1、Designation: D 5160 95 (Reapproved 2008)Standard Guide forGas-Phase Adsorption Testing of Activated Carbon1This standard is issued under the fixed designation D 5160; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last
2、 revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This guide covers the evaluation of activated carbons forgas-phase adsorption. It presents a procedure for determiningthe
3、dynamic adsorption capacity, No, and critical bed depth, dc, for an activated carbon used to remove a specific adsorbatefrom a gas stream under conditions chosen by the user.1.2 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.
4、3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use. Specific hazards
5、statements are given in Section 8.2. Referenced Documents2.1 ASTM Standards:2D 2652 Terminology Relating to Activated CarbonD 2854 Test Method for Apparent Density of ActivatedCarbonD 2867 Test Methods for Moisture in Activated CarbonD 3467 Test Method for Carbon Tetrachloride Activity ofActivated C
6、arbonE 300 Practice for Sampling Industrial Chemicals3. Terminology3.1 Definitions:3.1.1 breakthroughthe appearance in the effluent of aspecified concentration of an adsorbate of interest.3.1.2 Other terms relating to this guide are defined inTerminology D 2652.4. Summary of Guide4.1 An activated ca
7、rbon bed that contains a known amountof carbon is challenged with an adsorbate in a gas stream underconditions of flow rate, adsorbate concentration, temperature,pressure, and relative humidity set by the user. The time tobreakthrough of a specified concentration of adsorbate ismeasured. The measure
8、ment is repeated using the same con-ditions but varying the amount of carbon in the bed. For manypractical systems, a plot of breakthrough time versus amount ofcarbon is linear. The slope and x-intercept of this line can beused to calculate the dynamic capacity, No(expressed as gramsadsorbate/grams
9、carbon or grams adsorbate/cm3carbon) andcritical bed depth, dc, characteristic of the activated carbonunder the conditions used in the test.5. Significance and Use5.1 Activated carbon is used extensively for removing gasesand vapors from air or other gas streams. The physical andchemical characteris
10、tics of an activated carbon can stronglyinfluence its suitability for a given application. The procedurein this guide allows the evaluation of the dynamic adsorptioncharacteristics of an activated carbon for a particular adsorbateunder conditions chosen by the user. It is necessary that theuser choo
11、se test conditions that are meaningful for the appli-cation (see Section 9).5.2 This guide can also be used to evaluate activatedcarbons that have been impregnated with materials to enhancetheir effectiveness at removing gases otherwise poorly ad-sorbed on activated carbon.5.3 The procedure given in
12、 this guide is not generallyapplicable for evaluation of carbons used as catalysts for suchpurposes as decomposition of low levels of ozone or oxidationof SO2to SO3.5.4 The procedure given in this guide can be applied toreactivated or regenerated activated carbons.5.5 Fig. 1 shows the adsorbate conc
13、entration profile in anactivated carbon bed at breakthrough. The bed has a zone at theinlet in which the adsorbate concentration is equal to theinfluent concentration. In this region the carbon is at equilib-rium with adsorbate. The adsorbate concentration in theremainder of the bed drops until at t
14、he outlet it is equal to thebreakthrough concentration. The shorter the length of this masstransfer zone (adsorption zone), the more effectively the carbonin the bed is utilized.Abed whose depth is less than the lengthof this zone will show immediate appearance of adsorbate inthe effluent (breakpoin
15、t).1This guide is under the jurisdiction of ASTM Committee D28 on ActivatedCarbon and is the direct responsibility of Subcommittee D28.04 on Gas PhaseEvaluation Tests.Current edition approved Aug. 1, 2008. Published September 2008. Originallyapproved in 1991. Last previous edition approved in 2003 a
16、s D 5160 95 (2003).2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Ha
17、rbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.5.6 From the standpoint of best carbon utilization it isdesirable to choose a carbon which will give as short a masstransfer zone as possible under use conditions. However, inmany applications, high adsorptive capacity is more
18、importantthan a short mass transfer zone. In almost every application,bed pressure drop is also a primary consideration.5.7 In a few situations such as respiratory protection againstlow levels of extremely toxic gases such as radioactive methyliodide, a short mass transfer zone (that is, high adsorp
19、tion ratecoefficient) is more important than ultimate capacity. In othercases such as solvent recovery, a high dynamic capacity ismore important.5.8 Although the design of adsorber beds is beyond thescope of this guide, the following points should be considered.The bed diameter should be as large as
20、 possible in order tolower the pressure drop and to maximize the amount of carbonin the bed. Subject to pressure drop constraints, the deepestpossible carbon bed should be used. All else being equal, theuse of smaller particle size carbon will shorten the masstransfer zone and improve bed efficiency
21、 at the expense ofhigher pressure drop. If pressure drop considerations arecritical, some particle morphologies offer less resistance toflow than others.5.9 The two parameters obtained by the procedure in thisguide can be used as an aid in selecting an activated carbon andin sizing the adsorption be
22、d in which this carbon will be used.The best carbon for most applications should have a highdynamic capacity for the adsorbate Nocoupled with a shortmass transfer zone (small dc) when evaluated under theoperating conditions anticipated for the adsorber.6. Apparatus6.1 Sample TubeThis is often a vert
23、ically supportedcylindrical glass tube with diameter at least twelve times thediameter of the largest carbon particles present or 16 times themean diameter. The lower end of the tube must have a flatsupport for the carbon bed. Care should be taken to ensureuniformity of flow profile across the bed.
