|Title of Invention||
A PROCESS FOR THE PREPARATION OF DEALUMINATED CRYSTALLINE ALUMINOSILICATE ZEOLITE -Y.
|Abstract||A process for the preparation of dealuminated crystalline aluminosilicate zeolite-Y by treating aluminosilicate zeolite with an aqueous solution of an ammonium salt in a ratio of 1:8 to 1:12 w/v at a temperature in the range of 70-100°C, heating the resultant NH4Y zeolite in the presence of steam at a temperature in the range of 380-820°C, over a period in the range of 0.1 to 12 hours with the heating rate of 100°C per hour, treating the dealuminated zeolite obtained with a mineral acid in a ratio 1:8 to 1:12 for 0.25 to 2 hours to obtain dealuminated crystalline aluminosilicate zeolite-Y.|
|Full Text||The invention relates to a process for the preparation of the dealuminat ed crystalline alumino-sil icate zeolite. The invention more specifically relates to a process for the removal of frame work aluminium from crystalline aluminosilicate zeolite Y by controlled hydrothermal treatment to produce dealuminated zeolite-Y having increased silica to alumina ratio, decreased acid site density, increased acid site strength and having mesopores without significant loss of crystal l.inity. The dealuminated zeolite-Y prepared by the process of the present invention is thermally more stable and can be used efficiently in catalytic processes such as fluid catalytic cracking and hydrocracking, where high temperatures are used. The dealuminated zeolite Y prepared by the process of present invention can withstand the process conditions used in the regeneration of a used catalyst containing the same which involves burning of the deposited coke/residual hydrocarbon and, therefore, can be used Ln the preparation of the catalyst support/matrix of such catalysts as are used in the fluid catalytic cracking and hydrocracking operations. The retention of the activity and crystal1inity of the zeolite Y part of the catalyst is very essential for the success of a catalyst in these1 operations.
zeolite-Y is a crystalline aluminosilicate, synthesized in sodium form and, therefore, has substantial amount of the alkali metal. The cracking reactions conducted on. zeolite are acid-catalyzed reaction and as such the zeolite-Y is not
active as a cracking catalyst due to the absence of surface acidity because of the presence of alkali metal ions. Therefore, it is necessary to modify the Y type-zeolites to introduce the acidic catalytic sites and at the same time improve their thermal stability.
In the fluid catalytic cracking and hydrocracking processes a high boiling feed, such as the Bombay High vacuum gas oil (VGO) (BP 370-545°C) or the residual oil having high molecular weight, hydrocarbons is used. The size of these hydrocarbon molecules is large enough not to diffuse into the pores of zeolite Y. Dealumination creates mesopores and the large hydrocarbon molecules can diffuse into the zeolite pores thus making the full use of the zeolite present in the catalyst formulations. The desired acidity, mesoporosity and silica-to-alumina ratio can be achieved by controlled degree of dealumination required for a particular cracking reaction.
It is known in the art that zeolite Y can be dealuminated by either by a chemical or by a hydrothermal treatment. It is also known in the art that the unit cell size of the zeolite decreases as the degree of dealumination increases.
It is well-known to those skilled in the art that dealumination of zeolite Y by chemical treatment which removes the frame work aluminium in a volatile/or soluble form .is carried out by treatment with a chelating agent such
as ethylenediaminetetraacetic acid (H4EDTA), silicon tetrachlori.de (SiCl4) vapours, ammonium hexafluorosilicate [(NH4 )2 Si F6] in solution, or with fluorine gas (J. Scherzer in the ACS symposium series No. 248, 1983).
The aforementioned methods suffer from certain disadvantages such as the following
(i) The surface of the zeolite particle acquires
different gradients in the distribution of frame work aluminium to that of the interior/bulk, i.e, surface has lower number of aluminium atoms compared to the interior;
(ii) No mesopores are created when aluminium atom is replaced by a silicon atom;
(iii) Some part of the aluminium from the complex formed with the chelating agent such as EDTA is precipitated as aluminium hydroxide during the preparation involving washing with water resulting in blockage of the zeolite pores;
(iv) Use of fluorine gas and silicon tetrachloride is hazardous and poses handling and environmental problems.
In the alternate hydrothermal treatment method the zeolite Y in the ammonium form is heated with or without steam which causes partial dealumination of the zeolite frame work, but the aluminium atoms remain as alumina in
cages/channels of the zeolite as non-frame work debris. Which is removed by acid treatment. Mc Daniel and Maher (US Patent 3, 293, 192, Dec 20, 1966) disclosed the preparation of ultra-stable zeolite-Y by calcining NH4Y containing ~3% sodium oxide ( Naz o ) followed by further ammonium exchange and high temperature treatment.
