Activity, selectivity and stability of bimetallic catalysts inn-paraffin and cyclopentane reforming

AppliedCatalysis, 32 (1987)117-132 Elsevier Science Publishers B.V., Amsterdam

ACTIVITY,

SELECTIVITY

AND STABILITY

CYCLOPENTANE

REFORMING

J.M.

C.A. QUERINI,

PARERA,

Instituto Estero

117 -

Printed

OF BIMETALLIC

J.N. BELTRAMINI

de Investigaciones

in The Netherlands

en Catdlisis

CATALYSTS

IN n-PARAFFIN

AND

and N.S. FIGOLI y Petroquimica

- INCAPE - Santiago

de1

2654 - 3000 Santa Fe, Argentina.

(Received

25 August

1986, accepted

9 March

1987)

ABSTRACT Cataly ,tic activity, selectivit and stability under commercial conditions of and monometal lit (Pt/A1203, 30 kg cm- ?!) and bimetallic catalysts (Pt-Re-S/A1203 Pt-Ge/Al203, 15 kg cm-2) were compared in the reforming of nC5-nC1D paraffins, Under such conditions, the order of cyclopentane and methylcyclopentane. activity for n-paraffin transformation is Pt/A1203 > Pt-Re-S/A1203 > Pt-Ge/A1203 being Pt/A1203 the most active for hydrocracking, Pt-Re-S/A1203 for aromatization and Pt-Ge/Al203 for isomerization. Pt/A1203 has a minimum in coke formation and deactivation when n-heptane is fed, whereas on the bimetallics coke formation and deactivation increase from n-C5 with the increase in the n-paraffin length. Naphthenes of 5 C ring are the greatest coke producers on the three catalysts. Experiments with the bimetallics changing temperature showed that both catalysts have the same trend in selectivity, but for a similar selectivity the temperature must be 15-20°C higher in Pt-Ge/A1203 than in Pt-Re-S/A1203. These results and the comparison with literature data show the complexity of the phenomenon and the danger of extrapolating results to different experimental conditions.

INTRODUCTION Several

bifunctional

of naphtha Pt/A1203,

reforming.

metal-acid

catalysts

are used

was patented

[I]. Later,

Pt was promoted

bi or multimetallic

Ir, Pt-Re-Ir,

etc.,

does not mean

that Re, Sn and Ge are in the metallic

technical another

different

Pt-Re/A1203

with A1203

pretreatments. literature to metallic

depend

components

0166-9834/87/$03.50

compound

of Re associated

quoted

the oxidation

state;

and Biloen

with A1203

of catalyst

the conflicting

Science

to group VIII

Publishers

B.V.

obtaining Pt-Ge,

alumina.

PtThis

all or part of them

[2] stated

in which

with

Pt;

chlorine

preparation

points

that in

can

the surface

of view

state of Re. The same concepts

that do not belong

0 1987 Elsevier

Pt-Sn,

on chlorided

with Pt or forming

on the conditions

The same authors

regarding

supported

Sachtler

other metals

have Pt-Re,

process

monometallic

part of the Re can be associated

as a surface

The fractions

which

function"

to zero.

catalysts,

part can appear

be involved. compound

as "metallic

catalysts

catalyst,

with

the so-called

may have a valence

in the commercial

In 1949, the first bifunctional

and on in the

are applied

of the Periodic

Table.

118 Bowman

and Biloen

[3] found an interaction typical of alloying on Pt-Ge/A1203; +4 and Ge +* by reduction at 550°C and that they also found the presence of Ge +2 and Ge'. it was necessary to heat to 650°C to have Ge When

the element

Ir, the metallic selective

catalysts

the bimetallic

lower pressures selectivity

is passivated

catalyst.

have higher

and lower recycle

(savings

a more

is inactive,

like Sn or

of several

with hydrocarbons

besides

selectivity

cuts

catalysts,

one. For under

of a better

operational

catalysts

under

their

andnaphthacuts.

and stability

of Pt/A1203

[4], and then compared

with

during

the

C51 and with the reforming of a naphtha doped the same catalyst

Pt-Re-S/Al203

with those of Pt/A1203

units,

requirements).

using pure hydrocarbons

[61. In this paper,

bimetallic

the advantage

less gases)

heater

were studied

naphtha

in commercial

the mono and bimetallic

conditions,

reforming

than the monometallic

gas ratios with

In previous papers, the activity, pure hydrocarbons

compared

like Re or

thus obtaining

element

stability

and hydrogen,

to compare

operational

commercial

sulfur,

are operated,

in power and charge

It is interesting

reforming

with

the second

catalysts

(more aromatics

commercial

When

for hydrogenolysis,

is not necessary.

