Harmful solvent

The dense fluid that exists above the critical temperature and pressure of a substance is called a supercritical fluid. It may be so dense that, although it is formally a gas, it is as dense as a liquid phase and can act as a solvent for liquids and solids. Supercritical carbon dioxide, for instance, can dissolve organic compounds. It is used to remove caffeine from coffee beans, to separate drugs from biological fluids for later analysis, and to extract perfumes from flowers and phytochemicals from herbs. The use of supercritical carbon dioxide avoids contamination with potentially harmful solvents and allows rapid extraction on account of the high mobility of the molecules through the fluid. Supercritical hydrocarbons are used to dissolve coal and separate it from ash, and they have been proposed for extracting oil from oil-rich tar sands. 

As will happen, for example, with perfluorotriethylamine, a substance that is a good alternative reaction medium may be found for reactions and it can be easily recycled by simple extractive workup (Nakano and Kitazume, 1999). One of the most important issues in twenty-first century scientific society is the environmental problem. Thus far, there have been increasing demands for substitutes for toxic and/or harmful solvents like CH2CI2. Recently, inert and less toxic fluorous (perfluorinated) fluids have been recognized and are attracting attention as new alternative solvents (Fish, 1999). This fact shows the need to survey the scope and limitations of the utility of these liquids as alternative reaction media for reactions, which are of great current interest due to their unique reactivities and selectivities. 

Replace toxic or harmful solvents and chemicals with environmentally benign... 

Gerasimidis et ah, 2007). Although solvents have generally been successful in reducing the gossypol content of cottonseed products to quite low levels, how to completely remove the potentially harmful solvent residual is another challenging subject. 

Strychnine is prepared from the seeds by grinding them to a paste with slaked lime and water. The paste is dried and mixed with a suitable organic solvent (formerly benzene was used, but now less harmful solvents are substituted, e.g. chloroform). The slaked lime makes the mixture alkaline and under these conditions the strychnine dissolves readily in organic (i.e. oily) but not water-based solvents. The particulate debris is then removed by filtration and the liquid shaken with dilute sulphuric acid. This neutralises the effects of the lime and when the organic solvent and acid layers separate (cf. oil and vinegar salad dressing) the strychnine is dissolved in the latter. The organic solvent is decanted from the strychnine solution which is rendered alkaline by the addition of either ammonia or sodium hydroxide. This drastically reduces the... 

Extrusion is a simple and low-cost process of encapsulation with core-shell architecture, which is able to preserve probiotic cell viability, owing to the limited use of harmful solvents and the small stresses exerted on microbial cells. However, its use on large scale is limited by the slow process of capsule fabrication. In contrast, owing to its easier scalability, fluid-bed coating is more widely used in the encapsulation of probiotic cells. 

Quite apart from the harm solvents may do at concentrations greater than their TLV they can also overcome a person inhaling them by asphyxiation. The level of concentration at which this is likely to occur is 150 000 ppm (15%). The most volatile solvents will produce a saturated vapour of this strength at ambient temperature. 

Both native and regenerated cellulose can be used for the preparation of cellulose aerogels. Cellulose in native form, generally nanofibrillar such as bacterial cellulose and microfibrillated cellulose, has been proposed for the preparation of aerocellulose [77, 266]. Aerogels based on NFC can offer advantages from an environmental point of view, because NFC is obtained from renewable resources and no harmful solvents are required during the processing. 

The other option for future improvements, which is certainly being exercised as is shown in the above patents, is a rationalization of solvent composition. Here, regulations have played a progressive role in eliminating or reducing some very harmful materials. New inventions are still needed which aim to find more benign solvent mixtures or to replace resins which require aggressive or harmful solvents by ones which allow for more environmentally friendly compositions. 

Water-based acrylic paints provide no harmful solvents. They are easy to apply and a wide variety of colors is available. Lacquers contain solvents that evaporate allowing the paint coating to dry without chemical reaction. The lacquer must be carefully chosen so the solvent is compatible with the plastic being painted. Enamels are based on a chemical reaction that causes the coating film to form and harden. The effect of this reaction on the parent plastic part must be carefiilly noted. Certain plastics may require a primer to help improve the adhesion of the paint to the plastic. After coating, a top coat may also be required to improve the environmental or wear resistance of the paint. Two part paints, such as epoxy or urethane coatings, provide excellent adhesion qualities and do not require a top coat. 

In order to eliminate harmful solvents which are flammable and sometimes noxious, adhesives manufacturers have developed water-based adhesives, based on rubber latex or polymer dispersions, which set quickly due to the addition of an activator that reacts quickly with the base polymer and induces its quick coagulation. But the mixing should be done during the spraying in order to avoid any coagulation and clogging into the gun. 

It is a solvent-free process, eliminating the need to handle harmful solvents, and does not produce residual solvents. Additionally, due to the elevated temperatures applied, the presence of water or moisture in the environment is excluded, and therefore products sensitive to moisture can be easily formulated. 

Crystallinity can be tailored Potentially harmful solvent residues... 

---