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A History of the BP Fischer-Tropsch Catalyst from Laboratory to Full Scale Demonstration in Alaska and Beyond
Fischer-Tropsch Synthesis, Catalysts and Catalysis B.H. Davis and M.L. Occelli (Editors) © 2007 Elsevier B.V. All rights reserved.
37
A history of the BP Fischer-Tropsch catalyst from laboratory to full scale demonstration in Alaska and beyond Joep J.H.M. Font Freidea, John P. Collinsb, Barry Naya, and Chris Sharpc a
BP Exploration Operating Company, Chertsey Road, Sunbury on Thames, Middlesex, TW167LN b BP Exploration America Inc., 501 Westlake Park Blvd., Houston, TX 77079 c BP Chemicals, Hedon, Saltend, East Yorkshire HU128D5
1. Introduction This paper describes the development of BP’s Fischer-Tropsch (FT) catalyst from the early days of laboratory scale preparations and micro-reactor tests to commercial scale manufacture and operation at BP’s Gas to Liquids (GTL) demonstration facility in Nikiski, Alaska. A detailed description of the catalyst development activities, preparation methods, and experimental facilities is provided by Font Freide and coworkers [1]. The initial research was focused on catalyst development for a fixed bed reactor design. Recent activities include the commercial scale fixed bed tests in progress at Nikiski and development of a novel slurry-based reactor technology. 2. Catalyst Development The story of the BP FT catalyst began at BP’s Sunbury Research Centre in the early 1980’s when the search for a non-iron FT catalyst was initiated. Cobalt was chosen as the active metal for reasons of cost and availability. Flow-sheeting studies were used to define targets for catalyst performance. These targets required a catalyst capable of giving a single pass conversion of greater than 70 % with a C5+ productivity of greater than 150 g lcat-1 h-1 and selectivity to C5+ of greater than 80 %. For a viable fixed bed commercial process a catalyst life of 4 years was thought to be the minimum required. Laboratory evaluations of the FT catalysts were initially conducted in fixed bed micro-reactors. These have an internal diameter of approximately 9 mm and are fitted with 3.2 mm thermo-wells. Catalysts were tested as 250 – 500 micron particles usually diluted with an inert material of the same particle size. Activations were normally carried out in-situ by reduction with hydrogen prior to beginning testing.
38
The micro-reactor studies progressed in tandem with testing in a small pilot plant that was constructed to allow evaluation of formed catalysts that could be used in a commercial reactor, instead of the pressed powders tested in the micro-reactors. This larger scale testing was carried out in a 1" internal diameter reactor (120 ml cat.) fitted with a 5 zone heating system to ensure more isothermal operation and typically allowed 1-3 mm particles to be evaluated. The reactor tube internals were configured in such a way as to minimise the radial temperature profile and ensure that the reactor operated in a thermally stable regime. Many of the cobalt catalysts made during the initial screening studies showed good activities for CO conversion and high selectivity’s to liquid transportation fuels (> C5 hydrocarbons) but were found to be intolerant of CO2. It was a considerable problem since the natural gas is likely to contain CO2 and CO2 is also a by-product of syngas production. In addition the cobalt catalyst itself will make some CO2 via water gas shift. It was known that some methanol catalysts, not only tolerate CO2, but also require it in the syngas feed. For this reason it was decided to investigate a cobalt-based FT catalyst employing a similar catalyst formulation. The first of these new cobalt catalysts were made in 1986 by coprecipitation techniques using aqueous solutions with ammonium bicarbonate as the precipitant in a similar way to the methods used for methanol synthesis catalysts. The new catalysts were immediately found to be very active and selective catalysts for the conversion of syngas into hydrocarbons. A particularly attractive feature was their low methane make and tolerance of CO2. The CO2 tolerance was ascribed to the interplay between the support and the cobalt