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8-2013

Glucose and Cellobiose Adsorption onto ActivatedCarbonYu SunIndiana University of Pennsylvania

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GLUCOSE AND CELLOBIOSE ADSORPTION

ONTO ACTIVATED CARBON

A Thesis

Submitted to the School of Graduate Studies and Research

in Partial Fulfillment of the

Requirements for the Degree

Master of Science

Yu Sun

Indiana University of Pennsylvania

August 2013

ii

Indiana University of Pennsylvania School of Graduate Studies and Research

Department of Chemistry

We hereby approve the thesis of Yu Sun

Candidate for the degree of Master of Science August 28, 2013 Signature on File_____________________

John C. Ford, Ph.D. Associate Professor of Chemistry, Advisor

August 28, 2013 Signature on File_____________________

Jaeju Ko, Ph.D. Associate Professor of Chemistry

August 28, 2013 Signature on File_____________________

Nathan R. McElroy, Ph.D. Associate Professor of Chemistry

August 28, 2013 Signature on File_____________________

Keith Kyler, Ph.D. Assistant Professor of Chemistry

ACCEPTED ___________________________________ _____________________ Timothy P. Mack, Ph.D. Dean School of Graduate Studies and Research ______________

iii

Title: Glucose and Cellobiose Adsorption onto Activated Carbon Author: Yu Sun

Thesis Advisor: Dr. John C. Ford

Thesis Committee Members: Dr. Jaeju Ko Dr. Keith Kyler Dr. Nathan R. McElroy

Glucose and cellobiose are the simplest model compounds for cellulose.

Glucose is itself a valuable commodity. It is a food as well as a biorenewable

starting material for a variety of other materials.

However, certain fundamental data for this common material are scarce or

unavailable. For example, although activated carbon has long been used to

purify carbohydrates, published adsorption isotherms for glucose on carbon are

rare. We are unaware of any published adsorption isotherm for cellobiose on

carbon.

In this research, adsorption isotherms for glucose and cellobiose on

activated carbon were determined. The experiment was carried out using HPLC

and a derivatization method to quantify the saccharide concentrations before and

after adsorption. The Brauner-Emmet-Teller equation best fit the isotherm data.

For glucose, over the temperature range of 20-35°C, the adsorption equilibrium

constants gave a nonlinear van't Hoff plot, which can be rationalized by

consideration of the conformational equilbria involved.

iv

ACKNOWLEDGMENTS

The author wishes to express his gratitude to Dr. Ford for his patience,

guidance, support and encouragement. He would also like to thank his parents

for their financial support and encouragement.

v

TABLE OF CONTENTS

Chapter Page 1 INTRODUCTION ....................................................................................... 1 2 EXPERIMENTAL ....................................................................................... 8

2.1 Chemicals ..................................................................................... 8 2.2 Preparation of Activated Carbon ................................................. 10 2.3 HPLC System ............................................................................. 10 2.4 Other Equipment ........................................................................ 12 2.5 Procedure ................................................................................... 12

2.5.1 Preparing saccharide samples ........................................ 12 2.5.2 Derivatization procedure ................................................. 13

3 RESULTS AND DISCUSSION ................................................................. 15

3.1 Equilibration Time ........................................................................ 16 3.2 Preparation of Carbon ................................................................. 17 3.3 Isotherms of glucose and cellobiose ........................................... 20

3.3.1 Best-fit model ................................................................... 21 3.3.2 Comparison of fitted model parameters ........................... 28

3.4 Effect of temperature and thermodynamics of adsorption ........... 31

4 SUMMARY AND CONCLUSION ............................................................. 35

REFERENCES ................................................................................................... 37

APPENDICES .................................................................................................... 41

Appendix A - Langmuir parameters for glucose and cellobiose adsorbed to washed Darco G-60 activated carbon. ............. 41 Appendix B - BET parameters for glucose and cellobiose adsorbed to washed Darco G-60 activated carbon. ............. 41 Appendix C - Freundlich parameters for glucose and cellobiose adsorbed to washed Darco G-60 activated carbon. ............. 41

vi

LIST OF TABLES

Table Page

1 Characterizations of Darco G-60 Activated Carbon. ................................... 9

2 The Suppliers and Grades of all the Chemicals Used in This Research .......................................................................................... 10

3 The HPLC working conditions ...................................................................11 4 All Equipment Used In This Research .......................................................11

5 Langmuir parameters for glucose and cellobiose adsorbed to unwashed and washed Darco G-60 activated carbon .......................... 20

6 Statistical results for fitting model equations to adsorption isotherm data .......................................................................... 27

7 Brauner-Emmet-Teller parameters for glucose and cellobiose adsorbed to washed Darco G-60 activated carbon ................................... 29

vii

LIST OF FIGURES

Figure Page

1 Structure of glucose .................................................................................. 1

2 Structure of cellobiose. ............................................................................. 1

3 Solution concentrations of glucose and cellobiose in equilbrium with Norit SX carbon as a function of time............................. 17

4 Absorbance of MilliQ water, water from unwashed carbon, and water from washed carbon. ................................................. 18

5 Adsorption isotherms of glucose on washed and unwashed Darco G-60 activated carbon at 20°C, 25°C and 30°C. .......................... 19

6 Adsorption isotherm of glucose on Darco G-60 activated carbon at 20°C. ....................................................................... 23

7 Adsorption isotherm of glucose on Darco G-60 activated carbon at 25°C ........................................................................ 23

8 Adsorption isotherm of glucose on Darco G-60 activated carbon at 30°C. ....................................................................... 24

9 Adsorption isotherm of glucose on Darco G-60 activated carbon at 35°C. ....................................................................... 24

10 Adsorption isotherm of cellobiose on Darco G-60 activated carbon at 20°C. ....................................................................... 25

11 Adsorption isotherm of cellobiose on Darco G-60 activated carbon at 25°C. ....................................................................... 25

12 Adsorption isotherm of cellobiose on Darco G-60 activated carbon at 30°C ........................................................................ 26

13 Two possible ways of sugar molecules staying on the surface of activated carbon. (a) Sugar molecules sidewards lying on the surface of carbon. (b). Sugar molecules end-on, sticking up on the surface of carbon .......................................... 30

14 Adsorption isotherms of glucose on Darco G-60 activated carbon at 20°C, 25°C, ,30°C and 35°C. .................................. 32

15 Adsorption isotherms of cellobiose on Darco G-60 activated carbon at 20°C, 25°C, and 30°C. ............................................ 32

viii

16 Plot of lnKa1 and 1/T for glucose and cellobiose adsorption on G-60 activated carbon. ..................................................... 34

1

CHAPTER 1

INTRODUCTION

Glucose (C6H12O6) is a simple monosaccharide which is also called D-

glucose (the other stereoisomer, L-glucose is almost nonexistent in nature),

dextrose, blood sugar, corn sugar or grape sugar. Glucose, fructose and

galactose are three dietary monosaccharides, i.e., they can be absorbed directly

into the blood and metabolized. Glucose is the primary source of energy for cells

(1).

