[acs symposium series] zeolite synthesis volume 398 || synthesis of vpi-5

Chapter 21

Synthesis of VPI-5

Mark E. Davis1, Consuelo Montes1, and Juan M. Garces2

1Department of Chemical Engineering, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061 2Dow Chemical Company, Midland, MI 48640

We report here, for the first time, the synthetic procedures used to crystallize the aluminophosphate molecular sieve VPI-5. Two synthesis methods are illustrated. The step by step procedures are discussed i n d e t a i l and reveal the precise nature of synthesizing VPI-5.

The f i r s t discovery of a zeolite was recorded in 1756 (1). Since that time numerous natural and synthetic ze o l i t e s , s i l i c a polymorphs, and aluminophosphate-based molecular sieves have been reported. The largest ring i n these materials consists of 12 tetrahedral (12 T) atoms. This boundary has been in existence for over 180 years since the f i r s t zeolite to contain 12 T-atom rings, gmelinite, was discovered i n 1807 (1). Recently, we have synthesized the f i r s t molecular sieve with rings that possess greater than 12 T-atoms (2,3). Virginia Polytechnic Institute number 5 (VPI-5) is a family of aluminophosphate based molecular sieves with the same three-dimensional topology. The extra-large pores of VPI-5 contain unidimensional channels circumscribed by rings which have 18 T-atoms and possess free diameters of approximately 12 À (2,3).

We report here, for the f i r s t time, the synthesis procedures used to c r y s t a l l i z e the extra-large pore, aluminophosphate, molecular sieve VPI-5. Synthesis techniques for cr y s t a l l i z a t i o n of element substituted VPI-5 are forthcoming (Davis, M. E. , et a l . , Zeolites '89, in press)

Experimental Section

Pseudoboehmite alumina (Catapal-B) and 85 wt% H3PO4 were used exclusively as the aluminum and phosphorus starting materials. Aqueous (55 wt%) tetrabutylammonium hydroxide (TBA) and n-dipropylamine (DPA) were purchased from A l f a and Aldrich, respectively.

0097-6156/89/0398-0291$06.00/0 ο 1989 American Chemical Society

Dow

nloa

ded

by I

OW

A S

TA

TE

UN

IV o

n Se

ptem

ber

27, 2

013

| http

://pu

bs.a

cs.o

rg

Pub

licat

ion

Dat

e: J

uly

31, 1

989

| doi

: 10.

1021

/bk-

1989

-039

8.ch

021

In Zeolite Synthesis; Occelli, M., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

292 Z E O L I T E S Y N T H E S I S

A typical synthesis procedure involves the following steps: (i) alumina is slurried in water, ( i i ) phosphoric acid is diluted in water, ( i i i ) the phosphoric acid solution i s added to the alumina slurry, (iv) the aluminophosphate precursor mixture i s aged at ambient conditions, (v) an organic i s added to the precursor mixture and aged with rapid agitation to form the f i n a l gel, which (vi) is charged into the autoclave and heated. The gel composition can be written as

χ R · y A I 2 O 3 · ζ Ρ 2 0 5 · g H20.

Exploratory syntheses were accomplished i n 15 ml Teflon-lined autoclaves which were sta t i c a l l y heated at autogenous pressure in forced convection ovens. Larger autoclaves (300 ml, 600 ml, and above) have also been successfully employed. At specified times, the autoclaves were removed from the oven, quenched in cold water, and the pH of the contents measured. Product VPI-5 was recovered by slurrying the autoclave contents in water, decanting the supernatant l i q u i d , f i l t e r i n g the white solid, and drying the crystals in ambient air.

A Stoe 12 X-ray diffractometer was used to collect X-ray powder diffraction data. Figure 1 illustrates the X-ray powder diffraction pattern for VPI-5. Scanning electron micrographs were obtained using a Cambridge Instruments Stereoscan 200 scanning electron microscope.

