ITMI20010468A1 - MIXED ALUMINUM OXIDE AND PHOSPHORUS PROCEDURE FOR ITS PREPARATION AND USE AS A CATALYST - Google Patents

Description

Description of the industrial invention entitled:

"MIXED ALUMINUM AND PHOSPHORUS OXIDE, PROCEDURE FOR ITS PREPARATION AND ITS USE AS A CATALYST"

Background of the invention

Monoalkyl ethers of diphenols such as for example guaiacol (1-methoxy-2-hydroxybenzene) and guetol (1-ethoxy-2-hydroxybenzene) as well as other monoalkyl ethers of diphenols can be produced by condensation reaction (etherification) of catechol or other diphenols with an alkylating agent, catalyzing the above transformation through the use of a suitable material, having characteristics such as to favor the monoalkylation to oxygen, hence the formation of the monoalkyl ether. The reaction can be carried out in the gas phase, in the liquid phase or in the mixed phase, and the preferred alkylating agent is constituted by the corresponding alcohol.

Catalytic systems described in the patent literature consist of systems based on mixed oxides of boron and phosphorus, as claimed in patent EP 420 756 (1990), assigned to UBE Industries. This material is characterized by considerable catalytic activity, but its activity progressively decreases over time, since the active phase is slowly but progressively lost under the reaction conditions. To obviate this, it is necessary to coalesce volatile compounds of B and / or P, in order to prevent the loss of the active components by sublimation under reaction conditions. Alternatively, the decrease in activity can be obviated by raising the reaction temperature, but this leads to a decrease in selectivity in the desired product. The progressive disintegration of the active phase also leads to an impoverishment of the mechanical resistance characteristics of the extrudate or of the catalyst pellet.

In the patent FR 2,303,784, assigned to UBE Industries (1976) the use of a catalytic system based on Al / B / P / O is instead described, for which however it is still necessary to feed compounds of B and / or P to maintain performance in terms of reagent conversion unchanged over time.

Finally, in the patent EP 509,927 (1992), assigned to UBE Industries, the use of a catalyst consisting of a mixed oxide of

in which the relative ratios of the claimed components are included between (setting a = 1), b = 1.0-1.6, c = 0.05-0.5, d = 0.05-0.2. An alkali metal ion (typically potassium) can also be added to the composition (with relative ratio 0-0.9). With respect to the previous ones, this catalytic system has the advantage of having much more constant reactivity characteristics over time, and therefore does not require the coal-feeding of volatile compounds. The claimed catalyst is characterized by a specific surface area value of between 30 and 50 m2 / g after final heat treatment carried out at a temperature of between 300 and 600 ° C, preferably at a temperature of 400 ° C. This catalyst is used for the etherification reaction at a claimed temperature between 200 ° C and 400 ° C. It should be noted that according to what is claimed in the aforementioned patent, the absence of Ti or Si in the composition of the catalyst leads to a decrease in the selectivity in guaiacol (for the etherification reaction of catechol with methanol) and, above all, to a considerable decrease catalytic activity. The conversion at the temperature of 280 ° C in fact decreases from 64.7% to 46.3% (catalyst without Ti), to 55.7% (catalyst without Si); the selectivity decreases from 98.3% to 95.8% (catalyst without Ti), to 97.4% (catalyst without Si).

In consideration of the foregoing, it is desirable from an application point of view to develop a more active catalyst than those claimed or known, so as to be able to operate under relatively milder reaction conditions, and therefore to achieve acceptable conversions with high selectivities to monoethers. (for example guaiacol). The ideal is constituted by a system which can operate at reaction temperatures lower than those described in the patent literature, ie in conditions in which it is possible to achieve high selectivities to monoethers and to minimize the formation of undesirable products.

A catalytic system based on Al / P / O is described here, prepared by a different technique from that described in the patent literature, and which, compared to known systems, has the following advantages:

1) High specific surface area, between 50 and 100 m2 / g after calcination up to 400-800 ° C (preferably 400-650 ° C), obtained by virtue of the preparation method used, and therefore considerably higher than that of systems described in the literature and calcined at the same temperature.

2) By virtue of the characteristic referred to in the previous point, it is possible to carry out a consolidation heat treatment of the solid at temperatures higher than that described in the literature, for example at 600 ° C, while maintaining a high specific surface area, between 50 and 80 m2 / g, and therefore a high catalytic activity. A treatment at higher temperatures allows to obtain materials characterized by greater structural and morphological stability, therefore characterized by more stable catalytic performance over time.

