DE1668783C3 - - Google Patents

Description

can be used for a long time without any harmful effects. a formic acid sample in a brown bottle are Heating is continued until the content and at 60 ⁰ C. The color of the heated acid is then reduced to color forming impurities as compared with usual daily standard colors; That the acid finally obtained passes the acid color test as satisfactory. This time varies with the starting material, 5 Color after 168 hours at 60 ^° C. is not darker than the concentration of the impurities present 40 Pt-Co (»Standard Methods for the Examination and the Reaction Temperature. _o f \ v _ate r and Sewage "- 12th Edition American

It was further found that the presence of Public Health Assoc, New York 1960 pp. 111-113). Water in the mixture of acid and urea which since the usual storage conditions significantly increases the effectiveness of the treatment. The water may io are milder than in the accelerated test was festgejederzeit before or during the heating of the mixture is that a color of 40 Pt-Co after 168 hours of acid and urea or after heating at 60 ⁰ C-JE something equivalent is to a color of but before the distillation stage - are added, 20 Pt-Co for longer storage under normal conditions used to obtain the purified acid. 20 Pt-Co is also the one for commercial ones. The amount of water is not critical and the standard required, refined formic acid, usually varies between about 0.25 to 10 weight- The following examples illustrate the pre-

percent of acid to be treated; preferred invention without limiting it: about 0.5 to 3 percent by weight are used.

The method according to the invention provides a pro-Example 1

Pionic acid with a content of oxidizable maleria- 20 in this experiment was semi-refined propionlia of only 0.03% or less. The oxidizable acid from butane oxidation with the following Materials consist of the mentioned unsaturated composition used as the starting material: Compounds and other, low-boiling compounds. _ ".

impurities. One of the main tests for determining propionic acid ηΊ (\ ° /

the purity of propionic acid from oxidizable acrylic acid 0.70 ^

Materials is the hypobromite test. (“Reagent Che- United, low boiling point

micals and standards "- Rosin - 5th edition (1967) compounds U, r" / "

P. 11, D. Van Nostrand Co., Ltd.). According to the tech- ^Was f ^r ······ ■■ ······· · · · ■ ····· °. ⁴ %

The content of oxidizable oxidizable materials (according to Hypo-

Materials in pure propionic acid according to this test 30 (bromite analysis) 0.63 / _o

Do not exceed 0.05 percent by weight. The hypo ^{color in the} sulfuric acid test .... for measuring

bromite test is described below. ^{to dunlcel}

A solution of 15 g of sodium hydroxide in a flask was 600 g of the semi-refined

50 cm ^{3 of} distilled water are produced. For room propionic acid, 12 g of urea (2 ^{percent by weight of the temperature, 6 cm 3 of} bromine are added and the 35 propionic acid) and 30 g of water (5 percent by weight of the solution obtained with distilled water to 2 liters of propionic acid). This mixture was thinned. To carry out the analysis, 100 cm ^{3 are} heated to 122 ° C. for 16 hours, passed into a distilled water, 25 cm ^{3 of} the above sodium hypodermic device with an Oldershaw column with 45 plates of bromite solution and 10 cm ^{3 of} a 20% aqueous solution and distilled As head material, formate-free sodium solution in the specified 4 ° 10% by weight of the charge was collected in a reverse sequence in two alder flow ratios of 10: 1 provided with glass stoppers and discarded. meyer flask. The remaining 83% of the charge is placed in a flask with 10 cm ^{3 of} the propionic acid sample; the second of the distillate was at a reflux ratio flask serves as a comparison. The two flasks are collected by 3: 1. The purified propionic acid had left to stand for 15 minutes at room temperature, a content of oxidizable materials of 0.05% then 5 cm * 25% aqueous and, in the sulfuric acid test, a color of only potassium iodide and 10 cm ^{3 of} concentrated hydrochloric acid 10 pt. Co.

given. Then 0.1 n sodium thiosulphate up to Example 2

titrated to disappear the brown color and

the percentage of oxidizable materials according to 500 g of that described in Example 1, half of the determined using the following formula: refined propionic acid was admixed with 10 g of urea

and the mixture at 125 ° C for 120 hours.

