METHOD FOR THE HYDRODESCOMPOSITION OF AMMONIUM FORMIATES IN REACTION MIXES CONTAINING POLYOL The invention relates to the field of industrial organic chemistry. More precisely, the present invention provides a process for the effective decomposition of hydrogenation of trialkylammonium formate which is present in methylolalkanes and have been formed from the trialkylamine used as a catalyst in the preparation of the methylolalcanal and formic acid formed as a by-product. The condensation of formaldehyde with high alkanals of CH-acid to form methylolalcanales, in general dimethylolalcanales and trimethylolalcanales and the conversion of the obtained compounds into polyols is a widely used process in the chemical industry. Examples of important triols obtained in this way are trimethylolpropane, trimethylol ethane and trimethylolbutane, for which a widely used use has been found in the production of surface coatings, urethanes and polyesters. Additional important compounds are pentaerythritol, which is obtained by condensation of formaldehyde or acetaldehyde, and also neopentyl glycol of isobutyraldehyde and formaldehyde. Similarly, tetravalent alcohol pentaerythritol is frequently used in the surface coating industry, although it has also attained great importance in the production of explosives. The mentioned polyols can be prepared by several methods, one method is the Cannizzaro process which is further subdivided into the Cannizzaro inorganic process and the organic Cannizzaro process. In the inorganic variant, an excess of formaldehyde is reacted with that corresponding to the channel in the presence of stoichiometric amounts of an inorganic base such as NaOH or Ca (OH) 2. The methylolalcanal formed in the first stage reacts in the second stage with the excess of formaldehyde in a disproportionation reaction to form the corresponding polyol and the formate of the respective base, ie, for example sodium or calcium formate. In the Cannizzaro organic process, a ternary amine, generally a trialkylamine, is used instead of the inorganic base, the reaction proceeds as described above, with an equivalent of the ammonium formate of the corresponding amine that is formed. This can be further treated by appropriate methods, so that at least the amine can be recovered and returned to the reaction. The obtained crude polyol can be treated in several ways to obtain the pure polyol. A further development is the hydrogenation process in which an appropriate alkanal and formaldehyde are reacted with each other without the presence of at least stoichiometric amounts but of catalytic amounts of a ternary amine, generally from about 5 to 10 mol% . In this process, the reaction is stopped at the 2, 2-dimethylolalcanal phase which subsequently is converted to a trimethylolalkane by hydrogenation. A description of the effective process can be found in WO 98/28253 of the present applicant. A number of variants of this hydrogenation process are described, inter alia, in the patent applications DE-A-25 07 461, DE-A-27 02 582, DE-A-28 13 201 and DE-A-33 40 791. Although the hydrogenation process advantageously does not form stoichiometric amounts of the formate as in the organic Cannizzaro process, the trialkylammonium formate is formed as a product of a Cannizzaro cross reaction occurring in a small amount as a secondary reaction. The trialkylammonium formates react under particular conditions, for example, water extraction or heating of the obtained trimethylolalkane solutions, to form trialkylamine formate and trimethylolpropane. These decrease the production of trimethylolalkane and are difficult to disassociate without unpleasant degradation reactions. Therefore there is a particular interest in the removal of trialkylammonium forirtiates. DE 198 48 569 describes a process for the decomposition of ternary amine formates which are present as by-products in the trimethylolalkane solutions prepared by the organic Cannizzaro process. These formates decompose when heated, preferably in the presence of catalysts of a modified noble metal and under superatmospheric pressure, in hydrogen or carbon dioxide and / or water and carbon monoxide and the ternary amine. The formate conversions in this process are unsatisfactory, and the formation of additional byproducts is also observed. DE 101 52 525 describes the decomposition of trialkylammonium formates on heterogeneous catalysts comprising at least one metal of groups 8 to 12 of the Periodic Table, giving particular reference to catalysts containing copper-, nickel- and / or cobalt-. In addition, the aforementioned process has only a limited applicability for the effective treatment of a trimethylolalkane mixture obtained by the hydrogenation process in which only catalytic amounts of trialkylamine are used and the product mixture in this way, also contains only small amounts of trialkylammonium formate. It is an object of the present invention to provide a process which is suitable for the treatment of reaction mixtures obtained by the hydrogenation process and also those obtained by the organic