DE1618413A1 - Process for the production of aqueous formaldehyde solutions - Google Patents

Description

1618413 FARBENFABRIKEN BAYER AG

LEVEllKUSEN-Beyenrak G / Hg Petitioner Abbey

2 8 April hunt;

Process for the preparation of aqueous formaldehyde solutions

Process for the production of aqueous formaldehyde solutions by oxidative dehydrogenation of methanol are known. According to this process, a mixture of methanol vapor, Steam and air reacted on a silver catalyst at temperatures between 45o and 75o ° C. You can do this so that the methanol is completely converted to form a practically methanol-free aqueous formaldehyde solution. To do this, one works at higher catalyst temperatures. This embodiment brings with it greater losses of methanol through total oxidation, but can be applied to the downstream Do not rectify the formaldehyde solution. You can also work on incomplete methanol conversion (at a low catalyst temperature) and thus in the end achieves a much better utilization of the methanol, but must be the reaction product free from methanol by rectification (which is then used again will).

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The oxidation of methanol is in itself an exothermic process. However, it is not easy to use the heat released in this process to such an extent that the entire process takes place without external energy input. This is due to the fact that only the smaller part of the released heat energy at high temperatures, ie about the catalyst temperature 45o-75o ° C, occurs, while the larger part of the heat energy in the condensation of the water-formaldehyde vapor mixture at about 100 ° C and is released underneath. This thermal energy is therefore difficult to use. It has already been proposed to use this energy to heat a rectification column for formaldehyde solutions containing niethanol. To do this, however, this column must be operated at a considerable negative pressure and the methanol vapors leaving overhead must then be brought back to the pressure of the reactor by a compressor. The compressor is therefore in the flow of the conversion products. These products, especially the recycled methanol, are easily contaminated as a result. On the other hand, since the life of the silver catalyst is greatly reduced by impurities, this method is not yet completely satisfactory.

The present invention has the task of specifying a method after which the heat generated at a low temperature can be used for the formaldehyde production process

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can without interfering with the flow of reaction products are necessary.

A method for making methanol-free, aqueous Formaldehyde solutions by converting a mixture of methanol vapor, Water vapor and air on a silver catalyst at temperatures from 450-750 ° C, the vaporous reaction mixture with simultaneous indirect generation of steam is cooled to 100 - 200 ° C, the reaction gases then condensed in several stages and with the condensate, last with water, are washed, and wherein the generated water vapor to generate the methanol vapor-water vapor mixture from the corresponding liquids are used, characterized in that that the heat still contained in the 100-2oo ° C hot reaction gases including the heat of condensation with Absorbs water, which is partially evaporated at a negative pressure, the generated steam with a voltage below 1 ata, preferably compressed with the help of the generated steam of more than 1 ata and to generate the methanol-steam-water-steam-mixture resp. used for the rectification of the methanol-containing formaldehyde solution, and where the water which absorbs the heat energy is preferably the condensate of the steam of more than 1 ata used.

The two possible embodiments of the process - more complete and incomplete methanol conversion - are based on Le A 1o 723 - 3 -

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Figures 1 and 2 explained in more detail. These figures show similar devices for carrying out the method again, which are also the subject of the invention.

Figure 1 - practically complete methanol conversion - shows under:

(1) Evaporator for methanol-water mixture,

(2) superheater for methanol vapor-water vapor (heat exchanger),

(3) reactor with silver contact,

(4) Steam generator for superheated steam (heat exchanger),

(5) Condenser for cooling and partial condensation of the formaldehyde-water vapor mixture

(7), (8) and (9) absorber charged with condensate, (lo) absorber charged with water (l6),

(6) heat exchanger for dissipating the condensation heat from the condenser (5),

(ll), (l2) and (I?) heat exchangers,

(14) steam jet pump,

(15) condensate tank,

(16) water supply,

(17) to (21) circulation pumps.

The functioning of this device is as follows: in the Evaporator (l) are simultaneously introduced into methanol and water in liquid form and air and with the help of steam from more than 1 ata evaporated. The methanol vapor-water vapor mixture becomes

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then treated in the superheater (2) also with steam of more than 1 ata, then reacted on the silver catalyst in the reactor (3), cooled in the steam generator (4) with simultaneous generation of Steam of more than 1 ata and fed to the condenser (5). The condensate from this condenser is circulated through the heat exchanger (6) and its thermal energy (temperature about 7o 9o ° C) transferred there to water. This heat exchanger (6) is by the steam jet pump (14), which with 1o ata steam from steam generator (4) is operated, kept under negative pressure. Dadirch Part of the water evaporates in the heat exchanger (6) and is in the form of steam with a voltage below 1 ata in the steam jet pump (14) compressed and mixed with high tension steam. The vapor leaving the pump (14) with a voltage above 1 ata is fed to the heat exchangers (1) and (2) and their steam condensate partly via the condensate vessel (15) again as feed water in the circuit of the heat exchanger (6) and to Part of the feed water is fed to the steam generator (4). The remaining methanol-water vapor which has not condensed in the condenser (5) is completely in the downstream absorbers (7) # (8), (9) and (1o) condensed or absorbed in countercurrent, the heat exchangers (11), (12) and (12) take over the cooling. the Pumps (17) to (21) are used to maintain the various Cycles.

