WO2006046850A1 - Zeolite membrane - Google Patents

Zeolite membrane Download PDF

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Publication number
WO2006046850A1
WO2006046850A1 PCT/NL2004/000754 NL2004000754W WO2006046850A1 WO 2006046850 A1 WO2006046850 A1 WO 2006046850A1 NL 2004000754 W NL2004000754 W NL 2004000754W WO 2006046850 A1 WO2006046850 A1 WO 2006046850A1
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Prior art keywords
zeolite
layer
mesoporous
support
zeolite membrane
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PCT/NL2004/000754
Other languages
French (fr)
Inventor
Engela Elizabeth Mcleary
Jacobus Cornelis Jansen
Allard P. Friedrich
Original Assignee
Technische Universiteit Delft
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Priority to PCT/NL2004/000754 priority Critical patent/WO2006046850A1/en
Publication of WO2006046850A1 publication Critical patent/WO2006046850A1/en

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
    • B01D71/02—Inorganic material
    • B01D71/028—Molecular sieves
    • B01D71/0281—Zeolites
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
    • B01D71/02—Inorganic material
    • B01D71/028—Molecular sieves
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D67/00—Processes specially adapted for manufacturing semi-permeable membranes for separation processes or apparatus
    • B01D67/0039—Inorganic membrane manufacture
    • B01D67/0051—Inorganic membrane manufacture by controlled crystallisation, e,.g. hydrothermal growth
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
    • B01D69/10—Supported membranes; Membrane supports
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2323/00—Details relating to membrane preparation
    • B01D2323/24—Use of template or surface directing agents [SDA]
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2325/00—Details relating to properties of membranes
    • B01D2325/04—Characteristic thickness

