Vyas Morla MTP 734

Evaluation of Metal Organic Frameworks for Desulfurization

by

MORLA VYAS

Department of Chemical EngineeringIndian Institute of Technology, Guwahati

May, 2012

OUTLINE

INTRODUCTION

OBJECTIVES

LITERATURE REVIEW

EXPERIMENTAL WORK

RESULTS AND DISCUSSIONS

CONCLUSIONS

INTRODUCTION Environment

Air Pollution

Sulfur Emissions

Combustion of Fuels Combustion of Fuels

Gasoline and Diesel Fuels

Can`t we reduce these Emissions ????

Yes

Environmental Regulations

Euro III ( Concentration of [S] < 150 ppm) Euro IV ( Concentration of [S] < 25 ppm)

INDIA

BS III ( Concentration of [S] < 150 ppm) BS IV ( Concentration of [S] < 50 ppm)

Is there any methods to maintain these Sulfur concentrations ????

Methods Like

Oxidative and Bio Desulfurization

Ultra sound assisted Desulfurization

Extraction

Hydro Desulfurization Hydro Desulfurization

Adsorption

The first three methods are good at regulating the sulfur concentrations but these are not able to meet the present environmental regulations

HDS as an Conventional Technology

Principle: Converts Sulfur in to H2S

Advantages : Sulfur concentrations to less than 50 ppm very effectively Eliminates non aromatic sulfur compounds

Disadvantages : Requires high temperatures (~ 898 K) Requires high temperatures (~ 898 K) Requires high pressures (60 100 atm) High operating costs Frequent catalyst poisoning Ineffective in eliminating aromatic sulfur species like

Benzothiophene Dibenzothiophene 4,6-DMDBT

Decrease in octane ratings ( due to increase in temperature for the removal of organic sulfur species)

Here Comes Liquid Phase Adsorption

Advantages:

Requires Low temperature and low pressures (ambient conditions) Hydrogen is not required Low energy demands for the process Potential to regenerate the spent adsorbent Reduction of oil loss in the beds

Importance:

Selectively removes sulfur compounds from transportation fuels by the pi-complexation ( a weak chemica bond) adsorption. Refractory sulfur compounds bind strongly to the pi-complexation sorbents because of a better electron donation and back donation ability[01]

[01]Ralph T. Yang,Desulfurization of Transportation Fuels by Adsorption, Vol. 46, No. 2, pp. 111150, 2004

Adsorbents like :

Activated Carbon

Silica gel

Activated Alumina

Carbon Molecular sieves

Zeolites

Metal organic Frameworks

MOFs Consist of metal cations linked by polyfunctional organic linkers yielding porous three-dimensional networks.

Advantages:

High Surface Area

Easy Regeneration

Tunable structures

OBJECTIVE:

This Project focuses on

Synthesis and characterizing the adsorbents

Choosing the better adsorbent based on the effective removal of sulfur

species

Investigation of relationship between structures of the adsorbent

framework and sulfur adsorption

S. No Type of Adsorbent

Sulfur Species

removed

Work done Results at optimum

conditions

References

1. Cu-BTC-MOF

Thiophene and Tetra hydro thiophene (THT)

Investigated Zn containing MOF`s and Cu containing MOF`s (prepared by electro chemical methods) and found Cu containing MOF`s having higher potential towards the

78 wt% of the sulfur content was removed from the Thiophene based oils and 86 wt% for THT based oils

Sabine Achmann et.

al ,2010[2]

Literature Survey

potential towards the removal of thiophenes and THT in low sulfur gasoline and diesel fuels.

oils

2. Copper containing MOF

Benzothiophene, Thiopheneand tetra hydro thiophene

Investigated Al containing MOF`s ,Fe containing MOF`s and Cu containing MOF`s and observed C300 has high adsorption capacity.

