Process for catalytic conversion of low value hydrocarbon streams to light olefins

Abstract

A process for catalytic conversion of low value hydrocarbon streams to light olefins in comparatively higher yields is disclosed. Propylene is obtained in amounts higher than 20 wt. % and ethylene higher than 6 wt. %. The process is carried out in a preheated cracking reactor having a single riser and circulating an FCC catalyst. The riser is divided into three temperature zones in which different hydrocarbon feeds are introduced. An oxygenate feed is introduced in the operative top zone in the riser. Heat for the endothermic cracking is obtained by the exothermic reaction of converting the oxygenate feed into gas and/or from a regenerator in which the spent FCC catalyst is burnt.

Claims

1. A process for obtaining light olefins comprising the following steps: i. providing a pre-heated cracking reactor comprising a riser maintained at a pressure in the range of 0.5 to 3 bar, charged with a solid acidic FCC catalyst, said riser being provided with at least three temperature zones; a first zone operative at the bottom of the riser having a temperature in the range of 650 C. to 750 C., a second intermediate zone having a temperature in the range of 580 C. to 650 C. operative at a point above the first zone and a third zone operative at the top of the riser, above the second zone, having a temperature in the range of 500 C. to 620 C.; ii. feeding a first hydrocarbon feed comprising C4 hydrocarbons and a paraffinic stream to the first zone at a weight hourly space velocity of 0.2 h.sup.1 to 50 h.sup.1, feeding a second hydrocarbon feed comprising olefinic naphtha to the second intermediate zone at a weight hourly space velocity of 5 h.sup.1 to 100 h.sup.1, feeding a third hydrocarbon feed comprising heavy hydrocarbons to the third zone at a weight hourly space velocity of 40 h.sup.1 to 200 h.sup.1; iii. cracking the first, second and third hydrocarbon feeds sequentially along the riser, thereby producing light olefins; wherein additional heat is provided to the riser by: introducing an oxygenate feed comprising methanol to the third zone and converting the oxygenate feed to olefins; and optionally burning coke formed in a spent FCC catalyst in a regenerator at a temperature of 650 to 750 C. in the presence of oxygen to generate hot gases and feeding the hot gases to the first zone.

2. The process as claimed in claim 1, wherein said paraffinic stream comprises 4 to 6 carbons; the second hydrocarbon feed comprises C5-C12 olefinic naphtha; the third hydrocarbon feed comprises at least one heavy hydrocarbon selected from the group consisting of gas oil, vacuum oil, atmospheric oil/vacuum residue, slurry oil, crack-able cycle oil and heavy crude; and the oxygenate feed further comprises at least one of ethanol and ether.

3. The process as claimed in claim 1, wherein the weight proportion of said C4 hydrocarbon stream varies from 10 to 30 wt %, with respect to the total feed weight and comprises an olefin content from 30 to 80 vol %; the weight proportion of the paraffinic stream varies from 5 to 30 wt %, with respect to the total feed weight; the weight proportion of the second hydrocarbon feed varies from 20 to 95 wt %, with respect to the total feed weight; the weight proportion of the third hydrocarbon feed varies from up to 25 wt %, with respect to the total feed weight; and the amount of the oxygenate feed varies in the range of from up to 66 wt %, with respect to the total feed weight.

4. The process as claimed in claim 1, wherein the third hydrocarbon feed and the oxygenate feed are fed to the third zone through two separate injection points.

5. The process as claimed in claim 1, wherein the residence time of the oxygenate feed is 0.5 sec, based on the oxygenate feed flow rate.

6. The process as claimed in claim 1, wherein the oxygenate feed is converted to ethylene and propylene.

7. The process as claimed in claim 1, wherein at least one of the first, second, and third zone is further divided into at least one subzone.

8. The process as claimed in claim 1 wherein the cracking process comprises the stops of separating a spent FCC catalyst from the cracked gaseous stream.

9. The process as claimed in claim 1, wherein the step of burning the spent FCC catalyst in the regenerator includes the step of obtaining hot regenerated catalyst and producing heat nearly equivalent to the heat required for endothermic cracking of the hydrocarbon feeds in the riser and a pressure in the range of 1 to 3 bar.

10. The process as claimed in claim 1, wherein the cracking process further comprises recycling a regenerated catalyst to the cracking reactor.

11. The process as claimed in claim 1, wherein the FCC catalyst comprises a large pore size zeolite selected from the group consisting of USY, REUSY, Beta and combinations thereof, wherein the large pore size zeolite is further doped with alkaline earth metal(s) selected from the group consisting of Ca, Mg, Sr and combinations thereof, such that the weight proportion of the alkaline earth metal(s) vary from 500 to 20,000 ppm.

12. The process as claimed in claim 1, wherein the FCC catalyst comprises at least one large pore size zeolite in combination with additives that include medium pore size zeolite selected from the group consisting of ZSM-5, ZSM-11, ZSM-22, SAPO-11 and combinations thereof, wherein the medium pore size zeolite additive is a phosphate stabilized zeolite comprising a silica to alumina ratio in the range of 20 to 80; and wherein the weight proportion of the medium pore size zeolite in the additive ranges from 5 to 60 wt % and the weight proportion of said large pore size zeolite ranges from 0.1 to 35 wt %.

13. The process as claimed in claim 1, wherein the light olefins comprising propylene and ethylene are obtained in an amount higher than 20 wt % and 6 wt %, respectively.

14. The process as claimed in claim 1, which includes the step of preheating the hydrocarbon feeds before introducing them into the riser.

15. The process as claimed in claim 1, further comprising controlling at least one of a group of steps comprising preheating the hydrocarbon feeds, controlling the feed rates of the feeds and diluting the feeds with steam.