Cellobiose ((HOCH2CHO(CHOH)3)2O) is a disaccharide which is consisted

of two glucose units linked by a β bond. Cellobiose can be hydrolyzed to glucose

with specific enzyme or acid (2). The structures of glucose and cellobiose are

given below in Figure1 and Figure2.

Figure 1. Structure of glucose. The structure shown is β-D-glucose in the pyranose form. This is the preferred form in aqueous solution at 25°C.

Figure 2. Structure of cellobiose. Because of the flexibility of the structure, cellobiose has many possible configurations. The structure shown here is one possible configuration: α-D-glucopyranosyl β-D-glucopyranoside.

2

Cellulose is the most abundant, renewable biopolymer (3). In industry, it is

an important raw material. It plays a central role in the global carbon cycle and

has the potential to be more widely used as a source of fuels and commodity

chemicals in the future. Insoluble cellulose is a linear polymer of anhydroglucose

units joined by β(1-4) linkages, with degrees of polymerization (DP, the number of

repeating units) from 100 to 20000. While cellulose is frequently called a

polymer of glucose, cellobiose is the actual monomeric unit of cellulose (4). The

DP of a cellulosic material is an important measurement for functionally based

models of enzymatic cellulose hydrolysis as well as for paper-making and other

applications (5).

Short fragments of cellulose whose DP are from 2 to 12 are termed

cellodextrins. The cellodextrins are soluble when DP≤6 and slightly soluble when

6 < DP <12. The most common cellodextrins are cellobiose (DP=2), cellotriose

(DP=3), cellotetraose (DP=4), cellopentaose (DP=5), and cellohexaose (DP=6).

(6) These oligosaccharides have special properties which include solubility in

nonaqueous or partially aqueous solvents and a melting point which increases

with increasing molecular weight (8). Cellodextrins are intermediates in the

production of glucose from cellulose.

Cellulose has the potential to serve as a renewable carbon or energy

resource for the microbial production of fuels and chemical feedstocks in the

future but it is hard to utilize cellulose directly in many industrial processes. As

one of the United States' most abundant renewable resources, about one billion

tons of cellulose-containing residues are generated annually (7) and glucose can

3

be produced from cellulose (8). If these residues could be utilized well, there is a

potential for yielding over 6×1011 pounds of a valuable chemical feedstock,

glucose, from which fuel alcohol and other fermentation derived chemicals can

be made (7). Over 109 tons of “waste” cellulose is generated annually in the

United States, which is a huge waste. The cellulose has the potential to be

reused but much of it is discarded directly (9).

Activated carbon is a form of carbon which has been processed, usually

with oxygen or steam, to create many small pores of low pore volume and thus

produce a very large surface area available for adsorption or chemical reactions

(1). “The use of special manufacturing techniques results in highly porous carbon

that has surface areas of 300-2,000 square meters per gram.” (10) Activated

carbon is a widely used adsorbent for the removal of a wide range of

contaminants from liquids and gases. It is also used to adsorb a product to purify

it. For example, the activated carbon can be used to adsorb a solvent from a

process stream, and the adsorbed product can be subsequently desorbed on-site

for reuse (2).

The meaning of “adsorb” is: when an adsorbent adsorbs an adsorbate, the

adsorbate attaches to the adsorbent by chemical attraction. The surface area is

an important factor for an adsorbent. Activated carbon is a good adsorbent

because of its huge surface area which gives it many bonding sites. When

certain chemicals pass next to the carbon surface, they attach to the surface and

are trapped (11). Activated carbon is good at adsorbing organic chemicals. Many

other chemicals can not be adsorbed by activated carbon. In other words, under

4

appropriate conditions, an activated carbon filter can adsorb target chemicals

and ignore others. It also means that, if all of the bonding sites are filled, an

activated carbon filter doesn’t work anymore. At that point the filter must be

replaced (6).

Activated carbon is commonly used for purification of sugar liquors. Sugar

liquors include solutions of starch hydrolyzate which contains a mixture of mono-,

di-, oligo- and higher polysaccharides, as well as sugar solutions derived from

cane, beet and corn sources. The term, oligosaccharide, refers to a carbohydrate

containing from 2 to 8 simple sugars linked together, while the term,

“polysaccharide,” refers to a carbohydrate containing more that 8 simple sugars.

A starch hydrolyzate is an aqueous mixture of sugar components derived from

acid, enzyme or other treatment of starchy materials (6).

The purification of sugar liquors including corn syrup, cane sugar and

relatively impure solutions of dextrose is one of the oldest established industrial

chemical procedures. Aqueous solutions of certain sugars such as glucose are

produced industrially in the hydrolysis of amylaceous or cellulosic materials. For

example, large amount of glucose solutions are producing by the hydrolysis of

starch in the manufacture of corn syrup, corn sugar and dextrose. These

solutions contain minor but significant amounts of other sugars which can’t be

removed by conventional refining procedures. One use of activated carbon is for

the decolorization of sugar liquors. Typically the powdered activated carbon is

slurried with the impure liquor one or more times followed by filtration of the

decolorized liquor. Decolorization is also accomplished by passing the liquors

5

through a column of granular activated carbon. By these procedures, color-

causing impurities can be removed, which are small amounts of oligosaccharides

present in the liquor (6).

In addition to its industrial uses, activated carbon has been important in

laboratory purification for many years. It is frequently used to remove impurities

from synthetic products, and is known as “decolorizing carbon.” It has been an

important adsorbent in chromatography as well (12), and is frequently used in

carbohydrate and oligosaccharide purification (6).

In adsorbent-adsorbate interaction research, the ability to predict the

“absorbability” for a given adsorbent from a specific adsorbate is an important

objective (13). Isotherm data is important for a better understanding of the

purification process of glucose as well as improving preparative separations of

cellodextrins using activated carbon. Isotherm data can reflect the adsorption

ability well. The adsorption isotherm is a curve giving the functional relationship

between adsorbate and adsorbent in a constant-temperature adsorption process.

