Cellulose triacetate hollow fiber

Permeability Properties of Cellulose Triacetate Hollow-Fiber Membranes for One-Pass Seawater Desalination... 

Samples examined were 1) Cellulose triacetate hollow fibers, CTAHF, as spun. In distilled water 2) CTAHF stretched for eight days In water with a 3.57 gram weight (22 psi stress). In distilled water 3) CTAHF air dried for two weeks. In an unsealed capillary ... 

The commercialized RO modules consist of cellulose triacetate hollow-fiber type and polyamide spiral-wound type. The cellulose triacetate hollow-fiber RO modules are used around the world for seawater desalination mainly because of excellent features such as a chlorine tolerance and fouling resistance. 

This summary describes the history of cellulose triacetate RO membrane, description of cellulose triacetate hollow-fiber RO modules of Toyobo for seawater desalination, actual operation results, and recent RO modules of cellulose triacetate including most recently developed advanced modules. 

A hollow-fiber-type module was developed and a fundamental patent was filed by Dow Chemical in 1960. An RO module using the cellulose triacetate hollow fiber is indicated there (Mahon, 1966). A significant portion of research and development at Dow Chemical was carried out based on its research contract with OSW, and the development results of the RO module for brackish water was published in 1970 and for seawater in 1974. The RO module using cellulose triacetate hollow fiber for brackish water was marketed in 1974 (Dance et al., 1971 Ammons and Mahon, 1974). 

Research and development of the hollow-fiber-type module using a cellulose acetate membrane was conducted by Monsanto, Toyobo, and others, in addition to Dow Chemical. Toyobo announced an RO module for one-pass desalination of seawater that used the cellulose triacetate hollow-fiber membrane module in 1979 (Orofino, 1970 Ukai et al., 1980). 

Dance, E. L., Davis, T. E., Mahon, H. I., McLain, E. A., Skiens, W. E., and Spano, J. O. (1971). Development of cellulose triacetate hollow fiber reverse osmosis modules for brackish water desalination. Report No. 763. U.S. Office of Sahne Water Res. Develop. Progr., New York. 

Data of WRPC. The Water Reuse Promotion Center(WRPC) in JAPAN has been engaged in development of sea water desalination by reverse osmosis since 197. At IDEA meeting at Mexico city 1976,the first redults were reported with two types of modules, du Dont hollow fine fiber module B-10 and UOP s cellulose triacetate ultrathin spiral wound module,tested at their laboratory at Chigasaki beach. Then the WRPC has adopted two types of modules made in Japan, Toray new type of spiral wound module made from cellulose acetate and Toyobo s cellulose triacetate hollow fine fiber module. 

Currently, Toyobo markets the Hollosep cellulose triacetate hollow fine fiber for RO applications (Hollosep is a registered trademark of Toyobo Company, Ltd, Osaka, Japan). 

Separex s,41-43 Grace Membrane Systems cellulose ester,60 Envirogenics GASEP (trademark of Envirogenics Company)64 cellulose triacetate spiral-wound membranes, and Dow cellulose acetate hollow fibers are used to produce a salable product from sour gas streams. 

Polymer Plasticizer. Nylon, cellulose, and cellulose esters can be plasticized using sulfolane to improve flexibiUty and to increase elongation of the polymer (130,131). More importantly, sulfolane is a preferred plasticizer for the synthesis of cellulose hoUow fibers, which are used as permeabiUty membranes in reverse osmosis (qv) cells (131—133) (see Hollow-FIBERMEMBRANEs). In the preparation of the hoUow fibers, a molten mixture of sulfolane and cellulose triacetate is extmded through a die to form the hoUow fiber. The sulfolane is subsequently extracted from the fiber with water to give a permeable, plasticizer-free, hoUow fiber. 

As Figure 5.12 shows, Toray s PEC-1000 crosslinked furfuryl alcohol membrane has by far the best sodium chloride rejection combined with good fluxes. This explains the sustained interest in this membrane despite its extreme sensitivity to dissolved chlorine and oxygen in the feed water. Hollow fine fiber membranes made from cellulose triacetate by Toyobo or aromatic polyamides by Permasep (Du Pont) are also comfortably in the one-stage seawater desalination performance range, but the water fluxes of these membranes are low. However, because large-surface-area, hollow fine fiber reverse osmosis modules can be... 

Hollow fine fiber modules made from cellulose triacetate or aromatic polyamides were produced in the past for seawater desalination. These modules incorporated the membrane around a central tube, and feed solution flowed rapidly outward to the shell. Because the fibers were extremely tightly packed inside the pressure vessel, flow of the feed solution was quite slow. As much as 40-50 % of the feed could be removed as permeate in a single pass through the module. However, the low flow and many constrictions meant that extremely good pretreatment of the feed solution was required to prevent membrane fouling from scale or particulates. A schematic illustration of such a hollow fiber module is shown in Figure 3.47. 

Cellulose ester membranes (e.g., cellulose acetate, cellulose diacetate, cellulose triacetate, cellulose propionate, cellulose butyrate, cellulose cyanoethal-ate, cellulose methacrylate, and mixtures of these) can be employed for the acid components of a natural gas stream. The membranes can be either flat films or hollow fibers. 

This is analogous to the extraction of sugars with boronic acids described earlier. The recovery of phenylalanine from a fermentation broth has been simplified by using a microporous poly(tetrafluoroethylene) membrane with tri-/j-octylmethylammonium chloride in toluene in the pores.133 Phenylalanine can also be separated using the quaternary ammonium salt with 2-nitrophenyl octyl ether in a cellulose triacetate membrane.134 Kerosene flowing in hollow fiber membranes can remove 99.9% of organic pollutants, such as benzene, p dichlorobenzenc, chloroform, and carbon tetrachloride, from wastewater outside the fibers.135... 

Membranes with pores having pore diameters in the nanometer range ean be obtained by pyrolysis. Molecular sieves can be prepared by controlled pyrolysis of thermoset polymers [poly(vinylidene chloride), poly(furfuryl alcohol), cellulose, cellulose triacetate, polyacrylonitrile (PAN), and phenol formaldehyde] to obtain carbon membranes, or of silicone rubbers to obtain silica filters. For example, carbon molecular sieves can be obtained by pyrolysis of PAN hollow fibers in an inert atmosphere, which leads to dense membranes whose pores are opened by oxidation, initially at 400°-500°C and finished at 700°C [15]. These membranes are used to separate O2 /N2 mixtures. Le Carbone-Lorraine deposits a resin into a tubular macroporous substrate and then by pyrolysis creates a thin (< 1 pm) carbon active layer. Silicon rubber tubes can be pyrolyzed in an inert atmosphere at temperatures around 700°C followed by oxidation in air at temperatures from 500° to 900°C [16]. The membranes are composed almost completely of Si02 with pores having a maximum porosity of 50% and diameters fi om 5 to 10 nm. The permeabilities for He, H2, O2, and Ar range from 0.5 to 5 x 10 m s Pa. 

C. Pan, Permeation of water vapor through cellulose triacetate membranes in hollow fiber form, J. Appl. Polym. Sci., 1978, 22, 2307-2323. 

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