U.S. patent application number 11/160021 was filed with the patent office on 2006-12-07 for rdx composition and process for its manufacture.
This patent application is currently assigned to SCHLUMBERGER TECHNOLOGY CORPORATION. Invention is credited to Karri A. Brock, Philip Kneisl.
Application Number | 20060272756 11/160021 |
Document ID | / |
Family ID | 36571748 |
Filed Date | 2006-12-07 |
United States Patent
Application |
20060272756 |
Kind Code |
A1 |
Kneisl; Philip ; et
al. |
December 7, 2006 |
RDX Composition and Process for Its Manufacture
Abstract
An explosive composition can be produced by dissolving RDX in a
volume of a first solvent to form a first solution, and adding a
second solvent to the first solution. The second solvent is
miscible with the first solvent, but RDX is soluble in the second
solvent to an extent no greater than 1 g RDX/100 g of the second
solvent. Precipitated RDX crystals can be recovered. The RDX
crystals can have a crystal density of less than 1.80
g/cm.sup.3.
Inventors: |
Kneisl; Philip; (Pearland,
TX) ; Brock; Karri A.; (Santa Fe, TX) |
Correspondence
Address: |
SCHLUMBERGER RESERVOIR COMPLETIONS
14910 AIRLINE ROAD
ROSHARON
TX
77583
US
|
Assignee: |
SCHLUMBERGER TECHNOLOGY
CORPORATION
300 Schlumberger Drive
Sugar Land
TX
|
Family ID: |
36571748 |
Appl. No.: |
11/160021 |
Filed: |
June 6, 2005 |
Current U.S.
Class: |
149/92 |
Current CPC
Class: |
C06B 25/34 20130101;
C06B 21/0066 20130101 |
Class at
Publication: |
149/092 |
International
Class: |
C06B 25/34 20060101
C06B025/34 |
Claims
1. A process for making an explosive, comprising: dissolving RDX in
a volume of a first solvent to form a first solution; adding a
second solvent to the first solution, wherein the second solvent is
miscible with the first solvent, and wherein RDX is soluble in the
second solvent to an extent no greater than 1 g RDX/100 g of the
second solvent; and recovering precipitated RDX crystals.
2. The process of claim 1, wherein RDX is soluble in the first
solvent to an extent greater than 5 g RDX/100 g of the first
solvent.
3. The process of claim 1, wherein the first solvent is an organic
solvent having about 2-10 carbon atoms.
4. The process of claim 1, wherein the first solvent is acetone,
dimethylsulfoxide, or dimethylformamide.
5. The process of claim 1, wherein the second solvent is water.
6. The process of claim 1, wherein the second solvent is added in a
volume that is about 2-10 times the volume of the first
solvent.
7. The process of claim 1, wherein the recovered RDX crystals have
a crystal density of less than 1.80 g/cm.sup.3.
8. The process of claim 7, wherein the recovered RDX crystals have
a surface area of greater than about 1.15 m.sup.2/g.
9. An explosive prepared by a process comprising: dissolving RDX in
a volume of a first solvent to form a first solution; adding a
second solvent to the first solution, wherein the second solvent is
miscible with the first solvent, and wherein RDX is soluble in the
second solvent to an extent no greater than 1 g RDX/100 g of the
second solvent; and recovering precipitated RDX crystals.
10. The explosive of claim 9, wherein RDX is soluble in the first
solvent to an extent greater than 5 g RDX/100 g of the first
solvent.
11. The explosive of claim 9, wherein the first solvent is an
organic solvent having about 2-10 carbon atoms.
12. The explosive of claim 9, wherein the first solvent is acetone,
dimethylsulfoxide, or dimethylformamide.
13. The explosive of claim 9, wherein the second solvent is
water.
14. The explosive of claim 9, wherein the second solvent is added
in a volume that is about 2-10 times the volume of the first
solvent.
