WO2012095256A1

WO2012095256A1 - Method for the hydrogenation of 1,4-butynediol in the gaseous phase to form tetrahydrofurane

Info

Publication number: WO2012095256A1
Application number: PCT/EP2011/073933
Authority: WO
Inventors: Rolf Pinkos; Olga OSETSKA; Lucia KÖNIGSMANN
Original assignee: Basf Se
Priority date: 2011-01-12
Filing date: 2011-12-23
Publication date: 2012-07-19
Also published as: WO2012095709A1

Abstract

The invention relates to a method for the catalytic hydrogenation of 1,4-butynediol at least at the decomposition temperature of 1,4-butynediol to form tetrahydrofurane. According to the method, 1,4-butynediol is evaporated in a hydrogen-containing gas flow and is hydrogenated in the gaseous state on at least one catalyst that contains at least one of the elements of groups 7 to 11 of the periodic system.

Description

Process for the hydrogenation of 1, 4-butynediol to tetrahydrofuran in the gas phase

Description The present application includes, by way of reference, US Provisional Application 61/431868 filed Jan. 12, 2011.

The inventive method relates to the catalytic hydrogenation of 1, 4-butynediol (BID) to tetrahydrofuran (THF) in the gas phase on heterogeneous catalysts in the presence of hydrogen.

THF is widely used as a solvent and serves as a starting material for polytetrahydrofuran. It is produced worldwide in several hundred thousand tons per year.

As a gateway various options are known. Thus, it is possible to prepare maleic anhydride based on butane and hydrogenate it, for example as diester, to THF, GBL (gamma-butyrolactone), BDO (1,4-butanediol) (K. Weissermel, H.-J. Arpe, Industrielle Organische Chemie, 5th edition 1998, page 408). Furthermore, the acid-catalyzed cyclization of 1,4-butanediol is a common access route for THF (K. Weissermel, H.-J. Arpe, Industrielle Organische Chemie, 5th edition, 1998, page 113).

The technology for the production of THF, which is the most widely used worldwide, is cyclization of 1, 4-butanediol, which in turn mostly by the hydrogenation of 1, 4-butynediol as described for example in DE-A 19641707, usually under considerable pressure between 2 and 30 MPa. It must be ensured in the reaction of butynediol that this can decompose under thermal stress, especially in the presence of impurities, especially metals and their salts. This is generally the case for the pure substance already at 160 ° C, especially above 200 ° C. Impurities, especially heavy metals, can further reduce this decomposition temperature.

It would be economically desirable due to low investment costs if the hydrogenation of 1,4-butynediol would directly yield THF without isolation of 1,4-butanediol as an intermediate.

Methods for the direct production of THF from butynediol are described exclusively in the liquid phase. These are industrially (industrially) currently not exercised. DE-A 2029557 describes a process for the direct production of THF from 1,4-butynediol in the liquid phase. According to the disclosure of DE-A 2029557, butynediol is added in the liquid phase in the presence of a solvent over a catalyst having hydrogenation and acid function THF and water reacted. The reworking of the examples shows that the process is not feasible. It is mainly butanediol as a product found, but only negligible amounts of THF.

The present invention was therefore based on the object of providing a process for the catalytic hydrogenation of 1,4-butynediol to THF which, with good selectivities and high catalyst service lives, is an industrially advantageous, because of its cost-effective, direct access to THF from 1, 4 Butynediol allows. It has now surprisingly been found that THF can be obtained in high yield by catalytic hydrogenation of 1,4-butynediol at least at the decomposition temperature of 1,4-butynediol by evaporation of 1, 4-butynediol in a hydrogen-containing gas stream and gaseous at least one catalyst containing at least one of the elements of groups 7 to 11 of the Periodic Table hydrogenated.

The temperature during evaporation and the hydrogenation temperature are in the range of 160-330 ° C, preferred are 160-300 ° C, particularly preferred are 170-280 ° C. The temperature at which 1, 4-butynediol is evaporated, it may be lower than the hydrogenation temperature in the aforementioned temperature range. The pressure during evaporation and hydrogenation is 0.05 MPa (Mega Pascal) to 10 MPa absolute, preferably 0.1 to 6 MPa are absolute, more preferably 0.15 to 2 MPa are absolute. The pressure during evaporation corresponds at least to the pressure of the hydrogenation.

