Cobalt-based processes

Economics. Comparison of the material and energy balance for our process and the cobalt-based BASF higher olefin process (8), we foimd that our process reduced the capital investment required by over 50% due to the fact that we require far fewer unit operations, and because the operating pressure is much lower. In sutmnary, the thermomorphic solution developed by TDA allows easy catalyst recycle, which, when coupled with the lower pressure operation possible with Rh catalysts (compared to the cobalt-based process) lowers both capital and operating costs for current oxidation (oxo) plants of similar capacity. 

The solvent water reliably averts the risk of fire, which was inherent in the old cobalt-based process as a result of leaking highly flammable, metal carbonyls. The technique with its "built-in extinguishing system" reliably prevents such fires, and the painstaking... 

Assume that the basic mechanism of the Monsanto process is valid for the cobalt-based process. What would be the crucial hypothetical catalytic... 

Whereas extraction with an organic solvent is not desirable from an environmental point of view, supercritical CO2 represents an environmentally benign and clean alternative as demonstrated/461 If the process is run continuously, as depicted in Figure 4.5, it can even compete with the industrial cobalt-based process/47,61,621 Careful tuning is, however, required and the effects of different ionic liquids, temperature, gas composition and substrate flow rate are all important. 

Rhodium-based processes dominate in the hydroformylation of propene. On the other hand, the production capacity of cobalt-based processes has remained at a virtually constant level in the C4 field for years (Figure 7). 

Several explanations may be taken into account for only a small decrease in importance an existing high-pressure infrastructure which is also used for the hydroformylation of olefins higher than propene, where cobalt-based processes are advantageous a combined cobalt recovery and recycle system for the hydroformylation of different olefins and the use of tail gases from low-pressure hydroformylation units. 

When used as a catalyst, cobalt does not compare favorably to rhodium, particularly in terms of its activity and selectivity. Nevertheless, cobalt-based processes remain competitive for hydroformylating highly branched olefinic isomer mixtures containing internal double bonds. In addition to the problem... 

Xie and Subramaniam investigated theoretical options for a rhodium-based process for octenes. Their goal was a process that, when compared to cobalt-based processes, would be particularly efficient in terms of reaction technology and catalyst recycling [16]. Another process design requirement was a significantly lower investment cost than that of conventional cobalt-based processes. 

If a sensitivity analysis regarding the makeup rate is carried out, this shows that the CXL process with 72 wt% toluene as a solvent and a makeup rate of 0.5% incurs production costs of 416 million, and with a makeup rate of 1% production costs of 425 million, which are higher than the conventional cobalt-based process (all values relate to a production capacity of 150 000 mt/y). With this analysis, it must be said that in the recent past there have been periods when the price of rhodium was much higher than assumed here. Therefore, from an economic aspect it is very important that rhodium losses are kept to a minimum. 

An example of such recychng in a parallel reaction system is in the Oxo process for the production of C4 alcohols. Propylene and synthesis gas (a mixture of carbon monoxide and hydrogen) are first reacted to ra- and isobutyraldehydes using a cobalt-based catalyst. Two parallel reactions occur ... 

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. 

In recent years, the spraying process has been adapted for hard facing, using the chromium-nickel-boron alloys which have become known as Colmonoy. More recently still, the cobalt-base Stellite alloys have also been used. These materials in powder form are sprayed on to the surface in the usual way. The deposit is afterwards heat treated by a torch, so that fusion takes place. The process is often known as spray-welding. Such coatings are primarily used for hard facing under wear conditions, but as the Anal surface is nickel-chromium or cobalt-chromium they exhibit very high anticorrosive properties. 

Consequently, as a result of increasing environmental pressure many chlorine and nitric acid based processes for the manufacture of substituted aromatic acids are currently being replaced by cleaner, catalytic autoxidation processes. Benzoic acid is traditionally manufactured (ref. 14) via cobalt-catalyzed autoxidation of toluene in the absence of solvent (Fig. 2). The selectivity is ca. 90% at 30% toluene conversion. As noted earlier, oxidation of p-xylene under these conditions gives p-toluic acid in high yield. For further oxidation to terephthalic acid the stronger bromide/cobalt/manganese cocktail is needed. 

The catalysts used in hydroformylation are typically organometallic complexes. Cobalt-based catalysts dominated hydroformylation until 1970s thereafter rhodium-based catalysts were commerciahzed. Synthesized aldehydes are typical intermediates for chemical industry [5]. A typical hydroformylation catalyst is modified with a ligand, e.g., tiiphenylphoshine. In recent years, a lot of effort has been put on the ligand chemistry in order to find new ligands for tailored processes [7-9]. In the present study, phosphine-based rhodium catalysts were used for hydroformylation of 1-butene. Despite intensive research on hydroformylation in the last 50 years, both the reaction mechanisms and kinetics are not in the most cases clear. Both associative and dissociative mechanisms have been proposed [5-6]. The discrepancies in mechanistic speculations have also led to a variety of rate equations for hydroformylation processes. 

The first reduction in the cobalt-based polymer is metal-centered, resulting in the appearance of a new MLCT transition, with the second reduction being ligand-centered. For the nickel-based polymer, in contrast, both redox processes are ligand-based. 

Along with catalyst activity, product selectivity is a key issue in cobalt-based FTS.1 For GTL processes the preferred product is long-chain waxy hydrocarbons. It is well known that FT reaction conditions have an important effect on product selectivities. High temperatures and H2/CO ratios are associated with higher methane selectivity, lower probability of hydrocarbon chain growth, and lower olefinicity in the products.105... 

In this work, a detailed kinetic model for the Fischer-Tropsch synthesis (FTS) has been developed. Based on the analysis of the literature data concerning the FT reaction mechanism and on the results we obtained from chemical enrichment experiments, we have first defined a detailed FT mechanism for a cobalt-based catalyst, explaining the synthesis of each product through the evolution of adsorbed reaction intermediates. Moreover, appropriate rate laws have been attributed to each reaction step and the resulting kinetic scheme fitted to a comprehensive set of FT data describing the effect of process conditions on catalyst activity and selectivity in the range of process conditions typical of industrial operations. 

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