Characterization of Dual-Function Cracking Catalyst Mixtures - ACS

Chapter 12

Characterization of Dual-Function Cracking Catalyst Mixtures Effects of Sepiolite Addition on Metal Passivation 1

2

Mario L. Occelli and J. M. Stencel Downloaded by YORK UNIV on July 10, 2012 | http://pubs.acs.org Publication Date: September 12, 1988 | doi: 10.1021/bk-1988-0375.ch012

1

Unocal Science & Technology Division, Unocal Corporation, P.O. Box 76, Brea, CA 92621 Kentucky Center for Energy Research, P.O. Box 13015, Lexington, KY 40512 2

X-ray photoelectron spectroscopy (XPS) has been used to characterize s e p i o l i t e - c o n t a i n i n g DFCC mixtures i n an effort to explain the high metals tolerance o f t h i s type o f c a t a l y s t . High resolution electron spectra show vanadium to be present mostly as V(V). Hydrogen reduction experiments indicate that i n a DFCC strong metal-sepiolite interactions e x i s t and that pas sivation is probably the results o f inert compounds formation. Raman spectroscopy indicates that vana dates, such as MgV O and Mg V O , are formed; phase impurities i n the sepiolite used may alter the nature of the vanadate generated upon steam aging. S e p i o l i t e passivates most o f the nickel via formation of non i n t e r a c t i v e silicate-like materials. Heating a t high temperatures induces migration o f nickel to the interior and of vanadium to the exterior of the catalyst surface. Metal-surface interactions are observed also i n Ni-loaded kaolin microspheres; however, V on kaolin behaves l i k e bulk V O with respect to reduction, thus explaining t h i s c l a y ' s inability to passivate V-contaminants. 2

6

2

2

7

2

5

The d e l e t e r i o u s e f f e c t s t h a t metals contaminants have on f l u i d c r a c k i n g c a t a l y s t s (FCC) a c t i v i t y and product s e l e c t i v i t i e s can be d r a s t i c a l l y reduced by adding t o t h e FCC heat s t a b l e m a t e r i a l s w i t h metals scavenging p r o p e r t i e s ( 1 - 3 ) . Metals t r a n s p o r t experiments and microprobe a n a l y s i s have " I n d i c a t e d t h a t t h e dual f u n c t i o n c r a c k i n g c a t a l y s t s (DFCC) high V - t o l e r a n c e can be e x p l a i n e d by t h e gas phase t r a n s p o r t o f t h i s metal from the c r a c k i n g component t o t h e d i l u e n t where i t i s i r r e v e r s i b l y sorbed and p a s s i v a t e d ( 4 ) . In a t y p i c a l c r a c k i n g u n i t , s t e a m - s t r i p p i n g o f occluded hydrocarEbns from the c a t a l y s t surface i s performed a t temperatures i n t h e 480-550°C range. The severe hydrothermal treatment, such as t h a t a t which vanadium has been observed t o m i g r a t e , i s necessary t o reduce the s t r u c t u r a l and c a t a l y t i c p r o p e r t i e s o f c e r t a i n f r e s h commercial c a t a l y s t s t o e q u i l i b r i u m values (aging) i n a s h o r t ( l e s s than 10 h) p e r i o d o f t i m e . Higher temperatures (650 t o 750°C) a r e seen by t h e °

0097-6156/88/0375-0195$06.00/0 1988 American Chemical Society

In Fluid Catalytic Cracking; Occelli, M.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

FLUID CATALYTIC CRACKING: R O L E IN M O D E R N REFINING

196

c a t a l y s t i n t h e r e g e n e r a t o r where steam r a r e l y exceeds t h e 20% limit. However, d u r i n g the o x i d a t i v e decomposition and removal o f carbonaceous d e p o s i t s , temperatures on the c a t a l y s t s u r f a c e can be s i g n i f i c a n t l y higher than measured v a l u e s . In t h i s paper, XPS and Raman spectroscopy have been used t o study the chemical s t a t e and l o c a t i o n of Ni and V contaminants. The e f f e c t s o f thermal and hydrothermal treatments on c a t a l y s t s u r f a c e p r o p e r t i e s , and the r o l e o f s e p i o l i t e i n promoting metals t o l e r a n c e has been observed and r e p o r t e d . Experimental Samples P r e p a r a t i o n . A Ca-vanadate sample was prepared by p r e s s i n g a C a C 0 - V 0 mixture a t 10,000 lbs/1 min and then h e a t i n g t h e r e s u l t i n g l o a f e r i n a i r a t 800°C/lh {$). A melt was obtained t h a t gave an x-ray d i f f r a c t o g r a m c o n s i s t e n t w i t h JCPDS p a t t e r n No. 23-137 f o r CaVpOg, see f i g u r e IA. Several Mg-vanadates were prepared by high temperature c a l c i n a t i o n o f Mg0-V 0 mixtures w i t h d i f f e r e n t Mg0/V 0 r a t i o s . Heating i n a i r a t 1006°L/lh a wafer w i t h Mg0/V 0 = 3 fprepared as d e s c r i b e d above) gave a compound w i t h a m e l t i n g p o i n t i n the 1100-1200°C range having an x-ray d i f f r a c t o g r a m c o n s i s t e n t w i t h JCPDS p a t t e r n No. 19-779 f o r NgoV-Og, see Figure I E . Trace amounts of VoCL and/or MgV 0 c o u l a be present i n t h i s sample. Heating 5 t 650°C a mixture w i t h Mg0/Vp0 ~1.0 gave com pounds w i t h x-ray d i f f r a c t o g r a m s c o n s i s t e n t w i t h JCPDS p a t t e r n No 34-14 f o r MgVpCL ( 6 ) , see Figure IB. S i m i l a r l y , heating a t 650°C or 850°C a m i x t u f V w i t h Mg0/V 0, = 2.0 gave a-MgV 0 and 3-Mg V 0 , r e s p e c t i v e l y ; see JCPDS p a t t e r n s No 31-816, No 29-077 and Figures 1C-1D. A Mg-vanadate sample from Atomergic was found to be a MgV 0g2 2°7 c o n t a i n i n g t r a c e amounts of V 0 and of a phase which c o u l a not be i d e n t i f i e d , see Figure IF. D i f f e r e n t i a l thermal a n a l y s i s (DTA) data was o b t a i n e d using a DuPont 1090 thermal a n a l y z e r u s i n g 0.04 SCF/h of a i r as purging gas and h e a t i n g r a t e s o f 10°C/min. A l l powder d i f f r a c t i o n measurements were obtained w i t h a Siemens D-500 d i f f r a c t o m e t e r a t a scan r a t e o f l°/min u s i n g monochromatic Cu-K r a d i a t i o n . The p r e p a r a t i o n of DFCC mixtures c o n t a i n i n g s e p i o l i t e has been d e s c r i b e d elsewhere ( 4 ) .

