Process for production of high octane gasoline from straight run light naphtha on Pt containing HZSM - 5 molecular sieve catalyst

Abstract

The present invention relates to a process for the production of high-octane gasoline from straight run light naphtha on Pt containing HZSM-5 molecular sieve catalyst. The preparation of the catalyst for the process does not involve the steps of steaming and acid leaching before the actual catalytic application. The mentioned catalyst is environmentally friendly as the preparation does not involve the use of hazardous mineral acids, viz., HCl, HNO3 etc.

Description

FIELD OF THE INVENTION

[0001] The present invention relates to a process for the production of high-octane gasoline from straight run light naphtha on Pt containing HZSM-5 molecular sieve catalyst. More particularly the present invention relates to a process for the utilization of straight run light naphtha feedstock available from various refineries, into value added aromatics with low amounts of benzene which can be used as blending stocks for improvement of octane number in gasoline fuel. In addition to high-octane gasoline liquid product, some amounts of gas by-product are also obtained which can be used as domestic fuel (LPG).

BACKGROUND OF THE INVENTION

[0002] The fast growing automobile population as well as increasing pressure from environmental legislators has resulted in demand for good quality gasoline in the country. The focal point for the improvement of gasoline quality, at present is centered around benzene content of 5% (V/V) with already lead free gasoline available in India (Ref. Report of Sub-group on the Refining for IXth plan 1996). It is stated that some of the refiners will be unable to meet the specification of benzene leading to gasoline production loss. To address the benzene problem in gasoline it is suggested to increase IBP of reformer feed by adjusting naphtha splitter cut point which leads to substantial loss in gasoline production volume and increased quantities of light naphtha. As a result increasing interest is shown in the development of new catalysts and processes, which allow production of gasoline with sufficiently high octane numbers, making use of unconventional low value feed stock such as light naphtha into standard gasoline production. In addition to this, the demand for LPG is also growing much faster in India at growth rate of 12 to 13 percent per year. The corresponding deficit of LPG in 2000-01 is 4 million tons and expected to increase up to 7.8 million tons by the year 2010-2011 (Sundar Rajan Committee Report on Hydrocarbon perspective 1996, Ref LPG News of India, March '96, p 17).

[0003] Light naphtha is one of the least viable petroleum feed stocks treated today. Projected production of straight run light naphtha cut (IBP-130) other than catalytic reforming feed in India indicates 1-1.25 MMTPA (million metric tons) of light naphtha is available from various refineries in 1996-97. Light naphtha mainly contains C5 and C6 hydrocarbons (30 to 40 wt %) depending upon the source. Due to high percentage of n-paraffins in light naphtha it has lower research octane number (RON) and high RVP (Reid Vapour Pressure) due to n- and i-pentanes, hence it cannot be used directly for gasoline blending. Thus, the conversion of light naphtha into other petroleum and petrochemical products gains significance in this scenario.

[0004] Conventionally, gasoline is being produced from the Catalytic reforming process of naphtha and Fluid catalytic cracking units from various refineries. The indigenous gasoline production by refineries with low benzene content will be inadequate to meet the demands in future like at present. The catalyst used for reforming process is monometallic Pt/Al2O3 or PtRe/Al2O3 bimetallic catalyst. Although these processes are used all over the world, there are number of limitations in the use of these catalysts. The conventional catalyst is not effective in promoting aromatization of light naphtha rich in C5 hydrocarbons. The catalyst is also not very effective in promoting the aromatization of straight chain paraffins such as n-hexane and n-heptane present in the feed that remain unconverted. On the other hand, LPG production either from refineries or from gas fields is not enough to meet the demands. The import situation is also not encouraging, as only a few private entrepreneurs have actually created facilities for import market. Therefore the increasing demand for good quality gasoline and increasing gap between LPG deficit and import capacity also indicates the need to develop novel processes for the production of gasoline as well as LPG from cheaply available feed stocks, viz., light naphtha.

[0005] There are reports in the literature on the conversion of these straight chain paraffins into aromatics, using zeolites and metal-doped zeolites as catalyst.

[0006] Reference is made to a process developed by Mobil researchers (Ind. Eng. Chem. Process. Design Dev., 25 (1986) wherein the preparation of aromatics from variety of feedstock such as pyrolysis gasoline, unsaturated gases from catalytic cracker, paraffinic naphtha and LPG have been described. Reference is also made to (Patent of Russia Federation No 1141704, Appl. 17.06.1983) wherein method of producing gasoline fractions from gas condensate over HZSM-5 catalyst has described. The limitation of this process is that it utilizes long range naphtha (80-180° C.) which is also a feedstock for catalytic reforming unit.

