US3917706A - Production of secondary alkyl primary amines - Google Patents

Abstract

A process for producing secondary alkyl primary amines from nparaffins where a portion of the paraffin is nitrated to nitroparaffin along with the formation of nitrated and oxygenated by-products, where the nitroparaffin is substantially hydrogenated to the amine, and where the amine is separated from a mixture composed of unreacted paraffin, nitroparaffin, and by products, which comprises catalytically hydrogenating the mixture composed of paraffin, nitroparaffin and by-products in a plurality of zones where the initial hydrogenation is conducted at a temperature of from about 250* to 500*F., where hydrogenation in a subsequent zone is conducted at a temperature of from about 600* to 750*F. and recycling the hydrogenated product for nitration with the n-paraffin.

Description

United States Patent [1 1 Hudson, Jr. et al.

[ Nov. 4, 1975 PRODUCTION OF SECONDARY ALKYL PRIMARY AMINES both of NY.

[73] Assignee: Texaco, Inc., New York, NY.

[22] Filed: Dec. 26, 1973 21 Appl. No.: 428,641

[52] US. Cl 260/583 M; 260/644; 260/688 [51] Int. Cl. C07C 85/11; C07C 85/00;

C07C 87/04 [58] Field of Search 260/583 M, 644, 688

[56] References Cited UNITED STATES PATENTS 3,470,252 9/1969 Doyle et al 260/583 M Primary Examiner.loseph P.. Brust Attorney, Agent, or Firm-Thomas H. Whaley; C. G. Ries; George J. Darsa [57] ABSTRACT A process for producing secondary alkyl primary amines from n-paraffins where a portion of the paraffin is nitrated to nitroparaffin along with the formation of nitrated and oxygenated by-products, where the nitroparaffin is substantially hydrogenated to the amine, and where the amine is separated from a mixture composed of unreacted paraffin, nitroparaffin, and by products, which comprises catalytically hydrogenating the mixture composed of paraffin, nitroparaffin and by-products in a plurality of zones where the initial hydrogenation is conducted at a temperature of from about 250 to 500F., where hydrogenation in a subse quent zone is conducted at a temperature of from about 600 to 750F. and recycling the hydrogenated product for nitration with the n-paraffin.

10 Claims, No Drawings PRODUCTION OF SECONDARY ALKYL PRIMARY AMINES i This invention relates to the production of amines and more specifically to the production of secondary alkyl primary amines having from 6 to 30 carbon atoms from paraffin hydrocarbons. In particular, this invention relates to a continuous process for the production of high purity secondary alkyl primaryamines from paraffin hydrocarbons.

Processes for the production of secondary alkyl primary amines from paraffin hydrocarbons have been previously described in, for example, US. Pat. No. 3,470,252. In general, thesamines have been prepared by nitrating from to 50 weight per cent of the paraffin to nitroparaffin employing, for example, nitric acid, nitrogen dioxide or dinitrogen tetroxide and thereafter reducing the nitroparaffin with hydrogen in the presence of a hydrogenation catalyst. The product resulting from the nitration and hydrogenation reaction provides not only the desired amine but additionally contains unreacted paraffin, nitroparaffin and by-products of each of the previous reactions. Amines of high purity are recovered from the hydrogenated nitroparaffin product employing various separation techniques, as for example, the methods developed and disclosed in US. Pat. No. 3,470,251.

The formation and buildup of substantial amounts of by-products seriously reduces the attractiveness and selectivity of the process, particularly in continuous processsing where unconverted paraffin and by-products are contemplated for recycle to the initial nitration stage. The process would be substantially improved by providing recycle feedstock possessing a reduced by-product content.

