吸附20110517

1、活性炭吸附活性炭吸附ADSORPTIONAbsorption: the process of accumulating substances that are in solution on a suitable interface.Absorbate: the substance that is being removed from the liquid phase at the interface.Absorbent: the solid, liquid or gas phase onto which the adsorbate accumulates.Adsorption is used

2、in drinking water treatment to remove organic contaminants:Taste and odor-causing chemicalsSynthetic organic chemicalsColor forming organicsSome disinfection by-produce precursorsAdsorption is used in wastewater treatment as a polishing process for water that has already received normal biological t

3、reatment to remove a portion of the remaining dissolved organic matter.Historical Development一、 吸附原理 吸附剂：固体表面有吸附水中溶解及胶体物质的吸附剂：固体表面有吸附水中溶解及胶体物质的能力能力,比表面积很大的活性炭等具有很高的吸附能力。比表面积很大的活性炭等具有很高的吸附能力。吸附剂吸附剂 粉末状活性炭粉末状活性炭 粒状活性炭（园柱状、球状），粒径粒状活性炭（园柱状、球状），粒径24mm主要有活性炭、磺化煤、沸石、硅藻土、焦炭、木炭等。主要有活性炭、磺化煤、沸石、硅藻土、焦炭、木炭等。活性炭的

4、制造活性炭的制造木材、煤、果壳木材、煤、果壳高温炭化高温炭化隔绝空气，隔绝空气，600炭渣炭渣活性炭活性炭活化活化,800900活化剂：活化剂：ZnCl2蒸汽高温活化蒸汽高温活化 1.比表面积比表面积 每每g活性炭所具有的表面积。活性炭的比表面积为：活性炭所具有的表面积。活性炭的比表面积为：5001700m2/g，99.9%的表面积在多孔结构颗粒的内部。的表面积在多孔结构颗粒的内部。活性炭的细孔构造和分布活性炭的细孔构造和分布2.细孔构造细孔构造 小孔：小孔：2nm，0.150.90mL/g，占比表面积的，占比表面积的95%以上，起吸附作用，吸附以上，起吸附作用，吸附量以小孔吸附为主。量以小孔

5、吸附为主。过渡孔：过渡孔：2100nm，0.020.10mL/g，占比表面积，占比表面积25 n mMesopores 1 nm and 25nmMicropores 1 nmPowdered activated carbon (PAC): with a diameter of less than 0.074mm (200 sieve)Granular activated carbon (GAC): with a diameter of greater than 0.1mm (140 sieve) GACPACTotal surface aream2/g700-1300800-1800Bulk

6、 densityKg/m3400-500360-740Particle density, wetted in waterKg/L1.0-1.51.3-1.4Particle size range0.1-2.36 mm5-50 mAsh % 8 6Moisture as packed%2-83-10二、影响吸附的因素衡量衡量指标指标吸附能力吸附能力吸附速度吸附速度固体吸附剂用吸附量衡量固体吸附剂用吸附量衡量单位质量吸附剂在单位单位质量吸附剂在单位时间内所吸附的物质量时间内所吸附的物质量吸附吸附阶段阶段颗粒外部颗粒外部扩散阶段扩散阶段孔隙扩散孔隙扩散阶段阶段吸附反应吸附反应阶段阶段吸附质从溶液中扩

7、散到吸附吸附质从溶液中扩散到吸附剂表面剂表面吸附质在吸附剂孔隙中继续吸附质在吸附剂孔隙中继续向吸附点扩散向吸附点扩散吸附质被吸附在吸附剂孔隙吸附质被吸附在吸附剂孔隙内的吸附点表面内的吸附点表面吸附速度主要取决于外部扩散速度和孔隙扩散速度。吸附速度主要取决于外部扩散速度和孔隙扩散速度。外部扩外部扩散速度散速度与溶液浓度成正比与溶液浓度成正比与吸附剂的比表面积的大小成正与吸附剂的比表面积的大小成正比比吸附剂颗粒直径越小，速度越快吸附剂颗粒直径越小，速度越快增加溶液与颗粒间的相对运动速度，增加溶液与颗粒间的相对运动速度，可提高速度可提高速度孔隙扩孔隙扩散速度散速度吸附剂颗粒越小，速度越快吸附剂颗粒越