% oxidizable material = ~ ' ''kept. Then 25 g of water were added and the

10 specific gravity mixture at 100 mm Hg by an Oldershaw

⁵⁵ column with 45 trays means distilled. As head material

^ cm 'of N-normal- required for the sample was 117 g at a reflux ratio of 5: 1 Mg ^ nmtMAciht ». collected and discarded. Then one

B = SÄE ^ Äikich ^ robe necessary reflux ratio of 2: 1 a main run of 328% N-normal sodium thiosulphate. _β Der obtained by Natrmmhypobrpm ^ analysis

60 certain oxidizable content of propionic acid

The presence of color-forming bodies in the materials was 0.05%; the color in the sulfur propionic acid is determined by the 6 cm ³ acid test was 10 Pt-Co. 98% sulfuric acid at 2O ⁰ C to 100 cm ³ of Example 3

Propionic acid is added and then after 1 hour

20 ⁰ C formed color with a set of standard colors 65 To 500 g of the half-compared, refined propionic acid described in Example 1 were added 10 g of urea and the presence of 25 g of water with formic acid. The mixture of impurities that formed was then determined by heating to 125 ^° C. for 120 hours and then at 100 mm Hg

distilled through a 45 tray Oldershaw column. After removing and discarding a head material of 114 g, the main run was 308 g refined propionic acid collected. According to the sodium hypobromite test, this material contained only 0.03% oxy- dable materials; the color in the sulfuric acid test was only 5 Pt-Co.

Example 4

To 2000 g of the semi-refined propionic acid described in Example 1, 40 g of urea and 100 g of water were added, the mixture was heated to 123 ° C. for 24 hours and then passed through a at 100 mm Hg Oldershar · column with 45 trays distilled. That at 224 g of overhead material removed at a reflux ratio of 10: 1 was discarded; total were then 1625 g of purified propionic acid were collected at a reflux ratio of 2: 1. This main fraction contained 0.04 per cent oxidizable materials Sodium hypobromite analysis; the color from the sulfuric acid test was 10 Pt-Co.

Example 5

50 g of water and 20 g of urea were added to 1000 g of the semi-refined propionic acid described in Example 1, the mixture was ^{heated to 115 to 120 °} C. for 144 hours and then passed through a filled column of 60 cm length and a diameter of 2.5 cm distilled. After removing 104 g of the top fraction, a main fraction of 758 g of purified propionic acid was collected. This material contained 0.03% oxidizable materials according to sodium hypobromite analysis; the color in the sulfuric acid test was 10 Pt-Co.

Example 6

In this experiment, crude propionic acid was used as the bottom stream from the acetic acid distillation column butane oxidation was used. This raw material had the following composition:

Propionic acid 73.27% Formic acid 0.11% Acetic acid 9.75% * ⁵

Water 0.02%

United butyrolactone, acrylic acid, butyric acid and low boiling materials 16.33%

Oxidizable materials 0.78% Color in the sulfuric acid test for measuring

too dark

10 g of urea and 25 g of water were added to 500 g of this crude propionic acid, the mixture Heated to 122 ° C for 24 hours and passed through an Oldershaw column at 45 trays at a pressure of 150 mm Hg distilled. As head material, 96 g was removed at a reflux ratio of 10: 1 and discarded. The propionic acid fraction, weighing 279 g, was distilled at a reflux ratio of 3: 1. This purified propionic acid had an oxidizable material content of 0.05% and less Sulfuric acid color test has a value of 10 Pt-Co.

Example 7.

The method according to the invention was carried out continuously in the laboratory. The starting point The semi-refined propionic acid used had the following composition.

Propionic acid 97.2% Acetic acid 0.85% Acrylic acid 0.68%

Water 0.40%

Combined, other impurities 0.77% Oxidizable materials 0.80% Color in the sulfuric acid test for measuring

too dark

Two 5-1 flasks equipped with stirrers and condensers were so connected that the first overflowed into the second; the second piston was in turn attached to one Point 10 trays or the tray attached to the side of an Oldershaw column with 40 trays.

A solution was made from the above semi-refined propionic acid and 2% urea and 2% water. The flasks were charged with 7,130 g of the propionic acid-urea-water solution and ^{heated to 125 °} C. for 36 hours. Thereafter, the temperature was kept at 125 ⁰ C, while in addition propionic acid-urea-water solution at a rate of 105 ^, 'hours. was pumped into the first flask. This resulted in an average residence time of 35 hours in the reaction vessels. When the solution was pumped into the first flask, solution flowed at the same rate into the second reactor and from there into the distillation column. The latter operated at 150 mm Hg with a reflux ratio of 10: 1. About 10% overhead material was removed and the residue, consisting of purified propionic acid, was withdrawn from the bottom of the column at a steady rate. According to analysis, the purified propionic acid obtained in this way has an oxidizable material content of only 0.05% in each case at 7.5, 23, 32 and 48 hours after the start of charging to the distillation device; the color in the sulfuric acid test was 10 Pt-Co.

