DE102006009839A1 - A process for hydrogenating methylolalkanals to low acetal polyhydric alcohols - Google Patents

Abstract

Process for the preparation of polyhydric alcohols with a low acetal content by catalytic hydrogenation of methylolalkanals of the general formula, $ F1 in which R <SUP> 1 </SUP> and R <SUP> 2 </SUP> independently of one another have a further methylol group or an alkyl group 1 to 22 carbon atoms or an aryl or aralkyl group with 6 to 33 carbon atoms, in the liquid phase on a hydrogenation catalyst, characterized in that by adding at least one tertiary amine, an inorganic base or an inorganic or organic acid to the hydrogenation feed a pH of 7.0 to 9.0 is set in the hydrogenation.

Description

The The invention relates to a process for the production of polyvalent ones Alcohols with low acetal contents by catalytic hydrogenation of methylolalkanals in the liquid phase on a hydrogenation catalyst in which a pH of the hydrogenation from 7.0 to 9.0.

The catalytic hydrogenation of carbonyl compounds, e.g. aldehydes to produce simple and functionalized alcohols in the production lines of the basic chemicals industry. This is especially true for the hydrogenation of aldehydes via oxo synthesis or aldol reaction accessible are.

By Aldol reaction of alkanals with excess formaldehyde in the presence of stoichiometric amounts At base Methylolalkanale be accessible. From WO 01/51438 It is known, inorganic hydroxides such as sodium hydroxide or calcium hydroxide as a base. WO 98/28253 and DE-A 1 957 591 Amines as basic aldolization catalysts and WO 98/29374 basic ion exchangers. The methylolalkanal is prepared by these methods as 20 to 80 wt .-% aqueous solution receive. The pH of this aqueous solution is only 3.5 to 6.0, since the basic aldolization catalyst also catalyzes the Cannizzaro reaction of formaldehyde to formic acid, which in turn at least partially neutralizes the base.

Want Polyhydric alcohols such as pentaerythritol, neopentyl glycol or Trimethylolpropane from aqueous Methylolalkanal solutions manufacture, must these solutions be hydrogenated.

These Hydrogenation is generally carried out at temperatures above 80 ° C. It become schisms the methylol group to free aldehyde, the Cannizzaro reaction of formaldehyde to formic acid and above In addition, ether, ester and acetal formation observed in the hydrogenation reactor. These side reactions lead to low hydrogenation selectivities and to low yields of polyhydric alcohol.

moreover Many hydrogenation catalysts are not stable under these conditions. In particular catalysts based on the oxides of aluminum and Silicon as known from EP-A 44 444 and WO 95/32171, lose in the presence of these aqueous Methylolalkanallösungen Hydrogenation conditions of activity, what according to experience over the Lasting a few months leads to significantly lower sales.

According to the invention was found that at constant composition of the hydrogenation feed (Hydrierfeed) due to the catalyst aging, the pH in the hydrogenation reactor sinks. As a result, side reactions occur in the hydrogenation reactor between already formed products such as the 1,3-diols neopentyl glycol (NPG) and trimethylolpropane (TMP) and their starting compounds, the aldehydes hydroxypivalaldehyde (HPA) or dimethylol butanal (DMB) leading to the formation of acetals.

Industrially could the lowering of the hydrogenation activity of the catalyst at least partially compensated by the fact that the hydrogenation temperature gradually increased becomes. By temperature increase In addition, the Formiatzersetzung can be increased again, resulting in a higher one pH value leads. In addition to the uneconomical increased Energy consumption this measure means, on the other hand take side reactions above a certain temperature strong too, which too elevated Use figures (consumption of starting materials) or to impure product to lead.

So For example, in the hydrogenation of hydroxypivalaldehyde or of dimethylolbutanal to the corresponding alcohols neopentyl glycol (NPG) and trimethylolpropane (TMP) with increasing temperature Retroaldol reaction takes place. The resulting aldehydes are too unwanted Hydrogenated byproducts (in NPG, isobutanol and methanol, for TMP 2-methylbutanol, 2-ethyl-1,3-propanediol and methanol) and the yield is reduced accordingly. In the case of NPG synthesis is also at elevated Temperature also the formation of the cyclic acetal of NPG and hydroxypivalaldehyde (HPA) reinforced observed. This byproduct is not distillative to NPG separate and lead therefore a more impure product of value. Furthermore, promote high Temperatures the thermal Tishchenko reaction of HPA to hydroxypivalic acid neopentyl glycol ester (HPN). In the case of TMP production, corresponding TMP-dimethylol butanal acetals occur on, which significantly reduce the yield and thus the economic efficiency minimize the process.

