700
I N D U S T R I A L A N D ENGINEERING CHEMISTRY
require no heat treatment following the completion of the fabricating operations, nor do these properties change with time due to age-hardening. A true appreciation of the characteristics of magnesium alloys and their suitability for aircraft and other work requiring maximum strength and endurance with a minimum of weight is obtained when their properties are compared with those of other commercial metals. (Tables IV and V) Table IV shows the property data as ordinarily expressedt h a t is, in terms of pounds per square inch. Heat-treated Dowmetal castings are thus seen to be equal to the highstrength heat-treated aluminum-alloy castings, rolume for volume. Wrought Dowmetal has approximately the same fatigue endurance limit as duralumin, but somewhat lower tensile properties. The real advantages to be gained by the use of these ultra-light magnesium alloys in place of the heavier metals are shown in Table V where a comparison is made from the standpoint of equal weights of the various metals. I n this case the cross-sectional area of the aluminum and magnesium parts have been increased until they weigh the same as the steel section. On this basis Dowmetal castings are decidedly superior to aluminum-alloy castings, while wrought Dowmetal is superior to both duralumin and steel. The possibilities in the practical application of magnesium
Vol. 22, No. 7
alloys are just becoming apparent. A few years ago they were scarcely known to industry. Today they are available in most forms required by the designing engineer. Foundry technic, fabrication methods, and alloy compositions have been so perfected that construction parts made from magnesium alloys are recognized as having the properties and stability demanded of a modern ultra-light weight metal. Larger production and improvements in plant operation are lowering costs to the point where magnesium is now in competition with the heavier metals. It seems safe to predict that the day is not far distant when the magnesium industry will develop to an extent little dreamed of by those not acquainted with the properties of the metal. Literature Cited Abegg, Handbuch der anorganischen Chemie, Vol. 11, p. 34 (1905). Bunsen, Pogg. Ann., 92, 618 (1854). Bur. Mines, Mineral Resources, 1915 through 1928. Bussy, J. chim. med., 6, 141 (1830); Pogg. A n n . , 18, 140 (1830). Clarke, U . S . Geol. Survey, Bull. 695, 35 (1920). Clarke and Washington, Proc. Nut. Acud. Sci., 8, 108 (1922); Washington, A m . J . Sci., [5] 9, 351 (1925); Washington, Smithsonian Rept. 1920, p. 269. Deville and Caron, A n n . chim. phys., 67, 340 (1863). Gann and Winston, IND. ENG. CHEM.,19, 1193 (1927). Metnllborse, 19, 1604 (1929).
Evaporation of Caustic Soda to High Concentrations b y Means of Diphenyl Vapors' W. L. Badger, C. C. Monrad, and H. W. Diamond DEPARTMENT OF CHEMICAL ENGINEERING, UNIVERSITY OF MICHIGAN, ANN ARBOR,MICII.
The dehydration of caustic soda in a forced circulaconsidered an advantage, but tion evaporator has been accomplished in semi-plant a p p a r a t u s in which later developments indicated scale equipment using diphenyl vapor as a heating evaporation could be that the high freezing point of medium. The highest concentration obtained was carried out with high-temdiphenyl was also an advanslightly over 98 per cent NaOH. tage in some respects. h'aphperature vapors as a heating Heat-transfer coefficients for both condensing dimedium are so extensive and thalene was rejected partly phenyl and boiling caustic are reported. In all cases so obvious that no general because sufficient information the major resistance to heat flow was the film of cond i s c u s s i o n is n e c e s s a r y . was not available regarding densed diphenyl vapor. The diphenyl coefficient was During the winter of 1927-28 its stability and partly befound to increase with temperature difference and to it was decided to build an cause of its pronounced tendbe nearly independent of vapor temperature. exnerimental evanorator for ency to sublime. Dibenzyl study of s u c h p r o b l e m s . proved t o have very low This paper and one on the condensation of vapors by C. C. stability. The above information, together with the fact