US2415817A - Method of preparing amines - Google Patents

Description

Feb. 18, 1947.

E. J. GOHR ETAL umnon OF PREPARING mums Filed Aug. 24, 1943 M I KIN Patented Feb. 18, 1947 METHOD OF PREPARING AMINES I Edwin J. Gohr and Frank T. Barr, Summit, and

Bruno E. Roetheli, Cranford, N. J., assignors to Standard Oil Developm ration of Delaware ent Company, a corpo- Application August 24, 1943, Serial No. 499,768

The present invention relates to improvements in the manufacture of aromatic amines and more particularly it relates to the catalytic reduction of nitro aromatics, such as nitro xylene, to form the corresponding amino compounds.

It has been known that certain. aromatic amines, such as xylidines, are very valuable blending agents in the manufacture of aviation gasoline. These addition compounds greatly" improve the performance of the aviation gasoline, particularly its rich mixture performance, 1. e., where high fuel to air ratiosare used, as during take-off from the ground, when the plane suddenly is accelerated in flight, or when the plane is flying at maximum speed. A lean mixture for perfect combustion performance contains about 0.065 lb. of aviation fuel per pound of air.

Thlsmixture is preferred when an airplane is 2 Claims. (01,261)?580.)

going and related endsby causing the reduction to take place under temperature conditions \which prevent explosions or violent decomposition of the nitro aromatics, by carrying out the reduction in stages and introducing nitro aromatic feed and a coolant into the system between stages, the amount of coolant being sufficient to absorb the heat of reaction to the extent that the temperature during the reaction cannot ex-- cruising at less than full speed. On the-other hand, when it is necessary to develop more power for some reason, such as during take-off from the ground, greater power can be obtained from an engine of given size by adjusting the ratio of fuel to air in the cylinders to exceed the foregoing lean mixture ratio; that is to say, the fuel to air ratio may be increased to from about 0.09 to 0.12 lb. of fuel per pound of air.

There has recently been developed a method for testing the rich mixture performance of an aviation gasoline. This method is known as the A. F. D.-3C test. In effect, this test determines what is termed the indicated mean effective pressure, hereinafter sometimes abbreviated as I. M. E. P. Normally an aviation gasoline which has an aviation octane number (when it contains 4 cc. of lead tetraethyl per gallon) of 100 and a rich mixture performance or I. M. E. P., accord ing to the A. F. D.-3C test, of 200 lbs. per square inch, meets current specifications for 100 o ctane gasoline. When certain amino aromatic compounds, such as xylidine, are added to a gasoline, its power output is increased without causing knocking and the rich mixture performance of the gasoline is said to be increased. Thus, the utility of aromatic amines, such as xylidine, as addition agents to aviation gasoline is obvious.

Our present invention as heretofore indicated relates to a continuous process for producing aromatic amines as previously indicated, in a man her which is cheaper, so far, and more expedi-- tious than prior processes. In brief compass, we subject a nitro aromatic to catalytic reduction under closely controlled conditions of temperature to produce maximum quantities of desired amines of good quality, We accomplish the foreceed a safe maximum temperature.

The main object of our present invention therefore is to produce aromatic amines continuously under controlled conditions in a process which is safe, economical and otherwise commercially feasible.

In the accompanying. drawing, we have shown diagrammatically an apparatus layout in which a preferred modification of our invention may be carried into practical effect and which will serve toafford, in connection with the following description, a better understanding of the nature and purpose of our invention.

Referring in detail to the drawing, we shall describe the method of producing xylidine from nitro xylene, with the understanding that the invention is not limited to the precise details about to be disclosed but rather serves to illustrate our invention. 1 a

Speaking generally at first, we are about to describe an operation in which we charge to the reactor hydrogen gas, nitroxylene .and xylidine, i the latter being the coolant or temperature controlling substance.

Of course, the nitro xylene feed may and usually does contain dinitroand/or trinitro xylene, and in making xylidine we may remove the undesired dinitro and trinitro xylene by any suitable method, such as by steam distillation or by vacuum distillation, or by a combination of vacuum and steam distillation. However, in our'process, due to the closetemperature it is not necessary to remove'poly nitro aromatics. The xylidine isomers are each goodblending agents in aviation fuels, that is to say, the ortho-,

para'-,' r metaXyIidinesare-each' satisfactory additives.

