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Effect of catalyst preparation on NiAl2O3 poisoning by thiophene
The Chemzcal
Englneemng
Journal,
Effect of catalyst
49 (1992)
preparation
45-48
45
on Ni-Al,03
poisoning
by thiophene
Stanka ZrnCe\& Department
of Chemzcal
Reactwn
Engzneerxng,
Unzverszty
of Zagreb,
Zagreb
(Croatia)
Hem-&a Melder and DeJan PlavG Rude-r BoSknvzc Instatule,
P 0
Box
1016, Zagreb
(Crontza)
(Recewed July 23, 1991)
Abstract The mfluence of expet-unental
concklons such as the temperature of calcmatlon and peUetmg pressure on Nl-A1203 deactivation by ttiophene III benzene hydrogenation LS outlmed and discussed It was found that benzene hydrogenation over unpolsoned mckel catalyst LS a structure-msensltlve reaction However, its u-&ubltlon by thophene produced structure sensltnlty the reactlon rate &as less sensltlve to thophene for large tuckel crystalbtes (formed durmg catalyst calcmatlon at Hugh temperatures followed by reduction), than for small crystalhtes Thus, the structure sensltn%y of poison adsorptlon unparted an apparent structure sensltlvlty to the rnti reactlon m the presence of a poison m the feedstream (secondary structure sensltlvlty) The pore structure of the catalyst pellet du-ectly mfluences the degree of Muslon resistance of both the mam and the polsonmg reactlons It was found that hgher mass transfer resistances mcrease the hfe-tune of the pellets whrle a lower mass transfer resistance mcreases the overall effectiveness factor
1. Introduction
2. Experimental
The deactlvatlon of a catalyst by sulphur or sulphur-contammg compounds and the consequent decrease m catalyst effectiveness is a very common
2 1 Catalyst preparatzon The method chosen for preparation of a catalyst 1s based on a patent of McArthur [ 15 ] which clauns the production of nickel alurmna catalyst by deposltlon-precipitation of nickel hydroxide onto a support by thermal decomposltlon of nickel ammo complexes To prepare the nickel ammo complex solution 20 g of mckel nitrate hexahydrate m 20 cm’ of dlstrlled water and 1 cm3 of concentrated nitric acid were dissolved and 25 cm3 of concentrated ammonia was added slowly under vigorous stu-nng A 2 M aqueous solution of sodnun hydroxide was very slowly added to this solution until the pH was 10 5 10 g of ahnnuuum oxide support prepared by the authors [ 161 were added to tlus solution The solution was heated to 363 K, wtie carbon dioxide was passed through it and Uus resulted m a rapid decrease of the pH to a value of 7.5 After a few hours a further decrease m the pH was observed and at that pomt the synthesis was stopped The product was filtered, washed wth hot d&tied water to the negative reactlon on sodnun and dned overrught at 393 K Samples were c+ned at 643 and
and unportant ious methods
problem UI mdustry Therefore, varhave been considered m order to
unprove the thloreslstance properties of the catalytic system TIE can be done by creatmg a new catalyst design m which the active phase 1s protected either geometncally (location mslde a catalyst pellet) [ l-51 or chemically (proxumty of a compound havmg a higher af%uty for sulphur) [6-81 In both cases, the mtnns~c thloreslstance of the active metal phase 1s not modified and polsorung 1s only delayed The only way to alter the mtrmslc thoreslstance of a metal 1s by modlfymg its electronic properties, and thus may be done by changmg the acid-base propertles of the carrier, by alloymg, or by changtng the metallic particle size [g-14]. The present paper 1s concerned mth the tluoresistance of NL-A1203 catalyst m which the nickel particle sue and pore structure of the support have been modtied The extent of these variations was followed usmg benzene hydrogenation, either pure or contammg thlophene as a poison
0300-9467/92/$5
00
section
0 1992 - ELsewer Sequoia
AU nghts
reserved
TAEILE
1 PIns~cal
properties
flame-Ionization detector, Pye Umcam DP 88 computmg Integrator) were the same as used pre\lously
of the catalyst
Tabletmg pressure (t cm-?)
