Composition and a process for preparation of attrition resistant cracking catalyst suitable for enhancing light olefins

Abstract

The present invention relates to a composition of attrition resistant attrition resistant catalyst particularly for FCC catalyst additives such as ZSM-5, bottom cracking additive/residue upgradation additive and GSR additive comprising aluminum phosphate binder wherein said binder comprising of 1.5 to 2.9 moles equivalent of monobasic acid for each mole of mono-aluminum phosphate (MAP). Further, the aluminum phosphate binder is added to the catalyst additive to ensure effective binding of catalyst as well as preserving catalyst activity with high selectivity towards light olefins including LPG.

Claims

1. An attrition resistant hydrocarbon cracking catalyst additive composition comprising 10-70% wt % zeolite, 5-20 wt % colloidal silica, 10-60 wt % clay, 1-10 wt % phosphate and 1-15 wt % aluminium phosphate binder, wherein the aluminium phosphate binder is a reaction product of mono aluminium phosphate and an aluminium compound in the mole ratio of 1:1 to 1:2.5: wherein said zeolite is selected from mordenite, ZSM-5, beta, ZSM-11 with silica alumina ratio ranging from 8 to 500.

2. The composition as claimed in claim 1, wherein said additive has ABD above 0.75 gm/cc, AI based on ASTM D-5757 is less than 5 and average particle size is in the range of 80-100 microns.

3. The composition as claimed in claim 1, wherein said aluminium compound is selected from salts of aluminum.

4. The composition as claimed in claim 3, wherein said salts of aluminum are selected from the group comprising of aluminum nitrate, aluminum sulphate, alumina chloride, aluminum acetate and aluminum oxalate.

5. The composition as claimed in claim 4, wherein said salts of aluminum in-situ generates monobasic acid.

6. The composition as claimed in claim 5 wherein the monobasic acid varies from 1.5 to 2.9 moles per mole of aluminum phosphate binder.

Description

DESCRIPTION OF THE PRESENT INVENTION

(1) In general, aluminium phosphate solution prepared as per the prior art literature contains very high concentration of free acid such as mono-basic acid which is detrimental to catalyst activity. It is found, application of such aluminium phosphate as a binder though provides ABD to the catalyst, but due to presence of acid, it is found to be detrimental to catalyst and hence not suitable to be used in catalyst composition.

(2) Further, the catalyst which provides activity and selectivity towards light olefins, the ABD and AI resistance are found to be on the lower side. In order to ensure the catalyst retention in the process unit for a longer period, it is desirable to further increase the AI of the catalyst product.

(3) While the invention is susceptible to various modifications and/or alternative processes and/or compositions, specific embodiment thereof has been shown by way of example in the drawings and tables and will be described in detail below. It should be understood, however that it is not intended to limit the invention to the particular processes and/or compositions disclosed, but on the contrary, the invention is to cover all modifications, equivalents, and alternative falling within the spirit and the scope of the invention as defined by the appended claims.

(4) The graphs, tables, formulas, protocols have been represented where appropriate by conventional representations in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having benefit of the description herein.

(5) The following description is of exemplary embodiments only and is not intended to limit the scope, applicability or configuration of the invention in any way. Rather, the following description provides a convenient illustration for implementing exemplary embodiments of the invention. Various changes to the described embodiments may be made in the function and arrangement of the elements described without departing from the scope of the invention.

(6) Accordingly, the main embodiment of the present invention relates to an attrition resistant hydrocarbon cracking catalyst additive composition comprising an aluminium phosphate binder, wherein the aluminium phosphate binder is a reaction product of mono aluminium phosphate and an aluminium compound in the mole ratio of 1:1 to 1:2.5.

(7) In other embodiment, the present invention relates to an attrition resistant hydrocarbon cracking catalyst additive composition comprising an aluminium phosphate binder, wherein the aluminium phosphate binder contains 1.5 to 2.9 moles equivalent of monobasic acid for each mole of mono aluminium phosphate.

(8) In another embodiment, the present invention relates to an attrition resistant hydrocarbon cracking catalyst additive composition wherein said composition comprises of 10-70 wt % zeolite, 5-20 wt % colloidal silica, 10-60 wt % clay, 1-10 wt % phosphate and 1-15 wt % aluminium phosphate binder.

(9) In one another embodiment, said zeolite is selected from mordenite, ZSM-5, beta, ZSM-11 with silica alumina ratio ranging from 8 to 500.

