Title of Invention	"A PROCESS FOR THE CONVERSION OF NATURAL GAS LIQUID TO LIQUEFIED PETROLEUM GAS AND HIGH OCTANE GASOLINE"
Abstract	A process for the conversion of natural gas liquid to liquefied petroleum gas and high octane gasoline by contacting natural gas liquid as feed stock containing hydrocarbon having carbon atoms in the range of C5 to C9 with the modified ZSM-5 zeolite catalyst at a weight hourly space velocity ranging from 4-10 hrs-1, at a temperature in the range of 400-500°C, at a pressure in the range of 5-25 kg/cm2 Ibs for 24 hours, optionally in the presence of inert gas separating the liquid petroleum gas high octane gasoline and other products of the resultant reaction mixture from first reactor by known methods, carrying out in-situ regeneration of catalyst in reactor for 24 hours by oxidative combustion, repeating the conversion of natural petroleum gas to liquified petroleum gas and high octane gasoline in the reactor is carried out followed by in-situ regeneration of catalyst bed.

Title of Invention

"A PROCESS FOR THE CONVERSION OF NATURAL GAS LIQUID TO LIQUEFIED PETROLEUM GAS AND HIGH OCTANE GASOLINE"

Abstract

A process for the conversion of natural gas liquid to liquefied petroleum gas and high octane gasoline by contacting natural gas liquid as feed stock containing hydrocarbon having carbon atoms in the range of C5 to C9 with the modified ZSM-5 zeolite catalyst at a weight hourly space velocity ranging from 4-10 hrs-1, at a temperature in the range of 400-500°C, at a pressure in the range of 5-25 kg/cm2 Ibs for 24 hours, optionally in the presence of inert gas separating the liquid petroleum gas high octane gasoline and other products of the resultant reaction mixture from first reactor by known methods, carrying out in-situ regeneration of catalyst in reactor for 24 hours by oxidative combustion, repeating the conversion of natural petroleum gas to liquified petroleum gas and high octane gasoline in the reactor is carried out followed by in-situ regeneration of catalyst bed.

