DE2201434C3 - Process for the production of formaldehyde - Google Patents

Description

The water vapor mixture should be low. The Auxiliaries must be stable against alkali so that they are not destroyed while they are in the evaporator will and at the same time maintain its effect; Esters and acids are therefore out of the question. The Aid must be heavier than the sump drain or dissolve in it enough so that it does not dissolve enriches in the evaporator, such as B. in the case of silicone oils. It must be effective in such small amounts be sure that it does not interfere with further processing, even if some of it ends up in the end product.

Also, the effectiveness of a substance in a particular case cannot generally affect its Property as a defoamer. Many parameters play a role in foam formation Role, ζ. Β. Viscosity, surface tension, difference in surface tension, in a bubble and on the surface of the solution. Pure liquids do not produce durable foams (K. Edelmann, Textbook of Colloid Chemistry, Vol. 1, pp. 309 to 310 [VED, Berlin 1961], H. Freundlich, Kapillarchemie [Leipzig 1922 |, pp. 1091 to 1093). Type and amount of one suitable for a particular case Defoamer cannot be derived from known cases; the foaming effect is also one Substance or an impurity in a given medium cannot be foreseen (Ross, The Inhibition of Foaming [Rensselaer Polytechnic Institute. N. Y. 195O |, pp. II, 17, 21, 29; B i k e r m a η, Foams Theory and Applications [Reinhod Publ. Corp. 1953], pp. 74, 297).

It has now been found that formaldehyde can be obtained by evaporating a mixture of methanol and water followed by oxidative dehydrogenation of methanol in the presence of a catalyst Advantageously obtained at elevated temperature when the evaporation in the presence of a mixture of at least one alkanol with more than 7 carbon atoms and of at least one dialkyl ether, wherein each of the two alkyl groups contains more than 7 carbon atoms.

In view of the prior art, the method according to the invention surprisingly provides simpler ones and more economical way formaldehyde in good yield, better space-time yield and in good purity. The aforementioned difficulties and corresponding operational disruptions are avoided. The yield of formaldehyde per unit of time and thus the continuous rate of evaporation of the methanol solution is in the Usually 1.5 to 2.5 times the normal, failure-prone operation. These were beneficial results with the mixture of alkanols and ethers according to the invention with reference to the publications mentioned not to be expected; It is also known (German Offenlegungsschrift 1618438) that ether, like Dimethyl ether, and alkanols, such as isobutyl alcohol, interfere with the production of formaldehyde.

Suitable starting materials for the process are pure methanol or technical-grade methanol in a mixture with water; the concentration of the aqueous mixtures can expediently be between 50 and 95 Weight percent, preferably between 58 and 70 percent by weight of methanol, vary. Also raw methanol, as a rule, according to the German patent specifications in German Auslegeschrift 1,277,834 1,235,881 and 1,136,318 processes described by separating off a lower-boiling fraction or cleaned by treatment with oxidizing agents and / or alkalis can be used will.