1, 4-butynediol can be used as a pure substance, but it is preferred to use 1, 4-butynediol as it is obtained from the synthesis stage for 1, 4-butynediol. This technical butynediol contains, for example, water, propynol, formaldehyde free or bound as hemiacetals or full acetals, methanol and small amounts, generally less than 1% of acetylene, dissolved or solid substances such as catalyst components from the 1, 4-butynediol synthesis catalyst (eg copper salts such as Copper acetylides that increase the disintegration of butynediol) or salts that come from a pH control, such as Sodium formate, oligomeric or polymeric secondary components (so-called cuprene), C5 and Cß components, which are due to impurities in the acetylene used or side reactions in Butindiolsynthese. If no, for example by distillation, from technical 1, 4-butynediol available pure butynediol is used, the water content in the feedstock 5 - 89 wt .-%, particularly preferably 20 - 70 wt .-%. The 1,4-butynediol content is generally from 10 to 90% by weight, preferably from 20 to 80%, particularly preferably from 30 to 70% by weight. The propynol content is generally less than 10% by weight, preferably less than 5% by weight, more preferably less than 3% by weight. Formaldehyde calculated as the sum of formaldehyde itself, hydrate, acetal or hemiacetal has a content of less than 5 wt .-%, preferably less than 2 wt .-%, more preferably less than 1 wt .-%. The methanol content is below 50 wt .-%, preferably below 5 wt .-%, more preferably below 1 wt .-%. The content of non-volatile constituents is generally less than 2% by weight, preferably less than 1% by weight, more preferably less than 0.1% by weight.

The evaporation of the 1, 4-butynediol-containing stream is usually carried out at pressures which correspond at least to the later hydrogenation pressure. However, it is also possible the pressure of evaporation of 1, 4-butynediol higher, for example, to choose up to 0.5 MPa higher. By such an increased pressure occurring pressure losses, for example by pipelines, fittings, catalysts, heat exchangers can be compensated.

The evaporation of the 1, 4-butynediol is carried out in the presence of hydrogen-containing gas in known per se for evaporation apparatuses, for example in one or more falling-film evaporators, thin-film evaporators, Wendelrohlverdampfern, single or multi-fluid nozzles, Tubes filled with inert materials in cocurrent or countercurrent with hydrogen, natural circulation evaporators, forced circulation evaporators, kettle-type evaporators or steam boilers. In this case, the 1, 4-butynediol-containing gas stream to achieve the desired reactor inlet temperature of the hydrogenation reactor, further heated.

As a heat input for the evaporation, a corresponding preheated hydrogen-containing gas stream can be used in addition to hydrogen helium, nitrogen and carbon dioxide and, if cycle gas from the hydrogenation is used, methane, ethane, propane, butane, methanol, dimethyl ether, ethanol, propanol, Butanol, carbon monoxide, THF and water may contain. These components have a mass fraction of the gas stream, which is generally less than 50%, preferably less than 40%, preferably less than 30%. However, it is also possible to produce an indirect heat transfer, for example by an electric heating or heat transfer medium such as steam or oil.

For example, if high boilers such as cuprene and salts are present in the butynediol-containing stream, the feed stream for evaporation containing 1,4-butanediol can be used

Butindiol high-boiling components are added. These high boiling components prevent solidification, e.g. salts in the evaporator. These high boilers may e.g. Alcohol, ester, ether, urea, urethane, amide-containing substances. By way of example, mention may be made of glycerol and its oligomers and sokalan brands. The high boilers, which can be added based on butynediol with 0.001 to 5 weight percent, are then discharged together with the salts and Cuprenen from the 1, 4-butynediol and preferably burned to produce energy.

The catalyst used in the process according to the invention has as active component for the hydrogenation at least one of the elements from groups 7 to 11 from the periodic table of the elements. These elements may be in the form of one or more metals or in the form of low-valency compounds of these metals, such as, for example, as oxides, which are also hydrogenation-active. Of the hydrogenation-active elements of groups 7 to 11 of the Periodic Table of the Elements, the catalyst preferably has Mn, Re, Fe, Ru, Co, Rh, Ir, Ni, Pd, Pt, Cu and / or Au, particularly preferably Ru, Rh, Ir, Ni, Pd and / or Pt, in particular preferably Pd as the sole active component from the groups of the Periodic Table of the Elements.

