US2206813A - Pbocess of nitbamng hedbocabbong - Google Patents

Description

Jill 2, 1940.

H, B. HASS'EIAL PROCESS OF NITRATING HYDROCARBONS Filed Aug. 31, 1936 Recieuer Patented J l a UNITED S- success or Aren't mo rrirmiooannoxs poration of Indiana Application August a1, 1936, Serial No. 98.63; Claims. (cl. zoo-s44) Our invention relates to the nitration of saturated aliphatic hydrocarbons, and more particularly to the nitration of saturated hydrocarbons of the paraflin series having" in excess of two car- 5 bon atoms, by means of nitrogen dioxide.

Numerous efforts have been made in the past to develop a satisfactory method of obtaining nitro derivatives of the saturated hydrocarbons. vRegardless of availability and cheapness of the latter, however, no practical commercial process has been developed prior to that disclosed in United States Patent No. 1,967,667, of July 24, 1934, granted to us with Byron M. Vanderbilt as co-inventor. According to that process, saturated aliphatic hydrocarbons having from three to eight carbon atoms, and especially those having secondary or tertiary carbon atoms, are nitrated in the gaseous or vapor phase by the aid of vapors obtained by heating nitric acid, which contain nitrogen dioxide mixed with other substances.

We have now found that we may also obtain eflective vapor phase nitration of hydrocarbons higher than those having eight carbon atoms, such as decane, eicosane, triacontane, or paraflln wax, which is a mixture of a number of high molecular weight hydrocarbons.

We have also found that saturated aliphatic hydrocarbons may be more satisfactorily nitrated by substantially pure nitrogen dioxide in place of the vapors formed by heating nitric acid. The use of substantially pure nitrogen dioxide permits improvements in operating procedure which will be apparent from the description of our improved process which follows. Among such improvements are these: By using substantially pure nitrogen dioxide we can obtain more nearly optimum yields, over a wider temperature range, and thus eliminate the necessity for such precise temperature control as is necessary for obtaining such optimum yields, at any given space velocity when vapors of nitric acid are used. Also, by using nitrogen dioxide substantially free from water and nitric acid, we facilitate operation M under pressure, lessen condensation, obtain a more selective nitrating action on secondary and tertiary carbon atoms, and obtain greater economy in the recovery of the nitrating agent used.

Our process may be illustrated by reference to the figure, which shows a laboratory apparatus suitable for the application of our process. In

the apparatus shown in the diagram, carbon dioxide, or other inert gas, passes through the pipe J, the rate of flow of the inert gas being regulated 55 by the aid of the flow-meter F. The carbon dioxide bubbles through liquid nitrogen dioxide in the cylinder A, the temperature of which is regulated by the bath B maintained slightly below the boiling point of the nitrogen dioxide. By reguco lating the flow of carbon diomde through the liquid nitrogen, dioidde the proportion of gaseous nitrogen dioxide to hydrocarbon in the reaction mixture may be changed as desired. It is to be understood, however, that other suitable methods of regulating the proportion of nitrogen dioxide to hydrocarbon may be employed without departing from the scope of our invention. In commercial scale operations, for example, the carbon dioxide, or other inert gas, may be dispensed with, if desired, and the gaseous or liquid nitrogen dioxide pumped into the system at determined rates in order to give the desired proportion of reactants.

The hydrocarbon to be nitrated enters the system in a gaseous state through the pipe K, the amount of gas admitted being regulated by the aid of the flowmeter F, or other suitable means. The gaseous reactants meet at L and pass through the coil R maintained at the reaction temperature. This may be accomplished by any suitable means permitting satisfactory temperature control, such as, for example, by the use of electrical heating coils, a molten lead bath or a bath of the molten eutectic mixture of sodium nitrite and potassium nitrate, a bath of this latter type being represented as C in the drawing.

The gaseous reaction products pass through a condenser D where part of the nitrated product is condensed and collected in the receiver E, preferably surrounded by an ice bath G. The uncondensed gases are then preferably conducted to an auxiliary condenser H, cooled by a solid carbon dioxide bath I, or a refrigerating coil, which serves to remove the greater part if not all of the remainder of the nitroparafiins and a substantial portion of any nitrogen dioxide and hydrocarbon remaining in the gaseous reaction mixture. The uncondensed gases leave the system at M and. consist mainly of unreacted hydrocarbon together with smaller proportions of carbon dioxide, carbon monoxide, nitric oxide, and nitrogen dioxide. Obviously,'however, the composition of the gaseous by-products depends to a large extent upon the particular reactants employed and whether or not an inert diluent gas is used to regulate the admixture of the nitrogen dioxide with the hydrocarbon being nitrated.

