INDUSTRIAL AND ENGINEERING CHEMISTRY
March 1948
general unit operations equipment such as filter presses, pumps, and centrifugals, which can be adapted to almost any unit process. Here the fundamental chemical changes are initially applied and the equipment is checked for proper design and adaptability to the economic factors of a specific industry. To stimulate further research and also to enable practicing chemical engineers to make better use of the present state of knowledge, INDUSTRIAL AND ENG~NEERINQ CHEMISTRY is now organizing a yearly review of unit processes, the first of which is scheduled to appear in the early fall. This presentation will be by a group of men experienced in the particular unit process discussed.
381
LITERATURE CITED
(1) Furnas, C. C., ed., “Rogers’ Manual of Industrial Chemistry,” 6th ed., New York, D. Van Nostrand Co., 1942. ed., “Unit Processes in Organic Synthesis,” 3rd (2) Groggins, P. H., ed., New York, McGraw-Hill Book Co., 1947. (3) Houge2 0. A., and Watson, K. M., “Chemical Process Principles, Part 1 (1943),2 and 3 (1947),New York, John Wiley &
Sons. Newman, Trans.Am. Inst. Chem. Engrs., supplement to 34, No. 3a. 6 fJulv 26. 1938): Ibid.. 32. 568 (1936). (5) Shreve, R . N.,“Chemical Process Industries,” New York, McGraw-Hill Book Go., 1945. (6) Shreve, R. N., IND. ENG.CHEM.,32,145 (1940). (4)
R ~ C E I V ESeptember D 22, 1947.
CONTINUOUS PROCESS FOR PRODUCTION OF 2,Z-DINITROPROPANE W. I. Denton, R. B. Bishop, and E. M. Nygaard SOCONY-VACUUM LABORATORIES, PAULSBORO, N. J.
T. T. Noland R. T. VANDERBILT COMPANY, NEW YORK 17, N. Y.
THEdata presented
here show that, by operating at the proper conditions, 2-nitropropane can be nitrated with nitric acid to give 2,2-dinitropropaneYa valuable combustion modifier for Diesel fuels. Optimum conditions are: pressure, 990 to 1200 pounds per sqpare inoh; temperature, 400’ to 450’ F. (204-232’ C.); molar ratio, 1 mole of nitric acid to 1 mole of 2-nitropropane when using 70% nitric acid; space velocity, 1.0. Conversions per pass of 11 to 14 mole YO of the 2-nitropropane charged are obtained under these conditions with ultimate yields above 50%. For commercial exploitation more detailed yield and corrosion data are necessary.
that nitration at a lower temperature would be necessary t o preserve the length of the carbon chain. It also appeared advisable t o maintain a 1.iquid phase or a borderline liquid-vapor phase by the use of elevated pressures, as liquid-phase nitration seems t o favor polynitration. The preliminary experiments carried out indicated that 2nitropropane was not further nitrated by concentrated nitric acid at atmospheric pressure and reflux temperatures. The
T
=
H E observation that 2,2-dinitropropane is an extremely effective combustion modifier for Diesel fuels (6, 6) stimulated efforts to find a direct and economical method for its preparation. The recent commercial availability of 2-nitropropane made it appear a likely starting material for the synthesis of 2,2-dinitropropane. This paper presents data on a process for the production of 2,2-dinitropropane from 2;nitropropane. The vapor phase nitration of paraffin hydrocarbons as reported by Hass and co-workers ( 1 , s ) produces all possible mononitro pro’ducts of the starting paraffin plus all the mononitro products of a degradation series of the paraffin. However, substantially no polynitro paraffins are produced. Urbanski and Slon ( 7 ) nitrated propane with nitrogen tetroxide at’temperatures above 100’ C. They report the formation of 1-nitropropane (boiling point indicates it was fl-nitropropane) and 1,3-dinitropropane but no 2,2-dinitropropane. Hass, Dorsky, and Hodge (9) nitrated propane a t 248’ C. with nitrogen dioxide. Although various mononitro paraffins were produced, no polynitro paraffins were formed. Konowalow (4) states that dinitro compounds might be formed by the action of nitric acid on mononitro compounds but restricted his work to compounds having more than five carbon atoms. Gem-dinitro compounds were not among the dinitro compounds described by him. Since vapor phase nitration produced cracking as shown by the presence of mononitrated degradation products, it appeared
-
-~
~
~
Figure 1. Control Panel
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Vol. 40, No. 3