MM Telkmar et al., Journal of Molecular Catalysis A: Chemical (2002), 187 (1), 81-93 and R. Chaudhah et al. Applied Catalysis (1987), 29 (1), 141-59) disclose that catalysts based on palladium in liquid phase hydrogenation is preferably used when incomplete conversion in the hydrogenation of the 1, 4-butynediol is desired and 1, 4-butenediol to be the desired product. It is therefore surprising that palladium catalysts according to the process of the invention in the gas phase lead directly to THF. The metal content (active component) of the catalysts which can be used in the process according to the invention is generally between 0.001 and 100% by weight. In the case of catalysts which are generally prepared by metal salt precipitation at 1-100% by weight of metal content, preferably 5-90% by weight, particularly preferably 10-80% by weight. For catalysts by impregnation are prepared, the metal content is from 0.001 to 50 wt .-%, particularly preferably 0.01 to 20 wt .-%, particularly preferably from 0.1 to 10 wt.%.

The catalysts used in the process according to the invention may additionally contain at least one element or element compound selected from the elements of groups 1 to 16 of the Periodic Table of the Elements and the lanthanides. These elements or element compounds may contain or may also be added deliberately, for example as a promoter for the reaction and / or as a carrier for the active component. The catalyst used in the process according to the invention is preferably a supported catalyst.

The promoter content of the catalyst may be up to 25 wt .-%, preferably 0.001 to 15 wt .-%, particularly preferably 0.01 to 13 wt .-% amount. Examples include alkali or alkaline earth metal components such as hydroxides, oxides, carbonates or salts of organic or inorganic acids, e.g. to vary the basic properties of the catalysts. Furthermore, sulfur, phosphorus, silicon and aluminum components can serve to modify catalysts in their acidity. For example, sulfuric acid or phosphoric acid may be anchored to the catalyst. Especially in the case of catalysts based on carbon, e.g. Activated carbon, the acidic property of the carrier can also be adjusted by the coal is treated, for example, with hydrochloric, sulfuric, phosphoric or nitric acid. This can take place before or after the impregnation with active component, preferably before.

As catalysts precipitation, carrier, or Raney type catalysts can be used, the preparation of which is described for example in Ullmanns, Encyclopedia of Industrial Chemistry, 4th Edition, 1977, Volume 13, pages 558-665.

As carrier materials of the supported catalysts preferably used in the process according to the invention, for example, aluminum oxides, titanium oxides, zirconium dioxide, silicon dioxides, silicon carbide, phyllosilicates, clays, e.g. Montmorillonite, silicates such as magnesium or aluminum silicates, zeolites and activated carbons are used. Preferred support materials are aluminas, titanium dioxides, silica, zirconia and activated carbons.

Of course, mixtures of different carrier materials can also serve as carriers for catalysts which can be used in the process according to the invention.

These carriers may also be already finished monoliths, for example made of ceramic, Si0 ₂ , Al ₂ 0 ₃ , etc., or, for example, corrugated surfaces, which are later rolled up so that they give a cylindrical shape that can be flowed through or, for example, wire mesh, which also can be brought into shape.

Suitable catalysts for the inventive hydrogenation of 1, 4-butynediol to THF are heterogeneous catalysts, which are preferably used as moldings. Among the shaped bodies are understood in this application, for example, grit, strands and tablets. These moldings can also be hollow bodies to increase the surface, such as hollow cylinders, stars and trilobes. In the process according to the invention, preference is given to used in the form of chippings, tablets and strands. These moldings have diameters of 0.1 - 20 mm. Preference is given to 1 to 10 mm, more preferably 1 to 5 to 7 mm. The length of the catalyst body is not critical, but should generally not be less than the diameter. Preferred lengths of the shaped catalyst bodies are 1-50 mm.

The preparation of the supported catalysts used according to the invention is carried out by applying the active component or else the combinations of active components which can be applied together or one behind the other. The application can be carried out according to methods known per se, for example by impregnation, precipitation, sputtering. The active components are generally in the form of a thin layer on the support. In the case of application by sputtering while the content of active material based on the carrier is less than 0.001 wt.%. Preferred here is a content of active component of 0.00001 to 0.5 wt .-%.

Furthermore, Raney type catalysts, for example Raney nickel, Raney copper, Raney cobalt, Raney nickel / molybdenum, Raney nickel / copper, Raney nickel / chromium, Raney nickel / chromium / iron, Raney nickel / Palladium or rhenium sponge suitable for the inventive method. Raney nickel / molybdenum catalysts can be prepared, for example, by the method described in US-A 4,153,578. However, these catalysts are also marketed, for example, by the company Degussa, 63403 Hanau, Germany. A Raney nickel-chromium-iron catalyst is marketed, for example, under the trade name Catalyst Type 1 1 112 W® by Degussa.