Cannizzaro process. In addition, this process should make it possible to decompose trialkylammonium formates with high conversions which have been possible to use in known processes of the prior art. In addition, this decomposition should lead to decomposition products which can be easily handled on an industrial scale and which do not trigger secondary reactions, thus providing a more economical process for preparing high purity trimethylolpropane. It has been found that this object is achieved by a process of removal of trialkylammonium formate from methylolalkanes which have been obtained by the condensation of formaldehyde with a high aldehyde, a process comprising decomposing trialkylammonium formate at an elevated temperature in the presence of a gas containing hydrogen in addition to a catalyst comprising ruthenium supported on titanium dioxide. The methylolalkanes which have been treated by the process of the present invention are, for example, neopentyl glycol, pentaerythritol, trimethylolpropane, trimethylolbutane, trimethylolethane, 2-ethyl-1,3-propanediol, 2-methyl-1,3-propanediol, glycerol, dimethylolpropane, dipentaerythritol and 1,1-, 1,2-, 1,3- and 1,4-cyclohexanedimethanol. In the process of the present invention, preference is given to the removal, under hydrogenation conditions, of the trialkylammonium formates of trimethylolalkanes that have been prepared by the organic Cannizzaro process or the hydrogenation process. Preference is given to purified trimethylolalkanes, particularly preferably trimethylolpropane, hereinafter referred to as TMP for short, prepared by the hydrogenation process. The preparation of crude TMP containing trialkylammonium formate by the Cannizzaro process is described, for example, in DE 198 48 569. In the hydrogenation process, the TMP is obtained by condensation of n-butylaldehyde with formaldehyde in the presence of catalytic amounts. of a ternary amine and the subsequent catalytic hydrogenation of the dimethylolbutanal mixture formed. This crude TMP does not contain any alkali metal or alkaline earth metal formates or other impurities that are formed in the inorganic Cannizzaro process. Likewise, the crude TMP contains only small amounts, from about up to 10% in moles, of trialkylammonium formates or free trialkylamine, unlike the product obtained from the organic Cannizzaro process. The crude TMP that comes from the hydrogenation and is to be subjected to the purification process of the present invention comprises trimethylolpropane and water together with methanol, trialkylamine, trialkylammonium formate, alcohols and linear and branched long chain diols, for example methylbutanol or ethylpropanediol, addition products of formaldehyde and methanol in trimethylolpropane, acetals such as TMP acetal of dimethylolbutyraldehyde and di-TMP. Good results are obtained using crude hydrogenation products comprising from 10 to 40% by weight of trimethylolpropane, from 0 to 10% by weight of 2,2-dimethylolbu anal, from 0.5% to 5% by weight of methanol, from 0 to 6% by weight of methylbutanol, from 1 to 10% by weight of trialkylammonium formate, from 0 to 5% by weight of 2-ethyl-propanediol, from 0.1 to 10% by weight of heaters such as di-TMP or other addition products and from 5 to 8% by weight of water. Crude hydrogenation products having such a composition can be obtained, for example, by the process described in WO 98/28253. Prior to the purification of the present invention to decompose the trialkylammonium formate, the crude hydrogenation product can first be treated by continuous distillation as described in Examples 2 and 3 of DE-A-199 63 435. However, the purification according to the present invention of the crude hydrogenation products is preferably carried out without prior treatment by distillation. The present invention further provides a catalyst comprising ruthenium supported on shaped titanium dioxide bodies which are obtained by the treatment of commercial titanium dioxide, before or after shaping, with from 0.1 to 30% by weight of an acid in the which titanium dioxide is barely soluble, whose catalyst is used in the process of the present invention. The ruthenium can be used either in the form of a pure metal or as a compound thereof, for example an oxide or a sulfide. The catalytically active ruthenium is applied by methods known per se, preferably in prefabricated T1O2 as support material. A preferred titanium dioxide support can be obtained for use with the ruthenium-containing catalyst as described in DE 197 38 464 by treating commercial titanium dioxide, before or after shaping with from 0.1 to 30% by weight, with based on titanium dioxide, an acid in which titanium dioxide is barely soluble. Preference is given to the use of titanium dioxide in the modification of anatase. Examples of suitable acids are formic acid, phosphoric acid, nitric acid, acetic acid and stearic acid. Ruthenium as an active component can be applied in the form of a ruthenium salt solution to the titanium dioxide support obtained in this manner, using one or more impregnation steps. The