PARTIAL PRESSURE PROCESSES
“Partial pressure distillation”, “stum distilbtion”, and “azeotropic distillation” an t e r n used to repment the phenomenon of additive partial pressures due to the mutual immiscibility of many pain of liquids, as well as the methodc of carrying out separating operations and chemical reactions involving one or both of the liquids of the pair. The applications to industrial process are numerous, and tremendous tonnages of materials are separated or manufactured in many different industries by some of the methods described above, othen of the processes or operations described hwe been worked only on a small scale.
1106
swtmba, 1s41
INDUSTRIAL A N D ENG INBERING CHEMISTRY
equilibrium relations be predicted VpAPORliquid for only of pairs of liqui-. e., thoae which e r f d y immisdble and t h w which are perfectly can
+ma
sua
rain-
cible.
In the hit oam the individual vapor pmsmrea of the respective matetiah am additive; in every other case more complicated reJations are involved. Thus, the compdtion of the vapm may be found from the law of additive vapor pressurea, which stgtee that the ratio of the molar percentages of the two constituene in the vapor is the same aa the ratio of the individual partial pressuresat that temperature. Pok mbly a more convenient way of e x p m thie relation is to h t e that the hiling point of the mixture may be found by plotting the individual vapor pressures on the ordinata of merent temperatures, graphi~dyadding these pressures on these ordinaten, and debmining the intersection of the latter m e with the absciem repwenting the desired operating pmure. If, for example, 760 mm. is the pressure at whiah the b o i i temperatwe is desired, the intersection of the 760 nun. line with the additive curve wiU give the boiling temperature of a mixture of the liquids or the wcalled azstropic point.
TaLing, for example, b e n e and water aa the insoluble liquids, the b o i i point of the first is 80.Zo and of the second, 100° C., and the hiling point or place at which the pressure of the combination rescbes 760 mm.is 89.26' C., with 8.83 per cent water and 91.17 per cent bemsene. Thus, the efiective C. when in boiling point of water has been reduced to 69.?Ba8" the presence of bemne. A deecription of a new method of plotting and calculating t h m relations waa recently p r e mted (17).
This addition of the pressures of immiscible liquids is tsken advantage of in industrialopemtions, often 8 p O h of 88 aseotropic distillation, partial pressure distillation, or steam distillation.
h m DWiUdion The most cornmoll u ~ of e partialpressura distillstionis the practice of e h n l distillationwbich is used d y for lowering the &&ve boiling point of one compound. In thin case the othw compormd is ahno& water, added as steam, and it wrvm to bringover ahigher boillng material at Bmne temperaturebelow the boiling point of water. &nee pairn of liquids which are Bubstentislly mutually inmluble are the o w whioh ahow the phenomenon in queation, the oondenaats rennlting after such a dietillation immediately aepsrates i n k two liquid pbaees; one is always water sutwnted with a rondl amount of the other liquid, and the m n d is the other liquid sutwnted with a damount of water. The water layer may Contsin only a fraation of a per cent of the other liquid dissolved in it, and there may be only a fraction of a per cent of water diemlvd in the other liquid hyer. But the respective partial pressures must be the same from each layer, Bince thelayem are in equilibrium; and either m a W would distill fmm one layer into the other if merent vspor pHssures prewiled in the two phases. Thus, although Lmzene saturata a water layer when dholved to the extant of only one psrt in many hundred, the vapor pressure of b e out of that water layer is the m e as that of the b e from itd own layer, which is practically pure b e . The two layem will thus smell the m e . It is evident that, because of the high vapor pressure of b e n e from the water layer and the d amount therein, the die solved benzene will all evsporste away rapidly. The separation of one material which has an additive vapor p m r e with water from another material which does not obey thcsalawemay b e d by such a psrtial p m u r e distillation. A oeud laboratmy analysis for water in various
1101
solids or liquids is by the addition of toluene or some other wahinmluble subetanae to act aa an entasioar; then after condensation of the sreotropic mixture or vapors of the steam dietiustion, the insolubletoluene and water are separated and the amount of water is meesured. This system is uwfd only if the d d or liquid being analyzed has no other mated wbich will form a partial preswua distillaton with the entrsiner under the conditio= of the experiment. Commonly 8pOken of aa a staam diewlstion is the 8eparation of water from glycerol. This is not a steam distillation in the e8nw the term is used elnewhere, even thongh steam is ueed and ie added dire& to the materisl King diswled (as it is in many other distillati-. g., ihe beer still of an alcohol plant). Water and glsoerol are soluble liquids, they do not have additive vapor pre6muen, the boiling point of the diawlstion is a l m p higher than that of water at the name pmaure, and no psrtial preamre dietillation is found since them is a more complicated relation between the vapor and liquid compoeitions, as shown by the usual type of zy or vapor composition diagram of a pair of miscible liquids. Dehydration 01
