Polycyclic aromatic hydrocarbon adsorbent

Abstract

To provide an adsorbent for polycyclic aromatic hydrocarbons containing clay minerals such as sepiolite and attapulgite, which exhibits excellent removal rates for polycyclic aromatic hydrocarbons. [Solution] An adsorbent comprising at least one of sepiolite and attapulgite, wherein, in the pore distribution measured by mercury intrusion, the volume of pores in the range of pore diameter 10 nm or more and 100 nm or less is in the range of 0.50 mL / g or more and 2.00 mL / g or less, and the volume of pores in the range of pore diameter 10 nm or more and 30 nm or less is in the range of 0.40 mL / g or more and 1.20 mL / g or less.

Description

[Technical Field]

[0001] This invention relates to an adsorbent for adsorbing polycyclic aromatic hydrocarbons. [Background technology]

[0002] Polycyclic aromatic hydrocarbons are carcinogenic and, when burned, lead to the generation of soot (particulates), so their removal is desired in various fields. For example, Patent Document 1 discloses a method for removing polycyclic aromatic hydrocarbons contained in diesel fuel by adding 30g to 150g of heat-treated clay, obtained by treating acidic clay at a temperature of 80°C to 250°C under air circulation for 3 to 10 hours, to 1000ml of diesel fuel in a diesel fuel tank. Patent Document 2 discloses a method for adsorbing sulfur compounds and polycyclic aromatic hydrocarbons in hydrocarbon oil using biomass that has been carbonized at 300 to 900°C or activated after carbonization. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2019-151761 [Patent Document 2] Japanese Patent Publication No. 2007-284337 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] While various adsorbents for adsorbing polycyclic aromatic hydrocarbons are known, no adsorbent containing at least one of sepiolite and attapulgite that exhibits excellent removal rates for polycyclic aromatic hydrocarbons has been known until now.

[0005] The present invention aims to provide an adsorbent for polycyclic aromatic hydrocarbons comprising at least one of sepiolite and attapulgite, which exhibits excellent removal rates for polycyclic aromatic hydrocarbons. [Means for solving the problem]

[0006] The inventors of the present invention have found that the above problems can be solved by using an adsorbent comprising at least one of sepiolite and attapulgite, wherein, in the pore distribution measured by mercury intrusion, the volume of pores in the range of 10 nm to 100 nm in diameter is in the range of 0.50 mL / g to 2.00 mL / g, and the volume of pores in the range of 10 nm to 30 nm in diameter is in the range of 0.40 mL / g to 1.20 mL / g, and have completed the present invention. [Effects of the Invention]

[0007] According to the present invention, an adsorbent for polycyclic aromatic hydrocarbons containing clay minerals such as sepiolite and attapulgite can be provided, which exhibits excellent removal rates for polycyclic aromatic hydrocarbons. [Brief explanation of the drawing]

[0008] [Figure 1] This shows the pore distribution of the adsorbent obtained by the mercury intrusion method in Example 1. [Modes for carrying out the invention]

[0009] This invention includes an invention relating to an adsorbent for removing polycyclic aromatic hydrocarbons (hereinafter also referred to as "the adsorbent of the present invention"). The adsorbent of the present invention will be described in detail below.

[0010] [Adsorbent of the present invention] The adsorbent of the present invention comprises at least one of sepiolite and attapulgite, and in the pore distribution measured by mercury intrusion, the volume of pores with a pore diameter in the range of 10 nm to 100 nm is in the range of 0.50 mL / g to 2.00 mL / g, and the volume of pores with a pore diameter in the range of 10 nm to 30 nm is in the range of 0.40 mL / g to 1.20 mL / g.

[0011] The adsorbent of the present invention comprises at least one of sepiolite and attapulgite. In the adsorbent of the present invention, sepiolite is an adsorbent for adsorbing polycyclic aromatic hydrocarbons. Sepiolite is a type of clay mineral, and is a chain-like clay mineral that differs from common clay minerals such as kaolin and talc, which are layered clay minerals. A typical chemical structure of sepiolite is shown in the following formula (1).