The bimetallic this reason

to Pt is very active

function

and stable

Ge, sulfidation

economy

added

properties

and Pt-Ge/Al203,

for n-paraffins

of two

are studied

and cyclopentanes

and

reforming.

EXPERIMENTAL The following percentages -

catalysts

on the catalyst

Pt(0.37)/A1203-Cl(D.90),

were

used (numbers

between

prepared

according

-

The metal

-

dispersion,

calculated

Commercial

Pt(0.33)-Re(0.32)/A1203-Cl(0.90);

dispersion

of 65% (by chemisorption

fided with

a 0.06 mol% H2S in H2 stream

H2 was passed Commercial n-Pentane, cyclopentane bed, were

to [SJ was 80%.

as provided

of O2 at 25°C).

as

has a total metallic

This catalyst

was sul-

at 500°C and 1 atm for 4 h, and then yielding

0.03%

S.

Pt(0.37)-Ge(0.24)/A1203-Cl(0.81). n-hexane,

n-heptane,

n-octane,

Erba RP, dehydrated

activity

n-decane,

by passage

cyclopentane

through

and stability

were determined

test using a bench scale flow equipment

The test included

hydrocarbon

according

CK-300

(Amsterdam)

and methyl-

a molecular

sieve 4 A

used as feed.

deactivation

4; WHSV

Cyanamid

over for 8 h at the same temperature

Carlo

Catalytic

conditions

are the weight

to 171, using alumina

(Sg = 200 m2 g-1, Vg = 0.48 cm3 g-') from Ketjen support.

brackets

dried at 120°C):

three

similar

periods

at 515°C.

to the commercial

for the bimetallic

of an accelerated

described

elsewhere

[9,10].

and third

period were under -2 (P = 30 kg cm ; H2: -2 and P = 15 kg cm ; H2:hydrocarbon =

ones for each catalyst

= 8; WHSV = 6 h-' for Pt/A1203

= 4 h-'

The first

by means

catalysts)

for 7 h. The second

period was

119 under more

severe

for Pt/A1203 bimetallic

catalysts)

On starting

515°C before

feeding

period).

produced

Conversion

on the catalysts

and expressed

and Pt-Ge/A1203,

changing

as weight

at each temperature

room to

kept for 2 h at

during

squalane after

operated

of the catalyst period

liquid yield

in temperature

programmed

by combustion-

and selectivity

using n-heptane in 10°C steps,

the chromatographic

in these experiments

and

on the catalysts.

on activity

from 450 to 550°C

(severe

data using alOOmx

the test was determined

percent

is

in total conversion

the second

total conversion,

runs were performed

before

after stabilization,

and the difference

is taken as a measure

of temperature

the temperature

conditions

rate from

and was

from on line gas chromatography

coated with

To see the influence A1203

in the first period, activity,

to each product,

column

Coke content

volumetry,

at constant

hydrogen,

by the coke deposited

were calculated

0.2 mm capillary mode.

conversion of catalyst

the first and third periods

selectivities

was heated

over 6 h in flowing

the hydrocarbon.

hydrocarbon

deactivation

= 4; WHSV = 6 h-l

= 2 and WHSV = 4 h-l for the

for 20 h.

(515°C)

taken as a measure between

(P = IO kg cm-*; H*:hydrocarbon

the run, the catalyst

run temperature

Total

conditions

and P = 3.5 kg cm -*; H*:hydrocarbon

were similar

analysis.

of Pt-Re-S/

as feed and remaining

Other

to those during

one hour

operational

the first

period

of the test.