Full Text	The present invention relates to a process for the conversion of Natural Gas Liquid to Liquefied Petroleum Gas and High Octane Gasoline. In particular this invention relates to process and apparatus for converting Natural Gas Liquid (NGL) from gas to Liquefied Petroleum Gas (LPG) and high-octane gasoline pool component. In particular it relates to technique for operating a swing mode catalytic reactor system using acid zeolite catalyst capable of facilitating low selectivity for fuel gas and down stream separation unit for enhanced on spec LPG recovery. NGL is one of the least viable petroleum feed stock treated today. Substantial quantities are available of this low value feed stock from various gas fields. NGL mainly contains C5 and C6 hydrocarbons (35 to 70 wt%) depending upon source and boiling range. Due to high percentage of n-paraffins in NGL it has lower octane number and exhibit higher Reid Vapor Pressure (RVP) restricting its use as gasoline pool blending stock. Thus, conversion of NGL into other petroleum and petrochemical products gains significance in this scenario. Moreover, increasing deficit of LPG in India and in other South -East Asian countries, demands the process technologies for the production of LPG from low value feed stocks. The demand projection trends of LPG indicate about growth of 12-13% growth rate of LPG per year in India. The corresponding deficit of LPG in 1996-97 was about 2 million tons and is expected to increase up to 7.8 millions tons by year 2010-2011 (Sunder Rajan Committee Report on Hydrocarbon perspective 1996, Ref LPG News of India, March 96, p17). In view of the above value addition to light hydrocarbons (mainly Cs and Ce Range) is extremely desirable. In addition to the basic work derived from modified ZSM-5 type zeolite catalysts, a number of discoveries and evolutions have contributed to the development of a new process, known as NGL (or Naphtha) to Gas and Gasoline (NTGG) process. Applicability of this process and technology at low capacities of operation is another key issue, which facilitates its retrofitting to the existing LPG recovery plants for NGL. There are reports in the literature on the conversion of straight chain paraffins into aromatics, using zeolites and metal doped zeolites as catalyst. Reference may be made to a process developed by Mobil researchers (Ind. Eng. Chem. Process. Design Dev., 25 (1986) wherein the preparation of aromatics from variety of feed stock such as pyrolysis gasoline, unsaturated gases from catalytic cracker, paraffinic naphtha and LPG have been described. Another reference may be made to (Hydrocarbon Processing Sept., 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 Gringemouth refinery in Scotland. Yet another reference may be made to US patent nos. 3,960,978 and4,021,502 by Plank, Rosinski and Givens, where in conversion of Ca - Cs olefins alone or in admixture with parrafinic components, in to higher hydrocarbons over crystalline zeolites having controlled zeolite has been described. Still another reference may be made to US patent 4,996,381 dated Feb. 26, 1991 where in an aromatization process is described for increased conversion of C2-C12 aliphatic hydrocarbons to aromatic hydrocarbons using a highly purified recycle stream. Still another reference may be made to US patent 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. Yet another reference may be made to (US patent 5,026,938 dated 25th June' 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. The limitation of the all the processes described in above patents is mainly related to the production of aromatics from olefins or paraffins of Ce - Ci2 range and Cs-Cs range. Still another reference may be made to (IPA No. 2627/DEL/96-dated 29/11/96) 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 frame work alumina. The shortcoming of the above process is a 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. The carrier gas is used in the above process in molar ratio of N2/HC=2, so the N2 cost will be a disadvantage to the economy of the process. The main objective of the present invention is to provide a process for the conversion of Natural Gas Liquid to Liquefied Petroleum Gas and High Octane Gasoline Another objective of the present invention is to provide a process for the conversion of NGL to LPG along with high octane gasoline as a blender to boost the octane number by using a catalyst system containing acidity modified ZSM-5 zeolite composite. Yet another objective of the present invention is to provide a process which utilizes NGL (Natural Gas Liquid) containing more than 25 types of hydrocarbon components for the production of LPG unlike the other existing processes. Still another objective of present invention is to convert Cs and Ce paraffinic components efficiently to produce LPG unlike the conventional reforming processes. Still another objective of the present invention is to provide a process which also effectively converts feed n-paraffinic components to iso-paraffins and feed benzene to C? or higher aromatics to provide advantages of meeting gasoline specs for Octane number and Benzene content respectively. Still another objective of the present invention is to produce LPG and high octane gasoline pool component from NGL with minimal yields of low cost dry gas (Ci+C2) for an improved economics. Still another objective of the present invention is to develop above process, which is safe and environmentally acceptable. Still another objective of the present invention is to evolve a reactor system and swing logic for the synchronized and simultaneous operation of two reactors, one being used for NGL conversion and other being regenerated by burning coke laid down on the catalyst. Still another objective of the present invention is to optimize operating conditions and develop an energy efficient process scheme to provide enhanced on spec LPG recovery without using a compressor. Still another objective of the present invention is to develop the process, which can be retrofitted to existing LPG recovery plants from Natural Gas. In the drawings accompanying this specification figure 1 represents is a simplified process flow diagram showing connectivity and sequencing between major unit operations. Figure 2 represents a schematic system diagram showing a process equipment and flow line configuration for a preferred embodiment. Figure 3 represents a process side diagram showing major process control function. Figure 4 represents a regeneration loop diagram showing all necessary control scheme required to implement reactor swing logic. Figure 5 represents the schematic of handling hot releases to flare from the NTGG process. Accordingly, the present invention provides process for the conversion of natural gas liquid to liquefied petroleum gas and high octane gasoline which comprises : a) contacting natural gas liquid as feed stock containing hydrocarbon having carbon atoms in the range of C5 to C9 with the modified ZSM-5 zeolite catalyst at a weight hourly space velocity ranging from 4-10 hrs"1, at a temperature in the range of 400-500°C, at a pressure in the range of 5-25 kg/cm2 Ibs for 24 hours, optionally in the presence of inert gas, b) separating the liquid petroleum gas high octane gasoline and other products of the resultant reaction mixture from first reactor by known methods, c) carrying out in-situ regeneration of catalyst in reactor for 24 hours by oxidative combustion, d) repeating the conversion of natural gas liquid to liquefied petroleum gas and high octane gasoline in the reactor is carried out as in step( b) and step ( c) followed by in-situ regeneration of catalyst bed e) carrying out in- situ regeneration of catalyst in reactor for at least 24hours by oxidative combustion, f) repeating the conversion of LPG to NGL and high octane gasoline in the reactor is carried out as in step b and step c followed by in- situ regeneration of catalyst bed In an embodiment of the present invention the regeneration of the catalyst bed is carried out in two steps. In yet another embodiment of the present invention the first step of regeneration is carried out at a temperature in the range of 350 - 400°C in the presence of oxygen in the range of 0.5 to 1.0 vol%. In yet another embodiment of the present invention the second step of regeneration is carried out at a temperature in the range of 480 - 550°C in the presence of oxygen in the range of 1.5 to 5.0 vol%. In yet another embodiment of the present invention the use of inert gas is optional. In yet another embodiment of the present invention weight hourly space velocity is preferably in the range 4-6 hrs"1. In yet another embodiment of the present invention the reactor temperature is preferably in range of 440-460°C. In yet another embodiment of the present invention reactor pressure is preferably in the range of 10-20 kg/cm2abs. In yet another embodiment of the present invention the top product from debutanizer is used to produce Liquefied Petroleum Gas (LPG) of desired specification. In yet another embodiment of the present invention heavier hydrocarbons obtained by oligomerization of the feedstock is fractionated in a lower pressure product splitter unit to produce gasoline of required final boiling point In yet another embodiment of the present invention the catalyst is a novel acidity modified ZSM-5 zeolite In yet another embodiment of the present invention the process conditions viz. pressure can be varied 5-25 kg/cm2 temperature can be varied 400 - 500°C to control the Cg+ aromatic content in the product in order to improve the catalyst life against the coke lay down. In still another embodiment of the present invention the novel process developed can operate for various NGL feed stocks that are varying in Cs, iC5, C6, C7 hydrocarbon components without significantly effecting the product yields. In still another embodiment of the present invention the catalyst system containing acidity modified ZSM-5 zeolite composite used is such as prepared by extrudates controlled steaming without acid leaching step. In still another embodiment of the present invention the reactor system includes at least two reactors to facilitate in-situ catalyst regeneration at least after every 24 hours in one the reactors system. In still another embodiment of the present invention the reaction temperature may be increased continuously at constant intervals in order to get a constant product yield patterns, if necessary. The General Process Description: The flow diagram of Figure 2 represents the overall NTGG process. The feedstock to the NTGG plant is supplied through the conduit 10 and small inventory is maintained in the vessel 12 for feeding the reactors. The feed is pressurized to the process pressure by pump 14 and heated using hot reactor effluents in the exchange 16. The feed stock is finally heated in the in the furnace 18 to achieve reaction temperature. The hot, fully