Molecular sieve abstract
Molecular sieve compositions having three-dimensional microporous
framework structures of LiO.sub.2 AlO.sub.2 PO.sub.2 and SiO.sub.2
tetrahedral oxide units are disclosed. These molecular sieves have
an empirical chemical composition on an anhydrous basis expressed
by the formula: wherein "R" represents at least one organic
templating agent present in the intracrystalline pore system; "m"
represents the molar amount of "R" present per mole of
(Li.sub.w Al.sub.x P.sub.y Si.sub.z)O.sub.2 ; and "w",
"x", "y" and "z" represent the mole
fractions of lithium, aluminum, phosphorus and silicon, respectively,
present as tetrahedral oxides. Their use as adsorbents, catalysts,
etc. is also disclosed.
Molecular sieve claims
We claim:
1. Crystalline molecular sieves having three-dimensional microporous
framework structures of LiO.sub.2 AlO.sub.2 PO.sub.2 and SiO.sub.2
tetrahedral units having an empirical chemical composition on an
anhydrous basis expressed by the formula:
wherein "R" represents at least one organic templating
agent present in the intracrystalline pore system; "m"
represents the molar amount of "R" present per mole of
(Li.sub.w Al.sub.x P.sub.y Si.sub.z)O.sub.2 and has a value of zero
(0) to about 0.3; and "w", "x", "y"
and "z" represent the mole fraction of lithium, aluminum,
phosphorus and silicon, respectively, present as tetrahedral oxides,
said mole fractions being such that they are within the pentagonal
compositional area defined by points A, B, C, D and E of FIG. 1
The crystalline molecular sieves having a characteristic X-ray powder
diffraction pattern which contains at least the d-spacings set forth
in one of the following Tables L and LA,
2. Crystalline molecular sieves according to claim 1 wherein the
mole fractions of lithium, aluminum, phosphorus and silicon present
as tetrahedral oxides are with the hexagonal compositional area
defined by points a, b, c, d, e and f of FIG. 2.
3. The crystalline molecular sieves according to claim 1 or claim
2 wherein "m" is not greater than about 0.15.
4. The crystalline molecular sieves of claim 1 or 2 wherein w+z
is not greater than about 0.20.
5. Process for preparing crystalline molecular sieves having three-dimensional
microporous framework structures of LiO.sub.2 AlO.sub.2 PO.sub.2
and SiO.sub.2 tetrahedral units having an empirical chemical composition
on an anhydrous basis expressed by the formula:
wherein "R" represents at least one organic templating
agent present in the intracrystalline pore system; "m"
represents the molar amount of "R" present per mole of
(Li.sub.w Al.sub.x P.sub.y Si.sub.z)O.sub.2 and has a value of zero
to about 0.3; and "w", "x", "y" and
"z" represent the mole fractions of lithium, aluminum,
phosphorus and silicon, respectively, present as tetrahedral oxides,
said mole fractions being such that they are within the pentagonal
compositional area defined by points A, B, C, D, and E of FIG. 1
the crystalline molecular sieves having a characteristic X-ray powder
diffraction pattern which contains at least the d-spacings set forth
in one of the following Tables L and LA,
the process comprising providing a reaction mixture composition
at an effective temperature and for an effective time sufficient
to produce said molecular sieves, said reaction mixture composition
being expressed in terms of molar oxide ratios as follows:
wherein "R" is an organic templating agent; "a"
is the amount of "R" and is an effective amount greater
than zero to about 6; "b" has a value of between zero
and about 500; and "s", "t", "u" and
"v" represent the mole fractions, respectively, of lithium,
aluminum, phosphorus and silicon in the (Li.sub.s Al.sub.t P.sub.u
Si.sub.v)O.sub.2 constituent, and each has a value of at least 0.01.
6. Process according to claim 5 wherein "s", "t",
"u" and "y" are within the area defined by points
F, G, H, I and J of FIG. 3.
7. Process according to claim 5 wherein "a" is not greater
than about 0.5.
8. Process according to claim 5 wherein "b" is from about
2 to about 500
9. Process according to claim 8 wherein "b" is from about
2 to about 300.
10. Process according to claim 9 wherein "b" is not greater
than about 20.
11. Process according to claim 10 wherein "b" is not
greater than about 10.
