NTNU

Department of Petroleum Engineering and Applied Geophysics

Modelling absorption drying of natural gas

Luká Polák

May 2009

Trondheim

ii

Summary

This report deals with dehydration of natural gas. Possibilities and different ways of drying

natural gas are described theoretically. The main focus is on absorption drying using

triethylene glycol, its benefits and disadvantages.

Then, the dehydration is simulated with Aspen Hysys software. The minimum glycol mass

flow and specific glycol circulation rate is calculated. Currently Hysys is used to obtain TEG-

water equilibrium data. Further, the graphical solution and analytical solution (Kremser-

Brown equation) are used to estimate the number of theoretical stages in a absorption column.

iii

List of Content

1 Introduction ................................................................................................................... - 6 - 2 Dehydration of natural gas ............................................................................................ - 7 -

2.1 Direct cooling ........................................................................................................ - 7 - 2.2 Indirect cooling...................................................................................................... - 7 - 2.3 Adsorption ............................................................................................................. - 7 - 2.4 Absorption ............................................................................................................. - 8 -

3 TEG Dehydration unit ................................................................................................... - 9 - 3.1 Dehydration process .............................................................................................. - 9 - 3.2 Regeneration process............................................................................................. - 9 -

4 Hysys modelling of dehydration process..................................................................... - 10 - 4.1 Equations of state................................................................................................. - 10 - 4.2 Conditions and compositions of inlet streams..................................................... - 11 - 4.3 TEG-water equilibrium........................................................................................ - 11 -

5 Results ......................................................................................................................... - 12 - 5.1 Hysys simulation ................................................................................................. - 12 - 5.2 Graphical solution of absorption process ............................................................ - 14 - 5.3 Analytical solution of absorption process ........................................................... - 14 -

6 Conclusion ................................................................................................................... - 16 - 7 References ................................................................................................................... - 17 -

iv

List of Tables

Table 1: TEG-water equilibrium data, mole fraction x in liquid phase and mole fraction y in

vapour phase. X and Y are relative mole fractions......................................................................I

List of Figures

Figure 1: Diagram of water content of natural gas [2] .............................................................. II

Figure 2: Process flow diagram for glycol dehydration unit ....................................................III

Figure 3: Flow sheet of drying process ....................................................................................III

Figure 4: Flow sheet of case for obtaining equilibrium data....................................................IV

Figure 5: Conditions of all streams from the case obtaining equilibrium data.........................IV

Figure 6: Composition of all streams from first step obtaining equilibrium data .....................V

Figure 7: Conditions of inlet and outlet streams used in absorption drying process.................V

Figure 8: Composition of inlet and outlet streams calculated for minimum TEG flow rate ....VI

Figure 9: Estimation of theoretical stages of absorption column by using graphical solution.VI

Figure 10: Trendline through the equilibrium data for obtaining constant k ...................... VII

v

Nomenclature

a

Parameter of Peng-Robinson equation of state

A

Effective absorption factor

b Parameter of Peng-Robinson equation of state

G Molar flow rate of gaseous phase entering in the column

k Constant of the linear equilibrium equation

L

Molar flow rate of liquid phase entering in the column

m

Mass flow rate

N Number of theoretical stages

P

Pressure

q

Volume flow rate

R

Universal gas constant (8.314 J.K-1.mol-1)

T

Temperature

V Molar volume

x

Molar fraction of water in liquid phase

y

Molar fraction of water in vapour phase

Acentric factor

Mass density

BTEX Benzene, toluene, ethylbenzene, xylens

DEG Diethylene glycol

EG Monoethylene glycol

GCR Glycol circulation rate

TEG Triethylene glycol

T4EG Tetraethylene glycol

VOC Voltaic organic compounds

Subscripts

c

Critical

in

Inlet stream

out

Outlet stream

- 6 -

1 Introduction

Natural gas to be transported by pipeline must meet certain specifications. In addition to

specifications regarding delivery pressure, rate, and possibly temperature, other specifications

include maximum water content (water dew point), maximum condensable hydrocarbon

content (hydrocarbon dew point) and allowable concentrations of contaminants such as H2S,

CO2, mercaptans, minimum heating value, and cleanliness (allowable solids content). This

report focuses on basic principles of removing water from natural gas and modelling of this

process.