phase both in the oxidized and reduced forms. The general belief is that the support stabilizes the cobalt phase such that the catalyst can be operated at the higher temperatures, required to maintain activity despite competitive adsorption by CO2, without any loss in stability. Other investigators e.g. Shell have used similar strategies [2]. Early catalyst life studies indicated a steady deactivation of the catalyst, regardless of preparation method. Improvements in preparation, formulation and activation eventually lead to an increase in catalyst life. Methane selectivity of > 10 % with larger catalyst particles was ascribed to bed geometry and diffusional problems [3]. Many different particle sizes and catalyst shapes were investigated including pellets, spheres and extrudates. Similar procedures and reactor internals to those used in the 1” reactor were developed to allow testing of large particles in the small micro-reactors. Results correlated extremely well with those achieved in the 1" tube and thus allowed all future testing of full size catalyst pellets to be undertaken in fixed bed micro-reactors, with confidence. It became clear early in the development program that the target of a 4 year catalyst life was only likely to be met if the catalyst could be regenerated in-situ. Investigations showed that the catalyst was best regenerated using
39
conventional wax removal, oxidation and then re-reduction techniques. However, the success of regenerations was highly variable with many failing for no apparent reason. An in-depth correlation study revealed that small changes in the chemical composition of the catalyst had a drastic effect on the ability of the catalyst to regenerate fully. It was found that parts per million levels of certain contaminants in the Fischer-Tropsch catalyst could be massively detrimental to regeneration effectiveness. The source of these contaminants was traced to the base component chemicals and also the water used in various stages of the preparation. Elimination of the impurities improved the effectiveness of the catalyst regeneration and it was possible to completely regenerate a catalyst after 8000 hours on stream 3. In-House Pilot Manufacturing Facility. In 1989 a pilot manufacturing facility was built for the scale up of a variety of catalysts. The purpose of this facility was to allow in-house production of catalysts at a scale of up to 100kg via co-precipitation, impregnation, extrusion, pelletization or granulation. Concern over the high projected cost of the co-precipitated FT catalyst led to a search for cheaper alternatives. Impregnation of cobalt via cobalt nitrate salts onto bulk support material gave catalysts of similar performance to coprecipitated catalysts in the laboratory, particularly when a support with high surface area was used. Therefore, manufacturing efforts focused on development of an aqueous impregnation route for large scale catalyst production. Initially, the aqueous impregnation routes were beset with problems due to cobalt hydrolysis reactions that were amplified by the presence of the support material. The rate and extent of these reactions was highly dependent on, for instance, cobalt source, metal concentration, temperature and time. However, after much work, the chemistry was understood well enough to allow aqueous solutions to be used for impregnation. The ultimate performance of catalysts in the FT reaction (activity, selectivity and stability) could be directly related to the structure of the catalyst precursors. Detailed recipes were required to ensure that the correct precursors were made during the impregnation and subsequent calcination steps. Extruded catalysts were made by means of a Winkworth extruder. This could produce a range of shaped (tri-lobe, quadri-lobe, star shapes etc) and cylindrical extrudates at 10 kg h-1 scale with 1 – 4 mm diameter. A wide variety of lubricants and binding additives were investigated to aid the extrusion process and improve the crush strength of the resulting extrudates. Finding additives that improved the physical properties of the extrudate but did not interfere with the FT chemistry proved to be a challenge but eventually suitable additives were found.
