DE1285995B - Process for the production of aqueous formaldehyde solutions by oxidation of methanol vapor - Google Patents

Description

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It is known to combine formaldehyde with the normal silver catalyst in a tech-oxidation and dehydrogenation from methanol and air ruffled plant in itself already causes a pressure drop of as oxidant and crystallized silver than 50 to 130 torr and also to produce the after catalyst at elevated temperatures. Switched scrubber also causes a pressure drop. In practice, if you generally take a steam effect, you would have to carry out the formaldehyde absorption with a formaldehyde-water mixture, which is 50 to 75 times a fairly high vacuum. It is known, however, that methanol contains and conducts this amount by weight, that the absorption in a vacuum is worse and incompletely mixed with air at temperatures between more constant than at normal or slightly above 500 and 700 ° C. over a catalyst from crystalline pressure. In addition, the apparatus must have enlarged silver. The used for this method io and be protected against ingress of air, since the reactor thus consists essentially of a formaldehyde emission of up to 20 ° / ₀ hydrogen ent-catalyst zone, can hold from an adjoining and thus there is danger of explosion. With an intermediate piece and a downstream cooler. this process has the advantage of higher yields. This downstream cooler is used to pay the price of too great a technical effort. The gases leaving the reaction space to cool down and to 15 Furthermore, it is from FIAT report 999, p. 3, paragraph 2, condense. The condensate is then washed with known to produce formaldehyde from methaso much water that aqueous formaldehyde nol a catalyst made of silver crystals with a solution of the commercial concentrations of diameter between 0.15 and 1.25 mm to expire. The exhaust gas, which is insoluble in water, contains next to turns. The coarser crystals come to lie below nitrogen, only hydrogen, carbon dioxide, carbon. The exact catalyst structure from the lenmonoxide and traces of methanol, oxygen, formaldehyde reactors of IG colors is in this and formaldehyde. It cannot be mentioned as heating gas or literature, but can be found in BIOS report 104, annex sheet 11, used for the production of pure nitrogen. given composition is as follows:

The conversion of the methanol on the crystallized 35 4 percent by weight

Silver catalyst can now penetrate in two ways: Silver crystals 0.2 to 0.4 mm in diameter

be guided. If you put z. B. a methanol-water 44 percent by weight

Mixture with 60 to 80 percent by weight of methanol-silver crystals, 0.4 to 0.75 mm in diameter

content and the temperature at the catalyst is 38.6 percent by weight

with the added amount of air to 500 to 600 ° C, 30 silver crystals 0.75 to 1 mm in diameter in this way a 30 to 45 percent by weight 13.4 percent by weight formaldehyde solution can be obtained, which still contains 3 to 25 Ge silver crystals over 1 mm in diameter contains methanol by weight, d. i.e., the methanol catalyst layer thickness 10 mm Conversion was largely incomplete. The mold dust components are less than 0.2 mm in diameter aldehyde yields that are achieved are, however, not used according to this reference, things are very high and, taking into account, something that does not belong to the state of the art unreacted methanol normally 88 to the older proposal (German patent specification 1231229) 91 mole percent. Since such methanol-containing form- formaldehyde is converted into methanol Aldehyde solutions are expensive because of the content of methanol with oxygen in the gas phase and are only usable to a limited extent Methanol mostly removed by distillation crystals used, which are at least 50 weight and so recovered. The distillation causes a percentage of crystals with a basket size of 1.25 to 5.0 mm but additional costs and a deterioration in quality exist and where the height of the catalyst layer because the normal distillation conditions should be between 15 and 50 mm. From the two However, this patent specification shows that the formic acid content of the formaldehyde solution is doubled to tripled. even when working according to this method in the exhaust gas

