ENGINEERING. DESIGN. AND PROCESS DEVELOPMENT the natural gas I\-ithout attempting t o nitrate the methane present. -4lthough the propane t o nit,ric acid ratio \?as as high as 37 and the ethane to nitric acid was as high as 68, it was not possible to obtain conversions to nitroparaffins appreciably greater than those in the opt,imum run E-20 in Table I, in which the propane t o nitric acid was 0.448 and the ethane t o nitric acid was 0.826. The experimental data suggest, the conclusion that in the nitration of a mixture of hydrocarbon gases, the distribution of t,he products of nitration and the over-all conversions do not correspond to v h a t TTould be expected from the nitration of these hydrocarbon components separately.
References (1) Bachman, G. B.. Addison, L.SI.,H e i v e t t , J. V.,Kohn, SIillikan, A,, J . Oro. C'liem., 17, ROO (1952).
(2) Bachman, G . B., .Itvoori, hi. T., arid Pollack, AI,, I b i d . . publication pending. ( 3 ) Rachman, 0. B., I-Iass, 13. 13.. and Addison, L. M., Ibrd., 1 7 , 014 (1952). (1) Bachman, G . B., Hass, 13. 13.. a n d Hev-ett, J. V.,Ib;d., 17, 92s
(1952).
The authors are indebted to the Commercial Solvents Corp. and the Purdue Research Foundation for financial assistance in the form of a fellowship and t o the analytical department of the Commercial Solvents Corp. for the inass spectrographic aiialvsw of the nitroparaffin samples produced in this work.
V.,aud Mllikal1, A. G., I b ; d . , 17, 93.5 (1982). Bachman, G. B., and Kohn, L., Ibid.. 17, 942 (1952). Hass, H. B.,and Alexander, L. G.. 1x11. EKG.CHEM..41, 2266 (1949). Hass, H. E., and Patterson, J. A , Ibid., 30, 67 (1938). Riley, E . , Ph.D. thesis. E'urdue University (1911). Walsh, A. D.. Tmne. F a r u d a ~SOC.,42, 269 (1946).
(5) Rachman, G. B., H e n e t t , 3 . (Gj
(7)
Acknowlledgment
I..,and
(8) (9) (10)
RWEITEDfor review Septemher 1 4 , 1953. ACCEPTEDFebruary 12, 1054. This paper is part of t h e P h . D tliesis of XI. Pollack, Purdue University, I'ebruary 1953.
e FRITZ MEISSNER
GEORGE The
WANNSCHAFF
Firm of J . Meissner, Cologne, G e r m m y
AND
DONALD F. OTHMER Pofyfechnic fnsfifufe, Brooklyn I , N . Y.
This article and the one following are based on the operations of plants which have been built in Germany utilizing this process. At the present time the company is putting additional plants into operation which incorporate a number of improvements. It seemed advisable to sacrifice some detail in the present articles with the expectation of publishing later comparative data between earlier plants operating by this continuous process and these new plants. In continuous processing of nitrotoluenes there is no change of temperatures, pressures, or concentrations of any of the reactants at any point with respect to time, and only a movement of {he reaction components or mass, from point to point, is necessary to control conditions so that they are always at the optimum. Once set, these conditions are more readily maintained t h a n with batch operations, because the reaction is very responsive to minor adjustments. Coytinuous processing equipment i s always filled to optimum capacity; thus the entire heat transfer surface is always operative. The flow of cooling water removes heat exactly as fast as it is generated without changing the reaction temperature and precise and instantly variable proportioning pumps or meters maintain concentrations. Because rates of flow and reaction are always optimum, the size of equipment is only a fraction of that of batch equipment, and the labor of operation is greatly reduced. Only a small amount of the sensitive product is in the plant a i any time.
