DE102004012114A1 - Process for the preparation of tetrahydrofuran - Google Patents

Abstract

The invention relates to a process for the preparation of THF (tetrahydrofuran) by reacting a 1,4-butanediol-containing reaction mixture over a heteropoly acid, wherein the reaction mixture, based on the heteropolyacid, less than 0.2 wt .-% iron ions.

Description

The The invention relates to a process for the preparation of tetrahydrofuran (THF) by reaction of a 1,4-butanediol-containing reaction mixture on a heteropolyacid, wherein the reaction mixture, based on the heteropolyacid less as 0.2 wt .-% iron ions.

method for the production of THF from 1,4-butanediol have long been known. In K. Weissermel, H.-J. Arpe, Industrial Organic Chemistry, VCH Verlagsgesellschaft, D 69451 Weinheim, 1994, page 111, is the Reaction of 1,4-butanediol to THF by dehydration under Addition of phosphoric acid, sulfuric acid or acidic ion exchangers. This is the acidified with 1,4-butanediol is heated and supplemented to the extent by 1,4-butanediol, as Distilled out THF / water.

Also for the Cyclization of 1,4-butanediol to THF are suitable catalysts Heteropolyacids. The cyclization to THF leaves usually perform easily, if you are pure heteropolyacids used, as they are available in the chemicals trade. Because the pure heteropolyacids are expensive, it is desirable the amounts as possible small, but at least a long lifetime of the heteropolyacids too guarantee. The disadvantage is that for a long time Use of heteropolyacids often their activity sinks. All the more so, if the reactions, as technically common practice, in running metallic reactors become.

The rapid deactivation of the heteropolyacid catalyst proves especially in continuous operations and processes with reused catalyst as particularly disadvantageous since they to falling sales leads.

It Therefore, the task was a simple and inexpensive Process for the preparation of THF from 1,4-butanediol on a heteropolyacid catalyst to provide consistent sales, even when reused Heteropolyacid catalyst, guaranteed and deactivation of the heteropolyacid catalyst to a large extent avoids.

Surprisingly has now become a process for the production of THF by reaction of 1,4-butanediol-containing reaction mixtures in the presence a heteropolyacid, characterized in that the reaction mixture based on the heteropoly less than 0.2 wt .-% iron ions, found.

Under In this application, iron ions are in particular iron ions of the Oxidation levels (+ II) and (+ III) understood. The determination of the Content of the reaction mixture of iron ions is carried out in a known per se Way by atomic absorption spectrometry.

Of the Iron ion content of the reaction mixture should be 0 to 0.2% by weight, preferably less than 0.1% by weight, more preferably less than 0.05% by weight, be particularly preferred, the reaction mixture is free from Iron ions. The one used to reduce the iron content of the reaction mixture Method is not critical in itself. Under reaction mixture is in the present application, the heteropolyacid, staged Understood 1,4-butanediol-containing reaction mixture.

preferred activities to avoid the harmful Iron ion contents are the avoidance of the use of iron ion-containing Heteropolyacids. The heteropolyacid used should therefore be less than 0.5% by weight, preferably less than 0.1% by weight, more preferably below 0.05 wt .-% iron ions.

Furthermore, the use of apparatus, in particular of reactors and lines, with which the heteropolyacids come into contact from glass, enamel or plastics is recommended. Since this is often not possible or very expensive in large-scale processes, measures are necessary to minimize the effect of heteropolyacids on metallic, iron-containing reactor walls, pipelines, pumps, etc. as much as possible. It has surprisingly been found that the consistent exclusion of active oxygen is of crucial importance. By active oxygen is meant oxygen in the form of, for example, air or dissolved oxygen or peroxides and hydroperoxides, especially in the form of organic hydroperoxides. Since the effect of active oxygen can also have a cumulative effect, it must be ensured that even small quantities which are constantly fed to the reaction system are avoided as far as possible. It is recommended, based on the duration of the process molar oxygen amounts, based on moles of heteropolyacid used, of less than 1000, preferably less than 100, more preferably klei ner 50. Advantageously, the polymerization is carried out under an inert gas atmosphere. As inert gases, for example, nitrogen, carbon dioxide or noble gases can serve, preferably nitrogen. The inert gases should be as oxygen-free as possible. The reaction mixture containing 1,4-butanediol is preferably degassed with nitrogen before the reaction in the usual way.

is to avoid an advent of iron ions, or should one already previously used and therefore (partially) deactivated catalyst be regenerated, so is the use of ion exchangers in the H form recommended. In this case, the heteropolyacid-containing Reaction mixture intermittently or continuously for iron ion removal over the Ion exchangers are passed.

