Page 20 - Principles of Catalyst Development
P. 20

6                                                        CHAPTER  1

                Although  the  importance of increasing selectivity is  different for each
            process,  in  the  case  of industrial  operations  with  large  throughputs,  small
            improvements  may  lead  to  large  benefits.  For example,  a  1 %  increase  in
            gasoline yield in catalytic cracking amounts to an extra one million gallons
            a  day  for  the  United  States, thereby lowering dependence on  imports.(9)
                Deactivation rates enter significantly into process design.  Not only are
            yield-time relationships established, but also type of reaction and mode of
            operation  (e.g.,  fixed  or  fluidized  bed).(lO)  Lifetime  decline  can  have  a
            profound  effect  on  the  engineering  and  economics  of  a  process.  Small
            changes  that improve  lifetime can  have  a  large  payoff.  An  example  is  the
            introduction  of  bimetallics  in  catalytic  reforming.  Adding  rhenium  to
            platinum  on  alumina  greatly  decreased  the  deactivation  rate  from  both
            coking and sintering.  Not only did  the catalyst last longer and  require less
            regeneration  (thus  vastly  simplifying  process  configurations),  but  lower
            pressure operations were possible, giving improved selectivity to high-octane
            aromatics. (II)
                Priorities  in  today's  industry  emphasize  more  efficient  utilization  of
            feedstocks and energy. Most effort is placed on improving existing processes
            rather than developing new ones. With this in mind and with an awareness
            of the direction of current research, it is the author's opinion that the relative
            order of importance  is  selectivity> deactivation> activity.



            1.2.  ORGANIZATION  OF  CATALYSIS


                Before  proceeding  with  our  discussion,  we  should  perhaps  briefly
            acknowledge  the  different  but  complementary  divisions  of catalysis  now
            existing  within  industrial  and  academic  fields.  They  are  homogeneous,
            heterogeneous, and enzyme catalysis.  Each has its own structure and disci-
            plines, involving researchers from  varying backgrounds. There are special-
           ized  journals  and  meetings  catering  to  each.  Unfortunately,  attempts  at
           cross-fertilization  have  not  been  too  successful,  which  is  regrettable since
           each has  much  to  learn from  the  others.



            1.2.1.  Homogeneous Catalysis
               The  catalyst  is  the  same  phase  as  the  reactants  and  products.(12)
           Examples are hydrolysis of esters by acids (liquid-liquid), oxidation of S02
           by N0 2  (vapor-vapor), and decomposition of potassium chlorate by Mn02
           (solid-solid). Usually, the liquid phase is  most common, with both catalyst
           and reactants in solution.
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