Definitions

  • the invention is directed to novel and improved, zeolite based membranes.
  • Molecular sieve membranes such as zeolite membranes have been proposed for uses such as molecular separations, reactions, and combined separations and reactions.
  • Such membranes sometimes referred to as molecular sieve membrane composites or zeolite membrane composites, comprise a zeolite layer, or other inorganic layer capable of molecular separations, on porous substrates. Additionally, the zeolite layer may have a catalytic functionality present in the layer itself, in some cases inherently, or in the form of a proximately-located catalytically active material.
  • Zeolite membranes belong to the group of siliceous microporous membranes, which are based on one of the most versatile inorganic building blocks, i.e. silica tetrahedral units, and are comprised of amorphous and crystalline materials which are both typically created by hydrolysis/condensation, sol-gel and solidification or crystallisation processes.
  • amorphous materials characterized by a moderately narrow pore size distribution as well as modest (hydro)thermal stability, offer the possibility to produce in a facile way, thin as well as defect- free membranes.
  • zeolites allow the precise control of the pore size, offer high stability as well as high specific surface areas and are, therefore, also promising candidates for the preparation of inorganic membranes.
  • Applications of zeolite membranes in industry in, e.g., gas separation has, however, been limited mainly because of difficulties in producing ultra-thin, defect-free (composite) zeolite membranes on a large scale.
  • Continuous layers of crystalline zeolite material are extremely difficult to realize.
  • Promising SEM pictures from the top or of a cross-section of the crystalline layer are often published. However, artificial and systematic failures in the layer are frequently reported and have been well-analysed.
  • the continuity of the layer which is virtually invisible with microscopic imaging, is more reliably determined from permeation experiments, which, in contrast to the microscopic observations, often indicate imperfections in the microporous phase.
  • Hurdles to overcome in the preparation of a continuous layer are, in particular, the systematic imperfections.
  • One of the most crucial of these is the ever-occurring triangularly shaped gap between growing crystals on the support. In the frequently occurring event that three crystallites do not grow parallel to each other on the support this gap will form.
  • the mass of nutrient supplied to this gap will preferentially attach on the closest and fastest growing crystal faces, increasing the secondary nucleation rate as well and, thus, preventing the crystals from fully closing these gaps.
  • Tubular zeolite membranes are especially preferred, as they can be used easily in all kinds of equipment and industrial applications. However, those tubes suitable for these uses, having sufficient mechanical strength, are only available in alumina or stainless steel.
  • a further object is to provide a zeolite based membrane, not having the disadvantages of the prior art membranes.
  • the invention thus concerns a zeolite based membrane comprising a support based on macroporoias alumina of stainless steel and a substantially pinhole free zeolite membrane layer.
  • the membrane comprises a mesoporous, amorphous silica base layer attached to the macroporous support and said zeolite layer on top of said mesoporous layei 1 .
  • said substantially pinhole free zeolite membrane is directly attached to the macroporous support.
  • a suitable macroporous support is provided with a mesoporous layer. This is achieved by applying a precursor solution of the mesoporous layer on the surface of the support, preferably on the inside of a tubular support.
  • a suitable method is described in US patent No. 6,358, 486, the content of which is incorporated herein by w ⁇ ay of reference.
  • This method comprises heating a mixture of water, inorganic oxiide and a compound that binds to the inorganic oxide by hydrogen bonding to produce a solid inorganic oxide (preferably silica), having both mesopores and micropores. This oxide is subsequently hydrothermally treated to reduce tlie amount of micropores.
  • a solid inorganic oxide preferably silica
  • the mesoporous layer is based on at least one inorganic oxide, preferably a silica.
  • the zeolite layer is preferably based on alumina-silicate zeolites, although other zeolites can also be used, such as those based on titania.
  • Preferred zeolites are MFI, Y, ⁇ , SIL-I, SIL-2, ZSM-5, ZSM-Il, ZSM- 22, FER, MOR, BEA, Clathrasils, and other high Si/Al ratio zeolites.
  • the presence of the mesoporous layer is used as a basis for growing the zeolite top layer. Due to the presence of a concentrated amount of building blocks in the mesoporous, continuous silicate layer, the growth of a faultless zeolite layer, partly by converting the mesoporous layer and partly by growing from a feed solution, is easy.
  • the supported mesoporous layer was calcined and subsequently a standard, aqueous zeolite feed solution was provided comprising zeolite precursor compounds and a suitable template. Under zeolite growth conditions the zeolite membrane is formed on top of the mesoporous layer. In view of the presence of the mesoporous, continuous surface with a high specific surface area, the relatively high nucleation rate and the anticipated growth rate promote a pinhole free zeolite layer.
  • the second embodiment of the present invention is based thereon, that mesoporous silica precursor layers seem to facilitate and promote the formation of a continuous layer of zeolite in the best way.
  • mesoporous silica precursor layers seem to facilitate and promote the formation of a continuous layer of zeolite in the best way.
  • mesoporous layer After activation of the mesoporous layer by calcination, it could easily be converted to a substantially pinhole-free zeolite phase by impregnation with, a suitable template/zeolite feed solution followed by conversion of the nxesoporous material under standard zeolite synthesis conditions.
  • the complete disappearance of the mesoporous phase is most probably due to Ostwald's rule of successive phase transformation. Indeed, zeolites are more stable than amorphous mesoporous materials.
  • the crystals orient d Tiring growth based on their aspect ratio along the largest crystal dimension, i.e. parallel to the support.
  • An essential feature of the invention is the combination of a specific support with a zeolite membrane layer that is substantially pinhole-free.
  • Pinholes are defined as openings in the membrane having a size in excess of the pore size of the particular zeolite.
  • the pore size of the membrane (zeolite) is generally between 0.1 and 1 nm.
  • the presence of pinholes can be determined by permeation experiments, using a compound having a size with is at least 50% larger than the pore size of the zeolite.
  • a membrane can be considered pinhole free when no pores larger than the zeolite pores are present.
  • An other method for determining tlie presence of pinholes is based on the adsorption behaviour of a gaseous mixture of linear and branched alkanes with the same number of carbon atoms, for example n-butane and iso- butane or n-hexane and iso-hexane.