[0012] Mg4Si6O 15 (OH)2·6H2O (1)

[0013] Sepiolite occurs as a naturally occurring mineral, and its chemical composition can vary depending on its origin and refining method. However, even if the chemical composition differs, if a sepiolite diffraction pattern is obtained in the X-ray diffraction of the adsorbent, it can be determined that the adsorbent contains sepiolite. Furthermore, if the adsorbent is made using sepiolite as a raw material, it can be presumed that the adsorbent contains sepiolite.

[0014] Furthermore, in the adsorbent of the present invention, attapulgite is an adsorbent medium for adsorbing polycyclic aromatic hydrocarbons. Attapulgite is a natural silicate mineral mainly composed of hydrated magnesium and aluminum silicate, and is also called acid clay. A typical chemical structure of attapulgite is shown in the following formula (2).

[0015] Mg(Al 0.5-1 Fe 0-0.5 )Si4O 10 (OH)·4H2O (2)

[0016] Similar to the aforementioned sepiolite, if diffraction patterns derived from these can be confirmed by X-ray diffraction, it can be determined that this adsorbent contains attapulgite. In addition, even in the case of an adsorbent using attapulgite as a raw material, it can be determined that this adsorbent contains attapulgite.

[0017] Furthermore, the adsorbent of the present invention may contain both sepiolite and attapulgite.

[0018] The content rates of sepiolite and attapulgite in the adsorbent of the present invention are preferably 30% by mass or more, more preferably 40% by mass or more, and particularly preferably 50% by mass or more, as a ratio with respect to the mass of the adsorbent. When the content rates of sepiolite and attapulgite increase, more polycyclic aromatic hydrocarbons can be adsorbed. The content rates of sepiolite and attapulgite in the adsorbent of the present invention may be 90% by mass or less, may be 80% by mass or less, and may be 70% by mass or less. The content rates of sepiolite and attapulgite can be estimated from the mixing ratio when manufacturing the adsorbent. Also, it can be estimated from the chemical composition of the adsorbent using the aforementioned chemical structural formulas (1) and (2).

[0019] The adsorbent of the present invention has a pore volume of pores with a pore diameter in the range of 10 nm or more and 100 nm or less in the pore distribution measured by the mercury intrusion method in the range of 0.50 mL / g or more and 2.00 mL / g or less. In the adsorbent of the present invention, pores with a pore diameter in the range of 10 nm or more and 100 nm or less are pores effective for the diffusion of a medium containing polycyclic aromatic hydrocarbons, and are particularly effective for the diffusion of a liquid medium. The adsorbent of the present invention, in addition to containing an adsorbent medium such as sepiolite and attapulgite, has many such pores, so that the removal of polycyclic aromatic hydrocarbons is accelerated. The pore volume of pores with a pore diameter in the range of 10 nm or more and 100 nm or less may be 2.00 mL / g or less, may be 1.75 mL / g or less, and may be 1.50 mL / g or less.

[0020] The adsorbent of the present invention has a pore distribution measured by mercury intrusion, in which the volume of pores with a diameter in the range of 10 nm to 30 nm is in the range of 0.40 mL / g to 1.20 mL / g. In the adsorbent of the present invention, pores with a diameter in the range of 10 nm to 30 nm are effective pores for the diffusion of hydrocarbon oils containing polycyclic aromatic hydrocarbons. In addition to containing adsorbents such as sepiolite and attapulgite, the adsorbent of the present invention has many such pores, which allows for the efficient removal of polycyclic aromatic hydrocarbons contained in hydrocarbon oils, which have a small difference in polarity compared to polar solvents such as water. The volume of pores with a diameter in the range of 10 nm to 30 nm may be 1.20 mL / g or less, 1.10 mL / g or less, or 1.00 mL / g or less.

[0021] The adsorbent of the present invention preferably has a total pore volume of 0.40 mL / g or more, and more preferably 0.50 mL / g or more, determined from the pore distribution measured by the mercury intrusion method. A larger total pore volume leads to faster removal of polycyclic aromatic hydrocarbons. The adsorbent of the present invention may have a total pore volume of 1.80 mL / g or less, 1.50 mL / g or less, or 1.20 mL / g or less, determined from the pore distribution measured by the silver intrusion method.