40
Drying and subsequent calcination of the catalyst pre-cursors were found to be critical steps in producing a catalyst with desirable characteristics for FT (activity, selectivity and life). Drying of large batches of catalyst was carried out in an APV Mitchell oven which could be charged with up to 100 kg of catalyst for fan-assisted air drying at temperatures below 200qC. The use of multiple trays allowed thin bed depths to be achieved resulting in more constant drying characteristics. A variety of different equipment was used for calcinations. An OMI 8CA-135 belt furnace with an 8 inch wide conveyor belt and heated length of 3.5 m was temperature controlled in seven zones (plus pre-heat and cooling zones). Belt speeds ranged from 2.5 to 25 cm/min and it could reach a temperature of 1100qC with air or nitrogen atmospheres. Three sampling points for oxygen concentration allowed continuous oxygen monitoring and throughput would generally be in the range 10 –100 kg depending on residence time. An EFCO furnace comprised two chambers with an 800qC upper limit that could hold purged boxes of 100 liter capacity. The boxes used up-flow through a fine mesh onto which the catalyst (ca 25 kg) was charged before loading into the oven. Various calcinations gases could be used and the apparatus included on-line analysis and logging of inlet and outlet streams for CO, CO2, NOx, NH3, CH4, O2, humidity content and total hydrocarbon content, plus flow pressure and temperature recordings. 4. Pilot Plant Operations. In 1992 a purpose built FT pilot plant at BP Chemicals Saltend site near Hull in North East England was modified and started up for the first time with a prototype of the new FT catalyst. The plant employed a 6 meter salt-cooled tube of commercial diameter designed to simulate a single tube in a commercial multi-tubular reactor. Initial tests employing formed powder granular catalysts in this unit indicated similar performance to that observed at Sunbury in microreactor tests. This powder granule formulation was translated into a shaped extrudate catalyst offering acceptable pressure drop characteristics. The new extrudate catalyst exhibited the high activity/selectivity and cycle time > 7000 hours normally achieved using powder catalyst, and was regarded as a suitable candidate for a commercial fixed-bed process. 5. Catalyst Specifications. In order to progress from prototype catalysts to a version capable of commercial scale production, not only does the catalyst preparation route need to be specified in considerable detail but also, the specification of the finished catalyst needs to be defined. A set of physical and chemical characteristics needed to be determined which fully defined the catalyst and then, for each of
41
these characteristics an acceptable value, or more usually a range of values, was set. Physical parameters used to specify the finished catalyst were as follows: x BET surface area as measured by nitrogen porosimetry x Mean pore diameter x Skeletal density x Mercury intrusion volume x Mercury pore area x Mercury particle density x Mercury skeletal density x Extrudate diameter, length x Attrition resistance and bulk crush strength The definition of the chemical specification was more complex. For instance not only did the cobalt loading and the levels of numerous elements, some present in only in trace amounts, need to be specified but also measures of the state of the cobalt oxide were also required. Techniques used to “fingerprint” the active phases included X-ray diffraction (XRD) to determine crystallite phase sizes and temperature programmed reduction (TPR). The TPR experiments were run with hydrogen and conditions were chosen to produce a characteristic trace with sharp peaks. The temperatures corresponding to these peaks were indicative of the “reducibility” of the cobalt and proved to be strongly correlated with catalyst performance under process conditions. Electron microscope techniques were used to determine the distribution of the active phase throughout the extrudates to ensure it was uniform. The Catalyst Specification proved to be essential for moving into the next phase of development. 6. Commercial Manufacture. Based on the success of in-house catalyst manufacturing efforts and the encouraging performance in FT evaluations, it was decided in 1991 to investigate production of large quantities of catalyst at the tonnage scale. This was beyond the capabilities of the equipment available in-house so it was decided to approach catalyst manufacturers with a view to selecting one to move forward with. Proposals were sought from six leading manufacturers and discussions were held with three companies. One manufacturer was selected, who was willing and capable of working to BP’s timescale. Key aspects of the manufacturing proved to be sourcing the correct raw materials, validating and guaranteeing their quality, as well as the quality of the water used. It took a year of painstaking analysis to confirm which trace impurities introduced in the commercial manufacturing route were detrimental to catalyst performance and to eliminate these from the production method. Two batches were made at the two ton scale and tested in
