Hydrocarbons Synthesis from CO

Kravtsov, A.V., Moizes, O.E., Usheva, N.V., and Yablonskii, G.S. 1988. Kinetic model for hydrocarbon synthesis from CO and H2 accounting for its intragroup distribution. React. Kinet. Catal. Lett. 36 201-6. 

Iron has a rich surface coordination chemistry that forms the basis of its important catalytic properties. There are many catalytic applications in which metallic iron or its oxides play a vital part, and the best known are associated with the synthesis of ammonia from hydrogen and nitrogen at high pressure (Haber-Bosch Process), and in hydrocarbon synthesis from CO/C02/hydrogen mixtures (Fischer-Tropsch synthesis). The surface species present in the former includes hydrides and nitrides as well as NH, NH2, and coordinated NH3 itself. Many intermediates have been proposed for hydrogenation of carbon oxides during Fischer-Tropsch synthesis that include growing hydrocarbon chains. 

It can also be obtd as a by-product of hydrocarbon synthesis from CO and H2, and as a by-product of methanol synthesis from these gases. The oldest method of alcohol prepn is by fermentation of grains, molasses and carbohydrates. It can also be prepd by fermentation of sulfite pulp. Alcohol prepd from grains is known as grain alcohol and it is used in prepn of beverages (Refs 1, 11 12)... 

Kolbel and coworkers (3) have calculated the formation enthalpies for hydrocarbon synthesis from CO/H2 at mainly on the basis of Equations... 

Discovery of hydrocarbon synthesis from CO and H2 on iron catalysts... 

C. Preparation of so-called capsular FT synthesis catalysts [90], with the nucleus being the catalyst of hydrocarbon synthesis from CO and and the outer shell is the zeolite membrane (Fig. 8). The depth of the zeolite shell controls the transport of CO and... 

For industrial hydrogenation of vegetable and animal oils in Russia a Raney type nickel was prepared by Bag and co-workers (64). Preparation of detergents from hydrogenated fats has been reported (11). Reviews of these so-called skeleton catalysts were published by Russian investigators, for instance, by Lel chuk and co-workers (197). These catalysts have also been discussed with reference to hydrocarbon synthesis from water gas (148). Lel chuk (197) states that Raney nickel is more drastic for water gas synthesis than are the skeleton nickel catalysts prepared by Bag, and that Bag s copper-nickel skeleton catalysts approach nickel in their activity. Destructive hydrogenation under mild conditions was said to be possible with Bag s skeleton catalyst as described by Lel chuk. 

In order to produce ethanol by COj hydrogenation, the catalyst should have two functions C-C bond formation and C-0 bond partial preservation. In the case of the CO/Hj feed gas system, the former is industrially performed in Fischer-Tropsch synthesis, while the latter in methanol synthesis. K/Fe oxides catalyst, being effective in Fischer-Tropsch synthesis, was found to produce C-C bond in COj hydrogenation. It converted COj into CO, alcohols, and hydrocarbons. Cu-Zn oxides catalyst, practically used in methanol synthesis from CO/CO2/H2 mixture, was found unable to produce C-C bond it converted CO, to CO and methanol without any other detected compounds. 

In order to elucidate the role of CO in COj hydrogenation, activity tests were carried out with the feed gas, in which CO2 was partly replaced with CO. The results are illustrated in Figure 3. It shows that the ratios of the yields of ethanol, methanol, and hydrocarbons (C1 C5) scarcely changed with the replacement of CO2 by CO. The total yield of the products increased with an increase in the CO/CO2 ratio. The total yield dependence on the CO/CO, ratio is attributable to the difference of reactivity between CO and CO2. In Figure 2 CO selectivity remained low in the whole range. These results shown in Figure 2 and 3 suggest that ethanol was produced directly from CO2 as well as CO. In methanol synthesis from CO/CO2/H2 mixture, it was reported that methanol is produced directly both from CO and CO, [3]. 

The Co-MgO-ZSM-5 catalyst was prepared as a physical mixture of cobalt hydroxycarbonate, MgO and NaZSM-5. It was found to be active in the hydrocarbon synthesis from the products of biomass gasification. The addition of CO2 caused a decrease of the growth factor while that of N an increase. ... 

When 002 is added to a synthesis gas feed to a promoted iron catalyst, 0 is found in the CO just as expected for a catalyst that is active for the WGS reaction. However, the observation of the much higher content of the hydrocarbon products than is present in the CO is surprising (Figure 23). If the production of hydrocarbons was from CO only, the CH4 should have the same C/mole as CO and the activity of a hydrocarbon of carbon number n should have n times the activity of the CO. Thus, for initiation and chain growth by the carbon derived from CO, we would anticipate the C/mole in the hydrocarbon products to follow curve 1 of Figure 23. However, irrespective of whether curves 2 or 3 best fit the data for the hydrocarbons, it is apparent that all of the products have a much higher activity than is possible if they are derived from CO. 

Hydrocarbon synthesis from syngas (Fischer-Tropsch reactions) can be carried out over the catalysts prepared from Co- and Cu-containing LDHs. The products include methane, higher paraffins, and olefins as well as methanol. The loading of Co and Cu determines the selectivity for each compound. For instance, Co-rich catalysts give more paraffins, while Co-poor ones lead to methanol (615). 

