GB2179563A - Use of modified layered clay catalysts in reactions capable of catalysis by protons - Google Patents

Abstract

Layered clays in which the interlamellar charge, as defined by their Cation Exchange Capacities (C.E.C.s), are sufficient only to permit expansion of the sheets to accommodate a single liquid layer are used as catalysts in reactions capable of catalysis by protons. Typically montmorillonite clays having a reduced C.E.C. of about 25 to about 45 may be used.

Description

SPECIFICATION Use of modified layered clay catalysts in reactions capable of catalysis by protons The present invention relates generally to layered clays and in particular to the use of modified layered clays as catalysts in reactions capable of catalysis by protons.

Broadly, the clay minerals are all aluminosilicates. Two groups, the amorphous (I) and the crystalline (II) may generally be distinguished. The present invention is not concerned with the amorphous clays, otherwise known as the allophanes, largely because they are of comparatively little interest as catalysts.

Clay minerals of group (II) can be broadly subdivided into the following four groups: (a) Two-layer sheet types, such as the kandites. In these, the sheets are composed of units of one layer of silica tetrahedrons and one of alumina octahedrons, each double layer sheet being then separated from the next by an interlameliar space of 8 Angstroms or more.

(b) Three-layer sheet types, such as the smectites, micas and vermiculites. Here the sheet structures are composed of successive layers of tetrahedral silica, octahedral alumina and tetrahedral silica (TOT). The central layer of each sheet (layer) may be dioctahedral or trioctahedral and again the sheets are separated by an interlamellar space.

This group is further sub-divided into: (i) expanding (swelling), eg montmorillonite, vermiculite, and some brittle micas, and (ii) non-expanding, eg pyrophyllite, illite and micas.

(c) Regular mixed layer types, such as the chlorites.

(d) Chain structure types with chains of silica tetrahedrons linked by octahedral groups of oxygens and hydroxyls with Al or Mg atoms, for example sepiolite.

Of these, clays of type (d) are of no interest in the context of the present invention which is principally though not exclusively concerned with clays of type (b). The idealised basic structure of clays of type (b) is that of pyrophyllite which has the basic formula Si8A14020(OH)4 but the important members of the group are the montmorillonites, vermiculites and micas. The TOT structure is obviously fully charge balance in pyrophyllite and thus, since there is no charge excess or deficiency, the interlamellar space is neutral and is, in nature, occupied by "neutral" water molecules. In practice many variants of this structure occur for a variety of reasons. For example the central octahedral layer may be occupied not by two 3-valent cations (eg Awl3+) but by three 2-valent cations (eg Mg2+).The former comprise the class of dioctahedral clays, the latter the ciass of trioctahedral clays, which it is readily apparent, have no charge deficiency or excess in the sheet. Furthermore, only partial replacement, ie one M2+ for one M3+, results in a residual surplus of negative charge in the structure and this leads to the necessity to introduce balancing cations into the interlamellar space together with solvent. Moreover, substitution of A13+ for Si4+ in the tetrahedral layer is possible. This leads to the formation of alternative groups or sub-groups depending upon the identities and extents of ion substitution.Thus, a general representation of the available variants on the pyrophyllite structure is: MZ+(x+yalz(y)n[(M12+t M13+)(6-Y)+ (OH)2Si4~XAlxO1o](X+Y)- here MZ+(x+y/z represents interlamellar (balancing) cations, Y represents H20 (or other swelling liquid) and the square bracket describes the silicate layer. x andy are the charges of the cations substituted in the tetrahedral layer and octrahedral layers, respectively. It is the flexibility of this formulation that allows such a range of values of x andy, and hence of (x+y) and so defines the various mineral types and their properties. The following annotated table for a series of related materials, all having A13+ as the dominant ion in the octrahedral layer, illustrates the point.All, of course, are by definition dioctahedral varieties.

x+y Group Sub-Group Variety o Pyrophyllite 0.250.55 Smectites Montmorillonite Montmorillonite 0.550.69 Vermiculites Vermiculite Vermiculite 0.660.88 Mica Illite Illite 1.S2.0 Mica Mica Muscovite Although pyrophyllite (x+y = 0) is non-swelling, all others of (x+y) up to about 0.7 will undergo swelling, those of x+y greater than about 0.7 are non-swelling.