Due to these side reactions, in particular the acetal formation, the temperature increase is a means of keeping constant the hydrogenation activity of an aging catalyst and thus avoiding the Ace valley formation is limited by economic factors such as yield and product purity. Acetals in this application are understood to mean the cyclic 6-ring acetals which the polyhydric alcohol can form with aldehydes contained in the hydrogenation feed, especially with the corresponding methylolalkanal.

According to the invention was now found that the pH in the hydrogenation reactor crucial Influence on the catalyst activity, the hydrogenation result and has the acetal formation. The pH in the hydrogenation reactor becomes crucial by its formic acid content certainly. An influence on the pH value continues to have the Hydrolysis of HPN to NPG and hydroxypivalic acid (HPS).

Formic acid, which was formed during the aldolization as a byproduct of a Cannizzaro reaction from formaldehyde, is decomposed in the course of the industrially operated hydrogenation to CO ₂ and H ₂ or to CO and H ₂ O. CO and CO ₂ can be detected in the exhaust gas of the hydrogenation. The decomposition rate of the undesirable by-product formic acid depends, in addition to the temperature, crucially on the age of the catalyst. With increasing age of the catalyst, the decomposition rate of formic acid also decreases permanently under constant reaction conditions.

in the Generally, the hydrogenation reactor is used on a large scale to provide good drainage the hydrogenation heat to ensure, with a high circulation ratio operated, that is the circulation quantity is chosen larger than the amount of fresh feed (feed of the fresh feed). Therefore corresponds the pH in the reactor to the pH of the hydrogenation, but is significantly higher as the pH of the hydrogenation feed. The difference in pH between Feed and discharge are determined by the activity of the catalyst relative to the Decomposition of formic acid, and determined by temperature, exhaust gas quantity and load.

Out In the prior art, methods are already known in which was tried over the pH value to influence the hydrogenation result.

PCT / WO 2004/092097 describes a hydrogenation process in which the hydrogenation feed is neutralized by adding a base with the goal negative Effects of pH on the mechanical stability of the catalyst carrier to prevent.

The JP 2004-182622 describes a hydrogenation process in which the pH to pH 5.5-7.5 is set in the hydrogenation feed. At lower pH's was a discharge of the active metal from the catalyst observed what to a continuous loss of activity of the catalyst led.

Of the The invention therefore an object of the invention, a process for the preparation of polyhydric alcohols by catalytic hydrogenation of methylolalkanals in which polyhydric alcohols with low acetal content made accessible at good yields and long service lives of the catalyst can be.

in der R¹ und R² unabhängig voneinander eine weitere Methylolgruppe oder eine Alkylgruppe mit 1 bis 22 C-Atomen oder eine Aryl- oder Aralkylgruppe mit 6 bis 33 C-Atomen bedeuten, in der Flüssigphase an einem Hydrierkatalysator, dadurch gekennzeichnet, dass durch Zusatz mindestens eines tertiären Amins, einer anorganischen Base oder einer anorganischen oder organischen Säure zum Hydrierfeed ein pH-Wert von 7,0 bis 9,0 im Hydrieraustrag eingestellt wird.This object is achieved by a process for the preparation of polyhydric alcohols by catalytic hydrogenation of Methylolalkanalen the general formula

in which R ¹ and R ² independently of one another are a further methylol group or an alkyl group having 1 to 22 C atoms or an aryl or aralkyl group having 6 to 33 C atoms, in the liquid phase on a hydrogenation catalyst, characterized in that by addition at least one tertiary amine, an inorganic base or an inorganic or organic acid to Hydrierfeed a pH of 7.0 to 9.0 is set in the hydrogenation.

The inventive method allows an effective pH control in the hydrogenation reactor. pH fluctuations and the adverse influence of an aging catalyst on the Acetal formation can be avoided. Polyhydric alcohols are in good yield and accessible with low acetal, wherein by the inventive method very good service life of the catalyst can be achieved.

