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Pergamon C h e m i c a l n g i a u ~ e d n g c ie n c e , o l . 5 1 , N O . I , p . 2 9 3 3 - 2 9 3 5 , 1 9 9 6C o p y r ig h t O 1 9 9 6 E lsev ie r Sc i en ~ L tdPd n t~ l in G r ea t B ri tain . A l l r i~ ts

0 0 0 9 -2 5 0 9 /9 6 $ 1 5 . 0 0 + 0 . 0 0S 0 0 0 9 . 2 . ~ 9 ( 9 ~ 0 0 1 7 7 - 7

C A T A L Y S T D E V E L O P M E N T F O R T H ES E L E C T I V E M E T H Y L A T I O N O F C A T E C H O L

S . P O R C H E T , L . K I W I - M I N S K E R , R . D O E P P E R , A . R E N K E NInstitut d e G-tnie Chimique, Ecole P olyteclmique F~dtrale de L ausanne,CH-1015 Lausan ne, Switzerland

Ab stra ct - Gas-phase alkylation of catechol with m ethanol on T-alumina and mo dified "t-alumina catalystsis s tudied experimentally. By lim iting the con version to X < 0 .3, the formation of polymethylated speciescan be av oided and only the three isom ers guaiacol, 3-methylcatechol and 4-methylcatechol are observed.Optimising the catalyst composition and the reaction conditions, a selectivity of 0.75 for the industriallymost valuable product 3-methylcatechol can be obtained.

I N T R O D U C T I O NSyn the s i s o f a lk y lc a te c ho l s i s a n impor ta n t p roc e s s in f ' me c he mic a l s p rodu c t ion . The s e s u b s ta nc e s a re w ide lyu s e d in the s yn the s i s o f f la vou r ing a ge n t s , a g r i c u l tu ra l c he m ic a l s a nd pha rma c e u t i c a l s ( F ie ge e t a l. , 1991).P re v iou s ly T- AI2 0 3 w a s f ou n d to b e a n e f f e c t ive c a t a ly s t f o r the ga s - pha s e me thy la t ion o f c a t e c ho l w i th me tha no la s me thy la t ion a ge n t ( Po rc he t e t a l ., 1993) . The re a c t ion l e a ds to m a ny d i f f e re n t a lk y la t e d p rodu c t s . Th e re a c t ionc o n d i ti o n s h a v e b e e n o p t i m i s e d t o a v o i d t h e f o r m a t i o n o f p o l y m e t h y l a t ed p r o d uc t s .

O H O H

+ C H 3 O H ~ . . . . . . .( A I ) ( A 4 )

O H O H

2 ) ( A 3 ) C H 3

p o l y m e t h y l a t e dp rodu c t s

Fig. 1 Reaction scheme of catechol methylationThe th re e p r ima ry p rodu c t s a re gu a ia c o l ( A2 ) , 3 - me thy lc a te c ho l ( A3 ) , 4 - me thy lc a te c ho l ( A4 ) ; t he y a re f o rme d b ypr im a ry me thy la t ion o f c a t e c ho l ( A1). A t low c onve rs ion a nd in the t e mpe ra tu re ra nge o f 2 60 - 3 10 C , the ox yg e n-a lk y la t ion i s f a vou re d , e . g . t he m a in p rodu c t i s gu a ia c o l . Th e c a rb on- a lk y la t ion i s ma in ly o r tho - s e l e c t ive .

P re v iou s s tu die s o f phe n o l a lk y la t ion w i th me tha no l s how e d tha t t h i s t ype o f r e a c t ion i s ve ry s e ns i t ive to thea c id ic a nd b a s i c p rope r t i e s o f the c a t a ly s t s u r fa c e ( Ta na b e e t a l. , 197 6 ; V e in e t a l ., 1994 ) . D i f f e re n t me ta l i ons a s2+ + .+ 2+ 3+ -C a , K , L I , M g o r r un s a s B a n d F a r e a d d e d t o y - a lu m i n a i n o r d e r t o m o d i f y t h e s e s u r fa c e p r o p e r ti e s(Ler cher e t a l. , 1984; Ber teau e t a l ., 1987, 1989; Jurczyk e t a l ., 1989) . Th e purp ose o f th is wo rk is to increas e thes e le c t iv i ty f o r the 3 - m e thy lc a te c ho l th rou gh a c a t a ly s t mod i f i c a tion .