Description

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING

(1) FIG. 1 illustrates a schematic presentation of Thermo Neutral Catalytic Conversion process, in accordance with the present disclosure.

DETAILED DESCRIPTION

(2) The disclosure will now be described with reference to the embodiments shown in the non-limiting accompanying drawings. The embodiments do not limit the scope and ambit of the disclosure. The description relates purely to the exemplary preferred embodiments of the disclosure and its suggested applications.

(3) The diagrams and the description hereto are merely illustrative and only exemplify the disclosure and in no way limit the scope thereof.

(4) Accordingly, a process for improved production of light olefins by catalytically cracking a hydrocarbon feed stock in a single riser is disclosed in the present disclosure wherein the improved production of light olefins from hydrocarbon feedstock is produced under thermally sustained cracking conditions using a single riser system.

(5) As used herein the term thermo-neutral refers to a heat-balanced cracking reaction wherein the heat requirement for endothermal cracking is met by heat released by an exothermal cracking of oxygenate or burning the coke deposited on catalyst surface during regeneration process of catalyst.

(6) As used herein the term fresh feed refers to a hydrocarbon feed introduced in the reaction zone for conversion and does not include any re-cycled product from that of reaction zone.

(7) As used herein the term riser refers to a part of the reactor used in a fluid catalytic process.

(8) As used herein the term, difficult to crack refers to crack-ability of olefinic C4 hydrocarbon streams and paraffinic C.sub.4-C.sub.6 hydrocarbon streams.

(9) As used herein the term moderate to crack refers to crack-ability of olefinic naphtha streams (C.sub.5-C.sub.12).

(10) The term easy to crack as used in the present disclosure refers to crack-ability of gas oil, vacuum gas oil, atmospheric/vacuum residue, slurry oil, crack-able cycle oil, heavy crude and oxygenate like methanol, ethanol, ether and the like.

(11) The process as disclosed in the present disclosure is a thermo-neutral cracking process wherein the heat requirement for endothermal cracking of hydrocarbon feedstock is accomplished by simultaneously executing the endothermic and exothermic cracking in the same riser. Alternatively, the heat-balanced conditions are provided by burning the coke deposited on cracking catalyst surface in a catalyst regenerator to produce heat equivalent to the heat required for endothermal cracking. The thermo-neutral catalytic conversion of hydrocarbon feedstock in accordance with the present disclosure is typically accomplished in a single riser wherein the cracking conditions including the type and ratio of hydrocarbon feeds, cracking catalyst, temperature, pressure and the riser configuration are optimized to procure light olefins in improved yield.

(12) The above described objects of obtaining light olefins in improved yield by employing thermally sustained cracking reaction in a single riser are accomplished by cracking the hydrocarbon feedstock in a sequential manner wherein diverse range of hydrocarbon feeds having different cracking behavior are catalytically cracked in a sequential manner. The sequential cracking of hydrocarbon feeds is carried out in a way so as to maintain the thermo-neutral or heat-balanced conditions during entire catalytic cracking process.

(13) As described above, the thermo-neutral condition during catalytic cracking is typically sustained by performing the endothermal and exothermal cracking in the same riser or by burning the coke deposited on catalyst surface in the catalyst regenerator. The heat produced during catalyst regeneration or coke burning is further utilized in endothermal cracking of feed.

(14) Typically, the feed stocks having difficult, moderate or easy cracking behavior are employed in the process of the present disclosure. The feeds having difficult to moderate cracking behavior are low coke making feedstock, whereas the feeds having easy crack-ability are usually high coke making feeds or oxygenates that crack exothermally.

(15) Typically, the feeds having difficult crack-ability comprises at least one hydrocarbon feed selected from the group consisting of olefinic C.sub.4 hydrocarbons and paraffin having 4 to 6 carbons.

(16) Typically, the feeds having moderate crack-ability comprise olefinic naphtha streams having 5 to 12 carbons.

(17) Typically, the higher coke making feeds having easy crack-ability are heavy hydrocarbons that include at least one selected from the group consisting of gas oil, vacuum gas oil, atmospheric/vacuum residue, slurry oil, crack-able cycle oil and heavy crude.

(18) The hydrocarbon feeds of the present disclosure further comprises oxygenate for exothermal cracking. The oxygenate typically includes at least one selected from the group consisting of methanol, ethanol and ether.

(19) The sequential cracking of hydrocarbon feedstock in accordance with the present disclosure is carried in a single riser. The single riser is a multizone riser having different zones for sequential cracking the hydrocarbon feeds. The multizone riser comprises high, intermediate and low severity zones for sequentially cracking the feeds having difficult, moderate and easy cracking behavior.

(20) The sequential catalytic cracking process of the present disclosure is further described in light of the schematic depiction of thermo-neutral catalytic process (refer to FIG. 1 of the accompanying drawing). The system as employed in the sequential catalytic cracking process of the present disclosure comprises a reaction section 100 and 101, a regeneration section 105 and 106 and a product separation section 110.

(21) The reaction section includes a riser 101 and a reactor 100 wherein feeds having different cracking behavior are introduced separately in a sequential manner particularly from low coke making feed to high coke making or from feeds having difficult crack-ability to feeds having easy crack-ability in the different reaction zones of the single riser.

(22) The thermo-neutral cracking process of the present disclosure comprises at least one reaction selected from the group consisting of (i) endothermally cracking the feeds having C.sub.4 hydrocarbons to heavy hydrocarbons, sequentially followed by cracking the exothermal oxygenate or (ii) burning the coke deposited on catalyst surface in a catalyst regenerator to provide heat required for endothermal cracking of feeds having C.sub.4 hydrocarbons to heavy hydrocarbons.