The operation of our process will be specifically illustrated by the nitration of isobutane. Carbon dioxide gas, at the rate of two liters per hour, was passed through the cylinder of nitrogen dioxide A, maintained at approximately 18 C. At the same time gaseous isobutane was passed through the flowmeter F, at a rate of fifty liters per hour. The two gaseous reactants after mixing at L were passed through the coil R of 17 ml. capacity, maintained in a NaNOz-KNO: salt bath kept at a temperature of 420 C. The exit gases were cooled in the water cooled condenser D and then passed through the receiver E, and the auxiliary condenser H which was cooled by solid carbon dioxide, and the nitrated products were collected in both vessels E and H. The nitrated product thus obtained represented 41% of the theoretical conversion of the nitrogen dioxide to.

nitro compounds.

The procedure outlined above for the nitration of isobutane is applicable to other saturated nonbenzenoid hydrocarbons having more than two carbon atoms, such as, for example, propane, n-butane, pentane, hexane, heptane, octane, decane, eicosane, triacontane, cyclohexane, decahydronaphthalene, etc., as well as mixtures of hydrocarbons, such, for example, as paraflin wax. With the different hydrocarbons, however, the rate of reaction varies somewhat, and hence in order to obtain the best results in any particular case it is usually necessary to vary to some extent the temperature of reaction, the proportion of the reactants, and the space velocity of the reaction mixture. These slight variations in operating conditions, however, ordinarily present no particular difiiculties. When, for example, it isv desired to operate-at some particular temperature the space velocity of the reaction mixture may be regulated by observing the gases from the reaction vessel and adjusting the space velocity so acterot the hydrocarbon, determine the exact ratios below which it is impractical to go on account of danger of explosions. On the other hand, increasing the ratio of hydrocarbon to nitrogen dioxide increases the conversion of the nitrogen dioxide to nitro compounds. The cost of handling and recirculating large excesses of hydrocarbon limits 'from a practical and economical point of view-the upper limits of the ratio of hydrocarbon to nitrogen dioxide. In the case of isobutane, a practical ratio for -most purposes appears to be of the order of 4 6 mol parts'of hydrocarbon to 1 mol part of nitrogen dioxide. As the molecular weight of the hydrocarbon increases, the molecular ratio of hydrocarbon to nitrogen dioxide may be decreased.

The temperature may be varied through a fairly wide range without greatly affecting the degree of conversion, although it is necessary to vary the space velocity to compensate for temperature changes. Temperatures ranging from 300 C. to 600 C. may in general be employed. For most purposes a temperature of theorder of 475 C. is satisfactory.

The data shown in the following table will illustrate the results obtained by our process when carried out according to the example set forth that the brown color characteristic of nitrogen above.

Table i halrinountbof Al nlglnt Rate of Partial T lSuace velocity, Cony rocar on o a, pressure emperaere reac an s version, Hydrocarbon weight in weight in figgg of reacture, C. per liter space percent grams grams tants per hour N O:

at 13. e 2 0. 908 420 3, 530 is 66 15, 0 2 0. 968 475 3, 580 17 40. 4 15. 4 3. 4 0. 971 515 14, 400 12 40. 4 14. 1 3. 6 0. 970 550 14, 18

97. 2 16. 4 2 0. 968 420 3, 560 44 l 86. 4 13. 8 .2 D. 968 480 3, 530 25 129. 7 15. 4 8 O. 967 450 13, 530 36 86. 4 2i. 2 2 0. 971 540 8, 360 29. 2 64. 8 14. l 4 0. 971 7 540 15, 940 39. 2 108. 1 18 9 4 0. 968 525 15, 280 39. 4

dioxide is no longer, or only barely, visible therein. By way of example, if an operating temperature of 475 C. is selected, the space velocity for the reaction mixture used in the isobutane example described above may be variedbetween 3000 and 20,000, the preferred range, however, being between 8000 and 15,000.

The proportion of hydrocarbon to nitrogen dioxide may be varied within fairly wide limits. By decreasing the proportion of hydrocarbon to nitrogen dioxide the conversion of the hydrocarbon is increased. This proportion of hydrocarbon, however, should not be lowered sufliciently to approach too closely an explosive mixture. The presence or absence of inert gases and the character and amount of same, as well as the char- As has previously been pointed out, our invention is applicable to the vapor phase nitration of liquid or normally solid hydrocarbons as well as gaseous hydrocarbons. For example, nitrations of decane and cetane were efiected in an apparatus similar to that shown in Figure 1 with the exception that the flow-meter F was omitted, the rate of flow of the hydrocarbon being controlled in the liquid state; a vaporizer for the hydrocarbons was inserted in the bath C preceding the reaction coil R; and the COz-NOz mixture was introduced into the reaction coil R in the form of a jet, simultaneously with the vaporized hydrocarbon. The data shown in Table II illustrate the results obtained when operating according to this procedure.

