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 octagen and hexagen, 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:
FIELD OF THE INVENTION 
     The present invention relates to a complete process for working up returned and residual explosives which contain both fusible binders and crystalline high-energy explosives. 
     BACKGROUND OF THE INVENTION 
     Previously, no useful processes have been available 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. 
     SUMMARY OF THE INVENTION 
     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 octagen and hexagen, to be reused. An additional advantage of the novel process is, furthermore, that it is also the octagen and hexagen, whose manufacture results in the greatest degree of environmental pollution. 
     In addition, the novel process enjoys the advantage that solvents which are used in it are, processed in accordance with constituent processes which are included in the invention. As a result 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 relevant 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 related nitramines octagen and hexagen. As a rule, octagen and hexagen are used separately. However hexagen, since it and octagen are prepared by what is, in principle the same synthesis, can be present as an impurity, particularly in somewhat older octagen batches. This is, per se, a complication when reusing octagen since there are currently strict standards for the lowest content of hexagen in newly manufactured octagen-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 compared 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. octagen together with trotyl as binder and hexagen together with trotyl as binder, respectively, and also compressed octagen and hexagen 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. 
     That which follows provides a general description of the process in all its different stages. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The flow diagrams elucidate the following different parts and steps of the invention. 
     FIG. 1 represents a flow diagram for the recovery of explosive. 
     FIG. 2 represents a flow diagram for leaching stage 1. 
     FIG. 3 represents a flow diagram illustrating the working up of HMX and BLO/NMP. 
     FIG. 4 represents a flow diagram for recrystallization stage 3. 
     FIG. 5 represents a flow diagram for working up BLO/NMP stage 5:2. 
     FIG. 6 represents a flow diagram for working up BLO/NMP stage 5:2. 
    
    
     DESCRIPTION OF THE INVENTION 
     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 temperature, an elevated temperature can be required, principally 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 fulfill the main requirements which are relevant in this context, namely exhibiting a sufficiently 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, the remainder 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 octagen and it is not known how much hexagen this octagen might contain, or if it is already evident from the start that the octagen does not meet current standards, an additional leaching stage is then required in order to remove contaminating quantities of hexagen. The effectiveness of this leaching stage is based on the appreciably higher solubility of the hexagen in at least some solvents. In the leaching stage, all the hexagen 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 elevated temperature, which is, in turn, clearly advantageous. While a dissolution temperature on the order of approximately 105° C. does not dissolve the octagen completely, the hexagen is completely dissolved at this temperature. Once all the hexagen has been dissolved, the temperature of the mother liquor is lowered to a point at which virtually all the previously dissolved octagen has precipitated out in crystalline form while all the hexagen is still present in solution. A pure crystalline octagen, whose crystal form does not meet current requirements, is obtained as a residue by filtering the resulting mother liquor. In order to obtain octagen 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 octagen is regulated so that the desired crystal size and form is obtained. For this purpose, the solubilizing 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 β-octagen 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 octagen which is contained in the residual product and returned product is completely free of hexagen or that the crystalline high-energy product consists solely of hexagen. 
     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 nitramines adding water to almost 50% by weight, whereupon all the remaining octagen or hexagen, 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 includes 6 pages of flow diagrams. 
     
         ______________________________________Description of the method for leaching returned explosive.______________________________________STAGE 1 LEACHING.    Additions:   150 liters, 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 (&lt;10%) which has been   sucked dry is now overlaid with 30 liters   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 liters 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 (&lt;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 liters 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- When the temperature has reached the  tion: programmed temperature (105° C.), it is   maintained at this value so that the   water and toluene vapors can escape; the   boiling paint 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 liters 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-   ableSTAGE 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 l of water and 300 liters 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- The volatilization continues until the  ZATION: 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.: &gt;99% toluene, &lt; 1% water.STAGE 5 WORKING UP THE BLO/NMP.  1. PRECIPITATING THE EXPLOSIVE FROM TKE BLO/NMP Additions:     250 liters 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 liters 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 ELO/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 bail at 55-60° C.; the              vapor 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.______________________________________