US1950875A - Process for the vaporization of formamide - Google Patents

Description

March 13, 1934. H. A. BOND PROCESS FOR THE VAPORIZA'I'ION OF PORMAMIDE Filed July 9, 1931 INVENTOR. W A. B01707 Patented Mar. 13, 1934 UNITED STATES PATENT FFIQE PROCESS FOR THE VAPORIZATION OF FORMAMIDE Application July 9, 1931, Serial No. 549,585

Claims.

This invention relates to the vaporization of formamide and more particularly to the vaporization of formamide from metal Vaporizers.

" Because of its high boiling point, around 200 U C. at atmospheric pressure, and because of the decomposition of formarnide into carbon monoxide and ammonia, when heated, the problem of vaporizing formamide has heretofore presented considerable diiiiculty. To avoid this decomposition it has previously been proposed to vaporize formamide at reduced pressure and it has further been proposed to vaporize formamide from surfaces heated above 215 C. without allowing the substantial accumulation of liquid forniamide on the vaporizing surface. The heretofore proposed methods of vaporizing formamide are costly, require more or less elaborate apparatus, necessitate careful control and therefore are not entirely satisfactory. Although the decomposition is small, solids stick to the hot surface and heat conduction becomes poor. Moreover, there is tendency when the liquid strikes the hot surface for it to agglomerate in droplets which evaporate with explosive effect and give uneven evaporation.

One object of this invention is to provide a process for vaporizing accumulated liquid formamide from a metal surface without appreciable decomposition of the formamide and at substantially atmospheric pressure. A further object of this invention is to simplify and improve the vaporizing of formamide. Further objects will be apparent hereinafter.

The invention comprises vaporizing formamide from a heat conducting surface upon which said formamide is allowed to accumulate in a shallow pool which covers a substantial portion of the surface. Metal surfaces are particularly useful since their rate of heat conduction is greater than that of other materials.

The accompanying drawing shows in crosssection an apparatus suitable for carrying out the process of this invention. Referring to the drawing 1 is a metal base plate in which are embedded electrical elements 2. Metal cover 3, of such construction as to form a vapor space 10, is flanged on top of base plate 1. 4 is an inlet pipe for liquid formamide having its terminus 5 within the cover 3 and close to the base plate 1; 6 is an outlet pipe for formamide vapor; several openings as at 7 are provided in the base plate in which thermocouples or other temperature measuring devices may be inserted; 8 is a well of metal extending into the outlet tube into which a thermometer 9 is inserted.

The invention will now be further described in terms of the accompanying drawing.

Liquid formamide is flowed into the vaporizer through pipe l and spread as a shallow pool over a portion of the massive base plate 1, which is heated by means of heating elements 2 to a temperature of preferably between about 200 to 400 C. The vaporizer is tilted or sloped toward the liquid inlet at an angle of a few degrees so that the liquid accumulates near the inlet end; this tilting or slope will cause a uniform horizontal or transverse spread of liquid and favor the formation of a shallow pool with its deeper portions near the inlet end. It will be found in general that the shallow pool of liquid formamide may cover a substantial portion of the vaporizing surface and may cover the entire surface. The temperature of the vaporizer plate near the inlet end will ordinarily be maintained at about the boiling point of formamide, while nearer the exit end the temperature may be considerably higher, it may attain 300 to 400 0., or even more, on those portions of the vaporizer surface which are not covered by liquid. I prefer to vaporize at temperatures of 200-400" C.

To further clarify the invention, a specific example is given below, which however, should not be taken to limit the invention to the specific details shown therein.

Example An apparatus similar to that shown in the drawing was employed consisting of a forged aluminum base plate 2" thick by 12" wide by 24" long. 12 nichrome heating elements extending transversely through the base, having a capacity of about 2 kilowatts each at 110 volts were uniformly spaced lengthwise of the base plate and embedded therein. The formamide was introduced through an aluminum pipe in diameter which terminated above the base plate 1. The outlet pipe for formamide vapor was also aluminum and was 1%" in diameter.. Two thermocouples were inserted in the holes provided in the base plate of the vaporizer, one near the inlet end and a second beyond the edge of the liquid pool of forrnamide accumulated in the vaporizer. The apparatus was tilted at an angle of about 2 toward the inlet end. The entire vaporizer was thoroughly insulated with powdered magnesia contained in a rectangular sheet iron shell surrounding the vaporizer.

