Measuring the Density of Bitumen and its Relevance

Bitumen is a combination of different organic substances. It occurs naturally and can also be obtained from crude oil. At ambient temperature, bitumen is often very thick or even solid. In other words: highly viscous. Density is an economically relevant factor: It affects the return on sales.

Imagine that a large amount of bitumen is transported – as usual – by tanker ship from A to B. The “blending” of the bitumen is done directly on the tanker. Before the ship can sail out again it must be ensured that the volume of bitumen corresponds with the agreed amount. The customers want to know the mass of the sold bitumen. To determine these values a density measurement is carried out. The quicker the density value is determined, the better – the time a ship spends in the port is very costly.

Time is money

The most common method for determining the density of semi-solid bituminous materials is ASTM method D70. This is a measurement using a pycnometer: To start with the pycnometer must be calibrated. To do this the first step is to weigh the pycnometer and then fill it with water. The next step is to heat the device to 25 °C or 60 °F for approx. 30 minutes in a water bath. Afterwards the pycnometer must be dried and weighed again. The sample is then heated, which takes a further 30 minutes or so. Following this the sample can be filled into the pycnometer. It takes around 40 minutes more for the sample to cool down to 60 °F or 25 °C. At that point the pycnometer can be weighed again. Water is then added and the stopper is used to loosely close the pycnometer so that no air bubbles can form. The pycnometer is then thermostatted for at least a further 30 minutes. After the pycnometer has been dried it is weighed again. Now the density can be calculated. Without including the time for a thorough cleaning of the pycnometer, this measuring procedure already takes around 120 minutes – and all the while the tanker is waiting. Human influence makes this method – similar to measurement with a hydrometer – prone to errors. This can result in the measurements having to be repeated. This increases the costs because the tanker has to wait longer.

Quicker and better: digital density measurement

To obtain results quicker and more easily it is possible to carry out analysis with a digital density meter. DMA 4200 M was specially designed for the petroleum industry and can measure all samples such as crude oil, intermediate products, tar, bitumen, liquid gas and highly viscous liquids. In contrast to the two old-fashioned methods – measurement with a pycnometer or hydrometer – this type of measurement only needs a very low sample volume.

DMA 4200 M

The heart of DMA 4200 M is an oscillating U-tube made of Hastelloy, a material which has much higher chemical resistance to sour gas and hydrochloric acid than stainless steel. It can be used at all points in the refining process and is the only instrument of its type which is perfectly suited for measuring “heavy” samples such as bitumen, tar and VGO (Vacuum Gas Oil) in the laboratory. DMA 4200 M automatically calculates the density value for the required temperature using built-in API tables. This means the results for the tanker ship would be available immediately because a measurement of the already liquid sample only takes twelve minutes. The results of a double measurement are available in less than half an hour and then the tanker is free to leave the port. After the measurement the measuring cell can be cleaned quickly with just a small amount of solvent. 10 mL to 15 mL are enough. This is just a quarter of the volume which is required by the conventional methods. This not only helps the refineries to save additional money but is also environmentally friendly and safe.
With DMA 4200 M you can take a well-deserved break.

Would you like to learn more about measurements on bitumen and asphalt? The Eurasphalt & Eurobitume Congress takes place for the sixth time from June 1 to 3 – this year in Prague. Anton Paar is of course taking part. Visit us at Booth 85.