Process for determining the distillation characteristics of liquid petroleum products by express mini-distillation and apparatus permitting implementation of this process

Process for determining the distillation characteristics of liquid petroleum products by express mini distillation, characterised by the fact that it includes the following steps:

• 1. a volume of the order of 5 to 15 ml of the sample to be analysed is introduced into a distillation flask co-operating with a heating element at its lower part and provided with a pressure detector and two inertialess temperature sensors permitting measurement on the one hand of the true value of the temperature of the sample in the liquid phase and on the other the true value of the temperature of the sample in the vapour phase at a level situated a little below the inlet of the outlet tube with which the distillation flask is equipped,
• 2. the distillation flask is heated with a constant heating intensity depending on the nature of the sample to be analysed so as to progressively boil it,
• 3. the vapour pressure in the distillation flask is constantly measured at the level of the inlet of the outlet tube, as are the true values of the temperatures of the sample in the liquid phase TL and the vapour phase TS and the curves are plotted representing the variations in this pressure and these temperatures as a function of time τ1,
• 4. the primary and secondary derivatives are established of the curve representing the variations of the temperature of the sample in the liquid phase and in the vapour phase:
• ⅆ T S ⅆ τ 1 ;
• ⁢ ⅆ T L ⅆ τ 1 ;
• ⁢ ⅆ 2 ⁢ T S ⅆ τ 1 2 ;
• ⁢ ⅆ 2 ⁢ T S ⅆ τ 1 2
• and the temperature is deduced of initial boiling in the liquid phase TLIBP which corresponds to the point for which ⅆ 2 ⁢ T L ⅆ τ 1 2 = 0 ,
• 5. the temperature of initial boiling in the vapour phase TSIBP is determined which corresponds to the time for which a commencement of increase of pressure is observed.
• 6. the temperature TLEND is determined for which the value indicated by the temperature sensor which measures the true value of the temperature of the sample in the liquid phase corresponds to the value indicated by the sensor which measures the temperature of the sample in the vapour phase and by convention this temperature TLEND is considered to be equal to the final boiling temperature in the vapour phase TSFBP,
• 7. the volumetric percentage of sample distilled νV is determined from curves representing the variations as a function of τ1 in the pressure of vapour P in the distillation flask and in the true value of the temperature of the sample in the vapour phase TS by the function:
• v Vi = [ Sf ⁢ ( Ti S , Pi ) Sf ⁢ ( T S , P ) , V i res ]
• in which Sf(TS,P) depends on the area situated below the pressure curve in the distillation process while Sf(TiS, Pi) depends on the fraction of this area at the time τli, and Vires represents the volume of liquid in the distillation flask at the time τli,
• 8. the molar percentage of sample distilled νM as a function of the true value of the temperature of this sample in the vapour phase TS is determined by the function νMi=f(νVi, ρi, TSi) in which ρi represents the molar density at the time τli,
• 9. the final boiling temperature in the liquid phase TLFBP is determined by interation in accordance with the formula:
• T FBP L = T END L + ( T END L - T FBP L ) [ v END ( 1 - v END ) / a ] ⁢ ⁢ 1 / k
• in which νEND represents the molar percentage of sample distilled at the temperature TLEND and a and k are coefficients of the mathematical model of distillation corresponding to the empirical formula:
• v M = a ⁢ ⁢ τ k ( 1 + a ⁢ ⁢ τ k )
• calculated by iteration from the equation:
• ln ⁢ ⁢ ( v Mi 1 - v Mi ) = ln ⁢ ⁢ a + k ⁢ ⁢ ln ⁢ ⁢ τ i
• in which:
• τ i = T i L - T IBP L T FBP L - T i L
• calculating each step a new value of TFBPL up to the moment when:
• TFBPL(n)−TFBPL(n-1)≦1° C.
• 10. the molar percentage of sample distilled as a function of the true value of the temperature of this sample in the vapour phase is recalculated so as to take account of the residues and losses of sample in the vapour phase by the formula:
• νMi=ν′Mi+ΔLi+ΔSi
• in which ΔSi represents the percentage of vapour phase in the course of distillation, ΔLi the percentage of liquid phase at the moment of its formation by condensation and νMi the molar percentage of sample distilled taking the residues into consideration,
• 11. the volumetric percentage of sample distilled νVi as a function of the true value of the temperature of this sample in the liquid phase is determined by the formula:
• νVi=f(νMi, ρi, TiL)
• 12. and the corresponding curve is traced.