The extent of DBT at temperatures close to ambient is eight times higher on C300 MOF`s

G.Blanco-Brieva et. al , 2011 [3]


Sulfur species

removed


conditions

References

3. Ag+/Al-MSU-S

Benzo thiophenes and Di Benzo thiophenes (DBT)

Investigated Ag+ exchanged mesoporous material Al-MSU-S for gasoline containing 600 ppmw of BT and DBT

The sulfur species were brought to less than 10 ppmws

Chunmei Meng et. al 2010 [4]

Contd

4. Activated Carbon Fibre

BT,DBT before HDS and after HDS 4-MDBT;4-6 DMDBT; 2,4,6-

TMDBT

Activated carbon ber (ACF) was selected in this study asan adsorbent because it showed rather low pressure drop and

high performance among the activated carbon materials and the twice use of bed is possible

Removed the

sulphur content from 300 ppms to less than 10 ppms

Yosuke Sano et. al 2005 [5]


Sulfur species

removed


conditions

References

5Activated

carbonImpregnated with CuCl and PdCl2

4,6-dimethyl di benzo

thiophene,BT,DBT

Considered JP-5, a jet fuel that has sulphur content of 1172 ppm and investigated metal impregnated oxides, zeolite 5A,13X,Y zeolites of various

65% sulphuradsorptioncapacity wasobserved forfirstregeneration

Hermen A. Zinnen 1999 [6]

Contd

of various metal cation forms..

regeneration and 54% for second regeneration

Sulfur Species

We have chosen Dibenzothiophene as our sulfur species

Why Dibenzothiophene????

Structure

Two benzene rings

Single sulfur atom (Hindered)

At very High temperatures (~900oC) DBT can At very High temperatures (~900oC) DBT can be removed

But at those temperatures the aromaticitywill be lost.

Hence, Liquid phase adsorption explored3 Dimensional structure of DBTSource : Ben mills et al.,

Metal organic Frameworks

We have chosen three different MOFs Cu-BTC Cr-BDC MIL-53 (Al)

What is the Importance of Choosing these MOFs????

Cu-BTC Coordinatively unsaturated metal center Stable structure Stable structure

Cr-BDC Open metal centers High surface area and large pore volume

MIL-53 (Al) Stable structure Partially saturated metal center Flexible framework

This Involves

Synthesis Characterization Adsorption Equilibrium Measurements

Synthesis:

Experimental Work

Adsorbent Reactants Temperature

(K)

Time

(h)

Product Recovery

Cu-BTC

[7]

[Cu3(BTC)2], [Cu

(NO3)2.3H2O ,

Ethanol, DMF,

Methanol and

Deionized water

373 10

Filtration and Soxhleted

with methanol, for

removal of excess DMF.

Product is dried in hot air

oven at 353 K

Adsorbent Reactants Temperature

(K)

Time

(h)

Product Recovery

Cr-BDC

[8]

Cr(NO3 )3.9H2O ,

BDC, Hydrofluoric

acid, DMF,ethanol

& Deionized water

493 8

Filtration and Washed

thoroughly with DMF

and dried in oven at 423

K in hot air oven for

overnight. For 200 mg of

373 20 the product,15 ml of

ethanol is added.

MIL 53(Al)

[9]

Al(NO3)2.9H2O,

Terephthalic acid,

DMF, and

Deionized water

493 72

Filtration and Washed

with Deionized water. For

removal of excess BDC

1 gm of product is added

with 25 ml of DMF and

keep for heating at 333 K

for 15 h

010

20

30

40

25 225 425

We

igh

t, m

g

Temperature , C

Characterization

Thermo Gravimetric analysis plot for Cu-BTC MOF

0

2

4

6

8

10

12

14

16

18

20

0 100 200 300 400 500 600

We

igh

t, m

g

Temperature C

Thermo Gravimetric analysis plot for Cr-BDC MOF

Thermo Gravimetric Analysis

0

2

4

6

8

10

12

14

16

0 200 400 600 800

We

igh

t, m

g

Temperature (oC)

Thermo Gravimetric analysis plot for MIL-53(Al) MOF

Metal Organic

Framework

BET Surface

Area (m2/gm)

Pore

volume

(cm3/gm)

Cu-BTC1668 0.828

Cr-BDC3300 1.38

MIL-53 (Al)1215 0.59

Textual Properties of Metal Organic frameworks

Adsorption Equilibrium Measurements:

To study the behavior of Metal organic Frameworks in Liquid phase adsorption, we followed a definite Protocol

Protocol Involves Six Steps:

Preparation of Synthetic Fuel mixtures

Synthesizing the Metal organic Framework Synthesizing the Metal organic Framework

Activating the Metal organic Framework

Loading the MOF to the fuel mixtures

Equilibrating the Fuel mixture

Analyzing the Fuel mixture

Equilibrium Experiments for Liquid phase adsorption

Allowed to distribute

Done by shaking at 200 rpm in an Incubator shaker

Time estimated for equilibration is 24 hrs

Adsorbent was filtered and the clear solution is collected

This unknown concentration (After adsorption) was analyzed in analyzing equipments This unknown concentration (After adsorption) was analyzed in analyzing equipments

Finally we will get the extent of adsorption done by measuring the removal of the subjected species on to the adsorbent.

