Patented Oct. 21, 1941 ‘ ‘2,260,258

UNITED STATES ‘PATENT OFFICE 2,260,258 ‘PRODUCTION, OF NITROHYDROCABBONS Jerome Martin, Terre Haute, Ind., assignor to Commercial Solvents Corporation, Terre Haute, 11111., a corporation of Maryland No Drawing‘. Application April 24, 1939, , Serial‘ No. 269,792 ~ 7 Claims. (01. 260-644) My invention relates to the "production of ous'manner, although intermittent treatment nitrohydrocarbons. More speci?cally, my inven will be satisfactory if e?ected at suf?ciently short _ - tion relates to an improvement in-the production intervals. By means of this preventive treat , of- nitrohydrocarbons by the direct vapor phase ment, it is possible to operate the process con ' nitration of hydrocarbons. tinuously, with little or no deactivation of the The vapor phase nitration of saturated hydro vessel taking place. In fact, I have been able carbons is described in U. S. Patent 1,967,667 of to secure continuous operation over a ‘period H. B. Hass et al., U. S. Patent 2,071,122 of H.‘ B. , of many months, with no apparent deactivation Hass et al.,~ and in copending application Serial , whatever, i. e., no apparent decrease from the No. 98,634 of H. B. Hass et al. According to 10 ‘initial maximum yields. and conversions. this process, saturated hydrocarbonsand nitric In carrying out the preventive treatment of acid vapor or nitrogen, dioxide are contacted in my present invention, it is merely necessary to a reaction vessel maintained at a sufficiently high introduce intermittently or continuously into the temperature to insure vapor phase conditions reaction vessel one of the known reactivating . at the pressures employed. 15 agents. It is desirable that the material be in Although the vapor phase nitration process troduced in such a manner that it can contact gives satisfactory initial yields and conversions, the entire inner surface of the vessel, and for it has been found that there is a tendency for this reason I prefer to disperse the treating agent these yields and conversions to drop‘oif under in a ?nely-divided form in the reactant vapors continued operation. This e?ect appears to be 20 entering the vessel. Thus, a ?nely-divided solid similar to the deterioration or poisoning of a may be suspended in the entering gas stream, or catalyst in a catalytic reaction, but as there is a molten material, or a solution or suspension, no catalyst employed in the process, the explana may be atomized into the entering gas stream. ’ tion of the phenomenon is not clear. It appears When employing nitric acid rather than 7 that after a certain period of operation, the in nitrogen dioxide as the nitrating agent, a very terior walls of the reaction vessel acquire reac convenient method for carrying out my present tion-inhibiting characteristics. The reaction invention consists in vaporizing the nitric acid vessel in this condition is described as “deacti by contacting the liquid acid with amolten salt vated,” and it has been found that the deac bath, at least one of the components, of which tivated reaction vessel can again be “reactivated” 30 constitutes a reactivating agent. . In this method by treatment with various reactivating agents, of operation, the contact of the cold acid with as described in co-pending application Serial No. the molten salt bath gives rise to pronounced 272,152 of E. B. Hodge et a1. Although the reac turbulence, with resulting entrainment of salt tivating treatment is generally successful in in vparticles in the vapor stream leaving the vapor creasing the yields and conversions after the 35 izing vessel. In the absence of undue .ba?le reaction vessel has become deactivated, it is not e?ects, the entrained particles are carried into always possible to completely reactivate, i. e., to the reaction vessel and contact the inner sur ‘obtain again the initial maximum yields and faces thereof to effect the desired preventive conversions. Furthermore, the reactivation treatment. It will be evident, of course, that treatment is undesirable in continuous commer 40 various other mechanical equivalents for intro cial operation, since it involves stopping the proc ducing ?nely-divided reactivating agents may be ess, e?fecting the reactivation treatment, and employed, and it is to be understood that my again starting up the process. , ' invention is not limited to the mechanical details I have now discovered that the materials of this operation. , I which have previously been found to be effective 45 My process for continuously treating the reac-' in remedying the deactivated condition of a re-_ tion vessel may be used in conjunction with any action vessel may also, be satisfactorily employed of the known methods for carrying out the vapor as preventive agents to preclude’ the initial oc ~ phase nitration process. Any combination of currence of deactivation. In accordance with my , . reactants and reaction conditions known to be present invention, the reaction vessel is treated 50 operative for vapor phase nitration may be ‘em with the reactivating agent during the operation ployed in conjunction .with the present preven of the nitration process, and before any deac- ' tive treatment. The known , nitrating agents, tivation