RESULTS n-Paraffins Figure

Activity. paraffins

1 shows the values

fed as a function

is taken as a measure transformed

of the catalytic

into products

to activities

deactivation

and n-C6 reforming, number.

is the less active Selectivity. reforming

activity

per 100 g of feed.

of the second

30 kg cm-*) and Pt-Re-S/A1203

atoms

atoms

at the end of the first period

the accelerated

carbon

of the total

of their carbon

hydrocracking: fed x lO*/total

conversion

as.grams

the third one

respectively.

have different

of feed

lines correspond (after

Pt/A1203

activities

activities

are similar

for paraffins

of higher

Under

experimental

conditions

of this work

Pt-GelA1203

catalyst

for all the n-paraffins

selectivity

(at

for n-C5

whereas

Percent

is defined

and is defined

and during

of the n-

The total

Full and dashed

period),

(at 15 kg cm-')

conversion

number.

tested.

for each type of products

of n-paraffins

as:

conversion

to n-paraffins

of lower carbon

atom number

than that

conversion.

isomerization:conversion

to isomers

the n-paraffin

fed x lO*/total

aromatization:

conversion

of equal or smaller

carbon

conversion.

to aromatics

x lO*/total

conversion.

atom number

than

120 cyclization:

conversion

to non-aromatic

cyclic

hydrocarbons

x lOLltotal

con-

version. The sum of these four selectivities includes

the formation

genation

involving

generally

called

of C,, which

is 100%. Our definition

is produced

only the metallic

function.

mainly

of hydrocracking

by cracking

This metallic

and hydro-

raction

is

hydrogenolysis.

* t

90 x

Pt-Re-S/Al203

l

Pt -Ge/A12

*-

/_

/I ‘x’

\

/

\ ‘\

\

30 ‘t

FIGURE

1

carbon

atoms

Total

deactivated

.A ‘a

\

w’ I

I

I

I

6

7

8

9

10

NUMBER

OF

CARBON

I

5

conversion

of n-paraffins

Dashed

to define

conversion

i-C4 (isomerization formation:

Figure

9 --.

lines,

ATOMS

as a function

catalysts.

activity

of their number

Full lines,

in the third

activity

period

of

at the end

(catalyst

by coke).

formation:

methane

/

/

i

for mono and bimetallic

It is important gas

/

I

of the first period.

--._I(,

/

r\ \\

I

O3

other

selectivities:

n-C4 (hydrocracking ;2* c3' x 10 /total conversion.

to C,,

product) conversion

to Cl x lO'/total

2 shows the selectivities,

products)

and to

conversion.

in the first

period

of the test, for the

2

Dashed

to cyclization

(C,-C4).

J

as a function

and hydrocracking

ATOMS

.

ISOMERIZATION

9

fed.

of monometallic

7

AROMATIZATION

CYCLIZATION

Pt-Ge /A1203

of the number of carbon atoms of the n-paraffin

isomerization

CARBON

aromatization,

DE

HY DROCRACKING

line, C, formation.

catalysts

Pt-Re-S/A1203

ISOMERIZATION

(naphthenes),

NUMBER

Dotted

from ref. 141) and bimetallic

Selectivities

line, gas formation

partially

FIGURE

AROMATIZATION

Pt/AL20,

(data

E

122 TABLE

1

Average

selectivity

reforming

on mono and bimetallic

at the end of the first

of the accelerated

deactivation

Reaction

catalysts

(I) period

for n-paraffins

and during

the third

(C,-C,,) period

(III)

test.

Catalyst:

Pt/A1203

Period:

I

Pt-Re-S/A1203

III

Pt-Ge/A1203

III

I

I

III

Hydrocracking

45

38

31

32

23

27

Isomerization

27

41

38

47

51

56

26

17

29

18

24

13

2

4

2

3

2

4

[4]) and bimetallic

catalysts.

Aromatization

’

Cyclization

monometallic able that,

(partially

of the n-C5 to gaseous reforming

on Pt-Ge/A1203

monometallic

catalyst

but the bimetallics Methane

(dotted

The maximum

selectivity

gas formation

length

values

decreases.

are shown

values

for the third period

Pt/AlpG3,

Pt-Ge/A1203

&Stability. du$ng,the

Table

The

in n-C8,

small on the bimetallic from n-C6 reforming

the C, production

on Pt/A1203

the length of the paraffin

in Table

isomerization

The average

1. The values

of carbon

test when

deposited

n-paraffins

by

for the first

in a similar

2 shows the amount

from

(from n-C5

in Figure

and aromatization

respectively.