vaporized feed is then fed to one of the reactors of reactor system 20 (20 A or 20 B, whichever is in process loop). Reactor effluent after getting cooled in exchanger 16 is mixed uncondensed gases, mainly C1 and C2, from debutanizer column 32 top. This combined stream is trim cooled in air cooler 22 and partially condensed stream 23 is routed to drum 24. Vapor stream, 60, from drum 24 is the dry gas and may be sent to the fuel gas header. Liquid from vessel 24 is pumped to debutanizer column 32 via exchangers 28 and 30, acting as column 42 bottom product cooler and condenser respectively. The debutanizer column may be tray type or packed vertical fractionating column with a reboiler 40 and reflux loop 34, 36, 38. Top product 66 from the debutanizer column 32 is LPG rich stream, which is routed to light end fractionator of the existing LPG plant hence facilitating a good retrofit. The bottom product 33 from column 32 is directly sent to column 42 (heavy end fractionator, HEF) which separates the heavy ends (220°C+) from high octane gasoline. . The HEF column too may be tray type or packed vertical fractionating column with a reboiler 43 and reflux loop 30, 44, 46. The top product from HEF 42 is high-octane gasoline and can be blended with gasoline range hydrocarbons as octane booster. The heavy ends of relatively small yields can be routed to diesel pool. In the present invention the reactor in process loop is kept on stream until the coke content increases from 0% at the start of run (SOR) to about 20 weight % at the end of the run (EOR) at which stage it is regenerated by burning the coke in the presence of controlled oxygen. Typically after every 24 hrs a reactor needs to be regenerated by coke burning. During this period no increase in reactor temperature is envisaged and EOR is signaled by maximum allowable increase in liquid flow through pump 26. At this stage reactor is taken in regeneration loop to burn off the deposited coke. In the present invention the regeneration loop comprises of compressor 58, exchanger 52, furnace 50, cooler 54 and knock out (KO) drum 56 to facilitate in situ catalyst regeneration. This compressor takes suction from phase separator 56. The gas is then heated in feed /effluent exchanger 52 against the hot gases from the reactor and then in the regeneration furnace 50 to 370 °C before being fed to the reactor 20 B (or 20 A), in the regeneration loop. Burning off the coke, producing CCX and HLO generates the catalyst. Cooled reactor effluents in exchanger 52 are further cooled in air cooler 54 and fed to knock out drum 56. The condensed water formed due to coke burning gets collected in KO drum and drained out intermittently. The KO drum 56 is maintained at temperature 40 to 55 °C and pressure 5 to 7 kgs in order to minimize water content in regeneration gas which other wise will damage the catalyst. The coke-burning rate is closely controlled by monitoring the oxygen content in the circulating regeneration gas through air intake at compressor suction. This is maintained at less than 0.8 vol. % so that temperature rise across the reactor is does not exceed 90 °C. Once the temperature rise across the reactor ceases to exist the Oxygen concentration is increased to 2 Vol% and temperature is gradually increased to 520°C. This condition is maintained for at least one hour or until all evidence of burning has ceased. Once the regeneration is complete, the temperature is reduced to the reaction temperature and system is purged free of oxygen by nitrogen. Now the reactor is ready to be taken in the process loop. A typical process control system is presented in Figure 3. This schematic instrumentation drawing shows the basic process unit and interconnecting process flow lines of Figure 2 in solid lines. Control signal lines and instruments activating for process instrumentation are depicted as dashed lines with conventional instrument mode abbreviation; TC = Temperature Control, PC = Pressure Control, FC = Flow Control and LC = Level Control, AC = Composition Control, TDC = Temperature differential control . These are general guidelines only and may be adapted to control requirements of any NTGG plant. REACTOR SWING LOGIC: The reactor swing logic employed in NTGG process is included as a preferred embodiment of the present invention. To swing the reactors between process and regeneration loops, a programmable logic controller is employed to control the sequencing of valve operations during all the stages of reactor system operation. Figure 4 shows the valves required to be operated and the sequencing, to achieve the reactor swing. At the time of swing, conditions in each reactor, steps involved to achieve the swing and estimated time for each step are described as follows: Referring Figure 4, the valves used to describe the swing logic are numbered as P1, P1B, P2, P3, P3B, P4 in process loop lines, R1, R2, R3 and R4 in regeneration loop lines across the reactors. Valves L1, L2, L3 and L4 are additional valves in the regeneration loop to facilitate the swing. Sequencing of the valves in Figure 4 is as follows (Table Removed) Following reactor conditions typically represents the starting point for this cyclic operation, once in 24 hours: Reactor A in process loop and ready to be taken in regeneration loop. It is at process temperature (say 450 deg C), pressure (say 20 kg/cm2, abs) and with HC atmosphere in the reactor. Reactor B already regenerated but still in regeneration loop and ready to be taken in process loop. It has been brought to the process temperature (say 450 deg C), after regeneration but is at regeneration pressure (say 6 kg/cm2, abs) and with N2 atmosphere. Regeneration loop is in Oxygen free N2 environment. Reactor swing at these conditions is achieved by isolating regeneration loop from the reaction section by opening by pass valve L3, closing valves L1 and then L2 and subsequently valves R3 and R4. Now the Reactor 20B is taken in process loop by opening Reactor 20B inlet valve P3B (i.e. P3 by pass valve with orifice). Orifice in by pass line allows pressure in reactor 20B to gradually build up typically to 20 kg/cm2 from 6 kg/cm2 abs. Once the process pressure is achieved in the reactor B, valve P4 at reactor outlet opens up. Opening of reactor 20B inlet valve P3 and closing valve P3B follows this. At this stage reactor 20B is in process loop while the catalyst in reactor 20A is coked and is to be isolated from process loop. This is done by closing reactor 20A inlet valve P1 and then reactor 20A outlet valve P2. Reactor 20 A is now taken in regeneration loop by opening Valve L4 to release hydrocarbons at high pressure to flare header. Once the pressure in the reactor 20A is reduced, valve L4 is closed and the residual hydrocarbons are purged by opening inlet valves R1 & L1 as well as outlet valves R2 & L2 and closing valve L3. This is done by circulating Nitrogen in regeneration loop at 6 kg/cm2 with net N2 intake and circulating it at 450 C and releasing the N2 to have knockout drum at lowest possible pressure (say 2 kg /cm2a). This pressure swing in the regeneration loop is repeated till HC in purge gas is During HC purge operation catalyst bed is cooled at a rate of ~40 °C per hr to a temperature of 370 °C by controlling regeneration furnace outlet temperature. Nitrogen circulation rate is maintained large enough (say about 700 kg/hr) to provide enough thermal capacitance of the circulating media, critical to avoid temperature runaway during the coke burning as described above. Once the reactor is regenerated, as evident by no temperature rise across the reactors, even at 520°C and circulating gas with 2 vol% oxygen, it is inertized by purging oxygen from the regeneration loop. This is done by stopping the airflow to the regeneration. Nitrogen is kept circulated and regeneration loop pressure is reduced to the lowest possible pressure (at least 2 kg/cm2, a). This is again increased to 6 kg/cm2a, in the reactor and after circulating the gas for about 5 minutes it is purged such that K.O. drum 56 is at the lowest possible pressure ( at least 2 kg/cm2 a). Simultaneously reactor is cooled at a rate of ~ 40 °C/ hr to the process temperature. The pressure swing in the regeneration loop is repeated till the Oa concentration in the regeneration loop is 2000 ppm. At this point of regeneration cycle reactors are at following conditions: Reactor A :is at process temperature, at about 6 kg/cm2a pressure, with oxygen free environment and regenerated i.e. ready to be taken to process loop Reactor B is also at process temperature, at about 20 kg/cm2 a pressure, with hydrocarbon atmosphere and coke laid down on the catalyst i.e. to be taken in the regeneration loop. Regeneration loop is in Oxygen free N environment. Time required to regenerate each reactor is about 24 hrs. Reactor 20B by this time is required to be regenerated. This is the complete cycle at the end of which Reactor 20A is regenerated and Reactor 20B is in Process and ready to be taken for regeneration. At this point of reactor swing and regeneration cycle, the situation is reverse of that described above as the starting point of the cyclic operation, that is Reactor 20B in process loop and Reactor 20A in regeneration loop. The steps already described are exactly applicable for this situation to take Reactor 20A in process loop and Reactor 20B in regeneration loop with following equivalence of the valves. P1 =P3 P1B = P3B R1 =R3 P2 = P4 R2 = R4 L4=L5 Valves L1, L2 and L3 are the unchanged in both the situations. HOT FLARE RELEASE SCHEME: In the present invention the hot streams is released to the existing to flare headers designed normally for low temperatures. This facilitates retrofitting of the NTGG process to the existing LPG recovery plants without going for a new flare header. The cases for hot flare release from NTGG plant and their routing is as follows: There are two possible cases for hot release from the reaction section at process temperatures (say about 450 °C or above). Case 1 :HC purge from a reactor at the time of reactor swing This situation of intermittent purge of hot hydrocarbons (Temp ~ 450 ° C or higher) arises at the time of reduction in reactor pressure from process pressure (say 20 kg/cm2 ) to about 4 kg/cm2 before a reactor could be taken from process loop to regeneration loop as described above. This requires hot hydrocarbons to be released in about 30 seconds. Referring Figure 5, this release is routed through a cooler 102 and knockout pot 100 by opening Valve L4 for reactor 20A or Valve L5 for reactor 20B. Case 2 : Hot hydrocarbon release from reactor safety valves (108 A/B or 116) in case reactor blocked operation: This hot release is expected at the time when reactor in process line is subjected to blocked discharge situation. Referring Figure 5, this hot safety release is routed as bypass of reactors 20A or 20B through the existing cooling facilities 16 and 22 provided