The exchangeable cations in the interlamellar space, which balance the residual negative layer charge, are normally hydrated but, in fact, a host of solvating molecules may be intercalated along with, or in place of, water. The number of exchangeable cations, as reflected by the Cation Exchange Capacity (C.E.C.), is primarily fixed by the layer charge, with defects at layer edges perhaps adding a further 510%.

It is now very well documented that certain cation-exchanged, for example A13+ or H±exchanged, layered clays are very strong Bronsted acids which property renders them very active as catalysts in a wide variety of reactions capable of catalysis by protons, see for example our European patent publications Nos. 0031687 and 0031252. It is generally believed in the art that the catalytic activity of such clays increases with increasing C.E.C. One problem associated with the use of layered clays as catalysts in certain reactions is their instability, caused by the tendency of the layers to collapse at high temperatures and under hydrothermal conditions, with associated loss of catalytic activity.Attempts to improve the stability of layered clays have involved the introduction into the interlamellar space of various metal compounds, thereby forming "piliars". Representative of the art relating to pillared layered clays may be mentioned US Patents Nos. 4,216,188; 4,248,739; 4,510,257 and 4,515,901 for example. Although such methods demonstrably provide layered clays of improved stability, this is offset to some extent by a loss in catalytic activity as compared with the activity of non-pillared layered clays.

We have now suprisingly found that the particle stability of layered clays in polar solvents can be improved and at the same time an acceptable catalytic activity retained, without introducing pillars, by reducing their C.E.C. Moreover, reducing the C.E.C. of layered clays can alter their selectivity to products in proton catalysed reactions in which they are employed as catalysts.

Accordingly, the present invention provides a process for carying out a reaction capable of catalysis by protons wherein there is used as catalyst a layered clay in which the interlamellar charge, as defined by its C.E.C., is sufficient only to permit expansion of the sheets to accommodate a single liquid layer.

Layered clays for use as catalysts in the process of the invention may be prepared from natural or synthetic layered clays by a variety of methods. One method comprises cation-exchanging a cationexchangeable layered clay with a solution comprising a source of either alkali metal or alkaline earth metal cations and a source of ions capable of migrating into vacant cation-exchangeable sites in the octahedral layer of the clay, exchanging alkali or alkaline earth metal cations with catalytically active cations and finally heating the cation-exchanged clay at elevated temperature, the cation-exchanges and heating being effected under conditions which do not destroy the lamellar structure of the clay. It will be apparent to those skilled in the art that many variations on this technique are possible.Thus, it is possible to eliminate a step by effecting a single cation-exchange with catalytically active cations and a source of ions capable of migrating into vacant cation-exchangeable sites. Another method comprises simply heating in a controlled manner a cation-exchangeable layered clay which has been cation-exchanged with cations capable of migrating into non-exchangeable positions in the octahedral layer of the clay. The controlled heating may be effected at a temperature suitably in the range from 200 to 5000C, for example about 400 C, for a period sufficient to produce a single liquid layer in the interlamellar region of the layered clay, which period may suitably be less than one hour, preferably about 2 hour or less.The heating may be effected in the presence of catalytically active cations or their precursors, for example ammonium ions which are converted by thermal decomposition into hydrogen ions, or in the presence of alkali metal or alkaline earth metal cations which may thereafter be cation-exchanged with catalytically active cations.

Whilst the layered clay may be any of the layered clays (a) to (c) as hereinbefore described, it is preferably a smectite or vermiculite, even more preferably a smectite, for example montmorillonite.