The principal source of by-products is derived from the initial nitration involving reaction between the nitrating agent, such as nitrogen dioxide, dinitrogen tetroxide and nitric acid, and the paraffin. In addition to the principal nitroparaffin product, there is produced through a series of complex mechanisms a plurality of other materials including nitrites, nitrates, olefins, ketones, alcohols, acids and polyfunctionals, such as nitroalcohols, dinitroparaffins, nitroketones and nitroolefins. While caustic washing of the nitrated product as disclosed in the art removes some of the by-product, primarily the acids, a substantial amount of by-product is passed on to the amine forming hydrogenation step. Following hydrogenation of the nitroparaffin to the amine, the by-products can, in effect, constitute up to 35 weight per cent of the liquid hydrogenation product excluding unreacted paraffin. It will be appreciated that the propensity of the reaction'to form by-products seriously reduces the selectivity of the process insofar as production of nitroparaffin and ultimately secondary alkyl primary amines are concerned. Moreover, in continuous processing where recycle of the predominantly unreacted paraffin streams containing unconverted nitroparaffin and by-products to the initial nitration stage is contemplated, there will occur in the course of long periods of operation a substantial buildup of contaminating by-products interfering with the orderly conversion at high selectivy of the paraffin to the amine, which ultimately leads to a highly unsatisfactory and cost-prohibitive operation. H

I-Ieretofore, the mixture of paraffin,'nitroparaffin and by-products was hydrogenated at temperatures of from about 450 to 600F. under hydrogen pressures of from 200 to 4,000 p.s.i.g. in the presenceof known and conventional hydrogenation catalysts. Temperatures below 450F. were taught as not giving appreciable hydrogenolysis and temperatures in excess of 600F. were to be avoided as the same caused undesirable isomerization, cracking and coking of the hydrocarbons. Further, the oxygenated by-products such as alcohols are dehydrogenated to undesired olefins. Consequently, hydrogenating the mixture in accordance with the known procedure provided only partial hydrogenolysis of the mixture such that a considerable amount of incompletely converted by-products are recycled to the initial nitration reactions.

It is therefore an object of this invention to provide a process for selectively converting paraffin hydrocarbons'to secondary alkyl primary amines.

Another object of'this invention is to provide a process for the production of secondary alkyl primary amines from n-paraffins wherein the by-product content of recycle stream is substantially reduced.

Yet another object of this invention is to provide a process wherein secondary alkyl'primary amines are prepared from n-paraffins by means of a continuous process wherein the byproduct content in the recycle stream is substantially reduced and where the amines are recovered in high purity.

Other objects and advantages will become apparent from a reading of the following detailed description and examples.

SUMMARY OF THE INVENTION Broadly this invention contemplates a process for producing secondary alkyl primary amines from nparaffins wherein a portion of the n-paraffin is nitrated to form a nitroparaffin along with nitrated and oxygenated by-products, where the nitroparaffin is substantially hydrogenated to the amine and where the amine is separated from a mixture of' unreacted paraffin, unconverted nitroparaffm and by-products, the improvement which comprises:

a. hydrogenating the mixture in the presence of a hydrogenation catalyst in a plurality of reaction zones in series wherein initial hydrogenation of the mixture is conducted at a temperature of from about 250 to 500F., preferably from about 350 to 475F. and

subsequent hydrogenation of the mixture is conducted at a temperature of from about 600 to 750F., preferably from about 650 to 710F.; and

b. recycling the hydrogenated product of (a) for nitration with the n-paraffin.

The mixture of unreacted n-paraffin, nitroparaffin and by-products hydrogenated and recycled in accordance with the instant invention, is derived from a paraffin hydrocarbon or paraffin hydrocarbon mixtures containing from 6 to 30 carbon atoms, initially nitrated and subsequently hydrogenated to the corresponding amine. Typical paraffin hydrocarbons include n-hexane, n-heptane, n-octane, n-decane, n-dodecane, n-tetradecane, n-pentadecane, n-o ctadecane, n-eicosane,

n-pentacosane, n-triacontane and mixtures thereof.

urea or solvent dewaxing, which are capable of recovering n-paraffins from mixtures of isoparaffins, naphthenes, aromatics and n-paraffins. Mixtures of n-paraffins having from 6 to 10, or to 14, or 14 to 17 carbon atoms can be obtained by absorption of molecular sieves. Likewise, mixtures containing from to 21 carbon atoms, or to carbon atoms can be obtained by means of urea or solvent dewaxing and are also contemplated as starting materials.

