Extraction Technology

Extraction Process Figure 8.1 Typical liquid-liquid extraction process.

Typical Extractor Light Phase Dispersed Heavy Phase Dispersed Out Light Phase Out Heavy Phase In Heavy Phase In Light Phase In Light Phase In Heavy Phase Out Heavy Phase Out Light Phase Dispersed Heavy Phase Dispersed

Typical Extractor Light Phase Dispersed Extract Out Feed In Solvent In Raffinate Out Light Phase Dispersed

Liquid-liquid Equilibrium Phase I Phase II

Design Methods Theoretical Trays Hunter – Nash graphical method Aspen Packed Tower Height Seibert et al. Sieve Tray Efficiency

Hunter – Nash Graphical Method Blender Material Balance M = F + S = RNp+ E1 M xM = F xF + S yS = RNp xNp + E1y1

Hunter – Nash Graphical Method Figure 8.14 Location of product point.

D “P” Point 100 lbs 181 lbs D = 81 lbs 10 lbs 90 lbs 171 lbs

Hunter – Nash Graphical Method Figure 8.15 Location of operating point.

Hunter – Nash Graphical Method Figure 8.18 Determination of minimum solvent to feed ratio.

Hunter – Nash Graphical Method Figure 8.17 Determination of the number of equilibrium stages.

Graphical Method Example In a continuous counter-current train of mixer settlers, 100 kg/hr of a 40 wt % acetone / 60 wt % water solution is to be reduced to 10 wt % acetone by extraction with pure 1,1,2 trichloroethane (TCE) at 25 C. Find: The minimum solvent rate At 1.8 times the minimum solvent rate, find the number of mixer settlers required. Water Phase ( wt %) TCE Phase ( wt %) C2H3Cl3 Water Acetone 0.73 82.23 17.04 73.76 1.10 25.14 1.02 72.06 26.92 59.21 2.27 38.52 1.17 67.95 30.88 53.92 3.11 42.97 1.60 62.67 35.73 47.53 4.26 48.21 2.10 57.00 40.90 40.00 6.05 53.95 3.75 50.20 46.05 33.70 8.90 57.40 6.52 41.70 51.78 26.26 13.40 60.34

Acetone E1min F Mmin RNp s Water TCE

Acetone E1 F M RNp s TCE Water

10 Minute Problem A feed stream “C” of 100 kg/min containing 30 mass percent solute “A” is being contacted in a single stage stirred contactor with 50 kg/min of pure solvent “S” (equilibrium figure below). Determine the composition and amount of the resulting raffinate and extract streams.

Extractor Sieve Tray Photo of Sieve tray

Trayed Extractor Efficiency (Treybal Empirical Model) Where: Ht = tray spacing (ft) Ud = superficial dispersed phase velocity Uc = superficial continuous s = interfacial tension (dyne/cm)

Interfacial Tension

Trayed Extractor Efficiency (Seibert Model) Kod,r Kod,f Seibert, A.F. and Fair, J.R., “Mass-Transfer Efficiency of a Large-scale Sieve Tray Extractor,” Ind. Eng. Chem. Res., 32 (10): 2213-19 (1993).

Trayed Extractor Efficiency Correction of k d,r from Seibert Table VI Equation 16

Trayed Extractor Efficiency dVS

Trayed Extractor Efficiency

Trayed Extractor Hydraulics

Packed Liquid-liquid Extraction IMTP Pall Rings Structured

Packed Extractor Design (Hydraulics) Seibert, A.F., Reeves, B.E., and Fair, J.R., “Performance of a Large-scale Packed Liquid-Liquid Extractor,” Ind. Eng. Chem. Res. 29 (9); 1901-07 (1990).

Packed Extractor Design (Hydraulics)

Packed Extractor Design (Mass Transfer)

Extraction Equipment Selection Depends on: - solvent recovery economics - viscosities, interfacial tension, solids - product/solvent value - flowrates - risk assessment - operation experience

Static Columns Spray Tower Packed Tower (a)

Static Columns Sieve Tray Light liquid out Operating interface Heavy liquid in Light liquid in Heavy liquid out Operating interface Perforated plate Downcomer Coalesced dispersed Sieve Tray

Oldshue-Rushston Column Develop in 1950s Many commercial installations Solids handling Viscosities to 500 cP Differential contactor

Reciprocating Plate Extractor (Karr) Developed in 1959 Many commercial installations V. High Volumetric Efficiency Vary tray amplitude and frequency Caution at low interfacial tensions Tray movement can clean walls Differential contactor Scale-up to the 0.38 power on diameter Other variations (e.g. VPE)

Podbielniak Horizontal centrifugal extractor High efficiency Short residence time Minimum inventory Light phase out Light phase in Heavy phase in Heavy phase out

Mixer-Settler Wide range of designs Handle wide range of flow ratios Easy start-up Easy to clean/inspect Batch operations Larger equipment Handles solids Low headroom Occupy much floor space Can add stages Interstage pumping often required High solvent inventory

Hollow Fiber Extractor Solvent Out Solvent In Feed In Feed Out Developed in 1980s Modified in 1990s Stage contactor Low organic solvent to aqueous feed ratios Few commercial extraction applications Many commercial gas/liquid applications

Stichlmair (1980)