impregnated support is subsequently dried and, if desired, calcined. However, it is also possible to precipitate the ruthenium from a ruthenium salt solution, preferably by sodium carbonate, in a titanium dioxide present as a powder in an aqueous suspension. The precipitates are rinsed, dried, if desired, calcined and shaped. In addition, volatile ruthenium compounds, for example ruthenium acetyl acetonate or ruthenium carbonyl, can be carried to the gas phase and applied to the support in a manner known per se (chemical vapor deposition). The supported catalysts obtained in this way can be of all known finishing forms. Examples are extruded, pellets or granules. Before use, the ruthenium catalyst precursors are reduced by treatment with a hydrogen-containing gas, preferably above 100 ° C. The catalysts are preferably passivated by oxygen-containing gas mixtures, preferably air / nitrogen mixtures, from 0 to 50 ° C, preferably at room temperature, before they are used in the process of the present invention. It is also possible to install the catalyst in oxidic form in the hydrogenation reactor and to reduce it under reaction conditions. The catalyst of the present invention has a ruthenium content of 0.1 to 10% by weight, preferably from 2 to 6% by weight, based on the total weight of the catalyst comprising the catalytically active metal and support. The catalyst of the present invention can have a sulfur content from 0.01 to 1% by weight, based on the total weight of the catalyst, with the determination of sulfur that is carried out coulometrically. The ruthenium surface area is from 1 to 20 m2 / g, preferably from 5 to 15 m2 / g, and the BET surface area (determined in accordance with DIN 66 131) is from 5 to 500 m2 / g, preference from 50 to 200 m2 / g. The catalysts of the present invention have a pore volume from 0.1 to 1 ml / g. In addition, the catalysts have a hardness for cutting from 1 to 100 N. The supported catalyst containing ruthenium in titanium dioxide described above which is used according to the present invention for the decomposition of trialkylammonium formate present in the crude TMP it is also suitable for the hydrogenation of the TMP precursor (2,2-dimethylolbutanal). The use of the same catalyst for the hydrogenation of dimethylolbutanal and for the decomposition of trialkylammonium formate is particularly economical, since the decomposition of the trialkylammonium formate can in this case be carried out in the hydrogenation reactor of the hydrogenation process described in WO 98. / 28253 and no additional reactor is necessary. However, the decomposition of the trialkylammonium formates by the process of the present invention can likewise be carried out in a separate reactor. In the process of the present invention, the decomposition of the trialkylammonium formates is generally carried out from 100 to 250 ° C, preferably from 120 to 180 ° C. The pressures are generally used above lxlO6 Pa, preferably in the range from 2xl06 to 15x106 Pa. The process of the present invention can be carried out either continuously or in batch form, with preference given to a continuous process. In a continuous process, the amount of crude trimethylolalkane from the hydrogenation process or the organic Cannizzaro process is preferably from about 0.05 to about 3 kg per liter of catalyst per hour, more preferably from 0.1 to about 1 kg per liter of catalyst per hour . The process of the present invention is carried out under hydrogenation conditions, that is, using a hydrogenation gas added from an external source. As hydrogenation gases, it is possible to use any gases comprising free hydrogen and not containing harmful amounts of catalyst poisons, for example CO. For example, it is possible to use malodorous gases from a reformer. Preference is given to the use of pure hydrogen. The process of the present invention is illustrated by the examples below.
EXAMPLES I. Preparation of the curved TMP by the method of WO 98/28 253 An apparatus comprising two agitable and heat-stable vessels connected to each other by means of spill tubes and having a total capacity of 72 1 was supplied with a fresh aqueous formaldehyde solution (4 300 g / 1 in the form of an aqueous solution of a consistency of 40%) and n-butylaldehyde (1 800 g / h) and with fresh trimethylamine as catalyst (130 g / h) in the form of an aqueous solution with a consistency of 45%. The reactors were maintained at 40 ° C. The outlet was fed directly into the top of a film evaporator with superimposed column (steam for heating of 11 bar) and fractionally distilled there under atmospheric pressure to give an upper product of low boiling temperature consisting essentially of -butylaldehyde, ethyl acrolein, formaldehyde, water and trimethylamine and a lower product of high boiling temperature. The upper product was continuously condensed and recirculated to the reactors described above. The boiling high temperature base product of the evaporator (approximately 33.5 kg / h) was mixed continuously with a fresh trimethylamine catalyst (50 g / h, in the form