US3111538A

US3111538A - Continuous manufacture of explosive liquid nitric acid esters

Info

Publication number: US3111538A
Application number: US638780A
Authority: US
Inventors: Jr Frederic S Stow
Original assignee: Hercules Powder Co
Current assignee: Hercules Powder Co
Priority date: 1957-02-07
Filing date: 1957-02-07
Publication date: 1963-11-19
Anticipated expiration: 1980-11-19

Description

Nov. 19, 1963 F. s. sTow, JR 3,111,538

CONTINUOUS MANUFACTURE OF EXPLOSIVE LIQUID NITRIC ACID ESTERS Filed Feb. 7, 1957 i FRESH FORTIFYING ACID 34 LIQUID 2| POLYHYDRIC NITRATING /l6 ALCOHOL ACID REACTOR 7 33 SPENT ACID STORAGE 32 FRESH 35 37 WASH uoum 9 ACID WASTE L 36 RECOVERY WASH LIQUID STAGE 1 46 a LQ JL I FFRESH WASH l u um 57 2/ Q STAGE 11 J I 3"" I as FRESH 9 k as I WASH LIQUID 66 e7 e4 68 l FIG I STAGEIII PURIFIED 7| EXPLOSIVE l 38 ESTER FREDERIC S. STOW,JR. INVENTOR.

BY 52... 9? 023m...

AGENT United States Patent 3,111,538 CDNTKNUGUS MANUFACTURE 0F EXPLOSlWE LlQUlD NHTRI AQID EgTERS Frederic S. Stow, 31"., Wiimingtou, Deh, assignor to Hercules Powder Company, Wilmington, Del, a corporation of Delaware Filed Feb. 7, 1%7, Ser. No. 638,780 11 (Ilaims. (Cl. 260467) The present invention relates to the continuous manufacture of explosive liquid nitric acid esters of rapidly esterifiable liquid polyhydric alcohols, and is an improvement over copending application Serial No. 612,832, filed September 28, 1956 by Charles D. McKinney, now US. Patent 2,951,866. More particularly, the present invention relates to a novel cyclic process for the continuous manufacture of nitroglycerin, nitroglycols, and mixtures thereof.

Heretofore, various methods for the continuous manufacture of explosive liquid nitric acid esters have been proposed because such methods inherently should be less hazardous and more economical than the well-established and conventional batch process for manufacturing these explosive compounds. However, previously proposed continuous nitration processes have always involved various mechanical mixing devices in the nitrating zo e to effect intimate mixing of the nitrating acid with the liquid alcohol. Such mechanical devices in the nitrating zone always involve the element of hazard when dealing with highly sensitive materials such as nitroglycerin and the like. Moreover, extensive circulation, recirculation, and a relatively long residence time of the reaction mixture in the nitrating zone are characteristics of a majority of the previously proposed methods, and such features are inherently undesirable because they favor side reactions. Furthermore, prior art methods for purification and stabilization of explosive liquid nitric acid esters have been slow and tedious and inherently hazardous, since such methods involve treatment of relatively large amounts of such explosive esters in concentrated form while such esters are still in an impure unstable state.

It is, therefore, the principal object of the present invention to provide an improved cyclic process for the continuous manufacture of explosive liquid nitric acid esters which overcomes the various undesirable features of prior art methods.

A further object is provision of a continuous cyclic process which is unique in its simplicity and relative freedom from hazard in comparison to prior art methods.

Another object is provision of a continuous cyclic process in which there is a minimum amount of explosive liquid nitric acid ester in concentrated form at any point in the process at any time.

Still other objects of this invention include:

Provision of :a continuous cyclic process in which there is a minimum of side reaction encountered, and an exceptionally pure product is obtained;

Provision of a continuous cyclic process in which positive control of the process is easily and readily accomplished;

Provision of a continuous cyclic process which requires only simple, relatively inexpensive equipment and buildings in comparison to prior art methods.

Other objects will become apparent from the following description of the invention, the novel features and combinations being set forth in the appended claims.

Generally described, the continuous manufacture of explosive liquid nitric acid esters of polyhydric alcohols in accordance with this invention comprises continuously feeding a stream of polyhydric alcohol through a tubular path to a tubular reaction zone, simultaneously and continuously feeding a stream of nitrating acid through 3,l 1 1,538 Patented Nov. 19, 1963 a second tubular path to said tubular reaction zone, im-- pinging the separate streams of polyhydric alcohol and nitrating acid upon each other at sufficient ilow rates to form a turbulent reaction mixture stream in the tubular reaction zone, continuously advancing the resultant reaction mixture stream through the tubular reaction zone at a flow rate corresponding to a Reynolds number of at least about 1000 until substantially all of the polyhydric alcohol has reacted with the nitrating acid to form explosive liquid nitric acid ester, continuously discharging the reaction mixture stream into a separating zone and there continuously separating spent nitrating acid from impure explosive liquid nitric acid ester, recovering the separated spent nitrating acid and fortifying part thereof with concentrated nitric acid and concentrated sulfuric acid and recycling the fortified mixture as the nitrating acid for the nitration reaction, purifying the separated impure explosive liquid nitric acid ester by continuously mixing a stream thereof with a stream of aqueous washing liquid to form an intimate dispersion of said ester in said washing liquid and then continuously separating explosive liquid nitnic acid ester from washing liquid and Withdrawing purified explosive liquid nitric acid ester from the process.