takes place. This treatment is con - ,such as nitric acid vapor or nitrogen dioxide, tinued during the operation of the nitration may be utilized, and any of the various hydro process, and is‘ preferably effected in a contmu 55 carbons may be nitrated. My improved process 2 2,260,258 is particularly effective in the nitration of the saturated hydrocarbons, such as methane, vention, and among these I prefer to employ the ethane, propane, butanes, pentanes, hexanes, alkali metal compounds. In general, it is desir cyclohexane, and the like, utilizing nitric acid able to utilize a reactivating agent which is vapor as the nitration agent. molten under the conditions employed in the nitration reaction, in order to insure adequate Known reactivating agents are available for contact of the treating agent with the entire in the treatment of deactivated vessels at reactiv ating temperatures throughout the entire oper ner surface of the vessel; and for this reason, as well as for greater activity, certain of the ative range for the nitration reaction, and I have alkali metal compounds are to be preferred. found that such agents are e?'ective at the same temperatures for preventing deactivation when 10 For use in the molten salt bath for vaporizing employed in the present procedure. It is prob nitric acid for the process, the reactivating agent able that materials requiring relatively high tem should preferably constitute a n1tric acid salt perature for eil’ecting reactivation will be eifec which is stable in the presence of nitric acid at tive to prevent deactivation at lower temper the temperature of the salt bath. The alkali 15 metal nitrates and mixtures of these nitrates with atures; but it is unnecessary to attempt such other‘ nitric acid salts are particularly satisfac applications since there are a great many mate tory for use as the vaporizing salt bath. A large rials readily available which are active at even the lowest temperatures employed in the nitra number of salt mixtures are available for this tion process. In general, temperatures of 250° purpose, so that a salt bath of suitable melting C. to 800° C., or even higher, may be employed 20 point may readily be chosen, depending upon the for the nitration reaction, depending upon the desired operating pressure (which, of course, con space velocity. The preventive treatment of my trols the boiling point of the nitric acid). In present invention is effective throughout this en general, it is preferable to employ a salt mixture tire range, but I prefer to operate within the which is stable in the molten state at 60° to 100° range 350° C., to 500° C., to secure optimum yields 25 0., above the boiling point of nitric acid at the and conversions. operating pressure, and to operate at such tem The remaining operating conditions for the re perature in order to insure adequate heat trans action, such as pressure and space velocity, may fer. Since most of the nitric acid salts melt at be chosen in accordance with prior practices, the relatively high temperatures, it' is convenient to limiting values, of course, being dependent upon 30 employ mixtures having minimum melting points, the temperature employed, and the particular or eutectic points. The following is a representa tive list of suitable salt mixtures for this pur reactants. These conditions, however, have no pose: direct bearing upon the preventive treatment of the present invention, and may be varied widely in accordance with known procedures for this 35 Minimum Maximum Composition melting melting type of reaction. point point Any suitable type of apparatus for vapor phase reactions of this general nature may be utilized SodiumLithium nitrate..... nitrate ______._ “C. °C. when carrying out my present procedure. Reac 40 Potassium nitrate 120 334 tion vessels of di?'erent materials of construction Potassium nitrate. . Silver nitrate _____ .. 131 334 differ in their deactivating tendencies, copper, Rubidium nitrate Silver nitrate ______. . 136' 310 aluminum, iron, and the ferrous alloys appar Sodium nitrate... ently being the most easily deactivated. Stain- _ Thallium nitrate 162 308 less steel is particularly‘ suited for the construc Lithium nitrate 45 Silver nitrate... 172 255 tion of apparatus of this type, and my process Sodium nitrate... Potassium nitrate ______. . adequately inhibits deactivation of this mate Calcium nitrate.-. 561 rial. The particular structure of the apparatus Potassium nitrate. Thallium nitrate- - is not critical, but it is desirable that the nitra Sodium nitrate.. - 334 tion reaction vessel be of such form and be so 50 Potassium nitrate. Lead nitrate ...... 357 positioned that the treating agent can readily Potassium nitrat contact the entire inner surface thereof. Lead nitrate- -- Sodium nitrate“ 357 It will also be obvious that certain precautions Potassium nitrate should be taken to prevent the solid treating Strontium nitrate ...... 570 Potassium nitrate. material from blocking the flow of the reactants Calcium nitrate. """""" h 561 through the reaction vessel, or through the aux Sodium nitrate. Potassium nitrat iliary apparatus. Likewise, when employing the Barium nitrate.. 