US2384415A - Continuous production and stabilization of nitrates of cellulose or nitrates of other alcohols like starch - Google Patents

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Sept. 4, 1945. E. BERL 2,334,415

CONTINUOUS PRODUCTION AND STABILIZATION 0F NITRATES OF CELLULOSE OR NITRATES OF OTHER ALCOHOLS LIKE STARCH Filed March 27, 1941 Jbll/e): t l quor:

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IN V EN TOR.

ATTORNEY Patented Sept. 4,

con'rmuous PRODU ZATION OF NITRA ON AND ST S 0F CELLULOSE OB NI'IRATES OF OTHER ALCOHOLS LIKE STABCH Ernst Berl, Pittsburgh, Pa.

Application March 27, 1941, Serial No. 385,580

13 Claims. (Cl. 260-220) The continuous production and stabilization of cellulose nitrates or nitrates of other alcohols like starch has been tried rather often but up to now without any industrial success. The diillculties were that the speed of nitration was not high enough so that during a rather short treatment of the material to be nitrated with the nitrating acid it was not possible to introduce the necessary amount oi nitrogen into the molecule of the alcohol. Certain constructions gave nitrates which represented mixtures of nitrates with higher and lower nitrogen content and, therefore, of low industrial value. p The removal of the, spent acid 1 from the nitrated material and the further stabilization took a long time so that the goalquick nitration-and quick, complete elimination oi, the absorbed and adhering spent acid, and

quick stabilization-has not been realized up to now.

It has been found that the following described way represents a solution of this problem. In the same machines in which cellophane is produced, or in other appropriate constructions, dried, thin sheets of permeable paper made from cellulose practically free of foreign substances, like lignin, lower carbohydrates, oils, fats, and ash components, and with a low content of beta and gamma cellulose are introduced in a mixed acid which is composed of nitric acid, phosphoric acid, and a few percent (440%) of free phosphoric acid anhydride. One can at the same time easily introduce several sheets of cellulosic material which are kept separated by rods or any other simple arrangement. The relative movement of mixed acid oi this kind toward the continuously introduced sheets of thiscellulose paper weighing not more than 30 or 40 grams per sq. meter, but preferably only about 20 grams per sq. meter, can be made in counter current or in parallel stream.

The very astonishing fact has been found that then the nitration under formation of a highly nitrated material with about 13.95% of nitrogen can be eiiected in only a few seconds or minutes. Another unexpected effect is that the nitric acid content of this mixed acid which inthe fresh acid may be 50 to 60% can be reduced to a few tenths of a percent in the spent acid during this nitration. No appreciable attack of the formed highly nitrated cellulose through the resulting, nearly nitric-acid-iree, spent acid can be observed. The nitration can be can'ied out at roomtemperature or somewhat elevated temperature (50-70 C.)

without any appreciable degradation of the cellulose molecule. The nitration can be carried out:

also at lower temperatures than room temperature. Then the solubility of the resulting cellulose nitrate is aiiected and partly or wholly insoluble cellulose nitrates can be obtained, in spite of the high degree of nitration. This change in the solubility characteristics may be of importance for the production of certain smokeless powders.

The same results can be obtained with a mixture of water-free nitric acid and glacial acetic acid which may contain some acetic anhydride. This mixture will contain to of an anhydrous nitric acid. It can be used under exactly the same conditions as the mixed acid composed of nitric acid and phosphoric acid and phosphoric acid anhydride at normal, slightly elevated, or at lower temperature.

One can use also mixtures of these mixed acids; in other words, mixed acid composed of nitric acid, phosphoric acid, glacial acetic acid and phosphoric acid anhydride. 7

The reason for the high speed of nitration is the swelling of cellulose and cellulose nitrate in phosphoric acid and iii-glacial acetic acid. This swelling enlarges the internal surface of the material and diffusion and backdiiiusion of acids are facilitated.

The resulting nitrates contain one-half or more percent'of bound nitrogen (13.8.-14.0% N) more than can be obtained with sulfuric acid containing mixed acids (maximum nitrogen content after stabilization 13.3% N). The spent acid can be pressed out by passing the material through rollers so that the nitrated material contains relatively little adheringfspent acid. can be removed very quickly by washing first with cold and then with warm water. Again by passage through rollers, the adhering liquid can be pressed out. I

e The strengthening of spent acid resulting from a treatment of cellulose or other alcohols with phosphoric acid containing mixed acid can be. carried out with strong nitric acid and the addi- 'tion of either P205 or meta phosphoric acid (HPOa) so that the original strength will result. Using nitrating mixtures of nitric acid and glacial acetic acid, the addition of water-free nitric acid, and the addition of I acetic anhydride or ketene brings the spent acid back to the composition of the original nitrating mixture.

It is very remarkable that the nitration process of cellulose or other alcohols with mixed acid composed either of nitric acid, phosphoric acid and free P205 or of nitric acid, glacial acetic acid with or without additional amounts of acetic anquickly under formation of oxalic acid and other 10 organic acids on one hand, and nitrososulphuric acid on the other hand. Therefore, spent acids after several repetitions of nitrations result which are very impure and which give rise to a strong decomposition during subsequent nitrations. Theorganic part is then burned to carbon dioxide and the nitric acid is transformed into dangerous lower nitric oxides. These disadvantages are not observed with these aforementioned mixtures containing phosphoric acid, or acetic acid. or both. This also simplifies considerably the whole process.