(23) The sequential cracking comprises the cracking of C.sub.4 hydrocarbons stream 102 at the bottom riser, cracking of paraffinic streams 117 having 4 to 6 carbons at higher elevation of C.sub.4 stream injection 102, cracking of predominantly olefin streams like olefinic naphtha streams 121 having 5 to 12 carbons at higher elevation of paraffinic C.sub.4-C.sub.6 streams injection and optionally, the cracking of methanol 122 or higher coke making heavy feedstock 123 at the top of the riser. The process of the present disclosure comprises inclusion of at least one of the following feeds; oxygenate stream (methanol, ethanol and ether) and third hydrocarbon stream (higher coke making heavy feedstock).

(24) The C.sub.4 hydrocarbon feed as injected in the bottom riser is typically a fresh hydrocarbon feed. In one of the embodiments, a recycled C.sub.4 hydrocarbon stream 115 generated during sequential catalytic process of the present disclosure is injected with fresh C.sub.4 hydrocarbon stream at the bottom riser to maximize light olefin production. The recycled C.sub.4 hydrocarbon stream 115 is mixed with fresh C.sub.4 hydrocarbon feed 102 only when the recycle C.sub.4 hydrocarbon stream 115 comprises minimum of 30 vol % olefin. In another embodiment, the fresh C.sub.4 hydrocarbon stream 102 or combination of fresh C.sub.4 hydrocarbon stream 102 with recycled stream 115 is diluted with steam prior their injection at the bottom riser.

(25) The C.sub.4 stream 102 including the C.sub.4 recycle stream 115 is cracked in riser bottom. The cracking of C.sub.4 hydrocarbon feed is typically carried out by contacting the feed with a FCC catalyst at suitable cracking conditions of temperature and pressure. The cracking of C.sub.4 hydrocarbon feed at the bottom riser is typically carried out at a temperature varying from 650 C. to 750 C.; most preferably at 660 C. to 680 C. The weight hourly space velocity (WHSV) is typically maintained in the range of from 0.2 hr.sup.1 to 50 hr.sup.1, preferably 1 to 25 hr.sup.1 and most preferably 1 to 10 hr.sup.1.

(26) The paraffinic stream having 4 to 6 carbons 117 is introduced above C.sub.4 injection at the bottom riser having high severity cracking conditions. The paraffinic C.sub.4-C.sub.6 stream 117 is typically introduced at a distance equivalent to 1 to 1.5 s vapor residence time of C.sub.4 stream 102. The weight proportion of paraffinic C.sub.4-C.sub.6 streams 117 introduced in the riser varies from 5 to 30 wt %, with respect to the weight of total fresh feed wherein initial boiling point (IBP) varies from 35 C. to 50 C. and final boiling point varies from 200 C. to 221 C. The paraffinic stream having aromatic contents not more than 20 vol %, preferably less then 10 vol % is preferred.

(27) The paraffinic stream having 4 to 6 carbons 117 is injected as a fresh feed. In another embodiment, the paraffinic stream having 4 to 6 carbons 117 is injected with a recycle naphtha stream 118 obtained from separation tank 110 of the present disclosure.

(28) The cracking of paraffinic C.sub.4-C.sub.6 stream 117 is carried out by contacting the feed with the FCC catalyst at a temperature of 630 C. to 690 C., most preferably 650 C. to 680 C. The WHSV during paraffinic cracking is typically maintained in the range of from 5 to 100 hr.sup.1, most preferably 50 to 80 hr.sup.1.

(29) After introducing paraffinic C.sub.4-C.sub.6 stream, olefinic naphtha stream having 5 to 12 carbons injected at a point above the paraffinic C.sub.4-C.sub.6 feedstock injection points so that paraffinic feed (C.sub.4-C.sub.6) 117 acquires vapor residence time of 1 to 1.5 s. The weight proportion of olefinic naphtha streams (C.sub.5-C.sub.12) 121 introduced in the riser varies from 20 to 95 wt % of total fresh feed, most preferably 50 to 95 wt. %.

(30) The olefin content of C.sub.5 to C.sub.12 olefinic naphtha stream varies from 30 to 70 vol %, most preferable from 45 to 55 vol %. The cracking of moderate to easy cracking feed i.e. olefinic naphtha stream having 5 to 12 carbons 121 is carried out at a temperature of 580 C. to 650 C. The weight hourly space velocity during catalytic cracking of olefinic naphtha feed varies from 5 to 100 hr-1.

(31) The high coke making feed i.e. heavy hydrocarbons are injected at the top of the riser having low severity cracking conditions above olefinic naphtha streams having 5 to 12 carbons 121 injection points. The cracking of high coke making feed is typically carried out at temperature varying in the range of 500 C. to 620 C., most preferably 570 C. to 620 C. and with WHSV varying from 40 to 200 hr-1. The weight proportion of higher coke making heavy hydrocarbon stream 123 injected at the top of the riser varies from 0 to 25 wt %, most preferably 10 to 15 wt %, with respect to the weight of total fresh feed. The high coke making feed is introduced as a fresh feed. In another embodiment, a recycle CSO stream 119 obtained from separation tank 110 is injected with the high coke making feed.

(32) In one of the embodiments, the thermo-neutral sequential cracking of the present disclosure comprises the exothermic cracking of oxygenate feed to provide heat required for the endothermic cracking of hydrocarbon feeds having C.sub.4 to heavy hydrocarbons. The oxygenate feed as employed in the present disclosure typically include at least one selected from the group consisting of methanol, ethanol and ether.

