FR2459213A1 - Removing processing solvent from propellant casting powders - by adding miscible organic liq. which is not a solvent for the powder - Google Patents

Abstract

Propellant powders of the single, double base, modified double base or composite type are dried, to remove residual processing solvent, prior to casting by contacting them with an organic solvent which is miscible with the residual solvent but which is not a solvent for the powder. Pref. the process is carried out at 60-160 degrees F for 2-30 days. The powder is esp. kept immersed in the org. solvent until it is to be cast into a propellant. The process avoids dangerous heat-drying of the powder and the need for subsequent handling of dry powders.

Description

 The invention relates to a drying process for molding powders used in the manufacture of propellant compositions.

 According to a first aspect, the invention relates to an extraction process for removing from a molding powder for propellant composition the liquid solvent remaining after the manufacture of this powder. The invention also relates to a method of removing the "process solvent" remaining in the raw molding powder by drying in the liquid phase and maintaining the dried liquid molding powder thus retained moistened with the drying liquid to a liquid. at and including the beginning of the molding step, which eliminates the risks incurred during the conventional thermal drying of the raw powder and during the subsequent manipulation of the dry material obtained.

 In the manufacture of molded propellant compositions some or all of the components are formed into a particulate molding powder which is then introduced into a mold and molded by passing a suitable molding liquid through the mass obtained to form a molded powder. filling the voids is then carried out polymerization of the mass obtained under conditions of time and temperature suitable for the formation of a homogeneous solid propellant composition.

The molding powder is preferably any suitable smoke-free base or double base composition which, in a manner known per se, comprises additional components selected from ethyl centrality (diethylurea symmetrical), diphenylamine and dibutyl phthalate. potassium sulfate or any other similar product. The following table gives examples of these formulations.

<tb><SEP> Parts <SEP> for <SEP> hundred <SEP> parts
<tb><SEP> Composition <SEP> of <SEP> powder <SEP> of <SEP> total <SEP> of <SEP><SEP> powder <SEP> of <SEP> molding
<tb><SEP> of <SEP> molding <SEP> 1 <SEP> 2 <SEP> 3 <SEP> 4 <SEP> 5
<tb> Nitrocellulose <SEP> 91.0 <SEP> 75.0 <SEP> 40, o <SEP> 30.0 <SEP> 20.0
<tb> Nitroglycerin <SEP> 17.0 <SEP> 27.5 <SEP> 10.0 <SEP> 10.0
<tb> Ammonium perchlorate <SEP><SEP> 30.0 <SEP> 28.0 <SEP> 7.0
<tb> Cyclotetramethylene
<tb><SEP> tetranitramine <SEP> 36.0
<tb> Powder <SEP> aluminum <SEP> 29.0 <SEP> 25.0
<tb> Resorcinol <SEP> 1.5 <SEP> 2.0 <SEP> 1.0
<tb> 2-Nitrodiphenylamine <SEP> 2.0 <SEP> 2.0 <SEP> 1.0 <SEP> 1.0 <SEP> 1.0
<tb> Dioctyl <SEP> Phthalate <SEP> 4.0
<tb> Stearate <SEP> of <SEP> Lead <SEP> 3.0
<tb> Salicylate <SEP> of <SEP> Lead <SEP> 3.0
<tb> Beta <SEP> Resorcyclate <SEP> of <SEP> Lead <SEP> 3.0 <SEP>
<Tb>

 The individual components of the molding powder are mixed with a sufficient amount of a suitable process solvent to form an extrudable or kneadable slurry.

 The material -pateuse is then transformed into particles, dried in an oven and fed to the molds. A series of operations of this type consists of forming the pasty mass and then extruding it into strands, cutting the pasty strands into granules, removing the process solvent from the granules by drying in an oven, sifting the dry granules to remove fines and oversize particles, to transfer the dried granules to storage, to transfer the dried granules from the storage to the molding station, to discharge them by gravity into the molding unit and to mold the granules by pass a plasticizer into the voids of the granular mass and then polymerize, generally at room temperature, for a sufficiently long period to effect the swelling and the jelly-like thinking of the granules and thus to form a homogeneous mass of solid propellant composition having the ballistic and mechanical properties required.

 The risks existing in the handling of the dry powder are numerous. It can easily be understood that the handling of these dry powders during melting, shaping, sieving and other processes leads to dust formation, collisions, interparticle friction of the dry particles as they pass through. one or more of these operational steps, all of which result in high particle sensitivity to accidental initiation, especially because of the electrostatic charges that are inherently developing under these conditions.

