June,
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T H E JOURNAL OF INDUSTRIAL A N D ENGINEERING CHEMISTRY
vent tank t o t h e still through a heat exchanging and vapor rectifying system; and from t h e still t o t h e absorber through t h e heat exchanger i n t h e direction opposite t o t h a t followed on its way t o t h e still, through t h e oil cooler, and finally through t h e oil pump. The gas t h a t is liberated in t h e still passes through t h e rectifier t o remove any oil t h a t it may carry, through a condenser for t h e condensation of whatever gasoline m a y be obtained a t pressures only slightly above atmospheric, and then through a compressor and second condenser for t h e separation of such gasoline as can be secured. T h e proper design and method of operation of a n absorption plant must be determined for each different p l a n t . At t h e present time i t would be rare indeed t o 'build a plant t o fit a particular need t h a t would not require modifications after it is p u t into use, and t h e most efficient method of operation can be determined only after a n extended period of experimentation.
It may be estimated t h a t t h e average absorption plant operates a t an efficiency of 50 t o 6 0 per cent, computed on t h e actual gasoline content of t h e gas, although some few plants may perhaps reach efficiencies of 7 0 t o 80 per cent. The highest efficiency t h a t i t is practicable t o maintain will vary considerably with t h e individual conditions, b u t i t is safe t o state t h a t this efficiency has not yet been reached, and will not be reached until thorough investigations have been made in t h e matters of plant design and plant operation. CHOICE O F METHOD
For t h e purpose of considering Khat method, or methods, should be employed i n recovering gasoline from natural gas, t h e following classification may be made: ( I ) Lean gas, containing less t h a n 0.5 gal. gasoline per M cu. f t . of gas; ( 2 ) moderately rich gas, containing from 0.5 t o 3 gal. gasoline per M cu. f t . of gas; ( 3 ) rich gas, containing more t h a n 3 gal. gasoline per M cu. f t . of gas. I---Lean gas is usually compressed for t h e purpose of transporting i t t o t h e point of consumption, b u t this compression would not ordinarily cause t h e condensation of gasoline. The absorption method may be employed on gas of this character, provided its gasoline content is sufficient t o make t h e project a financial success. The absorption method has been successfully employed where t h e gasoline production has amounted t o less t h a n 0.1 gal. per M cu. ft. of gas. 2--The compression of a moderately rich gas for transmission purposes may not result in t h e condensation of gasoline if t h e pressure required is low, b u t gasoline will be condensed if high pressures are necessary. I n a gas of this sort t h e gasoline removal will by no means be complete, even a t high pressures, on account of t h e low initial partial pressures of t h e gasoline hydrocarbons, and either t h e refrigeration or t h e absorption method may be applied on t h e residual gas, t h e choice depending upon t h e local conditions. If t h e absorption method is t o be employed, t h e pressure need not be raised above t h e point required for
549
transmission of t h e gas, while if t h e refrigeration method is t o be employed, t h e gas should be compressed t o 2 5 0 t o 300 lbs. before expansion, according t o t h e usual procedure. 3-A rich gas should be compressed primarily for its gasoline content. I n this case, on account of t h e higher initial partial pressure of t h e gasoline constituents, t h e efficiency of gasoline extraction will be much higher t h a n i n t h e previous case and treatment of residual gas by refrigeration or absorption method would yield b u t little gasoline of marketable character. T o t r e a t a rich gas by t h e absorption method a t low pressure is a n alternative t h a t may possibly have desirable features i n exceptional cases. I t will, of course, be understood t h a t no definite figures can be given for t h e gasoline content a t which t h e direct compression method begins t o be applicable, nor for t h e gasoline content a t which t h e compression method can be made so efficient t h a t no treatment of residue gas is advisable. The figures t h a t have been given for t h e purpose of setting limits between Classes I , 2 , and 3 are, therefore, only approximate and dependent t o a considerable extent upon t h e nature of t h e gas t o be treated. S U 11N A R Y
I-The principles forming t h e foundation of t h e compression! refrigeration and absorption methods for t h e production of gasoline from natural gas have been enunciated and t h e relationships between t h e different methods have been explained. Incidentally, i t has been shown t h a t t h e absorption method is essentially a n indirect compression method, in which t h e gasolineforming constituents of a gas are concentrated in small space by fractional solubility before t h e compression method is applied. 11-A table of properties of t h e principal gasoline constituents and curves showing t h e vapor pressures of some of these hydrocarbons a t different temperatures have been inserted for convenience of reference. 111-The applications of t h e different methods have been discussed. T h e absorption method is employed exclusively for lean gas and t h e compression method almost exclusively for rich gas. For moderately rich gas, the production may be largely by t h e compression method, or largely by t h e absorption method, as t h e situation demands. THE USE OF PARACOUMARONE RESIN IN VARNISHES By W. W. King, F. W. Bayard and F. H. Rhodes H.
