Bull. SOC. Chim. Belg. vo1.93/n0 8-9/1984 SKWD W Q U I B O P IBETIHC ON BIDPOTUUTDIC CATALYSTS bwain-la-neuva, 29 - 30 October, 1984

FAST AND SLOW STEPS OF HYDRODESULFURIZATION

Hans Schulz and DAC-VOng DO Engler-Bunte-Institut, UniversitPt KArhruhe, 75 Karlaruhe, FRG

ABSTRACT Two model mixturem (2-methylthiophene, phenol, o-toluidine, ethylbenzene

And benzothiophene, 0-cremol, aniline, 0-xylene) were used to characterize acti- vity and melectivity of different sulfur resistent catalysts for rimultaneoum IDS, HDO, HDN and hydrogenation of aromaticm. 2-methyltetrahydrothiophene and dihydrobenzothiophene were found am intermediatern. A mechanimm for the HDS- reaction i m discussed And Compared to the HDN mechanimm of quinoline.

INTRODUCTION Wheream in Petroleum the mulfur is most abundant to contaminate the hydro-

carbon products, o i l s from COAl - obtained Via hydrogenation or pyrolysis - con- tain higher amounts of nitrogen And oxygen. Simultaneoum removal of these ele- ment. i m then of importance A S already investigated by Mathiam Pier (1). On the other hand hydrogen conmumption during hydrotreating mhall be AS low as pos- mible. BQCAUSe Of thesa practical impliCAtiOnS it Appear# Of interest to cha- racterize hydrotreating catalymts with respect to their specific activities for the mentioned reactions. Such data would then be of theoretical importance

Hydrogenative removal of 8 , N, 0 from organic compoundm obvioumly concerns mul- tistep roactionr and to undermtand the overall conversionm And the mode of ca- talymt action does therefore imply the knowledge of the reaction scheme And the nature of tha individual reaction mteps. In the firmt part of thim paper simul- taneoum conversion of four melected compounds in A temt mixture am A function of reaction temperature is demcribed AS applied to typiaal hydrotreating cata- lysts. Then desulfurization of 2-methylthiophene And benzothiophene is regar-

A h 0 beCaUSe they could help to dircriminate individual CAtAlySt functions.

ded in detail And the nature Of individual reaction steps deduced from the 9-9-

rimental data And compared with reaction Steps Of hydrodenitrogenation which have been observed with quinoline.

EXPERIMENTAL The fOllWing CAtalyStS have been umed I

1) CoMo/A1203 (6-B); Supplied by BASF, Trade number M 8-10, Co-content 4 wt-9, --content 9 wt-9, BET murface Area 220 m2/g, pore volume 0 . 5 cm /g, AmOunt in the reactor 1 ml (0.47 g).

2) CoNo/A1203 (5-C); Supplied by Shell, Trade number S 444, Co-content 3 wt-9, no-content 9 wt-9, BET murface Area 220 m2/g, pore volume 0.50 m /g, amount in the reactor 1 ml (0.673 9).

no-content 10 wt-9, BET area 150 m2/g, pore volume 0.6 cm /g, amount in the reactor 1 ml (0 .660 9).

3

2

3) NlNo/A1203 (2-8); Supplied by BASF, Trade number kl 8-21, Ni-content 2.4 wt-9, 3

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NiXO/A1203 (3-A); Harrhaw UT 500, Ni 3.8 wt-8, XO 10.3 wt-t, BET area 225 m2/g, poro volumo 0.5 am3/g, .mount i n tho reactor 1 m l (0.756 9 ) . Y1W/Al2OJ ( 9 - B ) ; Suppliod by RASP (M 7-11), Ni-content 3 wt -a , W-contont 20 wt-8, BET aroa 248 m2/g, pore volumo 0.5 cm3/g, amount i n t h e roac tor 1 m l

NiW/A120j-Si02 ( 1 1 - A ) , Harrhaw Ni-4301, N i 5 wt-8, W 19 wt-t, BET 228 m2/g, p r o volurm 0.37 c m /g, Mount i n t h e reactor 1 m l (0.804 g ) .

(0.805 g ) .

3

A f ixed bod reac tor , ar dorcribod i n (2,3) ha8 boon appl ied. Tho product8 wore analyzod by garchromatography (2,3) . Roridenco t i m e ( T ~ ~ ~ ) i r dofined an volum. of t h e c a t a l y s t l a y e r i n tho roac tor (1 m l ) devided by the gar flow of reactant. ( a t reac t ion p r e r r u r e and roact ion tomperature) . tion8 aro given togethor with tho r o s u l t r i n tho corrosponding table. and dia- grams.

