December, 1933
INDUSTRIAL A S D ESGINEERING
when one-quarter full, will have a cross section of 0.25 and a wetted perimeter of 1.5, making the equivalent diameter 0.67 inch. 2. Calculate the actual velocity. If this i j not given directly in the statement of the problem, it can be most readily calculated thus : u = 40 M / p A u = 40 V / A
3. Calculate AI‘ by means of Equations 2c, ;3c, 5c, or 6c, using the equivalent diameter and actual velocity. VISCOSITY. I n all the above equations, viscosity is expressed in centipoises, as most data in the literature are generally given in terms of poises or centipoises (the centimeter-gram-second unit). Petroleum products are a common exception to this statement, the viscosity being generally expressed in the arbitrary units of commercial viscometers. Such data can be converted to kinematic viscosity by Herschel’s chart ( 2 ) , and then to centipoises by multiplying by one hundred times the specific gravity. I n stream-line flow, pressure drop is directly proportional to viscosity, but diameter to give a stated pressure drop varies as the fourth root of the viscosity. I n turbulent flow, pressure drop is proportional only to the fourth t o fifth root of viscosity, and diameter to give a stated pressure drop varies as about the ninth root of viscosity. Because of this widely varying importance of viscosity the required accuracy of the data will vary. In some cases, a fair guess is enough, in others, the best available data should be used. CONVERSION FACTORS. Frequently required conversion factors are:
CHEMISTRY
1319
M = p V AH
1 gal. of water/min.
= 144 A = 0.5 M
(17)
Pfo
(18)
I .
(igaj
500 lb./hr. 1-in. head of water = 0.0362 lb./s . in. 1-in. head of mercury = 0.491a 1b.qsq. in.
(19b) (20) (21)
=
Multiplied by 12.6/13.6 if both limbs of the mercury are submerged in water.
Conversion factors to obtain consistent units in the footpound-second system are given in Table 11. TABLE11. CONVERSION FACTORS TO OBTAIN CONSISTENT UNITE SYMBOLOF UKIT A d
f Q AH
L
MULTIPLY BY: 1/144 1/12 0.00750
S s > i B o L OF
UNIT
.M P
MULTIPLY BT: 1/3.6 144
L!P R
144 4960.3
1
T
1 1
U
1 1
V
1/3.6 0.000672 1
ACKROWLEDQMENT The temperature change of a gas flowing in a conduit was pointed out and calculated by E, F. von Wettberg. A careful check on all the equations was made by H. G. Hyland. LITERATURE CITED (1) (2) (3) (4) (5) (6)
Furnas, C. C., Bur. Mines, Bull. 307, 126 (1929). International Critical Tables, Vol. I, p. 33, McGraw-Hill, 1926. Keevil and McAdanis, Chem. & M e t . Eng., 36,464 (1929). Swindin, N., “Flow of Liquid Chemicals in Pipes,’’ Benn, 1922. Trinks, “Industrial Furnaces,” Vol. I, p. 262, W h y , 1926. Wilson, McAdams, and Seltzer, J. IXD. ENQ. C H ~ M .14, , 105 (1922).
RECEIVED August 5 , 1933.
Sulfur Forms in Crude Viscose Rayon Yarn PHILIPC. SCHERER, JR., The Virginia Polytechnic Institute, Blacksburg, Va.
