Clay materials modified with amino acids for purification processes of biogas and natural gas

Joanna Juźków

1

Clay materials modified with amino acids for purification processes

of biogas and natural gas

Joanna Juźków

Instituto Superior Técnico, Lisbon, Portugal

Poznan University of Technology, Poznań, Poland

_________________________________________________________________________________________

ABSTRACT

Biogas and natural gas purification is an issue of a great industrial importance. Due to decrease of calorific

value of the fuel, corrosion and dry ince formation as a result of carbon dioxide presence in methane, the

concentration of CO2 needs to be reduced to ppm level. Adsorption on a natural sorbent has drawn the attention

of researchers recently, as a low-cost, environmentaly friendly and effective way of gas treatment. In the present

research samples of montmorillonite were intercalated with amino acids: glycine, arginine and L-histidine at pH

7 and pH 5 in order to enhance adsorption properties of the clay materials. The obtained adsorbents were

analyzed with FTIR, XRD, thermogravimetry with DSC and nitrogen adsorption-desorption. Conducted tests

confirmed retention of amino acid molecules in the clay structure and increase of porosity of materials in the

result of intercalation. Investigations of methane and carbon dioxide adsorption on the prepared samples were

conducted and adsorption isotherms were plotted. Clays intercalated with arginine and L-histidine adsorbed

more CO2 than in case of glycine. Materials prepared at pH 5 showed better results than samples obtained at pH

7. The adsorbent with the highest adsorption capacity was ARG-5 with 0.80 mmol/g of CO2 adsorbed. The most

selective material for CH4/CO2 separation was L-HIST-5, which up to 0.7 molar fraction of CH4 adsorbed only

CO2 from the mixture at relatively low pressure 100 kPa. The obtained results showed a promising possibility

for further application of intercalated clay materials in industrial gas treatment processes.

Keywords: adsorption, montmorillonite, amino acids, methane purification, carbon dioxide separation

_________________________________________________________________________________________

1. Introduction

Nowadays fossil fuels are by far the most dominant

energy sources and provide about 80% of total

world energy consumption. There is a strong

necessity to cut the utilization of fossil fuel energy

resources due to their significant environmental

impact connected with the emission of greenhouse

gases and pollutants [1]. As effect of fossil fuels

consumption, the atmospheric CO2 concentration

has been elevated from 280 ppm in pre-industrial

period to nearly 400 ppm in present times, what

contributed to a significant climate change [2]. One

of most promising renewable energy sources is

biomass, as it is considered as one of the most

suitable ways of energy storage, being a real

alternative to fossil fuels, as it is abundant, clean

and carbon neutral [3]. In Europe, biomass

currently accounts for around 2/3 of renewable

energy and will play a key role in reaching the

Clay materials modified with amino acids for purification processes of biogas and natural gas

Joanna Juźków

2

target approved by the renewable sources by 2020

[1]. Biogas is produced by anaerobic digestion of

biomass, in the industry is generated at sewage

treatment plants, landfills, sites with industrial

processing industry and at digestion plants for

agricultural organic waste [4]. Biogas is an

alternative for energy production, that has

advantages of being eco-friendly source of energy,

in that the calorific value of biogas is equal to that

of half litre of diesel oil. (6 kWh/m3) [5]. The final

result of a series of decomposition reactions of

organic matter are methane, carbon dioxide and

water as main products [6]. When CO2 and other

impurities are removed during the upgrading

process, the methane concentration increases and

thus the resulting biomethane can be utilized as an

alternative to natural gas [7]. Natural gas itself,

although cannot be referred to as the green energy,

its use has many advantages over the use of other

conventional fuels. Burning NG produces less CO2

and more water vapour per energy unit than burning

gasoline or diesel [8]. For methane distribution

through pipelines or liquefaction in order to

transport it for long distances the impurities

contained in methane (in form of biogas or natural

gas) need to be removed [9]. Presence of CO2

lowers calorific value of the fuel and can cause dry

ice formation. Methane for domestic use is required

to have 97% or higher purity [10]. Among different

technologies developed for methane treatment,

adsorption on the low-cost adsorbents in gaining

more attention, as method relatively cheap, simple

and environmental-friendly. Natural clays are an

interesting group of adsorbents, regarding their

layered structure and extraordinary properties, like

ion-exchange, swelling and possibility of

intercalation of particles between the layers [11-13].

