The conversion of 2-propanol over chrysotile

361

Applied Catalysis, 10 (1984) 361-368 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands

THE CONVERSION

Sadakatsu

SUZUKI and Yoshio

Department Tokyo

OF 2-PROPANOL

of Chemical

OVER CHRYSOTILE

ON0

Engineering,

Tokyo

Institute

of Technology,

Meguro-ku,

152, Japan.

(Received

3 January

1984, accepted

12 March

1984)

ABSTRACT Layered magnesium silicates with chrysotile structure were synthesized under hydrothermal conditions from the alkaline gels containing magnesium and silicon sources with varying ratio of Na20/Si02. The morphology and the thermal stability of the synthesized materials were characterized by electron microscopy, X-ray diffraction analysis, thermal analysis and surface area measurement. The conversion of 2-propanol (dehydration and dehydrogenation) was carried out over the materials in order to clarify the acid-base character of their surfaces, which were found to depend greatly on the Na20/Si02 ratio of the starting gel.

INTRODUCTION Chrysotile

Mg3(OH)4Si205

under hydrothermal and silicon

sources

from alkaline

active

Such applications

metal cations,

or part of the Mg(I1) Robson depended

like Ni(II),

that the physical

on the pH or on the Na20/Si02

2.5 and 2.0, and between

a change

is to examine

chrysotile reaction

centers,

Co(II) and Al(III),

in place of all

form of the synthesized

chrysotile

gel. Thus, thick wall

from gels with Na20/Si02

materials

in physical

properties

ratios between

while thin flakes were formed

and dehydrogenation

with changing

for 2-propanol

[4,53. Cracking

by

of isopropylbenzene

structure

was tested over

Na20/Si02

ratios. The

character

of the surfaces,

proceed

0 1984 Elsevier Science Publishers B.V.

crystal

conversion

for the acid-base of alcohols

is accompanied

The aim of the present work

from gels with varying

should give a good diagnosis

respectively

properties

activity

synthesized

form of a crystal

of the material.

in catalytic

Thus, catalytic

0166-9834/84/$03.00

by

could be obtained

1.5 and lower.

the change

since dehydration

for a

were reviewed

active materials

2.0 and 1.5, respectively,

that the change

in the surface

of chrysotile.

magnesium

with its high

or as a support

of the material

ratio of the starting

tubes and thin wall tubes were produced

It is expected

together

in the structure.

[3] reported

at ratios of about

and can be synthesized

or gel containing

structure

may be useful as a catalyst

species.

Swift [23. It is also known that catalytically by incorporating

silicate

solution

[I]. Because of its defined

surface area, chrysotile catalytically

is a layered magnesium

conditions

over acidic and basic was also examined.

362 EXPERIMENTAL The various

physical

the literature

[1,3]. Sodium metasilicate

mol) were dissolved magnesium

into water.

chloride

H20/Si02

forms of chrysotile

crystals

(0.15 mol) with stirring.

added.

was added an aqueous

Water was further

ratio to 65. The pH of the resulting

in an autoclave

(0 - 0.2

solution

of the

gel ranged from 7 to 13, depending

The resultant

mixture

and heated at 543 K for 24 h. After cooling,

determined

by the BET method.

thermal

analysis

was then placed

the insoluble

and dried at 383 K. The surface area of the produced Differential

to

added to adjust

was washed

were made with Shimadzu

according

(0.1 mol) and sodium hydroxide

To this solution

upon the amount of sodium hydroxide

were prepared

materials

product was

and thermogravimetry

TG-200, DT-POB and DTG-20 instruments, raising the temper-1 . Electron micrographs and X-ray diffraction patterns

ature at a rate of 5 K min were taken with JEOL-200cx The reactions was placed benzene)

and Phillips

were carried

PW/Oll instruments,

out in a continuous

in a reactor of silica tubing.

was delivered

by a motor-driven

The reactant syringe

respectively.

flow reactor.

The catalyst

(2-propanol

or isopropyl-

to be vaporized

in a preheating -1 (W/F) were 44 g h mol

zone of the reactor containing quartz. The contact times -1 and 78 g h mol for the reaction of 2-propanol and isopropylbenzene, Products

RESULTS

were analyzed

respectively.

by gas chromatography.