8、小，速度越快对于同一种活性炭，在恒定温度下平衡吸附量对于同一种活性炭，在恒定温度下平衡吸附量x/m仅是平仅是平衡浓度衡浓度 e的函数，此时的函数，此时x/m与与 e的关系称为等温吸附线。的关系称为等温吸附线。初始浓度初始浓度 i容积容积V活性炭活性炭质量质量m开始开始平衡浓度平衡浓度 e容积容积V活性炭活性炭质量质量m平衡平衡到达吸附平衡时，单位到达吸附平衡时，单位质量活性炭的吸附量为质量活性炭的吸附量为mVmxei)(对于一种活性炭来说，实验证明对于一种活性炭来说，实验证明x/m值是平衡浓度值是平衡浓度 e和温度的函数和温度的函数对于特定的活性炭于特定的原水，对于特定的活性炭于特定的原水，x

9、/m与与 e的函数是一定的。的函数是一定的。Langmuir 吸附等温线吸附等温线eebmxbmx1)/(0BET 吸附等温线吸附等温线)/)(1(1)()/(0seeseBmxBmxFreundlich 吸附等温线吸附等温线nefKmx/1x/m ex/m eSurface layerMultiple layerx/m eExample:A tricholoroethene (TCE) isotherm was performed on Calgon F400 GAC. A total of 25 isotherm points were determined using 250-ml am

10、ber bottles with Teflon-lined screw caps. The dosage of GAC varied in each bottle. The GAC used was powdered from virgin stock GAC, washed, and dried to a constant weight before use. Pure TCE was added to a solution containing organic free laboratory water to yield a TCE initial concentration of abo

11、ut 10,000 g/L. The weight of the bottles and the caps were recorded prior to filling the bottles with GAC dosage and the TCE solution. The bottles were filled headspace free to prevent any TCE from volatizing out of the solution. A total of eight extra empty bottles were filled and allowed to equili

12、brate. The extra bottles were used as blanks to measure the initial concentration used in the isotherm. All the bottles were placed on a rotating device and rotated at 25 rev/min for a period of 14 days. The bottles were then removed from the tumbler and the carbon was allowed to settle for a few ho

13、urs, and a sample was drawn from each bottle and the TCE concentration was analyzed using a gas chromatograph. Based on the raw data given below, calculate the average initial liquid-phase concentration from the equilibrated blanks and the equilibrium adsorbent-phase concentration. Plot the correspo

14、nding values of qe and Ce on arithmetic and log-log paper to determine the nature of the distribution. A summary of the GAC dosages, solution volume, and equilibrated blanks is provided below:Example:p Experimental data: Carbon type: F-400 Temperature: 13 C Chemical: TCE pH:6.8 Carbon size: 200 400S

15、ample No.Dosage D, gVolume V,mlTCE Liquid-Phase concentration Ce, g/L10.44254247.1320.39002251.24.530.34427252.54.140.26784252.48.150.20674253.615.560.18305251.118.970.16521251.424.580.14041252.174.390.12416252.157100.10836249.6109110.09418254.7162.5120.08320253.0213.6130.07332251.0144.9140.05380251

16、.2643.1150.04752255.1872.6160.03956252.31109.1170.03315251.51476.9180.02696255.12699.8190.02189254.63271.9200.01609253.04858.4210.01072251.76263.2220.00544251.58427.3230.00343252.310009.8240.00164252.99875.5250.06273253.0352.6p Equilibrated blank data:Sample No.Equilibrated Blank C0, g/L110,48628,40

17、1311,355410,205510,415612,912712,025811,123p isotherm datasolution:1. Calculate the average initial TCE aqueous-phase concentration in g/L: LgC/865,108123,11025,12912,12415,10205,10355,11401, 8486,1002. Calculate the equilibrium adsorbent-phase concentration in g/g. The required computations for sam

18、ple 1 is shown below:ggLggLCMVqee/6065/)3865,10(44254. 02471. 0)1 (865,10) 1 () 1 () 1 (/)865,10()(0LgCMVCCMVqeeeSample No.Ce, g/Lqe, g/g136065.024.5699.534.17966.048.110231.0515.513309.0618.914877.8724.516496.4874.319374.795721945.61010924776.411162.528944.612213.632390.313144.936699.6Sample No.Ce,

19、 g/Lqe, g/g14643.147728.915872.653643.6161109.162221.6171476.971227.2182699.877263.3193271.988317.9204858.494452.8216263.2108054.9228427.3112712.72310009.8249875.525352.642339.3solution:3. Plot the TCE isotherm data on arithmetic and log-log paper.Arithmetic log-log推导的基本假定推导的基本假定吸附剂表面吸附剂表面吸附层厚度吸附层厚度

