Recovered solvent value

The extract is vacuum-distilled ia the solvent recovery column, which is operated at low bottom temperatures to minimise the formation of polymer and dimer and is designed to provide acryUc acid-free overheads for recycle as the extraction solvent. A small aqueous phase in the overheads is mixed with the raffinate from the extraction step. This aqueous material is stripped before disposal both to recover extraction solvent values and minimise waste organic disposal loads. 

The cobalt catalyst can be introduced into the reactor in any convenient form, such as the hydrocarbon-soluble cobalt naphthenate [61789-51 -3] as it is converted in the reaction to dicobalt octacarbonyl [15226-74-17, Co2(CO)g, the precursor to cobalt hydrocarbonyl [16842-03-8] HCo(CO)4, the active catalyst species. Some of the methods used to recover cobalt values for reuse are (11) conversion to an inorganic salt soluble ia water conversion to an organic salt soluble ia water or an organic solvent treatment with aqueous acid or alkah to recover part or all of the HCo(CO)4 ia the aqueous phase and conversion to metallic cobalt by thermal or chemical means. 

The crystalline fractions are now systematically recrystallized from methanol. The head crop is recrystallized from about 600 cc. of this solvent, and the remaining crops are crystallized in order from the successive mother liquors. At each stage the volume of the solution is adjusted by addition or distillation of solvent so that from one-third to one-half of the salt crystallizes. A series of large Erlenmeyer flasks, fitted with a reflux condenser or distilling head as required, is convenient for the purpose. The recrystallization is continued, using fresh or recovered solvent, until the head fraction has [a]i> — 2.8° or less (c = 4, methanol). It is unnecessary to take rotation values until the crystalline appearance and solubility behavior of the head fraction become approximately constant. Usually five to seven recrystallizations are necessary for purification. When pure, the head fraction is removed from the series and the recrystallization of the remaining crops is continued as long as it appears profitable. The final mother liquor from each series is reserved. 

These inks contain high concentrations of low-boiling solvents, and the usual practice is to dilute them further in the press room. The large volume of solvents emitted makes incineration impractical, but these solvents may be absorbed on activated charcoal, and removed l steam distillation when the charcoal is saturated. The recovered solvents may be re-used or sold however, it may be impractical to fractionate some recovered solvent blend that boil in the same temperature range, which lessens their value considerably. Therefore, although this approach is also technically and economically feasible, the difficulty in procuring the solvents used for dilution may restrict the continued use of these solvent-based inks and, hence, the adoption of solvent recovery approach. 

One can expect to achieve, in selling recovered solvent, 70-80% of the virgin solvent price. The cost of recovery, not including transport, will typically lie in the range 150-300/Te so that the cheaper solvents will have a negative value loaded on transport at the solvent user s works. 

A continuous process in which the contaminated water flowing to the air stripper may contain 1000 ppm of dissolved solvent still needs a solvent of y P > 250 000 to begin to make solvent recovery from stripping air a profitable recovery proposition. It may, of course, be necessary for achieving regulatory approval whatever the value of the recovered solvent. 

Organic solvents that are soluble in water can have large values when stripped out, but because of subsequent purification costs and the large range of possible concentrations in the waste water, no helpful indication of the possible economics can be made. It will be clear when considering the costs of stripping that it is possible for the value of the recovered solvent to pay for the removal of pollution from the effluent. 

The use of disposable powdered AC to remove involatile solvents (and other high-boding organic contaminants) from the air-stripped water is likely to raise the water to reusable quality but yields no further recovered solvent. In addition, cost is incurred for disposal of spent carbon. Costs will be affected by the value of pollutant removed by the AC but a further outlay of US 0.4—0.5/m would be realistic. Thus the cost for a combination of air stripping, liquid-phase polishing with AC and recapture of... 

If techniques are used which allow reuse of recovered solvent, the emission limit value in waste gases shall be 150... 

Rubber conversion (>15) 20(1) 25< 25% of solvent input techniques are used which allow reuse of recovered solvent, the emission limit value in waste gases shall be 150. The fugitive emission value does not include solvent sold as part of products or preparations in a sealed container... 

The basic principles of some generally accepted gas cleaning processes for solvent removal are given in Table 22.1.2. For more than 70 years adsorption processes using activated carbon, in addition to absorption and condensation processes, have been used in adsorptive removal and recovery of solvents. The first solvent recovery plant for acetone was commissioned for economic reason in 1917 by Bayer. In the decades that followed solvent recovery plants were built and operated only if the value of the recovered solvents exceeded the operation costs and depreciation of the plant. Today sueh plants are used for adsorptive purification of exhaust air streams, even if the return is insufficient, to meet environmental and legal requirements. 

Solvent values from these two streams are easily recovered. First, only a single purge stream may be necessary. Second, water can be removed as a contaminant by passing the cooled stream through a bed of desiccant such as mol sieves (molecular sieves. Footnote 93). Third, dried solvent materials may be returned to tbe tank from which the binary azeotrope is formulated. 

And there is a final category — the positive value of the recovered solvent. This category is one of the two... 

Wet solvent Is also produced within this process by regeneration of the adsorbent bed with steam. A financial credit is given for the value of the recovered solvent because it can be reused for cleaning operations. But since no financial charge was made for the solvent when It was a pollutant in the emitted air, the credit for value of the recovered solvent is a windfall. 

The value of recovered solvent is negligible relative to the cost of producing it (except for CFC-113 ). 

Recovery is shown in the images of Figures 4.47 to 4.60 as a positive number because it is more easily seen in these plots. Recognize that the monetary value of recovered solvent is negligible from an overall standpoint (except for CFC-113 because of its unusual purchase price). 

Since two insoluble phases must form for an extraction operation, point Af, must lie within the heterogeneous liquid area, as shown. The mininimn amount of solvent is thus found by locating Af, at D, which would then provide an infinitesimal amount of extract at G, and the maximum amount of solvent is found by locating Af, at AT, which provides an infinitesimal amount of raffinate at L. Point L also represents the r finate with the lowest possible C concentration, and if a lower value were required, the recovered solvent S would have to have a lower C concentration. 

At the Ford Motor Company s spark plug plant in Fostoria, Ohio, trichloroethylene vapor in the air from degreaser units is recovered by adsorption on activated carbon. Two 72-in.-diameter adsorbers are used, each containing 1,300 lb of carbon pellets. The system is reported to be capable of recovering 400 to 450 gal. of liquid trichloroethylene per day with a collection efficiency of over 90%. Operating costs were only about 3% of the value of the recovered solvent (Anon.. 1969). 

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