c
OXTINUOUS nitration of aromatic hydrocarbons has been studied for many decades. The dye firm of hIeieter, Lucius, and Bruning ( l a ) in 1906 patented a continuous inrthod for preparing aromatic mononitro hydrocarbons. The firm \Veiler-ter-Meer ( 1 9 ) >The Westfahlen Explosive A.G. (20), and Tiubierschlry (8) all described apparatus and processes. Uaxter and Beule (3,4) describe processes for the nitration of phenol, also for benzene, toluene, and cresol. The many patents granted clearly showed that continuou. processes would have great advantages, but only relatively small amounts of materials were produced. Especially in the eaplosives industry, which is one of the most conservative of the chemical industries, resistance t o change has been tremendous. The firm of Meissner succeesfully developed and operated on a 00111-
718
niercial scale in 1928 the trc.hiiiqucs of Schmid (2 6). Thereupon a continuous process for nitroglycerin was introduced t o the explosives industry, and today 45 continuous working plants for nitroglycerin have been built using this process and the further iiiodifications and refinenleiits that have been added. Four plants that were built as early as 1929 and 1930 are still in production. The advantages demonstrated by the success of the continuous nitration of glycorol encouraged the study of other continuous nitrations. Thus, the firm Meixsner developed procemes arid plants for the continuous nitration of glycol, diglyol. priilawythritol, and aromatic hydrocarbons. This papcr deals, howrver, only with the development of processes for the nitration of aromatic hydrocarbons.
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 46, No. 4
UNIT PROCESSES Until the present process. which is covered by patents or patent applications in the industrialized countries, the continuous nitration of aromatic hydrocarbons was done only on a small scale because of troubles with equipment. For the continuous process there are several requirements: 1. Precise metering and addition of starting materials 2. Exact and continuous determinntion of product material 3. Method and data for calculating the maximum rate of nitration in :I given volume of equipment 4. Simple apparatus for the continu o ; ~separation of final materials D. Method and equipment for continuous washing and drying
From the accumulated experience in the continuous process for nitrating glycerol, Meissner (10) worked out a simple process for the continuous nitration of aromatic hydrocarbons in 1934. This process was used in various plants, among others a GO-ton-per-day plant for the Westfahlen Explosive A.G. This process has since been improved to realize the major advantages that are not possible with the discontinuous procehs. Figure 1 is a comparism of continuous and batch process plants, for the production of aromatic hydrocarbons. For the continuous production of trinitrotoluene there are additional problems present as compared to other nitrations, but the continuous method is very attractive because of its much larger safety possibilities. I n England in Korld War I a trinitrotoluenc plant using a continuous process mas reported t o be in production ( 1 ) . Several other patents may also be mentioned-Chance &: Hunt Ltd., Holley and Mott (6,6) and Staatsmijnen (18),and a German application of the Dynamite A.G. presently on filc. Besides these, the firm Meissner developed a hitherto undisclosed process in World War I1 and operated one plant for Dynamite, A.G. There was published, however, a German Patent (11j on the continuous washing of trinitrotoluene, somewhat rclated to the one on continuous washing of nitroglycerin ( I O ) .
Suggested Continuous Processes for Nitration of Aromatic Hydrocarbons The following four basic processes have been described foi the continuous nitration of aromatic h\,drocarbons. Vapor Phase Nitration. lT7ilhelm( 2 1 )described such a orocess A continuously mixed stream of the aromatic hydrocarbon and nitric acid or nitric oxide was passed over a catalyst-e.g., silica gel-condensed and separated. Unreacted parts were recycled, and no sulfuric acid was used. This process, as do all gaseous reactions, requires large volumes for reactors compared to the relatively small units used with liquid phase reaction.; There are also other references in the literature (2, 17). Partial Pressure. The continuous partial pressure process with the use of nitric acid alone developed by Othmer and coworkers (13-16) used a boiling mixture of approximately Gl% nitric acid and hydrocarbon to nitrate the hydrocarbon. The resulting water was continuously removed from the reaction by a partial pressure distillation and was decanted overhead from the hydrocarbon. This process has resulted in dinitration ab well as mononitration, and it has the advantage that i t discharges no spent acid for reconcentration. Counterflow. The hydrocarbon to be nitrated is mixed counter-
April 1954
Continuous Nitration Units in Pilot Plant
rurrcntlp with a udual nitrating medium (8). For example, a suitable column is filled with sulfuric-nitric acid mixture, and a t the bottom, benzene is introduced in droplets t o rise thro1.lgh the acid mixture and be removed at the top. Fresh acid mixture is added a t the top, while exhausted acid is removed a t the bottom. This process requires no moving parts; however, the slow motion of the liquids and the large cross section of column required makes the removal of heat of reaction difficult. Furthermore, emulsions are a problem if sufficiently fine droplets are used. S o industrial use of this method has been reported. Parallel-Flow. Here the nitric-sulfuric acid mixture is thoroughly agitated in a reaction vessel of suitable material and may pass to several others in series with the hydrocarbon in order t,o obt'ain completion of the degree of nitration desired (19, 19).
