Recycling of solvent

Solvent Recovery. Most of the activated carbon used in gas-phase applications is employed to prevent the release of volatile organic compounds into the atmosphere. Much of this use has been in response to environmental regulations, but recovery and recycling of solvents from a range of industrial processes such as printing, coating, and extmsion of fibers also provides substantial economic benefits. 

Undoubtedly cost factors and environmental considerations (recycling of solvents, less toxic or less ha2ardous materials) wih lead to increasing industrial appHcation of this methodology. 

Figure 5.189. Modification of EQMULTI with recycle of solvent.

In other related areas, such as solution polymerization and bulk polymerization, the removal/recycling of solvents or unreacted monomer has been extensively investigated [108-112]. The methods used are based on lateral heat-dependent operations such as evaporation and steam-stripping, or non-lateral heat-dependent operations that include a variety of extraction procedures. 

Recycling of solvent waste and stop dumping (Closing the Loop). 

The figures calculated are prior to any recycling of solvent. Two of the four waste streams are easily recyclable by distillation. 

The final approach to the reduction of eluent consumption is the optimal recycling of solvents. Indeed, preparative and industrial chromatography can be designed as a unit operation that includes solvent recycling dry feed mixture is injected while dry separated compounds are recovered. Many techniques can be applied depending on the situation in isocratic (that is with a constant mobile phase composition) or gradient conditions, and with organic and/or supercritical eluents. 

Separation of organic/aqueous phases Treatment and discharge of aqueous phase Distillation of organic phase Recycling of solvent Distillation of organic phase... 

Typical other parts of the plant apart from the cell room are storage facilities for starting materials and end products, equipment for safety and environment protection, purification systems for products and by-products, facilities for recycling of solvents and electrolytes, energy supply, and process control. 

Recycles of solvents, catalysts, unconverted feed materials, and byproducts are found in many processes. Most processes contain at least one material recycle, and some may have six or more. Furthermore, when energy is recovered by process-to-process heat transfer, then energy recycles are created, as discussed in Section 4.5.4. 

Figure 6 Conceptual flow sheet comprising fractional extraction and back-extraction unit with recycle of solvent stream. Assumption R is preferentially extracted ( > Ks)...

Teehnol., 44, pp. 79 4 (2005)]. Another process that exploits a phase transition to facilitate separation and recycle of solvent alter extraction utilizes ethylene oxide-propylene oxide copolymers in aqueous two-phase extraction of proteins [Persson et al.,/. Chem. Teehnol. Bioteeh-nol., 74, pp. 238-243 (1999)]. After extraction, the polymer-rich extract phase is heated above its LCST to form two layers an aqueous layer containing the majority of protein and a polymer-rich layer that can be decanted and recycled to the extraction. 

A well-designed Purex plant aims for as complete recycle of solvent as possible, to minimize costs of solvent makeup and disposal. Solvent from the uranium purification section usually contains so few contaminants or degradation products that it can be reused a number of times without cleanup. On the other hand, solvent that has processed solutions containing hi activity of fission products and plutonium carries traces of these contaminants, uranium, nitric acid, dibutyl phosphate, and other radiolytic degradation products of TBP and dodecane. Uranium and plutonium should be recovered because of their value. Fission products should be removed to prevent product contamination in later cycles. Dibutyl phosphate should be removed because it forms strong complexes with tetravalent zirconium and plutonium that would impair ability of the solvent to reject zirconium and separate plutonium from uranium. 

Recycling of solvents is possible with this method too. Ethyl acetate can be recovered during the vacuum evaporation by use of a dry-ice trap. The dimethyl-formamide can be recovered by vacuum distillation. 

This section describes the requirements for rejection of materials, reprocessing and reworking, recovery and recycling of solvents in the process, and customer returns of materials. 

The stream conditions shown in Figure 14.1 are from the dynamic simulation of the process at steady-state conditions with the recycle of solvent loop closed. This loop did not converge in the steady-state Aspen Plus simulation. Other simulation issues are discussed in the next section. 

The recycling of solvents in dry cleaning is very important, because solvents are too expensive for single use. Three different systems are used for the cleaning of the solvent in order for it to be recycled ... 

Other waste reduction can be realized by the better production scheduling, use of dry filters in the spray booth, prevention of leakage from the spray gun, separation of wastes, and recycling of solvents by distillation. 

The pharmaceutical sector is somewhat different to the others in that substantial internal recycling of solvents already occurs. The actual process throughput of solvents is 3-5 times the figures shown in the table, which represent make-up quantities. Most modern pharmaceutical plants are fully integrated for waste management, and solvent that cannot be recycled is destroyed by thermal oxidation. Some spent solvent is supplied to third party toll recoverers with the recovered material ending up in the thinners and cleaners market. The quantities are small, however, because of the reluctance of the manufacturers, for reasons of safety and confidentiality, to release waste process materials which could contain trace amounts of pharmaceutical products. 

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