Ultraclean processing

In the last few years, a number of factors have led practitioners to abandon the concept of ultraclean processing (reducing the level of contaminants to below the level detectable with state-of-the-art equipment). The approach that seems to have taken hold instead is that of just clean enough, which requires a fundamental understanding of the specific effects of contaminants and as a consequence, the ability to define tolerable levels of contaminants. In the next section we review the characterization tools that can be used in this context. 

So far, only presses with rollers arranged side-by-side, were presented. Although most of the presses with horizontal feed and rollers on top of each other are small, manufactured by relative newcomers to the field, and applied in the pharama-ceutical industry for ultraclean processing, Fig. 8.128g.l and g.2 are examples of large machines of this design. 

Components of the Suggested Novel Ultraclean Process for the Production of the Ultraclean Fuel Hydrogen... 

Another modification is the use of microbubble column flotation (13). In this process, smaller bubbles are generated to enhance the recovery of micrometer-sized particles. A countercurrent flow of feed slurry is also used to further enhance the bubble—particle attachment. The process is capable of produciug ultraclean coals containing less than 0.8% ash. 

More recendy, the molten caustic leaching (MCL) process developed by TRW, Inc. has received attention (28,31,32). This process is illustrated in Eigure 6. A coal is fed to a rotary kiln to convert both the mineral matter and the sulfur into water- or acid-soluble compounds. The coal cake discharged from the kiln is washed first with water and then with dilute sulfuric acid solution countercurrendy. The efduent is treated with lime to precipitate out calcium sulfate, iron hydroxide, and sodium—iron hydroxy sulfate. The MCL process can typically produce ultraclean coal having 0.4 to 0.7% sulfur, 0.1 to 0.65% ash, and 25.5 to 14.8 MJ/kg (6100—3500 kcal/kg) from a high sulfur, ie, 4 wt % sulfur and ca 11 wt % ash, coal. The moisture content of the product coal varies from 10 to 50%. 

Researchers at the Brush-Wellman Laboratory (Ebnore. Ohio) have developed a bench-scale, inert-gas atomization method for producing ultraclean, spherical powders, which then can be hot isostatic processed. 

Kawahara H. Ultraclean Surface Processing of Silicon Wafers. Berlin Springer-Verlag 1998. p 456. 

Advanced syngas cleaning and conditioning processes are needed that efficiently remove contaminants at high temperatures, producing ultraclean syngas. 

Approaches to ultradeep HDS include (a) improving catalytic activity by new catalyst formulation for HDS of 4,6-DMDBT, (b) tailoring reaction and process conditions, and (c) designing new reactor configurations. Design approaches for ultradeep HDS focus on how to remove 4,6-DMDBT in gas oil more effectively. One or more approaches may be employed by a refinery to meet the challenges of producing ultraclean fuels at affordable cost. 

Current progress in HDS via improvement of conventional catalysts, reactors, and processes or development of new catalysts, reactors, and processes has allowed the refining industry to be able to produce the low-sulfur fuels to meet the new EPA regulation. However, the current HDS technology is still difficult or costly to produce the ultraclean liquid hydrocarbon fuels for fuel cell applications. Adsorptive desulfurization and ODS are two promising alterable technologies for ultradeep desulfurization of hydrocarbons fuels for fuel cell applications. 

This symposium series book describes the recent advances in various aspects (production, processing, upgrading, and utilization) of such recent research and development efforts related to ultraclean transportation fuels from a variety of hydrocarbon feedstocks (coal, petroleum coke, biomass, waste oil, and natural gas). 

Fig. 6.2-80 Two drum film coaters installed in the ultraclean environment of pharmaceutical processing (courtesy Driam, Eris-kirch/Bodensee, Germany)...

The stability and maintenance of a cleaned surface is often more critical than the final surface state which is achieved after the cleaning process. Storage in an ultraclean, controlled environment, a very expensive but most effective measure is usually seldom required. Instead of using a universal protection device, it is often easier and cheaper to identify the undesirable contaminants and to eliminate them from the storage environment. Such contaminants are usually the airborne ones, including various types of dust particles, atmospheric condensates of chemical vapours, and, last but not least, water vapour. The use of some preventive measures is, therefore, well worth considering. Contact with dust may be reduced drastically by storing the parts in a closed container or in a clean bench. 

Budde, K.J., Determination of organic contamination from polymeric construction materials for semiconductor technology. Mater. Res. Soc. Symp., Proc. Ultraclean Semiconductor Processing Technology and Surface Chemical Cleaning and Passivation, 1995, 386, 165-176. 

Indirect coal liquefaction first gasifies the coal with steam to form synthesis gas (syngas—a mixture of hydrogen and carbon monoxide). The sulfur is removed from this gas and the mixture is adjusted according to the desired product. The synthesis gas is then condensed over a catalyst—the Fischer-Tropsch process— to produce high-quality, ultraclean products. 

Nevertheless, since it relies on the abrasive properties of metal oxide particles suspended in a colloidal dispersion, the activity of the chemical reagents, a relatively softer polymeric pad, and a wafer carrier to hold the wafer face down to achieve the nanolevel wafer and die scale planarity, it is tmly counterintuitive in its scope. The side containing the active elements of each and every wafer, always processed in an ultraclean and extremely low particle environment, is exposed to bHlions of abrasive particles multiple times, and after each pass all the particles and the chemical agents in the dispersion need to be completely removed from the wafer surface during post-CMP processing to prevent surface contamination and degradation. In spite of this, CMP has proven to be... 

As discussed in the introduction of this preface, it is now important to develop creative talents in chemical engineers. Chapter 8 aims to do this by offering two examples of novel processes one for the efficient production of the ultraclean fuel hydrogen and the other for the production of the clean fuel ethanol through the biochemical path of utilizing lingo-cellulosic wastes. Readers can expect to use the tools provided earlier in this book in order to develop these novel processes and modes of operation without the need of the expensive pilot plant stage. 

Novel Reforming Process for the Efficient Production of the Ultraclean Fuel Hydrogen from Hydrocarbons and Waste Materials... 

Main Characteristics of the Suggested Novel Ultraclean/Efficient Reforming Process Configuration... 

NOVEL REFORMING PROCESS FOR THE EFFICIENT PRODUCTION OF THE ULTRACLEAN FUEL HYDROGEN FROM HYDROCARBONS AND WASTE MATERIALS... 

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