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7-Homogeneity reduces electrolytic corrosion, and has no effect on complete corrosion. %-Other influences-catalysis, nature of surface, strained areas in t h e alloy, etc.-are operative, b u t have not been included in this investigation. It is doubtful whether in practice either form of corrosion ever occurs t o t h e exclusion of t h e other. I n complete corrosion, dezincification occurs as a secondary process b y t h e displacement of copper from t h e solution, and since electrolytic corrosion usually takes place in contact with the air, primary oxidation of the alloy is possible. GASOLINE FROM NATURAL GAS. I-METHOD REMOVAL By R. P. Anderson
OF
UNITSD NATURAL GAS CO., OIL CITY, PENNSYLVANIA Received December 31, 1919
The hydrocarbon content of natural gas consists essentially of a mixture of such hydrocarbons of t h e parafin series as exert an appreciable vapor pressure at t h e temperature of gas production. Similarly natural gas gasoline consists essentially of a mixture of those hydrocarbons of natural gas t h a t may exist in liquid form a t atmospheric temperatures and pressures, As natural gas hydrocarbons, there may be included t h e normal and various isomeric compounds from methane t o undecane, inclusive; and as constituents of natural gas gasoline, all of t h e natural gas hydrocarbons except methane, ethane, propane, a n d butane. For convenience of reference, various d a t a concerning t h e normal paraffin hydrocarbons from methane t o undecane, inclusive, are given i n Table I. The constituents of natural gas gasoline may be removed from natural gas and collected in liquid form by either t h e compression, t h e refrigeration, or t h e absorptiogz method. I n t h e general discussion which follows no attempt will be made t o consider details of apparatus or operation; on t h e contrary, t h e present purpose is merely t o present briefly t h e principles and applications of the different methods and t o bring out t h e relationships t h a t exist between them.’ COMPRESSION METHOD
The compression method for t h e production of gasoline operates on the well-understood principle t h a t t h e vapor pressure of a substance is independent of t h e pressure on t h e gas of which t h e vapor forms a part. Accordingly, when t h e pressure on the gas is increased, t h e partial pressure of the vapor increases only until its saturation pressure is reached, and from this point, increase in pressure results in condensation of increasing amounts of t h e vapor as liquid. The amount of t h e substance remaining in vapor form is 1 For details, consult the following publications of the Bureau of Mines: “The Condensation of Gasoline from Natural Gas,” by Burrell, Seibert and Oberfell, Bulletin 88 (1915). “12xtraction of Gasoline from Natural Gas by Absorption Methods,” by Burrell, Biddison and Oberfell, Bulletin 120 (1917). “Recovery of Gasoline from Natural Gas by Compression and Refrigeration,” by Dykema, BuZZetzn 151 (1918). “llecent Developments in the Absorption Process for Recovering Gasoline from Natural Gas,” by Dykema, Bulletin 176 (1919).
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inversely proportional t o the number of compressions employed, using t h e pressure a t which t h e partial pressure becomes equal t o saturation pressure as a basis. For example, if a gas is saturated with pentane vapor a t atmospheric pressure, compression t o z atmospheres will condense one-half t h e pentane; if t h e gas is onetenth saturated, compression t o I O atmospheres will be necessary t o increase t h e partial pressure t o t h e saturation point and this last pressure must be doubled t o cause condensation of one-half t h e pentane vapor. Such difficulties as are encountered in t h e efficient operation of a compression plant result from t h e simultaneous condensation of t h e several mutually soluble hydrocarbons t h a t constitute natural gas gasoline. What is t r u e when pentane is t h e only condensable substance no longer holds when other condensable substances are present. The saturation pressure for each gasoline hydrocarbon is influenced by t h e other condensable hydrocarbons and varies as condensation becomes more and more nearly complete. The result is t h a t t h e most efficient method of operating a compression plant for t h e production of gasoline can be determined, a t the present time, only by experiment.
