adsorption labwork

8/10/2019 Adsorption Labwork

http://slidepdf.com/reader/full/adsorption-labwork 1/20

Universität Duisburg – Essen

Fakultät für Ingenieurwissenschaften

Abteilung Maschinenbau

Institut für Energie- und Umweltverfahrenstechnik,

Verfahrenstechnik / Wassertechnik

Prof. Dr. Ing. habil. Rolf Gimbel

Dr. Ing. Ralph Hobby

M. Sc. Grit Hoffmann

M. Sc. Mathis Keller

M. Sc. Anik Deutmarg

M. Sc. Lucas Landwehrkamp

Practical Course “Technical Engineering Water”

Adsorption

First Name: Second Name:

Matriculation number:



2

Content

1. Introduction ................................................................................................................... 3

2. Main goals of the experiments....................................................................................... 9

3. Experimental procedure .............................................................................................. 10

4. Interpretation of data................................................................................................... 16

5. Literature..................................................................................................................... 17



3

1 Introduction

For about 80 years activated carbon has been used for drinking water treatment. The

primary treatment goal was the removal of taste, odour and colour causing

substances and the removal of chlorine.

Over the past 30 years activated carbon has been increasingly used for the removal

of organic micropollutants. These substances are present in quite low concentrations

in surface waters and may also be present in ground water due to a long-term

anthropogenic pollution.

These so called organic micropollutants include: chlorinated carbohydrates,

pesticides, pharmaceuticals and endocrine disrupting compounds.

Activated carbon is used as granular activated carbon in deep bed filters (GACadsorber) or as powdered activated carbon (PAC) which is added to the water e. g.

as a suspension. In a GAC-adsorber, the adsorption process occurs if the water

passes the activated carbon layer. Using the conventional PAC, the process PAC is

added at an appropriate point of the water treatment plant. After sufficient contact

time for the adsorption process, PAC is removed from the treated water with

sedimentation and/or a rapid sand filtration (Sontheimer et al., 1985a).

Figure 1 represents schematically the adsorption process for a single substance with

PAC in a continuously stirred tank reactor (CSTR) and for a single substance in aGAC-adsorber, assuming ideal conditions. Using the PAC process the maximum

solid phase concentration (adsorbed single substance onto the activated carbon)

qmax, PAC can be achieved using the operation line which starts at the influent

concentration cin of the CSTR and ends at the adsorption equilibrium point on the

isotherm of the single substance with the effluent concentration ceff, PAC (t=∞). The

concentration ceff, PAC (t=∞) is in equilibrium with the solid phase concentration

qmax, PAC. The slope of the operation line is given by the ratio of the volume of water

V and the mass of PAC m.

In a GAC adsorber the theoretical maximum solid phase concentration is much

higher in comparison to a conventional PAC process. This is due to the filter effect, i.

e. in a GAC layer it is possible to achieve the maximum solid phase concentration

qmax, PAC of a single substance which equilibrates with the influent concentration cin.

But, regarding real conditions the maximum solid phase concentration may be

reduced enormously due to preloading effects by natural organic substances which

are present in natural water.



4

0

140

0 1,1Liquid-phase concentration c

S o l i d - p h a s e

c o n c e n t r a t i o n

q

Isotherm

qmax, PAC

CinCeff,PAC (t=∞∞∞∞)

q = f(c)

-V/m

V

m

PAC: Operation line with

slope -V/m

qmax, GAC

V, cin V, ceff, PAC

. .

CSTR with PAC

V, cin

ceff, GAC

V

.

.

G A C a

d s o r b e r

Ceff,GAC (t=0)

Ceff,GAC (t=∞∞∞∞)

PAC

Figure 1: Schematic view of the adsorption process using PAC in a CSTR and using a GAC

adsorber assuming ideal conditions

For the understanding and for the design of an adsorption process with activated

carbon, it is essential to know about the:

• special characteristics of activated carbon,

• adsorption equilibrium,

• adsorption kinetics,

• process design

The raw material and the conditions of the activation process influence the structure

of the pore system, the inner surface and also the adsorption characteristics of an

activated carbon. One very important adsorption characteristic is the adsorption

equilibrium, which will be described in the following chapter.

1.1 Description of adsorption equilibria

1.1.1 Adsorption equilibria of single substances

For the design and operation of an adsorption process for water treatment it is

necessary to characterise the raw water as well as the activated carbon. Thus, it is

necessary to know the adsorption capacity of the activated carbon and also the

adsorption kinetic. The adsorption capacity can be determined by an adsorption

isotherm. An adsorption isotherm describes the adsorption equilibrium in a closed

system, which consists of a solution with a single dissolved organic substance and



5

an amount of activated carbon brought in contact with the solution. If adsorption

equilibrium is reached after sufficient contact time, a constant concentration of the

substance remains in the solution. There is also a constant solid-phase

concentration of the substance, which has been adsorbed on the activated carbon.

