Batch reactor fresh catalyst

The condensation of methyl N—phenyl carbamate witli IICHO to methylene diphenyl diurethane has been studied in a batch reactor in the presence of cation exchanged resins. Unlike conventional H0SO4 catalyst, fresh resin catalysts did not form a byproduct N—benzyl compound. However, accumulation of water from repeated uses of the catalyst caused a decreased activity and the formation of the byproduct. The deactivated catalyst could be completely regenerated by drying in vacuo. Ethylacetate and toluene were found to be efficient solvents with the resin catalysts. 

The major advantage of the use of CuHY as a catalyst for this reaction is the ease with which it can be recovered from the reaction mixture by simple filtration if used in. a batch reactor (alternatively it can be used in a continuous flow fixed bed reactor). We have carried out the heterogeneous asymmetric aziridination of styrene until completion, filtered and washed the zeolite then added fresh styrene, PhI=NTs and solvent, without further addition of chiral bis(oxazoline), for several consecutive experiments. The yield and the enantioselectivity decline slightly on reuse we have found that adsorbed water can build up within the pores of the zeolite on continued use and we believe that this is the cause of loss of activity and enantioselection. However, full enantioselectivity and yield can be recovered if the catalyst is simply dried in air prior to reuse, or alternatively the catalyst can be recalcined and fresh oxazoline ligand added. 

In a pilot campaign, altogether 17,392 kg of 3 were produced in 182 batches, each run in a 630 L hydrogenation reactor. The average yield was 92.2%, the average content was 99.0%, with <0.5% of the isomer 4. In all 1% yield was lost in 19 of the total 182 batches due to incomplete conversion. This was almost certainly caused by incursion of oxygen, probably in the H2 or N2 lines. All attempts to revitalize a reaction that had stopped, through addition of fresh catalyst, were unsuccessful. The toluene solvent was successfully recycled after distillation under N2. 

The term moving bed arises from the mode in which the spent catalyst is replaced. The catalyst bed is displaced periodically downward by gravitational forces. The fresh catalyst enters at the top of the reactor, and the deactivated catalyst leaves the reactor through the bottom. Liquid flow can be supplied either cocurrently or countercurrently with respect to the movement of the bed. The rate of deactivation determines how frequently the catalyst is replaced. Commonly, catalyst replacement is a batch operation and is done once or twice a week [68]. 

Contrary to experiments in fixed-bed continuous reactors, deactivation of catalytic reactions performed in batch modes can be hidden, as the observed behavior could be similar to first-order kinetics. Then it is advisable to perform experiments adding a fresh catalyst (Fig. 9.46) or recychng the catalyst (Fig. 9.47). 

There is a definite need, therefore, for systems that combine the advantages of high activity and selectivity of homogeneous catalysts with the facile recovery and recycling characteristic of their heterogeneous counterparts. This can be achieved by employing a different type of heterogeneous system, namely liquid-liquid biphasic catalysis, whereby the catalyst is dissolved in one liquid phase and the reactants and product(s) are in a second liquid phase. The catalyst is recovered and recycled by simple phase separation. Preferably, the catalyst solution remains in the reactor and is reused with a fresh batch of reactants without further treatment or, ideally, it is adapted to continuous operation. 

Oxidation reaction experiments were performed in a 300 mL stainless-steel high pressure reactor vessel (Parr Instraments Co., USA, 5521) operated under isothermal batch mode at 413 K, 2 MPa of oxygen pressure and stirred at 500 rpm to optimize the mass transfer in the liquid phase. For every run a fresh feed of aqueous phenol solution of 20 mmol L and 4 g L of the catalyst was introduced to the reaction vessel. The liquid phase was analyzed by HPLC on a Pursuit XRs 5 C18 150 while the gas phase was analyzed in a GC equipped with a Porapak Q packed column. 

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