DE1299640B - Process for the production of trioxane - Google Patents

Description

The production of trioxane by trimerizing formaldehyde is known from the literature. It is made from aqueous formaldehyde solutions Catalysis with strong acids at elevated temperature Trioxane formed and distillative removed from the reaction mixture. However, side reactions easily occur in these processes one that will reduce the yield. So z. B. the concentration of the used Formaldehyde solution do not exceed 60 percent by weight, otherwise it will take effect the acid serving as a catalyst promotes the formation of paraformaldehyde. Paraformaldehyde is insoluble in the reaction medium and at the temperatures used from 90 to 100 "C difficult to remove by depolymerization. On the other hand, cause too high acid concentrations in the reaction medium disproportionation reactions of the Formaldehyde, with methyl formate, formic acid, methylal as well as other by-products develop. When using the p-toluenesulfonic acid also mentioned in the literature there is also a reaction of the aromatic nucleus with the formaldehyde, which leads to resinification. When using sulfuric acid z. B. the concentration Do not exceed 8 percent by weight, otherwise the yield will be greatly reduced will.

Above all, however, these methods have the disadvantage that only one Part of the formaldehyde added in the unit of time is converted and as a trioxane-formaldehyde-water mixture can be removed from the reaction medium by distillation, d. that is, the response times are long or large equipment is required. However, if you increase the throughput faster distillation rate, then the level of polymeric formaldehyde decreases in the distillate, and the trioxane formation decreases.

There is also a method in which it is attempted by addition of foreign substances, such as alkali or alkaline earth metal chlorides, or of glycerol, the reaction temperature in the aqueous phase and thus to increase the rate of formation of the trioxane.

The substances added here, however, interfere with the implementation the formation of by-products.

Finally, a process has become known in which as a catalyst an acidic ion exchanger is used. However, with this method only a low hourly throughput of a maximum of 170/0 of the formaldehyde used and only a conversion of 550 / o of the formaldehyde used can be achieved.

In addition, the use of an ion exchanger is insofar disadvantageous, since this is only slight in the 100 to 1800 C hot reaction solution Has lifetime.

The inventive method for the preparation of trioxane from at least 600/0 aqueous formaldehyde solutions by heating to at least 95 ° C in the presence an acid catalyst and distillation of the trioxane formed is thereby characterized in that the reaction is carried out in an emulsion consisting of the aqueous Formaldehyde solution, an acidic solution against formaldehyde at temperatures above 1000 C Medium stable, inert oily component and an alkyl, aryl, alkylaryl or. Aralkylsulfonic acid as an emulsifier and catalyst, at a temperature above 95 "C performs.

In the process according to the invention, the trimerization takes place Formaldehyde to trioxane in an oil-water emulsion as an interfacial reaction. the as The acids used in the catalyst are also emulsifiers for the oil-water emulsion. With this procedure it is possible to use reaction temperatures above 1000 C as well to use high formaldehyde and acid concentrations without the above Having to fear side reactions. The trioxane formed is not in the oily phase dissolved, but expelled immediately. This also makes the The formation of new trioxane from the formaldehyde present in the emulsion is favored.

Aqueous formaldehyde concentrates are used whose formaldehyde content is at least 600 /. In general, formaldehyde concentrates are used between 60 and 80 percent by weight, preferably 70 percent by weight, formaldehyde.

As an acid catalyst and emulsifier, for. B. alkyl, aryl, Alkylaryl or aralkylsulfonic acids containing one or more sulfonic acid groups per Contain molecule in question.

The concentration of sulfonic acids is generally between 20 and 50 percent by weight, based on the amount of formaldehyde in the concentrate. But there are also other sulfonic acid concentrations outside this range possible; in particular, in contrast to the previously known methods, the acid concentration be chosen very high, without noticeable disproportionation reactions of the used Having to fear formaldehyde. The catalysts to be used at the same time act as emulsifiers, can be used individually or as a mixture.