Under Hydrierfeed is in this application a Methylolalkanal of the general Formula I containing aqueous Solution, in particular an aqueous solution containing 20 to 80% by weight of methylolalkanal understood. Such a hydrogenation feed is preferred according to WO 98/28253 or DE-A 1 957 591 prepared by reacting aldehydes with formaldehyde.

It The procedure is that the aldehyde with the 1- to 8-fold Amounts of formaldehyde reacted in the presence of a tertiary amine (aldolization) and the reaction mixture thus obtained is separated into two solutions, being a solution that mentioned Methylolalkanal and the other solution has unreacted starting material. This last solution will attributed to the reaction. The Separation is carried out by distillation or simple separation the aqueous from the organic phase. The aqueous solution containing the methylolalkanal can be used as Hydrierfeed in the process according to the invention.

It but it is also possible the watery methylolalkanal as hydrogenation feed by other methods of the prior art, for example, according to those known from WO 01/51438, WO 97/17313 and WO 98/29374 Process to produce.

In A preferred variant of the method according to the invention becomes a particular one Low-formaldehyde or formaldehyde-free aqueous methylolalkane solution as Hydrierfeed used. In a low-formaldehyde Methylolalkanallösung the content of formaldehyde below 5 wt .-%. The separation of formaldehyde from the Aldolisierungsaustrag, for example, according to WO 98/28253 can be obtained according to those known from the prior art Process, for example by distillation, take place.

at the methylolalkanal of the general formula I is preferred dimethylolalkanal, pentaerythritol or hydroxypivalaldehyde.

Of the Hydrogenation feed is conducted in front of the hydrogenation reactor inlet with tertiary amine, inorganic base or inorganic or organic acid until the hydrogenation discharge, which is taken after the reactor outlet, a pH of 7.0 to 9.0, for the preparation of neopentyl glycol preferably has a pH of 8.0 to 9.0, for the preparation of trimethylolpropane has a pH of 6.0 to 8.0. It is also possible, the hydrogenation feed and the tertiary one Amine, the inorganic base or the inorganic or organic acid separated feed into the reactor and mix there.

As suitable tertiary amines listed in DE-A 25 07 461 amines are exemplified. As tertiary amines, tri-n-C _{1 to} C ₄ -alkylamines are preferred and trimethylamine, triethylamine, tri-n-propylamine and tri-n-butylamine are particularly preferred. In general, up to 10% by weight (based on the hydrogenation feed) of the tertiary amine is added to the pH control in the process according to the invention. The amine can be used as a pure substance or as an aqueous solution.

amines are particularly beneficial to use for pH adjustment, as they are with formic acid form thermally decomposable salts, which after the hydrogenation again can be split. Thus, a salt attack can be avoided and the tertiary amine can be recycled in the process.

suitable Inorganic bases are the carbonates, bicarbonates and hydroxides the alkali and alkaline earth metals.

Especially advantageous is the use of the same tertiary amine in the aldolization process to the methylolalkanal - the Condensation of higher Aldehyde and formaldehyde - and in the hydrogenation.

When inorganic or organic acids can According to the invention mineral acids such as Hydrochloric acid, sulfuric acid or phosphoric acid or organic acids like citric acid, acetic acid or ethylhexanoic acid be used. Preferably, acetic acid is used. In general are 0 and 3 wt.% (Based on the hydrogenation Feed) of a 10% aqueous solution the acid added for pH control The pH is measured with the known techniques, preferably with a glass electrode and a pH meter.

Catalysts which can be used according to the invention are catalysts suitable for hydrogenations, which preferably contain at least one metal from subgroup 8 to 12 of the Periodic Table of the Elements such as Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Zn, Cd, Hg, preferably Fe, Co, Ni, Cu, Ru, Pd, Pt, particularly preferably Cu, preferably on a customary carrier material, more preferably on one of the oxides of titanium, zirconium koniums, hafnium, silicon and / or aluminum. The catalysts which can be used according to the invention can be prepared by processes known from the prior art for the preparation of such supported catalysts. Preference may also be given to using supported catalysts comprising copper on an alumina- or titania-containing support material in the presence or absence of one or more of the elements magnesium, barium, zinc or chromium. Such catalysts and their preparation are known from WO 99/44974.