Combined Parallel-Flow and Counterflow Process The combination of both parallel-flow and counterflo\y of nitrating acid and hydrocarbon may be made to conaiderable advantage. Thus, there will be parallel-flow of the acid mixture and the toluene, through one, two, or more nitrating vessels A decanter is then utilized t o separate the two liquid streams, and they may next be flowed countercurrently t o still other mising tanks. The outflows of the second group of tanks or nitrators are combined in counterflow with the streams from the next major series of vesselas operating in parallel f l o ~ . Such a combined parallel-flow and counterflow process may I)e described utilizing six special units: 1. The proportioning contrivances for separately feeding measured streams of mixed acid and hydrocarbon into the system 2. The main nitrator 3. One or more secondary nitrators 4. One special fitted tank 5 and 6. Two continuous separators
Together with a stream of hydrocarbon, the mixed acid is fed into the main nitrator via the measuring equipment. The size of this unit and other factors are so cont,rolled that the nitration may he completed substantially in this one vessel. Adequate means are provided t o remove the heat generated. The reaction mass flows from the main nitrator to a second and possibly a third nitrator where the reaction is completed almost quantitatively. These vessels are in parallel flow. The mononitrotoluene contains approximately 1$& of toluene as it flows into a con-
INDUSTRIAL AND ENGINEERING CHEMISTRY
719
ENGINEERING, DESIGN, AND PROCESS DEVELOPMENT
1-
I
Figure 1 .
I
I
I
Comparison of Plants for Production of Aromatic Mononitrohydrocarbons
Upper drawing shows a semicontinuous process and lower drawing, continuous process of same doily productive capacity. Equipment for the two plants i s drawn to the same scale to indicate the considerable difference in size and cost of the equipment, buildings, and processing materials
120
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
Vol. 46,No. 4
UNIT PROCESSES tinuous decanter, which continuously separates spent acid from nitrotoluene passing to subsequent washing units. The spent acid flows continuously from the decanter to a speriallp fitted tank into which is fed the continuous stream of fresh toluene from the proportioning equipment. This unit utilizes any nitric acid remaining, which may be from 1 to 3% so that the remaining acid is practically free of nitric acid. From this continuous apparatus the reaction mass overfloics as fast as the components are added to another continuous decanter where the mixed toluene and some nitrotoluene are separated from the final sptmt acid. The mixture is then passed into the main nitrator; this arrangement represents a counterflow principle as compared t o the parallel flow of the main nitrating units. The Taste acid is immediately concentrated without the necessity of prior denitration, because it contains only about 0.3% nitric acid and less than 0.5% aromatic material. One major equipment advantage of this process is that no centrifugal pumps are rrquired. There are always difficulties nith centrifugal pumps in handling acids of this typc. Special stainless steels are used for all the equipment. Description of Equipment. Rotameters or other standard equipment may be utilized. The accuracy of measuring must be within 1%. The main nitrator of this plant has been constructed based on the exporience of many years, and its cooling surfaces are of such design that they map be increased to any desired large amount and especially so that there is excellent heat transfer. Furthermore, the shape of the stirrer and the special design of the apparatus guarantee a thorough mixing of the reaction components. Secondary nitrators are simply cylindrical tanks with an outside cooling jacket and an inside cooling coil. ,4 good agitator gives thorough dispersion of the reaction components. The continuous decanter may be any one of several suitable types, or it may be merely a n open tank with suitable piping connections. The preferred type has, however, a number of specially arranged bafie plates and no moving parts so that it is particularly suitable for use with explosives. Washing Process. The washing system employs the mixed parallel and countercurrent principle in order to use the least amount of water and to minimize the loss of nitrotoluene. The wash water is added through the usual measuring