15. The explosive of claim 9, wherein the recovered RDX crystals
have a crystal density of less than 1.80 g/cm.sup.3.
16. The explosive of claim 15, wherein the recovered RDX crystals
have a surface area of greater than about 1.15 m.sup.2/g.
17. RDX crystals having a crystal density of less than 1.80
g/cm.sup.3.
18. The RDX crystals of claim 17, wherein the RDX crystals have a
surface area of greater than about 1.15 m.sup.2/g.
19. The RDX crystals of claim 17, wherein detonation of the RDX
crystals can be initiated with less than about 100 mJ.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates generally to explosives and
processes for manufacturing such explosives.
[0002] The explosive hexahydro-1,3,5-trinitro-s-triazine is often
referred to as RDX. Two processes have been used commercially to
manufacture RDX. The first is direct nitration, which produces type
A RDX. In this process, hexamethylenetetramine is reacted with
nitric acid at 30.degree. C. or less. The direct nitration method
is not widely used today for economic reasons. The second process,
known as the Bachmann process, is currently the most common method
used to manufacture RDX. It produces type B RDX. In this process,
hexamethylenetetramine is reacted with nitric acid in the presence
of ammonium nitrate and acetic anhydride.
[0003] The primary difference between the two types of RDX is that
type A is essentially pure, while type B is contaminated with HMX.
However, for practical purposes, both processes yield RDX of
essentially identical utility. In both processes, the raw RDX is
further purified and the crystal morphology is modified by
recrystallization.
[0004] RDX is commonly manufactured in a wide range of particle
sizes (grades) from 25 microns to 600 microns in diameter by
recrystallization. Recrystallized RDX may also be ground, for
example in a fluid energy mill, to obtain finer particles ranging
from 2 to 25 microns in diameter. However, all RDX commercially
produced today consists of orthorhombic crystals with a density in
the range of 1.80-1.82 grams/cm.sup.3. This form of RDX has been
designated as the .alpha. polymorph, or RDX(I). The exact crystal
density of a given lot of RDX is a function of purity (i.e., HMX
content), and the absence or presence of crystal defects and
inclusions.
[0005] A .beta. polymorph of RDX has been reported in the
literature. The stability of .beta.-RDX is unknown and no
measurements of physical properties or sensitivity have been
reported other than the crystal morphology is dendritic.
[0006] RDX is an explosive material and therefore is used in a
variety of applications in which controlled explosions are useful.
In these applications, it is necessary to initiate the detonation
of the RDX, and of course it is important to do so in a safe
way.
[0007] A slapper detonator is a device that offers a relatively
high degree of initiation safety. Slapper detonators function by
rapidly discharging voltage through a low inductance circuit. The
circuit comprises a high-voltage spark gap switch (typically
500-3,500 volts), a high-voltage low-inductance capacitor
(typically 500-3,500 volts and 0.1-0.2 .mu.F), and an
exploding-foil initiator (EFI) bridge. The entire circuit
inductance is typically 20-50 nH, and sometimes less (1-20 nH).
Discharging such a circuit causes a current of several thousand
amperes to flow through the EFI bridge, which in turn causes the
EFI bridge to explode. The exploding bridge then accelerates a
polymeric flyer (typically a thin polyamide film) across a short
gap, where it slaps a pellet of a secondary explosive, causing the
secondary explosive to detonate.
[0008] Many explosives have been detonated in a laboratory setting
by slapper detonators, such as HNS, PETN, CL-20, TNT, RDX, HMX, and
various formulations made from such explosives. However, such
laboratory initiation systems typically function at high voltages
with large capacitors and discharge energies of 250 mJ to 1,225 mJ.
Such systems are generally unsuitable for use outside the
laboratory. To be useful outside the laboratory, experience has
shown that it is desirable to significantly reduce the firing
voltage and capacitor size (firing energy) of the circuit. While
this can be accomplished to some degree by designing the electrical
firing circuit to be more efficient, ultimately the minimum firing
energy is controlled by the sensitivity of the explosive.