24、The support shouldcontribute as little as possible to the total pressure drop of thebed. For this reason, fritted glass supports are often undesir-able. Fine mesh stainless steel screens supported if necessaryby heavier screens may be used. Commercially availablespunbonded polyester nonwovens having
25、 both high strengthand very low pressure drop may also be used as veryconvenient supports for tests in small tubes.NOTE 1Atest fixture in which the bed is held in place at both top andbottom requires less skill to obtain reproducible results. An 8.8 cmdiameter aluminum fixture with a perforated plat
26、e that screws down ontothe bed from above has been used successfully at bed depths from 1 to 3.5cm. A diagram of this fixture is shown in Fig. 2.6.1.1 Flow should be downward through the sample toavoid disturbing the bed. For tests on small amounts of carbon,a ground glass outer joint at the top of
27、the tube allows easyconnection and disconnection from the challenge gas withoutdisturbing the bed. It is very easy to disturb the packing of asmall bed. Preferably these should not be moved after loading.6.1.2 The length of the sample tube must be several timesgreater than the critical bed depth of
28、the activated carbon underthe test conditions chosen.6.2 Fill DeviceFor small beds the sample tube can beloaded using the vibration feed device described in TestMethod D 2854. The bottom of the delivery funnel should havethe same diameter as the sample tube. It is desirable to allowthe carbon to fal
29、l at least 10 cm from the bottom of the deliveryfunnel to the top of the bed. For larger beds, the best packingis obtained when the carbon falls through a loading columnwhich contains screens to evenly distribute the carbon acrossthe bed.3The column should have the same cross section as thebed.7. Ha
30、zards7.1 Carbons containing toxic or radioactive adsorbatesshould be disposed of in accordance with applicable federal,state, and local regulations.3British patent 606,867.FIG. 1 Concentration Profile of an Activated Carbon Bed atBreakthroughFIG. 2 Test Fixture for Gas-Phase Adsorption Testing of Ac
31、tivatedCarbonD 5160 95 (2008)27.2 Certain gases and vapors have very high heats ofreaction as they chemisorb on a carbon surface. At highconcentrations, enough heat can be liberated to cause ignitionof the carbon bed if oxygen is present. An example ischemisorption of high concentrations of phosphin
32、e or arsine onwhetlerized carbon.7.3 Another hazard is encountered when large quantities ofeasily oxidizable substances such as hydrazines are adsorbedon carbon from an inert gas stream. When these carbons areexposed to air, they often ignite as oxidation rapidly takesplace. The same materials adsor
33、bed in low concentrations froman air stream cause no problems since the oxidation occursslowly during the adsorption process.7.4 Adsorption of high concentrations of strong oxidizerssuch as ozone (formation of ozonides), fluorine, hydrogenperoxide, or nitric acid vapors can result in ignition orexpl
34、osion of the carbon bed.8. Selection and Preparation of Activated Carbon8.1 A representative sample should be obtained and pre-pared for testing in accordance with Practice E 300.8.2 The particle size distribution of the activated carbonmust be considered if several different carbons are to becompar
35、ed using this procedure.All other things being equal, anactivated carbon consisting of smaller particles will possess ahigher adsorption rate and hence a smaller critical bed depth,dc, than one consisting of larger particles. Therefore, carbonsthat have different particle sizes should not be compare
36、dagainst each other using critical bed depth. However, thedynamic capacities, No, calculated using this guide are directlycomparable regardless of particle size distribution. For manyapplications, the dynamic capacity is more important than thecritical bed depth.8.3 Since pre-adsorbed water can stro
37、ngly affect adsorptionof both organic vapors and reactive gases, the water content ofeach carbon sample tested should be determined using TestMethod D 2867. Impregnated carbons are often sold containingup to about 20 % by weight water to increase their capacity forreactive gases.8.4 The carbon tetra
