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INDUSTRIAL AND E N G I N E E R I N G C H E M I S T R Y
Hydrogenation Products of Naphthalene C. H. S. T u p h o l m e - 6,
Hamilton
Gardens,
THE value of tetrahydronaphthalene as a means for removing naphthalene deposits from town gas mains and apparatus has been known in America and Germany for some years, where this product is known as tetralin. More recently the same product has been marketed in this country under the name "Tetranap." Tetrahydronaphthalene is formed by the hydrogenation of pure naphthalene in the presence of a suitable catalyst. The four added hydrogen atoms take up positions on one ring of the naphthalene, giving a partially saturated, but extremely stable, product. Tetralin or Tetranap at ordinary temperatures and pressures is a water-white liquid, insoluble in water but miscible with practically all organic solvents in all proportions, and is an excellent solvent for a wide range of oils, waxes, and resins. It is a very stable compound, and does not char or decompose until relatively high temperatures are reached, roughly in the range 800° to 850° F. It is non-poisonous, and Continental experiments have shown that even internal dosage indicates only very slight toxic effects. The merit of tetrahydronaphthalene for town gas mains lies in the fact t h a t , being a close chemical relative of naphthalene, it has the power of absorbing larger quantities of naphthalene than a n y of the other solvents in present use. This solvent power a t ordinary temperatures is approximately three times as great as that of gas oil. Tetranap, being a definite chemical compound and having undergone purification treatment in its manufacture, contains no naphthalene as an. impurity. Its vapor pressure makes it ideal for use as a solvent for naphthalene and gums deposited in meters and gasburning appliances. Since t h e boiling point of T e t r a n a p is rather high (206° C ) , its volatility is fairly low a t ambient temperatures; t h u s considerable amounts of this material are not required to saturate the gas. However, even if large quantities are added, the effect of T e t r a n a p on the gas will be slightly to raise the calorific value. On t h e other hand, it has a volatility high enough so that there will always be a sufficient quantity of Tetranap present t o absorb the naphthalene from the gas. The dew points of naphthalene and T e t r a n a p are so close that whenever there is a condensation of naphthalene, there will be a corresponding condensation of Tetranap and these two will precipitate in mutually soluble proportions, so t h a t it will be impossible to get crystallized naphthalene in the mains. According t o Imperial Chemical Industries, Ltd., the makers of Tetranap, by injecting Tetranap into t h e gas stream the troubles caused by naphthalene deposition may be satisfactorily overcome. Although only a relatively small amount of T e t r a n a p is necessary to saturate the gas, there will always be sufficient vapor present to insure that, where condensation of naphthalene occurs, a corresponding condensation of Tetranap will also occur sufficient to dissolve the naphthalene and to maintain it in solution. The T e t r a n a p may be introduced into the gas by one of two methods. In t h e hot process, the hot Tetranap vapor from a n electrically heated unit is added in measured quantities to the gas stream. T h e cold process consists essentially of adding the T e t r a n a p t o the gas in t h e form of a. mist or fog; it may be atomized by a. secondary compressed gas stream or b y
N.London,
England
injecting it through a nozzle by means of a small compressor. The cold process appears to be more uniform in working and in t h e distribution of Tetranap in the main gas stream. I n addition to preventing the deposition of naphthalene, the T e t r a n a p fog condenses in the form of a thin layer on the internal surface of the gas mains, thus minimizing oxidation and effectively preventing corrosion and rust formation. Tetranap is also claimed to exert a beneficial action on the leather diaphragms of meters, etc., rendering them flexible and gas-tight. T h e cost of the process will, of course, depend on t h e naphthalene content of the gas, the cost of power, etc. The usual consumption of Tetranap lies between 50 and 05 grains of Tetranap per 100 cu. ft. of gas, giving a cost (including cost of power) of about 0.25 d. per 1000 cu. ft. of gas treated. T h e other hydrogenated product of naphthalene is decahydronaphthalene which has special value as a solvent and thinner for paint and varnish. According to a report, Imperial Chemical Industries, Ltd., has recently put into operation a new process for the manufacture of decahydronaphthalene which has served to bring down the price substantially and also to insure a domestic source for a product which has hitherto been imported. Decahydronaphthalene is the fully hydrogenated form of naphthalene, and as manufactured by I. C. I. is a water-white liquid of exceptional purity, with a pleasant terpene-like odor, not unlike t h a t of turpentine. The comparative d a t