w. JAYNE LABORATORY, THEB A R R E T T CO., FRANKFORD, PHILADELPHIA, PENNSYLVANIA Received January 9, 1920
Paracoumarone resin, t h e artificial resin prepared by t h e polymerization of t h e coumarone and indene in certain aromatic naphthas, is now manufactured and sold in considerable quantities i n t h e United States, and is finding application in various industries. The process for t h e manufacture of this material has recently been so perfected t h a t large quantities of lighter color and higher melting point t h a n t h a t previously obtainable are now available for commercial purposes. This resin posscsses certain properties which
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render i t particularly suitable for use as a varnis8 gum t o replace ester gum or t h e more expensive kauri a n d other foreign gums. I n this laboratory a considerable amount of work has been done t o determine t h e advantages of paracoumarone resin as a varnish gum, the most satisfactory procedure for making varnishes from paracoumarone resin, and t h e general properties of these varnishes. G E N E R A L P R O P E R T I E S OF P A R A C O U M A R O N E R E S I N
Aromatic naphthas distilling between 160' and zoo' C. contain considerable amounts of indene, coumarone, and their homologs. When such naphthas are agitated with strong sulfuric acid these compounds are polymerized, the polymerization products remaining in solution in t h e naphtha. Similar polymerization may be effected by t h e action of certain metallic salts-for example, aluminum chloride-or b y simply heating t h e naphtha under pressure. When the naphtha is separated from the polymerizing agent, neutralized, and distilled t o remove unpolymerized material, there remains a liquid residue which, on cooling, solidifies t o the resinous material known as "paracoumarone resin." The technical resin consists essentially of a mixture of t h e polymerization products of coumarone, indene, and their homologs. The degree of polymerization has not been definitely determined. Some authorities have stated t h a t t h e resin is a tetra-polymer, while other results have indicated t h a t , in some cases, at least, the resin molecule is built u p from eight simple molecules. Some work done in this laboratory has indicated t h a t the resin is a t least an octo-polymer, and t h a t t h e lower values obtained by previous observers were due t o the presence of impurities in t h e resins examined by them. Chemically, paracoumarone resin differs from t h e ordinary varnish resins in t h a t i t is a neutral body, insoluble in alkalies. I t is true t h a t some samples of technical paracoumarone resin have shown an apparent, and very low, "acid number," but this has been due t o impurities. The resin is unattacked by acid (with t h e exception of strong sulfuric acid and nitric acid), ammonia, and soap solution; and is practically insoluble in alcohol. The unbsual chemical inertness of paracoumarone is of particular value in connection with its use as a varnish resin, since it renders t h e varnish films more resistant t o alkalies, soap solutions, alcohol, fruit acids, and other materials by which t h e common varnish resins are attacked. Physically, paracou marone resin when properly prepared is a brittle, amorphous material, somewhat resembling rosin in appearance. The poorer grades are black b u t t h e varnish grades vary in color from reddish brown (similar t o Grade E rosin) through orange-yellow t o very pale yellow (similar t o WW rosin). Inferior grades may be cloudy, but t h e varnish grades are clear. Paracoumarone is apparently not a true solid, b u t a highly supercooled liquid. When heated, i t does not melt sharply, b u t gradually softens and finally liquefies. It does not, therefore, possess a t r u e melting point. However, a n apparent "melting point" may be deter-
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mined by forming a cube of t h e material around a copper wire, heating this cube in an air bath under definite and constant conditions, and noting t h e temperature a t which the material becomes sufficiently fluid t o drop from t h e wire. By this test rosin shows a melting point of approximately 100' C., while Manila gum melts at 127' t o 135' C. The apparent melting point of paracoumarone resin varies from 85' to 20 j ' C. We have found, however, t h a t paracoumarone with a melting point lower t h a n 125' C. is not suitable for varnish work since varnishes made with t h e low melting paracoumarone tend t o remain tacky for a rather long time. Paracoumarone melting above 14j ' C. has not yet been prepared in commercial quantities. The varnish grade of paracoumarone now available has a melting point between 125' and 145' C., although it is expected t h a t resin melting above 145' C. can soon be supplied if there is any demand for such highmelting material. Paracoumarone resin, like rosin and other varnish gums, possesses t h e property of delaying t h e polymerization of tung oil by heat, so t h a t a mixture of tung oil and paracoumarone resin may be safely bodied by heating to 300' C., although straight tung oil would polymerize a t this temperature. PREPARATION