Due to them it is possible to introduce molecules of

other compounds into the clay’s structure, tuning

their properties.

In the present work a natural clay - montmorillonite

(MMT) was intercalated with three different amino

acids: glycine, arginine and L-histidine in order to

enhance its adsorptive properties. Amino acid

intercalated clay materials are capable of CO2

retention due to the presence of amine groups in the

amino acid structure. Glycine, as the simplest

amino acid, contains only one NH2 group in the

structure. L-histidine and arginine, having

additional basic amino groups side chains are

expected to show enhanced adsorption properties

[13, 14]. Amino acids can be considered as green

compounds, as being one of main building blocks

of living organisms are eco-friendly and do not

cause contamination when released to the

environment.

2. Materials preparation

Natural montmorillonite (MMT) clay from

Wyoming, USA has been used as a raw material for

adsorbents preparation. For the clay’s surface

functionalization three different amino acids:

glycine, arginine and l-histidine (Sigma Aldrich,

purity >99%) were used. Two samples, at pH 5 and

pH 7 were prepared for each kind of amino acid and

also a sample of non-intercalated MMT. In order to

prepare amino acid intercalated clay adsorbents the

following procedure was applied. 2 g of clay was

added to 100 mL of distilled water and mixed for 3

h using magnetic stirrer. 50 mL of 0.03 M solution

of amino acid was prepared by dissolving adequate

amount of amino acid in distilled water. All

solutions were obtained at room temperature. Then,

the amino acid solution was added to the clay and

pH of the mixture was adjusted to the required

value using 0.05 M HCl solution. The acid solution

was prepared by dilution of HCl solution (Carlo

Erba, 37%) with distilled water. The clay mixture

was mixed with amino acid solution overnight in

Clay materials modified with amino acids for purification processes of biogas and natural gas

Joanna Juźków

3

the room temperature. The next day it was removed

from stirrer and centrifuged with centrifuge (NF400

– N400R Nüve). Next the supernatant was

discarded and the sample was washed with distilled

water at room temperature and dried in the oven

overnight. The obtain material was milled with a

mortar and stored in a plastic container. Six kinds

of adsorbents were prepared: three at pH 7,

intercalated with glycine (GLY-7), arginine (ARG-

7) and L-histidine (L-HIST-7). Also three materials

at pH 5 were obtained, GLY-5, ARG-5 and L-

HIST-5, respectively. Schema of adsorbents

preparation is shown in the Fig. 1.

Fig. 1. Schema of adsorbents preparation.

3. Characterization methods

FTIR spectra of prepared adsorbents were collected

along with spectra of pure amino acids used for

montmorillonite intercalation – glycine, arginine

and L-histidine. The analysis was conducted using

KBr pellet method. First KBr pellet was obtained

by milling KBr with a mortar and pressurizing it.

The KBr pellet was used to obtain the background

spectra. The pellets of investigated samples were

prepared by mixing adsorbent material with KBr in

proportion 2:3, milling with a mortar and

pressurizing to produce the final pellet. The sample

spectra was collected by subtraction of background

KBr spectrum from the spectrum of pellet

containing KBr and sample material. The

investigation of FTIR was conducted with use of a

Nicolet 6700 Fourier transform IR

spectrophotometer (256 scans, resolution 4 cm-1

) in

the wavenumber range from 400 to 4000 cm-1

.

X-ray diffraction spectra of pressed powder

samples were prepared for pure MMT and each

type of amino acid-intercalated MMT. X-ray

powder diffraction patterns in range from 3o to 10

o

were obtained with a Phillips PW 1730

diffractometer with automatic data acquisition

(APD Phillips v3.6B software using a Cu anode

(λ=1.5406 Ǻ)).

