njit-etd1961-002 - New Jersey Institute of Technology

METHOD OF CALCULATIONThe critical constants of formaldehyde wereevaluated using Lydersen's correlations 8,¹0 basedon atomic and structural contributions which could bedue to either the -CHO or the -C = 0 group. Based onthe -C = 0 group contribution, the calculated criticalcompressibility factor Zc of formaldehyde was greaterthan the value of water. This was not likely, becausethe value of the dipole moment of water, which is ¹.84 ¹5,is less than that of formaldehyde, 2.27 ¹5 . Therefore,the decision was made to estimate all critical constantsbased on -CHO group contribution.Calculations of the vapor pressure from -¹9 ° C. tothe critical point were based on Riedel's correlation ¹¹,¹² .The thermodynamic values of specific volume,enthalpy and entropy in both the saturated and superheatedregions were determined from the correlations ofLydersen, Greenkorn, and Hougen 9 . These correlationswere derived from the theory of corresponding states andevaluation of 82 different compounds for which P-V-T dataand critical constants were known.All data available for calculations in this paperare listed in Section ¹.The procedure of calculation for the establishmentof the thermodynamic properties of formaldehyde was asfollows:-(A) The critical temperature was predicted usingLydersen's method 8 ' 10 which is a modification ofthe Guldberg rule. The Lydersen method forcritical temperature relates critical temperature,Tc , to the normal boiling temperature, Tb, and 9 which