FIG.1
I n actual practice t h e degree of compression varies from a few pounds t o about 300 lbs., depending upon the kind of gas being treated. I n some cases a high vacuum is maintained on old wells in oil-bearing sands from which t h e original gas has almost entirely been withdrawn. The more volatile portions of t h e oil are gradually vaporized and only a slight pressure is required t o condense these as gasoline after they reach t h e surface of t h e earth. On t h e other hand, some natural gases give no condensation of gasoline a t 300 lbs. pressure. Gases t h a t yield much less t h a n 0.5 gal. per M cu. ft. of gas a t 300 lbs. pressure are not usually compressed for their gasoline content. Additional condensate may usually be obtained b y using pressures higher t h a n 300 lbs., but butane and propane are its principal constituents and these of course cannot be retained by themselves in liquid form a t atmospheric pressure and room temperature. There is no question b u t what butane may remain in solution in
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
548 A
B
C
T ~ B L I-PROPERTIES E D E
Vol.
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OF NATURALGAS HYDROCARBONS
F G Specific Gravity
---
H Gravity BaumC Scale
I
Vapor Pressure
J K Cu. Ft. Gal. Vapor per M per Cu. f t . Gal. Sat. Vapor
L B. t. u. per Cu. f t . 1008.5 1763.2 2.5 18 3273 4027 4782 5537
Melting Point Boiling Point Gas Liquid 60° F. NAME Formula c. ' F. C. OF. Air = 1 Water = 1 In. Hg Methane CH4 -184.0 -299.0 -160.0 -256.0 . . . . . . 0.554 ... .. Ethane CzHe -172.1 -277.8 -84.1 -119.4 1.038 Propane. CaHs -187.8 -206.2 -44.1 -47.4 1.523 Butane C4H10 -135.0 -211.0 +0.3 +32.5 2.007 0:6i)O ' II%:3 6i:OO Pentane CsHn -130.8 -203.4 36.4 97.7 2.491 0.626 93.6 13.99 2;:s 17:i Hexane CsHlr -94.0 -137.2 69.0 156.2 2.975 0.663 81.2 3.82 24.2 5.26 CIH16 -97.1 Heptane -142.8 98.4 209.2 3.459 0.688 73.5 1.02 21.6 1.57 Octane CsHis -56.6 -69.9 125.5 257.9 3.944 0.707 68.0 0.31 19.5 0.53 6291 Nonane CQHZO -51.0 -59.8 150.5 302.9 4.428 0.722 63.9 0.16 17.7 0.30 7046 Decane ClaHm -32.0 -25.6 173.0 343.4 4.912 0,734 60.7 0.08 16.2 0.16 7801 Undecane CIIHZ~ -25.6 -14.1 194.5 382.1 5.396 0.743 58.4 0.03 15.0 0.07 8555 COLUMNS B A N D D-The values for the melting and boiling points t h a t are given in Columns B and D were taken from the 1918 edition of Van &'ostrand's "Chemical Annual." The boiling point of ethane was determined a t a pressure 749 mm., and that of nonane a t 759 mm.; otherwise the figures are for 760 mm. COLUMN F-Theoretical specific gravities are given in Column F. They were computed from the formula sp. gr. = 0.4842 n 0.07, in which n represents the number of carbon atoms in the hydrocarbon molecule (see Anderson, THIS JOURNAL, 11 (1919), 299). COLUMN G-The figures in Bernthsen's "Organic Chemistry," 1912 Edition, page 30 form the basis of Column G , corrections having been applied to obtain the ratio of the weights of hydrocarbon and water a t G O O F . No correction has been' made t o the value for butane which was determined a t its boiling point. Degrees, COLUMNH-The Baume scale figures in Column H were computed from the values in Column G by the formula: 140 Baume = sp, Gr, 60",600 F,-130, in accordance with the procedure adopted by the Bureau of Standards. (See Circular 67.) COLUMN I-The vapor pressures a t 60' F. given in Column I were taken from curves prepared from tables in Landolt-Bbrnstein, "Physikalisch-chemische Tabellen " with the exception of the values of nonane and undecane, which were gotten from the others by interpolation. C O L ~ MJ-The N volume of dry vapor a t 60' F. and 30 in. mercury corresponding t o one gallon of the important gasoline hydrocarbons, as given in Column J, was computed from the formula: Wt. gallon water a t 60' F. X Sp. Gr. Hydrocarbon (Water = 1) 8.328 Sp. Gr. Hydrocarbon (Water = 1) ' Wt. cu. ft. dry air a t 60' F. 30 in. Mer. X Sp. Gr. Hydrocarbon (Air = 1) = 0.07650 Sp Gr Hydrocarbon (Air = 1) COLUMN K-Column K shows the theoretical yield of the various gasoline hydrocarbons expressed in gal.' pe; M cu. ft. of gas a t 60' F. and 30 in. mer1000 = Vapor Pressure X 33.3 , cury. The yields were computed by the formula: Gal. per M cu. ft.=Vapor Pressure 30 c u f t . per gal. Cu. ft. per gal. COLUMN I,-The heating value of dry gas a t 60' F 30 in. mercury, as given in Column L, was computed from the formula: B. t. u. percu. ft. = 253.8 754.7 n,in which n represents the number of carbon atgms in the hydrocarbon molecule.
