PRODUCTION OF HIGH YIELDS OF LIGHT OLEFINS FROM HEAVY HYDROCARBONS

Abstract

A process for conversion of hydrocarbon feedstock into lighter olefins of C.sub.2 to C.sub.4 carbons, the process comprising of cracking the hydrocarbon feedstock in a reactor in the presence of a catalyst. The catalyst for short contact time catalytic cracking process of heavy hydrocarbons having contact time less than 1 second to produce light olefins of C.sub.2 to C.sub.4 carbon in the range of 40 to 60 wt % on fresh feed basis in a fluidized bed reactor which is concentric downflow reactor in presence of catalyst consisting of ultra-stable Y zeolite in the range of 5-10 wt %, 4 to 8 wt % of pentasil zeolite, 2.5-5 wt % of bottom selective material, 0.5-2 wt % of rare earth and 75-88 wt % of support material.

Claims

1. A process for conversion of hydrocarbon feedstock into lighter olefins of C.sub.2-C.sub.4 carbons in the presence of catalyst system comprising of 7-10 wt % of an ultra-stable Y zeolite; 4-8 wt % of shape selective pentasil zeolite; 2.5-5 wt % of bottom selective material; 0.5-2 wt % of rare earth metals; and 75-88 wt % of support material wherein the cracking of feedstock is carried out in the temperature of range of 550° C. to 650° C., weight hourly space velocity (WHSV) in the range of 100-300 hr-1 and a pressure in the range of 1-4 kg/cm.sup.2 g in a reactor which is essentially a concentric downflow reactor and wherein the ratio of catalyst to hydrocarbons is 25-40 wt/wt, and wherein 0 to 50% of the products from the concentric downflow reactor is being recycled and wherein the process yields upto 65 wt % of fresh feed as light olefins of C.sub.2-C.sub.4 hydrocarbons.

2. The process as claimed in claim 1, wherein the coked catalyst is separated from the cracked hydrocarbons at the exit of the concentric downflow reactor through a stripper, and is transferred to the regenerator in the presence of an oxygen containing gas and at a temperature ranging from 650° C. to 750° C. to burn off the coke and provide a regenerated catalyst having a coke on catalyst less than 0.1 wt %, wherein coked catalyst is continuously circulated between the regenerator and concentric downflow reactor.

3. The process as claimed in claim 1, wherein the residence time of catalyst in the concentric downflow reactor is in the range of 0.1 to 1 seconds.

4. The process as claimed in claim 1, the products having a boiling range above 200° C. are partly recycled back into the stripper section at one or more locations.

5. The process as claimed in claim 1, the products having a boiling range above 200° C. are partly recycled back into the regenerator section at one or more locations.

6. The process as claimed in claim 1, wherein the cracking of feedstocks carried out in the temperature of 620-640° C. and WHSV of 120-150 hr-1 and a catalyst to hydrocarbon ratio of 35-40 wt/wt.

7. The process as claimed in claim 1, wherein the catalyst is a catalyst system comprising of 8-9 wt % of an ultra-stable Y zeolite; 6-7 wt % of shape selective pentasil zeolite; 4-5 wt % of bottom selective material; 0.5-1 wt % of rare earth metals; and 80-82 wt % of support material.

Description

DESCRIPTION OF THE INVENTION

[0022] The present invention provides a catalyst with short contact time for conversion of heavy hydrocarbon feed to light olefins especially carbon number 2 to 4 in a fluidized bed reactor in presence of a micro spherical catalyst.