The pure or crude methanol can by one of the known processes (U 11 m a η η, loc. Cit., Vol. 12, pp. 402 ff.), In particular a letterpress process. Lately it is methanol also produced by the so-called low-pressure process ίο add carbon monoxide and hydrogen to methanol Pressures below 150 at and at temperatures below 300 'C implemented. As catalysts for that Low-pressure processes are those with a content of copper, zinc and a third element, z. B. chromium, or a difficult to reducible metal of the II. To IV. Group of the periodic table used. Such catalysts are for example in British patents 1010 871 and 1159 035. Also pure or raw methanoi produced by a low pressure process can be used for the method according to the invention. Evaporation is in the Usually in one of the well-known evaporator systems (Uli mann, loc. Eil., B. I. O. S. Final Report No. 1331; F.J.A.T. Final Report No. 999) at a temperature of the evaporator liquid of the top one Evaporator bottom from 68 to 100 ° C., preferably from 68 to 88 ° C., without pressure or under pressure, expedient under a pressure of 1.0 to 1.8at, discontinuously or advantageously carried out continuously. The aqueous methanol solution becomes a mixed solvent of at least one alkanol with more than 7 carbon atoms, preferably 8 to 24, in particular from 8 to 12 carbon atoms, and of at least one dialkyl ether, in which each of the two alkyl groups have more than 7, preferably from 8 to 24, in particular from 8 to 12 carbon atoms contains, added. The dialkyl ethers may optionally be from one another and / or from the alkanols contain different alkyl groups. The alkyl groups can be branched or advantageous be straight chain. In general, from 0.0001 to 0.8, preferably from 0.0005 to 0.1 percent by weight is used Solvent mixture, based on methanol (calculated 100%). Appropriate to come Mixtures of 1 to 5 alkanols and 1 to 5 dialkyl ethers are possible, the number of alkanol components is advantageously greater than the number of dialkyl ether components. Total quantities of 50 to 900, expediently from 100 to 400 percent by weight of alkanols, based on the total amount of Ethers, are beneficial.

Mixtures with 2 to 5 alkanols and 1 to 3 dialkyl ethers, the two alkyl groups of which are identical to one another and the alkyl group of an alkanol present, are preferred. For example, octyl, nonyl, decyl, undecyl, lauryl, tridecyl, myristyl, pentadecyl, cetyl, heptadecyl, stearyl, nonadecyl, aracyl, heneicosyl, behen alcohol and corresponding ethers are possible . Such mixtures are obtained, for example, in the distillation of fatty alcohols which are prepared by various processes (U 11-mann, loc. Cit., Vol. 7, p. 440 ff.), Expediently by an oxo process. In particular, fractions of such fatty alcohol distillation having a boiling point at 760 Torr 80-280 ° C, preferably 145-250 ° C, in particular 150-210 ⁰ C, is advantageous. Such fat

alcohol fractions, which are unier with the name thick oil are known, in general have refractive indicesni? from 1.425 to 1.451 and densities <* ¥ from 0.76 to 0.79. The mixtures expediently have saponification numbers below 20 and acid numbers below 1. If necessary, unsaturated fatty alcohols or corresponding ethers can be present, the iodine number the mixture is therefore appropriately below 2. The aforementioned fatty alcohol fractions (thick oils) are generally in an amount from 0.0001 to 08, preferably from 0.0005 to 0.1, in particular from 0.002 to 0.01 percent by weight based on methanol (calculated 100 ° .Ό), used. The thick oils admixtures of up to 5 percent by weight ester, e.g. B. nonyl acetate and up to Contains 0.5 percent by weight of water.

The evaporation can be carried out as follows: A methanol-containing, aqueous formaldehyde solution, to which the aforementioned solvent mixture, in particular a thick oil, has been added, is evaporated at the aforementioned temperature. You can use directly or indirectly heated evaporators and types of evaporators, for example tube, Robert, Kestner, forced circulation, multi-stage evaporator; Rectification columns, e.g. B. sieve tray, Oldershaw, glass tray, bubble cap, valve tray column, use. Evaporation rates of 1000 to 20,000 kg of water-methanol vapor per hour and / or feed rates of 1000 to 20,000 kg per hour of aqueous methanol solution with a content of 58 to 70 percent by weight (calculated 100 ^β Ό) are useful. In continuous operation, the methanol solution can be fed to the evaporator sump, the upper third or, expediently, the uppermost base of the evaporator. The solvent mixture (thick oil) can preferably be fed in together with the methanol solution or separately; a separate feed line can be at any point in the evaporator; it is advantageously located above the uppermost tray, for example 20 to 50 cm above the uppermost sieve base plate. The solvent mixture can be added batchwise or continuously. In the case of discontinuous metering, it is usually sufficient to enter the appropriate amount for this period at intervals of 1 to 25 hours. In the case of thick oils, in view of the small amount and the high viscosity, it is advisable to first prepare a solution in a suitable solvent, e.g. B. methanol, or a suspension in a methanol solution. Examples of the solubility of thick oils are summarized in the following table:

solvent solubility
(g thick oil in 100 g solvent) Methanol
60 weight percent
Methanol
40 percent by weight
water infinitely miscible
0.5

