December, 1929
IXDUSTRIAL A,VD ENGINEERISG CHEMISTRY
I n consideration of the initial cost of investment and the present undeveloped state of the market for this acid and its salts, it is impossible to fix even a tentative price for this product. It is felt, however, that with the establishment of a finished process and the stabilization of demand on a reasonable scale, gluconic acid and calcium gluconate may be produced a t a price comparable with that of citric acid. The writers realize that there are still several important factors t o be worked out if the process is to be established on an efficient industrial basis. Among these are large-scale sterilization of a plant in which an open-pan process is employed, large-scale inoculation of the pans, and large-scale sterilization of the sugar solutions and their distribution to the fermentation pans without contamination. ’These problems are clearly recognized and acknowledged, but it is beyond the scope of the work of this division to investigate them. They are by no means insoluble. In the hands of it competent
1203
chemical engineer with a knowledge of industrial biological processes they should be readily and satisfactorily worked out. Bibliography Amelung, 2 . physiol. Chem., 166, 161 (1927). Bernhauer, Biochem. Z., 153, 517 (1924). Bernhauer, I b i d . , 197, 278, 287 (1928). Butkewitsch, Ibid., 164, 177 (1924); 182, 99 (1927). Falck and Kapur, Ber., 67, 920 (1924). Herrick and May, J . B i d . Chem., 77, IS5 (1928); U. S. Patent 1,726,067 (1929). Herzfeld and Lenart, Z . Ver. deut. Zucker-Znd., 69, 122 (1919). Ling and Nanji, J . Soc. Chem. I n d . , 41, 28T (1922). hlay, Herrick, Thom, and Church, J . Biol. Chem., 75, 417 (1927). Molliard, CompL. rend., 174, 881 (1922); 178, 41 (1924). Stoll, U. S. Patent 1,648,368 (1927). Stoll and Kussmaul, U. S. Patent 1,703,755 (1929). Takahashi and Asai. Proc. I m p . Acad. Japan, 3, NO.2, 85 (1927). Wehmer, Biochem. Z., 191, 418 (1928).
Line Coordinate Charts for Representing Chemical Engineering Data‘ Edw. A. RavenscroftZ DEPARTMENT O F CHEMICAL
MICHIGAN, AXN ARBOR,
MICH.
The purpose of this paper is to show how line coIn brief, then, any straight HE system of line coordinates may profitably be employed by the chemical line in the Cartesian system ordinates is probably as old as or older than engineer. The principle of line cogrdinates is exrepresents a linear equation the more familiar Cartesian plained, and the relative merits of charts constructed b e t w e e n x and y, and any coordinates, I n general, line in line coordinates and in Cartesian coordinates are point on this line represents coordinates are not so condiscussed. Five examples of line coordinate charts are a solution to the equation. venient or clear as Cartesian given, together with their method of construction and In the line coordinate system coordinates for graphically their use. any point represents a linear reprejenting the relation beequation between x and y, tween two variables; but in some cases they do present dis- and any straight line drawn through this point represents tinct advantages. a solution to the equation. It is clear, then, that a series of straight lines in Cartesian coordinates reduces to a series of Comparison of Cartesian and Line Coihdinates points when transformed into line coordinates. It may be Plane Cartesian coordinate axes consist of two perpendicu- further shown that a series of lines passing through a comlar lines. Any corresponding set of values for two variables, mon point of intersection in Cartesian coordinates reduces to say x and y, is represented by a point so located that its a series of points all lying along a straight line in line coprojection on the x axis reads x, and its projection on the ordinates. If the straight lines in the Cartesian system are y axis reads y. Figure 1 is such a system. On it is plotted all parallel (infinite intersection), then the points to which X, a linear relation between 2 and y-namely, 29 - x = 2. they reduce in line coordinates will all lie on a line parallel Line coordinate axes consist of two parallel straight lines. to the coordinate axes. Any corresponding set of values for the two variables z and If the relation between x and y is empirical and does not y is represented by a transverse straight line