Page 56 - Principles of Catalyst Development
P. 56

CATALYST  DEVELOPMENT                                            43
            feedstocks,  products, processing routes, or conditions from those normally
            used. Direct liquefaction of coal is a recent example; low-density polyethyl-
            ene is  another.
                Modification of an existing process involves a change either in conver-
            sion, selectivity, lifetime, or operating conditions. The need may come from
            changes  in  economics,  feedstocks,  products  and  energy  supplies  or from
            problems encountered in established units.  For example, steam reforming,
            as  practiced until the  1960s, was a fairly  low-pressure process.  In order to
            take advantage of more economical centrifugal compressors, it was desirable
            to  raise  pressure in  the  reformer.(l)  Higher pressures required  more active
            and robust catalysts.  It is  interesting that the solution to this  problem was
            to  increase  silica  in  the  support,  thereby  generating  a  new  problem.  At
            higher  steam  pressures,  silica,  which  is  volatile,  leaves  the  catalyst,  and
            deposits  on  lower-temperature  equipment  downstream.  Thus  a  second-
            generation solution was  needed.(49)
                Whether new or existing, it is desirable at this point to make a detailed
            analysis  of similar processes. This  helps to  focus  upon potential problems
            and  also  define  the  direction  of the  development.  For  example,  in  direct
            coal  liquefaction, comparison with  hydrotreating of heavy petroleum frac-
            tions  was  useful  to establish similarities and differences.(78)
                Detailed comparisons are time consuming and tedious, but well worth
            the  effort.  It is  wise  to  follow  a  systematic  procedure such  as  the  "check
            list" in Appendix 4.  Only in  this way is  it certain that all  relevant data are
            included and nothing overlooked. If conscientiously carried out, the exercise
            is  not  only  informative but often  generates  creative  and  innovative  ideas.



           3.3.  DEFINE  PROBLEM  AND  OBJECTIVES

                Catalyst problems vary from case to case. Increased activity or improved
           selectivity  may  be  called  for,  or  decreased  deactivation.  Perhaps  it  is  a
            question  of devising  satisfactory  regeneration  procedures.  In  some  cases
           cost and availability of catalyst components may be the factor.  Analyses of
           similar  processes  are  helpful  in  establishing  reasonable  levels  and  limits.
           Just  how  much activity  is  required? What selectivity is  sufficient?  What is
           the minimum regeneration cycle?
                Next,  we  must  define  the  precise  objectives  necessary  to  solve  these
           problems,  and  this  can  be  very  critical.  For example,  activity,  selectivity,
           and  deactivation  problems  may  exist  because  of  either  chemical  or
           diffusional  factors.  Which is  it? The answer determines the  route of future
           development.  If chemical  properties are to be adjusted, then modification
           of  surface  composition  is  necessary.  On  the  other  hand,  correction  for
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