EXPERIMENTALCatalysts preparationPu re T- a lu mina ( AI - 3 98 2 , Enge lha rd , N L) i s u s e d a s s t a r ting ma ter ia l . The mod i f i e d c a ta ly s t s a re p re pa re d b y w e tc a p i l l a ry impre gna t ion w i th a q u e ou s s o lu t ions o f n i t ra t e s a l ts . H 3 B O3 a nd N H 4 F s o lu t ions a re u s e d in the c a s e o fB 3+ a nd F" impre gna t ion .

2 9 3 3

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293 4 S. PORCHEr t al .T h e c o n c e n t r a t i o n o f t h e s o l u t io n s a r e a d j u s t e d t o g e t th e r e q u i r e d r a t i o i o n / A 1 3 + ( a t o m i c - % ) b y v a r y i n g t h ea m o u n t o f n i t r a te s a d d e d t o y - a l u m i n a . B e f o r e i m p r e g n a t i o n , ~ , - al u m in a i s d r i e d a t 2 0 0 C f o r 2 h o u r s. A f t e r 8 h o u r sa t 5 0 C t h e i m p r e g n a t e d s a m p l e s a r e c a l c i n a t e d i n a i r d u r i n g 8 h o u r s a t 6 2 0 C .A p p a r a t u s a n d c a ta l y t ic t e s tT h e r e a c t a n ts a r e p r e m i x e d w i t h w a t e r a n d t h e s o l u t io n s a r e f e d i n to t h e e v a p o r a t o r u si n g a m i c r o - f e e d p u m p . T h ec a t a l y t i c r e a c t i o n is c a r r i e d o u t i n th e t e m p e r a t u r e r a n g e o f 2 6 0 - 3 1 0 C a n d a t 1 01 .3 k P a i n a s ta i n l e s s s t e e l t u b u l a rf i x e d - b e d r e a c t o r ( F i g . 2 ) . T o c h a n g e t h e r e s i d e n c e t i m e i n t h e r e a c t o r , t h e m o l a r i n l e t f l o w ( F o ) a n d t h e c a t a l y s tm a s s ( m c, t) a r e v a r i e d i n t h e r a n g e o f 5 .1 0 - 2 < Fo < 1 0 m o l . h l a n d 2 .1 0 : < m c a < 3"10 - 1 kg .

ator

be dr

condensatereceiver foranalysis

, (

>< 1

condense~

vent

Fig. 2 Sch ema tic layou t of the experimental apparatusT h e r e a c t i o n m i x t u r e i s c o n d e n s e d a t t h e r e a c t o r o u t l e t a n d c o l l e c t e d f o r a n a ly s i s . T h e p r o d u c t d i s t r ib u t i o n i sd e t e r m i n e d q u a n t i t a ti v e l y b y H P L C : t h e s e p a r a t io n i s a c c o m p l i s h e d a t r o o m t e m p e r a t u r e o n a N u c l e o s i l 5 C ~c o l u m n ( m o b i l e p h a s e C H 3 C N : H 2 0 = 1 : 9 m o l a r ra t i o , f lo w r a t e = 1 m l . m i n - I, o p e r a t i n g p r e s s u r e = 1 8 M P a ) . T h es i g n a l s a r e o b s e r v e d w i t h U V d e t e c t i o n a t L = 2 7 0 n m .

0 . 0 4 r

X- - 0 .03 .

}40.02.