Likewise, methanol and water can be separated discontinuously or advantageously continuously from each other and the solvent mixture, advantageously thick oil, one or the other component add continuously or discontinuously. To the boiling of the evaporator sump during the addition not to be interrupted, it is expedient to bring the components or mixtures fed in beforehand to a temperature close to the temperature of the sump.

The methanol-water-vapor mixture emerging from the evaporator is, advantageously in a mixture with the recirculated exhaust gas and optionally

ίο with inert gas, fed to the reaction chamber. A suitable inert gas for the process is, for example, nitrogen. The vapor mixture is expediently mixed at the same time with the oxidizing agent and with the exhaust gas and / or inert gas.

Both pure oxygen and free oxygen can be used as the oxidizing agent Use gases, especially air. Oxygen and methanol are expediently in a molar ratio of 0.3 to 0.6, in particular from 0.4 to 0.5 mol of acid

substance per mole of methanol or methanol and air, advantageously in a molar ratio of 1 mole of methanol applied to 1.4 to 2.9 moles of air. The oxidation is, if appropriate, in the presence of 1 to 2, advantageous 1 to 1.65 moles, especially 1.3 to 1.5 moles

made as exhaust gas per mole of methanol.

For the method according to the invention, any Silberkata '> sators are suitable, for. B. in the German Auslegeschrift 1 231 229 and Ullmann's Encyclopedia of Techniques; n Chemistry, Vol. 7,

P. 659 ff., Described. Two-layer silver catalysts, e.g. B. in the German Auslegeschrilt 1 294 360 and listed in German Offenlegungsschrift 19 03197.1 Catalysts. Regarding the production of the catalyst

tors and carrying out the corresponding reaction with these catalysts, reference is made to the publications mentioned. A preferred embodiment of the process according to the invention consists in carrying out the reaction on a two-layer catalyst, the lower layer being 15 to 40 mm, in particular 20 to 30 mm, and at least 50 percent by weight of crystals with a grain size of 1 to 4 mm, in particular 1 to 2 , 5 mm and the upper layer has a thickness of 0.75 to 3, in particular 1 to 2 mm and consists of crystals with grain sizes of 0.1 to 1, in particular 0.2 to 0.75 mm, and this catalyst with 1 to 3 t, in particular 1.4 to 2.4 t of methanol per m ^{2 of} catalyst bed cross-section and hours

de to burden. Catalyst bed diameters are preferably used for large-scale implementation of at least 0.5, expediently 1 to 3 m.

The oxidation is carried out in the rest of the known manner by z. B. a gas mixture

Methanol vapor, water vapor, air, optionally inert gas and expediently exhaust gas in the aforementioned Amounts at temperatures of about 550 to 750 ° C, in particular 600 to 700 ° C, through the silver catalyst directs.

The process is generally carried out continuously at pressures between 0.5 and 2 at, preferably between 0.8 and 1.8 at. It is advantageous to cool the reaction gases leaving the catalyst zone within a short time, for example in less than ₁₀ seconds, e.g. B. to temperatures of 350 ° C. The cooled gas mixture is then expediently fed to an absorption tower in which the formaldehyde is added