(33) Preferably, the methanol 122 in an amount of from 20 to 40 wt %, with respect to the weight of total fresh feed is introduced at the top portion of the riser having low severity cracking conditions. The methanol 122 is injected with high coke making heavy hydrocarbon feed 123 at same elevation of riser, which is typically higher than that of olefinic naphtha stream. The low severity zone of the single riser comprises two separate injection points for injecting heavy hydrocarbon feed and oxygenate separately at the same elevation point. The weight proportion of the third feed varies from 0 to 25 wt %, with respect to the total feed weight and the amount of oxygenate feed varies in the range of 0 to 66 wt %, with respect to the total feed weight. Typically, when the weight proportion of the third feed is 0, the weight proportion of the oxygenate feed is not 0 and when the weight proportion of the oxygen feed is 0, the weight proportion of the third feed is not 0. The residence time of oxygenate feed is typically maintained at 0.5 sec based on only oxygenate flow rate.

(34) The weight ratio of heavy hydrocarbon feed to methanol typically varies from 0 to 1. The cracking of oxygenate feed is typically carried out the top of the riser under low severity cracking conditions that include the cracking temperature of 500 C. to 620 C., most preferably 500 C. to 600 C. and weight hourly space velocity of 40 hr.sup.1 to 200 hr.sup.1. The pressure in the top of riser reactor is in the range of 0.5 to 3.0 bar (g).

(35) The each severity zone of the single riser of the present disclosure is further subdivided into more than one subzone depending on the crack-ability of individual feedstock. The operation control of each zone is provided and maintained by altering the feed preheat temperature and steam dilution to the combined hydrocarbon stream entering to each zone. The desired WHSV in each zone is additionally achieved by altering the riser diameter, length and injection of the hydrocarbon and dilution steam.

(36) The product vapors coming out of the reactor section 100, wherein the spent catalyst is separated from cracking products, goes to the separation section 110 through conduit 109. The separation section 110 consists of fractionation columns and gas concentration section. The cracking products are further separated into different products like dry gas 111, ethylene 112, propylene 113, C.sub.4 116, naphtha 120, light cycle oil (LCO) 114 and clarified slurry oil (CSO) 124. Out of these streams, a portion or complete C.sub.4 stream 115 is recycled back through conduit and injected at the bottom riser along with fresh C.sub.4 stream 102 to increase the yield of C.sub.2 and C.sub.3 olefin products. A portion or complete naphtha stream 118 is also recycled back through conduit along with fresh Paraffinic C.sub.4-C.sub.6 stream 117 to provide an additional conversion across the overall process system. A portion or complete CSO stream 119 is recycled back through conduit along with fresh heavy hydrocarbon feed 123 to provide additional coke deposition on catalyst to satisfy heat requirement.

(37) The spent catalyst recovered from reactor 100 passes from reactor stripper section through spent catalyst stand pipe 104 and is introduced to the regeneration section which consists of a combustor 106 and regenerator vessels 105. In the regenerator section, the catalyst is contacted with oxygen containing gas such as air 107, at the temperature range of 650 to 750 C., pressure of 1 to 3 bar(g) to remove coke deposited on the spent catalyst. The oxygen containing gas is introduced into the regenerator through conduit 107 and combustion gases pass from regenerator by way of conduit 108. The regenerated hot catalyst then passes from regenerator to the riser through regenerated catalyst standpipe 103. The heat generated during regeneration of spent catalyst is further utilized for heating the feeds while contacting feeds with regenerated catalyst. The sequential thermo-neutral catalytic process of the present disclosure produces light olefins that typically include ethylene and propylene in an amount higher than 6 wt % and 20 wt % respectively.

(38) The catalyst as employed in the present disclosure for cracking the hydrocarbon feeds under thermo-neutral conditions is typically a FCC catalyst comprising at least one large pore zeolite selected from the group consisting of USY REUSY, beta or combination thereof. The FCC catalyst as employed in the present disclosure is further used in combination with an additive (pentasil zeolite) selected from the group consisting of ZSM-5, ZSM-11, ZSM-22, SAPO-11 and combinations thereof. Typically, the additive is a medium pore zeolite. The ZSM 5-additive is typically a phosphate stabilized zeolite having silica to alumina ratio in the range of 20 to 80, most preferably 30 to 40. Typically, the weight proportion of the ZSM-5 zeolite in the additive varies from 5 to 60 wt %, most preferably 20 to 30 wt %; whereas the weight percent of the large pore size zeolite ranges from 0 to 35 wt %. The product selectivity of FCC catalyst is further enhanced by doping the additive with alkaline earth metals that typically include at least one selected from the group consisting of Ca, Mg and Sr. The concentration of alkaline earth metal typically varies from 500 to 20000 ppm, more preferably from 5000 to 10000 ppm, without adversely affecting activity of catalyst.

(39) The FCC catalyst as employed in the cracking process of the present disclosure is prepared by employing the process as disclosed in our co-pending Indian patent application no. 1955/MUM/2011 and PCT application PCT/IN2011/000599. However, ZSM-5 zeolite and ReUSY or USY based catalyst available in commercial markets can also be used in the present disclosure.

(40) The embodiments herein and the various features and advantageous details thereof are explained with reference to the non-limiting embodiments in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.

Illustrative Example

(41) According to the present disclosure, there is provided a sequential multizone, multifeed & thermo neutral catalytic cracking process. The process comprising of sequential multizone reaction section in a single riser divided into high, intermediate and low severity zones for sequential cracking of wide range of feedstock from C.sub.4 to residue including both olefinic and paraffinic naphtha streams as further distinguished by difficult to crack, moderate to crack, easy to crack and high coke making feedstock. (refer to FIG. 1 for Schematic depiction of Thermo Neutral Catalytic Conversion (TNC2) process). The operational control of each zone is maintained by altering the feed preheat temperature, feedstock flow rate and steam dilution to the combined hydrocarbon stream entering each zone and whereas the desired WHSV in each zone is additionally achieved in the design by altering the riser diameter, length and location of the injection point for hydrocarbon and dilution steam.