Surfxe area (m’ g-y
Pore \olume
ALerage dnnieter
(cm'
(Iull)
Eff dfi coefficient (IO cm’ s-‘)
15 30 50
3 10 285 ‘69
0 638 0 450 0 328
89 62 17
s9 3 1 t ,3
g-1)
pore
[201 Reactton condltlons were
693 K m afl for 16 h After dg?ng and calcmatlon the powder was pressed mto pellets (5 x 5 mm) at various tabletmg pressures (1 5, 3 and 5 t cm-“) The mfluence of the pressure of pelletmg on the physIca charactenstws of the catalyst IS gwen m Table 1 PItor to use, the catalyst was reduced Z?L sllu m flo\\umg hydrogen for 10 h at ‘7-l3 K This temperature was chosen because It was found to gwe the highest catalyst actlvrty for benzene hydrogenation wthout resiltmg m catalyst witeruig 2 2 Apparatus and ploceclure The metal content (200/o NI) of the catalyst was determmed by comparmg the mltlal and final metal concentrations of the mmpregnatlon solution The specific surface areas were obtamed accol dmg to the BET method from the nitrogen adsorption Isotherms at 7’i K and a Lalue of 0 163 nm’ tor the cross-se&on of Ihe adsorbed N-, molecule Pore volumes 1%ere measured usmg the mercury porosmmeter method X-ray powder dtiractlon (XRD) patterns were recorded by ‘an X-ray dfiractometer with filtered Cu Kn ladlatlon All spectra displayed charactenstlc bands for NtO and y-Al,O, The diameter of the metal crystalhte was detemunecl flom XRD hne broadenmg usmg the Scherrer equation [ 171 (see Append= A)
d =r4A/p
cos e
(1)
where d IS the partwle size, A IS the X-ray wavelength, p 1s the peak wdth at half-mruunum, and 0 IS the dflractlon angle The mean diameter of the crystalhtes mcre,ases wth the temperature of calcmatlon from 3 6 nm at 623 K to 5 8 nm at 693 K The degree of mckel reduction and the degree of dlsperslon of the reduced phase were detennmed by the pulse chromatographlc method described by Duprez and coworkers [ 18, 191 The degree of reduction (m per cent) R
3 I Eflect of ctrlcmnt~on tempefatu)e ii7hen studjmg the effect of calcmatlon temperature on the catalytic behawour of powdered NI--.M,O~ m benzene hydrogenation (when the reactton mMurc does not contam poem) we found that the temperature at whwh the catalyst had been calcmecl does not play a dommant role At the begmnmg of the reactlon penod the catalyst shoned a decline UI xtnlty, but after about 40 nun a steaclJ state was reached (Fig 1) The decre‘asmg rates of hydrogenation l\xh tmle could be due to
01
10
20
30
40
50
60
t,/min
Rg 1 Effect of c~stalhte sue on benzene com’erslon catalyst) 0 3 6 run, 0 5 8 nm
(fresh
S
Znu%vrc
et al
/ Nz-A1,03
mth the catalyst surface After the reaction rate measurements, pure hydrogen was passed over the catalyst Wthm 1 h the adsorbed lntermedlates of benzene were hydrogenated to cyclohexane, which left the surface, and the catalyst actlvlty was restored As seen m E’lg. 1, a change m calcmatlon temperature has no effect on the catalyst actlvlty although the diameter of the metal crystallite mcreases mth temperature from 3 6 nm at 623 K to 5 8 nm at 693 K As benzene hydrogenation over the unpoisoned catalyst does not depend on crystallite sEe it can be concluded that benzene hydrogenation IS a structure-msensltlve reaction The data are m agreement mth results of BarbIer et al. 1241 who mvestlgated benzene hydrogenation to cyclohexane over Pt-A120J catalyst However, NI-A&O~ mhlbltlon by thlophene caused a strong structure sensltlvlty (F’lg 2)) for benzene hydrogenation, large crystalhtes were less sensltlve to ttiophene mhlbltlon than small crystalhtes Thus, the structure sensltlvlty of the poison adsorption unparted an apparent structure sensltlvlty to the mam reaction m the presence of a poison m the feed-stream Manogue and Katzer [25] call such phenomena “secondary structure sensitlmty” as dlstmct from the “pnmary structure sensitlmty” whch IS reserved for the structure sensltlvlty of the mam reaction m the absence of poison 3 2 Eflect of pe1Letan.g pressure The Threle modulus for unpunty polsonmg is the prune pore dlffuslon parameter and the life-tune of the catalyst depends on it [ 26 1 The Thiele modulus &, for the polsonmg reaction may be expressed as 1271 & =z&/DJ’~