The values of interatomic spacing were calculated

on the basis of θ values from the Bragg law:

, where: d – the interplanar distance

[Ǻ], θ – the scattering angle [o], n – the positive

integer (n=1), λ – the wavelength of incident wave

(λ=1.5406 Ǻ). The clay expansion in result of

intercalation was calculated by subtracting the

value of the interlayer spacing of MMT from the

value of interlayer spacing of intercalated materials.

Experiments of thermogravimetry with differential-

scanning calorimetry were conducted using an

apparatus Setaram TG-DSC 111. All the samples

were analyzed regarding mass loss and heat flow

during heating. The analysis was conducted in the

temperature range from 25 oC to 700

oC and speed

5 oC/min.

In the nitrogen adsorption-desorption analysis the

capillary condensation of nitrogen inside pores

allows for evaluation of porous volume and pore

size distribution in the sample. Clay adsorbents

were analyzed by nitrogen (Air Liquide, 99.999%)

adsorption-desorption with NOVA 2200e

Quantachrome at -196 oC. The samples were

previously degassed for 2.5 h at 150 oC under

vacuum conditions.

Clay materials modified with amino acids for purification processes of biogas and natural gas

Joanna Juźków

4

4. CO2 and CH4 adsorption measurements

Pure gas adsorption isotherm experiments were

performed on a high-pressure adsorption line. The

central element of the adsorption line was a

stabilization cell of calibrated volume enclosed

between three valves and connected with pressure

tranducer, which allowed for precise measurement

of pressure of the gas inside. The left valve was

connected to the pressurized gas bottles (switched

between methane, carbon dioxide and helium), that

supplied the gas used for adsorption properties

investigation. The right valve was connected to the

diffusion pump and allowed for creating vacuum

conditions inside the line and degassing of the

sample. The bottom valve was connected to the cell

with powder of investigated adsorbent material

inside. The cell and the stabilization cell were

submerged in the water bath, in order to conduct the

experiments in the conditions of controlled

temperature. For degassing of the sample vacuum

pump and diffusion pump were applied in the line.

The liquid nitrogen was used for removal of

contaminations from the line by their condensation

in the trap. The general scheme of high pressure

adsorption line installation is presented in the Fig 2.

Fig. 2. Scheme of the adsorption line

The sample powder ca. 1.5 g was placed inside the

cell, which was connected to the adsorption line

and degassed under vacuum conditions with

diffusion pump for 2.5 h at 150 oC using oven with

thermocouple for temperature control. Next, the cell

was cooled down to the room temperature and the

cell factor measurements were conducted. In order

to calculate the cell factor extrapure helium

(Praxair, purity 99.999%) was introduced into the

cell at pressures increasing accordingly to the order:

200, 400, 600 and 1000 kPa. After opening the cell

valve, the resulting pressure decrease was used to

calculate the cell factor. For adsorbents prepared at

pH 7 the cell factor was calculated at 25oC, for

adsorbents at pH 5 at 25 and 45 oC. The cell with

sample and calibrated cell were submerged in

waterbath for temperature control. After finishing

the calibration helium was eliminated from the cell

under vacuum.

Next, investigation of adsorption isotherms were

conducted using pressurized gases: methane (Air

Liquide, purity 100%) and carbon dioxide (Criolab,

purity 99.995%). In order to obtain the isotherms

portions of gas were purged into the cell starting

from 200 kPa and doubling the pressure each time

up to the value of 1000 kPa. The value of pressure

drop was noted after reaching equilibrium pressure

and the amount of the gas adsorbed was calculated.

After finishing the experiment the powder was

cleaned removing the gas by heating for ca. 1 h at

150 oC in vacuum conditions.

On the basis of obtained results adsorption

isotherms of carbon dioxide and methane

adsorption on amino acid intercalated MMT were

plotted. The isotherms show results obtained at 25

oC for clay based adsorbents at pH 7 and at 25 and

45 oC for adsorbents produced at pH 5. The

obtained results were fitted into virial equation. The

analytical expressions were further applied for

calculations of selectivity of materials and

adsorption of carbon dioxide and methane from the

binary mixture.

