Initiation catalysts

Some fabrication processes, such as continuous panel processes, are mn at elevated temperatures to improve productivity. Dual-catalyst systems are commonly used to initiate a controlled rapid gel and then a fast cure to complete the cross-linking reaction. Cumene hydroperoxide initiated at 50°C with benzyl trimethyl ammonium hydroxide and copper naphthenate in combination with tert-huty octoate are preferred for panel products. Other heat-initiated catalysts, such as lauroyl peroxide and tert-huty perbenzoate, are optional systems. Eor higher temperature mol ding processes such as pultmsion or matched metal die mol ding at temperatures of 150°C, dual-catalyst systems are usually employed based on /-butyl perbenzoate and 2,5-dimethyl-2,5-di-2-ethyIhexanoylperoxy-hexane (Table 6). 

Raw material costs should be estimated by direct computation from flow rates and material prices. The flow rates are deterrnined from flow sheet material balances. The unit prices are obtained from vendors, company purchasing departments, or the Chemical Marketing Reporter. For captive raw materials produced internally, a suitable transfer price must be estabHshed. Initial catalyst charges can be treated as a start-up expense, working capital component, or depreciable capital, depending on the expected catalyst life and cost. Makeup catalyst is frequendy treated as a raw material. 

An ingenious application of Corey s ylide (1) was discovered by the Shea group in 199 7 51,52 ugjj g trialkylboranes as initiator/catalyst and 1 as the monomer, a living... 

Addition of styrene to a green solution of naphthalene" Na+ in tetrahydrofuran leads to an instantaneous change of color from green to red. Styrene polymerizes rapidly and quantitatively within a few seconds, and when the reaction is completed, addition of water converts the red solution of polystyryl carbanions into colorless solution of polystyrene. After precipitation of the polymer it was shown spectroscopically25 that the residual solution contains an amount of naphthalene equal to that used in the preparation of the initiating catalyst. This observation confirms the proposed mechanism of initiation of the polymerization. 

IGT selected Harshaw Ni-0104T nickel-on-kieselghur catalyst formed in 4 X y in. cylindrical pellets for the initial catalyst charge to the methanation section of the HYGAS pilot plant. This selection was based on high activity over a range of temperatures (274°-516°C) and space velocities. Catalyst activity life tests were conducted for 1420 hrs without deterioration (Table I) consequently, we felt that suitable longevity could be obtained in the pilot-plant methanation reactors. 

As shown on Figure 9.1 when the circuit is opened (I = 0) the catalyst potential starts increasing but the reaction rate stays constant. This is different from the behaviour observed with O2 conducting solid electrolytes and is due to the fact that the spillover oxygen anions can react with the fuel (e.g. C2H4, CO), albeit at a slow rate, whereas Na(Pt) can be scavenged from the surface only by electrochemical means.1 Thus, as shown on Fig. 9.1, when the potentiostat is used to impose the initial catalyst potential, U r =-430 mV, then the catalytic rate is restored within 100-150 s to its initial value, since Na(Pt) is now pumped electrochemically as Na+ back into the P"-A1203 lattice. 

The palladium(O) complex undergoes first an oxydative addition of the aryl halide. Then a substitution reaction of the halide anion by the amine occurs at the metal. The resulting amino-complex would lose the imine with simultaneous formation of an hydropalladium. A reductive elimination from this 18-electrons complex would give the aromatic hydrocarbon and regenerate at the same time the initial catalyst. 

Feed ratio hydrogen/CCbFo Figure 1. Initial catalyst performance. 

Six catalysts available from Evonik Degnssa were tested initially (Catalysts A-F in Table 10.1). 

We monitored the percent conversion of epichlorohydrin and enantiomeric excess of the recovered S-epichlorohydrin with time by using GC-FID. Approximately 54% conversion and >99% ee were obtained in about 4 h reaction time. After 4 h, the epichlorohydrin was removed under vacuum at room temperature and diol was removed at a temperature of 329 K. The recovered catalyst was further treated in the HKR of racemic mixture of fresh epichlorohydrin. In the second run, we observed a decrease in the conversion and ee compared to the fresh catalyst. The Co-salen was again recovered after the second run by removing all the products under vacuum and recycled two more times. With each subsequent HKR reaction, the conversion and ee were found to decrease with time (22). Table 43.1 summarizes the initial rates and ee s determined from the four runs without intermediate catalyst regeneration. Interestingly, the initial catalyst activity was resumed when the catalyst was regenerated with acetic acid prior to recycle. 

