STRUCTURE OF WATER/SOLIDS/ASPHALTENES AGGREGATESAND THEIR SETTLING BEHAVIOR IN SOLVENT-DILUTED BITUMEN

摘要

Emulsified water droplets (WD), dispersed solids (DS), and precipitated asphaltenes (PA)form aggregates when bitumen emulsions are treated with aliphatic solvents. TheWD/DS/PA aggregates in solvent-diluted bitumen exhibit zone settling mode and thesettling rate is strongly influenced by aggregate structure. Procedures and experimentaltechniques have been developed for determining structural parameters of the aggregatessuch as average porosity, diameter, density, volume fraction, and Richardson-Zakiparameter. It has been found that the size and compactness of the WD/DS/PA aggregatesdepend on properties of the solvent used to dilute the bitumen emulsion and also onmixing conditions e.g. mixing temperature. Choosing the appropriate solvent andadjusting mixing conditions can thus greatly enhance settling rate. In this study, bitumenfroth was diluted with a 50/50 mixture of n-pentane and n-hexane (C5C6) and with nheptane(C7) at mixing temperatures ranging from 30oC to 120oC. It was found in settlingtests that the volume fraction of aggregates in the hindered settling zone was 0.12 to 0.13.Lighter solvent generated aggregates with lower porosity while heavier solvent producedhigher-porosity aggregates. Elevating the mixing temperature led to larger aggregates andresulted in a significant increase in settling rate. The effect of the permeability of theporous structure of the aggregates on settling rate was analyzed and was found to beinsignificant unless the porosity of the aggregates is very high (e.g. above 0.8).