NITRATION The nitration of the paraffin hydrocarbons to secondary mono-nitroparaffms is conducted in a liquid-vapor process. The paraffin hydrocarbon along with the upgraded recycle hydrogenated stream provided herein is contacted with a nitrating agent, such as nitrogen dioxide, dinitrogen tetroxide or nitric acid, at a temperature of from about 250 to 500F. at pressures ranging from atmospheric to 20 atmospheres thereby converting from about 5 to about 50 per cent of the paraffin hydrocarbon principally to the corresponding secondary mono-nitroparaffin. By secondary mono-nitroparaffin we mean that the nitro group is predominantly located on other than the paraffms terminal carbon atom.

Illustrative mono-nitroparaffms include 2 or 3- nitrohexane, 2, 3 or 4-nitroheptane, 2, 3 or 4-nitrooctane, 2, 3, 4 or S-nitrodecane, 2, 3, 4, 5 or 6-nitroundecane, 2, 3, 4, 5 or 6-nitrododecane, 2, 3, 4, 5, 6 or 7-nitrotridecane, 2, 3, 4, 5, 6 or 7-nitrotetradecane, 2, 3, 4, 5, 6, 7, 8 or 9-nitrooctadecane and mixtures thereof. The amount of nitrating agent employed can vary within wide limits, as for example, from about 0.05 to 0.55, preferably 0.1 to 0.3, moles of nitrating agent per mole of paraffin. Any excess nitrating agent can be recovered alongwith, for example, nitric oxide, a gaseous reaction by-product, the latter in continuous operations subsequently oxidized to nitrogen dioxide and the nitrating agent stream recycled for reintroduction into the nitration reaction zone.

In the course of nitration, reaction by-products are formed including C to C ketones, alcohols, carboxylic acids, nitrites, nitrates and multifunctional by-products, such as dinitroparaffins, nitroalcohols, nitroketones, nitroolefins, nitroacids and trinitroparaffins. These by-products are carried along in the liquid crude nitration product after separation of such off-gases as nitrogen, nitrous oxide, carbon dioxide, carbon monoxide, nitric oxide, water and unreacted nitrating agent. The crude nitrated liquid product typically comprises from 5 to weight percent nitroparaffin and from 0.5 to 15 weight percent by-products.

I-IYDROGENATION TO AMINE The secondary mono-nitroparaffins described above contained in the crude liquid nitrated product are substantially hydrogenated to secondary alkyl primary amines at average conversion temperatures ranging from about 100 to 450F. in the presence of conventional and well-known hydrogenation catalysts. Preferably the crude liquid product is caustic washed in an aqueous medium prior to the hydrogenation where some of the by-products deleterious to hydrogenation catalyst life are removed.

The crude liquid hydrogenated product comprises C to C n-paraffin, secondary alkyl primary amine and lesser amounts of secondary alkyl secondary amine, alcohols, ketones, unconverted nitroparaffin, water and polyfunctionals such as nitroamines, aminoketones and aminoalcohols. Conventional recovery procedures may be employed for recovering the desired primary amine as by distilling the hydrogenated product by stepwise fractionation. Alternatively, the amine may be converted and recovered as an amine salt by reaction of the crude liquid product with an inorganic acid followed by further treatment of the amine salt with alkali and thereafter recovering the primary amine by distillation. In a highly preferred procedure the amine containing liquid hydrogenation product is treated with carbon dioxide at about 15 to C. under pressures ranging from 100 to 500 p.s.i.g. where the hydrogenated product is admixed with from about 1 to 10 moles of carbon dioxide per mole of amine present in the hydrogenation product until substantial quantities of an amine-carbon dioxide complex are formed in mixture with paraffins and by-products. This mixture is thereafter contacted wtih from about 1 to 5 parts by weight of alkanol-water solvent mixture substantially saturated with carbon dioxide. Contacting the paraffin and the complex with the solvent mixture, for example, methanol-water, causes a solvent phase to form containing substantially all of the nitroparaffin by-products and secondary amine. It will be appreciated that the separation technique employing carbon dioxide is selective in removing primary amine and rejecting secondary amine. Separation employing a strong inorganic acid extracts both primary and secondary amines which can be subsequently separated by distillation after neutralization. The solvent phase is thereafter heated to about 60 to C., or alternative the pressure of the solvent phase is reduced, thereby springing the amine and flashing off carbon dioxide and a portion of the solvent. The amine is recovered from residual solvent by distillation or a combination of distillation and decantation and the purity of the amine recovered is in excess of 98 weight per cent.