Downloaded by YORK UNIV on July 10, 2012 | http://pubs.acs.org Publication Date: September 12, 1988 | doi: 10.1021/bk-1988-0375.ch012

3

2

5

?

2

q

5

2

?

5

fi

5

?

2

2

?

2

y

2

Mg

V

m i x t u r e

2

5

X-Ray P h o t o e l e c t r o n Spectroscopy. M a t e r i a l s i n powdered form, were pressed i n t o t h i n , 13-mm diameter wafers and then mounted on a 4-sided sample probe a t t a c h e d t o a Leybold-Hereaus LHS-10 XPS/Auger/ISS instrument. The base pressure i n t h i s instrument i s 2 x 1 0 ~ bar whereas samples were g e n e r a l l y analyzed a t a pressure of 2x10" b a r . A f t e r s p e c t r a l a c q u i s i t i o n w h i l e u s i n g Mg Κ x-ray e x c i t a t i o n , the samples were Ar bombarded f o r 10 minutes to expose f r e s h sub-surface r e g i o n s . The s p u t t e r p r o f i l e removal r a t e f o r the c a t a l y s t s was estimated from separate s p u t t e r i n g experiments oç s p e c i a l l y prepared 1.4 nm/min f o r Ni and 2.0 nm/min f o r S i . A r s p u t t e r i n g was a l s o used as an i n d i c a t o r o f the r e d u c i b i l i t y of the Ni s p e c i e s . The c a t a l y s t s were a l s o exposed t o 50 ml/min f l o w i n g H~ a t a pressure o f 1.5 bar and a temperature o f 420°C f o r p e r i o d s or 15 t o 75 minutes. These exposures were f a c i l i t a t e d by use o f the high pressure-high temperature r e a c t o r attached to the s i d e o f the LHS-10 8



12. O C C E L L I AND S T E N C E L

Dual-Function Cracking Catalyst Mixtures 197

3'i. TWO

35. - THETA

âlT (DEGREES)

Figure 1. X-ray d i f f r a c t o g r a m s o f (A) CaV 0 , (B) MgV O , (C) a - M g V 0 , (D) e - M g ^ V ^ , (E) f ^ O g / a R d (F) MgV*0°-Mg V 0 mixture. 9

2

2

fi

?

fi

7


2

2

7


198

a n a l y s i s chamber._ After exposure, the r e a c t i o n chamber was evacuated t o 10" b a r a f t e r which the sample was moved i n t o a p r e p a r a t o r y chamber and f i n a l l y to the a n a l y s i s chamber. A t y p i c a l time to c o o l , evacuate and move the sample t o the a n a l y s i s p o s i t i o n i s 10 minutes. A l l b i n d i n g energies r e p o r t e d have been c o r r e c t e d f o r charging by assuming t h a t the ubuiquitous C I s band i s l o c a t e d a t 284.6 eV.


