Cobalt catalysts pressure

Goal Upgrading via Fischer-Tropsch. The synthesis of methane by the catalytic reduction of carbon monoxide and hydrogen over nickel and cobalt catalysts at atmospheric pressure was reported in 1902 (11). 

During World War II, nine commercial plants were operated in Germany, five using the normal pressure synthesis, two the medium pressure process, and two having converters of both types. The largest plants had capacities of ca 400 mr / d (2500 bbl/d) of Hquid products. Cobalt catalysts were used exclusively. 

Prior to 1975, reaction of mixed butenes with syn gas required high temperatures (160—180°C) and high pressures 20—40 MPa (3000—6000 psi), in the presence of a cobalt catalyst system, to produce / -valeraldehyde and 2-methylbutyraldehyde. Even after commercialization of the low pressure 0x0 process in 1975, a practical process was not available for amyl alcohols because of low hydroformylation rates of internal bonds of isomeric butenes (91,94). More recent developments in catalysts have made low pressure 0x0 process technology commercially viable for production of low cost / -valeraldehyde, 2-methylbutyraldehyde, and isovaleraldehyde, and the corresponding alcohols in pure form. The producers are Union Carbide Chemicals and Plastic Company Inc., BASF, Hoechst AG, and BP Chemicals. 

The original catalysts for this process were iodide-promoted cobalt catalysts, but high temperatures and high pressures (493 K and 48 MPa) were required to achieve yields of up to 60% (34,35). In contrast, the iodide-promoted, homogeneous rhodium catalyst operates at 448—468 K and pressures of 3 MPa. These conditions dramatically lower the specifications for pressure vessels. Yields of 99% acetic acid based on methanol are readily attained (see Acetic acid Catalysis). 

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. 

A Belgian patent (178) claims improved ethanol selectivity of over 62%, starting with methanol and synthesis gas and using a cobalt catalyst with a hahde promoter and a tertiary phosphine. At 195°C, and initial carbon monoxide pressure of 7.1 MPa (70 atm) and hydrogen pressure of 7.1 MPa, methanol conversions of 30% were indicated, but the selectivity for acetic acid and methyl acetate, usehil by-products from this reaction, was only 7%. Ruthenium and osmium catalysts (179,180) have also been employed for this reaction. The addition of a bicycHc trialkyl phosphine is claimed to increase methanol conversion from 24% to 89% (181). 

In a typical process adiponitrile is formed by the interaction of adipic acid and gaseous ammonia in the presence of a boron phosphate catalyst at 305-350°C. The adiponitrile is purified and then subjected to continuous hydrogenation at 130°C and 4000 Ibf/in (28 MPa) pressure in the presence of excess ammonia and a cobalt catalyst. By-products such as hexamethyleneimine are formed but the quantity produced is minimized by the use of excess ammonia. Pure hexamethylenediamine (boiling point 90-92°C at 14mmHg pressure, melting point 39°C) is obtained by distillation, Hexamethylenediamine is also prepared commercially from butadience. The butadiene feedstock is of relatively low cost but it does use substantial quantities of hydrogen cyanide. The process developed by Du Pont may be given schematically as ... 

The carbonylation of methanol is currently one of the major routes for acetic acid production. The basic liquid-phase process developed by BASF uses a cobalt catalyst at 250°C and a high pressure of about 70... 

Cobalt catalysts such as HCo(CO)4 are widely used for hydroformyla-tion of higher alkenes, despite the higher temperatures and pressures required. The main reason for this is that these catalysts are also efficient alkene isomerization catalysts, allowing a mix of internal and terminal alkenes to be used in the process. Catalyst recovery is more of a problem here, involving production of some waste and adding significantly to the complexity of the process. A common recovery method involves treating the catalyst with aqueous base to make it water soluble, followed by separation and subsequent treatment with acid to recover active catalyst (4.3). 

The rhodium catalyst has several distinct advantages over the cobalt catalyst it is much faster and far more selective. The higher rate is in process terms translated into much lower pressures (the cobalt catalyst is operated at pressures of 700 bar). Nickel- and palladium-based catalysts have also been reported, but no applications have resulted from these. The mechanism for group 10 metals has not been studied (see Section 9.3.2.3). 

Cobalt carbonyls are the oldest catalysts for hydroformylation and they have been used in industry for many years. They are used either as unmodified carbonyls, or modified with alkylphosphines (Shell process). For propene hydroformylation, they have been replaced by rhodium (Union Carbide, Mitsubishi, Ruhrchemie-Rhone Poulenc). For higher alkenes, cobalt is still the catalyst of choice. Internal alkenes can be used as the substrate as cobalt has a propensity for causing isomerization under a pressure of CO and high preference for the formation of linear aldehydes. Recently a new process was introduced for the hydroformylation of ethene oxide using a cobalt catalyst modified with a diphosphine. In the following we will focus on relevant complexes that have been identified and recently reported reactions of interest. 