D
URING manufacture of rayon by the viscose process a certain quantity of sulfur or sulfur ccimpounda is deposited in the crude viscose filament. Since such sulfur content detracts from the clarity and dyeing properties of the product, a desulfurizing step must be used to remove such sulfur content. This treatment has been empirically developed, but little attention has been paid to the manner of combination of sulfur in the rayon. In order to obtain a clear picture of the problem, certain speculations as to the nature of the changes and reactions occurring during the formation of the rayon filament may prove of value. During the spinning, viscose is extruded from the very small spinneret opening into an acid bath. At the instant of contact with the acid the outer portion of the viscose is regenerated into a thin skin of cellulose which acts as a membrane separating a core of unregenerated viscose from the acid bath. Further regeneration of the viscose proceeds by the osmotic passage of the bath acid through the membrane and takes place wholly within the first formed outer skin or shell of the filament. During such regeneration it may be assumed that the reaction between the acid and the viscose results in the production of the following compounds : cellulose, hydrogen suliide, sodium sulfide, sodium thiocarbonates of various compositions, sodium sulfate, and colloidal sulfur; and, when the regeneration is not
complete, some cellulose xanthate remains. It is also possible that any or all of these products might react with the newly regenerated cellulose to form organic sulfur compounds or complexes. There is also the possibility that the sulfuric acid of the bath might also react with the cellulose. We may therefore assume that the rayon on the spool probably contains the above possible forms of sulfur. The wet spool is next placed in a washing machine and pure water circulated through the threads until no more salts or acids are detectable. Since such washing occurs by osmotic passage of the salts through the cellulose membrane into the water, it is apparent that water-soluble salts would largely be eliminated by such a process. The possible sulfur compounds present may then be considered to be slight traces of sodium sulfide which may be adsorbed on the cellulose owing to its alkaline nature, sodium thiocarbonates, colloidal sulfur, which could not pass the membrane, and various unknown organic sulfur compounds or complexes. During the drying process which usually follows, it is possible that any inorganic sulfur products still remaining may react with cellulose to form organic sulfur compounds of an unknown nature. The crude dry rayon yarn may then be assumed to have present a mixture of colloidal free sulfur and organic sulfur derivatives of unknown nature. Organic sulfur derivatives prepared from cellulose are
I N D U ST R I A L A N D E N G I N E E R I NG C H E M I ST R Y
1320
VOl. 25, No. 1 2
If n-e omit from the average the results grouped under I11 in which long times were used and those under I1 in which excessive concentrations of alkalies were used, it is apparent that treatment by a large number of varied reagents removes in 10 seconds an average of about half of the total sulfur present. This would indicate that there might be a t least DETERMINATION OF SULFURFORM two kinds of sulfur present, one removable by aqueous soluExperiments were run in an effort to obtain some informa- tion regardless of the type of solution used and the second tion as t o the form in TThich sulfur exists in rayon. One series removable only under special conditions of reagent and temof experiments (B) studied the action of various reagents perature. The experiments grouped under I11 indicate that upon the sulfur content of rayon. This series shows that this last form of sulfur is removed by a hydrolytic reaction there are apparently two general types of sulfur present. which is retarded by the presence of acids and hastened by The first of these is a sulfur comibnation which may be readily that of alkalies. Analytical methods of separation were next attempted and a removed by any aqueous solution and even by cold water. There is, however, a second type of sulfur combination present rough separation into three types of sulfur compounds was which may only be removed by hot alkaline solution. This made. Total sulfur is defined as all the sulfur present in the indicates that the last portion requires a hydrolysis of some compound regardless of its combined form. Free sulfur is union between sulfur and some other radical before removal that sulfur which can be extracted with 0.5 per cent caustic may occur. Before considering the individual experiments, soda solution and which upon acidification yields hydrogen it may be well to show the speed with which rayon sulfur sulfide subsequently determined by any of the usual methods. may be removed by efficient desulfurizing agents. This is The difference between the free sulfur and the total sulfur is indicated in series A (Table I) in which small skeins of known combined sulfur. Under total sulfur are determined all sulfur content were dipped into the indicated solutions for the sulfate, sulfite, thiosulfate, sulfide, sulfur, and organic sulfur compounds present. Under free sulfur are determined any given time and then analyzed for total sulfur content. sulfides, sulfur, and a portion of the organic sulfur comOF DESULFCRIZATION TABLEI. SERIESA, RAPIDITY pounds present. The combined sulfur then would give TOTALSULFUR theoretically any sulfur in the form of sulfate or other oxides REAQENTTIM= T ~ M P . Original Final of sulfur, either in inorganic or organic combination. See. C. % % 0.71 3 80 None With this in mind, certain other experiments were run. Trace 0.40 3 80 Trace 3 80 0.76 In series C (Table 111) samples of rayon of known sulfur 0.02 0.36 80 1 content were treated as indicated and the remaining sulfur 0.07 0.44 80 30 0.13 0.44 10 80 determined analytically in the three forms. 0.71 None 3 80
usually highly colored as is instanced by the preparation of a sulfur black from cellulose waste and sodium sulfide by fusion. The coloring matter in crude rayon which makes necessary the subsequent bleaching step may be of this nature.