2,2-dinitropropane. The reaction temperature was controlled by immersing the preheater and reactor in a molten salt bath. The liquid product was analyzed by diluting the product with an equal volume of water and steam distilling the mixture in a n eight plate fractionating column. Dissolved oxides of nitrogen were driven off initially followed by a 2-nitropropane-water mixture which distilled at 88-90' C. This fraction separatedinto a 2-nitropropane layer and a ivater layer. The actual amount of 2-nitropropane was obtained by measuring each layer and applying a suitable correction for the solubility of water in 2nitropropane and 2-nitropropane in water. The next fraction distilled over from 98" t o 100" C. and was a mixture of water and 2,2-dinitropropane. The 2,2-dinitropropane lower layer solidi-
LIQUID
W P
PRODUCT WT
Figure 2. Flow Diagram
reaction was then tried in a Carius tube under pressure. These batch experiments are given in Table I. Small amounts of 2,2-dinitropropane and Iarge amounts of decomposition products were obtained. Since the amounts of both products increased with increased temperature, and since longer reaction times only increased the amount of decomposition products, a flow system using limited contact time was designed. This consisted of an all-stainless steel unit capable of withstanding elevated temperatures and pressures. Figure 1 shows the control panel on the outside of the bomb cell which housed the unit. The charge materials, 2-nitropropane and 70% nitric acid, were mutually soluble, and therefore the desired molar proportions could be mixed together and pumped to the reactor by displacement with oil. When nitric acid of 55% concentration or less was used, separation of the mixture occurred at room temperature; consequently the two components had to be pumped separately. A flow diagram of the system is sholvn in Figure 2. I n actual operation the mixture of 2-nitropropane and nitric acid was pumped through a stainless steel preheater tube of 0.25-inch outside diameter into 'a reactor consisting of a 0.75inch pipe-size stainless steel tube 40 inches long, packed with glass beads to increase the contact surface. The products leaving the reactor were passed through a water condenser and then reduced to atmospheric pressure through a needle valve; after that they were further cooled with an ice condenser, and the gaseous decomposition products were separated from the liquid product. The products were measured and analyzed. The gaseous product contained decomposition products from the nitroparaffin, recoverable oxides of nitrogen, and free nitrogen. The liquid product contained unreacted charge materials plus
TABLE I. NITRATION OF Run N0.a
Reaction Time, OF. ("C.) Min.
N-5 N-6 N-14
Reflux 305 (152) 350 (177)
Temp.,
{:::)
390 (199)
120 30 30 30
N-8 N-23
390(199) 380 (193)
9 10
N-16
410 (210) 390 (199)
17 30
E:)
a
2-XITROPROPANE Unreacted ZNitropropane Recovered Reactor Wt. % Nil Effect of Temperature
3-necked Erlenmeyer flask Carius tube Stainless steel tube Stainless steel tube
30 50 50 10
Effect of Reaction Time Carius tube 50 Stainless steel tube 48 (520-lb. pressure) Stainless steel tube 25 Stainless steel tube 10
Figure 3. Preheater after Explosion
fied upon chilling and was weighed directly after the water was decanted. -1 study was made of the following variables: pressure, t e m p e r a t u r e , space velocity, reactant ratio, and effect of dilution with water; each of these will be discussed ind i v i d u a l l y . All of t h e graphs plotted from the Figure 4. Preheater study of the variables are Corrosion on the basis of number of moles of 2,a-dinitropropane formed divided by the number of moles of 2-nitropropane charged. Sitration reactions, are known to become uncontrollably violent, and this condition is accentuated when the unit is initially pIaced under pressure. Consequently every safety precaution sliould be taken. This reaction has been found t o be safe during operation within the limits and under the conditions to be described. Figures 3 and 4 illustrate what occurs when these limits are exceeded. Figure 3 is a picture of the preheater after an explosion which resulted while running outside of None safe operating conditions. Figure 4 is actual size, Trace 12 whereas Figure 3 is enlarged. The stainless steel 16 tube shown in the pictures is normally rated as safe at a working pressure of 10,000 pounds per 20 square inch and has a bursting pressure of about 19 60,000 pounds per square inch. 10
16'
In all runs but N-23 a molar ratio of concentrated (70%) nitric acid to 2-nitropropane of N-23 was 1:1.25. Pressure was not measured except in run h'-23.
1:l was used.