Results and Discussion

We have synthesized VPI-5 with a variety of organic agents such as amines and quaternary ammonium cations. The synthesis procedure depends upon the type of organic agent and we w i l l i l l u s t r a t e an "amine" synthesis with DPA and a "quat." synthesis with TBA. Table I l i s t s reproducible procedures. We have provided an example of a "small" scale synthesis (DPA) and a f a i r l y "large" scale synthesis (TBA) to show that these procedures can be scaled-up. Below we discuss the essential details of these two procedures. VPI-5 that has been crystallized with the use of DPA and TBA w i l l be denoted DPA-VPI-5 and TBA-VPI-5, respectively.

Synthesis Using DPA. The synthesis of DPA-VPI-5 is summarized in Table I and is f u l l y described as follows. Upon combining the alumina slurry with the phosphoric acid solution, the pH of the precursor mixture rises with aging (see Fig. 2). Thus, the phosphoric acid i s slowly reacting with the alumina. The pH stabilizes around 1.2-1.3 after approximately 1.5 hours. This aging process i s important for the formation of VPI-5. If the precursor mixture is not aged and a l l other steps of the procedure followed, H3 (4,J>) i s usually c r y s t a l l i z e d . H3 i s an aluminophosphate hydrate ( A I P O 4 · 1.5 H20) f i r s t synthesized by d'Yvoire (4) . The structure of H3 has been solved (5) and contains 4,6, and 8 membered rings. Aging times as long as approximately 10 hours s t i l l y i e l d VPI-5. Upon addition of the DPA to the s t i r r i n g precursor mixture the pH immediately increases to above 3 and then gradually climbs to a f i n a l value of approximately 3.75 (see Fig. 2). Again, the aging of the complete

Dow

nloa

ded

by I

OW

A S

TA

TE

UN

IV o

n Se

ptem

ber

27, 2

013

| http

://pu

bs.a

cs.o

rg

Pub

licat

ion

Dat

e: J

uly

31, 1

989

| doi

: 10.

1021

/bk-

1989

-039

8.ch

021


DAVIS ET AL. Synthesis ofVPI-5

2© d ( Â ) 5.38 16.43 100 9.32 9.49 2

10.75 8.23 14 14.26 6.21 6 16.16 5.48 2 18.68 4.75 6 21.76 4.08 20 21.92 4.05 22 22.39 3.97 14 22.56 3.94 15 23.59 3.77 10 24.46 3.64 4 26.12 3.41 2 27.17 3.28 16 28.19 3.17 5 28.96 3.08 7 29.48 3.03 4 30.28 2.95 8 30.88 2.90 5 32.71 2.74 7 34.05 2.63 2 35.86 2.50 3 38.32 2.35 3

Figure 1 0 X-ray powder diffraction pattern of VPI-5,

Dow

nloa

ded

by I

OW

A S

TA

TE

UN

IV o

n Se

ptem

ber

27, 2

013

| http

://pu

bs.a

cs.o

rg

Pub

licat

ion

Dat

e: J

uly

31, 1

989

| doi

: 10.

1021

/bk-

1989

-039

8.ch

021


Tabl

e I.

Sy

nthe

sis

Proc

edur

es for

VPI-5

Wit

h DPA

and

TBA

DPA

1· 6.9

g of

pseudoboehmite

are

slur

ried in

20

g of w

ater

2.

10 g o

f wa

ter

are added

to 11.5

g of

ph

osph

oric

aci

d 3.

The

phos

phor

ic a

cid

solu

tion is

added t

o th

e al

umin

a sl

urry t

o form a

pre

curs

or mix

ture

4.

The

prec

urso

r mi

xtur

e is

aged

for 1.5-2

hour

s at a

mbient

con

diti

ons

with

ag

itat

ion

5.

5.1

g of

DPA ar

e added

to the

pre

curs

or

mixt

ure

and

the

resu

ltin

g ge

l aged

wit

h ag

itat

ion

for 1.5-2

hour

s at

ambient

con

diti

ons

6.

The

reac

tion mi

xtur

e is

hea

ted at

142°C for

20-24

hour

s

gel

comp

osit

ion:

DPA

· Al

o0_

· P.0_ · 40 H_0

2 3

2 5

2

TBA

1.

55 g

of ps

eudo

boeh

mite

are

slu

rrie

d in

150

g of

wat

er

2.