Clay materials modified with amino acids for purification processes of biogas and natural gas

Joanna Juźków

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Table 1. θ values for basal peak obtained in XRD plots for MMT and amino acid modified MMT materials, corresponding

interlayer spacing and expansion of MMT in the effect of amino acid intercalation.

MMT pH 7 pH 5

GLY-7 ARG-7 L-HIST-7 GLY-5 ARG-5 L-HIST-5

θ [o] 3.600 3.4845 3.3230 3.4045 3.4300 3.4215 3.4170

d [Ǻ] 12.27 12.67 13.29 12.97 12.86 12.91 12.92

expansion [Ǻ] - 0.40 1.02 0.70 0.59 0.64 0.65

Fig. 3. XRD plots for amino acid modified materials obtained at pH 7 and pH 5.

5. Results and discussion

Regarding the data obtained with FTIR method for

amino acid intercalated samples, the FTIR analysis

could not provide reliable proof for the presence of

amino acid molecules in the clay structure for all

the investigated materials. According to a big

dilution of amino acids in clay material in was very

difficult to obtain noticeable peaks for respective

peaks in the spectra. Also the peaks coming from

the raw material – montmorillonite influenced to

the great extent the plot of spectra, covering the

presence of amino acids. Materials obtained at pH 7

gave no characteristic peaks visible in spectra and

only peaks characteristic for MMT were observed.

Samples prepared at pH 5 showed some peaks that

could correspond to the amino acids presence,

although it was hard to relate them to specific

vibrations.

In XRD analysis a characteristic, strong and sharp

basal reflection for the MMT plot can be observed

for θ equal to 3.6o. For all the amino acid modified

samples shift of the basal peak to smaller θ values

was noticed (Fig. 3.). It indicates increase of

interlayer spacing in the structure of investigated

materials, what can be explained by expansion of

clay structure caused by intercalation of amino acid

molecules. The results of calculated interlayer

spacing along with values of MMT structure

expansion are presented in the Table 1.

The basal spacing for the pure MMT was calculated

as 12.27 Ǻ, which is characteristic value of basal

spacing for clay materials, usually enclosed

between 12 to 14 Ǻ. It can be noticed that the

greatest expansion of spacing is present in case of

ARG-7, equal to 1.02 Ǻ, which is followed by L-

HIST-7 with the value of 0.70 Ǻ. The least

expanded material of all the investigated samples

was GLY-7 with expansion corresponding to 0.40

Ǻ. Adsorbent samples obtained at pH 5 presented

medium expansion with values located between

marginal results for materials at pH 7. Among

0

20

40

60

80

100

3 4 5 6 7 8 9 10

inte

nsi

ty [

a. u

.]

2θ [o]

pH 5

MMTGLYARGL-HIST

0

20

40

60

80

100

3 4 5 6 7 8 9 10

inte

nsi

ty [

a. u

.]

2θ [o]

pH7

MMTGLYARGL-HIST

Clay materials modified with amino acids for purification processes of biogas and natural gas

Joanna Juźków

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Fig. 4. TG DSC plots for adsorbents prepared at pH 7 and pH 5.