RECYCLE I-IYDROGENATION The unreacted nitroparaffin and by-products of the nitration and hydrogenation reactions in admixture with the paraffin separated above are upgraded and made suitable for recycle and introduction to the initial nitration reaction by means of a plural stage hydrogenation treatment. Typically the recycle mixture contemplated for hydrogenolysis in accordance with the instant invention is predominantly C to C n-paraffin containing from 0 to 5 weight per cent unconverted nitroparaffin and from 0.5 to 15 weight per cent of all byproducts. Representative of the by-products are C and C oxygenated, nitrated or nitrooxidized materials illustrated by alcohols, ketones and polyfunctionals including nitroketones, nitroalcohols, nitrates, nitrites and dinitroparaffins. The mixture may also contain aminated by-products such as secondary amines, aminoketones, aminoalcohols and unextracted amine product. The feed for the plural stage hydrogenation treatment can also include such by-product streams from the process as, for example, the bottoms from the amine distillation which consist of primarily secondary amines and polyfunctional products as aminoalcohols or aminoketones. Also, the organic material sprung with acid from the caustic extract generated in contacting the crude nitration product contains organics which can be converted to paraffins for recycle and the paraffin stream derived from the initial vacuum distillation of the crude amines can be added to the recycle mixture intended for hydrogenolysis. These waste streams,

when upgraded in accordance with the instant invention, eliminate the need for special handling and disposal and at the same time provide for the recovery of valuable feedstock. The mixture can contain some or all of the aforementioned by-products in varying amounts depending upon the conditions and reaction employed for the initial nitration of the paraffin, the subsequent hydrogenation of the nitroparaffin to primary amine and the procedure employed for separating and recovering the secondary alkyl primary amine.

It has now been found that the above mixture of nparaffin, nitroparaffin and by-products can be essentially converted to a recycle stream composed of at least 98 and preferably 99 weight per cent or higher of the original C to C n-paraffin purity while deterring cracking or isomerization of the paraffin and the formation of coke and where the material suitable for recycle to the initial nitration reaction is substantially free of olefins, isomerized n-paraffins, oxygenates and cracked light hydrocarbons. The stream suitable for recycle is provided by catalytically hydrogenating the mixture in a plurality of zones where initial hydrogenation is conducted at a temperature of from about 250 to 500F., preferably between about 350 and 475F., for a time of sufficient duration whereby unconverted nitroparaffins are hydrogenated to amines and unstable oxygenates such as nitrites and nitrates are converted to more thermally stable forms. In general, the initial hydrogenation converts the nitroparaffin and unstable oxygenated by-products to, for example, amines, am ides, diamines and alcohols.

Following the initial hydrogenation, the mixture is subsequently hydrogenated at a temperature of from about 600 to 750F., preferably between about 650 and 710F., for a time of sufficient duration whereby primary amines, secondary amines, alcohols, ketones, aminoalcohols, amides, and diamines contained in the mixture are substantially converted to n-paraffins.

An additional hydrogenation treatment may in some instances be desirable as, for example, where the liquid product hydrogenated at about 600 to 750F. is found to contain small amounts of olefins. Such an additional hydrogenation treatment can be conducted at from about 450 to 650F. whereby the olefins are converted to n-paraffin.

