Bartók, Mihály

Notheisz, Ferenc

Pálinkó, István

Pálinkó István

Notheisz Ferenc

Bartók Mihály

SZTE Publicatio Repozitórium - SZTE - Repository of Publications

Effect of Iodine on Platinum-CatalyzedCombustion ofNuclear PowerResidual Hydrogen inPlants491109lstv5n PAr-rr.rr6, Ferenc NorHErsz and Mihaly BnnrorDepartment of Organic Chemistry, Jbzsef Attila University, Szeged,Dom t1r 8. Hungary. H-6720INTRODUCTIONIn the secondary  cyc le  o f  a  nuc lear  power  p1ant ,  hydrogen ls  produced.  I ts; oncen t ra t i on  i s  1ow ,  abou t  2% tn  a t r ,  bu t  neve r the less  i t  mus t  be  e l im ina ted  be -cause of  the danger  o f  exp l -os ion.  Tvuo main methods are cur rent ly  used for  th isp rocess :  ( r )  i t s  ca ta l y t i c  combus t i on ,  o r  ( i i )  i t s  bu rn ing  i n  f l ame .  I n  t he  f o r -' ne r  p rocess ,  a  P t lA l r0 .  ca ta l ys t  i s  app l i ed .  Du r i ng  t he  ope ra t i on  o f  t he  p1an t ,severaf  e lements  and 6of ipounds are formed,  a .g .  iod ine,  which may behave as cata-lys t  po isons.  In  th is  paper  r , re  repor t  on resu l ts  concern ing the po ison ing ef fec t, r f  iod ine on the t ransformat ion of  hydrogen in  a i r  over  a  Pt /  AI r0 ,  cata lys t .The  reac t i on  cond i t i - ons  do  no t  exac t l y  m im ic  t he  rea l  s i t ua t i on  i n  t he  p lan t ,es the iod ine concent ra t ion in  th is  work  is  much h lgher  than can be expected inthe  p lan t  and  t he  P t lA l rO . .  i s  no t  t he  i ndus t r i a l  ca ta l ys t  ( i t  was  made  i n  ou rl abo ra to ry ) ;  none the less , ' i t  seemed  wo r th r vh i l e  t o  ca r r y  ou t  t he  i nves t i ga t i - on  be -^ * ' ^ - ^ t  t o  ou r  knov , l l edge ,  ve ry  l i t t l e  i n fo rma t i on  i s  ava i l ab le  abou t  t heL d L t J t t ,  d  L  I E d Jr n i qnn inn  c f f en l  s f  i od ine  on  any  k i nd  o f  me ta l - ca ta l yzed  t r ans fo rma t i on  (1 ,  2 ) .EXPERIMENTALA 2 .5% hyd rogen - i n -a i r  m i x tu re  was  p repa red  by  m ix i ng  H ,  and  N"  w i t h  0 ,  i n  a' :a l ib ra ted ro tameter .  Th is  mix ture was passed through a f low reSctor  eQuipped, r i th  a  co ld  t rap af ter  the reactor  and wi th  a  sampl ing dev ice.  The react ion wasrun  ove r  a  0 .43% P t /A l r0 .  ca ta l ys t ,  p repa red  by  imp regna t i on .  The  samp les  we reanalyzed by gas chromato$r5phy.  The s ignal  o f  hydrogen t4 /as moni tored.The po ison ing exper iments  were per formed wi th  I r .  Iod ine was p laced in  a  satu-ra tor  and i ts  vapor  was washed by the gas s t ream 6nto the cata lys t .  The iod ine; t r eam co r responded  app roxLma te l y  t o  a  15  Pa  gas  f l ow .  Expe r imen ts  w i t hou t  po i -son r {ere per formed in  the temperature range 32J-723 K,  and the po ison ing measure-rnen ts  a t  52J - l 2J  K .RESULTS AND DISCUSSIONThe  ac t i v i t y  o f  t he  ca ta l ys t  b ,as  app rec iab le  ( conve rs ion :  B l%)  even  a t  323  K .Thrs  act i -v i ty  j "ncreased wi th  e levat ion o f  temperature,  but  fu l l  convers ion re-' lu i red 123 K.  I t  rvas surpr is ing though that  the temperature range 423-12 i  K com-monly  appl red in  the p lant  is  not  enough for  the complete  removal  o f  res idual  hy-' l rogen.  Th is  sor t  o f  se l f -po ison ing is  qu i - te  probably  due to  the b lock ing ef fec t, r f  adsorbed u la ter .  lvh ich desorbs complete lv  on lv  a t  lZJ  K.C a l a l y t r c  S c t e n c e  a n d  T e c h r . r o l o g y ,  V o l u m e  ' 1Copyrrqht (!" 1991 by Kodansha LtdI .  P [ l i n k o  e r  r r lTreatment wi th iodine exefted a dramat ic ef fect  on the catalyst .  