that hlonrad2 represent the first results of this investigation. diphenyl was made available in quantity by the Federal Phosphorus Company, who actively coiiperated through the Selection of Working Substance entire problem, placed the final decision on diphenyl. Considerable thought was given to the selection of a maConsiderable time was spent in determining the various terial that could be 'used as a high-temperature heating physical and thermal properties of diphenyl. Some demedium. ii substance with a high condensing temperature terminations were made, and some properties were cala t ordinary pressures was desired, since the temperature con- culated from various equations proposed in the literature. trol is easy if latent heat rather than sensible heat is trans- A very extensive investigation has been conducted by the ferred. There were available mercury, diphenyl, diphenyl Federal Phosphorus Company, and on the completion of oxide, naphthalene, and other hydrocarbons of high molecular their work all the data on the physical properties of weight. Mercury vapor was considered and discarded mainly diphenyl will be published. At present it is sufficient t o because of its poisonous nature and the difficulty of holding say that the boiling point of diphenyl a t atmospheric presit in experimental apparatus. The choice between diphenyl sure is 492" F. and at 140 pounds gage is 750" F. I t s latent and diphenyl oxide was not easy to make, but preliminary heat a t atmospheric pressure is 138, and a t 140 pounds gage information indicated that diphenyl oxide was not so stable is 97 B. t. u. per pound. The specific heat of the liquid as diphenyl. The low melting point of diphenyl oxide was varies between 0.4 and 0.6 in the temperature range of 200" to 700" F. I t s melting point is 156.6" F. 1 Received May 5,1930. Presented before the meeting of the American The first application that suggested itself was that of Institute of Chemical Engineers, Detroit, Mich , June 4 t o 6, 1930 dehydrating caustic soda with a view to eliminating the ex2 T o appear In a subsequent issue
HE possibilities of an
T
IND UXTRIAL AND ENGINEERING CHEMISTRY
July, 1930
701
A EVAPORATOR VAPCRHIAD
8 C D
D l P H E N n JACMET EVAFURATING TU8E
DIPHENYL VAPOR LINli
E
SURFACE CONDENSER
F
SURFACE CONDENSER DRIP TANKS
G
DlPHENYL MELTING TANKS
H 1 J
DIPHENYL HELTING T U 0 E S
K
GAS BURNER
VICTORS F O R PUMPS ELECTRIC HEATERS
L DIPHENYL CIRCULATING PUMP M DIPHENYL F L A W CHAMBER
N 0 P Q
DIPHENYL
DRIP RECEIVERS
ORlFICL P L A T E C l i Y I T l C CIRCULhTIH,; CAUSTIC STORAGE
PUMP
TAN6
3 ! D I P H E N n VENT LINES S DPMENYL DRIP RICEIVEQS EQUALIZER LINE T THERMOCOUPLES U DIPYENIL DRIP LlNE
v W
STEAM CWLS PUMP
CASING VfNT
/j
Figure 1-Experimental
Evaporator and Diphenyl Boiler
pensive and inefficient caustic pot. This paper reports the results obtained from this application. Apparatus
As there was no previous experience to act as a guide, it became necessary to design the apparatus on the basis of rather general considerations. Many difficulties were met and the apparatus had to be modified many times. I n the final form, however, most of the difficulties were eliminated, so that it is believed that the application of diphenyl to hightemperature evaporation is entirely practical. DIPHENYL BoILER-The diphenyl boiler used in the experiments is strictly a laboratory affair and does not correspond to the design of even small commercial units. The design was based on two conditions: first, that the apparatus should be as simple and as easy to assemble as possible; and second, that it should employ electrical heat if possible, because of ease and simplicity of control. The method adopted consisted essentially in pumping diphenyl through pipe containing electric heaters and allowing the mixture of vapor and liquid to escape tangentially into a flash chamber. The original boiler was later modified by adding gas heat to t h e outside of the circulating pipes. The diphenyl boiler is shown in Figure 1. It consists of a welded steel flash chamber, M, 20 inches in diameter by 48 inches high. From the bottom of this flash chamber liquid diphenyl was withdrawn by a 2-inch centrifugal pump. 1,. and pumped through two pieces of 2-inch extra heavy iron pipe, H , each about 70 inches long, connected with return bends as indicated. Into this pipe were inserted four 6-kilowatt Chromalox immersion heaters, J . From the end of this pipe the mixture of liquid and vapor was conducted by a tangential inlet into the flash chamber. Gas burners, K , were added below the two pieces of 2-inch pipe. The diphenyl