Alcohol
If history rather than logic is followed, the most complim distillation method will cated example of the partial p he considered Grst. Young in 1902 argned that, aince t h e ~ ~ ~ ~ . w i t h w a t e r a t a b o u t B g ' C . why not u8e this method of lowering the boiling point of water to separate the approximatdy 6 per cent water from ita C. B. M. (constan&biling mixture) with alcohol at 78" C. Unfortunately simple addition of partial pressures does not hold for benzene and water when alcohol is added, pmibly because h m i e and water are not insoluble when alcohol is present. Insteed,an even lower boiling mixture containing alcohol waa found; and thin ternary azeotrope (the first one discovered) bo& at 68.5" C. and conbins 18.6 per cent alcohol, 7.4 per cent water, and 74.1 per cent benaane. It condensas to give two layers. The lower one, 16 per cent of the total volume, contains about 31 per cent water, 11 per cent b e , and 68 per cent alcohol, while the upper layer, containing 84 per cent of the total volume, contain80.5 per cent water, 84.6 per cent benzene, and 15.0 per oent almhol. Many process and patent8 have been worked out on the basis of these and related data aa noted by Keyen (6)and a r (r). The desire has been to simplify the process to a partial pressure dietillstion involving only the additive vapor pressure of some entrainer and the water without the additional efiect of the vapor pressures of the dcohol. This has been done, and a prooess deacrihed (M) in which the added material is ether and the p m u r e of the distillation column is considerably higher than atmaspheric in order to tske advantage of more favorable vapor pressure relations at higher temperaturea Thus, at a higher temperature than the atmospheric boiling p&t, the ratio of the vapor pressure of ether to thatof waterislowerthanatlowertemperat~andpreesurea, and fewer pounds of ether are required per pound of water removed. The operation, by being reduced to the simple additive psJtial pressure distillation, is simpler and q n i r e a much less equipment than previous proc%ases because no alcohol distills over to be eeparated in the water layer in the decanter and subsequently rectified in another unit. For the same reaeon the heat reqnirementa are much lower becaw additionsl distillation operationsare eliminated.
(m
Use d Liquid Being Dried as Entrain-
*
Methanol is the only volatile alcohol which dcea not form C. B. M. of one type or another with water. Most other
1106
I N D U S T R I A L A N D E N G I N $ B R I N Q CHBMISTRY
alcohol8 except ethanol form C. B. M. because of the addition of partisl VBpO' premma, although the other lower dcobols have d c m t mutual miscibility with water to prevent the theoretical addition of vapor pressure to give C. B. M. with the exact c o m p i t i m which would be predieted. Butyl alcohol hss an sseotropia mkture at 92.26' C. with 63 per cent water, and on condenention two k u i d layers are formed. Butyl alcohol is emnetmm d t o r e m o v e water from various materials by displarAng and dissolvhg water. It is then dried by subjecting the saturated solution to a didling action whereby the water steam distills with the ($8). butyl alcohol it& and in 80 removed from the @fm There are other materials, e'ther containing dissolved water or d i d v e d in watar, from whch the water may be separated by nsing the material itself as the entrainer. One of these is furfural. It is obtained along with water and other ma& rials from the acid hydmlysis of cellulosic substances; and one of the step in ita puriBaation is the dehydration by an aseotropic dietillstion (14). Correct application of the principles of sseotmpic distillstion reaulta in the complete separation and purification of furfural and the several materials produced with it in mme prowme#, without any additional expenditure of heat. Wentworth (96) considered the special caw where the solubility in a water layer approximstestheaseotropicratio,ssitdceainthecaseofetherandof methyl ethyl ketone. A rectifying column is dfor all of these dehydrating dik tillations, 88 in others where the lowest b o i i g constituent is desired 88 the overhead pmduct. In a partislp m dik tillation, the minimum-boii constituent is the amtropic mixture, which is condensed and decanted. The water layer may be returned if the object is separation of the entrainer from other materials; or the solvent or entrainer lam may be returned if the object is the ultimate dehydration of the entrainer or of some other materiel. The return of one layer acta as d u x to hold down higher boiling materials or other ratios of water and entrainer; and sometimes the layers are psssed to Merent columns to e5ect their Bubstgntial purification. Thus, the water layer from a decanter following a butyl alcobd dehydrating still is passed to a wahtripping column where the b u b o 1 is didled o@ in a prdhl preesune distihtion; the eame vapor oompoeition as the first de hydrating distillation is ohtdned, and pure water remains. The wet butanol is passed back to the original dehydrating column, and the dry butsnol paws off the base of the h n t column as the bigbe&boiling constituent.