All known inorganic and organic ion exchangers, as known, for example, from Ullmann's Encyclopedia of Industrial Chemistry, 6th Edition, electronic release, 2000, can be used to remove the iron ions from the reaction mixture. Suitable acidic ion exchangers, also called cation exchangers, strongly acidic ion exchanger, bonded to an organic polymeric backbone benzene groups sulfonic acid groups are contained, and, for example in the form of the commercial products Amberlite ^® IR 120, Amberjet ^® 1200 H and Duolite ^® C20 from Rohm & Haas , Darmstadt, Dowex ^® HCR from Dow Chemical, Midland, Michigan, USA, Lewatit ^® K2621 and Lewatit ^® S100 from Bayer AG, Leverkusen will distribute, in all possible forms, such as granular or as a gel. Also suitable are weakly acidic ion exchangers, generally polyacrylates which are sold for example in the form of commercial products Amberlite ^® IRC 76 and Duolite ^® C433 from Rohm & Haas, Darmstadt. Also suitable are clays and zeolites in the H form.

The reaction of 1,4-butanediol into THF in the presence of heteropolyacids as catalyst is carried out in a manner known per se, as described, for example, in JP-A 61-126 080. Heteropolyacids which are used according to the invention are inorganic polyacids which, in contrast to isopolyacids, have at least two different central atoms. Heteropoly acids are formed from weak polybasic oxygen acids of a metal such as chromium, molybdenum, vanadium and tungsten and a nonmetal such as arsenic, iodine, phosphorus, selenium, silicon, boron and tellurium as partial mixed anhydrides. Examples include the dodecatungstophosphoric acid H ₃ (PW ₁₂ O ₄₀ ) or the decamolybdophosporic acid H ₃ (PMo ₁₂ O ₄₀ ). The heteropolyacids may also contain actinides or lanthanides as the second central atom (Z. Chemie 17 (1977), pages 353 to 357 and 19 (1979), 308). The heteropolyacids can generally be described by the formula H _8-n (Y ⁿ M ₁₉ O ₄₀ ) where n is the valence of the element Y (eg boron, silicon, zinc) (see also Heteropoly- and Isopoly-oxomalates, Berlin, Springer 1983). Suitable catalysts for the process according to the invention are phosphotungstic acid, phosphomolybdic acid, silicon molybdic acid and silicotungstic acid, and dodecatungstophosphoric acid and decamolybdatophosphoric acid are preferred.

The Heteropolyacids used as catalysts can be both dried (1 to 10 moles of water / mole of heteropolyacid) or undried (10 to 40 moles of water / heteropolyacid) in the cyclization can be used. The amount of heteropolyacid used is preferred 0.05 to 1 wt .-%, based on the reaction mixture.

The inventive method has the advantage that the used 1,4-butanediol containing Reaktoinsmischungen not pre-purified on an acid catalyst prior to conversion to THF Need to become. 1,4-Butanediol is at the same productivity of heteropolyacid over long periods cyclized to THF without significant amounts of by-products.

The Reaction of 1,4-butanediol-containing reaction mixtures THF is in the liquid phase carried out.

The in the reaction used as feed used 1,4-butanediol Reaction mixtures can can be obtained by known methods.

So For example, a reaction mixture containing 1,4-butanediol are used, which according to the Reppe method of acetylene and Formaldehyde and subsequent Hydrogenation of the resulting 1,4-butynediol is obtained, or by Acetoxylation or chlorination of butadiene.

The hydrogenation effluent of the hydrogenation of a compound selected from maleic acid, maleic acid monoesters, maleic diesters, maleic anhydride and an intermediate product resulting from their hydrogenation can also be used as feed. Such intermediates are, for example Succinic anhydride, γ-butyrolactone, succinic acid or succinic diester. The hydrogenation effluent from the hydrogenation of butynediol or maleic diesters is particularly preferably used as feed in the conversion to THF.