42
the Hull pilot plant (1993), as well as the Sunbury micro-reactors in 1997. The basic recipe of the catalyst remained unaltered during this period. 7. Nikiski Demonstration Plant. The sanction for the 300 bpd GTL demonstration plant in Nikiski, Alaska was given in July 2000. In addition to demonstration of the fixed bed FT process and catalyst described in this paper this facility will also demonstrate the Compact Reformer syngas generation technology jointly developed by BP and Davy Process Technology. A commercial hydrocracking process is the final step leading to the synthetic crude product. A total of 45 tonnes of the FT catalyst was manufactured for the demonstration plant including extra catalyst as back up. Prior to manufacture of the full 45 tonnes a 2 ton test batch was made and validated at the Davy Process Technology R&D Centre in Stockton, England during 2000. Once validation had been signed off, production of the full 45 tonne order commenced. The full order was delivered to Nikiski during the latter half of 2001. Validation tests carried out on representative samples taken during the manufacture confirmed that the production had gone to plan. This validation was done in Stockton as well as in BP’s new facilities at Sunbury during 2001 and 2002. Loading of the catalyst into the multi-tube reactor (several thousand narrow tubes) was a challenge. Hence a specialist catalyst loading company was contracted in to carry out a loading trial. The trial was successful with minimal fines production during both transportation and the actual loading itself. This success was mirrored when the catalyst was loaded at Nikiski during October of 2001. In less than a week the loading was completed and verified through pressure drop testing. The Nikiski plant underwent extensive commissioning and prestart-up tests during 2002 and early 2003 and the first product was made on 21st July, 2003. It was a truly historic day in BP’s quest to deliver an economic FischerTropsch process to the market. The Nikiski test program has continued through 2003 and 2004 with the aim of demonstrating the following features of the FT process: x x x
Steady operation for an extended period A managed catalyst activity decline with a 4 year target life Compatible operation with the Compact Reformer x Minimal loss in performance after multiple start ups and shutdowns Progress has been steady since production of the first liquid product. Extended operation has been achieved quite easily. Catalyst performance has been relatively stable through the multiple start ups and shutdowns and during extended operation. Encouraging results have also been achieved with regard to the carbon number distribution of the FT wax with alpha values ranging from
43
0.92 to 0.95. While continued operation is needed to achieve the test program goals, there have already been many lessons learned that will help pave the way for commercial plants. 8. Novel Reactor Technology Development. An attractive feature of the fixed bed operating mode employed at Nikiski is its operational simplicity since there are no moving parts and no need to separate catalyst from the product. A disadvantage is the lower catalyst productivity that is obtained compared to slurry reactors due to heat and mass transfer limitations. In collaboration with Davy Process Technology, BP began development work on a novel slurry-based Fischer-Tropsch reactor technology in 2000. Key aspects of the reactor operation involve the mixing of syngas and liquid catalyst suspension in a high shear zone followed by syngas conversion to liquid hydrocarbons in a post mixing zone [4]. The intensive mixing of syngas and the catalyst suspension allows smaller catalyst particle sizes to be employed compared with conventional slurry and fixed bed technologies reducing the formation of unwanted by products such as methane. Mass transfer is also improved due to the production of micron-sized gas bubbles that enhance the contact between the gaseous reactants, liquid medium, and solid catalyst particles. As in any slurry based process, complex hydrodynamic behavior complicates the scale up to a commercial size unit. Therefore, computational modeling supported by cold flow x-ray mapping tests on a pilot reactor prototype has been used to assist the reactor development efforts. Operation of a 2 bpd Fischer Tropsch pilot plant began in 2003 and has continued through 2004 at the BP Chemicals Saltend site.
44
References (1) Font Freide, J.H.M.; Gamlin, T.D.; Graham, C; Hensman, R.J.; Nay, B.; Sharp, C. Topics in Catalysis, 2003, 26(1-4), 3. (2) EP 142 887, 9th November, 1984, Process for the preparation of hydrocarbons. (3) Iglesia, E.; Reyes, S.C.; Soled, S.L., Advances in Catalysis, 1993, 39, 199. (4) US 6635682 B2, 21st October, 2003, Process for converting synthesis gas into higher hydrocarbons.
