ISO 10370 Petroleum products - Determination of carbon residue - Micro method
9 Test procedure
9.1 With the oven at a temperature < 100 °C, place the vial holder, loaded as in 8.3, into the oven chamber and secure lid. Purge with nitrogen for at least 10 min at 600 ml/min. Subsequently, decrease the purge to 150 ml/min and heat the oven slowly to 500 °C at a rate of 10 °C/min to 15 °C/min.
9.2 Hold the oven at 500 °C +/- 2 °C for 15 min. Then shut off furnace power and allow the oven to cool freely while under a nitrogen purge of 600 ml/min. When the oven temperature is < 250 °C, remove the vial holder for further cooling in the desiccator.
NOTE 1 After the samples are removed from the oven, the nitrogen purge may be shut off.
If the sample foams or spatters causing loss of sample, discard and repeat the test.
NOTE 2 Spattering may be due to water that may be re-moved by prior gentle heating under reduced pressure, followed by a nitrogen sweep. Alternatively, a smaller size may be used.
If another test is to be run, remove the lid to allow faster cooling.
NOTE 3 A subsequent test may be started when the oven has cooled to below 100 °C.
WARNING - Do not open the oven to air at any time during the heating cycle, as the introduction of air (oxygen) may form an explosive mixture with the volatile coking products formed. Do not open the oven until the oven temperature has fallen to below 250 °C during the cooling step. Maintain the nitrogen flow until after the vial holder has been removed from the oven.
Either locate the coking oven in a laboratory exhaust hood for safe venting of smoke and fumes, or install a vent line from the oven exhaust to the laboratory exhaust system, being careful not to create negative pressure in the line.
9.3 Handling the vials with forceps, transfer them to the desiccator and allow them to cool to room temperature.
Weigh each cooled vial to the nearest 0.1 mg and record its mass.
Discard the used glass sample vials.
9.4 Examine the condensate trap at the bottom of the oven chamber; empty if necessary and replace.
WARNING - The condensate trap residue may contain some carcinogenic materials, and contact with them should be avoided. They should be properly disposed of according to acceptable procedures.
10 Calculation
Calculate the mass percentage of carbon residue in the original sample, or in the 10 % (V/V) distillation residue, to the nearest 0.01 % (m/m), µCR, using the following formula:
µCR = [(m3 - m1)/(m2 - m1)] x 100
where
m1 is the mass of the empty vial, in grams;
m2 is the mass of vial + test portion, in grams;
m3 is the mass of vial + residue, in grams.
For the relationship of carbon residue by micro method (this International Standard) to carbon residue by Conradson method (see ISO 6615), Annex A may be used.
