Process for the halogen modification of aluminophosphate molecular sieves and a product so produced

A process for treating crystalline aluminophosphates to provide aluminophosphates having modified catalytic properties. The crystalline aluminophosphates are contacted with a halogen-derived compound at an effective temperature and for an effective time to alter the surface characteristics of the aluminophosphates with resulting modification of catalytic properties.

BRIEF SUMMARY OF THE INVENTION 
1. Technical Field 
This invention is directed in general to a process for the treatment of 
crystalline aluminophosphate molecular sieves to provide adsorptive and 
modified catalytic properties. This invention is directed to 
aluminophosphate molecular sieves which have been treated with fluorine, 
chlorine, bromine, iodine, interhalogen compounds, boron trifluoride, 
phosphorus trifluoride, phosphorus pentafluoride and mixtures thereof 
whereby the changes in surface characteristics of the aluminophosphate 
result in changes in the adsorptive properties and/or catalytic 
properties. 
2. Background Art 
Although there are a few notable exceptions, the vast majority of 
naturally-occurring and synthetic crystalline molecular sieves contain 
most if not all of the framework atoms as AlO.sub.4 -tetrahedra, i.e., 
framework aluminum atoms, together with the SiO.sub.4 -tetrahedra, 
comprise the zeolite crystal framework. Relatively few molecular sieves 
have been extensively studied which do not contain aluminum and silicon as 
the essential framework constituents. 
Although it is generally accepted that the aluminum-containing structural 
units in an aluminosilicate provide the so-called "acid-sites" which 
account for the catalytic activity of zeolites in such hydrocarbon 
conversion reactions as catalytic cracking, the various sites in 
aluminophosphates are not to be similarly viewed owing to the different 
framework constituents. Since it is believed that the cation sites are 
responsible in one or more ways for the adsorptive preference of most 
zeolites for strongly polar molecules such as water, i.e. their 
hydrophilic character, one can only speculate the effect of various 
treatment processes on different molecular sieves when such molecular 
sieves are vastly different in terms of their acid sites as a result of 
different framework structures. 
A number of different techniques have heretofore been proposed to remove 
framework aluminum atoms from aluminosilicates to create 
aluminum-deficient lattice structures having fewer cation sites, and 
consequently less hydrophilicity and more hydrophobicity, and altered 
catalytic activities. One of the more common early techniques for 
dealuminizing zeolites involves contacting either the hydrogen or the 
decationized form of the zeolite with a known chelating agent for 
aluminum, such as ethylenediamine tetracetic acid (EDTA) or acetylacetone, 
and removing aluminum as an organometallic complex. A more recent and more 
widely used procedure involves prolonged contact of non-metallic cation 
forms of zeolites with steam at elevated temperatures which can exceed 
800.degree. C. The most relevant processes for treatment of 
aluminosilicates are discussed hereinafter. 
U.S. Pat. No. 4,297,335 describes crystalline aluminosilicate zeolite 
compositions which have been treated with a fluorine gas mixture to alter 
the framework aluminum content and cation sites and thereby enhance the 
hydrophobic character of the zeolites. The fluorine gas mixture is 
comprised of (i) from 0.1 to 20 volume percent fluorine, (ii) from zero to 
21 volume percent oxygen and (iii) as the remainder, one or a mixture of 
two or more inert gases, preferably nitrogen. The starting crystalline 
aluminosilicate zeolite compositions have at least 50 percent of the 
framework aluminum atoms not associated with metal cations and are 
contacted with the fluorine gas mixture at a temperature of from about 
50.degree. F. to 400.degree. F. 
Copending U.S. patent application Ser. No. 363,560, filed Mar. 30, 1982, 
now abandoned and commonly assigned, describes a process for enhancing the 
hydrophobicity of crystalline aluminosilicate zeolites having an initial 
SiO.sub.2 /Al.sub.2 O.sub.3 molar ratio of at least 5. The zeolites are 
treated with pure chlorine gas at a temperature of from about 200.degree. 
C. to about 1000.degree. C. and thereafter purged with a purge gas, i.e., 
nitrogen, to remove entrapped chlorine gas from the treated zeolite. This 
treatment results in modification of both the adsorptive properties, i.e., 
enhanced hydrophobicity, and the catalytic properties of the zeolites. 