In general, hydrogenation in each of the plural reaction zones is undertaken in the presence of hydrogen pressures ranging from about 100 to 1,500 p.s.i.g. for periods of from 0.1 to 5 hours. In continuous processing, the mixture can be introduced into each of the plural zones at space velocities of from 0.2 to 10 v./v./hr. Conventional hydrogenation catalysts can be employed in each zone as, for example, nickel, cobalt, molybdenum, platinum, palladium and rhodium. The catalysts may be supported on kieselguhr, silica, carbon or alumina as is known in the art. Preferably, we employ an alumina supported Group VIII metal or a mixture of Group VIB and VIII metal. A highly preferred catalyst is composed of nickel-molybdenum or cobalt-molybdenum on an alumina support.

The plural stage hydrogenation of the mixture ultimately intended for recycle provides an improved and upgraded material having an n-paraffin content of 99 weight per cent and higher. The purity of the recycle material is related to the plural zone hydrogenation described above in that the mixture separated from the amine while originally unstable to temperatues of 600F. and higher with regard to components therein being subject to isomerization, cracking and coking, can be subjected to such elevated temperatures if the initial hydrogenation at the lower temperatures is previously undertaken. It is believed that the components responsible for the lack of staiblility at temperatures of 600F. and higher are the unconverted nitroparaffin and oxygenated by-products which according to the instant invention are essentially converted to forms more stable to elevated temperatures thereby deterring cracking, isomerization and coking.

The instant process embodying the improvements related to upgrading recycle stream provides a highly selective process for the production of secondary alkyl primary amines. These amines can be employed as mold-release agents, emulsion freeze-thaw stabilizers, pigment dispersing agents, polyurethan catalysts and anti-caking anti-dusting agents. The amines can also be used as corrosion inhibitors, deleterious bacterial control agents, sludge dispersants and as detergents and deicers in gasolines.

In order to more fully illustrate the nature of this invention and the manner of practicing the same, the following examples are presented. In these examples the best mode contemplated for carrying out the invention is set forth.

EXAMPLE I A continuous process for converting n-paraffins to secondary alkyl primary amines is undertaken by providing a fresh water-white C to C n-paraffm hydrocarbon composition having the following carbon chain length distribution on a weight per cent basis: C 11.1, C 28.7, C 32.2, c 26.9, C 1.1. To 10.7 weight per cent of fresh normal paraffins there is mixed 89.3 weight per cent of previously processed and upgraded recycle paraffins according to the instant invention.

940 pounds per hour of the paraffin hydrocarbon charge are nitrated with 60 pounds per hour of nitrogen dioxide wherein nitration proceeds at 330F. under a pressure of 4 p.s.i.g. Off-gases comprising paraffin, nitrogen dioxide, nitric oxide, nitrous oxide, nitrogen, carbon dioxide, carbon monoxide and water are withdrawn, the off-gases partially condensed, and condensed paraffin recycled. Nitric oxide in the overhead gas is oxidized to nitrogen dioxide, the oxidized gas cooled to condense nitrogen dioxide, and the liquefied nitrating agent recycled. Non-condensible gases including nitrogen, ntiric oxide, nitrous oxide, carbon monoxide and carbon dioxide are vented.

977 pounds per hour of the crude nitrated paraffin 1 product comprising weight per cent n-paraffin, 14.7 weight per cent nitroparaffin and 4.4 weight per cent by-products including oxidized paraffin and polyfunctionals of which 0.6 weight per cent are ketones, 1.2 weight per cent are nitrites and 0.5 weight per cent are nitrates are continuously caustic washed with about 70 pounds per hour of 10 per cent aqueous sodium hydroxide in a line mixer at 200F. and 50p.s.i.g. The resulting aqueous layer is separated in a settler and removed. The organic layer is washed at F. and 50 p.s.i.g. with 27 pounds per hour of water in a conventional countercurrent extraction tower. The washed nitrated product contains 129 pounds per hour of nitrated paraffin and 833 pounds per hour of n-paraffin and other materials that include 0.43 weight per cent ketones, 0.95 weight per cent nitrites and 0.41 weight per cent nitrates.

