DE721300C - Process for the separation of water from liquids containing water and formic acid with high formic acid concentrations - Google Patents

Description

Process for the separation of water from water-formic acid High Formic Acid Liquids The removal of water from hydrous Formic acid causes difficulties because these two substances are known to be one Form high-boiling mixture (Kp7oo 107, z °, 22.5o / "water). For separating the water and for the production of high-percentage or anhydrous formic acid (bp, oo ioo, 47 °) one has proposed numerous methods based on the most varied of principles are based. Also the use of auxiliary materials, the low-boiling mixtures with water form, one has given for the purpose of azeotropic drainage. Already the multitude of the methods and numerous variations of each method cover that difficulty of the problem.

The surprising observation has now been made that the isopropyl formate excellent for azeotropic dewatering of water-formic acid Liquids of high formic acid concentration are suitable; Isopropyl formate from Kp.ZO 66 ° forms a low-boiling mixture with water of KP ... 62 °, because at Room temperature 4. Separate volume percent water. This separated water is practically free from formic acid, even if the water content is that to be dehydrated Formic acid is very small.

Formic acid esters are particularly easy to use because you can use them does not need to be prepared beforehand, but by simply adding the alcohols to the can produce aqueous formic acid by esterification, since formic acid esters are known arise from the components very easily. Of course, you can also use the finished one Esters going out.

Isopropyl formate significantly outperforms similar substances that have already been used for the dehydration of formic acid. The table shows comparative tests which have been carried out with the formic acid esters of various lower alcohols and which show the great superiority of isopropyl formate. In each of the two comparative experiments, 300 g of 76.30 /, i'-formic acid were boiled with 60 g of the alcohol in question for 1 hour until esterified and then distilled with the aid of a column 50 mm in length and 40 mm in diameter. The distillate separates into an ester layer, which runs back into the boiling vessel, and an aqueous layer. The latter was collected in portions of 10 cc and the free formic acid content was determined. The columns of the table indicate the distillation times in minutes, calculated from the beginning of the experiment, and the percentages of formic acid in each 10 cc of the separated annual layer. n-propyl formate n-butyl formate @ see-butyl formate 'i-propyl formate i-propyl ether Low boiling temperature 5 to; 6 ° 8o to 8 - ° do to (gf: ° 62 ° 6o to 6d, ° Minutes I minutes "minutes @" minutes minutes., . Water fraction i ... 25 0.35 20 20.9 30 0.46 25 o, 18 17 o i 18.4 - 2 ... 40 1.38 35 26.1 5o! 1.14 45 o, 16,300 1 28.1 - 3 .. 65 8 45 35.4 7o 8.48 85 o, 16 - 4 .. 2o5 2 7.75 65 32.6 go 1o, 3 12o o, 15. - 5 .. 9 o 354 i 12o 16.45 16o ,, o, 32 I. - 6 ... io5 36.7 16o 19.6 225 1.24 -. . i 225 2O, 8,390 2.1 Eth -, - lformate gives only traces of water separation. In the case of n-propyl formate, no separation of an aqueous layer took place on further distillation due to the high formic acid content in the distillate. Also i-Propylätlier, which does not belong to the group of esters. which is also a derivative of i-propyl alcohol, behaves in the same way.

The tests were carried out under the same conditions as possible; the column is deliberately chosen with only modest effectiveness. The experimental set-up is made in such a way that the effectiveness of the distillation is just sufficient, the binary To form mixture of isopropyl formate and water; at the same time -tends that the binary The mixture is formed during the entire distillation period, but the distillation residue is still present very poor in water. In contrast, other formic acid esters such as n-propyl fortnate form and sec-butyl formate, only initially an approximately pure binary mixture. As soon as however If there is less water in the distillation residue, the effectiveness is sufficient the column no longer, an almost pure low-boiling mixture, consisting of your Esters and water. Formic acid is found in increasing amounts in the aqueous The distillate layer accumulates until so much formic acid passes into the distillate, that there is no longer any separation of layers. In the case of the n-butyl formate, At the beginning a strongly formic acid-containing boiling mixture was formed. n-propyl formate has already been proposed for azeotropic dehydration of formic acid. Around to achieve the same thing with this aid or the other formic acid esters as with isopropyl formate, the columns are much more efficient and the work of distillation is increased necessary. The direct comparison under the severe conditions of the experiment shows the great superiority of isopropyl formate.

The formic acid content of the aqueous layer is then clear Comparison of the effectiveness of the various substances and proves their superiority of isopropyl formate via similar substances. If one continues the experiment with isopropyl formate going any longer, practically all of the formic acid is obtained in anhydrous form Conditions. This goal is achieved much more easily when using more highly effective Distillation columns, as are customary for such fractionations.

