IT201800006967A1 - Solid composition for heterogeneous catalysis and related preparation process - Google Patents

Description

Description of the patent application for industrial invention entitled:

"Solid composition for heterogeneous catalysis and related preparation process"

Technical field of the invention

The present invention relates to a composition for heterogeneous catalysis and a process for its preparation.

Known technique

The use of catalysis in the chemical industry has long been known in the preparation of a wide range of chemical products.

Among the different types of catalysis that exist, heterogeneous catalysis, i.e. in which the catalyst and the reactants are in two different phases, has multiple advantages, such as easier separation of the catalyst after the reaction, to the advantage of its recycling. Often the catalyst is in the solid phase, which allows to increase the number of process options and to reduce the polluting discharges of the process, while the reactants are in the liquid phase.

Among the known catalysts, acid catalysts are widely used, and have various advantages when they are in solid form, including in particular a lower environmental impact.

In this context, the use of superacid perfluorosulfonated resins, in particular Nafion® and Aquivion®, as catalysts of reactions in the liquid phase has been known for some time. Their superacid properties exhibit a very high catalytic activity, but their low surface area value leads to poor accessibility of acid sites.

A problem of known superacid solid catalysts is that they are not suitable for a heterogeneous catalysis of a gas phase reaction, such as the catalytic dehydration of ethanol to obtain ethylene. This reaction arouses great interest as it allows ethylene, a compound widely used in the chemical industry, to be obtained from sources other than fossil sources.

Brief summary of the invention

The object of the present invention is therefore to provide a composition which has a good catalyzing effect for the reactions in the gaseous phase.

Another purpose of the invention is to provide a process for the preparation of the catalyst composition.

These and other objects are achieved by a composition according to claim 1, by a use according to claim 6 and by a process according to claim 9.

The dependent claims define possible advantageous embodiments of the invention.

Description of embodiments of the invention

In general, the solid composition for heterogeneous catalysis comprises a support material and a superacid perfluorosulfonated resin supported by the aforementioned support material.

By superacid we mean that the perfluorosulfonated resin has a very high Hammett acidity, typically ranging from -11 to -13.

According to the invention, the superacid perfluorosulfonated resin includes Aquivion® and the support material has a surface area greater than or equal to 5 m <2> / g.

It has been possible to verify that the fact of having a support material with a surface area value of at least 5 m <2> / g confers catalytic activity on the solid composition for reactions carried out in the gas phase.

According to a preferred embodiment, the support material comprises SiO2 or TiO2. Other materials are possible, for example Al2O3 or CeO2.

It has in fact been found that Aquivion® coupled to SiO2 or TiO2 has a good reaction catalysis activity in the gas phase.

It has also been observed that the solid composition in which the support material is titania allows to obtain better results both in terms of efficiency and in terms of selectivity of the reaction.

It should be noted that Aquivion® is a perfluorosulfonated resin based on a SSC fluorinated ionomer, or short side chain, of formula (I).

According to a possible embodiment, the superacid perfluorosulfonated resin is in the form of a homogeneous dispersion on the support material, that is, it forms a coating on the support material.

Alternatively, the superacid perfluorosulfonated resin can be in the form of a dispersion on the surface of the support material, but without completely coating the surface thereof. Obtaining one or the other form depends on the preparation process used, as will be better specified below.

Preferably the solid composition has a granulate form, and even more preferably a granulate form in which the granules have a substantially spherical irregular shape. The dimensions of the obtained granules are comprised between some tens and some hundreds of microns.

With the present invention it is also intended to protect the use of the composition described above as a heterogeneous catalyst.

It is intended to preferably protect the use of the composition as a heterogeneous catalyst in a gas phase reaction.

It is also noted that thanks to the above composition, a way has been found to use Aquivion® in a catalysis of a gas phase reaction. It is also intended to protect this use in the present invention.

A process for the preparation of the solid composition described above is also the subject of the protection.