Water, advantageously in countercurrent, comes from the gas consideration. Preference is given to oxides of the

mixture is washed. Iron and molybdenum, without carrier materials

A part of the remaining exhaust gas is left, or expediently on a carrier, for use then escape and the other one leads z. B. after the in the German Offenlegungsschrift expediently back into the reaction cycle. The 5th process portion of the exhaust gas described in 1,932,892 and 2,050,096, which is added to the reaction. One used, for example, in one used, is from 1 to 2 mol, based on the embodiment shown, an amount from 5 to 15 , 1 mole of the methanol fed to the reaction. The expedient 5 to 10 percent by weight of methanol, be exhaust gas essentially contains nitrogen, water added to the amount by weight of air. In continuous, carbon dioxide, carbon monoxide, water, methanol, io borrowed operation, at least 0.1 is expediently allowed Argon and usually from 0.1 to 0.5 grams to 1 kg, preferably 0.2 to 0.7 kg of methanol each Formaldehyde in the cubic meter of exhaust gas. It is useful - hour and liter of catalyst in the presence of the Katamäßig with a basic compound - advantageously react lysators.

in an amount that a pH of at least 10, the catalyst can from 3 to 20, preferably 11 to 13.5, adjusts - and / or oxides from 4 to 15 percent by weight oxides of iron and dating agents, then treated with the remaining grains of molybdenum, based on a carrier, contain advantageous components of the starting mixture of the reaction as a silicate carrier. As a rule, mixed and then fed back into the reaction chamber, the oxides are fed in at a ratio of 1. The basic compounds are mainly Fe ₂ O ₃ to 3 to 12 _{parts by weight MoO 3} , preferably alkalis, such as solid or dissolved in water, preferably 1 part by weight Fe ₄ O, to 5 to 7 Ge hydroxides, oxides or carbonates of the alkali - or parts of MoO ₃ . Optionally, alkaline earth metals or other alkaline cobalt, nickel, chromium, tungsten, aluminum substances, for example alkali alcoholates, strongly basic, oxide, phosphorus trioxide or phosphorus pentoxide in a generally high-boiling amine such as triethanol amount of 0 , 5 to 5, preferably 0.5 to 3 geamin, in question. The oxidizing agent is about 5 percent by weight, based on the support, or, for example, hydrogen peroxide, sodium peroxide in the case of unsupported catalysts in an amount of aqueous solution; Perborates, percarbonates, expediently from 0.1 to 2 percent by weight, based on the moderate in a mixture with water; Potassium permanganate together with the amount of oxide, to be present in the catalyst, or chromic acid, expediently in the form of an aqueous solution. In general, alkali, 0.5 to 10 percent by weight solutions are suitable as silicate carriers. Alkaline earth silicates, in particular calcium silicates, magnesia In general, 0.02 to 10 g oxide silicate, zinc silicate, cerium silicate, zirconium silicate, solvent are used, based on one cubic meter of exhaust gas. minium silicate or their mixtures are used. The treatment is generally carried out at one temperature. Silicates can also be used as aluminosilicates, borosilicates temperature between 20 and 150 ° C, without pressure or under pressure, or zeolites are preferably carried out continuously. Also is a 35 speaking magnesium silicate. If necessary, two-stage treatment with both components, they keep additives such as alkali sulfates or oxides, z. B. preferably first with a basic compound and soda glasses, sulfate glasses, potash glasses, potassium sulfate glasses, then with the oxidizing agent, possible. Preferred Also silicates with different cations in the fabric are suitable for the treatment of the exhaust gas that is in the German, z. B. in the form of silicates see Offenlegungsschrift 2 022 818 described 40 of the type of olivine, phenacite, titanite, chrysolite, method used. Benitoite, axinite, cordierite, milarite, steatite, ortho-

If necessary, one can use in the case of verwenklas, plagioclase, albite.

