METHOD OF WORKING UP MIXED EXPLOSIVES

Abstract: The present invention relates to a method of working up and recovering returned explosives which are principally of the military type and which contain both fusible and non-fusible crystalline substances. In accordance with the invention, the returned explosive is treated in a multi-stage process which includes a first leaching stage for removing the non-crystalline, preferably fusible, component of the explosive in the form of trotyl, wax or plastic. The substance used in the leaching stage, principally toluene, does not affect the crystalline components of the explosive. The collected leaching liquid is separated off and the toluene, together with its dissolved content of trotyl or wax, is conveyed onwards for working up. The toluene which is recovered during the working up is returned to the process while the remaining filtrate from the filtration stage is treated with solvent which dissolves the crystalline high-energy explosives octogen and hexogen, respectively, which are relevant in this connection, which explosives, in a subsequent process stage, are precipitated out in the form of new crystals which, after a possible recrystallization, are ready to be reused. The solvent which is used in this connection is returned to the process.

Description: METHOD OF WORKING UP MIXED EXPLOSIVES The present invention relates to a complete process for working up those returned and residual explosives which contain both fusible binders and crys¬ talline high-energy explosives. The object of the invention is to provide a process for working up mixed explosives of the above- mentioned types with the intention of enabling at least the most valuable of the components contained therein, namely the crystalline high-energy explosives octogβn and hexogen, respectively, to be reused. An additional advantage of the novel process is, furthermore, that it is also the octogβn and hexogen, respectively, whose manufacture, in our hands, results in the greatest degree of environmental pollution. Previously, no useful processes have been avail¬ able for working up mixed explosives which are relevant in this present case. As a result, residual and returned quantities of these explosives have regularly been sent for destruction. By contrast, residual and returned quantities of pure trotyl explosives have been reused to a substantial degree. In addition, the novel process enjoys the advan¬ tage that solvents which are used in it are, in their turn, worked up in accordance with constituent processes which are included in the invention, as a result of which the solvents can be circulated continuously in the main process. Both fusible explosive binders such as trotyl and other non-explosive binders of the wax or plastic type can be included in the mixed explosives which are rel¬ evant in connection with the present invention. The crystalline high-energy explosives which are relevant in this context consist, as has already been mentioned, of the nitramines octogen and hexogen, respec¬ tively, which are related to each other and which, as a rule, are used separately, although the hexogen, since it and octogen are prepared by what is in principle the same synthesis, can be present as an impurity in somewhat older octogen batches, in particular. This is, per sβ, a complication when reusing octogen since there are now- adayβ strict standards for the lowest content of hexogen in newly manufactured octogen-containing products. While the novel process does not reduce the quantities of residual product which have to be destroyed to zero, it does represent a clear improvement as com- pared with the previous technology, when everything was sent for destruction. The mixed explosives which will probably in the main be relevant in connection with the novel process are octol and hexotol, i.e. octogen together with trotyl as binder and hexogen together with trotyl as binder, respectively, and also compressed octogen and hexogen products containing wax or plastic as binder. The novel process is defined in the subsequent patent claims and also illustrated in the form of flow diagrams in the attached figures. In addition, the process has, in all its stages, been illustrated by a number of constituent examples. For the rest, we shall, in that which follows, provide a general description of the process in all its different stages. In accordance with the present invention, the first treatment stage (stage 1) involves a leaching of the starting substance, which can be residues from ongoing production or returned products from different types of fallen ammunition. The leaching is carried out using a solvent which is suited to the relevant binder. While the leaching normally takes place at room tempera¬ ture, an elevated temperature can be required, princi¬ pally in connection with compressed products of the abovementioned type. Toluene and xylene, in particular, are suitable for this purpose. However, there are also other solvents which fulfil the main requirements which are relevant in this context, namely exhibiting a βuffi- ciently high degree of solubility for the binders which are present, while exhibiting the lowest possible degree of solubility for nitramines. After having filtered off the