.4ug.,
1920
T H E J O U R N A L O F ILVDL’STRIAL A N D E N G I N E E R I N G C H E M I S T R Y
GASOLINE FROM NATURAL GAS. 11-USE OF CHARCOAL IN DETERMINING THE GASOLINE CONTENT OF NATURAL GAS By R. P. Anderson and C. E. Hinckley UNITED NATURAL GAS COMPANY, OIG CITY, PENNSY&VANIA
Received December 31, 1919
The first paper of this series was devoted t o a discussion of the methods t h a t may be employed for t h e commercial extraction of gasoline from natural gas. For the purpose of determining whether a gasoline plant shall be installed on gas from a given source and in determining what t h e nature of t h e plant shall be, a knowledge of the gasoline content of t h e gas is of prime importance. Methods of determining t h e approximate gasoline content of natural gas, embodying the same principles as are used in t h e production of gasoline commercially, have been employed by the various companies engaged in this industry. All of these methods have undesirable features, and t h e need for a new method by which tests can be made more quickly and more simply has been strongly felt. With t h e recent production of large amounts of gasmask charcoal, far superior as a n adsorbent t o any hitherto prepared, came t h e utilization of this material for determining t h e gasoline content of natural gas, and results of some of the experimental work on this new method have already been pub1ished.l I n t h e present paper t h e authors present t h e results t h a t they have obtained in standardizing t h e procedure for t h e use of charcoal in gas testing and in developing a portable testing outfit. M E T H O D OF G A S O L I N E A D S O R P T I O N
I n t h e experiments t o be described 8 t o 14 mesh charcoal obtained from t h e National Carbon Company a n d known by them as activated carbon, No. 4 mix, was employed in glass tubes about 0.8 in. in diameter. Each t u b e was filled t o a depth of about 8 in. and t h e removal of t h e gasoline-forming constituents from t h e gas was effected b y passing i t through two of these tubes in series. The weight of t h e charcoal in each t u b e amounted t o about one ounce. Among t h e variables which might influence t h e yield of gasoline t h e following have been studied: ( a ) R a t e of flow of gas through charcoal, ( b ) quantity of gas treated, (c) moisture content of gas and charcoal, and ( d ) temperature of gas and charcoal. ( a ) R A T E O F F L O W O F GAS-In varying t h e rate of flow of gas through t h e charcoal i t was found t h a t , on a gas yielding 0.1j gal. gasoline per M CU. f t . , rates from 2 0 t o 5 0 cu. f t . per hr. gave about t h e same results.@ Inasmuch as t h e amount of gas required for a test is’ small, t h e effect upon t h e yield of gasoline of employing higher rates was not determined. During t h e passage of natural gas through charcoal, adsorption of each of its constituents presumably takes place t o a certain extent. I t is possible t o conceive 1 OberfeU, Shinkle and Meserve, THIS JOURNAL, 11 (1919), 197; Oberfell and Burrell, GQSRecord, 121 18 (1919), 45. a I n these and subsequent experiments where the effect of a certain variable was being studied, the experiments were performed in pairs, the conditions being the same except for a single variable. I n this way the ettect of unavoidable variations in the quality of the gas was eliminated.