2

Raman Spectroscopy. Raman s p e c t r a were recorded on a Spex Ramalog 1403 spectrometer equipped w i t h a cooled RCA GaAs p h o t o m u l t i p l i e r tube (CA 31034-02). The 4880 angstrom l i n e o f an argon-ion l a s e r (Spectra Physics model 165) was used t o generate Raman s c a t t e r e d l i g h t . The l a s e r power impinging on the sample was l i m i t e d t o 50 mW. A l l s p e c t r a were recorded w i t h a s p e c t r a l r e s o l u t i o n of 5 cm" . S i g n a l pulses from t h e p h o t o m u l t i p l i e r were passed through an a m p l i f i e r / d i s c r i m i n a t o r ( P r i n c e t o n A p p l i e d Research model 1182) and counted by a N i c o l e t data system. T y p i c a l l y , 50 scans per sample were averaged i n order t o o b t a i n s p e c t r a w i t h good s i g n a l - t o - n o i s e r a t i o s . Samples were prepared f o r Raman measurements by p r e s s i n g the V-loaded s e p i o l i t e i n t o one cm-diameter wafers w i t h a pressure of approximately 1000 p s i . Each wafer was mounted i n a sample h o l d e r and placed i n the sample chamber o f the spectrometer. The sample h o l d e r r o t a t e d a t a r a t e of approximately 500 rpm i n order to a v o i d temperature-induced chemical m o d i f i c a t i o n of the sample by the i n c i d e n t l a s e r beam. R e s u l t s and D i s c u s s i o n X-Ray R e s u l t s . A f t e r an endotherm w i t h peak minimum a t about 125°C, the DTA p r o f i l e f o r s e p i o l i t e i s e s s e n t i a l l y f e a t u r e l e s s u n t i l 680°C where a second endotherm w i t h peak minimum a t 830°C begins. Between 830°C and 900°C, there i s a sharp exotherm w i t h peak maximum a t 848°C. S i m i l a r r e s u l t s have been r e p o r t e d by Grim ( 8 ) . X-ray a n a l y s i s o f the c a l c i n e d samples i n d i c a t e t h a t a t 68U°C c r y s t a l water begins t o be l o s t and a t 800°C, 9Q '-|2 30^ U ' some q u a r t z ( a - S i 0 ) i s a l s o present, see Figure 2A. The phase t r a n s i t i o n a t 848°C represents r e c r y s t a l 1 i z a t i o n o f the m a t e r i a l i n t o orthorombic MgSiO- ( e n s t a t i t e ) ; some m o n o c l i n i c MgSiO( C l i n o e n s t a t i t e ) may a l s o have formed. A f t e r c a l c i n a t i o n a t 540°C/10 h, s e p i o l i t e c o n t a i n i n g 5% V g i v e s an x-ray d i f f r a c t o g r a m i n agreement w i t h t h a t f o r M g ^ S i ^ O ^ O H ) . , Figure 2B. C a l c i n a t i o n of the same t o g e t h e r w i t h some q u a r t z , Figure 2C; vanadates formation c o u l d not be observed. The steam aged sample i s e s s e n t i a l l y e n s t a t i t e w i t h a d d i t i o n a l peaks a t 2θ = 21.77° and 29.39°, see arrows i n F i g u r e 2D. The peak a t 2Θ = 21.77° c o u l d be due to the presence of high temperature q u a r t z . The peak a t 2θ = 29.39° i s c o n s i s t e n t w i t h the presence o f MgVÔg. However, s i n c e o t h e r s t r o n g d i f f r a c t i o n l i n e s t y p i c a l o f t h i s compound are not p r e s e n t , these r e s u l t s cannot be i n t e r p r e t e d as i n d i c a t i v e of the presence of MgV 0g. m

Si

0

0H

I S

O B S E R V E D

2

2

Raman R e s u l t s . Raman s p e c t r a of two types of steam-aged (732°C/10h, ~100% steam) s e p i o l i t e granules c o n t a i n i n g 5% V and of s e v e r a l (unsupported) r e f e r e n c e vanadates are shown i n Figures 3 and 4.




Dual-Function Cracking Catalyst Mixtures

i4. TWO

Figure 2. X-ray (A) c a l c i n a t i o n and c a l c i n a t i o n at 800°C/lh and

26. - THETA

"IE

57

(DEGREES)

d i f f r a c t o g r a m o f Spanish s e p i o l i t e a f t e r : i n a i r a t 800°C/lh; (B) l o a d i n g w i t h 5% V i n a i r a t 540 C/lOh; (C) sample Β c a l c i n e d (D) sample D steam-aged.


199



200

300

400

500

600 700 WAVENUMBER

800 (CM )

900

1000

1100

1

F i g u r e 3. Raman s p e c t r a o f : (A) Spanish s e p i o l i t e c a l c i n e d a t 800°C; (B) Spanish s e p i o l i t e c o n t a i n i n g 5% V, c a l c i n e d a t 800°C/lh, (C) Sample Β steamed, (D) I M V - s e p i o l i t e c o n t a i n i n g 5% V, c a l c i n e d a t 800°C/lh, and (E) Sample D steamed.



12. OCCELLI AND S T E N C E L

_J 300

ι


ι

, ι

. ι ι I . ι χ ι 500 600 700 800 900 W A V E N U M B E R cnv

400

• ι 1000

1

F i g u r e 4. Raman s p e c t r a o f unsupported: (A) C a V 0 , (B) MgV 0,., (C) a-Mg V 0 , (D) S-Mg V 0 , (E) MgV 0.-Mg V l) m i x t u r e âfid (F) M g V ^ / i t d dl 9

