Preparation and porosity of cellulose triacetate reverse osmosis membranes

doi:10.1016/0376-7388(95)00191-3

Journal of Membrane Science

Volume 109, Issue 2, 24 January 1996, Pages 223-230

https://doi.org/10.1016/0376-7388(95)00191-3 Get rights and content

Abstract

Good cellulose triacetate reverse osmosis membranes have been prepared by the phase separation technique. The membrane properties were influenced by the membrane casting dope composition, mostly by the dioxane/acetone ratio and the maleic acid content in the casting dope. The distinctive membrane performances were caused by different pore size distributions and various numbers of pores in the membranes skin. The improved pore size distribution analysis and the calculation of both the effective number of pores and the active part of the membranes surface area have shown a wide spectrum of the network pore sizes and usually one size group of bigger aggregate pores.

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Cellulose triacetate (CTA) is a bio-based chiral polymer with the rare property of forming homogenous solid blends with several compounds. The controlled modification of the conformational freedom of the polymer chains by plasticizers could enable the tuning of its selectivity towards optical isomers. We survey the blends of CTA with four individual ionic liquids (ILs), with a focus on the action of the individual counter ions. Blends of CTA with four ILs being, the combinations of two cations (BMIM and BMPy) and two anions (Tf₂N and TfO), were studied using thermal analysis methods (TGA, DMA), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy and sorption tests. Blends containing the ILs with Tf₂N, which undergoes cis-trans stabilization, were less effective plasticizers of CTA than the TfO-based ILs when sensed as decreases in the temperatures of glass transition (T_g) and degradation (T_d). The exchange of the cations caused discernible but far smaller changes of T_g and T_d. All studied ILs caused the disappearance of the Raman band of CTA at 702 cm⁻¹, which we assign to the skeletal vibrations of the pyranose ring using the ab-initio calculation, and pronounced wavenumber shifts of the bands of the methoxy group (at 1163 cm⁻¹) and pyranose ring (at 1075 and 1085 cm⁻¹) in CTA. This indicates the increased intra-chain mobility and physical interactions between CTA and IL. TEM analysis confirmed the existence of interactions between the ILs and CTA chain, and the amplification of plasmon resonance. Sorption uptakes of some enantiomers (carvone, 1-phenylethanol and 1-amino-2-propanol) confirmed the chiral behavior of the CTA-based polymers. For instance, the sorption uptake of (S)-(−)-1-phenylethanol in pure CTA was by 30 % higher than that of (R)-(+)-1-phenylethanol. Moreover, the sorption uptakes of (R)-(+)- and (S)-(−)- carvone enantiomers increased by 47 % and 260 %, respectively, due to blending CTA with 20 wt % of [BMPy][TfO].
Reverse osmosis desalination: A state-of-the-art review
2019, Desalination
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As a result, conventional techniques such as thermoporometry, gas adsorption-desorption, and bubble point cannot be employed for determining the pore size [117,118]. Typically, for RO membrane, the pore size and PSD are determined indirectly by means of solute transport method utilizing separation data of reference solutes [117,119–123]. Also, membrane's flux dependency on pressure can be used to determine characteristic parameters that can be related to PSD [121].
Water scarcity is a grand challenge that has always stimulated research interests in finding effective means for pure water production. In this context, reverse osmosis (RO) is considered the leading and the most optimized membrane-based desalination process that is currently dominating the desalination market. In this review, various aspects of RO desalination are reviewed. Theories and models related to concentration polarization and membrane transport, as well as merits and drawbacks of these models in predicting polarization effects, are discussed. An updated review of studies related to membrane modules (plate and frame, tubular, spiral wound, and hollow fiber) and membrane characterization are provided. The review also discusses membrane cleaning and different pre-treatment technologies in place for RO desalination, such as feed-water pre-treatment and biocides. RO pre-treatment technologies, which include conventional (e.g., coagulation-flocculation, media filtration, disinfection, scale inhibition) and non-conventional (e.g., MF, UF, and NF) are reviewed and their relative attributes are compared. As per the available literature, UF, MF and coagulation-flocculation are considered the most widely used pre-treatment technologies. In addition, this review discusses membrane fouling, which represents a serious challenge in RO processes due to its significant contribution to energy requirements and process economy (e.g., flux decline, permeate quality, membrane lifespan, increased feed pressure, increased pre-treatment and membrane maintenance cost). Different membrane fouling types, such as colloidal, organic, inorganic, and biological fouling, are addressed in this review. Principles of RO process design and the embedded economic and energy considerations are discussed. In general, cost of water desalination has dropped to values that made it a viable option, comparable even to conventional water treatment methods. Finally, an overview of hybrid RO desalination processes and the current challenges faced by RO desalination processes are presented and discussed.