100

g of

wat

er a

re added t

o 90 g

of

phos

phor

ic a

cid

3.

The

phos

phor

ic a

cid

solu

tion i

s added

to the

al

umin

ium

slur

ry t

o fo

rm a

pre

curs

or mix

ture

4.

The

prec

urso

r mi

xtur

e is

aged

for 1.5-

3 ho

urs

at a

mbient

con

diti

ons

with n

o ag

itat

ion

5.

186

g of

55

wtj

TBA

are added

to the

pr

ecur

sor mi

xtur

e and

the

resu

ltin

g ge

l vi

goro

usly

agi

tate

d fo

r ap

prox

imat

ely

2 ho

urs at

ambient

con

diti

ons

6.

The

reac

tion m

ixtu

re i

s he

ated

at

150

C fo

r 24 h

ours

gel

comp

osit

ion:

TBA

. Al

0

. Ρ 0

. 50 HO

Dow

nloa

ded

by I

OW

A S

TA

TE

UN

IV o

n Se

ptem

ber

27, 2

013

| http

://pu

bs.a

cs.o

rg

Pub

licat

ion

Dat

e: J

uly

31, 1

989

| doi

: 10.

1021

/bk-

1989

-039

8.ch

021


21. DAVIS ET AL. Synthesis ofVPI-5 295

gel i s important. Since the pH slowly rises during this time period, a chemical reaction is occurring. If the gel is aged for too long of period, e.g., 24 hours, H3 is crystallized rather than VPI-5.

τ ι 1 1 1—ι 1 1 Γ Gel Preporot ion Crys ta l l i za t ion

0 I 1 1 I I I I I I I 0 40 80 120 160 200 0 8 16 24 32

Minutes Hours Time

Figure 2. pH versus time for the synthesis of DPA-VPI-5.

The c r y s t a l l i z a t i o n of VPI-5 occurs at 142°C, and the crystallization time is fast. From Figures 2 and 3 i t is observed that within five hours the pH of the autoclave contents has reached a plateau and the product is quite crystalline. In Figure 3 we illus t r a t e the degree of cr y s t a l l i n i t y estimated from X-ray powder d i f f r a c t i o n data as a function of time. Since VPI-5 quickly crystallizes, the values shown at short times are rough estimates only. Notice, however, that the DPA-VPI-5 is not stable for long periods of time in the mother liquor, and that the loss of c r y s t a l l i n i t y is not accompanied by a change in pH. We specify a cry s t a l l i z a t i o n time of 20-24 hours in Table I since we have observed that slight variations in the procedure normally lengthen the time for the onset of crystallization. However, we almost always observe the highest c r y s t a l l i n i t y in the samples which have been crystallized for 20-24 hours.

The crystallization temperature can be varied ± 5°C with no adverse effects. At temperatures above 150°C VPI-5 forms with H3 then quickly decomposes and ultimately AlPO^-ll is crystallized. At temperatures around 125°C the solid product is amorphous at 24 hours but eventually forms H3 after several days.

Table II illustrates the effect of gel composition on the fi n a l product crystallized using the procedure l i s t e d in Table I.

Dow

nloa

ded

by I

OW

A S

TA

TE

UN

IV o

n Se

ptem

ber

27, 2

013

| http

://pu

bs.a

cs.o

rg

Pub

licat

ion

Dat

e: J

uly

31, 1

989

| doi

: 10.

1021

/bk-

1989

-039

8.ch

021


Tabl

e II

. Va

riat

ion in

Gel

Com

posi

tion W

ith DPA

Synt

hesi

s

Prep

arat

ion

DPA

Al Ο

2 3

Ρ 0 2U5

H 20

Resu

lt

1 2 3 4 5 6 7 8 9 10

11

1.0

1.0

1.0

0.5

2.0

1.00

1.10

0.90

0.75

1.25

1.00

1.00

1.00

1.00

1.00

1.00

1.00

1.00

1.00

1.00

1.00

0.75

1.25

1.00

1.00

1.00

1.00

40

40

40

40

40

40

40

35

45

40

40

VPI-5

VPI-5

VPI-5

VPI-5 + H3

unknown*

unknown*

H3 + unknown*

VPI-5

with

sl

ight

ly

lowe

r cr

ysta

llin

ity

VPI-5 + H3*»