[0022] The adsorbent of the present invention may contain a pore-forming agent. For example, by including chemically stable inorganic particles such as silica, alumina, silica-alumina, and calcium silicate with specific particle sizes as a pore-forming agent, pores of various sizes can be imparted to the adsorbent. The unique pore distribution of the adsorbent of the present invention can also be produced by methods other than those containing a pore-forming agent, as will be described later. The adsorbent of the present invention, by containing a pore-forming agent, is superior to the adsorbent without a pore-forming agent in terms of strength and chemical stability. The content of the pore-forming agent is preferably 10% by mass or more, more preferably 20% by mass or more, and particularly preferably 30% by mass or more, as a percentage of the mass of the adsorbent. Furthermore, the content of the pore-forming agent is preferably 70% by mass or less, more preferably 60% by mass or less, and particularly preferably 50% by mass or less. When the content of the pore-forming agent is reduced, the content of sepiolite and attapulgite can be increased, so that more polycyclic aromatic hydrocarbon compounds can be removed.

[0023] The adsorbent of the present invention may contain a reinforcing agent. A reinforcing agent is an agent that increases the physical strength of the adsorbent. For example, the physical strength of the adsorbent can be increased by adding fibrous inorganic oxides. Since increasing the size of the adsorbent tends to decrease its physical strength, a reinforcing agent can be added to compensate for this. Also, when the adsorbent of the present invention is manufactured without using a pore-forming agent, the physical strength of the adsorbent tends to be low, so it is preferable to include a reinforcing agent. The reinforcing agent content is preferably 1% by mass, more preferably 3% by mass or more, and particularly preferably 5% by mass or more, as a percentage of the mass of the adsorbent. Furthermore, it is preferably 20% by mass or less, more preferably 15% by mass or less, and particularly preferably 10% by mass or less. When the reinforcing agent content is low, the content of sepiolite and attapulgite can be increased, so that more polycyclic aromatic hydrocarbons can be adsorbed.

[0024] The adsorbent of the present invention may contain at least one of sepiolite and attapulgite, and may also contain components other than the pore-forming agent and the reinforcing agent. The content thereof is preferably 5% by mass or less, more preferably 3% by mass or less, and particularly preferably 1% by mass or less.

[0025] The specific surface area of the adsorbent of the present invention is preferably 80 m 2 / g or more, more preferably 110 m 2 / g or more, and particularly preferably 140 m 2 / g or more. When the specific surface area increases, the polycyclic aromatic hydrocarbons contained in the hydrocarbon oil are likely to diffuse to the inside of the adsorbent. As a result, the removal rate of the polycyclic aromatic hydrocarbons contained in the hydrocarbon oil increases. The specific surface area in the present invention refers to the specific surface area determined by the BET one-point method. The specific surface area of the adsorbent of the present invention may be 300 m 2 / g or less, may be 250 m 2 / g or more, and may be 200 m 2 / g or less.

[0026] In addition to the aforementioned pores, the adsorbent of the present invention preferably has developed pores with a pore diameter exceeding 0 nm and not exceeding 1 nm. In the adsorbent of the present invention, the pores in this pore diameter range are derived from sepiolite and attapulgite. When the crystal structures of sepiolite and attapulgite are developed, the pores in this pore diameter range are also developed, and more polycyclic aromatic hydrocarbons can be adsorbed. The pores with such a small pore diameter are measured by a gas adsorption method rather than the aforementioned mercury intrusion method. Specifically, in the pore size distribution (vertical axis: Log differential pore volume, horizontal axis: pore diameter) obtained from the adsorption isotherm measured by the nitrogen adsorption method, the height of the peak appearing in the pore diameter range exceeding 0 nm and not exceeding  1 nm is preferably 0.15 mL / g or more, and particularly preferably 0.25 mL / g or more. The height of this peak may be 0.80 mL / g or less, may be 0.70 mL / g or less, and may be 0.60 mL / g or less.

[0027] The shape of the adsorbent of the present invention may be spherical, columnar (including cylindrical and tetrahedron-shaped), or similar. Its size (minimum length of the adsorbent's outer shape) is preferably 0.5 mm or more, and more preferably 1 mm or more. A larger adsorbent size reduces pressure loss when a medium containing polycyclic aromatic hydrocarbons is passed through it. Its size is preferably 10 mm or less, and more preferably 6 mm or less. A smaller adsorbent size increases the contact area between the adsorbent and the medium containing polycyclic aromatic hydrocarbons, thus accelerating the removal of polycyclic aromatic hydrocarbons.

