Solvent recovery wastes

WASTE RECOVERY PROCESSES INVOLVING SOLVENT EXTRACTION... 

Packed-column SFC also is suitable for preparative-scale enatioseparations. Compared with preparative LC, sub- or supercritical fluid chromatography results in easier product and solvent recovery, reduced solvent waste and cost, and higher output per unit time. Because of its reduced sample capacity, SFC usually allows the separation of 10-100 mg samples per run. Chromatographers can compensate for these sample amounts by using shorter analysis times and repetitive injections (Wolf and Pirkle, 1997). 

As shown in Figure 3.7, since 1995 there has been a large reduction in the amount of solvent wastes directly released, treated, and used for energy recovery on-site. There have also been moderate reductions in the amount of wastes used for energy recovery and treatment off-site. However, there were increases in every other form of on- and off-site waste treatment. In 2006, about 70% of solvent waste was treated for disposal or recycled. The remaining 30% was either directly released or treated for energy recovery. The fractions of solvent wastes treated and recycled are very close to the values reported earlier by Lee-Jeffs and Constable in 2008 (A. Lee-Jeffs, private communication D.J.C. Constable, private communication). This shows an increasing trend in the amount of solvents recycled in order to reduce... 

Supercritical fluid extraction (SFE) has been demonstrated as a technique that has eliminated some of the tedious steps of current liquid-liquid and solid-liquid extraction procedures. SFE also offers cleaner extracts, less sample handling and equivalent or better recoveries to conventional technologies. As a technique, it is cost effective, time efficient and low in solvent waste generation. 

H. Reinhardt, Some Problems in Metal Waste Recovery Using Solvent Extraction, Hydrometallurgy 81, FI (1981). 

The hydrophobic nature of the activated carbons is best suited for the solvent vapor recovery applications because most industrial waste gas streams containing organic solvents are saturated with water vapor. Activated carbons can retain a large fraction of their dry adsorption capacities for organic compounds in presence of high humidity. Table 22.3 shows a few examples of this behawor [22]. Most polar adsorbents (zeolites, alumina, and silica gels) will not be effective for this appHcation. 

This chapter ends with a brief survey of efforts to extend asymmetric hydrogenation by operating in defined phases, unusual media, at surfaces or on soHd supports. In part, this chemistry is driven by the demands for clean technology in fine chemicals manufacturing the absence of solvent waste is an attractive goal. In addition, commercial considerations dictate that soluble metal catalysts should not contaminate the product. The operational criterion for impurity control is often delectabihty, and hence improvements in analytical techniques serve to increase the demand for complete catalyst recovery. The rarely reaUzed prospect of a recyclable asymmetric catalyst serves to provide a further stimulus to developments in this area. 

SFE has been demonstrated to be a good extraction technique for A-nitrosamines in rubber products. In addition, SFE allows fast analysis with a reduction in solvent waste, time, and manipulation. Although recoveries are not too good, especially for the smaller A-nitrosamines, SFE could be considered as a useful tool to determine these analytes, considering that through its selectivity it provides quite clean extracts in one step." Reche et al." determined A-nitrosamines in latex products by combining supercritical fluids and chemical derivatization. The addition of a denitrosation reagent into the extractor combined with an adequate liquid trap allows elucidation of the presence of A-nitrosamines as well as their potential precursors. 

A. M. Baniel, A. M. Eyal, and J. Mizrahi, Acid-base solvents in recovery of mineral acids from waste streams, Proceedings of 2nd Int. Conf Sep. Sci.,... 

Solvents for recovery are frequently contaminated with solutes that have a negligible vapour pressure and are waste materials for disposal, possibly even for land-fill if they are solid or highly viscous and have a high flash point after treatment. These solvents can arise in different ways. 

Because of its wide usage as a degreasing solvent, the most commonly met contaminant of trichloroethylene is a mixture of high-boiling hydrocarbons. Provided this waste has not been contaminated with other solvents, the recovery of trichloroethylene for further degreasing use is easy. It can either be by steam distillation or by vacuum distillation or a combination of both techniques. The distillate will form two easily separating phases with a very low concentration of water in the recovered solvent. 

The above described process is an in-process recovery of raw materials, which are used for production of a final product. Such processes are developed in industry to make technology more efficient or to reduce waste. In fabric coaling, the edge trimming produces 6 to 10% of all wastes. Recovery of raw materials is essential for the coated fabric industry. This initiated munerous attempts in developing plasticizer (among other raw materials) recovery systems based on the solvent extraction or the steam distillation processes. Two reasons hinder the use of these processes economy and quality of the plasticizer. Production usually involves several different plasticizers, which are difficult and costly to separate. ... 

Imposes a cost because some of the costly solvent mixture is lost as the soils are disposed as waste, and also because the dilute rinse water is treated to recover the water. Because the cleaning agent is a multi-component solvent mixture, recovery and reconstitution of it from the waste soil concentrate is seldom attempted. Incineration of the soil concentrate is a common disposal technique. 

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 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. 

It is possible to dispense with the extraction step if the oxidation section is operated at high propylene concentrations and low steam levels to give a concentrated absorber effluent. In this case, the solvent recovery column operates at total organic reflux to effect a2eotropic dehydration of the concentrated aqueous acryflc acid. This results in a reduction of aqueous waste at the cost of somewhat higher energy usage. 

Water formed in the reaction as well as some undesirable by-products must be removed from the acetic acid solvent. Therefore, mother Hquor from the filter is purified in a residue still to remove heavies, and in a dehydration tower to remove water. The purified acetic acid from the bottom of the dehydration tower is recycled to the reactor. The water overhead is sent to waste treatment, and the residue still bottoms can be processed for catalyst recovery. Alternatively, some mother Hquor from the filter can be recycled directiy to the reactor. 

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. 

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