3) By virtue of the characteristics described in points 1 and 2 it is possible to obtain an active system even in the absence of the Si and Ti components. It is therefore possible to prepare catalysts characterized by a lower cost, and by simpler preparative procedures, and in general by better reproducibility, since the preparation and composition parameters are significantly lower.

4) The catalysts prepared according to the procedure described in the present patent can operate in lower temperature conditions than those described in the literature, and therefore in more favorable conditions both in terms of selectivity to the desired product, and in terms of life times of the catalyst itself. . In fact, lower temperatures slow down the phenomena, however always present, of hydrolysis of the phosphate and at the same time reduce the formation of heavy products and therefore the deactivation problems. For example, it is possible to achieve a conversion of catechol between 20 and 30% at a temperature of 190 ° C, with selectivity in guaiacol greater than 99% for more than 1,300 hours of reaction in flow, without any decrease in reactivity. The unconverted reagent can then be easily recycled into the reaction environment.

Description of the invention

The object of the present invention is a catalyst for the oxygen monoalkylation (monoetherification) of polyhydroxybenzenes by reaction between these compounds and an alcohol, more particularly for the reaction between dihydroxybenzenes and CrC6 alcohols, preferably C1-C4, linear or branched, saturated or unsaturated. The reaction can be carried out in gas phase, or in mixed phase, with high conversion of the limiting reagent, and with high selectivity to the product of monoalkylation to oxygen (1-alkoxy-2-hydroxybenzene, for example 1-methoxy-2-hydroxybenzene or guaiacol), and with low selectivity to other undesirable products, such as complete etherification products (e.g. veratrol). A further advantage of the catalyst described in the present invention is constituted by the possibility of carrying out the reaction for very long life times without observing deactivation of the catalyst, both in terms of activity and selectivity, and without the need to co-feed together with the compound reagents intended mainly to maintain the performance of the catalyst itself remains unchanged over time. Typically, the feeding of these compounds is necessary in the case of catalytic systems known in scientific and patent literature, such as systems based on boron, phosphorus and oxygen, and they consist of alkylborates, alkyl phosphates or other volatile compounds of boron and phosphorus. This operation is necessary as the catalyst progressively loses activity due to the slow but continuous hydrolysis of the mixed compound based on B / P / O in the reaction environment, and the release of boron and phosphorus in the form of volatile compounds. The creation of a vapor pressure by continuously feeding compounds of B and P prevents or at least slows down the deactivation process. However, the continuous feeding of the aforesaid compounds entails an additional burden for the process, both in terms of the costs of the reagents and in terms of operations relating to the separation of said compounds from the unconverted reactants and from the products. Furthermore, the presence of compounds of B and / or P, potentially hydrolyzed in the presence of water vapor, can lead to undesired corrosion phenomena downstream of the reactor itself.

The catalyst described in the present invention is able to operate in the absence of "doping" compounds fed continuously to the reactor, and does not show any phenomenon of decrease in catalytic activity and performance in general (in terms therefore of selectivity and yield to the product desired) over at least 1,300 hours of reaction. The most important advantage of the material described here is in any case constituted by the possibility of operating under reaction temperature conditions lower than those claimed in the literature; in fact the system described here works effectively at the temperature between 170 ° and 200 ° C, preferably at the temperature of 190 ° C, therefore outside the temperature range claimed for example in the patent EP 509.927 (1992), assigned to UBE Industries . The catalyst object of the present invention consists of aluminum oxide and phosphorus oxide present in the form of mixed oxide of aluminum and phosphorus, Al / P / O, where the atomic ratio between aluminum and phosphorus is between 0.40 and 1.0, preferably between 0.60 and 0.80. Contrary to what is described in other patents which claim materials based on phosphates, the addition of other doping components in the composition of the catalyst itself is not necessary to increase the stability and activity of the catalyst itself.

The preparation of the catalytic material described in the present invention consists of a co-precipitation of a mixed compound of Al and P, precursor of the final catalyst. In general, the preparation is made starting from a water-soluble aluminum compound and a water-soluble phosphorus compound. The two compounds are dissolved, and then the coprecipitation of the elements is carried out by varying the pH of the solution, with the obtaining of a precursor which is then filtered, dried and finally treated in air at high temperature. The methodology described below is an example of the procedure used for the preparation of the catalyst described in the present invention, but does not constitute a limitation to the claims of this invention. In fact, the most important conditions for obtaining a precursor suitable for the preparation of a catalyst having the characteristics suitable for use for the monoetherification reaction under the conditions described in the present patent are: i) the preparation of a homogeneous solution, and ii) the co-precipitation of Al and P in the form of oxohydrates by controlling the pH of the above solution. Therefore, any type of soluble compound of Al and P which satisfies the above mentioned criteria can be used for the purpose of the present invention.