In a preferred embodiment of the invention, [the tubular reaction zone is uncooled and the temperature of the reaction mixture in the tubular reaction zone is controlled within safe operating limits by regulating the temperature of the nitrating acid and by regulating the proportions, respectively, of the nitrating acid and of the polyhydric alcohol which are mixed together by impingement to form the reaction mixture. Operating with an uncooled tubular reaction zone promotes a more rapid reaction which is desirable, and in fact is an impontant advantage of the present invention. Moreover, although not necessary in practicing this invention, it has been found desirable to cool the mixture of explosive liquid nitric acid ester and spent nitrating acid upon completion of the nitration reaction and prior to separation, since this promotes a more complete recovery of the product. While cooling can he eifected in a separate vessel following discharge of the reaction mixture from the tubular reaction zone, such cooling is more conveniently and efficiently accomplished in a tubular cooling zone forming an extension of the tubular reaction zone. Preferably, but not necessarily, the reaction mixture stream is advanced through the tubular reaction zone, and the tubular cooling zone when employed, at a flow rate corresponding to a Reynolds number of at least about 2100 and sufficient to maintain turbulent flow in the reaction mixture.

Whereas the preferred practice of this invention employs an uncooled tubular reaction zone, the invention is by no means limited in this respect, for the invention can also be practiced satisfactorily with a tubular reactor, all or part of which is associated with cooling means.

It is an important characteristic of this invention that there are no moving parts, obstructions, or constrictions in the tubular reactor. Turbulent flow, brought about by impinging the two reactant streams upon each other at sufiicient flow rates, is relied upon as the sole means for elfectuating intimate dispersion of the polyhydric alcohol in the nitrating acid, and for maintaining the intimate dispersion in the reaction mixture in the tubular reactor. it is a further characteristic of this invention that the reaction mixture positively and continuously advances through the tubular reactor without recirculation, and residence time of the reaction mixture in the tubular reactor is limited to only a few seconds, suflicient to complete the nitration reaction, and'cool the product if desired, before discharging the reaction mixture stream into the separating zone.

in the preferred practice of this invention, the reaction mixture, upon completion of the nitration reaction and containing explosive liquid nitric acid ester dispersed in spent nitrating acid, is discharged into a centrifugal separating zone in which spent nitrating acid is continuously separated from acid impure explosive liquid nitric acid ester. Centrifugal separation has a distinct advantage over separation by settling in that only a very small amount of explosive ester is present in concentrated form while in an impure unstable state. Also, during purification of the impure ester it is preferred to centrifugally separate explosive liquid nitric acid ester from washing liquid in order to minimize the quantity of explosive ester in concentrated form at any one time or point during purification.

A preferred embodiment of the invention has been chosen for purposes of illustration and description and is shown in the accompanying drawing forming a part of the specification, wherein reference symbols refer to like parts wherever they occur and wherein gauges and other conventional auxiliary equipment have been omitted for the sake of simplicity.

FIG. 1 is a diagrammatic drawing illustrating the features of this invention.

FIG. 2 is a fragmentary, cross-sectional view illustrating one embodiment for the junction of the two tubular reactant feed lines with the tubular reactor of this invention.

FIG. 3 is a diagrammatic, cross-sectional view of one preferred form of injection mixing chamber employed for intimately mixing and dispersing explosive liquid nitric acid ester with aqueous washing liquid during purification.

Referring to the drawing, liquid polyhydric alcohol from supply tank 11 via line 12 is fed through metering pump 13 in predetermined proportions via line 14 to tubular reactor 15. Simultaneously nitrating acid from supply tank 16 via line 17 is fed through pump 18 in predetermined proportions via line 19 to tubular reactor 15. 21 is a refrigerating brine coil in acid supply tank 16 for precooling the nitrating acid. Valve 22 in line 19 is a throttle valve for regulating the flow of nitrating acid when employing a centrifugal pump. Valve 22 be comes unnecessary when a metering pump or similar constant feed means is employed instead of a centrifugal pump.

Valve 23 in line 14 is a quick opening by-pass valve which is normally closed. However, upon shutdown for any reason, this valve can be instantly opened to shut ofi the supply of alcohol to the reaction zone and return the alcohol stream via line 24 to alcohol supply tank 11. Such a quick opening by-pass valve normally is not employed in the nitrating acid line, since nitrating acid is employed to sweep out the tubular reactor upon shutting down for any reason.

It will be seen from the drawing that

feed lines

14 and 19 converge and junction with tubular reactor at one end thereof, and in the embodiment illustrated the two feed lines and the tubular reactor form a simple T-tube section, free of moving parts, obstructions, or constrictions as illustrated in FIG. 2. The separate streams of polyhydric alcohol and precooled nitrating acid thus converge and impinge upon each other to form a turbulent reaction mixture at the point where the two feed lines junction with the tubular reactor.

The turbulent reaction mixture is then advanced through the tubular reactor 15 at a flow rate corresponding to a Reynolds number of at least about 1000, preferably at a flow rate corresponding to a Reynolds number of at least about 2100, suificicnt to maintain turbulent flow in the reaction mixture, and is discharged from tubular reactor 15 at 25 into separating zone 26 Where the explosive liquid nitric acid ester is separated from the spent nitrating acid. 27 is a conventional refrigerated brine bath having inlet 7 and outlet E which is associated dwith at least part of tubular reactor 15 adjacent the discharge end thereof when it is desired to cool the reaction mixture prior to discharge of the reaction mixture to a separating zone.

The reaction mixture upon discharge into separating zone 26 is continuously separated into spent nitrating acid and acid impure explosive liquid nitric acid ester, Spent nitrating acid is recovered and passed via line 28 to spent acid storage tank 29. Part of the spent nitrating acid from storage tank 29 is passed via line 31, pump 32, and line 33 to nitrating acid storage tank 16, where it is fortified with predetermined amounts of fresh concentrated nitric and sulfuric acids introduced via line 34 to reconstitute nitrating acid for the nitration reaction. The fortified mixture is then recycled via line 17, pump 13, and line 1 to tubular reactor as nitrating acid for the nitration reaction.

The remainder of the spent nitrating acid which aecumulates in spent acid storage tank 2% is drawn oil and sent to acid recovery via line 35, pump 36, and line 37.