Water vapor is probably the most common undesirable component found in untreated natural

gas. The main reason for removing water vapor from natural gas is that water vapor becomes

liquid water under low temperature and/or high-pressure conditions. Specifically, water

content can affect long-distance transmission of natural gas due to the following facts:

Liquid water and natural gas can form hydrates that may plug the pipeline and other

equipment.

Natural gas containing CO2 and/or H2S is corrosive when liquid water is present.

Liquid water in a natural gas pipeline potentially causes slugging flow conditions

resulting in lower flow efficiency of the pipeline.

Water content decreases the heating value of natural gas being transported [1].

Solubility of water in natural gas increases with temperature and decreases with pressure. The

water content of natural gas is shown in Figure 1. The diagram covers saturation conditions

for temperatures from -50 °C to 200 °C, and pressures from 0.1 MPa to 80 MPa [2].

Water content of untreated natural gases generally is in the order of a few grams of water per

standard cubic meter of gas (hundreds lbm/MMscf); while gas pipelines normally require

water content to be in the range of 90

120 mg/Sm3 (6 8 lbm/MMscf). The water content in

deep water pipelines must be even lower than the previous requirement. The water content of

natural gas is indirectly indicated by the dew point, defined as the temperature where the

natural gas is saturated with water vapor at a given pressure [1, 3].

- 7 -

2 Dehydration of natural gas

Dehydration systems used in the natural gas industry fall into four categories in principle:

Direct cooling

Indirect cooling (Expander or Joule-Thomson valve)

Adsorption

Absorption

2.1 Direct cooling

The ability of natural gas to contain water vapor decreases as the temperature is lowered at

constant pressure. During the cooling process, the excess water in the vapor state becomes

liquid and is removed from the system. Natural gas containing less water vapor at low

temperature is output from the cooling unit. The gas dehydrated by cooling is still at its water

dew point unless the temperature is raised again or the pressure is decreased. It is often a good

practice that cooling is used in conjunction with other dehydration processes. Glycol may be

injected into the gas stream ahead of the heat exchanger for instance to reach lower

temperatures before expansion into a low temperature separator [1].

2.2 Indirect cooling

Expansion is a second way of natural gas cooling. It can be achieved by the expander or

Joule-Thomson valve. These processes are characterized by a temperature drop to remove

condensed water to yield dehydrated natural gas. The principal is the similar to the removal of

humidity from outside air as a result of air conditioning. Gas is forced through a constriction

called an expansion valve into space with a lower pressure. As a gas expands, the average

distance between molecules grows. Because of intermolecular attractive forces, expansion

causes an increase in the potential energy of the gas. If no external work is extracted in the

process and no heat is transferred, the total energy of the gas remains the same. The increase

in potential energy thus implies a decrease in kinetic energy and therefore in temperature [4].

2.3 Adsorption

Solid desiccant dehydration, also known as solid bed, utilizes the adsorption principles for

removing water vapor. Adsorbents used include silica gel (most commonly used), molecular

- 8 -

sieve (common in natural gas vehicle dryers), activated alumina and activated carbon. The

wet gas enters into an inlet separator to ensure removal of contaminants and free water. The

gas stream is then directed into an adsorption tower where the water is adsorbed by the

desiccant. When the adsorption tower approaches maximum loading, the gas stream is

automatically switched to another tower allowing the first tower to be regenerated.

Heating a portion of the mainstream gas flow and passing it through the desiccant bed

regenerates the loaded adsorbent bed. The regeneration gas is typically heated in an indirect

heater. The undersaturated regeneration gas is then passed through the bed removing water

and liquid hydrocarbons. These liquid components have to be removing from gas for two

main reasons. First reason is present the water can allow natural gas hydrates forming. Second

reason is a lot of corrosive and aggressive compounds (H2S, CO2) can be absorbed in this

liquid phase. The regeneration gas exits the top of the tower and is cooled most commonly

with an air-cooled heat exchanger. Condensed water and hydrocarbons are separated and the

gas is recycled back into the wet gas inlet for processing [4].

2.4 Absorption

The fourth method of dehydration utilizes liquid desiccant and it is the most commonly used

for dehydrating natural gas moved through transmission lines. Method removes water from

the gas stream by counter current contact, in a tray type contactor tower, with tri-ethylene

glycol (TEG). Natural gas enters the unit at the bottom of the adsorber tower and rises through

the tower where it contacted with the TEG solution flowing downward across bubble trays.