[0028] The bulk density of the adsorbent of the present invention is preferably 0.10 g / mL or more, more preferably 0.20 mL / g or more, and particularly preferably 0.30 g / mL or more. A higher bulk density allows more adsorbent to be packed into the adsorption column, thus enabling the adsorption of more polycyclic aromatic hydrocarbons. The bulk density of the adsorbent of the present invention is preferably 0.70 g / mL or less, more preferably 0.60 mL / g or less, and particularly preferably 0.50 mL / g or less. A lower bulk density reduces the impact when packing the fixed-bed adsorption column and the load applied after packing, thereby suppressing the collapse and pulverization of the adsorbent.

[0029] The adsorbent of the invention can remove polycyclic aromatic hydrocarbons contained in various media, and can remove polycyclic aromatic hydrocarbons contained in hydrocarbon oils more efficiently. Furthermore, the aforementioned media may be liquid or gas. The adsorbent of the present invention can remove polycyclic aromatic hydrocarbons more efficiently even in liquids, where the removal efficiency of liquid polycyclic aromatic hydrocarbons tends to be lower compared to gases.

[0030] The adsorbent of the present invention has a unique pore distribution. For example, such a pore distribution can be imparted by a method of preparing secondary particles containing sepiolite and attapulgite, with particles of different sizes being prepared and mixed to form a molded body. Alternatively, it can be imparted by a method of mixing sepiolite and attapulgite with a gas generating agent, forming a molded body, and then removing the gas generating agent by heat treatment or the like. Furthermore, it can also be imparted by mixing sepiolite and attapulgite with a pore-forming agent and forming a molded body. The method of manufacturing the adsorbent of the present invention will be described in detail below using the method of mixing with a pore-forming agent as an example, but the method of manufacturing the adsorbent of the present invention is not limited to this method.

[0031] A method for producing the adsorbent of the present invention by mixing a pore-forming agent comprises the following steps (1) to (3).

[0032] (1) A molding precursor preparation step, which involves mixing at least one of sepiolite and attapulgite with a pore-forming agent and a solvent to prepare a molding precursor. (2) Molding process to obtain an adsorbent precursor by molding the molding precursor into pellets. (3) A drying step in which the adsorbent precursor is dried at a temperature of 700°C or lower to obtain an adsorbent.

[0033] [(1) Preparation of molding precursor] The above manufacturing method includes a molding precursor preparation step of preparing a molding precursor by mixing at least one of sepiolite and attapulgite with a pore-forming agent and a solvent. In this step, a clay-like kneaded material containing each component of the adsorbent of the present invention is prepared.

[0034] In this process, the mixing of sepiolite and attapulgite is preferably 30% by mass or more, more preferably 40% by mass or more, and particularly preferably 50% by mass or more, based on the total amount of solids excluding the solvent. As the mixing ratio of sepiolite and attapulgite increases, an adsorbent capable of adsorbing more polycyclic aromatic hydrocarbons is obtained. This mixing ratio may be 90% by mass or less, 80% by mass or less, or 70% by mass or less.

[0035] The mixing ratio of the pore-forming agent in this process is preferably 10% by mass or more, more preferably 20% by mass or more, and particularly preferably 30% by mass or more, based on the total amount of solids excluding the solvent. Furthermore, this mixing ratio is preferably 70% by mass or less, more preferably 60% by mass or less, and particularly preferably 50% by mass or less. Lowering this mixing ratio allows for an increase in the content of sepiolite and attapulgite, thereby enabling the removal of more polycyclic aromatic hydrocarbon compounds.