Table II I Amount of Amount Partial Space velocity, hydrocarbon of N0 Rate of pressure Temperaliters reactants Comer Hydrocarbon flow of 00 sion erweight in weight in of reacture, C. or liter s ace p grams liters/hr. tan 9 per cent N0;

DQ011118 158 9 5. 5 0. 891 330 472 Z; Octane 36 8. 2 5. 5 0. 846 320 317 25 The vapor phase nitration of normally solid hydrocarbons may be illustrated by the nitration of parafin wax in which case an apparatus similar to that employed in the nitration of the liqdid hydrocarbons in the preceding example was used, with the exception that all of the hydrocarbon was placed in the vaporizer and a stream of carbon dioxide was passed through the molten Wax, the rate of hydrocarbon feed being controlled by the rate of carbon dioxide flow. Nitrations were effected under the operating conditions shown in Iable 111.

ess will naturally occur to those skilled in the art. It is to be understood that any such modifications or the use of any equivalents which would naturally occur to those skilled in the art are included within the scope of our invention.

It is to be understood, also. that with respect to the nitration of hydrocarbons having more than eight carbon atoms we do not limit ourselves to the use of substantially pure nitrogen dioxide as the nitrating agent, but may also use less pure materials such as nitrogen dioxide obtained by thermal decomposition of nitric acid, in which Table III Amount Rate of Rate of Space velocity of'hydro- 3 33 flow of CO1 flow oi CO; gigg Tem liters reactant-s Hydrocarbon carbofiit, weigh? tlgxoggh h iglmuglg P of s per litelil space weig 1 y rocar on per our in grams m grams liters/hr. liters/hr. acmnts lamfiin wax..- 155 29. 5 3. 2 8. 6 0.636 375-400 217 Do i 50 I 41 1. 2 32 0. 800 300-335 150 Conversions were not calculated for these nitrations in view of the unknown molecular composition of the original hydrocarbon mixture and of the products, but in both cases satisfactory nitrations were secured as evidenced by complete utilization of the N02 and isolation of nitro compounds in the products.

It is to be understood, of course, that our invention is not to be construed as limited to .the particular procedures set forth in the above examples. Numerous modifications of the process will naturally occur to those'skilled in the art. For example, the process may be operated in a cyclic manner if desired. The exit gases from the condensation and scrubbing systems contain nitrogen oxides, carbon monoxide, carbon dioxide, water vapor, nitroparafiins and hydrocarbons, the amounts and proportions of which vary wide- 1y with the particular hydrocarbon being nitrated, the proportion of reactants used, and the character of the recovery system. In the case 01 low boiling hydrocarbons such as, for example, propane and isobutane, the greater portion of the unreacted hydrocarbon may remain in the exit gases after the condensation of the nitroparaflins. In such cases, additional hydrocarbon and nitrogen dioxide may be added to give a gas mixture of substantially the original composition, which may then be recirculated through the reaction system. 7

Likewise, if desired, the exit gases may be compressed sufiiciently to permit the separation of unconverted hydrocarbon from the nitric oxide, carbon monoxide, etc., and the nitric oxide'then reconverted to nitrogen dioxide. The entire nitration operation may even be carried out under sufliciently elevated pressures to cause liquefaction of the unconverted hydrocarbon in the receiver along with the nitroparafllns. It mayalsobe conducted under reduced pressure, which is often desirable in the case of higher boiling hydrocarbons. Numerous other modifications of our proccase the nitrogen dioxide need not be separated from any undecomposed nitric acid.

Now having described our invention, what we claim is:

1. A process for the production of nitrohydrocarbons which comprises chemically combining, by contacting wholly in the vapor phase, substantially pure nitrogen dioxide and a saturated hy drocarbon containing more than two carbon atoms, at a temperature of 300 to 600 C.

2. A process for the production of nitrohydrocarbons which comprises chemically combining, by contacting wholly in the vapor phase, substantially pure nitrogen dioxide and a saturated hyiii drocarbon containing more than two carbon atoms, at a temperature of approximately 475 C.

3. The continuous process of nitrating saturated hydrocarbons .having in excess of two carbon atoms, which comprises passing a mixture of substantially pure nitrogen dioxide and a saturated hydrocarbon through a reaction vessel maintained at a temperature between 300 and 600 0., and regulating the space velocity of the reactants so that the characteristic brown color of nitrogen dioxide is practically invisible in the gaseous reaction products.

4. A continuous process for the production of nltrohydrocarbons which comprises chemically combining, by contacting wholly in the vapor phase, substantially pure nitrogen dioidde and a saturated hydrocarbon containing more than two carbon atoms, at a temperature of 300 to 600 C., and at a space velocity of 3,000 to 20,000.

5. A process of nitrating a saturated aliphatic hydrocarbon having more than 2 carbon atoms, which comprises producing contact between and chemically combining such saturated aliphatic hydrocarbon and substantially purenitrogen d1- oxlde, with both reagents wholly in the gas or vapor phase.

I HENRY B. BASS.

EDWARD 2B. HODGE.

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