synthesis of zsm-5 with hexamethylineimine

5/28/2018 Synthesis of ZSM-5 with hexamethylineimine

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ByImteaz AhmedPhD candidate

Green Nanomaterials Research Center& Dept. of Chemistry

Kyungpook National UniversityRepublic of Korea


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IntroductionExperimental

Results and discussion

Summary

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Introduction


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Zeolite ZSM-5 with an MFI structure is one of

the most widely used and studied structures

because of its special pore structure, good

stability and high acidity.

Especially, ZSM-5 has been very widely used

in various chemical industries for acid

catalyses.

So far, ZSM-5 has been prepared with tetra-n-

propyl ammonium hydroxide (TPAOH) as a

templating molecule (template) or structure-

directing agent. However, the cost of TPAOH

is very high.

Pore structure of ZSM-5

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In this study, the facile synthesis of ZSM-5 from

gels using a HMI template under varying reaction

conditions (such as Al2O3/SiO2, HMI/SiO2and H2O/

SiO2ratios, pHs, reaction times, etc.) was reported.

Especially the effects of MW aging were shown forthe synthesis of ZSM-5 from gels containing the

HMI template.

The obtained ZSM-5 was used in the dehydration of

simple alcohols such as ethanol and n-butanol, and

the results were also compared with those obtainedwith a commercial ZSM-5 zeolite in order to

estimate the potential applications of the produced

ZSM-5 zeolite.

3 dimensional structure of

ZSM-5

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7

15.1 g TEOS was hydrolyzed in

13.7 mL 0.3 M aqueous

solution of HCL at room temp.

for 2 h to get the gel mixture.

An aqueous solution was

obtained by mixing NaAlO2,

NaOH, hexamethylen eimine

(HMI) and water.

the above two solutions were placed in MW at 60 oC for 1

h to give the final synthesis gel mixture. The composition

of the gel was: SiO2 : X NaOH : Y AlO2: Z HMI : 20 H2O.

+

Finally, the slurry was transferred to a Teflon-lined stainless steel

autoclave and left to crystallize statically at 150 C. Products from the

synthesis were separated by centrifugation, followed with washing

with deionized water and air-drying at 100 C.

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XRD:

Bruker D2 Phaser

SEM:

Hitachi, S-4300

N2 ads.: Micromeritics,

Tristar II 3020

pH:

Horiba pH meter F-51

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N2

M.F.C

Feed

F.I.D

200

200

ReactionTemp. :

200450

Flow diagram of the processes Equipment used for the processes

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Results and discussion


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Sample

Synthesis conditions Textural properties

MW aging

temp.

[oC]

Synthesis

time

[d]

HMI/SiO2

ratio

H2O/SiO

2

ratio

BET

surface area

[m2/g]

Micropore

volume

[cm3/g]

Total pore

volume

[cm3/g]

A 30 3 0.6 20 248 0.09 0.14

B 60 3 0.6 20 333 0.13 0.23

C 90 5 0.6 20 308 0.11 0.19

D 120 5 0.6 20 292 0.11 0.18

E 60 3 1.2 20 312 0.12 0.19

F 60 3 0.6 12 325 0.12 0.20

Comm. - - - - 360 0.16 0.28

MW aging time was 1 h and the synthesis temp. was

175 oC. SiO2 to Al2O3molar ratio was taken as 60.

Typical composition: SiO2: 0.017 Al2O3: 0.075

Na2O: 0.6 HMI : 20 H2O0.0 0.2 0.4 0.6 0.8 1.0

0

30

60

90

120

A

B

C

D

E

F

Comm.

Quantityadsorbed(cm

3/g)

Relative pressure (P/Po)

N2adsorption isotherms

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0 20 40 60 80 100 1200.00

0.25

0.50

0.75

1.00

Relativecrystallinity

Time (h)

(b)

5 10 15 20 25 300

5000

10000

15000

20000

25000

(a)

Calculated

Intensity(a.u.)

2 theta (deg)

96 h

72 h

48 h

36 h

24 h

18 h

6 h12 h

XRD patterns Relative crystallization curve

The XRD patterns matched nicely with those of the ZSM-5 (MFI) structure,suggesting that ZSM-5 zeolite can be obtained from the HMI template under suitable

conditions.

The X-ray crystallinity of the ZSM-5 increased with the reaction time up to 72 h and

there was no change in the XRD pattern with further increase in time up to 96 h.