It is very remarkable that the stabilization can be carried out very quickly in a very short time (fractions of or several minutes) with pecial stabilization methods because phosphoric acid or glacial acetic acid containing mixed acids do not form mixed esters of cellulose of the type of cellulose sulfato nitrates which results from the nitration of cellulose with sulfuric acid containing mixed acids and which are relatively difiicult to decompose. A treatment with swelling agents like alcohol or with mixtures of swelling and nonswelling agents like alcohol and benzene which are kept at or near the boiling point is sufilcient to remove quickly those substances which cause the instability. Those substances are mostly nitrates of lower carbohydrates which are present in the cellulosic material before nitration. -A.fter repeated treatment with hot alcohol, or hot alcohol-hydrocarbon mixtures, or alcohol-chlorinated hydrocarbon mixtures, and following drying if necessary, one has obtained in a continuous process which lasts only a few minutes completely stable cellulose nitrates which contain up to 13.95% of bound nitrogen. In most cases the alcohol-containing material, after stabilization can be used without the complete removal of alcohol for the production of smokeless powder, plastic masses, etc. The excess of alcohol or alcohol-containing liquid may be eliminated by pressing out or by centrifuging. Through this special kind of nitration and stabilization, the resulting nitrates show a stability which is higher than the stability of the best stabilized cellulose nitrate's made with acids containing sulfuric acid. 'The production of the latter-mentioned stabilized materials takes more than 100 times longer than the processes of nitration and stabilization described in this specification.

It is remarkable that nitrates with very high stability can be'obtained without having those nitrated fibers pulped. The classical stabilization by boiling with .diluted acids and diluted alkalis does not give satisfactory results with long fibers. They have to be cut into short pieces by pulping which costs time and power. These expenditures can be avoided by the use of a stabilization process whereby swelling. but not dissolving, agents remove mixed esters like cellulose nitratosulfates, furthermore, strongly adsorbed mineral acids and nitrates and nitrites of lower carbohydrates, for example. dextrose nitrates.

assure the same machines which are used now for the production of Cellophane, or films, or foils can be used with. relatively small changes for the continuous production of cellulose nitrates in. form of those nitrated and stabilized sheets. For other alcohols, for example, sugar, starch. slic- ,erine, glycol, or pentaerythrite, etc., other approphoric acid which may contain iron and aluminum salts. Comparative experiments have shown that filter cloth made with an acid mixture composed of sulfuric acid, nitric acid and water was destroyed by a treatment with a 70% phosphoric acid at 70 0. within 12 hours, and that filter cloth made with a mixture of phosphoric acid, nitric acid and PzOs, or with glacial acetic acid and water-free nitric acid, showed the same attack after '1 to 14 days under the same conditions of corrosion. These tissues nitrated according to the prescription of this patent specification can be used also with the greatest success as powder bags for military purposes.

The accompanying drawing shows an apparatus for carrying out the continuous process as above described; the scope of the invention, however, is not limited to the particular apparatus shown.

Figure 1 shows a longitudinal section, and

Figure 2 shows a top view of the apparatus.

The apparatus consists of along container divided in compartments for the nitrated bath, for a washing bath (cold or hot) and for a stabilization bath with swelling agents. Transverse rollera are arranged near the bottom and near the top of the compartments for continually conducting through the container a continuous sheet of cellulose material. These rollers are suitably arranged to present a large surface of the sheet to the respective baths. The compartments may also be equipped with baiiies. Inlets and outlets are provided in each compartment for admitting and withdrawing respectively the bath liquids. The hot water bath compartment may be fitted with a steam inlet for heating the water. The

stabilization bath compartment may also be fitted with an outlet for the solvent vapors generated its scope, will readily occur to the expert. The

scope of my invention is therefore deemed to be limited by the appended claims only.

I claim: 1. A process of manufacturing cellulose nitrates comprising treating a cellulose-containing material with a mixed acid comprising water-free nitric acid, water-free phosphoric acid and phosphoric acid anhydride.

2. A process'of manufacturing cellulose nitrates An interesting feature of this process is that 7 comprising treating a cellulose-containing material with a mixed acid comprising water-free.

nitric acid, water-tree acetic acid and acetic anhydrlde.

4. A process according to claim 1, wherein said water-tree phosphoric acid anhydride is present in a proportion of between 4% and 10%.

5. A process of manufacturing cellulose nitrates comprising treating the cellulose-containing material with a mixed acid comprising water-free nitric acid and water-tree phosphoric acid and phosphorous pentoxide whereby the ratio oi nitric acid to phosphoric acid varies between 3:1 and 1:100.

6. In the process according to claim 1, the step of stabilizing the non-pulped nitrated cellulose with a swelling agent.

"I. In the process according to claim 1, the step of stabilizing the pulped ni-trated cellulose with a swelling agent.

8. In the process according toclaim 5, the step of stabilizing the unpulped nitrated cellulose with a swelling agent.

9. In theprocessaccordingtoclaim5,thestep of stabilizing the pulped nitrated cellulose with a swelling agent.

10. A process of manufacturing nitrates of allphatic alcohols comprising treating said alcohols with a mixed acid comprising water-tree nitric acid, water-free phosphoric acid and phosphorous pentoxide.

11. A process of manufacturing nitrates oi aliphatic alcohols comprising treating said alcohols with a mixed acid comprising water-tree nitric acid, glacial acetic acid and acetic acid anhydride.

vl2. A process of manufacturing nitrates of starch. treating said finely divided starch with a mixed acid comprising water-free nitric acid, water-tree phosphoric acid and phosphorous 2o pentoxide.

13. A process according to claim 11, the step of stabilizing the nitrated aliphatic alcohol with a swelling, but not dissolving, agent.

' ERNST BERL.

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