. INDUSTRIAL AND ENGINEERING CHEMISTRY
364
Surprisingly enough 1 0 0 ~ nitric o acid gave only 4.0 mole r0 conversion per pass. A maximum of 11.5 mole yo conversion per pass was obtained at a dilution of water. Figure 9 indicates that high conversions can be obtained with water dilution ratios of 25 to 75 mole %. This is an extremely valuable characteristic since it makes the use of highly concentrated nitric acid unnecessary. Water as a diluent may be used advantageously in proportions of from 10 to 80 mole %.
Vol. 40, No. 3
LITERATURE CITED (1) Hass, ISD. EBG.CHEY.,35, 1146-52 (1943). (2) Hass, Dorsky, and Hodge, I b s . , 33,1138-43 (1941). 381 251-3 (lg4'). (3) Howe and H a s s 7 1 b i d . 9 (4) Konowalow, J . Russ. Phys. SOC.,31,57-69 (1899). >lcCracken, 8 , patent2,387,279 (1945). (6) McCracken and Nygaard, Ibid., 2,387,403 (1945). (7) Urbanski and Slon, Compt. rend., 203,620-2 (1936).
u,
RECEIVED September 22, 1947.
CONTINUOUS PROCESS FOR ACETYLATION OF THIOPHENE John Kellett and H. E. Rasmussen SOCONY-VACUUM LABORATORIES, PAULSBORO, N. J.
THEliquid
phase acetylation of thiophene with acetic anhydride, giving acetic acid as by-product, may be accomplished at temperatures of 100" to 400" F. by use of reaction times from 1 hour to a few minutes, respectively. The catalyst may be heterogeneous promoted type or homogeneous type. A continuous process is described wherein essentially complete conversion of acetic anhydride to product is obtained in, a single pass, charging 2 moles of thiophene to 1 of acetic anhydride. The reaction temperature is about 325" F. and the reaction time 5 minutes. The catalyst is a 1.3Yo concentration, based on total charge, of 8570 orthophosphoric acid in homogeneous liquid phase with the reactants. The excess thiophene is recovered and recycled.
R
ECENT publications from these laboratories (6, 7 ) describe the production of thiophene in pilot plant quantities from n-butane and sulfur. The resultant availability of thiophene in appreciable quantities has made feasible the investigation of its use as a starting material for other chemicals. Steinkopf (8) described the acetylation of thiophene with acetic anhydride and acetyl halides in the liquid phase using catalytic amounts of P205. Hartough and Kosak described the acetylation of thiophene in the liquid phase using catalytic amounts of iodine, hydriodic acid, and zinc chloride (2, 3 ) . The same authors have submitted for publication a paper which describes the acetylation of thiophene with oxymineral acids. Hartough, Kosak, and Sardello described the same acetylation using surface active catalysts (4). The present aork was undertaken to develop the most attractive of the latter reactions into a continuous process. This paper descrlbes the resulting process wherein acetic anhydride and thiophene are reacted in the presence of small amounts of phosphoric acid catalyst to give acetyl thiophene id yields approaching 100%. PROCEDURE
USED. The thiophene used in the investigation was obtained from the 100-pound-per-day unit previously described (6) and was better than 99% pure as determined by freezing point and mass spectrographic analysis, the detectable pre. dominant impurity being carbon disulfide. The acetic anhydride was supplied by Carbide and Carbon Chemicals Company and was analyzed for acetic anhydride and acetic acid by the method of Radcliffe and hledofski ( 5 ) . The results of several analyses indicated a mean purity of 97% by weight acetic anhydride, the major impurity being acetic acid. The phosphoric acid was Baker's analyzed 8570, ortho, specific gravity 1.71 at 15" C. The heterogeneous type catalyst used was a synthetic silica-alumina active clay in pellet form of the type used in comhfATERIALS
mercial catalytic cracking. The promoted catalyst was prepared by adding 30% by weight of the phosphoric acid described to the pelleted catalyst while stirring to obtain uniform acid distribution. The catalyst was then air-dried at 300" F. for 6 to 12 hours before introduction into the reactor PROCESS AND APPARATUS. Either acetic anhydride or acetyl chloride may be used as the acetylation agent; acetic anhydride was chosen because it precludes the formation of hydrogen chloride gas, which would eliminate the use of conventional steel equipment and would complicate the setting up of a continuous process. The investigation was carried out in two parts, (a)the liquidphase reaction of acetic anhydride and thiophene catalyzed by heterogeneous contact-type catalyst, promoted with H3POa, and ( b ) the same reaction catalyzed with small amounts of HSP04 in homogeneous phase with the reactants. The latter was evolved as a consequence of findings in the first part of the work, and resulted in a better process and in higher conversions. The reaction pressure was found to be unimportant since the liquid phase reaction involved no appreciable volume change. The pressure used was that necessary to maintain the reaction mixture liquid at the temperature used, usually 50 to 100 pounds gage. One aim in the development of the process was to achieve essentially complete conversion of the acetic anhydride in a single pass; this would eliminate its recovery from the product stream for recycling. This necessitated the use of excess thiophene; hence all conversions are expressed in terms of acetic anhydride converted to product. REACTION USING CONTACT CATALYSTS
The process consisted essentially of pumping a stream of mixed thiophene and acetic anhydride (usually 3 moles to 1 mole) through a thermostated bed of silica-alumina catalyst promoted with 30% by weight of 85% orthophosphoric acid. A diagrammatic flow sheet of the apparatus is given in Figure 1. The unit consisted of a 30-gallon glass-lined charge vessel in which the reactants were premixed; a positive displacement Hills-IIcCanna metering pump with Hastalloy D piston and SS 304 pump body with vertical-composite, double-check valves having Hastalloy D cones and SS 304 seats; preheater; reactor; reactor effluent cooler; and product receiver. The receiver, a 30-gallon Pfaudler glass-lined stirring autoclave, was also used for washing and neutralizing the product stream, and subsequentlr as still pot for topping the unreacted thiophene. The reactor, having a catalyst capacity of 2500 cc., consisted of a &foot length of 2-inch IPS (iron pipe size) 27% chromium (type 446 steel) pipe wrapped with two 500-watt, helix-wound, ball and socket, bead-insulated electrical-resistance heaters.
March 1948
INDUSTRIAL AND ENGINEERING CHEMISTRY (0O-LB.GAGE
385
the amount of thiophene. This method, of analysis was fast and reasonably accurate, and provided a means of rapid control analysis. Analysis of phosphoric acid as phosphorous in the product stream (leached from the catalyst) was by Goodloe's method (1). Where necessary this amount of phosphoric acid was applied as a correction t o the titrations, There was found to be a definite leaching out of the phosphoric acid, which resulted in deterioration of catalyst activity. HOMOGENEOUS; LIQUID-PHASE CATALYST
The marked deterioration of catalyst activity ' which was found to occur in using the promoted
contact type resulted in progressively lower conversions as a run proceeded. I n order to counteract this condition, it was reasoned that Pump system A used where no HsPO, was charged; system A-B used where HaPo' was the addition of phosphofic acid to the charge charged stream in amounts about equal to that leached out might maintain catalyst activity. ConHeater input was controlled by means of Variacs. Temperasequently, the addition of 1%by weight of phosphoric acid was ture measurement in the reactor was made by means of thermomade to the charge pot consisting of a mixture of 3 moles of thiophene to 1 of acetic anhydride. Immediately after the couples in a thermowell extending the length of the reactor bed through a bottom welded header. An insulated skin thermoaddition a sharp increase in temperature of the Contents was couple a t the exit of the preheater gave the preheat temperature. noted, and subsequent titration of this mixture revealed that All charge and effluent lines in contact with the reaction mixture about 65% of the acetic anhydride had reacted. Pumping were '/a-inch IPS 18-8 (type 304) stainless steel tubing. A %inch this mixture in the usual manner over a batch of Catalyst steel union above the product take-off line on the reactor served whose activity had diminished because of previous runs brought as point of withdrawal or changing solid catalyst. A 300the conversion to loo%, a value which is realized in the first pound steel-tube pressure gage was in the top half of the union. part of a normal run using fresh promoted catalyst. In the runs made where the reactor consisted of a bed of solid This observation suggested the use of small amounts of phoscatalyst, the charge, consisting of thiophene and acetic anhyphoric acid as homogeneous catalyst instead of the promoted type dride (3 moles to 1 mole) previously mixed in the 30-gallon charge of contact catalyst. Consequently, one