Caustic fusion of 6-methyl~2-sodium naphthalenesulfonate R. NORRIS SHREVE AND F. R. LLOYD* PURDUE
A laboratory pressure
autoclave was used to investigate the effect of concentration of alkali, amount of alkali in excess, temperature, and type of alkali on the conversion of 6-methyl2-naphthol by the caustic fusion of 6-methyl-2-sodium naphthalenesulfonate. These data were compared with conversion data for the fusion of 2-sodium naphthalenesulfonate. The conversion of 6-methyl-2-naphthol is a direct function of concentration of alkali, and is little affected by the amount of alkali in excess. A moderate increase in reaction temperature serves to increase the conversion considerably. The fusion time may be shortened and conversion increased by the use of a mixture of sodium hydroxide and potassium hydroxide as the fusion agent. The reaction rate is greater in the 6methyl-2-naphthol reaction than in the 2-naphthol reaction.
S A result of the recent commercial availability of 2-methylnaphthalene in relatively pure form from coal tar distillation, wide interest has been stimulated in the products of combination of this material in organic syntheses. An extended research program has been in progress at Purdue University to develop uses for this chemical through the sulfonation reaction. Previous investigators (1,6,6, 9) have made a thorough study of the sulfonation of 2-methylnaphthaleneJ and Stoltenberg (10) has made an exploratory study of the caustic fusion of 6-methyl-2sodium naphthalenesulfonate to produce 6-methyl-2-naphthol. The present work is an outgrowth of the last in an effort to obtain sufficient data on the fusion reaction for specification of optimum conditions for large scale operation. The only previous literature reference to the fusion of 6-methyl2-sodium naphthalenesulfonate was that reported by Dziewonski, Schoenowna, and Waldman (3) with potassium hydroxide as the hydrolyzing agent a t a temperature of 280" to 300" C. The technique of fusion of aromatic sodium sulfonates in general, however, is well described (4, 8) and it was expected that a similar method could be applied to the fusion of this material. The reaction may be generalized as: RSO&a
+ 2NaOH +RONa + NazSOa + HzO
The method used by Stoltenberg was substantially identical with that described by Shreve (8) for the commercial production of 2-naphthol in an open fusion pot. The details were modified slightly to permit reaction on a 30-gram scale in a 300-ml. nickel crucible. The reactor was equipped with a Chrome1 wire stirrer of the Hershberg type bent t b scrape the walls. The reaction temperature was 295" to 300" C. and a nitrogen blanket was employed to help reduce oxidation of the reactants. Bn investigation was made of the effect of amount of sodium hydroxide in excess upon the curves of time us. yield between the limits of 50 and 500% excess alkali. From the data shown in Figure 1 (solid lines) it is apparent that the best yield (38.4%) was obtained with 500% excess sodium hydroxide in a fusion time of 2 hours. All curves reflect the very heavy oxidation of product which occurred after exposure to the fusion conditions for 2 hours. The maximum is considerably below the commercial yield of 74% obtained in the production of the 1 Present
address, Eli Lilly & Company, Indianapolis, Ind.
UNIVERSITY, LAFAYETTE, IND.
homologous 2-naphthol in a fusion time of 6 hours with 15 to 20% excess sodium hydroxide. From a comparison of these figures, it was concluded that 6-methyl-2-naphthol is so much more sensitive to decomposition than 2-naphthol that a much larger amount of alkali should be used and the fusion time should be shortened to 2 hours. The maximum points in the curves of the exploratory results, however, corresponded to a change in the fusion mass from a uniform melt to a lumpy solid. That this change in consistency is not paralleled in the commercial 2-naphthol reaction indicates that the small scale of operation might be an important cause of the decomposition of 6-methyl-2-naphthol. Undoubtedly, the change from liquid to solid could cause local overheating and subsequent oxidation of the reaction product. With this point in mind, it w&sdecided, as a preliminary study for the present work, to determine a few data on the fusion of 2-sodium naphthalenesulfonate with which the exploratory results could be more rigorously compared.