It is also possible, however, to choose the reaction conditions still at least 0.36% carbon oxide so that the methanol is almost completely. A considerable part of the methanol is therefore over-converted. In the 30 to 40 percent by weight obtained, the formaldehyde stage is also oxidized, percent formaldehyde solutions then remain. There has now been an improved method for producing a maximum of up to 1 percent by weight of residual production of aqueous formaldehyde solutions by methanol. Such formaldehyde solutions can practically be used universally for the oxidation of methanol vapor with an oxygen. You put them z. B. forth from a containing gas in the presence of water vapor on a water-methanol mixture with 50 to 63 weight a silver catalyst, cooling, condensing the percent methanol at catalyst temperatures between 55 reaction gas mixture, washing out the residual gas with see 580 to 700 ° C each according to the activity of the catalyst. Water and separation of the aqueous formaldehyde this case, one obtains formaldehyde yields, based on solvent from the exhaust found that characterized gekennzeicheingesetztes methanol of usually about 84, to net that one uses a silver catalyst, at most 87.5 ° / _0th The content of the oxides of carbon to _^7/8 of its weight of silver crystals of the substance (ie carbon dioxide and carbon monoxide) in the exhaust 60 0.75 to 3 mm in diameter and about ^x / e ^of silver gas amounts to approximately 4.9 to 5 , 9 percent by volume. crystals below 0.3 mm and that

In the literature it is also mentioned that one of the gases leaving the catalyst in a

Percentage by volume of the oxides of carbon in a time of less than 0.1 seconds so that the

Exhaust gas up to 4.4 percent by volume and even up to the carbon monoxide content of the exhaust gas not more than 0.23 vol-

2.6 percent by volume can be reduced if you increase the 65 percent by volume.

Gases under reduced pressure (680 or 250 Torr) in In the method according to the invention it is

allows the catalyst chamber to enter. The formaldehyde required that the residence time of the in the catalyst

This improves the yield accordingly. converted gas in the intermediate zone before

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Cooler less than 0.1 seconds, in particular less. The methanol conversion took place at 625 to 635 ° C

than 0.02 seconds. instead of. The pressure in front of the catalyst was 802 torr.

With this procedure practically the reaction gases were after cooling in the no more carbon monoxide (CO content about 0.1 to catalyst cooler in an absorption system after -0.2 Percentage by volume compared to before 0.8 to 1.4 volume 5 cooled, condensed and with additional water percent). The carbon dioxide content of the exhaust gas drops washed. Formed from 875 kg of pure methanol when working on complete methanol conversion of 745 kg of formaldehyde in the form of a 29 weight earlier 3.8 to 4.4 percent by volume to 3.4 to 3.6 percent by volume solution, plus 0.007 percent by weight percent and, if the methanol conversion is incomplete, formic acid is still 0.9 percent by weight methanol down to 2.2 to 2.8 percent by volume. This will contain io. According to this, the formaldehyde yield was obtained high formaldehyde yields, with about 90.8 mol incomplete methanol conversion of 93 to 95 mol percent based on the methanol used.

percent, with practically complete methanol conversion The exhaust gas, its composition during the

from 90 to 91 mol percent, based on the test used, was automatically monitored, consisted of:

Methanol. 15 3.30 to 3.50 percent by volume carbon dioxide

It was surprising that the reduction was 0.11 to 0.18 volume percent carbon oxide
the zone between the catalyst bed and the catalyst - 18.2 to 17.3 percent by volume of hydrogen
cooler, however strong, on the formaldehyde yield 0.3 to 0.6 percent by volume oxygen
although there is already a considerable amount of nitrogen remaining in this zone
There is a temperature drop, and in the normal 20.
technical reactors the residence times also already comparative experiment
are very small. Since the reduction in size of this zone in an experimental reactor in which the residence time of the mainly affects the prevention of the formation of reaction gases in the zone between the catalyst and carbon oxide and in the case of the incomplete catalyst cooler was approximately 0.04 seconds, methanol conversion was practically only the 25th If a normal silver crystal catalyst, which changes the concentration of carbon dioxide, has to be incorporated into silver crystals with a diameter of approximately one should assume that carbon dioxide consists mainly of 0.2 to 1 mm. In this experimental catalyst and carbon oxide, on the other hand, in the main reactor, an intimate mixture of
thing after the catalyst, possibly by decomposing 9.73 kg / h of pure methanol vapor,
setting of formaldehyde according to equation 30 and 6.8 kg / h water vapor

ΗΓΗΟ + CO 4. H ^{approx. 13} ' ^{7 Nm3 / h air} '

HCHO ^ CO + H ₂ initiated.

are formed. The methanol conversion took place at 630 to 640 ° C

It was also amazing that the expected took place. The pressure in front of the catalyst was 825 torr.

