Process of preparing a high-energy softening agent

Details Process of preparing a high-energy softening agent Process of preparing a high-energy softening agent

2000-03-13

2001-07-17

Richter, Johann (Department: 1621)

Organic compounds -- part of the class 532-570 series

Organic compounds

Amino nitrogen containing

C564S111000

Reexamination Certificate

active

06262301

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a continuous process of preparing N-alkyl-nitratoethylnitramines (or NENA-compounds), and in a particularly preferred embodiment a continuous process of preparing butyl-nitratoethylnitramine (butyl-NENA). Further, the invention relates to a plant for effecting such a continuous process.
BACKGROUND OF THE INVENTION
Nitroethylnitramines, in the field known as NENA-compounds, (nitratoethyl-nitramine), have recently been discovered to be potentially very useful ingredients in propellants and explosives (The NENA compounds constitute a large family of energetic plasticizers). This is due to an increasing demand for developing less sensitive propellants and explosive compositions. A large group of NENA-compounds are useful—methyl, ethyl, propyl, butyl etc..
wherein R
1
is alkyl.
Alkyl-NENAs include a nitrate ester as well as a nitramino group, and as a consequence thereof, the NENA compounds are of high interest to both the pro-pulsion, rocket propultion, and military high explosives for low sensitivity ammunition. Alkyl-NENAs has numerous advantages as energetic materials. A well known property is the ability to readily plasticize cellulosic polymers (such as e.g. nitrocellulose) to yield a new type of double-base propellants. These double-base propellants offer very low molecule weight combustion gases (less than 20), which in turn provides for a higher driving force (impetus) at any given flame temperature than the conventional gun propellants or alternatively a lower flame temperature at any given impetus level. Alkyl-NENAs have also been demonstrated to be successful as ingredients in more modern propellant and explosive compositions, particularly as plasticizers in polymeric materials such as poly-NIMMO, HTPE and others.
PRIOR ART
Alkyl-NENAs were first discovered in the early part of the second world war (most probably in 1942) by the research scientists George Wright and Walter Chute at the University of Toronto. At the same time the US Navy was searching for a new flashless gun propellant. Alkyl-NENAs appeared to be a promising solution. The research on Alkyl-NENAs quickly spread to other laboratories in other universities. Seven U.S. patent applications were filed on the same day, Dec. 30, 1944; George Wright and Walter Chute (U.S. Pat. No. 2,461,582, U.S. Pat. No. 2,462,052), Alfred Blomquist and Fred Fiedorek (U.S. Pat. No. 2,481,283, U.S. Pat. No. 2,485,855, U.S. Pat. No. 2,678,946 and U.S. Pat. No. 2,669,576) and John Kincaid (U.S. Pat. No. 2,698,228).
In the last years particularly the interest for butyl-NENA has been increasing. By substituting butyl-NENA for NG (nitroglycerin) in propellants and explosives and thus contributing to an increased safety, this type of propellants and explosives were able to comply with the present military requirements of advanced ammunition. Butyl-NENA has improved thermochemical properties, and is in addition a particularly good nitrocellulose plasticizer. It is expected that butyl-NENA can be used as an important, energetic material.
The NENA-compounds are synthetized batch-wise in a two-step synthesis starting from commercially accessible alkylaminoethanols having a low price by using concentrated nitric acid followed by scavenging the water formed using acetic acid anhydride. By the nitration the hydroxyl group is converted to a nitrate ester group, and the amine group to a nitramine group.
wherein R
1
is alkyl.
wherein R
1
is alkyl.
U.S. Pat. No. 2,678,946 was granted on May 18, 1954. Alfred Blomquist and,Fred Fiedorek were mentioned as inventors in the patent. This patent relates to a process of preparing nitroxy alkylnitramines, in which the examples among others show the preparation of methyl-NENA (example II) and ethyl-NENA (example III). Claim
1
of said patent claims a process of preparing nitroxy alkylnitra-mines, wherein a secondary amine reacts with an equivalent amount of anhydrous nitric acid forming a liquid reaction mixture. This liquid reaction mixture is reacted with an equivalent amount of a water scavenging acid anhydride in the presence of a small amount of halide ion forming catalyst.
Shen Qiong-hua et al (28
th
International Conference of ICT, Jun. 25-28, 1996, Karlsruhe, P133-1) discloses a method of preparing butyl-NENA batchwise in a laboratory scale by the use of very small amounts of starting materials. Nitric acid is initially cooled in an ice/salt water bath, whereupon n-butyl-ethanolamine is added below the liquid surface to the acid with vigorous stirring. The temperature is kept below 22° C. After all the amine is added, the mixture is left with stirring in about 50 minutes. A mixture of acetic acid anhydride and zinc chloride is then added to the mixture at such a rate that the temperature is kept below 35° C. When the entire mixture of acetic acid and zinc chloride is added, the reaction mixture is left for about 1 hour with stirring and then poured into an ice bath. Butyl-NENA separates as a yellowish liquid in the bottom of the ice-bath. Shen Qiong-hua et al concluded that the optimalized reaction conditions for the preparation of butyl-NENA was a reaction temperature of below 22° C. in the first part of the reaction and a reaction of below 35° C. in the second part of the reaction. The reaction time should be about 2.5 hours. In one experiment Shen et al obtained 98.9% purity and 84% yield. In the other experiments the purity was never better than 97% when the yield was higher than 67%.
The literature does not exhaustingly disclose the preparation of Alkyl-NENAs in a larger scale than 5 liters (P. A. Silver and F. Stanley. Hercules Aero-space Division, Hercules Incorporated, Allegany Ballistics Laboratory, Maryland). The total reaction time for step one of the reaction was 4.5 hours, and the addition time for the second step of the reaction was 2.5 hours. The product phase was separated and washed three times, each time having a washing time of about 1 hour per wash. Total time for the synthesis of butyl-NENA in this 5 liter flask was stated to be as much as 10 hours. No yield or purity of the product prepared by the process in a 5 liter scale is presented.
Generally the technology of nitration includes very exothermic reactions. The synthesis of Alkyl-NENAs is so far no exception. Reaction step 1, in which alkylethanol amine is added to cold nitric acid, is a very exothermic reaction. The additon of the amine must be effected below the liquid surface to avoid “spark spheres”. Controlling the rate of addition, amount added and sufficient cooling of the reaction flask is thus of great importance when alkylethanolamine is added to nitric acid. It is also important that nitric acid is not allowed to enter the addition tube of the alkylethanolamine.
Formation of sparks quickly arises in the nitration acid when the alkyletha-nolamine is added, and this is not kept under control. At a larger scale (100 I, 1000 I or largers reactors) this reaction step is expected to be particularly dangerous, and extensive and well planned measures are required before such a reaction is performed.
It is disclosed in the literature that the reaction mixture from the first step should be left with stirring for about 1 hour before a second step is entered. A mixture of acetic acid anhydride is added to a halide ion forming catalyst by the addition to the reaction mixture from the first step. Also this reaction is an exother-mic reaction, but the development of heat is less drastic than in the first part of the reaction. It is disclosed in the literature that the final reaction mixture after step two should be left for about 1 hour with stirring before the reaction mixture is poured into ice water. After this mixture is discharged into ice water, the Alkyl-NENAs will separate as distinct liquid phases in the bottom of the drowning vessel (exception: methyl-NENA which will be precipitated as crystals). The product phase must be separated, and the product washed several times before it is separated and dried.
SUMMARY OF THE INVENTION
It was therefore an object

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