Initiators Catalysts Co-catalysts Stereo modifiers Mineral oil (catalyst carriers)... 

Polymerization of Styrene Initialed by Zr(benzyl)t Dependence of Molecular Weight (M ) on Initial Catalyst Concentrations at 30°C in Toluene [Ml. = 6M... 

The polymerization of 2-(diethylamino)ethyl methacrylate, DEAEMA, was studied under different conditions. It was shown that the best system providing narrow molecular weight distribution polymers involved the use of p-toluenesulfonyl chloride/CuCl/HMTETA as the initiator/catalyst/ligand at 60 °C in methanol [72]. Taking advantage of these results, well-defined PDEAEMA-fr-PfBuMA block copolymers were obtained. The synthesis was successful when either fBuMA or DEAEMA was polymerized first. Poor results with bimodal distributions were obtained when CuBr was used as the catalyst. This behavior was attributed to the poor blocking efficiency of PDEAEMA-Br and the incomplete functionalization of the macroinitiator. 

As discussed earlier, it is generally observed that reductant oxidation occurs under kinetic control at least over the potential range of interest to electroless deposition. This indicates that the kinetics, or more specifically, the equivalent partial current densities for this reaction, should be the same for any catalytically active feature. On the other hand, it is well established that the O2 electroreduction reaction may proceed under conditions of diffusion control at a few hundred millivolts potential cathodic of the EIX value for this reaction even for relatively smooth electrocatalysts. This is particularly true for the classic Pd initiation catalyst used for electroless deposition, and is probably also likely for freshly-electrolessly-deposited catalysts such as Ni-P, Co-P and Cu. Thus, when O2 reduction becomes diffusion controlled at a large feature, i.e., one whose dimensions exceed the O2 diffusion layer thickness, the transport of O2 occurs under planar diffusion conditions (except for feature edges). 

Fig. 3. Relative activity of Rh catalyst activated by RC1. Initial catalyst composition = h mil (EttRhCl). + lOOmAf RC1.

Figure 2. Hg production as a function of added Rus(CO)lg concentration 5 g NMes, 15 g HgO, solution diluted to 100 mL with THF, 415 psi CO, 100°C, 5 h. The abscissa reflects the Ru carbonyl concentration based on initial catalyst loadings clearly it does not reflect true [Rus(CO)lg].

We take the results of a series of experiments conducted by Morgan (1967, his Fig. 23) at pH 9, 9.3, and 9.5. He used an initial Mn11 concentration of 4.5 x 10-4 molar, a carbonate concentration of 1.6 x 10-3 molar, and an oxygen partial pressure of 1 atm. We can figure an approximate value for the rate constant l<+ from oxidation rate at the end of the experiment, when the mass of catalyst is known from the depletion of Mn11, then estimate the initial catalyst mass from that value and the oxidation rate at the onset of reaction. Running the simulation, we can refine the two numbers until prediction matches observation. 

Here, we take the initial catalyst mass as 2 mg, and set a rate constant of 3 x 1012 molal-4 s-1, which gives good results. As shown in Figure 28.2, the reaction starts slowly, increases in rate as the catalyst accumulates, then decreases to zero as the supply of reduced manganese is depleted. 

In this case, we find we can match the experimental results using a single value for the rate constant, but an initial catalyst mass that depends on pH, as shown in Figure 28.3. Here, we take the rate constant to be 1013 molal-4 s-1, and use initial catalyst masses of 6 mg at pH 9.5, 5 mg at pH 9.3, and 0.6 mg at pH 9. This form of the rate law seems more satisfactory than the previous form, since we might reasonably expect the amount of catalyst, perhaps an MnC03 colloid, initially present to be greatest in the experiments conducted at highest pH, but the rate constant to be invariant. 

Fig. 28.3. Concentration of Mn11 versus time in simulations of the autocatalytic oxidation of manganese at pH 9.0, 9.3, and 9.5, at 25 °C, compared to results of laboratory experiments (symbols) by Morgan (1967). Simulations made assuming rate law of a form carrying mMa++, rather than mMnn. Rate constant in the simulations is taken to be 1013 molal-4 s-1, and the initial catalyst mass is 0.6 mg (pH 9.0), 5 mg (9.3), and 6 mg (9.5).

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