--
I n the experiments given under series B (Table 11) small skeins of rayon of known sulfur content were treated as indicated, and the amount of sulfur remaining was determined analytically. TABLE11. SERIES B, ACTION O F CHEMICALS ON SULFUR CONTENT OF RAYON -SULFUR--? GROUP -.--R~AGENT--I
% I
I1
0 . 1 NaOH 0.2 0.3 0.5 2 NazSOa 5 10
I11 0.02 0.02 0.02 0.02 0.02 0.02
IV
V VI
Water Water Water Acetic acid Acetic acid Acetic acid NazCOa NarCOa NazCOs
2 Oxalic acid 1 Hydroquinone 1 Hydroquinone
10 NasPO4 10 Narc03
TEMP. C. 80 80 80 80 80 80 80
TIME
Original OrigiRerenal maining maining"
%
%
%
10 10 10 10
0.51 0.51 0.51 0.51
0.36 0.33 0.33 0.28
70.6 64.7 62.7 54.9
10 10 10
0.51 0.51 0.51
Trace Trace Trace
None None None
15 min. 30 min. 60 min. 15 min. 30 min. 60 min. 15 min. 30 min. 60 min.
0.43 0.43 0.43 0.43 0.43 0.43 0.43 0.43 0.43
0.20 0.16 0.08 0.31 0.1s 0.17 None 0.01 0.03
80 80
80
10 10 15min.
0.51 0.51 0.51
0.43 0.30 0.34
84.3 58.8 66.6
80 80
10 10
0.51 0.51
0.36 0.38
70.6 74.5
80 80 SO 80
100 100
100 100 100 100 100 100 100
Sec.
.. .. .. .. .. .. .. ..
..
SO
10 10 10 10 10 10
50 Glycerol 75 Glycerol
105 115
10 10
0.43 0.43
0.19 0.24
44.2 55.9
2 8 NHiOH
15
10
0.43
0.21
48.8
Ca(0H)r satd. 3 Ba(0H)z 3 (NHdZCOa 3 Bas 1 KOH 16nCIr
so
56.8 Av. %- original sulfur remaining after treatment a This column gives the percentage of the origjnal percentage of sulfur which remains in the yarn after treatment. Thus in the first experiment of Froup I 0.36 per cent sulfur remains o u t of an original of 0.51 per cent. "this in 'therefore 70.6 per cent of the total sulfur originally in the yarn.
TABLE111. SERIESC, ASALYTICALMETHODSOF SEPARATING SULFUR YREAGEXT-
TEMP.
c.
%
...
...
None Water Water Benzene Acetic acid in alcohol 2 HISO, 2 HC1 1 NazS
100 20 80 80 40 40 80
i
TIME Min.
..
15 30 15 15 5 5
15
-SULFUR Total
-
Free Combined
%
%
%
0.88 0.49 0.78 0.81 0.39 0.70 0.62 None
0.27 0.18 0.26 0.25 0.22 0.25 0.24 None
0.61 0.31 0.52 0.56 0.17 0.45 0.38 None
In series C, although the total sulfur is somewhat reduced in the experiments, this reduction takes place almost entirely in the combined sulfur and the free sulfur is little affected by the reagents used. Calculation of the results shows that an average of 86.6 per cent of original free sulfur remains after treatment. This would indicate that the free sulfur is in a form difficult to remove by any except hot alkaline reagents as already indicated above. I n series D (Table IV) rayon yarns of known sulfur content were extracted in a Soxhlet extractor for 2-hour periods as indicated and then analyzed for sulfur remaining. TABLEIv.
SERIES
REAGENT None Water Alcohol Benzene
D,
SULFUR SEPARATION IN SOXHLET EXTRACTOR
FREES %
COVBINED
% 0.40 Trace 0.20 0.27
0.13 Trace 0.08 0.12
0.27 None 0.12 0.15
TOTAL
%
I n series D, again it is apparent that the removal of the free sulfur is definitely a hydrolytic process in that water will completely remove it whereas alcohol and benzene remove very little. DISCUSSION OF RESULTS I n the earlier consideration of the various steps during the Spinning of rayon, it was pointed out that the tota1 sulfur
December, 1933
INDUSTRIAL AND ESGISEERING CHEMISTRY
present may be, owing to an efficient washing step, restricted to any colloidal occluded sulfur and to sulfur which may be in combination with the cellulose present. Consideration of the analytical methods and their results indicate that such sulfur is of two types. One of these, the free sulfur, must then be in the form of organic sulfides or of occluded colloidal sulfur in order to give hydrogen sulfide upon analysis. It is difficult to understand why, if this were in the form of colloidal sulfur, it was not completely extracted by benzene in series C and D but was completely extracted by water. If in the form of organic sulfides, it might well be hydrolyzed to soluble compounds by water and yet remain insoluble in benzene. It is indicated then that the free sulfur probably consists of sulfide compounds with cellulose or cellulose residues. I n the same way the combined sulfur may be compounds of the higher oxides of sulfur with cellulose--for example,
1321
the sulfate, formed by the direct action of residual spin bath acid. Sulfates of cellulose are, in general, quite soluble in water or are a t least readily hydrolyzed thereby. It would be difficult to account for the fact that benzene would extract half of the total combined sulfur if it were in the form of adsorbed inorganic salts.