The process for preparing the composition comprises the steps of

a) preparing an aqueous suspension of superacid perfluorosulfonated resin and support material;

b) applying the superacid perfluorosulfonated resin on the support material; And

c) remove the solvent.

With reference to step a), it is meant the preparation of a single suspension in which both the superacid perfluorosulfonated resin and the support material are present.

According to a possible form of the process, the application step b) comprises an impregnation step under mechanical stirring, and the solvent removal step c) comprises a solvent drying step.

In this case, the preparation of the solid composition takes place by "Wet Impregnation", ie the impregnation of the support material with the perfluorosulfonated resin in conditions of excess solvent.

The impregnation phase under mechanical stirring can take place by means of a magnetic stirrer or by means of a rotovapor. The drying step can be carried out at atmospheric pressure or under vacuum. Furthermore, the support material can be provided in the form of powder or pellets.

The best results were obtained with the support material in the form of powder, with stirring using a magnetic stirrer and drying under atmospheric pressure.

Note that by preparing the composition through impregnation, the solid composition obtained presents the superacid perfluorosulfonated resin in the form of a dispersion on the support material, but not of the coating.

According to another form of the preparation process, step b) of application includes a step of spraying the solution in a liquid nitrogen bath, and step c) of removing the solvent comprises a step of sublimation of the solvent.

In this form of the procedure, the composition is prepared through "Spray Freeze Drying", which involves a freeze-drying of a compound previously sprayed directly in a cryogenic solution, in particular liquid nitrogen.

The "Spray Freeze Drying" is already used in the food or pharmaceutical sector, but has not yet been used to synthesize a heterogeneous catalyst. It is also known that this technique allows one material to be encapsulated in another, which is in line with the fact that the solid composition obtained by “Spray Freeze Drying” has the superacid perfluorosulfonated resin forming a coating on the support material. The latter is encapsulated in the resin.

Examples

Example 1

The composition according to the invention is prepared through "Wet Impregnation".

The specific porosity of the support material in powder form is measured, in order to determine the amount of solvent (in this case water) to be used during the synthesis. This quantity of water corresponds to ten times that necessary to completely fill the porosity.

The support material and the superacid perfluorosulfonated resin are then placed in a beaker in excess of water and stirred with a magnetic stirrer for three hours at a temperature of 60 ° C. The quantities of the two compounds are suitably calculated to obtain catalysts with a known composition.

The solvent is then evaporated by rotovapor, and the powders obtained are dried in an oven at 150 ° C at atmospheric pressure overnight.

Subsequently the calcination of the dried catalysts is carried out for 3 hours at the temperature of 300 ° C.

Finally, the powders obtained are pelletized. The catalysts thus prepared and the products used are indicated in table 1.

Table 1: catalysts prepared through "Wet Impregnation"

Example 2

The composition according to the invention is prepared containing Aquivion® and SiO2 through "Spray Freeze Drying".

First of all, the superacid perfluorosulfonated resin and SiO2 mixtures are prepared. For this purpose a colloidal silica dispersion available on the market is used, and it is acidified by treating it with an ion exchange resin (DOWEX 50x8). The purpose of this phase is to reduce the pH of the silica dispersion, which is around values equal to 8. With such a high pH, the addition of Aquivion® would lead to an almost instantaneous flocculation. The pH of the silica dispersion is lowered to a value of 4.

The acidified silica dispersion is then diluted and added drop by drop to a 20% concentrated dispersion of Aquivion® to ensure correct atomization of the mixture.

The mixture is then stirred for about 24 hours by means of a ball milling containing grinding bodies of zirconia with a diameter of 5 mm.

The mixture thus obtained is made to flow, by means of a peristaltic pump, towards a nozzle with a diameter of 100 µm, towards which a flow of nitrogen at a pressure of 0.4 bar is also fed, which allows the atomization of the suspension.

The suspension is then atomized in a beaker containing liquid nitrogen, at a temperature of -196 ° C, kept under stirring.