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of a variation in t h e ratio of t h e adsorbed gasolineforming constituents t o t h e other adsorbed substances, as a result of a variation in t h e rate of flow of t h e gas. Since t h e efficiency of recovery in liquid form of t h e gasoline hydrocarbons adsorbed by t h e charcoal is a function of the amount of gas liberated from t h e charcoal during t h e distillation process, t h e variation in t h e ratio mentioned above would affect t h e yield of gasoline a t rates which would give complete removal of t h e gasoline-forming constituents from t h e gas. While this factor might prove important under certain conditions, i t is evident t h a t i t has b u t little effect between rates of 2 0 and 50 cu. f t . per hr. for the gas which was employed. For t h e relationship between rate of flow and charcoal temperature, see ( d ) . ( b ) Q U A N T I T Y OF G A S TREATED-The quantity Of gas t o be employed t o obtain t h e maximum yield of gasoline can be determined only b y experiment. If too small an amount of gas is used t h e ratio of adsorbed gasoline-forming constituents t o other adsorbed substances is low and, on distilling t h e gasoline vapor from t h e charcoal, t h e efficiency of recovery of t h e gasoline is also low, on account of t h e low partial pressure of t h e gasoline hydrocarbons in t h e gas liberated from t h e charcoal. On the other hand, if too much gas is passed through t h e charcoal, t h e gasoline-forming constituents are not completely adsorbed, and a low yield may therefore result. I t is quite possible, in the case of certain natural gases, t h a t t h e efficiency of gasoline recovery in t h e distillation process might increase more rapidly t h a n t h e efficiency of adsorption would decrease as the amount of gas first exceeds t h e limit for complete removal of t h e gasoline hydrocarbons, and, under these conditions, a maximum yield will be obtained when t h e volume of gas is in excess of t h a t from which t h e charcoal can remove t h e gasoline hydrocarbons with I O O per cent efficiency. For the amount of charcoal t h a t has been specified, t h e volume of gas t h a t should be employed may vary with t h e character of the gas from a fraction of I cu. f t . t o 3 0 cu. f t . or more. As regards t h e gases t h a t t h e authors have examined, t h e volume of gasoline recovered from t h e first charcoal tube should be between 5 and I O cc., while t h e volume obtained from t h e second t u b e should not exceed a few tenths of I cc. A larger volume in t h e second tube indicates t h e use of too large a quantity of gas. The importance of using t h e proper volume of gas is shown by t h e d a t a of Table I obtained on a lean gas of about 0.65 specific gravity. TABLE I Volume of Gas Cu. Ft. 2.7 5.5 10.9 16.4 21 .8
Volume Gasoline Recovered, C c . First Tube Second Tube Total 0.3 0.3 1.1 T&e 1.1 3.3 0.1 3.4 7.0 0.2 7.2 9.0 0.3 9.3
Yield Gasoline Gal. per M Cu F t . 0.029 0.053 0.082 0 116 0.113
I n view of t h e rather narrow limits within which t h e gas volume must sometimes be chosen, i t is important, in examining a natural gas for gasoline for t h e first time, t o make at least three different determinations with different volumes of gas, using whatever informa-
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tion may be available in deciding what volumes t o employ. (6) M O I S T U R E
CONTENT
OF
GAS
AND
CHARCOAL-
Experiments were performed t o determine t h e effect upon t h e yield of gasoline of drying t h e gas before passing it through t h e charcoal, in some cases using charcoal in equilibrium with t h e air of t h e laboratory as regards moisture content, and in others using charcoal t h a t had been dried a t 150' C. Drying t h e gas alone gave an increase in yield of about 5 per cent as t h e average of three experiments, and drying both gas and charcoal gave an increase in yield of about 8 per cent as t h e average of t h e same number of determinations. Inasmuch as t h e gas volumes employed were probably slightly in excess of t h e volumes t h a t would give a maximum yield, i t seems likely t h a t t h e effect of drying t h e gas and charcoal could be made still smaller by using t h e proper gas volumes. At any rate, t h e increase in yield as a result of drying t h e gas and charcoal seems scarcely worth t h e extra effort, and in subsequent determinations no attempt has been made t o modify t h e natural water coiitent of either t h e gas or charcoal. ( d ) T E M P E R A T U R E O B G A S A N D CHARCOAL--TiC'hile i t is realized t h a t t h e activity of charcoal is affected by its temperature, i t is felt t h a t such changes in a t mospheric temperature as are met with in t h e ordinary conditions of testing would have b u t little effect upon t h e yield of gasoline. On t h e other hand, when natural gas is first passed through charcoal considerable heat is evolved and when t h e flow of gas is rapid t h e temperature of t h e charcoal may momentarily be raised