A Coalescing Filter for Liquid-Liquid Separation and Multistage Extraction in Continuous-Flow Chemistry

Abstract

Presented here is the design and performance of a coalescing liquid-liquid filter, based on low-cost and readily available meltblown nonwoven substrates for separation of immiscible phases. The performance of the coalescer was determined across three broad classes of fluid mixtures: (i) immiscible organic/aqueous systems, (ii) a surfactant laden organic/aqueous system with modification of the type of emulsion and interfacial surface tension through the addition of sodium chloride, and (iii) a water-acetone/toluene system. The first two classes demonstrated good performance of the equipment in effecting separation, including the separation of a complex emulsion system for which a membrane separator, operating through transport of a preferentially wetting fluid through the membrane, failed entirely. The third system was used to demonstrate the performance of the separator within a multistage liquid-liquid counterflow extraction system. The performance, robust nature, and scalability of coalescing filters should mean that this approach is routinely considered for liquid-liquid separations and extractions within the fine chemical and pharmaceutical industry.

Figure 1

(a) Schematic showing coalescence of droplets on fibers of media, and separation of suspended phase from the continuous phase downstream of the filter. (b) SEM image of meltblown PBT filter media as used in this work (200 μm scale for reference).

Figure 2

(a) Sectional view of the coalescing filter housing. Photograph of (b) the assembled laboratory scale coalescing filter and (c) assembled coalescing filter, CSTR fReactor mixers and pump.

Figure 3

Schematics of (a) the pump actuated control system, (b) the valve actuated control system.

Figure 4

Flow schematics for single stage separations using (a) coalescing separator level controlled with pump and (b) membrane separator with (integral) pressure control. (c) 3-Stage counter-current multistage separator using coalescing media.

Figure 5

Percentage of water and 1-butanol collected at each outlet of the coalescing filter during operation at 10 mL/min (total) and image of separation on downstream side of media.

Figure 6

Average percentage of organic phase collected at the organic outlet depending on the (a) number of filter layers and (b) as a function of the HLD values.

Figure 7

Images of samples collected at the organic and aquous outlet for water–surfactant–toluene mixtures (A–D, Table 4). The blue hatch has been added to indicate where no liquid is present within the vials.

Figure 8

Percentage of acetone extracted from the aqueous phase, depending on phase ratio and number of extraction stages. The x-axis label S#₁PR#₂ shows the number of stages (#₁) and the phase ratio of aqueous to organic phase (#₂). The extraction percentage is compared to the percentage found in batch as well as by the Aspen thermodynamic model. Batch data for single step extraction is shown, together with predicted results for sequential, multistep batch extractions.