326
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
The equipment for this conrersion consisted of a concrete mixer, two large wooden tanks, and necessary pump, steam, and water lines. It was assembled as shown in Figure 2. A charge of 200 pounds of ore (ground to 200 mesh), 40 pounds of sodium carbonate (a 25 per cent excess), and 15 gallons of hot water were placed in the concrete mixer. A temperature of about 90" C. was maintained by blowing live steam into the slurry in the mixer during operation. The mixer was allowed to rotate for one hour, and the course of the reaction followed by determining the residue insoluble in dilute hydrochloric acid (Figure 3 ) . Further operations were limited to a 30-minute period of agitation, after which the charge was dumped into a 350gallon tank. One day's operation of 1400 to 1600 pounds of ore about filled the tank. After standing overnight to settle, the clear liquor on top was pumped off, more water added, and the slurry pumped to a 400-gallon tank. This was worked twice by decantation in 24 hours, and the thick slurry taken to a plate dryer. Less than one per cent of water-soluble material remained in the dried product.
SULFONATI
Vol. 35, No. 3
Acknowledgment
The pilot-plant experiments were carried out by Edward Ammer of the Manufacturers Mineral Company of Seattle. Literature Cited (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14)
Booth, U. S. P a t e n t 2,112,903 (April 5, 1938). Caldwell and Boyd, IXD. ENG.CHEM.,34, 230-3 (1942). Doumani and Kobe, Ibid., 31, 264-5 (1939). Elledge a n d H i r s c h , U. S. P a t e n t 2,106,131 (Jan. 18, 1938). Gallo, Ann. chim. applicata. 25, 628-31 (1935). Ibid., 26, 109-15 (1936). Harness, U. 8.Bur. Mines, Circ. 7200 (1942). Kobe and Doumani, 2. anorg. allgem. Chem., 232, 319--24 (1937). Kobe, H a m m , a n d Leipper, IND. EKG.CHEM.,32, 981-3 (1940). Kobe and Handlin, unpublished work. Kolthoff, "Volumetric Analysis", Vol. 11, pp. 418-21, New York, John Wiley & Sons, 1929. Piva, Giorn. chim. i n d . applicata, 5, 279-84 (1923). Thomas, U. 5 . P a t e n t 1,936,806 (Nov. 28, 1933). Townley, Whitney, and Felsing, J . Am. Chem. Soc., 59, 631-3 (1937) I
APHTHALENE
Application of Partial-Pressure Distillation Donald
F. Othmer,
Joseph
J.
Jacobs, Jr., and Wilbur
J.
Buschmann
POLYTECHNIC INSTITUTE, BROOKLYN, N. Y.
ANY processes in the chemical industry involve the removal of water from aqueous solutions or as formed during a chemical reaction. I n the former case the unit operations of distillation and evaporation are usually applied, although in certain special cases the partial pressure method-i. e., removal of the water as a constantboiling mixture with a n added immiscible liquid-has proved desirable ( 5 ) . I n the latter case, where the water formed during a reaction affects the rate, chemical dehydrating agents have been used. An example is sulfuric acid in nitration and sulfonation reactions; it has been proposed (4, 6, 7 ) to use the partial-pressure method for the removal of this water produced in both the sulfonation and nitration of benzene. An immiscible liquid was added in each case to remove the water as a constant-boiling mixture by distillation. A logical extension of the sulfonation of benzene is the sulfonation of other aromatics. P-Naphthalene sulfonic acid is necessary for the manufacture of P-naphthol, an important dye intermediate; and it was felt that the partialpressure method might be applicable to the sulfonation of naphthalene. Chemistry of Naphthalene Sulfonic A c i d s
The number of sulfonic acids of naphthalene, naphthol, and naphthylamine is extremely large, and their importance is growing. More and more technical applications for the acids are being found. The sulfonic acids of naphthalene can be converted to a- or @-naphthol, the most important dye intermediates in the production of a z o dyes. When naphthalene is sulfonated, two isomeric inonosulfonic acids are formed. The temperature of the sulfonation determines the relative amount of each obtained. It
has not been possible to produce one form of the sulfonic acid alone. A mixture of the two is alrrays formed. When the reaction is performed at 40" C., the a-rnonosulfonate is the predominate form:
When the sulfonation is carried out at 40" C., the ratio of alpha/beta form is close t o 96/4. When the sulfonation temperature is raised to 160" C., the beta compound represents 86 per cent of the total sulfonic acids formed. A number of isomers may be formed on further sulfonation, and their separation is usually difficult. The isolation of the individual sulfonic acids have always presented a problem in industry. At present the monosulfonation of naphthalene is usually carried out with a 25 to 40 per cent excess of sulfuric acid, of 93 to 98 per cent strength. In the preparation of the alpha compound, the sulfuric acid is placed in a reaction container and the naphthalene is added, keeping the temperature below 60" C. When the beta form is desired, the naphthalene is melted and the acid is added to the hydrocarbon, maintained a t a temperature of 160-165" C. To determine the completion of a reaction, samples are taken a t intervals and steam-distilled. When no naphthalene is steam-distilled, the reaction is complete. When naphthalene-2-sulfonic acid is the desired product, the alpha form of the acid is decomposed by dry steam and is removed with the naphthalene by steain distillation.