12. Process according to claim 5 wherein the source of phosphorus
in the reaction mixture is orthophosphoric acid.
13. Process according to claim 5 wherein the source of phosphorus
in the reaction mixture is orthophosphoric acid and the source of
aluminum is at least one compound selected from the group consisting
of pseudo-boehmite and aluminum alkoxides.
14. Process according to claim 13 wherein the aluminum alkoxide
is aluminum isopropoxide.
15. Process according to claim 5 wherein the source of lithium
is selected from the group consisting of oxides, hydroxides, alkoxides,
chlorides, bromides, iodides, sulfates, nitrates, carboxylates and
mixtures thereof.
16. Process according to claim 5 wherein the source of lithium
is lithium orthophosphate.
17. Process according to claim 5 wherein the silicon source is
silica.
18. Process according to claim 5 wherein the silica source is a
tetraalkyl orthosilicate.
19. Process according to claim 5 wherein the organic templating
agent is a quaternary ammonium or quaternary phosphonium compound
having the formula:
wherein X is nitrogen or phosphorus and each R is an alkyl or aryl
group containing from 1 to 8 carbon atoms.
20. Process according to claim 5 wherein the organic templating
agent is an amine.
21. Process according to claim 5 wherein the templating agent is
selected from the group consisting of tetrapropylammonium ion; tetraethylammonium
ion; tripropylamine; triethylamine; triethanolamine; piperidine;
cyclohexylamine; 2-methyl pyridine; N,N-dimethylbenzylamine; N,N-dimethylethanolamine;
choline; N,N-dimethylpiperazine; 14-diaziabicyclo-(222) octane;
N-methyldiethanolamine; N-methylethanolamine; N-methylpiperidine;
3-methylpiperidine; N-methylcyclohexylamine; 3-methylpyridine; 4-methylpyridine;
quinuclidine; N,N'-dimethyl-14-diazabicyclo (222) octane ion;
tetramethylammonium ion; tetrabutylammonium ion; tetrapentylammonium
ion; di-n-butylamine; neopentylamine; di-n-pentylamine; isopropylamine;
t-butylamine; ethylenediamine; pyrrolidine; 2-imidazolidone; di-n-propylamine;
and a polymeric quaternary ammonium salt .sub.x wherein x is a value
of at least 2.
22. Molecular sieves prepared by calcining, at a temperature sufficiently
high to remove at least some of any organic templating agent present
in the intracrystalline pore system, the crystalline molecular sieves
having three-dimensional microporous framework structures of LiO.sub.2
AlO.sub.2 PO.sub.2 and SiO.sub.2 tetrahedral units having an empirical
chemical composition on an anhydrous basis expressed by the formula:
wherein "R" represents at least one organic templating
agent present in the intracrystalline pore system; "m"
represents the molar amount of "R" present per mole of
(Li.sub.w Al.sub.x P.sub.y Si.sub.z)O.sub.2 and has a value of zero
to about 0.3; and "w", "x", "y" and
"z" represent the mole fractions of lithium, aluminum,
phosphorus and silicon, respectively, present as tetrahedral oxides,
said mole fractions being such that they are within the pentagonal
compositional area defined by points A, B, C, D, and E of FIG. 1
the calcined crystalline molecular sieves having a characteristic
X-ray powder diffraction pattern which contains at least the d-spacings
set forth in one of the following Tables L and LB,
Molecular sieve description
FIELD OF THE INVENTION
The instant invention relates to a novel class of crystalline microporous
molecular sieves and to the method of their preparation. The invention
relates to novel lithium-aluminum-phosphorus-silicon-oxide molecular
sieves containing framework tetrahedral oxide units of lithium,
aluminum, phosphorus and silicon. These compositions may be prepared
hydrothermally from gels containing reactive compounds of lithium,
aluminum, phosphorus and silicon capable of forming framework tetrahedral
oxides, and preferably at least one organic templating agent which
functions in part to determine the course of the crystallization
mechanism and the structure of the crystalline product.