Preliminary Investigation of 2-Naphthol Reaction A small supply of pure 2-sodium naphthalenesulfonate was prepared by the method described by Shreve ( 8 ) ,and this material was used to establish time vs. yield curves for the 2-naphthol reaction on a 30-gram scale. The reactor as described above was modified to include a stainless steel lid to increase the effectiveness of the nitrogen blanket, and a stainless steel thermometer well to permit continuous measurement of the fusion temperature. The Hershberg stirrer was replaced by a stainless steel horseshoe-type stirrer which was carefully fitted and centered by hand in the nickel reactor. A diagram of this apparatus is shown in Figure 2. Fusions were made in this reactor at 295' to 300 C. with 100 and 500% excess sodium hydroxide by the method deswibed by Stoltenberg (10). The results are shown (dashed) in Figure 1for comparison with the exploratory work. O
Considering the modifications of the reactor, the unavoidable differences in experimental technique, and the different reactants, the agreement among these data is good. In all runs, approximately the same conditions of reaction consistgncy were noted in the 2-naphthol reaction as had been observed in the 6-methyl-2naphthol reactions of the exploratory work. The curve maxima corresponded with a rapid loss of fluidity of the charge, and this point marked the beginning of a rapid darkening of the fusion color and a strong evolution of %naphthol fumes. It thus became apparent that low yields and heavy decomposition in the 6methyl-2-naphthol reaction could not be justified by an assumption of hypersensitivity of the product to oxidation, for these yields were closely approximated under similar conditions with a material which is known from industrial experience to be very stable under moderate fusion conditions. It is well known that satisfactory flyidity of a fusion mass is dependent upon the presence of 10% or more of water in the melt to depress the melting point of the alkali A very rapid loss of water from the reaction would be expected in a small scale fusion because of the relatively large surface area exposed to the atmosphere; hence an attempt was made to improve the fluidity of the charge by adding water to the melt during the course of the fusion. Several different rates of water addition were tried up to the limit where control of the reaction temperature was lost, but the mass still solidified a t 2 to 2.5 hours as before. The reactor was weighed periodically during some of these water addition runs, and the appreciable increase in the weight of the reactor in811
INDUSTRIAL AND ENGINEERING CHEMISTRY
812
dicated that 1 to 3% of the added water actually found its way into the fusion mass, but this was not enough t o increase the firnpidity of the fusion appreciably From a practical point of view, it was useless to run the reaction after solidification, and the fact that the data were not comparable with large scale fusions because of the large surface-volume ratio precluded the use of this 5c
YUMERALS INDICATE HUNDREDS OF % (t----o 6-METHYL-2-NAPHTHOL
e-------+ I-NAPHTHOL
HOOH IN EXCESS
RUNS
RUNS
40
z
3c
0
-1
w
2c
IC
I
1
I
2
3
4
5
Val. 42, No. 5
Description of Pressure Reactor The autoclave was designed for 800 pounds per square inch gage pressure and is diagramed in Figure 3. The vessel consisted of a body turned from a solid block of mild steel with a central cavity bored to receive a 100-ml. nickel crucible by a force fit to serve as an alkali-resistant liner. Asquare butt milled at the base of the body was used to hold the apparatus during assembly. A stainless steel head was provided with a hole for the entrance of a 0.125-inch stainless steel thermocouple well, a stirring shaft hole at the center, and an oblique passage for the introduction of nitrogen to the vessel. The thermowell was sealed with silver solder at both surfaces of the head, and the shaft passage was fitted with a bronze bearing at the middle with threaded packing cavities above and below. The nitrogen passage connected with the shaft entrance at the bearing and was designed so that a positive nitrogen pressure could be maintained between the two packing glands, thus reducing the pressure drop across each packing and thereby reducing the possibility of leakage of water vapor from the reaction cavity. The shaft packing was l/lti-inch asbestos cord impregnated with graphite, and it was compressed by stainless steel packing nuts drilled to admit the stirrer shaft. The stirrer itself w&s made from a piece of 1/1&ch st'ainlesssteel sheet' cut to shape and riveted t o a short length of 0.5-inch stainless steel shaft. The paddle was carefully filed to fit the crucible with the blades inclined so as to serape material down from the side walls and toward the center. The 0.25-inch stainless steel drive shaft was secured to the 0.5inch paddle stub shaft by a threaded connection inside the reaction cavity. A copper gasket beheen head and body gave a gastight seal when the sealing ring was in place. The sealing ring screwed onto the body and carried six 0.5-inch cap screws around its circumference. These cap screws, when tightened, bore directly on a case-hardened bearing ring which transmitted their compression to the head, and thus served to seal the reaction cavity. The stirring shaft was rotated at 150 r.p.m. by a laboratory stirring motor through a 4 to 1 gear reducer,
6
TIME (HrS)
Figure 1. Effect of Excess Sodium Hydroxide on Yield of Naphthols in Open Pot Fusions at 300' C.