H3

amorphous

•Most

like

ly d

ense

phase a

lumi

noph

osph

ate

••Re

quir

ed l

onge

r cr

ysta

lliz

atio

n ti

me

Dow

nloa

ded

by I

OW

A S

TA

TE

UN

IV o

n Se

ptem

ber

27, 2

013

| http

://pu

bs.a

cs.o

rg

Pub

licat

ion

Dat

e: J

uly

31, 1

989

| doi

: 10.

1021

/bk-

1989

-039

8.ch

021


21. DAVIS ET AL. Synthesis of VPI-5 297

100 -

° 50-

12 16 20 24 Crystallization Time, hours

Figure 3. Degree of c r y s t a l l i n i t y estimated from X-ray powder diffraction data versus crystallization time.

Notice that small compositional variations (preparations 1-3) are allowable. However, ± 25% variations in gel composition do not cryst a l l i z e pure DPA-VPI-5. It is interesting to note that the water content is important and that excess DPA (preparation 11) hinders the crystallization of VPI-5.

Synthesis With TBA. As with the DPA-VPI-5 crystallization, the TBA synthesis involves the use of a precursor aluminophosphate mixture. (This is summarized also in Table I.) However, there is an important distinction between the two types of syntheses during step 4. When TBA is used, the precursor mixture is not agitated. The quiescent mixture exhibits a pH profile in time nearly that with agitation (see Figures 2 and 4). If the precursor mixture is agitated during aging, either TBA-VPI-5 is formed and accompanied by H3 or only H3 is crystallized.

The precursor gel is vigorously agitated just prior to the addition of TBAOH. When the TBAOH i s combined with the aluminophosphate mixture the pH instantly rises to around 5. The fi n a l pH is dependent upon the degree of mixing during addition of TBAOH. Incomplete mixing produces pH's below 5 and can lead to the formation of impure TBA-VPI-5 (with small amounts of H3 present).

The TBA gel crystallizes VPI-5 rapidly and reaches a fi n a l pH equivalent to that observed with DPA (see Figures 3 and 4). For reasons similar to those outlined in the DPA synthesis, we specify approximately 24 hours of crystallization time when using TBA (in Table I). Notice that the TBA-VPI-5 does not decompose in the mother liquor. We have observed that the TBA-VPI-5 is stable in the mother liquor for many days. It is interesting that the fi n a l pH of the TBA and DPA syntheses are approximately the same yet the TBA-VPI-5 is stable while the DPA-VPI-5 is not.

Dow

nloa

ded

by I

OW

A S

TA

TE

UN

IV o

n Se

ptem

ber

27, 2

013

| http

://pu

bs.a

cs.o

rg

Pub

licat

ion

Dat

e: J

uly

31, 1

989

| doi

: 10.

1021

/bk-

1989

-039

8.ch

021


298 ZEOLITE SYNTHESIS

τ 1 Γ

Gel Preparat ion Crys ta l l i za t ion

0 40 80 120 160 200 0 8 Γ6 24, 32 Minutes Hours

Time

Figure 4. pH versus time for the synthesis of TBA-VPI-5.