Isotherms were plotted to understand the behavior of the adsorbents at different temperatures and to identify conditions for which high adsorption capacities can be obtained.

Sulfur Analysis

These can be carried out on

The fuel mixture need to be analyzed before and after the Adsorption, to know the extent of adsorption

We prepared Concentrations ranging from 100 ppm(S) to 6000 ppm(S) for our analysis

These can be carried out on

High Performance Liquid Chromatography

UV-Visible Spectrophotometer

GC/MS Spectroscopy

Determination of DBT concentrations in UFLC (Ultra Fast Liquid Chromatography):

Results and Discussion:

Column selected: C-18 (ZORBAX-ODS)

Wavelength range : 220 nm

Detector :UV-Visible

Stationary phase (A): Deionised water (HPLC grade)

Typical chromatogram for DBT+ n-heptane (500ppmw DBT) mixture using UFLC

Deionised water (HPLC grade)

Mobile phase (B): Methanol (HPLC grade)

Flow rate (A): 0.2 ml/min

Flow rate (B) : 0.8 ml/min

Pressure : 13.9 Mpa

Amount injected: 0.10 ml

Observation:

Compound of interest dibenzothiophene is detected at the retention time of 16-17.5 minutes( Retention Time) range.

Contd.Calibration Plot:

y = 1E-05x + 1.6411R = 0.998

0

100

200

300

400

500

600

700

800

900

1000

pp

mw

DB

T

Analysis:

50 ppmw DBT 950ppmw DBT

A plot of ppmw DBT verses these chromatogram areas gives the required calibration plot.

0

0 20000000 40000000 60000000 80000000 100000000

Area

Calibration plot of dibenzothiophene + n-heptane fuel mixture [11]

Observation:

From the trend line pattern it is obvious that analysing equipment is best suitable for the concentrations ranging upto around 900 ppmw DBT

[11]P.Poddar Adsorptive Desulfurization of Liquid Fuels, BTP thesis,Dept of chemical engineering,IITG

Contd.Dibenzothiophene on Cu-BTC:

0

20

40

60

80

100

120

Am

ou

nt

Ad

sorb

ed

( g

S/

kg M

OF)

298 K

313 K

328 K

Experiments were conducted at three different temperatures

298 K 313 K 328 K

0

0 1000 2000 3000 4000 5000

Concentration, ppmwS

Adsorption isotherms of DBT on Cu-BTC at 298 K, 313 K and 328 K

Observation:

It is evident that adsorption potential of this material is higher at 313 K than on 298 K and still lesser for 328 K

Reasons: At low temperatures, the adsorption process is basically governed by weak Van der Waals forces

At higher temperatures Chemisorption, and probably chemical reaction [12] is dominant showing in increase in adsorption potentials

[12] Zhang ZY, Adsorptive removal of aromatic organosulfur compounds over the modied NaY zeolites. Appl Catal B: Environ 2008;82:110

Contd.Dibenzothiophene on Cr-BDC:

0

20

40

60

80

100

120

Am

ou

nt

Ad

sorb

ed

(gS

/ kg

MO

F)

298 K

313 K

328K


298 K 313 K 328 K

0

0 1000 2000 3000 4000 5000


Adsorption isotherms of DBT on Cr-BDC at 298 K, 313 K and 328 K

Observation:

It is evident that adsorption potential of this material is slightly higher at 313 K than on 298 K and still lesser for 328 K

Reasons: At low temperatures, the adsorption process is basically governed by weak Van der Waals forces

At higher temperatures Chemisorption, and probably chemical reaction [12] is dominant showing in increase in adsorption potentials

Contd.Dibenzothiophene on MIL-53 (Al):

0

20

40

60

80

100

120

140

0 1000 2000 3000 4000

Am

ou

nt

Ad

sorb

ed

( g

S/ k

g M

OF)

