TECHNICAL FIELD

The present invention relates to the field of catalys for use in chemical reactions and more specifically to a novel catalyst element intended for use in a reacto wherein a chemical reaction takes place by contacting a lyophobic fluid with a lyophilic fluid to accomplish a reaction in the presence of the catalyst in said element In this context the element according to the invention has turned out to improve drastically the yield of a gas-liquid reaction, e.g. a liquid phase hydrogenation, but is of value in all cases where a lyophobic reactant is reacted with a lyphilic reactant within or upon the catalyst. Furthermore, the invention relates to a proces for the preparation of said elements as well as the use of said element in a reactor wherein a lyophobic fluid i reacted with a lyophilic one.

BACKGROUND OF THE INVENTION

As was mentioned above the present invention has turn out to give considerable advantages in connection with liquid phase hydrogenations, and in view of that the in¬ vention will primarily be described and exemplified in connection therewith. However, the idea of the invention is not in any way restricted to this type of reaction but should be generally applicable to chemical reactions of the kind referred to.

Liquid phase hydrogenations are very commonly used processes within the chemical industry, from very large petrochemical plants to small apparatuses of the type that is utilized inter alia within the pharmaceutical industry. In the manufacture of so-called fine or perform ance chemicals of a complex nature the synthesis method often comprises a large number of stages. Obviously it is of great importance that the yield of each stage will be a maximum yield to have the possibility of obtaining a

total yield which is econi ically competitive. Therefore, the selective action of the catalyst will be decisive in a liquid phase hydrogenation as well as in every other step of the total synthesis. In this connection the probl with reference to liquid phase hydrogenations can be schematically illustrated by means of the following simpl example.

A compound B containing a hydroxyl amine group is to be prepared from the corresponding nitro compound A. Thro the fact that the desorption of B from the catalyst sur¬ face is relatively slow time permits B to be hydrogenated further to the corresponding amine compound C, and in vie of that the yield of B will be low. To varying extents this is applicable to many consecutive, catalytic reactio Variations of hydrogen pressures and temperatures have very small influences upon the yield, which means that the hydrogenation step must be supplemented with an exten sive and in some cases energy consuming processing step. From this example it is apparent that already very small improvements as to catalyst efficiency can mean important contribution to and savings in connection with the techni within this field.

An improvement of the technique in connection with catalytical reactions is disclosed in Swedish Lay-Open Print No. 7114167-5. The technique disclosed therein is based on an improvement of the non-wettability of the catalyst carrier, i.e. carbon, by means of at maximum the same amount of polytetrafluoroethylene as of the catalyst carrier. According to said Swedish Lay-Open Print the manufacture of the catalyst particles having improved non-wettability properties is accomplished by mixing said catalyst particles with polytetrafluoroethylene in the form of an emulsion, the water then being evaporated by means of heat to the formation of a pure mixture of cata- lyst particles and polytetrafluoroethylene. The catalyst particles having improved non-wettability properties can then be utilized in a bed or shaped to an element and giv some improvements of the yield as compared to particles

which have not been treated in this way to obtain non- wettability.

As to catalysts for e.g. gas-liquid reactions reference can also be made to Derwents Abstract 73066B/4 DE-A-2835943, EP-A1-066 676, EP-A1-085 350, DE-B2-210401 and US-A-4 259 209 but neither of these documents dis¬ closes or suggests the combination of features which are essential to the present invention as described more in detail below. On the contrary the most relevant of said documents are based on wet methods comprising impregna¬ tion with a solution of a precursor of the final catalys in a solvent, e.g. chloroplatinic acid in acetone, which obviously means a more or less uncontrolled penetration of the catalyst into the porous material and no continuo layer on the surface of the porous carrier but rather some kind of "islands" of the catalyst particles.

DISCLOSURE OF THE INVENTION

In accordance with the present invention it has been shown that considerably improved yields can be obtained in reactions of the above-mentioned type if another stru ure is imparted to the catalyst element than according t Swedish Lay-Open Print No. 7114167-5. This improvement i of such a kind that it could be called a difference in nature rather than a difference in degree, which opens possibilities never dreamt of within the field of cataly reactions. The improvement obtained is unexpected in vi of the fact that also in the present case the catalyst element comprises a lyophobic and a lyophilic part. How- ever, the structure of the catalyst element is completel different, and apparently the fact that the catalytical reactions take place with other rates and optionally als according to other mechanisms than according to the prio art is ascribable to this novel structure, although the vention is not limited by any specific theory in this connection.