Further oxperinmntal condi-

RESULTS AND DISCUSSION Tho conversion of a model mixture cana ls t ing o f 2-methylthiophene, phonol,

t c lu id ino and ethylbanzono ham boon so lec ted f o r reprosonta t ive ly r e f l e c t i n g HDS, H W , HDN reac t ionr and hydrogonation of aromatic r i n g r during f u e l o i l hydrotroating. A recond mixturo cons i r tod of benzothiophene, o-crosol, a n i l i n e and o-xylono. Sul fur bonded i n tho thiopheno r i n g has a comparatively low reac- t i v i t y . Oxygen is found mainly am phenol ic OH-groups i n l i q u i d product. from coal. I n thorn. producte mostof t h e ni t rogon i r found as NU2 group8 a t tached t o aromatic r ings . In Figure 1 t h e degroor of converrion of tho ind iv idua l compo- nontr of mod01 mixture 1 a r o rhown ar a funct ion o f roact ion tuapera ture f o r t h r e e typical catalyst.. r p o c i f i c a c t i v i t y of a c a t a l y s t f o r on. of t h e reactionr i n quer t ion can be quant i f iod by meanr of the tuaporature f o r a 50 8 converrion (Tso) which can bo taken o a r i l y f r a n tho f iguro.

Roact ivi ty o f tho compounds of tho mixture and ar w e l l

Roact ivi ty of tho componentr of tho model mixture i r thus found t o be charac te r i rod by t h e following T50 valuer :

2-lhthylthiophone % 27OOC Phenole % 31OOC Toluidine % 35OOC

Ethylbanzone % 45OoC

Dorulfur izat ion is much oarier than dooxygonation and deoxygenation than donitrogenation. Tho i s o l a t o d aromatic r i n g i r very re r imtent drogonation.

is e a r i o r a g a i n r t hy-

REACTIONTEMPERATURE , OC

Whon canparing T50 valuer f o r tho ram0 re- a c t i o n and d i f f o r o n t c a t a l y r t s (Figure 1, Table 1) i n order t o diecr iminate s p e c i f i c

F I G . 1. Degree of conwrnion of the individual c o pound8 of a tent drture cannistkrg of 2- Methylthiophme, Phonol. dolu id ine . and Ethylbenzene u M i a n of reaction t a r

mtrua ior three catelymtr. - 96.7 bu. Pm - Pph - PT - 0.5 bar, K 2 Pw 0.67 b u , P y - 0.1 bar. Teff 7.2 - 10.2 I ) .

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TABLE 1 Reaction temperatures for a 50 5 convemion (T Mixture I : 2-MethylthiopheneD phenol, o-toluidrae, ethylbenzene Nixture I1 : Benzothiopheru, o-cnrol. aniline, 0-mlene Catrlysts : Colb/A1203, I W b / A l 2 O 3 and RiW/A1203

p ~ b - 0.67 bar.

) of tho campouuda in a model mixture. 50

Total pressure : 100 bar; Partial pressure : ~II, - 96.7 bar . &r Poq 0.5

0 pCr PA 0.5 bar. pw 0 0.67 bar; 912s 0 0 , l bar, Teff 7.2 - 10 8

Cmpounda to

be converted r;l

r CoHD/A1203 (6-B) AiMo/A1203 (2-B)

HiW/A1203 (9-B)

I Reaction Temperatures (T50) in OC 1 268 237 323 358 359 356 540* 535- 273 244 303 333 334 333 424 42 1

273 241 302 339 348 338 432 418

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FIG. +

3.

FIG. 4. Composition of the products (vithout feed

phene as a h c t i o n of reridonce time

Composition of feed stream : Q2 - 96.7 by , Q2s 0.1 bar, g h 0.5 bar (Mdi- t 1 O n r l Compounds : Pph 9 0,s bar, pEb - 0.67 bar,) T - 25OoC.

., ccmpound) of conversion of 2-mthylthio-

(COHD/A1$3, 5-C)

Product c w s i t i o n ( i n C-%) as a function of re r idmca time for uthyl thioghene con- verrion of &&/Al 0 (5-C). h p r i t i o n of f e d atroam : Q 2 s - 0.1 b u ,

T - 25OoC.