O.Ol.

o.bs oho o.'15 oN 0}5t~ dm ce t in~ o f ca t~ao l , z ' [h .kgrno l ]

Fig .3 Di f fe ren t ia l convers ion and y ie lds on - /-a lumina a f te r in i t i a l deac t iva t ion ;temp erature = 270"C, Pl ,o = 12.7 kPa, P~.o = 12.7 kPa, P6,o = 7 6.0 kPa

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Catalyst development for the selective methylation of catechol 2935To t e s t t he d i f f e re n t c a t a ly s ts , t he re a c t ion i s r e s t r i c te d to the p r ima ry me thy la t ion : c a t e c ho l c o nve rs ion i s l imi t e dto va lu e s o f X < 0 .0 5 a l low ing the re a c t ion to b e c a rr ie d ou t in the d i f f e ren t i a l k ine t i c r e g ion ( F ig . 3 ). Thes ta nda rd re a c ta n t s f e e d i s a s o lu t ion w i th a mo la r ra tio c a t e c ho l : me tha no l : w a te r = 1 : 1 :6 tha t c o r re s ponds toin it ia l p a r t i a l p re s s u re s o f 12 .7 k Pa f o r e a c h re a c ta n t a nd 7 6 .0 k Pa f o r w a ter . The in i ti a l r e a c t ion ra t e o f c a t e c ho l( -R~o) is meas ured un der s tea dy-s ta te co ndi t ion s af te r 8-10 hours of the ca ta lys t ac t iv i ty s tab i lisa tion and is used toc om pa re the c a t a ly s t s a c t iv ity . Th e d i f fe re n t i a l s e le c tiv it ie s ( si ,o ) f o r the mon om e thy la t e d p rod u c t s ( u nde r s t e a dy-s t a t e c ond i t ions ) a re u s e d to c om pa re the d i f f ere n t c a t aly st s:

R i o Y i , o / x ' Y i ,os i, o = - - _ i =2 , 3 , 4 wh ere -c ,_ mcat- R I o X / z ' X F l o

R E S U L T SThe s pe c i f i c s u r fa c e a re a s o f the s tud ied c a ta ly s t s a re l is t ed in Ta b le 1 . Pu re y - a lu mina e x hib it s a B .E T. s u r f a c ea re a o f 165 m2 .g ~ . Th e s u r f a c e a re a s r e m a in a lm os t u nc ha ng e d a f t e r i nc o rpo ra t ion o f B 3+, L i+ a n d M g 2+ wit h 5%o f i o n c o n t e n t (a t o m i c - % ) b u t d e c r e a s e i n t h e c a s e o f C a2 and K +. A re duct io n o f th is a rea is a lso obse rved withh ighe r M g2 + - c on ten t : t he po re s i ze d i s t r ib u t ion s how s a s m a l l de c re a s e o f the a ve ra ge m e s oporo u s d ia me te r f o rmo d i f i e d y - a lu mina a nd a g lob a l de c re a s e o f a ll d i a me te r s w i th ion c on te n t h ighe r tha n 7 .5 %

Ta b le 1C ha ra c te r i s t i c s o f the d i f f e re n tc a ta ly s t s

C a ta ly s t I on c on te n t

( a to m i c - % )~ -A1203i .IF / 7-A1203 7.53 +B / ?-A1203 5Ca 2+ / ?-A1203 5K + / ?-A1203 5Li + / y-AI203 5M g 2+ / ?-A1203 5M g 2+ / ?-A1203 7.5M g 2+ / ?-A1203 10

I Spe c i f i c B .E .T .a re a

(m2.g -1)

Initial rate-Rio

(mol.kg-a .h-1)

Differential selectivities( - )

