Physical Properties of Liquid Crystals in Athabasca Bitumen Fractions S. Reza Bagheri, † Brady Masik, † P. Arboleda, ‡ Q. Wen, ‡ K. H. Michaelian, ‡ and John M. Shaw* ,† † Department of Chemical and Materials Engineering, University of Alberta, Edmonton, Alberta T6G 2V4, Canada ‡ CanmetENERGY, Natural Resources Canada, Devon, Alberta T9G 1A8, Canada ABSTRACT: Naturally occurring amphotropic liquid-crystals were recently identified in unreacted hydrocarbon resources and resource fractions from around the world, including Athabasca bitumen. Liquid crystal forming constituents are present in both asphaltene and maltene fractions and appear to be an important class of materials that is missed entirely during conventional hydrocarbon characterization, i.e.: SIMDIST or SARA analysis. In this contribution, some physical properties of liquid crystals in Athabasca asphaltenes and maltenes identified using experimental methods as diverse as polarized light microscopy, differential scanning calorimetry (DSC), and mid- and near-infrared photoacoustic spectroscopy with depth profiling are reported. Liquid crystals, comprising materials with an aromaticity between that of maltenes and asphaltenes, form irreversibly on the surface of both asphaltene particles and maltene drops on heating. At higher temperatures the liquid crystals become isotropic but remain on particle surfaces. Liquid crystals do not reappear on cooling or subsequent reheating unless the samples are frozen and crushed between heating cycles. The interdependence of these phase properties on sample thermal and mechanical history may help explain unexpected and frequently deleterious surface and interfacial phenomena arising during Athabasca bitumen production and processing. ■ INTRODUCTION Liquid-crystals were recently observed in unreacted petroleum fractions including Athabasca, Maya, and Cold Lake pentane asphaltenes, Safaniya heptane asphaltenes and a fraction of Athabasca bitumen were extracted with supercritical n-pentane (SFE6). 1 The liquid crystals form between 338 and 341 K for the pentane asphaltenes, 370 K for Safaniya heptane asphaltenes, and 316 K for SFE6. The liquid crystals disappear between 423 and 435 K for the pentane asphaltenes, 433 K for C7 Safaniya asphaltenes, and 373 K for SFE6. These materials also exhibit liquid crystalline domains in the presence of toluene vapor at room temperature. 1 Compounds that exhibit liquid crystalline properties in a defined temperature range between the melting point and the transition to the isotropic liquid state are called thermotropic. Compounds that show liquid crystalline properties by the addition of solvents are called lyotropic. For this type of liquid crystal, concentration constitutes an additional degree of freedom. Compounds that exhibit both types of behavior are termed amphotropic or amphitropic. 2 The liquid crystals observed in unreacted petroleum fractions belong to this latter group. Following these initial observations, detailed studies related to the thermophysical properties, physical structure, and chemical composition of the liquid crystals were initiated. For example, liquid crystal rich material extracted from Athabasca pentane asphaltenes comprises more than 10,000 different constituents. Their mean molecular size is smaller than asphaltenes, and they are enriched in heteroatoms relative to asphaltenes. Detailed chemical composition data are reported separately. 3 This material is distinct from carbonaceous mesophase, 4-9 a nematic discotic (disk-like) liquid crystal phase formed during petroleum coking 6 and liquid crystal rich material separated from isotropic pitch using supercritical toluene 10 and pentane. 11 The liquid crystal rich material investigated here appears to share some characteristics with liquid crystals observed at bitumen-water interfaces during production, 3,12-14 but this link requires further elaboration. Naphthenic acids and their salts also form liquid crystals at oil- water interfaces. 15 However, though present, such constituents appear to comprise a minor fraction of the liquid crystal forming material. Possible attributions are also found in cognate literatures. For example, plastic crystals exhibit crystal-like positional order with local rotational disorder and mobility, 16 and Funaki et al. 17 suggested that orientation and stress- induced plasticization can produce domains in polarizing optical microscopy that resemble Maltese crosses. Basic physical structures for liquid crystals are well established. They include the following: columnar liquid crystals, that have long-range order in two dimensions, e.g.: array of liquid tubes; smectic liquid crystals, that have quasilong-range order in one dimension, e.g.: liquid layers stacked on one another; and nematic liquid crystals, that have positional short-range order and orientational long-range order. 18 Many individual molecules and classes of molecules are known to form liquid crystals: small elongated organic molecules, discoid organic molecules, and long helical rod like molecules, which may include single or multiple oxygen, nitrogen, and sulfur substitutions. 18-20 Binary mixtures also form discotic 21 and nematic 22 liquid crystals through cooperative interaction even if the individual components do not do so on their own. These phenomena have been known for some time. 23 Liquid crystals involving multiple components, as would appear to be the case for asphaltenes and heavy oil fractions, is a less well-developed subject. The transition from solid to liquid crystal states is also known to be complex as are the resulting physical states and their properties. 24 Metastable Received: February 27, 2012 Revised: June 23, 2012 Published: June 25, 2012 Article pubs.acs.org/EF © 2012 American Chemical Society 4978 dx.doi.org/10.1021/ef300339v | Energy Fuels 2012, 26, 4978-4987