(2)
because the deactivation rate of Ni-AIPOB by Quophene m benzene hydrogenation m terms of normahzed actlvlty 1s 12
by thwphene
47
-da/dt=k,C,ad=k,‘ad
(3)
powmzng
The effective dtiuslvlty of a poison III the porous catalyst D,, 1s a function of pore diameter As no change m physical charactenstlcs of the nickel catalyst after benzene hydrogenation was detected, we assumed that the effective dlffuslvlty is uniform throughout the catalyst pellet and that it remams unaffected by the polsonmg process, which does not apply II-Ithe case of the catalyst cokmg reaction [28, 291 As seen III Table 1, there are three pore diameters, 8 9, 6 2 and 4 7 nm, used III the calculations These median pore catalysts correspond to Thlele moduh of 2 63,3 14 and 3 94 respectively The effect of catalyst deactlvatlon by thlophene was measured by momtonng benzene conversion agamst tune Catalyst actlvlty a at tune t IS defined as the net rate of formatlon of cyclohexane at the tune for which the catalyst has been on stream to the corresponding net rate measured usmg a fresh catalyst Typical actiW.y-tune plots for catalysts wth dflerent pore radu are shown m Fig 3 The results mdicate that for lower values of Thiele modulus, polsomng of the catalyst particles IS completed LIImuch less tune than for the large values, z e mternal mass transfer resistances tend to mcrease the hfe-tune of poisoned catalyst particles The overall effectiveness of the catalyst pellet dunng its active life can be characterized by an effectiveness factor q’ =
observed rate mtrmsic rate at pellet surface condltlon for fresh catalyst
(4)
representmg the combmed effects of tiuslon and deactivation III terms of pellet surface con&tions I+gure 4 displays the change of effectiveness factor mth dunenslonless tune 8 defined as
I
h OOo
6
0
4
0
q
t/mIn
F’x$ 2 Effect of crystalhte we on benzene conversion (wth polsomng) 0 3 6 nm, 0 5 8 nm
t/mln 3 Effect of catalyst pelletmg pressure on catalyst actlwty 0, p= 1 5 t cm-‘, i-=8 9 run, 0, p=3 0 t cmm2, ?=6 2 nm, A p=5 0 t cmm2, P=4 7 m Rg
6
Fig -1 Effect of catalyst pore dlanleter on catalyst nctl\ltg decay, overall effectneness factor L’S dnnenslonless tune 9, i=89 nnl, c&=267. l . r=62 nnl, 9,=3 l-1. 0, i=4; fun, 6,=3 94
15 lb
(5) for the catalyst wth iVarIous pore dlarneters It can be seen that the effectiveness factor mcIeases wth mcreasulg pore clwneter However , smce the larger pores c‘an accommodate more I>OMUI, ttw sunultaneousl~ decre‘ases the catalyst hfe This means that III the case of lmpunty po~sonutg. wtll the optrmal pore structiue of the catnl3st pellet the optunsl relatlonshlp between effectn eness
1; 18 19 30 31 7’ 23 24 ‘5 36
4. Conclusions
17 38
The mfonuatlon collected m this work per-nuts us to draw the followuig co~icliis~o~is Benzene hydrogenation over unpolsoned NI-.4&O, catalyst 1s a structure-msensltlve reactIon Catalyst ulhlbltlon by poison caused structure sensltnlty to the mam ~eactlon. I c secortdary structure sensltI\ity The pore cllameter of the NI-Al,O, pellet mfluences the degrees of dfiuslon res&ance The higher mass transfer reslskance mcre‘ases the hfe-tmie of the pellets while the lower IIIL?SS transfer mcreases the overall effectiveness factor
29
References 1 F Shadman-Yazdl &and E E Petersen, Chmn Erg Srz , 27 (197’) 2’27 2 G B De Lancey, Chat Eny SC2 , 28 (1973) 105 J E R Becker and J Wel, J Cufnl, -76 (1977) 3X 4 L Hegedus and A McCabe, UI B Delrnon and G Froment (eds ), C’afnlgst Lkx-l~~wfwn, Elsewer tinsterdam. 1950, p -171 5 L L Hegedus and J C Summers, I C17tcrl. -IS (1977) 345
Appendix
A: Nomenclature
catalyst actn7tj thlophene concentration (11101 cl111 - ‘) deactlvatlon order effectl\‘e dlffuslon coefficient for poison (Ill’
s-
‘)
concentration of thlophene correspondmg to complete dcactwatlon (mol dm- ‘) consmnt of deactwatlon rate (mul‘) characterlstlc dunenslon of pellet (mm) mean pore diameter (run) tune (mm) benzene conversIon mmununl