[0023] In an embodiment of the present invention the heavy hydrocarbon feedstock is converted into high yield of light olefins through a concentric downflow reactor in presence of micro spherical catalyst consisting of a large pore component having silica to alumina ratio at least 10, a medium pore component having silica to alumina ratio at least 30, a non crystalline silica alumina component, phosphate compound, a rare earth compound and a non active support material. The large pore component is essentially the Y zeolite having the pore size between 7 to 10 Å. The medium pore zeolite is essentially the shape selective pentasil zeolite. Cracking the heavy hydrocarbon feedstock in a concentric downflow reactor in presence of multifunctional micro spherical catalyst consisting of ultra stableY zeolite in the range of 5-10 wt %, 4-8 wt % of shape selective pentasil zeolite, 2.5-5 wt % of active material which is bottom selective material, 0.5-2 wt % of rare-earth, rare-earth materials are essentially Lanthanum and cerium and 75-88 wt % of support material. Bottom selective material is essentially the mesoporous acidic alumina used to pre-crack the heavy hydrocarbons before entering into the y zeolite. Cracking of hydrocarbons is carried out in the temperature range of 550-650° C. and weight hourly space velocity (WHSV) in the range of 100-300 hr-1, the contact time in the concentric downflow reactor being maintained in the range of 0.1-1 second, the catalyst is present in the range of 15-45 wt % of the hydrocarbon feedstock in the reactor, pressure in the range of 1 to 4 kg/cm.sup.2 g, steam to hydrocarbon in the ratio of 0.1 to 1.0 wt/wt. The process produces total light olefins yield (C.sub.2, C.sub.3 and C.sub.4 carbon atoms) ranging up to 40 to 65 wt. % of the fresh petroleum-based feedstock. The other gaseous products produced in the process are methane, ethane, propane, butane, and hydrogen. The liquid product produced in the process can be fractionated as per the desired cut range. The catalyst gets deactivated during the cracking step due to deposition of coke.

[0024] The separation of coked catalyst is carried out at the end of the cracking step in the reactor. The catalyst is separated from cracked products. The separator to the concentric down flow reactor is able to separate the catalyst and the cracked hydrocarbons in a very short time. Lower part of reactor is used as stripper to strip off the entrapped hydrocarbons from the catalyst using steam. The coked catalyst is then transferred to the regenerator which is positioned at the top through a lift line using air as the transferring medium.

[0025] The carbon, hydrogen, sulfur & nitrogen deposits on the catalyst are burnt in the regenerator in presence of oxygen at a temperature of 650-750° C. for regeneration of the catalyst.

[0026] The regenerated catalyst is then sent to the concentric downflow reactor for cracking the heavy hydrocarbons into light olefins. As the catalyst used in the process is highly coke selective, the coke yield required for satisfying the heat balance may not be possible. In such cases recycle of CLO and LCO range products can be sent to stripper as coke precursors for generating additional coke. In one of the embodiments, a part of CLO and LCO range products can be recycled to regenerator for burning and generating additional heat so as to supply the heat required by the reactor. The process conditions and catalyst being used in the examples are for illustration purpose only. The present invention can be used for any such feedstocks and shall include any feedstocks like C.sub.4, Residue hydrocarbons like reduced crude oil and Vacuum Residue, Hydrotreated Vacuum Gas Oil (HDT-VGO), hydrocracker bottom.

[0027] Coke selective catalyst means the catalyst when operated with the same operating conditions and feed results in a lower coke yield. This can be seen in the data generated in Example-3, where the products obtained using the different catalyst system with different reactor configuration is provided. It can be seen that the FCC catalyst provides a coke yield of 6.2 wt %, whereas the catalyst of the present invention provides a coke yield of 4.6 wt %. In actual plant, the use of coke selective catalyst will reduce the delta coke in the system. Delta coke is defined as the coke present on the circulating catalyst. The use of high coke selective catalyst will result in reduced delta coke demanding higher catalyst circulation for a given reaction temperature resulting in higher catalytic conversion and thereby improved product yields. In one of the embodiments, the LCO and CLO generated in the process is recycled in the stripper at multiple locations so as to maximize its conversion and coke yield.

[0028] Example-1 provides the data for Conventional FCC process utilizes up flow riser configuration where the contact time of in the catalyst and hydrocarbon move upwards, is in the range of 2-2.5 seconds. Due to relatively high contact time, the undesired products such as coke and dry gas increases, it is also observed that when the temperature is increased the propylene selectivity of LPG increases whereas the ethylene selectivity in dry gas and butylenes selectivity in LPG decreases. But the overall olefins yield increases with temperature parabolically. In Example-2 the data generated for the downflow system where hydrocarbon feed and catalyst contact and move co-currently downward with a contact time of catalyst and hydrocarbon in the range of 0.5-1 second, there is an improvement in the product selectivity due to the narrow residence time operated in this setup. However, the product conversion also reduces due to the reduced contact time. The disadvantage of the present step has been overcome by using the catalyst of present invention. In the present invention in Example-3, the product conversion is increased by increasing the reaction temperature with the new catalyst system for improving the yields of light olefins using a concentric downflow reactor with contact time of catalyst and hydrocarbon in the range of 0.5-1 second. The data generated indicates higher Light Olefins (C.sub.2-C.sub.4) as compared to the other system, lower coke yield and higher propylene selectivity in LPG.