.
Dehydraflon of Acetic Acid
The use of entrainers for separating water from aqueous solutions of acetic acid (since the separation of the water by &might mMcation is practically im+ble because of the p&ty of b o i i points) has been described in many pa& enta and in Various articles (16, 16). The operation here is Munewhat simpler than in the case of ethsnbl dehydration since acetic acid itself has no C.B. M. with water. It is not difficult to 6nd entrainers which do not have a b i i C.B. M. with acetic acid, m d no entrainers am known which form a tarnary C.B. M. with acetic acid and water. Nevertheless, it is intereating from a technical standpoint because of the bundrads of times as much anhydrous acetic acid as anhydrous alcohol which is &tilled industdly, because of the added di5cultiea to be overcome due to impwitiw in the liquids handled industrially, and because of the vapor-liquid and liquid-liquid extraction phenomena which proceed in the distilling column simultaneously With the usual operations of condeneation and re-evaporation. The homologs of acetic acid dl form C. B. M. with water; and formic acid, in particular, is more difficult to dehydrata
VoL 33, No. 9
because of the relative mutability of the pure wid, becaw of ita maximum C. B. M. with water, and because of ita tendency to form amtropic mixtures with many liquid which may be wed as entrainers for dehydrating acetic acid. Thin latter property baa been used as a means of separating formic acid by secotropicallydistilling it away from the acetic acid. A new procese, involving further adaptations of the partial p m distillation technique, has recently been developed which reduces to a fraction the steam and equipment require mente hitherto thought ne(16). Other Operations Involving Liquids
A mder number of proceases have bean developed to utilize entrainers for removing other materials from nonaqueous solutions. In sepmting miKturas of hydrocarbons (ai), probably because of the relative insolubility of certain liquids in some hydrocarbons, the reapective partial preaurea of entrainer and the particular bydmcaraOn may be regsnled as additive, at least as a first approximation. It is in& eating to note that the several liquids mentioned as enorsinem for specific hydrocarbons d y contgin bydroxyl gmups, which may account for the relative insolubility with the respective hydrocarbons and hence the additive vapor pres ~ u 4 &Examples of the UBB of entrainers for the separation of hydrocarbon mixturea have slso been cited in various patenta covering commercial prooease%-e. g., Field (3) who
&pt.rmba. lsll
I N D U S T R I A L A N D E N G l[NBERXNG C I i t Y I S T R Y
r
tem cyclohqane from hensene by an aseotmpic diution with wetone. 33Xamplea of wueous solutions of liclllids ha* very low or ne.&ible vap& preanve rue the solutions of &-mineral sci& such an sulfuric and phqhoric. Kerowne and other liqnidaam we3 ns enbinem (lS),and the water may be removed becsuse of ita partial preanve with the kerosene. The lowering of the &active h o i i point of water is important in this esse; and a continuouspmceea operating in a dig tilling column is conducted to dehydrate the acid. The dee tion of a petroleum fraotion, b m , which will be entirely unsttecked by the concentrated sulfuric acid is diEcult, Degradation producta of the hydrocarbons are almast slway8 obtained, and it is qudonable whether these 10of &lUhW be kept to WOMmiCd amount. Dohydration of Solids and d Aqueous Solutions of Solida
of higher boiling water-insoluble c ~ r m In general, the pounds or “entrained allows the entrhing of a given amount of water with a mlaller amount of entrainer owing to the lower vapor p m of the high-boiling entrainer with rerpect to the vapor pnrunve of the water. Thus, a lower amount of added heat over that required for evaputing the water itaelf is neoemuy to m o v e a given amount of water with higher boiling enbinem. On the other hand, the &dive boiling temperature (that ofthe aseotmpc mixhue) incresaes with inof the normJ boiling point of the entrainer; and if it in desired to keep this ns low m p d b l e , a lower b o w entrainer will be used. If the operating temperaturemust be kept low and heat consumption is dw to be kept down, it is oftan denirable to conduct the operation nnder a partial vacuum by utili5iug a h i g k h o i i e n t r a i n e r . Inthiscasethede&dIowratio of entrainer to water may be s e d becsuw the ratio of ree.pective vapor pis low (although this will not be a constent at all t e m p e r a h ) ; and the desired low teollpusture may be dby oombinstion of the dfecta of vacuum