Molecular sieve abstract
Crystalline molecular sieve materials such as high silica zeolites
are manufactured using an organic template comprising an optically
active enantiomer such as an enantiomer of 3(.+-.) methyl piperidine
-N,N-dimethyl bromide. A new zeolite materials is identified.
Molecular sieve claims
We claim:
1. A process for the production of a synthetic crystalline molecular
sieve material by the use of a reaction mixture containing an organic
template material characterised in that the template is an enantiomer.
2. A process as claimed in claim 1 wherein the template is an amine
or ammonium enantiomer.
3. A process as claimed in claim 2 wherein the template is an piperidine
enantiomer.
4. A process as claimed in claim 1 for the production of a crystalline
high silica zeolite molecular sieve comprising forming an aqueous
reaction mixture containing a template comprising an enantiomer
and sources of R.sub.2 O.sub.3 SiO.sub.2 and optionally M.sub.2
O.sub.3 in the molar proportions ##EQU2## wherein R indicates an
alkali metal and M indicates one or more metals selected from B,
Al, V, Cr, Mr, Fe, Ga, As, Mo or Sb, hydrothermally treating the
reaction mixture at a temperature of from 100.degree. C. to 300.degree.
C. and a pressure of from 1 to 100 bars until crystallisation occurs
and separating the crystalline product so formed.
5. A process as claimed in claim 4 wherein the molar proportions
of the reactants are ##EQU3## and R is Na and M is Al.
Molecular sieve description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a novel process for the preparation of
crystalline, synthetic molecular sieve materials and materials so
produced.
2. Summary of the Invention
By `molecular sieve` is meant herein microporous three dimensional
framework materials having pores generally in the 2 to 20 Angstroms
size range which are capable of use for molecular separations. The
framework may consist of or comprise, for example, aluminosilicate,
aluminophosphate or silica.
According to one aspect of the present invention there is provided
a process for the production of a synthetic crystalline molecular
sieve material characterised by the use in the reaction mixture
of an organic template comprising an optically active enantiomer.
It has now been found that by the use of the novel templates described
above the synthesis may be controlled to produce different products
than would be produced using the corresponding racemic form of the
template and that novel zeolites may be produced thereby.
The present invention is particularly, although not exclusively,
concerned with the preparation of high silica zeolites or their
silica analogues. By "high silica zeolite" is meant a
zeolite having the general formula:
where R is one or more alkali metal or alkaline earth metals of
valency n preferably sodium, M.sub.2 O.sub.3 is an oxide of one
or more of B, Al, V, Cr, Mn, Fe, Ga, As, Mo or Sb but preferably
Al, x is a charge balancing quantity of R, y is from 0 to 1 z is
more than 6 for example from 10 to 5000 and W is at least 0 for
example from 0 to 2000. While zeolites having a lesser content of
silica such as the traditional zeolites A, X and Y may be manufactured
readily without the assistance of an organic template material high
silica zeolites are generally synthesised with the assistance of
an organic template material present in the reaction medium. Such
synthesis may be accomplished by including sources of the constituents
of the zeolite in an aqueous reaction medium containing the template
material and heating, generally, under elevated pressure until crystallisation
has taken place. Very suitably the proportions of the sources of
the constituents are such as to provide a reaction medium having
the following composition in terms of oxide mole ratios. ##EQU1##
where R, and M have the values above defined. Suitably, the alkali
metal may be provided by the hydroxide and/or by the use of an alkali
metal silicate; the SiO.sub.2 may be provided by the use of a silica
hydrosol or gel, by silicic acid or by said sodium silicate; and
the metal M may be provided by the sodium metallate, for example,
aluminate or by the use of a metallosilicate, for example aluminosilicate.
Alternative sources of the desired ingredients will be well known
to those versed in the art. Suitably, the synthesis may be carried
out under alkaline conditions, at a temperature of from 100.degree.
C. to 300.degree. C. and at a pressure of from about 1 to 100 bars
which may, if desired, be generated autogenously. The zeolite so
formed may be separated, washed free of residual reaction medium,
dried and calcined to remove residual template materials and/or
to reduce or remove water of crystallisation.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. I is an x-ray diffraction pattern obtained upon the product
of the preparation I(a) obtained in the Example I.
FIG. II is the NMR spectra (29.sub.si MAS) obtained on the product
of Preparation I(a) of Example I.
FIG. III is the isotherm for adsorption of isobutane on the product
of Preparation I(a), Example I.
FIG. IV is an X-ray diffraction pattern of a novel zeolite of the
invention.
FIG. V is an X-ray diffraction pattern of the product of synthesis
(b) in Example I.
DETAILED DESCRIPTION OF THE INVENTION
Very many specific zeolite synthesis have been described in detail
in the literature and many of these are summarised in the book "Molecular
Sieves" by D. W. Breck (1974 John Wiley & Sons). A major
characteristic of these syntheses is not the mole ratio of reactants,
although this may to an extent be tailored to the type of zeolite
required, but the particular organic template to be used to produce
a desired zeolite type. British Pat. No. 1161974 for example, specifies
the use of a tetrapropyl ammonium hydroxide template to produce
zeolite ZSM5 the oxide mole ratios of reactions being specified
very broadly as follows:
The templates specifically disclosed above are substantially all
non-optically active and incapable of existing as racemates. An
exception to this is 3-methyl piperidine which is listed as being
suitable for use in the synthesis of an aluminophosphate molecular
sieve (ALPO-5). This compound exists as a racemate.
An enantiomer of 3-methyl piperidine may be prepared by separation
from the racemate, for example by the process described in our copending
European Patent Application claiming the same priority dates as
the present application or by direct synthesis. The process of said
European Patent Application is to utilise a crystalline molecular
sieve having an assymetric crystal structure such as zeolite ZSM11
zeolite Theta I or silicalite II, the silica analogue of ZSM11
which are assymetric zeolites and may be prepared as described in
British Pat. No. 1339501 European Patent Specification No. 0057049
and Nature Vol 280 Aug. 23 1979 pages 664-665 respectively as
a stereoselective adsorbent for one enantiomer of a racemate, the
channels of the molecular sieve being partially blocked, when that
molecular sieve is not itself enantiomorphic, by an enantiomer separable
from those which constitute the racemate being adsorbed. By such
means an eluate relatively concentrated in one enantiomer may be
produced and the concentration thereof may be increased as required
by recycling.
Examples of other enantiomers which may be used according to the
present invention are compounds belonging to the groups quaternary
ammonium compounds, amines, alcohols, and heterocyclic compounds
and may be selected, for example, from the list of chiral building
blocks on pages 1067 to 1069 of the FLUKA (Fluorochem Limited) Catalogue
No. 14 1984-5 for example alphapinene, 2 methyl butanol or piperidium
compounds such as the 3-methyl piperidine-N,N-dimethyl cation or
a cobalt interpenetration complex as Co.sup.+3 bis(ethylene diamine)
or other Co.sup.+3 complexes with low molecular weight ligands containing
for example not more than 4 carbon atoms.
There is a growing need for more, or relatively concentrated, enantiomers
which, although they may be common in nature are often produced
in the racemic form by synthesis. One method for achieving the required
separation is by stereoselective adsorption of one enantiomer onto
an assymetric crystalline molecular sieve as disclosed above.
It is postulated that the zeolites produced by the present invention
may be assymetric either in the sense of possessing two sets of
pores of opposite symmetry, or in the sense of being enantiomeric
and that, if so, they may exhibit chiral adsorption properties relative
to racemic mixtures. |