- 96.7 bar, - 0.5 b a r ? h i t i o n a l ccpp0Udr Pph 0.5 bu. pEb 0.67 bar),

S e l e c t i v i t y of 2-methylthiophene conversion with d i f f e r e n t c a t a l y s t s a t 250'C and a t about t h e samo degree of conversion (b 20%) is reported i n Table 2 . Romarkably g r e a t d i f fe rences h a w been observed. much more a c t i v e than tho o thers . The same degree of conversion is obtained i n l o s s than 1/3 of tho residence t i m e .

The CoMo/A1203 c a t a l y s t is

TABLE 2

Comporition of the products obtainrd fmn 2-methylthiophene with four di f fe ren t hydro-

t r e a t i n g ca ta lys t s a t a c m p u a b l e degree of conversion.

additional compounds : pph - b0 0.5 bar, pn - 0.67 bu) (T 25OoC, Ptotal .I 100 bar, 96.7 bar, m2s 0.1 bar, p ~ h 0.5 bar

Catalyst 1 Conv. 1 T eff 1 Compos. of products, Mol-% I

sec. I c;l P I I i iMo/U2O3 ( 3 - A)

20 liW/A1203-Si02 ( 11 - A) 15 14 22

Pantoner 1 Pentane I

With tho CoNo/Al2O3 c a t a l y s t 6 0 mole-% of t h e productsare tetrahydrothiophene. With tho NiW/AIZOJ t h e corrosponding f i g u r e is only 1 4 mole-% of te t rahydrothio- phono. Of g r e a t interest is a l s o the molar ratio of pentenes t o pentano i n the product. With tho CoNo/A1203 c a t a l y r t t h i s ra t io is about 1. tho concontrat ion of t h e pentenes i s up t o t h r e e times higher than t h e con- cont ra t ion o f pentane. 2-mothylthiophene desul fur iza t ion with CoMo/A1203 as compared to t h e o ther hy- d r o t r e a t i n g catalyst.. Whon roac t ing the model mixture 11, t h e dihydrobensothiophene is observed as

With t h e o t h e r c a t a l y s t s

Again we see a g r e a t d i f fe rence i n t h e behaviour f o r

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an i n t e n m d i a t e ( f i g u r a 5 ) . From this ethylbenzene i s formed as t h e hydrocar- bon product. A t r e l a t i v e l y high temperature ( > 330'C) hydrogenation of t h e ethylbenzene starts.

FIO. 5 . hoduct coqmsition ( in C-%) an a function of reaction t q n t u r e for benrothiophene conversion on &h/Al 03. feed rtreaa : h2 - 9t .7 bar, pH2s - 0.1 bar, (Additional cOllpoUn& : Pcr P h 0 . 5 bar. PQ. 0.67 bar). Tcff 7.2 - 10.2 I.

Composition of

The above r e r u l t s r h a l l be discussed fur- t h e r on t h e b a r i s of appropr ia te reac t ion schemes. Schema 1 genera l izes t h e f ind ings f o r 2- methylthiophene. In a f a s t reac t ion (1) 2-

REACTIONTEMPERATURE , OC

wthyl th iophene is hydrogenated t o 2-methyltetr~hydrothiophene !a a r e l a t i v e l y r t a b l e intermediate . o t h e r c a t a l y s t s . lesr a c t i v e than the o ther c a t a l y s t s . The next intermediate which can be obser-

This reac t ion is f a s t e r with tha CoMo/A1203 than with t h e However f o r t h e next s t e p of r i n g s c i s s i o n t h e CoMo/A1203 is

SCHEME 1 : iiydrodmuliuization of 2- Methylthiophene.

?@[TI %m +n ved 1s the o l e f i n . El iminat ion of H2S is very f a r t a f t e r t h e r i n g ' has been opened. This corresponds

111 (21 131 1 0 1 I 1 i I SLOW DfACllol , 1 F I s l REACllOW t o t h e known minor s t a b i l i t y of

m r c a p t a n e s ( 6 ) . Olef in hydroge- nat ion i s genera l ly f a s t i n a11 the hydro t rea t ing systems. When regarding aga in t h e two s t e p s of bond s c i r r i o n which is necessary t o e l imina te t h e s u l f u r it is to be concluded t h a t t h e C-S bond i n the f i v e membered r i n g is much less reac- t i v e than t h a t i n a mercaptane. Thus breaking of t h e C-S bonds murf no t a t a l l be the rlow r t e p s in hydrodesul fur i ia t ion .