20、被吸附水分子被吸附水分子未被吸附水分子未被吸附水分子未被吸附物质分子未被吸附物质分子被吸附物质分子被吸附物质分子假定被吸附的水分子和物质颗粒的数目分别为假定被吸附的水分子和物质颗粒的数目分别为n1s和和n2s个；未被吸附的水分子和物质个；未被吸附的水分子和物质颗粒的数目分别为颗粒的数目分别为n1和和n2个个由于水分子与吸附颗粒大小相同，单位吸附剂表面的吸附点位一定（由于水分子与吸附颗粒大小相同，单位吸附剂表面的吸附点位一定（ n1s+n2s =n，单，单位吸附剂表面共有位吸附剂表面共有n个个 0面积），单位吸附剂表面所能容纳的颗粒总数是一定的。面积），单位吸附剂表面所能容纳的颗粒总数是一定的。

21、吸附剂表面上吸附与脱落过程相平衡吸附剂表面上吸附与脱落过程相平衡未被吸附的物质颗粒数目未被吸附的物质颗粒数目+ +被吸附的水分子数目被吸附的水分子数目被吸附的物质颗粒数目被吸附的物质颗粒数目+ +未被吸附的水分子数目未被吸附的水分子数目即即n2+ n1sn2s+ n1n2+ n1sn2s+ n1上式得到平衡常数上式得到平衡常数2112nnnnKssnnnss21ssnnnnnK2221)(1/nKb snnbnnb222)1 (2221nbnnbns除以除以Avogadro常数常数LnbLnmxbmx2201)/(Lne2b=bLeebmxbmx1)/(01、求吸附公式的常数、求吸附公式的常数

22、-图解法图解法Langmuir 公式公式00)/(11)/(1)/(1mxmxbmxe00)/(1)/(1)/(mxbmxmxee(x/m)01/b(x/m)0O1/ e1/(x/m)1/b(x/m)01/(x/m)0O e e /(x/m) e1eebmxbmx1)/(0BET公式公式)/)(1(1)()/(0seeseBmxBmx00)/(1)/(1)/)(mxBmxBBmxseese(B-1)/(x/m)0O e / s e /( s- e)( x/m)(B-1)/B(x/m)0 s值估计偏高值估计偏高 s值估计偏低值估计偏低未知未知Freundlich公式公式feKnmxlglg1lg

23、nefKmx/1线性化线性化lgKf1/nOlg elg(x/m)Example: Determination of Freundlich and Langmuir isotherm parametersFor the experimental isotherm data given below, determine the Freundlich and Langmuir isotherm parameters. Apply linear regression to determine the isotherm parameters. Solution:p Experimental data:

24、 Carbon type: F-400 Temperature: 13 C Chemical: TCE pH:7.5-8 Carbon size: 200 400 Equilibrium time: 31daysSample No.CA, mole/LqA, mole/g123.673726.6745033.2631840.32212150.16985.260.11475.81. Determine Langmuir isotherm parameters.1/(x/m)0=slope=0.0013g/ mole(x/m)0=769.23 mole/g=1.01 105 g/g1/b(x/m)

25、0=intercept=0.0033g/Lb =3.00 10-3L/ gExample: Determination of Freundlich and Langmuir isotherm parametersFor the experimental isotherm data given below, determine the Freundlich and Langmuir isotherm parameters. Apply linear regression to determine the isotherm parameters. Solution:2. Determine Fre

26、undlich isotherm parameters.1/n=slope=0.4327lg Kf=intercept=2.28314327. 04327. 04327. 0)(68.60)100039.131(1000139.1319 .191)(9 .191mgLgmgmgggmolemoleLgmgmoleggmolemoleLgmoleKfFreundlich isotherm equation provides a better fit of the data than the Langmuir model.Powdered activated carbonPowdered acti

27、vated carbon is primarily used in the treatment of taste and odor compounds and the treatment of low concentrations of pesticides and other organic micropollutants. The convenience of PAC is that it can be employed periodically in a conventional treatment plant with minimum capital cost. For example

28、, PAC can be used during summer months for surface water sources containing taste and odor compounds resulting from algal blooms. It is also be employed to remove chemical pollution (pesticides and herbicides) carried in spring runoff.Factors that influence PAC performance Location of PAC additionTh

29、e most promising locations for PAC addition: (1) at the raw-water intake, (2) in the rapid-mix tank, and (3) in a slurry contactor (separately designed for PAC).Point of additionAdvantages disadvantagesPowdered activated carbonFactors that influence PAC performance impact of disinfectants and oxidan