J. Scherzer (J. of Catalysis 54, (1978) p.285 reported the preparation of highly dealuminated zeolite Y having silica-to-alumina ratio over 100 by hydrothermal treatment of NH4Y followed by acid extraction. The unit cell size of the dealuminated zeolite Y ranges from 24.18 to 24.27 A°. The resulting product has very little frame work aluminium, consequently poor acidity and hence cannot make a satisfactory cracking catalyst.
Pei-shinng E. Dai, David E. Sherwood et al in their US Patent 5, 069, 890 Dec. 3, 1991 disclosed the preparation of dealuminated Y zeolites using the commercially available ultrastable zeolite Y of Union Carbide and superultra stable zeolite Y of PQ corporation. The non-frame work alumina is not removed in these preparations.
However, the available hydrothermal treatment methodology of dealuminating the zeolite Y does not define the conditions of temperature and duration of the hydrothermal treatment in order to achieve controlled and desired degree of dealumination. Further the available
methodology invariably includes an intermediate calcination step during the exchange of NaY to NH4Y.
The objective of the present invention is therefore, to provide an improved process for the preparation of dealuminated zeolite Y to get a product having the desired thermal stability, acid sites strength, specific silica-to-alumina ratio, high crystallinity and activity as a result of the creation of rnesopores which can be used in preparing superior cracking catalysts.
In carrying out the present invention, as a result of extensive investigations carried out by us, we found it advantageous to avoid the intermediate calcination step during the exchange of NaY zeolite to the NH4Y zeolite in that the resulting product is more crystalline than what it would be if it were subjected to repeated heat treatment.
Accordingly, the present invention provides an improved process for the preparation of dealuminated crystalline alumirio-sil icate , zeolite specially Y type zeolite which compri ses.
(a) treating alumino-silicate zeolite with an aqueous
ammonium salt solution at a temperature in the
range 70-100°C to bring down the sodium content in
the alumino silicate zeolite to less than 1%,
(b) heating the resultant NH4Y zeolite at a temperature
range of 380-820°C, over a period in the range of
0.1 to 12 hrs in the presence of steam in a controlled manner to achieve the degree of dealumination in the range of 10-90% and
(c) treating the dealuminated zeolite Y obtained from
step (b) with a mineral acid to further enhance the
crystal1inity and the pore size of the zeolite and
(d) if desired treating the zeolite formed by
conventional methods to reduce the sodium content
in the zeolite Y formed to less than 0.1%.
The extent of dealumination in dealuminated zeolite is conventionally determined from the unit cell size verses aluminium atom per unit cell (Breck and Flanigen; Ketzen Catalyst Symposium 86 page 4, fig-1) derived from the X-Ray diffraction data on the sample. The degree of dealuminatin increases with the decrease in unit cell size.
The unit cell size and crystallinity of dealuminated zeolite Y were determined by X-ray diffraction method using ASTM D-3942-85 and D-3906-85 standard procedures respectively.
The degree of dealumination to within desired ~5% is achieved by controlling the rate of heating, temperature, duration and the amount of steam. The desired pore structure having mesopores of (50-200 A° dia) can be obtained by modifying the conditions mentioned above. It is known that
faster heating rate will create larger pores but with crystallinity loss (J. Biswas and I.E. Maxwell, Applied Catalysis, 63 ((1990) p. 227).
The non-frame work alumina debris is removed by mineral acids such as HNO3 and HC1 . Removal of non-frame work alumina improves the effective pore dia, increases total acidity, crystal1inity and reduces the sodium content to 50% dealuminated zeolite and decreases in case of The invention may be practiced as illustrated in the following examples. It may, however, be construed that the following examples are only representative and do not limit the scope of the invention.
This examples illustrates the process for obtaining 20% dealuminated zeolite Y.
(A) Exchange of NaY to NH4Y lOOg. NaY (LZY-52) of
Union Carbide, on anhydrous basis, was slurried in a litre solution of ~18% NH4NO3 in demineral ized water. The slurry was refluxed for 2 hours, filtered, and the solid washed with demineralized water to remove the excess NH4NO3 and the sodium
salt. The cake was dried at 110°C. The entire operation contacting the cake with similar concentration of the ammonium salt solution, reflux ing filtering and drying at 110°C was repeated thrice. At the end of the 4th cycle >90% sodium was exchanged. The crystallinity of NH4Y thus prepared was >100% and the unit cell size 24.70 to 24.73 A° with respect to the starting material. NaY (LZY-52) 100% and 24.68 A° (Table 1).
