Cellulose acetate membrane modules

Development of Commercial Cellulose Acetate Membrane Modules... 

Reverse Osmosis. This was the first membrane-based separation process to be commercialized on a significant scale. The breakthrough discovery that made reverse osmosis (qv) possible was the development of the Loeb-Sourirajan asymmetric cellulose acetate membrane. This membrane made desalination by reverse osmosis practical within a few years commercial plants were installed. The total worldwide market for reverse osmosis membrane modules is about 200 million /yr, spHt approximately between 25% hoUow-ftber and 75% spiral-wound modules. The general trend of the industry is toward spiral-wound modules for this appHcation, and the market share of the hoUow-ftber products is gradually falling (72). 

Currently, approximately one billion gal/day of water are desalted by reverse osmosis. Half of this capacity is installed in the United States, Europe, and Japan, principally to produce ultrapure industrial water. The remainder is installed in the Middle East and other desert regions to produce municipal drinking water from brackish groundwater or seawater. In recent years, the interfacial composite membrane has displaced the anisotropic cellulose acetate membrane in most applications. Interfacial composite membranes are supplied in spiral-wound module form the market share of hollow fiber membranes is now less than... 

Removal of carbon dioxide is the only membrane-based natural gas separation process currently practiced on a large scale—more than 200 plants have been installed, some very large. Most were installed by Grace (now Kvaerner-GMS), Separex (UOP) and Cynara and all use cellulose acetate membranes in hollow fiber or spiral-wound module form. More recently, hollow fiber polyaramide (Medal) membranes have been introduced because of their higher selectivity. 

The treatment of ADUF by reverse osmosis [13] was found to be useful in concentrating activity in small volume while making a larger volume of the decontaminated effluent for direct disposal after required dilution. Porous cellulose acetate membranes were used in plate module configurations. The concentration of ammonium nitrate in the permeate stream is not very different from that of the contaminated retentate. With the addition of flocculating aids, the decontamination factors in the range of 1000 with VRFs in the range of 100 were achieved. 

Development of a Cellulose Acetate Membrane and a Module for Hemofiltration... 

In pilot plant experiments we have used a 7 m DDS-module type 40 with tight cellulose acetate membranes type DDS-990. Concentration has been performed at pH = 4.0-4.5 in a batch system at ambient temperature using 30 kp/m2 delivered by a Rannie piston pump. 

Figure 6.3927 shows a two-stage cascade for the purification and dehydration of sour gases, mainly removing C02 and H2S. Again, spiral wound modules with asymmetric cellulose acetate membranes are employed. It should be noted, that in this case as in all other cases discussed here, no compressors had to be installed. This is the main reason why these applications show excellent payback times. 

Figure 14.7 Photographs of UOP membrane plants using spiral-wound modules of cellulose acetate membranes for CO2 separation, (a) Plant compact enough to be moved when the gas field is exhausted after a few years of operation capacity of lOOOONnrp/h membrane designed to reduce CO2 gas from 6% to 2%. (b) A 600000sdNm /h unit designed to reduce CO2 gas from 5.7% to 2%...

Figure 15.1 A gas treatment skid for hydrogen recovery from the 1980 s containing cellulose acetate membranes as spiral wound modules. Image courtesy of W. R. Grace, Copyright (1988) W. R. Grace...

Gas permeation systems typically use hollow-fiber or spiral-wound membranes, although hollow-fiber systems are more common tBaker. 2004k Cellulose acetate membranes are used for carbon dioxide recovery, polysulfone coated with silicone rubber is used for hydrogen purification, and conposite membranes are used for air separation. The feed gas is forced into the membrane module under pressure. Retentate, which does not go through the membrane, will become concentrated in the less permeable gas. Retentate exits at a pressure that will be close to the input pressure. The more permeable species will be concentrated in permeate. Permeate, which has passed through the membrane, exits at low pressure. The operating cost for a gas permeator is the cost of conpression of the feed gas and the irreversible pressure difference that occurs for the gas that permeates the membrane. A typical hollow-fiber unit will contain 5000 m membrane area per m at a cost of approximately 200/m. ... 

