A new perspective on the measurements of wax appearance temperature: Comparison between DSC, thermomicroscopy and rheometry and the cooling rate effects

Knowledge on wax appearance temperature (WAT), amongst other properties, is essential in designing the facilities involved in the transportation and processing of waxy crude oil. Several measurement techniques and equipment are currently available to measure the WAT. However, differences in the values measured from different measurement platforms may result in conflicting decisions. In this work, the WAT of several crude oils, representing mild, medium and severe waxy crude oils are measured utilizing current advanced and precise equipment; a micro differential scanning calorimeter (micro-DSC) capable of providing measurements at low cooling rates, a cross polar microscopy (CPM) coupled with an image processing technique and a controlled stress rheometer. Several rheological protocols to measure WAT especially at low shear and strains to better replicate the static cooling measurements in the micro-DSC as well as under CPM are assessed. The effects of cooling rate on the WAT and wax aggregation as well as the WAT comparison from the various equipments under cooling rate of 1 degrees C/min are explored and discussed in detail. The results show that the WAT measured from different platforms is highly influenced by the precipitation rate, the type of wax (micro or macro crystalline), the cooling rate as well as the imposed shear. The advancement of micro-DSC and rheometer technology provides better sensitivity for WAT measurement than microscopy observation under CPM.