30、ts on PAC performanceFor the removal of MIB and geosmin, oxidants such as chlorine and potassium permanganate have a negative impact on PAC removal of taste and odor compounds. The impact is the greatest when oxidants is added simultaneously with the PAC.For example, when oxidants is added with PAC,

31、 removal efficiencies for MIB decrease by as much as 50-75%; while geosmin can decrease by as much as 20-40%. impact of organic matter on PAC performanceBy either pore blockage or competing for adsorption sites, OM can reduce the adsorption capacity of micropollutants in PAC. Consequently, single-so

32、lute isotherms performed in organic free water will predict a higher capacity than would be observed for PAC dosages in natural water containing OM. impact of contact time on PAC performanceTypically, PAC added in a conventional plant has contact times between 0.5 and 2h, which is not sufficient to

33、utilize fully the capacity of the PAC for micropollutants. For example, it was reported that for 90% removal of atrazine, the contact time could be decreased from 4h to 30min if the PAC dosage was increased from 23 to 32 mg/L.吸附公式的直接应用必须是吸附过程在较短时间内达到平衡，一般应用于粉末活性炭吸附公式的直接应用必须是吸附过程在较短时间内达到平衡，一般应用于粉末活性炭

34、例题：废水中含有机物的浓度为例题：废水中含有机物的浓度为20mg/L，用粉末活性炭做吸附试验，吸附迅速达到平衡，用粉末活性炭做吸附试验，吸附迅速达到平衡，数据用数据用Langmuir公式处理后得出公式处理后得出b=0.13L/mg，(x/m)0=0.345mg/mg。按。按CSTR处理考虑，处理考虑，池子容积为池子容积为60000升，流量为升，流量为100L/s,出水有机物浓度要求不超过出水有机物浓度要求不超过1mg/L。在开始运行时，。在开始运行时，先按反应器容积每升加活性炭先按反应器容积每升加活性炭20g，流出的活性炭经分离后在回流到反应器，直到完全饱，流出的活性炭经分离后在回流到反应器，

35、直到完全饱和后再补充新炭，计算每秒钟补充的活性炭量。和后再补充新炭，计算每秒钟补充的活性炭量。解：按解：按Langmuir公式求公式求 e=1.0mg/L时的时的x/m值值)/(0397. 0113. 011345. 013. 01)/(0mgmgbmxbmxee令每秒钟投加的活性炭的量为令每秒钟投加的活性炭的量为Mmg，因投加的新活性炭故，因投加的新活性炭故(x/m)0=0值，有物料恒算值，有物料恒算100(20-1)=M(0.0397-0)M=1900/0.0397=47858mg/s=47.9g/s每每mg活性炭对有机物的吸附潜力为活性炭对有机物的吸附潜力为0.345mg，而实际中只利用

36、了，而实际中只利用了0.0397mg例题：废水中含有机物的浓度为例题：废水中含有机物的浓度为20mg/L，用粉末活性炭做吸附试验，吸附迅速达到平衡，用粉末活性炭做吸附试验，吸附迅速达到平衡，数据用数据用Langmuir公式处理后得出公式处理后得出b=0.13L/mg，(x/m)0=0.345mg/mg。按。按CSTR处理考虑，处理考虑，池子容积为池子容积为60000升，流量为升，流量为100L/s,出水有机物浓度要求不超过出水有机物浓度要求不超过1mg/L。在开始运行时，。在开始运行时，先按反应器容积每升加活性炭先按反应器容积每升加活性炭20g，按下图所示的逆流吸附操作，计算每秒钟补充的活性，

37、按下图所示的逆流吸附操作，计算每秒钟补充的活性炭量。炭量。 1CSTR1(x/m)1解：解：CSTR2的平衡浓度的平衡浓度 2=1.0mg/L时的时的(x/m)2=0.0397mg/mg20mgL-1100L/sM/ gs-1x/m 2CSTR2(x/m)2 1/mgL-1M/ gs-1(x/m)21mgL-1M/ gs-10100L/s在第二个在第二个CSTR中只有进水的有机物浓度中只有进水的有机物浓度 1未知，对未知，对CSTR2中的有机物做物料恒算中的有机物做物料恒算LmgM/) 11000397. 0(1 1是是CSTR1中平衡浓度，由此可求中平衡浓度，由此可求CSTR1中的吸附量中的