S 2 , 0 S 3 , 0 S 4 , 0

16514417 114615017 1167156140

0 .13 50 .13 20 .14 40.0060.0010.0550.1130 .0 920.043

0.71 0.260.70 O.250.75 0.240.74 0.240.70 0.250.60 0 .390.34 0.620 .30 0 .660.53 0.44

0.030.050.010.020.050.010.040.040.03

D i f f e r e n t i a l r e a c t o r : c a t a l y s t s c r e e n i n gAf te r a s t a b i li s a t ion pe r io d o f 8 - 10 hou rs , a c t iv i ty o f ? -a lu mina a nd mod i f i e d ? - a lu mina c a ta ly s t s r e ma ins c onsta nt .Th e c a ta ly t ic ac t iv i ty , e xpressed b y the in it ial reac t io n ra te ( -R~o) , and th e d if ferentia l se lec t iv i t ies ( sl o) on pu re?- a lu mina a nd on v a r iou s m od i f i e d c a ta ly s t s a t 2 7 0 C ( Ta b le 1 ). C a ta ly s ts m od i f i e d w i th F , B 3+, ~2+ a nd K +exhib i t the same prod uct se lect ivi t ies as pure ?-A1203 whe reas the ir ac t iv i ty is decreased. This los t of ac t iv i tyde pe nds on the io n typ e u s e d a nd i s pa r t i c u la r ly s e ve re f o r C a 2+ a nd K +.

W ith Li*-m odif ied ca ta lys ts , a rema rkable se lect ivi . ty increase fo r the des i red 3-m ethy lca tec hol is observed.But the mo s t s ignif ica nt cha nge is ob ta ine d with Mg2+-modif ied cata lys ts : the d if feren t ia l se lec t iv i ty s3 ,o can beimpro ve d u p to 0 .65.D e a c t i v a t i o nUn der d if ferent ia l cond i t ions pure ?-a lum ina a nd F " , B 3+, Ca 2+, K + and Li+-modified ca ta lys ts d eac t iva te witho utinf luenc ing the d if ferent ia l se lec t iv i t ies . In the c ase of Mg2+-modified ca ta lys ts , i t is in te res t ing to not ice th a t thed i f f e re n t i a l s e l e c t iv i t i e s c ha nge du r ing the f h s t hou rs on s t r e a m ( F ig . 4 ) : t he s e l e c t iv i ty f o r 3 - me thy lc a te c ho linc re a s e s w h i l e the re l a t ive f o rma t ion o f gu a ia c o l is r e du c e d . Th e e f f e c t o f th i s p re - t re a tme n t , w h ic h i s a lw a y sf a vou ra b le to the de s i re d p rodu c t , i s mo re o r l e s s impor ta n t de pe nd ing on M g2+ conten t.

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0.20

2:- " 0 . 1 5 -i

0.8

~ 0.10-

.~ 0.05-

0.80 .7 J

~ 0.6 t.4i . 3 - 0 . 2 -

- 1 ~ o S 3 , o

S ~ o

mv v v v v v 0 .~ o ~ ~ o ~ 5Time on s t r e ~ t [11]

, . S ~ oI _v - - -

- 0 . 6

- 0 . 4

- 0 . 2

0.020

Fig.4. Deactivation o f Mg 2+ /~,.A1203 (5 %) catalyst; temperature = 270C,Pl,o = 12.7 kPa, Ps,o = 12.7 kPa, P6,o = 76 .0 kPa, z' = 0.38 h.kg'mol-t

2936 S. PORCH~et al .

C a t a l y s t s m o d i f i e d w i t h M g 2+2+M g - mod i f i e d " / -a lu mina is o f pa r ti c u la r in t e re s t du e to the f a c t t ha t 3 - me thy lc a te c ho l s e l e c t iv i ty inc re a s e s w i th