equipment. The nitrated hydrocarbon is mixed with fresh nrater in the first of two washing columns. From the top of this column the mixture flows into a first decanter where the acid water is separated from the nitrotoluene. The acid water is discharged, and the nitrotoluene layer is added to a second washing column with wash water from a third decanter. A measured amount of alkali is also added to neutralize the remaining acid. The mixture flows from the top of the second column into the second decanter and is separated into alkaline wash water, which is wasted, and nitrotoluene which goes into the third washing column. Here, metered fresh water washes any entrained alkali. The mixture flows from the top of this washer into the third decanter. The nitrotoluene leaves the third decanter and flows either to the drying area or storage. The wash water from the third decanter goes, as previously mentioned, to the second column as wash water. Washing Equipment. The various washing towers and decanters exposed to acid are built of the same stainless steels as April 1954
Continuous Washing Units in Pilot Plant are the nitrators, although the alkali and the neutral units may be of carbon steel. At the bottom of the columns, inlet wash water and nitrotoluene layer are thoroughly emulsified with jets of compressed air. The mixture rises to the top of the column where there is a n increase in cross section to allow air separation from the liquid, which overflows. This washing system has no moving parts which is a major advantage with explosives such as nitroglycerin and trinitrotoluene. Raw Materials and Finished Product. The initial materials are 96 to 98% sulfuric acid, about 60% nitric acid, and nitration grade toluene. The quantity of sulfuric acid used must be such t h a t the sulfuric acid content of the final acid is about 70%. The loss is about 1% of that used. The nitric acid quantity required is only about 1.5% greater than the theoretical amount required to give a loss of 1.5% of that used. The molar yield of nitrotoluene is about 98% based on the toluene added. The product contains less than 1% of toluene, less than 0.5% of dinitro products, and is completely neutral. The acid after separation contains about 70% sulfuric acid, less than 0.5% suspended toluene and nitrotoluene. Since it contains not more than 0.3% nitric acid, i t can be concentrated directly without being denitrated. The amount of alkali used is dependent upon the qualitj of the raw materials used: i t is never greater than 0.5% of the nitrotoluene washed. Plant Conditions. The personnel requirement for a unit of 20 to 60 tons per day (the latter is the largest recommended size in a single unit) and for both the nitration and the Rashing stages is one man per shift. Because of the particularly simple construction and operation of the unit, i t is possible to shut down in about 10 minutes. rlfter such a shutdown, i t may be in continuous operation again in about 10 minutes if the unit has not been emptied. Only for a very long shutdown are the several units emptied. The space requirement for a 20-ton unit is about 17,000 cubic feet.
Trinitrotoluene Production The continuous production of trinitrotoluene is dependent upon the same principle as the production of the mononitrotoluene described-namely, the combined parallel countercurrent flows. Figure 2 shows a plant for the continuous production of trinitrotoluene. The nitration is carried out in three stages: nitration of toluene to mononitrotoluene; nitration of mononitrotoluene to dinitrotoluene; and nitration of dinitrotoluene to trinitrotoluene.
INDUSTRIAL AND ENGINEERING CHEMISTRY
72I
ENGINEERING, DESIGN, AND PROCESS DEVELOPMENT
Comparison of Continuous aind Batch Nitration Processes Batch Process 1. The time required for chargin" tlie unit and for its discharge $ about the same as t h a t required for the operation itself. Besides tlie loss of time and production capacity, there is t h e disadvantage t h a t the cooling surface present can be utilized for only half the time and must, therefore, he a t least twice as large for this reason alone.
Continuous Process 1.
very slow rate of reaction and a very long time of nitration, particularly because the cooling surface in the usual batch unit i F very small in comparison t o the volume.
side. The value of the coefficient is in any case very low for the transfer of heat from tlir acid to the metal wall. 4
5.
6.
