Solvent-based processes

Aqueous scouring is expensive in terms of water use and effluent treatment and it can cause entanglement of delicate wool fibres. Solvent scouring offers an effective alternative but it is essential that the solvent does not enter the environment. Earlier solvent-based processes included the use of perchloroethylene in which 8-18% water had been emulsified with a surfactant. Current processes are based on hexane (de Smet process), 1,1,1-... 

In contrast, the Biotechnologische Forschungsgesellschaft has used a solvent-based process for the recovery of poly(3HB) from A. latus. The cells were harvested by centrifugation and the poly(3HB) was subsequently extracted from the suspended cells with methylene chloride and precipitated from the solvent by the addition of water. After drying a polyester with 99% purity was obtained [15]. The process also included the recovery of the solvent. 

Thirdly, the economy of the whole process seems to be very favourable. The tremendous reaction rate makes the reactor very small. The concentration of the substrate in the solvent ( i.e., the loading) is crucial, as in any other solvent-based process. Single-phase conditions have been achieved at a loading of 15 - 20 wt.% for different lipids at a total pressure of 150 bar [29,35]. This would allow a moderate solvent recirculation. Based on these results, a company has decided to build a pilot plant, which will be put into operation in Goteborg, Sweden, during the spring of 2001. 

Dinitrogen tetraoxide (N2O4) selectively oxidizes some of the primary hydroxyl groups. One solvent-based process involves selective oxidation of starch with N204 in the presence of oxygen119 to give a product with 75% uronic acid units. Co-builders for use with zeolites have been produced by oxidation and hydrolysis of starch with a gas phase of N02/N204 in a fluidized bed.120... 

Figure 3.5 HMF production using a solvent-based process (1 two-phase reactor, 2 evaporator, 3 condenser, 4 extractor).

Atarget of 25% recycling for 2003, aiming for 50% by 2005, has been set. This is based on a mechanical cryogenic unit which will require additional capacity or be augmented via a solvent based process (www.vinyl2010.org). 

At high syngas pressure, physical solvent-based processes become increasingly attractive, for example, the Rectisol and Selexol processes. There are more than 55 Selexol plants worldwide, treating natural and syngas.51 The Selexol process solvent is a mixture of dimethyl ethers of polyethylene glycol, and has the formulation... 

Emulsion polymerization is the basis of many industrial processes, and the production volume of latex technologies is continually expanding—a consequence of the many environmental, economic, health, and safety benefits the process has over solvent-based processes. A wide range of products are synthesized by emulsion polymerization, including commodity polymers, such as polystyrene, poly(acrylates), poly (methyl methacrylate), neoprene or poly(chloroprene), poly(tetrafluoroethylene), and styrene-butadiene rubber (SBR). The applications include manufacture of coatings, paints, adhesives, synthetic leather, paper coatings, wet suits, natural rubber substitutes, supports for latex-based antibody diagnostic kits, etc. ... 

Kalinwasky, 1 st Shirley Int. Seminar on solvent based processing of textiles, Manchester (Oct 1969). 

A number of solvent-based processes have been developed to remove H S from gas streams [1, 2]. Separation of H S is achieved through preferential chemical reaction (chemical solvents), differential physical solubility (physical solvents), or a combination of both mechanisms (hybrid solvents) [1,2]. Choice of process type is primarily related to the partial pressure of H S in the stream [1, 2]. Chemical solvents have very high absorption capacities for H S at low partial pressures, but become less effective as the reactive agent approaches saturation [1,2]. For physical solvents, the solubility of H S typically increases in a linear fashion with increasing H S partial pressure (i.e., Henry s Law behavior) [1, 2]. 

One of the best known and most influential developments in the use of SCCO2 was based on the work of Kurt Zosel in the early 1960s, where SCCO2 played a key role in the extraction of caffeine from coffee, which has obvious benefits to the consumer over alternative, solvent-based processes." This is now carried out industrially on a huge scale, producing many thousands of tons of decaffeinated coffee per year. Liquid and supercritical CO2 are routinely used for the extraction of natural products, particularly hops and essential oils, and this is now considered to be a relatively mature area of CO2 technology. 

Mixture with water. Whether it arises in the solvent-based process or in some part of the recapture of the solvent, it is very common to find that the solvent is contaminated with water. Removal of water is a simple matter in many cases but in others it is so diftrcult that restoration to a usable purity may prove to be uneconomic. 

Solvent extraction is an operational definition for a solvent-based process to isolate soluble material from the complex and heterogeneons mixtnre, which is coal. Unless the separation process is specified, including filter pore size or centrifngation clearing factor, the material isolated is not well defined and may not be the same as that isolated in other laboratories. This is especially true for coals subject to weathering. 

With the end of the battery research, the need for processing became evident, as new ideas connected with LEDs emerged. These demanded a kind of solvent-based processing technique. On the basis of work by Elsenbaumer et al. [44], a variety of soluble conductive polymers and solvents, even for doped polyaniline, have been proposed. This question was discussed shortly in Section 1.2. Here, only conductive polymers will be discussed. 

Fuel oxidation and CO2 separation are carried out in a single unit composed of two (or three in one case) adiabatic reactors, and no other exotic processes are required while using solvent-based processes. Air separation unit, which is very expensive from an energy point of view, is required only if there is not complete fuel conversion in the CLC loop. 

It is likely that solvent-based processing of recovered plastics will grow in the future as part of the overall global infrastructure for plastics recovery. Economies of scale will help to cover the overhead costs required to meet demanding environmental and safety requirements for chemical processing. Some advantages and disadvantages of solvent-based separation processed are summarized here ... 

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