37
A history of the BP Fischer-Tropsch catalyst from laboratory to full scale demonstration in Alaska and beyond Joep J.H.M. Font Freidea, John P. Collinsb, Barry Naya, and Chris Sharpc a
BP Exploration Operating Company, Chertsey Road, Sunbury on Thames, Middlesex, TW167LN b BP Exploration America Inc., 501 Westlake Park Blvd., Houston, TX 77079 c BP Chemicals, Hedon, Saltend, East Yorkshire HU128D5
1. Introduction This paper describes the development of BP’s Fischer-Tropsch (FT) catalyst from the early days of laboratory scale preparations and micro-reactor tests to commercial scale manufacture and operation at BP’s Gas to Liquids (GTL) demonstration facility in Nikiski, Alaska. A detailed description of the catalyst development activities, preparation methods, and experimental facilities is provided by Font Freide and coworkers [1]. The initial research was focused on catalyst development for a fixed bed reactor design. Recent activities include the commercial scale fixed bed tests in progress at Nikiski and development of a novel slurry-based reactor technology. 2. Catalyst Development The story of the BP FT catalyst began at BP’s Sunbury Research Centre in the early 1980’s when the search for a non-iron FT catalyst was initiated. Cobalt was chosen as the active metal for reasons of cost and availability. Flow-sheeting studies were used to define targets for catalyst performance. These targets required a catalyst capable of giving a single pass conversion of greater than 70 % with a C5+ productivity of greater than 150 g lcat-1 h-1 and selectivity to C5+ of greater than 80 %. For a viable fixed bed commercial process a catalyst life of 4 years was thought to be the minimum required. Laboratory evaluations of the FT catalysts were initially conducted in fixed bed micro-reactors. These have an internal diameter of approximately 9 mm and are fitted with 3.2 mm thermo-wells. Catalysts were tested as 250 – 500 micron particles usually diluted with an inert material of the same particle size. Activations were normally carried out in-situ by reduction with hydrogen prior to beginning testing.
38
The micro-reactor studies progressed in tandem with testing in a small pilot plant that was constructed to allow evaluation of formed catalysts that could be used in a commercial reactor, instead of the pressed powders tested in the micro-reactors. This larger scale testing was carried out in a 1" internal diameter reactor (120 ml cat.) fitted with a 5 zone heating system to ensure more isothermal operation and typically allowed 1-3 mm particles to be evaluated. The reactor tube internals were configured in such a way as to minimise the radial temperature profile and ensure that the reactor operated in a thermally stable regime. Many of the cobalt catalysts made during the initial screening studies showed good activities for CO conversion and high selectivity’s to liquid transportation fuels (> C5 hydrocarbons) but were found to be intolerant of CO2. It was a considerable problem since the natural gas is likely to contain CO2 and CO2 is also a by-product of syngas production. In addition the cobalt catalyst itself will make some CO2 via water gas shift. It was known that some methanol catalysts, not only tolerate CO2, but also require it in the syngas feed. For this reason it was decided to investigate a cobalt-based FT catalyst employing a similar catalyst formulation. The first of these new cobalt catalysts were made in 1986 by coprecipitation techniques using aqueous solutions with ammonium bicarbonate as the precipitant in a similar way to the methods used for methanol synthesis catalysts. The new catalysts were immediately found to be very active and selective catalysts for the conversion of syngas into hydrocarbons. A particularly attractive feature was their low methane make and tolerance of CO2. The CO2 tolerance was ascribed to the interplay between the support and the cobalt phase both in the oxidized and reduced forms. The general belief is that the support stabilizes the cobalt phase such that the catalyst can be operated