(285d) Experimental Investigation of a Multi-Stage Counter-Current Rotating Packed Bed for Distillation

Experimental Investigation of a Multi-Stage Counter-Current Rotating Packed Bed for Distillation

Authors: Daniel Sudhoff*, Mathias Leimbrink, Philip Lutze, Andrzej Górak

Keywords:

Rotating Packed Bed, Distillation, centrifugally-enhanced separation, process intensification

* Dipl.-Ing. Daniel Sudhoff

TU Dortmund University

Phone: +49 (0) 231/ 755 6002

Email: Daniel.sudhoff@bci.tu-dortmund.de

Web: www.fvt.bci.tu-dortmund.de

To meet future global challenges for the chemical and bio-chemical production processes such as lower lifetimes and the demand of innovative products but also to produce products more sustainable, the processes need improvements. Besides others, more flexible processes are necessary to be able to react to changing compositions of a bio-based feedstock, to meet changing market needs and to enable a quicker entry to market for new products. To fulfill these requirements processes are needed that either dynamically adapt the changing requirements quickly or can quickly be rearranged by modular devices and modular process parts. For both cases compact apparatuses are required that have a sufficient number of degrees of freedom and a wide range of operation.

The so called HIGEE-technology (“high gravity”) is an example of a promising technology to meet these process demands for fluid separations. Therefore a high gravity field is created and the liquid and vapor are contacted inside this field. A promising possibility to realize a phase contactor applying a high centrifugal field are rotating packed beds (RPBs). In these machines a cylindrically shaped packing is rotating at a high rotational speed. The liquid is introduced to the center of this rotating packing and is therefore radially accelerated along the packing. The vapor is introduced to the outer casing and driven through the packing to the center of the rotor by a slightly enlarged pressure. The phase contact inside the packing occurs at applied forces that are a multiple of the gravitational force.

The high applied forces to the liquid enable a very high throughput of liquid and vapor as well as the use of high performance packings with a very high surface area. High turbulence with large interfacial areas are created and quick mass and heat transfer between the phases are enabled. This gives the opportunity for high capacities at short residence times and low space requirements. Additionally, the rotational speed that has a high influence on the separation efficiency of the RPB is an additional degree of freedom. Due to these advantages RPBs can be applied to meet the above mentioned requirements for chemical production plants.

Despite these advantages RPBs have not been established as phase contactors yet in the chemical industry. Although several studies, on the application of RPBs for absorption processes and for the production of nano-particles have shown its feasibility, no sufficient investigations of distillation processes in RPBs have been published yet. The few available results have been achieved with lab scale apparatuses with small radial lengths of the packing. Therefore, systematic investigations to understand energy, mass and impulse transport phenomena and the influence of equipment and operating parameters are lacking.

To fill this gap a novel rotating packed bed with three consecutive rotors at pilot scale for distillation has been developed (Multi-Stage Counter-Current Rotating Packed Bed, MSCC-RPB) and build. The details of the MSCC-RPB have as well been presented in a previous work as its hydrodynamic operating limits and an approach for the evaluation and comparison of the performances of RPBs for distillation [1].

In this work the hydrodynamic behavior with regard to pressure drop and hold-up have been investigated. Additionally, the separation performance of the MSCC-RPB for distillation has been characterized with as suitable water-alcohol test system. The influence of the parameters rotational speed, feed location and vapor and liquid load have been determined. The results are presented and evaluated on a basis of absolute reference values (integrated centrifugal acceleration, integrated liquid and vapor loads) as have already introduced in an earlier work [1]. Finally, the separation efficiency of the MSCC-RPB for distillation is compared to a pilot scale distillation column with structured packing existing at the same laboratory. For this purpose an established and in previous works successfully applied mass transfer model for the distillation column is used to determine the required packing height of a distillation column to achieve the same separation efficiency as the MSCC-RPB.

[1] Sudhoff, D.; Lutze, P.; Górak, A.: Multi-Stage Counter-Current Rotating Packed Bed for Distillation; presentation at AIChE Spring Meeting 2013, San Antonio, USA.