  • high separation factors up to 50 may be obtained at temperatures between room temperature and about 125 0 C due to the preferential adsorption of the linear alkane .
  • Knudsen diffusion will occur, resulting in the absence of separation.
  • the macroporous support generally possesses pores with an average pore size (by volume) between 5 nm and IOOOO nm.
  • Mesopores are defined as pores with a size from 10 nm to 100 nm.
  • the support material to be used in the membrane of the present invention is based on alumina or stainless steel.
  • the alumina is generally an ⁇ -alumina, whereas the stainless steel is selected form the various nickel based steel materials.
  • the support is preferably in the form of a tube, of a thickness that provides sufficient mechanical strength for the application for which it is envisaged. Further the shape (diameter, length and thickness) should be such that it can easily be accommodated in the reactor/separator in which it is to be used. Preferred dimensions are for a stainless steel tube and alumina tube are about 80x1x0.8 cm.
  • the process of preparing a zeolite membrane according to the invention is based on a first step comprising applying a mesoporous layer on the support.
  • the method has been described in US patent No. 6,358,486.
  • This three-dimensional mesoporou.s material which may be synthesized from triethanolamine/silica solutions, exhibits properties somewhat in between those of crystalline and amorphous materials.
  • this mesoporous layer is used as a precursor building phase for zeolites, thus being converted completely into a continuous microporous phase.
  • the amorphous silica film is commonly prepared with tetraethylorthosilicate, TEOS, as silica source.
  • the silica sol is applied to a macroporous support by dip -coating or spin-coating at a relatively low temperature. At elevated temperatures the liquid film is homogeneously converted into a gel phase. Preferably the temperature over the film is constant during phase transitions.
  • the amorphous silica layer on the support is by no means a stagnant, dry system.
  • a wide variety of chemical and physical changes still takes place, such as i) polymerization, increasing the connectivity of the gel network, ii) syneresis, resulting in a reduction of the solid/liqxiid surface areas, and iii) coarsening and phase separation.
  • Monoineric silica species can be released from the gel via hydrolysis reactions to form Si(OH) 3O" and Si(OH)2 ⁇ 2 2 " that will in turn preferentially react with OH-groups on the support in order to decrease the interfacial energy. This process leads to the formation of a homogeneous amorphous layer on the support, which exhibits an increasing degree of order with time/aging.
  • a relatively thin and continuous amorphous silica layer can be achieved, since the gel network has the ability to 'bridge' the almmina or stainless steel support surface macropore openings (diameter ca. 2.5 nrn).
  • the thickness of the coating applied can be as small as 30 nm. Generally tbie thickness does not exceed 5 pm. It has been well-established that the tliinner the silica layer, the fewer trie chances of crack development, since strong interactions of the silica layer with the support prevent lattice relaxation in the plane of the coating.
  • sol-gel-derived oxides neither the oxide framework nor the pore structure is ordered, whereas the surface of the support tubes is often composed of crystalline ⁇ -alumina.
  • amorphous phases like silica can accommodate such a lattice on an atom-length-scale.
  • the mesoporous layer is used to anchor the zeolite to the sxxpport, but it also serves as feed for the zeolite synthesis, resulting in part conversion of the layer into zeolite. This is accomplished by feeding a zeolite synthesis solution to the surface of the mesoporous layer and heating for a time sufficiently to grow the zeolite.
  • alumina to provide acidity.
  • a multi-functional membrane is provided, which, may be used for combined separation/reaction systems.
  • the mesoporous layer is completely converted into a zeolite.
  • the mesoporous layer is activated by calcination and then impregnated with an aqueous template solution, preferably a 25 % aqueous solution of TPA + (tetrapropylammonium-ion).
  • This template-loaded mesoporous coating is subsequently immersed in a standard zeolite (such as MFI) synthesis solution of template/silica in an autoclave for a few hours at elevated temperature. After cooling and washing a continuous layer of oriented crystallites of zeolite can be observed. The xnesoporous phase is completely disappeared.
  • the thickness of the resulting zeolite membrane layer is generally the same as the thickness of the original mesoporous layer, i.e. from about 30 nm to 5 ⁇ m.
  • an aluminate such as sodium aluminate in the template solution, thereby generating Br ⁇ nsted acidity in the zeolite.
  • the nucleation and crystal growth rate must be extremely high in order to grow small crystallites with, rough surfaces in such a way that they form a continuous phase.
  • Th.e nucleation and crystallisation rate could indeed be extremely high at the support surface as this was achieved with the high concentration of silica nutrient of the solid mesoporous material with a thickness of a few micrometers.
  • This material had a specific surface area of about 1000 m 2 /g.
  • the interface of the silica and the TPA+ solution was, thus, high.
  • the pore wall being curved provides a higher degree of supersaturation of nutrient locally and, therefore, a higher nucleation rate compared to that associated with surfaces of lesser curvature.
  • the membranes of the invention can suitably be applied to various separation processes, but also for catalysing chemical reactions, optionally in combination with simultaneous separation of the reactarxts. Examples are processes limited by a thermodynamic equilibrium which might benefit from integrating separation and reaction in either a catalytic membrane or membrane configuration.
  • gas-phase reaction carried out in plug-flow may benefit from ttte membranes of the present invention.
  • examples are hydrogenation, isomerisation, hydro-isomerisation and other reactions.
  • tetraethylortosilicate and tripropylamine were mixed, and a % wt.% solution of tetraethylammoniixm hydrocide was added. After one hour the viscous solution was dipcoated onto an ⁇ -alumina tube. The tube was heated in a hot-air oven at 100°C to convert the solution to a gel. After completion of the reaction the temperature was raised to 180°C to remove the volatile components (water and alcohol) .
  • the mesoporous layer was subsequently produced by calcining the material at 550°C, to remove the TEA.
  • the mesoporous layer was impregnated with a zeolite synthesis mixture, including the template for the zeolite synthesis, in this case tetrapropylammonium bromide.
  • the zeolite was synthesized. If acidity is required, it is possible to add sodium-aluminate to the template solution, thereby introducing aluminum in the zeolite.
  • the material is calcined at 550 0 C to remove the template.
  • the resulting zeolite, MFI had the structure as given in the figure, wherein a) and b) denote the different directions of crystallization.
  • the thickness of the zeolite layer was 500 nm.
  • the zeolite was tested for pirxholes by bringing it in contact with a mixture of n-butane and iso-butane at 110 0 C. No Knudsen diffusion was noted, which means that there were no pinholes in the membrane.