intersecting yield a straight line in Cartesian coordinates but rather a the x axis at x and the y axis a t y, as shown in Figure 2 . It smooth curve of some sort, in transferring to line coordinates is this line that is the basis of the name “line coordinates.” the coordinate lines representing corresponding values of On it is plotted the point X, representing the linear rela- x and y will be found to form in general an envelope of tantion 2y - z = 2. It can be proved by analytical geometry gents to some transverse curved line. Corresponding values that any straight line drawn through X will intersect the x and of x and y are read by drawing a straight-line tangent to y axes a t values of x and y which will satisfy the above equa- the envelope and reading x and y a t its intersections with the tion ( 3 ) . coordinate axes. This is the basis of tangential coordinates, I n Figure 1 there is located a point P, the coordinates of of which line coordinates are a special branch. Representwhich are (2, y). Since this point lies on A, its coordinates ing a non-linear relation between x and y by this method represent vnlues of x and y that satisfy the equation repre- is not so convenient as the customary curve in Cartesian sented by A. I n Figure 2 there is drawn a straight line P , coordinates. There is no simple relation between the Cartesian the coordinates of whirh are (2, y). Since this line passes curve and the envelope in line coordinates. There are other through X, its coordinates represent values of x and y that relations between these two coordinate systems, but they lie satisfy the equation represented by the point X. Some- bpyond the scope of this paper (1,3,10). times the name “point equations” is used in place of “line It may be added that corresponding scales are used in the coordinates” because of this fact. two systems. Thus, if the relation between x and y can be represented as a straight line by plotting log x against y 1 Received M a y 27, 1929. 2 Present address, 677 Valley Road, Glencoe, Ill. in Cartesian coordinates, the straight line may be condensed
T
‘
E N G I X E E R I N G , b-XIVERSITY O F
Vol. 21, No. 12
INDUSTRIAL AND ENGINEERING CHEiMISTRY
1204
to a point by laying off log x on one axis in line coordinates and y on the other. Many other combinations a t once suggest themselves. If a given straight line in Cartesian coordinates has a positive slope, then by laying off the line coordinat,e axes in opposite directions from any convenient starting points, the straight line will condense to a point lying between the axes. On the other hand, if the line coordinate axes are laid off in the same direction, the point will lie either to the right or left of the coordinate axis, depending upon the relative scale moduli of the two axes. For Cartesian lines of negative slope the reverse holds.
CARTESIAN COORDINATES
/
6v)
O
L
0
I
2
I
I
I
I
4
X
I
I
I
6 8 AXIS
I
I
I
I
I
I
Vapor Pressure Chart
Figure 3 shows a vapor pressure chart in line codrdinates for fifty substances. Duhring's rule was used to obtain linear vapor-pressure curves. All the substances represented have been placed in one of two groups-the associating liquids and the non-associating liquids. I n plotting the data for substances of the former group, water has been used as the reference substance; in plotting the latter, hexane has been used. The rules laid down by Rechenberg (9) for determining to which of these two groups a given substance may belong have been summarized briefly and the summary has been put on the chart for convenience. On the chart will be found a temperature and a pressure scale. The temperature scale is arithmetic, and the pressure scale is an arithmetic scale of the boiling point of the reference substance at the same pressure, graduated in terms of that pressure. Hence, the chart reads directly temperature and pressure without the use of steam tables. On one side of the pressure scale are plotted graduations with hexane as the reference substance, on the other side with water as the reference substance. This makes one chart serve for all substances. On the chart have been plotted points representing the vapor-pressure curves of fifty substances. Each point has been numbered and the substance for which each number stands is given in the accompanying key.
