DE1183896B - Process for the purification of gaseous formaldehyde - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Boarding school KL: C 07 c

German KL: 12 ο - 7/01

Number: 1 183 896

File number: F39306IVb / 12o

Filing date: March 22, 1963

Opening day: December 23, 1964

The invention relates to a method for removing contaminants from crude formaldehyde gases, as obtained, for example, by pyrolysis of paraformaldehyde. The procedure is in Presence of a washing liquid at elevated temperatures at which polymerization of the formaldehyde is not carried out.

Several processes are already known for the purification of crude formaldehyde gases. In principle knows you have two options, once cleaning at low temperatures, which is always a lossy one Pre-polymerization of the formaldehyde is connected, and on the other hand the purification through Washing the formaldehyde with washing liquids at higher temperatures (over 80 ° C). In these procedures the prepolymerization does not take place. The washing procedures of this type are primarily based on removal directed by water that occurs when ionic catalysts are used for subsequent polymerization interferes with polyoxymethylenes.

In detail z. B. the following methods are known: According to German patent specification 1 140 921 can chemically almost pure formaldehyde is obtained if the formaldehyde vapors are partially polymerized leaves. Here you have to keep the prepolymerization low by complex measures in order to achieve a To achieve a good yield, or the yield drops so much that the losses are economically viable Exceed measure.

German Patent 1 106 748 describes the purification of formaldehyde with dicarboxylic acid anhydride made in liquid form, for example, a stream of formaldehyde gas is through a Melt passed by maleic anhydride. In this process there is a risk that the anhydride will collapse escapes with the formaldehyde and thus contaminates the formaldehyde again. As the acid anhydride In this process, a chemical reaction with the impurities in the formaldehyde occurs is received, it is consumed in this process. Regeneration is therefore hardly possible.

According to Belgian patent specification 623 900, the alkali or alkaline earth salt of an ion exchanger is used for Purification and drying of formaldehyde used. This procedure requires a very expensive and laborious preparation and regeneration of the ion exchangers and also very large quantities of exchangers. It is therefore unsuitable for technical use.

The treatment of gaseous formaldehyde with washing liquids is z. As described in U.S. Patent 2,785,651. There is a process used to purify formaldehyde
gaseous formaldehyde

Applicant:

Paint factories Bayer Aktiengesellschaft,

Leverkusen

Named as inventor:

Dr. Ernst-Ulrich Köcher;

Dr. Kuno Wagner, Leverkusen;

Dr. Karl-Ludwig Schmidt, Opladen;

Kurt Klinkmann, Monheim

gas washed with polyethylene glycol dialkyl ether. The purified formaldehyde obtained can be with Tin (II) catalysts polymerize to a usable polyoxymethylene, but the production this washing liquid is much more expensive, since the polyethers used have previously undergone an alkylation must be subjected, d. H. an additional process step with work-up is required.

According to Austrian patent specification 225 682, esters of polyalkylene glycol are used as washing liquid used, especially ethyl acetate. This process aims in particular at the removal of water, but accepts that the formaldehyde is caused by acid split off from the ester, especially acetic acid, becomes contaminated again. However, traces of acids in particular interfere with the polymerization with tin (II) catalysts very.

According to German Patent 1,090,191, the washing liquid used is cyclohexylformaldehyde hemiacetal used. In this process, a significant part of the formaldehyde is absorbed by the washing liquid and must be recovered in a cumbersome way. As the basis of this hemiacetal Alcohol lying in the working temperature range must have such a low vapor pressure that it removes formaldehyde not contaminated, this process cannot be carried out at higher temperatures. The low working temperatures, however, require prepolymerization of the formaldehyde and thus further losses in yield.

According to the process of the invention, on the other hand, formaldehyde can be obtained with such purity that This is for the polymerization on special metal catalysts, z. B. tin (II) compounds are suitable. Here does the content of the? Formaldehyde to impurities

409 759/398

3 4

such as methanol, methylal and especially the temperature, the water content area plays a subordinate role at normal pressure; this can be between 80 and 140 ° C. Under reduced more than 0.5 ° / ₀ and up to about 5 ° o of /. The metal catalysts used there are sensitive to lower (about 60 ^c C) or higher minimum catalyst poisons, which are also used in raw temperatures. It is most advantageous if it contains formaldehyde gases, the nature of which is generally the lowest possible temperature, but at which little has been known so far. Under the pressure conditions chosen, a form may be aldol-like condensation-aldehyde polymerization just not taking place, products and their decomposition or secondary products that can be used

even in the smallest amounts, possibly through chelation, complete or preferably only partial regeneration education or oxidative or reductive effect can be used again. Most beneficial is one Deactivate the catalyst. Washing cycle in which a bypass flow of about