The Raney catalysts are also preferably used as moldings. e.g. tableted or extruded, however, it is also possible to add alloy granules to e.g. Treat caustic soda so that only an outer layer of the grain is leached and releases the active Raney layer. Such grains then have, for example, diameters between 1 and 10 mm.

When using precipitated or supported catalysts, these are preferably reduced before the beginning of the reaction at 20 to 500 ° C in the hydrogen or hydrogen / inert gas stream, this can be done for example already during heating of the reactor to start temperature in the presence of hydrogen. The reduction temperature depends on the desired degree of reduction and the temperature required for the active component. Thus, Pd, which is present for example as PdO on a support, temperatures of 20 - 100 ° C, co-oxides, however, 200-300 ° C for activation with hydrogen. This reduction can be carried out directly in the hydrogenation reactor. If the reduction is carried out in a separate reactor, the catalysts may be removed before being removed at e.g. 30 ° C with oxygen-containing gas mixtures see surface passivated. The passivated catalysts in this case may be used in the hydrogenation reactor prior to use in a nitrogen / hydrogen stream at e.g. 180 ° C activated or used without activation.

For the process according to the invention, one type of catalyst can be used. But it is also possible to use mixtures of several catalysts. These mixtures can be present as a quasi-homogeneous mixture or as a so-called structured bed, in which individual reaction zones with quasi-homogeneous catalyst bed are present. It is also possible to combine the methods, ie, for example, at the beginning of the reaction, a type of catalyst to use a mixture further back.

In a preferred embodiment of the process according to the invention, in addition to at least one of the catalysts described above, which comprises at least one of the elements from groups 7 to 11 from the Periodic Table of the Elements as the active component for the hydrogenation, an acidic catalyst which has no hydrogenation properties is used , but is able to convert 1, 4-butanediol to THF and water. As the acid catalyst, in this particular embodiment of the process according to the invention, aluminum oxides, titanium oxides, zirconium dioxides, silicas, phyllosilicates, clays, e.g. Montmorillonites, silicates such as magnesium or aluminum silicates, zeolites and acidified activated carbons. To enhance acidity, the usual methods can be used, e.g. Application of sulfuric or phosphoric acid. It is important that no basic components such as amines or possibly volatile or entrained salts, which can neutralize the acidic sites, come on the acidic catalyst.

There are a number of possibilities for the large-scale implementation of hydrogenation. After evaporation of the 1, 4-butynediol or the 1, 4-butynediol-containing stream, preferably by means of hydrogen flow and heating, the butynediol-containing gas stream passes into the hydrogenation reactor. After the hydrogenation, the gas stream is cooled, the product is largely separated from hydrogen and the product stream is further worked up. The remaining hydrogen is partially removed, a part, preferably recycled as recycle gas.

For the hydrogenation, a fresh hydrogen-containing gas stream is used, which in addition to hydrogen, e.g. nor helium, nitrogen and carbon dioxide, with a mass fraction of the gas stream, which is generally less than 5%, preferably less than 1%, more preferably less than 0.5%.

The catalyst loading of the hydrogenation according to the invention is generally from 0.01 to 3 kg of 1, 4-butynediol (I catalyst ^» h). Catalyst loadings of 0.05 to 2, particularly preferably 0.1 to 1 kg 1, 4-butynediol / 1 catalyst ^»h are preferred.

The molar ratio of hydrogen to be consumed by hydrogenation to 1,4-butynediol used is at least 2: 1, preferably 2 to 4: 1, for the advantageous reaction. After the reaction, excess hydrogen can be discharged. It is preferred, during evaporation or during the reaction, to have a higher molar ratio between hydrogen and butynediol or its reaction products, for example from 4 to 400 to 1, preferably from 20 to 300 to 1, particularly preferably from 40 to 200 to 1. Dies can be achieved by the preferred cycle gas mode in which at least a portion of the hydrogen or hydrogen gas stream contained in the circuit. The amount of hydrogen consumed chemically by the hydrogenation and by discharge is supplemented. In a preferred embodiment, a portion of the recycle gas is discharged to inert Remove connections. The recirculated hydrogen can also be used to evaporate the 1, 4-butynediol in the process of the invention.