The azeotropic distillation with isopropyl formate is now also Extremely useful for esterifying alcohols with formic acid. Isopropyl formate itself can easily be obtained in pure form by distillation the components in the molar ratio and separation of the water from the distillate. So far you have z. B. for alcohols with boiling points that are higher than those of the Formic acid, initially finite excess aqueous formic acid, for example from about 75 ', 0. corresponding to the high-boiling mixture of formic acid and water, heated, until equilibrium was reached. Then you have the aqueous formic acid distilled off and further esterified with excess 95% formic acid, water-containing formic acid is again distilled off and now the esterification is still a few Repeated times with 100% formic acid. You had to do this cumbersome and wasteful Accept the way you work if you are fairly well-educated Esterification wanted to achieve, since the foriniate is often difficult to separate from the associated alcohols are.

By using: the method of manufacture according to the invention from anhydrous formic acid to esterification reactions with formic acid succeeds it, .with almost the theoretical amounts of formic acid, quantitative esterifications of alcohols to perform. You only need the esterification mixture for the Adding the necessary amount of isopropyl formate to a distillation column or the necessary amount of isopropyl alcohol and the corresponding excess of formic acid to use; Esterification catalysts can be present.

Amotropic esterifications with formic acid: I n-butanol (column iooommlong, 5ommZ, without catalyst). 370 g n-butanol. (= 5 mol) -f- 345 g formic acid (= 7.5 mol) + 1 g isopropyl formate.

Water theor. = 9o g, found = 90 g in 2s / 4 hours with o, i2 ° /, acid, 100% esterification.

II n-hexanol (column 100 mm long, 50 mm-0 ", without catalyst). 3o69 n-hexanol (= 3 mol) -E- 152 g formic acid (= 3.3 mol) + 180 g isopropyl formate.

Water theor. = 54 g, found = 54 g in 11 / "hours, acid-free, 100% esterification. III Technical cetyl alcohol (equiv. Wt. = 2 10.6) (column 100 mm long, 50 mm X # ', without catalyst) g technical cetyl alcohol (= 0.85 mol) + 43 g formic acid (= 0.94 mol) + 180 g isopropyl formate.

Water theor. = 15, q..9, gef. = 15.5 g in 2 hours, acid-free, 100% esterification, techn. Cetyl formate Kplo 1.6o to 218 °, at ordinary temperature soaked with oil: IV benzyl alcohol (column 300 mm length, 20 mm -0 ', without catalyst). 54 g of benzyl alcohol (= 0.5 mol) + 28 g of formic acid (= 0.6 mol) + 50 g of isopropyl formate.

Water theor. = 9 g, found = 9 g in three and a half hours as an average of 10% acid, 100% esterification. -V ethylene glycol. With an excess of 70% formic acid, 100% esterification was achieved using 511 % toluenesulphonic acid as catalyst and isopropyl formate as auxiliary liquid.

VI glycerine. With 50% excess formic acid and 30/0 toluene: sulfonic acid as a catalyst and isopropyl formate as an auxiliary liquid was 100% esterification achieved.

The degree of esterification is always determined by determining the esterification number ,controlled. In the case of ethylene glycol and glycerine, esterification took place without a catalyst only very slowly forward, so it was with the help of catalysts quickly brought to an end. A 100% esterification can also be approximated with the theoretical amount of formic acid excess can easily be achieved if you have a slightly takes longer response times into account.

The formic acid dehydration and esterification reactions described can be modified in detail in many ways, for example by the aqueous formic acid or the esterification mixtures into the distillation column or other parts of the system and below: dehydrated formic acid or Formic acid ester withdraws. The reactants can also go to the still be submitted. The method is intended to have the usual variants and embodiments these basically known reaction procedures include.

It has been proposed to use lower fatty acids from aqueous solution Isopropyl ether in a mixture with esters, i.a. also isopropyl formate, to extract. This method is suitable to approximate the fatty acids from their dilute solutions Isolate anhydrous, but it is not usable to use formic acid with a low water content to be freed from water, as highly concentrated formic acid with isopropyl ether and Isopropyl formate is miscible.

Claims (1)

PATENT CLAIM: Process for dewatering liquids containing formic acid by azeotropic distillation using a propyl ester of formic acid, characterized in that from liquid mixture, ischen, formic acid and Contain water with high formic acid content or in those with the presence of formic acid Water is formed chemically, the water with the help of isopropyl formate removed solely by known azeotropic distillation