DE2123181C3 - Boric Acid Recovery - Google Patents

Description

The result relates to a process for continuous P-recovery of the boric acid used as catalyst in the cyclohexane oxidation from the aqueous Phase of the product mixture obtained after hydrolysis of the reaction mixture by extraction with Oxidation products of cyclohexane oxidation or mixtures thereof.

It is known that the partial oxidation of cyclohexane with atmospheric oxygen in the presence of Boric acid obtained reaction mixtures are then hydrolyzed and saponified. From the organic jo In the phase of these reaction mixtures, a pure cyclohexanone / cyclohexanol mixture is obtained by distillation. For example is in U.S. Patent 32 43 449 a such procedure is described.

During the hydrolysis of the reaction mixture, the Most of the boric acid was recovered from the aqueous phase. A smaller part of boric acid will do However, it is lost because a certain amount of hydrolysis water is removed from the hydrolysis cycle because of the in this water dissolved and enriched organic 4η see impurities (cycloliexanediols, mono- and dicarboxylic acids) must feed out. From the Dutch Patent specification 67 06 296 it is known that such compounds by by-product formation in the Reactors reduce the selectivity of the oxidation. Hence the so-called mother liquor discharge inevitable. The dissolved boric acid is lost if no suitable measures are taken Recovery can be taken.

Two methods are known for recovering boric acid from the mother liquor:

D ₁ ¹ S first method is described in French patent specification 15 72 834 and consists of crystallization and subsequent centrifugation. However, this procedure is disadvantageous since the crystals obtained from the mother liquor are not very pure. The Dutch patent specification 67 06 296 can be seen, for example, that a certain percentage of organic carbon in the boric acid must not be exceeded. With the normal recovery of the major part of boric acid from the circulating water of the hydrolysis by crystallization and centrifugation, it is possible to remain below this limit without difficulty. The crystals that are obtained from the mother liquor by this process (ή, however, are too unclean to be added directly to the reaction; therefore post-treatment, e.g. washing, is necessary.

If you want the above-mentioned difficulties and the not inconsiderable costs of a crystallization system around, a second method can be used. It consists of a selective extraction the above-mentioned impurities (organic acids and diols) from the hydrolysis circuit water. This has the effect that significantly less mother liquor is fed out, and the boric acid losses decreases. Such an extraction process is described in Belgian patent 6 33 933. the entire aqueous phase, containing d-.e-mentioned boric acid and some of the organic impurities from the reaction, is treated extractive between hydrolysis and crystallization Extracting agent a ketone or an alcohol, preferably cyclohexanone or cyclohexanol, is used.

A disadvantage of this procedure is that all of the hydrolysis water is subjected to Extraktio.i and therefore correspondingly large amounts of extractant are obtained for work-up. Another The disadvantage is that a second circuit is necessary and thus the outlay on equipment enlarged. In addition, the greater the extractant content, the greater the loss of boric acid the extra medicine.

There has now been a process for the continuous recovery of Jer in the cyclohexane oxidation as Boric acid used as the catalyst from the aqueous phase of the after hydrolysis of the reaction mixture resulting product mixture by extraction with oxidation products of the cyclohexane oxidation or their mixtures and recycling of the purified aqueous phase found, which is characterized is that after hydrolysis of the reaction mixture, the aqueous phase is concentrated. Boric acid through Crystallization separates and separates and extracted a partial stream of the filtrate.

The advantages of this procedure can be seen in the fact that much smaller amounts of extractant and much less expensive apparatus can be used. Another benefit is there in that a bottom product from the cyclohexane oxidation plant is used as the extractant instead of a distillate can be used. That made up of cyclohexanol (88%) and cyclohexanone (7%) has lower-boiling components (1%), such as alcohols and higher-boiling fractions (4%), such as esters, diols, ethers, the same good extraction properties like the distilled bottom product, a mixture of cyclohexanol (92%) and cyclohexanone (8th%).

In contrast to the last-mentioned product mixture, the extractant used according to the invention is used not subjected to distillation or other energy-consuming purification to recover it. The extractant is added to the saponification where it is combined with the organic phase from hydrolysis is treated with alkali. All acids and some of the diols that are normal with the Mother liquor discharge are discharged, then go together with the others, less or not water-soluble acids as dissolved sodium salts from the saponification in the wastewater. The remaining diols are removed in the distillation.

In order to clarify this procedure and to give a complete overview, we will use one The flow diagram describes the plant with the attached extraction apparatus. The parts of the Method that does not directly affect the invention

concern appropriate procedures.

