Solvent Recovery and Reuse

successful implementation of a solvent recovery system will depend on the savings it will yield. Although solvent recovery systems can cut down on the purchasing of fresh solvents and waste disposal, they also require an input of energy to operate while producing wastes of their own. If a solvent system is 

5 Allen, D.T., and Shonnard, D.R. (2002) Green Engineering Environmentally Conscious Design of Chemical Processes, Prentice Hall, Upper Saddle River, NJ, pp. 475-489. 

11 United States Environmental Protection Agency (1997) EPA Office of Complience Sector Notebook Project Profile of the Pharmaceutical Manufacturing Industry, United States Environmental Protection Agency, Washington DC, pp. 17-57. 

12 LaPorte, T.L, and Wang, C. (2007) Curr. Opin. Drug Discovery Dev., 10, 738-745. 

13 Gad, S.C. (2008) Pharmaceutical Manufacturing Handbook Production and Processes, John Wiley Sons, Inc, Hoboken, NJ, pp. 881-895. 

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Fischer and co-workers undertook a LCA of the 26 organic solvents which they had already assessed in terms of EHS criteria (see above).They used the Eco-solvent software tool (http //www.sust-chem.ethz.ch/tools/ecosolvent/), which on the basis of industrial data considers the birth of the solvent (its petrochemical production) and its death by either a distillation process or treatment in a hazardous waste incineration plant. For both types of end-of-life treatment, environmental credits were granted where appropriate, e.g. solvent recovery and reuse upon distillation. The results of this assessment are shown in Figure 1.2. From an LCA perspective, tetrahydrofuran (THF), butyl acetate, cyclohexanone and 1-propanol are not good solvents. This is primarily due to the environmental... 

Solvents are selected to increase reaction rates, to increase the reproducibility and ease of running reactions, and to ensure that the desired quality and yield of product is reached. Other important considerations are to decrease waste and allow for efficient solvent recovery and reuse. Each of these goals has a direct efiect on productivity and product cost for a manufactured product. In early stages of development, providing material by any means is crucial, and solvents are selected to ensure that the desired product can be prepared within the timeline with minimal difficulty. 

Mobile phase costs Solvent, salts, and also water (especially highly purified water (HPW) and water for injection (WFI) typically in bioprocesses) could have a big impact on the purification costs. Similarly in small molecule purification, solvent cost is a very important cost factor and requires an intensive investigation regarding solvent recovery and reuse. 

Solvent recovery and reuse—The reuse of organic solvents in a BPC system is widespread, especially given the increased cost of these materials and the environmental difficulties sometimes associated with their proper disposal. This reuse is achieved through defined procedures for the recovery of the solvents from distillates, extractions, and spent mother liquors. Where recovered solvents are utilized in the production of a BPC, the validation of the recovery process is strongly recommended. The validation of the recovery... 

Of course, Hovione s particular approach applies only to their own manufacturing programme. The techniques can be applied generally, with specific modification for particular circumstances, to any manufacturing operation, provided the economics are attractive. As new techniques are developed for solvent recovery and reuse they can be easily incorporated into established systems if the total approach strategy, adopted by Hovione, is in place. 

Green chemistry imposes additional constraints on the product and process characteristics. The issues are different for different product sectors and industries. Thus, the specialty chemicals and the pharmaceuticals industries use many different types of synthetic organic reactions. The product volume may be small, but the purities expected are very high. They are very dependent on solvents, as both reactants and products are often solids, and produced molecules may possess toxicity and have other effects on the environment. The most important issues are atom efficiency of individual reactions, solvent recovery and reuse, use of benign solvents, product toxicity, and product end-of-life. Such data for all their raw materials and products may not be available. 

A method for the polymerization of polysulfones in nondipolar aprotic solvents has been developed and reported (9,10). The method reUes on phase-transfer catalysis. Polysulfone is made in chlorobenzene as solvent with (2.2.2)cryptand as catalyst (9). Less reactive crown ethers require dichlorobenzene as solvent (10). High molecular weight polyphenylsulfone can also be made by this route in dichlorobenzene however, only low molecular weight PES is achievable by this method. Cross-linked polystyrene-bound (2.2.2)cryptand is found to be effective in these polymerizations which allow simple recovery and reuse of the catalyst. 