(B) Dealuminabion of NH4Y
This example illustrates the process for ~20% dealumination. Appx. 35g of NH4Y, prepared as described in step (A), was taken in a steel cell which was fitted in a muffle furnace. The furnace was heated slowly at. a rate of 100°C/hr. At 250°C, the water injection into the cell was started at a rate of ~5ml/hr through a coiled tube fitted at one end of the steel cell. The steam escaped through steel Lube fitted at the other end of the steel cell. The furnace was switched off when it attained 400°C. The water injection was also stopped and the steel cell was cooled. The crystal1inity and the unit cell size of the product were 85.5% and 24.60 A° respectively (Table 1) as determined by XRD. By this method ~20% dealumination was effected.
Appx. 35 g. of NH4Y prepared as described in step A of Example 1 was taken in a steel cell fitted in a muffle furnace. The furnace was heated slowly at a rate of 100°C/hr. At 250°C, the water injection was started to inject in steel cell at a rate of ~20ml/hr. The temperature was kept constant at 500°C for 2 hrs. The sample was cooled without steam. The crystal!inity and the unit cell size of the product, as determined by XRD, were 81.91% and 24.43 A° respectively (Table-]). The dealumination effected was ~50%.
Appx. 35g NH4 Y prepared as per step A of example 1 was taken in a steel cell which was fitted in a muffle furnace. The furnace was heated slowly at a rate of 100°C/hr. At 250°C, the water was started to inject in steel cell at a rate of ~20ml/hr. The temperature was held at 500°C for 1.5 hours and finally at 600°C for 1 hour. The sample was cooled in presence of steam till a temperature of 500°C was attained and further without steam. The crystallinity and unit cell size by XRD was 84.9% and 24.39 A" respectively (Table-1). The dealumination effected was ~60%.
Appx. 35g NH4Y prepared as per step A of example 1 was taken in a steel cell which was fitted in a muffle furnace. The furnace was heated slowly at a rate of 100°C/ hr. At 250°C water was started to inject in steel cell at a rate of ~20ml/hr. The temperature was held at 500°C and 600°C for a period of 2 hours each and finally for 1 hour at 780°C. The sample was cooled in steam till a temperature of ~500°C was attained and further without steam. The crystal 1 ini ty arid unit cell size by XRD, of the product, as determined were 73.5% and 24.31 A° respectively (Table-1). The dealumination effected was ~80%.
The dealuminated zeolite Y samples as obtained in example 1,2,3 and 4 have non-frame work aluminium as alumina debris in zeolite cage/channels which causes the blockage of effective pore dia of zeolite.
This example illustrates the process of removal of non-frame work alumina by the acid extraction of 60% dealuminated zeolite Y. lOg zeolite slurried in 85ml N HCl was refluxed for 30 minutes, filtered and washed free of chloride ions with demineralized water and dried at 110°C for 16 hrs. The crystall ini ty and unit cell size by XRD after acid extraction were 87.6% and 24.38 A° respectively as compared to 84.9% and 24.39 A° respectively before acid extraction.
From the information given in the table it can be inferred that there is loss of crystallinity in dealuminated zeolite-Y w.r.t. starting material i.e. NaY. The unit cell size of dealuminated zeolite Y decreases as the degree of dealuminat.ion i nc reases .
We Claim :
1. An improved process for the preparation of dealuminated
crystalline aluminosilicate zeolite,
zeolite, which comprises.
(a) treating aluminosilicate zeolite with an aqueous
solution of an ammonium salt in a ratio of 1:8 to 1:12 w/v
at a temperature inthe range of 70-1000C
(b) heating the resultant NH4Y zeolite in the presence
of steam at a temperature in the range of 380-
820°C, over a period in the range of 0.1 to 12
hours with the heating rate of 100°C per hour.
(c) treating the dealuminated zeolite obtained from
step (b)in a ratio of 1:8 to 1:12 for 0.25 to 2 hours and to
obtain dealuminated crystalline alumino silicate
zeolite-y with a mineral acid.
2. An improved process as claimed in claim 1 where in the
ammonium salt used is selected from NH4NO3, NH4C1,
(NH4 )2 S04
3. An improved process as claimed in claim 1 and 2 where in
the concentration of the ammonium salts ranges from
4. An improved process as claimed in claimsl-3 where in the
mineral acid used in step (C) is HC1 , arid the
concentration ranges from 0.1-6 N.
5. An improved process for the preparation of dealuminated
crystalline alumino-silicate zeolite especially Y type
zeolite substantially as herein described with reference
to the examples.
|Indian Patent Application Number||1247/DEL/1995|
|PG Journal Number||04/2008|
|Date of Filing||04-Jul-1995|
|Name of Patentee||COUNCIL OF SCIENTIFIC AND INDUSTRIAL RESEARCH|
|Applicant Address||RAFI MARG, NEW DELHI-110001, INDIA.|
|PCT International Classification Number||B01J 29/04|
|PCT International Application Number||N/A|
|PCT International Filing date|