The crude nitrated paraffin composition is intro duced at an inlet temperature of 200F. to a hydrogenation reactor containing a hydrogenation catalyst composed of one weight per cent palladium on carbon at a liquid hourly space velocity of 2.0 volumes ofliquid per volume of catalyst per hour. Hydrogenation is conducted under a hydrogen pressure of 560 p.s.i.g. and up to a maximum conversion temperature of 410F. Following hydrogenation; substantially all of the nitroparaffin is reduced. to amine. Hydrogen, ammonia and some water are removed as gases and remaining water and ammonia are decanted from the recovered crude hydrogenation product at 110F.

950 pounds per hour of crude hydrogenation product comprising 834 pounds per hour of n-paraffins and miscellaneous by-products including 0.49 weight per cent amines (secondary) and 0.52 weight per cent ketones, 100 pounds per hour of secondary alkyl primary amine, about 1 pound per hour of unconverted nitroparaffins and 15 pounds per hour of water and ammonia are contacted and saturated with 87 pounds per hour of carbon dioxide at 300 p.s.i.g. and 110F. thereby forming an amine-carbon dioxide complex. The carbon dioxide saturated-crude hydrogenation product is countercurrently contacted in a tower with 1,500 pounds per hour of a solvent mixture comprising 40 per cent methanol and 60 per cent water, the solvent mixture having been previously saturated with 50 pounds per hour of carbon dioxide at 300 p.s.i.g. and 110F. Upon contacting of the carbon dioxide saturated crude hydrogenation product with the solvent mixture, the primary amine complex transfers from the predominantly paraffin stream to the solvent stream.

The amine depleted paraffin stream is subsequently reduced to atmospheric pressure in a flash drum whereupon carbon dioxide therein is removed overhead. The amine-enriched solvent stream is heated to a temperature of 150F. and introduced to a flash tower maintained at atmospheric pressure where carbon dioxide, along with some methanol and water, is removed overhead. The amine-rich liquid from the flash tower is passed through a fractionator where methanol, residual carbon dioxide and some water are removed overhead. The bottom stream containing water and crude amines separates as two phases, namely a water phase containing some methanol and amines, and a crude amine phase containing some water.

.110 pounds per hour of the crude amine phase are heated to 248F. and flashed at 160 mm. Hg thereby removing as overhead substantially all of the residual methanol and water, along with some organic materials. After condensation, the organic matter in the overhead is separated from the aqueous layer and combined with the flashed amine phase. The flashed crude amine phase is thereafter vacuum-distilled at 20 mm. Hg and 200F. to remove overhead residual methanol, water, paraffinic hydrocarbons and lighter than C amines. Finally, the amine phase is vacuum distilled at 10 mm. Hg and 300F. to produce 100 pounds per hour of finished amine containing 98.5 weight per cent secondary alkyl primary amine.

The amber colored amine-depleted paraffln stream from the rafflnate flash drum is combined with the predominantly paraffinic waste streams derived from vacuum distilling the crude amines to form a recycle stream comprising about 98 weight per cent n-paraffin, 0.15 weight per cent nitroparaffins and about 1.85 weight per cent by-products. The mixed recycle stream is introduced into an initial hydrogenation zone at the rate of -840 pounds per hour and hydrogenated at 400F. with 17 pounds per hour of hydrogen at 500 p.s.i.g. at a liquid hourly space velocity of 3.0 in the presence of a nickel-molybdenum on alumina catalyst. The product of the initial hydrogenation zone is introduced into a subsequent hydrogenation zone at the rate of 840 pounds per hour and hydrogenated at 660F. with 16 pounds per hour of hydrogen at 500 p.s.i.g. at a liquid hourly space velocity of 1.5 in the presence of a nickel-molybdenum on alumina catalyst. After separating hydrogen, ammonia and water, the hydrogenated water-white product is essentially free of nitrated and oxygenated by-products, contains 3 ppm of nitrogen, possesses a Bromine Index of 41 and is recycled for introduction to the nitration reactor. The system for producing the amines continues to operate for long periods of time without interruption.

