Contamination process improvement

Water as an impurity accelerates the oxidation rate. Figure 4 compares growth curves for Si02 under dry and steam conditions. Halogens can also be introduced to the oxidation process, thereby reducing sodium ion contamination. This improves dielectric breakdown strength, and reduces interface trap density (15). 

Beneficiation processes to remove contaminants and improve the overall quality of ash have been developed. The amount of ash that is... 

PSA operates much the same way as PAC beds, but the intent is to have a more continuous process. That is, the effluent stream is never stopped and diverted from one PSA bed to the next. Usually, there is a series of PSA beds in continuous operation at one time to increase the removal efficiency of the contaminant and improve the regeneration capability. 

The constraints are usually (1) the existing plant, equipment, and layout, and (2) the existing feedstocks (although one might allow different trace contaminants) and economic constraints of budget and profitability. For process improvement and waste... 

Mixed polymer streams can be handled in addition to a certain level of nonplastic contaminants, which improves the economy of the process. Even paper and food can be pyrolysed simultaneously to give other chemical products. Consequently the method is ideal for commingled plastics and composites [25], An additional advantage is that when contamination can be reduced to a minimum, both the matrix and the reinforcing material can be recovered from polymer-based composites. 

The Mukaiyama aldol reaction is beyond doubt a brilliant triumph of modem synthetic organic chemistry however, the reaction products are contaminated with pre-activated silyl enol ethers derived from the carbonyl compounds with stoichiometric amounts of silylation agent and base. In addition, silylated wastes are inherently formed. Circumventing the pre-activation process improves atom efH-ciency in this case, the carbonyl nucleophiles react directly with the carbonyl electrophiles in the presence of catalyst. The first Bronsted acid-catalyzed direct aldol reactions have been achieved using chiral Hg-BINOL-derived phosphoric acid 96 (Scheme 28.12) [66], The aldol products (127) have syn-configurations and, thus, this reaction is complementary to (S)-proHne catalysis in Brpnsted acids, which in general yields the anti configuration [11]. 

Three approaches have been identified that reduce susceptibility of CA resists to airborne contamination. In the first, process engineering changes such as the addition of special activated carbon filters to the environmental chambers surrounding the exposure tools (76,79), overcoating the resist with a soluble protective film to isolate the resist from the environment (77,80,81), or modifications of the process flow to minimize the time interval between exposure and post-exposure bake have been shown to improve CA resist processibibty. 

Nearly every chemical manufacturiag operation requites the use of separation processes to recover and purify the desired product. In most circumstances, the efficiency of the separation process has a significant impact on both the quality and the cost of the product (1). Liquid-phase adsorption has long been used for the removal of contaminants present at low concentrations in process streams. In most cases, the objective is to remove a specific feed component alternatively, the contaminants are not well defined, and the objective is the improvement of feed quality defined by color, taste, odor, and storage stability (2-5) (see Wastes, industrial Water, industrial watertreati nt). 

Because of the development of electronic appHcations for WF, higher purities of WF have been required, and considerable work has been done to improve the existing manufacturing and purification processes (20). Most metal contaminants and gaseous impurities are removed from WF by... 

Improved feedstock pretreatment is important to minimize catalyst consumption and reduce subsequent spent-catalyst handling requirements. Selective hydrogenation of dienes can be used to reduce acid consumption, both in HF and H2SO4 alkylation (29). More effective adsorptive treating systems have been appHed to remove oxygen-containing contaminants that are frequently introduced in upstream processing steps. 

Contaminant by-products depend upon process routes to the product, so maximum impurity specifications may vary, eg, for CHA produced by aniline hydrogenation versus that made by cyclohexanol amination. Capillary column chromatography has improved resolution and quantitation of contaminants beyond the more fliUy described packed column methods (61) used historically to define specification standards. Wet chemical titrimetry for water by Kad Eisher or amine number by acid titration have changed Httle except for thein automation. Colorimetric methods remain based on APHA standards. 

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