The invention relates to a process for 10 to 30% of a regeneration stage. the Purification of gaseous formaldehyde by loading. Regeneration can be done with the help of ion exchangers treatment with an organic liquid can be carried out at er 15. Acid ion exchangers come higher temperature, which is characterized, but only taken into account if previously in the Waschdaß the treatment of the crude formaldehyde gas, medium amounts of dissolved aldehyde, for example by if necessary together with a low volatility blowing out with inert gases, have been completely removed. Hydrocarbon, with at least one hy- With advantage, basic ion exchangers, Aludroxylgruppe containing alkylene glycol polyether with 20 miniumoxide, activated carbon, sodium carbonate in common Molecular weight between 300 and 5000, which in a suitable form, e.g. B. as a fine powder or as granules the polyether chain by replacing an oxygen atom or in a thin layer on solid support materials by a sulfur or nitrogen atom or used. A simple one may also suffice under certain circumstances Acetal group can be modified, at temperatures blowing out with inert gas or steam, from 80 to 140 ° C and normal pressure, 25 In the following examples, the purity of the the minimum temperatures at negative pressure or formaldehyde purified according to the invention by the Overpressure are lower or higher. Molecular weight of the PpIy produced by polymerization: -

The molecular weight of these washing fluids is shown by oxymethylene. The crude formaldehyde gas must be between 300 and 5000 so that, on the one hand, a suspension of Paraderen The vapor pressure is so low that no noteworthy formaldehyde is allowed to enter a hot pyrolysis zone Transition into the gas phase takes place, on the other hand, natural gas flow is generated. Through the subsequent the viscosity of the liquid is not too high, so gas scrubbing was the water and methanol content that the flow through a scrubbing column interfering gases is not significantly reduced. The effective free he follows. Viscosities of about 2 poise at the speed of the washing operation manifested themselves in a chosen one Operating temperatures can still be taken into account. Liquids whose vision has been detected are preferred, as well as a reduction in the cosities up to about 1.0 poise. impurities acting as catalyst poisons, the

These alkylene glycol polyethers, which can be branched or unbranched in a substantial increase in molecular weights, can be expressed by polymers of the formaldehyde polymers obtained. As a sation of alkylene oxides or by etherification 40 relative measure of the molecular weights, the viscose of diols is used, whereby the use of tatszabj [η] (intrinsic viscosity), which by measuring the amines, hydrazines, alkylene sulfides or sulfur flow time of 0.5 ° / ₀ solution of an acetylated diol containing z. B. thiodiglycol, as well as ali- polyoxymethylene sample in butyrolactone at 150 ° C in phatic aldehydes, z. B. formaldehyde, numerous an Ubbelohde viscometer was determined. The variations of the characteristics of these polyether back 45 viscosity [η] is the measured viscosity of the clear melting point, viscosity, basicity and oxy- solution in the following relationship: dationsbeständigkeit possible. The manufacturing process for optionally modified polyether diols r ■, __ j · 1 ⁷ V. are described in the literature. In detail, <■ _ <><;' for example the following, more than one hydroxyl group 50 viscosity of the solution

containing alkylene glycol polyethers :% ~.

Addition products of ethylene oxide or propylene viscosity of the solvent

oxyds to di- and higher-functional alcohols such as

ω, ω ' -dihydroxyethylene glycol polyether, ω, ω'-dihy- Example 1 ₍

hydroxypropylene glycol ether, copolymers of 55 A through continuous pyrolysis of paraforrri ethylene oxide and propylene oxide and / or styrene oxide, aldehyde in diesel light oil (bp 220 to 320 ° C) Copolymers of tetrahydrofuran with alkylene 130 ° C generated formaldehyde stream was from below oxides, condensation products from polyfunctional ones passed through a jacket-heated sensor column, Alcohols (hexanediol, thiodiglycol) - given by the washing liquid from above. To if in a mixture with other di- or higher-function 60 passage through the column was the purified one nellenAlkoholeniGlycerin.Trimethylolpropa ^ hexane-formaldehyde mixed with steam, condensed and triol and pentaerythrate). the acid content in the aqueous solution thus obtained

The washing operation can be determined by simple flooding, by potentiometric titration. The preferred but in a countercurrent scrubbing column such No. 1 was carried out with diesel light oil as scrubbing liquid will. The ability is expediently carried out. Here are only minor lonne with a jacket heater or other heating amounts of formic acid removed, so that this experiment provided with the help of which the desired as a comparison to the following experiments No. 2 to 10 Temperature can be maintained. Is to be regarded as operational.

Tabel

\ / α ** o Π ^ * rl Washing liquid Flow Washing formaldehyde Formic acid,% *) before 0.075 v ersiiL / fl
No. speed temperature throughput after the cleaning 0.075 Diesel light oil l / h ⁰ C g / h 0.067 0.075 1 Polypropylene glycol i ¹ ) 1.65 100 200 0.019 0.075 2 the same 1.0 100 100 0.011 0.075 3 the same 1.65 100 100 0.004 0.075 4th C ¹ ) + 5% ( ² ) 2.0 100 135 0.007 0.075 5 ( ^x ) + 5% ( ³ ) 1.55 100 200 0.006 0.075 6th Polyethylene glycol ( ⁴ ) 1.6 100 200 0.006 0.075 7th the same 1.95 100 210 0.008 0.075 8th ( ⁴ ) + 5% ( ⁵ ) 1.55 100 210 0.004 9 ( ⁴ ) + 5% ( ³ ) 1.55 100 210 0.003 10 1.55 100 210

*) The stated values are the mean values from at least two analysis results.

