Therefore, the preparation and characterization of low-cost ceramic membranes is always an incentive to increase the industrial cost-effectiveness of membrane technology. The performance characteristics of the prepared ceramic membranes were studied for the treatment of oil-in-water (o/w) emulsions and MF mosambi juice in a blind mode of operation.
Major research areas in membrane technology 7
Preparation and Characterization of Ceramic Membranes
Treatment of Oily Wastewater using Ceramic Membrane
Related theory of membrane fouling mechanism 66
Microfiltration of Mosambi Juice using Ceramic Membranes
Microfiltration of Oily Wastewater and Mosambi Juice using B3 Membrane
Preparation of Cellulose Acetate - Ceramic Composite Membranes
Conclusions and Scope of Future Work 165-172
Microfiltration of Mosambi Juice Using Prepared Ceramic Membranes 168 Preparation of Cellulose Acetate-Ceramic Composite Membranes 170 .
Appendix 185-187
Notations
Rf resistance to immediate membrane fouling during MF (m2/m3) Corrosion resistance provided by the interlayer (m2.s.kPa/m3). Rt total membrane resistance during MF (m2/m3) Upper resistances provided by the upper layer (m2.s.kPa/m3).
Greek letters
Introduction
Background
- Classification of membranes
- Classification of membrane separation processes
- Industrial applications of membranes
Symmetric and asymmetric solid-phase membranes are mainly used for pressure membrane separation processes. These membranes are used to remove divalent ions and small molecules from solutions.
Major research areas in membrane technology
As shown, membrane materials research is a central theme that enables the development of conventional and novel functional materials that provide utility, low cost, and durable performance. Therefore, for any industrial application of membranes, the emphasis is on the development of suitable membrane materials.
Membrane materials and trade offs
- Polymeric membranes
- Ceramic membranes
- Polymeric vs. ceramic membranes
- Polymer - ceramic composite membranes
The most useful feature of the ceramic membranes is their ability to tolerate strong doses of chlorine (up to 2000 mg/L in certain cases). These features accompanied by slightly higher costs (cost of ceramic support) are beneficial for applications where polymeric membranes are preferred over the ceramic membranes.
General methods for membrane preparation
- Symmetric ceramic membranes
- Asymmetric ceramic membranes
- Polymer - ceramic composite membranes
The sol-gel process involves the transition from the slip coat technique to the colloidal level. The vapor deposition method involves the deposition of the polymeric film by condensation of vapor on the membrane support.
State of the art
- Preparation of ceramic membranes Literature survey
- Preparation of polymer - ceramic composite membranes Literature survey
- Applications of membrane technology
- Treatment of oil-in-water emulsions Literature survey
- Clarification of mosambi juice Literature survey
The cost of these membranes is significantly high due to the higher cost of the precursors used for the preparation of these membranes. Xiangli et al., [29] presented nonlinear models to express the flux (and thus the hydraulic resistance) and selectivity of the polymer-ceramic composite.
Objectives of present study
Organization of the thesis
Preparation and Characterization of Ceramic Membranes
Experimental
- Raw materials
- Membrane preparation
- Characterization techniques .1 Structural characterizations
- Permeation characterizations Experimental set up
- Chemical stability
TGA and DTA (Make: Mettler Toledo, USA; Model: TGA/SDTA 851e) of the sample mixtures were performed to identify the temperature regimes where the predominant weight losses (and hence transformations) occur in the membrane. The average pore diameter of the area ( ) from the SEM analysis of the membrane was estimated by assuming the cylindrical porous texture of the membrane as;. The membrane was held in the Teflon layer and sealed with epoxy resin (Mseal, Pidilite Industries Ltd, Mumbai, India).
After calculating the dg values, the effective porosity (ε q2 ) of the membrane was calculated using Eq. 2.4), the first term (intercept) corresponds to the Knudsen permeability and the second term (slope) corresponds to the viscous permeability. Permeation experiments using pure water (deionized water) were performed to determine the hydraulic permeability ( ) and hydraulic pore diameter ( ) of the membrane.
Results and discussion
- Characterization of clay materials
- Structural characterization of membranes .1 Thermogravimetric analysis
- Phase characterization by XRD analysis
- Surface morphology
- Pore size analysis based on SEM
- Porosity and structural density
- Permeation characterization of membranes .1 Membrane compaction
- Hydraulic pore diameter, permeability and effective permeable area factor The variation of hydraulic pore diameter and hydraulic permeability of the membranes with
- Gas transport
- Comparative study of pore diameters from different methods
- Chemical stability
- Cost of the membranes
Due to this reason, the porosity of the membrane decreased with an increase in sintering temperature. From the figures it can be observed that the structural density of the membrane increased with an increase in sintering temperature. Similarly, for composition B membranes, the porosity and structural density of the membrane sintered at 800 oC were 34.4 % and 1280 kg/m3, respectively.