respect to 2+pure7-alu min a wit hou t big" lost o f catal ytic a ctiv ity (t able 1). The2. sele ctiv ity S3,o is s trongly, dep end enton the M g - c on te n t (F ig . 5 ) . I n the c onc e n t ra t ion ra nge o f 5 - 7 .5 % o f M g , i t pa s s e s th rou gh a m a x im u m o f S3,o =0 .65 a nd 3 - me thy lc a te c ho l b e c o me s the m a in p rodu c t u nde r d i f fe re n t i a l c ond i tions . I t is w or thw hi l e to no te tha ton ly the re l a t ive f o rma t ions o f gu a ia c o l a nd 3 - me thy lc a te c ho l a re a f f e c te d b y the p e rc e n ta ge o f M g 2 a dde d to~ ,- alumina : the ox y ge n- a lk y la t ion i s r e du c e d in f a vou r o f c a rb on- a lk y la t ion , b u t the r ing me thy la f ion s t a ys l a rge lyo r tho - s e le c t ive . Th e b e ha v iou r o f the s e M g2 + -mod if ie d c a ta ly s ts i s ve ry s e ns i t ive to the pu r i ty o f the re a c ta n t s .

0.1.0.0

S3 , o

~ 0 2 5 ; 0 7 5 1 ~ 0

Fig .5 Differential selectivities of the monom ethylated products as function of Mg2+ adde d to y-AI203;temperature = 270"C, Pl.o = 12.7 kPa, Ps,o = 12.7 kPa, P6,o = 76.0 kPa, x ' = 0.38 h.kg.mol -i

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Catalyst developm ent for the select ive methylat ion of catechoi 2937Integral reactorA s p r e s e n t e d i n F i g . 1 , t h e t h r e e m o n o m e t h y l a t e d i s o m e r s a r e f o r m e d b y d i r e c t a l k y l a t i o n o f c a t e c h o l w i t hm e t h a n o l . T h e f o r m a t i o n r a te o f 4 - m e t h y l c a t e c h o l i s sl o w c o m p a r e d t o t h e p r o d u c t i o n r a t e s o f t h e o t h e r s p e c i e sw h i c h i s f a v o u r a b l e b e c a u s e i t is a n u n d e s i r e d s t a b l e p r o d u c t . O n t h e o t h e r h a n d g u a i a c o l i s i t s e l f a m e t h y l a t i o na g e n t : i t d e c o m p o s e s i n a r e v e r s e r e a c t i o n to c a t e c h o l a n d m e t h a n o l o r c a n b e t r a n s f o r m e d b y r e a r r a n g e m e n t t o t h ed e s i r e d 3 - m e t h y l c a t e c h o l ( P o r c h e t e t a l , 1 9 9 4 ). T h e r e f o r e t h e o v e r a l l y i e l d Y 2 s h o w s t h e t y p i c a l r e a c t i o n p a t h o fa n i n t e r m e d i a t e p r o d u c t . T h e y i e l d o f 3 - m e t h y l c a t e c h o l i n c r e a s e s w i t h c a t e c h o l c o n v e r s i o n w h e r e a s t h e g u a i a c o ly i e l d p a s s e s a m a x i m u m v a l u e a s s h o w n f o r p u r e , f -a l u m in a i n F i g . 6 .A ) . H o w e v e r t h e m o n o m e t h y l a t e d p r o d u c t sr e a c t w i t h a l k y l a t i o n a g e n t s to f o r m s t a b l e h i g h e r m e t h y l a t e d s p e c ie s . T h e r e a c t i o n h a s t h e r e f o r e t o b e s t o p p e d a ta n o p t i m a l c o n v e r s io n .

A s t h e d i f f e r e n t i a l s e l e c t i v i t y o f 3 - m e t h y l c a t e c h o l i s c o n s i d e r a b l y i m p r o v e d u s i n g M g 2 + - m o d i f ie d c a t a ly s t s , t h eo b t a i n a b l e i n t e g r a l s e l e c t i v i t y c a n b e i n c r e a s e d to v a l u e s u p t o 0 . 7 5 f o r a c a t e c h o l c o n v e r s i o n o f X = 0 . 28 . T h i sc o r r e s p o n d s t o a 1 5 0 % h i g h e r y i e l d c o m p a r e d t o p u r e ~ / -a lu m in a a t th e s a m e c o n v e r s i o n a s s h o w n i n F i g . 6 . b ).