(42) The properties of different feedstock used for different examples are given in Table 1.

(43) TABLE-US-00001 TABLE 1 Characterization of different feedstock Light Coker Naphtha (LCN) Clarified Slurry Oil (CSO) Feed Kg/m3 682.2 1071 Density @ 15 C. Distillation Volume % Weight % Initial C. 39 188 Boiling Point 5% C. 294 30% C. 56 360.5 50% C. 65 390 70% C. 76 424 90% C. 87 487 FBP C. 101 605

Example 1

(44) This example illustrates the concept of thermal neutrality with the regeneration of catalyst by combining endothermic cracking of Light Coker Naphtha (LCN) with exothermic cracking of Methanol over hydrothermally deactivated ZSM-5 additive. The physico-chemical properties of fresh ZSM-5 additive are given in Table 2.

(45) TABLE-US-00002 TABLE 2 Physico-chemical properties of ZSM-5 zeolite based catalyst ZSM-5 based catalyst Total Surface area, m2/gm 140 Total zeolite Surface area, 110 m.sup.2/g Chemical Analysis, wt. % Al.sub.2O.sub.3 18.70 Na.sub.2O 0.11 P.sub.2O.sub.5 11.98 ABD, g/cc 0.75 Attrition Index(ASTM) 3.12 Particle Size Distribution, wt. % 40 micron 6 60 28 80 53 100 72 APS 77

(46) The above ZSM-5 additive was hydro thermally deactivated separately at 800 C., atmospheric pressure for 20 hours using 100% steam. 10 g of hydrothermally deactivated ZSM-5 additive was loaded in fixed fluid bed micro reactor. The micro reactor is electrically heated to maintain the catalyst bed temperature of 620 C. The LCN as mentioned in Table 1 was cracked in the fluidized bed reactor for time of stream (TOS) of 30 seconds at 620 C. temperature and atmospheric pressure wherein vapor residence time is lower than 0.5 sec. Immediately after cracking, catalyst bed was stripped with nitrogen for removing all strippable hydrocarbons and cracked gas along with strippable hydrocarbon which was collected and measured under chilling condition was analyzed to get gas yield. The coke on catalyst was burnt off using air at 750 C. temperature, wherein coke was measured by passing flue gas to on-line IR analyzer. The collected liquid product was analyzed in typical SIMDIST analyzer to get different liquid product. This experiment gave yield pattern of LCN as mentioned in column-1 of Table 3.

(47) As explained above, another experiment was carried out without burning of coke deposited on catalyst. Once stripping was over, methanol was cracked on spent catalyst bed for TOS of 30 sec at 620 C. temperature and atmospheric pressure wherein vapor residence time was less than 0.5 sec. The yield pattern from Methanol cracking is summarized in column-2 of Table 3.

(48) TABLE-US-00003 TABLE 3 Yields from heat neutral cracking of LCN and Methanol LCN & Methanol LCN Methanol (1:1.40) Yield, wt. % Column-1 Column-2 Column-3 Dry gas (excluding 4.82 5.57 5.26 ethylene) Ethylene 10.58 10.48 10.52 Propylene 19.73 14.11 16.45 38.14 23.67 29.70 Gasoline (C5-221 C.) 43.63 4.58 20.85 Coke 2.09 0.7 1.28 221 C..sup.+ (water) 0.74 (55) 32.39

(49) The above data shows that even though spent additive have some coke due to cracking of LCN, the residual activity of additive is enough for selectively cracking of methanol. Therefore, sequential cracking of LCN followed by methanol provide better yield of olefin from methanol even at very high temperature. The coke make (2.09 wt. %) from Light Coke Naphtha feed is low as compared to the required coke of 5.7 wt. % (on feed) to supply the total heat required for preheating, vaporization and cracking the feed. The net heat demand for Light Coker naphtha is 346 Kcal/kg. The combined heat released from cracking of methanol alone and from burning its coke (0.7 wt. % on feed) is more than required for preheating and vaporizing methanol; net surplus heat is 192.2 Kcal per kg of methanol. The surplus heat released by cracking 1.4 kg of methanol is sufficient to preheat, vaporize and crack one kg of Light Coker naphtha. Hence, 1 kg of LCN is required to be cracked with 1.40 kg of methanol to make process heat neutral and estimated products are summarized in column-3 of Table 3. Therefore, LCN is to be cracked followed by cracking of methanol with residence time of less than one second. Heat generated in the regenerator from burning of the coke deposited during sequential cracking of LCN and Methanol on the catalyst also contributes in meeting the heat demand of the process.

(50) TABLE-US-00004 TABLE 4 Heat neutrality of Cracking LCN with Methanol LCN& Methanol LCN Methanol (1:1.40) Reactor temperature C. 620 620 620 Regent temperature C. 700 700 700 Cat to oil Wt/wt. 13.33 12.28 13.42 Actual Coke yield Wt % 2.09 0.7 0.81 feed Heat required for heating and Kcal 328.23 364.46 799.43 vaporizing feed Heat of cracking Kcal 91.35 560 632.66 Heat from coke burning Kcal 153.74 72.09 166.76 Net Heat Demand Kcal 265.8 266.0 0.0 Required Coke for heat Wt % 5.70 1.90 1.27 balance feed

Example 2

(51) This example further illustrates thermal neutrality by combining endothermic cracking of LCN with cracking of heavy feed like clarified Slurry oil (CSO) over mixed catalyst consisting of equal proportions of hydrothermally deactivated ZSM-5 additive and ultra-stable Y zeolite based FCC catalyst. CSO is a product from FCC unit from cracking of vacuum gas oil. In this experiment, ZSM-5 additive as mentioned in Table 2 has been used. However, physico-chemical properties of FCC catalyst used in this experiment are shown in Table 5.