Acid impure explosive liquid nitric acid ester from separating zone 26 is then subjected to one or more stages of purification as found necessary to obtain a stable product tree of acidity. To accomplish the necessary purification, acid impure explosive liquid nitric acid ester from separating zone 26 flows via line 38 to mixing zone 39 where the stream of the impure ester is mixed with a stream of aqueous Washing liquid introduced to mixing zone 39 via line 21, pump 42, and line 43 to form a fine dispersion of expiosive liquid nitric acid ester in washing liquid. The aqueous dispersion of explosive liquid nitric acid ester then fiows via line 44 to separating Zone 45 where explosive liquid nitric acid ester is separated from washing liquid. Washing liquid from separating zone 45 is discarded via line 46. The above operations of dispersing explosive liquid nitric acid ester in aqueous washing liquid in mixing zone 39 followed by separation therefrom in separating Zone 45 constitutes one stage of purification, and is designated as stage I purification. Additional stages of purification, when necessary, involve the same operations of mixing followed by separation as employed for stage I purification, and are designated as stage II purification and stage III purification.

If the separated explosive liquid nitric acid ester from stage I purification is found by test to be free of acid and of sufficient stability, it is then withdrawn from the process via

lines

47 and 43. When only a single stage of purification is necessary to prepare a stable product free of acidity, washing liquid is supplied to stage '1 via lines 9 and 41, pump 42, and line 4-3 to mixing zone 39. However, when additional purification is found necessary, washing liquid for stage I purification is provided by recycling separated washing liquid from stage II purification via

lines

51 and 41, pump 42, and line 43 to mixing zone 39. Explosive liquid nitric acid ester which is not sufficiently purified and stabilized by stage I purification is subjected to additional purification in stage II. Partially purified explosive liquid nitric acid ester from separating zone 45 fiows via lines 4-7 and 49 to mixing zone 52 where the stream of the partially purified ester is mixed with a stream of aqueous washing liquid introduced to mixing zone 52 via line 53, pump 54, and line 55 to again form a fine dispersion of explosive liquid nitric acid ester in washing liquid. The aqueous dispersion of explosive liquid nitric acid ester then flows via line 56 to separating zone 57 where explosive liquid nitric acid ester is separated from washing liquid. Washing liquid from separating zone 57 is then recirculated via

lines

51 and 41, pump 42, and line 43 to mixing zone 39 where it is employed as washing liquid for stage I purification. If the separated explosive liquid nitric acid ester from stage II purification is found by test to be free of acid and of sufiicient stability, it is then withdrawn from the process via

lines

58 and 59. When two stages of punification are suificient to prepare a stable product free of acidity, washing liquid is supplied to stage II purification via

lines

61 and 53, pump 54, and line 55 to mixing zone 52. However, when additional purification is found necessary, washing liquid for stage II purification is provided by recycling separated washing liquid from stage III purification vi-a

lines

62 and 53, pump 54, and line 55 to mixing zone 52.

Explosive liquid nitric acid ester which is not sufficiently purified and stabilized by two stages of purification is subjected to additional purification in stage Iii. Partially purified explosive liquid nitric acid ester from separating zone 57 flows via

lines

58 and 63 to mixing zone 64 where the stream of partially purified ester is mixed with a stream of aqueous washing liquid introduced to mixing zone 64 via line 6-5, pump 66, and line 67 to again form a fine dispersion of explosive liquid nitric acid ester in washing liquid. The aqueous dispersion of explosive liquid nitric acid ester then flows via line 68 to separating zone 69 where purified explosive liquid nitric acid ester is separated from washing liquid and is withdrawn from the process via line 7-1. Washing liquid from separating zone 69 is then recirculated via

lines

62 and 53, pump 54, and line 55 to mixing zone 52 Where it is employed for stage II purification.

In the preferred practice of this invention, it has been found desirable to precool the nitrating acid, since this practice affords a practical means for controlling and regulating the nitration reaction. Although it is convenient to cool the nitrating acid in supply tank 16 as i1- lustrated, the invention is not limited in this respect. Accordingly, therefore, cooling means can be employed to cool the nitrating acid at any desirable and convenient point along the path of flow of nitrating acid in the system before the nitrating acid reaches the reaction zone. For example, if desired, the acid can be cooled before it reaches supply tank 16 or between supply tank 16 and tubular nitrator 15. However, the invention is not limited to employment of precooled nitrating acid, and the invention can be practiced quite satisfactorily with uncooled nitrating acid, since other means have been disclosed herein for controlling and regulating the nitration reaction.

In the embodiment illustrated, feed lines 14 and '19 and tubular reactor 15 form a simple T-tube section. Hot ever, the invention is not limited to employment of a T- tube, since the only requirement is that the feed lines converge and junction with the tubular reactor so that the feed streams of polyhydric alcohol and nitrating acid will impinge upon each other. Accordingly, any geometrical configuration for the junction of the feed lines with the tubular reactor which will accomplish the purposes of this invention is within the scope of this invention.

The rates of flow of the reactant streams are regulated so that upon impingement upon each other, they form a turbulent reaction mixture wherein the polyhydric alcohol is intimately dispersed throughout the nitrating acid. No further mixing is required. This is indeed surprising since heretofore it has been considered necessary to provide mechanical stirring devices. The present invention, on the other hand, relies solely on turbulent flow created by impinging the reactant streams upon each other at flow rates sufficient to initiate turbulent flow in the resulting reaction mixture.