Abstract

The invention is directed to a zeolite based membrane comprising a support based on macroporous alumina of stainless steel and a substantially pinhole free zeolite membrane layer.

Description

Title: Zeolite membrane
The invention is directed to novel and improved, zeolite based membranes.
Molecular sieve membranes such as zeolite membranes have been proposed for uses such as molecular separations, reactions, and combined separations and reactions.
Such membranes, sometimes referred to as molecular sieve membrane composites or zeolite membrane composites, comprise a zeolite layer, or other inorganic layer capable of molecular separations, on porous substrates. Additionally, the zeolite layer may have a catalytic functionality present in the layer itself, in some cases inherently, or in the form of a proximately-located catalytically active material.
Zeolite membranes belong to the group of siliceous microporous membranes, which are based on one of the most versatile inorganic building blocks, i.e. silica tetrahedral units, and are comprised of amorphous and crystalline materials which are both typically created by hydrolysis/condensation, sol-gel and solidification or crystallisation processes.
On the one hand, amorphous materials, characterized by a moderately narrow pore size distribution as well as modest (hydro)thermal stability, offer the possibility to produce in a facile way, thin as well as defect- free membranes.
On the other hand, zeolites allow the precise control of the pore size, offer high stability as well as high specific surface areas and are, therefore, also promising candidates for the preparation of inorganic membranes. Applications of zeolite membranes in industry in, e.g., gas separation has, however, been limited mainly because of difficulties in producing ultra-thin, defect-free (composite) zeolite membranes on a large scale. Continuous layers of crystalline zeolite material are extremely difficult to realize. Promising SEM pictures from the top or of a cross-section of the crystalline layer are often published. However, artificial and systematic failures in the layer are frequently reported and have been well-analysed. The continuity of the layer, which is virtually invisible with microscopic imaging, is more reliably determined from permeation experiments, which, in contrast to the microscopic observations, often indicate imperfections in the microporous phase.
Hurdles to overcome in the preparation of a continuous layer are, in particular, the systematic imperfections. One of the most crucial of these is the ever-occurring triangularly shaped gap between growing crystals on the support. In the frequently occurring event that three crystallites do not grow parallel to each other on the support this gap will form.
The mass of nutrient supplied to this gap will preferentially attach on the closest and fastest growing crystal faces, increasing the secondary nucleation rate as well and, thus, preventing the crystals from fully closing these gaps.
Tubular zeolite membranes are especially preferred, as they can be used easily in all kinds of equipment and industrial applications. However, those tubes suitable for these uses, having sufficient mechanical strength, are only available in alumina or stainless steel.
Up to now the provision of a zeolite membrane on an alumina or stainless steel support always resulted in an imperfect membrane, presumably due to the difficulty of growing a zeolite on a macroporous support of alumina or stainless steel in a continuous coating.
Accordingly it is an object of the invention to overcome these problems. A further object is to provide a zeolite based membrane, not having the disadvantages of the prior art membranes. The invention thus concerns a zeolite based membrane comprising a support based on macroporoias alumina of stainless steel and a substantially pinhole free zeolite membrane layer.
In a first embodiment of the present invention the membrane comprises a mesoporous, amorphous silica base layer attached to the macroporous support and said zeolite layer on top of said mesoporous layei1. In a second embodiment, said substantially pinhole free zeolite membrane is directly attached to the macroporous support.
The preparation of the membrane comprises various steps. In tbte first step, which is common to both embodiments, a suitable macroporous support is provided with a mesoporous layer. This is achieved by applying a precursor solution of the mesoporous layer on the surface of the support, preferably on the inside of a tubular support. A suitable method is described in US patent No. 6,358, 486, the content of which is incorporated herein by w^ay of reference.
This method comprises heating a mixture of water, inorganic oxiide and a compound that binds to the inorganic oxide by hydrogen bonding to produce a solid inorganic oxide (preferably silica), having both mesopores and micropores. This oxide is subsequently hydrothermally treated to reduce tlie amount of micropores.
The mesoporous layer is based on at least one inorganic oxide, preferably a silica. The zeolite layer is preferably based on alumina-silicate zeolites, although other zeolites can also be used, such as those based on titania. Preferred zeolites are MFI, Y, β, SIL-I, SIL-2, ZSM-5, ZSM-Il, ZSM- 22, FER, MOR, BEA, Clathrasils, and other high Si/Al ratio zeolites.