a issued b y I. C. I. show that it is not on the score of price alone (for it is now considerably cheaper than turpentine) t h a t it m a y be used with advantage to replace turpentine as a paint thinner, and also, in many cases, the most costly solvents which are today becoming increasingly employed. Such intrinsic properties as a very high flash point, leading to a reduction of the fire risks normally run with the more usual thinner, an absence of toxicity shown by prolonged tests and practical use; and a solvent power of exceptional range where paint and varnish materials are concerned, are claimed for it by the manufacturers. " D e c , " as this product is called, is stated t o give stable solutions with a variety of driers, notably with cobalt linoleate, which is often unstable in white spirit solution. Its general solvency is illustrated in a number of comparative tables, in which the solubilities in Dec of a large range of natural and synthetic waxes, bitumens, and glyptal type resins are set out against the corresponding values for turpentine and Rumanian white spirit. It is interesting to note that t h e kauributanol test shows it is slightly superior to turpentine in solvent power. The limits of its miscibility with ethyl alcohol a n d methanol are clearly shown by solubility diagrams for the systems Dec-anhj-drous ethyl alcohol-water, and D e c methanol-water, respectively. I t is pointed o u t t h a t , whereas the evaporation rate of this product per se is comparatively low, the ultimate drying t i m e of paints and varnishes is substantially unaffected, while examples are cited in which this is actually more rapid than with turpentine or white spirit. I t is further claimed that the film properties and flow of paints and varnishes containing it are superior to those of the corresponding mixtures with tur-
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pentine or white spirit. Greater abrasion resistance has been demonstrated by the Air Ministry ''scratch t e s t , ' and such defects as wrinkling, silking, and webbing, especially of varnishes, are stated to be reduced by its use. Small amounts are also claimed to improve the brushing properties of paints which otherwise would have poor flow, and white paints thinned with it a: e claimed to give no discoloration with metallic driers. In its anti-skinning properties, and in respect to such requirements as hiding power and gloss, it is fully the equal of turpentine, and it has no lifting or softening effect on t h e undercoat.
Notes from Y e n c h i n g University CHOLARSHIP awards for advanced S study, recently granted to science graduates of Yenching University, include two scholarships in chemistry for study in Great Britain, by the British Boxer Indemnity F u n d ; one scholarship for work on motor fuels a t Yenching University, by the China Foundation; and one scholarship for s t u d y in America on vegetable oils b y the Shansi Provincial Government. Tsai Liu-sheng has received a grant of $500 for continuing his work on the preparation of activated charcoal from Chinese raw materials. Students from seventeen universities in China competed this year for the awards in physics offered b y t h e Sun Yat Sen Memorial Foundation. Of the three for the best B.S. theses, two were awarded to Yenching students, as well as three prizes for excellence in written examinations. Six: papers on biochemistry and nutrition were presented by members of the university staff a t t h e annual meeting of the Chinese Physiological Society held in Peiping in April. Nine candidates passed their examinations for the master's degree in June, 1935, three in the Department of Chemistry. The Mass Education Movement under the leadership of Y. C. James Yen is reorganizing its rural reconstruction program, and the agricultural work is being organized into an Agricultural Experiment Station. C. F. Wu is to be released from part of his teaching work a t Yenching University to serve as director and also as head of the Division of Economic Entomology of the station. A new freshman curriculum is being placed in operation at the university, beginning with the fall of 1935, in accordance with which first-year students will have an opportunity to take one course in each of t h e three laboratory sciences— biology, chemistry, and physics—and will not decide on their major subject of s t u d y until the close of the freshman year. The introductory courses in biology and chemistry are being recast as onesemester courses. Chang Ch'uan, in charge of the leather laboratory of the Department of Chemistry, a few years ago traveled through Shensi as a member of a commission charged with preparing plans for industrial development. Interest in the possibilities of the leather industry has been growing in this p a r t of China. An appointee of the Kansu Provincial Government is spending the summer semester as a special student in the laboratory and recently a request has come from the Suiyuan administration for two Yenching graduates to organize a model tannery for the district. COLLEGE OF NATURAL SCIENCE, YENCHING UNIVERSITY, PEIPING, CHINA
From Science Notes