(10) In further embodiment, said attrition resistant cracking catalyst additive has ABD above 0.75 gm/cc, AI based on ASTM D-5757 is less than 5 and average particle size in the range of 80-100 microns.

(11) In a preferred embodiment, said aluminium compound is selected from salts of alumina.

(12) In another embodiment, said salts of alumina are selected from the group comprising of alumina nitrate, alumina sulphate, alumina chloride, alumina acetate and alumina oxalate wherein said salts of alumina in-situ generates monobasic acid.

(13) In one another embodiment, said attrition resistant hydrocarbon cracking catalyst additive composition has LPG selectivity up to 27 wt %, propylene selectivity upto 8.9 wt %, at 5 wt % concentration in base catalyst.

(14) In further embodiment, the present invention relates to a process of preparation of attrition resistant cracking catalyst additive composition comprising: a) preparing a mono aluminum phosphate (MAP) by reacting the aluminium trihydrate slurry with desired amount of H.sub.3PO.sub.4 at 70-90 C. for the 1-3 h duration; b) preparing an aluminium phosphate binder by reacting the mono aluminium phosphate (MAP) prepared in step (a) with an aluminium compound in a mole ratio of 1:1 to 1:2.5; c) preparing phosphated zeolite slurry by adding di-ammonium hydrogen phosphate to zeolite; d) preparing clay-silica-alumina phosphate slurry by adding kaolin clay slurry and the aluminium phosphate binder solution of step (b) to ammonium polysilicate; e) preparing additive precursor slurry by adding the phosphated zeolite slurry of step (c) to the clay-silica-alumina phosphate slurry of step (d); and f) spray drying and calcining the additive precursor slurry of step (e) to obtain the additive composition.

(15) In one of the preferred embodiments, the present invention relates to a process for preparation of aluminium phosphate binder for an attrition resistant cracking catalyst additive comprising reacting mono-aluminium phosphate with aluminium compound wherein the monobasic acid derived from aluminium compound are present in ratio of 1.5 to 2.9 moles equivalent for each mole of mono-aluminium phosphate.

(16) In another embodiment, the present invention relates to a process for preparation of aluminium phosphate binder by reacting mono-aluminium phosphate with aluminium compounds wherein said aluminium compounds are selected from salts of alumina.

(17) In one of the preferred embodiments of the present invention, salts of alumina are selected from the group comprising of alumina nitrate, alumina sulphate, alumina chloride, alumina acetate and alumina oxalate.

(18) In another preferred embodiment of the present invention, salts of alumina are selected from the group consisting of alumina nitrate, alumina sulphate, alumina chloride, alumina acetate and alumina oxalate.

(19) In yet another embodiment, the present invention relates to process of preparation of aluminium phosphate binder by reacting mono-aluminium phosphate (MAP) with salts of alumina in the ratio of 1:1 to 1:2.5.

(20) In further embodiment, the present invention relates to aluminium phosphate binder for attrition resistant catalyst additive wherein said binder is prepared by reacting mono-aluminium phosphate with aluminium compounds with the proviso that the monobasic acid derived from the aluminium compounds are present in ratio of 1.5 to 2.9 moles equivalent for each mole of mono-aluminium phosphate.

(21) In a preferred embodiment, the zeolite used in preparation of attrition resistant cracking catalyst additive composition is selected from mordenite, ZSM-5, beta, ZSM-11 with silica alumina ratio ranging from 8 to 500. In the most preferred embodiment, the zeolite used in the catalyst additive composition is ZSM-5.

(22) In another preferred embodiment, the above said monobasic acid is derived from aluminium compounds such as salts of alumina selected from the group consisting of alumina nitrate, alumina sulphate, alumina chloride, alumina acetate and alumina oxalate.

(23) The process of the present invention provides a water soluble aluminium phosphate binder having a controller amount of mono-basic acid (up to 2.9 moles equivalent for each mole of mono-aluminium phosphate) which keeps aluminium phosphate bonder in free flowing liquid state.

(24) In another embodiment, the present invention relates to the attrition resistant cracking catalyst composition consisting of 10-70 wt % of zeolite, 5-20 wt % colloidal silica, 10-60 wt % clay, 1-15 wt % of aluminium phosphate binder and 1-10 wt % phosphate, wherein said aluminium phosphate binder is a reaction product of mono aluminium phosphate and an aluminium compound in the mole ratio of 1:1 to 1:2.5 with a proviso that for each mole of mono-aluminium phosphate there exists 1.5 to 2.9 moles equivalent of monobasic acid.