Isotherm data of cellodextrins adsorption onto carbon is important because it can

give a better understanding of the purification process of cellodextrins solution,

which may help people to make a better industrial purification plan. Although the

purification of sugar liquors is one of the oldest established industrial chemical

procedures (11), very little relative isotherm data is published. Relative isotherm

data is useful in understanding the process more exactly and may help to

increase the working efficiency. The adsorption of cellodextrins onto carbon may

also be a good method to produce cellodextrins from cellulosic waste. Isotherm

6

data would be useful in modeling such a method. For example, studies of the

competitive adsorption of cellodextrins onto carbon need the individual isotherms

of each component as basic supporting information. And isotherm data are

invaluable for studies of adsorption energetics.

Activated carbon is extensively used in the purification of sugars, both

industrially and in the laboratory. Little or no published information is available

concerning the thermodynamics of the interaction between the carbon surface

and simple carbohydrates. Here, the isotherms of glucose and cellobiose

adsorption onto activated carbon under different temperatures are presented and

the adsorption of the simplest cellodextrin is studied. The important part of this

research is how to quantify the concentration of sugar before and after

adsorption. A derivatization method was used for the determination of the

concentration of sugar. The reducing ends of glucose and cellobiose can react

with 4-aminobenzoic acid ethyl ester. The amount of product can be used to

determine the original concentration of sugar. The concentration of product is

determined by a HPLC system. The method is available for oligosaccharides.

Brauner-Emmet-Teller (BET) isotherm equation was fit to the data. The BET

equation can be mathematically represented by:

Here, Γmono is the surface concentration of the sugar that corresponds to

monolayer coverage of the interface.Ka1 is the equilibrium constant for adsorption

of the sugar on the solid, and Ka2 is the equilibrium constant for adsorption on

sites that are already occupied by adsorbed molecules (14).

7

The adsorption process is temperature sensitive. Isotherms of glucose and

cellobiose were obtained under 20°C, 25°C and 30°C respectively. There is

obvious difference between the isotherms under different temperature. The

influence of temperature was studied. Basically the adsorption ability increased

with the increasing of temperature in this temperature range. And the isotherms

of glucose were compared with the isotherms of cellobiose. While the molecule

size of cellobiose is larger than that of glucose, approximately equal numbers of

molecules are adsorbed at monolayer coverage.

8

CHAPTER 2

EXPERIMENTAL

Isotherms were determined using the static method (15). Basically a known

mass of adsorbent was equilibrated with a known volume of adsorbate solution of

known concentration. After equilibration, the concentration of adsorbate

remaining was measured, and the amount adsorbed calculated from the

difference in the initial and final concentrations.

Glucose or cellobiose is not readily detected by the UV absorbance detector

of the HPLC. Two detection methods were employed: early work was performed

using a pulsed-amperometric detector (PAD). PAD is a well-known method of

detecting carbohydrates;(16) the carbohydrates are chromatographed in a

strongly basic mobile phase, rendering them anions. They are detected by

oxidization at a gold electrode. Unfortunately, an instrumental failure caused us to

adopt an alternative quantitation method.

Subsequently, a derivatization method was used. This method employed for

derivatization of glucose and cellobiose at their reducing end with p-

aminobenzoic ethyl ester (ABEE). (17) The details of the method are given below.

All work on washed carbon was performed using this derivatization method.

2.1 Chemicals

The adsorbents used were Norit SX and Darco G-60 activated carbons (both

Norit Company). All reported isotherms were measured using the Darco G-60

activated carbon, as that material is frequently used in saccharide purification

9

and analysis (6). The manufacturer's characterization of Darco G-60 is provided

in Table 1, taken from the Norit data sheet. The water used in this research was

obtained from a Millipore Direct-Q® 8 UV-R (EMD Millipore, Billerica, MA). The

grades and suppliers of the other chemicals used are listed in Table 2.

Table 1. Characterizations of Darco G-60 Activated Carbon. This is the carbon most commonly used for cellodextrin purification. These data are from the data sheet supplied by Norit America, the manufacturer

Characterization Tests Results of Tests

Methylene blue adsorption, g/100 g 15 min

Iron, Zacher method, ppm as Fe 200 max

Moisture, % as packed 12max

Water solubles, % 0.50 max

Acid soluble ash, % 0.7

pH, water extract 6

Ash, % 4

Bulk density, tamped, g/mL 0.40

Bulk density, tamped, ib/ft3 25

Particle size, laser, d5, um 5.5

Particle size, laser, d50, um 34

Particle size, laser, d95, um 125

Food Chemical Codex Passes

10

Table 2. The Suppliers and Grades of all the Chemicals Used in This Research

Compound Grade Supplier

Acetonitrile HPLC Fisher Scientific

Methanol Laboratory Fisher Scientific

Acetic Acid Glacial Laboratory Emdchemicals

ABEE Laboratory Fisher Scientific

Sodium Cyanoborohydride

Laboratory MP Biomedicals

Cellobiose Chemical Purpose Eastman Organic Chemicals

Glucose Reagent Fisher

2.2 Preparation of Activated Carbon

Prior to use, 4 g of activated carbon powder was stirrred 1000ml MillliQ

water for 4 hours, and the water exchanged three times. The carbon was then

collected by filtration and dried prior to use. Several batches of washed carbon

were combined to provide the material used for isotherm determinations.

2.3 HPLC System

Initially, the carbohydrate concentrations were determined by high

performance anion exchange (HPAE) liquid chromatography with A Shimadzu

LC-20, consisting of a LC-20AT pump, a SIL-20ADvp auto-sampler, and a CTO-

20Acvp column oven, will provide the basic chromatography. A Bioanalytical

Systems Model SPD-10A(V)vp was used as a pulsed-amperometric detector

(PAD). The quadrupole-potential waveform recommended by Rocklin et al (18).

was used.

11

As mentioned above, an equipment problem caused us to change to a

derivatization-based determination, using reductive amidation to form UV-

fluorescent derivatives according to the reaction scheme show in Figure 4. This

aminobenzoic acid ethyl ester (ABEE) derivatization is common in carbohydrate

analysis (19). The derivatized products are separated from one another and the

unreacted ABEE by reversed-phase liquid chromatography using the HPLC

working conditions given in Table 3. For this work, a RF-20A Fluorescence

Detector (Shimadzu) was used.