EXAMPLE [I An amine-depleted C to C paraffin stream composed of about 3 weight per cent by-products including nitroparaffins, ketones, secondary amines, alcohols, nitrates, nitrites and polyfunctional derivatives of the nparaffln similar to Example I was introduced into a hydrogenation reactor containing a nickel on kieselguhr hydrogenation catalyst at the rate of 3.3 pounds per hour and hydrogenated at 610 to 615F. with 0.03 pounds per hour of hydrogen at about 600 p.s.i.g. Sampling of the off-gas shows it to contain 7 per cent methane thereby demonstrating that substantial hydrocracking has occurred.

EXAMPLE [II An amine-depleted C to C paraffin stream composed of about 2 weight per cent by-products including nitroparaffins, ketones, secondary amines, alcohols, nitrates, nitrites and polyfunctional derivataives of the n-paraffin similar to Example I was preheated to an average temperature of 635F. under a hydrogenation pressure of 550 p.s.i.g. through a bed of porcelain saddles and introduced to a hydrogenation reactor. After hours of processing, the pressure drop across the preheater section rose rapidly to the order of 50 p.s.i.g. Upon examination of the preheater bed it was found that the saddles were blackened and fused together thereby demonstrating the thermal instability of the mixture.

EXAMPLE IV An amine-depleted n-paraffin stream containing 1.4 weight per cent nitroparaffin and 0.5 weight per cent of carbonyl compounds was passed over a bed of porcelain saddles at a liquid hourly space velocity of 0.6 together with hydrogen introduced at the rate of 2,200 SCF hydrogen per barrel of liquid feed and at temperatures of 450 and 550F. for periods of 8 hours. At 450F., the product contains about 0.4 per cent nitroparaffin and at 550F. no nitroparaffin. No amines are formed and the carbonyl concentrations are not decreased at either 450 or 550F. While the porcelain saddles are blackened in 8 hours at 450F., a thick gummy black residue is formed at 550F.

These experiments indicate that the nitroparaffin is unstableat 450F. and above although no hydrogenation takes place in the absence of a hydrogenation catalyst. Continued operation at 550F. will ultimately lead to the formation of a plug thereby stopping the flow of feed.

EXAMPLE v A feedstock comprising 0.7 weight per cent amine bottoms, 0.7 weight per cent of oxygenated paraffins sprung from the caustic extract stream and 98.6 weight per cent of amine-depleted paraffin, the feedstock having a Bromine Index of 108, a Total Base Number of 0.97 and Total Nitrogen of 580 p.p.m., is hydrogenated in two stages at 500 p.s.i.g. and with a hydrogen flow of 3 SCF per pound of charge. The catalyst used in each stage is nickel-molybdenum on alumina. The initial stage reactor operates at 400F. and 3.0 weight hourly space velocity and the subsequent stage reactor is operated at 700F. and 1.5 W.I-I.S.V. The product formed after initial and subsequent hydrogenation has a Bro mine Index of 262, a Total Base Number of 0.03 and Total Nitrogen of 2 p.p.m. By additionally hydrogenating the product at 620F. at 3.0 W.H.S.V., 500 p.s.i.g. and 3 SCF of hydrogen, the Bromine Index is reduced to below 50 and the color of the product is water-white.

We claim:

1. In a process for producing secondary alkyl primary amines from n-paraffins having from 6 to 30 carbon atoms wherein a portion of said n-paraffin is nitrated to form a nitroparaffin along with nitrated and oxygenated by-products, where said nitroparaffin is substantially hydrogenated to said amine and where said amine is separated and recovered from a mixture of unreacted paraffin, unconverted nitroparaffin and by-products, the improvement which comprises:

a. hydrogenating said mixture in the presence of a hydrogenation catalyst in a plural stage hydrogenation treatment under a hydrogen pressure of from about 100 to 1500 p.s.i.g. wherein 10 initial stage hydrogenation of said mixture is conducted at a temperature of from about 250 to 500F. and subsequent stage hydrogenation of said mixture is conducted at a temperature of from about 600 to 750F. and

b. recycling said hydrogenated product of (a) for nitration with said n-paraffin.