 The present invention relates to a method of removing the process solvent from the pasty mixture of molding powder while maintaining said powder in a wet state up to (and including) its placement in the mold for the step This eliminates the risks inherent in conventional drying in an oven and the handling of dry powders.

 According to the invention, the powder particles containing the residual process solvent, originating from the manufacture of the powder, are dried in the liquid phase to remove the solvent in order to be in a state allowing their molding to form a propellant composition. Drying in the liquid phase is carried out by contacting the powder particles with an organic solvent constituting the drying liquid, which is miscible with the residual process solvent but which has practically no solvent action for the components of the powder. and hardly penetrates the interior of the particles; the liquid phase drying action comprises diffusing the process solvent through the solid phase of the molding powder particles and passing said solvent from the surfaces of the particles to the drying liquid which is in direct contact with them. The drying liquid functions essentially as an extraction solvent but in a unique manner, that is, its selective solvent action occurs at the surfaces of the particles of the molding powder since there is hardly any penetration of the drying liquid inside the particles. The drying liquids used for the implementation of the process according to the invention of extraction solvents can thus be qualified while specifying the uniqueness of both the extraction solvent and the process.

 Although all the liquids having the properties defined above can be used as liquid seals in the practical application of the invention, it is preferred to use liquid saturated aliphatic hydrocarbons and mixtures thereof and particularly one or more compounds belonging to the group of hexanes, heptanes, octanes and nonanes and preferably n-hexane, n-heptane or mixtures n-hexane / n-heptane.

 Among the known process solvents used in the manufacture of the pasty molding powder particles described above, mention may be made of acetone, ethanol, iso-propanol and n-propanol. n-butanol, iso-butanol, toluene, ethyl acetate, n-butyl acetate, isobutyl acetate, tetrahydrofuran, methyl ethyl ketone, diethyl ketone and ethyl ether. These solvents can be used alone or in mixtures, according to different ratios.

 The invention is applicable to the drying of particles of molding powder of any suitable shape or size.

 In practice, however, it is preferred to start from granules cut from strands produced by extrusion of the pasty mass and that is why the particles of molding powder will be called most often simply granulated, but it is understood that the present invention can not be limited to this type of particles.

 Drying in the liquid phase according to the invention can be carried out under all suitable conditions of contacting. In general, this drying is carried out for a period ranging from 2 to 30 days at temperatures ranging from 21 ° to 38 ° C., although it is possible, if desired, to work at higher temperatures, up to 710C, a range of 15.6 to 71 ° C generally bringing together the temperature conditions applied; the ratio of the drying liquid to the pasty particulate mass of the molding powder, although significantly depending on the concentration gradient of the process solvent between the pasty mass and the drying liquid, is generally between 1: 1 and 10: 1, by weight, although higher ratios can advantageously be used up to about 15: 1.

 The following examples will furthermore illustrate the invention without limiting it: they relate to the removal of the process solvent from the raw powder granules according to the liquid drying method of the invention.

Example 1
700 g (without process solvent) of a pasty mass of molding powder are formed by mixing the components in the presence of about 295 g of an acetone-ethanol mixture, as a process solvent, the acetone volume ratio. ethanol being about 1.5: 1. The pasty mass is then extruded into strands of circular cross-section, having a diameter of approximately 36.8 mm and then the strands are cut into green granules of approximately 38.1 mm. The composition of the molding powder (without the solvent )is the following
Component% by weight
Nitrocellulose 28.0
Nitroglycerin 9.5
Ammonium perchlorate 42.5
Aluminum powder i4,0
Resorcinol 1.5 2-Nitrodiphenylamine 1.0
Zirconium fibers 3,5
In each series of tests, a portion of the mass of green granules is brought into contact with n-heptane, which is miscible with the solvent acetone-ethanol remaining in the granules but has a low, if any, solvent action for the solvents. components of the granules. The tests were carried out under certain conditions of duration, temperature and stirring not only to demonstrate the liquid phase drying of the granules according to the invention but also to illustrate the relationships existing between the above variables. All the tests were carried out in using 10 parts by weight of n-heptane per one part by weight (solvent-free basis) of the mass of granules a sample of granules is removed from contact with the nheptane at cumulative time intervals and analyzed for its n-content. heptane, acetone and ethanol to measure the degree of drying in the liquid phase achieved, that is to say the drying of granules without acetone-ethanol noticeable sanipénétration granules by n-heptane. The results are collated in Table I.