deactivation

increases

of each type of product

were calculated

(III)

n-C6, and

2; the

way. The highest correspond

to

on the catalysts

were

fed. Pt shows

th% m&ir&m deposition when the feed is n-C7. On the bimetallic catalysts, .I ca_?boq formation is always increased on increasing the n-paraffin length. Fi&r3'3rshows pe$o$

$3 the test

Fipr512or mihm&n

the drop

in total conversion

(difference

each catalyst).

with

is important

is found with

The aromatization

and Pt-Re-S/A1203,

accelerated

of n-C5

is particularly

and hydrocracking

for the three catalysts.

(I) of the test are the areas

to hydrocracking,

most

reforming.

period

seTectivities .,

cracks

is very small.

2) is very

catalyst,

by increasing

the isomerization

the paraffin

from n-C5

It is notice-

Pt/A1203

in the zone n-C6 to n-C8.

to isomerization

with n-C5;

behavior

of C, was 2.1% produced

and n-hexane

selectivity

on the bimetallics

This

lines in Figure

amount

conditions,

i-C5 is the main product

where gas formation

On the monometallic

only for n-pentane

to n-C,o)

while

and Pt-Ge/A1203.

has a minimum

the greatest

these maxima,

operational

have a maximum

formation

Pt-Re-S/A1203.

increasing

products,

on Pt-Re-S/A1203

remarkable

catalysts:

from ref.

under the corresponding

in values

between between

the first and the third

full and dashed

In the case of Pt/A1203,

&hen the feed is n-C7 whereas

the

the curve

with the bimetallics

lines

presents

in a

the deactivation

123 TABLE

2

Coke deposited n-Paraffin

on the catalysts

fed

(wt%) after

the test.

Pt/A1203

Pt-Re-S/A1203

n-C5

0.79

0.97

1.35

n-C6

0.44

2.25

3.90

Pt-Ge/A1203

n-C7

0.25

3.95

5.15

n-CB

0.61

5.40

5.50

n-c1o

1.29

7.52

6.00

!3 1

7

Pt /A1203

I

7

5

6

7 8 OF CARBON

NUMBER

FIGURE

3 Drop

deposition

in total conversion

as a function

increases

with the length

period

of the test is much

(and coke formation)

10

of carbon

of accelerated atoms

of the paraffin.

higher with

are higher

9 ATOMS

as a consequence

of the number

always

t

I

I

of the n-paraffin

As the severity

the bimetallics,

on the bimetallics

coke

the falls

fed.

of the second in activity

than on the monometallic

catalyst. As shown formation accelerated

in Table

increased

1, aromatization on the three

coke deposition.

decreased

catalysts

and isomerization

during

and naphthenes

the third period,

after

the

124 TABLE

3

Reforming

of cyclopentane.

and conversion during

Total conversion,

to each productb

the third

(III)

period

of the deactivation

Pt/A1203

101.50

on cit.

c2

(7 h) and

Pt-Ge/Al203

I

III

18.68

5.67

9.97

3.08

100.08

99.64

100.91

99.74

3.94

cl

on catalyst

test.

III

I

9.89

106.58

Liquid yield Carbon

III

46.58

conversion

carbon

(I) period

Pt-Re-S/A1203

I Total

liquid yield,

at the end of the first

-

9.76

-

11.2

Oa

0.02

0.14

0.03

0.10

0

0.87

0.13

0.49

0.15

0.20

0.06

c3 i-C4

1.20

0.19

1.00

0.23

0.05

0.05

0.28

0

0.18

0

0

0

n-C4

0.64

0

0.45

0.03

0.08

0

2.25

5.05

0.30

2.89

0.10

0

0.13

0.22

0

0

21 .93a

i-C5 olef.

0

C5

n-C5

20. 25a

6.05

6.81

0.98

3.75

0

CPe

0.74

1.25

2.98

3.66

2.66

2.87

BZ

0.24

0

0.14

0

0

0

CH

0

0

0.31

0

0.11

0

Toluene

0.44

0

0.74

0.07

0.13

0

EBz

0

0

0.07

0

0

0

m-xyl

0

0

0.11

0

0

0

o-xyl

0

0

0.07

0

0

0

LThe first analysis Ci = paraffin Bz = benzene;

with

(at 44 min) showed i carbon

atoms;

CH = cyclohexane;

9.9% Cl, 12.5%

n = normal;

E = ethyl;

i-C5 and 8.3% n-C5.

i = iso; CPe = cyclopentene;

xyl = xylene.