stream of acetic anvessel (reactants and products are miscible in all proportions) hydride and thiophene and another of acetic anhydride and phoswas pumped through the reactor at the rate necessary to give phoric acid, the latter equal to 1%by weight of the total charge, the desired residence time. (Since later runs were made with no were processed using a double-pump Hills-McCanna unit in solid catalyst present, all reaction time figures in the results are place of the single pump of the previous unit. The acetic an. presented as residence time.) Before run data were taken, the hydride, sufficient to maintain the 3:l thiophene:anhydride unit was allowed to come to equilibrium by pumping enough ratio, was divided between the two streams. The initial run UScharge to fill completely the reactor and take-off lines with liquid ing a 1-hour reaction time at 218' F. resulted in about 98% cona t the pressure used (usually 50 pounds), plus a similar volume version of the acetic anhydride with the same reactor with no excess to purge out the initial quantity of material. Thus, if solid catalyst present. The feasibility of the reaction thus esthe residence time were to be 1 hour and the reactor catalyst bed tablished, the next step was the design of a unit specifically for 2500 cc. with 50% free space, the pumping rate was regulated to the homogeneously catalyzed reaction. 1250 cc. per hour and maintained for 2 hours before the first sample wm taken. Data taken were pumping rate, reactor temperature at three to five equally spaced points DISPLACEMENT in the catalyst bed, reactor skin temperature, preheat temperature, and pressure. The time at which a run sample was taken and the exact interval of time during which it wae taken while maintflining the pressure constant were also noted. The weight of this sample compared to the charge rate then gave the material balance. Analysis of the product and charge streams for acetic acid and for acetic anhydride wa8 made by titrating weighed samples by the method previously described. The moles of acetylthiophene in the product stream were assumed to be equal to the moles of acetic anhydride converted to acetic acid, and this amount was checked consequently by distillation of the product. T h t weight difference ANHYDROE IARGE between the original sample and the total Figure 2. Flow Sheet of Experimental Acetylthiophene Unit Using weight of acetylthiophene and acetic acid wm Homogeneous Catalyst Figure 1. Flow Sheet of Experimental Acetylthiophene Unit Using Heterogeneous Catalyst
'
*
*
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INDUSTRIAL AND ENGINEERING CHEMISTRY
386
Figure 2 is a diagrammatic flow sheet of the modified unit. Three separate streams consisting of thiophene and acetic anhydride were charged by means of the double pump unit previously described, and the 85% phosphoric acid was charged by means of a special pump. The required addition of phosphoric acid to the reaction was a t a low rate, in the range 8 t o 80 cc. per hour. These rates were handled accurately a t the pressures used (50 to 100 pounds gage) by means of a displacement cylinder made from 3 feet of I-inch IPS stainless tubing (volume 550 cc.) used in conjunction with the pump. Light transformer oil was pumped into the top of the displacement cylinder with a '/l-inch piston pump with Hills-McCanna check valves of the type previously described. 100
Vol. 40, No. 3
It seemed of interest, in view of the results obtained, t o compare plain silica-alumina (active clay) type catalyst with the promoted catalyst. Figure 3 is a plot of this comparison, run 12 (Table I) being plotted with the data obtained under the same conditions with the untreated catalyst. The plain surface active catalyst gave a good conversion initially, which dropped off rapidly, whereas the phosphoric acid-promoted catalyst, in addition to giving a higher conversion initially, also exhibited a more sustained activity, dropping off a t a slower rate. This would seem to indicate that the surface activity of the former is easily poisoned by some phenomena, such as sludge formation on the catalyst; whereas the latter is more slowly deactivated, perhaps predominantly because of the leaching out of the phosphoric acid. Both conditions were found to exist. Inspection of the used catalyst revealed a gummy deposit, and analysis of the effluent stream where the promoted catalyst was used revealed the presence of constantly diminishing amounts of phosphoric acid (analyzed as phosphorous).