The suspension is fed in such a way as to obtain an outgoing flow from the nozzle that is intermittent, in order to avoid freezing of the suspension on the nozzle, and its consequent obstruction. It is also preferable to keep the nozzle moving, to avoid the deposit of fluid on the outlet hole.

By operating in this way, a granulation of the mixture is obtained. The equipment used is a LAB-SCALE LS-2 granulator.

The frozen particles obtained are then removed from the beaker, placed in metal plates and transferred to the freeze-drying chamber, where the solvent is sublimated.

Sublimation begins at a pressure of 1.5 mbar and at a temperature of -1 ° C. The temperature is then increased until it reaches 25 ° C, in order to increase the speed of sublimation. During this phase, the temperature of the granulate must not exceed 0 ° C before the pressure exceeds 6 mbar (pressure corresponding to the triple point of water), otherwise the ice would melt and, consequently, the collapse of the granulate.

The freeze-drying phase has a total duration of 48 hours.

The catalysts thus prepared and the products used are indicated in table 2.

Table 2: catalysts prepared by “Spray Freeze Drying” with SiO2 as support material

Example 3

The composition according to the invention is prepared containing Aquivion® and TiO2 through "Spray Freeze Drying".

First a TiO2 dispersion is prepared, using commercially available Titania P25. The dispersion is carried out in water with an acidic pH (HCl solution with a pH of about 3) to inhibit flocculation during mixing with Aquivion® and keep the dispersion stable.

The dispersion is then homogenized in an ultrasonic bath for 15 minutes, and is subsequently mixed with a dispersion of Aquivion®. The mixture thus obtained is then in turn homogenized by ultrasound for 15 minutes and in a ball mill for one night.

The subsequent spraying and freeze-drying phases are identical to those described in example 2.

The catalysts thus prepared and the products used are indicated in table 3.

Table 3: catalysts prepared by “Spray Freeze Drying” with TiO2 as support material

Example 4

The catalytic activity of the catalysts according to the invention is studied in the model reaction in the gas phase of dehydration of ethanol, as per scheme 1.

The plant in which the reaction takes place consists of three sections: a feeding section, including a volumetric pump for the injection of liquid ethanol via syringe and electronic nitrogen and helium flow regulators; a reaction section, consisting of a fixed bed glass reactor, with sintered glass septum, placed inside an oven; and a product analysis section, comprising a gas chromatograph equipped with a TCD detector.

It is noted that ethanol is injected in the liquid state, and is then vaporized through the use of heating bands that allow the reagent and reaction products to be kept in the gaseous phase along all the lines of the plant.

Before each reaction, the catalyst loaded in the plant is subjected to a pre-treatment of dehumidification, feeding through the reaction section a flow of N2 (40 ml / min) at 150 ° C for 1 hour. In this way the moisture present on the surface of the catalyst is completely removed. after pretreatment, the nitrogen flow to the reactor is closed, and in its place a flow of He is introduced, which acts as a carrier for ethanol.

In the tests performed, all the reactions were carried out with a contact time of 1s, feeding ethanol at 1% by volume in helium and using catalysts with a 30-40 mesh, i.e. in the form of powder whose dimensions are between 30 mesh and 40 mesh (where mesh represents the number of meshes per square inch of the sieve).

Catalytic activity of catalysts with SiO2 and Aquivion®

Table 4: catalyzed dehydration reactions of ethanol, conducted at a temperature of 200 ° C

The results of the tests show that the composite catalysts according to the invention allow to significantly increase the conversion yields of ethanol into ethylene and diethyl ether.

With an Aquivion® load of 17% (compound 1-1) the reaction is not selective, as the productions of ethylene and diethyl ether are the same. By increasing the load of Aquivion® to 29% and 40% (compounds 1-2 and 1-3) the selectivity of the reaction is increased, in favor of a much better ethylene yield than the diethyl ether yield.

With the same load of Aquivion®, an increase in the acid load from 1.02 to 1.51 mmol SO3H / g (compounds 1-3 and 1-4) allows to increase the conversion efficiency of ethanol as well as the selectivity of the reaction in favor of the formation of ethylene.