EFFECTS O F VARIABLES
TEMPERATURE. The most critical variable is temperature. The effect of increasing the tem-
#
March 1948
383
INDUSTRIAL AND ENGINEERING CHEMISTRY 16 0
.o 2
$8 p '8g
12
8
a
i 4 0 880 Temperature
300
' F.
460
0
640
Figure 5. Effect of Temperature
2400
Figure 6. Effect of Pressure
N0z
+
800 1600 Pressure, Lb./Sq.Inch
NO2
+
Mixture, XCHsdHCHi XHNO, 1.5 XHzO; space velocity, 1.0; pressure, 900 pounds per square inch
I
+
Mixture, XCBsCHCHs X " O a f 1.5 XHzO. space velocity, 1.0; temperature, 400' F. (204' C.); biack dot a t right of graph is average value of t w o point.
16
a 0
2
12
c m
a:
6 : se&
8
-0)
-
i
4 40
80
60
100
Mole % of 70% Nitric Acid 2.0
0
4.0
6.0
Space Velocity (Vol. Charged per Hr. per Vol. of Reactor)
Figure 7. NO1
Effect of Space Velocity
+
+
Mixture, XCHskHCks XHNOa 1.5 XHzO; temperature, 400' F. (204' C.); curve A , 1200 pounds per square inchi curve B, 900 pounds per square inch; ourve C, 400 pounds pcr square inch
Figure 8. Effect of Mixture Temperature, 400' F: (204O C.); pressure. 900 poundm per Square inch; space velocity 1.0
$ m 12
tic!
vk 8;
8
90
perature while holding all other variables constant is illustrated in Figure 5. The optimum conversion under these conditions (14 mole % per pass) occurs at temperatures between 400' and 450' F. (204-232' C.). As the temperature is raised above this point the amount of decomposition increases and consequently lower ultimate yields are obtained. At a temperature of 500' F. (260' C.) explosions are noted, and a t 575' F. (302' C.) the detonations become violent and almost continuous. At this latter temperature no 2,2-dinitropropane is recovered, and, while most of the products are gaseous, the liquid product which is recovered is basic even though concentrated nitric acid is one of the charge materials. Since space velocity and temperature are interrelated it is likely that, a t higher space velocities, the curve will be displaced to the right to give a higher optimum temperature. PRESSURE. The increase in the conversion per pass effected b y increasing the pressure is graphically shown in Figure 6. Pressures in excess of 1200 pounds per square inch give smaller increases in conversion per equal increment of pressure rise than are obtained for the same increment of pressure rise below 1200 pounds per square inch. Somewhat improved ultimate yields are obtained, however, at the higher pressures. I n the 900- t o 1200-pound pressure range the average conversion per pass is 12 mole %. When pressures below 200 pounds per square inch are used, the amounts of 2,2-dinitropropane formed decrease rapidly. SPACE VELOCITY.I n Figure 7 the effect of space velocity (volume liquid charged per hour per volume reactor) a t various pressures is shown. At the lower pressures a space velocity of 1.0 seems optimum, and small changes in space velocity result in decreased conversions. At 900 pounds per square inch, in-
s.a
4 0
80
40
120
Mole % Water
Figure 9. Effect of Dilution with Water NOn
+
+
Mixture, XCHa&HCH* XHNO, YHzO; temperature, 400' F. (204' C.); pressure, 900 pounds per square inch; space velocity, 1.0
creasing the space velocity from 1.0 to 5.0 decreases the conversion per pass from 12 to 6.5 mole %. Space velocities below 0.5 seem to offer little advantage. MOLARRAno: A study of the result of varying the pioportions of the charge materials (2-nitropropane and 70% nitric acid) is plotted in Figure 8. As the mole per cent of 70% nitric acid is increased more of the 2-nitropropane is converted to 2 , s dinitropropane per pass. However, s higher ultimate yield of 2,2-dinitropropane might be obtained under conditions which give a lower conversion per pass. For example, when using a charge containing nitric acid, the amount of 2,%dinitropropane obtained per pass from the 2-nitropropane might be higher than would be obtained when using 75 mole % nitric acid, but more decomposition in the former case may reduce the ultimate yield below that obtained in the latter case. DILUTION WITH WATER. The effect of increasing the proportion of nitric acid as shown by Figure 8 is modified by the concurrent increase in the amount of water diluent. This water dilution effect is illustrated in Figure 9. Keeping a 1:l molar ratio of 2-nitropropane and 100% nitric acid a t all times, the amount of water was varied over the range of 0 to 80 mole %.
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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 orthophosphoricacid 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.
