I X D U S T R I A L A N D ENGINEERIXG C H E M I S T R Y
24
Vol. 18. s o . 1
Some Critical Constants of Furfural' By W. V. Evans and M. B. Aylesworth NORTHWESTERN U N I V E R S I T Y ,
EVANSTON, ILL.
OR ninety-five years furfuraldehyde,ordinarily abbrevi-
(160.5' to 160.7' a t 742 mm.), of BrUhll3 (161.4' to 161.8' ated as furfural, has been known to chemists; yet until at 754.5 mm.), and of Mains4 (161.7' at 760 mm.) seem to recent years it has not been available in any large quan- have been performed with any great degree of accuracy, tity. The cost of production has prevented a broad and it was thought of value to determine the boiling point of this thorough study of this compound. At the present time fur- furfural and see if the value of Mains could be checked. A fural is being produced at the rate of about a ton a day. 2-liter flask was charged with 1 liter of pure furfural and the Through the courtesy of the Miner Laboratories of Chicago thermometer set so that the bulb was completely covered by the writers have had at their disposal an unlimited supply of escaping vapor. The temperature was taken on a certified furfural and because of the abundance of the product at thermometer. The pressure as read on a calibrated baromtheir command they are able eter. The corrected atmosto purify it to a very high pheric pressure was 744.0 degree. I n view of this fact mm. The corrected value The values for the boiling point and refractive init seemed a favorable time of t h e t e m p e r a t u r e was dex of furfural have been redetermined on a specially to check some of the phys160.9' C. Using the value purified sample of furfural and found to be 161.7' C. ical constants of long stand0.05 degree for the change at 760 mm. and 1.52608 for the D line of sodium. These ing in the literature and to in boiling point per millivalues check the values of Mains for the boiling point do some new work. meter of pressure (the value and those of Bruhl for the refractive index. The constants investiobtained by Mains, as well The critical solution temperature curve for the sysgated w e r e t h e b o i l i n g as by the authors, from the tem furfural water has been determined. The curve point, refractive index, and vapor pressure curve in the is found to fit the curve of Mains but to disagree with the critical solution temperneighborhood of the boiling Rothmund's results. ature curve of the furfuralpoint) the writers obtained The critical solution temperature has been deterwater system. The new as the boiling point of furmined and found to be 120.9OC., whereas Rothmund work consisted of taking the fural 161.7' C. at 760 mm. found 122.7' C. v a p o r pressure curve of It might be added here that The critical solution concentration was found to be furfural. by dividing the absolute 50.7 per cent furfural, whereas Rothmund found 51 boiling point by 8500, which per cent. preparation of Pure is an empirical rule, we obFurfural The vapor pressure curve for furfural has been detertain 0.051 degree as the mined from 40" C. to 170.6'C., or from a pressure of change in boiling point with The pure furfural used in 8 to 966 mm. pressure. this work was prepared from If we calculate this value technical furfural in the folfrom the Clausius-Clapeylowing manner: S o d i u m carbonate, amounting to 7 per cent by weight of the tech: ron equation, using the value 107.91 calories as the latent nical furfural, was added and the mixture distilled over an heat of vaporization found by Matthews16we obtain the oil bath. The distillate was collected over a 3-degree range. value 0.048' C. This value, 161.7' a t 760 mm., is in agreeAbout 60 per cent (estimated) of the original amount came ment with Mains' value for the boiling point. At another time the corrected pressure was 755.1 mm. and over a t this temperature. The liquor was distilled again, using 2 per cent sodium carbonate. The distillate was col- the corrected temperature 161.4' C. From the equation lected over a 1-degree range, from 158.4' to 159.4' C. (un- (760 - 755.1) X 0.05 the boilingpoint is 161.65'C. a t 760mm. corrected). ,The purpose of the sodium carbonate was to Refractive Index neutralize traces of pyromucic acid. The third distillaThe refractive index of this sample of furfural was detertion was carried on slowly and the distillate collected at mined on a Pulfrich refractometer, using all precautions to 159.3' C. (uncorrected). One liter of this constant-boiling furfural was placed in a insure purity and proper temperature control, since this is round-bottom Pyrex flask to which a fractionating column the largest source of error. The prism was hydraulically was attached, and distilled i n vacuo a t a pressure of 6 mm. connected to a thermostat whose temperature was kept at The almost colorless liquid was condensed and by the use of 20.0' C. The sodium flame was kept in an adjoining room a five-way distributing receiver collected in different contain- and the light introduced through a n orifice. The temperaers without breaking the vacuum. The distillate of least color ture of the liquid was taken before and after reading with a coming over at constant temperature was chosen as pure fur- short bulb thermometer. The temperature of the room was fural. However, to insure its purity further, the clear liquid approximately 20" C. Hence, by proper control the rewas once more distilled and kept in sealed, dark brown fractive index could be taken when the room, the prism, bottles. Whenever the furfural was allowed to stand more and the liquid were all at 20" C. This was done and the refractive index of furfural at this temperature for the D line than 3 days it was redistilled before using. was 1.52608, which figure is in exact agreement with that Boiling Point obtained by Briihl.3 This value was checked twice and T h e boiling points of furfural previously given in the lit- finally accepted as the refractive index. mature rangeTrom 160" to 168' C. Since only those of Schiff2 I Ann., 3911, 7 (1886).
