WO2012004808A1

WO2012004808A1 - Apparatus and process for gas to liquid (gtl) conversion

Info

Publication number: WO2012004808A1
Application number: PCT/IN2011/000444
Authority: WO
Inventors: Ravikumar Balivada; Rajesh Muralidhar Badhe; Alok Sharma; Brijesh Kumar; Santanam Rajagopal; Ravinder Kumar Malhotra; Anand Kuamr
Original assignee: Indian Oil Corporation Ltd.
Priority date: 2010-07-08
Filing date: 2011-07-04
Publication date: 2012-01-12

Abstract

This invention relates to an apparatus and a process for conversion of syngas into one or more hydrocarbons in presence of Fisher-Tropsch catalyst comprising in-situ catalyst activation in a separate fluid bed reactor. Activation is carried out in the dry phase in flowing hydrogen atmosphere in fluidised condition in a separate fluid bed reactor. The activated catalyst is transferred to the main slurry reactor with flowing hydrogen. Filters are provided outside the slurry reactor and separated wax product is recycled back to the reactor.

Description

APPARATUS AND PROCESS FOR GAS TO LIQUID (GTL) CONVERSION

FIELD OF THE INVENTION [001] The present invention relates to gas to liquid (GTL) conversion. This invention particularly relates to a novel design of reactor system for GTL process for the conversion of syngas (CO+H₂ mixture) into a wide range of hydrocarbons from methane to heavy waxes. This invention also relates to a process for the same. BACKGROUND OF THE INVENTION

[002] The present invention discloses an inventive design of a reactor system and a process thereof for GTL conversion, preferably for syngas into a wide range of hydrocarbons from methane to heavy waxes in the presence of Fisher-Tropsch catalyst (iron or cobalt based) which includes dry phase catalyst activation in a separate fluid bed reactor and the recycling back the separated wax product to the slurry reactor. Natural gas which is one of the earth's cleanest and most abundant natural resources, can be used to produce liquid fuels and a range of petrochemical feedstocks. The present invention is aimed to provide a much more efficient apparartus and a process for GTL conversion for syngas in this area to meet the growing demand of the consumers.

[003] Conversion of Gas to Liquids, generally referred to as GTL, is increasingly attracting the interest of the global Refining Industry for both sustainability and environmental reasons. Several studies estimate a total GTL production capacity of 1.5-2 million barrels per day by 2015. GTL technologies can potentially be used to convert the Natural Gas to a variety of valuable end products, including liquid fuels such as Diesel & Gasoline, Methanol, Dimethyl Ether (DME), Ethanol, Diethyl ether, Olefins, Propylene oxide and Vinyl monomers. These products have enormous existing and potential markets as fuels for transportation, electric power generation and as feedstocks for other chemicals.

[004] Diesel fuel from GTL is an ultra clean product serving as a tool for refiners to meet current and future strict fuel quality standards. Automotive diesel fuel from the GTL process contains no sulfur, no aromatics and has a cetane number of 70 or higher. Such diesel fuel is generally compatible with conventional crude diesel and can either be used as a pure component in automotive diesel engines or through dilution of the existing diesel pool.

[005] In general, "GTL" refers to the chemical transformation of natural gas into hydrocarbon liquid. Following are major synthesis routes for GTL.

- Fischer-Tropsch

- Methanol (subsequently methanol to olefins for fuels)

- Dimethylether (DME)

[006] For all the above three routes, the first step is production of syngas (CO+H₂ mixture) by natural gas reforming or coal gasification. The second step is a Fischer-Tropsch reaction, which converts syngas into a wide range of hydrocarbons from methane to heavy waxes. Since 1902, Sabatier and Senderens reported the hydrogenation of CO over nickel to produce methane, the catalytic production of liquid hydrocarbons and other organic molecules from syngas has been investigated. In 1925, Franz Fischer and Hans Tropsch announced the synthesis of higher hydrocarbons at atmospheric pressure over nickel and cobalt catalysts.

[007] The Fischer-Tropsch reaction can be carried out in different kinds of reactor vessels. Currently, there is much interest in using a slurry reactor for this process because it is relatively inexpensive to build and operate and gives excellent heat and mass transfer which promotes high reaction rates.

[008] A slurry reactor is a vessel containing the catalyst suspended in a liquid hydrocarbon. The syngas is brought in at the bottom of the vessel and bubbled up through the reactor. As the bubbles contact the catalyst, the Fischer-Tropsch reaction takes place.

[009] In the Fischer-Tropsch synthesis (F-T) unit, the syngas is converted to hydrocarbons, via a complex combination of reactions that can be simplified as follows:

2n H₂ + n CO - (-CH₂-)„ + n H₂0

(2n+l ) H₂ + n CO - C_n H_2n+2 + n H₂0

[010] The Fischer Tropsch synthesis reactions are highly exothermic and 155 KJ heat is liberated per reacted carbon atom. The rapid removal of the heat of reaction is one of the main considerations in reactor design for Fischer Tropsch synthesis. [Oi l] At present two Fischer Tropsch synthesis operating modes exist: a high temperature mode working at 300-350°C with an iron-based catalyst. This mode is generally used to obtain gasoline and linear low molecular olefins. The second operating mode works at low temperatures, i.e., 200-240°C, with either iron or cobalt catalysts and is mainly used for the production of high molecular linear waxes.