The Hydrogenation of maleic diesters can be carried out in a known manner in the gas or liquid phase. For example, dimethyl maleate by hydrogenation on a catalyst, e.g. Copper chromite, under increased Pressure and elevated Temperature to be implemented in the gas phase. The recovered hydrogenation discharge, which are used as feed in the reaction according to the invention can, contains generally 5 - 85 Wt% butanediol and 15-95 % By weight of alcohol, preferably 10 to 70% by weight of butanediol and 15 to 70% by weight of alcohol, more preferably 15 to 60% by weight of butanediol and 15 to 50% by weight of alcohol. In addition, products such as ã-butyrolactone or succinic diester in the range to e.g. 30 wt .-%, be contained. The contents of ã-butyrolactone or succinic diester are generally for the process is not critical. Furthermore, water can be in any Salary be present, as well as small amounts of other compounds. It is possible, that in the hydrogenation already THF is present, the THF content for the process is not critical and e.g. between 10 and 30 wt .-% may be.

Instead of the entire hydrogenation can also only a partial stream of the hydrogenation fed to the conversion to THF become. The reaction product of the reaction to THF may be the same Refill towers supplied be like the unreacted substream of the hydrogenation, because both have similar impurities and by-products. So do not need for comparable separation tasks to be operated different equipment.

In the method according to the invention for the production of THF the reaction mixture alcohols are added. In general will be aliphatic alcohols, which are preferably monovalent used. Especially preferred are monohydric aliphatic alcohols having 1 to 7 carbon atoms, of these are methanol, ethanol, iso- and n-propanol and n-butanol very particularly preferred.

The Reaction takes place at 50 to 300 ° C, preferably at 65 to 270 ° C, more preferably at 65 to 240 ° C. It is in a print area (Absolute pressure) of 0.5 to 80 bar, preferably 0.8 to 60 bar, more preferably 1 to 40 bar performed. The reaction can be carried out continuously or batchwise. The continuous driving is preferred.

In dependence from the chosen ones Temperature and pressure conditions can be the formed THF and Water and optionally the added alcohol from the liquid in the gaseous Phase over or in the liquid Phase remain. At low reaction pressures, the product stream becomes the reactor gaseous leave. This is the preferred embodiment.

The Inflow amount is in general 1000 kg / h per kg of catalyst, preferably 500 kg / h, more preferably 300 kg / h.

Of the Sales of the present in the reaction mixture 1,4-butanediol THF is generally 99 to 100%. Thus, the discharge corresponds to the Reaction of 1,4-butanediol to THF (Cyclisierungsaustrag) substantially its feed composition, with the difference that in the feed contained 1,4-butanediol was converted to THF and water. Of the Contains Cyclisierungsaustrag generally THF, water of reaction and optionally alcohol. In addition, you can e.g. γ-butyrolactone and Contain succinic acid ester be. They are not affected by the reaction.

Based The composition of the Cyclisierungsaustrags it becomes clear that in the reaction of 1,4-butanediol-containing reaction mixtures to THF to heteropolyacid, optionally not significant in the presence of other alcohols Formation of by-products, such as intermolecular ethers Reaction or olefins occurs.

The Cyclisierungsaustrag can be worked up by distillation methods known in the art. EP-B 0 485 484 describes various processes for recovering THF from mixtures containing THF, one or more low-boiling alcohols and water. Thus, the extraction can be carried out for example by extractive distillation with the addition of another component such as 1,4-butanediol, water, ethylene glycol and others. EP-B 0 485 484 further describes a process for recovering THF from said mixtures comprising two consecutive distillations, the first being conducted at a lower pressure than the second, and a condensation carried out between the distillations. The by-product enriched mixture obtained from the second distillation is mixed with the stream the first distillation condenses again, and the recovered in the second distillation pure THF is separated.

In a preferred embodiment becomes the reaction of the invention carried out in a tubular reactor with attached column. Of the Reactor may e.g. a stirring or loop reactor, or the bottom of a column.

THF is an important solvent for many High polymers and furthermore serves for the production of polytetramethylene glycol, an intermediate in the production of polyurethanes and Spandex fibers is.

The explain the following examples the invention additionally.

example

When Butanediol is used such, in a conventional manner after Reppe made from acetylene, formaldehyde and hydrogen has been.

Determination of iron ion content by atomic absorption spectrometry (AAS)

0.2 to 0.3 g of the sample of the reaction mixture are dissolved in 10 ml of 2-propanol solved. This sample solution is diluted with further propanol-2 in the ratio 1:10 and 1:20.

The Measurement of these two solutions carried out by atomic absorption, graphite tube technology with Zeeman background compensation according to the procedure of standard addition.

gauge:

• AAS spectrometers, e.g. Fa. Varian type "SpectraAA 880"

Measurement conditions: Wavelength Fe: 248.3 nm Gap: 0.2 nm dosing: 10 μl Limit of quantitation: 1 mg / kg in the sample.

