Single-Pellet Crush Strength Testing of Catalysts - American Chemical

Chapter 37

Single-Pellet Crush Strength Testing of Catalysts P. K . Brienza

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A S T M , 1916

1

Race Street, Philadelphia, PA 19103-1187

ASTM D-32 Committee on Catalysts has developed a standard test method for single pellet crush strength for formed catalyst shapes. This standard was issued under the fixed designation D-4179. The method is applicable to regular catalyst shapes such as tablets and spheres. Extrudates, granular materials and other irregular shapes are excluded. The committee continues to work on the development of a method for the single pellet crush strength testing of extrudates. S i n g l e p e l l e t c r u s h t e s t i n g has p l a y e d an i n t e g r a l p a r t i n i n d u s t r y f o r many y e a r s . Pharmaceutical companies, f o r example, c o n s i d e r t h e mechanical strength o f m e d i c i n a l t a b l e t s t o be an i m p o r t a n t p r o p e r t y . (1) With t h e development o f c a t a l y t i c p r o c e s s e s such as r e f o r m i n g , h y d r o c r a c k i n g and h y d r o t r e a t i n g , which u t i l i z e formed p a r t i c l e s , s i n g l e p e l l e t crush s t r e n g t h t e s t s were d e v i s e d by t h e m a n u f a c t u r e r s and u s e r s o f such c a t a l y s t s . These t e s t s were d e v e l o p e d i n order to determine the a b i l i t y of the c a t a l y s t p a r t i c l e s to m a i n t a i n i n t e g r i t y d u r i n g u s e i n c a t a l y t i c r e a c t o r s . (2) Due to v a r i a t i o n s i n sampling procedures, i n s t r u m e n t a t i o n , t e s t methods and p r e t r e a t m e n t c o n d i t i o n s , t h e r e has been g r e a t d i f f i c u l t y i n obtaining a g r e e m e n t among t h e t e s t s p e r f o r m e d i n d i f f e r e n t l a b o r a t o r i e s . (2) ASTM C o m m i t t e e D-32 o n C a t a l y s t s was o r g a n i z e d i n o r d e r t o s t a n d a r d i z e c a t a l y s t t e s t i n g and a Task Group b e g a n w o r k i n g on s i n g l e p e l l e t c r u s h m e t h o d s w i t h t h e formation of the committee. Two r o u n d r o b i n t e s t i n g p r o g r a m s w e r e c a r r i e d o u t u s i n g s p h e r e s , t a b l e t s and e x t r u d a t e s . Testing c o n d i t i o n s were c o n t r o l l e d i n o r d e r t o m i n i m i z e i n t e r - l a b o r a t o r y v a r i a t i o n s ; however, t h e use of Chairman of A S T M D32.02 Subcommittee on Physical-Mechanical Properties of A S T M D-32 Committee on Catalysts. Mailing address: 66 Emerson Avenue, Apt. B 18, Wall, NJ 07719

0097-6156/89/0411-0407$06.00/0 o 1989 American Chemical Society

In Characterization and Catalyst Development; Bradley, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