t o a temperature of 50' or 60' C. or even higher i n t h e case of gases rich in easily adsorbable constituents. If a thorough study of t h e effect of t h e rate of flow of gas upon the yield of gasoline were t o be made with t h e idea of increasing t h e accuracy of t h e charcoal method, t h e heat of adsorption would probably prove a n important factor, especially with gases of large gasoline content. One experiment has been performed in which gas from t h e same source was passed a t t h e same rate through two charcoal tubes in parallel, one of t h e tubes being heated by a steam jacket. The gas escaped from t h e steam-heated tube a t a temperature of about 90' C. and from t h e other t u b e a t an average temperat u r e of 18' C. T h e gasoline recovery from t h e hot tube amounted t o 60 per cent of what was obtained from t h e other tube. METHOD O F G A S O L I N E R E C O V E R Y
The following methods of recovery of gasoline from t h e charcoal have been tried: 1-Heating with mineral oil 2-Heating with glycerol 3-Heating with steam 4-Dry heating under reduced pressure
Heating with mineral oil is t h e method t h a t has been generally employed. I. H E A T I N G W I T H M I N E R A L oIL-The addition O f mineral oil t o saturated charcoal a t ordinary temperatures results in t h e liberation of t h e greater part, a t least, of the adsorbed substances. This operation
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causes t h e oil t o foam considerably, due t o t h e escape of gas. The gasoline-forming constituents remain dissolved i n t h e oil, except for t h e portion t h a t i s unavoidably carried off with t h e escaping gas. T h e application of heat results in t h e liberation of more gas and in t h e distillation of gasoline. The method of procedure was t o place t h e charcoal from one t u b e in a 1 2 j cc. distillation flask and to cover t h e charcoal with about 50 cc. of mineral seal oil, free from low-boiling hydrocarbons. After foaming had ceased heat was applied t o t h e flask, and t h e gasoline distilled and collected i n t h e usual fashion. The gasoline ceased t o distil over a t a vapor temperature of about 140' C., and from this point continued heating caused t h e temperature t o rise rapidly t o t h e initial distillation point of t h e oil. Care must be taken t o discontinue t h e distillation before t h e oil distils over in quantity. The use of oils more viscous t h a n mineral seal oil i s t o be avoided on account of t h e difficulties t h a t arise from excessive foaming. T h e oil distillation method works satisfactorily, t h e only important objection being t h a t a trace of oil is volatilized and carried over with t h e gasoline vapor, slightly affecting t h e amount and specific gravity of t h e distillate. 2. H E A T I N G WITH GLYCEROL-Glycerol can b e used as a substitute for oil in recovering gasoline from t h e saturated charcoal. It has t h e advantage over oil in t h a t t h e gasoline is not contaminated with a foreign substance. It has t h e disadvantage of being much more expensive, a n objection which can be partially overcome by recovering t h e glycerol for repeated use. 3. H E A T I N G W I T H STEAai-The attempt was made t o distil t h e gasoline from t h e charcoal with steam, but, a t t h e end of 30 min. heating, only one-half as much gasoline had been obtained as was obtained b y t h e use of oil, and t h e method was abandoned. 4. D R Y HEATIXG-Heating t h e dry charcoal was found t o be unsatisfactory. I n one case, a sample of saturated charcoal was heated for 2 . j hrs. under a 2 2 in. vacuum. The vapor temperature reached 145" C. and t h e temperature of t h e charcoal was probably as high as 2 0 0 ° C. for a portion of t h e time, and y e t b u t 6 0 per cent of t h e gasoline content of t h e charcoal was removed. P O R T A B L E A P P A R A T U S F O R F I E L D CSE
The apparatus for using charcoal in testing natural gas for gasoline can, on account of its small bulk, be readily adapted t o a portable apparatus for field use. The carrying case designed by t h e authors is shown in Fig. I . DESCRIPTION-This case is about 1 2 in. high, 1 2 in. broad, and 8 in. deep, external dimensions. It i s divided into two parts by a vertical partition placed midway between t h e front and back of t h e case. T h e portion of t h e case in front of t h e partition provides space for a n orifice meter, A, and two charcoal tubes, B, all of which are attached t o t h e partition i n t h e positions i n which they are t o be used. Suitable connecting tubes permit of passing t h e gas through t h e meter and then through t h e two charcoal tubes in
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1920
T H E JOURNAL OF INDUSTRIAL A N D ENGINEERING CHEMISTRY
series. The sliding door in front is removed when t h e apparatus is in use t o render t h e meter and tubes easily accessible, and a small door a t t h e left provides a n opening for bringing t h e gas t o t h e meter through E, and for exchanging charcoal tubes.
