Halogenated solvent recovery

The following spent non-halogenated solvents xylene, acetone, ethyl ace- (I) tate, ethyl benzene, ethyl ether, methyl isobutyl ketone, n-butyl alccAol, cyclohexanone, and methanol and the still bottoms from the recovery of these solvents. 

F002 - The following spent halogenated solvents tetrachloroethylene, methylene chloride, trichloroethylene, 1,1,1-trichloromethane, chlorobenzene, l,l,2-trichloro-l,2,2-trifluoroethane, ortho-dichlorobenzene, and trichlorofluoromethane orthodichlorobenzene and trichlorofluoromethane all spent solvent mixtures/blends containing, before use, a total of 10% or more (by volume) of one or more of the above halogenated solvents or those solvents listed in FOOl, F004, F005, and stiU bottoms from the recovery of these spent solvents and spent solvent mixtures. 

Non-halogenated solvent extraction (antisolvent method) Haloferax mediterranei Acetone Purity 98.4% recovery 91.4% [3]... 

Non-halogenated solvent extraction Comamonas sp. EB172 recombinant Cupriavidus necator NaOH and water Purity 96.6% recovery 96.9% [32]... 

Non-halogenated solvent extraction Recombinant Cupriavidus necator Water and ethanol Purity 81% recovery 95% [33]... 

Non-halogenated solvent extraction Ralstonia eutropha Methyl isobutyl ketone, methyl ethyl ketone, butyl acetate and ethyl acetate Purity 99% recovery 84% for methyl isobutyl ketone [34]... 

Non-halogenated solvent extraction Mixed microbial cultures DMC or combination with NaClO Recovery 82% 137]... 

Lopez-Abelairas and co-workers [30] proposed and compared a few recovery methods, namely sulfuric acid with bleaching steps, and NaClO, NaOH and NaOH with a halogenated solvent (one acid treatment and three alkaline treatments). It was found that the PHA extracted from the acid treatment exhibited the highest purity (98%) and lowest polymer degradation. In addition, this extraction method gave the lowest recovery cost it was therefore concluded to be the best choice for PHA recovery in this study. 

Figures 21.2 and 21.3 explain the plasticizer recovery system from scrap cable. Cable coating contains 20-25 wt% plasticizer (frequently DOP). Halogenated solvent is selected because it is non-flatrmiable but also because it dissolves DOR Figure 21.3 shows that the plasticizer is recovered by evaporation of the solvent. This may give mixture of plasticizer(s) with other additives (e.g., stabilizers).

This approach requires a bit more method development, but it is clearly well worth the effort when the same method needs to be used for thousands or hundreds of thousands of samples. Method development starts with purchasing 6—12 halogenated solvent analogs and empirically measuring (screening) extraction recoveries. Once a high-recovery solvent is found, execution of the cleanup is simple add solvent and mix by pipette, then centrifuge. 

Currently, most PHA extraction processes are based on halogenated solvent extraction which is costly and may cause environmental problems and toxicity to humans. Thus, it seems that a practical commercial extraction system with a clean, simple and efficient process for PHA recovery at a reasonable cost focusing on a non-halogenated solvent extraction-based recovery needs to be developed. However, halogen-free methods require further adjustment, depending on both significant process parameters and external factors influencing their performance, to make the process suitable for polymer recovery on an industrial scale. 

At ambient temperature and pressure, hexafluoroacetone is a (toxic) gas, and catalyst recovery is impractical. As a nonvolatile alternative, Sheldon et cd. employed perfluoroheptadecan-9-one. After completion of the epoxidation, this catalyst can be recovered from halogenated solvents such as dichloroethane or TFE by simple cooling of the reaction mixture [39]. Furthermore, this long-chain perfluorinated ketone has the potential for immobilization in fluorous phases. When appHed to epoxidation with perfluoroheptadecan-9-one as catalyst, TFE gave yields of epoxide comparable to those obtained in dichloroethane. However, to achieve good yields of add-sensitive epoxides, buffering by Na2HP04 was necessary. 

FOOl— The spent halogenated solvents used in degreasing tetrachloroethylene, trichloroethylene, methylene chloride, 1,1,1-trichloroethane, carbon tetrachloride, and the chlorinated fluorocarbons and sludges from the recovery of these solvents in degreasing operations... 

This technology has been used to treat polychlorinated biphenyls (PCBs), halogenated and nonhalogenated solvents, semivolatile organic compounds (SVOCs), polynuclear aromatic hydrocarbons (PAHs), pesticides, herbicides, fuel oils, benzene, toluene, ethylbenzene, and xylenes (BTEX), and mercury. This system has also treated Resource Conservation and Recovery Act (RCRA) hazardous wastes such as petroleum refinery wastes and multisource leachate treatment residues to meet RCRA Land Disposal Restrictions (LDR) treatment standards. 

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