at the higher temperatures, required to maintain activity despite competitive adsorption by CO2, without any loss in stability. Other investigators e.g. Shell have used similar strategies [2]. Early catalyst life studies indicated a steady deactivation of the catalyst, regardless of preparation method. Improvements in preparation, formulation and activation eventually lead to an increase in catalyst life. Methane selectivity of > 10 % with larger catalyst particles was ascribed to bed geometry and diffusional problems [3]. Many different particle sizes and catalyst shapes were investigated including pellets, spheres and extrudates. Similar procedures and reactor internals to those used in the 1” reactor were developed to allow testing of large particles in the small micro-reactors. Results correlated extremely well with those achieved in the 1" tube and thus allowed all future testing of full size catalyst pellets to be undertaken in fixed bed micro-reactors, with confidence. It became clear early in the development program that the target of a 4 year catalyst life was only likely to be met if the catalyst could be regenerated in-situ. Investigations showed that the catalyst was best regenerated using
39
conventional wax removal, oxidation and then re-reduction techniques. However, the success of regenerations was highly variable with many failing for no apparent reason. An in-depth correlation study revealed that small changes in the chemical composition of the catalyst had a drastic effect on the ability of the catalyst to regenerate fully. It was found that parts per million levels of certain contaminants in the Fischer-Tropsch catalyst could be massively detrimental to regeneration effectiveness. The source of these contaminants was traced to the base component chemicals and also the water used in various stages of the preparation. Elimination of the impurities improved the effectiveness of the catalyst regeneration and it was possible to completely regenerate a catalyst after 8000 hours on stream 3. In-House Pilot Manufacturing Facility. In 1989 a pilot manufacturing facility was built for the scale up of a variety of catalysts. The purpose of this facility was to allow in-house production of catalysts at a scale of up to 100kg via co-precipitation, impregnation, extrusion, pelletization or granulation. Concern over the high projected cost of the co-precipitated FT catalyst led to a search for cheaper alternatives. Impregnation of cobalt via cobalt nitrate salts onto bulk support material gave catalysts of similar performance to coprecipitated catalysts in the laboratory, particularly when a support with high surface area was used. Therefore, manufacturing efforts focused on development of an aqueous impregnation route for large scale catalyst production. Initially, the aqueous impregnation routes were beset with problems due to cobalt hydrolysis reactions that were amplified by the presence of the support material. The rate and extent of these reactions was highly dependent on, for instance, cobalt source, metal concentration, temperature and time. However, after much work, the chemistry was understood well enough to allow aqueous solutions to be used for impregnation. The ultimate performance of catalysts in the FT reaction (activity, selectivity and stability) could be directly related to the structure of the catalyst precursors. Detailed recipes were required to ensure that the correct precursors were made during the impregnation and subsequent calcination steps. Extruded catalysts were made by means of a Winkworth extruder. This could produce a range of shaped (tri-lobe, quadri-lobe, star shapes etc) and cylindrical extrudates at 10 kg h-1 scale with 1 – 4 mm diameter. A wide variety of lubricants and binding additives were investigated to aid the extrusion process and improve the crush strength of the resulting extrudates. Finding additives that improved the physical properties of the extrudate but did not interfere with the FT chemistry proved to be a challenge but eventually suitable additives were found.