9

9

7

1

9 1

9 7

7

9

9

9

fi o

7

3


9

202


Band p o s i t i o n s and i n t e n s i t i e s , to g e t h e r w i t h vanadates data from the l i t e r a t u r e (9) a r e given i n Table I . The parent s e p i o l i t e does not c o n t a i n VÔg nor t e t r a h e d r a l VO- s p e c i e s , Figure 3A. However, a f t e r impregnation w i t h 5% V and c a l c i n a t i o n i n a i r , broad peaks appear and f u r t h e r broadening o f these bands occur upon steaming, Figures 3B and 3C. Such broadening could be caused by Η-bonding o r , more l i k e l y , by the presence o f a h i g h l y d i s p e r s e d vanadate phase. In c o n t r a s t , s p e c t r a o f a l l t h e r e f e r e n c e (unsupported) vanadates c o n t a i n narrow and w e l l d e f i n e d Raman bands. Figure 4. Bands a t about 885, 845 and 525 cm present i n s p e c t r a o f ( V 0 ) - c o n t a i n i n g samples (such as C d V 0 (9) and the M g V 0 - M g V 0 mixture) a r e i n general agreement w i t n bancis i n the s p e c t r a o f the V - c o n t a i n i n g S p a n i s h , s e p i o l i t e s , see Table L. Furthermore, two bands, one a t 959 cm and the o t h e r a t 885 c m , i n the spectrum o f CaVJDg and MgV 0 a r e a l s o i n c l o s e p r o x i m i t y w i t h bands observed i n l:he V - c o n t a i n i n g Spanish s e p i o l i t e . Evidence o f M g J L O g and a - M g V 0 formation c o u l d not be observed i n t h i s s e p i o l i t e sample, see F i g u r e 3. Vanadium-surface i n t e r a c t i o n s a r e e a s i l y a f f e c t e d by t h e presence o f phase i m p u r i t i e s i n the s e p i o l i t e sample. D i f f e r e n t vanadates a r e formed on a s e p i o l i t e r i c h i n c a l c i t e and dolomite (obtained from I n d u s t r i a l M i n e r a l s Venture (IMV), Amargosa V a l l e y , Nevada). T h i s grade o f s e p i o l i t e was used t o generate c r a c k i n g data w i t h V-contaminated DFCC d e s c r i b e d i n the patent l i t e r a t u r e (1_). On the r e l a t i v e l y pure Spanish s e p i o l i t e , Vanadium forms mainly MgV 0 &Mg V 0 mixtures whereas on t h e I M V - s e p i o l i t e , a t h i r d pnase ( M g ^ O g ) 4s a l s o o b t a i n e d , see Figures 3D and 3E. In f a c t , bands a t 868 cm" η and 929 cm" a r e w e l l i n agreement w i t h the strong^-band a t 863 cm" i n Mg~V 0 and w i t h the s t r o n g band a t 921, cm" i n MgV 0 . S i m i l a r l y , Bands a t 882, 860, 845 and 788 cm" i n t h e spectrum o f B-Mg VJD a r e a l s o observed i n steam-aged (V-loaded) I M V - s e p i o l i t e gr^mifles, see Table I . V a r i a t i o n s i n Raman bands i n t e n s i t y a r e a t t r i b u t e d t o changes i n t h e r e l a t i v e amounts o f [ V 0 ] , [ V 0 ] and [ V 0 ] u n i t s present. I t i s b e l i e v e d t h a t , a t t h e hydrothermal c o n d i t i o n s a t which c r a c k i n g c a t a l y s t s a r e t e s t e d , vanadium migrates from a D F C C s host p a r t i c l e and when i t reaches the metal scavenger ( s e p i o l i t e ) , i t i s trapped on the metal scavenger s u r f a c e as a s t a b l e vanadate. When using Spanish s e p i o l i t e , V p a s s i v a t i o n i s a t t r i b u t e d t o the forma t i o n o f M g V 0 g - M g ^ V 0 - l i k e m i x t u r e s . When s e p i o l i t e admixed w i t h c a l c i t e and oblonntie ( I M V - s e p i o l i t e ) i s used as a V-scavenger, a t h i r d phase, probably M Q O V O O Q » i s a l s o formed. ^ G r i f f i t h and Lesniai< (#) have r e p o r t e d t h a t i s o l a t e d [ V 0 ] ions a r e present i n C d V 0 and i n aqueous [ V 0 ] " s o l u t i o n s , buch i s o l a t e d ions c o u l d be expected t o form i n tire steam-aged s e p i o l i t e m a t r i x where they would produce an i n t e n s e band a t ca 885 cm w i t h weaker bands a t ca 850 ,cm and 525 c m , see Table I . However, the band a t about 1014 cm" i n the V-loaded s e p i o l i t e s (observed i n the 2 6" 2 2°7 ) could r e s u l t from combination and/or over tone modei Dut i t i s o f s u f f i c i e n t s t r e n g t h t o siwgest t h a t p r o tonated s p e c i e s (such as [ H V 0 ] o r [ H V 0 g ] ) have formed w i t h i n the s e p i o l i t e . Protonatfon o f a t e r m i n a l Ύ^Ο group w i l l tend to both i n c r e a s e the bond order and v i b r a t i o n a l frequency o f the remaining V=0 groups and cause broadening o f the v i b r a t i o n a l bands. 2

7

2


2

2

2

7

2

g

2

2

g

7

2

2

2

2

g

7

?

R

1

2

2

6

2

7

?

2

2

2

g

7

2

2

M g V

0

7

M g

V

?

7

2

7

m i x t u r e

2

7

10

2


7

g


O C C E L L I AND S T E N C E L

TABLE

I. RAMAN SPECTRA OF V-LOADED (5%) S E P I O L I T E S AND REFERENCE , . COMPOUNDS (APPROXIMATE R E L A T I V E I N T E N S I T I E S GIVEN IN P A R E N T H E S I S ) ' ' Q

SAMPLE V 0 2

WAVENUMBER

5

[(V0 ) "] 3


4

[Pb (V0 ) Cl] 5

4

MgV 0 2

CaV 0 2

3

[

(

ν

(6),

780

(2)

829

799

(2) (3),

(10),

921

(10),

836

6

(10),

885 ( 5 . 5 ) ,

877

(10),

848 ( 3 ) ,

2

7

2°7^ς

L

L

]

8

9

7

7

(

948

1

0

)

'

(1),

(1.5),

MgV 0 -Mg V 0 Mg V 0 2

2

2

7

8

5

< >

0

2)

919 621

1014 ( 3 ) ,

7

6

6

8

(5.5),

631

9

0-Mg,V O

2

788 ( 4 . 5 ) ,

959

a-Mg-ν,Ο-.