[0009] The current state of the art is the low-energy foil
initiator (LEFI) These devices typically function with firing
energies below 100 mJ. To this end, explosives have been developed
that have fine particle size and high surface area, such as HNS-IV,
PETN, and CL-20, which can be initiated with less than 100 mJ.
However, each of these explosives has significant problems. HNS-IV
is difficult to manufacture and purify, and therefore is expensive.
PETN has excellent sensitivity and an acceptable price, but has
marginal thermal stability for non-laboratory applications. CL-20
is expensive and cannot be recrystallized to a very small particle
size. It is therefore just barely sensitive enough for a LEFI
application.
[0010] There is a need for new explosive materials that can be
initiated by LEFI devices, and that overcome at least some of the
above-described problems.
SUMMARY OF THE INVENTION
[0011] One aspect of the present invention is a process for making
an explosive. The process comprises dissolving RDX in a volume of a
first solvent to form a first solution, and adding a second solvent
to the first solution. The second solvent is miscible with the
first solvent, but RDX is soluble in the second solvent to an
extent no greater than 1 g RDX/100 g of the second solvent. RDX
crystals are precipitated and can be recovered.
[0012] Another aspect of the invention is an explosive prepared by
the above process. The explosive comprises primarily RDX, but can
also contain smaller amounts of other materials such as HMX.
[0013] Another aspect of the invention is RDX crystals having a
crystal density of less than 1.80 g/cm.sup.3.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is an enlarged illustration of type B RDX
particles.
[0015] FIG. 2 is an enlarged illustration of RDX particles of the
present invention.
[0016] FIG. 3 is a schematic diagram of a perforating system of the
present invention.
DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
[0017] The present invention relates to a novel form of RDX that
can be used in the perforation of well casing, among other
applications.
[0018] The production of the novel form of RDX begins with a
particulate RDX composition. This starting composition contains
primarily RDX (e.g., at least about 90 wt % RDX on a dry solids
basis, and in some embodiments at least about 99 wt % RDX), but it
can also contain smaller amounts of other explosive or
non-explosive substances, such as HMX. Type B RDX is one suitable
starting material.
[0019] The RDX is dissolved in a first solvent to form a first
solution. RDX should be soluble in this first solvent to an extent
of greater than 1 g RDX/100 g solvent. In various embodiments of
the invention, the solubility of RDX in the first solvent is
greater than 5 g/100 g, 10 g/100 g, or 25 g/100 g. (All solubility
figures in this patent are at room temperature unless otherwise
stated.) The concentration of RDX in the solution will generally be
about 1-50 wt %, although higher or lower concentrations can be
used in some situations.
[0020] The first solvent will typically be an organic solvent, for
example one having about 2-10 carbon atoms. Ketones are one group
of suitable solvents. Specific examples of suitable first solvents
include acetone, dimethylsulfoxide, and dimethylformamide.
[0021] A second solvent is then added to the solution, in order to
cause "crash" precipitation of RDX particles. The second solvent is
miscible with the first solvent, but RDX is much less soluble in
the second solvent than in the first solvent. In various
embodiments of the invention, RDX is soluble in the second solvent
to an extent no greater than 1 g of RDX/100 g of the second
solvent, or in some cases no greater than 0.1 g/100 g. Suitable
examples of second solvents include water and various dilute
aqueous solutions.
[0022] The second solvent can be added in an excess compared to the
volume of the first solvent in the solution. For example, the
second solvent can be added in a volume that is about 2-10 times
greater than the volume of the first solvent. Even more of the
second solvent can be used, although it may be economically
undesirable in many cases. In contrast, if the amount of the second
solvent used is too small, the resulting crystals will not have the
desired properties and will not function as an EFI explosive. The
solution can be agitated during and/or after the addition of the
second solvent.