BACKGROUND OF THE INVENTION
Molecular sieves of the crystalline alumino-silicate zeolite type
are well known in the art and now comprise over 150 species of both
naturally-occurring and synthetic compositions. In general the crystalline
zeolites are formed from corner-sharing AlO.sub.2 and SiO.sub.2
tetrahedra and are characterized by having pore openings of uniform
dimensions, having a significant ion-exchange capacity and being
capable of reversibly desorbing an adsorbed phase which is dispersed
throughout the internal voids of the crystal without displacing
any atoms which make up the permanent crystal structure. Other crystalline
microporous compositions which are not zeolitic, i.e. do not contain
AlO.sub.2 tetrahedra as essential framework constituents, but which
exhibit the ion-exchange and/or adsorption characteristics of the
zeolites are also known. Metal organosilicates which are said to
posses ion-exchange properties, have uniform pores and are capable
of reversibly adsorbing molecules having molecular diameters of
about 6.ANG. or less, are reported in U.S. Pat. No. 3941871 issued
Mar. 2 1976 to Dwyer et al. A pure silica polymorph, silicalite,
having molecular sieving properties and a neutral framework containing
neither cations nor cation sites is disclosed in U.S. Pat. No. 4061724
issued Dec. 6 1977 to R. W. Grose et al.
A recently reported class of microporous compositions and the first
framework oxide molecular sieves synthesized without silica, are
the crystalline aluminophosphate compositions disclosed un U.S.
Pat. No. 4310440 issued Jan. 12 1982 to Wilson et al. These materials
are formed from AlO.sub.2 and PO.sub.2 tetrahedra and have electrovalently
neutral frameworks as in the case of silica polymorphs. Unlike the
silica molecular sieve, silicalite, which is hydrophobic due to
the absence of extra-structural cations, the aluminophosphate molecular
sieves are moderately hydrophilic, apparently due to the difference
in electronegativity between aluminum and phosphorus. Their intracrystalline
pore volumes and pore diameters are comparable to those known for
zeolites and silica molecular sieves.
In U.S. Pat. No. 4440871 there is described a novel class of
silicon-substituted alumino-phosphates which are both microporous
and crystalline. The materials have a three dimensional crystal
framework of PO.sub.2.sup.+, AlO.sub.2.sup.- and SiO.sub.2 tetrahedral
units and, exclusive of any alkali metal or calcium which may optionally
be present, an as-synthesized empirical chemical composition on
an anhydrous basis of:
wherein "R" represents at least one organic templating
agent present in the intracrystalline pore system; "m"
represents the moles of "R" present per mole of (Si.sub.x
Al.sub.y P.sub.z)O.sub.2 and has a value of from zero to 0.3 the
maximum value in each case depending upon the molecular dimensions
of the templating agent and the available void volume of the pore
system of the particular silicoaluminophosphate species involved;
and "x", "y", and "z" represent the
mole fractions of silicon, aluminum and phosphorus, respectively,
present as tetrahedral oxides. The minimum value for each of "x",
"y", and "z" is 0.01 and preferably 0.02. The
maximum value for "x" is 0.98; for "y" is 0.60;
and for "z" is 0.52. These silicoaluminophosphates exhibit
several physical and chemical properties which are characteristic
of aluminosilicate zeolites and aluminophosphates.
In U.S. Pat. No. 4500651 there is described a novel class of
titanium-containing molecular sieves whose chemical composition
in the ass-synthesized and anhydrous form is represented by the
unit empirical formula:
wherein "R" represents at least one organic templating
agent present in the intracrystalline pore system; "m"
represents the moles of "R" present per mole of (Ti.sub.x
Al.sub.y P.sub.z)O.sub.2 and has a value of between zero and about
5.0; and "x", "y" and "z" represent
the mole fractions of titanium, aluminum and phosphorus, respectively,
present as tetrahedral oxides.
In U.S. Pat. No. 4567029 there is described a novel class of
crystalline metal alumino-phosphates having three-dimensional microporous
framework structures of MO.sub.2 AlO.sub.2 and PO.sub.2 tetrahedral
units and having an empirical chemical composition on an anhydrous
basis expressed by the formula:
wherein "R" represents at least one organic templating
agent present int he intracrystalline pore system; "m"
represents the moles of "R" present per mole of (M.sub.x
Al.sub.y P.sub.z)O.sub.2 and has a value of from zero to 0.3; "M"
represents at least one metal of the group magnesium, manganese,
zinc and cobalt; "x", "y", and "z"
represent the mole fractions of the metal "M", aluminum
and phosphorus, respectively, present as tetrahedral oxides.