F
1 Received August 3, 1925. , A n n . , 330, 103 (1883).
4
6
Chcm. Me:. Eng., 36, 779 (1922). Getman, J . Phys. Chcm., 29, 395 (1925).
INDUSTRIAL A N D ENGINE%RING CHEMISTRY
January, 1926
Critical Solution Temperature Curve for Furfural-Water System
RothmundG has studied the mutual solubilities of furfural and water in relation to their critical solution point. Since no data on the purity of the original furfural are given, it was thought useful to determine this curve with what was considered a pure sample of furfural. Mains4has determined this curve, but only to the boiling point of water-furfural mixtures. The method used in this determination was largely the same as Rothmund's. A Pyrex test tube of the mixture, of known amounts of furfural and water, was sealed and heated in a bath. The temperature at which the two layers disappeared was recorded and when cooled the temperature at which the two liquid phases appeared was also recorded. The mean of these two temperatures was taken as the solution temperature of that particular tube. By using a series of such tubes, in which ratio of furfural to water was changed, a series of temperatures was obtained. These temperatures were plotted against concentration and a curve obtained from this series of points. The test tubes used in the determination had a volume of about 25 cc. The clean dry tubes were heated in an oxygen flame about 3 cm. from the open end and drawn down until a small opening, about 3 mm. in diameter remained for the introduction of the liquid. The method of filling consisted of drawing out delivery pipets into capillaries about 1 mm. in diameter and 3 mm. in length. The pipets were fitted vertically by means of clamps and so adjusted that they could be raised or lowered. By this construction the tip of the pipet could be lowered into a test tube, the liquid released, and the pipet raised without touching the inside of the narrow opening of the test tube. This greatly reduced the chance of escape of the
. ...*
*"*I
.
*.I
L
"1
D
la-,
h
.t
70
30
f'
10
e 0
'
1
I
10
20
30
Figure 1-Curve
i
I
40
SO
) 60
I
j
70
&
I
1
YO
/oo
P€R CENT FURfURAL for Solution Temperature of FurfuralWater System
liquid by evaporation when the tube was finally sealed. Definite quantities of the liquids were introduced into the tubes by weighing a tube before and after the admission of each liquid. The tube was then sealed in an oxygen flame and weighed again to detect any loss by evaporation. I n no case was there more than 2 mg. loss due to evaporation. The tube was then introduced into a bath and thoroughly shaken during heating. Z. physik. Chcm., 86,
454 (1898).