in the process for normal operation, which is subsequently be handled by pressure safety valves provided down stream the reactor. CATALYST: In the present invention the catalyst used is a novel acidity modified ZSM-5 zeolite in which parent ZSM-5 zeolite composite is prepared according to our earlier patent No.2627/DEL/96 dated 29/11/96. The as synthesized Na-ZSM-5 powder is calcined at 540°C in air for about 4-6 hrs to burn off the template molecules. This calcined Na-ZSM-5 powder is ion exchanged with ammonium nitrate solution to obtain NH4-ZSM-5. The novelty of present catalyst is such that the HZSM-5 form obtained by calcining the NH4-ZSM-5 powder at 450°C was extrudated with commercial alumina binder in the range of 40 to 70 wt% to the zeolite catalyst, using 3% glacial acetic acid. These extrudates are oven dried and calcined in the range of 400-600°C in the presence of air for 5 hrs. To modify the acidity and acid strength distribution of this catalyst, the extrudates in the HZSM-5 form are steamed between 300-500°C under 100% steam for a period of 3-6 hrs to optimize the performance. Another novelty of the present catalyst from the above patent is such that the acid leaching step has been eliminated to reduce the fuel gas yield to 4 wt % from 12 wt % further which improves the production of high octane gasoline as blender to boost octane during NGL conversion. The physico-chemical properties of the zeolite catalyst are as follows: Characteristics of Parent HZSM-5: Pore Volume=0.32127; Silica-Alumina Ratio(SAR)= 30-50 XRD Crystallinaty =>99%; Crystal Size= Catalyst = Acidity modified ZSM-5; Zeolite -Alumina Binder Ratio=60:40 Shape = Cylindrical form; Diameter = 1.5 - 2.0 mm Bulk Density = 0.55 - 0.75 gm/cc; Crushing Strength (Kg)=5-8Kg Surface area = 400 - 450 m2/g ; Total Acidity = 0.49-0.54 mm/gm The novelty of the present invention lies in the process to convert natural gas liquid preferably in the range C5- C6 hydrocarbons into liquefied petroleum gas and high octane gasoline using modified ZSM -5 zeolite catalyst optimized to reduce the dry gas yield. The process has been developed to facilitate its retrofitting in existing LPG recovery unit taking the advantage of existing LPG recovery unit, existing flare release system and availability of feed at high pressure. A safe reactor swing logic and associated controls are evolved to operate this fast deactivating catalyst in fixed bed reactor thus making the process economical viable at low capacity. The following examples are given by way of illustration of the present invention and therefore should not be construed to limit the scope of the present invention. Example 1 A method for the preparation of acidity modified ZSM-5 zeolite catalyst as described in our patent application No.2627/DEL/96 dated 29/11/96 A mixture of tetra propyl ammonium bromide [ N ( C3 H7 ) Br], aluminium sulphate [AI2 ( 804)3 ] • H2 O and deionised water were aded to silica gel under stirring. The chemical composition of the initial gel was 3Na2 O : AI2 Oa: 30 SiO2 : 825 H2 0. The pH of the reaction gel was controlled at 10.5 by adding 3.5 ml of 1:1 H2 S04 solution. The crystallization of the reaction mixture was carried out at 150°C in an autoclave for 3.5 days. The solid was filtered, washed with hot water and then dried at 80 °C. The zeolite sample thus obtained was calcined at 480 °C for 12 hours in presence of dry air to remove organic matter. The ion exchange of zeolite samples was carried out by submitting the samples to 3 cycles of ion exchange with 0.2N solution of NhU NO3 at 80 °C for 4 hours followed by filtration and washing with hot water. This zeolite material was subjected to steam treatment at 300°C . Steam treated zeolite sample (10g) was mixed with 85 ml. 1N HCI and refluxed for 30 minutes, filtered and washed free of chlorides ions with demineralized water and dried at 110 °C for 16 hours. Extrudates of the zeolite sample prepared and modified as above were made using alumina as binder in a proportion of 65% by weight of zeolite and 35% by weight of binder. Example 2 The feed stock characteristics of natural gas liquid used in this process for a preparation of LPG /propane along with a gasoline by product are shown below. About 40cc of the catalyst (24 g) as prepared in Example 1 in extruded from of 1/16" diameter is loaded in a fixed bed reactor. The liquid product was analyzed using a gas Chromatograph fitted with Tetra Cyano Ethoxy Propionitrile column and FID detector. The gaseous products were analyzed using Squalane column. Characteristics of Natural Gas Liquid (NGL) Feed stock: Density at 15°C= 0.695; RVP (Kg/cm2 at 38°C)= 0.560 Research Octane Number (RON) = 74 ASTM°C IBP - 37.2 10 - 48.3 30 - 54.0 50 - 59.8 70 - 67.6 90 - 86.6 FBP - 120.2 Feed Composition (wt %): C5 Paraffins - 34.9 C6 Paraffins - 43.0 Ce Aromatics - 4.9 C/and higher hydrocarbons - 17.2 TOTAL - 100 This example describes the yields of product LPG and high-octane gasoline obtained in the NTGG process from the NGL feed stock along with high-octane gasoline characteristics. The ranges in yield of individual product component and gasoline characteristics that can be obtained in this process are given. Table 1 :Characteristics of Gas and Liquid Products obtained in NTGG process Feed : Natural Gas Liquid (NGL) of Vaghodia Reaction Temperature = 400°C to 500°C Pressure = 5 to 25 kg/cm2 Reactor: Bench Scale Reactor of 100 gm-catalyst capacity (Table Removed) Example 3 This example illustrates the results of the effect of process parameters on the yield and composition of LPG. The process parameters are varied in the range reported in Table 2 such that severity of operation increases for the four cases A,B,C and D. For each case product analysis is reported in Table 2: Table 2 .-Flexibility in process operation : Variation in Yield and composition of LPG Feed : Natural Gas Liquid (NGL); Reaction Temperature = 450°C to 480°C Pressure = 10 to 20 kg/cm2 WHSV = 5 to 6 hr-1 The product yields for the four operating cases in increasing severity are as follows. (Table Removed) Example 4 This example illustrates the effect of run length on the product yield viz. Fuel Gas (C1+C2), LPG (C3+C4), liquid product and their composition. In the run length of 37 hrs, the product was analyzed at various intervals and results are presented in Table 3. Table 3 : Catalyst Stability Studies Feed : Natural Gas Liquid (NGL) Reaction Temperature = 450°C WHSC = 6.0 hrs'1 Pressure = 20 kg/cm2, abs (Table Removed) Example 5 This example describes the effect of change of NGL composition on the product yield. This reaction was conducted at optimum process conditions and the results were given in table 4. Table 4 : Effect of Feed Composition on Ex -Reactor Yields Conditions: As they are given in Table 4. (Table Removed) Example 6 This example illustrates the effect of catalyst regeneration on the product yields in the process of present invention for the LPG production from NGL. The product yields patterns before and after the regeneration are given in the table 5. Table. 5 : Reproducibility of the Ex-reactor yields after the Regeneration Process Feed = Natural Gas Liquid(NGL); Reaction Temperature = 450°C Pressure = 20 kg/cm2 WHSV = 6hr'1 (Table Removed) The main advantages of the present invention are: 1. The process of the present invention converts all types of hydrocarbon components present in the feed NGL viz. Paraffins, iso-paraffins, naphthenes and benzene into LPG and high octane components e.g. iso-paraffinic and aromatic hydrocarbons with a high selectivity with a single catalyst system. 2. NGL which is not potential feed stock for catalytic reformers, can be effectively converted to value added LPG and high-octane gasoline products. 3. The catalyst used in this process is relatively low cost and eco-friendly and it does not involve the acid leaching with hazardous mineral acids such as HCI during preparation. 4. The catalyst used in this process reduces dry gas ex-reactor yields from 12 to 4 wt% with increase of high-octane liquid product, thereby improves the economics of this process. 5. LPG, which is a major product in the present process, can meet the great industrial and domestic demands. 6. The process does not require hydrogen. 7. The process also does not require use of corrosive organic chloride additives. 8. The high-octane liquid by-product obtained in the process can be used as a gasoline blender to boost octane number. 9. The process of present invention can be retrofitted with existing LPG recovery plants from NGL located at remote thus avoiding the difficult NGL transportation for further processing and the existing LPG supply network can be used to reach the market place. 10. This process is economically viable even at low capacities due to reduction in investment by retrofitting it to the existing LPG recovery units. We claim : 1. A process for the conversion of natural gas liquid to liquefied petroleum gas and high octane gasoline which comprises : a) contacting natural gas liquid as feed stock containing hydrocarbon having carbon atoms in the range of C5 to C9 with the modified ZSM-5 zeolite catalyst at a weight hourly space velocity ranging from 4-10 hrs" \ at a temperature in the range of 400-500°"C, at a pressure in the range of 5-25 kg/cm2 Ibs for 24 hours, optionally in the presence of inert gas, b) separating the liquid petroleum gas high octane gasoline and other products of the resultant reaction mixture from first reactor by known methods, c) carrying out in-situ regeneration of catalyst in reactor for 24 hours by oxidative combustion, d) repeating the conversion of natural gas liquid to liquified petroleum gas and high octane gasoline in the reactor is carried out as in step( b) and step ( c) followed by in-situ regeneration of catalyst bed. 2 A process as claimed in claims 1-3 wherein weight hourly space velocity is preferably in the range 4-6 hrs"1 3. A process as claimed in claims 1-4 wherein the reactor temperature is preferably in the range of 440-460°C. 4. A process as claimed in claims 1-5 wherein reactor pressure is preferably in the range of 10-20 kg/cm2lbs. 5. A process as claimed in claims 1-7 wherein heavier hydrocarbons obtained by oligomerization of the feedstock is fractionated in a lower pressure product splitter unit to produce gasoline of required final boiling point. 6. A process as claimed in claims 1-8 wherein the catalyst used is a novel acidity modified ZSM-5 zeolite. 7. A process as claimed in claims 1-9 wherein the process conditions viz. pressure can be varied 5-25 kg/cm2 temperature can be varied 400- 500°C to control the C9+ aromatic content in the product in order to improve the catalyst life against the coke lay down. 8. A process for the conversion of natural gas liquid to liquefied petroleum gas and high octane gasoline substantially as herein described with reference to the examples and drawings accompanying this specification.