CHARACTERIZATION AND CATALYST DEVELOPMENT


408

i d e n t i c a l c r u s h t e s t i n s t r u m e n t s was not r e q u i r e d . T e s t equipment used i n c l u d e d l o a d c e l l h a r d n e s s testers, i n - h o u s e d e s i g n e d computer o p e r a t e d s y s t e m s and commercial crush t e s t apparatus. R e p r e s e n t a t i v e samples were p r o v i d e d and a t e s t p o r t i o n o f 50 t o 200 p e l l e t s was o b t a i n e d by r i f f l i n g or s p l i t t i n g . The samples were then h e a t e d a t 400°C f o r 3 h o u r s and c o o l e d i n a d e s i c c a t o r , s i n c e m o i s t u r e a b s o r p t i o n by h y g r o s c o p i c c a t a l y t i c m a t e r i a l s has been shown t o a f f e c t c r u s h i n g s t r e n g t h . (3) The c o m p r e s s i o n t e s t i n g d e v i c e was r e q u i r e d t o have a c a l i b r a t e d gauge and a s y s t e m t h a t p r o v i d e d a u n i f o r m r a t e o f f o r c e a p p l i c a t i o n i n t h e range o f 1 t o 10 l b f / s . The s i n g l e c a t a l y s t p e l l e t s o f s p h e r e s and t a b l e t s ( i n r a d i a l o r i e n t a t i o n ) were p l a c e d between the f l a t a n v i l s o f t h e c o m p r e s s i o n t e s t i n g i n s t r u m e n t by use of t w e e z e r s or o t h e r s u i t a b l e d e v i c e . F o r c e was then a p p l i e d a t a u n i f o r m r a t e i n t h e range o f 1 t o 10 l b f / s u n t i l t h e p e l l e t s c r u s h e d or c o l l a p s e d . When a l l t h e p e l l e t s i n t h e sample were t e s t e d , the a v e r a g e c r u s h s t r e n g t h , s t a n d a r d d e v i a t i o n and 80% s p r e a d were reported. The 80% s p r e a d was d e f i n e d as t h e range i n which 80% o f t h e i n d i v i d u a l p e l l e t s t r e n g t h s a r e e x p e c t e d t o f a l l , a s s u m i n g t h a t i n d i v i d u a l p e l l e t s form a normal d i s t r i b u t i o n . R e s u l t s o f t h e second round r o b i n t e s t i n g o f s p h e r e s and t a b l e t s a r e shown i n T a b l e s I and I I . These d a t a are i n c l u d e d i n ASTM R e s e a r c h R e p o r t Number 1004 f o r S t a n d a r d T e s t Method D-4179 f o r S i n g l e P e l l e t C r u s h S t r e n g t h o f Formed C a t a l y s t S h a p e s . Table

I.

Test Sample

Product

Characteristics

Mean Crush Strength(1)

( l b s . force)

Within-Sample

Variation

Std.

T y p i c a l 80% Spread(3)

Dev.(2)

1/8" S p h e r e s (EAS-480)

19.27

6.75

1/8" T a b l e t s (GSAT-480)

16.43

5 . 38

(1)

Mean o f 6 t e s t s

each by

(2)

A v e r a g e v a l u e o f the w i t h i n - s a m p l e d e v i a t i o n (S.D.) o f the 36 t e s t s .

(3)

Based on:

Mean S t r e n g t h

6

10.6

to

27.9

9.5

to

23.3

laboratories.

+ 1.28

S.D.

standard

within


sample.

37.

BRIENZA

Table


Test

409

Single-Pellet Crush Strength

Sample

I I . Test

Precision

(lbs.

Within a Laboratory 95% R e l i a b i l i t y of Mean o f 95% O v e r a l l 100 P e s . ( 1 ) Repeatability(2)

force) Between Labs 95% S p r e a d of Laboratory Means

1/8" S p h e r e s (EAS-480)

+ 1.40

+ 1.47

+ 1.15 (4)

1/8" T a b l e t s (GSAT-480)

+ 1.13

+ 1.34

+ 1.97

as +1.96 x S.D. w i t h i n - s a m p l e t V l O O

1)

Calculated

2)

I n c l u d e s R e l i a b i l i t y o f Mean o f 100 p i e c e s , p l u s w i t h i n - d a y and d a y - t o - d a y l a b o r a t o r y v a r i a t i o n .

3)

C a l c u l a t e d as +1.96 x S.D. o f l a b o r a t o r y a r o u n d g r a n d mean o f a l l l a b o r a t o r i e s .