(25) In a preferred embodiment, a calculated amount of an ion radical in the form of salts of alumina (i.e. aluminium compounds) is added to the catalyst to ensure effective binding of catalyst as well as preserving catalyst activity with high selectivity towards olefins.

(26) It is observed that the selectivity of olefins (LPG) is found to be 26.96% in the present invention compared to 23.41% in the additive prepared by using process disclosed in U.S. Pat. No. 528,636.

(27) In another preferred embodiment, the zeolite catalyst used for preparation of attrition resistant catalyst is converted to phosphated zeolite slurry by combining the zeolite catalyst with phosphate source such as di-ammonium hydrogen phosphate in aqueous medium before adding it to the binder.

(28) In one of the preferred embodiments, the zeolite is selected from the source comprising of mordenite, ZSM-5, beta, ZSM-11 with silica alumina ratio ranging from 8 to 500.

(29) In further embodiment, the attrition resistant cracking catalyst additive composition can be used from 1-40 wt % with a base catalyst to produce LPG up to 27 wt % and up to 8.9 wt % of propylene.

(30) In a preferred embodiment, the composition of present invention has LPG selectivity up to 27 wt %, propylene selectivity up to 8.9 wt % at 5 wt % concentration in base catalyst.

(31) Further, the binder of the present invention allows loading of zeolite as high as 70 wt % at the same time maintaining attrition index. The proposed binder ensures smoother catalyst surface free of pits and cracks and the application of binder of this invention allows un-interrupted production of catalyst due to reduction in viscosity of catalyst precursor slurry which results in increase of catalyst throughput. Thus prepared binder has maximum of up to 2.9 moles of mono-basic acid against three moles per mole of mono-aluminium phosphate prepared by conventional method. Introduction of calculated amount of anion radical in the form of salts of aluminium will ensure effective binding of catalyst as well as preserving catalytic activity with high selectivity towards olefins.

(32) In the conventional method the aluminium phosphate is prepared using the aluminium nitrate and phosphoric acid as alumina and phosphate precursors. U.S. Pat. No. 5,194,412 to Roberie et. al. disclosed the following equation for preparation of aluminium phosphate:
Al(NO.sub.3).sub.3+H.sub.3PO.sub.4.fwdarw.AlPO.sub.4+3HNO.sub.3(1)

(33) In the present invention, aluminium phosphate binder is prepared by reacting mono aluminium phosphate with salts of alumina. The aluminium phosphate is prepared according to the following equation in the present invention:
Al(H.sub.2PO.sub.4).sub.3+2Al(NO.sub.3).sub.3+9H.sub.2O.fwdarw.3AlPO.sub.4+6HNO.sub.3+9H.sub.2O(2)

(34) The equation (2) indicates that as per present invention, 2.0 moles of monobasic acids are formed as byproduct for the preparation of each mole of aluminum phosphate binder. Contrary to this, in the prior art reference (U.S. Pat. No. 5,194,412), 3 moles of monobasic acids are formed as byproduct for each mole of aluminium phosphate binder, as shown in equation (1).

(35) As in the present invention, the ratio of MAP: alumina salts are varied in the range of 1:1 to 1:2.5, therefore the formation of the monobasic acid varies from 1.5 to 2.9 moles per mole of aluminium phosphate binder.

(36) The invention will now be explained with the help of following examples. However, the scope of the invention should not be limited to these examples as the person skilled in the art can easily vary the proportion of the ingredients and combinations.

(37) TABLE-US-00001 TABLE 1 Feed properties Sr No Attributes Unit Value 1 Density @ 15 C. g/cc 0.881 2 Kinematic Viscosity @ Cst 6.59 100 C. 3 Distillation, D-1160 4 IBP C. 311 5 5% C. 387 8 30% C. 430 9 50% C. 447 10 70% C. 470 11 Sulphur ppmw 300 1 Total N2 ppmw 47 13 CCR wt % 0.09

(38) Table 1 depicts the typical feed properties of a representative feed used in the refinery for FCC. The representative feed is used to evaluate the different additives under similar conditions.