March, 1943
INDUSTRIAL AND ENGINEERING CHEMISTRY
327
t b b In extending the technique of partial-pressure evaporation t o the sulfonation of naphthalene, several of the process variables have been investigated. Naphthalene was sulfonated with as little as one per cent excess sulfuric acid; high yields were obtained by removing the water formed during the reaction in i t s constant-boiling mixture with kerosene. The maximum yield was found when exactly the stoichiometric quantity of water was distilled from the reaction flask. When a lesser quantity of water was removed, the reaction did not go to completion, when more than the theoretical amount of water was removed (as was sometimes the case), this was evidently possible only because of decomposition or charring of product, with resulting lower yield. The effect of varying the amounts of exc2ss sulfuric acid was also investigated. Sulfone formation was found to b e a function of the amount of water removed in the partial-pressure distillation. Since naphthalene i s soluble i n kerosene, the recovery of any unreacted naphthalene i s very simple in this method. Because of the reduction in the amount of excess acid required, the excellent heat control which i s possible, as well as the general simplification in procedure, the use of kerosene in a partial-pressure distillation in the sulfonation of naphthalene appears to offer some advantages over conventional methods) a continuous process can probably be utilized.
A study of rates of sulfonations has shown that, as the water of reaction is formed, the rate of sulfonation will decelerate. Unless Figure 7. Sulfonation Appathis water is reratus moved so as to prevent excess dilution, Flask with liquid-sealed agitator and thermometer, condenser for reflux, the reaction will with calibrated moisture determinastop a t a definite tion tube for decanting water i n sulfuric acid concencondensate (heavy layer) and retration, different for turning o i l layer t o flask. each organic substance. Therefore, it is of great economic importance to remove this water of reaction, either mechanically or by chemical combination. Various methods have been devised to accomplish this purpose: 1. CSEOF OLEUM. This method for keeping up the sulfur trioxide concentration has been used for some time; the excess sulfur trioxide combines with the water of reaction to form sulfuric acid. This method has been proved practical in the disulfonation of benzene and ne hthalene. The oleum and organic compound should be addef gradually and concurrently to a large volume of the cyclic acid, thus taking up the water of reaction as quickly as it is formed. 2. USE OF VACUUM.Reduced pressure (1,b), as a means of removing the water of reaction, has some technical advantage in the sulfonation of phenol and benzene.
EVALUATION OF LOSSES.I n the sulfonation processes used, the following losses are incurred (a), which are those commonly encountered in the case of naphthalene sulfonation to form ,&naphthalene sulfonic acid:
Proposed Method The removal of water in this process is essentially a partialpressure evaporation, involving, however, several complications. The water must be formed by the reaction before it can be removed. When the water is formed, it dissolves the sulfuric acid in the reaction mass. Since sulfuric acid
has a great affinity for water, the vapor pressure of water is considerably lowered. I n all cases various hydrocarbon fractions were added to the reaction, so that the combined vapor pressure of the diluent and the water was greater than atmospheric pressure and thus sufficient t o boil the water out of the sulfuric acid. This was, in effect, the same as the use of a vacuum equal to the difference of the atmospheric and the partial pressure of the diluent. To perform the reaction a t optimum conditions and t o produce the maximum amount of naphthalene-2-sulfonic acid, the reaction must take place a t 160-165" C. The diluent must be chosen, therefore, t o boil within a range close t o this temperature. SULFONATION APPARATUS.The sulfonations qere performed in a three-neck one-liter flask, fitted with a 15-cc. moisture determination tube, a water-cooled reflux condenser, and a thermometer (Figure 1). The agitator was fitted into the middle neck of the flask and consisted of a glass rod with the end bent into a paddle. This simple blade was enough to keep the acid layer dispersed throughout the kerosene layer. Lubricating oil was used in the seal, which consisted of two concentric copper pipes, fitted with corks and a glass tube. The heat was supplied by a Bunsen burner.
Separation of Reaction Products One of the most difficult problems to be faced in a sulfonation process is the separation of the reaction products. If only one sulfonic acid is formed, the simplest method is to convert the sulfonic acid to the salt of an alkaline earth. When several isomers are formed, as with naphthalene, the method is more complex. In all subsequent discussions, it was assumed that a constant amount of 15 per cent asulfonic acid was always formed. The analytical scheme was concerned onlv with the total amount of naDhthalene sulfonic acid formed. " Several possible methiods of separation were tried. Recovery of the pure naphthalene sulfonic acids by crystallization did not give quantitative results despite the use of hydrochloric acid for salting out the pure acids. Fractional precipitation of the sodium salts was attempted but found to be inadequate. The method of analysis finally adopted follows.