Table 3. The HPLC working conditions

Mobile phase 70% of MilliQ water mixing with 30% of ACN.

Flow rate 1.0mL/min

Column 40°C

Injection volume 5μl

Table 4. All Equipment Used In This Research

Equipment Supplier

Dry Bath Fisher Brand

Centrifuge Micro Centrifuge Model 235B

Balance Lab companion

SI-300R Lab companion

RF-20A Fluorescence Detector Shimadzu

Pulsed Amperometric Detector Bioanalytical Systems, Inc, West Lafayette, IN USA

LC-20AT pump Shimadzu

SIL-20 ACHT Auto Sampler Shimadzu

CTO-20A Column Oven Inc, Rescek Corporation, IN USA

12

2.4 Other Equipment

Other equipment included a dry bath instrument, a thermostatted shaker, a

centrifuge, and an analytical balance, also listed in Table 4.

2.5 Procedure

Initial experiments with the PAD showed us that the linear range of the

detector allowed concentrations at least as high as 10 mM but that the lower limit

of quantitation (LOQ) was affected by the choice of high concentration. This is

because the PAD detector signal is sent to an analog-to-digital converter (ACD)

in the Shimadzu system and the resolution of the ADC determines the LOQ.

Adjusting the amplification to allow a smaller LOQ reduces the maximum

concentration represented without clipping. Consequently, the upper limit of

concentration used to some extent affected the lowest concentration used in a

given experiment.

2.5.1 Preparing saccharide samples

Saccharide solutions were prepared with concentrations ranging from 0.0 to

the 5.0mM, with. 11 different concentrations used for each trial: 0.0mM, 0.5mM,

1.0mM 1.5, 2.0mM, 2.5mM, 3.0mM, 3.5mM, 4.0mM, 4.5mM, 5.0mM.

The isotherms were measured as follows:

(i) 0.1 gram of activated carbon were placed in stoppered glass tubes.

(ii) 8mL of each saccharide solution was added to each tube.

13

(iii) The tubes were incubated with shaking at a fixed temperature for at least 8

hours to make sure the saccharide has enough time to adsorb carbon.

(Preliminary experiments indicated that the adsorption of glucose is essentially

complete in 1 hour at room temperature.)

(iv) The carbon was allowed to settle, and an aliquot taken for analysis.

2.5.2 Derivatization procedure

The derivatization reagent was prepared by mixing 7.0mL methanol and

820μL of glacial acetic acid, then adding 3.30 gram of ABEE and, 0.7 gram of

sodium cyanoborohydride were added. The ABEE did not dissolve well at room

temperature, so water bath was used to make solvent warm (around 50°C).

After the adsorption process was finished, the 10μL aliquot of each

saccharide solution before adsorption (11 samples) and after adsorption (11

samples) was put in separated 6×50mm tube. Next, 40μL of ABEE reagent ( the

method of making it was described before) was added to each tube, and the

tubes were placed in a dry bath instrument for 1 hour at 80°C. After 1 hour, the

reaction mixtures were cooled to room temperature, 200 μL of MillliQ water and

200 μL of chloroform were added to each tube, the tubes vortexed for 5 seconds,

and allowed to stand for 1 minute. The mixture separated into two layers—an

upper clear aqueous layer and a lower muddy layer. Fifty μL of the clear upper

aqueous layer was put in a HPLC vial and 400 μL of MilliQ water was added. The

saccharide concentrations before and after adsorption were then measured by

14

HPLC. The only change to collect data at different temperatures was to change

the incubation temperature.

The concentration of each saccharide solution before adsorption was known,

so a linear relationship between saccharide solution concentration and the HPLC

peak area could be determined, which was used to calculate the final

concentration of each saccharide solution after adsorption. Because the volume

of each solution and the weight of carbon were known, the amount of saccharide

adsorbed per gram of carbon (in units of μg/g) could be calculated. Thus, a

series of adsorption data points were determined. Langmuir, Freundlich and BET

equations were fit to the data by nonlinear least squares regression using the

Solver tool in Microsoft Excel.

15

CHAPTER 3

RESULTS AND DISCUSSION

For each experiment, a calibration curve relating the HPLC-determined peak

areas to the prepared saccharide prior to exposure to carbon was prepared.

These calibration curves were described by linear equations. Next, the

saccharide concentration of each solution following adsorption was determined

using the calibration curve. Because the volume of each solution and the weight

of carbon powder were also known, the adsorption capacity of carbon (CS) could

be calculated and expressed in μmol/g .

Then, the isotherm could be determined with CS as the dependent variable

and CM (equilibrium solution concentration) as the independent variable. However,

fitting of adsorption isotherm equations to experimental data is an important

aspect of data analysis. An adsorption isotherm gives the functional relationship

between adsorbate and adsorbent in a constant-temperature adsorption process

(20). A large number of such functional relationships have been applied (14).

One of the more widely used models is the Langmuir model. This model is

based on a simple statistical consideration involving adsorption onto a surface

with a finite number of equivalent sites (21). The Langmuir model has been

applied extensively, even in situations where non-equivalent populations of

adsorption sites are clearly evident (22). While it is highly unlikely that activated

carbon contains a homogeneous population of adsorption sites, the Langmuir

model is so appeallingly simple that it is included here.

16

In contrast, the Freundlich isotherm model is usual considered as empirical,

although it can be derived from an adsorption model where the adsorption

energy decreases exponentially as the number of adsorbed molecules increases.

The Freundlich model has found widespread use and has previously been

applied to mono- and oligosaccharides adsorbed onto activated carbons (23).

Adsorption is also frequently described by the Brauner-Emmet-Teller (BET)

isotherms model. The BET model allows multi-layer adsorption, with each layer

following Langmuir-like behavior (24).

3.1 Equilibration Time

Adsorption isotherms require that the solution concentration of the adsorbate

comes to equilibrium with the adsorbed concentration. Thus, it is necessary to

first determine the length of time required for the establishment of that equilibrium.

Figure 3 shows the solution concentrations of glucose and cellobiose in

equilbrium with Norit SX carbon as a function of time. In each case, 1.00 mL of

10 mM sugar was mixed with 10.0 mg of the carbon and shaken for the indicated

period of time at rom temperature. Following centrifugation and HPLC-PAD

analysis, the remaining solution concentrations were determined. The figure

shows that equilbrium was reached quickly, and that two-hour equilibration times

were adequate. To ensure equilibrium, all isotherm measurements were

performed using overnight (8-12 hours) equilibration times.