Morphology. Figures 5 , 6 , and 7 show scanning electron micrographs which i l l u s t r a t e the morphology of TBA-VPI-5, DPA-VPI-5, and H3 respectively. The TBA-VPI-5 crystals have "needle-like" morphology and are aggregated into bundles. The crystals are approximately 10 microns in length and are submicron in diameter. We suspect that the c-axis and thus the 12 Â pore is oriented in the direction of the needle length. On the other hand, the DPA-VPI-5 shows large spherical aggregates (greater than 100 microns). Inspection of these aggregates reveals particles which adopt a variety of morphologies. Spheres of approximately 5 microns are observed as well as needles (see Figure 6 b ) . From adsorption experiments (ref. 3, sample 1 - TBA-VPI-5, sample 2 -DPA-VPI-5), i t has been determined that the void volume of TBA-VPI-5 is equivalent to DPA-VPI-5. Therefore, the 5 micron spheres in DPA-VPI-5 are not impurities but must also be DPA-VPI-5 with a different or very small crystal habit. The morphology of H3 is illustrated since i t typically is the impurity present when VPI-5 is not crystallized properly. H3 is observed as spherical aggregates of approximately 20 micron diameter. These aggregates are easily distinguished from TBA-VPI-5 by optical microscope. However, since DPA-VPI-5 grows in large spherical aggregates i t is more d i f f i c u l t to differentiate from H3 with only a optical microscope. However, we presently are able to do so and use the difference in size (Λ/ 100 μ versus Λ/20 μ) as the distinguishing feature.

Adsorption. Table III shows the adsorption capacity of AlPO^-5 and VPI-5 for various adsorbates. A l l values l i s t e d are obtained at P/P 0 - 0.4. The data f or A I P O 4 - 5 (except f o r

Dow

nloa

ded

by I

OW

A S

TA

TE

UN

IV o

n Se

ptem

ber

27, 2

013

| http

://pu

bs.a

cs.o

rg

Pub

licat

ion

Dat

e: J

uly

31, 1

989

| doi

: 10.

1021

/bk-

1989

-039

8.ch

021


21. DAVIS ET Synthesis ofVPI-5 299

Figure 5. Scanning e l e c t r o n micrographs of TBA-VPI-5. (A) bar s i z e i s 50 microns, (B) bar s i z e i s 20 microns.

Dow

nloa

ded

by I

OW

A S

TA

TE

UN

IV o

n Se

ptem

ber

27, 2

013

| http

://pu

bs.a

cs.o

rg

Pub

licat

ion

Dat

e: J

uly

31, 1

989

| doi

: 10.

1021

/bk-

1989

-039

8.ch

021



Figure 6. Scanning electron micrographs of DPA-VPI-5. (A) bar size is 100 microns, (B) bar size is 20 microns.

Dow

nloa

ded

by I

OW

A S

TA

TE

UN

IV o

n Se

ptem

ber

27, 2

013

| http

://pu

bs.a

cs.o

rg

Pub

licat

ion

Dat

e: J

uly

31, 1

989

| doi

: 10.

1021

/bk-

1989

-039

8.ch

021



Figure 7. Scanning electron micrographs of H3. (A) bar size is 100 microns, (B) bar size is 20 microns.

Dow

nloa

ded

by I

OW

A S

TA

TE

UN

IV o

n Se

ptem

ber

27, 2

013

| http

://pu

bs.a

cs.o

rg

Pub

licat

ion

Dat

e: J

uly

31, 1

989

| doi

: 10.

1021

/bk-

1989

-039

8.ch

021


Tabl

e II

I.

Adso

rpti

on cap

acit

y of

mol

ecul

ar s

ieve

s at

P/P

= 0.4

Capa

city

, cm^/g

Kine

tic

Diam

eter

, X

Adso

rbat

eb Al

PO^-

50 VPI-5

3.46

°2

0.146

0.228

4.30

n-Hexane

0.139

0.198

6.00

Cycl

ohex

ane

0.145

0.156

6.20

Neopentane

0.137

0.148

8.50

Trii

sopr

opyl

benz

ene

0.02

1a

0.117

From

Dav

is e

t al

., J.

Am. Chem.

Soc,

sub

mitt

ed.

bAds

orpt

ion

at room

temp

erat

ure

exce

pt f

or 0

whic

h was

perf

orme

d at

eit

her

liqu

id

N 2 or

02 te

mper

atur

es.

cFro

m re

f, 6. D

ownl

oade

d by

IO

WA

ST

AT

E U

NIV

on

Sept

embe

r 27

, 201

3 | h

ttp://

pubs

.acs

.org

P

ublic

atio

n D

ate:

Jul

y 31

, 198

9 | d

oi: 1

0.10

21/b

k-19

89-0

398.