More specifically the catalyst element according to the invention is characterized in that it is in the for of a porous lyophobic, e.g. hydrophobic, body which has a pore size essentially below 20 μm, and is provided with a surface layer having a thickness of at most 100 of lyophilic, e.g. hydrophilic, catalyst particles with a size essentially below 50 μm, across part of its peri phery only, said catalyst layer having been formed by sintering and/or pressing the catalyst particles into the porous, lyophobic body.

Thus, the present invention is based upon a combina¬ tion of features which have hitherto not been utilized in this art and which have now been shown to give out- standing reaction rates e.g. in gas-liquid reactions.

In the present case the term "lyophobic" means that between the solid phase, i.e. the porous body, and the fluid referred to there are weak binding forces only (no affinity), while "lyophilic" has the opposite meanin i.e. that there are strong forces between the solid phas and the fluid (strong affinity) or that the solid phase is easily wetted by the fluid referred to. If said flui is water the corresponding expressions are "hydrophobic" and "hydrophilic", respectively. Last-mentioned case represents a preferable embodiment of the invention, but the invention is applicable also to other liquids, e.g. when hydrogenating fatty acids. However, in general the invention is useful for all combinations of gas-liquid,

liquid-liquid and gas-gas, which means that synonymously to lyophilic-lyophobic the fluids could be said to be essentially non-miscible with each other. From the above- mentioned it can also be gathered that the term "fluid" is utilized in a broad sense, i.e. for liquids as well as gases.

In connection with the invention the term catalyst mea a lyophilic catalyst per se or a catalyst supported by a lyophilic carrier. An essential feature in connection wit the invention is thus that the catalyst element has the structure of a lyophobic porous part and a lyophilic cata lyst. Of importance is also that the catalyst is present merely in the form of a surface layer on the lyophobic, porous material and that said layer does not either cover the whole surface of said porous material. In accordance with the prior art according to Swedish Lay-Open Print No. 7114167-5 it could be expected that a structure of a catalyst element where lyophilic portions are present al- ternatingly with lyophobic portions throughout the whole element would represent the best conditions for the react between for instance a gas and a hydrophilic liquid. On the contrary, however, it has been shown in accordance wi the invention that this is not the case and that complete ly unexpected reaction rates of a completely other order of magnitude are obtained with a structure of the element in accordance with the present invention.

From the above-mentioned it can be gathered that a surface layer of catalyst means that the major part or po tion of the catalyst, e.g. more than 50 V by weight there of, should not be embedded so deeply in the lyophobic material that the separate catalyst particles will be ^' completely surrounded by lyophobic material but that merely part of their peripheries are in direct contact with the lyophobic material. Therefore, a suitable method of preparation for an element according to the invention means that, which is also disclosed more in detail below, a porous element of the lyophobic material is firstly manufactured and that said element is subsequently coated with a catalyst layer in any suitable way.

Another consequence of the above-mentioned is that the catalyst layer should not be made especially thick, as this does not give any further contribution to the improve ment of the reaction rates but with time tends to lower the rate again due to a longer way of transportation for the lyophilic fluid. This also means that the catalyst costs can be reduced by means of the present invention, which also means an important contribution to the art within this field, since these costs as is well known are generally high. Therefore, the thickness of the catalyst layer is at most 100 p , preferably at most 50 μm, and it should preferably be within the range of 5 - 25 μm and even within the range of 5 - 15 μm.

Another important feature of the invention is that the catalyst layer has been formed by a "dry" technique, as obviously another structure is obtained thereby as compared to previously known "wet" techniques, in additio to the fact that this of course also means a much simpler and cheaper method of manufacture. One embodiment of this dry technique means that the catalyst layer of the elemen has been formed by the sintering of catalyst particles into the porous, lyophobic body. In this case the catalyst particles are preferably not only loosely applied onto the surface and then sintered but the sintering operation is preferably performed in connection with a pressing opera¬ tion such that the catalyst particles are pressed some distance into the lyophobic material. Alternatively mere pressing can be utilized to adhere the catalyst particles to the surface of the porous body. In this context it should also be noted that the term pressing should be interpreted in its broad sense, i.e. the measure need not be made in a press but could of course also be made in any conventional way, e.g. by rolling, etc.