[0007] Reference is made to (Hydrocarbon Processing September 1989 p 72) wherein a process developed jointly by UOP Inc. and British Petroleum based on gallium doped zeolite catalyst has been reported. In this process LPG was converted into BTX aromatics and the process has been demonstrated in a large-scale pilot plant of the British Petroleum Grangemouth refinery in Scotland. Reference is also made to U.S. Pat. No. 5,026,938 dated 25 Jun. 1991 wherein a process for converting a gaseous feed stock containing C3-C5 paraffins into aromatics hydrocarbons by contacting the feed with gallosilicate molecular sieve catalyst has been described.

[0008] The draw back of all these processes is that these are mainly related to the production of aromatics from paraffins of C3-C5 range which are in high demand as LPG in India.

[0009] Reference is made to U.S. Pat. No. 5,125,415, dated June 1992 wherein the use of Pt—Sn-ZSM-5 catalyst for the production of mono-alkyl aromatics from C8 n-paraffins containing feed stocks has been described. The limitation of the above process is production of xylenes from C6-C8 hydrocarbons. Reference is also made to Indian Patent Application No. 010/DEL/2001 dated May 1, 2001 wherein a process for the conversion of natural gas liquid (NGL) into liquefied petroleum gas (LPG) and high-octane gasoline over modified ZSM-5 zeolite has been reported. The limitation of above process is that zeolite catalyst was modified by steaming method and it produces more LPG (55 wt %) than aromatics (22 wt %).

[0010] Reference is made to Indian Patent Application No. 2627/DEL/96-dated 29 Nov. 1996 wherein a process for the preparation of a novel modified ZSM-5 zeolite has been reported. In this process zeolite catalyst was modified by steaming method followed by acid leaching to remove the extra framework alumina.

[0011] The limitations of the above process are firstly formation of high quantity (8-12 wt %) of dry gas (C1+C2) during the n-heptane conversion which will be a loss to the economy of the process. Secondly the preparation of ZSM-5 catalyst in this process involves acid leaching step which involves the use of hazardous mineral acids viz. HCl.

OBJECTS OF THE INVENTION

[0012] The main object of the invention is to provide a process for the production of high-octane gasoline from straight run light naphtha on platinum containing HZSM-5 molecular sieve catalyst, which obviates the drawbacks as detailed above.

[0013] Another object of the invention is to provide a process for the conversion of light naphtha into high octane low benzene content unleaded gasoline as a blender to boost the octane number along with LPG as by product by using a catalyst system containing platinum supported ZSM-5 zeolite composite.

[0014] Another object of the present invention is to provide a process for the preparation of platinum metal modified ZSM-5 zeolite catalyst by impregnation method with out acidity modification by steaming and acid leaching steps.

[0015] Yet another object of the invention is to provide a process, which utilizes the straight run light naphtha containing up to 35 hydrocarbon components for the production of high-octane gasoline unlike the other existing processes.

[0016] Still another object of invention is to convert C5-C7 paraffinic and C6-C8 naphthenic components efficiently to produce high-octane gasoline.

[0017] Another object of invention is to provide a process that produces in addition to n-paraffinic and naphthenic components, isoparaffins; benzene and other aromatics present in the feed also can be effectively converted to give high octane gasoline with low benzene content and LPG.

SUMMARY OF THE INVENTION

[0018] Accordingly the present invention provides a process for the production of high-octane gasoline from straight run light naphtha over a Pt containing HZSM-5 molecular sieve catalyst which comprises

[0019] i) impregnating 0.1-2.0% wt % of Pt from tetramine platinum chloride on a HZSM-5 zeolite extrudate,

[0020] ii) drying the zeolite extrudate followed by calcination,

[0021] iii) loading the Pt impregnated zeolite extrudate in a high pressure reactor and reducing it

[0022] iv) cooling the Pt impregnated zeolite bed and then increasing the bed temperature

[0023] v) passing light naphtha through the bed to obtain a mixture of high octane gasoline and LPG and separating the high octane gasoline from the mixture.

[0024] In one embodiment of the invention, in step (ii) the zeolite extrudate is dried at a temperature of about 110° C. and for a period of 10-12 hrs and then calcined at a temperature in the range of 400-600° C. for a period of 1-4 hrs in static air.