In U.S. Pat. No. 4544143 there is described a novel class of
crystalline ferroaluminophosphates having a three-dimensional microporous
framework structure of FeO.sub.2 AlO.sub.2 and PO.sub.2 tetrahedral
units and having an empirical chemical composition on an anhydrous
basis expressed by the formula
wherein "R" represents at least one organic templating
agent present in the intracrystalline pore system; "m"
represents the moles of "R" present per mole of (Fe.sub.x
Al.sub.y P.sub.z)O.sub.2 and has a value of from zero to 0.3; and
"x", "y" and "z" represent the mole
fractions of the iron, aluminum and phosphorus, respectively, present
as tetrahedral oxides.
The instant inventions relates to new molecular sieve compositions
comprising framework tetrahedral units of LiO.sub.2.sup.-3 AlO.sub.2.sup.-,
PO.sub.2.sup.+ and SiO.sub.2.
DESCRIPTION OF THE FIGURES
FIG. 1 is a ternary diagram wherein parameters relating to the
instant compositions are set forth as mole fractions.
FIG. 2 is a ternary diagram wherein parameters relating to preferred
compositions are set forth as mole fractions.
FIG. 3 is a ternary diagram wherein parameters relating to the
reaction mixtures employed in the preparation of the compositions
of this invention are set forth as mole fractions.
SUMMARY OF THE INVENTION
The instant invention relates to a new class of lithium-aluminum-phosphorus-silicon-oxide
molecular sieves having a crystal framework structure of LiO.sub.2.sup.-3
AlO.sub.2.sup.-, PO.sub.2.sup.+ and SiO.sub.2 tetrahedral oxide
units. These new molecular sieves exhibit ion-exchange, adsorption
and catalytic properties and, accordingly, find wide use as adsorbents
and catalysts. The members of this novel class of compositions have
crystal framework structures of LiO.sub.2.sup.-3 AlO.sub.2.sup.-,
PO.sub.2.sup.+ and SiO.sub.2 tetrahedral units and have an empirical
chemical composition on an anhydrous basis expressed by the formula:
wherein "R" represents at least one organic templating
agent present in the intracrystalline pore system; "m"
represents the molar amount of "R" present per mole of
(Li.sub.w Al.sub.x P.sub.y Si.sub.z)O.sub.2 and has a value of zero
to about 0.3; and "w", "x", "y" and
"z" represent the mole fractions of lithium, aluminum,
phosphorus and silicon, respectively, present as tetrahedral oxides.
These molecular sieve compositions comprise crystalline molecular
sieves having a three-dimensional microporous framework structure
of LiO.sub.2.sup.-3 AlO.sub.2.sup.-, PO.sub.2.sup.+ and SiO.sub.2
tetrahedral units. The instant molecular sieve compositions are
characterized in several ways as distinct from heretofore known
molecular sieves, including the aforementioned ternary compositions.
The instant molecular sieves are characterized by the enhanced thermal
stability of certain species and by the existence of species heretofore
unknown for binary and ternary molecular sieves.
The molecular sieves of the instant invention will be generally
referred to by the acronym "LiAPSO" to designate the framework
of LiO.sub.2.sup.-3 AlO.sub.2.sup.-, PO.sub.2.sup.+ and SiO.sub.2
tetrahedral units. Actual class members will be identified by denominating
the various structural species which make up the LiAPSO class by
assigning a number and, accordingly, are identified as "LiAPSO-i"
wherein "i" is an integer. This designation is an arbitrary
one and is not intended to denote structural relationship to another
material(s) which may also be characterized by a numbering system.
DETAILED DESCRIPTION OF THE INVENTION
The instant invention relates to a new class of lithium-aluminum-phosphorus-silicon-oxide
molecular sieves comprising a crystal framework structure of LiO.sub.2.sup.-3
AlO.sub.2.sup.-, PO.sub.2.sup.+ and SiO.sub.2 tetrahedral oxide
units. These new molecular sieves exhibit ion-exchange, adsorption
and catalytic properties and, accordingly, find wide use as adsorbents
and catalysts.