manure of silver catalysts also amines after It can also use other support materials, which in the German Offenlegungsschrift 2 116947 z. B. quartz, alumina, silicon carbide, porcelain or the processes described. The amines 45 magnesium oxide or rutile can be used. They can be used in pure form or in solution. Carrier materials can arrive in crystalline, amorphous formation, whereby under the reaction conditions or sintered state are used. Also in inert solvents such as water; Alkenols, e.g. B. fused alumina is well suited. Before ethanol or preferably methanol; or, correspondingly, carriers come into consideration which are an internal corresponding mixture. Generally 50 surface areas between 0 and 5 m ^a / g. Solutions of 20 to 60 percent by weight can be used in the form of granules, pills, rings and amine. It is also possible to use mixtures of, advantageously, spheres with a diameter of amines. Use the temperature of 3 to 12 millimeters. The amine solution or the amine is advantageously between The catalyst consists of particles of any, see 20 and 80 ° C. You can use the amine from the 5; , add but preferably spherical in shape with iron passage mixture in the evaporator, in the züge- diameter of 4 to 12, preferably from 6 to 10 MiHiftihrte water metering, or it can be to-meter and a surface area of below 10, vorsammen with the methanol m the evaporator, preferably from 0.01 to 5 m * / g catalyst. In general. The amine is expediently pumped or a spherical silicate carrier is used, an amine solution onto the boiling liquid which is treated with an aqueous solution of molybdenum and steamer or iron salts in the liquid to be evaporated. Regarding the Katalyim umlaut. Sator production is based on the aforementioned patents

In the case of the use of metal oxides, reference can be made.

the known processes under the corresponding The oxidation of methanol is used when

corresponding conditions (U 11 m a η η, loc dt., as well as «5 formation of the aforementioned oxides usually with a

the processes listed in the prior art) temperature between 280 and 420 ^° C., preferably

carried out, whereby for such cases the pre- between 320 and 370 ° C, unpressurized or under pressure,

said exhaust gas recirculation generally not in discontinuous or preferably continuously

accomplished. The reaction can be designed as follows: A reactor is equipped with the one in the above Way prepared catalyst filled. A tubular reactor is advantageously used as the reactor external cooling and any number of tubes, e.g. B. up to 15,000, which is expediently free of Internals, e.g. B. heat shafts are. In a preferred embodiment, the inner diameter is of the tubes at least 25 millimeters, in particular 30 to 34 millimeters, and the length of the Tubes 0.5 to 5 meters. After the reaction, the reaction mixture is generally according to the Above-mentioned procedure when using silver catalysts worked up and the formaldehyde absorbed.

The formaldehyde which can be produced by the process of the invention is disinfectant, tanning agent, Reducing agent and valuable raw material for the production of synthetic resins, adhesives and Plastics. With regard to the use, reference is made to the cited volume by U11 m a η η, p. 670.

The parts given in the following examples are parts by weight.

example 1

In an evaporator column with three sieve trays, an hourly mixture of 40 parts of crude ethanol (24 parts of methanol, calculated 100%, 0.16 part of alkali) and 16 parts of water is evaporated at 1.2 atm and 70 ° C, with 71 parts per hour of air mixed and the steam-air mixture reacted over a silver catalyst (250 parts) at 1.2 at and 68O ^{0 C.} The silver catalyst consists of a lower, 20 mm thick layer of silver with a grain size of 1.5 to 3 mm and an upper, 1 mm thick layer of silver with a grain size of 0.2 to 1 mm. The loading is 1.9 t of methanol per m ^{2 of} catalyst bed cross section and hour. The reaction mixture is cooled to 150 ° C. and dissolved in 5.2 parts of water per hour in a Ricscl tower.