[0025] In another embodiment of the invention, the treated Pt impregnating zeolite extrudate is reduced inside the high pressure reactor in step (iii) by passing hydrogen for a period in the range of 2-5 hours at a temperature in the range of 400-500° C. and at a flow rate in the range of 8-12 l/h into the reactor.

[0026] In yet another embodiment of the intention, in step (iv) the Pt impregnated zeolite bed is first cooled to a temperature of about 300° C. under nitrogen atmosphere and the bed temperature thereafter increased to a range of 300-600° C.

[0027] In a further embodiment of the invention, in step (v) of the process, light naphtha is passed through the bed at a weight hourly space velocity in the range of 1 to 8 hrs−1 and at a pressure in the range of 1 to 25 kg/cm2 and in the absence of nitrogen.

[0028] In another embodiment of the invention the light naphtha feedstock comprises light naphtha containing C6 to Cg range paraffins and naphthenes.

[0029] In another embodiment of the invention the reaction temperature is in the range of 400-500° C.

[0030] In yet another embodiment of the invention the pressure is in the range of 1-10 kg/cm2.

[0031] In another embodiment of the invention the weight hourly space velocity of light naphta is in the range of 2-8 hrs−1.

[0032] In another embodiment of the invention the Research Octane Number (RON) of straight light naphtha fraction is increased from 64 to 97 in the product with gain of 34 units.

[0033] In another embodiment of the invention the platinum impregnated ZSM-5 zeolite composite used is prepared by incipient wetness method.

[0034] In another embodiment of the invention the catalyst used is regenerated by oxidative combustion.

[0035] In another embodiment of the invention the total amount of platinum metal added into HZSM-5 molecular sieve is in the range of 0.1 to 1.1 wt %.

[0036] In another embodiment of the invention the catalyst used results in the reduction of the sulfur content in light naphtha feed stock from 50 ppm level sulfur to 10 ppm level sulfur in the obtained product.

[0037] In another embodiment of the invention the pressure is varied to in order to increase the aromatic content and decrease the LPG in product mixture.

DETAILED DESCRIPTION OF THE INVENTION

[0038] In the present invention, preparation of the catalyst for the process does not involve the steps of steaming and acid leaching before the actual catalytic application. The mentioned catalyst is environmentally friendly as the preparation does not involve the use of hazardous mineral acids, viz., HCl, HNO3 etc.

[0039] The detailed steps of the process are:

[0040] About 18 cc of the catalyst (13 g) in extruded form of 1.5 to 2 mm diameter is loaded in a fixed bed, down flow, high pressure reactor. Before the test runs, the catalyst is reduced at 450° C. with H2 gas for 4 hours with flow rate of 10 l/h. It is cooled down to 300° C. in N2 flow and heated again to desired reaction temperature. The light naphtha is pumped by plunger type feed pump and N2 flow was stopped totally. Reactor effluents are cooled before being fed to high-pressure separator. The vapors from separator are purged, while the liquid phase is sent to stabilizer column.

[0041] Regeneration of the deactivated catalyst in reactor is carried out by conventional procedure using air and nitrogen mixture. The liquid product is analyzed using a gas Chromatograph fitted with Tetra Cyano Ethoxy Propionitrile column and FID detector. The gaseous products are analyzed using Squalane column.

[0042] The process conditions controls the C1+C2 (dry gas) yield, which is not desired in the gasoline process. In order to reduce the duration of regeneration of the catalyst thereby to improve the catalyst life against the coke lay down, 0.4 wt % of platinum metal is doped on HZSM-5 catalyst. The process can operate for maximization of LPG as well by simply altering process parameters. The catalyst used in present process is a novel platinum supported HZSM-5 zeolite in which parent ZSM-5 zeolite composite was procured from Zeolyst international (Lot No. 1822-43). The zeolite to binder ratio of HZSM-5 extrudates was 80:20. These extrudates were impregnated with 0.4 wt % of Pt from tetraamine platinum chloride (Aldrich) solution. These extrudates were oven dried at 110° C. for 12 hrs and then processed to calcination at 500° C. for 3 hrs in static air.

[0043] The Physico-chemical properties of the zeolite catalyst are as follows:

[0044] Characteristics of Parent HZSM-5:

[0045] Si—Al ratio (SAR): 100; XRD Crystallinity: 99%; Catalyst: Pt/HZSM-5; Shape: Cylindrical form; Diameter: 1.5-2.0 mm; Bulk Density: 0.7-0.75 gm/cc; BET Surface Area: 350400 m2/g.