INDUSTRIAL AND ENGINEERING CHEMISTRY
328
ANALYSIS.The sulfonation mass was dissolved in 200 cc. of water. The resulting solution was so darkened by tar and carbon that clarification was necessary. Because carbon and tar pass through ordinary filter paper, the commercial filtration method was adopted (1). Decolorizing charcoal was added to the solution, it was brought t o a boil and then filtered, and the process was repeated until the solution was a straw color.
Vol. 35, No. 3
The solutions were neutralized with hot hydrated lime, and the gypsum was filtered off, dried, and weighed. The remainder of the solutions were evaporated in casseroles a t about 95" C. The calcium sulfonic acids were then weighed. These determinations checked one another within 2 per cent and checked the true figures within 2 per cent. The asulfonic acid forms a monohydrate; therefore, the determination will be slightly low. This error is not serious because the molecular weights are so high and also because the alpha form is only about 15 per cent of the total yield. EXPERIMENTAL PROCEDURE. The naphthalene was dissolved in the diluent, and the mixture was heated t o boiling in the reaction flask. The sulfuric acid (commercial 93 per cent acid) was fed in gradually from a dropping funnel discharging below the surface of the liquid. Varsol, a sulfuric-acid-treated kerosene (supplied by Colonial Beacon Oil Company) was fractionated and the cut of 165-175' C. was collected. This fraction was used as the diluent in all runs. The temperature in the reaction mass was always 160" C. Several preliminary runs were made a t different ratios of kerosene to naphthalene in a given batch; it was found that 4 parts of kerosene to 1 part of naphthalene provided enough liquid to make the batch fluid and easy to handle without substantial charring.
'/.Y! y 80 -1
70
0 -1 W
F60bE X C E S SIb S U L F2U10R I C
ACID d0
-
P41E0R C E N 50 T
Figure 2. Effect of Excess Sulfuric Acid on Y i e l d o f Sulfonic Acid in Preliminary Experimen ts
The total volume of solution was measured, and an aliquot portion used for analysis. The solution was exactly neutralized with calcium hydroxide, the end point being determined by adding phenolphthalein. The solution was then evaporated to about half its volume or about seven times the weight of the reactants dissolved in the sample, and then filtered hot. The gypsum was separated from the calcium salts in solution. The solution was cooled in an ice bath, and the precipitated salts were filtered. The remaining solution was evaporated to dryness to obtain all of the sulfonates. Before the sulfonation mass was analyzed, the solution of acids and tar was left to stand a t least overnight. Some of the tar and sulfones settled out of solution and this facilitated filtration. To make sure there was no serious error in the method of analysis, two blank runs were made. To make these runs, some of the free sulfonic acids were needed. The first step, therefore, was t o prepare some free acid; some of the filtered solution from a run made previously was evaporated to about half its volume. This point was approximated by a boiling point of 115" C. The solution was cooled, and half its volume of strong hydrochloric acid was added. The vessel containing the acid was placed in an ice bath. After a few minutes white crystals appeared in the liquid until the mass seemed almost solid. These crystals were filtered and dried; special precautions had to be taken, because the beta form is deliquescent. Air which had been dried by bubbling through concentrated sulfuric acid and passing through a drying tube was passed over the acids in a sealed container. The acids were then in the dry condition. DETERMINATIONS. Two equal samples of the acid were removed from the drying vessel and quickly weighed. To duplicate the conditions in this experiment, weighed amounts of 93 per cent sulfuric acid were placed in the beakers with the sulfonic acids. Each sample was diluted with ten times its weight of water. The solutions were heated to boiling and passed separately through activated charcoal to see if any was absorbed. The charcoal was washed with water, and the washings were added to the filtrate.
Effect of Excess A c i d
Excess sulfuric acid is necessary in ordinary sulfonations to take up the water formed during the reaction. The use of excess acid in a partial-pressure sulfonation also tends to increase the dehydrating effect and thus influence the yields. Several runs were made with varying amounts of excess acid but a constant amount of removed water (Table I, Figure 2).