TABLE I
Pellet analysis
Percent by weight
Portion of Total Time Fraction granules cumulative acetone acetone tested contact n-hep- Etha- Acetone and etha (grams) (minutes) tane nol tone ethanol nol origi (dry basis)
added
Test 1 - Contact at 250C 100 O - 4.39 8.67 13.06 -
15 0.31 4.74 5.92 10.66 0.82
30 0.15 4.25 4.92 9.17 0.70
60 0.34 3.81 4.40 8.21 0.63
120 0.08 2.83 3.70 6.53 0.50
360 0.19 2.16 2.62 4.78 0.37
1440 0.09 1.15 1.60 2.75 1.21
Test 2 - 250C contact with stirring during 360 pre
minutes 100 O - 4.39 8.67 13.06 -
0.12 4.25 5.46 9.71 0.74
30 o, o8 4.14 5.06 9.20 0.70
60 o, og 3.36 4.22 7.58 o, 58
120 o, o8 2.90 3.58 6.48 0.50
360 0.08 2.26 2.68 4.94 0.38
1440 o, og 1.15 1.60 2.75 0.21
Test 3 - Contact at 37,8 C 100 -0 - 5,68 8,33 14,01 -
15 o, ol 3.44 5.15 8.59 0.61
30 o, o6 3.41 5.14 8.55 0.63
60 o, og 3,32 4,27 7,59 0,54
120 0.08 2.65 3.49 6.14 0.55
1440 0.27 0.71 1.34 2.05 0.15
Test 4 - Contact at 48,90C 100 O - 5,68 8,33 14,01 -
15 o, lo 4, o8 5.34 9.42 0.67
30 o, lo 3.36 4.48 7.84 0.56
60 o, î6 3.31 4.02 7.33 0.52
0.14 2.05 2.71 4.76 0.34
1440 0.40 o, 89 1.33 2.22 0.16
Test 5 - Contact at 600c
O - 5.68 8.33 14.01 -
15 o, 17 3.05 4.24 7.29 0.52
30 0.17 2.86 4, o4 6.90 o, 4g
60 0.18 2.30 3.10 5.40 0.39
120 0.17 1.38 2.68 4, o6 0.29
1440 0.41 0.41 0.73 1.14 o, o81
The tests summarized in Table I demonstrate that, when the contact temperature of the drying liquid and the particles of the raw molding powder are increased, the drying speed is also increased, that is to say the removal of the solvent process of the raw powder.

Example 2
A part of another mass of 700 g of raw molding powder of the same composition as that of Example 1 and formed according to the method described in Example 1, including the use as a process solvent of the acetone-solvent. ethanol of composition similar to that of the solvent of Example 1, is brought into contact with n-heptane at 600C in a series of tests, in order to demonstrate the drying in the liquid phase according to the invention, at this temperature, during a unique duration of 72 hours; another part of the same mass of 700 g of raw pellets is put in contact, in another series of tests with n-heptane, under the same conditions and for the same period of time, except that the contact is made in three separate steps of 24 hours each which means that after each period of 24 hours the n-heptane is removed from the molding powder and replaced with fresh n-heptane. The two series of tests are carried out using 10 parts by weight of n-heptane of very high purity for one part by weight of granular mass.

In each test a portion of the granules were removed from contact with n-heptane at the end of each indicated cumulative period and analyzed as described in Example 1. The results of these tests are collated in Table II.

TABLE II
Pellet analysis
Percent by weight
Portion of Total Time Fraction granules cumulative acetone acetone tested contact n-hep- etha- and etha- (grams) (minutes) tane nol tone ethanol nol origi (dry basis)
added
Test 1 - 600C - Single Step 00 0 - 5.83 7.89 13.72 -
24 0.61 0.35 0.52 0.87 0.063
48 0.89 0.22 0.48 0.87 0.052
72 - 0.23
Test 2 - 600C - Three steps, each 24 hours at equilibrium 100 0 - 5.83 7.89 13.72 -
24 0.62 0.79 o, 88 1.67 0.12
48 0.53 0.13 0.31 o, 44 0.32
72 0.42 0.00 0.25 0.25 0.018
The data collected in Table II show that the multistage operation corresponds to lower levels of process solvent in the raw molding powder and, therefore, corresponds to an increase in drying efficiency compared to the single step.

Example 3
Another mass of 700 g of granules of raw molding powder of the same composition as that of Example 1, including the use of the acetone-ethanol process solvent of the same composition and in the same proportions as those indicated in FIG. Example I: is brought into contact with n-heptane under different temperature conditions, weight ratio n-heptane / mass of solid granules, and extraction in multi-steps to illustrate the influence of these variables on the drying in the liquid phase according to the invention.