TABLE I. CONTINUOUS ACETYLATION OF THIOPHESE IN LIQUID PHASE
20
0
6
12
18
24
30
Hr. from Beginning of R u n
Figure 3. Comparison of Promoted and Unpromoted Catalyst I
Temperature, 2 1 2 O F.; residence time 1 houri preanure. 50 pounds gag-. R u n 12, curve A , silica-alumina catalyst p l u s 30 weight % &PO( (2500 cc.)c run 13, curve B. silica-alumina catalyst (2500~0.).HsPO4 in product stream at point x , 2.51 %; at point y , 0.07 %
The two main charge streams (thiophene and acetic anhydride) were separately preheated with steam, the steam pressure controlling the temperature of preheat. The two preheated streams then joined the minute phosphoric acid stream, and the mixture was sent through a stainless steel autoclave mixer of 450-cc. capacity. The reactor consisted of a 40-foot coiled section of 1/4-inch IPS stainless steel tubing (750 cc. volume) in a steam chest, the amount of steam pressure controlling the reaction temperature. Part of the runs were made using the mixer only as the reactor, in which case the reactor coil was by-passed. All connecting lines and fittings were 1/4-inch IPS stainless tubing, except the phosphoric acid lines which were 0.14-inch I.D. stainless tubing. Thermocouples were placed in the exits of the preheaters and in the mixer. A calibrated Weston dial-type thermometer gave the steam temperature in the reactor. The mechanics of running the unit mere the same as those described for the previous unit. When the system exhibited liquid pressure, indicated by a rapid rise of pressure with the outlet valve closed, the phosphoric acid pump was started and the line valve connecting it to the charge stream was opened, the displacement cylinder having been pressured initially to reaction pressure. Sufficient time for the attainment of steady conditions was allowed before the unit was considered on stream.
+
(Catalyst, SiOz-AlzOs, 30% H s P O ~ pressure, ;, 50 lb./sq. in. gage; mole ratio th1ophene:acetic anhydride, 3 :1) Residence Recovery wt.% Based Vol. Charge Time, Hr. t o Vol. Based on A,czO Wt. Yo on Run Run Reactor Temp. in AozO Sample, Catalyst, Free Space NO. F Charge Reacted Wt. % Additively 1 158 0.45 29.7 75.6 99 2.5 2 0.45 30.0 158 100 5.5 68.0 3 158 29.5 1.0 67.0 98 7.45 4 29.5 1.0 185 81.0 95 8.75 5 212 29.5 1.0 94 86.0 10.1 239 6 29.5 1.0 91.2 98 11.35 266 7 29.5 1.0 99 12.65 96.0 8 29.5 294 1 .o 13.95 98.6 96 29.5 212 9 0.5 15.25 75.6 99 10 212 2.0 29.5 16.55 87.4 99 11 29.5 212 1.0 17.85 74.0 97 12 (start) 29.5 220 1 .o 98.2 99.6 0 12 (finish) 220 1.0 14.2 08.2 29.5 85.4
HOMOGENEOUS-TYPE PHOSPHORIC ACIDCATALYST.The first run using &Po4 catalyst in homogeneous phase with the reactants was made as previously described to counteract the leaching of the acid from the promoted catalyst. Several runs were made in the same reactor as was used for the contact catalyst work; the charge as described was phosphoric acid mixed with part of the acetic anhydride. I n making this mixture a sharp heat of solution was noted. In seeking a mechanism for the P206-catalyzedacetylation, Steinkopf (8) postulated the ionowing reactions:
0
0
4I/- 0 - L C H a
+
0
0
RESULTS
CONTACT-TYPE CATALYSTS.The results obtained using a silica-alumina type of catalyst promoted with phosphoric acid are given in Table I. Runs 1through 11were made at different times, using the same catalyst. Run 12 was a long uninterrupted one starting with fresh catalyst; conversions a t the start and a t the finish are given. Two things are obvious from this table: Conversions are favored by higher temperatures and longer residence time; and catalyst activity decreases markedly with throughput, and this is true whether several short runs or one long run are made.