In the first embodiment, the presence of the mesoporous layer is used as a basis for growing the zeolite top layer. Due to the presence of a concentrated amount of building blocks in the mesoporous, continuous silicate layer, the growth of a faultless zeolite layer, partly by converting the mesoporous layer and partly by growing from a feed solution, is easy. In this embodiment, the supported mesoporous layer was calcined and subsequently a standard, aqueous zeolite feed solution was provided comprising zeolite precursor compounds and a suitable template. Under zeolite growth conditions the zeolite membrane is formed on top of the mesoporous layer. In view of the presence of the mesoporous, continuous surface with a high specific surface area, the relatively high nucleation rate and the anticipated growth rate promote a pinhole free zeolite layer.
The second embodiment of the present invention is based thereon, that mesoporous silica precursor layers seem to facilitate and promote the formation of a continuous layer of zeolite in the best way. After activation of the mesoporous layer by calcination, it could easily be converted to a substantially pinhole-free zeolite phase by impregnation with, a suitable template/zeolite feed solution followed by conversion of the nxesoporous material under standard zeolite synthesis conditions. The complete disappearance of the mesoporous phase is most probably due to Ostwald's rule of successive phase transformation. Indeed, zeolites are more stable than amorphous mesoporous materials.
As the layer is relatively thin, the crystals orient d Tiring growth based on their aspect ratio along the largest crystal dimension, i.e. parallel to the support.
An essential feature of the invention is the combination of a specific support with a zeolite membrane layer that is substantially pinhole-free. Pinholes are defined as openings in the membrane having a size in excess of the pore size of the particular zeolite. The pore size of the membrane (zeolite) is generally between 0.1 and 1 nm. The presence of pinholes can be determined by permeation experiments, using a compound having a size with is at least 50% larger than the pore size of the zeolite. When using a trans-membrane pressure of at least 0.5 bar, a membrane can be considered pinhole free when no pores larger than the zeolite pores are present. An other method for determining tlie presence of pinholes is based on the adsorption behaviour of a gaseous mixture of linear and branched alkanes with the same number of carbon atoms, for example n-butane and iso- butane or n-hexane and iso-hexane. In absence of pinholes, high separation factors (up to 50) may be obtained at temperatures between room temperature and about 1250C due to the preferential adsorption of the linear alkane . On the other hand, in the presence of pinholes Knudsen diffusion will occur, resulting in the absence of separation.
The macroporous support generally possesses pores with an average pore size (by volume) between 5 nm and IOOOO nm.
Mesopores are defined as pores with a size from 10 nm to 100 nm. The support material to be used in the membrane of the present invention is based on alumina or stainless steel. The alumina is generally an α-alumina, whereas the stainless steel is selected form the various nickel based steel materials.
The support is preferably in the form of a tube, of a thickness that provides sufficient mechanical strength for the application for which it is envisaged. Further the shape (diameter, length and thickness) should be such that it can easily be accommodated in the reactor/separator in which it is to be used. Preferred dimensions are for a stainless steel tube and alumina tube are about 80x1x0.8 cm.
The process of preparing a zeolite membrane according to the invention is based on a first step comprising applying a mesoporous layer on the support. The method has been described in US patent No. 6,358,486. This three-dimensional mesoporou.s material, which may be synthesized from triethanolamine/silica solutions, exhibits properties somewhat in between those of crystalline and amorphous materials. In one embodiment, this mesoporous layer is used as a precursor building phase for zeolites, thus being converted completely into a continuous microporous phase. The amorphous silica film is commonly prepared with tetraethylorthosilicate, TEOS, as silica source. The silica sol is applied to a macroporous support by dip -coating or spin-coating at a relatively low temperature. At elevated temperatures the liquid film is homogeneously converted into a gel phase. Preferably the temperature over the film is constant during phase transitions.
After gelation, the amorphous silica layer on the support is by no means a stagnant, dry system. A wide variety of chemical and physical changes still takes place, such as i) polymerization, increasing the connectivity of the gel network, ii) syneresis, resulting in a reduction of the solid/liqxiid surface areas, and iii) coarsening and phase separation. In the coated layer on the support an equilibrium exists between the monomeric/oligomeric species and the gel network. Monoineric silica species can be released from the gel via hydrolysis reactions to form Si(OH) 3O" and Si(OH)2θ22" that will in turn preferentially react with OH-groups on the support in order to decrease the interfacial energy. This process leads to the formation of a homogeneous amorphous layer on the support, which exhibits an increasing degree of order with time/aging.