Advantages of the present invention in comparison to prior art methods and apparatus employing mechanical stirring devices to disperse the polyhydric alcohol in the nitrating acid reside in more rapid and uniform dispersion, improved control, and greatly improved safety. In comparison to aspirators of the venturi type, one important advantage of the present invention resides in control. An aspirator relies on vacuum to suck or pull the relatively viscous liquid polyhydric alcohol into the jet stream of nitrating acid. Accordingly, variations in temperature of the polyhydric alcohol or variations in the velocity of the jet stream materially aflect flow of the alcohol stream. To overcome such variations, a throttle valve must he employed in the alcohol line to adjust and regulate flow, and requires constant attention and frequent adjustment. On the other hand, alcohol feed from a metering pump in accordance with the preferred practice of this invention does not require constant attention and frequent adjustment. Moreover, since an aspirator requires that friction losses of head between the venturi and the discharge be low, it is necessary to employ short, substantially straight transport lines in the region between the venturi and the discharge for satisfactory operation. Accordingly, transport of the reaction mixture through an integral cooler coil, or any long lines between the venturi and the discharge, would entail sufficient downstream friction losses of head to seriously impair or even prevent satisfactory operation of the aspirator. Furthermore, it has been definitely established that the nitration reaction is only partly completed in the aspirator itself. Accordingly, provision must be made for completing the reaction in an auxiliary vessel under controlled temperature conditions before discharging to a separating zone. The present invention, on the other hand, is not burdened with these shortcomings.

According to the present invention, the turbulent reaction mixture is advanced through the tubular reaction zone at a flow rate corresponding to a Reynolds number of at least about 1000 and preferably at a flow rate corresponding to a Reynolds number of at least about 2100, sufficient to maintain turbulent flow in the reaction mixture. Reynolds numbers, according to Badger and McCabe, Elements of Chemical Engineering, 1936, ed., page 28, are readily calculated from the following engineering formula: Reynolds number= Using metric units,

D=inside diameter of tube in cm.

u=linear velocity of liquid stream in cm./ sec. =density of liquid in g./ ml.

,u=viscosity of liquid in poises At Reynolds number above about 2100, the flow of a liquid in smooth tubes assumes a completely turbulent character. For the purposes of this invention, completely turbulent flow is not necessary, and successful nitrations have been made at Reyonolds numbers of approximately 1000. However, to keep the reaction time to a minimum and the efficiency of the heat exchange at a maximum, it is desirable that the Reynolds number be at least about 2100.

In the embodiment illustrated, part of tubular reactor 15 adjacent the discharge end thereof is associated with a conventional heat exchange means 27. However, it is important to note that the invention is not limited in this respect, since the invention can be practiced quite satisfactorily with a tubular reactor entirely free of cooling means. On the other hand, under certain circumstances, the entire tubular reactor can be surrounded by a brine bath or equivalent heat exchange means, if desired. In a preferred embodiment of the invention, however, part of the tubular reactor adjacent to the converging feed tubes is not cooled, since this promotes a more rapid reaction which is desirable. In this case, precooled nitrating acid is relied upon to absorb the heat of reaction and control the temperature of the reaction mixture Within safe operating limits. In practicing this invention, it has been found that temperatures up to about 70 C. in the reaction mixture during nitration are quite feasible.

However, upon substantial completion of the nitration reaction, it is desirable to cool the reaction mixture contain ing the explosive liquid nitric acid ester product dispersed in spent acid to a temperature below about 50 C. before separating the product from the spent acid. In accordance with one embodiment of this invention, the nitration reaction is carried out in an uncooled tubular reaction zone with temperatures ranging from about 30 7 C. to about 50 C. in the reaction mixture, and upon substantial completion of the nitration reaction, the reaction mixture is then cooled in a tubular cooling zone below about 20 C. before separating the product from the spent acid.

The nitration reaction commences immediately upon mixing of the two reactants and, although not instantaneous as the prior art would lead one to believe, it is nevertheless very rapid under the preferred conditions of the invention, being substantially complete Within a matter of one second or less, and seldom, if ever, longer than about 3 seconds. It will be apparent, therefore, that residence time of the reaction mixture in the tubular reaction zone need be of only very brief duration, but should be still.- cient to accomplish substantial completion of the nitration reaction. The length of the tubular reaction zone for any particular tubular reactor to accomplish the purposes of this invention can be readily ascertained by fixing thermocouples at fixed points along the tubular reactor and noting temperatures. The point of maximum temperature rise corresponds closely with completion of the nitration reaction. Similarly, the length of a tubular cooling zone, when employed, to cool the reaction mixture to any desired tempeature, also can be readily ascertained by thermocouple readings.

The inside diameter of the tubular reactor will be governed largely by the projected production throughput ca pacity desired from the apparatus, keeping in mind the Reynolds number requirements of the invention.

Although metering pumps, such as gear pumps, are preferred for positively feeding and proportioning the two reactant streams to the tubular reactor, the invention is not limited in this respect, since any known means for accomplishing the positive feed and proportioning of liquid feed streams is equivalent for the purposes of this invention, for example, pressure exerted by a constant hydraulic head, or pressure exerted by gas under constant pressure, pressure accumulators, or the like, or any combination of such means.

Although explosive liquid nitric acid ester could be separated from spent nitrating acid by conventional settling methods, such separation cannot achieve the full benefits of the present invention, for settling methods of separation entail accumulation of relatively large amounts of explosive liquid nitric acid ester in concentrated form and in an impure unstable state. Accordingly, in practicing this invention in its preferred embodiment, explosive liquid nitric acid ester is centrifugally separated continuously from spent nitrating acid, and the separated impure ester is flowed through as short a transport line as practical to a mixing zone where the stream of explosive ester is continuously redispersed in a stream of aqueous Washing liquid to purify and stabilize the explosive ester. Preferably, the separated impure ester is gravity-flowed from the centrifugal separator through a relatively short unconstricted tubular path to the mixing zone where it is redispersed in washing liquid.