; Onemodiflcation of "our invention involves the following procedure: nitroxylene is withdrawn from. storage tank I through line 2, pumped by pump E'through line 1 with coolant amine product withdrawn from storage 32 by line 32-"a and pump 33 and forced via line 39 into line 1, where it mixes with hydrogen from line 9, whereuponthe mixture is forced into a, heat exchanger I0.

thence discharged via line l2 into a heater [4 where it is heated to a temperature ofabout 350 F. to 400 F. and thence discharged via line 13 into the top of a cylindricalireactor 20 containing catalyst. It will be noted from the drawing that the catalyst is disposed in the reactor in the form of four separated beds C-l, C-2, C-3, and C-4, and between the beds there are spaces 5-1, 8-2, and 8-3, the latter forming mixing cham bers into which a cooling fluid, subsequently to be fully identified, and nitro aromatic feed are introduced. It will be further noted that in the modification we have shown, the depth of the catalyst beds C-l,. C2, C3, and -4 in: creases progressively downward. The beds of catalyst are supported respectively on screens G-l,

G-J. Catalysts such as molybdenum sulfide or a mixture of nickel sulfide and tungsten sulfide, either as such or on suitable supports, are preferably employed. However, .it is pointed out that a wide variety of catalysts may be used, including the oxides and sulfides of the II, IV, V, V1, and VIII group of the periodic system.

Since the present operation is carried out in liquid phase by maintaining a pressure of 500-5000 lbs. in the reactor 20, it is essential that the catalyst be one which will resist physical distintegration. We have found that an excellent catalyst for the purpose intended is molybdenum sulfide supported on charcoal; for example, a-catalyst containing from -40% molybdenum sulfide, the balance being charcoal, with 10-20% molybdenum sulfide preferred.

As will be noted from the drawing, we inject into the reactor a portion of the nitro aromatic and coolant without preheating the same. For this purpose, we prefer to use a portion of the product from storage 32 which is drawn off through line 32-11 and forced by pump 33 into line 34 where it mixes with nitroxylene from storage conductedto line 34 via line 8. The mixture then enters pipe 35, thence passes into manifold 3B and thereafter into the reactor 20 via branch lines 31, 38, and 39. We have shown three points of injection into the reactor of the nitro xylene and amine product, but obviously injections at a lesser or greater number of points may be made. It will be noted also that branch lines 31, 38, and 39 each carry respectively proportioning orifices 40, M, and 42, by means of which orifices the amount of coolant delivered through any given branch line may be controlled.

This direct injection of a major portion of the nitro loody without preheating and mixed with thecoolant into spaced points in the system is our preferred procedure.

Y Hereinafter, we have set forth in a table proportions of feed and coolant injected at the several points. At this point we shall state that sufficient coolant is added via pipes-31, and 33 to cool the mixture in 8-4, 8-2, and 5-3 to around 350 F. and to prevent the temperature in a subsequent state from exceeding 475 F.

Under the conditions stated and in the presence of one of the catalysts mentioned, the nitro compound undergoes reduction and the products of the reaction are withdrawn from the reactor 20 through pipe 50, pass through heat exchanger 10, thence passed via line 52 into a cooler 53 and thence passed byline 55 into a separator 30.

From the separator 60 the amine product and water formed in the process are withdrawn through line 02 and delivered to means 30 for separating water, e. g., distillation equipment. The separation of water at this point, however, is optional. The water if separated is withdrawn system through line 5 as desired, as previously pointed out.