reactor for the collection of significant or reliable data for extrapolation to large scale operation. The scale of operation could not be increased, as the facilities a t hand were not adequate for %lie preparation of the large amount of &methyl-2-sodium nq~hthalenesulfonatewhich would be required for a broad network of data. It was therefore necessary to devise a method for p:eventing the escape of water from the reaction mass and thus to si .nulate large scale operation more closely in this respect. The water could be retained in contact with the fusion by using a closed autoclav$ which would also reduce oxidation effects and pcmnit more accurate temperature control through the use of eicctrical heating. Although the control problem could be satisf;ictorily solved in this way, the use of such a device presented a r t a i n difficulties in interpretation of the data by reason of the negligible oxidation effects to be expected and the fact that the oourse of the reaction would be changed, though slightly, by the application of the pressure necessary to keep the water inside the reactor. A further disadvantage of this method of attack, which was discovered later in the work, was that the small scale of the reaction tends to reduce the effectiveness of agitation, as the total charge is not great enough t o submerge the agitator and to keep the reactants localized in, the bottom of the crucible by the force of their own weight as in a large scale industrial fusion. These objections could be lessened somewhat if there were some basis for comparison with known results in an open pot fusion. Because such data are known over a wide range of conditions for $lie fusion of 2-sodium naphthalenesulfonate, it was decided to make parallel runs with this salt in order to have a basis of comparison with large scale data for the fusion of 6-methyl-2-sodium naphthalenesulfonate in a pressure reactor. This procedure would also permit conservation of the available 6-methyl-%sodium naphthalenesulfonate by using the 2-naphthol data for exploratory purposes as well.
4STlRRER
SALT E A T H
BUNSEN BURNER
Figure 2. Diagram of Open Reactor for Preliminary Fusions
Auxiliary e uipment included a device for holding the autoclave during assembqy and an electrical heating jacket. The former Ria8 made from a 2.5-inch length of 4-inch pipe fastened to a stationary platform, and the heater was formed from a 5-inch length of 44nch pipe and a 3-inch length of 5-inch pipe welded together coaxially to a 0.5-inch annular ring of mild steel. This ring formed a shoulder inside the heater which supported the reactor by the sealing ring. The heater was wrapped with a layer of asbestos paper over which two 600-watt Nichrome wire heating coils were wound. One of these coils was arranged for connection across the 120-volt line, and the other was connected t o a Variac transformer
INDUSTRIAL A N D E N G I N E E R I N G C H E M I S T R Y
May 1950
for control purposes. The whole heater was insulated with 1.5 inches of glass wool. The fusion temperature was measured by an iron-constantan thermocouple inserted in the well, and was recorded every minute on a Micromax automatic recordtr.
Experimental Procedure The experimental procedure was identical for both fusion reactions, but is described specifically here for the 6-methyl-2naphthol runs. A reaction paste was made by mixing 25 grams of 6-methyl-2sodium naphthalenesulfonate with the desired amount of water, to this was added the solid alkali, and the mixture was stirred until the pellets had dissolved. The paste was transferred to the reaction cavity, the autoclave was assembled, and the head bolts were tightened. The assembly was placed in the preheated heater, the stirrer started, and the nitrogen inlet connected to the nitrogen cylinder. A nitrogen pressure of 500 pounds per square inch gage was applied, and the upper packing nut was tightened until the escape of gas was no longer audible. The heating cycle required 45 to 60 minutes with both heaters across 120 volts, but the reaction temperature,. once attained, could be easily maintained with a single coil through the Variac. The thermocouple was inserted in the well early in the heating period, and during the whole reaction showed temperature control well within a 5' C. range. At the conclusion of a run, the reactor was removed from the heater and immersed immediately in a bath of cold circulating water. The cold autoclave, upon removal from the quenching bath, was unsealed, and the fused product (solid at room temperature) was chipped out of the crucible and placed in a porcelain mortar. The lumps were dissolved by grinding with hot reactor washings, and the 400 to 500 ml. of brown solution thus obtained were clarified by passing through a hot-jacketed Biichner funnel. The cake was washed with several portions of hot 10% sodium hydroxide solution, and the alkaline filtrate was transferred to a 1-liter separatory funnel and acidified with 50% sulfuric acid to a pH of 5. The white 6-methyl-2-naphthol thus "sprung" rose BRONZE BEARING UPPER
SHAFT PPCKING NUT
I
PACKING
STIRRING
/
SHAFT
WELL
SEALING RING
, I INCH I Figure 3.