38、吸附量) 11000397. 0(13. 01) 11000397. 0(345. 013. 0)(1MMmxCSTR1中的有机物做物料恒算中的有机物做物料恒算将将(x/m)1和和 (x/m)2带入上式带入上式Mmxmx)()()20(100211MMMM0397. 0) 11000397. 0(13. 01) 11000397. 0(345. 013. 0)11000397. 0(20100解上式得解上式得M=12550mg/s=12.5g/s吸附柱的设计通常是在已知活性炭的吸附性能、运行负荷和吸附柱高度条吸附柱的设计通常是在已知活性炭的吸附性能、运行负荷和吸附柱高度条件下求吸附所能维持的时

39、间，或者确定吸附时间条件下求吸附柱高度。件下求吸附所能维持的时间，或者确定吸附时间条件下求吸附柱高度。活性炭的活性炭的吸附性能吸附性能设计指标设计指标出出水水物物质质浓浓度度 i b xVbVx累计产水量累计产水量出出水水物物质质浓浓度度 i b xVbVx累计产水量累计产水量 出出水水物物质质浓浓度度 i b xVbVx累计产水量累计产水量出出水水物物质质浓浓度度 i累计产水量累计产水量 吸附能力没吸附能力没有得到发挥有得到发挥 厚度厚度吸附层吸附层的吸附能力的吸附能力f厚度吸附层的吸附能力出来的吸附能力厚度吸附层中没有发挥f%100LfL吸附柱的饱和百分数(x/m)x(x/m)yy ydy

40、在体积微元内，吸在体积微元内，吸附量与该时刻该体附量与该时刻该体积微元内的有机物积微元内的有机物浓度表现平衡关系，浓度表现平衡关系，可以用等温吸附线可以用等温吸附线来描述来描述在体积微元内，单位时间内从在体积微元内，单位时间内从水中去除的有机物的量水中去除的有机物的量=单位单位时间内被吸附的有机物的量时间内被吸附的有机物的量在体积微元内，单位时间内从水中去除的有机在体积微元内，单位时间内从水中去除的有机物的量物的量=单位时间内被吸附的有机物的量单位时间内被吸附的有机物的量假设吸附反应为一级反应，反应物有效浓度应当为（假设吸附反应为一级反应，反应物有效浓度应当为（ - e）cemkadtd)(t

41、mkaei303. 2lg未知未知通过搅拌吸通过搅拌吸附试验求附试验求ka对于单位截面积的体积微元对于单位截面积的体积微元dykadFem)(0到到y积分积分 b到到 积分积分bemdkaFyibemdkaF)()1 (10ydfi e i等温吸等温吸附线附线操作线操作线x/m0 e 为求假定单位时间内活性炭吸附的有机物量与单位时间内通过假定单位时间内活性炭吸附的有机物量与单位时间内通过单位吸附柱截面面积的有机物量成正比单位吸附柱截面面积的有机物量成正比常数mxFm/=i时，该直线通过(x/m) i点 - e为吸附为吸附的推动力的推动力Fro the case where the mass t

42、ransfer rate is fast and the mass transfer zone is a sharp wave front, a steady-state balance around a carbon contactor reactor yields:Accumulation = inflow outflow- amount absorbed00eGACeQC tQC tmqQ= volumetric flowrate, L/h;Ce= final equilibrium concentration of absorbate, mg/L;C0= initial concent

43、ration of absorbate, mg/L;qe= adsorbent phase concentration after equilibrium, mg adsorbate/g adsrobentt= time, h;mGAC=mass of absorbent, g;The adsorbent usage rate is defined as GACmQt0eeCCqIf it is assumed that the mass of the adsorbate in the pore space is small compared to the amount adsorbed, t

44、hen the term QCet can be neglected.The adsorbent usage rate is given 0GACemCQtqTo quantify the operational performance of GAC contactor, the following terms have been developed and are used commonly:1. Empty-bed contact time (EBCT)bbfbfVA DDEBCTQv AvEBCT= empty bed contact time, hVb= volume of GAC i

45、n contactor, m3Q= volumetric flowrate, m3/hAb= cross sectional area of GAC filter bed, m2D= length of GAC in contactor, mvf= linear approach velocity, m/h2. Activated carbon densityGACGACbmV GAC= density of GAC, g/LmGAC= mass of GAC, g3. Specific throughput, expressed as m3 of water treated per gram

46、 of carbonSpecific throughput3/bGACGACV tQtmgmEBCTm()bGACbGACV ttEBCTVEBCT4. Carbon usage rate (CUR), expressed as gram of carbon per m3 of water treated5. Volume of water treated for a given EBCT, expressed in liters, Lmassof GAC for givenEBCTLGACusagerate6. Bed life, expressed in days, d3/GACmg mQtCURvolumeof water treated for givenEBCTdQEXAMPLE