This was due to the reason that higher sintering temperatures enable densification of the porous. The material cost of the membranes was estimated at 130 and 220 $/m2 for composition A and composition B membranes, respectively.
Experimental
- Membrane
- Preparation of oil-in-water emulsions
- Microfiltration of oil-in-water emulsions
- Membrane cleaning
The purpose of these experiments was to observe the effect of oil concentration and pressure difference across the membrane on the permeate flux and oil rejection efficiency of the membrane. The formation of the stable emulsion was further tested by regularly measuring the droplet size distribution, the absorption at a wavelength of 235 nm, the pH and the viscosity of the emulsions. After a period of two weeks, coalescence of the oil droplets was observed, leading to the formation of a thin oil film on the water surface.
Dead-run MF experiments of synthetic o/w emulsions were performed in the experimental setup shown in Fig.2.2 (chapter 2). The pure water flux (PWF) of each membrane was verified before and after cleaning the membrane.
Related theory of membrane fouling mechanism
Cake filtration corresponds to a scenario where particles larger than the average pore size accumulate on the membrane surface and form a "cake" (Fig. 3.1d). Thereby, the cake grows over time and provides an additional porous barrier (and thus hydraulic resistance) against the penetrating liquid. The appropriateness and competence of different fouling models can be confirmed by comparing the values of the correlation coefficient (R2) obtained from the linear regression analysis.
Results and discussion
- Emulsion droplet size distribution
- Effect of trans-membrane pressure and oil concentration on flux
- Effect of trans-membrane pressure and oil concentration on rejection
- Identification of competent flux decline mechanism
Figures 3.5 - 3.8 illustrate the suitability of the full pore blocking, standard pore blocking, intermediate pore blocking and cake filtration models for all oil concentrations, respectively. Furthermore, in Table 3.2 for the same regime it can also be observed that R2 values for all other models (standard pore blocking, complete pore blocking and intermediate pores). Therefore, it was concluded that intermediate pore blocking followed by cake filtration represent the most representative values. competent combination of fouling mechanisms for the observed decrease in membrane flux.
Also, droplets in the µm range either enter the pores or are rejected by the membrane and contribute to intermediate pore blocking and cake filtration. Henceforth, it is clear that the pertinent flux decline will constitute an initial phase of intermediate pore blocking followed by cake filtration.
Microfiltration of Mosambi Juice using Ceramic Membranes
Experimental
- Membrane
- Juice preparation and pre-treatment
- Microfiltration studies
- Membrane cleaning
- Analytical methods
Enzymatic pretreatment of the liquid was performed by heating the liquid at 42 oC for 100 minutes with enzyme concentration of 0.0004 w/v%. The suspension was then heated at 90 oC for 5 min in a water bath to inactivate the remaining enzyme in the liquid. Finally, the liquid was cooled to room temperature (25 oC) and centrifuged at 4000 rpm for 20 minutes.
Acidity measurements were made by titrating a 10 mL sample of juice with 0.1 N NaOH until the pH of the solution reached 8.2 and was expressed as % by weight of anhydrous citric acid equivalent. The viscosity of the juice samples was measured using a glass Oswald capillary viscometer (Manufacturer: Pisco, India; Model: D 30797).
Applicable theory
The pH of the samples was measured using a water and soil analysis kit (Make: VSI Electronics, India; Model: VSI-06D1,). During a MF run, the membrane is fouled by the suspended solids which cause variations in the morphological properties of the membrane (εm,. For composite membrane since the thickness of the cake/gel layer varies negligibly with respect to the pore length (lcm ≈ lm) ), Cf.
Further, the rate of decrease over time indicates the degree of membrane fouling. In other words, a slower time change indicates a lower degree of membrane fouling.