[0029] Feed properties of the feedstocks used in this invention have been tabulated in the table 1 below:

TABLE-US-00001 Hydrotreated Hydrocracker Feed Description UOM VGO Bottom Density @ 15° C. kg/m.sup.3 899.1 843 CCR wt % 0.05 0.08 Sulphur wt % 0.04 0.007 H.sub.2 content wt % 13.4 14.8

[0030] Catalyst Components Used in the Present Invention

TABLE-US-00002 Catalyst Components UOM CAT-A Large pore component wt % 10.1 Medium pore component wt % 6.2 Non Crystalline component wt % 1.75 Phosphate  w % 5.9 Rare earths wt % 0.2 Non active support Material wt % 75.9

Example-1

[0031] Effect of Temperature on Product Yields/Light Olefins Selectivity with Temperature in Riser

[0032] Reactor [0033] Feedstock used: Hydrotreated VGO [0034] Catalyst: FCC catalyst with 10 wt % of pentasil zeolite [0035] Catalyst loading into the reactor: 8 gms [0036] Simulated Contact Time: 2.5 seconds

TABLE-US-00003 Exp Ref No # 1739 1732 1735 1743 Temperature ° C. 550 600 620 650 Fuel gas wt % 2.1 5.6 8.1 12.9 LPG wt % 35.1 39.2 37.3 32.8 Coke wt % 3.1 5.2 6.2 9.0 Ethylene wt % 2.8 6.0 7.0 9.7 Propylene wt % 14.0 17.5 18.1 1 17.4 Butylenes wt % 9.2 10.2 10.8 8.9

Example-2

[0037] Concentric downflow reactor Vs Riser Reactor [0038] Feedstock used: HDT VGO [0039] Catalyst: FCC catalyst with 10 wt % of pentasil zeolite

TABLE-US-00004 1709 Exp Ref No Concentric Reactor 1735 Downflow Configuration # Riser Reactor Simulated Sec 2.5 0.7 Contact time Temperature ° C. 620 620 Fuel gas wt % 8.1 6.9 LPG wt % 37.3 36.8 Coke wt % 6.2 5.9 Ethylene wt % 7.0 6.6 Propylene wt % 18.1 18.1 Butylenes wt % 10.8 10.9 Propylene selectivity wt % 48.6 49.1 in LPG Total Light Olefins wt % 36.0 35.6 (C.sub.2 + C.sub.3 + C.sub.4)

Example-3

[0040] Effect of Catalyst and Reactor Configuration [0041] Feedstock used: Hydrotreated VGO

TABLE-US-00005 Concentric Concentric Reactor Configuration Riser Downflow Downflow Catalyst FCC FCC CAT-A Catalyst Catalyst Simulated Contact Time Se 2.5 0.7 0.7 Exp Ref No # 1735 1709 1781 Temperature ° C. 620 620 620 Fuel gas wt % 8.1 6.9 6.7 LPG wt % 37.3 36.8 38.7 Coke wt % 6.2 5.9 4.6 Ethylene wt % 7.0 6.6 11.2 Propylene wt % 18.1 18.1 22.2 Butylenes wt % 10.8 10.9 10.8 Propylene selectivity in LPG wt % 48.6 49.1 57.2 Total Light Olefins wt % 36.0 35.6 44.2 (C.sub.2 + C.sub.3 + C.sub.4)

Example-4

[0042] Effect of High Activity catalyst with different feedstocks in Concentric Downflow Reactor Catalyst: CAT-A

TABLE-US-00006 Hydrotreated Hydrocracker Feedstocks VGO Bottoms Catalyst CAT-A CAT-A Exp Ref No # 1781 916 Temperature ° C. 620 620 Fuel gas wt % 6.7 15.9 LPG wt % 38.7 56.4 Coke wt % 4.6 0.9 Ethylene wt % 11.2 11.2 Propylene wt % 22.2 30.7 Butylenes wt % 10.8 19.5 Propylene selectivity in LPG wt % 57.2 54.51 Total Light Olefins wt % 44.2 61.4 (C.sub.2 + C.sub.3 + C.sub.4)

Advantages of the Invention

[0043] The following are the technical advantages of the present invention over the prior arts [0044] 1. High yields of total light olefins. [0045] 2. High light olefins selectivity.