and partia p m evaporation. C A O ~SODA. C The mnod of watsr fmm aqueous caustic soda hss been described (18) using kemsene ns the entrainer. This nerved to m o v e the water at a tempersture lower by 500° F. or more than that required by the usual caustic fusion process. Because of this lower operating temperature and the fact that the pmceea may be operated cantinuouely, the heat require6nenta are only a fraction of thoee required by the usual method; a new form of caustic eoda is produced which in crystalline io nature and p ceaw several advant?gea in um. These resulta have since been s u b t i a t e d on a pilot plsnt with a capacity of 0.6 ton per day. From the engineering standpoint the handling in a diawling column of a lfuge amount of d d s represents some new mechanical problems. Thin tendency for plugging, due to the settling out of the cawtic, and the uecesnity for allowing the time required for the complete d e hydration of the particles, due to the neees881y di5usion of water from the imide of the particle to the outaide, repreeent two of the problem which have beem s u d u l l y solved in the application of this p r o m to dehydrating caustic and other solutions or solid d t a having water of crystallisaton in pilot plant work by the Vulcan Copper & Supply C o m p w (Fleure 2).
The dective boding temperature may not be determined fmm the addition of the vapor preenvee of the entrainer and pure water, h o e the vapor pressure of the water out of the material being dehydrated may be only a erndl fraction of the vapor prrssure of pure water itsell. In thin case the dective boiling point is obtained after adding partial pres-
1109
unrw of water from the solution in question and of the entrainer. It may be higher than the boiling point of pure water, althongh dwayn much lower than that of water boiling out of the material in question. Sometima, ns in the c ~ d eof dehydratiag caustic aoda solutions, the we of a distilling column with a fed of the originalmlution at or near the top plate servm to rectify toward the comt aseotmpic point; but in no we could the b o i tempersture at the top of the column be expected to be below that point found from plotting the sums of tbe partial p m u w of entrainer and the partial pressunvl of the feed solution at Merent temperaturea bnd determining the intersection of thin curve with the desired o p t i n g pressures. Omm S o m . The dehydration of solutions (or molecular additions of water to solids) using kemmm ns an entrainer has been developed and patented for general use by Kokatnur (8). It is appsrent.that some special advantage must be mured in such a p r o m to outweigh the faat that the entrainer haa to be distilled along with the water, which CBU~BB an inin the thewetid heat consnmption. Aa mentioned under “Causticfkdn’’, the totel heat reqnired, due to more dEcient application of heat or for other m n s , may be comidembly leas even with this addition; i. e., in ‘the rem o d of water from caustic sods solutions, about 0.7 pound of kerosene must be W d for each pound of water removed. %idea the reduction in temperature and improvement of general operation and product with caustic, there rue some other advantages which may be gaiaed in working with diffemlt materials. One of these is the prevention or subSbtie,l elimination of hydrolysis which occurs in the ordinary evaporation of many d t a such an msgDeeium chloride with six mol& of water of crystdimtion. This gow to the oxychloride when water is drawn off in the ordinary way at 4%’ C. The lowering of the tanperahreby the removalof the water in the pence of keKlsene cuts down to a large extent the hydmlyais which otherwise occurs. using stiu other mlventa with lower h o i i pointa, such ea pentachlomthane, the temperamay be lowered still further and the hyddynh praot i d y eliminated. Calcium chloride and other chlorides hsve ales been m l d u l l y treated in thismanner. “ALLOY CB&YIU.” Another advantage which may often be important is the securing of an extremely intimate mixture of two materials. In the we of two solids dissolved in watar-for example, caustic sods and soda &-the usual evaporation of the solution d t a in the cryeMimtion of one of the solids in a substantisly pure form or in some 6xed ratio determined by the solubility relations of the given combination. The dehydration of a solution containing two or more solids diaeolved in water by distilling with an entrainer mulb in tbe formation of minute dropleta of the aqueous solution d i s p e d in the entrainer p k . The two soli& are h l v e d in each droplet in whatever ratio hss been