Through the contact, the gas gives up its water vapor to the TEG. The water laden TEG is

circulated in a closed system, where the water is boiled from the TEG. The regenerated TEG

then is recirculated to the contacting tower [1, 5].

Water vapor is removed from the gas by intensive contact with a hygroscopic liquid desiccant

in absorption dehydration. The contact is usually achieved in packed or trayed towers. Glycols

have been widely used as effective liquid desiccants. Dehydration by absorption with glycol is

usually more attractive economically than dehydration by solid desiccant when both processes

are capable of meeting the required dew point. Glycols used for dehydrating natural gas are

ethylene glycol (EG), diethylene glycol (DEG), triethylene glycol (TEG), and tetraethylene

glycol (T4EG). Normally a single type of pure glycol is used in a dehydrator, but sometimes a

- 9 -

glycol blend is economically attractive. TEG has gained nearly universal acceptance as the

most cost effective of the glycols, due to its superior dew point depression, operating cost, and

operation reliability [1, 2, 6].

3 TEG Dehydration unit

Triethylene glycol has been successfully used to dehydrate sweet and sour natural gases over

wide ranges of operating conditions. Dew point depression of the order of 30 °C to 70 °C can

be reached at gas pressures ranging from 0.25 to 17 MPa and gas temperatures between 4 °C

and 70 °C [2]. The dew point depression obtained depends on the equilibrium dew point

temperature, for a given TEG concentration and contact temperature. Increased glycol

viscosity may cause problems at lower contact temperature. Thus, heating of the natural gas

may be desirable. Very hot gas streams are often cooled prior to dehydration to prevent

vaporization of TEG.

3.1 Dehydration process

A typical glycol dehydration unit is shown in Figure 2. The feed gas must be cleaned to

remove all liquid water and hydrocarbons, wax, sand, drilling muds, and other impurities.

These impurities can be removed using an efficient scrubber, separator, or even a filter

separator for very contaminated gases. Integral separators at the bottom of the contactor are

common. The regenerated glycol is pumped to the top tray of the contactor. The glycol

absorbs water as it flows down through the contactor, countercurrent to the gas flow [1].

Dried gas is exiting from the top of the contactor. This gas required the water concentration

specification. Water-rich glycol is removed from the bottom of the contactor (absorber),

passes through the reflux condenser coil and flashes off most of the soluble gas (VOC,

BTEX) in the flash tank. Then the water-rich glycol flows through the rich-lean

(glycol/glycol) heat exchanger to the regenerator. In some cases, cloth and charcoal filters are

added in between the flash tank and the regenerator.

3.2 Regeneration process

In the regenerator, absorbed water is distilled from the glycol at near atmospheric pressure by

application of heat. The regeneration heat is provided by a natural gas burner. The common

temperature of regeneration process is under 204 °C. The regenerated lean glycol exiting the

- 10 -

surge drum, is first partly cooled in the lean-rich exchanger then is pumped through the glycol

cooler before being recirculated to the contactor.

4 Hysys modelling of dehydration process

Aspen Hysys software was used for modelling of a dehydration process. Aspen Hysys is used

for steady state simulation, design, performance monitoring and optimization of oil and gas

production, gas processing and petroleum refining industries.

4.1 Equations of state

In the present work, thermodynamic behavior of the TEG water system was represented by

means of the Peng-Robinson equation of state. Models based on a cubic equation of state

generally guarantee good phase equilibrium predictions over a wide range of temperature and

pressure. This is important in view of modelling the multicomponent system in the natural gas

dehydration units, where it is necessary to account for the presence of gases and for the high

operating pressure of the absorption column [7].

The Peng-Robinson equation is written as [7]:

)()(

.

)( bVbbVV

a

bV

RTP

(1)

The parameters are given by [7]:

c

c

P

TRa

22

45724.0

(2)

c

c

P

RTb 07780.0

(3)

where P

is the pressure, V the molar volume, T

the temperature, R

the universal gas

constant (8.314 J·K-1·mol-1), cT the critical temperature, cP the critical pressure and alpha

function, , is a function of reduced temperature cr TTT /

and acentric factor

defined by

[8]:

25.0

2 126992.054226.137464.01cT

T

(4)

1logcP

P

(5)

- 11 -

The mixing rules, [7], are used to calculate mixture parameters. The Peng-Robinson equation

is widely used for hydrocarbons and related components over broad ranges of temperature and

pressure. It is accurate enough for calculating enthalpy and entropy departures, vapor-liquid

equilibrium, liquid densities and vapor density in natural gas processing and many petroleum-

related operations. The Peng-Robinson equation is accurate in the critical region.

