Pulping processes chemical, various

Hydrogen sulfide Refinery gases, crude oil, sulfur recovery, various chemical industries using sulfur compounds Petroleum and chemicals Kraft pulping process Foul odor of rotten eggs irritating to eyes and respiratory tract darkening exterior paint... 

Various modifications have been made to the conventional chemical pulping process to increase the extent and selectivity of delignification. Delignification occurs through the... 

Wood is converted into pulp by mechanical, chemical, or semichemical processes. Sulfite and kraft (sulfate) are the common chemical processes, and neutral sulfite is the principal semichemical process (NSSC). Coniferous wood species (softwoods) are the most desirable, but the deciduous, broad-leaved species (hardwoods) have gained rapidly in their usage and constitute about 25 percent of pulp-wood. Table 28.2 summarizes the conditions utilized with the various pulping processes,... 

Conventional sulphite pulping processes use aqueous solutions of sulphur dioxide at various pH levels. Sulphite solutions differ in their content of sulphur dioxide, bisulphite ions and sulphite ions, as shown in Figure 13.9. At a low pH of between 1 and 2 the sulphite liquor contains about 50% sulphurous acid and bisulphite ions respectively at a pH of 4 to 5 it contains approximately 100% bisulphite ions and at a pH of 8 to 10 it consists almost entirely of sulphite ions. When allowance is made for chemical charge, it is the pH and the relative amounts of bisulphite and sulphite ions that chiefly control the mode of pulping. In the original acid sulphite process... 

The paper-making process consists of various steps from pulp production, pulp processing and chemical recovery, pulp bleaching, and stock preparation to paper manufacturing. 

The Kraft process is not only the dominant chemical pulping process, but also the most important overall concerning the various production methods. Several studies have been reported on modeling of continuous digesters at different levels of complexity. Michelsen and Foss (1996) have developed a dynamic model that describes the transfer... 

The determination of Cr, Ni and Pb require the addition of NH4H2PO4 to samples for matrix modification. Most elements in pulp effluent occur in pg L concentrations (As, Ba, Co, Li, Sr, Sn) while some, such as Na, Ca, Mg, Si and K (naturally present in wood or added to pulp during processing in various chemicals), occur in mg L concentrations. Mass spectrometry may be employed for certain elements that are present in very low concentrations < 1 pg L (Ag, Mo, Sb, Tl) and the combination of elements determined by this method offers a characterization of pulp and paper mill effluent in water. Mercury is determined by cold vapour AAS where the detection limit is 0.1 pg-Hg L L... 

Sulfite processes vary by the alkali used. These inelude calcium, magnesimn, sodium and ammonium. The alkali affects the process in various ways. Solubility varies from highly soluble sodium and ammonium throughout the full pH range, to calcium that is soluble only at very low pH. Ammonium-based sulfite has the fastest pulping rate, sodium the slowest. Chemical recovery is easiest with magnesimn, most difficult with sodimn. 

Paper surfaces have unique complexities which can challenge surface modification efforts. Some are manufactured from chemical pulps and are known as wood-free papers. Other varieties of paper can be tree-free . The kraft process is the most widely practiced technique for pulp manufacturing and can produce particularly strong, unbleached paper products that are utilized for bags, but are often further processed into various plys to develop corrugated packaging. 

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