[012] Cobalt catalyst has the advantages of being more active for F-T reaction with very little activity for the water gas shift reaction. Iron has considerable activity for water gas shift, resulting in potential yield losses by converting CO to C0₂. However, Cobalt is more expensive than iron. Due to its high activity and long life, cobalt-based Fischer-Tropsch catalyst is currently the catalyst of choice.

[013] F-T catalysts are required to be activated with hydrogen in dry phase prior to use.

Conventionally activation of these catalysts is carried out in the main GTL slurry reactor.For complete activation of the catalyst in dry phase, highly efficient and well designed sparger is needed for good contact between catalyst and Hydrogen.

[014] To address the above issues, the present invention is aimed at avoiding or overcoming the difficulties or limitations encountered in the complete activation of the catalyst used in the GTL process in the dry phase in the existing technology. Moreover, it will also be advantageous to provide a novel design of the reactor system used in the GTL process which ensures complete activation of the catalyst in the dry phase under fluidization conditions in separate reactor thereby maintaining good contact between catalyst and hydrogen. In addition, it will also be advantageous to reduce or eliminate the need for inert gas for purging of oxygen from the system required in the existing art. A process for the same is also desirable. The present invention realizes some of these advantages. SUMMARY OF THE INVENTION

[015] Accordingly, the present invention is intended to provide a novel designed reactor apparatus for conversion of syngas into one or more hydrocarbons in presence of Fisher-Tropsch catalyst. More particularly, the present invention is intended to provide an apparatus with a slurry reactor and a separate fluid bed reactor for insitu activation of the Fisher-Tropsch catalyst in fluidised condition in dry phase with flowing hydrogen and transfer of the activated catalyst to the main slurry reactor by flow of hydrogen gas.

[016] In one embodiment, the present invention provides anapparatus for conversion of syngas into a wide range of hydrocarbons from methane to heavy waxes in presence of Fisher- Tropsch catalyst (iron based or iron and cobalt based)in a slurry reactor characterised in that the said apparatus having a separate fluid bed reactor upstream of the slurry reactor for insitu activation of the catalyst in fluidised condition with flowing hydrogen added with means for transfer of the activated catalyst to the main slurry reactor by flow of hydrogen gas for carrying out the conversion process.

[017] The slurry reactor of the present invention is a conventional Continuous-flow

Stirred Tank Reactor (CSTR) with stirring, sparger and filters for uniform distribution of the syngas and seperation of reaction products.

[018] The process of the present invention for converting syngas into one or more hydrocarbons in presence of Fisher-Tropsch catalyst includes insitu catalyst activation in a separate fluidized bed reactor using flowing hydrogen and transferring the activated calalyst to a slurry reactor where the FT conversion is carried out.. The velocity of hydrogen gas used in the catalyst activation is in the range of 1.0-1.5 times of minimum fluidisation velocity with bed expansion in a range of 5-50%. DESCRIPTION OF THE INVENTION

[019] According to this invention there is provided an apparatus for conversion of syngas (CO+H₂ mixture) into a wide range of hydrocarbons from methane to heavy waxes in presence of Fisher-Tropsch catalyst (iron based or iron and cobalt based) in a slurry reactor characterised in that a separate fluid bed reactor is provided outside and upstream of the the slurry reactor for in-situ activation of the catalyst in fluidised condition with flowing hydrogen added with means for transfer of the activated catalyst to the main slurry reactor by flow of hydrogen gas for carrying out the conversion process.

[020] This invention also provides for a process for converting syngas (CO+¾ mixture) into a wide range of hydrocarbons from methane to heavy waxes in presence of Fisher-Tropsch catalyst (iron based or iron and cobalt based) in a slurry reactor characterized in that the catalyst is activated in-situ under controlled heating in a separate fluid bed reactor outside and upstream of the slurry reactor under fluidised condition with flowing hydrogen followed by transfer of the activated catalyst to the main slurry reactor for carrying out the conversion process.

[021] This activation is carried out in the dry phase in flowing hydrogen atmosphere in fluidised condition in a separate fluid bed reactor. The velocity of hydrogen in the activation step is in the range of 1.0-1.5 times of minimum fluidisation velocity with bed expansion in the range of 5-50%. The catalytic conversion of syngas is carried out in conventional CSTR with stirring and sparger for uniform distribution of syngas. Filters are provided within the slurry reactor for retaining the catalyst particles. The said filters also can be provided within the slurry reactor with back flushing arrangement with high pressure syngas or nitrogen for periodic cleaning of the filters. The filters can also be provided outside the slurry reactor and separated wax product is recycled back to the reactor.

[022] To validate the concept, a cold flow prototype equipment has been designed and fabricated for simulating catalyst activation in fluidised condition with proper transfer methodology for the catalyst after activation. Simulation of catalyst fluidisation has been carried out by optimising gas velocity for proper fluidisaton. Experiments have been carried out with different gas velocities which are in the range of 1.0 to 1.5 times the minimum fluidisation velocity. The minimum fluidisation velocity (u_m/) has been calclulated using the following expresssion.