0
!'-O-b-CHa
ll
0
+ !'-OH I1
6
-
Q
PzOa
+ CH,COOH
(3)
March 1948
387
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
P 120
i
i
240 360 Reaction Temp., O F.
l
l
]
100
180 260 Reaction Temp.,
340
420
I?. Figure 5. Effect of VaryingThiopheneAcetic Anhydride Ratio
480
Figure 4. Effect of Varying Amount of Homogeneous Catalyst, HaPo,, on Conversion
Homogeneous catalyst, 1% HaPOd; time, 1 hour
reaction
Reaction time, 1 hour; acetic anhydridein charge, 25 to 29 weight 70
p
90
$
62 60
2
se
6
30
0
0
0.6
Figure 6.
1.0 1.5 Reaction Time, Hr.
2.0
4
8 Reaction Time, Min.
12
16
Figure 7. Effect of Varying Temperature and Thiophene-Acetic Anhydride Ratio
Effect of Variation of Reaction Time on Conversion
Homogeneous catalyst, HnP04 1%by weight
Homogeneous catalyst, 1 % Hap@; reaction-temperature, 145' F.
m,
The heat effect may be due to the formation of active complexes similar to these postulated by Steinkopf. The runs made in the chamber-type reactor are given in Table I1 and are plotted in Figures 4 and 5, which show the effect of variations of the catalyst concentration as a function of temperature and the ratio of reactants as a function of temperature, respectively, and in Figure 6, which shows the effect of various reaction times with other variables kept constant. Several variables to the reaction appeared obvious as a result of this work. The conversion of acetic anhydride to product appears to be not only dependent upon €he concentration of catalyst, temperature, time of reaction, and molar ratio of reactants but also upon the manner in which the phosphoric acid catalyst is introduced. For example, the heating effect on mixing phosphoric acid with acetic anhydride has an effect. Figure 6 shows that as the reaction time a t 145' F. is increased, the conversion increases up to about 83% during a 1-hour reaction time. Longer reaction times result in no further increase in conversion, whereas, i f the temperature is higher initially, reaction times shorter than 1 hour can achieve 100% conversion, Thus there seem to be, in effect, two competing reactions: (a) the desired acetylation, and (b) the removal of phosphoric acid, possibly due to the formation of a stable complex with the reactants or products which destroys catalytic activity. If the reaction rate of b is slower than that of a, which seems true at ceitain conditions in view of the results, then the promotion of short reaction times would be advantageous. For this reason the last described unit-modified to provide separate preheating of the main reactant stream, injection of the phosphoric acid catalyst directly into the preheated reactants, and rapid mixing-was designed and put in operation. The results obtained are given in Table 111. Runs 1 through 7 were made using the reaction system shown in Figure 2. These runs indicate that high conversions are pussible with low reaction
times. Since the capacity of the pumps was reachedin these runs, it was found necessary to by-pass the reactor coil and use only the mixer as reactor to get still shorter reaction times. Runs 8 through 27 were made in this system. Comparison of run 11, Table I1 (conversion 90.5%), with run 25, Table I11 (conversion 89.5%), made at approximately the same temperature, reactant molar ratio, and catalyst concentration (the former with a reaction time of 1 hour and the latter hour) shows about a fourfold increase in reaction rate. Figures 7 and 8 are plots of the data recorded in Table I11 and show the variation of molar ratio and temperature as a function of reaction time, and the variation of reaction time and molar ratio as a function of temperature, respectively. One undesirable feature of the continuous autoclave type of reactor is that equilibrium is never reached since, in the turbulent
TABLE 11. CONTINUOUS ACETYLATION OF THIOPHENE IN LIQUID PHASE
Run NO..
