This thesis focuses on determining the feasibility of the forward osmosis (FO) process for the concentration of freshly brewed black tea extract. The feasibility of the concentration of tea extract using the FO process was investigated in this thesis. A one-dimensional mathematical model of the given FO process has been developed for the concentration of tea extract using the FO process.
- Introduction to the Membrane Process
- Overview of Membrane Processes in Food and Beverage Processing Industries
- Fundamentals of the Forward Osmosis Process
- Draw solute
- Forward osmosis membranes
- Challenges of FO operations
- Motivation
- Importance of developing a mathematical model for hollow fiber forward osmosis
- Importance of non-thermal membrane process in concentration of black tea
- Importance of suitable food-grade draw solute for liquid food concentrate using
- Importance of development of hydrogel as a draw solute for the concentration of
- Summary and Scope of Research
- Objectives
- Organisation of the Thesis
Appropriate selection of the solute and FO membrane plays an important role in the progress of the FO process. Due to the asymmetric nature of the FO membrane, the orientation of the membrane significantly affects the FO process. Therefore, this suggests that CP cannot be avoided in the FO process regardless of the membrane orientation used.
Fundamentals of Forward Osmosis Process
- Forward osmosis membranes
- Draw solute
Table 2.4 summarizes the advantages and disadvantages of the FO process in the liquid food and beverage processing industry. The feasibility of the FO process for the concentration of liquid food and drink has been studied by researchers. Despite these advantages, the large-scale application of the FO process for liquid food concentration has yet to be confirmed.
Black Tea
- Black tea catechins
- Method of extraction, isolation, and concentration of tea catechins
- Concentration of the extracted constituent
- Identification and quantification of tea catechin
- Application of extracted tea catechins in food and beverage processing industries
Identification and quantification of tea catechins are used to determine the concentration, yield and purity of the catechin in the final product. Tea catechins have the potential to be used in muscle nutrition for inhibiting lipid oxidation during storage. Tea catechins such as EGCG and epicatechin inhibit the growth of Helicobacter pylori, a common ulcer-causing bacterium.
Literature Closure and Research Gaps
Development of a One-Dimensional Mathematical Model for the Concentration of
- Overview of hollow fiber forward osmosis (HFFO) membranes
- Flux equation for FO membranes
- Concentration polarisation
- Mass balance equation for HFFO membranes
- Tank mass balance equation
The term ∆π represents the osmotic pressure gradient at the surface of the active layer (AL) and the interface of the support and active layers. The solute penetrates the membrane in the opposite direction of the water flow (ie from draw to feed solution). The reverse solute flux (𝐽𝑠) is a function of the solute permeability coefficient (B) of the membrane AL and the solute concentration gradient at the membrane AL.
Depending on the membrane orientation, the FS and DS are allowed to pass through either shell lumen side of the membrane module. Due to the continuous dilution and concentration of DS and FS, a non-uniform osmotic driving force is present along the length of the module. The 𝜋𝑑𝑚 and 𝜋𝑓𝑚 represent the osmotic pressure at the active layer of the membrane surface on the draw and feed side, respectively.
The effective driving force for osmosis only exists at the interface of the selective (active) layer. While the membrane is only permeable to water and the solute in the membrane accumulates in the supporting layer of the membrane, this phenomenon is called internal concentration polarization (ICP). The term 𝐶𝑓𝑚 indicates the FS concentration at the interface of the selective support layer and can be expressed as the sum of the two components.
The water and reverse solute flux was expressed in terms of the structural parameter (S), pure water permeability (𝐿𝑝), solute permeability coefficient (B) and mass transfer coefficient (k).
Process Flow-Sheet Simulation
Materials
For the synthesis of hydrogels, the polymers (such as polyvinyl alcohol 'PVA', poly(diallyldimethylammonium chloride) 'polyDADMAC') and monomers (such as acrylic acid and N₋Isopropylacrylamide 'NIPAM') were purchased from Sigma-Aldrich. The crosslinker (such as N,N'₋ methylenebisacrylamide solution 'MBA' and glyoxal) and initiator (ammonium persulfate 'APS') were purchased from Merck. The standards for essential tea components were purchased from Catechin (C), Epicatechin (EC), Epigallocatechin (EGC), Epigallocatechin Gallate (EGCg), Epicatechin Gallate (ECG), Gallic Acid and Caffeine Anhydrous were purchased from Sigma Aldrich.
The hollow fiber forward osmosis (HFFO) membrane module and flat sheet membranes used in this were supplied by Aquaporin Asia Pvt. All chemicals used in this study were of high quality and were used further without any modification.
Methodology
- Preparation of feed solution
- Selection of draw solution
- Selection of suitable forward osmosis membrane
- Analytical methods
- Experimental Setup for HFFO module performance study
- Synthesis of hydrogel
- FO experimental setup for performance analysis of hydrogel
The support layer of the membrane consists of a polyester mesh (PE) embedded in a polysulfone substrate (PSF) and the active layer is formed by a dense selective polyamide (PA) layer with integrated aquaporin proteins coated on the lumen side of the fibers. void [141]. The quality of the concentrated tea extract (liquid food) was evaluated in terms of the concentration change of the essential tea components. The elemental composition analysis of the synthesized hydrogel was evaluated using energy dispersive X-ray spectroscopy (EDX) (Make: Zeiss, Germany, Model: Sigma 300).