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5 10 15 20 25 300

1500

3000

4500

After 3 dIntensity(a.u.)

2 theta (degree)

After 7 d

(c)

5 10 15 20 25 300

2000

4000

6000

8000

After 7 d

After 3 d

Intensity(a.u.)

2 theta (degree)

(a)

5 10 15 20 25 300

1000

2000

3000

4000

After 3 d

After 7 d *

*

*

**

**

(b)

Intensity(a.u.)

2 theta (degree)

*

5 10 15 20 25 300

300

600

900

1200

(d)

Intensity(a.u.

)

2 theta (degree)

After 7 d

After 3 d

Only MW aging was very effective in the ZSM-5

synthesis up to 4 d (after 7 d, an unknown impurity phase

was observed);

Aging under conventional heating was not efficient (aging

by conventional heating at 60 oC and aging at room

temperature led to amorphous materials and MFI/MOR

mixed zeolites (after 7 d), respectively)

Syntheses without aging led only to amorphous materials.

MW, 60 oC, 1 h Stirred, 25 oC, 20 h Stirred, 60 oC, 20 h

Without significant aging

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5 10 15 20 25 30 35 400

5000

10000

15000

20000

25000SiO

2/Al

2O

3= 80

SiO2/Al

2O

3= 60

SiO2/Al

2O

3= 40

SiO2/Al

2O

3= 20

SiO2/Al

2O

3= 10

Intensity

(a.u.)

2 theta (degree)

ZSM-5 was obtained from gels with a

SiO2/Al2O3 ratio of 40 60. A

SiO2/Al2O3 ratio of 80 or 10 leads to

an amorphous phase.

Zeolite gmelinite (GME structure) was

obtained at a SiO2/Al2O3ratio of 20.

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10 15 20 25 300

4000

8000

12000

16000

H2O / SiO

2= 12

H2O / SiO2= 16

H2O / SiO

2= 20

H2O / SiO

2= 60

Intensity(a.u.)

2 theta (degree)

(a)

10 15 20 25 300

10000

20000

30000

40000

HMI / SiO2= 1.2

HMI / SiO2= 0.6

HMI / SiO2= 0.3

Intensity(a.u.)

2 theta (degree)

(b)

Effect of water content Effect of HMI content

A very diluted precursor (H2O/SiO2=60) led to amorphous materials, and a ZSM-5

with low crystallinity was obtained with precursors having a low HMI content

(HMI/SiO2=0.3).

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5 10 15 20 25 300

5000

10000

15000

20000

Intensity(a.u.)

2 theta (degree)

pH 9.8

pH 11.5

pH 12.3

pH 12.8

pH 13.5

the pH of the precursor was also very important

for the crystallization of ZSM-5 zeolites.

A pH of 12.8 was the optimum basicity for the

synthesis.

Higher and lower pH led to poor crystallinity

and amorphous (or dense-phase) materials,

respectively.

Even though the synthesis condition is quitenarrow, highly porous ZSM-5 can be

synthesized.

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10 20 300

2500

5000

7500

10000

240 min

120 min

60 min

30 min

10 min

Intensity(a.u.)

2 theta (degree)

A long or short aging time (at 60 oC) was not

effective for the crystallization of ZSM-5, and

60 min were the optimum duration for aging.

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5 10 15 20 25 300

7000

14000

21000

28000

30oC

60oC

90oC

120oC

Intensity(a.u.)

2 theta (degree)

(b)

5 10 15 20 25 300

5000

10000

15000

20000

30oC

60 oC

90oC

120oC

Intensity(a.u.)

2 theta (degree)

(a)

The crystallinity of the zeolite decreased as the aging temperature increased

above 60 oC.

The optimum aging temperature was 60 oC because a low temperature of 30oC was also not effective to produce highly crystalline ZSM-5.

3 d synthesis 5 d synthesis

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100 200 300 400 500

H-ZSM-5 (HMI)

H-ZSM-5 (comm.)

Intensity(a.u.)

Temp. (oC)

synthesis temp. = 175 oC,

Synthesis time = 3 d,

SiO2/Al2O3= 60.

The ammonia-TPD, confirms the acid strength and

acid concentration of H-ZSM-5(HMI) obtained with

the HMI template are very similar to those of a

commercial ZSM-5 zeolite (H-ZSM-5(Comm.)).