4.2 Conditions and compositions of inlet streams

An absorption column with 3 trays was used for the natural gas drying process simulation.

The process flow sheet is shown in Figure 3. Triethylene Glycol (TEG) was used as the

absorption medium. The TEG contained 0.5 wt. % of water, which is typical amount for

industrial drying units. The stream of TEG flowed down from the top of the column through

the contactor countercurrent to the natural gas stream and absorbed water.

An inlet gas stream was used, whose composition is similar to that of the Kristin field, [9],

located in the south-western part of the Halten Bank, in the Norwegian Sea. Natural gas

conditions were 30 °C temperature and 8000 kPa pressure, which are typical for industrial

drying units. A 9.15·10-6 Sm3/day molar flow of natural gas stream was used, which

corresponded to half of the gas rate on the Kristin platform. The standard volume (conditions

15 °C temperature and 101.325 kPa pressure) corresponded to 8.67·10-6 Nm3/day (conditions

0 °C and 101.325 kPa). The flow rate of TEG depended on the required water dew point

specification of outlet pipeline gas.

4.3 TEG-water equilibrium

Data describing the equilibrium between TEG and water are important for graphical

(McCabe-Thiel) solution of absorption drying process. Numerous data on the TEG-water (and

natural gas) system have been reported [11, 12]. However, there are severe discrepancies in

reported equilibrium values and the computing methods are very complicated.

Equilibrium data were obtained from one simple case created in Hysys. Figure 6 shows this

case. Natural gas stream and triethylene glycol stream were mixed and then were separated in

two streams in the two phase separator. The composition of natural gas stream was similar to

the composition of the absorption drying process (composition of Kristin natural gas). The

conditions were also similar (30 °C temperature and 8000 kPa pressure). Conditions of all

streams are shown in Figure 5.

- 12 -

Triethylene glycol stream had the same conditions as the natural gas stream and had variable

content of water (molar fraction from 0.02 to 0.36). First example (0.98 molar fraction of

TEG and 0.02 molar fraction of water) is shown in the Figure 6. The equilibrium molar

fractions of water for vapour and liquid phase calculated by Hysys are 9·10-6 and 15722·10-6

respectively. Equilibrium data necessary for graphical solution were obtained in the same way

and are reported in Table 1.

5 Results

5.1 Hysys simulation

The absorption drying process flow sheet is shown in Figure 3. Beyond the flow rate of TEG

stream, the composition and conditions of both inlet streams were described. The flow rate of

absorption medium depends on the required water dew point specification of outlet pipeline

gas. The required dew point specification was -18 °C temperature at 7000 kPa pressure in this

work [9]. The required specification corresponds to water vapour content of 40.66·10-6 mole

fraction.

A 3653 kg/h minimum flow rate of TEG with 0.5 wt. % of water was calculated. Mass flow

rate calculations are shown in Figure 7 and Figure 8.

Glycol circulation rate is preferably used instead of mass or volume flow rate. Glycol

circulation rate means volume of circulating glycol per kilogram of absorbed water. The

minimum mass flow rate of TEG (3653 kg/h) corresponds to 15.6 L L TEG/kg H2O absorbed.

Most economical industrial designs utilize circulation rates of about 15 40 L L TEG/kg H2O

absorbed. Common circulation rate design is 25 L TEG/kg H2O absorbed [1]. Glycol

circulation rate calculated by Hysys provides agreement with this data.

The glycol circulation rate [L TEG/kg H2O absorbed]:

OH

TEG

m

qGCR

2

(6)

where:

TEG

TEG

TEG

mq

(7)

- 13 -

outOHinOHOH mmm 222

(8)

...TEGq volume flow rate of TEG [L/h]

...TEGm mass flow rate of TEG [kg/h]

...TEG mass density of TEG (calculated by Hysys: 1127.44 kg/m3)

...2OHm flow rate of absorber water [kg/h]

...2 inOHm flow rate of water in the inlet stream of gas (from Hysys: 219.72 kg/h)

...2 outOHm flow rate of water in the outlet stream of gas (from Hysys: 11.80 kg/h)

Then the glycol circulation rate is:

absorbedOHkgTEGLGCR 23 /58.1510

80.1172.21944.1127

3653

For most common glycol circulation rate ( absorbedOHkgTEGLGCRMC 2/25 ), the mass

flow rate of TEG is 5860.5 kg/h.