(Homogeneous ratslyst, HaPO4; chamber reactor) H B P O ~ Mole Based Ratio Reacon ThioAm0 in tion Total phene: Total AcrO AczO Time, Temp., Char e Charge, Reacted, 1 F. wt. Charge wt. % wt. % HI. 25.4 98.4 1.01 3.6 0.92 100 3.6 25.35 1.02 26.0 85.2 0.56 29.6 68.1 0.51 27.6 93.0 3.2 0.52 27.6 99.6 3.2 0.27 62.3 28.6 3.0 0.29 27.5 33.1 3.2 0.25 28.3 80.3 3.1 0.99 36.2 83.8 2.1 36.2 90.5 2.1 1 .o 36.2 97.5 1.01 2.1 36.0 1.07 75.6 2.2 33.8 83.5 0.95 2.4 29.2 90.7 2.9 0.96
1:;
Reoovsry Based
on Run Sample, wt.% 97 100 98.3 99.2 99.3 99 99.5 99.8 99.4 98.5 99.5 99.8 99.2 99 99.5
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INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 40, No. 3
100
TABLE 111. CONTINUOUS ACETYLATION OF THIOPHENE IN LIQUIDPHASE
90 4.
s
2
j
8
5
(Homogeneous catalyst, HaPO4; HaPo4 Mo!e Based Ratio Reacon Thiotion Total pheneTime, Temp., Charge, Am0 Hr. ' F. Wt. % Charge
80
Run
70
NO.
,"
60
1 2 3 4 5
' I
50 225
250
275
Temperature,
300
325
F.
6
7
3.1 2.9 2.9 3.1 2.9
0.5 0.96 0.99 0.99 0.99 0.99 1.0
3.0
2. 1
AczO Reacted, Wt. %
27.5 28.8 28.8 27.5 28.6 28.2 36.2
89.9 94.4 99.5 99.1 100 99.7 86. 5
k'
Homogeneous catalyst, 1% HaPOa
13
Recovery Based on Run Sample,
Wt. % 98.6 98.3 98.4 100 99.5 98.0 98. 0 96.5 97.5
9
10 11 12
mixing action, a portion of the charge is mixed to the point in the autoclave where it leaves with the effluent before it has any appreciable reaction time (short circuiting). Thus conversions never quite reach 10070, whereas in the coil reactor, where a reaction gradient from inlet to outlet exists, conversions of 100% were obtainable. The acetylation reaction is markedly exothermic. A sharp heat rise in the mixer always occurred and was more pronounced in the high-rate runs. I n some cases the temperature in the mixer rose above the desired reaction temperature. It was therefore necessary to trace the mixer with copper tubing windings, through which cooling water could be run, to maintain isothermal conditions. If initial preheating of the reactants is provided to start the reaction when the phosphoric acid catalyst is injected into the mixture, the rcaction proceeds without the addition of further heat. I n fact it is necessary to remove part of the heat. This may feasibly be done on a large scale by exchanging it to the reactants to supply part of the preheat load. I n the above work described here, most of the runs liere made using a ratio of thiophene to acetic anhydride of 3 t o 1. I n the operation of the process, the excess thiophene would be fractionated from the products and recycled. Thus it would be desira-
200 148 172 206 270 255 250
AczO in Total Char e Wt.
8
Figure 8. Effect of Varying Reaction Time and Thiophene-Acetic Anhydride Ratio
.
