Polyacrylonitrile hollow fibers

Y. Maeda, M. Tsuyumoto, H. Karakane and H. Tsugaya, Separation of water-ethanol mixture by pervaporation through hydrolyzed polyacrylonitrile hollow fiber membranes, Polymer J., 1991, 23, 501-512 N. Schamagl, K.-V Peinemann, A. Wenzlaff, H.-H. Schwarz and R.-D. Behling, Dehydration of organic compounds with SYM-PLEX composite membranes, J. Membr. Sci., 1996, 113, 1-5. 

Y. Maeda, M. Tsuyumoto, H. Karakane and H. Tsuyumoto, Separation of water-ethanol mixture by pervaporation through hydrolyzed polyacrylonitrile hollow fiber membranes, Polym. J., 1991, 23, 501-511. 

An enzymatic production process for Diltiazem (54), a coronary vasodilator and calcium channel blocker, was started in 1993 by Tanabe Seiyaku, Japan [7, 77]. The epoxide (2i, 3S)-52 is a key intermediate in this synthesis (Scheme 17) and can be produced via asymmetric hydrolysis of rac-52 catalyzed by Serratia marescens lipase immobilized on spongy layers. The whole process takes place in a polyacrylonitrile hollow fiber membrane reactor and produces (2i, 3S)-52 in yields of 40-45%. The hydrolyzed product (2S,3i )-53 is not stable under the prevailing reaction conditions and decarboxylates to aldehyde 55, a strong enzyme deactivator. The aldehyde needs therefore to be removed, which is achieved by continuous filtration of its bisulfite adduct 56. Using this enzymatic process it was possible to bring down the number of required steps en route to 54 from nine to five. This process is also carried out by other companies (e.g., DSM) with a worldwide annual production of 1001. 

For membrane solvent extraction, Schlosser et al. [114] provided a comprehensive review for organic acid separation and recovery. Large-scale utilization of membrane solvent extraction [107,115,116] modules in pharmaceutical/chemical plants is used. Lopez and Matson [115] demonstrated enzymatic resolution of diltiazem precursor using hydrophilic polyacrylonitrile hollow fibers and an aqueous-organic interface on the outside surface of these fibers. Klaassen and Jansen [116] and Porebski et al. [107] illustrated the use/ performances of modules of porous hydrophobic PP hollow fibers in chemical plants achieving aqueous-to-organic and organic-to-aqueous solvent extraction, respectively. 

The bank of 60 m commercial-scale membrane reactor modules in diltiazem production facility employing hydrophilic polyaCTylonitrile hollow fibers was demonstrated. This example describes enzymatic resolution of diltiazem precursor using hydrophilic polyacrylonitrile hollow fibers and an aqueous-organic interface on the outside surface of these fibers (Eigure 4.16) [1,3,116]. 

Polyacrylonitrile hollow fibers fabricated at Gulf South Research Institute were used. Their hydraulic permeability was 9x 10 cm/s atm, the wall thickness 50 /x, the inside diameter 200 microns and the wall micropore diameter about 100 A. Hollow fibers (150) assembled in bundles with a total surface area of 140 cm were washed first with water, and then with methanol and dried by passing nitrogen gas through them for one hour. They were immersed in a mixture of 4-VP and a,co-dihaloalkane (2 1 molar). The reaction was permitted to proceed for 10 days in case of dibromo ethane and 2 days in the case of dibromohexane. A cross section of a typical fiber is shown in Figure 5. 

Yin, J., N. Coutris, and Y. Huang. 2012. Experimental investigation of aligned groove formation on the inner surface of polyacrylonitrile hollow fiber membrane. Journal of Membrane Science 394 57-68. 

Figure 3 is a scanning electron micrograph of polyacrylonitrile hollow fiber used for ultrafiltration. A large number of voids can be seen in the wall and there are thin and compact layers on both the outer and inner surfaces of the wall. The balance between these two kinds of structures affect the properties of the membrane. The electron micrograph of a cross section of the outside surface of the polyacrylonitrile hollow fiber shows that the pore size of the network close to the outer surface is smaller than that of the inner part. 

The microstructure of the polyacrylonitrile hollow fiber for the hemofilter artificial kidney is somewhat different from that for industrial ultrafiltration. The number of voids, their location, and their shapes are different from those of the ultrafiltration membrane for industrial use. 

Bei, W., Xiao-Quan, S., and Shu-Guang, X. (1999). Pieconcentration of ultratrace rare earth elements in seawater with 8-hydroxyquinoUne immobilized polyacrylonitrile hollow fiber membrane for determination by inductively coupled plasma mass spectrometry. Analyst (London) 124(4), 621. 

Yang, M.-C., and Tong, J.-H. (1997). Loose ultrafiltration of proteins using hydrolyzed polyacrylonitrile hollow fiber. J. Membr. Sci. 132, 63. 

Hollow-fiber permeators, 26 22 Hollow fibers, 13 389-390 cellulose ester, 26 19 cellulosic, 26 18-20 ion-exchange, 26 15 mechanical considerations and dimensions for, 26 5-7 natural polymer, 26 23 polyacrylonitrile, 26 23 polyamide, 26 21-22 post-treatment of, 26 13-14 preparation of, 26 3 production of, 19 757 with sorbent walls, 26 26 technology of, 26 27 wet spinning of, 25 816, 817-818 Hollow-fiber spinning processes, 26 7-12 Hollow fiber spinning technology,... 