17

Figure 3. Solution concentrations of glucose and cellobiose in equilbrium with Norit SX carbon as a function of time. Ten mL of 10.0 mM aqueous solute was mixed with 100 mg of carbon, and samples withdrawn at the indicated times. Analysis with performance by high-performance anion exchange chromatography using pulsed-amperometric detection. 3.2 Preparation of Carbon

Initial studies were performed using Norit SX carbon, and quantifying the

adsorbed sugar by HPLC. For the temperature studies, the carbon was changed

to Darco G-60 which the carbon most often recommended for the separation of

sugars (25). Both these carbons were used as supplied.

However, an instrumental issue caused us to attempt to perform some work

using absorbance at 191 nm to quantify the amount of sugar adsorbed. Figure 4

shows the absorbance spectrum of the carbon blank, i.e., 100 mg of carbon were

shaken in MilliQ purified water for 12 hours and centrifuged. Figure 4 also shows

the absorbance spectrum of the water itself, the absorbance spectrum obtained

when the carbon was first washed with water and dried before weighing.

18

Figure 4. Absorbance of MilliQ water, water from unwashed carbon, and water from washed carbon. The absorbance of the MilliQ water was recorded directly, without contact with carbon. The other two curves represent the absorbances of water which had been in contact with unwashed or washed Darco G-60 activated carbon for 8 hours, then recovered by filtration.

While the washing procedure did not remove all water-soluble material,

washing reduced it considerably, as revealed by the difference in the spectra of

water from unwashed carbon and water from washed carbon. More extensive

washing did not significantly reduce the absorbance from this unknown water-

soluble material, nor did washing with glacial acetic acid prior to washing with

water (data not shown). Washing with boiling water was also effective at reducing

the amount of water soluble material, but did not eliminate the absorbance

observed in subsequent washes (data not shown).

19

Figure 5. Adsorption isotherms of glucose on washed and unwashed Darco G-60 activated carbon at 20 °C, 25°C and 30°C. Data fit with Langmuir equations.

Figure 5 shows adsorption isotherms obtained on washed and unwashed

Darco G-60 activated carbon at several temperatures. Each data set is fit to the

Langmuir Equation:

QKC1

QK

mq

Where K is the equilibrium constant, Q is surface concentration of the adsorbate

on the carbon, C is final concentration. The resultant best-fit parameters are

given in Table 5. As received, the Darco G-60 activated carbon had a water-

soluble, UV-active substance adsorbed to the surface. This material increased

the affinity of the surface for glucose, and significantly decreased the saturation

capacity of the surface for glucose, as calculated by the Langmuir equation.

These results strongly suggest that work performed on unwashed adsorbent

does not necessarily reflect the adsorption properties of that adsorbent. And it

20

must be noted that, while the washing employed here reduced the amount of

water-soluble substance, it was not eliminated. Hence, these isotherms, while

likely more correct than those obtained on unwashed activated carbon, may not

completely reflect adsorption to the carbon surface.

All subsequent work was done using Darco G-60 carbon which had been

washed extensively with MilliQ-purified water, dried at 60C, and stored in a

sealed container.

Table 5. Langmuir parameters for glucose and cellobiose adsorbed to unwashed and washed Darco G-60 activated carbon

Solute Adsorbent Temp K Q (μg/g)

Glucose Unwashed carbon 20 0.30 207.64

Glucose Unwashed carbon 25 0.40 172.22

Glucose Unwashed carbon 30 0.32 218.17

Glucose Washed carbon 20 0.03 1028.27

Glucose Washed carbon 25 0.01 2818.68

Glucose Washed carbon 30 0.03 920.59

Glucose Washed carbon 35 0.06 478.46

Cellobiose Washed carbon 20 0.98 210.02

Cellobiose Washed carbon 25 0.52 333.77

Cellobiose Washed carbon 30 0.85 279.31

3.3 Isotherms of glucose and cellobiose

Figures 6-9 show the adsorption isotherm data for glucose adsorbed to

Darco G-60 carbon at 20, 25, 30 and 35°C, respectively. In each case, the

experimental data is shown as points, while lines corresponding to best-fit BET,

Freundlich, and Langmuir equations are also shown. Figures 10-12 show similar

21

adsorption isotherm data for cellobiose,also adsorbed to Darco G-60, at 20, 25,

and 30°C, respectively.

3.3.1 Best-fit model

To select the model in best agreement with the experimental data, the

reduced sum of squared residuals (RSSν), Akaike’s information criterion(AIC)

(26), and the mean absolute percentage error (MAPE) are shown in Table 6. The

RSSν is approximately the reduced chi-squared of the fit, that is, it is the sum of

the square of the distances of each point from the fitted line, divided by the

degrees of freedom of the fit:

1N

)y-(y

RSSv

2

1

ifit

np

N

i

Where yi is experimental amount adsorbed, yfit is calculated amount adsorbed, N

is the number of data, and np is the number of parameters in model. It is widely

used in fitting; the smaller the RSSν,the better the fit. The AIC is a similar statistic,

but derived from information theory. It is given by:

K2N

SSlnNAIC

Where N is the number of data points, K is the number of parameters fit by the

regression plus one, and SS is the sum of the square of the vertical distances of

the points from the curve. Again, the smaller value of the AIC corresponds to the

better fit. The advantage of using the AIC is that it allows direct comparison of

different models, while, strictly speaking, the RSSν should only be used to

22

compare nested models, such as the Langmuir and BET models. MAPE is

commonly used in quantitative forecasting methods because it produces a

measure of relative overall fit. The absolute values of all the percentage errors

are summed up and the average is computed (27). It is given by:

n

t t

tF

1

t

A

A

n

1MAPE

Where At is experimental amount adsorbed, Ft is calculated amount adsorbed, n

is the number of data.

Comparing the RSSν values, the fit of the BET equation model has given the

smallest values in 6 of 7 isotherms; for the AIC model statistic, the fit of the BET

equation has gave smaller values in 6 of 7 isotherms. In the case of cellobiose at

20°C, the Freundlich equation fits the data slightly better than the BET equation.

In comparing the MAPE values, the fit of the BET equation model gave the

smallest values in all of 7 isotherms.The BET and the Freundlich equations both

fit the data better than the Langmuir equation. So the BET model is generally the

best-fit model. However, in the present work, the BET equation is used sole due

to it providing the best fit of the data points, not for any implied mechanistic

information.

