Selectivity Fischer-Tropsch process

A particularly favourable application would be in the synthesis of MTBE and TAME. The selective reaction of methanol with the branched alkene would enable the straight chain alkenes to be recycled through the isomerization catalyst. Since the methanol for such a process would likely be synthesised from CO and Hg it would be possible to run this process in parallel with an alkene selective Fischer-Tropsch process to achieve a self contained conversion of CO and to a high octane fuel blend stock. 

Epoxides such as ethylene oxide and higher olefin oxides may be produced by the catalytic oxidation of olefins in gas-liquid-particle operations of the slurry type (S7). The finely divided catalyst (for example, silver oxide on silica gel carrier) is suspended in a chemically inactive liquid, such as dibutyl-phthalate. The liquid functions as a heat sink and a heat-transfer medium, as in the three-phase Fischer-Tropsch processes. It is claimed that the process, because of the superior heat-transfer properties of the slurry reactor, may be operated at high olefin concentrations in the gaseous process stream without loss with respect to yield and selectivity, and that propylene oxide and higher... 

Espinoza, R.L., Shingles, T., Duvenhage, D.J., and Langenhoven, P.L., Method of modifying and controlling catalyst selectivity in a Fischer-Tropsch process. U.S. patent 6,653,357, Sasol Technology, Nov. 25, 2003. 

Van Der Laan, G.P. 1999. Kinetics, selectivity and scale up of the Fischer Tropsch process. PhD dissertation, Rijksunivertiteit Groningen. 

In view of the size of operation being contemplated, it is unlikely that homogeneous catalysts will play a primary role in the production of synthetic oil. However, from the standpoint of the chemical industry, the complex mixture of products obtained from the classical Fischer-Tropsch process is generally unattractive owing to the economic constraints imposed by costly separation/purification processes. What is needed is a catalyst system for the selective conversion of CO/H2 mixtures to added-... 

X. Huang and C. B. Roberts, Selective Fischer-Tropsch synthesis over an A1203 supported cobalt catalyst in supercritical hexane, Fuel Process Technol., 2003, 83, 81-99. 

Another, highly selective oligomerisation reaction of ethene should be mentioned here, namely the trimerisation of ethene to give 1-hexene. Worldwide it is produced in a 0.5 Mt/y quantity and used as a comonomer for ethene polymerisation. The largest producer is BP with 40 % market share utilizing the Amoco process, formerly the Albemarle (Ethyl Corporation) process. About 25 % is made by Sasol in South Africa where it is distilled from the broad mixture of hydrocarbons obtained via the Fischer-Tropsch process, the conversion of syn-gas to fuel. The third important process has been developed by Phillips. 

In the very active field of unmodified nanoparticles recent discoveries have been made on size-selective Fischer-Tropsch catalysts that convert selectively CO and H2 into hydrocarbons there is a strong dependence of activity, selectivity and Hfetime on Co particle size. This topic of unmodified, supported or unsupported, nanoparticles is outside the scope of this chapter [74, 75]. Nevertheless, we mention discoveries made by Degussa, who have patented a process for H2O2 synthesis from molecular oxygen and molecular hydrogen with nanosized Pd particles (6 A) [76]. 

The properties of these new materials as catalyst support were tested on Fischer-Tropsch process (CO-H2 reaction) in a fixed bed differential reactor. Three materials were tested a) CON, a conventional activated carbon b) SC-155 (G40.60) and c) C-155 (G20.20). All of them were previously iron doped until 5% metallic iron wt/wt was reached. The test conditions were Reaction temperature =270°C H2/CO ratio=3, pressure = latm. The main properties of the tested catalyst supports and their performance in the first hour test are shown in Table 2. SC-155 (G40.60) and C-155 (G20.20) were selected for this test in order to compare materials with near the same specific surface area but with different structural composition, and CON was selected because it is of common use and has very different texture characteristics respect to the other two materials. 

Iron catalysts have found only limited use in usual hydrogenations, although they play industrially important roles in the ammonia synthesis and Fischer-Tropsch process. Iron catalysts have been reported to be selective for the hydrogenation of alkynes to alkenes at elevated temperatures and pressures. Examples of the use of Raney Fe, Fe from Fe(CO)5, and Urushibara Fe are seen in eqs. 4.27,4.28, and 4.29, respectively. 

As part of the work undertaken by APCI under contract to the DOE, to develop a slurry phase Fischer-Tropsch process to produce selectively transportation fuels, a study of the hydrodynamics of three phase bubble column reactors was begun using cold flow modelling techniques (l ). Part of this study includes the measurement of solid concentration profiles over a range of independent column operating values. 

Fischer-Tropsch process. The methane selectivity is t)q)ically 30-60 mol%. This significant selectivity for methane formation implies that the rate of hydrogenation of the "Ci" species is of the same order of magnitude as the rate of chain growth. The Fischer-Tropsch process is economical only if a major fraction of the carbon in the synthesis gas is converted to long-chain hydrocarbons and not more than about 10% is converted to methane (41). 

Other carbogenic sieves were active for shape selective hydrogenations [55], for oxidative dehydrogenations, deep oxydations of chlorinated hydrocarbons, and in the Fischer-Tropsch process. 