The alkali metal cation may suitably be sodium. An ion capable of migrating into vacant cationexchangeable sites in the octahedral layer of the clay is lithium. Examples of catalytically active cations include hydrogen ions and metal cations other than alkali and alkaline earth metal cations, for example chromium, aluminium, cobalt, nickel, iron, copper and vanadium ions. Sources of the aforesaid ions may suitably be the metal salts, for example the halides. Generally, aqueous solutions of the salts may be employed. It is important that cation-exchange is carried out under conditions which do not destroy the lamellar structure of the clay. Suitably the temperature may be less than 100 C, preferably less than 50"C and even more preferably less than 30 C, for example ambient temperature.The cation-exchanged clay may suitably be heated to a final temperature in the range 200 to 300"C, for example about 250"C.

The effect of incorporating a cation capable of migrating into vacant cation-exchangeable sites in the octahedral layer of the clay is to reduce the C.E.C. of the clay. The amount by which the C.E.C. must be reduced is to a value sufficient only to permit expansion of the sheets to accomodate a single liquid layer.

This amount will vary depending upon the nature of the clay used as the starting material. Using montmorillonite, for example, the C.E.C. may range from about 20 meq/100 g and may be as high as about 50 meq/100 g. It is preferred to use a montmorillonite having a reduced C.E.C. of about 25 to about 45, even more preferably from about 25 to about 35 meq/100 g because such clays, whilst exhibiting maximum catalytic activity, are substantially non-swelling.

In a preferred embodiment, the reduced C.E.C. clays are silanised, suitably by the method described in our copending European application No. 85300038.8, which comprises hydrolysing in the presence of a layered clay a hydrolysable silicon compound, for example a tetraalkoxysilane such as tetraethoxysilane, in the absence of a polymeric cationic hydroxy inorganic metal complex. Silanising the reduced C.E.C. layered clay can improve both its catalytic activity and its stability.

The process of the invention may be applied to a wide variety of reactions capable of catalysis by protons, including the following: (i) a process forthe production of an ester by reacting either an olefin or an olefin oxide with a carboxylic acid, (ii) a process for the production of an ether by reacting either an olefin or an olefin oxide with an alcohol, (iii) a process for the production of an alcohol by reacting an olefin with water, (iv) a process for the production of an alkyl aromatic hydrocarbon by reacting an aromatic hydrocarbon with an alkylating agent selected from olefins and C2 or higher alcohols, (v) a process for the transalkylation of alkyl aromatic hydrocarbons, (vi) a process for the dealkylation of alkyl aromatic hydrocarbons, (vii) a process for the conversion of either a primary or secondary aliphatic alcohol into an ether, and (viii) a process for the conversion of an olefin oxide into an ether.

The aforesaid are only representative of the variety of reactions capable of catalysis by protons to which the process of the present invention is applicable. Conditions under which such processes are operated are by now well established in the art, representative of which may be mentioned the aforesaid EP-A-0031687 and EP-A-0031252. Afeature of operating certain of the aforesaid processes using reduced C.E.C. layered clays as catalysts is that the selectivity to desirable products can be modified.

The process of the present invention will now be further illustrated by reference to the following Examples.

C.E.C. Determination Each individual clay sample was exchanged with NH4+. 1 g of the dried material was then boiled for 30 minutes in 50 ml of 1N NaOH (aq). The gaseous ammonia evolved was passed through a water-cooled condenser into 25 ml (V) of 0.1 N HCl(aq)(N1). This was then titrated with 0.1N NaOH(aq)(N2) to a titre volume, T, using phenolphthalein indicator. The C.E.C. is then given by: C.E.C. = 102 (VN1 - TN2) (meq/100 g) Preparation of Reduced C.E.C. Clays Series A (i) Cation Exchange A 1% w/w suspension of Gel-White L, a montmorillonite having a C.E.C. of 101 + 8 meq/100 g dried clay, was stirred at room temperature for 6h in a 1 N aqueous solution of the chloride salt of the exchanging cation. The supernatant liquid was discarded and the whole process repeated.The exchanged clay was then washed with deionised water and centrifuged repeatedly until no chloride ion could be detected in the washings.