[0046] The composition of straight run light naphtha used in this process has been analyzed by GC is shown below.

[0047] Light naphtha Feed Composition (wt %): 1 Carbon No. n-paraffin i-paraffin Naphthenes Aromatics C4 0.4 0.1 — — C5 4.5 5.5  1.5 — C6 4.7 7.2 11.5 2.3 C7 5.0 7.5 21.5 5.9 C8 4.0 3.6 11.5 3.2

[0048] The following examples are given by way of illustration and therefore should not be construed to limit the scope of the present invention.

EXAMPLE—1

[0049] This example describes the characteristics of the high-octane gasoline liquid product and LPG obtained in the present process from light naphtha feed stock. Yields of individual product components that are obtained are given. Analysis is based on GC fitted with Tetra Cyano Ethoxy Propionitrate column and FID detector. 2 TABLE 1 Characteristics of Feed and Liquid Products of this process Process conditions: Catalyst: Pt/HZSM-5; Feed: light naphtha of Numaligharh refinery; Reaction Temperature: 450° C.; Pressure: 3 kg/cm2; WHSV: 6 hr−1; TOS: 24 hrs; Reactor: Micro Reactor of 25 gm-catalyst capacity. Light naphtha Liquid Component Feed (wt %) Product (wt %) Dry Gas 0 1.0 LPG (C3 + C4) 0 13.5 Total Paraffins* 42.6 11.3 Total Aromatics 11.4 60.0 Benzene content 2.3 8.6 Density of the Liquid (g/cc) 0.7230 0.7498 Research Octane No. (RON) 64.4 97.4 Sulphur (ppm) 43.3 10.2 RVP of liquid (kPa at 38° C.) 41.2 67.6 Existent gum (g/m3) — 17.0 Potential gum (g/m3) — 89.0 Distillation a. Initial Boiling Point(° C.) 44.1 46.3 b. Recovery up to 70° C.(% vol) 20.0 20.0 c. recovery up to 100° C. 70.0 50.0 d. recovery up to 180° C. nil 95.0 e. Final boiling point(° C.) 132.4 210.5 f. Residue (% vol) 1.2 3.3 *excluding C6-C8 naphthenes of 46 wt %

[0050] Table 1 shows conversion of light naphtha feed stock having RON of 64 into aromatics rich (60%) liquid product with low benzene content having RON 97.4. 85 wt % of high-octane gasoline was produced from low value feedstock, which also met environmental regulations on gasoline in terms of low benzene content and low sulphur level.

EXAMPLE—2

[0051] This example illustrates the results of effect of temperature on product distribution of aromatics (BTX) in liquid product, LPG and dry gas. Gaseous and liquid products were analyzed by same method mentioned in example 1. 3 TABLE 2 Effect of Temperature on Product Yields Process conditions: Catalyst: Pt/HZSM-5; Feed: light naphtha; Pressure: 20 kg/cm2; WHSV: 6 hr−1; TOS: 24 hrs Temperature (° C.) 400 450 500 Ex-reactor yield (Wt % based on the feed) Dry gas 2.5 2.0 3.5 LPG 24.4 21.5 31.6 C3 14.4 14.1 20.9 C4 10.0 7.4 10.6 C5-C8 (Sat) 51.6 50.5 13.6 Aromatics (BTX) 16.4 20.8 43.4 C9+ 5.1 5.2 7.9 RON 80.0 90.4 9

[0052] Table-2 shows that yield of aromatics (BTX) increases with increase of temperature and optimum temperature for the present process was chosen as 450° C. due to formation of less coke during reaction.

EXAMPLE—3

[0053] This example includes results of effect of pressure on yields and composition of aromatics and LPG. The product analysis is presented in table-3. 4 TABLE 3 Effect of Pressure on Product Yields Process conditions: Catalyst: Pt/HZSM-5; Feed: Straight run light naphtha; Temperature: 450° C.; WHSV: 6 hr−1; TOS: 24 hrs Pressure (kg/cm2) 20 3 Ex-Reactor Yields (Wt % based on the feed) Dry gas 2.0 1.0 LPG 21.5 13.5 C3 14.1 8.0 C4 7.4 5.5 C5-C8 (Sat) 50.5 21.7 Aromatics (BTX) 20.8 60.0 C9+ 5.2 3.8 RON 90.4 97.4

[0054] The experimental results reported in table-3 shows that the decrease of pressure increases the BTX production with decrease in yields of LPG. The optimum pressure for this process was fixed at 3 Kg/cm2 due to more aromatic formation.