Aluminum trichloride hexahydrate and 85% o-phosphoric acid are dissolved in water; in particular, the Al compound is dissolved in an aqueous acid solution for HC1, keeping the solution temperature close to the ambient one (and avoiding the hydrolysis of the compound and the consequent formation of the aluminum hydroxide precipitate). Phosphoric acid is then added to this solution and co-precipitation of the mixed compound is carried out by adding ammonium hydroxide up to a pH of about 7, which is then maintained. Alternatively, it is possible to add by dripping the solutions containing Al and P to a solution at pH 7 (for example containing ammonium acetate), and to maintain the pH at this value by adding ammonia or other basic compounds.

The precipitate, which is generally (but not necessarily) in the form of a gel, is preferably dried at 120-150 ° C, and finally calcined in air for a few hours (alternatively, the coprecipitate can be subjected directly to calcination). Calcination takes place up to temperatures between 400 and 800 ° C, preferably between 400-650 ° C, and even more preferably following the following program:

heating from room temperature to 280-320 ° C at a rate of about 10 ° C / minute;

permanence at 280-320 ° C for 3-5 hours;

further heating up to 580-620 ° C at a rate of about 10 ° C / minute;

permanence at 580-620 ° C for 3-5 hours.

The final form of the catalyst can be any suitable for use in a fixed bed reactor, such as extrusions, cylinders or granules, prepared using known technologies.

The described procedure constitutes an example of heat treatment, but the conditions do not constitute a limitation to the claims of this invention. In fact, the intermediate temperatures, the heating gradients and the isotherm times can be conveniently modified, in order to optimize the heat treatment according to the quantity of catalyst that is prepared.

The heat treatment must be carried out in such a way as to favor the removal of volatile compounds, according to the known technique in industrial practice. This is an essential condition for obtaining a catalyst characterized by a high surface area.

As an alternative to ammonium hydroxide (or gaseous ammonia) as a precipitating agent, you can use primary, secondary or tertiary amines with CrC4 alkyls, or even tetra- (C1-C4) alkylammonium hydroxides.

This procedure allows to obtain a solid characterized by a specific surface area greater than 50 m2 / g.

The fundamental difference with respect to the preparations described in the literature is evident in the different methodology. The catalyst described in UBE EP 509.927 is prepared by dispersing aluminum hydroxide Al (OH) 3 in water, and kept under stirring in suspension, under reflux conditions (T 100 ° C). A titanium oxide sol and a silica sol are then added to the suspension in the appropriate quantities to reach the desired atomic ratio, and finally 85% phosphoric acid is added. The resulting suspension mixture is left under stirring and heating for a few hours, and the resulting paste is dried, formed and finally calcined in air at a temperature of 400 ° C. The procedure does not therefore pass through the complete dissolution of the Al reagent, and therefore the final compound necessarily suffers from the original characteristics of the aluminum hydroxide used. The surface area described in the aforementioned patent after treatment at 400 ° C is between 30 and 50 m2 / g, therefore lower than that obtained with the preparation developed by us.

In the catalyst described in the present application, in particular in the final compound after heat treatment, the atomic ratio Al / P must be between 0.5 and 1.0, preferably between 0.6 and 0.8. Lower or higher ratios lead to a worsening of the catalytic performance, especially in terms of selectivity to the product of interest. Different ratios also lead to life times, understood as the time in which the catalytic performance remains sufficiently stable, between two successive regenerations, which are considerably lower, due to the disintegration of the particles (extruded or pellets) of catalyst and the deposit on the surface. of it of carbonaceous products or pitches.

In the case of the catalyst according to the present invention, it is however possible to carry out a regeneration heat treatment, should deactivation phenomena occur due to covering the catalyst with pitch or carbonaceous products in general. A typical regeneration treatment can be carried out at temperatures between 450 ° and 650 ° C and more conveniently at 650 ° C, in an air stream. At this temperature it is possible to completely remove the products that have led to deactivation, while lower temperatures would not lead to complete removal of them. A further advantage of the system described in the present invention therefore consists in the possibility of carrying out an effective regeneration, should the need arise, at a temperature similar to that of calcination and consolidation of the catalyst itself. The advantage is that the regeneration treatment does not lead to changes in the characteristics compared to the fresh catalyst.