predetermined. The evaporationand dehydration are conducted with such rapidity and the dropleta m so dthat the cry8tdliBation of the two materids occurs simultaneously on the same nuclei rather than successively on Werent nuclei. This result8 in a mixture of the deeired and predetermined cornpaition crJ%tallised out of each droplet. A@ pulvernlent, crystalline material, which is almost moleaulsr in the degm of mixing, is obtained of any desired composition. The name “alloy chemic&” haa been given to tbis type of mixture he caw the constituente are ea uniformly dispersed in h e cry* tals d t i n g froman aqueoussolution an in an alloy resulting fromthe crystallizationof matmi& dissolved in each other. MIXINOOB COATINO Caymu. A modification of this process may be utilized where for some reseon it is desirable to have a core of one material coated with another. Such a syetem might be that of a mixture of ptaaaium and d u m ni-
1110
I N D U S T R I A L A N D ENGINEERING CHEMISTRY
Vol. 33, N o . 3
3. E P O I W N T FOB W O W 0 75 TONS OF W A DAILY ~ BY A PABF I O W
TIM.
tratea, where it might be deaired to coat the datively hygruscopic salt, sodium nitmte, with the relatively nonhygroscopic salt, potassium nitrate. In this caw a batch of seed crystals of sodium nitrate would 6mt be made and added to the entrainer and a concentrated solution of potassium nitrate. This would be boiled to remove the water and precipitate a mating of the potassium salt on the seed crystals of the sodium salt as nuclei. It would he necessary to control the ratio of the amount or concentration of the solution added to the solid salt 80 as to get the right amount of coating or the desired ratio of the two dts. A further step is the expansion of this coating prowsa to include other mixing owrations where one of the components is more or less insoluhlefor example, in the proposed mixing of the constituents of black gun powder. Carbon particles of the deaired degree of 6neneaa may be coated with d u l t d j e d v e d in a solvent which would he removed either by ordinary evaporation or by partial pressure evaporation while maintaining suitable agitation. Then a solution of potassium nitrate is added and precipitated on the coated carbon particles by partial pressure evaporation in the presence of an entrainer. Experiments along these linea indicate an improved p r o m and product due to the relative simplicity and eafety of such a mixing operation and the nniformity of prcduct which will result.
Use of Partial Pressures in Chemical Reactions The most familiar procew in which a ESTERIPTCATION. partial pressure distillation is used to help or complete a chemical reaction is probably the manufacture of esters which datea back to Wade (83, #4). In his work and the literature and patents of many others, the water which is formed by the combination of an alcohol and an acid is removed in a partial pressure distillation of the water with the ester or alcohol or both. A summary of these prowsaes is given by Key- (6). These operations become rather complicated in their attempts to @e full advantage of the various consht-hoiling mixtures, both homogeneous and heterogeneous, involved hetween alwhol, ester, and water,
FmssW PBOcEea
and in some casea between one or more of them and an entrainer which is not a component of the reaction but is a d d 4 to it. In the wee of acetic acid, the most commonly wed. acid, as noted above there is no C. B. M. involving it and water or any other of the components although some of the. other acids do have such aaeotropic mixtww to complicate. further the neoeassry distillation steps. SOAP MAKING. Kokatnw (10) used partial pressure dig tillation for the revem reaction-aapordication of an oil or fa&o-t give the resulting soap of the fatty acid and the a l e hol, glycerol. Kerosene is Sirnost completely immiscible. with glycerol, and the two form a partial p r m r e distillation at about ZOOo C. under atmoepberic pressure and at a lower temperature under partial vacuum. The reaction of saponification may be made to go to completion in a few minutes, and the mixed vapors of the volatile constituente are condgnsed and eeparated. The glycerol IS m o v e d 88 a product of high strength and commercial purity to give an eoonomid method of glycerol recovery. The kerosene may be. ~JIuxedto the system. The process bas been further d e veloped (4) to give a semicontinuous or continuous p r o m . with necessiy modifioations of temperatures and pressures. to m o v e entirely the glycerol and kerosene from the soap. A commercially desirable form of soap is obtained which in.