Full Text

The present invention relates to a process for the conversion of Natural Gas Liquid to Liquefied Petroleum Gas and High Octane Gasoline.
In particular this invention relates to process and apparatus for converting Natural Gas Liquid (NGL) from gas to Liquefied Petroleum Gas (LPG) and high-octane gasoline pool component. In particular it relates to technique for operating a swing mode catalytic reactor system using acid zeolite catalyst capable of facilitating low selectivity for fuel gas and down stream separation unit for enhanced on spec LPG recovery.
NGL is one of the least viable petroleum feed stock treated today. Substantial quantities are available of this low value feed stock from various gas fields. NGL mainly contains C5 and C6 hydrocarbons (35 to 70 wt%) depending upon source and boiling range. Due to high percentage of n-paraffins in NGL it has lower octane number and exhibit higher Reid Vapor Pressure (RVP) restricting its use as gasoline pool blending stock. Thus, conversion of NGL into other petroleum and petrochemical products gains significance in this scenario.
Moreover, increasing deficit of LPG in India and in other South -East Asian countries, demands the process technologies for the production of LPG from low value feed stocks. The demand projection trends of LPG indicate about growth of 12-13% growth rate of LPG per year in India. The corresponding deficit of LPG in 1996-97 was about 2 million tons and is expected to increase up to 7.8 millions tons by year 2010-2011 (Sunder Rajan Committee Report on Hydrocarbon perspective 1996, Ref LPG News of India, March 96, p17).
In view of the above value addition to light hydrocarbons (mainly Cs and Ce Range) is extremely desirable. In addition to the basic work derived from modified ZSM-5 type zeolite catalysts, a number of discoveries and evolutions have contributed to the development of a new process, known as NGL (or Naphtha) to Gas and Gasoline (NTGG) process. Applicability of this process and

technology at low capacities of operation is another key issue, which facilitates its retrofitting to the existing LPG recovery plants for NGL.
There are reports in the literature on the conversion of straight chain paraffins into aromatics, using zeolites and metal doped zeolites as catalyst.
Reference may be made to a process developed by Mobil researchers (Ind. Eng. Chem. Process. Design Dev., 25 (1986) wherein the preparation of aromatics from variety of feed stock such as pyrolysis gasoline, unsaturated gases from catalytic cracker, paraffinic naphtha and LPG have been described.
Another reference may be made to (Hydrocarbon Processing Sept., 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 Gringemouth refinery in Scotland.
Yet another reference may be made to US patent nos. 3,960,978 and4,021,502 by Plank, Rosinski and Givens, where in conversion of Ca - Cs olefins alone or in admixture with parrafinic components, in to higher hydrocarbons over crystalline zeolites having controlled zeolite has been described.
Still another reference may be made to US patent 4,996,381 dated Feb. 26, 1991 where in an aromatization process is described for increased conversion of C2-C12 aliphatic hydrocarbons to aromatic hydrocarbons using a highly purified recycle stream.
Still another reference may be made to US patent 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.

Yet another reference may be made to (US patent 5,026,938 dated 25th June' 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.
The limitation of the all the processes described in above patents is mainly related to the production of aromatics from olefins or paraffins of Ce - Ci2 range and Cs-Cs range.
Still another reference may be made to (IPA No. 2627/DEL/96-dated 29/11/96) 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 frame work alumina.
The shortcoming of the above process is a 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. The carrier gas is used in the above process in molar ratio of N2/HC=2, so the N2 cost will be a disadvantage to the economy of the process.
The main objective of the present invention is to provide a process for the conversion of Natural Gas Liquid to Liquefied Petroleum Gas and High Octane Gasoline
Another objective of the present invention is to provide a process for the conversion of NGL to LPG along with high octane gasoline as a blender to boost the octane number by using a catalyst system containing acidity modified ZSM-5 zeolite composite.
Yet another objective of the present invention is to provide a process which utilizes NGL (Natural Gas Liquid) containing more than 25 types of

hydrocarbon components for the production of LPG unlike the other existing processes.
Still another objective of present invention is to convert Cs and Ce paraffinic components efficiently to produce LPG unlike the conventional reforming processes.
Still another objective of the present invention is to provide a process which also effectively converts feed n-paraffinic components to iso-paraffins and feed benzene to C? or higher aromatics to provide advantages of meeting gasoline specs for Octane number and Benzene content respectively.
Still another objective of the present invention is to produce LPG and high octane gasoline pool component from NGL with minimal yields of low cost dry gas (Ci+C2) for an improved economics.
Still another objective of the present invention is to develop above process, which is safe and environmentally acceptable.
Still another objective of the present invention is to evolve a reactor system and swing logic for the synchronized and simultaneous operation of two reactors, one being used for NGL conversion and other being regenerated by burning coke laid down on the catalyst.
Still another objective of the present invention is to optimize operating conditions and develop an energy efficient process scheme to provide enhanced on spec LPG recovery without using a compressor.
Still another objective of the present invention is to develop the process, which can be retrofitted to existing LPG recovery plants from Natural Gas.
In the drawings accompanying this specification figure 1 represents is a simplified process flow diagram showing connectivity and sequencing between major unit operations.

Figure 2 represents a schematic system diagram showing a process equipment and flow line
configuration for a preferred embodiment.
Figure 3 represents a process side diagram showing major process control function.
Figure 4 represents a regeneration loop diagram showing all necessary control scheme required
to implement reactor swing logic.
Figure 5 represents the schematic of handling hot releases to flare from the NTGG process.
Accordingly, the present invention provides process for the conversion of natural gas liquid to
liquefied petroleum gas and high octane gasoline which comprises :
a) contacting natural gas liquid as feed stock containing hydrocarbon having carbon
atoms in the range of C5 to C9 with the modified ZSM-5 zeolite catalyst at a
weight hourly space velocity ranging from 4-10 hrs"1, at a temperature in the
range of 400-500°C, at a pressure in the range of 5-25 kg/cm2 Ibs for 24 hours,
optionally in the presence of inert gas,
b) separating the liquid petroleum gas high octane gasoline and other products of
the resultant reaction mixture from first reactor by known methods,
c) carrying out in-situ regeneration of catalyst in reactor for 24 hours by oxidative
combustion,
d) repeating the conversion of natural gas liquid to liquefied petroleum gas and
high octane gasoline in the reactor is carried out as in step( b) and step ( c)
followed by in-situ regeneration of catalyst bed

e) carrying out in- situ regeneration of catalyst in reactor for at least 24hours by
oxidative combustion,
f) repeating the conversion of LPG to NGL and high octane gasoline in the
reactor is carried out as in step b and step c followed by in- situ regeneration
of catalyst bed
In an embodiment of the present invention the regeneration of the catalyst bed is
carried out in two steps.
In yet another embodiment of the present invention the first step of regeneration
is carried out at a temperature in the range of 350 - 400°C in the presence of
oxygen in the range of 0.5 to 1.0 vol%.
In yet another embodiment of the present invention the second step of
regeneration is carried out at a temperature in the range of 480 - 550°C in the
presence of oxygen in the range of 1.5 to 5.0 vol%.
In yet another embodiment of the present invention the use of inert gas is
optional.
In yet another embodiment of the present invention weight hourly space velocity
is preferably in the range 4-6 hrs"1.
In yet another embodiment of the present invention the reactor temperature is
preferably in range of 440-460°C.
In yet another embodiment of the present invention reactor pressure is preferably
in the range of 10-20 kg/cm2abs.

In yet another embodiment of the present invention the top product from
debutanizer is used to produce Liquefied Petroleum Gas (LPG) of desired
specification.
In yet another embodiment of the present invention heavier hydrocarbons
obtained by oligomerization of the feedstock is fractionated in a lower pressure
product splitter unit to produce gasoline of required final boiling point
In yet another embodiment of the present invention the catalyst is a novel acidity
modified ZSM-5 zeolite
In yet another embodiment of the present invention the process conditions viz.
pressure can be varied 5-25 kg/cm2 temperature can be varied 400 - 500°C to
control the Cg+ aromatic content in the product in order to improve the catalyst
life against the coke lay down.
In still another embodiment of the present invention the novel process developed
can operate for various NGL feed stocks that are varying in Cs, iC5, C6, C7
hydrocarbon components without significantly effecting the product yields.
In still another embodiment of the present invention the catalyst system
containing acidity modified ZSM-5 zeolite composite used is such as prepared by
extrudates controlled steaming without acid leaching step.
In still another embodiment of the present invention the reactor system includes
at least two reactors to facilitate in-situ catalyst regeneration at least after every
24 hours in one the reactors system.

