Liquid-based processing

There is little doubt that intrepid entrepreneurs will continue to champion ideas for the application of ionic liquids. Without a doubt, further uses of these materials will be found and justified for commercial use. However, the perceived disadvantages, and particularly the toxicity issues, will temper enthusiasm until the data obtained provide reassurances that an ionic-liquid-based process satisfies all the economic, toxicological, safety, and (in the pharmaceutical industry) FDA regulatory criteria to justify implementation. 

For ionic liquid based process liquors, the contrary can be assumed. Due to their relatively high prices and anticipated costs for discharge of spent liquors a breakthrough of ionic liquids in plating applications can be expected to be linked... 

From the perspective of a chemical engineer, who eventually will scale up any ionic liquid based process developed in the laboratory, whether a solvent melts at -30°C or -80°C makes very little difference. The viscosity of the solvent, on the other hand, is much more important, which for ionic liquids is usually high. Table 2.3 lists the viscosity data of a series of ionic liquids together with some molecular solvents for comparison purposes. Considerably more extensive series of physical properties of ionic liquids can be found elsewhere/21 221 the aim here is to illustrate general trends and principles. 

Supercritical fluids possess characteristics that make them interesting for use as polymerization media. A supercritical fluid exists at temperatures and pressures above its critical values. In the supercritical state, the fluid exhibits physical and transport properties intermediate between the gaseous and liquid state. This is illustrated in Table 2. SCFs have liquid-like densities, but gas-like diffusivities. These intermediate properties can provide advantages over liquid-based processes. In particular, the higher diffusivities of SCFs reduce mass transfer limitations in diffusion-controlled processes. Additionally, lower energy is required for processing the supercritical fluid because its viscosity is lower than that of most liquids, and because the need to vaporize large quantities of liquid is avoided. 

The French Petroleum Institute has developed an ionic liquid based process for the dimerization of alkenes (Dimersol process) and it has been patented as the Difasol process. Interestingly, it can be retrofitted and operated in existing Dimersol plants. However, its biphasic nature offers several advantages over the traditional, homogeneous Dimersol process (Table 10.6). 

It should be possible to use compressed metal powders as, for example, a catalytic filter, but the present authors are not aware of any industrial examples of this. Raney metals powders, however, have been employed in some liquid-based processes in shallow beds through which reactants pass. Because Raney metals are fine grained, pressure drop can be a problem so it is more common to use them in an unstructured way in slurry reactors, as, for example, formerly in the oils and fats industry [3]. Raney metals can have high surface areas when freshly prepared, but this decreases quickly in use, particularly when exposed to elevated temperatures. Pressure drop considerations are less significant for beds of metal granules, but there is less effective use of metal than with fine powders. For granules, surface areas in the region of 30-35 cm g are typical for silver used in... 

In 2002 BASF established the first dedicated industrial-scale ionic liquid-based process [7]. The so-called BASIL process (BASIL = Biphasic Acid Scavenging utilizing Ionic Liquids) is used for the synthesis of alkoxyphenylphosphines, which are important raw materials in the production of BASF s Lucirines (Scheme 9-3), substances that are used as photoinitiators to cure coatings and printing inks by exposure to UV light. 

To afford a sufficient separation the amount of ionic liquid added has to be in the range of 30 to 50 wt.%. This sounds like a large percentage, but is an even smaller quantity than that usually needed with a classic entrainer like dimethylformamide (DMF). In all cases the entrainer has of course to be recycled. Figure 9.6 shows a generic flow chart for the ionic liquids-based process. 

Fig. 9-6 Generic flow chart for the ionic liquid-based process. The ionic liquid is acting as an extractant, washing down compound B. Compound A is released and can be distilled as a pure compound at the head of the column. B is removed at the bottom. The ionic liquid is recycled into the process after having removed residual B in a falling film evaporator.

The Institut Francaise du Petrol (IFP) was the first to develop an ionic liquid-based process to a pilot scale. This is the DIFASOL technology which can be used for the dimerization of olefins. This process is described in detail in Section 5.4 of this book. 

Adsorption processes have a number of competitors, including primarily distillation, extractive and azeotropic distillation, absorption, solvent extraction, and, more recently, membrane-based processes. Vapor-liquid-based processes and, in particular, distillation are especially formidable competitors because of their relatively simple flowsheets. Thus, if a separation can be performed easily by distillation, it will usually be the process of choice, based on relatively low capital costs and tolerable, if not low, energy costs. In addition, systems of distillation columns can oftentimes be energy integrated to effect lower energy costs per unit of feed processed than for stand-alone columns. 

Microfabrication is a process used to generate physical devices onto substrates. These devices are formed by structures with dimensions from millimeter to nanometer range. Figure 3.1 shows a piece of silicon (Si) wafer with devices after the completion of the fabrication. Over the years, microfabrication has advanced significantly from the established semiconductor fabrication processes used for integrated circuits (ICs) to diverse materials and processes such as polymers, liquids, soft lithography, and liquid-based processes. 

Precursors for Aqueous and Liquid-Based Processing of Ferroelectric Thin Films... 

---