A thermometer was inserted in the well at the outlet end to measure the temperature of the formamide vapor produced. Liquid formamide vapor per day.

was flowed into the apparatus at the rate of 142 grams per minute and formamide vapor collected therefrom at substantially the same rate. Vaporization was carried out at substantially atmospheric pressure. The temperature near the inlet end and beneath the accumulated pool of formamide varied from 195 to 210 C. Tests indicated that about to of the vaporizing surface was covered by the liquid formamide. The average temperature of the vaporizer beyond the point occupied by the pool of formamide was 374 C. varying from 365 to 395 C. in a series of measurements. The average temperature of the vapor in the outlet pipe was 280 C. This temperature is the average of several taken over a one hour period. Tests on the percentage decomposition of formaniide in apparatus of this type have shown that the loss was in all cases less than 1.5% and frequently as low as 0.5%.

While the apparatus has been described as made of aluminum, other metals which do not deleteriously affect the decomposition of formamide, for example copper, brass, iron or steel may be used. A metal surface covered with an adherent nonreactive thin oxide layer, for example, ZnO or A1203 may also be used, subject to the same restrictions. Good heat conducting surfaces are preferable.

The dimensions of the vaporizer will depend upon the scale of operation desired. I prefer to employ a relatively massive metal base plate to facilitate heat transfer and ballast and to introduce the liquid at one or more points close to the surface of said vaporizer base plate to avoid uneven spreading and spattering. The heating elements should be spaced and otherwise arranged to produce a uniform temperature over the vaporlzing surface. I have found it advisable to so arrange them that when the apparatus is empty various parts of the vaporizing surface will not show more than to C. difference in temperature when heat is applied.

The apparatus described above is capable of vaporizing up to 500 lbs. or more of forrnamide This vaporizer is serviceable for any amount of vaporization up to its full rated capacity which will be attained when the entire vaporizing surface is substantially covered by liquid. The temperature of the vaporizing will depend on the amount of formamide present and the rate of heat supply; if correct, this rate of heating should be such that should the formamide input cease such liquid as remains on the surface will be completely evaporated within 5-10 minutes. The temperatiu'e may also be adjusted by heating so that portions of the vaporizer surface not covered by liquid formamide will not in general exceed 400 C., i. e., the surface of the vaporizer will vary from about the boiling point of formamide up to about 400 C. The rate of heating should permit vaporization to take place at a sufficient rate so that the liquid formamide does not remain exposed to high temperatures for periods of more than 5 to 10 minutes and preferably not more than l-2 minutes, since otherwise the rate of decomposition, which is of the order of 1 to 2% per minute, may become excessive.

The advantages of this process he in its simplicity of operation and in the effective and speedy evaporation of formamide without substantial decomposition losses due to the formation of carbon monoxide and ammonia. It is particularly useful where a rapid supply of substantially pure formamide vapor is desired. It has been found to give excellent results when. used in connection with a converter such as that described in U. S. P. 1,675,366, wherein said vapors are converted to hydrocyanic acid and water by a process requiring formamide of high purity.

I claim:

1. A process for vaporizing formainide comprising maintaining a shallow pool of formamide over a substantial portion of a surface heated to a temperature above the atmospheric boiling point of formamide.

2. A process for vaporizing formamide comprising flowing liquid formamide over a metal surface heated to 200 to 400 C., and continually maintaining a shallow liquid pool on a substantial portion of said surface.

3. A process for vaporizing formamide comprising flowing liquid formamide over an aluminum surface heated to 200 to 400 C. and continually maintaining a shallow pool on a substantial portion of said aluminum surface.

4. In the vaporization of formamide the step comprising exposing said formamide in a shallow pool to a heated metal surface selected from the group consisting of aluminum, brass, copper, iron and steel.

5. In the vaporization of formamide the step comprising exposing said formamide in a shallow pool to a heated metal surface selected from the group consisting of aluminum, brass, copper, iron and steel, said surface being coated with a thin adherent non-reactive oxide layer.

I-IARLAN A. BOND.

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