Diagram of Pressure Reactor
'9
HUMERALS INDICATE %
813
NaQH
IN
FUSION
SOLUTION
d
90
" 10
I
Q
O
1
I
I
I
I
l
2
3
4
S
TIME
I
S
7
8
1
9
(Hrr)
Figure 4. Effect of Concentration of Fusion Solution 0: Conversion at 100% Excess Sodium Hydroxide at 295 to 300' C.
to the surface of the salt solution, and the whole mixture was allowed to cool. The 6-methyl-2-naphthol was easily separated from the acidified mixture by extraction with 25-ml. portions of ether in six to eight stages. The ether extract was accumulated in a tared 70ml. weighing bottle and evaporated to incipient crystallization of the naphthol, then cooled and crystallized. The solid product was weighed, mixed well, and sampled for analysis. The analytical procedure employed was a slightly modified form of a method proposed by Wilkie ( I I ) , which is based upon the quantitative substitution of an iodine atom at the 1- position of the naphthalene nucleus in very faintly alkaline solution at 60' C. The accuracy of the assay was established as within 1%of the correct value for this type of product. The crude products obtained from eight to ten runs (analysis 60 to 80% methylnaphthol) were combined and distilled a t 5 to 6 mm. of pressure. The solid distillate was recrystallized from dilute ethyl alcohol to produce a material melting a t 128.5" C. The above melting point agrees well with the accepted literature values for the melting point of the pure material ( 2 , 7). The melting point obtained for the distilled product of the 2naphthol runs was 122' C.
Experimental Data Several practice runs were made with the pressure reactor described above t o develop experimental technique, overcome mechanical defects of the system, check the data for reproducibility, and determine the limits of alkali concentration over which the reaction could feasibly be studied. Within the limits chosen, the reaction product was uniform and well localized in the bottom of the reactor, thus indicating a satisfactory intimacy of phase contact. The fact that in no case was the fusion product a lumpy solid as in the open pot reaction substantiated the principle that the presence of water is necessary for a smoothly fused reaction. Five different series of runs were made with the two sodium sulfonates under identically varied conditions. The data were collected under conditions to investigate the effects of concentration of the alkali fusion solution, amount of alkali in excess, reaction temperature, and type of alkali. The specific conditions for each series may be listed as follows:
814
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 NUMERALS
NaOH
%
IN
looT
FUSION SOLUTION
90
90
--
80-
80
--
70
-.
70
8
INDICATE
-3
60--
2
P
r
6 0
NUMERALS INDICATE
%
Vol. 42, No. 5 NaOH IN FUSION
SOLUTION
60-.
2
g
50-
so--
w
2
8
40-
30t
O
i/
-4&NAPHTHOL
/;,
C-
- -*
40--
PUNS
6-METHYL-2-NAPHTHOL
RUNS
1
2
J
A
5
TIME
6
7
8
RUNS
e---+6-METHYL-&NAPHTHOL
O Y 0
/
0
&NAPHTHOL
C-----C
9
I
I
I
1
1
RUNS
I
3
4
(Hrs)
1 1 TIME (Hrs)
6
I
7
8
t 9
Figure 5. Effect of Concentration of Fusion Solution on Conversion at 507' Excess Sodium Hydroxide at 295" to 300' C.
Figure 6. Effect of Concentration of Fusion Solution on Conversion at 1Oq' Excess Sodium Hydroxide at 295' to 300" C.