Cyclopentanes Table

3 shows the reforming

was the most active is defined

as the volume

liquid yield Pt/A1203,

is higher

n-C5

of cyclopentane

and Pt-Ge/A1203

of liquid

products

than 100% because

2.26% on Pt-Re-S/Al

cyclopentane ducts:

catalyst

0

on the three catalysts; the least active.

(C,+) per 100 ml of feed. This

the gas formation

and 0.43% on Pt-Ge/A1203)

(CP) (0.75 g cm- 5 ) 3.IS higher

ring opening, to cyclopentene

the gas formation

catalysts.

(2.99% on

Coke deposition

of

of the main pro-

Ring opening

and the isomerization,

(CPe) is increased.

is small

and the density

than the densities

(0.63 g cms3) and i-C5 (0.62 g cm-").

on the mono than on the bimetallic

Pt/A1203

The liquid yield

is more extensive deactivates

the

but the dehydrogenation

125 TABLE

4

Reforming catalyst

(III)

of methylcyclopentane. and conversion

periods

Total

to different

of the deactivation

Total

conversion

Liquid yield Carbon

III

carbon

Pt-Ge/A1203

I

I

III

III

67.30

98.10

13.20

89.20

11.50

93.20

96.90

80.30

98.70

84.00

99.00

13.00

12.50

0.87

0.60

1.37

0.23

0.52

0.16

0.94

0.73

1.69

0.37

0.76

0.23 0.11

4 n-C4

0.56

0.39

1.15

0.10

0.49

0.55

0.47

1.06

0.23

0.46

0.13

I-butene

0

0

0

0.07

0

0

i-C5

0.65

0.22

0.92

0.04

0.29

0.02

n-C

0.44

0.24

0.65

0.07

0.18

0.03

ZAB

1.97

0.36

0.80

0

0.59

0

CPe

0

0

0

0.74

0

0.05

CP

0

0

0.36

0

0

0

23DMB

0

2MP

12.34

1.09

0.58

0.36

0.72

0.21

9.06

3.67

0.66

3.39

0.35

3MP

8.10

6.55

2.68

0.57

2.31

0.30

n-C6

11.99

14.60

3.40

3.12

4.19

2.71

62

45.48

28.07

78.20

3.71

74.2

3.27

MCPe

0

0

0.08

2.74

0.43

3.05

CH

7.49

4.42

0

0.59,

0.01

0.64

n-C

7 Toluene

0

0.09

0.17

0

0

0.14

0.12

0.12

0.61

0.11

0.39

0.06

EBz

0

0.07

0.25

0

0.12

0

m-xyl

0.07

0.13

0.41

0.11

0.17

0

o-xyl

0.05

0.05

0

0

0

0

aSame

symbols

as Table

on

(I) and third

Pt-Re-S/A1203

3.09

c3 i-C

the first

91.60

on cat.

cl + c2

liquid yield,

during

test.a

Pt/Al203 I

conversion,

products

3. CP = cyclopentane;

D = di; M = methyl;

B = butane;

P = pentane.

Table catalysts,

4 shows the results conversion

dehydroisomerization

of methylcyclopentane

is higher to benzene

reforming.

than that of CP and the main Bz. Pt-Ge/A1203

For the three reaction

is the more selective

is the catalyst

126 for dehydroisomerization

to Bz. The smallest

Pt-Ge/Al203

(2.23%),

and the highest

the highest

activity

for opening

amount

affects

(2MP) is higher

(3MP) on the three catalysts

the n-C6 production

of gases

during

to a lesser extent

is produced

(5.27%).

the 5 C ring producing

of n-C6 and 2-methylpentane

methylpentane

amount

by Pt-Re-S/Al203

Pt/A1203

C6 paraffins.

than the amount period

by

shows

The

of 3-

I; coke deposition

than the production

of its

isomers. In the mono as well as in the bimetallic coke producers.

