In the "Chemical Process Computations" by Raghu Raman, Elsevier Applied Science Publishers LTD, ISBN 0-85334-341-1,I found Peng Robinson equation in the form:
P=R*T/(V-b)- a(T)/(V*(V+b)+b*(V-b)),
where
b=0,0778*R*Tc/Pc,
a(T)=0,45724*(R^2)*(Tc^2)/Pc*alfa(T),
alfa^0,5=1+m*(1-Tr^0,5),
m=0,37464+1,54226*FI-0,26992*FI^2;
Tc=critical T
Tr= reduced T
Pc =critical P
and acentric factor FI if not known, could be estimated as
FI=(3/7)*Tbr/(1-Tbr)*LOG(Pc/101,3)-1
where Tbr is the reduced normal boiling point.
You can refer to many Chemical Engineering Thermodynamic book. You can also refer to Process Engineering Simulation model such as HYSYS Thermodynamic Base manual or PRO/II Technical reference data.