In tlie continuous p r o c e s ~ the apparatus is always filled P O that the entire cooling w r f a c e of the unit can always be utilized With respect to the .i,oluine. the continuous nitration unit has a n unusually large ratio of coolinn surface and almost anv desirez amount of surface inay be added iu tlie deaisn uwd.
7.
sary under normal woiking conditions, and the reaction mixture merely moves from one unit to the other. Since the units are always completely filled. the cooling surface can be utilized without interruption.
2.
3.
KO charging of the unit is neces-
3. T h e continuous nitration apparatus that has been developed and successfnlly used l i a y a paytirularly intensire mixing and agitation of the reaction med i u m .A comparatively excrllent heat tiansfer rorfficient is u l i tairied.
In the batch processes retilrdine of the reaction can easily occur a t the start of tlie p r o c c ~ ss i n r r in this etage one O T the ottiei components is being addivl. If tlie temperature drops too niucli -for example. by too rapid a n addition of this componenta retardation of the reaction can take place. When the temperature does increase the reartion may start again too rnpidly hrcause of the escess of the coinponent and poor heat transfer. From this nonuniform and sometimes uncontrollable reaction. there may be evaporation losses and even possihiy boilin. over or explosions. I t i i t h r r ( ~ fore necessary to select carefullv trainril and responsible workf>is for the operation.
1
I n batch nitrations. one of the reaction components is added initially in the nitrat,ion apparatus. while the other reaction component is added in m r a s u r r ~ l amounts, regulated by hand. In the reaction mixture, the acids Pass through all possible conrentrations and the hvdrocaihon
5.
Beeause of good mixing in tlic rontinuous nitrators the reaction \ eiocity is always high enougli e ~ e nafter a considerable teiliverature drop, t o prevent a large and instantaneously occurring temperature rise. Should a larger than usual quantity of heat h a r e t o be removed, the continuous unit tias, in cornparison t o the volume. iiianv times the cooling surface of t h e batch apparatus as ~vvell as a much larger heai transfer coeffirient. On the other hand, it is almost impossihle in the continuous process t o have a retarding or a n upswing of the reaction sinrr the unit, after the start, practicalll- runs automatically and only minor adiustnients hereafter are necessaiy. as it oprrates under conditions which are almayq uniiorm. By workinq according to the continuons process, therefore. especiallv alAe personnel are n o t required.
In the continuous procr?ss, composition of t h e reaction ture in each single apparat always constant. I t is possi to adiust the necessary conditions for the nitration to sccurp a n optimum. Conditions alp chosen and readily maintained t o prevent side reactions almost completely. Bv the continuous feeding the quality of the end product is practically independent of the operating personnel.
for the prevention of side react,ions can be utilized for on13 part of t h e reaction time.
It is not w e n t i a l that the nitration he cariied out completely to the end in each stage-for e x a m p l ~in , the fiist step the nitrotoluene need not be pule but may contain 10 or even 20% toluene without disadvantage. On the other hand, t h r secnond stage can go so far as t o give some trinitrotoluenr without dieadvantage. Adequate cooling surface is then provided for this. I n each single stage, the toluene and nitrotoluene niivtuie anti the nitric acid-sulfuric acid mixture are in parallel flow and. :ts noted above, also in countercurrent flow as regards the seieial stages. The residual acids of the higher stages are u s ~ din the nitrations of the lower stages after addition of nitric acid ap required. This places the stages in countercurrent flow and produces an excellent grade or C I initrotoliiene. 722
Batch Process In mononitration according to the batch method, the toluene is added, usually initially, and the acids are thereafter added from time to time. A t the operating temperatures the toluene has a corresponding high vapor pressure and presents danger oi flammability. Also, t h e quantity of the hydrocarbon present in the nitration apparatus is considerable. (If the toluene ia added t o the excess mixed acid. there may still be a relatively high vapor pressure a t the teniperature encountered, and formation of dinitrotoluene cannot be avoided, this prevents safi: distillation )or separation of the monoisomers.) As a result of the large volume of nitration apparatus in the batch process, there ii. a large q J a n tity of explosive in the nitration building.
8 . An advantage of the batch process is t h a t i t can be operated i n 8 hours time; henae, i t is nor necessary t o operate the unit a t night.
i?.