>
1 0 1 2 1 4
FIG. 2
Application of Line Coordinates
Suppose it is desired to represent graphically data involving three variables, z, y, and z, and further that for any value of z the relation between z and y may be represented by a straight line in Cartesian coordinates by scaling the axes with the proper f(z) and f(y). When constructing charts to represent the relations between x , y, and z, it has been customary to draw a series of straight lines for the relation between z and y for particular values of z, marking each line with the value of z it represents. I n general these lines are not parallel and do not have a common point of intersection, and may even criss-cross in a confusing manner. Interpolation between these lines for intermediate values of z is difficult and rather inaccurate. Construction of a chart for these same data in line coordinates is no more difficult. Each straight line reduces to a point, and in general these points will be found to define a smooth curve which may be graduated with the corresponding values of z. The chart has become greatly simplified. Two coordinate axes and one curved line have replaced a mass of perhaps fifty lines on a background of perpendicular coordinates. Besides this it is no longer necessary to rely on hazy interpolation between curves. There are some disadvantages to line coordinates. If data are not exactly representable by a straight line in Cartesian coordinates, they will not define a sharp point when transferred into line coordinates. If the data are erratic, there will result a small area filled with many intersections. It is then difficult to decide on a suitable point to represent the average of these intersections. I n such a case it is best first to plot the data in Cartesian coordinates, draw the most representative straight line, and transfer this line directly into line coordinates. The reproduction and discussion of several line coordinate charts will make apparent the wide application and the general utility of this type of chart to the designing chemical engineer.
xi 2
1
0
LINE COORDINATES
Table A-Key to Vapor Pressure Chart (Figure 3) Arranged bv similar substances: Butane. . . . . . . . . . ..50 Isopropyl alcohol. . . .34 Chlorobenzene.. . . . .. 2 2 Pentane . . . . . . . . . . .47 Isobutyl alcohol, . . . . 2 7 Bromobenzene., . . . . . 1 4 Hexane. . . . . . . . . .42 Isoamyl alcohol. . . . .20 Iodobenzene . . . . . . . . 6 Heptane . . . . . . . . . .32 Formic a d d . . . . . . . . .33 o-Xylene.. . . . . . . . . ..17 Octane. . . . . . . . . . .. 2 4 Acetic acid. . . . . . . . . 2 6 m-Xylene.. . . . . . . . ..18 Nonane., . . . . . . . . . l 5 Propionic acid.. .... .16 $-Xylene . . . . . . . . . ..19 Decane. . . . . . . . . . . . 9 Butyric acid. . . . . . ..11 Silicon tetrachloride. .45 Isopentane. . . . . . . . . 4 8 n-Valeric acid. . . . . . . 3 Carbon tetrachloride.40 n-Caoroir acid. . . . . . 1 Chloroform . . . . . . . ..35 ~so%tt& Bcid. . . . . .12 Ethyl formate.. . . . . .43 Ethyl acetate.. . . . . .37 Methyl alcohol. . . . .39 Ethyl propionate, . . .31 Thiophenol. . . . . . . . . .10 Ethyl alcohol.. . . . . .36 Ethyl butyrate. .... .25 Benzaldehyde. . . . . . . 8 28 Ethyl chloride.. , , , .49 Bromine. , , 44 2 23 Ethyl bromide. . , , . .46 Diethyl oxalat 7 Ethyl iodide. . . . . . .. 4 1 Arranged by number: 18-%Xylene 35-Chloroform I - w C a p r o i c acid 19-#-Xylene 36-Ethyl alcohol 2-Diethyl oxalate 20-Isoamyl alcohol 37-Ethyl acetate 3-n-Valeric acid 21-Ethyl benzene 38-Benzene 4-Phenol 22-Chlorobenzene 39-Methyl alcohol 5-Aniline 23-n-Butyl alcohol 40-Carbon tetrachloride 6-Iodobenzene 41-Ethyliodide 7-n-Heptyl alcohol 24-Octane 25-Ethyl butyrate 42-Hexane 8-Benzaldehyde 26-Acetic acid 43-Ethyl formate 9-Decane 27-Isobutyl alcohol 44-Bromine 10-Thiophenol 28-n-Propyl alcohol 45-Silicon tetrachloride 11-Butyric acid 29-Water 46-Ethyl bromide 12-Isobutyric acid 30-Toluene 47-Pentane 13-Propyl benzene 14-Bromobenzene 31-Ethyl propionate 4s-Isopentane 15-Nonane 32-Heptane 49-Ethyl chloride 50-Butane 16-Propionic acid 33-Formic acid 17-&Xylene 34-Isopropyl alcohol I
-
.
..
INDUSTRIAL A N D ENGINEERING CHEMISTRY
December, 1929
240
VAPOR PRESSURE CHART
ASSOCIATING LIQUIDS:
700
600
40 I
I
600
I. INORGANIC COMPDS.
500
2. ALL ACIDS 3. PRI.& SEC. SAT'D
ALIPHATIC 400 4. TRIPLE
ALCOHOLS UNSAT'D
1205
200
ti
I
I I
L
I
7g
8
0
--
-+--
I
1
I
I
46' ($47
$48 I
490 I I
I
I
I
650
NOTE: FOR K E Y T O NUMBERS SEE TABLE A
1206
INDUBTRIAL AND Eh-GINEERING CHEMISTRY
LATENT AS A
HEAT r 40
necessarily space themselves uniformly along the dotted line connecting them all. However, for rough approximations they may be assumed to be sufficiently uniformly spaced so that interpolation or extrapolation may be made f o r t h o s e members of a series for which data are lacking.
lo
F U N C T I O N OF TEMPERATURE
,,
0’ 50
Latent Heat Chart
Curves representing the variation of latent heat with temperature may be cono2 55 v e r t e d into straight lines in Cartesian coordinates by use of an empirical interp o l a t i o n similar to Duhring’s rule for vapor pressures. Thus, instead of plot120 ting latent heat against boiling temperature directly, the boiling temperature is plotted against the temperature a t which a suitable key substance has the same 140 latent heat. a The straight lines resulting from appli3 cation of this method with benzene as the 0 0 Q. 15 16 170 160 f, key substance were used as the basis for n c o n s t r u c t i n g the line-coordinate latent I heat chart of Figure 4. Two scales were w 180 first put on the chart y-namely, a boilIing point scale and a scale of the corresponding boiling point of the key substance. Both scales are arithmetic; the KEY: latter, however, being graduated in terms of the latent heat of the key substance, N-PENTANE - 7 BENZENE - - - - - 18 k 2 0 0 thereby making the chart read directly N-HEXANE - - - I O FLUORBENZENE - - 14 temperature and latent heat. These two scales were placed on the outer edges of N-HEPTANE- - 12 CHLORBENZENE - - 15 220 the chart in order better to distribute the N - O C T A N E - - - 13 BROMBENZENE - - - 4 points representing the latent heat curves of various substances. Eighteen of these ISOPENTANE - - - 5 1,ODOBENZENE - - points were next plotted on the chart. DllSOPROPYL - - 8 The data for the chloro-compounds were DIISOBUTYL - - - 9 CARBON DISULPHIDE 11 t a k e n from t h e International Critical Tables ( 5 ) and the data for the other HEXAMETHYLENE - 1 6 CHLOROFORM - - - 3 substances were taken from Young (19). ETHYL ETHER - - 6 The points representing various related substances, such as the hydrocarbons, do Figure 4 not seem to have any systematic location The vapor-pressure data for these fifty substances have on the chart. Interpolations and extrapolations such as were been taken directly from Rechenberg (9), whose vapor-pres- made on the vapor-pressure chart are therefore impossible on sure data have been leveled with Duhring’s rule and are there- this chart. fore directly available for constructing the chart without Boiling Point Chart for Electrolytic Caustic Solutions further modification. The points representing the various members of a homologous series have been connected with The data for constructing Diihring lines for this system dotted lines. These lines are not straight, the one involv- published by Monrad and Badger (1) were used in making ing the alcohols being particularly curved. This means the chart shown in Figure 5. Two scales were put on the that the Diihring lines for a homologous series as customarily chart-one for the temperature and the other for the corredrawn on Cartesian coordinates do not quite intersrct a t a sponding boiling point of water also graduated in terms of common point. This statement is not in agreement with pressure. The points corresponding to various concentrathe conclusion reached by Carr and Murphy ( 2 ) . These tions of caustic were found to define a smooth curve. The authors extended the customary Diihring lines far beyond curve was drawn and graduated in terms of the concentrathe normal limits of a Duhring line chart to find the com- tion of caustic. Thus the chart is direct-reading for temmon point of intersection, There are inherent mechanical perature, pressure, and concentration. errors in this construction that are not present in the line coordinate method, But in either case, whether the exact Liquid-Vapor Equilibrium Chart for Hexane-Octane concurrency of the Diihring lines for a homologous series Mixtures of hexane and octane of varying composition is admitted or not, the construction in line coordinates is have been shown by Leslie and Carr to follow Duhring’s a simpler and easier way to represent the relation. It should be added, further, that the points representing rule (6). Their data have been used in constructing the the various members of a series in this construction do not chart of Figure 6. The temperature and pressure scales /---
”
e
T’ol. 21, s o . 12
-
-
IIVDUSTRIAL AND EXGINEERIXG CHE-VISTRY
December, 1929
and the points on the curve representing the composition of the boiling liquid were plotted in a manner similar to that used in constructing the boiling point chart for caustic solutions, It seems quite reasonable that the condensing points of a vapor mixture of given composition follow Duhring'q rule, as do the boiling points of a liquid mixture of given composition. Assuming this, it is possible to locate a point on the chart corresponding to all the condensing points under various pressures of a vapor of given composition. This assumption was made and the resulting points were found to define a smooth curve which was graduated in terms of the composition of the vapor. The chart therefore reads directly the boiling point and composition of liquid and of vapor at any desired pressure. d chart of this nature should prove particularly valuable in predicting the performance of fractionating columns under various pressures.
1207
where a = average specific heat of dry air b = average specific heat of water vapor r u = latent heat of water a t wet bulb temperature, B. t. u. per pound t, = wet bulb temperature, O F. t = temperature of air, ' F. H = humidity o f air, pounds water vapor per pound dry air
For any given adiabatic cooling curve t, and rtu are constant. Integrating the above equation and calling c the arbitrary constant: ln(r,
- bt,
+ bt) = In a + bH
Since H = H, when t = tu, r,
=
C
+ bH,
__
a
and
Humidity Chart Y,
Since its publication in 1912, the Grosvenor ( 4 ) humidity chart has been widely used in drier design. I n this country there hare been practically no published improvements of this chart. That it is unnecessarily complicated and that line coordinates have a truly wide application can be seen from the fact that the author has succeeded in condensing all the data found on the low-range Grosvenor chart onto a line coordinate chart of five scales, shown in Figure 7 . 800 -=i Perhaps the most important part of the Grosvenor chart is the series of adiabatic cooling lines, by means of which 700 the humidity of the air may be found from the wet- and dry-bulb temperatures. 600 Each one of these lines represents an over-all heat balance connecting an ini\ \ tial and final condition of the air. It 500 does not represent the true path of the air as it cools from a partially saturated condition to a saturated state. Rather, the true path is represented by a smooth curve drawn through the end points of all 400 the adiabatic cooling lines radiating from 5 a given point on the saturation curve. It I is these true-path curves that must be I 300 used in calculating the humidity or temW perature of unsaturated air leaving an U 3 adiabatic drier. m If the humidity and temperature co- Yw, ordinate scales of the Grosvenor chart can U a be so modified that the true-path adia200 batic cooling curves become straight lines, a 0 it will be possible to construct a line co- n 4 ordinate chart that may be used to de- > 150 termine humidity directly from wet- and dry-bulb temperatures, or will readily and accurately solve the type of drier problem just mentioned. With the line coordinate chart it is unnecessary to int e r p o l a t e between true-path curves or 100 guess a t which of the radiating adiabatic cooling lines is the proper one to follow 80 in a given case. The following basic differential equation for the adiabatic cooling of air by 60 evaporation has been derived by Walker, Lewis, and McAdams (11):
- bt, + bt
=
r,(a
a
+ bHJ
+ bH
Rearranging:
SYSTEM:
NaOH- H_,Q
(SAT'D WITH NaCl)
BOILING POINTS & VAPOR
PRESSURES
P
$
(a
+ bH)dt
- [f,
+ b(t - t,)]dH
0
70
a I
8z
INDUSTRIAL A N D ENGINEERING CHEMISTRY
1208 IOoo
3-
900 -
-800 --700 --
LIQUID AND
-
TEMPERATURE
3
v) v)
w
a: n
-
I- \ \
--
--200--
150 7
-
-
90 80 -
100-
70
--
60 -
-
50
-
--
W
a 2
3OOk,
I
VARYING
PRESSURE.
120-
.
