Bleaching operations

Ni-Cr-Mo Ni-Mo Ni-Cu Chlorination processes Processes involving HCl and nonoxidising acidic chlorides Production and Distillation columns containing acidic chlorides HF alkylation Fluorination Applications where no pitting and no loss of reflectivity are necessary Valves, Bleaching operations Handling Pickling of... 

During preparation of peracetic acid solutions for textile bleaching operations, the reaction mixture must be kept acid. Under alkaline conditions, highly explosive diacetyl peroxide separates from solution [1], An excess of the anhydride has the same effect [2],... 

An explosion in flour-bleaching operations was attributed to violent decomposition of the basic nitrate [1], which is an impact-, friction- and heat-sensitive explosive [2]. The instability is associated with the presence of reducant and oxidant functions in the same molecule. The previous formulation as tin(II) nitrate oxide is revised to that above. 

The increasing demands on the pulp and paper industry to reduce emissions from bleaching operations has lead to modifications of the cooking process to provide a pulp that requires a decreased amount of bleaching. This is accomplished by decreasing the amount of residual... 

The fat refining and bleaching operation is carried out to remove impurities that would cause color and odor in the finished soap. The wastewater from this source has a high soap concentration, treatment chemicals, fatty impurities, emulsified fats, and sulfuric acid solutions of fatty acids. Where steam is used for heating, the condensate may contain low-molecular-weight fatty acids, which are highly odorous, partially soluble materials. 

Methods. A typical hydrogen peroxide bleaching operation consists of treatment of a 20% HPL solution in 60-75% aqueous ethanol with 25-50% hydrogen peroxide (by weight) on lignin derivative at 80°C. The reaction medium is adjusted to pH 2 by the addition of HC1, or to pH >12-13 by NaOH. Color loss is determined by UV/VIS absorbance measurements on suitably diluted samples. 

The pulps listed in Fig. 1 are characterized on an unbleached basis as produced by processes conventionally called pulping processes. In many instances, these pulps must be further treated chemically to remove residual lignin, hemicellulose, and color bodies before they can be considered suitable for use in specific applications. This further treatment is called bleaching, and the bleaching operation is actually an extension of the pulping process. 

The direct electrochemical oxidation (no cell divider membrane) of wastewater has been employed in the textile industry. Typically, this industry produces an organic-contaminated wastewater that also contains sodium chloride sodium chloride is desirable in promoting anodic oxidation. The presence of sodium chloride is fortuitous for textile manufacturers since the hypochlorite byproduct produced in the electrochemical oxidation process is used for textile bleaching operations.24... 

The Kraft process that is widely used in wood pulping leaves behind 5% to 8% by weight of residual modified lignin in the pulp. This residual is responsible for the characteristic brown color of the pulp and is commercially removed by the use of bleaching agents such as chlorine and chlorine oxides [32], Bleaching operations produce dark-brown effluents that contain toxic and mutagenic chlorinated products that constitute an environmental... 

Pulp and paper mills are a much smaller source of PCDD/Fs in the environment than in the past. In 1988, the EPA and the US pulp and paper industry collaborated on the 104-Mill Study to measure levels of dioxins in effluent, sludge and pulp from 104 bleached chemical wood pulp and paper mills in the US. The study estimated the total discharge from all US pulp and paper mills to be 1188 g TEQ yr 1.18 In response to these findings, the pulp and paper industry expended more than SI billion dollars to reduce TCDD and TCDF formation during bleaching operations.19 The 1993 estimated discharge from all US pulp and paper mills is 97.2 g TEQ (Table 2). 

Mechanical pulp contains approximately 20% m/m lignin, a coloured, random polyaromatic polymer. The objective of the bleaching operation is to destroy the chromophoric groups without substantial removal of the lignin. Mechanical pulp products are currently used for newsprint and packaging. 

Carotenoids and chlorophylls are the major lipochromes of vegetable oils. Cmde regular sunflower oil is not particularly rich in carotenoids (as palm oil is) or in chlorophylls (like rice bran, rapeseed, olive, and avocado oils). This gives cmde regular sunflower oil its light-amber color, turning to pale yellow upon the bleaching operation. 

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