To evaluate an adsorption isotherm defined quantities mi of activated carbon are

added to several bottles containing the same defined volumes V of solution with a

single substance initial concentration c0 . The solutions with the activated carbon are

mixed intensively to bring the carbon into contact with the solution. The adsorption

equilibrium is usually reached after a contact time of about 24 to 72 hours. In the

solution remains an equilibrium concentration c of the single substance and a solid-

phase concentration q, which describes the quantity of the adsorbed substance. This

can be described by the following mass balance

V c m q V c m qo o⋅ + ⋅ = ⋅ + ⋅ (1.1.1)

If the initial solid-phase concentration of the unused carbon qo= 0 then

( )q V

mc co= ⋅ − (1.1.2)

A single adsorption equilibrium point is shown in Figure 2.

Figure 2: Determination of an equilibrium point of an adsorption isotherm



6

The figure shows the solid-phase concentration of an adsorbable single substance

as a function of the liquid-phase concentration. At starting point the concentration in

the liquid phase is equal c0 (c=c0) and the solid-phase concentration q0=0.

Depending on contact time the liquid-phase concentration becomes lower and the

solid-phase concentration increases according the mass balance 1.1.2. This

relationship is described by an operation line with the slope of –V/m, which connects

the point c0 on the abscissae and the equilibrium point q=f (c). In figure 1.1.2. can be

seen, that several equilibrium points are necessary to determine an adsorption

isotherm. In this case equilibrium points were determined by the variation of the ratio

V/m resp. the slope of the operation lines.

Figure 3: Adsorption isotherm and equilibrium points which are obtained by the variation of the

ratio V/m with constant initial concentration co



7

There are different equations to describe the measured adsorption equilibrium

points. In the following the so-called „Langmuir isotherm equation“ and the

„Freundlich isotherm equation“ are described.

The Langmuir isotherm equation can be derived based on two kinetic equations

according equations 1.1.3 and 1.1.4. Equation 1.1.3 describes the rate of adsorption

dependent on free adsorption sites of the activated carbon resp. the difference

between the maximum solid phase concentration qm and the occupied adsorption

sites given by q. Equation 1.1.4 describes the rate of desorption dependent on the

solid-phase concentration resp. the occupied adsorption places. K1 and K2 are rate

constants.

( )r K q q cAds m= ⋅ − ⋅1 (1.1.3)

r K qDes = ⋅2 (1.1.4)

If equilibrium is reached adsorption rate is equal desorption rate

DesAds rr = (1.1.5)

and the Langmuir isotherm equation is given by equation 1.1.6:

q q K c

K cm

L

L

= ⋅⋅

+ ⋅1, K

K

KL =

1

2

(1.1.6)

KL is the Langmuir-constant, qm the maximum solid-phase concentration if a

monomolecular layer on the carbon surface is assumed, c is the liquid-phase

concentration at adsorption equilibrium point and q is the solid-phase concentration

at adsorption equilibrium point. For the experimental evaluation of KL and qm a

linearisation of equation 1.1.6. is useful

c q K q q m Lm

1111⋅

⋅

+= (1.1.7)

This regression is strongly biased toward fitting the data in the low concentration

range. Another possible linearisation (1.1.8) should also be considered. It has some

bias toward fitting the data in the middle and high concentration range.

(1.1.8)



8

The Langmuir isotherm equation has two limits:

( )lim q c q K cc o

m L= ⋅ ⋅

→

(linear isotherm) (1.1.9)

( )lim q c qc

m=

→ ∞

(horizontal isotherm) (1.1.10)

The linear range of the isotherm is also called as the Henry’s law range, because

equation 1.1.9 is similar to Henry’s law which describes the solubility of gases in

liquids. At high liquid-concentrations the solid-phase concentration is not dependent

on the liquid-phase concentration. Thus the adsorption isotherm becomes horizontal.

Because of these two limits it becomes evident, that the description of experimentally

determined equilibrium points is often not exactly enough by the use of Langmuir

isotherm equation.

More often the Freundlich isotherm equation is used to describe the adsorption

isotherm for a single substance.

q K cFn

= ⋅ , (1.1.11)

Therein KF is the Freundlich constant and n is the Freundlich exponent. These twoparameters can be determined easily by nonlinear regression or by linear regression

of equation 1.1.11 which has to be transformed to

lg lg lgq K n cF= + ⋅ (1.1.12)

The Freundlich isotherm equation allows very often a better description of an

adsorption isotherm in a wide concentration range.



