Modified Technogenic Asphaltenes as Enhancers of the Thermal Conductivity of Paraffin

Abstract

The low thermal conductivity of paraffin and other organic phase change materials limits their use in thermal energy storage devices. The introduction of components with a high thermal conductivity such as graphene into these materials leads to an increase in their thermal conductivity. In this work, we studied the use of inexpensive carbon fillers containing a polycyclic aromatic core, due to them having a structural similarity with graphene, to increase the thermal conductivity of paraffin. As such fillers, technogenic asphaltenes isolated from ethylene tar and their modified derivatives were used. It is shown that the optimal concentration of carbon fillers in the paraffin composite, which contributes to the formation of a structural framework and resistance to sedimentation, is 5 and 30 wt. %, while intermediate concentrations are ineffective, apparently due to the formation of large aggregates, the concentration of which is insufficient to form a strong framework. It has been found that the addition of asphaltenes modified with ammonium persulfate in acetic acid significantly increases the thermal conductivity of paraffin by up to 72%.

Size matters: asphaltenes with enlarged aromatic cores promote heat transfer in organic phase-change materials

“…It is noteworthy that the ASP2 molecule resembles the structure of so-called “technogenic” asphaltenes isolated from ethylene tar samples in ref. 16 and 28. The aliphatic periphery of this molecule consists of several methyl and ethyl groups, so that the ASP2 molecular weight amounts to about 500 g mol −1 in accordance with a peak molecular weight value observed through the matrix assisted laser desorption/ionization (MALDI) spectroscopy for the most probable “technogenic” asphaltene molecules considered in ref.…”

“…Recent experiments and computer simulations have suggested that asphaltenes can be used as fillers for paraffin-based phase-change materials. [14][15][16] These materials are promising for developing domestic thermal energy storage systems, but their low thermal conductivity limits their performance by reducing charging and discharging rates. Adding asphaltenes to paraffin has been found to increase its thermal conductivity, thus enhancing the practical prospects of these materials.…”

“…Adding asphaltenes to paraffin has been found to increase its thermal conductivity, thus enhancing the practical prospects of these materials. 15,16 Chemical modification of asphaltenes has also been shown to affect their aggregation behavior and control the thermal conductivity of the systems. [14][15][16] Moreover, it has been established that the sedimentation stability of paraffin-based blends filled with asphaltenes can be improved using polymer compatibilizers such as poly(3-hexylthiophene).…”

“…15,16 Chemical modification of asphaltenes has also been shown to affect their aggregation behavior and control the thermal conductivity of the systems. [14][15][16] Moreover, it has been established that the sedimentation stability of paraffin-based blends filled with asphaltenes can be improved using polymer compatibilizers such as poly(3-hexylthiophene). 17 Most previous studies considered asphaltenes of the socalled ''island'' type, whose cores chemically resembled small ''flakes'' of graphene.…”

“…23,24 Asphaltene samples can also be subjected to pyrolysis at high temperatures to change the core sizes due to polymerization/ depolymerization reactions. 25 In addition, Gorbacheva et al 16 have shown that the pyrolysis of hydrocarbon feedstock can yield so-called ''technogenic'' asphaltenes with high condensation and an almost complete absence of heteroatoms in polycyclic cores. Despite the availability of these methods, the precise control of the chemical structure of asphaltene molecules and the size of their cores remains an excessively complex experimental task.…”