More carbon

of the n-paraffins

tested

was deposited

catalysts

cyclopentanes

are major

from CP and MCP than deposited

by any

(n-C5 to n-C,6).

100

450

FIGURE 4 1, Total

500 TEMPERATURE

Conversion

of n-heptane

conversion;

hydrocracking

2, conversion

and hydrogenolysis

,*C

as a function

of temperature

to isomerization products;

products;

4, conversion

on Pt-Re-S/A1203. 3, conversion

to aromatization

to pro-

ducts.

Runs at different Figures

4 and 5 show the conversion

as a function Both catalysts (at 464°C

temperatures

of temperature show a similar

for Pt-Re-S/Al203

of n-heptane

for Pt-Re-S/A1203 trend;

to each group of products

and Pt-GelA1203,

isomerization

passes

and 486°C for Pt-Ge/A1203),

respectively.

through

a maximum

and hydrocracking

and

127

TEMPERATURE FIGURE Legends

5

Conversion

of n-heptane

the same as in Figure

aromatization

always

increase.

,*C

as a function

of temperature

The n-heptane

total conversion

and reaches

100% at 520°C with Pt-Re-S/A1203;

with

and reaches

100% at 540°C.

observed

isomerization Conversion

to isomers

Pt-Ge/A1203. Pt-Ge/Al203

The main

at low temperatures

The trend requires

reactions

while

Pt-Ge/A1203

and hydrocracking

and to aromatic

520°C on Pt-Re-S/A1203,

on Pt-GelAl203.

4.

products

a similar

is similar

value

15-20°C

is 24% at 450°C

on both catalysts

at higher

higher

are

temperatures.

have the same value (22%) is reached

for both catalysts,

a temperature

is 52% at 450°C

(24%) at

at 535°C on

but for the same results

than that required

by Pt-Re-S/

A1203.

DISCUSSION The simplified follows

reaction

network

for catalytic

reforming

on n-heptane

[lo]:

.

aromatization

n-heptane

isomerization

toluene aromatization T i-heptane -1

hydrocracking

light paraffins (C,-Cc)

is as

128

According forming

to this scheme,

of n-paraffins;

functional

mechanism

a bifunctional cracking

a) cyclization

controlled

reaction

to lighter

controlled

there are three types of reactions

controlled

paraffins,

by the acidic

middle

of the paraffinic

called

hydrogenolysis)

mainly

C,. i-Heptane

and aromatization,

by the acidic

by the acidic

produced

function chain

function,

either

function,

and producing

mainly

only the metallic

is an intermediate

product

which

can be transformed

contact

time or temperature,

or by using a more active

produced outlet.

from

i-C7 will decrease,

This simple

reaction

products

conditions,

Pt/Al203

selectivity producing

There

the lowest

and Pt-Ge/A1203

4 and 5) and the paraffin

Regarding produces

bimetallic

many

than Pt/Al203

that the reforming

1 and Figure

was made

pressure. because

by operating

Under

these

hydrocracking

was

a) the Pt/A1203

Pt-Re-S/Al203

was the catalyst

the highest

differences

2.

depend

liquid yield,

on temperature

feed.

selectivity,

more aromatics

the different

in Table

the one with These

being the main reaction.

On the other

of i-C7 at the reactor

for this behavior:

pressure.

into

increasing

and light paraffins

reforming

liquid yield

are two reasons

more aromatics,

(Figures

as was shown

used commercial

and b) the high hydrogen

isomerization

stated

produced

the amount

of n-paraffins

its most commonly

by

catalyst.

of toluene

can be used to explain

reforming,

the comparison

under

the main reaction.

scheme

of paraffins

In our studies, each catalyst

reaction

increasing

(generally

and producing

is increased

the amount

at the

mechanism

function

this transformation

is deactivated,

mechanism

the rupture

and light paraffins;

if the catalyst

by a bi-

and c) hydro-

by a bifunctional

toluene

hand,

produced

b) isomerizat-ion, also

[II] or by a monofunctional

involving

in the re-

authors

[12,13],

of n-C7 produces

more

agree

that Pt-Re-S/Al203

and Aboul-Gheit

et al. Cl41

isomerization

on Pt-Ge/A1203

than on Pt/A1203. The length of the n-paraffin (Figure

2) showed

temperature,

kinetic

trend;

increment

than

from n-C6 up,

The reasons

feasibility

the length

increases.