(ii) C. E. C. Reduction Co-ionic Na+ and Li+ exchanged clays were heated at 2000C for 24h, the Na+ then being removed by cation-exchange with A13+ as described in (i) above. The C.E.C.s of the reduced charge clays are as listed in Table 1.

TABLE 1

Sample C.E.C. (meq/100 g) Sample C.E.C. (meq/100 g) Al 10118 A4 4614 A2 92 + 8 AS 30 1 3 A3 74 1 6 A6 24 t 3 A13+ exchange was assumed to be quantitative and the exchangeable A13+ concentration, [Al3+]ex, data quoted are inferred from the C.E.C. measurements.

Series B A Wyoming montmorillonite having an initial C.E.C. of 85 meq/100 g was divided into 2 portions. One portion was cation-exchanged at room temperature with 1N NaCI solution, centrifuged and washed with water and the other portion was exchanged in identical manner with 0.5N LiCI solution.

The Li±exchanged clay and the Na±exchanged clay were mixed in the form of an aqueous paste in the proportions shown in Table 2 and heated at 60C for 6 to 8 hours. After standing overnight at room temperature the paste was dried in vacuo and heated at 250"C for 24 hours.

Finally the clay was exchanged with cold H2SO4, washed, centrifuged, dried and its C.E.C. determined.

The C.E.C.s of the reduced charged clays are listed in Table 2.

TABLE 2

WtofNa±clay Wt of Li±clay C.E.C.

Sample (g) (g) meq/100 g B1 40 4 64 82 35 8 51 83 20 20 31 84 10 30 30 B5 10 25 24 B6 5 35 21 Examples 1 to 5 and Comparison Test 1

0.3 g catalyst (Series A) was placed in a stainless steel reactor of internal volume 20 ml and 3 ml cyclohexylamine was added. The sealed reactor was placed in an oven thermostatically controlled at 216"C.

After 4 hours the reactor was cooled and its contents analysed.

Analyses were conducted with a Pye Unican GCD chromatograph equipped with a temperature programming facility. The injection port was held at 200"C with the flame ionisation detector at 300"C. Dried N2 carrier gas flowed at 20 ml/minute. The column used was an 11 feet x 8 inch O.D. stainless steel column packed with 8% w/wApiezon-M/2% KOH on 100--120 mesh Chromasorb P-AW (designated A) temperature programmed at 1 OO"C for 3 minutes and then 800/minute to 180"C. The results are given in Table 3.

TABLE 3

C.E.C. Total Product Yield Example meq/100 g (mol % final mixture) 1 24 33.4 2 30 25.1 3 46 26.8 4 74 29.3 5 92 26.4 Comp Test 1 101 27.9 Examples 6 to 10 and Comparison Test 2

0.3 g catalyst (Series A) was placed in a stainless steel reactor of internal volume 20 ml and 3 ml of reactant (2.05 ml hexene + 0.95 ml acetic acid) was added. The sealed reactor was placed in an oven thermostatically controlled at 160"C. After 4 hours the reactor was cooled and its contents analysed as described in Examples 1 to 5 except the column used was a 17 feet x 8 inch O.D. stainless steel column containing 10.7% w/w Carbowax 20M on 120140 mesh Chromasorb P-AW DMCS (designated B) temperature programmed at 50"C for 10 minutes, then 40/minute to 180 C.

The results are given in Table 4.

TABLE 4

Relative Selectivity* C.E.C. Total Product Yield Example meq/100 g (mol % final mixture) S2-hex S3-hex Sisom 6 24 14.3 64.3 12.7 23.0 7 30 29.7 31.0 8.9 60.1 8 46 34.5 26.5 10.8 62.8 9 74 33.9 25.5 9.8 64.6 10 92 33.5 24.0 10.4 65.6 Comp Test 2 101 34.1 23.2 10.5 66.5 * S2~hex; S3-hex;; S,sOm = relative selectivity for hex-2-yI, hex-3-yl esters and hexene isomers respectively.