As was mentioned above the catalyst particles have a particle size that is essentially below 50 μm and that is for instance within the range of 5-10 μm. In this case the term particle size means the largest extension in any direction. An interesting shape of the particles is the

spherical shape, said size being represented by the diameter.

As concerns the porosity of the lyophobic material it is of course desirable to have as high porosity as possi to reduce the transportation time for the lyophobic flui However, the upper limit thereof is determined by the requisite strength of the element referred to, which mus be decided for each separate case. Generally, however, a porosity within the range of 20-50 % can be suitable, bu higher values and even very high values, exceeding 90 t, can be useful in certain cases where the strength requir ments can be lowered.

A suitable material for the lyophobic body is polytet fluoroethylene which has turned out to give superior res in experiments, but the inventive idea is applicable to any other type of lyophobic, preferably hydrophobic, mat rial to which the desired porosity can be imparted, e.g. other plastics or polymeric materials.

With reference to the catalyst it is often easily ava able in the form of catalyst particles supported on an inert carrier, and such catalyst particles have turned o to be well suited for utilization at the invention. Exam of such catalysts are palladium on alumina and palladium on carbon.

Many different shapes or configurations can be impart to the catalyst element according to the invention, but specially interesting shape is a plate, said plate being provided with the surface layer of the catalyst across t part thereof which is intended to contact the lyophilic fluid. Thus, porous catalyst plates are useful in chemic reactors having a filter-press configuration where the lyophilic fluid is allowed to pass on one side of the pl in this case the catalyst-coated part thereof, and the lyophobic fluid is allowed to pass on the opposite side thereof. Such plates are preferably mounted in plastic frames in any desired number, where every second flow is a lyophilic fluid and every second is a lyophobic one.

These fluids can be passed in the same direction or in th opposite direction relative to each other, i.e. concurren ly or countercurrently respectively.

Another interesting use of the catalyst element accord to the invention is as a so-called packing element for us in a packed column. In this case any of those shapes whic are conventional within the field of packed columns can be imparted to said element. Such columns are often used by feeding a gas at the bottom and liquid at the top ther i.e. counter current conditions are used. The matter how great portion or part of the periphery of said packing elements which should be coated by a surface layer of the catalyst to obtain optimum results at this use is decided by a person skilled in the art in each separate case. Moreover, the invention relates to a pτocess for the preparation of the above-mentioned catalyst element. As wa mentioned above a preferable process means that a surface layer of catalyst is sintered across or over a part of the periphery of the porous lyophobic body. This can for instance be accomplished by simply strewing or spreading • catalyst particles over that part of the surface of the lyophobic material which is to be coated and then perform¬ ing a heating operation up to the sintering temperature o the material referred to to sinter the catalyst particles into thesurface. In connection therewith there is preferabl also used a pressing operation to press catalyst particles some distance into the lyophobic material. Said pressing operation can for instance be performed after said sinter operation, i.e. while the material is in a cold state. Furthermore, it is possible, as has already been mentione to utilize mere pressing.

Finally, the invention relates to a use of the catalyst element described above in a reactor intended for a chemic reaction where a lyophobic fluid is brought into contact with a lyophilic fluid for a reaction in the presence of the catalyst within the element.

As was mentioned above a preferable use in this connec¬ tion is the use of the catalyst element in the form of a

plate in a chemical reactor wherein the lyophilic fluid is contacted with the lyophobic fluid from opposite sides of said plate, that part of the plate which is provided with the surface layer of the catalyst being faced towards the lyophilic fluid.

Another embodiment of said use is the use of the cata¬ lyst element in the form of a packing element in a packed column where a lyophobic fluid is contacted with a lyo¬ philic one.

DRAWINGS

The invention will now be described more in detail in connection with the accompanying drawings , on which

Fig. 1a shows schematically the structure of a catalyti element according to the prior art;

Fig. 1b shows schematically the structure of a catalyti element according to the present invention;

Fig. 2 shows schematically the laboratory reactor where in a catalyst element in the form of a plate has been utilized to perform the experiments described below; and

Fig. 3 shows schematically a packed column wherein the catalyst element according to the invention in the form of packing elements has been utilized to perform the experi¬ ments described below.