Example 8

Semi-refined propionic acid of the following composition was used in this experiment:

Propionic acid 98.2% Content of oxidizable Materials 0.63% Sulfuric acid color test for measuring

too dark

Then urea was added to a concentration of 2 percent by weight of the propionic acid Mixture was heated and sampled, distilled and tested at various times. the Results were as follows:

P Ii t

Reaction
time
hours Content of
oxidizable materials
in the product
% Sulfuric acid test 0
3
16
40 0.63
0.34
0.10
0.06 fails
fails
passed
passed

The addition of 1% urea for this semi-refined propionic acid at 8O ⁰ C followed by the immediate

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Vacuum distillation; thus became a distilled propionic acid containing oxidizable materials of 0.60% obtained. The sulfuric acid test gave a dark color.

The addition of 2% urea and 5% water to the semi-refined propionic acid at 146 ° C was followed by the immediate vacuum distillation to give a product with an oxidizable material content of 0.13% which developed a dark color in the sulfuric acid test.

If 2 % urea was added to this semi-refined propionic acid and the mixture was heated to various temperatures for 4 hours, the content of oxidizable materials decreased as the heating time increased; however, the propionic acid obtained did not pass the sulfuric acid color test.

temperature
⁰ C Content of
oxidizable materials
in the product
% Sulfuric acid test 75
135
141 0.57
0.14
0.07 fails
fails
fails

Even the use of 5% urea did not provide propionic acid, which after 4 hours of heating Sulfuric acid color test passed. Although in this case the oxidizable material content of 0.63% was reduced to 0.07%, the color-forming impurities were not removed.

The results of Example 8 and in the part immediately above show that a propionic acid With a low content of oxidizable materials that only passes the sulfuric acid color test Using both urea and a longer heating time can be obtained. Although the addition of urea alone in some cases, without the heating stage, increases the content of oxidizable substances Seems to decrease materials, the propionic acid obtained passes the sulfuric acid color test not.

Other additives such as sodium acetate, zinc chloride, ammonium chloride, aqueous ammonia, dilute sulfuric acid, air, etc., may be present in the propionic acid mixture, but they showed no advantage over the method described.

In an experimental pair in which to the semi-refined crude acid used in Example 8

2% urea and 5% water were added, the mixtures were ^{heated to 125 °} C. for 96 hours and to 120 ^° C. for 144 hours. The purified propionic acid was recovered by atmospheric distillation; these acids had an oxidizable material content of 0.02 and 0.03%, respectively. Both passed the sulfuric acid color test.

Example 9

In a flask was placed semi-refined formic acid of 99.5% purity containing a total of about 0.5% acetic acid and water and about 20 parts per million of unknown color-forming impurities and 2% by weight of urea was added. The mixture was ^{heated to 100 °} C. for 1 hour and then distilled to obtain purified formic acid. The acid was checked for the presence of color-forming impurities

ao the procedure described above. As a comparison, the untreated, semi-refined formic acid was tested at the same time. The results are summarized in Example 10.

Example 10

A mixture thereof, semi-refined formic acid with a content of 1% urea and 2% of added water was heated for 1 hour at 10O ⁰ C, distilled and tested for the presence of color-forming impurities. The results are summarized in the following table:

Pt-Co color
after heating control 9 example 10 ,. to 60 ° C for 10 0 0 hours 40 24 hours 50 48 hours 80 20th 5 ⁴⁰ 72 hours .... 1-Gardner 25th 10 96 hours - 40 15th 240 hours -

The data show that the control failed the color test immediately after the start of the experiment, and after After 72 hours of heating, the Pt-Co paint series could no longer be used; it was the essential one darker Gardner range of standard colors necessary. The formic acid purified according to the invention did not develop unsatisfactory color even after 240 hours (10 days) of heating.