solvent with binder dissolved in it, and, where appropriate, having washed the solid residual product, that which now remains is a solid product which consists of the whole of the nitramine content of the original mixed explosive. If the nitramine in question consists of octogen and it is not known how much hexogen this octogen might contain, or if it is already evident from the start that the octogen does not meet current standards, an addi¬ tional leaching stage is then required in order to remove contaminating quantities of hexogen. The effectiveness of this leaching stage is based on the appreciably higher solubility of the hexogen in at least some solvents. In the leaching stage in question, all the hexogen is dissolved, at an elevated temperature, preferably greater than 105°C, in a solvent which is suitable for the purpose, such as gamma-butyrolactone (BLO) or N-methyl-2- pyrrolidone (NMP) . Any toluene and water residues which remain from the preceding leaching stage are also removed in connection with increasing the temperature to the abovementioned higher temperature, which is, in turn, clearly advantageous. While a dissolution temperature of the order of approximately 105°C does not dissolve the octogen completely, the hexogen is completely dissolved at this temperature. Once all the hexogen has been dissolved, the temperature of the mother liquor is lowered to a point at which virtually all the previously dissolved octogen has precipitated out in crystalline form while all the hexogen is still present in solution. A pure crystalline octogen, whose crystal form does not meet current requirements, is obtained as a residue by means of filtering the resulting mother liquor. In order to obtain octogen of the desired particle size, a recrystallization stage is required in which the same solvents are used as in the previously mentioned second leaching stage but in which the precipitation of the crystalline octogen is regulated so that the desired crystal size and form is obtained. For this purpose, the βolubilizing power of the solvent can be altered both by lowering the temperature and adding water. The crystal modification (α- or β- ) which is obtained has been found to depend on which solvent is used in the recrystallization, and solvents which are relevant in this context have been found to yield a 0-octogen which is virtually 100% pure. Exactly as in previous stages, the mother liquor which is obtained at this point is sent for working up so that it can subsequently be returned to the process. The concluding recrystallization stage can be used, directly after the leaching stage, for removing the binder provided it is known either that the octogen which is contained in the residual product and returned product is completely free of hexogen or that the crystalline high-energy product consists solely of hexogen. The process stages which remain to be discussed within the scope of the invention consist of the working up of the different solvents, in which the toluene, or, alternatively, the xylene, from the original leaching stage is worked up by being driven off from the mother liquor obtained in this stage and is then condensed and returned to the process. When the solvent is driven off, the binder precipitates out of the remaining water and can be collected for combustion. The solvents in the form of BLO and NMP from the subsequent treatment stages are freed from remaining nitramineβ by means of adding water to almost 50% by weight, whereupon all the remaining octogen or hexogen, respectively, precipitates out and can be collected, after which the solvent itself is freed from remaining water by distillation. As has previously been mentioned, the invention has been illustrated by the attached method description, which also in¬ cludes 6 pages of flow diagrams which should not require any detailed description. As has also been pointed out previously, the invention is defined in the subsequent patent claims. The flow diagrams will elucidate the following different parts and steps of the invention. Figur 1 Flow diagram for the recovery of explosive. Figur 2 Flow diagram for leaching stage 1. Figur 3 Working up of HMX and BLO/NMP. Figur 4 Flow diagram for recrystallization stage 3. Figur 5 Flow diagram for working up BLO/NMP stage 5:2. Figur 6 Flow diagram for working up BLO/NMP stage 5:2. Description of the method for leachinσ returned explos¬ ive. STAGE 1 LEACHING. Additions: 150 litres of toluene are added to a stirred apparatus and the stirring is started and the speed of revolution is adjusted to approximately 60 revolutions/minute. 