Depending on the membrane orientation, FS and DS (Model: VND-380-SP1, M/s Lunar Motors, India) are pumped through the shell or tube side of the HFFO membrane module. Before each experiment, the HFFO membrane module was first stabilized by passing DI water through the lumen and tube side of the module. When the mass of the FS tank reached 1.179 kg, the circulation of FS and DS to the membrane was completed.
Then, the shell side of the module was sealed and the tube side of the membrane module was flushed with DI water for another 25 min. The performance of the synthesized hydrogel was evaluated based on hydrogel swelling and removal ability. Wd and Wt represent the weight (in g) of the dried and swollen hydrogel at time 't'.
The given pilot study suggests the feasibility of the given 3-layer design of the membrane module.
Performance Analysis of HFFO Membrane Module for Tea Concentration using:85
- Multi-component inorganic draw solution
The efficiency of the FO process was determined in terms of water flux, SRSF, and the concentration of essential tea components in the final product. The selection of an appropriate DS is a crucial component for the successful development of the FO process. The selection of appropriate DS is a crucial component for the successful development of the FO process.
The feasibility of the identified multicomponent inorganic salt solutions was investigated as a potential DS for the concentration of liquid food (tea extract) using the FO process. Since, the water flux (Jw) is a function of the osmotic pressure gradient between DS and FS. The quality of the concentrated tea extract was measured in terms of the concentration of essential tea components.
The change in the concentration of essential tea components represents the improved quality of the final tea concentrate (Table 5.3). The quality of the final tea concentrate was assessed based on the concentration of essential tea components. The quality of tea extract obtained by both the conventional brewing process and tea powder was evaluated in relation to the concentration of essential tea components.
The influence of the composition of the grout solution on the quality of the final product was determined by the change in the concentration of the essential tea component.
Simulation and Design Analysis of HFFO Membrane Module
- Model simulation and validation for single component inorganic draw solution
- Process flow-sheet simulation for the concentration of tea extract
The above study suggests that the FO process is a viable technique for the concentration of brewed tea extract and the developed model was able to predict the performance of the given FO process. It is said that the performance of HFFO membrane modules strongly depends on the flow rate FS and DS [210]. Thus, to understand the role of operating flow rate (both FS and DS).
Increased flux resulted in increased flux, demonstrating the dominance of ECP on the active side of the membrane. Theoretically, the increased flow configuration is attributed to the reduction of ECP by decreasing the mass transfer coefficient with the flow. The introduction of a higher feed rate reportedly disrupts the thick layer of liquid on the AL.
Like the FS flow rate, the applied DS flow rate also influences the performance of the HFFO module. The impact of DS flow rate on FO performance can theoretically be explained by the more severe effect of DS flow rate on diluting internal and external concentration polarization. Furthermore, the sweep-two-parameter function should be used to study the dependence of two-parameter response at the end of the integration interval (Figure 5.10).
As discussed in the previous section, the DS and FS flow rates significantly affect the overall FO performance, and the same trend was observed in this study.
Performance Analysis of Hydrogel as Draw Solute for Forward Osmosis Process
- Effect of different stimuli on hydrogel regeneration
- Forward osmosis performance of the synthesised hydrogel
The reduced membrane performance was due to the surface morphology of the synthesized hydrogel due to repeated cycles of swelling and deswelling (Figure 5.11 (c, d). The change in surface morphology of the hydrogel subsequently reduced the water flux in the FO process. The reduction in FO performance could also be from DECP due to the reduced swelling capacity of the hydrogel on the membrane surface.
An internal osmotic pressure gradient can control the swelling capacity of the hydrogel (this is related to the number of ionic functional groups. The cross-linking density plays an important role in determining the absorption properties of the hydrogel. Although the inclusion of NIPAM does not play a role play a significant role in improving the swelling capacity of the hydrogel.
This swelling and deflating of the synthesized hydrogel continued until the change in water flux (L m−2 h−1) became constant. This means that the cross-linker concentration has no significant effect on the unloading properties of the hydrogel. To overcome the given problem, the solvent must be simultaneously removed from the polymer network to maintain the swelling ability of the synthesized hydrogel.
The leaching of loose polymer components could be possible due to the continuous swelling and deflating of the hydrogel during the 5-cycle FO process.
Wenten, Advances in forward osmosis (FO) membrane for liquid food concentration, IOP Conf Ser Mater Sci Eng. Shi, Recent developments and future challenges of hydrogels as entrained solutes in the forward osmosis process, Voda (Switzerland). Tang, Design optimization modeling research of osmosis hollow fiber modules, J Memb Sci.
Wenten, Advances in forward osmosis (FO) membrane for concentration of liquid foodstuffs, in: IOP Conf. Wang, Composite polymer hydrogels as pulling agents in forward osmosis and solar dewatering, Soft Matter. Simon, Composite polymer hydrogels as traction agents in forward osmosis and solar dewatering, Soft Matter.
Fang, Forward osmosis with electro-responsive P(AMPS-co-AM) hydrogels as attractants for desalination, J Memb Sci. Yang, Performance evaluation of electroresponsive hydrogels as attractant agent in forward osmosis desalination, Desalination. Tessaro, Membrane concentration of liquid foods by forward osmosis: Process and quality view, J Food Eng.
Li, Athermal advanced osmosis process for liquid egg white concentration: efficiency and process improvement. Hu, Investigation of food preservatives as solutes in forward osmosis process for juice concentration, J Memb Sci. Mohanty, Ibrar Ibrar, Ali Altaee (2022) Feasibility of poly(vinyl alcohol)/poly(diallyldimethylammonium chloride) polymer network hydrogel as a draw solution for forward osmosis process.