100% excess NaOH, 295-300' C., 24.7-53.7'% NaOH concentration (Figure 4) Series I b 50% excess NaOH, 295-300' C., 24.i-41 .O% NaOH roncentration (Figure 5 ) Series IC 10% excess XaOH, 295-300' C., 24.7-33.2% Na0I-I aoncentration (Figure 6) Series I1 10% excess NaOHy 24.7% NaOH concentration, temperature lovels of 295-300°, 320-325', and 345-350' C. (Figures 9 and 10) Series I11 10% excess alkali, 24.7% alkali concentration as NaOH, 295-300' C., operate with pure NaOH, pure KOH, and an equimolar mixture of the two (Figures 11 and 12)
ditions. The importance of fluidity is exaggerated somewhat in this study because of the method of investigation and the scale of the reaction. In an industrial fusion, the reaction is started by adding the sodium sulfonate slowly, over a period of about an hour, to the fused caustic at the reaction temperature. During this addition period, the reaction is in progress, and little difficulty is experienced in maintaining a fluid charge, even with relatively high concentrations of sodium hydroxide in the fusion solution. In addition, the weight and volunie of the reactants are sufficient t o
Series I a
The data of series I are cross-plotted in Figures 7 and 8 to show the effect of alkali in excess a t constant concentration.
90
90-
80
Discussion of Results Natural Limitations of Method. In the specification of the limits of investigation for the series I runs, the maximum concentration of alkali was d e c r e a s e d as t h e amount of alkali in excess was decreased. This is based upon a fluidity consideration which has not been discussed previously, but which was found to be an outstanding variable in the reaction under these con-
"'T -
'0°7
-.
70-
2
9
t
0-
2ol
30
-- --+
CMETHYL-&NAPHTHOL
RUNS
IO
4
--hri
----e
-
40
2-NAPHTHOL RUNS
301
t - - + 6-METHYL-2-NAPHTHOL
t
10
- 0
5ol----
I
60-
9 hrs. r
RUNS
lot SO EXCESS NaOH
Id0 0
Figure 7. Effect of Excess Alkali with 33.2q' Sodium Hydroxide at 295' to 300' C.
04
;
0
IO
I 50 EXCESS NOOH
100
(%I
Figure 8. Effect of Excess Alkali with 24.77~Sodium Hydroxide at 295" to 300'C.
May 1950
INDUS9RIAL AND ENGINEERING CHEMISTRY
keep the reaction well localized, and the stirring blades submerged, almost without regard to the consistency. The use of a closed autoclave, however, necessitated a departure from the standard procedure, as all the reactants must be mixed before charging to the vessel, and the mixture did not become well condensed until fusion had taken place. Thecombination of these two effects produced anunsatisfactory reaction which was not reproducible in conversion whenever the initial charge did not have a certain minimum degree of fluidity. In this case, the material became distributed around the interior of the reactor and adhered to the paddle in such a way that satisfactory agitation was not obtained, and the reactants did not reduce to a smooth fusion melt. As is to be expected, a low yield was invariably the result. The initial fluidity of the charge, however, was dependent upon the total amount of water present (the sodium sulfonate charge was constant for all runs), but because the amount of water varied inversely with concentration and directly with amount of alkali, it was necessary to reduce concentration as the amount of alkali was reduced in order to preserve the minimum fluidity required for satisfactory operation. Thus, for each quantity of alkali in excess, the concentration was varied from 24.7% sodium hydroxide up to the natural maximum indicated by the above considerations. A second related effect was noted between the two sodium sulfonates used, in that fluidities of the cold charges were not comparable under identical conditions; 6-methyl-2-sodium naphthalenesulfonate charges were always noticeably less fluid than corresponding 2-sodium naphthalenesulfonate charges and hence the natural maximum alkali