CONCLUSION The general picture derivable from the results obtained is that there is a portion of the sulfur present in some form readily removed by almost any aqueous solution. The best guess as to the form of this is that of easily hydrolyzable or water-soluble sulfates of organic residues. The residue, which is more difficult to remove, is assumed to be in the form of some sulfide combination with cellulose. RECEIVED July 27, 1933.
Volatilization of Fluorine in Manufacture of Phosphorus and Phosphoric Acid by Furnace Processes D. S. REYNOLDSAND K. D. JACOB, Bureau of Chemistry and Soils, Washington, D. C. HOSPHATE rock is the principal source of the fluosilicates-chiefly the barium, magnesium, and sodium salts-used for various agricultural, industrial, and technical purposes, such as the control of plant pests ( I ) , the moth-proofing of fabrics ( I d ) , the preservation and hardening of cement and concrete ( 7 ) ,the treatment of rubber latex (4), the manufacture of glass (19) and enamels (20), the electrolytic refining of lead (6) and antimony (RZ),and laundry purposes (24). The commercial grades of domestic phosphate rock usually contain approximately 3.3 to 3.9 per cent fluorine (8, 10, 13, 1'9, and the average fluorine content of all phosphate rock produced in this country at present is probably close to 3.7 per cent. In the manufacture of ordinary superphosphate approximately 25 per cent of the fluorine in the phosphate rock, equivalent to about 20 pounds of fluorine per long ton of rock, is volatilized ( I O ) , principally as silicon 1etrafluoride, and the greater portion can be recovered in the form of hydrofluosilicic acid by washing the gases with water. I n normal years of fertilizer production approximately 20,000 short tons of fluorine are volatilized in the manufacture of superphosphate in the United States. However, only a portion of the total fluorine volatili,zed is recovered, the majority of the plants allowing it to go to waste. I n recent years furnace methods for the production of high-grade phosphoric acid (5, 12, 23) have comc into prominence in this country, and it is anticipated that these methods will play an important part in the future phosphate fertilizer industry. Klugh (12) states that the fluorine volatilized from phosphate rock during the electric furnace manufacture of phosphoric acid has a very strong corrosive effect on all refractories commonly used in building conduits for handling the hot furnace gases, and it is known that a certain amount of fluorine, principally in the form of silicon tetrafluoride, escapes from the Cottrell precipitators used for the recovery of the phosphoric acid. Data on the quantity of fluorine volatilized in the manufacture of phosphorus and phosphoric
acid by furnace processes are of interest from the standpoint of furnace operation and also in connection with the possible recovery of fluorine compounds from the furnace gases. Inasmuch as such data were not available in the literature, several experiments and analyses were made to obtain information on the subject. TABLEI. VOLATILIZATIOS OF FLUORISE FROM SMALL MIXTURES OF FLORIDA LAKD-PEBBLE PHOSPHATE, CARBON, AND SILICA (Mixtures heated f o r 0.5 hour in a graphite tube furnace in a n atmosphere of dry nitrogen) COMPOSITION O F X f I X T T R E TEMP. F \'OLATILIZED P VOLATILIZED 8.5 grams phosphate rock,b 1.5 gram8 carbon
5.95 grams phosphate rock, 2.55 grams silica,C 1.5 grams carbon
c.
%"
%"
1100
6.6
6.8
1300
14.3
49.1
1300
16.3
96.2
1400
9.7
98.8
a Percentage of total in original phosphate rock. b Containing 3.87 per cent fluorine, 8.98 per cent total silica, and 31.62 per cent PnOn. c I n addition to the silica present in the phosphate rock.
EXPERIMENTS IS LABORATORY FURNACE I n these experiments 10-gram mixtures of 200-mesh Florida land-pebble phosphate and carbon, and of pebble phosphate, carbon, and silica (quartz) were heated in an atmosphere of dry nitrogen for 0.5 hour in the graphite-tube resistance furnace previously described (3, 9 ) . The volatilization of fluorine was determined from the total fluorine content of the residue as compared with that of the original charge. The fluorine content of the phosphate rock, and also that of the other phosphate rocks and the sintered phosphate matrix discussed elsem-here in this paper, was determined by the TTillard and Winter method (25, 26). This method may give low results, however, when used on slags containing acid-decomposable silicates. Consequently, all