23

Figure 6. Adsorption isotherm of glucose on Darco G-60 activated carbon at 20°C. Data fit with Langmuir, Freundlich and BET equations.

Figure 7. Adsorption isotherm of glucose on Darco G-60 activated carbon at 25°C. Data fit with Langmuir, Freundlich and BET equations.

24

Figure 8. Adsorption isotherm of glucose on Darco G-60 activated carbon at 30°C. Data fit with Langmuir, Freundlich and BET equations.

Figure 9. Adsorption isotherm of glucose on Darco G-60 activated carbon at 35°C. Data fit with Langmuir, Freundlich and BET equations.

25

Figure 10. Adsorption isotherm of cellobiose on Darco G-60 activated carbon at 20°C. Data fit with Langmuir, Freundlich and BET equations.

Figure 11. Adsorption isotherm of cellobiose on Darco G-60 activated carbon at 25°C. Data fit with Langmuir, Freundlich and BET equations.

26

Figure 12. Adsorption isotherm of cellobiose on Darco G-60 activated carbon at 30°C. Data fit with Langmuir, Freundlich and BET equations.

27

Table 6. Statistical results for fitting model equations to adsorption isotherm data

Solute Model Temp (C) RSS1 AIC2 MAPE3

Glucose Langmuir 20 22.60 32.95 6.64%

BET 20 8.78 22.15 5.13%

Freundlich 20 16.50 29.80 7.41%

Langmuir 25 48.38 121.09 11.35%

BET 25 14.53 82.68 6.33%

Freundlich 25 41.54 116.37 13.54%

Langmuir 30 57.49 85.85 10.89%

BET 30 36.22 76.94 9.35%

Freundlich 30 54.19 84.61 9.95%

Langmuir 35 41.59 79.05 11.00%

BET 35 36.65 77.19 10.97%

Freundlich 35 38.48 77.42 11.17%

Cellobiose Langmuir 20 129.46 50.40 8.52%

BET 20 99.43 48.43 5.46%

Freundlich 20 98.58 47.68 8.28%

Langmuir 25 100.36 97.55 11.03%

BET 25 14.09 57.12 2.42%

Freundlich 25 29.18 71.61 4.38%

Langmuir 30 223.29 114.34 9.71%

BET 30 104.11 99.12 7.51%

Freundlich 30 158.42 107.13 8.65%

1. 1N

)y-(y

RSSv

2

1

ifit

np

N

i , reduced sum of squared residuals.

2. K2N

SSlnNAIC

, Akaike’s information criterion.

3.

n

t t

tF

1

t

A

A

n

1MAPE , mean absolute percentage error.

28

3.3.2 Comparison of fitted model parameters

Although the BET equation accounts for multi-layer adsorption and contains

a parameter which characterizes the attractive interaction between the adsorbed

solution and the free solute in solution (24), we do not propose that the

adsorption of glucose or cellobiose is mechanistically explained by the BET

model. Nonetheless, the Ka1 term in the BET model represents the affinity of the

adsorbent for the adsorbate, and is in the limit of infinite dilution, the Henry's Law

constant for that system. Thus, the fitted Ka1 values should be, if not identical to,

proportional to the true equilibrium constants of interest.

The values of the best-fit BET equations are shown in Table 6. Comparing

the Ka1 values for glucose at different temperatures, there is not a obvious

tendency regarding to the increasing of temperature from 20 to 35°C.

On the other hand, with the increasing of temperature, the Ka1 values of

cellobiose increase, and the Γmono values decreases. This implied that with the

increasing of temperature, the affinity of the carbon for the cellobiose is

increasing and the adsorption capacity is decreasing.

Comparing the Ka1 and Γmono values of glucose with those of cellobiose, we

can see, the Ka1 and Γmono values of cellobiose are significant larger than those of

glucose, which can indicate that the affinity of activated carbon for cellobiose is

much stronger than that for glucose. And the adsorption capacity of activated

carbon for cellobiose is also larger than that of glucose, when expressed in μg/g.

However, when the adsorption capacity is expressed in μmol/g, it is nearly

identical for the two sugars.

29

Table 7. Brauner-Emmet-Teller parameters for glucose and cellobiose adsorbed to washed Darco G-60 activated carbon

Adsorbate Temperature Ka11 Ka2

1 Γmono1 (μg/g) Γmono1 (μmol/g)

Glucose 20 0.75 0.16 47.98 0.27

Glucose 25 1.34 0.19 38.26 0.21

Glucose 30 1.36 0.17 44.79 0.25

Glucose 35 0.84 0.13 55.39 0.31

Cellobiose 20 2.55 0.12 118.89 0.35

Cellobiose 25 3.03 0.19 112.11 0.33

Cellobiose 30 4.27 0.21 108.97 0.32

The average Ka2 value of glucose (excepting 35C) is 0.17 +/- 0.02 while the

average Ka2 value of cellobiose is0.17 +/- 0.05. Ka2 is the equilibrium constant for

adsorption on the second layer of carbon. The Ka2 values of glucose seem to be

the same as the Ka2 values of cellobiose. Of course this does not prove that the

adsorption equilibrium of glucose and cellobiose on the second layer are identical,

but does suggest that behavior. However, in the concentration range of these

experiments, an entire curve for the second layer of any isotherm was not

measured, and the existence of a second layer is not firmly established, so the

similarity comparation of Ka2 values is suggestive but not conclusive.

As we can see in Table 7, the Γmono values of cellobiose with unit μg/g are

almost twice of glucose. However, in units of μmol/g, the Γmono values are almost

constant. This implies similarity in the conformation of sugar molecules on the

surface of carbon. In general, one can imagine two ways for the sugar molecules

30

to adsorb the carbon surface, either sidewards lying on the surface or end-on,

sticking up on the surface.

(a)

(b)

Figure 13. Two possible ways of sugar molecules staying on the surface of activated carbon. (a) Sugar molecules sidewards lying on the surface of carbon. (b). Sugar molecules end-on, sticking up on the surface of carbon.

Γmono represents the surface concentration of the adsorbate on the carbon

which corresponds to a monolayer - full coverage of the interface. If the glucose

and cellobiose are sidewards lying on the surface when adsorbed (Figure 13a),

the Γmono values (in molar terms) of glucose would be expected to be different

31

from those of cellobiose because the length and surface area of glucose are

different from cellobiose. Similarly, if glucose is adsorbed flat while cellobiose is

adsorbed sticking up, the Γmono values would likely be different as well. However,

if glucose and cellobiose are both sticking up on the surface of carbon (Figure

13b), the interface area of each sugar molecule occupying should be the same,

and the Γmono values of glucose and cellobiose would be the same in terms of

moles adsorbed per unit area. The Γmono values of glucose and cellobiose in

Table 6 are almost constant, consistant with the analysis above that both glucose

and cellobiose are adsorbed end-on, sticking up from the surface of activated

carbon.