Determination of oxygen content

Execution:

Of the Proportion of the dissolved Oxygen in liquids was by stripping with an inert gas and subsequent detection determined by means of an electrochemical measuring cell.

In a measuring device (small glass vessel with inlet tube, the in a glass frit ends)) was one with the to be analyzed Substance readily miscible, unreacted liquid submitted. It can also be a subset of the sample to be analyzed. Through the measuring cell and the liquid submitted then became so long the stripping gas (N2) passed until the measuring device oxygen-free was. This can be controlled by the indication of the oxygen cell. An aliquot of the sample was then inserted into the template through a septum metered with the help of a syringe and the measuring process started. The optimal mixing of the two liquids is through ensures the bubbling stripping gas. The end of the measuring process was reached when the signal of the oxygen measuring cell again reached the same level as before the sample addition. The measuring signal of the oxygen cell was determined by means of a laboratory data system recorded and evaluated.

Calibration:

to Calibration of the measuring arrangement was in the measuring cell with the liquid template using a gas-tight syringe a defined amount of a calibration gas dosed with known oxygen content and the measurement signal obtained evaluated with the help of the laboratory data system.

Equipment:

• Measuring device with septum and inlet tube with frit
• Strippgasversorgung
• Electrochemical oxygen measuring cell ('Hersch cell', for example from TELEDYNE, Type B 1)
• Laboratory data system
• Calibration gas with known oxygen content in inert gas
• Flüssigdosierspritzen
• gas-tight syringe (for Kalibiergas)

Cyclization to THF

Comparative example

A 5 l reactor of high-alloy stainless steel, for example with 18 chromium, such as X ₆ CrNiTi18-20 with 0.06% carbon, 18% chromium, 10 nickel and a maximum of 48% titanium and iron, with stirrer and attached column was half filled with 1,4-butanediol and 1 g of commercial tungstophosphoric acid was added. The mixture was heated to 175-180 ° C. Distilled mixture of THF and water was continuously replaced with fresh butanediol (0.5 kg / h). After 100 hours of operation, the productivity had fallen by 0.1 kg / h, after 200 h in total by 0.2 kg / h. It was then cooled and the reactor opened for sampling. The reaction solution had a light brown color.

Subsequently was restarted under the last conditions. It was found, that productivity after another 3 h already by another 0.1 kg / h had fallen. The Reaction was stopped and the reaction mixture was analyzed. 0.2% by weight were found, based on the heteropolyacid used Iron ions (detected as iron) in the reaction mixture. The reaction mixture was strongly brown colored and contained brown solid particles.

example

Above Example described was repeated, with the difference that the butanediol previously degassed with pure nitrogen, the Experimental apparatus before and during The reaction is purged with pure nitrogen and rendered inert and when opening the Reactor after 200 h by nitrogen blanketing air access excluded has been. After these total of 203 hours of testing, the productivity decrease was only 0.05 kg / h. The iron analysis of the reaction mixture revealed only 0.02% by weight of iron. In addition to a slight browning of the reaction mixture, were not insoluble To see ingredients.

Claims (7)

A process for the preparation of THF by reacting a 1,4-butanediol-containing reaction mixture over a heteropoly acid, characterized in that the reaction mixture, based on the heteropolyacid, less than 0.2 wt .-% iron ions. Method according to claim 1, characterized in that that the reaction mixture containing 1,4-butanediol, according to the Reppe Process of acetylene and formaldehyde followed by hydrogenation of the resulting 1,4-butynediol or by acetoxylation or chlorination was obtained from butadiene or a hydrogenation of the hydrogenation a connection selected from maleic acid, maleic monoesters, maleic diesters and maleic anhydride and one of the intermediates resulting from the hydrogenation, is. Method according to claim 1 or 2, characterized the content of iron ions is less than 0.1% by weight. Method according to one of claims 1 to 3, characterized that as heteropolyacid Dodecanwolframatophosphorsäure and / or decamolybdatophosphoric acid is used. Method according to one of claims 1 to 4, characterized that the reaction is carried out at a temperature of 50 to 300 ° C. Method according to one of claims 1 to 5, characterized that the reaction is carried out in a pressure range of 0.5 to 80 bar. Method according to one of claims 1 to 6, characterized 1,4-butanediol with extensive exclusion of oxygen is cyclized.