298 K

313 K

328 K

Reasons: At low temperatures, the adsorption process is


298 K 313 K 328 K

0 1000 2000 3000 4000


Adsorption isotherms of DBT on MIL-53 (Al) at 298 K, 313 K and 328 K

adsorption process is basically governed by weak Van der Waals forces

Observation:

It is evident that adsorption potential of this material is slightly higher at 313 K than on 298 K and lesser for 328 K

Adsorption potentials at 298 K and 313 K haven`t shown significant changes, resembling that there is no effect of chemisorptions at 313K

Contd.Correlation of MOFs based on Temperature Kinetics:

0

20

40

60

80

100

120

140

0 1000 2000 3000 4000 5000Am

ou

nt

Ad

sorb

ed

(gS

/ kg

of

MO

F)


Cu-BTC

Cr-BDC

MIL-53(Al)

Observation:

MIL-53 (Al) is having more adsorption capacity than other two mofs

Cu-BTC is competitive with MIL-53 (Al) because of its still adsorbing potentials

0

20

40

60

80

100

120

140

0 2000 4000 6000

Am

ou

nt

Ad

sorb

ed

( g

S/ k

g o

f M

OF)


Cu-BTC

Cr-BDC

MIL-53 (Al)

Correlation among the adsorption isotherms of DBT on the three MOFs (Cu-BTC, Cr-BDC and MIL-53 (Al) ) at 298 K.


Observation:

Same trend is observed at 313 K

Contd.Correlation of MOFs based on Temperature Kinetics:

0

20

40

60

80

100

120

140

Am

ou

nt

Ad

sorb

ed

( g

S /

kg o

f M

OF)

Cu-BTC

Cr-BDC

MIL-53 (Al)

0

0 1000 2000 3000 4000 5000



Observation:

MIL-53 (Al) is having more adsorption capacity than other two mofs

Cu-BTC is less competitive with MIL-53 (Al) at this temperature (328 K)

Contd.

0

20

40

60

80

100

120

140

290 300 310 320 330

Exte

nt

of

adso

rpti

on

( g

S/ k

g M

OF) MIL-53 (Al)

Cu-BTC

Cr-BDC

Variation of Adsorption amounts:

290 300 310 320 330

Temperature K

Variation of dibenzothiophene (DBT) adsorption capacity for Cr-BDC and MIL-53 (Al) at equilibrium concentration (3400 ppmwS) and Cu-BTC at 3400 ppmwS

Observation:

No distinct pattern is noticed

Extent of adsorption is maximum at 313 K for Cu-BTC and Cr-BDC

Extent of adsorption at 298 K , 313 K and 328K are more or less equal for MIL-53 (Al)

Contd.Comparison with existed Sorbents:

40

60

80

100

120

140

Exte

nt

of

Ad

sorp

tio

n (

g S

/ kg

So

rbe

nt)

Extent of DBT adsorption at 298 K (2500 ppmw S) for Cu-BTC, Cr-BDC,MIL-53 (Al), MOF-5, MOF-177, MOF-505 [13] , Y-Zeolites[03], Activated carbons[14]

[13] Adam J. Matzger, Liquid Phase Adsorption by Microporous Coordination Polymers: Removal of OrganosulfurCompounds, J. AM. CHEM. SOC. 2008, 130, 69386939[14]

0

20

MIL-53 (Al) Cu-BTC Cr-BDC MOF-5 MOF-505 MOF-177 Y-Zeolites Activated Carbon

Exte

nt

of

Ad

sorp

tio

n (

g S

/ kg

So

rbe

nt)

Sorbents

Why this higher and lower adsorption amounts ???

Factors effecting adsorption

Surface areas pore volumes

Liquid phase adsorption Impact of structure Impact of structure Role of metals Role of ligands Role of host-guest interactions

Comparison with existed Sorbents: Surface areas

SorbentsMetal

involvedLigand

BET

Surface

Area

(m2/gm)

Pore volume

(cm3/gm)

Amount Adsorbed

(g S / kg Sorbent)