FIG I-PORTABLE TESTING OUTFIT
,4ccess t o t h e rear section of t h e case is obtained by a sliding door i n its top. This portion of t h e case is divided into ten vertical compartments of t h e proper size t o hold additional charcoal tubes, leaving a larger compartment a t t h e left for additional charcoal, rubber tubing, needle valves, etc. When ready for use, with 1 2 tubes filled with charcoal, t h e weight is 14 lbs. The orifice meter was constructed by sealing a platinum disk containing a n opening 0.15 in. in diameter in t h e glass tube a t A. The manometer C is filled with water and serves t o measure t h e differential pressure, and manometer D, containing mercury, indicates t h e gas pressure in excess of atmospheric a t t h e outlet of t h e orifice. T h e quantity of gas passing through t h e orifice is determined from t h e formula'
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To = standard temperature = 520' A. T = temperature of gas flowing through orifice, "A. Go = specific gravity of air = I G = specific gravity of gas flowing through orifice Before use t h e orifice meter should be calibrated against a n accurate displacement meter t o determine t h e value of K. The charcoal tubes shown in Fig. I are somewhat larger in diameter and shorter than those employed in t h e preliminary experiments. The internal diameter is about I in., and a column of charcoal about 6 in. long is placed in each tube. It is held firmly in place away from t h e rubber stoppers in t h e ends by t h e use of circular pieces of copp er gauze wedged into position. Where desirable aluminum tubes may be substituted for t h e glass tubes shown in t h e figure. Where field conditions are such t h a t a glass orifice meter would probably soon be broken, a metal meter may be substituted. A brass meter of t h e proper size t o fit into t h e portable case in place of t h e glass meter has already been constructed and installed. I t s form is shown in Fig. 2 . MASIPCLATION-The charcoal tubes are filled and connections made as shown in Fig. I . Connection is made from t h e gas supply through a needle valve and rubber tubing t o t h e inlet of t h e orifice meter, and gas is passed through t h e meter and charcoal tubes a t a definite r a t e for a definite time interval. Observations are made of t h e duration of t h e test, t h e differential pressure, h ' , t h e gas pressure a t orifice outlet, #, t h e barometric pressure, P, t h e gas t e m perature, T, and its specific gravity, G. The charcoal samples are taken t o t h e laboratory where their gasoline content is determined according t o t h e procedure already outlined. CALCULATION O F RESULTS-From t h e d a t a taken during t h e test, t h e amount of gas passed through t h e charcoal may be computed as outlined under t h e description of t h e apparatus. 55
Jonrs
*,WE
~ , V ~ i - C T / C W TO S
LCRE#.?,lFL Ann LSSYRC- +7,4W',"cr-
W,,-M
(2 = K w ' ~
in which Q = cu. ft. per hr., measured a t 6 0 " F., 30 in. mercury; K = constant; h = differential pressure measured when gas passes a t 60" F., and under a pressure of 30 in. mercury a t t h e orifice outlet. If gas is passed a t other than standard temperature and pressure, and if t h e specific gravity is different from t h a t of air, t h e formula must be amplified t o include these conditions, as follows:
FIG
P = barometric pressure, inches mercury, a t time of gas flow p = pressure in excess of atmospheric, inches mercury, a t orifice outlet Po = standard pressure = 30 in. mercury 1
T.R. Weymouth, Trans. A m . SOC. Mech. E m . ,
34 (1912), 1091.