A short  ( fmin) t reatment under an iodine stream caused complete deact ivat ion at  both 521 Kand 623 K. Swi- tching of f  the iodine stream and purging the catalyst  v ' r i th the re-actants for  some t ime resul ted in part ia l  react i -vat ion of  the catalyst  (523 K: aJ-hour  purge ,  26% ac t iv i t y  rega in ;  ra is ing  the  tempera ture  to  623 K:  a  l -hourpurge restores 9J% of the or ig inal  act iv i ty observed at  th is temperature).  Thecomple te ly  po isoned ca ta lys t  a t  623 K cou ld  be  par t ia l l y  rev i ta l rzed  a t  121 Kand on switching back the iodine stream only part ia l  deact ivat ion occurred (55%act iv i t y  loss  a f te r  l0  min  on  s t ream) .  A t  th is  tempera ture  B l% o f  the  or ig ina lact iv i ty was restored by only a 10-min pufge with the pure reactants.  The exper i -mental-  resul ts are summarized in Tables I  and 2.Table I  Temperature dependence Table 2 Effect  of  iodine treatment and react ionof unpoisoned react ion t i : : :9rr?; , t l r rouOh (a) purging with reactantr  r ,LUcrn,  \u, /  ra is ing temperatureemp.( K )I ,  t reatmentL / \ ( m ] n ,purge withreac tan t  (h )convers ion( o t \\ / o )52J6 2 J1 2 J ( bq,1 0r ( a )? ( a )l ( a  )t ( a ,,t r<^>0tr1 1t - r2 i0BO3 58 1At lower  tempepatures,  the iod ine s t ream resu l ts  in  complete  coverage of  thesur face v ia  mul t i layer  adsorpt ion wi th  both phys ica l ly  and chemica l ly  adsorbedspec ies.  The pure reactant  f low removes the excess iod ine and the chemisorbedlaye r  does  no t  cove r  t he  en t i r e  su r face  ( J ) :  pa r t i a l  r eac t i va t i on  occu rs .  A t  t heh ighest  temperature appl ied,  there is  extens ive iod ine desorpt ion;  complete  deac-t ivat ion does therefore not  occur ,  even under  an iod ine s t ream, and in  i ts  ab-sence a shor t  purge ur i th  the pure reactants  prov ides an easy react ivat ion route.CONCLUSIONSThe above set -up and resu l ts ,  in  sp i te  o f  the d i f ferences f rom the rea l  condi -t i ons ,  i nd i ca te  t he  f o l l ow ing  f i nd ings :  ( i )  i n  t he  ope ra t i ng  range  o f  t he  p lan t ,se l f -po ison ing of  the cata lys t  occurs ,  ( i i )  i -od ine po ison ing is  det r imenta l  tothe cata lys t  ( the descr ibed set -up can be regarded as an acce lerated po ison ingprocedure) .  Upon exposure to  a  10-*  Pa iod ine r '1ow,  0 .17 sur face iod ine coveragedeve lops  ove r  P t ( i 11 )  unde r  UHV cond i t i ons  ( l ) .  Consequen t l y ,  t he  ca ta l y t i c  com-bust ion o f  res idual  hydrogen can be safe ly  appl ied in  nuc lear  power  p lants  onJ-yunder  r igorous check ing condi t ions.REFERENCES( 1 )  J o y n e r ,  R . W . , a n d  P e n d r y ,  J . 8 . ,  C a t a l .  L e t . 1 , 1  ( 1 9 8 8 ) ;  C a d d o c k ,  P . 0 . ,J o y n e r ,  R . W . ,  a n d  W i l l i a m s ,  P . 8 . ,  C a t a l .  L e t . 2 , 2 1  ( 1 9 8 9 ) .Q )  X . - 1 .  Z h o u ,  a n d  W h i t e  J . M . ,  J .  P h y s .  C h e m .  9 4 ,  2 6 4 t  ( 1 9 9 0 ) ;  L i u ,  Z . - V . ,A k h t e r ,  S . ,  R o o p ,  8 . ,  a n d  W h i t e ,  J . M . ,  J .  A m .  C h e m .  S o c .  1 1 0 ,  B 7 0 B  ( i 9 B B ) .( l )  S t i c k n e y ,  J . L . ,  R o s a s c o , S . D . ,  S o n g ,  D . ,  S o r i a g a , M . P . ,  a n d  H u b b a r d ,  A . T . ,S u r f .  S c i .  l J O ,  3 ? 6  ( f 9 8 l ) .t e m p .  ( K ) conve rs ion (%)

Effect of Iodine on Platinum-Catalyzed Combustion of Residual Hydrogen in Nuclear Power Plants

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Effect of Iodine on Platinum-Catalyzed Combustion of Residual Hydrogen in Nuclear Power Plants

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