This arrangement reduces the heat of condensation of the formaldehyde-water vapor mixture so far recovered that the whole

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Device can work without external heat supply. Cooling water is no longer required for the condenser (5). the The amount of heat recovered depends on the negative pressure in the heat exchanger (6). This negative pressure can be through the Control the steam jet (14) so that the whole system does not have any needs more external energy supply.

Figure 2 shows the embodiment for incomplete Methanol conversion. With this device, more highly concentrated formaldehyde solutions can be produced completely free of methanol will. In the figure:

(1) Infeed for methanol and water,

(2) evaporator for methanol-water mixture with air supply,

(3) Superheater for a methanol vapor / water vapor mixture,

(4) reactor with silver catalyst,

(5) steam generator for superheated steam,

(6) Condenser to cool down the partial condensation

the formaldehyde-methanol-water vapor mixture,

(7) Heat exchanger to dissipate the heat of condensation of the Capacitor (6),

(8), (9), (lo) absorbers charged with condensate, (11), (12), (IJ) coolers (heat exchangers for these absorbers),

(14) absorber filled with water,

(15) heat pump (compressor),

(16) distillation column for formaldehyde-methanol-water mixture,

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(17) heat exchanger for heating the column (16),

(18) Heat exchanger for additional heating of the column (l6) with fresh steam,

(19) to (24) circulation pumps.

The operation of this device is as follows: At the feed point (l) becomes water and methanol in a weight ratio of 5o: 5o mixed to Io i 90 and fed to the evaporator (2). Hler will this mixture evaporates and mixed with air, then superheated in the heat exchanger (3) and reacted in the reactor (4). the The temperature of the reactor should be around 500 - 65o ° C so that the methanol conversion remains incomplete. In the heat exchanger (5) the reaction gases give off their heat to water * They will give up Chilled about 12o ° - 15o ° C, with steam of about 2 ata is generated; The gases are then fed to the condenser (6), condensed there and the condensate via the heat exchanger (7) circulated. The heat side of this heat exchanger is under reduced pressure, so part of it of the water it contains evaporates. The steam obtained in this way, with a voltage below 1 ata, is increased to about 1 ata is compressed and used to heat the column (l6) via the heat exchanger (17). The column (16) can with negative pressure operate. The steam from the heat exchanger (5) is used to heat the evaporator (2) and the superheater (3) used. If the steam obtained in the heat exchanger (7) is not sufficient to heat the column (l6), the heat

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exchanger (18) can also be heated with fresh steam. In the absorbers (8), (9) and (11) the absorber (6) uncondensed gases washed in countercurrent with condensate and completely condensed. The last capacitor (14) will charged with water. A methanol-containing formaldehyde solution is removed from the condenser (6) or absorber (8), which the Column (16) is fed and separated there by distillation. That Methanol passing over at the top of this column is fed in again at (1), the methanol-free formaldehyde solution to the bottom of the Removed from column (16).

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Example 1 .

During the production of formaldehyde (according to FIG. 1), a mixture of preheated to 90.degree. C. is placed in the reactor (3) 2o kg / h methanol vapor,

15 kg / h water vapor and

27.5 Nnr ⁵ / h air

initiated. The methanol conversion takes place at 625 ° C. with a 9o.2 molar yield, based on the ₅ methanol used. In the reactor cooler (4) 1o ata steam is generated, with the help of a steam radiator (H) (Figure 1) the vacuum steam generated in the first condensation stage (5) or in the associated heat exchanger (6) from o _s 32 ata to one Pressure of 1 ^ 5 is applied o The resulting amount of steam travels from * the input methanol-water mixture to evaporate in the evaporator (1) and the methanol-water-air mixture in the superheater (2) to a temperature of ea "9o ° C to overheat.

Is applied under the same Yerhältnissen the ICondensatlonswärme without Mutzung erfataifflgagemäß kg ein® Zusatzdasapfmenge of k ₉ 4 = 5 * 6 / h of steam needed J © NaOH, the amount of the added water _s with di © absorption column (io) at the point (16), creates a Jo = up to 59 Gei'j _o = ^ ige formaldehyde solution,;, which can contain up to 1 Gev / O = ^ methanol _D

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If the ratio of the mongrel the evaporator (1) tapering methanol-water mixture in a ratio of 7o: brought j5o and catalyst temperature adjusted to 580 ⁰ C, then the methanol in the reactor Umstz - incomplete. This gives a formaldehyde solution of 37-42% by weight of formaldehyde, which contains above-mentioned 10-12% methanol. The yield of formaldehyde, based on converted methanol, is very high and is approx. 94.9 mol-56.