of an aqueous solution of a 45% consistency) and was introduced into the a heatable tube reactor which was provided with a random fill and had an empty volume of 12 1. The reactor was maintained at 40 ° C. The outlet from the rear of the reactor was continuously introduced into the upper part of an apparatus for further distillation, namely the removal of formaldehyde (steam for heating to 11 bar), and fractionally distilled there to give a superior product of Low boiling temperature consisting essentially of ethyl acrolein, water and trimethylamine and a high boiling temperature base product. The upper low boiling temperature product (27 kg / h) was continuously condensed and recirculated to the first stirring vessel, while the lower high boiling temperature product was collected. The base product obtained in this manner consisted essentially of water together with dimethylolbutyraldehyde, formaldehyde and traces of monomethylolbutyraldehyde. Then it underwent a continuous hydrogenation. For this purpose, the reaction solution was hydrogenated at 90 bar and 115 ° C in a main reactor operated in a circulation / downflow mode and downstream of the reactor operated in the circulation mode. The catalyst was prepared by an analogous method to catalyst J in DE 198 09 418. It comprises 40% CuO, 20% Cu and 40% Ti02.The apparatus used comprised a heated main reactor 10 m in length (internal diameter: 22 mm) and a heated rear reactor 5.3 meters long (internal diameter: 25 mm). The flow around the circuit was 25 1 / h of liquid, and the feed to the reactor was set at 4 kg / h. Consequently, 4 kg / h of the hydrogenation product were removed. The hydrogenation product had the following composition: 22.6% by weight of TMP, 1.93% by weight of dimethylolbutanal, 1.4% by weight of methanol, 1.1% by weight of methylbutanol, 0.7% by weight of ethylpropanediol, 1.2% by weight of adducts of TMP with formaldehyde and methanol, < 0.1% by weight of TMP formate, 1.2% by weight of G-dimethylbutanal acetals, 2.9% by weight of high heaters, 0.57% by weight of trimethylammonium formate and 62% by weight of water. II. Measurement of porosity The porosity of the catalysts was determined by the Hg intrusion method corresponding to DIN 66 133. III. Determination of the BET surface area The BET surface area of the catalyst was determined in accordance with DIN 66 131. IV. Determination of the hardness for the cut To determine the hardness for the cut, specimens were split by a cutter. The force that had to be applied to the cutter to cut through the specimen is the hardness for cutting in N (newton). V. Determination of the formate content by ion chromatography. The formate content was determined by ion chromatography according to DEV ISO 10304-2.
Example 1: Preparation of the Ru / Ti02 catalyst 121.3 g of ruthenium nitrosyl nitrate solution (content of Ru: 10.85% by weight) were diluted with water in 90 ml. 250 g of extruded titanium dioxide extrudates of 1.5 mm having a BET surface area of 104 m2 / g and a porosity of 0.36 ml / g, which had been produced as described in DE 197 38 463, example 3, were slowly impregnated with the ruthenium solution. The wetted extrudates were subsequently dried at 100 ° C for 2 hours and at 120 ° C for 16 hours. The catalyst was activated by reduction using 10 1 standard / h of hydrogen and 10 1 standard / h of nitrogen at 300 ° C for a period of 4 hours. The catalyst is subsequently passivated by means of air / nitrogen mixtures at room temperature. The finished catalyst extrudates had a Ru content of 4.2% by weight, a BET surface area of 103 m2 / g, a pore volume of 0.26 ml / g, a ruthenium surface area of 12 m2 / g and a hardness for the cut of 21.2 N.
Examples 1 to 4 The TMP used was prepared as described above, the composition having 22.6% by weight of TMP, 1.93% by weight of dimethylolbutanal, 1.4% by weight of methanol, 1.1% by weight of methylbutanol, 0.7% by weight of ethylpropandiol, 1.2% by weight of TMP adducts with formaldehyde and methanol, < 0.1% by weight of TMP formate, 1.2% by weight of dimethylbutanal acetals of TMP, 2.9% by weight of high heaters, 0.57% by weight of trialkylammonium formate and 66.2% by weight of water. 180 ml of this crude solution were treated with hydrogen at 180 ° C and 90 bar in the presence of a catalyst as indicated in table 1, which had been pre-reduced to 180 ° C and 25 bar. After one hour, the dimethylolbutanal content was determined by gas chromatography. The formate concentration was determined by means of ion chromatography. The results obtained are summarized in table 1.
GC analysis (detection without water) Determination by means of chromatography of DMB = 2, 2-dimethylbutanal
It can be seen from the table that the ammonium formate can be catalytically decomposed with high conversions at 150 ° C on the ruthenium catalysts used according to the present invention and these catalysts are significantly more effective than the copper, nickel and cobalt catalysts . The analysis of malodorous gas indicates that methane is the main product of the decomposition of the formate.