concentration for the former was always below that of the latter. This effect was quantitatively evaluated at low sodium hydroxide concentrations by means of solubility tests in alkaline solutions. These tests showed that the solubility of 6-methyl-2-sodium naphthalenesulfonate in alkali weaker than 16% sodium hydroxide is slightly less than half the solubility of 2-sodium naphthalenesulfonate. By operating within the prescribed limits of concentration of alkali, reasonable uniformity of agitation was assured by the fact that the fusion appeared to be well localized and condensed when the reactor head was removed. This contention was further
'"1
validated by the fact that the data reported were consistently reproducible within 2% in all cases where check runs were made. This was considered a suitable degree of precision in view of the heterogeneity of the reaction and the purpose for which the data were intended. Effect of Concentration of Alkali. Examination of the curves of Figures 4 to 6 shows that the conversions in the 6-methyl-2naphthol runs were below the corresponding conversions of 2naphthol for the major part of the fusion, but there is a distinct tendency for the former to exceed the latter later in the reaction period. This indicates that the former reaction is slow starting, but its rate is greater for the bulk of the fusion. The slow starting may be explained by the poorer fluidity of the 6-methyl2-naphthol reaction charges, as this characteristic tends to impede reduction to a smooth melt; hence the phase contact is not as intimate in the first stages of the reaction. After the attainment of fluidity, however, a more rapid reaction takes place with the resulting tendency toward higher conversions after 6 hours. This was qualitatively substantiated by the observation that for long runs there was little apparent difference between the degree of condensation of product in the two reactions, but for short runs the 6-methyl-2-naphthol product was definitely less well localized and condensed than the 2-naphthol product. The conversion level is directly related to alkali concentration for the 6-methyl-Znaphthol runs, as is to be expected; however, the 2-naphthol data are &nomalousin this respect. The lack of strict correlation in the 2-naphthol runs between concentration and conversion indicates that other factors tend to affect conversion significantly over the range of concentrations selected. By kinetic principles, a direct relationship is normal, but kinetic theory assumes freedom from such nonideal effects as imperfect agitation and nonuniformity of the reaction charge. In this case, the system is extremely sensitive to the fluidity of the charge, and the conversion is largely dependent upon the intimacy of contact between the phases. Because the fluidity of the charge is in'versely dependent on alkali concentration, it is not unreasonable to conclude that in certain ranges the tendency toward reduction in conversion by reduction in alkali concentration is more than counteracted by the tendency toward increased conversion by
looT
'
-
295-300% 320-3258'C
3
345-35OoC
o----O &NAPHTHOL
2-NAPHTHOL
e-
2
I
-
2ol
RUNS
- 4 6-METHYL-&NAPHTHOL
RUNS
20
RUNS
e------. 6-METHYLZ-NAPHTHOL
RUNS
10
10
0
*
815
I
1
o
i
i
d
4
5
6
I
I
7
B
1
9
TIME (nrsl
Figure 9. Effect of Fusion Temperature on Conversion at 10% Excess Sodium Hydroxide and 24.7% Sodium Hydroxide Concentration
O U e95 300 505 310 315 320 325 330 3 3 5 340 3 4 s 350 AVERAOE FUSION TEMPERATURE Po)
Figure 10. Effect of Fusion Temperature on Conversion at 10% Excess Sodium Hydroxide and 24.7% Sodium Hydroxide Concentration
I N D U S T R I A L A N D ENGINEERING CHEMISTRY
816
Vol. 42, No. 5
looT
70
g 5 0 40
P-NAPHTHOL
0----4
RUNS
*-----e 6-METHYLL-NAPHTHOL 50s505,
IloOH,
i
J
/' C-----O
&NAPHTHOL
RUNS
O---~6-ME'fNYL-k-NAPHTHOL
RUNS
RUNS
W% KOH
295-5OO'C Io!