The LiAPSO molecular sieves of the instant invention comprise a
framework structure of LiO.sub.2.sup.-3 AlO.sub.2.sup.-, PO.sub.2.sup.+
and SiO.sub.2 tetrahedral units having an empirical chemical composition
on an anhydrous basis expressed by the formula:
wherein "R" represents at least one organic templating
agent present in the intracrystalline pore system; "m"
represents the molar amount of "R" present per mole of
(Li.sub.w Al.sub.x P.sub.y Si.sub.z)O.sub.2 and has a value of zero
to about 0.3 but is preferably not greater than about 0.15; and
"w", "w", "y" and "z" represent
the mole fractions of lithium, aluminum, phosphorus and silicon,
respectively, present as tetrahedral oxides. The mole fractions
"w", "x", "y" and "z" are
generally defined as being within the pentagonal compositional area
defined by points A, B, C, D and E of the ternary diagram of FIG.
1. Points A, B, C, D and E of FIG. 1 have the following values for
"w", "x", "y", and "z":
______________________________________ Mole Fraction Point x y
z + w ______________________________________ A 0.60 0.38 0.02 B
0.38 0.60 0.02 C 0.01 0.60 0.39 D 0.01 0.01 0.98 E 0.60 0.01 0.39
______________________________________
In a preferred subclass of the LiAPSO molecular sieves the values
of "w", "x", "y" and "z"
in the above formula are within the hexagonal compositional area
defined by the points a, b, c, d, e and f of the ternary diagram
which is FIG. 2 of the drawings, said points a, b, c, d, e and f
representing the following values for "w", "x",
"y" and "z":
______________________________________ Mole Fraction Point x y
z + w ______________________________________ a 0.60 0.38 0.02 b
0.38 0.60 0.02 c 0.01 0.60 0.39 d 0.01 0.39 0.60 e 0.39 0.01 0.60
f 0.60 0.01 0.39 ______________________________________
Especially preferred molecular sieves of this invention are those
in which w+z is not greater than about 0.20.
The LiAPSOs of this invention are useful as adsorbents, catalysts,
ion-exchangers, and the like in much the same fashion as aluminosilicates
have been employed heretofore, although their chemical and physical
properties are not necessarily similar to those observed for aluminosilicates.
LiAPSO compositions are generally synthesized by hydrothermal crystallization
from a reaction mixture containing reactive sources of lithium,
aluminum, phosphorus and silicon, preferably an organic templating,
i.e., structure-directing agent, preferably a compound of an element
of Group VA of the Periodic Table, and/or optionally an alkali or
other metal. The reaction mixture is generally placed in a sealed
pressure vessel, preferably lined with an inert plastic material
such as polytetrafluoroethylene and heated, preferably under autogenous
pressure, at a temperature between 50.degree. C. and 250.degree.
C., and preferably between 100.degree. C. and 200.degree. C., until
crystals of the LiAPSO product are obtained, usually for a period
of from several hours to several weeks. Crystallization times of
from about 2 hours to about 30 days are generally employed with
from about 4 hours to about 20 days, and preferably about 1 to about
10 days, being typically employed. The product is recovered by any
convenient method such as centrifugation or filtration.
In synthesizing the LiAPSO compositions of the instant invention,
it is preferred to employ a reaction mixture composition expressed
in terms of the molar ratios as follows:
wherein "R" is an organic templating agent; "a"
is the amount of organic templating agent "R" and has
a value of from zero (0) to about 6 and is preferably an effective
amount within the range of greater than zero (0) to about 6 and
desirably not greater than 0.5; "b" has a value of from
zero (0) to about 500 preferably between about 2 and about 300
desirably not greater than about 20 and most desirably not greater
than about 10; and "s", "t", "u" and
"v" represent the mole fractions of lithium, aluminum,
phosphorus and silicon, respectively, and each has a value of at
least 0.01. In a preferred embodiment the reaction mixture is selected
such that the mole fractions "s", "t", "u"
and "v" are generally defined as being within the pentagonal
compositional area defined by points F, G, H, I and J of the ternary
diagram of FIG. 3. Points F, G, H, I and J of FIG. 3 have the following
values for "s", "t", "u" and "v":
______________________________________ Mole Fraction Point t u
(v + s) ______________________________________ F 0.60 0.38 0.02
G 0.38 0.60 0.02 H 0.01 0.60 0.39 I 0.01 0.01 0.98 J 0.60 0.01 0.39
______________________________________
In the foregoing expression of the reaction composition, the reactants
are normalized with respect to the total of "s", "t",
"u" and "v" such that (w+x+y+z)=1.00 mole, whereas
in the examples the reaction mixtures are expressed in terms of
molar oxide ratios normalized to the moles of P.sub.2 O.sub.5. This
latter form is readily converted to the former form by routine calculations
by dividing the number of moles of each component (including the
template and water) by the total number of moles of lithium, aluminum,
phosphorus and silicon which results in normalized mole fractions
based on total moles of the aforementioned components.