 In each test, a portion of the granules was removed from contact with the extraction solvent at the end of each cumulative time period and analyzed as described in Example I. The results obtained are collated in Table III and illustrate the influence of the contact time on the effectiveness of the drying action.

TABLE III
Pellet analysis
Percent by weight
Portion of Total Time Fraction granules cumulative acetone acetone tested contact n-hep- Etha- Acetone and etha (grams) (minutes) tane nol tone ethanol nol origi (dry basis)
added
Test 1 - 600C - n-heptane ratio / granules 1: 1 by weight
Successive steps of 24 hours * 120 O - 4.04 7.64 11.68 -
48 0.68 l, lo 1.78 2.88 0.25
72 i, 14 0.92 1.23 2.15 0.18
144 1.10 0.21 o, 54 0.75 0.064
192 0.91 0.17 0.33 0.50 0.043
240 1.41 0.04 0.36 0.40 0.034
336 1.50 0.04 o, l9 0.23 0.020
Test 2 - 250C - n-heptane ratio / granules 1 :: 1 by weight
Successive steps of 24 hours * 120 0 - 4.04 7.64 11.68 -
48 0.46 2.02 3.29 5.31 o, 46
72 0.42 1.50 2.41 3.91 0.34
144 0.76 1.15 1.56 2.71 0.23
192 0.66 o, 80 1.02 1.82 0.16
240 0.76 0.49 0.72 1.21 0.10
336 0.82 0.42 0.62 1.04 o, o89
Test 3 - 250C - n-heptane ratio / granules 10: 1 by weight
One step
40 o - 4, o4 7.64 11.68 -
72 0.34 1.81 2.49 4.30 0.37
192 0.89 0.72 o, g 1.71 o, 15
336 0.61 0.22 0.52 0.74 0.063
Test 4 - 250C - n-heptane ratio / granules 1 :: 1 by weight
Single step 120 o - 4.04 7.64 11.68 -
72 0.79 2.60 4.26 6.86 0.59
192 0.25 o, 93 1.95 2.88 0.25
336 o, 54 0.22 0.52 0.74 0.012
Test 5 - 250C - First 24 hours (then 600C)
N-heptane ratio / granules 10 :: 1 by weight
Successive steps of 24 hours *
40 o - 4.04 7.64 11.68 -
24 0.5 1.99 3.82 5.81 0.50
48 o, 6g 0.52 0.86 1.38 0.12
72 0.53 - 0.27 0.27 0.023 120 0.92 o, 08 0.23 0.31 0.027
168 o, g6 - 0.18 0.18 0.015
360 0.70 - o, og o, og o, oo8
At the end of each successive 24 hour period, (regardless of the intervals between which the samples are analyzed), n-heptane is removed from the molding powder and replaced with fresh, high purity n-heptane.

 It should be noted that in some cases there may be a loss of components of the molding powder by the extraction solvent, which is a function of the extraction temperature, the solvent itself, and the components of the powder. For example, when 99% purity n-heptane, especially at elevated temperatures, eg 490C600C, is used as the drying liquid, and nitroglycerin as a component of the granules, some loss of this component can be seen in the process. extraction solvent. It is then sufficient to presaturate the drying liquid with the component (s) in order to regulate the solubility equilibrium and to minimize the component loss.

 These minor losses can also be virtually eliminated even without presaturation of the extraction solvent, by lowering the ratio of the drying liquid to the mass of molding powder to a level of, for example, from 0.5: 1 to 1: 1, and by performing the drying step at a low temperature adapted for example at 15.6-26.70C. Nevertheless, it is now preferred to pre-saturate the drying liquid with the components having a certain solubility in said liquid in order to minimize or virtually eliminate these losses, however small they may be.

 The invention enables the process solvent to be removed from the liquid-phase dry-drying powder particles without appreciable penetration of the drying liquid into the powder granules as is apparent from the low nheptane content of the granules. It is therefore one of the characteristics of the invention that not only can the drying liquid phase of the granules be carried out by a single extraction process with a solvent but also that the penetration of the granules by the solvent (drying liquid). is virtually zero which, in turn, allows the handling, storage and movement of the granules dried in the liquid phase, while they are wetted by contact with at least a residual portion of the extraction solvent.