38、chloride activity (CTA) determined byTest Method D 3467 is often used to qualify activated carbonsfor a particular use. It should be realized that these activitiesare a measure of the total micropore volume of an activatedcarbon sample. They say nothing about the distribution ofmicropore area among
39、pores of various sizes.At low adsorbateconcentrations, the smallest micropores are most effective.Therefore, a carbon with many small pores may have a highercapacity for a low concentration adsorbate than a carbon withgreater total micropore volume (higher activity) but fewer verysmall pores. Fig. 3
40、 shows a situation in which high activity isnot favorable. The 57.9 % CTA carbon in this figure isspecially activated to have a high proportion of very smallmicropores.9. Selection of Test Conditions9.1 The user of this guide must decide under what experi-mental conditions to evaluate the activated
41、carbon. The pre-ferred procedure is to use the same adsorbate concentration andsame gas stream velocity as will be encountered in theapplication. Other factors such as relative humidity, tempera-ture, pressure, and breakthrough concentration should alsocorrelate as closely as possible.9.2 Temperatur
42、e affects the capacity of the activated carbonthrough its effects on the adsorption isotherm and on diffusionrates. This is usually not a large effect over narrow ranges oftemperature for fairly non-volatile organic vapors (1).4It canbe much more significant for chemisorption.9.3 The relative humidi
43、ty (RH) of the challenge stronglyaffects the capacity and adsorption rate of the activated carbon(see Fig. 4). The RH of the challenge entering the carbon bedis the important parameter and should be carefully controlledespecially at high relative humidities. As mentioned in 8.3,pre-adsorbed water al
44、so strongly influences the adsorptioncharacteristics of the activated carbon. The strong dependenceof RH on temperature at high RH values requires goodtemperature control at the bed when working at high RH.Generally, physical adsorption of organic vapors on dry newcarbon shows little RH dependence u
45、nless the challenge RH ishigher than about 65 %. Chemisorption or catalytic activity isusually much more sensitive to RH.9.4 Accelerated TestsAt low adsorbate concentrationsthese tests can require considerable time. Therefore, attemptsare often made to accelerate the tests.9.4.1 The most common way
46、to accelerate this test is toincrease the concentration of adsorbate in the gas stream. Since4The boldface numbers in parentheses refer to a list of references at the end ofthe text.FIG. 3 Time to Breakthrough Versus Volume of CarbonD 5160 95 (2008)3this increases the driving force for adsorption, t
47、he dynamiccapacity of the carbon for the adsorbate Nowill be higher thanthat observed in the actual bed. This complicates bed sizingcalculations. More serious is the fact that a ranking of activatedcarbons for adsorption capacity at high concentrations ofadsorbate is not necessarily the same at low
48、concentrations.Differences among carbons can be surprisingly large especiallyat low concentrations and in the presence of high water vaporconcentrations. This consideration is especially important forcarbons used in odor control applications where typically theodorant is present in low concentration
49、 in a gas stream of highrelative humidity.These differences in adsorption isotherms aremuch more significant for physical adsorption than for chemi-sorption. Another effect of high adsorbate concentration isheating of the bed. This affects both the capacity and theadsorption rate of the carbon for the adsorbate. Large industrialadsorption beds operate almost adiabatically so accuratescale-up may require thermal insulation of a small lab column.Such considerations can be especially important in chemisorp-tion.9.4.2 Another and usually better way of accelerating the testis to i
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