0.25

0.20." 7~" 0 .15 .

0.10.

0.05.

0.000.00

I ~ ~ ~ 1 Y~

Y~

0.05 0.10 0.15 0.20 0.25 0.30C ~ r s i ~ x [ - ]

0.25

_ I 1~" o.15. . / ~ [

0.10.Y 2

0.05.

o o o~ x [ - I

Fig. 6.a) & b) Integral yields of the three monom ethylated products as function of catechol conversion; temperature:262"C (a), 270 "C (b), P l,o = 12.7 kPa , Ps,o = 12.7 kPa, P6,o = 7 6.0 "l 'l&a,x ' = 0.3 - 5.7 h,kg.mol . l

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2938 s. RCHET etal.CONCLUSIONOn pure y-alumina the selectivity for the desired product 3-methylcatechol can be optimised taking into accountthe initial formation rates of the monomethylated compounds and the consecutive rearrangement of guaiacol. Thisleads to a selectivity sj = 0.52 at a conversion of X = 0.28. Guaiacol and catechol must then be separated and maybe recycled.

It has been shown that the differential selectivity for 3-methylcatechol can be increased by modifying thecatalyst with Mg+. This leads to a selectivity sg = 0.75 at the same conversion and it decreases the amount ofguaiacol that has to be recycled.

ACKNOWLEDGEMENTThe authors gratefully acknowledge financial support by the Swiss National Science Foundation

NOMENCLATUREFOF O%* tP190RI O- R I OS ,s i , O

7 'XYy*,o

total molar flowmolar flow of catecholcatalyst massinitial partial pressure of iinitial formation rate of iinitial reaction rate of catecholselectivity of idifferential selectivity of itime on streamresidence time of catecholcatechol conversionintegral yield of idifferential yield of i

mo1.h -Imo1.h -kgkPamol.kg -.h-mol.kg-.h-

hh.kg.mol -I

indices i:2 guaiacol3 3-methylcatechol4 4-methylcatechol5 methanol6 water

REFERENCESBerteau, P., Ceckiewicz, S., Delmon, B., Role of the Acid-Base Properties of Aluminas, Modified y-Alumina, andSilica-Alumina in Butanol Dehydration, 1987, A&. Cutal., 31, 361.Berteau, P., Delmon, B., Modified Aluminas: Relationship Between Activity in 1-Butanol Dehydration andAcidity Measured by NH3 TPD, 1989, Cutul. Today, 5, 121.Fiege, H., Hamamoto, T., Iwata, T., Buysch, H.-J., Garbe, D., Paulus, W., Phenol Derivatives, in Ullrnunn sEncyclopedia of Industrial Chemistry, Vol. A19, VCH Verlagsgesellschaft, Weinheim, 1991, 3 13.Jurczyk, K., Kania, W., Base Properties of Modified y-Alumina, 1989, Appl. Cutul., 56,203.Lercher, J. A., Colombier, C., Noller, H., Acid-Base Properties of Alumina-Magnesia Mixed Oxides, 1984, J.Chem. Sot., Furuduy Trans. 1,80,949.Porchet, S., Su, S., Doepper, R., Renken, A., Methylienmg von Brenzcatechin in der Gasphase, 1993, Chem.-Zng.-Tech. 65, 203.Porchet, S., Su, S., Doepper, R., Renken, A., Heterogeneous Catalytic Methylation of Catechol, 1994, Chem. Eng.Technof. 17, 108.Tanabe, K., Nishizaki, T, The Selectivity of Oxide Catalysts for the Alkylation of Phenols with Methanol, inProceedings of the Sixt h Congress on Cutufy sis, vol. 2, London, 1977, 863.Velu, S., Swamy, C.S., Alkylation of Phenol with Methanol over Magnesium-Aluminium Calcined Hydrotalcites,1994, Appl. Cutuf., 119, 241.