In forming reaction mixtures from which the instant molecular sieves
are formed the organic templating agent can be any of those heretofore
proposed for use in the synthesis of conventional zeolite aluminosilicates.
In general these compounds contain elements of Group VA of the Periodic
Table of Elements, particularly nitrogen, phosphorus, arsenic and
antimony, preferably nitrogen or phosphorus and most preferably
nitrogen, which compounds also contain at least one alkyl or aryl
group having from 1 to 8 carbon atoms. Particularly preferred compounds
for use as templating agents are the amines, quaternary phosphonium
and quaternary ammonium compounds, the latter two being represented
generally by the formula R.sub.4 X.sup.+ wherein "X" is
phosphorus or nitrogen and each R is an alkyl or aryl group containing
from 1 to 8 carbon atoms. Polymeric quaternary ammonium salts such
as [(C.sub.14 H.sub.32 N.sub.2)(OH.sub.2 ].sub.x wherein "x"
has a value of at least 2 are also suitably employed. The mono,
di- and tri-amines are advantageously utilized, either alone or
in combination with a quaternary ammonium compound or other templating
compound. Mixtures of two or more templating agents can either produce
mixtures of the desired LiAPSOs or the more strongly directing templating
species may control the course of the reaction with the other templating
species serving primarily to establish the pH conditions of the
reaction gel. Representative templating agents include tetramethylammonium;
tetraethylammonium; tetrapropylammonium; and tetrabutylammonium
ions; tetrapentylammonium ions; di-n-propylamine; tripropylamine;
triethylamine; triethanolamine; piperidine; cyclohexylamine; 2-methylpyridine;
N,N-dimethylbenzylamine; N,N-dimethylethanolamine; choline; N,N'-dimethylpiperazine;
14-diazabicyclo (222) octane; N-methyldiethanolamine, N-methylethanolamine;
N-methylpiperidine; 3-methylpiperidine; N-methylcyclohexylamine;
3-methylpyridine; 4-methylpyridine; quinuclidine; N,N'-dimethyl-14-diazabicyclo
(222) octane ion; di-n-butylamine, neopentylamine; di-n-pentylamine;
isopropylamine; t-butylamine; ethylenediamine; pyrrolidine; and
2-imidazolidone. Not every templating agent will direct the formation
of every species of LiAPSO, i.e., a single templating agent can,
with proper manipulation of the reaction conditions, direct the
formation of several LiAPSO compositions, and a given LiAPSO composition
can be produced using several different templating agents.
The reactive phosphorus source is preferably phosphoric acid, but
organic phosphates such as triethyl phosphate have been found satisfactory,
and so also have crystalline or amorphous aluminophosphates such
as the AlPO.sub.4 composition of U.S. Pat. No. 4310440. Organophosphorus
compounds, such as tetrabutylphosphonium bromide, do not, apparently,
serve as reactive sources of phosphorus, but these compounds do
function as templating agents. Conventional phosphorus salts, such
as sodium metaphosphate, may be used, at least in part, as the phosphorus
source, but are not preferred.
Almost any reactive silicon source may be employed such that SiO.sub.2
tetrahedral units are formed in situ. The reactive silicon source
may be silica in the form of a silica sol, may be a fumed silica
or may be other conventional sources of silica used in zeolite synthesis
such as reactive solid amorphous precipitated silicas, silica gel,
alkoxides of silicon, tetraalkyl orthosilicates (for example, tetraethyl
orthosilicate), silicic acid, alkali metal silicates and the like.
The preferred aluminum source is either an aluminum alkoxide, such
as aluminum isoproproxide, or pseudoborehmite. The crystalline or
amorphous aluminophosphates which are a suitable source of phosphorus
are, of course, also suitable sources of aluminum. Other sources
of aluminum used in zeolite synthesis, such as gibbsite, sodium
aluminate and aluminum trichloride, can be employed but are not
preferred.