592 reactivating agent in the salt bath for vaporizing Sodium nitrate ______.. Calcium nitrate. .. nitric acid for the process, precautions must be Potassium nitrate.. 561 taken to prevent the entrained reactivating salt Barium nitrate.-... 60 Strontium nitrate. . 592 from separating completely from the vapor Sodium nitrate... . stream, prior to entering the reaction vessel. Lead nitrate . . . . Sodium nitrate 357 Such obvious precautions, and various equivalent Barium nitrate means for effecting the present process, will be Lead nitrate- . 592 obvious to those skilled in the art, and my in Potassium nitrate.. 65 Strontium nitrate ______. . 570 vention is not to be construed as limited to any Sodium nitrate... - . Strontium nitrate- . 570 mechanical details for this purpose. Lithium nitrate- . . . Any of the known reactivating agents, such as Potassium nitrate. those described in co-pending application, Serial Barium nitrate..._. . 592 Potassium nitrate ...... No. 272,152, referred to above, may be employed Barium nitrate...... } 70 Sodium nitrate... 502 as the agents for preventing deactivation in ac Barium nitrate--. cordance with the present invention. Reactivat 592' ing agents, chosen from the class consisting of the alkali and alkaline earth metal compounds If the reactivating agent is to be introduced di are particularly suited for use in the present in rectly into the reaction vessel or into the entering 75 gas stream, instead of being employed in the 2,260,258 3 nitric acid vaporizer, the nitric acid salts still will be sufdcient to completely prevent deactiva constitute the preferred materials, but the reacti tion of the reaction vessel. Much larger amounts vating agents may also be satisfactorily employed of thereactlvating agent may, of course, be em in the form‘ of other active compounds, either in ployed, and it is usually desirable to provide a organic or .organic. In view of the presence of factor of safety in this respect. A large excess nitric acid in the reaction chamber, ant7 of the will not adversely affect the reaction, and will compounds employed will be at least partially merely involve mechanical and economic consid transformed into thecorresponding nitric acid erations. The optimum or minimum amounts to salt during the course of the nitration reaction; - effect this end in any particular. case can, of For this reason it is desirable to utilize the nitric 10 course, readily be determined by preliminary ex acid salts initially, or to employ compounds such periment. ' as the hydroxides or carbonates, which will not My invention ‘may be illustrated by the follow- ' form by-products di?lcult to separate from the ing speci?c example: reaction products. Various other compounds, Nitric acid (13.5 N.) was vaporized by drop such as sulfates, phosphates, chromates, halides, 15 ping the liquid acid onto the surface of a molten and the like, which are known to be reactivating salt bath comprising approximately equal parts agents, will serve satisfactorily as preventive by weight of sodium and potassium nitrates. The ' agents in the present invention, but are less desir salt bath was maintained at approximately 230° able than the nitrates, hydroxides, or carbonates, 0., and the acid was vaporized at a rate of ap-' in view.of the nature of the reaction products ob 20 proximately 9 kilograms'per hour. The result tained in the partial transformation ‘ of these ing nitric acid vapor, together with the small compounds into the corresponding nitrates. amount of entrained sodium and potassium ni It is desirable, although not essential, that the‘ trates, was mixed with propane gas and imme , reactivating agents for introduction directly into ' diately introduced into-a stainless iron reaction the reaction, vessel, or into the entering gas vessel of 0.84; liter capacity, maintained at 430 stream, be molten at the reaction temperature. 445° C. The propane ‘feed rate was approxi Many of the individual compounds, such as the mately 10 kiloliters per hour (760 mm. Hg; 25° ’ alkali metal hydroxides and nitrates, have melt 0.). The initial yield of nitrohydrocarbons ob ing points within the desired operating tempera tained was approximately 2.8 liters per hour, and ture- range. However, numerous other com 30 this yield was maintained in continuous opera pounds which are active reactivating agents, have tion for 60 days. At the end of this period of much higher melting points, and it is therefore operation, there was no apparent decrease in the convenient to employ mixtures having minimum quantity of molten salt in the vaporizing bath, melting points, or eutectic points. The following but a very small amount of salt was collected at is a representative list of such mixtures: 35 the exit of the reaction vessel during the opera tion. In a similar experiment in which the nitric Minimum acid was vaporized by admixture with super Composition melting heated propane, and no reactivating agent was point employed as a preventive of deactivation, the yield fell to 1.5 liters per hour after 5 days of ° 0. 40 operation. Sodium hydroxide ______.. 184 Potassium hydroxide. . _ It is to be understood, of course, that the above Sodium hydroxide . . _ _ . 