The discharge rate of hydrogen, calculated as a proportion of the hydrogen chemically consumed by hydrogenation, is 100 to 0.1%. Preferred are 50 to 0.2%, more preferably 20 to 0.3%. The lower, the less hydrogen is removed, the more economical the process. The discharge can be done on the one hand by exhaust gas, on the other hand, by the dissolved portion of hydrogen in the cooled, liquid product stream. The discharge takes place in order to discharge inert or secondary components. Inerts may be introduced, for example, by the hydrogen, e.g. Hey, N2, C02. Secondary components may be, for example, methane, ethane, propane, butane, methanol, dimethylethanol, ethanol, propanol, butanol and carbon monoxide, which form in the reaction. Other components in the recycle gas stream may be desired reaction products such as THF and water. It is advantageous if the inerts, products, water and minor components are not too concentrated in the recycle gas because they reduce the partial pressure of hydrogen. They should have a share of less than 50% in the recycle gas. A special case is carbon monoxide, possibly also carbon dioxide, since these can reduce the activity of the active components. The proportion of carbon monoxide and / or carbon dioxide in the cycle gas should therefore be less than 10%, preferably less than 5%, particularly preferably less than 1%. A considerable advantage of the method according to the invention is that THF contained in the circulating gas does not decompose or only very slightly decomposes. It has surprisingly been found that THF remains unchanged at least 99% even on the second pass through the catalyst. Although complete condensation of the product is desirable, the minimum condensation temperature needed to condense the product stream is not critical due to the described stability of the THF, which can save energy. The condensation temperature is generally from -78 ° C to 70 ° C, preferably from -15 ° C to 40 ° C, more preferably from -10 ° C to 30 ° C.

The temperature control in the hydrogenation reactor is preferably carried out so that the temperature along at least the length of the catalyst bed increases, regardless of the type of reactor used. If one were to induce a cooling along the catalyst bed, especially in the first zone of the catalyst, there would be the danger of condensation, which would then lead to the deactivation of the catalyst by coking. The temperature increase at least along the first quarter of the catalyst bed is 1 - 100 ° C, preferably 2 to 80 ° C, particularly preferably 5 to 60 ° C. After reaching the maximum temperature, depending on the reactor type (eg tube bundle reactor), the reaction temperature may drop again. This is understood as the inlet temperature, the temperature of the gas stream, with which this meets the catalyst. After leaving the catalyst bed or the hydrogenation reactor, the gas stream (hydrogenation output) is cooled in one or more stages to the extent that a liquid phase, the product mixture, is formed. This is preferably done at the same pressure level as the reaction itself. Cooling can take place via air and water coolers, refrigeration systems or other technical aids.

As a reactor or as reactor types for the inventive hyration in the gas phase, for example, tube bundle reactors, shaft reactors or fluidized bed reactors can be used. A special feature would be the microcrystalline reactor, which is particularly advantageous if you want to remove the heat of the reaction very efficiently in order to keep the temperature of the reaction as constant as possible. The individual reactors or reactor types can also be used as a combination. The process according to the invention is preferably carried out continuously.

Before working up, the liquid product mixture is generally depressurized to a lower pressure level, provided that the hydrogenation reaction was carried out under pressure, for example to 0.1 to 0.5 MPa absolute. In the process, dissolved hydrogen-containing gas is released, which is either discharged or recycled.

Subsequently, the liquid product mixture can be separated by known methods, preferably distillatively. In industrial (large-scale) processes, the separation is preferably carried out continuously in several columns. A work-up can for example be designed as follows: The liquid hydrogenation product passes into a first column (a), in which all THF together with water, preferably only the portion of water which is the THF / water

Azeotrope at the set pressure corresponds to other low boilers at pressures of 0.05 to 0.3 MPa are separated from the absolute higher boiling components. The THF-containing stream is separated further in a second column (b), preferably at pressures above the first, for example at 0.15 to 1.5 MPa. The resulting

THF / water low-boiling azeotrope can be completely or only partially recycled to the first column. Existing low-boiling components, such as e.g. Methanol, can be completely or partially discharged at the top of the column. Since these low boilers, for example, methanol, still contain THF, this mixture, depending on the amount, in one or more separate column (s) can be further separated. The high-boiling product of the column (b), THF, can already be salable as such, if you want purities over 99.9%, be finely purified in another column. The high-boiling product of the column (a) which mostly consists mainly of water, can for example be disposed of (sewage treatment plant or incineration).