I
I
O
I
2
9
4
4
6
7
8
0
TIME (hrs)
Figure 11. Effect of Type of Alkali at 10% Excess Alkali and 24.7 yo Sodium Hydroxide Concentration
the coricurrent increase in fluidity and intimacy of phase contact The relatively small apparent effect of concentration on conversion in this anomalous range is a further indication of this behavioi. Although the same inconsistency was not noted in the 6methyl-2-naphthol runs, it is possible that a similar behavior might be observed over a different range of concentrations. Effect of Amount of Alkali in Excess. Examination of the cross plots (Figures 7 and 8) shows the effect of amount of alkali on conversion to be in appaient opposition to the principle of mass action, for an inciease in the amount of alkali has either no appreciable effect or else a moderate negative effect on conversion during a given fusion period. This result also disagrees superficially with the exploratory work (Figure 1) The total reaction volume, however, is subject to a wide variation at constant concentration between the limits of alkali in excess investigated, so that the concentration of sodium sulfonate may change by as much as 50% at 24.7% concentration. The effect of this variation is in such a direction as t o oppose the effect of quantity of alkali charged. In the exploratory work, the opposite effect was observed because the amount of water present was not controlled; hence as the amount of alkali was increased, the sodium sulfonate was diluted, in effect, by sodium hydroxide alone, and the anomaly was thus suppressed. From this consideration, it is apparent that the amount of alkali in excess has a smaller effect on conversion than the concentration of the sodium sulfonate, if the amount of water present is controlled. Effect of Temperature. Because in the series I1 runs the concentration and amount of alkali were maintained constant, the effect of consistency of the reaction mass was not observed, except that elevation of the temperature tends to produce a well fused reaction somewhat earlier in the run, thus inducing a higher rate in the earlier part of the fusion. The curves of Figures 9 and 10 indicate that the 6-methyl-2-naphthol reaction is more sensitive t o an increase in temperature than the 2-naphthol reaction. This is probably due in large part to the shortening of the initial fusion period a t elevated temperatures. The 320' to 325" C operating temperature is the optimum for both reactions under these conditions, for very high yields are produced in relatively short periods. Raising the temperature to 345" to 350" C. results in less favorable conversions due to more vigorous side reactions+.g., ether and sulfone formation
,I , 0
60 MOLE % KOH IN FUSION
I
100
Figure 12. Effect of Potassium Hydroxide in Fusions at lOY6 Excess Alkali and 24.7y0 Sodium Hydroxide Concentration
Ternperature elevation kvould rinturally be expected to inureaac: the oxidation eflect in open pot reactions; however, this side reaction had no effect on the result*sof this study. Effect of Type of Alkali. The curves of Figures 11 and 12 shoiv that the use of potassium hydroxide as a fusion agent improves the conversion over sodium hydroxide, as agent, but an equimolar mixture of the two results in conversions superior to either pure alkali. This behavior may be just,ified by thc observation t'hat this mixture corresponds roughly to the eutectic composition for mixtures of these two bases and is therefore capa,ble of producing a more fluid reaction mass, as it is a t a teniperature well above its melting point. In addition, the alkali naphtholate produced is a mixture of the potassium and sodiuni salts, and therefore an additional melting point lowering effect is introduced. Better phase contact, is thus assured by using the mixture, and a higher conversion results. The 2-naphthol reaction is more strongly affected by a change in the type of alkali than thv 6-methyl-2-naphthol reaction, for in the former the conversion curves tend to show maxima, thus indicating that side reactions are degrading the product even at this relatively low fusion t,erriperature.
Conclusions The presence of water in a fusion reaction mass is necessary to preserve the fluidity of the charge. Open pot fusion on a small scale is unsatisfactory, as the fusion mass is subject to heavy decomposition cnusedby local overheating and poor agitation, In the pressure reacbor, the amount; of alkali in excess lias a small effect on the naphthol conversions of the sodium sulfonates studied. Over the range investigated, the conversion of 6-methyl-2naphthol is directly related to the alkali concentration in the fusion solution. Conversions of naphthols are heavily dependent upon the consistency of the fusion mass. With controlled composition of the fusion mixture, the conversion of the naphthols is dependent upon the concentration of the sodium sulfonate. An increase in temperatiirr inerrasps t,he reaction rat)(!in t,he
May 1950
INDUSTRIAL AND ENGINEERING CHEMISTRY
fusion of sodium naphthalenesulfonates, but also increases the rates of the side reactions. Conversion in fusions with pure potassium hydroxide as agent is greater than in those with sodium hydroxide as agent, but an equimolar mixture of the two gives a higher conversion than either pure alkali.
Literature Cited (1) Czenkusch, E. L., unpublished M.S. thesis in chemical engineering, Purdue University, February 1948. (2) Dziewonski, K., and Chromik, T., Bull. intern. m a d . polon. sci ,
classe sei. math., 1938A,541-50. (3) Dziewonski, K., Schoenowna, J., and Waldman, C., Ber., 58B, 1211-18 (1925).