ch02

1



triisopropylbenzene) are from Union Carbide (6). The VPI-5 data were obtained using a McBain-Bakr apparatus and the samples were activated by heating to 350°C under vacuum overnight (Davis et a l . , J. Am. Chem. Soc, submitted). ΑΙΡΟ^-δ adsorbs oxygen and the hydrocarbons l i s t e d except for triisopropylbenzene. The triisopropylbenzene is too large to penetrate the 12 T-atom ring. Notice that the adsorption capacity of AlPO^-5 is the same, within experimental error, for a l l adsorbates listed. VPI-5 reveals two phenomena not observed for AlPO^-5. First, triisopropylbenzene is adsorbed. Second, the adsorption capacity monotonically decreases with increasing adsorbate size. Since VPI-5 contains pores that are s l i g h t l y larger than 12 Â, a l l adsorbates other than triisopropylbenzene have the possibility of f i t t i n g more than one molecule across the diameter. In other words, packing of adsorbate molecules may be important in these extra-large pores. Further evidence to support this ideas is provided elsewhere (Davis et a l . , J. Am. Chem. Soc, submitted).

Perfluorotributylamine (PFTBA) has a kin e t i c diameter greater than 10 Â (Λ, 10.5 Â ) . After repeated attempts to adsorb PFTBA into VPI-5, we were convinced that our data were influenced by e x t r a c r y s t a l l i n e adsorption. Thus, we performed PFTBA desorption experiments u t i l i z i n g a thermogravimetric analyzer in which the off-gas was transferred into a mass spectrometer. A I P O 4 - 5 was used for comparison since PFTBA cannot adsorb in a 12 T-atom ring. A I P O 4 - 5 and VPI-5 were loaded with PFTBA. Next, A I P O 4 - 5 was heated to 100°C in flowing helium in the apparatus described previously. After several hours, a stable weight was obtained (PFTBA loss observed i n the mass spectrometer). Upon heating AlPO^-5 to_550°C, no further weight loss was observed. Thus, PFTBA can be desorbed from an A I P O 4 surface by flowing helium at 100°C. The same treatment was employed for VPI-5. After reaching a stable weight in flowing helium at 100°C, the sample was heated to 550°C. Several higher temperature desorption peaks were due to the loss of PFTBA. We interpret this result to indicate that PFTBA can adsorb within the 18 T-atom rings of VPI-5. Thus, adsorption of molecules with kinetic diameters above 10 Â is possible with VPI-5.

Acknowledgments

We thank the National Science Foundation and the Dow Chemical Company for support of this work through the Presidential Young Investigator Award to M.E.D.

Literature Cited 1. Breck, D. W., Zeolite Molecular Sieves: Wiley: New York,

1974; p. 188. 2. Davis, M. E.; Saldarriaga, C.; Montes, C.; Garces, J.;

Crowder, C. Nature 1988, 331, 698. 3. Davis, M. E.; Saldarriaga, C.; Montes, C.; Garces, J.;

Crowder, C. Zeolites 1988, 8, 362. 4. d'Yvoire, F. Bull. Soc. Chim 1962, 1762. 5. Pluth, J. J.; Smith, J. V. Nature 1985, 318, 165.

Dow

nloa

ded

by I

OW

A S

TA

TE

UN

IV o

n Se

ptem

ber

27, 2

013

| http

://pu

bs.a

cs.o

rg

Pub

licat

ion

Dat

e: J

uly

31, 1

989

| doi

: 10.

1021

/bk-

1989

-039

8.ch

021



6. Wilson, S. T.; Lok, Β. M.; Messina, C. Α.; Flanigen, Ε. M. Proceedings of the Sixth International Zeolite Conference. Butterworths: Survey, 1985; p. 97.

RECEIVED December 22, 1988

Dow

nloa

ded

by I

OW

A S

TA

TE

UN

IV o

n Se

ptem

ber

27, 2

013

| http

://pu

bs.a

cs.o

rg

Pub

licat

ion

Dat

e: J

uly

31, 1

989

| doi

: 10.

1021

/bk-

1989

-039

8.ch

021


[acs symposium series] zeolite synthesis volume 398 || synthesis of vpi-5

Documents