was melted in an external melting tank, G, with steam coils, V , and all vents, R , from all parts of the apparatus were conducted to this melting tank. The pump casing was vented to the top of the flash chamber by a separate r e n t line, W , independent of all other vents. E\ A P O R A T O R -el-aporator T~~ consisted of a single nickel inch i. d., inch o. d., and 12 feet long. I t was tube, C, surrounded by a jacket, B, of 3-inch extra heavy iron pipe. The nickel tube was originally rolled into steel tube sheets a t either end of this jacket, but it was found that the nickel was too soft to give a satisfactory grip, and short ferrules of monel metal were placed inside the tube a t the tube sheets to give additional strength to the joint. A ll/s-inch Kingsford pump, P , was located so that it discharged first through an orifice plate, 0 , and then into the bottom of the evaporator tube. The top of the evaporator tube was connected to a vapor head, A , originally made of 14-inch flanged iron pipe, but later of cast iron. The inlet for the vapor into the vapor head was tangential, and from the bottom of the vapor head the liquid was withdrawn to the circulating pump. From the top of the vapor head the vapors passed through a surface condenser. E , connected to a vacuum pump. It was thought a t one time that it would be desirable to operate the apparatus under a vacuum, but all the runs reported i n this paper were made with atmospheric pressure in the evaporator. The condensate from the surface condenser was collected in calibrated drip receivers, F. The feed solution n’as contained in a sheet-monel storage tank, 8. The diphenyl vapor was introduced into the top of t h e jacket around the evaporating tube by pipe D, and t h e condensate was withdrawn from t h e bottom of the jacket b y pipe I: and collected in drip receivers N. The drip tanks were welded steel vessels, 14 inches in diameter and 30 inches high,
July, 1930
703
ISDIISTRIAI, 4 X D ESGIA%ERISG CHE.1fIXTRY
pressures was iiied arid the couples found to be the sanie up to 700°F. It was not possihle to calibrate the other couples in place, but since they checked the calibrated couple within 1" F. a t all teinperatures, and since this calibrated couple 7%as rechecked occasionally in the laboratory arid fouiid to be constant, it is believed that all the readings rep x t e d in this paper are accurate to the = 1 F. hawe hit-iiaiiiely l I E C H i \ I C iL DIFFICCLTIES-In the caustic side of the system the difficultiec due to corrosion have already been m e n t i o n e d . The ube of nickel and nickel-cast i r m has apparently been satisfactory for the purposes of the laboratory up to the highebt concentrations reached-iiaqiely, 98 per cent KaOH. The iiickel parts appear to be unattacked. The nickel-cast-iron vapor head, the cast-.ron fittings, aiid tlie steel shaft of tlie circulating puiiip nere attacked. This attack was sufficient to discolor the cauqtic badly, but not sufficient to indicate an unduly short life of the parts The nickel-cast-iron casing and impeller on the circulating pump nere apparentlv unattacked after ahout a year s use The cast-iron Mereo cocks were a iource of some difficulty, ac they could he operated when hot but were practically iinpxsible to manipulate when cold. The only other m i m e of trouble oii the caustic side n as the packing in the circulating pump. The only packing which would withstand the action of hot coiicentrated cau+c n a s a laiiiinated copper packing, John Crane S o . 