(52) TABLE-US-00005 TABLE 5 Physico-chemical properties of fresh FCC catalyst FCC catalyst Total Surface area, m.sup.2/g 336 Total zeolite Surface area, m.sup.2/g 226 Pore volume, cc/g 0.35 ABD, g/cc 0.78 Chemical Analysis, wt. % Al.sub.2O.sub.3 29.37 Na.sub.2O 0.28 Re.sub.2O.sub.3 0.85 Particle Size Distribution, wt. % 40 micron 4 80 67 APS 70 Attrition Index(ASTM) 2.52

(53) LCN and clarified slurry oil (CSO) were cracked separately in fixed fluid bed reactor in presence of equal amount of ZSM-5 additive and FCC catalyst and yield pattern were summarized in Table 6.

(54) TABLE-US-00006 TABLE 6 Yield from cracking light Coker naphtha with heavy feed LCN& CSO LCN CSO (1:0.495) Yields, wt. % Column-1 Column-2 Column-3 Dry gas (excluding 4.15 4.50 4.27 ethylene) Ethylene 9.24 2.23 6.92 Propylene 20.02 3.03 14.39 LPG 37.77 5.56 27.11 Gasoline (C5-221 C.) 43.63 4.05 30.52 Coke 2.41 10.72 5.16 221 C..sup.+ 2.8 72.94 26.02

(55) The coke make (2.41 wt. %) from Light Coke Naphtha feed is low as compared to the required coke of 5.7 wt. % (on feed) to supply the total heat required for preheating, vaporization and cracking the feed. As shown in Table 7, the net heat demand for Light Coker naphtha is 242 Kcal/kg. The additional coke required for heat balancing is provided by cracking of heavy cycle oil which makes 10.72 wt. %. The heat released by burning the coke from heavy feed is more than required for preheating and vaporizing heavy feed; net surplus heat is 490 Kcal per kg of the heavy feed. The surplus heat released by cracking 0.495 kg of heavy feed is sufficient to preheat, vaporize and crack one kg of Light Coker naphtha. Thus cracking of LCN in combination with a heavy feed like Cycle oil makes the process heat neutral i.e. it does not require burning fuel oil/torch oil in the regenerator to supply external heat to run the process

(56) TABLE-US-00007 TABLE 7 Heat neutral cracking with regeneration by combining Light Coker feed with Heavy feed LCN& CSO LCN CSO (1:0.495) Column-1 Column-2 Column-3 Reactor temperature C. 620 620 620 Regenerator temperature C. 700 700 700 Cat to oil Wt/wt. 15.48 13.83 14.80 Kinetic Coke yield Wt % 2.41 10.726 5.02 feed Heat required for heating/ Kcal 328.23 145.18 473.41 vaporizing feed Heat of cracking Kcal 91.35 2.83 94.18 Heat from burning Kcal 177.28 390.57 567.85 available coke Net Heat Demand after Kcal 242.30 242.30 0.0 coke burning Coke for Heat balance Wt % 5.70 4.07 5.16 feed

Example 3

(57) This example illustrate concept of sequential cracking of feedstock depending on their crack-ability. LCN and n-hexane feedstock were separately cracked in fixed fluid bed micro reactor at different reactor temperature in presence of ZSM-5 zeolite based catalyst as explained in example 1. The yield patterns are summarized in Table 8. As shown in the Table 8, when both light Coker naphtha (LCN) and N-hexane are cracked at same conditions of 620 C., LCN cracks to produce high yield of propylene and ethylene with lower coke and dry gas yield, whereas N-hexane has lower yields of propylene and ethylene under same conditions. Increasing cracking severity (reaction temperature of 675 C.) improves the yield of Propylene and Ethylene for low cracking N-hexane whereas easily crack-able LCN substantially increases the yield of the undesirable products like dry gas and coke as compared to improvement in the yields of light olefins. Thus, feeds having different crack-ability need to be injected at different locations to provide optimum cracking severity to obtain maximum yields of Light olefins and to minimize undesirable products like coke and dry gas. In a single riser, this can be achieved by sequential cracking of N-hexane followed by LCN at two different locations along the riser length. As described in process description section, riser bottom temperature is in the range of 650 to 750 degree C. and catalyst has highest activity, hence, riser bottom is the ideal location to inject least crack-able material like C.sub.4 streams, saturated C.sub.4-C.sub.6 hydrocarbons etc. In summary, the high active catalyst and high severity zones at riser bottom provide flexibility to crack least crack-able hydrocarbon materials in a compact configuration using single riser and reactor.

(58) TABLE-US-00008 TABLE 8 Importance of sequential cracking in single riser - effect of operating severity Catalyst ZSM 5 ZSM 5 ZSM 5 ZSM 5 Feed LCN LCN N-HEXANE N-HEXANE Reactor 620 675 620 675 Temperature, C. Catalyst-to-Oil, wt./wt. 13.33 13.33 13.33 13.33 YIELDS, wt. %: Coke 2.09 6.67 1.88 3.93 Dry gas(excluding 4.82 8.71 7.17 13.04 ethylene) Ethylene 10.58 14.20 7.40 11.56 Propylene 19.73 23.32 13.06 17.84 LPG 38.14 39.47 26.25 31.39 Gasoline (35-221 C.) 43.63 30.44 57.12 39.96