4)

Based on c l a s s i f y i n g one o f t h e 6 r e p o r t i n g l a b o r a t o r i e s as an o u t l i e r . For a l l 6 l a b o r a t o r i e s the f i g u r e h e r e was +5.56.

means

S t a n d a r d D-4179 s p e c i f i c a l l y e x c l u d e s t h e t e s t i n g o f g r a n u l a r m a t e r i a l s , o t h e r i r r e g u l a r shapes and extrudates. I t was n e v e r p l a n n e d t o i n c l u d e i r r e g u l a r l y shaped m a t e r i a l s w i t h i n t h e s c o p e o f a s i n g l e p e l l e t c r u s h t e s t method; however, e x t r u d a t e t e s t i n g was included i n the o r i g i n a l procedure. T h i s was done by m o d i f y i n g one o f t h e f l a t a n v i l s t o form a 0.125 i n . b a r shaped c r o s s s e c t i o n on t h e a n v i l and r e p o r t i n g r e s u l t s as l b f / 0 . 1 2 5 i n . ( F i g u r e 1) The i n t e r l a b o r a t o r y p r e c i s i o n f o r e x t r u d a t e c r u s h s t r e n g t h t e s t i n g was so p o o r i n b o t h o f t h e round r o b i n s , t h a t i t was d e c i d e d t o p u b l i s h t h e method f o r r e g u l a r shapes o n l y , and have t h e t a s k group c o n t i n u e t o work t o improve e x t r u d a t e t e s t i n g . A s u b s e q u e n t round r o b i n , u s i n g t h r e e e x t r u d e d a l u m i n a s a m p l e s , showed n o t o n l y m u l t i - l a b e r r o r b u t poor w i t h i n - l a b r e p r o d u c i b i l i t y as w e l l ( T a b l e I I I ) . The p a r t i c i p a t i n g l a b o r a t o r i e s t h e n r e s p o n d e d t o a d e t a i l e d q u e s t i o n n a i r e regarding exact t e s t methodology. I t was d i s c o v e r e d t h a t t h r e e l a b o r a t o r i e s were u s i n g t e s t i n g p r a c t i c e s o u t s i d e t h e method. Two o f the l a b s were w i t h d r a w n from t h e r o u n d r o b i n , one b e c a u s e t h e f o r c e a p p l i c a t i o n d i d n o t comply w i t h t h e p r o c e d u r e r e q u i r e m e n t s and a s e c o n d b e c a u s e sample e x p o s u r e was t o o l o n g and t e s t i n g was n o t r e p e a t e d . The t h i r d l a b o r a t o r y repeated the t e s t using the c o r r e c t f o r c e a p p l i c a t i o n and d a t a from an a d d i t i o n a l l a b were


410


V 0.125" o r 3.18

Y

mm-


: A

F i g u r e 1. Method o f t e s t f o r r a d i a l of e x t r u d e d c a t a l y s t s h a p e s .

Table

III.

Extrudate

Extrudate Designat ion

Within sample var i a t i o n (+ 2S)

lbf

Strength

B

+.21

+ 4 .6%

+ .90

D

+.15

+ 2 . 3%

F

+.37

+ 5.0%

J E

J-5

% of X

lbf

+5.5%

+.43

+ 5.6%

+ . 75 +3.8%

+.34

+ 3 . 7%

+ 1 .22

+6.2%

+.65

+ 6.3%

+. 39

+ 4 . 3% + 1 .41

+5.1%

+.81

+ 5.6%

+.59

+ 5 . 2% + 1 . 45 +5.5%

+.92

+ 5.6%

+ 5 . 2%

+ 5 . 4% +12.9%

+. 33

+ 7 . 2% + 2 .67

+16.4% +.98

D

+.97

+15.1% + 1.92

+9.6%

F +1.82

+24.9% + 2 .55

+13.1%

J

+22.3% + 2 .05

+ 7 .4% +1.30

+30.9% + 2.42

+ 9 .2% +2.58

+2.00

Avg

% of X

+ 4.3%

B

E +3.50

MULTILAB ERROR

strength

K-6

l b f % of X

Avg TOTAL WITHIN LAB ERROR (+ 2S)

R a d i a l Crush

M-9

Lab

crush

+.90 +.82

+ 9.6% + 8.1% + 8 . 9% +15.8%

+20.1%

+11.1%

+ 11 . 1%

+69.3%

+45.3%

+64.6%



37.