500. Kheii two rings of this were used, backed nit11 t n o or three rings of asbestos packing, no difficulty was experienced in keeping the stuffing box tight over long periods of time. On the diphenyl side the mechanical difficulties were not bo great as had been expected. I t was known that diphenyl was extreinely fluid when hot and mould penetrate through leaks that would not he shown by water or steam teste. The nelds 011 the diphenyl chaqber and the drip receivers leaked slightly a t the start, but the leaki were easily peened shut with a hammer. The various joints in t h e pipe handling liquid diphenyl were first made with forged steel fittings, because it was thought that it would be necessary to meld all these joints. As a matter of fact. it was not found difficult to make a n ordinary screwed joint without welding that would hold diphenyl. This was accoinplislied by coatiiig the threads with a litharge-copper oxideglycerol cement. The valves in the diphenyl system gave considerable trouble. Ordinary 300-pound brass valves were used I n the sizes employed. the
e nz k1
@ >
Vul. 22>s o . 7
INDUSTRIAL A N D ENGl .VEERING CHEii41STRY
704
Finure 4-Causric
E~ap~sfor
stuffing boxes werc not sat,isfactory and leaked diphenyl vapor. A i:ommerrial instalkition s h d d haw more expensive yalvcs with niore carefully dcsigned striffing boxes, but ot,hcr than leakage around thi cni no difficulty was experienced. The packing on the diphenyl circulating pump was t,hc soi~rceof thc ppat,est difficulty. The original dcsigii of this pump had a split stuffing box which was exceedingly difficult to keep tight. It is [rractically inipossihle to liold liquid dipiirnyl at high pressures with ordinary asbestos packing, but, a sinall ainorint of cooling water freezes tho diplieiiyl in the packing and makm a satisfaot,ory seal. Later the split s t u f i i i g box was replaced with a single cast-iron stuffing box, and alt.hoogli t,liis was tiglit 1.0 water at low temperatures it. proved to have tiny leaks which herarne apparent at high t,ernperatures and allownd water t,o leak into the diphmyl. A satisfactory seal was obtained only when a casthronze u~aterc,ooled stuSiig box was pnrviderl. With this there has heen no difficiiltp whatever in ki:epiu piirrip tight to diphenyl. The diphenyl piinip, as or ly designed, gave contiiiiial because the studs and bolts difficulty at the juint in t.hF, e, were of poor quality a i d not on close enough centers. The sanic difficiilty was experienced with t,he studs which held the Jergusou gagic glassns to the diphenyl drip recxivers. At the teinperatures of (,peratirin the tuds were too weak t.o stand ary to make tight joints and were easily twisted off. Substilnting studs and bolts t u n i e d from riioderately higli carbon steel solved this difficulty on both t,lie gage glasses and the pomp casing. Considerable trouble was experienced from burning out of Imt this was always due to a failiiro of the circulating purrip, cit,her from poor vcnting or from h s c n dipheilyl in tlie lilies. Inasinuch as tlie electrirally heated boiler is purely a laboratory rnaked~iftand does not represent commercial design, this feature is not considered important. All parts of the apparatus handliiig diphenyl are traced with high-pressure steam lines and heavily insulated. With t,his provision it is not difficult. to start the apparatus and to keep it free from freeze-ups.
Figure 5--Top of Diphenyl-Heated Caustic EVapOlatDr
R.4nra~1os (ir~im Since tiic apparatus had a ratlicr luge extcrna and a sirisll heating surface, and since it was to opexate a t relatively high temperatures, t,lie radiation correction became of importance. Kariiaiion was deterrxiined by filling t,he vapor space with diphenyl a coustant pressure and niairitaining this until a iver full of condensate had heeri obtain~d. Iteadings were taken at frequent int,er.rvalsduring this tinir. Tho radiation correctiorr was expressed in millimeters of diplienyl collertrd per minute in the drip receivers, and is plotted in 0 CU-
-
Candant
Temprratvrr Balh
Figure 6-Junctiona for Tempersfure Measurements.
INDUSTRIAL AXD ENGINEERING CHEMISTRY
July, 1930
705
Figure 8. It was found possible to obtain very satisfactory checks between duplicate determinations. Radiation runs were also made with both increasing and decreasing diphenyl temperatures in order to obtain the effect of changes in the heat capacity of the apparatus due to fluctuations in temperature during a run. I t was found that unless the temperatures varied by inore than * 10" F. this effect was negli-
F.