Example 4

(59) This example illustrates importance of sequential injection over co-injection of feedstock. To make the process heat balanced, very high coke yielding (heavy) feeds are required to be cracked along with lighter feeds since lighter feeds do not make sufficient coke. In the single riser, if heavy feeds are injected prior to the lighter feeds or are co-injected at same location, the heavy feed will coke and deactivate the catalyst and will render it ineffective for cracking lighter feeds, ultimately deteriorating the overall yields. Using experimental setup as explained in example 1, cracking data for LCN and CSO were generated at 600 degree reaction temperature and atmospheric pressure, catalyst to oil ratio of 13.33 using TOS of 30 sec. Results are summarized in Table 9. Furthermore, LCN and CSO were mixed in equal proportion and co-injected into reactor maintaining reaction conditions as above. In case, LCN is cracked followed by CSO at above condition, the expected yield is estimated to be average of two individual yields as shown in column-3 of Table 9. As can be seen from Table 9, in case co-feeding, propylene yield was lower than the yields obtained by sequential feeding. Moreover, overall conversion also comes down while co-cracking the two feeds. It is worth to mention that sequential cracking in reverse order i.e., COS cracking followed by LCN cracking will deteriorate the yield pattern in comparison with co-feeding. This is ensured that the high coke making (heavy) feedstock needs to be introduced in the last zone of the riser.

(60) TABLE-US-00009 TABLE 9 Effect of co-injecting heavier and lighter feeds on yields. Catalyst Name ZSM 5 ZSM 5 ZSM 5 ZSM 5 Feed Name CSO LCN Averaged for 50:50 LCN and CSO CSO:LCN Reactor 600 600 600 Temperature, C. Catalyst-to-Oil, 13.33 13.33 13.33 13.33 wt./wt. Column-1 Column-2 Column-3 Column-4 Yields, wt. %: Coke 15.11 1.78 8.44 7.49 Dry gas(excluding 1.90 2.52 2.21 3.05 ethylene) Ethylene 1.39 8.59 4.99 5.06 Propane 0.22 3.20 1.71 2.45 Propylene 1.72 20.94 11.33 8.80 LPG 2.92 40.00 21.45 17.04 Gasoline 2.21 46.10 24.15 16.38 221 C..sup.+ 76.48 1.05 38.77 51.02

Example 5

(61) This example illustrate that the optimum catalyst mix is required to maximize yield of light olefins in a single riser from feeds having wide difference in crack ability. As per prior art, ZSM 5 zeolite based catalyst gives highest propylene yield and conversion for light feeds like LCN and N-hexane while heavy feed like clarified slurry oil (CSO) gives highest conversion with Y zeolite based catalyst. To find an optimum mix of ZSM-5 and Y zeolite, each of the three feeds viz. LCN, N-Hexane and CSO were cracked with each of 50 wt. % ZSM 5 crystal, 45 wt. % Y Zeolite crystal and 25 wt. % ZSM 5 crystal with 22.5 wt. % Y Zeolite crystal mixture based catalyst. The typical properties of ZSM-5 and USY based catalyst are shown in previous examples. Different experimental data generated in experimental set up which is explained in example-1. From table 10, it is observed that for light feeds like LCN and N-hexane, yield of light olefins and conversion are similar with 50 wt. % ZSM 5 crystal and with 25 wt. % ZSM 5 crystal+22.5 wt. % Y Zeolite crystal, but with 45 wt. % Y Zeolite crystal, the light olefin yields and conversion are the lowest from the three catalyst mixes. For heavy feed CSO, though 45 wt. % Y Zeolite crystal gives highest conversion but the yield of light olefins are lower than those obtained with 25 wt. % ZSM 5 crystal+22.5 wt. % Y Zeolite crystal mix. With CSO as feed, 50 wt. % ZSM 5 crystals give lowest conversion and lowest light olefin yields. Overall, it is observed that for light feeds, the yields of light olefins are similar for 45 wt. % Y Zeolite crystal and for 25 wt. % ZSM 5 crystal+22.5 wt. % Y Zeolite crystal mixtures and is better than with 45 wt. % Y Zeolite crystal case. For CSO also, mixture of 25 wt. % ZSM 5 crystal+22.5 wt. % Y Zeolite crystal gives highest yield of light olefins though conversion is lower than with 45 wt. % Y Zeolite crystal. Therefore, catalyst composition needs to be selected depending on the feed composition to be cracked in riser.

(62) TABLE-US-00010 TABLE 10 Optimum catalyst composition for different feeds 25 wt. % 25 wt. % 25 wt.% ZSM 5 ZSM 5 ZSM 5 crystal + crystal + crystal + 45 wt. 22.5 45 wt. 22.5 wt. 45 wt. 22.5 50 wt. % % Y wt. % Y 50 wt.% % Y % Y 50 wt. % % Y wt.% Y ZSM 5 Zeolite Zeolite ZSM 5 Zeolite Zeolite ZSM 5 Zeolite Zeolite Catalyst crystal crystal crystal crystal N- crystal N- crystal N- crystal crystal crystal Feed LCN LCN LCN HEXANE HEXANE HEXANE CSO CSO CSO Reactor 620 620 620 675 675 675.0 620.0 620 620 Temperature, C. Catalyst- 13.33 13.33 13.33 13.33 13.33 13.33 13.33 13.33 13.33 to-Oil, wt./wt. YIELDS, wt. %: Coke 2.10 2.16 2.41 3.93 3.11 4.13 11.94 12.07 10.73 Dry Gas 4.82 3.79 4.15 13.04 9.71 12.77 2.76 5.99 4.49 Ethylene 10.58 3.67 9.24 11.56 7.98 10.79 1.70 1.73 2.23 Propylene 19.73 13.88 20.03 17.84 13.63 18.87 2.03 2.71 3.03 LPG 38.14 28.27 37.77 31.39 23.48 32.43 3.51 5.84 5.56 Gasoline 43.63 60.60 45.45 39.96 55.45 39.14 2.87 6.16 4.05 221 C..sup.+ 0.74 1.51 0.98 0.13 0.28 0.83 77.22 68.21 72.94

