Liquids Recycling for Reuse

To recycle the palladium catalyst used for the Mizoroki-Heckreaction, a reaction using Pd/C as a heterogeneous catalyst was performed in [bmimJIPFe]. Ethyl cin-namate 86 was extracted simply from the ionic liquid using diethyl ether or hexane (Scheme 32). After the reaction, the Pd/C remained suspended in the ionic liquid, suitable for reuse. Since the EtsN+n formed in the course of the Mizoroki-Heck reaction accumulates in the [bmimJfPFe], slightly lower yields were obtained for successive runs. However, washing the ionic liquid with water removed any iodide salt present. 

The liquid waste processing system is provided for use in the processing and handling of radioactive wastes generated during various modes of plant operation. The system is designed to receive, segregate, process, monitor, and recycle for reuse all primary... 

The author likes to thank the many researchers who responded to his request about their experience with ionic liquids recycling and reuse. Very deep thanks shoidd go to Dr. G. W. Meindersma (Eindhoven University of Technology, The Netherland) for the invaluable... 

Two separate 2.1 L reservoirs contain the catalyst and product phases and the contents are fed into the reactor through a standard liquid mass flow controller. The contents of the reactor can be sampled from a pressure fed sample tube. The pressurized liquid reactor products exit the reactor through a pressure control valve, which reduces the pressure to atmospheric, and the liquid contents are delivered to a continuous decanter where the phases separate. The catalyst phase then settles to the bottom where it is drained for recycle and reuse, while the product phase is collected into a 4.2 L reservoir. 

When viewing effluent treatment methods, it is clear that the basic problem of safely disposing of waste material is, in many cases, not so much solved but moved from one place to another. If a method of treatment can be used that allows material to be recycled or reused in someway, then the waste problem is truly solved. However, if the treatment simply concentrates the waste as concentrated liquid, slurry or solid in a form that cannot be recycled, then it will still need to be disposed of. Landfill disposal of such waste is increasingly unacceptable, and thermal oxidation causes pollution through products of combustion and liquors from scrubbing systems. The best method for dealing with effluent problems is to solve the problem at source by waste minimization. 

Although several noble-metal nanoparticles have been investigated for the enantiomeric catalysis of prochiral substrates, platinum colloids remain the most widely studied. PVP-stabilized platinum modified with cinchonidine showed ee-values >95%. Several stabilizers have been also investigated such as surfactants, cinchonidinium salts and solvents, and promising ee-values have been observed. Details of a comparison of various catalytic systems are listed in Table 9.16 in one case, the colloid suspension was reused without any loss in enantioselectiv-ity. Clearly, the development of convenient two-phase liquid-liquid systems for the recycling of chiral colloids remains a future challenge. 

An efficient and convenient methodology for the aerobic oxidation of alcohols catalysed by sol-gel trapped perruthenate and promoted by an encapsulated ionic liquid in supercritical carbon dioxide solution has been reported. The reaction is highly selective and useful for substrates otherwise difficult to oxidize.263 A four-component system consisting of acetamido-TEMPO-Cu(C104)2-TMDP-DABCO has been developed for aerobic alcohol oxidation at room temperature. The catalytic system shows excellent selectivity towards the oxidation of benzylic and allylic alcohols and is not deactivated by heteroatom-containing (S, N) compounds. The use of DMSO as the reaction medium allows the catalysts to be recycled and reused for three runs with no significant loss of catalytic activity.264... 

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