*
817
(4) Groggins, P. H., et al., “Unit Processes in Organic Synthesis,” 3rd ed., New York, McGraw-Hill Book Co., 1947. ( 5 ) Kruder, G. A,, unpublished Ph.D. thesis in chemical engineering, Purdue University, February 1948. (6) Miller, J. R., unpublished M.S. thesis in chemical engineering, Purdue University, February 1948. (7) Royer, R., Hoi, B., and Woi, H. K., Bull. soc. chim., 12, 904-8 (1945).
Shreve, R. N., Color Trade J . , 14, 42-7 (1924). (9) Shreve, R. N., and Lux, J. H., IND.ENG.CHEW,35, 306-12
(8)
(1943). * (10) Stoltenberg, D. R., unpublished M.S. thesis in chemical engi. neering, Purdue University, June 1948. (11) Wilkie, J. M., J. SOC.Chem. Ind., 30, 398-402 (1911). RECEIVEDJanuary 12, 1950.
Continuous flow stirred tank reactor systems Development of Transient Equations DONALD R. MASON’ AND EDGAR L. PIRET UNIVERSITY OF MINNESOTA, MINNEAPOLIS 14, MI”.
Exact mathematical expressions are developed which completely describe the concentration changes that occur in continuous stirred tank reactor systems during transient periods of operation. The reactant and product concentrations are given as functions of time when single, simultaneous, consecutive, or reversible first-order reactions occur in the system, or when a nonreacting system is being purged of its contents. These expressions are applicable when the system is changing from one steady-state operating condition to another, and under certain circumstances when the system is being started
up or shut down. The mathematical solutions are given for systems of vessels all having the same volumes, all having different volumes, and combinations thereof, as well as for multitemperature-level systems. These extremely general equations for the transient states could be readily obtained by using the Laplace transformation method for solving the linear differential rate equation for the system. This method has definite advantages over the more specific mathematical methods which have been used in this field, and it should find applications in many other branches of chemical engineering.
R
equation is obtained which can be applied to systems of vessels all having equal volumes, or unequal volumes, or combinations thereof. The feed component concentration initially in each vessel and in the feed stream may be different from zero, and furthermore be independently different from each other. This equation is applicable when the system is being purged of its contents, or when single or simultaneous first-order irreversible reactions are being carried out in the system. The individual tanks need not be operated at the same temperatures. This most general equation, which is developed below, describes the operation when the system is changing from one steady-state operating condition to another, and under certain conditions when the system is being started up or shut down. Solutions have also bceri worked out for some cases of simultaneous, consecutive, and reversible first-order reactions. The equations that are presented in this paper could also be applied to first-order reactions in fluid catalyst units if no volume change occurs in the reacting system, and if the concentrations are uniform throughout each individual unit. These equations may also be appIied to irreversible secondorder reactions in these types of systems if one reactant is in such large excess that its concentration throughout the system may be assumed to be constant. Continuous stirred tank reactor system have the following characteristics, which must be well understood. The basic assumption is made that the concentration of each individual tank or reaction compartment is uniform throughout its contents, and
ECENTLY considerable interest ( 3 , 4 , 7-9,18, IS) has been shown in the development of design equations for continuOUS stirred tank reactor systems-i.e., for system in which a solution flows continuously through a row of reaction compartments as shown in Figure 1. In a recent paper, Eldridge and Piret ( 4 ) have given a brief review of the field and have presented a useful method for designing such systems. Their method is applicable for the steady-state operating condition only. In addition to the steady-state condition of operation, certain transient conditions arise whenever the system is started up, changed from one set of operating conditions to another, or shut down. At such times the steady-state operating equations do not adequately describe the behavior of the system. To derive the equations that do apply in these circumstances, a rate equation for the system must be solved. To date this rate equation has always been solved by Ham and Coe ( 6 ) , MacMullin and Weber ( I S ) , Kirillov ( 9 ) , Kandiner (8), and Johnson and Edwards (7) using the classical mathematical methods, which become difficult very rapidly as the complexity of the system increases. As a result only a limited number of cases have been solved. These cases and their solutions are included in Tables 111, IV, and V. In this paper the Laplace transform method of solving linear constant coefficient differential difference equations is used to solve in a relatively simple manner the rate equation of the system for a wide variety and number of conditions. A most general 1
Present address, Bell Telephone Laboratories, Inc., Murray Hill, N. J.