75 kg of returned octol are added in a net basket. Leaching: While the leaching can be carried out at room temperature, it can also be carried out at higher temperatures, for example 40°. The leaching time also varies with the size of the added lumps; if, for example, the leaching takes 1 hour at 40°, it takes 2 hours at 20°, and larger lumps take a longer time to dissolve. The leaching can be regarded as being finished when there are no lumps to be seen in the slurry and when the net bas¬ ket does not contain any lumps. Normally, it has been found that the leaching time is approximately 3 hours on a factory scale and at room temperature. Filtration: The filtration takes place in a usual manner with the mixture being tapped off down into a suction filter which is coupled to a vessel for collecting the leaching liquid. The leached octogen is sucked as dry as possible in order to facilitate the subsequent overlaying. The toluene/TNT liquid is sucked into a col¬ lecting tank using a membrane pump. Overlaying: The product cake (<10%) which has been sucked dry is now overlaid with 30 litres of pure toluene in order to remove the last remnants of the trotyl; this is carried out with the membrane pump being switched off so that the liquid has plenty of time to disperse within the cake. After this, as much as possible of the overlying liquid is sucked off into the collecting tank. Washing: 50 litres of cold water are now dispersed over the product cake in the same way as when overlaying and with the membrane pump being switched off. The water is then sucked off to the greatest extent possible, preferably down to a moisture content of less than 10%. Samples are taken in order to determine the trotyl content and moisture content and also the content of toluene and hexogen. RESULTS . Using an incoming composition consisting of 76.3% octogen and 23.7% trotyl, the following typical results were obtained after leaching 10 tonnes of worked-up octol: Octogen content: 99 .39% Hexogen content: 0 . 61% Trotyl content: 0 . 03% Toluene content: 0 . 04% Water content: 5 . 9% STAGE 2 PURIFICATION OF LEACHED PRODUCT. (Leaching 2) In order to achieve the purest of the grades in Mil-H-45444 (< 0.2% hexogen), an additional purification step is required for the purpose of removing the hexogen which is present in the octogen (up to 1.5%) and removing the remaining toluene. This is done with the aid of solvents, in this case BLO. This additional purification is carried out principally when precipitating grades directly out of the solvent using water. Additions: 350 litres of BLO from a container located outside the factory are added to the apparatus using a membrane pump and a hose. 125 kg of leached octogen are weighed, in accordance with protocol, into a cask or barrel and added to the apparatus while stirring. Heating: The heating is regulated from the control room using a program regulator and a sui¬ table program (up to 120°C) ; the appar¬ atus is heated with hot water. Volatiliza¬ tion: When the temperature has reached the programmed temperature (105°C) , it is maintained at this value so that the water and toluene vapours can escape; the boiling point of the toluene/water azeotropic mixture is approximately 86°C. Cooling: When all the toluene/water has been vol¬ atilized and all the octogen is wholly or partially dissolved, the batch is then cooled down to 15°C, either using a cool¬ ing program or else manually. Filtration: When tapping-off, the bottom valve under the apparatus is opened and the product is tapped off down into a suction filter for separating the solvent and the explo¬ sive. The tapped-down batch has first to sediment, and, after that, the mother liquor is sucked off into an intermediate vessel so that it can be reused. Washing: The remaining octogen cake is washed with 100 litres of water, after which the cake is sucked as dry as possible, preferably to a water content of less than 10%. Emptying: The octogen in the suction filter is scooped out manually into either plastic boxes or plastic barrels in which it is then transported away for storage. RESULTS: Typical results from these leachings, now that we have to date purified approximately 5 tonnes, are as follows: Octogen content: 99.95% Hexogen content: 0.05% Trotyl content: 0.01% Toluene content: Not detect¬ able STAGE 3 RECRYSTALLIZATION TO MIL-SPEC. GRADE AND DESIRED PARTICLE SIZE. Recrystallization to approved grades in accordance with specification Mil-H-45444 is effected using the method described in Swedish Patent Application 8401857-1. STAGE 4 WORKING UP THE LEACHING LIQUID. The leaching liquid, containing up to 25% trotyl dis¬ solved in toluene, is worked up in batches. The volatile toluene is distilled off in an apparatus provided with a stirrer. ADDITIONS: 100 1 of water and 300 litres of leaching liquid are added to the apparatus while stirring. HEATING: The mixture is heated so that the azeotropic mixture of toluene/water (86°C) evaporates. The heating is regulated in accordance with a regulator program. VOLATILI¬ ZATION: The volatilization continues until the temperature has risen to greater than 95°C, when the volatilization is termin¬ ated. FILTRATION: The remaining spent wash consisting of water, trotyl and small quantities of toluene is tapped off, while hot, down into a water-containing suction filter while stirring; when the trotyl comes into contact with the cold water it sol¬ idifies into granules which are then easy to drain. The volatilized toluene is reused in the process. The granulated trotyl can be combusted in the customary manner. RESULTS: > 99% toluene, < 1% water. STAGE 5 WORKING UP THE BLO/NMP. 1. PRECIPITATING THE EXPLOSIVE FROM THE BLO/NMP Additions: 250 litres of BLO/NMP mother liquor from a container located outside the factory are added to the apparatus using a mem¬ brane pump. The speed of revolution of the stirrer is adjusted to 100 rpm. Precipitation: 250 litres of water