A variant of this workup is, especially if methanol contents in the hydrogenation> 0.2% are present, the methanol in the column combination (a) + (b) by recycling a

(B) in (a) until the water stops flowing from column (a) into the column (b) together with the methanol / THF azeotrope (b) in THF / methanol-containing low-boiler stream. As a result, all water, together with excess methanol, discharged via the bottom of the column (a).

If any desired value products are included, such as, for example, 1, 4-butanediol and / or gamma butyrolactone, they can either be isolated in pure form or, after removal of water and other undesirable components such as propanol and butanol, are recycled to the reaction. A preferred variant is to treat the high-boiler stream of the column (a), if it still contains 1, 4-butanediol, by means of an acid catalyst in such a way that the butanediol is cyclized to THF. This can be done directly with the high-boiling stream of the column (a), or even after separation of components, so that the butanediol is present in concentrated form. Catalysts for this cyclization can be homogeneously dissolved or heterogeneous as a suspension or fixed. The cyclization can take place in fixed catalysts in gas or liquid phase, otherwise in the liquid phase. The temperatures here are in the range of 80 to 300 ° C, preferably at 90 to 250 ° C. As catalysts of its inorganic acids, such as sulfuric acid, phosphoric acid or heteropolyacids such as dibromophosphoric, organic acids such as sulfonic acids, acidic ion exchange resins and acidic, inorganic solids such as zeolites, metal oxides such as S1O2 or AI2O3, called metal mixed oxides such as montmorillonites.

The quality of the THF is based on market standards. Thus, the THF meets the usual required GC purities, the color and other key figures.

The invention will be explained in more detail in the following examples.

Examples The analysis of the product was carried out by gas chromatography. The product compositions given are all calculated to be anhydrous. The 1, 4-butynediol used was prepared by reacting acetylene with formaldehyde on Cu / Bi catalysts according to Reppe. The technical 1, 4-butynediol used had 50 wt .-% butynediol, 47 wt .-% water, 1 wt .-% formaldehyde, about 1% propynol and small amounts of other components such as cuprene, Cu compounds, salts such as sodium on. The pure 1,4-butynediol was as

40% aqueous solution before. The indicated conversion is that of the used 1,4-butynediol. The selectivity data still take into account 1, 4-butynediol or intermediate to be hydrogenated. In this case, as intermediates 1, 4-butenediol, 4-hydroxybutyraldehyde and acetals derived therefrom, gamma-butyrolactone (GBL) or butanediol (BDO) were taken into account as compounds still to be hydrogenated or reacted to give THF.

example 1

In the example, hydrogenation was carried out with pure 1,4-butynediol as a 40% strength aqueous solution at normal pressure. This 1, 4-butynediol solution was pumped continuously into an externally heated reactor tube (diameter 2.7 cm). The tube was fitted with glass rings at the top (30 ml). This zone was used as the evaporator section, in which butynediol / water and hydrogen (300 liters / h) heated to the hydrogenation temperature indicated in Table 1 and a vapor on a second zone (hydrogenation zone) in the reactor tube, in which the catalyst indicated in Table 1 was ( 20 ml) was passed. After the reactor tube, the gaseous reactor discharge was cooled to about 20 ° C and collected auskondensierendes product. The exhaust gas was passed through a cold trap at - 78 ° C while further condensed out product. The two condensates were combined for the purpose of analysis. The catalyst was activated prior to the reaction in a hydrogen stream. The result is summarized in Table 1. Table 1 :

1 THF = tetrahydrofuran

2 BDO = 1, 4-butanediol

3 GBL = gamma-butyrolactone

4 BID = 1, 4-butynediol

Examples 2 to 5

In these examples, under elevated pressure aqueous pure or technical

1, 4-Butynediol in Example 5 (marked with *) in an evaporator containing metal fill rings and externally heated by oil to 240 ° C, evaporated in a hydrogen stream and in a reactor tube filled with catalyst (100 ml unless otherwise stated indicated in Table 2 or catalysts, The reactor tube was designed as a double-jacket tube, the outside being oiled or cooled The reaction effluent was cooled and the condensed product was depressurized via a valve to atmospheric pressure while the gaseous phase was passed through A small proportion of the gas was discharged as exhaust gas, and as much hydrogen was introduced into the reaction via a fresh gas supply as hydrogen was consumed by the reaction and exhaust gas, thereby keeping the reaction pressure constant Table 2. The conversion of butynediol was in all cases For the calculation of selectivity, products such as 1,4-butenediol and 4-hydroxybutanal and its acetals, gamma-butyrolactone (GBL) or butanediol (BDO) were also included as compounds still to be hydrogenated or reacted to give THF.