K i t h respect to the large volume of the apparatus a unit for the production of 20 'tons per d a y of mononitrotoluene together with the wash unit requires about 67.000 cubio feet of space.
0.
Continuous Process In the continuous process t i w first nitration unit converts s u b stantially the toluene into nitrotoluene. The vapor pressure o i the toluene present in the uitration mixture is therefore so small that there is little or no danger of vapori%ation. The amount ut flammable substances in the continuouv nitration apparatus ih w r y small. Furthermore, i l l the continuous process tht. nitrotoluene-toluene mixture ih always emulsified b y acid anti t h e danger of flammability 0 1 detonation has been shown bs experiments t o be praqticall? eliminated. This is a malor advantage of t h e continuous unit.
7 . The quantities of explosive present in the nitration apparatus iu the continuous process are about 1 i a 0 of those of t h e same daily capacity in the batch process. 8.
K i t h the continuous process [it3scribed here i t is possible to sh!; t down the unit a t any time within 10 to 15 minutes. I n the prep& ration of t h e mono- and dinitroliydrocarbons, it is possiblr for t h e unit t o reach normal running conditions in 1 0 to 1:) minutes, even after i t has been shut down overnight. Th(. schedule may also he acconiniodated to an 8-hour day.
$1
The continuous nitration ani1 washing plant needs only about 17.000 cubic feet of space bi,cause of the small size and ~ r n i r l l number of t h e units. 'Phis rfisults in decidedly lower equiijinent and building costs.
If the vwy highest grade material is requiwd, thc mononitrat'iori stpp and acid flow must be separated from the di- and tririitration. In the first stage a mixed acid suited for this particxlai, purpose is employed. The reason for this is that, after the nitration from mono- to dinitrotoluene, the mixed acid contains riitri,. oxides that are strongly oxidizing. Also, the mononitrotoluene preparcd from the residual actid of the di-stage contains some dinitxotoluene and ie not suit:ilil(x for a fractional distillation for the separation of the mono isomers. Particularly for the production of trinitrotoluene of higl; freezing point for military purposes, it is important to w p a r a k (hi- distillation and fract,ionation) t,he mononitrotolwnc. into the three isomers formed in the mononitration. For the following nitration, either the o-nitrotolucm alone i$ used (the para is used mainly for dyestuff purposes) or the mixture of 0- and p-nitrotoluene. The purpose of the separation is to remove the tn-nitrotoluene, Iyhich upon further nitration yields the asymnietric trinitrotoluene, which great,ly lowers the freezing point. In order t o obtain the desired high freezing product,, c-nitrotoluene !vas used almost, exclueively during World War 11 in Germany to produce trinitrotoluene for thow military purposes that require a high freezing point. The standard process as used and improved in the United States during World War I1 has been very adequately described (?), Comparison may thus readily be made between what has been said to be t,he best of the batch proccsees and the continuoil8 process.
Continuous Washing of Trinitrotoluene The continuous washing of trinitrotoluene is carried out according to the parallel-countercurrent principle in the mouonitrotoluene wash described. The equipment is the same, h i the FT aih unit Is naturally somewhat la~grr.
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 46, No. 4
Figure 2.
Plant for Continuous Production of Trinitrotoluene
Buildings 2, 3, 4, and 5 housing critical operations are built inside familiar earthen embankments to minimize effect of any possible hazard. Embankments are pierced by passogeways with offsets, and entrances are also shielded by minor earth works. Buildings and structures for other facilities, including storage and distillation of liquid materials and production of mononitrate are outside the earthen embankments 1 = Packing house 2 = Granulation 3 = Crystalline sulfite washing plant and TNT-drying plant 4 = TNT washing plant 5 = Di- and trinitration plant 6 = Absorption 7 = HzSOa concentration plant 8 = HNOa concentration plant 9 = Preparation of washing agents 10 = Compressed air plant 1 1 = Heating plant 12 = Acid storage for di- and trinitration 13 = Acid storage for mononitration 14 = Plant for distillation and separation of mononitrotoluene 15 = Store far toluene and mononitrotoluene 16 = Mononitration plant 17 = Monawashing plant
A
16
A
Sirice the dcsircd syninictric a-tririitrotolue~ie is more stable toward the sodium sulfite than the asymmetric p- and y-trinitrotoluenes, the latter are easily converted by the sulfite iiito the corresponding water-soluble sodium sufonates which are then completely removcd from the trinitrotoluene ivith the water wash. The reinoval of the tetranitrometliane is dependent upon an analogous reaction. Because of the very small requirements o i sulfuric and nitric acids and of toluene above the theoretical in this continuous process as coinpared with the regular batch process, it follows that riot as many impurities must hc removed by washing. Less water is also used because of the very efficient, washers that have been developed. The problems of waste disposal and stream pollution arc thus comparativrly small for production by this method.