OF
VARNISHES
FROM
PARACOUMARONE
RESIN
We have prepared paracoumarone varnishes of varying oil content, ranging from 5 gal. of oil per I O O lbs. of resin t o 40 gal. of oil per I O O lbs. of resin. I n all of these varnishes t h e oil used has been a mixture of I j parts of pure raw linseed oil and I O O parts of China wood oil. Cobalt linoleate was used as t h e drier, using 1.5 lbs. of drier per I O O lbs. of oil. I n most of these varnishes we have used, as a thinner, a heavy, refined, coal-tar paint solvent distilling completely above 160 ' C., although some lots have also been made up with pure gum turpentine, petroleum base turpentine substitute, and other turpentine substitutes. We have confined our work so largely t o varnishes thinned with the coal-tar solvent because we have found t h a t such varnishes are in every respect equal t o varnishes thinned with t h e more expensive turpentine. The varnishes thinned with petroleum naphthas have not always been satisfactory because some of these naphthas have contained enough paraffin t o cause a slight dulling of t h e films from the varnishes made from them, a n d because some of these varriishes have shown a tendency t o become turbid when allowed t o stand a t temperatures below 3 z ' F. The most satisfactory procedure for making up these paracoumarone varnishes was found t o be as follows: Place t h e mixed linseed and China wood oil in t h e varnish kettle and add t h e required amount of paracoumarone resin, preferably broken u p into fairly small lumps. Heat t h e mixture a t t h e rate of about 2 . 5 ' C. (4.5' F.) per minute t o a final temperature of 290' t o 320' C. ( 5 55' t o 610' F.). (The temperatures given are corrected for t h e emergent stem of t h e thermometer.) We have found t h a t with t h e resins having t h e higher melting points i t is essential t o carry 6he heating to t h e higher temperatures in order t o ohfain
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thorough incorporation of t h e resin with t h e oil, a n d t o prevent the clouding and wrinkling of films made from t h e finished varnishes. When t h e desired final temperature is reached, remove t h e kettle from t h e fire and allow t h e mixture t o cool. As soon as t h e temperature has fallen t o near t h e boiling point of t h e thinner t o be used, add t h e thinner and mix well. The amount of thinner is, of course, determined b y t h e t y p e of varnish and by t h e desired final viscosity of t h e varnish. When t h e thinned mixture has cooled t o well below 100' C., add t h e required amount of drier solution, prepared b y adding 10.0 parts of cobalt linoleate (cut in thin pieces) t o 84.2 parts of raw linseed oil, heating t h e mixture t o 200' C. for 2 hrs., adding 42.1 parts of bodied China wood oil, continuing the heating (with frequent stirring) at 2 0 0 " C. for one hour, cooling t o 160" C., and pouring t h e resulting solution into 600 parts of coalt a r naphtha paint solvent. T h e final drier solution contained 1.03 per cent of cobalt. PROPERTIES O F PARACOUMARONE RESINS
All of t h e varnishes which have been prepared have been clear and free from sediment. I n color they have been as light or lighter t h a n the commercial varnishes now on t h e market. The color of t h e finished varnish, of course, depends upon t h e color and amount of t h e original paracoumarone resin. The very pale varnishgrade resins give very light varnishes, which, when properly applied, dry t o form almost colorless films; while t h e darker grades give slightly yellowish films. All of t h e varnishes, when properly applied, set t o the touch in 3 hrs. and dried hard in less t h a n 2 0 hrs. T h e resulting films were clear and free from cloudiness and tackiness, smooth, brilliant, and very light in color. The rubbing qualities of t h e varnishes were determined b y t h e following test: T o a maple panel (IS in. b y 6 in.) was applied a coat of varnish, well rubbed in, which was allowed t o dry for 48 hrs. and was then lightly sandpapered. A second coat was then applied, allowed t o dry for 48 hrs., and lightly sandpapered. A third coat was applied, allowed tQdry for 7 2 hrs., polished t o a satin finish with ground pumice and water, and finally polished with a little linseed oil. All of t h e varnishes, from t h e 5 gal. varnish t o t h e 40 gal, varnish, inclusive, gave smooth coats, free from impel-fections and with a smooth, satiny luster. The water-resisting properties of t h e varnishes were determined b y t h e following test:' Baspwood panels were filled with a coat of drop black oil, thinned with turpentine and drier, and allowed t o dry for a t least I O days. Two successive coats of varnish were then applied, t h e first coat being allowed t o dry for 48 hrs., a n d lightly sandpapered. When t h e second coat had dried €or 7 2 hrs. t h e panel was placed at an angle of 4 j O and a gentle stream of cold water was allowed t o flow down t h e middle of it for r 8 hrs. A small stream of boiling hot, distilled water was allowed t o flow on another portion of t h e panel for 1 Based on test described in U. S. Railroad Administration Speci6catioxsfer Spar VPmish, May 1, 1918.