BRIENZA

411


added. ( T a b l e I V ) . The r e v i s i o n s s i g n i f i c a n t l y r e d u c e d t h e d i f f e r e n c e s among l a b o r a t o r i e s , h o w e v e r , t h e r e s u l t s remained u n s a t i s f a c t o r y . The T a s k G r o u p t h e n d e c i d e d t o c o n d u c t a r o u n d r o b i n u s i n g p e n c i l l e a d s i n an a t t e m p t t o e s t a b l i s h a non-hygroscopic (albeit non-catalytic) standard. Results of t h i s round r o b i n (excluding laboratories u s i n g o t h e r t h a n 0.125 i n . a n v i l s ) , s h o w n i n T a b l e V, s t i l l demonstrate a less than s a t i s f a c t o r y i n t e r l a b o r a t o r y v a r i a t i o n i n c r u s h r e s u l t s among n i n e laboratories using d i f f e r e n t pieces of crush strength apparatus. I n a d d i t i o n , one o f t h e l a b o r a t o r i e s conducted experiments which i n d i c a t e d moisture

Table

IV.

Extrudate

Summary

Extrudate Designat ion

100 Within Sample Variation (+ 2S)

TOTAL WITHIN LAB ERROR ( + 2S)

Radial

Crush

of Revised

M-9

Strength

Results

J-5

K_J5

LAB

lbf

% OF X

D

+.15

+2.3%

+ . 75

+ 3.8%

+.34

+3.7%

F

+.37

+5.0%

+ 1.22

+ 6.2%

+.65

+6.3%

J

+.39

+4.4%

+ 1.41

+ 6.0%

+.81

+5.8%

I

+.44

+5.6%

+ 1 . 49

+ 6 . 0%

+.77

+6.2%

G

+.35

+4.1%

+ 1.22

+ 5 . 3%

+.70

+5.7%

Avg

+.34

+ 4 . 2 8 % + 1 . 22

+5.46%

+.65

+5.5%

D

+.97

+ 1 5 . 1 % + 1 .92

+ 9 . 6%

+.90

+9.6%

F

+1.82

+ 2 4 . 9 % + 2 .55

+ 1 3 . 1 % +.8 2

+8.1%

+ 8 . 7%

+1.30

+9.3%

J

lbf

+ 2 . 0 0 + 2 2 . 6 % + 2 . 05

% OF X

lbf

% OF X

I

+0.96

+ 1 2 . 4 % + 2 .63

+10.6%

+1.37

+11.0%

G

+2.08

+ 2 4 . 7 % + 5 . 06

+22.4%

+3.58

+27.8%

+19.9%

+13.6%

+13.2%

LAB-TOLAB DIFFERENCES

+20.9%

+19.2%

+31.8%

MULTI-LAB ERROR

+28.8%

+23.5%

+34.5%

Avg



412


Table

1.

Grand

Average

V.

Crush Strength T e s t on P e n c i l

Round R o b i n Leads

a n d Mean S t a n d a r d

Deviations

LABORAP E N C I L LEAD: P E N C I L LEAD: TORY B SOFT T Y P E R HB MEDIUM T Y P E R CODES GRAND MEAN GRAND MEAN AVE STD. AVE STD. (X) DEV. (X) DEV. lbf.

l b f .

PENCIL LEAD: H MED HARDTYPE R GRAND MEAN AVE STD. (X) DEV. l b f .