It will be apparent, of course, that any of the conventional methods known to the art can be employed for washing and stabilizing the acid impure explosive liquid nitric acid ester. However, in order to achieve the maximum benefits of the invention, it is preferred to fiow a stream of the acid impure explosive liquid nitric acid ester from the centrifugal separator in which it is separated from spent nitrating acid through a relatively short length of unconstricted tubing to an injection mixing zone Where the stream of acid impure ester is continuously redispersed in a stream of aqueous washing liquid. Any conventional injector consisting essentially of a main pipe, through which the stream of aqueous washing liquid is propelled, and an auxiliary pipe, jet, nozzle, tube, or orifice, through which the stream of explosive liquid nitric acid ester is injected into the main stream of washing liquid and in which the velocity of flow in the main pipe induces a flow of material in the auxiliary pipe, is suitable for the purposes of this invention. A preferred embodiment of this invention contemplates the use of an eductor-type injection mixing device in which a main jet stream of washing liquid sucks or aspirates the stream of explosive liquid nitric acid ester into the main stream of washing liquid to form an emulsion of such explosive ester in the washing liquid. FIG. 3 illustrates an eductor'type injection mixing device in accordance with the preferred practice of this invention. A flow rate corresponding to a Reynolds number of at least about 2100 is generally preferred in the eductor to assure intirnate dispersion of the explosive ester in the washing liquid. injection mixing zones 3%, 52 and 64 can all embody injection mixing devices in a preferred embodiment of the invention.

To achieve the maximum benefits from the present invention, it is preferred to centrifugal'ly separate explosive liquid nitric acid ester from its emulsion in washing liquid in the one or more stages of purification employed in this invention, for by centrifugal separation the amount of explosive liquid nitric acid ester accumulated in concentrated form at any point in the system is reduced to the absolute minimum, particularly since it is preferred to employ the shortest practical lengths of transport pipes between the separators and the injection mixing zones, during which the explosive liquid nitric acid ester is in concentrated form. Since the explosive ester is in emulsified form in washing liquid during transport from the injection mixing zones to the separating zones, there is relatively no danger of detonation. This is because this invention contemplates the use of at least about 2 parts by weight of washing liquid per part of explosive liquid nitric acid ester, and preferably at least about 3 parts washing liquid per part of explosive ester. At 2 parts washing liquid per part of explosive ester, the emulsions of explosive ester in washing liquid are highly insensitive to shock, and at ratios of 3:1 or more of washing liquid, such emulsions cannot be detonated.

It will be apparent from inspection of the drawing that when more than one stage of purification is employed, the washing procedure in accordance with the preferred practice of this invention is, in effect, a countercurrent washing procedure, since washing liquid from the first stage is discarded and the separated washing liquid from each succeeding stage of purification is recycled to the preceding stage as washing liquid therein. Accordingly in multistage puriiication, according to this invention, fresh washing liquid contacts explosive liquid nitric acid ester which is already in an advanced stage of purification. If desired, of course, the recycled stream of washing liquid can be augmented with fresh washing liquid at convenient points between stages, as for example, from either line 61 or 9, or both. As an alternative to countercurrent washing in stages, fresh washing liquid may be employed for each stage of washing and purification and discarded at the end of the washing stage in which it is employed.

Explosive liquid nitric acid esters in accordance with this invention include all such esters obtainable by substantially complete nitration of liquid polyhydric alcohols, such as, by way of example, glycerin, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1,2- butanediol, l,3-butanediol, 2,3-butanediol, isopropyl ethylene glycol, glycerol ct-chlorohydrin, and the like, to obtain glycerol trinitrate, ethylene glycol dinitrate, diethylene glycol dinitrate, triethylene glycol dinitrate, propylene glycol dinitrate, 1,2-butanediol dinitrate, 1,3-butanediol dinitrate, 2,3-butanediol dinitrate, isopropyl ethylene glycol dinitrate, glycerol rx-chlorohydrin dinitrate, and the like. Mixtures of explosive liquid nitric acid esters obtainable by nitrating mixtures of two or more liquid polyhydric alcohols in any proportion also come within the scope of this invention, as for example, mixtures of nitroglycerin and nitroglycol. Solid polyhydric alcohols, such as nitroisobutylglycerol for example, dissolved in glycerol or glycol, upon nitration in accordance with this invention also form mixtures of explosive liquid nitric acid esters.

Nitrating acid according to this invention contains between about 18% and about 40% nitric acid, between about 45% and about 70% sulfuric acid, and between about 1 1% and about 17% water by weight. Although the process may be initiated with nitrating acid composed entirely of fresh nitric and fresh sulfuric acids, the present invention is directed to a continuous cyclic process in which a predetermined amount of the recovered spent nitrating acid is fortified with a predetermined amount of concentrated nitric acid and concentrated sulfuric acid, and the fortified mixture is recycled as the nitrating acid for the nitration reaction. For economic reasons it is desirable to utilize as much as possible of the recovered spent nitrating acid for fortification and recycle as reconstituted nitrating acid. Accordingly, the fortifying acid should be composed of substantially anhydrous nitric acid, at least about 98.5% nitric acid, and anhydrous sulfuric acid preferably containing some free sulfur trioxide (commonly termed oleum). Typical mixed fortifying acid for the purposes of this invention will contain between about 50% and about 85% nitric acid, between about 15% and about 50% sulfuric acid, and between about and about sulfur trioxide. in general, spent acid in accordance with this invention will contain between about 3% and about 32% nitric acid, bet-ween about 48% and about 77% sulfuric acid, and between and about 2 4% water by weight, and will contain small percentages of explosive liquid nitric acid ester and oxides, usually on the order of about 25 explosive liquid nitric acid ester and from less than 0.01% to about 0.11% oxides. Between about 2 parts and about 8 parts by weight of spent nitrating acid per part of fortifying acid is employed in practicing this invention.

The nitrating acid preferably, but not necessarily, is precooled to a temperature between about -]-5 C. and about -10-C. before being fed to the tubular nitrating zone. Between about 6 parts and about 30 parts by weight of nitrating acid per part of liquid polyhydric alcohol has been employed in the practice of this invention. A preferred range is between about 10 parts and about parts by weight nitrating acid per part of polyhydnic alcohol.