3

846

6

[Cd V 0 ] 2

997 ( 1 0 ) , 827 ( 1 0 ) ,

730 ( 4 ) ,

8

1

(1),

(1),

(

2

)

'

902

570

923

(10),

863

827

(2)

729 ( 7 . 5 ) ,

523

5

0

3

(

670 ( 6 ) ,

605

(8)

(0.5) 555

789

(1.5)

(0.5)

2

(10),

)

873 ( 3 . 5 ) ,

842

(3),

723

845

(4.5),

(1.5),

(0.5)

898 ( 5 ) , 523

1014 ( 2 ) , (10),

0

(6.5),

(INTENSITY)

1

723 ( 1 . 5 ) ,

820 ( 2 ) ,

920 ( 1 ) , 740

cm"

882

(10),

860

(3),

788

(1.5)

882

(6.5),

845 ( 4 ) ,

840

(4)

732

(4),

522

5% V / S p - S e p , Steam 5% V / S p - S e p ,

CA

1014 ( 1 . 5 ) ,

952

1014

925 ( 4 . 5 ) ,

(2.5),

(2.5),

885

(10),

850 ( s h ) ,

525

(1)

898 ( s h ) ,

885 ( 1 0 ) ,

850 ( 5 ) ,

525

(1)

5% V / I M V - S e p , Steam 5% V / I M V - S e p , CA

1013 ( 1 ) , 929 ( 9 . 5 ) , 868 ( 1 0 ) , 1015 ( 0 . 5 ) , 929 ( 1 0 ) , 867 ( 9 ) , 770

sh -

(3),

690

(0.5),

530

848 ( 9 ) , 835 ( 5 ) , 773 (3) 849 ( 8 . 5 ) , 836 ( 5 . 5 ) , 788

(1)

shoulder


(2),

(1)


204

A l t e r n a t e l y , c o n s i d e r a b l e anion d i s t o r t i o n o f [V0~] groups i n [ V 0 y ] - u n i t s has been suggested to cause V-0 s t r e t c h i n g modes near 1000 cm" (JJ_). Such d i s t o r t i o n would be expected to be more impor t a n t i n the pure Spanish s e p i o l i t e than i n the i m p u r i t y - l a d e n IMV c l a y . As a r e s u l t , the r e l a t i v e i n t e n s i t y of the 1014 cm" band i s g r e a t e r i n the Spanish s e p i o l i t e than i n the IMV s e p i o l i t e sample. Wormsbecher and coworkers {]2) have proposed t h a t a t the c o n d i t i o n s (700°C, 20% steam) used to regenerate c r a c k i n g c a t a l y s t s , a v o l a t i l e H^VO- species i s formed causing the d e s t r u c t i o n o f the z e o l i t e . th and coworkers (9,10) i n s t u d y i n g the Raman and i n f r a r e d s p e c t r a of aqueous vanadates,-were a b l e to demonstrate the presence of [ V 0 ~ r ~ (pH V(IV)[1000°C,CA] > V(IV)[850°C,CA] > V(IV)[732°C, steamed], fts seen in t h e s p u t t e r e d samples, V ( I I I ) s p e c i e s c o u l d not be observed ( a f t e r H - r e d u c t i o n experiments) i n any o f the s e p i o l i t e samples s t u d i e d . In c o n t r a s t , when p l a c e d on k a o l i n , vanadium reduces t o V(IV) and V ( I I I ) s p e c i e s and the V ( I I I ) / V ( I V ) r a t i o seems indepen dent o f t h e thermal pretreatment used t o age t h i s c l a y . S i m i l a r l y , V 0 can be reduced t o a combination o f V(IV) and V ( I I I ) s p e c i e s . These r e s u l t s t o g e t h e r w i t h those i n Tables I I and I I I show t h a t V i n t e r a c t s w i t h the s e p i o l i t e s u r f a c e . Steaming a t tempera t u r e s t y p i c a l l y encountered i n the r e g e n e r a t o r o f an FCC u n i t would not d e s t r o y t h i s i n t e r a c t i o n . Upon c a l c i n a t i o n a t 850°C t h e V becomes more r e d u c i b l e than i n 732°C steamed c l a y , but s u b s t a n t i a l l y h i g h e r temperatures (1000°C) than those u s u a l l y seen i n FCCU opera t i o n s a r e r e q u i r e d before these V - s e p i o l i t e i n t e r a c t i o n s a r e broken and vanadium migrates t o the c l a y s u r f a c e . Such m i g r a t i o n produce compounds t h a t a r e not as e a s i l y H -reduced as V 0,-. Meisenheimer (13) has r e p o r t e d t h a t f r e s h l y vanadiumcontaminated a l u m i n o s T l i c a t e c a t a l y s t s r e q u i r e d i n excess o f f o u r hours a t 750°C f o r f u l l r e d u c t i o n o f V(V) t o V ( I I I ) ; f o u r hours a t 500°C r e s u l t e d i n 70% -30% V ( I I I ) - V ( I V ) m i x t u r e s . A t the s h o r t c o n t a c t times (4-8 seconds) and temperatures (480-520°C) e x i s t i n g i n the c r a c k i n g zone (the r i s e r ) o f a FCC u n i t , V(V) r e d u c t i o n t o V ( I V ) w i l l probably be i n c o m p l e t e , ( V 0 , + w = VpO, + H 0, AG = -33.5 Kcal/m) ( 1 4 ) . Reduction o f V o / t f f V 0 ^ i s ntft as f a v o r a b l e ( V 0 - + W = Vo0~ + H 0, AG = -17.4 Xcal/m). In the p r e s e n t c a s e , H t r e a t m e n r o f ν 6 a t 400°C f o r one hour r e s u l t e d i n 30% V ( I I I )


?

ς

2

g

2

2

7

9

R

0

2

2

5

2

2

9

9

?

?

9

2

9

2

?

ς



TABLE

II.

THE XPS BINDING ENERGIES (eV) OF ELEMENTS IN 2% V LOADED KAOLIN, 2% V LOADED S E P I O L I T E CATALYSTS AND IN REFERENCE COMPOUNDS

V2

Sample



Pv?

ûll

102. 6

50.2

532.0

102. 9

50.6

531.8

102. ,7

50.4

532.0

102. ,7

50.7

515.3

530.0

103. .0

50.7

850*C,

CA

517.1

2%V/Sep,

850'C,

H

517.0

2%V/Sep,

1000'C,

CA

517.0

2%V/Sep,

1000'C,

SP

517.3

515.8

2%V/Sep,

1000"C,

H

517.0

?