25
The glycerol bath used in the determination was rapidly stirred and the temperature controlled so that the bath could be held constant for as much as 10 minutes or heated as slowly as desired. Certified thermometers were used in t h e experiment. Two strong electric lights were placed behind the bath so that a very clear view of the tube and contents was possible a t all times. I n making a n observation a prescribed method was followed. The tube was placed in the bath and heated slowly until the contents of the tube appeared as one phase. The bath was then allowed to cool until the turbidity that accompanies the dissolution appeared. This practice served a twofold purpose: first, i t gave the approximate temperature necessary to cause a homogeneous solution; second, it tested the strength of the sealed tube, if the temperature was above the boiling point of the mixture. The bath was once more heated very slowly until with vigorous shaking the liquid cleared. The temperature was recorded and the bath cooled slowly. The temperature at which the first sign of immiscibility appeared was recorded. This procedure was repeated until the two temperatures were very close together and could be duplicated any number of times. The mean of these two temperatures was taken as the solution temperature for that particular tube. Mention should be made of the form this turbidity took at different concentrations. Three typical forms describe this behavior. When the concentration of furfural was about 10 per cent, the appearance and disappearance of turbidity were extremely hard to discern. Very fine particles could be seen with the naked eye, and as the temperature gradually increased it was necessary to use a very strong lens in order to see the particles and observe their behavior. Between 2 and 4 hours' observation was required before results were obtained that would check. Constant shaking between readings was also necessary a t all times. When the furfural and water were present in nearly equal proportions the transition was very abrupt. During heating the turbidity would gradually wane and suddenly disappear, while during cooling a dense cloud would form suddenly. When, however, the mixture was rich in furfural an entirely different behavior was noted. There was no real turbidity. During rising temperature the last particles of water would remain as visible particles on the sides of the tube. With constant shaking these particles nyould dissolve slowly, leaving a homogeneous phase. Upon cooling there was no turbidity, for the water that came out of the solution would adhere as tiny droplets to the side of the tube. When the temperature was raised or lowered the accurate consistency of this behavior was remarkable, for the two temperatures required did not differ by more than 0.2 or 0.3 degree. I n general, then, the behavior inside the tube could be anticipated by merely noting the concentration, for any behavior was a modification of the two extreme types mentioned above. About twenty-five observation tubes were used in determining the curve. Table I shows the data obtained and gives the percentage of furfural in each tube, the temperature of appearing and disappearing of two phases, and the mean temperature. Figure 1 gives the curve obtained by plotting the mean temperature against concentration. The values obtained by Rothmund and the values obtained by Mains are also given here for comparison. Rothmund's curve is higher than the curve obtained by the authors; his critical point is almost 2 degrees higher; and his critical solution concentration differs by 0.6 per cent from that of the authors. On the right-hand side of the diagram, however, Rothmund's curve fits into this new curve. The authors' curve, it may be noted, fits exactly into the curve obtained by Mains by an entirely different method.
INDUSTRIAL A N D ENGINEERING CHEMISTRY
26 Table I Furfural Per cent 47.37 50.54 48.98 50.69 27.84 72.19 65.03 83.03 88.79 91.83 56.34 33.77 9.82 22.39 50.30 20.75 9.03 15.04 94.9 50.4
c.-
Mean 120.8 120.9 120.85 120.85 113.1 115.1 119.15 95* 95 73.6 53.35 120.5 117.9 53.1 106.1 120.9 102.8 39.5 85.8 27.85
120.0
The graph of the curve represents the solubility of the furfural-water system. The highest point of this curve comes a t 120.9” C . and the critical solution concentration is 50.7 per cent furfural. It is interesting to note the flatness of the curve a t the higher temperatures. Table I1 CENT FURFURALFurfural layer Observed CI c2 C1 2 92.2 50.7 90.9 50.7 89.1 50.65 87.2 50.65 84.9 50.7 81.8 50.7 76.5 50.75 61.0 50.75 50.7
Temgerature C.