them the most expanded material was L-HIST-5

amounting to 0.65 Ǻ. The least expanded material

was GLY-5 with expansion of 0.59 Ǻ. In the TG

DSC analysis (Fig. 4) the raw MMT the first loss of

mass of ca. 7% was observed between 30 and 115

oC, which contributed to the release of water

physically adsorbed on the clay. It corresponded to

the endothermic peak that could be observed on the

heat flow in the same range of temperatures. During

further heating the mass of MMT remained

constant until 600 oC. The sharper decrease of mass

beyond 600 oC resulted from destruction of clay

structure under high temperature. For intercalated

clays prepared at pH 7 analogous mass loss due to

water evaporation can be noticed, but with smaller

mass decrease indicated; approximately 4% for L-

HIST-7 and 6% for GLY-7 and ARG-7. Next,

another small decrease of mass (around 1%) was

observed, which also reflected in slight

endothermic peak on the heat flow plot, that

contributed to the loss of water adsorbed in the

pores. Further slow decrease of mass was observed

for GLY-7 and L-HIST-7 (ca. 5% and 6%

respectively) in the region of 300 to 600 oC In case

of ARG-7 no significant mass decrease was

observed in this region. However, corresponding

strong endothermic decrease in the heat flow can be

noticed. It indicated decomposition of adsorbed

amino acids from the interlayer space of clays. In

case of materials obtained at pH 5 analogical mass

loss along with characteristic endothermic peaks

can be observed in the range of 15 to 115 oC

contributing to the water loss. The mass loss

contributing to amino acids removal amounted to

13% for ARG-5, 6% for GLY-5 and 7% for L-

HIST-5., what indicates more efficient intercalation

Table 2. Porosity and surface properties characteristics of pure MMT and amino acids modified MMT materials.

-18

-13

-8

-3

2

70

75

80

85

90

95

100

15 215 415 615

he

at fl

ow

[mV

]

mas

s [%

]

temperature [oC]

pH7MMT GLY ARG L-HIST

-18

-13

-8

-3

2

70

75

80

85

90

95

100

15 215 415 615

he

at fl

ow

[mV

]

mas

s [%

]

temperature [oC]

pH5MMT GLY ARG L-HIST

MMT pH 7 pH 5

GLY-7 ARG-7 L-HIST-7 GLY-5 ARG-5 L-HIST-5

BET surface area [m2/g] 20 34 22 14 35 35 9

micropore volume [cm3/g] 0 0 0 0 0 0 0

micropore area [cm2/g] 1 0 0 0 0 0 2

external surface area [cm2/g] 18 34 22 14 35 35 7

total pore volume [cm3/g] 0.032 0.054 0.044 0.037 0.072 0.074 0.025

Clay materials modified with amino acids for purification processes of biogas and natural gas

Joanna Juźków

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The results of nitrogen adsoption-desorption

analysis were gathered in the Table 2. GLY-5 and

ARG-5 show the best porosity and surface

properties among all the adsorbents prepared, with

surface area amounting to 35 m2/g and total pore

volume 0.074 cm3/g for ARG-5 and 0.072 cm

3/g for

GLY-5. Both adsorbents intercalated with L-

histidine; L-HIST-7 and L-HIST-5 exhibited

relatively low development of surface area, 14

cm2/g and 7 cm

2/g respectively, which was lower

than for MMT with 18 cm2/g. ARG-7 and GLY-7

presented medium values of surface area with 22

cm2/g and 34 cm

2/g respectively and pore volume

0.044 cm3/g and 0.054 cm

3/g respectively.

As presented in the Fig. 5, at pH 7 the highest

adsorption capacity towards carbon dioxide was

shown by ARG-7 with the value of 0.46 mmol/g at

high pressures and it was the only material among

intercalated clays, that showed better adsorption

abilities than raw MMT with CO2 retention

amounting to 0.25 mmol/g at high pressures. Both

GLY-7 and L-HIST-7 exhibited lower amount of

CO2 adsorbed with results of 0.08 and 0.023

mmol/g respectively. In case of methane

adsorption, amounts of gas adsorbed were lower

than for carbon dioxide for all the investigated

adsorbents. Amount of CH4 retained by GLY-7 was

very low (0.003 mmol/g) and below the sensitivity

of the method. For this reason results of this

adsorption isotherm are not presented on the graph.

Fig. 5. Adsorption isotherms of carbon dioxide and methane adsorption at 25oC on amino acid intercalated MMT samples

prepared at pH 7.

Fig. 6. Adsorption isotherms of carbon dioxide and methane adsorption at 25oC on amino acid intercalated MMT samples

prepared at pH 5.