I7
Acknowledgment The acidic trinitrotoluene is rvashed M ith water to remove acids, neutralized with sodium bicarbonate, then with sodium sulfite in order to wash a t least a portion of the asymmetric trinitrotoluenes and to remove the tetranitromethane held in the trinitrotoluene. Finall) the trinitrotoluene is washed repeatedly with water in order to remoTTe the last traces of sodium sulfite and other water-soluble impurities. The washing liquids are led countercurrent to the trinitrotoluene stream, and the trinitrotoluene losses are thus held t o a minimum. The sulfite ash replaces a nitro group from the trinitrotoluene with a sulfonic group. Rater-soluble sodium salts of the dinitrotoluene sulfonic acid are thus formed.
CsH, CH, (NO&
+ NanSOd
4
CsHz.CH, ( NO2)*.SOsNa April 1954
+ NaNOz
Apprcchtion is expressed to the firm of J. hleissner for permission lo present this material. Literature Cited (1) Am. SOC.Metals Review, p. 366R-8R (Oct. 15,1919). ( 2 ) Avanesov, D., and Vyatskin, J., Khim. Referat. Z h u r . , 2, KO. 5, 43 (1939). (3) Raxter, J. G., Brit. Patent 125,160 (June 22, 19lG). (4) Beule, P. de, Bull. soc. chim. Belges, 42, 27-79 (1933). (5) Chance & Hunt, Ltd., Holley, A. E., and Mott, 0. E., Byit. Pat-
ent 124,461 (Jan. 7, 1916). ( 6 ) Ibid., 125,140 (June 10, 1916). (7) Kirk-Othmer, "Encyclopedia of Chemical Technology," vol. 6, pp. 45-6, Xew York, Interscience Encyclopedia, h e . , 1951. (8) Kubierschky, K., Ger. Patent 287,799 (March 31, 1914).
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
723
ENGINEERING, DESIGN, AND PROCESS DEVELOPMENT (9) LIeissner, J., Brit. Patent 465,570 (Oct. 23, 1036) ; Ger. Patent 655.339 (Jan. 13, 1938). (10) Ibid., Ger. Patent 710,826 (;\up. 14, 1941). (11) Ibid., 732,742 (Feb. 11, 1943). (12) Meister, Lucius, and Brcining (now Farbwerke, floch8t), Ger. Patent 201,623 (June 10. 190G). (13) Othmer, D. F., ISD. ENG.CHEM.,33, 1106-12 (1941). (14) Othmer. D. F., Jacobs, J. J., and I , e ~ J., ~ ~ Ibid., , 34, 246 (1942). (15) Othmer, D. F., and Kleinhans, H., Ibid., 36, 447 (1941). (16) Sohmicl, Arnold, Z . ges. Schiess-rc. Sprengstoflw., 22, 169-73. 201-6 (1927).
(17) Shorygin, P. P., Topchiev, A. V. and Ananina, V., A , , 6.Gen. Chmi. ( C S.8.R ) , 8, 981 5 (1938). (18) StaatEmijnen, Limburg, Holland, Gel. Patent 858,245 ( S o v . 25, 1948'1 _. _. I .
(19) Weiler-ter-Neer, Uerdingen "Rh. (now Chem. Fabrikon), I b f d . , 228,544 (July 24, 1909). (20) TVestfkIisch-.4nhaltische Sprengstoff A.G., Ibid., 274,854 (Sept. 27, 1912). (21) Wilhelm, H., U. S.Patent 2,109,873 (hlarch 1, 1938). Rhzcaivm for review December 2, 1953.