of the n-paraffin,

kinetic

found

that the values

are not are

the length

kinetics

of the

is higher follow

a

the rate of all the

reaches

the highest

were found for Pt/A1203

the reforming

when

are of

The increment

[15]. The reaction

level. These

n-C,g on Pt(0.30)/A1203

decreases

two reactions

and on increasing

and the rate of aromatization results

at the same

and hydrogenolysis

is increased

Krane et al. [I61 studying

Our results

for this behavior

[15]. The other

equilibrium,

in isomerization

by increasing

in selectivity.

and the isomerization

Hydrocracking

limitations

the thermodynamic

in aromatization

authors:

nature.

by the thermodynamic

reactions

increases

is increased.

to thermodynamic

n-paraffin,

similar

length

and thermodynamic

subjected limited

that on the three catalysts,

the aromatization

the n-paraffin

is very important

by several

of n-C6, n-C+,

n-C8,

of the rate constants

n-Cg and

for dehydro-

129 TABLE

5

Relative

reaction

rates of n-C6 and n-C7 under severe

reforming

conditions.

Paraffin Reaction n-C Isomerization

n-C7

6

10

13

Aromatization

1

4

Hydrocracking

3

4

cyclization

are 0.00, 0.58,

of hydrocracking 0.27,

0.32, 0.35,

cyclization

that the reactivity

increases

of hydrocarbons,

mass,

the aromatization

increasing

more.

general

main differences these

increase

reactions

therefore,

on passing

for naphtha

reforming

in Table

is the most

for rapid

to our results It seems

regarding

changes

added

state different

of n-paraffins

and Pt-Ge/A1203. function

of these catalysts

having

with Ge. This affects

rates

5. The value

and according

catalysts

by the acidic

on the second metal an oxidation

molecular

reaction

and Pt-Ge/A1203.

and aromatization

Pt-Re-S/A1203

are controlled

the acid functions

controlled

that the highest

[18],

that a

of

length.

for isomerization between

of paraffins

Kmak and Stuckey

from n-C6 to n-C7, aromatization

in the case of Pt-Re-S/A1203,

with the paraffin

Selectivities

are shown

[17] showed

is proportional

The relative

All these data refer to Pt/A1203,

trend exists

selectivity

conditions,

of n-C6 is taken as unity and isomerization

All the rates

the same happens

showed

are

in dehydro-

for aromatization

the lower paraffins. catalyst

value)

and Dynkina

from n-C6 to n-C,o.

concentrations,

react before

of n-C6 and n-C7 for a commercial

reaction.

i.e., the increase

under reforming

of magnitude

and the values

hydrocracking

Rabinovich

and that the rate constant

plots of hydrocarbon

paraffins

(highest

than in hydrocracking.

by two orders

in their weight

1.81 and 2.54 respectively,

of the chain

0.55 and 1.24 respectively,

is higher

to the molecular

1.33,

in the middle

to zero with

the acid function

It is considered of the catalyst

should

to Pt. Re can be associated

are the

be different

either

the support.

and the selectivities

with

that

[Ill, depending

Pt or,

The same is true for reactions

by this function.

The main

reaction

of cyclopentane

reforming

is ring opening.

Pt/A1203

most active

catalyst

and Pt-Ge/A1203

the

active

the smallest

amount

of gas. For cyclopentane

sPlectivities Regarding operational Coughlin

to those

for n-paraffins

coke formation conditions

reforming,

less

producing

the catalysts

present

similar

reforming.

on mono and bimetallic

catalysts

were the same for all the catalysts),

et al. [ZO] and Parera

is the

et al. [12] found

(in each study, Guisnet

that Pt-Re-S/A1203

et al. [19], produces

130 less coke than Pt/A1203.