EXAMPLE —4

[0055] This example illustrates effect of weight hourly space velocity on yield and composition of high-octane gasoline and LPG. The product analysis presented in Table-4. 5 TABLE 4 Effect of Weight Hourly Space Velocity on Product Yields Process conditions: Catalyst: Pt/HZSM-5; Feed: Straight run light naphtha; Temperature: 450° C.; Pressure: 3 kg/cm2; TOS: 24 hrs WHSV (hr−1) 6.0 2.0 Ex-Reactor Yields (Wt % based on the feed) Dry gas 1.0 1.3 LPG 13.5 38.4 C3 8.0 22.1 C4 5.5 16.3 C5-C8 (Sat) 21.7 11.8 Aromatics (BTX) 60.0 37.4 C9+ 3.8 11.1 RON 97.4 94.8

[0056] From the above table-4, it is shown that the increase of WHSV to 6 decreases the LPG yield and increases aromatic yields with similar dry gas yields.

EXAMPLE —5

[0057] This example illustrates effect of run length on product yield viz. BTX, LPG and their composition. In run length of 24 hrs, product was analyzed at various intervals and results are presented in table-5. 6 TABLE 5 Catalyst Stability Studies Process conditions: Catalyst: Pt/HZSM-5; Feed: Straight run light naphtha; Temperature: 450° C.; WHSV: 6.0 hrs−1; Pressure: 3 Kg/cm2 Time (hrs on - stream) 8 16 24 Ex-Reactor Yields (Wt % based on the feed) Dry gas 1.5 0.9 1.0 LPG 27.2 20.7 13.5 C3 16.1 12.6 8.0 C4 11.0 8.1 5.5 C5-C8 (Sat) 15.5 22.3 21.7 Aromatics (BTX) 47.4 50.9 60.0 Benzene 4.5 7.2 8.6 Toluene 16.5 21.3 25.7 Xylene + EB 26.4 22.4 25.7 C9+ 8.4 5.2 3.8 RON 84.0 90.0 97.4 Total 100 100 100

[0058] Table-5 shows consistent yield patterns of BTX in Liquid product and decrease in yields of LPG at WHSV of 6 hrs−1 persists over the run length of 24 hrs.

EXAMPLE—6

[0059] This example explains the effect of catalyst regeneration on the product yields in the present process of high-octane gasoline production from light naphtha. The products yield patterns before and after the regeneration was given in the table-6. 7 TABLE 6 Reproducibility of the Ex-reactor yields before and after the Regeneration Process Process conditions: Catalyst: Pt/HZSM-5; Feed: light naphtha; TOS: 24 hrs; Reaction Temperature: 400° C.; Pressure: 20 kg/cm2; WHSV: 6 hr−1 Process Performance Before Regeneration After Regeneration Ex-Reactor Yields (Wt % based on the feed) Dry gas 0.5 0.4 LPG 12.5 10.9 C3 7.2 6.0 C4 5.3 4.9 C5-C8 (Sat) 76.1 78.5 Aromatics (BTX) 10.7 10.0 C9+ 0.2 0.2 RON 80.0 78.6 Total 100 100

[0060] Table-6 shows the similar yield patterns of BTX aromatics in liquid product and LPG in both before and after the regeneration of the catalyst indicating the complete removal of coke lay down during the reaction.

[0061] The main advantages of the present invention are:

[0062] 1. The process of the present invention converts all types of hydrocarbon components present in the light naphtha feed viz. Paraffins, isoparaffins, naphthenes and benzene into aromatic hydrocarbons, isoparaffinic and LPG, at high selectivity with single catalyst system.

[0063] 2. Light naphtha, which does not have potential use as conventional reformer feed stock, can be used as a feed in this process.

[0064] 3. The catalyst used in this process is ecofriendly and it does not involve acid leaching with hazardous mineral acids such as HCl during preparation.

[0065] 4. The catalyst used in this process reduces dry gas yields to 2 wt % with increase of high-octane liquid product and thereby improves the economics of this process.

[0066] 5. LPG, which is a by-product in the present process, can meet the industrial and domestic demands.

[0067] 6. The process does not require hydrogen during feed cut in.

[0068] 7. The process also does not require use of corrosive organic chloride additives.

[0069] 8. The high-octane liquid a major product obtained in the process can be used as a gasoline blender to boost octane number.