The reactive source of lithium can be introduced into the reaction
system in any form which permits the formation in situ of a reactive
form of lithium, i.e., reactive to form the framework tetrahedral
oxide unit of lithium. Compounds of lithium which may be employed
include oxides, alkoxides, hydroxides, chlorides, bromides, iodides,
sulfates, nitrates, carboxylates (e.g., acetates) and the like.
Phosphates can also be employed.
While not essential to the synthesis of LiAPSO compositions, stirring
or other moderate agitation of the reaction mixture and/or seeding
the reaction mixture with seed crystals of either the LiAPSO species
to be produced or a topologically similar aluminophosphate, aluminosilicate
or molecular sieve composition, facilitates the crystallization
procedure.
After crystallization the LiAPSO product may be isolated and advantageously
washed with water and dried in air. The as-synthesized LiAPSO generally
contains within its internal pore system at least one form of the
templating agent employed in its formation. Most commonly the organic
moiety derived from an organic template is present, at least in
part, as a charge-balancing balancing cation as is generally the
case with as-synthesized aluminosilicate zeolites prepared from
organic-containing reaction systems. It is possible, however, that
some or all of the organic moiety is an occluded molecular species
in a particular LiAPSO species. As a general rule the templating
agent, and hence the occluded organic species, is too large to move
freely through the pore system of the LiAPSO product and must be
removed by calcining the LiAPSO at temperatures of 200.degree. C.
to 700.degree. C., and preferably 350.degree. C. to 600.degree.
C. to thermally degrade the organic species. In a few instances
the pores of the LiAPSO product are sufficiently large to permit
transport of the templating agent, particularly if the latter is
a small molecule, and accordingly complete or partial removal thereof
can be accomplished by conventional desorption procedures such as
are carried out in the case of zeolites. It will be understood that
the term "as-synthesized" as used herein does not include
the condition of the LiAPSO phase wherein the organic moiety occupying
the intracrystalline pore system as a result of the hydrothermal
crystalline process has been reduced by post-synthesis treatment
such that the value of "m" in the composition formula:
has a value of less than 0.02. The other symbols of the formula
are as defined hereinabove. In those preparations in which an alkoxide
is employed as the source of lithium, aluminum, phosphorus and/or
silicon, the corresponding alcohol is necessarily present in the
reaction mixture since it is a hydrolysis product of the alkoxide.
It has not been determined whether this alcohol participates in
the synthesis process as a templating agent. For the purposes of
this application, however, this alcohol is arbitrarily omitted from
the class of templating agents, even if it is present in the as-synthesized
LiAPSO material.
Since the present LiAPSO compositions are formed from LIO.sub.2
AlO.sub.2 PO.sub.2 and SiO.sub.2 tetrahedral units which, respectively,
have a net charge of -1 -1 +1 and 0 the matter of cation exchangeability
is considerably more complicated than in the case of zeolitic molecular
sieves in which, ideally, there is a stoichiometric relationship
between AlO.sub.2.sup.- tetrahedra and charge-balancing cations.
In the instant compositions, an AlO.sub.2.sup.- tetrahedron can
be balanced electrically either by association with a PO.sub.2.sup.+
tetrahedron or a simple cation such as an alkali metal cation other
than lithium, a cation of lithium present in the reaction mixture,
a proton (H.sup.+) or an organic cation derived from the templating
agent. Similarly, an LiO.sub.2.sup.-3 tetrahedron can be balanced
electrically by association with PO.sub.2.sup.+ tetrahedra, a cation
of lithium present in the reaction mixture, a simple cation such
as an alkali metal cation other than lithium, organic cations derived
from the templating agent, a proton (H.sup.+) or other divalent
or polyvalent metal cations introduced from an extraneous source.
It has also been postulated that non-adjacent AlO.sub.2.sup.- and
PO.sub.2.sup.+ tetrahedral pairs can be balanced by Na.sup.+ and
OH-- respectively [Flanigen and Grose, Molecular Sieve Zeolites-I,
ACS, Washington, DC (1971)].