Difficulties in heating up the catalyst by 35 The reaction gases were after cooling in the

extreme reduction of the distance between the catalytic converter cooler in an absorption system after

Sator and contact cooler, whereby the heat is cooled down, condensed and with additional water

would have been significantly improved, did not occur, washed.

although the power of the heat source is not enhanced. 850 kg of methanol evolved into 691 kg of mold. (The silver catalyst must for starting aldehyde 40 in the form of a 30,2gewichtsprozentigen Löder reaction by an external heat source to min- solution that are least preheated in addition 0.006 weight percent formic acid 400 to 500 ⁰ C). still contained 1.0 percent by weight of methanol. Since the residence time of the methanol was actually the formaldehyde yield, based on the silver catalyst, is still much shorter than the amount of methanol used in the zone, about 86.8 mol percent, between the catalyst and the cooler, various types of exhaust gas, its composition during the lent assumed that the reaction was not only automatically monitored in the experiment, consisted of: catalyst, but also takes place behind it. After 3.9 to 4.1 percent by volume CO ₂
but the methanol conversion achieved by us is just as 0.8 to 1.3 percent by volume of CO
is high, as in the older type reactors, 17.2 to 16.0 percent by volume of H _{2 is}
from the fact that the formaldehyde formation is 50 0.4 to 0.6 percent by volume O ₂
plays exclusively in the contact bed. Remainder N ₂

Example 2

In an experimental reactor, a silver catalyst consisting of crystals in the experimental reactor described in Example 1 was built up. This 55, a silver catalyst was disposed with the crystal there beKatalysator sat with ⁷ / s us ^a silver crystals of signed structure. The residence time in 0.75 to 3 mm and ^x / e ^of silver crystals under the zone between catalyst and catalyst cooler 0.3 mm, especially below 0.15 mm, together. It was about 0.0043 seconds.

The thickness of the catalyst layer was about 10 mm. The in this experimental reactor was an intimate

Catalyst bed was installed in the reactor so that 60 mixture of

the residence time of the gases in the zone between cataly- 9.73 kg / h pure methanol vapor,

Sator and catalyst cooler about 0.0037 seconds and 4.17 kg / h of water vapor

fraud. In this experimental reactor, an intimate ^{air of about 10.9 m 3} / h was generated

Mixture of initiated.

9.73 kg / h of pure methanol vapor, 65 The reaction took place at 58O ⁰ C. The pressure was 6.8 kg / h of steam and upstream of the catalyst was 796 Torr. The reaction was ^{about 13.2 Nm 3} / h of air, gases were introduced into the catalyst after cooling, after-cooled in an absorption system,

condensed and washed with additional water. From 850 kg of methanol were 604 kg of formaldehyde in In the form of a 40.2 percent by weight solution, which (in addition to 0.008% formic acid) is still 11.3 percent by weight Contained methanol. About 680 kg of methanol were converted. According to this, the formaldehyde yield was based on the amount of methanol reacted, about 94.7 mol percent. The exhaust gas had the following composition:

2.4 to 2.7 percent by volume carbon dioxide

0.13 to 0.2 volume percent carbon oxide 17.4 to 17.0 volume percent hydrogen 0.3 to 0.8 percent by volume of oxygen, the remainder being nitrogen

The exhaust gas composition was automatically monitored during the experiment.

about 722 kg / h formaldehyde in the form of a 30.5 percent by weight solution, the other 0.005 percent by weight Formic acid still contained 0.8 percent by weight of methanol. The formaldehyde yield was based on methanol used, 88.1 mol percent. The methanol conversion took place at about 625 ° C. The pressure in front of the catalyst was 807 to 825 torr.