Cyclohexane is conveyed via line 10 together with meta-boric acid from line 26 to reaction part 1 pumped, where it is partially oxidized with air. The product stream with unreacted cyclohexane, Cyclohexanol, cyclohexanol boric acid ester, cyclohexanone and impurities go through line 11 together with fresh water 12 and hydrolysis circuit water 13 zi'Ki hydrolysis part 2. After separation is the organic phase via line 14 to the saponification section 3 pumped There it is washed with an alkali solution over LeKung 15. After depositing and separating the aqueous alkali solution via line 16, the organic phase is pumped to the cyclohexane column 4. The unreacted cyclohexane is recovered and returned to the reaction via line 20. The bottom product 18 is subjected to an initial distillation 5 and a residue separation 6 by distillation. Pure distillate is via line 22, lead substances are via line 21 and Residues discharged via line 23. The boric acid is recovered after separation in the Hydrolysis part by crystallization 7 and centrifugation 8.

From the water cycle of the hydrolysis via lines 24, 25, 13 and 12, a partial flow 27 is formed so-called mother liquor, discharged The modification of the method according to the invention relates to the Extraction system 9 switched on after discharge. The extractant is switched on and off via line 29 Recirculated via 30 The purified mother liquor runs via line 28 back into the water cycle.

The following examples serve to explain the process in more detail.

Example I.

8 kg reaction product the cyclohexanol, cyclohexanol boric acid ester, Cyclohexanone, cyclohexanediols and organic acids are kept at 80 "C for 15 Stirred minutes with 4,000 kg of hydrolysis water from the system. The water contains 7% boric acid and has the Acid number 28. After separation, 7.8 kg of 5 organic phase and 4.13 kg of aqueous phase with 17% are obtained Boric acid and an acid number of 32. Approx. 1.3 kg are distilled off from this solution; i.e., it is narrowed, until a mash with 25% boric acid is obtained. It is filtered warm (45 ° C). 100 g of the filtrate (8.5% boric acid;

ίο acid number 31) are seven times with 35 g of bottom product stirred at 50 ° C. for 15 minutes. After the last separation there are 90 g of aqueous phase 8.2% boric acid and acid number 5, and a total of 255 g of organic phase. These 255 g become the 7.87 kg of organic phase from the hydrolysis and with 800 g of 4% sodium hydroxide solution for 15 minutes touched. The organic phase is washed with water and in an Older Shaw column with 50 soils fractionated. This gives 6.85 kg of cyclohexane, 0.01 kg of water, 0.0 "kg of lower boiling points Proportions and 0.97 kg of pure cyclohexamine / cyclohexano! - Mixture. 0.07 kg of residue remain. These factions agree in terms of quality with those a comparison sample without extraction. However, the proportion of residue in the comparative sample is high lower.

JO

Example 2

1000 ml of mother liquor are three times in a row with each 350 ml of new bottom product for 15 Stirred at 55 ° C for minutes. The same experiment is carried out with distilled bottom product and bottom product forerun repeated The following table shows the analysis results before and after the extractions:

% org. Acids % C acids % Diols % C % Boron Diols acid Mother liquor 5.91 2.9 4.38 2.7 9.35 with bottom product extr. 2.27 1.1 1.71 1.1 8.30 with bottom product distillate extr. 2.16 1.1 1.47 0.9 8.50 with bottom product flow extr. 2.27 1.1 1.57 1.0 7.90

Conclusion: The extraction properties of the raw bottom product are equivalent to the other products.

example

1000 ml mother liquor are five times in a row with 350 ml each time new bottom product for 15 Stirred minutes at 55 ° C. The table below shows the analysis results of the mother liquor before and after the 5 extractions:

% org. Acids

% C acids% diols

% C
Diols

% Boric acid

Mother liquor
after extr.

7.6 1.7

3.8 0.8

Calculations based on this show that 7 to> 8 extraction stages are required in order to reduce diols and acids to 10% of their original concentration 3.47
0.67

2.2
0.4

8.1
6.3

bring. For this purpose, a total of 2 to 2.5 parts of crude bottom product are required for 1 part of mother liquor.

For this purpose I sheet drawings

Claims (1)

Claim: Process for the continuous recovery of the cyclohexane oxide as a catalyst boric acid used from the aqueous phase of the resulting after hydrolysis of the reaction mixture Product mixture by extraction with oxidation products of cyclohexane oxidation or their Mixing and recycling of the purified aqueous phase, characterized in that after hydrolysis of the reaction mixture, the aqueous phase is concentrated, boric acid by crystallization separates and separates and extracted a partial stream of the filtrate. ,