A

1 0 . 73

2. 09

11 . 92

2 . 00

1 6 . 53

B

10.76

0.48

10.78

0.48

14.18

0.638

C

11.39

0.77

11.89

0.87

15.71

1.44

D

14.00

0.92

15.47

1.40

20.87

2.34

F

13.12

1.83

14.06

1.46

16.95

2.54

G

10.07

1.16

10.53

1.09

13.45

1.63

H

11.39

1.40

12.46

1.44

15.62

2.15

I

14.07

1.43

15.23

1.30

20.40

2.48

J

13.78

1.75

14.20

1.67

18.85

3.410


3 . 25


37.

BRIENZA


413

a b s o r p t i o n by t h e p e n c i l l e a d s , s i n c e c r u s h i n g s t r e n g t h i n c r e a s e d a f t e r d r y i n g f o r 3 h o u r s a t 100*C. A t a s u b s e q u e n t m e e t i n g o f ASTM D-32 C o m m i t t e e o n C a t a l y s t s , t h e Task Group d e c i d e d t o r e v i s e t h e e x t r u d a t e t e s t p r o c e d u r e t o e x c l u d e t h e u s e o f t h e 0.125 in. anvil. I n s t e a d , a procedure used i n t h e l a b o r a t o r i e s o f s e v e r a l members o f t h e g r o u p , i n w h i c h e x t r u d a t e p a r t i c l e s a r e measured f o r l e n g t h and crushed b e t w e e n f l a t a n v i l s , w i l l be a d o p t e d . In addition, the method w i l l i n c l u d e t h e use o f a f l o w o f d r y n i t r o g e n over t h e p a r t i c l e s during the t e s t . This alternate procedure w i l l t e s t t h e v a l i d i t y o f t h e group's a s s u m p t i o n t h a t t h e two main causes o f d i f f e r e n c e s i n t e s t r e s u l t s a r e t h e v a r i a t i o n s c a u s e d by t h e a n v i l and by m o i s t u r e a b s o r p t i o n . An a d d i t i o n a l r o u n d r o b i n , u t i l i z i n g several v a r i e t i e s o f e x t r u d e d a l u m i n a w i l l be c a r r i e d o u t . Conelus i o n A t e s t method f o r s i n g l e p e l l e t c r u s h t e s t i n g o f c a t a l y t i c s p h e r e s a n d t a b l e t s w a s d e v e l o p e d b y ASTM C o m m i t t e e D-32 o n C a t a l y s t s . A procedure f o rthe s i n g l e p e l l e t crush strength of extrudates that gives s a t i s f a c t o r y i n t e r l a b o r a t o r y v a r i a t i o n i s y e t t o be attained. An a l t e r n a t e m e t h o d w i l l t e s t t h e a s s u m p t i o n that t h e i n t e r l a b o r a t o r y v a r i a t i o n s , seen i n a l l round r o b i n s , were c a u s e d by m o i s t u r e a b s o r p t i o n d u r i n g t e s t i n g and t h e use o f a s p e c i a l i z e d a n v i l i n t h e t e s t instrument. Acknowledgments Laboratories p a r t i c i p a t i n g i n these studies include A l l i e d - S i g n a l E n g i n e e r e d M a t e r i a l s R e s e a r c h C e n t e r , Akzo Chemie, S h e l l , Monsanto, Exxon, Haldor-Topsoe, Union C a r b i d e , M a 1 1 i n c k r o d t , N o r t o n , G e n e r a l M o t o r s , W. R. G r a c e , E n g e l h a r d , A m e r i c a n C y a n a m i d , C r i t e r i o n , A r c o , United Catalyst, Ashland, F i l t r o l , Gulf, A i rProducts, and Amoco.

Literature 1. 2. 3.

Cited

Brook, D.B.; Marshall, K. J . Pharmaceutical Sciences 1968 57, 481. Beaver, E.R. Chem. Eng. Prog. 1975 , 71 44. Adams, A.R.; Sartor, A . F . ; Welch, J . G . Chem. Eng. Prog. 1975 71 35.

Received June 20, 1989


Single-Pellet Crush Strength Testing of Catalysts - American Chemical

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