H. K. Beyer and I. Belenykaja, A New Method for the Dealumination of 
Faujasite-Type Zeolites, Catalysis be Zeolites, Printed in the 
Netherlands, 203-209 (1980) describes the dealumination of faujasite-type 
zeolites, particularly Y zeolites, using silicon tetrachloride as the 
dealuminizing agent. This dealumination process is carried out at high 
temperatures ranging from about 457.degree. C. to about 557.degree. C. 
French Pat. No. 2,303,764 describes a process for increasing the molar 
ratio of SiO.sub.2 /Al.sub.2 O.sub.3 in the crystalline skeleton of 
zeolites having SiO.sub.2 /Al.sub.2 O.sub.3 molar ratios of less than 5. 
The zeolites are first dehydrated by heating to a temperature of at least 
400.degree. C. in a reactor equipped with at least one opening in the 
presence of air or inert gases. Thereafter, gases containing chlorine 
and/or hydrochloric acid are reacted with the dehydrated zeolite at 
temperatures between 400.degree. C. and 700.degree. C. It is stated that 
the zeolite product can then be treated by washing with aqueous solutions 
of ammonium salts or salts which give ammonium ions, strong aqueous 
mineral acids, caustic soda or alkaline solutions, or distilled water. 
Example 11 illustrates that the capacity of adsorption of zeolites with 
respect to water vapor is practically not altered by treatment of the 
zeolites according to the process described therein. 
In copending U.S. Ser. No. 403,928, filed Aug. 2, 1982, now abandoned but 
followed by divisional application Ser. No. 725,503, filed Apr. 24, 1985, 
now U.S. Pat. No. 4,569,833, commonly assigned, is a process which 
involves the treatment of aluminosilicates and aluminophosphates with 
silicon tetrafluoride. The process involves silicon substitution or 
rearrangement of the framework tetrahedral atoms. 
None of the aforementioned items disclose a process for treating 
crystalline aluminophosphates according to the present invention in which 
the crystalline aluminophosphates are treated with a gas mixture 
containing: (i) from 0.1 to 100 volume percent of a halogen-derived gas 
comprising at least one of fluorine, chlorine, bromine, iodine, 
interhalogen compounds, boron trifluoride, phosphorus trifluoride and 
phosphorus pentafluoride; (ii) from zero to 21 volume percent oxygen; and 
(iii) optionally, as the remainder, one or a mixture of two or more inert 
gases. 
SUMMARY OF THE INVENTION 
The present invention provides a process for treating aluminophosphates. 
The process generally comprises contacting a crystalline aluminophosphate 
with a gas comprising: 
(i) from 0.1 to 100 volume percent of a halogen-derived gas comprising at 
least one of fluorine, chlorine, bromine, iodine, interhalogen compounds, 
boron trifluoride, phosphorus trifluoride and phosphorus pentafluoride; 
(ii) from zero to 21 volume percent oxygen gas; and 
(iii) optionally, as the remainder, one or a mixture of two or more inert 
gases, preferably nitrogen. 
A preferred embodiment of the present invention comprises contacting the 
aluminophosphate obtained from the treatment with the halogen-derived gas 
with an aqueous solution of salt, such as an ammonium salt solution, for a 
sufficient time to remove fluoride species, such as AlF.sup.++ and 
AlF.sub.2.sup.+, from the treated crystalline aluminophosphate. In 
addition the final crystalline aluminophosphate can be treated after the 
instant process by calcination at temperatures from 100.degree. C. up to 
the crystal destruction temperature of the crystalline aluminophosphate 
and by rehydration or by a combination of ion exchange, calcination and 
rehydration treatments in any order.

DETAILED DESCRIPTION OF THE INVENTION 
The crystalline aluminophosphates employed in the instant invention 
include, among others, those described in U.S. Pat. No. 4,310,440 and, in 
particular, to the species denominated therein as AlPO.sub.4 -5, 
AlPO.sub.4 -8, AlPO.sub.4 -9, AlPO.sub.4 -11, AlPO.sub.4 -12, AlPO.sub.4 
-14, AlPO.sub.4 -16, AlPO.sub.4 -17, AlPO.sub.4 -18, AlPO.sub.4 -20, 
AlPO.sub.4 -22, AlPO.sub.4 -25, AlPO.sub.4 -26, AlPO.sub.4 -28, and 
AlPO.sub.4 -31. Reference to one of the aforementioned species is meant 
herein to denominate that species as described in U.S. Pat. No. 4,310,440. 