Claims (1)

1 2 initially obtained raw material usually has a propionic acid content below about 75 percent by weight So far, propionic acid was made by reacting with Process for the purification of formic acid or an oxidizing agent such as potassium permanganate ge-propionic acid by means of urea in the heat, 5 cleans This method is, however, inexpedient d a d u r c h e k e η η ζ e i c h η e t that one of the large amounts of oxidizing agent are necessary The acid to be purified is urea in a concenic acid and the propionic acid with the metal compound underneath Tration of 0.2 to 5 percent by weight and, if necessary, the formation of the corresponding metal propionate up to 10 percent by weight of water is yawing. adds a mixture composed of formic acid and urea from German patents 866 78b 869 070 for at least 0.25 hours to 883 605, and from German Auslegeschrift 1050 770 a temperature of 40 to 150 ^° C. or a process known for the separation of high molecular weight propionic acid and urea mixture of straight-chain aliphatic compounds by means of at least 16 hours to a temperature of urea. These reactions produce 120 to 150 ⁰ C heated with stirring and then 15 inclusion compounds, the formation of which is essentially the pure acid by fractionation Distillation borrowed physical forces are effective, i.e. none wins. Reaction takes place in the chemical sense, inflammatory accordingly, on the other hand, there is a reaction of urea with the impurities, including unsaturated ones -, ο connections, while the latter in the known process remain unchanged. In the German patent specification 1 132 911 a In common methods of making ants, methods of purifying 2 to 4 carbon atoms acid and propionic acids by oxidation of aliphatic-containing saturated fatty acids by treatment Typical alkanes are formed in complex mixtures, 25 with hydrogen in the presence of a hydrogenation die then described by a series of extractions catalyst and under pressure. To that and distillations into their individual components must, however, make processes economical be separated. So in the oxidation aliphatic the catalysts will be recovered, for which purpose Typical alkanes of 3 to about 6 carbon atoms are required in costly recovery. In the liquid phase, a mixture is obtained which essentially plays a role in catalytic processes of this type borrowed from acetic acid and other acids, including the poisoning of the catalyst during the Contains ethers, ketones or aldehydes. This mixture reaction plays a big role. According to the invention These problems fall through complex extractions and distillation, since such a catalyst does not tions are separated, which is also used, among other things. Formic acid and propionic acid obtained - verden. The subject of the present invention is a These two acids are usually obtained in a process by which formic acid or propionic purity of over 95%, but acid of improved purity and free from color-forming, the refined, distilled acids still contain minor impurities is obtained.
Amounts of undesirable impurities caused by the inventive method for purifying the usual extractions and distillations not 40 formic acid or propionic acid using urea in can be removed. the warmth is characterized by the fact that the The acid to be purified, obtained in this way, contains urea in one concentration acid trace amounts of unknown impurities from 0.2 to 5 percent by weight and optionally up to conditions that add an undesirable 10 percent by weight of water during storage, one out Cause color formation. All previous attempts 45 formic acid and urea existing mixture to remove these impurities were without at least 0.25 hours at a temperature of Success, so that the formic acid obtained in this way in 40 to 150 ° C or one from propionic acid and urine Uses were limited. existing mixture for at least 16 hours The propionic acid obtained from the hydrocarbon oxidation by distillation at a temperature of 120 to 150 ^° C. with stirring contains impurities and then the pure acid by fractions, which, after the addition of sulfuric acid, wins a neat distillation. form brown color. Furthermore, the distilled The amount of urine required according to the invention Propionic acid some impurities with boiling matter depends on the points of presence in the starting material very close to that of propionic acid, the amount of impurities. Usually amounts to which therefore by physical cleaning measures 55 they are at least about twice the stoichiomenon be completely removed from the propionic acid tric amount of the total amount present be able; their presence in these small amounts of impurities. The additives used prevent that the propionic acid the commercial concentration is preferably between about 0.25 to Regulations. The main constituents present are 2 percent by weight. The impurities are acrylic acid and unsaturated acids. 60 The pressure used in the reaction is not tones, such as methylpropenyl ketone and methylbutenyl- crucial, and the reaction can take place at atmospheric ketone, together with other, low-boiling, verical or superatmospheric pressure impurities. The semi-refined, distilled Propion- are led. acid usually contains about 0.5 to 1% acrylic acid. and about 0.01 to 0.3% unsaturated ketones and others, 65 preferably between about 30 minutes to about 24 hours of low boiling point Impurities. Although this that that what depends on the temperature used; in general, in the distilled propionic acid in propionic acid in particular about 16 to 40 hours, areas of contamination are found, the In both cases, prolonged heating