Catalysts synthesized by spraying and lyophilization show slightly higher or equal yields compared to compounds synthesized by impregnation. Comparing the results obtained with compounds 1-3 and 2-4 (which have the same load of Aquivion® and the same acid load) we observe an equal conversion efficiency of ethanol, and a slightly higher selectivity in favor of the formation of ethylene with the catalyst synthesized by Spray Freeze Drying.

Catalytic activity of catalysts with TiO2 and Aquivion®

Table 5: catalyzed dehydration reactions of ethanol, conducted at a temperature of 150 ° C

Composite titania-based catalysts exhibit significantly higher catalytic activity than titania alone.

With an Aquivion® load of 40% (compound 1-5) excellent conversion yields of ethanol and excellent selectivity in favor of the formation of ethylene are obtained.

It is noted that the results of table 5 are obtained with reactions carried out at 150 ° C, while those of table 4 were obtained with reactions at 200 ° C. Globally, at equal compositions, compounds with TiO2 have a higher catalytic activity than compounds with SiO2.

Example 5

Tests were performed at different temperatures to verify the influence of the variation of this parameter on the catalytic activity of the composite catalysts.

Table 6: catalytic activity of some composite catalysts as a function of the reaction temperature

The catalytic activity of composite catalysts with Aquivion® and SiO2 or TiO2 increases with temperature. This increase in catalytic activity results in an increase in the conversion of ethanol, and an increase in the selectivity of the reaction in favor of the formation of ethylene.

From these results it can be seen that catalysts with TiO2 as support material have optimal yields at lower temperatures than catalysts with SiO2 as support material.

Table 7: comparison between the catalytic activities at 200 ° C of composite catalysts with SiO2 and TiO2

At the same compositions and under the same reaction conditions, TiO2-based catalysts have a better catalytic activity than SiO2-based catalysts, both in terms of ethanol conversion and in terms of ethylene formation.

It is also noted that, again with the same compositions and under the same reaction conditions, the catalysts synthesized by spraying and lyophilization have a better catalytic activity than the catalysts synthesized by impregnation.

To the described embodiments of the solid composition for heterogeneous catalysis according to the invention, the skilled person, in order to satisfy specific contingent needs, can make numerous additions, modifications, or replacements of elements with other functionally equivalent ones, without however departing from the scope of the attached claims.

Claims (11)

Claims 1. A solid composition comprising - a support material; And - a superacid perfluorosulfonated resin supported by said support material; characterized by the fact that the superacid perfluorosulfonated resin includes Aquivion®, and the support material has a surface area greater than or equal to 5m <2> / g. 2. Composition according to claim 1, wherein the support material comprises SiO2 or TiO2. Composition according to claim 1 or 2, wherein the superacid perfluorosulfonated resin is in the form of a coating on the support material. Composition according to claim 1 or 2, wherein the superacid perfluorosulfonated resin is in the form of a dispersion on the surface of the support material. 5. Composition according to any one of the preceding claims, having the form of granulate in which the granules have a substantially spherical irregular shape. 6. Use of the composition according to any one of the preceding claims as a heterogeneous catalyst. 7. Use according to the preceding claim in a gas phase reaction. 8. Use of Aquivion® in a heterogeneous catalysis of a gas phase reaction. 9. Process for preparing the composition according to any one of claims 1 to 5, comprising the steps of a) preparing an aqueous suspension of superacid perfluorosulfonated resin and support material; b) applying the superacid perfluorosulfonated resin on the support material; And c) removing the solvent; in which the superacid perfluorosulfonated resin includes Aquivion® and the support material includes SiO2 or TiO2. 10. Process according to the preceding claim, wherein step b) comprises an impregnation step under mechanical stirring and step c) comprises a solvent drying step. 11. Process according to the preceding claim, wherein step b) comprises a step of spraying the solution in liquid nitrogen and step c) comprises a step of sublimation of the solvent.