In addition the crystalline aluminophosphate, denominated AlPO.sub.4 -33, 
disclosed in copending U.S. Ser. No. 480,698, filed Mar. 31, 1983, now 
U.S. Pat. No. 4,473,663, issued Sept. 25, 1984 and incorporated herein by 
reference thereto, may be employed herein. The crystalline 
aluminophophates of U.S. Pat. No. 4,310,440 are generally described as 
having a framework structure whose chemical composition expressed in terms 
of mole ratios of oxides is: Al.sub.2 O.sub.3 : 1.0.+-.0.2 P.sub.2 O.sub.5 
; each of said framework structures being microporous in which the pores 
are uniform and have nominal diameters within the range of about 3 to 
about 10 Angstroms, an intracrystalline adsorption capacity for water at 
4.6 torr and 24.degree. C. of at least 3.5 weight percent, the adsorption 
and desorption of water being completely reversible while retaining the 
same essential framework topology in both the hydrated and dehydrated 
state. 
The terms "halogen-derived gas" and "halogen-derived compounds" are 
employed herein to include at least one of the group consisting of 
fluorine, chlorine, bromine, iodine, interhalogen compounds, boron 
trifluoride, phosphorus trifluoride and phosphorus pentafluoride. The term 
"interhalogen compounds" denominates compounds formed from two or more 
halogens, e.g., ClF.sub.3 and BrF.sub.5. 
The crystalline aluminophosphates may be calcined at above about 
100.degree. C. for a period of about 0.1 hours or more prior to being 
contacted with a halogen-derived gas mixture comprising: (1) from 0.1 to 
100 volume percent of a halogen-derived gas, preferably from about 0.25 to 
about 50 volume percent and more preferably from about 1 to about 25 
volume percent of a halogen-derived gas; (2) from zero to 21 volume 
percent oxygen and (3) optionally, as the remainder, one or a mixture of 
two or more inert gases. The inert gas is preferably present in an amount 
from about 50 to about 99.75 volume percent and is preferably one or a 
mixture of two or more inert gases such as nitrogen, helium, argon and the 
like. When oxygen and nitrogen are present in the gas mixture, the use of 
dry air is particularly beneficial. The inert gas acts as a diluent to 
adjust the halogen-derived gas concentration to a desired level. Low 
concentrations of the halogen-derived gas in the gas mixture are desirably 
and effectively used in the process of this invention. However, the gas 
mixture can contain higher concentrations up to 100 volume percent of the 
halogen-derived gas. 
The crystalline aluminophosphates are contacted with halogen-derived gas at 
an effective temperature and is preferably from about 20.degree. C. to 
about 200.degree. C. for an effective period of time to affect the surface 
characteristics of the aluminophosphate. The more preferred temperature 
for contacting the halogen-derived gas with the crystalline 
aluminophosphate is from about 20.degree. C. to about 100.degree. C. and 
most preferably is at about room temperature (18.degree. C. to 22.degree. 
C.). The process of this invention is preferably carried out at ambient 
pressure (14.7 psia), however both atmospheric and superatmospheric 
pressure conditions may be employed in this process. In general, the 
effective contact time can vary from a few minutes or less to several 
hours or longer, i.e., from 1 minute or shorter to 10 hours or longer. The 
preferred contact time is from about 10 minutes to about four hours. It is 
readily appreciated that the required contact time will be influenced by 
the reaction temperature, total pressure, concentration and flow rate of 
the halogen-derived gas mixture, concentration and choice of the 
crystalline aluminophosphate and other factors. The process of the present 
invention is suitably conducted under operative conditions which give 
reasonable reaction rates and, of course, the desired modification of the 
crystalline aluminophosphates. 
After the crystalline aluminophosphates are contacted with halogen-derived 
gas under the above described operational conditions, the 
aluminophosphates are preferably treated with an aqueous solution of at 
least one salt for a sufficient period of time to remove at least some of 
any fluoride species associated with the treated crystalline 
aluminophosphate. Aqueous salt solutions of ammonium or aluminium are 
generally employable. The removal of the fluoride species can prevent the 
corrosion of equipment utilized in carrying out the process of the present 
invention and also equipment used in processes employing the halogen 
treated aluminophosphates such as catalytic cracking reactions. The 
crystalline aluminophosphates are preferably contacted one or more times, 
most preferably three times, with an aqueous solution of ammonium or metal 
ion (e.g. alkali, alkaline earth or aluminium) in a conventional manner. 
This step is preferably conducted under operative conditions which give 
essentially complete removal of residual fluoride species from the 
crystalline aluminophosphate. The preferred aqueous solution for use in 
this step is an ammonium salt solution, such as a 10% ammonium chloride or 
acetate solution. 