Gt eek sym bok overall effectlbeness factor dunensIonless tune ;: Thlete modulus for polsontng 4,
reactton
Englneemng
Journal,
Effect of catalyst
49 (1992)
preparation
45-48
45
on Ni-Al,03
poisoning
by thiophene
Stanka ZrnCe\& Department
of Chemzcal
Reactwn
Engzneerxng,
Unzverszty
of Zagreb,
Zagreb
(Croatia)
Hem-&a Melder and DeJan PlavG Rude-r BoSknvzc Instatule,
P 0
Box
1016, Zagreb
(Crontza)
(Recewed July 23, 1991)
Abstract The mfluence of expet-unental
concklons such as the temperature of calcmatlon and peUetmg pressure on Nl-A1203 deactivation by ttiophene III benzene hydrogenation LS outlmed and discussed It was found that benzene hydrogenation over unpolsoned mckel catalyst LS a structure-msensltlve reaction However, its u-&ubltlon by thophene produced structure sensltnlty the reactlon rate &as less sensltlve to thophene for large tuckel crystalbtes (formed durmg catalyst calcmatlon at Hugh temperatures followed by reduction), than for small crystalhtes Thus, the structure sensltn%y of poison adsorptlon unparted an apparent structure sensltlvlty to the rnti reactlon m the presence of a poison m the feedstream (secondary structure sensltlvlty) The pore structure of the catalyst pellet du-ectly mfluences the degree of Muslon resistance of both the mam and the polsonmg reactlons It was found that hgher mass transfer resistances mcrease the hfe-tune of the pellets whrle a lower mass transfer resistance mcreases the overall effectiveness factor
1. Introduction
2. Experimental
The deactlvatlon of a catalyst by sulphur or sulphur-contammg compounds and the consequent decrease m catalyst effectiveness is a very common
2 1 Catalyst preparatzon The method chosen for preparation of a catalyst 1s based on a patent of McArthur [ 15 ] which clauns the production of nickel alurmna catalyst by deposltlon-precipitation of nickel hydroxide onto a support by thermal decomposltlon of nickel ammo complexes To prepare the nickel ammo complex solution 20 g of mckel nitrate hexahydrate m 20 cm’ of dlstrlled water and 1 cm3 of concentrated nitric acid were dissolved and 25 cm3 of concentrated ammonia was added slowly under vigorous stu-nng A 2 M aqueous solution of sodnun hydroxide was very slowly added to this solution until the pH was 10 5 10 g of ahnnuuum oxide support prepared by the authors [ 161 were added to tlus solution The solution was heated to 363 K, wtie carbon dioxide was passed through it and Uus resulted m a rapid decrease of the pH to a value of 7.5 After a few hours a further decrease m the pH was observed and at that pomt the synthesis was stopped The product was filtered, washed wth hot d&tied water to the negative reactlon on sodnun and dned overrught at 393 K Samples were c+ned at 643 and
and unportant ious methods
problem UI mdustry Therefore, varhave been considered m order to
unprove the thloreslstance properties of the catalytic system TIE can be done by creatmg a new catalyst design m which the active phase 1s protected either geometncally (location mslde a catalyst pellet) [ l-51 or chemically (proxumty of a compound havmg a higher af%uty for sulphur) [6-81 In both cases, the mtnns~c thloreslstance of the active metal phase 1s not modified and polsorung 1s only delayed The only way to alter the mtrmslc thoreslstance of a metal 1s by modlfymg its electronic properties, and thus may be done by changmg the acid-base propertles of the carrier, by alloymg, or by changtng the metallic particle size [g-14]. The present paper 1s concerned mth the tluoresistance of NL-A1203 catalyst m which the nickel particle sue and pore structure of the support have been modtied The extent of these variations was followed usmg benzene hydrogenation, either pure or contammg thlophene as a poison
0300-9467/92/$5
00
section
0 1992 - ELsewer Sequoia
AU nghts
reserved
TAEILE
1 PIns~cal
properties
flame-Ionization detector, Pye Umcam DP 88 computmg Integrator) were the same as used pre\lously
of the catalyst
Tabletmg pressure (t cm-?)