The vaporizer always contains 60 parts of liquid. After three hours of operation, a strong foaming. 10 hours after the start, the foam layer is 210 cm high and covers all of them three evaporator trays. The liquid level indicator shows an apparent fluctuation in the liquid level of ± 100 cm. Also an addition of 0.5 parts of 50 percent strength by weight sodium hydroxide solution does not reduce foam formation. Now it becomes 0.0005 Parts thick oil (consisting of 60 percent by weight nonyl alcohol, 10 percent by weight octyl alcohol, 5 percent by weight Decyl alcohol, 3 percent by weight dodecyl alcohol, 2 percent by weight myristyl alcohol and 10 percent by weight of dinonyl ether and 10 percent by weight of dioctyl ether), dissolved in one part a mixture of 60 percent by weight of raw methanol and 40 percent by weight of water within Added for 2 minutes. Immediately after the addition; the foam disappears completely, the evaporator bottoms remain free and the liquid boils calmly. Fluctuations in the liquid level are not flour detectable. After this one-time addition of thick oil, the foam occurs until the system is switched off after lOTagen no longer on. The discharge before the addition of thick oil is on average 14.0 parts per hour Formaldehyde, after the addition 19.7 parts of formaldehyde.

Example 2

An evaporator column with two sieve trays are 61 parts per hour of a mixture of 40 percent by weight of water and 60 percent by weight of raw methanol are supplied. The mixture is at 1.4 at and 74 ° C evaporated and implemented analogously to Example 1. The inflowing mixture contains 0.08 percent by weight Sodium hydroxide. A 2 cm thick layer of foam forms on the upper floor, on which lower soil a layer of 30 cm. Analogous to example 1 are all disturbances of the evaporation rate and the delay in boiling can be observed.

Then, within 10 minutes, 0.2 parts of an oil percent strength by weight aqueous methanol solution are added and 0.0006 parts thick oil (consisting of 50 percent by weight nonyl alcohol, 5 percent by weight Octyl alcohol, 5 percent by weight lauryl alcohol, 20 percent by weight dinonyl ether, 18 percent by weight Dioctyl ether, 0.2 percent by weight water, 1.8 percent by weight acetic acid onyl ester) was added. The foam collapses immediately after the addition, the starting mixture evaporates without disturbance, the system remains foam-free until it is switched off (2 days after addition). The yield before the addition of thick oil is 22 parts of formaldehyde per hour, and 30.0 parts of formaldehyde after the addition.

Example 3

In a batch carried out analogously to Example 2, 0.0003 parts per hour of thick oil are continuously added of the composition 70 percent by weight decyl alcohol, 10 percent by weight octyl alcohol, 8 percent by weight Dodecyl alcohol, 10 percent by weight didecyl ether and 2 percent by weight acetic acid decyl ester admitted. The evaporation takes place without disturbance. The system remains until it is switched off (60 Days) foam-free. The hourly output is 29.9 parts of formaldehyde.

S- *

552

Claims (2)