0.49 0.52 0.51 0.25 0.17 0.08 0.08
mixer-coil reactor)
100
99.1 99.8 98.1 98.8 99.5 100 100 100 100 100 99.9 99.3 97.5 99.5
14 15 16 17 18 19 20 21 22 23 24 25 26 27
100 99.6 98.1
CONSTANTS OF MATERIALS USEDIY TABLE IV. PHYSICAL PROCESS Density, dZo Thiophene Aceticanhydride -4cetic acid 2-Aoetvlthiophene
1.064 1.082 1.049 1.17
Boiling Point a t 760 him.,
C. 84.1 139.6 118.1 214
Viscosity, Bbs. Cp. 0.662 0.91 0,122 ..*
Specific Heat, Cal./G.
... 0:ik ...
Heat of Vapoii- Mel&ng zation, Point, Cal./G. C.
...
66.2 96.8 89.7
-38.3 -73 16.7 10.2
ble to keep down the amount of excess thiophene to decrease the recycle load to a minimum. Further, for a unit of a given size it would be desirable to increase the severity of reaction conditions RECYCLE T H I O P H E N E ( 6 % ACETIC ACID) -0 STORAGE to obtain the highest throughput allowable, still maintainTO V A C U U M ing complete conEJECTOR version of the acetic anhydride c h a r g e For best economic operation this should be to the point where heat costs, corrosion, or degradation predominate to ACETYLTHIOPHENE TO STORAGE detract from the process. The amount of catalyst used, also, should be kept low since it is not readily recovered. The approximate optimum operating conditions for the I I BOTTOMS TECI. I C A L unit described using D ~ L ~ ACLTI~. E ACID TO AC ETY Ll IOPHENE CAUSTIC TO STORAGE STORAGE TO ST ? A G E OR OR TO the coil reactor were AMMONIA FURTHER TREAT M E N T found to be: thiophene to acetic anFigure 9. Condensed Flow Sheet of Commercial Unit for Production of Acetylthiophene Y
I
I
.
March 1948
INDUSTRIAL AND ENGINEERING CHEMISTRY
hydride ratio 2 to 1; temperature 325" F., reaction time 5 minutes, and catalyst concentration 1.33% based on total reactants by weight. The conversion obtained was essentially 100%. TREATMENT OF PRODUCT STREAM
\
In all the experimental runs the acetic acid, unreacted acetic anhydride when present, and phosphoric acid were water-washed from the product and last traces removed with ammonia solution. The thiophene was then topped out, first at atmospheric pressure and last traces a t about 20 inches of vacuum. The product was distilled under vacuum (20 mm. absolute pressure) in a 30gallon glass and glass-lined column. The purity of the final constant-boiling product was 99% or better. Transition cuts were rejected t o redistillation. No materials heavier than acetyl thiophene were distillable under these conditions. After a 20gallon batch of product had been run, a small amount of black tarry material remained in the still pot. This amounted to approxymately 0.470 of Dhe crude topped product and contained some acetyl thiophene because of column holdup. This residue was not analyzed but probably consists partly of polymers of thiophene. Commercially it would be desirable to recover the by-product acetic acid either to convert to acetic anhydride for re-use in the process or to market as the acid. Figure 9 is a flow sheet for a possible commercial unit. I n the operation of the process, using excess thiophene and converting all the acetic anhydride, the reaction, assuming a charge ratio of 2 moles of thiophene to 1 of acetic anhydride, may be written:
2C,TT,S
-
+ (CH,CO),O + 1% &PO4 CdH3SCOCH3 + CH,COOH + CaH4S + 1%
Hap04
Thus the product stream contains three major components and IL small amount of phosphoric acid. The main physical
389
properties of the products along with those of acetic anhydride are given in Table IV. Because of the wide differences in boiling points, the product components are readily separable by distillation. A study of the binary system thiophene-glacial acetic acid revealed an azeotrope boiling at 182' F. containing 4.5% by weight of acetic acid. However, this composition returned to the process as recycle thiophene has no undesirable effect on the reaction. Actually, in the operation of the process, because of limitations of column efficiency, thiophene containing 6% acetic acid is returned to the process. In the proposed scheme the separations are carried out in two columns. The thiophene and acetic acid are stripped overhead in a first column operating under slight vacuum, and the crude product and phosphoric acid withdrawn as bottoms. In the second column operating a t atmospheric pressure, the thiopheneacetic acid azeotrope is taken overhead to recycle, and the acetic acid withdrawn as bottoms. A third column may be used to distill the acetylthiophene for the production of pure grades after phosphoric acid hae been caustic-washed and density-separated from the crude product. LITERATURE CITED
