The Effects of Ultrasonic Treatment On the Viscosity of Athabasca Bitumen And Bitumen-solvent Mixtures

Abstract

Heavy oils and bitumens may be considered to be composed or chemical constitutive molecules belonging to two distinct categories, namely, the malthenes (soluble in 40 volumes of n-pentane) and the asphaltenes (soluble in roluene but insoluble in n-pentane).
The spatial organization of malthenes and asphaltenes leads to the macrostructural and microstructural properties of which
viscosity is of paramount importance for production, transportation and processing considerations., Such spatial organization causes an increase in viscosity with an increase in asphaltene concentration. Hence the high viscosity of Athabasca bitumen is, at least, partly due to its high asphaltene content (>15 wt.%).

Experimental results suggest that viscosity depends not only on asphaltene concentration but also on the molecular weight of the asphaltenes. For example, higher molecular weight asphaltene units have greater tendencies to form aggregates of larger sizes. and therefore, provide greater resistance to flow,. The process of aggregate formation is a complex one and is not well understood. However, this process can be reversed by breaking up the aggregates with the application of energy in the form of high shear or heat. We have examined the effect of ultrasonic energy on the viscosity or Athabasca bitumen and its mixtures with olher solvents and solutions via break up of asphaltene aggregates. In this paper, we report the results of our experimental work.

Introduction

Bitumens produced from Alberta tar sand formations such as The Athabasca formation have viscosities higher than 100,000 mPas (cP) at room temperature Pipeline specifications require viscosities of less than 120 mPas measured at 20 ºC. As a result hey can not be transported through a heated pipeline and addition of lighter diluents to reduce viscosity prior to transportation via a conventional pipeline, the latter is widely used in Alberta.

With the projected increase in bitumen and heavy oil production and the dwindling supply of light condensate, the diluent method of bitumen and heavy oil transportation will become increasingly difficult. Projections are that condensate supplies may not be sufficient enough to transport the growing volumes of Alberta bitumens and heavy oils by the early 1990's ⁽¹⁾.
As a result the search for other viable options has been underway for sometime. One notable development in this area is the oil-in-water emulsion technology, commercially known as the Transoil process, where the viscosity of the bitumen is reduced by forming an oil-in-water emulsion prior to transportation and subsequent recovery of the bitumen upon emulsion break up. The oil-in-water emulsion technology requires a two stage emulsification process at the upstream end and a de-emulsification process at the downstream end of the pipeline. The bitumen that is recovered from de-emulsification process essentially remains as viscous as the original bitumen and needs to be subjected to various upgrading stages. Successful field trials of this technology has been reported ⁽²⁾. One traditional viscosity reduction process involving low seventy thermal cracking, known as visbreaking, is superior to oil-in-water transportation to the sense that it not only reduces viscosity, but also upgrades the bitumen to some extent. This reduces the upgrading effort required in a downstream refinery.