is routed. All of these impurities will ever occur Claim: according to the manufacturing process and storage of the methanol in different amounts and numbers of processes for the production of formaldehyde components. by evaporation of a mixture of metha- 5 In the evaporation of such mixtures of menol and water and subsequent oxidizing ethanol and water, difficulties often and often arise in the considerable dehydrogenation of methanol in the presence of a chemical measure: The evaporation catalyst at elevated temperature, thereby speed decreases, the evaporator sump is marked that the evaporation in holds back liquid, and it occurs at the upper presence of a mixture of at least one io area of the evaporating methanol solution. ■ larger alkanols with more than 7 carbon atoms and amounts of foam with relatively large E; . Iblasen of at least one dialkyl ether, in which each and mostly relatively solid consistency. At the same time the two alkyl groups have more than 7 carbon, the pressure in the evaporator can increase and the atoms it contains is carried out. Liquid mixed with the air with the 15 increasingly a dense layer of foam form. In some cases the foam is carried away, gets onto the catalyst and disrupts or The invention relates to a method of production which prevents the conversion of the methanol. Just in treatment of formaldehyde by evaporation of a large-scale plant, where generally from 60-mix of methanol and water in the presence of 20 to 95 weight percent methanol solutions of Meneine Mixture of alkanols and Dialkyläthem conditions in H) OO to 20,000 kg of methanol solution per hour and subsequent catalytic, oxidizing vaporization can be done after 1 to 16, often already hydrogenation of methanol. at intervals of 1 to 3 hours, the pressure of It is from Ullmann's Encyclopedia of technical · usually 1.2 aul 1.5 to 1.8 at rise when Chemie, Vol. 7 (1956), p. 659 ff., Known that * 5 a two-bottom evaporator column is used. Methanol in the form of an aqueous, e.g. B. 55 oigen At the same time, the amount of evaporated Lo-methanol solution increases evaporated in an evaporator, the solution per hour to 70 to 80 ° υ of its original Vapor mixture mixed with air and then the Mc value off. ethanol on a silver or metal oxide catalyst All these difficulties lead to mostly oxidizing dehydrated. As water, condensation is used. Water, but also non-chlorine, appropriately disinfected, are operational interruptions in relation to tetcs befiebsvvasscr used. As process water inlet and heat supply necessary. This slöin this is where groundwater comes in. by suitable construction of the Spring water, surface water, such as river water, evaporator only in certain cases reduced who-drinking water, Boiler feed water and occasionally 35 den. Even so, step accordingly beforehand also consider seawater. Depending on the origin and designed evaporators in long-term operation Treatment of the water used can cause numerous disorders of the mentioned form and their causes Contain substances as an impurity, e.g. B. Metal salts are often unknown and not only in the evaporator such as Ferric chloride, alkaline earth compounds are to be sought in shape construction. The cause of this the hardness of the water, alkali salts, metals such as zinc or difficulties mostly lies in the type and Aluminum or copper e.g. from pipe materials, Ni amount of impurities present in the mixture, Nitrites, phosphates, organic decomposition probes, but their effect in individual cases mostly not products like phenols. Raw materials can be used as a foreseeable raw material. In particular, there seems to be a certain ethanol or pure methanol, the alkali content of raw methanol to promote the foam effect. Likewise is obtained by fractional distillation, an increase in the alkali content or a be turned. Depending on the manufacturer, raw methanol can be switched from raw methanol to pure treatment process (Ullmann's encyclopedia of technical-methanol as a starting material give away considerable disruptions Chemistry, Vol. 2, p. 398 ff.) In its combination of causes. The German Offenlegungsschrift 1 618 438 Settlement vary and contains generally of 95 teaches (p. 2, 1st paragraph) that alkalis die Schaumbilbis 70 percent by weight of methanol, from 1 to 29 percent in this context, and underweight percent Water and from 0.1 to 6 percent by weight emphasizes the importance of using particularly Impurities. Grain pure methanol as impurities. Foam once formed z. B. Alkaline compounds such as sodium formate, layers are difficult to remove, as can Sodium hydrogen carbonate, sodium carbonate, Na- cleaning the evaporator again foam in let trium acetate, sodium sulphide, sodium methylate, ca.55 appear in the cleaning water, lium hydroxide, sodium hydroxide; Formic acid; In the industry. e.g. in paper production, Aldehydes such as acrolein, glyoxal, propionaldehyde, textile dyeing or de-acetaldehyde used in textile printing; Ketones such as acetone and butanone-2; Foamers are for corresponding aqueous treatment glycol; Hexane; Dimethyl ether; organic or baths, e.g. B. washing baths, mercerization liquors, inorganic Connections, e.g. B. Formiate or 6 ° thought. They do not solve these difficulties or Sulphides of metals such as iron, chromium, copper, inadequate. Defoamer or aluminum, Zinc, magnesium; Sulfur compounds for the difficulties mentioned gene such as dimethyl sulfide; Esters such as B. Dimethyl in methanol-water mixtures were previously in terephthalate; Amines such as monomethylamine, Dirne- connection with the production of formthylamine, Trimethylamine; Ammonia in question. Ins- 65 aldehyde not described. In addition, a special are alkaline impurities in which such aids also meet conditions, Usually present because the ones in the methanol are unsuitable for the many defoamers: The Acid in almost all synthesis processes with alkali new- volatility with steam or methanol-