241 example is illustrative only, and does not limit Rubidium hydroxide. . Potassium hydroxide. . _ } 306 the scope of my invention. Likewise, the various Rubidium hydroxide. _ reactivating agents and mixtures containing such Potassium s _... . } 333 45 Potassium nitrate_.._ agents, listed above, are not to be construed as Sodium bor e ______} 475 limiting the scope of my invention. Any of the Calcium phosphate. _ Lithium earbonate_-_ } 492 various agents which are active to reactivate a Potassium carbonate . deactivated vessel, are operative for preventing Lithium sulfate- _ . } 551 Cadmium sulfate- . ~ 50 deactivation in accordance with the present pro Lithium sulfate. . - } 596 cedure. Similarly, any of the various methods Sodium suli'ate_.--tungstate... _ _ . } 630 for effecting the nitration reaction may suitably Potassium tungstate . be employed in conjunction with the present pro Potassium sulfate___ } 6S0 Manganese sulfate. ..-. . cedure. In general it may be said that any equiv Potassium carbonate.-- . } 753 55 alents or modi?cations, which would naturally Calcium carbonate ...... occur to those skilled in the art, are included The amount of reactivating agent which; it is within the scope of my invention. necessary to, use for prevention of deactivation My invention now having been described, what I claim is: ' of the reaction vessel, will of course depend to 1. In a process for the vapor phase nitration some extent upon the nature of the agent used, 60 of hydrocarbons, the improvement which com a and the means employed for effecting contact of prises introducing a, reactivating agent, effective the agent with the interior walls of the vessel. in decreasing the reaction-inhibiting character Thus, a reactivating agent which is molten at the istics of the deactivated nitration reaction vessel reaction temperature may‘ generally be employed walls, into said nitration reaction vessel during in smaller amounts than a material which is solid 65 Similarly, smaller amounts v the course of the nitration reaction. at such temperature. 2. ma process for the vapor phase nitration of the reactivating agent will be required if the of hydrocarbons, the improvement which com apparatus is suitably designed to afford ease of prises introducing into'the reaction vessel, dur contact of the material ‘with the entire inner ing the course of the reaction, a reactivating surface of the reaction vessel. In any case, how 70 ever, the amount required is extremely small agent for nitration reaction vessels, selected from compared to the quantities of reactants simulta the group consisting of the ‘substantially water neously used in the process. In general, it may 'soluble salts of the alkaline earth metals,v the be said that less than 0.1% of reactivating agent, salts of the alkali metals, and the bases of the based on the weight of the nitric acid employed, 75 alkali metals and the alkaline earth metals. 4 2,260,258 3. In a process for the vapor phase nitration of hydrocarbons, the improvement which com ing nitric acid vapors and entrained reactivating prises continuously introducing into the nitration agent into said nitration reaction vessel. reaction vessel, during the course of the reaction, 6. In a process in which nitric acid is vaporized a reactivatlng agent, e?ective in decreasing the and the resulting vapors are reacted with satu reaction-inhibiting characteristics of the deacti rated hydrocarbons in the vapor phase to form vated nitration reaction vessel walls, which is nitrohydrocarbons, theimprovement which com molten at the reaction temperature. prises vaporizing said nitric acid by contact with 4. In a process for the vapor phase nitration a molten salt bath containing a reactivating of saturated hydrocarbons, the improvement agent for nitration reaction vessels‘ selected from which comprises continuously introducing into the group consisting of the substantially water the stream of reactant gases entering the nitra soluble salts of the alkaline earth metals, the tion reaction vessel, 2. ?nely-divided reactivating salts of the alkali metals, and the bases oi.‘ the agent for nitration reaction vessels selected from alkali metals and the alkaline earth metals, and the alkali metal compounds which are molten introducing the resulting nitric acid vapors and at the nitration reaction temperature. entrained reactivating agent into the nitration 5. In a process in which nitric acid is vaporized reaction vessel. -' _ and the resulting vapors are reacted with satu 7. In a process in which nitric acid is vaporized, rated hydrocarbons in the vapor phase to form and the resulting vapors are reacted with satu nitrohydrocarbons, the improvement which com rated hydrocarbons in the vapor phase to form prises vaporizing said nitric acid by contact with 20 nitrohydrocarbons, the improvement which com a molten salt bath containing a reactivating prises vaporizing said nitric acid by contact with agent, effective in decreasing the reaction-inhibit a molten salt bath containing an alkali metal ing characteristics of the deactivated nitration nitrate, and introducing the resulting nitric acid reaction vessel walls, and introducing the result vapors and entrained alkali metal nitrate into the 25 nitration reaction vessel. JEROME MARTIN.