When the aluminophosphates have been calcined such crystalline 
aluminophosphates can be rehydrated or washed with distilled water for a 
sufficient time to remove entrapped metal halides, if any, from the 
framework of the aluminophosphate(s). Metal halides such as alkali metal 
halides, alkaline earth metal halides and aluminum halides are removed 
from the crystalline aluminophosphate structure. Such metal halides can 
occupy the pore volume surface and cause high water adsorption near 
saturation. Because many metal halides sublime at relatively low 
temperatures, the calcination treatment step at the indicated elevated 
temperatures can also be used to remove impurities from the 
aluminophosphate. In general, the washing time can vary from a few minutes 
to several hours or longer. The total washing time will be influenced by 
the concentration and choice of crystalline aluminophosphate, the amount 
of metal halides blocking the pore structure of the aluminophosphate and 
other factors. The water washing step of the present invention is 
preferably conducted to remove essentially all metal halides from the 
treated crystalline aluminophosphate. 
In some instances it is desirable to have residual halogen-derived 
compounds present in an amount between about 0.05 and about 6 percent by 
weight halogen based on the total weight of the treated product and 
preferably between about 0.1 and about 5 percent by weight halogen, since 
some catalytic reactions may benefit from the presence of halogen present 
as a result of treatment with such halogen-derived compounds. 
The treated crystalline aluminophosphate (treated with halogen-derived gas) 
can further undergo calcination at a temperature of from about 100.degree. 
C. up to the crystal destructon temperature of the aluminophosphate. This 
calcination step may remove non-metallic cations such as ammonium cations 
from the crystalline aluminophosphate. The calcination step, in addition 
to the process step involving contacting the halogen-derived gas with the 
aluminophosphate(s), provides for high purity aluminophosphate products. 
The crystalline aluminophosphate compositions prepared in accordance with 
the process of the present invention can be used as selective adsorbents 
or as catalysts in hydrocarbon conversion processes, for example, 
catalytic cracking processes wherein said hydrocarbon is contacted with a 
treated aluminophosphate at effective hydrocarbon conversion conditions. 
Representative hydrocarbon conversion processes include: cracking; 
hydrocracking; alkylation for both the aromatic and isoparaffin types; 
isomerization, including xylene isomerization; polymerization; reforming, 
hydrogenation, dehydrogenation; transalkylation; dealkylation; 
hydrodecyclization; hydrofining; dehydrocylization; and disproportionation 
processes. Further, these compositions may be employed to separate 
molecular species from admixture with molecular species having a less 
degree of polarity by contacting said mixture with said treated 
aluminophosphates, preferably activated by heating at greater than 
100.degree. C., having at least one of the more polar molecular species 
whereby molecules of the more polar molecular species are selectively 
adsorbed into intracrystalline pore system thereof. 
Although this invention has been described with respect to a number of 
details, it is not intended that this invention should be limited thereby. 
The examples which follow are intended solely to illustrate the 
embodiments of this invention which to date have been determined and are 
not intended in any way to limit the scope and the intent of this 
invention. 
EXPERIMENTAL PROCEDURE 
In carrying out the process of this invention, it is advantageous to 
utilize a reactor having means for evacuating the gases therefrom as well 
as means for regulating the temperature. The reactor used in the examples 
for contacting the aluminophosphates with halogen-derived gas is an 
enclosed mild steel container resistant to corrosion by halogen-derived 
gas. The reactor is approximately 17 inches in length by 10 inches in 
width with a height of 4 inches and a total volume of approximately 11.8 
liters. The reactor is equipped with a removable lid and a 1/4 inch 
stainless steel tubing inlet and outlet. The reactor is heated with a hot 
plate or an oven. The temperature of a sample in the reactor was measured 
with a thermocouple embedded in the sample. The temperature of the reactor 
is controlled to .+-.5.degree. C. with a temperature controller and the 
flow of halogen-derived gas and/or diluent was controlled with a series of 
rotometers. The aluminophosphates are placed inside the reactor in Teflon 
containers measuring approximately 4 inches in length by 4 inches in width 
with a height of 1 inch. The halogen-derived gas is thoroughly mixed in a 
mixing chamber or cylinder before entering the reactor. Gas escaping from 
the reactor is directed to a scrubber system consisting of a soda lime 
trap vented to the top of a hood. The general procedure includes: (1) 
introducing the aluminophosphate starting material into the reactor; (2) 
adjusting the temperature to the indicated temperatures in the examples; 
(3) removing the bulk of the air over the aluminophosphate sample by means 
of a vacuum pump (a pressure of about 10.sup.-3 Torr is adequate) or 
flushing with nitrogen gas; (4) introducing the halogen-derived gas and/or 
diluent mixture at a minimal flow rate which results in a continuous flow 
of the gas mixture through the system for a period of time, e.g. about 1 
minute to about 10 hours; and (5) evacuating or flushing the reactor to 
remove residual halogen-derived gas. Thereafter, the treated 
aluminophosphate may be treated with an aqueous solution, i.e., ammonium 
salt solution, for a sufficient time to remove any aluminum fluoride 
cation species, i.e. AlF.sup.++ and AlF.sub.2.sup.+, from the treated 
aluminophosphate. The final aluminophosphate product may then be stored in 
a sealed container to prevent reaction with water vapor. 