Washing liquid for purifying and stabilizing the explosive liquid nitric acid ester may be water, but preferably is an aqueous solution of a substance having a mild alkaline reaction, such as sodium carbonate, sodium bicarbonate, ammonium carbonate, and the like, the principal function of such mild alkaline substances being to neutralize any acid in the explosive liquid nitric acid ester. The concentration of such acid neutralizers may be as low as 0.5% by weight in the aqueous solution, and can range upward in concentration until saturated solutions thereof are obtained. As noted hereinbefore, at least about 2 parts by weight of aqueous washing liquid per part of explosive liquid nitric acid ester will be employed in washing and stabilizing said ester in accordance with this invention, and preferably at least about 3 parts washing liquid per part of said ester.

The following example sets forth a specific embodiment of the invention. It is to be understood that this example is purely illustrative and not to be construed as a limitation of the invention.

Example In this example the tubular reactor consisted of an uncooled coiled 20-foot length of Mr-inch inside diameter stainless steel tubing joined at one end thereof by means of a /2-111011 inside diameter T-tube section, as illustrated in the drawing, with the nitrating acid and polyhydric alcohol feed lines, each of /2 -inch inside diameter, and at the other end thereof joined to a coiled 50-foot length of /2 -inch inside diameter stainless steelv tubing surrounded by a refrigerating bath. The nitrating acid was chilled in its storage tank by means of a refrigerating brine coil.

In carrying out this example, a mixture of ethylene glycol and 20% glycerin by weight was continuously pumped from a storage tank to the tubular reactor at the rate of 208.8 lb./ hour. Nitrating acid, containing 23.3% nitric acid, 64.3% sulfuric acid, 10.3% water, and 2.1% of a mixture of approximately 80% ethylene glycol dinitrate and 20% glycerol trinitrate, and precooled in its storage tank to 0 C., was contiuously pumped to the tubular reactor at the rate of 3079.6 lb./hour. The feed ratio of precooled nitrating acid to the alcohol mixture was thus 14.7:1. The two feed streams were impinged upon each other in the tubular nitrating zone to form a turbulent reaction mixture having an initial temperature of 6 C., and the turbulent reaction mixture was continuously advanced through the tubular nitrating Zone at the rate of 6.17 ft./sec. Reynolds number was calculated to be 4640. The maximum temperature reached by the reaction mixture in the tubular nitrating zone was 40.7 C. The reaction mixture was then continuously passed through the tubular cooling zone and was continuously discharged from the tubular reactor at the rate of 3288.4 lb./ hour and at a temperature of 17 C. into a centrifugal separator of the type described in application Serial No. 520,267, now Patent No. 2,840,303, filed July 6, 1955 by Joseph Stuart II, spinning at 3000 r.p.m. Spent nitrating acid at the rate of 2751.9 lb./hour, and composed of 9.32% nitric acid, 71.68% sulfuric acid, 15.98% water, and 3.02% of a mixture of approximately 80% ethylene glycol dinitrate and 20% glycerol trinitrate, was recovered from the centrifugal separator and was stored in a stainless steel storage tank. Spent nitrating acid from the spent acid storage tank was pumped at the rate of 2111.1 lb./hour to the nitrating acid storage tank where it was mixed with fresh fortifying acid composed of 53.69% nitric acid, 37.60% sulfuric acid, and 8.71% sulfuric trioxide at the rate of 968.5 lb./hour, and the fortified mixture was recycled as nitrating acid for the nitration reaction. Spent nitrating acid from the spent acid storage tank at the rate of 640.8 lb./hour was sent to acid recovery.

An acid impure mixture of explosive liquid nitric acid esters composed of approximately 80% ethylene glycol dinitrate and 20% glycerol trinitrate by weight was drawn from the centrifugal separator at the rate of 536.5% lb./ hour, of which 493.4 lb./ hour was the mixed explosive liquid nitric acid esters and the balance consisted substantially of nitric acid. This acid impure mixture of explosive liquid nitric acid esters was then purified and stabilized in three stages countercurrently, employing 6.1% solution of sodium carbonate in water as the washing liquid in the following manner.

Fresh washing liquid entered the stagewise purification in stage HI where it was pumped at the rate of 1210 lb./hour through an eductor to aspirate a gravity-flow stream of partially purified mixed explosive liquid nitric acid esters from stage II purification into the main jet stream of washing liquid, thereby emulsifying the partially purified ester in the fresh washing liquid. The aqueous emulsion thus formed was delivered to the bowl of a centrifuge of the type employed for separating acid impure mixed explosive liquid nitric acid esters from spent nitrating mixture, from which centrifuge 489.8 lb./hour of purified stabilized mixed explosive liquid nitric acid esters was drawn off by gravity-flow and was collected in a storage tank. Separated wash liquid from the centrifuge of stage III purification was recycled to stage II purification where it was pumped through an eductor to aspirate a gravity-flow stream of partially purified mixed explosive liquid nitric acid esters from stage I purification into the main jet stream of washing liquid, thereby emulsifying the partially purified ester from stage I purification in the recycle washing liquid from stage III purification. The aqueous emulsion thus formed was delivered to the bowl of a centrifuge of the type employed in stage Ill, from which partially purified mixed explosive liquid nitric acid esters were drawn oif and delivered by gravity-flow 1 1 to stage III purification. Separated wash liquid from the centrifuge of stage II purification was recycled to stage I purification where it was pumped through an eductor to aspirate a gravity-flow stream at the rate of 53 6.5 lb./ hour of acid impure mixed explosive liquid nitric acid esters. separated from spent nitrating acid, into the main jet stream of washing liquid, thereby emulsifying the acid impure esters, separated from spent nitrating acid, in the recycle washing liquid from stage H purification. The aqueous emulsion thus formed was delivered to the bowl of a centrifuge of the type employed in stages 11 and III, from which partially purified mixed explosive liquid nitric acid esters were drawn off and delivered by gravit flow to stage II purification. Separated wash liquid from the centrifuge of stage I purification was discarded at the rate of 1256.7 lb./hour. 3.6 lb./hour of mixed explosive liquid nitric acid esters was lost during the three-stage purification through solution in the soda water wash. The recovered stabilized purified mixed explosive liquid nitric acid esters contained 18.42% nitrogen by weight. Theoretical nitrogen content is 18.44% for a product consisting of 80% ethylene glycol dinitrate and glycerol trinitrate.

