(55f) Packing Structure Capable of Sub-Centimeter HETP for High Purity Distillation of Low Relative Volatility Compounds

Achieving a high separation factor with mixtures of low relative volatility typically requires a large numbers of stages and very tall columns, even with advanced structured packings.  The challenge is exacerbated by vapor and liquid phase dispersion when a high purity product is demanded.  A novel microchannel technology is presented that utilizes layered structures to precisely control the mass transfer length-scale in the liquid phase to a fraction of a millimeter, thereby enabling sub-centimeter height of a theoretical plate (HETP).  Furthermore, both the liquid and vapor phase flows are laminar, which reduces dispersion and allows high purity to be achieved even with low relative volatility mixtures.  Experiments conducted with low concentrations of 1,4-dimethyl cyclohexane and 3-methyl heptane in octane successfully demonstrated HETP values below 0.5 cm for relative volatilities of 1.03 and 1.24, respectively.  The lack of HETP dependence on relative volatility is evidence that dispersion is not limiting product purity.  Scale-up of the technology is discussed.