In still another embodiment of the present invention the reaction temperature may be increased continuously at constant intervals in order to get a constant product yield patterns, if necessary.
The General Process Description:
The flow diagram of Figure 2 represents the overall NTGG process. The feedstock to the NTGG plant is supplied through the conduit 10 and small inventory is maintained in the vessel 12 for feeding the reactors. The feed is pressurized to the process pressure by pump 14 and heated using hot reactor effluents in the exchange 16. The feed stock is finally heated in the in the furnace 18 to achieve reaction temperature. The hot, fully vaporized feed is then fed to one of the reactors of reactor system 20 (20 A or 20 B, whichever is in process loop). Reactor effluent after getting cooled in exchanger 16 is mixed uncondensed gases, mainly C1 and C2, from debutanizer column 32 top. This combined stream is trim cooled in air cooler 22 and partially condensed stream 23 is routed to drum 24. Vapor stream, 60, from drum 24 is the dry gas and may be sent to the fuel gas header. Liquid from vessel 24 is pumped to debutanizer column 32 via exchangers 28 and 30, acting as column 42 bottom product cooler and condenser respectively. The debutanizer column may be tray type or packed vertical fractionating column with a reboiler 40 and reflux loop 34, 36, 38. Top product 66 from the debutanizer column 32 is LPG rich stream, which is routed to light end fractionator of the existing LPG plant hence facilitating a good retrofit. The bottom product 33 from column 32 is directly sent to column 42 (heavy end fractionator, HEF) which separates the heavy ends (220°C+) from high octane gasoline. . The HEF column too may be tray type or packed vertical fractionating column with a reboiler 43 and reflux loop 30, 44, 46. The top product from HEF 42 is high-octane gasoline and can be blended with gasoline range hydrocarbons as octane booster. The heavy ends of relatively small yields can be routed to diesel pool.

In the present invention the reactor in process loop is kept on stream until the coke content increases from 0% at the start of run (SOR) to about 20 weight % at the end of the run (EOR) at which stage it is regenerated by burning the coke in the presence of controlled oxygen. Typically after every 24 hrs a reactor needs to be regenerated by coke burning. During this period no increase in reactor temperature is envisaged and EOR is signaled by maximum allowable increase in liquid flow through pump 26. At this stage reactor is taken in regeneration loop to burn off the deposited coke.
In the present invention the regeneration loop comprises of compressor 58, exchanger 52, furnace 50, cooler 54 and knock out (KO) drum 56 to facilitate in situ catalyst regeneration. This compressor takes suction from phase separator 56. The gas is then heated in feed /effluent exchanger 52 against the hot gases from the reactor and then in the regeneration furnace 50 to 370 °C before being fed to the reactor 20 B (or 20 A), in the regeneration loop. Burning off the coke, producing CCX and HLO generates the catalyst. Cooled reactor effluents in exchanger 52 are further cooled in air cooler 54 and fed to knock out drum 56. The condensed water formed due to coke burning gets collected in KO drum and drained out intermittently. The KO drum 56 is maintained at temperature 40 to 55 °C and pressure 5 to 7 kgs in order to minimize water content in regeneration gas which other wise will damage the catalyst. The coke-burning rate is closely controlled by monitoring the oxygen content in the circulating regeneration gas through air intake at compressor suction. This is maintained at less than 0.8 vol. % so that temperature rise across the reactor is does not exceed 90 °C. Once the temperature rise across the reactor ceases to exist the Oxygen concentration is increased to 2 Vol% and temperature is gradually increased to 520°C. This condition is maintained for at least one hour or until all evidence of burning has ceased. Once the regeneration is complete, the temperature is reduced to the reaction temperature and system is purged free of oxygen by nitrogen. Now the reactor is ready to be taken in the process loop.

A typical process control system is presented in Figure 3. This schematic instrumentation drawing shows the basic process unit and interconnecting process flow lines of Figure 2 in solid lines. Control signal lines and instruments activating for process instrumentation are depicted as dashed lines with conventional instrument mode abbreviation; TC = Temperature Control, PC = Pressure Control, FC = Flow Control and LC = Level Control, AC = Composition Control, TDC = Temperature differential control . These are general guidelines only and may be adapted to control requirements of any NTGG plant. REACTOR SWING LOGIC:
The reactor swing logic employed in NTGG process is included as a preferred embodiment of the present invention. To swing the reactors between process and regeneration loops, a programmable logic controller is employed to control the sequencing of valve operations during all the stages of reactor system operation. Figure 4 shows the valves required to be operated and the sequencing, to achieve the reactor swing. At the time of swing, conditions in each reactor, steps involved to achieve the swing and estimated time for each step are described as follows:
Referring Figure 4, the valves used to describe the swing logic are numbered as P1, P1B, P2, P3, P3B, P4 in process loop lines, R1, R2, R3 and R4 in regeneration loop lines across the reactors. Valves L1, L2, L3 and L4 are additional valves in the regeneration loop to facilitate the swing.
Sequencing of the valves in Figure 4 is as follows
(Table Removed)
Following reactor conditions typically represents the starting point for this cyclic operation, once in 24 hours:
Reactor A in process loop and ready to be taken in regeneration loop. It is at process temperature (say 450 deg C), pressure (say 20 kg/cm2, abs) and with HC atmosphere in the reactor.
Reactor B already regenerated but still in regeneration loop and ready to be taken in process loop. It has been brought to the process temperature (say 450 deg C), after regeneration but is at regeneration pressure (say 6 kg/cm2, abs) and with N2 atmosphere.
Regeneration loop is in Oxygen free N2 environment.
Reactor swing at these conditions is achieved by isolating regeneration loop from the reaction section by opening by pass valve L3, closing valves L1 and then L2 and subsequently valves R3 and R4.
Now the Reactor 20B is taken in process loop by opening Reactor 20B inlet valve P3B (i.e. P3 by pass valve with orifice). Orifice in by pass line allows pressure in reactor 20B to gradually build up typically to 20 kg/cm2 from 6 kg/cm2 abs. Once the process pressure is achieved in the reactor B, valve P4 at reactor outlet opens up. Opening of reactor 20B inlet valve P3 and closing valve P3B follows this.
At this stage reactor 20B is in process loop while the catalyst in reactor 20A is coked and is to be isolated from process loop. This is done by closing reactor 20A inlet valve P1 and then reactor 20A outlet valve P2.
Reactor 20 A is now taken in regeneration loop by opening Valve L4 to release hydrocarbons at high pressure to flare header. Once the pressure in the reactor 20A is reduced, valve L4 is closed and the residual hydrocarbons are purged by opening inlet valves R1 & L1 as well as outlet valves R2 & L2 and closing valve L3. This is done by circulating Nitrogen in regeneration loop at 6 kg/cm2 with net N2 intake and circulating it at 450 C and releasing the N2 to have knockout drum at lowest possible pressure (say 2 kg /cm2a). This pressure swing in the regeneration loop is repeated till HC in purge gas is During HC purge operation catalyst bed is cooled at a rate of ~40 °C per hr to a temperature of 370 °C by controlling regeneration furnace outlet temperature. Nitrogen circulation rate is maintained large enough (say about 700 kg/hr) to provide enough thermal capacitance of the circulating media, critical to avoid temperature runaway during the coke burning as described above. Once the reactor is regenerated, as evident by no temperature rise across the reactors, even at 520°C and circulating gas with 2 vol% oxygen, it is inertized by purging oxygen from the regeneration loop. This is done by stopping the airflow to the regeneration. Nitrogen is kept circulated and regeneration loop pressure is reduced to the lowest possible pressure (at least 2 kg/cm2, a). This is again increased to 6 kg/cm2a, in the reactor and after circulating the gas for about 5 minutes it is purged such that K.O. drum 56 is at the lowest possible pressure ( at least 2 kg/cm2 a). Simultaneously reactor is cooled at a rate of ~ 40 °C/ hr to the process temperature. The pressure swing in the regeneration loop is repeated till the Oa concentration in the regeneration loop is 2000 ppm. At this point of regeneration cycle reactors are at following conditions:
Reactor A :is at process temperature, at about 6 kg/cm2a pressure, with oxygen free environment and regenerated i.e. ready to be taken to process loop
Reactor B is also at process temperature, at about 20 kg/cm2 a pressure, with hydrocarbon atmosphere and coke laid down on the catalyst i.e. to be taken in the regeneration loop.
Regeneration loop is in Oxygen free N environment.
Time required to regenerate each reactor is about 24 hrs. Reactor 20B by this time is required to be regenerated. This is the complete cycle at the end of which Reactor 20A is regenerated and Reactor 20B is in Process and ready to be taken for regeneration.
At this point of reactor swing and regeneration cycle, the situation is reverse of that described above as the starting point of the cyclic operation, that is Reactor 20B in process loop and Reactor 20A in regeneration loop. The steps already described are exactly applicable for this situation to take Reactor 20A in process loop and Reactor 20B in regeneration loop with following equivalence of the valves.
P1 =P3
P1B = P3B
R1 =R3
P2 = P4
R2 = R4
L4=L5 Valves L1, L2 and L3 are the unchanged in both the situations.
HOT FLARE RELEASE SCHEME:
In the present invention the hot streams is released to the existing to flare headers designed normally for low temperatures. This facilitates retrofitting of the NTGG process to the existing LPG recovery plants without going for a new flare header. The cases for hot flare release from NTGG plant and their routing is as follows:
There are two possible cases for hot release from the reaction section at process temperatures (say about 450 °C or above).
Case 1 :HC purge from a reactor at the time of reactor swing
This situation of intermittent purge of hot hydrocarbons (Temp ~ 450 ° C or higher) arises at the time of reduction in reactor pressure from process pressure (say 20 kg/cm2 ) to about 4 kg/cm2 before a reactor could be taken from process loop to regeneration loop as described above. This requires hot hydrocarbons to be released in about 30 seconds. Referring Figure 5, this release is routed through a cooler 102 and knockout pot 100 by opening Valve L4 for reactor 20A or Valve L5 for reactor 20B.
Case 2 : Hot hydrocarbon release from reactor safety valves (108 A/B or 116) in case reactor blocked operation:
This hot release is expected at the time when reactor in process line is subjected to blocked discharge situation. Referring Figure 5, this hot safety release is routed as bypass of reactors 20A or 20B through the existing cooling facilities 16 and 22 provided in the process for normal operation, which is subsequently be handled by pressure safety valves provided down stream the reactor.