EXAMPLES

Example-1

Additive Prepared as Per Example-7 of U.S. Pat. No. 7,517,827 and Increased Zeolite Content from 25 wt % to 40 wt %

(39) 98.63 gm of Pural SB grade alumina (having loss on ignition of 23.96 wt %) was made into a slurry with 425 gm of Demineralised (DM) water. The slurry was peptized with 21.52 gm of formic acid (85% concentration). 682.72 gm of ZSM-5 zeolite (loss on ignition 12.12 wt %) having silica to alumina molar ratio of 30 was made into a slurry with 700 gm of 10% ammonia solution followed by addition of 27.7 gm phosphoric acid (85%) to produce a zeolite slurry having pH of 7.8. 758.02 gm of kaolin clay (having loss on ignition 14.91 wt %) was made into a slurry with 800 gm DM water and kept under vigorous stirring while 191.53 gm of ortho-phosphoric acid (concentration 85 wt %) was added. Earlier prepared alumina gel and zeolite slurry were added to the clay-phosphate slurry one after another under vigorous stirring. Final slurry having a pH of about 2.9 was spray dried in a counter current spray drier having two fluid nozzles. Spray dried product was calcined at 550 C.

(40) Calcined additive showed ABD of 0.78 g/cc and ASTM D5757 attrition index of 12. The catalyst is then steam de-activated and evaluated in Advanced Cracking Evaluation R+ Micro Activity Test unit at 5 wt % concentration in base catalyst. Physical properties along with performance results are shown in Table 2 & 3.

Example-2

Preparation of Additive Using Aluminium Phosphate Binder as Per Example-2 of U.S. Pat. No. 5,286,369

(41) 83.41 gm of di-ammonium hydrogen phosphate (DAHP) was dissolved in 500 gm of DM water and 454.55 gm of ZSM-5 zeolite (loss on ignition 12 wt %) having silica to alumina molar ratio of 30 was added to it under stirring to form phosphated zeolite slurry having pH of 7.2. 399.62 gm of kaolin clay (having loss on ignition 14.92 wt %) was made into a slurry with 400 gm DM water and kept under vigorous stirring while 664.45 gm of aluminium phosphate prepared as per the method mentioned in the Example-2 of U.S. Pat. No. 5,286,369 was added followed by addition of 333.33 gm of ammonium poly-silicate to form clay-silica-alumina phosphate slurry. Earlier prepared phosphated zeolite slurry was added to clay-silica-alumina phosphate slurry under vigorous stirring to form final ZSM-5 precursor slurry. The final slurry having a pH of about 0.5 was spray dried in a counter current spray drier having two fluid nozzles. Spray dried product was calcined at 550 C.

(42) Calcined catalyst showed ABD of 0.79 g/cc and ASTM D5757 attrition index of 1.9. The catalyst is then steam de-activated and evaluated in Advanced Cracking Evaluation R+ Micro Activity Test unit at 5 wt % concentration in base catalyst. Physical properties along with performance results are shown in Table 2 & 3. Though the additive possess attrition index 1.9, but it shows inferior activity.

Example-3

Preparation of Mono-Aluminium Phosphate

(43) 223.94 gm of aluminium trihydrate (LOI=34 wt %) was dispersed in 380 gm of DM water to form alumina slurry then 1002.59 gm of phosphoric acid (85 wt %) was added to it to under stirring condition, while the mixture was maintained at a temperature of 70 C. and was kept for 1 hr to obtain clear solution of mono-aluminium phosphate. Solution was then cooled down to room temperature for use in additive preparation.

Example-4

Preparation of Additive Employing Mono-Aluminium Phosphate Prepared as Per Example-3

(44) 83.41 gm of di-ammonium hydrogen phosphate (DAHP) was dissolved in 500 gm of DM water and 454.55 gm of ZSM-5 zeolite (loss on ignition 12 wt %) having silica to alumina molar ratio of 30 was added to it under stirring to form phosphated zeolite slurry having pH of 7.2. 399.62 gm of kaolin clay (having loss on ignition 14.92 wt %) was made into a slurry with 400 gm DM water and kept under vigorous stirring while 174.31 gm of mono-aluminium phosphate (LOI=42.63) as prepared under Example-3 was added followed by addition of 333.33 gm of ammonium poly-silicate to form clay-silica-alumina phosphate slurry. Earlier prepared phosphated zeolite slurry was added to clay-silica-alumina phosphate slurry under vigorous stirring to form final ZSM-5 precursor slurry. The final slurry having a pH of about 0.7 was spray dried in a counter current spray drier having two fluid nozzles. Spray dried product was calcined at 550 C.

(45) Calcined additive has ABD of 0.65 g/cc and ASTM D5757 attrition index of 3.9. The additive is then de-activated and evaluated in Advanced Cracking Evaluation R+ Micro Activity Test unit at 5 wt % concentration level along with base catalyst. Physical properties along with performance results are shown in Table 2 & 3. The additive shows lower activity.