In this way a relatively thin and continuous amorphous silica layer can be achieved, since the gel network has the ability to 'bridge' the almmina or stainless steel support surface macropore openings (diameter ca. 2.5 nrn). The thickness of the coating applied can be as small as 30 nm. Generally tbie thickness does not exceed 5 pm. It has been well-established that the tliinner the silica layer, the fewer trie chances of crack development, since strong interactions of the silica layer with the support prevent lattice relaxation in the plane of the coating.
In sol-gel-derived oxides, neither the oxide framework nor the pore structure is ordered, whereas the surface of the support tubes is often composed of crystalline α-alumina. In contrast to crystalline coatings like zeolites, amorphous phases like silica can accommodate such a lattice on an atom-length-scale.
Based on the high concentration of silica on the support (close to melt or even solid) and the fact that there is no need of other building blocks (as would be the case for zeolite coatings), extremely high nucleation rates and continuous phases can be achieved.
In the first embodiment the mesoporous layer is used to anchor the zeolite to the sxxpport, but it also serves as feed for the zeolite synthesis, resulting in part conversion of the layer into zeolite. This is accomplished by feeding a zeolite synthesis solution to the surface of the mesoporous layer and heating for a time sufficiently to grow the zeolite.
In this embodiment there is also the possibility to include further functionality in the mesoporous layer, for example alumina to provide acidity. In this way a multi-functional membrane is provided, which, may be used for combined separation/reaction systems.
As indicated above, in the second embodiment the mesoporous layer is completely converted into a zeolite. The mesoporous layer is activated by calcination and then impregnated with an aqueous template solution, preferably a 25 % aqueous solution of TPA+ (tetrapropylammonium-ion). This template-loaded mesoporous coating is subsequently immersed in a standard zeolite (such as MFI) synthesis solution of template/silica in an autoclave for a few hours at elevated temperature. After cooling and washing a continuous layer of oriented crystallites of zeolite can be observed. The xnesoporous phase is completely disappeared. The thickness of the resulting zeolite membrane layer is generally the same as the thickness of the original mesoporous layer, i.e. from about 30 nm to 5 μm. In case it is required to include catalytic activity in the zeolite, it is possible to include an aluminate, such as sodium aluminate in the template solution, thereby generating Brønsted acidity in the zeolite.
To obtain a continuous layer, the nucleation and crystal growth rate must be extremely high in order to grow small crystallites with, rough surfaces in such a way that they form a continuous phase. Th.e nucleation and crystallisation rate could indeed be extremely high at the support surface as this was achieved with the high concentration of silica nutrient of the solid mesoporous material with a thickness of a few micrometers. This material had a specific surface area of about 1000 m2/g. The interface of the silica and the TPA+ solution was, thus, high. Additionally, the pore wall being curved provides a higher degree of supersaturation of nutrient locally and, therefore, a higher nucleation rate compared to that associated with surfaces of lesser curvature. As indicated earlier, the membranes of the invention can suitably be applied to various separation processes, but also for catalysing chemical reactions, optionally in combination with simultaneous separation of the reactarxts. Examples are processes limited by a thermodynamic equilibrium which might benefit from integrating separation and reaction in either a catalytic membrane or membrane configuration.
In general gas-phase reaction carried out in plug-flow may benefit from ttte membranes of the present invention. Examples are hydrogenation, isomerisation, hydro-isomerisation and other reactions.
Example
At room temperature tetraethylortosilicate and tripropylamine were mixed, and a % wt.% solution of tetraethylammoniixm hydrocide was added. After one hour the viscous solution was dipcoated onto an α-alumina tube. The tube was heated in a hot-air oven at 100°C to convert the solution to a gel. After completion of the reaction the temperature was raised to 180°C to remove the volatile components (water and alcohol) .
The mesoporous layer was subsequently produced by calcining the material at 550°C, to remove the TEA. The mesoporous layer was impregnated with a zeolite synthesis mixture, including the template for the zeolite synthesis, in this case tetrapropylammonium bromide. At 1800C in an oven the zeolite was synthesized. If acidity is required, it is possible to add sodium-aluminate to the template solution, thereby introducing aluminum in the zeolite. Finally the material is calcined at 5500C to remove the template.
The resulting zeolite, MFI, had the structure as given in the figure, wherein a) and b) denote the different directions of crystallization. The thickness of the zeolite layer was 500 nm. The zeolite was tested for pirxholes by bringing it in contact with a mixture of n-butane and iso-butane at 1100C. No Knudsen diffusion was noted, which means that there were no pinholes in the membrane.