Ternperd!ure,
Figure 8
Figure 7
Method of Operation
Commercial flake caaustic was dissolved to an approximately 50 per cent solution in the storage tank. This was about as strong as could be conveniently handled ai room teniperature without danger of freezing. The length of the individual experiments was usually kept short so that there would be no excessive change in concentration between the beginning and the end of the experiment. For a time the experiments were carried out during the clay, but the delay in thawing out the caustic lines and the diphenyl lines and getting the apparatus u p to temperature was so great that it became necessary to keep the apparatus hot throughout the 2-2 hours, although the numerical data were largely taken during the day. The calculation of the r m i l t s presented certain difficulties. Total heat transferred was determined from the volume of condensed diphenyl collected in the drip tanks S o determinations mere made of the quality of the diphenyl vapor as i t reached the jacket of the evaporator. If it was not dry and saturated at this point, the coefficients as calculated are in error. The concentration of the caustic varied qoniewhat during a run and consequently its boiling point varied. Further, the actual 1 emperature of the liquid over the length of the tube was higher than the boiling point, owing to the combined effects of hydrostatic head and friction. The difficulty of determining the mean liquid temperature was so great that it was considered out of the question for this work, consequently the results were calculated on the basis of the boiling temperature of the caustic as it left the appara-
tus. The results, therefore, are apparent heat-transfer coeKcients corrected for the elevation in boiling point of the solution. It was finally decided to base the calculations on the boiling temperature of the caustic at the end of a run rather than the average Over the whole run, largely for the sake of simplifying the calculations. The change in concentration during the short runs employed was small and therefore the error so introduced was not great. The coefficients thus determined are inore useful in design than the more scientific true coefficients. These result5 coTer such a wide range of concentrations that the data are sufficient for any ordinary purpose of design. I n the first experiments no thermocouple was placed in the caustic as the primary interest was in the diphenyl film coefficients. At the end of a run the supply of diphenyl vapor was shut off and the tube allowed to come to liquid temperature. I n later runs a thermocouple was placed in the liquid just beyond the evaporator tube, and temperatures
--'L 3 0 230
300
400
500
Bciltng
Gerlvh--- -----o Von bn+ropoPrrd Scl-mer
point
60
O F
-
Figure 9
mere taken during the run. These two methods checked very well. Especially a t the higher concentrations, i t was not feasible to remove samples for specific gravity determinations, and the number of runs was so great that it was not considered
Vol. 22, s o . 7
TSDUSTRIAL $ N D E,VGISEERlAFTGCHEMISTRY
706
feasible to determine the concentration by analysis. The boiling points of strong solutions have been reported by Gerlach ( 2 ) ,and by von Antropoff and Sommer ( I ) . These data are given in Figure 9. The data of Gerlach were used up t o 50 per cent and the data of von Antropoff and Sominer above 50 per cent. Concentrations mere calculated from the observed boiling point and the above data. The operation of the evapor a t o r and the data taken are obvious from Figure 1.
A
+ Q
-5-
14
H e a t - T r a n s f e r Coefficients
KO attempt was made to calculate coefficients when the temperature differences were less than 10" F., as the a c c u r a c y of the thermocouples is too lorn to give such results any precision. All runs in which the pressure of the diphenyl was less than atmospheric were discarded, as a slight leakage of air into the d i p h e n y l space would seriously affect the results. The data for some of the runs are contained in the accompanying tables. The headings of the various columns are self-explanatory with the exception of certain mathematical symbols which have the following significance:
s"
0. L?
0
= temperature d r o p
between diphenyl vapor and outside surface of tube U, = diphenyl film coefficient in B. t. u. p e r s q u a r e foot per hour per degree Fahrenheit On; = temperature d r o p through metal of tube, in degrees Fahrenheit OL = temperature d r o p b e t w e e n inside s u r f a c e of tube and circulating liquid L'L = caustic film coefficient in B. t. u. per square f o o t per degree Fahrenheit per hour
It is believed that the accuracy of the coefficients reported in Tables I and I1 and plotted in Figures 10 and 11 was approximately 5 per cent. The spattering
I N D UXT RI ill, A S D E NGI S E ERI S G CH E AVIIXTRY
July, 1930
Correnird. o n
\Id@?