From (6) and (7):

TEGOHMCTEG mGCRm 2 (9)

Because the mass of absorbed water is constant, (molar fractions of water in both gas streams

are constant) and mass density of TEG is constant, (temperature and pressure are constant) the

mass flow rate of TEG is:

hkgmTEG /54.586044.112780.1172.21925

For this mass flow of TEG and 3 theoretical stages, Hysys calculates a molar fraction of water

in the outlet gas of 28.78·10-6 mol/mol, which is well within the required water content

specification (40.66·10-6 mol/mol).

- 14 -

5.2 Graphical solution of absorption process

One way to estimate the number of theoretical stages for absorption column is a graphical

solution as shown in Figure 9. The equilibrium curve is created from equilibrium data

obtained in chapter 4.3. The processing curve is created like a linear line from two points. The

first point [xin, yout] represents the top of the column. The value xin is the water fraction in the

inlet glycol stream and the value yout is the water fraction in the outlet gas stream. The second

point of processing line [xout, yin] represents the bottom of the column and values xout, yin are

the fractions of water in the outlet glycol stream respectively in the inlet gas stream [13].

It was necessary to accomplish three equilibrium steps between processing line and

equilibrium curve for achieve the required water content specification. These three steps are

corresponding to three theoretical stages of the absorption column.

5.3 Analytical solution of absorption process

Analytical solution is another way to estimate the number of theoretical stages of absorption

column. It is given by the following equation, often referred to as the Kremser (or Kremser-

Brown) equation [13]:

AAAyy

yyN N

ln

1111ln

01

01

(10)

where:

...N number of theoretical stages ...1Ny molar fraction of water in inlet gas stream (calculated by Hysys: 7.56·10-4)

...1y molar fraction of water in outlet gas stream (calculated by Hysys: 2.88·10-6)

...0y molar fraction of water in vapour phase in equilibrium with 00 xky

...0x molar fraction of water in inlet TEG stream (calculated by Hysys: 4.02·10-2)

The value A is called effective absorption factor and is calculated by [13]:

kG

LA

(11)

where: ...L molar flow of liquid phase entering in the column (calculated by Hysys: 40.46 kmol/h) ...G molar flow of gaseous phase entering in the column (calculated by Hysys: 16124 kmol/h)

The constant k represents the equilibrium. Figure 10 is shown the obtaining of the value k . The points of equilibrium data were interlaid with the linear trendline and the value k was obtained from the equation of this trendline. ( 41051.6k ; see figure 10)

- 15 -

Then:

95.386.3ln

1

86.3

1

86.3

11

1062.21088.2

1062.21056.7ln

86.31051.601.16124

46.40

1062.21002.41051.6

56

54

3

5240

N

A

y

Analytical solution gives result the absorption column need 4 theoretical stages.

- 16 -

6 Conclusion

Hysys model, based on cubic Peng-Robinson equation of state, provides satisfactory

agreement with industrial data. The Hysys process simulation offers a suitable tool to

determine many operating parameters, such as mass flow rates, molar flow rates and glycol

circulation rate.

A 3653 kg/h triethylene glycol minimum mass flow rate was determined for a three stages

absorption column, where the outlet gas required water content was specified. It corresponds

to 15.6 L TEG/kg H2O absorbed specific circulation rate (Most economical industrial designs

employ circulation rates of about 15-40 L TEG/kg H2O absorbed). For most common glycol

circulation rate (25 L TEG/kg H2O absorbed) and three theoretical stages the required water

content specification was reached. Four theoretical stages were then calculated.

Graphical solution of the same absorption process was built on the equilibrium data obtained

from simple Hysys case. This solution estimated three theoretical stages for absorption

column.

The number of theoretical stages was also estimated by the analytical calculation. Kremser-

Brown equation for this method was used. This equation gave as result of 4 theoretical stages.

- 17 -

7 References

[1] Guo, B., Ghalambork, A., (2005): Natural Gas Engineering Handbook, Gulf Publishing

Company, p. 123 147.

[2] Gas Processors Suppliers Association (2004): GPSA Engineeering Data Book, 12th

Edition, p. 20-23 20-29.