AND DISCUSSION

Physical

forms of chrysotile

Electron

micrographs

shape of the products starting tubular

(1 g)

of some of the products greatly

gel, in agreement crystals

with the description

100 - 300

the tubular

shape became obscure

ratio over 1.6 and below

chrysotile,

respectively,

The specific materials

in reference

amorphous.

from gels with Na20/Si02

[3]. At Na20/Si02

= 2,

As the Na20/Si02

ratio

l(b) and (c)). At a Na20/SiD2 The products

1.5 will be called

after the designation

1. The physical

(or the pH) of the

l(a). The outer and inner diameters

(Figures

surface area of the products

obtained

ratio

and 50 - 70 A, respectively.

ratio of 1.13, the product was apparently Na20/Si02

are shown in Figure

on the Na20/Si02

were formed as shown in Figure

of the tubes were decreased,

depended

tube-type

by Robson

paralleled

from gels with

and flake-type

[3].

morphology.

For the

ratio 1.0 - 1.1, the specific with

ratio.

area was about 130 m2 g-1.

For tube-type

chrysotile,

the specific

The values were in good agreement The change diffraction

in the structure

patterns

line became weaker

of the materials

respectively.

ratio increased,

The trend was particularly to diffraction

This indicates

ratios.

by X-ray every diffraction

significant

in the lines

from the (020) and the

that significant

in the piling of the layers at higher Na20/Si02

Na20/Si02

[3].

was also evidenced

(Figure 2). As the Na20/Si02

and broader.

at 2e = 12.1 and 24.4", which correspond (004) planes,

surface

with those in reference

increasing

surface

area was about 400 m ' g-I. The surface area decreased

irregularity

occurs

363

(a)

(b)

FIGURE

1

Electron

ratio of (a) 2.00,

micrographs

of chrysotiles

(b) 1.50 and (c) 1.38.

prepared

from gels with Na20/Si02

364

b

A

C

-

10

FIGURE 2

20

FIGURE 3

30 “29

X-ray diffraction

SiO2 ratio of (a) 2.00,

300

patterns

Thermogravimetric (a) tube-type

(b) flake-type

I

I

40 50 I degree

I

60

of chrysotile

70

prepared

from gels with Na,O/

(b) 1.75 and (c) 1.13

500 700 900 Temparature I K

chrysotile;

I

1

I

chrysotile

300

1100

analysis chrysotile prepared

500

900 700 Temparaturc I K

and differential prepared

thermal

1100

analysis

from gel with Na20/SiOp

from gel with Na20/Si02

of = 2.00,

= 1.13,

e

10 FIGURE 4

X-ray diffraction

temperatures; (d) calcined

20

30

pattern

(a) as prepared,

40 50 028 /degree of tube-type

(b) calcined

at 973 K, (e) calcined

60

70

chrysotile

calcined

at 773 K, (c) calcined

at 1073 K and (f) calcined

at various

at 873 K,

at 1173 K.

365 Thermal

stability

The results materials

of thermogravimetric

prepared

and thermal

from gels with Na20/Si02

differential

analyses

of the

ratio of 2.00 and 1.13 are shown

Figure

3. The tube-type

chrysotile

change

of the structure

occurs at 1050 K. In the case of the flake-type

dehydration

proceeds

calcination

temperature

pattern

was in conformity

was kept in an electric

As shown in Figure 4, calcination indicating

partial dehydration

disappearance

range indicating

of the tube-type with results

furnace

at 773 K decreased

of the crystal.

of all the diffraction calcined

of the thermal

the intensity

Calcination

indicative

lines,

over 973 K showed

of 2-propanol

ratios was carried

conversion

of 2-propanol

the conversion different.

out at 453

was obtained

With the flake-type product

samples.

flake-type

over samples

of new

to forsterite

materials

samples

cannot

above,

to a difference

than with the tube-type

Figure 6 shows the temperature

was observed

of both acidic

not mean thattherewere activity

by differences

in the surface

differs

between

in surface

structure

of the

of Z-propanol

[4,5]. Thus, the results

proceed shown in

samples. of 2-propanol

increased

conversion

with reaction

at all temperatures

over tube-

temperature.

studied,

confirming

The the

and basic sites.

The fact that dehydration

dehydrogenation

of the

sites exist on the surfcae of the flake-

dependence

The total conversion

area of the materials

and dehydrogenation

that much more acidic

of acetone

while for the

activity

the large difference

be explained

sites and basic sites, respectively

type chrysotile.

were also

exclusively

at 453 K shows that dehydration

It is known that dehydration

type samples

occurred

gel is low. Since the surface

area and should be ascribed

Figure 5 indicated

The products

is higher when the Na20/Si02

and flake-type

over acidic

samples.

dehydration

5, 100%

samples at 513 K. In contrast,

was formed with about 40% selectivity

at most by a factor of three, as described

materials.

from gels with different

and 513 K. As shown in Figure

for flake-type

samples,

(acetone)

The conversion

ratio of the starting

activity.

that the formation

prepared

was only 5 - 7% for the tube-type

the dehydration

presence

dehydration.

of 2-propanol

The conversion

formation

temperatures.