Dibenzothiophene

Cu-BTC Copper

1,3,5-

benzenetricarboxylic

acid

1668 0.828 68.1

Cr-BDC Chromium

1,4-

benzenedicarboxyli

c acid

3300 1.38 57.3

1,4-

MIL-53 (Al) Aluminium

1,4-

benzenedicarboxyli

c acid

1215 0.59 118.6

MOF-5[13] Zinc

1,4-

benzenedicarboxyli

c acid

2900 1.04 40

MOF-177[13] Zinc1,3,5-

benzenetribenzoate4630 1.69 20

MOF-505[13] Copper

3,3,5,5-

biphenyltetracarbox

ylic acid

1830 0.71 35

[13] Adam J. Matzger, Liquid Phase Adsorption by Microporous Coordination Polymers: Removal of OrganosulfurCompounds, J. AM. CHEM. SOC. 2008, 130, 69386939

Contd.Reasons behind higher and lower adsorption:

Role of Cation on the S-M (Sulfur-Metal) interactions with alter in Ligand

40

60

80

100

Exte

nt

of

Ad

sorp

tio

n (

gS/

kg

of

MO

F)

298 K313 K

298 K 313 K 328 K

328 K Observation:

Here the Cation Copper ( Cu2+ ) is same for both the Materials

0

20

40

Cu-BTC Cu-DABCO Cu-BTC Cu-DABCO Cu-BTC Cu-DABCO

Exte

nt

of

Ad

sorp

tio

n (

gS/

kg

of

MO

F)

Metal organic frameworks

298 K 313 K 328 K

Possess greater (S-M) interactions and leads to higher adsorption for Cu-BTC than on Cu-DABCO

Extent of DBT adsorption at equilibrium (3500 ppmw S) for Cu-BTC andCu-DABCO [11]

[11]P.Poddar Adsorptive Desulfurization of Liquid Fuels, BTP thesis,Dept of chemical engineering,IITG

Contd.Reasons behind higher and lower adsorption: Role of Ligand on the S-M (Sulfur-Metal) interactions with alter in Cation

40

60

80

100

120

140

Exte

nt

of

adso

rpti

on

(g

S/ k

g o

f M

OF) Observation:

Here the CationAluminium (Al3+ ) and Iron (Fe2+) is different for both the Materials

But the ligands are identical

0

20

MIL-53 (Al) MIL-53 (Fe)

Exte

nt

of

adso

rpti

on

(g

S/ k

g o

f M

OF)

Metal organic frameworks

Extent of DBT adsorption at equilibrium (3500 ppmw S) for MIL-53(Al)and MIL-53(Fe) [03]at 313K

identical

Thus possess 6 times higher adsorption for MIL-53 (Al) than on MIL-53 (Fe)

[03] G.Blanco-Brievaa, Effectiveness of metalorganic frameworks for removal of refractory organo-sulfur compound present in liquid fuels, Fuel Vol:90, 2011

Conclusion:

In this study

The metal organic frameworks Cu-BTC, Cr-BDC and MIL-53 (Al) were synthesised and characterisation of these frameworks were also carried out.

The metal organic frameworks Cu-BTC, Cr-BDC and MIL-53 (Al) were synthesised and characterisation of these frameworks were also carried out.

Explored Sulfur adsorption measurements on these MOFs

Our studies explored that these MOFs have promising adsorption potentials than existing Sorbents employed for desulfurization of organosulfur compounds till yet

MIL-53 (Al) has higher adsorption potentials than Cu-BTC and Cr-BDC

Cu-BTC is more competitive with MIL-53 (Al) than Cr-BDC due to its still adsorbing capacities

It was explored that the structure of these organo sulfur compounds plays an important role along with the structure of MOF and other parameters like -Complexation and pore volumes and surface areas in deciding the adsorption potentials of these MOFs employed in this work

It has been demonstrated that the extent of dibenzothiophene (DBT) adsorption at temperatures close to ambient (304 K) is higher for all three mofs employed in this work

The very high adsorption capacity of these (MIL-53(Al)) and Cu-BTC) substrates makes it a potential candidate to be employed in the removal of remaining refractory S-compounds in

Contd.

potential candidate to be employed in the removal of remaining refractory S-compounds in previously desulfurized liquid fuels.

Future work

Evaluating these organo sulfur compounds like BT(benzothiophene) and DBT( dibenzothiophene) on mofs like MOF-74 with change in metal (w.r.t. Mg,Ni, and Co), which is showing higher adsorption potentials for CO2 adsorption till now.