CATALYST:
In the present invention the catalyst used is a novel acidity modified ZSM-5 zeolite in which parent ZSM-5 zeolite composite is prepared according to our earlier patent No.2627/DEL/96 dated 29/11/96. The as synthesized Na-ZSM-5 powder is calcined at 540°C in air for about 4-6 hrs to burn off the template molecules. This calcined Na-ZSM-5 powder is ion exchanged with ammonium nitrate solution to obtain NH4-ZSM-5. The novelty of present catalyst is such that the HZSM-5 form obtained by calcining the NH4-ZSM-5 powder at 450°C was extrudated with commercial alumina binder in the range of 40 to 70 wt% to the zeolite catalyst, using 3% glacial acetic acid. These extrudates are oven dried and calcined in the range of 400-600°C in the presence of air for 5 hrs. To modify the acidity and acid strength distribution of this catalyst, the extrudates in the HZSM-5 form are steamed between 300-500°C under 100% steam for a period of 3-6 hrs to optimize the performance. Another novelty of the present catalyst from the above patent is such that the acid leaching step has been eliminated to reduce the fuel gas yield to 4 wt % from 12 wt % further which improves the production of high octane gasoline as blender to boost octane during NGL conversion. The physico-chemical properties of the zeolite catalyst are as follows:
Characteristics of Parent HZSM-5:
Pore Volume=0.32127; Silica-Alumina Ratio(SAR)= 30-50
XRD Crystallinaty =>99%; Crystal Size= Catalyst = Acidity modified ZSM-5; Zeolite -Alumina Binder Ratio=60:40
Shape = Cylindrical form; Diameter = 1.5 - 2.0 mm

Bulk Density = 0.55 - 0.75 gm/cc; Crushing Strength (Kg)=5-8Kg Surface area = 400 - 450 m2/g ; Total Acidity = 0.49-0.54 mm/gm
The novelty of the present invention lies in the process to convert natural gas liquid preferably in the range C5- C6 hydrocarbons into liquefied petroleum gas and high octane gasoline using modified ZSM -5 zeolite catalyst optimized to reduce the dry gas yield. The process has been developed to facilitate its retrofitting in existing LPG recovery unit taking the advantage of existing LPG recovery unit, existing flare release system and availability of feed at high pressure. A safe reactor swing logic and associated controls are evolved to operate this fast deactivating catalyst in fixed bed reactor thus making the process economical viable at low capacity.
The following examples are given by way of illustration of the present invention and therefore should not be construed to limit the scope of the present invention.
Example 1
A method for the preparation of acidity modified ZSM-5 zeolite catalyst as described in our patent application No.2627/DEL/96 dated 29/11/96
A mixture of tetra propyl ammonium bromide [ N ( C3 H7 ) Br], aluminium sulphate [AI2 ( 804)3 ] • H2 O and deionised water were aded to silica gel under stirring. The chemical composition of the initial gel was 3Na2 O : AI2 Oa: 30 SiO2 : 825 H2 0. The pH of the reaction gel was controlled at 10.5 by adding 3.5 ml of

1:1 H2 S04 solution. The crystallization of the reaction mixture was carried out at 150°C in an autoclave for 3.5 days. The solid was filtered, washed with hot water and then dried at 80 °C. The zeolite sample thus obtained was calcined at 480 °C for 12 hours in presence of dry air to remove organic matter. The ion exchange of zeolite samples was carried out by submitting the samples to 3 cycles of ion exchange with 0.2N solution of NhU NO3 at 80 °C for 4 hours followed by filtration and washing with hot water. This zeolite material was subjected to steam treatment at 300°C . Steam treated zeolite sample (10g) was mixed with 85 ml. 1N HCI and refluxed for 30 minutes, filtered and washed free of chlorides ions with demineralized water and dried at 110 °C for 16 hours. Extrudates of the zeolite sample prepared and modified as above were made using alumina as binder in a proportion of 65% by weight of zeolite and 35% by weight of binder.
Example 2
The feed stock characteristics of natural gas liquid used in this process for a preparation of LPG /propane along with a gasoline by product are shown below. About 40cc of the catalyst (24 g) as prepared in Example 1 in extruded from of 1/16" diameter is loaded in a fixed bed reactor. The liquid product was analyzed using a gas Chromatograph fitted with Tetra Cyano Ethoxy Propionitrile column and FID detector. The gaseous products were analyzed using Squalane column.
Characteristics of Natural Gas Liquid (NGL) Feed stock:
Density at 15°C= 0.695; RVP (Kg/cm2 at 38°C)= 0.560
Research Octane Number (RON) = 74
ASTM°C
IBP - 37.2
10 - 48.3

30 - 54.0
50 - 59.8
70 - 67.6
90 - 86.6
FBP - 120.2
Feed Composition (wt %):
C5 Paraffins - 34.9
C6 Paraffins - 43.0
Ce Aromatics - 4.9
C/and higher hydrocarbons - 17.2
TOTAL - 100
This example describes the yields of product LPG and high-octane gasoline obtained in the NTGG process from the NGL feed stock along with high-octane gasoline characteristics. The ranges in yield of individual product component and gasoline characteristics that can be obtained in this process are given.
Table 1 :Characteristics of Gas and Liquid Products obtained in NTGG process
Feed : Natural Gas Liquid (NGL) of Vaghodia
Reaction Temperature = 400°C to 500°C
Pressure = 5 to 25 kg/cm2