Water layer
T
c1
50 60 70 80 90
9.2 10.5 12.2 14.1 16.5 19.6 25.0 40.5
100
110 120 120.9
-PER
+
Table I1 gives the temperatures and concentrations taken from the graph, and when the law of rectilinear diameters of Cailletet and Mathias is applied it is found to hold excellently. The equation is 2
= A +BT
Rothmund found the constant B to be zero. Precisely, it results from his work as - 0.003, which of course may be considered zero. His value for A is 50.9. The mean value of A when calculated according to the formula from his work is 51.3, and he gives for his critical solution vaIue, which should be 51.3, the value 51. The writers’ mean value for B is - 0.00071, which is much nearer an actual zero value than 0.003. The writers’ mean value of A , calculated from their work, is 50.80, and their experimental mean value is 50.7. The difference between their lowest and highest values for B is 0.01, while Rothmund’s value for B showed a variation of 0.025. Also, Rothmund’s experimental value of A showed greater variation from the mean value of A than the authors’, Rothmund’s value of A varies from 52.55 to 49.80, a variation of 2.75. The authors’ value for A is from 51.20 to 50.65, a variation of 0.55. Rothmund obtained a critical solution temperature of 122.7” C. and a critical solution concentration of 51 per cent furfural. Near the top of his curve the points are few, too few to determine the nature of the curve near the critical solution temperature. One point, which is above the curve, indicates the highest temperature reached and yet is a considerable distance from the critical solution concentration. Apparently, the critical solution temperature was found by interpolation over a considerable range. This method would not reveal flatness, often found near the critical solution temperature on such curves. Also, it is graphically impossible to locate the points just mentioned on a smooth curve. Furthermore, Rothmund submitted no other constant by which the liquid he used could subsequently be identified aa pure furfural. His values of TI and TZvary
Vol. 18, No. 1
by as much as 1 degree, while the writers’ values differ at most by 0.4 degree. Rothmund’s method was very similar to that used by the writers with one exception. He retained the long capillary at the end of his tube. This might possibly interfere with a thorough mixing, but would not account for the high temperature. His idea was to decrease the size of the air space above his liquid. Yet a calculation will show that a volume of air equal to the volume of the liquid will not seriously change the concentration of either liquid phase. The evaporation of the two liquids will in part compensate for any change in concentration. Also, a change due to this source would merely affect the shape of the curve and would not prevent obtaining the highest temperature value. On the other hand, a tube practically full of furfural will prevent a shaking of the liquid and so the obtaining of true solubility-which the writers found to be the chief source of error. Mains4 has published data for the mutual solubility of the furfural and water system. His method consisted of holding the temperature constant and shaking the mixture of the two liquids and analyzing the two layers. His curve does not include points above the boiling point of his system. Vapor Pressure Curve for Furfural An apparatus was set up for vacuum distillation, as described in the purification process. The following modification was used, however: The Hyvac pump was connected to a 10-liter bottle by a tube through one hole of a three-hole stopper. I n the second hole a tube equipped with an external stopcock was sealed. A glass tube ran from the third hole of the stopper to a T-tube, one fork of which went to the mercury manometer. The manometer was 5 mm. in diameter and was half filled with purified mercury. This construction would register pressures from 1 to 1500 mm., for the mer-
-‘I
Pf
wo
* . m*I
0
B
P
b
,
o
20
40
60
go
/eo
/zo
T€M P€RA TUP€
(40 /60
- “6.
/a0
Figure %Vapor Pressure Curve of Furfural
cury could either be drawn up one side of the manometer by suction or could be forced up the other side by pressure. The lower pressures were controlled by the use of the vacuum pump in conjunction with the variable intake of the stopcock. The high pressures were obtained by forcing compressed air into the bottle through the stopcock and when the desired pressure was obtained the stopcock could be closed. During the distillation this large bottle served as a cushion, or in other words, as an agent to damp out small
INDUSTRIAL AND ENGINEERING CHEMISTRY
January, 1926
fluctuations in pressure. The temperatures were read from 0.1 degree thermometers that were checked against the two certified thermometers previously mentioned. The initial temperature was taken at atmospheric pressure to make sure the liquid was constantly boiling. Temperature
160.9 159.0
140.2 131.6 92.3
Table I11 Pressure Temperature Mm. Hg c. 744 120.3 707 163.8 411 170.6 310 39.9 69 154.4
Pressure
Mm. Hg 214 812 966 8 625
Table I11 gives the corrected temperature and pressure recorded.
27
Figure 2 shows the graph obtained by plotting temperature against pressure. It is interesting to note that dp/dt is approximately constant for a large region in the neighborhood of the boiling point. From the table the change in temperature for a change in pressure of 1 mm. is 0.05 degree in the boiling point region. This value is obtained also from the Clausius-Clapeyron equation, as previously stated. Getmans found the association constant of furfural to be 1.11 to 1.14. I n the upper regions of the curve no difficulty was experienced; but in the extreme lower part of the curve temperature fluctuations of 0.5 to 1 degree were encountered. An inspection of the graph will show that this fluctuation might be expected in this part of the curve.
Amounts of Soap and Builder Necessary to Soften Water of Different Degrees of Hardness' By H. B. Robbins, H. J. MacMillan, and L. W. Bosart THEPROWER& GAMBLE Co., IVORYDALE, OHIO
sen because it is a fair averThe cost of softening water with a built soap in which age temperature of the varithe question frequently soda ash is the builder is practically independent of the ous suds operations in a steam arises as to the most ecoproportion of builder which the soap contains. laundry and is approximately nomical of different methods The tests indicate that in laundry practice where the temperature employed in of procedure in the use of dehard water is used it is uneconomical to use soap alone home washing processes. tergents, e s pe cia11 y w h e n or soap and builder together as a softener. For maxiDetergent solutions were hard water is used; for exmum economy soda ash should first be added with made up using powdered soap ample, whether it is more agitation, allowing it a little time to react with the with commercial soda ash as economical to use a pure soap water before adding the soap. the builder and with distilled or a soap containing a builder The amount of soda ash to add for waters of different water as the solvent. The such as sodium carbonate, or, degrees of hardness in order to arrive at the minimum soap was a very pure tallow if both soap and builder are cost for producing suds is shown. With water of zero soap containing 95 per cent used, whether it is more ecohardness there is no practical difference in the cost of of anhydrous soap and about nomical to use them together treatment whether a built soap is used or the soda ash 2 per cent of electrolytes and or to add first a c e r t a i n is added first and then the soap. glycerol, which occur in all amount of builder for the sake commercial soaps, the reof its softening effect on the water and thegfinish the softening with the soap. To answer mainder being water. The soda ash was the ordinary commercial grade containing about 99 per cent anhydrous sothese questions this work was undertaken. I n the tests that follow, the hardness will be expressed in dium carbonate. These same detergents were used in all the grains of calcium carbonate per U. S. gallon. I n the case of tests. magnesium, its equivalent in terms of calcium carbonate will The costs were figured throughout on a basis of 10 cents a be used. Hardness figures are those determined by alcoholic pound for soap containing 95 per cent anhydrous soap and soap solution standardized against calcium carbonate or, more 1.5 cents a pound for soda ash. At the time of writing, prices literally, against the calcium chloride equivalent of calcium are somewhat higher than these figures. The ratio of the carbonate. present costs of soap and builder is approximately the same, With the exception of the waters described in Part 11, however. It seemed advantageous to use decimal cost figall the hard water was prepared in the laboratory by adding ures for this work, since it would facilitate any calculation to calcium and magnesium chlorides to distilled water in such current prices. proportion that two-thirds of the hardness was due to calPart I-Laboratory Scale Experiments cium and one-third (expressed in CaC03 equivalents) was due to magnesium. This ratio is the average taken from analyses . The composition of the detergent solutions is shown in of water from all parts of the United States. Table I. The method for determining hardness is in accord with Table I-Composition of Detergent Solutions that recommended by the American Public Health Associa(1 gramaf detergent materia1 in 100 cc. of solution) Soap Soda ash tion.2 I n determining hardness by means of alcoholic soap Solution Gram Gram solution, the hard waters were diluted to less than 5 grains 1 1.00 0.25 2 0.75 per gallon, as recommended. I n the softening operations 0.50 3 0.50 with soap and builder, or soap alone, however, the hard waters 4 0.25 0.75 were used without dilution, so as to obtain conditions comThe hard waters were titrated with the detergent solutions parable with those found in a laundry using hard water. All tests were made at 130' F. This temperature was cho- in the following manner:
N LAUNDRY practice
I
1
t
Received August 4, 1925. Standard Methods of Water Analysis, 1920, p. 31.
Fifty cubic centimeters of hard water were placed in a narrowmouth, 6-ounce bottle for titration with the detergent solution.