Solution polymerization can use various solvents, primarily aUphatic and aromatic hydrocarbons. The choice of solvent is usually dictated by cost, avaHabihty, solvency, toxicity, flammabiUty, and polymer stmcture. SSBR polymerization depends on recovery and reuse of the solvent for economical operation as well as operation under the air-quaUty perrnitting of the local, state, and federal mandates involved. 

The mbber is then separated from its solvent by steam stripping. The viscous cement is pumped into a violently agitated vessel partly full of boiling water. The hexane flashes off and, together with water vapor, passes overhead to a condenser and to a decanter for recovery and reuse after drying. Residual unpolymerized ethylene and propylene appear at the hexane condenser as noncondensibles, and are recovered for reuse after drying. The polymer, freed from its carrier solvent, falls into the water in the form of cmmb. 

The problem with solvents is not so much their use, but the inefficiencies associated with their recovery and reuse. High volatility, whilst being an extremely useful property, leads to solvent losses to the environment. If a process consists of a reaction stage and a purification stage, solvents may be used and lost at each stage, as shown schematically in Figure 1.20a. Real chemical processes may include several separation steps, with further opportunities for solvent loss. 

This section describes catalytic systems made by a heterogeneous catalyst (e.g., a supported metal, dispersed metals, immobilized organometaUic complexes, supported acid-base catalysts, modified zeolites) that is immobilized in a hydrophilic or ionic liquid catalyst-philic phase, and in the presence of a second liquid phase—immiscible in the first phase—made, for example, by an organic solvent. The rationale for this multiphasic system is usually ease in product separation, since it can be removed with the organic phase, and ease in catalyst recovery and reuse because the latter remains immobilized in the catalyst-philic phase, it can be filtered away, and it does not contaminate the product. These systems often show improved rates as well as selectivities, along with catalyst stabilization. 

HRP/IL phase. The electrical conductivity of the PANI films prepared by solvent casting from the aqueous solutions showed a relatively high and similar value even after the fifth run (Fig. 12), which demonstrates the validity of our approach and the ease of recyclability and reuse of the enzyme inside the IL. For the PEDOT, the process of recovery and reuse was successfully repeated up to ten times using the same HRP/EDOT catalytic phase (Fig. 13), further confirming the success of the synthetic approach and the ease of recyclability and reuse of the enzyme inside the EDOT monomer phase. 

Wong, H., Pink, C., Ferreira, F., and Livingston, A. (2006) Recovery and reuse of ionic liquids and palladium catalyst for Suzuki reactions using organic solvent nanofiltration. Green Chem., 8, 373-379. 

Finally, it should be noted that Lewis acids and bases can also be used in other non-conventional media, as described in Chapter 7, e.g. fluorous solvents, supercritical carbon dioxide and ionic liquids by designing the catalyst, e.g. for solubility in a fluorous solvent or an ionic liquid, to facilitate its recovery and reuse. For example, the use of the ionic liquid butylmethylimidazolium hydroxide, [bmim][OH], as both a catalyst and reaction medium for Michael additions (Fig. 2.45) has been recently reported [151]. 

The subject of alternative reaction media (neoteric solvents) also touches on another issue which is very relevant in the context of this book recovery and reuse of the catalyst. This is desirable from both an environmental and an economic viewpoint (many of the catalysts used in fine chemicals manufacture contain highly expensive noble metals and/or (chiral) ligands. 

THE GOAL use less expensive solvents and grades of solvents increase ease of recovery and reuse. 

Recovery and reuse of solvents may have great financial impact for manufacturing operations. Usually solvents are recovered by distillation, with optional aqueous washes before distillation. High-boiling solvents such as DMF and DMSO are difficult to recover, so they often are used only once, then sent to waste disposal. Solvents may be chosen for decreased water solubility and to decrease the burden on water processing facilities. All waste-water streams that contacted organic solutions should be considered to be contaminated with that solvent and solute, as very few compounds are truly insoluble. ... 

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