Solvent-based recovery methods

Fig. 1. General overview of a PHA production process. All PHA production processes consist of a fermentation and a recovery step, followed by polymer processing for specific applications. In many cases the fermentation is divided into two stages, a biomass production and a PHA accumulation stage (for further detail see text). Several methods for recovery of the material have been described, of which solvent-based and non-solvent-based recovery protocols are illustrated...

Sample Cleanup. The recoveries from a quick cleanup method for waste solvents based on sample filtration through a Elorisd and sodium sulfate column are given in Table 2 (40). This method offers an alternative for analysts who need to confirm the presence or absence of pesticides or PCBs. 

Many of the charcoal tube methods are based on NIOSH Method P CAM 127 (4) for organic solvents. In this method, a known volume of air is drawn through a charcoal tube to trap organic vapors, the charcoal is transferred to a vial, and the sample is desorbed with carbon disulfide. The sample is analyzed by gas chromatography (GC) with flame ionization detection (FID). Most methods use CS2 as the desorption solvent because it yields good recoveries from charcoal and produces a very low flame response. 

A method for determining CDDs in municipal incinerator fly ash has been reported (Alexandrou and Pawliszyn 1990). The method uses supercritical fluid extraction (SFE) to recover CDDs from fly ash samples prior to GC. Supercritical fluid extraction is faster and less expensive than the typically used Soxhlet extraction and gives quantitative removal of CDDs and CDFs from fly ash. Extracts obtained using SFE will still require additional clean-up steps prior to analysis. Supercritical C02 has also been used to assist solvent-based extraction of CDDs from soils (Friedrich and Kleibohmer 1997). In this case, the supercritical fluid was combined with accelerated solvent extraction (liquid extractions conducted under elevated temperature and pressure) to provide good recoveries relative to Soxhlet extractions. 

The resulting filter cakes contain around 40-60% of polyether polyol. In order to improve the yield of the polyether, in some technologies the polyether is extracted with a solvent and, after the distillation of the solvent, 90-95% of the polyether retained in the filter cake is recovered. Low price solvents are used, such as n-hcxanc, hexane fractions, toluene, etc. A recovery method for polyether retained in the filter cakes, based on the extraction with PO in a closed system, was developed [57]. 

By the end of the decade, most printers using solvent-based inks will have installed engineering controls to abate their solvent emissions. Of the various abatement methods available, thermal oxidation and solvent recovery using carbon adsorption have found widespread use. 

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. 

To satisfy the Resource Conservation and Recovery Act (1977) and its amendment for hazardous and solid waste (1984), the 80(K) Series Methods have been designed to analyze solid waste, soUs, and groundwater. In particular, methods 8240/8260 require the use of a purge-and-trap device in conjunction with packed or capillary GC/MS, respectively, for the analysis of purgeable organic compounds. Methods 8250/8270 concern analyses for the less-volatile bases, neutrals, and acids by GC/MS after extraction from the matrix by an organic solvent. 

The stopping solution composition was based on experiments showing that lowering the pH from 9 to 5 to 1 reduced formation of cis-DMNM, perhaps because this prevented elution of the amine from the column, and that addition of ammonium sulfamate lowered cis-DMNM formation, relative to the situation where ascorbate alone was used as a nitrite trap. The hexane wash of the column was introduced to remove a large peak near the solvent front in the GC-TEA, perhaps due to neutral fats. Using the described procedure, the recovery of 70-160 ng NMOR added to 2 g semisynthetic diet was 92 + 19% (mean + S.D. for 13 measurements). The recovery of 227 ng NMOR from 5-8 g whole mouse homogenate using the Iqbal method was 101 + 57% for 7 measurements. 

---