Schulz, H., Claeys, M., and Harms, S. 1997. Effect of water partial pressure on steady state Fischer-Tropsch activity and selectivity of a promoted cobalt catalyst. Stud. Surf. Sci. Catal. 107 193-200. 

Carbon deposition from CO on a cobalt catalyst at low pressures is known to be a structure-sensitive process. CO is adsorbed molecularly on the low index surfaces (Co (0001)), but its dissociation occurs on the Co (1012), Co (1120), and polycrystalline surfaces.5762 Deposition of carbon on Co (1012) and the probable formation of Co3C have been established by Auger emission spectroscopy (AES) and low-energy electron diffraction (LEED) techniques.66... 

Additionally, the following factors are believed to have an increase in the amount of carbon deposited on cobalt catalysts higher reaction temperature,39-63 lower H2/CO ratio,63 higher CO partial pressures,59 and cleaner (sulfur-free) synthesis gas.33-64... 

Beitel, G. A., de Groot, C. P. M., Oosterbeek, H., and Wilson, J. H. 1997. A combined in-situ PM-RAIRS and kinetic study of single-crystal cobalt catalysts under synthesis gas at pressures up to 300 mbar. J. Phys. Chem. B 101 4035-43. 

The most difficult problem to solve in the design of a Fischer-Tropsch reactor is its very high exothermicity combined with a high sensitivity of product selectivity to temperature. On an industrial scale, multitubular and bubble column reactors have been widely accepted for this highly exothermic reaction.6 In case of a fixed bed reactor, it is desirable that the catalyst particles are in the millimeter size range to avoid excessive pressure drops. During Fischer-Tropsch synthesis the catalyst pores are filled with liquid FT products (mainly waxes) that may result in a fundamental decrease of the reaction rate caused by pore diffusion processes. Post et al. showed that for catalyst particle diameters in excess of only about 1 mm, the catalyst activity is seriously limited by intraparticle diffusion in both iron and cobalt catalysts.1... 

Meanwhile, Wacker Chemie developed the palladium-copper-catalyzed oxidative hydration of ethylene to acetaldehyde. In 1965 BASF described a high-pressure process for the carbonylation of methanol to acetic acid using an iodide-promoted cobalt catalyst (/, 2), and then in 1968, Paulik and Roth of Monsanto Company announced the discovery of a low-pressure carbonylation of methanol using an iodide-promoted rhodium or iridium catalyst (J). In 1970 Monsanto started up a large plant based on the rhodium catalyst. 

Bertole et al.u reported experiments on an unsupported Re-promoted cobalt catalyst. The experiments were done in a SSITKA setup, at 210 °C and pressures in the range 3-16.5 bar, using a 4 mm i.d. fixed bed reactor. The partial pressures of H2, CO and H20 in the feed were varied, and the deactivation, effect on activity, selectivity and intrinsic activity (SSITKA) were studied. The direct observation of the kinetic effect of the water on the activity was difficult due to deactivation. However, the authors discuss kinetic effects of water after correcting for deactivation. The results are summarized in Table 1, the table showing the ratio between the results obtained with added water in the feed divided by the same result in a dry experiment. The column headings refer to the actual experiments compared. It is evident that adding water leads to an increase in the overall rate constant kco. The authors also report the intrinsic pseudo first order rate-coefficient kc, where the overall rate of CO conversion rco = kc 6C and 0C is the coverage of active... 

The influence of water on the rate of CO hydrogenation over y-Al203-supported cobalt catalysts has been the subject of several studies. Table 2 gives an overview of the reported effects. As can be seen the observed effects range from negative to positive, for a range of catalyst compositions and supports used. There are also examples of this effect in the patent literature, e.g. Eri et al,44 who addressed the effect of water on an a-Al203 supported cobalt catalysts. When the inlet water partial pressure was 4.6 bar, the CO conversion increased from 24 to 30%. Thus, a positive impact of water was recorded. 

Li et al 9 also reported on the selectivity to C02, attributed to the WGS reaction (Fig. 6). Cobalt catalysts have a low activity towards the WGS, but some C02 is always detected in the product. The C02 selectivity increases almost linearly with increasing residence time (1/SV), and is doubled with added water (about 15% water added), the rate of C02 formation being proportional to the resulting water pressure. 

Butanal by hydroformylation of propene is the most important oxo product in terms of volume. Six million metric tons per year of butanals were consumed in 2003, vis-a-vis a capacity of 7.6 million metric tons. Highly chemo- and regioselective processes based on ligand-modified rhodium catalysts have been developed and replaced the original cobalt high pressure technology. 

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