P
s.ptember, 1941
INDUSTRIAL AND ENQINEERING CHEMISTRY
FIQ4. DEUIYDBATION OF AN ORQANICACID AND &TEE BY A PmTm. h s s u m PBoaas R' ht, baee heater of the &tilling col-, bowing s t e m controls; below, detail. of m. ereotmpic column,showmg feedmg &ion.
comparable to soap heads or flskes iL .-r.iity of dissolving. A further advantage is that a k e m n e or naphtha fraction suitable for inclusion in the linal soap for laundry or other work may be used as the entrainer; and by ite incomplete removal, a s o - d e d naphtha soap containing any desired amount of solvent may be produced. Another step allows the incorporation of other hydrocarbons into the soap 80 as to produce lubricating greases of Herent characteristics. Because of the method of manufacture, t h w greases are more homogeneous and present g r e a h re Bistance to moisture than greases made by other proceasas. Metallic soaps-i. e., those of other metals hesides sodium for use in other special usea--have slso been made in this manner which ia much simpler than the eeveral+tep process. In these causticixstions, 88 in other caustic proceasea, the use of the crystalline caustic prepared by the partial pressure method above describd has been found advantageous in several ways. Comparable to the distillation of g l y m l ia the partial p m u r e distillation of another material than water, using Lemeane 88 entrainer in the separation of fatty acids from rosin. aa in the French p r o w (3).
SULFONATION AND CAUSTIC FUSION.Benmne bss been d o n a t e d , using kerosene 88 an entraiw for removing the water of reaction, to give benzene sulfonic acid 88 the fint step in making phenol, as indicated by Kokatnur (ff)and O t h e r and byes (M).Certain advantages of speed of resotion, due to the higher operating temperature possible at atmospheric pressure, to the control of the d o n , and to the purity of pmduct due to absenoe of sulfoneformstion, have been indicated. The m u d step (9), the fusion of the multing sodium d t to give phenol, has also been advantageously operated in the presence of Isemme to give a mwther and mom controllable reaction,low cauatic (1.5 per rent over theory), high yields, and a pmduct wbich is in a form to be d y Purifiad. The experimental work indimtea the importance of intimate contact (hem obtsined by high speed agitation) between the entrainer and the p h giving off water, so that the vapor-liquids equilibrium condition may be approached. A large enough number of other s d f ~ ~ t i and ~ n caustic s fusions for making resorcinol, pcreaol, @-naphthol, eta., have been made to indicate that the use of partial pressure &tilation may be regarded as a tool of g e n d utility in this field. NITRATION.Benzene baa been nitrated in a continuous e proceas operated in a distilling column with a feed of b and a feed of nitric acid, using the b e n e itself an the entrainer for moving the water of reaction s~ well 88 that present in the nitric acid. The vaporous mixture is condensed, the condensate layer decanted, the water layer removed. and the benzene returned to the column. Nitrobenzene is removed from the base of the column either 88 such or in a solution with b e n e which may be Beparated in a subsequent fractionation. Monc- and dinitrotoluene have been prepared similarly by the use of nitric acid alone rather than by mixed acids containing sulfuric for the removal of the water hy chemical combination. Partial pressure diswlstion takes the place of chemical dehydration much more economically. Of particular utility in the nitration of toluene by this method (besides the elimination of the nuisance and expense of mixed acid recovery) would be the suggested application to mixturee of aliphatic hydrocarbons and toluene. The Beparation of toluene to pmduce TNT present% some dif-
INDUSTRIAL AND ENQINEERING CHEMISTRY
1112
ficultiea due to the fact tbat the aliphatic hydrocarbons have the m e b o i i range 88 the aromatic hydrocarbon, toluene, although some extrsotion methoda are suitable (f),and 88 mentioned above, aneotmpic distillation iteelf with an added entrainermaybeuaedforseparatinghydmaarbons.Thepderentisl nitration of the toluene to the mononitrate might be conducted using the comparatively inert aliphatic hydrocarbons as entrainer% for the water formed. The m o n o n i b toluene d t i n g could be readily separated by dietilling off the aliphatica. This step is little more expanaive than sew ration methods and is directed toward the ~ end. EThe I relatively innocuousmononitrateformedmay then be shipped or carried to a higher stage of nitration. Them nitration operations are described in patent applications (it,18). Dehydrating Oils
Castor oil has been dehydrated (f S) by the use of a cablyst such as sodium acid sulfate in the presence of -e, which sds as an entrainer for the water moved. The vapor of h y d m a r h n prewnta oxidation of the oil, and dehydration proceeds to u greater extent than is otherwise poseible. Other nondrying oils, such 88 soybean, have bean aimjJarly treated to give oils which have definite drying properties and poasible utility in the field of paints and varnishes. The dehydration p r o w has been carried further to give plaatic materials of a rubbery nature, although the chemistry of the reactions themselves and of the 6nal products are not completelyknown at this time.