Claims

Claims
1. Zeolite based membrane comprising a support based on nαacroporous alumina of stainless steel and a substantially pinhole free zeolite membrane layer.
2. Zeolite membrane according to claim 1, wherein said substantially pinhole free zeolite membrane layer consists of a mesoporous silica "base layer attached to the macroporous support and said zeolite layer on top of said mesopoπnis layer.
3. Zeolite membrane according to claim 1, wherein said substantially pinhole free zeolite membrane layer is directly attached to the macroporous support.
4. Zeolite membrane according to claim 1-3, wherein the maxroporous support is an alumina tube.
5. Zeolite membrane according to claim 1, obtainable by a pxocess comprising providing a macroporous support of stainless steel or alumina, applying a layer of silica precursor, preferably by dipcoating, converting this layer into a mesoporous silica layer and converting the mesoporous layer into a substantially pinhole free zeolite.
6. Zeolite membrane according to claim 5, wherein the step of converting the mesoporous layer into substantially pinhole free zeolite comprises providing a source of zeolite precursor and forming a zeolite layer on top of the mesoporous layer, while at the same time converting part of the mesoporous layer irrto zeolite.
7. Zeolite membrane, wherein the macroporous support is in the shape of a tube.
8. Zeolite membrane according to claim 1-7, wherein the zeolite layer has a thickness of 3O nm to 5 μm.
9. Zeolite membrane according to claim 1-8, wherein the zeolite is MFI, Y, β, SIL-I, SIL-2, ZSM-5, ZSM-Il, ZSM-22, FER, MOR, BEA, Clathrasils, or other high Si/Al ratio zeolites.
10. Process for the production of the zeolite membrane of claim 1-9, said process comprising providing a mesoporous silica layer on the macorporous alimina or stainless steel support, and converting the mesoporous support to a zeolite, or growing a zeolite on top of the macroporous support from a conventional zeolite synthesis solution.
11. Separation process for the separation of components from a mixture thereof, whexein a zeolite membrane according to any one of the claims 1-9 is used.
PCT/NL2004/000754 2004-10-27 2004-10-27 Zeolite membrane WO2006046850A1 (en)

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US10369528B2 (en) * 2014-11-25 2019-08-06 Mitsubishi Chemical Corporation Porous support-zeolite membrane composite, and method for producing porous support-zeolite membrane composite
US11141703B2 (en) 2014-11-25 2021-10-12 Mitsubishi Chemical Corporation Porous support-zeolite membrane composite, and method for producing porous support-zeolite membrane composite

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