AccEP,r&D
I'ehruary 18, 1954.
Continuous Production of Hexamethylenetetramine FRITZ MEISSNER
AND
ERNST SCHWIEDESSEN
DONALD
The Firm o f J. M e h e r , Cologne, Germany
,
F.
OTHMER
Polyfechnic Inrtifufe, Brooklyn I, New York
A
new continuous process for hexamethylenetetramine production allows the direct addition of the formaldehyde and the ammonia in the gaseous phase to the reactor. The formaldehyde may come directly and unpurified from an efficient and specially devised oxidation unit fed with methanol and integrally a part of the production unit. The heats of hydration of the two gases and the heat of the reaction accomplished in an aqueous phase are removed by vaporization of water from the reactor, which i s actually a specially fitted still pot. In order to prevent losses of either ammonia or formaldehyde gas, their effective concentrations in the reactor must be very low, or they would pass off with the vapors and be lost to the reaction. The optimum temperature of the reaction may be controlled b y varying the total pressure at which the reaction mixture i s allowed to boil or b y controlling the partial pressure by the presence of noncondensable gases. The reaction under these desirable conditions i s extremely fast. In continuous plant reactors i t is from 2 to 3 metric tons per day for a reactor of relatively small size with a yield on a one-pass basis of above 99% for both ammonia and formaldehyde. The solid hexamine i s removed continuously from the reactor either as fine white crystals or as a solution of any desired concentration. The heat of the reaction and of the hydration of the starting gases performs the entire water removal and eliminates the need of additional evaporative equipment and heat.
H
E X A ~ I E T H Y L E ~ E T E T R ~ or ~ ~ hexamine I I S ~ ~ has hecri
known for nearly 100 years as product of the reaction of 6 molecules of formaldehyde and 1 nlolecules of ammonia (6'). This inteiesting and symmetrical chemical structure has been carefully investigated. The carbon atoms are so positioned that lines joining them form a regular octahedron, and the nitrogen atoms are at the points of a circumscribed pyramid. \Then nitrated, hexamine gives compounds that are among the most powerful explosi One is knovr-n as Cyclonit, but in this country it is generally called Hezogen or RDX. This ingwdient of the so-called blockbuster bombs caused the production of hexamine t o reach very high levels in the United States, Germany, and ot8her countries participating in \Torid \Tar 11. Its application in peacetime iucludes important uses in the production of molding plastics, vulcanization accelerators, and various Raterproof resins and adhesives. Hexamine is the starting material for the production of various phsrmaceut'icals.
Prior Development of Hexamine Production Methods Hexamine is formed by the reaction of aqueous ammonia Trith aqueous formaldehyde arcording to the following reaction: 1
See summary on page 718.
724
+
GCH,O C 4KH3 4 CaHi?K\'r GHz0 The reaction is jtrongly exothermic. The normally expected tomnperature rise should not, take place, since at, too high a temperature there is the danger of producing by-products. Early Commercial Production. The first plants for production of hexamine operat,ed at, a react,ion temperat,ure of about 20" C., and used aqueous solutions of formaldehyde and ammonia as raiv materials. In some cases (2) a part of the ammonia was gaseous. The Ion- reaction temperature and the relatively great, heat of reaction have always been difficult t o rontrol. To provide the cooling Eurfaces, large unit,s of correspondingly large volumes were necessary. The procedure was batchwise and required a8 much as 36 hours per charge. Thc hexamine obtained in solution (10 to 20% depending on the concent,ration of the raw materials) was concentrated in vacuum (about 40 mm. Hg.) until hexamine was crystallizcd during a continuous addition of a,mmonia. After this operation, requiring 24 hours, thc product obtained was recrpstallizcd t o pharmaceutical grade hexamine ( S , ? ) . Continuous Processes Using Anhydrous Ammonia. J,ater development work was aimed a t making the process continuous, increasing the speed of the reaction, and obtaining a more con-
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 46,No. 4
