CHAPTER IV RESULT AND DISCUSSION
4.4. Permeate flux profile of surfactant-enhanced ultrafiltration system for dye
65 Another important information is the knowledge of thermodynamic parameters, such as, a change in Gibbs free energy (ΔG) is important. To understand the feasibility of such solubilization process. Therefore, the Gibbs free energy of solubilization (ΔG) was calculated for remazol red RB as well as remazol blue TQ.
The ΔG of Sapindus rarak saponin was found to be -12.283 and -13.388 KJ.mol-1 for remazol red and blue, respectively. As for the pure commercialized saponin the ΔG were -11.821 and -12.634 kJ.mol-1 for remazol red and blue respectively. The negative value of Gibbs free energy of solubilization (ΔG) suggests that, the solubilization of the dyes in saponin micelle was a feasible and spontaneous process. The ln Km, and Gibbs free energy of solubilization (ΔG) of both the dyes, are summarized in Table 4.4.
Table 4.4 Molar solubilization power (SP), ln Km and ΔG of solubilization of pure saponin and extract of S.rarak for remazol dye, at 27oC
Remazol Dye
Type of Surfactant
Solubilization power (SP) (mM/mM)
ln Km Gibbs free energy (ΔG) (KJ.mol-1)
Red RB
Extract S.rarak 0.251 4.924 -12.283
Pure Saponin 0.199 4.739 -11.821
Blue TQ
Extract S.rarak 0.239 5.367 -13.388
Pure Saponin 0.192 5.065 -12.634
4.4. Permeate flux profile of surfactant-enhanced ultrafiltration system for
66 ultrafiltration process with feed solution in various saponin concentration. The flux profile of each run was presented in the Figure 4.13.
(a)
(b)
Figure 4.13 Variation of the observed permeate flux of remazol red RB and Tq Blue with time at room temperature and pressure of 1.5 bar
Figure 4.13 shows the observed normalized flux of remazol red RB and Tq blue compared to time. The permeate flux of all variables were slightly decline with the processing time and then remained almost constant for the rest of the experiment. This flux (J) constant value is considered as the steady state permeate flux. The phenomenon of flux decline is mainly due to the concentration
Time (minutes)
0 20 40 60 80 100 120
Normalized Flux (J/J0)
0.0 0.2 0.4 0.6 0.8 1.0 1.2
R.Red 0 CMC R.Red 0.5 CMC R.Red 1 CMC R.Red 1.5 CMC R.Red 2 CMC
Time (minutes)
0 20 40 60 80 100 120
Normalized Flux (J/J0)
0.0 0.2 0.4 0.6 0.8
R.Blue 0 CMC R.Blue 0.5 CMC R.Blue 1 CMC R.Blue 1.5 CMC R.Blue 2 CMC
67 polarization effect and membrane fouling (Huang et al., 2014), although osmotic pressure and precipitation could also contribute to flux decline (Zaghbani et al., 2007). Concentration polarization appears as a result of a local increase of solutes concentration close to the membrane surface. Membrane fouling was mainly due to gel layer formation and pore blocking, occurs as a result of deposition and accumulation of solutes on the membrane surface and within the membrane pores (El-Abbasi et al., 2011). With the addition of saponin, the surfactant micelles generate a deposited layer over the membrane surface (concentration polarization), thus increasing the resistance against the solvent flux through the membrane. As a result, in the initial stage of MEUF experiments, the micelles are accumulated near the membrane surface, producing a sharp decline of permeate flux due to concentration polarization and gradual formation of gel layer. As the filtration proceeds, the gel layer becomes denser, leading to a slow flux decline. In the final stage, the membrane fouling is fixed and the permeate flux reaches the steady state value (Huang et al., 2014). Besides, the increment of the osmotic pressure difference across the membrane (related to micelles concentration in permeate and retentate streams) reduces the effective TMP and, as a result, the permeate flux decreases with operation time (Zaghbani et al., 2007). The similar result was also found in the previous study using ionic and non-ionic surfactant to remove emerging contaminants (Acero et al., 2017), removal of cadmium ions (Li et al., 2011) and recovery of phenolic compound (Victor-Ortega et al., 2017). Removal of various indigosol reactive dye using cationic and anionic surfactant, SDS and CPC, also shows a similar flux profile with this study (Aryanti et al., 2016).
In absence of saponin, the remazol red solution was showing more rapid flux decline at the end, while the blue one showing a rapid decline at the beginning of UF process. This phenomena associated with the molecular weight difference of the two dyes. The dyes molecular weight were 668.999 g/mol and 1098.062 g/mol, for remazol red rb and remazol tq blue, respectively. The molecule of remazol tq blue was bigger in size. It will starts blocked the membrane pores as soon as the process begin. This direct pore blocking causing the flux decline rapidly in the beginning of the process. However, the flux was then only slightly declined after
68 40 minutes of UF. This was because of too much deposition of dye molecule in the surface of the membrane. Where, there is a possibility of the excess dye molecule to be carried out again by the feed current. Meanwhile, the remazol red rb molecules were small and way smaller than the membrane pore, which is 10.000 Da. In the UF process, the red dye molecule will just through the membrane pore easily, which gives a rather high and stable flux profile. However, the deposit of dye molecule inside the membrane pore or surface cannot be denied. After 60 minutes of filtration process, the deposit of dye molecules start to affect the flux profile. The flux profile decline rapidly in the end of the filtration process because of the continuously blocked membrane pores.
Figure 4.13 also shows the effect of saponin addition to the flux profile. The feed without any addition of saponin has the highest flux. In general, the flux value is decreased with the increase of saponin concentration on the feed solution, both for above or below its CMC. The addition of saponin at 2 times CMC having a lowest normalized flux on both remazol red rb and blue tq. This is due to the interaction of saponin molecule with the pollutant where the pollutant is entrapped in the micelle saponin structure. An ionic reactive dyes, such as remazol red rb and remazol blue tq, can be solubilized into the hydrophobic and hydrophilic medias in micelles, or dissociate to ions which are adsorbed on the surfactant micelles (Zaghbani et al., 2009; Bielska et al., 2009). Addition of saponin (surfactant) molecule in the feed solution at a concentration above the CMC generates the formation of surfactant micelles (Chang et al., 2011). In general, the micelle structure is the hydrophobic region in the internal core, and hydrophilic region in the external side. The hydrophobic core had the ability to solubilize hydrophobic or less polar molecule. As for the polar or charged layer of the external side, micelle has the more hydrophilic characteristic (Acero et al., 2017). Based on this fact, the pollutant molecule will be trapped in the innermost part of the micelle outer region, whit hydrophilic character. This hydrophilic side of surfactant micelle had the tendency to attached one to each other in low aqueous solution. The micelles forms a layer and blocking the water to get through the membrane, resulting to the lower of flux. However, this layers are not permanent, proving by the rather stable
69 flux. The micelle surfactant molecule can goes on to the retentate again because of the feed flow. On both type of dye, the addition of saponin higher than its CMC showing a similar result. The solution with addition of saponin at 1.5 and 2 times of CMC was showing a similar normalized flux. It is indicating that the addition of excess saponin will not generates more blocking in the membrane. Yet its effect to the rejection capability was definitely important.