10

3. Experimental Procedure

3.1 Materials

− Hach-Lange DR5000 spectrophotometer

− balance

− volumetric flasks (100 ml, 2 L)

− powdered activated carbon: NORIT SA-UF (Suspension) 200 mg/L

− powdered activated carbon: Jacobi PAC-MG (Suspension) 200 mg/L

− “Schott” bottles

− lab gloves

− multi magnetic stirrer and stir bars

− pipettes and pipette tips

− dispenser (100 ml)

− narrow neck bottles (100 ml)

− filtration unit ”suction pump, glass fibre filters

− ultrapure water

− beakers

− stopwatch

− diclofenac (DFC) stock solution 0.4 g/L

− NaHCO3 solution 0.05 mol/L

− MgSO4 solution 0.02 mol/L

− CaCl2 solution 0.03 mol/L

− 1 M HCL / 1 M NaOH



11

3.2 Guidelines for carrying out the experiments

3.2.1 Preparation of synthetic drinking water

All experiments are carried out in synthetic drinking water. Although it is suitable for human

consumption, tap water still contains a residual concentration of natural organic matter

(NOM). This NOM is also adsorbed on activated carbon. Therefore, the use of tap water for

the experiment would lead to a so called “multisolute system”, in which the substances

compete with one another for the adsorption sites on the activated carbon surface. Synthetic

drinking water in contrast contains no NOM, thus, it is possible to create a system that

contains just one adsorbable substance (in our case diclofenac).

Preparation of 5 L synthetic drinking water: Use a 5 L volumetric flask to prepare the

synthetic drinking water. Add ~2 L of ultrapure water into the volumetric flask, then pipette

the right amounts of NaHCO3 solution, MgSO4 solution and CaCl2 solution into the volumetric

flask and fill it up to the mark with ultrapure water. Do not mix the salt solutions undiluted, as

precipitation might occur!

Adjust the pH-value of the synthetic drinking water to 7.5 by dropwise addition of

hydrochloric acid / sodium hydroxide solution.

Calculation of the right amount of salt stock solution: The concentrations of different ions in

synthetic drinking water are listed in table 1.

Table 1: Ion concentration

IonConcentration

[mg/L]

Na+ 11.5

Ca2+

12

Mg2+

5

HCO3- 30.5

Cl- 21

SO42- 19

− Calculate the ion concentration in the synthetic drinking water in mol /L.

− Calculate the right volume of stock solution you have to add for the preparation of 5 L

synthetic drinking water (for concentrations of salt stock solutions see section 3.1).

You may find figure 4 helpful in case you have problems with the calculation.



12

Figure 4: Instruction for the calculation of different parts for preparing a solution

Table 2: Calculated volumes

Stock solution

volume needed for

preparation of 5 L synthetic

drinking water [mL]

NaHCO3 0.05 mol/L FILL IN RIGHT VOLUME

MgSO4 0.02 mol/L FILL IN RIGHT VOLUME

CaCl2 0.03 mol/L FILL IN RIGHT VOLUME

3.2.2 Calibration

Perform a 6-point calibration using DFC concentrations between 0 and 5 mg/L. The

absorption maximum of DFC is at 276 nm; accordingly you have to adjust the

spectrophotometer to that wavelength (ask supervisor). The DFC stock solution has aconcentration of 0.4 g/L. Prepare standard solutions in the concentration range mentioned

above:

− use one volumetric flask to prepare a dilution of the stock solution if necessary

− add the (calculated) volume of DFC stock solution into a volumetric flask (100 ml)

− fill it up to the mark with synthetic drinking water

− prepare also one flask without DFC for the blank

After carefully shaking the flasks, measure the extinction of each standard solution using the

spectrophotometer. Note the displayed extinction. Plot a calibraton curve to get the



14

the bottles No. K 0 – No. K 9. Add the volume of PAC suspension to get a concentration of

10 mg PAC/L in each bottle with a time delay of 30 seconds. Than take samples after 2.5, 5,

10, 15, 30, 60, 90, 120 and 150 minutes contact time. For a better understanding see

Figure 6. The procedure of taking a sample is described in the next chapter.

Figure 6: Experimental procedure for kinetic experiment

Stop this experiment when adsorption equilibrium is reached (that is the case when the

extinction of a sample is equal or higher than the extinction of the sample measured before).

The samples (No. 0 – No. 9), prepared in part 1 of the experiment have also reached

adsorption equilibrium now (stop experiment, measure samples).