METER
The yield of gasoline expressed in gallons per fvI cu. f t . is then computed from t h e following formula: Gal. gasoline per M cut. f t . of gas a t 6 0 " F., 3 0 in. Cc. gasoline recovered X 0 . 2 6 4 2 , in which mercury = Cu. f t . gas treated 0.2642 represents t h e number of gallons t o one liter. It will be noticed t h a t t h e use of an orifice meter i n measuring t h e amount of gas treated involves a knowledge of one more factor t h a n t h e use of a displacement meter, v%., t h e specific gravity of t h e gas. The labor involved in determining specific gravity is slight and is usually amply justified by t h e information t h a t is t h u s obtained concerning t h e relationship between t h e Y
h' = observed differential pressure
2-oRlFICE
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specific gravity of a gas and its gasoline content as determined by t h e charcoal method. It should be stated t h a t in none of the methods i n use for the determination of the gasoline content of natural gas is all of t h e gasoline recovered in liquid form. The charcoal method probably gives larger yields t h a n any other method commonly employed. The highest obtainable efficiency will no doubt depend t o a considerable extent on the nature of t h e gas being treated. SUMWARY
I-The use of charcoal in testing gas for gasoline has been investigated. This has involved a study of the conditions under which t h e gas should be treated and of t h e conditions under which t h e adsorbed gasoline should be recovered. 11-A portable testing outfit has been described a n d directions for its use have been prepared. THE EXTRACTION OF BITUMENS FROM MINERAL AGGREGATE‘ By M. R. Walczak and H.I. Rice CHICAGO LABORATORY, THEBARRETT COMPANY, CHICAGO, ILL Received March 6, 1920
I n investigations of the behavior of bituminous road materials there has been a long-felt need of some method by which a binder could be recovered for further examination from a bituminous aggregate without materially changing its character and particularly its consistency. it has been t h e usual practice to extract with solvents such as benzene or carbon disulfide either by digestion and decantation or in some form of. extractor of which t h e “Forrest Hot Extractor”2 and the “Reeve Centrifuge Extractor”3 are representative types. These methods are entirely satisfactory for the quantitative determination of bitumen content of an aggregate or for the recovery of an aggregate for purposes of further examination. The bitumen may be recovered by evaporation of the solvent, and several methods of manipulation have been suggested,a b u t by none of them can one be sure of obtaining the bitumen in t h e exact condition in which it existed before extraction, particularly if i t contained volatile matter which is removed with the solvent. Moreover, in t h e recovery of t a r bitumens by t h e above methods the free carbon is left with the aggregate and the characteristics of the bitumen are changed accordingly. With the above objections in mind, t h e authors have succeeded in developing a method and apparatus which appears t o oRer a large possibility of success, particularly in the recovery of fluid or semi-fluid t a r bitumen without any material change in character or consistency through the r e ~ o v e r y process. This method is based on the principle of specific gravity where t h e two substances, bitumen and minParticularly adapted to tar bitumens. Forrest, Proc. Am. Soc. Testing Materials, 13 (1913), 1069. 8 “Reeve Centrifugal Extractor: Methods for the Examination of Bituminous Road Material,” by Prevost Hubbard and Charles S. Reeve, W S. Dept. of Agriculture. Office and Public Roads, Bulletin 314 (1915). 4 “Testing of Bitumens for Paving Purposes,” by A. W. Dow. Proc. Am. ,506. Testing Mater%&, 1903, 360. “The Modern Asphalt Pavement,” by Clifford Richardson. 1
* C. N.
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era1 aggregate, each mutually insoluble in the other, the bitumen having a low specific gravity (approximately I . 2 a t 60’ F.) and t h e mineral matter a higher specific gravity (approximately 2.70), are separated by t h e use of a solution of a n (approximately) inert salt of a gravity intermediate between t h e other two substances, thereby floating the bitumen while allowing the mineral matter t o remain as a sediment. The materials used i n this work were: t h e mineral aggregate, consisting of a mixture of standard limestone, passing a three-quarter inch screen; a standard torpedo sand, mixed in t h e proportion of three t o one; and aqueous sodium carbonate as the intermediate solution. This was considered t h e best adapted for the purpose because of its ready solubility, and because of its inertness t o t h e t a r bitumen in question, as its only probable action on t h e t a r mixture would be solvent action upon the tar-acid content. Tests were made t o determine this point by thoroughly shaking 7 j cc. of t h e sodium carbonate solution (sp. gr. I . 2 7 t o I. 2 8 a t 60’ F.) with 2 5 cc. of dry t a r acids a t 140’ F., allowing t o settle in a separatory funnel graduated t o 0 .I cc. and noting any increase or decrease in either the soda solution or t h e upper layer of t a r acids present. No variation of volume of either substance was noted, b u t after removal of the soda solution and its slight acidification with sulfuric acid t h e odor of t a r acids was noted, but no layer or measurable quantity of acids was present. Actual operation of this method confirmed the view that the solvent action could be neglected. The t a r bitumen used in t h e experiment varied from a fluid t a r t o a soft pitch readily indented with t h e finger. APPARATUS
An ordinary, twoliter, vertical copper still was fitted with a tightly fitting funnel-shaped lid or cover fastened t o t h e still body with six screws and a rubber gasket. A flanged glass tube about I . j in. in diameter was fastened t o t h e top of the funnel lid by means