Example 2

In the preparation of methanol-free formaldehyde solutions according to Figure 2, the reactor (4) z. B. one preheated to 1oo ° C Mixed from

74.9 kg / h methanol vapor,

25 kg / h water © i.-dßsnpf and 1o2 MtB ⁵ A air

forwarded. Di © Ksfehanolumsetzung proceeds at about 600 ⁰ C, with only a portion (86 approximately - $ 87) of the methanol is converted. However, the formaldehyde yield, based on converted methanol, is very high and amounts to 94.5 mol = JiL. In the reactor cooler (3), steam of 2.5 afea is generated, which is used to evaporate the water-methanol layer and to overheat the water-methanol mixture. Air mixture is used. The absence of steam is taken from the steam network * In Figure ^3, the first condensation stage (6) is compressed by the condensation of formaldehyde, water and methanol vapor from öj25 ata generated and with the aid of a heat pump (15) to 1, o3 ata, of the for heating Methanol-formaldehyde separation column

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Ji

is used, whereby approx. 90 % of the amount of steam can be saved (Premd steam consumption approx. 6.5 kg / h). The 1.03 ata steam can therefore be used in the column because it is operated under a vacuum of 400-520 Torr.

This gives a methanol-free formaldehyde solution of about 5o - 52 percent -.% Formaldehyde. If the input methanol: water ratio is changed to 85:15, it is even possible to obtain a formaldehyde solution with approx. 60% by weight of formaldehyde, depending on the amount of additional water required for complete washing out of the exhaust gas for the absorption column (14).

Under the same conditions, without using the heat of condensation for the separation of the methanol-formaldehyde mixture, approx. 63 kg of steam are used per hour.

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Claims (2)

Claims . Process for the production of methanol-free, aqueous formaldehyde solutions by reacting a mixture of methanol vapor, water vapor and air over a silver catalyst at temperatures of 45o - 75o ° C, the vaporous reaction mixture being cooled to 100 - 200 ° C with simultaneous indirect generation of steam, the reaction gases then condensed in several stages and washed with the condensate, finally with water, and the water vapor generated is used to generate the methanol vapor-water vapor mixture from the corresponding liquids, characterized in that the 1oo - 2oo ° C hot reaction gases absorbs any heat including the heat of condensation with water, which is partially evaporated at a negative pressure, the generated steam is compressed with a voltage below 1 ata, preferably with the help of the generated steam of more than 1 ata and to generate the methanol vapor-water vapor Mixture or for rec tification of the methanol-containing formaldehyde solution is also used, and the condensate of the steam of more than 1 ata is preferably used as the water absorbing the heat energy. Le A 1 ο 723 -12- 009 8 4 4/1819 2. Apparatus for carrying out the procedure according to Inspmieäi 1, consisting of (1) Evaporator for methanol-water mixture, (2) superheater for methanol vapor-water vapor (heat exchanger), (3) reactor with silver contact » (4) Steam generator for superheated steam (heat exchanger), (5) Condenser for cooling and partial condensation of the Formaldehyde-water vapor mixture (7) 3 (8) and (9) absorber charged with condensate ₃ (1o) absorber charged with water (16), (6) heat exchanger for dissipating the condensation heat from the condenser (5), (11), (12) and (1 j5) heat from t from rather,
(14) steam jet pump, Condensate tank ,, Water supply,
to (21) circles, Device for performing the method aaaeh claim 1, consisting of (1) Infeed for methane ©! and water, (2) 1 / evaporator for methanol-water mixture with air supply, (3 | 'superheater for .MethanoMaTripi' -Was er stampf-Semiscla, (4) reactor with Le A io723 - «3 - Ί6Ί84 1 y (5) steam generator for superheated steam, (6) Condenser to cool down the partial condensation the formaldehyde-methanol-steam mixture, (7) Heat exchanger to dissipate the heat of condensation of the Capacitor (6), (ö) t ί9) »ίΐό) absorber charged with condensate, (11), (12), {13) cooler (heat exchanger for these absorbers), absorber filled with water, heat pump (compressor), (16) distillation column for formaldehyde-methanol-water mixture, (17) heat exchanger for heating the column (16), (18) Heat exchanger for additional heating of the column { tu) with fresh steam, (19) to (24) circulation pumps. Le K Io 723 - 1 * - Q0B84A / 1819 JlS . Blank page