Mg2p

531.7

2%V/Sep,

2

Si2p

515.3

2%V/Sep,

Steam

517.3

515.4

532.1

102. .9

50.6

2%V/Sep,

Steam

SP

517.0

514.6

532.1

102, .9

50.8

2%V/Sep,

Steam

H

516.9

515.6

531.7

102. .6

50.2

?

2%V/Kaolin,

540 C,

CA

516.6

530.8

102 .2

2%V/Kaolin,

540'C,

H

516.2,

514.6

531.4

102 .5

517.1,

516.2

531.7

103 .3

516.3,

515.0

532.0

103 .4

e

2%V/Kaolin,

Steam

2%V/Kaolin,

Steam

MgV 0

H

2

2

AR

517.2

SP

517.2

514.7

Mixture

H

2

517.4

515.6

CaV 0 ,

AR

517.4

CaV 0 ,

SP

516.6

514.2

CaV 0 ,

H

516.9

515.3

2

6

Mg V 0 2

2

2

2

2

?

6

6

6

2

V 0 ,

AR

517.2

V 0 ,

H

516.0

2

2

CA:

5

5

2

Calcined;

Steam:

Steamed,

H : 2

2

AR:

530.0

532.0

529.9

532.2

530.2

531.7

529.5 529.3

530.2

1 nr.,

50.0

....

529.8

1.5

ATM; SP:

50.0 50.4

530.4

514.7

H - t r e a t e d , 400'C,

732*C/10 h r ;

532.0

... ... ... — ... -

Ar-Sputtered;

As-received.


....


208

TABLE

III.

ATOMIC RATIO IN TWO METALS-LOADED

CLAYS

AND

REFERENCE COMPOUNDS


Mg/Si

V/Si(x10 )

Mq/V

2

2%

V/Sep, 8 5 0 C ,

CA

0.52

0.53

98.0

2%

V/Sep, 850 C,

H

0.54

0.68

79.0

2%

V/Sep, 850 C,

SP

-

-

-

2%

V/Sep, 1000'C,

CA

0.53

6.6

8.0

2%

V/Sep, 1000'C,

SP

0.75

3.6

2.1

2%

V/Sep, 1000'C,

H

0.95

8.8

11.0

2%

V/Sep, Steam,

AR

0.75

0.63

119.0

2%

V/Sep, Steam,

SP

0.72

0.61

118.0

2%

V/Sep, Steam,

H

0.70

0.87

80.0

2%

V/Sep, Bulk*

0.64

3.8

17.1

e

e

e

2

2

2

_

5.1

-

-

7.2

-

-

6.2

-

-

6.3

-

AR

-

-

SP

-

-

1.2

H

-

-

3.0

2%V/Kaolin,

1000 ,

CA

2%V/Kaolin,

1000 ,

H

e

e

2%V/Kaolin,

Steam

2%V/Kaolin,

Steam,

MgV 0 2

6

Mg V 0 2

2

7

Mixture

H

2

2

2

*From chemical

1.6

analysis.



TABLE

IV.

Dual-Function Cracking Catalyst Mixtures

DISTRIBUTION OF V - S P E C I E S

IN

2% V-LOADED

CLAYS

AND REFERENCE COMPOUNDS


V(V) 2% V / S e p ,

850*C,

CA

2% V / S e p ,

850 C,

H

2% V / S e p ,

1000'C,

CA

2% V / S e p ,

1000 C,

H

2% V / S e p ,

Steam

2% V / S e p ,

Steam,

e

e

77

£

1000°,

CA

2%V/Kaolin,

1000°,

H

2

2%V/Kaolin,

Steam

2%V/Kaolin,

Steam,

H

2

2

-

6

Mg V 0 Mix., 2

2

7

54

46

80

20

88

12

100 0

57

65

35

0

52

AR

100

H

82

2

CaV 0 ,

AR

100

CaV 0 ,

H

70

2

2

6

6

2

V 0 ,

AR

100

V Ο

H

-

2

5

23

100

2

2%V/Kaolin,

MgV 0

vnin

100

2

H

VHV)

43

48

18

30

70

30



210


formation (Table I V ) . However, none of the V-loaded s e p i o l i t e granules c o u l d be reduced to V(111) probably because of s t r o n g V-sepiolite interactions. The r e l a t i v e ease w i t h which VpCL can be reduced t o V ( I I I ) i n a l u m i n o s i l i c a t e s i n d i c a t e t h e e x i i r e n c e o f weak m e t a l - s u r f a c e i n t e r a c t i o n s and the i n a b i l i t y o f the s u r f a c e to e f f e c t i v e l y pass i vate vanadium. S i m i l a r l y , V on K a o l i n (and metakaolin) e x i s t mostly as the " f r e e " oxide and can ( i n p a r t ) be reduced to V ( I I I ) s p e c i e s . T h e r e f o r e , DFCC systems c o n t a i n i n g metakaolin microspheres (or amorphous a l u m i n o s i l i c a t e s (15)) should not be as e f f e c t i v e as s e p i o l i t e i n p a s s i v a t i n g metals TTke Ni and V. In f a c t , DCC mix t u r e s loaded w i t h 5000 ppm N i - e q u i v a l e n t s ( t h a t i s 0.6% V + 0.38% Ni) are not metals r e s i s t a n t when metakaolin i s used as a metals scavenger ( 1 ) : GRZ-1 60.0 37.6 5.2 0.58

Conversion (V% FF) G a s o l i n e (V% FF) Carbon (Wt% FF) Hydrogen (Wt% FF)