Results and discussion
- Effect of pretreatment on juice quality
- Effect of pore size on permeate flux
- Effect of operating pressure on permeate flux
- Effect of membrane pore size on permeate juice quality
- Effect of operating pressure on permeate juice quality
- Analysis of membrane fouling mechanism
- Phenomenological modeling
- Effect of membrane morphology on total resistance
- Effect of operating pressure on total resistance
- Effect of membrane morphology on membrane fouling characteristics
- Effect of pressure on membrane fouling characteristics
- Long term storage studies
With an increase in the pore size of the membranes (A1 to A4), the quality of the juice decreased marginally. A reduction in permeate juice quality for A4 membrane was due to the larger pore diameter of the membrane. From the table it can be seen that color, clarity, viscosity and AIS of the permeate juice varied marginally for both CJ and ETCJ.
This indicated that the fouling of the membrane follows a power law trend with an increase in From the table, it can be observed that overall quality of the CJ and ETCJ degrades with time, with a higher degradation rate for CJ.
Microfiltration of Oily Wastewater and Mosambi Juice using B3 Membrane
Experimental
Results and discussion
- Microfiltration of oil-in-water emulsions
- Identification of flux decline mechanism for oil-in-water emulsions The identification of flux decline mechanism for MF of o/w emulsions was carried out using
- Microfiltration of mosambi juice
- Identification of flux decline mechanism for mosambi juice
- Permeate quality after filtration
- Long term storage studies
From these figures it can be observed that the decrease in permeate flux can be explained by either cake filtration model or a combination of two different pore blocking models. It was observed that R2 values of cake filtration model varied in the range of for the entire duration. Therefore, the hypothesis that flux decrease of the membrane was due to the cake filtration appears to be consistent during the dead-end MF of o/w emulsions.
An increase in permeate flux with ∆P was due to the higher driving force across the membrane. Therefore, it was concluded that flux drop due to intermediate pore blocking followed by cake filtration is the most competent combination of fouling mechanisms.
Comparison between A1 and B3 membranes performance
- Microfiltration of oil-in-water emulsions
- Microfiltration of mosambi juice
This is due to the fact that the porosity and average pore size of the membrane and therefore the effective permeability factor (εmdl2) of A1 is higher than membrane B3. However, for the B3 membrane, the average membrane pore size was lower than the oil droplet size. Therefore, the oil rejection efficiency of membrane B3 was relatively higher (less than 1%) than that of membrane A1.
This was due to the reason that porosity and average pore size of membrane and thus effective permeability factor of composition A membranes was higher than that of the B3 membrane. However, due to its lower pore size, permeate juice quality was better for B3 membrane than composition A membranes (Tables 4.3, 4.4 and 5.5).
Preparation of Cellulose Acetate - Ceramic Composite Membranes
Experimental
- Raw materials
- Preparation of composite membranes
- Characterization methods
Surfaces other than the top surface of the support were covered with Teflon tape to prevent CA deposition. During this time, acetone evaporates from the top layer and thereby contributes to pore formation and thus to membrane morphology and separation capacity [10]. Characterization techniques include the structural characterization of the support and composite membranes by SEM, flux characterization using gas (air) and liquid (water) permeation, densification studies and solute rejection experiments using BSA.
The pH of the feed solution was kept constant at 7.2, as a change in pH can increase adsorptive fouling of membranes [96]. In addition, intermolecular forces between BSA molecules and membranes will dominate and affect the performance of the membranes if the pH of the solution changes [97].
Theoretical considerations
This intermediate layer played an important role in the stability of the membrane and the bonding of the top layer to the ceramic support. The structural and morphological properties of the interlayer mainly depended on the pore size and porosity of the support, as well as the concentration of CA used for dip coating. The growth of the upper CA layer was predicted after the formation of the intermediate layer [45].
The growth rate of the CA top layer was also largely dependent on the CA concentration in the solution, structure and morphology of the interlayer [12, 15]. Rcoat can also be expressed as the sum of the interlayer resistances ( ) and the top layer resistance ( ) axis.
Results and discussion
- Surface morphology
- Gas permeability
- Membrane compaction
- Hydraulic permeability
- Protein rejection
- Assessment of different hydraulic resistances
- Phenomenological models for parameter dependency
- Membrane parameters
- Dip coating parameters
- Error analysis
From the figure, it was observed that with an increase in both CA concentration and dipping time, the pore size of the membrane decreased. With an increase in CA concentration in acetone, the viscosity and density of the solution increased. However, an increase in effective porosity of the membrane was observed when the CA concentration was increased to 6 wt.
This was due to the fact that, with an increase in both dipping time and CA concentration, the average pore size of the membrane decreases and upper layer thickness increases. This increase was due to the reduction in pore size of the membranes with an increase in CA concentration and dip time.