---
I
UNDER &
COMPOSITIONS
-
2 loo+l ---
---
d
a
OCTANE
-----
----
4 0 0 :
W
-
140-
---
500:
VAPOR
A T EQUlLlBRlUM
600- -
2
HEXANE
SYSTEM:
A
- - .\ --E
2 S O _-
drier is found by connecting the temperature and humiditv of the enterinn air with a straight line. “This line will-intersect the wet-bulb curve a t the proper adiabatic cooling point. The intersections of any line drawn through this point and the H and t scales give the temperature and humidity of the air corresponding to some other point in the drier. If the line is drawn through the exit air temperature, the exit humidity is read a t once and vice versa. It is often desirable to know the latent heat of water a t any temperature when making drier calculations. Therefore, the w e t - b u l b temperature scale has been graduated on the other side in terms of 20 the corresponding latent heat of water. Both these latent heat data and the vapor pressure data for water used in making 4o this chart were taken from the International Critical Tables ( 5 ) . I n order to make the chart read humid 50 E volume directly, it is necessary to find 0 suitable scales for H and t so that lines > of c o n s t a n t humid volume plotted on C a r t e s i a n coordinates will be straight. z Let V = humid volume in cubic feet of wet air per pound dry air. From the gas
4
-
---
-4 L s \ z I-
Vol. 21, No. 12
6>*,
I - \ \ -m 40 -(3
-z-I -0
359
2
--
-20 ---0-
-
Figure 6
t
) -t 18.02 ( =
5
100
+ 460 492
)
+ 0.0405 H ) ( t + 460)
V
0.0252
+ 0.0405H - 460
+
If t is plotted against 1/(0.0252 0.0405H), in Cartesian coordinates, lines of constant humid volume will be straight. This is the basis of the left half of the humidity chart. The same t scale is used and a new H scale constructed a t the extreme left. The locus of points of constant humid volume is a smooth, almost straight curve which is graduated in terms of humid volume on one side and its re-
December, 1929
IiVDUXTRIAL AND ENGINEERING CHEMISTRY
HUMIDITY
-
LBS. HzO/ LB. DRY AIR
HUMID H ~ A T- B.T.U.
HUMIDITY
-
/ LB. DRY AIR
LBS. H ~ O /LB. DRY AIR
1209
1210
INDUSTRIAL AND ENGINEERING CHEMISTRY
of 1000 pounds per hour on the dry basis. The air leaves a t 130’ F. Calculate (a) humidity of entering air, ( b ) humidity of exit air, (c) evaporation of water from stock in pounds per hour, (d) volume of entering air, ( e ) volume of exit air. Solution (shown on chart). (a) Connect wet- and dry-bulb temperatures of entering air with a straight line and read the humidity of the entering air on the scale a t the right-hand edge as 0.0538 pound water per pound dry air. ( b ) Since wet-bulb temperature is constant throughout drier, draw a straight line through the intersection of the line drawn to solve part (a) with the wet-bulb temperature scale and through 130’ F. on the dry-bulb scale. Read the humidity of the exit air on the right-hand humidity scale as 0.0645 pound water per pound dry air. (c) Water evaporated = lOOO(0.0645 0.0538) = 10.7 pounds per hour. (d) Connect 170’ F. on the dry-bulb temperature scale with 0.0538 on the left-hand humidity scale and read the humid volume as 17.25 cubic feet wet air per pound dry air. Volume of entering air is therefore 17,250 cubic feet per hour, (e) By similar method, volume of exit air is 16,380 cubic feet per hour.
-
Conclusion There is a similarity between line coordinate charts and the more familiar nomographic charts. The two should not
Vol. 21, No. 12
be confused, however. The five charts described in this article are examples of the wide adaptability of line coordinates to chemical engineering data. The reader may adopt this method to construct other charts to suit his particular needs. Literature Cited (1) Brodetsky, “A First Course in Nomography,” G. Bell & Sons, Ltd., London, 1920. (2) Carr and Murphy, J . A m . Chem. Soc.. 51, 116 (1929). (3) d’Ocagne, “Traite de Nomographie,” p. 158, Gauthier-Villars, Paris, 1921. (4) Grosvenor, T r a m . 4 m . Znst. Chem. Eng., 1, 184 (1912). ( 5 ) International Critical Tables, Vol. V, McGraw-Hill Book Co., Inc. (6) Leslie and Carr, IND.ENG.CHEM.,17,810 (1925). (7) Monrad and Badger, Zbid., 21, 40 (1929). (8) Partington and Schilling. “Specific Heats of Gases.” E. Benn, t t d . , 1924. (9) Rechenberg, “Distillation,” Selbstverlag von Schimmel & Co., 1923. (10) Runge, “Graphical Methods,” Columbia University Press, 1912. (11) Walker, Lewis, and McAdams, “Principles of Chemical Engineering,” p. 458, RIcGraw-Hill Book Co.. Inc., 1927. (12) Young, Sci. Proc. R o y . Dublin Soc., 12,374 (1910).