GRZ-1 D i l u t e d w i t h 40% o f : MetakaofTn Sepiolite 49.4 66.8 33.8 44.6 3.1 4.2 0.34 0.33

DFCC mixtures c o n t a i n i n g 40% s e p i o l i t e and 60% GRZ-1 are e q u a l l y e f f e c t i v e i n p a s s i v a t i n g high (10,000 wtppm) l e v e l s o f vanadium i m p u r i t i e s (]_). In both c a s e s , m e t a k a o l i n microspheres do n o t i n t e r a c t w i t h vanadium o r vanadium i n the presence o f n i c k e l thus a c t i n g as i n e r t d i l u e n t s d e c r e a s i n g both c r a c k i n g a c t i v i t y and gasoline s e l e c t i v i t y GRZ-1 57.0 40.0 2.5 0.20

Conversion (V% FF) G a s o l i n e (V% FF) Carbon (Wt% FF) Hydrogen (Wt% FF)

GRZ-1 D i l u t e d w i t h 40 wt% o f : Metakaolin Sepiolite 51.0 66.2 37.5 45.7 2.3 3.6 0.16 0.15

Vanadium pentoxide ( V 0 ) melts a t 658°C, forming an oxygend e f i c i e n t semiconductor corrtaîning V(IV) ions as d e f e c t s capable of r e a c t i n g w i t h Group I I A m e t a l s , a l k y l metals and aluminum ( 1 6 ) . The r e s i s t a n c e t o V - d e a c t i v a t i o n o f DFCC c o n t a i n i n g sepioTTte granules ( o r s e p i o l i t e i n a c a l c i t e - d o l o m i t e m a t r i x ) d e s c r i b e d i n the patent l i t e r a t u r e ( 1 ) , c o u l d be a t t r i b u t e d to s t a b l e vanadates f o r m a t i o n . A t the c o n d i t i o n s encountered d u r i n g steam s t r i p p i n g , r e a c t i o n s of the type: V 0 + xMg(0H) = 9γ 9°ί5+χ) 2 ° o c c u r ; 1 < χ < 3. S i m i l a r l y , d u r i n g ttffc o x i d a t i v e decomposition o f carbonaceous deposits i n the regenerator: V 0 + xMgO = Mg V 0 / n . Calcium compounds are b e l i e v e d t o hwe a secondary r o r e i n p a s s i v a t i n g V - i m p u r i t i e s s i n c e the data i n Table I I I shows t h a t c a l c i u m vanadate i s more e a s i l y reduced ( a t t e s t c o n d i t i o n s ) than magnesium vanadates. Depending on the host FCC c o m p o s i t i o n , the metal r e s i s t a n c e of the DFCC mixture c o u l d be enhanced by the presence of f r e e L a 0 which c o u l d form LaV0 (17). 2

R

Μ

2

5

ν

+

2

2

x H

2

5

5 +

9

?

d


c o u l d

12.



The Ni 2 p spectra from 2% N i - l o a d e d s e p i o l i t e ( c a l c i n e d a t 850°C) a f t e r rf/ treatment i s shown i n Figure 6 along w i t h t h e synthesized curve p r o f i l e and f i t t e d Ni peaks l o c a t e d a t 856.8, 854.6, and 852.2 eV. The p o s i t i o n s f o r these Ni peaks a r e i n agreement with those expected from compounds such as N i S i C L , NiO and Ni m e t a l , r e s p e c t i v e l y . Heating a t 400°C i n hydrogen d i d not reduce the reference NiSiO- species whereas NiO was e a s i l y reduced. Hence, the data i n Figure 6 suggests t h a t u n r e a c t i v e Ni i s p r e s e n t , probably the r e s u l t of strong N i - s e p i o l i t e i n t e r a c t i o n s . Formation of a s t a b l e s i l i c a t e l i k e g a r n i e r i t e (a N i - c h r y s o t i l e l i k e compound) has probably o c c u r r e d , see Figure 5. Atomic r a t i o s ( N i / S i , Mg/Si and Mg/Ni) are shown i n Table V. A f t e r c a l c i n a t i o n at 850°C, the N i / S i r a t i o i n Ni-loaded s e p i o l i t e increases s l i g h t l y from 0.73 to 0.74 a f t e r s p u t t e r i n g and to 0.88 a f t e r H^-reduction a t 400°C. The N i / S i r a t i o i n the sample c a l c i n e d a t 1000*C i s 50% lower than i n samples c a l c i n e d a t lower temperat u r e s . A f t e r s p u t t e r i n g t h e r a t i o increases t o 1.1 from 0.48. These r e s u l t s suggest t h a t whereas high temperature c a l c i n a t i o n cause vanadium to migrate from the i n t e r i o r to the e x t e r i o r of the c l a y s u r f a c e , n i c k e l migrates i n t o t h e bulk o f t h e s e p i o l i t e granules a f t e r c a l c i n a t i o n a t 1000°C. Steaming (at 732°C) enhances d r a m a t i c a l l y the o b s e r v a b i l i t y of Ni on the s e p i o l i t e s u r f a c e . This enhancement i s noted i n both N i / S i and Mg/Ni atomic r a t i o s i n Table V. N i c k e l migration to the surface o r an increase i n Ni d i s p e r s i o n could account f o r such enhanced o b s e r v a b i l i t y . However, the behavior o f the Ni during H^-reduction i n the N i - l o a d e d s e p i o l i t e s , i s independent o f t h e o D s e r v a b i l i t y of the N i . Hence, s e p i o l i t e s t a b i l i z e s N i , i r r e s p e c t i v e of i t s s t a t e of d i s p e r s i o n . S t a b i l i z a t i o n may r e s u l t from the formation o f r e l a t i v e l y l a r g e N i c r y s t a l l i t e p a r t i c l e s having a NiSiOo-1 i k e surface and a Ni-NiO core. In the case o f a h i g h l y dispersed N i , s t a b i l i z a t i o n could be t h e r e s u l t o f i n t e r a c t i o n between very small Ni p a r t i c l e s and the s e p i o l i t e surface to form a stable nickel s i l i c a t e . When supported on k a o l i n i t e , Ni o b s e r v a b i l i t y i s independent of the thermal pretreatment used t o age the c a t a l y s t ; however, i t s s p e c i a t i o n o r i n t e r a c t i o n with t h i s c l a y change a f t e r steaming. In f a c t , whereas 2% Ni on k a o l i n i s approximately 60% r e d u c i b l e a f t e r c a l c i n a t i o n , the steamed sample i s not, probably because o f the formation o f a s t a b l e N i - s i l i c a t e s o r even a surface s p i n e l phase l i k e Ni-aluminate.