It is well admitted that the first step of the hydrocarbons synthesis from syngas is the CO dissociation on a metallic center (Co°, Fe°, or Co-Fe in the present case). CO dissociation into Cgurf and CO2 has been studied on the partially Lai j,Coo.4Feo,603 5 solids [43]. The results clearly show that the rate of CO dissociation increases almost linearly with the lanthanum deficiency. This is associated with the increased amount of reduced metal (2.1 wt% for y = 0-10.9 wt% for y=0A). The metal particles size has also an effect. For y = 0.4, CO dissociation is lower when catalysts were initially calcined at 900 °C (12% of CO conversion for 14.1 wt% of metal of average particle size of 28 nm) compared to those calcined at 750 °C (19% of CO conversion for 10.9 wt% of metal of average particle size of 10 nm). The larger size of particles led to a lower surface/volume ratio and to a decrease of CO dissociation. 

On the basis of the assumptions of model <22> and <23> the Fischer-Tropsch synthesis in a slurry phase BCR has been modeled [37, 38]. As this hydrocarbon synthesis from synthesis gas (CO + H2) is accompanied by considerable volume contraction, it is clear that gas flow variations have to be accounted for. The developed models are useful to evaluate experimental data from bench scale units and to simulate the behavior of larger scale Fischer-Tropsch slurry reactors. Though only simplified kinetic laws were applied, the predictions of the model are in reasonable agreement with data reported from 1.5 m diameter demonstration plant. Fig. 12 shows computed space-time-yields (STY) as a function of the inlet gas velocity. As the Fischer-Tropsch reaction on suspended catalyst takes place in the slow reaction regime, it is understood that STY passes through a maximum in dependence of uqo- The predicted maximum is in striking agreement with experimental observations [37]. 

The Fischer-Tropsch process can be considered as a one-carbon polymerization reaction of a monomer derived from CO. The polymerization affords a distribution of polymer molecular weights that foUows the Anderson-Shulz-Flory model. The distribution is described by a linear relationship between the logarithm of product yield vs carbon number. The objective of much of the development work on the FT synthesis has been to circumvent the theoretical distribution so as to increase the yields of gasoline range hydrocarbons. 

By selection of appropriate operating conditions, the proportion of coproduced methanol and dimethyl ether can be varied over a wide range. The process is attractive as a method to enhance production of Hquid fuel from CO-rich synthesis gas. Dimethyl ether potentially can be used as a starting material for oxygenated hydrocarbons such as methyl acetate and higher ethers suitable for use in reformulated gasoline. Also, dimethyl ether is an intermediate in the Mobil MTG process for production of gasoline from methanol. 

Steam reforming of CH4 CH4 + H2O = CO + 3H2 NH3 synthesis from the elements Hydrogenation of CO and CO2 to form hydrocarbons (Fischer-Tropsch syndresis)... 

These observations, coupled with the findings of Muetterties et al. that none of a large number of mononuclear coordination catalysts examined showed any activity for the H2/CO reaction (53), lend further support to the idea that more than one metal center is necessary for the catalytic formation of hydrocarbon products from synthesis gas. 

With reference to the homogeneous catalyst systems thus far reported for the synthesis of hydrocarbons/chemicals from carbon monoxide and hydrogen, only the anionic rhodium systems of Union Carbide show any appreciable shift activity. With neutral species of the type M3(CO)12 (M = Ru or Os), only small quantities of carbon dioxide are produced under the synthesis conditions (57). 

When the Fe-MnO catalyst is analyzed after use in the Fischer-Tropsch reaction (the synthesis of hydrocarbons from CO and H2), the XRD pattern in Fig. 6.2 reveals that all metallic iron has disappeared. Instead, a number of weak reflections are visible, which are consistent with the presence of iron carbides, as confirmed by Mossbauer spectroscopy [7]. The conversion of iron to carbides under Fischer-Tropsch conditions has been studied by many investigators and has been discussed in more detail in Chapter 5 on Mossbauer spectroscopy. 

The ODH of ethylbenzene to styrene is a highly promising alternative to the industrial process of non-oxidative dehydrogenation (DH). The main advantages are lower reaction temperatures of only 300 500 °C and the absence of a thermodynamic equilibrium. Coke formation is effectively reduced by working in an oxidative atmosphere, thus the presence of excess steam, which is the most expensive factor in industrial styrene synthesis, can be avoided. However, this process is still not commercialized so far due to insufficient styrene yields on the cost of unwanted hydrocarbon combustion to CO and C02, as well as the formation of styrene oxide, which is difficult to remove from the raw product. 

The first step toward making liquid fuels from coal involves the manufacture of synthesis gas (CO and H ) from coal. In 1925, Franz Fischer and Hans Tropsch developed a catalyst that converted CO and at 1 atm and 250 to 300°C into liquid hydrocarbons. By 1941, Fischer-Tropsch plants produced 740 000 tons of petroleum products per year in Germany (Dry, 1999). Fischer-Tropsch technology is based on a complex series of reactions that use to reduce CO to CH groups linked to form long-chain hydrocarbons (Schulz, 1999) ... 

The FTS was established in 1923 by German scientists Franz Fischer and Hans Tropsch. The main aim of FTS is the synthesis of long-chain hydrocarbons from CO and Hj gas mixture. The FTS is described by the set of equations (Schulz, 1999) ... 

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]. 

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