EXPERIMENT I

A number of experiments were performed with the cata¬ lyst element in the form of plates to hydrogenate p-nitro benzoic acid to p-amino benzole acid in the presence of palladium as a catalyst, the experimental conditions and results being the following: Materials of the catalyst plates

The material consisted of an inert hydrophobic powder and active metal on different types of carrier powders. Said inert powder consisted of non-porous particles with a size of 30-50 μm. The carrier particles were porous (avera pore diameter 10 nm) and had a particle size of about 5 μm

The catalytic material utilized was of three different types, of which two are commercially available. These two were 10 % of Pd-on-alumina and 10 I of Pd-on-carbon. The third type consisted of 1.9 % of Pd-on-NiO/Si0 ₂ obtained by impregnating the carrier with palladium(II)chloride sol tion (500 moles/m ) in concentrated ammonia followed by a drying operation with nitrogen and a reduction operatio with hydrogen at 450°C for 1 hour and 3 hours, respective

In addition to said powder materials the plates also contained reinforcing mesh of nickel wire (0.16 mm) or glass fibres (0.2 mm).

Manufactures and characteristics of the plates

The catalytic plates were manufactured in a hydraulic

2 press at a pressure of from 450 to 7S0 kp/cm (44.1 MPa to 73.6 MPa). Length and width, respectively, of the plat used in the hydrogenations were about 150 x 56 mm, the geometric area in contact with each of the two reactants

2 being 73 cm .

The inter-particle pores of the plates were dependent on the hydraulic pressure during the manufacture and was determined to between 1 and 5 μm.

The plates consisted of two different layers, viz. a catalytic layer on the liquid side and a hydrophobic laye on the gas side. The hydrophobic layer which was manufact ured from polytetrafluoroethyleneparticles, permits a free passage for the gas across.this layer to the catalyt layer. The catalytic layer consisted either of a mixture of polytetrafluoroethylene particles and catalyst particl (prior art) or of catalyst particles only (the present in vention). Dependent on the thicknesses and the compositio of the different layers and the placings of the reinforce ments mesh the tested plates can be divided into two cate gories: a) Plates according to the prior art (I, II and III), where the catalytic layer was thicker than the polytetra¬ fluoroethylene layer. The catalytic layer consisted of catalytic particles as well as polytetrafluoroethylene particles. A nickel mesh was placed within the catalytic layer close to the boundary between the two layers.

This structure is shown schematically in Fig. 1a, wherei the reference numeral 1 represents the polytetrafluoro¬ ethylene layer and the reference 2 represents the cataly layer, while 3 relates to said nickel mesh. b) Plates according to the invention (IV, V, VI and V wherein the catalytic layer was very thin as compared to the polytetrafluoroethylene layer. The catalytic layer consisted of catalytic particles only. A glass fibre mes or net was placed in the polytetrafluoroethylene layer. This structure of the plate is shown schematically in

Fig. 1b, where the polytetrafluoroethylene layer has bee marked with 4, the catalytic layer with 5 and the glass fibre net with 6. The reactor In the utilized laboratory reactor the catalytic plat was arranged between two thick end plates of stainless steel, as is shown schematically in Fig. 2, where the c lytic plate is numbered 7 and the end plates 8 and 9, re pectively, with inlets and outlets for gas and liquid, respectively, as well as grooves on the interior sides o the end plates for the mounting of meshes or nets which cause a turbulent flow. Hydrogenations and analyses

A hydrogenation of p-nitrobenzoic acid in the form of an aqueous solution (100 moles/m ) at 81 C was used for a determination of the efficiency of the porous plate as a catalyst in a module of the cell reactor. The hydrogen pressure was 9.8 bars. Data for the used plates and the obtained results are presented in Tables 1 and 2.

Table 1

CATALYST ELEMENTS MANUFACTURED IN ACCORDANCE WITH THE PRIOR ART.

Hydrogenation of 0.1 molar p-nitrobenzoic acid. 81°C. Hydrogen pressure 9.8 bars (0.98 MPa).