Having described the physical steps in our process, we shall now set forth in more detail a prel0 ferred modification thereof by means of a specific example, with the understanding that the precise details we are about to enumerate are purely illustrative and do not impose any limitation on our invention. Thus for each 100 gallons of nitro l5 xylene fed to the reactor we prefer to operate under the following conditions:

It will be understood, of course, that the foregoing'example is purely illustrative and that we 30 may use a coolant other than amine product. For example, we may use water, a hydrocarbon or any other material which would not undergo chemical reaction. It would be virtually impossible to set forth precise information for all pos- 5 sible cooling fluids that may be used and it is believed to be unnecessary since the foregoing -data clearly indicate our process. It should be pointed out, however, that our preferred procedure is to introduce all of the hydrogen at one time, say with that portion of the feed stream fed to the top of the reactor, but our preferred procedure, as previously indicated, includes introducing a mixture of the nitro feed and coolant to several points in the system, the coolant serving to cool the reaction products and to be present in suflicient quantity to absorb that portion of the heat of reaction in a stage, following the addition of the coolant, which would cause temperature increase of reactants above the ioregoing maximum.

Heretofore we have described our operation carried out in liquid phase. If we operate in vapor phase, that is where the feed and the diluent are vaporized by the heat of hydrogenation from each preceding stage, it is desirable to operate in a series of reaction chambers of increasing size, either in a single tower or in a succession of individual towers. In vapor phase operation conditions will differ from those shown 30 above because of changes in heat balance imposed by consideration of latent heats of vaporization. In such an operation it will be desirable to obtain complete mixing of vapors before charging to the catalyst bed, and hence provision should be made for flash chambers between catalyst beds.

To recapitulate briefly, we have devised a process for continuously reducing aromatic nitro compounds to the corresponding amines. Our

invention relates to the production 01' aniline, toluidine, xylene and similar amino aromatics from the corresponding nitro aromatics by reduction thereof. In the reduction of an amine there is. an appreciable evolution of heat (approximately 200,000 to 220,000 B. t. u.s per pound the separator 30 through moi of N02 converted to NI-Iz) or about 540,000 B. t. u. per barrel of nitro xylene charged. Moreover, the nitro xylenes, particularly the diand possibly the tri-nitro compounds, tend to decompose vigorously at temperature levels between 500 F. and 800 F. so that safety in operation demands the use of a rather low temperature of operation, say not higher than 600 F. Furthermore, close temperature of operation or temperature control is desirable in order to maintain maximum possible reaction rates compatible with safety. This, however, would entail the removal of heat at the rate of liberation and if conducted by indirect heat exchange would involve the use of tremendous exchanger surfaces because the temperature level is relatively low so that the corresponding temperature differences through .films would be quite low.

We have found that the most convenient method of dissipating the heat is by adding cooler liquid capable of absorbing heat to the catalyst chamber at various points in the system. The use of gas entails the recirculation of excessive volumes of this material and since circulation rates must be high, equipment sizes will be excessive at low pressures so it is necessary from the standpoint of economy with respect to equipment to operate at pressures within the range of from about 2500 to 3500 lbs. per sq. in. Operation with liquid diluent, however, is possible at moderate or low pressures, i e., 125 to 600 lbs. per. sq. in., the pressure of operation being dictated largely by the resistance to flow encountered in passing the liquid through the system.

Numerous modifications of our invention will be apparent to those who are familiar with this art.

What we claim is: 1. The method of continuously reducing aromatic nitro compounds which comprises providing a reaction zone containing a plurality of spaced beds of a catalyst consisting essentially of I molybdenum sulfide on charcoal, introducing into one of said beds of said catalyst in said reaction zone a mixture of aromatic nitro compound, an

amine and hydrogen, causing the said mixture to flow through the said bed of catalyst whereby at least a portion of the aromatic .nitro compound is reduced to the corresponding amine, iniecting a mixture of aromatic amine and ,aromatic nitro compound into the reaction zone at points between the spaced beds of catalyst, causing the latter introduced mixture of aromatic amine and aromatic nitro compound to flow through the beds of catalyst at temperatures sufliciently high to causereduction of the nitro aromatic compound to the corresponding amine, maintaining sufficient aromatic amine in said reaction zone by injection of said amine to prevent the temperature prevailing in the reaction zone from exceeding a desired maximum, and recovering amino aromatics from said reaction zone.

2. The method set forth in claim 1 in which the mixture of aromatic amine and aromatic nitro compound contacts beds of catalyst of increasingly greater length as they proceed through the reaction zone.

EDWIN J. GOHR. FRANK T. BARR. BRUNO E. ROETHELI.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS.

Kise Aug. 11, 1942

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