Cobalt high-pressure process

In none of the technically applied processes complete conversion of the reactants is achieved in a single pass. The conversion of propene, for example, can be as low as 25-30% per pass (LPO gas recycle process) or amount to more than 95 % (cobalt high-pressure process) as a consequence of several process variables (temperature, pressure, catalyst, reactant concentration, and residence time of reactants). Consequently, in every case an unconverted portion remains which, after separation from the product, has to be recycled (or partially vented to avoid accumulation of inerts) or used in a second stage. For LPO processes with limited olefin conversion, especially, several solutions have been proposed for arranging single reactors in series as a cascade [147]. 

The minimum mass concentration of toluene needed to keep the ligand in solution is 33wt%. Table 9.1 shows the investment costs for the CXL process assuming 72 wt% solvent and a variant without solvent. The conventional process corresponds to a cobalt high-pressure process (see Section 9.3.1). The following discussion about process economy relates to production plants with a capacity of 150 000 mt/y of Cg aldehyde. All data is based on pure process simulations. 

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. 

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. 

Introduction of a high pressure process employing homogeneous cobalt catalysts. 

The advantages of this new process are the high n/i ratio and the low formation of heavy ends (1.5%) and alcohols (1%) without any formation of formates. In the original cobalt-based high-pressure process the n/i ratio was 67/33, with substantial formation of heavy ends (6.7%), alcohols (6.6%) and pentylformates (4.2%).350 The n-valeraldehyde product is oxidized with molecular oxygen to n-valeric acid, the trimethylolpropane, pentaerythritol, or dipentaerythritol esters of which are used as lubricants.350... 

The low-pressure oxo process based on rhodium complex catalysts has largely replaced the older, high-pressure process, which used cobalt carbonyls as catalyst. The low-pressure process is operated at about 100°C and 200psig. A new generation oxo process with bisphosphite modified rhodium catalyst is shown schematically in Fig. 10.5. 

In the oxide-silicate ores nickel is so disseminated within the laterite that conventional ore-dressing methods do not work. The ore is often treated directly in py-rometallurgical processes, high-temperature reduction with carbon. This process yields ferronickd. Laterite ores are also leached with sulfuric acid in a high-tem-perature, high-pressure process. Nickel and cobalt are separated from purified solutions by solvent extraction. 

The alkalized zinc oxide—chromia process developed by SEHT was tested on a commercial scale between 1982 and 1987 in a renovated high pressure methanol synthesis plant in Italy. This plant produced 15,000 t/yr of methanol containing approximately 30% higher alcohols. A demonstration plant for the lEP copper—cobalt oxide process was built in China with a capacity of 670 t/yr, but other higher alcohol synthesis processes have been tested only at bench or pilot-plant scale (23). 

Ma.nufa.cture. Nickel carbonyl can be prepared by the direct combination of carbon monoxide and metallic nickel (77). The presence of sulfur, the surface area, and the surface activity of the nickel affect the formation of nickel carbonyl (78). The thermodynamics of formation and reaction are documented (79). Two commercial processes are used for large-scale production (80). An atmospheric method, whereby carbon monoxide is passed over nickel sulfide and freshly reduced nickel metal, is used in the United Kingdom to produce pure nickel carbonyl (81). The second method, used in Canada, involves high pressure CO in the formation of iron and nickel carbonyls the two are separated by distillation (81). Very high pressure CO is required for the formation of cobalt carbonyl and a method has been described where the mixed carbonyls are scmbbed with ammonia or an amine and the cobalt is extracted as the ammine carbonyl (82). A discontinued commercial process in the United States involved the reaction of carbon monoxide with nickel sulfate solution. 

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). 

Cobalt in Catalysis. Over 40% of the cobalt in nonmetaUic appHcations is used in catalysis. About 80% of those catalysts are employed in three areas (/) hydrotreating/desulfurization in combination with molybdenum for the oil and gas industry (see Sulfurremoval and recovery) (2) homogeneous catalysts used in the production of terphthaUc acid or dimethylterphthalate (see Phthalic acid and otherbenzene polycarboxylic acids) and (i) the high pressure oxo process for the production of aldehydes (qv) and alcohols (see Alcohols, higher aliphatic Alcohols, polyhydric). There are also several smaller scale uses of cobalt as oxidation and polymerization catalysts (44—46). 

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... 

The hypothesis that the cobalt carbonyl radicals are the carriers of catalytic activity was disproved by a high pressure photochemistry experiment /32/, in which the Co(CO), radical was prepared under hydroformylation conditions by photolysis of dicobalt octacarbonyl in hydrocarbon solvents. The catalytic reaction was not enhanced by the irradiation, as would be expected if the radicals were the active catalyst. On the contrary, the Co(C0)4 radicals were found to inhibit the hydroformylation. They initiate the decomposition of the real active catalyst, HCo(C0)4, in a radical chain process /32, 33/. 

Of the three catalytic systems so far recognized as being capable of giving fast reaction rates for methanol carbonylation—namely, iodide-promoted cobalt, rhodium, and iridium—two are operated commercially on a large scale. The cobalt and rhodium processes manifest some marked differences in the reaction area (4) (see Table I). The lower reactivity of the cobalt system requires high reaction temperatures. Very high partial pressures of carbon monoxide are then required in the cobalt system to... 

The systems that we investigated in collaboration with others involved intermolecular and intramolecular electron-transfer reactions between ruthenium complexes and cytochrome c. We also studied a series of intermolecular reactions between chelated cobalt complexes and cytochrome c. A variety of high-pressure experimental techniques, including stopped-flow, flash-photolysis, pulse-radiolysis, and voltammetry, were employed in these investigations. As the following presentation shows, a remarkably good agreement was found between the volume data obtained with the aid of these different techniques, which clearly demonstrates the complementarity of these methods for the study of electron-transfer processes. 

As a result of the higher stability the process can be (and must be ) operated at lower pressure (25-100 bar versus 200-300 bar for HCo(CO)4). The higher stability can be explained by the electron donation of the phosphine to the electron deficient cobalt carbonyl thus strengthening the Co-CO bonds. The phosphine complex is less active than the tetracarbonyl complex and therefore the reaction is carried out at higher temperatures (170 °C versus 140 °C). The temperature is "dictated" by the rate required the high pressures in the tetracarbonyl system are needed to prevent decomposition of the carbonyls to metal and CO. 

Raffinate-II typically consists of40 % 1-butene, 40 % 2-butene and 20 % butane isomers. [RhH(CO)(TPPTS)3] does not catalyze the hydroformylation of internal olefins, neither their isomerization to terminal alkenes. It follows, that in addition to the 20 % butane in the feed, the 2-butene content will not react either. Following separation of the aqueous catalyts phase and the organic phase of aldehydes, the latter is freed from dissolved 2-butene and butane with a counter flow of synthesis gas. The crude aldehyde mixture is fractionated to yield n-valeraldehyde (95 %) and isovaleraldehyde (5 %) which are then oxidized to valeric add. Esters of n-valeric acid are used as lubricants. Unreacted butenes (mostly 2-butene) are hydroformylated and hydrogenated in a high pressure cobalt-catalyzed process to a mixture of isomeric amyl alcohols, while the remaining unreactive components (mostly butane) are used for power generation. Production of valeraldehydes was 12.000 t in 1995 [8] and was expected to increase later. 

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