Materials and Methods
2.3 Experimental studies
2.3.2 Three phase experimental studies with BLM [2, 3]
The laboratory scale BLM setup for the three phase experiments is shown in Fig. 2.3. The set up consists of cuboidal shaped glass container (75mm × 75 mm × 63 mm) with magnetic stirrers.
The cell is divided into two compartments by a thin glass plate of thickness 5 mm. In order to ensure no channeling between the compartments, a blank test was carried out by keeping colored (crystal violet) solution in one compartment and water in the other. Both liquids were stirred continuously for 24 h by magnetic stirrers and the intensity of the color of liquids in both compartments was then measured with UV-vis. spectrometer at 584 nm. There was no change in the absorbance which confirmed no channeling between the compartments. The results of leakage test are incorporated in Appendix-II.
Two different BLM configurations can be set up depending on the density of the membrane phase. This research work deals with membrane phase which is lighter than the aqueous phases and the BLM set-up is made accordingly. The feed and the strip phases are placed in respective compartments in such a way that the level of these liquids remain well below the top of the separating wall. The membrane phase liquid is then poured from the top in such a way that the height of the membrane phase clears the top of the glass wall and thus creates a bridge between the feed and strip phases for possible diffusion of solute through the membrane phase. Care is
Materials and Methods taken so that there is no leakage/accidental mixing of these phases. Aqueous phases were continuously stirred by magnetic stirrer and stirring speeds (rpm) were controlled by voltage regulators. Sufficient care had been taken to prevent unwanted mixing of feed and strip phases.
Moreover, the stirrer speed was regulated in such a way that neither it allows formation of any emulsions at the feed/membrane interface nor it disturbs the membrane interface.
Figure 2.3: Schematic of BLM set up
The three phase experiments were carried out in the BLM set-up as described above. Area of membrane/aqueous interface was 19.5 × 10-4 m2 at both sides. Catechin was transferred through these interfaces. The volumes of feed phase as well as receiving phase were 50 mL each and the volume of LM phase was 30 mL. Continuous stirring of aqueous phases ensured the solution to be well mixed and the bulk concentration to be uniform throughout. Three mL sample of both aqueous phases was collected periodically for determination of catechin concentration in UV-vis spectrophotometer.
Chapter-II 2.3.3 Three phase experimental studies with FS-SLM
2.3.3.1 Set-up
The FS-SLM apparatus consisted of two cylindrical vessels (internal diameter 55 mm and height 95 mm) connected with pipes which are joined by flanges. A flat-sheet support membrane along with ML impregnated in its pores is placed in between the flanges as shown in Fig. 2.4. Two mechanical stirrers (Make: Remi; Model: RGQ 121/D) were used for stirring of aqueous phases in both the vessels whose effective volume is 130 mL each. The whole membrane disc was of 47 mm in diameter and the contact area of the membrane with each aqueous phase was 11.3× 10-4 m2.
2.3.3.2 Solid membrane support
Various polymeric membranes were used as support for the organic phase such as polytetrafluoroethylene (PTFE), Nylon 6, polyvinylidenefluoride (PVDF) and polyether sulphone (PES). The pore diameter of the support membrane was taken from the supplier and the porosity of supports was taken from the literature. The thickness of the support materials was measured by thickness measurement instrument (Litematic, VL-50).
Table 2.2: Characteristics of polymeric membrane supports Support
material
Pore size, d (µm)
Thickness, L (µm)
Porosity ( ε)
Tortuosity (τ)
( ετ/L) (µm-1)
PTFE 0.2 77.2 0.51 2.92 0.019
PVDF 0.2 88.5 0.45 3.4 0.017
Nylon, 6 0.2 102 0.40 4.0 0.015
PES 0.2 107 0.5 3.0 0.014
Materials and Methods 2.3.3.3 Preparation of FS-SLM
The membrane liquid (ML) was immobilized into the pores of the flat sheet polymeric membrane. First the support material is immersed into the ML for at least 24 hours. It was then taken out and the excess liquid was wiped out gently from the flat surface by good quality non- fibrous tissue. It was fitted between two flanges connected to feed and strip compartments as described before.
2.3.3.4 Experimental procedure
Both aqueous phases were stirred using mechanical stirrer in order to reduce concentration polarizations of solute at the interfaces. Before the start of experiments including that of fed- batch system, required amount of electrolyte (NaCl) was dissolved either one or both aqueous phases in order to enhance the stability of LM. The rationale of the stability has been explained in the later chapter. Feed and strip phase samples (about 3 mL) were periodically taken out and catechin concentration was determined using UV-vis spectrophotometer (Perkin Elmer, Model:
Lambda 35) at 279 nm wavelength (for catechin). The concentrations of individual catechins were measured by HPLC in case of experiments with real extract of green tea leaves. All experiments were carried out in triplicate and results are shown with standard error bars.
Chapter-II
Figure 2.4: Schematic of FS-SLM set-up
2.3.4 Hollow fiber membrane (HFM) module