Fischer reactors used

The principal reactors used are fluidized bed reactors, called Synthol reactors, in which the feed gas entrains an iron catalyst powder in a circulating flow. The suspension enters the bottom of the fluidized bed reaction section, where the Fischer-Tropsch and the gas shift reactions proceed at a temperature of from 315 to 330°C. These reactions are highly exothermic, as described previously, and the large quantity of heat released must be removed. The products in gaseous form together with the catalyst are taken off from the top of the reactor. By decreasing the gas velocity in another section, the catalyst settles out and is returned for reuse. The product gases are then condensed to the liquid products. 

Synthesis gas contains a mixture of carbon monoxide and hydrogen and can be obtained from the combusfion of coa) or natural gas. This gas can be used to produce synthetic crude by the Fischer-Tropsch reaction. Describe two industrial reactors used to convert synthesis gas to a mixture of hydrocarbons by the Fischer-Tropsch process. 

The goal of using solid-state electrolytic reactors is not only to generate electrical power, but also to combine this with an industrially important catalytic reaction, such as dissociation of oxygen-containing compounds like NO [40,41], quantitative oxidation of NH3 to NO [42-44], oxidation of SO2 [45], and methanol [46], ethylene epoxidation [46], or Fischer-Tropsch synthesis [47]. The cross-flow reactor used in this type of study (Fig. 10) [48,49] has a solid electrolyte consisting of yttria-doped zirconia. The plates are electrically connected in series, with a varying number of plates in parallel. The oxidant flow channels... 

The Fischer-Tropsch reactions were discussed in Example 1-4. A sehematie of the Sasol slurry reactor, used to make wax, is shown in Figure E12-4.1. In the slurry reactor, a typical reaction stoichiometry might be... 

Introduction of CO + (760 Torr) in a molar ratio 2 1 in the glass equipment was followed by a stepwise increase of temperature from 25 up to 200°C. Analysis of the gas phase gave the results represented on Figure la. At 176°C the conversion of CO to hydrocarbons is close to 1 % with mainly propylene (32%), methane (26,1 %) ethylene (9,2 %), 1-butene (7,3 %), cis-2-butene (3,6 %), trans-2-butene (5,5 %), isobutene (1 %) and C, hydrocarbons (7 %). All the paraffins except methane are present in much smaller amount than olefins. Figure (lb) represents typical results obtained in Fischer-Tropsch synthesis in a dynamic reactor using a catalyst derived from Fe CO) jj/A Oj (3e). 

Figure L Reactor used for Fischer-Tropsch synthesis (a)fixed bed reactor, (b) slurry phase reactor...

Larger scale Fischer-Tropsch synthesis runs were performed in a pilot plant slug-flow slurry reactor using 3-8kg catalyst as well as in a slurry phase bubble column demonstration unit using 500-1500kg catalyst. The reaction conditions were similar to those in the laboratory CSTR runs. The reactor wax production varied between 5 and 30kg per day for the pilot plant runs and up to 60 bbl/day for the demonstration unit. On-line catalyst samples were taken for particle size distribution measurements and Scanning Electron Microscope analyses. 

Fischer-Tropsch synthesis is another industrially important case where the quest for a catalyst with higher rate as well as selectivity continues. This synthesis is exothermic, and catalysts with higher activity (higher rates) will impose a burden on the heat exchanging capacity of the multiphase reactor used. Development of better catalysts must be accompanied by multiphase reactors that can cater to the higher exotherm associated with faster rates. Section 3.4.1.4 discusses the various available reactor options. 

Haynes WP, Baird MJ, Schehl RR, Zarochak MF. Fischer-Tropsch studies in a bench-scale tube wall reactor using magnetite, Raney iron and taconite catalysts. ACS Division of Petroleum Chemistry Preprints, Anaheim, CA, March 12-17, 1978. 

Stem D, Bell AT. Heinemann H. Effects of mass transfer on the performance of slurry reactors used for Fischer-Tropsch synthesis. Chem. Eng. Sci. 1983 38 597-605. 

Figure 6.11.11 Reactors used for Fischer-Tropsch processes. Adapted from Moulijn, Makkee, and Van Dlepen (2004).

Shell operated its middle-distillate synthesis process (SMDS) in Malaysia from 1993 to 1997, but closed the facility in 1997 while better Fischer-Tropsch catalysts were being developed for future operation. Synthesis gas produced by the Shell partial oxidation process was converted to dhstillates and waxes in a tubular high-pressme Fischer-Tropsch reactor. A sluny phase reactor using an improved catalyst is being developed (40-46 atm 120-130°C). 

The Fischer-Tropsch reaction is essentially that of Eq. XVIII-54 and is of great importance partly by itself and also as part of a coupled set of processes whereby steam or oxygen plus coal or coke is transformed into methane, olefins, alcohols, and gasolines. The first step is to produce a mixture of CO and H2 (called water-gas or synthesis gas ) by the high-temperature treatment of coal or coke with steam. The water-gas shift reaction CO + H2O = CO2 + H2 is then used to adjust the CO/H2 ratio for the feed to the Fischer-Tropsch or synthesis reactor. This last process was disclosed in 1913 and was extensively developed around 1925 by Fischer and Tropsch [268]. 