The whole membrane module is composed of six racks, each of them consisting of eleven pressure vessels, operated in parallel, designed to house one spiral wound membrane each. The pressure vessels were originally equipped with cellulose acetate membranes specifically developed for PRO. During the first period, the plant operation has been optimized and the performance has been monitored, resulting in a power density lower than 0.5 W/m. Next, thin film composite membranes developed for PRO were installed in early 2011. So far the measured power density has reached nearly 1 W/m, which is a major improvement compared to the cellulose acetate membranes originally installed. Based on this preliminary experience, Statkraft plans to build a full-scale 25 MW osmotic power plant by 2015 [20]. 

In this type of module a number of membranes of tubular shape are encased in a container. For example, 18 tubes are connected in scries by headers at both ends of the Nitto NTR-1500-PI 8A module. Figures 7.9 and 7.10 show the structure of the module. Cellulose acetate membranes are formed in the internal wall of the support tube of 12-mm internal diameter The tubular membranes so prepared are inserted into plastic tubes with many holes, which are mounted in a module container. The feed liquid flows inside the tube, and the permeate flows from the inside to the outside of the membrane tube and is collected at the permeate outlet. There are also tubular modules in which the feed is supplied to the outside of the membrane tube. The main features of the tubular module are... 

Membrane compaction involves the compressing of the membrane itself that, in essence, makes the membrane denser or thicker which reduces the flow and salt passage through it. Compaction can occur under higher feed pressure, high temperature, and water hammer. (Water hammer occurs when the RO high-pressure feed pump is started and there is air trapped in the membrane modules—see Chapter 6.2.) Most brackish water membranes, when operated properly, experience a minimal degree of compaction. However, seawater membranes and cellulose acetate membranes... 

To overcome the problems of cellulose acetate membranes, many synthetic polymeric materials for reverse osmosis were proposed, but except for one material, none of them proved successful. The only one material, which could remain on the market, was the linear aromatic polyamide with pendant sulfonic acid groups, as shown in Figure 1.2. This material was proposed by DuPont, which fabricated very fine hollow fiber membranes the modules of this membrane were designated B-9 and B-10. They have a high rejection performance, which can be used for single-stage seawater desalination. They were widely used for mainly seawater or brackish water desalination and recovery of valuable materials such as electric deposition paints, until DuPont withdrew them from the market in 2001. 

Gulf General Atomic was funded by OSW and developed a spiral-wound-type module. Moreover, the company applied for the patent of the basic stmcture in 1964. In the patent, the example that used the cellulose diacetate membrane of Loeb and Sourirajan was indicated (Westmoreland, 1968). The improvement was performed after that in each company, and the spiral-wound-t5 e module using a cellulose acetate membrane was put on the market by many companies, such as UOP, Hydranautics, Envirogenics, Toray Industries, and Daicel. 

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). 

Ullrafiltration processes have proved successful for the treatment of effluents, the treatment of black liquor, bleaching effluents and paper machine wash waters. They have also found use in the treatment of Kraft process effluents and there is increasing use of ultrafiltration to recover lignosulphonate and alkali lignin from the spent Uquors to produce other products. Reverse osmosis is used in the pulp and paper industry for concentration of sulphate liquor, using plate and frame modules and cellulose acetate membranes. Reverse osmosis is also used in the treatment of bleach effluents after various pretreatment stages. 

Membrane modules have found extensive commercial appHcation in areas where medium purity hydrogen is required, as in ammonia purge streams (191). The first polymer membrane system was developed by Du Pont in the early 1970s. The membranes are typically made of aromatic polyaramide, polyimide, polysulfone, and cellulose acetate supported as spiral-wound hoUow-ftber modules (see Hollow-FIBERMEMBRANEs). 

In 1968 we started investigations of RO applications for desalting brackish water. In the course of the investigations, we have found the spirally wound module of asymmetric cellulose acetate RO membrane shows excellent durabilities against fouling materials and free chlorine. 

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