Examples 11 to 15 and Comparison Test 3

0.3 9 catalyst (Series A) was placed in a stainless steel reactqr of internal volume 20 ml and 3 ml of npentanol was added. The sealed reactor was placed in an oven thermostatically controlled at 200 C. After 4 hours the reactor was cooled and its contents analysed as described in Examples 6 to 10, ie using column B, except that the column was operated isothermally at 1500C.

The results are given in Table 5.

TABLE 5

Relative Selectivity* C.E.C. Total Product Yield Example meq/100 g (mol % final mixture) Si.ie Sl.2e Spe 11 24 21.6 73.5 5.2 21.4 12 30 43.5 66.5 4.3 29.2 13 46 54.7 57.7 3.9 38.4 14 74 54.5 52.3 4.5 43.2 15 92 54.0 48.9 5.0 46.1 Comp Test 3 101 54.5 46.5 5.0 48.4 * S1,1e; S1,2e; Spe= relative selectivity for 1,1 ether, 1,2 ether and pentenes respectively.

Examples 16to 19 and Comparison Test4

0.3 9 catalyst (Series A) was placed in a stainless steel reactor of internal volume 20 ml and 3 ml of reactant (1.85 ml 2-methylpropene + 1.15 ml ethanol) was added. The sealed reactor was placed in an oven thermostatically controlled at 100"C. After 24 hours the reactor was cooled and its contents analysed as described in Examples 6 to 10, ie using column B, except that the column was programmed at 555C for 8 minutes and then at 8"/minute to 1 500C.

The results are given in Table 6.

TABLE 6

C.E.C. Total Product Yield Relative Selectivity* Example meq/100 9 (mol % final mixture) 5t-BEE St-BUOH SDIM 16 24 73.5 96.4 1.6 2.0 17 30 67.0 93.5 3.8 2.7 18 74 69.0 94A 4.0 1.7 19 92 74.8 93.7 3.8 2.5 Comp Test 4 101 68.8 93.7 4.1 2.2 * St-BEE; St-BuOH; SDIM = relative selectivity for t-butyl ethyl ether, t-butanol and alkene dimers.

Examples 20 to 25 - Propene Hydration An autoclave was charged with 2 g of clay catalyst (Series 8 Table 2), 40 ml propene and 50 ml of water and the mixture was heated at 2000C for 2.5 hours under 50 bar pressure of nitrogen. The products were analysed by gas chromatography.

The results are given in Table 7.

TABLE 7

Clay C.E.C. % wt propan-2-ol in Example Sample (meq/100 g) products 20 B1 64 0.7 21 B2 51 1.1 22 B3 31 4.4 23 84 30 3.5 24 B5 24 0.2 25 B6 21 Trace Example 26 An autoclave was charged with 2 g of silanised clay catalyst (Series B, clay 81 of Table 2 - silanised by the method described in our copending European Application No. 85 300038.8) of C.E.C. 64,40 ml of propene and 50 ml of water and the mixture was heated at 200"C for 2.5 hours under 50 bar pressure of nitrogen. The products were analysed by gas chromatography.The product contained 3.9% wt propan-2-ol, as compared with 0.7% wt propan-2-ol for the corresponding non-silanised reduced C.E.C. clay.

Example 27 An autoclave was charged with 2 g of silanised clay catalyst (Series B, clay B6 of Table 2 -- silanised by the method described in our copending European Application No. 85 300038.8), 40 ml of propene and 50 ml of water. The mixture was heated at 200"C for 2.5 hours under 50 bar pressure of nitrogen. The products were analysed by gas chromatography. The product contained 0.7% wt propan-2-ol in the products as compared with a trace for the corresponding non-silanised reduced C.E.C. clay.