It is evident from the foregoing description that this invention provides an eminently satisfactory method for the continuous production of explosive liquid nitric acid esters, having distinct advantages over prior art methods for nitration of liquid polyhydric alcohols. The principal advantages of the invention reside in the attainment of the objectives as set forth hereinbefore.

What I claim and desire to protect by Letters Patent is:

1. A continuous cyclic process for the production of explosive liquid nitric acid esters of polyhydric alcohols which comprises continuously force feeding a stream of liquid, saturated aliphatic polyhydric alcohol through a tubular path to an uncooled elongated tubular liquid phase reaction zone which is free of obstructions and constrictions, simultaneously and continuously force feeding a stream of precooled nitrating acid through a second tubular path to said uncooled elongated tubular liquid phase reaction zone, said nitrating acid containing between about 18% and about 40% nitric acid, between about 45% and about 70% sulfuric acid and between about 11% and about 17% water by weight, the ratio of said nitrating acid to said polyhydric alcohol being between about 6 parts and about parts per part of polyhydric alcohol by weight, bringing the separate force-fed streams of polyhydric alcohol and nitrating acid together so that said streams impinge upon each other from directly opposing directions at sufiicient flow rates to form a turbulent liquid reaction mixture stream in the uncooled elongated tubular liquid phase reaction zone, the impingement of said force-fed streams upon each other from directly opposing directions being the sole means for mixing the polyhydric alcohol with the nitrating acid, continuously advancing the resultant liquid reaction mixture stream through the uncooled elongated tubular liquid phase reaction zone at a flow rate corresponding to a Reynolds number of at least about 1,000 to react substantially all of the polyhydric alcohol with the nitrating acid to form explosive liquid nitric acid ester, continuously passing the liquid reaction mixture stream from the uncooled elongated tubular liquid phase reaction zone into an elongated tubular cooling zone and advancing said reaction mixture stream through said cooling zone at a flow rate corresponding to a Reynolds number of at least about 1,000 to cool said reaction mixture stream, continuously discharging the cooled reaction mixture stream from the elongated tubular cooling zone into a separating zone and there continuously separating spent nitrating acid from acid impure explosive liquid nitric acid ester, recovering the separated spent nitrating acid, fortifying part of the recovered spent nitrating acid with concentrated nitric acid and concentrated sulfuric acid and recycling the resulting fortified acid as the nitrating acid for the nitration 12 reaction, purifying the separated acid impure explosive nitric acid ester by continuously mixing a stream thereof with a stream of aqueous washing liquid and then continuously separating explosive liquid nitric acid ester from washing liquid, and withdrawing purified explosive llqllid nitric acid ester from the process.

2. A continuous cyclic process for the production of explosive liquid nitric acid esters of polyhydric alcohols which comprises continuously force feeding a stream of liquid, saturated aliphatic polyhydric alcohol through a tubular path to an uncooled elongated tubular liquid phase reaction zone which is free of obstructions and constrictions, simultaneously and continuously force feeding a stream of precooled nitrating acid through a second tubular path to said uncooled elongated tubular liquid phase reaction zone, said nitrating acid containing between about 18% and about nitric acid, between about and about sulfuric acid and between about 11% and about 17% water by weight, the ratio of said nitrating acid to said polyhydric alcohol being between about 6 parts and about 30 parts per part of polyhydric alcohol by weight, bringing the separate force-fed streams of polyhydric alcohol and nitrating acid together so that said streams impinge upon each other from directly opposing directions at sutficient flow rates to form a turbulent liquid reaction mixture stream in the uncooled elongated tubular liquid phase reaction zone, the impingement of said force-fed streams upon each other from directly opposing directions being the sole means of mixing the polyhydric alcohol with the nitrating acid, continuously advancing the resultant liquid reaction mixture stream through the uncooled elongated tubular liquid phase reaction zone at a flow rate corresponding to a Reynolds number of at least about 1,000 to react substantially all of the polyhydric alcohol with the nitrating acid to form explosive liquid nitric acid ester, continuously passing the liquid reaction mixture stream from the uncooled elongated tubular liquid phase reaction zone into an elongated tubular cooling zone and advancing said reaction mixture stream through said cooling zone at a flow rate corresponding to a Reynolds number of at least about 1,000 to cool said reaction mixture stream, continuously discharging the cooled reaction mixture stream from the elongated tubular cooling zone into a separating zone and there continuously separating spent nitrating acid from acid impure explosive liquid nitric acid ester, recovering the separated spent nitrating acid, fortifying part of the recovered spent nitrating acid with concentrated nitric acid and concentrated sulfuric acid and recycling the resulting fortified acid as the nitrating acid for the nitration reaction, purifying the separated acid impure explosive liquid nitric acid ester in stages, in each stage of purification continuously mixing a stream of explosive liquid nitric acid ester with a stream of aqueous washing liquid and then separating said explosive liquid nitric acid ester from said washing liquid, discarding the washing liquid separated in the first stage of purification, and recycling the washing liquid separated in each succeeding stage of purification to the preceding stage of purification as the washing liquid therein and witdrawing purified explosive liquid nitric acid ester from the process.

3. The process in accordance with claim 1 in which the reaction mixture stream is advanced through the tubular reaction zone at a fiow rate corresponding to 21 Reynolds number of at least about 2100, sufiicient to maintain turbulent flow in said reaction mixture.

4. The process in accordance with claim 1 in which the polyhydric alcohol is glycerin.

5. The process in accordance with claim 1 in which the polyhydric alcohol is ethylene glycol.

6. The process in accordance with claim 1 in which the polyhydric alcohol is a mixture of glycerin and ethylene glycol.

7. The process in accordance with claim 1 in which the reaction mixture is discharged into a centrifugal $631311 rating zone in which spent nitrating acid is continuously separated from acid impure explosive liquid nitric acid ester.