[0036] The pore-forming agent in this process is preferably a chemically stable inorganic particle such as silica, alumina, silica-alumina, or calcium silicate. Furthermore, its average particle diameter is preferably in the range of 1 μm to 50 μm, and more preferably in the range of 5 μm to 40 μm. In this process, the average particle diameter refers to the median diameter (D50) in the volume-based particle size distribution measured using a laser diffraction particle size analyzer. When a pore-forming agent with an average particle diameter within the aforementioned range is used in this process, a large number of pores with a diameter of 10 nm to 100 nm tend to be produced. Additionally, when wet silica is used as the pore-forming agent, the specific surface area tends to be larger. Wet silica is amorphous silica synthesized in a liquid. Because wet silica has a small primary particle size, its specific surface area tends to be higher.

[0037] The solvent in this process is a component that fixes the aforementioned sepiolite and attapulgite with the pore-forming agent to form a precursor suitable for molding. In this process, either an inorganic solvent or an organic solvent can be used as the solvent, but the use of an inorganic solvent is preferred, and the use of water is more preferred. The mixing ratio of the solvent varies depending on the properties of the aforementioned components, so it is difficult to uniquely determine a preferred range, but it is preferable to mix it in a range of 10% by mass or more and 70% by mass or less of the total amount of the molding precursor. If the amount of solvent added is small, the aforementioned components tend to fix together and become granular, and such a molding precursor can be suitably used as a precursor for tablet molding. On the other hand, if the amount of solvent added is large, the fixing of the aforementioned components progresses further and tends to become clay-like, and such a molding precursor can be suitably used as a precursor for extrusion molding.

[0038] The mixing method used in this process is a conventionally known method. For example, mixing can be done using a high-speed mixer, mill, etc. Mixing can also be done using a kneader. These mixing methods can be selected as appropriate, taking into consideration manufacturing efficiency, etc.

[0039] [(2) Molding process] In this step, the molding precursor obtained in the previous step can be molded using conventionally known methods. For example, it can be molded into pellets using tableting, extrusion molding, etc. When using tableting, it is preferable to set the granular molding precursor in a tablet forming machine and apply a constant pressure. The shape of the cylinder used at this time can determine the shape of the adsorbent that is ultimately obtained. Furthermore, it is preferable to use extrusion molding in this step. Compared to tableting, extrusion molding is less likely to damage the pores derived from the pore-forming agent. For example, the clay-like molding precursor can be extruded using a single-screw auger extruder or a disc pelletizer. The shape of the die used at this time can determine the shape of the adsorbent that is ultimately obtained.

[0040] [(3) Drying process] In this step, the adsorbent precursor obtained in the previous step can be dried using conventionally known methods. For example, air drying, heat drying, vacuum drying, or a combination thereof can be used. The drying temperature is preferably 700°C or lower, more preferably 500°C or lower, and particularly preferably 300°C or lower. This is to prevent the properties of each component contained in the adsorbent precursor from changing due to heat. In particular, at high temperatures, the structures of sepiolite and attapulgite may change.

[0041] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0042] [Measurement method or evaluation method] Various measurements and evaluations were performed as follows:

[0043] [1] Pore distribution using mercury adsorption method Approximately 3 g of the adsorbent obtained in each example was placed in a porcelain crucible, heated at 120°C for 1 hour, then cooled to room temperature in a desiccator to obtain a sample for measurement. The sample was then measured using the mercury intrusion method (mercury contact angle: 150 degrees, surface tension: 480 dyn / cm).

[0044] [2] Pore distribution using nitrogen adsorption method Approximately 3 g of the adsorbent obtained in each example was placed in a porcelain crucible, heated at 120°C for 1 hour, and then cooled to room temperature in a desiccator to obtain a sample for measurement. N2 adsorption measurements were then performed using a BELSORP-mini II manufactured by Microtrac-Bel. The pore distribution of the adsorbent was calculated from the obtained N2 adsorption isotherm using the BJH method. The maximum value of the volume distribution in the pore diameter range of 0 to 1.0 nm was determined with the Y axis representing the volume distribution (dVp / dlogdp).

[0045] [3] Specific surface area Approximately 30 mL of the adsorbent obtained in each example was placed in a porcelain crucible (Type B-2), heated at 120°C for 1 hour, and then cooled to room temperature in a desiccator to obtain a sample for measurement. Next, 1 g of this sample was taken and the specific surface area (m²) of the sample was measured using a fully automated surface area analyzer (MultiSorb 12, manufactured by Yuasa Ionics Co., Ltd.). 2 The concentration (per g) was measured using the BET method.