Example-5

Preparation of Aluminium Phosphate Binder Based on Mono-Aluminium Phosphate (MAP) Prepared as Per Example-3 where the Mole Ratio of MAP: Al(NO3)3.9H2O is 1:1

(46) 799.9 gm of mono-aluminium phosphate (LOI=42.63) as prepared under Example-3 was diluted with 310 gm of DM water and then 552.14 gm of Al(NO.sub.3).sub.3.9H.sub.2O was added under stirring to it and kept for 30 min to form aluminium phosphate binder solution.

Example-6

Preparation of Additive Using Aluminium Phosphate Binder Prepared as Per Example-5

(47) 83.41 gm of di-ammonium hydrogen phosphate (DAHP) was dissolved in 500 gm of DM water and 454.55 gm of ZSM-5 zeolite (loss on ignition 12 wt %) having silica to alumina molar ratio of 30 was added to it under stirring to form phosphated zeolite slurry having pH of 7.2. 399.62 gm of kaolin clay (having loss on ignition 14.92 wt %) was made into a slurry with 400 gm DM water and kept under vigorous stirring while 328.41 gm of aluminium phosphate (LOI=69.55) as prepared under Example-5 was added followed by addition of 333.33 gm of ammonium polysilicate to form clay-silica-alumina phosphate slurry. Earlier prepared phosphated zeolite slurry was added to clay-silica-alumina phosphate slurry under vigorous stirring to form final ZSM-5 additive precursor slurry. The final slurry having a pH of about 0.6 was spray dried in a counter current spray drier having two fluid nozzles. Spray dried product was calcined at 550 C. Calcined additive has ABD of 0.68 g/cc and ASTM D5757 attrition index of 3.5. The additive is then de-activated and evaluated in Advanced Cracking Evaluation R+ Micro Activity Test unit at 5 wt % concentration level along with base catalyst. Physical properties along with performance results are shown in Table 2 & 3. The additive shows lower activity.

Example-7

Preparation of Aluminium Phosphate Binder Based on Mono-Aluminium Phosphate (MAP) Prepared as Per Example-3 where the Mole Ratio of MAP: Al(NO3)3.9H2O is 1:2

(48) Aluminium nitrate solution prepared by dissolving 716.53 gm of Al(NO.sub.3).sub.3.9H.sub.2O in 310 gm of DM water was added to 519.09 gm of mono-aluminium phosphate (LOI=42.63) as prepared under Example-3 under stirring and kept for 30 min to form ready to use aluminium phosphate binder of present invention.

Example-8

Preparation of Additive Using Aluminium Phosphate Binder Prepared as Per Example-7 of Current Invention

(49) 399.62 gm of kaolin clay (having loss on ignition 14.92 wt %) was made into a slurry with 400 gm DM water and kept under vigorous stirring while 430.48 gm of aluminium phosphate (LOI=76.77) as prepared under Example-7 was added followed by addition of 333.33 gm of ammonium polysilicate to form clay-silica-alumina phosphate slurry. To clay-silica-alumina phosphate slurry, 1038 gm of phosphate zeolite prepared similar to procedure of Example-2 was added under vigorous stirring to form final ZSM-5 precursor slurry. The final slurry having a pH of about 0.5 was spray dried following the procedure of example-1. The green catalyst was calcined. Calcined additive has ABD of 0.78 g/cc and ASTM D5757 attrition index of 2.9. The additive is then steam de-activated and evaluated in Advanced Cracking Evaluation R+ Micro Activity Test unit at 5 wt % concentration level along with base catalyst. Physical properties along with performance results are shown in a Table 2A & 2B. The additive shows higher activity towards production of LPG.

Example-9

Preparation of Aluminium Phosphate Binder Based on Mono Aluminium Phosphate (MAP) Prepared as Per Example-3 where the Mole Ratio of MAP: Al(NO3)3.9H2O is 1:2.5

(50) Aluminium nitrate solution prepared by dissolving 761.94 gm of Al(NO.sub.3).sub.3.9H.sub.2O in 310 gm of DM water was added to 441.52 gm of mono-aluminium phosphate (LOI=42.63) as prepared under Example-3 under stirring and kept for 30 min to form ready to use aluminium phosphate binder of present invention.