3.4 Effect of temperature and thermodynamics of adsorption

Figure 14 shows the isotherms of glucose at 20°C, 25°C, and 30°C. The

amount adsorbed increased with increased temperature in this temperature

range. Interestingly, the isotherm of glucose at 35°C showed less adsorption than

the lower temperatures. The 35°C isotherm shown represents two independent

sets of data, acquired on different days using the same reagents and techniques

as were used for the data acquired at lower temperatures. (Actually, each

isotherm in Figures 14 and 15 represent two independent experiments.) Hence,

this decrease in adsorption is most likely real, not some odd experimental error. A

possible explanation for this oddity will be presented below.

For cellobiose, the isotherms were similar in that the amount adsorbed

increased with the increasing of temperature. The isotherms of cellobiose are

32

shown in Figure15.

Figure 14. Adsorption isotherms of glucose on Darco G-60 activated carbon at 20°C, 25°C, 30°C and 35°C. Original data points are omitted to make the curves clear.

Figure 15. Adsorption isotherms of cellobiose on Darco G-60 activated carbon at 20°C, 25°C, and 30°C. Original data points are omitted to make the curves clear.

According to van 't Hoff equation: , where K is the

equilibrium constant, ΔHo is standard enthalpy change, T is temperature, ΔSo is

33

standard entropy change. Thus, -lnK should have linear relationship with 1/T if

ΔHo keeps constant. Figure 16 shows ln Ka1 vs 1/T for the BET parameters fit to

the adsorption data of glucose and cellobiose. While three data is hardly

definitive, the plot for adsorption of cellobiose onto carbon does appear

reasonably linear. But the adsorption data for glucose onto carbon does not show

a linear relationship. The limited number of data do allow for experimental error

as being the originating factor of this curvature in the van't Hoff plot, but it is also

possible that ΔHo is temperature sensitive in this regime. Again, the isotherm at

each temperature represents two entirely independent experiments. Thus it

seems most likely that -lnK and 1/T don’t have a linear relationship because ΔHo

is changing with temperature. One possible explanation for this nonlinearity is the

temperature-dependence of the structure of glucose. While we refer to the

adsorbate as “glucose,” it is in fact an equilibrium mixture of α-glucopyranose, β-

glucopyranose, the corresponding glucofuranoses, and the open-chain form (1).

The equilibria among these forms are temperature dependent (28). Thus, the

adsorption being modeled as a single component system is actually a complex,

competitive adsorption system, which may account for the van't Hoff nonlinearity

as well as, e.g., the decreased adsorption of glucose at 35°C.

34

Figure 16. Plot of lnKa1 and 1/T for glucose and cellobiose adsorption on G-60 activated carbon. The upper tendency line is for three cellobiose data points at 20°C, 25°C and 30°C. The other tendency with the same length and similar slop is for glucose data points at 20°C, 25°C and 30°C. The longest tendency line is for all the four glucose data points at 20°C, 25°C, 30°C and 35°C.

The data for glucose in Figure 16 show a strong deviation from linearity, if

taken as a whole. Over the 20-35°C range, the least-squares best straight line is

y = -760x + 2.6,

corresponding to a weakly endothermic adsorption process. However, if we

consider Figure 16 to represent two distinct adsorption processes for glucose,

then the adsorption processes for glucose and cellobiose are both endothermic

from 20°C to30°C, and they have very similar ΔHo values, while for glucose, it is

exothermic from30°C to 35 . This interpretation also implies a significant change

for glucose in the entropy associated with the adsorption process, i.e.,

significantly different mechanisms above and below 30°C. Given the energetics

associated with hydrogen bonding, and the large numbers of possible hydrogen

bonds, this is not impossible. However, additional data should be gathered to

substantiate the behavior before making any such interpretation.

35

CHAPTER 4

SUMMARY AND CONCLUSION

In this research, the adsorption behaviors of glucose and cellobiose on

activated carbon was examined. The experiment was carried out using HPLC to

measure the concentrations of solutions after adsorption using a derivatization

method for the detection of glucose and cellobiose by HPLC. Langmuir,

Freundlich, and BET equations were fit to the adsorption data; the BET equation

gave the best fit by a number of statistical criteria.

From the isotherms, the amount of cellobiose adsorbed increases with

increasing temperature in the temperature range examined. The amount of

glucose adsorbed onto carbon is almost the same as the amount of cellobiose

adsorbed, when measured in moles per gram, which means they are apparently

adsorbed to the surface in the same way, standing on the surface of carbon with

the same cross-sectional area. The thermodynamic analysis shows the

adsorption process for glucose from 20°C to 30°C is exothermic and from 30°C

to 35°C is endothermic; for cellobiose from 20°C to 30°C the process is

exothermic. The adsorption behavior is likely complicated by the conformational

equilibria for these species.

This study indicates areas for further research: (a) Additional measurements

of glucose isotherms in the 10-30°C region, to better refine the thermodynamic

parameters associated with this adsorption. (b) Additional measurements of

these isotherms beyond 30°C, which appear to be controlled by different

thermodynamic parameters. Of course, the temperature sensitive conformational

36

equilibria for glucose must be considered. (c) Isotherm determinations for

additional cellodextrins, e.g., cellotriose, cellotetraose, etc. (d) Competitive

adsorption isotherms. This last is particularly interesting as providing insight into

the chromatographic conditions best suited for preparative isolation of individual

cellodextrins.

37

REFERENCES

1. Activated Carbon. Wikipedia [Online]; Wikipedia, Posted Jul 30, 2013.

http://en.wikipedia.org/wiki/Activated_carbon (accessed Aug 7, 2013).

2. Cellobiose. Wikipedia [Online]; Wikipedia, Posted Aug 2, 2013.

http://en.wikipedia.org/wiki/Cellobiose (accessed Aug 7, 2013).

3. Gilbert, R. D.; Kadla, J. E. Biopolymers from Renewable Resources;

David L. Kaplan, Eds.; VCH: New York, 1998; p 47.