?5D@ .c
\
I
33 4C
1
50
--I1
ao
-0
60
% 51 *;~gi.E5
r-1 I 1
1
,-
1
I 1
I 1
I
33 9
0ZOO -2-2
93
300
I
,
I
I
bo
in$
poirt of cabs' c ,
150 pounds gage) it was practically impossible to keep t h e gage glasses on the drip receivers tight, and consequently t h e diphenyl condensate was returned directly to the boiler and no measurements could be made. Considering that the whole apparatus mas evoli-ed de nor'o, with no precedent or previous-experience, and that in spite of this caustic was almost completely dehydrated, it is believed that a properly designed commercial apparatus for concentrating caustic soda with diphenyl would be entirely practical. Aside from the information on heat-transfer coefficients which are reported in this paper, the principal result is that caustic has been dehydrated in a continuous apparatus with entirely negligible mechanical difficulties. Acknowledgment
6300
2,000
Atmospheric
70 7
"i
Figure 10
of the points for the liquid film coefficient in Figure 10 is probably due to variations in the conditions of velocity, temperature drop, purity of solution, etc. Figure 11 shows the diphenyl film coefficient C:~I plotted versus tempwature drop. No marked effect of temperature of the vapor was noted, but yjo0 + the coefficient was found to increase with increasing temperature difference. The spattering of the zdzo points and the application of Kusselt's theory of vapor condensation (dotted line) is explained in the article on the condensation of vapom2 An interesting feature of this work is the fact e that, under the conditions employed, the liquid film coefficient is so high compared with the diphenyl film coefficient that the latter controls. I n runs J U 59 to 65 some of the thermocouples were $ 2''' broken so that only over-all coefficients could be determined, and it is interesting to note that these are only slightly lower than the diphenyl film coefficients.
The authors wish to express their indebtedness to t h e Swenson Evaporator Company, who financed the entire program, and without whose assistance the work could not have been completed.
>
I
I
I
1
i
I
~
.:
~
:-
. .
!
Theoretical
I
Concentration Obtained
I n these experiments caustic was actually concentrated to 98.2 per cent. No data are reported f o r concerltrations in excess of 92 per cent, however, because at the diphenyl pressures employed for the higher caustic concentrations (about
*..
Figure 11
L i t e r a t u r e Cited
"
z,
Antropofl, , and Sommer, phrsik, , 123, 161 (1926) c2) Gerlach, anal, Chem,, 26, 413 (1887), (3) Othmer and codts, IND ENG.CHEM , 20, 124 (1928).
z,
Establishment of Standards for Gages
War on Food and Clothing Pests
The establishment of national standards for pressure and vacuum gages was recommended a t a general conference held in New Pork City on May 15 under the auspices of the American Standards Association. Thirty-five representatives of rnanufacturers and users of pressure and vacuum gages and of technical, governmental, and safety bodies having an interest in such gages were present. In accordance with the recommendations of the conference, the scope of the committee's work will include nomenclature and definitions ; rules and specifications for installation and use; method of testing; method of expressing allowable errors; accuracy requirements; capacity ratings; connections; indicator hands and stop pins; dials and graduations; bezel rings and attachments; case sizes and mounting holes. The conference favored, in general, the development of specifications which would tend to unify the external features of gages of the indicating types, and permit a reasonable amount of interchangeability between the various makes. Representatives of the steam power interests, petroleum refineries, traction interests, gas and chemical interests were particularly eager t o have the standardization undertaken. One group pointed out that a t present it was necessary t o carry in stock 72 gages of the same size in order to meet the demands of those to r h o m they sold their product.
To develop more effective fumigants for treating insectinfested grain, foodstuffs, carpets, and clothing, scientists of the Department of Agriculture have tested more than 300 compounds. The results of the tests are reported in Technical Bulletin 162-T. More than 6000 tests were made, and about 100,000 insects were killed in determining the efficacy of these compounds. The investigators used rice weevils in the tests. Of the 309 compounds tested, 66 killed all the weevils by the end of a 24-hour period. Eighteen of the compounds killed the weevils in the minimum dosage which ranges from 1 to 4 pounds per 1000 cubic feet. The fumigants were then tested for their effect upon the germination of wheat. Only a few of the materials that give promise as insecticides had a bad effect on seed grain. Seventeen compounds promising commercially were tested in a fumigation vault with a capacity of 500 cubic feet. Two of these, ethylene oxide and ethyl monochloroacetate, proved slightly more effective than carbon disulfide. These two compounds killed the weevils a t a dosage of 1 pound per 1000 cubic feet. Ethylene dichloride, mixed with carbon tetrachloride a t the rate of 3 parts to 1 by volume, was effective a t a dosage of 6 pounds per 1000 cubic feet. The department regards this mixture as a highly promising fumigant because of its low cost, its effectiveness, its lack of fire hazard, and its comparative harmlessness to human beings.
