carbon black, wherein the densified carbon black has an increase in density of from about 100% to about 500% over the undensified carbon black, and wherein the adsorbent does not include a binder.

26. The adsorbent of claim 25, wherein said densified carbon black has a I II 16 density of at least about 0.29 g/cm 3

27. The adsorbent of claim 25, wherein the densified carbon black has a nitrogen surface area of at least about 600 m 2 /g.

28. A process for adsorbing a gas with an adsorbent consisting essentially of a densified carbon black, said process including the step of contacting said gas with said adsorbent for a sufficient time to adsorb at least a portion of said gas.

29. A process of claim 28, wherein said densified carbon black has a density of at least about 0.29 g/cm 3 DATED this 18th day of December, 1997. CABOT CORPORATION 0 0* o WATERMARK PATENT TRADEMARK ATTORNEYS o LEVEL 4, AMORY GARDENS S2 CAVILL AVENUE ASHFIELD N.S.W. 2131 AUSTRALIA KJS:PJM:GL DOC 018 AU2231095.WPC