The exhaust gas had the following composition: 3.5 to 3.7 percent by volume carbon dioxide 0.5 to 0.6 volume percent carbon oxide 15.8 to 17.0 volume percent hydrogen 0.6 to 0.8 volume percent oxygen Remainder nitrogen

Example 3

In a technical reactor, the catalyst bed was installed so that the residence time of the reaction gases in the zone between the catalyst bed and the catalyst cooler was about 0.012 seconds. (The end Reasons of operational safety - in particular because of the hardly calculable thermal expansion possibilities - the distance compared to the reactor specified in Example 1 has been increased slightly, which of course increased the residence time.) The structure of the silver crystal catalyst corresponded that in example 1.

An intimate mixture of 875 kg / h of pure methanol vapor was introduced into this reactor 660 kg / h water vapor and

about 1130 Nm ³ / h air

2. Comparative experiment

A catalyst made of silver crystals (the silver crystals had a diameter of 0.2 to 1 mm) arranged in a layer about 10 mm thick. the The zone between the catalyst and the catalyst cooler was so large that the residence time of the reaction gases under normal load was approximately 0.095 seconds.

An intimate mixture of 615 kg / h of pure methanol vapor, 464 kg / h of water vapor and 850 Nm ^s / h of air was introduced into this reactor
initiated.

The reaction took place at 630 to 640 ° C. The pressure in front of the catalyst was 840 to 860 torr. The reaction gases were after leaving of the catalyst cooler in the absorption system after-cooled, condensed and with additional

initiated.

The reaction gases were washed in water after cooling.
Catalyst cooler in a normal absorption From 615 kg of pure methanol, 488 kg of molding plant were cooled, condensed and washed with additional aldehyde in the form of a 30.5 percent by weight solution of water. An average of 740kg / h were obtained, which, in addition to 0.008 percent by weight of formaldehyde, which still contained 1 percent by weight of residual methanol in the waste acid due to the addition of water, sorption system in the form of a 30.2 percent by weight except 0.004 percent by weight amei on methanol used, 84.8 mol percent,
sens acid still contained 0.7 percent by weight of methanol.

The formaldehyde yield was based on the amount used Methanol, 90.2 mole percent.

The methanol conversion took place at about 625 ° C. The pressure in front of the catalyst was 810 bis 825 torr. The exhaust gas had the following composition - The exhaust gas, its composition automatically was determined, consisted of

3.9 to 4.3 volume percent carbon dioxide 0.9 to 1.3 volume percent carbon oxide 15.5 to 16.2 percent by volume hydrogen, remainder nitrogen.

Settlement:

3.6 to 3.7 volume percent carbon dioxide 0.16 to 0.23 volume percent carbon oxide 16.6 to 17.9 percent by volume hydrogen, 0.3 to 0.8 percent by volume oxygen, remainder nitrogen

1. Comparative experiment

The same technical reactor had previously been designed so that the residence time in the zone between the catalyst bed and the catalyst cooler was about 0.048 seconds. With a silver catalyst whose structure corresponded to that of Example 1, we obtained 875 kg / h of pure methanol vapor, 660 kg / h of water vapor, at the following reactor feed rates,
1150 Nm ^s / h air

Claims (1)

Claim: Process for the preparation of aqueous formaldehyde solutions by oxidation of methanol vapor with an oxygen-containing gas in the presence of water vapor over a silver catalyst, cooling, condensation of the reaction gas mixture, washing out of the residual gas with water and separation of the aqueous formaldehyde solution from the exhaust gas, characterized in that a silver catalyst is used which ⁷ / s of its weight is composed of silver crystals of 0.75 to 3 τη τη diameter and ¹ Zs ^of silver crystals below 0.3 mm and that the gases leaving the catalyst are so cooled in a time of less than 0.1 seconds that the carbon monoxide content of the exhaust gas does not rise above 0.23 percent by volume.