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Vapour pressure

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Reference
Endpoint:
vapour pressure
Type of information:
experimental study
Adequacy of study:
key study
Study period:
2011
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
guideline study with acceptable restrictions
Qualifier:
according to
Guideline:
OECD Guideline 104 (Vapour Pressure Curve)
Deviations:
no
Qualifier:
according to
Guideline:
EU Method A.4 (Vapour Pressure)
Deviations:
no
GLP compliance:
not specified
Type of method:
effusion method: by loss of weight or by trapping vaporisate
Temp.:
25 °C
Vapour pressure:
1.6 other: mPa

Results obtained in the measurement of the vapour pressures of Castor Oil, reaction with Soybean Oil.

 Cell  m / mg  p / Pa  m / mg  p / Pa
 T / °C = 24.91 t = 02h58m07s  T / °C = 29.92  t = 22h37m16s
 IV  0.1  0.0012  0.5  0.0008
 V  0.2  0.0024  0.6  0.0009
 VI  0.1  0.0012  0.7  0.0011
    T / °C = 48.94  t = 20h09m50s   T / °C = 39.22  t = 23h47m27s
 IV  0.5  0.009  0.1  0.0002
 V  0.2  0.0004  0.1  0.0002
 VI      0.1  0.0002
     T / °C = 39.21 t = 74h15m43s     
 IV  0.1  0.00005    
 V  0.1  0.00005    
 VI  0.1  0.00005    

m : is the mass of effused compound

t : is the effused time

As seen in the graph, the result of the measurements is not a typical vapour pressure line. Instead, it can be verified from the chronological order of the experiments that the calculated value for the vapour pressure was always inferior to what would be expected considering the previous experiment. This is especially clear in the experiments 4 and 5, performed at the same temperature. The peculiarity of these results is due to the fact that the measured compound is a UVCB product. As the experiments are performed, the more volatile compounds effuse readily, leading to a change in the composition of the condensed phase, which in the next experiment will show a lower vapour pressure as the composition becomes richer in the less volatile compounds. The first experiment is therefore the only which can be considered to reproduce the vapour pressure of the sample received from the customer. Based on this value, vapour pressures for other temperatures can be estimated, although with limited precision. This can be done considering typical values of the enthalpies of vaporization, which determines the change of pressure with temperature. For the sample in question, the vapour pressure is expected to vary a 10 fold per 30 °C. Further measurements could be performed by a static method, which is not sensitive to the purity of to the composition of the samples, being therefore more suitable for UVCB products. However, given the results obtained in the first experiment with the Knudsen effusion method at 25 °C, the vapour pressure of the compound is too low to be quantified by the static method, unless the study is performed at a much higher temperature. A solution to the problem would be to repeat the experiments using in each experiment a new sample, rather than sample used in the previous experiment. The following table shows the value measured at the temperature of 25 °C, and values derived for other relevant temperatures, using on an empirical method based on a typical value of enthalpy of vaporization.

Vapour pressures of Castor Oil, reaction with Soybean Oil calculated for relevant temperatures. The values have an uncertainty of around 50%.

 T /K  T / °C  p / mPa  p / mbar (hPa)
 293.15  20.0  1.0 (b)  0.00001
 298.15  25.0  1.6 (a)

 0.000016

 323.15  50.0  13 (b)  0.00013
 328.15  55.0  20 (b)  0.00020

a – value determined experimentally;

b – Value estimated from the experimental value obtained for 25 °C.

Conclusions:
The vapour pressure of the substance was determined as 1.6 mPa (0.000016 mbar = hPa) at 25 °C
Executive summary:

The vapour pressure of the substance was determined using the Knudsen effusion method (mass-loss technique), according to OECD guideline 104 and EU method A.4.

The quality of the apparatus was previously verified with the measurement of well known reference compounds.

Experiments were performed at temperatures between 25 °C and 49 °C. The results did not allow the establishment of an acceptable relation between the vapour pressure of the compound and temperature, due to the fact that the measured sample is a UVCB product. As experiments are performed, the more volatile components present in the sample effuse readily, leading to a change in the composition of the condensed phase, which from one experiment to the next will exhibit a lower vapour pressure, since the composition becomes richer in the less volatile compounds.

The first experiment however, can be considered to reproduce the vapour pressure of the sample received from the customer. This experiment yielded a value of 1.6 mPa (0.000016 mbar = hPa) for the vapour pressure of the sample at 25 °C.

Description of key information

The vapour pressure of the substance was determined as 1.6 mPa (0.000016 mbar = hPa) at 25 °C

Key value for chemical safety assessment

Vapour pressure:
0 hPa
at the temperature of:
25 °C

Additional information

The vapour pressure of the substance was determined using the Knudsen effusion method (mass-loss technique), according OECD guideline 104 and EU method A.4.

The quality of the apparatus was previously verified with the measurement of well known reference compounds.

Experiments were performed at temperatures between 25 °C and 49 °C. The results did not allow the establishment of an acceptable relation between the vapour pressure of the compound and temperature, due to the fact that the measured sample is a multi-component product. As experiments are performed, the more volatile components present in the sample effuse readily, leading to a change in the composition of the condensed phase, which from one experiment to the next will exhibit a lower vapour pressure, since the composition becomes richer in the less volatile compounds.

The first experiment however, can be considered to reproduce the vapour pressure of the sample received from the customer. This experiment yielded a value of 1.6 mPa (0.000016 mbar = hPa) for the vapour pressure of the sample at 25 °C.