Example 6

(63) This example illustrates the performance of ZSM-5 zeolite based catalyst for improving yields of light olefins. Three different ZSM-5 based catalyst i.e, (i) commercial ZSM-5 additive as shown in example 1, an ultra-stable ZSM 5 zeolite based catalyst as disclosed in PCT application PCT/IN2011/000599 and alkaline metal modified ZSM 5 as disclosed in Indian patent application no. 1955/MUM/2011 were evaluated in the experimental set up as explained in example 1. The performance of these catalysts are compared for LCN as feed as shown in Table 11. As compared to the commercially available ZSM 5, ultrastable ZSM 5 based additive is shown to give highest yields of light olefins. Alkaline metal doped commercial ZSM 5 additive produces light olefin yields comparable to commercial ZSM 5 additive but additionally reduces yield of dry gas. Thus the alkaline metal modified commercial ZSM 5 can be used to reduce Dry gas yield while maximizing C3 olefin yield at high severity.

(64) TABLE-US-00011 TABLE 11 Effect of ZSM-5 zeolite stabilization process Catalyst Commercial Ca modified ZSM 5 Ultrastable ZSM 5 (10000 ppm Ca ZSM-5 Additive as content) additive example 1 (Indian patent appl. no. (PCT/IN2011/ 1955/MUM/2011) 000599) ZSM 5 crystal 50 50 40 content, wt. % Feed LCN LCN LCN Reactor 620 620 620 Temperature, C. Catalyst-to-Oil, 13.33 13.33 13.33 wt./wt. Yields, wt. %; Coke 2.09 2.00 2.12 Dry 4.82 3.37 5.28 gas(excluding ethylene) Ethylene 10.58 8.70 11.91 Propylene 19.73 20.41 20.31 LPG 38.14 36.60 40.69 Gasoline 43.63 48.50 38.18 221 C. 0.74 0.83 1.82

Example 7

(65) This example illustrates the possibility of using different heavier hydrocarbon feedstock in place of CSO as described in previous examples. Crude oil which are difficult to process because of its high metal content, high TAN value, high viscosity or low API value are called opportunity crude. These crudes are available at lower market price than other light crude oil. Internationally known feedstock such as Mangla, DOBA, DAR were cracked in experimental set up described in example 1 using FCC equilibrium(Ecat) catalyst at 600 C., atmospheric pressure, TOS of 30 sec at 13.33 catalyst to oil ratio. The major physic-chemical properties of Ecat and cracking data for various feed are given in Table 12 and 12A respectively.

(66) TABLE-US-00012 TABLE 12 Physico-chemical properties of Ecat Parameters Total Surface Area, m.sup.2/g 166 Total Zeolite Surface area, m.sup.2/g 105 MAT activity, wt. % 72 Metals on Ecat, PPM Nickel 339 Vanadium 670 Phosphorus 1.36 Al.sub.2O.sub.3 38.2 Re.sub.2O.sub.3 0.79 Particle Size Distribution, micron 20 0 40 2 45 3 80 32 APS 96

(67) As can be seen from Table 12A, processing these crudes in place of CSO in present disclosure will not only provide required coke yield for heat balance but also improve overall yield slate. It is observed that, compared to CSO, coke yield is almost same for these crudes however, LPG, propylene and gasoline yields are much higher. This makes processing of opportunity crude oils in place of CSO much more attractive.

(68) TABLE-US-00013 TABLE 12A Direct crude processing as high coke making feedstock Catalyst E-CAT E-CAT E-CAT E-CAT Feed Mangla DOBA DAR CSO Reactor Temperature, C. 600 600 600 600 Catalyst-to-Oil, wt./wt. 13.33 13.33 13.33 13.33 Yields, wt. %: Coke 16.76 16.83 16.82 16.97 Dry gas (excluding ethylene) 3.82 4.29 4.60 4.74 Ethylene 6.10 5.04 5.78 1.95 Propylene 19.96 15.41 18.05 2.88 LPG 44.61 35.06 39.67 6.12 Gasoline 19.44 23.44 21.43 4.71 Other Products 9.27 15.35 11.69 65.52
Technical Advantages

(69) Technical advantages of the present disclosure lie in providing a process for catalytic conversion of hydrocarbon feedstock to lower olefins with improved yield that involve: 1. catalytic cracking of diverse range of hydrocarbon feedstocks having difficult, moderate and easy cracking behavior in a sequential manner; 2. the sequential cracking of diverse range of hydrocarbon feedstocks in a single riser wherein the single riser being divided into multizones for executing the sequential cracking; and 3. thermo-neutral conditions during entire catalytic cracking process wherein the thermo-neutral conditions are accomplished in the single riser reactor by employing sequential cracking of hydrocarbon feeds or sequentially cracking the feeds in the multizones riser followed by burning the coke deposited on the catalyst surface to provide the heat required for endothermal cracking.

(70) Throughout this specification the word comprise, or variations such as comprises or comprising, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.

(71) The use of the expression at least or at least one suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the disclosure to achieve one or more of the desired objects or results.

(72) Whenever a range of values is specified, a value up to 10% below and above the lowest and highest numerical value respectively, of the specified range, is included in the scope of the disclosure.

(73) The numerical values mentioned for the various physical parameters, dimensions or quantities are only approximations and it is envisaged that the values higher/lower than the numerical values assigned to the parameters, dimensions or quantities fall within the scope of the disclosure, unless there is a statement in the specification specific to the contrary.

(74) Any discussion of documents, acts, materials, devices, articles or the like that has been included in this specification is solely for the purpose of providing a context for the invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the invention as it existed anywhere before the priority date of this application.

(75) The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.