Surfxe area (m’ g-y
Pore \olume
ALerage dnnieter
(cm'
(Iull)
Eff dfi coefficient (IO cm’ s-‘)
15 30 50
3 10 285 ‘69
0 638 0 450 0 328
89 62 17
s9 3 1 t ,3
g-1)
pore
[201 Reactton condltlons were
693 K m afl for 16 h After dg?ng and calcmatlon the powder was pressed mto pellets (5 x 5 mm) at various tabletmg pressures (1 5, 3 and 5 t cm-“) The mfluence of the pressure of pelletmg on the physIca charactenstws of the catalyst IS gwen m Table 1 PItor to use, the catalyst was reduced Z?L sllu m flo\\umg hydrogen for 10 h at ‘7-l3 K This temperature was chosen because It was found to gwe the highest catalyst actlvrty for benzene hydrogenation wthout resiltmg m catalyst witeruig 2 2 Apparatus and ploceclure The metal content (200/o NI) of the catalyst was determmed by comparmg the mltlal and final metal concentrations of the mmpregnatlon solution The specific surface areas were obtamed accol dmg to the BET method from the nitrogen adsorption Isotherms at 7’i K and a Lalue of 0 163 nm’ tor the cross-se&on of Ihe adsorbed N-, molecule Pore volumes 1%ere measured usmg the mercury porosmmeter method X-ray powder dtiractlon (XRD) patterns were recorded by ‘an X-ray dfiractometer with filtered Cu Kn ladlatlon All spectra displayed charactenstlc bands for NtO and y-Al,O, The diameter of the metal crystalhte was detemunecl flom XRD hne broadenmg usmg the Scherrer equation [ 171 (see Append= A)
d =r4A/p
cos e
(1)
where d IS the partwle size, A IS the X-ray wavelength, p 1s the peak wdth at half-mruunum, and 0 IS the dflractlon angle The mean diameter of the crystalhtes mcre,ases wth the temperature of calcmatlon from 3 6 nm at 623 K to 5 8 nm at 693 K The degree of mckel reduction and the degree of dlsperslon of the reduced phase were detennmed by the pulse chromatographlc method described by Duprez and coworkers [ 18, 191 The degree of reduction (m per cent) R
3 I Eflect of ctrlcmnt~on tempefatu)e ii7hen studjmg the effect of calcmatlon temperature on the catalytic behawour of powdered NI--.M,O~ m benzene hydrogenation (when the reactton mMurc does not contam poem) we found that the temperature at whwh the catalyst had been calcmecl does not play a dommant role At the begmnmg of the reactlon penod the catalyst shoned a decline UI xtnlty, but after about 40 nun a steaclJ state was reached (Fig 1) The decre‘asmg rates of hydrogenation l\xh tmle could be due to
01
10
20
30
40
50
60
t,/min
Rg 1 Effect of c~stalhte sue on benzene com’erslon catalyst) 0 3 6 run, 0 5 8 nm
(fresh
S
Znu%vrc
et al
/ Nz-A1,03
mth the catalyst surface After the reaction rate measurements, pure hydrogen was passed over the catalyst Wthm 1 h the adsorbed lntermedlates of benzene were hydrogenated to cyclohexane, which left the surface, and the catalyst actlvlty was restored As seen m E’lg. 1, a change m calcmatlon temperature has no effect on the catalyst actlvlty although the diameter of the metal crystallite mcreases mth temperature from 3 6 nm at 623 K to 5 8 nm at 693 K As benzene hydrogenation over the unpoisoned catalyst does not depend on crystallite sEe it can be concluded that benzene hydrogenation IS a structure-msensltlve reaction The data are m agreement mth results of BarbIer et al. 1241 who mvestlgated benzene hydrogenation to cyclohexane over Pt-A120J catalyst However, NI-A&O~ mhlbltlon by thlophene caused a strong structure sensltlvlty (F’lg 2)) for benzene hydrogenation, large crystalhtes were less sensltlve to ttiophene mhlbltlon than small crystalhtes Thus, the structure sensltlvlty of the poison adsorption unparted an apparent structure sensltlvlty to the mam reaction m the presence of a poison m the feed-stream Manogue and Katzer [25] call such phenomena “secondary structure sensitlmty” as dlstmct from the “pnmary structure sensitlmty” whch IS reserved for the structure sensltlvlty of the mam reaction m the absence of poison 3 2 Eflect of pe1Letan.g pressure The Threle modulus for unpunty polsonmg is the prune pore dlffuslon parameter and the life-tune of the catalyst depends on it [ 26 1 The Thiele modulus &, for the polsonmg reaction may be expressed as 1271 & =z&/DJ’~