Sasol Fischer-Tropsch Process. 1-Propanol is one of the products from Sasol s Fischer-Tropsch process (7). Coal (qv) is gasified ia Lurgi reactors to produce synthesis gas (H2/CO). After separation from gas Hquids and purification, the synthesis gas is fed iato the Sasol Synthol plant where it is entrained with a powdered iron-based catalyst within the fluid-bed reactors. The exothermic Fischer-Tropsch reaction produces a mixture of hydrocarbons (qv) and oxygenates. The condensation products from the process consist of hydrocarbon Hquids and an aqueous stream that contains a mixture of ketones (qv) and alcohols. The ketones and alcohols are recovered and most of the alcohols are used for the blending of high octane gasoline. Some of the alcohol streams are further purified by distillation to yield pure 1-propanol and ethanol ia a multiunit plant, which has a total capacity of 25,000-30,000 t/yr (see Coal conversion processes, gasification). 

Medium Pressure Synthesis. Pressures of 500—2000 kPa (5—20 atm) were typical for the medium pressure Fischer-Tropsch process. Cobalt catalysts similar to those used for the normal pressure synthesis were typically used at temperatures ranging from 170 to 200°C ia tubular "heat exchanger" type reactors. 

These reactors for hquids and liquids plus gases employ small particles in the range of 0.05 to 1.0 mm (0.0020 to 0.039 in), the minimum size hmited by filterability. Small diameters are used to provide as large an interface as possible since the internal surface of porous pellets is poorly accessible to the hquid phase. Solids concentrations up to 10 percent by volume can be handled. In hydrogenation of oils with Ni catalyst, however, the sohds content is about 0.5 percent, and in the manufacture of hydroxylamine phosphate with Pd-C it is 0.05 percent. Fischer-Tropsch slurry reac tors have been tested with concentrations of 10 to 950 g catalyst/L (0.624 to 59.3 IbiTi/fF) (Satterfield and Huff, Chem. Eng. Sci., 35, 195 [1980]). 

The Fischer-Tropsch reaction is highly exothermic. Therefore, adequate heat removal is critical. High temperatures residt in high yields of methane, as well as coking and sintering of the catalyst. Three types of reac tors (tubular fixed bed, fluidized bed, and slurry) provide good temperature control, and all three types are being used for synthesis gas conversion. The first plants used tubular or plate-type fixed-bed reactors. Later, SASOL, in South Africa, used fluidized-bed reactors, and most recently, slurry reactors have come into use. 

Shell Gas B.V. has constructed a 1987 mVd (12,500 bbhd) Fischer-Tropsch plant in Malaysia, start-up occurring in 1994. The Shell Middle Distillate Synthesis (SMDS) process, as it is called, uses natural gas as the feedstock to fixed-bed reactors containing cobalt-based cat- yst. The heavy hydrocarbons from the Fischer-Tropsch reactors are converted to distillate fuels by hydrocracking and hydroisomerization. The quality of the products is very high, the diesel fuel having a cetane number in excess of 75. 

L. Seglin Why has Lurgi selected the hot gas recycle process for methanation rather than the isothermal reactor (ARGE) design which they used for the Fischer-Tropsch plant in SASOL s plant in South Africa ... 

This you cannot do in an adiabatic reactor unless you go to extremely high mixing ratios of fresh feed and recycle gas. In summary, it is a question of selectivity, which is the reason for using the isothermal reactor for Fischer-Tropsch. An adiabatic reactor with a waste heat boiler is cheaper than an isothermal feactor, and hence it is used for methanation. 

The catalytic hydrogenation of fatty oils, the desulfurization of liquid petroleum fractions by catalytic hydrogenation, Fischer-Tropsch-type synthesis in slurry reactors, and the manufacture of calcium bisulfite acid are familiar examples of this type of process, for which the term gas-liquid-particle process will be used in the following. 

Various methods may be used for the determination of gas holdup—for example, displacement measurements and tracer experiments. Farley and Ray (F2) have described the use of gamma-radiation absorption measurement for the determination of gas holdup in a slurry reactor for the Fischer-Tropsch synthesis. 

Catalysts were tested for activity in the Fischer-Tropsch reaction using a fixed-bed reactor. The catalyst (0.4 g) was reduced in situ in flowing hydrogen at 425°C for 7 h prior to testing. The test was performed under 2/1 H2/CO at 20 bar total pressure. The initial flow was 64 ml/min, but this was reduced after 24 h to increase the conversion. A final reading of activity and selectivity was taken after 100 h on stream. 

ICP) measurements. The catalytic performance of the nanocatalysts was finally tested in the Fischer-Tropsch synthesis carried out in a fixed bed reactor. The obtained results were compared with literature data of commercially used Fischer-Tropsch catalysts. 

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