As an inert oily constituent, those oils come into consideration that are stable under the reaction conditions, especially paraffin oil and synthetic ones Lubricating oils, for example isomerized polyethylene, are suitable.

The reaction temperatures are from 95 to 150 ° C., preferably at 101 to 104 "C.

The emulsion is preferably composed of 1 part of formaldehyde concentrate and 1.5 to 3 parts of oil content, but other amounts of oil content are also possible, and composed of sulfonic acids.

The inventive method is particularly suitable for continuous Execution.

The technical progress of the process according to the invention lies especially in the high conversion, the high yield and in the possibility of one high throughput that does not result in an increased formation of undesirable by-products connected is.

It is therefore possible to work with high space-time yields.

The resulting crude trioxane is in a known manner by extraction, Steam distillation or freezing cleaned.

The following examples explain the process according to the invention: Example 1 a) In an enamel reaction vessel equipped with a stirrer and heating bath 600 parts by weight of paraffin oil (DAB VI) are heated to 90 ° C. Now 300 parts by weight a 700/0 aqueous formaldehyde solution, which is also heated to 90 ° C, added. 45 parts by weight of alkyl sulfonic acids, which contain 14 to 16 carbon atoms and which have an average molecular weight of 300 have, added, forming an emulsion. Afterward the heating bath temperature is increased to 105 ° C, with the distillation of the crude trioxane begins and goes over at about 96 ° C. The Rohtrioxan is in one with water charged cooler condenses.

After one hour, 300 parts by weight of distillate are obtained has the following composition: 150 parts by weight of trioxane, 48 parts by weight Formaldehyde, 3 parts by weight of by-product, 99 parts by weight of water.

The throughput per hour is therefore 1000 / o of the weight used of formaldehyde solution and the conversion of formaldehyde 730 / o. 970 / o of the turnover Formaldehyde is obtained as trioxane. b) Comparative experiment without paraffin oil 300 parts by weight of 65% formaldehyde solution are used in the apparatus described above submitted and without the addition of paraffin oil 45 parts by weight of alkyl sulfonic acids, the Contains 14 to 16 carbon atoms and has an average molecular weight from 300 have, added with stirring. The reaction mixture foams very strongly; at 99 ° C., 100 g of a distillate pass over in the course of one hour, the following composition has: 26 parts by weight of trioxane, 28 parts by weight of formaldehyde, 4 parts by weight of by-products, 42 parts by weight of water.

The throughput per hour is thus 33 percent by weight of the weight of formaldehyde solution used. The conversion is 460 / o of the formaldehyde used. 87% of the converted formaldehyde is obtained as trioxane. With this procedure, noticeable amounts of paraformaldehyde are deposited in the apparatus. c) Comparison with Example 1, a) of German Auslegeschrift 1 135 491. The technical progress of the process according to the invention, in particular with regard to the conversion and the yield, results from the data in the table below German Auslegeschrift 1135491 Method according to the invention [(Example 1, a)] [(Example 1, a)] Use of raw materials ....... 300 parts paraformaldehyde 600 parts paraffin oil (96 0 / o = 288 parts 1000 10 mold- 45 parts alkyl sulfonic acids aldehyde) 300 parts of formaldehyde concentrate 175 parts water (70% = 210 parts 100 ovo mold (about 62% formaldehyde solution) aldehyde) 45 parts ion exchanger Temperature ............... 100 ° C 105 ° C Distillation time ....... 1.5 and 2 hours 1 hour Distillate ............... 52 parts of trioxane 150 parts of trioxane 24 parts of formaldehyde 48 parts of formaldehyde 1 part by-product 3 parts by-product 23 parts of water 99 parts of water Throughput per hour a maximum of about 17 0 / o of the formaldehyde used 100 0 / o of the formaldehyde content aldehyde concentrate centrates Sales ............... 550 / o of the paraformaldehyde used 73 01o of the 100% formaldehyde used after a total of 8 hours aldehydes after 1 hour Yield .... .... .... 91%, based on the conversion 97 ovo Example 2 According to the method described in Example 1, a), 600 parts by weight of 70% aqueous formaldehyde solution preheated to 900 ° C. are introduced into the reaction vessel every hour after the start of the distillation of the crude trioxane. Every hour, 600 parts by weight of a distillate are removed which consists of 316 parts by weight of trioxane, 95 parts by weight of formaldehyde, 180 parts by weight of water and 9 parts by weight of by-products. The throughput is thus 100010 of the weight of the formaldehyde solution used, the conversion 77% of the formaldehyde used, 97% of the converted formaldehyde being obtained as trioxane.

