22 Concentration and Recovery of є-Caprolactam from the Process Waste Stream Y. NAKAGAWA1, Y. NOGUCHI2, M. KURIHARA3, N. KANAMARU1, and T. TONOMURA1 Downloaded by PENNSYLVANIA STATE UNIV on July 2, 2012 | http://pubs.acs.org Publication Date: January 1, 1985 | doi: 10.1021/bk-1985-0281.ch022
1
Technical Development Department, Toray Industries, Inc., 3-Chome, Sonoyama, Otsu, Shiga 520, Japan Technical Department, Nagoya Plant, Toray Industries, Inc., 9-1 Ooe-cho, Minato-ku, Nagoya, Aichi 455-91, Japan 3 Pioneering Research and Development Laboratories, Toray Industries, Inc., 3-Chome, Sonoyama, Otsu, Shiga 520, Japan 2
PEC-1000 membrane exhibits excellent RO performance in the field of separation for water-soluble organic compounds with lowmolecular-weight as well as in the seawater desalination. After the basic test and the field test, a commercial plant for concentration and recovery of є-caprolactam has been on continuous operation for two years. RO system is constructed as so-called "Christmas Tree" and 250 t/d of feedwater containing less than 0.1 % of є-caprolactam is concentrated to 5 % and returned to the "Nylon-6" production process through evaporation process. It was most important to take care of fouling for designing and operating the RO systems since the feedwater contains considerable amount of suspended materials. Flux decline is controlled by periodical cleaning with anionic detergent. On the concentration and recovery of valuable materials from their aqueous solutions, reverse osmosis (RO) technology has been expected to be employed for the pur poses not only of saving energy to recover it but also of environmental pollution problems. Moreover, it is considered to be able to separate organic compounds of remarkably lower molecular-weight than with ultrafiltra tion (UF). However, the practical applications of this technology by means of conventional RO membranes, so far, have been limited due to the insufficiently low solute rejection of low molecular-weight organic compounds such 0097-6156/85/0281-0283$06.00/0 © 1985 American Chemical Society
In Reverse Osmosis and Ultrafiltration; Sourirajan, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.
Downloaded by PENNSYLVANIA STATE UNIV on July 2, 2012 | http://pubs.acs.org Publication Date: January 1, 1985 | doi: 10.1021/bk-1985-0281.ch022
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as ethanol or acetic acid. Therefore, it has also been necessary to develop a membrane of very high performance to overcome this limitation in this work. Frang et al. reported that the separation of lowmolecular-weight organic compounds including various functional groups in dilute aqueous solution (0.1 % by weight were not so effective as that of inorganic salts for all the membranes tested (1). Since then, many newly developed RO membranes have been examined for the selective separation performance of valuable materials in aqueous solutions by RO technology. PEC-1000 membrane has excellent RO performance (especially in solute rejection), which may lead to wider applications in both fields of seawater desalination and concentration and recovery of valuable materials (£-£) . In this paper, basic examination and application to RO system design and operation for the concentration and recovery of e-caprolactam are reported as one of the successful examples for the latter case. Steps toward Planning RO Systems for Recovery of Valuable Materials Before planning RO systems for the concentration and recovery of valuable materials, following examinations and estimations are to be employed. 1st step. Basic separation performance of the objective solute. 2nd step. Effects of operating conditions on RO performance. 3rd step. Durability test. 4th step. Investigation on pretreatment and/or cleaning, 5th step. Designing of RO system after feasibility investigation. Basic RO Performance of PEC-1000 Membrane From the comparative RO performance data of PEC-1000 membrane and several conventional RO membranes to the solutes such as e-caprolactam, dimethylformamide and dimethylsulfoxide, PEC-1000 membrane is known to be by far superior to NS-200 membrane as well as other conventional membranes (2^5^) . Pusch et al. examined the RO performance to benzyl alcohol and 1,4-dioxane as well as sodium chloride with various kinds of RO membranes (2) and reported the excellent rejection by PEC-1000 membrane. Further, Ohya et al. reported the possibility for concentration of ethanol (£,£) , ethyleneglycol (10) and other solutes by RO technology using PEC-1000 membrane. Similarly the performance data of PEC-1000 membrane and those in the literatures (11-13) of the other commercialized membranes were comparecT and those of PEC-1000 membrane showed high solute rejections even to various kinds of water-soluble organic compounds of
In Reverse Osmosis and Ultrafiltration; Sourirajan, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.
Downloaded by PENNSYLVANIA STATE UNIV on July 2, 2012 | http://pubs.acs.org Publication Date: January 1, 1985 | doi: 10.1021/bk-1985-0281.ch022
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NAKAGAWA ET AL.
Concentration and Recovery of e-Caprolactam
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low-molecular-weight such as ethanol, phenol, acetic acid, and e-caprolactam (4-6). Basic RO performance of PEC-1000 membrane for various kinds of organic compounds in aqueous solutions are tabulated in Table I. The membrane rejects quite sufficiently many of organic solutes and it exhibits its potential application to a variety of fields where the application of conventional RO membranes are recognized as quite impractical. Based on the basic performance of PEC-1000 membrane for various solutes in aqueous solution, long-term field tests were conducted on the PEC-1000 membrane elements for e-caprolatam, acetic acid and ethylene glycol solutions (3^i.) . In all cases, the RO performance remained stable for about one year without the deterioration of membrane performance. PEC-1000 membrane is not resistant to oxidative substances, where dissolved oxygen (DO) as well as chlorine affects the membrane (2) • Therefore, it is very important to remove such oxidative substances from a viewpoint of durability of the membrane. Chlorine and DO can be easily removed by reducing reagents such as sodium bi-sulfite (SBS) or sodium sulfite. DO can be also removed by physical method such as vacuum deaeration. The level of DO in the latter two cases (acetic acid and ethylene glycol) is controlled below 1 ppm not by SBS dosing but by bubbling and sealing with nitrogen gas. Background of RO Plant Planning for e-Caprolactam Concentration As shown in Table I, e-caprolactam, which is the raw material or monomer of "Nylon-6", is separated or rejected over 99.9% by PEC-1000 membrane. Therefore, the concentration and recovery of e-caprolactam by RO technology using PEC-1000 membrane elements was expected to be practical. There is a limit of concentration to be concentrated from the viewpoint of osmotic pressure which, for example, is estimated to be about 20 atms at 10% by weight of e-caprolactam solution at 35°C. Consequently, it is necessary to apply RO technology in combination with other separation processes such as evaporation to obtain pure e-caprolactam. There are several kinds of aqueous e-caprolactam solutions originating from the processes of "Nylon-6" production as follows: A. Water extracts from nylon tips or nylon fibers. B. Distillates from the evaporator for the recovery of e-caprolactam from the water extracts described in case A. C. Distillates from the evaporator for the production of e-caprolactam. D. Waste streams from other processes for the production of e-caprolactam. The solute, e-caprolactam in case A is concentrated by
In Reverse Osmosis and Ultrafiltration; Sourirajan, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.
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