15

3.2.4 Sampling

To take a sample, prepare the filtration unit (see figure 7) as follows:

Figure 7: Filtration unit

− place the filtration unit on an empty narrow neck bottle, put a glass fibre filter and the

sample reservoir on the filter holder and fix them with the clamp

− switch on the suction pump and close the aeration valve and filter your sample

− place the filtration unit on the wash bottle and rinse the sample reservoir with ~ 20 ml

water

− use a new glass fibre filter and filter the next sample into another empty narrow neck

bottle

− measure the extinction of the filtrate

3.2.5 Experiment 2: Adsorption of Diclofenac using Jacobi PAC MG

Repeat experiment 1 using the second activated carbon “Jacobi PAC MG”.



16

4. Interpretation of data

For the first and the second experiment plot the adsorption kinetics for each carbon type,

check the time which is necessary to reach the equilibrium and compare the two different

activated carbon brands (Discuss the results in a few sentences!). Are there differences?Why?

Furthermore plot and discuss the adsorption isotherms for each carbon type → solid-phase

concentration, q [g DFC/kg PAC] against liquid-phase concentration, c [mg DFC/L].

Make a linear regression using the Langmuir equation as well as the Freundlich equation for

each carbon brand and discuss which model is more suitable to describe the adsorption of

DFC onto PAC. Please keep in mind that there are two types of Langmuir regression.

Calculate the maximum solid-phase concentration qmax and the Langmuir constant KL as wellas the Freundlich exponent n and the Freundlich constant KF for each carbon brand and

compare both carbon brands using these values, especially with respect to their adsorption

capacity. If there are any differences, how can they be explained concerning the different

characteristics (see data sheet for each carbon brand in appendix and check the meaning of

different carbon characteristics in the literature or the internet)?

Your report should include group colour, all necessary graphs and your discussion.



17

5. Literature

Sontheimer, H., Frick, B.R., Fettig, J., Hörner, G., Huebele, C., Zimmer, G. (1985):

Adsorptionsverfahren zur Wasserreinigung

DVGW Forschungsstelle am Engler – Bunte Institut der Universität Karlsruhe (TH)

von Kienle, H., Bäder, E. (1980): Aktivkohle und ihre industrielle Anwendung

Ferdinand Enke Verlag



017687A

Date Issued

Customer

Quantity

Certificate of AnalysisLot #

w w w . j a c o b i . n e t

Product

PO #

AquaSorb 5000, PAC-MG

Parameter Method Value Unit

Iodine number ASTM D4607 1470 mg/g

Moisture content (as packed) ASTM D2867 4,6 %

Total ash content ASTM D2866 12,4 %

Particle size by Laser

- 325 ( - 0.045) 100

US mesh mm %

Universität Duisburg

Muster

03 August 2010

No Match

Certified by NSF to

ANSI/NSF Standard 61

Jacobi Carbons

is certified to

ISO 9002:2000

......................................................................................

Karl Krause, Quality Manager



Datenblatt

Wasser

Dokument-Nummer

SAUF

Produkt / Anwendung

Aktivkohlepulver

Version

10 Februar 2010

Norit Nederland BV

Nijverheidsweg-Noord 723812 PM AmersfoortP.O. Box 1053800 AC AmersfoortThe Netherlands

T: +31 33 46 48 911F: +31 33 46 17 429E: [email protected]: www.norit-ac.com

Norit SA UF

Norit SA UF ist ein Aktivkohlepulver mit hervorragenden kinetischen Eigenschaften, die auf seineultrafeine Teilchenstruktur zurückzuführen sind. Norit SA UF besitzt ein sehr hohes

Adsorptionsvermögen für eine Reihe von Verbindungen und findet besonders Anwendung in der Trinkwasserbehandlung. Da strenge Überkorn-Anforderungen gelten, eignet sich Norit SA UFbesonders in Kombination mit Hohlfaser-Ultrafiltrationsmembranen. Norit SA UF wird mittelsDampfaktivierung aus ausgewählten Rohstoffen hergestellt.

Norit SA UF erfüllt die Anforderungen des U.S. Food Chemical Codex (6. Ausgabe, 2008). Sie wird imRahmen eins Qualitätssystems hergestellt, das die Anforderungen des CDX HACCP erfüllt. Dasentsprechende Zertifikat der Registrierung ist auf Anfrage erhältlich.

SPEZIFIKATIONEN

Jodzahl min. 1000 -

Korngröße > 400 µm max. 0.0 Gew.-%

Korngröße > 180 µm max. 0.1 Gew.-%

Feuchte (verpackt) max. 5 Gew.-%

ALLGEMEINE EIGENSCHAFTEN

Jodzahl 1100 -

Methylenblauadsorption 24 g/100 g

Phenoladsorption 5 Gew.-%

Innere Oberfläche (B.E.T.) 1200 m2/g

Schüttdichte (gestampft) 225 kg/m3

Korngröße D50 5 µm

Aschegehalt 10 Gew.-%

pH alkaline -

Feuchte (verpackt) 2 Gew.-%

adsorption labwork

Documents