(2)
because the deactivation rate of Ni-AIPOB by Quophene m benzene hydrogenation m terms of normahzed actlvlty 1s 12
by thwphene
47
-da/dt=k,C,ad=k,‘ad
(3)
powmzng
The effective dtiuslvlty of a poison III the porous catalyst D,, 1s a function of pore diameter As no change m physical charactenstlcs of the nickel catalyst after benzene hydrogenation was detected, we assumed that the effective dlffuslvlty is uniform throughout the catalyst pellet and that it remams unaffected by the polsonmg process, which does not apply II-Ithe case of the catalyst cokmg reaction [28, 291 As seen III Table 1, there are three pore diameters, 8 9, 6 2 and 4 7 nm, used III the calculations These median pore catalysts correspond to Thlele moduh of 2 63,3 14 and 3 94 respectively The effect of catalyst deactlvatlon by thlophene was measured by momtonng benzene conversion agamst tune Catalyst actlvlty a at tune t IS defined as the net rate of formatlon of cyclohexane at the tune for which the catalyst has been on stream to the corresponding net rate measured usmg a fresh catalyst Typical actiW.y-tune plots for catalysts wth dflerent pore radu are shown m Fig 3 The results mdicate that for lower values of Thiele modulus, polsomng of the catalyst particles IS completed LIImuch less tune than for the large values, z e mternal mass transfer resistances tend to mcrease the hfe-tune of poisoned catalyst particles The overall effectiveness of the catalyst pellet dunng its active life can be characterized by an effectiveness factor q’ =
observed rate mtrmsic rate at pellet surface condltlon for fresh catalyst
(4)
representmg the combmed effects of tiuslon and deactivation III terms of pellet surface con&tions I+gure 4 displays the change of effectiveness factor mth dunenslonless tune 8 defined as
I
h OOo
6
0
4
0
q
t/mIn
F’x$ 2 Effect of crystalhte we on benzene conversion (wth polsomng) 0 3 6 nm, 0 5 8 nm
t/mln 3 Effect of catalyst pelletmg pressure on catalyst actlwty 0, p= 1 5 t cm-‘, i-=8 9 run, 0, p=3 0 t cmm2, ?=6 2 nm, A p=5 0 t cmm2, P=4 7 m Rg
6
Fig -1 Effect of catalyst pore dlanleter on catalyst nctl\ltg decay, overall effectneness factor L’S dnnenslonless tune 9, i=89 nnl, c&=267. l . r=62 nnl, 9,=3 l-1. 0, i=4; fun, 6,=3 94
15 lb
(5) for the catalyst wth iVarIous pore dlarneters It can be seen that the effectiveness factor mcIeases wth mcreasulg pore clwneter However , smce the larger pores c‘an accommodate more I>OMUI, ttw sunultaneousl~ decre‘ases the catalyst hfe This means that III the case of lmpunty po~sonutg. wtll the optrmal pore structiue of the catnl3st pellet the optunsl relatlonshlp between effectn eness
1; 18 19 30 31 7’ 23 24 ‘5 36
4. Conclusions
17 38
The mfonuatlon collected m this work per-nuts us to draw the followuig co~icliis~o~is Benzene hydrogenation over unpolsoned NI-.4&O, catalyst 1s a structure-msensltlve reactIon Catalyst ulhlbltlon by poison caused structure sensltnlty to the mam ~eactlon. I c secortdary structure sensltI\ity The pore cllameter of the NI-Al,O, pellet mfluences the degrees of dfiuslon res&ance The higher mass transfer reslskance mcre‘ases the hfe-tmie of the pellets while the lower IIIL?SS transfer mcreases the overall effectiveness factor
29
References 1 F Shadman-Yazdl &and E E Petersen, Chmn Erg Srz , 27 (197’) 2’27 2 G B De Lancey, Chat Eny SC2 , 28 (1973) 105 J E R Becker and J Wel, J Cufnl, -76 (1977) 3X 4 L Hegedus and A McCabe, UI B Delrnon and G Froment (eds ), C’afnlgst Lkx-l~~wfwn, Elsewer tinsterdam. 1950, p -171 5 L L Hegedus and J C Summers, I C17tcrl. -IS (1977) 345
Appendix
A: Nomenclature
catalyst actn7tj thlophene concentration (11101 cl111 - ‘) deactlvatlon order effectl\‘e dlffuslon coefficient for poison (Ill’
s-
‘)
concentration of thlophene correspondmg to complete dcactwatlon (mol dm- ‘) consmnt of deactwatlon rate (mul‘) characterlstlc dunenslon of pellet (mm) mean pore diameter (run) tune (mm) benzene conversIon mmununl
Gt eek sym bok overall effectlbeness factor dunensIonless tune ;: Thlete modulus for polsontng 4,
reactton