Carter

et al. C.211 stated

is more stable

than Pt/A1203,

both produce

to the results

in this paper,

Franck

with

n-C7 that the coke content

and Martin0

run under similar

the first produces

times more

Our results

show that the deactivating

were

was observed

produced

with n-C5

predominantly, genolysis

is less important. products,

affected

e.g.,

It is interesting

(see Table

to analyze

is a demanding

site [23]. A small amount

paraffins

of metal

to the metallic genolysis

the ring rupture

[24]; the higher

and smaller deposition decrease

to Gault

producing

the ratio the larger is higher

from ring rupture deposit

eliminates

As a conclusion, monometallic

is nonselective

from

is sensitive MCP hydro-

producing

the

33% 3MP, 67% 2MP and 0% n-C6. The ratio to infer the size of the Pt crystals According

the first

when the catalyst similar

on the acidic

on selectivity

the large ensembles

the bimetallic

one. The second metal

of 2MP,

metal

ring they

influence

Ir by van of carbon

Sites

causing

intermediates.

catalysts changes

A similar

in the case of

of contiguous

to the singlesite

and secondly,

that the presence

coke

by a

or nonselective

function.

was found

as a possibility,

Then,

The concentrations

reactions

4, in

of the test

to the one produced

crystallites.

in several

to Table period

is coked.

not in the ratio of selective

they are consumed

shift from the multisite

atoms

only one or a

selectivity

et al. [24], during

the crystals.

in selectivity

et al, [25] who stated,

the surface

metal

C, formation

that require

than 0.5 during

the third period,

has an effect

of the carbonaceous Senden

reactions

the reaction

in the size of the metallic

could originate

of parafThe C,

20% 3MP, 40% 2MP and 40% n-C6. On large Pt crystals,

the ratio

firstly

(rupture

of several

poisoning

than other

3MP and n-C6 are however, rupture;

is less

on the metal is enough to decrease

Also the MCP ring opening

is selective

during

since they produce

reaction

an ensemble

of coke

can be taken as a guide by which

our catalysts

hydro-

-giving paraffins).

extent

distribution

occurs

reforming

1).

requiring

according

The highest

deactivation

Isomerisation

atoms.

structure;

severe

differently

isomerised.

of many atoms,

on small Pt crystallites

statistical

3MP/n-C6

reaction

of ensembles

to a higher

small number

behave

on catalyst

hydrogenolysis

In C,.

the hydrogenolysis

formation

higher and

show that

functions.

but the most

of cyclopentanes

as active

the number

of coke depends

poisoned.

Bimetallics

C, and ring opening

conditions

on the catalyst

n-C5 is mainly

by coke deposition

fins giving

greatly

action

In n-C5 reforming

most severely

different

experiments

times

on Pt(0.37)-Ge(0.24)

operational

in C,. reforming,

reforming.

a reaction

in their

is three

coke than the second.

and how the coke is deposited

coke deposits

Pt-Re/A1203

of coke. Similarly

[22] found

Our experiments

on Pt(O.33)-Re(0.32)/A1203,

selectivity

amounts

of Pt(O.6)-Ge(0.22)/A1203

than that of Pt(O.6)-Re(O,6)/Al,O,.

thirteen

that although

similar

have better

selectivity

not only the metallic

than the

function

but

on a

131 also the acidic trolled

one and as the main

by the acidic

The main change

is the decrease

When Ge is the second the lowest,

metal,

producing,

compared

of n- and i-paraffins S/A1203 changing better.

selectivities results

can be quite

mono and bimetallic content

of metal

selectivity

catalysts

catalyzed

are deactivated

atoms of the metallic

and other catalysts on the methods

These

catalyst

Pt-Re-

but can be

of preparation

activities

and

in the-behavior

by the operational

differences

amount

found when comparing

the differences

are affected

on the catalysts.

in activity

and a higher

of aromatics;

treatments,

influence

are

in isomerization.

At one temperature,

amount

The differences

who studied

and, consequently,

The reactions opening)

different.

authors

is small,

depend

for different

of the catalysts;

from several

change

and selectivity

selectivity

the decrease

into aromatics.

the greatest

are expected.

of n- and i-paraffins.

an increase

with the monometallic

selectivities

activity

and con-

changes

and the hydrocracking

at the same temperature,

producing

the temperature,

and activation

in hydrocracking

the activity

is transformed

is the catalyst

Catalytic

are bifunctional selectivity

at the usual temperatures,

When Re is the second metal, and hydrocracking

reactions

those marked

function,

conditions

the

of and

catalyst

stability.

on the metallic

function

in a way that suggests

(C, formation

a decrease

and 5C ring

in the number

of

ensembles.

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1: 16 17 18

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