at 873 K led to

had taken place. Most of the new peaks were ascribed

tube-type

analyses.

of each line,

of complete

of materials

tube-type

with

for 12 h at designated

substance(s)

Na20/Si02

an inhomogeneous

chrysotile

The patterns

Conversion

chrysotile,

material.

in X-ray diffraction

The chrysotile

between 800 and 900 K and further

over a much wider temperature

nature of the flake-type The change

is dehydrated

in

no

exclusively

occurred

over flake-type

basic sites over flake-type

of the materials

To check this possibility,

samples,

could be masked

poisoning

materials,

might

since the

by high dehydration

of the acidic

sites by pyridine

366

s

. 60

Na20

FIGURE 5

Dependence

starting

of Z-propanol

gels; reaction

temperature

100

-

80

-

<60

1.5

I SiO2

conversion (0)

on the Na2O/SiO2

513 K and (A)

ratio of the

453 K.

-

9

e40

-

20

-

O-

500 600 700 Reaction Temparature I K

FIGURE 6

Dependence

of 2-propanol

tube-type

chrysotile

(0)

conversion

total conversion,

on the reaction

(0)

temperature

propene yield,

(A)

over

acetone

yield.

was attempted

as shown in Figure 7. The reaction

pure2-propanol.

100% conversion

After 2 h, pyridine

was added to the feed. The conversion

decreased

gradually,

expected.

At the same time, acetone

indicating

sites exist also on the surface absence

was started

of dehydrogenation

at 633 K by feeding

to propene and to diisopropylether

to dehydration

that acidic sites contribute started

to be formed.

of the flake-type

activity

products

to dehydration,

as

This implies that basic

materials,

is due to its masking

was observed.

and the apparent

by the very high activity

for dehydration.

Cracking

of isopropylbenzene

The activities

of various

chrysotile

materials

for isopropylbenzene

cracking

367

stream h5

3

Time on

FIGURE 7

Effect of pyridine

over flake-type

addition

I

on the conversion

chrysotile.

Experimental

under reaction

conditions

to propene

and acetone

data is in the text. Reaction

temperature

633 K.

were examined

since the reaction conversions obtained

of isopropylbenzene

cracking

did not proceed

from gels with Na20/Si02 conformity Bronsted

over Brdnsted

acid sites. The initial

were 23, 18 and 11% for the flake-type

from the gels with Na20/Si02

In contrast,

of W/F = 78 g mol h -I, 573 K, 101 kPa,

was known to proceed

ratio of 1.06, 1.13 and 1.38, respectively. over any of the tube-type

materials

ratio of 1.63, 1.30 and 2.00. These results

with the results

materials

of dehydration

of Z-propanol.

acid sites exist only on the flake-type

obtained

are in good

It is concluded

that

chrysotile.

Origin of acidic and basic sites It is clear that the surface acidic

of chrysotile

sites, but has a basic character.

of chrysotile the surface character

has no Brdnsted

should resemble

acidity

anions

It is expected

structure

those of silica or magnesium from a partially

have a nucleophilic

tendency

similar

has few.

that the ideal crystal

since all the OH groups

of the surface may originate

where oxygen

with tubular

(SiOH and MgOH) on

hydroxide.

The basic

dehydroxylated

MgOH layer,

to those on magnesium

oxide. The high acidity chrysotile

and basic character on the details amorphous cation similar

of flake-type

structure.

materials

[61, although

of the preparation

the extent method.

mixed oxides was considered

in an oxide structure structures

(flake-type).

could come from incompleteness

It is known that amorphous

depends

of the

has both acidic

on the ratio of MgO/SiO*

The origin

to be related

of another

could be formed

silica-magnesia

of the acidity to incorporation

metal cation

in the ill-defined

of the of a metal

[7]. It is conceivable structure

and

that

of chrysotile

368 REFERENCES 1 2 3 4 5 6 7

W. Nell, H. Hirscher and W. Syberts, Kolloid Z., 157 (1958) 1. H.E. Swift, in "Advanced materials in Catalysis", J.J. Burton and R.L. Garten, Eds., Academic Press, New York and London, (1977) 230. H.E. Robson, US Patent 3,804,701; 3,852,165. G.V. Krylov, in "Catalysis by Nonmetals", Academic Press, New York (1970) 116. T. Yashima, H. Suzuki and N. Hara, J. Catal., 33 (1974) 486. H. Niiyama and E. Echigoya, Bull. Chem. Sot. Japan, 45 (1972) 938. K. Tanabe, T. Sumiyoshi, K. Shibata, T. Kiyoura and J. Kitagasa, Bull. Chem. Sot. Japan, 47 (1974) 1064.