Methylene chloride recovery

The solvent used to form the dope is evaporated during the extrusion process and must be recovered. This is usually done by adsorption on activated carbon or condensation by refrigeration. For final purification, the solvent is distilled. Approximately 3 kg of acetone, over 99%, is recovered per kg of acetate yam produced. Recovery of solvent from triacetate extmsion is similar, but ca 4 kg of methylene chloride solvent is needed per kg of triacetate yam extmded. 

Environmental Impact. The volume of waste remover from these products is remarkably increased when compared to methylene chloride, petroleum, and oxygenate removers, since both /V-methy1pyrro1idinone and dibasic esters have low vapor pressures. Recovery of the remover after use is difficult because the finish is tesolubili2ed by the remover. A representative dibasic ester formula appears below for a thickened water rinse finish remover. 

Trichloroethylene use has declined as a result of environmental concerns. However, trichloroethylene may replace some 1,1,1-trichloroethane appHcations. Perchloroethylene used in small businesses for dry cleaning will be regulated for emissions under the same guidelines as those that govern the large chemical producers. This will cause replacement of perchloroethylene for those appHcations where recovery is uneconomical. Methylene chloride has been classified as a suspected carcinogen and its use will decline in aerosol and paint stripping appHcations because of health concerns. 

The checkers carried out this recrystallization by dissolving triphenylene in a minimum of methylene chloride maintained at reflux. Pentane was slowly added to this solution up to 90% recovery was achieved. 

Benzothiadiazole 1,1-dioxide can be conveniently assayed and characterized without isolation by forming its adduct with cyclopentadiene.5 The following procedure illustrates characterization, for assay the same procedure can be applied to an aliquot, with all amounts scaled down in proportion. The dried ether extract of 1,2,3-benzothiadiazole 1,1-dioxide prepared from 1.43 g (0.0080 mole) of sodium 2-aminobenzene-sulfinate is concentrated to about 20 ml at 0°, and 20 ml. of acetonitrile at —20° is added. Twenty milliliters of cold, freshly prepared cyclopentadiene6 is added The mixture is kept overnight at —10° to 0°. Solvent and excess cyclopentadiene are removed by evaporation at 0° under reduced pressure to leave 1.20-1.28 g. (64-68% based on sodium 2-aminobenzenesulfinate) of crude 1-1 adduct, mp. 87° (dec.). For purification it is dissolved in 20 ml. of methylene chloride, 70 ml. of ether is added, and the solution is kept at —70°. Adduct decomposing at 90° crystallizes recovery is about 75%. From pure, crystalline 1, 2, 3-benzothiadiazole 1,1-dioxide the yield of adduct is 92-98%. 

The recovery of the product is described in outline in Figure 95. Essentially the process involves separating the broth and mycelium by filtration, extracting the mycelium with acetone and methylene chloride. Combining these extracts with the broth and re-extracting with methylene chloride. The extract is washed with 2% sodium bicarbonate, evaporated and re-dissolved in methylene chloride. The product is allowed to crystallise from the methylene chloride. 

Water samples are acidified and extracted with solvent (Kawamura and Kaplan 1983 Muir et al. 1981). Clean-up steps may be used (Kawamura and Kaplan 1983). Methylene chloride is often used as the extracting solvent, and it may interfere with the nitrogen-phosphorus detector. In this case, a solvent-exchange step is used (Muir et al. 1981). Analysis by GC/NPD or GC/MS provides specificity (Kawamura and Kaplan 1983 Muir et al. 1981). Accuracy is acceptable (>80%), but precision has not been reported. Detection limits were not reported, but are estimated to be 0.05-0.1 pg/L (Muir et al. 1981). Detection limits at the low ppt level (ng/L) were achieved by concentrating organophosphate esters on XAD-2 resin. The analytes were solvent extracted from the resin and analyzed by GC/NPD and GC/MS. Recovery was acceptable (>70%) and precision was good (<10% RSD) (LeBel et al. 1981). 

A method for sediment involves Soxhlet extraction followed by filtration, and concentration to 5 mL. The residue is diluted with water, acidified, extracted with methylene chloride, and then the extracts are dried and evaporated to dryness. The residue is cleaned up on an alumina column. Analysis is performed by GC/NPD. Good recovery (81-97%) and precision (>15% RSD) were reported detection limits were not reported (Muir et al. 1981). 

In contrast, the Biotechnologische Forschungsgesellschaft has used a solvent-based process for the recovery of poly(3HB) from A. latus. The cells were harvested by centrifugation and the poly(3HB) was subsequently extracted from the suspended cells with methylene chloride and precipitated from the solvent by the addition of water. After drying a polyester with 99% purity was obtained [15]. The process also included the recovery of the solvent. 

Gustavson et al. (2000) developed a convenient and novel solid phase extraction (SPE) method for the removal of methyl oleate from SPMD dialysates containing PAHs. A small SPE column (1 g or 0.5 g) containing a dual-zone silica (normal phase)-based restricted-access sorbent (Diazem, Midland, MI, USA) is used for the separation. The capacity of this sorbent to remove methyl oleate is about 1.8% (lipid/sorbent wt wt ). The PAHs are eluted with 19 mL of hexane and methylene chloride (97 3 VV ) and recoveries of all PAHs are typically >72%. 

As shown in Tab. 11.5, multi-component catalyst (27) matches the activity of its corresponding monomer (4), promoting efficient RCM of (19) in just 15 minutes at 40 °C. The reaction mixture was passed through a short column in methylene chloride to isolate the desired product. Subsequent washing of the silica with diethyl ether led to quantitative recovery of the dendritic catalyst. 400 MHz NMR analysis revealed that 13% of the styrene ligands on the dendrimer were va-... 

High-performance liquid chromatography (HPLC), followed by GC/MS, has been used to fractionate and then quantitate the aliphatic and aromatic hydrocarbons present in liquid fuel precursors in order to determine the fuel potential of the compounds. Kerosene had the advantage of not requiring any sample preparation. Other light fuel oils may require the use of methylene chloride as a solvent prior to HPLC analysis (Lamey et al. 1991). The sensitivity, precision, and recovery of this method were not reported. 

Figure 2. HPLC chromatograms obtained for sulfathiazole standard compared with a honey control and honey fortified at 1.0 ppm (80% recovery). Mobile phase 95% methylene chloride-5% methanol flow rate 1.5 ml/min 0.2 Pg of sulfathiazole injected as standard extract injected equivalent to 40 mg of honey.

A method for the determination of diazinon in human serum has recently been published by researchers at the Centers for Disease Control and Prevention (Liu et al. 1994) in which 2-dimensional chromatography was used to determine 15 pesticides in 4 minutes. Supercritical fluid extraction (SFE) was used to recover pesticides into methylene chloride and this extract was analyzed using two 2-meter columns connected by an on-column thermal desorption modulator. Sensitivity for diazinon was reported to be 1.8 pg on-column no details about overall recoveries were provided. 

Methods found for the determination of diazinon in animal products also used homogenization with a polar organic solvent as the first step in residue recovery. Toyoda et al. (1990) isolated diazinon from milk via partition into methylene chloride after extraction of the milk with 70% acetonitrile in water. Based on GC/FPD, an LOD of 10 ppb and a recovery of 89% (3.8% relative standard deviation) at 100 ppb were reported. Diazinon residues in eggs were studied (Leoni et al. 1992) after blending the eggs with acetone and partitioning into dichloromethane and acetone followed by C18-silica SPE. Based on GC/FPD analysis, an LOD of 1 ppb and a recovery of 93% at 13 ppb were reported. 

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