0

0,2

0,4

0,6

0,8

1

0 200 400 600 800 1000

nad

s[m

mo

l/g]

p [kPa]

CO2

ARG-7 L-HIST-7 GLY-7 MMT

0

0,2

0,4

0,6

0,8

1

0 200 400 600 800 1000

nad

s[m

mo

l/g]

p [kPa]

CH4

L-HIST-7 ARG-7

0

0,2

0,4

0,6

0,8

1

0 200 400 600 800 1000

nad

s[m

mo

l/g]

p [kPa]

CO2

ARG-5 L-HIST-5 GLY-5 MMT

0

0,2

0,4

0,6

0,8

1

0 200 400 600 800 1000

nab

s[m

mo

l/g]

p [kPa]

CH4

GLY-5 ARG-5 L-HIST-5

Clay materials modified with amino acids for purification processes of biogas and natural gas

Joanna Juźków

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Fig. 7. Adsorption isotherms of carbon dioxide adsorption at 25oC and 45oC on amino acid intercalated MMT samples

prepared at pH 5.

Methane retained on ARG-7 and L-HIST-7 reached

value of 0.11 mmol/g. Due to low amounts of gases

adsorbed at 25 oC, for the materials prepared at pH

7 adsorption at higher temperature (45 oC) was not

conducted.

For pH 5 (Fig. 6.) the amounts of carbon dioxide

adsorbed increased for all the intercalated clays in

comparison to the values obtained at pH 7, with the

best result for ARG-5, equal to 0.80 mmol/g. It was

the highest amount of carbon dioxide adsorbed

among all experiments conducted in presented

research. The second value belonged to L-HIST-5

with 0.53 mmol/g of CO2 adsorbed. The material of

lowest adsorptive properties was GLY-5, which

retained 0.32 mmol/g. All adsorbents prepared at

pH 5 exhibited better adsorption of carbon dioxide

than raw MMT material. ARG-5 and L-HIST-5 are

capable of adsorbing over 0.4 mmol/g of CO2 at

pressures lower than 200 kPa. It indicates the

possibility to conduct the adsorption process at

lower pressure, what is favourable from technical

and economical point of view for further

implementation to industrial-scale processes. The

amounts of methane adsorbed were significantly

lower than CO2.

As it can be noticed in Fig. 7, at 45 oC ARG-5

showed the highest adsorption properties with 0.72

mmol/g of all the samples investigated at pH 5.

Although L-HIST-5 presented slightly lower results

with final amount of carbon dioxide adsorbed equal

to 0.64 mmol/g, it obtained better results than

ARG-5 at lower pressures, reaching 0.5 mmol/g at

240 kPa. GLY-5 was the material with the lowest

adsorptive properties, reached 0.32 mmol/g. It

should be pointed out, that even though it was

expected, that at higher temperature the adsorbents

would exhibit lower properties of adsorption, GLY-

5 and L-HIST-5 reached higher amounts of carbon

dioxide adsorbed at 45 oC than in case of the

experiment conducted at 25 oC.

Fig. 8. Selectivity of aminoacid intercalated MMT

adsorbents against pressure.

0

0,2

0,4

0,6

0,8

1

0 200 400 600 800 1000

nad

s[m

mo

l/g]

p [kPa]

25 oCL-HIST-5 ARG-5 GLY-5 MMT

0

0,2

0,4

0,6

0,8

1

0 200 400 600 800 1000

nad

s [m

mo

l/g]

p [kPa]

45 oCL-HIST-5 ARG-5 GLY-5

1

21

41

61

81

101

121

141

161

181

201

0 200 400 600 800 1000

Se

lectivity

p / kPa

L-HIST-5

ARG-5

GLY-5

L-HIST-7

ARG-7

Clay materials modified with amino acids for purification processes of biogas and natural gas

Joanna Juźków

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Fig. 9. Phase diagrams at 100 kPa describing separation of CH4 between gaseous and adsorbed phase as a function of mole

fraction of CH4 in adsorbed phase (left up) and phase diagrams for L-HIST-7, ARG-7, L-HIST-5, ARG-5 and GLY-5.

Among materials used for experiences L-HIST-5

presented the best selectivity properties. (Fig. 8.)