2. A process according to claim 1 wherein said initial hydrogenation is conducted at. a temperature of from about 350 to 475F.

3. A process according to claim 1 wherein said subsequent hydrognation is conducted at a temperature of from about 650 to 710F.

4. A process according to claim 1 wherein said hydrogenating in step (a) is conducted in said zones at a liquid hourly space velocity of 0.2 to 10.

5. A process according to claim 1 wherein said mixture hydrogenated in (a) is additionally hydrogenated at 450 to 650F. prior to recycling in (b).

6. A process according to claim 1 wherein (a) is conducted in the presence of a Group VIII metal on alumina catalyst.

7. A process according to claim 6 wherein said catalyst is nickel-molybdenum on alumina.

8. A process according to claim 6 wherein said catalyst is cobalt-molybdenum on alumina.

9. A process according to claim 1 wherein said nitroparaffin and by-products are aqueous caustic washed, recovering an aqueous solution, separating organic materials from said aqueous solution and introducing said organic materials to said mixture in (a).

10. A process according to claim 1 wherein said separated amine is distilled to separate a by-product stream and introducing said by-product stream to the mixture in (a).

Claims (10)

1. IN A PROCESS FOR PRODUCING SECONDARY ALKYL PRIMARY AMINES FROM N-PARAFFINS HAVING FROM 6 TO 30 CARBON ATOMS WHEREIN A PORTION OF SAID N-PARAFFIN IS NITRATED TO FORM A NITROPARAFFIN ALONG WITH NITRATED AND OXYGENATED BY-PRODUCTS, WHERE SAID NITROPARAFFIN IS SUBSTANTIALLY HYDROGENATED TO SAID AMINE AND WHERE SAID AMINE IS SEPARATED AND RECOVERED FROM A MIXTURE OF UNREACTED PARAFFIN, UNCOVERED NITROPARAFFIN AND BY-PRODUCTS, THE IMPROVEMENT WHICH COMPRISES: A HYDROGENATING SAID MIXTURE IN THE PRESENCE OF A HYDROGENATION CATALYST IN A PLURAL STAGE HYDROGENATION TREATMENT UNDER A HYDROGEN PRESSURE OF FROM ABOUT 100 TO 1500 P.S.I.G. WHEREIN INITIAL STAGE HYDROGENATION OF SAID MIXTURE IS CONDUCTED AT A TEMPERATURE OF FROM ABOUT 250* TO 500*F AND SUBSEQUENT STAGE HYDROGENATION OF SAID MIXTURE OS CONDUCTED AT A TEMPERATURE OF FROM 600* TO 750*F. AND B. RECYCLING SAID HYDROGENATED PRODUCT OF (A) FOR NITRATION WITH SAID NIPARAFFIN.

2. A process according to claim 1 wherein said initial hydrogenation is conducted at a temperature of from about 350* to 475*F.

3. A process according to claim 1 wherein said subsequent hydrognation is conducted at a temperature of from about 650* to 710*F.

4. A process according to claim 1 wherein said hydrogenating in step (a) is conducted in said zones at a liquid hourly space velocity of 0.2 to 10.

5. A process according to claim 1 wherein said mixture hydrogenated in (a) is additionally hydrogenated at 450* to 650*F. prior to recycling in (b).

6. A process according to claim 1 wherein (a) is conducted in the presence of a Group VIII metal on alumina catalyst.

7. A process according to claim 6 wherein said catalyst is nickel-molybdenum on alumina.

8. A process according to claim 6 wherein said catalyst is cobalt-molybdenum on alumina.

9. A process according to claim 1 wherein said nitroparaffin and by-products are aqueous caustic washed, recovering an aqueous solution, separating organic materials from said aqueous solution and introducing said organic materials to said mixture in (a).

10. A process according to claim 1 wherein said separated amine is distilled to separate a by-product stream and introducing said by-product stream to the mixture in (a).