8. The process in accordance with claim 1 in which the separated acid impure explosive liquid nitric acid ester is purified in stages, in each stage continuously mixing a stream of an explosive liquid nitric acid ester with a stream of aqueous washing liquid and then separating said explosive liquid nitric acid ester from said Washing liquid, and in which said explosive liquid nitric acid ester entering each succeeding stage is more pure than said ester entering the preceding stage.

9. The process in accordance with claim 8 in which a gravity-flow stream of explosive liquid nitric acid ester is continuously injection mixed with a stream of washing liquid in each stage of purification.

10. The process in accordance with claim 2 in which the separated acid impure explosive liquid nitric acid ester is purified in each stage by continuously aspirating a stream thereof into a main stream of aqueous washing liquid, and then centrifugally separating explosive liquid References Cited in the file of this patent UNITED STATES PATENTS 449,687 Maxim Apr. 7, 1891 1,705,699 Aaronson Mar. 19, 1929 2,737,522 Nilsson Mar. 6, 1956 OTHER REFERENCES Chemical Engineers Handbook 3rd ed. (1950), p. 1203, McGraw-Hill Book Co., NY.

Claims

1. A CONTINUOUS CYCLIC PROCESS FOR THE PRODUCTION OF EXPLOSIVE LIQUID NITRIC ACID ESTERS OF POLYHYDRIC ALCOHOLS WHICH COMPRISES COTINUOUSLY FORCE FEEDING A STREAM OF LIQUID, SATURATED ALIPHATIC POLYHYDRIC ALCOHOL THROUGH A TUBULAR PATH TO AN UNCOOLED ELONGATED TUBULAR LIQUID PHASE REACTION ZONE WHICH IS FREE OF OBSTRUCTIONS AND CONSTRICTIONS, SIMULTANEOUSLY AND CONTINUOUSLY FORCE FEEDING A STREAM OF PRECOOLED NITRATING ACID THROUGH A SECOND TUBULAR PATH TO SAID UNCOOLED ELONGATED TUBULAR LIQUID PHASE REACTION ZONE, SAID NITRATING ACID CONTAIINING BETWEEN ABOUT 18% AND ABOUT 40% NITRIC ACID, BETWEEN ABOUT 45% AND ABOUT 70% SULFURIC ACID AND BETWEEN ABOUT 11% AND ABOUT 17% WATER BY WEIGHT, THE RATIO OF SAID NITRATING ACID TO SAID POLYHYDRIC ALCOHOL BEING BETWEEN ABOUT 6 PARTS AND ABOUT 30 PARTS PER PART OF POLYHYDRIC ALCOHOL BY WEIGHT, BRINGING THE SEPARATE FORCE-FED STREAMS OF POLYHYDRIC ALCOHOL AND NITRATING ACID TOGETHER SO THAT SAID STREAMS IMPINGE UPON EACH OTHER FROM DIRECTLY OPPOSING DIRECTIONS AT SUFFICIENT FLOW RATES TO FORM A TURBULENT LIQUID REACTION MIXTURE STREAM IN THE UNCOOLED ELONGATED TUBULAR LIQUID PHASE REACTION ZONE, THE IMPINGEMENT OF SAID FORCE-FED STREAMS UPON EACH OTHER FROM DIRECTLY OPPOSING DIRECTIONS BEING THE SOLE MEANS FOR MIXING THE POLYHYDRIC ALCOHOL WITH THE NITRATING ACID, CONTINUOUSLY ADVANCING THE RESULTANT LIQUID REACTION MIXTURE STREAM THROUGH THE UNCOOLED ELONGATED TUBULAR LIQUID PHASE REACTION ZONE AT A FLOW RATE CORRESPONDING TO A REYNOLDS NUMBER OF AT LEAST ABOUT 1000 TO REACT SUBSTANTIALLY ALL OF THE POLYHYDRIC ALCOHOL WITH THE NITRATING ACID TO FORM EXPLOSIVE LIQUID NITRIC ACID ESTER, CONTINUOUSLY PASSING THE LIQUID REACTION MIXTURE STREAM FROM THE UNCOOLED ELONGATED TUBULAR LIQUID PHASE REACTION ZONE INTO AN ELONGATED TUBULAR COOLING ZONE AND ADVANCING SAID REACTION MIXTURE STREAM THROUGH SAID COOLING ZONE AT A FLOW RATE CORRESPONDING TO A REYNOLDS NUMBER OF AT LEAST ABOUT 1000 TO COOL SAID REACTION MIXTURE STREAM, CONTIUNUOUSLY DISCHARGING THE COOLED REACTION MIXTURE STREAM FROM THE ELONGATED TUBULAR COOLING ZONE INTO A SEPARATING ZONE AND THERE CONTINUOUSLY SEPARATING SPENT NITRATING ACID FROM ACID IMPURE EXPLOSIVE LIQUID NITRIC ACID ESTER, RECOVERING THE SEPARATED SPENT NITRATING ACID, FORTIFYING PART OF THE RECOVERED SPENT NITRATING ACID WITH CONCENTRATED NITRIC ACID AND CONCENTRATED SULFURIC ACID AND RECYCLING THE RESULTING FORTIFIED ACID AS THE NITRATING ACID FOR THE NITRATION REACTION, PURIFYING THE SEPARATED ACID IMPURE EXPLOSIVE NITRIC ACID ESTER BY CONTINUOUSLY MIXING A STREAM THEREOF WITH A STREAM OF AQUEOUS WASHING LIQUID AND THEN CONTINUOUSLY SEPARATING EXPLOSIVE LIQUID NITRIC ACID ESTER FROM WASHING LIQUID, AND WITHDRAWING PURIFIED EXPLOSIVE LIQUID NITRIC ACID ESTER FROM THE PROCESS.