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2 0 min. All of t h e varnishes formed films which withstood perfectly t h e action of t h e cold water, showing no dulling, whitening, or other effects. The I O , 15, and 2 0 gal. varnishes stood up perfectly under t h e hot water test. The j gal. varnish, after exposure t o t h e hot water test, showed a very faint, cloudy surface film which was apparent only on close inspection, and which was readily and completely removed b y polishing with a little linseed oil.
Weathering tests on panels coated with t h e 5 , I O , 2 0 , 30, and 40 gal. varnishes, respectively, showed t h a t they were fully as resistant to weathering as any of t h e varnishes of similar oil content now on t h e market. The long-oil varnishes from paracoumarone resin stood up particularly well under this test, being noticeably more resistant to weathering t h a n was any one of t h e eight standard commercial spar varhishes used for comparison purposes. I n hardness, toughness, and elasticity, t h e varnish films from paracoumarone varnish were similar t o t h e films from the best commercial varnishes. We have found t h a t t h e cobalt linoleate may be replaced b y a manganese drier (acetate or linoleate) with equally satisfactory results, although a somewhat larger amount of t h e manganese drier is required t o give t h e same drying time. The use of manganese dioxide as a drier has not been altogether satisfactory, as it causes t h e varnish t o darken. From these results, i t is apparent t h a t varnishes properly prepared from paracoumarone resin (m. p . 1 2 5 " to 145' C ), China wood oil, linseed oil, cobalt or manganese (acetate or linoleate) drier, and heavy refined coal-tar naphtha are light in color, have excellent drying and rubbing qualities, and are as tough, as hard, and as resistant t o hot and cold water and t o weathering as are t h e best commercial varnishes.
15,
A D V A N T A G E S OF P A R A C O U M A R O N E R E S I X AS A VARNISI-I
GUM
I n considering t h e advantages t o be gained by using paracoumarone resin as a varnish gum, t h e following facts must be taken into consideration: I-Paracoumarone resin can be obtained a t a price approximately equal t o t h a t of ester gum, and much below t h a t of the better grades of kauri and other imported gums. 2-It is offered for sale in quantity in a number of different grades, so t h a t material of the desired melting point and qolor can be secured. 3-It is free from dirt, sticks, etc., so t h a t t h e varnish manufacturer is relieved of t h e trouble and expense of sorting or purifying t h e resin or of settling or filtering t h e varnish t o remove impurities due t o dirt in t h e resin, 4-It contains essentially no material which is volatilized during t h e "cooking" of t h e varnish. T h u s all of t h e resin remains in t h e finished varnish, while rosin and other varnish gums are partially decomposed during t h e "cooking" giving volatile products and allowing only a portion of t h e resin t o remain in t h e varnish.
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j-The remarkable chemical inertness of paracoumarone renders t h e varnishes very resistant t o t h e action of ammonia, lye, soap, and other alkalies; vinegar, fruit acids, a n d other acids; and alcohol or alcoholic solutions.
viscosity, specific gravity, elasticity, and time of drying. These tests were followed b y noting brilliancy, uniformity of film, and t h e effect of water upon panels of wood coated with t h e varnish.
THE WEARING QUALITY OF EXTERIOR VARNISHES COMPARED WITH THEIR PHYSICAL AND CHEMICAL ANALYSES By W. T. Pearce
T h e percentages of total resins, rosin, total oils, turpentine, turpentine substitutes, and ash were determined with reasonable accuracy. We have not a t tempted as yet t o identify t h e resin although this will be taken up within t h e next few months.