voL33,No.o
Literature Cited Bbtnsgar. 8. 8., .nd Ward, P. J.. IND. ENa. h. 31, ,196 (1988). Field, Edmond, U. 8. Patent 2,212,810(Aw.27,1940). %ob. E.E..IbX. l,fIB7,171 (April 9,19.36). Jaoob, J. J., patent application. Keyed, D. B.. Im. &a. h. 21.888 ,(19Zs). ma..u,1000 (1032). Kkr. M., “Fabrihtnn wn sbmlutem llllmhd m& Ver-dung da Zuaatrmittel N Motor-T~eibtoffen.” 2nd ad.. Hdle a. W e , W. Knapp. 1937. Kokatnur. V. R. (to Autoxym, ha.), Brit. Patent 409,862 (JUIYaa. 1837) and u. 8. Patent SPPECS~~OW. KokaQlur. V.R., U.8.Patent 1,007.480 (April 24.1828).
m.. i,sia,w (JUIY~, ioai).
m., a.iii,97a (Maoh 22. isas).
mid,pstent applioatioM. Kokatnur, V. R., and Jacobs, J. J., patazlt applloatio~. Main&0.E.,Chen. d Md.Bw., 28,778,841(1922). Other, D.F . , m . , 4&91 (June, 1941). Otbmer. D.F.. IND. ha. h. 27.2E4 , (1086).
m.. 31,841 (1940).
Othmes, D.F., and Jwbs, J. T . . M . . 32,164 (1940).
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DESIGNING EFFICIENT ERUIPMENT qu+V. A
d
Buffalo Foundry & Machine Company. Buffalo, N. Y.
Problems of design of kettles for use in chemical plan@are reviewed from the standpoint of the designer and fabricator. Materials of construction, agitation, heat transfer, and details of design affecting operation are diuuaed.
of the most common pieces of zed for u multitude of purposes. It may be used for the mixing of e d y miscible liquids, for the diwlving of solids in liquids, and for the mixing or compounding of viscous liquids. Kettles are required to operate through large rangeeof temperature und pressure, and must be so designed that their contents may be heated or cooled in order that the prowas mction may procead properly. They must frequentlywithstand corrosion and are constructed of suitahle corrosion-resisting materialf~.Kettles van‘ in size according to the requirements of the process for which they are to be used. Some kettles may hold only a few quarts, others thousands of gallons. Some kettles may be used for a variety of purposes. A reaction may be carried out, then it may be necessary to evaporate water with a thick viscous material resulting. Again chemicals may be charged as liquids which, as they react, produce 6mt a pasty m&88 which becomes almost solid and finally u granular material which must be discharged from the kettle. The kettle must operate under 80 wide a variety of conditions that it has been difEcult to analyze. Much has been published concerningheat transfer rates in heat exchangers, condensars, evaporators, etc., and on drying operations, distillation, and other unit operations. However, there is tittle in the litera-
ture to guide the designer of the humble and versatile kettle; yet frequently the initial operations upon which the yield and themfore economy of the whole process depends are c a r ried out in kettles. Materials of Construction
Until recently the only chemical-resistant material uvauahle at reasonable cost was cast iron. Veesels fabricated from steel plate were used for many purposes but were less reliable than cast iron since they gave trouhle at riveted or welded jointa. The cast iron vessels were seamless and uniform throughout. Today a large number of corrosion-&stant materials areuvailable. There is a large vuriety of Bt9inless steels ranging from the simple 18 niOkel-8 chrome to the more complex alloys containing titanium and columbium. Each of the many alloys has definite properties which make it particularly suitable for certain applications. Since the price of the more complex alloys is much greater than tbat of the simpler ones, the purchaser of stainlw steel equipment should make sure tbat the apparatus is fabricated from the particular grade of stainless steel which is beat suited to the purpose. Many of the large chemical companies which purchase
