1、Designation: D 5160 95 (Reapproved 2003)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 (e) 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 as thestandard.1.3 This standard does not purport to address all of thes
4、afety 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 hazardsstatements are given in Section 8.2. Referenced Documen
5、ts2.1 ASTM Standards:2D 2652 Terminology Relating to Activated CarbonD 2854 Test Method for Apparent Density of ActivatedCarbonD 2867 Test Method for Moisture in Activated CarbonD 3467 Test Method for Carbon Tetrachloride Activity ofActivated CarbonE 300 Practice for Sampling Industrial Chemicals3.
6、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 carbon bed that contains a known amountof carbon is challe
7、nged 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 measurement is repeated using the same con-ditions but varying
8、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 carbon or grams adsorbate/cm carbon) andcritical bed dep
9、th, 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 characteristics of an activated carbon can stronglyinfluence its su
10、itability 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 choose test conditions that are meaningful for the appli-cat
11、ion (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 this guide is not generallyapplicable for evaluation of
12、 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 concentration profile in anactivated carbon bed at breakthro
13、ugh. 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 the outlet it is equal to thebreakthrough concentration.
14、The shorter the length of this masstransfer zone (adsorption zone), the more effectively the carbonin the bed is utilized. A bed whose depth is less than the lengthof this zone will show immediate appearance of adsorbate inthe effluent (breakpoint).1This guide is under the jurisdiction of ASTM Commi
15、ttee D28 on ActivatedCarbon and is the direct responsibility of Subcommittee D28.04 on Gas PhaseEvaluation Tests.Current edition approved Oct. 1, 2003. Published Dec. 2003. Originally approvedin 1991. Last previous edition approved in 1998 as D 5160 95 (1998).2For referenced ASTM standards, visit th
16、e 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 Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,
17、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 importantthan a short mass transfer zone. In almost every a
18、pplication,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 adsorption ratecoefficient) is more important than ultimate capac
19、ity. 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 possible in order tolower the pressure drop and to maximiz
20、e 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 at the expense ofhigher pressure drop. If pressure drop co
21、nsiderations 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 bed in which this carbon will be used.The best carbon for mos
22、t 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 vertically supportedcylindrical glass tube with diameter at lea
23、st 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. The support shouldcontribute as little as possible to the t
24、otal 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 both high strengthand very low pressure drop may also be u
25、sed as veryconvenient supports for tests in small tubes.NOTE 1A test 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 plate that screws down ontothe bed from above has been used su
26、ccessfully 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 the tube allows easyconnection and disconnection from the
27、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 the activated carbon underthe test conditions chosen.6.2 F
28、ill 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 fall at least 10 cm from the bottom of the deliveryfunnel to
29、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. Hazards7.1 Carbons containing toxic or radioactive adsorbate
30、sshould 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 ActivatedCarbonD 5160 95 (2003)27.2 Certain gases and vapors
31、 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 phosphine or arsine onwhetlerized carbon.7.3 Another hazard is enc
32、ountered 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 adsorbed in low concentrations froman air stream cause no probl
33、ems 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 orexplosion of the carbon bed.8. Selection and Preparation of Ac
34、tivated 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 becompared using this procedure. All other things being equal, ana
35、ctivated 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 comparedagainst each other using critical bed depth. However, th
36、edynamic 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 strongly affect adsorptionof both organic vapors and reactive
37、 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 tetrachloride activity (CTA) determined byTest Method D 3467 i
38、s 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 pores of various sizes. At low adsorbateconcentrations, t
39、he 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 shows a situation in which high activity isnot favorabl
40、e. 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 carbon. The pre-ferred procedure is to use the same adso
41、rbate 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 Temperature affects the capacity of the activated carbonthrough it
42、s 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 humidity (RH) of the challenge stronglyaffects the capacity an
43、d 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 also strongly influences the adsorptioncharacteristics of
44、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 unless the challenge RH ishigher than about 65 %. Chemiso
45、rption 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 to accelerate this test is toincrease the concentration
46、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 (2003)3this increases the driving force for adsorption, the dynamiccapacity of the carbon for the adsorbate Nowil
47、l 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 concentrations.Differences among carbons can be surprisi
48、ngly 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 in a gas stream of highrelative humidity. These differe
49、nces 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 increase the flow rate through the bed while maintainingt