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+
+
natural gas gasoline for considerable periods of time a t temperatures of 6 0 ' t o 70' F., b u t t h e losses of t r u e gasoline constituents along with the butane make it undesirable t o condense much of t h e latter i n t h e process of gasoline manufacture. The heat of compression of t h e gas is usually removed b y cooling with water. It is possible t o cool t h e gas t o about soo F. by t h e use of deep-well water, or t o even lower temperatures by t h e use of creek water in t h e winter time in certain localities, but it is probable t h a t , on t h e average, t h e gas from which gasoline is t o be obtained is not cooled below 60' F. by t h e use of water. T h e temperature t o which t h e compressed gas is cooled is a n important thing from t h e point of view of efficiency of condensation, as will be readily understood from a n inspection of Fig. I , which contains pressure-temperature curves of t h e normal paraffin hydrocarbons, butane t o octane, inclusive. T o illust r a t e t h e importance of this cooling, t h e maximum pentane content of a gas is 3 j per cent less a t 50' t h a n a t 7 0 ' F., t h e hexane content 38 per cent less, and t h e heptane content 48 per cent less. T o accomplish t h e same result by increasing the pressure, while maintaining t h e temperature a t 70' F., t h e number of compressions would have t o be increased by 54 per cent in the case of pentane, b y 61 per cent in t h e case of hexane, a n d by 9 2 per cent i n t h e case of heptane. R E F R I G E R A T I O N METHOD
Refrigeration methods are sometimes resorted t o in order t o lower t h e temperature of t h e gas below t h a t which may be obtained by t h e use of air or water. T h e usual procedure is t o utilize t h e cooling effect obtained by t h e expansion of t h e compressed gas, especially in those cases where i t is not necessary t o deliver t h e gas at high pressure. T h e expansion may take place through a n orifice or valve, or in a n expansion engine, t h e cooled expanded gas being made t o absorb heat from t h e high pressure gas in various forms of heat exchanger of t h e counter-current type. T h e cooling
effect t h a t is obtained through a n orifice or valve i s small and generally quite unsatisfactory. By t h e use of expansion engines, t h e temperature of t h e high pressure gas may be cooled t o o o F., or lower if desirable. The expansion engine has not as yet been widely used in t h e eastern states. ABSORPTIOK
METHOD
If a mineral oil is placed in contact with n a t u r a l gas, i t dissolves a portion of each of t h e hydrocarbons present in t h e gas, t h e percentage efficiency of t h e absorption increasing with t h e molecular weight of t h e hydrocarbon. If this oil be subsequently heated, a gas is liberated which differs from t h a t which was treated with t h e oil in t h a t i t contains a much higher concentration of t h e heavier, or gasoline, hydrocarbons. If t h i s liberated gas be cooled, condensation of gasoline m a y occur, and additional gasoline may be obtained b y compressing a n d re-cooling this gas. I n a word, then, t h e absorption process of producing natural gas gasoline consists in t h e preparation from a natural gas of a n artificial gas mixture in which t h e greater part of t h e gasoline-forming hydrocarbons of t h e natural gas h a v e been concentrated and from which gasoline may easily be condensed by application of t h e principles of t h e compfession method. It is evident then, from this point of view, t h a t t h e absorption method is especially suited t o the t r e a t m e n t of natural gases from which gasoline cannot be condensed, or a t best only very incompletely, b y direct compression and cooling. I n practice, natural gas is treated continuously with the absorbing oil, quite commonly a t pressures considerably above atmospheric, i n vertical absorbers i n which t h e gas enters a t t h e bottom a n d leaves a t t h e t o p , and oil enters a t t h e t o p a n d leaves at t h e bottom. After leaving the absorber t h e course of t h e oil is normally as follows: From t h e absorber through a t r a p t o t h e vent t a n k where t h e gas liberated from t h e oil as a result of t h e drop in pressure is withdrawn; from t h e
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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
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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
