In the chemical and petrochemical industry, distillation is by far the most important and the most widely applied separation technology and also the largest consumer of energy, especially in the separation of azeotropic mixtures. Besides, the demanding environment conditions stimulate process industry to look for more environmentally friendly and energy efficient production processes. Hence any new separation technology that can lead to important improvements in terms of sustainable development criteria has an incentive to be researched.

Frictional Diffusion, briefly FricDiff, is an alternative separation technology, which emerged from the concepts of reduced energy usage and avoiding hazardous solvents [2].

FricDiff is based on the difference in diffusion rate of two components when diffusing through a third component, so-called counter gas (sweep). In the FricDiff concept, the separation occurs because the light components in the feed mixture diffuse at a higher rate into the counter gas than the heavy components. This difference results into the enrichment of the heavy components on the feed side. The heavy components have a larger molecular weight, and experience therefore more friction with the sweep gas. This friction between the molecules occurs in the pores of a barrier (porous layer), where the feed components and sweep gas diffuse counter-currently.

Previous work dealt with retention of the valuable products either in the feed stream (e.g. isopropanol-water) [2,3] as well as in the sweep stream (e.g. hydrogen- hydrocarbon mixture). For these configurations, the effect of design parameters and operating conditions on the performance of a single tube FricDiff module was studied. A model considering Hagen-Poiseuille flow for feed and sweep side as well as the Binary Friction Model [1] for transport through the porous layer was employed [2,3]. In these studies, only modest enrichments on the order of 65% could be achieved in a single tube FricDiff unit. Such performance is not uncommon for kinetic separation principles but economically not favorable.

In this present work, possibilities to achieve higher purity of the product using FricDiff are therefore investigated. For this purpose, simulation results are analyzed via three different key performance indicators namely enrichment factor, recovery and productivity. Their dependency on the design parameters such as the range of pore size, tube dimensions, the sweep ratio and the flow rate is quantified. The conditions allowing for higher purity separations using FricDiff will be discussed. The simulation results support the claim that the novel FricDiff technology is a sustainable separation method also applicable for tasks of strong enrichment.

Based on these results, a design-case has chosen for a test unit which is under construction now. This unit shall demonstrate the technical viability of FricDiff technology under industrial conditions.

References:

[1] P.J.A.M. Kerkhof, M.A.M. Geboers; Analysis and extension of the theory of multi-component fluid diffusion; Chemical Engineering Science 60 (2005) 3129 – 3167

[2] M.A.M. Geboers, P.J.A.M. Kerkhof, P. Lipman, F. Peters; FricDiff: A novel separation concept. Separation and Purification Technology 56 (1): 47-52 (2007)

[3] A. Selvi, B. Breure, J. Gross, J. de Graauw and P.J. Jansens; Basic parameter study for the separation of a isopropanol–water mixture by using FricDiff technology; Chemical Engineering and Processing, 46 (2007) 810-817.