The reactivity of the catalyst prepared for the etherification reaction of diphenols or in general of polyhydroxybenzenes is analyzed with a laboratory flow reactor, containing the catalyst in the desired form. In particular, the reactants (the diphenol and the alcohol) are fed together or separately to the reactor, possibly after vaporization in an evaporator. A carrier gas, preferably nitrogen, can be used to carry the reactants onto the catalyst bed located inside the reactor. This can be made of steel, glass or quartz. The catalytic bed temperature is maintained at the desired level by a suitable heating system. The reaction temperature can be maintained in a range between 170 and 220 ° C, more conveniently between 180 and 200 ° C.

The reagents can consist of i) as regards the polyhydroxybenzenes, catechol, hydroquinone or resorcinol (diphenols), or the same ones having, however, on the aromatic ring substituent groups such as methyl groups or halogen atoms, and ii) as regards the alcohols, from methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol and others up to 6 carbon atoms, possibly also unsaturated.

The tests were carried out by loading 7.5 ml of catalyst into a laboratory microreactor, feeding 3 g / h of a liquid mixture consisting of 50% by weight of catechol and 50% of methanol, and with a carrier gas flow equal to 35 Nml / min. The reaction temperature was varied between 190 - 200 ° C (Examples) and 275 ° C (Comparative Examples).

EXAMPLES

Example 1

59.2 g of A1C13.6H20 are dissolved in 200 ml of 0.5 N HCl (190 ml H20 10 ml HCl 37%), kept under stirring. Subsequently 21 ml of H3P04 at 85% by weight are added. The solution remains clear. NH4OH conc. drop by drop (about 90 ml), until reaching a pH of about 7. A precipitate is formed, which is subsequently dried on a buchner-type filter, until a paste is obtained. The pasta is then dried in an oven at 120 ° C for 12 hours, until a dry, white mass is obtained. The solid is then treated in a high temperature air current, using the following program: from room temperature to 300 ° C with a speed of 10 ° / min, maintaining the temperature of 300 ° C for 4 hours, subsequent heating from 300 to 600 ° C with a speed of 10 ° / min, maintaining the temperature of 600 ° C for 4 hours. The surface area of the sample thus obtained is equal to 74 ± 5 m2 / g. The solid is then granulated by compression, granulation and sieving until granules with size between 0.5 and 1 mm are obtained. The analytical Al / P ratio in the final catalyst, determined by plasma spectrometry, is equal to 0.64 ± 0.04.

Example 2

The preparation is the same as that described in Example 1, except that the relative quantities of A1C13.6H20 and H3P04 are equal to 20 g and 8.1 ml, respectively. The analytical Al / P ratio in the final catalyst, after heat treatment, is equal to 0.67 ± 0.04.

Comparative example 3

The preparation is the same as that described in Example 1, except that the relative quantities of A1C13.6H20 and H3P04 are equal to 90.0 g and 21.0 ml. The Al / P ratio in the final catalyst, after heat treatment, is equal to 0.95 ± 0.04.

Example 4

The catalyst whose preparation is described in example 1 was tested in the monoetherification reaction of catechol with methanol, using the reaction conditions described above. In particular, a reaction temperature of 190 ° C was used. The test results, obtained over a life time of 1300 hours of reaction, are summarized in the table.

Example 5

The catalytic tests were carried out on the catalyst whose preparation is described in example 1, and under the same reaction conditions as in example 4, except that the reaction temperature is equal to 200 ° C.

Comparative example 6

The catalytic tests were carried out on the catalyst whose preparation is described in example 1, and under the same reaction conditions as in example 4, except that the reaction temperature is equal to 275 ° C.

Comparative example 7

The catalytic tests were carried out on the catalyst whose preparation is described in example 2, and under the same reaction conditions as in example 4, except that the reaction temperature is equal to 275 ° C.

Comparative example 8

The catalytic tests were carried out on the catalyst whose preparation is described in comparative example 3, and in the same reaction conditions of example 4, except that the reaction temperature is equal to 275 ° C.

Table

Summary of catalytic reactivity tests in catechol monoalkylation

* reaction time means the time elapsed from the start of the catalytic tests.

Example 9

Proceed as in example 5 using ethanol as etherifying agent, instead of methanol. The test results obtained over a catalyst life time of 600 hours are:

conversion of catechol 24%

selectivity to guetol 96%

From the evidence listed above it can be deduced that:

1) The catalyst described in example 1 maintains its reactivity characteristics for at least 1300 hours of reaction, with a conversion of more than 20% and selectivity in guaiacol of 99.1-99.2% (example of reactivity 4).

2) The catalyst described in example 1 shows a drop in selectivity to guaiacol if tested at temperatures above 200 ° C; especially at the temperature of 275 ° C (also reported in the examples of patent EP 509.927) the selectivity drops to 96.54% (comparative example of reactivity no. 6).

