On the Viscosity and Pipe Transport Behavior of Pure Ionic Liquids and Their Mixtures with Conventional Solvents

This work addresses two interconnected topics: the viscosity-temperature behavior of ionic liquids and the techno-economic aspects of their pipe transport. A diverse selection of ionic liquids, conventional solvents, and their mixtures—covering a wide viscosity range—was analyzed under transport conditions representative of industrial processes. Based on an extensive experimental database compiled from the literature, new empirical correlations were developed to estimate the viscosity-temperature relationships of ionic liquids, using only their viscosities at 298.15 K. Rigorous simulations of pipe transport were conducted using the Pipe Segment model in Aspen HYSYS. A continuous transition in transport behavior was observed, ranging from highly viscous ionic liquids to low-viscosity solvents and their mixtures. This observation enables the use of heuristics developed for conventional fluids in the design of transport operations involving ionic liquids, provided that their specific characteristics are appropriately considered. Under the conditions and economic scenarios analyzed, the most cost-effective strategy for transporting viscous fluids involves using pipes with the largest feasible internal diameter, regardless of whether they are constructed from carbon steel or stainless steel. The use of conventional solvents as viscosity reducers does not appear to be economically viable, except when they are already present as impurities in the ionic liquid following purification. This may, additionally, reduce the cost associated with ionic liquid recovery. Leveraging heat integration instead of relying on external heating fluids for the thermal conditioning of ionic liquids can reduce transport costs by enabling operation at higher temperatures, which increases fluid velocity without exceeding the pressure drop limit.