are sluiced down into the apparatus in ordered to precipitate the explosive out of the mother liquor; the precipitation takes place at room temperature or lower. Filtration: When tapping-off, the bottom valve under the apparatus is opened and the product is tapped off down into a suction filter. The tapped-down batch has first to sedi¬ ment and, after that, the mother liquor, consisting of approximately 50% BLO/NMP and 50% water, is sucked off into the intermediate vessel, after which it is transferred into containers so that it can then be transported away to be worked up. Washing: The remaining BLO/NMP is washed away with water and conveyed to the effluent point. Emptying: The explosive in the suction filter is scooped out manually into either plastic boxes or plastic barrels and then trans¬ ported away for storage and subsequent recrystallization. 2. WORKING UP THE BLO/NMP MOTHER LIQUOR. The working up of the BLO/NMP water takes place in two stages; firstly, the water is distilled off and then, in stage 2, the BLO/NMP is distilled off. Both these stages take place under reduced pressure. The following description presents a nor¬ mal work-up. Additions: The mother liquor consisting of BLO/NMP water is collected in a distillation still. The pressure is lowered to -95 kPa using a vacuum pump. Heating: The temperature in the still is raised using hot water or steam in the jacket of the apparatus (max 130°C) . Distillation 1: The water begins to boil at 55-60°C; the vapour is cooled down in the condenser and collected in a receiving vessel; the water can then be tapped off to the effl¬ uent point. Distillation 2: The temperature rises in the still once there is no water left, and rises to approximately 125°C at which point the BLO/NMP is volatilized; the distillation is continued until 10% of the spent wash remains in the still. Water is added to the remainder of the spent wash and the whole is allowed to pass to the effluent point. The volatilized BLO/NMP is tapped off into containers and is reused in the process. Results: Typical values when working up BLO/NMP: 98% BLO/NMP, 2% water.

Claims: PATENT CLAIMS 1. Method of working up returned and residual quantities of those mixed explosives which, in addition to explosive and/or non-explosive binders of the trotyl type or, in the latter case, plastics or wax, also include nitramines in the form of one or more of the crystalline high-energy explosives octogen and hexogen, respectively, with the intention of enabling at least some of the components contained therein to be reused, characterized in that the binders, in a first leaching stage, are leached out using a first solvent which is suited for the purpose and which dissolves trotyl, relevant plastic and/or wax, but only partially dissolves nitramines, in that the nitramines contained in the solid substance which is obtained after this leaching stage, after filtering the resulting mother liquor in the form of the said first solvent with binders dissolved in it, are dissolved in a second solvent which is able to dissolve nitramines of the octogen or hexogen, respect¬ ively, type, while the binder, which is dissolved in the mother liquor obtained from the first leaching stage, is separacely precipitated out in solid form and collected, by means of the solvent being distilled off and then condensed for reuse in the first leaching stage of the process, while the nitramines which are dissolved in the second solvent are, after filtering off any remaining solid substance, precipitated out, by means of altering the degree of saturation of the resulting solution, in the form of crystals whose size and shape is modified in a desired manner in accordance with known technology and which are separated off for reuse while solvent which remains after this precipitation is purified by means of distillation and then returned to the process. 2. Method, according to Claim 1, of recovering from the starting material, when the crystalline high-energy explosive contained in the starting material consists of octogen whose possible degree of contamination with hexogen is not known, or is known to exceed current standards, octogen having a degree of purity which meets the said standards, characterized in that the solid residual substance which is obtained after the first leaching stage is, in an intermediate stage between the first leaching stage and the final dissolution and recrystallization of the crystalline explosive, leached in a solvent of the type used in the concluding crystal- lization stage and then precipitated out under such conditions that all the hexogen remains in solution, after which the resulting solid substance is filtered off and conveyed onwards to the recrystallization stage. 3. Method according to Claim 1 or 2, characterized in that the solvent in the leaching stage consists of toluene or xylene. 4. Method according to any one of Claims 1 - 3, characterized in that gamma-butyrolactone (BLO) and/or N- methyl-2-pyrrolidone (NMP) is/are used as solvent(s) in the recrystallization stage and possible intermediate stage.

Inventors: NYQVIST JAN-OLOF, NYQVIST, JAN-OLOF
Applicants: BOFORS EXPLOSIVES AB, NYQVIST JAN OLOF, NYQVIST, JAN-OLOF
Application year: 1995
Main classification: F42D5
IPC codes: C06B21