3 / 2




212

Binding Energy, e V

Figure 6. The XPS spectrum and Ni 2 P curve f i t f o r a sample of Spanish s e p i o l i t e (loaded w i t h 2% lir and c a l c i n e d a t 850°C) a f t e r H r e d u c t i o n a t 400°C/lh. 1 / p

?




TABLE V.

ATOMIC RATIOS IN

2% NI-LOADED

CLAYS

AND REFERENCE COMPOUNDS


SamDle

Ni/Si

(xlO ) 2

Mq/Si

Mg/Ni

2% N i / S e p ,

850'C,

CA

0.73

0.64

88

2% N i / S e p ,

850*C,

SP

0.74

0.88

119

2% N i / S e p ,

850 C,

H

0.88

0.64

73

2% N i / S e p ,

l O O O ' C , CA

0.48

0.59

123

2% N i / S e p ,

1000'C,

SP

1.1

0.91

83

2% N i / S e p ,

1000'C,

H

-

-

e

2

2% N i / S e p ,

Steam,

2% N i / S e p ,

Steam,

H

2% N i / S e p ,

Steam,

SP

2% N i / S e p ,

Bulk

2

2

-

1.9

0.54

29

1.7

0.47

28

-

-

20

0.65

3.3

2%Ni/Kaolin,

540 C,

CA

7.4

2%Ni/Kaolin,

540'C,

H

4.9

-

-

4.5

_

_

5.0

-

-

e

2%Ni/Kaolin,

Steam

2%Ni/Kaolin,

Steam,

H

2

2

Ni-Chrysotile,

AR

50

0.12

0.24

Ni-Chrysotile,

SP

33

0.12

0.36

Ni-Chrysotile,

H

34

-

-

CA

2

= Calcined; H

2

« H - t r e a t e d 400'C, 2

Steam = Steamed, 7 3 2 ' C ,

10 h r ;

1 nr.,

1.5

ATM; SP = A r - s p u t t e r e d ;

AR = A s - r e c e i v e d .


214


Acknowledgments The many useful d i s c u s s i o n s and support r e c e i v e d from the Unocal A n a l y t i c a l Department s t a f f a r e g r a t e f u l l y acknowledged. S p e c i a l thanks a r e due t o D r . E . G o l d i s h , Mr. M . B e l l , and D r . P . R i t z f o r x - r a y , e l e c t r o n microprobe and Raman measurements. F i n a l l y , we would l i k e t o thank TOLSA S . A . f o r p r o v i d i n g the sample o f s e p i o l i t e used i n t h i s study.

LITERATURE CITED O c c e l l i , M.L. and Kennedy, J.V., i n U.S. Patent No. 4,465,588 (1984). 2. O c c e l l i , M.L. and Swift, H.E., i n U.S. Patent No. 4,466,884 (1984). 3. O c c e l l i , M. L. i n U. S. Patent No. 4,615,996 (1986). 4. O c c e l l i , M. L. i n "Advances i n C a t a l y t i c Cracking" Symposium preprints. New Orleans, LA, 1987, V o l . 32, p. 658-662. 5. Perez, G . , Frit, B., Bouloux, J. C. and Galy, J., C. R. Aud. Sc. P a r i s , t.270, 952 (1970). 6. Ng, H. N . and Calvo, C., Canadian J. Chem. 50, 3619 (1972). 7. C l a r k , G. M. and Morley, R., J. S o l i d State Chem. 14,429 (1976). 8. Grim, R. E., "Clay Minerology," 2nd Ed. McGraw-Hill (1968), p. 290. 9. Griffith, W. P., Lesniak, P. J. B., Chem. Soc. (A) 1066 (1969). 10. Griffith, W. P. and Wickins, T. D., J. Chem. Soc. (A), 1087 (1966). 11. Hanuza, J., Hermanowicz, K., Oganowski, W. and Trzebiatowska, Bull. P o l . Acad. Sci. 31, 139 (1984). 12. Worsbecher, R. F., Peters, A. W., and Maselli, J. M., J. Catal. 100, 130 (1986). 13. Meisenheimer, R. G., J. Catal., 1, 356 (1962). 14. Reed, J. B., "Free Energy of Formation of Binary Compounds," MIT Press, Cambridge, MA (1971). 15. Occelli, M.L. and Kennedy, J.V. i n G.B. Patent No. 2,116,062A (1983). 16. C l a r k , R.J., The Chemistry of Vanadium and Titanium. Elsevier (1968). 17. W. Rudorff and H. Becker, Z. Naturfossel, 96, 613 (1954). RECEIVED February 25, 1988 Downloaded by YORK UNIV on July 10, 2012 | http://pubs.acs.org Publication Date: September 12, 1988 | doi: 10.1021/bk-1988-0375.ch012

1.


Characterization of Dual-Function Cracking Catalyst Mixtures - ACS

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