Oxidative addition to ruthenium and osmium four-coordinate complexes occurs readily. These complexes are excellent starting materials for group VIII complexes. Addition of formaldehyde to complexes M(CO)L(PPh3)2 (L = CO or PPhs selection of L is metal dependent) leads to oxidative addition products, a reaction of relevance to Fischer-Tropsch processes. The ruthenium complex is proposed as an intermediate only the osmium complex has been isolated ... 

Catalysis by Metal Ousters in Zeolites. There is an increasing interest in the use of metal clusters stabilized in zeolites. One objective of such work is to utilize the shape and size constraints inherent in these support materials to effect greater selectivities in typical metal-catalysed reactions. Much work has been concerned with carbon monoxide hydrogenation, and although the detailed nature of the supported metals so obtained is not well understood, there is clear evidence of chain limitation in the Fischer-Tropsch process with both RuY zeolites and with HY and NaY zeolites containing Fe3(CO)22- In the former case there is a drastic decline in chain-growth probability beyond C5- or C10-hydrocarbons depending upon the particle size of the ruthenium metal. 

The synthesis of light alkenes by modification of the Fischer-Tropsch process is recognised as an important route to high value fuel components (refs. 1,2). The essential requirement of the F-T catalyst is high selectivity towards alkenes, suppression of methane and resistance to coking under conditions which favour the formation of hydrogen deficient products. 

Even more spectacular results in terms of the increasing importance of nanocatalysis for bulk industrial processes have recently been reported by Kuipers and de Jong [32, 33]. By dispersing metallic cobalt nanoparticles of specific sizes on inert carbon nanofibers the authors were able to prepare a new nano-type Fischer-Tropsch catalyst. A combination of X-ray absorption spectroscopy, electron microscopy, and other methods has revealed that zerovalent cobalt particles are the true active centers which convert CO and H2 into hydrocarbons and water. Further, a profound size effect on activity, selectivity, and durability was observed. Via careful pressure-size correlations, Kuipers and de Jong have found that or cobalt particles of 6 or 8nm are the optimum size for Fischer-Tropsch catalysis. The Fischer-Tropsch process (invented in 1925 at the Kaiser-Wilhelm-Institute for... 

Statoil has been involved in Fischer-Tropsch based GTL technology development since the mid 1980 s (Rytter et al.,1990). In order to maximize distillate production, a low temperature, cobalt catalyst based Fischer-Tropsch technology has been selected. A slurry bubble column reactor offers the best performance in terms of economy of scale, throughput and yield, but presents several technical challenges. A highly active and selective cobalt catalyst is needed and must be adapted to suit the requirements of the slurry reactor. Separation of wax from the slurry is another critical aspect of this technology. Statoil has developed a supported cobalt catalyst and a continuous filtration technique that forms the heart of the Fischer-Tropsch process. 

Selective Fischer-Tropsch wax hydrocracking -opportunity for improvement of overall gas-to-liquids processing... 

Shape-selective reaction of methanol with ZSM-5 catalysts. Hydrocarbons that exceed the ideal size for gasoline are retained in the zeolite pores untU they have been catalytically shortened enough to escape. The product spectrum of this process is far more favorable than that of the Fischer-Tropsch process. 

As the production route from coal via methanol to automotive fuels has an edge on the coal-based Fischer-Tropsch process not only because of its high selectivity but also in view of its higher efficiency, there are today signs in South Africa - which possesses some of the richest coal deposits in the world - that methanol will play a role as an intermediate or finished product in future automotive fuel production. 

The structural promoter functions to provide a stable, high-area catalyst, while the chemical promoter alters the selectivity of the process. The effectiveness of the alkali metal oxide promoter increases with increasing basicity. Increasing the basicity of the catalyst shifts the selectivity of the reaction toward the heavier or longer-chain hydrocarbon products (Dry and Ferreira, 1967). By the proper choice of catalyst basicity and ratio, the product selectivity in the Fischer-Tropsch process can be adjnsted to yield from 5% to 75% methane. Likewise, the proportion of hydrocarbons in the gasoline range ronghly can be adjnsted to produce 0%-40% of the total hydrocarbon yield. 

Fig. 5. Relation between the selectivities of the hydrocarbon cuts for the high temperature Fischer-Tropsch process. The selectivities are on a C atom % basis.

Important unfunctionalized acyclic alkenes used in industry are ethene (C2) and propene (C3), isomeric butenes (C4), octenes (Cg), and olefins up to a chain length of C g. In general, a distinction is made between short-chain (C3, C4), medium-chain (C5-C42), and long-chain (C13-C19) 0x0 products. Some linear a-olefins (LAOs), such as 1-butene, 1-hexene, 1-octene, or 1-decene, can be extracted selectively from Fischer- Tropsch processes. As exemplarily conducted in Sasol s SYNTHOL process, a range of olefins with a broad distribution of odd and even carbon numbers can be obtained [9, 10]. In the case of low-cost ethylene, dimerization may produce 1-butene. Trimerization or tetramerization produces 1-hexene and/or 1-octene [11]. 

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