[0070] 9. This process is economically profitable and depending on the capital investment the pay back period will be 1.5 to 3 years.

[0071] 10. The process maintains constant production of high-octane gasoline pool by utilization of light naphtha from reformate.

[0072] 11. The catalyst can desulphurize the synthesized gasoline to 10 ppm from 50 ppm of light naphtha feed.

Claims

1. A process for the production of high-octane gasoline from straight run light naphtha over a Pt containing HZSM-5 molecular sieve catalyst which comprises

(i) impregnating 0.1-2.0 wt % of Pt from tetramine platinum chloride on a HZSM-5 zeolite extrudate,

(ii) drying the zeolite extrudate followed by calcination,

(iii) loading the Pt impregnated zeolite extrudate in a high pressure reactor and reducing it

(iv) cooling the Pt impregnated zeolite bed and then increasing the bed temperature

(v) passing light naphtha through the bed to obtain a mixture of high octane gasoline and LPG and separating the gasoline from the mixture.

2. A process as claimed in claim 1 wherein in step (ii) the zeolite extrudate is dried at a temperature of about 110° C. and for a period of 10-12 hrs and then calcined at a temperature in the range of of 400-600° C. for a period of 1-4 hrs in static air.

3. A process as claimed in claim 1 wherein the treated Pt impregnating zeolite extrudate is reduced inside the high pressure reactor in step (iii) by passing hydrogen for a period in the range of 2-5 hours at a temperature in the range of 400-500° C. and at a flow rate in the range of 8-12 l/h into the reactor.

4. A process as claimed in claim 1 wherein in step (iv) the Pt impregnated zeolite bed is first cooled to a temperature of about 300° C. under nitrogen atmosphere and the bed temperature thereafter increased to a range of 300-600° C.

5. A process as claimed in claim 1 wherein in step (v) of the process, light naphtha is passed through the bed at a weight hourly space velocity in the range of 1 to 8 hrs−1 and at a pressure in the range of 1 to 25 kg/cm2 and in the absence of nitrogen.

6. A process as claimed in claim 1 wherein the light naphtha feedstock comprises light naphtha containing C6 to C8 range paraffins and naphthenes.

7. A process as claimed in claim 1 wherein the reaction temperature is in the range of 400-500° C.

8. A process as claimed in claim 1 wherein the reaction pressure is in the range of 1-10 kg/cm2.

9. A process as claimed in claim 1 wherein the weight hourly space velocity of light naphta is in the range of 2-8 hrs−1.

10. A process as claimed in claim 1 wherein the Research Octane Number (RON) of straight light naphtha fraction is increased from 64 to 97 in the product with gain of 34 units.

11. A process as claimed in claim 1 wherein the platinum impregnated ZSM-5 zeolite composite used is prepared by incipient wetness method.

12. A process as claimed in claim 1 wherein the catalyst used is regenerated by oxidative combustion.

13. A process as claimed in claim 1 wherein the total amount of platinum metal added into HZSM-5 molecular sieve is in the range of 0.1 to 1.1 wt %.

14. A process as claimed in claim 1 wherein the catalyst used results in the reduction of the sulfur content in light naphtha feed stock from 50 ppm level sulfur to 10 ppm level sulfur in the obtained product.

15. A process as claimed in claim 1 wherein the pressure is varied to in order to increase the aromatic content and decrease the LPG in product mixture.

16. A process for the production of high-octane gasoline from straight run light naphtha on Pt containing HZSM-5 molecular sieve catalyst which comprises

(i) impregnating 0.1-2.0 wt % of Pt from tetramine platinum chloride on HZSM-5 zeolite extrudate,

(ii) drying the zeolite extrudate at a temperature of about 110° C. for a period of 10-12 hrs followed by calcination at a temperature of 400-600° C. for a period of 1-4 hrs in static air,

(iii) loading the treated Pt impregnated zeolite extrudate in a high pressure reactor and reducing it by passing of hydrogen for a period of 2-5 hours at a temperature of 400-500° C. at a flow rate of 8-12 l/h into the reactor

(iv) cooling the Pt impregnated zeolite bed to a temperature of about 300° C. under nitrogen atmosphere and increasing thereafter further bed temperature to 300-600° C.

(v) passing light naphtha through the bed at weight hourly space velocity ranging from of 1 to 8 hrs−1 at a pressure in the range of 1 to 25 kg/cm2 in the absence of nitrogen to obtain a mixture of high octane gasoline and LPG and separating the gasoline from the mixture.