(26g) Future Perspectives of Using Hollow Fibers as Structured Packings In Light Hydrocarbon Distillation

In many industrial countries, olefin and paraffin are the largest chemical commodities. These chemicals are the major building blocks for petrochemical industry. Each year, petroleum refining, consumes 4,500 TBtu/yr in separation energy, making it one of the most energyintensive industries in the United States. Just considering liquefied petroleum gas (ethane/propane/butane) and olefins (ethylene and propylene) alone, the distillation energy consumption is about 400 TBtu/yr in US. In practice, distillation columns require 100 to 200 trays to achieve the desired separation. The height of a transfer unit (HTU) of conventional packings is typical in the range of 36 – 48 inch. Since petroleum distillation is a mature technology, incremental improvements in column/tray design provide only a few percent improvements in the performance. However, each percent saving in net energy use amounts to

 
savings of 10 TBtu/yr and reduces 0.2 MTon/yr of CO2 emissions. In this work, we explored using several non-selective membranes, which are commercially available, as the structured packings to replace the conventional packing materials used in light hydrocarbon distillations.  We found the lowest HTU for the hollow fiber column to be < 20 cm, which is appreciably better than conventional packing materials. We also compare separation efficiency and operational stability in the distillation processes of two pairs of light hydrocarbon mixtures (iso-/n-butane and propylene/propane) using the hollow fiber packings. Because of a slightly larger relative volatility of iso-/n-butane than that of propane/propylene, a wider and a more stable operational range is obtained for the former pair. Within the loading range of F-factor < 2.0 Pa0.5, a pressure drop on the vapor side is not sensitive to the vapor velocity whereas the pressure drop on the liquid side increases linearly with the liquid velocity. Nevertheless, the pressure drops of hollow fibers packings are not engineering barriers for their applications in distillations. The effects of membrane morphology and module packing density on the separation efficiency will be discussed. The thermal stability study of those hollow fibers suggests that polypropylene, polyvinylidene fluoride, and polyimide are stable after a long time exposure to light hydrocarbons. Future perspectives of using hollow fibers as structured packings in distillationand other separation processes will be also discussed.