[3] Gironi, F., et al, (2007): Modelling triethylene glycol

water system for natural gas

dehydration, 8th International Conference on Chemical and Process Engineering, Chemical

Engineering Transactions, ISBN 88-95608-00-6, p. 881

886.

[4] Kittel, C., Kroemer, H., (1980): Thermal Physics, W. H. Freeman. ISBN 0-7167-1088-9,

p. 336 337.

[5] Lyons, W., C., Plisga, G., J., (2005): Standard Handbook of Petroleum and Natural Gas

[6] Speight, J., G., (2007): Natural Gas: A Basic Handbook, Gulf Publishing Company

Engineering (2nd Edition), Elsevier

[7] Peng, D., Y., Robinson, D., B., (1976): A New Two-Constant Equation of State, Ind. Eng.

Chem., Fundam., 15(1), p. 59-65

[8] Twu, H., C., et al, (2005): Advanced equation of state method for modeling TEG-water

for glycol gas dehydration, Fluid Phase Equilibria, 228-229, p. 213-221

[9] Gudmundsson, J., S., Private communication, (NTNU), 11. 2. 2009

[10] Oi, L., E., (2003): Estimation of tray efficiency in dehydration absorbers, Chem. Eng.

Pr., 42, p. 867-878

[11] Herskowitz, M., Gottlieb, M., (1984): Vapor-liquid equilibrium in aqueous solutions of

various glycols and poly(ethylene glycols), J. Chem. Eng. Data, 24, p. 173-175

[12] Bestani, B., Shing, K., S., (1989): Infinite-dilution activity coefficients of water in TEG,

PEG, glycerol and their mixtures in the temperature range of 50

140 °C, Fluid Phase

Equilib., 50, p. 209-221.

[13] Gudmundsson, J., S., (2009): Prosessering av petroleum, Department of Petroleum

Engineering and Applied Geophysics, Norwegian University of Science and Technology,

p. 89 95.

[14] ISEE

International Sustainable Energy Exchange, http://www.hart-isee.com/,

24.6.2009

I

Appendix A

Table 1: TEG-water equilibrium data, mole fraction x in liquid phase and mole fraction y in vapour phase. X and Y are relative mole fractions obtained from simple Hysys case (see chapter 4.3).

molar fraction of water in inlet TEG

stream

x (mol/mol) y (mol/mol) X = x/(1-x) Y = y/(1-y)

0.02 0.015722 0.000009 0.015973 0.000009 0.04 0.031514 0.000018 0.032539 0.000018 0.06 0.047376 0.000028 0.049733 0.000028 0.08 0.063312 0.000038 0.067591 0.000038 0.11 0.087355 0.000052 0.095716 0.000052 0.14 0.111574 0.000068 0.125586 0.000068 0.17 0.135974 0.000084 0.157373 0.000084 0.20 0.160566 0.000100 0.191279 0.000100 0.23 0.185358 0.000117 0.227532 0.000117 0.26 0.210359 0.000135 0.266398 0.000135 0.29 0.235580 0.000153 0.308182 0.000153 0.32 0.261035 0.000172 0.353244 0.000172 0.34 0.278140 0.000186 0.385310 0.000186 0.36 0.295359 0.000199 0.419163 0.000199

II

Appendix B

Figure 1: Diagram of water content of natural gas [2]

III

Figure 2: Process flow diagram for glycol dehydration unit [14]

Figure 3: Flow sheet of drying process

IV

Figure 4: Flow sheet of case for obtaining equilibrium data

Figure 5: Conditions of all streams from the case obtaining equilibrium data

V

Figure 6: Composition of all streams from first step obtaining equilibrium data

Figure 7: Conditions of inlet and outlet streams used in absorption drying process

VI

Figure 8: Composition of inlet and outlet streams calculated for minimum TEG flow rate

Figure 9: Estimation of theoretical stages of absorption column by using graphical solution

VII

Equation of linear trendline of equilibrium data

y = 0,000651011711503x

0,00000

0,00002

0,00004

0,00006

0,00008

0,00010

0,00012

0,00014

0,00016

0,00018

0,00020

0,00 0,05 0,10 0,15 0,20 0,25 0,30

x (mol/mol)

y (m

ol/m

ol)

Figure 10: Trendline through the equilibrium data for obtaining constant k (see chapter 5.3).