C ¹⁾ ß), Cu 'dihydroxy-propylene glycol [l, 2 -] - Polyether, molecular weight 2000, viscosity at 80 ⁰ C: 0.35 poise.

( ² ) Polypropylene glycol ether modified with ethylene diamine and ethylene oxide, branched.

( ³ ) Polypropylene glycol ether modified with ethylene diamine, molecular weight about 2400.

⁽⁴⁾ ω, ω'-dihydroxy-ethylene glycol polyether, molecular weight 1550 viscosity at 8O ⁰ C: 0.50 poise.

( ₅ ) Polypropylene glycol ether modified with ethylene diamine, molecular weight about 500.

Example 2
as in Example 1 produced continuous

Formaldehyde gas stream was, as described there, washed and passed into cooled methylene chloride, until the solution had absorbed about 4 percent by weight formaldehyde gas, which as polyoxymethylene failed. The catalyst used in the individual experiments was 25% before the start added to the polymerization, while the remaining 75% during the approximately 30 minute polymerization were added dropwise. The polymerization temperature was 20 to 30 ° C. After the end of the polymerization the deposited polyoxymethylene was filtered off with suction, air-dried and in a known manner acetylated. Comparative experiment No. 11 demonstrates that the formaldehyde washing carried out according to the invention the specific problems of the polymerization of hydrous formaldehyde over suitable metal catalysts is fair; when using ionic catalysts as in experiment no. 11 Obtain technically unusable polyoxymethylenes.

Tabel

Washing liquid Washing catalyst Lot*) M. VCIaUdJt
No. temperature Weight (I) **) ⁰ C Tri-n-butylamine percent 0.11 11 (1) **) 100 Sn (II) octoate 0.01 1.48 12th (1) **) 100 Sn (II) -bis-methoxyethyl- 0.3 1.43 13th 100 carbonate 0.3 ( ⁴ ) **) Sn (II) octoate 1.87 14th Tetraethylene glycol 100 Sn (II) octoate 0.3 1.25 15th a, co-dimethyl ether according to 100 0.3 U.S. Patent 2,780,652

*) Based on formaldehyde.
**) See under table 1.

Example 3

A formaldehyde gas stream obtained by pyrolysis of paraformaldehyde, which is diluted with methylene chloride vapor in a ratio of about 1: 1, is introduced through ^{lines heated to 100 °} C. into a polymerization vessel in which methylene chloride has been placed. At the same time, a solution of Sn (II) octoate in methylene chloride is metered evenly into the polymerization vessel as a contact. (0.3 percent by weight Sn (II) octoate, based on formaldehyde.) After an approximately 3% suspension of the polymer has been reached, the introduction is ended, the polymer is filtered off, acetylated and the intrinsic viscosity is determined.

In case A the test is carried out as described above, in the FaIIeB formaldehyde methylene chloride-gas mixture is a countercurrent hot wash at 100 ⁰ C in a washing tower filled with Raschig rings, subjected. 50 liters of polypropylene glycol are used as scrubbing liquid per kilogram of formaldehyde gas. The polypropylene glycol is slightly branched and has an average molar weight of 4000.

The viscosity number increases considerably during washing:

A [η] = 0.92

B ". M = 1.25

The polypropylene glycol used as washing liquid is circulated, with regeneration with activated charcoal and sodium carbonate is interposed by adding the glycol via an appropriate Column filling is sent. This regeneration, along with other impurities, removes acid from the Polypropylene glycol removed. The acid values of polypropylene glycol that can be titrated against phenolphthalein is before regeneration 6.9 meq. / l, after regeneration 0.7 meq. / l.

Claims (3)

Patent claims: 1. Process for the purification of gaseous formaldehyde by treatment with an organic one Liquid at elevated temperature, characterized in that the treatment the crude formaldehyde gas, possibly together with a low volatile hydrocarbon, with at least one hydroxyl group containing alkylene glycol polyether with a molecular weight between 300 and 5000, which in the polyether chain by replacing an oxygen atom with a sulfur or nitrogen atom or an acetal group can be modified, at temperatures of 80 to 140 ° C and normal pressure is carried out, the minimum temperatures being lower or higher in the case of underpressure or overpressure lie. 2. The method according to claim 1, characterized in that that the treatment with a ω, ω'-dihydroxyethylene glycol polyether is carried out with a molecular weight between 500 and 4000. 3. The method according to claim 1, characterized in that the treatment with an ω, ω'-dihydroxypropylene glycol ether is carried out with a molecular weight between 500 and 4000. Considered publications:
German Auslegeschriften Nos. 1 090 191, 1 106 749, 752, 1 140 921; Austrian Patent No. 2,780,652;
Belgian Patent No. 623,900;
Czechoslovak Patent No. 99,988. 409 759/398 12.64 Bundesdruckerei Berlin