function dk_dP=dK_dP(T,P)
% Compute VLE constants
% T : Temperature [K]
% P : Pressure    [bar]

% Antoine Equation Parameters
%               A       B        C
a(1,1)=Antoine(T,3.0457 , 71.6152,  3.19 );       % Hydrogen     H2
a(2,1)=Antoine(T,4.50706, 791.300, -6.422);       % Ethane       C2H6
a(3,1)=Antoine(T,4.53678,1149.360, 24.906);       % Propane      C3H8
a(4,1)=Antoine(T,3.85002, 909.650,-36.146);       % Butane       C4H10
a(5,1)=Antoine(T,3.98920,1070.617,-40.454);       % Pentane      C5H12
a(6,1)=Antoine(T,4.02832,1268.636,-56.199);       % Heptane      C7H16  (P)
a(7,1)=Antoine(T,3.97710,1330.402,-56.946);       % Cycloheptane C7H14  (N)
a(8,1)=Antoine(T,4.14157,1377.578,-50.507);       % Toluene      C7H8   (A)

p(1,1)=a(1);                                      % Hydrogen     H2
p(2,1)=2*(a(2)+a(3)+a(4))/3;                      % Gas/LPG
p(3,1)=a(6);                                      % P
p(4,1)=a(7);                                      % N
p(5,1)=a(8);                                      % A

dk_dP=diag(-p./P^2);
return