The second adsorbent was ARG-7 followed by

ARG-5. The least selective materials were L-HIST-

7 and GLY-5. It is remarkable, that for while

samples with low selectivity, the selectivity is not

much dependent on pressure (GLY-5, L-HIST-7,

ARG-5). For materials highly selective, selectivity

grows significantly with increase of pressure.

The graphs presented in the Fig 9. show that L-

HIST-5 has best adsorptive properties among all the

investigated samples. Up to 0.7 molar fraction of

CH4 contained in the mixture, no adsorption of this

gas is exhibited and only CO2 is being retained with

amount of 0.3 mmol/g of CO2 adsorbed. The

retention of CO2 remains predominant up to 0.96

molar fraction of CH4 in the binary mixture. ARG-7

shows exclusivity of CO2 adsorption until 0.25

molar fraction of CH4 with retention of CO2 equal

to 0.34 mmol/g at this point. Interesting properties

were also shown by ARG-5 with the highest

retention of both pure gases, with values amounting

to 0.44 mmol/g for CO2 and 0.1 mmol/g for CH4.

Very poor selectivity and adsorption properties

were shown by L-HIST-7 and GLY-5.

6. Conclusions

Intercalation process was successful for all the

materials prepared. Due to insertion of amino acid

molecules into the interlayer space expansion of

montmorillonite structure was observed on XRD

spectra, as well as for all the samples, except for L-

HIST-5, increase of surface area and total pore

volume was noted. The CO2 adsorption was

strongly enhanced by intercalation with amino

acids.Higher adsorption capacity was obtained for

adsorbents prepared at pH 5. It can be explained by

greater retention of amino acids by clay material at

this pH due to protonation of amine groups of

amino acids, what causes the increase of their

availability for carbon dioxide adsorption. The

material with highest adsorption capacity towards

CO2 was ARG-5 with 0.80 mmol/g. Both arginine

0

0,1

0,2

0,3

0,4

0,5

0 0,5 1

ad

so

rbed

am

ount / m

mo

l g -

1

yCH4

CO2CH4Total

ARG-7

0

0,1

0,2

0,3

0,4

0,5

0 0,5 1

ad

so

rbed

am

ount / m

mo

l g -1

yCH4

CO2

CH4

Total

L-HIST-7

0

0,1

0,2

0,3

0,4

0,5

0 0,5 1

ad

so

rbed

am

ount / m

mo

l g -

1

yCH4

CO2CH4Total

GLY-5

0

0,1

0,2

0,3

0,4

0,5

0 0,5 1

ad

so

rbed

am

ount / m

mo

l g -

1

yCH4

CO2CH4Total

ARG-5

0

0,1

0,2

0,3

0,4

0,5

0 0,5 1

ad

so

rbed

am

ount / m

mo

l g -

1

yCH4

CO2

CH4

Total

L-HIST-5

0

0,2

0,4

0,6

0,8

1

0 0,5 1

y CH

4

xCH4

L-HIST-5

ARG-5

GLY-5

L-HIST-7

ARG-7

Clay materials modified with amino acids for purification processes of biogas and natural gas

Joanna Juźków

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and L-histidine intercalated clays showed

satisfactory results and their adsorption capacity

towards carbon dioxide was higher than in case of

raw montmorillonite. Adsorption on glycine

intercalated samples did not give promising results.

For the tests conducted at temperature 45 oC at pH

5, the amount of carbon dioxide adsorbed was

higher for ARG-5 and GLY-5 than at 25 oC.

Retention of methane by intercalated clays gave

lower results than for CO2 for all materials. In terms

of selectivity L-HIST-5 was the best adsorbent,

adsorbing exclusively CO2 up to 0.7 molar fraction

of CH4 in the binary mixture and predominant CO2

retention up to 0.96 molar fraction of CH4. Amino

acid modified montmorillonite adsorbents showed

promising results for CO2 and CH4 separation.

Regarding their low-cost, environmental friendly

character and selectivity, they can be successfully

applied in the industrial separation processes.

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