SCHOOL OF CHEMISTRY AND TECHNOLOGY, NORTHDAKOTA AGRICULTURAL COLLEGE,AGRICULTURAL COLLEGE,N. D. Received December 4, 1919 INTRODUCTION
The varnishes used were purchased in quart or halfgallon cans from stores, or sent i n by t h e manufacturer for t h e purpose of this investigation, and, in most cases, represent the better grades of the product. All were exterior varnishes except Nos. 1 1 , 1 2 , and 13, which were interior varnishes included for purposes of comparison. A similar s t u d y of a large number of interior and floor varnishes is i n progress. The status and reliability of methods of varnish analysis have already been discussed b y t h e writer.l It is t h e aim of this a n d subsequent investigations t o obtain such d a t a t h a t both the public and the varnish maker may determine t h e true value of any varnish. Some of t h e most vital questions are: How little oil may a varnish contain and still be good? What must be t h e limits of the resin-oil ratios in exterior, interior, floor, and automobile varnishes? What must be t h e limit t o t h e amount of thinner used? How much rosin may a varnish contain? S E R V I C E TEST
T h e doors of several buildings on the college campus were selected, so t h a t each varnish would have a northern, eastern, southern, and western exposure, and so t h a t i n three cases all of them would be on t h e same piece of wood. I n other cases, two were placed on t h e same piece of wood a n d t h e positions so varied t h a t they would be acted upon in t h e same way. On t h e north doors and wooden pillars of one of t h e buildings all t h e varnishes were in three cases placed on t h e same piece of wood, t h e old film was entirely removed, and one coat of liquid filler and two coats of varnish applied, t h e filler and first coat being rubbed down with fine emery paper. T h e wood was measured and a definite amount was allotted t o each varnish. I n all other cases t h e old coat was rubbed smooth and three coats of varnish were applied. At t h e end of 9 mos. exposure t h e luster and condition (checking, cracking, washing, whitening) of t h e film were studied. Three months later another thorough study was made. The results were i n excellent agreement with each other and showed t h a t fair methods were used. It will be necessary t o make a third examination a t t h e end of 2 yrs. service t o differentiate between t h e better varnishes. OTHER PHYSICAL
TESTS
T h e color, clearness, odor, consistency, and working a n d flowing under the brush were first noted; then t h e 1
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CHEMICAL ANALYSIS
M E T H O D S O F X A K I N G P H Y S I C A L TESTS
VISCOSITY-An Engler viscosimeter was used for t h e viscosity a n d the usual method was followed, IOO cc. of the varnish being allowed t o run out. SPECIFIC GRAVITY-A Westphal balance was sufficiently accurate for t h e specific gravity determination. TIME OF DRYING-A thin coat of varnish was applied t o a glass plate and allowed t o stand away from t h e dust a t a n angle of 60'. T h e coat was examined frequently a n d t h e time required for drying recorded. ELASTICITY-The glass plate used in the drying test was scratched with a knife, and t h e smoothness of t h e cut was noted. A heavy sheet of cardboard was then coated with simple sirup and a coat of varnish applied. When this h a d dried, t h e film was removed by placing t h e cardboard in water. At definite intervals the elasticity was determined a s follows: A halfinch strip of film was clamped a t both ends between two smooth pieces of wood. One end was clamped t o a n a r m attached t o a vertical wooden beam nailed t o a heavy base. On t h e beam was placed a metric scale and one of t h e binders on t h e free end of t h e film served as a n indicator. A weight was hung from a wire stirrup attached t o t h e free end, a n d t h e distance in millimeters which the film stretched before breaking constituted t h e measure of t h e elasticity. B R I L L I A N C Y , L U S T E R A X D S P O N G E TEST-The varnished panel was examined for luster a n d uniformity of coat, considering nearly all of t h e varnishes a t t h e same time and comparing t h e m with each other. A sponge made of felt was placed on one end of t h e panel a n d kept moist for a definite period of time. If t h e varnish failed t o whiten, t h e panel was placed i n water for definite periods. It was then removed a n d allowed t o d r y before examination. METHODS U S E D I N C H E M I C A L A N A L Y S I S VOLATILE THINNERTFifty grams of varnish were weighed into a half-liter Erlenmeyer flask, and subjected t o steam distillation, t h e flask being heated in a n oil bath a t 130' C. until no more volatile oil was carried over. T h e distillate, usually 500 cc. in volume, was collected in a separatory funnel and allowed t o settle, t h e water run off, a n d t h e oil transferred t o a tared flask and weighed. I n calculating the volatile thinner i t was assumed t h a t t h e water which distilled over had dissolved 0.4 g. per I O O cc. (We did not use t h e values obtained by this method, as the non-volatile method is more accurate.)
