Petrochemistry (001-050)

The water content of diesel fuel and petrol (gasoline) is determined according to Karl Fischer. Because of the low water content the determinations are carried out by coulometric titration.

Determination of tar acids in coal tar products. This procedure may also be applied to the determination of a range of weakly acidic organic compounds such as carboxylic acids, hydroxy acids, phenols, phenolic acids, keto-enols, imides and aromatic nitro compounds¹.

¹ Vaughan, G. A. Thermometric and Enthalpimetric Titrimetry. Van Nostrand Reinhold Co. Ltd (1973)

In principle the 774 Oven Sample Processor can be used with all samples that release their water when heat is applied. However, the KF oven method is essential whenever direct volumetric or coulometric Karl Fischer titration is impossible because the sample contains interfering components or, due to its consistency, is difficult to place in the titration vessel.

The combination of the 774 Oven Sample Processor with coulometric Karl Fischer titration (756 or 831 KF Coulometer) is ideal for samples with a low water content. Foodstuffs, pharmaceutical products, plastics or mineral oil products can be analyzed fully automatically and extremely accurately. On the other hand, a volumetric Karl Fischer titration using a KF Titrino is to be preferred for samples with a very high water content (>50%).

In accordance with the gas extraction principle the water is driven out of the heated sample by a stream of dry carrier gas and transferred to the titration vessel, where the water is determined by KF titration.

For temperature-sensitive samples, e.g. foodstuffs, the water can be released gently at lower temperatures by simultaneous extraction with methanol. In this way it is possible to prevent any water being released by decomposition.

This Application Bulletin uses examples from the food, pharmaceutical, plastics and petrochemical industries to describe automatic Karl Fischer water determination using the 774 Oven Sample Processor and a KF Coulometer. Information concerning the combination of the Oven Sample Processor with a volumetric KF titrator is given in brackets.

Humus in the soil is made up of decayed organic substances. The humus content is used for the evaluation of the exchanger capacity, the water-binding capacity of the soil structure and the biological activity.

Under heating, a potassium dichromate/sulfuric acid mixture will decompose organic substances to form carbon dioxide and water. A known amount of potassium dichromate is added to an accurately weighed-out amount of soil. After the reaction the amount of potassium dichromate consumed is proportional to the humus content of the soil.

Max. 15 samples can be titrated fully automatically with the 676 Sample Changer. After the titration the used solution is aspirated off into a waste container using a 683 Diaphragm Pump and the sample vessels are rinsed.

Non-aqueous titrations, particularly those in nonpolar solvents with a low conductivity, are strongly affected by electrostatic charges to the extent that the evaluation of the titration curves may be extremely difficult or even impossible. With the 6.2129.000* Differential Amplifier Metrohm has created a useful tool with which easily evaluable titration curves can be obtained even under difficult conditions.

* In Titrinos the differential amplifier is already built in.

The determination of the acid or base number plays a significant part in the analysis of petroleum products. This is shown by the numerous standard procedures in use the world over (internal specifications of multinational companies, national and international specifications of ASTM, DIN, IP, ISO, etc.). These procedures differ mainly in the composition of the solvents and titrants used. Fortunately, the days of the work-intensive use of pH meters, glass burets and color indicators seem to be over. Modern titrators are gradually replacing time-consuming manual titrations as well as the calculation of the results.

This Bulletin describes the determination of the acid and base number in petroleum products by means of automatic potentiometric titration.

The determination of the lead content in engine fuels has gained considerable importance since the introduction of the catalytic converter technique. Even small contents of lead interfere with the effectiveness of the catalysts or may destroy them. On the other hand, there are still many vehicles on the roads which run on leaded fuel (addition of tetraalkyl lead). Here also the knowledge of the lead content is of interest.

With reference to DIN 51769 and ASTM 0-1269 a simplified procedure for the determination of lead in petrochemical products is described. The products are digested with HCl and the lead compounds are converted to lead(II) chloride. After extraction with water, the inverse voltammetric Pb determination is carried out.