[0023] The addition of the second solvent will cause precipitation
of RDX particles. The particles can be recovered, for example by
filtration, and then washed and dried. The final RDX composition
can be essentially pure RDX, or it can contain smaller amounts of
other substances, such as HMX. In contrast to the RDX that has been
commercially available in the past, the RDX has a crystal density
of less than 1.80 g/cm.sup.3. In some cases, the RDX has a crystal
density of about 1.65-1.73 g/cm.sup.3. In some embodiments of the
invention, the RDX has a surface area of greater than about 1.15
m.sup.2/g.
[0024] The detonation of RDX produced by the above-described
process can generally be initiated with less energy than what is
required to initiate previously-known RDX compositions. In some
embodiments of the invention, detonation of the RDX can be
initiated with less than about 100 mJ, or in some cases, less than
about 75 mJ.
[0025] FIG. 1 shows a sample of type B RDX at 100.times.
magnification, while FIG. 2 shows a sample of the RDX of the
present invention at 790.times. magnification.
[0026] The RDX composition of the present invention can be used in
a variety of applications. For example, it can be used in
perforating the casing of subterranean wells, mining, construction
blasting, and many other applications that are well known in the
explosive industry.
[0027] FIG. 3 shows a schematic view of the use of the RDX
composition to perforate a well casing. A borehole 10 has been
drilled down from the surface of the earth into a subterranean
formation 12. The borehole has been lined with casing 14, which
generally takes the form of a cylindrical pipe. At some depth or
depths in the borehole, the surrounding formation 12 contains oil
and/or gas. In order for the oil and/or gas to pass from the
formation into the borehole and up to the surface, it is necessary
to perforate the casing. This can be done with a perforating gun
16, which can be lowered into the well to the desired depth on a
wireline 18 or using other means that are known in the oil
industry.
[0028] The perforating gun 16 comprises a plurality of shaped
charges 20, each of which contains an explosive material. This
explosive material can be the RDX produced as described above,
alone or in combination with other materials that are suitable for
use in an explosive composition. Detonation of the explosive
material in the shaped charge 20 can be initiated by a low-energy
foil initiator 22. When an electrical signal is sent via a control
line from a control device at the surface (not shown in FIG. 3),
the initiator 22 causes the detonation of the shaped charge 20. The
explosive force from the shaped charge 20 is directed primarily
horizontally to the left in FIG. 3, such that a perforation is
formed in the casing, allowing oil and gas in the formation to flow
into the borehole.
[0029] It should be understood that the arrangement shown in FIG. 3
is only one example of how the RDX of the present invention could
be used in the perforation of well casing.
[0030] Specific embodiments of the present invention can be further
understood from the following example.
EXAMPLE 1
[0031] RDX crystals were prepared by crash precipitation. Type B
RDX was dissolved in acetone to make a 10% by weight solution. A
large excess of deionized water was added to this solution with
vigorous stirring to precipitate fine particle size RDX. The
precipitated RDX crystals were filtered from the liquid and washed.
The resulting RDX was dried at 50-55.degree. C. overnight in a
drying oven. The measured BET surface area of the precipitated RDX
was in excess of 1.2 m.sup.2/g. When examined by light microscope,
the RDX crystals appeared to be polycrystalline and orthorhombic.
However, when the crystal density of the crash-precipitated RDX was
checked by helium pyconometer, the crystal density was found to be
1.69 g/cm.sup.3, which is significantly different than the starting
material (ca. 1.80-1.82 g/cm.sup.3).
[0032] The RDX crystals were successfully detonated in a low-energy
exploding foil initiator (LEFI) at 72 mJ (1300 volts, 0.085
.mu.F).
[0033] The preceding description is not intended to be an
exhaustive list of every possible embodiment of the present
invention. Persons skilled in the art will recognize that
modifications could be made to the embodiments described above
which would remain within the scope of the following claims.
* * * * *