Farther are copper-containing supported catalysts as they are e.g. in WO 95/32171 and in EP-A 44 444 and DE-A 1 957 591 disclosed catalysts for the hydrogenation of the invention suitable.

The Hydrogenation can be carried out batchwise or continuously e.g. in a reactor bed filled with a catalyst bed, in which the reaction solution over the catalyst bed e.g. in trickle or sump mode, as in DE-A 1 941 633 or DE-A 2 040 501 described, is passed. It can be beneficial attributed a partial flow of the reaction, optionally with cooling, and again over to direct the fixed catalyst bed. This circulation method is preferably with a ratio operated from circuit to feed of 10: 1 to 20: 1. As well it may be advantageous to hydrogenate in several consecutive to conduct switched reactors, for example, in 2 to 4 reactors, wherein in the individual reactors before the last reactor, the hydrogenation reaction only up to a partial conversion from e.g. 50 to 98% performed and only in the last reactor, the hydrogenation is completed. It may be appropriate the hydrogenation from the previous reactor prior to its entry to cool in the subsequent reactor, for example by means of coolers or by spraying cold gases, such as hydrogen or nitrogen or introducing a Partial stream of cold reaction solution.

The Hydrogenation temperature is generally between 50 and 180 ° C, preferably 90 and 140 ° C. As the hydrogenation pressure are generally 10 to 250 bar, preferably 20 to 120 bar applied.

The Hydrogenation can be carried out with the addition of an inert solvent. As a solvent are water, cyclic ethers such as THF or dioxane, as well as acyclic Ether usable, as well as lower alcohols, e.g. Methanol, ethanol or 2-ethylhexanol.

Otherwise, any Hydrogenation methods are used and hydrogenation catalysts are used, as for the hydrogenation of aldehydes usual and described in detail in the standard literature.

example 1

Hydrogenation of hydroxypivalaldehyde to neopentyl glycol

hydrogenation

1.1 mol of isobutyraldehyde were reacted with 1 mol of formaldehyde in the form of a 40 % solution and 4 mol% of trimethylamine, based on isobutyraldehyde, at 75 ° C for 1 h touched. The reaction solution was concentrated by at low pressure low boilers such as Isobutyralydehyde and part of the water were distilled off. The resulting bottoms consisted of 75% by weight hydroxypivalaldehyde, 20% by weight of water and about 5% by weight of other organic secondary components.

catalyst Preparation

All percentages stated under this sub-item, to the extent that Unless otherwise stated,% by weight. The percentages given Compositions refer to the oxidic constituents the finished catalysts.

feedstocks were a 20% by weight sodium carbonate solution and an aqueous one solution I containing 2.67% by weight of Al and 5% by weight of Cu in the form of their nitrates.

at the precipitation was in a precipitation boiler at 80 ° C solution I and soda solution so metered that a pH of 5.6 was established.

The precipitation mixture was transferred to a larger stirred tank and there at 80 ° C with soda solution adjusted to a pH of 7.9. Then the suspension was on passed a filter press.

The Mixture was then filtered and washed with water nitrate-free. The filter paste was suspended in water and in a spray tower with hot air at 130-150 ° C outlet temperature dried. This is followed by a calcination at a temperature of 375-390 ° C. Subsequently The powder with 3 wt .-% graphite as an aid to tablets with 3 × 3 mm tabletted.

The obtained tablets were now in a heated rotary tube at a temperature of 600 ° C during 60 minute calcined.

The catalyst consisted of 55% CuO and 45% by weight Al ₂ O ₃ , had a specific surface area (BET) of 95 m ² / g, a Hg porosity of 0.38 ml / g with a shaking weight of 1042 g / l on.

150 ml of this Cu / Al ₂ O ₃ catalyst were in a tubular reactor at 190 ° C by passing a mixture of 5 vol.% Hydrogen and 95 vol.% Nitrogen (total volume 50 Nl / h) depressurized for 24 h.

hydrogenation

The starting solution was the mixture described above as Hydrierfeed. This mixture was from 0 to 7 wt .-% (based on the hydrogenation Feed) of a 15 wt .-% aqueous solution of trimethylamine (2 to 5 wt .-% (based on the hydrogenation Feed) or a 5 wt .-% aqueous solution of citric acid in Comparative Examples) was added to each set to the specified in Table 1 pH of the hydrogenation. The hydrogenation feed thus obtained was pumped over the catalyst in a hydrogenation reactor with liquid circulation (circulation: feed = 10: 1) with a catalyst loading of 0.4 kg _HPA / I _cat × h in trickle mode at 40 bar and 120 ° C.

a Comparison of the method according to the invention with the comparative examples V1 and V2, in which the pH of the Hydrieraustrags each outside the range of the invention is shown in Table 1.

to pH measurement was using a pH meter from the company Knick Model 766 a glass electrode N1041A from Schott used.