40
Drying and subsequent calcination of the catalyst pre-cursors were found to be critical steps in producing a catalyst with desirable characteristics for FT (activity, selectivity and life). Drying of large batches of catalyst was carried out in an APV Mitchell oven which could be charged with up to 100 kg of catalyst for fan-assisted air drying at temperatures below 200qC. The use of multiple trays allowed thin bed depths to be achieved resulting in more constant drying characteristics. A variety of different equipment was used for calcinations. An OMI 8CA-135 belt furnace with an 8 inch wide conveyor belt and heated length of 3.5 m was temperature controlled in seven zones (plus pre-heat and cooling zones). Belt speeds ranged from 2.5 to 25 cm/min and it could reach a temperature of 1100qC with air or nitrogen atmospheres. Three sampling points for oxygen concentration allowed continuous oxygen monitoring and throughput would generally be in the range 10 –100 kg depending on residence time. An EFCO furnace comprised two chambers with an 800qC upper limit that could hold purged boxes of 100 liter capacity. The boxes used up-flow through a fine mesh onto which the catalyst (ca 25 kg) was charged before loading into the oven. Various calcinations gases could be used and the apparatus included on-line analysis and logging of inlet and outlet streams for CO, CO2, NOx, NH3, CH4, O2, humidity content and total hydrocarbon content, plus flow pressure and temperature recordings. 4. Pilot Plant Operations. In 1992 a purpose built FT pilot plant at BP Chemicals Saltend site near Hull in North East England was modified and started up for the first time with a prototype of the new FT catalyst. The plant employed a 6 meter salt-cooled tube of commercial diameter designed to simulate a single tube in a commercial multi-tubular reactor. Initial tests employing formed powder granular catalysts in this unit indicated similar performance to that observed at Sunbury in microreactor tests. This powder granule formulation was translated into a shaped extrudate catalyst offering acceptable pressure drop characteristics. The new extrudate catalyst exhibited the high activity/selectivity and cycle time > 7000 hours normally achieved using powder catalyst, and was regarded as a suitable candidate for a commercial fixed-bed process. 5. Catalyst Specifications. In order to progress from prototype catalysts to a version capable of commercial scale production, not only does the catalyst preparation route need to be specified in considerable detail but also, the specification of the finished catalyst needs to be defined. A set of physical and chemical characteristics needed to be determined which fully defined the catalyst and then, for each of
41
these characteristics an acceptable value, or more usually a range of values, was set. Physical parameters used to specify the finished catalyst were as follows: x BET surface area as measured by nitrogen porosimetry x Mean pore diameter x Skeletal density x Mercury intrusion volume x Mercury pore area x Mercury particle density x Mercury skeletal density x Extrudate diameter, length x Attrition resistance and bulk crush strength The definition of the chemical specification was more complex. For instance not only did the cobalt loading and the levels of numerous elements, some present in only in trace amounts, need to be specified but also measures of the state of the cobalt oxide were also required. Techniques used to “fingerprint” the active phases included X-ray diffraction (XRD) to determine crystallite phase sizes and temperature programmed reduction (TPR). The TPR experiments were run with hydrogen and conditions were chosen to produce a characteristic trace with sharp peaks. The temperatures corresponding to these peaks were indicative of the “reducibility” of the cobalt and proved to be strongly correlated with catalyst performance under process conditions. Electron microscope techniques were used to determine the distribution of the active phase throughout the extrudates to ensure it was uniform. The Catalyst Specification proved to be essential for moving into the next phase of development. 6. Commercial Manufacture. Based on the success of in-house catalyst manufacturing efforts and the encouraging performance in FT evaluations, it was decided in 1991 to investigate production of large quantities of catalyst at the tonnage scale. This was beyond the capabilities of the equipment available in-house so it was decided to approach catalyst manufacturers with a view to selecting one to move forward with. Proposals were sought from six leading manufacturers and discussions were held with three companies. One manufacturer was selected, who was willing and capable of working to BP’s timescale. Key aspects of the manufacturing proved to be sourcing the correct raw materials, validating and guaranteeing their quality, as well as the quality of the water used. It took a year of painstaking analysis to confirm which trace impurities introduced in the commercial manufacturing route were detrimental to catalyst performance and to eliminate these from the production method. Two batches were made at the two ton scale and tested in