Example-10

Preparation of Additive Employing Aluminium Phosphate Binder Prepared as Per Example-9 of Current Invention

(51) The catalyst was prepared similar to the Example-8 and evaluated except binder, employing 475.29 gm of binder (LOI=78.96) of Example-9. Calcined additive has ABD of 0.77 g/cc and ASTM D5757 attrition index of 3.1. The additive is then de-activated and evaluated in Advanced Cracking Evaluation R+ Micro Activity Test unit at 5 wt % concentration level along with base catalyst. Physical properties along with performance results are shown in Table 2 & 3. The additive shows higher activity towards production of LPG.

Example-11

Preparation of Additive as Per Example-8 by Replacing ZSM-5 with Beta Zeolite Having Si/Al Mole Ratio 20

(52) Calcined additive has ABD of 0.75 g/cc and ASTM D5757 attrition index of 3.5.

(53) TABLE-US-00002 TABLE 2 Additive composition and their physical properties prepared as per Example-1 to 11 Example-1 Prepared as per U.S. Pat. No. 7,517,827 Example 2 Example 4 Example 6 Example 8 Example 10 Example 11 Binder AlPO4, wt % 0 10 (Prepared 10 (Prepared 10 (Prepared 14 (Prepared 10 (Prepared 10 (Prepared as per U.S. Pat. as per as per as per as per as per No. 5,286,369) Example 3) Example 5) Example 7) Example 9) Example 7) PSB Alumina 5 0 0 0 0 0 0 ZSM-5 Zeolite, wt % 40 40 40 40 40 40 0 Beta zeolite 0 0 0 0 0 0 40 Clay, wt % 43 34 34 34 34 34 34 H.sub.3PO.sub.4 (as PO.sub.4), wt % 12 0 0 0 0 0 0 (NH.sub.4).sub.2HPO.sub.4 as PO.sub.4. Wt % 0 6 6 6 6 6 6 SiO.sub.2 0 10 10 10 10 10 10 ABD, gm/cc 0.78 0.79 0.65 0.68 0.78 0.77 0.75 Attrition Index, ASTM 12 1.9 3.9 3.5 2.9 3.9 3.5 D5757

(54) TABLE-US-00003 TABLE 3 Performance results of additive prepared as per Example-1 to 10 Base Catalyst + Base Catalyst + Base Catalyst + Base Catalyst + Base Catalyst + Base Catalyst + 5 wt % Additive 5 wt % Additive 5 wt % Additive 5 wt % Additive 5 wt % Additive 5 wt % Additive of Example-1 of Example-2 of Example-4 of Example-6 of Example-8 of Example-10 Cat/oil 6.87 6.87 6.87 6.87 6.87 6.87 220 C. Conversion, 78.50 78.63 79.06 79.53 79.63 79.60 wt % Coke 3.48 3.35 3.55 3.49 3.41 3.41 DG 1.78 1.77 1.78 1.80 1.79 1.79 LPG (including 24.99 23.41 23.91 24.33 26.46 26.96 propylene) Propylene 8.24 7.60 7.84 7.95 8.73 8.90 Gasoline (C5-160 C.) 38.55 40.05 40.27 40.19 38.82 38.29 HN (160-220 C.) 9.70 10.05 9.55 9.72 9.15 9.15 LCO (220-360 C.) 14.63 14.85 14.49 14.12 14.10 14.10 Bottom (370 C.+) 6.87 6.52 6.45 6.35 6.27 6.30
Table 2 depicts the physico-chemical properties of different additive formulations. As mentioned earlier ABD and AI of the sample prepared in example 2 (U.S. Pat. No. 528,636) is better than that of additive prepared in the present invention. The additive given in example 2 is prepared using aluminium nitrate as alumina precursor that results into production of excess of HNO.sub.3 (3 moles per mole of aluminium phosphate binder). This destabilizes the ZSM-5 zeolite structure and deactivates during the preparation as well as equilibration. The above fact can be represented using the following equation.
Al(NO.sub.3).sub.3+H.sub.3PO.sub.4.fwdarw.AlPO.sub.4+3HNO.sub.3

(55) Table 3 clearly reflects the deactivation of ZSM-5 additive wherein LPG yield using example 2 is 23.41% vis-a-vis 26.96% for the additive formulation of the present invention.

(56) Calculated amount of aluminium nitrate is added during the preparation of aluminium phosphate binder and amount nitric acid (by-product) is controlled. This methodology is optimized in a way that the additive formulation will have better attrition index (ASTM D-5757)<5 and ABD>0.75 gm/cc and at the same time deactivation ZSM-5 zeolite is controlled. In a nutshell, the customized binder used in the present invention attains the desired physico-chemical properties and also retains the catalytic activity with high selectivity towards olefins.