Table 2

1 THF = tetrahydrofuran

2 BDO = 1, 4-butanediol

3 GBL = gamma-butyrolactone

Adjustment of the examples of DE-A 2029557

Example 6 of DE-A 2029557

According to Example 6 of DE-A 2029557 140 g of 1, 4-butynediol were hydrogenated in 360 g of water in the liquid phase on a 5% palladium on activated alumina catalyst at 10.3 MPa and 275 ° C. Only decomposition products and water in the hydrogenation effluent could be detected. THF was not found.

Examples 2, 3 and 4 of DE-A 2029557

According to Examples 2, 3 and 4 of DE-A 2029557, butynediol was hydrogenated. In the hydrogenation of the adjustment of Example 2 with Pd on activated alumina spheres as a catalyst found in addition to <3 wt .-% THF, especially n-butanol and water. In the case of Ni- and Ru-containing catalysts according to Examples 3 and 4 only water was found in the discharge. In the exhaust gas, in addition to low (<1%) THF, mainly hydrocarbons from methane to butane were detected. Comparison example with DE-A 2029557

Analogously to Example 6 of DE-A 2029557, a 40% strength aqueous butynediol solution at 10.3 MPa at 225 ° C on a 5% palladium on activated alumina catalyst (5% Pd / Al2O3) in the liquid phase hydrogenated. In the liquid hydrogenation discharge were found in addition to polymeric residues a variety of components. About 14% by weight of n-propanol, 10% by weight of n-butanol and 20% by weight of THF were found. The total amount of organic parts in the hydrogenation output corresponded to 10% of the originally used amount of butynediol. The selectivity for THF was only 2%.

Example 6

According to the invention, a 40% strength aqueous butynediol solution was hydrogenated in the gas phase at an inlet temperature of 225 ° C. and 0.9 MPa on a catalyst containing 5% Pd / Al 2 O 3 (5% palladium on activated alumina). In the hydrogenation, 75% by weight of THF, 20 wt .-% of n-butanol and in each case less than 1 wt .-% gamma-butyrolactone, 1, 4-butanediol and n-propanol were found. The selectivity to THF was 75% since the butynediol conversion was complete.

Claims

claims

A process for preparing tetrahydrofuran by hydrogenating 1, 4-butynediol, characterized in that 1, 4-butynediol evaporated in a hydrogen-containing gas stream and gaseous at least one catalyst containing at least one of the elements from groups 7 to 1 1 of the Periodic Table contains the elements is hydrogenated.

A method according to claim 1, characterized in that the temperature at which 1, 4-butynediol is evaporated and the hydrogenation temperature 160 to 300 ° C.

Method according to one of claims 1 or 2, characterized in that the pressure at which 1, 4-butynediol is evaporated, at least equal to the pressure of the subsequent hydrogenation.

Process according to claims 1 to 3, characterized in that the hydrogenation is carried out at a pressure of 0.5 to 10 MPa.

Process according to claims 1 to 4, characterized in that the temperature at which 1,4-butynediol is hydrogenated is 160 to 300 ° C.

Process according to claims 1 to 5, characterized in that the catalyst contains at least one of the elements selected from Mn, Re, Fe, Ru, Co, Rh, Ir, Ni, Pd, Pt, Cu and Au.

Process according to claims 1 to 6, characterized in that the catalyst contains Pd as active metal.

Process according to claims 1 to 7, characterized in that two catalysts with elements from groups 7 to 1 1 of the Periodic Table of the Elements are used, one of which contains Pd as active metal.

Process according to claims 1 to 8, characterized in that the catalyst (s) contains a support selected from the oxides of aluminum, titanium, zirconium oxide, silica, clays, silicates, zeolites and activated carbon.

Process according to claims 1 to 9, that additionally an acidic catalyst without hydrogenating properties is used.

Process according to claims 1 to 10, that the molar ratio of hydrogen to in-fed 1, 4-butynediol during the hydrogenation is at least 2.

12. The method according to claims 1 to 1 1, characterized in that the hydrogenation is carried out with Kreisgasfahrweise.