Effects of Temperature and Pressure on the Upper Explosive Limit of Methane-Oxygen Mixtures‘ C. M. Cooper and P. J. Wiezevich DEPARTMENT OF CHEMICAL EKOINEERING, MASSACHUSETTS INSTITUTE OF TECHNOLOGY. CAMBRIDGE, MASS.
A new apparatus of the make-and-break type has surprising to find that anybeen developed for the ignition of gaseous mixtures a t mentation has been done thing which alters the heat high temperatures and pressures. With this apparatus by various investigators losses to the s u r r o u n d i n g s the explosive limits of methane-oxygen mixtures have o n t h e explosive limits of affects the explosive limits. been investigated a t pressures up to 230 atmospheres methane-air mixtures a t ordiThus, by gradually decreasand temperatures up to 480’ C. nary temperatures and presing the diameter of the tube It has been found t h a t the lower the oxygen concenused for the determinations, sures. Recently ($) higher tration or the temperature, the higher the pressure repressures have been used with the explosive l i m i t s come quired for the successful ignition of the mixture; and the same materials, but few closer and closer together unconversely, as either pressure or temperature is indata are available for methtil finally, for v e r y n a r r o w creased, the amount of oxygen necessary to form a ane-oxygen mixtures. This tubes, it appears that there combustible mixture is decreased. A t temperatures is no gas composition which work was u n d e r t a k e n in above 400” C. spontaneous reaction begins to occur. will ignite a n d p r o p a g a t e order to obtain information Complete consumption of the oxygen does not take flame. concerning the effects of templace on the explosion of the mixtures a t high pressure. perature a n d p r e s s u r e o n Previous Work the upper explosive limit of methane-oxygen mixtures. The limits of inflammability for gases and vapors a t orThe “expl&ve limit” or “limit of inflammability” of an dinary conditions have been determined by various investiinflammable gas, vapor, or solid suspension with oxygen or gators (9, 10, $0, 33). The effect of pressures up to 10 any medium capable of supporting combustion may be atmospheres has also been studied (2, 29, 24, $5, /to),and defined as that composition which when ignited will just sup- results published after the completion of the present study (2) port its own combustion. Consider a typical case. If meth- give the effect of pressures up to 400 to 500 atmospheres ane is mixed with air a t room temperature and pressure, for various gas and vapor mixtures with air. At atmosit is found that mixtures containing less than about 5 per pheric pressure and room temperature the upper and lower cent methane will not burn. Compositions from 6 per cent limit mixtures of methane and air contain, respectively, 14.02 to 14 per cent burn when ignited, while those containing more and 5.24 per cent oxygen. At pressures below atmospheric than 14 per cent will not ignite. The composition containing the limits gradually narrow and meet a t about 9 per cent 6 per cent methane is known as the lower limit mixture. methane for a pressure of 140 mm. (20” (2.). At 10 atmosSimilarly the 14 per cent mixture is the upper limit mixture. pheres pressure the upper limit becomes 14 and the lower 6.5 When a limit mixture burns, part of the heat liberated by per cent, while a t 100 atmospheres the corresponding limits the burning of one layer of gas is used in heating the adjacent are 36 and 7 per cent. layer to the ignition temperature. The remainder of the Experiments on the effect of temperature a t low pressures heat is lost by radiation and conduction. It is therefore not have also been made (,9, 25, 38) with methane-air mixtures. The limits widen continually as the temperature is increased, 1 Received August 12, 1929.
I
1 T H E past much experi-