Flow-through experiments and determination of the selectivity of these materials for BT and DBT in the presence of other aromatic compounds found in fuels are can be made to assess the practicality of desulfurization by adsorption to MOFs.

References[2] Sabine Achmann, Gunter Hagen, Martin Hmmerle, Itamar Malkowsky, Christoph Kiener, Ralf Moos, Sulfur Removal from Low sulphur Gasolineand Diesel Fuel by Metal Organic Frameworks, Chem. Eng. Technol. 2010, 33, No. 2, 275280

[3] G.Blanco-Brievaa, J.M. Campos-Martina, S.M. Al-Zahrani and J.L.G. Fierroa, Effectiveness ofmetalorganic frameworks for removal of refractory organo-sulfur compound present in liquidfuels, Fuel Vol:90, 2011

[4]Chunmei Meng, Yunming Fang, Lijun Jin, Haoquan Hu, Deep desulfurization of modelgasoline by selective adsorption on Ag+/Al-MSU-S , Catalysis Today 149 (2010) 138142

[5] Yosuke Sano, Kazuomi Sugahara, Ki-Hyouk Choi, Yozo Korai, Isao Mochida , Two-stepadsorption process for deep desulfurization of diesel oil , Fuel 84 (2005) 903910adsorption process for deep desulfurization of diesel oil , Fuel 84 (2005) 903910

[6] Hermen A. Zinnen Removal of organic sulphur compounds from FCC Gasoline usingRegenerable Adsorbents, US Patent number 5,935,422 Aug 10 1999

[7] Pradip C Ph.D. Thesis, Indian Institute of Technology, Guwahati, 2009

[8] Pradip chowdhury, Chaitanya Bikkina, and Sasidhar Gumma* Gas adsorption properties ofthe Chromium based Metal Organic Framework MIL 101 J.Phys.Chem.C 2009, 113, 6616-6621

[9] Rowsell, J. L. C., and Yaghi, O. M., Metalorganic frameworks: a new class of porousmaterials, Micropor. Mesopor. Mater., 73, 3-14 (2004)

Chemisorption:

-Complexation: The DewarChattDuncanson model is a model in organometallic chemistry , which

Chemisorption is a sub-class of adsorption , driven by a chemical reaction occurring at the exposed surface.

A new chemical species is generated at the adsorbent surface (e.g. corrosion, metallic oxidation).

The strong interaction between the adsorbate and the substrate surface creates new types of electronic bonds ionic or covalent, depending on the reactive chemical species involved

Back up

The DewarChattDuncanson model is a model in organometallic chemistry , which explains the type of chemical bonding between an alkene and a metal (pi-complex) in certain organometallic compounds.

The model is named after Michael J.S. Dewar , Joseph Chatt and L.A. Duncanson

The pi-acid alkene donates electron density into a metal d-orbital from -symmetry bonding orbital between the carbon atoms.

The metal donates electrons back from (a different) filled d-orbital into the empty antibonding orbital. Both of these effects tend to reduce the carbon-carbon bond order, leading to an elongated C-C distance and a lowering its vibrational frequency.[14]

[14] Olefin co-ordination compounds. Part III. Infra-red spectra and structure: attempted preparation of acetylene complexes J. Chatt and L. A. Duncanson, J. Chem. Soc., 1953,

Back up: for UFLC

ZORBAX-ODS: [10] Highly retentive reversed phase liquid chromatographic column packing based on the ZORBAX Microparticulate silica support This bonded phase packing is formed by the monomolecular bonding of octadecysilane groups to the surface of the particles Maximum surface area coverage is maintained to produce these columns with exceptional reproducibility of performance C-18 bonded phases are well established for the seperation of non polar and low polarity solutes Stronger retentive power for non polar compounds

Choice of Mobile phase: Methanol [10]

As our fuel mixture is basically a non polar mixture, we need our compound to be retended by the column So, we need a partially aqueous solvents to serve our purposeMethanol is a strong organic solvent and it is chosen as our mobile phase An increase in the retention is basically governed by increasing the water content of the mobile phase Hence we have chosen the binary mixture composition of flow as

Methanol : 0.8ml/min Deionised water : 0.2ml/min

[10] Instrumental Liquid chromatography: A practical manual on High performance liquid chromatography, by N.A Parris

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Vyas Morla MTP 734