[0046] [4] Bulk density 50g of the adsorbent obtained in each example was dropped by gravity into the upper opening of a 250ml graduated cylinder to fill it, and the volume (V1) when the top of the packed layer was made horizontal was measured and calculated using the following formula.

[0047] Bulk density = 50 / V1 [g / mL]

[0048] [5] Polycyclic aromatic hydrocarbon adsorption test The adsorbents obtained in each example were packed tightly into a reaction tube to a layer height of 20 mm and attached to an adsorption test apparatus. The reaction tube was pre-treated at 150°C for 1 hour under nitrogen flow and then cooled to room temperature. Subsequently, xylene containing 0.1 mM indeno[1,2,3-cd]pyrene as a polycyclic aromatic hydrocarbon was flowed at a rate of 1 ml / min. Ten minutes after the start of flow, the flowed liquid was sampled for 5 minutes, and the ultraviolet-visible absorption spectrum of the liquid was measured using a 10 mm quartz cell. The absorbance of the absorption band at 365 nm, which originates from indeno[1,2,3-cd]pyrene, was determined in the ultraviolet-visible absorption spectra of the liquid before and after the adsorbent flow. The greater the decrease in absorbance from the liquid sampled before flow to the liquid sampled after flow, the higher the adsorption capacity for polycyclic aromatic hydrocarbons can be evaluated.

[0049] [Raw materials] Sepiolite; manufactured by IMV NEVADA, THERMOGEL Attapulgite; manufactured by IMV NEVADA, Min-U-Gel-200 Wet-processed silica; manufactured by Oriental Silicas Corporation, Toxil 928, average particle size 11 μm Calcium silicate; Tomita Pharmaceutical Co., Ltd., FLORITE R, average particle size 30 μm

[0050] [Example 1] 336 g of sepiolite, 275 g of wet silica as a pore-forming agent, and 450 g of deionized water were mixed in a kneader to obtain a clay-like molding precursor. This molding precursor was molded in an extrusion molding machine to obtain an adsorbent precursor. This adsorbent precursor was dried in an electric dryer at 120°C for 12 hours. Further drying at 200°C for 3 hours yielded adsorbent molded into cylindrical shapes with a diameter of 1.2-1.3 mmφ and a height of 3-5 mm. The measurements and evaluations described in [1]-[5] above were performed on this adsorbent. The results are shown in Table 1. The pore distribution obtained by the mercury intrusion method in measurement [1] is shown in Figure 1.

[0051] [Example 2] 221 g of sepiolite, 235 g of attapulgite, 165 g of wet silica as a pore-forming agent, and 480 g of deionized water were mixed in a kneader to obtain a clay-like molding precursor. Subsequent steps and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0052] [Example 3] 316 g of attapulgite, 275 g of wet silica as a pore-forming agent, and 500 g of deionized water were mixed in a kneader to obtain a clay-like molding precursor. Subsequent steps and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0053] [Example 4] 470 g of sepiolite, 150 g of calcium silicate as a pore-forming agent, and 510 g of deionized water were mixed in a kneader to obtain a clay-like molding precursor. Subsequent steps and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0054] [Comparative Example 1] 631 g of sepiolite and 420 g of deionized water were mixed in a kneader to obtain a clay-like molding precursor. Subsequent steps and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0055] [Comparative Example 2] 631 g of attapulgite and 420 g of deionized water were mixed in a kneader to obtain a clay-like molding precursor. Subsequent steps and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0056] [Comparative Example 3] 316 g of sepiolite, 336 g of attapulgite, and 410 g of deionized water were mixed in a kneader to obtain a clay-like molding precursor. Subsequent steps and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0057] [Table 1]

Claims

[Claim 1] An adsorbent for removing polycyclic aromatic hydrocarbons, It comprises at least one of sepiolite and attapulgite, In the pore distribution measured by the mercury intrusion method, the volume of pores with a diameter between 10 nm and 100 nm is in the range of 0.50 mL / g and 2.00 mL / g, and the volume of pores with a diameter between 10 nm and 30 nm is in the range of 0.40 mL / g and 1.20 mL / g. Adsorbent.

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