promoter is also accompanied by a significantly reduced amount of the principal impurity, p-carboxybenzaldehyde. Under proper conditions rc-butane plus fractional amounts of the standard quantity of methyl ethyl ketone can serve as an excellent promoter, Dr. Behun says. The need for the ketone can be eliminated completely under other conditions. Optimum concentrations of n-butane appear to be in the range of 1.5 to 5.0 moles of n-butane per mole of p-xylene. However, the higher concentrations of n-butane can be used at higher pressures, which may be of further usefulness in continuous processing. Although Dr. Behun's work was done primarily in the batch mode, attention was given to the problems of continuous production, particularly with respect to the problems of recycle. The chief concern was accumulation of possible contaminants with sustained recycle, but no major effect on activity of the oxidation system was observed during studies simulating continuous recycle. The conclusion reached was that a continuous system using n-butane or combinations of n-butane and methyl ethyl ketone is possible. The possibility of using n-butane in combination with materials other than methyl ethyl ketone also was investigated. None of the other materials, including hydrogen peroxide, butene-1, acetaldehyde, and acetoin, were successful, Dr. Behun says. Aliphatic promoters other than nbutane were also examined but none showed any cost/performance advantages over n-butane. n-Butane also was used as a promoter for the oxidation of alkylaromatics other than p-xylene. In the cases of m-xylene and mesitylene, there was an acceptable level of conversion; however, the work was not pursued. All that can be said at present is that n-butane appears to be a valuable promoter for making various aromatic carboxylic acids via oxidation.
Method improves paper encapsulation 168lHrfa MhTioMhL meaiMG Among techniques for modifying cellulosic materials with polymers, coating with preformed polymers has been practiced for some time. In recent years, however, in situ polymerization, interfacial polymerization, and encapsulation have proved more effective. At the University of Montreal's chemistry department, Dr. Robert H. Marchessault has developed a unique kind of encapsulation that permits not only the coating of paper but also the prep-
aration of polymeric mats that reproduce the structure of the paper from which they were formed. Dr. Marchessault's technique is based on previous work done elsewhere, in which an organometallic, usually triethylaluminum, is added to a dry cellulose suspension in a titanium tetrachloride/hydrocarbon mixture. The reaction products between titanium tetrachloride and the organometallic precipitate on the cellulose, thereby establishing the catalyst for polymerization of ethylene, which is bubbled through the reaction solvent. This procedure has been used primarily to encapsulate individual pulp fibers, which can then be formed into sheets using conventional papermaking processes. The drawback, Dr. Marchessault explained during a symposium on new developments in cellulose technology, held by the Cellulose, Paper, and Textile Division, is that the catalyst is formed outside the fiber surface and it takes more time to precipitate than is desired. It would be preferable, he says, to have a process in which the catalyst is deposited throughout the fiber matrix. Such processes exist but Dr. Marchessault believes he has devised the simplest one yet.
He treats the paper matrix with a solution of titanium tetrachloride in a solvent such as isopentane. The paper is then passed into an evaporator, where the solvent is removed, leaving titanium tetrachloride uniformly distributed throughout the matrix. The paper sheet is then exposed to the organometallic compound, in vapor or liquid form, thereby forming a finely dispersed Ziegler-Natta type catalyst in the matrix. Subsequent exposure to the olefin monomer results in rapid polymerization within the matrix. The paper that results is impervious to water and can be handled as would any other kind of paper. But, an added advantage is that the cellulose in the matrix can be dissolved and a microporous polyolefin membrane results. The membrane retains the paperlike structure after the cellulose has been removed, providing a replica of the original sheet. One of the areas in which the new encapsulation technology has been found useful is that of making filter media with better strength, insolubility, and chemical resistance than is exhibited by paper. The technique also has been successfully applied to other woven and nonwoven fabrics.
Plasma technique for osmosis membranes 168TH rfO IfdOfiL MNGOIMG A new method for preparing reverse osmosis membranes has been demonstrated at the University of California, Berkeley. The method involves use of a plasma produced in an electric discharge to deposit a thin polymer film on the surface of a porous substrate such as glass, polysulfone, or cellulose acetate-nitrate. Dr. Alexis T. Bell, professor of chemical engineering at the university, says that solute rejection is accomplished by the polymerized film. Dr. Bell described advantages of the technique, compared to conventional casting methods, during a symposium on commercial potential for arc and plasma processes, held by the Division of Industrial and Engineering Chemistry: The finished membrane can be prepared and stored dry; the substrate and film compositions can be selected independently; and the rejecting layer can be made very thin, thereby making it possible to prepare membranes with unusually high water fluxes. An additional advantage is that many conventional and nonconventional polymers can be polymerized in a plasma. However, not all polymers are suitable for membranes. Previous work has shown that efficient membranes require that the polymer rejection layer should be moderately hydrophilic.
Many hydrophilic organic polymers react in plasma to form hydrophobic polymers. As a class, only nitrogencontaining compounds, particularly olefinic amines, heteroaromatic amines, and aromatic amines have been found to form good reverse osmosis membranes. The specific objectives of Dr. Bell's work included identifying preparation condition influences on reverse osmosis characteristics of the final membrane and evaluating membrane performance as a function of applied pressure, feed concentration (of salt), and feed temperature. Two types of substrates were used. One was MF Millipore material with an average pore size of 0.025 millimicron and a water permeability of 400 X 10- 5 gram per second per sq. cm. per atm. The second was a cellulose acetate-cellulose nitrate film manufactured by Gulf Environmental Systems. It had similar characteristics. The monomer used for the deposited film was in all cases allylamine. As a result of tests, Dr. Bell concluded that the main resistance to water flow and the main cause for salt rejection was the plasma-polymerized film. Since the properties of the allylamine film are highly controllable by means of plasma variations, membranes with a wide range of osmotic characteristics can be prepared by the method. The substrate is thus no longer the limiting factor in membrane preparation. Sept. 23, 1974 C&EN
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