• NPG = Neopentylglykol

The analysis of the acetal content of the obtained polyhydric alcohol was carried out by means of gas chromatography (GC) on an HP5 column from J & W, injector: 280 ° C, the detection was carried out with FID (flame ionization detector). Table 1 shows NPG-HPA acetal contents at the respective pH values. Table 1:

• NPG = neopentyl glycol

Example 2

Hydrogenation of dimethylolbutanal (DMB) to Trimethylolpropane (TMP)

hydrogenation

Of the Hydrierfeed was according to example 6 of PCT / WO 98/28253.

catalyst activation

300 ml of a Cu / TiO ₂ catalyst J WO 99/44974% nitrogen (total volume 150 Nl / h)% hydrogen and 95 volume were in a tubular reactor at 190 ° C by passing a mixture of 5 Vol.. Depressurized activated for 24 h.

hydrogenation

The starting solution was the mixture described above as Hydrierfeed. Between 0 and 3% by weight (based on the hydrogenation feed) of a 10% strength aqueous solution of citric acid were added to the mixture in order to adjust the pH of the hydrogenation effluent stated in Table 2. The thus obtained hydrogenation feed was run in trickle mode at 80 bar H ₂ pressure over the heated to 120 ° C reactor. The load was 0.4 kg dimethylol butanal (DMB) / (I _cat. * H). Part of the hydrogenation effluent was added to the feed again (circulation mode). The ratio of circulation to feed was 10: 1. Table 2 shows averaged conversions and selectivities over several days at different pH values. The pH was measured from samples of the reactor effluent at room temperature.

a Comparison of the method according to the invention with Comparative Examples V3 and V4, in which the pH of the Hydrieraustrags each outside the range of the invention is shown in Table 2.

to pH measurement was using a pH meter from the company Knick Model 766 a glass electrode N1041A from Schott used.

• TMP = Trimethylolpropan

The analysis of the acetal content of the resulting polyhydric alcohol was carried out by means of gas chromatography (GC) on an HP5 column from J & W, injector: 280 ° C. The detection was done with FID. Table 2 shows averaged TMP-DMB acetal levels over several days at the respective pH values. Table 2

• TMP = trimethylolpropane

Claims (10)

A process for the preparation of polyhydric alcohols with low acetal contents by catalytic hydrogenation of Methylolalkanalen the general formula

in which R ¹ and R ² independently of one another are a further methylol group or an alkyl group having 1 to 22 C atoms or an aryl or aralkyl group having 6 to 33 C atoms, in the liquid phase on a hydrogenation catalyst, characterized in that by addition at least one tertiary amine, an inorganic base or an inorganic or organic acid to Hydrierfeed a pH of 7.0 to 9.0 is set in the hydrogenation. Method according to claim 1, characterized the hydrogenation feed contains less than 5% by weight of formaldehyde Method according to claim 1 or 2, characterized that a tri-n-alkylamine is used. Method according to one of claims 1 to 3, characterized trimethylamine, triethylamine, tri-n-propylamine and or tri-n-butylamine is added. Method according to one of claims 1 or 2, characterized the acetic acid is added. Method according to one of claims 1 to 5, characterized the hydrogenation catalyst comprises at least one metal of the subgroups 8 to 12 of the Periodic Table of the Elements. Method according to one of claims 1 to 6, characterized that it is a supported catalyst is. Method according to claim 7, characterized in that that as a carrier material the oxides of titanium, zirconium, hafnium, silicon and / or aluminum be used. Method according to one of claims 6 to 8, characterized that the hydrogenation catalyst copper on an alumina or Titanium dioxide-containing carrier material in the presence or absence of one or more of the elements magnesium, Barium, zinc or chromium. Method according to one of claims 1 to 9, characterized that it is hydroxypivalaldehyde, pentaerythritol or dimethylolbutanal is.