4. Cellulose. Wikipedia [Online]; Wikipedia, Posted Aug 3, 2013.

http://en.wikipedia.org/wiki/Cellulose (accessed Aug 7, 2013).

5. Zhang, Y. H. P; Lynd, L. R. Determination of the Number Average Degree of

Polymerization of Cellodextrins and Cellulose with Application to

Enzymatic Hydrolysis. Biomacromolecules. 2005, 1510-1515.

6. Urbanic, J. E. Purification of Sugar Liquors with Activated Carbon. U. S.

Patent 4,502,890, March 5, 1985.

7. Huebner, A.; Ladisch, M. R.; Tsao, G. T. Preparation of Cellodextrins: An

Engineering Approach. Biotechnology and Bioengineering. 1978,

1669-1677.

8. Muhammad, I. A.; Ghufrana, S. Applied and Environmental Microbiology.

1991, 655-659.

9. Dorsey, J. G.; Fanali, S.; Giese, R. W.; Haddad, P. R.; Lee, H. K.; Poole, C.

F.; Riekkola, M. L.; Schoenmakers, P. J.; Tanaka, N. Journal of

Chromatography. 1978, 147, 185-193.

10. Shahaf, D. Respiratory Hoods. U.S. Patent 20,030,075,173, May 1, 2003.

38

11. Holly, A. C.; Scott, H. M.; Sallavanti, R. A. Multi-functional Protective

Materials and Methods for Use. U.S. Patent 0,161,631, July 3, 2008.

12. Cassidy, H. G.; Weissberger, A. Techniques of Organic Chemistry volume

V—adsorption and chromatography; Cassidy, H. G, Eds.; VCH: New

York, 1951; pp 190-192.

13. Vander, K. A.; Qiang, D.; Aburub, A.; Wurster, D. E. Modified Langmuir-like

Model for Modeling the Adsorption from Aqueous Solutions by Activated

Carbons. Langmuir. 2005, 21, 217-224.

14. Park, H. M.; Moon, D. J. Adsorption Equilibria of CFC-115 on Activated

Charcoal. J. Chem. Eng. 2003, 48, 908–910.

15. Falade, K. O.; Adetunji, A. I.; Aworh, O. C. Adsorption isotherm and heat of

sorption of fresh- and osmo-oven dried plantain slices. European Food

Research and Technology. 2003, 217, 230-234.

16. Zook, C. M.; LaCourse W. R. Pulsed Amperometric Detection of

Carbohydrates in Fruit Juices Following High Performance Anion

Exchange Chromatography. Current Separations. 1995,14, 2.

17. Momenbeik, F.; Khorasani, J. H. Analysis of Sugars by Micellar Liquid

Chromatography with UV Detection. Acta Chromatographica. 2006, 16.

18. Rocklin, R. D.; Clarke, A. P.; Weitzhandler, M. Improved Long-Term

Reproducibility for Pulsed Amperometric Detection of Carbohydrates

Via a New Quadrupole-Potential Waveform. Anal Chem. 1998, 70,

1496-1501.

19. Kwon, H.; Kim, J. Determination of Mono-and Oligosaccharides

39

Derivatized with p-Aminobenzoic Ethyl Ester by Reverse Phase HPLC.

Analytical Science and Technology. 1995, 8, 4.

20. Isotherm. Wikipedia [Online]; Wikipedia, Posted Aug 1, 30, 2013.

http://en.wikipedia.org/wiki/Isotherm (accessed Aug 7, 2013).

21. Langmuir Equation. Wikipedia [Online]; Aug 5, 2013. Wikipedia, Posted Jul

30, 2013. http://en.wikipedia.org/wiki/Langmuir_equation (accessed

Aug 7, 2013).

22. Murilo, F.; Luna, T.; Antonio, A.; Eduardo, D. Trindade; Silva, I. J. Removal

of Aromatic Compounds from Mineral Naphthenic Oil by Adsorption. Ind.

Eng. Chem. 2008, 47, 3207-3212.

23. Lee, J. W.; Kwon, T. O.; Moon, S. Adsorption of Monosaccharides,

Disaccharides, and Maltooligosaccharides on Activated Carbon for

Separation of Maltopentaose. Carbon. 2004, 42, 371–380.

24. BET theory. Wikipedia [Online]; Aug 5, 2013. Wikipedia, Posted Jul

30, 2013. http://en.wikipedia.org/wiki/BET_theory (accessed Aug 7,

2013).

25. Ikan, R. Natural Product-A Laboratory Guide. Kaplan, D. L., Eds.;

Academic Press: New York, 2007; pp 84-86.

26. Motulsky, H.; Christopoulos, A. Fitting Models to Biological Data Using

Linear and Nonlinear Regression. Oxford University Press: Oxford, U.K.,

2003; pp143-144.

27. Mean Absolute Percentage Error. John Galt.

http://www.johngalt.com/galt_university/mape.shtml.

40

28. Los, J. M.; Simpson, L. B. The Mutarotation and Ionization of d-glucose in

Alkaline Solution. Wiley Online Library. 1954, 73, 941–958.

41

APPENDIX

Table A, B, C give the least-squares, best-fit parameters for Langmuir, BET and Freundlich isotherm equations for each set of adsorption data. Each set of adsorption data represents two separate trials, performed on different days. Appendix A. Langmuir parameters for glucose and cellobiose adsorbed to washed Darco G-60 activated carbon.

Glucose onto washed carbon Cellobiose onto washed carbon

Temp K Q K Q

20 0.026 1028.30 0.98 210.02

25 0.010 2818.69 0.52 333.77

30 0.033 920.59 0.85 279.31

35 0.064 478.46

Appendix B. BET parameters for glucose and cellobiose adsorbed to washed Darco G-60 activated carbon.

Glucose onto washed carbon Cellobiose onto washed carbon

Temp Ka1 Ka2 Γmono Ka1 Ka2 Γmono

20 0.75 0.16 47.98 2.55 0.12 118.89

25 1.34 0.19 38.26 3.03 0.19 112.11

30 1.36 0.17 44.80 4.27 0.21 108.97

35 0.84 0.13 55.39

Appendix C. Freundlich parameters for glucose and cellobiose adsorbed to washed Darco G-60 activated carbon.

Glucose onto washed carbon Cellobiose onto washed carbon

Temp K 1/n K 1/n

20 24.09 0.96 97.51 2.06

25 24.658 0.90 111.16 1.65

30 30.57 1.09 120.85 1.83

35 29.90 1.17