SCHEME 2 : liydrod.sulfurization of &nzc- qy+@+[Q]*y@rn t hiophene . I l l 121 (31

6 Conversion of benzothiophene is fas- - 3 - 2 - 1 ter than t h a t of 2-mothylthiophene (Tab le 11 and -the Intermediate

would be an aromatic marcaptane with t h e SH-group a t tached t o the aromatic r ing . However this is not observed a t a l l . The S-H group i r s p l i t o f f from t h e r i n g and t h e ethylbenzene is formed. With respec t to C-S bond cleavaue it is con- cluded t h a t t h e bond of r u l f u r to t h e r i n g ir SO weak t h a t it can be e a s i l y s p l i t through hydrogenolysis without any hydrogenation of t h e aromatic r ing. When regarding t h e f u r t h e r conversion of a l i p h a t i c mercaptane in te rmedia tes t h e i r r e a c t i v i t y w i l l ba SO high t h a t any of tho t h r e e p o s s i b i l i t i e s of H2S e l imina t ion appear poss ib le (Scheme 3) : Acid ca ta lyBis , hydrogenolysis, ther - m a l reac t ion . Formation of o l e f i n s through hydrogenolysis is p i c t u r e d i n

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/

\ R. D

Schom 4 . Tho chemimorbod a l k y l group (i), obtained v i a opening of tho C-S

bond, can bo demorbed not only ammociativoly ( roac t ion I i n Sahomo 4 ) t o y i e l d a p a r a f f i n , bu t almo dimmociativoly ( reac t ion 3) t o y i o l d an o l o f i n . T h i s roac- t i o n ham 0.g. analoqiom i n aymtonu of p a r t i a l o l o f i n hydrogenation and hydrocar- bon formation by tho Pimchor Tropach reac t ion ( 7 ) .

8- 4 : h-tion of olefins during hydmgenolyris

poundl through dirso- ciatiwe &rorption Of

r;r + [ C-E] ;;;' * of organic ruliur cem-

1 2 ruryl rpecier. -

C H ~ - C H ~ - C H Z C H Z C H ~ - C H Z - C H Z - C H ~ Tho olefinm obtainod from 2-

- 5 e rnethylthiophono are a mixtu- re of imonwrom. Thia l a in- d i c a t i v o for p a r t i a l mocon-

dary o l a f i n hydrogenation which i r a 8 8 O C i a t O d t o doublo bond mhift v i a a common intormmdiato (Scheme 511 ( 7 ) .

8- 5 : Double bond shift of olafinr during t h e i r partial hydmgelution.

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The lart Scheme 6 concerns hydrodonitrogenation of qulnoline (8,9). In con- tra8t to the reactlon of benzothlophene the product of rlng openlng, the propyl- aniline (2) l a very stable. The bond of N to the aromatic rlng l r not split and the aromatic rlng must be hydrogenated in a .low reactlon (6) prior the ell- mlnatlon of amonla.

rzn. - W H ~ I sss I

S- 6 : Reaction network for the HDN of quinoline.

This comparison shows, that in hydrodesulfurization and hydrodenltrogenation very different reactlon stepr are decisive, hcwever generally speaking the slow rtepr in moat of the reactlon sequence6 are one. of hydrogen transfer which tranrform the heterocompound lnto a more reactive intermediate and final steps of bond breaking between carbon and the hetermtom will then be easy.

ACKNOWLEDGMENT

fiir Forschung und Technologle. Thir work was supported by the grant ET 1302 A of the Bunderminlaterium

REFEFtENCES 1. M. Pler, 2. Elektrochem., 57, 456 (1933). 2. Dac-Vong Do, Dissertation, Unlversitlt Karlrruhe 1982.

Fortrchr. Ber. VDI Z., Rolhe 3, Nr 69, VDI Verlag G m b H , DUrreldorf 1982. 3. H. Schulz, Dac-Vong Do, W. Kahler, U. Schon, Van Hung Nguyen, Forschungsbe-

rlche T 83-175, BMFT-FB-T 83-175, Fachlnformatlonszentrum, Karlrruhe. 4. C.H. Amberg, J. Laam Commaon Met. 36, 339 (1974). 5. P.E. U.rsoth, J. Catal., 47, 300 (1977). 6. P. Selfrled, DlSSertatlOn, Universltlt Karlrruhe (1978). 7. H. Bchulz, Proc. 5th Int. Sympor. Heterogeneous Catalyst., Varna, Oct. 3-4,

8. C.N. Satterfield, J.F. Cochetto, Ind. Eng. Chem., PDD, 20, 53 (1981). 9. H.D. Elchhorn, Dissertation, Universltat Karhruhe (1979).

(1983).

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