Examples 28 to 33 - Propan-2-ol Dehydration The reactions were carried out in a small scale continuous flow apparatus using a 5 ml catalyst bed (Series B reduced C.E.C. layered clays). 30 ml/hour propan-2-ol was passed over the catalyst at a pressure of 12 bar and a temperature of 200"C. The products were analysed by gas chromatography.

The results are given in Table 8.

TABLE 8

Product Selectivity (%) Unreacted Clay C.E.C. Diisopropyl propan-2-ol Example Sample (meq/100 g) Propene - ether (%) 28 85 38 20 40 29 B1 64 36 21 43 30 B2 51 46 16 36 31 B3 31 20 4.4 75 32 B4 30 17 3 80 33 B6 21 24 2.7 73

Claims (14)

1. A process for carrying out a reaction capable of catalysis by protons wherein there is used as catalyst a layered clay in which the interlamellar charge, as defined by its C.E.C., is sufficient only to permit expansion of the sheets to accomodate a single liquid layer.

2. A process according to claim 1 wherein the layered clay for use as the catalyst is prepared by cationexchanging a cation-exchangeable layered clay with a solution comprising a source of either alkali metal or alkaline earth metal cations and a source of ions capable of migrating into vacant cation-exchangeable sites in the octahedral layer of the clay, exchanging alkali or alkaline earth metal cations with catalytically active cations and finally heating the cation-exchanged clay at elevated temperature, the cation-exchanges and heating being effected under conditions which do not destroy the lamellar structure of the clay.

3. A process according to claim 2 wherein the cation-exchange with catalytically active cations is effected in the same step as cation-exchange with a source of ions capable of migrating into vacant cationexchangeable sites.

4. A process according to claim 1 wherein the layered clay for use as a catalyst is prepared by heating in a controlled manner a cation-exchangeable layered clay which has been cation-exchanged with cations capable of migrating into non-exchangeable positions in the octrahedral layer of the clay.

5. A process according to claim 4 wherein the heating in a controlled manner is effected at a temperature in the range from 200 to 5005C for a period sufficient to produce a single liquid layer in the interlamellar region of the layered clay.

6. A process according to any one of claims 2 to 5 wherein the cation-exchangeable layered clay from which the layered clay for use as a catalyst is prepared is a smectite-type clay.

7. A process according to any one of claims 2 to 6 wherein the ion capable of migrating into vacant cation-exchangeable sites in the octahedral layer is the lithium cation.

8. A process according to any one of claims 2 to 7 wherein the catalytically active cations are hydrogen ions.

9. A process according to any one of claims 2 to 7 wherein the catalytically active cations are metal cations, the metal being either chromium, aluminium, cobalt, nickel, iron, copper or vanadium.

10. A process according to any one of the preceding claims wherein the catalyst is a montmorillonite having a CEC in the range from 20 to 50 meq/100 g.

11. A process according to any one of claims 1 to 9 wherein the catalyst is a montmorillonite having a CEC in the range from 25 to 45 meq/100 g.

12. A process according to any one of claims 1 to 9 wherein the catalyst is a montmorillonite having a CEC in the range from 25 to 35 meq/100 g.

13. A process according to any one of the preceding claims wherein the catalyst is silanised.

14. A process according to any one of the preceding claims wherein the reaction capable of catalysis by protons is either: (i) a process for the production of an ester by reacting either an olefin or an olefin oxide with a carboxylic acid, (ii) a process for the production of an ether by reacting either an olefin or an olefin oxide with an alcohol, (iii) a process for the production of an alcohol by reacting an olefin with water, (iv) a process for the production of an alkyl aromatic hydrocarbon by reacting an aromatic hydrocarbon with an alkylating agent selected from olefins and C2 or higher alcohols, (v) a process for the transalkylation of alkyl aromatic hydrocarbons, (vi) a process for the dealkylation of alkyl aromatic hydrocarbons, (vii) a process for the conversion of either a primary or secondary aliphatic alcohol into an ether, or (viii) a process for the conversion of an olefin oxide into an ether.