A completely different approach was taken by Koresh and Soffer (1980, 1986, 1987). Their preparation procedure involves a polymeric system like polyacrylonitrile (PAN) in a certain configuration (e.g. hollow fiber). The system is then pyrolyzed in an inert atmosphere and a dense membrane is obtained. An oxidation treatment is then necessary to create an open pore structure. Depending on the oxidation treatment typical molecules can be adsorbed and transported through the system. 

K. Watanabe and S. Kyo, Pervaporation Performance of Hollow-fiber Chitosan-Polyacrylonitrile Composite Membrane in Dehydration of Ethanol, J. Chem. Eng. Jpn 25, 17 (1992). 

Saufi S.M., and Ismail A.F. (2003) Development and characterization of polyacrylonitrile (PAN) based carbon hollow fiber membrane. Songklanakarin J. Sci. Technol. 24, 843-854. 

Carbon molecular sieve membranes. Molecular sieve carbons can be produced by controlled pyrolysis of selected polymers as mentioned in 3.2.7 Pyrolysis. Carbon molecular sieves with a mean pore diameter from 025 to 1 nm are known to have high separation selectivities for molecules differing by as little as 0.02 nm in critical dimensions. Besides the separation properties, these amorphous materials with more or less regular pore structures may also provide catalytic properties. Carbon molecular sieve membranes in sheet and hollow fiber (with a fiber outer diameter of 5 pm to 1 mm) forms can be derived from cellulose and its derivatives, certain acrylics, peach-tar mesophase or certain thermosetting polymers such as phenolic resins and oxidized polyacrylonitrile by pyrolysis in an inert atmosphere [Koresh and Soffer, 1983 Soffer et al., 1987 Murphy, 1988]. 

In dialysis, size exclusion is the main separation mechanism, while osmotic pressure and concentration difference drive the transport across two typically aqueous phases. While dialysis is used in some analytical separations, dialysis for the removal of toxins from blood (hemodialysis) is the most prominent application for hollow fiber technology in the biomedical field. The hemodialyzers are used to treat over one million people a year and have become a mass produced, disposable medical commodity. While the first hemodialyzers were developed from cellulosic material (Cuprophane, RC, etc.), synthetic polymers such as polyacrylonitrile, poly(ether) sulfone, and polyvinyl pyrrolidone are increasingly used to improve blood compatibility and flux. Hemodialyzer modules consist of thousands of extremely fine hollow fibers... 

The enantioselective hydrolysis is carried out in an organic-aqueous two-phase reactor (toluene/water), where the phase contact is established by a hydrophilic hollow-fiber membrane (polyacrylonitrile). The lipase is immobilized onto a spongy layer by pressurized adsorption. The productivity is about 40 kg trans-(2R,3S)-(4-methoxyphenyl) glycidic acid methyl ester m-2 a-1. This process has been operated since 1993. 

Polyacrylonitrile (PAN) has been used in the preparation of UP membranes for a long time [82, 83] due to its superior resistance to hydrolysis and oxidation. PAN is highly crystalline and relatively hydrophilic and is usually copolymerized with more hydrophilic monomers to improve processability and to make it less brittle. Hollow fibers can be prepared from PAN dissolved in nitric acid [84]. Preparation of PAN membranes by phase inversion from solutions in DMAC, DMF or NMP is also possible. An example is shown in Fig. 4.4. A Sumitomo patent [85] discloses the preparation of membranes from copolymers containing 89% acrylonitrile and 11% ethyl acrylate dissolved in DMF and formamide and coagulated in water. A microporous membrane is obtained. In order to make the membranes suitable for reverse osmosis, they were submitted to a plasma treatment in the presence of 4-vinyl pyridine. 

A suitable polymer material for preparation of carbon membranes should not cause pore holes or any defects after the carbonization. Up to now, various precursor materials such as polyimide, polyacrylonitrile (PAN), poly(phthalazinone ether sulfone ketone) and poly(phenylene oxide) have been used for the fabrication of carbon molecular sieve membranes. Likewise, aromatic polyimide and its derivatives have been extensively used as precursor for carbon membranes due to their rigid structure and high carbon yields. The membrane morphology of polyimide could be well maintained during the high temperature carbonization process. A commercially available and cheap polymeric material is cellulose acetate (CA, MW 100 000, DS = 2.45) this was also used as the precursor material for preparation of carbon membranes by He et al They reported that cellulose acetate can be easily dissolved in many solvents to form the dope solution for spinning the hollow fibers, and the hollow fiber carbon membranes prepared showed good separation performances. 

Lu et al. [Ill] later reported on the development of solid-state electrochemical linear actuators with a polyaniline yarn-in-hollow fiber configuration using an ionic liquid electrolyte. These yarn-in-hollow fiber actuators, which were constructed using a triflic acid-doped polyaniline solid fiber inserted into a triflic acid-doped polyaniline hollow liber. A porous polyacrylonitrile insert separated the two electrodes, which contained the [BMIM] [Bp4] electrolyte (Figure 2.27). It was demonstrated... 

Yang MC, Yu DG, Influence of precursor structure on the properties of polyacrylonitrile based activated carbon hollow fiber, J Appl Polym Sci, 59(11), 1725-1731, 1996. 

---