(1) Goodloe, P.,IND.ENO.CHEM., ANAL. ED.,9,527(1937). (2) Hartough, H., and Kosak, A., J. Am. Chem. Soc., 68, 2639 (1946). (3) Ibid., 69, 1012 (1947). (4) Hartough, H.:Kosak, A., and Sardello, J., Ibid., 69,1014 (1947). (5) Radcliffe, L. G., and Medofski, S., J. 8 0 0 . Chem. Ind., 36, 628 (1917). (6) Rasmusgen, H. E., Hansford, R. C., Sachanen, A. N., IND.ENG. CHEM.,38,376 (1946). (7) Rasmussen, H. E., and Ray, F. E., Chent. Inds., 60,593(1947). (8) Steinkopf, W.,"Die Chemie des Thiophen," p. 73,Verlag von Theodor Steinkopf, Dresden andsleipsig, 1941. R E C E I V ~September D 22, 1947.
VAPOR-PHASE HYDRATION OF ETHYLENE OXIDE .
R. R. Cartmell', J. R. Galloway2, R. W. Olson, and J. M. Smith PURDUE UNIVERSITY, LAFAYETTE, IND.
THEincreased demand for ethylene glycol, chiefly for use
P
as an antifreeze, has stimulated investigation of new methods of manufacture. One of these is based on the vapor-phase oxidation of ethylene with air, followed by the liquid-phase hydration of the ethylene oxide to glycol in weakly acidic, aqueous solutions. In this investigation a study was made of the possibility of carrying out the second step (the hydration reaction) i n the vapor phase by passing ethylene oxide and steam over a solid catalyst, thereby eliminating the purification difficulties encountered in the acidic liquid-phase process. Over a temperature range from 150' to 250' C. with acid-type catalysts, such as phosphoric acid on alumina, silica gel, thoria, etc., no glycol was obtained, although considerable quantities of aldehydes were formed in some instances. Silver oxide on an alumina carrier was found to be effective, conversions to glycol ranging from 20 to 30oJ,, with corresponding yield figures of about 80 and 40%. This yield is affected by catalyst age, increasing to an approximately constant value of 80% after about 5 hours of operation. The results suggest that, with a new catalyst, significant quantities of ethylene oxide are converted to a by-product which is held on the solid catalyst surface.
D
URING the last few years the demand for ethylene glycol has increased at a rapid rate, the total production reaching over 200,000,000pounds in 1944 (8). As a result there has been considerable interest in the development of new methods of manufacture to compete with the conventional 'Dhlorohydrin process (2, 3, 11). I n one'of these ethylene is first oxidized to ethylene oxide by passing air and ethylene over a silver oxide catalyst, on a suitable carrier, at temperatures from 200-300° C. (6, 6). I n the second step glycol is obtaihed by hydration of the oxide. This reaction has been investigated in the liquid phase; it was found to take place slowly when ethylene oxide is dissolved in pure water and much more rapidly in the presence of a small amount of acid (IO). Since the presence of acid in the liquid phaseprocess may make extensive purification necessary, it seems desirable to investigate the possibility of avoiding its use by carrying out the hydration in the vapor phase. This paper presents the results of a preliminary investigation of the vapor-phase process. The reaction C~H40(g) HnO(g)+(CH20H)2(g)is exothermic. The heat of reaction is +23,000 calories per gram mole a t 25 C. using Bichowsky and Rossini's (1)values for the heats of formation of the three compounds.' 1 Present addresa, California Research Corboration, Whittier, Calif. 9 Present address, Riohmond, Ind.
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