Development of graphene oxide-cellulose acetate nanocomposite reverse osmosis membrane for seawater desalination
2019, Composites Part B: Engineering
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Finally, the membrane was annealed at 80 °C for 10 min in water bath. According to previous studies [33–38], 15 wt% of cellulose acetate concentration was chosen to fabricate RO membrane and the membrane thickness were adjusted at 100 μm by the gate height of the doctor blade. To investigate the dependence of prepared membrane properties on GO concentration, four membranes called CA, CA-0.5% GO, CA-1% GO, CA-2% GO were fabricated with 0, 0.5, 1 and 2 wt% of GO, respectively.
Cellulose acetate (CA)/Graphene oxide (GO) nanocomposite membrane was prepared by phase inversion method. GO nanosheets were added to CA matrix with the aim of improving seawater desalination performance of asymmetric CA reverse osmosis (RO) membrane and enhancing mechanical and thermal stability. GO with grain size of 2.7 nm was synthesized through modified Hummer method and dispersed in CA matrix to prepare GO/CA nanocomposite membranes. The membranes were fabricated by casting of GO/CA onto a polyester fabric. The results showed that the GO concentrations would affect the morphology, hydrophilicity, porosity, roughness, mechanical strength and thermal stability of membranes. Incorporation of GO into the CA matrix changed the porosity structure from finger-like to sponge-like. Hydrophilicity nature, storage modulus and thermal stability of CA membranes were greatly improved with incorporation of 1 wt% GO. In addition, synthetic seawater salt rejection of CA membrane modified with 1 wt% GO at 25 bar was 1.8 times higher than that of pristine CA membrane, while flux of CA membrane exhibited small reduction with the presence of 1 wt% GO.
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On the one hand, the main obstacles in terms of CTA membrane fabrication were its poor solubility in organic water-miscible solvents by the phase separation method. On the other hand, it was easy to be compacted when testing at moderate or high operating pressures [16,17]. In our previous works, a kind of CTA RO membrane was successful fabricated by melting method in order to solve its poor solubility in organic water-miscible solvents [18].
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A novel procedure to fabricate quaternized cellulose triacetate reverse osmosis (QCTA-RO) membranes via the etherification procedure between partially hydrolyzed CTA-RO membrane and 3-chloro-2-hydroxypropyl-trimethyl ammonium chloride (CHPTAC) in alkaline solutions (pH = 9–11) for different reaction time (1, 2, 3 and 4 h) was proposed. The structure and performances of the obtained QCTA-RO membranes were characterized and their antibacterial performances against E. coli and S. aureus were evaluated through colony counting method. The results showed that quaternary amine group was successfully grafted on the surface of membrane via covalently bond without significant damage to morphology, mechanical performance and thermal stability. The permeation flux values increased with prolonging modification time to 3 h, while the salt rejection decreased slightly but remained above 92%. QCTA-RO membranes displayed good antibacterial activity against Gram-negative E. coli and Gram-positive S. aureus and their bactericidal rates were 78.7–89.0% and 64.7–76.6% respectively at the optimized modification time of 2–3 h.
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Chromophoric sensors were made based on 8-hydroxyquinoline immobilized onto a thin film of a polymer blend matrix. The thin films were made by the solution casting method using cellulose triacetate and polyethylene glycol (PEG 600) as plasticizer and pore-forming agent. Different contents of PEG 600 additive were investigated. The prepared films were characterized by FTIR and thermal analysis. The absorption and fluorescence spectra of different films were dependent on the content of PEG 600 with clear quenching of the fluorescence of the film that contains PEG 600 compared to that with zero content. This behavior was attributed to the collective effect of hydrogen bonding (intra- and intermolecular hydrogen bonding) that enhances the process of excited-state proton transfer. This result is favorable to a responsive sensor that shows fluorescence off in the absence of metal ions and fluorescence on upon metal ion chelation. The detection of 5 × 10⁻⁵ M of Al³⁺, Zn²⁺ and thallium (I) in aqueous solution has been observed with the fluorescence method. The result obtained is consistent with the enhancing effect of PEG 600 in the detectability of metal ions. Compared with the detection of Al³⁺ and Zn²⁺, the sensor shows better detection of thallium (I), with clear fluorescence spectra.

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Preparation and porosity of cellulose triacetate reverse osmosis membranes

Abstract

J. Membrane Sci.

Desalination

Desalination

Desalination

Sea water demineralization by means of an osmotic membrane

Adv. Chem. Ser.

The combined effects of evaporation and quench steps on asymmetric membrane formation by phase inversion

J. Polym. Sci., Polym. Phys. Ed.

Asymmetric cellulose acetate membranes

Method of making asymmetric cellulose triacetate membranes