The catalytic character of the aluminophosphates which have been treated 
with a halogen-derived gas were evaluated by test procedure involving the 
catalytic cracking of premixed n-butane at 2 mole percent in a helium 
stream. The mixture containing 2 mole percent n-butane in helium was 
obtained from Union Carbide Corporation. The mixture underwent cracking in 
a one-half inch (outside diameter) quartz tube reactor into which was 
added 0.5 to 5.0 grams at 20-40 mesh of crystalline molecular sieve sample 
to be tested. The crystalline molecular sieve sample was activated in situ 
for 60 minutes at 500.degree. C. under 200 cm.sup.3 /minute dry helium 
purge. The mixture containing 2 mole percent n-butane in helium is then 
passed at a rate of 50 cm.sup.3 /minute over the aluminophosphate sample 
for 40 minutes, with a product stream analysis carried out at 10 minute 
intervals. The first order rate constant was then calculated to determine 
the activity of the treated aluminophosphate as follows: 
First Order Rate Constant (cm.sup.3 /gm min)=F 1n (1-c)/W wherein F is the 
flow rate in cm.sup.3 /min., W is the activated aluminophosphate sample 
weight in grams and c is the mole fraction of n-butane consumed. 
The following examples are provided to illustrated the invention and are 
not intended to be limiting thereof: 
EXAMPLE 1 
AlPO.sub.4 -5 was evaluated for its n-butane cracking constant and had a 
value of 0.05. A five gram sample of AlPO.sub.4 -5 was calcined at 
600.degree. C. for 2 hours in air. The calcined sample was then ion 
exchanged in a 10 percent by weight solution of ammonium acetate in water 
under reflux conditions for 1 hour. The mixture was filtered and the solid 
washed with 500 cubic centimeters of distilled water. The reflux and water 
wash were repeated two additional times and the material dried in air. The 
n-butane cracking constant was determined by the procedure above 
described, and was 0.05. 
EXAMPLE 2 
AlPO.sub.4 -11 was evaluated to determine its n-butane cracking constant 
and was determined to have a value of 0.05. AlPO.sub.4 -11 was calcined 
and ion-exchanged by a procedure similar to that employed in example 1 for 
AlPO.sub.4 -5. The n-butane cracking constant of the ammonium exchanged 
AlPO.sub.4 -11 was 0.04. 
EXAMPLE 3 
Ten grams of AlPO.sub.4 -5 as the calcined extrudate was treated with 2.5 
volume percent fluorine in a nitrogen stream (volume percent fluorine 
based on the total volume of fluorine and nitrogen) for a period of 15 
minutes at a total flow rate of 1500 cubic centimeters per minute (cc/min) 
at room temperature (18.degree. C. to 22.degree. C.). A five gram portion 
of this sample was steamed for 2 hours and 45 minutes at a steam 
concentration of 16 percent by weight and a temperature of 600.degree. C. 
The steamed sample was analyzed by x-ray and observed to be highly 
crystalline and of substantially the same crystallinity of the starting 
material. The n-butane cracking constant of the steamed product was 0.50. 
EXAMPLE 4 
A ten gram sample of AlPO.sub.4 -5 was treated with 5 percent by volume 
fluorine in nitrogen (volume percent fluorine based on the total volume of 
fluorine and nitrogen) for 30 minutes at a flow rate of 1500 cc/min at 
room temperature (18.degree. C.-22.degree. C.) and then purged for 10 
minutes with nitrogen at a flow rate of 1500 cc/min. A portion of this 
sample was ammonium exchanged under reflux conditions and water washed as 
done in example 1. The product was dried and the n-butane cracking 
constant determined to be 0.22.