function cbsmin = vanmax(x);
%  
%  25 july 94
%  (c) b.w. bequette
%
%  finds the maximum of cbs with respect to fsov for
%  the van de vusse reaction
%
%  use matlab function fmin which finds the minimum of a function
%    take -cbs as the function to be minimized,
%    which is equivalent to maximizing cbs
%
%  fsov = steady-state space velocity, fs/v
%  cas  = steady-state concentration of a
%  cbs  = steady-state concentration of b
%  cafs = feed concentratioon of a
%
   k1 = 5/6;
   k2 = 5/3;
   k3 = 1/6;
   cafs = 10;
%
   fsov = x;
%
   cas1 = -(k1 + fsov)/(2*k3);
   cas2 = sqrt((k1+fsov)^2 + 4*k3*fsov*cafs)/(2*k3);
   cas  = cas1 + cas2;
%
   cbs    =  k1*cas/(fsov + k2);
   cbsmin = - cbs;