Reactor: Bench Scale Reactor of 100 gm-catalyst capacity
(Table Removed)

Example 3
This example illustrates the results of the effect of process parameters on the yield and composition of LPG. The process parameters are varied in the range reported in Table 2 such that severity of operation increases for the four cases A,B,C and D. For each case product analysis is reported in Table 2:
Table 2 .-Flexibility in process operation : Variation in Yield and composition of LPG
Feed : Natural Gas Liquid (NGL); Reaction Temperature = 450°C to 480°C Pressure = 10 to 20 kg/cm2

WHSV = 5 to 6 hr-1
The product yields for the four operating cases in increasing severity are as follows.
(Table Removed)
Example 4
This example illustrates the effect of run length on the product yield viz. Fuel Gas (C1+C2), LPG (C3+C4), liquid product and their composition. In the run length of 37 hrs, the product was analyzed at various intervals and results are presented in Table 3.
Table 3 : Catalyst Stability Studies
Feed : Natural Gas Liquid (NGL) Reaction Temperature = 450°C WHSC = 6.0 hrs'1 Pressure = 20 kg/cm2, abs

(Table Removed)

Example 5
This example describes the effect of change of NGL composition on the product yield. This reaction was conducted at optimum process conditions and the results were given in table 4.
Table 4 : Effect of Feed Composition on Ex -Reactor Yields
Conditions: As they are given in Table 4.
(Table Removed)
Example 6
This example illustrates the effect of catalyst regeneration on the product yields in the process of present invention for the LPG production from NGL. The product yields patterns before and after the regeneration are given in the table 5.
Table. 5 : Reproducibility of the Ex-reactor yields after the Regeneration Process
Feed = Natural Gas Liquid(NGL);
Reaction Temperature = 450°C
Pressure = 20 kg/cm2
WHSV = 6hr'1
(Table Removed)

The main advantages of the present invention are:
1. The process of the present invention converts all types of hydrocarbon
components present in the feed NGL viz. Paraffins, iso-paraffins, naphthenes
and benzene into LPG and high octane components e.g. iso-paraffinic and
aromatic hydrocarbons with a high selectivity with a single catalyst system.
2. NGL which is not potential feed stock for catalytic reformers, can be
effectively converted to value added LPG and high-octane gasoline products.
3. The catalyst used in this process is relatively low cost and eco-friendly and it
does not involve the acid leaching with hazardous mineral acids such as HCI
during preparation.
4. The catalyst used in this process reduces dry gas ex-reactor yields from 12 to
4 wt% with increase of high-octane liquid product, thereby improves the
economics of this process.
5. LPG, which is a major product in the present process, can meet the great
industrial and domestic demands.
6. The process does not require hydrogen.
7. The process also does not require use of corrosive organic chloride additives.
8. The high-octane liquid by-product obtained in the process can be used as a
gasoline blender to boost octane number.
9. The process of present invention can be retrofitted with existing LPG recovery
plants from NGL located at remote thus avoiding the difficult NGL
transportation for further processing and the existing LPG supply network can
be used to reach the market place.

10. This process is economically viable even at low capacities due to reduction in investment by retrofitting it to the existing LPG recovery units.

We claim :
1. A process for the conversion of natural gas liquid to liquefied petroleum gas and high octane gasoline which comprises :
a) contacting natural gas liquid as feed stock containing hydrocarbon
having carbon atoms in the range of C5 to C9 with the modified ZSM-5
zeolite catalyst at a weight hourly space velocity ranging from 4-10 hrs"
\ at a temperature in the range of 400-500°"C, at a pressure in the
range of 5-25 kg/cm2 Ibs for 24 hours, optionally in the presence of
inert gas,
b) separating the liquid petroleum gas high octane gasoline and other
products of the resultant reaction mixture from first reactor by known
methods,
c) carrying out in-situ regeneration of catalyst in reactor for 24 hours
by oxidative combustion,
d) repeating the conversion of natural gas liquid to liquified petroleum
gas and high octane gasoline in the reactor is carried out as in step( b)
and step ( c) followed by in-situ regeneration of catalyst bed.
2 A process as claimed in claims 1-3 wherein weight hourly space
velocity is preferably in the range 4-6 hrs"1
3. A process as claimed in claims 1-4 wherein the reactor temperature is
preferably in the range of 440-460°C.

4. A process as claimed in claims 1-5 wherein reactor pressure is
preferably in the range of 10-20 kg/cm2lbs.
5. A process as claimed in claims 1-7 wherein heavier hydrocarbons
obtained by oligomerization of the feedstock is fractionated in a lower
pressure product splitter unit to produce gasoline of required final
boiling point.
6. A process as claimed in claims 1-8 wherein the catalyst used is a novel
acidity modified ZSM-5 zeolite.
7. A process as claimed in claims 1-9 wherein the process conditions viz.
pressure can be varied 5-25 kg/cm2 temperature can be varied 400-
500°C to control the C9+ aromatic content in the product in order to
improve the catalyst life against the coke lay down.
8. A process for the conversion of natural gas liquid to liquefied petroleum
gas and high octane gasoline substantially as herein described with
reference to the examples and drawings accompanying this
specification.

Documents:

10-del-2001-abstract.pdf

10-del-2001-claims.pdf

10-del-2001-correspondence-others.pdf

10-del-2001-correspondence-po.pdf

10-del-2001-description (complete).pdf

10-del-2001-drawings.pdf

10-del-2001-form-1.pdf

10-del-2001-form-19.pdf

10-del-2001-form-2.pdf

10-del-2001-form-3.pdf

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Patent Number

230855

Indian Patent Application Number

10/DEL/2001

PG Journal Number

13/2009

Publication Date

27-Mar-2009

Grant Date

28-Feb-2009

Date of Filing

05-Jan-2001

Name of Patentee

COUNCIL OF SCIENTIFIC AND INDUSTRIAL RESEARCH

Applicant Address

RAFI MARG, NEW DILHI-110 001, INDIA.

Inventors:

#	Inventor's Name	Inventor's Address
1	PERUPOGU VIJAYANAND	INDIAN INSTITUTE OF PETROLEUM, DEHRADUN-248005,INDIA
2	NAGABHATLA VISWANADHAM	INDIAN INSTITUTE OF PETROLEUM, DEHRADUN-248005,INDIA
3	YOGESH KUMAR KUCCHAL	INDIAN INSTITUTE OF PETROLEUM, DEHRADUN-248005,INDIA
4	JAI KRISHNA GUPTA	INDIAN INSTITUTE OF PETROLEUM, DEHRADUN-248005,INDIA
5	ALOK SAXENA	INDIAN INSTITUTE OF PETROLEUM, DEHRADUN-248005,INDIA
6	CHIUNCHU RAGHUVERA PRASAD	GAS AUTHOITY OF INDIA LIMITED,16,BHIKAIJI CAMA PLACE,CEW DELHI 110066,INDIA
7	HAR PARKASH CHANDNA	GAS AUTHOITY OF INDIA LIMITED,16,BHIKAIJI CAMA PLACE,CEW DELHI 110066,INDIA
8	KUMAR DE	GAS AUTHOITY OF INDIA LIMITED,16,BHIKAIJI CAMA PLACE,CEW DELHI 110066,INDIA
9	RANJAN GHOSH	GAS AUTHOITY OF INDIA LIMITED,16,BHIKAIJI CAMA PLACE,CEW DELHI 110066,INDIA
10	ASHIM KUMAR NANDI ROY	GAS AUTHOITY OF INDIA LIMITED,16,BHIKAIJI CAMA PLACE,CEW DELHI 110066,INDIA
11	RACI AGARWAL	GAS AUTHOITY OF INDIA LIMITED,16,BHIKAIJI CAMA PLACE,CEW DELHI 110066,INDIA

PCT International Classification Number

C10G 5/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA