Cobalt catalysts concentrations

The study of the crosshnking of dimethacrylate-based VERs using scanning/isothermal DSC and DMTA describes the correlation between the reaction kinetics, as well as the relaxational behavior, cure temperature and peroxide and cobalt catalyst concentration [195]. An increase in the methylethylketone peroxide concentration increased the polymerization rate and reduced the gel time. The use of cobalt octoate as the promoter also reduced the gel time but retarded the reaction rate, except at very low concentrations. This could be explained by the dual role of the cobalt species as a catalyst of the formation of radicals from MEKP (Scheme 30) ... 

Butane LPO conducted in the presence of very high concentrations of cobalt catalyst has been reported to have special character (2,205,217—219). It occurs under mild conditions with reportedly high efficiency to acetic acid. It is postulated to involve the direct attack of Co(III) on the substrate. Various additives, including methyl ethyl ketone, -xylene, or water, are claimed to be useful. 

A one-step LPO of cyclohexane directly to adipic acid (qv) has received a lot of attention (233—238) but has not been implemented on a large scale. The various versions of this process use a high concentration cobalt catalyst in acetic acid solvent and a promoter (acetaldehyde, methyl ethyl ketone, water). 

A thkd method utilizes cooxidation of an organic promoter with manganese or cobalt-ion catalysis. A process using methyl ethyl ketone (248,252,265—270) was commercialized by Mobil but discontinued in 1973 (263,264). Other promoters include acetaldehyde (248,271—273), paraldehyde (248,274), various hydrocarbons such as butane (270,275), and others. Other types of reported activators include peracetic acid (276) and ozone (277), and very high concentrations of cobalt catalyst (2,248,278). 

The three chemical reactions in the toluene—benzoic acid process are oxidation of toluene to form benzoic acid, oxidation of benzoic acid to form phenyl benzoate, and hydrolysis of phenyl benzoate to form phenol. A typical process consists of two continuous steps (13,14). In the first step, the oxidation of toluene to benzoic acid is achieved with air and cobalt salt catalyst at a temperature between 121 and 177°C. The reactor is operated at 206 kPa gauge (2.1 kg/cm g uge) and the catalyst concentration is between 0.1 and 0.3%. The reactor effluent is distilled and the purified benzoic acid is collected. The overall yield of this process is beheved to be about 68 mol % of toluene. 

The effects of manganese on the cobalt/bromide-catalyzed autoxidation of alkylaromatics are summarized in Figure 17. The use of the Mn/Co/Br system allows for higher reaction temperatures and lower catalyst concentrations than the bromide-free processes. The only disavantage is the corrosive nature of the bromide-containing system which necessitates the use of titanium-lined reactors. 

It should be noted that these results with the cobalt carbonyl phosphine catalysts may not apply over a wide range of conditions. At milder conditions of lower temperature and low catalyst concentration, the conversion of Co2(CO)8 to HCo(CO)3PR3 is only partially completed, even with up to 5/1 ratios of P/Co (22). 

For cobalt as catalyst, variations in reaction parameters have been studied as a means of controlling the product composition (or isomer ratio). Thus, variations in isomer ratio from 1 1 to about 4 1 were observed under widely differing conditions of temperature, catalyst concentration, partial pressure of hydrogen, and partial pressure of carbon monoxide. 

Conflicting results have been reported for the effects of catalyst concentration in the cobalt-catalyzed reaction. In early work, Hughes and Kirshenbaum (31) reported that these parameters were very influential in determining product composition high temperatures and high catalyst concentrations resulted in products containing decreased amounts of the... 

In the case of cobalt ions, the inverse reaction of Co111 reduction with hydroperoxide occurs also rather rapidly (see Table 10.3). The efficiency of redox catalysis is especially pronounced if we compare the rates of thermal homolysis of hydroperoxide with the rates of its decomposition in the presence of ions, for example, cobalt decomposes 1,1-dimethylethyl hydroperoxide in a chlorobenzene solution with the rate constant kd = 3.6 x 1012exp(—138.0/ RT) = 9.0 x 10—13 s—1 (293 K). The catalytic decay of hydroperoxide with the concentration [Co2+] = 10 4M occurs with the effective rate constant Vff=VA[Co2+] = 2.2 x 10 6 s— thus, the specific decomposition rates differ by six orders of magnitude, and this difference can be increased by increasing the catalyst concentration. The kinetic difference between the homolysis of the O—O bond and redox decomposition of ROOH is reasoned by the... 

Das et al.w recorded an increase in the CO conversion when 10% water was added to a bulk cobalt catalyst during FTS in a slurry CSTR. The positive influence lasted for three days, proving that the effect was not of a transitory nature. After termination of water addition, the CO conversion was about the same as before water addition. Adding 20% water caused the conversion to decline slightly, and as discussed above, also led to deactivation. The authors concluded that the addition of small amounts of water is beneficial for the CO conversion. However, there is a level where a further increase in the water concentration ceases to cause an increase in the CO conversion. 

A method for observing intermediates directly in the reaction cycle is in situ IR spectroscopy under reaction conditions. As early as 1975, Penninger published a contribution concerning in situ IR spectroscopic studies of cobalt carbonyl modified by tri-u-butylphosphine as a hydroformylation catalyst [58] at relatively low catalyst concentrations of 2 mmoll-1. The observed carbonyl... 

In the United States, benzoic acid is produced commercially by the liquid-phase oxidation of toluene [7,8]. A variety of cobalt catalysts (in the concentration range of 30-1000 ppm) are used for this purpose. 

Investigations of cobalt stability as a function of catalyst concentration, temperature, and CO partial pressure have been carried out in connection with cobalt-catalyzed hydroformylation (5658). The stability of Co2(CO)g in heptane is shown by Fig. 4, which relates to the equilibrium... 

Experiment 1. Effect of Carbon Catalyst on Oxidation of Cobalt(ll) to Cobalt (III) and Formation of Ethylenediamine and Effect of Cobalt on Formation of Ethylenediamine. Carbon dioxide-free air was bubbled through the reaction mixture. Nine determinations each of the amounts of ammonia volatilized, the ethylenediamine concentration, and the cobalt (II) concentration were made over a period of 18 hours. The results are shown in Figure 1. 

The use of water-soluble catalysts in this reaction has hardly been investigated. Ruthenium/edta (78) and cobalt/tppts (79) catalysts have been described. The use of palladium/tppms catalyst was also reported (80). When edta and tppms are used as ligands, leaching of the metal by the product stream takes place. In the case of the cobalt/tppts catalyst, a high CO partial pressure and a catalyst concentration of >8 mol% are necessary. The reason for this effect is not clear. 

Despite some differences, the mechanism of rhodium-catalyzed hydroformylation is very similar to that of the cobalt-catalyzed process.39-42 Scheme 7.1 depicts the so-called associative route which is operative when the ligand is in excess. Rhodium metal and many Rh(I) compounds serve as precursor to form21,22—in the presence of triphenylphosphine, CO and H2—the active species [RhH(CO)(PPh3)3] (5). At high CO partial pressure and low catalyst concentration without added PPh3, the [RhH(CO)2(PPh3)] monotriphenylphosphine complex instead of 6 coordinates the alkene and participates in the so-called dissociative route.21,39... 

Mechanism A is a generalised mechanism which was proposed for those metals where the frans-but-2-ene cis-but-2-ene ratio was around unity. This mechanism contains a variety of reversible steps which permit the conformational interconversion of the diadsorbed buta-1 3-diene. Consequently, the trans cis ratio will depend upon the relative rates of these reversible steps and the ratio may be much lower than would be expected if the relative surface concentrations of anti- and syn-diadsorbed buta-1 3-diene, species I and III, respectively, in Fig. 37, were similar to the relative amounts of anti- and syn-buta-1 3-diene in the gas phase. It was also suggested that the relative importance of the various steps in mechanism A may be different for different metals. Thus, for example, the type A behaviour of nickel and cobalt catalysts, as deduced from the butene distributions and a detailed examination of the butene AAprofiles [166], was... 

Catalyst-Inhibitor Conversion. The system 2,6,10,14-tetramethyl-pentadecane-bis(N-butylsalicylaldimino)cobalt(II) at 50°C. illustrates well the observed catalyst-inhibitor conversion (Figure 2). At low concentrations up to M/20,000 the metal chelate is a conventional catalyst no induction period is observed, and the reproducible initial autoxidation rates are proportional to the square root of catalyst concentration. From the curves shown in Figure 2 catalyst deactivation becomes apparent at... 

With cobalt as catalyst the plot of log [peracetic acid] vs. time was linear for each cobalt acetate concentration. The first-order rate constants obtained at different cobalt concentrations (k2 ) were plotted as a function of total cobalt (Cot) concentration, and the plot indicates a first-order dependence on total cobalt as shown in Figure 3. The experimental rate law for the cobalt-catalyzed decomposition is thus ... 

In the presence of manganese and cobalt acetates the reaction becomes very fast, and the intermediate AMP cannot be detected. The kinetics of these reactions were studied in a flow reactor, and the results gave a good second-order fit (first order in peracetic acid and first order in acetaldehyde) at different catalyst concentrations. The plot of [acetaldehyde] vs. [peracetic acid] was linear with a slope of 1, indicating that equimolar quantities of the two substances are reacting. A plot of the experimental second-order rate constants (k Co) as a function of catalyst concentration gave a very good first-order fit for cobalt acetate... 

Although the graft copolymer was obtained readily by the reaction of cw-1,4-polybutadiene with PVC in the presence of EtoAlCl alone, the addition of 0.001-0.1 mole of a cobalt compound per mole of the Et2AlCl yielded a gel-free product with superior properties. The preferred cobalt compound concentration was between 0.002 and 0.01 mole per mole of aluminum compound. The effective cobalt compounds were those generally used in polymerizing butadiene to cw-1,4-polybutadiene using the Et2AlCl-cobalt compound catalyst system. 

It has been observed that rapid isomerization accompanies the cobalt carbonyl-catalyzed hydrosilation of olefins (18). The reaction of equimolar amounts of a trisubstituted silane and dicobalt octacarbonyl has been shown to result in the formation of cobalt hydrocarbonyl (cf. Section IV). A very effective isomerization catalyst may be prepared by treatment of a solution of Co2(CO)8 in olefin ( 0.01 M) with a silicon hydride in sufficient quantity to slightly exceed the cobalt carbonyl concentration. 

---