Cleaning operations using organic solvents

For material accounting purposes, we can classify cleaning (unit) operations as follows  

Surface preparation of large manufactured components (stage before a coating is applied). 

Line cleaning (includes piping network and any associated tanks). 

Tank cleaning (mostly inner tank surfaces and any associated pipes). 

---

AH volatile organic solvents are toxic to some degree. Excessive vapor inhalation of the volatile chloriaated solveats, and the central nervous system depression that results, is the greatest hazard for iadustrial use of these solvents. Proper protective equipment and operating procedures permit safe use of solvents such as methylene chloride, 1,1,1-trichloroethane, trichloroethylene, and tetrachloroethylene ia both cold and hot metal-cleaning operations. The toxicity of a solvent cannot be predicted from its chlorine content or chemical stmcture. For example, 1,1,1-trichloroethane is one of the least toxic metal-cleaning solvents and has a recommended threshold limit value (TLV) of 350 ppm. However, the 1,1,2-trichloroethane isomer is one of the more toxic chloriaated hydrocarboas, with a TLV of only 10 ppm. 

Various other biphasic solutions to the separation problem are considered in other chapters of this book, but an especially attractive alternative was introduced by Horvath and co-workers in 1994.[1] He coined the term catalysis in the fluorous biphase and the process uses the temperature dependent miscibility of fluorinated solvents (organic solvents in which most or all of the hydrogen atoms have been replaced by fluorine atoms) with normal organic solvents, to provide a possible answer to the biphasic hydroformylation of long-chain alkenes. At temperatures close to the operating temperature of many catalytic reactions (60-120°C), the fluorous and organic solvents mix, but at temperatures near ambient they phase separate cleanly. Since that time, many other reactions have been demonstrated under fluorous biphasic conditions and these form the basis of this chapter. The subject has been comprehensively reviewed, [2-6] so this chapter gives an overview and finishes with some process considerations. 

Application of SPE to sample clean-up started in 1977 with the introduction of disposable cartridges packed with silica-based bonded phase sorbents. The solid phase extraction term was devised in 1982. The most commonly cited advantages of SPE over liquid-liquid extraction (LLE) as practiced on a macroscale include the reduced time and labor requirements, use of much lower volumes of solvents, minimal risk of emulsion formation, selectivity achievable when desired, wide choices of sorbents, and amenability to automation. The principle of operation consists of four steps (1) conditioning of the sorbent with a solvent and water or buffer, (2) loading of the sample in an aqueous or aqueous low organic medium, (3) washing away unwanted components with a suitable combination of solvents, and (4) elution of the desired compound with an appropriate organic solvent. 

Volatile organic chemicals are released during a number of industrial and manufacturing operations. For example, 1,3-butadiene is an important raw material in the manufacture of synthetic rubber During manufacture small amounts of the chemical escape into the air. Formaldehyde is a raw material used in the manufacture of a variety of building materials, such as phenol-formaldehyde and melamine resins. Many household products, such as cleaning products, varnishes, waxes, paints, and organic solvents, contain VOCs, which vaporize and escape easily into the atmosphere when they are used. For this reason, VOCs often build up indoors. 

Considerable time can be saved by cleaning each piece of equipment soon after use, for you will know at that point what contaminant is present and be able to select the proper method for removal. A residue is easier to remove before it has dried and hardened. A small amount of organic residue usually can be dissolved with a few milliliters of an appropriate organic solvent. Acetone (bp 56. TC) has great solvent power and is often effective, but it is extremely flammable and somewhat expensive. Because it is miscible with water and vaporizes readily, it is easy to remove from the vessel. Cleaning after an operation often can be carried out while another experiment is in process. 

Solvent extraction is widely used in laboratory applications on a very small scale but also on much larger industrial scale. In fact, the variety of materials, both organic and inorganic, that are processed using some form of solvent extraction is staggering. Moreover, the methods in which solvent extraction is applied to vastly different recovery and cleaning operations continues to grow... 

---