The LiAPSO compositions of the present invention may exhibit cation-exchange
capacity when analyzed using ion-exchange techniques heretofore
employed with zeolitic aluminosilicates and have pore diameters
which are inherent in the lattice structure of each species and
which are at least about 3.ANG. in diameter. Ion exchange of LiAPSO
compositions is ordinarily possible only after the organic moiety
present as a result of synthesis has been removed from the pore
system. Dehydration to remove water present in the as-synthesized
LiAPSO compositions can usually be accomplished, to some degree
at least, in the usual manner without removal of the organic moiety,
but the absence of the organic species greatly facilitates adsorption
and desorption procedures. The LiAPSO materials will have various
degrees of hydrothermal and thermal stability, some being quite
remarkable in this regard, and will function as molecular sieve
adsorbents and hydrocarbon conversion catalysts or catalyst bases.
In preparing the LiAPSO composition it is preferred to use a stainless
steel reaction vessel lined with an inert plastic material, e.g.,
polytetrafluoroethylene, to avoid contamination of the reaction
mixture. In general, the final reaction mixture from which each
LiAPSO composition is crystallized is prepared by forming mixtures
of less than all of the reagents and thereafter incorporating into
these mixtures additional reagents either singly or in the form
of other intermediate mixtures of two or more reagents. In some
instances the reagents admixed retain their identity in the intermediate
mixture and in other cases some or all of the reagents are involved
in chemical reactions to produce new reagents. The term "mixture"
is applied in both cases. Further, it is preferred that the intermediate
mixtures as well as the final reaction mixtures be stirred until
substantially homogeneous.
X-ray patterns of reaction products are obtained by X-ray analysis,
using standard X-ray powder diffraction techniques. The radiation
source is a high-intensity, copper target, X-ray tube operated at
50 Kv and 40 ma. The diffraction pattern from the copper K-alpha
radiation and graphite monochromator is suitably recorded by an
X-ray spectrometer scintillation counter, pulse height analyzer
and strip chart recorder. Flat compressed powder samples are scanned
at 2.degree. (2 theta) per minute, using a two second time constant.
Interplanar spacings (d) in Angstrom units are obtained from the
position of the diffraction peaks expressed as 2.theta. where .theta.
is the Bragg angle as observed on the strip chart. Intensities were
determined from the heights of diffraction peaks after subtracting
background, "I.sub.o " being the intensity of the strongest
line or peak, and "I" being the intensity of each of the
other peaks. Alternatively, the X-ray patterns may be obtained by
use of computer based techniques using copper K-alpha radiation,
Siemens type K-805 X-ray sources and Siemens D-500 X-ray powder
diffractometers available from Siemens Corporation, Cherry Hill,
N.J.
As will be understood by those skilled in the art, the determination
of the parameter 2 theta is subject to both human and mechanical
error, which in combination, can impose an uncertainty of about
.+-.0.4.degree. on each reported value of 2 theta. This uncertainty
is, of course, also manifested in the reported values of the d-spacings,
which are calculated from the 2 theta values. This imprecision is
general throughout the art and is not sufficient to preclude the
differentiation of the present crystalline materials from each other
and from the compositions of the prior art. In some of the X-ray
patterns reported, the relative intensities of the d-spacings are
indicated by the notations vs, s, m, w and vw which represent very
strong, strong, medium, weak and very weak, respectively.
In certain instances hereinafter in the illustrative examples,
the purity of a synthesized product may be assessed with reference
to its X-ray powder diffraction pattern. Thus, for example, if a
sample is stated to be pure, it is intended only that the X-ray
pattern of the sample is free of lines attributable to crystalline
impurities, not that there are no amorphous materials present.
The molecular sieves of the instant invention may be characterized
by their X-ray powder diffraction patterns and such may have one
of the X-ray patterns set forth in the following Tables A through
W, wherein said X-ray patterns are for the as-synthesized form unless
otherwise noted. In most cases, the pattern of the corresponding
calcined form will also fall within the relevant table. However,
in some cases the removal of the occluded templating agent which
occurs during calcination will be accompanied by sufficient relaxation
of the lattice to shift some of the lines slightly outside the ranges
specified in the relevant table. In a small number of cases, calcination
appears to cause more substantial distortion in the crystal lattice,
and hence, more significant changes in the X-ray powder diffraction
pattern. |