3) The catalyst described in example 2, prepared with an atomic ratio slightly different from that of example 1, shows comparable performances, under the same experimental conditions, with those of the catalyst described in example 1 (example of reactivity no. 7) .

4) The catalyst described in comparative example 3, characterized by an Al / P ratio substantially different from that of the catalysts described in examples 1 and 2), has a much worse catalytic behavior than that of the catalysts described in the present invention, especially in terms of selectivity to guaiacol (comparative example of reactivity No. 8).

Example 10

We proceed as in example No. 4 using isopropanol as an etherifying agent instead of methanol and operating under the following reaction conditions:

8.5 ml of catalyst loaded, 5 g / h of a liquid mixture consisting of 6% by weight of catechol and 94% of isopropanol, flow of the carrier gas equal to 25 N ml / min., reaction temperature equal to 140 ° C.

The results of the test, obtained over a catalyst life time equal to 90 hours of reaction, are:

catechol conversion: 25%

selectivity to monoether: 75%

Example 11

The catalyst whose preparation is described in Example 1 was tested in the monoetherification reaction of hydroquinone with methanol, using the reaction conditions described in Example No. 4, except that the reaction temperature is equal to 200 ° C and feeding the hydroquinone / methanol mixture at 1.2 g / hour.

The results of the test, obtained over a catalyst life time equal to 15 hours of reaction, are:

Hydroquinone conversion: 17%

selectivity to hydroquinone monomethylether: 96%

Claims (14)

CLAIMS 1. Mixed oxide of aluminum and phosphorus characterized by an atomic ratio Al: P between 0.4: 1. and 1: 1 and a surface area between 40 and 100 m2 / g. 2. Mixed oxide of aluminum and phosphorus according to claim 1, characterized by an atomic ratio Al: P between 0.6: 1 and 0.8: 1, and a surface area greater than 50 m2 / g. 3. Process for the preparation of a mixed oxide of aluminum and phosphorus according to claims 1-2, characterized in that: a) co-precipitates, from an aqueous solution of a water-soluble compound of aluminum and a water-soluble compound of phosphorus, a mixed compound of Al and P; b) said precipitate is subjected to drying at a temperature of between 80 and 180 ° C; c) the product obtained in b) is subjected to calcination in an air stream by gradually heating it from room temperature to a final temperature between 400 ° C and 800 ° C; 4. Process according to claim 3, characterized in that the precipitate obtained in a) is directly subjected to calcination. 5. Process according to claims 3 and 4, characterized in that aluminum chloride and phosphoric acid are used as water-soluble compounds of Al and P. 6. Process according to claims 3 to 5, characterized in that the co-precipitation is carried out by bringing the pH to about 7. 7. Process according to claims 3 to 6, characterized in that the coprecipitation is carried out by adding a base selected from the group consisting of ammonia, (C1-C4) primary, secondary and tertiary alkylamines, relative hydroxides and hydroxides of (C1 -C4) tetraalkylammonium. 8. Process according to claims 3, 5, 6 and 7, characterized in that the drying of the precipitate is carried out at a temperature between 100 and 150 ° C. 9. Process according to claims 3 to 8, characterized in that the calcination is carried out by gradually heating the product obtained according to claim 3b from room temperature to a final temperature of between 400 and 650 ° C. 10. Process according to claims 3-7, characterized in that the calcination is carried out according to the following program: from room temperature to 280 - 320 ° C at a rate of about 10 ° C / minute; permanence at 280 - 320 ° C for 3 - 5 hours; heating up to 580 - 620 ° C at a rate of about 10 ° C / minute; permanence at 580 - 620 ° C for 3 - 5 hours. 11. Process for the preparation of monoalkyl ethers of polyhydroxybenzenes possibly bearing alkyl groups or halogen atoms on the aromatic ring, by reaction with CrC6 alcohols, linear or branched, saturated or unsaturated, in gaseous, liquid or mixed phase, said reaction being catalyzed by a mixed oxide of aluminum and phosphorus according to claims 1-2. 12. Process according to claim 11, characterized in that one operates at temperatures between 170 ° C and 220 ° C. 13. Process according to claim 12, characterized in that one operates at temperatures not higher than 200 ° C. 14. Process according to claims 11-13, characterized in that the polyhydroxybenzene is selected from the group consisting of 1,2-, 1,3- and 1,4-dihydroxybenzene and the alcohol is selected from the group consisting of methanol, ethanol , propanol and isopropanol.