Contaminated solvent recycling

Our results suggest that due care should be taken when applying supercritical C02 as solvent in hydrogenation reactions. Platinum metals catalyze the reduction of C02 to CO (reverse water gas shift reaction) even at ambient temperature, and CO can poison the catalyst (e.g. in carbonyl reductions) and contaminate the recycled C02. 

Still several problems remain unsolved to make the DSHP-HPPO process economically viable (i) safety the reaction of H2 with O2 in the presence of a flammable solvent (methanol) puts high hurdles on safety (ii) removal of acid and bromide the Bronsted acid and the bromide needed to produce HP from the elements have to be removed before the generated H P solution can be used for epoxidation (iii) solvent recycle after the generated H P solution has been used for epoxidation, the methanol has to be separated and recycled. During work-up some additional by-products are formed formaldehyde, acetaldehyde, propionaldehyde, methyl formate, dimethoxymethane, 1,1-dimethoxyethane and 1,1-dimethoxypro-pane. These compounds are difflcult to separate (many make azeotropes with methanol), so the recovered methanol will be contaminated. However, even small amounts of aldehydes or formates can poison the Pd or Pd/Au catalyst. Additional equipment needed to solve these problems will increase the investment costs. 

Two compounds are currently of particular interest in paper and board. Diisopropyl naphthalene (DIPN) is a mixture of isomers that until recently were widely used in carbonless copy papers as ink solvents. Although it is currently being replaced it occurs as a persistent contaminant in recycled paper and board. Various studies have shown that it is able to migrate from paperboard into food. There is a draft CEN analytical method available. This method involves acetone extraction and quantification by GC-MS using diethyl naphthalene as an internal standard. There is currently no limit for DIPN but levels are being monitored to reduce concentrations in recycled paperboard. 

Any unused or uncontaminated solvent can be sent to a licensed reclaimer or to an approved incinerator. Any contaminated solvent may have to be analyzed by a method recommended by the solvent manufacturer prior to recycling in a licensed facility. The solvent producer should be able to answer any questions on recycling or disposal practices. Any disposal process must follow all local, state, and federal regulations... 

It should be noted that recycling comes with its own set of environmental concerns. One of the greatest of these is contamination of recycled materials with toxic substances. In some cases, motor oil, especially that collected from the individual consumer sector, can be contaminated with organohalide solvents and other troublesome impurities. Food containers pick up an array of contaminants and, as a... 

Low molecular cationic polymers or alum can also be used to flocculate pitch, ie, bind up the pitch so that it is retained in the sheet, to minimize pitch deposition on machine surfaces and fabrics (35,36). Alum is used commonly in newsprint operations (34). The addition of a nonionic surfactant with a hydrocarbon solvent to the wet end has shown some utility in preventing deposits of adhesive recycled furnish contaminants from forming on the paper... 

Effects of Impurities nd Solvent. The presence of impurities usually decreases the growth rates of crystalline materials, and problems associated with the production of crystals smaller than desired are commonly attributed to contamination of feed solutions. Strict protocols should be followed in operating units upstream from a crystallizer to minimize the possibiUty of such occurrences. Equally important is monitoring the composition of recycle streams so as to detect possible accumulation of impurities. Furthermore, crystalliza tion kinetics used in scaleup should be obtained from experiments on solutions as similar as possible to those expected in the full-scale process. 

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