Table I. Effect of Excess Acid on Yields (9.5 cc. water removed; 50 grams naphthalene and 150 grams diluent used) % Total Analysis of Reaction Mass, % Ex- Yield % A?id sene Tar cess Sulfonic Acid Acids, &SO4 Unre- Carboh- Sulfonic sultonles, Used % Used acted ized acid HISO, eto. 0 61.7 62.3 11.3 9.35 54.0 5.0 41.0 20 84.0 70.0 11.6 8.00 69.5 5.5 25.0 30 87.5 40 90.0 6b:o 2s:2 7:a5 7i:5 1415 1410
~z,,-
While excess sulfuric acid did increase the yield, it is shown later that better dehydrating conditions (optimum rates of agitation and heating and optimum values for other variables) will produce high yields with no excess acid. Effect of Amount of Water Removed
I n the preliminary runs the yields varied considerably with the amount of water removed from the reaction mass. The theoretical quantity of water produced by the reaction between naphthalene and the stoichiometric quantity of sulfuric acid is 7.04grams. If the water in the sulfuric acid is also taken into account, the total amount of water to be removed (using 1 per cent excess sulfuric acid) is 9.94 grams. However, even more than this amount could be removed simply by continuing the dehydration process. A series of reactions was carried out in which all conditions were kept constant except the amount of water removed. Fifty grams of naphthalene, 42.1 grams of sulfuric acid, and 150 grams of diluent were used in each run. The results in Table I1 and Figure 3-4 show that the optimum yield of the naphthalene sulfonic acids is obtained by removing
INDUSTRIAL AND ENGINEERING CHEMISTRY
March, 1943
329
was plotted against the amount of water given off in Figure 3C; D indicates the percentage of sulfonic acid in the reaction mass. I n both cases the best results are those obtained by the removal of nearly the theoretical amount of water. Optimum Conditions
I
ae
II
I
i
1
10 C
I II
1
I
1
I le
C. WATER REMOVED
Figure 3. Effect of Amount o f w a t e r Removed on Yields o f Sulfonic A c i d and on Formation of Insoluble Materials
The sulfonation of naphthalene involves several dehydrating reactions of which only one is desirable. Therefore, to determine optimum conditions, a dehydrating condition must be attained which has the least effect on the undesirable r e x tions and the maximum effect on the desirable ones. I n normal sulfonations and nitrations, this is accomplished by varying the quantity of sulfuric acid; in the partial-pressure method, i t can be done only by varying either the temperature or the rate or amount of water removal. Thus, a run was carried out with the stoichiometric amount of acid under the optimum conditions of correct amount of water withdrawal, slightly improved agitation, and somewhat higher rate of heating. Fifty grams of naphthalene were dissolved in 200 grams of kerosene, and 42.1 g a m s of 93 per cent sulfuric acid were charged into the reaction flask; the mass was then heated with violent agitation. A total of 10 cc. of water was removed, and the mass was analyzed for total sulfonic acid and sulfone. The yield of sulfonic acid, based upon naphthalene, was 96 per cent and the sulfone formation was 3.2 per cent. No unreacted sulfuric acid was found in the mass. The use of a diluent in this type of operation seemed to offer an opportunity for the development of continuous methods. A small packed glass column was set up in the laboratory, and sulfuric acid and a hydrocarbon solution of naphthalene were fed simultaneously to the top of the column, Kerosene vapors were passed countercurrently, and the water of reaction was continuously distilled out with the hydrocarbon. The sulfonation proceeded smoothly; yields comparable with batch operation were obtained by withdrawal and analysis of the bottoms product. Conclusions
the theoretical amount of water. Evidently, the removal of more water causes side reactions and excessive charring of the kerosene entrainer. Since the reaction producing sulfones involves the loss of an additional molecule of water, the amount of water taken off should have an effect on sulfone formation. Accordingly, the data forwater-insoluble materials (tar and sulfones) in Table I1 were plotted in Figure 3B. These insoluble materials are the sum of the degradation products from both the naphthalene and the kerosene since there is no simple analytical method available for differentiating between them. These data are not, therefore, directly comparable to those on yields in the second column. A sulfuric acid balance was made for these various runs and the percentage of original sulfuric acid which did not react
While the use of the partial-pressure method in the sulfonation of naphthalene has not been investigated exhauustively, enough of the optimum conditions have been determined to project the sulfonation of naphthalene in the presence of kerosene as having several advantages: 1. The use of excess acid can be eliminated without substantial loss of yield. 2. Temperature control can be maintained accurately by roper selection of the kerosene entrainer. Sudden surges of {eat will be merely absorbed as latent heat of the diluent. 3. Unreacted naphthalene can be recycled in the kerosene and thus recovery roblems are simplified. 4. It appears &at a continuous process might be developed for production use.
Literature Cited Table II.
Effect of Water Removed on Yields and on Formation of Insoluble Materials (Stoichiometric amount of acid used in each case) Total Analysis of Reaction Mass. % Yield Tar Cc. Sulfonic A?id % sulf on’es, Wate, Acids, UnreKerosene Sulfonic % acted Carbonized acid H&o4 eto. Removed 2.40 9.5 8.5 55.0 82.0 8.9 13.6 9.4 9.5 10.0 11.2 12.0
59.5 61.7 96.0 83.7 48.0
12.2 11.3 0 10.5 3.0
9.35 9.35