PTFE = polytetrafluoroethylene ABS = p-aminobenzoic acid

Table 2

CATALYST ELEMENTS MANUFACTURED IN ACCORDANCE WITH THE PRESENT INVENTION

Hydrogenation of 0.1 molar p-nitrobenzoic acid. 81°C. Hydrogen pressure 9.8 bar (0,98 MPa).

Catalyst layer J Reaction rate I moles of ABS thickness i s kg Pd

Catalyst * nm

Example IV 10% Pd on 0.010 alumina 6.06

PTFE = polytetrafluoroethylene ABS = p-aminobenzoic acid * = the total thickness of the catalyst element = 0.45 mm.

SUMMARY:

The obtained improvements as to reaction rates are very great and unexpected in the light of the fact that al the catalyst element according to the present invention has a lyophobic and a lyophilic part. Obviously those im- provements which were obtained in the experiments and which are improvements as to several exponents are effects of the structure of the catalyst element which is a com¬ pletely novel structure as compared to the prior art.

EXPERIMENT II

Two experiments were performed with the catalyst ele¬ ment in the form of packing elements for the hydrogena¬ tion of p-nitrobenzoic acid to p-aminobenzoic acid in the presence of palladium as a catalyst, the experimental conditions and results being the following: Materials of the catalyst packing elements

The material consisted of an inert hydrophobic powder and active metal on a carrier. The inert powder consisted of non-porous particles with a size of 30-50 μm. The carrie particles were porous (average pore diameter 10 nm) and h a particle size of about 5 μm. The used catalytic material was commercially available (10% Pd on carbon).

In addition to the powder material the catalyst elements contained a reinforcing mesh of glass fibres (0.2 mm).

Manufactures and characteristics of the packing elements

A catalyst element was firstly manufactured in the form of a plate. Said plate was prepared in a hydraulic press

2 at a pressure of 750 kp/cm (73.6 MPa). The inter-particle pores of the plate were determined to 2 μm.

The plate consisted of two different layers, viz. a catalytic layer on one side and a hydrophobic layer on the other side. The hydrophobic layer, which was manu- factured from polytetrafluoroethylene particles, permits a free passage for the gas through said layer to the cata¬ lytic layer. The catalytic layer consisted of catalyst particles only (the present invention) .

The catalytic layer which was very thin as compared to the polytetrafluoroethylene layer, consisted of catalytic particles only. A glass fibre mesh was placed within the polytetrafluoroethylene layer. This structure of the plate is presented schematically in Fig. 1b, where the poly¬ tetrafluoroethylene layer is numbered 4, the catalytic layer 5 and the glass fibre mesh 6.

The two experiments represent different methods of packing the column by dimensioning the filling or packing elements in the following ways. a) The plate was cut into strips with the dimensions 2 x 400 mm (thickness 0.45 mm) b) The plate was cut into strips with the dimensions 2 x 100 mm (thickness 0.45 mm)

The reactor

The utlizied column, which was a glass tube having a diameter of 50 mm and a height of 370 mm, was packed with the filling or packing elements. To distribute the nitro- benzoic acid flowing downwardly a layer of 3 mm glass beds was arranged on top of the packing elements. In this expe¬ riment hydrogen gas was fed concurrently. The total geo-

2 metric catalyst layer surface was 9.24 dm .

In Fig. 3 a packed column is schematically shown which is numbered 10, wherein the packing elements are placed in space 11 with glass beds 12 for the distribution of the liquid 13 fed to the column. The discharged liquid is num- bered 14. The gas flow passed into the column is numbered 15 while the gas flow leaving said column is numbered 16. Hydrogenations and analyses

A hydrogenation of p-nitrobenzoic acid in the form of an aqueous solution (100 moles/ ) thereof at 71°C was utilized for a determination of the efficiency of the reac as compared to a so-called slurry reactor. The hydrogen pressure was 1.2 bars. Data for the utilized catalyst ele¬ ment and the results obtained are presented in table 3.

Table 3 Catalyst elements in the form of packing elements in a packing column.

Hydrogenation of 0.1 molar p-nitrobenzoic acid 71°C. Hydrogen pressure 1.2 bars (0.12 MPa).

SUMMARY:

Obviously the improvements obtained which are improve¬ ments of several exponents (the literature discloses that packed columns have an efficiency factor of from 0.1 to 1.0 % of the slurry reactor) are a consequence of the structure of the catalyst element which is a completely novel structure as compared to that of the prior art.