42
the Hull pilot plant (1993), as well as the Sunbury micro-reactors in 1997. The basic recipe of the catalyst remained unaltered during this period. 7. Nikiski Demonstration Plant. The sanction for the 300 bpd GTL demonstration plant in Nikiski, Alaska was given in July 2000. In addition to demonstration of the fixed bed FT process and catalyst described in this paper this facility will also demonstrate the Compact Reformer syngas generation technology jointly developed by BP and Davy Process Technology. A commercial hydrocracking process is the final step leading to the synthetic crude product. A total of 45 tonnes of the FT catalyst was manufactured for the demonstration plant including extra catalyst as back up. Prior to manufacture of the full 45 tonnes a 2 ton test batch was made and validated at the Davy Process Technology R&D Centre in Stockton, England during 2000. Once validation had been signed off, production of the full 45 tonne order commenced. The full order was delivered to Nikiski during the latter half of 2001. Validation tests carried out on representative samples taken during the manufacture confirmed that the production had gone to plan. This validation was done in Stockton as well as in BP’s new facilities at Sunbury during 2001 and 2002. Loading of the catalyst into the multi-tube reactor (several thousand narrow tubes) was a challenge. Hence a specialist catalyst loading company was contracted in to carry out a loading trial. The trial was successful with minimal fines production during both transportation and the actual loading itself. This success was mirrored when the catalyst was loaded at Nikiski during October of 2001. In less than a week the loading was completed and verified through pressure drop testing. The Nikiski plant underwent extensive commissioning and prestart-up tests during 2002 and early 2003 and the first product was made on 21st July, 2003. It was a truly historic day in BP’s quest to deliver an economic FischerTropsch process to the market. The Nikiski test program has continued through 2003 and 2004 with the aim of demonstrating the following features of the FT process: x x x
Steady operation for an extended period A managed catalyst activity decline with a 4 year target life Compatible operation with the Compact Reformer x Minimal loss in performance after multiple start ups and shutdowns Progress has been steady since production of the first liquid product. Extended operation has been achieved quite easily. Catalyst performance has been relatively stable through the multiple start ups and shutdowns and during extended operation. Encouraging results have also been achieved with regard to the carbon number distribution of the FT wax with alpha values ranging from
43
0.92 to 0.95. While continued operation is needed to achieve the test program goals, there have already been many lessons learned that will help pave the way for commercial plants. 8. Novel Reactor Technology Development. An attractive feature of the fixed bed operating mode employed at Nikiski is its operational simplicity since there are no moving parts and no need to separate catalyst from the product. A disadvantage is the lower catalyst productivity that is obtained compared to slurry reactors due to heat and mass transfer limitations. In collaboration with Davy Process Technology, BP began development work on a novel slurry-based Fischer-Tropsch reactor technology in 2000. Key aspects of the reactor operation involve the mixing of syngas and liquid catalyst suspension in a high shear zone followed by syngas conversion to liquid hydrocarbons in a post mixing zone [4]. The intensive mixing of syngas and the catalyst suspension allows smaller catalyst particle sizes to be employed compared with conventional slurry and fixed bed technologies reducing the formation of unwanted by products such as methane. Mass transfer is also improved due to the production of micron-sized gas bubbles that enhance the contact between the gaseous reactants, liquid medium, and solid catalyst particles. As in any slurry based process, complex hydrodynamic behavior complicates the scale up to a commercial size unit. Therefore, computational modeling supported by cold flow x-ray mapping tests on a pilot reactor prototype has been used to assist the reactor development efforts. Operation of a 2 bpd Fischer Tropsch pilot plant began in 2003 and has continued through 2004 at the BP Chemicals Saltend site.
44
References (1) Font Freide, J.H.M.; Gamlin, T.D.; Graham, C; Hensman, R.J.; Nay, B.; Sharp, C. Topics in Catalysis, 2003, 26(1-4), 3. (2) EP 142 887, 9th November, 1984, Process for the preparation of hydrocarbons. (3) Iglesia, E.; Reyes, S.C.; Soled, S.L., Advances in Catalysis, 1993, 39, 199. (4) US 6635682 B2, 21st October, 2003, Process for converting synthesis gas into higher hydrocarbons.