Example 4
453 g of mold powder granules, dried in the liquid phase according to Example 1, and wet (the n-heptane covering the surface of the granules) are passed through a manufacturing line in a vertical mold for molding the granules in order to form a propulsive composition.

 The residual n-heptane is removed from the granules and then a slow stream of air is passed through the granules to remove the last traces of n-heptane from their surface. 136 g of nitroglycerine are then passed through the lowest part of the mold assembly, and from bottom to top, between the interstices of the granules, as a plasticizer or molding solvent, in accordance with common practice in molding of propellant compositions; the mass obtained is then kept in the mold for about 480 hours, between 21 and 250 ° C., and then for about 336 hours, at about 49 ° C., in order to carry out the polymerization necessary for the formation of a double base solid propellant composition, high burning rate, ready for firing, as a source of energy for the control of a projectile.

 A molding solvent other than nitroglycerine, for example triacetin, may be employed. The polymerization conditions have temperatures between 49 and 600 ° C. for a period of 168 to 816 hours depending on the formulation of the propellant composition, all according to the methods well known in the prior art.

 Although the invention has been more particularly described with reference to molding powders of the double base type, it can also be applied to molding powders of other types, such as those with a simple base or composite; the molding powder frequently contains, as a process residual solvent, acetone / ethanol mixtures in a volume ratio of from 0.8: 1 to 8.0: 1.

Claims (18)

 - Claims  l - Process for drying molding-type powder particles of the basic, double-base, double-base modified and composite type, containing residual process solvent from their manufacture, in order to bring said particles to the state dry for molding to form a propellant composition, characterized in that it comprises contacting said particles with an organic solvent miscible with said residual process solvent but which has substantially no solvent power vis-à-vis screwing components of said molding powder and not substantially penetrating said particles sufficiently to allow said process solvent to diffuse through said molding powder particles and escape along their surfaces into said organic solvent to obtain particles of molding powder dried in the liquid phase.  2 - drying process according to claim 1, characterized in that at least a portion of said organic solvent is maintained in substantially complete wetting relationship with the surfaces of the dried particles to the location of said particles to form to form the propulsive composition.  3 - Process according to claim 1, characterized in that the organic solvent is at least one liquid saturated aliphatic hydrocarbon.  4 - Process according to claim 2, characterized in that the organic solvent is at least one liquid saturated aliphatic hydrocarbon.  5 - Process according to claim 3, characterized in that the organic solvent is selected from the group comprising hexanes, heptanes, octanes and nonanes and mixtures of these compounds.  6 - Process according to claim 5, characterized in that the organic solvent is n-heptane.  7 - Process according to claim 5, characterized in that the organic solvent is n-hexane.  8 - Process according to claim 5, characterized in that the organic solvent is a mixture of n-heptane and n-texane.  NaN. 9. A process as claimed in any one of claims 1 to 3 and 5 to 8, characterized in that the weight ratio of the organic solvent to the molding powder particles is from 0.5: 1 to 15: 1.  10 - Process according to claim 9, characterized in that the duration and the contact temperature between the organic solvent or anhydride and the age / age particles are respectively between 2 and 30 days and between 15.6 and 710C.  11 - Process according to claims 9 and 10, characterized in that the temperature is between 15.6 and 27.70C and the weight ratio is not greater than 1: 1.  12 - Process according to claim 9, characterized in that the molding powder particles are cylindrical granules obtained by cutting a strand of green molding powder of cylindrical cross section.  13 - Process according to any one of claims 1, 3 and 5 to 12, characterized in that the drying in the liquid phase is carried out in a single step.  14 - Process according to any one of claims 1, 3 and 5 to 12, characterized in that the drying in the liquid phase is carried out in several steps, a separate portion of the organic solvent being used at each step.  15 - Process according to any one of claims 1, 3 5 to 10,12 to 14, characterized in that the organic solvent is saturated with at least one of the components of the molding powder before it comes into contact with the powder particles. molding.  16 - Process according to any one of claims 1 to 15, characterized in that the organic solvent is n-heptane and the process solvent is a mixture of acetone and ethanol in a volume ratio acetone / ethanol se ranging from 0.8: 1 to 8.0: 1.  17 - Process according to any one of claims 1 to 16, characterized in that the molding powder is a formulation of the double base type.  18 - Process according to any one of claims 1 to 17, characterized in that puts in place the dried particles of molding powder coated with organic solvent in a mold and then said organic solvent is removed from the mass of particles, vaporizes the residual organic solvent from the surface of the particles and molds the resulting mass to form the propellant composition.