Re_m/= SQRT ((¾* + Ar x K₂) - K,)

Where:

Re_mf. Reynolds number with u_m/

Re_OT/= (u_m/x d_p x £_g) / μ

Ar: Arquimedes number

Ar = (d_p ³ x £g X (£_s -€g) x g)V

Ki and K₂ are constants and are equal to 25.17 and 0.0373 respectively (Ref: Adanez et al 1990) d_p: Diameter of catalyst particle

ig. gas density

€_s: solid density g: gravity

μ: gas viscosity

[023] Based on the results of simulated activation and transfer mechanism, a pilot plant scale demonstration unit has been fabricated. It is expected that this can be scaled to any manufacturing scale desired.

DESCRIPTION OF THE INVENTION WITH REFERENCE TO ACCOMPANING DRAWING [024] Fig 1 illustrates the methodolgy of catalyst activation and design of complete unit.

[025] Hydrogen gas via line 1 and through control valve 2 is fed to the fluid bed reactor

3, which is filled with F-T catalyst. The dry phase activation of the catalyst is carried out in fluidised condition with flowing hydrogen. Hydrogen gas flow is controlled through control valve 2.

[026] Activation takes place in the Reactor 3 with controlled heating. Reactor 3 is designed based on experimental data generated in the cold flow prototype with bed expansion in the range of 30-50%. After the activation is complete, the catalyst is transfered by hydrogen gas via line 4 and through valve 5 to the main slurry reactor 14. The flow of ¾ required for complete transfer of the catalyst from reactor 3 to the reactor 14 has been determined experimentally using the prototype cold flow apparatus. Reactor 14 is a conventional CSTR with stirring and sparger for syngas and is also provided with filters for retaining catalyst particles inside the reactor. A pair of filters 14A and 14B with backflushing arrangement with high pressure syngas or nitrogen is provided for periodic cleaning of the filters. GTL reactions are carried out in reactor 14 in slurry phase, in which activated F-T catalyst is dispersed in wax. Alternatively, the filters can be provided outside the slurry reactor and separated wax product is recycled back to the reactor. The reaction effluent along with unconverted syngas is then sent via line 6 to the gas liquid separator 7. The unconverted gases are recycled back to the reactor 14 from separator 7 top via line 8, pressure control valve 9 and line 10. Liquid from the seaparor 7 is sent via line 11, level control valve 12 to the product storage via line 13.

Claims

CLAIMS:

1. An apparatus for conversion of syngas into a wide range of hydrocarbons from methane to heavy waxes in presence of Fisher-Tropsch catalyst (iron based or cobalt based) in a slurry reactor characterised in that a separate fluid bed reactor is provided outside the slurry reactor for in-situ activation of the catalyst in fluidised condition with flowing hydrogen upstream of the slurry reactor added with means for transfer of the activated catalyst to the main slurry reactor by flow of hydrogen gas for carrying out the conversion process.

2. An apparatus as claimed in claim 1 , wherein the activation is carried out in the dry phase.

3. An apparatus as claimed in claim 1, wherein the velocity of hydrogen in the activation step is in the range of 1.0-1.5 times of minimum fluidisation velocity with bed expansion in the region of 5-50%.

4. An apparatus as claimed in claim 1, wherein the slurry reactor is a conventional CSTR with stirring and sparger for uniform distribution of syngas.

5. An apparatus as claimed in claim 1, wherein filters are provided within the slurry reactor for retaining the catalyst particles.

6. An apparatus as claimed in claim 1, wherein filters are provided within the slurry reactor for retaining catalyst particles with back flushing arrangement with high pressure syngas or nitrogen for periodic cleaning of the filters.

7. An apparatus as claimed in claim 1, wherein filters are provided outside the slurry reactor and separated wax product is recycled back to the reactor.

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8. A process for converting syngas into a wide range of hydrocarbons from methane to heavy waxes in presence of Fisher-Tropsch catalyst (iron based or cobalt based)in a slurry reactor characterized in that the catalyst is activated in-situ under controlled heating in a separate fluid bed reactor outside the slurry reactor under fluidised condition with flowing hydrogen followed by transfer of the activated catalyst to the main slurry reactor for carrying out the conversion process.

9. A process as claimed in claim 8, wherein the activation of the catalyst is carried out in the dry phase.

10. A process as claimed in claim 8, wherein the velocity of hydrogen gas is in the range of 1.0-1.5 times of minimum fluidisation velocity with bed expansion in the region of 5-

50%.

11. A process as claimed in claim 8, wherein filters are provided within the slurry reactor for retaining catalyst particles within the reactor.

12. A process as claimed in claim 8, wherein filters are provided for retaining catalyst particles with back flushing arrangement with high pressure syngas or nitrogen for periodic cleaning of the filters.

13. A process as claimed in claim 8, wherein filters are provided outside the slurry reactor and separated wax product is recycled back to the reactor.

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