Example 3 According to the method described in Example 1, a) 200 parts by weight of paraffin oil (DAB VI) and 30 parts by weight of methanesulfonic acid below Emulsified stirring. 100 parts by weight of a 77% strength emulsion are allowed to enter this emulsion at 90.degree Run in formaldehyde solution within an hour and distill at a heating bath temperature of 105 ° C in the same period at 94 to 96 ° C head temperature a mixture of the following Composition from: 52 parts by weight of trioxane, 13 parts by weight of formaldehyde 1 part by weight By-product, 34 parts by weight of water.

The throughput per hour is 1000 / o of the weight used of formaldehyde solution and the conversion 69% of the formaldehyde used, of which 98% are converted to trioxane.

Example 4 In a reaction vessel equipped with a stirrer and heating bath 300 parts by weight of paraffin oil (DAB VI) are heated to 90 ° C. Now 250 parts by weight 700 /, aqueous formaldehyde solution, which is also heated to 900 ° C., is stirred in. 95 parts by weight of phenylethylsulfonic acid (C6H5 - CH2 - CH2 - SO3H) added, and the heating bath temperature is increased to 105 "C, where the distillation of the crude trioxane begins, which passes over at 96 and 97 ° C and is condensed in a cooler charged with water.

400 parts by weight of a 90 "C warm 70% formaldehyde solution are added every hour introduced into the reaction vessel and at the same time 400 parts by weight of distillate per Hour deducted from 192 parts by weight of trioxane, 86 parts by weight of formaldehyde, 2 parts by weight of by-products and 120 parts by weight of water.

The throughput per hour is thus 100 ovo of the weight used of formaldehyde solution and the conversion of formaldehyde 690 / o 990 / o of the converted formaldehyde are obtained as trioxane.

Example 5 According to the method described in Example 1, a) 600 parts by weight of paraffin oil (DAB VI), 300 parts by weight of 700% strength aqueous formaldehyde solution and 50 parts by weight of n-dodecylbenzenesulfonic acid reacted and distilled subject.

After hours of distillation, 300 parts by weight of the distillate are as follows Composition obtained: 144 parts by weight of trioxane, 51 parts by weight of formaldehyde, 3 parts by weight of by-product, 102 parts by weight of water.

The throughput per hour is therefore 1000 / o of the weight used the formaldehyde solution, the conversion 700 / o of the formaldehyde used, with 980 / o of the converted formaldehyde can be obtained as trioxane.

To separate off the trioxane, the distillate obtained is treated with methylene chloride stirred and extracted in an extraction column with methylene chloride.

The resulting water-containing solution of trioxane in methylene chloride is then distilled, the bottom product being an anhydrous, molten one Crude trioxane is obtained, which is again distilled over calcium oxide under nitrogen. 94,010 of the crude trioxane used are obtained as pure trioxane with a temperature of 64 ° C.

Claims (1)

Claim: Process for the production of trioxane from at least 60% aqueous formaldehyde solutions by heating to at least 95 ° C in the presence an acid catalyst and distilling off the trioxane formed, d a d u r c h g e k e n nz e i c h n e t that one consists of the reaction in an emulsion from the aqueous formaldehyde solution, one against formaldehyde at temperatures over 1000 C in an acidic medium stable, inert oily component and an alkyl, Aryl, alkylaryl or aralkylsulfonic acid as an emulsifier and catalyst, with one Temperature above 95 "C performs.