Moreover, the synthesized H-ZSM-5(HMI) has not

only weak but also strong acid sites. Therefore, the

ZSM-5(HMI) can be used in various acid-catalyzed

reactions.

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Ethanol 250 ~ 400 oC

N2pretreatment,

Feed = 0.1 cc/h,

Catalyst = 0.2g,

WHSV = 0.3

Temp.

Selectivity (mol %)

C2 C3 C4C5

/C6+

Benz

ene

Tolue

ne

Ethylbe

nzene

Xyle

ne

Cum

eneC9

+

250 oC 92.7 0.9 2.3 2.1 - - 0.2 0.4 0.1 1.1

400 oC 14.8 13.3 5.6 4.1 1.0 9.1 2.1 18.8 5.4 25.8

At the low temperature of 250 oC, ethanol is converted mainly into ethylene

through a dehydration reaction, similar to reported results.

Not only olefins but also aromatics such as xylenes and toluene were obtained

at 400o

C with the zeolite.

Aromatics are produced because of aromatization of the formed ethylene or

olefins. Therefore, the results of the ethanol conversion show the acidity of the

ZSM-5(HMI), in agreement with the ammonia TPD result.

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Temp. Zeolite

Selectivity (mol %)

C2 C3 C4C5

/C6+

Benz

ene

Tolu

ene

Ethy

lben

zene

Xyl

ene

Cu

me

ne

C9+

250 oC

H-ZSM-

5(Comm.) 0.1 0.9 79.3 6.4 1.2 2.9 0.3 2.3 2.8 3.9

H-ZSM-5(HMI) 0 1.2 94.8 0.5 0.2 1.5 0.1 1.1 0.2 0.1

400 oC

H-ZSM-

5(Comm.)8.6 16.3 8.8 7.3 1.2 13.3 1.5

20.

34.5 18.2

H-ZSM-5(HMI) 9.0 27.4 7.2 2.6 3.5 21.6 1.217.

22.8 7.4

Butanol 200 ~ 400 oC

N2pretreatment,Feed = 0.1 cc/h,

Catalyst = 0.2g,

WHSV = 0.3

HMI ZSM-5 (60), at 12 h

Temp. ZeoliteC

4

1-B T-2-B C-2-B

250 oCH-ZSM-5(Commercial) 14.9 53.3 31.8

H-ZSM-5(HMI) 16.6 50.9 32.6

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4 6 8 10 12

0

20

40

60

80

100

Conversion&

selectivity

Time (hr)

Conversion

C3

C4

C5C6

Aromatics

4 6 8 10 12

0

20

40

60

80

100

Conversion&

selectivity

Time (hr)

Conversion

C3

C4

C5C6

Aromatics

H-ZSM-5 (HMI) H-ZSM-5 (Comm.)

The two zeolites produced mainly butenes at 250 oC and the conversions, irrespective of

the zeolites, were very stable up to 12 h at that temperature.

The selectivity for butenes such as 1-butene, cis-2-butene and trans-2-butene did not

remarkably depend on the catalysts (Table 3).

The selectivity for butenes over H-ZSM-5(HMI) was higher than that over H-ZSM-

5(Comm.)

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10 m 1.0 m

H-ZSM-5 (HMI) H-ZSM-5 (comm.)

Higher crystal size was obtained for H-ZSM-5 synthesized from HMI.

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Commercially valuable ZSM-5 zeolite can be produced from gels containing HMI asan inexpensive template.

For the successful synthesis, selected conditions should be followed. Some of them

are strict aging under MW irradiation (60 oC for 1 h), a SiO2/Al2O3ratio of 40-60, pH of

~ 12.8 and so on.

When the aging time under MW was too long or too short, or when the aging

temperature was too high, only amorphous phase was produced.

The synthesized ZSM-5 was converted into H-ZSM-5 by ion exchange and could be

used in acid-catalyzed reactions because of the acidic property of the obtained H-ZSM-5.

The H-ZSM-5 produced by the HMI template was comparable to the commercial H-

ZSM-5 in TPD patterns and in its performance of dehydrating simple alcohols.

It can be concluded that the produced H-ZSM-5 can be used in various acid-catalyzed

reactions.

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Thank you for your kind attention

synthesis of zsm-5 with hexamethylineimine

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